Classifications

• • 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
  • C30B7/00—Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions
  • C30B7/10—Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions by application of pressure, e.g. hydrothermal processes
  • C30B7/105—Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions by application of pressure, e.g. hydrothermal processes using ammonia as solvent, i.e. ammonothermal processes
• • 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
  • H01L21/02367—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
  • H01L21/02518—Deposited layers
  • H01L21/02521—Materials
  • H01L21/02538—Group 13/15 materials
  • H01L21/0254—Nitrides

Definitions

• the invention relates to a bulk crystal of semiconductor material used to produce semiconductor wafers for various devices including optoelectronic devices such as light emitting diodes (LEDs) and laser diodes (LDs), and electronic devices such as transistors. More specifically, the invention provides a bulk crystal of group III nitride such as gallium nitride. The invention also provides a method of selecting seed crystals for growth of group III nitride bulk crystals.
• Gallium nitride (GaN) and its related group III nitride alloys are the key material for various optoelectronic and electronic devices such as LEDs, LDs, microwave power transistors, and solar-blind photo detectors.
• LEDs are widely used in displays, indicators, general illuminations, and LDs are used in data storage disk drives.
• heterogeneous substrates such as sapphire and silicon carbide because GaN substrates are extremely expensive compared to these heteroepitaxial substrates.
• group III nitride causes highly defected or even cracked films, which hinder the realization of high-end optical and electronic devices, such as high-brightness LEDs for general lighting or high-power microwave transistors.
• HVPE hydride vapor phase epitaxy
• this invention is intended to obtain crack-free bulk group III nitride crystals using any bulk growth method, such as growth in supercritical ammonia or from a melt of group III metals.
• the invention provides a method of growing bulk crystal of group III nitride using a seed crystal selected by (a) measuring x-ray rocking curves of the seed crystal at more than one point, (b) quantifying the peak widths of the measured x-ray rocking curves, and (c) evaluating the distribution of the quantified peak widths.
• the invention also includes the method of selecting a seed crystal for growing bulk crystal of group III nitride.
• FIG. 1 is an example of a process flow of this invention.
• FIG. 2 shows full width half maximum (FWHM) of 201 X-ray rocking curves from seed crystals (square dots), FWHM of 201 X-ray rocking curves from bulk GaN crystals using the corresponding seeds (diamond dots), and a photograph of a wafer sliced from the corresponding bulk GaN crystals, (a) for a seed with scattered distribution of FWHM, (b) for a seed with less scattered distribution of FWHM.
• the zero-point is at approximately the center of the seed's face along the longest line on an m-plane.
• XRD data in the examples was collected at various points across the seed crystal's face and along this line.
• the bulk crystal of the present invention is typically sliced to produce group III nitride wafers suitable for fabricating various optoelectronic and electronic devices such as LEDs, LD, transistors, and photodetectors by known techniques.
• Many optoelectronic and electronic devices are fabricated with thin films of group III nitride alloys (i.e. alloys of GaN, A1N and InN).
• the group III nitride alloys are typically expressed as GaxAl y Ini-x- y N (0 ⁇ 1, 0 ⁇ x+y ⁇ l). Since the group III metallic elements (i.e. Al, Ga, In) shows similar chemical characteristics, nitrides of these group III elements makes alloys or solid solution. In addition, crystal growth nature of these group III nitrides are quite similar.
• the device Due to limited availability and high cost of single crystalline substrates of group III nitride, these devices have been fabricated on so-called heteroepitaxial substrates such as sapphire and silicon carbide. Since the heteroepitaxial substrates are chemically and physically different from the group III nitride, the device typically has a high density of dislocations (10 8 ⁇ 10 10 cm "2 ) generated at the interface between the heteroepitaxial substrate and the device layer. Such dislocations deteriorate performance and reliability of devices, thus substrates composed of crystalline group III nitride such as GaN and A1N are favorable.
• ammonothermal growth which utilizes supercritical ammonia, has been developed.
• the ammonothermal method can produce GaN substrates with dislocation density less than 10 5 cm “2 .
• One advantage of the ammonothermal method is that bulk crystals having a thickness larger than 1 mm can be grown.
• the ammonothermal method can also be used to grow crystals having various dopants such as donors (i.e. electron), acceptors (i.e. hole) or magnetic dopants.
• donors i.e. electron
• acceptors i.e. hole
• magnetic dopants such as magnetic dopants.
• the current invention provides a method of making a bulk crystal of group III nitride in which a seed crystal is selected by (a) measuring x-ray rocking curves of the seed crystal at more than one point, (b) quantifying the peak widths of the measured x-ray rocking curves, and (c) evaluating the distribution of the quantified peak widths.
• FIG 1 presents a process flow of this invention.
• a seed crystal for growing bulk crystal of group III nitride such as GaN is prepared.
• Seed crystal is preferably a single crystal of group III nitride such as GaN.
• the orientation of the seed crystal can be c-plane, a-plane, m-plane or other semipolar planes, although c-plane crystal is preferable.
• the single-crystal seed may be grown by hydride vapor-phase epitaxy (HVPE), molecular beam epitaxy (MBE), metal organic vapor-phase epitaxy (MOVPE), ammonothermal growth, flux method, high-pressure solution growth or other method.
• HVPE hydride vapor-phase epitaxy
• MBE molecular beam epitaxy
• MOVPE metal organic vapor-phase epitaxy
• the seed crystal is measured with X-ray diffractometer to obtain rocking curves from more than one spot of the seed crystal.
• One example of selecting the measurement location is a straight line along one crystallographic orientation such as indirection or a-direction.
• Another example is to select points at intersections or within a square grid plotted over the seed's face.
• Another example is to take a statistically significant number of random measurements of the seed crystal's structure over the seed's face.
• off-axis diffraction such as 201 and 102 reflections is preferably used. This is because the off-axis reflections turned out to be more sensitive to the quality of the seed crystals for growing bulk crystals. Consequently, it is helpful to first determine which directions are more sensitive to crystal structure of the seed crystal for the particular seed used (e.g. c-plane, m-plane, a-plane), and then use those directions in measuring quality of crystal structure at various points across the surface of the seed.
• the particular seed used e.g. c-plane, m-plane, a-plane
• FWUM is commonly used although other methods of quantifying the peak width is also used.
• the peak width of the X-ray rocking curve represents the quality of microstructure of the crystal.
• the peak width is typically measured in the unit of arcsec, arcmin, or degree.
• statistic value such as a standard deviation can be used. Alternately, one can plot the peak width data on a graph, and visually determine the distribution of the data.
• the magnitude of data scattering can be evaluated in an absolute value with a unit of arcsec, arcmin or degree. Alternately, the magnitude of data scattering can be evaluated relative to a representative value such as a mean value of all data.
• the standard deviation is preferably less than 30% of the mean value, more preferably less than 20% of the mean value, or more preferably less than 10% of the mean value.
• the selected seed crystal will be used to grow a bulk crystal of group III nitride such as bulk GaN.
• group III nitride such as bulk GaN.
• Single crystalline GaN seed crystal having a basal plane of c-plane was prepared with HVPE.
• the thickness of the GaN seed was approximately 430 microns.
• X-ray rocking curves from 201 reflection were recorded from multiple spots of the nitrogen polar side of the seed crystal.
• the measurement was conducted along the m-direction with the spot separation of 0.5 mm.
• the peak width is quantified with FWHM in arcsec.
• the square dots in FIG. 2 (a) show FWHM at each measurement spot.
• the FWHM values have a large scattering.
• the mean value of the FWHM was 78 arcsec and the standard deviation was 29 arcsec, which was 37% of the mean value.
• the data scattering is seen throughout the scanned line.
• a bulk crystal of GaN was grown in supercritical ammonia using a high- pressure reactor.
• the chamber within the high-pressure reactor was divided into a lower part and an upper part with baffle plates.
• Approximately 15 g of poly crystalline GaN is used as a nutrient and approximately 3.1 g of sodium is used as a mineralizer.
• Mineralizer and the seed crystal were placed in the lower part of the high-pressure reactor and the nutrient was placed in the upper part of the high-pressure reactor.
• the high-pressure reactor was sealed, pumped to a vacuum and filled with anhydrous liquid ammonia.
• the volumetric ammonia fill factor was approximately 53%.
• the high-pressure reactor was heated at about 510 ⁇ 520°C to allow crystal growth of GaN on the seed.
• the resultant bulk GaN crystal has a thickness of approximately 5 mm.
• X-ray rocking curves from 201 reflection were measured at multiple spots on the surface of the grown bulk GaN crystal as described above and as described in Example 2.
• the FWHMs are plotted in FIG. 2(a) with diamond dots.
• the FWFDVIs from the grown bulk crystal also showed large scattering.
• the mean value of the FWFDVI was 89 arcsec and the standard deviation was 38 arcsec, which was 43% of the mean value.
• the bulk crystal was sliced into wafers with a multiple wire saw.
• the inset picture in FIG. 2(a) is a photograph of the sliced wafer. The wafer had numerous cracks.
• Example 2 Similar to Example 1, a c-plane GaN seed crystal was prepared with HVPE. The thickness of the GaN seed was approximately 430 microns. X-ray rocking curves from 201 reflection were recorded from multiple spots of the nitrogen polar side of the seed crystal. The measurement was conducted along a m-direction with spot separation of 0.5 mm. The peak width is quantified with FWHM in arcsec. The square dots in FIG. 2 (b) show FWHM at each measurement spot. As shown in the FIG. 2(b) the FWHM values have a small scattering. The mean value of the FWHM was 41 arcsec and the standard deviation was 7 arcsec, which was 17% of the mean value.
• the evaluation of the data scattering can be performed by combining a standard deviation, visual judgment and other criteria. For example, if we use the center portion of the data from the seed crystal in this example (FIG. 2(b)), the standard deviation can be smaller than 10% of the mean value. This way one can eliminate the edge effect of the measurement. Taking a correlation between the data scattering of the rocking curve peak width and cracking density, one can obtain a crack-free bulk crystal.
• the bulk GaN crystal obtained with the method disclosed in this invention contains no or reduced amount of cracks.
• the obtained crack-free bulk GaN crystals are sliced into wafers. These wafers are used for optical devices such as LEDs and laser diodes or electronic devices such as high-power transistors. Since cracks deteriorate performances and reliability of these devices significantly, this invention can improve the device performance and reliability.
• GaN seed crystal having thickness about 430 microns
• similar benefit of this invention can be expected for other thicknesses between 100 microns to 2000 microns.
• a bulk crystal as described, as made, or as used in any of the description above may have a thickness greater than or equal to: 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, for instance.

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• Crystals, And After-Treatments Of Crystals (AREA)

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• 2016
  • 2016-01-22 CN CN201680006774.2A patent/CN107208305A/zh active Pending
  • 2016-01-22 EP EP16703412.3A patent/EP3247824A1/en not_active Withdrawn
  • 2016-01-22 KR KR1020177023443A patent/KR102069277B1/ko active IP Right Grant
  • 2016-01-22 WO PCT/US2016/014522 patent/WO2016118862A1/en active Application Filing
  • 2016-01-22 JP JP2017538419A patent/JP6448155B2/ja active Active

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