A method for back thinning of a wafer

Abstract

The present application provides a method for back thinning of a wafer, which includes providing a wafer. The edge of the wafer includes a flat edge perpendicular to the <110> crystal orientation of the wafer. A grinding protective film is pasted on the front side of the wafer, and then the wafer is fixed on the wafer support disk of a thinning machine tool. The back side of the wafer is polished and thinned to obtain a thinned wafer sheet. Finally, the grinding protective film on the front side of the thinned wafer sheet is removed. By setting the flat edge of the wafer in a direction perpendicular to the <110> crystal orientation of the wafer, when a notch appears on the flat edge during the thinning process of the wafer, the microcracks generated will only expand in a direction parallel to the flat edge, and will not expand to the center of the wafer, avoiding chipping during the back thinning of the wafer and improving the yield of the back thinning of the wafer.

Description

Technical Field

[0001] The present application relates to the field of semiconductor-related technology, and in particular to a method for thinning the back side of a wafer. Background Art

[0002] In the manufacturing process of semiconductor integrated circuits, as the requirements for semiconductor devices become higher and higher, some semiconductor devices need to adopt a wafer backside thinning process to reduce the thickness of the wafer and change the conductivity and heat dissipation performance of the semiconductor substrate such as the silicon substrate, thereby improving the performance of the semiconductor device.

[0003] Existing semiconductor devices are usually manufactured on the shallow surface of the wafer, rather than using very thin wafers at the beginning. Therefore, before the wafer is thinned on the back side, a layer of blue film needs to be pasted on the front side of the wafer to protect the device structure manufactured on the front side of the wafer. However, the pasted blue film will form tensile stress on the front side of the wafer, and during the process of wafer thinning on the back side, the continuous reduction in substrate thickness will often form microcracks on the back side of the wafer. The combination of tensile stress and microcracks further expands the microcracks, causing the wafer to break. At the same time, the pressure applied to the wafer during thinning by the grinding wheel and grinding disc also leads to a further increase in the fragmentation rate of the wafer pasted with the blue film after thinning.

[0004] Therefore, how to provide a wafer backside thinning method that can reduce the wafer chipping rate during the backside thinning process has become an urgent problem to be solved in the art. Summary of the invention

[0005] The purpose of the present application is to provide a wafer backside thinning method, which can reduce the wafer cracking rate during the backside thinning process.

[0006] In a first aspect, an embodiment of the present application provides a method for thinning a wafer backside, comprising:

[0007] A wafer is provided, and a process preparation of a device structure is completed on the front side of the wafer; the edge of the wafer also includes a <110> Flat edges perpendicular to the crystal direction;

[0008] A grinding protection film is attached to the front side of the wafer to protect the device structure on the front side of the wafer;

[0009] The wafer is fixed on a wafer support plate of a thinning machine, and the front side of the wafer with the grinding protective film is in contact with the wafer support plate; the grinding head of the thinning machine grinds and thins the back side of the wafer to obtain a wafer thinning sheet;

[0010] The grinding protection film on the front side of the wafer thinning film is removed.

[0011] In a possible real-time solution, the step of sticking a grinding protection film on the front side of the wafer includes sticking the grinding protection film along a direction parallel to the flat edge.

[0012] In a possible real-time solution, the step of grinding and thinning the back side of the wafer by the grinding head of the thinning machine includes:

[0013] Roughly grinding and thinning the back side of the wafer to obtain a first roughly ground and thinned wafer with a first thickness parameter;

[0014] The first coarsely ground and thinned slice is finely ground and thinned to obtain the wafer thinned slice with preset thickness parameters.

[0015] In a possible real-time solution, the step of obtaining a first thickness parameter by rough grinding and thinning comprises:

[0016] The grinding head performs rough grinding and rapid thinning on the back side of the wafer at a second grinding speed to obtain a second rough grinding and thinning wafer with a second thickness parameter;

[0017] The grinding head performs rough grinding and slow thinning on the second roughly ground and thinned sheet at a first grinding speed to obtain a first roughly ground and thinned sheet with a first thickness parameter.

[0018] In a possible real-time solution, the second grinding plate speed is 3 μm / s, and the first grinding plate speed is 1.5 μm / s.

[0019] In a possible real-time solution, the second thickness parameter>the first thickness parameter>the preset thickness parameter.

[0020] In a possible real-time solution, before the step of removing the grinding protection film on the front side of the wafer thinning sheet, the thinning surface of the wafer thinning sheet is also subjected to etching treatment.

[0021] In a possible real-time solution, the step of etching the thinned surface of the wafer thinning sheet includes:

[0022] The wafer thinning sheet is placed in an etching device, and the thinning surface is subjected to etching treatment to remove surface defects of the thinning surface, wherein the etching solution of the etching treatment includes at least one or more of nitric acid, acetic acid or hydrofluoric acid solution.

[0023] In a possible real-time solution, the grinding protection film includes a blue film.

[0024] In a possible real-time solution, the device structure completed on the front side of the wafer includes an IGBT device structure.

[0025] Compared with the prior art, the present invention has at least the following beneficial effects:

[0026] The present application provides a wafer backside thinning method, comprising providing a wafer, wherein the edge of the wafer comprises a <110> The flat edge perpendicular to the crystal direction is to stick a grinding protective film on the front side of the wafer, fix the wafer on the wafer support plate of the thinning machine, grind and thin the back side of the wafer to obtain a wafer thinning sheet, and remove the grinding protective film on the front side of the wafer thinning sheet to complete the wafer back side thinning process. <110> In the direction perpendicular to the crystal direction, the microcracks generated when notches appear on the flat edge during the wafer thinning process only expand in the direction parallel to the flat edge and will not expand to the center of the wafer, thus avoiding the generation of cracks during the wafer thinning process and improving the yield of wafer back thinning.

[0027] The present application provides a wafer backside thinning method, which uses a step-by-step grinding method to thin the backside of the wafer, performs rapid grinding when the wafer has a large thickness parameter, and reduces the grinding speed when it is close to a preset thickness parameter, thereby improving the grinding and thinning efficiency, and effectively improving the uniformity and residual stress distribution of the wafer thinning surface, and at the same time reducing the incidence of microcracks caused by the grinding disc BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 It is a schematic flow chart of a method for thinning the back side of a wafer according to an embodiment of the present application. DETAILED DESCRIPTION

[0030] The following describes the implementation of the present application through specific embodiments, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. The present application can also be implemented or operated through other different specific implementations, and the details in the present application can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application.

[0031] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be internal communication between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to the specific circumstances. In addition, the terms "first" and "second" are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0032] In recent years, with the rapid development trend of semiconductor devices, IGBT devices have been widely used in the field of new energy vehicles and industrial motor drives. As the most critical and core part of the IGBT wafer, the back thinning process will directly affect the performance of the IGBT device and the uniformity of the performance of the IGBT device. In order to achieve better IGBT device performance, the requirement for the thickness of the IGBT wafer is that the thinner the better. However, as the thickness of the semiconductor substrate decreases after the back thinning of the wafer, microcracks often appear during the thinning of the back of the wafer, and such microcracks are prone to further expansion in subsequent processes.

[0033] Usually, the thinning process of IGBT wafer is as follows: stick a grinding protective film on the front of the wafer; thin the back of the wafer; remove the grinding protective film. The sticking grinding protective film will form tensile stress on the front of the wafer. The combination of tensile stress and microcracks generated by thinning the back of the wafer will promote the further expansion of microcracks, and under the promotion of the pressure applied to the wafer during the thinning of the grinding wheel and grinding disc, the wafer will eventually break.

[0034] After the above analysis, the applicant found that the position of the wafer flat edge will have a direct impact on wafer breakage. The surface of the IGBT wafer is usually (100) plane, and the flat edge is usually prepared at <110> The grinding protective film is pasted in the direction parallel to the flat edge. <110> When a notch appears on the flat edge of the crystal direction, the notch will produce <110> Microcracks that are perpendicular to the crystal direction are perpendicular to the direction of the flat edge. Therefore, when the direction of the microcracks is perpendicular to the direction of the grinding protective film, the tensile stress of the grinding protective film on the front of the wafer will be concentrated at the microcracks that are perpendicular to the flat edge. When the wafer is thinned to a certain thickness, the microcracks will expand in the direction perpendicular to the flat edge, causing the wafer to break. <110> When the direction is perpendicular to the crystal direction, the microcracks generated when a notch appears on the flat edge will no longer be perpendicular to it, but parallel to the flat edge, which is correspondingly parallel to the direction of sticking the grinding protective film. Therefore, as the wafer becomes thinner, the tensile stress of the grinding protective film on the front side of the wafer will no longer have the ability to expand the microcracks.

[0035] At the same time, the applicant also found that the back side thinning of the wafer adopts a step-by-step grinding method, which includes rapid grinding when the wafer has a larger thickness parameter and reducing the grinding speed when it is close to the preset thickness parameter. This can not only improve the efficiency of grinding and thinning, but also effectively improve the uniformity of the wafer thinning surface and the residual stress distribution, while also reducing the incidence of microcracks caused by the grinding disc.

[0036] Based on the above analysis, the present application provides a method for thinning the back side of a wafer. Figure 1 , including the following steps:

[0037] S1, providing a wafer, and completing the process preparation of the device structure on the front side of the wafer, and the edge of the wafer also includes a <110> A flat edge that is perpendicular to the crystal direction.

[0038] S2, pasting a grinding protection film on the front side of the wafer to protect the device structure on the front side of the wafer;

[0039] S3, fixing the wafer on the wafer support plate of the thinning machine, the front side of the wafer with the grinding protective film attached is in contact with the wafer support plate, and the grinding head of the thinning machine grinds and thins the back side of the wafer to obtain a wafer thinning sheet;

[0040] S4, removing the grinding protection film on the front side of the wafer thinning film.

[0041] In one embodiment, the surface of the wafer is a (100) plane, with a flat edge located at <110> The edge of the wafer perpendicular to the crystal direction. It should be noted that before the crystal ingot is processed into a sheet-shaped wafer, a flat edge is usually processed on the side of the crystal ingot to indicate the crystal direction doping type. <110> When a notch appears at the flat edge, the crack caused by the notch will usually also appear in the wafer along the vertical direction. <110> Extension in the direction of the crystal.

[0042] Optionally, the device structure completed on the front side of the wafer includes a power device, the power device includes an active region, a transition region and a terminal region, the terminal region surrounds the active region, the transition region is located between the active region and the terminal region, a device unit structure is formed in the active region, and a terminal structure is formed in the terminal region. Optionally, the power device includes an IGBT device, and the device structure includes an emitter region, a gate structure and a drift region. In other embodiments, the power device may also be a MOS device.

[0043] In one embodiment, the grinding protective film is pasted on the front side of the wafer and pasted in a direction parallel to the flat edge. The grinding protective film can protect the device structure located on the front side of the wafer, and pasting the grinding protective film in a direction parallel to the flat edge can effectively reduce the incidence of wafer breakage. The grinding protective film will generate vertical tensile stress on the front side of the wafer along the pasting direction, and pasting the grinding protective film in a direction parallel to the flat edge can make the microcracks generated by the flat edge notch consistent with the pasting direction of the grinding protective film, so that the microcracks can only expand in a direction parallel to the flat edge under the action of tensile stress, and cannot extend toward the center of the wafer.

[0044] It should be noted that the flat edge of the wafer in the prior art is set at <110> If the grinding protective film is pasted in the direction parallel to the flat edge in the crystal direction, the microcracks caused by the notch of the flat edge will be perpendicular to the pasting direction of the grinding protective film, so that the microcracks will expand in the direction perpendicular to the flat edge under the action of tensile stress, that is, extend toward the center of the wafer, causing damage to the device structure and fragmentation of the wafer.

[0045] Optionally, the grinding protection film includes a blue film.

[0046] In one embodiment, the grinding head of the thinning machine grinds and thins the back of the wafer in two steps: first, the back of the wafer is rough-ground and thinned with a coarse grinding wheel with a larger grain size, and then the coarse grinding wheel is replaced with a fine grinding wheel, and fine grinding and thinning are continued until the wafer is thinned to a preset thickness parameter to obtain a wafer thinned sheet. More than 60% of the wafer thinning thickness is removed by coarse grinding and thinning.

[0047] Optionally, in the rough grinding and thinning stage, the grinding head performs rough grinding and fast thinning on the back side of the wafer at a second grinding speed to obtain a second rough grinding and thinning sheet with a second thickness parameter; then the grinding head performs rough grinding and slow thinning on the second rough grinding and thinning sheet at the first grinding speed to obtain a first rough grinding and thinning sheet with a first thickness parameter, wherein the second thickness parameter>the first thickness parameter>the preset thickness parameter.

[0048] In this embodiment, the thickness of the wafer to be thinned is 625μm, and the second grinding speed is preferably 3μm / s for rough grinding and fast thinning on the back side of the wafer until the wafer is thinned to 145μm, i.e., the second thickness parameter. Then, the second grinding speed is adjusted to the first grinding speed, and the preferred value of the first grinding speed is 1.5μm / s, until the wafer is thinned to 120μm, i.e., the first thickness parameter. Finally, the coarse grinding wheel is replaced with a fine grinding wheel, and the wafer is continued to be thinned at a grinding speed of 1.5μm / s until the thickness is thinned to less than 100μm, thereby obtaining a thinned wafer with preset thickness parameters.

[0049] Rapid grinding is performed when the wafer has a larger thickness parameter, and the grinding speed is reduced when it is close to the preset thickness parameter. This can not only improve the efficiency of grinding and thinning, but also effectively improve the uniformity of the wafer thinning surface and the residual stress distribution, while also reducing the incidence of microcracks caused by the grinding disc.

[0050] In one embodiment, the thinned surface of the wafer thinning sheet that has completed the back thinning also includes a process of performing an etching treatment. The wafer thinning sheet is placed in an etching device and the thinning surface is subjected to an etching treatment. The damage to the thinning surface during the thinning process of the grinding sheet can be repaired, and the incidence of wafer cracking can be further reduced. The etching solution of the etching treatment includes at least one or more of nitric acid, acetic acid or hydrofluoric acid solution. After the etching-treated wafer thinning sheet is cleaned and dried, the grinding protective film attached to the front is removed, and the thinning process on the back of the wafer is completed.

[0051] The present application provides a wafer backside thinning method, comprising providing a wafer, wherein the edge of the wafer comprises a <110> The flat edge perpendicular to the crystal direction is to stick a grinding protective film on the front side of the wafer, fix the wafer on the wafer support plate of the thinning machine, grind and thin the back side of the wafer to obtain a wafer thinning sheet, and remove the grinding protective film on the front side of the wafer thinning sheet to complete the wafer back side thinning process. <110> In the direction perpendicular to the crystal direction, the microcracks generated when notches appear on the flat edge during the wafer thinning process only expand in the direction parallel to the flat edge and will not expand to the center of the wafer, thus avoiding the generation of cracks during the wafer thinning process and improving the yield of wafer back thinning.

[0052] The present application provides a wafer backside thinning method, which uses a step-by-step grinding method to thin the backside of the wafer, performs rapid grinding when the wafer has a large thickness parameter, and reduces the grinding speed when it is close to a preset thickness parameter, thereby improving the grinding and thinning efficiency, and effectively improving the uniformity and residual stress distribution of the wafer thinning surface, and at the same time reducing the incidence of microcracks caused by the grinding disc

[0053] The above is only a preferred implementation of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present application. These improvements and substitutions should also be regarded as the scope of protection of the present application.

Claims

1. A method for back thinning of a wafer, characterized in that, it includes: providing a wafer and completing the process preparation of the device structure on the front side of the wafer; an edge of the wafer further includes a flat edge perpendicular to the <110> crystal orientation direction of the wafer; pasting a grinding protective film on the front side of the wafer along a direction parallel to the flat edge for protecting the device structure on the front side of the wafer; fixing the wafer on a wafer support disk of a thinning machine tool, with the front side of the wafer pasted with the grinding protective film in contact with the wafer support disk; the grinding head of the thinning machine tool grinds and thins the back side of the wafer to obtain a wafer thin slice; removing the grinding protective film on the front side of the wafer thin slice.

2. The back thinning method according to claim 1, characterized in that, the step of the grinding head of the thinning machine tool grinding and thinning the back side of the wafer includes: rough grinding and thinning the back side of the wafer to obtain a first rough grinding thin slice with a first thickness parameter; fine grinding and thinning the first rough grinding thin slice to obtain the wafer thin slice with a preset thickness parameter.

3. The back thinning method according to claim 2, characterized in that, the step of obtaining the first rough grinding thin slice with the first thickness parameter includes: rough grinding and quickly thinning the back side of the wafer with the grinding head at a second grinding speed to obtain a second rough grinding thin slice with a second thickness parameter; rough grinding and slowly thinning the second rough grinding thin slice with the grinding head at a first grinding speed to obtain the first rough grinding thin slice with the first thickness parameter.

4. The back thinning method according to claim 3, characterized in that, the second grinding speed is 3μm / s and the first grinding speed is 1.5μm / s.

5. The back thinning method according to claim 3, characterized in that, the second thickness parameter > the first thickness parameter > the preset thickness parameter.

6. The back thinning method according to claim 1, characterized in that, before the step of removing the grinding protective film on the front side of the wafer thin slice, it further includes performing an etching treatment on the thinning surface of the wafer thin slice.

7. The back thinning method according to claim 6, characterized in that, the step of etching the thinning surface of the wafer thin slice includes: placing the wafer thin slice in an etching device and performing an etching treatment on the thinning surface to remove surface defects on the thinning surface, wherein the etching solution for the etching treatment includes at least one or more of nitric acid, acetic acid or hydrofluoric acid solution.

8. The back thinning method according to claim 1, characterized in that, the grinding protective film includes a blue film.

9. The back thinning method according to claim 1, characterized in that, the device structure completed on the front side of the wafer includes an IGBT device structure.

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