JP5518566B2 - Manufacturing method of nitride semiconductor free-standing substrate - Google Patents

Description

  The present invention relates to a method for manufacturing a group III nitride semiconductor free-standing substrate such as gallium nitride and a nitride semiconductor free-standing substrate.

  Group III nitride compound semiconductors (gallium nitride (GaN), indium gallium nitride (InGaN), gallium aluminum nitride (GaAlN), etc., hereinafter also simply referred to as nitride semiconductors) are blue, ultraviolet light emitting diodes (LEDs) and laser diodes. It has begun to play an important role as a material for (LD). In addition to optical elements, nitride semiconductors are excellent as a substrate material for electronic devices that take advantage of these features because they have good heat resistance and environmental resistance, or good high frequency characteristics.

However, nitride semiconductors are difficult to grow in bulk crystals, and gallium nitride free-standing substrates are only used in limited applications such as laser diodes where cost is not an issue. A gallium nitride growth substrate that is currently in wide use is a sapphire (Al ₂ O ₃ ) substrate, and there is a method of epitaxially growing gallium nitride on a single crystal sapphire substrate by metal organic vapor phase epitaxy (MOVPE method) or the like. Commonly used.

  On the other hand, thick gallium nitride is grown on a dissimilar substrate such as sapphire by an HVPE method (hydride vapor phase epitaxy), which has a high growth rate, and the interface between the substrate and the epitaxial layer using laser light. A method of obtaining a self-supporting substrate by dissolving and peeling (see Non-Patent Document 1), and further growing for a long time to produce a crystal mass called a boule or ingot, and slicing it A method for obtaining a self-supporting substrate is also being put into practical use (see Patent Documents 1 and 2).

  In addition, since the HVPE method allows epitaxial growth of gallium nitride at a relatively high speed, it is formed by epitaxial growth of an ultra-thick film of about 1 cm to 10 cm or more on a gallium nitride free-standing substrate by utilizing its characteristics. Attempts have been made to slice a single crystal ingot to obtain a large number of substrates (sliced substrates) and to polish a sliced surface of the sliced substrate to obtain a large number of gallium nitride free-standing substrates (Patent Document 1, 2). However, with this method, it has been difficult to stably obtain a gallium nitride free-standing substrate with high crystal quality.

  In addition, a relatively thick epitaxial growth substrate is fabricated by the HVPE method using a nitride semiconductor free-standing substrate as an epitaxial growth substrate, and the epitaxial growth substrate is sliced into two to produce a free-standing substrate with excellent crystal quality at low cost. A technique has been proposed (see Patent Document 3).

Japanese Patent Laid-Open No. 2000-12900 JP 2000-22212 A JP 2008-156189 A

Jpn. J. et al. Appl. Phys. Vol. 38 (1999) pt. 2, no. 3A, L217-219

  The method for manufacturing a nitride semiconductor free-standing substrate according to Patent Document 3 is excellent in productivity, but has the following problems. In this method, an epitaxial layer of a nitride semiconductor is formed in a shape raised on the outer periphery of the substrate during epitaxial growth, or a main surface (hereinafter referred to as a front main surface) that performs epitaxial growth out of the main surface of a seed substrate (seed crystal substrate). In particular, the outer peripheral portion of the main surface opposite to the main surface (hereinafter sometimes referred to as the back main surface, which is also simply referred to as the back surface in the sense of the side opposite to the surface on which epitaxial growth is performed). In some cases, a nitride semiconductor may grow. In particular, when a nitride semiconductor grows on the back main surface side, it becomes impossible to secure a reference surface for bonding to a slicing jig or a polishing plate at the time of two-division slicing or subsequent grinding and polishing processes, and chamfering of an epitaxial growth substrate And the controllability of the slices is worsened. Thus, when the slice surface has a gradient with respect to the target surface, a portion where the slice thickness is reduced is generated. As a result, extra grinding and polishing are required to remove the taper during wafer processing. For this reason, a nitride semiconductor epitaxial layer thicker than necessary must be formed during epitaxial growth.

  The present invention has been made in view of such problems, and suppresses the growth of nitride semiconductor on the back main surface and side surface of the seed substrate during the epitaxial growth of the nitride semiconductor, and provides a reference surface for slicing. An object of the present invention is to provide a method for manufacturing a nitride semiconductor free-standing substrate that can be secured.

The present invention has been made in order to solve the above-described problems. A nitride semiconductor of the same type as the seed substrate is epitaxially grown on the main surface of the nitride semiconductor free-standing substrate to be a seed substrate, and the epitaxial growth is performed. A method of manufacturing a nitride semiconductor free-standing substrate by slicing an epitaxial growth substrate, comprising at least a step of preparing a nitride semiconductor free-standing substrate to be the seed substrate, and at least one of the back main surface and side surfaces of the seed substrate. A step of forming a film made of SiO ₂ or Si ₃ N ₄ on the surface, a step of epitaxially growing a nitride semiconductor of the same type as the seed substrate on the front main surface of the seed substrate, and an epitaxial growth substrate on which the epitaxial growth has been performed Removing the deposit deposited on the coating film and the coating film; and A nitride semiconductor free-standing substrate, comprising: a step of slicing in parallel and dividing the main surface from which the main surface is removed into two as a reference plane, and manufacturing two nitride semiconductor free-standing substrates from one seed substrate A manufacturing method is provided.

A nitride semiconductor free-standing substrate, which is a seed substrate, is a method for manufacturing a nitride semiconductor free-standing substrate including the above steps and manufacturing two nitride semiconductor free-standing substrates from one seed substrate. Since the entire back main surface and at least a part of the side surface of the substrate are covered with SiO ₂ (silicon oxide) or Si ₃ N ₄ (silicon nitride), the growth of the nitride semiconductor on the back main surface and the side surface of the seed substrate during epitaxial growth can be achieved. Moreover, even if a small amount of deposition occurs, it is removed together with the coating, so that a reference plane parallel to the original back main surface of the seed substrate can be secured. As a result, when the epitaxial growth substrate after epitaxial growth is sliced in two, the thickness and parallelism can be controlled with reference to the reference plane, and the nitride semiconductor free-standing substrate having a desired shape can be sliced. can do. For this reason, it is possible to reduce the machining allowance for subsequent grinding and polishing, the thickness of the epitaxial growth can be reduced correspondingly, and high productivity can be realized.

  In this case, in the method for manufacturing a nitride semiconductor free-standing substrate according to the present invention, the main surface from which the film is removed after the deposit deposited on the film of the epitaxial growth substrate and the film are removed and before the slicing step. It is preferable to further include a step of forming a guide groove that guides a tool for chamfering and slicing the peripheral portion of the epitaxial growth substrate with reference to the reference plane.

  In the method for manufacturing a nitride semiconductor free-standing substrate according to the present invention, the main surface from which the coating is removed can be secured as a reference plane parallel to the original back main surface of the seed substrate. If the chamfering and the guide groove are formed as a surface, the chamfering and the guide groove can be formed with higher accuracy. In addition, since chamfering and guide groove formation can be accurately performed in this way, even a slice using a thin inner peripheral blade or thin wire can be sliced more uniformly, and the shape of the wafer after slicing is stable. Quality can be. Therefore, the machining allowance for subsequent grinding and polishing can be further reduced, the thickness of the epitaxial growth can be further reduced, and higher productivity can be realized.

  Furthermore, in this case, it is preferable that the depth and shape of the guide groove that guides the tool for slicing be matched with the chamfered shape of each substrate after slicing into the two divisions.

  Thus, if the depth and shape of the guide groove for guiding the tool for slicing are matched to the chamfered shape of each substrate after slicing in two, the nitride semiconductor free-standing substrate after slicing It becomes possible to play the role of wafer chamfering during wafer processing, processing distortion of the chamfered portion is suppressed, and a nitride semiconductor free-standing substrate having excellent mechanical strength can be manufactured.

  In the method for manufacturing a nitride semiconductor free-standing substrate according to the present invention, it is preferable to perform epitaxial growth with a thickness of 600 μm or more and 800 μm or less by the HVPE method in the epitaxial growth.

  As described above, if the epitaxial growth is performed by the HVPE method (hydride vapor phase growth method), the epitaxial growth can be performed at a high speed. Therefore, a nitride semiconductor free-standing substrate can be manufactured with high productivity. Further, if the thickness of the epitaxial layer grown by epitaxial growth is 600 μm or more, it is sufficient to slice the epitaxial growth substrate into two pieces to form two nitride semiconductors, and grow with high productivity by the HVPE method. be able to. If the thickness of the epitaxial layer grown by epitaxial growth is 800 μm or less, the epitaxial growth surface during epitaxial growth can be easily managed, and the crystal quality of the epitaxial layer can be maintained high.

  Moreover, it is preferable that the nitride semiconductor free-standing substrate to be the seed substrate and the nitride semiconductor free-standing substrate to be manufactured are gallium nitride free-standing substrates.

  Thus, if the nitride semiconductor free-standing substrate to be a seed substrate and the nitride semiconductor free-standing substrate to be manufactured are gallium nitride free-standing substrates, a high-quality gallium nitride free-standing substrate can be manufactured at low cost, Can be used for device applications.

  Moreover, it is preferable to grind and grind both main surfaces about the board | substrate which is not a board | substrate which has the said reference surface among the board | substrates after slicing in the said 2 division.

  Of the substrates that have been sliced in two, the substrate that is not the substrate having the reference surface, that is, the substrate that has the epitaxial growth surface has a larger thickness variation than the substrate that has the reference surface. It is preferable to adjust the thickness by grinding and polishing the surface.

The present invention is also a nitride semiconductor free-standing substrate, characterized in that it has a film made of SiO ₂ or Si ₃ N _{4 on} one of the main surfaces and at least a part of the side surface. Provide a self-supporting substrate.

If the nitride semiconductor self-supporting substrate has a film made of SiO ₂ or Si ₃ N _{4 on one} or all of its main surfaces and at least a part of the side surface, the main surface on the side where no film is formed is used. When a nitride semiconductor is epitaxially grown on the surface, it is possible to suppress the growth of the nitride semiconductor on the main surface and the side surface on the side on which the film is formed. Further, such a film made of SiO ₂ or Si ₃ N ₄ can be easily removed by etching or the like. Therefore, it is very suitable as a substrate for epitaxial growth.

  In this case, the nitride semiconductor free-standing substrate is preferably a gallium nitride free-standing substrate.

Thus, the nitride semiconductor free-standing substrate is a gallium nitride free-standing substrate, and has a film made of SiO ₂ or Si ₃ N _{4 on} one whole surface and at least a part of the side surface of the main surface of the gallium nitride free-standing substrate. If present, this substrate can be used as a seed substrate for epitaxial growth, and a gallium nitride free-standing substrate with high crystal quality can be manufactured at low cost, and can be used for various device applications. In addition, since nitride semiconductors have ion-bonding properties, they have strong cleavage properties, and chipping is likely to occur on the outer periphery of the wafer in each of the slicing, grinding, and polishing processes. By having a coating made of SiO ₂ or Si ₃ N ₄ on the side surface of the wafer, it is only on one side of the wafer divided into two, but there is also an effect that chipping in the processing step can be reduced.

  According to the method for manufacturing a nitride semiconductor free-standing substrate according to the present invention, the growth of the nitride semiconductor on the back main surface and side surface of the seed substrate during epitaxial growth can be suppressed, and even if a small amount of deposition occurs. Then, since it is removed together with the film, a reference plane parallel to the original back main surface of the seed substrate can be secured. As a result, when the epitaxial growth substrate is sliced into two, the thickness and parallelism can be controlled with reference to the reference plane, and the nitride semiconductor free-standing substrate having a desired shape can be sliced, and the wafer after slicing has a stable shape. Quality can be. For this reason, it is possible to reduce the machining allowance for subsequent grinding and polishing, the thickness of the epitaxial growth can be reduced correspondingly, and high productivity can be realized.

It is a flow sheet which shows the outline of an example of the manufacturing method of the nitride semiconductor self-supporting substrate concerning the present invention. It is a schematic sectional drawing of the seed substrate before epitaxial growth. It is a schematic sectional drawing of the epitaxial growth board | substrate after epitaxial growth. It is a schematic sectional drawing of the epitaxial growth board | substrate after removing a film. It is the schematic which shows a mode that chamfering and formation of a guide groove are performed before slicing into 2 parts. It is the schematic which shows the epitaxial growth board | substrate which performed chamfering and guide groove formation before slicing in 2 parts. It is a schematic sectional drawing which shows the two board | substrates after being sliced into 2 parts. It is a schematic block diagram which shows an example of the vertical HVPE epitaxial apparatus which can be used for this invention.

  Hereinafter, the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto. The present invention can be applied to various group III nitride semiconductors (group III metal nitrides such as aluminum, gallium, or indium, or mixed crystals thereof). In the following, a case where a gallium nitride free-standing substrate is mainly manufactured will be described as an example. FIG. 1 shows an outline of an example of a method for manufacturing a nitride semiconductor free-standing substrate according to the present invention.

  First, as shown in S1 of FIG. 1, a nitride semiconductor free-standing substrate to be a seed substrate (epitaxial growth substrate) is prepared (step S1). This seed substrate is the same type as the nitride semiconductor free-standing substrate to be finally produced. The nitride semiconductor free-standing substrate serving as a seed substrate may be manufactured by any manufacturing method. If it is a gallium nitride free-standing substrate, it can be manufactured by the manufacturing method described in Patent Documents 1 and 2, for example.

  In addition, as described above, the nitride semiconductor free-standing substrate as a seed substrate prepared here includes various group III nitride semiconductors (group III metal nitrides such as aluminum, gallium, or indium, or mixed crystals thereof) ). The substrate prepared here is preferably one in which crystal orientation, thickness, parallelism, and the like are controlled to predetermined standards.

  The seed substrate preferably has a diameter of 45 mm (1.8 inches) or more. In order to manufacture a device such as an LED industrially at low cost, a device having a larger substrate area is preferable. In addition, the size of the nitride semiconductor free-standing substrate that is finally produced is affected by the size of the seed substrate. Therefore, it is preferable to use such a large-diameter seed substrate.

Next, as shown in S2 of FIG. 1, a film made of SiO ₂ (silicon oxide) or Si ₃ N ₄ (silicon nitride) is formed on the entire back main surface and at least part of the side surface of the seed substrate (step) S2). As described above, in this specification, of the two main surfaces of the seed substrate, the main surface on the side where epitaxial growth is performed to form the epitaxial layer is referred to as the “front main surface”, and the main surface on the opposite side Is the “back main surface”.

FIG. 2 shows a schematic cross-sectional view of the seed substrate at this point, that is, before the epitaxial growth. A coating 111 made of SiO ₂ or Si ₃ N ₄ is formed on the entire back main surface 103 and at least a part of the side surface 104 of the seed substrate 101 to obtain a seed substrate 100 on which the coating is formed. At this time, no coating is formed on the front main surface 102 of the seed substrate.

  In FIG. 2, the seed substrate is formed on the entire side surface 104 of the seed substrate. However, the present invention is not limited to this, and the coating 111 may be formed on at least a part of the side surface 104 of the seed substrate. Further, it is preferable to form the coating 111 on the entire back main surface 103 side of the side surface 104. In FIG. 2, the side surface 104 of the seed substrate is simply illustrated so as to be perpendicular to the front main surface 102 and the back main surface 103. However, the side surface 104 of the seed substrate is usually chamfered.

  The formation of the film 111 in this step can be performed by various known methods. For example, it can be performed as follows. First, it is formed by atmospheric pressure CVD (Chemical Vapor Deposition). In the case of this atmospheric pressure CVD, etc., a part of the seed substrate 101 that does not intend to form the coating 111, that is, the outer periphery of the front main surface 102, etc., may form a coating. In such a case, it may be removed by an appropriate method such as etching or mirror polishing by CMP (Chemical Mechanical Polishing).

  After the coating 111 is formed on the back main surface 103 or the like of the seed substrate in this way, epitaxial growth is performed. Before that, as shown in S3 of FIG. 1, the epitaxial growth is performed on the front main surface 102 side where epitaxial growth is performed. It is preferable to perform mirror polishing by CMP (step S3). Moreover, you may perform washing | cleaning etc. after that. Thus, it is preferable to sufficiently smooth and clean the front main surface 102 of the seed substrate by mirror polishing or the like, and to improve the quality of the formed epitaxial layer. The mirror polishing or the like on the front main surface 102 can also serve as mirror polishing or the like for removing the coating formed around the front main surface 102 in step S2.

  Next, as shown in S4 of FIG. 1, a nitride semiconductor of the same type as the seed substrate 101 is epitaxially grown (that is, homoepitaxial growth) on the front main surface 102 of the seed substrate 101 (step S4). This epitaxial growth is preferably performed by the HVPE method (hydride vapor phase epitaxy), which can be epitaxially grown at a high speed of, for example, 100 μm / h or more, because a nitride semiconductor free-standing substrate can be manufactured with high productivity.

  FIG. 8 shows a vertical type HVPE apparatus as an example of an epitaxial growth apparatus that can be used in the present invention.

  The HVPE apparatus 1 includes a group III metal compound generation tube 8 that generates a group III metal compound inside a vertical reaction tube (chamber) 2. The group III metal compound production tube 8 is configured as follows. A group III metal boat 6 loaded with a group III metal, a reaction gas introduction pipe 4 for introducing hydrogen chloride as a carrier gas, for example, as a reaction gas, and a rectification for adjusting the flow of the generated group III metal compound gas A plate 10, a dilution gas introduction pipe 5 for introducing a dilution gas for adjusting the flow rate of the generated group III metal compound gas, and a group III metal compound blowing pipe 11 for blowing out the group III metal compound gas are provided. The group III metal compound production tube 8 is heated by the first heater 7. When a nitride semiconductor free-standing substrate containing a plurality of group III metal elements is manufactured, the ratio of the mixture of these metals may be adjusted and mounted on the raw material group III metal boat 6.

  The HVPE apparatus 1 further has an ammonia introduction tube 3 for introducing ammonia, a rotatable susceptor 13 on which a seed substrate 100 on which a film is formed is placed, and a reaction product deposited inside the vertical reaction tube 2. An internal protective tube 14 for preventing gas, a gas discharge tube 15 for discharging various gases, a second heater 9 for heating the substrate, and the like.

  Using the HVPE apparatus 1 having such a structure, homoepitaxial growth of a nitride semiconductor is performed as follows.

  First, the raw material group III metal mounted on the raw material group III metal boat 6 is heated to, for example, 800 to 850 ° C. by the first heater 7. A reaction gas such as hydrogen chloride is blown from the reaction gas introduction tube 4 to the molten raw material group III metal (for example, gallium) and reacted to cause a group III metal compound gas (III metal is gallium and the reaction gas is hydrogen chloride). In this case, gallium chloride) is produced.

  The generated group III metal compound gas passes through the rectifying plate 10 and is blown from the group III metal compound blowing tube 11 onto the seed substrate 100 on which the coating is formed, which is placed on the rotating susceptor 13. The flow rate of the group III metal compound gas can be adjusted by controlling the flow rate of the dilution gas (hydrogen, nitrogen, etc.) introduced by the dilution gas introduction pipe 5. The seed substrate 101 is heated by the second heater 9, and the group III metal compound gas reacts with the ammonia introduced from the ammonia introduction pipe 3, so that the group III nitride semiconductor is formed on the seed substrate 100 on which the film is formed. The epitaxial layer grows epitaxially.

  A schematic cross-sectional view of the epitaxial growth substrate after this epitaxial growth is shown in FIG. As shown in FIG. 3, in the epitaxial growth substrate 200, the epitaxial layer 201 is grown on the front main surface 102 of the seed substrate 101.

  Note that the thickness of the epitaxial layer 201 grown by epitaxial growth is preferably 600 μm or more. With such a thickness, the thickness is sufficient to be sliced into two pieces to form two nitride semiconductors, and can be grown with high productivity by the HVPE method. Further, it is preferable that the thickness of the epitaxial layer 201 is 800 μm or less because the epitaxial growth surface during the epitaxial growth can be easily managed and the crystal quality of the epitaxial layer 201 can be maintained high. In addition, unnecessary productivity reduction does not occur.

In epitaxial growth of a nitride semiconductor by the HVPE method, nucleation on a silicon oxide film (SiO ₂ ) or silicon nitride film (Si ₃ N ₄ ) is difficult to occur. Therefore, when these films are used, selective epitaxial growth, that is, on the film It is possible to grow a nitride semiconductor at a site to be epitaxially grown while suppressing the growth of the nitride semiconductor.

  Thus, the presence of the film 111 can suppress the growth of the nitride semiconductor on the back main surface and side surfaces of the seed substrate during the epitaxial growth. However, in the present invention in which a relatively thick epitaxial growth of, for example, 600 μm or more and 800 μm or less is performed, a nitride semiconductor is formed on a part of the coating 111 covering the back main surface and side surfaces of the seed substrate 101 as shown in FIG. Deposit 211 is deposited. In particular, the deposit 211 is likely to be deposited on the outer peripheral portion of the coating 111 covering the back main surface and side surfaces of the seed substrate 101. In addition, the deposit 211 is often polycrystalline.

  Next, as shown in S5 of FIG. 1, the deposit 211 and the coating 111 deposited on the coating 111 are removed (step S5). For example, after the deposit 211 is roughly removed by grinding or the like, the coating 111 can be removed by etching or the like. Further, when the amount of deposit 211 is very small, the deposit 211 can be removed at the same time by removing the film 111 by etching with a chemical solution such as hydrofluoric acid or phosphoric acid.

The film 111 made of SiO ₂ or Si ₃ N ₄ can be easily removed by etching. As an etchant used for removing the coating 111 by etching, it is preferable to use an etching solution in which the etching rate of the nitride semiconductor of the seed substrate 101 and the epitaxial layer 201 and the etching rate of the coating 111 are greatly different. For example, when the coating 111 is SiO ₂ , hydrofluoric acid (hydrofluoric acid) can be used as an etching solution.

  FIG. 4 shows a schematic cross-sectional view of the epitaxial growth substrate with the deposit 211 and the film 111 removed. The deposit 211 and the film 111 are removed, and a reference surface 303 parallel to the original back main surface of the seed substrate 101 (back main surface 103 in FIG. 2) is secured. The epitaxial layer 201 is still formed on the front main surface 102 of the seed substrate 101.

  After removing the deposit 211 and the film 111 deposited on the film 111 of the epitaxial growth substrate 200 in this way, the epitaxial growth substrate 200 is sliced into two parts. Before that, as shown in S6 of FIG. In addition, a guide groove that guides a tool (such as a slicing blade or a wire saw) for chamfering and slicing the peripheral portion of the epitaxial growth substrate 200 on the basis of the reference surface 303, that is, the main surface from which the film 111 has been removed. It is preferable to form (step S6).

  This step can be performed, for example, as follows. FIG. 5 shows how the chamfering and the guide groove are formed. In order to chamfer and form a guide groove, first, the epitaxial growth substrate 200 is placed on the adsorption stage 510.

  Next, grinding is performed using a chamfering and guide groove forming wheel 520 so that the outer peripheral portion of the epitaxial growth substrate 200 has a predetermined diameter. At this stage of grinding, the grinding surface becomes perpendicular to the stage rotation surface. FIG. 5 shows this stage. That is, the seed substrate 101 and the epitaxial layer 201 are laminated, and the outer peripheral portions thereof are substantially aligned vertically. If the initial seed substrate 101 has an orientation flat or a notch, it may be reprocessed at this stage. The side surface shape of the epitaxial layer 201 is preferably aligned with the seed substrate 101.

  Next, grinding is performed using a chamfering and guide groove forming wheel 520. At this time, it is preferable that the depth and shape of the guide groove for guiding the tool for slicing are matched with the chamfered shape of each substrate after slicing in two. This is because the wafer can be chamfered during wafer processing of each substrate after slicing, the processing distortion of the chamfered portion is suppressed, and a nitride semiconductor self-supporting substrate having excellent mechanical strength can be manufactured. . As the shape of the guide groove, a V-shaped groove, a U-shaped groove or the like can be appropriately selected.

  FIG. 6 shows an epitaxial growth substrate on which chamfering and guide groove formation have been performed. As shown in FIG. 6, the guide groove 204 is preferably formed not in the portion corresponding to the seed substrate 101 but in the epitaxial layer 201 in order to secure a machining allowance during slicing. In this case, as described above, the initial seed substrate 101 has an orientation flat or notch, and when the side surface shape of the epitaxial layer 201 is aligned with the seed substrate 101, a guide groove is formed in the orientation flat or notch portion. You don't have to.

  If the shape of the chamfering and guide groove forming wheel 520 shown in FIG. 5 is a shape having a vertical portion and a protrusion for groove formation, the outer peripheral portion of the epitaxial growth substrate 200 is ground (chamfered). ) And guide groove formation are preferable.

  In the present invention, since the reference surface 303 parallel to the original back main surface of the seed substrate 101 is secured, the chamfering and the guide groove 204 are formed on the basis of the reference surface 303, so that the chamfering and guiding can be performed with higher accuracy. The groove 204 can be formed.

  Next, as shown in S7 of FIG. 1, the epitaxially grown substrate is sliced in parallel and divided into two using the main surface from which the film 111 is removed as a reference plane, thereby obtaining two nitride semiconductor free-standing substrates (steps). S7). As a tool for slicing, for example, an inner peripheral blade with a blade thickness of 250 μm or less, a single wire saw with a wire diameter of 200 μm or less, or a single blade saw with a blade thickness of 250 μm or less is used. Can do. As described above, when the guide groove 204 shown in FIG. 6 is formed, the guide groove is sliced by applying a tool for slicing the guide groove.

  FIG. 7 shows a schematic cross-sectional view of two nitride semiconductor free-standing substrates after being divided into two parts. As shown in FIG. 7, the substrate after slicing the epitaxial growth substrate into two parts is a nitride semiconductor free-standing substrate 300 on the seed substrate 101 side having a reference surface 303, and a nitride semiconductor free-standing substrate having no reference surface ( A nitride semiconductor free-standing substrate 400 having an epitaxial growth surface). Both nitride semiconductor free-standing substrates 300 and 400 have slice planes 205a and 205b, respectively. When the guide groove 204 is formed in the epitaxial layer 201 as shown in FIG. 6, as shown in FIG. 7, the nitride semiconductor free-standing substrate 300 on the seed substrate 101 side having the reference surface 303 includes a seed substrate. A part 201a of the epitaxial layer divided on 101 is left. In this case, the nitride semiconductor free-standing substrate 400 having no reference plane is composed of a part 201b of the remaining divided epitaxial layer.

  After performing the two-slice in this manner, the nitride semiconductor free-standing substrate 300 having the reference surface 303 is ground, polished, etched, etc., as shown in S8 of FIG. Step S8).

  Thereafter, if necessary, as shown in S9 of FIG. 1, mirror polishing is performed (step S9), and the substrate can be used again as an epitaxial growth substrate, that is, a seed substrate.

  On the other hand, for the nitride semiconductor free-standing substrate 400 having no reference surface, it is preferable to grind and polish both main surfaces as shown in S8 'of FIG. 1 (step S8'). Further, it is preferable to perform etching. The nitride semiconductor free-standing substrate 400 that does not have a reference surface has an epitaxial growth surface, and has a larger thickness variation than the nitride semiconductor free-standing substrate 300 that has a reference surface, so both main surfaces are ground and polished. It is preferable to adjust the thickness by doing so.

  In this case, since the slice is performed using the guide groove, it is an advantage of the present method that the slice plane is very close to the crystal orientation (plane orientation) of the seed substrate. Between steps S5 and S6, a predetermined amount of the epitaxial surface is ground so as to be parallel to the reference surface 303 to form a secondary reference surface, and the plane orientation of the two-piece wafer 201b is made very close to that of the seed substrate. Can do. By processing in accordance with the reference plane, the crystal orientation of the wafer surface can be kept at the original orientation of the seed substrate at the stage where the mirror polishing step (S9) before epitaxial growth is completed.

  After that, as shown in S9 'of FIG. 1, a mirror polishing process before epitaxial growth is performed on the nitride semiconductor free-standing substrate 400 having no reference surface as necessary (step S9'). This can be used as a product wafer, or can be used as an epitaxial growth substrate, that is, a seed substrate.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this does not limit this invention.

  First, as shown in S1 of FIG. 1, a single crystal gallium nitride free-standing substrate (seed substrate) 101 for epitaxial growth in which crystal orientation, thickness, and parallelism are controlled to predetermined standards was prepared (step S1). This seed substrate was controlled to have a thickness of 400 μm ± 15 μm.

  Next, as shown in S2 and S3 of FIG. 1 and FIG. 2, the surface of the seed substrate 101 on which the epitaxial growth is not performed (that is, the back main surface 103) and the side surface 104 are oxidized with 500 nm of silicon by atmospheric pressure CVD. After depositing the film (coating film) 111, the silicon oxide film 111 that wraps around the outer peripheral portion of the surface on which the silicon oxide film 111 is not deposited (that is, the front main surface 102) and the silicon oxide film 111 deposited on the side surface 104 are formed. The surface was removed to a predetermined position with hydrofluoric acid, and then the surface main surface 102 was further cleaned as a mirror surface having a quality (epiready quality) that can be epitaxially grown using a colloidal silica-based abrasive (step S2). , S3).

  As shown in S4 of FIG. 1, an epitaxial layer 201 of gallium nitride having a center thickness of 800 μm is formed on the seed substrate 100 on which the silicon oxide film is formed by the HVPE apparatus 1 shown in FIG. 8 (step S4). . In this case, two seed substrates were introduced into the HVPE apparatus for epitaxial growth. The growth temperature for epitaxial growth was set to 1050 ° C., and the growth rate was set to 150 μm / hour.

  Next, as shown in S5 of FIG. 1, the polycrystalline (the deposit 211 of FIG. 3) grown on the outer peripheral corners on the silicon oxide film 111 of the substrate 200 on which the gallium nitride having the center thickness of 800 μm is epitaxially grown as described above. ) On the back main surface side of the seed substrate 101 is roughly removed using diamond abrasive grains having a particle diameter of 0.5 μm, and then the silicon oxide film 111 is removed by etching with hydrofluoric acid to be parallel to the initial back main surface 103. A surface (reference surface 303) was secured (step S5).

  Next, chamfering and guide groove formation were performed as shown in S6 of FIG. 1 (step S6). Specifically, first, the epitaxial growth substrate 200 is placed on the adsorption stage 510 (see FIG. 5), and after centering the epitaxial growth substrate 200, a diamond wheel (with chamfering and It was ground with a guide groove forming wheel 520). At this stage, the grinding surface was perpendicular to the stage rotation surface. In addition, the orientation flat was reprocessed on the epitaxial growth substrate 200 using the reference plane 303 as a reference in accordance with the orientation flat position of the seed substrate 101. Subsequently, by using the same diamond wheel (the chamfering and guide groove forming wheel 520 in FIG. 5), the lateral V groove is formed at a predetermined position of the chamfered portion of the epitaxial growth substrate 200, that is, at a position of 550 μm from the reference surface 303. Formed. At this time, the orientation flat portion was not V-grooved.

  Next, as shown in S <b> 7 of FIG. 1, the epitaxial growth substrate 200 was specifically sliced into two parts as follows using a wire saw (step S <b> 7). A diamond wire having a wire diameter of 200 μm was used as the slice wire. In order to prevent chipping at the end of slicing, an adhesive plate was bonded to the orientation flat portion with an epoxy resin, and then the epitaxial growth substrate 200 was set on the vacuum adsorption type two-slice slicing stage on the slice end side. Coolant was flowed during slicing, and the slicing speed was 0.2 mm / min.

  At this stage, two types of gallium nitride free-standing substrates (the nitride semiconductor free-standing substrates 300 and 400 shown in FIG. 7) were manufactured. Among these, the gallium nitride free-standing substrate on the side that is not back-coated with the silicon oxide film 111, that is, the gallium nitride free-standing substrate 400 having the epitaxial growth surface has a large variation in thickness, and is shown in S8 ′ of FIG. Thus, both the main surfaces were ground and polished (step S8 ′). Specifically, the slice plane 205b was used as a reference plane, and the substrate was ground in three stages with diamond abrasive grains having a diameter of 15 μm, 3 μm, and 0.5 μm to a predetermined thickness to ensure parallelism of the substrate.

  Thereafter, gallium nitride was etched in an alkaline solution to remove strain. A part of this free-standing substrate was returned to the step of forming a film on the back main surface (step S2), and the rest was subjected to mirror polishing before epitaxial growth (step S9 ') to obtain a product.

  For the other gallium nitride free-standing substrate (nitride semiconductor free-standing substrate 300 having the reference surface of FIG. 7), as shown in S8 of FIG. 1, the diamond surface of 3 μm diameter and 0.5 μm diameter on the slice surface 205a side is provided. The grains were ground in two steps to a predetermined thickness (step S8), and the chamfered portion was similarly ground with diamond grains having a diameter of 0.5 μm for a predetermined time. Thereafter, the entire gallium nitride free-standing substrate 300 was etched with an alkaline solution. A part of the self-supporting substrate was returned to the step (S2) of forming a film on the back main surface.

  As for the rest, as shown in S9 of FIG. 1, the slice surface 205a side of the gallium nitride free-standing substrate 300 is polished to a depth at which latent scratches are eliminated by using an abrasive based on colloidal silica, and epitaxial growth is performed. A self-supporting substrate having a surface capable of quality (epiready quality) was obtained (step S9).

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

100 ... Seed substrate on which a film is formed, 101 ... Seed substrate (nitride semiconductor free-standing substrate),
102 ... Front main surface, 103 ... Back main surface, 104 ... Side surface, 111 ... Coating,
200: Epitaxial growth substrate, 201: Epitaxial layer,
201a, 201b ... divided epitaxial layers,
204 ... Guide groove, 205a, 205b ... Sliced surface, 211 ... Sediment,
300 ... Nitride semiconductor free-standing substrate having a reference plane; 303 ... Reference plane;
400... A nitride semiconductor free-standing substrate having no reference plane,
510 ... Suction stage, 520 ... Chamfering and groove forming wheel,
DESCRIPTION OF SYMBOLS 1 ... Epitaxial growth apparatus (HVPE apparatus), 2 ... Vertical reaction tube (chamber),
3 ... Ammonia introduction pipe, 4 ... Reaction gas (hydrogen chloride) introduction pipe,
5 ... Gas introduction pipe for dilution,
6 ... Raw material group III metal (gallium) boat, 7 ... First heater,
8 ... Group III metal compound (gallium chloride) production tube, 9 ... Second heater,
10 ... Rectifying plate, 11 ... Group III metal compound (gallium chloride) blowing tube,
13 ... susceptor, 14 ... internal protective tube, 15 ... gas discharge tube.

Claims (6)

A method of manufacturing a nitride semiconductor free-standing substrate by epitaxially growing a nitride semiconductor of the same type as the seed substrate on a front main surface of a nitride semiconductor free-standing substrate to be a seed substrate, and slicing the epitaxially grown epitaxial substrate after the epitaxial growth. At least,
Preparing a nitride semiconductor free-standing substrate to be the seed substrate;
Forming a film made of SiO ₂ or Si ₃ N ₄ on the entire back main surface and at least part of the side surface of the seed substrate;
Epitaxially growing a nitride semiconductor of the same type as the seed substrate on the front main surface of the seed substrate;
Removing the deposit deposited on the film of the epitaxial growth substrate on which the epitaxial growth has been performed and the film;
A step of slicing the epitaxial growth substrate in parallel with a main surface from which the coating has been removed as a reference plane and dividing the substrate into two to produce two nitride semiconductor free-standing substrates from one seed substrate. A method for manufacturing a nitride semiconductor free-standing substrate.   After the deposit deposited on the film of the epitaxial growth substrate and the film are removed, and before the slicing step, the peripheral surface of the epitaxial growth substrate is chamfered using the main surface from which the film is removed as a reference surface. The method for manufacturing a nitride semiconductor free-standing substrate according to claim 1, further comprising a step of forming a guide groove for guiding a tool for slicing.   3. The nitride according to claim 2, wherein the depth and shape of the guide groove for guiding the tool for slicing are matched to the chamfered shape of each substrate after slicing in the two divisions. Manufacturing method of semiconductor free-standing substrate.   4. The method for manufacturing a nitride semiconductor self-supporting substrate according to claim 1, wherein the epitaxial growth is performed with an HVPE method to a thickness of 600 μm or more and 800 μm or less. 5.   The nitride semiconductor free-standing substrate according to any one of claims 1 to 4, wherein the nitride semiconductor free-standing substrate to be the seed substrate and the nitride semiconductor free-standing substrate to be manufactured are gallium nitride free-standing substrates. A method for manufacturing a substrate.   6. Both main surfaces of the substrate that is not the substrate having the reference surface among the substrates that have been sliced into two halves are ground and polished. The manufacturing method of the nitride semiconductor self-supporting substrate as described in 2.

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