CA2286019C - Recovery of surface-ready silicon carbide substrates - Google Patents
Recovery of surface-ready silicon carbide substrates Download PDFInfo
- Publication number
- CA2286019C CA2286019C CA002286019A CA2286019A CA2286019C CA 2286019 C CA2286019 C CA 2286019C CA 002286019 A CA002286019 A CA 002286019A CA 2286019 A CA2286019 A CA 2286019A CA 2286019 C CA2286019 C CA 2286019C
- Authority
- CA
- Canada
- Prior art keywords
- silicon carbide
- group iii
- epitaxial layer
- stress
- layer
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/005—Processes
- H01L33/0062—Processes for devices with an active region comprising only III-V compounds
- H01L33/0066—Processes for devices with an active region comprising only III-V compounds with a substrate not being a III-V compound
- H01L33/007—Processes for devices with an active region comprising only III-V compounds with a substrate not being a III-V compound comprising nitride compounds
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S438/00—Semiconductor device manufacturing: process
- Y10S438/931—Silicon carbide semiconductor
Abstract
A method is disclosed for recovering surface-ready silicon carbide substrates from heteroepitaxial structures of Group III nitrides on silicon carbide substrates. The method comprises subjecting a Group III nitride epitaxial layer on a silicon carbide substrate to a stress that sufficiently increases the number of dislocations in the epitaxial layer to make the epitaxial layer subject to attack and dissolution in a mineral acid, but that otherwise does not affect the silicon carbide substrate, and threafter contacting the epitaxial layer with a mineral acid to remove the Group III nitride while leaving the silicon carbide substrate unaffected.
Description
_1_ RECOVERY OF SURFACE-READY SILICON CARBIDE SUBSTRATES
Fie?d of the Invention The present invention relates to the manufacture of semiconductor devices from wide-bandgap materials, and in particular relates to a method of recovering silicon carbide substrates from composite structures of such substrates with Group III nitride epitaxial layers.
Backgrot.nd of the Invents on The present invention relates to the recent increase in the research, development, manufacture and use of electronic devices made from wide-bandgap semiconductors, specifically including silicon carbide (SIC) and Group III nitrides (I.e., Group III of the Periodic Table: B, A1, Ga, In, T1) such as gallium nitride (GaN). Both of these materials have generated such interest for several reasons. Silicon carbide is an attractive candidate material for semiconductor applications because of its wide bandgap (2.99 eV for alpha-SiC at 300K) and its other exceptional electronic, physical, thermal and chemical properties.
Gallium nitride, although not sharing all of the same physical properties as silicon carbide offers the electronic advantage of being a wide-bandgap (3.36 eV
at 300K) directtransition emitter. Stated somewhat differently, both silicon carbide and gallium nitride ° are ideal candidate materials for producing light emitting diodes (LEDs) that because of their wide bandgaps, are capable of emitting at higher energies.
_2_ In terms of the characteristics of light, higher energy represents higher frequencies and longer wavelengths.
In particular, gallium nitride and silicon carbide have bandgaps sufficiently wide to allow them to emit light in the blue portion of the visible spectrum (i.e., wavelengths of between about 455 and 492 nanometers, nm), a color that cannot be directly produced by most other semiconductor materials. A thorough discussion of optoelectronic devices, and their design, the theory behind their operation, is set forth in Sze, Physics of Semiconductor Devices, (1981), and particularly in Chapter 12, pages 681-742, with related discussions of photodetectors in Chapter 13 (page 743) and solar cells in Chapter 14 (page 790). Such background and theory will not be discussed further herein other than as necessary to describe the present invention.
In brief, however, silicon carbide is an indirect emitter, which means that a portion of the energy generated by each transition is generated as vibrational energy rather than as emitted light. In comparison, gallium nitride is a direct emitter in which all of the energy generated by a transition is emitted as light. Thus, at any given current input, gallium nitride offers the possibility for more efficient LEDs, than does silicon carbide. To date.
however, gallium nitride has not been produced in bulk crystal form, and thus in order to form an LED or other optoelectronic device from gallium nitride, epitaxial layers of gallium nitride must be formed on some suitable substrate material.
Conventionally, sapphire has been the preferred substrate material for gallium nitride because of its physical properties and because of the generally satisfactory crystal lattice match between gallium nitride and sapphire (A1203). Sapphire cannot be made electronically conductive, however, and thus the physical geometry of LEDs formed from gallium nitride epitaxial layers on sapphire substrates are typically of the "same side" variety rather than the generally more preferred "vertical" LED geometry. As used herein, the term "vertical" refers to an LED in which the ohmic contacts can be placed on opposite faces of the device rather than on a common face.
Accordingly, and in addition to its own advantageous electronic properties, silicon carbide provides an excellent substrate material for gallium nitride and other Group III nitride devices.
Accordingly, many recent advances in the production of blue LEDs have been based upon a combination of such gallium nitride epitaxial layers on silicon carbide substrates.
Although the manufacture of such GaN-SiC devices has progressed rapidly, epitaxial growth of such materials such as gallium nitride on silicon carbide continues to represent a complex process, and one in which a substantial proportion of attempts produce device precursors that are unsatisfactory for one or more reasons.
More particularly, a GaN on SiC LED typically consists of an SiC substrate with a back ohmic contact, one or more buffer layers on the SiC substrate that provide a crystal lattice transition between the SiC
and the GaN, and at least two epitaxial layers of gallium nitride on the buffer layer. The gallium nitride layers include at least one p-type layer and one n-type layer adjacent one another to form the p-n junction of the device. A top ohmic contact is usually made to the top layer of gallium nitride, or in some cases to another material that for some other desired reason forms the top layer of the device.
As well known to those of ordinary skill in this industry, semiconductor substrates are typically sliced from bulk crystals in the form of circular disks, generally referred to as "wafers," upon which various other layers, such as epitaxial layers of GaN, are formed. Because the bulk growth of silicon carbide and the preparation of silicon carbide wafers are both processes which represent significant technical challenge and economic investment, the wafers are in turn quite valuable. If, however, after the gallium nitride epitaxial layers are grown on the SiC wafer, they are found to be defective, or simply unsatisfactory from a desired quality standpoint, the entire wafer becomes a waste product.
Thus, a need exists for removing gallium nitride from silicon carbide in a manner that preserves the silicon carbide wafer, interestingly enough, the recent success of high quality epitaxial growth of gallium nitride on silicon carbide has exacerbated this problem. Namely, the high quality gallium nitride (and . ~_ CA 02286019 1999-10-12 a.
~' f r other Group III nitride) epitaxial layers required to produce appropriate LEDs, are similarly much more resistant to the normal techniques (typically wet or dry etching) used to remove unwanted material in conventional semiconductor processes. A thorough discussion regarding reactive ion etching of high quality gallium nitride. (and other Group III nitride) epitaxial layers, and the effect that film quality has on the etch rate is set forth in Hughes et al., Reactive Ion Etching of A1N, AlGaN, and GaN Using BC13, Proceedings of the First International Symposium on Gallium Nitride and Related Materials, Boston, MA, US
(27.11.-01.12.1995) , 395 MATERIAL RES. SOC'Y SYMP. PROC.
757-762 (1996). As noted in the article referenced above, the etch rate of A1N, AlGaN, and GaN, strongly depends on the film quality.
Object and Suxmnarv of the Invention Therefore, it is an object of the present invention to provide a method of recovering surface-ready silicon carbide substrates from heteroepitaxial structures of Group III nitrides on silicon carbide substrates, particularly when the Group III nitride layers are high quality crystalline materials.
The invention meets this object with the method of recovering such substrates by subjecting a Group III
nitride epitaxial layer on a silicon ca~'bide substrate to a stress that sufficiently increases the number of dislocations in the epitaxial layer to make the epitaxial layer subject to attack and dissolution in a AMENDED SHEET
~' . . . r, - r ' ~
r. , r r r r. r r~ r r r~ r r ~ r, r r. r mineral acid, but that otherwise does not affect the silicon carbide substrate, and thereafter contacting the epitaxial layer with a mineral acid to remove the Group III nitride while leaving the silicon carbide substrate unaffected.
Detailed Descries The invention is a method of recovering surface-ready silicon carbide substrates from heteroepitaxial structures of Group III nitrides on silicon carbide substrates. The method comprises subjecting the Group III nitride epitaxial layer on a H;'JI~I~:~G~a ~El~i~
silicon carbide substrate to a stress that sufficiently increases the number of dislocations in the epitaxial layer to make the epitaxial layer subject to attack and dissolution in a mineral acid, but that otherwise does not affect the silicon carbide substrate. Thereafter, the epitaxial layer is contacted with a mineral acid to remove the Group III nitride while leaving the silicon carbide substrate unaffected.
Because gallium nitride is the most commonly used Group III nitride for LEDs, the specification will often refer to gallium nitride. It will be understood, however, that the invention embraces all of the Group III nitrides described above, including binary, ternary, and tertiary nitrides. Such binary nitrides also include aluminum nitride (A1N) and indium nitride (InN). Ternary nitrides include those often referred to as "aluminum gallium nitride," and which are typically designated by the empirical formula AlXGa,_xN.
It will be understood that this general formula is used to refer to a variety of aluminum gallium nitride compounds that are in many ways similar, but that differ according to the atomic fractions of aluminum and gallium, with somewhat differing properties as well.
Tertiary Group III nitrides refer for example to indium aluminum gallium nitride, which is similarly designated In,~AlYGal_X_~,N. The reasons for using gallium nitride, aluminum, Y gallium nitride, or other ternary or tertiary nitrides are set forth in exemplary, but certainly not limiting, fashion in U.S. Patent No.
_7_ 5,523,589; 5,592,501; and 5,739,554; all of which are commonly assigned with the present invention.
Although the inventors do not wish to be bound by any particular theory of the invention, it appears that recent successes in the crystal growth of Group III
nitrides on silicon carbide has produced high-quality Group III nitride layers whose crystal structure is less susceptible to wet chemical attack than are Group III nitride layers produced by other techniques. Thus, although in one sense gallium nitride and other Group III nitrides have been recognized as being susceptible to wet chemical etch, the higher quality Group III
nitrides produced more recently are not so susceptible.
Accordingly, it appears that these higher quality gallium nitride epitaxial layers must be physically brought to a lower quality ("the stress step") before they can be successfully attacked with a wet chemical etch such as a mineral acid.
Furthermore, it will be understood that the crystal defects referred to herein, although frequently labeled as "dislocations," include, but are not limited to, slips, edge dislocations, and screw dislocations.
Accordingly, in preferred embodiments of the invention, there are several techniques for applying the stress.
A first technique is to raise the temperature of the substrate and the epitaxial layers to a temperature sufficient to dissociate the gallium nitride. In more preferred embodiments, this technique comprises heating the substrate and epitaxial layers to temperatures of _g_ about 1000°C in the presence of oxygen or argon. The equipment used for these heating steps is otherwise conventional in this art, and can be used to practice the invention without undue experimentation.
In another embodiment, the stress step comprises exposing the substrate and epitaxial layers to rapid thermal annealing (RTA). As used herein, rapid thermal annealing refers to the technique generally well understood in the semiconductor arts in which an item such as a semiconductor material is placed in a device that, because of its physical capabilities, can raise the temperature of the semiconductor material very quickly; i.e., on the order of about 10°C per second.
Again, although not wishing to be bound by any particular theory, it appears that when the lattice mismatch between the gallium nitride and silicon carbide (even in the presence of a buffer layer) is subjected to such rapid thermal stress (which is not expected in any ordinary use of the device), the mismatch creates or increases the number of defects in the crystal, particularly dislocation defects, that permit the mineral acid to attack and remove the Group III nitride.
In some embodiments, the rapid thermal annealing is carried out at relatively low pressure (e. g., about 10-6 torr), while in other circumstances, the rapid thermal annealing can be carried out in an ambient atmosphere (air) at high temperatures (e. g., 1050°C).
In yet another embodiment, the step of subjecting the Group III nitride layer to stress can comprise _g_ physically abrading the layer, for example by bombarding it with silicon carbide or aluminum oxide powders. It presently appears, however, that such physical abrasion methods may cause underlying damage to the silicon carbide substrate as well, which is a less desirable result.
In the preferred embodiments of the method, the step of contacting the epitaxial layer with a mineral acid comprises contacting the layer with phosphoric acid (H3P04) . Most preferably 85% H3P04, heated to about 170°C is used to remove the nitride epitaxial layers.
In a preferred embodiment, the etching apparatus comprises a quartz beaker and a Wollam condenser. The condenser keeps the H3P04 solution at 85% by preventing water from evaporating.
As noted above, the difficulty in removing the gallium nitride from the substrate relates back to the quality of the gallium nitride epitaxial layer, which in turn relates back to the method by which it is produced. Thus, in another aspect, the invention comprises the step of depositing the Group III nitride epitaxial layer on the substrate prior to the step of subjecting the layer to stress. More particularly, it has been found that electronically high quality Group III nitride epitaxial layers, and thus those hardest to remove, tend to be produced by metal organic chemical vapor deposition (MOCVD), and are typically of higher quality than those produced by vapor phase epitaxy (VPE). Although these processes are to a great extent similar, as used herein, vapor phase epitaxy refers to processes such as those in which a gas (such as a blend of hydrogen chloride and hydrogen) is bubbled through liquid gallium to produce a gallium chloride vapor, which is then directed to react with a nitrogen containing gas, typically ammonia (NH3), to form gallium nitride. Some VPE processes seem to inherently form dislocations and tend to capture chloride atoms or chloride ions in the resulting material.
Alternatively, MOCVD uses a metal organic compound (in which the Group III element is the metal) in the vapor phase. To some extent, the vapor phase compound will dissociate to form metal radicals. These radicals in turn react with the nitrogen containing gas (again typically ammonia) to form the Group III nitride.
Trimethyl gallium ( "TMG, " (CH3) 3Ga) is a preferred metal organic source for gallium.
Thus, in the present invention the step of depositing the Group III nitride epitaxial layer on the silicon carbide substrate preferably comprises MOCVD.
In turn, the MOCVD is preferably carried out from a vapor phase reaction between an organic Group III
compound such as TMG, and ammonia (NH3).
It will be understood, however, that the invention is not limited by the method in which the Group III
nitride layers are deposited. Other appropriate methods can include (but are not limited to) molecular beam epitaxy (MBE), the aforementioned VPE, and liquid phase epitaxy (LPE).
It has also come to be recognized in recent years that an appropriate buffer layer or layers positioned s between the silicon carbide substrate and the gallium nitride epitaxial layers can greatly improve the quality of those epitaxial layers. Thus, a preferred embodiment of the present invention further comprises depositing such a buffer layer on the silicon carbide substrate prior to the step of depositing the Group III
nitride epitaxial layers. Appropriate buffer layers are described in several of the patents already cited as well in U.S. Patent No. 5,393,993, which is commonly assiged with the present invention. The method of the invention removes these buffer layers as well.
In summary, the invention produces a silicon carbide wafer that is otherwise indistinguishable from wafers that have never carried Group III nitride epitaxial layers. Such recovered wafers can accordingly be used or processed in the same manner as "new" wafers, thus offering significant gains in the efficiency and economy of wafer and device production.
In the specification, there have been set forth preferred and exemplary embodiments, which have been included by way of example and not limitation, the scope of invention being set forth in the following claims.
Fie?d of the Invention The present invention relates to the manufacture of semiconductor devices from wide-bandgap materials, and in particular relates to a method of recovering silicon carbide substrates from composite structures of such substrates with Group III nitride epitaxial layers.
Backgrot.nd of the Invents on The present invention relates to the recent increase in the research, development, manufacture and use of electronic devices made from wide-bandgap semiconductors, specifically including silicon carbide (SIC) and Group III nitrides (I.e., Group III of the Periodic Table: B, A1, Ga, In, T1) such as gallium nitride (GaN). Both of these materials have generated such interest for several reasons. Silicon carbide is an attractive candidate material for semiconductor applications because of its wide bandgap (2.99 eV for alpha-SiC at 300K) and its other exceptional electronic, physical, thermal and chemical properties.
Gallium nitride, although not sharing all of the same physical properties as silicon carbide offers the electronic advantage of being a wide-bandgap (3.36 eV
at 300K) directtransition emitter. Stated somewhat differently, both silicon carbide and gallium nitride ° are ideal candidate materials for producing light emitting diodes (LEDs) that because of their wide bandgaps, are capable of emitting at higher energies.
_2_ In terms of the characteristics of light, higher energy represents higher frequencies and longer wavelengths.
In particular, gallium nitride and silicon carbide have bandgaps sufficiently wide to allow them to emit light in the blue portion of the visible spectrum (i.e., wavelengths of between about 455 and 492 nanometers, nm), a color that cannot be directly produced by most other semiconductor materials. A thorough discussion of optoelectronic devices, and their design, the theory behind their operation, is set forth in Sze, Physics of Semiconductor Devices, (1981), and particularly in Chapter 12, pages 681-742, with related discussions of photodetectors in Chapter 13 (page 743) and solar cells in Chapter 14 (page 790). Such background and theory will not be discussed further herein other than as necessary to describe the present invention.
In brief, however, silicon carbide is an indirect emitter, which means that a portion of the energy generated by each transition is generated as vibrational energy rather than as emitted light. In comparison, gallium nitride is a direct emitter in which all of the energy generated by a transition is emitted as light. Thus, at any given current input, gallium nitride offers the possibility for more efficient LEDs, than does silicon carbide. To date.
however, gallium nitride has not been produced in bulk crystal form, and thus in order to form an LED or other optoelectronic device from gallium nitride, epitaxial layers of gallium nitride must be formed on some suitable substrate material.
Conventionally, sapphire has been the preferred substrate material for gallium nitride because of its physical properties and because of the generally satisfactory crystal lattice match between gallium nitride and sapphire (A1203). Sapphire cannot be made electronically conductive, however, and thus the physical geometry of LEDs formed from gallium nitride epitaxial layers on sapphire substrates are typically of the "same side" variety rather than the generally more preferred "vertical" LED geometry. As used herein, the term "vertical" refers to an LED in which the ohmic contacts can be placed on opposite faces of the device rather than on a common face.
Accordingly, and in addition to its own advantageous electronic properties, silicon carbide provides an excellent substrate material for gallium nitride and other Group III nitride devices.
Accordingly, many recent advances in the production of blue LEDs have been based upon a combination of such gallium nitride epitaxial layers on silicon carbide substrates.
Although the manufacture of such GaN-SiC devices has progressed rapidly, epitaxial growth of such materials such as gallium nitride on silicon carbide continues to represent a complex process, and one in which a substantial proportion of attempts produce device precursors that are unsatisfactory for one or more reasons.
More particularly, a GaN on SiC LED typically consists of an SiC substrate with a back ohmic contact, one or more buffer layers on the SiC substrate that provide a crystal lattice transition between the SiC
and the GaN, and at least two epitaxial layers of gallium nitride on the buffer layer. The gallium nitride layers include at least one p-type layer and one n-type layer adjacent one another to form the p-n junction of the device. A top ohmic contact is usually made to the top layer of gallium nitride, or in some cases to another material that for some other desired reason forms the top layer of the device.
As well known to those of ordinary skill in this industry, semiconductor substrates are typically sliced from bulk crystals in the form of circular disks, generally referred to as "wafers," upon which various other layers, such as epitaxial layers of GaN, are formed. Because the bulk growth of silicon carbide and the preparation of silicon carbide wafers are both processes which represent significant technical challenge and economic investment, the wafers are in turn quite valuable. If, however, after the gallium nitride epitaxial layers are grown on the SiC wafer, they are found to be defective, or simply unsatisfactory from a desired quality standpoint, the entire wafer becomes a waste product.
Thus, a need exists for removing gallium nitride from silicon carbide in a manner that preserves the silicon carbide wafer, interestingly enough, the recent success of high quality epitaxial growth of gallium nitride on silicon carbide has exacerbated this problem. Namely, the high quality gallium nitride (and . ~_ CA 02286019 1999-10-12 a.
~' f r other Group III nitride) epitaxial layers required to produce appropriate LEDs, are similarly much more resistant to the normal techniques (typically wet or dry etching) used to remove unwanted material in conventional semiconductor processes. A thorough discussion regarding reactive ion etching of high quality gallium nitride. (and other Group III nitride) epitaxial layers, and the effect that film quality has on the etch rate is set forth in Hughes et al., Reactive Ion Etching of A1N, AlGaN, and GaN Using BC13, Proceedings of the First International Symposium on Gallium Nitride and Related Materials, Boston, MA, US
(27.11.-01.12.1995) , 395 MATERIAL RES. SOC'Y SYMP. PROC.
757-762 (1996). As noted in the article referenced above, the etch rate of A1N, AlGaN, and GaN, strongly depends on the film quality.
Object and Suxmnarv of the Invention Therefore, it is an object of the present invention to provide a method of recovering surface-ready silicon carbide substrates from heteroepitaxial structures of Group III nitrides on silicon carbide substrates, particularly when the Group III nitride layers are high quality crystalline materials.
The invention meets this object with the method of recovering such substrates by subjecting a Group III
nitride epitaxial layer on a silicon ca~'bide substrate to a stress that sufficiently increases the number of dislocations in the epitaxial layer to make the epitaxial layer subject to attack and dissolution in a AMENDED SHEET
~' . . . r, - r ' ~
r. , r r r r. r r~ r r r~ r r ~ r, r r. r mineral acid, but that otherwise does not affect the silicon carbide substrate, and thereafter contacting the epitaxial layer with a mineral acid to remove the Group III nitride while leaving the silicon carbide substrate unaffected.
Detailed Descries The invention is a method of recovering surface-ready silicon carbide substrates from heteroepitaxial structures of Group III nitrides on silicon carbide substrates. The method comprises subjecting the Group III nitride epitaxial layer on a H;'JI~I~:~G~a ~El~i~
silicon carbide substrate to a stress that sufficiently increases the number of dislocations in the epitaxial layer to make the epitaxial layer subject to attack and dissolution in a mineral acid, but that otherwise does not affect the silicon carbide substrate. Thereafter, the epitaxial layer is contacted with a mineral acid to remove the Group III nitride while leaving the silicon carbide substrate unaffected.
Because gallium nitride is the most commonly used Group III nitride for LEDs, the specification will often refer to gallium nitride. It will be understood, however, that the invention embraces all of the Group III nitrides described above, including binary, ternary, and tertiary nitrides. Such binary nitrides also include aluminum nitride (A1N) and indium nitride (InN). Ternary nitrides include those often referred to as "aluminum gallium nitride," and which are typically designated by the empirical formula AlXGa,_xN.
It will be understood that this general formula is used to refer to a variety of aluminum gallium nitride compounds that are in many ways similar, but that differ according to the atomic fractions of aluminum and gallium, with somewhat differing properties as well.
Tertiary Group III nitrides refer for example to indium aluminum gallium nitride, which is similarly designated In,~AlYGal_X_~,N. The reasons for using gallium nitride, aluminum, Y gallium nitride, or other ternary or tertiary nitrides are set forth in exemplary, but certainly not limiting, fashion in U.S. Patent No.
_7_ 5,523,589; 5,592,501; and 5,739,554; all of which are commonly assigned with the present invention.
Although the inventors do not wish to be bound by any particular theory of the invention, it appears that recent successes in the crystal growth of Group III
nitrides on silicon carbide has produced high-quality Group III nitride layers whose crystal structure is less susceptible to wet chemical attack than are Group III nitride layers produced by other techniques. Thus, although in one sense gallium nitride and other Group III nitrides have been recognized as being susceptible to wet chemical etch, the higher quality Group III
nitrides produced more recently are not so susceptible.
Accordingly, it appears that these higher quality gallium nitride epitaxial layers must be physically brought to a lower quality ("the stress step") before they can be successfully attacked with a wet chemical etch such as a mineral acid.
Furthermore, it will be understood that the crystal defects referred to herein, although frequently labeled as "dislocations," include, but are not limited to, slips, edge dislocations, and screw dislocations.
Accordingly, in preferred embodiments of the invention, there are several techniques for applying the stress.
A first technique is to raise the temperature of the substrate and the epitaxial layers to a temperature sufficient to dissociate the gallium nitride. In more preferred embodiments, this technique comprises heating the substrate and epitaxial layers to temperatures of _g_ about 1000°C in the presence of oxygen or argon. The equipment used for these heating steps is otherwise conventional in this art, and can be used to practice the invention without undue experimentation.
In another embodiment, the stress step comprises exposing the substrate and epitaxial layers to rapid thermal annealing (RTA). As used herein, rapid thermal annealing refers to the technique generally well understood in the semiconductor arts in which an item such as a semiconductor material is placed in a device that, because of its physical capabilities, can raise the temperature of the semiconductor material very quickly; i.e., on the order of about 10°C per second.
Again, although not wishing to be bound by any particular theory, it appears that when the lattice mismatch between the gallium nitride and silicon carbide (even in the presence of a buffer layer) is subjected to such rapid thermal stress (which is not expected in any ordinary use of the device), the mismatch creates or increases the number of defects in the crystal, particularly dislocation defects, that permit the mineral acid to attack and remove the Group III nitride.
In some embodiments, the rapid thermal annealing is carried out at relatively low pressure (e. g., about 10-6 torr), while in other circumstances, the rapid thermal annealing can be carried out in an ambient atmosphere (air) at high temperatures (e. g., 1050°C).
In yet another embodiment, the step of subjecting the Group III nitride layer to stress can comprise _g_ physically abrading the layer, for example by bombarding it with silicon carbide or aluminum oxide powders. It presently appears, however, that such physical abrasion methods may cause underlying damage to the silicon carbide substrate as well, which is a less desirable result.
In the preferred embodiments of the method, the step of contacting the epitaxial layer with a mineral acid comprises contacting the layer with phosphoric acid (H3P04) . Most preferably 85% H3P04, heated to about 170°C is used to remove the nitride epitaxial layers.
In a preferred embodiment, the etching apparatus comprises a quartz beaker and a Wollam condenser. The condenser keeps the H3P04 solution at 85% by preventing water from evaporating.
As noted above, the difficulty in removing the gallium nitride from the substrate relates back to the quality of the gallium nitride epitaxial layer, which in turn relates back to the method by which it is produced. Thus, in another aspect, the invention comprises the step of depositing the Group III nitride epitaxial layer on the substrate prior to the step of subjecting the layer to stress. More particularly, it has been found that electronically high quality Group III nitride epitaxial layers, and thus those hardest to remove, tend to be produced by metal organic chemical vapor deposition (MOCVD), and are typically of higher quality than those produced by vapor phase epitaxy (VPE). Although these processes are to a great extent similar, as used herein, vapor phase epitaxy refers to processes such as those in which a gas (such as a blend of hydrogen chloride and hydrogen) is bubbled through liquid gallium to produce a gallium chloride vapor, which is then directed to react with a nitrogen containing gas, typically ammonia (NH3), to form gallium nitride. Some VPE processes seem to inherently form dislocations and tend to capture chloride atoms or chloride ions in the resulting material.
Alternatively, MOCVD uses a metal organic compound (in which the Group III element is the metal) in the vapor phase. To some extent, the vapor phase compound will dissociate to form metal radicals. These radicals in turn react with the nitrogen containing gas (again typically ammonia) to form the Group III nitride.
Trimethyl gallium ( "TMG, " (CH3) 3Ga) is a preferred metal organic source for gallium.
Thus, in the present invention the step of depositing the Group III nitride epitaxial layer on the silicon carbide substrate preferably comprises MOCVD.
In turn, the MOCVD is preferably carried out from a vapor phase reaction between an organic Group III
compound such as TMG, and ammonia (NH3).
It will be understood, however, that the invention is not limited by the method in which the Group III
nitride layers are deposited. Other appropriate methods can include (but are not limited to) molecular beam epitaxy (MBE), the aforementioned VPE, and liquid phase epitaxy (LPE).
It has also come to be recognized in recent years that an appropriate buffer layer or layers positioned s between the silicon carbide substrate and the gallium nitride epitaxial layers can greatly improve the quality of those epitaxial layers. Thus, a preferred embodiment of the present invention further comprises depositing such a buffer layer on the silicon carbide substrate prior to the step of depositing the Group III
nitride epitaxial layers. Appropriate buffer layers are described in several of the patents already cited as well in U.S. Patent No. 5,393,993, which is commonly assiged with the present invention. The method of the invention removes these buffer layers as well.
In summary, the invention produces a silicon carbide wafer that is otherwise indistinguishable from wafers that have never carried Group III nitride epitaxial layers. Such recovered wafers can accordingly be used or processed in the same manner as "new" wafers, thus offering significant gains in the efficiency and economy of wafer and device production.
In the specification, there have been set forth preferred and exemplary embodiments, which have been included by way of example and not limitation, the scope of invention being set forth in the following claims.
Claims (9)
1. A method of recovering surface-ready silicon carbide substrates from heteroepitaxial structures of Group III nitrides on silicon carbide substrates by chemically removing the nitrides from the substrates;
characterized by:
subjecting a Group III nitride epitaxial layer on a silicon carbide substrate to a stress that sufficiently increases the number of dislocations in the epitaxial layer to make the epitaxial layer subject to attack and dissolution in a mineral acid, but that otherwise does not affect the silicon carbide substrate; and thereafter contacting the epitaxial layer with a mineral acid to remove the Group III nitride while leaving the silicon carbide substrate unaffected.
characterized by:
subjecting a Group III nitride epitaxial layer on a silicon carbide substrate to a stress that sufficiently increases the number of dislocations in the epitaxial layer to make the epitaxial layer subject to attack and dissolution in a mineral acid, but that otherwise does not affect the silicon carbide substrate; and thereafter contacting the epitaxial layer with a mineral acid to remove the Group III nitride while leaving the silicon carbide substrate unaffected.
2. A method according to Claim 1 wherein the step of subjecting the Group III nitride layer to stress comprises subjecting a layer of Al x Ga l-x-N to stress.
3. A method according to Claim 1 wherein the step of subjecting the Group III nitride layer to stress comprises subjecting a gallium nitride layer to stress.
4. A method according to Claim 1 wherein the stress step comprises heating the substrate and epitaxial layer to a temperature sufficient to cause the epitaxial layer to dissociate.
5. A method according to Claim 1 wherein the stress step comprises subjecting the substrate and epitaxial layer to rapid thermal annealing.
6. A method according to Claim 5 wherein the rapid thermal annealing is carried out at low pressure.
7. A method according to Claim 5 wherein the rapid thermal annealing is carried out in an ambient atmosphere at high temperature.
8. A method according to Claim 1 wherein the step of contacting the epitaxial layer with a mineral acid comprises contacting the layer with hot concentrated phosphoric acid.
9. A method according to Claim 1 wherein the step of subjecting the Group III nitride layer to stress comprises physically abrading the layer.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/840,961 US5923946A (en) | 1997-04-17 | 1997-04-17 | Recovery of surface-ready silicon carbide substrates |
| US08/840,961 | 1997-04-17 | ||
| PCT/US1998/006836 WO1998047185A1 (en) | 1997-04-17 | 1998-04-07 | Recovery of surface-ready silicon carbide substrates |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2286019A1 CA2286019A1 (en) | 1998-10-22 |
| CA2286019C true CA2286019C (en) | 2003-10-07 |
Family
ID=25283677
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002286019A Expired - Fee Related CA2286019C (en) | 1997-04-17 | 1998-04-07 | Recovery of surface-ready silicon carbide substrates |
Country Status (12)
| Country | Link |
|---|---|
| US (1) | US5923946A (en) |
| EP (1) | EP0976162B1 (en) |
| JP (1) | JP4063336B2 (en) |
| KR (1) | KR100569796B1 (en) |
| CN (1) | CN1123073C (en) |
| AT (1) | ATE299296T1 (en) |
| AU (1) | AU6887498A (en) |
| CA (1) | CA2286019C (en) |
| DE (1) | DE69830788T2 (en) |
| ES (1) | ES2244055T3 (en) |
| TW (1) | TW385487B (en) |
| WO (1) | WO1998047185A1 (en) |
Families Citing this family (20)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5679152A (en) * | 1994-01-27 | 1997-10-21 | Advanced Technology Materials, Inc. | Method of making a single crystals Ga*N article |
| US6533874B1 (en) | 1996-12-03 | 2003-03-18 | Advanced Technology Materials, Inc. | GaN-based devices using thick (Ga, Al, In)N base layers |
| AU747260B2 (en) | 1997-07-25 | 2002-05-09 | Nichia Chemical Industries, Ltd. | Nitride semiconductor device |
| US6459100B1 (en) * | 1998-09-16 | 2002-10-01 | Cree, Inc. | Vertical geometry ingan LED |
| US6503769B2 (en) * | 1998-10-26 | 2003-01-07 | Matsushita Electronics Corporation | Semiconductor device and method for fabricating the same |
| JP3770014B2 (en) | 1999-02-09 | 2006-04-26 | 日亜化学工業株式会社 | Nitride semiconductor device |
| DE60043536D1 (en) | 1999-03-04 | 2010-01-28 | Nichia Corp | NITRIDHALBLEITERLASERELEMENT |
| US6995032B2 (en) * | 2002-07-19 | 2006-02-07 | Cree, Inc. | Trench cut light emitting diodes and methods of fabricating same |
| KR101045160B1 (en) * | 2002-12-20 | 2011-06-30 | 크리 인코포레이티드 | Methods of forming semiconductor devices having self aligned semiconductor mesas and contact layers and related devices |
| US20050079642A1 (en) * | 2003-10-14 | 2005-04-14 | Matsushita Elec. Ind. Co. Ltd. | Manufacturing method of nitride semiconductor device |
| US7008861B2 (en) * | 2003-12-11 | 2006-03-07 | Cree, Inc. | Semiconductor substrate assemblies and methods for preparing and dicing the same |
| JP2006253172A (en) * | 2005-03-08 | 2006-09-21 | Toshiba Corp | Semiconductor light emitting element, semiconductor light emitting apparatus and method of manufacturing semiconductor light emitting element |
| US20060267043A1 (en) * | 2005-05-27 | 2006-11-30 | Emerson David T | Deep ultraviolet light emitting devices and methods of fabricating deep ultraviolet light emitting devices |
| TWI362769B (en) | 2008-05-09 | 2012-04-21 | Univ Nat Chiao Tung | Light emitting device and fabrication method therefor |
| TW201310692A (en) * | 2011-08-31 | 2013-03-01 | Solution Chemicals Inc | Reproducing method of LED substrate |
| CN102593285B (en) * | 2012-03-06 | 2014-07-09 | 华灿光电股份有限公司 | Method for recovering pattern sapphire substrate |
| KR101226904B1 (en) * | 2012-07-31 | 2013-01-29 | 주식회사 세미콘라이트 | Method of recycling a substrate used for depositng iii-nitride semiconductor thereon |
| KR101226905B1 (en) * | 2012-07-31 | 2013-01-29 | 주식회사 세미콘라이트 | Method of recycling a substrate used for depositng iii-nitride semiconductor thereon |
| CN103730548B (en) * | 2013-12-28 | 2016-07-06 | 福建省诺希新材料科技有限公司 | A kind of method utilizing high temperature oxidation stability gas to reclaim patterned sapphire substrate |
| TWI737610B (en) | 2015-05-20 | 2021-09-01 | 美商納諾光子公司 | Processes for improving efficiency of light emitting diodes |
Family Cites Families (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS50113500A (en) * | 1974-02-15 | 1975-09-05 | ||
| US3923567A (en) * | 1974-08-09 | 1975-12-02 | Silicon Materials Inc | Method of reclaiming a semiconductor wafer |
| US4009299A (en) * | 1975-10-22 | 1977-02-22 | Motorola, Inc. | Tin strip formulation for metal to glass seal diodes |
| JPS5343480A (en) * | 1976-10-01 | 1978-04-19 | Matsushita Electric Ind Co Ltd | Etching method of gallium nitride |
| JPS60960B2 (en) * | 1979-12-17 | 1985-01-11 | 松下電器産業株式会社 | Method for manufacturing gallium nitride light emitting device array |
| DE3725346A1 (en) * | 1987-07-30 | 1989-02-09 | Nukem Gmbh | METHOD FOR REUSE OF SILICON BASE MATERIAL OF A METAL ISOLATOR SEMICONDUCTOR (MIS) INVERSION LAYER SOLAR CELL |
| JPH02228470A (en) * | 1989-03-02 | 1990-09-11 | Toshiba Corp | Sputtering target |
| US5030536A (en) * | 1989-12-26 | 1991-07-09 | Xerox Corporation | Processes for restoring amorphous silicon imaging members |
| US5131979A (en) * | 1991-05-21 | 1992-07-21 | Lawrence Technology | Semiconductor EPI on recycled silicon wafers |
| US5393993A (en) * | 1993-12-13 | 1995-02-28 | Cree Research, Inc. | Buffer structure between silicon carbide and gallium nitride and resulting semiconductor devices |
| EP0668611A1 (en) * | 1994-02-22 | 1995-08-23 | International Business Machines Corporation | Method for recovering bare semiconductor chips from plastic packaged modules |
| US5523589A (en) * | 1994-09-20 | 1996-06-04 | Cree Research, Inc. | Vertical geometry light emitting diode with group III nitride active layer and extended lifetime |
| SE9501312D0 (en) * | 1995-04-10 | 1995-04-10 | Abb Research Ltd | Method of procucing a semiconductor device |
-
1997
- 1997-04-17 US US08/840,961 patent/US5923946A/en not_active Expired - Lifetime
-
1998
- 1998-04-07 JP JP54398498A patent/JP4063336B2/en not_active Expired - Lifetime
- 1998-04-07 EP EP98914546A patent/EP0976162B1/en not_active Expired - Lifetime
- 1998-04-07 CN CN98804197A patent/CN1123073C/en not_active Expired - Lifetime
- 1998-04-07 AT AT98914546T patent/ATE299296T1/en not_active IP Right Cessation
- 1998-04-07 ES ES98914546T patent/ES2244055T3/en not_active Expired - Lifetime
- 1998-04-07 KR KR1019997009641A patent/KR100569796B1/en not_active IP Right Cessation
- 1998-04-07 DE DE69830788T patent/DE69830788T2/en not_active Expired - Lifetime
- 1998-04-07 AU AU68874/98A patent/AU6887498A/en not_active Abandoned
- 1998-04-07 CA CA002286019A patent/CA2286019C/en not_active Expired - Fee Related
- 1998-04-07 WO PCT/US1998/006836 patent/WO1998047185A1/en active IP Right Grant
- 1998-04-17 TW TW087105882A patent/TW385487B/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| ATE299296T1 (en) | 2005-07-15 |
| EP0976162A1 (en) | 2000-02-02 |
| KR20010006551A (en) | 2001-01-26 |
| ES2244055T3 (en) | 2005-12-01 |
| CN1123073C (en) | 2003-10-01 |
| JP4063336B2 (en) | 2008-03-19 |
| CN1252895A (en) | 2000-05-10 |
| WO1998047185A1 (en) | 1998-10-22 |
| DE69830788D1 (en) | 2005-08-11 |
| JP2001525121A (en) | 2001-12-04 |
| TW385487B (en) | 2000-03-21 |
| CA2286019A1 (en) | 1998-10-22 |
| EP0976162B1 (en) | 2005-07-06 |
| US5923946A (en) | 1999-07-13 |
| KR100569796B1 (en) | 2006-04-10 |
| DE69830788T2 (en) | 2006-05-04 |
| AU6887498A (en) | 1998-11-11 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA2286019C (en) | Recovery of surface-ready silicon carbide substrates | |
| US5679152A (en) | Method of making a single crystals Ga*N article | |
| Okumura et al. | Growth and characterization of cubic GaN | |
| US6943095B2 (en) | Low defect density (Ga, A1, In) N and HVPE process for making same | |
| US20170186913A1 (en) | Formation of nitride-based optoelectronic and electronic device structures on lattice-matched substrates | |
| US7012016B2 (en) | Method for growing group-III nitride semiconductor heterostructure on silicon substrate | |
| WO1996041906A1 (en) | Bulk single crystal gallium nitride and method of making same | |
| Ghosh et al. | Reduced-stress GaN epitaxial layers grown on Si (1 1 1) by using a porous GaN interlayer converted from GaAs | |
| US10043662B2 (en) | Method of forming semiconductor substrate | |
| Tansley et al. | The contribution of defects to the electrical and optical properties of GaN | |
| US6906351B2 (en) | Group III-nitride growth on Si substrate using oxynitride interlayer | |
| US6623877B2 (en) | III nitride epitaxial wafer and usage of the same | |
| Moustakas | Epitaxial growth of GaN films produced by ECR-assisted MBE | |
| JP3758537B2 (en) | Method for producing group III nitride compound semiconductor | |
| Lee et al. | Improvements in the heteroepitaxy of GaAs on Si by incorporating a ZnSe buffer layer | |
| Davis et al. | Growth via Mocvd and Characterization Of GaN and AlxGa1− xN (0001) Alloys for Optoelectronic and Microelectronic Device Applications | |
| Willardson et al. | Gallium-Nitride (GaN) II | |
| Yam et al. | The growth of III-V nitrides heterostucture on Si substrate by plasma-assisted molecular beam epitaxy | |
| Sukach et al. | Structure and composition of gallium nitride films produced by processing gallium arsenide single crystals in atomic nitrogen | |
| Pearton et al. | Hydrogen Diffusion and Passivation in InGaAIN Alloys | |
| JP2003073195A (en) | Method for producing gallium nitride crystal and gallium nitride crystal |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |
Effective date: 20130408 |
|
| MKLA | Lapsed |
Effective date: 20130408 |