WO2014012237A1 - Method and apparatus for growing nitride-based compound semiconductor crystals - Google Patents

Method and apparatus for growing nitride-based compound semiconductor crystals Download PDF

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Publication number
WO2014012237A1
WO2014012237A1 PCT/CN2012/078899 CN2012078899W WO2014012237A1 WO 2014012237 A1 WO2014012237 A1 WO 2014012237A1 CN 2012078899 W CN2012078899 W CN 2012078899W WO 2014012237 A1 WO2014012237 A1 WO 2014012237A1
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Prior art keywords
gas
reactant
ammonia
zones
metalorganic
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PCT/CN2012/078899
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French (fr)
Inventor
Zhanchao HUANG
Chuan He
Yue Ma
Hungseob Cheong
Tao Song
Sal Umotoy
Bing Hu
Ming Xi
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Ideal Energy Equipment (Shanghai) Ltd.
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Priority to PCT/CN2012/078899 priority Critical patent/WO2014012237A1/en
Priority to CN201280001823.5A priority patent/CN104603328B/en
Publication of WO2014012237A1 publication Critical patent/WO2014012237A1/en

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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
    • C23C16/30—Deposition of compounds, mixtures or solid solutions, e.g. borides, carbides, nitrides
    • C23C16/301—AIII BV compounds, where A is Al, Ga, In or Tl and B is N, P, As, Sb or Bi
    • C23C16/303—Nitrides
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
    • C23C16/455—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating characterised by the method used for introducing gases into reaction chamber or for modifying gas flows in reaction chamber
    • C23C16/45523—Pulsed gas flow or change of composition over time
    • C23C16/45525—Atomic layer deposition [ALD]
    • C23C16/45544—Atomic layer deposition [ALD] characterized by the apparatus
    • C23C16/45548—Atomic layer deposition [ALD] characterized by the apparatus having arrangements for gas injection at different locations of the reactor for each ALD half-reaction
    • C23C16/45551—Atomic layer deposition [ALD] characterized by the apparatus having arrangements for gas injection at different locations of the reactor for each ALD half-reaction for relative movement of the substrate and the gas injectors or half-reaction reactor compartments
    • 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
    • C30B25/14—Feed and outlet means for the gases; Modifying the flow of the reactive gases
    • 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
    • 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

Definitions

  • the present invention generally relates to a Metalorganic Vapor Deposition (MOCVD) method and an apparatus for growing semiconductor crystal, more particularly for fabricating Nitride-based compound semiconductors with substantially high Al content between 20% and 100%.
  • MOCVD Metalorganic Vapor Deposition
  • MOCVD Metal organic chemical vapor deposition
  • MOCVD Metal organic chemical vapor deposition
  • epitaxy growth is initiated by the thermal pyrolysis of group II or III metal-organic sources and group VI or V hydrides, with the nitrogen or hydrogen as the carrier gas, injected into the reactor with pre-determined proportions.
  • group II or III metal-organic sources and group VI or V hydrides with the nitrogen or hydrogen as the carrier gas, injected into the reactor with pre-determined proportions.
  • Several reaction pathways compete in both vapor phase and on the surface of hot substrate, and the metal-organic source consumption in the vapor phase is an important factor affecting the composition of the deposited film, thereby its final opto-electronic properties.
  • reaction space in the reactor gas temperature, substrate temperature, gas flow field, and operating pressure, all play important roles in growing II- VI or III-V semiconductor materials and their alloys of desired properties.
  • MOCVD reactor design a great deal of focus has been put forward to better control aforementioned process parameters.
  • One particular area is the design of reactant gas distribution device, for its contribution to forming a uniformly mixed gaseous environment above the hot substrate where epitaxial growth takes place is believed to be essential in MOCVD process.
  • AlGaN/GaN materials system is used for different purposes.
  • Aluminum Gallium Nitride (AlGaN) has a direct transition band gap between 3.4 and 6.2 eV, thus it is often used as active region of UV LED, deep UV LED and UV detectors. It could also be used as buffer layer to block dislocations and relax the strains between active layers and underneath substrate to improve the device performance.
  • AlGaN Aluminum Gallium Nitride
  • the wavelength of the LED - the higher the Al content, the shorter the wavelength.
  • the Al content over the Ga content is greater than 40%.
  • the AlGaN/GaN super lattice (SL) used as buffer layers on Si substrate for LED or HEMT application the Al content is generally over 70%.
  • Al composition in the epitaxial film (solid phase) grown on the hot substrate is commonly controlled by the composition in the gaseous phase, gas flow velocity, and operating pressure.
  • the Al composition in the solid phase increases with that in the gaseous phaseto a point beyond which a saturation of Al content is reached.
  • a MOCVD method to synthesize Group III-V nitride-based compound semiconductor crystals with high Al content comprising:
  • a reactant gas distribution apparatus comprising:
  • an inlet side where at least one inlet connecting to metalorganic source reactant gas feed, at least one inlet connecting to ammonia reactant gas feed, and at least one inlet connecting purge gas,
  • a first gas distribution member connecting said inlet side, consisting of a gas connection channels isolating said metalorganic source reactant from said ammonia reactant and distributing reactant gases from said inlets to said reactant distributing zones;
  • a plurality of second gas distribution members connecting to said outlet side, each consisting of a plurality of gas outlets and gas connection channels distributing reactant gas from each of said reactant distribution zones to gas outlets that guide reactant gas flow to exit vertically to said outlet side; at least one third gas distribution member consisting of an inlet gas switch among metalorganic source reactant gas, ammonia reactant gas, and nitrogen purge gas feed, gas flow connection channels, and an outlet gas injector that guides reactant gas flow exiting gas injector horizontally to said outlet side.
  • One characteristic of this invention is that the reactants mix inhomogeneously in the gaseous environment to form a plurality of alternating zones, one rich in metalorganic source and the other rich in ammonia, immediately above the epitaxy substrates.
  • This inhomogeneously mixed gaseous phase reduces parasitic reaction to only regionswhere one zone rich in metalorganic source and the other rich in ammonia meet.
  • the hot epitaxy substrates continuously move under said alternating zones of reactants, passing each zone at the time scales from a few milliseconds to a few tens of milliseconds.
  • compound semiconductor crystals with high Al content between 20% and 100% can be made by an economical process ata reduced consumption rate of metalorganic precursors.
  • Fig. 1 illustrates the side view of part of the gas distribution apparatus
  • Fig. 2 illustrates the side view of the reaction spacing between the gas distribution apparatus and the substrates
  • Fig. 3a illustrates the side view of a first embodiment of the center gas injector
  • Fig. 3b illustrates the side view of a second embodiment of the center gas injector
  • Fig. 3c illustrates the side view of a third embodiment of the center gas injector
  • Fig. 4a illustrates the bottom view of part of one embodiment of the gas distribution apparatus
  • Fig. 4b illustrates the bottom view of part of another embodiment of the gas distribution apparatus
  • Fig. 5a illustrates the ammonia mass fraction on the plane of the substrate surface with one distance between the gas distribution apparatus and substrates by computer simulation
  • Fig. 5b illustrates the ammonia mass fraction on the plane of the substrate surface with another distance between the gas distribution apparatus and substrate by computer simulation
  • Fig. 6a illustrates side view of the reaction spacing between the gas distribution apparatus and the substrates at one time
  • Fig. 6b illustrates side view of the reaction spacing between the gas distribution apparatus and the substrates at another time
  • Fig. 7 illustrates the ⁇ -2 ⁇ scan curve by XRD for one AlGaN sample prepared in the MOCVD apparatus
  • Fig. 8 illustrates the ⁇ -2 ⁇ scan curve by XRD for another AlGaN sample prepared in the MOCVD apparatus
  • Fig. 9 illustrates the chart of the Al concentration in the AlGaN films prepared at different distances between substrate surface and gas delivering device
  • Fig. 10 illustrates the chart of the Al concentration in AlGaN films prepared with different Al composition in the gaseous phase.
  • Fig. 1 illustrates the side view of part of the gas distribution apparatus 100 that delivering the precursors into the reaction area.
  • the gas distribution apparatus 100 comprises an inlet side 110 and an outlet side 120. And there is a cooling system 130 in the gas distribution apparatus 100 at the inlet side 110. This cooling system can also be placed at outlet side 120.
  • the first gas distribution member 111 comprises a gas distribution channel which isolates the metalorganic precursors from the ammonia precursor, and distributes the metalorganic precursors to a plurality of second gas distribution member 121 at the outlet side 120 of the gas distribution apparatus.
  • Each of the second gas distribution members 121 for delivering metalorganic precursors comprises a plurality of gas outlets 131 to introduce metalorganic precursors into the reaction area with a vertical flow at the outlet side 120.
  • the first gas distribution member for metalorganic precursors 111 and the second gas distribution members for metalorganic precursors 121 can be made in one body.
  • one of the second gas distribution members 121 for delivering metalorganic precursors comprises 10 or more than 10 gas outlets 131.
  • the total area of the gas outlets 131 on one of the second gas distribution members 121 for delivering metalorganic precursors is greater than 5% and less than 75% of the area of one of the second gas distribution members 121.
  • the gas distribution member 112 comprises a gas distribution channel which isolates the ammonia precursor from the metalorganic precursors, and distributes the ammonia precursor to a plurality of second gas distribution members 122 at the outlet side 120 of the gas distribution apparatus.
  • Each of the second gas distribution members 122 for delivering ammonia precursor comprises a plurality of gas outlets 132 to introduce ammonia precursor into the reaction area with a vertical flow at the outlet side 120.
  • the first gas distribution member for ammonia 112 and the second gas distribution members for ammonia 122 can be made in one body.
  • one of the second gas distribution members 122 for delivering ammonia precursor comprises 10 or more than 10 gas outlets 132.
  • the total area of the gas outlets 132 on one of the second gas distribution members 122 for delivering ammonia precursor is greater than 5% and less than 75% of the area of one of the second gas distribution members 122.
  • the second gas distribution members 121 for delivering metalorganic precursors and the second gas distribution members 122 for delivering ammonia precursor are adjacent to each other.
  • the metalorganic precursors with the carrier gas are delivered vertically into the reaction spacing 201 between the gas distribution apparatus 100 and the substrates 210, as shown in Fig. 2, by a plurality of second gas distribution members 121, thereby forming a plurality of zones 141 rich in metalorganic precursors.
  • the ammonia precursor with carrier gas is delivered vertically into the reaction spacing 201 between the gas distribution apparatus 100 and the substrates 210, as shown in Fig. 2, by a plurality of second gas distribution members 122, thereby forming a plurality of zones 142 rich in ammonia precursor.
  • the zones 141 rich in metalorganic precursors and the zones 142 rich in ammonia precursor are adjacent to each other to form an inhomogeneous gaseous environment in the reaction spacing 201.
  • the gas outlets 131 and 132 in the gas distribution apparatus 100 can be straight holes, tapered holes, rectangular slits or any other possible configurations that are used for gas distribution.
  • the dimension of the gas outlets 131 and 132 is between 0.5 and 2mm, or larger than 2mm.
  • the gas distribution apparatus 100 comprises at least one gas inlet 103 connected to a third gas distribution member 113.
  • the inlet gas for the gas inlet 103 can be switched among metalorganic precursors, ammonia precursor, carrier gases and their mixtures.
  • the third gas distribution member 113 is connected to at least one gas injector 123 which delivers the inlet gas into the reaction spacing 201 horizontally.
  • the gas injector 123 has one slit gas flow opening around its perimeter or a plurality of separated gas flow openings, each of which is positioned in between projections of the second gas distribution members 121 and 122.
  • Fig. 3a shows the side view of a first embodiment of the gas injector 123.
  • the third gas distribution member 113 comprises a gas distribution channel 301 connected to the gas injector 123.
  • the gas injector 123 comprises a plurality of separated openings 302 to deliver nitrogen or hydrogen to the reaction spacing 201. After the gas flows out from each of the separated gas flow openings, the gas flows into the area between zones 141 rich in metalorganic precursors and the zones 142 rich in ammonia, thereby prohibitingdirect mixing of gas flows from gas outlets 131 and 132.
  • Fig. 3b shows the side view of a second embodiment of the gas injector 123.
  • the third gas distribution member 113 comprises a gas distribution channel 311 connected to the gas injector 123.
  • the gas injector 123 comprises a slit opening around its perimeter to deliver the metalorganic precursors or the ammonia precursor with carrier gas into the reaction area 210.
  • gas flows out from the slit gas flow opening around the perimeter of gas injector 123 an uniform gas layer is formed immediately outside of the injector, and this layer of uniform gas flow aids mixing between gas vertical gas flows from gas outlets 131 and 132.
  • Fig. 3c shows the side view of a third embodiment of the gas injector 123, with a combination of the first and second embodiments of the gas injector 123 shown in Fig. 3a and 3b.
  • the third gas distribution member 113 comprises a first gas distribution channel 321 to introduce nitrogen or hydrogen to the first layer of the gas injector 1231 and a second gas distribution channel 323 to introduce metalorganic precursors or ammonia precursor with carrier gas to the second layer of the gas injector 1232.
  • the first layer of the gas injector 1231 comprises a plurality of separated openings 322 to deliver nitrogen or hydrogen to the reaction spacing 201 to inhibit direct mixing of gas flows from gas outlets 131 and 132.
  • the second layer of the gas injector 1232 comprises a slit opening around its perimeter to deliver the metalorganic precursors or the ammonia precursor with carrier gas into the reaction area 210 to aid mixing between vertical gas flows from gas outlets 131 and 132.
  • the gas flow out from the opening 322 and that from 324 can be controlled independently.
  • the gas distribution apparatus is made of graphite or graphite coated with protective layer, silicon carbide, stainless steel or any other material which is compatible for the MOCVD process.
  • the substrates are made from one of A1203, Si, SiC, AIN, AlGaN or InAlGaN.
  • Fig. 4a illustrates the bottom view of part of one embodiment of the gas distribution apparatus 100.
  • the second gas distribution members 121 for delivering metalorganic precursors and the second gas distribution members 122 for delivering ammonia precursor have a fan shape and are adjacent to each other.
  • the gas injector 123 is at the center of bottom side of the gas distribution apparatus 100.
  • the gas injector 123 can be one of the embodiments illustrated in Fig. 3a to 3c, or any other configurations without departing from the invention.
  • the second gas distribution members 121 deliver the metalorganic precursors into the reaction spacing 201 vertically and form the zones rich in metalorganic precursors 141.
  • the concentration of metalorganic precursor in the zones rich in metalorganic precursors 141 is more than 1.2 times of that of the average concentration of metalorganic precursors in the whole reaction spacing 201.
  • the total volumetric gaseous flow rate through each of the zones rich in metalorganic precursors 141 is between 0.2 to lOL/min.
  • the second gas distribution members 122 deliver the ammonia precursor into the reaction spacing 201 vertically and form the zones rich in ammonia precursor 142.
  • the gas injector 123 delivers metalorganic precursors, ammonia precursor, nitrogen, hydrogen or a mixture of the above gases into the reaction area horizontally.
  • the concentration of ammonia precursor in the zones rich in ammonia precursors 142 is more than 1.2 times of that of the average concentration of ammonia precursors in the whole reaction spacing 201.
  • the total volumetric gaseous flow rate through each of the zones rich in ammonia reactant 142 is between 0.15 to 8L/min.
  • the zones rich in metalorganic precursors 141 constitutes between 15% and 85% of the reaction spacing 201.
  • the computer simulation by ANSYS FLUENT was carried out to estimate the ammonia mass fraction on the plane of the substrate surfaces with one embodiment of the gas distribution apparatus 100 with a small distance between the gas distribution member 100 and the substrates 210, as shown in Fig. 5a.
  • the mass fraction of ammonia in the zones 142 rich in ammonia precursor is 0.9, while that in the zones 141 rich in metalorganic precursor is 0.3. It can be concluded that the zones 142 rich in ammonia precursor contain majority of ammonia reactant within the reaction spacing 201 and the zones 141 rich in metalorganic precursors contain majority of metalorganic reactant within the reaction spacing 201, which indicate an inhomogeneous mixing of ammonia and metalorganic precursors.
  • Fig. 5b illustrates the ammonia mass fraction on the plane of the substrate surface with a large distance between gas distribution apparatus and the substrate by computer simulation.
  • the mass fraction of ammonia in the zones 142 rich in ammonia precursor is 0.8, while that in the zones 141 rich in metalorganic precursor is 0.5.
  • the concentration of ammonia precursor in the zones rich in ammonia 142 is 1.23 times of the average ammonia concentration in the whole reaction spacing 201.
  • the Al concentration in the fabricated nitride-based semiconductor compound can be controlled by controlling the distance between the gas distribution apparatus 100 and the substrates 210.
  • Fig. 4b illustrates the bottom view of part of another alternative embodiment of the gas distribution apparatus 100.
  • a plurality of second gas distribution members 121 for delivering metalorganic precursors and a plurality of second gas distribution members 122 for delivering ammonia precursor have a fan shape and are adjacent to each other.
  • a plurality of gas injectors 123 are in between the second gas distribution members 121 and 122. And the gas injectors 123 can be one of the embodiments illustrated in Fig. 3a to 3c, or any other configuration without departing from the invention.
  • the gas distribution members 121 deliver the metalorganic precursors into the reaction spacing 201 vertically and form the zones rich in metalorganic precursors 141.
  • the second gas distribution members 122 deliver the ammonia precursor into the reaction spacing 201 vertically and form the zones rich in ammonia precursor 142.
  • the gas injectors 123 deliver metalorganic precursors, ammonia precursor, nitrogen, hydrogen or a mixture of the above gases into the reaction area horizontally.
  • the substrates 210 are heated between 500 and 1350C and the pressure in the reaction space 210 is 50 to 800mbar.
  • the metalorganic precursor and ammonia are introduced into the reaction space 210 by the gas distribution apparatus 100.
  • a plurality of alternating zones 141 rich in metalorganic precursor and a plurality of alternating zones 142 rich in ammonia are formed.
  • the substrates 210 are rotated around an axis with 1 to 300rpm and are exposed to one of the alternating zones 141 rich in metalorganic precursor and in contact with the majority of the metalorganic precursor before and after they are exposed to one of the alternating zones 142 rich in ammonia and in contact with the majority of ammonia with the rotation of the substrate holding device.
  • the metalorganic precursor and ammonia react and form a layer of semiconductor compound with high Al content on the substrate surface.
  • An exemplary procedure is shown in Fig. 6a and 6b.
  • substrate 210a is under one of the second gas distribution member 121 delivering metalorganic precursors and substrate 210b is under one of the second gas distribution member 122 delivering ammonia precursor.
  • the substrates 210a and 210b have a relative motion to the gas distribution apparatus 100 in a time period t2-tl.
  • substrate 210a is under one of the second gas distribution member 122 delivering ammonia precursor
  • substrate 210b is under one of the second gas distribution member 121 delivering metalorganic precursors.
  • the substrates 210a and 210b are exposed to one of the alternating zones 141 rich in metalorganic precursor and in contact with the majority of the metalorganic precursor before and after they are exposed to one of the alternating zones 142 rich in ammonia and in contact with the majority of ammonia with the rotation of the substrate holding device.
  • the metalorganic precursor and ammonia react and form a layer of semiconductor compound with high Al content on the substrate surface.
  • the time period t2-tl is determined by the speed of the relative motion between the substrates 210 and the gas distribution apparatus 100 and the area of the second gas distribution member 121 and 122. In one embodiment of the invention, the time period t2-tl is longer than 4ms. In another embodiment of the invention, the relative motion between substrates 210 and gas distribution apparatus 100 is a kind of translational motion with a translational velocity less than 13m/s.
  • the gas feed of either metalorganic precursor or ammonia to the gas injector 123 is closed and an inhomogeneous gaseous environment is formed.
  • the substrates 210 are exposed to one of the alternating zones 141 rich in metalorganic precursor and in contact with the majority of the metalorganic precursor before or after they are exposed to one of the alternating zones 142 rich in ammonia and in contact with the majority of ammonia to form a layer of semiconductor compound with high Al content on the substrate surface.
  • the Al content is further increased when gas feed of nitrogen, serving as a separation gas, to the separated openings of the flow injector is open and separation gas flows into the area between zones rich in metalorganic precursors and the zones rich in ammonia, reducing the mixing of the two zones.
  • the gas feed of either metalorganic precursor or ammonia is open to feed to the slit opening around the perimeter of the gas injector 123 to aid mixing between gas vertical gas flows from gas outlets 131 and 132 and a more homogeneous gaseous environment is formed.
  • One example of the high Al content semiconductor compound was prepared with the disclosed method and gas distribution apparatus 100.
  • the ⁇ -2 ⁇ scan of XRD of the prepared AlGaN film is illustrated in Fig. 7.
  • the temperature of the substrate surfaces was between 500 to 1350°C and the pressure in the reaction spacing 201 was between 50 to 800mbar.
  • the metalorganic precursors were, but not limited to, TMGa and TMA1.
  • the Al concentration is defined as the molar concentration of Al divided by the molar concentration of total group III metal sources.
  • the Al concentration in the gaseous phase was 34.4%, and the Al concentration in the AlGaN film was estimated as 52.6% based on the XRD result, which was much higher than that in the gas phase.
  • the utilization of Al source is defined as the Al concentration in the synthesized solid semiconductor compound divided by the Al concentration in the gaseous phase, and in this case the utilization of Al source is larger than 1.5.
  • FIG. 8 Another example of the high Al content semiconductor compound was prepared with the disclosed method.
  • the temperature of the substrate surfaces was between 500 to 1350°C and the pressure in the reaction spacing 201 was between 50 to 800mbar.
  • the metalorganic precursors were, but not limited to, TMGa and TMAL.
  • the ⁇ -2 ⁇ scan by XRD of the prepared AlGaN films is illustrated in Fig. 8.
  • Two layers of AlGaN were prepared in the sample with different Al concentration in each layer, by adjusting the Al concentration in the gas phase.
  • the Al concentration in the gas phase for preparing the layer with low incorporated Al concentration is 19%, while that for the one with high incorporated Al concentration is 48.5%.
  • the ⁇ -2 ⁇ scan of XRD of the AlGaN sample showed two peaks for AlGaN, indicating an AlGaN layer with low incorporated Al concentration as 31.5% and another with high incorporated Al concentration as 80.2%, both of which are higher than that in the gas phase.
  • the utilization of Al source is larger than 1.5 for both low and high Al content semiconductor compound layers.
  • Fig. 9 illustrates the Al concentration in the exemplary AlGaN films prepared in the reaction spacing 201 with the method disclosed in this invention at different distances between the substrate 210 surfaces and the gas distribution apparatus 100. It showed that the Al concentration in the AlGaN film decreased when the distance between the substrate 210 surface and the gas distribution apparatus 100 became larger. When the distance between the gas distribution apparatus 100 and the substrates 210 became larger, the metalorganic precursors and the ammonia had a more homogeneous mixing due to longer diffusion distance. More metalorganic precursor reacted and was consumed with the ammonia in the gas phase, while less reached to the substrate 210 surfaces to form a layer of solid semiconductor compound, leading to a lower Al concentration in the layer. This indicates that the inhomogeneous mixing of ammonia and metalorganic precursors helps for preventing gas phase parasitic reaction and preparing the semiconductor compound with high Al content between 20% and 100% with the disclosed method.
  • Fig. 10 illustrates the Al concentration in the exemplary AlGaN films prepared in the reaction spacing 201 with the method disclosed in this invention with different Al concentration in the gas phase. It showed that Al concentration in the AlGaN film increased with that in the gas phase, and it is higher than that in the gas phase.
  • This high incorporation rate of Al into the AlGaN film prepared with the method disclosed in this invention brings additional benefit of reducing particle formation brought about by gas phase reaction between Al metalorganic precursor and ammonia.
  • the particle formation in the gas phase is a seriousproblem in commercial MOCVD reactors when being applied to growing Al containing nitride-based compound semiconductors. These particles, when migrating from gas phase to solid AlGaN, cause defects and low yield in the final devices.
  • the disclosed method and apparatus can also be used to synthesis A1N, AlInN, AlInGaN or any other nitride based semiconductor compound with high Al content between 20% and 100%, by applying different metalorganic precursors such as, but not limit to TMGa, TEGa, TMA1 and TMIn.

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Abstract

Disclosed are a MOCVD method and a gas distribution apparatus for fabricating nitride-based semiconductor crystals with high Al content between 20% and 100%, providing an inhomogeneous mixing of metalorganic and ammonia reactants in the gaseous environment to form a plurality of alternating zones, one rich in metalorganic source and the other rich in ammonia, immediately above the epitaxy substrates. This inhomogeneously mixed gaseous phase reduces parasitic reaction. In epitaxy process, the hot epitaxy substrates continuously move under said alternating zones of reactants, passing each zone at the time scales from a few milliseconds to a few tens of milliseconds.

Description

SPECIFICATION
METHOD AND APPARATUS FOR GROWING NITRIDE-BASED COMPOUND
SEMICONDUCTOR CRYSTALS
BACKGROUND OF THE INVENTIONFIELD
1. FIELD OF THE INVENTION
[0001] The present invention generally relates to a Metalorganic Vapor Deposition (MOCVD) method and an apparatus for growing semiconductor crystal, more particularly for fabricating Nitride-based compound semiconductors with substantially high Al content between 20% and 100%.
2. DESCRIPTION OF RELATED ART
[0002] Metal organic chemical vapor deposition (MOCVD) is widely used for the preparation of semiconductor thin films of single crystal III-V and II- VI group materials and alloys thereof. In a typical MOCVD reactor, epitaxy growth is initiated by the thermal pyrolysis of group II or III metal-organic sources and group VI or V hydrides, with the nitrogen or hydrogen as the carrier gas, injected into the reactor with pre-determined proportions. Several reaction pathways compete in both vapor phase and on the surface of hot substrate, and the metal-organic source consumption in the vapor phase is an important factor affecting the composition of the deposited film, thereby its final opto-electronic properties. Furthermore, reaction space in the reactor, gas temperature, substrate temperature, gas flow field, and operating pressure, all play important roles in growing II- VI or III-V semiconductor materials and their alloys of desired properties. In modern MOCVD reactor design, a great deal of focus has been put forward to better control aforementioned process parameters. One particular area is the design of reactant gas distribution device, for its contribution to forming a uniformly mixed gaseous environment above the hot substrate where epitaxial growth takes place is believed to be essential in MOCVD process.
[0003] The biggest application of MOCVD technique is by far the manufacturing of LED. More recent success in commercialization of GaN-based blue and green LEDs has enabled the broader adaption of LED general lighting. Typical reactants in MOCVD process for nitride-based compound semiconductors include Ga, Al, In metalorganic sources and anhydrous ammonia (NH3), with dopants and carrier gases. Apart from the advancement of visible light LED technology, the applications of using MOCVD to make ultra-violet (UV) wavelength LED's and photo detectors, deep UV LED's [1, 2,3 , 1. E. Monroy, F. Callea, J.L. Pau, E. Munoz, F. Omnes, B. Beaumont, P. Gibart, J. Crystal Growth 230 (2001) 537; 2. D. Walker, X. Zhang, A. Saxler, P. Kung, J. Xu, M. Razeghi, Appl. Phys. Lett. 70 (1997) 949; 3. Shur MS, Gaska R. Deep-ultraviolet light-emitting diodes. IEEE Trans Electron Dev 2010;1 : 12-25.], solar-blind photo detectors [4, R.McClintock, K.Mayes, A. Yasan, D. Shiell, P. Kung,M. Razeghi, Appl. Phys. Lett. 86 (2005) 011117.], power devices (Hight Electron Mobility Trasistor (HEMT), Field Effect Transistor (FET) )[ 5 Nariaki Ikeda, Jiang Li, Hironari Takehara, Takahiro Wada, Seikoh Yoshida, J C G, 275, 1091], and related photo-electronic devices based on Si substrates, are under exploration in recent years.
[0004] In these applications, AlGaN/GaN materials system is used for different purposes. Aluminum Gallium Nitride (AlGaN) has a direct transition band gap between 3.4 and 6.2 eV, thus it is often used as active region of UV LED, deep UV LED and UV detectors. It could also be used as buffer layer to block dislocations and relax the strains between active layers and underneath substrate to improve the device performance. For LED active layer, the wavelength of the LED - the higher the Al content, the shorter the wavelength. For deep UV-LED, the Al content over the Ga content is greater than 40%. For the AlGaN/GaN super lattice (SL) used as buffer layers on Si substrate for LED or HEMT application, the Al content is generally over 70%. [M.A. Mastro, C.R. Eddy Jr., D.K. Gaskill, N.D. Bassim, J. Casey, A. Rosenberg, R.T. Holm, R.L. Henry, M.E. Twigg, Journal of Crystal Growth, 287,610] In conventional MOCVD reactors, the incorporation of Al is difficult. The Al composition in the epitaxial film (solid phase) grown on the hot substrate is commonly controlled by the composition in the gaseous phase, gas flow velocity, and operating pressure. In a reactor where reactants in the gaseous phase is well mixed, the Al composition in the solid phase increases with that in the gaseous phaseto a point beyond which a saturation of Al content is reached. Further increase in Al content in the gaseous phase carries no effect on the Al content in the solid phase, rather, gives away to the parasitic reaction in the gaseous phase due to the highly active nature of the Al metalorganic source with ammonia. [Gas-Phase Parasitic Reactions and Al Incorporation of AlGaN Growth Using TPIS-MOCVD, Sunwoon Kim, Junho Seo, Kyuhan Lee, Haeseok Lee, Keunseop Park, Younghoon Kim and Chang-Soo Kim, Journal of the Korean Physical Society, Vol. 41, No. 5, November 2002, pp. 726-731]. It is also reported at high Al content in the gas phase will lead to non-uniformity of Al content in solid film and degrade the AlGaN material quality due to the parasitic reaction of TMA1 in the gas phase. [ K. Hoshino*, T. Someya, K. Hirakawa, Y. Arakawa, Journal of Crystal Growth, 237-239, 1163]
[0005] To reduce the consumption of Al in the metalorganic source in gaseous phase by parasitic reaction, increasing gas flow velocity and lowering operating pressure can be used; however, lowering operating pressure can alter other properties of the epitaxy film,. Another disclosed method of increasing Al content in the epitaxy layer is to introduce Al metalorganic source and NH3 into the reactor at different time steps so that the mixing of the twois reduced and thereforethe parasitic reaction is minimized [M. Takeuchi, H. Shimizub, R. Kajitani, K. Kawasaki ,Y. Kumagai, A. Koukituc, Y. Aoyagi, Journal of Crystal Growth, 298,336]. The time steps are on the scales of seconds. This method can lead to low utilization of metalorganic source and prolonged process time.
SUMMARY OF THE INVENTION
[0006] According to one aspect of the present invention, a MOCVD method to synthesize Group III-V nitride-based compound semiconductor crystals with high Al content, comprising:
heating epitaxy substrates to a temperature between 500 and 1350C;
introducing vertically to said epitaxy substrates gas flow of metalorganic source reactant, ammonia reactant and carrier gas into a reaction space at the same time through a reactant gas distribution apparatus positioned less than 5cm away from said epitaxy substrates; forming an inhomogeneous gaseous environment of a plurality of alternating zones rich in Al metalorganic source reactant and rich in ammonia reactant within said reaction space, wherein the zones rich in Al metalorganic source contain majority of Al metalorganic source reactant within said reaction space, wherein the zones rich in ammonia contain majority of ammonia reactant within said reaction space;
exposing said epitaxy substrates to said majority of Al metalorganic source reactant and to said majority of ammonia reactant in an alternating manner by the periodic relative motion between said epitaxy substrates and said inhomogeneous gaseous environment to grow epitaxy film;
terminating metalorganic source reactant introduction to reaction space at the end of synthesis.
[0007] According to another aspect of the present invention, a reactant gas distribution apparatus, comprising:
an inlet side, where at least one inlet connecting to metalorganic source reactant gas feed, at least one inlet connecting to ammonia reactant gas feed, and at least one inlet connecting purge gas,
an outlet side, where a plurality of metalorganic source reactant distribution zones distributing metalorganic source reactant and a plurality of ammonia reactant distribution zones distributing ammonia reactant; each of said metalorganic source reactant distribution zones andeach of said ammonia reactant distribution zones are adjacent;
a first gas distribution member, connecting said inlet side, consisting of a gas connection channels isolating said metalorganic source reactant from said ammonia reactant and distributing reactant gases from said inlets to said reactant distributing zones;
a plurality of second gas distribution members, connecting to said outlet side, each consisting of a plurality of gas outlets and gas connection channels distributing reactant gas from each of said reactant distribution zones to gas outlets that guide reactant gas flow to exit vertically to said outlet side; at least one third gas distribution member consisting of an inlet gas switch among metalorganic source reactant gas, ammonia reactant gas, and nitrogen purge gas feed, gas flow connection channels, and an outlet gas injector that guides reactant gas flow exiting gas injector horizontally to said outlet side.
[0008] One characteristic of this invention is that the reactants mix inhomogeneously in the gaseous environment to form a plurality of alternating zones, one rich in metalorganic source and the other rich in ammonia, immediately above the epitaxy substrates. This inhomogeneously mixed gaseous phase reduces parasitic reaction to only regionswhere one zone rich in metalorganic source and the other rich in ammonia meet. In epitaxy process, the hot epitaxy substrates continuously move under said alternating zones of reactants, passing each zone at the time scales from a few milliseconds to a few tens of milliseconds.
[0009] With the disclosed MOCVD method and gas distribution apparatus, compound semiconductor crystals with high Al content between 20% and 100% can be made by an economical process ata reduced consumption rate of metalorganic precursors.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Fig. 1 illustrates the side view of part of the gas distribution apparatus;
[0011] Fig. 2 illustrates the side view of the reaction spacing between the gas distribution apparatus and the substrates;
[0012] Fig. 3a illustrates the side view of a first embodiment of the center gas injector;
[0013] Fig. 3b illustrates the side view of a second embodiment of the center gas injector;
[0014] Fig. 3c illustrates the side view of a third embodiment of the center gas injector;
[0015] Fig. 4a illustrates the bottom view of part of one embodiment of the gas distribution apparatus;
[0016] Fig. 4b illustrates the bottom view of part of another embodiment of the gas distribution apparatus; [0017] Fig. 5a illustrates the ammonia mass fraction on the plane of the substrate surface with one distance between the gas distribution apparatus and substrates by computer simulation;
[0018] Fig. 5b illustrates the ammonia mass fraction on the plane of the substrate surface with another distance between the gas distribution apparatus and substrate by computer simulation
[0019] Fig. 6a illustrates side view of the reaction spacing between the gas distribution apparatus and the substrates at one time;
[0020] Fig. 6b illustrates side view of the reaction spacing between the gas distribution apparatus and the substrates at another time;
[0021] Fig. 7 illustrates the Ω-2Θ scan curve by XRD for one AlGaN sample prepared in the MOCVD apparatus;
[0022] Fig. 8 illustrates the Ω-2Θ scan curve by XRD for another AlGaN sample prepared in the MOCVD apparatus;
[0023] Fig. 9 illustrates the chart of the Al concentration in the AlGaN films prepared at different distances between substrate surface and gas delivering device;
[0024] Fig. 10 illustrates the chart of the Al concentration in AlGaN films prepared with different Al composition in the gaseous phase.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0025] Fig. 1 illustrates the side view of part of the gas distribution apparatus 100 that delivering the precursors into the reaction area. The gas distribution apparatus 100 comprises an inlet side 110 and an outlet side 120. And there is a cooling system 130 in the gas distribution apparatus 100 at the inlet side 110. This cooling system can also be placed at outlet side 120.
[0026] There is at least one inlet 101 for introducing metalorganic precursors into a first gas distribution member 111 for delivering metalorganic precursorswhich is connected to the inlet 101. The first gas distribution member 111 comprises a gas distribution channel which isolates the metalorganic precursors from the ammonia precursor, and distributes the metalorganic precursors to a plurality of second gas distribution member 121 at the outlet side 120 of the gas distribution apparatus. Each of the second gas distribution members 121 for delivering metalorganic precursors comprises a plurality of gas outlets 131 to introduce metalorganic precursors into the reaction area with a vertical flow at the outlet side 120. The first gas distribution member for metalorganic precursors 111 and the second gas distribution members for metalorganic precursors 121 can be made in one body.
[0027] In one preferred embodiment of the invention, one of the second gas distribution members 121 for delivering metalorganic precursors comprises 10 or more than 10 gas outlets 131.
[0028] In an alternative embodiment of the invention, the total area of the gas outlets 131 on one of the second gas distribution members 121 for delivering metalorganic precursors is greater than 5% and less than 75% of the area of one of the second gas distribution members 121.
[0029] There is at least one inlet 102 for introducing ammonia precursor into first gas distribution member 112 for delivering ammonia precursors which is connected to the inlet 102. The gas distribution member 112 comprises a gas distribution channel which isolates the ammonia precursor from the metalorganic precursors, and distributes the ammonia precursor to a plurality of second gas distribution members 122 at the outlet side 120 of the gas distribution apparatus. Each of the second gas distribution members 122 for delivering ammonia precursor comprises a plurality of gas outlets 132 to introduce ammonia precursor into the reaction area with a vertical flow at the outlet side 120. The first gas distribution member for ammonia 112 and the second gas distribution members for ammonia 122 can be made in one body.
[0030] In one embodiment of the invention, one of the second gas distribution members 122 for delivering ammonia precursor comprises 10 or more than 10 gas outlets 132.
[0031] In another alternative embodiment of the invention, the total area of the gas outlets 132 on one of the second gas distribution members 122 for delivering ammonia precursor is greater than 5% and less than 75% of the area of one of the second gas distribution members 122.
[0032] The second gas distribution members 121 for delivering metalorganic precursors and the second gas distribution members 122 for delivering ammonia precursor are adjacent to each other. The metalorganic precursors with the carrier gas are delivered vertically into the reaction spacing 201 between the gas distribution apparatus 100 and the substrates 210, as shown in Fig. 2, by a plurality of second gas distribution members 121, thereby forming a plurality of zones 141 rich in metalorganic precursors. The ammonia precursor with carrier gas is delivered vertically into the reaction spacing 201 between the gas distribution apparatus 100 and the substrates 210, as shown in Fig. 2, by a plurality of second gas distribution members 122, thereby forming a plurality of zones 142 rich in ammonia precursor. The zones 141 rich in metalorganic precursors and the zones 142 rich in ammonia precursor are adjacent to each other to form an inhomogeneous gaseous environment in the reaction spacing 201.
[0033] The gas outlets 131 and 132 in the gas distribution apparatus 100 can be straight holes, tapered holes, rectangular slits or any other possible configurations that are used for gas distribution. The dimension of the gas outlets 131 and 132 is between 0.5 and 2mm, or larger than 2mm.
[0034] The gas distribution apparatus 100 comprises at least one gas inlet 103 connected to a third gas distribution member 113. The inlet gas for the gas inlet 103 can be switched among metalorganic precursors, ammonia precursor, carrier gases and their mixtures. The third gas distribution member 113 is connected to at least one gas injector 123 which delivers the inlet gas into the reaction spacing 201 horizontally. The gas injector 123 has one slit gas flow opening around its perimeter or a plurality of separated gas flow openings, each of which is positioned in between projections of the second gas distribution members 121 and 122.
[0035] Fig. 3a shows the side view of a first embodiment of the gas injector 123. The third gas distribution member 113 comprises a gas distribution channel 301 connected to the gas injector 123. The gas injector 123 comprises a plurality of separated openings 302 to deliver nitrogen or hydrogen to the reaction spacing 201. After the gas flows out from each of the separated gas flow openings, the gas flows into the area between zones 141 rich in metalorganic precursors and the zones 142 rich in ammonia, thereby prohibitingdirect mixing of gas flows from gas outlets 131 and 132.
[0036] Fig. 3b shows the side view of a second embodiment of the gas injector 123. The third gas distribution member 113 comprises a gas distribution channel 311 connected to the gas injector 123. The gas injector 123 comprises a slit opening around its perimeter to deliver the metalorganic precursors or the ammonia precursor with carrier gas into the reaction area 210. When gas flows out from the slit gas flow opening around the perimeter of gas injector 123, an uniform gas layer is formed immediately outside of the injector, and this layer of uniform gas flow aids mixing between gas vertical gas flows from gas outlets 131 and 132.
[0037] Fig. 3c shows the side view of a third embodiment of the gas injector 123, with a combination of the first and second embodiments of the gas injector 123 shown in Fig. 3a and 3b. The third gas distribution member 113 comprises a first gas distribution channel 321 to introduce nitrogen or hydrogen to the first layer of the gas injector 1231 and a second gas distribution channel 323 to introduce metalorganic precursors or ammonia precursor with carrier gas to the second layer of the gas injector 1232. The first layer of the gas injector 1231 comprises a plurality of separated openings 322 to deliver nitrogen or hydrogen to the reaction spacing 201 to inhibit direct mixing of gas flows from gas outlets 131 and 132. The second layer of the gas injector 1232 comprises a slit opening around its perimeter to deliver the metalorganic precursors or the ammonia precursor with carrier gas into the reaction area 210 to aid mixing between vertical gas flows from gas outlets 131 and 132. The gas flow out from the opening 322 and that from 324 can be controlled independently.
[0038] The gas distribution apparatus is made of graphite or graphite coated with protective layer, silicon carbide, stainless steel or any other material which is compatible for the MOCVD process. And the substrates are made from one of A1203, Si, SiC, AIN, AlGaN or InAlGaN.
[0039] Fig. 4a illustrates the bottom view of part of one embodiment of the gas distribution apparatus 100. The second gas distribution members 121 for delivering metalorganic precursors and the second gas distribution members 122 for delivering ammonia precursor have a fan shape and are adjacent to each other. The gas injector 123 is at the center of bottom side of the gas distribution apparatus 100. The gas injector 123 can be one of the embodiments illustrated in Fig. 3a to 3c, or any other configurations without departing from the invention. The second gas distribution members 121 deliver the metalorganic precursors into the reaction spacing 201 vertically and form the zones rich in metalorganic precursors 141. The concentration of metalorganic precursor in the zones rich in metalorganic precursors 141 is more than 1.2 times of that of the average concentration of metalorganic precursors in the whole reaction spacing 201. The total volumetric gaseous flow rate through each of the zones rich in metalorganic precursors 141 is between 0.2 to lOL/min. The second gas distribution members 122 deliver the ammonia precursor into the reaction spacing 201 vertically and form the zones rich in ammonia precursor 142. The gas injector 123 delivers metalorganic precursors, ammonia precursor, nitrogen, hydrogen or a mixture of the above gases into the reaction area horizontally. The concentration of ammonia precursor in the zones rich in ammonia precursors 142 is more than 1.2 times of that of the average concentration of ammonia precursors in the whole reaction spacing 201. The total volumetric gaseous flow rate through each of the zones rich in ammonia reactant 142 is between 0.15 to 8L/min. The zones rich in metalorganic precursors 141 constitutes between 15% and 85% of the reaction spacing 201.
[0040] The computer simulation by ANSYS FLUENT was carried out to estimate the ammonia mass fraction on the plane of the substrate surfaces with one embodiment of the gas distribution apparatus 100 with a small distance between the gas distribution member 100 and the substrates 210, as shown in Fig. 5a. The mass fraction of ammonia in the zones 142 rich in ammonia precursor is 0.9, while that in the zones 141 rich in metalorganic precursor is 0.3. It can be concluded that the zones 142 rich in ammonia precursor contain majority of ammonia reactant within the reaction spacing 201 and the zones 141 rich in metalorganic precursors contain majority of metalorganic reactant within the reaction spacing 201, which indicate an inhomogeneous mixing of ammonia and metalorganic precursors. And the concentration of ammonia precursor in the zones rich in ammonia 142 is 1.5 times of the average ammonia concentration in the whole reaction spacing 201. In this way, the metalorganic precursor is prevented from the reaction with the ammonia and consumption in the gas phase. Thus more metalorganic precursor can reach the surface of the substrates 210 and be incorporated in the semiconductor compound to generate a solid film with high Al content. Fig. 5b illustrates the ammonia mass fraction on the plane of the substrate surface with a large distance between gas distribution apparatus and the substrate by computer simulation. The mass fraction of ammonia in the zones 142 rich in ammonia precursor is 0.8, while that in the zones 141 rich in metalorganic precursor is 0.5. The concentration of ammonia precursor in the zones rich in ammonia 142 is 1.23 times of the average ammonia concentration in the whole reaction spacing 201. The larger distance between gas distribution apparatus 100 and substrates 210, the more homogeneous the mixing of metalorganic and ammonia reactants. And the metalorganic precursors and ammonia have a complete homogeneous mixing when the distance between the gas distribution apparatus 100 and substrates 210 is larger than 50mm. The Al concentration in the fabricated nitride-based semiconductor compound can be controlled by controlling the distance between the gas distribution apparatus 100 and the substrates 210.
[0041] Fig. 4b illustrates the bottom view of part of another alternative embodiment of the gas distribution apparatus 100. A plurality of second gas distribution members 121 for delivering metalorganic precursors and a plurality of second gas distribution members 122 for delivering ammonia precursor have a fan shape and are adjacent to each other. A plurality of gas injectors 123 are in between the second gas distribution members 121 and 122. And the gas injectors 123 can be one of the embodiments illustrated in Fig. 3a to 3c, or any other configuration without departing from the invention. The gas distribution members 121 deliver the metalorganic precursors into the reaction spacing 201 vertically and form the zones rich in metalorganic precursors 141. The second gas distribution members 122 deliver the ammonia precursor into the reaction spacing 201 vertically and form the zones rich in ammonia precursor 142. The gas injectors 123 deliver metalorganic precursors, ammonia precursor, nitrogen, hydrogen or a mixture of the above gases into the reaction area horizontally. [0042] A MOCVD method to prepare semiconductor compound with high Al content between 20% and 100% is disclosed in the preferred embodiment of this invention, comprising:
(1) heating the epitaxy substrates to a temperature between 500 and 1350C;
(2) introducing spontaneously metalorganic source precursor, ammonia precursor and carrier gas into a reaction space;
(3) forming an inhomogeneous gaseous environment of a plurality of alternating zones rich in Al metalorganic source precursor and rich in ammonia precursor in the reaction space;
(4) exposing the epitaxy substrates to the majority of Al metalorganic source precursor and to the majority of ammonia precursor in an alternating manner by moving the epitaxy substrates periodically within the inhomogeneous gaseous environment;
(5) stopping metalorganic source precursor introduction to the reaction space at the end of synthesis.
[0043] In one embodiment of the disclosed method, the substrates 210 are heated between 500 and 1350C and the pressure in the reaction space 210 is 50 to 800mbar. The metalorganic precursor and ammonia are introduced into the reaction space 210 by the gas distribution apparatus 100. A plurality of alternating zones 141 rich in metalorganic precursor and a plurality of alternating zones 142 rich in ammonia are formed. The substrates 210 are rotated around an axis with 1 to 300rpm and are exposed to one of the alternating zones 141 rich in metalorganic precursor and in contact with the majority of the metalorganic precursor before and after they are exposed to one of the alternating zones 142 rich in ammonia and in contact with the majority of ammonia with the rotation of the substrate holding device. The metalorganic precursor and ammonia react and form a layer of semiconductor compound with high Al content on the substrate surface. An exemplary procedure is shown in Fig. 6a and 6b. At time tl, substrate 210a is under one of the second gas distribution member 121 delivering metalorganic precursors and substrate 210b is under one of the second gas distribution member 122 delivering ammonia precursor. The substrates 210a and 210b have a relative motion to the gas distribution apparatus 100 in a time period t2-tl. And at time t2, substrate 210a is under one of the second gas distribution member 122 delivering ammonia precursor and substrate 210b is under one of the second gas distribution member 121 delivering metalorganic precursors. Thus the substrates 210a and 210b are exposed to one of the alternating zones 141 rich in metalorganic precursor and in contact with the majority of the metalorganic precursor before and after they are exposed to one of the alternating zones 142 rich in ammonia and in contact with the majority of ammonia with the rotation of the substrate holding device. The metalorganic precursor and ammonia react and form a layer of semiconductor compound with high Al content on the substrate surface. The time period t2-tl is determined by the speed of the relative motion between the substrates 210 and the gas distribution apparatus 100 and the area of the second gas distribution member 121 and 122. In one embodiment of the invention, the time period t2-tl is longer than 4ms. In another embodiment of the invention, the relative motion between substrates 210 and gas distribution apparatus 100 is a kind of translational motion with a translational velocity less than 13m/s.
[0044] When preparing semiconductor compound with high Al content between 20% and 100%, the gas feed of either metalorganic precursor or ammonia to the gas injector 123 is closed and an inhomogeneous gaseous environment is formed. The substrates 210 are exposed to one of the alternating zones 141 rich in metalorganic precursor and in contact with the majority of the metalorganic precursor before or after they are exposed to one of the alternating zones 142 rich in ammonia and in contact with the majority of ammonia to form a layer of semiconductor compound with high Al content on the substrate surface. The Al content is further increased when gas feed of nitrogen, serving as a separation gas, to the separated openings of the flow injector is open and separation gas flows into the area between zones rich in metalorganic precursors and the zones rich in ammonia, reducing the mixing of the two zones.
[0045] When preparing semiconductor compound with low Al content between 0% and 20%, the gas feed of either metalorganic precursor or ammonia is open to feed to the slit opening around the perimeter of the gas injector 123 to aid mixing between gas vertical gas flows from gas outlets 131 and 132 and a more homogeneous gaseous environment is formed. [0046] One example of the high Al content semiconductor compound was prepared with the disclosed method and gas distribution apparatus 100. The Ω-2Θ scan of XRD of the prepared AlGaN film is illustrated in Fig. 7. The temperature of the substrate surfaces was between 500 to 1350°C and the pressure in the reaction spacing 201 was between 50 to 800mbar. The metalorganic precursors were, but not limited to, TMGa and TMA1. The Al concentration is defined as the molar concentration of Al divided by the molar concentration of total group III metal sources. The Al concentration in the gaseous phase was 34.4%, and the Al concentration in the AlGaN film was estimated as 52.6% based on the XRD result, which was much higher than that in the gas phase. The utilization of Al source is defined as the Al concentration in the synthesized solid semiconductor compound divided by the Al concentration in the gaseous phase, and in this case the utilization of Al source is larger than 1.5.
[0047] Another example of the high Al content semiconductor compound was prepared with the disclosed method. The temperature of the substrate surfaces was between 500 to 1350°C and the pressure in the reaction spacing 201 was between 50 to 800mbar. The metalorganic precursors were, but not limited to, TMGa and TMAL. And the Ω-2Θ scan by XRD of the prepared AlGaN films is illustrated in Fig. 8. Two layers of AlGaN were prepared in the sample with different Al concentration in each layer, by adjusting the Al concentration in the gas phase. The Al concentration in the gas phase for preparing the layer with low incorporated Al concentration is 19%, while that for the one with high incorporated Al concentration is 48.5%. The Ω-2Θ scan of XRD of the AlGaN sample showed two peaks for AlGaN, indicating an AlGaN layer with low incorporated Al concentration as 31.5% and another with high incorporated Al concentration as 80.2%, both of which are higher than that in the gas phase. The utilization of Al source is larger than 1.5 for both low and high Al content semiconductor compound layers.
[0048] Fig. 9 illustrates the Al concentration in the exemplary AlGaN films prepared in the reaction spacing 201 with the method disclosed in this invention at different distances between the substrate 210 surfaces and the gas distribution apparatus 100. It showed that the Al concentration in the AlGaN film decreased when the distance between the substrate 210 surface and the gas distribution apparatus 100 became larger. When the distance between the gas distribution apparatus 100 and the substrates 210 became larger, the metalorganic precursors and the ammonia had a more homogeneous mixing due to longer diffusion distance. More metalorganic precursor reacted and was consumed with the ammonia in the gas phase, while less reached to the substrate 210 surfaces to form a layer of solid semiconductor compound, leading to a lower Al concentration in the layer. This indicates that the inhomogeneous mixing of ammonia and metalorganic precursors helps for preventing gas phase parasitic reaction and preparing the semiconductor compound with high Al content between 20% and 100% with the disclosed method.
[0049] Fig. 10 illustrates the Al concentration in the exemplary AlGaN films prepared in the reaction spacing 201 with the method disclosed in this invention with different Al concentration in the gas phase. It showed that Al concentration in the AlGaN film increased with that in the gas phase, and it is higher than that in the gas phase. This high incorporation rate of Al into the AlGaN film prepared with the method disclosed in this invention brings additional benefit of reducing particle formation brought about by gas phase reaction between Al metalorganic precursor and ammonia. The particle formation in the gas phase is a seriousproblem in commercial MOCVD reactors when being applied to growing Al containing nitride-based compound semiconductors. These particles, when migrating from gas phase to solid AlGaN, cause defects and low yield in the final devices.
[0050] Besides the examples illustrated above, the disclosed method and apparatus can also be used to synthesis A1N, AlInN, AlInGaN or any other nitride based semiconductor compound with high Al content between 20% and 100%, by applying different metalorganic precursors such as, but not limit to TMGa, TEGa, TMA1 and TMIn.
[0051] Although the present invention has been described with respect to certainembodiments, examples, and applications, it will be apparent to those skilled in the art that various modifications and changes may be made without departing from the invention.

Claims

Claims
1. A MOCVD method to synthesize Group III-V nitride-based compound semiconductor crystals with high Al content, comprising:
heating epitaxy substrates to a temperature between 500 and 1350C;
introducing vertically to said epitaxy substrates gas flow of metalorganic source reactant, ammonia reactant and carrier gas into a reaction space at the same time through a reactant gas distribution apparatus positioned less than 5cm away from said epitaxy substrates,
forming an inhomogeneous gaseous environment of a plurality of alternating zones rich in Al metalorganic source reactant and rich in ammonia reactant within said reaction space, wherein the zones rich in Al metalorganic source contain majority of Al metalorganic source reactant within said reaction space, wherein the zones rich in ammonia contain majority of ammonia reactant within said reaction space;
exposing said epitaxy substrates to said majority of Al metalorganic source reactant and to said majority of ammonia reactant in an alternating manner by periodic relative motion between said epitaxy substrates and said inhomogeneous gaseous environment to grow epitaxy film;
terminating metalorganic source reactant introduction to reaction space at the end of synthesis.
2. The MOCVD method of claim 1, wherein the concentration of Al in synthesized nitride-based compound semiconductor crystals is between 15% and 100%.
3. The MOCVD method of claim 1, wherein the utilization of said Al metalorganic source reactant is greater than 1.
4. The MOCVD method in claim 1 , wherein the pressure of said reaction space is between 50mbar and 800mbar.
5. The MOCVD method in claim 1, wherein said metalorganic source reactant is TMA1.
6. The MOCVD method in claim 1, wherein said metalorganic source reactant is a mixture of TMA1, TEG and TMG
7. The MOCVD method in claim 1, wherein said metalorganic source reactant is a mixture of TMA1, TEG, TMG, and TMI.
8. The MOCVD method in claim 1, wherein total volumetric gaseous flow rate through each of said zones rich in metalorganic source reactant is between 0.2 to lOL/min.
9. The MOCVD method in claim 1, wherein total volumetric gaseous flow rate through each of said zones rich in ammonia reactant is between 0.15 to 8L/min.
10. The MOCVD method in claim 1, wherein said epitaxy substrates are made from one of:
A1203, Si, SiC, A1N, AlGaN, InAlGaN.
11. The MOCVD method in claim 1, wherein said epitaxy substrates move with a translational velocity less than 13m/s.
12. The MOCVD method in claim 1 , wherein said epitaxy substrates move with a rotational speed less than 300rpm.
13. The MOCVD method in claim 1, wherein said zones rich in metalorganic source constitutes between 15% and 85% of said reaction space.
14. The MOCVD method in claim 1, wherein time of one of said substrate passes through one of said zones is greater than 4ms.
15. The MOCVD method in claim 1, wherein particle formation in gas phase is reduced.
16. The MOCVD method of claim 1, wherein the distance from said gas distribution apparatus to said epitaxy substrate is used to control Al composition in solid phase.
17. The MOCVD method in claim 1, wherein each of said zones rich in Al metalorganic and each of said zones rich in ammonia is separated by zones of nitrogen or inert gas.
18. the MOCVD method of claim 1, wherein a flow layer of ammonia reactant horizontal to said epitaxy substrates is used to lower Al content in said epitaxy film.
19. The MOCVD method of claim 1, wherein a flow layer of metalorganic source reactant horizontal to said epitaxy substrates is used to lower Al content in said epitaxy film.
20. A reactant gas distribution apparatus, comprising: an inlet side, where at least one inlet connecting to metalorganic source reactant gas feed, at least one inlet connecting to ammonia reactant gas feed, and at least one inlet connecting purge gas;
an outlet side, where a plurality of metalorganic source reactant distribution zones distributing metalorganic source reactant and a plurality of ammonia reactant distribution zones distributing ammonia reactant; each of said metalorganic source reactant distribution zones and each of said ammonia reactant distribution zones are adjacent;
a first gas distribution member, connecting said inlet side, consisting of a gas connection channels isolating said metalorganic source reactant from said ammonia reactant and distributing reactant gases from said inlets to said reactant distributing zones;
a plurality of second gas distribution members, connecting to said outlet side, each consisting of a plurality of gas outlets and gas connection channels distributing reactant gas from each of said reactant distribution zones to gas outlets that guide reactant gas flow to exit vertically to said outlet side;
at least one third gas distribution member consisting of an inlet gas switch among metalorganic source reactant gas, ammonia reactant gas, and nitrogen purge gas feed, gas flow connection channels, and an outlet gas injector that guides reactant gas flow exiting gas injector horizontally to said outlet side.
21. The reactant gas distribution apparatus of claim 20, wherein said inlet side is cooled by a cooling system.
22. The reactant gas distribution apparatus of claim 20, wherein said first gas distribution member and said second gas distribution members are made in one body.
23. The reactant gas distribution apparatus of claim 20, wherein a plurality of separation members protruding out the surface of said outlet side between said metalorganic source reactant distribution zones and said ammonia reactant distribution zones.
24. The reactant gas distribution apparatus of claim 20, wherein the area of said gas outlets on said outlet surface is greater than 5% and less than 75% of the area of said gas distribution zones.
25. The reactant gas distribution apparatus of claim 20, wherein said apparatus is made of at least one of graphite, graphite coated with protection film, stainless steel, silicon carbide, and ceramic.
26. The reactant gas distribution apparatus of claim 20, wherein said gas outlets are in the shape of rectangular slits.
27. The reactant gas distribution apparatus of claim 20, wherein dimension of narrowest gas passage in said gas outlets is between 0.5 to 2 mm.
28. The reactant gas distribution apparatus of claim 20, wherein the number of said outlets in each of said second gas distribution members is greater than 10.
29. The reactant gas distribution apparatus of claim 20, wherein said gas injector has at least one slit gas flow opening around its perimeter.
30. The reactant gas distribution apparatus of claim 20, wherein said gas injector has a plurality of gas flow openings, each is positioned in between two of said second gas distribution members
PCT/CN2012/078899 2012-07-19 2012-07-19 Method and apparatus for growing nitride-based compound semiconductor crystals WO2014012237A1 (en)

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