JP2018118873A - Method for manufacturing nitride semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of easily achieving a large diameter and efficiently obtaining a free-standing substrate having low dislocation and high quality when obtaining a free-standing nitride semiconductor substrate having a main surface of a semipolar plane.SOLUTION: The method for manufacturing a nitride semiconductor substrate comprises: the first step of preparing a plurality of seed crystal substrates consisting of a nitride semiconductor single crystal, having a cross sectional shape rectangularly formed and having at least a main surface of a polar plane and a side surface of a nonpolar plane; the second step of arranging the plurality of seed crystal substrates on a base in the state of inclining the cross sectional shape at a predetermined inclination to form a stair shape by a part of the polar plane and the nonpolar plane on the side opposite to the base side; the third step of growing a nitride semiconductor single crystal on the stair shape to form a nitride semiconductor single crystal layer; and the fourth step of obtaining a free-standing nitride semiconductor substrate having a main surface of a semipolar plane from the nitride semiconductor single crystal layer.SELECTED DRAWING: Figure 1

Description

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

  In general, the nitride semiconductor layer constituting the light emitting element is formed on the polar face (C face) of the base substrate, but when the light emitting element is constituted using the nitride semiconductor layer formed on the polar face, An internal electric field is generated in the light-emitting layer of the light-emitting element, and the locations where electrons and holes are present are separated, which may reduce the light emission efficiency. Regarding this point, by forming a nitride semiconductor layer on a nonpolar surface such as an M surface or a semipolar surface such as a {11-22} surface instead of a polar surface, an internal electric field in the light emitting layer in the light emitting element is formed. It is theoretically predicted that the luminous efficiency will be improved.

  As a method for obtaining a nitride semiconductor substrate having a nonpolar surface or semipolar surface other than the polar surface as a main surface, for example, a desired surface can be obtained by slicing a bulk crystal thickened with a polar surface as a growth surface in the vertical direction. Has been proposed (see, for example, Patent Document 1). In addition, for example, a method of realizing nonpolar plane GaN by growing GaN on a high index plane sapphire or a silicon substrate has been studied (see, for example, Patent Document 2).

Japanese Patent No. 5271489 Japanese Patent No. 5252465

However, since it is difficult to grow crystals on nonpolar or semipolar surfaces other than polar surfaces, it is possible to efficiently obtain a high-quality epitaxial growth substrate having these surfaces on the surface using the above-described conventional technology. However, it is not always easy.
For example, in the case of the technique described in Patent Document 1, although there is an advantage that a low dislocation GaN single crystal can be used as a base substrate, the bulk crystal thickening is limited to about several millimeters thick. Even if a desired surface is cut out, only a substrate having a width of several mm can be obtained, and it is difficult to realize a large substrate.
For example, in the case of the technique described in Patent Document 2, although there is an advantage that a large-diameter substrate can be used, there is a possibility that high-quality crystals cannot be obtained because the growth is on a different substrate.

  In the present invention, when obtaining a nitride semiconductor free-standing substrate having a semipolar principal surface, it is possible to easily increase the diameter of the free-standing substrate, and to efficiently produce a high-quality free-standing substrate with low dislocations. It is an object to provide a technique that can be obtained.

According to one aspect of the invention,
A first step of preparing a plurality of seed crystal substrates made of a nitride semiconductor single crystal, having a cross-sectional shape formed in a rectangular shape, and having at least a main surface of a polar surface and a side surface of a nonpolar surface;
The plurality of seed crystal substrates are arranged on a base in a state where the cross-sectional shape is inclined at a predetermined inclination angle so that the polar surfaces are in contact with each other and a part of one of the polar surfaces is exposed. And the second step which makes the side opposite to the base side a stepped shape by a part of the polar surface and the nonpolar surface,
A third step of growing a nitride semiconductor single crystal on the step shape to form a nitride semiconductor single crystal layer;
A fourth step of obtaining a nitride semiconductor free-standing substrate having a semipolar principal surface from the nitride semiconductor single crystal layer;
A method for manufacturing a nitride semiconductor substrate is provided.

  According to the present invention, when obtaining a nitride semiconductor free-standing substrate having a semipolar principal surface, it is possible to easily realize a large-diameter free-standing substrate, and to provide a high-quality free-standing substrate with low dislocations. Can be obtained efficiently

It is sectional drawing which shows typically the outline | summary of the manufacturing procedure of the nitride semiconductor self-supporting substrate concerning one Embodiment of this invention. It is explanatory drawing which shows one structural example of the growth apparatus used for manufacture of the nitride semiconductor self-supporting substrate concerning one Embodiment of this invention. It is explanatory drawing (the 1) which shows typically the outline | summary of the crystal growth at the time of manufacturing the nitride semiconductor self-supporting substrate concerning one Embodiment of this invention. It is explanatory drawing (the 2) which shows typically the outline | summary of the crystal growth at the time of manufacturing the nitride semiconductor self-supporting substrate concerning one Embodiment of this invention.

<One Embodiment of the Present Invention>
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

(1) Manufacturing Method of Nitride Semiconductor Substrate FIG. 1 is a cross-sectional view schematically showing an outline of a manufacturing procedure of a nitride semiconductor free-standing substrate according to this embodiment.
In the present embodiment, a case where a substrate made of a single crystal of gallium nitride (GaN) (hereinafter also referred to as “GaN substrate”) is manufactured as an example of a free-standing substrate of a nitride semiconductor will be described.

The GaN crystal has a hexagonal crystal structure (wurtzite crystal structure). In such a hexagonal GaN crystal, examples of the polar face (polar face) include {0001} face and {000-1} face. In addition, examples of the nonpolar plane perpendicular to the polar plane include {10-10} plane and {11-20} plane.
In this specification, the polar plane is sometimes referred to as “C plane”, and in particular, the {0001} plane may be referred to as “+ C plane” and the {000-1} plane may be referred to as “−C plane”. Also, the {10-10} plane that is a nonpolar plane may be referred to as “M plane”, and the {11-20} plane that is also a nonpolar plane may be referred to as “A plane”. In this specification, when a specific index plane such as “C plane” or “M plane” is referred to, an off angle within 10 ° from each crystal axis measured with an accuracy within ± 0.01 ° is used. It is intended to include a surface within a range having an off-angle, preferably a surface having an off angle within 5 °, more preferably within 3 °. Here, the off-angle refers to an angle formed between the normal direction of the surface and the axial direction of the GaN crystal.
Further, the hexagonal GaN crystal has a semipolar plane which is a plane inclined from a nonpolar plane other than the polar plane. As the semipolar plane, for example, a {10-11} plane, a {10-12} plane, a {10-13} plane, {20−, inclined in the m-axis direction (axial direction perpendicular to the M plane) from the C plane 21} surface and the like. These {10-11} planes, {10-12} planes, {10-13} planes, and {20-21} planes are known as planes that are exceptionally easy to obtain flat surfaces by growth among semipolar planes. Yes.

  In this embodiment, the GaN substrate 20 having the semipolar main surface 21 is manufactured by sequentially performing “first step” to “fourth step” described below.

(First step: preparation of seed crystal substrate)
In the first step, a plurality of seed crystal substrates 10 are prepared as shown in FIG. The number of seed crystal substrates 10 to be prepared is not particularly limited, and may be appropriately determined according to the size, shape, etc. of the GaN substrate 20 to be manufactured.

  The seed crystal substrate 10 is a base (seed) for manufacturing the GaN substrate 20 and is made of a single crystal of GaN, which is an example of a nitride semiconductor, and has a rectangular cross-sectional shape. Of the four surfaces 11 and 12 surrounding the rectangular cross-sectional shape, the two main surfaces 11 facing each other are C-planes that are polar surfaces. More specifically, one of the two main surfaces 11 is a + C surface 11a, and the other surface is a -C surface 11b. Moreover, about the two side surfaces 12 which cross | intersect these surfaces 11, all become the M surface which is a nonpolar surface. In addition, although the case where the side surface 12 is an M surface is mentioned here as an example, the present invention is not limited to this, and may be an A surface as long as it is a nonpolar surface. In other words, the seed crystal substrate 10 only needs to have at least the polar main surface 11 and the nonpolar side surface 12.

  The rectangular cross-sectional shape is substantially the same for each of the plurality of seed crystal substrates 10. For example, the long side constituted by the C plane 11 is about 10 to 200 mm, and the short side constituted by the M plane 12 is 0.3. It can be considered that the thickness is about 5.0 mm. If the cross-sectional shapes of the plurality of seed crystal substrates 10 are substantially the same, it is possible to easily arrange them side by side as described later, and it is suitable for constructing the step shape described later. is there. In addition, the cross-sectional shape size mentioned here is only a suitable specific example, and this invention is not limited to this.

  The planar shape of the plurality of seed crystal substrates 10 may be, for example, rectangular, but is not particularly limited, and may be appropriately set as long as they can be arranged side by side as described later. Absent.

  In the present embodiment, such a plurality of seed crystal substrates 10 are obtained by dividing a GaN substrate 14 whose main surface 13 is a polar surface into a plurality of pieces. More specifically, it is assumed that the GaN substrate 14 is cleaved at the M-polar surface and divided into a plurality of pieces, thereby obtaining a plurality of seed crystal substrates 10.

  Therefore, in this embodiment, in the first step, first, as a base material used when obtaining a plurality of seed crystal substrates 10, as shown in FIG. 1A, GaN whose main surface 13 is a C-plane. A substrate 14 is prepared. The GaN substrate 14 may be any substrate prepared by, for example, epitaxially growing a GaN crystal on a base substrate, slicing the grown crystal and polishing the surface by a known method. In the current technical level, if the diameter is about 2 inches, the variation of the off angle in the main surface 13 (that is, the difference between the maximum value and the minimum value of the off angle) is compared with, for example, within 0.3 °. And a high-quality substrate with a small defect density and a low impurity concentration can be obtained relatively inexpensively.

  When the GaN substrate 14 is prepared, the GaN substrate 14 is then cleaved at the M-plane which is a nonpolar surface and divided into a plurality of pieces. The cleavage may be performed using a known method such as cutting using a laser scribing device. As a result, a plurality of seed crystal substrates 10 are obtained from the GaN substrate 14 as shown in FIG.

  Thus, in this embodiment, since the GaN substrate 14 is cleaved to obtain a plurality of seed crystal substrates 10, it is possible to easily obtain a plurality of homogeneous seed crystal substrates 10.

(Second step: Arrangement of seed crystal substrate)
In the second step, the plurality of seed crystal substrates 10 prepared in the first step are arranged side by side on a base 208 provided in the growth apparatus 200 described later.

  In arranging the plurality of seed crystal substrates 10, first, as shown in FIG. 1C, the cross-sectional shape of each of the seed crystal substrates 10 to be arranged is inclined at a predetermined inclination angle θ. The “predetermined inclination angle θ” here is an angle formed by the c-axis direction (axial direction perpendicular to the C-plane) in the cross-sectional shape and the normal direction of the base 208. The angle coincides with the angle formed between the C surface 11 and the upper surface of the base 208.

  The predetermined inclination angle θ is an important parameter in determining the semipolar plane that will be the main surface 21 of the finally obtained GaN substrate 20. That is, depending on the setting of the inclination angle θ, what kind of semipolar surface the main surface 21 becomes is determined. A specific example of the predetermined inclination angle θ and the relationship between the inclination angle θ and the semipolar plane will be described later in detail.

  When the cross-sectional shape is tilted at a predetermined tilt angle θ, each of the plurality of seed crystal substrates 10 is adjacent to the adjacent seed crystal substrate as shown in FIG. The ten C-planes 11 are in contact with each other, and are arranged side by side on the base 208 so that a part of one C-plane 11 is exposed. More specifically, the seed crystal substrates 10 are arranged on the surface of the base 208 so that one + C surface 11a and the other −C surface 11b of adjacent seed crystal substrates 10 are in contact with each other. At this time, a plurality of seed crystal substrates 10 having substantially the same cross-sectional shape are arranged on the surface of the base 208 that is a flat surface, but each seed crystal substrate 10 is tilted at an inclination angle θ. Therefore, when a plurality of seed crystal substrates 10 are arranged, a part of one C plane 11 of the adjacent seed crystal substrate 10 is exposed without being covered on the side opposite to the base 208 side. is there. By arranging the plurality of seed crystal substrates 10 side by side in this way, a part of the C surface 11 and the M surface exposed by the plurality of seed crystal substrates 10 are placed on the side opposite to the base 208 side. A staircase shape 15 is formed.

  The C plane 11 constituting the staircase shape 15, that is, the C plane 11 that is partially exposed when the plurality of seed crystal substrates 10 are arranged side by side, can be realized by either the + C plane or the −C plane. However, the + C plane (that is, {0001} plane) is preferable for the reason described later. Therefore, in the present embodiment, the plurality of seed crystal substrates 10 are arranged while defining the directions thereof so that the C plane 11 constituting the staircase shape 15 is the + C plane.

  For the C plane (in the present embodiment, + C plane) 11 constituting the staircase shape 15, the off-angle distribution in each of the plurality of seed crystal substrates 10 is preferably within 1 °. The off-angle distribution means a variation in off-angle between a plurality of seed crystal substrates 10 (that is, a difference between the maximum value and the minimum value of the off-angle), and is within 1 ° as described above. However, it is more preferably within 0.3 °, still more preferably within 0.15 °. Thus, by aligning the off-angle distribution of the C-plane 11 constituting the staircase shape 15, when a GaN crystal is grown on the staircase shape 15 as will be described in detail later, a high-quality crystal with low dislocations is formed. This is because it can be obtained.

  When arranging the plurality of seed crystal substrates 10 in a state inclined at a predetermined inclination angle θ, it is conceivable to use an arrangement jig 16 having an inclined surface inclined at the inclination angle θ. If the placement jig 16 is used, each of the plurality of seed crystal substrates 10 can be tilted easily and appropriately by arranging the C-plane 11 of the seed crystal substrate 10 along the inclined surface of the placement jig 16. It becomes possible to dispose it at an angle θ. For example, pyrolytic graphite (PG), carbon, quartz or the like having excellent heat resistance and mechanical strength is used as a material for forming the placement jig 16 for realizing the placement of the seed crystal substrate 10. Is preferred.

  The placement jig 16 may be a pair of a jig 16a on the side supporting the seed crystal substrate 10 and a jig 16b on the side holding the seed crystal substrate 10, but at least support them. If the side jig 16a is provided, the plurality of seed crystal substrates 10 can be disposed at an inclination angle θ. Further, the placement jig 16 is not necessarily required for the placement of the plurality of seed crystal substrates 10. For example, the upper surface of the base 208 on which the seed crystal substrate 10 is placed is made to have an inclined step shape. It doesn't matter.

(Third step: GaN crystal growth)
In the third step, a GaN crystal layer 22 is formed by growing a GaN crystal, which is a nitride semiconductor single crystal, on the step shape 15 formed by the plurality of seed crystal substrates 10 in the second step.

In this embodiment, the growth of the GaN crystal is performed using a hydride vapor phase epitaxy apparatus (HVPE apparatus).
FIG. 2 is a schematic diagram showing a specific example of the HVPE apparatus used in the present embodiment.

  The HVPE apparatus 200 includes an airtight container 203 made of a heat-resistant material such as quartz or alumina and having a film forming chamber 201 formed therein. In the film forming chamber 201, a susceptor 208 is provided as a base on which the plurality of seed crystal substrates 10 and the placement jig 16 are placed. The susceptor 208 is connected to a rotation shaft 215 included in the rotation mechanism 216, and is configured to be rotatable in accordance with the drive of the rotation mechanism 216. These susceptor 208 and rotating mechanism 216 are preferably made of carbon or carbon coated with silicon carbide (SiC), boron nitride (BN), or the like, and other members have less impurities. It is preferably composed of high purity quartz. In particular, members in regions exposed to high temperatures of 1300 ° C. or higher are preferably composed of alumina instead of high-purity quartz.

At one end of the hermetic vessel 203, a gas supply pipe 232a for supplying hydrogen chloride (HCl) gas into the gas generator 233a, a gas supply pipe 232b for supplying ammonia (NH ₃ ) gas into the film forming chamber 201, and A gas supply pipe 232 c for supplying nitrogen (N ₂ ) gas into the film formation chamber 201 is connected. A gas supply pipe 232d that supplies hydrogen (H ₂ ) gas is connected to the gas supply pipe 232c. The gas supply pipes 232a to 232d are respectively provided with flow rate controllers 241a to 241d and valves 243a to 243d in order from the upstream side. A gas generator 233a for storing Ga melt as a raw material is provided downstream of the gas supply pipe 232a. Connected to the gas generator 233a is a nozzle 249a that supplies gallium chloride (GaCl) gas generated by the reaction of HCl gas and Ga melt toward the seed crystal substrate 10 or the like disposed on the susceptor 208. ing. Nozzles 249b and 249c for supplying various gases supplied from these gas supply pipes toward the seed crystal substrate 10 and the like disposed on the susceptor 208 are connected to the downstream sides of the gas supply pipes 232b and 232c, respectively. Yes. The nozzles 249a to 249d are arranged to flow gas in a direction intersecting the surface of the susceptor 208.

  An exhaust pipe 230 that exhausts the inside of the film forming chamber 201 is provided at the other end of the hermetic container 203. The exhaust pipe 230 is provided with a pump (or blower) 231. A zone heater 207 for heating the inside of the gas generator 233 a and the seed crystal substrate 10 on the susceptor 208 to a desired temperature is measured on the outer periphery of the hermetic container 203, and the temperature in the film forming chamber 201 is measured in the hermetic container 203. A temperature sensor 209 is provided for each. Each member included in the HVPE apparatus 200 is connected to a controller 280 configured as a computer, and is configured such that processing procedures and processing conditions described later are controlled by a program executed on the controller 280.

In the third step, using the HVPE apparatus 200 having the above-described configuration, a GaN crystal is grown on the stepped shape 15 of the plurality of seed crystal substrates 10 by, for example, a processing procedure described below.
First, in the HVPE apparatus 200, Ga melt is accommodated as a raw material in the gas generator 233a. Then, while rotating the susceptor 208 and heating and exhausting the film formation chamber 201, H ₂ gas (or a mixed gas of H ₂ gas and N ₂ gas) is supplied into the film formation chamber 201. Further, in the state in which the inside of the film formation chamber 201 reaches a desired growth temperature and growth pressure and the inside of the film formation chamber 201 is in a desired atmosphere, gas is supplied from the gas supply pipes 232a and 232b, and a plurality of seeds are supplied. GaCl gas and NH ₃ gas are supplied as film forming gases onto the stepped shape 15 formed by the crystal substrate 10. These film forming gases may be supplied after being mixed with a carrier gas composed of H ₂ gas, N ₂ gas, or a mixed gas thereof. Further, the supply of NH ₃ gas is preferably started from the stage where the growth temperature reaches 500 ° C. from the viewpoint of preventing the seed crystal substrate 10 from being deteriorated.

  Thereby, in the third step, as shown in FIG. 1E, the GaN crystal is epitaxially grown on the staircase shape 15, and the GaN crystal layer 22 is formed.

Examples of the processing conditions for carrying out the third step include the following.
Deposition temperature (seed crystal substrate temperature): 980-1100 ° C., preferably 1050-1100 ° C.
Deposition pressure (pressure in the deposition chamber): 90 to 105 kPa, preferably 90 to 95 kPa
GaCl gas partial pressure: 1.5 to 15 kPa
NH ₃ gas partial pressure / GaCl gas partial pressure: 4 to 20
N ₂ gas partial pressure / H ₂ gas partial pressure: 0 to 1

Here, the epitaxial growth of the GaN crystal on the step shape 15 will be described in more detail.
FIG. 3 is an explanatory diagram (part 1) schematically showing an outline of crystal growth when the nitride semiconductor free-standing substrate according to the present embodiment is manufactured.

  In the third step, a GaN crystal is epitaxially grown on the step shape 15. As shown in FIG. 3A, the staircase shape 15 is configured such that the C plane (+ C plane in the present embodiment) 11 and the M plane 12 of the seed crystal substrate 10 are exposed. Epitaxial growth of GaN crystals generally has a higher growth rate when growing in the direction along the c-axis (arrow A direction in the figure) than when growing in the direction along the m-axis (arrow B direction in the figure). . Therefore, in the epitaxial growth of the GaN crystal on the staircase shape 15, the influence by the C face 11 becomes more dominant than the influence by the M face 12.

  In this case, if the C plane 11 constituting the step shape 15 is the + C plane (ie, {0001} plane), the + C plane is exposed during the epitaxial growth of the GaN crystal on the step shape 15. As shown in FIG. 3B, the polar directions of the GaN crystals to be epitaxially grown along the + C plane are aligned while receiving a dominant influence from the + C plane. Therefore, for example, unlike the case where the -C plane is exposed, there is a polarity inversion domain (inversion domain) in which the polarity of the GaN crystal is aligned and the polarity of the surrounding crystal is reversed. This is very suitable for obtaining a high-quality GaN crystal with low dislocations.

  In this case, if the off-angle distribution on the C plane 11 constituting the staircase shape 15 is within 1 °, even if GaN crystals are epitaxially grown on the plurality of seed crystal substrates 10, As a result, it becomes possible to obtain a high quality GaN crystal with low dislocations.

By the way, in the third step, the GaN crystal layer 22 obtained by epitaxial growth of the GaN crystal is formed on the step shape 15. Therefore, the GaN crystal layer 22 is formed through the following process.
FIG. 4 is an explanatory diagram (part 2) schematically showing an outline of crystal growth when the nitride semiconductor free-standing substrate according to the present embodiment is manufactured.

  In the initial stage of GaN crystal growth, the GaN crystal layer 22 has a surface shape that follows the stepped shape 15 as shown in FIG. However, as the growth of the GaN crystal continues and the GaN crystal layer 22 becomes thicker, as shown in FIG. 4B, the surface shape deviates from the stepped shape 15, and the GaN crystal layer 22 has a certain thickness (for example, , 500 μm or more), the surface becomes flat as shown in FIG. The surface of the GaN crystal layer 22 after planarization is a semipolar surface similar to the main surface 21 of the GaN substrate 20 finally obtained.

  About the GaN crystal layer 22 obtained through such a process, it is preferable that each GaN crystal constituting the GaN crystal layer 22 has the same polarity and has a low dislocation and a high quality. For that purpose, at least until the surface of the GaN crystal layer 22 is flattened, the epitaxial growth of the GaN crystal may continue to be affected by the + C plane 11a constituting the stepped shape 15. It is done.

  Therefore, for the plurality of seed crystal substrates 10 that form the staircase shape 15, as shown in FIG. 4 (d), just the semipolar plane of the GaN crystal layer 22 to be obtained in the third step is obtained. You may make it set the inclination at the time of arrange | positioning at a 2nd process to inclination | tilt angle (theta) + (alpha) so that the staircase shape 15 may become the positional relationship which has inclination (alpha) with respect to the surface 23. FIG. That is, in such a case, each inclination is set to the inclination angle θ + α so that the inclination angle when the seed crystal substrate 10 is arranged is increased by the inclination α with respect to the just surface 23. It is.

  Thus, if the inclination of each seed crystal substrate 10 is set to the inclination angle θ + α so that the staircase shape 15 has a positional relationship with the inclination α with respect to the just surface 23 (that is, the just surface 23 has If the GaN crystal is epitaxially grown on the staircase shape 15, the growth surface from the + C plane will continue to be exposed until the surface of the GaN crystal layer 22 is flattened. Become. Therefore, since the state in which the influence from the + C plane 11a constituting the staircase shape 15 continues to the epitaxial growth of the GaN crystal, the direction of the polarity of the GaN crystal to be epitaxially grown can always be made uniform, and low dislocations can be obtained. And is very suitable for obtaining high-quality crystals.

  That is, in the second step, the inclination at the time of arranging the plurality of seed crystal substrates 10 is set so that the growth surface from the + C surface 11a of the step shape 15 continues to be exposed until the growth surface of the GaN crystal layer 22 is flattened. If the inclination angle is set to θ + α, when the GaN crystal is epitaxially grown on the staircase shape 15 in the third step, it is possible to always align the polarity direction of the GaN crystal, and the low-dislocation and high-quality. It becomes feasible to obtain crystals.

  The specific magnitude of the inclination α may be about 0.2 to 3 °, for example. However, the present invention is not limited to this, and as described above, the influence from the + C surface 11a is affected. The size may be any size as long as the extended state continues.

  In the third step, it is conceivable to continue the epitaxial growth of the GaN crystal until the growth surface of the GaN crystal layer 22 is flattened, but this is not always necessary. If the self-standing substrate can be cut out, the epitaxial growth of the GaN crystal may be terminated at the stage before the growth surface of the GaN crystal layer 22 is flattened (that is, the stage where the influence of the staircase shape 15 remains). Even before the growth surface is flattened, the GaN crystal layer 22 is considered to be in a state in which the polar directions of the GaN crystals are aligned, and the self-standing substrate cut out from the GaN crystal layer 22 has high quality with low dislocations. Because.

After the epitaxial growth of the GaN crystal is completed and the GaN crystal layer 22 is formed on the staircase shape 15, the HVPE apparatus 200 supplies NH ₃ gas and N ₂ gas into the film forming chamber 201, While the film chamber 201 is evacuated, supply of HCl gas to the gas generator 233a, supply of H ₂ gas to the film formation chamber 201, and heating by the heater 207 are stopped. Then, when the temperature in the film formation chamber 201 becomes 500 ° C. or lower, the supply of NH ₃ gas is stopped, and then the atmosphere in the film formation chamber 201 is replaced with N ₂ gas to return to atmospheric pressure. The temperature inside the film chamber 201 is lowered to a temperature at which the film chamber 201 can be unloaded, and the plurality of seed crystal substrates 10 bonded by the GaN crystal layer 22 are unloaded from the film forming chamber 201.

(Fourth process: Cutting out a self-supporting substrate)
In the fourth step, a self-supporting substrate is cut out from the GaN crystal layer 22 obtained in the third step, thereby obtaining a GaN substrate 20 having a semipolar principal surface 21.

  Specifically, the GaN crystal layer 22 on the seed crystal substrate 10 carried out from the film formation chamber 201 of the HVPE apparatus 200 is sliced in parallel with the growth surface if the growth surface is flattened, The seed crystal substrate 10 is removed. Note that, even if the growth surface is not flattened, the slice is sliced in the direction in which the growth surface can be viewed. This slicing can be performed using, for example, a wire saw or an electric discharge machine.

  Thereby, as shown in FIG.1 (f), one or more self-supporting board | substrates (namely, GaN board | substrate 20 with the main surface 21 of a semipolar surface) can be obtained. Thereafter, the surface (semipolar surface) of the GaN substrate 20 is subjected to a predetermined polishing process to make this surface an epi-ready mirror surface. Note that the back surface of the GaN substrate 20 is a lapping surface or a mirror surface.

(2) Relationship between Inclination Angle and Semipolar Surface Next, in the manufacturing method of the above-described procedure, the relationship between the inclination angle θ of the seed crystal substrate 10 and the semipolar surface constituting the main surface 21 of the GaN substrate 20. This will be described in detail.

  As the semipolar surface constituting the main surface 21 of the GaN substrate 20, for example, a {10-11} plane, a {10-12} plane, a {10-13} plane that are exceptionally easy to obtain a flat surface by growth. Either a plane or a {20-21} plane is mentioned. When such a semipolar plane is targeted, a high-quality GaN substrate 20 can be realized by setting the inclination angle θ as described below.

(When targeting {10-11} plane)
For example, if the {10-11} plane is the target, the tilt angle θ of the seed crystal substrate 10 is set to 62 °. And each of the several seed crystal substrate 10 is arrange | positioned in the state inclined by inclination-angle (theta) set to 62 degrees. The setting value of the inclination angle θ at this time is a plurality of values in a state in which the inclination α is added to the setting value of the inclination angle θ and the amount of the inclination α is added (for example, 62.2 to 65 °). It is preferable to arrange the seed crystal substrate 10.

  By epitaxially growing a GaN crystal on the step shape 15 formed at such a set angle, it is possible to obtain a GaN crystal layer 22 having a flat {10-11} plane on the surface. Then, after the GaN crystal layer 22 is grown to a sufficient thickness, the GaN crystal layer 22 is sliced and the seed crystal substrate 10 on the back side is removed, so that the {10-11} plane becomes the main surface 21. It is possible to obtain a GaN substrate 20 that is a large-area and low-dislocation free-standing substrate.

(When targeting {10-12} plane)
For example, if the {10-12} plane is targeted, the tilt angle θ of the seed crystal substrate 10 is set to 43 °. And each of the several seed crystal substrate 10 is arrange | positioned in the state inclined by inclination-angle (theta) set to 43 degrees. The setting value of the inclination angle θ at this time is a plurality of values in a state where the inclination α is added to the setting value of the inclination angle θ and the amount of the inclination α is added (for example, in a state of 43.2 to 46 °). It is preferable to arrange the seed crystal substrate 10.

  By epitaxially growing a GaN crystal on the staircase shape 15 formed at such a set angle, it is possible to obtain a GaN crystal layer 22 having a flat {10-12} plane on the surface. Then, after the GaN crystal layer 22 is grown to a sufficient thickness, the GaN crystal layer 22 is sliced and the seed crystal substrate 10 on the back side is removed, so that the {10-12} plane becomes the main surface 21. It is possible to obtain a GaN substrate 20 that is a large-area and low-dislocation free-standing substrate.

(When targeting {10-13} plane)
For example, if the {10-13} plane is the target, the tilt angle θ of the seed crystal substrate 10 is set to 32 °. And each of the several seed crystal substrate 10 is arrange | positioned in the state inclined by inclination-angle (theta) set to 32 degrees. The setting value of the inclination angle θ at this time is a plurality of values in a state where the inclination α is added and the inclination α is added to the setting value of the inclination angle θ (for example, a state where the angle is 32.2 to 35 °). It is preferable to arrange the seed crystal substrate 10.

  By epitaxially growing a GaN crystal on the step shape 15 formed at such a set angle, it is possible to obtain a GaN crystal layer 22 having a flat {10-13} plane on the surface. Then, after the GaN crystal layer 22 is grown to a sufficient thickness, the GaN crystal layer 22 is sliced and the seed crystal substrate 10 on the back side is removed, so that the {10-13} plane becomes the main surface 21. It is possible to obtain a GaN substrate 20 that is a large-area and low-dislocation free-standing substrate.

(When targeting {20-21} plane)
For example, if the {20-21} plane is targeted, the tilt angle θ of the seed crystal substrate 10 is set to 75 °. And each of the several seed crystal substrate 10 is arrange | positioned in the state inclined by inclination-angle (theta) set to 75 degrees. The setting value of the inclination angle θ at this time is a plurality of values in a state (for example, a state in which the inclination α is added to the setting value of the inclination angle θ and the amount of the inclination α is added). It is preferable to arrange the seed crystal substrate 10.

  By epitaxially growing a GaN crystal on the step shape 15 formed at such a set angle, it is possible to obtain a GaN crystal layer 22 having a flat {20-21} plane on the surface. Then, after the GaN crystal layer 22 is grown to a sufficient thickness, the GaN crystal layer 22 is sliced and the seed crystal substrate 10 on the back side is removed, so that the {20-21} plane becomes the main surface 21. It is possible to obtain a GaN substrate 20 that is a large-area and low-dislocation free-standing substrate.

(3) Effects Obtained by the Present Embodiment According to the present embodiment, one or more effects shown below can be obtained.

(A) In the present embodiment, a plurality of seed crystal substrates 10 having a cross-sectional shape formed in a rectangular shape and having at least a polar main surface 11 and a nonpolar surface 12 are prepared (first step). They are arranged side by side in a state inclined at a predetermined inclination angle θ (second step), and a GaN crystal is grown on the stepped shape 15 formed thereby to form a GaN crystal layer 22 (third step). Then, a self-supporting substrate is cut out from the GaN crystal layer 22 to obtain a GaN substrate 20 having a semipolar main surface 21 (fourth step).
Therefore, in the case of obtaining the GaN substrate 20 having the semipolar main surface 21, it is possible to easily realize a large substrate diameter by arranging a plurality of seed crystal substrates 10 side by side (first step). Become.
Further, when arranging a plurality of seed crystal substrates 10, each seed crystal substrate 10 is disposed in an inclined state, and a polar surface is formed using a staircase shape 15 formed by a polar surface and a nonpolar surface formed thereby. Since the GaN crystal layer 22 is obtained by epitaxial growth on the stepped shape 15 where a part of the GaN crystal layer is exposed (second step to third step), a high-quality crystal is obtained with low dislocations.
Moreover, since the growth surface to be epitaxially grown may be the stepped shape 15 (third step), the polishing process for exposing the semipolar surface as the growth surface is not required, and the productivity of the GaN substrate 20 is improved. It is very useful for the purpose.
Furthermore, the GaN crystal layer 22 is grown on the stepped shape 15 (third step), and the GaN substrate 20 is obtained directly from the GaN crystal layer 22 (fourth step). It is very useful for improving the productivity of the GaN substrate 20 without requiring a polycrystalline binder or the like for holding. Moreover, since no polycrystalline region due to a binder or the like remains in the GaN substrate 20, it is very useful for obtaining a high-quality GaN substrate 20 with low dislocations.

(B) According to the present embodiment, when preparing a plurality of seed crystal substrates 10 (first step), the GaN substrate 14 whose main surface 13 is a polar surface is cleaved with a nonpolar surface and divided into a plurality of pieces. Thus, a plurality of seed crystal substrates 10 are obtained. Therefore, it becomes feasible to easily obtain a plurality of homogeneous seed crystal substrates 10 and is very suitable for obtaining high-quality crystals with low dislocations for the GaN crystal layer 22 grown on each seed crystal substrate 10. It is also very suitable for improving the productivity of the GaN substrate 20 and the like.

(C) According to the present embodiment, the polar surface constituting the staircase shape 15 is the {0001} plane (that is, the + C plane). Thus, if the polar plane is the + C plane, the + C plane is exposed during the epitaxial growth on the staircase shape 15. Therefore, the polarity direction of the GaN crystal to be epitaxially grown along the + C plane is determined. This is very suitable for obtaining high-quality crystals with low dislocations.

(D) As described in the present embodiment, the staircase shape 15 is in a positional relationship having an inclination α with respect to the semipolar plane just surface 23 of the GaN crystal layer 22 to be obtained in the third step. If the inclination at the time of arranging in the second step is set to the inclination angle θ + α, during the epitaxial growth of the GaN crystal on the staircase shape 15, the growth surface from the + C plane is maintained until the surface of the GaN crystal layer 22 is flattened. It will continue to be exposed. Therefore, since the state where the influence from the + C plane constituting the staircase shape 15 continues to the epitaxial growth of the GaN crystal, the direction of the polarity of the GaN crystal to be epitaxially grown can always be made uniform, and the low dislocation can be achieved. This is very suitable for obtaining high-quality crystals.
That is, in the second step, the inclination when arranging the plurality of seed crystal substrates 10 is inclined so that the growth surface from the + C plane of the step shape 15 continues to be exposed until the growth surface of the GaN crystal layer 22 is flattened. If the angle θ + α is set, in the third step, when the GaN crystal is epitaxially grown on the stepped shape 15, it becomes possible to always align the polarity direction of the GaN crystal, so that a high-quality crystal with low dislocations. It is feasible to obtain
The formation of the GaN crystal layer 22 may be completed at a stage before the growth surface is flattened (that is, a stage where the influence of the staircase shape 15 remains). Even before the growth surface is flattened, the GaN crystal layer 22 is considered to be in a state in which the polar directions of the GaN crystals are aligned, and the GaN substrate 20 cut out from the GaN crystal layer 22 has a low dislocation and a high quality. Because it becomes.

(E) As described in the present embodiment, if the off-angle distributions of the + C planes of the plurality of seed crystal substrates 10 are within 1 °, the off-angle distributions of the C planes constituting the staircase shape 15 are aligned. . Therefore, when a GaN crystal is grown on the staircase shape 15, it is possible to obtain a high-quality crystal with low dislocations.

(F) As described in the present embodiment, when the arrangement jig 16 having the inclined surface inclined at the inclination angle θ is used when arranging the plurality of seed crystal substrates 10, the inclined surface of the arrangement jig 16 is provided. By disposing the seed crystal substrate 10 along the C surface 11, each of the plurality of seed crystal substrates 10 can be easily and appropriately inclined at the inclination angle θ, and the GaN substrate 20. This is useful for improving productivity of the product.

<Other embodiments>
Although one embodiment of the present invention has been specifically described above, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention.

  In the above-described embodiment, in order to obtain a plurality of seed crystal substrates 10, the case where the GaN substrate 14 whose main surface 13 is a polar surface is cleaved with the M-plane which is a nonpolar surface is taken as an example. However, the present invention is not limited to this. For example, the GaN substrate 14 may be cleaved with an A-plane that is another nonpolar surface to obtain a plurality of seed crystal substrates 10. When the seed crystal substrate 10 obtained by cleaving on the A plane is used, the {11-21} plane and the {11-22} plane inclined from the C plane in the a-axis direction (axial direction perpendicular to the A plane) Alternatively, it is feasible to obtain the GaN substrate 20 having these semipolar planes on the main surface 21 with respect to the {11-23} plane or the like.

  Moreover, although the above-mentioned embodiment demonstrated the case where a hydride vapor phase epitaxy method (HVPE method) was used in the 3rd process of forming the GaN crystal layer 22 on the step shape 15, this invention is such an aspect. It is not limited to. For example, in the third step, a vapor phase growth method other than the HVPE method such as a metal organic chemical vapor deposition method (MOCVD method) may be used. Even in that case, the same effect as the above-described embodiment can be obtained.

Moreover, although the case where the nitride semiconductor was GaN was given as an example in the above-described embodiment, the present invention is not limited to such an aspect. That is, the present invention is not limited to GaN, but nitrides such as aluminum nitride (AlN), aluminum gallium nitride (AlGaN), indium nitride (InN), indium gallium nitride (InGaN), and aluminum indium gallium nitride (AlInGaN) The present invention can also be suitably applied to manufacturing a self-supporting substrate made of a crystal, that is, a nitride crystal represented by a composition formula of Al _x In _y Ga _1-xy N (0 ≦ x + y ≦ 1).

<Preferred embodiment of the present invention>
Hereinafter, preferred embodiments of the present invention will be additionally described.

[Appendix 1]
According to one aspect of the invention,
A first step of preparing a plurality of seed crystal substrates made of a nitride semiconductor single crystal, having a cross-sectional shape formed in a rectangular shape, and having at least a main surface of a polar surface and a side surface of a nonpolar surface;
The plurality of seed crystal substrates are arranged on a base in a state where the cross-sectional shape is inclined at a predetermined inclination angle so that the polar surfaces are in contact with each other and a part of one of the polar surfaces is exposed. And the second step which makes the side opposite to the base side a stepped shape by a part of the polar surface and the nonpolar surface,
A third step of growing a nitride semiconductor single crystal on the step shape to form a nitride semiconductor single crystal layer;
A fourth step of obtaining a nitride semiconductor free-standing substrate having a semipolar principal surface from the nitride semiconductor single crystal layer;
A method for manufacturing a nitride semiconductor substrate is provided.

[Appendix 2]
In the method for manufacturing a nitride semiconductor substrate according to appendix 1, preferably,
The plurality of seed crystal substrates are obtained by cleaving a nitride semiconductor single crystal substrate whose main surface is the polar surface at the nonpolar surface and dividing the substrate into a plurality of pieces.

[Appendix 3]
In the method for manufacturing a nitride semiconductor substrate according to appendix 1 or 2, preferably,
The polar surface constituting the staircase shape is a {0001} plane.

[Appendix 4]
In the method for manufacturing a nitride semiconductor substrate according to attachment 3, preferably,
The inclination angle when the plurality of seed crystal substrates are arranged is set so that the stepped shape has a positional relationship having an inclination with respect to the just plane of the semipolar plane.

[Appendix 5]
In the method for manufacturing a nitride semiconductor substrate according to appendix 3 or 4, preferably,
The inclination angle when the plurality of seed crystal substrates are arranged is set so that the growth surface from the stepped polar surface continues to be exposed until the growth surface of the nitride semiconductor single crystal layer becomes flat. .

[Appendix 6]
In the method for manufacturing a nitride semiconductor substrate according to any one of appendices 1 to 4, preferably,
The self-standing substrate is cut out from the nitride semiconductor single crystal layer in a state where the growth surface of the nitride semiconductor single crystal layer has a stepped shape.

[Appendix 7]
In the method for manufacturing a nitride semiconductor substrate according to any one of appendices 1 to 6, preferably,
The off-angle distribution at the polar face of the plurality of seed crystal substrates is within 1 °.

[Appendix 8]
In the method for manufacturing a nitride semiconductor substrate according to any one of appendices 1 to 7, preferably,
When arranging the plurality of seed crystal substrates, a jig having an inclined surface inclined at the inclination angle is used.

[Appendix 9]
In the method for manufacturing a nitride semiconductor substrate according to any one of appendices 1 to 8, preferably,
The inclination angle when arranging the plurality of seed crystal substrates is an angle having an inclination of 62 to 65 ° with respect to the surface of the base,
The semipolar plane in the self-standing substrate is a {10-11} plane.

[Appendix 10]
In the method for manufacturing a nitride semiconductor substrate according to any one of appendices 1 to 8, preferably,
The angle of inclination when arranging the plurality of seed crystal substrates is an angle having an inclination of 43 to 46 ° with respect to the surface of the base,
The semipolar plane in the self-standing substrate is a {10-12} plane.

[Appendix 11]
In the method for manufacturing a nitride semiconductor substrate according to any one of appendices 1 to 8, preferably,
The inclination angle when arranging the plurality of seed crystal substrates is an angle having an inclination of 32 to 35 ° with respect to the surface of the base,
The semipolar plane in the self-standing substrate is a {10-13} plane.

[Appendix 12]
In the method for manufacturing a nitride semiconductor substrate according to any one of appendices 1 to 8, preferably,
The inclination angle when arranging the plurality of seed crystal substrates is an angle having an inclination of 75 to 78 ° with respect to the surface of the base;
The semipolar plane in the self-standing substrate is a {20-21} plane.

  DESCRIPTION OF SYMBOLS 10 ... Seed crystal substrate, 11 ... Main surface (polar surface, C surface), 11a ... + C surface, 11b ...- C surface, 12 ... Side surface (nonpolar surface, M surface), 14 ... GaN substrate, 15 ... Staircase shape 16, 16a, 16b ... placement jig, 20 ... GaN substrate (nitride semiconductor substrate), 21 ... main surface (semipolar surface), 22 ... GaN crystal layer, 23 ... just surface

Claims (5)

A first step of preparing a plurality of seed crystal substrates made of a nitride semiconductor single crystal, having a cross-sectional shape formed in a rectangular shape, and having at least a main surface of a polar surface and a side surface of a nonpolar surface;
The plurality of seed crystal substrates are arranged on a base in a state where the cross-sectional shape is inclined at a predetermined inclination angle so that the polar surfaces are in contact with each other and a part of one of the polar surfaces is exposed. And the second step which makes the side opposite to the base side a stepped shape by a part of the polar surface and the nonpolar surface,
A third step of growing a nitride semiconductor single crystal on the step shape to form a nitride semiconductor single crystal layer;
A fourth step of obtaining a nitride semiconductor free-standing substrate having a semipolar principal surface from the nitride semiconductor single crystal layer;
A method for manufacturing a nitride semiconductor substrate comprising: 2. The nitride semiconductor substrate according to claim 1, wherein the plurality of seed crystal substrates are obtained by cleaving a nitride semiconductor single crystal substrate whose main surface is the polar surface at the nonpolar surface to divide into a plurality of pieces. Production method. The method for manufacturing a nitride semiconductor substrate according to claim 1, wherein the polar face constituting the step shape is a {0001} plane. 4. The nitride semiconductor according to claim 3, wherein the inclination angle when the plurality of seed crystal substrates is arranged is set so that the stepped shape has a positional relationship having an inclination with respect to the just plane of the semipolar plane. 5. A method for manufacturing a substrate. The inclination angle when the plurality of seed crystal substrates are arranged is set so that the growth surface from the stepped polar surface continues to be exposed until the growth surface of the nitride semiconductor single crystal layer becomes flat. The method for manufacturing a nitride semiconductor substrate according to claim 3 or 4.