US20050173715A1 - Nitride semiconductor devices and method of their manufacture - Google Patents

Nitride semiconductor devices and method of their manufacture Download PDF

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US20050173715A1
US20050173715A1 US10/514,261 US51426104A US2005173715A1 US 20050173715 A1 US20050173715 A1 US 20050173715A1 US 51426104 A US51426104 A US 51426104A US 2005173715 A1 US2005173715 A1 US 2005173715A1
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film
substrate
nitrogen
semiconductor substrate
semiconductor
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Takashi Kyono
Masaki Ueno
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Sumitomo Electric Industries Ltd
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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
    • C30B25/02—Epitaxial-layer growth
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/40—AIIIBV compounds wherein A is B, Al, Ga, In or Tl and B is N, P, As, Sb or Bi
    • C30B29/403—AIII-nitrides
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/40—AIIIBV compounds wherein A is B, Al, Ga, In or Tl and B is N, P, As, Sb or Bi
    • C30B29/403—AIII-nitrides
    • C30B29/406—Gallium nitride
    • 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
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02367—Substrates
    • H01L21/0237—Materials
    • H01L21/02387—Group 13/15 materials
    • H01L21/02389—Nitrides
    • H—ELECTRICITY
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    • 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
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02367—Substrates
    • H01L21/0237—Materials
    • H01L21/02387—Group 13/15 materials
    • H01L21/02395—Arsenides
    • 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
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02367—Substrates
    • H01L21/0237—Materials
    • H01L21/0242—Crystalline insulating materials
    • 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
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02367—Substrates
    • H01L21/02428—Structure
    • H01L21/0243—Surface structure
    • 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
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02436—Intermediate layers between substrates and deposited layers
    • H01L21/02439—Materials
    • H01L21/02455—Group 13/15 materials
    • H01L21/02458—Nitrides
    • 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
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02436—Intermediate layers between substrates and deposited layers
    • H01L21/02494—Structure
    • H01L21/02496—Layer structure
    • H01L21/02505—Layer structure consisting of more than two layers
    • 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
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/02521—Materials
    • H01L21/02538—Group 13/15 materials
    • H01L21/0254—Nitrides
    • 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
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02612—Formation types
    • H01L21/02617—Deposition types
    • H01L21/0262—Reduction or decomposition of gaseous compounds, e.g. CVD
    • H—ELECTRICITY
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    • 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
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02656—Special treatments
    • H01L21/02658—Pretreatments
    • H01L21/02661—In-situ cleaning
    • 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
    • Y10S438/906—Cleaning of wafer as interim step

Definitions

  • the present invention relates to nitride semiconductor devices such as light-emitting devices, and to methods of their manufacture; more specifically, the present invention relates to high-quality nitride semiconductor devices excelling in flatness and manufacturable at high yields, and to methods of manufacturing such devices.
  • the substrate is annealed with the object of ridding the substrate of contaminants (organic matter, moisture) adhering to it, and defects (scratches, strain, etc.).
  • this heating process is performed prior to the epitaxial film growth, the process is called “pretreating,” “preheating,” “cleaning,” “purification,” or simply “annealing.”
  • the substrate heating temperature in removing the contaminants and defects has been made at or above the temperature to which the substrate is heated in the deposition process for growing an epitaxial film onto the post-treated substrate (patent documents including Japanese Unexamined Pat. App. Pub. Nos. 2000-174341 and 2000-323752).
  • the motivation behind this is that it has taken over from a procedural operation, in methods of manufacturing silicon-based semiconductor devices, in which the substrate temperature for cleaning is made to be at or above the film-deposition temperature of the substrate—with cleaning being stressed, because the higher the substrate heating temperature in pretreating is made, the better cleaning will progress.
  • the substrate surface can be cleaned by making the temperature to which the substrate is heated in the pretreating process be at or above the temperature to which the substrate is heated in the film-deposition process.
  • An atmosphere from which source-material gas containing the Group 3B (Japanese periodic system) element has been omitted from among the ambient gases that are introduced in the film-deposition operation is generally employed as the annealing atmosphere.
  • the reason for this is because nitrogen tends to come loose from the surface part of the substrates, leading to surplus Group 3B element there, which is liable to produce roughness in the surface of a nitride semiconductor substrate. Accordingly, to keep roughness originating in the accumulation of surplus Group 3B element on the substrate surface from occurring, arrangements are made for an atmosphere as just noted that does not contain Group 3B element, and the escape of nitrogen from the substrate is controlled.
  • An object of the present invention is to make available nitride-based semiconductor devices, and a method of their manufacture, wherein epitaxial films excelling in flatness and crystallinity can be grown onto nitride semiconductor substrates.
  • a method according to the present invention of manufacturing nitride-based semiconductor devices is a method of manufacturing nitride semiconductor devices that are formed onto a semiconductor substrate that is a compound containing a Group 3B element for forming compounds with nitrogen, and nitrogen.
  • This manufacturing method includes steps of heating the semiconductor substrate to a film-deposition temperature, supplying to the substrate a film-deposition gas containing a source-material gas for the Group 3B element, together with a nitrogen source-material gas, and epitaxially growing onto the semiconductor substrate a thin film of a compound containing the Group 3B element and nitrogen.
  • the method is furnished with a step, in advance of the epitaxial growth step, of heating the semiconductor substrate to a pretreating temperature less than the film-deposition temperature, to clean the surface of the semiconductor substrate.
  • the substrate surface is cleaned by heating the substrate to a temperature lower than the substrate-heating temperature in the film deposition process.
  • the fact that the substrate heating temperature is comparatively high from the outset in the course of growing a nitride-semiconductor epitaxial film makes it possible to set the pre-heating temperature in the cleaning step to what will guarantee sufficient cleaning action. Satisfactory planarity along the substrate surface can therefore be ensured, and the flatness of the epitaxial film formed on the substrate surface proves to be superior as a result.
  • the substrate heating temperature will differ depending on the location of the temperature sensors or temperature gauges furnished in the thin-film formation equipment, or on how the instruments are mounted, it is sufficient that, according to the same temperature indicator within the film-deposition device, the heating temperature during cleaning is lower than the substrate temperature during film deposition—the absolute numerical value of the temperature will not be an issue.
  • a pretreatment gas in which the proportion of Group-3B-element source gas has been reduced below what it is in the film-deposition gas for the epitaxial growth step can be supplied.
  • lowering what the substrate temperature measures during the cleaning step minimizes the likelihood that precedential breaking away of nitrogen—originating in the fact that the vapor pressure of nitrogen is high—as well as accumulation of excess Group 3B element will occur, making it possible to avert degradation of the front-side planarity.
  • One example of the aforementioned pretreatment gas may be one made not to contain Group-3B-element source gas. Gas from which source-material gas containing the Group 3B element has been omitted from among the ambient gases that are introduced in the film-deposition step can be utilized as such a pretreatment gas. As a result, the necessity of having to seek out by trial and error the requirements for gas-supply during the cleaning process is eliminated, wherein the parameters for an efficient cleaning operation can be set.
  • Group 3B elements include Al (aluminum), Ga (gallium) and In (indium), wherein the fabrication at high yields of semiconductor devices in which semiconductors that are nitrides of these elements are the base—semiconductor devices of laminated construction, excelling in flatness over what has been conventional—becomes possible.
  • Nitride-based semiconductor devices by the present invention are furnished with a semiconductor substrate that is formed from a compound containing a Group 3B element for forming compounds with nitrogen, and nitrogen, and, formed onto the semiconductor substrate, with an epitaxial semiconductor film containing the Group 3B element and nitrogen.
  • the smoothness of the semiconductor substrate surface is 15 nm or less in root-mean-square roughness.
  • the planarity of the epitaxial film formed on the surface of the nitride semiconductor substrate can be made superlative. Having it that the RMS roughness exceeds 15 nm gives rise to hexagonal hillocks when the epitaxial film has been formed to a thickness of approximately 2 ⁇ m, in which case not only that epitaxial film, but also epitaxial films formed onto it turn out to be layers in which the crystallinity is spoiled, which degrades the device quality.
  • the epitaxial deposition would not grow into a continuous film when having been formed to a thickness on the order of 0.5 ⁇ m, on account of the unevenness in the substrate surface.
  • the root-mean-square roughness of the semiconductor substrate may, moreover, be rendered 5 nm or less.
  • the 10-point peak-and-valley mean roughness Rz of the epitaxial film may be 15 nm or less.
  • This configurational aspect not only makes excellent the crystallinity and flatness of the epitaxial film itself, but also contributes to guaranteeing the crystallinity and flatness of epitaxial films that are formed onto this epitaxial film.
  • the Rz roughness is determined based on peaks and valleys on an epitaxial film that is as noted above, in the state in which no thin films have been further grown onto the epitaxial film. Utilizing any sort of method as long as the method can detect roughness of the epitaxial film after it has been built up with semiconductor devices, measurement of the roughness may be by any sort of method as long as it can gauge the epitaxial smoothness.
  • the 10-point mean roughness Rz of the epitaxial film may, moreover, be rendered 7.5 nm or less. More outstanding flatness and crystallinity of the film are ensured as a result to enable high-quality semiconductor devices to be fabricated with good yields.
  • the front-side surface of the epitaxial film is kept from having peaks and valleys of 50 nm to 150 nm height appearing at a pitch of 100 ⁇ m to 150 ⁇ m.
  • the hexagonal hillocks on the epitaxial film are observed to be peaks and valleys of 50 nm to 150 nm height at a pitch of 100 ⁇ m to 150 ⁇ m. Having the RMS roughness of the semiconductor substrate be, as stated above, no more than 15 nm makes it so that the hexagonal hillocks do not arise.
  • the consequent benefit is that, excelling in flatness, the epitaxial film makes it possible to improve the crystallinity of films formed onto the epitaxial film.
  • FIG. 1 is a sectional view representing a blue LED that is a nitride semiconductor device in an embodiment of the present invention.
  • FIG. 2 is a diagram illustrating a method, in an embodiment of the present invention, of manufacturing nitride semiconductor devices.
  • FIG. 3 is views showing surface morphology in 10 ⁇ m ⁇ 10 ⁇ m of the surface of GaN substrates, being micrographs depicting the surface morphology of, in FIG. 3A , a raw substrate that had not been pretreated; in FIG. 3B , a GaN substrate that underwent pretreating at 1025° C.; and in FIG. 3C , a GaN substrate that underwent pretreating at 1150° C.
  • FIG. 4 is views showing observations by differential interference contrast microscopy of the surface of a semiconductor device in respective fabrication stages in the present invention, the views being photographs of, in FIG. 4A , the substrate after being pretreated at 1025° C.; in FIG. 4B , a GaN film having been grown to a layer thickness of 0.5 ⁇ m onto the substrate in FIG. 4A ; and in FIG. 4C , the GaN film having been grown to a layer thickness of 2 ⁇ m onto the FIG. 4A substrate.
  • FIG. 5 is views showing observations by differential interference contrast microscopy of the surface of a semiconductor device in respective fabrication stages in a comparative example, the views being photographs of, in FIG. 5A , the substrate after being pretreated at 1150° C.; in FIG. 5B , a GaN film having been grown to a layer thickness of 0.5 ⁇ m onto the substrate in FIG. 5A ; and in FIG. 5C , the GaN film having been grown to a layer thickness of 2 ⁇ m onto the substrate in FIG. 5A .
  • FIG. 6 is a diagram showing the results of measuring, using a stylus surface profilometer, the surface roughness of a GaN film corresponding to that in FIG. 4C , deposited at a thickness of 2 ⁇ m.
  • FIG. 7 is a diagram showing the results of measuring, using a stylus surface profilometer, the surface roughness of a GaN film corresponding to that in FIG. 5C , deposited at a thickness of 2 ⁇ m.
  • FIG. 1 is a diagram representing a light-emitting device that is a semiconductor device in an embodiment of the present invention.
  • a Ti—Al layer 9 that forms an n-type electrode is provided on the back side of a GaN substrate 1 in FIG. 1 .
  • An n-type buffer layer 2 consisting of a GaN film doped with Si is epitaxially grown onto the front side of the GaN substrate 1 .
  • An n-type cladding layer 3 consisting of an epitaxial film—an Al 0.07 GaN film—obtaining Si is formed onto the n-type buffer layer 2 .
  • An active layer 4 that is the light-emitting portion is situated between the n-type cladding layer 3 and a p-type cladding layer 5 .
  • the active layer 4 is formed as an In 0.2 GaN—GaN multi-quantum well structure.
  • the p-type cladding layer 5 atop the active layer 4 is formed as an Al 0.07 GaN film containing Mg as a dopant. In order to secure favorable crystallinity in these layers each is formed as an epitaxial film.
  • a p-type contact layer 6 consisting of a GaN film containing Mg, and further, atop that, a p-type electrode 7 consisting of a Ni—Au metal film are provided. Over that a pad electrode 8 is formed.
  • the front side of the GaN substrate 1 in the cleaning step undergoes a cleaning process whereby the substrate is heated to a temperature lower than the temperature of the substrate when in the film-deposition step.
  • Roughness in the front side of the GaN substrate 1 is thereby held down to being 15 nm or less in root mean square (RMS) roughness, and can moreover be brought to 5 nm or less.
  • RMS root mean square
  • the semiconductor-substrate front side minimizing roughness of the semiconductor-substrate front side and forming epitaxial films onto that front side enables the crystal properties of the epitaxial films to be made superb. As a result, the quality of light-emitting characteristics can be enhanced—such as in emission-efficiency improvement and in narrowed emission-beam width.
  • a further advantage is that enhancing the flatness of the n-type buffer layer 2 on the GaN substrate to simplify the structure of the light-emitting device enables yields to be improved. Peaks and valleys at a 100 ⁇ m to 150 ⁇ m pitch should not be present on the front-side surface of the n-type buffer layer; in other words, the layer should be made not to produce hexagonal hillocks. This may be realized, as discussed above, getting the RMS roughness of the semiconductor substrate to be 15 nm or less. Likewise, the 10-point mean roughness Rz of the epitaxial film surface can be rendered 15 nm or less. The roughness Rz can even be made 7.5 or less. Naturally, these curbs on the roughness, through improvement in crystal properties and improvement in flatness, contribute to improving the quality of the semiconductor devices and to improving manufacturing yields.
  • FIG. 2 is a diagram that explanatorily illustrates a method of manufacturing semiconductor devices as described above.
  • T 1 the substrate heating temperature in the cleaning step
  • T 2 the substrate heating temperature in the following film-deposition step.
  • the flow rate of the nitrogen source gas is given as N 1
  • G 1 may be zero.
  • Hydrogen gas and other source gases may be included as well.
  • the substrate heating temperature is given as T 2 , the flow rate of the nitrogen source gas as N 2 , and the flow rate of the Ga source gas as G 2 .
  • the substrate heating temperatures T 2 >T 1 and the condition that the flow rates of the Ga source gas be G 2 >G 1 ⁇ 0 is imposed.
  • the flow rate of the Ga source gas in the cleaning step is made lower than what it is in the film-deposition step, but the addition or subtraction of other source gases is not performed.
  • the following three events conflict with each other. Namely, the three events are: (g1) the breaking away of Ga and N; (g2) the supplying of Ga from the Ga source gas; and (g3) the supplying of N from the N source gas.
  • the three events are: (g1) the breaking away of Ga and N; (g2) the supplying of Ga from the Ga source gas; and (g3) the supplying of N from the N source gas.
  • pretreating gas supply requirements be the aforementioned film-deposition source-gas supply requirements minus the Ga source gas (Group III source gas).
  • Ga source gas Group III source gas
  • Making the preheating temperature lower than the film-deposition temperature rids the GaN substrate surface of imbalances from accumulation and breaking away of the atoms constituting the epitaxial film, even with a pretreating gas in which Ga source gas has been omitted from the film-deposition gases being employed.
  • a substrate front side of favorable flatness and crystallinity, suited to growing epitaxial films, can be achieved as a result. Since it involves only one parameter, optimizing the substrate temperature is easy compared with optimizing the preheating-gas supply conditions.
  • the temperatures at which nitride semiconductor films are deposited are fundamentally high, even with the preheating temperature made lower than the film-deposition temperature, there is no harm to the cleaning effectiveness.
  • the gas flow rate in supplying the source gases that, with the source gas for Ga or other Group III element being omitted, remain may be made the same as the gas flow rate during film deposition.
  • the pretreating temperature is lower than the film-deposition temperature, there will be no occurrence of the imbalances noted above. Therefore, simply by omitting the Ga source gas from the film-deposition-gas supply requirements as described above, optimization of the pretreating-gas supply requirements by designating an immense number of parameters need not be carried out.
  • a GaN substrate was utilized, and a cleaning process (pretreatment) was implemented on the GaN substrate, onto which a homoepitaxial film was thereafter deposited.
  • the pretreating conditions as film-deposition conditions are as noted below.
  • Substrate temperature Present invention example: 1025° C.;
  • Substrate temperature 1150° C.
  • the GaN substrate Utilized as the GaN substrate was a bulk crystal prepared by growing a thick GaN film onto a GaAs substrate with SiO 2 made the mask and thereafter removing the GaAs substrate.
  • the Ga source gas TMG was omitted, and ammonia as the nitrogen source gas, and nitrogen and hydrogen as the carrier gases alone were flowed according to the same flow parameters as those in the film-deposition conditions noted above.
  • the root-mean-square (RMS) roughness of the substrate after having undergone the pretreatment was assessed using atomic force microscopy (AFM).
  • AFM atomic force microscopy
  • FIG. 3 is micrographs made using AFM, showing 10 ⁇ m ⁇ 10 ⁇ m of roughness, for RMS calculations, along the front side of the GaN substrate.
  • the views show results for, in FIG. 3A , a GaN substrate with no pretreatment (raw substrate/comparative example); in FIG. 3B , a GaN substrate that underwent pretreating at a 1025° C. substrate temperature (present-invention example); and in FIG. 3C , a GaN substrate that, similarly as is conventional, underwent pretreating at a substrate temperature that was the same as the film-deposition temperature (comparative example).
  • RMS calculations for the foregoing samples within 2 ⁇ m ⁇ 2 ⁇ m and 10 ⁇ m ⁇ 10 ⁇ m bounds are set forth in the Table.
  • the sample pretreated at a substrate temperature that was the same 1150° C. that is the film-deposition temperature had an RMS roughness of over 20 nm; thus its surface roughness compared to that of the raw substrate on which pretreatment had not been carried out had grown drastically, deteriorating the substrate quality.
  • the size of a single gradation along the taxis in FIG. 3C is ten times that of the zaxes in FIGS. 3A and 3B , and although the magnitude of the disparity just noted is thus somewhat hard to discern, the disparity is unmistakable.
  • the 2 ⁇ m ⁇ 2 ⁇ m RMS roughness is 0.6 nm, which is markedly superior to the 1.3 nm of the raw substrate.
  • the 10 ⁇ m ⁇ 10 ⁇ m RMS roughness, 1.5 nm, is superior to the 2.0 nm of the raw substrate, and proved to measure one order of magnitude smaller than the 23.6 nm RMS roughness of the comparative example.
  • the substrate is cleaned without its flatness being harmed.
  • an epitaxial film onto a GaN substrate that has been pretreated at a substrate temperature of 1025° C. an atomically stepped surface in which the RMS roughness is 0.5 nm or less can be achieved.
  • FIG. 4 is views showing results of using differential interference contrast microscopy to observe, following stages, the surface of a sample in an example of the present invention.
  • FIG. 4A is a photograph in which a GaN substrate after being pretreated correspondingly to the substrate in FIG. 3B is observed by differential interference microscopy;
  • FIG. 4B is a photograph of a GaN film at the point at which it has been epitaxially grown, according to the foregoing film-deposition conditions, 0.5 ⁇ m thick onto the GaN substrate;
  • FIG. 4C is a photograph of the GaN film after it has been epitaxially grown 2 ⁇ m thick.
  • FIG. 4A is a photograph in which a GaN substrate after being pretreated correspondingly to the substrate in FIG. 3B is observed by differential interference microscopy
  • FIG. 4B is a photograph of a GaN film at the point at which it has been epitaxially grown, according to the foregoing film-deposition conditions, 0.5 ⁇ m thick onto the GaN substrate
  • FIG. 5 is views showing results of likewise using differential interference contrast microscopy to observe, following stages, the surface of a sample in a comparative example corresponding to that of FIG. 3C .
  • FIG. 5A is a photograph in which a GaN substrate after being pretreated correspondingly to the substrate in FIG. 3C is observed by differential interference microscopy;
  • FIG. 5B is a photograph of a GaN film at the point at which it has been epitaxially grown, according to the foregoing film-deposition conditions, 0.5 ⁇ m thick onto the GaN substrate;
  • FIG. 5C is a photograph of the GaN film after it has been epitaxially grown 2 ⁇ m thick.
  • FIGS. 6 and 7 are diagrams showing the results of measuring, using a stylus surface profilometer, the surface roughness of GaN films deposited at 2 ⁇ m thickness, corresponding to those in FIGS. 4C and 5C .
  • the surface roughness profile of the comparative example peaks and valleys whose height/depth is 50 nm to 150 nm, at a pitch of 100 ⁇ m to 150 ⁇ m are ascertainable. This is analogous to the roughness from the hexagonal hillocks verified in the FIG. 5C differential-interference-microscopy photograph.
  • FIG. 6 of the present-invention example on account of the film-deposition process having been carried out after pretreatment at 1025° C. was performed, no heavy roughness can be ascertained.
  • the amplitude of the roughness of the semiconductor substrate, etc. in the semiconductor devices of the present invention is based on the roughness prior to a thin film being formed on the substrate, etc.—with the description, including that of the mode for carrying out the invention, presuming that even once other thin films have been formed on the substrate, etc. the roughness will not undergo a significant change. Nevertheless, the actual amplitude of the roughness in the front side after it has been fabricated into semiconductor devices will depend significantly on the measuring method—particularly in implementations in which the surface roughness is exposed by etching, on the etching technique. And it will also depend on the precision of the device with which the roughness is measured. It is believed that, in determining the roughness amplitude of the surface of the respective areas in the semiconductor devices of the present invention, the best measuring method and the best measuring device have been specified.
  • nitride-based semiconductor devices and a method of their manufacture makes it possible to achieve nitride-based semiconductor devices containing epitaxial films excelling in flatness and crystallinity.

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EP1601009A8 (de) 2006-02-01
CA2495908A1 (en) 2004-09-16
US20080132044A1 (en) 2008-06-05
CN100580881C (zh) 2010-01-13
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TWI324424B (de) 2010-05-01
CN1698184A (zh) 2005-11-16
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EP1601009A4 (de) 2010-07-14
KR101036223B1 (ko) 2011-05-20
TW200423509A (en) 2004-11-01

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