Wafer flatness control method, system and storage medium

Abstract

This invention provides a wafer flatness control method, system, and storage medium, belonging to the field of semiconductor manufacturing technology. The flatness control method sets a deviation threshold based on the target thickness. If the thickness change amplitude is less than the preset thickness change threshold, the difference between the current thickness and the target thickness of each polishing region is calculated as a floating deviation. If the floating deviation is positive, it is compared with the deviation threshold. If the floating deviation is greater than or equal to the deviation threshold, the polishing pressure value of the polishing region is calculated, and polishing is performed. If the floating deviation is less than the deviation threshold, the polishing region is not polished. If the floating deviation is negative, the polishing region is also not polished. This method selects the desired polishing regions for polishing, avoiding direct re-polishing. This improves the uniformity of the overall wafer thickness after polishing, further reduces the thickness change amplitude, and improves wafer flatness.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor manufacturing technology, specifically relating to a wafer flatness control method, system, and storage medium. Background Technology

[0002] Wafer polishing is a key step in semiconductor manufacturing, mainly used to adjust the thickness, flatness, or surface quality of wafers to meet the requirements of subsequent processes. Common processes include mechanical polishing, chemical mechanical polishing, and dry polishing. In chemical mechanical polishing, a certain pressure is usually applied to the back of the wafer by a polishing head to make the front of the wafer adhere tightly to the polishing pad. The polishing head drives the wafer and the polishing pad to rotate in the same direction, so that the front of the wafer and the polishing pad generate mechanical friction to make the wafer surface flatter.

[0003] Chinese Patent Application No. CN202210706556.7 discloses a flatness control method, apparatus, device, and medium. The method includes: obtaining a current thickness value set of a target wafer, the current thickness value set including the current thickness values ​​of multiple different grinding areas of the target wafer; calculating the thickness change amplitude of the target wafer based on the current thickness value set; if the thickness change amplitude is greater than or equal to a preset thickness change threshold, calculating the current thickness deviation of different grinding areas based on the current thickness value of a reference grinding area of ​​the target wafer and the target thickness values ​​of multiple different grinding areas; calculating the target grinding pressure value of the grinding area based on the pressure value of the target wafer in the previous grinding by the machine, the current thickness deviation, and the thickness value removed by re-grinding; and controlling the machine to execute a preset chemical mechanical polishing process based on the grinding pressure value to improve the thickness uniformity of different grinding areas of the wafer.

[0004] Although this invention can adjust the grinding pressure of corresponding areas according to the thickness of different areas, thereby improving the uniformity of wafer flatness, it still has the following problems:

[0005] 1. During the synchronous application of polishing pressure to different areas based on their thickness, if the polishing pressures of two adjacent areas differ significantly, the pressure transmission will cause other polishing areas near the area with higher pressure to experience increased pressure, exceeding the required polishing force. This results in increased polishing thickness and affects the flatness of the wafer.

[0006] 2. Wafers typically require multiple grinding processes to achieve the desired thickness. If the thickness variation is less than the preset thickness variation threshold during each grinding process, directly re-grinding may ignore the cumulative effect of local thickness deviations. During grinding, areas that were originally thinner may experience a significant reduction in thickness after multiple grinding processes, resulting in a thickness that is too low. This is because direct re-grinding without adjusting the pressure will cause each grinding area to be ground, leading to excessive grinding of areas that were originally thinner, resulting in a decrease in wafer thickness uniformity.

[0007] Therefore, in order to solve the above problems, there is a need to provide a wafer flatness control method, system and storage medium. Summary of the Invention

[0008] The purpose of this invention is to provide a wafer flatness control method, system, and storage medium. It aims to solve the problems in the prior art where, during the synchronous application of polishing pressure to corresponding regions based on their thickness, if the polishing pressure difference between two adjacent regions is large, the wafer will deform due to the pressure difference. Furthermore, the pressure transmission will cause other polishing regions near the region with higher pressure to experience increased pressure, exceeding the required polishing force and resulting in increased polishing thickness, thus affecting wafer flatness. Additionally, since wafers typically require multiple polishing processes to reach the desired thickness, if the thickness change is less than a preset thickness change threshold during each polishing process, and polishing is directly repeated, the cumulative effect of local thickness deviations may be ignored. This could lead to a significant reduction in thickness in regions that were originally thinner after multiple polishing processes, resulting in a thickness below the required level and a decrease in wafer thickness uniformity.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] A method for controlling wafer flatness, the method comprising:

[0011] S1: Obtain the current thickness value of each grinding area of ​​the target wafer, select the area with the largest current thickness value as the reference area, and perform preliminary grinding with a set pressure value;

[0012] S2: Reacquire the current thickness values ​​of each grinding area of ​​the target wafer, construct the current thickness value set, calculate the thickness change amplitude of the target wafer. If the thickness change amplitude is greater than or equal to the preset thickness change threshold, proceed to S3. If the thickness change amplitude is less than the preset thickness change threshold, proceed to S4.

[0013] S3: Calculate the current thickness deviation of different grinding areas based on the target thickness value and current thickness value of each grinding area; calculate the grinding pressure value of each grinding area based on the grinding pressure value of the reference area, the grinding thickness and the current thickness deviation of each grinding area.

[0014] S4: Set the deviation threshold according to the target thickness value, calculate the floating deviation of each grinding area according to the target thickness value and the current thickness value of each grinding area, compare the floating deviation with the deviation threshold, filter the grinding areas, calculate the grinding pressure value of the corresponding grinding area according to S3, and perform grinding.

[0015] S5: Compare the grinding pressure values ​​of each grinding zone and prioritize grinding the zone with the highest grinding pressure value;

[0016] S6: Reacquire the current thickness value of other grinding areas of the target wafer, recalculate the current thickness deviation and grinding pressure value of other grinding areas, return to S5, and continue grinding other areas with the maximum grinding pressure value until the process is completely finished.

[0017] Preferably, S1 includes:

[0018] S11: Divide the grinding surface of the target wafer into multiple grinding areas along the direction close to the center;

[0019] S12: Measure the current thickness value of each grinding zone;

[0020] S13: Compare the current thickness values ​​of each grinding area and select the area with the largest current thickness value as the reference area;

[0021] S14: Set the initial grinding pressure value. The initial grinding pressure value should be lower than the target grinding pressure value to grind to the target thickness.

[0022] S15: Perform preliminary grinding on the reference area of ​​the wafer using the initial grinding pressure value.

[0023] Preferably, S2 includes:

[0024] S21: After the initial grinding, the current thickness value of each grinding area of ​​the target wafer is re-detected;

[0025] S22: Construct a set of current thickness values ​​for each grinding region, select the maximum and minimum values ​​among the current thickness values, calculate the difference, and use it as the thickness change amplitude;

[0026] S23: Set the thickness change threshold and compare the thickness change amplitude with the thickness change threshold;

[0027] S24: If the thickness change amplitude is greater than or equal to the thickness change threshold, proceed to S3;

[0028] S25: If the thickness change amplitude is less than the preset thickness change threshold, proceed to S4.

[0029] Preferably, S3 includes:

[0030] S31: Calculate the difference between the current thickness value in reference area S1 and the current thickness value in S2 to obtain the grinding thickness, and calculate the grinding ratio coefficient based on the grinding thickness and the initial grinding pressure value;

[0031] S32: Calculate the difference between the current thickness value and the target thickness value in S2 of each grinding area to obtain the current thickness deviation of each grinding area;

[0032] S33: The pressure adjustment value of each grinding zone is calculated based on the grinding ratio coefficient and the current thickness deviation of each grinding zone;

[0033] S34: The grinding pressure value of each grinding zone is calculated based on the initial grinding pressure value of the reference zone and the pressure adjustment value of each grinding zone.

[0034] Preferably, S4 includes:

[0035] S41: Set the deviation threshold based on the target thickness value;

[0036] S42: If the thickness change amplitude is less than the thickness change threshold, the difference between the current thickness value and the target thickness value of each grinding area will be calculated and used as the floating deviation.

[0037] S43: If the floating deviation is positive, it is compared with the deviation threshold. If the floating deviation is greater than or equal to the deviation threshold, the grinding pressure value of the grinding area is calculated by S3 and grinding is performed. If the floating deviation is less than the deviation threshold, the grinding area does not need to be ground.

[0038] S44: If the floating deviation is negative, then the grinding area does not need to be ground.

[0039] Preferably, S5 includes:

[0040] S51: Construct a set of grinding pressure values ​​for each grinding zone;

[0041] S52: Compare the grinding pressure values ​​of each grinding zone and select the grinding zone with the highest grinding pressure value as the priority grinding zone;

[0042] S53: Adjust the grinding pressure of the priority grinding area to the corresponding grinding pressure value, and grind the priority grinding area separately.

[0043] Preferably, S6 includes:

[0044] S61: Re-detect the current thickness value of other grinding areas, and recalculate the current thickness deviation and grinding pressure value of other grinding areas;

[0045] S62: Return to S5 and once again construct a set of grinding pressure values ​​for other grinding areas;

[0046] S63: Compare the grinding pressure values ​​of each grinding area again, select the maximum grinding pressure value for priority grinding, until all areas are ground.

[0047] A wafer flatness control system, comprising:

[0048] The polishing module is used to perform chemical mechanical polishing processes on the target wafer;

[0049] A measurement module is used to measure the current thickness values ​​of multiple different polishing zones of the target wafer;

[0050] The control modules are electrically connected to both the polishing module and the measurement module.

[0051] Preferably, the control module includes a storage unit and a processing unit. The storage unit stores a computer program, and the processing unit executes the computer program to implement the steps of the wafer flatness control method in any embodiment of this disclosure.

[0052] A wafer flatness control storage medium has a computer program stored thereon, which, when executed by a processing unit, implements the steps of the wafer flatness control method in any embodiment of this disclosure.

[0053] Compared with the prior art, the beneficial effects of the present invention are:

[0054] This invention can adjust the grinding pressure value of each area in real time by calculating the grinding pressure value of each area multiple times. By comparing the grinding pressure value of the required grinding area multiple times, the grinding area with the highest grinding pressure value is selected as the priority grinding area, and the priority grinding area is ground separately until all areas are ground. By grinding the area individually, the grinding effect caused by the large pressure being transmitted to other areas during synchronous pressure application can be effectively reduced.

[0055] This invention can set a deviation threshold based on the target thickness. If the thickness change amplitude is less than the preset thickness change threshold, the difference between the current thickness and the target thickness of each grinding area is calculated as a floating deviation. If the floating deviation is positive, it is compared with the deviation threshold. If the floating deviation is greater than or equal to the deviation threshold, the grinding pressure value of the grinding area is calculated and grinding is performed. If the floating deviation is less than the deviation threshold, the grinding area does not need to be ground. If the floating deviation is negative, the grinding area does not need to be ground. In this way, the required grinding areas are selected and ground without direct re-grinding. This can improve the uniformity of the thickness of the wafer after overall grinding, further reduce the thickness change amplitude, and improve the flatness of the wafer. Attached Figure Description

[0056] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0057] Figure 1 This is a schematic diagram of the overall process of the flatness control method of the present invention;

[0058] Figure 2 This is a schematic diagram of the specific process of step S1 of the present invention;

[0059] Figure 3 This is a schematic diagram of the specific process of step S2 of the present invention;

[0060] Figure 4 This is a schematic diagram of the specific process of step S3 of the present invention;

[0061] Figure 5 This is a schematic diagram of the specific process of step S4 of the present invention;

[0062] Figure 6 This is a schematic diagram of the specific process of step S5 of the present invention;

[0063] Figure 7 This is a schematic diagram of the specific process of step S6 of the present invention. Detailed Implementation

[0064] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0065] Example 1

[0066] During the process of adjusting the grinding pressure of corresponding areas according to the thickness of different areas and applying pressure synchronously, if the grinding pressure of two adjacent areas differs greatly, the stress field of adjacent grinding areas will be superimposed due to the influence of pressure transmission. This will cause the pressure on other grinding areas near the area with higher pressure to increase, exceeding the required grinding force, resulting in a larger grinding thickness and affecting the overall flatness of the wafer.

[0067] Please see Figures 1 to 7 The present invention provides the following technical solution: a wafer flatness control method, the method comprising:

[0068] S1: Obtain the current thickness value of each grinding area of ​​the target wafer, select the area with the largest current thickness value as the reference area, and perform preliminary grinding with a set pressure value;

[0069] S2: Reacquire the current thickness values ​​of each grinding area of ​​the target wafer, construct the current thickness value set, calculate the thickness change amplitude of the target wafer. If the thickness change amplitude is greater than or equal to the preset thickness change threshold, proceed to S3. If the thickness change amplitude is less than the preset thickness change threshold, proceed to S4.

[0070] S3: Calculate the current thickness deviation of different grinding areas based on the target thickness value and current thickness value of each grinding area; calculate the grinding pressure value of each grinding area based on the grinding pressure value of the reference area, the grinding thickness and the current thickness deviation of each grinding area.

[0071] S4: Set the deviation threshold according to the target thickness value, calculate the floating deviation of each grinding area according to the target thickness value and the current thickness value of each grinding area, compare the floating deviation with the deviation threshold, filter the grinding areas, calculate the grinding pressure value of the corresponding grinding area according to S3, and perform grinding.

[0072] S5: Compare the grinding pressure values ​​of each grinding zone and prioritize grinding the zone with the highest grinding pressure value;

[0073] S6: Reacquire the current thickness value of other grinding areas of the target wafer, recalculate the current thickness deviation and grinding pressure value of other grinding areas, return to S5, and continue grinding other areas with the maximum grinding pressure value until the process is completely finished.

[0074] Step S1 includes:

[0075] S11: Divide the grinding surface of the target wafer into multiple grinding areas along the direction close to the center;

[0076] S12: Measure the current thickness value of each grinding zone;

[0077] S13: Compare the current thickness values ​​of each grinding area and select the area with the largest current thickness value as the reference area;

[0078] S14: Set the initial grinding pressure value. The initial grinding pressure value should be lower than the target grinding pressure value to grind to the target thickness.

[0079] S15: Perform preliminary grinding on the reference area of ​​the wafer using the initial grinding pressure value.

[0080] On the polished surface of the wafer, multiple regions are divided from the center area to the edge area, namely the first polishing region, the second polishing region, and the Nth polishing region, etc., where N is the number of regions and should be set according to actual needs.

[0081] The current thickness of each polishing region of the target wafer is measured by optical interferometry and spectroscopic ellipsometric method. Both optical interferometry and spectroscopic ellipsometric method are existing technologies and will not be described in detail here.

[0082] In step S14, the initial grinding pressure value should be lower than the target grinding pressure value to the target thickness, where the target grinding pressure value should be obtained based on actual tests.

[0083] Example: The polishing surface of the wafer is divided into a first polishing region, a second polishing region, a third polishing region, a fourth polishing region, and a fifth polishing region. The current thicknesses detected in the first polishing region are 713 μm, the second polishing region is 720 μm, the third polishing region is 725 μm, the fourth polishing region is 735 μm, and the fifth polishing region is 730 μm. The target thickness is 720 μm, the preset thickness variation threshold is 20 μm, and the target polishing pressure obtained from the polishing experiment is approximately 15 kPa. Therefore, the initial polishing pressure can be 5 kPa. Comparing the current thicknesses of the first, second, third, fourth, and fifth polishing regions, the fourth polishing region has the largest current thickness of 735 μm. Therefore, the fourth polishing region is selected as the reference region, and the polishing pressure value of the fourth polishing region is adjusted to 5 kPa. The second polishing region is then polished separately first.

[0084] The purpose of selecting an initial grinding pressure value for initial grinding in step S1 is to calculate the grinding ratio coefficient under the current working environment based on the initial grinding pressure value and grinding thickness after the initial grinding of the target wafer, so as to avoid the impact of different grinding environments on the grinding ratio coefficient each time and improve the accuracy of grinding.

[0085] Since the thickness difference between wafers cut in the same batch is usually small during the wafer cutting process, grinding experiments are conducted on multiple wafers to obtain the target grinding pressure value, which should be the average value of multiple grinding pressure values ​​in the experiment.

[0086] The purpose of selecting the area with the largest current thickness value as the reference area is to adapt the initial grinding pressure value by using the largest thickness value, so as to avoid the thickness being lower than the target thickness after preliminary grinding in other areas, thus facilitating subsequent operations.

[0087] Step S2 includes:

[0088] S21: After the initial grinding, the current thickness value of each grinding area of ​​the target wafer is re-detected;

[0089] S22: Construct a set of current thickness values ​​for each grinding region, select the maximum and minimum values ​​among the current thickness values, calculate the difference, and use it as the thickness change amplitude;

[0090] S23: Set the thickness change threshold and compare the thickness change amplitude with the thickness change threshold;

[0091] S24: If the thickness change amplitude is greater than or equal to the thickness change threshold, proceed to S3;

[0092] S25: If the thickness change amplitude is less than the preset thickness change threshold, proceed to S4.

[0093] Step S3 includes:

[0094] S31: Calculate the difference between the current thickness value in reference area S1 and the current thickness value in S2 to obtain the grinding thickness, and calculate the grinding ratio coefficient based on the grinding thickness and the initial grinding pressure value;

[0095] S32: Calculate the difference between the current thickness value and the target thickness value in S2 of each grinding area to obtain the current thickness deviation of each grinding area;

[0096] S33: The pressure adjustment value of each grinding zone is calculated based on the grinding ratio coefficient and the current thickness deviation of each grinding zone;

[0097] S34: The grinding pressure value of each grinding zone is calculated based on the initial grinding pressure value of the reference zone and the pressure adjustment value of each grinding zone.

[0098] It should be noted that, considering that after applying pressure to one grinding area, other grinding areas near that area may also be ground due to the influence of the grinding pressure transmission, it is necessary to re-detect the current thickness of each grinding area.

[0099] Based on the above example, the current thickness values ​​of the first, second, third, fourth, and fifth polishing regions of the target wafer detected in S1 are 713μm, 720μm, 725μm, 735μm, and 730μm, respectively. After the reference region, i.e., the fourth polishing region, is polished with an initial polishing pressure of 5kPa, the current thickness values ​​of the first, second, third, fourth, and fifth polishing regions detected again in S2 are 713μm, 720μm, 723μm, 730μm, and 720μm, respectively. The thickness is 8μm. The reason for the grinding in the third and fifth grinding areas is that the grinding pressure in the fourth grinding area is transmitted to the third and fifth grinding areas. Since the current thickness of the reference area, i.e., the fourth grinding area, detected in S2 is 730μm, the difference between the current thickness of 735μm in the reference area S1 and the current thickness of 730μm in S2 is calculated to obtain a current thickness deviation of 5μm. Dividing 5μm by 5kPa gives a grinding ratio coefficient of 1μm / kPa. The difference between the current thickness in S2 of each grinding area and the target thickness is calculated to obtain the thickness deviation of each grinding area. The thickness deviations of the first, second, third, fourth, and fifth grinding regions are as follows: -7 μm, 0 μm, 3 μm, 10 μm, and 8 μm. The pressure adjustment values ​​for each grinding region are obtained by multiplying the thickness deviation of each region by the grinding ratio coefficient. The pressure adjustment values ​​for the first, second, third, fourth, and fifth grinding regions are -7 kPa, 0 kPa, 3 kPa, 10 kPa, and 8 kPa, respectively. The initial grinding pressure value of the reference region (5 kPa) is added to the pressure adjustment values ​​of each grinding region to obtain the grinding pressure value of each region. The grinding pressure value for the first region is -2 kPa (since the grinding pressure value is negative, the actual grinding pressure value should be 0 kPa), the second region is 5 kPa, the third region is 8 kPa, the fourth region is 15 kPa, and the fifth region is 13 kPa. Thus, the grinding pressure value of each grinding region is calculated.

[0100] Step S5 includes:

[0101] S51: Construct a set of grinding pressure values ​​for each grinding zone;

[0102] S52: Compare the grinding pressure values ​​of each grinding zone and select the grinding zone with the highest grinding pressure value as the priority grinding zone;

[0103] S53: Adjust the grinding pressure of the priority grinding area to the corresponding grinding pressure value, and grind the priority grinding area separately.

[0104] Step S6 includes:

[0105] S61: Re-detect the current thickness value of other grinding areas, and recalculate the current thickness deviation and grinding pressure value of other grinding areas;

[0106] S62: Return to S5 and once again construct a set of grinding pressure values ​​for other grinding areas;

[0107] S63: Compare the grinding pressure values ​​of each grinding area again, select the maximum grinding pressure value for priority grinding, until all areas are ground.

[0108] Based on the above example, further explanation is provided. A preset thickness change threshold of 15 μm is set. The current thicknesses of the first, second, third, fourth, and fifth grinding regions, re-detected in S2, are 713 μm, 720 μm, 723 μm, 730 μm, and 728 μm, respectively. The difference between the maximum value (730 μm) and the minimum value (713 μm) is calculated to obtain a thickness change amplitude of 17 μm, which is greater than 15 μm. Therefore, proceeding to S5, a set of grinding pressure values ​​is constructed: -2 kPa for the first grinding region, 5 kPa for the second, 8 kPa for the third, 15 kPa for the fourth, and 13 kPa for the fifth. 15 kPa is the highest, so the fourth grinding region is prioritized for grinding at 15 kPa. Due to the influence of grinding pressure transmission, the fifth and third grinding regions may be ground while the fourth grinding region is being ground. If 13 kPa and 8 kPa are directly applied to the fifth grinding region respectively... Grinding is performed in the first and second grinding areas. Because the grinding pressure in the third grinding area is significantly lower than that in the fourth grinding area, a pressure difference exists. Furthermore, due to the influence of the grinding pressure transmitted from the fourth grinding area, the actual grinding pressure in the third grinding area exceeds 8 kPa, resulting in a larger thickness. Therefore, step-by-step grinding is used to reduce the superposition of stress fields. This requires re-detecting the current thickness of the first, second, third, and fifth grinding areas in S6, recalculating the current thickness deviation and grinding pressure values ​​of these areas, and resetting the grinding pressure values ​​for each area. The area with the highest grinding pressure value is then selected for grinding, and this process continues until all areas are ground. By repeatedly calculating and adjusting the grinding pressure values ​​for each area, and by grinding the priority areas individually until all areas are ground, the impact of high pressure transmitted to other areas can be effectively reduced, improving the uniformity of the overall wafer flatness.

[0109] In step S6, if the grinding pressure value calculated for the corresponding area is less than or equal to 0 kPa, then the actual grinding pressure should be 0 kPa. There is no need to adjust the grinding pressure of that area, and there is no need to grind that area, which can improve the overall grinding efficiency.

[0110] The thickness of the polished area is affected by the pressure of the polishing head and the reaction force of the polishing pad. If two adjacent areas are polished simultaneously with pressure, the polishing pressure will differ significantly. Due to the influence of the larger polishing pressure, the stress field of the larger polishing pressure will be superimposed on the stress field of the adjacent area with smaller polishing pressure, resulting in a larger polishing pressure in the adjacent area. As the reaction force increases with the increased pressure, the polishing thickness of the adjacent area is greater than the actual thickness of all polished areas. When polishing separate areas, since there is no polishing pressure in the adjacent areas where the polishing pressure is applied, the adjacent areas are only affected by the pressure transmitted from the area where the pressure is applied, resulting in only partial polishing.

[0111] A wafer flatness control system, comprising:

[0112] The polishing module is used to perform chemical mechanical polishing processes on the target wafer;

[0113] The measurement module is used to measure the current thickness values ​​of multiple different polishing zones on the target wafer;

[0114] The control module is electrically connected to both the polishing module and the measurement module.

[0115] The control module includes a storage unit and a processing unit. The storage unit stores a computer program, and the processing unit executes the computer program to implement the steps of the wafer flatness control method in any embodiment of this disclosure.

[0116] It should be noted that the polishing module includes a polishing head, polishing pad, turntable, force application device, abrasive and abrasive nozzle. The polishing head is used to press the surface of the wafer to be polished against the rough polishing pad. The machine control module controls the force application device to apply a set pressure to the polishing head to polish the target wafer. The polishing pad is usually made of polyurethane material, which is of medium hardness and has a certain degree of elasticity. Its purpose is to adapt to the micro-unevenness of the wafer. This is existing technology and will not be described in detail.

[0117] A wafer flatness control storage medium stores a computer program thereon, which, when executed by a processing unit, implements the steps of the wafer flatness control method in any embodiment of this disclosure.

[0118] In summary, by using steps S5 and S6 to calculate the grinding pressure value of each region multiple times, the grinding pressure value of each region can be adjusted in real time. By comparing the grinding pressure values ​​of the regions to be ground multiple times, the region with the highest grinding pressure value is selected as the priority grinding region, and the priority grinding region is ground separately until all regions are ground. This can effectively reduce the grinding impact caused by the transmission of large pressure to other regions and improve the uniformity of the overall flatness of the wafer.

[0119] Example 2

[0120] Based on the above embodiments, the wafer needs to be polished multiple times to reach the required thickness. If the thickness change is less than the preset thickness change threshold during each polishing process, and the wafer is directly re-polished, the cumulative effect of local thickness deviation may be ignored. During polishing, the thickness of the originally thinner area may be significantly reduced after multiple polishings, resulting in a thickness that is too low. This is because direct re-polishing does not adjust the pressure, and each polishing area will be polished, resulting in the originally thinner area being over-polished multiple times, which leads to a decrease in the thickness uniformity of the wafer after polishing.

[0121] For example, in S2, the current thicknesses of the first, second, third, fourth, and fifth grinding regions of the target wafer are detected to be 714μm, 721μm, 725μm, 727μm, and 725μm, respectively. The preset thickness change threshold is 15μm. The thickness change amplitude calculated by subtracting 715μm from the maximum value of 727μm is 12μm, which is less than the preset thickness change threshold of 15μm. Therefore, re-grinding is performed directly. The grinding pressure value for re-grinding is the target grinding pressure value of 15kPa minus the initial grinding pressure value of 5kPa, which is approximately 10kPa. If the grinding pressure value of each region is 10kPa for grinding a certain thickness, it will cause the thinnest region, i.e., the first grinding region, to be ground to a thickness greater than the actual required thickness. This will cause the thickness of the first grinding region to become thinner, significantly lower than the target thickness, affecting the uniformity of the wafer thickness.

[0122] Please see Figure 3 and Figure 5 Step S4 includes:

[0123] S41: Set the deviation threshold based on the target thickness value;

[0124] S42: If the thickness change amplitude is less than the thickness change threshold, the difference between the current thickness value and the target thickness value of each grinding area will be calculated and used as the floating deviation.

[0125] S43: If the floating deviation is positive, it is compared with the deviation threshold. If the floating deviation is greater than or equal to the deviation threshold, the grinding pressure value of the grinding area is calculated by S3 and grinding is performed. If the floating deviation is less than the deviation threshold, the grinding area does not need to be ground.

[0126] S44: If the floating deviation is negative, then the grinding area does not need to be ground.

[0127] Based on the target thickness, a deviation threshold is set. Further explanation is provided below: the current thicknesses of the first, second, third, fourth, and fifth grinding regions of the target wafer detected in S2 are 714μm, 721μm, 725μm, 727μm, and 725μm, respectively. The preset thickness change threshold is 15μm. The thickness change amplitude calculated by subtracting 714μm from the maximum value of 727μm is 13μm, which is less than the preset thickness change threshold of 15μm. A deviation threshold of 5μm is set based on the target thickness of 720μm. The difference between the current thickness of each grinding region and the target thickness is calculated as the floating deviation. The floating deviation thicknesses for the first, second, third, fourth, and fifth grinding regions are -6μm, 1μm, 5μm, 7μm, and 5μm, respectively. Positive floating deviations are compared with the deviation threshold of 5μm. The floating deviations of 5μm, 7μm, and 5μm for the third, fourth, and fifth grinding regions are greater than or equal to the deviation threshold of 5μm. Since the floating deviation of the first grinding area is -6μm, which is negative, and the floating deviation of the second grinding area is 1μm, which is less than 5μm, the first and second grinding areas do not need to be ground, i.e., the grinding pressure value is 0kPa. The grinding pressure values ​​of the third, fourth, and fifth grinding areas are calculated through step S3, where the grinding ratio coefficient is 1μm / kPa. The grinding pressure values ​​of the third, fourth, and fifth grinding areas are obtained by multiplying the floating deviation by the grinding ratio coefficient, which is 5kPa, 7kPa, and 5kPa, respectively. Thus, the grinding pressure values ​​of the third, fourth, and fifth grinding areas are controlled by the CMP machine to reach 5kPa, 7kPa, and 5kPa, respectively. Then, grinding is carried out area by area in S5 and S6. By setting a deviation threshold, when the thickness change amplitude is less than the preset thickness change threshold, the required grinding area is selected for grinding instead of directly re-grinding. This can improve the uniformity of the thickness of the wafer after overall grinding, further reduce the thickness change amplitude, and improve the flatness of the wafer.

[0128] In summary, this invention, through step S4, sets a deviation threshold based on the target thickness. If the thickness change amplitude is less than the preset thickness change threshold, the difference between the current thickness and the target thickness of each grinding area is calculated as a floating deviation. If the floating deviation is positive, it is compared with the deviation threshold. If the floating deviation is greater than or equal to the deviation threshold, the grinding pressure value of the grinding area is calculated through S3, and grinding is performed. If the floating deviation is less than the deviation threshold, the grinding area does not need to be ground. If the floating deviation is negative, the grinding area does not need to be ground. This method selects the required grinding areas for grinding, without directly performing re-grinding, which can improve the uniformity of the overall wafer thickness after grinding, further reduce the thickness change amplitude, and improve the flatness of the wafer.

[0129] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlling wafer flatness, characterized in that, The method includes: S1: Obtain the current thickness value of each grinding area of ​​the target wafer, select the area with the largest current thickness value as the reference area, and perform preliminary grinding with a set pressure value; S2: Reacquire the current thickness values ​​of each grinding area of ​​the target wafer, construct the current thickness value set, calculate the thickness change amplitude of the target wafer. If the thickness change amplitude is greater than or equal to the preset thickness change threshold, proceed to S3. If the thickness change amplitude is less than the preset thickness change threshold, proceed to S4. S3: Calculate the current thickness deviation of different grinding areas based on the target thickness value and current thickness value of each grinding area; calculate the grinding pressure value of each grinding area based on the grinding pressure value of the reference area, the grinding thickness and the current thickness deviation of each grinding area. S4: Set the deviation threshold according to the target thickness value, calculate the floating deviation of each grinding area according to the target thickness value and the current thickness value of each grinding area, compare the floating deviation with the deviation threshold, filter the grinding areas, calculate the grinding pressure value of the corresponding grinding area according to S3, and perform grinding. S5: Compare the grinding pressure values ​​of each grinding zone and prioritize grinding the zone with the highest grinding pressure value; S6: Reacquire the current thickness value of other grinding areas of the target wafer, recalculate the current thickness deviation and grinding pressure value of other grinding areas, return to S5, and continue grinding other areas with the maximum grinding pressure value until the end; Wherein, S3 includes: S31: Calculate the difference between the current thickness value in reference area S1 and the current thickness value in S2 to obtain the grinding thickness, and calculate the grinding ratio coefficient based on the grinding thickness and the initial grinding pressure value; S32: Calculate the difference between the current thickness value and the target thickness value in S2 of each grinding area to obtain the current thickness deviation of each grinding area; S33: The pressure adjustment value of each grinding zone is calculated based on the grinding ratio coefficient and the current thickness deviation of each grinding zone; S34: The grinding pressure value of each grinding zone is calculated based on the initial grinding pressure value of the reference zone and the pressure adjustment value of each grinding zone. Wherein, S4 includes: S41: Set the deviation threshold based on the target thickness value; S42: If the thickness change amplitude is less than the thickness change threshold, the difference between the current thickness value and the target thickness value of each grinding area will be calculated and used as the floating deviation. S43: If the floating deviation is positive, it is compared with the deviation threshold. If the floating deviation is greater than or equal to the deviation threshold, the grinding pressure value of the grinding area is calculated by S3 and grinding is performed. If the floating deviation is less than the deviation threshold, the grinding area does not need to be ground. S44: If the floating deviation is negative, then the grinding area does not need to be ground.

2. The wafer flatness control method according to claim 1, characterized in that, S1 includes: S11: Divide the grinding surface of the target wafer into multiple grinding areas along the direction close to the center; S12: Measure the current thickness value of each grinding zone; S13: Compare the current thickness values ​​of each grinding area and select the area with the largest current thickness value as the reference area; S14: Set the initial grinding pressure value. The initial grinding pressure value should be lower than the target grinding pressure value to grind to the target thickness. S15: Perform preliminary grinding on the reference area of ​​the wafer using the initial grinding pressure value.

3. The wafer flatness control method according to claim 2, characterized in that, S2 includes: S21: After the initial grinding, the current thickness value of each grinding area of ​​the target wafer is re-detected; S22: Construct a set of current thickness values ​​for each grinding region, select the maximum and minimum values ​​among the current thickness values, calculate the difference, and use it as the thickness change amplitude; S23: Set the thickness change threshold and compare the thickness change amplitude with the thickness change threshold; S24: If the thickness change amplitude is greater than or equal to the thickness change threshold, proceed to S3; S25: If the thickness change amplitude is less than the thickness change threshold, proceed to S4.

4. The wafer flatness control method according to claim 3, characterized in that, S5 includes: S51: Construct a set of grinding pressure values ​​for each grinding zone; S52: Compare the grinding pressure values ​​of each grinding zone and select the grinding zone with the highest grinding pressure value as the priority grinding zone; S53: Adjust the grinding pressure of the priority grinding area to the corresponding grinding pressure value, and grind the priority grinding area separately.

5. The wafer flatness control method according to claim 4, characterized in that, S6 includes: S61: Re-detect the current thickness value of other grinding areas, and recalculate the current thickness deviation and grinding pressure value of other grinding areas; S62: Return to S5 and construct the grinding pressure values ​​of other grinding areas into a set of grinding pressure values ​​again; S63: Compare the grinding pressure values ​​of each grinding area again, select the maximum grinding pressure value for priority grinding, until all areas are ground.

6. A wafer flatness control system, wherein the wafer flatness control system is used to implement the wafer flatness control method as described in claim 5, characterized in that, include: The polishing module is used to perform chemical mechanical polishing processes on the target wafer; A measurement module is used to measure the current thickness values ​​of multiple different polishing regions of the target wafer; The control modules are electrically connected to both the polishing module and the measurement module.

7. The wafer flatness control system according to claim 6, characterized in that: The control module includes a storage unit and a processing unit. The storage unit stores a computer program, and the processing unit executes the computer program to implement the steps of the wafer flatness control method according to any one of claims 1 to 5.

8. A wafer flatness control storage medium, wherein a computer program is stored thereon, characterized in that, When the computer program is executed by the processing unit, it implements the steps of the wafer flatness control method according to any one of claims 1 to 5.

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