Method for reducing metal impedance and optimizing uniformity

Abstract

The invention provides a method for reducing metal impedance and optimizing uniformity, which comprises the following steps: pretreatment: putting a to-be-coated product into coating equipment, filling inert gas, starting an ion source to dissociate the inert gas by electrons to generate ions, bombarding the surface of the to-be-coated product by using the generated ions, and coating the to-be-coated product. And removing surface impurities, coating, and finally removing the protective glue and the film layer by using a lift process. The oxidation layer on the metal surface to be coated is pretreated, so that pure metal is exposed, and the overall impedance of the coated metal layer is reduced.

Description

Technical Field

[0001] The invention belongs to the field of metal film formation, relates to a process for coating metal films on silicon wafers, and specifically relates to a method for reducing metal impedance and optimizing uniformity. Background Art

[0002] Reducing impedance is one of the common requirements in circuit design. By selecting low-impedance materials, increasing the cross-sectional area of ​​the conductor, reducing the circuit length, using impedance matching circuits, using differential signal transmission, using special wiring techniques, selecting appropriate devices and optimizing grounding design, we can effectively reduce the impedance of the circuit and improve the efficiency of signal transmission. The process introduced this time is a method of reducing metal impedance and optimizing uniformity by improving production conditions during the metal film plating process to achieve better circuit performance. Summary of the invention

[0003] In order to overcome the problem in the prior art of processing one or more layers of metal film on the incoming wafer to form metal bumps, the reliability and appearance of the metal bumps meet the requirements, but the insufficient uniformity of the umbrella frame of the coating machine will lead to excessive impedance and uneven inner and outer circles when measuring electrical properties. The present invention reduces the impedance of the coated metal layer from a process perspective and provides a process method for reducing the impedance of the metal film and optimizing uniformity.

[0004] To achieve the above objectives, the present invention provides a pretreatment method for reducing the impedance of the metal film and optimizing the uniformity, which comprises placing the product to be coated into the coating equipment, filling it with inert gas and turning on the ion source to generate ions by electron dissociation of the inert gas, and using the generated ions to bombard the surface of the product to be coated to remove surface impurities.

[0005] Preferably, the surface of the product to be coated is metal.

[0006] Preferably, the coating equipment is an evaporative coating machine, and the coating vacuum degree is greater than 1.5*10^-3.

[0007] Preferably, the inert gas is one or a combination of argon, neon or helium.

[0008] Preferably, when the inert gas is used to bombard the surface of the product to be coated before coating, the correction plate of the coating machine is in a closed state. Preferably, the product pretreated with inert gas is vacuum coated, and the electron gun of the coating machine bombards the target material to form one or more metal film layers on the surface of the pretreated product.

[0009] Preferably, the current of the electron gun during film coating is 0.8-10A, and the correction plate of the coating machine is in an open state during film coating.

[0010] Preferably, the metal of the plated metal film layer includes one or more of Ni, Ag, Ti, Au, Cr, Al, and Cu.

[0011] Preferably, after the coating is completed, a liftoff process is used, and the reagent is dimethyl sulfoxide. The reagent is heated to 70-85° C. to remove the protective glue and the film layer.

[0012] Preferably, the plated metal film layers are Ni layer, Ag layer, Ni layer and Ti layer in sequence.

[0013] The beneficial effects of the present invention are as follows: The process of the present invention performs metal film coating according to a pre-designed film structure, and the film is coated in a prepared pattern. The film layer on the glue is removed by a liftoff process to expose the metal layer pattern. The process improvement of the present invention focuses on the pretreatment of the product before coating, that is, before coating the metal film, an inert gas and an ion source are used in the coating machine to pre-treat the oxide layer on the surface of the product to be coated, and the overall impedance of the metal film layer after coating is reduced by reducing the oxide content on the surface of the product to be coated; at the same time, the impedance uniformity is optimized by recycling the coating correction plate.

[0014] The improved pretreatment method provided in the present invention can directly use a conventional coating machine and has been successfully put into mass production. The test results and batch production results are in line with the normal product control requirements and have reached the level of exemption from inspection. While ensuring product quality, it greatly reduces the manpower and resources required for inspection. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is the process flow and pretreatment link diagram of the present invention; Figure 2 This is an example of the coating structure diagram of the product described in the present invention; Figure 3 This is an example of a comparison analysis diagram of the method of the present invention and the effect before and after improvement. DETAILED DESCRIPTION

[0016] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present application will be further described below in conjunction with specific embodiments.

[0017] The present invention provides a method for reducing metal impedance and optimizing uniformity, which comprises the following steps: The evaporator is used for coating, and the coating vacuum is set to be greater than 1.5*10^-3. Before coating, the ion source is turned on and only argon gas is filled in. The correction plate is not turned on, so that the ion beam of the ion source is fully diverged to the surface of the product, and the metal PAD to be coated is pre-treated with argon gas; Select a well-designed metal target and bombard it with the electron gun of the evaporation coating machine. The current of the electron gun of the evaporation coating machine is 1.3-4.3A. Vacuum coating is performed on the wafer products in the evaporative coating machine, and metal film layers of different thicknesses are coated on the surface of the wafer products; During the coating process, the crystal oscillator and light control system monitor the thickness of the film layer. After all the film layers reach the set film thickness value, the coating machine stops and slowly releases air to form a metal film layer with a total thickness that meets the customer's design requirements, and the coating is completed.

[0018] Using the liftoff process, the agent is heated to 70-85°C to remove the protective glue and film layer, so that the entire metal bump is completely exposed.

[0019] Testing: Use CP test machine to measure, including specially customized pin card to measure its electrical performance.

[0020] Example 1 This embodiment provides a method for reducing metal impedance and optimizing uniformity, which is based on the improved process of copper-aluminum alloy pad products. Figure 1 In the middle process, IQC: incoming material inspection; AOI: automatic optical defect inspection, after the coating, exposure and development are operated on the entire wafer substrate, the copper-aluminum alloy PAD wafer products that need to be coated are pre-treated with argon gas before coating: first turn on the ion source, only fill with argon gas, do not turn on the correction plate, and let the ion beam of the ion source diverge completely to the product surface; The evaporator coating is used, the coating vacuum is set to 1.5*10^-3, and the designed metal target is selected. The metal target is bombarded by the electron gun of the evaporator coating machine. The current of the electron gun of the evaporator coating machine is 1.3-4.3A; The wafer products in the evaporative coating machine are vacuum coated, and metal film layers of different thicknesses are coated on the surface of the wafer products; during the coating process, the crystal oscillator and light control system monitor the film thickness. After all the film layers reach the set film thickness value, the coating machine stops and slowly releases air to form a metal film layer with a total thickness that meets the design requirements, and the coating is completed. The coating results are shown in Figure 2 .

[0021] Using the liftoff process, the agent is heated to 70-85℃ to remove the protective glue and film layer, so that the metal bumps composed of the entire multi-layer metal film are completely exposed. The CP tester is used for testing, which contains a specially customized pin card to measure its electrical properties.

[0022] After testing, the impedance of the product prepared by this process is between 0.03~0.15Ω, and the uniformity is improved. See Table 1 below, Table 1 Improved impedance values ​​measured at different points on the same product

[0023] The product to be coated was not pre-treated with argon gas. The other processes were the same as the above steps. The test impedance was between 0.28 and 2.04Ω. See Table 2 below. Table 2 Impedance values ​​before improvement measured at different points on the same product

[0024] According to the R column in Table 1, the impedance is between 0.03 and 0.15Ω, and the uniformity is also improved. The comparison results before and after the improvement are shown in Figure 3 and Table 3, Table 3 .

[0025] The present invention provides a method for reducing metal film impedance and optimizing uniformity, which comprises the following steps: 1) Inert gas pretreatment of the product to be coated: Use a coating machine to coat the film, turn on the ion source, only fill it with inert gas, let the ion beam of the ion source diverge to the surface of the product to be coated, and pre-treat the product to be coated with inert gas; 2) Coating: The product to be coated is bombarded by the electron gun of the coating machine. The current of the electron gun of the coating machine is 0.8-10A, and vacuum coating is performed to form one or more metal film layers.

[0026] After the inert gas pretreatment is performed on the product to be coated in the coating machine, the present invention controls the current of the electron gun of the coating machine to vacuum coat the wafer product in the evaporative coating machine, and coats a metal film layer of corresponding thickness on the surface of the wafer product; and uses the liftoff process, the reagent is heated to 70-85°C to remove the protective glue and film layer. The present invention solves the problem that the effect of the metal film coating of the product changes with the fluctuation of the incoming materials of the front-end factory. Later, the present invention can be unaffected by the incoming materials and effectively control the performance and stability of the shipped products; the above data are all outer circle data comparisons, which shows that the present invention also solves the problem of large differences between the inner and outer circles of the coating.

[0027] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A pretreatment method for reducing metal film impedance and optimizing uniformity, characterized in that: Place the product to be coated into the coating equipment, fill it with inert gas and turn on the ion source to generate ions by electron dissociation of the inert gas. Use the generated ions to bombard the surface of the product to be coated to remove surface impurities.

2. The pretreatment method for reducing metal impedance and optimizing uniformity according to claim 1, characterized in that: The surface of the product to be coated is metal.

3. The pretreatment method for reducing metal impedance and optimizing uniformity according to claim 1, characterized in that: The coating equipment is an evaporative coating machine.

4. The pretreatment method for reducing metal impedance and optimizing uniformity according to claim 1, characterized in that: The inert gas is one or a combination of argon, neon or helium.

5. The pretreatment method for reducing metal impedance and optimizing uniformity according to claim 1, characterized in that: When inert gas is used to bombard the surface of the product to be coated before coating, the correction plate of the coating equipment is in the closed state.

6. The pretreatment method for reducing metal impedance and optimizing uniformity according to any one of claims 1 to 5, characterized in that: The product after inert gas pretreatment is vacuum coated, the coating vacuum degree is greater than 1.5*10^-3, and the electron gun of the coating equipment bombards the target material to form one or more metal film layers on the surface of the pretreated product.

7. The pretreatment method for reducing metal impedance and optimizing uniformity according to claim 6, characterized in that: During coating, the current of the electron gun is 0.8-10A, and the correction plate of the coating machine is in the open state.

8. The pretreatment method for reducing metal impedance and optimizing uniformity according to claim 6, characterized in that: The metal of the plated metal film layer includes one or more of Ni, Ag, Ti, Au, Cr, Al, and Cu.

9. The pretreatment method for reducing metal impedance and optimizing uniformity according to claim 6, characterized in that: After coating, the liftoff process is used, and the reagent is dimethyl sulfoxide. The reagent is heated to 70-85℃ to remove the protective glue and film layer.

10. The method for reducing metal impedance and optimizing uniformity according to claim 8, characterized in that: The plated metal film layers are Ni layer, Ag layer, Ni layer and Ti layer in sequence.

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