A method for improving the warping of thin sheets

Abstract

The present invention provides a method for improving wafer warpage, which includes providing a wafer; forming a first film layer with a first tensile stress on the front outer surface of the wafer; forming a second film layer with a second tensile stress on the back outer surface of the wafer, wherein the direction of the second tensile stress is opposite to that of the first tensile stress, so that the second tensile stress cancels out the first tensile stress. The present invention increases the tensile stress of the back film layer of the wafer, partially cancels out the tensile stress of the front film layer, reduces the overall stress of the wafer, so that the wafer will not warp and will not affect subsequent processing.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and particularly to a method for improving the warping of thin wafers. Background Art

[0002] During the production process of power device products in a wafer fab, due to the relatively thick film thickness and high process temperature, high stress is generated during the device manufacturing process. These wafers with high stress become severely warped after the thinning process, resulting in a series of problems such as machine alarms and high wafer breakage rates. In severe cases, it even affects the processing of thin wafers.

[0003] Power metal-oxide transistors based on superjunction technology have become the industry standard in the field of high-voltage switch converters. They offer lower static on-resistance and fewer gate and output charges, which helps maintain higher efficiency at any given frequency. Due to the influence of the stress of the polyimide (PI) layer, some superjunction (SJ) products have excessive warping during thin wafer processing, affecting the circulation of superjunction (SJ) products with a polyimide (PI) layer during yield testing.

[0004] In the prior art, usually by finding the stress level causing warping, optimizing the operation of the stress layer, and changing the stress of the metal film layer by adjusting the process temperature, the production efficiency is low and the improvement effect is also limited. Summary of the Invention

[0005] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a method for improving the warping of thin wafers, which is used to solve the problems that the wafers become severely warped after the thinning process in the prior art, resulting in a series of problems such as machine alarms and high wafer breakage rates, and even affecting the processing of thin wafers in severe cases.

[0006] To achieve the above object and other related objects, the present invention provides a method for improving the warping of thin wafers, including:

[0007] Step 1: Provide a wafer;

[0008] Step 2: Form a first film layer with a first stress on the front outer surface of the wafer;

[0009] Step 3: Form a second film layer with a second stress on the back outer surface of the wafer, where the second stress is opposite to the direction of the first stress, so that the second stress cancels the first stress.

[0010] Optionally, the first film layer in Step 2 is at least one of a passivation layer, a polyimide layer, a metal layer, and a trench layer.

[0011] Optionally, the wafer in step two warps towards the front side under the action of the first stress.

[0012] Optionally, the second film layer in step three is a metal layer.

[0013] Optionally, the forming method of the second film layer is sputtering with a nickel-vanadium alloy as the metal target, so that nickel and vanadium atoms of the metal target are deposited on the back side of the wafer.

[0014] Optionally, the material of the metal target is nickel-vanadium alloy.

[0015] Optionally, the sputtering increases the process time by reducing the power of the sputtering equipment, so that the thickness of the second film layer increases and the second stress increases.

[0016] Optionally, the sputtering cancels nitrogen in the process, so that the second stress increases.

[0017] Optionally, the second film layer is formed by one-time deposition, so that the second stress increases.

[0018] A thin sheet structure, comprising:

[0019] A wafer;

[0020] A first film layer formed on the front outer surface of the wafer and having a first stress;

[0021] A second film layer formed on the back outer surface of the wafer and having a second stress.

[0022] Wherein the second stress is opposite to the direction of the first stress, so that the second stress cancels the first stress.

[0023] Optionally, the first film layer is at least one of a passivation layer, a polyimide layer, a metal layer, and a trench layer.

[0024] Optionally, the second film layer is a metal layer.

[0025] Optionally, the material of the second film layer is nickel-vanadium alloy.

[0026] Optionally, the thin sheet structure can be formed by the method in any of the above steps.

[0027] As described above, the method for improving wafer warping of the present invention has the following beneficial effects:

[0028] The present invention increases the tensile stress of the back film layer of the wafer, partially cancels the tensile stress of the front film layer, reduces the overall stress of the wafer, so that the wafer does not warp and does not affect subsequent processing. Description of the Drawings

[0029] Figure 1 It shows a schematic diagram of the process flow steps provided by the present invention;

[0030] Figure 2 It shows a schematic diagram of the improved wafer cross-sectional structure provided by an embodiment of the present invention;

[0031] Figure 3 It shows a schematic diagram of yield detection comparison provided by an embodiment of the present invention. Detailed implementation manners

[0032] The following uses specific specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0033] Please refer to Figure 1 , the present invention provides a method for improving wafer warping, including:

[0034] Step 1, providing a wafer 1, which is a wafer thin sheet;

[0035] Step 2, forming a first film layer 3 with a first stress on the front surface of the wafer 1, and the first film layer 3 is formed as required in the actual production process;

[0036] In a possible implementation manner, the first film layer 3 in Step 2 is at least one of a passivation layer, a polyimide layer, a metal layer, and a trench layer. The material of the passivation layer can be an oxide or silicon nitride, and the material of the metal layer can be aluminum.

[0037] In a possible implementation manner, the first film layer 3 in Step 2 is a polyimide layer. Polyimide (abbreviated as PI) refers to a class of polymers containing imide rings (-CO-N-CO-) in the main chain and is one of the organic polymer materials with the best comprehensive performance. It can withstand high temperatures above 400 °C, the long-term use temperature range is -200 to 300 °C, some have no obvious melting point, high insulation performance, the dielectric constant is 4.0 at 103 Hz, and the dielectric loss is only 0.004 to 0.007.

[0038] The wafer 1 in Step 2 warps towards the front surface under the action of the first stress such as the polyimide layer.

[0039] Step 3, please refer to Figure 2 , forming a second film layer 2 with a second stress on the back surface of the wafer 1, wherein the second stress is opposite to the direction of the first stress, so that the second stress can offset the first stress and reduce the warping degree of the wafer 1.

[0040] In a possible implementation, the second film layer 2 in step three is a metal layer. In the prior art, there is only the first film layer 3 on the surface of the wafer 1, and its tensile stress is difficult to eliminate. After forming a metal layer on the back of the wafer 1, the tensile stress of its first film layer 3 can be offset.

[0041] In a possible implementation, the material of the second film layer 2 can be a nickel-vanadium alloy. The nickel-vanadium alloy target is a new type of semiconductor target. In engineering, the nickel-vanadium alloy target is used to replace the original nickel target and vanadium target. It can generate an adhesion layer and a barrier layer in one sputtering. At the same time, after adding a certain amount of vanadium to nickel, the nickel-based alloy is non-magnetic, which is also beneficial to magnetron sputtering. The nickel-vanadium alloy target used in engineering requires, especially for large-sized targets, high purity, uniform composition, fine grains, uniform structure, and the alloy is a strict single phase. The forming method of the second film layer 2 is to sputter with a nickel-vanadium alloy as the metal target, so that nickel and vanadium metal atoms are deposited on the back of the wafer 1.

[0042] In a possible implementation, sputtering reduces the power of the sputtering equipment and increases its process time, so that the grain structure of the second film layer 2 changes, and the tensile stress of the second film layer 2 can be increased.

[0043] In a possible implementation, sputtering cancels nitrogen during nickel-vanadium alloy sputtering, so that the grain structure of the second film layer 2 changes, and the tensile stress of the second film layer 2 can be increased.

[0044] In a possible implementation, the second film layer is formed by one-time deposition, so that the grain structure of the second film layer 2 changes, and the tensile stress of the second film layer 2 can be increased.

[0045] It should be understood that the above three implementation methods can all increase the tensile stress of the second film layer 2. They can be used alone or simultaneously. In a preferred implementation, the above three implementation methods can be used simultaneously when sputtering to generate the second film layer 2.

[0046] Please refer to Figure 2 , the present invention also provides a thin sheet structure, including:

[0047] Wafer 1;

[0048] The first film layer 3 formed on the front of the wafer 1 and having a first tensile stress;

[0049] The second film layer 2 formed on the back of the wafer 1 and having a second tensile stress;

[0050] Wherein the second tensile stress is opposite to the direction of the first tensile stress, so that the second tensile stress offsets the first tensile stress.

[0051] In a possible implementation, the first film layer 3 is at least one of a passivation layer, a polyimide layer, a metal layer, and a trench layer. The material of the passivation layer can be an oxide or silicon nitride, and the material of the metal layer can be aluminum.

[0052] In a possible implementation, the second film layer 2 is a metal layer.

[0053] In a possible implementation, the material of the second film layer 2 can be a nickel-vanadium alloy.

[0054] In a possible implementation, the sheet structure can be formed by the method in any of the above steps.

[0055] In a possible implementation, please refer to Figure 3 , the upper curve in the figure is the warp of the back surface of the wafer 1 before backside metallization, and the lower curve is the warp of the back surface of the wafer 1 after backside metallization. The unit is millimeter. From the detection data of the baseline group and the split condition groups 1 to 4 (split1 to 4), it can be obtained that the warp before the yield detection of the superjunction (SJ) product with a polyimide (PI) layer is reduced by 0.8 mm, from 2.6 mm to 1.8 mm.

[0056] It should be noted that the illustrations provided in this embodiment only schematically illustrate the basic concept of the present invention. Therefore, only the components related to the present invention are shown in the drawings, rather than being drawn according to the number, shape, and size of the components in actual implementation. The type, quantity, and ratio of each component in actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0057] In summary, in the present invention, the tensile stress of the back film layer is increased, partially offsetting the tensile stress of the front film layer, reducing the overall stress of the wafer, so that the wafer does not warp and does not affect subsequent processing. Therefore, the present invention effectively overcomes various disadvantages in the prior art and has high industrial utilization value.

[0058] The above embodiments only exemplarily illustrate the principles and effects of the present invention, rather than limiting the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A method for improving wafer warpage, characterized in that, At least including: Step 1: Provide a wafer after the thinning process; Step 2: Form a first film layer with a first stress on the front side of the wafer, and the first film layer is at least one of a passivation layer, a polyimide layer, a metal layer, and a trench layer; Step 3: Form a second film layer with a second stress on the back side of the wafer, the second film layer is a metal layer, and the forming method of the second film layer is sputtering with a metal target so that atoms of the metal target are deposited on the back side of the wafer, and the sputtering cancels nitrogen in the process to increase the second stress, wherein the second stress is opposite to the first stress in direction so that the second stress cancels the first stress.

2. The method for improving wafer warpage according to claim 1, wherein: The wafer in Step 2 warps towards the front side under the action of the first stress.

3. The method for improving wafer warpage according to claim 1, characterized in that: The material of the metal target is a nickel-vanadium alloy.

4. The method for improving wafer warpage according to claim 1, wherein: The sputtering increases the process time by reducing the power of the sputtering equipment to increase the second stress.

5. The method for improving wafer warpage according to claim 1, wherein: The second film layer is formed by one-time deposition to increase the second stress.

6. A wafer structure, characterized in that, Including: A wafer after the thinning process; A first film layer formed on the front side of the wafer and having a first stress, and the first film layer is at least one of a passivation layer, a polyimide layer, a metal layer, and a trench layer; A second film layer formed on the back side of the wafer and having a second stress, the second film layer is a metal layer, and the forming method of the second film layer is sputtering with a metal target so that atoms of the metal target are deposited on the back side of the wafer, and the sputtering cancels nitrogen in the process to increase the second stress; wherein the second stress is opposite to the first stress in direction so that the second stress cancels the first stress.

7. The wafer structure according to claim 6, wherein: The material of the second film layer is a nickel-vanadium alloy.

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