JP2010132473A - Growth method of gallium nitride crystal and production method of gallium nitride crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a growth method of a GaN crystal and a production method of the GaN crystal suppressing growth of a polycrystalline GaN crystal. <P>SOLUTION: The growth method of the GaN crystal includes steps of: preparing a base substrate (step 1); forming a mask layer having an aperture on the base substrate by using a resist (step 2); cleaning the base substrate and the mask layer with an acidic solution (step 3); cleaning the base substrate and the mask layer with an organic solvent (step 4) after the step S3 of cleaning with the acidic solution; and growing the GaN crystal on the base substrate and on the mask layer (step 5). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for growing a gallium nitride crystal and a method for producing a gallium nitride crystal.

  Gallium nitride (GaN) substrates having an energy band gap of 3.4 eV and high thermal conductivity have attracted attention as materials for semiconductor devices such as short-wavelength optical devices and power electronic devices. Such a GaN substrate manufacturing method is disclosed in Japanese Patent Application Laid-Open No. 2004-304203 (Patent Document 1). Patent Document 1 discloses a method for manufacturing a nitride semiconductor substrate by the following method.

14-17 is sectional drawing which shows typically the manufacturing process of the GaN substrate of the said patent document 1. As shown in FIG. As shown in FIG. 14, first, a nitride semiconductor 102 is grown on a heterogeneous substrate 101. Next, a protective film 103 is formed, a resist is further applied, and the protective film 103 made of silicon dioxide (SiO ₂ ) or the like is etched into a predetermined shape by photolithography so as to have a window portion. Next, as shown in FIG. 15, the first nitride semiconductor 104 is grown from the window portion of the protective film 103 with the nitride semiconductor 102 as a nucleus, and the first nitride semiconductor 104 is laterally formed on the protective film 103. When the first nitride semiconductor 104 is grown, the growth of the first nitride semiconductor 104 is stopped before the protective film 103 is completely covered. Next, as shown in FIG. 16, the protective film 103 of the first nitride semiconductor 104 is removed. Next, as shown in FIG. 17, the second nitride semiconductor 105 is grown on the first nitride semiconductor 104 from which the protective film 103 has been removed from the upper surface and side surfaces of the first nitride semiconductor 104. .
JP 2004-304203 A

  FIG. 18 is an enlarged view of a main part of FIG. As shown in FIG. 18, in the above-mentioned Patent Document 1, the present inventor has found that polycrystalline nuclei 111 are generated on the protective film 103. Further, the inventors have found a problem that when the polycrystalline nucleus 111 is generated, the polycrystalline first and second nitride semiconductors 104a and 105a grow on the nucleus 111. .

  Therefore, the present invention provides a GaN crystal growth method and a GaN crystal production method capable of suppressing the growth of a polycrystalline GaN crystal.

  As a result of earnest research, the present inventor has found that the problem that the polycrystalline GaN crystal grows in Patent Document 1 is caused by a reaction product derived from the resist used in forming the protective film 103. It was. In other words, it has been found that if a reaction product derived from a resist remains on the base substrate and the mask layer, the reaction product derived from the resist becomes a polycrystalline nucleus 111. That is, the present inventor has found that in the method of growing a GaN crystal using a mask layer, the formation of the mask layer affects the quality of the grown GaN crystal. Therefore, the present inventor has found the present invention as a result of earnestly studying the conditions for forming a mask layer that suppresses the growth of polycrystalline GaN crystals.

  That is, the GaN crystal growth method according to the present invention includes the following steps. First, a base substrate is prepared. Then, a mask layer having an opening is formed on the base substrate using a resist. Then, the acidic solution is washed on the base substrate and the mask layer. Then, after the step of washing with the acidic solution, the base substrate and the mask layer are washed with an organic solvent. Then, a GaN crystal is grown on the base substrate and the mask layer.

  According to the GaN crystal growth method of the present invention, by washing with an acidic solution, the reaction product remaining on the base substrate and the mask layer is decomposed into a hydrophilic part and a lipophilic part, and The hydrophilic part can be dissolved. As a result, the hydrophilic part of the reaction product can be removed. In the reaction product that could not be removed by the acidic solution, the lipophilic part is compatible with the lipophilic organic solvent. Therefore, the lipophilic part of the reaction product can be removed by washing with the organic solvent. For this reason, since the reaction product remaining on the base substrate and the mask layer can be removed separately in the hydrophilic portion and the lipophilic portion, the reaction product can be removed at the atomic level. Therefore, it is possible to suppress the growth of polycrystalline GaN using this reaction product as a nucleus.

  In the GaN crystal growth method, preferably, in the step of washing with the acidic solution and the step of washing with the organic solvent, ultrasonic waves are applied to the acidic solution and the organic solvent.

  Thereby, since the fine particles adhering to the surface of the base substrate and the mask layer can be removed, the generation of polycrystalline nuclei can be further suppressed.

  In the GaN crystal growth method, the mask layer is preferably made of silicon dioxide. Thereby, it is possible to realize the growth of the GaN crystal that effectively suppresses the generation of polycrystalline nuclei.

  In the GaN crystal growth method, preferably, the following steps are performed between the step of washing with the organic solvent and the step of growing the GaN crystal. A buffer layer made of GaN is formed on the base substrate. And a buffer layer is heat-processed at 800 degreeC or more and 1100 degrees C or less.

  By forming the buffer layer, the lattice constant matching between the base substrate and the GaN crystal can be relaxed. Further, by heat-treating the buffer layer at the above temperature, the buffer layer crystal can be changed from amorphous to single crystal. For this reason, the crystallinity of the GaN crystal can be improved.

  The method for producing a GaN crystal of the present invention includes a step of growing a GaN crystal and a step of removing the base substrate and the mask layer by any of the GaN crystal growth methods described above.

  According to the method for producing a GaN crystal of the present invention, since the GaN crystal growth method is used, the grown GaN crystal is suppressed from being polycrystalline. For this reason, by removing at least the base substrate and the mask layer, a GaN crystal in which polycrystals are suppressed can be manufactured.

  According to the GaN crystal growth method and the GaN crystal production method of the present invention, a polycrystalline GaN crystal is obtained by performing a step of washing the base substrate and the mask layer with an acidic solution and a step of washing with an organic solvent. Growth can be suppressed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
FIG. 1 is a schematic cross-sectional view showing a GaN crystal in the present embodiment. With reference to FIG. 1, the GaN crystal in this Embodiment is demonstrated.

  As shown in FIG. 1, GaN crystal 10 in the present embodiment has a main surface and a back surface opposite to the main surface. The GaN crystal 10 is, for example, a substrate or an ingot.

  In the GaN crystal 10, a region made of polycrystal is suppressed. For example, the region made of polycrystal is 33% or less, and preferably 12% or less. Further, the radius of curvature of the GaN crystal 10 is preferably 35 m or more, and more preferably 50 m or more.

  FIG. 2 is a flowchart showing a method for manufacturing a GaN crystal in the present embodiment. Next, with reference to FIG. 2, a method for manufacturing the GaN crystal 10 in the present embodiment will be described.

FIG. 3 is a cross-sectional view schematically showing the base substrate 11 in the present embodiment. As shown in FIGS. 2 and 3, first, the base substrate 11 is prepared (step S1). The prepared base substrate 11 may be GaN or a material different from GaN. As the heterogeneous substrate made of a material different from GaN, for example, gallium arsenide (GaAs), sapphire (Al ₂ O ₃ ), zinc oxide (ZnO), silicon carbide (SiC), or the like can be used.

FIG. 4 is a cross-sectional view for explaining a method of forming mask layer 13 in the present embodiment. FIG. 5 is a cross-sectional view schematically showing a state in which the mask layer 13 in the present embodiment is formed. Next, as shown in FIGS. 2, 4 and 5, a mask layer 13 having an opening 13a and made of SiO ₂ is formed on the surface of the base substrate 11 (step S2).

Step S2 for forming this mask layer 13 is performed as follows, for example. As shown in FIG. 4, first, an SiO ₂ layer 12 that is a material of the mask layer 13 is formed by, for example, vapor deposition. Next, a resist 15 is formed on the SiO ₂ layer 12 using, for example, a coater. Next, the mask pattern is transferred to the resist 15 using, for example, a stepper. This mask pattern can adopt an arbitrary shape such as a stripe shape or a dot shape. Next, the transferred portion of the resist 15 is dissolved to form a resist 15 having a pattern. Next, using the resist having this pattern as a mask, the SiO ₂ layer 12 not covered with the resist 15 is etched. Thereby, the opening part 13a can be formed. Thereafter, the resist 15 is removed. The removal method is not particularly limited, and for example, ashing can be used. Thereby, as shown in FIG. 5, the mask layer 13 having the opening 13a can be formed.

Although the mask layer 13 of the present embodiment is made of the SiO ₂ layer 12, the material of the mask layer 13 is not limited to SiO ₂ and may be SiN (silicon nitride), for example.

When the mask layer 13 is made of SiO ₂ , the surface roughness Rms of the mask layer 13 is preferably 2 nm or less, more preferably 0.5 nm or less, and even more preferably 0.2 nm or less. In the case of 2 nm or less, the number of remaining atoms on the surface can be reduced. In this case, the generation of polycrystalline nuclei produced by the reaction of at least one of Si atoms and O atoms with at least one of Ga atoms and N atoms supplied in Step S5 for growing a GaN crystal described later. Can be suppressed. In the case of 0.5 nm or less, the generation of polycrystalline nuclei can be further suppressed. In the case of 0.2 nm or less, the generation of polycrystalline nuclei can be further suppressed.

Here, the “surface roughness Rms” is based on JIS B0601 using an atomic force microscope (AFM) in a field of view of 50 μm or less in a mask layer 13 positioned substantially at the center, for example. It is a measured value. Moreover, it is preferable to measure the surface roughness of five or more samples with a pitch of 10 μm or less in a field of view of 50 μm or less in all directions. In this case, in the roughness curve of this sample, the value of the square root of the value obtained by averaging the squares of the deviation from the average line to the measurement curve is defined as the surface roughness Rms. Also, the openings 13a sized to be difficult to measure the surface roughness Rms due pitch, the surface of the SiO ₂ layer 12 roughness Rms when for example the formation of the SiO ₂ layer 12 as a material of the mask layer 13 Can be obtained as the surface roughness Rms of the mask layer 13.

FIG. 6 is a schematic diagram for explaining the radius of curvature of the mask layer 13 in the present embodiment. As shown in FIG. 6, when the mask layer 13 is formed of SiO _2, the radius of curvature R of the mask layer 13 is preferably at least 8m, more preferably at least 50 m. In the case of 8 m or more, since the strain energy of the mask layer 13 can be suppressed, at least one of Si atoms and O atoms of the mask layer 13 and at least Ga atoms and N atoms supplied in Step S5 for growing a GaN crystal described later. It can suppress reacting with one side. As a result, generation of polycrystalline nuclei can be suppressed. In the case of 50 m or more, the generation of polycrystalline nuclei can be further suppressed.

Here, the “curvature radius R” means a radius R when it is assumed that a curve connecting the surfaces of the mask layer 13 grown on the base substrate 11 forms an arc as shown in FIG. Such radius of curvature R, for example a curvature radius of the SiO ₂ layer 12 when forming the SiO ₂ layer 12 as a material of the mask layer 13 as measured, may be a curvature radius of the mask layer 13.

  Next, the base substrate 11 and the mask layer 13 are washed with an acidic solution (step S3). As the acidic solution, for example, sulfuric acid, hydrofluoric acid, hydrochloric acid, or the like can be used.

  In step S2 for forming the mask layer, since the resist 15 is used as described above, a reaction product derived from the resist may remain on the mask layer 13 in some cases. For this reason, the reaction product remaining on the base substrate 11 and the mask layer 13 is washed with an acidic solution, for example, a hydrophilic part having an OH group and a lipophilic part having an alkyl group, for example. It can be decomposed to dissolve the hydrophilic part. Therefore, the hydrophilic part of the reaction product can be removed.

  Next, the base substrate 11 and the mask layer 13 are washed with an organic solvent (step S4). As the organic solvent, for example, acetone, ethanol or the like can be used.

  After step S3 of washing with the acidic solution, a lipophilic part of the reaction product may remain. This lipophilic part is compatible with the organic solvent (easy to mix). For this reason, the lipophilic part of the reaction product remaining on the base substrate 11 and the mask layer 13 can be removed by washing with an organic solvent.

  In step S3 of washing with an acidic solution and step S4 of washing with an organic solvent, the reaction products remaining on the base substrate 11 and the mask layer 13 are separated into a hydrophilic part and a lipophilic part, respectively. Yes. For this reason, the reaction product derived from the resist can be removed at the atomic level.

  In step S3 of washing with an acidic solution and step S4 of washing with an organic solvent, it is preferable to apply ultrasonic waves to the acidic solution and the organic solvent. Specifically, vibration (or rocking) is applied to the acidic solution and the organic solvent as the cleaning liquid using, for example, an ultrasonic device as shown in FIG. FIG. 7 is a schematic cross-sectional view showing the processing apparatus used in step S3 for cleaning with an acidic solution and step S4 for cleaning with an organic solvent in the present embodiment. It is more effective to use ultrasonic waves having a frequency of 900 to 2000 kHz as the ultrasonic waves.

  As shown in FIG. 7, the processing apparatus has a cleaning bath 1 for holding a cleaning liquid 7 that is an acidic solution or an organic solvent, an ultrasonic wave generating member 3 installed on the bottom surface of the cleaning bath 1, and an ultrasonic wave generating member 3. And a control unit 5 for controlling the ultrasonic wave generating member 3. A cleaning liquid 7 is held inside the cleaning bath 1. Further, the cleaning liquid 7 is in a state in which a holder 9 for holding the base substrate 11 on which the plurality of mask layers 13 are formed is immersed. The holder 9 holds a base substrate 11 on which a plurality of mask layers 13 to be cleaned are formed. An ultrasonic wave generating member 3 is disposed on the bottom surface of the washing tub 1.

  When cleaning the base substrate 11 on which the mask layer 13 is formed in the step S3 for cleaning with an acidic solution and the step S4 for cleaning with an organic solvent, a predetermined cleaning liquid 7 is disposed in the cleaning bath 1 as shown in FIG. Then, the base substrate 11 on which the mask layer 13 held by the holder 9 is formed is immersed in the cleaning liquid 7 for each holder 9. In this way, the surfaces of the mask layer 13 and the base substrate 11 can be cleaned with the cleaning liquid 7.

  At this time, an ultrasonic wave may be generated by controlling the ultrasonic wave generating member 3 by the control unit 5. As a result, ultrasonic waves are applied to the cleaning liquid 7. For this reason, since the cleaning liquid 7 vibrates, the effect of removing impurities and fine particles from the mask layer 13 and the base substrate 11 can be enhanced. Further, the cleaning bath 1 may be placed on a swingable member such as an XY stage, and the member may be swung, so that the cleaning bath 1 is swung and the cleaning liquid 7 inside is stirred (swung). . Alternatively, the cleaning liquid 7 may be agitated (oscillated) by shaking the base substrate 11 on which the mask layer 13 is formed together with the holder 9 by manual work or the like. Also in this case, the effect of removing impurities and fine particles from the base substrate 11 and the mask layer 13 can be enhanced in the same manner as the application of ultrasonic waves.

  FIG. 8 is a cross-sectional view schematically showing a state in which the GaN crystal 17 in this embodiment is grown. Next, as shown in FIGS. 2 and 8, a GaN crystal 17 is grown on the base substrate 11 and the mask layer 13 (step S5). The growth method of the GaN crystal 17 is not particularly limited, and gas phase such as sublimation method, HVPE (hydride vapor phase epitaxy) method, MOCVD (metal organic chemical vapor deposition) method, MBE (Molecular Beam Epitaxy) method and the like. A growth method, a liquid phase growth method, or the like can be employed, and it is preferable to employ the HVPE method.

  The GaN crystal 17 can be grown by performing the above steps S1 to S5. When the GaN crystal 10 such as the GaN substrate shown in FIG. 1 is manufactured using the GaN crystal 17, the following steps are further performed.

  Next, the base substrate 11 and the mask layer 13 are removed from the GaN crystal 17 (step S6). The removal method is not particularly limited, and for example, a method such as cutting or grinding can be used.

  Here, the cutting means that the interface between the GaN crystal 17 and the mask layer 13 is mechanically divided (sliced) with a slicer having a peripheral edge of an electrodeposited diamond wheel, a wire saw, etc., and laser pulses and water molecules are separated. It means that the GaN crystal 17 and the mask layer 13 are mechanically divided by irradiating or spraying the interface between the GaN crystal 17 and the mask layer 13 or cleaving along the crystal lattice plane of the mask layer 13. Grinding refers to mechanically removing the base substrate 11 and the mask layer 13 with a grinding facility having a diamond grindstone.

  It should be noted that a chemical method such as etching may be employed as a method of removing the base substrate 11 and the mask layer 13.

  Further, in order to manufacture the GaN crystal 10 made of the GaN crystal 17, at least the base substrate 11 and the mask layer 13 are removed. However, the GaN crystal 17 in the vicinity of the base substrate 11 and the mask layer 13 may be further removed. .

  By performing the above steps S1 to S6, the GaN crystal 10 shown in FIG. 1 can be manufactured.

  The GaN crystal 10 may be further polished from the side where the base substrate 11 is formed. This polishing is an effective method when at least one of the front surface and the back surface of the GaN crystal 10 is used as a mirror surface, and for removing the work-affected layer formed on at least one of the front surface and the back surface of the GaN crystal 10. It is an effective method.

  As described above, the growth method of GaN crystal 17 and the method of manufacturing GaN crystal 10 according to the present embodiment include step S3 for cleaning base substrate 11 and mask layer 13 with an acidic solution, and step S3 for cleaning with acidic solution. After that, step S4 for cleaning the base substrate 11 and the mask layer 13 with an organic solvent is provided.

  Thereby, even if the reaction product derived from the resist remains on the base substrate 11 and the mask layer 13 after step S2 of forming the mask layer 13, the reaction product derived from the resist is made hydrophilic. It can be removed by dividing it into a part and a lipophilic part. For this reason, since the reaction product can be removed at the atomic level, it is possible to further suppress the growth of polycrystalline GaN using this reaction product as a nucleus. Therefore, the GaN crystal 17 with a reduced polycrystalline region can be grown.

  In the growth method of GaN crystal 17 and the manufacturing method of GaN crystal 10 in the present embodiment, the surface roughness Rms of mask layer 13 is preferably 2 nm or less.

  Thereby, since the surface area of the mask layer 13 can be reduced, the number of remaining atoms in the bond existing on the surface of the mask layer 13 can be reduced. For this reason, when the GaN crystal 17 is grown on the mask layer 13 (step S5), it is suppressed that at least one of Ga atom and N atom is bonded to at least one bond of Si atom and O atom. Can do. In addition, the number of atoms having a disordered crystal structure on the surface of the mask layer 13 can be reduced. As a result, the formation of GaN polycrystal nuclei on the mask layer 13 can be suppressed, and the GaN crystal 17 with a further reduced polycrystal region can be grown.

  In the growth method of GaN crystal 17 and the manufacturing method of GaN crystal 10 in the present embodiment, the curvature radius of mask layer 13 is preferably 8 m or more.

  Thereby, since the curvature of the surface of the mask layer 13 can be reduced, the strain energy of the mask layer 13 can be reduced. For this reason, it can suppress that at least one of the Si atom and O atom of the mask layer 13 couple | bonds with at least one of Ga atom and N atom at step S5 which makes the GaN crystal 17 grow. Therefore, the formation of GaN polycrystalline nuclei on the mask layer 13 can be suppressed. Therefore, it is possible to grow the GaN crystal 17 in which the polycrystalline region is further reduced.

(Embodiment 2)
The GaN crystal in the present embodiment is the same as the GaN crystal 10 in the first embodiment shown in FIG.

  FIG. 9 is a flowchart showing a method for manufacturing a GaN crystal in the present embodiment. Next, a method for manufacturing a GaN crystal in the present embodiment will be described. As shown in FIG. 9, the GaN crystal manufacturing method according to the present embodiment basically has the same configuration as the GaN crystal manufacturing method according to the first embodiment, but a buffer layer is further formed. Is different.

  Specifically, first, as shown in FIGS. 3 and 9, the base substrate 11 is prepared in the same manner as in the first embodiment (step S1).

  Next, as shown in FIGS. 5 and 9, a mask layer 13 is formed as in the first embodiment (step S2).

  Next, as shown in FIG. 9, the substrate is washed with an acidic solution (step S3) and washed with an organic solvent (step S4) as in the first embodiment.

  FIG. 10 is a schematic cross-sectional view showing a state in which the buffer layer 19 in the present embodiment is formed. Next, as shown in FIGS. 9 and 10, a buffer layer 19 made of GaN is formed on the base substrate 11 (step S7). By forming the buffer layer 19, it is possible to improve the lattice constant matching between the base substrate 11 and the GaN crystal 17 grown in step S5.

  In the present embodiment, the buffer layer 19 is grown on the base substrate 11 and in the opening 13 a of the mask layer 13. The method for forming the buffer layer 19 is not particularly limited. For example, the buffer layer 19 can be formed by being grown by a method similar to the method for growing the GaN crystal 17.

  Next, the buffer layer 19 is heat-treated at 800 ° C. or higher and 1100 ° C. or lower (step S8). The temperature for the heat treatment is preferably 800 ° C. or higher and 1100 ° C. or lower, and more preferably around 900 ° C. By performing the heat treatment in this temperature range, when the buffer layer 19 is amorphous, it can be changed from amorphous to single crystal. In particular, when the base substrate 11 is a GaAs substrate, it is effective to form a buffer layer 19 and perform heat treatment.

  The step S7 for forming the buffer layer 19 and the step S8 for heat treatment may be omitted. For example, when the base substrate 11 is a sapphire substrate, even if these steps S7 and S8 are omitted, the influence on the GaN crystal 17 to be grown is small. On the other hand, for example, when the base substrate 11 is a GaAs substrate, the crystallinity of the GaN crystal 17 to be grown can be improved by carrying out the steps S7 and S8.

  FIG. 11 is a schematic cross-sectional view showing a grown GaN crystal 17 in the present embodiment. Next, as shown in FIGS. 9 and 11, a GaN crystal 17 is grown (step S5). In the present embodiment, a GaN crystal 17 is grown on the mask layer 13 and the buffer layer 19. The rest is the same as in the first embodiment. The GaN crystal 17 can be grown by the above steps S1 to S5, S7 and S8.

  Next, as shown in FIG. 9, the base substrate 11 and the mask layer 13 are removed (step S6). In the present embodiment, the buffer layer 19 is further removed. The rest is the same as in the first embodiment. Through the above steps S1 to S8, the GaN crystal 10 shown in FIG. 1 can be manufactured.

  Since the other growth methods of GaN crystal 17 and the manufacturing method of GaN crystal 10 are the same as those in the first embodiment, the same members are denoted by the same reference numerals, and description thereof will not be repeated.

  As described above, the growth method of the GaN crystal 17 and the manufacturing method of the GaN crystal 10 according to the present embodiment are performed between the step S4 of washing with an organic solvent and the step S5 of growing the GaN crystal 17 in the buffer layer 19. And step S8 of heat-treating the buffer layer 19 at 800 ° C. or higher and 1100 ° C. or lower.

  Thereby, the lattice constant matching between the base substrate 11 and the growing GaN crystal 17 can be improved. Further, by heat-treating the buffer layer 19 at the above temperature, the crystal of the buffer layer 19 can be changed from amorphous to single crystal. For this reason, the crystallinity of the GaN crystal 17 can be improved. Therefore, it is possible to grow the GaN crystal 17 in which the polycrystalline region is further reduced.

(Embodiment 3)
The GaN crystal in the present embodiment is the same as the GaN crystal 10 in the first embodiment shown in FIG.

  Next, a method for manufacturing a GaN crystal in the present embodiment will be described. The GaN crystal manufacturing method according to the present embodiment basically has the same configuration as the GaN crystal manufacturing method according to the second embodiment, except that the buffer layer is also formed on the mask layer. Different.

  Specifically, as shown in FIG. 9, the base substrate 11 is prepared as in the first and second embodiments (step S1). Next, the mask layer 13 is formed as in the first and second embodiments (step S2). Next, as in the first and second embodiments, the substrate is washed with an acidic solution (step S3) and washed with an organic solvent (step S4).

  FIG. 12 is a schematic cross-sectional view showing a state in which the buffer layer 19 in the present embodiment is formed. Next, as shown in FIGS. 9 and 12, a buffer layer 19 made of GaN is formed on the base substrate 11 (step S7). In the present embodiment, the buffer layer 19 is grown on the opening 13 a of the mask layer 13 on the base substrate 11 and the mask layer 13. That is, the buffer layer 19 is grown so as to cover the entire mask layer 13.

Next, as in the second embodiment, the buffer layer 19 is heat-treated (step S8).
FIG. 13 is a schematic cross-sectional view showing a state in which the GaN crystal 17 is grown in the present embodiment. Next, as shown in FIGS. 9 and 13, a GaN crystal 17 is grown (step S5). In the present embodiment, a GaN crystal 17 is grown on the buffer layer 19. The rest is the same as in the second embodiment. The GaN crystal 17 can be grown by the above steps S1 to S5, S7 and S8.

  Next, as shown in FIG. 9, the base substrate 11 and the mask layer 13 are removed (step S6). In the present embodiment, the buffer layer 19 is further removed as in the second embodiment. Through the above steps S1 to S8, the GaN crystal 10 shown in FIG. 1 can be manufactured.

  Since the other growth methods of GaN crystal 17 and the manufacturing method of GaN crystal 10 are the same as those in the first embodiment, the same members are denoted by the same reference numerals, and description thereof will not be repeated.

  As described above, according to the present embodiment, the buffer layer 19 is formed so as to cover the entire mask layer 13. Therefore, polycrystalline nuclei are unlikely to be generated in the buffer layer 19 on the mask layer 13. Therefore, the GaN crystal 17 formed on the mask layer 13 is suppressed from generating polycrystals. In addition, since the lattice matching with the base substrate 11 can be relaxed by the buffer layer 19, the crystallinity can be improved. Therefore, it is possible to grow the GaN crystal 17 in which the polycrystalline region is further reduced and the crystallinity is further improved.

  In the present Example, the effect by having the process wash | cleaned with an acidic solution and the process wash | cleaned with an organic solvent was investigated.

(Invention Example 1)
In Example 1 of the present invention, the GaN crystal 17 was basically grown according to the first embodiment described above.

  Specifically, first, a base substrate 11 having a diameter of 60 mm and made of sapphire was prepared (step S1).

Next, a mask layer 13 made of SiO ₂ was formed on the base substrate 11 (step S2). Specifically, the SiO ₂ layer 12 was deposited on the base substrate 11 by sputtering under the conditions shown in Table 1 below. Thereafter, a resist 15 was formed on the SiO ₂ layer 12 and patterned by a reactive ion etching (RIE) method to form a mask layer 13 having an opening 13a.

In step S2 for forming the mask layer 13, when the SiO ₂ layer was formed, the surface roughness Rms and the radius of curvature were measured. The surface roughness Rms was measured in a visual field of 10 μm square with respect to a total of five points including the central part of the SiO ₂ layer and four points moved 100 μm vertically and horizontally from the central part. The radius of curvature was measured as shown in FIG. The results are shown in Table 1 below.

  Next, the base substrate 11 and the mask layer 13 were washed with an acidic solution (step S3). An ultrasonic solution was applied at room temperature for 15 minutes using hydrofluoric acid having a concentration of 25% as the acidic solution.

  Next, the base substrate 11 and the mask layer 13 were washed with an organic solvent (step S4). Acetone was used as the organic solvent, and ultrasonic waves were applied at room temperature for 15 minutes.

Next, a GaN crystal 17 was grown on the base substrate 11 and the mask layer 13 by HVPE (step S5). Specifically, the base substrate 11 on which the mask layer 13 was formed was put into a growth furnace. Then, ammonia (NH ₃ ) gas, hydrogen chloride (HCl) gas, and gallium (Ga) are prepared as raw materials for the GaN crystal 17, oxygen gas is prepared as a doping gas, and purity is 99.99 as a carrier gas. More than 999% hydrogen (H ₂ ) was prepared. Then, gallium chloride (GaCl) gas was generated by reacting HCl gas and Ga as Ga + HCl → GaCl + 1 / 2H ₂ . The GaCl gas and the NH ₃ gas are flowed together with a carrier gas and a doping gas so as to hit the base substrate 11 exposed from the opening 13a of the mask layer 13, and on the surface, at 1000 ° C., GaCl + NH ₃ → GaN + HCl + H ₂ To react. In the growth of the GaN crystal 17, the partial pressure of HCl gas was 0.001 atm and the partial pressure of NH ₃ gas was 0.15 atm. Thereby, the GaN crystal 17 of Inventive Example 1 was grown.

(Invention Examples 2 to 5)
In the inventive examples 2 to 5, the GaN crystal 17 was basically grown according to the second embodiment described above.

  Specifically, first, a base substrate 11 having a diameter of 60 mm and made of GaAs was prepared (step S1).

Next, a mask layer 13 made of SiO ₂ was formed on the base substrate 11 (step S2). In this step S2, it was the same as Example 1 of the present invention except that sputtering was performed under the conditions described in Table 1 below.

  Next, similarly to Example 1 of the present invention, the base substrate 11 and the mask layer 13 were washed with an acidic solution (step S3).

  Next, similarly to Example 1 of the present invention, the base substrate 11 and the mask layer 13 were washed with an organic solvent (step S4).

  Next, a buffer layer 19 made of GaN was formed on the base substrate 11 by HVPE (step S7). Specifically, the base substrate 11 on which the mask layer 13 was formed was put into a growth furnace, and the buffer layer 19 was formed under the conditions described in Table 1 below.

  Next, the buffer layer 19 was heat-treated at 900 ° C. in an atmosphere containing hydrogen and ammonia (step S8).

  Next, a GaN crystal 17 was grown on the base substrate 11 and the mask layer 13 by the HVPE method under the growth conditions shown in Table 1 below (step S5).

(Comparative Example 1)
First, a base substrate made of GaAs similar to Examples 2 to 5 of the present invention was prepared (step S1).

Next, sputtering was performed under the conditions described in Table 1 below to form a mask layer made of SiO ₂ on the base substrate.

  Next, similarly to Example 1 of the present invention, the base substrate 11 and the mask layer 13 were washed with an organic solvent (step S4).

  Next, a buffer layer was formed under the conditions described in Table 1 below. Next, this buffer layer was heat-treated under the conditions described in Table 1 below.

  Next, a GaN crystal was grown on the base substrate 11 and the mask layer 13 by the HVPE method under the growth conditions shown in Table 1 below.

(Measuring method)
For the GaN crystals of Invention Examples 1 to 5 and Comparative Example 1, the occupied area of the polycrystal and the curvature radius of the GaN crystal were measured. The occupied area of the polycrystal was measured as follows. Specifically, the entire area of a size of 2 inches was irradiated with a white LED, and a portion having high reflectivity was made into a polycrystal, and the whole was photographed with a CCD camera. And the part with the high reflectance of the image | photographed image was counted by the number of bits, and the ratio of the number of bits with respect to the whole GaN crystal was computed. As for the radius of curvature, the radius R was measured when it was assumed that the curve connecting the surfaces of the GaN crystal 17 would draw an arc as in the method shown in FIG.

(Measurement result)
As shown in Table 1, in the GaN crystals of Invention Examples 1 to 5 in which a GaN crystal was grown by washing with an acidic solution and an organic solvent after forming a mask layer, the region occupied by the polycrystal was 33. % And so on.

  On the other hand, in Comparative Example 1 which was not washed with an acidic solution, the grown GaN crystal had a polycrystal occupying region of 100%. Moreover, since many cracks occurred, the radius of curvature of the GaN crystal could not be measured. This is considered to be because a reaction product derived from a resist by the resist used when forming the mask layer remains on the base substrate and the mask layer, and a polycrystal nucleus is generated.

  As described above, according to this example, it was confirmed that the growth of the polycrystalline GaN crystal was suppressed by including the step of washing with the acidic solution and the step of washing with the organic solvent.

  Although the embodiments and examples of the present invention have been described above, it is also planned from the beginning to appropriately combine the features of the embodiments and examples. The embodiments and examples disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above-described embodiment but by the scope of claims for patent, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims for patent.

It is a schematic sectional drawing which shows the GaN crystal in Embodiment 1 of this invention. It is a flowchart which shows the manufacturing method of the GaN substrate in Embodiment 1 of this invention. It is sectional drawing which shows schematically the base substrate in Embodiment 1 of this invention. It is sectional drawing for demonstrating the method to form the mask layer in Embodiment 1 of this invention. It is sectional drawing which shows schematically the state in which the mask layer in Embodiment 1 of this invention was formed. It is a schematic diagram for demonstrating the curvature radius of the mask layer in Embodiment 1 of this invention. It is a cross-sectional schematic diagram which shows the processing apparatus used in the process wash | cleaned with the acidic solution of Embodiment 1 of this invention, and the process wash | cleaned with an organic solvent. It is sectional drawing which shows schematically the state which grew the GaN crystal in Embodiment 1 of this invention. It is a flowchart which shows the manufacturing method of the GaN crystal in Embodiment 2 of this invention. It is a schematic sectional drawing which shows the state in which the buffer layer in Embodiment 2 of this invention was formed. It is a schematic sectional drawing which shows the state which grew the GaN layer in Embodiment 2 of this invention. It is a schematic sectional drawing which shows the state in which the buffer layer in Embodiment 3 of this invention was formed. It is a schematic sectional drawing which shows the state which grew the GaN layer in Embodiment 3 of this invention. It is sectional drawing which shows typically the manufacturing process of the GaN substrate of the said patent document 1. FIG. It is sectional drawing which shows typically the manufacturing process of the GaN substrate of the said patent document 1. FIG. It is sectional drawing which shows typically the manufacturing process of the GaN substrate of the said patent document 1. FIG. It is sectional drawing which shows typically the manufacturing process of the GaN substrate of the said patent document 1. FIG. It is a principal part enlarged view of FIG.

Explanation of symbols

1 cleaning bath, 3 ultrasonic wave generating member, 5 control unit, 7 washings, 9 holder, 10 GaN crystal, 11 underlying substrate, 12 SiO ₂ layer, 13 a mask layer, 13a opening, 15 resist, 17 GaN crystal, 19 buffer layer.

Claims (5)

Preparing a base substrate;
Using a resist, forming a mask layer having an opening on the base substrate;
Washing the base substrate and the mask layer with an acidic solution;
After the step of washing with the acidic solution, the step of washing the base substrate and the mask layer with an organic solvent;
And a step of growing a gallium nitride crystal on the base substrate and the mask layer.   The method for growing a gallium nitride crystal according to claim 1, wherein in the step of washing with the acidic solution and the step of washing with the organic solvent, ultrasonic waves are applied to the acidic solution and the organic solvent.   The gallium nitride crystal growth method according to claim 1, wherein the mask layer is made of silicon dioxide. Between the step of washing with the organic solvent and the step of growing the gallium nitride crystal,
Forming a buffer layer made of gallium nitride on the base substrate;
The method for growing a gallium nitride crystal according to claim 1, further comprising a step of heat-treating the buffer layer at 800 ° C. or higher and 1100 ° C. or lower. A step of growing a gallium nitride crystal by the method of growing a gallium nitride crystal according to any one of claims 1 to 4,
And a step of removing the base substrate and the mask layer.

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