JP5644797B2 - Method for producing group III nitride semiconductor single crystal and method for producing GaN substrate - Google Patents

Description

  The present invention relates to a method for producing a group III nitride semiconductor single crystal and a method for producing a GaN substrate. More specifically, the present invention relates to a method for manufacturing a group III nitride semiconductor single crystal using a flux method and a method for manufacturing a GaN substrate.

  Semiconductor crystal fabrication methods include vapor phase growth methods such as metal organic chemical vapor deposition (MOCVD) and hydride vapor phase epitaxy (HVPE), molecular beam epitaxy (MBE), and liquid phase epitaxy. is there. The liquid phase epitaxy method includes a flux method using Na flux.

  In the flux method, before the GaN single crystal grows, part or all of the underlying layer (GaN or AlN) that becomes a seed crystal may disappear during the temperature rise of the flux. This phenomenon is called meltback. For example, Patent Document 1 discloses a technique for slightly growing a single crystal by maintaining the flux temperature at a temperature lower than the growth temperature of the single crystal to be grown (paragraph [0010] of Patent Document 1). ]). As a result, disappearance of the underlying layer is suppressed.

JP 2006-131454 A

By the way, when a GaN single crystal is grown on the underlayer by the flux method, the crystallinity of the GaN single crystal is the same as the crystallinity of the underlayer. That is, the dislocation density of the single crystal to be grown also inherits the dislocation density of the underlayer. A similar problem occurs in the case of Patent Document 1. In this case, the dislocation density is about 1 × 10 ⁶ / cm ² .

The smaller the dislocation density of such a GaN single crystal, the better. For example, the dislocation density is preferably 1 × 10 ⁵ / cm ² or less. Thus, in order to obtain a GaN single crystal having a smaller dislocation density value, it is necessary to significantly reduce the dislocation density during the growth of the GaN single crystal.

  On the other hand, when the GaN single crystal is grown using the flux method, the underlayer is subjected to meltback. The underlayer that has undergone meltback is often not flat and has irregularities. Then, due to the subsequent growth of the semiconductor single crystal, a part of the dislocation is bent and the dislocation extending from the uneven shape is reduced. Although this meltback reduces some of the dislocations, it is not sufficient. Since this meltback occurs non-uniformly, it is difficult to make the entire wafer low dislocation.

  It is further preferable that the semiconductor single crystal can be easily removed from the growth substrate. For example, it is suitable when a GaN single crystal having a low dislocation density is formed as a semiconductor single crystal and the GaN single crystal is used as a GaN substrate. Therefore, it is preferable to form a semiconductor single crystal that easily peels from the growth substrate.

  The present invention has been made to solve the above-described problems of the prior art. That is, the problem is that the growth substrate can be easily peeled and a Group III nitride semiconductor single crystal having excellent crystallinity can be produced, and a method for producing a Group III nitride semiconductor single crystal and a GaN substrate. Is to provide a method.

The method for producing a group III nitride semiconductor single crystal according to the first aspect is a method for producing a group III nitride semiconductor single crystal in which a group III nitride semiconductor single crystal is grown using a flux. Then, a mask layer forming step of forming a mask layer made of Al _x In _Y Ga _(1-XY) N (0 <X, 0 ≦ Y, X + Y ≦ 1) containing Al on the underlayer, and the mask layer Forming a recessed portion where the underlying layer is exposed at a plurality of locations by removing all of the thickness of the substrate and a part of the thickness of the underlying layer, and the group III nitride semiconductor single crystal does not cover the surface of the recessed portion As described above, the semiconductor single crystal forming step for growing the group III nitride semiconductor single crystal and the semiconductor single crystal separation step for peeling the group III nitride semiconductor single crystal from the underlayer are included. Then, in the semiconductor single crystal forming step, the ground layer exposed in the recess is melt-backed by the flux to widen the recess to expose the slope, and the amorphous portion filled with the flux component is formed in the recess. Then, a group III nitride semiconductor single crystal is grown from the surface of the mask layer to form a group III nitride semiconductor single crystal on the surface of the mask layer and on the amorphous portion.

  In this method for producing a group III nitride semiconductor single crystal, as the temperature in the crucible is raised, the underlying layer dissolves in the flux from the formed recess. Thereby, a recessed part spreads. Then, a group III nitride semiconductor single crystal is formed starting from the seed crystal on the surface of the mask layer. On the other hand, a cavity is formed at a location that was a recess. The term “cavity” as used herein means a portion where a semiconductor crystal does not grow (non-crystalline portion), and does not necessarily mean that a gas such as air is contained inside. Actually, flux is contained inside the cavity. Because of this non-crystalline portion, dislocation from the base layer is not inherited in the semiconductor single crystal to be formed. And the peeling strength between an amorphous part and a semiconductor single crystal is weak. Therefore, it is easy to separate the semiconductor single crystal from the growth substrate.

  In the method for producing a Group III nitride semiconductor single crystal according to the second aspect, in the semiconductor single crystal forming step, the (1,0, -1,1) plane of the underlayer is exposed by meltback, and then the Group III A nitride semiconductor single crystal is grown.

In the Group III nitride semiconductor single crystal manufacturing method according to the third aspect, an AlGaN layer is formed as a mask layer in the mask layer forming step. This is because the AlGaN layer is not only hardly dissolved in the flux, but also a high-quality single crystal can be grown.

In the method for producing a group III nitride semiconductor single crystal according to the fourth aspect, in the mask layer forming step, the Al composition ratio X in the mask layer is set in the range of 0.02 to 1.00. Within this range, the mask layer is difficult to dissolve in the flux.

In the method for producing a group III nitride semiconductor single crystal according to the fifth aspect, in the mask layer forming step, the Al composition ratio X in the mask layer is set in the range of 0.03 to 0.50. When it is within this range, a single crystal grown thereon can be formed with high quality.

In the method for producing a group III nitride semiconductor single crystal according to the sixth aspect , the c-plane of the underlayer is not exposed by meltback in the semiconductor single crystal formation step. This is also because the semiconductor single crystal can be prevented from covering the recess.

In the method for producing a group III nitride semiconductor single crystal according to the seventh aspect , the thickness of the mask layer is set in the range of 2 nm to 2 μm. Within this range, the mask layer is more difficult to dissolve in the flux, and the single crystal can be grown with high quality.

In the method for producing a group III nitride semiconductor single crystal according to the eighth aspect , a flux having a carbon (C) concentration in the range of 0.01 mol / l or more and 2 mol / l or less is used. Within this range, the solubility of the carbon in the flux increases, so the dissolution of the underlayer is promoted.

In the method for manufacturing a group III nitride semiconductor single crystal according to the ninth aspect, in the recess forming step, a recess having an opening width in the range of 1 μm to 500 μm is formed. This is because a concavo-convex shape having an appropriate size is formed on the underlayer at this time.

In the method for producing a group III nitride semiconductor single crystal according to the tenth aspect , the plurality of recesses are arranged in a lattice pattern on the surface of the mask layer. Therefore, the concave surface which consists of a hexagonal pyramid or the complex of a hexagonal pyramid is formed from the recessed part arrange | positioned at a grid | lattice form by meltback.

In the method for producing a group III nitride semiconductor single crystal according to the eleventh aspect , the plurality of recesses are arranged in stripes. Since the growth rate in the a-axis direction is high, more dislocations can be bent.

In the group III nitride semiconductor single crystal manufacturing method according to the twelfth aspect, the base layer forming step of forming a GaN layer as the base layer is provided before the mask layer forming step. The base layer can be dissolved by the melt back.

In the method for producing a group III nitride semiconductor single crystal according to the thirteenth aspect , the underlayer is a GaN substrate. In this case, the GaN substrate is dissolved by meltback. Then, the recess erodes to the GaN substrate.

In the group III nitride semiconductor single crystal manufacturing method according to the fourteenth aspect , the underlying layer is a GaN layer formed on a sapphire substrate. In this case, the GaN layer formed on the sapphire substrate is dissolved.

The method for producing a GaN substrate in the fifteenth aspect is a method for growing a GaN single crystal on a growth substrate using a flux. Then, a mask layer forming step of forming a mask layer made of Al _x In _Y Ga _(1-XY) N (0 <X, 0 ≦ Y, X + Y ≦ 1) containing Al on the underlayer, and the mask layer Removing the entire thickness of the substrate and a part of the thickness of the underlying layer, forming a recessed portion where the underlying layer is exposed at a plurality of locations, and a GaN single crystal so that the GaN single crystal does not cover the surface of the recessed portion. A semiconductor single crystal forming step for growing a crystal, and a semiconductor single crystal separating step for peeling the GaN single crystal from the underlayer. Then, in the semiconductor single crystal forming step, the ground layer exposed in the recess is melt-backed by the flux to widen the recess to expose the slope, and the amorphous portion filled with the flux component is formed in the recess. Then, a GaN single crystal is grown from the surface of the mask layer to form a GaN single crystal on the surface of the mask layer and on the amorphous portion.

  In this GaN substrate manufacturing method, as the temperature in the crucible is raised, the underlying layer dissolves in the flux from the formed recess. Thereby, a recessed part spreads. Then, a GaN single crystal is formed using the seed crystal on the surface of the mask layer as a base point. On the other hand, a cavity is formed at a location that was a recess. The term “cavity” as used herein means a portion where a semiconductor crystal does not grow (non-crystalline portion), and does not necessarily mean that a gas such as air is contained inside. Actually, flux is contained inside the cavity. Since there is this non-crystalline portion, dislocation from the base layer does not propagate to the semiconductor single crystal to be formed. The non-crystalline portion reduces the contact area between the base layer and the single crystal portion, and stress concentrates in the vicinity of the mask layer. Therefore, the semiconductor single crystal can be easily separated from the growth substrate.

  According to the present invention, a method for producing a group III nitride semiconductor single crystal and a method for producing a GaN substrate capable of producing a group III nitride semiconductor single crystal that is easy to peel off a growth substrate and excellent in crystallinity are provided. Is provided.

FIG. 6 is a view (No. 1) for describing the method for producing the group III nitride semiconductor single crystal according to the first embodiment. FIG. 6 is a view (No. 2) for explaining the method for producing the group III nitride semiconductor single crystal according to the first embodiment. FIG. 6 is a view (No. 3) for explaining the method for manufacturing the group III nitride semiconductor single crystal according to the first embodiment. FIG. 6 is a view (No. 4) for explaining the method for manufacturing the group III nitride semiconductor single crystal according to the first embodiment. FIG. 5 is a view (No. 5) for explaining the method for producing the group III nitride semiconductor single crystal according to the first embodiment. FIG. 6 is a view (No. 6) for explaining the method for manufacturing the group III nitride semiconductor single crystal according to the first embodiment. FIG. 7 is a view (No. 7) for explaining the method for producing the group III nitride semiconductor single crystal according to the first embodiment. It is FIG. (1) for demonstrating the manufacturing method of the group III nitride semiconductor single crystal which concerns on 2nd Embodiment. It is FIG. (2) for demonstrating the manufacturing method of the group III nitride semiconductor single crystal which concerns on 2nd Embodiment. It is FIG. (3) for demonstrating the manufacturing method of the group III nitride semiconductor single crystal which concerns on 2nd Embodiment. It is FIG. (4) for demonstrating the manufacturing method of the group III nitride semiconductor single crystal which concerns on 2nd Embodiment. It is a figure for demonstrating the manufacturing method of the group III nitride semiconductor single crystal which concerns on 3rd Embodiment.

  Hereinafter, specific embodiments will be described with reference to the drawings. However, these are examples and are not limited to these embodiments. And the thickness of each layer in each figure is shown conceptually and does not indicate the actual thickness.

  In the following embodiments, a mask layer that hardly causes meltback and a recess that mainly causes meltback are formed. And while exposing the exposed part of a recessed part, a recessed part is made into an amorphous part by growing a semiconductor single crystal from a mask layer to a horizontal direction. This prevents dislocation from the underlying layer from being taken over and facilitates separation from the growth substrate.

(First embodiment)
A first embodiment will be described. In the present embodiment, a group III nitride semiconductor single crystal is manufactured on a GaN substrate using a flux method.

1. Method for Producing Group III Nitride Semiconductor Single Crystal The method for producing a group III nitride semiconductor single crystal of the present embodiment includes the following steps.
(C) Mask layer forming step (D) Recessed portion forming step (E) Semiconductor single crystal forming step Accordingly, these steps will be described below in order.

1-1. (C) Mask layer forming step First, a GaN substrate G10 is prepared. The GaN substrate G10 is a GaN free-standing substrate. The dislocation density is about 5 × 10 ⁶ / cm ² . The GaN substrate G10 is also a base layer for forming a mask layer. Then, a mask layer 140 is formed on the GaN substrate G10. This mask layer 140 is a layer that is hardly subjected to meltback due to the flux supplied in the subsequent semiconductor single crystal formation step, or has a much slower etching rate than the underlayer. Thereby, the laminated body B11 as shown in FIG. 1 is obtained.

Here, the composition of the mask layer 140 is Al _X In _Y Ga _(1-XY) N (0 <X, 0 ≦ Y, X + Y ≦ 1). The mask layer 140 is preferably an AlGaN layer. The Al composition ratio X in the mask layer 140 is preferably 0.02 or more and 1.0 or less. In particular, as shown in Table 1, the Al composition ratio X in the mask layer 140 is preferably in the range of 0.03 to 0.50. When the Al composition ratio X is less than 0.03, the effect of meltback by the flux is large. If the Al composition ratio X is greater than 0.50, the crystal quality of the GaN crystal grown in the semiconductor single crystal formation step described later will be poor.

  And as shown in Table 1, the thickness of the mask layer 140 should just be in the range of 2 nm or more and 2 micrometers or less. When the thickness of the mask layer 140 is less than 2 nm, the effect of meltback described later is not sufficient. On the other hand, when the thickness of the mask layer 140 exceeds 2 μm, the crystal quality of the GaN crystal grown in the semiconductor single crystal formation step described later becomes poor.

[Table 1]
Al composition ratio of mask layer 0.03 or more and 0.50 or less Mask layer thickness 2 nm or more and 2 μm or less

1-2. (D) Concave formation step 1-2-1. Procedure for forming recesses Next, a plurality of recesses are formed in the laminate B11. As shown in FIG. 2, the entire thickness of the mask layer 140 and a part of the thickness of the GaN substrate G10 are removed, and the exposed recesses X11 of the GaN substrate G10 are formed at a plurality of locations. Thereby, as shown in FIG. 2, the seed crystal T10 in which the plurality of concave portions X11 are formed is manufactured. For example, photolithography may be used to form the recess X11. First, resist patterning is performed. Next, a plurality of recesses X11 are formed by removing the entire thickness of the mask layer 140 and a part of the thickness of the GaN substrate G10 by dry etching. At this time, the mask layer 140 after forming the concave portion X11 is a mask portion that covers the base layer. Then, the resist mask is removed. Thereby, the seed crystal T10 shown in FIG. 2 is obtained. Thereafter, the seed crystal T10 in which the plurality of concave portions X11 are formed is washed.

1-2-2. Seed Crystal Formed with Recesses As shown in FIG. 2, the recesses X <b> 11 are arranged on the mask layer 140 surface at regular intervals in a lattice shape. However, it does not necessarily have to be equally spaced. In FIG. 2, when the seed crystal T10 is viewed from the mask layer 140 side, the shape of the recess X11 is a square. However, the planar shape of the recess X11 is not limited to a square. It may be a polygon such as a hexagon. Further, it may be circular. Further, the shape is not limited to a symmetric shape with respect to the center point, and may be an asymmetric shape.

  FIG. 3 is a cross-sectional view showing the AA cross section of FIG. The recess X11 is a non-through hole that penetrates the mask layer 140 and covers a part of the thickness of the GaN substrate G10. The thickness of the mask layer 140 is in the range of 2 nm or more and 2 μm or less, but the depth D1 of the recess X11 is larger than the thickness of the mask layer 140. The depth D1 of the recess X11 is in the range of 1 μm to 5 μm. However, the formation of the recess X11 requires that a part of the GaN substrate G10, which is a GaN layer, is exposed on the bottom surface of the recess X11.

  And the width | variety (opening width) W1 of the opening part of the recessed part X11 exists in the range of 1 micrometer or more and 500 micrometers or less. Furthermore, the opening width W1 is more preferably in the range of 20 μm to 100 μm. If it is smaller than 1 μm, the depth of the meltback is not sufficient. This is because if the (1, 0, -1, 1) plane appears due to the meltback, the meltback does not proceed any further. If it is larger than 500 μm, it becomes difficult to control the meltback, and a uniform interface cannot be formed.

  And the space | interval W2 between the recessed part X11 and the adjacent recessed part X11 exists in the range of 2 micrometers or more and 500 micrometers or less. The interval W2 is more preferably in the range of 20 μm or more and 100 μm or less. When the interval W2 is less than 2 μm, the mask layer may be melted back by side etching. In that case, the area of the surface 142 to be the base point of the lateral growth of the semiconductor layer grown in the semiconductor single crystal formation step described later becomes non-uniform, and a semiconductor crystal with high crystallinity cannot be obtained.

  The recess X11 has a bottom surface G12 and side surfaces G11, 141. The bottom surface G12 is a part of the GaN substrate G10. The side surfaces G11 and 141 are substantially perpendicular to the surface 142 of the mask layer 140. The side surfaces G11 and 141 are formed over the GaN substrate G10 and the mask layer 140.

1-3. (E) Semiconductor Single Crystal Formation Step Next, a semiconductor single crystal layer is grown on the seed crystal T10 using a flux method which is a kind of liquid phase epitaxy method. The raw materials used here are shown in Table 2. Here, the Ga ratio is preferably 30% or less. Moreover, you may change carbon ratio within the range of 0 mol% or more and 2.0 mol% or less. That is, the flux may or may not contain carbon, but is more preferably in the range of 0.01 mol% or more and 2.0 mol% or less. The values in Table 2 are merely examples, and other values may be used.

  This semiconductor single crystal is, of course, a group III nitride semiconductor single crystal. For example, any of GaN, AlGaN, InGaN, AlInGaN, and the like may be used. First, the seed crystal T10 and the raw materials shown in Table 2 are weighed in a glove box in which the dew point and the oxygen concentration are controlled. Note that these are examples, and different values may be used. Next, the seed crystal T10 and the raw material are put into an alumina crucible. And the crucible is put in the inside of the inner container made from SUS. Then, the inner container is placed on the turntable inside the pressure container. Then, after the pressure vessel is evacuated, the pressure is increased and the temperature is increased.

[Table 2]
Ga 20g-80g
Na 20g-80g
C 0.1 mol% to 2.0 mol% (relative to Na)

  Here, Table 3 shows the conditions in the crucible used in the semiconductor single crystal formation step. The temperature is 870 ° C. The pressure is 3 MPa. Stirring is performed at 20 rpm. At that time, the rotation direction of the stirring member is appropriately reversed. The breeding time is 30 hours.

[Table 3]
Temperature 850 ° C-900 ° C
Pressure 3MPa-10MPa
Stirring conditions 0rpm ~ 100rpm
Training time 20-200 hours

  In this semiconductor single crystal formation step, the GaN substrate G10 exposed as the inner surface of the recess X11 is dissolved by meltback. Specifically, the bottom surface G12 and the side surface G11 are dissolved in the flux. On the other hand, the mask layer 140 is difficult to dissolve in the flux. However, since the GaN substrate G10 which is the base layer of the mask layer 140 is melted, the mask layer 140 is also slowly melted from the lateral direction. Thereby, the recessed part X11 becomes large. Specifically, it becomes deep in the vertical direction and slightly spreads in the horizontal direction. And as shown in FIG. 4, seed crystal T11 in which the hexagonal recessed part X12 was formed is manufactured. Here, the a-axis is perpendicular to the BB cross section. The m-axis is parallel to the BB cross section.

  FIG. 5 is a cross-sectional view showing a BB cross section in FIG. 4. The recess X12 has a slope G13 and a side surface 143. In the recess X12, the c-plane of the GaN substrate G10 is not exposed. The inclined surface G13 is inclined in such a direction that the opening width W3 increases as it approaches the surface 144. The slope G13 is a surface close to the (1, 0, -1, 1) surface. The side surface 143 is a side surface of the mask layer 140.

  As shown in FIG. 6, the GaN layer 150 grows after the flux is saturated by meltback and pressurization. This growth occurs after the slope G13 is exposed. Specifically, the GaN layer 150 grows using the seed crystal on the surface 144 of the mask layer 140 as a base point. Here, the GaN layer 150 grows from the surface 144 of the mask layer 140 in the lateral and upward directions in FIG. Here, the surface of the underlayer is formed with substantially (1, 0, -1, 1) plane. Nitrogen (N) is difficult to be supplied downward. For these reasons, no single crystal is formed in the recess X12, and the recess X12 becomes a cavity. Thus, the GaN layer 150 is grown by flux so that the GaN substrate G10 exposed in the recess X11 is melted back and the recess X12 is not covered.

2. 1. Group III nitride semiconductor single crystal produced 2-1. GaN Single Crystal As described in detail above, the GaN single crystal B12 is obtained as shown in FIG. 6 by the group III nitride semiconductor single crystal manufacturing method of the present embodiment. The GaN single crystal B12 has a GaN substrate G10, a mask layer 140, a GaN layer 150, and an amorphous part X13.

  The amorphous part X13 is a place where a semiconductor single crystal is not formed. And the non-crystal part X13 is a hollow part. In practice, however, the cavity is filled with a flux component. The amorphous portion X13 is surrounded by the slope G13 ((1, 0, -1, 1) plane) of the GaN substrate G10 and a part 152 of the bottom surface 151 of the GaN layer 150.

  The cross section of the GaN substrate G10, which is the base layer, has a concavo-convex shape in which concave and convex surfaces are alternately repeated. The slope G13 ((1, 0, -1, 1) plane) is exposed in the concave and convex portions. The slope G13 is a hexagonal pyramid-shaped concave surface. On the other hand, the c-plane (convex surface G15) is also exposed at the uneven convex portion. The mask layer 140 is disposed on the convex surface G15 of the GaN substrate G10 that is the underlayer.

2-2. Single Crystal Shape The GaN layer 150 is in contact with the mask layer 140 or the amorphous portion X13 at the bottom surface 151. A part 152 of the bottom surface 151 of the GaN layer 150 is in contact with the amorphous portion X13. Here, the shape of the part 152 of the bottom surface 151 in contact with the non-crystal part X13 is substantially hexagonal. The remaining part 153 of the bottom surface 151 of the GaN layer 150 is in contact with the mask layer 140. Note that the bottom surface 151 of the GaN layer 150 is flat. In addition, as will be described in an example described later, the film thickness of the GaN layer 150 can be set to about 1 mm.

2-3. Dislocation density of single crystal The GaN single crystal B12 of this embodiment has an amorphous part X13. Therefore, when the GaN layer 150 is grown from the GaN substrate G10, dislocations do not extend from a part 152 of the bottom surface 151 of the GaN layer 150. That is, some of the dislocations from the underlayer are not inherited. However, dislocations from the mask layer 140 are inherited. Thus, since part of dislocations from the underlayer is not inherited, the crystallinity of the GaN layer 150 is good. Specifically, the dislocation density value of the GaN layer 150 is 1 × 10 ⁴ / cm ² or less. Further, in this GaN layer 150, the dislocation density is uniform over the entire surface. This is because the plurality of formed recesses X11 are regularly arranged.

2-4. Single Crystal Separation In the GaN single crystal B12 of the present embodiment, the GaN layer 150 can be easily separated from the GaN substrate G10. This is because the stress due to the warp of the seed crystal is concentrated on the boundary surface between the seed crystal and the single crystal. It may peel off naturally when the temperature drops during growth. Moreover, it can also be made to peel by applying a light impact after completion | finish of cultivation. FIG. 7 shows the GaN layer 150 and seed crystal T11 after separation. Thus, the GaN layer 150 and the GaN substrate G10 are easy to peel off. This is because there is an amorphous part X13 between the growth substrate and the GaN layer 150.

  In this way, by forming a portion that is easy to melt back and a portion that is not so intended to block dislocations, it is possible to produce a group III nitride semiconductor single crystal that has excellent crystallinity and is easy to peel from the growth substrate it can.

3. Meltback control Meltback continues until the nitrogen concentration in the flux is saturated. Therefore, the degree of meltback can be controlled by changing the conditions shown in Table 4. By changing these conditions, the GaN layer 150 can be formed so as not to cover the recess X12. These conditions are the same in other embodiments described later.

[Table 4]
Temperature Solution composition ratio (Ga / Na)
Nitrogen pressure Time Carbon concentration

4). Modified example 4-1. Group III nitride semiconductor single crystal In the present embodiment, the GaN layer 150 is formed. However, it can also be applied to the production of other Group III nitride semiconductor single crystals. That is, it is possible to manufacture the _{Al X In Y Ga (1-} XY) N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1).

5. Summary As described in detail above, in the method for producing a group III nitride semiconductor single crystal of the present embodiment, the seed crystal T10 used in the flux method is one in which the recess X11 is formed. In this way, the GaN substrate G10 that mainly receives meltback and the mask layer 140 that hardly receives meltback are formed. Therefore, no single crystal is formed in the recess X12, and an amorphous portion X13 is formed in the recess X12. Dislocations are not inherited in the GaN layer 150 above the amorphous part X13. That is, the dislocation density of the formed GaN single crystal is sufficiently low. Therefore, a group III nitride semiconductor single crystal having excellent crystallinity can be formed.

  This embodiment is merely an example. Therefore, naturally, various improvements and modifications can be made without departing from the scope of the invention. The number of recesses formed in the seed crystal is actually larger than that shown in the figure.

(Second Embodiment)
A second embodiment will be described. In this embodiment, a GaN template formed on a sapphire substrate is used as the growth substrate. The other points are the same as in the first embodiment. Therefore, differences from the first embodiment will be described.

1. Method for Producing Group III Nitride Semiconductor Single Crystal The method for producing a group III nitride semiconductor single crystal of the present embodiment includes the following steps.
(A) Low-temperature buffer layer forming step (B) Underlayer forming step (C) Mask layer forming step (D) Recessed portion forming step (E) Semiconductor single crystal forming step Accordingly, these steps will be described below in order.

1-1. (A) Low temperature buffer layer formation process First, the low temperature buffer layer 320 is formed in the sapphire substrate S30 which is a growth substrate (refer FIG. 8). The sapphire substrate S30 is c-plane sapphire. Then, the low temperature buffer layer 320 is epitaxially grown on the sapphire substrate S30. Examples of epitaxial growth methods include metal organic vapor phase epitaxy (MOCVD), hydride vapor phase epitaxy (HVPE), molecular beam epitaxy (MBE), and liquid phase epitaxy. Any of these may be used. The low temperature buffer layer 320 is a layer made of GaN. Alternatively, it may be a layer made of AlN.

1-2. (B) Underlayer Formation Step Next, a GaN layer 330 is formed on the low temperature buffer layer 320 (see FIG. 8). The GaN layer 330 is a base layer. Here, the thickness of the GaN layer 330 is preferably in the range of 1.5 μm to 20 μm. In this underlayer forming step, any one of metal organic vapor phase epitaxy (MOCVD), hydride vapor phase epitaxy (HVPE), molecular beam epitaxy (MBE), and liquid phase epitaxy is used. May be used.

1-3. (C) Mask Layer Formation Step Then, a mask layer 340 is formed on the GaN layer 330 (see FIG. 8). The Al composition ratio and thickness of the mask layer 340 formed here may be the same as those shown in Table 1.

1-4. (D) Concave formation step Next, the concavity X31 is formed by photolithography. Thereby, seed crystal T30 as shown in FIG. 8 is manufactured. The recess X31 is the same as the recess X11 of the first embodiment (see FIG. 3). Here, the recess X31 is a non-through hole that penetrates the mask layer 340 and covers a part of the thickness of the GaN layer 330. The opening width W7 of the opening of the recess X31 is the same as the width W1 of the first embodiment (see FIG. 3). The depth D4 of the recess X31 is the same as the depth D1 of the first embodiment (see FIG. 3). An interval W8 between the recess X31 and the adjacent recess X31 is the same as the interval W2 of the first embodiment (see FIG. 3). Of course, different values may be used.

1-5. (E) Semiconductor Single Crystal Formation Step Next, a semiconductor single crystal layer is grown on the seed crystal T30 by a flux method which is a kind of liquid phase epitaxy method. The raw materials used here may be those shown in Table 2. The conditions used in the flux method may be those shown in Table 3.

  The GaN layer 330 is dissolved from the exposed portion by the meltback. Therefore, the recess X31 becomes deep and slightly expands in the lateral direction. Therefore, the recessed part X31 spreads and the recessed part X32 is formed as shown in FIG. The recess X32 is surrounded by the bottom surface S34, the slope 333, and the side surface 343. The bottom surface S34 is the c-plane of the sapphire substrate S30. That is, the c-plane of the sapphire substrate S30 is exposed. Here, the slope 333 is a (1, 0, -1, 1) plane.

After the flux is saturated by the meltback, the GaN layer 350 is grown with the seed crystal on the surface 344 of the mask layer 340 as a base point. In addition, GaN is not formed inside the recess X32 . Then, the GaN layer 350 grows from the upper part of the mask layer 340 in the lateral direction and the upward direction in FIG. Here, the GaN layer 350 is formed so as not to cover the recess X32. Therefore, GaN is not formed inside the recess X32. And the recessed part X32 turns into the amorphous part X33.

2. 1. Group III nitride semiconductor single crystal produced 2-1. GaN Single Crystal As described in detail above, the GaN single crystal B32 is obtained as shown in FIG. 10 by the method for producing a group III nitride semiconductor single crystal of this embodiment. The GaN single crystal B32 includes a sapphire substrate S30, a low-temperature buffer layer 320, a GaN layer 330, a mask layer 340, a GaN layer 350, and an amorphous part X33.

  The amorphous part X33 is a place where a semiconductor single crystal is not formed. And the non-crystal part X33 is a hollow part. In practice, however, the cavity is filled with flux. The amorphous portion X33 is surrounded by the slope 333 ((1, 0, -1, 1) plane) of the GaN layer 330, the bottom surface S34, the side surface 343, and a part 352 of the bottom surface 351 of the GaN layer 350. .

  The cross section of the GaN layer 330 that is the base layer has an uneven shape in which concave and convex surfaces are alternately repeated. A slope 333 ((1, 0, -1, 1) plane) is exposed in the concave and convex portions. The slope 333 is a hexagonal pyramid-shaped concave surface. On the other hand, the c-plane (convex surface 335) is also exposed at the uneven convex portion. The mask layer 340 is disposed on the convex surface 335 of the GaN layer 330 that is a base layer.

2-2. Single Crystal Shape The GaN layer 350 is in contact with the mask layer 340 or the non-crystal part X33 at the bottom surface 351. A part 352 of the bottom surface 351 of the GaN layer 350 is in contact with the amorphous part X33. Here, the shape of the part 352 of the bottom surface 351 in contact with the non-crystal part X33 is a hexagon. The remaining part 353 of the bottom surface 351 of the GaN layer 350 is in contact with the mask layer 340. Note that the bottom surface 351 of the GaN layer 350 is flat. In addition, as will be described in an example described later, the film thickness of the GaN layer 350 can be set to about 1 mm.

2-3. Dislocation density of single crystal The GaN single crystal B32 of the present embodiment has an amorphous part X33. Therefore, when the GaN layer 350 is grown from the sapphire substrate S30, dislocations do not extend from a part 352 of the bottom surface 351 of the GaN layer 350. That is, some of the dislocations from the underlayer are not inherited. However, dislocations from the mask layer 340 are inherited. Thus, since part of dislocations from the underlayer is not inherited, the crystallinity of the GaN layer 350 is good. The value of the dislocation density of the GaN layer 350 is 1 × 10 ⁴ / cm ² or less. Further, in this GaN layer 350, the dislocation density is uniform over the entire surface. This is because the plurality of formed recesses X31 are regularly arranged.

2-4. Single Crystal Separation In the GaN single crystal B32 of this embodiment, the GaN layer 350 can be easily separated from the sapphire substrate S30. This is because the stress due to the warp of the seed crystal is concentrated on the boundary surface between the seed crystal and the single crystal. It may peel off naturally when the temperature drops during growth. Moreover, it can also be made to peel by applying a light impact after completion | finish of cultivation. FIG. 11 shows the separated GaN layer 350 and seed crystal T31. Thus, the GaN layer 350 and the sapphire substrate S30 are easy to peel off. This is because there is an amorphous part X33 between the growth substrate and the GaN layer 350.

  In this way, by forming a portion that is easy to melt back and a portion that is not so intended to block dislocations, it is possible to produce a group III nitride semiconductor single crystal that has excellent crystallinity and is easy to peel from the growth substrate it can.

3. Modification 3-1. Group III nitride semiconductor single crystal In the present embodiment, the GaN layer 350 is formed. However, it can also be applied to the production of other Group III nitride semiconductor single crystals. That is, it is possible to manufacture the _{Al X In Y Ga (1-} XY) N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1).

4). Summary As described in detail above, in the method for producing a group III nitride semiconductor single crystal of the present embodiment, the seed crystal T30 used in the flux method is one in which the recess X31 is formed. Thus, the GaN layer 330 that mainly receives meltback and the mask layer 340 that hardly receives meltback are formed. Therefore, no single crystal is formed in the recess X32, and an amorphous part X33 is formed at the location of the recess X32. Dislocations are not inherited in the GaN layer 350 above the amorphous part X33. That is, the dislocation density of the formed GaN single crystal is sufficiently low. Therefore, a group III nitride semiconductor single crystal having excellent crystallinity can be formed.

  This embodiment is merely an example. Therefore, naturally, various improvements and modifications can be made without departing from the scope of the invention. The number of recesses formed in the seed crystal is actually more.

(Third embodiment)
A third embodiment will be described. In 3rd Embodiment, as shown in FIG. 12, the recessed part X41 is arrange | positioned at stripe form. The side surface 430 of the recess X41 is the a-plane of the GaN layer. That is, the a-plane of the GaN layer is exposed on the inner side surface of the recess X41. In this case, since the growth rate of GaN on the a-plane is fast, it is easily flattened. In FIG. 12, the opening width is indicated by W9. The interval is indicated by W10.

  Even in this case, an amorphous part is formed, and the dislocations of the formed group III nitride semiconductor single crystal are reduced. That is, a group III nitride semiconductor single crystal having excellent crystallinity can be formed.

(Fourth embodiment)
A fourth embodiment will be described. In the fourth embodiment, the GaN single crystal manufactured by the Group III nitride semiconductor single crystal manufacturing method described in the first to third embodiments is removed from the growth substrate, and The present invention relates to a method for manufacturing a GaN substrate.

1. Semiconductor Single Crystal Separation Step As described above, in the GaN single crystal in which the amorphous portions X13 and X33 are formed, the GaN layers 150 and 350 are easily separated from the growth substrate. This is because the adhesion strength with the underlayer is low because of the non-crystal parts X13 and X33. Therefore, as shown in FIGS. 7 and 11, the GaN single crystal and the growth substrate are separated. Moreover, you may utilize heating cooling using the difference of an expansion coefficient.

  Actually, a part of the mask layers 140 and 340 and the non-crystal parts X13 and X33 may remain attached to the GaN single crystal. Even in that case, there is no problem if the bottom surfaces 151 and 351 are cut.

2. Summary As described above in detail, the method for manufacturing a GaN substrate according to the present embodiment removes the GaN single crystal formed in the first to third embodiments from the growth substrate to form a GaN free-standing substrate. Is the method.

  Example 1 will be described. In this example, a sapphire substrate S30 was used as in the second embodiment. A sapphire substrate S30 having a diameter of 2 inches (50.8 mm) was used. Then, the MOCVD method was used to produce the seed crystal T10.

The carrier gas used here is hydrogen (H ₂ ), nitrogen (N ₂ ), or a mixed gas of hydrogen and nitrogen (H ₂ + N ₂ ). Ammonia gas (NH ₃ ) was used as a nitrogen source. Trimethylgallium (Ga (CH ₃ ) ₃ : hereinafter referred to as “TMG”) was used as the Ga source. Trimethylaluminum (Al (CH ₃ ) ₃ : hereinafter referred to as “TMA”) was used as the Al source.

  First, a layer made of GaN was formed as the low temperature buffer layer 120. Next, a GaN layer 130 was formed on the low temperature buffer layer 120. The thickness of this GaN layer is 8 μm. Next, an AlGaN layer 140 was formed on the GaN layer 130. The Al composition ratio in the AlGaN layer 140 was 0.1. The thickness of the AlGaN layer 140 is 100 nm.

  Subsequently, the recess X11 was formed by photolithography. The depth D1 of the recess X11 was 1 μm. The width W1 of the recess X11 was 20 μm. The interval W2 between the adjacent recesses X11 was 20 μm. Thereby, seed crystal T10 was created.

  Next, the seed crystal 10 was put together with the raw materials into the crucible. The material was 30 g of Ga, 30 g of N, and 80 mg of C. The carbon ratio in the flux at this time was 0.5 mol%. The temperature inside the crucible was set to 890 ° C. The pressure inside the crucible was 3 MPa. In order to grow crystals, the stirring member was stirred at 20 rpm while appropriately inverting the raw materials. The breeding time was 30 hours.

As a result, a GaN crystal having a thickness of 0.9 mm was obtained. It was confirmed by SEM that the cavity X13 was formed. The sapphire substrate S30 and the GaN crystal were separated when the temperature was lowered after the growth. The dislocation density of the obtained single crystal was 1 × 10 ⁴ / cm ² or less.

  Example 2 will be described. The conditions of the experiment performed in Example 2 are almost the same as the conditions of Example 1. The difference from Example 1 is that a GaN substrate having a diameter of 4 inches (101.6 mm) was used as in the first embodiment.

  As a result, a GaN crystal having a thickness of 1.5 mm was obtained. The temperature inside the crucible was cooled at a rate of 1 ° C./min. In addition, the GaN crystal naturally separated from the sapphire substrate S30.

320 ... low temperature buffer layer 330 ... GaN layer (underlayer)
140, 340 ... AlGaN layers 141, 143, 331, 341, 343 ... side surfaces 142, 144, 342, 344 ... surface 332 ... bottom surface 333 ... slope 150, 350 ... GaN layer 151 ... bottom surface 152 ... part 153 ... remaining G10 ... GaN substrate G11 ... side G12 ... bottom G13 ... slope S30 ... sapphire substrate S34 ... bottom T10, T11, T30, T31 ... seed crystals W1, W3, W7, W9 ... opening widths W2, W4, W8, W10 ... intervals D1, D2 , D4: Depth X11, X12, X31, X32, X41 ... Recess X13, X33 ... Non-crystalline part

Claims (15)

In a method for producing a group III nitride semiconductor single crystal using a flux to grow a group III nitride semiconductor single crystal,
A mask layer forming step of forming a mask layer made of Al _X In _Y Ga _(1-XY) N (0 <X, 0 ≦ Y, X + Y ≦ 1) containing Al on the underlayer;
A recess forming step of forming the exposed recesses of the base layer at a plurality of locations by removing the entire thickness of the mask layer and a part of the thickness of the base layer;
A semiconductor single crystal forming step of the group III nitride semiconductor single crystal growing said Group III nitride semiconductor single crystal so as not to cover the surface of the recess,
A semiconductor single crystal separation step of peeling the group III nitride semiconductor single crystal from the underlayer;
Have
In the semiconductor single crystal forming step,
The underlayer exposed in the recess is melt-backed by flux to widen the recess to expose the slope, and in the recess, an amorphous portion filled with a flux component is formed, and the surface of the mask layer The group III nitride semiconductor single crystal is grown from the surface to form the group III nitride semiconductor single crystal on the surface of the mask layer and the amorphous portion . A method for producing a semiconductor single crystal. In the manufacturing method of the group III nitride semiconductor single crystal of Claim 1,
In the semiconductor single crystal forming step,
The Group III nitride semiconductor single crystal is grown by exposing the (1, 0, -1, 1) plane of the underlayer by meltback, and then growing the Group III nitride semiconductor single crystal. Method. In the manufacturing method of the group III nitride semiconductor single crystal of Claim 1 or Claim 2 ,
In the mask layer forming step,
A method for producing a group III nitride semiconductor single crystal, comprising forming an AlGaN layer as the mask layer. In the manufacturing method of the group III nitride semiconductor single crystal of any one of Claim 1- Claim 3 ,
In the mask layer forming step,
A method for producing a group III nitride semiconductor single crystal, wherein the Al composition ratio X in the mask layer is in the range of 0.02 to 1.00. In the manufacturing method of the group III nitride semiconductor single crystal according to claim 4 ,
In the mask layer forming step,
A method for producing a group III nitride semiconductor single crystal, wherein the Al composition ratio X in the mask layer is in the range of 0.03 to 0.50. In the manufacturing method of the group III nitride semiconductor single crystal of any one of Claim 1- Claim 5 ,
In the semiconductor single crystal forming step,
A method for producing a group III nitride semiconductor single crystal, wherein the c-plane of the underlayer is not exposed by meltback. In the manufacturing method of the group III nitride semiconductor single crystal of any one of Claim 1- Claim 6 ,
A method for producing a group III nitride semiconductor single crystal, wherein the thickness of the mask layer is in the range of 2 nm to 2 μm. In the manufacturing method of the group III nitride semiconductor single crystal of any one of Claim 1- Claim 7 ,
A method for producing a group III nitride semiconductor single crystal, wherein the flux has a carbon (C) concentration within a range of 0.01 mol / l to 2 mol / l. In the manufacturing method of the group III nitride semiconductor single crystal of any one of Claim 1- Claim 8 ,
In the recess forming step,
A method for producing a group III nitride semiconductor single crystal, wherein a recess having an opening width in a range of 1 μm to 500 μm is formed. In the manufacturing method of the group III nitride semiconductor single crystal of any one of Claim 1- Claim 9 ,
The plurality of recesses are
A method for producing a group III nitride semiconductor single crystal, which is arranged in a lattice pattern on the surface of the mask layer. In the manufacturing method of the group III nitride semiconductor single crystal of any one of Claim 1- Claim 9 ,
The plurality of recesses are
A method for producing a group III nitride semiconductor single crystal, wherein the group III nitride semiconductor single crystals are arranged in a stripe shape. The method for producing a group III nitride semiconductor single crystal according to any one of claims 1 to 11 ,
Before the mask layer forming step,
A method for producing a group III nitride semiconductor single crystal comprising a step of forming an underlayer for forming a GaN layer as the underlayer. The method for producing a group III nitride semiconductor single crystal according to any one of claims 1 to 12 ,
The underlayer is
A method for producing a group III nitride semiconductor single crystal, which is a GaN substrate. The method for producing a group III nitride semiconductor single crystal according to any one of claims 1 to 12 ,
The underlayer is
A method for producing a group III nitride semiconductor single crystal, which is a GaN layer formed on a sapphire substrate. In a method for manufacturing a GaN substrate, in which a GaN single crystal is grown on a growth substrate using a flux,
A mask layer forming step of forming a mask layer made of Al _X In _Y Ga _(1-XY) N (0 <X, 0 ≦ Y, X + Y ≦ 1) containing Al on the underlayer;
A recess forming step of forming the exposed recesses of the base layer at a plurality of locations by removing the entire thickness of the mask layer and a part of the thickness of the base layer;
A semiconductor single crystal forming step of the GaN single crystal growing said GaN single crystal so as not to cover the surface of the recess,
A semiconductor single crystal separation step of peeling the GaN single crystal from the underlayer;
Have
In the semiconductor single crystal forming step,
The underlayer exposed in the recess is melt-backed by flux to widen the recess to expose the slope, and in the recess, an amorphous portion filled with a flux component is formed, and the surface of the mask layer The GaN single crystal is grown on the surface of the mask layer and the amorphous portion to form the GaN single crystal .

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