Method for controlling bending degree of silicon wafer through double-sided thinning

Abstract

The invention relates to the technical field of semiconductor manufacturing, and discloses a method for controlling the bending degree of a silicon wafer through double-sided thinning. The method aims to convert a double-sided thinning process from a passive'deformation generation source 'into an active'shape corrector'. The method comprises the following steps: acquiring a curvature value of an incoming silicon wafer and setting a final target curvature value; the target DSG morphology and the deformation quantity delta BOW needing to be introduced are calculated based on the morphology neutralization model, and the target thinning position and angle parameters of the grinding wheel are deduced according to the target DSG morphology and the deformation quantity delta BOW; dSG machining is carried out after collaborative adjustment of the thinning position and the angle of the grinding wheel is carried out; and finally, the machined morphology is subjected to detection and feedback fine adjustment. According to the method, through model prediction and process design, self-defined shaping of the final bending degree value of the silicon wafer is achieved, the silicon wafer is not limited by incoming materials, the bending degree value can be stably, efficiently and accurately regulated and controlled to the target range, and the product yield and the process flexibility are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and more specifically to a method for controlling the curvature of silicon wafers through double-sided thinning. Background Technology

[0002] In 12-inch silicon wafer manufacturing, bendability (BOW) is a key geometric parameter for measuring the local flatness of the central region of the wafer. Inadequate bendability can directly lead to lithography machine focusing failure, excessive overlay accuracy, and even serious production accidents such as transport debris, posing a fatal threat to product yield and process stability. Therefore, achieving precise control of bendability is an indispensable prerequisite for high-end chip manufacturing.

[0003] It is generally believed that the final curvature problem can be traced back to two upstream stages of silicon wafer processing: wire cutting and double-sided thinning DSG. Wire cutting easily causes overall wafer warping (WARP). This overall unevenness changes the relative height of the wafer center, thus setting an initial "base value" for subsequent curvature. The direct impact of the DSG process comes from its processing characteristics. Curvature is extremely sensitive to the material removal rate in the central region of the wafer. Even slight deviations in parameter settings can directly lead to excessive or insufficient grinding at the center point, resulting in a "center point problem"—a bulge or depression at the center point—and consequently, abnormal curvature.

[0004] Currently, the industry mainly relies on the following two approaches to control bending in the DSG process: 1) Incoming material screening and grouping: Grouping silicon wafers according to their initial morphology parameters (such as TTV, WARP) after wire cutting, and attempting to match different subsequent process parameters to different groups. This method acknowledges that existing processes cannot effectively handle incoming material fluctuations, resulting in low efficiency, lengthy processes, and inherent defects in the method's general applicability. 2) Passive parameter optimization in the DSG process: In the double-sided thinning (DSG) process, optimizing process parameters such as cooling water flow rate and rotation speed, as shown in CN118951894A and CN110098117A, limits the approach to fine-tuning within a given processing mode, suppressing bending by controlling processing stability. This is mainly because traditional concepts often attribute abnormal bending to "poor incoming wire cutting materials" or "deformation introduced by DSG processing," thus adopting "avoidance" or "suppression" strategies. Whether it's grouping incoming materials or attempting to "reduce" the deformation impact of DSG through process stabilization measures, the underlying logic is to treat the DSG process as a passive and uncontrollable "source of deformation." This "suppression" adjustment process means that the solution can only be repaired on the periphery, and cannot achieve universal and efficient precise control of bending that is not constrained by incoming materials. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for controlling the curvature of silicon wafers through double-sided thinning. This method aims to achieve "custom shaping" of the silicon wafer morphology, enabling precise control of its final curvature value to the target range through DSG processing without limiting the curvature of the wire-cut incoming material.

[0006] Through long-term process manufacturing exploration, the inventors have discovered a way to precisely control the curvature of silicon wafers within a target range after the double-sided thinning (DSG) process, achieving stable high-flatness wafers without relying on tedious screening and grouping of wire-cut incoming materials. The inventors found that DSG has traditionally been considered a passive "thinning" step, with the introduced deformation seen as a negative effect that needed to be overcome. The inventors creatively transformed the DSG process from a "deformation source" into an active "morphology corrector." Through in-depth analysis of the process chain, based on the understanding that the curvature of the final polished wafer is the superposition of the wire-cut incoming material's morphology and the DSG processing morphology, and that the polishing process chemically and mechanically amplifies this superposition effect, the inventors treated the DSG processing morphology as a controllable key variable. Based on this, the inventors established a method and specific techniques for actively controlling the DSG processing morphology to precisely regulate the final silicon wafer curvature.

[0007] In their exploration of the DSG process, the inventors realized that the distribution of grinding force on the center point of the silicon wafer directly determines the stress state at the wafer's center, thus dominating the sign and magnitude of the curvature value. Controlling the curvature essentially means controlling the symmetrical distribution of grinding force in the central region of the silicon wafer. Based on this, through theoretical analysis and repeated experimental verification, the inventors identified two key factors affecting the grinding force distribution: the thinning position of the grinding wheel (macroscopic lever arm) and the left-right vertical angle of the grinding wheel (microscopic force direction). The inventors discovered that systematically adjusting the thinning position (e.g., gradually shifting it to the left or right) produces a predictable and monotonic effect on the curvature. For example, shifting the thinning position to the right always results in a "bowl" shape. This is not accidental but determined by the physical nature of the changing grinding force lever arm. Further exploration revealed that adjusting the thinning position alone sometimes fails to achieve the ideal shape. Further, by adjusting the vertical and horizontal angles of the left and right grinding wheels in a coordinated manner according to specific rules (e.g., equal amplitude, opposite direction), a more refined "sculpting" of the shape can be achieved. Furthermore, position adjustment and angle adjustment have a strong synergistic effect. First, the main shape is set by position adjustment, and then fine-tuning is done by angle adjustment, which constitutes the optimal control strategy. Based on a large amount of data, the inventors have summarized a simplified shape neutralization model, which makes "custom shaping" for any incoming material and target value calculable and achievable on specific production lines and equipment.

[0008] Based on the above principles and findings, this invention provides a method for precisely controlling the curvature of silicon wafers during double-sided thinning, mainly comprising the following steps: Step 1: Obtain the initial morphology parameters (incoming material curvature value) of the silicon wafer after wire cutting; set the final curvature value according to the flatness requirements of the final product. The final curvature value is usually set to the expected curvature value after the silicon wafer is polished.

[0009] Step 2: Based on the morphology neutralization model, calculate and determine the morphology variable (ΔBOW) of the DSG process according to the initial morphology, i.e., the incoming material curvature value (BOW_incoming) and the final curvature value (BOW_final), and determine the target DSG morphology of the DSG process, i.e., the target curvature value (BOW_DSG); and derive the target thinning position and target angle parameters of the grinding wheel accordingly.

[0010] Step 3: Execute the following coordinated control procedure. After adjusting the thinning position of the grinding wheel, the left and right vertical angles, and the horizontal angles of the grinding wheel according to the following control procedure, perform DSG machining: I) Adjust the thinning position of the grinding wheel to the target thinning position to set the macroscopic trend of the silicon wafer curvature. Preferably, after adjusting the thinning position, the barometer of the DSG machine needs to be reset to zero to lock in the adjustment effect and prevent the machine's automatic compensation function from negating it.

[0011] II) Adjust the left-right vertical and horizontal angles of the grinding wheel to the target angle parameters to perform fine calibration of the silicon wafer morphology. The adjustment of the left-right vertical and horizontal angles is performed in preset adjustment units, each unit including asymmetrical changes in the vertical angle of the left and right grinding wheels and synchronized changes in the horizontal angle. The adjustment of the left-right vertical and horizontal angles of the grinding wheel includes at least one such adjustment unit.

[0012] Step 4: Inspect the morphology of the silicon wafer after DSG processing. If the target curvature value is not met, return to Step 2 for parameter fine-tuning. Then, execute Step 3 and this step according to the fine-tuned parameters until the target is met.

[0013] The morphology neutralization model in step two is: ΔBOW≈K×BOW_final-BOW_incoming-β. Here, BOW_final is the curvature value after the silicon wafer polishing process; BOW_incoming is the incoming material curvature value, i.e., the curvature value after silicon wafer wire cutting; and ΔBOW is the curvature value variable generated by the double-sided thinning (DSG) process. Based on the morphology neutralization model, the curvature value variable, ΔBOW, is calculated and determined. The coefficients K and β are empirical coefficients determined by fitting experimental data for a specific process line and specific equipment. The determination process is a process debugging process, employing systematic experimental design and regression analysis, as detailed below.

[0014] Step 1. Establish the model: BOW_final ≈ A × BOW_DSG + β, where A and β are constants, BOW_final is the curvature value after the silicon wafer polishing process, and BOW_DSG is the target curvature value after the silicon wafer double-sided thinning (DSG) process. After extensive research, the inventors discovered that from the completion of the DSG process to the final polishing process, forming a polished silicon wafer, the curvature morphology of the polished silicon wafer exhibits a near-linear "inheritance / transmission" of the DSG-formed morphology. A represents this inheritance / transmission coefficient. If A is close to 1, it indicates that polishing hardly changes the morphological trend formed by DSG; if A deviates from 1, it indicates that polishing amplifies or reduces this trend; β is the systematic deformation offset introduced by the polishing process itself. For a specific process line and specific equipment, coefficients A and β can be considered close to constants.

[0015] The incoming silicon wafer undergoes a certain deformation during the DSG process. The superposition of these two deformations forms the morphology of the silicon wafer after the DSG process, i.e.: BOW_DSG≈BOW_incoming+ΔBOW, where BOW_DSG is the curvature value after the double-sided thinning process (DSG); BOW_incoming is the curvature value after the wire cutting process; and ΔBOW is the curvature value variable generated by the double-sided thinning process (DSG).

[0016] Step 2. Model parameter determination process: A batch of wire-cut silicon wafers with sufficient morphological diversity (such as bending values ​​from negative to positive) were selected as experimental samples. The incoming bending value of each sample was accurately measured and denoted as BOW_incoming.

[0017] The DSG process is performed using a fixed, benchmark process parameter. After processing, the curvature value of the DSG process is measured (denoted as BOW_DSG).

[0018] Finally, the final curvature value (denoted as BOW_final) is measured after polishing.

[0019] Record the above three sets of data for all samples.

[0020] Based on the experience that BOW_final is a linear combination of BOW_DSG, the fitting model is set as: BOW_final ≈ A × BOW_DSG + β, where A and β are fixed coefficients. By using regression analysis tools such as the least squares method to fit the collected data, the coefficients A and β suitable for the specific process line and specific equipment can be obtained.

[0021] Get A and β, BOW_DSG≈(1 / A)×BOW_final-β, Then ΔBOW≈BOW_DSG-BOW_incoming≈(1 / A)×BOW_final-BOW_incoming-β; Assuming K=1 / A, the morphological neutralization model ΔBOW≈K×BOW_final-BOW_incoming-β is obtained.

[0022] When our goal is to obtain a flat, polished silicon wafer, i.e., when BOW_final=0, the morphology neutralization model simplifies: ΔBOW≈-BOW_incoming-β.

[0023] Ideally, if the polishing process does not alter the morphology, coefficients A and K should be close to 1, and β close to 0. However, in reality, polishing alters the morphology. Based on extensive practical experience, this invention demonstrates that while the value of coefficient K varies depending on the production line, it generally falls within a range with clear physical meaning: between 0.8 and 1.2.

[0024] The above method provides a scientific initial starting point and quantitative guidance for process debugging, significantly reducing the time spent on blind debugging. In actual production, fine-tuning can be performed based on the fitted coefficients, thereby quickly locking in the optimal process window.

[0025] In step three, adjusting the thinning position of the grinding wheel to the target thinning position, wherein setting the target thinning position includes determining the adjustment amount and direction of the thinning position, and the determination method is as follows: (1) Thinning position adjustment amount: The thinning position is adjusted in stages based on the hardness of the grinding wheel. The correspondence between the two is divided into several levels according to the type and age of the grinding wheel and abrasive, for example: Hardness grade H1 (soft): New grinding wheel or grinding wheel with high porosity abrasive as the main component.

[0026] Hardness grade H2 (medium): Standard grinding wheel in normal use.

[0027] Hardness grade H3 (hard): old grinding wheels or grinding wheels mainly composed of high-hardness, high-density abrasives.

[0028] Each hardness grade is assigned a base adjustment unit ΔP_base. For example, if ΔP_base = 20μm, then the actual adjustment ΔP matches the grinding wheel hardness grade: ΔP = n × ΔP_base, where n is the coefficient corresponding to the hardness grade. H1 (soft): n = 0.5~1.0, H2 (medium): n = 1.0~1.5, H3 (hard): n = 1.5~2.5. Therefore, when ΔP_base = 20μm, the adjustments for the above three hardness grades are 10~20μm, 20~30μm, and 30~50μm respectively.

[0029] Based on the determined ΔBOW value, the adjustment unit ΔP_base is determined. The absolute value of ΔBOW is proportional to the adjustment amount ΔP at the thinning position. The specific value of the adjustment unit ΔP_base can be determined based on an empirical database built from historical data. The larger the |ΔBOW| value, the larger the ΔP_base should be, and naturally, the larger the adjustment amount |ΔP| will also be.

[0030] (2) Regulations for determining the direction of thinning position adjustment: The direction of movement of the thinning position is determined by ΔBOW. When ΔBOW is negative (less than zero), it indicates that the DSG process needs to be processed towards a bowl shape, and the thinning position is adjusted to the right by ΔP. Adjusting the thinning position to the right means that the left grinding wheel moves ΔP closer to the silicon wafer, while the right grinding wheel moves ΔP further away from the silicon wafer; that is, both the left and right grinding wheels move ΔP to the right simultaneously.

[0031] When ΔBOW is positive (greater than zero), it indicates that the DSG process needs to be processed towards a dome shape, and the thinning position needs to be adjusted to the left by ΔP. Adjusting the thinning position to the left means that the left grinding wheel moves away from the silicon wafer by ΔP, while the right grinding wheel moves closer to the silicon wafer by ΔP. In other words, both the left and right grinding wheels move to the left by ΔP simultaneously.

[0032] With this set of rules, technicians no longer rely on guesswork based on experience when facing different grinding wheels, but instead make adjustments based on clear rules, thus achieving repeatability and standardization of operations.

[0033] In step three, the adjustments to the left and right vertical and horizontal angles are performed in preset adjustment units. Each adjustment unit consists of two simultaneous operations, including... Synchronous Operation 1) Asymmetrical Adjustment of Grinding Wheel Vertical Angle: The specific operation is as follows: adjust the vertical angle of the left grinding wheel by ΔV_L, and adjust the vertical angle of the right grinding wheel by ΔV_R, with |ΔV_L|=|ΔV_R|, but in the opposite direction, i.e., ΔV_R=-ΔV_L. The preferred values ​​for |ΔV_L| or |ΔV_R| are 5μm, 10μm, or 15μm. For example, using 10μm as a standard adjustment unit, when correcting excessively convex morphology (BOW_DSG>0), ΔV_L=-10μm and ΔV_R=+10μm.

[0034] Synchronous Operation 2) Linked Adjustment of Grinding Wheel Horizontal Angle: Specifically, the horizontal angles of the left and right grinding wheels are synchronized and reduced by a fixed value ΔH. The value of ΔH is typically 1 / 2 to 1 / 3 of the value of |ΔV_L| or |ΔV_R|. For example, when |ΔV_L| or |ΔV_R| is 10μm, ΔH is usually set to 5μm, meaning the horizontal angles of the left and right grinding wheels are reduced by 5μm simultaneously. This operation aims to compensate for potential stability issues caused by changes in the vertical angle, acting like a "stabilizer."

[0035] For example, for a centrally protruding morphology (BOW_DSG>0), the adjustment unit includes ΔV_L=-10μm, ΔV_R=10μm, and ΔH=5μm, meaning the left grinding wheel vertically decreases by 10 μm, the right grinding wheel vertically increases by 10 μm, and the horizontal angles of the left and right grinding wheels decrease by 5 μm. 1-4 adjustment units can be repeated until the morphology meets the requirements. As another example, for a centrally concave morphology (BOW_DSG<0), the adjustment unit includes ΔV_L=+10μm, ΔV_R=-10μm, and ΔH=5μm, meaning the right grinding wheel vertically decreases by 10 μm, the left grinding wheel vertically increases by 10 μm, and the horizontal angles of the left and right grinding wheels decrease by 5 μm. Here, BOW_DSG is derived from the formula BOW_DSG≈BOW_incoming+ΔBOW.

[0036] The present invention has the following advantages over the prior art.

[0037] This invention provides for the first time a complete, model-predictive-based methodology for bending control, transforming the DSG process from passive machining to active morphology design, and achieving a leap from "leveling control" to "design".

[0038] The above solution can significantly improve the process yield of bending from about 86% to over 98%.

[0039] This method does not rely on stringent requirements for incoming materials and has the ability to handle various abnormal BOW incoming materials, greatly enhancing the flexibility and stability of the production line.

[0040] By precisely controlling the BOW (Biode Surface Shape), it can be flexibly integrated with subsequent processes such as epitaxy to meet the customized needs of different customers for substrate morphology, thus creating new product possibilities. Attached Figure Description

[0041] Figure 1 This is a flowchart of a method for precisely controlling the curvature of a silicon wafer through double-sided thinning according to the present invention.

[0042] Figure 2 The 3D morphology of the silicon wafer after polishing and epitaxy of the double-sided thinning bending warp (BOW) controlled by the method of the present invention in Embodiment 8 of the present invention. Detailed Implementation

[0043] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. The following embodiments are provided to better understand the present invention, but not to limit its scope of protection.

[0044] like Figure 1 The diagram shown is a flowchart of a method for precisely controlling the curvature of a silicon wafer through double-sided thinning according to the present invention. The present invention will be further described below with reference to the flowchart and specific embodiments.

[0045] Example 1

[0046] This embodiment primarily addresses the issue of a bulge at the center of the incoming material, aiming for complete flatness of the polished wafer, i.e., a BOW (Browser Overhead) of approximately 0. This embodiment demonstrates how the method of this invention can correct a typical incoming material anomaly (center bulge) to flatness. The specific steps are as follows.

[0047] Step one, detection and judgment, corresponding to: Figure 1 Step 1 in the flowchart: The average incoming bending value of a certain batch of 12-inch silicon wafers after wire cutting was measured to be +8.5μm (shaped like a "bun"), and the WARP value was 22μm.

[0048] Step two, target setting and calculation, corresponding to... Figure 1 Step 2 in the flowchart: Target setting: The silicon wafer is required to be flat after polishing, so the final target curvature value (BOW_final) is set to 0μm.

[0049] Model calculation: Based on the pre-fitted morphology neutralization model parameters for this production line (A≈0.85~0.90, β≈-0.25~-0.30), taking A≈0.87 and β≈-0.28, then K=1.15; calculating ΔBOW≈K×BOW_final-BOW_incoming-β≈-8.22μm, the target curvature value for the DSG process is: BOW_DSG≈BOW_incoming+ΔBOW≈0.28. That is, in the DSG process, the silicon wafer is shaped into a "bowl" shape during DSG processing, and the deformation amount ΔBOW in the DSG process is approximately -8.22μm to neutralize the "bun" shape of the incoming material.

[0050] Adjusting the thinning position: Since ΔBOW is approximately -8.22μm, which is a negative number less than zero, according to the rules, the thinning position needs to be adjusted to the right. This batch uses a medium hardness (H2) grinding wheel, so n=1.5, and ΔP_base=20μm. Therefore, the adjustment amount of the thinning position ΔP=n×ΔP_base=30μm.

[0051] Adjusting the grinding wheel angle: |ΔV_L| or |ΔV_R| is selected as 10μm, and ΔH is taken as |ΔV_L| / 2. The grinding wheel angle adjustment is preset with 1 standard adjustment unit. According to the previously calculated BOW_DSG≈0.28, which is convex in the center, then ΔV_L= -10μm, ΔV_R = +10μm, ΔH =5μm. That is, the left grinding wheel is vertically reduced by 10 μm, the right grinding wheel is vertically increased by 10 μm, and the horizontal angle of the left and right grinding wheels is reduced by 5 μm.

[0052] Step 3, coordinated regulation and processing, corresponding to... Figure 1 Step 3 in the flowchart: Adjust the thinning position and grinding wheel angle according to the parameters in step two. After adjustment, immediately reset the barometer of the DSG machine to zero to lock the adjustment effect. Then perform DSG machining.

[0053] Step four, verification and feedback, corresponding to... Figure 1 Step four in the flowchart: After DSG processing, the BOW_DSG value is tested. It is close to the target (0.28μm) but not completely up to standard.

[0054] Feedback Fine-tuning: Return to step two and perform parameter fine-tuning. Since the morphology is close to the target, only the grinding wheel angle is fine-tuned, applying 0.5 adjustment units (i.e., parameters are halved: ΔV_L=-5μm, ΔV_R=+5μm, ΔH =2.5μm).

[0055] After reprocessing and inspection, the BOW_DSG value was 0.31μm, which is close to the target (0.28μm) and meets the requirements. It then proceeds to the polishing process.

[0056] Result: After polishing, the average final curvature value of this batch of silicon wafers was -0.3μm, successfully achieving "complete neutralization". The curvature value was calculated to have a pass rate of 95% according to the production line's conventional requirements.

[0057] Example 2

[0058] In this embodiment, the thinning position was adjusted.

[0059] Before DSG processing, the incoming silicon wafer after wire cutting measured a BOW of 10.9 μm and a WARP of 25 μm, with a central protrusion. The requirement is that the polished silicon wafer will have a convex shape, and the target curvature value (BOW_final) should be approximately 3.5 μm.

[0060] Model Calculation: Using the same production line as in Example 1, the pre-fitted morphology neutralization model parameters A≈0.85~0.90, β≈-0.25~-0.30 are taken as A≈0.87, β≈-0.28, then K=1.15; ΔBOW≈K×BOW_final-BOW_incoming-β≈-6.6μm is calculated, then the target curvature value of the DSG process is: BOW_DSG≈BOW_incoming+ΔBOW≈-4.3. That is, in the DSG process, the silicon wafer is processed into a "bowl" shape, and the deformation amount ΔBOW of the DSG process is about -6.6μm to neutralize the "bun" shape of the incoming material.

[0061] Adjusting the thinning position: According to the rules, the thinning position needs to be adjusted to the right. This batch uses a medium hardness (H2) grinding wheel, so n=1.5. Take ΔP_base=20μm, so the thinning position adjustment amount ΔP=n×ΔP_base=30μm.

[0062] After DBSG processing, the BOW (bulk warp) decreased from 10.9 μm in the incoming material to -4.10 μm, which is close to the target bend value of -4.3 μm for the DSG process.

[0063] Example 3

[0064] In this embodiment, the thinning position was adjusted.

[0065] Before DSG processing, the center point of the incoming silicon wafer after wire cutting is concave: BOW is -5.21μm. The requirement is that the polished silicon wafer will be convex, and the target curvature value (BOW_final) should be approximately 2.2μm.

[0066] Model calculation: Based on the pre-fitted morphology and model parameters of this production line, which are the same as those in Example 1, and with consistent fitting parameters, ΔBOW≈8.01μm is calculated. Therefore, the target curvature value of the DSG process is approximately 2.8μm. That is, in the DSG process, the silicon wafer is shaped into a "bun" shape during DSG processing, and the deformation amount ΔBOW of the DSG process is approximately 8.01μm to neutralize the "bowl" shape of the incoming material.

[0067] Adjusting the thinning position: Since ΔBOW is approximately μm, which is a positive number greater than zero, according to the rules, the thinning position needs to be adjusted to the left. This batch uses a medium hardness (H2) grinding wheel, so n=1.5, and ΔP_base=20μm. Therefore, the thinning position adjustment amount ΔP=n×ΔP_base=30μm.

[0068] According to the model calculation, ΔBOW is a positive number. In the BSG process, the thinning position is gradually moved to the left, with the left grinding wheel moving away from the wafer and the right grinding wheel moving closer to the wafer. The curvature is increased from the initial -5.21 to +2.88μm, which is close to the target of 2.8μm in the DSG process.

[0069] Example 4

[0070] In this embodiment, before DSG processing, the incoming silicon wafer after wire cutting has a WARP size of 14.5μm and a BOW size of 8.91μm.

[0071] The model calculation and adjustment of the thinning position are performed in the same way as in Example 2, and the grinding wheel angle is adjusted in the DSG machining process as follows.

[0072] Adjusting the grinding wheel angle: |ΔV_L| or |ΔV_R| is selected as 10μm, and ΔH is taken as |ΔV_L| / 2. The grinding wheel angle adjustment is preset with 1 standard adjustment unit. According to the abnormality of the incoming material with a central bulge, then ΔV_L = -10μm, ΔV_R = +10μm, ΔH = 5μm, that is, the left grinding wheel vertically decreases by 10μm, the right grinding wheel vertically increases by 10μm, and at the same time the horizontal angle of the left and right grinding wheels decreases by 5μm. Repeat three times.

[0073] The silicon wafer curvature measured after the DSG processing was approximately -3.65μm. This morphology is consistent with the incoming material, meaning that the DSG processing did not introduce any issues such as center point anomalies, which is very much in line with expectations.

[0074] Example 5

[0075] In this embodiment, the incoming silicon wafer after wire cutting before DSG processing has a WARP of 18.14 and a BOW of -9.06μm.

[0076] The model calculation and adjustment of the thinning position are performed in the same way as in Example 2, and the grinding wheel angle is adjusted in the DSG machining process as follows.

[0077] Adjusting the grinding wheel angle: |ΔV_L| or |ΔV_R| is selected as 10μm, and ΔH is taken as |ΔV_L| / 2. The grinding wheel angle adjustment is preset with 1 standard adjustment unit. According to the abnormality of the incoming material with a central concave shape, then ΔV_L=+10μm, ΔV_R=-10μm, ΔH=5μm, that is, the left grinding wheel vertically increases by 10μm, the right grinding wheel vertically decreases by 10μm, and at the same time the horizontal angle of the left and right grinding wheels decreases by 5μm, repeating 4 times.

[0078] The morphology test of this embodiment after double-sided thinning shows a BOW of 3.59.

[0079] Example 6

[0080] The goal of this embodiment is to achieve complete flatness of the polished wafer, i.e., the BOW of the polished silicon wafer is approximately 0.

[0081] Before DSG processing, the incoming silicon wafer after wire cutting has a BOW of -2.5~-3μm; double-sided thinning is controlled by adjusting the thinning position and grinding wheel angle in DSG.

[0082] Model calculation: Consistent with the production line of Example 1, A≈0.87, β≈-0.28, K=1.15; ΔBOW≈K×BOW_final-BOW_incoming-β≈2.47μm is calculated, then the target curvature value of the DSG process is: BOW_DSG≈BOW_incoming+ΔBOW≈-0.28. That is, in the DSG process, the silicon wafer is shaped into a "bun" shape during DSG processing, and the deformation amount ΔBOW of the DSG process is approximately 2.47μm to neutralize the "bowl" shape of the incoming material.

[0083] Adjusting the thinning position: Since ΔBOW is approximately 2.47μm, which is a positive number greater than zero, according to the rules, the thinning position needs to be adjusted to the left. This batch uses a medium hardness (H2) grinding wheel, so n=1.5, and ΔP_base=20μm. Therefore, the adjustment amount of the thinning position ΔP=n×ΔP_base=30μm.

[0084] Adjusting the grinding wheel angle: Select 10μm for either |ΔV_L| or |ΔV_R|, and set ΔH to |ΔV_L| / 2. The grinding wheel angle adjustment presets one standard adjustment unit. Based on BOW_DSG≈-0.28 with a central concave shape, ΔV_L = +10μm, ΔV_R = -10μm, ΔH = 5μm. That is, add 10 μm vertically to the left grinding wheel and 10 μm vertically to the right grinding wheel, while simultaneously reducing the horizontal angle of both grinding wheels by 5 μm. Repeat once. After the DSG process, the morphology is adjusted to be opposite to that of the wire-cut material, i.e., the BOW is 2.5~3μm. The two are "neutralized", and the BOW of the polished sheet after chemical mechanical polishing (CMP) is maintained at -0.09μm.

[0085] Example 7

[0086] This embodiment is designed according to the final target curvature value of the polished wafer, setting the expected BOW of the polished wafer to a "bowl" shape of approximately -5. Furthermore, the wire-cut incoming silicon wafer also exhibits a "bowl" shape. Through DSG processing with this "bowl" shape, the final BOW of the polished wafer after CMP reaches -4.6μm, close to the target of -5μm. Before DSG processing, the BOW of the wire-cut incoming silicon wafer is 0.48μm.

[0087] ΔBOW and the target BOW_DSG are calculated based on the morphology neutralization model pre-fitted for the production line.

[0088] Adjusting the thinning position: Since ΔBOW is approximately 3.41μm, which is a negative number greater than zero, according to the rules, the thinning position needs to be adjusted to the left. This batch uses a medium hardness (H2) grinding wheel, so n=1.5, and ΔP_base=20μm. Therefore, the adjustment amount of the thinning position ΔP=n×ΔP_base=30μm.

[0089] Adjusting the grinding wheel angle: Select 10μm for either |ΔV_L| or |ΔV_R|, and take ΔH as |ΔV_L| / 2. The grinding wheel angle adjustment is preset with one standard adjustment unit. Based on the "bowl" shape machining requirements, ΔV_L = -10μm, ΔV_R = +10μm, ΔH = 5μm. That is, the left grinding wheel vertical angle decreases by 10μm, the right grinding wheel vertical angle increases by 10μm, and simultaneously the horizontal angles of both grinding wheels decrease by 5μm. Repeat once. By adjusting the thinning position and grinding wheel angle in the DSG process, the DSG "bowl" shape is achieved after the DSG process. The BOW of the silicon wafer after CMP (polishing) is -4.6μm.

[0090] Example 8

[0091] In this embodiment, the thinning adjustment is carried out according to the final target of the epitaxial wafer curvature value. It is known that the BOW increment of the polished silicon wafer after epitaxy is 7~10μm. The customer requires the BOW of the silicon wafer after EPI to be 0~5μm. The curvature value of the polished wafer needs to be approximately between -7 and -5μm. Therefore, BOW_final can be set to -6μm.

[0092] Based on the bending value of the silicon wafer before thinning, i.e., BOW_incoming, ΔBOW can be obtained according to the model in the method of the present invention. The thinning adjustment method can be set according to this value to achieve the specific bending value of the epitaxial wafer that meets the customer's requirements.

[0093] Regardless of the quality of the wire-cut incoming material, after thinning and adjustment according to the method of the present invention, the DSG processed material will become a "large bowl" with the expected target curvature value, thus achieving the following: Figure 2The image in Figure A shows the 3D morphology of the polished silicon wafer. Even with a significant BOW increment of 7-10 μm during the epitaxial process, the curvature of the epitaxial silicon wafer after EPI still meets customer specifications within the range of 0-5. The 3D morphology image after epitaxy is shown below. Figure 2 Figure B in the middle.

[0094] Table 1. Summary of data from the above embodiments (unit: μm)

[0095] It should be noted that the specific model parameters in the above embodiments are merely examples to illustrate the substantive content of the present invention, but are not intended to limit the scope of protection of the present invention. Those skilled in the art can make adaptive adjustments based on the core inventive concept of the method according to the actual process lines, equipment, and other conditions used, to obtain models suitable for their process lines, equipment, and other conditions. All such adjustments should fall within the scope of protection of the present invention.

Claims

1. A method for controlling the curvature of a silicon wafer through double-sided thinning, characterized in that, Includes the following steps: S1, obtain the incoming bending value of the silicon wafer after wire cutting, denoted as BOW_incoming; set the target final bending value of the silicon wafer after polishing according to product requirements, denoted as BOW_final; S2, based on the morphology neutralization model, according to BOW_incoming and BOW_final, calculate the curvature deformation ΔBOW required for the DSG process and the target curvature value after DSG processing, namely BOW_DSG, and derive the target thinning position and target angle parameters of the grinding wheel accordingly. S3, Coordinated Control and Processing: Adjust the thinning position of the grinding wheel to the target thinning position, and adjust the left and right vertical angles and horizontal angles of the grinding wheel to the target angle parameters, and then perform DSG processing; S4. Detect the bending value of the silicon wafer after DSG processing. If it does not meet the BOW_DSG standard, return to step S2 for parameter fine-tuning and re-execute step S3 and this step until the standard is met.

2. The method for controlling the curvature of a silicon wafer through double-sided thinning according to claim 1, characterized in that, In step S2, the morphology neutralization model is: ΔBOW≈K×BOW_final-BOW_incoming-β, And, BOW_DSG≈BOW_incoming+ΔBOW, Here, coefficients K and β are constants determined by fitting process data from a specific production line.

3. The method for controlling the curvature of a silicon wafer through double-sided thinning according to claim 2, characterized in that, The coefficients K and β are determined through the following steps: A batch of sample silicon wafers were collected for BOW_incoming, processed under the reference DSG process parameters, and their BOW_DSG was measured. After polishing, their BOW_final was measured. The data was fitted using the linear model BOW_final≈A×BOW_DSG+β to obtain coefficients A and β; Let K = 1 / A, then we obtain the coefficients K and β in the morphology and model.

4. A method for controlling the curvature of a silicon wafer through double-sided thinning according to claim 2 or 3, characterized in that, The coefficient K ranges from 0.8 to 1.

2.

5. The method for controlling the curvature of a silicon wafer through double-sided thinning according to claim 1, characterized in that, In step S2, the target thinning location is determined in the following way: The direction of movement of the thinning position is determined by the sign of ΔBOW: if ΔBOW is negative, the thinning position is adjusted to the right; if ΔBOW is positive, the thinning position is adjusted to the left. The adjustment amount ΔP for the thinning position is determined based on the absolute value of ΔBOW and the hardness grade of the grinding wheel.

6. The method for controlling the curvature of a silicon wafer through double-sided thinning according to claim 5, characterized in that, The adjustment amount ΔP is calculated using the formula ΔP=n×ΔP_base, where ΔP_base is the unit of basic adjustment amount and n is a coefficient related to the hardness grade of the grinding wheel. The harder the grinding wheel, the larger the value of the coefficient n.

7. The method for controlling the curvature of a silicon wafer through double-sided thinning according to claim 1, characterized in that, In step S3, the target angle parameter is adjusted in preset adjustment units; each adjustment unit includes the following synchronously executed operations: Asymmetrical adjustment of the vertical angle of the grinding wheel: the vertical angle of the left grinding wheel is adjusted by ΔV_L, and the vertical angle of the right grinding wheel is adjusted by ΔV_R, and |ΔV_L|=|ΔV_R|, with opposite adjustment directions; Linked adjustment of grinding wheel horizontal angle: The horizontal angles of the left and right grinding wheels decrease synchronously by a fixed value ΔH, where the value of ΔH is 1 / 2 to 1 / 3 of the value of |ΔV_L| or |ΔV_R|.

8. A method for controlling the curvature of a silicon wafer through double-sided thinning according to claim 7, characterized in that... The value of |ΔV_L| or |ΔV_R| is 5μm, 10μm, or 15μm.

9. The method for controlling the curvature of a silicon wafer through double-sided thinning according to claim 1, characterized in that, In step S3, after adjusting the thinning position of the grinding wheel, the barometer of the DSG machine needs to be reset to zero.

10. The method for controlling the curvature of a silicon wafer through double-sided thinning according to claim 1, characterized in that, In step S1, the target final curvature value BOW_final is set to 0 μm to achieve complete flatness of the silicon wafer after polishing.

11. The method for controlling the curvature of a silicon wafer through double-sided thinning according to claim 1, characterized in that, The target final curvature value BOW_final mentioned in step S1 is set according to the specific requirements of the epitaxial process in order to achieve customized control of the curvature value of the epitaxial silicon wafer.

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