A method for fabricating a stepped metal bump structure

Abstract

This invention discloses a method for fabricating a stepped metal bump structure. The method involves depositing a metal seed layer on the first surface of a wafer; forming a first photoresist pattern on the surface of the metal seed layer through a first photoresist coating, exposure, and development process, with a first opening in the first photoresist pattern exposing the surface of the metal seed layer; forming a first metal structure through a first electroplating process within the first opening of the first photoresist pattern; removing the first photoresist layer; forming a second photoresist pattern on the surfaces of the metal seed layer and the first metal structure through a second photoresist coating, exposure, and development process, with a second opening in the second photoresist pattern exposing a portion of the surface of the metal seed layer; removing the exposed metal seed layer by wet etching; removing the second photoresist layer; and retaining the metal seed layer and the first metal structure to form a stepped metal structure. This invention simplifies the complex process of traditional multiple photolithography and electroplating steps, reduces production costs, minimizes environmental pollution, and improves production efficiency.

Description

Technical Field

[0001] This invention relates to the field of semiconductor packaging technology, and more specifically to a method for preparing a stepped metal bump structure. Background Technology

[0002] With the rapid development of microelectronics and semiconductor packaging technologies, the integration density of integrated circuit chips is constantly increasing, placing higher demands on wire bonding technology. In semiconductor packaging, electroplating is a key technology for fabricating metal electrodes and interconnects. However, traditional electroplating processes face numerous challenges when dealing with complex stepped structures. Typically, to fabricate metal electrodes thicker than 10 μm, a complex process involving multiple photolithography and electroplating steps is required, which not only increases production costs but may also lead to environmental pollution. These problems severely restrict the further development of semiconductor packaging technology, especially in advanced packaging fields requiring 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, high-bandwidth transmission across heterogeneous chips.

[0004] Existing bumps are mainly divided into two categories: solder ball bumps and copper pillar bumps. Compared with solder ball bumps, copper pillar bumps have smaller diameters and pitches, and their applications are becoming increasingly common, especially in high-density interconnects between high-density I / O chips such as HBM, CPU, DSP, and FPGA.

[0005] In conventional wafer-level fabrication of copper pillar bumps, the bump dimensions (diameter and height) are uniform. However, in actual production, some 3D packages have substrate surfaces that are not on the same plane, requiring the growth of bumps of varying sizes on the heterogeneous chips during subsequent flip-chip integration. Similarly, for wafer-level 3D integration where the substrates are not on the same surface, bumps of varying sizes need to be grown on the same wafer.

[0006] Existing technologies include methods for growing bumps of varying sizes on the same wafer:

[0007] Option 1: Incoming wafer - first sputtering - first photolithography - etching - second sputtering - second photolithography - electroplating.

[0008] Its disadvantages are that it involves two repeated sputtering processes, two photolithography processes, and then electroplating, making the process cumbersome and complex, and incurring high costs in terms of materials and time.

[0009] Option 2: Incoming wafer - first sputtering - first photolithography - first electroplating - second sputtering - second photolithography - second electroplating.

[0010] Its disadvantages are that it involves two repeated sputtering processes, two PR lithography processes, and two electroplating processes, making the process cumbersome and complex, and the cost of process materials and time is high.

[0011] Therefore, there is an urgent need for a new bump fabrication method that can simplify the process, reduce costs, and avoid environmental pollution, in order to meet the demand of modern semiconductor packaging for high-quality metal stepped bump structures. Summary of the Invention

[0012] To address the aforementioned issues, this invention provides a method for fabricating a stepped metal bump structure. This method employs a metal seed layer patterning combined with electroplating bumping to form the stepped bump structure. This overcomes the drawbacks of traditional techniques that require multiple photolithography and electroplating processes, reduces the number of photolithography and electroplating cycles, lowers production costs, and improves production efficiency. Simultaneously, it avoids the errors that may arise from multiple photolithography and electroplating processes in traditional methods, thereby enhancing product consistency and reliability.

[0013] On one hand, this invention discloses a method for preparing a stepped metal bump structure, the method comprising the following steps:

[0014] S1. Provide a wafer and deposit a metal seed layer on the first surface of the wafer;

[0015] S2. A first photoresist pattern is formed on the surface of the metal seed layer by coating a first layer of photoresist, exposure and development processes, and the first opening of the first photoresist pattern exposes the surface of the metal seed layer.

[0016] S3. A first metal structure is formed by electroplating within the first opening of the first photoresist pattern;

[0017] S4. Remove the first layer of photoresist, and form a second photoresist pattern on the surface of the metal seed layer and the first metal structure by applying a second layer of photoresist, exposure and development processes. The second opening of the second photoresist pattern exposes part of the surface of the metal seed layer; wherein, there is a second layer of photoresist between the second opening and the first metal structure.

[0018] 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.

[0019] Preferably, in step S1, a metal seed layer is deposited on the first surface of the wafer using a physical vapor deposition method.

[0020] Preferably, the metal seed layer includes an adhesive layer and a conductive layer arranged sequentially 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.

[0021] Preferably, the conductive layer of the metal seed layer is made of Cu.

[0022] Preferably, in step S2, a first layer of photoresist is spin-coated onto the surface of the metal seed layer at a spin speed of 2500-3500 r / min for 30-90 s, followed by pre-baking at 100℃ for 10-15 min, and exposure at 110-125 mJ / cm². 2 After baking at 100℃ for 1 min to 3 min, and developing for 30 s to 70 s, the first photoresist layer is 2 μm to 5 μm thick, thus creating the first photoresist pattern.

[0023] Preferably, the thickness of the first metal structure is 1μm-3μm.

[0024] Preferably, the method for removing the first / second layer of photoresist is a wet or dry photoresist removal process.

[0025] 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 preparation method are replaced with the following steps:

[0026] S4'. The first layer of photoresist is exposed and developed a second time to form a third photoresist pattern. The third opening of the third photoresist pattern exposes part of the surface of the metal seed layer, and the third opening is formed on the side of the first metal structure. The surface of the metal seed layer in the third opening and the surface of the first metal structure form a height difference.

[0027] S5', A second electroplating is performed 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 stepped shape. After removing the first layer of photoresist, the exposed metal seed layer is etched away.

[0028] Preferably, the first layer of photoresist is a positive photoresist.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] The method disclosed in this invention uses a metal seed layer patterning combined with electroplating bumping to form a stepped bump structure. 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.

[0031] The method disclosed in this invention only involves one sputtering operation, which simplifies the process flow and saves on process materials and time costs.

[0032] Meanwhile, the method disclosed in this invention also avoids the errors that may be caused by multiple photolithography and electroplating processes in traditional methods, thus improving the consistency and reliability of the product. Attached Figure Description

[0033] Figure 1 This is a flowchart illustrating the fabrication process of the stepped metal bump structure in Embodiment 1 of the present invention.

[0034] Figure 2 This is a schematic diagram of the wafer structure in Embodiment 1 of the present invention;

[0035] Figure 3 This is a schematic diagram of a wafer with a deposited metal seed layer in Embodiment 1 of the present invention;

[0036] Figure 4 This is a schematic diagram of the process flow for step S2 in Embodiment 1 of the present invention;

[0037] Figure 5 This is a schematic diagram of the process flow for step S3 in Embodiment 1 of the present invention;

[0038] Figure 6 This is a schematic diagram of the process flow for step S4 in Embodiment 1 of the present invention;

[0039] Figure 7 This is a schematic diagram of the process flow for step S5 in Embodiment 1 of the present invention;

[0040] Figure 8 This is a schematic diagram of forming a first photoresist pattern on a wafer in Embodiment 2 of the present invention;

[0041] Figure 9 This is a schematic diagram of the process flow for step S4' in Embodiment 2 of the present invention;

[0042] Figure 10 This is a schematic diagram of the process flow for step S5' in Embodiment 2 of the present invention;

[0043] Figure 11 This is a schematic diagram of the stepped metal bump structure in Embodiment 2 of the present invention.

[0044] Labeling: 1. Wafer; 101. First surface; 2. Metal seed layer; 3. First photoresist layer; 4. First photoresist pattern; 401. First metal structure; 5. Second photoresist layer; 6. Second photoresist pattern; 7. Second opening; 701. Third opening; 8. Second metal structure; 9. Detailed Implementation

[0045] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0046] Example 1

[0047] This embodiment discloses a method for fabricating a stepped metal bump structure. The method uses a patterned 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. This simplifies the complex process flow of traditional multiple photolithography and electroplating, reduces production costs, reduces environmental pollution, and improves production efficiency.

[0048] The process flow of this embodiment is as follows: Figure 1 As shown in the figure, Basic wafer 1 is the wafer 1. st Sputter is the first sputtering process, 1 st PR 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.

[0049] Specifically, the method includes the following steps:

[0050] S1, providing such Figure 2 The wafer 1 shown has a metal seed layer 2 deposited on its first surface 101, forming a structure as shown. Figure 3 The structure shown.

[0051] A metal seed layer 2 is deposited on the first surface 101 of wafer 1 using physical vapor deposition.

[0052] The metal seed layer 2 includes an adhesive layer and a conductive layer arranged sequentially 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. In this invention, the metal seed layer 2 uses Ti and Cu.

[0053] The thickness of the metal seed layer 2 is: 1000 Å for the Ti layer and 8000 Å for the Cu layer; the thickness of the metal seed layer 2 can be adjusted according to product and design requirements.

[0054] S2. A first photoresist pattern 4 is formed on the surface of the metal seed layer 2 by coating a first layer of photoresist 3, followed by exposure and development processes. 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 As shown.

[0055] A first layer of photoresist 3 was spin-coated onto the surface of the metal seed layer 2 at a spin speed of 2500 r / min - 3500 r / min for 30 s - 90 s. Pre-baking was performed at 100℃ for 10 s - 15 s, followed by exposure at 110 - 125 mJ / cm².2 After baking at 100℃ for 1-3 minutes, followed by development for 30-70 seconds, the thickness of the first photoresist layer 3 is 2μm-5μm, thus creating the first photoresist pattern 4. In actual operation, the thickness of the first photoresist layer 3 is determined according to the required height of the first metal structure 5 to be electroplated.

[0056] S3. A first metal structure 5 is formed by electroplating within the first opening 401 of the first photoresist pattern 4, as shown in the figure. Figure 5 As shown.

[0057] The thickness of the first metal structure 5 is 1μm-3μm. Specifically, during electroplating, a Ni layer and an Au layer can be selected, with the Ni layer being 1μm and the Au layer 0.5μm. This is only one embodiment provided by the present invention, and adjustments can be made according to actual needs.

[0058] The manufacturing method of the first metal structure 5 is the existing electroplating bumping technology. The size of the bumps is selected according to actual needs, which will not be elaborated here.

[0059] S4. Remove the first layer of photoresist 3, and form a second photoresist pattern 7 on the surfaces of the metal seed layer 2 and the first metal structure 5 by applying a second layer of photoresist 6, followed by exposure and development. The second opening 701 of the second photoresist pattern 7 exposes a portion of the surface of the metal seed layer 2. A second layer of photoresist 6 exists between the second opening 701 and the first metal structure 5, as shown in the specific structure below. Figure 6 As shown.

[0060] The second layer of photoresist 6 is reserved between the second opening 701 and the first metal structure 5 in order to reserve a part 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 part of the metal seed layer 2 is removed later, the reserved metal seed layer 2 and the first metal structure 5 can form a stepped metal structure.

[0061] S5. After removing the exposed metal seed layer 2 by wet etching, the second photoresist layer 6 is removed. The remaining metal seed layer 2 and the first metal structure 5 form a stepped metal structure, as shown in the schematic diagram below. Figure 7 As shown.

[0062] The method for removing the first and second layers of photoresist in this embodiment is either a wet or dry photoresist removal process, both of which are existing technologies and will not be described in detail here.

[0063] The method disclosed in this embodiment only requires one sputtering and one electroplating operation, which simplifies the process flow and saves on process materials and time costs.

[0064] Meanwhile, the method disclosed in this embodiment also avoids the errors that may be caused by multiple photolithography and electroplating processes in traditional methods, thus improving the consistency and reliability of the product.

[0065] Example 2

[0066] In the step-type metal bump structure fabrication method disclosed in this embodiment, steps S1 to S3 are the same as steps S1 to S3 in the fabrication method described in Example 1. In specific implementation, the thickness of the first photoresist layer can be set according to requirements and can be appropriately increased compared to Example 1. The electroplated first metal structure does not completely cover the first opening of the first photoresist pattern 4, forming a structure as shown in the figure. Figure 8 The structure shown.

[0067] In Example 1, steps S4 and S5 are replaced with the following steps:

[0068] S4'. A second exposure and development process is performed on the first photoresist layer 3 to form a third photoresist pattern. The third opening 8 of the third photoresist pattern exposes part 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. A height difference is formed between the surface of the metal seed layer 2 within the third opening 8 and the surface of the first metal structure 5. The specific structure is as follows: Figure 9 As shown.

[0069] S5', A second electroplating is performed on the surface of the metal seed layer 2 within the third opening 8 and the surface of the first metal structure 5 to form a second metal structure 9 with a stepped shape, the structure of which is as follows: Figure 10 As shown. Finally, after removing the first layer of photoresist 3, the exposed metal seed layer 2 is etched away, forming as shown. Figure 11 The stepped metal bump structure shown.

[0070] In this embodiment, the first layer of photoresist is a positive photoresist. Utilizing the properties of the positive photoresist (opening at the exposure location), the first layer of photoresist is patterned twice, optimizing the traditional process flow by eliminating steps such as electroplating-resist stripping, electroplating-etching, secondary sputtering, and secondary photoresist coating.

[0071] The preparation method in this embodiment only requires one sputtering and two photolithography processes on one photoresist, which simplifies the process flow and saves process materials and time costs.

[0072] The above descriptions are merely some embodiments of the present invention. It should be noted that those skilled in the art can make other modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for preparing a stepped metal bump structure, characterized in that, The method includes the following steps: S1. Provide a wafer and deposit a metal seed layer on the first surface of the wafer; S2. A first photoresist pattern is formed on the surface of the metal seed layer by coating a first layer of photoresist, exposure and development processes, and the first opening of the first photoresist pattern exposes the surface of the metal seed layer. S3. A first metal structure is formed by electroplating within the first opening of the first photoresist pattern; S4. Remove the first layer of photoresist, and form a second photoresist pattern on the surface of the metal seed layer and the first metal structure by applying a second layer of photoresist, exposure and development processes. The second opening of the second photoresist pattern exposes part of the surface of the metal seed layer; wherein, there is a second layer of photoresist 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 the first surface of the 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 sequentially 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 conductive layer of the metal seed layer is made of Cu.

5. The method according to claim 4, characterized in that, In step S2, a first layer of photoresist is spin-coated onto the surface of the metal seed layer at a spin speed of 2500-3500 r / min for 30-90 s, followed by pre-baking at 100℃ for 10-15 min and exposure at 110-125 mJ / cm. 2 After baking at 100℃ for 1 min to 3 min, and developing for 30 s to 70 s, the first photoresist layer is 2 μm to 5 μm thick, thus creating the first photoresist pattern.

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

7. The method according to any one of claims 1-6, characterized in that, The methods for removing the first and second layers of photoresist are either wet or dry photoresist removal processes.

8. The method according to claim 1, characterized in that, Replace steps S4 and S5 with the following steps: S4'. The first layer of photoresist is exposed and developed a second time to form a third photoresist pattern. The third opening of the third photoresist pattern exposes part of the surface of the metal seed layer, and the third opening is formed on the side of the first metal structure. The surface of the metal seed layer in the third opening and the surface of the first metal structure form a height difference. S5', A second electroplating is performed 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 stepped shape. After removing the first layer of photoresist, the exposed metal seed layer is etched away.

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

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