JP4511801B2 - Group III nitride crystal polishing method, group III nitride crystal and semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a method for polishing a group III nitride crystal and a group III nitride crystal used in a blue-violet light source for optical disks, an ultraviolet light source (LD, LED), a blue-violet light source for electrophotography, a group III nitride electronic device, and the like. And a semiconductor device.
[0002]
[Prior art]
  In recent years, group III nitride semiconductors such as GaN, InGaN, and AlGaN have been applied to light-emitting diodes, semiconductor lasers, electronic devices, and the like. However, since there is no group III nitride bulk crystal of good quality and practical size, a heteroepitaxial device is fabricated on a heterogeneous substrate such as a sapphire substrate or SiC substrate. For this reason, there are problems such as crystal defects, insulation, and difficulty in cleavage, and a high-quality device has not been realized.
[0003]
  Recently, research and development of bulk GaN crystals have progressed by vapor phase growth and melt growth, and GaN crystals of practical size and quality are being realized. However, unlike conventional semiconductor materials such as GaAs, InP, and Si, GaN crystals cannot be easily etched by acid or alkaline solution. Therefore, it is difficult to remove a region having defects or irregularities on the GaN crystal surface (hereinafter referred to as a surface damage layer).
[0004]
  For example, Patent Document 1 proposes that the surface damage layer is removed and recovered by heat treatment at 900 ° C. or higher in a mixed gas atmosphere containing ammonia. However, even with such a heat treatment, it is difficult to remove and recover scratches and large defects previously introduced on the surface of the group III nitride crystal. Usually, the surface of a bulk GaN crystal is flattened and mirror-finished by mechanical polishing, but scratches and defects called scratches are generated during the mechanical polishing. Although it is possible to reduce the scratches and defects by reducing the abrasive grain size of the abrasive during the mechanical polishing, it is difficult to completely remove the scratches and defects.
[0005]
  Other semiconductor materials such as GaAs, InP, and Si can be easily etched with an acid or an alkaline solution, so that the scratches and defects can be removed. In the case of a group III nitride crystal, however, That is difficult.
[0006]
  Even if the technique disclosed in Patent Document 1 described above is used, the scratches and defects cannot be completely removed. For this reason, for example, Patent Document 2 proposes the following. That is, (1) Polish for 10 seconds using a basic aqueous solution of 0.01N or more and a soft pad. (2) Replacing the etching agent with pure water and polishing for at least one minute. (3) Dry in a dry nitrogen gas stream.
[0007]
[Patent Document 1]
  JP 2000-252217 A
[0008]
[Patent Document 2]
  JP-T-2001-518870
[0009]
[Problems to be solved by the invention]
  However, when the inventors of the present application polished a GaN crystal based on the technique disclosed in Patent Document 2, scratches and defects could not be sufficiently removed. That is, when a high-quality bulk GaN crystal is used, it has been found that due to the completeness of the crystal, the polishing as in Patent Document 2 cannot obtain a sufficient polishing rate and polishing quality.
[0010]
  For this reason, group III nitride crystals having a crystal surface of sufficient quality have not been realized at present. As a result, high performance characteristics of group III nitride semiconductor devices have not been realized.
[0011]
  The present invention relates to a group III nitride crystal polishing method, a group III nitride crystal capable of reducing scratches and defects in polishing of a group III nitride crystal, and obtaining a sufficiently practical polishing rate and polishing quality. The object is to provide a semiconductor device.
[0012]
[Means for Solving the Problems]
  In order to achieve the above object, the invention according to claim 1 is directed to a group III metal and nitrogen grown from a mixed melt formed of an alkali metal and a substance containing at least a group III metal and a substance containing at least nitrogen. A group III nitride crystal composed of: a first fine particle dispersed in a solvent and a polishing solution having a pH value greater than 7;Then, after polishing the group III nitride crystal, the step of polishing the group III nitride crystal with a polishing liquid not containing fine particles is performed while applying ultrasonic waves.It is characterized by that.
[0015]
  Claims2The described inventionClaim 1In the method for polishing a group III nitride crystal described in 1), the group III nitride crystal is polished while being heated.
[0016]
  Claims3The described inventionA group III nitride crystal composed of a group III metal and nitrogen grown from a mixed melt formed of an alkali metal and a substance containing at least a group III metal and a substance containing at least nitrogen, Polishing with a polishing liquid in which fine particles are dispersed in a solvent and having a pH value greater than 7,Group III nitriding using second fine particles different from the first fine particles as abrasive grains before polishing the group III nitride crystal using a polishing liquid in which the first fine particles are dispersed in a solvent. It is characterized by performing a polishing process including mechanical polishing of a product crystal.
[0017]
  Claims4The described invention is claimed.3The group III nitride crystal polishing method described above is characterized in that the second fine particles have a hardness higher than that of the group III nitride.
[0018]
  Claims5The invention described in claim 1 to claim 14In the method for polishing a group III nitride crystal according to any one of the above, the first fine particles have a hardness smaller than that of the group III nitride crystal.
[0019]
  Claims6The invention described in claim 1 to claim 15A group III nitride crystal obtained by polishing the group III nitride crystal according to any one of the above.
[0020]
  Claims7The described invention is claimed.6A group III nitride crystal as described is used as a substrate.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0022]
(First embodiment)
  According to a first embodiment of the present invention, in a method for polishing a group III nitride crystal using a polishing liquid in which first fine particles are dispersed in a solvent, a pH value of the polishing liquid is set. It is characterized by being larger than 7.
[0023]
  Here, the fine particles are particles having a particle size of several tens of μm or less. The polishing liquid contains such fine particles dispersed therein, and the polishing liquid is an alkaline solution having a pH value higher than 7. Moreover, as a group III nitride crystal, GaN, AlN, InN, BN, or those mixed crystals are mentioned.
[0024]
  Normally, a group III nitride crystal is not etched with a liquid having a pH value higher than 7 at room temperature. However, in this first embodiment, the first fine particles are usually brought into contact with the group III nitride crystal, so that Even at a temperature at which etching is not performed, the etching reaction is assisted and etching becomes possible. That is, when the first fine particles come into contact with the group III nitride crystal, an etching reaction with an alkaline solution of the group III nitride crystal becomes possible. As a result, high-quality polishing with few scratches and defects is possible even at a high polishing rate. That is, high-quality polishing can be performed in a short time, and the cost can be reduced.
[0025]
(Second Embodiment)
  In the second embodiment of the present invention, the second fine particles different from the first fine particles are used as abrasive grains before the polishing by the group III nitride crystal polishing method of the first embodiment. A polishing step including mechanical polishing of the used group III nitride crystal is performed.
[0026]
  Here, the abrasive grains are particles for sharpening. That is, the second fine particles come into contact with the group III nitride crystal, and polishing proceeds by mechanically scraping the group III nitride crystal.
[0027]
  In this second embodiment, a machine using second fine particles different from the first fine particles of the first embodiment as abrasive grains prior to the III-nitride polishing step according to the first embodiment. By performing a polishing process including mechanical polishing, the second fine particles come into contact with the group III nitride crystal, and the group III nitride crystal is mechanically scraped, so that the polishing progresses. And it becomes possible to remove defects. That is, it is possible to produce a high-quality group III nitride crystal surface at high speed and low cost.
[0028]
  In the second embodiment, the second fine particles are preferably larger in hardness than the group III nitride. That is, when the group III nitride crystal is mechanically polished, the hardness of the fine particles affects the polishing rate, and the higher the fine particle hardness, the faster the polishing can be performed.
[0029]
  As described above, since the hardness of the second fine particles is larger than the group III nitride to be polished, scratches and defects can be removed at a higher speed. That is, it is possible to produce a high-quality group III nitride crystal surface at higher speed and lower cost.
[0030]
(Third embodiment)
  In the third embodiment of the present invention, after the group III nitride crystal polishing method of the first embodiment is polished, the step of polishing the group III nitride crystal with a polishing liquid not containing fine particles is performed. It is characterized by.
[0031]
  In the third embodiment, the fine particles can be removed from the group III nitride crystal and its vicinity by polishing with a polishing liquid that does not contain the fine particles. That is, after the polishing process of the group III nitride according to the first embodiment, the first fine particles used in the polishing process according to the first embodiment and the second fine particles are polished by a polishing liquid that does not contain fine particles. The second fine particles used in the polishing step of the embodiment can be removed, and by removing these fine particles, a high-quality group III nitride crystal surface free from fine particle residues can be produced.
[0032]
  If the fine particle residue remains, it becomes an impurity, which causes a problem in the subsequent group III nitride crystal growth process and device process. In other words, although a high-quality group III nitride crystal cannot be grown or a high-performance semiconductor device cannot be realized, in the third embodiment, a high-quality group III nitride without fine particle residue is obtained. Since a crystal surface of an object can be formed, a high-performance semiconductor device can be realized.
[0033]
  Note that, in the Group III nitride crystal polishing method of the third embodiment, the polishing step with the polishing liquid not containing fine particles can be performed while applying ultrasonic waves. When performing while applying ultrasonic waves, it becomes possible to remove fine particles more effectively. That is, the first fine particles and the second fine particles can be more effectively removed by applying ultrasonic waves during the polishing step using the polishing liquid not containing fine particles. That is, it is possible to more effectively produce a higher-quality group III nitride crystal surface free of fine particle residues. As a result, a higher quality group III nitride crystal surface can be produced at higher speed and lower cost.
[0034]
(Fourth embodiment)
  The fourth embodiment of the present invention is characterized in that, in the group III nitride crystal polishing method of the first embodiment, the group III nitride crystal is polished while controlling the heating.
[0035]
  In the fourth embodiment, the chemical reaction in the polishing can be advanced at a higher speed by polishing while controlling the heating. That is, by polishing while controlling the heating, the etching reaction can proceed at a higher speed. As a result, high-quality polishing with few scratches and defects can be performed at a higher polishing rate. That is, high-quality polishing can be realized at a lower cost.
[0036]
(Fifth embodiment)
  According to a fifth embodiment of the present invention, in the group III nitride crystal polishing method of any one of the first to fourth embodiments described above, the hardness of the first fine particles is higher than the hardness of the group III nitride crystal. It is small.
[0037]
  As described above, when the hardness of the first fine particles is smaller than the hardness of the group III nitride crystal, a higher quality group III nitride crystal surface can be formed. That is, when the hardness of the fine particles is smaller than the hardness of the group III nitride crystal, the damage given to the group III nitride crystal is reduced, and as a result, a higher quality polished surface can be made.
[0038]
  In the group III nitride crystal polishing method of each embodiment described above, the group III nitride crystal to be polished is a mixed melt formed of an alkali metal and a substance containing at least a group III metal, and at least A material composed of a Group III metal and nitrogen grown from a substance containing nitrogen can be used.
[0039]
  Here, the group III metal is Ga, Al, In or the like, and the alkali metal can be K, Na or the like. The substance containing nitrogen is a compound containing nitrogen as a constituent element, such as nitrogen gas, sodium azide, or ammonia.
[0040]
  A group III nitride crystal composed of a group III metal and nitrogen grown from a mixed melt formed of an alkali metal and a substance containing at least a group III metal and a substance containing at least nitrogen has defects. Since it is a low-stoichiometric high-quality crystal, a higher-quality group-III nitride crystal can be obtained by polishing this group-III nitride crystal using the polishing method of the present invention. .
[0041]
(Sixth embodiment)
  The sixth embodiment of the present invention is a group III nitride crystal obtained by polishing with the polishing method of each embodiment described above.
[0042]
  In the sixth embodiment, high-quality group III nitride crystals can be obtained by polishing with the polishing method of the present invention.
[0043]
(Seventh embodiment)
  The seventh embodiment of the present invention is a group III nitride semiconductor device in which the group III nitride crystal of the sixth embodiment is used as a substrate.
[0044]
  Here, the group III nitride semiconductor device is a light emitting device such as a light emitting diode or a semiconductor laser, a light receiving device such as a photodiode, or an electronic device such as a transistor or a diode.
[0045]
  In the seventh embodiment, since the group III nitride crystal of the sixth embodiment is used as a substrate, a high-quality and high-performance semiconductor device can be provided. .
[0046]
  Next, a more specific example of the present invention will be described.
[0047]
  FIG. 1 and FIG. 2 are views showing a first configuration example of a polishing apparatus for realizing a group III nitride crystal polishing method according to the present invention. 1 is a perspective view, and FIG. 2 is a cross-sectional view.
[0048]
  In the polishing apparatus of FIGS. 1 and 2, a polishing board 102 is installed on a turntable 101. The turntable 101 is connected to a motor (not shown) via a rotating shaft 103, and the rotation of the motor is transmitted to the turntable 101 via the rotating shaft 103 so that the turntable 101 and the polishing disc 102 rotate. It has become.
[0049]
  A polishing jig guide 104 is provided on the polishing board 102. A sample holder 105 is provided inside the polishing jig guide 104. The polishing jig guide 104 and the sample holder 105 are separate and move while in contact with each other. Further, a group III nitride crystal 108 to be polished is held below the sample holder 105. The group III nitride crystal 108 is usually attached to the sample holder 105 with wax or the like.
[0050]
  Further, a column 106 and a weight 107 are provided on the upper portion of the sample holder 105. The column 106 and the sample holder 105 are connected to each other, and the weight 107 is installed on the sample holder 105 so as to be fitted into the column 106. In this case, the weight applied to the group III nitride crystal 108 can be adjusted by adjusting the weight of the weight 107.
[0051]
  A polishing liquid tank 109 is provided above the polishing board 102, and a polishing liquid 112 is accommodated inside the polishing liquid tank 109. A liquid supply pipe 110 is connected to the lower side of the polishing liquid tank 109, and a valve 111 is provided in the middle of the liquid supply pipe 110. The polishing liquid 112 is introduced onto the polishing board 102 through the liquid feeding pipe 110. At this time, the amount of the polishing liquid introduced onto the polishing board 102 can be adjusted by the degree of opening and closing of the valve 111. It has become.
[0052]
  The group III nitride crystal can be polished as follows using a polishing apparatus as shown in FIGS.
[0053]
  As a specific example, GaN is used for the group III nitride crystal 108. Further, it is assumed that the weight 107 is used so that the load on the group III nitride crystal 108 is 0.5 MPa. Further, a NaOH (sodium hydroxide) aqueous solution is used as the polishing liquid 112. The polishing liquid 112 has a pH value greater than 7. Further, the polishing liquid 112 contains silica (SiO 2) as fine particles.₂) The particles are dispersed. The size of the silica particles is mainly distributed around a diameter of 50 nm. The polishing board 102 is made of polyurethane.
[0054]
  In this case, first, the valve 111 is opened so that the polishing liquid is sufficiently immersed in the polishing board 102. During polishing, a polishing liquid is appropriately introduced into the polishing board 102 so that the polishing liquid always wets the polishing board 102 and the GaN crystal 108. In this state, the turntable 101 is rotated and the GaN crystal 108 is polished for 5 minutes. The rotation speed at this time is 20 rpm. By appropriately holding the polishing jig guide 104, polishing proceeds using the rotation and revolution of the polishing jig guide 104. As a result, it is possible to obtain a flat GaN crystal surface on the order of nm with few scratches and defects on the crystal surface. In this case, the polishing time can be shortened by one digit or more as compared with the case where there is no silica particle.
[0055]
  In the above example, a GaN crystal is used as the group III nitride crystal, but the group III nitride crystal may be AlN, InN, BN, or a mixed crystal thereof other than GaN. The present invention can also be applied to. In the above example, NaOH is used as the polishing liquid. However, any polishing liquid may be used as long as the pH value of KOH or the like is 7 or more. That is, any alkaline solution may be used.
[0056]
  Silica particles as fine particles have a hardness lower than that of GaN crystals. In addition to silica, fine particles having a smaller hardness than GaN crystals such as MgO, ZnO, and Si can be used. Further, in the above-described example, the polishing board 102 is made of polyurethane, but the polishing board 102 has a hardness and a shape that does not damage the GaN crystal while holding the polishing liquid. Any material can be used.
[0057]
  In the above example, the polishing liquid 112 is dropped by its own weight, but it is also possible to introduce the polishing liquid 112 into the polishing disk surface using a pump or the like.
[0058]
  FIG. 3 is a diagram showing a second configuration example of a polishing apparatus in which the method for polishing a group III nitride crystal according to the present invention is used. The polishing apparatus of FIG. 3 differs from the polishing apparatus of FIG. 2 in that another polishing liquid tank, a polishing liquid, a liquid feed pipe, and a valve are provided. That is, a second polishing liquid tank 209, a second polishing liquid 212, a second liquid supply pipe 210, and a second valve 211 are further provided.
[0059]
  More specifically, in the polishing apparatus of FIG. 3, the second polishing liquid 212 is accommodated in the second polishing liquid tank 209. A second liquid supply pipe 210 is connected to the lower side of the second polishing liquid tank 209, and a second valve 211 is provided in the middle of the second liquid supply pipe 210. . The second polishing liquid 212 is introduced onto the polishing board 102 through the second liquid supply pipe 210. At this time, the amount of the polishing liquid introduced onto the polishing board 102 is set to the second level. The opening / closing degree of the valve 211 can be adjusted.
[0060]
  Here, as the second polishing liquid, for example, pure water can be used, and in the second polishing liquid, for example, alumina (Al₂O₃) Is distributed. Here, the alumina particles are distributed around a diameter of 300 nm.
[0061]
  The group III nitride crystal can be polished as follows using a polishing apparatus as shown in FIG.
[0062]
  As a specific example, a metal one is initially used for the polishing board 102. Then, the second valve 211 is opened so that the second polishing liquid is sufficiently immersed in the metal polishing disk 102. The second polishing liquid is appropriately introduced into the metal polishing disk 102 even during polishing so that the second polishing liquid always wets the polishing disk 102 and the GaN crystal 108. In this state, the turntable 101 is rotated and the GaN crystal 108 is polished for 30 minutes. The rotation speed at this time is 20 rpm. By appropriately holding the polishing jig guide 104, polishing proceeds using the rotation and revolution of the polishing jig guide 104.
[0063]
  After the polishing using the second polishing liquid is completed, the polishing disk 102 is exchanged from a metal one to a polyurethane one. Then, the first valve 111 is opened so that the first polishing liquid is sufficiently immersed in the polyurethane polishing disk 102. During the polishing, the first polishing liquid is appropriately introduced into the polyurethane polishing disk 102 so that the first polishing liquid always wets the polyurethane polishing disk 102 and the GaN crystal 108. In this state, the turntable 101 is rotated and the GaN crystal 108 is polished for 5 minutes. The rotation speed at this time is 20 rpm. By appropriately holding the polishing jig guide 104, polishing proceeds using the rotation and revolution of the polishing jig guide 104.
[0064]
  In the polishing using the above-described second polishing liquid and a metal polishing disk, even a GaN crystal having a large unevenness of several tens of μm can be planarized at high speed. However, since scratches and defects occur on the polished surface, polishing using the first polishing liquid is necessary. As a result of further polishing using the first polishing liquid, it is possible to obtain a GaN crystal surface flat on the order of nm with few scratches and defects on the crystal surface. In the polishing using the first polishing liquid, the polishing time can be shortened by one digit or more as compared with the case where there is no silica particle.
[0065]
  In the above example, alumina particles having a hardness higher than that of the GaN crystal are used as the second fine particles, but the second fine particles have a hardness higher than that of the GaN crystal such as SiC or diamond other than alumina. Things can be used.
[0066]
  FIG. 4 is a diagram showing a third configuration example of a polishing apparatus in which the group III nitride crystal polishing method according to the present invention is used. The polishing apparatus of FIG. 4 is different from the polishing apparatus of FIG. 3 in that another polishing liquid tank, a polishing liquid, a liquid feed pipe, and a valve are provided. That is, a third polishing liquid tank 309, a third polishing liquid 312, a third liquid supply pipe 310, and a third valve 311 are further provided.
[0067]
  More specifically, in the polishing apparatus of FIG. 4, the third polishing liquid 312 is accommodated in the third polishing liquid tank 309. A third liquid supply pipe 310 is connected to the lower side of the third polishing liquid tank 309, and a third valve 311 is provided in the middle of the third liquid supply pipe 310. . The third polishing liquid 312 is introduced onto the polishing board 102 through the third liquid supply pipe 310. At this time, the amount of the polishing liquid introduced onto the polishing board 102 is set to the third level. The valve 311 can be adjusted according to the degree of opening and closing.
[0068]
  Here, as the third polishing liquid, for example, pure water can be used, and the third polishing liquid does not contain fine particles such as the first and second polishing liquids.
[0069]
  The group III nitride crystal can be polished as follows using a polishing apparatus as shown in FIG.
[0070]
  As a specific example, a metal one is initially used for the polishing board 102. Then, the second valve 211 is opened so that the second polishing liquid is sufficiently immersed in the metal polishing disk 102. The second polishing liquid is appropriately introduced into the metal polishing disk 102 even during polishing so that the second polishing liquid always wets the polishing disk 102 and the GaN crystal 108. In this state, the turntable 101 is rotated and the GaN crystal 108 is polished for 30 minutes. The rotation speed at this time is 20 rpm. By appropriately holding the polishing jig guide 104, polishing proceeds using the rotation and revolution of the polishing jig guide 104.
[0071]
  After completion of the polishing using the second polishing liquid, the third valve 311 is opened, and the GaN crystal 108 is polished using the third polishing liquid. At this time, the turntable 101 is rotated so that the second polishing liquid can be removed, and the GaN crystal 108 is polished for 3 minutes. The rotation speed at this time is 20 rpm. The third valve 311 is opened so that the polishing liquid becomes flowing water (pure water that always flows).
[0072]
  Next, the polishing disc 102 is replaced with a polyurethane one from a metal one. Then, the first valve 111 is opened so that the first polishing liquid is sufficiently immersed in the polyurethane polishing disk 102. During the polishing, the first polishing liquid is appropriately introduced into the polyurethane polishing disk 102 so that the first polishing liquid always wets the polyurethane polishing disk 102 and the GaN crystal 108. In this state, the turntable 101 is rotated and the GaN crystal 108 is polished for 5 minutes. The rotation speed at this time is 20 rpm. By appropriately holding the polishing jig guide 104, polishing proceeds using the rotation and revolution of the polishing jig guide 104.
[0073]
  After the polishing using the first polishing liquid is completed, the third valve 311 is opened, and the GaN crystal 108 is polished using the third polishing liquid. At this time, the turntable 101 is rotated so that the first polishing liquid can be removed, and the GaN crystal 108 is polished for 3 minutes. The rotation speed at this time is 20 rpm.
[0074]
  The polishing method using the polishing apparatus in FIG. 4 differs from the polishing method using the polishing apparatus in FIG. 3 in that the polishing process using the third polishing liquid is performed after the polishing process using the second polishing liquid and the polishing process using the first polishing liquid. It is provided. As a result, the polishing liquid used in the polishing process with the second polishing liquid and the polishing process with the first polishing liquid (respectively, the first and second polishing liquids) can be removed, and a good crystal with fewer scratches and defects. A surface can be obtained.
[0075]
  FIG. 5 is a view showing a modification of the polishing apparatus of FIG. The polishing apparatus of FIG. 5 differs from the polishing apparatus of FIG. 4 in that an ultrasonic transducer plate 413 with a heater is inserted between the turntable 101 and the polishing board 102.
[0076]
  The ultrasonic vibrator plate 413 can apply ultrasonic vibration to the polishing board 102 during polishing. Moreover, since it is equipped with a heater, it is also possible to control the heating of the polishing board 102 and to heat it during polishing.
[0077]
  The group III nitride crystal can be polished as follows using the polishing apparatus as shown in FIG.
[0078]
  As a specific example, a metal one is initially used for the polishing board 102. Then, the second valve 211 is opened so that the second polishing liquid is sufficiently immersed in the metal polishing disk 102. The second polishing liquid is appropriately introduced into the metal polishing disk 102 even during polishing so that the second polishing liquid always wets the polishing disk 102 and the GaN crystal 108. In this state, the turntable 101 is rotated and the GaN crystal 108 is polished for 30 minutes. The rotation speed at this time is 20 rpm. By appropriately holding the polishing jig guide 104, polishing proceeds using the rotation and revolution of the polishing jig guide 104.
[0079]
  After completion of the polishing using the second polishing liquid, the third valve 311 is opened, and the GaN crystal 108 is polished using the third polishing liquid. At this time, the turntable 101 is rotated while applying ultrasonic vibration so that the second polishing liquid can be removed, and the GaN crystal 108 is polished for 3 minutes. The rotation speed at this time is 20 rpm. The third valve 311 is opened so that the polishing liquid becomes flowing water (pure water that always flows).
[0080]
  Next, the polishing disc 102 is replaced with a polyurethane one from a metal one. Then, the first valve 111 is opened so that the first polishing liquid is sufficiently immersed in the polyurethane polishing disk 102. During the polishing, the first polishing liquid is appropriately introduced into the polyurethane polishing disk 102 so that the first polishing liquid always wets the polyurethane polishing disk 102 and the GaN crystal 108. In this state, the turntable 101 is rotated and the GaN crystal 108 is polished for 5 minutes. The rotation speed at this time is 20 rpm. By appropriately holding the polishing jig guide 104, polishing proceeds using the rotation and revolution of the polishing jig guide 104.
[0081]
  After the polishing using the first polishing liquid is completed, the third valve 311 is opened, and the GaN crystal 108 is polished using the third polishing liquid. At this time, the turntable 101 is rotated while applying ultrasonic vibration so that the first polishing liquid can be removed, and the GaN crystal 108 is polished for 3 minutes. The rotation speed at this time is 20 rpm.
[0082]
  In the polishing apparatus provided with such an ultrasonic transducer plate 413, it is possible to increase the cleaning efficiency of the polishing liquid containing fine particles by applying ultrasonic vibration. Further, the cleaning efficiency can be further increased by heating.
[0083]
  As a result, a higher quality crystal surface can be realized at low cost.
[0084]
  In the above polishing example, ultrasonic vibration is applied only when the GaN crystal 108 is polished using the third polishing liquid. However, when polishing is performed using the first and second polishing liquids. However, ultrasonic vibration can be applied, and in this case, the polishing rate can be increased in the step of polishing using the first and second polishing liquids. Further, the polishing rate can be increased by heating.
[0085]
  FIG. 6 is a diagram showing a configuration example of a semiconductor device manufactured using the group III nitride crystal of the present invention. Note that the semiconductor device of FIG. 6 is configured as a semiconductor laser. 6 includes an n-type AlGaN cladding layer 602, an n-type AlGaN cladding layer 602, an n-type GaN substrate 601 using a group III nitride crystal (for example, GaN) polished by the group III nitride crystal polishing method of the present invention. A type GaN guide layer 603, an InGaN MQW (multiple quantum well) active layer 604, a p-type GaN guide layer 605, a p-type AlGaN cladding layer 606, and a p-type GaN contact layer 607 are sequentially grown by crystal growth.
[0086]
  As this crystal growth method, a thin film crystal growth method such as MO-VPE (metal organic chemical vapor deposition) method or MBE (molecular beam epitaxy) method can be used.
[0087]
  A ridge structure is formed in such a laminated film of GaN, AlGaN, and InGaN, and SiO₂The insulating film 608 is formed in a state where it is perforated only at the contact layer 607, and a p-side ohmic electrode (Au / Ni) 609 and an n-side ohmic electrode (Al / Ti) 610 are formed on the upper and lower portions, respectively. Yes.
[0088]
  In this semiconductor laser, laser current is emitted by injecting current from the p-side ohmic electrode 609 and the n-side ohmic electrode 610, and laser light is emitted in the direction of the arrow in FIG.
[0089]
  Since this semiconductor laser uses the group III nitride crystal (GaN crystal) of the present invention as a substrate, it has few crystal defects in the semiconductor laser device, has a large output operation and a long life. Further, since the GaN substrate is n-type, an electrode can be directly formed on the substrate, and the cost can be reduced. Further, the light emitting end face can be formed by cleaving, and in combination with chip separation, a low-cost and high-quality device can be realized.
[0090]
  In the above example, InGaN MQW is used as the active layer 604, but it is also possible to reduce the emission wavelength by using AlGaN MQW as the active layer 604. That is, in the present invention, since the GaN substrate has few defects and impurities, light emission from a deep order is reduced, and a highly efficient light-emitting device is possible even when the wavelength is shortened.
[0091]
  In the above example, the case where the present invention is applied to an optical device has been described. However, the present invention can also be applied to an electronic device. In other words, by using a GaN substrate with few defects, the GaN-based thin film epitaxially grown on the GaN substrate has few crystal defects. As a result, leakage current can be suppressed, the carrier confinement effect in the case of a quantum structure can be increased, A high-performance device can be realized.
[0092]
【The invention's effect】
  As described above, according to the invention of claim 1,A group III nitride crystal composed of a group III metal and nitrogen grown from a mixed melt formed of an alkali metal and a substance containing at least a group III metal and a substance containing at least nitrogen, Since fine particles are dispersed in a solvent and polished with a polishing liquid having a pH value greater than 7, higher-quality group III nitride crystals can be obtained.
[0093]
  Claims1According to the invention described above, the step of polishing the group III nitride crystal with the polishing liquid containing no fine particles is performed after the polishing by the method for polishing a group III nitride crystal according to claim 1.1The high quality crystal surface obtained by the above can be cleaned.
[0094]
  Claims1According to the described invention, the claims1In the Group III nitride crystal polishing method described above, the polishing step with the polishing liquid not containing fine particles is performed while applying ultrasonic waves.MoreThe crystal surface can be efficiently cleaned.
[0095]
  Claims2According to the described invention,Claim 1In the method for polishing a group III nitride crystal described in 1), since the group III nitride crystal is polished while being controlled by heating, the polishing rate can be further increased as compared with the first aspect.
[0096]
  Claims3According to the described invention,A group III nitride crystal composed of a group III metal and nitrogen grown from a mixed melt formed of an alkali metal and a substance containing at least a group III metal and a substance containing at least nitrogen, Polishing with a polishing liquid in which fine particles are dispersed in a solvent and having a pH value greater than 7,Group III nitriding using second fine particles different from the first fine particles as abrasive grains before polishing the group III nitride crystal using a polishing liquid in which the first fine particles are dispersed in a solvent. Since the polishing step including mechanical polishing of the product crystal is performed, the polishing rate can be further increased.
[0097]
  Claims4According to the described invention, the claims3In the Group III nitride crystal polishing method described above, since the second fine particles have a hardness higher than that of the Group III nitride, the polishing rate can be further increased.
[0098]
  Claims5According to the described invention, claims 1 to4In the method for polishing a group III nitride crystal according to any one of the above, since the first fine particles have a hardness lower than that of the group III nitride crystal, a higher quality crystal polished surface can be obtained. Can do.
[0099]
  Claims6According to the described invention, claims 1 to5Since the Group III nitride crystal is obtained by polishing with the Group III nitride crystal polishing method according to any one of the above, a high-quality and low-cost Group III nitride crystal is obtained. be able to.
[0100]
  Claims7According to the described invention, the claims6Since the described group III nitride crystal is a semiconductor device characterized by being used as a substrate, a high-quality and high-performance semiconductor device can be obtained.
[0101]
  The high performance here means, for example, a semiconductor laser or a light emitting diode, which has a high output and a long life that has not been realized in the past, and in the case of an electronic device, low power consumption, low noise, It can operate at high speed and high temperature, and the light receiving device has low noise and long life.
[Brief description of the drawings]
FIG. 1 is a diagram showing a first configuration example of a polishing apparatus in which a method for polishing a group III nitride crystal according to the present invention is used.
FIG. 2 is a diagram showing a first configuration example of a polishing apparatus in which the method for polishing a group III nitride crystal according to the present invention is used.
FIG. 3 is a diagram showing a second configuration example of a polishing apparatus in which the method for polishing a group III nitride crystal according to the present invention is used.
FIG. 4 is a diagram showing a third configuration example of a polishing apparatus in which the method for polishing a group III nitride crystal according to the present invention is used.
5 is a view showing a modification of the polishing apparatus of FIG.
FIG. 6 is a diagram showing a configuration example of a semiconductor optical device according to the present invention.
[Explanation of symbols]
101 turntable
102 Polishing machine
103 axis of rotation
104 Abrasive jig guide
105 Sample holder
106 prop
107 weight
108 Group III nitride (GaN) crystals
109 First polishing liquid tank
209 Second polishing liquid tank
309 Third polishing liquid tank
110 First liquid feeding pipe
210 Second liquid feeding pipe
310 Third liquid feeding pipe
111 First valve
211 Second valve
311 Third valve
112 First polishing liquid
212 Second polishing liquid
312 Third polishing liquid
413 Ultrasonic diaphragm with heater
601 n-type GaN substrate
602 n-type AlGaN cladding layer
603 n-type GaN guide layer
604 InGaN MQW active layer
605 p-type GaN guide layer
606 p-type AlGaN cladding layer
607 p-type GaN contact layer
608 SiO₂Insulation film
609 p-side ohmic electrode
610 n-side ohmic electrode

Claims (7)

A group III nitride crystal composed of a group III metal and nitrogen grown from a mixed melt formed of an alkali metal and a substance containing at least a group III metal and a substance containing at least nitrogen, microparticles were polished with large polishing solution than and pH values are dispersed in a solvent is 7, after polishing the III-nitride crystal, a step of polishing the III-nitride crystal by polishing solution containing no fine particles, A method for polishing a group III nitride crystal, which is performed while applying ultrasonic waves . 2. The method for polishing a group III nitride crystal according to claim 1 , wherein the group III nitride crystal is polished while being heated and controlled. A group III nitride crystal composed of a group III metal and nitrogen grown from a mixed melt formed of an alkali metal and a substance containing at least a group III metal and a substance containing at least nitrogen, Before polishing the group III nitride crystal using the polishing liquid in which the fine particles are dispersed in a solvent and having a pH value greater than 7, and the first fine particles are dispersed in the solvent. A method for polishing a group III nitride crystal, comprising performing a polishing step including mechanical polishing of a group III nitride crystal using second particles different from the first particles as abrasive grains. 4. The group III nitride crystal polishing method according to claim 3 , wherein the second fine particles have a hardness higher than that of the group III nitride. In the polishing method of a group III nitride crystal according to any one of claims 1 to 4, wherein the first fine particle is characterized by a hardness less than the hardness of the Group III nitride crystal III A method for polishing a group nitride crystal. A group III nitride crystal obtained by polishing the group III nitride crystal according to any one of claims 1 to 5 . A group III nitride crystal according to claim 6 is used as a substrate.

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