Preparation method of stepped metal bump structure

Abstract

The invention discloses a preparation method of a stepped metal bump structure. The method comprises the following steps: depositing a metal seed layer on a first surface of a wafer; forming a first photoresist pattern on the surface of the metal seed layer through a first layer of photoresist coating, exposure and development process, wherein a first opening of the first photoresist pattern exposes the surface of the metal seed layer; performing first electroplating in the first opening of the first photoresist pattern to form a first metal structure; the first layer of photoresist is removed, a second photoresist pattern is formed on the surface of the metal seed layer and the surface of the first metal structure through a second layer of photoresist coating, exposure and development process, and a second opening of the second photoresist pattern exposes part of the surface of the metal seed layer; after the exposed metal seed layer is removed through wet etching, the second layer of photoresist is removed, and the reserved metal seed layer and the first metal structure form a stepped metal structure. According to the method, the traditional complex technological process of multiple times of photoetching and electroplating is simplified, the production cost is reduced, the environmental pollution is reduced, and the production efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor packaging, and more particularly to a method for preparing a stepped metal bump structure. Background Art

[0002] With the rapid development of microelectronics and semiconductor packaging technology, the integration of integrated circuit chips has continued to increase, placing higher demands on wire bonding technology. In the semiconductor packaging process, electroplating is a key technology for preparing metal electrodes and interconnects. However, traditional electroplating processes present many challenges when dealing with complex step structures. Typically, in order to prepare metal electrodes with a thickness exceeding 10 μm, a complex process of multiple photolithography and electroplating is required, which not only increases production costs but can also cause environmental pollution. These problems have seriously restricted the further development of semiconductor packaging technology, especially in the field of advanced packaging that requires high density, short paths, and systematic integration.

[0003] Currently, wafer-level packaging technology has become a widely used packaging method due to its high packaging density, fast packaging speed and low packaging cost. High-density bumps are essential for achieving high-speed and high-bandwidth transmission of heterogeneous chips.

[0004] Existing bumps are mainly divided into two categories: solder ball bumps and copper pillar bumps. Compared to solder ball bumps, copper pillar bumps have a smaller diameter and pitch, and are increasingly used, especially in high-density interconnects between high-density I / O chips such as HBM, CPUs, DSPs, and FPGAs.

[0005] Conventional copper pillar bumps are fabricated at the wafer level, resulting in uniform bump sizes (diameter and height). However, in actual production, some 3D packages require bumps of varying sizes to be grown on heterogeneous chips during subsequent flip-chip integration because the substrate surfaces are not coplanar. Furthermore, for wafer-level 3D integration where the substrates are not coplanar, bumps of varying sizes must be grown on the same wafer.

[0006] In the prior art, there are the following solutions for growing bumps of different sizes on the same wafer: Solution 1: Incoming wafer - first sputtering - first photolithography - etching - second sputtering - second photolithography - electroplating.

[0007] Its disadvantage is that it requires two repeated sputtering operations, two photolithography operations, and then electroplating. The process flow is cumbersome and complicated, and the process material and time costs are high.

[0008] Solution 2: Incoming wafer - first sputtering - first photolithography - first electroplating - second sputtering - second photolithography - second electroplating.

[0009] Its disadvantage is that it requires two repeated sputtering operations, two PR lithography operations and two electroplating operations. The process flow is cumbersome and complicated, and the process material and time costs are high.

[0010] Therefore, there is an urgent need for a new bump preparation method that can simplify the process, reduce costs, and avoid environmental pollution to meet the needs of modern semiconductor packaging for high-quality metal step bump structures. Summary of the Invention

[0011] In order to solve the above problems, the present invention provides a method for preparing a stepped metal bump structure. The method adopts a method of combining metal seed layer patterning with electroplating bumping to form a stepped bump structure, which overcomes the shortcomings of traditional technology that requires multiple photolithography and electroplating, reduces the number of photolithography and electroplating cycles, reduces production costs, and improves production efficiency. At the same time, it avoids the errors that may be caused by multiple photolithography and electroplating in traditional methods, and improves product consistency and reliability.

[0012] In one aspect, the present invention discloses a method for preparing a stepped metal bump structure, the method comprising the following steps: S1. providing a wafer and depositing a metal seed layer on a first surface of the wafer; S2, forming a first photoresist pattern on the surface of the metal seed layer by coating a first layer of photoresist, exposing and developing the first photoresist pattern, wherein a first opening of the first photoresist pattern exposes the surface of the metal seed layer; S3, forming a first metal structure by electroplating in the first opening of the first photoresist pattern for the first time; S4, removing the first layer of photoresist, applying a second layer of photoresist on the surface of the metal seed layer and the first metal structure, and performing exposure and development processes to form a second photoresist pattern, wherein a second opening of the second photoresist pattern exposes a portion of the surface of the metal seed layer; wherein a second layer of photoresist exists between the second opening and the first metal structure; S5. After removing the exposed metal seed layer by wet etching, the second layer of photoresist is removed, and the remaining metal seed layer and the first metal structure form a stepped metal structure.

[0013] Preferably, in step S1 , a metal seed layer is deposited on the first surface of the wafer using a physical vapor deposition method.

[0014] Preferably, the metal seed layer includes an adhesive layer and a conductive layer arranged in sequence from bottom to top, the metal material of the adhesive layer is Ti, and the metal material of the conductive layer is any one or more combinations of Cr, Ni, Cu, Au or Al.

[0015] Preferably, the metal material of the conductive layer of the metal seed layer is Cu.

[0016] Preferably, in step S2, a first layer of photoresist is spin-coated on the surface of the metal seed layer at a spin speed of 2500-3500 r / min for 30s-90s, pre-baked at 100°C for 10 min-15 min, and exposed at 110-125 mJ / cm 2 , post-bake at 100℃ for 1 min-3min, develop for 30s-70s, the thickness of the first layer of photoresist is 2μm-5μm, and the first photoresist pattern is produced.

[0017] Preferably, the thickness of the first metal structure is 1 μm-3 μm.

[0018] Preferably, the method for removing the first photoresist layer / the second photoresist layer is a wet or dry stripping process.

[0019] On the other hand, the present invention also discloses a method for preparing a stepped metal bump structure, wherein steps S4 and S5 of the above-mentioned preparation method are replaced by the following steps: S4′, performing a second exposure and development process on the first layer of photoresist to form a third photoresist pattern, wherein a third opening of the third photoresist pattern exposes a portion of the surface of the metal seed layer, and the third opening is formed on a side of the first metal structure, and a height difference is formed between the surface of the metal seed layer in the third opening and the surface of the first metal structure; S5', performing a second electroplating on the surface of the metal seed layer in the third opening and the surface of the first metal structure to form a second metal structure with a step shape, removing the first layer of photoresist, and then etching to remove the exposed metal seed layer.

[0020] Preferably, the first layer of photoresist is a positive photoresist.

[0021] Compared with the prior art, the present invention has the following beneficial effects: In the method disclosed in the present invention, a method of forming a stepped bump structure by patterning a metal seed layer in combination with electroplating bumping is adopted, and the process flow is simplified to: sputtering-photolithography-electroplating-photolithography-etching; this simplifies the complex process flow of traditional multiple photolithography and electroplating, reduces production costs, reduces environmental pollution, and improves production efficiency.

[0022] In the method disclosed by the present invention, only one sputtering is performed, which simplifies the process flow and saves process materials and time costs.

[0023] At the same time, the method disclosed in the present invention also avoids the errors that may be caused by multiple photolithography and electroplating in traditional methods, thereby improving the consistency and reliability of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Flow chart of the preparation process of the stepped metal bump structure in Example 1 of the present invention; Figure 2 Schematic diagram of the structure of the wafer in Example 1 of the present invention; Figure 3 Schematic diagram of a wafer on which a metal seed layer is deposited in Example 1 of the present invention; Figure 4 Schematic diagram of the process flow of step S2 in Example 1 of the present invention; Figure 5 Schematic diagram of the process flow of step S3 in Example 1 of the present invention; Figure 6 Schematic diagram of the process flow of step S4 in Example 1 of the present invention; Figure 7 Schematic diagram of the process flow of step S5 in Example 1 of the present invention; Figure 8 is a schematic diagram of forming a first photoresist pattern on a wafer in embodiment 2 of the present invention; Figure 9 Schematic diagram of the process flow of step S4' in Example 2 of the present invention; Figure 10 Schematic diagram of the process flow of step S5' in Example 2 of the present invention; Figure 11 Schematic diagram of the stepped metal bump structure in Example 2 of the present invention.

[0025] Reference numerals: wafer 1; first surface 101; metal seed layer 2; first photoresist layer 3; first photoresist pattern 4; first opening 401; first metal structure 5; second photoresist layer 6; second photoresist pattern 7; second opening 701; third opening 8; second metal structure 9. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0027] Example 1 This embodiment discloses a method for preparing a stepped metal bump structure. The method uses patterning of a metal seed layer 2 combined with electroplating bumping to form a stepped bump structure. The process flow is simplified to: sputtering-photolithography-electroplating-photolithography-etching; it simplifies the complex process flow of traditional multiple photolithography and electroplating, reduces production costs, reduces environmental pollution, and improves production efficiency.

[0028] The process flow of this embodiment is as follows Figure 1 As shown in the figure, Basic wafer is wafer 1, 1 st Sputter is the first sputtering process, 1 stPR Photo is the first photolithography process, 1 st Planting is the first electroplating process, 2 nd PR Photo is the second photolithography process, and Etch Bumping is the etching bump process.

[0029] Specifically, the method includes the following steps: S1、Provide Figure 2 The wafer 1 shown in FIG. 1 has a metal seed layer 2 deposited on the first surface 101 of the wafer 1 to form a Figure 3 The structure shown.

[0030] A metal seed layer 2 is deposited on the first surface 101 of the wafer 1 by using a physical vapor deposition method.

[0031] The metal seed layer 2 includes an adhesive layer and a conductive layer arranged in sequence from bottom to top. The metal material of the adhesive layer is Ti, and the metal material of the conductive layer is any one or more of Cr, Ni, Cu, Au or Al. In the present invention, the metal seed layer 2 is made of Ti and Cu.

[0032] The thickness of the metal seed layer 2 is: 1000A for the Ti layer and 8000A for the Cu layer. The thickness of the metal seed layer 2 can be adjusted according to product and design requirements.

[0033] S2, a first layer of photoresist 3 is applied to the surface of the metal seed layer 2, and a first photoresist pattern 4 is formed by exposure and development process. The first opening 401 of the first photoresist pattern 4 exposes the surface of the metal seed layer 2. The specific structure is as follows Figure 4 shown.

[0034] Spin-coat the first layer of photoresist 3 on the surface of the metal seed layer 2 at a spin speed of 2500 r / min-3500 r / min for 30s-90s, pre-bake at 100°C for 10 min-15 min, and expose at 110-125 mJ / cm 2 , post-baking at 100°C for 1-3 minutes, developing for 30-70 seconds, and forming a first photoresist layer 3 with a thickness of 2μm-5μm to produce a first photoresist pattern 4. In actual operation, the thickness of the first photoresist layer 3 is determined according to the height requirement of the first metal structure 5 to be electroplated.

[0035] S3, forming a first metal structure 5 by electroplating in the first opening 401 of the first photoresist pattern 4 for the first time, the structure is as follows Figure 5 shown.

[0036] The thickness of the first metal structure 5 is 1 μm-3 μm. When electroplating, a Ni layer and an Au layer can be selected, with a Ni layer of 1 μm and an Au layer of 0.5 μm. This is only one embodiment provided by the present invention and can be adjusted according to actual needs.

[0037] The manufacturing method of the first metal structure 5 is the existing electroplating bumping technology. The size of the bump is selected according to actual needs and will not be described in detail here.

[0038] S4, remove the first layer of photoresist 3, apply a second layer of photoresist 6 on the surface of the metal seed layer 2 and the first metal structure 5, and form a second photoresist pattern 7 through exposure and development processes, and the second opening 701 of the second photoresist pattern 7 exposes a portion of the surface of the metal seed layer 2; wherein, there is a second layer of photoresist 6 between the second opening 701 and the first metal structure 5, and the specific structure is as follows Figure 6 shown.

[0039] The second layer of photoresist 6 is reserved between the second opening 701 and the first metal structure 5 in order to reserve a portion of the metal seed layer 2 at the edge of the first metal structure 5. After the second layer of photoresist 6 on the surface of the portion of the metal seed layer 2 is removed later, the retained metal seed layer 2 and the first metal structure 5 can form a stepped metal structure. S5, after removing the exposed metal seed layer 2 by wet etching, the second photoresist layer 6 is removed, and the remaining metal seed layer 2 and the first metal structure 5 form a stepped metal structure, the structural diagram of which is shown in FIG. Figure 7 shown.

[0040] The method for removing the first photoresist layer and the second photoresist layer in this embodiment is a wet or dry stripping process, both of which are existing technologies and will not be described in detail here.

[0041] In the method disclosed in this embodiment, only one sputtering and one electroplating are performed, which simplifies the process flow and saves process materials and time costs.

[0042] At the same time, the method disclosed in this embodiment also avoids the errors that may be caused by multiple photolithography and electroplating in traditional methods, thereby improving the consistency and reliability of the product.

[0043] Example 2 In the method for preparing the stepped metal bump structure disclosed in this embodiment, steps S1 to S3 are the same as steps S1 to S3 in the method for preparing the step-type metal bump structure described in Example 1. In specific implementation, the thickness of the first layer of photoresist can be set as required and can be appropriately thickened compared to Example 1. The first metal structure electroplated does not completely cover the first opening of the first photoresist pattern 4, forming a Figure 8 The structure shown.

[0044] In Example 1, steps S4 and S5 are replaced by the following steps: S4', perform a second exposure and development process on the first layer of photoresist 3 to form a third photoresist pattern, wherein the third opening 8 of the third photoresist pattern exposes a portion of the surface of the metal seed layer 2, and the third opening 8 is formed on the side of the first metal structure 5, and a height difference is formed between the surface of the metal seed layer 2 in the third opening 8 and the surface of the first metal structure 5. The specific structure is as follows: Figure 9 shown.

[0045] S5', a second electroplating is performed on the surface of the metal seed layer 2 in the third opening 8 and the surface of the first metal structure 5 to form a second metal structure 9 with a step shape, the structure of which is as follows: Figure 10 Finally, after removing the first layer of photoresist 3, the exposed metal seed layer 2 is etched away to form Figure 11 The stepped metal bump structure shown.

[0046] In this embodiment, the first layer of photoresist is a positive photoresist. Leveraging the properties of positive photoresist (openings at the exposure locations), the first layer of photoresist is patterned twice, eliminating the traditional process steps of plating-stripping, plating-etching, sputtering, and PR coating.

[0047] The preparation method of this embodiment only performs one sputtering and performs two photolithography processes on one photoresist, which simplifies the process flow and saves process materials and time costs.

[0048] The above are only some embodiments of the present invention. It should be pointed out that for ordinary technicians in this field, other variations and improvements can be made without departing from the creative concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a stepped metal bump structure, characterized in that: The method comprises the following steps: S1. providing a wafer and depositing a metal seed layer on a first surface of the wafer; S2, forming a first photoresist pattern on the surface of the metal seed layer by coating a first layer of photoresist, exposing and developing the first photoresist pattern, wherein a first opening of the first photoresist pattern exposes the surface of the metal seed layer; S3, forming a first metal structure by electroplating in the first opening of the first photoresist pattern for the first time; S4, removing the first layer of photoresist, applying a second layer of photoresist on the surface of the metal seed layer and the first metal structure, and performing exposure and development processes to form a second photoresist pattern, wherein a second opening of the second photoresist pattern exposes a portion of the surface of the metal seed layer; wherein a second layer of photoresist exists between the second opening and the first metal structure; S5. After removing the exposed metal seed layer by wet etching, the second layer of photoresist is removed, and the remaining metal seed layer and the first metal structure form a stepped metal structure.

2. The method according to claim 1, characterized in that In step S1 , a metal seed layer is deposited on a first surface of a wafer using a physical vapor deposition method.

3. The method according to claim 2, characterized in that The metal seed layer includes an adhesive layer and a conductive layer arranged in sequence from bottom to top. The metal material of the adhesive layer is Ti, and the metal material of the conductive layer is any one or more combinations of Cr, Ni, Cu, Au or Al.

4. The method according to claim 3, characterized in that The metal material of the conductive layer of the metal seed layer is Cu.

5. The method according to claim 4, characterized in that In step S2, the first layer of photoresist is spin-coated on the surface of the metal seed layer at a speed of 2500-3500 r / min for 30s-90s, pre-baked at 100°C for 10 min-15 min, and exposed at 110-125 mJ / cm 2 , post-bake at 100℃ for 1 min-3min, develop for 30s-70s, the thickness of the first layer of photoresist is 2μm-5μm, and the first photoresist pattern is produced.

6. The method according to claim 5, characterized in that The thickness of the first metal structure is 1 μm-3 μm.

7. The method according to any one of claims 1 to 6, characterized in that The method for removing the first layer of photoresist and the second layer of photoresist is a wet or dry stripping process.

8. The method according to claim 1, characterized in that Replace steps S4 and S5 with the following steps: S4′, performing a second exposure and development process on the first layer of photoresist to form a third photoresist pattern, wherein a third opening of the third photoresist pattern exposes a portion of the surface of the metal seed layer, and the third opening is formed on a side of the first metal structure, and a height difference is formed between the surface of the metal seed layer in the third opening and the surface of the first metal structure; S5', performing a second electroplating on the surface of the metal seed layer in the third opening and the surface of the first metal structure to form a second metal structure with a step shape, removing the first layer of photoresist, and then etching to remove the exposed metal seed layer.

9. The method according to claim 8, characterized in that The first layer of photoresist is a positive photoresist.

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