Gallium nitride substrate manufacturing method

Abstract

To provide a manufacturing method of a GaN substrate capable of shortening a manufacturing time.SOLUTION: A manufacturing method of a GaN substrate includes: preparing a GaN wafer 10 including a first principal surface 10a and a second principal surface 10b at an opposite side of the first principal surface 10a; forming a modified layer 11 in a surface direction of the GaN wafer 10 by irradiating the inside of the GaN wafer 10 with laser light L from the second principal surface 10b of the GaN wafer 10; and manufacturing the GaN substrate from the GaN wafer 10 by dividing the GaN wafer 10 with the modified layer 11 defined as a boundary. In preparing the GaN wafer 10, prepared is the GaN wafer 10 which consists of a hexagonal crystal and in which the first principal surface 10a and the second principal surface 10b are made into {1-100}m surfaces, and in forming the modified layer 11, the modified layer 11 is formed by irradiating the inside of the GaN wafer 10 with the laser light L so as to form irradiation marks for constituting the modified layer.SELECTED DRAWING: Figure 1C

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a gallium nitride (hereinafter also simply referred to as GaN) substrate by dividing a GaN wafer. [Background technology]

[0002] A manufacturing method for manufacturing GaN substrates by dividing a GaN wafer has been proposed (see, for example, Patent Document 1). Specifically, in this manufacturing method, a GaN wafer having a first main surface and a second main surface is prepared, and a laser beam is irradiated from the first main surface or the second main surface to form an affected layer inside the GaN wafer along the surface direction of the GaN wafer. Then, in this manufacturing method, the GaN wafer is divided at the affected layer as a boundary to manufacture GaN substrates. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-57103 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above manufacturing method, the plane orientation of the first and second principal surfaces is not particularly specified. Furthermore, according to the investigations of the present inventors, it has been confirmed that if the first and second principal surfaces are made to be the commonly used {0001} c-plane and an affected layer is formed along this c-plane, the manufacturing time for manufacturing a GaN substrate may become longer.

[0005] In view of the above, an object of the present invention is to provide a method for manufacturing a GaN substrate that can shorten the manufacturing time. [Means for solving the problem]

[0006] Claim 1 to achieve the above object~3 In the method for manufacturing a GaN substrate, a GaN wafer (100) is manufactured from a GaN wafer (10), the method comprising the steps of: preparing a GaN wafer having a first main surface (10a) and a second main surface (10b) opposite to the first main surface; irradiating the interior of the GaN wafer from the second main surface with laser light (L) to form an affected layer (11) along the surface direction of the GaN wafer; and dividing the GaN wafer at the affected layer to manufacture a GaN substrate from the GaN wafer; in the step of preparing a GaN wafer, a GaN wafer is prepared which is constituted by a hexagonal crystal structure and whose first and second main surfaces are {1-100} m planes; and in the step of forming the affected layer, the affected layer is formed by irradiating the GaN wafer with laser light so that irradiation marks (La) for constituting the affected layer are formed inside the GaN wafer. Furthermore, in claim 1, by forming the altered layer, the laser light is scanned in one direction in the surface direction of the gallium nitride wafer as the scanning direction, and the angle (θ) between the scanning direction and the a-axis direction is set to less than 60° so that an irradiation mark is formed. In claim 2, further, by forming the altered layer, the laser light is scanned in one direction in the surface direction of the gallium nitride wafer as the scanning direction, and the angle (θ) between the scanning direction and the a-axis direction is set to less than 50° so that an irradiation mark is formed. In claim 3, furthermore, by forming the altered layer, the laser light is scanned in one direction in the surface direction of the gallium nitride wafer as the scanning direction, and the angle (θ) between the scanning direction and the a-axis direction is set to less than 30° so that an irradiation mark is formed.

[0007] According to this method, a GaN wafer having a first main surface and a second main surface constituted by an m-plane is prepared, and a laser beam is irradiated to form an affected layer along the surface direction of the GaN wafer (i.e., the m-plane), thereby shortening the manufacturing time of the GaN substrate.

[0008] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and the specific components described in the embodiments described below. [Brief explanation of the drawings]

[0009] [Figure 1A] 2A to 2C are cross-sectional views illustrating a manufacturing process of the GaN substrate according to the first embodiment. [Figure 1B] 1B is a cross-sectional view showing a manufacturing process of the GaN substrate subsequent to FIG. 1A. [Figure 1C] FIG. 1C is a cross-sectional view showing the manufacturing process of the GaN substrate subsequent to FIG. 1B. [Figure 1D] 1D is a cross-sectional view showing a manufacturing process of the GaN substrate subsequent to FIG. 1C. [Figure 1E]1D and 1E are cross-sectional views showing the manufacturing process of the GaN substrate subsequent to FIG. [Figure 1F] FIG. 1C is a cross-sectional view showing the manufacturing process of the GaN substrate subsequent to FIG. 1E. [Figure 2] FIG. 2 is a diagram for explaining the crystal orientation of a GaN wafer. [Figure 3] FIG. 2 is a schematic diagram showing the path of laser light when the laser light is irradiated onto a GaN wafer. [Figure 4] 4 is a schematic diagram showing irradiation marks and a deteriorated layer on the wafer formed by the laser beam irradiated onto the region IV in FIG. 3. FIG. [Figure 5] FIG. 10 is a diagram showing the relationship between the angle with respect to the a-axis direction, the total output of the laser light, and the irradiation mark. [Figure 6A] 10 is a schematic diagram showing irradiation marks when the angle between the a-axis direction and the scanning direction is 0°. FIG. [Figure 6B] FIG. 10 is a schematic diagram showing irradiation marks when the angle between the a-axis direction and the scanning direction is 10°. [Figure 6C] FIG. 10 is a schematic diagram showing irradiation marks when the angle between the a-axis direction and the scanning direction is 20°. [Figure 7] FIG. 10 is a schematic diagram showing irradiation marks for forming a wafer alteration layer in a comparative example. [Figure 8A] 3A to 3C are schematic diagrams showing surfaces divided by the manufacturing method of the first embodiment. [Figure 8B] FIG. 10 is a schematic diagram showing surfaces divided by a manufacturing method of a comparative example. [Figure 9A] 10A to 10C are cross-sectional views showing a semiconductor chip manufacturing process including a GaN substrate manufacturing process according to the second embodiment. [Figure 9B] 9B is a cross-sectional view showing a manufacturing process of the semiconductor chip subsequent to FIG. 9A. [Figure 9C] 9C is a cross-sectional view showing the manufacturing process of the semiconductor chip subsequent to FIG. 9B. [Figure 9D] 9D is a cross-sectional view showing a manufacturing process of the semiconductor chip subsequent to FIG. 9C. [Figure 9E] FIG. 9E is a cross-sectional view showing the manufacturing process of the semiconductor chip subsequent to FIG. 9D. [Figure 9F]FIG. 9F is a cross-sectional view showing the manufacturing process of the semiconductor chip subsequent to FIG. 9E. [Figure 9G] FIG. 9C is a cross-sectional view showing the manufacturing process of the semiconductor chip subsequent to FIG. 9F. [Figure 9H] 9C is a cross-sectional view showing the manufacturing process of the semiconductor chip subsequent to FIG. 9G. [Figure 9I] 9H is a cross-sectional view showing a manufacturing process of the semiconductor chip subsequent to FIG. 9H. [Figure 9J] 9I. FIG. 9I is a cross-sectional view showing a manufacturing process of the semiconductor chip. [Figure 9K] 9J. FIG. [Figure 10] FIG. 1 is a schematic plan view of a GaN wafer. [Figure 11A] 10 is a schematic diagram illustrating a case where a deteriorated layer for a wafer is formed without forming a deteriorated layer for a chip. FIG. [Figure 11B] 10 is a schematic diagram illustrating a case where a deteriorated layer for a chip is formed and then a deteriorated layer for a wafer is formed. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following embodiments, parts that are identical or equivalent to each other will be denoted by the same reference numerals.

[0011] (First embodiment) A method for manufacturing a GaN substrate 100 according to the first embodiment will be described with reference to the drawings. The GaN substrate 100 according to this embodiment is suitable for use in, for example, a semiconductor device mounted on a vehicle such as an automobile for driving various electronic devices for the vehicle. In the following description, when indicating a crystal orientation, a bar (-) should normally be placed above the desired number. However, due to limitations on expression based on electronic filing, a bar is placed before the desired number in this specification.

[0012] First, in this embodiment, a bulk GaN wafer 10 having a first principal surface 10a and a second principal surface 10b is prepared as shown in FIG. 1A. The GaN wafer 10 of this embodiment is a hexagonal single crystal wafer with a crystal orientation as shown in FIG. 2. The GaN wafer 10 of this embodiment has the first principal surface 10a and the second principal surface 10b as {1-100} m-planes, and one of the plane directions of the first principal surface 10a and the second principal surface 10b is a c-axis direction along the <0001> direction or a-axis direction. For example, if the first principal surface 10a and the second principal surface 10b are (1-100) m-planes, the <0001> c-axis direction and the <0010> a-axis direction are directions along the plane directions of the m-planes. In this embodiment, as will be described later, the laser light L is irradiated from the second main surface 10b side, and therefore the second main surface 10b is made into a mirror surface by mirror polishing or the like. The mirror polishing is performed, for example, by polishing using a grinder or by CMP (short for Chemical Mechanical Polishing). Furthermore, the m-plane in this embodiment includes slight manufacturing errors and the like, and also includes, for example, a surface tilted by ±3° with respect to the m-plane. In other words, the first main surface 10a and the second main surface 10b in this embodiment can be said to be surfaces formed to be m-planes.

[0013] Next, as shown in FIG. 1B, a holding member 20 is placed on the first main surface 10a side of the GaN wafer 10. For example, a dicing tape having a base material 21 and an adhesive 22 is used as the holding member 20. The base material 21 is made of a material that is resistant to warping during the manufacturing process, such as glass, a silicon substrate, or ceramics. The adhesive 22 is made of a material whose adhesive strength can be changed, such as a material whose adhesive strength changes depending on temperature or light. In this case, the adhesive 22 is made of, for example, an ultraviolet-curing resin, wax, or double-sided tape.

[0014] 1C, laser light L is irradiated from second main surface 10b of GaN wafer 10 to form wafer-deteriorated layer 11 along the surface direction of GaN wafer 10 (i.e., the m-plane) at a position a predetermined depth D from first main surface 10a of GaN wafer 10. In this embodiment, this step involves preparing a laser device including a laser light source that oscillates laser light L, a spatial light modulator that modulates the laser light L output from the laser light source, a focusing lens that focuses the laser light L modulated by the spatial light modulator, a displaceable stage, and the like. The spatial light modulator is configured, for example, with a reflective liquid crystal (LCOS: Liquid Crystal on Silicon) or the like.

[0015] When forming the wafer altered layer 11, the GaN wafer 10 is placed on a stage, and the position of the stage or the like is adjusted so that the focal point of the laser light L is scanned relatively along the surface direction of the GaN wafer 10. In this embodiment, as shown in FIG. 3 , if one direction in the surface direction of the GaN wafer 10 is defined as the X-axis direction and the direction perpendicular to the X-axis direction is defined as the Y-axis direction, the laser light L is scanned as follows. That is, the laser light L is scanned along the X-axis direction, then shifted along the Y-axis direction, and then scanned again along the X-axis direction. Therefore, the scanning direction of the laser light L can be said to be the direction along the X-axis direction.

[0016] Furthermore, in this embodiment, when the laser light L is scanned along the X-axis direction, it is irradiated onto the GaN wafer 10 so that multiple irradiation marks La are simultaneously formed along the Y-axis direction in the in-plane direction of the m-plane, as shown in FIG. 4 . Note that the irradiation marks La are marks formed by irradiation with the laser light. Although not particularly limited, in this embodiment, the GaN wafer 10 is irradiated with laser light L that is split into six points so that six irradiation marks La are simultaneously formed along the Y-axis direction in the in-plane direction of the m-plane. By irradiating the laser light L in this way so that multiple irradiation marks La are simultaneously formed along the in-plane direction of the m-plane, it is possible to shorten the manufacturing time.

[0017] However, when irradiating the laser light L, as will be described later in detail, the irradiation is performed under conditions such that an irradiation mark La is formed at the position irradiated with the laser light L, as shown in Fig. 4. Also, as will be described later in detail, Fig. 4 is a schematic diagram based on the results when the laser light L is scanned in a direction parallel to the a-axis direction.

[0018] The GaN wafer 10 is irradiated with laser light L to form irradiation marks La, and a modified layer 11a is formed around the area where the irradiation marks La are formed, where gallium and nitrogen are decomposed by thermal energy. More specifically, the irradiation with laser light L causes nitrogen to evaporate as a gas and gallium to precipitate, forming the modified layer 11a. Furthermore, cracks 11b propagating from the modified layer 11a along the surface direction of the m-plane are formed in the GaN wafer 10. As a result, a wafer-deteriorated layer 11 composed of the modified layer 11a and the cracks 11b is formed inside the GaN wafer 10. According to the inventors' studies, it has been confirmed that in the case of a hexagonal crystal structure such as the GaN wafer 10 of this embodiment, cracks are likely to propagate along the c-axis direction of the surface direction of the m-plane.

[0019] 4 is a schematic diagram in which the interval between adjacent irradiation marks La in the Y-axis direction is adjusted so that adjacent modified layers 11a in the Y-axis direction are connected by cracks 11b. Also, Fig. 4 is a schematic diagram based on the results when irradiating with laser light L branched into six points, and is a schematic diagram based on the results when the pulse pitch (i.e., the interval between irradiation marks La in the a-axis direction) is 3 μm and the feed speed is 150 mm / s.

[0020] Here, the inventors further investigated the irradiation mark La and obtained the results shown in FIG. 5. FIG. 5 shows the angle with the a-axis direction, the total output of the laser light L, and the presence or absence of the irradiation mark La. In FIG. 5, the angle with the a-axis direction refers to the angle θ between the scanning direction of the laser light L (i.e., the X-axis direction) and the a-axis direction, and is, for example, the angle θ shown in FIGS. 6A to 6C. FIG. 6A is a schematic diagram of the irradiation mark La and the modified layer 11a when the angle θ is 0°, FIG. 6B is a schematic diagram of the irradiation mark La and the modified layer 11a when the angle θ is 10°, and FIG. 6C is a schematic diagram of the irradiation mark La and the modified layer 11a when the angle θ is 20°. Note that cracks 11b are omitted in FIGS. 6A to 6C. Furthermore, in FIG. 5, the total output of the laser light L is the total output of the laser light L split into multiple beams. For example, in the case where the laser light L is split into six points as in this embodiment, it is the total output of the laser light L split into six points.

[0021] As shown in FIG. 5, according to the inventors' investigations, although the exact principle is not clear, it has been confirmed that when the angle θ between the a-axis direction and the scanning direction is 60° or more, the irradiation mark La may not be formed when the total output is 1.0 μJ or less. It has also been confirmed that when the angle θ between the a-axis direction and the scanning direction is 50° or more, the irradiation mark La may not be formed when the total output is 0.6 μJ or less. It has also been confirmed that when the angle θ between the a-axis direction and the scanning direction is 30° or more, the irradiation mark La may not be formed when the total output is 0.4 μJ or less. The absence of the irradiation mark La means that neither the modified layer 11a nor the crack 11b is formed, and thus the wafer-degraded layer 11 is not formed even when the laser light L is irradiated.

[0022] Therefore, in this embodiment, when irradiating the laser light L, the laser light L is irradiated so that an irradiation mark La is formed at the position irradiated with the laser light L. Specifically, as described above, when scanning with the laser light L, whether or not the irradiation mark La is formed depends on the angle θ formed between the a-axis direction and the scanning direction. The condition for forming the irradiation mark La is that the angle θ formed between the a-axis direction and the scanning direction is 60° or more, 50° or more, or 30° or more, and the total output of the laser light L required changes depending on whether the angle θ formed between the a-axis direction and the scanning direction is 60° or more, 50° or more, or 30° or more. In other words, under the condition for forming the irradiation mark La, the boundary angles for the angle θ formed between the a-axis direction and the scanning direction are 60°, 50°, and 30°. Therefore, in this embodiment, the angle θ formed between the a-axis direction and the scanning direction is adjusted according to the total output of the laser light L so that the irradiation mark La is formed when scanning with the laser light L. Specifically, the angle θ formed between the a-axis direction and the scanning direction is adjusted within a range of 60° or more, less than 60°, less than 50°, or less than 30° according to the total output of the laser light L. Furthermore, when the angle θ between the a-axis direction and the scanning direction is adjusted to be less than 60°, irradiation marks La may be formed even if the total output of the laser light L is lowered, compared to when the angle θ between the a-axis direction and the scanning direction is set to be 60° or more.In this case, the configuration and adjustments of the laser device can be simplified.

[0023] 1D, auxiliary member 30 is placed on the second main surface 10b side of GaN wafer 10. Similar to holding member 20, auxiliary member 30 is made of, for example, a base material 31 and an adhesive 32 whose adhesive strength can be changed. In this case, the base material of auxiliary member 30 is made of, for example, glass, a silicon substrate, ceramics, etc., and adhesive 32 of auxiliary member 30 is made of, for example, ultraviolet curable resin, wax, double-sided tape, etc.

[0024] 1E, holding member 20 and auxiliary member 30 are gripped and a tensile force or the like is applied in the thickness direction of GaN wafer 10, and GaN wafer 10 is divided at wafer-forming layer 11 as the boundary (i.e., the starting point of division). One of the divided portions is designated as GaN substrate 100. In this embodiment, the portion supported by holding member 20 is designated as GaN substrate 100. Hereinafter, the surface of GaN wafer 10 from which GaN substrate 100 is divided is designated as first main surface 10a of the new GaN wafer 10. Furthermore, the surface of GaN substrate 100 from which GaN wafer 10 is divided is designated as other surface 100b of GaN substrate 100.

[0025] Thereafter, as shown in FIG. 1F, the first main surface 10a of the GaN wafer 10 and the other surface 100b of the GaN substrate 100 are planarized by performing a CMP (short for chemical mechanical polishing) method using a polishing device 40 or the like. In this embodiment, the GaN substrate 100 is manufactured from the GaN wafer 10 in this manner. Various semiconductor elements are then formed on this GaN substrate 100, and the GaN substrate 100 is divided into chip units, thereby manufacturing a semiconductor device using the GaN substrate 100. Furthermore, a new GaN wafer 10 is used to manufacture a plurality of GaN substrates 100 by repeating the steps from FIG. 1A onward.

[0026] According to the present embodiment described above, a GaN wafer 10 having a first principal surface 10a and a second principal surface 10b formed as an m-plane is prepared, and laser light L is applied to form a wafer-forming affected layer 11 along the surface direction (i.e., the m-plane) of the GaN wafer 10. The GaN wafer 10 is then divided using the wafer-forming affected layer 11 as a starting point to produce a GaN substrate 100. This reduces the manufacturing time required to produce the GaN substrate 100. Hereinafter, a comparative manufacturing method will be described in which the first principal surface 10a and the second principal surface 10b are formed as the {0001} c-plane and the wafer-forming affected layer 11 is formed along the c-plane to produce a GaN substrate 100 from the GaN wafer 10. The effects of this embodiment will be specifically described in comparison with the comparative manufacturing method.

[0027] First, according to the manufacturing method of this embodiment, the inventors' investigations confirmed that when the depth D was 200 μm, the feed rate was 150 mm / s, the total output of the laser light L was 1.0 μJ, and the laser light L was branched into six points to form the wafer-forming altered layer 11, it took 15 minutes to separate the GaN substrate 100 from the 2-inch GaN wafer 10.

[0028] On the other hand, when forming a wafer-use altered layer 11 along the c-plane as in the manufacturing method of the comparative example, cracks 11b are likely to form along the m-plane but are difficult to form along the c-plane, so it is preferable to use the method shown in FIG. 7. That is, the irradiation mark formed by first irradiating laser light L is defined as the main irradiation mark La, and the modified layer formed around the main irradiation mark La is defined as the main modified layer 11a. In this case, in the manufacturing method of the comparative example, it is preferable to irradiate additional laser light L at a position including between the main modified layers 11a to form additional irradiation marks Lb and additional modified layers 111b. Note that the main irradiation mark La in FIG. 7 can be considered to be equivalent to the irradiation mark La in this embodiment. In other words, the manufacturing method of the comparative example requires additional time for irradiating laser light L to form additional irradiation marks Lb compared to the manufacturing method of this embodiment.

[0029] Furthermore, the inventors' investigations have confirmed that when GaN substrate 100 is manufactured by the manufacturing method of the comparative example, the time required to separate GaN substrate 100 from 2-inch GaN wafer 10 is 300 minutes when the depth D is 200 μm, the feed rate is 150 mm / s, the total output of laser light L for forming main irradiation marks La is 1.4 μJ, and the total output of laser light L for forming additional irradiation marks Lb is 0.6 μJ. Therefore, the manufacturing method of GaN substrate 100 of this embodiment can sufficiently shorten the manufacturing time.

[0030] (1) In this embodiment, the wafer-use damaged layer 11 is formed along the surface direction (i.e., the m-plane) of the GaN wafer 10. As described above, the cracks 11b constituting the wafer-use damaged layer 11 tend to extend along the m-plane. Therefore, as shown in FIG. 8A, when the wafer-use damaged layer 11 is formed along the m-plane as in this embodiment, the average surface roughness Ra of each divided surface 10a, 100b was 0.26 μm, and the maximum unevenness difference was 2.3 μm. On the other hand, as shown in FIG. 8B, in the comparative example in which the wafer-use damaged layer 11 is formed along the c-plane, the average surface roughness Ra of each divided surface 10a, 100b was 2.9 μm, and the maximum unevenness difference was 22.9 μm. The maximum unevenness difference refers to the difference between the height of the most convex portion relative to the reference plane and the depth of the most concave portion relative to the reference plane. Therefore, the manufacturing method of this embodiment can reduce the surface roughness to approximately 1 / 10 of that of the comparative example.

[0031] Therefore, according to the manufacturing method of this embodiment, when performing the step of FIG. 1F, the amount of GaN removed during planarization can be reduced, thereby reducing material loss. Furthermore, since the amount of GaN removed during planarization can be reduced, the manufacturing time for planarization can also be shortened. Note that FIG. 8B is a schematic diagram of a surface obtained by forming the main irradiation marks La and the additional irradiation marks Lb as shown in FIG. 7 to form the wafer-use damaged layer 11, and dividing the wafer-use damaged layer 11 at the boundary.

[0032] (2) In this embodiment, the angle θ between the scanning direction of the laser light L and the a-axis direction is adjusted so that the irradiation mark La is formed. This allows the wafer altered layer 11 to be appropriately formed. In this case, for example, when the angle θ between the scanning direction and the a-axis direction is set to less than 60°, the irradiation mark La may be formed even if the total output of the laser light L is lowered, compared to when the angle θ between the a-axis direction and the scanning direction is set to 60° or more, and the configuration and adjustment of the laser device can be simplified.

[0033] (Second embodiment) A second embodiment will be described. This embodiment is different from the first embodiment in that the configuration of the GaN wafer 10 is changed. As the rest is the same as the first embodiment, a description thereof will be omitted here.

[0034] In this embodiment, first, as shown in FIG. 9A, a base wafer 50 made of GaN in the form of a bulk wafer is prepared, having one surface 50a and the other surface 50b. The base wafer 50 is a hexagonal single crystal wafer, and the crystal orientation is as shown in FIG. 2. In this embodiment, the one surface 50a and the other surface 50b of the base wafer 50 are {1-100} m-planes, and one direction in the planar direction of the first main surface 10a and the second main surface 10b is the c-axis direction along the <0001> direction or the a-axis direction. In addition, the base wafer 50 in this embodiment is doped with, for example, silicon, oxygen, germanium, or the like, and has an impurity concentration of 5×10 17 ~5×10 19 cm -3 The thickness of the base wafer 50 is arbitrary, but for example, a base wafer of about 400 μm is prepared.

[0035] Next, as shown in FIG. 9B, an epitaxial film 60 made of GaN having a thickness of about 10 to 60 μm is formed on one surface 50a of the base wafer 50 to prepare a GaN wafer 10 in which a plurality of chip formation regions RA are partitioned by cutting lines SL. In this embodiment, the epitaxial film 60 is + type epitaxial layer 61 and n - The n-type epitaxial layer 62 is formed in this order from the GaN wafer 10 side. + The epitaxial layer 61 is doped with silicon, oxygen, germanium, etc., and has an impurity concentration of 5×10 17 ~1×10 18 cm -3 It is said to be about. - The epitaxial layer 62 is doped with silicon or the like, and the impurity concentration is 1×10 17 ~4×10 17 cm -3 It is said to be about that level.

[0036] In addition, n - The epitaxial layer 62 is a portion on which one-side element components 71 such as a diffusion layer 72, which will be described later, are formed, and has a thickness of, for example, about 8 to 10 μm. + The type epitaxial layer 61 is a portion for ensuring the thickness of the semiconductor chip 110, which will be described later, and has a thickness of, for example, about 40 to 50 μm. + type epitaxial layer 61 and n - The thickness of the n-type epitaxial layer 62 can be arbitrarily determined, but in this case, the thickness of the n-type epitaxial layer 62 is set to ensure the thickness of the semiconductor chip 110 described later. + The n-type epitaxial layer 61 - It is thicker than the type epitaxial layer 62 .

[0037] Hereinafter, the surface of the GaN wafer 10 facing the epitaxial film 60 will be referred to as the first main surface 10a of the GaN wafer 10, and the surface of the GaN wafer 10 facing the base wafer 50 will be referred to as the second main surface 10b of the GaN wafer 10. As described above, the base wafer 50 is formed of a hexagonal crystal, the epitaxial film 60 is grown on the first main surface 10a of the base wafer 50, and the second main surface 10b of the GaN wafer 10 is formed on the other surface 50b of the base wafer 50. Therefore, the GaN wafer 10 is formed of a hexagonal crystal, and the first and second main surfaces 10a and 10b are configured as {1-100} m planes. Each chip formation region RA is formed on the first main surface 10a of the GaN wafer 10.

[0038] 9C, a typical semiconductor manufacturing process is performed to form, in each chip formation area RA, first-surface element components 71 of the semiconductor element, such as diffusion layers 72, gate electrodes 73, surface electrodes (not shown), wiring patterns, and passivation films. The semiconductor elements employed here may have a variety of configurations, including power devices such as high electron mobility transistors (HEMTs) and optical semiconductor elements such as light-emitting diodes. Thereafter, if necessary, a surface protection film made of resist or the like is formed on the first main surface 10a of the GaN wafer 10.

[0039] 9D, a process similar to that shown in FIG. 1B is carried out to place the holding member 20 on the first main surface 10a side of the GaN wafer 10.

[0040] Next, as shown in Fig. 9E, laser light L is irradiated from the second main surface 10b of the GaN wafer 10 to form chip-forming affected layers 12 along the cutting lines SL. In this embodiment, as shown in Fig. 10, the planar shape of each chip formation region RA surrounded by the cutting lines SL is rectangular.

[0041] In this embodiment, when performing this step, a laser device similar to the laser device used to form the above-described wafer altered layer 11 is prepared. Then, the GaN wafer 10 is placed on a stage, and the position of the stage or the like is adjusted so that the focal point of the laser light L is scanned relatively along the cutting line SL.

[0042] As a result, a chip-degraded layer 12 including a modified layer in which gallium and nitrogen are decomposed by thermal energy is formed on the cutting line SL, similar to the wafer-degraded layer 11. Note that the chip-degraded layer 12 is in a state in which minute voids are formed due to the separation of nitrogen.

[0043] Furthermore, in this embodiment, when forming the chip-forming affected layer 12, the stage or the like is moved appropriately, and the laser light L is irradiated so that the focal point moves to two or more different locations in the thickness direction of the GaN wafer 10. In this case, the chip-forming affected layers 12 are formed at different locations in the thickness direction of the GaN wafer 10, and the chip-forming affected layers 12 may be separated from each other or may be connected. Furthermore, when the focal point is moved to two or more different locations in the thickness direction of the GaN wafer 10, the focal point is moved from the first main surface 10a side toward the second main surface 10b side of the GaN wafer 10.

[0044] Furthermore, the chip alteration layer 12 of this embodiment is formed so that when forming the wafer alteration layer 11 shown in Figure 9F described below, nitrogen generated by forming the wafer alteration layer 11 can be released to the outside through the pores in the chip alteration layer 12.

[0045] Next, as shown in Figure 9F, a process similar to that shown in Figure 1C is performed, and laser light L is irradiated from the second main surface 10b of the GaN wafer 10 to form a wafer-like altered layer 11 along the surface direction of the GaN wafer 10 at a position at a predetermined depth D from the first main surface 10a of the GaN wafer 10.

[0046] In this case, in this embodiment, the wafer-use damaged layer 11 is formed so as to intersect with the chip-use damaged layer 12 or pass directly below the chip-use damaged layer 12. This makes it possible to prevent large distortions from being applied to each chip formation region RA when the wafer-use damaged layer 11 is formed.

[0047] That is, if the chip-use damaged layer 12 is not formed, as shown in FIG. 11A, nitrogen generated during the formation of the wafer-use damaged layer 11 is difficult to be released to the outside, and therefore the distortion of the GaN wafer 10 due to the formation of the wafer-use damaged layer 11 is likely to be large. On the other hand, in this embodiment, the chip-use damaged layer 12 is formed, and the wafer-use damaged layer 11 is formed so as to intersect with the chip-use damaged layer 12 or pass directly below the chip-use damaged layer 12. Therefore, as shown in FIG. 11B, nitrogen generated during the formation of the wafer-use damaged layer 11 is easily released to the outside through pores in the chip-use damaged layer 12. Therefore, the distortion of the GaN wafer 10 due to the formation of the wafer-use damaged layer 11 can be suppressed from becoming large, and the distortion applied to each chip formation region RA can be reduced.

[0048] The predetermined depth D when forming the wafer altered layer 11 is set depending on the ease of handling and pressure resistance of the semiconductor chip 110, which will be described later, and is about 10 to 200 μm. In this case, the location where the wafer altered layer 11 is formed varies depending on the thickness of the epitaxial film 60, and the wafer is formed either inside the epitaxial film 60, at the boundary between the epitaxial film 60 and the base wafer 50, or inside the GaN wafer 10. Note that FIG. 9F shows an example in which the wafer altered layer 11 is formed at the boundary between the epitaxial film 60 and the GaN wafer 10.

[0049] However, as will be described later, at least a part of the base wafer 50 in the GaN wafer 10 is reused as a recycled wafer 80. For this reason, the wafer-use altered layer 11 is preferably formed inside the epitaxial film 60 or at the boundary between the epitaxial film 60 and the base wafer 50. When the wafer-use altered layer 11 is formed inside the base wafer 50, the wafer-use altered layer 11 is preferably formed on the first main surface 10a side of the base wafer 50. Furthermore, when the wafer-use altered layer 11 is formed inside the epitaxial film 60, the wafer-use altered layer 11 is preferably formed on the n-type epitaxial film 60 that constitutes the semiconductor device. - Instead of the n-type epitaxial layer 62, + The epitaxial layer 61 is formed inside the epitaxial layer 61 .

[0050] In the following description, the portion of GaN wafer 10 on the second main surface 10b side of wafer-forming altered layer 11 will be referred to as recycled wafer 80, and the portion of GaN wafer 10 on the first main surface 10a side of wafer-forming altered layer 11 will be referred to as GaN substrate 100.

[0051] 9G, a process similar to that shown in FIG. 1D is performed to place auxiliary member 30 on the second main surface 10b side of GaN wafer 10. Then, as shown in FIG. 9H, holding member 20 and auxiliary member 30 are gripped and a tensile force or the like is applied in the thickness direction of GaN wafer 10, and GaN wafer 10 is divided into recycled wafer 80 and GaN substrate 100 at wafer-forming layer 11 as the boundary (i.e., the starting point of division). In other words, GaN wafer 100 is manufactured from GaN wafer 10, with one-side device constituent portion 71 formed in each chip formation region RA.

[0052] Hereinafter, the surface of GaN substrate 100 separated from recycled wafer 80 will be referred to as other surface 100b of GaN substrate 100, and the surface opposite other surface 100b will be referred to as one surface 100a of GaN substrate 100. Similarly, the surface of recycled wafer 80 separated from GaN substrate 100 will be referred to as one surface 80a of recycled wafer 80. Since wafer-forming layer 11 is formed along the surface direction of GaN wafer 10, one surface 80a of separated recycled wafer 80 will be an m-plane.

[0053] 9I, one surface 80a of recycled wafer 80 and the other surface 100b of GaN substrate 100 are subjected to CMP using polishing apparatus 40 or the like to flatten one surface 80a and the other surface 100b. Note that in FIG. 9I, one-surface-side device constituent portion 71 and the like formed on GaN substrate 100 are omitted.

[0054] Furthermore, the recycled wafer 80 whose one surface 80a has been flattened is used again as the base wafer 50 to carry out the steps shown in Fig. 9A and thereafter. This allows the base wafer 50 to be used multiple times to form the semiconductor chip 110 described later.

[0055] 9J, a typical semiconductor manufacturing process is performed to form other-side element components 91 of the semiconductor element, such as metal film 92 constituting a back surface electrode, on other surface 100b of GaN substrate 100. After the step of forming other-side element components 91 is performed, a heat treatment such as laser annealing may be performed as necessary to establish ohmic contact between metal film 92 and second main surface 10b of GaN wafer 10.

[0056] Next, as shown in FIG. 9K, the holding member 20 is expanded, and each chip formation area RA is divided using the chip-forming alteration layer 12 as a boundary (i.e., the starting point of branching), thereby forming a semiconductor chip 110. Thereafter, the adhesive strength of the adhesive 22 is weakened by heat treatment or light irradiation, and the semiconductor chip 110 is picked up by peeling the one surface 100a side from the adhesive 22. This completes the manufacturing of the semiconductor chip 110. Before dividing each chip formation area RA, if necessary, slits or the like may be formed in the metal film 92 at the boundary between each chip formation area RA, thereby easily dividing the metal film 92 into each chip formation area RA. In this case, a metal mask covering the divided areas may be prepared in the step of FIG. 9J to prevent the metal film 92 from being formed in the divided areas.

[0057] As described above, even if the GaN wafer 10 is constructed by stacking the base wafer 50 and the epitaxial film 60, the same effect as in the first embodiment can be obtained by forming the wafer altered layer 11 along the m-plane.

[0058] (1) In this embodiment, the GaN wafer 10 is constructed by stacking a base wafer 50 and an epitaxial film 60, and the characteristics of the semiconductor chip 110 to be manufactured can be easily changed by appropriately adjusting the impurity concentration of the epitaxial film 60, etc.

[0059] (2) In this embodiment, the recycled wafer 80 is reused as the base wafer 50. Therefore, it is not necessary to prepare a new base wafer 50 every time a semiconductor chip 110 is manufactured, and the base wafer 50 can be effectively used. Therefore, the productivity of the semiconductor chip 110 can be improved.

[0060] (3) In this embodiment, the chip-use damaged layer 12 is formed before the wafer-use damaged layer 11 is formed, and when the wafer-use damaged layer 11 is formed, nitrogen generated when the wafer-use damaged layer 11 is formed is released through the chip-use damaged layer 12. This reduces distortion generated in each chip formation area RA, thereby suppressing defects in the semiconductor chip 110.

[0061] (Other embodiments) Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and modifications within the scope of equivalents. In addition, various combinations and forms, as well as other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

[0062] For example, in each of the above embodiments, when the laser light L is irradiated onto the GaN wafer 10 by branching it into multiple beams, the number of beams can be changed as appropriate, and may be less than six-point branching or may be seven-point branching or more. Furthermore, when the laser light L is irradiated onto the GaN wafer 10, the laser light does not have to be branched.

[0063] In each of the above embodiments, after GaN wafer 10 is separated into GaN substrates 100, it is not necessary to planarize other surface 100b of GaN substrate 100. For example, when forming an optical semiconductor element or the like on GaN substrate 100, light can be extracted effectively by leaving the unevenness.

[0064] Furthermore, in the second embodiment, each chip formation region RA may be divided using a dicing blade or the like without forming the chip-forming layer 12. In this case, by dividing each chip formation region RA before forming the wafer-forming layer 11, it is possible to release nitrogen that is generated when forming the wafer-forming layer 11. However, when dividing each chip formation region RA using a dicing blade or the like, each chip formation region RA may be divided after performing the step of FIG. 9J. [Explanation of symbols]

[0065] 10 GaN wafers 10a First principal surface 10b Second principal surface 11. Deterioration layer for wafer 100 GaN substrate L laser light La irradiation trace

Claims

1. A method for manufacturing a gallium nitride substrate (100) from a gallium nitride wafer (10), comprising: providing the gallium nitride wafer having a first major surface (10a) and a second major surface (10b) opposite to the first major surface; forming an altered layer (11) along a surface direction of the gallium nitride wafer by irradiating a laser beam (L) from a second main surface of the gallium nitride wafer to an interior of the gallium nitride wafer; and dividing the gallium nitride wafer at the affected layer to produce the gallium nitride substrate from the gallium nitride wafer; The preparation of the gallium nitride wafer includes preparing a gallium nitride wafer having a hexagonal crystal structure, the first main surface and the second main surface being {1-100} m-planes, In forming the affected layer, the affected layer is formed by irradiating the gallium nitride wafer with the laser light so that an irradiation mark (La) for constituting the affected layer is formed inside the gallium nitride wafer; Furthermore, in forming the altered layer, the laser light is scanned in one direction in the surface direction of the gallium nitride wafer as the scanning direction, and the angle (θ) between the scanning direction and the a-axis direction is set to less than 60° so that the irradiation mark is formed.

2. A method for manufacturing a gallium nitride substrate (100) from a gallium nitride wafer (10), comprising: providing the gallium nitride wafer having a first major surface (10a) and a second major surface (10b) opposite to the first major surface; forming an altered layer (11) along a surface direction of the gallium nitride wafer by irradiating a laser beam (L) from a second main surface of the gallium nitride wafer to an interior of the gallium nitride wafer; and dividing the gallium nitride wafer at the affected layer to produce the gallium nitride substrate from the gallium nitride wafer; The preparation of the gallium nitride wafer includes preparing a gallium nitride wafer having a hexagonal crystal structure, the first main surface and the second main surface being {1-100} m-planes, In forming the affected layer, the affected layer is formed by irradiating the gallium nitride wafer with the laser light so that an irradiation mark (La) for constituting the affected layer is formed inside the gallium nitride wafer; Furthermore, in forming the altered layer, the laser light is scanned in one direction in the surface direction of the gallium nitride wafer as the scanning direction, and the angle (θ) between the scanning direction and the a-axis direction is set to less than 50° so that the irradiation mark is formed.

3. A method for manufacturing a gallium nitride substrate (100) from a gallium nitride wafer (10), comprising: providing the gallium nitride wafer having a first major surface (10a) and a second major surface (10b) opposite to the first major surface; forming an altered layer (11) along a surface direction of the gallium nitride wafer by irradiating a laser beam (L) from a second main surface of the gallium nitride wafer to an interior of the gallium nitride wafer; and dividing the gallium nitride wafer at the affected layer to produce the gallium nitride substrate from the gallium nitride wafer; The preparation of the gallium nitride wafer includes preparing a gallium nitride wafer having a hexagonal crystal structure, the first main surface and the second main surface being {1-100} m-planes, In forming the affected layer, the affected layer is formed by irradiating the gallium nitride wafer with the laser light so that an irradiation mark (La) for constituting the affected layer is formed inside the gallium nitride wafer; Furthermore, in forming the altered layer, the laser light is scanned in one direction in the surface direction of the gallium nitride wafer as the scanning direction, and the angle (θ) between the scanning direction and the a-axis direction is set to less than 30° so that the irradiation mark is formed.

4. 4. The method for producing a gallium nitride substrate according to claim 1, wherein after dividing the gallium nitride wafer, at least one of the two divided surfaces is flattened.

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