Semiconductor device manufacturing method and semiconductor wafer

Abstract

To provide a method for manufacturing a semiconductor device, which is capable of suppressing degradation in characteristics of devices due to a leaked laser beam.SOLUTION: A method for manufacturing a semiconductor device includes: preparing a processed wafer 10 in which an epitaxial layer 3 is stacked on a base material substrate 1 containing a gallium nitride single crystal; forming a device constituent part 11 constituting a part of a device, in a portion of the processed wafer 10 on a front surface 10a side; forming a modified layer extending in a direction along a front surface 10a, inside of the processed wafer 10, by applying a laser beam from a back surface 10b side of the processed wafer 10; and dividing the processed wafer 10 in a thickness direction starting from the modified layer. In the preparation of the processed wafer 10, there is prepared a processed wafer that includes a reflective layer 16 for reflecting the laser beam at a position, inside the epitaxial layer 3, separated from a planned formation position P1, where the modified layer is to be formed, by a predetermined distance D2 toward the front surface side 10a, the reflective layer containing a layer having a refractive index different from that of the gallium nitride single crystal.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a semiconductor device and a semiconductor wafer used in manufacturing the semiconductor device. [Background technology]

[0002] Patent Document 1 discloses a method for manufacturing a semiconductor device in which a semiconductor wafer containing a single crystal of gallium nitride (hereinafter simply referred to as GaN) is subjected to laser slicing. In this manufacturing method, a processed wafer (i.e., a semiconductor wafer) is prepared in which an epitaxial layer is stacked on a GaN wafer. The surface of the processed wafer facing the epitaxial layer is the front surface, and the surface of the processed wafer facing the GaN wafer is the back surface. After forming device components on the front surface of this processed wafer, laser slicing is performed. That is, a laser beam is irradiated from the back surface of the processed wafer to form a modified layer. Then, the processed wafer is sliced ​​in its thickness direction, starting from this modified layer.

[0003] When a modified layer is formed by irradiating a laser beam from the backside of a processed wafer, some of the laser beam leaks onto the front side of the processed wafer. When the leaked laser beam reaches the device components on the front side, the laser beam is absorbed by the device components and generates heat. The device characteristics are deteriorated when the device components are affected by this heat.

[0004] To prevent this, in the conventional manufacturing method described above, an absorption layer that absorbs laser light is formed on the processed wafer at a position closer to the front surface than the intended position for forming the modified layer. The laser light that leaks to the front surface of the processed wafer is absorbed by the absorption layer and converted into heat, thereby preventing the leaked laser light from reaching the device components on the front surface. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-96135 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the above-described conventional technology, heat generated by absorption of laser light in the absorption layer may result in the formation of a new modified layer, etc. In this way, heat generated by absorption of laser light in the absorption layer may adversely affect the GaN crystal constituting the device, and may adversely affect the characteristics of the device.

[0007] In view of the above, an object of the present invention is to provide a method for manufacturing a semiconductor device that can suppress deterioration of device characteristics due to leakage of laser light, and to provide a semiconductor wafer that can suppress deterioration of device characteristics due to leakage of laser light. [Means for solving the problem]

[0008] In order to achieve the above object, claims 1, 2 and 6 According to the invention described in the item (1), a method for manufacturing a semiconductor device includes: A processed wafer (10) is prepared in which an epitaxial layer (3) containing a gallium nitride single crystal is stacked on a gallium nitride wafer (1) containing a gallium nitride single crystal, the surface on the epitaxial layer side being a front surface (10a) and the surface on the gallium nitride wafer side being a back surface (10b); forming a front surface side device component (11) that constitutes a part of a device on a front surface side portion of a processed wafer; forming a modified layer (15) extending in a direction along the surface of the processed wafer inside the processed wafer by irradiating the inside of the processed wafer with laser light (La) from the back side of the processed wafer; Dividing the processed wafer into a device-configured wafer (30) on the front side and a backside wafer (40) on the back side, starting from the modified layer; In preparing the processed wafer, a reflective layer (16, 17) that reflects laser light is formed inside the epitaxial layer at a predetermined distance (D2) from the intended position (P1) where the modified layer is to be formed on the surface side, by including a layer with a refractive index different from that of the gallium nitride single crystal.

[0009] According to this, a reflective layer is formed on the processed wafer at a position closer to the front surface than the planned position for forming the modified layer. Therefore, when the modified layer is formed by irradiating the laser light, the laser light leaking from the planned position for forming the modified layer to the front surface side of the processed wafer can be reflected. Therefore, compared to when a reflective layer is not formed, it is possible to suppress the laser light from reaching the front surface side device component.

[0010] Furthermore, according to this, the reflective layer reflects the laser beam and does not absorb the energy of the laser beam, or absorbs less of the energy of the laser beam than the absorption layer of the above-mentioned conventional technology, which makes it possible to suppress or avoid heat generation due to absorption of the laser beam in the absorption layer of the above-mentioned conventional technology, and to suppress deterioration of device characteristics due to leakage of the laser beam.

[0011] Also, claims 11 and 12 According to the invention described in The semiconductor wafer used in the laser slicing process, which is cut starting from the modified layer (15) formed by the irradiation of laser light, is a gallium nitride wafer (1) containing a single crystal of gallium nitride; an epitaxial layer (3) laminated on the gallium nitride wafer and including a single crystal of gallium nitride; a surface-side device component (11) formed on the surface side of the laminate (10) of the gallium nitride wafer and the epitaxial layer, with the surface on the epitaxial layer side being the surface (10a) and the surface on the gallium nitride wafer side being the back surface (10b), and constituting a part of the device; a reflective layer (16, 17) disposed inside the epitaxial layer and extending widely in a direction along the surface, the reflective layer including a layer having a refractive index different from that of the gallium nitride single crystal, thereby being capable of reflecting laser light; Equipped with.

[0012] In the laser slicing process, a laser beam is irradiated from the back side into the inside of the laminate to form a modified layer inside the laminate that extends in a direction along the surface. At this time, a reflective layer is located on the front side of the laminate relative to the planned position where the modified layer is to be formed.

[0013] This allows the laser light leaking from the position where the modified layer is to be formed to the front side of the laminate to be reflected when the modified layer is formed by irradiating the laser light, thereby preventing the laser light from reaching the front side device component compared to when no reflective layer is formed.

[0014] Furthermore, according to this, the reflective layer reflects the laser beam and does not absorb the energy of the laser beam, or absorbs less of the energy of the laser beam than the absorption layer of the above-mentioned conventional technology, which makes it possible to suppress or avoid heat generation due to absorption of the laser beam in the absorption layer of the above-mentioned conventional technology, and to suppress deterioration of the device characteristics.

[0015] 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]

[0016] [Figure 1A] 2A to 2C are cross-sectional views illustrating a manufacturing process of the semiconductor device according to the first embodiment. [Figure 1B] 1B is a cross-sectional view showing a manufacturing process of the semiconductor device subsequent to FIG. 1A. [Figure 1C] 1C is a cross-sectional view showing a manufacturing process of the semiconductor device subsequent to FIG. 1B. [Figure 1D] 1D is a cross-sectional view showing a manufacturing process of the semiconductor device subsequent to FIG. 1C. [Figure 1E] 1D. FIG. [Figure 1F]1F is a cross-sectional view showing a manufacturing process of the semiconductor device subsequent to FIG. 1E. [Figure 1G] 1F is a cross-sectional view showing a manufacturing process of the semiconductor device subsequent to FIG. 1F. [Figure 1H] 1C is a cross-sectional view showing the manufacturing process of the semiconductor device subsequent to FIG. 1G. [Figure 1I] 1C is a cross-sectional view showing the manufacturing process of the semiconductor device subsequent to FIG. 1H. [Figure 1J] 1I. FIG. [Figure 2] FIG. 10 is a cross-sectional view of a processed wafer after an epitaxial process. [Figure 3] FIG. 1 is a diagram showing the relationship between the refractive index and the optical energy for each of GaN, AlGaN, and InGaN. [Figure 4] FIG. 10 is a diagram showing a change in output of laser light irradiated in a laser slicing process over time. [Figure 5] 10 is a cross-sectional view showing a laser slicing step in the manufacturing method of the semiconductor device of Comparative Example 1. FIG. [Figure 6] 10 is a cross-sectional view showing a laser slicing step in the manufacturing method of the semiconductor device of Comparative Example 2. FIG. [Figure 7] 4A to 4C are cross-sectional views showing a laser slicing step in the manufacturing method of the semiconductor device according to the first embodiment. [Figure 8] 3 is a cross-sectional view of a device configuration wafer after a laser slicing step in the manufacturing method of the semiconductor device according to the first embodiment. FIG. [Figure 9] 4 is a cross-sectional view of a device configuration wafer after a planarization step in the method for manufacturing the semiconductor device according to the first embodiment. FIG. [Figure 10] 10 is a cross-sectional view of a reflective layer formed on a processed wafer in a method for manufacturing a semiconductor device according to a second embodiment. FIG. [Figure 11] FIG. 1 is a graph showing the relationship between the critical thickness of an AlGaN layer on GaN and the Al concentration in the AlGaN. [Figure 12] FIG. 11 is a cross-sectional view of a processed wafer after an epitaxial step in a method for manufacturing a semiconductor device according to a third embodiment. [Figure 13]FIG. 10 is a graph showing the relationship between the absorption coefficient and the Si concentration. DETAILED DESCRIPTION OF THE INVENTION

[0017] 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.

[0018] (First embodiment) First, an outline of the method for manufacturing the semiconductor device of this embodiment will be described. In this manufacturing method, a substrate preparation step, an epitaxial step, a front surface device step, a laser slicing step, a planarization step, a back surface device step, and a dicing step are performed in this order.

[0019] In the substrate preparation step, as shown in FIG. 1A, a bulk wafer-shaped base substrate 1 containing single crystal GaN is prepared. The base substrate 1 is also called a GaN freestanding substrate, a GaN bulk substrate, or a GaN wafer. The base substrate 1 has a front surface 1a and a rear surface 1b on the opposite side. For example, the base substrate 1 is doped with conductive impurities such as silicon, oxygen, or germanium, and the impurity concentration is 1×10 18 cm -3 The base substrate 1 has a thickness of, for example, about 400 μm. The front surface 1a is a gallium surface, and the back surface 1b is a nitrogen surface.

[0020] 1B, in the epitaxial step, a GaN single crystal is epitaxially grown on the surface 1a of the base substrate 1 to form an epitaxial layer 3 containing the GaN single crystal. This results in a laminate in which the epitaxial layer 3 is stacked on the surface 1a of the base substrate 1, i.e., a processed wafer 10.

[0021] In the epitaxial layer 3 of this embodiment, n + type epitaxial layer 3a and n - The n-type epitaxial layer 3b is laminated in this order from the base substrate 1 side. +The epitaxial layer 3a is doped with conductive impurities such as silicon, oxygen, and germanium, and the impurity concentration is 1×10 18 cm -3 n - The epitaxial layer 3b is doped with a conductive impurity such as silicon, and the impurity concentration is 1×10 18 cm -3 The following is said to be true.

[0022] In addition, n - The epitaxial layer 3b is a portion where the surface side device components 11 such as the diffusion layer 12 described later are formed. + The epitaxial layer 3a is a portion for ensuring the thickness of the semiconductor chip S1, which will be described later. + type epitaxial layer 3a and n - The thickness of the epitaxial layer 3b may be arbitrarily determined, but in this case, the thickness of the semiconductor chip S1 is determined to be n. + The n-type epitaxial layer 3a - It is thicker than the type epitaxial layer 3b.

[0023] The surface of the processed wafer 10 facing the epitaxial layer 3 is the front surface 10a of the processed wafer 10. The surface of the processed wafer 10 facing the base substrate 1 is the back surface 10b of the processed wafer 10. As described above, the front surface 1a of the base substrate 1 is a gallium surface and the back surface 1b is a nitrogen surface, so that in the processed wafer 10, the front surface 10a is a gallium surface and the back surface 10b is a nitrogen surface. In this way, the substrate preparation step and the epitaxial step are performed to prepare the processed wafer 10 having the epitaxial layer 3 stacked on the base substrate 1.

[0024] In the surface device process, as shown in FIG. 1C, a surface-side device component 11 is formed on the surface 10a side of the processed wafer 10. The surface-side device component 11 constitutes part of a device. The surface-side device component 11 includes a functional layer, a conductive film, and an insulating film. Examples of devices include power devices such as vertical MOS transistors, optical semiconductor elements such as light-emitting diodes, and semiconductor lasers. Examples of the surface-side device component 11 include an impurity diffusion layer 12, a gate electrode 13, a surface electrode (not shown), a wiring pattern, a passivation film, and the like.

[0025] In the laser slicing step, a laser slice process is performed. Specifically, as shown in Fig. 1D, a holding member 20 for holding the processed wafer 10 is fixed to the front surface 10a side of the processed wafer 10. The holding member 20 has a base material 21 and an adhesive 22 whose adhesive strength can be changed.

[0026] In this state, as shown in FIG. 1E, a modified layer 15 is formed inside the processed wafer 10 by irradiating the inside of the processed wafer 10 with laser light La from the back surface 10b side of the processed wafer 10. The irradiated laser light La is a pulsed laser. A laser device (not shown) is used for this purpose. This laser device includes a laser source that oscillates the laser light La, a displaceable stage on which the processed wafer 10 is placed, and a focusing lens 200 for focusing the laser light La. This laser device oscillates the laser light La as pulses of a fixed duration. The wavelength of the laser light La is a wavelength that is transparent to the processed wafer 10. An optical system is set so that the focusing point of the irradiated laser light La is located at a predetermined depth position from the back surface 10b of the processed wafer 10 inside the processed wafer 10.

[0027] When forming the modified layer 15, the laser light L is irradiated via the condenser lens 200 while adjusting the position of a stage or the like so that the focal point of the laser light La is scanned relatively along the surface direction of the processed wafer 10. At the focal point, the laser light La is absorbed by the GaN crystal due to the action of multiphoton absorption, etc. As a result, a modified region in which Ga is precipitated is produced by the modification reaction of the following formula (1). GaN → Ga (solid) + 1 / 2N2 (gas) (1)

[0028] The focal point of the laser beam La is scanned relatively along the surface direction of the processed wafer 10, so that the modified portions formed at the focal point are connected in a planar shape. This forms a modified layer 15 that extends along the surface direction of the processed wafer 10. The surface direction is a direction parallel to the surface 10a.

[0029] Next, starting from the modified layer 15, the processed wafer 10 is divided into a device configuration wafer 30 on the front surface 10a side of the processed wafer 10 and a back surface wafer 40 on the back surface 10b side of the processed wafer 10, as shown in Figure 1F.

[0030] At this time, an auxiliary member 50 is fixed to the back surface 10b of the processed wafer 10. The auxiliary member 50 has, for example, a base material and an adhesive capable of changing adhesive strength. Then, while the holding member 20 and the auxiliary member 50 are gripped, a force is applied to the processed wafer 10 under appropriate conditions to separate the entire processed wafer 10 in the thickness direction of the processed wafer 10. An appropriate condition is, for example, heating the entire processed wafer 10 to a temperature equal to or higher than the melting point of Ga metal (i.e., 38°C). This causes the processed wafer 10 to be divided.

[0031] The surface of the device configuration wafer 30 on which the front surface side device configuration portion 11 is formed is the front surface 30a of the device configuration wafer 30. The surface of the device configuration wafer 30 on which it is divided is the back surface 30b of the device configuration wafer 30. The surface of the back surface side wafer 40 on which it is divided is the front surface 40a of the back surface side wafer 40. The back surface 30b of the device configuration wafer 30 and the front surface 40a of the back surface side wafer 40 each have an uneven surface with a height difference of several μm to several tens of μm.

[0032] 1G, the planarization step involves removing a portion of the back surface 30b of the device configuration wafer 30, and planarizing the back surface 30b of the device configuration wafer 30. The planarization is performed by grinding and polishing such as CMP (short for chemical mechanical polishing).

[0033] In the back surface device process, as shown in FIG. 1H, a back surface side device component 60 is formed on the back surface 30b side of the device configuration wafer 30. The back surface side device component 60 constitutes another part of the device. The back surface side device component 60 is a metal film 61 that constitutes a back surface electrode, etc. Thereafter, the holding member 20 is peeled off from the device configuration wafer 30.

[0034] In the dicing step, as shown in FIG. 1I, the device configuration wafer 30 is cut into a plurality of chips S1. At this time, a holding member 51 is fixed to the back surface 30b side of the device configuration wafer 30. The holding member 51 has a base material 52 and an adhesive 53 capable of changing adhesive strength. In this state, the device configuration wafer 30 is cut into pieces by a blade dicing method, a laser ablation method, a stealth dicing method, or the like. Note that the dicing step may be performed before the laser slicing step, the back surface device step, and the planarization step.

[0035] The semiconductor device manufacturing method of this embodiment includes a recycling step. In the recycling step, as shown in FIG. 1J, the front surface 40a of the back surface side wafer 40 separated in the laser slicing step is planarized. The planarization is performed by grinding and polishing, such as by a CMP method, using a polishing device 70. As a result, the back surface side wafer 40 is reclaimed and used as the base substrate 1 in the substrate preparation step. In this way, the base substrate 1 is repeatedly used, thereby reducing the substrate cost per device formation.

[0036] Next, the planned formation position of the modified layer 15 and the epitaxial process will be described in detail.

[0037] 2, in this embodiment, the planned formation position P1 of the modified layer 15 in the laser slicing step is the interface between the base substrate 1 and the epitaxial layer 3 of the processed substrate 10, i.e., a position that is a first distance D1 away from the front surface 1a of the base substrate 1 toward the front surface 10a of the processed substrate 10. The first distance D1 is preferably set corresponding to the thickness of the portion that is removed when the front surface 40a of the back surface-side wafer 40 is planarized in the recycling step.

[0038] For example, a portion of the back surface 40a of the wafer 40, approximately 20 μm thick from the surface 40a, is removed by grinding and polishing in the recycling process. In this case, the first distance D1 is set to 20 μm. This makes it possible to suppress a decrease in the thickness of the base substrate 1 when the surface 40a of the back surface 40a of the wafer 40 is planarized. Note that the first distance D1 is not limited to 20 μm and may be set to another distance greater than 0 μm and equal to or less than 30 μm.

[0039] In the epitaxial process, as shown in FIG. 2, a reflective layer 16 is formed inside the epitaxial layer 3. The reflective layer 16 includes a layer with a refractive index different from that of the GaN single crystal, thereby reflecting the laser light La irradiated in the laser slicing process described above. The laser light La is incident almost perpendicularly on the processed wafer 10. This reflection includes not only specular reflection but also diffuse reflection. Diffuse reflection is also called irregular reflection or scattering.

[0040] In this embodiment, the reflective layer 16 is composed of only one AlGaN layer, which has a refractive index different from that of single crystal GaN. The AlGaN layer is a layer composed of aluminum gallium nitride (hereinafter referred to as AlGaN). The reflective layer 16 reflects laser light at the interface between the reflective layer 16 and the portion of the epitaxial layer 3 composed of GaN.

[0041] Here, as shown in Figure 3, AlGaN has a different refractive index from GaN. Depending on the magnitude of the laser light energy, the refractive index of AlGaN can be lower or higher than that of GaN. For example, when the wavelength of the laser light is λ=532 nm, the energy of the laser light is E=2.33 eV. In this case, as shown in Figure 3, the value on the vertical axis at the intersection of the dashed line when the horizontal axis is 2.33 eV and the line showing the refractive index of each material is the refractive index of each material. In other words, the refractive index of GaN is 2.48. The refractive index of AlGaN is 2.25. Note that the refractive index of AlGaN shown in Figure 3 is the refractive index of Al x Ga 1-X is the refractive index when x=0.25 at N. The refractive index of AlGaN is N1, and the refractive index of GaN is N2. The reflectance R at the interface between the GaN portion and the reflective layer 16 when λ=532 nm is given by the following equation. The reflectance R is the ratio of the intensity of the reflected wave to the intensity of the incident wave. Below, the value of the reflectance R is shown as a percentage.

number

[0042] The position where the reflective layer 16 is formed is a position that is a predetermined distance D2 away from the planned formation position P1 of the modified layer 15 toward the front surface 10a of the processed wafer 10. The second distance D2 is preferably set to be equal to or less than the thickness of a portion of the device configuration wafer 30 that is to be removed in the planarization step described above. The second distance D2 is set to, for example, 10 μm or more and 30 μm or less.

[0043] In the epitaxial growth process, a GaN layer is formed to a thickness equal to the sum of the first distance D1 and the second distance D2 from the surface 1a of the base substrate 1. Then, an AlGaN layer is formed, for example, to a thickness of 10 nm or more and 30 nm or less, preferably about 20 nm. Then, a GaN layer is formed to a thickness of 10 μm or more and 200 μm or less. The GaN layer is a layer composed of single crystal GaN. The GaN layer and the AlGaN layer are formed successively using the HVPE method in the same epitaxial growth apparatus while varying the conditions (e.g., the type of source gas). However, since the AlGaN layer requires precise control of its thin thickness, MOCVD or MBE, which allow for more precise control of the film thickness, may be used instead of the HVPE method.

[0044] Next, the effects of this embodiment will be described in comparison with Comparative Examples 1 and 2. Comparative Example 1 differs from this embodiment in that, as shown in FIG. 5, a reflective layer 16 is not formed inside the epitaxial layer 3 in the epitaxial process. The other configurations of the manufacturing method for the semiconductor device are the same as those of this embodiment. Comparative Example 2 differs from this embodiment in that, as shown in FIG. 6, an absorption layer 100 that absorbs the energy of laser light is formed inside the epitaxial layer 3 instead of the reflective layer 16. The position where the absorption layer 100 is formed is the same as the position where the reflective layer 16 is formed. The other configurations of the manufacturing method for the semiconductor device are the same as those of this embodiment.

[0045] The laser light irradiated in the above-mentioned laser slicing process is a pulsed laser. Figure 4 shows a schematic waveform of the output of this pulsed laser with respect to time. The pulse width is several hundred ps to several tens of ns. At the beginning of the pulse width, a certain amount of time is required for the GaN crystal to undergo the reaction of the above formula (1). During this period, the laser light passes through the focal point. The laser light leaks toward the front-side device component 11. In other words, the laser light during this period becomes leaked light.

[0046] As shown in Figure 5, in Comparative Example 1, this short period of leaked light is absorbed by the front-side device component 11, for example, an electrode such as the gate electrode 13. That is, the front-side device component 11 absorbs the energy of the laser light and instantaneously converts it into thermal energy. This induces melting of the electrode 13, local annealing effects of the GaN crystal, and the like. These may adversely affect the device characteristics.

[0047] 6, in Comparative Example 2, the absorption layer 100 absorbs the leaked light, thereby preventing the leaked light from reaching the front-side device component 11. However, heat generated by the absorption of the laser light by the absorption layer 100 may cause the formation of a new modified layer in the epitaxial layer 3, which is a GaN crystal layer. Thus, heat generated by the absorption of the laser light La by the absorption layer 100 may adversely affect the GaN crystal layer that constitutes the device, and may adversely affect the device characteristics.

[0048] In contrast to this, in this embodiment, as shown in Fig. 2, a reflective layer 16 is formed at a position on the processed wafer 10 closer to the front surface 10a of the processed wafer 10 than the planned formation position P1 of the modified layer 15. Therefore, in the laser slicing step, the reflective layer 16 can reflect the leaked light, as shown in Fig. 7. Therefore, compared to a case where the reflective layer 16 is not formed, it is possible to suppress the leaked light from reaching the front surface side device component 11.

[0049] Furthermore, according to this, the reflective layer 16 reflects the laser light La, and does not absorb the energy of the laser light La, or absorbs less of the energy of the laser light La than the absorption layer 100 of Comparative Example 2. Therefore, it is possible to suppress or avoid heat generation due to absorption of the laser light that occurs in Comparative Example 2, and it is possible to suppress deterioration of device characteristics due to leakage of the laser light.

[0050] Furthermore, this embodiment also provides the following effect. The formation position of the reflective layer 16 is a position that is a second distance D2 away from the planned formation position P1 of the modified layer 15 toward the front surface 10a of the processed wafer 10. That is, as shown in FIG. 8, the formation position of the reflective layer 16 is a position that is a second distance D2 away from the back surface 30b of the device configuration wafer 30 divided in the laser slicing step. This second distance D2 is set to be shorter than the thickness D3 of the portion that is to be removed when the back surface 30b of the device configuration wafer 30 is planarized in the planarization step. For example, when the thickness D3 of the portion that is to be removed is about 20 μm to 25 μm, the second distance D2 is set to 15 μm.

[0051] 9, when a portion of the back surface 30b side of the device configuration wafer 30 is removed in the planarization step, the reflective layer 16 is also removed. This makes it possible to prevent the reflective layer 16 from remaining in the manufactured device.

[0052] The reflective layer 16 may be formed of one InGaN layer instead of one AlGaN layer, as long as it has a refractive index different from that of single-crystal GaN. The InGaN layer is a layer made of indium gallium nitride (hereinafter referred to as InGaN). As shown in FIG. 3, the refractive index of InGaN is sometimes lower and sometimes higher than that of GaN depending on the energy of the laser light. When the wavelength of the laser light is λ=532 nm, i.e., when the energy of the laser light is E=2.33 eV, the refractive index of GaN is 2.48, while the refractive index of InGaN is 2.43. Even when the reflective layer 16 is made of only one InGaN layer, the reflective layer 16 reflects the laser light at the interface between the reflective layer 16 and the GaN portion of the processed wafer 10.

[0053] (Second embodiment) In this embodiment, the configuration of the reflective layer is different from that of the first embodiment, but other configurations of the method for manufacturing the semiconductor device are the same as those of the first embodiment.

[0054] 10, the reflective layer 17 of this embodiment has a dielectric multilayer structure in which multiple pairs of AlGaN layers 171 and GaN layers 172 are alternately stacked, with one AlGaN layer 171 and one GaN layer 172 considered as one pair. In one pair of AlGaN layer 171 and GaN layer 172, the AlGaN layer 171 is located on the back surface 10b side of the processed wafer 10. Note that an AlGaN layer or the like (not shown) is formed on the front surface 10a side (i.e., the upper side in FIG. 10) of the GaN layer 172, which is located closest to the front surface 10a of the processed wafer 10 in the reflective layer 17, in order to distinguish it from the GaN epitaxial layer 3.

[0055] The AlGaN layer 171 is a first layer. The GaN layer 172 is a second layer having a different refractive index from the first layer. The refractive index of the AlGaN layer 171 is N1, and the refractive index of the GaN layer 172 is N2, for the wavelength λ of the laser light La used in the laser slicing process. The thickness of the AlGaN layer 171 is d1, and the thickness of the GaN layer 172 is d2. In this case, the thickness d1 of the AlGaN layer 171 and the thickness d2 of the AlGaN layer 171 are set to satisfy the following formula:

number

number

[0056] For example, when the wavelength of the laser light is λ=532 nm, N1=2.25, N2=2.48, and the thickness d1 of the AlGaN layer 171 and the thickness d2 of the GaN layer 171 are set to d1=59.1 nm and d2=54.3 nm.

[0057] In this way, by alternately stacking multiple sets of the AlGaN layers 171 and the GaN layers 172, a higher reflectance than that of the first embodiment can be obtained due to the effect of the "dielectric multilayer film." For example, by setting the number of sets to 5 or more and 20 or less, a sufficiently high reflectance can be obtained.

[0058] In this embodiment, too, a GaN layer is formed in the epitaxial step to a thickness equal to the sum of the first distance L1 and the second distance L2 from the surface 1a of the base substrate 1. Then, AlGaN layers 171 and GaN layers 171 having the above-mentioned thickness are formed alternately. These layers are formed by successively depositing the layers using the HVPE method while changing the conditions in the same epitaxial growth apparatus. However, since the formation of the reflective layer 17 requires precise control of the thin film thickness, MOCVD or MBE, which allow for more precise film thickness control, may be used instead of HVPE.

[0059] When forming an AlGaN layer (i.e., an AlGaN film) on GaN by epitaxial growth, there is a limit to the thickness at which the AlGaN layer can grow normally. This thickness is called the critical thickness. x Ga 1-x It is determined by the Al content x (that is, Al concentration) of N. Figure 11 shows an example of calculation results for the relationship between the critical thickness of an AlGaN layer and the Al concentration.

[0060] As shown in Figure 11, the critical film thickness when the Al concentration is 100% (i.e., AlN) is approximately 6 nm. As the Al concentration decreases from 100%, the critical film thickness increases. For example, when the Al concentration is 10%, the critical film thickness is approximately 97 nm. Therefore, it is possible to stack the above-mentioned AlGaN layer with d1 = 59.1 nm on a GaN layer.

[0061] Similarly, the critical thickness of a GaN layer (i.e., a GaN film) for AlGaN with an Al concentration of 10% is also about 97 nm, so it is possible to stack the above-mentioned GaN layer with d2 = 54.3 nm on an AlGaN layer.

[0062] The refractive index difference between AlGaN and GaN when the Al concentration is 10% is smaller than the refractive index difference between AlGaN and GaN when the Al concentration is 25% in the first embodiment. However, even when the Al concentration is as low as 10%, it is possible to increase the number of alternately stacked AlGaN layers 171 and GaN layers 172 and grow them. Therefore, due to the effect of the dielectric multilayer film structure, a much higher reflectance can be obtained than when the Al concentration is 25% in the first embodiment.

[0063] In this embodiment, the thickness d1 of the AlGaN layer 171 and the thickness d2 of the AlGaN layer 171 are set to satisfy the above formula. However, as long as the laser light La can be reflected by the reflective layer 17, the above formula does not have to be satisfied.

[0064] In this embodiment, an AlGaN layer 171 is used as the first layer on the back surface 10b of the processed wafer 10. A GaN layer 172 is used as the second layer on the front surface 10a of the processed wafer 10. However, a GaN layer may be used as the first layer and an AlGaN layer as the second layer. Alternatively, an InGaN layer may be used as one of the first and second layers and a GaN layer as the other. Alternatively, an InGaN layer may be used as one of the first and second layers and an AlGaN layer as the other. Alternatively, the first and second layers may each be composed of another layer on which a GaN single crystal can be epitaxially grown.

[0065] (Third embodiment) 12, in this embodiment, in the epitaxial step of the first embodiment, in addition to forming a reflective layer 16 inside the epitaxial layer 3, an absorbing layer 18 is also formed. The absorbing layer 18 is formed in a position of the epitaxial layer 3 of the processed wafer 10 that includes a position P1 where the modified layer 15 is to be formed.

[0066] The absorption layer 18 absorbs the laser light La irradiated in the laser slicing process. The absorption layer 18 is made of a single crystal of GaN containing P-type or N-type conductivity impurities, and is a layer with a high light absorption coefficient due to a higher concentration of conductivity impurities compared to the region of the epitaxial layer 3 of the processed wafer 10 excluding the absorption layer 18. For example, when Si is used as the conductivity impurity, as shown in FIG. 13, 18 cm -3 From 1×10 19 cm -3 When the absorption coefficient of the fluorine-containing compound increases to about 380 nm to 550 nm, the absorption coefficient of the fluorine-containing compound increases by about 3 to 4 times.

[0067] The thickness of the absorption layer 18 is, for example, 1 μm or more and 5 μm or less. Other configurations of the method for manufacturing the semiconductor device are the same as those in the first embodiment.

[0068] According to this embodiment, the absorption coefficient is high at the position P1 in the epitaxial layer 3 where the modified layer 15 is to be formed, i.e., at the focal point of the laser light La. Therefore, by irradiating the laser light La in the laser slicing process, the modified layer 15 can be efficiently formed inside the processed wafer 10. That is, the modified layer 15 can be formed even using laser light with a relatively low power density. Furthermore, light with a relatively low power density leaking from there can be reflected by the reflective layer 16. Therefore, compared to the first embodiment, it is possible to further suppress the leakage light from reaching the front-side device component 11.

[0069] As in the first embodiment, when a portion of the back surface 30b side of the device configuration wafer 30 is removed in the planarization step, the absorbing layer 18 is removed together with the reflective layer 16. Therefore, the absorbing layer 18 does not remain in the manufactured device.

[0070] In this embodiment, the absorbing layer 18 is formed in a position in the epitaxial layer 3 of the processed wafer 10 that includes the planned formation position P1 of the modified layer 15. However, the absorbing layer 18 may also be formed in a position in the epitaxial layer 3 of the processed wafer 10 between the planned formation position P1 of the modified layer 15 and the reflective layer 16. In this case, the absorbing layer 18 absorbs leaked light, and the reflective layer 16 reflects the leaked light that has passed through the absorbing layer 18. This makes it possible to further suppress the leaked light from reaching the front-side device component 11 compared to when only the reflective layer 16 is formed.

[0071] Moreover, instead of the reflective layer 16, the reflective layer 17 of the second embodiment may be used.

[0072] (Other embodiments) (1) In the above-described embodiments, the reflective layers 16 and 17 are removed in the planarization step, but they do not necessarily have to be removed.

[0073] (2) In each of the above-described embodiments, the planned formation position P1 of the modified layer 15 in the laser slicing process is inside the epitaxial layer 3. However, this is not limited to this case, and the planned formation position P1 of the modified layer 15 may be the position of the interface between the base substrate 1 and the epitaxial layer 3. The planned formation position P1 of the modified layer 15 may also be inside the base substrate 1. However, in either case, the reflective layers 16 and 17 are formed inside the epitaxial layer 3.

[0074] (3) The present invention is not limited to the above-described embodiments, and can be modified as appropriate within the scope of the claims, including various modifications and modifications within the scope of equivalents. Furthermore, the above-described embodiments are not unrelated to each other and can be combined as appropriate, except in cases where the combination is clearly impossible. Furthermore, in the above-described embodiments, it goes without saying that the elements constituting the embodiments are not necessarily essential, except in cases where they are specifically stated as essential or where they are clearly considered essential in principle. [Explanation of symbols]

[0075] 1. Base substrate, gallium nitride wafer 3 Epitaxial layer 10 Processed wafer, laminate 11. Surface side device component 15 Modified layer 16 Reflective layer 17 Reflective layer 30 Device-configured wafer 40 Backside wafer

Claims

1. A method for manufacturing a semiconductor device, comprising: A processed wafer (10) is prepared in which an epitaxial layer (3) including a gallium nitride single crystal is stacked on a gallium nitride wafer (1) including a gallium nitride single crystal, the surface on the epitaxial layer side being a front surface (10a) and the surface on the gallium nitride wafer side being a back surface (10b); forming a front surface side device component (11) constituting a part of a device on the front surface side portion of the processed wafer; By irradiating the inside of the processed wafer with laser light (La) from the back side of the processed wafer, a modified layer (15) extending in a direction along the surface is formed inside the processed wafer; Dividing the processed wafer into a device configuration wafer (30) on the front side and a back side wafer (40) on the back side, starting from the modified layer; In preparing the processed wafer, a reflective layer (16, 17) that reflects the laser light is formed by including a layer having a refractive index different from that of gallium nitride single crystal at a position inside the epitaxial layer that is a predetermined distance (D2) away from the intended position (P1) for forming the modified layer toward the surface side, and the reflective layer (16) is composed of only one layer having a refractive index different from that of gallium nitride single crystal, and the one layer is a layer made of aluminum gallium nitride or a layer made of indium gallium nitride.

2. A method for manufacturing a semiconductor device, comprising: A processed wafer (10) is prepared in which an epitaxial layer (3) including a gallium nitride single crystal is stacked on a gallium nitride wafer (1) including a gallium nitride single crystal, the surface on the epitaxial layer side being a front surface (10a) and the surface on the gallium nitride wafer side being a back surface (10b); forming a front surface side device component (11) constituting a part of a device on the front surface side portion of the processed wafer; By irradiating the inside of the processed wafer with laser light (La) from the back side of the processed wafer, a modified layer (15) extending in a direction along the surface is formed inside the processed wafer; Dividing the processed wafer into a device configuration wafer (30) on the front side and a back side wafer (40) on the back side, starting from the modified layer; In preparing the processed wafer, a reflective layer (16, 17) that reflects the laser light is formed inside the epitaxial layer at a position inside the epitaxial layer that is a predetermined distance (D2) away from the intended position (P1) for forming the modified layer toward the surface, by including a layer having a refractive index different from that of a gallium nitride single crystal, and the reflective layer (17) is configured as a multilayer in which a first layer (171) and a second layer (172) having a refractive index different from that of the first layer are stacked alternately in multiple sets.

3. The wavelength of the laser light is λ, and the refractive index of each of the first layer and the second layer with respect to the laser light is N １ , N ２ and the thickness of the first layer is d １ and the thickness of the second layer is d ２ When The thickness of the first layer and the thickness of the second layer are [Equation 2] [Equation 3] 3. The method for manufacturing a semiconductor device according to claim 2, wherein:

4. one of the first layer and the second layer is a layer made of gallium nitride, 4. The method for manufacturing a semiconductor device according to claim 2, wherein the other of the first layer and the second layer is a layer made of aluminum gallium nitride or a layer made of indium gallium nitride.

5. A method for manufacturing a semiconductor device as described in any one of claims 1 to 4, wherein in preparing the processed wafer, an absorption layer (18) that absorbs the laser light is formed at a position on the processed wafer that includes the position where the modified layer is planned to be formed, or at a position on the processed wafer between the position where the modified layer is planned to be formed and the reflective layer, and the absorption layer is a layer having a higher concentration of conductive impurities compared to the area of ​​the processed wafer excluding the absorption layer.

6. A method for manufacturing a semiconductor device, comprising: A processed wafer (10) is prepared in which an epitaxial layer (3) including a gallium nitride single crystal is stacked on a gallium nitride wafer (1) including a gallium nitride single crystal, the surface on the epitaxial layer side being a front surface (10a) and the surface on the gallium nitride wafer side being a back surface (10b); forming a front surface side device component (11) constituting a part of a device on the front surface side portion of the processed wafer; By irradiating the inside of the processed wafer with laser light (La) from the back side of the processed wafer, a modified layer (15) extending in a direction along the surface is formed inside the processed wafer; Dividing the processed wafer into a device configuration wafer (30) on the front side and a back side wafer (40) on the back side, starting from the modified layer; A method for manufacturing a semiconductor device, comprising the steps of: preparing the processed wafer; forming a reflective layer (16, 17) that reflects the laser light by including a layer having a refractive index different from that of a gallium nitride single crystal at a position inside the epitaxial layer that is a predetermined distance (D2) away from a position (P1) on the surface side where the modified layer is planned to be formed; and forming an absorption layer (18) that absorbs the laser light at a position on the processed wafer that includes the position where the modified layer is planned to be formed, or at a position on the processed wafer between the position where the modified layer is planned to be formed and the reflection layer; and preparing the processed wafer;

7. 7. The method for manufacturing a semiconductor device according to claim 5, wherein the thickness of the absorption layer is 1 [mu]m or more and 5 [mu]m or less.

8. a surface of the device configuration wafer on which the front surface-side device configuration portion is formed is a front surface (30a) of the device configuration wafer, and a surface of the device configuration wafer on which the device configuration portion is divided is a back surface (30b) of the device configuration wafer, The method for manufacturing a semiconductor device includes, after dividing the processed wafer, removing a portion of the back surface side of the device configuration wafer, 8. The method for manufacturing a semiconductor device according to claim 1, wherein the predetermined distance is equal to or less than a thickness (D3) of the portion to be removed in the removing step.

9. 9. The method for manufacturing a semiconductor device according to claim 8, wherein the predetermined distance is 10 [mu]m or more and 30 [mu]m or less.

10. 10. The method for manufacturing a semiconductor device according to claim 1, wherein in preparing the processed wafer, the backside wafer is used as the gallium nitride wafer.

11. A semiconductor wafer used in laser slicing, which is cut starting from a modified layer (15) formed by irradiation with laser light, A gallium nitride wafer (1) containing a single crystal of gallium nitride; an epitaxial layer (3) laminated on the gallium nitride wafer and containing a single crystal of gallium nitride; a surface-side device component (11) formed on the surface side of the laminate (10) of the gallium nitride wafer and the epitaxial layer, with the surface on the epitaxial layer side being a surface (10a) and the surface on the gallium nitride wafer side being a back surface (10b), and constituting a part of a device; a reflective layer (16, 17) disposed inside the epitaxial layer and extending widely in a direction along the surface, the reflective layer including a layer having a refractive index different from that of a gallium nitride single crystal, thereby being capable of reflecting the laser light; The reflective layer (16) is composed of only one layer having a refractive index different from that of a single crystal of gallium nitride, A semiconductor wafer, wherein the one layer is a layer made of aluminum gallium nitride or a layer made of indium gallium nitride.

12. A semiconductor wafer used in laser slicing, which is cut starting from a modified layer (15) formed by irradiation with laser light, A gallium nitride wafer (1) containing a single crystal of gallium nitride; an epitaxial layer (3) laminated on the gallium nitride wafer and containing a single crystal of gallium nitride; a surface-side device component (11) formed on the surface side of the laminate (10) of the gallium nitride wafer and the epitaxial layer, with the surface on the epitaxial layer side being a surface (10a) and the surface on the gallium nitride wafer side being a back surface (10b), and constituting a part of a device; a reflective layer (16, 17) disposed inside the epitaxial layer and extending widely in a direction along the surface, the reflective layer including a layer having a refractive index different from that of a gallium nitride single crystal, thereby being capable of reflecting the laser light; The reflective layer (17) is a multilayer structure in which a first layer (171) and a second layer (172) having a refractive index different from that of the first layer are stacked alternately in multiple pairs.

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