US20100124807A1 - Method of manufacturing semiconductor device having step gates - Google Patents

Method of manufacturing semiconductor device having step gates Download PDF

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US20100124807A1
US20100124807A1 US12/693,384 US69338410A US2010124807A1 US 20100124807 A1 US20100124807 A1 US 20100124807A1 US 69338410 A US69338410 A US 69338410A US 2010124807 A1 US2010124807 A1 US 2010124807A1
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active region
forming
semiconductor substrate
hard mask
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Byung Soo Eun
Jung Suk Lee
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SK Hynix Inc
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Hynix Semiconductor Inc
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    • A—HUMAN NECESSITIES
    • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01D—HARVESTING; MOWING
    • A01D34/00—Mowers; Mowing apparatus of harvesters
    • A01D34/01—Mowers; Mowing apparatus of harvesters characterised by features relating to the type of cutting apparatus
    • A01D34/412—Mowers; Mowing apparatus of harvesters characterised by features relating to the type of cutting apparatus having rotating cutters
    • A01D34/42—Mowers; Mowing apparatus of harvesters characterised by features relating to the type of cutting apparatus having rotating cutters having cutters rotating about a horizontal axis, e.g. cutting-cylinders
    • A01D34/62—Other details
    • 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
    • H01L29/66007—Multistep manufacturing processes
    • H01L29/66075—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials
    • H01L29/66227—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials the devices being controllable only by the electric current supplied or the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched, e.g. three-terminal devices
    • H01L29/66409—Unipolar field-effect transistors
    • H01L29/66477—Unipolar field-effect transistors with an insulated gate, i.e. MISFET
    • H01L29/66568—Lateral single gate silicon transistors
    • H01L29/66659—Lateral single gate silicon transistors with asymmetry in the channel direction, e.g. lateral high-voltage MISFETs with drain offset region, extended drain MISFETs
    • A—HUMAN NECESSITIES
    • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01D—HARVESTING; MOWING
    • A01D34/00—Mowers; Mowing apparatus of harvesters
    • A01D34/01—Mowers; Mowing apparatus of harvesters characterised by features relating to the type of cutting apparatus
    • A01D34/412—Mowers; Mowing apparatus of harvesters characterised by features relating to the type of cutting apparatus having rotating cutters
    • A01D34/42—Mowers; Mowing apparatus of harvesters characterised by features relating to the type of cutting apparatus having rotating cutters having cutters rotating about a horizontal axis, e.g. cutting-cylinders
    • A01D34/46—Mowers; Mowing apparatus of harvesters characterised by features relating to the type of cutting apparatus having rotating cutters having cutters rotating about a horizontal axis, e.g. cutting-cylinders hand-guided by a walking operator
    • A01D34/47—Mowers; Mowing apparatus of harvesters characterised by features relating to the type of cutting apparatus having rotating cutters having cutters rotating about a horizontal axis, e.g. cutting-cylinders hand-guided by a walking operator with motor driven cutters or wheels
    • A—HUMAN NECESSITIES
    • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01D—HARVESTING; MOWING
    • A01D34/00—Mowers; Mowing apparatus of harvesters
    • A01D34/01—Mowers; Mowing apparatus of harvesters characterised by features relating to the type of cutting apparatus
    • A01D34/412—Mowers; Mowing apparatus of harvesters characterised by features relating to the type of cutting apparatus having rotating cutters
    • A01D34/42—Mowers; Mowing apparatus of harvesters characterised by features relating to the type of cutting apparatus having rotating cutters having cutters rotating about a horizontal axis, e.g. cutting-cylinders
    • A01D34/54—Cutting-height adjustment
    • 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
    • H01L21/28—Manufacture of electrodes on semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/268
    • H01L21/28008—Making conductor-insulator-semiconductor electrodes
    • H01L21/28017—Making conductor-insulator-semiconductor electrodes the insulator being formed after the semiconductor body, the semiconductor being silicon
    • H01L21/28026—Making conductor-insulator-semiconductor electrodes the insulator being formed after the semiconductor body, the semiconductor being silicon characterised by the conductor
    • H01L21/28123—Lithography-related aspects, e.g. sub-lithography lengths; Isolation-related aspects, e.g. to solve problems arising at the crossing with the side of the device isolation; Planarisation aspects
    • H01L21/2815—Lithography-related aspects, e.g. sub-lithography lengths; Isolation-related aspects, e.g. to solve problems arising at the crossing with the side of the device isolation; Planarisation aspects part or whole of the electrode is a sidewall spacer or made by a similar technique, e.g. transformation under mask, plating
    • 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
    • H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
    • H01L29/06—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions
    • H01L29/10—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions with semiconductor regions connected to an electrode not carrying current to be rectified, amplified or switched and such electrode being part of a semiconductor device which comprises three or more electrodes
    • H01L29/1025—Channel region of field-effect devices
    • H01L29/1029—Channel region of field-effect devices of field-effect transistors
    • H01L29/1033—Channel region of field-effect devices of field-effect transistors with insulated gate, e.g. characterised by the length, the width, the geometric contour or the doping structure
    • H01L29/1037—Channel region of field-effect devices of field-effect transistors with insulated gate, e.g. characterised by the length, the width, the geometric contour or the doping structure and non-planar channel
    • 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
    • H01L29/40—Electrodes ; Multistep manufacturing processes therefor
    • H01L29/41—Electrodes ; Multistep manufacturing processes therefor characterised by their shape, relative sizes or dispositions
    • H01L29/423—Electrodes ; Multistep manufacturing processes therefor characterised by their shape, relative sizes or dispositions not carrying the current to be rectified, amplified or switched
    • H01L29/42312—Gate electrodes for field effect devices
    • H01L29/42316—Gate electrodes for field effect devices for field-effect transistors
    • H01L29/4232—Gate electrodes for field effect devices for field-effect transistors with insulated gate
    • H01L29/42372—Gate electrodes for field effect devices for field-effect transistors with insulated gate characterised by the conducting layer, e.g. the length, the sectional shape or the lay-out
    • H01L29/42376—Gate electrodes for field effect devices for field-effect transistors with insulated gate characterised by the conducting layer, e.g. the length, the sectional shape or the lay-out characterised by the length or the sectional shape
    • 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
    • H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
    • H01L29/76—Unipolar devices, e.g. field effect transistors
    • H01L29/772—Field effect transistors
    • H01L29/78—Field effect transistors with field effect produced by an insulated gate
    • H01L29/7833—Field effect transistors with field effect produced by an insulated gate with lightly doped drain or source extension, e.g. LDD MOSFET's; DDD MOSFET's
    • H01L29/7834—Field effect transistors with field effect produced by an insulated gate with lightly doped drain or source extension, e.g. LDD MOSFET's; DDD MOSFET's with a non-planar structure, e.g. the gate or the source or the drain being non-planar
    • 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
    • H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
    • H01L29/76—Unipolar devices, e.g. field effect transistors
    • H01L29/772—Field effect transistors
    • H01L29/78—Field effect transistors with field effect produced by an insulated gate
    • H01L29/7833—Field effect transistors with field effect produced by an insulated gate with lightly doped drain or source extension, e.g. LDD MOSFET's; DDD MOSFET's
    • H01L29/7835—Field effect transistors with field effect produced by an insulated gate with lightly doped drain or source extension, e.g. LDD MOSFET's; DDD MOSFET's with asymmetrical source and drain regions, e.g. lateral high-voltage MISFETs with drain offset region, extended drain MISFETs
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10B—ELECTRONIC MEMORY DEVICES
    • H10B12/00—Dynamic random access memory [DRAM] devices
    • H10B12/01—Manufacture or treatment
    • H10B12/02—Manufacture or treatment for one transistor one-capacitor [1T-1C] memory cells
    • H10B12/05—Making the transistor
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10B—ELECTRONIC MEMORY DEVICES
    • H10B12/00—Dynamic random access memory [DRAM] devices
    • H10B12/30—DRAM devices comprising one-transistor - one-capacitor [1T-1C] memory cells
    • H10B12/48—Data lines or contacts therefor
    • H10B12/488—Word lines

Definitions

  • the present invention relates to a semiconductor device and a method of manufacturing the same. More particularly, the present invention relates to a semiconductor device having step gates to improve overall signal transfer rate, and a method of manufacturing the same.
  • a gate stack is provided on a semiconductor substrate having a trench isolation film, and a source/drain junction region is provided on the semiconductor substrate at both sides of the gate stack.
  • a gate having such a structure is called a planar gate.
  • the planar gate has a short channel length between the source and drain, and therefore exhibits fast operating speed due to the low resistance of the channel.
  • the increased degree of integration of DRAM cells leads to a decrease in the size of the transistors, which in turn results in a shortened channel length between the source and drain.
  • SCF short-channel effects
  • the channel doping concentration has conventionally been increased in order to obtain desired magnitude of threshold voltage.
  • recess channel structures which are capable of inhibiting the above-mentioned issues without decreasing the degree of integration of the device via the lengthening of the effective channel by etching a portion of a substrate to a given depth, are being actively researched.
  • step gate stack structures in which the lower part of the gate is formed into a step shape, thereby being capable of lengthening the channel, are receiving a great deal of attention in the art.
  • FIG. 1 is a cross-sectional view showing a step gate structure of a semiconductor device having a recess channel in accordance with a conventional art.
  • trench isolation films 110 defining an active region are provided in a semiconductor substrate 100 .
  • the trench isolation films 110 are made of insulating films, for example oxide films.
  • Step gate stacks 120 are provided on the semiconductor substrate 100 , and the step gate stacks 120 take step-like profiles having upper/lower and vertical surfaces on lower parts thereof.
  • Source regions such as first impurity regions 130 and a drain region as a second impurity region 135 are provided on the semiconductor substrate 100 at both sides of the step gate stacks 120 .
  • a gate insulating film 101 is deposited at the lower part of the step gate stacks 120 . In addition, even though they are not shown in FIG.
  • bottom electrode films which are electrically connected to the first impurity regions 130 provided in the semiconductor substrate 100 , capacitors (not shown) including a dielectric film and top electrode film sequentially formed on the bottom electrode films, and a bit line stack (not shown) connected to the second impurity region 135 are formed on the substrate.
  • the step gate of the semiconductor device since the step gate of the semiconductor device has a long channel length due to the step-like profiles having upper/lower and vertical surfaces, it is possible to prevent the localized electric-field enhancement effects in source junctions without increasing the channel doping concentration, thus decreasing leakage current.
  • prolonged channel length results in increased resistance of the device which in turn decreases the signal transfer rate of the overall DRAM.
  • Embodiments of the present invention to provide a semiconductor device having step gates in order to improve the overall signal transfer rate thereof, and a method of manufacturing the same.
  • a semiconductor device having step gates includes a semiconductor substrate including first regions having relatively low steps at both ends of an active region defined by trench isolation films, a second region having a relatively high step at the central part of the active region, and a groove having a predetermined depth being formed at the central part of the second region; step gate stacks provided on the boundary between the first region and second region while exposing the groove of the second region; first impurity regions provided in the first regions exposed by the step gate stacks; and a second impurity region provided in the second region exposed by the step gate stacks while enclosing the groove of the second region.
  • the groove formed at the central part of the second region of the semiconductor substrate may be provided to have a depth shallower than that of the second impurity region.
  • the second region of the semiconductor substrate is a film formed via selective epitaxial growth.
  • the semiconductor device in accordance with the present invention may further include bottom electrode films electrically connected to the first impurity regions, capacitors including a dielectric film and top electrode film sequentially formed on the bottom electrode films, and a bit line stack connected to the second impurity region.
  • a method of manufacturing a semiconductor device having step gates comprises forming trench isolation films on a semiconductor substrate, using hard mask film patterns covering an active region thereof; removing a portion of the hard mask film patterns to expose a first surface and second surface of the active region, while allowing the first and second surfaces to be separated by the hard mask film patterns formed at the central part of the active region; forming selective epitaxial growth layers on the first and second surfaces of the active region; removing the hard mask film patterns; forming step gate stacks on the boundary between the semiconductor substrate of the active region and selective epitaxial growth layer; and forming first impurity regions and a second impurity region in the semiconductor substrate using the step gate stacks as an ion implantation mask.
  • the selective epitaxial layer may be grown using dichlorosilane, hydrochloric acid and hydrogen as source gases.
  • the method of the present invention may further include cleaning the exposed first and second surfaces of the active region after exposure.
  • the cleaning process can be carried out using a first cleaning solution comprising sulfuric acid and hydrogen peroxide and/or a second cleaning solution comprising hydrofluoric acid and ammonium fluoride.
  • the first cleaning solution may be a 4:1 mixture of sulfuric acid and hydrogen peroxide.
  • the second cleaning solution may be a 300:1 mixture of hydrofluoric acid and ammonium fluoride.
  • the method of the present invention may further include forming bottom electrode films electrically connected to the first impurity regions, and capacitors including a dielectric film and top electrode film sequentially formed on the bottom electrode films; and forming a bit line stack connected to the second impurity region.
  • FIG. 1 is a view illustrating a semiconductor device having step gates in accordance with a conventional art and a method of manufacturing the same;
  • FIG. 2 is a layout view illustrating a semiconductor device having step gates in accordance with one embodiment of the present invention and a method of manufacturing the same;
  • FIGS. 3 through 9 are views illustrating a semiconductor device having step gates in accordance with one embodiment of the present invention and a method of manufacturing the same.
  • FIG. 8 and FIG. 9 are views illustrating a semiconductor device having step gates in accordance with one embodiment of the present invention.
  • a semiconductor device having step gates in accordance with the present invention includes first regions 350 having relatively low steps at both ends of an active region defined by trench isolation films 320 and a second region 360 having a groove 346 having a predetermined depth formed at a central part of the active region.
  • Step gate stacks 400 are formed on the boundary between the first region 350 and second region 360 .
  • the step gate stacks 400 are formed so as to expose the groove 346 formed at the central part of the second region 360 .
  • First impurity regions 410 as source regions, are formed in the first regions 350 exposed by the step gate stacks 400 , and a second impurity region 420 , as a drain region, is formed in the second region 360 .
  • the second impurity region 420 is formed so as to enclose the groove 346 formed at the central part of the second region 360 .
  • gate insulating films 301 are formed on the lower parts of the step gate stacks 400 , and even though they are not shown in FIG. 8 , bottom electrode films, which are electrically connected to the first impurity regions 410 formed in the semiconductor substrate 300 , capacitors (not shown) including a dielectric film and top electrode film sequentially formed on the bottom electrode films, and a bit line 430 connected to the second impurity region 420 are formed.
  • a contact area between the second impurity region 420 formed in the second region 360 and lower surface of the bit line 430 connected to the second impurity region 420 becomes larger due to the presence of the groove 346 formed at the central part of the second region 360 , thereby being capable of lowering the contact resistance therebetween.
  • FIG. 2 is a layout view illustrating a method of manufacturing a semiconductor device having step gates in accordance with one embodiment of the present invention.
  • FIGS. 3 through 8 are views illustrating a semiconductor device having step gates in accordance with one embodiment of the present invention and a method of manufacturing the same.
  • hard mask film patterns 310 covering an active region 303 are formed on a semiconductor substrate 300 .
  • the hard mask film patterns 310 are made of a pad oxide film 305 and a pad nitride film 307 which are sequentially stacked.
  • trenches 302 for isolation of devices are formed by etching the semiconductor substrate 300 to a predetermined depth, using the hard mask film patterns 310 as an etch mask.
  • a burial-type insulating film (not shown) is formed on the hard mask film patterns 310 , for example using a high-density plasma oxide film, such that trenches 302 for isolation of devices are buried, and the burial-type insulating film is then subjected to a planarization process, for example chemical mechanical polishing (CMP), so as to expose the upper surface of the hard mask film patterns 310 , thereby forming trench isolation films 320 .
  • CMP chemical mechanical polishing
  • photoresist film patterns 312 are formed on the hard mask film patterns 310 , and the hard mask film patterns 310 are etched using the photoresist film patterns 312 as an etch mask so as to expose a first surface 330 and second surface 340 of an active region 303 in the semiconductor substrate 300 .
  • the first surface 330 and second surface 340 are regions in which the selective epitaxial layers having a step will be grown so as to form step gates.
  • the photoresist film patterns 312 for patterning the hard mask film patterns 310 as shown in the layout view of FIG. 2 , are formed into stripe shapes passing through both ends and the center of the active region 303 .
  • the photoresist film patterns 312 were removed and the semiconductor substrate 300 was subjected to a cleaning process so as to completely remove oxides present on the exposed first surface 330 and second surface 340 .
  • the cleaning process to remove oxides is carried out using a first cleaning solution comprising sulfuric acid (H2SO4) and hydrogen peroxide (H2O2) and/or a second cleaning solution comprising hydrofluoric acid (HF) and ammonium fluoride (NH4F).
  • the first cleaning solution may be a 4:1 mixture of sulfuric acid and hydrogen peroxide.
  • the second cleaning solution may be a 300:1 mixture of hydrofluoric acid and ammonium fluoride.
  • selective epitaxial layers 345 are formed on the first surface 330 and second surface 340 exposed due to the hard mask film patterns 310 , via use of selective epitaxial growth.
  • the selective epitaxial layers 345 are grown with a supply of dichlorosilane (SiCl2H2), hydrochloric acid (HCl) and hydrogen (H2) as source gases, at a temperature of about 850° C. and pressure of about 10 to 100 Torr.
  • the selective epitaxial layers 345 grown at a deposition rate of 600 ⁇ /min has a thickness of 400 ⁇ .
  • first regions 350 having relatively low steps are formed at both ends of the active region 303 adjacent to the trench isolation films 320 , and a second region 360 having a relatively high step and including a groove 346 having a predetermined depth is formed at the central part of the active region 303 .
  • a gate insulating film 301 is formed on the entire surface of the semiconductor substrate 300 , utilizing an oxide film, for example, and a gate conductive film (not shown) is formed on the gate insulating film 301 .
  • a metal silicide film (not shown) and a insulating capping film (not shown), which constitute gate stacks, are sequentially stacked on the gate conductive film, followed by patterning to form step gate stacks 400 on the boundary between the first region 350 of the semiconductor substrate 300 and the selective epitaxial layer 360 as the second region thereof.
  • the gate conductive film may be formed of a polysilicon film
  • the metal silicide film may be formed of a tungsten silicide film
  • the insulating capping film may be formed of a nitride film.
  • first impurity regions 410 namely source regions
  • a second impurity region 420 namely a drain region
  • first impurity regions 410 and second impurity region 420 are formed in the semiconductor substrate 300 using the step gate stacks 400 as an ion implantation mask. Even though they are not shown in FIG. 6 , after formation of the first impurity regions 410 and second impurity region 420 , bottom electrode films, which are electrically connected to the first impurity regions 410 , capacitors (not shown) including a dielectric film and top electrode film sequentially formed on the bottom electrode films, and a bit line 430 connected to the second impurity region 420 are formed.
  • a contact area between a bit line and a second impurity region, i.e., a drain region, is increased by provision of a groove formed at the central part of the second region, thus decreasing contact resistance therebetween and therefore the overall signal transfer rate of the device is improved.

Abstract

A semiconductor device having step gates includes a semiconductor substrate including first regions having relatively low steps at both ends of an active region defined by trench isolation films and a second region having a relatively high step at a central part of the active region, a groove having a predetermined depth being formed at the central part of the second region, step gate stacks formed on the boundary between the first region and second region while exposing the groove of the second region, first impurity regions formed in the first regions exposed by the step gate stacks, and a second impurity region formed in the second region exposed by the step gate stacks while enclosing the groove of the second region.

Description

    CROSS-REFERENCES TO RELATED APPLICATIONS
  • The present invention is a divisional of U.S. patent application Ser. No. 11/293,317, filed on Dec. 1, 2005, and claims priority of Korean patent application number 2005-28298, filed on Apr. 4, 2005, which are incorporated by reference in their entirety.
    • BACKGROUND OF THE INVENTION
  • The present invention relates to a semiconductor device and a method of manufacturing the same. More particularly, the present invention relates to a semiconductor device having step gates to improve overall signal transfer rate, and a method of manufacturing the same.
  • In conventional dynamic random access memories (DRAMs), a gate stack is provided on a semiconductor substrate having a trench isolation film, and a source/drain junction region is provided on the semiconductor substrate at both sides of the gate stack. A gate having such a structure is called a planar gate. The planar gate has a short channel length between the source and drain, and therefore exhibits fast operating speed due to the low resistance of the channel.
  • However, the increased degree of integration of DRAM cells leads to a decrease in the size of the transistors, which in turn results in a shortened channel length between the source and drain. As a result, short-channel effects (SCF) of the transistors become severe, thus decreasing the threshold voltage. In order to prevent a decrease of threshold voltage due to short-channel effects of the transistors, the channel doping concentration has conventionally been increased in order to obtain desired magnitude of threshold voltage.
  • However, such increased channel doping concentration leads to localized electricfield enhancement effects in source junctions and increased leakage current, thereby aggravating the refresh properties of DRAM memory cells. Therefore, recess channel structures, which are capable of inhibiting the above-mentioned issues without decreasing the degree of integration of the device via the lengthening of the effective channel by etching a portion of a substrate to a given depth, are being actively researched. Among such recess channel structures, step gate stack structures, in which the lower part of the gate is formed into a step shape, thereby being capable of lengthening the channel, are receiving a great deal of attention in the art.
  • FIG. 1 is a cross-sectional view showing a step gate structure of a semiconductor device having a recess channel in accordance with a conventional art.
  • As shown in FIG. 1, trench isolation films 110 defining an active region are provided in a semiconductor substrate 100. The trench isolation films 110 are made of insulating films, for example oxide films. Step gate stacks 120 are provided on the semiconductor substrate 100, and the step gate stacks 120 take step-like profiles having upper/lower and vertical surfaces on lower parts thereof. Source regions such as first impurity regions 130 and a drain region as a second impurity region 135 are provided on the semiconductor substrate 100 at both sides of the step gate stacks 120. A gate insulating film 101 is deposited at the lower part of the step gate stacks 120. In addition, even though they are not shown in FIG. 1, bottom electrode films, which are electrically connected to the first impurity regions 130 provided in the semiconductor substrate 100, capacitors (not shown) including a dielectric film and top electrode film sequentially formed on the bottom electrode films, and a bit line stack (not shown) connected to the second impurity region 135 are formed on the substrate.
  • As described above, since the step gate of the semiconductor device has a long channel length due to the step-like profiles having upper/lower and vertical surfaces, it is possible to prevent the localized electric-field enhancement effects in source junctions without increasing the channel doping concentration, thus decreasing leakage current. However, prolonged channel length results in increased resistance of the device which in turn decreases the signal transfer rate of the overall DRAM.
    • BRIEF SUMMARY OF THE INVENTION
  • Embodiments of the present invention to provide a semiconductor device having step gates in order to improve the overall signal transfer rate thereof, and a method of manufacturing the same.
  • In accordance with an aspect of the present invention, a semiconductor device having step gates includes a semiconductor substrate including first regions having relatively low steps at both ends of an active region defined by trench isolation films, a second region having a relatively high step at the central part of the active region, and a groove having a predetermined depth being formed at the central part of the second region; step gate stacks provided on the boundary between the first region and second region while exposing the groove of the second region; first impurity regions provided in the first regions exposed by the step gate stacks; and a second impurity region provided in the second region exposed by the step gate stacks while enclosing the groove of the second region.
  • The groove formed at the central part of the second region of the semiconductor substrate may be provided to have a depth shallower than that of the second impurity region. The second region of the semiconductor substrate is a film formed via selective epitaxial growth.
  • The semiconductor device in accordance with the present invention may further include bottom electrode films electrically connected to the first impurity regions, capacitors including a dielectric film and top electrode film sequentially formed on the bottom electrode films, and a bit line stack connected to the second impurity region.
  • In accordance with another aspect of the present invention, a method of manufacturing a semiconductor device having step gates is provided. The method comprises forming trench isolation films on a semiconductor substrate, using hard mask film patterns covering an active region thereof; removing a portion of the hard mask film patterns to expose a first surface and second surface of the active region, while allowing the first and second surfaces to be separated by the hard mask film patterns formed at the central part of the active region; forming selective epitaxial growth layers on the first and second surfaces of the active region; removing the hard mask film patterns; forming step gate stacks on the boundary between the semiconductor substrate of the active region and selective epitaxial growth layer; and forming first impurity regions and a second impurity region in the semiconductor substrate using the step gate stacks as an ion implantation mask. The selective epitaxial layer may be grown using dichlorosilane, hydrochloric acid and hydrogen as source gases.
  • The method of the present invention may further include cleaning the exposed first and second surfaces of the active region after exposure. The cleaning process can be carried out using a first cleaning solution comprising sulfuric acid and hydrogen peroxide and/or a second cleaning solution comprising hydrofluoric acid and ammonium fluoride. The first cleaning solution may be a 4:1 mixture of sulfuric acid and hydrogen peroxide. The second cleaning solution may be a 300:1 mixture of hydrofluoric acid and ammonium fluoride.
  • The method of the present invention may further include forming bottom electrode films electrically connected to the first impurity regions, and capacitors including a dielectric film and top electrode film sequentially formed on the bottom electrode films; and forming a bit line stack connected to the second impurity region.
    • BRIEF DESCRIPTION OF THE DRAWINGS
  • The present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
  • FIG. 1 is a view illustrating a semiconductor device having step gates in accordance with a conventional art and a method of manufacturing the same;
  • FIG. 2 is a layout view illustrating a semiconductor device having step gates in accordance with one embodiment of the present invention and a method of manufacturing the same; and
  • FIGS. 3 through 9 are views illustrating a semiconductor device having step gates in accordance with one embodiment of the present invention and a method of manufacturing the same.
    •  DETAILED DESCRIPTION OF THE INVENTION
  • Now, preferred embodiments of the present invention will be described in more detail with reference to accompanying drawings, such that those skilled in the art can easily practice the present invention. In the drawings, thicknesses of various layers and regions are exaggerated for clarity. Like numbers refer to like elements throughout the specification and drawings.
  • FIG. 8 and FIG. 9 are views illustrating a semiconductor device having step gates in accordance with one embodiment of the present invention.
  • Referring now to FIG. 8 and FIG. 9, a semiconductor device having step gates in accordance with the present invention includes first regions 350 having relatively low steps at both ends of an active region defined by trench isolation films 320 and a second region 360 having a groove 346 having a predetermined depth formed at a central part of the active region. Step gate stacks 400 are formed on the boundary between the first region 350 and second region 360. The step gate stacks 400 are formed so as to expose the groove 346 formed at the central part of the second region 360. First impurity regions 410, as source regions, are formed in the first regions 350 exposed by the step gate stacks 400, and a second impurity region 420, as a drain region, is formed in the second region 360. The second impurity region 420 is formed so as to enclose the groove 346 formed at the central part of the second region 360. In this case, gate insulating films 301 are formed on the lower parts of the step gate stacks 400, and even though they are not shown in FIG. 8, bottom electrode films, which are electrically connected to the first impurity regions 410 formed in the semiconductor substrate 300, capacitors (not shown) including a dielectric film and top electrode film sequentially formed on the bottom electrode films, and a bit line 430 connected to the second impurity region 420 are formed.
  • In such a structure, a contact area between the second impurity region 420 formed in the second region 360 and lower surface of the bit line 430 connected to the second impurity region 420 becomes larger due to the presence of the groove 346 formed at the central part of the second region 360, thereby being capable of lowering the contact resistance therebetween.
  • FIG. 2 is a layout view illustrating a method of manufacturing a semiconductor device having step gates in accordance with one embodiment of the present invention. FIGS. 3 through 8 are views illustrating a semiconductor device having step gates in accordance with one embodiment of the present invention and a method of manufacturing the same.
  • First, referring now to FIG. 3, hard mask film patterns 310 covering an active region 303 are formed on a semiconductor substrate 300. The hard mask film patterns 310 are made of a pad oxide film 305 and a pad nitride film 307 which are sequentially stacked. Then, trenches 302 for isolation of devices are formed by etching the semiconductor substrate 300 to a predetermined depth, using the hard mask film patterns 310 as an etch mask. Next, a burial-type insulating film (not shown) is formed on the hard mask film patterns 310, for example using a high-density plasma oxide film, such that trenches 302 for isolation of devices are buried, and the burial-type insulating film is then subjected to a planarization process, for example chemical mechanical polishing (CMP), so as to expose the upper surface of the hard mask film patterns 310, thereby forming trench isolation films 320.
  • Next, referring to FIG. 4, photoresist film patterns 312 are formed on the hard mask film patterns 310, and the hard mask film patterns 310 are etched using the photoresist film patterns 312 as an etch mask so as to expose a first surface 330 and second surface 340 of an active region 303 in the semiconductor substrate 300. The first surface 330 and second surface 340 are regions in which the selective epitaxial layers having a step will be grown so as to form step gates. The photoresist film patterns 312 for patterning the hard mask film patterns 310, as shown in the layout view of FIG. 2, are formed into stripe shapes passing through both ends and the center of the active region 303.
  • Next, referring to FIG. 5, the photoresist film patterns 312 were removed and the semiconductor substrate 300 was subjected to a cleaning process so as to completely remove oxides present on the exposed first surface 330 and second surface 340. The cleaning process to remove oxides is carried out using a first cleaning solution comprising sulfuric acid (H2SO4) and hydrogen peroxide (H2O2) and/or a second cleaning solution comprising hydrofluoric acid (HF) and ammonium fluoride (NH4F). Herein, the first cleaning solution may be a 4:1 mixture of sulfuric acid and hydrogen peroxide. The second cleaning solution may be a 300:1 mixture of hydrofluoric acid and ammonium fluoride.
  • Next, referring to FIG. 6, after performing the cleaning process, selective epitaxial layers 345 are formed on the first surface 330 and second surface 340 exposed due to the hard mask film patterns 310, via use of selective epitaxial growth. The selective epitaxial layers 345 are grown with a supply of dichlorosilane (SiCl2H2), hydrochloric acid (HCl) and hydrogen (H2) as source gases, at a temperature of about 850° C. and pressure of about 10 to 100 Torr. In this case, the selective epitaxial layers 345 grown at a deposition rate of 600 Å/min has a thickness of 400 Å.
  • Next, referring to FIG. 7, the hard mask film patterns 310 are removed. Then, first regions 350 having relatively low steps are formed at both ends of the active region 303 adjacent to the trench isolation films 320, and a second region 360 having a relatively high step and including a groove 346 having a predetermined depth is formed at the central part of the active region 303.
  • Referring to FIG. 8 and FIG. 9, a gate insulating film 301 is formed on the entire surface of the semiconductor substrate 300, utilizing an oxide film, for example, and a gate conductive film (not shown) is formed on the gate insulating film 301. Subsequently, a metal silicide film (not shown) and a insulating capping film (not shown), which constitute gate stacks, are sequentially stacked on the gate conductive film, followed by patterning to form step gate stacks 400 on the boundary between the first region 350 of the semiconductor substrate 300 and the selective epitaxial layer 360 as the second region thereof. The gate conductive film may be formed of a polysilicon film, the metal silicide film may be formed of a tungsten silicide film, and the insulating capping film may be formed of a nitride film.
  • Next, first impurity regions 410, namely source regions, and a second impurity region 420, namely a drain region, are formed in the semiconductor substrate 300 using the step gate stacks 400 as an ion implantation mask. Even though they are not shown in FIG. 6, after formation of the first impurity regions 410 and second impurity region 420, bottom electrode films, which are electrically connected to the first impurity regions 410, capacitors (not shown) including a dielectric film and top electrode film sequentially formed on the bottom electrode films, and a bit line 430 connected to the second impurity region 420 are formed.
  • As apparent from the above description, in accordance with the method of manufacturing a semiconductor device having step gates of the present invention, it is possible to form gate stacks having a step-like structure on the boundary between the first regions formed at both ends of the active region adjacent to the trench isolation films and second region consisting of the selective epitaxial layer, without etching a portion of the semiconductor substrate. In addition, a contact area between a bit line and a second impurity region, i.e., a drain region, is increased by provision of a groove formed at the central part of the second region, thus decreasing contact resistance therebetween and therefore the overall signal transfer rate of the device is improved.
  • Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (7)

1. A method of manufacturing a semiconductor device having step gates, the method comprising:
forming trench isolation films on a semiconductor substrate using hard mask film patterns covering an active region thereof;
removing a portion of the hard mask film patterns to expose a first surface and second surface of the active region, while allowing the first and second surfaces to be separated by the hard mask film patterns formed at a central part of the active region;
forming selective epitaxial growth layers on the first and second surfaces of the active region;
removing the hard mask film patterns;
forming step gate stacks on the boundary between the semiconductor substrate of the active region and selective epitaxial growth layer; and
forming first impurity regions and a second impurity region in the semiconductor substrate using the step gate stacks as an ion implantation mask.
2. The method according to claim 1, wherein the selective epitaxial growth layer is grown using dichlorosilane, hydrochloric acid and hydrogen as source gases.
3. The method according to claim 1, further comprising:
cleaning the exposed first and second surfaces of the active region after exposure thereof.
4. The method according to claim 3, wherein the cleaning process is carried out using at least one of first and second cleansing solutions, the first cleaning solution comprising sulfuric acid and hydrogen peroxide, the second cleaning solution consisting essentially of hydrofluoric acid and ammonium fluoride.
5. The method according to claim 4, wherein the first cleaning solution is a 4:1 mixture of sulfuric acid and hydrogen peroxide.
6. The method according to claim 4, wherein the second cleaning solution is a 300:1 mixture of hydrofluoric acid and ammonium fluoride.
7. The method according to claim 1, further comprising:
forming bottom electrode films electrically coupled to the first impurity regions, and capacitors including a dielectric film and top electrode film sequentially formed on the bottom electrode films; and
forming a bit line stack coupled to the second impurity region.
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