Method and equipment for thinning lithium tantalate bonded wafer

Abstract

The invention provides a method and equipment for thinning a lithium tantalate bonded wafer, and relates to the technical field of wafer thinning, initial surface type data is detected firstly, then the inclination angle of a coarse grinding wheel is adjusted according to the positive and negative values of the initial BOW value of the initial surface type data, and then the wafer is subjected to coarse thinning. And then the rough grinding surface type data of the thinned wafer are detected again, the inclination angle of the fine grinding wheel is adjusted according to the positive and negative values of the rough grinding BOW value of the rough grinding surface type data, and then fine thinning is conducted on the wafer. Compared with the prior art, the wafer is thinned through rough thinning and fine thinning, the inclination angle of the grinding wheel can be adjusted according to the BOW value before the thinning action, the grinding wheel can be better matched with the wafer in the thinning process, on one hand, the risk of brittle fracture such as edge breakage can be reduced, a subsurface damage layer can be slowed down, and therefore the service life of the grinding wheel is prolonged; and on the other hand, the wafer can be adaptively corrected, and the problem of serious warping caused by thinning is solved. And the quality of the thinned ultrathin lithium tantalate bonded wafer can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of wafer thinning, and more particularly, to a method and apparatus for thinning a bonded lithium tantalate wafer. Background Art

[0002] Lithium tantalate wafers, as an important semiconductor material, are widely used in fields such as sensors. With the development of technology, the demand for ultra-thin lithium tantalate wafers is increasing day by day. Lithium tantalate materials are mainly used in key devices such as high-performance filters, and their excellent material properties make them increasingly play an irreplaceable role.

[0003] In summary, due to the low hardness, high brittleness and strong anisotropy of lithium tantalate crystals, brittle fracture, warping, and deep subsurface damage layers are likely to occur during the thinning process. Therefore, the existing thinning methods are difficult to meet the mass production requirements of high-quality ultra-thin bonded wafers. Summary of the Invention

[0004] The purpose of the present invention is to provide a method and apparatus for thinning a bonded lithium tantalate wafer, which can effectively improve the quality of the thinned ultra-thin lithium tantalate bonded wafer, reduce the risk of brittle fracture during thinning, and solve the problem of serious warping caused by thinning.

[0005] In a first aspect, the present invention provides a method for thinning a bonded lithium tantalate wafer, including: Detecting the initial surface profile data of the wafer after cleaning, the initial surface profile data including an initial BOW value; Adjusting the inclination angle of the coarse grinding wheel relative to the thinning machine platform according to the positive or negative value of the initial BOW value, so that the coarse grinding wheel fits the initial surface profile of the wafer; Coarsely thinning the wafer; Detecting the rough grinding surface profile data of the wafer after coarse thinning, the rough grinding surface profile data including a rough grinding BOW value; Adjusting the inclination angle of the fine grinding wheel relative to the thinning machine platform according to the positive or negative value of the rough grinding BOW value, so that the fine grinding wheel fits the surface profile of the wafer after coarse thinning; Finely thinning the wafer; Detecting the fine grinding surface profile data of the wafer after fine thinning.

[0006] In an alternative embodiment, the step of adjusting the inclination angle of the coarse grinding wheel relative to the thinning machine platform according to the initial BOW value includes: If the initial BOW value is positive, the coarse grinding wheel is tilted inward towards the wafer by a first preset angle; If the initial BOW value is negative, the coarse grinding wheel is tilted outward away from the wafer by a second preset angle.

[0007] In an alternative embodiment, the first preset angle is 0.5° - 2°, and the second preset angle is 0.5° - 2°.

[0008] In an alternative embodiment, the step of adjusting the inclination angle of the fine grinding wheel relative to the thinning machine platform according to the positive or negative value of the rough grinding BOW value includes: If the rough grinding BOW value is positive, the fine grinding wheel is tilted inward toward the wafer by a third preset angle; If the rough grinding BOW value is negative, the fine grinding wheel is tilted outward toward the wafer by a fourth preset angle.

[0009] In an alternative embodiment, the third preset angle is less than 1°, and the fourth preset angle is 1° - 3°.

[0010] In an alternative embodiment, before the step of adjusting the inclination angle of the grinding wheel relative to the thinning machine platform according to the positive or negative value of the initial BOW value, the method further includes: Leveling the thinning machine platform so that the horizontal deviation of the thinning machine platform is less than or equal to 1 μm.

[0011] In an alternative embodiment, after the step of finely thinning the wafer, the method further includes: Pressing and grinding the wafer for a first preset time; After idling and grinding the wafer flat for a second preset time.

[0012] In an alternative embodiment, the first preset time is 2 - 3 s, and the second preset time is 5 - 10 s.

[0013] In an alternative embodiment, the mesh number of the coarse grinding wheel is 3000 - 4000; the mesh number of the fine grinding wheel is 6000 - 8000.

[0014] In an alternative embodiment, the initial surface profile data further includes the TTV value and the film thickness value of the wafer before thinning; the rough grinding surface profile data further includes the TTV value and the film thickness value of the wafer after rough thinning; the fine grinding surface profile data includes the TTV value, the film thickness value, and the LTV value of the wafer after fine thinning.

[0015] In a second aspect, an embodiment of the present invention provides a thinning device for a lithium tantalate bonded wafer, which is applicable to the foregoing thinning method. The thinning device includes: A surface profile detection device, which is used to detect the initial surface profile data of the wafer after cleaning, the rough grinding surface profile data of the wafer after rough thinning, and the fine grinding surface profile data of the wafer after fine thinning; A thinning machine platform, which is used to carry the wafer; A coarse grinding wheel for coarsely thinning the wafer. A fine grinding wheel for finely thinning the wafer. Wherein, the initial surface profile data includes an initial BOW value, the rough grinding surface profile data includes a rough grinding BOW value, and the thinning machine platform is further configured to adjust the inclination angle of the coarse grinding wheel relative to the thinning machine platform according to the positive or negative value of the initial BOW value, and to adjust the inclination angle of the fine grinding wheel relative to the thinning machine platform according to the positive or negative value of the rough grinding BOW value.

[0016] The beneficial effects of the embodiments of the present invention include: The thinning method and device for a lithium tantalate bonded wafer provided by the embodiments of the present invention can realize the thinning of the lithium tantalate bonded wafer. The method includes: first detecting the initial surface profile data of the wafer after cleaning, the initial surface profile data at least including an initial BOW value, and then adjusting the inclination angle of the coarse grinding wheel relative to the thinning machine platform according to the positive or negative value of the initial BOW value, so that the coarse grinding wheel can fit the initial surface profile of the wafer, and then coarsely thinning the wafer. Since the inclination angle of the coarse grinding wheel is changed according to the positive or negative value of the BOW value, the warping of the wafer can be preliminarily corrected during the coarse thinning process. Then, the rough grinding surface profile data of the wafer after thinning is detected again, the rough grinding surface profile data at least including a rough grinding BOW value, and then the inclination angle of the fine grinding wheel relative to the thinning machine platform is adjusted according to the positive or negative value of the rough grinding BOW value, so that the fine grinding wheel can fit the surface profile of the wafer after coarse thinning, and then finely thinning the wafer. Finally, the fine grinding surface profile data of the wafer after fine thinning is detected again. Compared with the prior art, the present invention realizes the thinning of the lithium tantalate bonded wafer by grading coarse thinning and fine thinning, and the inclination angle of the coarse grinding wheel or the fine grinding wheel is adjusted according to the BOW value before the thinning operation, so that the grinding wheel can better fit the wafer during the thinning process. On the one hand, the risk of brittle fracture such as chipping can be reduced, and the subsurface damage layer can be slowed down. On the other hand, the BOW value of the wafer can be adaptively corrected to solve the problem of serious warping caused by thinning. Therefore, the quality of the ultrathin lithium tantalate bonded wafer after thinning can be effectively improved. Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0018] Figure 1 It is a block diagram of the steps of the thinning method for a lithium tantalate bonded wafer provided by the embodiments of the present invention. Figure 2Schematic diagram of the wafer surface profile before thinning for the thinning method of the lithium tantalate bonded wafer provided in Embodiment 1 of the present invention; Figure 3 Schematic diagram of the wafer surface profile after thinning for the thinning method of the lithium tantalate bonded wafer provided in Embodiment 1 of the present invention; Figure 4 Schematic diagram of the wafer surface profile before thinning for the thinning method of the lithium tantalate bonded wafer provided in Comparative Example 1 of the present invention; Figure 5 Schematic diagram of the wafer surface profile after thinning for the thinning method of the lithium tantalate bonded wafer provided in Comparative Example 1 of the present invention; Figure 6 Schematic diagram of the wafer after thinning for the thinning method of the lithium tantalate bonded wafer provided in Comparative Example 2 of the present invention. Detailed implementation manners

[0019] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Generally, the components of the embodiments of the present invention described and illustrated in the accompanying drawings here can be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0021] It should be noted that: similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0022] In the description of the present invention, it should be noted that if terms such as "upper", "lower", "inner", "outer", etc. are used to indicate the orientation or positional relationship, it is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship when the product of the present invention is usually placed. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0023] In addition, if terms such as "first", "second", etc. are used only for distinguishing descriptions, they cannot be understood as indicating or implying relative importance.

[0024] An embodiment of the present invention provides a method for thinning a bonded lithium tantalate wafer, which can effectively improve the quality of the thinned ultra-thin bonded lithium tantalate wafer, reduce the depth of the subsurface damage layer, reduce the risk of brittle fracture during thinning, and solve the problem of serious warping caused by thinning.

[0025] See Figure 1 , the thinning method of the bonded lithium tantalate wafer provided by the embodiment of the present invention is used to thin the bonded lithium tantalate wafer, and the thinning method includes the following steps: S1: Detect the initial surface profile data of the wafer after cleaning.

[0026] First, the wafer to be thinned needs to be cleaned and then the surface profile is detected. When cleaning, a single-sided scrubber can be used to scrub the wafer. It should be noted that the initial surface profile data here includes the initial BOW value, TTV value (Total Thickness Variation) and film thickness value of the wafer before thinning, so the surface profile of the wafer before thinning can be detected.

[0027] It should be noted that the wafer needs to be bonded to the substrate for thinning here. The bonding process can refer to the existing wafer bonding process and will not be introduced in detail here. The wafers mentioned in this embodiment all refer to lithium tantalate wafers bonded to the substrate.

[0028] S2: Level the thinning machine platform.

[0029] Specifically, the thinning machine platform is used to carry the wafer and can achieve leveling in the X-axis and Y-axis directions. After leveling, the horizontal deviation of the thinning machine platform is less than or equal to 1 μm, that is, the inclination degree in the X and Y-axis directions after leveling needs to be ≤ 1 μm, so that the thinning machine platform keeps as horizontal as possible and serves as the subsequent adjustment reference.

[0030] S3: Adjust the inclination angle of the coarse grinding wheel relative to the thinning machine platform according to the positive and negative values of the initial BOW value.

[0031] Specifically, after leveling the thinning machine, the coarse grinding wheel can be first adjusted above the thinning machine platform, and the roller pressing side of the coarse grinding wheel remains horizontal. Then, the inclination angle of the thinning machine platform is adjusted according to the positive and negative values of the initial BOW value, and further the inclination angle of the coarse grinding wheel relative to the thinning machine platform and the wafer is adjusted to make the coarse grinding wheel fit the initial surface profile of the wafer.

[0032] It should be noted that the coarse grinding wheel fitting the initial surface profile of the wafer mentioned here means that the coarse grinding wheel corresponds to the BOW value of the wafer. If the BOW value is positive, the coarse grinding wheel can be adjusted to incline inward. Conversely, if the BOW value is negative, the coarse grinding wheel can be adjusted to incline outward.

[0033] Further, in the mass production process, the wafers can be divided into two categories for separate processing according to the positive or negative value of the initial BOW value here. The adjustment method of the coarse grinding wheel is as follows: if the initial BOW value is positive, the coarse grinding wheel is tilted inward toward the wafer by a first preset angle; if the initial BOW value is negative, the coarse grinding wheel is tilted outward toward the wafer by a second preset angle. Among them, the first preset angle is 0.5° - 2°, and the second preset angle is 0.5° - 2°. In actual adjustment, when the initial Bow value of the wafer to be thinned is positive, it indicates that the wafer is warped with a central convex shape. At this time, the coarse grinding wheel is tilted inward toward the wafer, and the adjustment angle is 0.5° - 2°. For example, any point value among 0.5°, 1°, 2° or any value between any two points can be adjusted. When the initial Bow value of the wafer to be thinned is negative, it indicates that the wafer is warped with a central concave shape. At this time, the coarse grinding wheel is tilted outward toward the wafer, and the adjustment angle is 0.5° - 2°. For example, any point value among 0.5°, 1°, 2° or any value between any two points can be adjusted.

[0034] S4: Coarsely thin the wafer.

[0035] Specifically, the lithium tantalate bonded wafer can be placed and fixed on the thinning machine platform, and the thinning program is set. The coarse thinning is divided into two stages of thinning. The rotational speed of the coarse grinding wheel is 1750 - 1850 rpm, the rotational speed of the platform is 301 - 401 rpm, the F1 feed rate is 1 - 2 μm / s, the removal amount is 20 - 50 μm, the F2 feed rate is 0.5 - 0.8 μm / s, and the removal amount is 3 μm. The mesh number of the coarse grinding wheel here can be 3000 - 4000.

[0036] S5: Detect the rough grinding surface profile data of the wafer after coarse thinning.

[0037] After coarse thinning, the thinning machine platform can be leveled again, and then the surface profile of the wafer is detected. The rough grinding surface profile data includes the rough grinding BOW value, TTV value, and film thickness value of the wafer after coarse thinning. Therefore, the surface profile of the wafer after coarse thinning can be detected.

[0038] S6: Adjust the inclination angle of the fine grinding wheel relative to the thinning machine platform according to the positive or negative value of the rough grinding BOW value.

[0039] Specifically, after detecting the surface profile data, the fine grinding wheel can be adjusted above the thinning machine platform first, and the roller pressing side of the fine brush wheel is kept horizontal. Then, according to the positive or negative value of the rough grinding BOW value, the inclination angle of the thinning machine platform is adjusted, so as to adjust the inclination angle of the fine grinding wheel relative to the thinning machine platform and the wafer, so that the fine grinding wheel fits the surface profile of the wafer after coarse thinning.

[0040] It should be noted that the fine grinding wheel proposed here conforms to the surface profile after wafer thinning, which means that the BOW value of the fine grinding wheel corresponds to that of the wafer. If the BOW value is positive, the coarse grinding wheel can be adjusted to incline inward. Conversely, if the BOW value is negative, the coarse grinding wheel can be adjusted to incline outward.

[0041] Furthermore, the adjustment method of the fine grinding wheel is as follows: if the BOW value of rough grinding is positive, the fine grinding wheel is inclined towards the inner side of the wafer by a third preset angle; if the BOW value of rough grinding is negative, the fine grinding wheel is inclined towards the outer side of the wafer by a fourth preset angle. Among them, the third preset angle is less than 1°, for example, any point value among 0°, 0.5°, 1° or any value between any two points can be adjusted; the fourth preset angle is 1° - 3°, for example, any point value among 1°, 2°, 3° or any value between any two points can be adjusted. It should be noted that since the fine grinding wheel for fine thinning wears more, regardless of the concavity and convexity of the center of the wafer surface profile, the angle of the fine grinding wheel needs to be adjusted as a whole by 0.5° - 1° towards the outer side of the wafer on the basis of the angle adjustment during rough thinning, that is, the third preset angle should be 0.5° - 1° smaller than the first preset angle, and the fourth preset angle should be 0.5° - 1° larger than the second preset angle, so as to facilitate chip evacuation and prevent the chips worn from the fine grinding wheel and the wafer particles from causing secondary damage to the processed surface.

[0042] S7: Perform fine thinning on the wafer.

[0043] Specifically, the fine thinning is divided into three segments of thinning. The rotational speed of the fine grinding wheel is 1250 - 1350 rpm, the rotational speed of the platform is 301 - 401 rpm, the feed rate of F1 is 0.4 - 0.6 μm / s, the removal amount is 7 μm, the removal rate of F2 is 0.2 - 0.4 μm / s, the removal amount is 2 μm, the removal rate of F3 is 0.1 - 0.3 μm / s, and the removal amount is 1 μm. The mesh number of the fine grinding wheel here can be 6000 - 8000.

[0044] Furthermore, after fine thinning, it is also necessary to press and grind the wafer for a first preset time, then idle and grind the wafer flat for a second preset time, and then slowly lift the fine grinding wheel. Among them, the first preset time is 2 - 3 s, and the second preset time is 5 - 10 s. In actual operation, after fine thinning, press and grind with the fine grinding wheel, idle and grind to remove a certain thickness, and then slowly lift. Specifically, after fine thinning, keep the position of the fine grinding wheel and idle and grind the wafer flat at the rotational speed of the fine grinding wheel of 1750 - 1850 rpm and the rotational speed of the platform of 301 - 401 rpm, press and grind for 2 - 3 s, the idle time is 5 - 10 s, the slow lift rate is 0.2 - 0.4 μm / s, and the slow lift height is 2 - 3 μm.

[0045] It should be noted that by pressing and grinding and idling and flattening for a period of time here, defects such as grinding wheel marks on the wafer surface can be further reduced, and the surface profile of the wafer can be repaired. Cooperating with the adjustment of the grinding wheel angle during thinning can reduce the surface defects of the wafer caused by poor thinning processing and avoid abnormalities such as excessive abrasion during subsequent wafer dicing processes.

[0046] S8: Detect the precision grinding surface profile data of the wafer after precision thinning.

[0047] Specifically, after precision thinning is completed, the surface profile of the wafer after precision thinning can be detected again. The precision grinding surface profile data includes the TTV value, film thickness value, and LTV value (Local Thickness Variation) of the wafer after precision thinning, which can effectively detect the thinning quality and provide corresponding feedback for the thinning process.

[0048] The thinning method provided by the embodiments of the present invention can effectively reduce surface defects such as grinding wheel marks. First, by adjusting the angles of the coarse grinding wheel and the precision grinding wheel to fit the surface profile of the wafer to be thinned, the thinning quality is better, and warpage can be reduced. Then, by increasing the pressing and grinding and idling time, surface defects such as grinding wheel marks on the wafer are reduced. The surface defects of the wafer caused by poor thinning processing are reduced, and abnormalities such as excessive insertion loss during subsequent wafer dicing processes are avoided. After repairing the surface profile of the wafer, the present invention avoids abnormalities such as Pr Peeling at the edge of the wafer and frequency shift of Saw devices in the subsequent process. In addition, due to the sorting process of the wafers according to the surface profile and batch processing according to the sorting results, the data consistency between wafers is greatly improved, ensuring the stability of the batch processing of wafers.

[0049] The embodiments of the present invention also provide a thinning device for a lithium tantalate bonded wafer, which is applicable to the aforementioned thinning method. The thinning device includes a surface profile detection device, a thinning machine platform, a coarse grinding wheel, and a precision grinding wheel. The surface profile detection device is used to detect the initial surface profile data of the wafer after cleaning, the coarse grinding surface profile data of the wafer after coarse thinning, and the precision grinding surface profile data of the wafer after precision thinning; the thinning machine platform is used to carry the wafer; the coarse grinding wheel is used to perform coarse thinning on the wafer; the precision grinding wheel is used to perform precision thinning on the wafer; wherein, the initial surface profile data includes the initial BOW value, the coarse grinding surface profile data includes the coarse grinding BOW value, and the thinning machine platform is further used to adjust the inclination angle of the coarse grinding wheel relative to the thinning machine platform according to the positive or negative value of the initial BOW value, and is used to adjust the inclination angle of the precision grinding wheel relative to the thinning machine platform according to the positive or negative value of the coarse grinding BOW value.

[0050] It should be noted that the thinning machine platform here can adjust the relative inclination angle of the coarse grinding wheel and the fine grinding wheel. The thinning equipment also includes other components such as a driving device, and its basic working principle and structure can refer to existing thinning equipment. In the prior art, ICP etching is also used to replace the grinding of the damaged layer on the back of the wafer by a fine grinding machine, so as to remove the deeper damage caused by the coarse grinding process, reduce the wafer warpage, and avoid the mechanical damage caused during the fine grinding process. However, this process flow uses the ICP etching process, which is more costly, more complex, and has a large gap in efficiency compared with direct fine grinding, and is not suitable for the mass processing requirements of the production line. In traditional technologies for grinding other materials, there are also solutions for angle adjustment during grinding. However, they usually directly adjust the grinding angle according to the wafer slope specification requirements. Compared with materials such as lithium tantalate that are softer and have fragile cleavage planes, this grinding device cannot perform targeted processing on wafers in batch, and the possibility of chipping during such processing will also increase. The embodiments of the present invention can effectively solve the above problems.

[0051] The thinning method and device for lithium tantalate bonded wafers provided by the embodiments of the present invention can achieve the thinning of lithium tantalate bonded wafers. The method includes: first, detecting the initial surface profile data of the wafer after cleaning, where the initial surface profile data at least includes the initial BOW value. Then, adjusting the inclination angle of the coarse grinding wheel relative to the thinning machine platform according to the positive or negative value of the initial BOW value, so that the coarse grinding wheel can fit the initial surface profile of the wafer, and then performing rough thinning on the wafer. Since the inclination angle of the coarse grinding wheel is changed according to the positive or negative value of the BOW value, the wafer warpage can be preliminarily corrected during the rough thinning process. Then, detecting the rough grinding surface profile data of the thinned wafer again, where the rough grinding surface profile data at least includes the rough grinding BOW value, and adjusting the inclination angle of the fine grinding wheel relative to the thinning machine platform according to the positive or negative value of the rough grinding BOW value, so that the fine grinding wheel can fit the surface profile of the wafer after rough thinning, and then performing fine thinning on the wafer. Finally, detecting the fine grinding surface profile data of the wafer after fine thinning. Compared with the prior art, the present invention realizes the thinning of lithium tantalate bonded wafers by grading rough thinning and fine thinning, and the inclination angle of the coarse grinding wheel or the fine grinding wheel is adjusted according to the BOW value before the thinning operation, so that the grinding wheel can better fit the wafer during the thinning process. On the one hand, the risk of brittle fracture such as chipping can be reduced, and the subsurface damage layer can be slowed down. On the other hand, the BOW value of the wafer can be adaptively corrected to solve the problem of serious warpage caused by thinning. And by increasing the pressing grinding and idling time, the surface defects such as wafer grinding marks are reduced. The surface defects of the wafer caused by poor thinning processing are reduced, and the abnormalities such as excessive insertion loss in the subsequent wafer dicing process are avoided. After repairing the surface profile of the wafer, the present invention avoids abnormalities such as PrPeeling at the wafer edge and frequency shift of Saw devices in the subsequent process. In addition, due to the sorting process of the wafers according to the surface profile and batch processing according to the sorting results, the data consistency between wafers is greatly improved, and the stability of the batch processing wafer process is ensured. Therefore, the quality of the ultrathin lithium tantalate bonded wafers after thinning can be effectively improved.

[0052] Example 1 S1: Use a single-sided brushing machine to brush a 6-inch lithium tantalate bonded wafer, and detect the TTV, BOW, and film thickness data of the wafer after cleaning.

[0053] S2: Level the thinning machine platform so that the horizontal deviation of the thinning machine platform in the X and Y axis directions is 1 μm.

[0054] S3: Classify the lithium tantalate bonded wafers after cleaning into two categories according to the positive or negative value of the BOW value and process them separately. When the Bow value of the wafer to be processed is positive, it indicates that the wafer has a convex warpage at the center. At this time, tilt the grinding wheel inward towards the wafer, and the adjustment angle is 1°. When the Bow value of the wafer to be processed is negative, it indicates that the wafer has a concave warpage at the center. At this time, tilt the grinding wheel outward towards the wafer, and the adjustment angle is 1°.

[0055] S4: Then place the lithium tantalate bonded wafer into a thinning machine, set the thinning machine program for rough thinning. The rough thinning grinding wheel speed is 1750 rpm, the platform speed is 301 rpm, the F1 feed rate is 1 μm / s, the removal thickness is 50 μm, the F2 feed rate is 0.5 μm / s, the removal amount is 3 μm, and start rough thinning; S5: Detect the wafer surface profile data TTV, BOW, and film thickness data after rough thinning.

[0056] S6: Set the thinning machine program and adjust the grinding wheel tilt angle. When the Bow value of the wafer to be processed is positive, it indicates that the wafer has a convex warp in the center. At this time, tilt the grinding wheel inward towards the wafer, and the adjustment angle is 0.5°. When the Bow value of the wafer to be processed is negative, it indicates that the wafer has a concave warp in the center. At this time, tilt the grinding wheel outward towards the wafer, and the adjustment angle is 1.5°.

[0057] S7: Set the thinning machine program for fine thinning. The fine thinning grinding wheel speed is 1250 rpm, the platform speed is 301 rpm, the F1 feed rate is 0.4 μm / s, the removal amount is 7 μm, the F2 removal rate is 0.2 μm / s, the removal amount is 2 μm, the F3 removal rate is 0.1 μm / s, the removal amount is 1 μm, and start fine thinning. After fine thinning, press and grind with a fine grinding wheel for 2 s, slowly lift after idling. After fine thinning, keep the grinding wheel position and idle and grind the wafer flat at a grinding wheel speed of 1750 rpm and a platform speed of 301 rpm. The idle time is 5 s, the slow lift rate is 0.2 μm / s, and the slow lift height is 2 μm.

[0058] S8: Detect the data such as TTV, LTV, BOW, and film thickness of the thinned wafer, and make feedback for program adjustment.

[0059] See Figure 2 and Figure 3 , Figure 2 is the wafer surface profile before thinning. It can be seen that it has a concave warp in the middle. Figure 3 is the wafer surface profile after thinning. It can be seen that the warp has been effectively improved. After inspection, after thinning the lithium tantalate bonded wafer using the thinning method of Embodiment 1 of the present invention, the wafer TTV < 1.5 μm, BOW < 2 μm, the thickness between wafers in a batch ≤ 1 μm, the surface roughness of the thinned wafer ≤ 10 nm. The thickness range of the wafer before thinning is 2640 - 3889 μm, and the thickness range of the wafer after thinning using the method of the present invention is 1732 - 2246 μm. Then the wafer thickness difference is improved from 1249 μm to 514 μm.

[0060] Comparative Example 1 S1: Use a single-sided scrubbing machine to scrub a 6-inch lithium tantalate bonded wafer, and detect the wafer TTV, BOW, and film thickness data after cleaning; S2: Level the thinning machine platform so that the horizontal deviation of the thinning machine platform in the X and Y axis directions is 1 μm.

[0061] S3: Place the lithium tantalate bonded wafer into the thinning machine, set the thinning machine program, the rough thinning grinding wheel speed is 1750 rpm, the platform speed is 301 rpm, the F1 feed rate is 1 μm / s, the removal thickness is 50 μm, the F2 feed rate is 0.5 μm / s, the removal amount is 3 μm, and start rough thinning.

[0062] S4: Detect the wafer surface profile data TTV, BOW, and film thickness data after rough thinning.

[0063] S5: Set the thinning machine program for fine thinning. The fine thinning grinding wheel speed is 1250 rpm, the platform speed is 301 rpm, the F1 feed rate is 0.4 μm / s, the removal amount is 7 μm, the F2 removal rate is 0.2 μm / s, the removal amount is 2 μm, the F3 removal rate is 0.1 μm / s, the removal amount is 1 μm, and start fine thinning. After fine thinning, the fine grinding wheel idles and then slowly lifts. After fine thinning, keep the grinding wheel position and idle and flatten the wafer at the grinding wheel speed of 1750 rpm and the platform speed of 301 rpm. The idle time is 5 s, the slow lift rate is 0.2 μm / s, and the slow lift height is 2 μm.

[0064] S6: Detect the data such as TTV, LTV, BOW, and film thickness of the wafer after thinning, and give feedback for program adjustment; See Figure 4 and Figure 5 , Figure 4 is the wafer surface profile before thinning. It can be seen that it is a concave warping in the middle. Figure 5 is the wafer surface profile after thinning. It can be seen that the warping has not been improved. After inspection, after thinning the lithium tantalate bonded wafer using the thinning method of Comparative Example 1, the wafer TTV < 1.5 μm, BOW is 9 - 10 μm, the thickness difference between wafers in the batch < 2 μm, the surface roughness of the wafer after thinning ≤ 10 nm, the wafer thickness range before thinning is 3207 - 3886 μm, and the wafer thickness range after thinning using the thinning method in Comparative Example 1 is 1664 - 2444 μm. Then, the wafer thickness difference changes from 679 μm to 780 μm, without any improvement, and the BOW value is too large, and the wafer warps.

[0065] Comparative Example 2 S1: Use a single-sided scrubbing machine to scrub a 6-inch lithium tantalate bonded wafer, and detect the wafer TTV, BOW, and film thickness data after cleaning; S2: Level the thinning machine platform so that the horizontal deviation of the thinning machine platform in the X and Y axis directions is 1 μm.

[0066] S3: Place the lithium tantalate bonded wafer into a thinning machine, set the thinning machine program. The rotation speed of the rough thinning grinding wheel is 1750 rpm, the rotation speed of the platform is 301 rpm, the feed rate of F1 is 1 μm / s, the removal thickness is 50 μm, the feed rate of F2 is 0.5 μm / s, the removal amount is 3 μm, and start rough thinning.

[0067] S4: Detect the wafer surface profile data TTV, BOW, and film thickness data after rough thinning.

[0068] S5: Set the thinning machine program for fine thinning. The rotation speed of the fine thinning grinding wheel is 1250 rpm, the rotation speed of the platform is 301 rpm, the feed rate of F1 is 0.4 μm / s, the removal amount is 7 μm, the removal rate of F2 is 0.2 μm / s, the removal amount is 2 μm, the removal rate of F3 is 0.1 μm / s, the removal amount is 1 μm, and start fine thinning.

[0069] S6: Detect the data such as TTV, LTV, BOW, and film thickness of the thinned wafer, and make feedback for program adjustment; See Figure 6 , Figure 6 For the schematic diagram of the surface of the thinned wafer, it can be seen that there are a large number of grinding marks on its surface. After inspection, after thinning the lithium tantalate bonded wafer by the thinning method of Comparative Example 2 of the present invention, the wafer TTV < 1.5 μm, BOW is 9 - 10 μm, the thickness difference between wafers in a batch < 2 μm, the surface roughness of the thinned wafer ≥ 20 nm, and the surface defects such as grinding marks on the wafer surface are not repaired. The thickness range of the wafer before thinning is 3207 - 3886 μm, and the thickness range of the wafer after thinning by the method of the present invention is 1668 - 2448 μm. Then, the wafer thickness difference changes from 679 μm to 780 μm, without any improvement, and the BOW value is too large, and the wafer warps.

[0070] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for thinning a lithium tantalate bonded wafer, characterized in that: include: Detecting initial surface data of the cleaned wafer, wherein the initial surface data includes an initial BOW value; Adjusting the inclination angle of the coarse grinding wheel relative to the thinning machine platform according to the positive or negative value of the initial BOW value, so that the coarse grinding wheel fits the initial surface shape of the wafer; performing rough thinning on the wafer; Detecting rough grinding surface data of the wafer after rough thinning, wherein the rough grinding surface data includes a rough grinding BOW value; According to the positive and negative values ​​of the rough grinding BOW value, the inclination angle of the fine grinding wheel relative to the thinning machine platform is adjusted so that the fine grinding wheel fits the surface shape of the wafer after rough thinning; Performing fine thinning on the wafer; Detect the fine grinding surface data of the wafer after fine thinning.

2. The method for thinning a lithium tantalate bonded wafer according to claim 1, characterized in that: The step of adjusting the inclination angle of the coarse grinding wheel relative to the thinning machine platform according to the initial BOW value comprises: If the initial BOW value is positive, the coarse grinding wheel is tilted toward the inside of the wafer to adjust a first preset angle; If the initial BOW value is negative, the coarse grinding wheel is tilted toward the outside of the wafer to adjust a second preset angle.

3. The method for thinning a lithium tantalate bonded wafer according to claim 2, characterized in that: The first preset angle is 0.5°-2°, and the second preset angle is 0.5°-2°.

4. The method for thinning a lithium tantalate bonded wafer according to claim 2, characterized in that: The step of adjusting the inclination angle of the fine grinding wheel relative to the thinning machine platform according to the positive and negative values ​​of the rough grinding BOW value comprises: If the rough grinding BOW value is positive, the fine grinding wheel is tilted toward the inside of the wafer to adjust a third preset angle; If the rough grinding BOW value is negative, the fine grinding wheel is tilted toward the outside of the wafer to adjust a fourth preset angle.

5. The method for thinning a lithium tantalate bonded wafer according to claim 4, characterized in that: The third preset angle is less than 1°, and the fourth preset angle is 1°-3°.

6. The method for thinning a lithium tantalate bonded wafer according to claim 1, characterized in that: Before the step of adjusting the inclination angle of the grinding wheel relative to the thinning machine platform according to the positive or negative value of the initial BOW value, the method further includes: The thinning machine platform is leveled so that the horizontal deviation of the thinning machine platform is less than or equal to 1 μm.

7. The method for thinning a lithium tantalate bonded wafer according to claim 1, characterized in that: After the step of fine thinning the wafer, the method further comprises: Press and grind the wafer for a first preset time; The wafer is idling and polished for a second preset time.

8. The method for thinning a lithium tantalate bonded wafer according to claim 7, characterized in that: The first preset time is 2-3s, and the second preset time is 5-10s.

9. The method for thinning a lithium tantalate bonded wafer according to claim 1, characterized in that: The initial surface shape data also includes the TTV value and film thickness value of the wafer before thinning; the rough-grinding surface shape data also includes the TTV value and film thickness value of the wafer after rough thinning; the fine-grinding surface shape data includes the TTV value, film thickness value and LTV value of the wafer after fine thinning.

10. A thinning device for lithium tantalate bonded wafers, suitable for the thinning method for lithium tantalate bonded wafers as claimed in claim 1, characterized in that: The thinning equipment for the lithium tantalate bonded wafer comprises: A surface shape detection device, the surface shape detection device is used to detect the initial surface shape data of the wafer after cleaning, the rough grinding surface shape data of the wafer after rough thinning, and the fine grinding surface shape data of the wafer after fine thinning; A thinning machine platform, the thinning machine platform is used to carry the wafer; A coarse grinding wheel, the coarse grinding wheel is used to roughly thin the wafer; A fine grinding wheel, the fine grinding wheel is used for fine thinning the wafer; Among them, the initial surface shape data includes an initial BOW value, the rough grinding surface shape data includes a rough grinding BOW value, and the thinning machine platform is also used to adjust the inclination angle of the rough grinding wheel relative to the thinning machine platform according to the positive and negative values ​​of the initial BOW value, and is used to adjust the inclination angle of the fine grinding wheel relative to the thinning machine platform according to the positive and negative values ​​of the rough grinding BOW value.

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