Wafer grinding and polishing method

Abstract

The present invention provides a method for grinding and polishing a wafer, belonging to the field of semiconductor technology, comprising the following steps: S1. performing primary grinding on the wafer by using an edge collapse process to obtain a semi-finished wafer; S2. performing secondary grinding on the semi-finished wafer by using an edge protrusion process to correct the thickness deviation of the semi-finished wafer and obtain a finished wafer; the order of the edge collapse process in step S1 and the edge protrusion process in step S2 can be adjusted. The method for grinding and polishing a wafer provided by the present invention changes the existing single grinding to double grinding. By superimposing the different processing effects of the two grinding methods, the unidirectional deviations brought by the single grinding process are offset against each other, so as to achieve the processing effect of lower thickness deviation between the central region and the edge region of the wafer, and improve the uniformity of the surface quality of the wafer.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductors, and more specifically, relates to a method for grinding and polishing a wafer. Background Art

[0002] The grinding and polishing of semiconductor wafers exist in multiple links of wafer substrate production and device production. The grinding and polishing process of the wafer will change the thickness of each position of the wafer and determine the thickness deviation of the wafer. Especially as the size of the wafer is getting larger, due to the increase in the area of the ground and polished wafer, the removal amount of grinding and polishing at different positions of the wafer is more uneven, resulting in a larger thickness deviation of the large-size wafer and an increase in processing difficulty. The non-uniformity of the wafer thickness will have an adverse impact on device production. Therefore, the uniform thickness of the large-size wafer is an important indicator to measure the wafer processing level. Summary of the Invention

[0003] An object of the present invention is to provide a method for grinding and polishing a wafer, aiming to solve the problem that the removal amount of grinding and polishing at different positions of the wafer is more uneven, resulting in a large thickness deviation of the wafer.

[0004] To achieve the above object, the technical solution adopted by the present invention is: providing a method for grinding and polishing a wafer, including the following steps:

[0005] S1. Perform primary grinding on the wafer using an edge collapse process to obtain a semi-finished wafer;

[0006] S2. Perform secondary grinding on the semi-finished wafer using an edge bulge process to correct the thickness deviation of the semi-finished wafer and obtain a finished wafer;

[0007] The order of the edge collapse process in step S1 and the edge bulge process in step S2 can be adjusted.

[0008] As another embodiment of the present application, the overall thickness of the wafer to be ground is , and the thickness of the wafer ground in step S1 is , and the thickness of the wafer ground in step S2 is , .

[0009] As another embodiment of the present application, before grinding in step S2, measure the thickness of the semi-finished wafer obtained in step S1 to determine the thickness deviation at different positions of the semi-finished wafer , ; calculate the required thickness deviation correction value , , and the thickness deviation of the finished wafer obtained after step S2 is processed is .

[0010] As another embodiment of the present application, in the edge collapse process, the grinding effect of the grinding fluid gradually decreases, and in the edge bulge process, the grinding effect of the grinding fluid gradually increases.

[0011] As another embodiment of the present application, the grinding fluid used in the edge collapse process contains polishing abrasive grains; the grinding fluid used in the edge bulge process contains agglomerated abrasive grains, and the agglomerated abrasive grains gradually disperse under the action of pressure to form polishing abrasive grains, and the grinding strength of the polishing abrasive grains is greater than that of the agglomerated abrasive grains.

[0012] As another embodiment of the present application, the polishing abrasive grains are single crystal or polycrystalline abrasive grains.

[0013] As another embodiment of the present application, both the edge collapse process and the edge bulge process use a polishing machine. As the wafer moves, the abrasive grains in the grinding fluid in the polishing machine move from the edge area of the wafer towards the center area of the wafer.

[0014] As another embodiment of the present application, the polishing machine can be a single-sided polishing machine or a double-sided polishing machine.

[0015] As another embodiment of the present application, in the edge collapse process, changing the processing pressure can adjust the wear time of the polishing abrasive grains, and changing the processing speed can adjust the length of the moving path of the polishing abrasive grains;

[0016] In the edge bulge process, changing the processing pressure can adjust the dispersion time of the agglomerated abrasive grains, and changing the processing speed can adjust the length of the dispersion path of the agglomerated abrasive grains.

[0017] As another embodiment of the present application, in both the edge collapse process and the edge bulge process, the width of the edge collapse or bulge of the wafer can be changed by changing the particle size of the polishing abrasive grains in the grinding fluid.

[0018] The beneficial effect of the wafer polishing and grinding processing method provided by the present invention is that: compared with the prior art, the wafer polishing and grinding processing method of the present invention changes the existing single grinding to two grindings. By superimposing the different processing effects of the two grinding methods, the unidirectional deviations brought by the single grinding processing are offset from each other, so as to achieve a processing effect with a lower thickness deviation between the center area and the edge area of the wafer, and improve the uniformity of the wafer surface quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0020] Figure 1 Schematic diagram of the working principle of the double-sided grinding and polishing machine provided by the embodiment of the present invention;

[0021] Figure 2 Schematic diagram of the wafer layout of the double-sided grinding and polishing machine provided by the embodiment of the present invention;

[0022] Figure 3 Schematic diagram of the working principle of the single-sided grinding and polishing machine provided by the embodiment of the present invention;

[0023] Figure 4 Schematic diagram of the wafer layout of the single-sided grinding and polishing machine provided by the embodiment of the present invention;

[0024] Figure 5 Effect diagram of the wafer after edge collapse process grinding provided by the embodiment of the present invention;

[0025] Figure 6 Effect diagram of the wafer after edge bulge process grinding provided by the embodiment of the present invention;

[0026] Figure 7 Schematic diagram of the finished wafer provided by the embodiment of the present invention.

[0027] In the figure: 1, rotating lower disk; 2, rotating upper disk; 3, polishing pad; 4, wafer; 5, rotating chassis; 6, downward pressing rotating disk; 7, adhesive layer; 8, carrier disk; 9, internal and external toothed ring; 10, working area; 11, planetary wheel tooling; 12, central area; 13, edge area. Detailed implementation manners

[0028] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] Please refer to Figures 1 to 7 , and now the grinding and polishing processing method of the wafer 4 provided by the present invention will be described. The grinding and polishing processing method of the wafer 4 includes the following steps:

[0030] S1. Perform primary grinding on the wafer 4 by using an edge collapse process to obtain a semi-finished wafer 4;

[0031] S2. Perform secondary grinding on the semi-finished wafer 4 by using an edge bulge process to correct the thickness deviation of the semi-finished wafer 4 and obtain a finished wafer 4;

[0032] The order of the edge collapse process in step S1 and the edge bulge process in step S2 can be adjusted.

[0033] The grinding and polishing method of the wafer 4 provided by the present invention, compared with the prior art, changes the existing single grinding to double grinding. By superimposing the different processing effects of the two grinding methods, the unidirectional deviations caused by the single grinding process are offset from each other, so as to achieve the processing effect of a lower thickness deviation between the central region 12 and the edge region 13 of the wafer 4, and improve the uniformity of the surface quality of the wafer 4.

[0034] The existing single grinding can only improve the degree of edge collapse or edge bulge of the wafer 4, reduce the thickness difference between the central region 12 and the edge region 13 of the wafer 4, and cannot fundamentally change the phenomenon of edge collapse or edge bulge, that is, the thickness difference between the central region 12 and the edge region 13 of the wafer 4 will gradually increase with the extension of the processing time of the wafer 4. And grinding and polishing essentially mean grinding off a certain thickness of the wafer 4, so the thickness determines that there will be an unavoidable thickness difference between the central region 12 and the edge region 13 of the processed wafer 4 .

[0035] It is now proposed to combine the edge collapse process and the edge bulge process, and process the two steps in series, so that the thickness of the edge collapse and the thickness of the edge bulge cancel each other out, so as to reduce the thickness difference of the wafer 4, and further reduce the phenomenon of edge collapse or edge bulge.

[0036] The formation principle of the edge collapse process is that under the action of pressure, the abrasive grains in the grinding fluid enter the gap between the wafer 4 and the polishing pad 3 from the edge of the wafer 4, and through the relative displacement during the processing, they play a grinding role. As the wafer 4 moves, the abrasive grains move from the edge region 13 of the wafer 4 to the central region 12 of the wafer 4. During the movement, the abrasive grains become dull due to the grinding wear at the edge of the wafer 4, and the grinding ability becomes poor. Therefore, the grinding thickness 、 of the edge of the wafer 4 、 is greater than the grinding thickness of the central region 12 of the wafer 4

[0037] Thereby forming an edge collapse morphology. 、 is greater than the grinding thickness of the edge of the wafer 4 , , thus forming an edge convex morphology.

[0038] During the processing, the sequence of the edge collapse process and the edge convex process can be adjusted.

[0039] Taking the overall thickness of the wafer 4 to be ground as , the thickness of the wafer 4 ground in step S1 , and the thickness of the wafer 4 ground in step S2 is , . Divide the required grinding thickness into two steps of the edge collapse process and the edge convex process for serial processing, that is, the total thickness ground by the two-step process is the total thickness required for the overall grinding of the wafer 4. Among them, the required grinding thickness values and can be the same or different.

[0040] Taking the example of performing the edge collapse process first and then the edge convex process. In step S1, the wafer 4 is ground using the edge collapse process to form a semi-finished wafer 4 with an edge collapse, and the grinding thickness of the central region 12 of this wafer 4 is less than the overall thickness value to be ground. In step S2, the wafer 4 is ground using the edge convex process. By using the principle that the grinding force on the central region 12 in the edge convex process is stronger, the central grinding thickness of the wafer 4 in step S2 is made greater than the grinding thickness of the edge region 13, thereby achieving the same grinding thickness for the central region 12 and the edge region 13.

[0041] Before grinding in step S2, the thickness of the semi-finished wafer 4 obtained in step S1 is measured to determine the thickness deviation at different positions of the semi-finished wafer 4 , ; calculate the required correction thickness deviation value , , and the thickness deviation of the finished wafer 4 obtained after the processing in step S2.

[0042] In the processing technology, taking the central region 12 as the measurement point, the grinding thickness of the wafer 4 is detected. That is, in step S1, the grinding thickness of the central region 12 of the wafer 4 is , and the thickness difference between the edge region 13 and the central region 12 is ; in step S2, the grinding thickness of the central region 12 of the wafer 4 is , and the thickness difference between the edge region 13 and the central region 12 is . According to the characteristics of the two processing technologies, and One is positive and the other is negative. The thickness deviation of the finished wafer 4 formed after the superposition of the two processes , whose absolute value < . That is, the thickness difference between the central region 12 and the edge region 13 of the wafer 4 after two grinding processes must be less than the thickness difference processed by the existing single grinding technology.

[0043] To smoothly implement the edge collapse process and the edge bulge process, the grinding effect in the grinding fluid during the edge collapse process gradually decreases, and the grinding effect in the grinding fluid during the edge bulge process gradually increases. There are abrasive grains in the grinding fluid. The abrasive grains enter between the wafer 4 and the polishing pad 3. When the polishing pad 3 and the wafer 4 move relative to each other, the abrasive grains polish the surface of the wafer 4.

[0044] During the grinding process, only by changing the composition of the abrasive grains and utilizing the characteristics of abrasive grains with different compositions, the adjustment of the grinding effect can be achieved, and the edge collapse process and the edge bulge process can be switched.

[0045] Specifically, the grinding fluid used in the edge collapse process contains polishing abrasive grains; the grinding fluid used in the edge bulge process contains agglomerated abrasive grains. Under the action of pressure, the agglomerated abrasive grains gradually disperse to form polishing abrasive grains. The grinding intensity of the polishing abrasive grains is greater than that of the agglomerated abrasive grains.

[0046] In the grinding fluid of the edge collapse process, polishing abrasive grains are directly used. The polishing abrasive grains are single-crystal or polycrystalline abrasive grains. The abrasive grains are diamond powder particles or abrasive grains of other materials. Since the polishing abrasive grains have a large grinding ability during polishing and will become blunt due to wear during the grinding process, and the grinding ability becomes poor, the grinding ability of the polishing abrasive grains gradually decreases and the grinding effect gradually decreases as they wear during the process of entering the central region 12 from the edge region 13. This makes the grinding thickness of the edge region 13 greater than the grinding thickness of the central region 12.

[0047] In the grinding fluid of the edge bulge process, agglomerated abrasive grains are used. The agglomerated abrasive grains are formed by bonding a large number of small, irregularly shaped abrasive grains together with a ceramic binder or a resin binder to form a combined abrasive grain mass with a certain size, shape, and strength. The agglomerated abrasive grains will disperse from large particles into small particles until they become polishing abrasive grains under the action of pressure.

[0048] During the processing, the agglomerated abrasive grains enter between the wafer 4 and the polishing pad 3 from the edge of the wafer 4. During the movement of the agglomerated abrasive grains from the edge region 13 towards the central region 12, the agglomerated abrasive grains are squeezed and dispersed during the movement until the agglomerated abrasive grains are decomposed into polishing abrasive grains after moving to the central region 12. Since the abrasive grains of the agglomerated abrasive grains are bonded together when not dispersed, the grinding ability is poor. As the agglomerated abrasive grains are dispersed, the polishing abrasive grains inside are dispersed, and the grinding ability of the polishing abrasive grains is large. Therefore, during the movement of the agglomerated abrasive grains, the grinding effect of the grinding fluid gradually increases.

[0049] In the edge bulge process, since the grinding ability of the grinding fluid gradually increases, during the process of the abrasive grains of the grinding fluid entering the central region 12 from the edge region 13, as the agglomerated abrasive grains are dispersed, its grinding ability gradually improves and the grinding effect gradually enhances. The grinding thickness of the edge region 13 is made smaller than the grinding thickness of the central region 12.

[0050] In the edge collapse process, changing the processing pressure can adjust the wear time of the polishing abrasive grains, and changing the processing speed can adjust the length of the movement path of the polishing abrasive grains; in the edge bulge process, changing the processing pressure can adjust the dispersion time of the agglomerated abrasive grains, and changing the processing speed can adjust the length of the dispersion path of the agglomerated abrasive grains. In both the edge collapse process and the edge bulge process, the width of the edge collapse or bulge of the wafer 4 can be changed by changing the particle size of the polishing abrasive grains in the grinding fluid. In both steps, the processing parameters can be adjusted to affect the width and thickness of the central region 12 and the edge region 13 of the wafer 4, so as to realize the grinding thickness distribution of different position regions of the wafer 4.

[0051] Both the edge collapse process and the edge bulge process use a polishing machine. As the wafer 4 moves, the abrasive grains in the grinding fluid in the polishing machine move from the edge region 13 of the wafer 4 towards the central region 12 of the wafer 4.

[0052] The polishing machine can be a single-sided polishing machine or a double-sided polishing machine.

[0053] When the polishing machine is a double-sided polishing machine, since the two surfaces of the wafer 4 are processed simultaneously, the rotation speeds of the upper and lower disks can be adjusted respectively, resulting in different relative displacement speeds on the upper and lower surfaces of the wafer 4. The processing process parameters are adjusted according to the upper and lower surfaces of the wafer 4 to realize the grinding thickness distribution of different position regions of the wafer 4. Thus, different surface morphologies are formed on the upper and lower surfaces. Matching the distribution of the total grinding thickness of the second grinding, different morphologies such as concave up and flat down, flat up and concave down, convex up and flat down, flat up and convex down, convex up and down, concave up and down, flat up and down, concave up and convex down, convex up and concave down can be formed; or the width and thickness of the central region 12 of the wafer and the edge annular region are adjusted to realize the change of different concave and convex curvatures, so as to realize the processing of products with different morphologies. Figure 7Four common crystal morphologies are listed below. Morphology a is a crystal morphology with flat upper and lower surfaces, morphology b is a crystal morphology with a convex upper surface and a flat lower surface, morphology c is a crystal morphology with a concave upper surface and a flat lower surface, and morphology d is a crystal morphology with a concave upper surface and a convex lower surface.

[0054] As Figure 1 and Figure 2 shown, the double-sided grinding and polishing machine has a rotating upper platen 2 and a rotating lower platen 1. Both the rotating upper platen 2 and the rotating lower platen 1 can rotate around their central axes. There is a planetary wheel tooling 11 between the rotating lower platen 1 and the rotating upper platen 2. The planetary wheel tooling 11 has a mounting station for limiting the wafer 4, and each planetary wheel tooling 11 has at least 2 mounting stations for the wafer 4. There is an internal and external gear ring 9 between the rotating lower platen 1 and the rotating upper platen 2. An annular working area 10 is formed between the internal and external gear rings 9. The planetary wheel tooling 11 is located in the working area 10 and is simultaneously meshed and connected with the internal and external gear rings 9. Multiple planetary wheel toolings 11 can be installed in the working area 10 at the same time.

[0055] During grinding, polishing pads 3 are provided on both the rotating upper platen 2 and the rotating lower platen 1. The rotating upper platen 2 and the rotating lower platen 1 simultaneously grind the upper and lower surfaces of the wafer 4 with the polishing pads 3 they are equipped with.

[0056] When the grinding and polishing machine is a single-sided grinding and polishing machine, the single-sided grinding and polishing machine can process one surface and then process the other surface, so it is easier to achieve the processing of different morphologies on the upper and lower surfaces than the double-sided grinding and polishing machine.

[0057] As Figure 3 and Figure 4 shown, the single-sided grinding and polishing machine includes a rotating chassis 5 and a downward-pressing rotating platen 6. The downward-pressing rotating platen 6 is located above the rotating chassis 5 and faces the rotating chassis 5. A carrier plate 8 is installed at the bottom of the downward-pressing rotating platen 6. The wafer 4 is fixed to the bottom of the carrier plate 8 through an adhesive layer 7. The lower end surface of the wafer 4 is attached to the polishing pad 3 on the rotating chassis 5. The grinding liquid is dropped onto the polishing pad 3 on the rotating chassis 5 and enters between the wafer 4 and the polishing pad 3 from the gap between them as the rotating chassis 5 rotates, for polishing the lower surface of the wafer 4.

[0058] Optionally, there are multiple downward-pressing rotating platens 6 above the rotating chassis 5, and multiple wafers 4 are bonded to the bottoms of the multiple downward-pressing rotating platens 6. Under the combined action of the rotating chassis 5 and the downward-pressing rotating platens 6, the multiple wafers 4 are polished.

[0059] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for grinding and polishing a wafer, characterized in that, The steps include the following: S1. Perform primary grinding on the wafer using the edge collapse process to obtain a semi-finished wafer; S2. Perform secondary grinding on the semi-finished wafer using the edge bulge process to correct the thickness deviation of the semi-finished wafer and obtain a finished wafer; The sequence of the edge collapse process in step S1 and the edge bulge process in step S2 can be adjusted; The grinding fluid used in the edge collapse process contains polishing abrasive grains; the grinding fluid used in the edge bulge process contains agglomerated abrasive grains. Under the action of pressure, the agglomerated abrasive grains gradually disperse to form polishing abrasive grains, and the grinding intensity of the polishing abrasive grains is greater than that of the agglomerated abrasive grains; Both the edge collapse process and the edge bulge process use a polishing machine. As the wafer moves, the abrasive grains in the grinding fluid in the polishing machine move from the edge area of the wafer towards the center area of the wafer; In the edge collapse process, changing the processing pressure can adjust the wear time of the polishing abrasive grains, and changing the processing speed can adjust the length of the movement path of the polishing abrasive grains; In the edge bulge process, changing the processing pressure can adjust the dispersion time of the agglomerated abrasive grains, and changing the processing speed can adjust the length of the dispersion path of the agglomerated abrasive grains.

2. The lapping and polishing method for a wafer according to claim 1, wherein, The overall thickness of the wafer to be ground is , the thickness of the wafer ground in step S1 , the thickness of the wafer ground in step S2 is , .

3. The lapping and polishing method for a wafer according to claim 2, wherein Before grinding in step S2, the thickness of the semi-finished wafer obtained in step S1 is measured to determine the thickness deviation at different positions of the semi-finished wafer , ; calculate the required corrected thickness deviation value , , the thickness deviation of the finished wafer obtained after the processing in step S2 .

4. The grinding and polishing method for a wafer according to claim 1, characterized in that, The grinding effect in the grinding fluid during the edge collapse process gradually decreases, and the grinding effect in the grinding fluid during the edge bulge process gradually increases.

5. The method for grinding and polishing a wafer according to claim 1, characterized in that, The polishing abrasive grains are single-crystal or polycrystalline abrasive grains.

6. The lapping and polishing method for a wafer according to claim 1, wherein, The polishing machine can be a single-sided polishing machine or a double-sided polishing machine.

7. The lapping and polishing method for a wafer according to claim 1, characterized in that, In both the edge collapse process and the edge bulge process, the width of the edge collapse or bulge of the wafer can be changed by changing the particle size of the polishing abrasive grains in the grinding fluid.

Images