Method for improving copper color difference in electroplating process

Abstract

The invention discloses a method for improving copper color difference occurring in the electroplating process, and belongs to the technical field of wafer electroplating. According to the method, a three-section electroplating process is adopted, and the waiting time (Q-Time) of nickel plating after copper plating is strictly controlled, so that the color difference problem can be effectively improved, the uniformity of a plating layer is ensured, and the product quality is improved. By adopting the optimal current density, the production cost can be reduced on the premise of meeting the process requirements. According to the method, the waiting time before nickel plating after copper plating is strictly controlled, it can be ensured that the electroplating process is completed within the preset time, the production efficiency is improved, and the conditions of reworking and scrapping caused by overtime of the process are reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of wafer electroplating, and particularly relates to a method for improving copper color difference during the electroplating process. Background Art

[0002] When electroplating Cu / Ni / Au on wafer products, rework is often caused by color difference problems in the electroplated copper. For the copper color difference problem that occurs during the electroplating process, it is due to the self-annealing phenomenon of copper during the electroplating process. That is, at room temperature, the recrystallization behavior of electroplated copper occurs. During the electroplating process, electroplated copper starts from the substrate, so self-annealing also starts from the bottom and grows upward. The copper grains will grow from the nanoscale to several micrometer scales. During the electroplating of copper, a large amount of impurities may accumulate between the bottom of the coating and the substrate, making it impossible for copper to form an orderly lattice. At the same time, the impurities will gradually be discharged to the surface of the coating with self-annealing, resulting in dark and rough crystals, and finally presenting a different color phenomenon on the product.

[0003] In addition to affecting the abnormal color of the copper coating, the self-annealing phenomenon will also cause inconsistent material properties, reduced strength and hardness, and even cause dislocations inside the material. And when annealing is carried out below the recrystallization temperature, some alloy materials may show a hardening phenomenon. Self-annealing is a natural process, so it is difficult to control and grasp its occurrence and development in the electroplating process. Therefore, when performing the electroplating copper process, it is necessary to strictly control the occurrence of the self-annealing phenomenon. The waiting time after electroplating copper and before electroplating nickel, that is, Q-Time, will affect the quality and performance of the coating during the process. The Q-Time needs to be controlled. If the time is too long, it is easy to cause the self-annealing phenomenon of the copper coating to end, and problems such as color spots and different colors will appear on the coating surface, and the production efficiency will be reduced. Therefore, controlling Q-Time is also very important. Summary of the Invention

[0004] In view of the above situation, in order to overcome the defects of the prior art, the present invention adopts a three-stage electroplating process to adjust the waiting time after electroplating copper and before electroplating nickel, so as to improve the quality of wafer electroplated products.

[0005] In order to achieve the above object, the following technical solutions are adopted: The present invention provides a method for improving copper color difference occurring during the electroplating process, including the following steps:

[0006] Prepare a wafer;

[0007] Perform electroplating of copper;

[0008] Perform electroplating of nickel;

[0009] Perform electroplating of gold;

[0010] After the electroplating copper step is completed, wait for 5h to 7h before performing electroplating of nickel;

[0011] The copper electroplating adopts a three-stage electroplating process, including the first-stage electroplating, the second-stage electroplating, and the third-stage electroplating.

[0012] Furthermore, the current density corresponding to the first-stage electroplating is 2-4 ASD.

[0013] Furthermore, the current density corresponding to the first-stage electroplating is 3 ASD.

[0014] Furthermore, the current density corresponding to the second-stage electroplating is 2 ASD.

[0015] Furthermore, the current density corresponding to the second-stage electroplating is 0.6 ASD.

[0016] Furthermore, the copper electroplating step includes:

[0017] Washing the wafer, electroplating copper, washing again, spin-drying, and detecting and measuring.

[0018] Furthermore, the nickel electroplating step includes:

[0019] Washing the wafer, pickling, washing again, electroplating nickel, and washing for the third time.

[0020] Furthermore, the gold electroplating step includes:

[0021] Washing the wafer, electroplating gold, and washing again.

[0022] ]>The beneficial effects of the present invention are:

[0023] (1) The three-stage electroplating process adopted by the present invention can effectively improve the color difference problem, ensure the uniformity of the coating, and improve the product quality.

[0024] (2) The present invention adopts the optimal current density to reduce the production cost on the premise of meeting the process requirements.

[0025] (3) The present invention strictly controls the waiting time after copper electroplating and before nickel electroplating, which can ensure that the electroplating process is completed within the predetermined time, improve the production efficiency, and reduce the rework and scrapping caused by process overtime. Description of the Drawings

[0026] Figure 1 It is a relationship diagram between the average grain size and the Q-Time after self-annealing during the self-annealing process of copper electroplating in the present invention;

[0027] Figure 2 It is an appearance image of copper grains with different Q-Times during the self-annealing process of copper electroplating in the present invention;

[0028] Figure 3This is the image after electroplating copper in the three-stage electroplating of the present invention.

[0029] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation to the present invention. Detailed implementation manners

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0031] Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to the described content can be applied to the present invention. The preferred implementation methods and materials described herein are only for illustration purposes and do not limit the content of this application.

[0032] The experimental methods in the following embodiments are all conventional methods unless otherwise specified. The test materials used in the following embodiments are all obtained from commercial channels unless otherwise specified.

[0033] Embodiment

[0034] A method for improving the copper color difference in the electroplating process includes the following steps:

[0035] 1. Prepare wafers:

[0036] Select wafers that meet the production requirements as the substrates to be processed, ensure that their surfaces are free of scratches, cracks and other defects, and their sizes and electrical properties meet the requirements.

[0037] 2. Perform copper electroplating:

[0038] Water washing: Wash the wafers with ionized water to remove surface impurities.

[0039] Copper plating: A three-stage electroplating process is adopted. The three-stage electroplating process divides the electroplating process into three different stages, each with a different current density. The purpose of staging is to adjust for different coating problems and improve uniformity. In the first stage, a high current is used to promote the formation of a large number of crystal nuclei, form a fine crystal structure, quickly form a dense bottom layer, shorten the deposition time, and reduce the influence of substrate surface defects on the coating. In the second stage, a medium current is used to adjust the deposition rate, promote grain refinement, avoid dendritic growth, and improve uniformity. In the third stage, a low current / pulse current is used to slow down the deposition rate, merge the grains, reduce the surface roughness, and reduce the color difference caused by the difference in light scattering. In some embodiments, the current density in the first stage can be set to: 2-4 ASD. ASD: That is, the current density, which is the current passing through the unit area of the workpiece surface, and its unit is A / m^2. In some embodiments, the current density in the first stage can preferably be set to: 3 ASD. In some embodiments, the current density in the second stage can be set to 2 ASD. In some embodiments, the current density in the third stage can be set to 0.6 ASD. By gradually adjusting the current density, the problem of different colors caused by copper self-annealing can be effectively improved, thereby effectively improving the color difference problem and ensuring the uniformity of the coating and improving the product quality problem..

[0040] Re-washing: After electroplating is completed, quickly immerse the wafer in deionized water again for cleaning to remove the residual electroplating solution and impurities on the wafer surface. Spin-drying: Place the wafer after washing in a spin-drying device and spin off the surface moisture at high speed.

[0041] Inspection and measurement: Use professional inspection equipment to comprehensively inspect the wafer after spin-drying. Use a high-precision film thickness gauge to measure the thickness of the copper coating, and use an optical profiler to detect the flatness of the coating. At the same time, with the help of a color difference meter, quantitatively analyze the color of the coating to accurately judge whether there is a color difference problem.

[0042] 3. Wait for 5-7 h after the copper plating step is completed for nickel plating:

[0043] The waiting time after copper plating and before nickel plating, that is, the waiting time Q-Time. Through a large number of rigorous experiments and data analysis, it can be known that the incubation period of copper electroplating recrystallization is about 3 h, and the recrystallization completion time is about 9 h. The copper plating basically completes the self-annealing behavior after 9 h. To balance cost and efficiency while ensuring the coating quality, after repeated verification, the waiting time Q-Time is set to 5-7 h, and the optimal waiting time Q-Time can be set to 6 h. During the waiting period, the wafer needs to be placed in a clean, dry and relatively stable environment of temperature and humidity to avoid adverse effects of environmental factors on the coating. For example, humidity changes may cause oxidation on the coating surface, which may affect the subsequent electroplating effect. By controlling the waiting time after copper plating and before nickel plating, the color difference and color spot problems caused by copper self-annealing during electroplating can be effectively eliminated.

[0044] 4. Perform nickel electroplating:

[0045] Water washing: Immerse the wafer after waiting in deionized water for cleaning to remove dust and impurities that may have adsorbed on the surface during the waiting process.

[0046] Pickling: Put the wafer after water washing into the pickling solution for pickling. Dilute hydrochloric acid or dilute sulfuric acid solution is generally selected as the pickling solution. Its function is to remove the naturally formed oxide layer on the wafer surface, make the surface in an active state, and enhance the adhesion between the nickel coating and the copper coating. The pickling time is usually controlled within 1 - 3 minutes. If the time is too short, the oxide layer may not be effectively removed; if it is too long, the copper coating may be over-corroded, affecting the overall coating quality. The concentration of the pickling solution needs to be precisely adjusted according to the wafer material and surface condition.

[0047] Water washing again: Immediately after pickling, put the wafer into deionized water for cleaning again to thoroughly remove the residual pickling solution and impurities on the surface. This step is crucial because the residual acid solution may react with the plating solution during the subsequent nickel electroplating process, destroying the stability of the plating solution and causing defects in the coating.

[0048] Nickel electroplating: Put the wafer after water washing again into the nickel electroplating tank for electroplating. In some embodiments, the nickel electroplating solution may consist of nickel sulfate, nickel chloride, boric acid, etc. Nickel sulfate provides nickel ions for electroplating, nickel chloride provides chloride ions to help improve the conductivity of the plating solution, and boric acid plays a buffering role to adjust the pH value and ensure the stability of the electroplating process.

[0049] Water washing for the third time: After nickel electroplating is completed, put the wafer into deionized water for cleaning to remove the residual nickel electroplating solution and impurities on the surface. This water washing aims to ensure the cleanliness of the wafer surface and prevent the residual plating solution from having an adverse effect on the subsequent gold electroplating. Parameters such as the water washing time and water flow state can be appropriately adjusted according to the actual situation.

[0050] 5. Perform gold electroplating:

[0051] Water washing: Immerse the wafer after nickel electroplating in deionized water for cleaning to remove impurities that may have adsorbed on the surface and provide a clean surface for gold electroplating.

[0052] Gold electroplating: Put the wafer after water washing into the gold electroplating tank for electroplating. The gold electroplating solution may consist of potassium gold cyanide, citric acid, potassium dihydrogen phosphate, etc. Potassium gold cyanide provides gold ions, and citric acid and potassium dihydrogen phosphate, etc. act as complexing agents and buffering agents, which help improve the quality and stability of the gold coating.

[0053] Water washing again: After gold electroplating is completed, put the wafer into deionized water for cleaning to remove the residual gold electroplating solution and impurities on the surface.

[0054] After completing copper, nickel, and gold electroplating:

[0055] Conduct a comprehensive inspection on the final electroplated products, including appearance inspection, coating thickness measurement, adhesion test, and color difference detection, to ensure that the products meet the relevant standards and customer requirements.

[0056] Result analysis

[0057] Figure 1 It shows the relationship between the average grain size and the Q-Time after self-annealing during the electroplated copper self-annealing process. The horizontal axis is the time after self-annealing, and the vertical axis is the average size (D) of the copper grains.

[0058] Figure 2 It is the appearance image of the copper grains with different Q-Time during the electroplated copper self-annealing process.

[0059] From Figure 1 and Figure 2 it can be seen that the size increases rapidly after 3h and then slows down and flattens after 9h. Thus, it can be determined that the incubation period of the recrystallization of electroplated copper is about 3h, and the completion time of recrystallization is about 9h. The electroplated copper basically completes the self-annealing behavior after 9h. Considering both the quality of the coating and cost efficiency, the optimal Q-Time is set to 6h.

[0060] Figure 3 It is the image of the electroplated copper after three-stage electroplating, and it can be seen that there is no abnormal color situation, meeting the requirements.

[0061] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

[0062] The above describes the present invention and its implementation manners. Such a description is not restrictive. What is shown in the drawings is only one of the implementation manners of the present invention, and the actual application is not limited thereto. Generally speaking, if those of ordinary skill in the art are inspired by it and, without departing from the purpose of the present invention, design similar ways and embodiments to this technical solution without creative efforts, they should all fall within the protection scope of the present invention.

Claims

1. A method for improving the copper color difference occurring in the electroplating process, characterized in that: It includes the following steps: Prepare the wafer; Perform copper electroplating; Perform nickel electroplating; Perform gold electroplating; After the copper electroplating step is completed, wait for 5h to 7h before performing nickel electroplating; The copper electroplating adopts three-stage electroplating, including the first-stage electroplating, the second-stage electroplating and the third-stage electroplating.

2. The method for improving the copper color difference occurring in the electroplating process according to claim 1, wherein: The current density corresponding to the first-stage electroplating is 2 to 4 ASD.

3. A method for improving the copper color difference occurring in the electroplating process according to claim 1, characterized in that: The current density corresponding to the first-stage electroplating is 3 ASD.

4. A method for improving the copper color difference occurring in the electroplating process according to claim 1, characterized in that: The current density corresponding to the second-stage electroplating is 2 ASD.

5. A method for improving the copper color difference occurring in the electroplating process according to claim 1, characterized in that: The current density corresponding to the third-stage electroplating is 0.6 ASD.

6. A method for improving the copper color difference occurring in the electroplating process according to claim 1, characterized in that: The copper electroplating step includes: Wash the wafer, perform copper electroplating, wash again, spin dry, and perform inspection and measurement.

7. A method for improving the copper color difference occurring in the electroplating process according to claim 2, characterized in that: The nickel electroplating step includes: Wash the wafer, perform pickling, wash again, perform nickel electroplating, and wash for the third time.

8. A method for improving the copper color difference occurring in the electroplating process according to claim 3, characterized in that: The gold electroplating step includes: Wash the wafer, perform gold electroplating, and wash again.

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