Semiconductor chip manufacturing method

Abstract

To provide a manufacturing method of a semiconductor chip capable of improving productivity.SOLUTION: A manufacturing method of a semiconductor chip includes the steps of constructing a processed wafer 10 using a GaN wafer 1, forming a one-side element-constituting portion 11 of a semiconductor element, forming a degraded layer 15 along the surface direction inside the processed wafer 10 by irradiating the other surface 10b side of the processed wafer with a laser beam L, dividing the processed wafer 10 into a chip-constituting wafer 30 and a recycled wafer 40 by dividing the processed wafer 10 with the deteriorated layer 15 as a boundary, removing a semiconductor chip S1 from the chip-constituting wafer 30, and using the recycled wafer 40 again as a GaN wafer. In the step of forming the degraded layer 15, the surface 210a opposite to the processed wafer 10 becomes flat on the other surface 10b side of the processed wafer 10, and irradiation with the laser beam L is performed with a cushioning material 210 made of a material having a refractive index of 1.8 or higher and equal to or lower than that of GaN.SELECTED DRAWING: Figure 1E

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a semiconductor chip containing gallium nitride (hereinafter also simply referred to as GaN). [Background technology]

[0002] A manufacturing method has been proposed in the past in which an epitaxial film is formed on a semiconductor wafer to form a processed wafer, and semiconductor elements are formed on the processed wafer, followed by dividing the processed wafer into chip units to manufacture semiconductor chips (see, for example, Patent Document 1). Specifically, in this manufacturing method, assuming that the surface of the processed wafer facing the epitaxial film is one surface and the surface of the processed wafer facing the semiconductor wafer is the other surface, first, one-surface element components constituting the one-surface side of the semiconductor element, such as a diffusion layer and a front surface electrode, are formed on the one surface side of the processed wafer. Next, the other surface side of the processed wafer is ground to a predetermined thickness, and other-surface element components constituting the other-surface side of the semiconductor element, such as a back surface electrode, are formed on the other surface side of the processed wafer. After that, the processed wafer is divided into chip units. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-207908 A Summary of the Invention [Problem to be solved by the invention]

[0004] Meanwhile, the present inventors have been studying a semiconductor chip including GaN, which has advantages such as a wide band gap and a high saturation velocity of electrons. When such a semiconductor chip is manufactured using the above-mentioned manufacturing method, the following occurs.

[0005] That is, a GaN wafer is prepared as a semiconductor wafer, and an epitaxial film made of GaN is grown on the GaN wafer to form a processed wafer. Then, after forming device components on one side of the processed wafer, the other side of the processed wafer is ground. After that, device components on the other side are formed, and the processed wafer is divided into chip units.

[0006] However, in this manufacturing method, the processed wafer is ground from the other side. In other words, the GaN wafer is ground. This requires a GaN wafer to be prepared for each semiconductor chip to be manufactured, which may reduce productivity.

[0007] In view of the above, an object of the present invention is to provide a method for manufacturing semiconductor chips that can improve productivity. [Means for solving the problem]

[0008] Claim 1 to achieve the above object and 3A method for manufacturing a semiconductor chip having a semiconductor element formed thereon includes preparing a GaN wafer (1) made of GaN and having one surface (1a) and another surface (1b) opposite to the one surface, the one surface being a gallium surface and the other surface being a nitrogen surface; forming an epitaxial film (3) on one surface of the GaN wafer, so that the surface on the epitaxial film side is one surface (10a) and the surface on the GaN wafer side is the other surface (10b), thereby forming a processed wafer (10) having a plurality of chip formation regions (RA) on one surface side; The method includes forming a one-side element component (11) of the processed wafer, irradiating the inside of the processed wafer from the other side with laser light (L) to form an altered layer (15) inside the processed wafer along the surface direction of the processed wafer, dividing the processed wafer at the altered layer as a boundary to divide the processed wafer into a chip-constituting wafer (30) on one side of the processed wafer and a recycled wafer (40) on the other side of the processed wafer, taking out semiconductor chips (S1) from the chip-constituting wafer, and using the recycled wafer again as a GaN wafer. In forming the altered layer, the surface (210a, 230a, 240a) opposite the processed wafer is flattened on the other side of the processed wafer, and irradiating the laser light with a buffer material (210, 230, 240) made of a material having a refractive index of 1.8 or more and less than that of GaN. In claim 1, the affected layer is formed by irradiating the processed wafer with laser light while the processed wafer is immersed in a solution (210) in which additive particles having a predetermined refractive index are dispersed as a buffer material. In claim 3, the affected layer is formed by irradiating the laser light to a sheet (240) having additive particles dispersed therein and having a predetermined refractive index as a buffer material, which is placed on the other side of the processed wafer.

[0009] According to this, recycled wafers are used again as GaN wafers. Therefore, it is not necessary to prepare a new GaN wafer every time a semiconductor chip is manufactured, and the GaN wafer can be used effectively. Therefore, the productivity of semiconductor chips can be improved. Also, when irradiating the processed wafer with laser light to form an altered layer, the processed wafer is irradiated with the laser light via a buffer material. Therefore, diffuse reflection of the laser light can be suppressed, and an altered layer can be suitably formed inside the processed wafer. Therefore, the productivity of semiconductor chips can be further improved.

[0010] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and specific components described in the embodiments described below. [Brief description of the drawings]

[0011] [Figure 1A] 2A to 2C are cross-sectional views illustrating a manufacturing process of the semiconductor chip in the first embodiment. [Figure 1B] 1B is a cross-sectional view showing a manufacturing process of the semiconductor chip subsequent to FIG. 1A. [Figure 1C] 1C is a cross-sectional view showing a manufacturing process of the semiconductor chip subsequent to FIG. 1B. [Figure 1D] 1D is a cross-sectional view showing a manufacturing process of the semiconductor chip subsequent to FIG. 1C. [Figure 1E] 1D; FIG. 1E is a cross-sectional view showing a manufacturing process of the semiconductor chip subsequent to FIG. [Figure 1F] 1C is a cross-sectional view showing a manufacturing process of the semiconductor chip subsequent to FIG. 1E. [Figure 1G] 1C is a cross-sectional view showing a manufacturing process of the semiconductor chip subsequent to FIG. 1F. [Figure 1H] 1C is a cross-sectional view showing a manufacturing process of the semiconductor chip subsequent to FIG. 1G. [Figure 1I] 1C is a cross-sectional view showing a manufacturing process of the semiconductor chip subsequent to FIG. 1H. [Figure 1J] 1I is a cross-sectional view showing a manufacturing process of the semiconductor chip following FIG. 1I. [Figure 1K] 1C is a cross-sectional view showing a manufacturing process of the semiconductor chip subsequent to FIG. 1J. [Diagram 2] FIG. 1 is a diagram showing the relationship between the refractive index and reflectance of a solution. [Diagram 3] 5A to 5C are cross-sectional views showing a manufacturing process of the semiconductor chip in the second embodiment. [Figure 4] 10A to 10C are cross-sectional views showing a manufacturing process of the semiconductor chip in the third embodiment. [Diagram 5] 10A to 10C are cross-sectional views showing a manufacturing process of a semiconductor chip according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other will be denoted by the same reference numerals.

[0013] (First embodiment) The first embodiment will be described with reference to the drawings. Hereinafter, a method for manufacturing a semiconductor chip S1 made of GaN will be described.

[0014] First, as shown in FIG. 1A, a GaN wafer 1 having one surface 1a and another surface 1b and in the form of a bulk wafer is prepared. For example, the GaN wafer 1 is doped with silicon, oxygen, germanium, etc., and has an impurity concentration of 5×10 17 ~5×10 19 cm -3 The GaN wafer 1 is prepared with a thickness of about 400 μm. The GaN wafer 1 of this embodiment has one surface 1a as a gallium surface and the other surface 1b as a nitrogen surface. After the manufacturing process of the semiconductor chip S1 described below is performed, the GaN wafer 1 is prepared by reusing a recycled wafer 40 shown in FIG. 1K, which will be described later.

[0015] Next, as shown in FIG. 1B, an epitaxial film 3 made of GaN having a thickness of about 10 to 100 μm is formed on one surface 1a of the GaN wafer 1 to prepare a processed wafer 10 having a plurality of chip formation regions RA. In this embodiment, the epitaxial film 3 is + A type epitaxial layer 3a and an n - The n-type epitaxial layer 3b is formed in this order from the GaN wafer 1 side. For example, + The epitaxial layer 3a is doped with silicon, oxygen, germanium, etc., and has an impurity concentration of 5×10 17 ~5×10 19 cm -3 It is said to be about that level. -The epitaxial layer 3b is doped with silicon or the like and has an impurity concentration of 1×10 17 ~4×10 17 cm -3 It is said to be about that level.

[0016] In addition, n - The epitaxial layer 3b is a portion on which the one-side element components 11 such as the diffusion layer 12 described later are formed, and has a thickness of, for example, about 8 to 10 μm. + The n-type epitaxial layer 3a is a portion for ensuring the thickness of the semiconductor chip S1 described later, and has a thickness of, for example, about 40 to 100 μm. + Type epitaxial layer 3a and n - The thickness of the n-type epitaxial layer 3b may be arbitrarily determined, but in this embodiment, the n-type epitaxial layer 3b is set to a value that ensures the thickness of the semiconductor chip S1. + The epitaxial layer 3a is - It is thicker than the type epitaxial layer 3b.

[0017] In the following, the surface of the processed wafer 10 facing the epitaxial film 3 is referred to as one surface 10a of the processed wafer 10, and the surface of the processed wafer 10 facing the GaN wafer 1 is referred to as the other surface 10b of the processed wafer 10. As described above, the one surface 1a of the GaN wafer 1 is a gallium surface and the other surface 1b is a nitrogen surface, so that the one surface 10a of the processed wafer 10 is a gallium surface and the other surface 10b is a nitrogen surface. Each chip formation region RA is formed on the one surface 10a side of the processed wafer 10.

[0018] Here, in this step, the process temperature for growing the epitaxial film 3 is about 1000°C. Therefore, when each epitaxial film 3 is formed, nitrogen is easily gasified and released from the processed wafer 10. Specifically, nitrogen is easily released from the nitrogen face, which is easily chemically activated. Therefore, in this embodiment, the other face 10b of the processed wafer 10 is the nitrogen face, so nitrogen is easily released from the other face 1b. Then, on the other face 10b of the processed wafer 10, fine irregularities U are formed due to the release of nitrogen.

[0019] Next, as shown in Fig. 1C, a front side process is performed, which is a process for the one surface 10a side of a general semiconductor manufacturing process. Specifically, as the front side process, ion implantation, deposition, wet process, etc. are appropriately performed to form the one surface side element components 11 of the semiconductor element such as the diffusion layer 12, the gate electrode 13, the surface electrode not shown, the wiring pattern, and the passivation film in each chip formation area RA. Note that the semiconductor element here may have various configurations, such as a power device such as a vertical MOS transistor, an optical semiconductor element such as a light emitting diode, a semiconductor laser, etc. Thereafter, a surface protection film made of a resist or the like is formed on the one surface 10a side of the processed wafer 10 as necessary.

[0020] In this step, there is a possibility that the chemical liquid used in the wet process may react with the processed wafer 10. In this case, the nitrogen surface, which is easily chemically active, easily reacts with the chemical liquid, and therefore the other surface 10b of the processed wafer 10 is in a state in which even finer irregularities U are formed.

[0021] Next, as shown in FIG. 1D, a holding member 20 is placed on one surface 10a of the processed wafer 10. For example, a dicing tape having a support base 21 and an adhesive 22 is used as the holding member 20. The support base 21 is made of a material that is not easily warped during the manufacturing process, such as glass, a silicon substrate, or ceramics. The adhesive 22 is made of a material that can change its adhesive strength, 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. However, the adhesive 22 is made of a material that maintains its adhesive strength even when forming the other surface side element component part 60 of FIG. 1G, which will be described later.

[0022] Next, as shown in FIG. 1E, laser light L is irradiated from the other surface 10b of the processed wafer 10 to form an altered layer 15 along the surface direction of the processed wafer 10 at a position a predetermined depth D from the one surface 10a of the processed wafer 10.

[0023] Specifically, a laser device is prepared that includes a laser light source that oscillates laser light L (not shown), a dichroic mirror arranged to change the direction of the optical axis of the laser light, i.e., the optical path, a displaceable stage on which the processed wafer 10 is placed, and a condenser lens 200 for condensing the laser light. When forming the deteriorated layer 15, the laser light L is irradiated through the condenser lens 200 while adjusting the position of the stage, etc. so that the focal point of the laser light L is relatively scanned along the surface direction of the processed wafer 10. As a result, the deteriorated layer 15 is formed on the processed wafer 10 along the surface direction. More specifically, by irradiating the laser light L, nitrogen evaporates as a gas and gallium is precipitated to form the deteriorated layer 15.

[0024] As described above, fine irregularities U are formed on the other surface 10b of the processed wafer 10. For this reason, if the laser light L is irradiated from the other surface 10b of the processed wafer 10 as it is, the laser light L may be diffused by the other surface 10b of the processed wafer 10, and the affected layer 15 may not be formed properly.

[0025] For this reason, in this embodiment, the laser light L is irradiated on the other surface 10b of the processed wafer 10 in a state where a buffer material is placed on the surface opposite to the processed wafer 10, the buffer material having a refractive index of 1.8 or more and less than that of GaN. The refractive index of GaN is about 2.38.

[0026] In this embodiment, a solution 210 in which a high refractive index material is dispersed in a water-based or oil-based solvent to set the refractive index to 1.8 to 2.38 is prepared in a container 220. Note that nanoparticles of TiO2, ZrO2, ZnSe, or the like are used as the high refractive index material. In this embodiment, the nanoparticles correspond to the added particles, the solution 210 corresponds to the buffer material, and the liquid surface 210a of the solution 210 corresponds to the surface of the buffer material.

[0027] Then, the processed wafer 10 is immersed in the solution 210 so that the other surface 10b of the processed wafer 10 faces the liquid surface 210a of the solution 210. Thereafter, in this state, the processed wafer 10 is placed on a stage, and the laser light L is irradiated from the other surface 10b side of the processed wafer 10. As a result, since the liquid surface 210a of the solution 210 is flat, first, diffuse reflection of the laser light L at the interface between the solution 210 and the outside air is suppressed.

[0028] The reflectance of the boundary between the solution 210 and the other surface 10b of the processed wafer 10 is expressed by the following formula 1, where R is the reflectance, N0 is the refractive index of the solution 210, and N1 is the refractive index of GaN.

[0029]

number

[0030] The relationship between the reflectance R and the refractive index N0 of the solution 210 is shown in FIG. 2. In this case, when the reflectance R is 0.02 or less, it is generally recognized that the minute unevenness U is not formed on the surface. In other words, when the reflectance R is 0.02 or less, it is recognized that the other surface 10b of the processed wafer 10 is not cloudy. The refractive index of the solution 210 in this embodiment is set to 1.8 to 2.38. Therefore, the reflectance R between the solution 210 and the other surface 10b of the processed wafer 10 is 0.02 or less. As a result, in this embodiment, the laser light L is also suppressed from being diffusely reflected at the interface between the processed wafer 10 and the solution 210. Therefore, in this embodiment, the deteriorated layer 15 can be suitably formed on the processed wafer 10.

[0031] Moreover, the solution 210 configured as described above is preferably configured to have a transmittance equal to or higher than that of GaN, which can suppress absorption of the laser light L in the solution 210 and more suitably form the affected layer 15 inside the processed wafer 10.

[0032] In this embodiment, the laser light L is irradiated while the condenser lens 200 is placed outside the solution 210 (i.e., in the open air). Although not particularly limited, in this embodiment, the laser light L used when forming the affected layer 15 has a wavelength range from infrared to visible light, and is set in consideration of the transmittance of the target wafer (i.e., the transmittance of GaN). In this embodiment, the processing point output, pulse width, etc. of such laser light L are appropriately adjusted to form the affected layer 15.

[0033] The predetermined depth D for forming the affected layer 15 is set according to the ease of handling and pressure resistance of the semiconductor chip S1, and is about 10 to 200 μm. In this case, the location where the affected layer 15 is formed varies according to the thickness of the epitaxial film 3, and the affected layer 15 is formed either inside the epitaxial film 3, at the boundary between the epitaxial film 3 and the GaN wafer 1, or inside the GaN wafer 1. Note that FIG. 1E shows an example in which the affected layer 15 is formed at the boundary between the epitaxial film 3 and the GaN wafer 1.

[0034] However, as described below, at least a portion of the GaN wafer 1 in the processed wafer 10 is reused as a recycled wafer 40. For this reason, the affected layer 15 is preferably formed inside the epitaxial film 3 or at the boundary between the epitaxial film 3 and the GaN wafer 1. When the affected layer 15 is formed inside the GaN wafer 1, the affected layer 15 is preferably formed on the one surface 1a side of the GaN wafer 1. When the affected layer 15 is formed inside the epitaxial film 3, the affected layer 15 is preferably formed on the n-type GaN layer 10 constituting the semiconductor element. - The n-type epitaxial layer 3b is not + It is preferable that the n-type epitaxial layer 3a is formed inside the n-type epitaxial layer 3a.

[0035] In the following description, the portion of processed wafer 10 on one side 10a side of deteriorated layer 15 is referred to as chip configuration wafer 30, and the portion of processed wafer 10 on the other side 10b side of deteriorated layer 15 is referred to as recycled wafer 40.

[0036] Next, although not shown, the processed wafer 10 with the altered layer 15 formed thereon is taken out from the solution 210 and washed. This makes it possible to prevent the steps of FIG. 1B and after from being performed with foreign matter attached when the GaN wafer 1 is used again by performing the step of FIG. 1K described later.

[0037] Next, as shown in FIG. 1F, an auxiliary member 50 is placed on the other surface 10b side of the processed wafer 10. Although the auxiliary member 50 is shown in a simplified manner in FIG. 1F, it is composed of, for example, a base material and an adhesive capable of changing the adhesive strength. In this case, the base material in the auxiliary member 50 is composed of, for example, glass, a silicon substrate, ceramics, etc., and the adhesive in the auxiliary member 50 is composed of, for example, ultraviolet curing resin, wax, double-sided tape, etc. Then, the support base 21 and the auxiliary member 50 are held and a tensile force or the like is applied in the thickness direction of the processed wafer 10, and the processed wafer 10 is divided into a chip-configured wafer 30 and a recycled wafer 40 with the affected layer 15 as the boundary (i.e., the starting point of the branching).

[0038] In the following description, the surface of the chip configuration wafer 30 on which the one-side element configuration portion 11 is formed is referred to as one surface 30a, the divided surface of the chip configuration wafer 30 is referred to as the other surface 30b, and the divided surface of the recycled wafer 40 is referred to as the one surface 40a. In addition, in each of the figures from FIG. 1F onwards, the affected layer 15 remaining on the other surface 30b of the chip configuration wafer 30 and the one surface 40a of the recycled wafer 40 are omitted as appropriate.

[0039] Thereafter, as shown in FIG. 1G, as the remaining semiconductor manufacturing process, a back surface process is performed on the other surface 30b of the chip configuration wafer 30 to form the other surface side element components 60 of the semiconductor elements, such as a metal film 61 that constitutes a back surface electrode.

[0040] Before the step of forming the other surface side element component 60, a step of planarizing the other surface 30b of the chip configuration wafer 30 by a CMP (short for chemical mechanical polishing) method or the like may be performed as necessary. FIG. 1G shows a diagram of the case where the other surface 30b of the chip configuration wafer 30 is planarized. After the step of forming the other surface side element component 60 is performed, a heat treatment such as laser annealing may be performed as necessary to make the metal film 61 and the other surface 30b of the chip configuration wafer 30 into ohmic contact.

[0041] 1H, a holding member 51 is placed on the other surface 30b side of the chip configuration wafer 30, that is, on the metal film 61 side. For example, a dicing tape having a base material 52 and an adhesive 53 is used as the holding member 51. Note that the adhesive 53 is made of a material capable of changing its adhesive strength, and for example, one whose adhesive strength changes depending on temperature or light is used.

[0042] 1I, the support base 21 attached to one surface 30a of the chip configuration wafer 30 is peeled off. Here, a process for reducing the adhesive strength of the adhesive 22 attaching the support base 21 to the chip configuration wafer 30 is performed, for example, UV irradiation is performed when the adhesive 22 is made of a UV resin adhesive.

[0043] 1J, the chip configuration wafer 30 is divided into individual chip units by a dicing saw, laser dicing, or the like to form each semiconductor chip S1. At this time, it is preferable to adjust the dicing depth so that the holding members 51 are not cut but remain connected while the chip configuration wafer 30 is divided into chip units.

[0044] Although the subsequent process for the semiconductor chips S1 is not shown, the holding member 51 is expanded to widen the gap between the semiconductor chips S1 at the diced cut portions. After that, the adhesive force of the adhesive 53 is weakened by heat treatment or light irradiation, and the semiconductor chips S1 are picked up. In this way, the semiconductor chips S1 are manufactured.

[0045] 1K, one surface 40a of the recycled wafer 40 configured as shown in FIG. 1F is planarized by performing a CMP method using a polishing device 70 or the like. The planarized recycled wafer 40 is then used as the GaN wafer 1, and the steps from FIG. 1A onward are performed again. This allows the GaN wafer 1 to be used multiple times to configure the semiconductor chip S1.

[0046] According to the present embodiment described above, the recycled wafer 40 is reused as the GaN wafer 1. Therefore, it is not necessary to prepare a new GaN wafer 1 every time the semiconductor chip S1 is manufactured, and the GaN wafer 1 can be effectively used. Therefore, the productivity of the semiconductor chip S1 can be improved.

[0047] In addition, in this embodiment, when the deteriorated layer 15 is formed on the processed wafer 10 by irradiating the laser light L, the laser light L is irradiated onto the processed wafer 10 through the solution 210. Therefore, when the deteriorated layer 15 is formed, the liquid surface 210a of the solution 210 becomes flat, so that the diffuse reflection of the laser light L at the interface between the solution 210 and the outside air can be suppressed. The refractive index of the solution 210 is set to be 1.8 or more and less than the refractive index of GaN. Therefore, the diffuse reflection of the laser light L at the interface between the other surface 10b of the processed wafer 10 and the solution 210 can also be suppressed. Therefore, the deteriorated layer 15 can be suitably formed inside the processed wafer 10, and the productivity of the semiconductor chip S1 can be improved.

[0048] (1) In this embodiment, the transmittance of the solution 210 is made higher than that of GaN, so that the absorption of the laser light L in the solution 210 can be suppressed. Therefore, the affected layer 15 can be more suitably formed inside the processed wafer 10.

[0049] Second embodiment A second embodiment will be described. In this embodiment, the configuration of the cushioning material is changed from that of the first embodiment. As the rest is the same as the first embodiment, the description will be omitted here.

[0050] In this embodiment, when irradiating the laser light L in the step of Fig. 1E, as shown in Fig. 3, a resist 230 is placed as a buffer material on the other surface 10b of the processed wafer 10, and the laser light L is irradiated. The resist 230 is made by hardening a liquid resist material in which a highly refractive material such as TiO2 is dispersed. The resist 230 has a flat surface 230a on the side opposite to the processed wafer 10, and is made of a material with a refractive index of 1.8 or more and less than the refractive index of GaN.

[0051] After the affected layer 15 is formed by irradiation with the laser light L, a stripping process using a remover liquid or ashing or other such process is performed to remove the resist 230 and clean the processed wafer 10.

[0052] According to the present embodiment described above, the laser light L is irradiated through the resist 230 as a buffer material, so that the same effects as those of the first embodiment can be obtained.

[0053] Third embodiment A third embodiment will be described. In this embodiment, the configuration of the cushioning material is changed from that of the first embodiment. As the rest is the same as the first embodiment, the description will be omitted here.

[0054] In this embodiment, when the laser light L is irradiated in the step of FIG. 1E, as shown in FIG. 4, the laser light L is irradiated in a state where a sheet 240 is attached as a buffer material to the other surface 10b of the processed wafer 10. The sheet 240 is made of a polymer-based sheet manufactured by dispersing a highly refractive material such as TiO2. The surface 240a of the sheet 240 opposite to the processed wafer 10 is flat, and is made of a material with a refractive index of 1.8 or more and equal to or less than that of GaN. The sheet 240 is pressed against the other surface 10b of the processed wafer 10 to be in close contact with the other surface 10b of the processed wafer 10.

[0055] After the affected layer 15 is formed by irradiation with the laser light L, the sheet 240 is peeled off and the processed wafer 10 is cleaned.

[0056] According to the present embodiment described above, the laser light L is irradiated through the sheet 240 serving as a buffer material, and therefore the same effects as those of the first embodiment can be obtained.

[0057] (Other embodiments) Although the present disclosure has been described based on the embodiment, it is understood that the present disclosure is not limited to the embodiment or structure. The present disclosure also encompasses various modifications and modifications within the equivalent range. 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 concept of the present disclosure.

[0058] For example, in each of the above embodiments, the epitaxial film 3 has a thickness of n - Alternatively, the n-type epitaxial layer 3b may be formed alone.

[0059] In each of the above embodiments, the metal film 61 may be formed without polishing the other surface 30b of the chip-configuration wafer 30 in the step of FIG. 1G. For example, when forming an optical semiconductor element as a semiconductor element, it is possible to effectively extract light from the other surface by forming an uneven structure on the other surface side of the semiconductor chip S1. Then, immediately after dividing the processed wafer 10 into the chip-configuration wafer 30 and the recycled wafer 40, the other surface 30b of the chip-configuration wafer 30 has the deteriorated layer 15 remaining thereon, and minute unevenness is formed. For this reason, when forming an optical semiconductor element, the other surface 30b of the chip-configuration wafer 30 may not be polished, and the unevenness of the deteriorated layer 15 may be utilized.

[0060] 1B, an epitaxial film may also be formed on the other surface 1b of the GaN wafer 1. This makes it easier to leave a predetermined thickness or more as the recycled wafer 40 even when the affected layer 15 is formed in the GaN wafer 1, and increases the number of times the wafer can be reused. Even in this configuration, minute irregularities U are formed on the other surface 10b of the processed wafer 10, so that the affected layer 15 can be suitably formed by irradiating the laser light through a buffer material as described above.

[0061] In the first embodiment, the condenser lens 200 may be disposed at the interface between the solution 210 and the outside air, as shown in Fig. 5. In this case, the laser light L condensed by the condenser lens 200 is emitted directly into the solution 210, so that the condensed laser light L is not affected by the interface between the solution 210 and the outside air. Therefore, the affected layer 15 can be more suitably formed inside the processed wafer 10. Note that, although Fig. 5 shows an example in which the condenser lens 200 is disposed at the interface between the solution 210 and the outside air, the condenser lens 200 may be disposed inside the solution 210. [Explanation of symbols]

[0062] 1a one side 1b Other side 1 GaN wafer 3 Epitaxial film 10 Processed wafer 10a one side 10b Other side 11. One-side element component 15 Degenerated layer 30 chip configuration wafer 40 Recycled Wafers 210a liquid level 210 Solution L Laser light S1 Semiconductor Chip

Claims

1. A method for manufacturing a semiconductor chip having a semiconductor element formed thereon, comprising the steps of: A gallium nitride wafer (1) is prepared, the wafer (1) being made of gallium nitride, having one surface (1a) and another surface (1b) opposite to the one surface, the one surface being a gallium surface and the other surface being a nitrogen surface; forming an epitaxial film (3) on the one surface of the gallium nitride wafer, the surface on the epitaxial film side being one surface (10a) and the surface on the gallium nitride wafer side being the other surface (10b), thereby forming a processed wafer (10) having a plurality of chip formation areas (RA) on the one surface side; forming one-surface-side element constituent parts (11) of the semiconductor element in the plurality of chip formation regions; forming an altered layer (15) along a surface direction of the processed wafer inside the processed wafer by irradiating a laser beam (L) into the inside of the processed wafer from the other surface side of the processed wafer; Dividing the processed wafer at the deteriorated layer as a boundary, thereby dividing the processed wafer into a chip configuration wafer (30) on one side of the processed wafer and a recycled wafer (40) on the other side of the processed wafer; Extracting a semiconductor chip (S1) from the chip configuration wafer; and reusing the recycled wafer as the gallium nitride wafer. In forming the affected layer, the surface (210a, 230a, 240a) opposite to the processed wafer is flattened on the other side of the processed wafer, and the laser light is irradiated in a state where a buffer material (210, 230, 240) made of a material having a refractive index of 1.8 or more and a refractive index equal to or less than that of the gallium nitride is disposed on the other side of the processed wafer; In forming the altered layer, the method for manufacturing a semiconductor chip includes irradiating the laser light while the processed wafer is immersed in a solution (210) in which additive particles having a predetermined refractive index are dispersed as the buffer material.

2. 2. The method for manufacturing a semiconductor chip according to claim 1, wherein the formation of the altered layer comprises irradiating the laser light through a focusing lens (200) and positioning the focusing lens in the solution or at the interface between the solution and the outside air.

3. A method for manufacturing a semiconductor chip having a semiconductor element formed thereon, comprising the steps of: A gallium nitride wafer (1) is prepared, the wafer (1) being made of gallium nitride, having one surface (1a) and another surface (1b) opposite to the one surface, the one surface being a gallium surface and the other surface being a nitrogen surface; forming an epitaxial film (3) on the one surface of the gallium nitride wafer, the surface on the epitaxial film side being one surface (10a) and the surface on the gallium nitride wafer side being the other surface (10b), thereby forming a processed wafer (10) having a plurality of chip formation areas (RA) on the one surface side; forming one-surface-side element constituent parts (11) of the semiconductor element in the plurality of chip formation regions; forming an altered layer (15) along a surface direction of the processed wafer inside the processed wafer by irradiating a laser beam (L) into the inside of the processed wafer from the other surface side of the processed wafer; Dividing the processed wafer at the deteriorated layer as a boundary, thereby dividing the processed wafer into a chip configuration wafer (30) on one side of the processed wafer and a recycled wafer (40) on the other side of the processed wafer; Extracting a semiconductor chip (S1) from the chip configuration wafer; and reusing the recycled wafer as the gallium nitride wafer. In forming the affected layer, the surface (210a, 230a, 240a) opposite to the processed wafer is flattened on the other side of the processed wafer, and the laser light is irradiated in a state where a buffer material (210, 230, 240) made of a material having a refractive index of 1.8 or more and a refractive index equal to or less than that of the gallium nitride is disposed on the other side of the processed wafer; In the method for manufacturing a semiconductor chip, the altered layer is formed by irradiating the laser light while a sheet (240) in which additive particles having a predetermined refractive index are dispersed is placed on the other side of the processed wafer as the buffer material.

4. 4. The method for manufacturing a semiconductor chip according to claim 1, wherein the buffer material has a higher transmittance than the gallium nitride.

Images