A method for manufacturing a copper foil sheet metal closure structure

Abstract

The application provides a preparation method of a copper foil metal cover structure, which comprises the following steps: S1, substrate selection; S2, cleaning; S3, photoetching; S4, electroplating; S5, glue removal; S6, secondary electroplating; S7, wet etching; and S8, using a chisel-off machine to chisel off the metal cover substrate to form an independent microstructure device. The application solves the stability problem of the Cu foil metal cover ultra-small microstructure process, improves the control precision of key process parameters of the metal cover preparation, the qualified rate of the microstructure preparation and the production capacity of the device, and has the advantages of low implementation cost and the like.

Description

Technical fields: This invention relates to the field of microwave radio frequency technology, specifically to a method for fabricating a copper foil metal capping structure for millimeter-wave avalanche diodes. Background technology: Avalanche diodes, a new type of microwave semiconductor power device developed from the mid-1960s, are officially called impact-ionization avalanche transit-time diodes (IMPATT). They are negative-resistance active devices with phase delay caused by the avalanche multiplication effect and transit-time effect. The working principle of IMPATT diodes utilizes the interaction between the impact ionization of charge carriers (electrons and holes) and transit time in the semiconductor device structure, enabling the diode to generate significant microwave power output at very high frequencies. IMPATT diodes have higher power levels than other types of diodes, such as silicon-based microwave transistors, gallium arsenide and indium phosphide Gunn bulk effect diodes, silicon-based CMOS devices, and compound semiconductor HEMT devices, at frequencies above 60 GHz up to 400 GHz. Currently, silicon-based avalanche diodes can oscillate over the entire millimeter-wave band from 30 to 300 GHz, with the highest oscillation frequency currently exceeding 400 GHz.

[0003] Metal caps provide hermetic sealing for devices, protecting them from oxidation by the external environment that could affect their electrical performance. Simultaneously, they serve as the input terminal for DC power supply, necessitating the rigidity of the metal cap. The fabrication of the microstructure layer of the metal cap is a critical process in cap manufacturing, requiring compliance with requirements for sealing welding, DC power supply, and capacitance / inductance.

[0004] Currently, the problems in capping preparation are: (1) Due to the small size of the cap, machining is difficult, and a large amount of oil stains are present on the surface during machining, which makes it impossible to apply adhesive in the photolithography process; the acetone cleaning method used in the existing technology cannot completely remove the oil, resulting in poor adhesion of the photoresist, which leads to drilling and etching in the subsequent process, incomplete structure, and the gold layer cannot adhere or has poor adhesion during the subsequent electroplating process, making it easy to fall off; (2) The etching rate is uncontrollable and the uniformity is poor when using dry etching for capping patterning process. After etching, the line morphology is not good and the line width accuracy is difficult to control; (3) If the dry etching method is used, even if the line morphology and line width accuracy can meet the technical requirements, the independent microstructure cannot be released, which seriously leads to the inability to produce the device in the subsequent assembly process. Summary of the Invention: The present invention aims to overcome the shortcomings of the prior art and provide a method for preparing a copper foil sheet metal capping structure.

[0006] This application provides the following technical solution: A method for preparing a copper foil sheet metal cap structure, characterized in that it includes the following steps: S1, substrate selection: selecting a copper foil disc with a diameter of 6 inches and a thickness of 2 mm as the substrate; S2. Cleaning: The substrate is polished with magnesium oxide powder, then placed in a solution of chromic acid, sulfuric acid and water in a ratio of 0.1:0.01:1 for cleaning. After cleaning, it is taken out, rinsed with water, and spun dry to complete the cleaning process. S3. Photolithography: HMDS is used to enhance the adhesion of the copper foil surface. Then, positive photoresist is spin-coated to a thickness of 1.0±0.1μm. The copper foil disc is then pre-baked in an oven. The photomask is then used to pattern-register and expose the copper foil disc on the photolithography machine. The surface of the copper foil disc is then developed. Finally, the copper foil disc is post-baked in an oven, thereby forming a prominent photolithographic pattern on the surface of the copper foil disc, completing the photolithography step. S4. Electroplating: The copper foil disc is placed in the electroplating equipment and gold electroplating process is used to form metal protrusions on the upper surface of the copper foil disc outside the photolithographic pattern, thus completing the electroplating step. S5. Resin Removal: Place the copper foil disc into an organic cleaning wet table to remove the photolithographic pattern on the surface of the copper foil disc, then clean it, and then dry it to complete the resist removal step. S6. Secondary electroplating: The copper foil disc is placed in the electroplating equipment and a gold film layer is prepared on the lower surface of the copper foil disc using the gold electroplating process, thus completing the secondary electroplating step; S7. Wet etching: Place the copper foil disc into a chemical etching wet table and etch a groove on the upper surface between the metal bosses. After etching, clean it and then dry it to complete the wet etching step. S8. Forming: Place the copper foil sheet on the support table of the chisel-separating machine and output pressure of 1000N to chisel away the metal cover substrate to form an independent microstructure device.

[0007] Based on the above technical solutions, the following further technical solutions are also possible: The cleaning processes in S2, S5, and S7 all use deionized water with a resistivity ≥15 MΩ·cm.

[0008] The purity of magnesium oxide powder in S2 is 98%; the amount of chromic acid 3 used is 100ml with a concentration of 99.70%; the amount of sulfuric acid used is 10ml with a concentration of 93.5-95.6%; and the amount of water used is 1L.

[0009] In S4 and S6, the metal protrusions and gold film layers are made of the same material, gold, with the same thickness of 24 μm ± 2 μm, and are prepared using the same parameters: a current density of 0.25 A / dm³.2 The flow rate of the plating solution was 12L / min, and the electroplating time was 6450s.

[0010] The corrosion solution used in the S7 chemical corrosion wet bench is prepared by mixing 99.90% acetic acid, 70% nitric acid, and 87% phosphoric acid in a ratio of 0.125:0.1:0.275.

[0011] Advantages of the invention: This invention has simple steps and is easy to implement. It solves the stability problem of the ultra-small microstructure process of Cu foil metal capping. It has the advantages of improving the control accuracy of key process parameters in metal capping preparation, the yield rate of microstructure preparation and device production capacity, and low implementation cost. Attached image description: Figure 1 This is a diagram showing the result after completing step S3; Figure 2 This is a diagram showing the result after completing step S4; Figure 3 This is a diagram showing the result after completing step S5; Figure 4 This is a diagram showing the result after completing step S6; Figure 5 This is a diagram after completing step S7. Detailed implementation method: like Figure 1-5 As shown, a method for preparing a copper foil sheet metal cap structure is characterized by the following steps: S1, substrate selection: a copper foil disc with a diameter of 6 inches and a thickness of 2 mm is selected as substrate 1.

[0014] S2. Cleaning: At room temperature, use 98% pure magnesium oxide powder to polish substrate 1. After cleaning, immerse it in a solution of 100ml of 99.70% chromic acid, 10ml of 93.5-95.6% sulfuric acid and 1L of water in a ratio of 0.1:0.01:1 for etching and acid washing until the copper foil of the substrate changes color to light reddish copper. Then remove it and rinse it with deionized water with a resistivity ≥15MΩ.cm. Finally, spin dry it to complete the cleaning step.

[0015] S3. Photolithography: To ensure adhesion between the photoresist and the substrate, HMDS is used to enhance adhesion on the upper surface of the substrate. Then, a positive photoresist is spin-coated onto the upper surface of the substrate to form a 1.0±0.1μm thick layer (not shown in the figure). The copper foil wafer is then pre-baked in an oven at 90±5℃ for 10±2 minutes. Finally, the photomask is used on the photolithography machine to perform pattern registration and exposure on the copper foil wafer, with an registration accuracy of ±0.05μm.

[0016] The surface of the copper foil disc is then developed using a 5% KOH solution at a temperature of 25±1℃ for 1±0.1 min. After rinsing with deionized water with a resistivity ≥15 MΩ·cm, the disc is centrifuged and dried. Finally, substrate 1 is placed in an oven for post-baking. The substrate 1 is sequentially placed in the oven at the following temperatures: first zone (120±5)℃, second zone (130±5)℃, and third zone (150±5)℃, for a total post-baking time of 20±2 min. This forms a prominent photolithographic pattern 2 on the surface of substrate 1, completing the photolithography step.

[0017] S4. Electroplating: The substrate 1 is placed in an electroplating machine and gold electroplating is used to form gold metal protrusions 3 on the surface of the substrate 1 outside the photolithographic pattern 2. The thickness of the metal protrusions 3 is 24μm±2μm, and the current density during electroplating is 0.25A / dm³. 2 The plating solution flow rate was 12L / min, and the electroplating time was 6450s to complete the electroplating step.

[0018] S5. Adhesive Removal: Substrate 1 is placed in the cleaning tank of the organic cleaning wet bench and immersed in the cleaning solution. The cleaning solution is a mixture of 99.90% dimethylformamide and 99.90% monoethanolamine in a (1:1) ratio. The cleaning solution is heated to 120±5℃, and the immersion time is 15±1 min. After cleaning, substrate 1 is removed and rinsed with deionized water with a resistivity ≥15MΩ·cm. Then, it is centrifuged and dried to complete the adhesive removal step.

[0019] S6. Secondary Electroplating: The substrate 1 is placed in an electroplating device and a gold electroplating process is used to prepare a gold film layer 4 on the lower surface of the substrate 1, thereby forming a metal bonding surface. The current density during electroplating is 0.25 A / dm³. 2 The plating solution flow rate was 12L / min, and the electroplating time was 6450s, completing the second electroplating step.

[0020] S7. Wet etching: At room temperature, the substrate 1 is immersed in the etching solution in the etching tank of the chemical etching wet table. The etching solution is a mixture of 99.90% acetic acid, 70% nitric acid, and 87% phosphoric acid in a ratio of 0.125:0.1:0.275.

[0021] A groove 5 was etched into the upper surface between the metal bosses 3. The depth of the groove 5 was 20 μm ± 2 μm, and the etching rate was 2000 Å / min. After etching, the substrate 1 was removed, rinsed with deionized water with a resistivity ≥15 MΩ·cm, and then centrifuged and dried to complete the wet etching step.

[0022] S8. Forming: Place the substrate 1 on the receiving table of the chisel machine and output pressure of 1000N to chisel away the metal cap substrate to form an independent microstructure device.

Claims

1. A method for preparing a copper foil sheet metal capping structure, characterized in that: It includes the following steps: S1, substrate selection: select a copper foil disc as the substrate (1). S2. Cleaning: The substrate is polished with magnesium oxide powder, then placed in a solution of chromic acid, sulfuric acid and water in a ratio of 0.1:0.01:1 for cleaning. After cleaning, it is taken out, rinsed with water, and spun dry to complete the cleaning process. S3, Photolithography: HMDS is used to enhance the adhesion of the copper foil surface, and then positive photoresist is spin-coated with a thickness of 1.0±0.1μm. Then, the copper foil disc is pre-baked in an oven. Then, the photolithography mask is used to pattern-register and expose the copper foil disc on the photolithography machine. Then, the surface of the copper foil disc is developed. Finally, the substrate (1) is post-baked in an oven, thereby forming a prominent photolithographic pattern (2) on the surface of the substrate (1), thus completing the photolithography step. S4. Electroplating: The substrate (1) is placed in the electroplating equipment and gold electroplating process is used to form metal bosses (3) on the upper surface of the substrate (1) outside the photolithographic pattern (2) to complete the electroplating step. S5. Resin removal: The photolithographic pattern (2) on the upper surface of the substrate (1) is removed by placing the substrate (1) into an organic cleaning wet table, then cleaning it, and then drying it to complete the resist removal step. S6. Secondary electroplating: The substrate (1) is placed in the electroplating equipment and a gold film layer (4) is prepared on the lower surface of the substrate (1) using the gold electroplating process to complete the secondary electroplating step; S7. Wet etching: Place the substrate (1) in a chemical etching wet table and etch a groove (5) on the upper surface between the metal bosses (3). After etching, clean it and then dry it to complete the wet etching step. S8. Forming: Place the copper foil sheet on the support table of the chisel-off machine and output pressure of 1000N to chisel off the metal cover substrate to form an independent microstructure device. The cleaning processes in S2, S5 and S7 all use deionized water, and the resistivity of the deionized water is ≥15MΩ.cm. The purity of the magnesium oxide powder in S2 is 98%; the amount of chromic acid used is 100 ml with a concentration of 99.70%; the amount of sulfuric acid used is 10 ml with a concentration of 93.5-95.6%; and the amount of water used is 1 L.

2. The method for preparing a copper foil sheet metal capping structure according to claim 1, characterized in that: The metal protrusions (3) and gold film layer (4) formed in S4 and S6 are made of the same material, gold, with the same thickness of 24μm±2μm, and are prepared using the same parameters, with a current density of 0.25A / dm. 2 The flow rate of the plating solution was 12L / min, and the electroplating time was 6450s.

3. The method for preparing a copper foil sheet metal capping structure according to claim 1, characterized in that: The corrosion solution used in the S7 chemical corrosion wet bench is prepared by mixing 99.90% acetic acid, 70% nitric acid, and 87% phosphoric acid in a ratio of 0.125:0.1:0.275.

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