JP2019112268A - GaN SUBSTRATE, AND MANUFACTURING METHOD THEREOF - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a GaN substrate which is hard to be thermally etched even when used for a crystal growth treatment performed under a temperature condition of 1200 ° C. or higher, for example. Each of the front surface and the back surface is composed of a GaN single crystal, and etching of the front surface and the back surface when heated to a temperature of 1200 to 1400 ° C. under an inert gas atmosphere at a pressure of 1 to 105 kPa. The rate is less than 20 μm / hr. [Selection diagram] Fig. 1

Description

  The present invention relates to a GaN substrate and a method of manufacturing the same.

  When manufacturing a nitride semiconductor free-standing substrate or when manufacturing a semiconductor device such as a light emitting element or a high speed transistor, for example, a substrate (GaN substrate) made of a crystal of gallium nitride (GaN) is prepared. In some cases, a process of epitaxially growing crystals may be performed (see, for example, Patent Document 1).

JP, 2011-016680, A

  When the above-mentioned crystal growth process is performed under a temperature condition of, for example, 1200 ° C. or more, the GaN substrate may be lost by thermal etching.

  An object of the present invention is to provide a GaN substrate which is difficult to be thermally etched even if it is used for crystal growth processing performed under temperature conditions of, for example, 1200 ° C. or higher.

According to one aspect of the invention:
The respective etching rates of the front surface and the back surface when heated to a temperature of 1200 ° C. to 1400 ° C. in an inert gas atmosphere at a pressure of 1 to 50 kPa A GaN substrate is provided that is less than 20 μm / hr.

  According to the present invention, it is possible to provide a GaN substrate which is not easily thermally etched even when it is used for crystal growth processing performed under temperature conditions of, for example, 1200 ° C. or higher.

1 is a cross-sectional view of a GaN substrate according to an embodiment of the present invention. It is the schematic of the vapor phase growth apparatus used when making a crystal grow. FIG. 3 is a cross-sectional view showing a manufacturing step of the GaN substrate according to the embodiment. FIG. 3 is a cross-sectional view showing a manufacturing step of the GaN substrate according to the embodiment. FIG. 3 is a cross-sectional view showing a manufacturing step of the GaN substrate according to the embodiment.

<One embodiment>
Hereinafter, a GaN substrate 10 according to an embodiment of the present invention will be described. A technique for growing a GaN crystal using the GaN substrate 10 as a seed crystal substrate will be described.

(1) Configuration of GaN Substrate The configuration of the GaN substrate 10 will be described. FIG. 1 is a cross sectional view schematically showing the configuration of a GaN substrate 10. The GaN substrate 10 has a base GaN substrate 20, a GaN layer 30, and a GaN layer 40. Hereinafter, the GaN substrate 10 is also referred to as “substrate 10”, base GaN substrate 20 as “base substrate 20”, GaN layer 30 as “layer 30”, and GaN layer 40 as “layer 40”.

  A GaN crystal layer grown using the substrate 10 as a seed crystal substrate may be referred to as a full growth film. The GaN film 100 shown in FIG. 1 is an example of a full growth film. Hereinafter, the GaN film 100 is also referred to as a “film 100”.

  Base substrate 20 is formed of a wurtzite structure, that is, a hexagonal single crystal GaN, and has a main surface 21 which is a gallium (Ga) surface and a main surface 22 which is a nitrogen (N) surface. However, the GaN single crystal constituting underlying substrate 20 includes inversion domain (ID) 24 which is a portion in which the polarity is inverted with respect to substrate portion 23 having a predetermined polarity, and ID 24 has thickness of underlying substrate 20. It penetrates in the longitudinal direction. The “single crystal” in the present specification is not limited to a crystal not including ID, but also includes a crystal having a plurality of IDs. The base substrate 20 is, for example, a disk having a diameter of 2 to 6 inches. The thickness of the base substrate 20 is preferably a thickness that allows the base substrate 20 to be self-supporting, for example, a thickness of 0.4 to 1.0 mm.

  The main surface 21 is a region composed of a Ga polar region 21g which is a region composed of Ga polar faces (+ c face, (0001) face) and an N polar face (−c face, (000-1) face) And an N-polar region 21 n. The Ga polarity region 21 g is a region where the base portion 23 is exposed to the main surface 21, and the N polarity region 21 n is a region where the ID 24 is exposed to the main surface 21. The main surface 22 includes an N-polar region 22n which is a region constituted by an N-polar surface, and a Ga-polar region 22g which is a region constituted by a Ga-polar surface. The N-polar region 22 n is a region in which the base portion 23 is exposed to the main surface 22, and the Ga-polar region 22 g is a region in which the ID 24 is exposed to the main surface 22.

  Major surface 21 includes N-polar region 21n in addition to Ga-polar region 21g, and the ratio of N-polar region 21n in major surface 21, that is, the ratio of the area of N-polar region 21n to the total area of major surface 21, is 50. Less than%. Such a principal surface 21 is referred to as "Ga surface". Main surface 22 includes Ga polarity region 22g in addition to N polarity region 22n, and the ratio of N polarity region 22n in main surface 22, that is, the ratio of the area of N polarity region 22n to the total area of main surface 22, is 50 It is over%. Such a principal surface 22 is referred to as "N-plane".

  Base substrate 20 is manufactured by appropriately using a known technique for growing a GaN crystal containing an ID. For example, there is known a technology that facilitates generation of ID by adjusting the V / III ratio of the source gas in hydride vapor phase epitaxy (HVPE). Further, for example, there is known a technique of generating an ID in a predetermined area by using a mask pattern. The N-polar region 21n of the main surface 21 and the Ga-polar region 22g of the main surface 22 can be formed to have a predetermined shape, arrangement or the like, in other words, the Ga-polar region 21g of the main surface 21 and The N-polar region 22 n of the main surface 22 can be formed to have a predetermined shape, arrangement, and the like. The shape and arrangement of the ID may be random.

  In the base substrate 20 illustrated in the present embodiment, a plurality of IDs 24 are dispersedly disposed on the main surface 21 and the main surface 22, and the main surface 21 includes a plurality of sea-like Ga polar regions 21 g and a plurality of island shapes. The main surface 22 is composed of a sea-like N-polar region 22n and a plurality of island-like Ga-polar regions 22g.

The ID 24 is uniformly distributed, for example, in the major surface 21 and in the major surface 22. The median value of the distribution of the number density (ID number density) of the N-polar regions 21 n on the main surface 21 is, for example, about 3000 pieces / cm ² . At this time, the standard deviation of the ID number density is, for example, preferably 1000 particles / cm ² or less, more preferably 300 particles / cm ² or less. If this is generalized, the standard deviation of the ID number density on the major surface 21 is preferably 1/3 or less of the median value, and more preferably, as a measure that the ID 24 is uniformly distributed. Is 1/10 or less.

  Layer 30 is composed of a GaN crystal epitaxially grown in the N-polar direction from N-polar region 21 n of main surface 21, that is, in the −c-axis direction, and covers the entire surface of main surface 21. The surface of the layer 30 opposite to the major surface 21 constitutes one major surface 11 of the substrate 10, and the major surface 11 is composed of an N-polar surface. Between the Ga polar region 21 g of the main surface 21 and the layer 30, there may be a void 13 which is a space in which a GaN crystal is not formed.

  Layer 40 is composed of a GaN crystal epitaxially grown in the N-polar direction from N-polar region 22 n of main surface 22, and covers the entire surface of main surface 22. The surface of the layer 40 opposite to the major surface 22 constitutes the other major surface 12 of the substrate 10, and the major surface 12 is composed of an N-polar surface. Between the Ga polar region 22 g of the main surface 22 and the layer 40, there may be a void 14 which is a space in which a GaN crystal is not formed.

  As described above, in the substrate 10, both the major surface 11 and the major surface 12 are formed of N-polar surfaces. The N-polar surface of the GaN crystal is characterized in that its thermal decomposition resistance is higher than that of the Ga-polar surface and it is difficult to be thermally etched.

The thermal etching rate (hereinafter, also simply referred to as etching rate) of the Ga polar face of the GaN crystal is, for example, 20 μm under conditions of nitrogen gas (N ₂ gas) atmosphere at a pressure of 1 to 105 kPa and a temperature of 1200 to 1400 ° C. Depending on conditions, it may reach a size of about 1000 μm / hr or more, and in some cases about 2000 μm / hr or more. The thermal etching rate of the Ga-polar surface is N ₂ gas also when the inert gas that constitutes the atmosphere is made of a rare gas such as argon (Ar) or a mixed gas of N ₂ gas and a rare gas. In the case of using as atmosphere gas. When the atmosphere of the GaN crystal contains a crystal growth atmosphere described later, ie, a halide such as gallium trichloride (GaCl ₃ ), hydrogen nitride such as ammonia (NH ₃ ), hydrogen (H ₂ ), etc. The thermal etching rate of the Ga polar face may be larger than the above etching rate.

In contrast, the etching rate of the N-polar surface of the GaN crystal is smaller than that of the Ga-polar surface, eg, _{N 2} gas atmosphere at a pressure of 1～105KPa, under the conditions of a temperature of 1200 to 1400 ° C., 20 [mu] m / The size is less than hr, preferably less than 10 μm / hr. Under N ₂ gas atmosphere at a pressure of 1 to 10 5 kPa, the etching rate of the N-polar surface of GaN crystal is less than 0.5 μm / hr at a temperature of 1200 ° C. to less than 1300 ° C., at a temperature of 1300 ° C. to 1350 ° C. It has been confirmed that the size is less than 4 μm / hr and less than 10 μm / hr at a temperature of more than 1350 ° C. and not more than 1400 ° C. Even when the inert gas that constitutes the atmosphere is made of a rare gas such as Ar or a mixed gas of N ₂ gas and a rare gas, the thermal etching rate of the N-polar surface is N ₂ gas as an atmosphere gas. It is similar to that in the case of In addition, even when the atmosphere of the GaN crystal is a crystal growth atmosphere (an atmosphere containing a halide, hydrogen nitride, H _2, etc. described later), the thermal etching rate of the N-polar surface is, for example, less than 40 μm / hr. It has been confirmed that it is much smaller than the thermal etching rate of the Ga-polar surface, for example, the size is preferably less than 20 μm / hr.

By setting the substrate 10 to the above-described configuration, in the crystal growth process when using it as a seed crystal substrate as described later, the substrate 10 is heated to a temperature of 1200 to 1400 ° C. under an inert gas atmosphere at a pressure of 1 to 105 kPa. The etching rate of each of the major surface 11 and the major surface 12 when heated can be, for example, less than 20 μm / hr, preferably less than 10 μm / hr. Further, the substrate 10, described later crystal growth atmosphere when heated to the temperature conditions mentioned above under (a halide, hydrogen nitride, an atmosphere containing H _2, etc.), each of the etching rate of the main surface 11 and major surface 12 For example, the size may be less than 40 μm / hr, preferably less than 20 μm / hr.

(2) Method of Manufacturing GaN Substrate A method of manufacturing the substrate 10 will be described. FIG. 2 is a schematic view of a growth apparatus 200 used for vapor phase growth processing of a GaN crystal. 3 to 5 are cross sectional views schematically showing the manufacturing process of the substrate 10.

  A growth apparatus 200 and a crystal growth process for growing a GaN crystal in an N-polar direction by using the growth apparatus 200 will be described with reference to FIG. The growth apparatus 200 is made of a heat-resistant material such as quartz, and includes an airtight container 203 in which the growth chamber 201 is formed. In the growth chamber 201, a susceptor 208 as a supporting member for holding the growth substrate 150 is provided. The susceptor 208 is connected to the rotation shaft 215 of the rotation mechanism 216 and is configured to be rotatable.

  The growth substrate 150 has a base surface 151 including an N-polar surface of GaN crystal as a base for crystal growth. The growth substrate 150 may be of different structure depending on the particular crystal growth process. As described later in detail, the growth substrate 150 is the base substrate 20 when the layer 30 is grown, and is the laminate 15 of the base substrate 20 and the layer 30 when the layer 40 is grown. A laminate 10 of substrate 20, layer 30 and layer 40, ie substrate 10.

A gas supply pipe 232a for supplying GaCl ₃ gas, a gas supply pipe 232b for supplying NH ₃ gas, and a gas supply pipe 232c for supplying N ₂ gas are connected to one end of the airtight container 203, respectively. A gas supply pipe 232 d for supplying H ₂ gas is connected to the gas supply pipe 232 c. On the downstream side of the gas supply pipes 232a to 232c, nozzles 249a to 249c for supplying various gases supplied from the gas supply pipes toward the growth substrate 150 held on the susceptor 208 are connected, respectively. .

In the gas supply pipe 232a, a gas generator 233a and a valve 243a are provided in order from the upstream side of the gas flow. A solid raw material (solid GaCl ₃ ) which is solid at normal temperature is accommodated in the gas generator 233a. Outside the gas generator 233a, a heater 207a is provided for heating the solid raw material to obtain a vaporized gas (GaCl ₃ gas). A gas supply pipe 232 e for supplying N ₂ gas as a carrier gas is connected to the gas generator 233 a. The GaCl ₃ gas generated in the gas generator 233a is carried into the growth chamber 201 by the carrier gas supplied from the gas supply pipe 232e. The gas supply pipes 232a and 232e are provided with pipe heaters (not shown) for preventing liquefaction and solidification of the GaCl ₃ gas.

In the gas supply pipes 232b to 232e, flow controllers 241b to 241e and valves 243b to 243e are provided in this order from the upstream side of the gas flow. A bypass pipe 232f is connected between the upstream side of the valve 243e of the gas supply pipe 232e and the downstream side of the valve 243a of the gas supply pipe 243a. The bypass pipe 232 f is provided with a valve 243 f. By opening the valve 243 f in a state where the valves 243 e and 243 a are closed, it is possible to bypass the gas generator 233 a and supply N ₂ gas into the growth chamber 201.

  At the other end of the airtight container 203, an exhaust pipe 230 for exhausting the inside of the growth chamber 201 is provided. The exhaust pipe 230 is provided with a pump 231. A zone heater 207 for heating the growth substrate 150 held on the susceptor 208 to a desired temperature is provided on the outer periphery of the hermetic container 203. In the airtight container 203, a temperature sensor 209 that measures the temperature in the growth chamber 201 is provided. Each member included in the growth apparatus 200 is connected to a controller 280 configured as a computer, and a program executed on the controller 280 is configured to control processing procedures and processing conditions to be described later.

For example, the crystal growth processing by the growth apparatus 200 is performed by executing the following processing procedure. First, the growth substrate 150 is charged into the airtight container 203 (held in) and held on the susceptor 208. Further, the solid raw material accommodated in the gas generator 233a is heated and vaporized by the heater 207a to generate GaCl ₃ gas. Further, the gas supply pipes 232a and 232e are heated to a desired temperature. Then, while performing the heating and evacuation of deposition chamber 201, the valve 243a, 243 e, with closed 243b, opening the valve 243 c, 243 d, the 243f appropriate, _{H 2} gas into the deposition chamber 201, or, _{H 2} Supply a mixed gas of gas and N ₂ gas. Then, the valve 243 f is closed and the valves 243 a, 243 e and 243 b are opened in a state where the inside of the growth chamber 201 reaches a desired processing temperature and pressure and the atmosphere in the growth chamber 201 becomes a desired atmosphere. A GaCl ₃ gas and an NH ₃ gas are supplied to the lower surface 151 of the growth substrate 150. Thereby, a GaN crystal grows in the N-polar direction on the lower surface 151 of the growth substrate 150. The supply of NH ₃ gas may be started prior to the supply of GaCl ₃ gas. In order to enhance the in-plane uniformity of the GaN crystal grown on the base surface 151, it is preferable to carry out the crystal growth process with the susceptor 208 rotated. When the crystal growth is completed, the valves 243 e, 243 a and 243 b are closed and the valve 243 f is opened to stop the supply of the GaCl ₃ gas and the NH ₃ gas into the growth chamber 201. Thereafter, the temperature of the growth chamber 201 is lowered while the supply of the N ₂ gas into the growth chamber 201 is continued, the processed growth substrate 150 is carried out of the airtight container 203, and the crystal growth process is completed.

The following are illustrated as processing conditions.
Temperature of gas generator 233a: 90 to 110 ° C.
Temperature of gas supply pipes 232a and 232e: 200 to 210 ° C.
Carrier gas flow rate: 80 to 120 sccm
Partial pressure of NH ₃ gas / partial pressure of GaCl ₃ gas in growth chamber 201: 18 to 22
Processing temperature (temperature of growth substrate 150): 1200 to 1400 ° C., preferably 1250 to 1300 ° C.
Processing pressure (pressure in growth chamber 201): 90 to 105 kPa, preferably 90 to 95 kPa

  The crystal growth performed here is growth in the N-polar direction, as described above. The growth in the N-polar direction is difficult to proceed under the temperature conditions adopted in the growth in the Ga-polar direction, that is, the growth in the + c-axis direction, ie, the temperature conditions of 900 to 1100 ° C. Therefore, in the present embodiment, by setting the temperature condition high as described above, the growth in the N-polar direction is made to proceed at a practical rate, for example, at a rate of 80 to 90 μm / hr. .

  In the crystal growth processing as described above, the GaN crystal is epitaxially grown in the N-polar direction from the N-polar surface included in the base surface 151. Even in the case where the base surface 151 includes a Ga polar face, the growth rate from the N polar face to the N polar direction in the crystal growth processing at a high temperature as described above is Fast enough compared to speed. The GaN crystal grown in the N-polar direction also grows in the in-plane direction. Thus, when the GaN crystal layer is grown to a certain thickness, the Ga polarity surface included in the base surface 151 is covered. Thus, not only in the case where the entire surface of base surface 151 is made up of an N-polar surface, but also in the case where base surface 151 includes a Ga-polar surface, the entire surface of base surface 151 is grown in the N-polar direction. A GaN crystal layer covering the

  The manufacturing process of the substrate 10 will be described with reference to FIGS. 3 to 5. Please refer to FIG. The base substrate 20 is prepared, and the base substrate 20 is introduced into the airtight container 203 of the growth apparatus 200 as the growth substrate 150. The base substrate 20 is held on the susceptor 208 such that the main surface 21, that is, the Ga surface becomes the base surface 151.

  Please refer to FIG. By performing the above-described crystal growth processing on base substrate 20, GaN crystal is grown in the N-polar direction from N-polar region 21n on main surface 21 to form layer 30. The layer 30 is grown to a thickness such that at least the Ga polar region 21g is covered and the entire main surface 21 is covered. At the time of growth of the layer 30, a void 13 may be formed between the Ga polar region 21g of the main surface 21 and the layer 30, due to the difficulty of growing a GaN crystal on the Ga polar region 21g. .

  After the layer 30 is grown, the processed growth substrate 150, that is, the laminate 15 of the base substrate 20 and the layer 30 is unloaded from the inside of the hermetic container 203. Thus, a laminate 15 having the major surface 11 whose entire surface is formed of the N-polar surface of GaN single crystal is obtained. In addition, you may obtain the main surface 11 by grind | polishing the outermost layer of the grown layer 30 as needed.

  Please refer to FIG. The stack 15 of the base substrate 20 and the layer 30 is introduced as the growth substrate 150 into the airtight container 203 of the growth apparatus 200. The stacked body 15 is held on the susceptor 208 such that the main surface 22 of the base substrate 20, that is, the N surface becomes the base surface 151. In other words, while the layer 30 is being grown, the base substrate 20 is turned over and held on the susceptor 208.

  Then, by performing the above-described crystal growth process on the stacked body 15, a GaN crystal is grown in the N-polar direction from the N-polar region 22 n on the major surface 22 to form the layer 40. The layer 40 is grown to a thickness such that at least the Ga polar region 22g is covered and the entire major surface 22 is covered. At the time of growth of the layer 40, an air gap 14 may be formed between the Ga polar region 22g of the main surface 22 and the layer 40 due to the difficulty of growing a GaN crystal on the Ga polar region 22g. .

  After the layer 40 is grown, the growth substrate 150 after processing, that is, the laminate of the base substrate 20, the layer 30, and the layer 40, ie, the substrate 10, is unloaded from the inside of the hermetic container 203. Thus, the substrate 10 having the major surface 12 whose entire surface is formed of the N-polar surface of GaN single crystal is obtained. In addition, you may obtain the main surface 12 by grind | polishing the outermost layer of the grown layer 40 as needed.

  In this manner, the GaN crystal is grown in the N-polar direction from the N-polar region 21 n and the n-polar region 22 n on the main surface 21 and the main surface 22 of the base substrate 20 respectively. Substrates 10 can be manufactured, each of which is configured with an N-polar surface.

  In the above description, the layer 30 is first grown on the major surface 21 and then the layer 40 is grown on the major surface 22. First, the layer 40 is grown on the major surface 22, Next, the layer 30 may be grown on the main surface 21 surface. Among these embodiments, the embodiment in which the layer 30 is grown first is preferable for the following reasons, for example.

  Under the high temperature conditions in the crystal growth process of the present embodiment, the Ga polar surface is easily thermally etched compared to the N polar surface. Therefore, the main surface 21 that is the Ga surface is more easily etched than the main surface 22 that is the N surface, that is, the wider Ga polarity region 21 g is etched. By growing the layer 30 first, the main surface 21 is protected by the layer 30 in the later growth of the layer 40, and etching of the main surface 21 can be suppressed. On the other hand, in the embodiment in which the layer 40 is grown first, since the major surface 21 is exposed in the growth of the layer 40, the wide Ga polarity region 21g is easily etched and a large amount of decomposition products by etching may be generated. is there. Then, the decomposition product may adversely affect the growth of the later layer 30 by covering the N-polar region 21 n.

  The Ga polarity region 21 g of the main surface 21 is wider than the Ga polarity region 22 g of the main surface 22. Due to this, covering the entire surface of the major surface 21 with the layer 30 covering the Ga polar region 21g is easier than covering the entire surface of the major surface 22 with the layer 40 covering the Ga polar region 22g. Absent. The layer 30 may be formed thicker than the layer 40 in order to improve the certainty that the entire main surface 21 is covered. In addition, the void 13 formed on the main surface 21 is wider than the void 14 formed on the main surface 22 in correspondence to the Ga polarity region 21 g being wider than the Ga polarity region 22 g. May be there. Note that, since the Ga polarity region 21g is wide, in the growth of the layer 30 from the N polarity region 21n, the contribution of the growth in the in-plane direction becomes large. Thereby, in the layer 30, a reduction in defect density is expected compared to the layer 40.

(3) Crystal Growth Processing on GaN Substrate A crystal growth processing for forming a film 100 by growing a GaN crystal on the substrate 10 using the substrate 10 as a seed crystal substrate will be described. This process can be performed, for example, using the growth apparatus 200. Hereinafter, the main surface to be the lower ground surface 151 of the seed crystal substrate may be referred to as “front surface”, and the opposite surface, that is, the main surface on the susceptor 208 side may be referred to as “back surface”.

  Refer back to FIG. The substrate 10 is introduced into the airtight container 203 of the growth apparatus 200 as the growth substrate 150. For example, the substrate 10 is held on the susceptor 208 such that the main surface 11 is the base surface 151, that is, the main surface 11 is the surface 11.

  Then, the film 100 is grown on the surface 11 by performing the above-described crystal growth process on the substrate 10. Since the entire surface 11 of the surface 11 is composed of the N-polar surface, the film 100 is epitaxially grown from the entire surface 11 in the N-polar direction. After the film 100 is grown to a predetermined thickness, the processed growth substrate 150, that is, the substrate 10 which is a seed crystal substrate, and the stack of the film 100 which is a true growth film are unloaded from the airtight container 203. After growth, the film 100 is separated from the substrate 10 and sliced to obtain a new GaN substrate from the film 100. The substrate 10 after the film 100 is separated may be used again as a seed crystal substrate.

  Here, as a comparison form, a mode is considered in which a normal GaN substrate in which the entire surface is composed of N-polar surfaces and the entire surface is composed of Ga-polar surfaces is used as a seed crystal substrate. In the comparative embodiment, under the above-described temperature conditions, thermal etching of the back surface proceeds excessively, which causes the seed crystal substrate to disappear in a short time. On the other hand, the substrate 10 which is the seed crystal substrate of the present embodiment has excellent thermal etching resistance because each of the front surface 11 and the back surface 12 is formed of an N-polar surface. Thereby, in the present embodiment, even if the temperature condition is set high as described above, it is possible to avoid the disappearance of the seed crystal substrate in a short time. That is, in the present embodiment, the growth time of the film 100 can be extended, and a thick film 100 can be obtained.

As described above, the etching rate of the surface 11 and the back surface 12 composed of the N-polar surface is less than 20 μm / hr, preferably 10 μm, under an inert gas atmosphere at a pressure of 1 to 105 kPa and a temperature condition of 1200 to 1400 ° C. It is less than / hr. In addition, as described above, the etching rates of the front surface 11 and the back surface 12 configured by the N-polar surface are the crystal growth atmosphere (atmosphere containing halide, hydrogen nitride, H ₂ etc.) and temperature conditions of 1200 to 1400 ° C. Less than 40 μm / hr, preferably less than 20 μm / hr.

  In addition, although the aspect which makes the main surface 11 of the board | substrate 10 the surface was illustrated in the above-mentioned description, the aspect which makes the main surface 12 of a substrate the surface may be sufficient. Among these embodiments, the embodiment in which the main surface 11 is the front surface, that is, the embodiment in which the main surface 12 is the back surface is preferable for the following reasons, for example.

  A layer 40 defining the major surface 12 is laminated to the major surface 22. Therefore, by making the main surface 12 the back surface, even if the entire thickness of the layer 40 is etched during the growth of the film 100, it becomes the main surface 22 of the base substrate 20, that is, the N surface. Etching of the underlying substrate 20 can be suppressed. On the other hand, in the aspect in which the main surface 12 is the front surface, that is, in the aspect in which the main surface 11 is the back surface, the main surface 21 which is a Ga surface is Since it is exposed, the base substrate 20 is easily etched. Base substrate 20 has a thickness of 0.4 to 1.0 mm, for example. Therefore, even if the entire thickness of the layer 40 is etched by using the main surface 12 as the back surface, the base substrate 20 is thereafter at least 10 under the temperature conditions described above. The time, in some cases 20 hours, will not disappear. In the embodiment in which the main surface 12 is the surface, the layer 30 disposed on the back side has its entire thickness during the growth of the film 100 (more specifically, the entire surface of the Ga polar region 21 g It is preferable to be thick enough that the entire thickness of the covering portion is not etched.

  The substrate 10 preferably has a void 13 or a void 14. The presence of the air gap 13 or the air gap 14 weakens the force by which the film 100 is restrained by the substrate 10, and the stress generated in the film 100 can be relaxed. It is more preferable that the air gap 13 or the air gap 14 be present between the underlying substrate 20 and the film 100 in order to relieve stress more effectively. Also, the effect of relieving stress is greater as the gap is wider. Therefore, the presence of the air gap 13 between the base substrate 20 and the film 100 is more preferable than the case where the air gap 14 is present. That is, from such a viewpoint, it is more preferable to grow the film 100 on the main surface 21 side which is the Ga surface of the base substrate 20 with the main surface 11 as the surface. As described above, since the defect density reduction in the layer 30 is expected, the film 100 epitaxially grown on the layer 30 has higher crystal quality than the film 100 epitaxially grown on the layer 40. It is also expected. From such a point of view as well, the main surface 11 may be used as the surface.

  The ID 24 is preferably uniformly distributed in the main surface 21 and the main surface 22 of the base substrate 20. As a result, the in-plane distribution of the air gaps 13 and the air gaps 14 can be made uniform, and the effect of stress relaxation on the film 100 by the air gaps 13 and 14 can be made uniform in the plane. Further, by uniformly distributing the ID 24, the behavior of the layer 30 covering the Ga polar region 21 g on the major surface 21 and the behavior of the layer 40 covering the Ga polar region 22 g on the major surface 22 are in plane. Since it can approach uniformly, the part which is hard to be covered by the layer 30 on the main surface 21, and the part which is hard to cover by the layer 40 on the main surface 22 can be hard to produce.

(4) Effects Obtained by the Present Embodiment According to the present embodiment, one or more effects described below can be obtained.

(A) The main surface 11 and the main surface 12 of the substrate 10 are each formed of an N-polar surface which is difficult to be thermally etched, so that the substrate 10 has a temperature of 1200 to 1400 ° C. under an inert gas atmosphere at a pressure of 1 to 105 kPa. It is possible to set the etching rate of each of the main surface 11 and the main surface 12 when heated to a temperature, for example, to a size of less than 20 μm / hr, preferably less than 10 μm / hr. In addition, the etching rates of the main surface 11 and the main surface 12 when the substrate 10 is heated to the above-described temperature conditions in the above-mentioned crystal growth atmosphere (atmosphere including halide, hydrogen nitride, H _{2 and the} like) For example, the size can be less than 40 μm / hr, preferably less than 20 μm / hr. Thus, the substrate 10 of the present embodiment can be suitably used as a seed crystal substrate in crystal growth processing where temperature conditions need to be set high as described above, for example, growth processing of GaN crystals in the N-polar direction. It becomes possible. That is, epitaxial growth in the N-polar direction of the GaN crystal can be favorably performed on one main surface of the substrate 10, and thermal etching can be suppressed during the growth of the GaN crystal on the other main surface.

(B) Such a substrate 10 has a main surface 21 (an example of “surface on the front side”) including the Ga polar region 21 g and the N polar region 21 n (main surface including the Ga polar region 22 g and the N polar region 22 n) 22 (an example of “back side surface”), that is, the base substrate 20 having ID 24 and the N polarity region 21 n of the main surface 21 are grown to cover the main surface 21, and the main surface 11 of the substrate 10 ( It grows from the layer 30 (an example of a "front side GaN layer") which comprises "an example of a (front) face" with an N-polar face and the N-polar region 22n of the major surface 22, and covers the major surface 22 The main surface 12 (an example of the “back side”) of the substrate 10 can be configured as the substrate 10 having a layer 40 (an example of the “back side GaN layer”) formed of an N-polar surface.

  By using base substrate 20 including an N-polar surface and a Ga-polar surface for each of main surface 21 and main surface 22, a GaN crystal is grown in the N-polar direction on each of main surface 21 and main surface 22; And layer 40 can be obtained. Thereby, the board | substrate 10 in which both surfaces of the main surface 11 and the main surface 12 were comprised by N polar surface can be implement | achieved.

(C) The substrate 10 has the air gap 13 disposed between the main surface 21 of the base substrate 20 and the layer 30, and the air gap 14 disposed between the main surface 22 of the base substrate 20 and the layer 40. It is preferable to have at least one. Thereby, the stress generated in film 100 grown using substrate 10 as a seed crystal substrate can be relaxed.

(D) The ID 24 is preferably uniformly distributed in the major surface 21 and the major surface 22 of the base substrate 20. Thereby, the effect of stress relaxation to the film 100 by the air gaps 13 and 14 can be made uniform in the plane, and a portion which is not easily covered by the layer 30 on the main surface 21 and a layer 40 on the main surface 22 are covered. It is possible to make it hard to produce parts that are difficult to be damaged.

Other Embodiments
The present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the scope of the invention. In addition, various embodiments and modifications may be combined as appropriate.

  In the above-mentioned embodiment, in the main surface 21 and in the main surface 22, the base portion 23 is integrally and continuously disposed continuously in the form of a sea, and the ID 24 is dispersedly disposed in a plurality of islands. Although the base substrate 20 is illustrated, the shapes and the arrangement of the base portion 23 and the ID 24 may be appropriately changed as needed. For example, the ID 24 may be arranged to divide the base 23 into a plurality of parts. Also, for example, the ID 24 may be integrally, continuously, and have a shape (for example, a lattice shape, a meander shape, and the like) spread in the main surface. Base substrate 20 has main surface 21 configured of at least one Ga polar region 21g and at least one N polar region 21n, and is configured of at least one Ga polar region 22g and at least one N polar region 22n. The main surface 22 is provided.

  In the above-described embodiment, the base substrate 20 in which the ratio of the N-polar region 21 n in the main surface 21 is lower than the ratio of the N-polar region 21 n in the main surface 22 is illustrated. By using such base substrate 20, the characteristics of the substrate 10 can be made different between the main surface 21 side and the main surface 22 side. Specifically, for example, on the main surface 21 side where the ratio of the N-polar region is low, that is, the Ga surface, the wide air gap 13 is easily formed, and the defect density of the layer 30 is easily reduced. On the other hand, it is easy to cover the entire surface of the main surface 22 with the layer 40 on the main surface 22 side where the ratio of the N-polar region is high, that is, the N surface. However, base substrate 20 only needs to have both main surfaces including the N polarity region, and the ratio of N polarity region 21 n in one main surface 21 to the ratio of N polarity region 21 n in the other main surface 22 May be equal.

As described in the above embodiment, to form the layer 30, the layer 40 and the film 100, the growth of the GaN crystal in the N-polar direction is performed under high temperature conditions of 1200 ° C. or higher. Such a growth method of the GaN crystal in the N-polar direction is not limited to the above-described method, and the following method may be used. For example, the GaN crystal may be grown by a Tri-HVPE method in which a Ga source material is reacted with Cl ₂ gas or the like in a growth chamber in which crystal growth is performed to generate GaCl ₃ gas. Also, for example, in a state where the growth chamber reaches the processing conditions of 1 to 100 kPa and 1100 to 1400 ° C., and the atmosphere in the growth chamber becomes a desired atmosphere, the vapor of Ga containing no halogen element as source gas is applied to the growth substrate. may be grown GaN crystal by non-halogen VPE method supplies the NH ₃ gas. Further, for example, with the growth chamber reaching the processing conditions of 1 to 105 kPa and 1200 to 1400 ° C. and the atmosphere in the growth chamber becoming a desired atmosphere, the growth substrate is treated with trimethylgallium (TMG) gas as a source gas. The GaN crystal may be grown by a high temperature MOCVD method that supplies NH ₃ gas. The etching rate of the N-polar surface is less than 40 μm / hr, preferably less than 20 μm / hr, under the crystal growth atmosphere and temperature conditions in these methods.

In the above-mentioned embodiment, although the aspect which makes a GaN crystal grow as a full growth film was illustrated using substrate 10 as a seed crystal board, the crystal grown as a full growth film is not limited to a GaN crystal. For example, nitride crystals such as aluminum nitride (AlN), aluminum gallium nitride (AlGaN), indium nitride (InN), indium gallium nitride (InGaN), and aluminum gallium indium nitride (AlInGaN), that is, Al _x In _y Ga _{1- A} Group III nitride crystal represented by a composition formula of _xy N (0 ≦ x + y ≦ 1) may be grown as a true growth film.

<Preferred embodiment of the present invention>
Hereinafter, preferred embodiments of the present invention will be additionally stated.

(Supplementary Note 1)
The respective etching rates of the front surface and the back surface when heated to a temperature of 1200 ° C. to 1400 ° C. in an inert gas atmosphere at a pressure of 1 to 50 kPa GaN substrate less than 20 μm / hr.

(Supplementary Note 2)
The inert gas contains at least one of N ₂ gas and / or noble gas.
The GaN substrate according to appendix 1.

(Supplementary Note 3)
An underlying GaN substrate having a front side including a Ga polar region and an N polar region and having a rear side including a Ga polar region and an N polar region;
A front-side GaN layer grown from the N-polar region of the front-side surface, covering the front-side surface, and having the surface made up of N-polar surfaces;
A back side GaN layer grown from the N polarity region of the back side surface, covering the back side surface, and forming the back side with an N polarity surface;
The GaN substrate according to claim 1 or 2, further comprising:

(Supplementary Note 4)
An air gap in which a GaN crystal is not formed, which is disposed between the front surface and the front GaN layer;
An air gap in which the GaN crystal is not formed, which is disposed between the back surface and the back GaN layer
The GaN substrate according to appendix 3, comprising at least one of:

(Supplementary Note 5)
The ratio of the N-polar region in the front side surface is lower than the ratio of the N-polar region in the rear side surface,
The GaN substrate according to Appendix 3 or 4.

(Supplementary Note 6)
The thickness of the front side GaN layer is thicker than the thickness of the back side GaN layer,
The GaN substrate according to appendix 5.

(Appendix 7)
The N-polar regions are dispersedly arranged in the front side surface, and the standard deviation of the number density of the N-polar regions in the front side surface is preferably 1/3 or less of the median, more preferably Is less than 1/10,
The GaN substrate according to appendix 5 or 6.

(Supplementary Note 8)
The proportion of the N-polar region in the front side surface is equal to the proportion of the N-polar region in the rear side surface,
The GaN substrate according to Appendix 3 or 4.

(Appendix 9)
Preparing an underlying GaN substrate having a front side including a Ga polar region and an N polar region and having a rear side including a Ga polar region and an N polar region;
Growing a front side GaN layer covering the front side surface from the N polarity region of the front side surface, and the surface of the front side is formed of an N polar surface;
Growing a back side GaN layer covering the back side from the N polarity region of the back side, and the back side comprising an N polarity face;
Method of manufacturing a GaN substrate having

(Supplementary Note 10)
In the step of growing the front side GaN layer, forming an air gap in which a GaN crystal is not formed, which is disposed between the front side surface and the front side GaN layer;
In the step of growing the back side GaN layer, forming a void in which a GaN crystal is not formed, which is disposed between the back side surface and the back side GaN layer.
Do at least one of the
Appendix 9. The method of manufacturing a GaN substrate according to appendix 9.

(Supplementary Note 11)
Among the steps of growing the front side GaN layer and growing the back side GaN layer, the step of growing the side of the front side and the back side on the side having a lower ratio of the N polarity region The process is carried out prior to the step of growing on the surface with the higher proportion of the N polarity region,
A method of manufacturing a GaN substrate according to claim 9 or 10.

(Supplementary Note 12)
The respective etching rates of the front surface and the back surface when heated to a temperature of 1200 ° C. to 1400 ° C. in an inert gas atmosphere at a pressure of 1 to 50 kPa Less than 20 μm / hr,
An underlying GaN substrate having a front side including a Ga polar region and an N polar region and having a rear side including a Ga polar region and an N polar region;
A front-side GaN layer grown from the N-polar region of the front-side surface, covering the front-side surface, and having the surface made up of N-polar surfaces;
A back side GaN layer grown from the N polarity region of the back side surface, covering the back side surface, and forming the back side with an N polarity surface;
Preparing a GaN substrate having
Growing a GaN crystal in the N polarity direction on the surface;
Method of manufacturing a GaN crystal having

(Supplementary Note 13)
The surface is a surface of the surface and the back surface, which is disposed on the side of the surface on the front side and the surface on the back side where the ratio of the N polarity region is lower.
The manufacturing method of the GaN crystal as described in appendix 12.

10 GaN substrate (seed crystal substrate)
20 base GaN substrate 30, 40 GaN layers 11, 12, 21, 22 main surfaces 13, 14 air gaps 21 g, 22 g Ga polar regions 21 n, 22 n N polar regions 100 GaN film (full growth film)

Claims (10)

  The respective etching rates of the front surface and the back surface when heated to a temperature of 1200 ° C. to 1400 ° C. in an inert gas atmosphere at a pressure of 1 to 50 kPa GaN substrate less than 20 μm / hr. The inert gas contains at least one of N ₂ gas and / or noble gas.
The GaN substrate according to claim 1. An underlying GaN substrate having a front side including a Ga polar region and an N polar region and having a rear side including a Ga polar region and an N polar region;
A front-side GaN layer grown from the N-polar region of the front-side surface, covering the front-side surface, and having the surface made up of N-polar surfaces;
A back side GaN layer grown from the N polarity region of the back side surface, covering the back side surface, and forming the back side with an N polarity surface;
The GaN substrate according to claim 1 or 2, which has An air gap in which a GaN crystal is not formed, which is disposed between the front surface and the front GaN layer;
An air gap in which the GaN crystal is not formed, which is disposed between the back surface and the back GaN layer
The GaN substrate according to claim 3, having at least one of: The ratio of the N-polar region in the front side surface is lower than the ratio of the N-polar region in the rear side surface,
The GaN substrate according to claim 3 or 4. The thickness of the front side GaN layer is thicker than the thickness of the back side GaN layer,
The GaN substrate according to claim 5. The N-polar regions are dispersedly arranged on the front side surface, and the standard deviation of the number density of the N-polar regions on the front side surface is 1/3 or less of the median.
A GaN substrate according to claim 5 or 6. The proportion of the N-polar region in the front side surface is equal to the proportion of the N-polar region in the rear side surface,
The GaN substrate according to claim 3 or 4. Preparing an underlying GaN substrate having a front side including a Ga polar region and an N polar region and having a rear side including a Ga polar region and an N polar region;
Growing a front side GaN layer covering the front side surface from the N polarity region of the front side surface, and the surface of the front side is formed of an N polar surface;
Growing a back side GaN layer covering the back side from the N polarity region of the back side, and the back side comprising an N polarity face;
Method of manufacturing a GaN substrate having In the step of growing the front side GaN layer, forming an air gap in which a GaN crystal is not formed, which is disposed between the front side surface and the front side GaN layer;
In the step of growing the back side GaN layer, forming a void in which a GaN crystal is not formed, which is disposed between the back side surface and the back side GaN layer.
Do at least one of the
A method of manufacturing a GaN substrate according to claim 9.

Images