Silicon carbide wafer thinning processing method based on femtosecond laser

Abstract

The invention discloses a femtosecond laser-based silicon carbide wafer thinning processing method, which comprises the following steps of: arranging a to-be-processed SiC wafer on a vacuum chuck, and acquiring the thickness and processing size information of the to-be-processed SiC wafer; obtaining a femtosecond laser processing path according to the thickness and processing size information of the SiC wafer; and based on the processing path, carrying out thinning processing on the SiC wafer by using femtosecond laser processing equipment. Based on the femtosecond laser processing technology, the cutting size of the step surface of the SiC wafer is consistent, materials are removed uniformly, the section quality of the step surface is good during cutting, the edge is free of edge breakage and cracks, and the requirement for feature processing of the SiC wafer at present is met.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser processing, and in particular relates to a silicon carbide wafer thinning processing method based on femtosecond laser. Background Art

[0002] The pulse width of femtosecond laser can be as short as 2.6fs, and the pulse duration is much shorter than the energy release time of the excited carriers in the material. The carrier temperature can reach more than 10K within a few femtoseconds, while the lattice temperature is at room temperature, and the carrier thermal diffusion effect is small, so "cold" processing can be achieved, so the processing accuracy is high and the thermal damage is small. After multi-stage chirped pulse amplification technology, the peak power intensity can reach up to 1023W / cm 2 As mentioned above, femtosecond laser can ionize almost any material and process a wide range of materials. And because the ablation threshold of femtosecond laser processing materials is low, it is easy for femtosecond laser to reach the ablation value of the material and process the material. By controlling the energy of femtosecond laser, the processing area can be smaller than the spot size, and super-diffraction processing of local micro-size can be performed. By controlling the processing path designed by software, femtosecond laser can process complex surface structures.

[0003] As a typical hard and brittle material, SiC single crystal has a Mohs hardness of 9.2 to 9.5, second only to diamond, which makes the processing and manufacturing process of SiC single crystal substrates more difficult. At present, the main manufacturing process of SiC single crystal substrates is divided into several important stages: cutting → rough grinding → fine grinding → polishing. With the market demand and the increasing maturity of SiC growth technology, the demand for large-diameter SiC single crystal substrates and the corresponding processing technology are becoming increasingly higher. Compared with traditional SiC wafer processing methods, how to process SiC wafers that meet the characteristic requirements, high quality, high efficiency, high yield, low cost, and low damage has become an important research direction in the current field of silicon carbide single crystal substrate processing.

[0004] The Mohs hardness of SiC single crystal is very high. When cutting large-sized and ultra-thin SiC wafers with traditional diamond wire, it is difficult for the coolant to enter the cutting area during the cutting process, resulting in an increase in the temperature of the cutting area. While the wafer surface undergoes phase change due to the high temperature, the shavings and powder cannot be removed in time, causing the wafer to break and affecting the processing quality. In addition, a single processing mode cannot meet specific processing requirements. For example, how to process a step surface with a diameter of 90mm and a depth of 200μm on a thin wafer cannot be achieved with traditional cutting technology. Therefore, how to optimize the processing technology of SiC wafers and design new processing methods has become an urgent problem to be solved. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a femtosecond laser-based silicon carbide wafer thinning processing method. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0006] The present invention provides a femtosecond laser-based silicon carbide wafer thinning processing method, comprising:

[0007] S1: placing a SiC wafer to be processed on a vacuum chuck, and obtaining thickness and processing size information of the SiC wafer to be processed;

[0008] S2: Obtaining a femtosecond laser processing path according to the thickness and processing size information of the SiC wafer;

[0009] S3: Based on the processing path, the SiC wafer is thinned using a femtosecond laser processing device.

[0010] In one embodiment of the present invention, the vacuum suction cup comprises a suction cup body and an edge support ring arranged on the periphery of the suction cup body, wherein:

[0011] The suction cup body is provided with a plurality of mounting threaded holes for fixing the vacuum suction cup on a workbench, and the SiC wafer is placed on the suction cup body;

[0012] A vacuum pipe connection hole is also provided in the middle of the suction cup body, through which vacuum is drawn to fix the SiC wafer, and a plurality of internal support columns are also provided on the suction cup body, and the plurality of internal support columns are arranged in a ring array;

[0013] The edge support ring is used to support the edge of the SiC wafer, and the multiple internal support columns are used to support the lower surface of the SiC wafer.

[0014] In one embodiment of the present invention, the processing size information includes the size and thickness of the SiC wafer after processing.

[0015] In one embodiment of the present invention, the processing path includes a positioning path and an arc processing path, wherein:

[0016] The positioning path is the starting point of each arc processing path and is used for positioning the femtosecond laser; the arc processing path is used for arc cutting to remove a predetermined thickness of material on the SiC wafer.

[0017] In one embodiment of the present invention, the positioning path is a line segment arranged along the radial direction of the SiC wafer; the arc processing path includes a plurality of circular paths of different diameters, wherein the diameter of the minimum arc processing path is the minimum diameter required for processing, the diameter of the maximum arc processing path is the diameter of the SiC wafer to be processed, and the difference in radius between adjacent circular paths of the plurality of circular paths of different diameters is 40-60 μm.

[0018] In one embodiment of the present invention, S3 includes:

[0019] Based on the processing path, the femtosecond laser processing device is used to control the femtosecond laser processing head to move to the intersection of the maximum arc processing path and the positioning path, and thinning processing is performed along the maximum arc processing path with the intersection as the starting point; after the maximum arc processing path completes a circle of processing, the femtosecond laser processing head returns to the intersection and moves outward from the intersection along the positioning path a predetermined distance, and then completes another circle of processing along the current arc processing path. After the femtosecond laser processing head returns to the starting point of the current arc processing path, it moves outward along the positioning path a predetermined distance; the execution is repeated, and the arc processing paths are superimposed in sequence from small to large until the step surface cutting of the entire SiC wafer is completed.

[0020] In one embodiment of the present invention, the predetermined distance is 40-60 μm.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] Traditional wire cutting cannot meet the needs of cutting large-size, ultra-thin SiC wafer step surfaces. The present invention proposes a silicon carbide wafer thinning processing method based on femtosecond laser, which solves the current needs of SiC wafer feature processing. Based on femtosecond laser processing technology, the cutting size of the SiC wafer step surface is consistent, the material is removed evenly, the section quality of the step surface is good during cutting, and there is no edge collapse crack.

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a flow chart of a femtosecond laser-based silicon carbide wafer thinning processing method provided in an embodiment of the present invention;

[0025] Figure 2 is a structural schematic diagram of a vacuum suction cup provided by an embodiment of the present invention;

[0026] Figure 3 is a top view of a processing path provided by an embodiment of the present invention;

[0027] Figure 4 is a schematic diagram of a femtosecond laser processing device provided by an embodiment of the present invention;

[0028] Figure 5 It is a schematic diagram of the processing process of a femtosecond laser-based silicon carbide wafer thinning processing method provided in an embodiment of the present invention.

[0029] Description of reference numerals:

[0030] 1- Suction cup body; 2- Edge support ring; 3- Mounting threaded hole; 4- Vacuum pipe connection hole; 5- Internal support column. DETAILED DESCRIPTION

[0031] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, a femtosecond laser-based silicon carbide wafer thinning processing method proposed in the present invention is described in detail below in combination with the accompanying drawings and specific implementation methods.

[0032] The above and other technical contents, features and effects of the present invention are clearly presented in the following detailed description of the specific implementation modes in conjunction with the accompanying drawings. Through the description of the specific implementation modes, the technical means and effects adopted by the present invention to achieve the predetermined purpose can be more deeply and specifically understood. However, the attached drawings are only for reference and explanation purposes and are not used to limit the technical solutions of the present invention.

[0033] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants are intended to cover non-exclusive inclusion, so that an article or device including a series of elements includes not only those elements, but also other elements that are not explicitly listed. In the absence of more restrictions, the elements defined by the statement "including one..." do not exclude the existence of other identical elements in the article or device including the elements.

[0034] Embodiment 1

[0035] Since the pulse width of femtosecond laser is narrow, the peak power is high, and the laser energy is concentrated in a small area, even if the single photon energy is lower than the wide bandgap energy, the femtosecond laser can still be absorbed by the wide bandgap semiconductor through nonlinear absorption. Therefore, micro-nano structures can be easily obtained through femtosecond laser processing. This embodiment provides a method for thinning silicon carbide wafers based on femtosecond laser.

[0036] See also Figure 1 , Figure 1 The flowchart of a femtosecond laser-based silicon carbide wafer thinning method provided by an embodiment of the present invention. The thinning method includes:

[0037] S1: placing a SiC wafer to be processed on a vacuum chuck, and obtaining thickness and processing size information of the SiC wafer to be processed.

[0038] Before the SiC wafer to be processed is cut, it is first mounted and placed on a specific vacuum chuck. Figure 2 , Figure 2 It is a schematic diagram of the structure of a vacuum suction cup provided by an embodiment of the present invention. The vacuum suction cup comprises a suction cup body 1 and an edge support ring 2 arranged on the periphery of the suction cup body 1, wherein the suction cup body 1 is provided with a plurality of mounting threaded holes 3 for fixing the vacuum suction cup on a workbench, and the SiC wafer is placed on the suction cup body 1; a vacuum pipe connection hole 4 is also provided in the middle of the suction cup body 1, and vacuum is drawn through the vacuum pipe connection hole 4 to fix the SiC wafer to avoid position movement during processing; a plurality of internal support columns 5 are also provided on the suction cup body 1, and the plurality of internal support columns 5 are arranged in a ring array; the edge support ring 2 is used to support the edge of the SiC wafer, and the plurality of internal support columns 5 are used to support the lower surface of the SiC wafer to prevent cracking and damage.

[0039] Furthermore, the vacuum suction cup is connected to a vacuum pump through a pipeline. When the vacuum pump is turned on, the SiC wafer is adsorbed to the surface of the vacuum suction cup through negative pressure to ensure that there is no shaking, thereby ensuring the processing quality.

[0040] In this embodiment, the material to be processed is not limited to SiC single crystal wafers, but can also be any other hard and brittle material to be processed, which generally has a circular outer contour. Therefore, the processing size here generally refers to the processing radius or diameter.

[0041] The processing size information includes the size and thickness of the processed wafer. That is, before processing, it is necessary to obtain the original thickness of the SiC wafer to be processed and the size and thickness after processing.

[0042] S2: Obtaining a femtosecond laser processing path according to the thickness and processing size information of the SiC wafer.

[0043] In this embodiment, the processing path mainly includes a positioning path and an arc processing path. The positioning path is the starting point of each arc processing path and is mainly used for positioning the femtosecond laser; the arc processing path is used for arc cutting to remove a predetermined thickness of material on the SiC wafer to form a corresponding removal depth.

[0044] The specific process of obtaining the femtosecond laser processing path is: draw the wafer cutting size according to the CAD program, then use CAM software to simulate the path, and then import it into CNC for processing. For details, please refer to Figure 3 , Figure 3It is a top view of a processing path provided by an embodiment of the present invention. The positioning path is a line segment set along the radial direction of the SiC wafer; the arc processing path includes a plurality of circular paths of different diameters, wherein the diameter of the smallest arc processing path is the minimum diameter required for processing, the diameter of the largest arc processing path is the diameter of the SiC wafer to be processed, and the difference in radius between adjacent circular paths of the plurality of circular paths of different diameters is 40-60 μm.

[0045] S3: Based on the processing path, the SiC wafer is thinned using a femtosecond laser processing device.

[0046] See also Figure 4 , Figure 4 Schematic diagram of a femtosecond laser processing device provided by an embodiment of the present invention. Figure 4 As shown, the optical path mainly comes from the laser generated by the laser generator and two amplified light sources. Inside the amplifier, there are two optical path amplification systems to amplify the seed light, and then the amplified light beam is focused on the workpiece through the focusing objective lens. Two computers control the MaiTai controller and two Ascend controllers respectively. The current size, pulse repetition frequency, etc. can be changed through these two computers. At the same time, the laser shutter can be manually adjusted to control the laser switch.

[0047] The SiC wafer sample is mounted on an XYZ translation stage. The computer that controls the movement of the stage is equipped with μFab software, which can be used to adjust the position of the focal plane relative to the material surface, change the power of the laser, control the laser switch, set the processing path, and control the XYZ stage processing process.

[0048] Based on the above processing path, during the processing, the arc cutting path is superimposed from small to large in sequence, the minimum arc diameter is the minimum diameter required for processing, and the maximum arc diameter is the diameter of the wafer. Through the positioning path, the arc processing path is accumulated according to a certain processing width, thereby completing a certain width and depth of material removal on the surface of the SiC wafer, forming a cutting of the SiC wafer step surface.

[0049] The femtosecond laser processing device controls the movement of the femtosecond laser processing head from the inside to the outside based on the above processing path, and the arc processing path is used to remove each circle of SiC single crystal wafer material. Specifically, based on the processing path, the femtosecond laser processing device controls the femtosecond laser processing head to move to the intersection of the maximum arc processing path and the positioning path, and performs thinning processing along the maximum arc processing path with the intersection as the starting point; after the maximum arc processing path completes a circle of processing, the femtosecond laser processing head returns to the intersection, and moves outward from the intersection along the positioning path a predetermined distance, specifically 40-60μm, and then completes another circle of processing along the current arc processing path, and the femtosecond laser processing head returns to the starting point of the current arc processing path; this is repeated, and the arc processing paths are superimposed from small to large until the step surface cutting of the entire SiC wafer is completed.

[0050] See also Figure 5 , Figure 5 This is a schematic diagram of the processing process of a femtosecond laser-based silicon carbide wafer thinning processing method provided by an embodiment of the present invention. Taking the need to cut a circular step as an example, during the cutting process, based on the processing path, the femtosecond laser processing device controls the femtosecond laser processing head to move to the intersection of the maximum arc processing path and the positioning path, that is, the positioning path where the innermost side of the step to be cut is located, and the intersection is used as the starting point to perform thinning along the maximum arc processing path; after the maximum arc processing path completes a circle of processing, the femtosecond laser processing head returns to the starting point of the arc, and moves 40-60μm outward from the starting point of the arc along the positioning path, that is, moves to another adjacent circle, and then completes another circle of processing along the current arc processing path, and the femtosecond laser processing head returns to the starting point of the current arc processing path; repeating this, the arc processing paths are superimposed from small to large, until the step surface cutting of the entire SiC wafer is completed. It can be seen that as the arc cutting paths are superimposed from small to large, a certain depth is removed around the SiC wafer to achieve a step surface.

[0051] The present invention proposes a silicon carbide wafer thinning processing method based on femtosecond laser. Based on the femtosecond laser processing technology, the cutting size of the SiC wafer step surface is consistent, the material is removed evenly, the section quality of the step surface is good during cutting, and there is no edge collapse crack, which solves the current demand for SiC wafer feature processing.

[0052] In the several embodiments provided by the present invention, it should be understood that the apparatus and method disclosed by the present invention can be implemented in other ways. For example, the apparatus embodiments described above are only illustrative, for example, the division of the modules is only a logical function division, and there may be other division methods in actual implementation, for example, multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed.

[0053] In addition, each functional module in each embodiment of the present invention may be integrated into one processing module, or each module may exist physically separately, or two or more modules may be integrated into one module. The above-mentioned integrated module may be implemented in the form of hardware or in the form of hardware plus software functional modules.

[0054] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A femtosecond laser-based silicon carbide wafer thinning method, characterized in that: include: S1: placing a SiC wafer to be processed on a vacuum chuck, and obtaining thickness and processing size information of the SiC wafer to be processed; S2: Obtaining a femtosecond laser processing path according to the thickness and processing size information of the SiC wafer; S3: Based on the processing path, the SiC wafer is thinned using a femtosecond laser processing device.

2. The femtosecond laser-based silicon carbide wafer thinning method according to claim 1, characterized in that: The vacuum suction cup comprises a suction cup body (1) and an edge support ring (2) arranged on the periphery of the suction cup body (1), wherein: The suction cup body (1) is provided with a plurality of mounting threaded holes (3) for fixing the vacuum suction cup on a workbench, and the SiC wafer is placed on the suction cup body (1); A vacuum pipe connection hole (4) is also provided in the middle of the suction cup body (1), and vacuum is drawn through the vacuum pipe connection hole (4) to fix the SiC wafer. A plurality of internal support columns (5) are also provided on the suction cup body (1), and the plurality of internal support columns (5) are arranged in a ring-shaped array. The edge support ring (2) is used to support the edge of the SiC wafer, and the plurality of internal support columns (5) are used to support the lower surface of the SiC wafer.

3. The femtosecond laser-based silicon carbide wafer thinning method according to claim 1, characterized in that: The processing size information includes the size and thickness of the SiC wafer after processing.

4. The femtosecond laser-based silicon carbide wafer thinning method according to claim 1, characterized in that: The processing path includes a positioning path and an arc processing path, wherein: The positioning path is the starting point of each arc processing path and is used for positioning the femtosecond laser; the arc processing path is used for arc cutting to remove a predetermined thickness of material on the SiC wafer.

5. The femtosecond laser-based silicon carbide wafer thinning method according to claim 4, characterized in that: The positioning path is a line segment arranged along the radial direction of the SiC wafer; the arc processing path includes a plurality of circular paths with different diameters, wherein the diameter of the smallest arc processing path is the minimum diameter required for processing, the diameter of the largest arc processing path is the diameter of the SiC wafer to be processed, and the difference in radius between adjacent circular paths in the plurality of circular paths with different diameters is 40-60 μm.

6. The femtosecond laser-based silicon carbide wafer thinning method according to claim 1, characterized in that: The S3 includes: Based on the processing path, the femtosecond laser processing device is used to control the femtosecond laser processing head to move to the intersection of the maximum arc processing path and the positioning path, and thinning processing is performed along the maximum arc processing path with the intersection as the starting point; after the maximum arc processing path completes a circle of processing, the femtosecond laser processing head returns to the intersection and moves outward from the intersection along the positioning path a predetermined distance, and then completes another circle of processing along the current arc processing path. After the femtosecond laser processing head returns to the starting point of the current arc processing path, it moves outward along the positioning path a predetermined distance; the execution is repeated, and the arc processing paths are superimposed in sequence from small to large until the step surface cutting of the entire SiC wafer is completed.

7. The femtosecond laser-based silicon carbide wafer thinning method according to claim 6, characterized in that: The predetermined distance is 40-60 μm.

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