JP2014162713A - Method for manufacturing a nitride semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method for providing an excellent nitride semiconductor substrate having an excellent orientation of a crystal axis in the manufacture of a nitride semiconductor substrate, by causing a crystal growth of a nitride semiconductor substrate in a warpage-reduced seed substrate.SOLUTION: A method for manufacturing a nitride semiconductor substrate 11 raises a seed substrate 10 having a seed crystal 12 on the principal plane of a substrate, to a temperature optimum for the crystal growth of a nitride semiconductor layer 13, and the nitride semiconductor layer 13 and the seed substrate 10 are peeled after the nitride semiconductor layer 13 was crystally grown on the seed crystal 12, thereby to manufacture a nitride semiconductor substrate 1. At the time of producing the seed substrate 10, the warpage corresponding to that of the seed substrate 10 by the temperature rise is effected in the seed substrate 10 in a direction opposite to the direction, in which the seed substrate 10 is warped by the temperature rise.

Description

  The present invention relates to a method for manufacturing a nitride semiconductor substrate.

  In recent years, the demand for LEDs (Light Emitting Diodes) as a light source, in particular, the demand for light emitting diodes such as blue LEDs and white LEDs has increased rapidly. For blue LEDs and white LEDs, GaN, InGaN and similar nitride semiconductors manufactured by epitaxial growth are used. Further, nitride semiconductors are attracting attention as electronic device materials because they can operate at high power and high frequency because of their high electron mobility and wide band gap.

In general, a crystal of a nitride semiconductor (for example, GaN) used for a light emitting diode or a transistor is formed on a sapphire substrate or a silicon substrate by vapor phase epitaxial growth. The dislocation density of the GaN crystal obtained by this method is usually relatively high, about 10 ⁸ cm ⁻² to 10 ⁹ cm ⁻² , so that the crystal quality is poor. This is due to the large lattice constant difference between the sapphire substrate (or silicon substrate) and GaN. In order to solve such a problem of dislocation density, an GaN crystal having a GaN crystal itself as a substrate is not manufactured, but an GaN crystal is grown on a sapphire substrate (or a silicon substrate). It is optimal to produce a crystal substrate.

  For example, Patent Document 1 is cited as a document disclosing a method for manufacturing a GaN single crystal substrate. Patent Document 1 manufactures a seed substrate in which a seed crystal (GaN) is grown on the main surface of a sapphire substrate by metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or HVPE. Then, a GaN single crystal is grown on the main surface of the seed substrate by a liquid phase epitaxial growth (LPE) method using sodium (Na) as a flux at an optimum crystal growth temperature (about 800 ° C. to 1000 ° C.), Thereafter, a method of manufacturing a GaN single crystal substrate made of a GaN single crystal by naturally separating the seed substrate and the GaN single crystal by a stress caused by a temperature drop from the crystal growth temperature to room temperature (about 25 ° C.) is disclosed. Yes.

According to this manufacturing method, the dislocation density of the GaN single crystal becomes a value of about 10 ⁴ cm ⁻² , which can be made smaller than the dislocation density (10 ⁸ cm ⁻² to 10 ⁹ cm ⁻² ) of the epitaxial substrate. The quality of GaN crystals can be improved.

  Furthermore, in Patent Document 1, when the GaN single crystal and the seed substrate are naturally separated, the GaN single crystal and the seed substrate are prevented from being cracked by the stress applied to the GaN single crystal. A method of manufacturing a GaN single crystal substrate manufactured by providing a plurality of gaps at the interface is disclosed.

  As a result, the seed substrate and the GaN single crystal can be peeled from the gap provided at the interface between the seed substrate and the GaN single crystal even if a stress is generated due to a thermal change when the temperature is lowered from the crystal growth temperature to the room temperature. , It is possible to prevent cracks in the GaN single crystal.

Japanese Patent Laid-Open No. 2004-247711

  In the method for manufacturing a GaN single crystal growth substrate of Patent Document 1, when a GaN single crystal is grown by liquid phase epitaxial growth (LPE) using sodium (Na) as a flux, the crystal growth temperature is from room temperature (about 25 ° C.). It is necessary to heat the seed substrate to (800 ° C. to 1000 ° C.). During this temperature increase, the seed substrate is warped due to the difference in thermal expansion coefficient between the seed substrate and the seed crystal layer, and the seed substrate is warped immediately before crystal growth of the GaN single crystal.

  When a GaN single crystal is grown on the main surface of the seed substrate where warpage has occurred, the GaN single crystal grows on the main surface of the seed substrate based on the warped shape. There has been a problem that a GaN single crystal substrate having poor crystallinity is produced.

  The present invention has been made in view of the above points, and the object of the present invention is to reduce warpage when a nitride semiconductor layer is grown on a main surface of a seed substrate in the manufacture of a nitride semiconductor substrate. An object of the present invention is to provide a manufacturing method for manufacturing a high-quality nitride semiconductor substrate having a good crystal axis orientation by crystal growth of a nitride semiconductor layer on the seed substrate.

  In the method of manufacturing a nitride semiconductor substrate according to the present invention, a seed substrate having a seed crystal on the main surface of the substrate is heated to a temperature optimum for crystal growth of the nitride semiconductor layer, and the nitride is formed on the seed crystal. A method of manufacturing a nitride semiconductor substrate by separating the nitride semiconductor layer and the seed substrate after crystal growth of a semiconductor layer, wherein the temperature is increased in advance when the seed substrate is manufactured. The warping amount corresponding to the warping amount of the seed substrate is warped in the direction opposite to the direction in which the seed substrate warps due to the temperature rise.

  According to such a specific matter, when the seed substrate is manufactured, the amount of warpage corresponding to the amount of warping of the seed substrate due to the temperature rise to a temperature optimum for crystal growth of the nitride semiconductor layer is previously increased. Since the seed substrate is warped in the opposite direction to the direction in which the seed substrate is warped, even if the seed substrate is heated to the optimum temperature for crystal growth of the nitride semiconductor layer after the seed substrate is manufactured, Stress is applied in the direction in which the warpage is relaxed. That is, since the seed substrate immediately before the crystal growth is reduced in warpage and becomes almost flat, the crystal axis orientation of the nitride semiconductor layer is good even if the nitride semiconductor layer is grown on the seed substrate. A good quality nitride semiconductor substrate can be manufactured.

  In the method for manufacturing a nitride semiconductor substrate, the seed crystal is obtained by forming a convex portion on a main surface of the seed crystal when the seed substrate is manufactured.

  Due to such specific matters, a convex portion is formed on the main surface of the seed crystal, and a nitride semiconductor layer is grown on the convex portion, so that the contact area between the nitride semiconductor layer and the main surface of the seed crystal is reduced. The nitride semiconductor layer and the seed substrate can be easily peeled off.

  The nitride semiconductor substrate manufacturing method, wherein the nitride semiconductor layer has a crystal growth on the seed crystal through the through holes after disposing a mask having a plurality of through holes on the seed crystal. The mask is peeled off from the nitride semiconductor layer together with the seed substrate after the crystal growth.

  By arranging a mask having a through-hole on the seed crystal by such a specific matter, the nitride semiconductor layer is grown through the through-hole of the mask, so that no complicated process is required and simple. By this method, the contact area between the nitride semiconductor layer and the seed crystal can be further reduced. Thereby, the natural separation between the seed crystal and the nitride semiconductor layer can be more easily performed.

  The method of manufacturing a nitride semiconductor substrate, wherein the seed substrate is obtained by warping the seed substrate until the amount of warpage is reached by reducing the thickness of the seed substrate. Suppose that there is.

  By such a specific matter, the seed substrate can be warped by processing that is a simple method before the crystal growth step.

  In the above method for manufacturing a nitride semiconductor substrate, the seed substrate is obtained by warping until the amount of warpage is reached by heat treatment when the seed substrate is manufactured.

  Due to such specific matters, unlike the case where the substrate is warped by processing, generation of processing waste can be suppressed.

  The method for manufacturing a nitride semiconductor substrate, wherein the seed substrate is obtained by growing a seed crystal on a main surface of the substrate until the amount of warpage is reached when the seed substrate is manufactured. Suppose that there is.

  Since the substrate is warped simultaneously with the growth of the seed crystal due to such a specific matter, the seed substrate can be warped by a small number of steps without requiring a new step of warping the substrate.

  According to the present invention, in the manufacture of a nitride semiconductor substrate, when the nitride semiconductor layer is crystal-grown on the main surface of the seed substrate, the nitride semiconductor layer is crystal-grown on the seed substrate with reduced warpage, A manufacturing method for manufacturing a high-quality nitride semiconductor substrate with good crystal axis orientation can be provided.

In the manufacturing method of the nitride semiconductor substrate which concerns on this invention, it is explanatory drawing which shows the seed substrate manufacturing process of 1st embodiment. In the manufacturing method of the nitride semiconductor substrate which concerns on this invention, it is explanatory drawing which shows the seed substrate manufacturing process of 2nd embodiment. In the method for manufacturing a nitride semiconductor substrate according to the present invention, (a) is a plan view of the seed substrate of the third embodiment, (b) is a sectional view taken along line II-II in (a), (c). These are sectional drawings which show the modification of the seed substrate of 3rd embodiment. 1 is a schematic diagram of a crystal growth apparatus for manufacturing a nitride semiconductor substrate according to the present invention. FIG. 5 is an explanatory diagram showing a process of crystal growth of the nitride semiconductor layer of the first embodiment in the method for manufacturing a nitride semiconductor substrate according to the present invention. 4 is a plan view of a mask used for crystal growth of a nitride semiconductor layer in the method for manufacturing a nitride semiconductor substrate according to the present invention. FIG. In the method for manufacturing a nitride semiconductor substrate according to the present invention, it is an explanatory view showing a process of crystal growth of the nitride semiconductor layer of the third embodiment.

  In the method for manufacturing a nitride semiconductor substrate according to the present invention, the seed substrate 10 having the seed crystal 12 on the main surface of the substrate 11 is heated to a temperature optimum for crystal growth of the nitride semiconductor layer 13 (see FIG. 4). In this manufacturing method, the nitride semiconductor layer 13 and the seed substrate 10 are naturally separated after the nitride semiconductor layer 13 is grown on the seed crystal 12, and the nitride semiconductor substrate 1 is manufactured. At the time of manufacturing, the amount of warpage corresponding to the amount of warping of the seed substrate 10 due to temperature rise is previously warped in the direction opposite to the direction of warping of the seed substrate 10 due to temperature rise. .

  Hereinafter, embodiments of the present invention will be described step by step regarding a seed substrate manufacturing process for manufacturing a seed substrate and a crystal growth process for manufacturing a nitride semiconductor substrate by crystal growth of a nitride semiconductor layer on the seed substrate. To do.

○ First embodiment
[Seed board manufacturing process]
First, the manufacturing process of the seed substrate 10 will be described with reference to FIG. 1A.

  FIG. 1A is an explanatory view showing a seed substrate manufacturing process in the method for manufacturing a nitride semiconductor substrate according to the present invention.

  As a material for the substrate 11, for example, sapphire, silicon carbide, silicon, or the like can be used. The thickness of the substrate 11 is preferably 0.3 mm or more from the viewpoint of the handling of the substrate 11 and the quality of the seed crystal 12 grown on the substrate 11 thereafter, and is preferably 2.0 mm or less from the viewpoint of the price of the substrate. In this embodiment, a sapphire substrate having a diameter of 50 mm, a thickness of 0.43 mm, and a principal surface having a C-plane is used.

  The substrate 11 is warped in advance in a direction opposite to the direction in which the seed substrate 10 warps due to the temperature rise, with a warp amount corresponding to the amount that the seed substrate 10 warps due to the temperature rise in the crystal growth step described later. Here, the “warping amount” is a distance L from the center of the concave surface of the substrate to the horizontal surface when the concave surface of the substrate 11 is placed on the horizontal surface (see FIG. 1A). This amount of warpage can be measured by a known measuring device such as a grazing incidence interference type measuring device.

After warping the substrate 11, the seed crystal 12 is grown on the main surface of the substrate 11. The seed crystal 12 is crystal-grown by a conventionally known crystal growth method such as a metal organic chemical vapor deposition (MOCVD) method or a hydride vapor phase epitaxy (HVPE) method. In the present embodiment, GaN is grown as a seed crystal 12 on the substrate 11 by MOCVD. More specifically, after setting the substrate 11 having warpage in the chamber of the MOCVD apparatus, the inside of the chamber is cleaned with a pressure of 100 Torr and a temperature of 1240 ° C. in a hydrogen atmosphere. After cleaning the inside of the chamber, the temperature inside the chamber is lowered to 715 ° C., the pressure is set to 400 Torr, source gases such as trimethyl gallium (TMG) and ammonia (NH ₃ ) are supplied into the chamber, and a low temperature GaN buffer layer is formed on the substrate 11. Grow. After growing the low-temperature GaN buffer layer, the temperature in the chamber is raised to 1310 ° C., the pressure is set to 200 Torr, and a seed crystal 12 of GaN having a desired film thickness is grown on the low-temperature GaN buffer layer.

  The film thickness of the seed crystal 12 is preferably 3 μm to 20 μm from the viewpoint of the quality of the seed crystal 12 and the ease of natural peeling between the seed crystal 12 and the nitride semiconductor layer 13 described later. Further, the warpage amount of the seed substrate is preferably 70 μm to 110 μm as the warpage amount corresponding to the amount of warpage of the seed substrate 10 due to the temperature rise in the crystal growth step described later. In general, the amount of warping of the seed substrate 10 can be increased by increasing the thickness of the seed crystal 12.

  As described above, in the seed substrate manufacturing process, the amount of warpage corresponding to the amount of warping of the seed substrate 10 due to the temperature rise in the crystal growth process described later is warped in the opposite direction to the direction in which the seed substrate 10 warps due to the temperature rise. The seed substrate 10 can be manufactured.

  In addition, although the main surface of the sapphire substrate of the present embodiment has been described as the C plane, the main surface of the sapphire substrate may be another crystal plane such as an A plane or an R plane.

[Crystal growth process]
Next, a process of manufacturing the nitride semiconductor substrate by growing the nitride semiconductor layer 13 on the seed substrate 10 will be described with reference to FIGS.

  FIG. 3 is a schematic diagram of a crystal growth apparatus for manufacturing a nitride semiconductor substrate according to the present invention. FIG. 4 shows a method for crystallizing a nitride semiconductor layer according to the first embodiment in the method for manufacturing a nitride semiconductor substrate according to the present invention. FIG. 5 is an explanatory view showing a process of growing, and FIG. 5 is a plan view of a mask used for crystal growth of a nitride semiconductor layer in the method for manufacturing a nitride semiconductor substrate according to the present invention.

  In order to grow the nitride semiconductor layer 13 on the seed substrate 10, a crystal growth apparatus 30 is used. The crystal growth apparatus 30 includes a pressure vessel 31 and a nitrogen gas supply source 38 for supplying nitrogen gas into the pressure vessel 31 (see FIG. 3).

  The pressure vessel 31 is connected to a vacuum pump (not shown) that depressurizes the inside of the pressure vessel 31 through a gas exhaust pipe 36. Inside the pressure vessel 31, a crucible 33 that accommodates the seed substrate 10 described above, a reaction vessel 32 that accommodates the crucible 33, and a heater 34 that heats the reaction vessel 32 are provided.

  The diameter of the crucible 33 is large enough to accommodate the seed substrate 10 described above, and the material of the crucible 33 needs to have heat resistance in a high temperature atmosphere during crystal growth. In this embodiment, a high-purity alumina crucible having a diameter of about 80 mm is used.

  The reaction vessel 32 is made of a heat-resistant member such as stainless steel or hastelloy, and a heater 34 is disposed so as to surround the reaction vessel 32. In addition, a gas supply pipe 35 for supplying nitrogen gas from a nitrogen gas supply source 38 is inserted into the reaction container 32, and a pressure regulator 37 for adjusting the pressure in the reaction container 32 is provided in the gas supply pipe 35. Is provided.

  Using this crystal growth apparatus 30, the nitride semiconductor layer 13 is crystal-grown to manufacture the nitride semiconductor substrate 1. That is, the temperature of the seed substrate 10 is increased to an optimum temperature for crystal growth of the nitride semiconductor layer 13, and after the nitride semiconductor layer 13 is grown on the seed crystal 12, the nitride semiconductor layer 13 and the seed substrate 10 are grown. And the nitride semiconductor substrate 1 is manufactured.

  Here, the nitride semiconductor layer 13 to be crystal-grown in the present embodiment is crystal-grown on the seed crystal 12 through each through-hole 21 after disposing a mask 20 having a plurality of through-holes 21 on the seed crystal 12. It is a thing. After the crystal growth, the mask 20 is naturally peeled off from the nitride semiconductor layer 13 together with the seed substrate 10.

  The mask 20 has a plurality of through holes 21 arranged regularly (see FIG. 5). The shape of the through hole 21 is preferably a circular shape so that the nitride semiconductor layer 13 can be easily crystal-grown in the through hole 21, but may be a quadrangular shape, a hexagonal shape, or the like.

  The interval between the through holes 21 is d, and the width of the through holes 21 is W. The distance d is preferably in the range of 0.1 mm to 1.0 mm from the viewpoint of crystallinity of the nitride semiconductor layer and from the viewpoint of peelability between the nitride semiconductor layer 13 and the substrate 11 described later. The width W is preferably in the range of 0.1 mm to 1.0 mm from the viewpoint of ease of crystal growth of the nitride semiconductor layer. As the mask material, a material having high temperature resistance such as sapphire or alumina is used. The mask used in the present embodiment is made of sapphire having a diameter of 60 mm and a thickness of 0.4 mm, the interval d between the through holes 21 is 0.5 mm, and the width w of the through holes 21 is 0.5 mm.

  Hereinafter, a specific manufacturing process will be described step by step with reference to FIG.

  First, in the crucible 33, after containing the raw material such as Ga metal, Ga alloy, and Ga compound, the flux composed of Na, and the seed substrate 10 having the convex warpage of the main surface described above, the main surface of the seed substrate 10 is accommodated. A mask 20 is arranged. Then, the crucible 33 is introduced into the reaction vessel 32, and the reaction vessel 32 is installed in the pressure vessel 31. Furthermore, the inside of the pressure vessel 31 is sealed, the inside of the pressure vessel 31 is replaced with an inert gas, the atmosphere in the pressure vessel 31 is kept constant, and the pressure in the pressure vessel 31 is set to 1 MPa. In addition, by using Na as a flux, crystal growth of a nitride semiconductor layer can be performed under relatively low pressure and low temperature conditions in crystal growth described later. In addition to Na, an alkali metal (for example, Potassium) may be used.

  Next, the temperature of the reaction vessel 32 is raised to the crystal growth temperature (about 800 ° C. to 1000 ° C.) of the nitride semiconductor layer 13 (for example, GaN) by the heater 34. As a result, a solution 39 (see FIG. 3) in which a raw material such as Ga metal and a flux are melted is manufactured, and stress is applied to the seed substrate 10 as the temperature rises, and the warpage of the seed substrate 10 is alleviated. That is, the amount of warping of the seed substrate 10 is reduced.

  After the temperature is raised to the crystal growth temperature of the nitride semiconductor layer 13 by the heater 34, the pressure regulator 37 is adjusted to 3.6 MPa in the pressure vessel 31 and nitrogen gas is supplied from the nitrogen gas supply source 38 into the reaction vessel 32. Supply. As a result, the nitrogen crystal, Ga metal, flux, etc. react with the seed crystal 12 on the main surface of the seed substrate 10, and the nitride semiconductor layer 13 is grown on the seed crystal 12 through the through holes 21 of the mask 20. The At this time, the warpage of the seed substrate 10 is sufficiently reduced. That is, since the shape of the seed substrate 10 immediately before the crystal growth is in a substantially flat state, even if the nitride semiconductor layer 13 is grown on the main surface of the seed substrate 10, the crystal axes are aligned, and the orientation A good nitride semiconductor layer 13 can be grown on the main surface of the seed substrate 10. When the crystal growth time is 120 hours, the thickness of the nitride semiconductor layer 13 is about 1.4 mm.

  After growing the nitride semiconductor layer 13, the heater 34 is turned off, and the temperature in the reaction vessel 32 is lowered to room temperature over 10 hours. The seed substrate 10 and the nitride semiconductor layer 13 are naturally separated from each other by the stress generated when the temperature is lowered applied to the seed substrate 10 and the nitride semiconductor layer 13. At this time, the nitride semiconductor layer 13 is crystal-grown on the seed substrate 10 through the through-hole of the mask, and since the contact area between the seed substrate 10 and the nitride semiconductor layer 13 is small, the seed substrate 10 is reduced by a small stress. And the nitride semiconductor layer 13 can be separated. Therefore, generation of cracks in the nitride semiconductor layer 13 can be prevented.

  Thereafter, the separated nitride semiconductor layer 13 is taken out from the crystal growth apparatus 30, and a nitride semiconductor substrate 1 is manufactured by performing a cleaning step using an organic solvent or an acid as necessary.

Second Embodiment Next, a second embodiment of the method for manufacturing a nitride semiconductor substrate according to the present invention will be described with reference to FIG. 1B. Since this embodiment is different from the first embodiment only in the method of warping the seed substrate in the seed substrate manufacturing process, only the difference will be described below, and the same components are denoted by the same reference numerals and the same components are denoted by the same reference numerals. Description is omitted.

  FIG. 1B is an explanatory diagram showing a seed substrate manufacturing process according to the second embodiment in the method for manufacturing a nitride semiconductor substrate according to the present invention.

[Seed board manufacturing process]
In this embodiment, the substrate 11 is not warped before the crystal growth of the seed crystal 12 described in the first embodiment, but when the seed crystal 12 is grown on the substrate 11, the substrate 11 is warped by a predetermined amount. The seed substrate 10 is warped by growing the seed crystal 12 until Thereby, as the seed crystal 12 is grown on the substrate 11, the thickness of the seed crystal 12 becomes thicker. As a result, the substrate 11 can be warped to a predetermined warpage amount, so that the substrate is newly warped. The seed substrate 10 can be warped by a small number of steps without requiring a step.

  Note that the warpage of the seed substrate 10 may be changed by processing the substrate 11 and changing the thickness of the substrate 11 after the seed substrate 10 is manufactured.

  After that, by performing the crystal growth step described in the first embodiment, it is possible to provide a method for manufacturing a high-quality nitride semiconductor substrate with good crystal axis orientation of the GaN single crystal.

* About Examples 1-3 Next, Examples 1-3 of this embodiment are explained.

  In the present embodiment, in the seed substrate manufacturing process, by changing the film thickness condition of the seed crystal 12 at the time of crystal growth of the seed crystal 12, the seed substrates 10 having different warpage amounts are manufactured, and the various substrates 10 are subjected to the crystal growth process. The orientation distribution of the nitride semiconductor substrate 1 manufactured by applying the above is measured. The orientation distribution was measured by rocking curve measurement of X-ray diffraction measurement.

Example 1
In the seed substrate manufacturing process, when the thickness of the GaN seed crystal 12 was 7.0 μm, the warpage amount of the seed substrate 10 was 70 μm. The orientation distribution of the nitride semiconductor substrate 1 manufactured by subjecting the seed substrate 10 to the crystal growth step was 0.20 °.

Example 2
In the seed substrate manufacturing process, when the thickness of the GaN seed crystal 12 was 8.0 μm, the warpage amount of the seed substrate 10 was 85 μm. The orientation distribution of the nitride semiconductor substrate 1 manufactured by subjecting the seed substrate 10 to the crystal growth process was 0.14 °.

Example 3
In the seed substrate manufacturing process, when the thickness of the GaN seed crystal 12 was 9.0 μm, the warpage amount of the seed substrate 10 was 90 μm. The orientation distribution of the nitride semiconductor substrate 1 manufactured by subjecting this seed substrate to the crystal growth step was 0.16 °.

  All the nitride semiconductor substrates 1 manufactured according to Examples 1 to 3 have an orientation distribution of less than 0.20 °. In general, it can be said that the nitride semiconductor substrates 1 of Examples 1 to 3 have good crystallinity because the crystallinity is good when the orientation distribution is 0.20 ° or less. The results of Examples 1 to 3 are shown in Table 1.

□ Examples 4 to 6 Next, Examples 4 to 6 of the present embodiment will be described.

  In this embodiment, in the seed substrate manufacturing process, after the seed crystal 12 is grown on the substrate 11, the substrate is mechanically polished to change the thickness condition of the substrate 11, thereby manufacturing the seed substrates 10 having different warpage amounts. Then, the orientation distribution of the nitride semiconductor substrate 1 manufactured by subjecting the various substrates 10 to the crystal growth process is measured. As described above, the orientation distribution was measured by half-width measurement by rocking measurement of X-ray diffraction measurement.

Example 4
In the seed substrate manufacturing process, when the thickness of the substrate 11 was set to 0.35 μm by mechanical polishing, the warpage amount of the seed substrate 10 was 73 μm. The orientation distribution of the nitride semiconductor substrate 1 manufactured by subjecting the seed substrate 10 to the crystal growth step was 0.17 °.

Example 5
In the seed substrate manufacturing process, when the thickness of the substrate 11 was set to 0.40 μm by mechanical polishing, the warpage amount of the seed substrate 10 was 82 μm. The orientation distribution of the nitride semiconductor substrate 1 manufactured by subjecting the seed substrate 10 to the crystal growth step was 0.12 °.

Example 6
In the seed substrate manufacturing process, when the thickness of the substrate 11 was 0.43 μm, the warpage amount of the seed substrate 10 was 85 μm. The orientation distribution of the nitride semiconductor substrate 1 manufactured by subjecting the seed substrate 10 to the crystal growth process was 0.14 °.

  All of the nitride semiconductor substrates 1 manufactured according to Examples 4 to 6 have an orientation distribution of less than 0.20 °, and can be said to be nitride semiconductor substrates 1 with good crystallinity. The results of Examples 4 to 6 are shown in Table 2.

Third Embodiment Next, a third embodiment of the method for manufacturing a nitride semiconductor substrate according to the present invention will be described with reference to the drawings. Only differences from the first embodiment and the second embodiment will be described, and the same components will be denoted by the same reference numerals and description thereof will be omitted.

[Seed board manufacturing process]
First, the manufacturing process of the seed substrate 10 will be described with reference to the drawings. 2A is a plan view of a seed substrate according to a third embodiment, and FIG. 2B is a cross-sectional view taken along line II-II in FIG. (C) is sectional drawing which shows the modification of the seed substrate of 3rd embodiment.

  In the seed substrate manufacturing process of the present embodiment, when the seed substrate 10 is manufactured, the amount of warpage corresponding to the amount of warping of the seed substrate 10 due to the temperature rise in the crystal growth step described later is set in advance. It is assumed that the seed substrate 10 is warped in the direction opposite to the direction in which the seed crystal 12 is formed, and the seed crystal 12 is formed with a convex portion 12 a on the main surface of the seed crystal 12.

  The warpage amount of the seed substrate 10 of this embodiment needs to be warped to the warpage amount (70 μm to 110 μm) described in the first embodiment and the second embodiment in order to form the convex portion 12 a on the main surface of the seed substrate 10. However, it is sufficient to warp the seed substrate 10 so that the warping amount is about 0 μm to 40 μm.

  Patterning of the main surface of the seed crystal 12 is performed on the main surface of the seed crystal 12 by growing the seed crystal 12 on the substrate 11 and using a photolithography technique, an etching technique, or the like by a known method. In this embodiment, after a predetermined pattern is formed on the main surface of the seed crystal, the seed crystal 12 is etched to form a plurality of dots (convex portions 12a) (see FIG. 2C).

  Here, the patterning of the main surface of the seed crystal 12 is in the form of regularly arranged dots in order to control the crystal growth of the nitride semiconductor layer 13 in the crystal growth step described later (FIG. 2A )reference). In addition, not only a dot shape but a stripe shape having a convex portion may be used.

  The interval between the convex portions 12a of the dots is d, and the width of the convex portion 12a is W. The distance d is preferably in the range of 0.1 mm to 1.0 mm from the viewpoint of crystallinity of the nitride semiconductor layer 13 and the peelability of the nitride semiconductor layer 13 and the substrate 11 described later. Further, the width W of the convex portion 12a is preferably in the range of 0.1 mm to 1.0 mm from the viewpoint of ease of crystal growth of the nitride semiconductor layer. In the present embodiment, the distance d between the convex portions 12a is 0.5 mm, and the width W of the convex portions 12a is 0.5 mm.

  Further, by performing a surface treatment or the like on the patterning surface of the main surface of the seed crystal 12, the amount of warpage of the seed substrate 10 can be changed.

  As described above, the amount of warpage corresponding to the amount of warping of the seed substrate 10 due to the temperature rise in the crystal growth step described later is warped in the opposite direction to the direction of warping of the seed substrate 10 due to the temperature rise, A plurality of concave and convex shapes can be formed on the main surface of the seed crystal 12.

  The seed crystal 12 is not etched until the seed crystal 12 reaches the substrate 11 as shown in FIG. 2B, but the etching is stopped in the middle of the seed crystal 12 to form an uneven shape. It does not matter (see FIG. 2C). By changing such a concavo-convex shape, the amount of warpage of the seed substrate 10 can be changed.

[Crystal growth process]
Next, a process of manufacturing the nitride semiconductor substrate by growing the nitride semiconductor layer 13 on the seed substrate 10 will be described with reference to FIG.

  FIG. 6 is an explanatory diagram showing a process of crystal growth of the nitride semiconductor layer of the third embodiment in the method for manufacturing a nitride semiconductor substrate according to the present invention.

  The nitride semiconductor substrate of this embodiment is manufactured using the crystal growth apparatus 30 described in the first embodiment.

  First, in the crucible 33, a seed substrate 10 having raw materials such as Ga metal, Ga alloy, and Ga compound, a flux made of Na, and dots (convex portions 12a) on the main surface is accommodated. Then, the crucible 33 is introduced into the reaction vessel 32, and the reaction vessel 32 is installed in the pressure vessel 31. Furthermore, the inside of the pressure vessel 31 is sealed, the inside of the pressure vessel 31 is replaced with an inert gas, the atmosphere in the pressure vessel 31 is kept constant, and the pressure in the pressure vessel 31 is set to 1 MPa.

  Next, the temperature of the reaction vessel 32 is raised by the heater 34 to about 800 ° C. to 1000 ° C. which is the crystal growth temperature. As a result, a solution 39 (see FIG. 3) in which a raw material such as Ga metal and a flux are melted is manufactured, and stress is applied to the seed substrate 10 as the temperature rises, and the warpage of the seed substrate 10 is alleviated. That is, the amount of warping of the seed substrate 10 is reduced.

  After the temperature is raised to the crystal growth temperature of the nitride semiconductor layer 13 (GaN) by the heater 34, the pressure regulator 37 is adjusted to 3.6 MPa in the pressure vessel 31, and from the nitrogen gas supply source 38 to the reaction vessel 32. Supply nitrogen gas. As a result, nitrogen gas, Ga metal, flux, etc. react with the seed crystal 12 on the main surface of the seed substrate 10, and the nitride semiconductor layer 13 is formed on the dots (projections 12 a) of the seed crystal 12 and on the side surfaces of the seed crystal 12. Crystal is grown. Here, since the nitride semiconductor layer 13 is not grown on the substrate 11, the contact area between the seed crystal 12 and the nitride semiconductor layer 13 can be reduced. Further, since the warpage of the seed substrate 10 is sufficiently reduced and the shape of the seed substrate 10 immediately before crystal growth is in a substantially flat state, the nitride semiconductor layer 13 is grown on the main surface of the seed substrate 10. Even if they are used, the crystal axes are aligned. Therefore, the nitride semiconductor layer 13 with good orientation can be grown on the main surface of the seed substrate 10. When the crystal growth time is 120 hours, the thickness of the nitride semiconductor layer 13 (GaN) is 1.4 mm.

  After growing the nitride semiconductor layer 13, the heater 34 is turned off, and the temperature in the reaction vessel 32 is lowered to room temperature over 10 hours. The substrate 11 and the seed crystal 12 are naturally separated by the stress generated when the temperature is lowered applied to the seed substrate 10 and the nitride semiconductor layer 13. At this time, since the contact area between the seed crystal 12 and the nitride semiconductor layer 13 is small, the stress applied to the nitride semiconductor layer 13 can be reduced, and the occurrence of cracks in the nitride semiconductor layer 13 can be prevented. .

  Thereafter, the separated nitride semiconductor layer 13 is taken out from the crystal growth apparatus 30, and a nitride semiconductor substrate 1 is manufactured by performing a cleaning step using an organic solvent or an acid as necessary.

□ Examples 7 and 8 Next, Examples 7 and 8 of the present embodiment will be described.

-Example 7
In this embodiment, in the seed substrate manufacturing process, after the seed crystal 12 is grown on the substrate 11, dots (convex portions 12 a) are formed on the main surface of the seed crystal 12 so that the warpage amount is 10 μm. Manufactured.

  Thereafter, the orientation distribution of the nitride semiconductor substrate 1 manufactured by subjecting the seed substrate 10 to a crystal growth step was 0.14 °.

Example 8
In this embodiment, in the seed substrate manufacturing process, after the seed crystal 12 is grown on the substrate 11, dots (convex portions 12 a) are formed on the main surface of the seed crystal 12, and the warpage amount is 20 μm. Manufactured.

  Thereafter, the orientation distribution of the nitride semiconductor substrate 1 manufactured by subjecting the seed substrate 10 to the crystal growth step was 0.10 °.

  The nitride semiconductor substrates manufactured according to Example 7 and Example 8 both have an orientation distribution of less than 0.20 °, and can be said to be nitride semiconductor substrates with good crystallinity. The results of Example 7 and Example 8 are shown in Table 3.

  As described above, according to the first to third embodiments, the nitride semiconductor substrate manufacturing method according to the present invention is optimal for crystal growth of the nitride semiconductor layer 13 in advance when the seed substrate 10 is manufactured. Since the seed substrate 10 is warped in a direction opposite to the direction in which the seed substrate 10 is warped by the temperature increase, the amount of warpage corresponding to the amount of warping of the seed substrate 10 by raising the temperature to the temperature is kept. Even if the temperature is raised to an optimum temperature for crystal growth of the nitride semiconductor layer 13 after manufacture, the seed substrate 10 can grow the nitride semiconductor layer 13 without being affected by warpage.

  That is, since the seed substrate 10 before the crystal growth of the nitride semiconductor layer 13 is in a substantially flat state, even if the nitride semiconductor layer 13 is grown on the seed substrate 10, the crystal axis of the nitride semiconductor layer 13 is increased. Therefore, a high-quality nitride semiconductor substrate can be manufactured.

The structure and effect of the present invention The method for manufacturing the nitride semiconductor substrate 1 according to the present invention is such that the seed substrate 10 having the seed crystal 12 on the main surface of the substrate 11 is brought to a temperature optimum for crystal growth of the nitride semiconductor layer 13. A method of manufacturing a nitride semiconductor substrate 1 by peeling the nitride semiconductor layer 13 and the seed substrate 10 after raising the temperature and growing the nitride semiconductor layer 13 on the seed crystal 12. When the crystal 12 is manufactured, the seed substrate 10 is warped in advance in a direction opposite to the direction in which the seed substrate 10 warps due to the temperature rise, in advance, the amount of warpage corresponding to the amount that the seed substrate 10 warps due to the temperature rise. And

  According to such a specific matter, when the seed substrate 10 is manufactured, the amount of warpage corresponding to the amount of warping of the seed substrate 10 is increased in advance by raising the temperature to the optimum temperature for crystal growth of the nitride semiconductor layer 13. Since the seed substrate 10 is warped in the direction opposite to the direction in which the seed substrate 10 is warped by the temperature rise, the temperature is raised to the optimum temperature for crystal growth of the nitride semiconductor layer 13 after the seed substrate 10 is manufactured. Stress is applied in the direction in which the warpage of the seed substrate 10 is eased. That is, since the seed substrate 10 immediately before the crystal growth of the nitride semiconductor layer 13 is in a substantially flat state, the crystal axis of the nitride semiconductor layer 13 is obtained even if the nitride semiconductor layer 13 is grown on the seed substrate 10. A good quality nitride semiconductor substrate 1 with good orientation can be manufactured.

  In the nitride semiconductor substrate manufacturing method described above, the seed crystal 12 is obtained by forming the convex portion 12a on the main surface of the seed crystal 12 when the seed substrate 10 is manufactured. .

  Due to such specific matters, when the convex portion 12a is formed on the main surface of the seed crystal 12, and the nitride semiconductor layer 13 is grown on the convex portion 12a, the nitride semiconductor layer 13 and the main surface of the seed crystal 12 are Therefore, the nitride semiconductor layer 13 and the seed substrate 10 can be easily peeled off.

  In the method of manufacturing the nitride semiconductor substrate 1 described above, the nitride semiconductor layer 13 is formed on the seed crystal 12 through the through holes 21 after the mask 20 having the plurality of through holes 21 is disposed on the seed crystal 12. The mask 20 is peeled off from the nitride semiconductor layer 13 together with the seed substrate 10 after the crystal growth.

  Due to such a specific matter, the nitride semiconductor layer 13 is grown through the through hole 21 of the mask 20 by disposing the mask 20 having the through hole 21 on the seed crystal 12. The contact area between nitride semiconductor layer 13 and seed crystal 12 can be further reduced by a simple method that does not require a process. Thereby, the natural separation between the seed crystal 12 and the nitride semiconductor layer 13 can be performed more easily.

  In the method for manufacturing the nitride semiconductor substrate 1 described above, when the seed substrate 10 was manufactured, the seed substrate 10 was obtained by warping the seed substrate to a warp amount by reducing the thickness of the seed substrate. Suppose that it is a thing.

  Due to such specific matters, the substrate 11 can be warped by a simple process before the crystal growth step.

  In the method of manufacturing the nitride semiconductor substrate 1 described above, when the seed substrate 10 is manufactured, the seed substrate 10 is obtained by growing the seed crystal 12 on the main surface of the substrate 11 until the amount of warpage is reached. Suppose that

  Because the substrate 11 is warped simultaneously with the growth of the seed crystal 12 by such specific matters, the seed substrate 10 can be warped by a small number of steps without requiring a new step of warping the substrate 11.

  The above-described embodiments and examples of the present invention are all examples of the present invention, and are not of a nature that limits the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Nitride semiconductor substrate 10 Seed substrate 11 Substrate 12 Seed crystal 12a Protrusion part 13 Nitride semiconductor layer 20 Mask 21 Through-hole 30 Crystal growth apparatus 31 Pressure vessel 32 Reaction vessel 33 Crucible 34 Heater 35 Gas supply piping 36 Gas exhaust piping 37 Pressure Regulator 38 Nitrogen gas source 39 Solution

Claims (5)

After the seed substrate having a seed crystal on the main surface of the substrate is heated to a temperature optimum for crystal growth of the nitride semiconductor layer, and the nitride semiconductor layer is grown on the seed crystal, the nitride semiconductor A method for producing a nitride semiconductor substrate by peeling a layer and the seed substrate,
At the time of manufacturing the seed substrate, the seed substrate is warped in advance in a direction opposite to the direction in which the seed substrate warps due to the temperature rise, in an amount corresponding to the amount of warping of the seed substrate due to the temperature rise. A method for manufacturing a nitride semiconductor substrate. A method for manufacturing a nitride semiconductor substrate according to claim 1,
The method for manufacturing a nitride semiconductor substrate, wherein the seed crystal is obtained by forming a convex portion on a main surface of the seed crystal at the time of manufacturing the seed substrate. A method for manufacturing a nitride semiconductor substrate according to claim 1,
The nitride semiconductor layer is obtained by disposing a mask having a plurality of through holes on the seed crystal and then growing the crystal on the seed crystal through the through holes. A method for producing a nitride semiconductor substrate, comprising: peeling the mask together with the seed substrate from a physical semiconductor layer. A method for manufacturing a nitride semiconductor substrate according to any one of claims 1 to 3,
At the time of manufacturing the seed substrate, the seed substrate is obtained by growing a seed crystal on the main surface of the substrate until the warp amount is reached. . A method for manufacturing a nitride semiconductor substrate according to any one of claims 1 to 3,
At the time of manufacturing the seed substrate, the seed substrate is obtained by warping the seed substrate until the warpage amount is reached by reducing the thickness of the seed substrate. .

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