Wafer thinning method and wafer thinning system

Abstract

The invention discloses a wafer thinning method and a wafer thinning system, and the method comprises the steps: carrying out the modification of a to-be-thinned surface of a wafer under the induction of laser when the wafer is thinned, enabling a material of a region, irradiated by the laser, of the to-be-thinned surface to be modified, converting at least part of the region of the to-be-thinned surface from a first material to a second material, the to-be-thinned surface subjected to modification treatment is thinned, under the same thinning condition, the thinning rate of the first material is smaller than that of the second material, and based on the second material formed after modification, the thinning process difficulty of the to-be-thinned surface of the wafer is reduced, and the thinning rate of the wafer is increased.

Description

Technical Field

[0001] The present application relates to the technical field of wafer thinning process, and more specifically, to a wafer thinning method and a wafer thinning system. Background Art

[0002] Wafer thinning is an important process in integrated circuit manufacturing. Thinning the back side of the wafer before packaging can reduce the height and volume of the chip package, improve the heat dissipation effect of the chip, and reduce the power consumption of the chip, which is very helpful for improving the performance of the chip.

[0003] At present, the main processing methods used for wafer thinning include wet etching, atmospheric pressure plasma etching, grinding, and chemical mechanical grinding. Atmospheric pressure plasma etching is a technology that uses CF4 gas to perform dry chemical etching on silicon wafers. Its processing method is to introduce CF4 gas into the plasma zone under atmospheric pressure and pure argon filling environment, so that CF4 undergoes thermal decomposition due to high temperature, and active fluorine reacts with silicon to generate volatile substances of SiF4, thereby achieving the purpose of material removal. Wet etching is to immerse the wafer in an acidic solution (HF / KOH / phosphoric acid / HNO3), and remove the surface material of the silicon wafer by chemically reacting the solution with the wafer to generate soluble substances. Grinding and grinding are to achieve uniform removal of wafer surface material through the mechanical friction between the abrasive particles fixed in the grinding disc and the wafer surface. Multiple grindings are required to thin the wafer to the desired thickness.

[0004] According to the thinning mechanism, the existing wafer thinning methods can be classified into chemical etching and mechanical grinding, which are widely used in the thinning of Si wafers. However, for the third-generation semiconductors represented by SiC and the fourth-generation semiconductors represented by single-crystal diamond, due to their extremely high hardness (SiC Mohs hardness is 9, single-crystal diamond Mohs hardness is 10), greater brittleness and strong chemical stability (difficult to react with strong acids and alkalis at room temperature) and other material properties, the existing chemical etching and mechanical grinding thinning methods have the problem of difficult material removal and low thinning rate. Summary of the invention

[0005] In view of this, the present application provides a wafer thinning method and a wafer thinning system, and the scheme is as follows:

[0006] On one hand, the present application provides a wafer thinning method, comprising:

[0007] Under laser induction, modifying the surface to be thinned of the wafer so that the material of the area of ​​the surface to be thinned irradiated by the laser is modified, and converting at least a part of the area of ​​the surface to be thinned from the first material to the second material;

[0008] Thin the surface to be thinned after the modification treatment. Under the same thinning conditions, the thinning rate of the first material is less than that of the second material.

[0009] Preferably, in the above wafer thinning method, before the modification treatment of the surface to be thinned, it further includes:

[0010] Pre-treat the surface to be thinned to increase the crystal defects in the surface to be thinned.

[0011] Preferably, in the above wafer thinning method, the method for pre-treating the surface to be thinned includes:

[0012] Perform ion doping in the surface to be thinned, or etch the surface to be thinned with a chemical reagent.

[0013] Preferably, in the above wafer thinning method, the method of using a laser to modify the surface to be thinned includes:

[0014] Use a laser to scan the surface to be thinned without gaps;

[0015] Or,

[0016] Use a laser to scan the surface to be thinned based on a preset scanning path to form a modified area related to the scanning path on the surface to be thinned; wherein, in at least one radial direction of the wafer, non-modified areas are reserved between the modified areas; the non-modified areas are used to reduce the friction force during subsequent thinning treatment.

[0017] Preferably, in the above wafer thinning method, in at least one radial direction of the wafer, the surface to be thinned after the modification treatment includes: alternately arranged modified areas and non-modified areas; the modified areas are the second material, the hardness of the first material is greater than that of the second material; the non-modified areas are the first material; the depth of the modified areas is not greater than the required thinning thickness of the wafer.

[0018] Preferably, in the above wafer thinning method, the modified area is a spiral structure;

[0019] Or, the modified area is a grid structure.

[0020] Preferably, in the above wafer thinning method, in at least one radial direction, the modified areas are evenly distributed on the surface to be thinned;

[0021] In at least one radial direction, the depth of the modified areas gradually decreases.

[0022] Preferably, in the above wafer thinning method, in at least one radial direction, the depth of the modified areas remains uniformly unchanged;

[0023] In at least one radial direction, the distribution density of the modified areas decreases in sequence.

[0024] On the other hand, the present application also provides a wafer thinning system, including:

[0025] A laser device for modifying the surface to be thinned of the wafer, so that the irradiated area of the surface to be thinned by the laser is modified under the induction of the laser, and at least part of the area of the surface to be thinned is converted from a first material to a second material, and the hardness of the first material is greater than that of the second material;

[0026] A thinning device for thinning the surface to be thinned after the modification treatment.

[0027] Preferably, in the above wafer thinning system, it further includes:

[0028] A pretreatment device for pretreating the surface to be thinned before the modification treatment of the surface to be thinned, so as to increase the crystal defects in the surface to be thinned.

[0029] As can be seen from the above description, in the wafer thinning method and the wafer thinning system provided by the technical solution of the present application, when thinning the wafer, under the induction of the laser, the surface to be thinned of the wafer is modified, so that the material of the irradiated area of the surface to be thinned by the laser is modified, and at least part of the area of the surface to be thinned is converted from a first material to a second material. After the surface to be thinned after the modification treatment is thinned, under the same thinning conditions, the thinning rate of the first material is less than that of the second material. Based on the second material formed after the modification, the thinning process difficulty of the surface to be thinned of the wafer is reduced, and the thinning rate of the wafer is increased. Description of the Drawings

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0031] The structures, ratios, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those who are familiar with this technology to understand and read, and are not used to limit the limited conditions that can be implemented by the present application. Therefore, they do not have technical essence. Any modification of the structure, change of the proportional relationship or adjustment of the size should still fall within the scope covered by the technical content disclosed in the present application without affecting the effects that the present application can produce and the purposes that can be achieved.

[0032] Figure 1 It is a process flow chart of a wafer thinning method provided by an embodiment of the present application;

[0033] Figure 2 is a top view of the wafer facing the surface to be thinned before the modification treatment;

[0034] Figure 3 is Figure 2 a sectional view of the wafer shown in the A-A' direction;

[0035] Figure 4 is a top view of the wafer after a modification treatment method;

[0036] Figure 5 is Figure 4 a sectional view of the wafer shown in the A-A' direction;

[0037] Figure 6 is a side view of the wafer after the thinning treatment;

[0038] Figure 7 is a process flow chart of another wafer thinning method provided by an embodiment of the present application;

[0039] Figure 8 is a schematic diagram of a laser scanning path provided by an embodiment of the present application;

[0040] Figure 9 is based on Figure 8 a sectional view of the wafer in the A-A' direction after the modification treatment along the laser scanning path shown;

[0041] Figure 10 is a top view of the wafer after another modification treatment method provided by an embodiment of the present application;

[0042] Figure 11 is a top view of the wafer after yet another modification treatment method provided by an embodiment of the present application;

[0043] Figure 12 is a schematic diagram of the principle of thinning the wafer by mechanical grinding;

[0044] Figure 13 is a side view of the wafer after thinning by conventional mechanical grinding;

[0045] Figure 14 is a sectional view of the modified wafer along a radial direction;

[0046] Figure 15 is a top view of the wafer after yet another modification treatment method provided by an embodiment of the present application;

[0047] Figure 16 is a schematic diagram of the structure of a laser device provided by an embodiment of the present application;

[0048] Figure 17 is a schematic diagram of the principle of converting the light field intensity distribution of the beam shaping module;

[0049] Figure 18 Schematic structural diagram of a thinning device provided by an embodiment of the present application. Specific implementation manners

[0050] The following will clearly and completely describe the embodiments in the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0051] To make the above objects, features, and advantages of the present application more obvious and understandable, the present application will be further described in detail below with reference to the accompanying drawings and specific implementation manners.

[0052] Reference Figures 1-6 as shown in Figure 1 is a process flow chart of a wafer thinning method provided by an embodiment of the present application, Figure 2 is a top view of the wafer facing the surface to be thinned before the modification treatment, Figure 3 is Figure 2 a sectional view of the wafer shown in the A-A' direction, Figure 4 is a top view of the wafer after a modification treatment manner, Figure 5 is Figure 4 a sectional view of the wafer shown in the A-A' direction, Figure 6 is a side view of the wafer after the thinning treatment. The wafer thinning method includes:

[0053] Step S11: Under the induction of a laser, perform a modification treatment on the surface 111 to be thinned of the wafer 11, so that the material in the laser-irradiated area of the surface 11 to be thinned is modified, and at least part of the area of the surface 111 to be thinned is converted from a first material to a second material.

[0054] The structure of the wafer 11 before the modification treatment is as shown in Figure 2 and Figure 3 shown. The whole of the wafer 11 is the first material. After the modification treatment, the structure of the wafer 11 is as shown in Figure 4 and Figure 5 shown. The area irradiated by the laser is converted from the first material to the second material. In the schematic diagrams of the wafer 11 in the embodiments of the present application, the first material and the second material are respectively indicated by different filling patterns.

[0055] Step S12: Perform a thinning treatment on the surface 111 to be thinned after the modification treatment. Under the same thinning conditions, the thinning rate of the first material is less than the thinning rate of the second material.

[0056] After the thinning process, the structure of the wafer 11 is as Figure 6 shown, Figure 6 where the dashed line in Figure 6 indicates the height position of the surface 111 to be thinned before the thinning process.

[0057] In the wafer thinning method provided by the embodiments of the present application, before thinning the surface 111 to be thinned of the wafer 11, through laser induction, the surface 111 to be thinned of the wafer 11 is modified to convert at least part of the area of the surface 111 to be thinned from a first material to a second material. Since under the same thinning conditions, the second material has a larger thinning rate relative to the first material, the second material is more convenient for thinning, and the thinning rate of the wafer can be increased.

[0058] A semiconductor laser can be used to emit laser light to modify the wafer 11.

[0059] The laser light emitted by the laser 21 is pulsed laser light, and the pulse width can be 10 ps to 800 ps. Preferably, the pulse width can be set to 20 ps, or 40 ps, or 60 ps; the repetition frequency is no more than 1 MHz for single pulses. Preferably, the single pulse can be set to no more than 0.2 MHz, or 0.5 MHz, or 0.8 MHz, etc.; the laser is near-infrared light, and the wavelength range can be 0.8 μm to 1.1 μm, and the central wavelength of the laser can be 0.9 μm, or 1.0 μm. The laser power can be 0.2 W to 1.2 W. Preferably, the laser power can be 0.5 W or 0.8 W. The diameter of the light spot irradiated on the surface of the wafer 11 is 20 μm to 80 μm; preferably, the diameter of the light spot can be 50 μm, or 70 μm.

[0060] As described below, by controlling the parameters of the laser, a modified area 14 with a required graphic structure can be formed within the wafer surface, so as to facilitate subsequent thinning processing and improve the thickness uniformity of the wafer 11 after the thinning process.

[0061] The thickness removed from the wafer 11 through the thinning process is not less than the maximum depth of the second material within the surface 111 to be thinned, so as to ensure that after the thinning process is completed, the second material in the wafer 11 is completely removed, and only the wafer part of the first material remains.

[0062] Among them, the wafer 11 is a semiconductor wafer, and can be a high-hardness wafer with a Mohs hardness of not less than 9, such as a SiC wafer or a single-crystal diamond wafer, etc. Among them, the Mohs hardness of the SiC wafer is about 9, and the Mohs hardness of the single-crystal diamond wafer is about 10. Based on the wafer thinning method provided by the embodiments of the present application, the thinning rate of high-hardness wafers with a Mohs hardness of not less than 9 can be greatly increased.

[0063] It should be noted that in the embodiments of the present application, the wafer 11 is not limited to high-hardness wafers such as SiC wafers or single-crystal diamond wafers, but can also be semiconductor wafers with a relatively small Mohs hardness such as GaN wafers or Si wafers. The solution of the present invention can be adopted to further improve the thinning efficiency of various wafers.

[0064] This wafer thinning method can be carried out under normal pressure. Under laser induction, the area of the wafer 11 irradiated by the laser can generate high temperature, and carbonization, oxidation or nitridation, etc. can occur under the action of gases such as oxygen, carbon dioxide, and nitrogen, so that the area of the wafer surface irradiated by the laser is modified. The modification treatment of the wafer 11 can be carried out under normal pressure without the need for a low-pressure vacuum condition, realizing a simple process. Moreover, before the thinning treatment, based on the laser modification treatment, at least part of the area of the surface 111 to be thinned is converted into a modified area 14 with a loose physical structure and a small hardness, which can reduce the difficulty of subsequent thinning treatment and improve the overall processing efficiency. Moreover, the laser has the advantages of non-contact processing, fast scanning speed and high efficiency, and the mechanical damage to the wafer 11 during the modification treatment is small. After laser scanning, the difficulty of mechanically grinding the modified area 14 is reduced, the mechanical force applied to the surface of the wafer 11 is small, the mechanical damage to the wafer 11 becomes smaller, the risk of fragmentation is reduced, and at the same time, the thinning efficiency is greatly improved.

[0065] Reference Figure 7 shown in Figure 7 is a process flow chart of another wafer thinning method provided by the embodiments of the present application. The wafer thinning method shown includes:

[0066] Step S21: Pretreat the surface 111 to be thinned to increase the crystal defects in the surface 111 to be thinned.

[0067] Step S22: Under laser induction, perform a modification treatment on the surface 111 to be thinned of the wafer 11, so that the material in the area of the surface 111 to be thinned irradiated by the laser is modified, and at least part of the area of the surface 111 to be thinned is converted from a first material to a second material.

[0068] Step S23: Perform a thinning treatment on the surface 111 to be thinned after the modification treatment. Under the same thinning conditions, the thinning rate of the first material is less than the thinning rate of the second material.

[0069] Based on Figure 1 the wafer thinning method shown, Figure 7 In the wafer thinning method shown, before performing the modification treatment on the surface 111 to be thinned, it further includes: pretreating the surface 111 to be thinned to increase the crystal defects in the surface 111 to be thinned.

[0070] Figure 7In the wafer thinning method shown, before the surface 111 to be thinned of the wafer 11 is subjected to a modification treatment, crystal defects on the surface to be thinned are increased through a pretreatment, which can break the chemical bonds of the first material in the wafer 11, thereby improving the surface activity of the wafer, reducing the laser-induced energy consumption, improving the modification efficiency, facilitating subsequent modification of the wafer surface by laser, and improving the thickness uniformity of the wafer 11 after the thinning treatment.

[0071] Optionally, in Figure 7 the wafer thinning method shown, the method for pretreating the surface 111 to be thinned includes: performing ion doping within the surface 111 to be thinned. The ion physical bombardment during the ion doping process can break the lattice structure, thereby generating defects within the surface 111 to be thinned, or chemically etching the surface 111 to be thinned, and the lattice structure is etched by a chemical reagent, thereby generating defects within the surface 111 to be thinned.

[0072] Through the above pretreatment, not only can the crystal defects within the surface 111 to be thinned of the wafer be increased, facilitating subsequent modification of the wafer surface by laser, but also the mirror structure of the surface 111 to be thinned of the wafer can be destroyed, reducing the reflection of the laser, making it more convenient for the laser-irradiated area to absorb laser energy, improving the utilization rate of laser energy, and increasing the rate of the modification treatment.

[0073] In an implementation manner of the embodiment of the present application, the method for modifying the surface 111 to be thinned by laser includes: scanning the surface 111 to be thinned without gaps by laser. In this implementation manner, the entire surface 111 to be thinned of the wafer 11 is scanned without gaps, so that the entire surface 111 to be thinned of the wafer 11 is modified. In this manner, the structure of the wafer 11 after modification can be as Figure 4 and Figure 5 shown. Since the entire surface 111 to be thinned is modified, the second material that is relatively easy to be thinned is present on the side of the wafer 11 facing the surface 111 to be thinned, which can greatly improve the subsequent thinning rate. Along the radial direction of the wafer, the depth of the modified area within the surface 111 to be thinned can be uniformly unchanged as Figure 5 shown, or as described below, in the area from the center to the edge of the wafer, the depth of the modified area is set to gradually decrease; or it can be adjusted according to needs. Using laser modification is convenient for setting the scanning path 13 of the required graphic structure, and thus convenient for precisely controlling the graphic structure and depth of the modified area 14.

[0074] Referring to Figure 8 and Figure 9 shown, Figure 8 is a schematic diagram of the laser scanning path provided by the embodiment of the present application, Figure 9 is based on Figure 8Cross-sectional view of the wafer after modification along the A-A' direction of the laser scanning path shown. In this method, the method of using a laser to modify the surface 111 to be thinned includes: using a laser to scan the surface 111 to be thinned based on a preset scanning path 13 to form a modified region 14 related to the scanning path 13 on the surface 111 to be thinned; wherein, in at least one radial direction of the wafer 11, non-modified regions 15 are reserved between the modified regions 14; the non-modified regions 15 are used to reduce the friction force during subsequent thinning processing. In this method, the modified region 14 is a spiral structure, corresponding to the spiral scanning path 13. At this time, the laser scans the wafer surface from the center of the wafer 11 along the spiral scanning path 13 to form a spiral-structured modified region 14.

[0075] When the surface 111 to be thinned has both a modified region 14 and a non-modified region 15, the non-modified region 15 and the modified region 14 can form a convex surface texture on the surface 111 to be thinned, which can reduce the friction force. The principle of reducing the friction force is explained as follows: The existence of the surface texture reduces the grinding contact area between the grinding disk and the wafer surface, can effectively reduce the contact surface friction coefficient, and thus reduces the friction force; and when lubricated with grinding fluid, the lubricating liquid can penetrate into the cross grooves of the texture, improving the lubrication performance of the surface, and can also play a role in improving the surface friction performance. Compared with the surface 111 to be thinned without a surface texture, the lubrication performance of the surface 111 to be thinned with a surface texture can be significantly improved, especially for the pattern structure of the cross groove texture (such as the graphic structure in which the modified region 14 and the non-modified region 15 are alternately arranged in multiple wafer radial directions), and its friction coefficient can be reduced by up to 48.1%.

[0076] When the wafer 11 is modified based on the set scanning path 13 to form a modified region 14 with a preset graphic structure, along the wafer radial direction, the scanning pitch of the laser on the surface 111 to be thinned is not greater than 200 μm. Optionally, the scanning pitch can be set to 100 μm, or 120 μm, or 15 μm, etc. It can be set that the scanning pitch range within the wafer center region is 20 μm to 50 μm, such as it can be 30 μm or 40 μm; near the wafer edge region, the scanning pitch range is 100 μm to 200 μm, such as it can be 130 μm, or 150 μm, or 180 μm, etc. Based on the required graphic structure of the modified region 14 and the non-modified region 15, the spot size and the scanning pitch are set, and the embodiments of the present application do not limit the scanning pitch.

[0077] When the width of the non-modified region 15 is less than the set width threshold, it can be more easily thinned and removed during subsequent thinning processing, which not only does not affect the thinning efficiency, but also can reduce the friction force during the thinning process, and can improve the flatness and smoothness of grinding.

[0078] In addition, based on the non-uniform surface modification process with the set scanning path 13, the modified regions 14 and non-modified regions 15 arranged alternately are formed, which can buffer the thermal stress of the wafer 11 during the laser scanning process, prevent the wafer 11 from warping, and further prevent the subsequent wafer thinning quality from being affected by the warping problem. Optionally, the modified regions 14 with uniform distribution can be set in the surface 111 to be thinned, so that the wafer 11 is heated evenly during the modification process, and the wafer 11 is prevented from warping during the modification process.

[0079] It should be noted that Figure 8 only the scanning path 13 of the laser is simply shown, and the spot size of the laser is not shown. The spot size of the laser is positively correlated with the size of the modified region 14 in the radial direction of the wafer. The scanning path 13 and the spot size of the laser can be set based on the graphic structure of the required modified region 14 and non-modified region 15 in the surface 111 to be thinned, so as to form the modified region 14 and non-modified region 15 with the required graphic structure.

[0080] Among them, the graphic structure of the modified region 14 in the surface 111 to be thinned is the same as or similar to the graphic structure of the scanning path 13. When the scanning path 13 with a spiral structure as Figure 8 shown is adopted, a spiral-structured modified region 14 can be formed in the surface 111 to be thinned.

[0081] The graphic structure of the scanning path 13 can be set based on requirements to form the modified region 14 and non-modified region 15 with the required graphic structure, not limited to the Figure 8 scanning path 13 with a spiral structure as shown. For example, the scanning path 13 can also include multiple sub-paths distributed in parallel to form a modified region 14 with a graphic structure as Figure 10 shown in the surface 111 to be thinned; or it can also include multiple first sub-paths along the first direction and multiple second sub-paths along the second direction, where the first direction and the second direction intersect and are both parallel to the surface 111 to be thinned, so as to form a modified region 14 with a graphic structure as Figure 11 shown in the surface 111 to be thinned.

[0082] Refer to Figure 10 shown Figure 10 For the top view of the wafer after another modification process provided by the embodiment of the present application, in this method, multiple parallel modified regions 14 are formed on the surface 111 to be thinned of the wafer 11, and the corresponding scanning path 13 includes multiple parallel sub-paths, so as to form a modified region 14 with a graphic structure as Figure 10 shown in the surface 111 to be thinned.

[0083] Refer to Figure 11 shown Figure 11The top view of the wafer after another modification method provided by the embodiment of the present application. In this method, a grid-shaped modified area 14 is formed on the surface 111 to be thinned of the wafer 11, and the corresponding scanning path 13 includes a plurality of first sub-paths along the first direction and a plurality of second sub-paths along the second direction. The first direction and the second direction intersect and are both parallel to the surface 111 to be thinned, so as to form a modified area 14 with a graphic structure as shown in Figure 11 in the surface 111 to be thinned.

[0084] It should be noted that the top views of the wafer after modification in the embodiments of the present application are all top views facing the surface 111 to be thinned. The maximum depth of the modified area 14 does not exceed the thickness to be removed by thinning the wafer 11.

[0085] As shown in Figures 8-11 , in at least one radial direction of the wafer 11, the surface 111 to be thinned after modification includes: alternately arranged modified areas 14 and non-modified areas 15; the modified area 14 is a second material, and the hardness of the first material is greater than that of the second material; the non-modified area 15 is the first material; the depth of the modified area 14 is not greater than the thinning thickness required for the wafer.

[0086] Based on requirements, the modified area 14 in the surface 111 to be thinned can be set as any one of a grid structure, a spiral structure, and a parallel line structure. The embodiments of the present application do not limit the graphic structure of the modified area 14.

[0087] Arranged in at least one radial direction of the wafer 11 with alternately arranged modified areas 14 and non-modified areas 15 can buffer the thermal stress in the wafer 11 during the laser irradiation process, prevent the wafer 11 from warping, and the non-modified area 15 can also reduce the grinding friction in the subsequent thinning process and improve the thinning quality.

[0088] In the embodiments of the present application, the method for thinning the modified wafer 11 includes: mechanically grinding the surface 111 to be thinned by the grinding disk of a mechanical grinding device to thin the wafer 11.

[0089] Referring to Figure 12 and Figure 13 shown, Figure 12 is a schematic diagram of the principle of thinning the wafer by mechanical grinding, Figure 13 is the rear view of the wafer after thinning by conventional mechanical grinding of the wafer. Among them, Figure 12 is the top view, Figure 12The two dashed arcs are used to indicate the edge of the polishing pad when the polishing pad and the wafer 11 are in different relative positions. Based on these two dashed arcs, it can be seen that during the polishing process of the polishing pad moving from left to right, relative to the central region of the wafer 11, the edge region of the wafer 11 has a shorter contact line length with the polishing pad, such as Figure 12 the length of the overlapping part of the left dashed line and the wafer 11 in is less than the length of the overlapping part of the right dashed line and the wafer 11. Since the frictional force is proportional to the contact line length, based on the shorter contact line, the edge region of the wafer 11 has a greater polishing speed, which will cause the wafer to be thinned as Figure 13 shown, resulting in the problem of thicker in the middle and thinner at the edges. In addition, during the mechanical polishing process, there is polishing liquid between the polishing pad and the surface 111 to be thinned. During the mechanical polishing process, since the edge region of the wafer 11 can achieve the exchange of polishing liquid faster than the middle region, the thinning speed of the edge region of the wafer 11 is greater than that of the middle region, which will also cause the problem of thicker in the middle and thinner at the edges after the wafer 11 is thinned. To solve this problem, the Figure 14 or Figure 15 modified region 14 with the graphic structure shown in can be used.

[0090] Refer to Figure 14 shown, Figure 14 is a cross-sectional view of the modified wafer along a radial direction. In this method, in at least one radial direction, the modified regions 14 are evenly distributed in the surface 111 to be thinned; in the above at least one radial direction, the depth of the modified regions 14 gradually decreases from the center to the edge. Therefore, when the thinning process is carried out under the same polishing conditions, the central region of the wafer 11 has a greater polishing rate relative to the edge region, so as to compensate for the thickness difference caused by the larger exchange rate of the polishing liquid in the edge region of the wafer, so that after the thinning process, the central region and the edge region of the wafer have a relatively consistent thickness, improving the thickness uniformity of the thinned wafer 11. During the laser scanning process, by dynamically controlling the laser parameters, the depth of the laser-induced modified region 14 can be accurately controlled, so that the depth of the modified region 14 gradually decreases in the direction from the center to the edge of the wafer 11. Based on the accurate control of the laser parameters, the graphic structure of the modified region can also be accurately controlled. It can be set along a radial direction of the wafer 11, so that the modified regions 14 with different distances from the center of the circle have different widths. For example, the modified region near the central region of the wafer 11 has a larger width, and the modified region 14 near the edge region of the wafer 11 has a smaller width.

[0091] The uniform distribution of the modified regions 14 in the surface 111 to be thinned can be, as Figure 11 shown, the uniform distribution in multiple radial directions, or, as Figure 10 shown, the uniform distribution in a single radial direction. The embodiments of the present application do not limit this.

[0092] Reference Figure 15 as shown Figure 15 is a top view of a wafer after another modification method provided by an embodiment of the present application. Combining Figure 9 and Figure 15 as shown, in this method, in at least one radial direction, the depth of the modified region 14 is uniformly unchanged, and in the above at least one radial direction, the distribution density of the modified region 14 decreases in sequence. Therefore, when the thinning process is carried out under the same grinding conditions, the central region of the wafer 11 has a larger grinding rate relative to the edge region, so as to compensate for the above thickness difference caused by the larger exchange rate of the grinding fluid in the edge region of the wafer, so that after the thinning process, the central region and the edge region of the wafer have relatively consistent thickness, and the uniformity of the thickness of the wafer 11 after thinning is improved.

[0093] It should be noted that in the embodiment of the present application, during the laser modification process, when the spot size of the laser beam irradiated on the surface 111 to be thinned remains unchanged, the widths of the modified regions 14 in different regions on the wafer surface can be made the same. In other methods, the spot size of the laser beam irradiated on the surface 111 to be thinned can also be dynamically adjusted, so that the width of the modified region 14 gradually decreases from the central region to the edge region of the wafer. This method can also make the central region of the wafer 11 easier to thin relative to the edge region, and can improve the thickness uniformity of the wafer 11 after the thinning process.

[0094] In the wafer thinning method provided by the embodiment of the present application, the wafer 11 is thinned by a mechanical grinding device, which is a new type of wafer thinning method combining laser modification and mechanical grinding. The laser modification process can induce modification changes such as carbonization or oxidation of the surface material of the wafer 11, so as to form a modified region 14 with a loose physical structure and a lower material hardness on the surface of the wafer 11. When the wafer 11 is a SiC or single crystal diamond wafer, the material of the modified region 14 is graphite, and when the wafer 11 is a GaN wafer, the material of the modified region is Ga2O3. After the modification process is completed, the modified region 14 is removed by mechanical grinding. The laser modification process has strong controllability, can accurately control the graphic structure of the modified region 14, and does not introduce other additional impurities, which is convenient for improving the efficiency of the subsequent thinning process.

[0095] When the thinning thickness is greater than the maximum depth of the laser modification process, the above wafer thinning method can be repeated multiple times to thin the wafer 11 to the required thickness.

[0096] In order to improve the laser scanning efficiency, the wafer 11 is modified by using laser with a shaped light field. Through shaping, the light field intensity distribution of the laser is converted from a Gaussian distribution to a flat-top distribution, increasing the spot area of the laser irradiating on the wafer 11, thereby increasing the irradiation area of the laser on the surface 111 to be thinned, and improving the laser scanning efficiency. The laser with a flat-top distribution has a larger spot area, which can make the laser have a larger irradiation area on the surface 111 to be thinned, making the width of the modified area 14 larger and improving the modification efficiency.

[0097] As can be seen from the above description, the wafer thinning method provided by the embodiments of the present application at least includes the following

[0098] Beneficial effects:

[0099] Before the thinning process, based on the laser modification process, at least part of the surface 111 to be thinned is converted into a modified area 14 with a loose physical structure and a small hardness, which can reduce the difficulty of subsequent thinning process and improve the overall processing efficiency. Moreover, the laser has the advantages of non-contact processing, fast scanning speed and high efficiency, and the mechanical damage to the wafer 11 during the modification process is small. After laser scanning, the difficulty of mechanical grinding of the modified area 14 is reduced, the mechanical force applied to the surface of the wafer 11 is small, the mechanical damage to the wafer 11 is reduced, the risk of fragmentation is reduced, and at the same time, the thinning efficiency is greatly improved.

[0100] The light field intensity of the laser can be converted into a flat-top distribution to increase the laser spot size, so as to increase the interaction area between the laser and the wafer 11, improve the modification efficiency, and further improve the efficiency of the entire thinning process.

[0101] The required graphic structure of the modified area 14 can also be formed by setting the laser scanning path 13 to relieve the thermal stress during the modification process of the wafer 11, so as to relieve or even avoid the warping problem of the wafer 11 caused by the photothermal effect of the laser. Preferably, the laser scanning path 13 is set as a spiral structure and scanned outward from the center of the wafer 11 to better relieve the thermal stress during the modification process of the wafer 11.

[0102] Due to the good controllability of the laser energy and high energy utilization rate, by controlling the laser energy, the modified region 14 with the required depth can be accurately formed, such that the depth of the modified region 14 in the central region of the wafer is larger, and the depth of the modified region 14 in the edge region is smaller, so as to compensate for the thickness difference between the edge region and the central region during the mechanical grinding process of the wafer, and solve the problem that the wafer is thicker in the middle and thinner at the edge due to factors such as the contact angle difference, contact area difference, and grinding fluid exchange speed difference between the grinding disk and the wafer 11 during the mechanical grinding process. Or, by controlling the distribution density difference of the modified region 14 from the center to the edge of the wafer, the problem that the wafer is thicker in the middle and thinner at the edge due to factors such as the contact angle difference, contact area difference, and grinding fluid exchange speed difference between the grinding disk and the wafer 11 during the mechanical grinding process is solved.

[0103] Based on the above wafer thinning method, another embodiment of the present application further provides a wafer thinning system. The wafer thinning system includes: a laser device, which is used to perform a modification process on the surface 111 to be thinned of the wafer 11, such that the irradiated area of the surface 111 to be thinned by the laser undergoes modification under the induction of the laser, and at least a part of the surface 111 to be thinned is converted from a first material to a second material, and the hardness of the first material is greater than that of the second material; a thinning device, which is used to perform a thinning process on the surface 111 to be thinned after the modification process.

[0104] Through the wafer thinning system provided by the embodiments of the present application, the above wafer thinning method can be executed to thin the wafer 11, and the thinning of the wafer 11 is realized by combining laser modification and mechanical grinding, thereby improving the thinning efficiency and the thickness uniformity of the wafer 11 after thinning.

[0105] In the wafer thinning system provided by the embodiments of the present application, the laser device can be as Figure 16 shown.

[0106] Refer to Figure 16 shown, Figure 16 which is a schematic structural diagram of a laser device provided by an embodiment of the present application. The shown laser device includes: a laser 21, which is used to emit laser; a three-dimensional displacement platform 27, which is used to place the wafer 11; a control computer 28, which is respectively connected to the laser 21 and the three-dimensional working platform 27, and can control the working states of the laser 21 and the three-dimensional working platform 27.

[0107] Optionally, the laser 21 can be a semiconductor laser. The laser emitted by the laser 21 is pulsed laser, the pulse width can be 10 ps to 800 ps, the repetition frequency is no more than 1 MHz for single pulse, the laser is near-infrared light, and the wavelength range can be 0.8 μm to 1.1 μm. The laser power can be 0.2 W to 1.2 W. The diameter of the light spot irradiated on the surface of the wafer 11 is 20 μm to 80 μm. It is easy to know that the laser parameters can be set based on requirements, and are not limited to the numerical range provided in the embodiments of the present application.

[0108] When the wafer 11 is modified based on the set scanning path 13 to form the modified area 14 with a preset graphic structure, along the radial direction of the wafer, the scanning pitch of the laser on the surface 111 to be thinned is no more than 200 μm. It can be set that the scanning pitch range in the central area of the wafer is 20 μm to 50 μm, and in the area close to the edge of the wafer, the scanning pitch range is 100 μm to 200 μm. Based on the graphic structures of the required modified area 14 and non-modified area 15, the spot size and scanning pitch are set, and the embodiments of the present application do not limit the scanning pitch.

[0109] Among them, the three-dimensional workbench 27 can respond to the control of the control computer 28 to adjust the height in the vertical direction and the position in the horizontal direction. In the embodiments of the present application, when performing the modification process, the position of the wafer 11 can be controlled to be fixed, and the laser is controlled by a mechanical device to scan along the set scanning path 13 on the wafer to form the modified area 14 with the required graphic structure, or the laser irradiation position is fixed, and the three-dimensional workbench 27 is controlled to drive the wafer 11 to scan along the set scanning path 13 to form the modified area 14 with the required graphic structure.

[0110] Further, the laser device further includes a half-wave plate 22, and the half-wave plate is located in the optical path between the laser 21 and the wafer 11. The half-wave plate 22 is used to solve the polarization problem in laser transmission by adjusting the polarization state of the laser emitted by the laser 21, and improve the transmission quality and reliability of the optical signal.

[0111] Further, the laser device further includes a beam expander 23, and the beam expander 23 is located in the optical path between the laser 21 and the wafer 11. The beam expander 23 is used to expand the diameter of the laser beam and reduce the divergence angle of the laser beam.

[0112] Further, the laser device further includes a reflector 24, and the reflector 24 is located in the optical path between the laser 21 and the wafer 11. The reflector 24 is used to change the laser transmission direction to reduce the size of the laser device.

[0113] Further, the laser device further includes a beam shaping module 25, and the beam shaping module 25 is located in the optical path between the laser 21 and the wafer 11. The mirror 24 can convert the light field intensity distribution of the laser from a Gaussian distribution to a flat-top distribution.

[0114] Refer to Figure 17 as shown, Figure 17 which is a schematic diagram of the principle of converting the light field intensity distribution of the beam shaping module. In the left figure, the laser light field distribution is a Gaussian distribution, and in the right figure, the laser light field distribution is a flat-top distribution. Modifying the wafer 11 based on the flat-top distribution laser can increase the size of the laser spot on the surface of the wafer 11 and improve the modification efficiency.

[0115] Further, the laser device further includes a focusing lens 26, and the laser device emits the laser for modifying the wafer 11 through the focusing lens 26. Other optical devices in the laser device are located in the optical path between the laser 21 and the focusing lens 26. The focusing lens can achieve planar focusing of the laser, improving the laser modification efficiency and the laser energy utilization rate.

[0116] It should be noted that in the optical path between the laser 21 and the wafer 11, it may include one or more of a half-wave plate 22, a beam expander 23, a mirror 24, a beam shaping module 25, and a focusing lens 26. When there is a focusing lens 26, other optical devices need to be placed in the optical path between the focusing lens 26 and the laser 21. Other optical devices between the focusing lens 26 and the laser 21 can be one or more of a half-wave plate 22, a beam expander 23, a mirror 24, and a beam shaping module 25, and the arrangement order of other optical devices in the laser transmission direction can be set based on requirements, not limited to Figure 16 the shown manner.

[0117] In the wafer thinning system provided by the embodiments of the present application, the thinning device can be as Figure 18 shown.

[0118] Refer to Figure 18 as shown, Figure 18 which is a structural schematic diagram of a thinning device provided by the embodiments of the present application. The shown thinning device includes a mechanical grinding device. The mechanical grinding device includes a grinding disk 31, and the grinding disk 31 can mechanically grind the surface 111 to be thinned of the wafer 11 that has been modified based on the grinding liquid to achieve thinning of the thickness of the wafer 11.

[0119] In Figure 18 the shown figure, there is a modified area 14 with a gradually decreasing depth from the center to the edge along a wafer radius in the surface 111 to be thinned of the wafer 11 to improve the thickness uniformity of the thinned wafer.

[0120] In the wafer thinning system provided by the embodiments of the present application, it further includes: a pretreatment device. Before performing surface modification on the surface to be thinned, the pretreatment device is used to pretreat the surface 111 to be thinned to increase crystal defects in the surface 111 to be thinned. Among them, the pretreatment device can be an ion implantation device for ion implanting the surface 111 to be thinned, or the pretreatment device can be an etching device capable of chemically etching the surface 111 to be thinned.

[0121] In this specification, the various embodiments are described in a progressive, or parallel, or a combination of progressive and parallel manners. The key point of each embodiment is to illustrate the differences from other embodiments. For the same or similar parts among the various embodiments, reference can be made to each other.

[0122] It should be noted that in the description of the present application, it should be understood that the descriptions of the drawings and embodiments are illustrative rather than restrictive. The same reference numerals throughout the embodiments of the specification identify the same structures. Additionally, for the sake of understanding and easy description, the drawings may exaggerate the thickness of some layers, films, panels, regions, etc. At the same time, it can be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, the element can be directly on the other element or there may be intermediate elements. Additionally, "on" means positioning the element on or below another element, but essentially does not mean positioning on the upper side of another element according to the direction of gravity.

[0123] The orientation or positional relationship indicated by the terms "upper", "lower", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present application 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 should not be construed as a limitation to the present application. When a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be intermediate components present simultaneously.

[0124] It also should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variation thereof is intended to cover non-exclusive inclusion, such that an article or device including a series of elements not only includes those elements but also includes other elements not explicitly listed, or further includes elements inherent to such article or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of additional identical elements in the article or device including the above elements.

[0125] The foregoing description of the disclosed embodiments enables those skilled in the art to practice or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A wafer thinning method, comprising: Under laser induction, performing a modification treatment on the surface to be thinned of the wafer, so that the material in the irradiated area of the surface to be thinned by the laser is modified, and at least part of the area of the surface to be thinned is converted from a first material to a second material; Performing a thinning treatment on the surface to be thinned after the modification treatment, and under the same thinning conditions, the thinning rate of the first material is less than the thinning rate of the second material.

2. The wafer thinning method according to claim 1, before performing the modification treatment on the surface to be thinned, further comprising: Performing a pretreatment on the surface to be thinned to increase crystal defects in the surface to be thinned.

3. The wafer thinning method according to claim 2, the method for performing the pretreatment on the surface to be thinned includes: Performing ion doping in the surface to be thinned, or etching the surface to be thinned with a chemical reagent.

4. The wafer thinning method according to claim 1, the method for making the surface to be thinned modified by laser includes: Scanning the surface to be thinned by laser without gaps; Or, Using laser to scan the surface to be thinned based on a preset scanning path to form a modified area related to the scanning path on the surface to be thinned; wherein, in at least one radial direction of the wafer, non-modified areas are reserved between the modified areas; the non-modified areas are used to reduce the friction during subsequent thinning treatment.

5. The wafer thinning method according to claim 1, on at least one radial direction of the wafer, the surface to be thinned after the modification treatment comprises: Alternately arranged modified areas and non-modified areas; The modified area is the second material, and the hardness of the first material is greater than the hardness of the second material; The non-modified area is the first material; the depth of the modified area is not greater than the required thinning thickness of the wafer.

6. The wafer thinning method according to claim 5, the modified area is a spiral structure; Or, the modified area is a grid structure.

7. The wafer thinning method according to claim 5, in the at least one radial direction, the modified areas are evenly distributed on the surface to be thinned; In the at least one radial direction, the depth of the modified areas gradually decreases.

8. The wafer thinning method according to claim 5, in the at least one radial direction, the depth of the modified areas remains uniformly unchanged; In the at least one radial direction, the distribution density of the modified areas decreases in sequence.

9. A wafer thinning system, comprising: A laser device, which is used to perform a modification treatment on the surface to be thinned of the wafer, so that the irradiated area of the surface to be thinned by the laser is modified under the induction of the laser, and at least part of the area of the surface to be thinned is converted from a first material to a second material, and the hardness of the first material is greater than the hardness of the second material; A thinning device, which is used to perform a thinning treatment on the surface to be thinned after the modification treatment.

10. The wafer thinning system according to claim 9, further comprising: A pretreatment device, which is used to perform a pretreatment on the surface to be thinned before performing the modification treatment on the surface to be thinned to increase crystal defects in the surface to be thinned.

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