Manufacturing method for direct chemical plating redistribution layer based on aluminum pad

Abstract

The invention discloses a method for manufacturing a redistribution layer based on direct chemical plating of an aluminum pad, and relates to the technical field of semiconductor processing, and the method comprises the following steps: wafer cleaning, photoresist coating, PAB soft baking, RDL exposure, developing, Descum treatment, activating treatment, RDL chemical plating and photoresist removal. According to the invention, a necessary, expensive and complex sputtering UBM process in traditional semiconductor packaging is abandoned, and a simplified process for directly forming RDL on the surfaces of dielectric layers such as an aluminum bonding pad, a passivation layer and polyimide at one time through selective activation and chemical plating technologies is creatively developed; meanwhile, due to the fact that a metal interface layer is reduced, the stress problem caused by mismatching of thermal expansion coefficients is solved, and better interface integrity is provided through direct combination of the chemical plating metal layer and the aluminum pad.

Description

Technical Field

[0001] This invention relates specifically to the field of semiconductor processing technology, and more specifically to a method for fabricating a redistribution layer based on direct chemical plating of an aluminum pad. Background Technology

[0002] In the field of semiconductor packaging, aluminum pads on silicon wafers serve as a critical interface for connecting chips to external circuits, and their surface treatment processes directly affect the reliability, conductivity, and production cost of the package. As semiconductor devices move towards miniaturization and high density, the requirements for surface metallization and redistribution (RDL) processes on aluminum pads are becoming increasingly stringent.

[0003] In semiconductor packaging, aluminum pads require UBM sputtering to address issues such as poor adhesion to subsequent soldering materials. Currently, mainstream sputtering methods include titanium (Ti) and copper (Cu) layers, as well as titanium-tungsten (TiW) and gold (Au) layers; these are widely used in various semiconductor packaging scenarios, and are particularly suitable for surface treatment of high-precision, small-sized pads. Rewiring technology involves fabricating an insulating layer and metal wiring on the wafer surface to redistribute the chip pad positions, meeting the advanced packaging requirements of multi-chip integration and heterogeneous integration. Current RDL fabrication typically uses polyimide (PI) as the insulating layer and copper (Cu) as the metal wiring, formed through processes such as photolithography, electroplating, or sputtering.

[0004] Existing technologies require the additional fabrication of a UBM layer, involving the use of sputtering equipment. This equipment is expensive to purchase, and the sputtering process is energy-intensive and has a long production cycle. Furthermore, the high cost of target materials such as Ti and Cu further increases the overall process cost and reduces production efficiency. Moreover, the adhesion between the UBM layer and the aluminum pad depends on the quality of the Ti adhesion layer. If there are problems such as impurity contamination or fluctuations in deposition parameters during sputtering, delamination between the Ti layer and the aluminum pad or Cu layer can easily occur. The presence of multiple interfaces increases the risk of unstable coating adhesion, thus affecting packaging reliability. Therefore, we propose a method for fabricating a redistribution layer based on direct chemical plating of the aluminum pad, eliminating the UBM layer fabrication step. Photoresist coating and chemical plating of the RDL are performed directly on the aluminum pad, passivation layer, or PI layer, reducing equipment investment and sputtering target consumption, shortening the production cycle, and lowering the overall process cost. Summary of the Invention

[0005] The purpose of this invention is to provide a method for fabricating a redistribution layer based on direct chemical plating of an aluminum pad. This method eliminates the need for the UBM layer preparation process and allows for direct photoresist coating and chemical plating of the RDL on the aluminum pad, passivation layer, or PI layer. This reduces equipment investment and sputtering target consumption, shortens the production cycle, and lowers the overall process cost, thereby solving the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for fabricating a redistribution layer based on direct chemical plating of aluminum pads includes the following steps: S1: Wafer cleaning, using an ethanol solution to ultrasonically clean the surface of the wafer to remove organic contaminants such as grease and dust, and then using plasma to clean the wafer surface. S2: Photoresist coating, photoresist is spin-coated onto the wafer surface; S3: PAB soft bake, bake in a baking pan at 90-120℃ for 240 seconds; S4: RDL exposure, using a scanning lithography machine, ultraviolet light is used to expose the photoresist through the photomask; S5: Development. Immerse the wafer after the above operation in the developing solution for 400-800 seconds, then rinse with deionized water and dry. S6: Descum treatment, using oxygen plasma treatment, equipment power of 200-400W, operation time of 30-60 seconds; S7: Activation treatment. After the above treatment, the wafer is placed in an activation solution, which is a mixture of 0.2% palladium chloride, 1.5% hydrochloric acid, and deionized water with a pH of 1.2-1.5. The wafer is immersed in the solution at 40°C for 6 minutes while the solution is stirred at 140 rpm to ensure that palladium catalyst particles are uniformly adsorbed on the surface of the wiring area. After activation, the wafer is rinsed with deionized water for 4 minutes to remove residual activation solution. S8: RDL plating, immersing the wafer in an 85℃ plating solution for 10 minutes. The plating solution is a mixture of nickel sulfate with a concentration of 25g / L, sodium hypophosphite with a concentration of 20g / L, and sodium citrate with a concentration of 30g / L. The pH of the mixture is adjusted to 8.5-9.0 by ammonia water. Subsequently, a nickel seed layer is deposited, and a thicker nickel plating solution is used. The nickel plating solution consists of 35 g / L nickel sulfate, 25 g / L sodium hypophosphite, 35 g / L ammonium citrate, and 0.05 g / L stabilizer, with a pH of 8.8-9.2. The solution is immersed at 90°C for 35-50 minutes to increase the thickness of the nickel layer. At the same time, nitrogen gas is introduced to prevent oxidation of the plating solution, thus achieving electroless deposition and forming an RDL conductive path. S9: Photoresist removal. The wafer is immersed in an alkaline stripping solution at 60-70℃ for 15-30 minutes to remove the remaining photoresist. After cleaning, it is dried to obtain the finished product.

[0007] As a further technical solution of the present invention, in step S3, the PAB soft baking evaporates most of the solvent in the photoresist, causing it to solidify and enhancing its adhesion to the wafer surface.

[0008] As a further technical solution of the present invention, in step S5, the exposed photoresist area is dissolved by a developing solution. A designed circuit pattern opening is formed on the photoresist layer, exposing the dielectric layer area where metal needs to be deposited underneath.

[0009] As a further technical solution of the present invention, in step S7, a palladium catalytic layer is deposited on the surface of the RDL wiring region after activation, providing a catalytic center for the subsequent autocatalytic reaction of chemical plating.

[0010] As a further technical solution of the present invention, step S8 involves depositing metal in the activated dielectric layer region using a chemical plating method to form the final RDL circuit.

[0011] As a further technical solution of the present invention, the stabilizer in step S8 is at least one of thiourea, 2-mercaptobenzothiazole or potassium iodate.

[0012] As a further technical solution of the present invention, the alkaline stripping solution in step S9 is an aqueous solution containing organic amines or quaternary ammonium bases, and its working temperature is 60-70℃.

[0013] Compared with the prior art, the beneficial effects of the present invention are: This invention abandons the expensive and complex sputtering UBM process required in traditional semiconductor packaging, and creatively develops a simplified process that directly forms RDL on the surface of aluminum pads, passivation layers and dielectric layers such as polyimide in one step through selective activation and chemical plating technology. Meanwhile, by reducing the metal interface layer, stress problems caused by the mismatch of thermal expansion coefficients are reduced, and the direct bonding between the electroless metal plating layer and the aluminum pad provides better interface integrity. Attached Figure Description

[0014] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Please see Figure 1 In this embodiment of the invention, the following steps are included: S1: Wafer cleaning, using an ethanol solution to ultrasonically clean the surface of the wafer to remove organic contaminants such as grease and dust, and then using plasma to clean the wafer surface. S2: Photoresist coating, photoresist is spin-coated onto the wafer surface; S3: PAB soft bake, bake in a baking pan at 90-120℃ for 240 seconds; S4: RDL exposure, using a scanning lithography machine, ultraviolet light is used to expose the photoresist through the photomask; S5: Development. Immerse the wafer after the above operation in the developing solution for 400-800 seconds, then rinse with deionized water and dry. S6: Descum treatment, using oxygen plasma treatment, equipment power of 200-400W, operation time of 30-60 seconds; S7: Activation treatment. After the above treatment, the wafer is placed in an activation solution, which is a mixture of 0.2% palladium chloride, 1.5% hydrochloric acid, and deionized water with a pH of 1.2-1.5. The wafer is immersed in the solution at 40°C for 6 minutes while the solution is stirred at 140 rpm to ensure that palladium catalyst particles are uniformly adsorbed on the surface of the wiring area. After activation, the wafer is rinsed with deionized water for 4 minutes to remove residual activation solution. S8: RDL plating, immersing the wafer in an 85℃ plating solution for 10 minutes. The plating solution is a mixture of nickel sulfate with a concentration of 25g / L, sodium hypophosphite with a concentration of 20g / L, and sodium citrate with a concentration of 30g / L. The pH of the mixture is adjusted to 8.5-9.0 by ammonia water. Subsequently, a nickel seed layer is deposited, and a thicker nickel plating solution is used. The nickel plating solution consists of 35 g / L nickel sulfate, 25 g / L sodium hypophosphite, 35 g / L ammonium citrate, and 0.05 g / L stabilizer, with a pH of 8.8-9.2. The solution is immersed at 90°C for 35-50 minutes to increase the thickness of the nickel layer. At the same time, nitrogen gas is introduced to prevent oxidation of the plating solution, thus achieving electroless deposition and forming an RDL conductive path. S9: Photoresist removal. The wafer is immersed in an alkaline stripping solution at 60-70℃ for 15-30 minutes to remove the remaining photoresist. After cleaning, it is dried to obtain the finished product.

[0017] In this embodiment, in step S3, the PAB soft baking evaporates most of the solvent in the photoresist, causing it to solidify, enhancing its adhesion to the wafer surface, and improving the linewidth stability during exposure.

[0018] In this embodiment, in step S5, the exposed photoresist area is dissolved by a developing solution. A pre-designed circuit pattern opening is formed on the photoresist layer, exposing the dielectric layer area where metal needs to be deposited underneath.

[0019] In this embodiment, after activation in step S7, a palladium catalytic layer is deposited on the surface of the RDL wiring region to provide a catalytic center for the subsequent autocatalytic plating reaction.

[0020] In this embodiment, step S8 involves depositing metal in the activated dielectric layer region using a chemical plating method to form the final RDL circuit.

[0021] In this embodiment, the purpose of step S1 is to remove contaminants, particles, and the natural oxide layer from the wafer surface to ensure the adhesion and quality of the subsequent thin film.

[0022] In this embodiment, the purpose of step S2 is to uniformly coat the wafer surface with a layer of photoresist as a mask for subsequent pattern transfer.

[0023] In this embodiment, the purpose of step S6 is to remove photoresist residue and surface contaminants to avoid affecting the uniformity of subsequent activation layer deposition and to ensure the adhesion between the electroplated metal and the substrate.

[0024] In this embodiment, the stabilizer in step S8 is at least one of thiourea, 2-mercaptobenzothiazole, or potassium iodate.

[0025] In this embodiment, the alkaline stripping solution in step S9 is an aqueous solution containing organic amines or quaternary ammonium bases, and its working temperature is 60-70℃.

[0026] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0027] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style of the specification is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for fabricating a direct electroless plated redistribution layer based on aluminum pads, characterized in that: The method comprises the following steps: ​ S1: wafer cleaning, using ethanol solution to ultrasonic clean the surface of the wafer, remove grease, dust and other surface organic contaminants, and then use plasma to clean the surface of the wafer; S2: photoresist coating, spin coating photoresist on the surface of the wafer; S3: PAB soft baking, baking in the baking tray at a temperature of 90-120℃ for 240s; S4: RDL exposure, using a scanning photolithography machine, exposing the photoresist to ultraviolet light through a mask; S5: development, immersing the wafer after the above operation in a developing solution for 400-800s, then rinsing with deionized water, and drying after rinsing; S6: Descum treatment, using oxygen plasma treatment, the equipment power is 200-400W, and the operation time is 30-60s; S7: activation treatment, immersing the wafer after the above treatment in an activation solution, the activation solution is a mixture of 0.2% palladium chloride, 1.5% hydrochloric acid and deionized water, the pH value is 1.2-1.5, and the wafer is immersed at a temperature of 40℃ for 6min, while the activation solution is stirred at a speed of 140rpm, so that the palladium catalytic particles are uniformly adsorbed on the surface of the RDL wiring area; after activation, rinsing with deionized water for 4min to remove residual activation solution; S8: RDL plating, immersing the wafer in 85℃ plating solution for 10min, the plating solution is a mixture of 25g / L nickel sulfate, 20g / L sodium hypophosphite and 30g / L sodium citrate, and the pH value of the mixture is adjusted to 8.5-9.0 by ammonia water; then depositing a nickel seed layer, replacing the thickening type plating nickel solution, the plating nickel solution is a mixture of 35g / L nickel sulfate, 25g / L sodium hypophosphite, 35g / L ammonium citrate and 0.05g / L stabilizer, the pH value is 8.8-9.2, and the wafer is immersed at a temperature of 90℃ for 35-50min to thicken the nickel layer; at the same time, nitrogen is introduced to prevent the plating solution from being oxidized; realizing electroless plating deposition to form an RDL conductive path; S9: photoresist removal, immersing the wafer in an alkaline stripping solution at a temperature of 60-70℃ for 15-30min to remove the remaining photoresist, and drying after cleaning to obtain a finished product.

2. The method for fabrication of direct electroless re-routed layers on aluminum pad based substrates according to claim 1, wherein: In the step S3, the PAB soft baking evaporates most of the solvents in the photoresist, solidifies the photoresist, and enhances the adhesion to the surface of the wafer.

3. The method for fabrication of direct electroless re-routed layers on aluminum pad based interconnects of claim 1, wherein: In the step S5, the exposed photoresist area is dissolved by the developing solution. The designed circuit pattern opening is formed on the photoresist layer, and the dielectric layer area below which metal needs to be deposited is exposed.

4. The method for fabrication of direct electroless re-routed layers on aluminum pad based interconnects of claim 1, wherein: In the step S7, the palladium catalytic layer is deposited on the surface of the RDL wiring area after activation, which provides a catalytic center for the subsequent self-catalytic plating reaction.

5. The method for fabrication of direct electroless re-routed layers on aluminum pad based interconnects of claim 1, wherein: In the step S8, the metal is deposited on the activated dielectric layer area by chemical plating method to form the final RDL circuit.

6. The method for fabrication of direct electroless re-routed layers on aluminum pad based interconnects of claim 1, wherein: In the step S8, the stabilizer is at least one of thiourea, 2-mercaptobenzothiazole or potassium iodate.

7. The method for fabrication of direct electroless re-routed layers on aluminum pad based interconnects of claim 1, wherein: In the step S9, the alkaline stripping solution is an aqueous solution containing organic amine or quaternary ammonium base, and the working temperature is 60-70℃.

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