A method for preparing a protective layer for the junction morphing mesa of a semiconductor chip

Abstract

A method for preparing a protective layer for the junction termination of a semiconductor chip addresses the problems of existing technologies, such as simple processes, thin and uneven protective layers, irregular shapes, air inclusions leading to weak adhesion, and insufficient moisture resistance, corrosion resistance, shock resistance, high insulation, and oxidation resistance. This invention utilizes the properties of cured silicone rubber, including moisture resistance, corrosion resistance, shock resistance, high insulation, high temperature resistance, and strong adhesion. By introducing high-vacuum degassing technology, elastic plastic sealing technology, high-temperature preliminary curing, and high-temperature high-vacuum full curing, the organic components in the silicone rubber are fully volatilized, transforming its linear structure into a network structure. This makes the silicone rubber more chemically stable and fully leverages its unique properties to protect the junction termination of the semiconductor chip, increasing the blocking voltage of the semiconductor chip from 3000V to over 8500V, significantly improving the chip's blocking voltage capability.

Description

Technical Field

[0001] This invention relates to the field of semiconductor design and manufacturing technology, and specifically to a method for preparing a protective layer for the junction termination surface of a semiconductor chip. Background Technology

[0002] As is well known, every practical device has a PN junction termination. When the PN junction is suddenly interrupted from the external environment, the electric field (commonly known as the surface electric field) in the junction termination region suddenly concentrates, leading to a decrease in the surface breakdown voltage. Therefore, the breakdown voltage of the junction termination region is often lower than that of the bulk planar junction. Junction termination mesa is a specially designed surface to reduce the concentration of the local electric field on the surface, increase the surface breakdown voltage, and make the actual breakdown voltage of the device closer to that of the bulk planar junction. If the junction termination mesa is exposed to the outside environment without protection, it easily attracts charged ions from the air, increasing the leakage current on the junction termination surface and reducing the breakdown voltage. Therefore, effective protection of the junction termination mesa is essential.

[0003] Silicone rubber material is composed of high molecular weight dimethyl polysiloxane with a molecular weight of over 800,000. Its structure is similar to that of silicon. It has the functions of moisture resistance, corrosion resistance, shock resistance, high insulation, high temperature resistance, and strong adhesion. In addition, its shrinkage rate during curing is extremely small, so it is particularly suitable for deep potting insulation protection material for electronic components.

[0004] The existing technology is spin coating + high-temperature curing, such as Figure 1 As shown, the semiconductor chip 1 is placed on the stage S1 and rotated. Liquid silicone rubber is squeezed and applied to the stage 4 of the semiconductor chip 1. Then, it is cured at high temperature to become a chemically stable silicone rubber 5. The silicone rubber 5 has the properties of moisture resistance, corrosion resistance, shock resistance, high insulation and high adhesion to protect the terminal shaping stage 4 from the erosion of pollutants in the external environment.

[0005] like Figure 2 As shown, Figure 1 Along the structural diagram of A-A', the semiconductor chip 1 and the molybdenum sheet 2 are bonded together at high temperature by the aluminum foil 3, which protects and supports the semiconductor chip 1 and facilitates the shaping of the mesa 4 at the semiconductor chip junction terminal and other process operations. Figure 1 As shown, the rotating stage S1 slot is secured to the edge of the molybdenum sheet 2, and its height cannot exceed the thickness of the molybdenum sheet 2; otherwise, the protective layer of the silicone rubber 5 will be torn when the chip is removed after the silicone rubber 5 is fully coated. It is evident that the protective layer of the silicone rubber 5 obtained by the rotary coating method suffers from uneven thickness, irregular shape, and the potential for air pockets within the adhesive, resulting in deficiencies in insulation strength, oxidation resistance, corrosion resistance, and adhesion.

[0006] It is evident that the spin coating method combined with high-temperature curing is simple, but the protective layer is thin, uneven in thickness, and irregular in shape. Air pockets are easily trapped within the adhesive, resulting in weak adhesion and limited moisture resistance, corrosion resistance, shock resistance, high insulation, and oxidation resistance. Currently, it can only protect semiconductor chips with voltages below 3000V. Summary of the Invention

[0007] To overcome the problems of existing technologies, such as simple process, thin and uneven protective layer, irregular shape of protective layer, easy presence of air in the adhesive, resulting in weak adhesion, poor moisture resistance, corrosion resistance, shock resistance, high insulation and oxidation resistance.

[0008] This invention provides a method for preparing a protective layer for the junction termination mesa of a semiconductor chip, the method comprising:

[0009] Step 1: After the semiconductor chip terminal is shaped, immerse it in ACF cleaning solution to clean it, and then place it in a clean oven to dry.

[0010] Step 2: Pour the raw material silicone rubber into a stainless steel storage tank H, seal it and perform vacuum treatment to remove the air mixed in during the pouring process into the stainless steel storage tank H, which would affect the performance of the silicone rubber.

[0011] Step 3: Assemble the mold M and the sealing material T1 together using the circular plate Y, and fix them to the inner wall of the cylindrical stainless steel N using screws L.

[0012] Step 4: Place the semiconductor chip in the center of the mold M and the sealing material T1, cover the mold and the special sealing material T1, and apply pressure P, which is 30±5KN. At this time, the sealing material T1 below the mold M, the edge of the semiconductor chip 1, the sealing material T1 above the upper mold M, and the inner wall of the cylindrical stainless steel N form a sealed cavity Q1.

[0013] Step 5: Open the B vent valve and inject nitrogen under high pressure. Press the silicone rubber into the cavity Q1 through the pipe G. Inject the silicone rubber from the left injection port Z1 and let it out from the right overflow port Z2 for at least 5 seconds. After the air in the cavity Q1 is purged, first block the right outlet Z2 and then inject the silicone rubber again under high pressure from the left injection port Z1. The purpose is to increase the density of the silicone rubber in the cavity.

[0014] Step 6: Heat the cylindrical stainless steel N to initially solidify the silicone rubber surface, making it easier to remove the semiconductor chip from the mold M;

[0015] Step 7: Remove the semiconductor chip with the preliminary cured protective layer from the mold M and place it in an oven for complete curing. This evaporates the volatile organic compounds in the silicone rubber, causing the silicone rubber to change from a liquid to a solid state, thus stabilizing the chemical properties of the silicone rubber protective layer.

[0016] The protective layer of the silicone rubber is composed of polysiloxane with a molecular weight of 80±10,000 molar units. The height h1 of the upper surface is 8±1 cm; the width w1 is 10±1 cm; the height h2 of the sidewall is 13±1 cm; and the width w2 of the lower surface is 3±1 cm.

[0017] The final adhesive strength of the protective layer of the silicone rubber is greater than 5±1N; the tensile strength of the silicone rubber is greater than 20±2MPa; the hardness is 30±2ShoreA; and the insulation strength is greater than 15±1kv / mms.

[0018] The sealing material T1 is made of polytetrafluoroethylene, with a polished surface and coated with a non-adhesive chemical film. The material is a Teflon coating with a film thickness of 2.0±0.5μm. The circular plate Y is compatible with the sealing material T1.

[0019] The cleanroom drying oven achieves a cleanliness level of ISO CLASS 1 and a temperature of 250±2℃.

[0020] The vacuum treatment achieves a high vacuum level of 1.5 × 10⁻⁶. -1 Pa, evacuate for 30-50 minutes.

[0021] The cylindrical stainless steel N is heated to a temperature of 175±5℃ for a time of 5±2min.

[0022] The oven temperature and baking time are 240℃ / 24h, and the vacuum degree is 2.0×10⁻⁶. -2 Pa.

[0023] The pressure for re-injecting glue at the left-end glue injection port Z1 is 1.5 × 10⁻⁶. +1 Pa.

[0024] The present invention has the following beneficial effects:

[0025] 1. This invention utilizes the principles of moisture-proof, corrosion-proof, shock-proof, high insulation, high temperature resistance, and strong adhesion of cured silicone rubber. By carefully studying and improving the process technology, and introducing high vacuum degassing technology, the air content in silicone rubber is greatly reduced, thereby improving the insulation strength, oxidation resistance, and corrosion resistance of silicone rubber.

[0026] 2. This invention introduces a special material sealing process, which not only prevents the mold from leaking during high-pressure injection, but also improves the density of the silicone rubber, and makes the silicone rubber regular, uniform, and with a thick protective layer, thus improving the protective effect.

[0027] 3. This invention introduces a special material polishing process and a non-stick film coating process, which ensures that the shape of the silicone rubber protective layer is not damaged when the chip is removed after the silicone rubber has been initially cured in the mold, thus guaranteeing quality and improving work efficiency.

[0028] 4. This invention introduces a high-temperature, high-vacuum curing process, which allows the organic components in the silicone rubber to fully volatilize, transforming the linear structure into a network structure. This makes the chemical properties of the silicone rubber more stable and fully utilizes its moisture-proof, corrosion-proof, shock-proof, high insulation, and high adhesion properties. It protects the semiconductor chip junction terminal surface, increasing the blocking voltage capability of the semiconductor chip from 3000V to over 8500V. This significantly improves the blocking voltage capability of the semiconductor chip, while reducing leakage current at the blocking voltage, improving the consistency of device parameters, and increasing the yield.

[0029] 5. Practice has also proven that for chips below 3000V, the yield of the silicone rubber protective layer prepared by this invention is at least 20% higher than that prepared by the traditional coating method. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of an existing spin coating method.

[0031] Figure 2 It is a semiconductor chip protected by the existing spin coating method.

[0032] Figure 3 This is a schematic diagram of the high-temperature and high-pressure injection method of the present invention.

[0033] Figure 4 yes Figure 3 A magnified view of a portion of the image.

[0034] Figure 5 This is a schematic diagram of the silicone rubber protective layer structure of the semiconductor chip of the present invention.

[0035] The following are the symbols and their meanings: 1. Semiconductor chip; 2. Molybdenum sheet; 3. Aluminum foil; 4. Mesh surface; 5. Silicone rubber. Detailed Implementation

[0036] This embodiment provides a method for preparing a protective layer for the junction termination mesa of a semiconductor chip, including the following steps:

[0037] Step 1: After the semiconductor chip terminal mesa 4 is shaped, immerse it in ACF cleaning solution to clean it, and then place it in a clean oven to dry.

[0038] Step 2: Pour the raw material silicone rubber 5 into the stainless steel storage tank H, seal it and perform vacuum treatment to remove the air mixed in during the pouring process of silicone rubber 5 into the stainless steel storage tank H, which would affect the performance of silicone rubber 5.

[0039] Step 3: Assemble the mold M and the sealing material T1 together using the circular plate Y, and fix them to the inner wall of the cylindrical stainless steel N using screws L.

[0040] Step four, as Figure 4The semiconductor chip 1 is placed in the center of the mold M and the sealing material T1. The mold and the special sealing material T1 are covered and pressure P is applied. The pressure is 30±5KN. At this time, the sealing material T1 below the mold M, the edge of the semiconductor chip 1, the sealing material T1 above the upper mold M and the inner wall of the cylindrical stainless steel N form a sealed cavity Q1.

[0041] Step 5: Open the B vent valve and inject nitrogen under high pressure. Press the silicone rubber 5 into the cavity Q1 through the pipe G. Inject the silicone rubber from the left injection port Z1 and let it out from the right overflow port Z2 for at least 5 seconds. After the air in the cavity Q1 is purged, first block the right outlet Z2 and then inject the silicone rubber from the left injection port Z1 under high pressure. The purpose is to increase the density of the silicone rubber 5 in the cavity.

[0042] Step 6: Heat the cylindrical stainless steel N to initially solidify the surface of the silicone rubber 5, making it easier for the semiconductor chip 1 to be removed from the mold M;

[0043] Step 7: Remove the semiconductor chip 1 with the preliminary cured protective layer from the mold M and place it in an oven for complete curing. This evaporates the volatile organic compounds in the silicone rubber 5, causing the silicone rubber 5 to change from a liquid to a solid state, thus stabilizing the chemical properties of the protective layer of the silicone rubber 5.

[0044] The protective layer of the silicone rubber 5 is composed of polysiloxane with a molecular weight of 80±10,000 molar units. The upper surface height h1 is 8±1 cm; the width w1 is 10±1 cm; the sidewall height h2 is 13±1 cm; and the lower surface width w2 is 3±1 cm.

[0045] The final adhesion of the protective layer of the silicone rubber 5 is greater than 5±1N; the tensile strength of the silicone rubber 5 is greater than 20±2MPa; the hardness is 30±2ShoreA; and the insulation strength is greater than 15±1kv / mms.

[0046] The sealing material T1 is made of polytetrafluoroethylene, with a polished surface and coated with a non-adhesive chemical film. The material is a Teflon coating with a film thickness of 2.0±0.5μm. The circular plate Y is compatible with the sealing material T1.

[0047] The cleanroom drying oven achieves a cleanliness level of ISO CLASS 1 and a temperature of 250±2℃.

[0048] The vacuum treatment achieves a high vacuum level of 1.5 × 10⁻⁶. -1 Pa, evacuate for 30-50 minutes.

[0049] The cylindrical stainless steel N is heated to a temperature of 175±5℃ for a time of 5±2min.

[0050] The oven temperature and baking time are 240℃ / 24h, and the vacuum degree is 2.0×10⁻⁶.-2 Pa.

[0051] The pressure for re-injecting glue at the left-end glue injection port Z1 is 1.5 × 10⁻⁶. +1 Pa.

[0052] like Figure 3 As shown, open the B vent valve and inject nitrogen. Inject silicone rubber 5 into cavity Q1 through pipe G, allowing the right end overflow port Z2 to overflow for at least 5 seconds. After the air in cavity Q1 is purged, first block the right end outlet Z2, then inject silicone rubber again under high pressure at the left end injection port Z1. The purpose is to increase the density of silicone rubber 5 in the cavity. Then, heat the cylindrical stainless steel N to 175±5℃ and cure the silicone rubber 5 at high temperature for 2 minutes, allowing the surface of silicone rubber 5 to be initially cured and formed. Since the special sealing material T1 is made of polytetrafluoroethylene, it has a certain degree of flexibility, which facilitates sealing with surrounding materials after pressure, preventing leakage during high-pressure injection. The surface of the special sealing material T1 is polished and coated with a non-stick chemical film, so the silicone rubber 5 is not torn when removing the mold M and taking out the chip after the silicone rubber surface is initially cured and formed, ensuring the integrity of the shape of silicone rubber 5 and improving the efficiency of injection.

[0053] Then, semiconductor chip 1 was placed in a high-temperature vacuum of 2.0 × 10⁻⁶ for 24 hours at 240°C. -2 The Pa oven fully cures the silicone rubber 5, evaporating the volatile organic compounds in it. The silicone rubber 5 changes completely from a linear structure to a mesh structure, transforming it from a liquid to a solid state and stabilizing its chemical properties.

[0054] like Figure 5 As shown, the semiconductor chip 1 and the molybdenum sheet 2 are sintered together at high temperature by aluminum foil 3, which provides support and protection for the semiconductor chip 1 and facilitates subsequent machining processes such as grinding, etching, passivation, and protection of the junction termination mesa 4 of the semiconductor chip 1. The shape of the junction termination mesa 4 of the semiconductor chip 1 is protected by a protective layer of silicone rubber 5, wherein the upper surface height h1 is 8±1cm; the width w1 is 10±1cm; the sidewall height h2 is 13±1cm; and the lower surface width w2 is 3±1cm.

[0055] The use of high-vacuum degassing significantly reduces the air content in silicone rubber 5, improving its insulation strength, oxidation resistance, and corrosion resistance. High-temperature and high-pressure mold injection increases the density of the adhesive. Although the process is complex, the injection protective layer is thick, uniform, and regular, improving the quality of the silicone rubber protective layer. This allows the blocking voltage of the silicone rubber-protected semiconductor chip to exceed 8500V from 3000V, significantly improving the chip's blocking voltage capability, reducing leakage current at the blocking voltage, and improving the consistency of device parameters and yield.

[0056] As shown in Table 1, for chips below 3000V, the yield of the silicone rubber 5-layer preparation method prepared by this invention is at least 20% higher than that prepared by the traditional coating method.

[0057] Table 1. Comparison of blocking voltage characteristics of semiconductor chips with different serial numbers from the same batch protected by different technologies:

[0058]

[0059]

[0060] As can be seen, the yield rate increased by 30%.

Claims

1. A method for preparing a protective layer for the junction termination mesa of a semiconductor chip, characterized in that, Includes the following steps: Step 1: After the semiconductor chip (1) terminal surface (4) is shaped, immerse it in ACF cleaning solution to clean it, and then place it in a clean oven to dry. Step 2: Pour the raw material silicone rubber (5) into a stainless steel storage tank, seal it and perform vacuum treatment to remove the air mixed in during the pouring process of silicone rubber (5), which affects the performance of silicone rubber (5). Step 3: Assemble the mold and sealing material together using a circular plate clamp, and fix them to the inner wall of the cylindrical stainless steel with screws. Step 4: Place the semiconductor chip (1) in the center of the mold and sealing material, cover the mold and the special sealing material, and apply pressure of 30±5KN. At this time, the sealing material under the mold, the edge of the semiconductor chip (1), the sealing material above the upper mold and the inner wall of the cylindrical stainless steel form a sealed cavity. Step 5: Open the vent valve and inject nitrogen under high pressure. Press the silicone rubber (5) into the cavity through the pipe. Inject the silicone rubber from the left end injection port and let the rubber out from the right end overflow port for at least 5 seconds. After the air in the cavity is exhausted, first block the right end outlet port and then inject the rubber under high pressure from the left end injection port. The purpose is to increase the density of the silicone rubber (5) in the cavity. Step 6: Heat the cylindrical stainless steel to allow the surface of the silicone rubber (5) to be initially cured and formed, making it easier for the semiconductor chip (1) to be removed from the mold; Step 7: Take the semiconductor chip (1) with the preliminary cured protective layer out of the mold and put it into the oven for complete curing. This will evaporate the volatile organic compounds in the silicone rubber (5) and change the silicone rubber (5) from liquid to solid, thus stabilizing the chemical properties of the protective layer of the silicone rubber (5). The protective layer of the silicone rubber (5) is composed of polysiloxane with a molecular weight of 80±10,000 molar units, an upper surface height of 8±1 cm, a width of 10±1 cm, a sidewall height of 13±1 cm, and a lower surface width of 3±1 cm. The final adhesion force of the protective layer of the silicone rubber (5) is greater than 5±1N, the tensile strength of the silicone rubber (5) is greater than 20±2MPa, the hardness is 30±2ShoreA, and the insulation strength is greater than 15±1kv / mms. The sealing material is made of polytetrafluoroethylene, with a polished surface and coated with a non-stick chemical film. The material is a Teflon coating with a film thickness of 2.0±0.5μm. The circular plate is compatible with the sealing material.

2. The method for preparing a protective layer for a semiconductor chip junction termination mesa as described in claim 1, characterized in that, The cleanroom drying oven achieves a cleanliness level of ISO CLASS 1 and a temperature of 250±2℃.

3. The method for preparing a protective layer for a semiconductor chip junction termination mesa as described in claim 1, characterized in that, The vacuum treatment achieves a high vacuum level of 1.5 × 10⁻⁶. -1 Pa, evacuate for 30-50 minutes.

4. The method for preparing a protective layer for a semiconductor chip junction termination mesa as described in claim 1, characterized in that, The cylindrical stainless steel was heated to 175±5℃ for 5±2 minutes.

5. The method for preparing a protective layer for a semiconductor chip junction termination mesa as described in claim 1, characterized in that, The oven temperature and baking time are 240℃ / 24h, and the vacuum degree is 2.0×10⁻⁶. -2 Pa.

6. The method for preparing a protective layer for a semiconductor chip junction termination mesa as described in claim 1, characterized in that, The pressure for re-injecting glue at the left-end glue injection port is 1.5 × 10⁻⁶. +1 Pa.

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