Wafer and processing thereof
By cleaning the back side of the wafer with an alkaline solution before photolithography, the problem of white crystal defects at the edge of the back side of the wafer was solved, improving the wafer processing quality and reducing the risk of wafer breakage.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANGHAI INTEGRATED CIRCUIT EQUIPMENT & MATERIALS INDUSTRY INNOVATION CENTER CO LTD
- Filing Date
- 2022-12-20
- Publication Date
- 2026-06-02
AI Technical Summary
White crystalline defects appear on the back edge of the wafer after photolithography, which can accumulate in subsequent processes and may lead to wafer breakage.
Before photolithography, the back side of the wafer is cleaned with an alkaline solution to neutralize residual acidic substances. This includes cleaning with a weak alkaline solution and at a specific temperature to remove chemical residues from the edges of the back side of the wafer.
This effectively avoids the generation of white crystal defects, improves wafer quality, and reduces the risk of wafer breakage.
Smart Images
Figure CN115985758B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of integrated circuit manufacturing, and in particular to a wafer and its processing technology. Background Technology
[0002] In the field of integrated circuit manufacturing, the back-end copper interconnect process involves multiple metals (such as copper, titanium, and aluminum). Since the lithography machine is shared by both the front and back ends, a wet back-cleaning process is performed before lithography to prevent contamination of the wafer by metals from the back end. This removes metal ions from the back side of the wafer, avoiding the risk of metal contamination during lithography. However, engineers have discovered that after lithography, varying amounts of white crystalline defects appear on the back edge of the wafer during the back-end copper interconnect process. If these defects are not addressed, the white crystals will gradually accumulate after multiple wet back-cleaning, lithography, and dry lithography processes, eventually forming noticeable white crystalline defects on the back edge of the wafer. This can prevent the wafer from being properly mounted on the cavity stage or even cause the wafer to break within the cavity.
[0003] Therefore, how to solve the above-mentioned technical problems should be a key focus for those skilled in the art. Summary of the Invention
[0004] The purpose of this application is to provide a wafer and its processing technology to avoid white crystal defects on the back edge of the wafer and improve wafer quality.
[0005] To address the aforementioned technical problems, this application provides a wafer fabrication process, comprising:
[0006] Obtain the wafer after back cleaning;
[0007] The back side of the wafer is cleaned using an alkaline solution to neutralize any acidic substances remaining on the back side of the wafer after back cleaning.
[0008] The wafer, after being cleaned with the alkaline solution, is subjected to photolithography.
[0009] Optionally, cleaning the back side of the wafer using an alkaline solution includes:
[0010] The back side of the wafer is cleaned using a weakly alkaline solution, wherein the pH value of the weakly alkaline solution is in the range of 8 to 9.5, including the endpoint values.
[0011] Optionally, cleaning the back side of the wafer using a weakly alkaline solution includes:
[0012] The back side of the wafer is cleaned using a mixed solution comprising ammonia and water.
[0013] Optionally, cleaning the back side of the wafer using a weakly alkaline solution includes:
[0014] The back side of the wafer is cleaned using a mixed solution comprising ammonia, hydrogen peroxide, and water.
[0015] Optionally, in the mixed solution, the volume ratio of ammonia, hydrogen peroxide and water ranges from 1:1.5:100 to 1:2:30, including the endpoint values.
[0016] Optionally, cleaning the back side of the wafer using a weakly alkaline solution includes:
[0017] The back side of the wafer is cleaned with a weakly alkaline solution at a preset temperature below 60 degrees Celsius for a cleaning time of 30 to 60 seconds, including the endpoint values.
[0018] Optionally, obtaining a back-cleaned wafer includes:
[0019] The back side of the wafer is cleaned using an acidic solution to remove metal ions from the back side of the wafer.
[0020] This application also provides a wafer obtained by any of the wafer processing techniques described above.
[0021] The wafer processing technology provided in this application includes: obtaining a wafer after back cleaning; cleaning the back side of the wafer with an alkaline solution to neutralize the acidic substances remaining on the back side of the wafer after back cleaning; and performing photolithography on the wafer after cleaning with the alkaline solution.
[0022] As can be seen, in this application, during wafer processing, after back cleaning, the back side of the wafer is cleaned with an alkaline solution before photolithography. The alkaline solution neutralizes any acidic substances remaining on the back side after back cleaning. Because the acidic substances remaining after back cleaning are neutralized and removed, even if there are chemical residues on the back edge after photolithography, white crystal defects will not occur on the back edge of the wafer, improving wafer quality and avoiding the risk of breakage during subsequent wafer fabrication.
[0023] In addition, this application also provides a wafer having the above-mentioned advantages. Attached Figure Description
[0024] To more clearly illustrate the technical solutions of the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0025] Figure 1 This is a flowchart of a wafer fabrication process provided in an embodiment of this application. Detailed Implementation
[0026] To enable those skilled in the art to better understand the present application, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some embodiments of the present application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0027] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.
[0028] As described in the background section, after wet back cleaning and photolithography, some white crystalline defects will appear on the back edge of the wafer. If the defects on the back edge of the wafer are not addressed, after multiple wet back cleaning, photolithography, and dry etching processes, the white crystals will gradually accumulate, eventually forming a more obvious white crystalline defect on the back of the wafer. This may lead to the wafer not being able to be adsorbed on the stage in the cavity or directly cause the wafer to break within the cavity.
[0029] In view of this, this application provides a wafer fabrication process, please refer to... Figure 1 ,include:
[0030] Step S101: Obtain the wafer after back cleaning.
[0031] It should be noted that this application does not limit the method of obtaining the wafer; any method can be chosen. Optionally, as one possible implementation, obtaining the back-cleaned wafer includes:
[0032] The back side of the wafer is cleaned using an acidic solution to remove metal ions from the back side of the wafer.
[0033] The specific operating steps of wet back cleaning are well known to those skilled in the art, and will not be described in detail here.
[0034] As another possible implementation, a wafer that has already undergone wet back cleaning can be directly obtained, that is, the wet back cleaning process step is not required in this wafer processing technology.
[0035] Step S102: Clean the back side of the wafer with an alkaline solution to neutralize the acidic substances remaining on the back side of the wafer after back cleaning.
[0036] During wet back-side cleaning, after etching the back of the wafer with a strong acidic solution, pure water is used to rinse away any remaining acidic substances on the back surface. However, the design of a single-wafer cleaning device has limited ability to clean the wafer edges, so residual acidic substances remain on the back of the wafer. This application does not limit the use of alkaline solutions; any solution that can neutralize the residual acidic solution on the back of the wafer is acceptable.
[0037] It should be noted that after cleaning with an alkaline solution, the back side of the wafer is rinsed with pure water.
[0038] Step S103: Perform photolithography on the wafer after it has been cleaned with the alkaline solution.
[0039] The specific steps for photolithography on the back side of a wafer are well known to those skilled in the art and will not be described in detail here.
[0040] Although white crystal defects may appear on the back side of the wafer after wet back cleaning and photolithography, the cause of these defects has not been discovered in the art, and therefore this defect cannot be resolved at present. The skill of the person applying this application has, through exploration and research, discovered the cause of the white crystals.
[0041] Through a series of disassembly experiments, the technical personnel of this application discovered that in the back-end copper interconnect process, neither wet back cleaning nor photolithography (coating, exposure, and development) of the wafer back side resulted in the precipitation of white crystalline defects at the wafer back edge. Therefore, it is believed that the white crystalline defects at the wafer back edge are caused by the combined effects of back cleaning and photolithography (coating and development).
[0042] The technical personnel of this application analyzed the causes of the back edge defects and found that there were two main reasons:
[0043] First, due to the design of the back cleaning equipment, although pure water is used to rinse the residual acid liquid on the back surface of the wafer after etching with strong acid liquid, the design of the single-wafer cleaning equipment has limited cleaning ability for the wafer edges. Therefore, a very small amount of acidic substances remain on the wafer edges.
[0044] Secondly, in the photolithography process, during the coating and developing steps, there is also the issue of photoresist or photoresist cleaning solution (OK73) and developer (such as TMAH (Tetramethylammonium Hydroxide)) penetrating to the back side of the wafer. Although pure water is used to clean the back side of the wafer during the developing step, the cleaning ability is limited, and trace amounts of chemicals from the photolithography process remain at the edges of the wafer.
[0045] The presence of these two chemical substances as residues leads to defects such as white crystalline material appearing on the back side of the wafer.
[0046] In this application, during wafer processing, after back cleaning, the back side of the wafer is cleaned with an alkaline solution before photolithography. The alkaline solution neutralizes any acidic substances remaining on the back side after back cleaning. Because the acidic substances remaining after back cleaning are neutralized and removed, even if there are chemical residues at the edge of the back side after photolithography, white crystal defects will not occur at the edge of the back side of the wafer, improving wafer quality and avoiding the risk of breakage during subsequent wafer fabrication.
[0047] In wet back-side cleaning, after etching the back side of the wafer with a strong acidic solution, pure water is used to rinse away any remaining acidic substances on the back surface. However, the design of a single-wafer cleaning device has limited edge cleaning capabilities, so the amount of acidic substances remaining on the back side is small. To ensure the acid-base neutralization reaction proceeds and to prevent excessive etching of the back side of the wafer by the alkaline solution, resulting in pits, in one embodiment of this application, based on the above embodiments, cleaning the back side of the wafer with an alkaline solution includes:
[0048] The back side of the wafer is cleaned using a weakly alkaline solution, wherein the pH value of the weakly alkaline solution is in the range of 8 to 9.5, including the endpoint values.
[0049] To ensure the smooth progress of the acid-base neutralization reaction, the back side of the wafer is cleaned using a weakly alkaline solution, including:
[0050] The back side of the wafer is cleaned with a weakly alkaline solution at a preset temperature below 60 degrees Celsius for a cleaning time of 30 to 60 seconds, including the endpoint values.
[0051] The preset temperature, cleaning time, and pH value of the weakly alkaline solution are interrelated, and the specific values depend on the situation.
[0052] It should be noted that this application does not limit the types of weakly alkaline solutions; you may choose to use your own.
[0053] Optionally, as one possible implementation, cleaning the back side of the wafer with a weakly alkaline solution includes cleaning the back side of the wafer with a mixed solution comprising ammonia and water.
[0054] However, this application does not specifically limit the above cleaning. In other embodiments of this application, cleaning the back side of the wafer with a weak alkaline solution includes cleaning the back side of the wafer with a mixed solution including ammonia, hydrogen peroxide and water.
[0055] In the mixed solution, the volume ratio of ammonia, hydrogen peroxide and water can range from 1:1.5:100 to 1:2:30, including the endpoint values.
[0056] By adding hydrogen peroxide to a weakly alkaline solution, the acidic substances remaining after back cleaning can be neutralized by the weakly alkaline solution, while particles remaining on the back of the wafer after previous process steps can be removed.
[0057] This application has been verified through extensive experiments. By using ammonia, hydrogen peroxide, and water mixed in a certain proportion (pH value controlled at 8-9.5), and the temperature selected below 60 degrees Celsius, after targeted back cleaning of the wafer back side, no white crystal precipitation was observed at the edge of the wafer back side after 24 hours of observation under an optical microscope.
[0058] In other words, in the back-end copper interconnect of integrated circuit manufacturing, after back cleaning, by adding a wet single-wafer cleaning equipment and setting preset parameters in the process menu of the equipment, a weak alkaline chemical solution can be used to perform targeted acid-base neutralization on a specific area of the back edge of the wafer, which can effectively avoid the risk of wafer breakage in subsequent wafer fabrication.
[0059] This application also provides a wafer obtained by the wafer processing technology described in any of the above embodiments.
[0060] In this embodiment, after wet back cleaning and before back-side photolithography, the wafer is cleaned with an alkaline solution to neutralize any acidic substances remaining on the back side after back cleaning. Because the acidic substances remaining after back cleaning are neutralized and removed, even if there are chemical residues on the back edge after photolithography, white crystal defects will not be generated on the back edge of the wafer, improving wafer quality and avoiding the risk of breakage during subsequent wafer fabrication.
[0061] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the method section.
[0062] The wafer and its processing technology provided in this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this application. It should be noted that those skilled in the art can make several improvements and modifications to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.
Claims
1. A wafer fabrication process, characterized in that, include: Obtain the wafer after back cleaning; The back side of the wafer is cleaned using an alkaline solution to neutralize any acidic substances remaining on the back side of the wafer after back cleaning. Photolithography is performed on the wafer after it has been cleaned with the alkaline solution. Cleaning the back side of the wafer using an alkaline solution includes: The back side of the wafer is cleaned using a weakly alkaline solution, wherein the pH value of the weakly alkaline solution is in the range of 8 to 9.5, including the endpoint values.
2. The wafer fabrication process as described in claim 1, characterized in that, Cleaning the back side of the wafer using a weakly alkaline solution includes: The back side of the wafer is cleaned using a mixed solution comprising ammonia and water.
3. The wafer fabrication process as described in claim 1, characterized in that, Cleaning the back side of the wafer using a weakly alkaline solution includes: The back side of the wafer is cleaned using a mixed solution comprising ammonia, hydrogen peroxide, and water.
4. The wafer fabrication process as described in claim 3, characterized in that, In the mixed solution, the volume ratio of ammonia, hydrogen peroxide and water ranges from 1:1.5:100 to 1:2:30, including the endpoint values.
5. The wafer fabrication process as described in claim 1, characterized in that, Cleaning the back side of the wafer using a weakly alkaline solution includes: The back side of the wafer is cleaned with a weakly alkaline solution at a preset temperature below 60 degrees Celsius for a cleaning time of 30 to 60 seconds, including the endpoint values.
6. The wafer fabrication process as described in claim 1, characterized in that, Obtaining a back-cleaned wafer includes: The back side of the wafer is cleaned using an acidic solution to remove metal ions from the back side of the wafer.
7. A wafer, characterized in that, The wafer is obtained by the wafer processing technology as described in any one of claims 1 to 6.