Method for reducing stress of wafer, wafer and preparation method of wafer

Abstract

The invention relates to the technical field of wafer preparation, in particular to a method for reducing wafer stress, a wafer and a preparation method of the wafer. The method for reducing the stress of the wafer comprises the following steps: carrying out stress test on an original wafer to obtain a stress value and distribution; designing a photomask according to a stress test result and manufacturing the photomask; coating polyimide on the reverse side of the tensile stress of the original wafer and patterning according to the shape of a photomask; and then curing. The method can eliminate or reduce the influence of the strong stress generated in the process on the wafer and the subsequent process thereof, and has the advantages of convenient process implementation, easily available materials and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of wafer preparation, and in particular to a method for reducing wafer stress, a wafer and a preparation method thereof. Background Art

[0002] Wafer refers to the silicon wafer used to make silicon semiconductor circuits, and its original material is silicon. After high-purity polysilicon is dissolved, silicon crystal seeds are added, and then slowly pulled out to form cylindrical single crystal silicon. After grinding, polishing, and slicing, the silicon crystal rod forms a silicon wafer, that is, a wafer. Wafers usually have stress that causes product deformation and affects subsequent processes. For example, in the multi-layer RDL process, the deep trench process in devices such as insulated gate bipolar transistors (IGBTs) and through silicon vias (TSVs), the filling of deep trenches will produce strong internal stress on the wafer, which will change the shape of the wafer, thereby deteriorating the lithography accuracy during lithography, and the lithography machine will not be able to achieve good adsorption of the wafer during the lithography process, and the lithography operation cannot be performed; at the same time, the large stress itself will significantly increase the risk of wafer breakage during the transportation process or the dicing process. Therefore, how to reduce the adverse effects of wafer stress on device technology has become an important research and development topic in the semiconductor manufacturing process.

[0003] In view of this, the present invention is proposed. Summary of the invention

[0004] The purpose of the present invention is to provide a method for reducing wafer stress, a wafer and a method for preparing the same. The method provided by the embodiment of the present invention can eliminate or reduce the influence of strong stress generated in the process on the wafer and its subsequent processes, and has the advantages of convenient process implementation and easy acquisition of materials.

[0005] The present invention is achieved in that:

[0006] In a first aspect, the present invention provides a method for reducing wafer stress, comprising: performing a stress test on a wafer original to obtain stress values ​​and distribution;

[0007] Design and manufacture photomasks based on stress test results;

[0008] Coating polyimide on the tensile stress reverse side of the wafer original piece and patterning it according to the shape of the photomask;

[0009] Then solidify.

[0010] In an optional embodiment, the polyimide is selected from at least one of positive photosensitive polyimide, negative photosensitive polyimide and non-photosensitive polyimide.

[0011] In an optional embodiment, the polyimide is a polyimide having a cured film loss rate of 1%-50%.

[0012] In an alternative embodiment, the curing temperature is 150-500°C.

[0013] In an alternative embodiment, patterning includes baking, exposure and development.

[0014] In an optional embodiment, the thickness of the polyimide film formed after curing is 5-20 μm.

[0015] In an optional embodiment, the thickness of the polyimide film formed after curing is 15-20 μm.

[0016] In an optional embodiment, the method comprises: removing the cured polyimide film;

[0017] Preferably, the removal method is plasma oxidation removal.

[0018] In a second aspect, the present invention provides a method for preparing a wafer, which includes the method for reducing wafer stress as described in any one of the aforementioned embodiments.

[0019] In a third aspect, the present invention provides a wafer, which is prepared by the wafer preparation method described in the aforementioned embodiment.

[0020] The present invention has the following beneficial effects: the embodiment of the present invention tests the stress of the original wafer, designs a graphic distribution corresponding to the stress distribution according to the test results, and manufactures a cured polyimide film layer. The polyimide coated on the original wafer shrinks after curing to produce tensile stress, thereby offsetting the stress of the original wafer, thereby improving or offsetting the negative impact of stress on the original wafer. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention 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 creative work.

[0022] Figure 1 A schematic flow chart of a method for reducing wafer stress provided by an embodiment of the present invention;

[0023] Figure 2 A schematic diagram of stress magnitude and distribution of a method for reducing wafer stress provided by an embodiment of the present invention;

[0024] Figure 3 A schematic diagram of a photomask for a method of reducing wafer stress provided by an embodiment of the present invention;

[0025] Figure 4 A schematic diagram of a screenshot of an original wafer in the method for reducing wafer stress provided by an embodiment of the present invention;

[0026] Figure 5 A schematic screenshot of a method for reducing wafer stress provided in an embodiment of the present invention showing a polyimide pattern being arranged on the original wafer. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0028] In a first aspect, the present invention provides a method for reducing wafer stress, the flow chart of which is shown in FIG. Figure 1 ,include:

[0029] A polyimide is prepared, and the polyimide is a polyimide that is currently available and directly available. Specifically, the polyimide is a polyimide with a cured film loss rate of 1%-50%. For example, it is at least one of positive photosensitive polyimide, negative photosensitive polyimide and non-photosensitive polyimide. Specifically, it includes but is not limited to AS-PI-311P, AS-PI-411N and SP 483.

[0030] Perform stress test on the original wafer to obtain stress value and distribution, see Figure 2 The original wafer may be a wafer after a certain step in the wafer preparation process is completed. The stress may be detected by a stress testing device in the prior art.

[0031] Then, according to the stress test results, including but not limited to the stress distribution, direction, and size information of the wafer original, the mask pattern is designed and the mask is produced. For example, the mask pattern can be seen in Figure 3 .

[0032] Next, polyimide is coated on the tensile stress reverse side of the wafer original piece and patterned according to the shape of the photomask.

[0033] The patterning step is a method and step known in the art, and will not be described in detail in the present embodiment. For example, it includes corresponding baking, exposure, development and other processes. If it is non-photosensitive polyimide, it is necessary to add photoresist patterning.

[0034] Then, curing is performed by heating the polyimide. The curing temperature is 150-500°C, for example, any value between 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C and 500°C.

[0035] The curing steps include but are not limited to heating, curing temperature maintenance, cooling and other steps, which can be a single curing temperature maintenance, or curing at different stages. The above curing steps can be selected according to actual conditions, and the steps are steps known to those skilled in the art, and will not be described in detail in the embodiments of the present invention.

[0036] The schematic diagrams of the structure of the original wafer before and after polyimide curing are shown in Figure 4 and Figure 5 .

[0037] The embodiment of the present invention prepares a polyimide film layer by stress testing, and performs graphic design and curing according to the stress test results, and then utilizes the effect that the polyimide film will shrink and produce tensile stress after curing, and then the stress of the original wafer is used to improve or offset the negative impact of stress on the wafer. At the same time, the embodiment of the present invention enhances the shrinkage of polyimide by selecting a curing temperature, provides higher tensile stress, and then can better offset the stress of the original wafer. In summary, the embodiment of the present invention selects polyimide, performs graphic design, and selects a suitable curing temperature, and then the overall stress value and distribution of the polyimide film can be adjusted, thereby achieving a balanced adjustment of the stress of the original wafer.

[0038] The thickness of the polyimide film formed after curing is 5-20 μm, for example, any value between 5-20 μm, such as 5 μm, 10 μm, 15 μm and 20 μm, or a range between any two values, for example, preferably 15-20 μm.

[0039] Cooling after solidification is performed to make the wafer surface flat.

[0040] Furthermore, the cured polyimide film may or may not be removed, depending on the production step or production requirements. Methods for removing the cured polyimide film include but are not limited to selecting oxygen plasma for oxidation removal.

[0041] In a second aspect, the present invention provides a method for preparing a wafer, which includes the method for reducing wafer stress as described in any one of the aforementioned embodiments.

[0042] In a third aspect, the present invention provides a wafer, which is prepared by the wafer preparation method described in the aforementioned embodiment.

[0043] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0044] Example 1

[0045] An embodiment of the present invention provides a method for reducing wafer stress, comprising:

[0046] The stress of the 8-inch process wafer was tested using a stress tester. The stress value and distribution obtained by the test were 32.5MPa, and the stress distribution diagram was 26.3MPa in the X direction and 41.5MPa in the Y direction. Then, the graphic design was carried out according to the above stress, and the mask was prepared.

[0047] Then, positive photosensitive polyimide AS-PI-311P was spin-coated on the back of the 8-inch process wafer, and then heat-treated (pre-baked) at 120°C for 3 minutes using a hot plate (coating and developing device Mark-7 manufactured by Tokyo Electron Ltd.) to form a pre-baked film with a thickness of 10 μm. Using a pre-designed mask, an i-line stepper (manufactured by Nikon Corporation, NSR-2005i9C) was used at 50 to 400 mJ / cm 2 Exposure, 10mJ / cm 2 The obtained prebaked film was exposed by a step of . After exposure, it was developed with cyclopentanone for 90 seconds and then rinsed with PGMEA to obtain a developed film. Using an inert oven, the temperature was raised to 350°C at a rate of 3.5°C / min under the condition that the oxygen concentration was below 20 ppm, and the heat treatment was performed at 350°C for 1 hour. The wafer was taken out when the temperature became below 50°C.

[0048] Embodiment 2-8

[0049] Embodiments 2-8 respectively provide a method for reducing wafer stress. The method for reducing wafer stress is referred to the method for reducing wafer stress in Embodiment 1, and the operation is basically the same as that in Embodiment 1, except that some conditions are different, as follows:

[0050] Example 2

[0051] The AS-PI-411N in Example 1 was changed to non-photosensitive polyimide SP483.

[0052] Example 3

[0053] The AS-PI-411N in Example 1 was changed to the negative photosensitive polyimide AS-PI-311P. Meanwhile, the developing solution was replaced by a 2.38% TMAH aqueous solution, and the rinsing solution was replaced by water.

[0054] Example 4

[0055] The coating thickness of Example 1 was changed from 10 μm to 5 μm.

[0056] Example 5

[0057] The coating thickness of Example 1 was changed from 10 μm to 15 μm.

[0058] Example 6

[0059] The coating thickness of Example 1 was changed from 10 μm to 20 μm.

[0060] Example 7

[0061] The curing temperature of Example 1 was changed from 350°C to 500°C.

[0062] Example 8

[0063] The curing temperature of Example 1 was changed from 350°C to 150°C.

[0064] Comparative Example 1

[0065] The 8-inch process wafer provided in Example 1 is not processed in any way.

[0066] Test example

[0067] The wafers of Examples 1 to 6 and Comparative Example 1 were subjected to stress testing. Specifically, the stress of the wafers was measured using a stress testing device FLX2908 (manufactured by KLA Tencor Corporation).

[0068] Among them, the situation of 40MPa (excluding 40) or above is considered insufficient, that is, it is judged as D; the situation of 40MPa (including 40) or less and greater than 30MPa (excluding 30) is considered good, that is, it is judged as C; the situation of 30MPa (including 30) or less and greater than 20MPa (excluding 20) is considered better, that is, it is judged as B; the situation of less than 20MPa (including 30) is considered the best, that is, it is judged as A.

[0069] The results are shown in Table 1 below.

[0070] Table 1 Stress test results

[0071]

[0072] According to Table 1, the wafers formed by the methods 1-6 provided in the embodiments of the present invention all have relatively small stress, and the stress is even lower after the film thickness is increased. Compared with the embodiments, the stress of the wafers not treated in the comparative examples is higher. This further illustrates that the methods provided in the embodiments of the present invention can effectively reduce the stress of the wafers.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for reducing wafer stress, characterized in that: include: Perform stress test on the original wafer to obtain stress value and distribution; Design and manufacture photomasks based on stress test results; Coating polyimide on the tensile stress reverse side of the wafer original piece and patterning it according to the shape of the photomask; Then solidify.

2. The method for reducing wafer stress according to claim 1, characterized in that: The polyimide is selected from at least one of positive photosensitive polyimide, negative photosensitive polyimide and non-photosensitive polyimide.

3. The method for reducing wafer stress according to claim 2, characterized in that: The polyimide is a polyimide with a cured film loss rate of 1% to 50%.

4. The method for reducing wafer stress according to claim 1, characterized in that: The curing temperature is 150-500℃.

5. The method for reducing wafer stress according to claim 1, characterized in that: Patterning includes baking, exposure and development.

6. The method for reducing wafer stress according to claim 1, characterized in that: The thickness of the polyimide film formed after curing is 5-20 μm.

7. The method for reducing wafer stress according to claim 6, characterized in that: The thickness of the polyimide film formed after curing is 15-20 μm.

8. The method for reducing wafer stress according to claim 1, characterized in that: include: removing the cured polyimide film; Preferably, the removal method is plasma oxidation removal.

9. A method for preparing a wafer, characterized in that: The method comprises the method for reducing wafer stress as described in any one of claims 1 to 8.

10. A wafer, characterized in that: It is prepared by the wafer preparation method described in claim 9.

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