CA2197491C - Ferroelectric capacitor and method for manufacturing thereof - Google Patents
Ferroelectric capacitor and method for manufacturing thereof Download PDFInfo
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- CA2197491C CA2197491C CA002197491A CA2197491A CA2197491C CA 2197491 C CA2197491 C CA 2197491C CA 002197491 A CA002197491 A CA 002197491A CA 2197491 A CA2197491 A CA 2197491A CA 2197491 C CA2197491 C CA 2197491C
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- 239000003990 capacitor Substances 0.000 title claims abstract description 58
- 238000004519 manufacturing process Methods 0.000 title claims description 16
- 238000000034 method Methods 0.000 title claims description 16
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 30
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 30
- 239000010703 silicon Substances 0.000 claims abstract description 30
- 239000000758 substrate Substances 0.000 claims abstract description 21
- 238000007254 oxidation reaction Methods 0.000 claims description 49
- 230000003647 oxidation Effects 0.000 claims description 46
- 239000000126 substance Substances 0.000 claims description 21
- 229910019897 RuOx Inorganic materials 0.000 claims description 16
- 229910003070 TaOx Inorganic materials 0.000 claims description 16
- 229910003087 TiOx Inorganic materials 0.000 claims description 16
- HLLICFJUWSZHRJ-UHFFFAOYSA-N tioxidazole Chemical compound CCCOC1=CC=C2N=C(NC(=O)OC)SC2=C1 HLLICFJUWSZHRJ-UHFFFAOYSA-N 0.000 claims description 16
- 238000004544 sputter deposition Methods 0.000 claims description 13
- HTXDPTMKBJXEOW-UHFFFAOYSA-N iridium(IV) oxide Inorganic materials O=[Ir]=O HTXDPTMKBJXEOW-UHFFFAOYSA-N 0.000 claims description 7
- 230000001590 oxidative effect Effects 0.000 claims description 7
- 229910002673 PdOx Inorganic materials 0.000 claims 6
- 229910019020 PtO2 Inorganic materials 0.000 claims 6
- YKIOKAURTKXMSB-UHFFFAOYSA-N adams's catalyst Chemical compound O=[Pt]=O YKIOKAURTKXMSB-UHFFFAOYSA-N 0.000 claims 6
- 229910003445 palladium oxide Inorganic materials 0.000 abstract description 35
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 abstract description 19
- 229910052760 oxygen Inorganic materials 0.000 abstract description 19
- 239000001301 oxygen Substances 0.000 abstract description 19
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 abstract description 7
- 229910052814 silicon oxide Inorganic materials 0.000 abstract description 7
- JQPTYAILLJKUCY-UHFFFAOYSA-N palladium(ii) oxide Chemical compound [O-2].[Pd+2] JQPTYAILLJKUCY-UHFFFAOYSA-N 0.000 abstract 2
- KDLHZDBZIXYQEI-UHFFFAOYSA-N palladium Substances [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 48
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 45
- HBEQXAKJSGXAIQ-UHFFFAOYSA-N oxopalladium Chemical compound [Pd]=O HBEQXAKJSGXAIQ-UHFFFAOYSA-N 0.000 description 35
- 239000010408 film Substances 0.000 description 32
- 229910052763 palladium Inorganic materials 0.000 description 21
- 229910052697 platinum Inorganic materials 0.000 description 17
- 239000010936 titanium Substances 0.000 description 17
- 230000005621 ferroelectricity Effects 0.000 description 12
- 230000015556 catabolic process Effects 0.000 description 8
- 238000006731 degradation reaction Methods 0.000 description 8
- 239000013078 crystal Substances 0.000 description 7
- 239000000463 material Substances 0.000 description 7
- 230000032683 aging Effects 0.000 description 6
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 4
- 239000011259 mixed solution Substances 0.000 description 4
- 229910052719 titanium Inorganic materials 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 3
- 230000003247 decreasing effect Effects 0.000 description 3
- 230000010287 polarization Effects 0.000 description 3
- 238000007669 thermal treatment Methods 0.000 description 3
- 229910020684 PbZr Inorganic materials 0.000 description 2
- 230000002265 prevention Effects 0.000 description 2
- 238000005546 reactive sputtering Methods 0.000 description 2
- 238000003980 solgel method Methods 0.000 description 2
- 238000004528 spin coating Methods 0.000 description 2
- 239000007858 starting material Substances 0.000 description 2
- 239000010409 thin film Substances 0.000 description 2
- 235000009421 Myristica fragrans Nutrition 0.000 description 1
- 241000282320 Panthera leo Species 0.000 description 1
- 229910001252 Pd alloy Inorganic materials 0.000 description 1
- 230000032798 delamination Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000012212 insulator Substances 0.000 description 1
- 239000001115 mace Substances 0.000 description 1
Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/86—Types of semiconductor device ; Multistep manufacturing processes therefor controllable only by variation of the electric current supplied, or only the electric potential applied, to one or more of the electrodes carrying the current to be rectified, amplified, oscillated or switched
- H01L29/92—Capacitors with potential-jump barrier or surface barrier
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
- H01L21/3205—Deposition of non-insulating-, e.g. conductive- or resistive-, layers on insulating layers; After-treatment of these layers
- H01L21/32051—Deposition of metallic or metal-silicide layers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- H01L27/02—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier
- H01L27/04—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier the substrate being a semiconductor body
- H01L27/08—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier the substrate being a semiconductor body including only semiconductor components of a single kind
- H01L27/0805—Capacitors only
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L28/00—Passive two-terminal components without a potential-jump or surface barrier for integrated circuits; Details thereof; Multistep manufacturing processes therefor
- H01L28/40—Capacitors
- H01L28/55—Capacitors with a dielectric comprising a perovskite structure material
- H01L28/56—Capacitors with a dielectric comprising a perovskite structure material the dielectric comprising two or more layers, e.g. comprising buffer layers, seed layers, gradient layers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L28/00—Passive two-terminal components without a potential-jump or surface barrier for integrated circuits; Details thereof; Multistep manufacturing processes therefor
- H01L28/40—Capacitors
- H01L28/60—Electrodes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L28/00—Passive two-terminal components without a potential-jump or surface barrier for integrated circuits; Details thereof; Multistep manufacturing processes therefor
- H01L28/40—Capacitors
- H01L28/60—Electrodes
- H01L28/65—Electrodes comprising a noble metal or a noble metal oxide, e.g. platinum (Pt), ruthenium (Ru), ruthenium dioxide (RuO2), iridium (Ir), iridium dioxide (IrO2)
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L28/00—Passive two-terminal components without a potential-jump or surface barrier for integrated circuits; Details thereof; Multistep manufacturing processes therefor
- H01L28/40—Capacitors
- H01L28/60—Electrodes
- H01L28/75—Electrodes comprising two or more layers, e.g. comprising a barrier layer and a metal layer
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
- H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
- H01L21/768—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics
- H01L21/76838—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the conductors
- H01L21/76841—Barrier, adhesion or liner layers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L28/00—Passive two-terminal components without a potential-jump or surface barrier for integrated circuits; Details thereof; Multistep manufacturing processes therefor
- H01L28/40—Capacitors
- H01L28/55—Capacitors with a dielectric comprising a perovskite structure material
Abstract
A dielectric capacitor having excellent dielectric properties which comprise s a silicon oxide layer (4), a lower electrode (12), a ferroelectric layer (8) , and an upper electrode (15) formed on a silicon substrate (2). The lower electrode (12) is formed of palladium oxide, and so is the upper electrode (15). Palladium oxide prevents the permeation of oxygen through the dielectr ic layer (8), thus offering a dielectric capacitor having excellent dielectric properties.
Description
A Ferroelectric Capacitor and a Method far Manufacturing Thereof Field of the Invention The present invention relates to a ferroelectric capacitor and, more specifically, to improvement of the ferroelectricity and ot;r.er characteristics of the capacitor.
Background art Fig. 10 shows a conventional ferroelectric capacitor. A silicon o~:idation layer 4 is formed on a silicon substrate 2. A lower electrode 6 made of platinum is provided thereon. A PZT (PbZr~ Til_~_ Oj) film 8 as a ferroelectric layer is formed on the lower electrode 6, and an upper electrode 10 made of platinum is provided thereon.
Thus, the ferroelectric capacitor is formed by the lower electrode 6, the PZT fi1_m 8 and the upper electrode 10.
The reason to u~;Ee platinum for the lower electrode 6 is as follows. The PZT i=ilm 8 must be formed on a layer which can be oriented, because the ferroelectricity of PZT
is degraded when the PZ'7, film is formed on a layer made of amorphous material, since the PZT film cannot be oriented.
Meanwhile, the lower electrode 6 must be insulated from the silicon substrate 2, therefore, the silicon oxidation layer 4 is formed on the silicon substrate 2. The silicon oxidation layer 4 is amorphous. In general, although a layer formed on an amorphous material becomes nonorientable, a layer made of platinum has a characteristic of becoming orientable even when it is formed on the amorphous matex-ial.
Therefore, platinum is used for forming the lower electrode because of the reason dc~;~cribed above.
However, the con~rentional ferroelectric capacitor has the following problf~m to be resolved.
The problem is degradation of ferroelectricity 3~~ caused by frequent rove=rsion of polarization, aging and leakage of oxygen from t:he ferroelectric substance (PZT), since platinum has a tendency of allowing oxygen and Pb to pass through it. In other words, there is high probability of leakage of oxygen and Pb contained in the ferroelectric substance between the cclumnar crystals of platinum, as shown in Fig. 11. The ~:roblem also arises in a capacitor using a dielectric substance having high dielectric constant.
Disclosure of the present invention It is an object of the present invention to provide a ferroelectric capacitor having less degradation of ferroelectricity caused by frequent inversion of polarization and aging or. a dielectric capacitor maintaining high dielectric constant., both of which resolve the problem described in the above.
The word "capacitor" in the present invention defines structure havinct electrodes on both sides of an insulator, also it is a concept having the structure stated in the above regardless of whether it is used for electric storage.
In accordance wi.t:h a first embodiment of the invention, a ferroelect~~_Lc capacitor comprises:
a lower e.lectrocle having an oxidation layer including at least one 7_ayer selected from a WOx layer, a TiOx layer, a TaOx layer, an IrO, layer, a PtO, layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer, a dielectric lager comprising either a ferroelectric substance or a dielectric substance having a high dielectric constant, the dielectric layer being formed on the lower.
electrode, and an upper electrode formed on the dielectric layer.
By providing the lower electrode with at least one oxidation layer selected from a WOx layer, a TiOx layer, a TaOx layer, an Ir02 layer, a Pt0-. Layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer, it is possible to prevent leakage of o:~ygen from the dielectric layer <~s well as suppressing degradation of ferroelectricity by aging.
Preferably, the lower electrode comprises a conductive layer which includes at least one layer selected from a W layer, a Ti layer, a Ta layer, an Ir layer, a Pt layer, an Ru layer, an ~.e layer, a Pd layer and an Os layer on the oxidation layer, and a ferroelectric layer is formed on the conductive layer.
More preferably, the lower electrode is formed on a silicon oxidation layer located on a substrate, and the lower electrode has a cc>ntact layer in contact with the silicon oxidation layer.
By providing the lower electrode with a conductive layer which includes at. least one layer selected from a W
layer, a Ti layer, a T<~ ,'~ayer, an Ir layer, a Pt layer, an Ru layer, an Re layer, a Pd layer and an Os layer on the oxidation layer and providing a ferroelectric layer on the conductive layer, leakage current can be decreased.
In accordance wi.t;h a second embodiment of the invention, a ferroelectric capacitor comprises:
a lower electrode, a dielectric lager comprising either a ferroelectric substance or a dielect:r:_c substance having a high dielectric constant, the dielectric: layer being formed on the lower-electrode, and an upper electrode formed on the dielectric layer and including at least one layer selected from a WOx layer, a TiOx layer, a TaOx la;rer, an IrO,, layer, a PtO~ layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx laye r.
By providing the upper electrode with at least one oxidation layer selected from a WOx layer, a TiOx layer,. a TaOx layer, an IrO~ layer, a Pt0= layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer, it is possible to prevent leakage of oxygen from the dielectric layer as well as suppressing degradation of ferroelectricity by aging.
Preferably, the lower electrode is formed on a silicon oxidation layer located on a substrate, and the lower electrode has a contact layer in contact with the silicon oxidation layer.
In accordance with a third embodiment of the invention, a ferroelectric capacitor comprises:
a lower e:Lectrode having an oxidation layer including at least one 1_ayer selected from a WOx layer, a TiOx layer, a TaOx layer,. an IrO, layer, a PtO> layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer, a dielectric la~~er comprising either a ferroelect:ric substance or a dielectric substance having a high dielectric constant, the dielectric: layer being formed on the lower electrode, and an upper electrode having an oxidation layer including at least one 7_ayer selected from a WOx layer, a TiOx layer, a TaOx layer, an IrO, layer, a PtOlayer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer.
By providing both the upper and the lower electrode with at least one oxidation layer selected from a WOx layer, a TiOx layer, a TaOx lays=_r, an IrO, layer, a PtO~ layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer, it is possible to prevemr_ leakage of oxygen from the dielectric layer as wel=L as suppressing degradation of ferroelectricity by aging.
Preferably, the lower electrode comprises a 3~ conductive layer which :includes at least one layer seler_ted from a W layer, a Ti las~~~r, a Ta layer, an Ir layer, a I?t layer, an Ru layer, an Re layer, a Pd layer and an Os layer on the oxidation layer, and a ferroelectric layer is formed on the conductive layer-.
More preferably, the lower electrode is formed on a 5 silicon oxidation layer Located on a substrate, and the lower electrode has a cc>ntact layer in contact with the silicon oxidation layer.
By providing at least one layer selected from a W
layer, a Ti layer, a Ta 7_ayer, an Ir layer, a Pt layer, an Ru layer, an Re layer, ~~ Pd layer and an Os layer on the oxidation layer and providing a dielectric layer on the conductive layer, leakage current can be decreased.
Thus, in accordance with the invention, a ferroelectric capacitor which offers excellent ferroelectricity and h:ic~h dielectric property is attainable.
In accordance wi.t;h a further aspect of the invention, a method of manufacturing a ferroelectric capacitor comprises the :steps of:
forming at least: one oxidation layer selected from a WOx layer, a TiOx layer, a TaOx layer, an IrO~ layer, a Pt~O
layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer on a substrat;f=_ as a lower electrode by sputtering, forming either ~i ferroelectric film or a dielectric layer having a high die=Lc=ctric constant on the lower electrode as a dielectr_Lc layer, and forming an upper electrode on the dielectric layer.
In accordance wit=h a second method embodiment of: the invention, a method of manufacturing a ferroelectric capacitor comprises the ;steps of:
3~ forming at least: one layer selected from a W layer, a Ti layer, a Ta layer, an Ir layer, a Pt layer, an Ru layer, an Re layer, a Pd layer and. an Os layer on a substrate as a base layer by sputtering, oxidizing a surface of the base layer, forming either a ferroelectric film or a dielectric layer having a high dielectric constant on the base layer as a dielectric layer, a surface of the base layer being oxidized, and forming an upper electrode on the dielectric layer.
In accordance with a third method embodiment of the invention, a method of manufacturing a ferroelectric capacitor comprises the :steps of:
forming either a. ferroelectric film or a dielectric layer having a high dielectric constant on a lower electrode as a dielectric layer, dTld forming at least. one oxidation layer selected from a WOx layer, a TiOx layer, a TaOx layer, an IrO~ layer, a Pt=O
layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer on the dielectric layer as an upper electrode by sputtering.
In accordance wi.t:h a fourth method embodiment of the invention, a method of r:ranufacturing a ferroelectric capacitor comprises the :steps of:
forming a lower electrode on a substrate, forming either a ferroelectric film or a dielectric layer having a high dielectric constant on the lower electrode as a dielectric layer, forming at lea:~t; one layer selected from a W layer, a Ti layer, a Ta layer, <~n Ir layer, a Pt layer, an Ru layer, an Re layer, a Pc3 layer and an Os layer on the dielectric layer as a base layer by sputtering, and oxidizing a surface of the base layer.
In accordance w~t:h a fifth method embodiment of the invention, a method of manufacturing a ferroelectric capacitor comprises the steps of:
forming at least: one layer selected from a W layer, a Ti layer, a Ta layer, an Ir layer, a Pt layer, an Ru layer, an Re layer, a F?ct layer and an Os layer on a substrate as a base layer by sputtering, forming at least one layer selected from a W layer, a Ti layer, a Ta layer, an Ir layer, a Pt layer, an Ru layer, an Re layer, a Pd layer and an Os layer on a surface of the base layer as a conductive layer, forming a thin conductive :Layer on a surface of the conductive layer and oxidizing the conductive layer on the surface of which 1S COVE'7=ed with the thin conductive layer, forming either a ferroelectric film or a dielectric layer having a high die7_ectric constant on the conductiz~e layer as a dielectric l~~;rer, the conductive layer being oxidized, and forming an upper electrode on the dielectric layer.
Preferably, the step of oxidization is carried out within the step of form,'~ng the dielectric layer.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a view showing the structure of a ferroelectric capacitor :in an embodiment of the present invention.
Fig. 2 is a diagram showing a nonvolatile memory using a ferroelectric c<~pacitor 22.
Fig. 3A, Fig. 3F3,, Fig. 3C and Fig. 3D show successive stages in the fabrication of the ferroelectric 3C capacitor.
Fig. 4 is a view showing the structure of the ferroelectric capacitor when a contact layer 30 is provided.
Fig. 5 is a view showing the structure of the ferroelectric capacitor when a dielectric layer 90 having 3~, high dielectric constant is provided.
Fig. 6 is a view showing the structure of a ferroelectric capacitor in another embodiment of the present invention.
Fig. 7 illustrates the mechanism whereby the palladium oxidation layer prevents leakage of oxygen from the ferroelectric film.
Fig. 8A, Fig. f.3B, Fig. 8C and Fig. 8D are flow charts showing manufactux-ing processes of the ferroelectr.ic capacitor shown in Fig. E>.
Fig. 9 is a view showing another embodiment of the present invention that carries out oxidation of palladium after forming a thin plat:inum layer.
Fig. 10 is a view showing the structure of a ferroelectric capacitor in the prior art.
Fig. 11 is a view showing leakage of oxygen through the lower electrode 6 mace of platinum.
THE BEST MODE OF PREFERRED EMBODIMENT
TO CARRY OUT THE PRESENT INVENTION
Fig. 1 shows the structure of a ferroelectric capacitor fabricated in accordance with a first embodiment of the present invention.. In the ferroelectric capacitor, a silicon oxidation layer 4, a lower electrode 12, a ferroelectric film (ferroelectric layer) 8 and an upper electrode 15 are formed on a silicon substrate 2. The lower electrode 12 is made of palladium oxide (PdOx), and the upper electrode 15 is a~_so formed by palladium oxide (PdOx).
As shown in Fig. 11 which illustrates the conventional ferroelectric capacitor, oxygen contained i.n the ferroelectric film 8 passes through the platinum layer 6 having columnar crystal:. Palladium oxide is used for t:he lower electrode 12 in the present embodiment. Since the palladium oxide layer la? does not have columnar crystal:, it is hard for the oxygen t:o pass through it. Therefore, shortage of oxygen in the ferroelectric film 8 can be prevented. Shortage of oxygen can also be prevented by the upper electrode 15 which does not have columnar crystal~~.
Thus, the ferroelectric_Li~y of the ferroelectric film 8 is improved. Remarkable irnprovement of ferroelectricity degradation caused by u~,e of remanent polarization Pr is observed when either of_ t:he upper electrode 15 or the lower electrode 12 is made of_ palladium oxide in comparison with when either one of the electrodes is composed of platinum.
Since both of th.e lower electrode 12 and the upper electrode 15 are made of: palladium oxide in the embodiment described above, the electrodes made of palladium oxide ensure prevention of leakage of oxygen and Pb. Certain prevention of leakage can be expected when either of the electrodes is made of palladium oxide.
The ferroelectric~ capacitor described above can be used for a nonvolatile memory when it is combined with a transistor 24 as shown in Fig. 2.
Fig. 3A, Fig. 38, Fig. 3C and Fig. 3D show successive stages in the fabrication of a ferroelectric capacitor according to t:he present invention. A silicon oxidation layer 4 is foz~med by carrying out thermal oxidation of a surface of the silicon substrate 2 (Fig. 3.A).
In this embodiment, the :silicon oxidation layer 4 is formed with a thickness of 600 nm. A palladium oxide formed on the silicon oxide layer 4 bar reactive sputtering method using palladium as a target i;~ defined as the lower electrode 12 (Fig. 3B). The lower a:'~ectrode 12 is formed with a thickness of 200 nm.
A PZT film is formed on the lower electrode 12 as the ferroelectric film f3 by sol-gel method (Fig. 3C). A
mixed solution of Pb (CH-:COO) ,~3H~0, 2r (t-OC9H5) ,~ and Ti (i-OC3H~) 4 is used as a starter. The mixed solution i~;
dried at a temperature o.f 150 °C (hereinafter indicated in Celsius) after carrying ~~ut spin coating, then pre-baking is carried out at a tempera~ure of 400 °C for 30 seconds under dried air atmosphere. ~fhermal treatment at a temperature over 700 °C is carried out under O, atmosphere after carrzring out the processes descr:i:oed for 5 times. Thus, the 3= ferroelectric film 8 having a thickness of 250 nm is formed.
In this embodiment, the PZT film is formed at a ratio of x equals 0.52 in PbZruTi_.,0; (hereinafter the material is indicated as PZT (52 ~ 48)).
Further, a layer of palladium oxide is formed on. the ferroelectric film as the upper electrode 15 by reactive sputtering method (Fig. 3D). The upper electrode 15 is 5 formed with a thickness of 200 nm. Thus, the ferroelect.ric capacitor is completed. Any one of WOx, TiOx, TaOx, IrO~~, Pt02, ReOx, RuOx, OsOx can be used for the palladium oxide.
In the case of forming a layer made of ferroelect:ric substance on one of the oxidation layers, orientation of the 10 ferroelectric substance is degraded. In order to maintain the orientation, the lager made of ferroelectric substance can be formed on a conductive layer formed on the oxidation layer. The conductive 7_ayer may be selected from of at least one of the following: a W layer, a Ti layer, a Ta layer, an Ir layer, a Pt: layer, an Ru layer, an Re layer, an Os layer and the like. Further, leakage of the ferroelectric substance can be decreased by providing the conductive layer.
Fig. 4 shows they structure of a ferroelectric capacitor fabricated in accordance with another embodiment of the present invention. In this embodiment, a layer made of titanium (having a thickness of 5 nm) is provided between the lower electrode 12 c~Tld the silicon oxidation layer 9: as a contact layer 30. In general, palladium oxide and silicon oxide do not contact t:ic~htly with each other. Therefore, there is a probability of degradation of ferroelectricit:y occurring due to partia7_ delamination of a layer consisting of an alloy of palladium oxide and silicon oxide. To resolve the degradation, the titanium layer 30 which can be contacted tightly with t:he silicon oxide layer 4 is provided in this embodiment, so that the ferroelectricity is improved. The titanium .Layer can be formed by sputtering.
Although the titanium layer is used as the contact layer 30 in the embodiment described above, any other materials which improve contact can be utilized. For instance, a layer made of platinum can be used for the contact layer.
Background art Fig. 10 shows a conventional ferroelectric capacitor. A silicon o~:idation layer 4 is formed on a silicon substrate 2. A lower electrode 6 made of platinum is provided thereon. A PZT (PbZr~ Til_~_ Oj) film 8 as a ferroelectric layer is formed on the lower electrode 6, and an upper electrode 10 made of platinum is provided thereon.
Thus, the ferroelectric capacitor is formed by the lower electrode 6, the PZT fi1_m 8 and the upper electrode 10.
The reason to u~;Ee platinum for the lower electrode 6 is as follows. The PZT i=ilm 8 must be formed on a layer which can be oriented, because the ferroelectricity of PZT
is degraded when the PZ'7, film is formed on a layer made of amorphous material, since the PZT film cannot be oriented.
Meanwhile, the lower electrode 6 must be insulated from the silicon substrate 2, therefore, the silicon oxidation layer 4 is formed on the silicon substrate 2. The silicon oxidation layer 4 is amorphous. In general, although a layer formed on an amorphous material becomes nonorientable, a layer made of platinum has a characteristic of becoming orientable even when it is formed on the amorphous matex-ial.
Therefore, platinum is used for forming the lower electrode because of the reason dc~;~cribed above.
However, the con~rentional ferroelectric capacitor has the following problf~m to be resolved.
The problem is degradation of ferroelectricity 3~~ caused by frequent rove=rsion of polarization, aging and leakage of oxygen from t:he ferroelectric substance (PZT), since platinum has a tendency of allowing oxygen and Pb to pass through it. In other words, there is high probability of leakage of oxygen and Pb contained in the ferroelectric substance between the cclumnar crystals of platinum, as shown in Fig. 11. The ~:roblem also arises in a capacitor using a dielectric substance having high dielectric constant.
Disclosure of the present invention It is an object of the present invention to provide a ferroelectric capacitor having less degradation of ferroelectricity caused by frequent inversion of polarization and aging or. a dielectric capacitor maintaining high dielectric constant., both of which resolve the problem described in the above.
The word "capacitor" in the present invention defines structure havinct electrodes on both sides of an insulator, also it is a concept having the structure stated in the above regardless of whether it is used for electric storage.
In accordance wi.t:h a first embodiment of the invention, a ferroelect~~_Lc capacitor comprises:
a lower e.lectrocle having an oxidation layer including at least one 7_ayer selected from a WOx layer, a TiOx layer, a TaOx layer, an IrO, layer, a PtO, layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer, a dielectric lager comprising either a ferroelectric substance or a dielectric substance having a high dielectric constant, the dielectric layer being formed on the lower.
electrode, and an upper electrode formed on the dielectric layer.
By providing the lower electrode with at least one oxidation layer selected from a WOx layer, a TiOx layer, a TaOx layer, an Ir02 layer, a Pt0-. Layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer, it is possible to prevent leakage of o:~ygen from the dielectric layer <~s well as suppressing degradation of ferroelectricity by aging.
Preferably, the lower electrode comprises a conductive layer which includes at least one layer selected from a W layer, a Ti layer, a Ta layer, an Ir layer, a Pt layer, an Ru layer, an ~.e layer, a Pd layer and an Os layer on the oxidation layer, and a ferroelectric layer is formed on the conductive layer.
More preferably, the lower electrode is formed on a silicon oxidation layer located on a substrate, and the lower electrode has a cc>ntact layer in contact with the silicon oxidation layer.
By providing the lower electrode with a conductive layer which includes at. least one layer selected from a W
layer, a Ti layer, a T<~ ,'~ayer, an Ir layer, a Pt layer, an Ru layer, an Re layer, a Pd layer and an Os layer on the oxidation layer and providing a ferroelectric layer on the conductive layer, leakage current can be decreased.
In accordance wi.t;h a second embodiment of the invention, a ferroelectric capacitor comprises:
a lower electrode, a dielectric lager comprising either a ferroelectric substance or a dielect:r:_c substance having a high dielectric constant, the dielectric: layer being formed on the lower-electrode, and an upper electrode formed on the dielectric layer and including at least one layer selected from a WOx layer, a TiOx layer, a TaOx la;rer, an IrO,, layer, a PtO~ layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx laye r.
By providing the upper electrode with at least one oxidation layer selected from a WOx layer, a TiOx layer,. a TaOx layer, an IrO~ layer, a Pt0= layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer, it is possible to prevent leakage of oxygen from the dielectric layer as well as suppressing degradation of ferroelectricity by aging.
Preferably, the lower electrode is formed on a silicon oxidation layer located on a substrate, and the lower electrode has a contact layer in contact with the silicon oxidation layer.
In accordance with a third embodiment of the invention, a ferroelectric capacitor comprises:
a lower e:Lectrode having an oxidation layer including at least one 1_ayer selected from a WOx layer, a TiOx layer, a TaOx layer,. an IrO, layer, a PtO> layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer, a dielectric la~~er comprising either a ferroelect:ric substance or a dielectric substance having a high dielectric constant, the dielectric: layer being formed on the lower electrode, and an upper electrode having an oxidation layer including at least one 7_ayer selected from a WOx layer, a TiOx layer, a TaOx layer, an IrO, layer, a PtOlayer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer.
By providing both the upper and the lower electrode with at least one oxidation layer selected from a WOx layer, a TiOx layer, a TaOx lays=_r, an IrO, layer, a PtO~ layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer, it is possible to prevemr_ leakage of oxygen from the dielectric layer as wel=L as suppressing degradation of ferroelectricity by aging.
Preferably, the lower electrode comprises a 3~ conductive layer which :includes at least one layer seler_ted from a W layer, a Ti las~~~r, a Ta layer, an Ir layer, a I?t layer, an Ru layer, an Re layer, a Pd layer and an Os layer on the oxidation layer, and a ferroelectric layer is formed on the conductive layer-.
More preferably, the lower electrode is formed on a 5 silicon oxidation layer Located on a substrate, and the lower electrode has a cc>ntact layer in contact with the silicon oxidation layer.
By providing at least one layer selected from a W
layer, a Ti layer, a Ta 7_ayer, an Ir layer, a Pt layer, an Ru layer, an Re layer, ~~ Pd layer and an Os layer on the oxidation layer and providing a dielectric layer on the conductive layer, leakage current can be decreased.
Thus, in accordance with the invention, a ferroelectric capacitor which offers excellent ferroelectricity and h:ic~h dielectric property is attainable.
In accordance wi.t;h a further aspect of the invention, a method of manufacturing a ferroelectric capacitor comprises the :steps of:
forming at least: one oxidation layer selected from a WOx layer, a TiOx layer, a TaOx layer, an IrO~ layer, a Pt~O
layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer on a substrat;f=_ as a lower electrode by sputtering, forming either ~i ferroelectric film or a dielectric layer having a high die=Lc=ctric constant on the lower electrode as a dielectr_Lc layer, and forming an upper electrode on the dielectric layer.
In accordance wit=h a second method embodiment of: the invention, a method of manufacturing a ferroelectric capacitor comprises the ;steps of:
3~ forming at least: one layer selected from a W layer, a Ti layer, a Ta layer, an Ir layer, a Pt layer, an Ru layer, an Re layer, a Pd layer and. an Os layer on a substrate as a base layer by sputtering, oxidizing a surface of the base layer, forming either a ferroelectric film or a dielectric layer having a high dielectric constant on the base layer as a dielectric layer, a surface of the base layer being oxidized, and forming an upper electrode on the dielectric layer.
In accordance with a third method embodiment of the invention, a method of manufacturing a ferroelectric capacitor comprises the :steps of:
forming either a. ferroelectric film or a dielectric layer having a high dielectric constant on a lower electrode as a dielectric layer, dTld forming at least. one oxidation layer selected from a WOx layer, a TiOx layer, a TaOx layer, an IrO~ layer, a Pt=O
layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer on the dielectric layer as an upper electrode by sputtering.
In accordance wi.t:h a fourth method embodiment of the invention, a method of r:ranufacturing a ferroelectric capacitor comprises the :steps of:
forming a lower electrode on a substrate, forming either a ferroelectric film or a dielectric layer having a high dielectric constant on the lower electrode as a dielectric layer, forming at lea:~t; one layer selected from a W layer, a Ti layer, a Ta layer, <~n Ir layer, a Pt layer, an Ru layer, an Re layer, a Pc3 layer and an Os layer on the dielectric layer as a base layer by sputtering, and oxidizing a surface of the base layer.
In accordance w~t:h a fifth method embodiment of the invention, a method of manufacturing a ferroelectric capacitor comprises the steps of:
forming at least: one layer selected from a W layer, a Ti layer, a Ta layer, an Ir layer, a Pt layer, an Ru layer, an Re layer, a F?ct layer and an Os layer on a substrate as a base layer by sputtering, forming at least one layer selected from a W layer, a Ti layer, a Ta layer, an Ir layer, a Pt layer, an Ru layer, an Re layer, a Pd layer and an Os layer on a surface of the base layer as a conductive layer, forming a thin conductive :Layer on a surface of the conductive layer and oxidizing the conductive layer on the surface of which 1S COVE'7=ed with the thin conductive layer, forming either a ferroelectric film or a dielectric layer having a high die7_ectric constant on the conductiz~e layer as a dielectric l~~;rer, the conductive layer being oxidized, and forming an upper electrode on the dielectric layer.
Preferably, the step of oxidization is carried out within the step of form,'~ng the dielectric layer.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a view showing the structure of a ferroelectric capacitor :in an embodiment of the present invention.
Fig. 2 is a diagram showing a nonvolatile memory using a ferroelectric c<~pacitor 22.
Fig. 3A, Fig. 3F3,, Fig. 3C and Fig. 3D show successive stages in the fabrication of the ferroelectric 3C capacitor.
Fig. 4 is a view showing the structure of the ferroelectric capacitor when a contact layer 30 is provided.
Fig. 5 is a view showing the structure of the ferroelectric capacitor when a dielectric layer 90 having 3~, high dielectric constant is provided.
Fig. 6 is a view showing the structure of a ferroelectric capacitor in another embodiment of the present invention.
Fig. 7 illustrates the mechanism whereby the palladium oxidation layer prevents leakage of oxygen from the ferroelectric film.
Fig. 8A, Fig. f.3B, Fig. 8C and Fig. 8D are flow charts showing manufactux-ing processes of the ferroelectr.ic capacitor shown in Fig. E>.
Fig. 9 is a view showing another embodiment of the present invention that carries out oxidation of palladium after forming a thin plat:inum layer.
Fig. 10 is a view showing the structure of a ferroelectric capacitor in the prior art.
Fig. 11 is a view showing leakage of oxygen through the lower electrode 6 mace of platinum.
THE BEST MODE OF PREFERRED EMBODIMENT
TO CARRY OUT THE PRESENT INVENTION
Fig. 1 shows the structure of a ferroelectric capacitor fabricated in accordance with a first embodiment of the present invention.. In the ferroelectric capacitor, a silicon oxidation layer 4, a lower electrode 12, a ferroelectric film (ferroelectric layer) 8 and an upper electrode 15 are formed on a silicon substrate 2. The lower electrode 12 is made of palladium oxide (PdOx), and the upper electrode 15 is a~_so formed by palladium oxide (PdOx).
As shown in Fig. 11 which illustrates the conventional ferroelectric capacitor, oxygen contained i.n the ferroelectric film 8 passes through the platinum layer 6 having columnar crystal:. Palladium oxide is used for t:he lower electrode 12 in the present embodiment. Since the palladium oxide layer la? does not have columnar crystal:, it is hard for the oxygen t:o pass through it. Therefore, shortage of oxygen in the ferroelectric film 8 can be prevented. Shortage of oxygen can also be prevented by the upper electrode 15 which does not have columnar crystal~~.
Thus, the ferroelectric_Li~y of the ferroelectric film 8 is improved. Remarkable irnprovement of ferroelectricity degradation caused by u~,e of remanent polarization Pr is observed when either of_ t:he upper electrode 15 or the lower electrode 12 is made of_ palladium oxide in comparison with when either one of the electrodes is composed of platinum.
Since both of th.e lower electrode 12 and the upper electrode 15 are made of: palladium oxide in the embodiment described above, the electrodes made of palladium oxide ensure prevention of leakage of oxygen and Pb. Certain prevention of leakage can be expected when either of the electrodes is made of palladium oxide.
The ferroelectric~ capacitor described above can be used for a nonvolatile memory when it is combined with a transistor 24 as shown in Fig. 2.
Fig. 3A, Fig. 38, Fig. 3C and Fig. 3D show successive stages in the fabrication of a ferroelectric capacitor according to t:he present invention. A silicon oxidation layer 4 is foz~med by carrying out thermal oxidation of a surface of the silicon substrate 2 (Fig. 3.A).
In this embodiment, the :silicon oxidation layer 4 is formed with a thickness of 600 nm. A palladium oxide formed on the silicon oxide layer 4 bar reactive sputtering method using palladium as a target i;~ defined as the lower electrode 12 (Fig. 3B). The lower a:'~ectrode 12 is formed with a thickness of 200 nm.
A PZT film is formed on the lower electrode 12 as the ferroelectric film f3 by sol-gel method (Fig. 3C). A
mixed solution of Pb (CH-:COO) ,~3H~0, 2r (t-OC9H5) ,~ and Ti (i-OC3H~) 4 is used as a starter. The mixed solution i~;
dried at a temperature o.f 150 °C (hereinafter indicated in Celsius) after carrying ~~ut spin coating, then pre-baking is carried out at a tempera~ure of 400 °C for 30 seconds under dried air atmosphere. ~fhermal treatment at a temperature over 700 °C is carried out under O, atmosphere after carrzring out the processes descr:i:oed for 5 times. Thus, the 3= ferroelectric film 8 having a thickness of 250 nm is formed.
In this embodiment, the PZT film is formed at a ratio of x equals 0.52 in PbZruTi_.,0; (hereinafter the material is indicated as PZT (52 ~ 48)).
Further, a layer of palladium oxide is formed on. the ferroelectric film as the upper electrode 15 by reactive sputtering method (Fig. 3D). The upper electrode 15 is 5 formed with a thickness of 200 nm. Thus, the ferroelect.ric capacitor is completed. Any one of WOx, TiOx, TaOx, IrO~~, Pt02, ReOx, RuOx, OsOx can be used for the palladium oxide.
In the case of forming a layer made of ferroelect:ric substance on one of the oxidation layers, orientation of the 10 ferroelectric substance is degraded. In order to maintain the orientation, the lager made of ferroelectric substance can be formed on a conductive layer formed on the oxidation layer. The conductive 7_ayer may be selected from of at least one of the following: a W layer, a Ti layer, a Ta layer, an Ir layer, a Pt: layer, an Ru layer, an Re layer, an Os layer and the like. Further, leakage of the ferroelectric substance can be decreased by providing the conductive layer.
Fig. 4 shows they structure of a ferroelectric capacitor fabricated in accordance with another embodiment of the present invention. In this embodiment, a layer made of titanium (having a thickness of 5 nm) is provided between the lower electrode 12 c~Tld the silicon oxidation layer 9: as a contact layer 30. In general, palladium oxide and silicon oxide do not contact t:ic~htly with each other. Therefore, there is a probability of degradation of ferroelectricit:y occurring due to partia7_ delamination of a layer consisting of an alloy of palladium oxide and silicon oxide. To resolve the degradation, the titanium layer 30 which can be contacted tightly with t:he silicon oxide layer 4 is provided in this embodiment, so that the ferroelectricity is improved. The titanium .Layer can be formed by sputtering.
Although the titanium layer is used as the contact layer 30 in the embodiment described above, any other materials which improve contact can be utilized. For instance, a layer made of platinum can be used for the contact layer.
Though the PZT film is used as the ferroelectric film 8 in the embodiment. described above, any other materials can be utilized as long as the materials are ferroelectric _oxide. For_ instance, Ba~Ti~O,., can be used for the ferroelectric film.
Fig. 5 shows the structure of a ferroelectric capacitor fabricated in accordance with yet another embodiment of the present; invention. A dielectric layer 90 having high dielectric constant is used for the ferroelectric film 8 in this embodiment. The lower electrode 12 made of pa7_ladium oxide is provided on the silicon oxide layer 4, and a high dielectric thin film made of SrTi03, (Sr, Ba)TiO, having perovskite structure is formed thereon as the dielectric layer 90. In this embodiment, ferroelectricity is improved in the same manner as in the embodiment using the ferroelectric substance. In other words, it is clear that t=he advantages offered by using the ferroelectric layer can also be obtained by utilizing a dielectric layer having high dielectric constant.
Fig. 6 shows the structure of a ferroelectric capacitor fabricated in accordance with yet another embodiment of the present invention. In this embodiment, the silicon oxidation layer 4, the lower electrode 12, t:he ferroelectric film (ferroelectric layer) 8 and the upper electrode 15 are provided on the silicon substrate 2. The lower electrode 12 cons_Lsts of a palladium layer 11 and a palladium oxide layer 13 formed thereon. Also, the upper electrode 15 consists o:= a palladium layer 7 and a palladium oxide layer 9 formed thf=_:reon.
3C Fig. 7 is an en~-urged view of the vicinity of the lower electrode 12. Since the palladium layer 11 has columnar crystals, the oxygen contained in the ferroelectric film 8 passes through the palladium layer 11. A palladium oxide layer 13 is formed on the upper surface of the 3~, palladium layer 11 in this embodiment. Therefore, it i;~
possible to prevent shortage of oxygen contained in the ferroelectric film 8 by forming the palladium oxide layer 13 as described above. The upper electrode 15 obtains the same advantage which the lowe~x~ electrode 12 offers as described above.
Since both of th.e palladium oxide layers are formed in the lower electrode 1.2. and the upper electrode 15 respectively in this embodiment, it is possible to obtain a ferroelectric capacitor having excellent ferroelectricity as well as having less in:~Luences of aging. Certain advantages as described above can be observed when either of the lower electrode 12 or the uppE:r electrode 15 is formed by the structure described abov=e .
Fig. 8A, Fig. BE~, Fig. 8C and Fig. 8D show successive stages in thE> fabrication of the ferroelectri.c capacitor described above. The silicon oxidation layer 4 is formed by carrying out thermal oxidation of a surface of the silicon substrate 2 (Fic~. 8A). In this embodiment, the silicon oxidation layer 4 is formed with a thickness of 600 nm. The palladium oxide layer 11 is formed on the silicon oxide layer 4 by utilizing palladium as a target (Fig. 8B).
The palladium oxide layE~r_ 13 is formed by carrying out a thermal treatment at a temperature of 800 °C for one minute under OZatmosphere. 'fhc~ palladium layer 11 and the palladium layer 13 thus formed are defined as the lower electrode 12. The lower electrode 12 is formed with a thickness of 200 nm.
A PZT film is formed on the lower electrode 12 as the ferroelectric film f3 by sol-gel method (Fig. 8C). A
mixed solution of Pb (CH:C.'00) ~~3H,0, Zr (t-OC4H5) ~ and Ti(i-OC3H~)9 is used as a starter. The mixed solution i~~
dried at a temperature o:E 150 °C (hereinafter indicated in celsius) after carrying out spin coating, then pre-baking is carried out at a temperature of 400 °C for 30 seconds under dried air atmosphere. ~Clzermal treatment at a temperatux-e over 700 °C is carried out under O: atmosphere after carrying out the processes descr_i.bed above for 5 times. Thus, the ferroelectric film 8 having a thickness of 250 nm is formed.
In this embodiment, the :PZT film is formed at a ratio of x equals 0.52 in PbZr~ Tii_h O, (hereinafter the material i~;
indicated as PZT (52 ~ 48)).
Further, the palladium 7 is formed on the ferroelectric film 8 by sputtering method. Then, the palladium oxide layer 9 is formed on a surface of the palladium layer 7 by carrying out a thermal treatment at, a temperature of 800 °C for one minute under O;, atmosphere (Fig. 8D). The palladium layer 7 and the palladium oxide layer 9 thus formed are defined as the upper electrode 1.5.
The upper electrode 15 i;~ formed with a thickness of 200 nm.
Thus, the ferroelectric capacitor is completed.
It is also preferable to form the contact layer 30 in the ferroelectric capacitor as described in Fig. 4.
The process which oxidizes a surface of the palladium described above can be applied not only to the ferroelectric film, but also to the dielectric layer having high dielectric constant: described above, so that the same advantages can be expected.
As described above, though leakage of oxygen can be prevented by oxidizing t~lze surface of the palladium layer, orientation of the ferroE=lectric layer is degraded by formation of the pallad_i.um oxide on its surface. This problem can be resolved by formation of at least one conductive layer on the palladium oxide layer 13, selected from a W layer, Ti laye,-, Ta layer, Ir layer, Pt layer, Ru layer, Re layer, Os layf=:r or the like, as mentioned above.
The problem can also be :resolved by forming the lower electrode as follows.
At first, a plat~:inum layer 80 (thin film conductive substance) is formed very thinly on the palladium layer 11 as shown in Fig. 9. The platinum layer 80 is formed in a.
thickness of 30 nm. Ths=reafter, a thermal treatment is carried out. The platinum layer is not oxidized because the platinum layer 80 exposed on the surface does not react to 3~~ oxygen. Also, leakage of oxygen is shut out by formation of palladium oxygen between crystals of the palladium layer 11 located under the plat.i:num layer 80 as a result of oxidization of the crystals, because the platinum layer 80 is formed thinly. Therefore, the lower electrode 12 which can shut out leakage of oxygen whilst maintaining good orientation can be formed.
The palladium :~~~yer 11, being formed the thin platinum layer 80 and trim being oxidized can also be u~>ed as the lower electrode 7_2 by itself. The palladium layer 11 can be used as the conductive layer having good orientation in the embodiment of improving orientation by providing a conductive layer (a pal7_adium layer, a platinum layer and the like) having good or-_Lentation in the palladium layer formed by sputtering.
Also, all of the embodiments described in the above can be applied not only t:o a ferroelectric capacitor using the ferroelectric film but also to a capacitor using a dielectric layer having high dielectric constant. Exactly the same advantage offered by applying the present invention to the ferroelectric fi7_m can be obtained when the present invention is applied to t=he dielectric layer having high dielectric constant.
LVhile the invention has been described in its preferred embodiments, ~t is to be understood that the words which have been used are words of description rather than limitation and that changes within the purview of the appended claims may be rnade without departing from the true scope and spirit of the invention in its broader aspect~~.
Fig. 5 shows the structure of a ferroelectric capacitor fabricated in accordance with yet another embodiment of the present; invention. A dielectric layer 90 having high dielectric constant is used for the ferroelectric film 8 in this embodiment. The lower electrode 12 made of pa7_ladium oxide is provided on the silicon oxide layer 4, and a high dielectric thin film made of SrTi03, (Sr, Ba)TiO, having perovskite structure is formed thereon as the dielectric layer 90. In this embodiment, ferroelectricity is improved in the same manner as in the embodiment using the ferroelectric substance. In other words, it is clear that t=he advantages offered by using the ferroelectric layer can also be obtained by utilizing a dielectric layer having high dielectric constant.
Fig. 6 shows the structure of a ferroelectric capacitor fabricated in accordance with yet another embodiment of the present invention. In this embodiment, the silicon oxidation layer 4, the lower electrode 12, t:he ferroelectric film (ferroelectric layer) 8 and the upper electrode 15 are provided on the silicon substrate 2. The lower electrode 12 cons_Lsts of a palladium layer 11 and a palladium oxide layer 13 formed thereon. Also, the upper electrode 15 consists o:= a palladium layer 7 and a palladium oxide layer 9 formed thf=_:reon.
3C Fig. 7 is an en~-urged view of the vicinity of the lower electrode 12. Since the palladium layer 11 has columnar crystals, the oxygen contained in the ferroelectric film 8 passes through the palladium layer 11. A palladium oxide layer 13 is formed on the upper surface of the 3~, palladium layer 11 in this embodiment. Therefore, it i;~
possible to prevent shortage of oxygen contained in the ferroelectric film 8 by forming the palladium oxide layer 13 as described above. The upper electrode 15 obtains the same advantage which the lowe~x~ electrode 12 offers as described above.
Since both of th.e palladium oxide layers are formed in the lower electrode 1.2. and the upper electrode 15 respectively in this embodiment, it is possible to obtain a ferroelectric capacitor having excellent ferroelectricity as well as having less in:~Luences of aging. Certain advantages as described above can be observed when either of the lower electrode 12 or the uppE:r electrode 15 is formed by the structure described abov=e .
Fig. 8A, Fig. BE~, Fig. 8C and Fig. 8D show successive stages in thE> fabrication of the ferroelectri.c capacitor described above. The silicon oxidation layer 4 is formed by carrying out thermal oxidation of a surface of the silicon substrate 2 (Fic~. 8A). In this embodiment, the silicon oxidation layer 4 is formed with a thickness of 600 nm. The palladium oxide layer 11 is formed on the silicon oxide layer 4 by utilizing palladium as a target (Fig. 8B).
The palladium oxide layE~r_ 13 is formed by carrying out a thermal treatment at a temperature of 800 °C for one minute under OZatmosphere. 'fhc~ palladium layer 11 and the palladium layer 13 thus formed are defined as the lower electrode 12. The lower electrode 12 is formed with a thickness of 200 nm.
A PZT film is formed on the lower electrode 12 as the ferroelectric film f3 by sol-gel method (Fig. 8C). A
mixed solution of Pb (CH:C.'00) ~~3H,0, Zr (t-OC4H5) ~ and Ti(i-OC3H~)9 is used as a starter. The mixed solution i~~
dried at a temperature o:E 150 °C (hereinafter indicated in celsius) after carrying out spin coating, then pre-baking is carried out at a temperature of 400 °C for 30 seconds under dried air atmosphere. ~Clzermal treatment at a temperatux-e over 700 °C is carried out under O: atmosphere after carrying out the processes descr_i.bed above for 5 times. Thus, the ferroelectric film 8 having a thickness of 250 nm is formed.
In this embodiment, the :PZT film is formed at a ratio of x equals 0.52 in PbZr~ Tii_h O, (hereinafter the material i~;
indicated as PZT (52 ~ 48)).
Further, the palladium 7 is formed on the ferroelectric film 8 by sputtering method. Then, the palladium oxide layer 9 is formed on a surface of the palladium layer 7 by carrying out a thermal treatment at, a temperature of 800 °C for one minute under O;, atmosphere (Fig. 8D). The palladium layer 7 and the palladium oxide layer 9 thus formed are defined as the upper electrode 1.5.
The upper electrode 15 i;~ formed with a thickness of 200 nm.
Thus, the ferroelectric capacitor is completed.
It is also preferable to form the contact layer 30 in the ferroelectric capacitor as described in Fig. 4.
The process which oxidizes a surface of the palladium described above can be applied not only to the ferroelectric film, but also to the dielectric layer having high dielectric constant: described above, so that the same advantages can be expected.
As described above, though leakage of oxygen can be prevented by oxidizing t~lze surface of the palladium layer, orientation of the ferroE=lectric layer is degraded by formation of the pallad_i.um oxide on its surface. This problem can be resolved by formation of at least one conductive layer on the palladium oxide layer 13, selected from a W layer, Ti laye,-, Ta layer, Ir layer, Pt layer, Ru layer, Re layer, Os layf=:r or the like, as mentioned above.
The problem can also be :resolved by forming the lower electrode as follows.
At first, a plat~:inum layer 80 (thin film conductive substance) is formed very thinly on the palladium layer 11 as shown in Fig. 9. The platinum layer 80 is formed in a.
thickness of 30 nm. Ths=reafter, a thermal treatment is carried out. The platinum layer is not oxidized because the platinum layer 80 exposed on the surface does not react to 3~~ oxygen. Also, leakage of oxygen is shut out by formation of palladium oxygen between crystals of the palladium layer 11 located under the plat.i:num layer 80 as a result of oxidization of the crystals, because the platinum layer 80 is formed thinly. Therefore, the lower electrode 12 which can shut out leakage of oxygen whilst maintaining good orientation can be formed.
The palladium :~~~yer 11, being formed the thin platinum layer 80 and trim being oxidized can also be u~>ed as the lower electrode 7_2 by itself. The palladium layer 11 can be used as the conductive layer having good orientation in the embodiment of improving orientation by providing a conductive layer (a pal7_adium layer, a platinum layer and the like) having good or-_Lentation in the palladium layer formed by sputtering.
Also, all of the embodiments described in the above can be applied not only t:o a ferroelectric capacitor using the ferroelectric film but also to a capacitor using a dielectric layer having high dielectric constant. Exactly the same advantage offered by applying the present invention to the ferroelectric fi7_m can be obtained when the present invention is applied to t=he dielectric layer having high dielectric constant.
LVhile the invention has been described in its preferred embodiments, ~t is to be understood that the words which have been used are words of description rather than limitation and that changes within the purview of the appended claims may be rnade without departing from the true scope and spirit of the invention in its broader aspect~~.
Claims (15)
1. A ferroelectric capacitor comprising:
a lower electrode having an oxidation layer including at least one layer selected from a WOx layer, a TiOx layer, a TaOx layer, an IrO2 layer, a PtO2 layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer, a dielectric layer comprising either a ferroelectric substance or a dielectric substance having a high dielectric constant, the dielectric: layer being formed on the lower electrode, and an upper electrode formed on the dielectric layer.
a lower electrode having an oxidation layer including at least one layer selected from a WOx layer, a TiOx layer, a TaOx layer, an IrO2 layer, a PtO2 layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer, a dielectric layer comprising either a ferroelectric substance or a dielectric substance having a high dielectric constant, the dielectric: layer being formed on the lower electrode, and an upper electrode formed on the dielectric layer.
2. A ferroelectric capacitor in accordance with claim 1, wherein the lower electrode comprises a conductive layer which includes at least one layer selected from a W layer, a Ti layer, a Ta layer, an Ir layer, a Pt layer, an Ru layer, an Re layer, a Pd layer and an Os layer on the oxidation layer, and wherein a ferroelectric layer is formed on the conductive layer.
3. A ferroelectric capacitance in accordance with claim 1 or claim 2, wherein the lower electrode is formed on a silicon oxidation layer located on a substrate, and wherein the lower electrode has a contact layer in contact with the silicon oxidation layer.
4. A ferroelectric capacitor comprising:
a lower electrode, a dielectric layer comprising either a ferroelectric substance or a dielectric substance having a high dielectric constant, the dielectric layer being formed on the lower electrode, and an upper electrode formed on the dielectric layer and including at least one layer selected from a WOx layer, a TiOx layer, a TaOx layer, an IrO2 layer, a PtO2 layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer.
a lower electrode, a dielectric layer comprising either a ferroelectric substance or a dielectric substance having a high dielectric constant, the dielectric layer being formed on the lower electrode, and an upper electrode formed on the dielectric layer and including at least one layer selected from a WOx layer, a TiOx layer, a TaOx layer, an IrO2 layer, a PtO2 layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer.
5. A ferroelectric capacitor in accordance with claim 4, wherein the lower electrode is formed on a silicon oxidation layer located on a substrate, and wherein the lower electrode has a contact layer in contact with the silicon oxidation layer.
6. A ferroelectric capacitor comprising:
a lower electrode having an oxidation layer including at least one layer selected from a WOx layer, a TiOx layer, a TaOx layer, an IrO2 layer, a PtO2 layer, an RuOx layer, an ReOx layer, a PdOx layers and an OsOx layer, a dielectric layer comprising either a ferroelectric substance or a dielectric substance having a high dielectric constant, the dielectric layer being formed on the lower electrode, and an upper electrode having an oxidation layer including at least one layer selected from a WOx layer, a TiOx layer, a TaOx layer, an IrO2 Layer, a PtO2 layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer.
a lower electrode having an oxidation layer including at least one layer selected from a WOx layer, a TiOx layer, a TaOx layer, an IrO2 layer, a PtO2 layer, an RuOx layer, an ReOx layer, a PdOx layers and an OsOx layer, a dielectric layer comprising either a ferroelectric substance or a dielectric substance having a high dielectric constant, the dielectric layer being formed on the lower electrode, and an upper electrode having an oxidation layer including at least one layer selected from a WOx layer, a TiOx layer, a TaOx layer, an IrO2 Layer, a PtO2 layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer.
7. A ferroelectric capacitor in accordance with claim 6, wherein the lower electrode comprises a conductive layer which includes at least one layer selected from a W layer, a Ti layer, a Ta layer, an Ir layer, a Pt layer, an Ru layer, an Re layer, a Pd layer and an Os layer on the oxidation layer, and wherein a ferroelectric layer is formed on the conductive layer.
8. A ferroelectric capacitor in accordance with claim 6 or claim 7, wherein the lower electrode is formed on a silicon oxidation layer located on a substrate, and wherein the lower electrode has a contact layer in contact with the silicon oxidation layer.
9. A method for manufacturing a ferroelectric capacitor comprising the steps of:
forming at least ones oxidation layer selected from a WOx layer, a TiOx layer, a TaOx layer, an IrO2 layer, a PtO2 layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer on a substrate as a lower electrode by sputtering, forming either a ferroelectric film or a dielectric layer having a high dielectric constant on the lower electrode as a dielectric layer, and forming an upper electrode on the dielectric layer.
forming at least ones oxidation layer selected from a WOx layer, a TiOx layer, a TaOx layer, an IrO2 layer, a PtO2 layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer on a substrate as a lower electrode by sputtering, forming either a ferroelectric film or a dielectric layer having a high dielectric constant on the lower electrode as a dielectric layer, and forming an upper electrode on the dielectric layer.
10. A method of manufacturing a ferroelectric capacitor comprising the steps of:
forming at least one layer selected from a W layer, a Ti layer, a Ta layer, an Ir layer, a Pt layer, an Ru layer, an Re layer, a Pd layer and an Os layer on a substrate as a base layer by sputtering, oxidizing a surface of the base layer, forming either a ferroelectric film or a dielectric layer having a high dielectric constant on the base layer as a dielectric layer, a surface of the base layer being oxidized, and forming an upper electrode on the dielectric layer.
forming at least one layer selected from a W layer, a Ti layer, a Ta layer, an Ir layer, a Pt layer, an Ru layer, an Re layer, a Pd layer and an Os layer on a substrate as a base layer by sputtering, oxidizing a surface of the base layer, forming either a ferroelectric film or a dielectric layer having a high dielectric constant on the base layer as a dielectric layer, a surface of the base layer being oxidized, and forming an upper electrode on the dielectric layer.
11. A method of manufacturing a ferroelectric capacitor comprising the steps of:
forming either a ferroelectric film or a dielectric layer having a high dielectric constant on a lower electrode as a dielectric layer, and forming at least one oxidation layer selected from a WOx layer, a TiOx layer, a TaOx layer, an IrO2 layer, a PtO2 layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer on the dielectric layer as an upper electrode by sputtering.
forming either a ferroelectric film or a dielectric layer having a high dielectric constant on a lower electrode as a dielectric layer, and forming at least one oxidation layer selected from a WOx layer, a TiOx layer, a TaOx layer, an IrO2 layer, a PtO2 layer, an RuOx layer, an ReOx layer, a PdOx layer and an OsOx layer on the dielectric layer as an upper electrode by sputtering.
12. A method of manufacturing a ferroelectric capacitor comprising the steps of:
forming a lower electrode on a substrate, forming either a ferroelectric film or a dielectric layer having a high dielectric constant on the lower electrode as a dielectric layer, forming at least one layer selected from a W layer, a Ti layer, a Ta layer, an it layer, a Pt layer, an Ru layer, an Re layer, a Pd layer and an Os layer on the dielectric layer as a base layer by sputtering, and oxidizing a surface of the base layer.
forming a lower electrode on a substrate, forming either a ferroelectric film or a dielectric layer having a high dielectric constant on the lower electrode as a dielectric layer, forming at least one layer selected from a W layer, a Ti layer, a Ta layer, an it layer, a Pt layer, an Ru layer, an Re layer, a Pd layer and an Os layer on the dielectric layer as a base layer by sputtering, and oxidizing a surface of the base layer.
13. A method of manufacturing a ferroelectric capacitor comprising the steps of:
forming at least one layer selected from a W layer, a Ti layer, a Ta layer, an Ir layer, a Pt layer, an Ru layer, an Re layer, a Pd layer and an Os layer on a substrate as a.
base layer by sputtering, forming at least one layer selected from a W layer, a Ti layer, a Ta layer, an Ir layer, a Pt layer, an Ru layer, an Re layer, a Pd layer and an Os layer on a surface of the base layer as a conductive layer, forming a thin conductive layer on a surface of the conductive layer, oxidizing the conductive layer on the surface of which is covered with the thin conductive layer, forming either a ferroelectric film or a dielectric layer having a high dielectric constant on the conductive layer as a dielectric layer, the conductive layer being oxidized, and forming an upper electrode on the dielectric layer.
forming at least one layer selected from a W layer, a Ti layer, a Ta layer, an Ir layer, a Pt layer, an Ru layer, an Re layer, a Pd layer and an Os layer on a substrate as a.
base layer by sputtering, forming at least one layer selected from a W layer, a Ti layer, a Ta layer, an Ir layer, a Pt layer, an Ru layer, an Re layer, a Pd layer and an Os layer on a surface of the base layer as a conductive layer, forming a thin conductive layer on a surface of the conductive layer, oxidizing the conductive layer on the surface of which is covered with the thin conductive layer, forming either a ferroelectric film or a dielectric layer having a high dielectric constant on the conductive layer as a dielectric layer, the conductive layer being oxidized, and forming an upper electrode on the dielectric layer.
14. A method for manufacturing a ferroelectric capacitor in accordance with claim 10, claim 12 or claim 13, wherein the step of oxidization is carried out within the step of forming the dielectric layer.
15. A method for manufacturing a ferroelectric capacitor in accordance with claim 13, wherein the thin conductive layer is made of Pt.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JPHEI7-172142 | 1995-07-07 | ||
| JP17214295A JP3929513B2 (en) | 1995-07-07 | 1995-07-07 | Dielectric capacitor and manufacturing method thereof |
| PCT/JP1996/001883 WO1997003468A1 (en) | 1995-07-07 | 1996-07-05 | Dielectric capacitor and process for preparing the same |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2197491A1 CA2197491A1 (en) | 1997-01-30 |
| CA2197491C true CA2197491C (en) | 2002-01-01 |
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| Application Number | Title | Priority Date | Filing Date |
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| CA002197491A Expired - Fee Related CA2197491C (en) | 1995-07-07 | 1996-07-05 | Ferroelectric capacitor and method for manufacturing thereof |
Country Status (8)
| Country | Link |
|---|---|
| US (5) | US6454914B1 (en) |
| EP (2) | EP0785579B1 (en) |
| JP (1) | JP3929513B2 (en) |
| KR (1) | KR100385446B1 (en) |
| CN (1) | CN1085411C (en) |
| CA (1) | CA2197491C (en) |
| DE (1) | DE69633554T2 (en) |
| WO (1) | WO1997003468A1 (en) |
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-
1995
- 1995-07-07 JP JP17214295A patent/JP3929513B2/en not_active Expired - Fee Related
-
1996
- 1996-07-05 EP EP96922252A patent/EP0785579B1/en not_active Expired - Lifetime
- 1996-07-05 CA CA002197491A patent/CA2197491C/en not_active Expired - Fee Related
- 1996-07-05 WO PCT/JP1996/001883 patent/WO1997003468A1/en active IP Right Grant
- 1996-07-05 KR KR1019960706383A patent/KR100385446B1/en not_active IP Right Cessation
- 1996-07-05 DE DE69633554T patent/DE69633554T2/en not_active Expired - Fee Related
- 1996-07-05 EP EP04076904A patent/EP1467400A3/en not_active Withdrawn
- 1996-07-05 CN CN96190228A patent/CN1085411C/en not_active Expired - Fee Related
-
1997
- 1997-02-20 US US08/812,059 patent/US6454914B1/en not_active Expired - Lifetime
-
2002
- 2002-08-08 US US10/215,844 patent/US6693791B2/en not_active Expired - Lifetime
-
2003
- 2003-08-29 US US10/651,435 patent/US6873517B2/en not_active Expired - Fee Related
-
2004
- 2004-12-16 US US11/015,082 patent/US7057874B2/en not_active Expired - Fee Related
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- 2006-04-12 US US11/279,495 patent/US7443649B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| WO1997003468A1 (en) | 1997-01-30 |
| US20050098819A1 (en) | 2005-05-12 |
| EP1467400A3 (en) | 2004-10-20 |
| US20020189933A1 (en) | 2002-12-19 |
| EP0785579B1 (en) | 2004-10-06 |
| EP1467400A2 (en) | 2004-10-13 |
| US6873517B2 (en) | 2005-03-29 |
| JPH0922829A (en) | 1997-01-21 |
| US20040036105A1 (en) | 2004-02-26 |
| US7443649B2 (en) | 2008-10-28 |
| US6693791B2 (en) | 2004-02-17 |
| CN1085411C (en) | 2002-05-22 |
| US20060170021A1 (en) | 2006-08-03 |
| DE69633554T2 (en) | 2005-10-13 |
| EP0785579A1 (en) | 1997-07-23 |
| JP3929513B2 (en) | 2007-06-13 |
| US7057874B2 (en) | 2006-06-06 |
| CA2197491A1 (en) | 1997-01-30 |
| KR100385446B1 (en) | 2004-09-08 |
| CN1155943A (en) | 1997-07-30 |
| KR970703049A (en) | 1997-06-10 |
| DE69633554D1 (en) | 2004-11-11 |
| US6454914B1 (en) | 2002-09-24 |
| EP0785579A4 (en) | 1998-10-14 |
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