SiC semiconductor device and method for manufacturing SiC semiconductor device

Abstract

The purpose of the present invention is to provide a SiC semiconductor device having a property whereby the strength of the SiC semiconductor device can be increased as much as possible when the SiC semiconductor device (1) is cut from a SiC semiconductor wafer (11) by SnB technology. Correspondingly, a manufacturing method for manufacturing the SiC semiconductor device is provided. The SiC semiconductor device is obtained by forming a scribe line (L) on a SiC semiconductor wafer (11) by using a scribe tool and then applying an external force along the scribe line (L) to break the SiC semiconductor wafer (11). In a side wall surface of a SiC semiconductor device (1), a vertical pattern (TL) is formed which extends from a plastic deformation region of a Si surface and a predetermined depth other than a vertical crack region formed directly below the plastic deformation region to a C surface. The longitudinal lines (TL) satisfy either the following conditions: "straight line-shaped", and "when the lower surface is a C surface, the outer angle (theta) at the intersection between the longitudinal lines (TL) extending upward from the C surface and the bent lines (KL) formed by bending the longitudinal lines (TL) for the first time is within 10 degrees".

Description

Technical Field

[0001] The present invention relates to a SiC (silicon carbide) semiconductor device and a method for manufacturing the SiC semiconductor device. Background Art

[0002] Generally, the manufacturing process of semiconductor devices is divided into a process of manufacturing a semiconductor wafer, a process of forming a plurality of semiconductor elements (semiconductor electronic circuits) on the semiconductor wafer, a process of dividing the semiconductor wafer on which the semiconductor elements are formed to obtain semiconductor chips (semiconductor devices), and a process of manufacturing semiconductor devices using the semiconductor chips.

[0003] As a method for dividing (cutting out) a semiconductor wafer, a blade dicing method is representative, and there is also a technique disclosed in Patent Document 1.

[0004] Patent document 1 discloses a breaking technology (Scribing and Breaking, hereinafter sometimes referred to as SnB), which comprises: a process of forming a scribe line on a first main surface side provided with a metal film, breaking the metal film and extending a vertical crack into the interior of the substrate along a predetermined breaking position; and a process of abutting a breaking rod from a second main surface side where no metal film is provided, thereby breaking the substrate with the metal film at the predetermined breaking position.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Re-Publication of Patent "Re-Publication No. 2019 / 082724" Summary of the invention

[0008] Problems to be solved by the invention

[0009] SiC semiconductor wafers have Si and C surfaces. Usually, the Si surface is used as the mounting surface for configuring the back electrode, and the opposite C surface becomes the non-mounting surface. When cutting out a SiC semiconductor device (SiC semiconductor chip) from a SiC semiconductor wafer, SnB can be used, and the device can be broken by scratching from either the Si surface or the C surface. The side to be scratched can be selected according to the structure and manufacturing process of the semiconductor chip. In the aforementioned patent document 1, scratching is performed from the Si surface, and breaking is performed from the C surface side, thereby obtaining a SiC semiconductor device.

[0010] Various characteristics and performances are required for SiC semiconductor devices obtained from SiC semiconductor wafers. Among them, the applicant has conducted intensive research on verification and evaluation of the state of residual stress in SiC semiconductor devices, solder wettability, and the like.

[0011] On the other hand, evaluations related to the state of the cross section (side wall) of SiC semiconductor devices and the strength of the SiC semiconductor devices themselves have not been conducted so far. That is, SiC semiconductor devices used for power devices and the like may be damaged due to heat generation, stress load, etc. during use, and although it is expected that the reliability of strength will be improved, the optimal SnB conditions for improving the strength of SiC semiconductor devices and the properties of SiC semiconductor devices (the state of the chip cross section) are still unclear.

[0012] In view of the above problems, an object of the present invention is to provide a SiC semiconductor device having properties that can maximize the strength of the SiC semiconductor device when the SiC semiconductor device is cut out from a SiC semiconductor wafer by SnB (Scribing and Breaking), and a method for manufacturing the SiC semiconductor device.

[0013] Solutions to Solve Problems

[0014] In order to achieve the above-mentioned purpose, the following technical solutions are adopted in the present invention.

[0015] The SiC semiconductor device of the present invention is obtained by forming a scribe line on a SiC semiconductor wafer using a scribe tool and then applying an external force along the scribe line to break the wafer. The SiC semiconductor device is characterized in that a longitudinal line is formed on the side wall surface of the SiC semiconductor device, which is continuous to the C surface from a specified depth other than a plastic deformation region of the Si surface and a vertical crack region formed directly below the plastic deformation region, and the longitudinal line satisfies the following conditions (1) or (2).

[0016] (1) The longitudinal lines are straight.

[0017] (2) When the lower surface is defined as the C surface, the outer angle of the intersection formed by the longitudinal lines extending upward from the C surface and the bent lines formed by the first bending of the longitudinal lines is within 10°.

[0018] The manufacturing method of a SiC semiconductor device of the present invention is characterized in that a SiC semiconductor device is obtained in the following manner, wherein a longitudinal texture is formed on the side wall surface of the SiC semiconductor device, which is continuous from a specified depth excluding a plastic deformation region of the Si surface and a vertical crack region formed directly below the plastic deformation region to the C surface, and the longitudinal texture satisfies the following conditions (1) or (2).

[0019] (1) The longitudinal lines are straight.

[0020] (2) When the lower surface is defined as the C surface, the outer angle formed by the intersection of the longitudinal lines extending upward from the C surface and the bent lines formed by the first bending of the longitudinal lines is within 10°.

[0021] Effects of the Invention

[0022] According to the present invention, stable separation can be performed when dividing a SiC semiconductor wafer, and defects during breakage can be reduced, so that the strength of the manufactured SiC semiconductor device can be improved as much as possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 FIG. 1 is a diagram schematically showing a side wall surface of a SiC semiconductor device.

[0024] Figure 2 This is a photograph of the side wall surface of a SiC semiconductor device.

[0025] Figure 3 These are photographs of the side wall surfaces of SiC semiconductor devices cut out under various conditions.

[0026] Figure 4 It is a diagram showing the method and conditions of the strength test of the SiC semiconductor device.

[0027] Figure 5 FIG. 1 is an example showing the results of a strength test of a SiC semiconductor device.

[0028] Figure 6 This is a diagram schematically showing an example of a SiC semiconductor wafer for obtaining the SiC semiconductor device of the present invention. DETAILED DESCRIPTION

[0029] An embodiment of a SiC semiconductor device of the present invention will be described with reference to the drawings. The embodiment described below is an example of a specific embodiment of the present invention, and the structure of the present invention is not limited to this specific example.

[0030] In this embodiment, a 4H (Hexagonal)-SiC single crystal is used as an example of a SiC single crystal composed of hexagonal crystals. The SiC semiconductor device 1 obtained in the present invention is suitable for products such as SiC power devices, SiC high-frequency devices, and compound semiconductors.

[0031] First, the SiC semiconductor wafer 11 will be described. It should be noted that the SiC semiconductor wafer 11 may be simply referred to as a "wafer 11", and the SiC semiconductor device 1 may be simply referred to as a "chip 1".

[0032] exist Figure 6Schematically showing a wafer 11. The wafer 11 is a base material for obtaining the chip 1 of the present invention. In the present embodiment, the wafer 11 includes a semiconductor layer, and the semiconductor layer includes a 4H-SiC single crystal.

[0033] The wafer 11 is formed in a disc shape and has a first main surface 13 on the Si side, a second main surface 14 on the C side, and a wafer side wall surface 15 connecting the first main surface 13 and the second main surface 14. A plurality of element formation regions 12 corresponding to the chip 1 are formed on the first main surface 13. A notch 16 is formed on the wafer side wall surface 15. The notch is called an orientation plane (OF), which is a mark indicating the crystal orientation of the SiC single crystal. For example, 1 to 2 orientation planes 16 are provided. By breaking the wafer 11, a plurality of chips 1 are cut out. The size of the chip 1 is, for example, about 5 mm×5 mm, the thickness is about 1 mm or less, and includes a SiC semiconductor layer.

[0034] In the present embodiment, the chips 1 are cut out from the wafer 11 by SnB (Scribing and Breaking).

[0035] Specifically, after a scribing line L is formed on the Si surface of the wafer 11 using a scribing tool, an external force is applied along the scribing line L to break the wafer 1 to obtain the chip 1. In addition, as a major feature of the present embodiment, a longitudinal line TL is formed on the side wall surface of the chip 1, which is continuous from a predetermined depth excluding the plastic deformation region of the Si surface and the vertical crack region formed directly below the plastic deformation region to the C surface, and the longitudinal line TL satisfies the following conditions (1) or (2).

[0036] (1) The longitudinal lines TL are straight lines.

[0037] (2) When the lower surface is defined as the C surface, the outer angle θ of the intersection formed by the longitudinal grain TL extending upward from the C surface and the bent grain KL formed by the first bending of the longitudinal grain is within 10°.

[0038] If condition (2) is described in another way, there is a longitudinal line TL extending upward from the C surface and a bending line KL formed by the first bending of the longitudinal line TL. In this specification, the smaller angle of the intersection of the longitudinal line TL and the bending line KL is considered to be the external angle θ or the intersection angle θ. The external angle θ (absolute value) is within 10°.

[0039] Figure 1 1 is a diagram schematically showing the side wall surface of the chip 1 .

[0040] like Figure 1As shown on the right side of , a longitudinal line TL is formed on the side wall surface of the chip 1, which is continuous from a specified depth to the C surface except for the plastic deformation area of ​​the Si surface and the vertical crack area formed directly below the plastic deformation area. If the longitudinal line TL is a straight line, stable separation can be achieved when the chip is divided, and the adverse conditions during fracture are reduced, thereby improving the strength of the manufactured chip 1.

[0041] On the other hand, Figure 1 As shown on the left side of the chip 1, a longitudinal texture TL is formed on the side wall surface of the chip 1, which is continuous to the C surface from a specified depth excluding the plastic deformation area of ​​the Si surface and the vertical crack area (about 3~10% relative to the thickness of the substrate) formed directly below the plastic deformation area. Regarding the longitudinal texture TL, when the lower surface is set as the C surface, when the external angle θ (intersection angle θ) of the intersection formed by the longitudinal texture TL extending upward from the C surface and the bent texture KL formed by the first bending of the longitudinal texture TL is larger than 10°, the strength of the manufactured chip 1 is low.

[0042] Figure 2 This is an example of a photograph actually taken of the condition of the side wall surface of the chip 1 .

[0043] When scribing the wafer 11, if the pressing force applied to the scribing tool is an appropriate load, Figure 2 On the other hand, if the pressing force applied to the scribing tool deviates from the appropriate load (low load), the outer angle θ of the intersection is larger than 10°.

[0044] Specifically, in Figure 2 In the case of the photo on the right side of the image, the pressing force applied to the scribing tool during scribing is P=6.67N, which is an appropriate load. When scribing is performed based on this pressing force and the chip 1 is cut out, a longitudinal grain TL is formed that is continuous to the C surface from a specified depth other than the plastic deformation area of ​​the Si surface and the vertical crack area formed directly below, and the longitudinal grain TL is a straight line. The applicant conducted in-depth research and found through various experiments that the appropriate load range for the 4H-SiC, t=0.35mm chip 11 is about 5~8N.

[0045] On the other hand, a photograph of the side wall surface of the chip 1 when the pressing force applied to the scribing tool is set to a low load (=4.27N) is shown below. Figure 2. It is clear from the photo that when scratched with a low load, the longitudinal lines TL bend at least twice in the same plane, forming longitudinal lines TL that are significantly different from the above-mentioned appropriate load (=6.67N). On the other hand, when scratched with a low load, basically no vertical crack area was observed. That is, when scratched with a low load, it is difficult to form vertical cracks, so the direction of crack progression becomes unstable during fracture, and the indentation load during fracture increases. When completely separated, the ends of the substrate (C-side) contact each other under the impact of the fracture, resulting in defects and reduced strength.

[0046] Here, the scribing tool is a wheel type, the wheel diameter is 2 mm, and the front end angle of the wheel is 140°.

[0047] It should be noted that, when the load is higher than the appropriate load, there are problems such as horizontal cracks and collapse on the Si surface side, so it is basically necessary to avoid scribing with a high load higher than the appropriate load specified in the present invention. In addition, the applicant found that when the bare wafer is cut by SnB, horizontal cracks are less likely to occur when the blade tip angle of the scribing tool is an obtuse angle compared to an acute angle, and the strength of the Si surface becomes higher (the C surface does not change). By properly selecting the blade tip angle, a more appropriate load can be applied.

[0048] Figure 3 The photographs are magnified images of the side wall surfaces of the chips 1 obtained after the wafer 11 was scratched at various loads and the chips 1 were cut out.

[0049] about Figure 3 In the evaluation of the bending strength, a bending force is applied to the cut chip 1 by a bending test method, and the applied force when it breaks is taken as the bending strength.

[0050] Regarding the bending test method and test conditions, such as Figure 4 As shown in the figure, a 5 mm square chip 1 is used as a test sample, and the test sample is supported from below at a distance of 3 mm. On this basis, the center of the test sample is pressed from above at a speed of 1 mm / min, and the pressing force when the test sample breaks is used as the bending strength (bending strength). At this time, the test sample is set in a manner that the cross section parallel to the OF is perpendicular to the test fixture, and the load is applied from the Si surface side.

[0051] The greater the bending strength, the higher the strength of the chip 1. The applicant has found that in order to obtain a high-strength chip 1, it is necessary to set the pressing force during scribing to an appropriate load in SnB.

[0052] As the appropriate load for the scribing tool, when the load force (pressing force) is 5.07N or 6.67N, the bending strength of the chip 1 becomes a larger value, resulting in a high-strength chip 1. A longitudinal line TL is generated on the side wall surface of such a chip 1, and the longitudinal line TL satisfies any one of the following conditions: (1) it is a straight line; (2) when the lower surface is set as the C surface, the outer angle θ of the intersection formed by the longitudinal line TL extending upward from the C surface and the bent line KL formed by the first bending of the longitudinal line TL is within 10°.

[0053] On the other hand, when the load on the scribing tool is low (3.47N, 4.27N), the bending strength of the chip 1 becomes a smaller value, resulting in a chip 1 with low bending strength. A longitudinal line TL that draws an arc from bottom to top is generated on the side wall surface of such a chip 1. When the lower surface is set as the C surface, the outer angle θ of the intersection formed by the longitudinal line TL extending upward from the C surface and the bent line KL formed by the first bending of the longitudinal line TL becomes greater than 10°.

[0054] It should be noted that if Figure 3 As can be seen in the photo (2) with a load of 3.47N, the initial bending direction of the longitudinal grain TL is not constant. When the longitudinal grain TL extending upward from the C surface is first bent, it may be bent to the left or to the right. Regardless of the bending direction, when the outer angle θ of the intersection formed by the longitudinal grain TL extending from the C surface and the bending grain KL connected to it is within 10°, it becomes a high-strength chip 1 (a chip 1 with high bending strength).

[0055] exist Figure 3 In the figures, the cases where the evaluation of bending strength is described as “high (*)” or “low (*)” indicate that the results were estimated from other experimental results (a state in which longitudinal grains TL were generated in the cross section) without performing a strength test.

[0056] Figure 5 An example of evaluation of bending strength is shown.

[0057] If the chip 1 is cut out by scribing with an appropriate load, a linear longitudinal grain TL is generated on its side wall surface, and the average bending strength is 1300 MPa, with a maximum value of 2000 MPa. On the contrary, if the chip 1 is cut out by scribing with a low load, arc-shaped grains are generated on the side wall surface, and the average bending strength is 1000 MPa, with a maximum value of only 1500 MPa.

[0058] In order to obtain the side wall surface described above, in other words Figure 1 , Figure 2 In this embodiment, the chip 1 having the side wall surface shown is obtained by the following method.

[0059] First, a scribing tool (eg, a scribing wheel) is used to form a scribing line L on the wafer 11 , and then an external force is applied along the scribing line L to break the wafer 11 , thereby obtaining the chip 1 .

[0060] That is, the wafer 11 can be broken into chips 1 using a scribing device for forming the scribing line L and a breaking device for breaking by applying an external force along the scribing line L. Figure 6 The method of forming the scribe lines L on the wafer 11 and breaking the wafer 11 along the scribe lines L to obtain a plurality of chips 1 is called SnB (Scribing and Breaking).

[0061] For example, the scribing line L can be formed by rolling the blade tip of the scribing wheel (a ridge formed on the outer circumference of a circle) along the outer circumference of the wafer 11 in a state of being pressed against the wafer 11. As a scribing tool, a fixed blade (diamond pen, etc.) can also be used instead of the scribing wheel.

[0062] The force pressing the scoring wheel can be obtained by setting the pressing force to an appropriate load. Figure 1 , Figure 2 Side wall surface as shown.

[0063] Regarding the pressing force, the applicant has conducted various experiments and the results are shown as follows: Figure 3 As a result, it was found that by pressing the scribing wheel with a force of 5N to 8N and pressing it against the wafer 11, a chip 1 having a side wall surface in either (1) or (2) can be obtained.

[0064] (1) The longitudinal lines TL are straight lines.

[0065] (2) When the lower surface is defined as the C surface, the outer angle θ formed by the intersection of the longitudinal grain TL extending upward from the C surface and the bent grain KL formed by the first bending of the longitudinal grain TL is within 10°.

[0066] It should be noted that various devices other than the SnB device can be used as a device for obtaining the chip 1 from the wafer 11. The scribing device and the breaking device constituting the SnB device may be an integrated device or a separate device. In addition, the appropriate load band varies depending on the thickness of the substrate and the pattern formed on the surface of the substrate.

[0067] As described above, if the chip 1 satisfies the conditions that "the longitudinal line TL is straight" or "when the lower surface becomes the C surface, the external angle θ of the intersection formed by the longitudinal line TL extending upward from the C surface and the bent line KL formed by the first bending of the longitudinal line TL is within 10°" on the side wall surface of the chip 1, then the chip 1 can be stably separated during chip manufacturing, and the undesirable conditions during breakage are reduced, thereby making it possible to increase the strength of the manufactured chip 1 (especially the three-point bending strength of the C surface) as much as possible.

[0068] It should be noted that the embodiments disclosed herein are illustrative in all aspects and should not be considered as restrictive. In particular, in the embodiments disclosed herein, matters not explicitly disclosed, such as working conditions, operating conditions, dimensions and weight of structures, etc., are matters that can be easily selected by a person skilled in the art by referring to the problems to be solved, solutions, functions and effects, etc. of the present invention disclosed in this specification.

[0069] Description of Reference Numerals

[0070] 1 SiC semiconductor device (chip)

[0071] 11 SiC semiconductor wafer

[0072] 12 Element formation area

[0073] 13. First wafer main surface

[0074] 14. Second wafer main surface

[0075] 15 Wafer sidewall

[0076] 16 Orientation Plane

[0077] L Score Line

[0078] TL longitudinal grain

[0079] KL Bend pattern.

Claims

1. A SiC semiconductor device, which is obtained by forming a scribe line on a SiC semiconductor wafer using a scribe tool and then applying an external force along the scribe line to break the wafer, The SiC semiconductor device is characterized in that A longitudinal texture is formed on the side wall surface of the SiC semiconductor device, which is continuous from a predetermined depth to the C surface except for a plastic deformation region of the Si surface and a vertical crack region formed directly below the plastic deformation region, and the longitudinal texture satisfies the following conditions (1) or (2): (1) The longitudinal lines are straight lines. (2) When the lower surface is defined as the C surface, the outer angle of the intersection formed by the longitudinal lines extending upward from the C surface and the bent lines formed by the first bending of the longitudinal lines is within 10°.

2. A method for manufacturing a SiC semiconductor device, wherein a SiC semiconductor device is obtained by forming a scribe line on a SiC semiconductor wafer using a scribe tool and then applying an external force along the scribe line to break the SiC semiconductor device. The method for manufacturing a SiC semiconductor device is characterized in that: A SiC semiconductor device is obtained in the following manner, wherein a longitudinal texture is formed on the side wall surface of the SiC semiconductor device, which is continuous from a predetermined depth to the C surface except for a plastic deformation region of the Si surface and a vertical crack region formed directly below the plastic deformation region, and the longitudinal texture satisfies the following conditions (1) or (2): (1) The longitudinal lines are straight lines. (2) When the lower surface is defined as the C surface, the outer angle of the intersection formed by the longitudinal lines extending upward from the C surface and the bent lines formed by the first bending of the longitudinal lines is within 10°.

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