Flatness optimization equipment and method for silicon wafer polishing

Abstract

The invention discloses flatness optimization equipment and method for silicon wafer polishing, and the method comprises the steps: polishing a silicon wafer through grinding cloth, and executing a first repairing action of the grinding cloth in a first preset period; the grinding cloth executes silicon wafer polishing after the first repairing action, and detects the Tapper value of the silicon wafer in a second preset period; according to the Taper value of the silicon wafer, the second repairing action of the grinding cloth is executed, or the polishing action of the grinding cloth on the silicon wafer continues to be executed. According to the flatness optimization equipment and method for silicon wafer polishing, the surface of the grinding cloth is mechanically scrubbed through the polishing piece with the surface covered with the diamond piece, and the flatness of the silicon wafer is improved; siOx blockage on the surface of the grinding cloth is effectively removed, the micropore structure of the grinding cloth is exposed again, the material removal rate of the polishing process is recovered, and meanwhile the problem of poor flatness of a silicon wafer is solved through uniform micropore distribution on the regenerated surface.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon wafer processing, and in particular to a device and method for optimizing the flatness of silicon wafer polishing. Background Art

[0002] During the rough polishing process of silicon wafer mirror polishing, due to the long-term use of the grinding cloth, its surface morphology and material removal characteristics will gradually deteriorate, which is specifically manifested as knots on the surface of the silicon wafer (microscopic bumps formed by uneven local material removal) and overall flatness parameters (such as Taper value, local thickness deviation) exceeding the process window. The reasons are: 1. During the polishing process, due to the high grinding temperature, the small holes of the grinding cloth are blocked by the abrasive, resulting in uneven removal of the silicon wafer by the grinding cloth, forming knots and the morphology of the fixed plate will also change, resulting in poor flatness of the silicon wafer; 2. With the difference in the wear of the grinding layout, the Taper value deteriorates, resulting in poor flatness of the silicon wafer.

[0003] In response to the above problems, the existing technology mainly adopts three types of countermeasures: 1) based on online monitoring data or experience cycles, directly replace the grinding cloth after the flatness deteriorates; 2) rinse the surface of the grinding cloth with a high-pressure water jet to try to remove the sintered materials that block the micropores; 3) use a diamond brush to brush the grinding cloth in a forward rotation to restore the surface roughness.

[0004] However, the above method has obvious limitations: frequent replacement of grinding cloth leads to rising production costs, and shutdown for cloth replacement causes production capacity loss; high-pressure water washing can only remove loose residues on the surface and has limited effect on deep sintering blockages; although mechanical repair of diamond brushes can temporarily improve the surface morphology, the flatness of the silicon wafer is difficult to control. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a flatness optimization device and method for silicon wafer polishing, which can ensure the flatness of the silicon wafer during the polishing process.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions.

[0007] The present application provides a flatness optimization device for silicon wafer polishing, comprising a mounting frame and a positioning plate and a rotating plate rotatably connected to the mounting frame, and also comprising a first power unit and a second power unit respectively used to drive the positioning plate and the rotating plate to rotate;

[0008] The rotary disk is coaxial with the positioning disk and is located on the side of the positioning disk away from the ground. A lifting device is fixedly provided on the end surface of the rotary disk close to the positioning disk. The telescopic end of the lifting device faces the positioning disk and is fixedly provided with a mounting disk. A polishing piece is fixedly provided on the end surface of the mounting disk close to the positioning disk.

[0009] Wherein, the polishing member comprises a substrate, and a plurality of diamond pieces are fixedly arranged in a circular array about its own central axis on the end surface of the substrate close to the positioning plate;

[0010] The positioning plate is used to place the grinding cloth, and when the lifting device is in the extended state, the diamond piece on the polishing piece at the corresponding position can abut against the grinding cloth placed on the positioning plate;

[0011] When the rotary disk is rotating, the diameter of the rotating track circle of the polishing piece is not less than the diameter of the grinding cloth placed on the positioning disk.

[0012] It is further defined that in the above-mentioned device for optimizing the flatness of silicon wafer polishing, a plurality of lifting devices are fixedly provided on the end surface of the rotary disk close to the positioning disk, and the plurality of lifting devices are arranged in a circular array about the central axis of the rotary disk;

[0013] Wherein, a polishing piece is installed on at least one of the lifting devices.

[0014] It is further defined that in the above-mentioned flatness optimization device for silicon wafer polishing, the second power unit includes a polishing motor fixedly arranged on a mounting frame, and the turntable is fixedly arranged on a power output shaft of the polishing motor.

[0015] It is further defined that in the above-mentioned device for optimizing the flatness of silicon wafer polishing, a protective cover is fixedly provided on the mounting frame, and a cavity with an opening facing one side of the polishing motor is provided in the protective cover;

[0016] Wherein, the positioning plate is located in the cavity of the protective cover.

[0017] The present application also provides a method for optimizing the flatness of silicon wafer polishing, which is used in any of the above-mentioned devices for optimizing the flatness of silicon wafer polishing, comprising:

[0018] Polishing the silicon wafer by means of the grinding cloth, and performing a first repairing action of the grinding cloth in a first predetermined period;

[0019] The first repair action is specifically:

[0020] The grinding cloth is placed on the positioning plate, and the polishing piece is moved until the diamond piece abuts against the surface of the grinding cloth;

[0021] The positioning disk rotates in a first direction, and the rotating disk rotates in the first direction and the second direction for a predetermined time respectively;

[0022] The first direction and the second direction are specifically opposite rotation directions.

[0023] It is further defined that in the above-mentioned method for optimizing flatness of silicon wafer polishing, the first predetermined period is specifically set to 10 hours;

[0024] Wherein, in the first repairing action, the turntable first rotates in the second direction for 3 minutes and then rotates in the first direction for 1 minute.

[0025] It is further defined that the above-mentioned method for optimizing the flatness of a silicon wafer polishing further comprises:

[0026] The polishing cloth performs silicon wafer polishing after the first repairing action, and detects the Taper value of the silicon wafer in a second predetermined period;

[0027] Based on the Taper value of the silicon wafer, a second repairing action of the grinding cloth is performed, or the grinding cloth continues to polish the silicon wafer;

[0028] The second predetermined period is not greater than the first predetermined period, and the second repair action is specifically:

[0029] The grinding cloth is placed on the positioning plate, and the polishing piece is moved until the diamond piece abuts against the surface of the grinding cloth;

[0030] When the Taper value exceeds the error threshold and is positive, the positioning plate rotates in the first direction and the rotating plate rotates in the first direction;

[0031] When the Taper value exceeds the error threshold and is negative, the positioning plate rotates in the first direction and the rotating plate rotates in the second direction.

[0032] It is further defined that in the above-mentioned method for optimizing flatness of silicon wafer polishing, the second predetermined period is specifically set to 5 to 10 hours.

[0033] It is further defined that in the above-mentioned flatness optimization method for silicon wafer polishing, the error threshold is specifically set to -1.5 μm to +1.5 μm.

[0034] Further defined, in the above-mentioned method for optimizing the flatness of silicon wafer polishing, the method for detecting the Taper value is specifically as follows:

[0035] Taking the bottom surface of the silicon wafer as a reference plane, respectively obtaining the thickness of the silicon wafer at a first reference point and a second reference point, wherein the Taper value is specifically the thickness at the first reference point minus the thickness at the second reference point;

[0036] The first reference point is specifically set to be the center point of the arc edge of the silicon wafer, and the second reference point is specifically set to be the center point of the flat edge of the silicon wafer.

[0037] The present invention has at least the following beneficial effects:

[0038] 1. Mechanically scrub the surface of the grinding cloth with a polishing piece covered with diamond pieces to effectively remove SiO on the surface of the grinding cloth. x Blockage re-exposes the microporous structure of the polishing cloth, which not only restores the material removal rate of the polishing process, but also improves the poor flatness of the silicon wafer by regenerating the uniform micropore distribution on the surface;

[0039] 2. The grinding cloth is repaired by two-way grinding through the diamond piece to maintain balance and effectively remove SiO on the surface of the grinding cloth. x Blockage, reduce the problem of poor local Taperb of silicon wafer;

[0040] 3. Based on the detection results of the Taper value of the silicon wafer, the repair rotation direction between the grinding cloth and the polishing part is adjusted. This dynamic adjustment strategy realizes closed-loop control of the total thickness deviation value and the local thickness deviation value by actively correcting the surface morphology of the grinding cloth, avoiding the need to repair the grinding cloth after the flatness of the silicon wafer has problems, and suppressing the abnormal taper problem of the silicon wafer caused by the deterioration of the surface condition of the grinding cloth from the root. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a schematic diagram of the structure of a flatness optimization device for silicon wafer polishing according to an embodiment of the present application;

[0042] Figure 2 This is a schematic structural diagram of a "polishing member 400" in a flatness optimization device for silicon wafer polishing according to an embodiment of the present application;

[0043] Figure 3 It is a schematic diagram of the structure of the "silicon wafer 500" in the embodiment of the present application.

[0044] Reference numerals

[0045] Mounting frame 100, protective cover 110, positioning plate 200, polishing motor 310, rotating plate 320, lifting device 330, mounting plate 340, polishing piece 400, substrate 410, diamond piece 420, silicon wafer 500, first reference point 510, second reference point 520. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present application to clearly describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments in the present application belong to the scope of protection of this application.

[0047] The terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, and are not used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable under appropriate circumstances, so that the embodiments of the present application can be implemented in an order other than those illustrated or described here, and the objects distinguished by "first", "second", etc. are generally of one type, and the number of objects is not limited. For example, the first object can be one or more. In addition, "and / or" in the specification and claims represents at least one of the connected objects, and the character " / " generally indicates that the objects associated with each other are in an "or" relationship.

[0048] The flatness optimization device and method for silicon wafer polishing provided in the embodiments of the present application are described in detail below with reference to the accompanying drawings through specific embodiments and their application scenarios.

[0049] like Figure 1 , Figure 2 As shown, an embodiment of the present application provides a flatness optimization device for silicon wafer polishing, including a mounting frame 100 and a positioning plate 200 and a turntable 320 rotatably connected to the mounting frame 100, and also includes a first power unit for driving the positioning plate 200 to rotate and a second power unit for driving the turntable 320 to rotate.

[0050] The turntable 320 is coaxial with the positioning disk 200 and is located on the side of the positioning disk 200 away from the ground. A lifting device 330 is fixedly provided on the end surface of the turntable 320 close to the positioning disk 200. The telescopic end of the lifting device 330 faces the positioning disk 200 and is fixedly provided with a mounting disk 340. A polishing part 400 is fixedly provided on the end surface of the mounting disk 340 close to the positioning disk 200.

[0051] The polishing member 400 includes a substrate 410 and a plurality of diamond pieces 420 arranged in a circular array about the central axis of the substrate 410 and fixedly disposed on an end surface of the substrate 410 close to the positioning plate 200 .

[0052] The end surface of the positioning plate 200 close to the turntable 320 is used for placing the grinding cloth. When the lifting device 330 is extended, the diamond piece 420 on the polishing piece 400 at the corresponding position can abut the grinding cloth placed on the positioning plate 200. When the turntable 320 is rotating, the diameter of the rotating trajectory circle of the polishing piece 400 is not less than the diameter of the grinding cloth placed on the positioning plate 200.

[0053] Initially, the lifting device 330 is in a retracted state, and a large distance is maintained between the polishing piece 400 and the positioning disk 200. At this time, the staff can place the grinding cloth on the positioning disk 200, while ensuring that the grinding cloth is coaxial with the rotation axis of the positioning disk 200; when the grinding cloth is placed, the lifting device 330 is extended, and the diamond piece 420 on the polishing piece 400 abuts against the surface of the grinding cloth, and then the positioning disk 200 is driven to rotate by the first power unit, and the rotating disk 320 is driven to rotate by the second power unit. At this time, the polishing piece 400 revolves around the central axis of the positioning disk 200. Since the diameter of the rotating trajectory circle of the polishing piece 400 is not less than the diameter of the grinding cloth, it can ensure full coverage of the grinding cloth and achieve surface repair of the grinding cloth.

[0054] It is understandable that during the working process of the grinding cloth, the small holes on its surface are easily x Traditional brushes cannot remove the small pores on the surface of the abrasive cloth that are clogged with abrasives.

[0055] In the embodiment of the present application, the above-mentioned device for optimizing the flatness of silicon wafer polishing is used to mechanically scrub the surface of the grinding cloth by using the polishing piece 400 covered with a diamond piece 420 on the surface to effectively remove SiO x The clogging re-exposes the microporous structure of the polishing cloth, which not only restores the material removal rate of the polishing process, but also improves the poor flatness of the silicon wafer by regenerating a uniform micropore distribution on the surface.

[0056] In a preferred embodiment, Figure 1 , Figure 2 As shown, a plurality of lifting devices 330 are fixedly provided on the end surface of the rotary disk 320 close to the positioning disk 200 , and the plurality of lifting devices 330 are arranged in a circular array about the central axis of the rotary disk 320 .

[0057] At least one lifting device 330 is equipped with a polishing piece 400 .

[0058] It is understandable that, through the multiple lifting devices 330, the number of polishing pieces 400 during the repair of the grinding cloth can be adjusted, thereby increasing the repair frequency and the repair speed.

[0059] In a preferred embodiment, Figure 1 As shown, the second power unit includes a polishing motor 310 fixedly disposed on the mounting frame 100 , and a turntable 320 fixedly disposed on a power output shaft of the polishing motor 310 .

[0060] It is understandable that the configuration of the second power unit is not limited to the above-mentioned one, as long as it can realize the rotational drive of the turntable 320, which will not be elaborated here.

[0061] In a preferred embodiment, Figure 1 As shown, a protective cover 110 is fixedly provided on the mounting frame 100 , and a cavity is provided in the protective cover 110 with an opening facing one side of the polishing motor 310 .

[0062] The positioning plate 200 is located in the cavity of the protective cover 110 .

[0063] It is understandable that the protective cover 110 can provide a closed repair environment for the grinding cloth, thereby preventing grinding waste and grinding liquid from splashing out.

[0064] The embodiment of the present application provides a method for optimizing the flatness of silicon wafer polishing, which is used in the device for optimizing the flatness of silicon wafer polishing in the above embodiment, including:

[0065] Step S1, polishing the silicon wafer by means of a grinding cloth, and performing a first repairing action of the grinding cloth in a first predetermined period;

[0066] The first repair action is as follows:

[0067] The grinding cloth is placed on the positioning plate 200, and the polishing piece 400 is moved until the diamond piece 420 abuts against the surface of the grinding cloth;

[0068] The positioning disk 200 rotates in the first direction, and the rotating disk 320 rotates in the first direction and the second direction for a predetermined time respectively;

[0069] The first direction and the second direction are specifically opposite rotation directions.

[0070] In the embodiment of the present application, the above-mentioned method for optimizing the flatness of silicon wafer polishing is adopted, and the grinding cloth is repaired by bidirectional grinding through the diamond piece 420, so as to maintain balance and effectively remove SiO x Blockage and reduce the problem of poor local Taperb on the silicon wafer.

[0071] In a preferred implementation, the first predetermined period is specifically set to 10 hours.

[0072] In a preferred embodiment, the positioning plate 200 rotates in the first direction, and the rotating plate 320 rotates in the second direction for 3 minutes and then rotates in the first direction for 1 minute.

[0073] It is understandable that the rotation form of the turntable 320 in the first repair action is not limited to the above-mentioned one, and in the actual brushing process, the brushing time of the turntable 320 in the first direction and the second direction can be flexibly adjusted based on experimental data.

[0074] In a preferred embodiment, it also includes:

[0075] Step S2, the polishing cloth performs silicon wafer polishing after the first repairing action, and detects the Taper value of the silicon wafer in a second predetermined period;

[0076] Step S3: Based on the Taper value of the silicon wafer, a second repairing action of the grinding cloth is performed, or the grinding cloth continues to polish the silicon wafer.

[0077] The second predetermined period is not greater than the first predetermined period. In step S3, the second repair action is specifically:

[0078] The grinding cloth is placed on the positioning plate 200, and the polishing piece 400 is moved until the diamond piece 420 abuts against the surface of the grinding cloth;

[0079] When the Taper value exceeds the error threshold and is positive, the positioning disk 200 rotates in the first direction, and the rotating disk 320 rotates in the first direction for a predetermined time;

[0080] When the Taper value exceeds the error threshold and is negative, the positioning plate 200 rotates in the first direction and the rotating plate 320 rotates in the second direction for a predetermined time.

[0081] It is understandable that during the polishing process of silicon wafers, due to the influence of the fixed plate and the grinding cloth, the bird's-eye view of the silicon wafer after polishing may appear inclined. The inclined shape of the silicon wafer is called Taper, and the total thickness deviation is significantly affected by the Taper value. Therefore, during the production process, the total thickness deviation and local thickness deviation of the product are controlled according to the Taper value.

[0082] In an embodiment of the present application, the above-mentioned flatness optimization method for silicon wafer polishing is adopted, and based on the detection result of the Taper value of the silicon wafer, the repair rotation direction between the grinding cloth and the polishing piece 400 is adjusted. The dynamic adjustment strategy realizes closed-loop control of the total thickness deviation value and the local thickness deviation value by actively correcting the surface morphology of the grinding cloth, thereby avoiding the need to repair the grinding cloth after the flatness problem occurs on the silicon wafer, and suppressing the abnormal taper problem of the silicon wafer caused by the degradation of the surface state of the grinding cloth from the root.

[0083] In a preferred implementation, the second predetermined period is specifically set to 5 to 10 hours.

[0084] In a preferred implementation, the error threshold is specifically set to -1.5 μm to +1.5 μm.

[0085] According to the test results, when the Taper value is controlled within the error threshold (-1.5μm~+1.5μm), the total thickness deviation value level can reach 1.5±1.0um.

[0086] In a preferred embodiment, in step S2, the method for detecting the Taper value is specifically as follows:

[0087] Taking the bottom surface of the silicon wafer as a reference plane, the thickness of the silicon wafer at the first reference point 510 and the second reference point 520 are obtained respectively. The Taper value is specifically the thickness at the first reference point 510 minus the thickness at the second reference point 520 .

[0088] The second reference point 520 is specifically set as the center point of the flat side of the silicon wafer, and the first reference point 510 is specifically set as the center point of the arc side of the silicon wafer.

[0089] It is understandable that if Figure 3 As shown, silicon wafer 500 has an arc edge and a flat edge, a first reference point 510 is set at the center point of the arc edge, and a second reference point 520 is set at the center point of the flat edge. The thickness at the first reference point 510 minus the thickness at the second reference point 520 is the Taper value. Since there is a difference in thickness at the first reference point 510 and the second reference point 520, the Taper value may be positive or negative. When the Taper value exceeds the error threshold, the repair rotation direction between the grinding cloth and the polishing piece 400 can be adjusted based on the positive and negative values ​​of the Taper value.

[0090] It should be noted that, in this article, the terms "comprise", "include" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise one..." do not exclude the presence of other identical elements in the process, method, article or device including the element. In addition, it should be pointed out that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in reverse order according to the functions involved, for example, the described method may be performed in an order different from that described, and various steps may also be added, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

[0091] The embodiments of the present application are described above in conjunction with the accompanying drawings, but the present application is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present application, ordinary technicians in this field can also make many forms without departing from the purpose of the present application and the scope of protection of the claims, all of which are within the protection of the present application.

Claims

1. A flatness optimization device for silicon wafer polishing, characterized in that: It includes a mounting frame, a positioning plate and a rotating plate rotatably connected to the mounting frame, and also includes a first power unit and a second power unit for driving the positioning plate and the rotating plate to rotate respectively; The rotary disk is coaxial with the positioning disk and is located on the side of the positioning disk away from the ground. A lifting device is fixedly provided on the end surface of the rotary disk close to the positioning disk. The telescopic end of the lifting device faces the positioning disk and is fixedly provided with a mounting disk. A polishing piece is fixedly provided on the end surface of the mounting disk close to the positioning disk. Wherein, the polishing member comprises a substrate, and a plurality of diamond pieces are fixedly arranged in a circular array about its own central axis on the end surface of the substrate close to the positioning plate; The positioning plate is used to place the grinding cloth, and when the lifting device is in the extended state, the diamond piece on the polishing piece at the corresponding position can abut against the grinding cloth placed on the positioning plate; When the rotary disk is rotating, the diameter of the rotating track circle of the polishing piece is not less than the diameter of the grinding cloth placed on the positioning disk.

2. The flatness optimization device for silicon wafer polishing according to claim 1, characterized in that: A plurality of lifting devices are fixedly provided on the end surface of the rotary disk close to the positioning disk, and the plurality of lifting devices are arranged in a circular array about the central axis of the rotary disk; Wherein, a polishing piece is installed on at least one of the lifting devices.

3. The flatness optimization device for silicon wafer polishing according to claim 1, characterized in that: The second power unit comprises a polishing motor fixedly arranged on a mounting frame, and the turntable is fixedly arranged on a power output shaft of the polishing motor.

4. A flatness optimization device for silicon wafer polishing according to claim 1 or 3, characterized in that: A protective cover is fixedly provided on the mounting frame, and a cavity is provided in the protective cover with an opening facing one side of the polishing motor; Wherein, the positioning plate is located in the cavity of the protective cover.

5. A method for optimizing the flatness of silicon wafer polishing, characterized in that: The flatness optimization device for silicon wafer polishing as claimed in any one of claims 1 to 4, comprising: Polishing the silicon wafer by means of the grinding cloth, and performing a first repairing action of the grinding cloth in a first predetermined period; The first repair action is specifically: The grinding cloth is placed on the positioning plate, and the polishing piece is moved until the diamond piece abuts against the surface of the grinding cloth; The positioning disk rotates in a first direction, and the rotating disk rotates in the first direction and the second direction for a predetermined time respectively; The first direction and the second direction are specifically opposite rotation directions.

6. A method for optimizing flatness of silicon wafer polishing according to claim 5, characterized in that: The first predetermined period is specifically set to 10 hours; Wherein, in the first repairing action, the turntable first rotates in the second direction for 3 minutes and then rotates in the first direction for 1 minute.

7. A method for optimizing the flatness of silicon wafer polishing according to claim 5 or 6, characterized in that: Also includes: The polishing cloth performs silicon wafer polishing after the first repairing action, and detects the Taper value of the silicon wafer in a second predetermined period; Based on the Taper value of the silicon wafer, a second repairing action of the grinding cloth is performed, or the grinding cloth continues to polish the silicon wafer; The second predetermined period is not greater than the first predetermined period, and the second repair action is specifically: The grinding cloth is placed on the positioning plate, and the polishing piece is moved until the diamond piece abuts against the surface of the grinding cloth; When the Taper value exceeds the error threshold and is positive, the positioning plate rotates in the first direction and the rotating plate rotates in the first direction; When the Taper value exceeds the error threshold and is negative, the positioning plate rotates in the first direction and the rotating plate rotates in the second direction.

8. The method for optimizing the flatness of silicon wafer polishing according to claim 7, characterized in that: The second predetermined period is specifically set to be 5 to 10 hours.

9. The method for optimizing flatness of silicon wafer polishing according to claim 7, characterized in that: The error threshold is specifically set to be -1.5 μm to +1.5 μm.

10. The method for optimizing the flatness of silicon wafer polishing according to claim 7, characterized in that: The method for detecting the Taper value is specifically as follows: Taking the bottom surface of the silicon wafer as a reference plane, respectively obtaining the thickness of the silicon wafer at a first reference point and a second reference point, wherein the Taper value is specifically the thickness at the first reference point minus the thickness at the second reference point; The first reference point is specifically set to be the center point of the arc edge of the silicon wafer, and the second reference point is specifically set to be the center point of the flat edge of the silicon wafer.

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