A step-by-step wafer edge chamfering process

Abstract

The present application relates to the technical field of semiconductor manufacturing, in particular to a step-by-step progressive wafer edge chamfering process, which comprises a first grinding step: driving a first profiled grinding wheel to grind the wafer edge according to a first set of grinding parameters to form an intermediate profile on the wafer edge, the intermediate profile at least containing a first bevel with a predetermined included angle with the wafer surface; a second grinding step: driving a second profiled grinding wheel to grind the intermediate profile according to a second set of grinding parameters to at least remove part of the first bevel to form a final target round profile. By designing a profile progressive forming strategy of first forming a bevel intermediate profile and then modifying it to a circular arc target profile, the grinding contact area is gradually transitioned from surface contact to line contact, avoiding the edge collapse and stress concentration caused by one-time extrusion of the profiled grinding wheel, and the stress concentration coefficient of the wafer edge is reduced.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, specifically to a step-by-step wafer edge chamfering process. Background Technology

[0002] In semiconductor manufacturing, after silicon wafers are diced, their edges are sharp, leaving a layer of cutting damage on the surface, while mechanical stress and oxygen impurities lurk inside. These edge defects can easily cause chipping, stress concentration, and even fragmentation in subsequent chip manufacturing processes, directly affecting chip manufacturing yield and device reliability.

[0003] To eliminate the aforementioned defects, wafer edge chamfering is widely used. Existing chamfering processes typically employ high-speed rotating diamond grinding wheels to grind the edges of silicon wafers, shaping the edges into R-shaped or multi-corner blunt rounded profiles through a single-pass grinding or a simple two-step rough-fine grinding process.

[0004] Patent application CN202411703387.7 discloses a wafer chamfering device and method, which performs two feeds along the wafer's radial and thickness directions using a first feed unit and a second feed unit, respectively, enabling the acquisition of different wafer edge chamfer morphologies with a single grinding wheel. However, the two feeds in this scheme are merely a decomposition in the grinding direction, and the grinding profile is still formed in one step, that is, directly grinding out the final target profile. Its essence is still the conventional approach of rough grinding for shaping and fine grinding for finishing, lacking progressive coordination between the various processes.

[0005] It can be seen that the existing wafer edge chamfering process has the following technical problems: (1) During single-stage grinding, the contact area between the grinding wheel and the wafer edge is large and the grinding force is concentrated, which easily leads to edge chipping and stress concentration at the edge; (2) The simple rough grinding-fine grinding division lacks the progressive design of the contour shape. The rough grinding stage removes a large amount but does not consider the transition shape of stress release, resulting in a deeper subsurface damage layer. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the present invention aims to provide a step-by-step progressive wafer edge chamfering process, which achieves the gradual release of wafer edge stress and the layer-by-layer thinning of the subsurface damage layer through a dual progressive strategy of contour progressive forming and energy progressive control, thereby solving the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides a step-by-step wafer edge chamfering process, including a first grinding step: driving a first forming grinding wheel to grind the wafer edge according to a first set of grinding parameters to form an intermediate profile on the wafer edge, wherein the intermediate profile includes at least a first inclined surface forming a predetermined angle with the wafer surface;

[0008] Second grinding step: Drive the second forming grinding wheel and grind the intermediate contour according to the second set of grinding parameters to remove at least part of the first inclined surface and form the final target blunt round contour.

[0009] Wherein, the abrasive grain size of the first forming grinding wheel is coarser than that of the second forming grinding wheel, and the radial feed pressure in the first set of grinding parameters is greater than that in the second set of grinding parameters. The axial removal amount of the first grinding step and the axial removal amount of the second grinding step are progressively decreasing.

[0010] As a further improvement to this technical solution, the intermediate contour formed by the first grinding step also includes a first bottom plane that connects with the first inclined surface; the second grinding step completely removes the first inclined surface and grinds at least a portion of the first bottom plane into an arc segment of the target blunt round contour.

[0011] As a further improvement to this technical solution, the angle between the first inclined surface of the intermediate contour and the upper surface of the wafer is 30°-60°, and the first bottom plane is parallel to the wafer surface.

[0012] As a further improvement to this technical solution, the grinding wheel speed in the first set of grinding parameters is lower than the grinding wheel speed in the second set of grinding parameters, and / or axial ultrasonic vibration is applied in the first grinding step, while no axial ultrasonic vibration or an amplitude smaller than that applied in the second grinding step is applied.

[0013] As a further improvement to this technical solution, the abrasive grain size of the first forming grinding wheel is between #600 and #1000, and the abrasive grain size of the second forming grinding wheel is between #2000 and #4000; the total radial removal depth of the first grinding step is 3 to 8 times the total radial removal depth of the second grinding step.

[0014] As a further improvement to this technical solution, before the first grinding step, a pre-chamfering step is also included: the wafer edge is pre-ground using a third forming grinding wheel to form an initial inclined surface with an angle greater than 60° to the wafer surface; the first inclined surface in the first grinding step is further ground based on this initial inclined surface.

[0015] As a further improvement to this technical solution, between the first grinding step and the second grinding step, there is also a step of dressing the first forming grinding wheel in place; and the frequency and feed rate of the dressing are adjusted in real time according to the grinding resistance feedback in the first grinding step.

[0016] As a further improvement to this technical solution, the target blunt round profile is a multi-corner type or an R-shaped profile, the intermediate profile is a stepped profile, and the second grinding step rounds the convex corners of the stepped profile into a multi-corner type or an R-shaped blunt round profile.

[0017] As a further improvement to this technical solution, the wafer edge chamfering equipment includes a multi-axis linkage grinding head, with a first forming grinding wheel and a second forming grinding wheel replaceably mounted.

[0018] The control unit is configured to drive the multi-axis linkage grinding head according to different preset radial feed pressure, axial removal curves and grinding wheel speed in the first grinding step and the second grinding step, respectively, so as to achieve progressive grinding from the intermediate contour to the target blunt round contour.

[0019] As a further improvement to this technical solution, the control unit also includes a grinding resistance monitoring module. The monitoring module is configured to collect grinding resistance signals in the first grinding step in real time, and output dressing control signals according to the grinding resistance signals to adjust the in-situ dressing frequency and feed rate of the dressing tool installed on the multi-axis linkage grinding head.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. This step-by-step wafer edge chamfering process uses a progressive contour forming strategy that first forms the beveled middle contour and then trims it into the rounded target contour. This allows the grinding contact area to gradually transition from surface contact to line contact, avoiding edge chipping and stress concentration caused by the single extrusion of the forming grinding wheel, and reducing the stress concentration coefficient at the wafer edge.

[0022] 2. This step-by-step progressive wafer edge chamfering process uses a three-stage progressive scheme of pre-chamfering, intermediate contouring, and final contouring. Combined with the coordinated progressive control of radial feed pressure, grinding wheel speed, and removal amount between rough grinding and fine grinding, the grinding energy is reduced step by step, and the depth of the subsurface damage layer is reduced. It is particularly suitable for edge processing of ultra-thin wafers and wafers made of hard and brittle materials, and can effectively avoid cracking.

[0023] 3. This step-by-step wafer edge chamfering process ensures the consistency of multi-wafer processing by introducing in-situ dressing closed-loop control based on grinding resistance feedback between grinding steps, thereby improving the consistency of wafer edge contours within a batch. Attached Figure Description

[0024] The accompanying drawings described herein are for illustrative purposes only.

[0025] Figure 1 This is a schematic diagram of the intermediate contour formed in the first grinding step of Embodiment 1 of the present invention;

[0026] Figure 2 This is a schematic diagram of the target R-shaped blunt circle profile formed in the second grinding step of Embodiment 1 of the present invention;

[0027] Figure 3 This is a schematic diagram of the stepped intermediate contour formed in the first grinding step of Embodiment 2 of the present invention;

[0028] Figure 4 This is a schematic diagram of the target multi-corner blunt round profile formed in the second grinding step of Embodiment 2 of the present invention;

[0029] Figure 5 This is a schematic diagram of the module connections of the control unit of the present invention;

[0030] Figure 6 This is a comparison diagram of the subsurface damage layer depth of various embodiments and comparative examples of the present invention;

[0031] Figure 7 This is a comparison diagram of the stress concentration factors of various embodiments and comparative examples of the present invention. Detailed Implementation

[0032] The specific embodiments of the present invention are only used to explain the purpose of the present invention.

[0033] Please see Figures 1-7 As shown, the present invention provides a step-by-step progressive wafer edge chamfering process, and the wafer edge chamfering equipment used includes a multi-axis linkage grinding head, which can be replaced with a first forming grinding wheel and a second forming grinding wheel;

[0034] The control unit is configured to drive the multi-axis linkage grinding head according to different preset radial feed pressure, axial removal curves and grinding wheel speed in the first grinding step and the second grinding step, respectively, so as to achieve progressive grinding from the intermediate contour to the target blunt round contour.

[0035] The control unit also includes a grinding resistance monitoring module, which is configured to collect grinding resistance signals in the first grinding step in real time and output dressing control signals based on the grinding resistance signals to adjust the in-situ dressing frequency and feed rate of the dressing tool installed on the multi-axis linkage grinding head.

[0036] The process includes a pre-beveling step: the wafer edge is pre-ground using a third forming grinding wheel to form an initial bevel with an angle greater than 60° to the wafer surface;

[0037] First grinding step: Drive the first forming grinding wheel to grind the edge of the wafer according to the first set of grinding parameters to form an intermediate profile at the edge of the wafer. The intermediate profile includes at least a first inclined surface at a predetermined angle to the wafer surface. The first inclined surface is formed by further grinding based on the initial inclined surface.

[0038] The first forming grinding wheel undergoes in-situ dressing; and the frequency and feed rate of in-situ dressing are adjusted in real time based on the grinding resistance feedback in the first grinding step.

[0039] The second grinding step involves driving the second forming grinding wheel to grind the intermediate contour according to the second set of grinding parameters, at least removing a portion of the first inclined surface to form the final target blunt round contour. The target blunt round contour is a multi-corner or R-shaped contour, while the intermediate contour is a stepped contour. The second grinding step rounds the convex corners of the stepped contour into a multi-corner or R-shaped blunt round contour. The abrasive grain size of the first forming grinding wheel is coarser than that of the second forming grinding wheel, and the radial feed pressure in the first set of grinding parameters is greater than that in the second set of grinding parameters. The axial removal amount in the first grinding step and the axial removal amount in the second grinding step decrease progressively.

[0040] Specifically, the intermediate profile formed by the first grinding step also includes a first bottom plane that connects with the first bevel; the second grinding step completely removes the first bevel and grinds at least a portion of the first bottom plane into an arc segment of the target blunt round profile. The angle between the first bevel of the intermediate profile and the upper surface of the wafer is 30°-60°, and the first bottom plane is parallel to the wafer surface.

[0041] Furthermore, the grinding wheel speed in the first set of grinding parameters is lower than the grinding wheel speed in the second set of grinding parameters, and / or axial ultrasonic vibration is applied in the first grinding step, while no axial ultrasonic vibration or an amplitude smaller than that applied in the second grinding step is applied.

[0042] Furthermore, the abrasive grit size of the first forming grinding wheel is between #600 and #1000, and the abrasive grit size of the second forming grinding wheel is between #2000 and #4000; the total radial removal depth of the first grinding step is 3 to 8 times the total radial removal depth of the second grinding step.

[0043] Example 1

[0044] This embodiment provides a step-by-step wafer edge chamfering process for performing R-shaped edge chamfering on a silicon wafer with a diameter of 300mm.

[0045] Pre-chamfering step: Using a third forming grinding wheel with a grit size of #600, the edge of the wafer is pre-ground at a speed of 4000 r / min to form an initial bevel with an angle of 65° to the upper surface of the wafer, and the radial removal depth is 0.35 mm.

[0046] The first grinding step involves mounting a #800 grit first forming grinding wheel on a multi-axis grinding head and driving it to rotate at 4500 r / min. The radial feed pressure is set to 12 N. This further grinds the pre-beveled initial bevel, forming an intermediate profile consisting of the first bevel (which forms a 45° angle with the upper surface of the wafer) and the first bottom plane (which is parallel to the wafer surface). In this step, axial ultrasonic vibration with an amplitude of 8 μm and a frequency of 20 kHz is applied, resulting in a total radial removal depth of 0.30 mm. During the grinding process, the grinding resistance monitoring module collects resistance signals in real time. When the resistance value exceeds a preset threshold, the control unit issues a dressing signal to perform in-situ dressing of the first forming grinding wheel.

[0047] The second grinding step: Replace the first forming grinding wheel with a grit size of #3000, drive the grinding wheel to rotate at a speed of 6500 r / min, set the radial feed pressure to 4N, and do not apply axial ultrasonic vibration. Perform fine grinding on the intermediate contour, completely remove the first bevel, and grind the first bottom plane into the bottom arc segment of the target R-shaped blunt round contour, with a total radial removal depth of 0.06 mm.

[0048] After processing, the edges of the wafer are inspected.

[0049] Example 2

[0050] The difference between this embodiment and Embodiment 1 is that the target blunt round profile is a multi-corner profile. The intermediate profile formed in the first grinding step is a stepped profile, containing two levels of stepped surfaces. The second grinding step rounds off the convex corners of the stepped profile to form a multi-corner blunt round profile. The remaining steps and parameters are the same as in Embodiment 1.

[0051] Comparative Example 1

[0052] The conventional single-pass chamfering process is employed: using a #2000 forming grinding wheel at a speed of 5500 r / min and a radial feed pressure of 8 N, an R-shaped target profile is ground in one pass, with a total radial removal depth of 0.36 mm. No ultrasonic vibration is applied, and there is no intermediate profile transition.

[0053] Comparative Example 2

[0054] The chamfering process employs a conventional rough grinding-fine grinding method: In the rough grinding step, an #800 grinding wheel is used with a radial feed pressure of 12N, a rotation speed of 4500 r / min, and a radial removal depth of 0.30 mm, directly grinding out the rough grinding contour—not the intermediate contour of the bevel, but a direct contour-following rough grinding. In the fine grinding step, a #3000 grinding wheel is used with a radial feed pressure of 4N, a rotation speed of 6500 r / min, and a radial removal depth of 0.06 mm, to refine the rough grinding contour. There is no progressive design of the contour shape between the two steps; the rough grinding contour is simply an enlarged version of the target contour.

[0055] Comparative Example 3

[0056] The wafer chamfering apparatus and method disclosed in application number CN202411703387.7 are adopted: the target R-shaped profile is directly formed by two feeds of grinding along the radial and thickness directions of the wafer using a single grinding wheel. The total removal depth of the two feeds is 0.36 mm.

[0057] Experimental Example

[0058] 1. Testing Method

[0059] (1) Edge surface roughness: The edge of the chamfered wafer was measured using a white light interferometer ZYGO NewView 9000. Eight measurement points were evenly distributed around the edge of each wafer, and the average value was taken.

[0060] (2) Subsurface damage layer depth: The thickness of the damage layer was measured by observing the wafer edge cross section using the cross section polishing method and scanning electron microscope. Four measurement points were taken for each wafer, and the average value was taken.

[0061] (3) Edge chipping rate: After chamfering, the wafer edge is inspected around the entire circumference using a high-magnification optical microscope (200×). The number of edge defects with a chipping width ≥ 5μm is counted as a percentage of the total number of inspection points. 36 points are evenly distributed around the circumference of each wafer for inspection.

[0062] (4) Stress concentration factor: The stress at the edge of the wafer is detected by micro Raman spectrometer, and the residual stress value is calculated based on the Raman frequency shift. The ratio of the maximum residual stress value to the average residual stress value is used as the stress concentration factor.

[0063] (5) Three-point bending strength: In accordance with semiconductor industry standards, the chamfered wafer is processed into a strip sample with dimensions of 50mm×10mm×wafer thickness. A universal testing machine is used to perform a three-point bending test with a span of 30mm and a loading rate of 0.5mm / min. The fracture load is recorded and the bending strength is calculated.

[0064] (6) Intra-batch consistency (CPK value): The edge contour radius of 25 wafers in the same batch after chamfering is measured, and the process capability index CPK is calculated.

[0065] 2. Test Results

[0066] Table 1 shows a comparison of the chamfering effects of each embodiment and the comparative example;

[0067] Table 1

[0068] Testing items Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Surface roughness Ra (μm) 0.032 0.035 0.087 0.052 0.061 Subsurface damage layer depth (μm) 3.8 4.1 11.2 7.6 8.3 Edge chipping rate (%) 0.8 1.1 8.3 4.7 5.2 Stress concentration factor 1.12 1.15 1.68 1.42 1.51 Three-point bending strength (MPa) 486 472 352 408 391 Intra-batch CPK value 1.72 1.65 — 1.12 1.08

[0069] 3. Results Analysis

[0070] As shown in Table 1:

[0071] (1) Surface quality: The surface roughness Ra of Example 1 is 0.032 μm, which is significantly better than that of Comparative Example 1 (0.087 μm), Comparative Example 2 (0.052 μm), and Comparative Example 3 (0.061 μm). This shows that a smoother edge surface can be obtained by progressively forming the intermediate contour of the inclined plane + plane, combined with the synergistic progressive control of the rough and fine grinding parameters.

[0072] (2) Damage control: The subsurface damage layer depth of Example 1 was only 3.8 μm, which is much lower than that of Comparative Example 1 (11.2 μm), Comparative Example 2 (7.6 μm), and Comparative Example 3 (8.3 μm). This shows that contour progressive forming combined with energy progressive control can effectively reduce the subsurface damage layer layer by layer, avoiding deep damage caused by a single large removal amount or simple rough and fine grinding.

[0073] (3) Regarding edge chipping resistance: The edge chipping rate of Example 1 was 0.8%, which was much lower than that of Comparative Example 1 (8.3%), Comparative Example 2 (4.7%) and Comparative Example 3 (5.2%). The introduction of the inclined surface profile changed the grinding contact from surface contact to line contact, effectively dispersed the grinding stress, and significantly reduced the risk of edge chipping.

[0074] (4) Regarding stress distribution: The stress concentration factor of Example 1 is 1.12, which is significantly lower than that of Comparative Example 1 (1.68), Comparative Example 2 (1.42), and Comparative Example 3 (1.51). This indicates that contouring effectively eliminates stress concentration points at the wafer edge, resulting in a more uniform stress distribution.

[0075] (5) Mechanical strength: The three-point bending strength of Example 1 was 486 MPa, which was significantly higher than that of Comparative Example 1 (352 MPa), Comparative Example 2 (408 MPa) and Comparative Example 3 (391 MPa). The elimination of stress concentration and the thinning of the damaged layer jointly improved the mechanical strength of the wafer.

[0076] (6) In terms of batch consistency: The CPK value of Example 1 reached 1.72, which is much higher than that of Comparative Example 2 (1.12) and Comparative Example 3 (1.08). This is due to the real-time maintenance of the grinding wheel state by the in-situ dressing closed-loop control, which ensures the consistency of multi-wafer processing.

[0077] (7) Multi-corner profile - Example 2: Although the processing difficulty of multi-corner profile is higher than that of R-type, the various indicators of Example 2 are still significantly better than those of the comparative examples, proving that the step-by-step progressive strategy of the present invention is also applicable to the chamfering processing of multi-corner profile.

[0078] 4. Conclusion

[0079] The experimental data above show that, through a dual progressive strategy of contour progressive forming and energy progressive control, this invention reduces the stress concentration factor at the wafer edge by approximately 30%-45%, decreases the subsurface damage layer depth from 8-12 μm in conventional processes to 3-5 μm, stably controls the surface roughness Ra below 0.04 μm, improves the three-point bending strength by approximately 19%-38%, and increases the in-batch CPK value from 1.0-1.2 to above 1.6. This invention significantly improves the surface quality and mechanical strength of the wafer edge while ensuring processing efficiency, and has significant industrial application value.

[0080] Industrial applicability

[0081] The step-by-step wafer edge chamfering process provided by this invention can be widely used in the edge chamfering processing of various semiconductor wafers such as silicon wafers, silicon carbide wafers, and gallium nitride wafers in the semiconductor manufacturing field. It is especially suitable for precision chamfering of 12-inch and larger wafers and ultra-thin wafers, and has broad industrial application prospects and significant economic benefits.

[0082] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A step-by-step wafer edge chamfering process, characterized in that, The first grinding step includes: driving a first forming grinding wheel to grind the edge of the wafer according to a first set of grinding parameters to form an intermediate profile at the edge of the wafer, the intermediate profile including at least a first inclined surface at a predetermined angle to the wafer surface; Second grinding step: Drive the second forming grinding wheel and grind the intermediate contour according to the second set of grinding parameters to remove at least part of the first inclined surface and form the final target blunt round contour. Wherein, the abrasive grain size of the first forming grinding wheel is coarser than that of the second forming grinding wheel, and the radial feed pressure in the first set of grinding parameters is greater than that in the second set of grinding parameters. The axial removal amount of the first grinding step and the axial removal amount of the second grinding step are progressively decreasing.

2. The step-by-step progressive wafer edge chamfering process according to claim 1, characterized in that: The intermediate profile formed by the first grinding step also includes a first bottom plane that connects with the first inclined surface; the second grinding step completely removes the first inclined surface and grinds at least a portion of the first bottom plane into an arc segment of the target blunt round profile.

3. The step-by-step progressive wafer edge chamfering process according to claim 2, characterized in that: The angle between the first inclined surface of the intermediate contour and the upper surface of the wafer is 30°-60°, and the first bottom plane is parallel to the wafer surface.

4. The step-by-step wafer edge chamfering process according to claim 3, characterized in that: The grinding wheel speed in the first set of grinding parameters is lower than the grinding wheel speed in the second set of grinding parameters, and / or axial ultrasonic vibration is applied in the first grinding step, while no axial ultrasonic vibration or an amplitude smaller than that applied in the second grinding step is applied.

5. The step-by-step progressive wafer edge chamfering process according to claim 4, characterized in that: The abrasive grit size of the first forming grinding wheel is between #600 and #1000, and the abrasive grit size of the second forming grinding wheel is between #2000 and #4000; the total radial removal depth of the first grinding step is 3 to 8 times the total radial removal depth of the second grinding step.

6. The step-by-step progressive wafer edge chamfering process according to claim 5, characterized in that: Before the first grinding step, a pre-chamfering step is also included: the wafer edge is pre-ground using a third forming grinding wheel to form an initial inclined surface with an angle greater than 60° to the wafer surface; the first inclined surface in the first grinding step is further ground based on this initial inclined surface.

7. The step-by-step wafer edge chamfering process according to claim 6, characterized in that: Between the first grinding step and the second grinding step, there is also a step of dressing the first forming grinding wheel in place; and the frequency and feed rate of the dressing are adjusted in real time according to the grinding resistance feedback in the first grinding step.

8. The step-by-step progressive wafer edge chamfering process according to claim 7, characterized in that: The target blunt round profile is a multi-corner type or an R-shaped profile, and the intermediate profile is a stepped profile. The second grinding step rounds the convex corners of the stepped profile into a multi-corner type or an R-shaped blunt round profile.

9. The step-by-step wafer edge chamfering process according to claim 8, characterized in that: The wafer edge chamfering equipment used includes a multi-axis linkage grinding head, with a first forming grinding wheel and a second forming grinding wheel that can be interchangeably mounted; The control unit is configured to drive the multi-axis linkage grinding head according to different preset radial feed pressure, axial removal curves and grinding wheel speed in the first grinding step and the second grinding step, respectively, so as to achieve progressive grinding from the intermediate contour to the target blunt round contour.

10. The step-by-step progressive wafer edge chamfering process according to claim 9, characterized in that: The control unit also includes a grinding resistance monitoring module, which is configured to collect grinding resistance signals in the first grinding step in real time and output dressing control signals based on the grinding resistance signals to adjust the in-situ dressing frequency and feed rate of the dressing tool installed on the multi-axis linkage grinding head.

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