JP2014229843A - Method for manufacturing silicon carbide semiconductor device and silicon carbide semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a silicon carbide semiconductor device and a silicon carbide semiconductor device, capable of improving throughput and efficiency percentage.SOLUTION: A method for manufacturing a silicon carbide semiconductor device comprises: preparing an SiC wafer 1 having a bevel-shaped outer peripheral end; forming a breakdown voltage structure 6 in a surface layer on a front surface 2 of the SiC wafer 1; forming a deposition oxide film 12 on the front surface 2 of the SiC wafer 1 and protecting the front surface 2 of the SiC wafer 1; thinning the thickness of the SiC wafer 1 to 150 μm by grinding the SiC wafer 1 from a rear surface side of the SiC wafer 1; and removing a corner 14 of the outer peripheral end on a grinding surface 4a of the SiC wafer 1 by evaporating the SiC by irradiating the corner 14 of the outer peripheral end on the grinding surface 4a of the SiC wafer 1 with a laser 13. The corner 14 of the outer peripheral end on the grinding surface 4a of the SiC wafer 1 removed by laser processing includes a region of not more than 500 μm from a side surface to the inside of the SiC wafer 1.

Description

  The present invention relates to a method for manufacturing a silicon carbide semiconductor device and a silicon carbide semiconductor device.

  A semiconductor element using silicon carbide (SiC) as a semiconductor material is expected as a next-generation semiconductor element of a semiconductor element using silicon (Si) as a semiconductor material. The reason is that the SiC semiconductor element can reduce the resistance of the element in the ON state to a hundredth compared to the Si semiconductor element, and can be used in a higher temperature environment (for example, 200 ° C. or more). This is because there are various advantages. These advantages are obtained by the characteristics of SiC itself that the band gap of SiC is about three times as large as that of Si and that the dielectric breakdown electric field strength of SiC is nearly one order of magnitude larger than that of Si.

  As SiC devices (silicon carbide semiconductor devices), Schottky barrier diodes (SBDs), planar type vertical MOSFETs (insulated gate field effect transistors), and the like have been commercialized so far. In recent years, as a method for further reducing the resistance of an SiC device, in an SBD using SiC as a semiconductor material (hereinafter referred to as SiC-SBD), a semiconductor substrate which has been conventionally about 350 μm thick is thinned to a thickness of 150 μm or less. A method for reducing the thickness to a thickness has been proposed (for example, see Non-Patent Document 1 below).

  As another method for manufacturing a SiC device, a laser beam sufficient to vaporize and cut silicon carbide to be irradiated is directed to one surface of a portion of silicon carbide, and a portion of silicon carbide is applied. There has been proposed a method of performing dry etching on a portion of silicon carbide in order to remove by-products generated when the laser beam is cut (see, for example, Patent Document 1 below). In Patent Document 1 described below, by-products such as slag-like substances remaining on the surface of a cut semiconductor material, particularly on the surface of a wafer filled with a device precursor, are removed by dry etching.

Japanese Patent Application Laid-Open No. 11-505666

R. Rupp, 4 others, Performance of a 650V SiC Diode with Reduced Chip Thickness (Performance of a 650V SiC Diode Chip Thickness), Materials Science Forum Volumes 20 (17) Materials Science Forum Volumes 717-720 (2012)), (Switzerland), Trans Tech Publications, May 2012, p. 921-924

  However, when the back surface of the SiC wafer is ground, there is a possibility that the outer peripheral end of the SiC wafer protrudes outwardly with respect to the back surface of the SiC wafer due to the back surface grinding. This point-shaped protrusion may occur when, for example, the back surface of the SiC wafer is ground until the thickness of the SiC wafer reaches about 150 μm. In this way, when the pointed protrusion on the outer peripheral edge of the wafer comes into contact with the wafer cassette during storage of the SiC wafer, dust is generated due to the wafer cassette being scraped or the pointed protrusion at the outer peripheral edge of the wafer. There is a problem that the semiconductor wafer is damaged (cracked, chipped, etc.) due to the impact when it contacts the wafer cassette.

  Conventionally, when using a Si wafer, before or after the backside grinding of the Si wafer, the outer peripheral edge of the Si wafer is ground by an edge grinder or the like to obtain a smooth predetermined shape, and then occurs at the outer peripheral edge of the Si wafer. Grinding damage is removed by wet etching. For this reason, when using a Si wafer, the point-shaped protrusion part produced in the peripheral edge part of Si wafer by back surface grinding can be removed. However, when this method is applied to a SiC wafer, since SiC is a hard material, there is a problem that it takes time to grind the outer peripheral end portion.

  Further, since SiC is a chemically stable material, wet etching is difficult, and there is a problem that grinding damage caused by grinding of the outer peripheral edge of the SiC wafer cannot be removed. If grinding damage remains on the outer peripheral edge of the SiC wafer, in the subsequent process steps, for example, the grinding damage at the outer peripheral edge of the SiC wafer may be the starting point when the heat treatment is heated or lowered.

  An object of the present invention is to provide a method for manufacturing a silicon carbide semiconductor device and a silicon carbide semiconductor device capable of improving the non-defective product rate in order to eliminate the above-mentioned problems caused by the prior art. Another object of the present invention is to provide a method for manufacturing a silicon carbide semiconductor device and a silicon carbide semiconductor device capable of improving the throughput in order to eliminate the above-described problems caused by the prior art.

  In order to solve the above-described problems and achieve the object, the present inventor has conducted extensive research and as a result, after grinding the main surface of the SiC wafer, the SiC at the outer peripheral end of the ground surface of the SiC wafer is irradiated by laser irradiation. It has been found that by evaporating and rounding (chamfering), the throughput can be improved and the yield rate can be improved by preventing dust and wafer cracking. In addition, if the processing is performed in a minute area that chamfers the outer peripheral edge of the ground surface of the SiC wafer, debris (fine debris generated by processing) does not scatter to the area where the device structure is formed, and the yield rate decreases. I found it not. The present invention has been made based on such knowledge.

  In order to solve the above-described problems and achieve the object of the present invention, a method for manufacturing a silicon carbide semiconductor device according to the present invention has the following characteristics. First, a grinding process is performed to grind the back surface of a semiconductor substrate made of silicon carbide to reduce the thickness of the semiconductor substrate. Next, a laser beam is irradiated to the outer peripheral end portion of the back surface after grinding of the semiconductor substrate, and the outer peripheral end portion of the back surface of the semiconductor substrate after grinding is evaporated and selectively removed.

  In the method for manufacturing a silicon carbide semiconductor device according to the present invention, in the above-described invention, in the removing step, the laser is irradiated at an angle of 30 degrees or more and 60 degrees or less with respect to the back surface after grinding of the semiconductor substrate. It is characterized by that.

  The method for manufacturing a silicon carbide semiconductor device according to the present invention is characterized in that, in the above-described invention, in the removing step, the laser is irradiated to a region within 500 μm inward from the side surface of the semiconductor substrate.

  In the method for manufacturing a silicon carbide semiconductor device according to the present invention, the wavelength of the laser is 1030 nm or less in the above-described invention.

  In the method for manufacturing a silicon carbide semiconductor device according to the present invention, the spot diameter of the laser is not less than 10 μm and not more than 60 μm in the above-described invention.

  In the above-described invention, the method for manufacturing a silicon carbide semiconductor device according to the present invention is characterized in that, in the grinding step, the thickness of the semiconductor substrate is reduced to a thickness of 150 μm or less.

  In order to solve the above-described problems and achieve the object of the present invention, a silicon carbide semiconductor device according to the present invention is a silicon carbide semiconductor device manufactured using the above-described method for manufacturing a silicon carbide semiconductor device. The outer peripheral end of the back surface of the semiconductor substrate made of silicon carbide is chamfered.

  In the silicon carbide semiconductor device according to the present invention, in the above-described invention, the outer peripheral end portion of the back surface of the semiconductor substrate has a shape in which a region within 500 μm is chamfered inside from the side surface of the semiconductor substrate. It is characterized by.

  In the silicon carbide semiconductor device according to the present invention as set forth in the invention described above, the semiconductor substrate has a thickness of 150 μm or less.

  According to the above-described invention, the corner of the outer peripheral edge of the ground surface of the SiC wafer (semiconductor substrate) is removed by laser ablation after the back surface grinding, so that the SiC wafer can be formed in a short time without causing damage. The outer peripheral end of the grinding surface can be processed into a predetermined shape. In addition, dust and wafer cracks can be prevented in subsequent processes.

  According to the method for manufacturing a silicon carbide semiconductor device and the silicon carbide semiconductor device according to the present invention, it is possible to improve the yield rate. Moreover, according to the method for manufacturing a silicon carbide semiconductor device and the silicon carbide semiconductor device according to the present invention, there is an effect that the throughput can be improved.

It is sectional drawing which shows the state in the middle of manufacture of the silicon carbide semiconductor device concerning embodiment. It is sectional drawing which shows the state in the middle of manufacture of the silicon carbide semiconductor device concerning embodiment. It is sectional drawing which shows the state in the middle of manufacture of the silicon carbide semiconductor device concerning embodiment. It is sectional drawing which shows the state in the middle of manufacture of the silicon carbide semiconductor device concerning embodiment. It is sectional drawing which shows the state in the middle of manufacture of the silicon carbide semiconductor device concerning embodiment. 6 is a plan view showing a silicon carbide surface after laser ablation processing in Example 2. FIG.

  A preferred embodiment of a method for manufacturing a silicon carbide semiconductor device and a silicon carbide semiconductor device according to the present invention will be described below in detail with reference to the accompanying drawings. In the present specification and the accompanying drawings, it means that electrons or holes are majority carriers in layers and regions with n or p, respectively. Further, + and − attached to n and p mean that the impurity concentration is higher and lower than that of the layer or region where it is not attached. Also, in this specification, in the Miller index notation, “−” means a bar attached to the index immediately after that, and “−” is added before the index to indicate a negative index. Note that, in the following description of the embodiments and the accompanying drawings, the same reference numerals are given to the same components, and duplicate descriptions are omitted.

(Embodiment)
A method for manufacturing a silicon carbide semiconductor device according to an embodiment will be described by taking as an example the case of manufacturing (manufacturing) a Schottky barrier diode (SBD) using SiC as a semiconductor material. FIGS. 1-5 is sectional drawing which shows the state in the middle of manufacture of the silicon carbide semiconductor device concerning Embodiment. First, as shown in FIG. 1, for example, an n-type 4H—SiC single crystal epitaxial wafer having a diameter of 3 inches is prepared as an n-type semiconductor wafer (semiconductor substrate) 1 (hereinafter referred to as a SiC wafer). The initial thickness (before thinning) of the SiC wafer 1 may be 350 μm, for example. The initial thickness of the SiC wafer 1 is the thickness of the SiC wafer 1 before the SiC wafer 1 is put into the manufacturing process.

  Further, the outer peripheral end 3 of the front surface 2 of the SiC wafer 1 and the outer peripheral end 5 of the back surface 4 are chamfered (beveled), and the thickness decreases from the center side toward the outer peripheral end, for example. It has a shape. Specifically, the outer peripheral ends 3 and 5 of the SiC wafer 1 may be beveled, for example. The front surface 2 of the SiC wafer 1 may be, for example, a (0001) surface (so-called Si surface). Next, a step of patterning a resist film or an oxide film formed on the front surface 2 of the SiC wafer 1 to form an ion implantation mask (not shown), and using this ion implantation mask as a mask, impurities are ionized. The step of implanting 11 is repeated to selectively form the pressure resistant structure 6 on the surface layer of the front surface 2 of the SiC wafer 1.

  The breakdown voltage structure 6 is a region that relaxes the electric field on the front surface 2 side of the SiC wafer 1 and maintains the breakdown voltage, and surrounds the outer periphery of the active region through which current flows in the on state. As the breakdown voltage structure 6, for example, a p-type impurity such as aluminum (Al) may be implanted to form a p-type region guard ring, or an n-type impurity such as phosphorus (P) may be implanted to form a p-type. An n-type region may be formed inside the region guard ring to form a double guard ring. Next, heat treatment is performed to activate the impurities implanted 11 into the SiC wafer 1.

  Next, a deposited oxide film 12 having a thickness of, for example, 1.0 μm is formed on the front surface 2 of the SiC wafer 1 as a surface protective film that protects the front surface 2 of the SiC wafer 1 during back surface grinding described later. To do. Next, as shown in FIG. 2, the SiC wafer 1 is placed on, for example, a stage (not shown) with the front surface 2 facing down, and the SiC wafer 1 is ground from the back surface 4 side to obtain SiC-SBD. Grind to the position of the product thickness used as. Henceforth, let the back surface of the SiC substrate after grinding to the position of product thickness be the grinding surface 4a. The back surface grinding of the SiC wafer 1 is performed a plurality of times by gradually reducing the grain size of the wheel abrasive grains, thereby reducing the grinding damage on the grinding surface 4a of the SiC wafer 1 as well as making the SiC wafer 1 thinner. This is preferable.

  Specifically, the thickness of the SiC wafer 1 is reduced to, for example, about 155 μm by first grinding the back surface 4 of the SiC wafer 1 using a first wheel (not shown). And by grinding the back surface 4 of the SiC wafer 1 second using a second wheel having finer abrasive grains than the first wheel, the thickness of the SiC wafer 1 is further ground by about 5 μm, so that the SiC wafer 1 Grinding damage caused by the first grinding on the grinding surface 4a is removed. As a 1st wheel, you may use the diamond wheel which consists of a grindstone of the abrasive grain in the range whose particle size (diameter) is about 5 micrometers-10 micrometers, for example. As a 2nd wheel, you may use the diamond wheel which consists of a grindstone of the abrasive grain in the range whose particle size is about 2 micrometers-about 4 micrometers, for example.

  Next, as shown in FIG. 3, the SiC wafer 1 is irradiated with a laser 13 to evaporate (vaporize) the SiC wafer 1 by irradiating the corner 13 at the outer peripheral end of the back surface after grinding (grinding surface 4 a). The corner 14 at the outer peripheral edge of the ground surface 4a is removed (laser ablation process). Thereby, the outer peripheral end portion of the grinding surface 4a of the SiC wafer 1 is processed into a smooth predetermined shape. The corner 14 at the outer peripheral end of the grinding surface 4 a of the SiC wafer 1 is a connecting portion between the grinding surface 4 a of the SiC wafer 1 and the side surface of the SiC wafer 1. The incident angle of the laser 13 (the angle formed between the ground surface 4a of the SiC wafer 1 and the laser 13) θ is determined in consideration of the alignment accuracy (alignment accuracy) of the processing apparatus (not shown). For example, it is preferably about 30 to 60 degrees. The reason is as follows.

When the incident angle θ of the laser 13 is within the above range (about 45 ± 15 degrees), the irradiation area of the laser 13 is the projected area of the laser 13 onto the grinding surface 4a of the SiC wafer 1. Therefore, the irradiation area of the laser 13 can be made wider than when the incident angle θ of the laser 13 described later is close to an angle θ _V perpendicular to the grinding surface 4a of the SiC wafer 1 (θ≈θ _V ). . Further, in the case where an incident angle θ of a laser 13 described later is close to an angle θ _H that is horizontal with respect to the grinding surface 4a of the SiC wafer 1 (θ≈θ _H ), the grinding surface 4a of the SiC wafer 1 is moved in the depth direction. The reaching depth of the laser 13 can be increased. Therefore, the irradiation range of the laser 13 can be set within an allowable range in consideration of the alignment accuracy of the processing apparatus, and the laser beam 13 can be stably irradiated to the corner portion 14 at the outer peripheral end of the grinding surface 4a of the SiC wafer 1. can do.

On the other hand, when the incident angle θ of the laser 13 is θ≈θ _V , the irradiation area of the laser 13 is about the area of a circle having the spot diameter (diameter) R of the laser 13 as a diameter (= π · (R / 2) ² ). It becomes. For this reason, when the irradiation area of the laser 13 is narrower than the laser irradiation at an oblique incident angle θ within the above range and the alignment accuracy in the horizontal direction on the grinding surface 4a of the SiC wafer 1 is poor, the grinding of the SiC wafer 1 is performed. There is a possibility that the laser 13 is not irradiated to the corner 14 at the outer peripheral end of the surface 4a. Further, the closer to the incident angle θ≈θ _H of the laser 13, the shallower the laser 13 reaches the ground surface 4 a of the SiC wafer 1. For this reason, when the alignment accuracy in the direction horizontal to the grinding surface 4a of the SiC wafer 1 is poor, the laser 13 reaches a deep position from the grinding surface 4a of the corner 14 at the outer peripheral end of the grinding surface 4a of the SiC wafer 1. There is a risk of not. Therefore, there is a possibility that the outer peripheral end portion of the grinding surface 4a of the SiC wafer 1 cannot be processed into a predetermined shape.

  The wavelength of the laser 13 may be, for example, 1030 nm or less. Preferably, the wavelength of the laser 13 should be less than or equal to the wavelength having energy greater than or equal to the band gap of SiC. For example, 4H—SiC mainly used as a power semiconductor material among SiC compounds (SiC polytype). It is preferable that it is 380 nm or less having energy of band gap (3.26 eV) or more. This is because the corner 14 at the outer peripheral end of the grinding surface 4a of the SiC wafer 1 can be removed in a shorter time.

  The spot diameter R of the laser 13 is preferably in the range of 10 μm to 60 μm, for example. The reason is as follows. This is because when the spot diameter R of the laser 13 is larger than 60 μm, the irradiation range of the laser 13 becomes too wide, and the scattering range of debris (fine debris) generated by the irradiation of the laser 13 increases. In addition, since the energy density of the laser 13 decreases as the spot diameter R increases, it is necessary to increase the irradiation energy of the laser 13 as the irradiation range of the laser 13 increases. This is because the processing apparatus is increased in size. On the other hand, when the spot diameter R of the laser 13 is smaller than 10 μm, the laser 13 may not be applied to the corner portion 14 at the outer peripheral end of the grinding surface 4 a of the SiC wafer 1.

  Through the steps so far, as shown in FIG. 4, the outer peripheral end portion 5 a after processing the ground surface 4 a of the SiC wafer 1 has a shape in which the thickness decreases from the central portion side toward the outer peripheral end portion 5 a, for example. . Specifically, the width w of SiC to be removed by laser ablation processing (that is, the width of the corner portion 14 at the outer peripheral end portion of the grinding surface 4a of the SiC wafer 1) is, for example, within 500 μm from the side surface of the SiC wafer 1 to the inside. There should be. The depth d of SiC to be removed by laser ablation (that is, the thickness of the corner 14 at the outer peripheral end of the grinding surface 4a of the SiC wafer 1) is equal to or less than the thickness of the SiC wafer 1. The reason is that when the SiC removal range exceeds the range defined by the width w and the depth d, debris generated by the laser ablation processing is scattered to the active region, and the device characteristics may be deteriorated. is there. The shape of outer peripheral end 5a after processing of grinding surface 4a of SiC wafer 1 may be the same as the shape of outer peripheral end 3 of front surface 2 of SiC wafer 1.

  Next, the deposited oxide film 12 is removed. Next, as shown in FIG. 5, an interlayer insulating film 7 and a front surface electrode 8 are formed on the front surface 2 of the SiC wafer 1 by a general method, and the back surface is formed on the ground surface 4 a of the SiC wafer 1. Electrode 9 is formed. The front surface electrode 8 is an anode electrode (Schottky electrode) and is in contact with the front surface 2 and the pressure-resistant structure 6 of the SiC wafer 1 in the active region. The end of the front electrode 8 may extend on the interlayer insulating film 7. The back electrode 9 is a cathode electrode (ohmic electrode) and is in contact with the entire grinding surface 4a of the SiC wafer 1. Thus, the silicon carbide semiconductor device according to the embodiment is completed.

Example 1
Next, in accordance with the method for manufacturing the silicon carbide semiconductor device according to the above-described embodiment, SiC-SBD (hereinafter referred to as Example 1) was manufactured under the above-described various conditions. That is, in Example 1, the corner 14 at the outer peripheral end of the grinding surface 4 a of the SiC wafer 1 is removed by laser ablation processing using the laser 13. In Example 1, the irradiation conditions of the laser 13 are as follows. The spot diameter R of the laser 13 was 60 μm, and the incident angle θ was 45 degrees. The wavelength of the laser 13 was 1030 nm, and the pulse width was 800 nm. The repetition frequency of the laser 13 was 10 kHz, and the average output was 35 W. As a comparison, a SiC-SBD (hereinafter referred to as a conventional example) in which the corners of the outer peripheral end of the ground surface of the SiC wafer were removed by grinding using an edge grinder was produced. The manufacturing method of the conventional example other than the processing method of the outer peripheral end portion of the ground surface of the SiC wafer is the same as that of the first embodiment.

  And about Example 1 and the prior art example, it verified about the processing time of the outer peripheral edge part of the grinding surface of a SiC wafer, and a non-defective rate. As a result, in Example 1, the scanning speed of the laser 13 is 100 mm / second, and the laser ablation processing time of the outer peripheral end portion (including the orientation flat) of the grinding surface 4a of one SiC wafer 1 having a diameter of 3 inches is included. Was 5 seconds. On the other hand, in the conventional example, the grinding time of the outer peripheral end portion of the grinding surface of the SiC wafer was 2 minutes.

  Furthermore, about Example 1 and the conventional example, the cross section of the outer peripheral edge part after the process of the grinding surface of a SiC wafer was observed with the transmission electron microscope (TEM). As a result, in Example 1, it was confirmed that no crack was generated in the outer peripheral end portion 5a after the processing of the ground surface 4a of the SiC wafer 1. On the other hand, in the conventional example, it was confirmed that a crack of a maximum of 100 μm was generated at the outer peripheral end portion after processing the ground surface of the SiC wafer. Therefore, in the first embodiment, the wet etching process for removing damage, which has been conventionally performed after the grinding of the outer peripheral end portion of the SiC wafer, can be omitted.

  Therefore, the outer peripheral end 5a after processing of the ground surface 4a of the SiC wafer 1 is damaged by removing the corner 14 at the outer peripheral end of the ground surface 4a of the SiC wafer 1 by laser ablation processing as in the first embodiment. It was confirmed that the processing time of the outer peripheral end portion of the grinding surface 4a of the SiC wafer 1 can be significantly shortened compared to the conventional example without leaving any residual.

  Further, in Example 1, in the steps after the laser ablation processing step of the outer peripheral end portion of the grinding surface 4a of the SiC wafer 1, dust caused by the outer peripheral end portion 5a after processing of the grinding surface 4a of the SiC wafer 1, It was confirmed that the SiC wafer 1 was not cracked and the yield rate could be improved. The reason is that the outer peripheral end 5a of the grinding surface 4a of the SiC wafer 1 can be processed into a smooth predetermined shape as in the conventional example, so that the outer peripheral end of the SiC wafer 1 is, for example, a wafer cassette during the manufacturing process. This is presumed to be because the probability of contact with the battery could be reduced.

  Example 1 is an example manufactured under the laser conditions within the optimum ranges of the incident angle θ, wavelength, and spot diameter R of the laser 13 described in the method for manufacturing the silicon carbide semiconductor device according to the above-described embodiment. Even when other laser conditions are within the above range, the same effects as those of the first embodiment are obtained.

(Example 2)
The scattering range of debris that is scattered when the corner 14 at the outer peripheral end of the grinding surface 4a of the SiC wafer 1 is removed by laser ablation processing was verified. Patent Document 1 discloses that a non-defective product rate of a SiC device is reduced due to debris that is scattered when a SiC wafer is laser-diced. Therefore, 4H-SiC was laser ablated and the debris scattering range was examined. Specifically, as Example 2, a groove 22 is formed in 4H—SiC 21 by laser ablation under the same laser conditions as in Example 1, and the state in the vicinity of the groove 22 of 4H—SiC 21 is measured by a scanning electron microscope (SEM). Was observed. The thickness of 4H—SiC 21 was 150 μm, and the width t1 of the groove 22 was about 60 μm. The acceleration voltage of the electron beam of SEM was 15 kV, and the vicinity of the groove 22 was observed at a magnification of 100 times. The result is shown in FIG. 6 is a plan view showing a silicon carbide surface after laser ablation processing in Example 2. FIG.

  From the results shown in FIG. 6, the debris generated by the laser ablation processing for forming the groove 22 is in the range of about 50 μm from the processing end (upper side wall of the groove 22) to the outside of the groove 22 (indicated by the arrow 23) It was confirmed that it was distributed in the range indicated by the dotted line from the upper part of the side wall of the groove 22. In FIG. 6, in the part surrounded by two dotted lines, the white part in the area | region of the width | variety shown with the arrow of the code | symbol 23 is debris. As a result, as shown in the method for manufacturing the silicon carbide semiconductor device according to the above-described embodiment, a minute region (such as the above-described SiC wafer 1 of the SiC wafer 1) such as the corner 14 of the outer peripheral end of the grinding surface 4a of the SiC wafer 1 is shown. In the case of laser ablation processing with a width w and a depth d (SiC removal range from the side surface), debris extends to the active region where the device structure is formed (from the outer peripheral edge 3, 5a of the SiC wafer 1 to the region inside 2000 μm). Was not scattered, and it was confirmed that the device characteristics were not adversely affected.

  As described above, according to the embodiment, after the back surface grinding, the outer peripheral end portion of the ground surface of the SiC wafer is removed by laser ablation processing. It is possible to prevent the protrusion from protruding outward with respect to the wafer back surface. For this reason, dust and wafer cracking can be prevented in the subsequent steps, and the yield rate can be improved. In addition, according to the embodiment, after grinding the back surface, the corner of the outer peripheral edge of the ground surface of the SiC wafer is removed by laser ablation, so that the ground surface of the SiC wafer can be obtained in a short time without causing damage. Can be processed into a predetermined shape. As described above, since the outer peripheral end portion of the SiC wafer is not damaged, damage to the outer peripheral end portion of the SiC wafer can be prevented as a starting point, and the SiC wafer can be prevented from cracking. Thereby, the yield rate can be improved. Further, according to the embodiment, when processing the outer peripheral end portion of the SiC wafer grinding surface, the outer peripheral end portion of the SiC wafer grinding surface is not damaged. The process for removing can be omitted. Therefore, throughput can be improved.

  As described above, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the embodiment, a case where a SiC-SBD is manufactured has been described as an example. However, for example, a SiC (metal-oxide-semiconductor) type semiconductor device using SiC as a semiconductor material has another configuration SiC device. It is applicable to. In the embodiment, the (0001) plane of the SiC wafer is used as the front surface, and the (000-1) plane (so-called C plane) serving as the back surface is ground. The present invention can also be applied to the case where the crystal plane is a front surface.

  In the embodiment, the case where a breakdown voltage structure is formed on the outer peripheral end side of the SiC wafer and a device structure is formed in a region surrounded by the breakdown voltage structure has been described as an example. A device structure or a breakdown voltage structure may be formed in each region. Further, the protective film for protecting the front surface of the SiC wafer is not limited to the deposited oxide film but may be a resist film, for example. In the present invention, the case where SiC is used as a semiconductor material is described as an example. However, the present invention is not limited to this, and other materials having a band gap larger than Si are used as a semiconductor material. It can also be applied when used as a material. Further, the present invention is similarly established even when the conductivity type is reversed.

  As described above, the method for manufacturing a silicon carbide semiconductor device and the silicon carbide semiconductor device according to the present invention are useful for a silicon carbide semiconductor device in which a semiconductor substrate is thinned to reduce resistance by grinding.

DESCRIPTION OF SYMBOLS 1 SiC wafer 2 The front surface of a SiC wafer 3 The outer peripheral edge part of the front surface of a SiC wafer 4 The back surface of a SiC wafer 4a The position of the product thickness of a SiC wafer (the grinding surface of a SiC wafer)
5 outer peripheral end of back surface of SiC wafer 5a outer peripheral end after processing of ground surface of SiC wafer 6 breakdown voltage structure 7 interlayer insulating film 8 front surface electrode 9 back surface electrode 11 ion implantation 12 deposited oxide film 13 laser 14 SiC wafer Corner of the outer peripheral edge of the grinding surface

Claims (9)

Grinding the back surface of the semiconductor substrate made of silicon carbide, and reducing the thickness of the semiconductor substrate;
A removal step of selectively removing by irradiating the outer peripheral edge of the back surface after grinding of the semiconductor substrate and evaporating the outer peripheral edge of the back surface after grinding of the semiconductor substrate;
The manufacturing method of the silicon carbide semiconductor device characterized by the above-mentioned.   2. The method of manufacturing a silicon carbide semiconductor device according to claim 1, wherein in the removing step, the laser is irradiated at an angle of 30 degrees or more and 60 degrees or less with respect to the back surface after grinding of the semiconductor substrate.   3. The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein in the removing step, the laser is irradiated to a region within 500 μm inward from a side surface of the semiconductor substrate.   The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein the wavelength of the laser is 1030 nm or less.   The spot diameter of the said laser is 10 micrometers or more and 60 micrometers or less, The manufacturing method of the silicon carbide semiconductor device as described in any one of Claims 1-4 characterized by the above-mentioned.   The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein in the grinding step, the thickness of the semiconductor substrate is reduced to a thickness of 150 μm or less. A silicon carbide semiconductor device manufactured using the method for manufacturing a silicon carbide semiconductor device according to any one of claims 1 to 6,
A silicon carbide semiconductor device, wherein an outer peripheral end portion of a back surface of a semiconductor substrate made of silicon carbide is chamfered.   8. The silicon carbide semiconductor device according to claim 7, wherein an outer peripheral end portion of the back surface of the semiconductor substrate has a shape obtained by chamfering a region within 500 μm from the side surface of the semiconductor substrate.   9. The silicon carbide semiconductor device according to claim 7, wherein a thickness of the semiconductor substrate is 150 μm or less.

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