JP6032087B2 - Method for producing group 13 nitride crystal substrate - Google Patents

Description

  The present invention relates to a method for manufacturing a group 13 nitride crystal substrate, and more particularly to a method for manufacturing a group 13 nitride crystal substrate characterized by a grinding process.

  Group 13 nitride crystals typified by gallium nitride are used in light-emitting devices such as light-emitting diodes and laser diodes, and high-frequency and high-power electronic devices such as high electron mobility transistors (HEMT) and heterojunction bipolar transistors (HBT). It is useful as an applied substance. For this reason, it is required to manufacture a nitride semiconductor substrate having good crystallinity and a flat surface with good reproducibility while minimizing individual differences.

Group 13 nitride crystals can be obtained by vapor phase methods such as metal organic vapor phase epitaxy (MOCVD), molecular beam epitaxy (MBE) or hydride vapor phase epitaxy (HVPE), or liquid phase epitaxy (LPE). The crystal is grown on a substrate by a crystal growth method such as a liquid phase method.
The nitride semiconductor crystal obtained by such a method is subjected to morphological processing such as slicing or grinding to adjust the shape, but the crystal surface is rough in the crystal after morphological processing such as slicing or grinding, and the device structure remains as it is. It cannot be distributed to the market as a nitride semiconductor substrate for production. For this reason, the crystal surface is usually ground and polished.

For polishing the crystal surface, methods such as mechanical polishing and chemical mechanical polishing are known.
For example, Patent Document 1 describes that the surface is smoothed by three stages of rough polishing, precision polishing, and chemical mechanical polishing (CMP). Further, it is said that the surface of the wafer can be reduced to be a mirror surface by using loose abrasive grains as a physical polishing action and gradually reducing the grain size of the abrasive grains.
Patent Document 2 discloses surface grinding using fixed abrasive grains. Grinding with a fixed abrasive grain having an average particle diameter of 2 to 5 μm and a GaN surface Rms of 5 nm to 200 nm. A method is described.

JP 2004-335646 A JP 2005-112641 A JP2011-218545A

However, polishing using loose abrasive grains as described in Patent Document 1 has a very low polishing rate and requires a considerable amount of time to smooth the crystal surface, and shortens the polishing time for production. However, there is a demand for cost reduction.
On the other hand, when using fixed abrasive grains, the grinding rate is higher than when using free abrasive grains, but when the grain size of the abrasive grains is small, there was a problem such as the stone being easily clogged. As described in Patent Document 2, it has been used only when rough grinding is performed mainly using fixed abrasive grains having relatively large grain sizes and finishing to a high surface roughness state. .

Further, in the study by the present inventors, especially when fixed abrasive grains having a small particle diameter are used, if the processing load (stress applied to the crystal) is increased in order to increase the grinding rate, the grindstone itself is damaged. I came to find the problem that the grinding rate would decrease.
The present invention is a group 13 nitride crystal substrate having a good surface with a small surface roughness, which can solve the above-mentioned problems and can efficiently perform grinding using a fixed abrasive having a small particle size. It is an object to provide a manufacturing method.

The inventors of the present invention have made extensive studies to solve the above problems, and found that the above problems can be solved by setting the stress applied to the Group 13 nitride crystal during the grinding process to a specific range, thereby completing the present invention. I let you.
That is, the present invention is as follows.
(1) A method for producing a Group 13 nitride crystal substrate by grinding a Group 13 nitride crystal using a grindstone to which abrasive grains having an average particle size of less than 1.0 μm are fixed. A method for producing a Group 13 nitride crystal substrate, wherein a stress applied to the Group 13 nitride crystal during processing is 0.75 kg / cm ² or less.
(2) The method for producing a Group 13 nitride crystal substrate according to (1), wherein the grindstone is a grindstone in which abrasive grains are embedded with a bonding agent, and the abrasive grains are diamond.
(3) The method for producing a Group 13 nitride crystal substrate according to (2), wherein the bond agent is a vitrified bond.
(4) The Group 13 nitride crystal according to any one of (1) to (3), wherein the Group 13 nitride crystal has a Vickers hardness of 13 GPa or more and a fracture toughness value of 4 or more. A method for manufacturing a substrate.
(5) The method for producing a Group 13 nitride crystal substrate according to any one of (1) to (4), wherein the Group 13 nitride crystal is a gallium nitride crystal.
(6) The Group 13 nitride crystal according to any one of (1) to (5), wherein the ratio represented by the removal volume of the Group 13 nitride crystal / the grinding wheel wear volume is 0.03 or more. A method for manufacturing a substrate.
(7) The production of the Group 13 nitride crystal substrate according to any one of (1) to (6), wherein the grinding step is performed until the surface roughness Rms of the Group 13 nitride crystal is 5 nm or less. Method.

  According to the Group 13 nitride crystal substrate manufacturing method of the present invention, it is possible to efficiently produce a surface having a small surface roughness by grinding using a fixed abrasive having a small particle size. Moreover, it is possible to grind at a high grinding rate without damaging the grindstone itself. Furthermore, according to the manufacturing method of the present invention, it is possible to provide a high-quality group 13 nitride crystal substrate having a small surface roughness and suppressing generation of scratches.

It is a figure which shows the relationship between the stress concerning a crystal | crystallization in Examples 1-3 and the comparative example 1, and a grinding rate. It is a figure which shows the relationship between the stress concerning a crystal | crystallization, and a grinding rate in a reference example.

  The method for producing a Group 13 nitride crystal substrate of the present invention will be described in detail below. The description of the constituent elements may be based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.

In the present invention, the group 13 nitride crystal substrate means a substrate made of a group 13 nitride crystal, and the group 13 nitride crystal is, for example, a Ga _x Al _y In _1-xy N crystal (wherein 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), and specific examples include gallium nitride, aluminum nitride, indium nitride, and mixed crystals thereof. The plane index of the main surface of the group 13 nitride crystal substrate of the present invention is not particularly limited, and may be any of a C-plane that is a polar plane, an A-plane that is a nonpolar plane, an M-plane, or a semipolar plane. In the present specification, the “main surface” means the widest surface among the surfaces existing in the crystal, and is a surface on which normal crystal growth should be performed. Further, in this specification, the “off angle” is an angle representing a deviation of a certain surface from the exponential surface. Further, in this specification, when referring to the C, M, A, or specific index plane, a range having an off angle within 10 ° from each crystal axis measured with an accuracy within ± 0.01 °. Including the inner face. The off angle is preferably within 5 °, more preferably within 3 °.

In the present invention, a crystal having a surface on which an epitaxial layer is formed in order to form a semiconductor element is referred to as a substrate. In general, morphological processing such as slicing, grinding and polishing is performed from an as-grown crystal to obtain a substrate. In the present invention, a substrate in the middle of processing is not called a substrate but called a crystal.
Grinding is generally a process mainly for the purpose of form processing and refers to a process using fixed abrasive grains. A method for performing grinding is not particularly limited, and examples thereof include fixed abrasive grains in which diamond abrasive grains, silicon carbide abrasive grains, and the like are fixed with a binder, and processing is performed using abrasive grains having a relatively large grain size. It is done. According to the manufacturing method of the present invention, the surface roughness Rms can be reduced and the fine surface condition can be adjusted by selecting the size of the abrasive grains in grinding.

On the other hand, polishing is generally a process aimed mainly at reducing distortion caused by surface processing. In the present invention, it mainly refers to chemical mechanical polishing (CMP).
In the present invention, the plate refers to a plate to which a thirteenth crystal group nitride crystal (hereinafter sometimes simply referred to as a crystal) is attached in order to attach the crystal to the apparatus during grinding or polishing. The plate surface to which the crystal is attached is preferably flat in order to obtain a substrate having a uniform thickness after grinding and polishing.

In the method for producing a Group 13 nitride crystal substrate of the present invention, a Group 13 nitride crystal is ground by grinding a Group 13 nitride crystal using a grindstone to which abrasive grains having an average grain size of less than 1.0 μm are fixed. A method of manufacturing a physical crystal substrate, wherein a stress applied to the group 13 nitride crystal during grinding is set to 0.75 kg / cm ² or less.
The grinding process uses a grindstone in which abrasive grains are fixed, a group 13 nitride crystal is fixed to the plate, the crystal surface to be ground is applied to the grinding surface of the grindstone, and if necessary, a polishing solution is poured, The crystal plane is shaved by rotating the plate and the grindstone. As the crystal surface is ground, the distance between the crystal surface and the ground surface increases and grinding does not proceed. Therefore, the plate or the grindstone is brought close to each other so that the crystal surface and the ground surface come into contact with each other. That is, it is necessary to send the group 13 nitride crystal to the grindstone. In this specification, the speed at which the group 13 nitride crystal is moved to approach the grindstone is referred to as “feed speed”, and it is sufficient that the crystal surface and the ground surface are brought into contact with each other. A grindstone may be sent.

  In this way, since the crystal surface and the grinding surface come into contact with each other and grinding proceeds, the group 13 nitride crystal is in a state of being stressed. That is, the stress applied to the Group 13 nitride crystal is a load generated between the contacting crystal and the grindstone, and is the same as the force with which the crystal is pressed against the grindstone. Normally, it is considered that the grinding progresses faster when the force with which the crystal is pressed against the grindstone is large, but the stress is also exerted when the crystal is pushed into the grindstone when the grindstone cannot be cut due to clogging of the grindstone. To rise. The stress applied to the group 13 nitride crystal is calculated by measuring the load applied to the grindstone with a load cell and dividing the value by the area of the crystal plane.

Conventionally, when using fixed abrasive grains, it has been considered that the greater the stress applied to the group 13 nitride crystal, the greater the grinding rate. However, according to the study by the present inventors, when the grain size of the abrasive grains is relatively large, the grinding rate increases with the stress applied to the group 13 nitride crystal, but the average grain diameter of the abrasive grains is 1 In the case of using a grindstone having a diameter of less than 0.0 μm, it has been found that if the stress applied to the group 13 nitride crystal is larger than a specific range, the grinding rate is rather lowered. This is because when a small abrasive grain is fixed and used as a grindstone, the member for holding the abrasive grain is usually made of a soft material so as to prevent clogging and facilitate the self-growth of the grindstone. Therefore, when the stress applied to the Group 13 nitride crystal is large, the member itself for holding the abrasive grains cannot withstand the stress, and the grindstone is damaged, leading to a decrease in the grinding rate. It was thought. Further, when the grindstone is damaged, the dropped abrasive grains and members for holding the abrasive grains are caught during the grinding process, which may cause defects such as scratches on the crystal surface.

Therefore, as a result of intensive studies, it is possible to achieve both improvement of the grinding rate and reduction of damage to the grindstone by setting the stress applied to the group 13 nitride crystal during grinding to 0.75 kg / cm ² or less. became. As a result, the grinding time can be significantly shortened, leading to cost reduction in surface processing, and since there is no damage to the grindstone, it is possible to suppress scratches on the crystal surface caused by it. In particular, when the grain size of the abrasive grains used is small or when the feed rate is large, such an effect becomes more prominent, which is preferable. In order to improve the grinding rate, it is preferred that the stress applied to the Group 13 nitride crystal during grinding and 0.2 kg / cm ² or more, more preferably, to 0.4 kg / cm ² or more, It is preferably 0.7 kg / cm ² or less, and more preferably 0.5 kg / cm ² or less.

  The feed rate is not particularly limited as long as the stress applied to the group 13 nitride crystal during grinding can be adjusted within the above range, but is preferably 5 μm / min or more, more preferably 6 μm because the grinding rate is increased. / Min or more, more preferably 8 μm / min or more, and preferably 20 μm / min or less, and more preferably 15 μm / min or less in order to prevent excessive stress exceeding the strength of the grindstone.

The abrasive grains used in the grinding process are not particularly limited, and examples thereof include diamond, silicon carbide, silica, alumina, and the like. Among them, diamond is preferable. A larger abrasive grain has a higher grinding rate but a higher surface roughness. Therefore, it is preferable to finally grind the surface with a small particle size so that the surface roughness Rms is 5 nm or less, more preferably 3 nm or less, and even more preferably 2.5 nm or less. Specifically, the average particle size of the abrasive grains is less than 1.0 μm, preferably 0.8 μm or less, more preferably 0.7 μm or less, and even more preferably 0.5 μm or less. .
Here, in the present specification, the average grain size of the abrasive grains means an arithmetic average based on the size of the abrasive grain diameter, and the reference abrasive grain diameter is a dynamic light scattering method, a laser diffraction method, a centrifugal sedimentation method, or the like. It is a value measured using FFF method, electrical detection band method, etc.

The grindstone is not particularly limited as long as the abrasive grains are fixed, and examples thereof include a grindstone in which abrasive grains are embedded with a bonding agent such as resin bond, vitrified bond, metal bond, or a grindstone in which abrasive grains are embedded in a metal surface plate. It is done. Among them, a grindstone in which abrasive grains are embedded in a vitrified bond is preferable because of many pores and good chip discharge.
In the grinding process, the rotation speed of the plate and the grindstone is preferably 100 rpm or more, more preferably 200 rpm or more. On the other hand, the upper limit is preferably 500 rpm or less, more preferably 400 rpm or less.

In the grinding process in the production method of the present invention, it is preferable to perform dressing treatment on the grinding wheel during the grinding process in order to prevent the grinding wheel from being clogged and the grinding rate from being lowered. As a timing for performing the dressing process, it is preferable to perform the dressing process when the stress applied to the group 13 nitride crystal is 0.3 to 0.6 kg / cm 2 during the grinding process. To shorten the time required for the overall process, more preferably when carrying out the dressing process as a stress applied to the crystal 0.35 kg / cm ² or more, further it may be 0.4 kg / cm ² or more preferable. In addition, in order to efficiently replace the abrasive grains, 0.55
More preferably, it is kg / cm ² or less, and further preferably 0.5 kg / cm ² .

  When dressing is performed during grinding, grinding can be performed continuously when a single grindstone is used in the grinding process. In other words, it is not necessary to replace the grindstone to carry out the dressing process or to remove the grindstone from the crystal, and the rotation of the plate and grindstone is not stopped during the dressing process, and the grindstone and the crystal are always in contact with each other. Can be ground. On the other hand, when changing the grain size of the abrasive grains, the grindstone may be replaced. The method for performing the dressing process during the grinding process is not particularly limited, and a known grinding apparatus having two or more rotation mechanisms is used to perform grinding with a grindstone on one rotation axis while using the other rotation axis. A method of performing a dressing process, a method of spraying a slurry containing loose abrasive grains smaller than the abrasive grains contained in the grindstone on the grinding surface of the grindstone, and a jet of cleaning liquid at a high pressure on the grinding surface of the grindstone The method of doing is mentioned.

  Among these, it is preferable to perform the dressing process using a known grinding apparatus having a rotation mechanism of two or more axes. For example, an apparatus as described in JP 2011-218545 A cited as Patent Document 3 is used. it can. In such a dressing process, the grinding surface of the grindstone can be dressed by rotating the grindstone and / or the dressing grindstone while bringing the dressing grindstone into contact with the grinding surface of the grindstone.

Although it does not specifically limit as a dressing grindstone, It is preferable to use the dressing grindstone which contains the dressing abrasive grain whose hardness is smaller than the abrasive grain contained in a grindstone, and embedded the abrasive grain with bond agents, such as resin and vitrified bond. Specifically, alumina, silica, silicon carbide, or the like can be used as the dressing abrasive grains, and the average particle diameter is 0.25 μm or more, although the particle diameter depends on the particle diameter of the abrasive grains contained in the grinding wheel for grinding. More preferably, it is 0.5 μm or more, preferably 5 μm or less, and more preferably 3 μm or less. The dressing grindstone is preferably selected as appropriate according to the abrasive grain size of the grinding stone to be ground, and the grain diameter of the dressing grindstone is preferably close to the grain size of the grinding stone to be ground.
As the bonding agent for the dressing grindstone, vitrified bond or phenol resin is preferably used.

In the manufacturing method of the present invention, since the stress applied to the group 13 nitride crystal during the grinding process is controlled within a specific range, it is possible to suppress the wear of the grindstone to the minimum necessary. Specifically, the ratio (grinding ratio) represented by the removal volume of the group 13 nitride crystal / the grinding wheel wear volume is preferably 0.03 or more, more preferably 0.05 or more, and 0 More preferably, it is 1 or more. Here, the removal volume of the Group 13 nitride crystal and the grinding wheel wear volume can be obtained by measuring the respective volumes before and after the grinding step and calculating the difference.
In addition, when performing dressing during grinding, the grinding ratio should be maintained at a higher level because the dressing is performed before clogging occurs and the grinding wheel's processing capacity decreases, thereby promoting self-growth of the grinding wheel. Is preferable.

Although it does not specifically limit as a group 13 nitride crystal | crystallization which grinds, From the standpoint of the effect of the present invention, it is preferable that the Vickers hardness is 13 GPa or more and the fracture toughness value is 4 or more. Such crystals are hard and difficult to grind, and have a relatively high fracture toughness value. Therefore, the chips of the crystals cut by the grinding process tend to agglomerate, and the crystal chips and abrasive grains agglomerate. It is presumed that problems such as clogging of the grindstone and formation of recesses on the crystal surface are likely to occur. If the manufacturing method of the present invention is applied to such a crystal, a high-quality crystal surface can be obtained more easily than before. Among them, when the fracture toughness value is 8 or more, cracks are hardly generated and the grinding process is relatively easy. Therefore, it is preferable to apply to a crystal having a fracture toughness value of less than 8 in terms of achieving the effect of the present invention remarkably. . Moreover, it is preferable because the effect of the present invention is remarkably exerted on a crystal having a cleavage property, which is a crystal in which cracks are likely to occur during grinding.
Further, the surface of the group 13 nitride crystal to be ground is not particularly limited, but is preferably the main surface of the group 13 nitride crystal. The plane orientation of the group 13 nitride crystal to be ground is not particularly limited, but is a polar plane such as C plane or -C plane, a nonpolar plane such as A plane or M plane, (20-21) Or a semipolar surface such as (20-2-1) can be mentioned.

The Group 13 nitride crystal is specifically represented by a Ga _x Al _y In _1-xy N crystal (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), specifically, gallium nitride, Examples thereof include aluminum nitride, indium nitride, and mixed crystals thereof. Among these, it is preferable to apply to gallium nitride having a Vickers hardness of 15 GPa and a fracture toughness value of 5.7.
Generally, a group 13 nitride crystal substrate is obtained by subjecting an as-grown crystal to processing such as slicing, grinding, and polishing. In general, the grinding process of the present invention involves chamfering the side surfaces after slicing the as-grown crystal, and subjecting the back surface or surface to rough surface grinding or etching using a grindstone with a larger abrasive grain size as necessary. This is performed on the thirteenth nitride crystal. These processes should just employ | adopt a well-known method, and a processing method and an order are not limited. Moreover, said process is an example and it does not necessarily have to perform the grinding process of this invention with respect to the crystal which performed all such processes.

In the present invention, it is preferable to further perform a chemical mechanical polishing step on the surface of the nitride semiconductor crystal obtained by grinding. The chemical mechanical polishing step is a step of removing the work-affected layer present on the surface of the nitride semiconductor crystal. By removing the work-affected layer present on the crystal surface by this step, a high-quality nitride semiconductor substrate having no work-affected layer can be provided.
The chemical mechanical polishing step can be performed by employing a known method, and for example, using a colloidal silica slurry and a suede pad is exemplified. A known material may be used for the suede pad, and examples thereof include polyurethane.
The particle size of the abrasive grains (colloidal silica) contained in the colloidal silica slurry is usually 10 nm or more, and preferably 30 nm or more. The upper limit is usually 100 nm or less. The pH of the colloidal silica slurry is preferably 0.8 or more and 2.5 or less.

The polishing speed of chemical mechanical polishing is not particularly limited, and in the case of polishing by rotation, the normal rotation speed is 50 rpm or more and 200 rpm or less. Further, the pressure at the time of disposing the crystal facing the plate is not particularly limited, and is usually 100 g / cm ² or more and 1500 g / cm ² or less. About a polishing rate, what is necessary is just to adjust suitably according to polishing conditions.
The nitride semiconductor substrate after completion of chemical mechanical polishing preferably has a surface roughness Rms of 1 nm or less.
The nitride semiconductor substrate obtained by the production method of the present invention becomes a product through a cleaning process usually performed after polishing.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, it is not limitedly interpreted only to the specific form shown in the following Examples.

<Example 1>
Three gallium nitride crystals having a diameter of 56 mm and a thickness of 470.5 μm and having a C-plane as a main surface were prepared. In order to polish the gallium (Ga) face of the crystal, the nitrogen (N) face of the three crystals was attached to the plate with wax, and this was made into one batch.
The thickness is 468 under processing conditions of a grinding wheel rotational speed of 400 rpm, a plate rotational speed of 400 rpm, a dressing grinding wheel rotational speed of 200 rpm, a stress applied to the crystal of 0.16 kg / cm ² or less, and a plate (crystal) feed rate of 10 μm / min. The Ga surface was ground to a thickness of .9 μm to obtain a gallium nitride substrate. At this time, a grindstone in which diamond abrasive grains having an average grain size of less than 1 μm were fixed with vitrified bond, and a grindstone having a # 42000 grindstone was used. Moreover, as a dressing grindstone, a grindstone in which green silicon carbide abrasive grains having an average grain size of about 3 μm were fixed with phenol and a grindstone count of # 5000 was used.
In addition, when the stress applied to the crystal during grinding is 0.16 kg / cm ² , the clogging of the grindstone is eliminated by carrying out the dressing treatment of the grindstone, and the sharpness is kept constant by keeping the stress applied to the crystal constant. I tried to keep it.

  The grinding rate is 8.35 μm / h, the ratio (grinding ratio) represented by the removal volume / the grinding wheel wear volume is 0.05, and the surface roughness Rms of the Ga surface of the obtained gallium nitride substrate is 1. It was 62 nm. The surface roughness was measured using one Dimension 5000 manufactured by Digital Instruments, with a measurement range of 10 μm square, and one sheet per batch. The results of Examples 1 to 3 and Comparative Example 1 are shown in FIG.

<Example 2>
Example 1 except that the stress applied to the crystal was 0.47 kg / cm ² or less and that the dressing treatment of the grindstone was performed when the stress applied to the crystal during grinding was 0.47 kg / cm ^2. In the same manner as above, grinding was performed to obtain a gallium nitride substrate. The grinding rate is 27.5 μm / h, the ratio (grinding ratio) represented by the removal volume / the grinding wheel wear volume is 0.13, and the surface roughness Rms of the Ga surface of the obtained gallium nitride substrate is 2.3. It was 09 nm.

<Example 3>
Example 1 except that the stress applied to the crystal was 0.60 kg / cm ² or less, and the dressing treatment of the grindstone was performed when the stress applied to the crystal during grinding was 0.60 kg / cm ^2. In the same manner as above, grinding was performed to obtain a gallium nitride substrate. The grinding rate is 20.0 μm / h, the ratio (grinding ratio) represented by the removal volume / the grinding wheel wear volume is 0.10, and the surface roughness Rms of the Ga surface of the obtained gallium nitride substrate is 0.00. It was 80 nm.

<Comparative Example 1>
Example 1 except that the stress applied to the crystal was 0.81 kg / cm ² or less, and the dressing treatment of the grindstone was performed when the stress applied to the crystal during grinding was 0.81 kg / cm ^2. In the same manner as above, grinding was performed to obtain a gallium nitride substrate. The grinding rate is 14.5 μm / h, the ratio (grinding ratio) represented by the removal volume / the grinding wheel wear volume is 0.03, and the surface roughness Rms of the Ga surface of the obtained gallium nitride substrate is 2. It was 43 nm. In addition, the grinding stone itself collapsed during the grinding process, and the abrasive grains and the bonding agent dropped off, resulting in many scratches on the crystal surface.

<Comparative example 2>
Three gallium nitride crystals having a C plane with a diameter of 50 mm and a thickness of 420 μm were prepared. In order to polish the gallium (Ga) face of the crystal, the nitrogen (N) face of the three crystals was attached to the plate with wax, and this was made into one batch.
For the polishing of the Ga surface, first mechanical polishing (first lapping) is performed using a slurry containing diamond loose abrasive grains having an average particle diameter of 3 μm, and then a slurry containing diamond loose abrasive grains having an average grain diameter of 1 μm is used. Second mechanical polishing (second lapping) was performed, and finally, third mechanical polishing (third lapping) was performed using a slurry containing diamond free abrasive grains having an average particle diameter of 1 μm or less to obtain a gallium nitride substrate. The processing rate of the first lapping is 6.89 μm / h, the second
The lapping processing rate was 1.2 μm / h, and the third lapping processing rate was 0.53 μm / h. The thickness of the obtained gallium nitride substrate was 394 μm, and the surface roughness Rms of the Ga surface was 2.51 nm.

<Example 4>
One gallium nitride crystal having a diameter of 50 mm and a thickness of 338 μm and having a main surface with an off angle of 2 ° in the <000-1> (−c axis) direction from the (10-10) plane was prepared. In order to polish the main surface of the crystal, the back surface of the crystal was affixed to the plate with wax to make one batch.
Grinding wheel rotational speed 400 rpm, plate rotational speed 400 rpm, dressing grinding wheel rotational speed 200 rpm, the stress applied to the crystal is 0.45 kg / cm ² or less, and the plate (crystal) feed rate is 10 μm / min, and the thickness is 336 μm. The main surface was subjected to grinding processing until a gallium nitride substrate was obtained. At this time, a grindstone in which diamond abrasive grains having an average grain size of less than 1 μm were fixed with vitrified bond, and a grindstone having a # 42000 grindstone was used. Moreover, as a dressing grindstone, a grindstone in which green silicon carbide abrasive grains having an average grain size of about 3 μm were fixed with phenol and a grindstone count of # 5000 was used.
In addition, when the stress applied to the crystal during the grinding process reaches 0.45 kg / cm ² , the clogging of the grindstone is eliminated by carrying out the dressing treatment of the grindstone, and the sharpness is kept constant by keeping the stress applied to the crystal constant. I tried to keep it.

  The grinding rate was 0.19 μm / h. In addition, the grinding wheel itself did not collapse during the grinding process, and the abrasive grains and the bonding agent did not fall off.

<Example 5>
A gallium nitride crystal having a diameter of 50 mm and a thickness of 343 μm as a crystal and having a major surface with an off angle of 5 ° in the <000-1> (−c axis) direction from the (10-10) plane; A gallium nitride substrate was obtained by grinding in the same manner as in Example 4 except that the main surface was ground until the thickness became 340 μm. The grinding rate was 0.66 μm / h. In addition, the grinding wheel itself did not collapse during the grinding process, and the abrasive grains and the bonding agent did not fall off.

<Example 6>
A gallium nitride crystal having a diameter of 50 mm and a thickness of 340 μm as a crystal and having a main surface having an off angle of 5 ° in the <000-1> (−c axis) direction from the (10-10) plane; The main surface was ground until the thickness was 338 μm, the stress applied to the crystal was 0.23 kg / cm ² or less, and the stress applied to the crystal during grinding was 0.23 kg / cm ^2. At this point, grinding was performed in the same manner as in Example 4 except that the dressing treatment of the grindstone was performed, and a gallium nitride substrate was obtained. The grinding rate was 13.38 μm / h. In addition, the grinding wheel itself did not collapse during the grinding process, and the abrasive grains and the bonding agent did not fall off.

<Example 7>
The crystal used was a gallium nitride crystal having a diameter of 50 mm and a thickness of 338 μm, and the main surface was a (20-2-1) plane, the main surface was ground until the thickness became 336 μm, and the crystal was applied The stress was adjusted to 0.23 kg / cm ² or less, and the grinding stone dressing process was performed when the stress applied to the crystal during the grinding process was 0.23 kg / cm ² , as in Example 4. Grinding was performed to obtain a gallium nitride substrate. The grinding rate was 5.52 μm / h. In addition, the grinding wheel itself did not collapse during the grinding process, and the abrasive grains and the bonding agent did not fall off.

<Reference example>
As a grindstone used for grinding, a grindstone in which diamond abrasive grains having an average grain diameter of 1 to 2 μm are fixed by vitrified bond, a grindstone having a grindstone count of # 10000 is used. As a dressing grindstone, Grinding was performed in the same manner as in Example 1 using a dressing grindstone in which white alumina abrasive grains having an average grain size of about 1.5 μm were fixed with vitrified bond and having a grindstone count of # 10000. It was.
At this time, stress applied to the crystal 0.11 kg / cm ² or less, 0.32 kg / cm ² or less, 0.55 kg / cm ² or less, perform grinding while changing such that the 2.70 kg / cm ² or less A gallium nitride substrate was obtained. The grinding rate in each case was 18.7 μm / h, 51.1 μm / h, 197.0 μm / h, 334.1 μm / h. From this, it was confirmed that when a grindstone having an average grain size of 1 μm or more is used, the grinding rate increases as the stress applied to the crystal increases. The result of the reference example is shown in FIG.

Claims (7)

A method for producing a group 13 nitride crystal substrate by grinding a group 13 nitride crystal using a grindstone having an abrasive having an average particle size of less than 1.0 μm. A method for producing a Group 13 nitride crystal substrate, wherein a stress applied to the Group 13 nitride crystal is 0.75 kg / cm ² or less.   The method for producing a Group 13 nitride crystal substrate according to claim 1, wherein the grindstone is a grindstone in which abrasive grains are embedded with a bonding agent, and the abrasive grains are diamond.   The method for producing a Group 13 nitride crystal substrate according to claim 2, wherein the bond agent is a vitrified bond.   The method for producing a Group 13 nitride crystal substrate according to any one of claims 1 to 3, wherein the Group 13 nitride crystal has a Vickers hardness of 13 GPa or more and a fracture toughness value of 4 or more.   The method for producing a Group 13 nitride crystal substrate according to any one of claims 1 to 4, wherein the Group 13 nitride crystal is a gallium nitride crystal.   The method for producing a Group 13 nitride crystal substrate according to any one of Claims 1 to 5, wherein a ratio expressed by a removal volume of the Group 13 nitride crystal / a grinding wheel wear volume is 0.03 or more.   The method for producing a Group 13 nitride crystal substrate according to any one of claims 1 to 6, wherein the grinding step is performed until the surface roughness Rms of the Group 13 nitride crystal is 5 nm or less.

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