A method for stripping photoresist containing gold-tin patterns and a method for preparing wafer chips

Abstract

The present invention discloses a method for stripping photoresist containing gold-tin patterns and a method for preparing a wafer chip, belonging to the field of integrated circuit manufacturing and packaging. After the wafer is patterned by photolithography to form a gold-tin alloy layer, the photoresist is removed, comprising the following steps: S8, immersing the wafer in an acetone solution, ultrasonically applying a current of 0.2A to 1A for 10 to 30 minutes, and then immersing the wafer in an isopropyl alcohol solution for 1 to 10 minutes; S9, removing the photoresist using a plasma stripper to obtain a wafer chip product. The present invention utilizes the synergistic effect of wet and dry stripping processes without damaging the properties of the gold-tin alloy to rapidly obtain a gold-tin wafer product free of photoresist residue.

Description

Technical Field

[0001] The present invention relates to the field of integrated circuit manufacturing and packaging, and more particularly to a method for stripping a photoresist containing a gold-tin pattern and a method for preparing a wafer chip containing the gold-tin pattern. Background Art

[0002] Photolithography, a core process in wafer manufacturing, transforms the circuit topology on the mask into the physical pattern on the wafer surface through the synergistic effect of deep ultraviolet light and photosensitive polymers. The line width accuracy directly determines transistor density and chip performance. This process accounts for 32%-35% of chip manufacturing costs, primarily due to its high precision requirements and susceptibility to defects. Photoresist stripping, a critical step, requires thorough removal of the unexposed resist layer while ensuring no damage to the wafer substrate or metal layers.

[0003] To achieve this goal, wet stripping techniques remove uncured colloids through the selective interaction of solvent molecules with them. Common stripping solutions include N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), and acetone. NMP and DMSO easily penetrate the skin and can cause harm, while acetone is relatively less toxic and less expensive. Dry stripping methods, such as plasma stripping, can precisely remove residual colloids and are more adaptable to complex structures.

[0004] In the field of integrated circuit manufacturing and packaging, gold-tin alloys (such as Au80Sn20 or Au75Sn25) have significantly higher tensile and shear strengths than tin-silver-copper (SAC) alloys, effectively mitigating the propagation of solder joint cracks caused by thermal stress, and are therefore widely used. When traditional wet stripping is used to strip photoresists from integrated circuits containing gold-tin alloy patterns in manufacturing and packaging, the problem of uneven penetration due to surface tension is becoming increasingly prominent at high aspect ratios. When traditional dry stripping is used to strip photoresists from integrated circuits containing gold-tin alloy patterns in manufacturing and packaging, in an unprotected atmosphere, at temperatures exceeding 200°C, tin will gradually oxidize to tin oxide (SnO2), affecting the wettability of the solder interface and increasing the risk of leakage. The chemical activity of oxygen radicals in plasma is much higher than that of gaseous oxygen, and can induce metal oxidation at lower temperatures.

[0005] The above background technology is for facilitating understanding of the present invention and is not a known technology disclosed to the general public before the application of the present invention. Summary of the Invention

[0006] In response to the above problems, the present invention provides a method for preparing a wafer chip containing a gold-tin pattern, aiming to solve the problem of photoresist stripping in the field of integrated circuit manufacturing and packaging containing a gold-tin alloy pattern.

[0007] A method for stripping photoresist containing gold-tin patterns, wherein after a wafer is patterned by photolithography to form a gold-tin alloy layer, the photoresist is removed, comprising the following steps: S8, immersing the wafer in an acetone solution, ultrasonically applying an electric current of 0.2A to 1A for 10 to 30 minutes, and immersing the wafer in an isopropyl alcohol solution for 1 to 10 minutes; and S9, removing the photoresist using a plasma stripper to obtain a wafer chip product.

[0008] Optionally, in S8, the immersion in the acetone solution is divided into two immersions, and the acetone solution used for each immersion is a newly prepared acetone solution.

[0009] Optionally, in S9, the plasma stripping conditions are: power of 100 W to 200 W, oxygen flow rate of 50 sccm to 150 sccm, and time of 1 min to 10 min.

[0010] Optionally, the photoresist is a negative photoresist.

[0011] Optionally, the wafer is a four-inch alumina substrate or a four-inch aluminum nitride substrate.

[0012] The present invention also provides a method for preparing a wafer chip containing gold-tin patterns.

[0013] A method for preparing a wafer chip containing a gold-tin pattern comprises the following steps:

[0014] S1, performing the first photolithography patterning on the wafer substrate;

[0015] S2, sputtering a titanium layer, a platinum layer, and a gold layer in sequence to form an activated metal layer;

[0016] S4, immerse in acetone solution, ultrasonicate at 0.2A~1A current for 10min~30min, immerse in isopropyl alcohol solution for 1min~10min;

[0017] S5, performing a second photolithography patterning;

[0018] S6, evaporation of gold-tin alloy;

[0019] S8, immersed in acetone solution, ultrasonicated at 0.2A~1A current for 10min~30min, immersed in isopropyl alcohol solution for 1min~10min;

[0020] S9, plasma stripping machine removes photoresist to obtain wafer chip products.

[0021] Optionally, after S2 and before S4, S3 is further included, and a blue film is pasted to assist in removing the photoresist blue film and the blue film is torn off after it is pasted; after S6 and before S8, S7 is further included, and a blue film is pasted to assist in removing the photoresist blue film and the blue film is torn off after it is pasted.

[0022] Optionally, in S8, the immersion in the acetone solution is divided into two immersions, and the acetone solution used for each immersion is a newly prepared acetone solution.

[0023] Optionally, in S9, the plasma stripping conditions are: power of 100 W to 200 W, oxygen flow rate of 50 to 150 sccm, and time of 1 min to 10 min.

[0024] Optionally, the photoresist is a negative photoresist.

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

[0026] The present invention firstly uses a wet-process liquid acetone+isopropyl alcohol+specific ultrasonic current, and the high polarity can efficiently penetrate into the photoresist-substrate interface, preferentially dissolving uncrosslinked polymer chains, and having minimal impact on the solidified exposed area. Excessive current density will cause severe cavitation, which may break the stripped photoresist fragments into smaller particles. However, these particles may be temporarily suspended in the liquid due to solution turbulence or surface charge, and subsequently redeposited on the surface due to solvent volatilization or liquid flow stagnation. Excessively low current density cannot effectively destroy the bonding force between the photoresist and the substrate, and the residue is removed more thoroughly with low toxicity. Then, for the photoresist fragments remaining on the metal and substrate after wet cleaning, the photoresist is ashed in an oxygen atmosphere and a specific plasma power in the shortest time. The oxygen flow rate and power will lead to oxidation of the gold-tin alloy surface, and Sn will be gradually oxidized into SnO2 or SnO, and even form holes, which will damage the subsequent gold-tin weldability. Excessively low oxygen flow rate and power will prevent the photoresist from being oxidized into CO2 and H2O. Not only is the photoresist completely removed, but the gold-tin content is also guaranteed to change little, which does not affect subsequent chip packaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0028] Figure 1 This is the image of the present invention at a total ultrasound current of 0.6 A for 25 minutes;

[0029] Figure 2 This is the image after the wet method + oxygen drying method of the present invention;

[0030] Figure 3 This is the image of the present invention after a total ultrasound of 25 min at a current of 0.2 A;

[0031] Figure 4This is the image of the present invention after 25 minutes of total ultrasound at a current of 1 A;

[0032] Figure 5 This is the image of the present invention at a total ultrasound current of 0.6 A for 20 minutes;

[0033] Figure 6 This is the image after the wet method + argon dry method of the present invention;

[0034] Figure 7 This is the image after the wet method + oxygen and argon dry method of the present invention. DETAILED DESCRIPTION

[0035] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to a fixed connection, an indirect connection via an intermediate medium, internal communication between two components, or an interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0036] In the description of the present invention, it should be understood that the terms "upper," "lower," "front," "back," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They do not indicate or imply that the devices or elements referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limiting the present invention. In the description of the present invention, "plurality" means two or more, unless otherwise specifically specified.

[0037] The terms "first", "second", "third", "fourth", etc. (if any) in the specification of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can, for example, be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0038] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0039] The following specific embodiments are used to describe the technical solution of the present invention in detail. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described in detail in some embodiments.

[0040] In the present invention, photolithography patterning refers to the process of transferring the pattern to be formed to the wafer through the mask pattern through the steps of coating, exposure, and development of photoresist.

[0041] In the present invention, the wafer is a four-inch alumina substrate or a four-inch aluminum nitride substrate.

[0042] In the present invention, the photoresist is preferably a negative photoresist.

[0043] Example 1

[0044] A method for preparing a wafer chip product containing a gold-tin pattern is prepared by the following steps in sequence:

[0045] S1. Perform photolithography patterning on a four-inch wafer substrate.

[0046] S2. Sputtering a titanium layer, a platinum layer, and a gold layer in sequence to form an activated metal layer.

[0047] S3. Apply the blue film and gently wipe the surface of the blue film back and forth with a dust-free cloth so that the blue film is completely in contact with the activated metal layer. Then tear off the blue film. The activated metal layer on the photoresist will stick to the torn blue film, thereby completely exposing the photoresist.

[0048] During operation, place a layer of dust-free cloth under the substrate to prevent damage to the back.

[0049] S4. Remove photoresist: immerse in a clean acetone solution and sonicate at 0.6 A for 10 minutes (first sonication), then immediately place in another clean acetone solution and sonicate at 0.6 A for 15 minutes (second sonication) to prevent the photoresist from being re-adsorbed on the surface of the metal layer. Then immerse in a clean isopropyl alcohol solution for 5 minutes, immediately rinse with deionized water, spin dry, and dry.

[0050] Clean acetone solution refers to a freshly prepared acetone solution, and clean isopropyl alcohol solution refers to a freshly prepared isopropyl alcohol solution.

[0051] S5, performing photolithography patterning again.

[0052] S6, evaporation of gold-tin alloy (Au75Sn25).

[0053] S7, apply the blue film, and gently wipe the surface of the blue film back and forth with a dust-free cloth so that the blue film is completely in contact with the gold-tin layer. Then tear off the blue film, and the gold-tin layer on the photoresist will stick to the torn blue film, thereby completely exposing the photoresist.

[0054] During operation, place a layer of dust-free cloth under the substrate to prevent damage to the back.

[0055] S8, remove photoresist: immerse in clean acetone solution, ultrasonicate at 0.6 A current for 10 min (first ultrasonication), then immediately place in another clean acetone solution and ultrasonicate at 0.6 A for 15 min (second ultrasonication). The purpose of timely liquid change is to prevent the photoresist from re-adsorbing on the surface of the metal layer. Then immerse in isopropyl alcohol solution for 5 min, immediately rinse with deionized water, spin dry and dry. The image is as follows Figure 1 .

[0056] S9, plasma degumming machine removes the glue to obtain wafer chip products with no photoresist residue (the plasma product picture is as follows Figure 2 ): The plasma stripping machine was vacuumed to 0.320 mbar, the power was 100 W, the oxygen flow rate was 100 sccm, and the time was 3 min.

[0057] As can be seen from the picture, there is no photoresist residue on the wafer chip product.

[0058] The gold-tin composition of S9 wafer chip products was tested using XRF, and the test results are shown in Table 1.

[0059] Comparative Example 1

[0060] Compared with Example 1, the difference is:

[0061] (1) In S4 and S8, the ultrasonic current is 0.2 A;

[0062] ⑵ After S8 is completed, it stops and does not proceed to the subsequent process.

[0063] S8 rear image Figure 3 As can be seen from the figure, there are still some photoresist residues from the photolithography patterning in S5 on the wafer chip product, indicating that the photoresist removal in S8 and S9 was not thorough.

[0064] Comparative Example 2

[0065] Compared with Example 1, the difference is:

[0066] (1) In S4 and S8, the ultrasonic current is 1 A;

[0067] ⑵ After S8 is completed, it stops and does not proceed to the subsequent process.

[0068] S8 rear image Figure 4 As can be seen from the figure, there are still some photoresist residues from the photolithography patterning in S5 on the wafer chip product, indicating that the photoresist removal in S8 and S9 was not thorough.

[0069] Comparative Example 3

[0070] Compared with Example 1, the difference is:

[0071] (1) In S4 and S8, the second ultrasound time was 10 min;

[0072] ⑵ After S8 is completed, it stops and does not proceed to the subsequent process.

[0073] S8 rear image Figure 5 As can be seen from the figure, there are still some photoresist residues from the photolithography patterning in S5 on the wafer chip product, indicating that the photoresist removal in S8 and S9 was not thorough.

[0074] Comparative Example 4

[0075] Compared with Example 1, the difference is that after S7, S8 is not performed and the process directly enters S9.

[0076] Comparative Example 5

[0077] Compared with Example 1, the difference is that in S9, the time is 1 min.

[0078] The gold and tin components of wafer chip products were tested using XRF. The test results are shown in Table 1.

[0079] Comparative Example 6

[0080] Compared with Example 1, the difference is that in S9, the time is 2 minutes.

[0081] The gold and tin components of wafer chip products were tested using XRF. The test results are shown in Table 1.

[0082] Comparative Example 7

[0083] Compared with Example 1, the difference is that in S9, the power is 200 W.

[0084] The gold and tin components of wafer chip products were tested using XRF. The test results are shown in Table 1.

[0085] Example 2

[0086] Compared with Example 1, the difference is that in S9, argon is introduced instead of oxygen.

[0087] After dry Figure 6 ,Will Figure 6 and Figure 2 In contrast, surface dirt and small black spots still remain, and the removal efficiency is low. This is mainly because argon plasma mainly uses physical bombardment, which is effective for brittle or loose residual adhesive, but has limited effect on tightly chemically cross-linked photoresist and cannot decompose organic matter through oxidation reaction.

[0088] Example 3

[0089] Compared with Example 1, the difference is that in S9, in addition to oxygen, argon is also introduced, the oxygen flow rate is 80 sccm, and the argon flow rate is 20 sccm.

[0090] After dry Figure 7 ,Will Figure 7 and Figure 2 In comparison, there are no small black spots over a large area of ​​the surface, but due to insufficient oxygen content, the oxygen free radicals do not completely react with the organic components in the photoresist, and a small amount of residual glue still exists.

[0091] Comparing Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3, in the manufacture of wafer chip products with gold-tin patterns, in the photoresist stripping in the presence of gold-tin alloy, in the process of combined wet and dry stripping, under the conditions of dry process and other conditions such as stripping liquid, an ultrasonic current of 0.6 A can completely strip the photoresist, 1 A is the second best, and 0.2 A is the worst.

[0092] Table 1 Composition ratio of gold-tin alloy

[0093]

[0094] Comparing Example 1 with Comparative Examples 5 to 7, under the same conditions of thorough removal of the photoresist (i.e., the wet cleaning conditions remain unchanged), with other conditions unchanged, the tin content gradually increases with time at a small rate; with other conditions unchanged, when the power is doubled, the growth rate of the tin content increases. This shows that Example 1 ensures that the change in the gold-tin content is small and does not affect subsequent chip packaging, while also being able to completely remove the photoresist.

[0095] The present invention can not only completely remove the photoresist, but also ensure that the gold-tin content does not change much, and does not affect subsequent chip packaging.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for stripping a photoresist containing a gold-tin pattern, characterized in that: After the wafer is patterned by photolithography to form a gold-tin alloy layer, removing the photoresist includes the following steps: S8, immersed in acetone solution, ultrasonicated at 0.6 A current for 10 min to 30 min, immersed in isopropyl alcohol solution for 1 min to 10 min; S9, a plasma stripper is used to remove the photoresist to obtain a wafer chip product. The plasma stripper is vacuumed to 0.320 mbar, the power is 100 W, the oxygen flow rate is 100 sccm, and the time is 3 minutes; The gold-tin alloy is Au80Sn20 or Au75Sn25.

2. The method for stripping a photoresist containing a gold-tin pattern according to claim 1, wherein: In S8, the immersion in the acetone solution is divided into two immersions, and the acetone solution for each immersion is a newly prepared acetone solution.

3. The method for stripping a photoresist containing a gold-tin pattern according to claim 1, wherein: The photoresist is a negative photoresist.

4. The method for stripping a photoresist containing gold-tin patterns according to claim 1, wherein: The wafer is a four-inch alumina substrate or a four-inch aluminum nitride substrate.

5. A method for preparing a wafer chip containing a gold-tin pattern, characterized in that: The following steps are involved: S1, performing the first photolithography patterning on the wafer substrate; S2, sputtering a titanium layer, a platinum layer, and a gold layer in sequence to form an activated metal layer; S4, immerse in acetone solution, ultrasonicate at 0.2A~1A current for 10min~30min, immerse in isopropyl alcohol solution for 1min~10min; S5, performing a second photolithography patterning; S6, evaporation of gold-tin alloy; S8, immersed in acetone solution, ultrasonicated at 0.6 A current for 10 min to 30 min, immersed in isopropyl alcohol solution for 1 min to 10 min; S9, a plasma stripper is used to remove the photoresist to obtain a wafer chip product. The plasma stripper is vacuumed to 0.320 mbar, the power is 100 W, the oxygen flow rate is 100 sccm, and the time is 3 minutes; The gold-tin alloy is Au80Sn20 or Au75Sn25.

6. The method for preparing a wafer chip containing a gold-tin pattern according to claim 5, characterized in that: After S2 and before S4, S3 is also included, and a blue film is pasted to assist in removing the blue film of the photoresist and the blue film is torn off after the film is pasted; after S6 and before S8, S7 is also included, and a blue film is pasted to assist in removing the blue film of the photoresist and the blue film is torn off after the film is pasted.

7. The method for preparing a wafer chip containing a gold-tin pattern according to claim 5, wherein: In S8, the immersion in the acetone solution is divided into two immersions, and the acetone solution for each immersion is a newly prepared acetone solution.

8. The method for preparing a wafer chip containing a gold-tin pattern according to claim 5, wherein: The photoresist is a negative photoresist.

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