Backside illuminated image sensor pad opening method

Abstract

The application provides a back-illuminated image sensor pad opening method, comprising the following steps: making a recognition pattern on the back surface of a wafer according to the pattern surface of the wafer by a suess photoetching machine; bonding the wafer and a sensor wafer into an integrated structure and thinning the sensor wafer; recognizing the recognition pattern by the suess photoetching machine and exposing a pad pattern on the sensor wafer; and post-processing the pad pattern to realize pad opening. The technical scheme can realize the opening of the back-illuminated image sensor pad by using low-cost equipment.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing, and in particular to a method for opening pads of a back-illuminated image sensor. Background Technology

[0002] The basic structure of a back-illuminated sensor wafer consists of a carrier wafer and a sensor wafer bonded together perpendicularly face-to-face. This results in the patterned surface of the back-illuminated sensor wafer being located at the bonding interface. Because silicon at the bonding interface obstructs laser and halogen light, conventional lithography machines cannot recognize the markings at the bonding interface, thus failing to identify the patterned surface and preventing the pads from being opened. Currently, the industry generally uses blind opening technology or infrared alignment technology to solve this problem. Blind opening technology uses wafer notches for mechanical alignment, then etches away 4-20 micrometers of silicon at specific locations to expose the alignment marks, allowing the pads to be opened using a conventional lithography machine. Infrared alignment technology uses an infrared light source to penetrate the silicon and identify the markings at the bonding interface, enabling pad opening. However, blind opening technology adds a lithography and deep silicon etching process, and deep silicon etching equipment is expensive. Infrared alignment technology requires an infrared lithography machine, which is often even more expensive. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of existing technologies and propose a method for opening the pads of a back-illuminated image sensor, which can achieve the opening of the pads of a back-illuminated image sensor using low-cost equipment.

[0004] To achieve the above objectives, the present invention adopts the following specific technical solution:

[0005] The back-illuminated image sensor pad opening method according to an embodiment of the present invention includes: S100, forming an identification pattern on the back side of a wafer using a Sousser lithography machine based on the patterned surface of the wafer; S200, bonding the wafer and the sensor wafer, patterned surface to patterned surface, into an integral structure, and thinning the sensor wafer; S300, identifying the identification pattern using the Sousser lithography machine and exposing a pad pattern on the sensor wafer; S400, performing post-processing on the pad pattern to open the pads.

[0006] It should be noted that the SUSS lithography machine is also known as the Suss lithography machine. The price of the Suss lithography machine is much lower than that of infrared lithography machines and deep silicon etching equipment. The Suss lithography machine can create recognition patterns on wafers and can also recognize patterns on patterned surfaces. However, the Suss lithography machine cannot recognize the marks at the bonding interface, and therefore cannot recognize the patterned surface at the bonding interface, and cannot open the pads of back-illuminated sensors.

[0007] The back-illuminated image sensor pad opening method of this invention achieves at least the following beneficial effects: Before bonding the carrier wafer and the sensor wafer, a Seuss lithography machine is used to identify the patterned surface of the carrier wafer (the patterned surface of the carrier wafer is the front side of the carrier wafer), and an identification pattern is created on the back side of the carrier wafer. After bonding, the patterned surface of the carrier wafer is located at the bonding interface, but the identification pattern created before bonding is located on the back side of the carrier wafer and not at the bonding interface. Therefore, the identification pattern created before bonding can be identified, and the pads of the sensor wafer are opened by identifying the identification pattern created before bonding, thereby realizing the pad opening of a back-illuminated image sensor using a low-cost Seuss lithography machine.

[0008] According to some embodiments of the present invention, step S100 includes:

[0009] S110. Apply a protective film to the graphic surface;

[0010] S120. Flip the wafer so that the back side of the wafer faces upward and remove the back seal structure of the wafer.

[0011] S130. Apply adhesive to the back side of the carrier wafer;

[0012] S140. The wafer is fed into the Sous lithography machine, the Sous lithography machine identifies the patterned surface of the wafer, and the pattern is exposed on the back side of the wafer.

[0013] S150. Develop, etch, and remove the resist from the back side of the carrier wafer.

[0014] According to some embodiments of the present invention, the protective film is one of a blue film, a UV film, or a high-temperature resistant film.

[0015] According to some embodiments of the present invention, step S120 includes thinning and cleaning the back side of the carrier wafer, wherein the thinning thickness is 3-80 micrometers.

[0016] According to some embodiments of the present invention, step 100 further includes: after thinning and cleaning the back side of the carrier wafer, depositing silicon dioxide on the back side of the carrier wafer to a thickness of 0.2-2 micrometers. According to some embodiments of the present invention, the identification pattern is a cross mark.

[0017] According to some embodiments of the present invention, the thickness of the sensor wafer is reduced to 4-20 micrometers.

[0018] According to some embodiments of the present invention, step S300 includes: S310, placing the sensor wafer above the carrier wafer, and applying adhesive to the surface of the sensor wafer; S320, passing the sensor wafer and the carrier wafer into the Suez lithography machine, identifying the identification pattern on the carrier wafer through the Suez lithography machine, and exposing pad patterns on the sensor wafer.

[0019] According to some embodiments of the present invention, the identification pattern is identified by utilizing the back-side alignment function of the Suss lithography machine, and the pad pattern is exposed on the back side of the sensor wafer.

[0020] According to some embodiments of the present invention, step S400 includes: developing, etching and removing the resist from the sensor wafer.

[0021] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0022] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0023] Figure 1 This is a flowchart of a method for opening pads of a back-illuminated image sensor according to an embodiment of the present invention;

[0024] Figure 2 This is a flowchart of step S100 according to an embodiment of the present invention;

[0025] Figure 3 This is a flowchart of step S300 according to an embodiment of the present invention. Detailed Implementation

[0026] In the following description, embodiments of the invention will be described with reference to the accompanying drawings. In the description below, the same modules are denoted by the same reference numerals. Where the same reference numerals are used, their names and functions are also the same. Therefore, their detailed description will not be repeated.

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0028] Front-illuminated image sensor wafers have patterns and markings on their surface, allowing for pad opening via conventional photolithography. However, back-illuminated image sensor wafers are fundamentally composed of a carrier wafer and a sensor wafer, with their patterned faces perpendicularly stacked and bonded together. Therefore, the patterned face of the carrier wafer is located at the bonding interface. Due to silicon's blocking effect on laser and halogen light, conventional photolithography machines cannot recognize the markings at the bonding interface, thus failing to identify the patterned face and preventing pad opening.

[0029] Therefore, the present invention provides a method for opening the pads of a back-illuminated image sensor, which aims to achieve the opening of the pads of a back-illuminated image sensor using a less expensive and lower-cost Suss lithography machine.

[0030] The back-illuminated image sensor pad opening method provided in the embodiments of the present invention, such as... Figure 1 As shown, the process includes: S100, creating an identification pattern on the back side of the carrier wafer using a Sous lithography machine based on the patterned surface of the carrier wafer; S200, bonding the carrier wafer and the sensor wafer into an integrated structure and thinning the sensor wafer; S300, identifying the identification pattern using a Sous lithography machine and exposing the pad pattern on the sensor wafer; S400, performing post-processing on the pad pattern to open the pads.

[0031] The patterned surface is generally located on the front side of the wafer. In this solution, before bonding the carrier wafer and the sensor wafer, an identification pattern is made on the back side of the carrier wafer based on the patterned surface. After the carrier wafer and the sensor wafer are bonded, although the patterned surface of the carrier wafer is at the bonding interface and cannot be identified, the identification pattern on the back side of the carrier wafer can be identified normally. Therefore, the pad pattern can be exposed on the sensor wafer based on the identification pattern and the subsequent pad opening process can be performed.

[0032] In existing technologies, the deep silicon etching equipment used in blind-opening processes and the infrared lithography machines used in infrared alignment processes often cost tens of millions of RMB or more, resulting in high production costs. This method can be implemented using a Suez lithography machine or other lithography machines, which are much cheaper and significantly reduce production costs.

[0033] The SUSS lithography machine is priced much lower than infrared lithography machines and deep silicon etching equipment. It can create identification patterns on wafers and recognize patterns on patterned surfaces. However, it cannot recognize marks at bonding interfaces, and therefore cannot recognize patterned surfaces at bonding interfaces, thus it cannot open the pads of back-illuminated sensors.

[0034] A carrier wafer can be a wafer that has no circuitry and only serves as a carrier, or it can be a wafer with logic circuitry that serves as a signal processing device. Creating identification patterns on a carrier wafer has almost no or minimal impact on the carrier wafer.

[0035] In step S100, an identification pattern is created on the back side of the wafer using a Sousser lithography machine based on the patterned surface of the wafer. This identification pattern is then used in subsequent processes to open the solder pads.

[0036] In step S200, the carrier wafer and the sensor wafer are bonded together as a single structure with patterned surfaces facing each other, and the sensor wafer is thinned. After the carrier wafer is processed, the bonding and thinning processes can be performed on the carrier wafer and the sensor wafer.

[0037] In step S300, the identification pattern is identified using a Suez lithography machine, and the pad pattern is exposed on the sensor wafer. After the carrier wafer and the sensor wafer are bonded, the patterned surface of the carrier wafer is located at the bonding interface and cannot be identified. Therefore, the sensor wafer is exposed by identifying the identification pattern created in step S100, and the exposed pattern is the pad pattern.

[0038] Step S400: Post-processing is performed on the pad pattern to open the pads. After the pad pattern is exposed on the sensor wafer, the pads can be opened through post-processing.

[0039] Before bonding the carrier wafer and the sensor wafer, a Suez lithography machine is used to identify the patterned surface of the carrier wafer (the patterned surface of the carrier wafer is the front side of the carrier wafer) and to create an identification pattern on the back side of the carrier wafer. After the carrier wafer and the sensor wafer are bonded, the patterned surface of the carrier wafer is at the bonding interface. However, the identification pattern created before bonding is on the back side of the carrier wafer and not at the bonding interface, so the identification pattern created before bonding can be identified. By identifying the identification pattern created before bonding, the pads of the sensor wafer are opened, thereby realizing the opening of the pads of the back-illuminated image sensor using a low-cost Suez lithography machine.

[0040] According to some embodiments of the present invention, such as Figure 2 As shown, step S100 includes: S110, applying a protective film to the patterned surface; S120, flipping the wafer so that the back side of the wafer faces upward, and removing the back seal structure of the wafer; S130, applying adhesive to the back side of the wafer; S140, feeding the wafer into the Suez lithography machine, using the Suez lithography machine to identify the patterned surface of the wafer, and exposing the pattern on the back side of the wafer; S150, developing, etching, and removing the adhesive from the back side of the wafer.

[0041] Step S110: Apply a protective film to the graphic surface to protect the graphic pattern and prevent it from being stained or scratched in subsequent processes.

[0042] According to some embodiments of the present invention, the protective film is one of a blue film, a UV film, or a high-temperature resistant film.

[0043] Step S120: Flip the wafer so that the back side of the wafer faces upward and remove the back seal structure of the wafer.

[0044] Use a vacuum pen to flip the wafer so that the back side of the wafer is facing up and the patterned side is facing down. Remove the back seal structure on the back side of the wafer to expose the silicon on the back side.

[0045] According to some embodiments of the present invention, step S120 includes thinning and cleaning the back side of the wafer, wherein the thinning thickness is 3-80 micrometers.

[0046] The back side of the carrier wafer is thinned, and the thickness of the material removed during the thinning process is 3-80 micrometers, so that the back seal structure of the carrier wafer is completely removed.

[0047] When the material removal thickness is less than 3 micrometers, the back cover structure of the carrier wafer is not completely removed; when the material removal thickness is greater than 80 micrometers, it will affect the carrier wafer.

[0048] After thinning the carrier wafer, clean the back side of the carrier wafer to avoid the waste generated during the thinning process affecting subsequent processes.

[0049] Clean the back side of the carrier wafer using deionized water or Cleaning Solution No. 1.

[0050] Understandably, other chemical solutions can also be used to clean the back side of the wafer.

[0051] According to some embodiments of the present invention, step 100 further includes: after thinning and cleaning the back side of the carrier wafer, depositing silicon dioxide on the back side of the carrier wafer at low temperature by chemical vapor deposition, with a deposition thickness of 0.2-2 micrometers.

[0052] After removing the back seal structure, the silicon on the carrier wafer is exposed. In some cases, the back side of the carrier wafer needs to be made of other materials. Taking silicon dioxide as an example, when silicon dioxide is required on the back side of the carrier wafer, silicon dioxide deposition is performed on the back side of the carrier wafer, and a deposition thickness of 0.2-2 micrometers is sufficient to meet the requirements.

[0053] It is understood that the deposition material can also be other materials, and the embodiments of the present invention are not limited thereto.

[0054] It is understandable that when the silicon on the back of the wafer meets the process requirements, there is no need to deposit material on the back of the wafer.

[0055] Step S130: Apply photoresist to the back side of the carrier wafer.

[0056] Step S140: The wafer is fed into the Suez lithography machine, which identifies the patterned surface of the wafer and exposes the pattern on the back side of the wafer.

[0057] Using the back-side alignment function of the SUSCH lithography machine, markings on the patterned surface are identified, and the identification pattern is exposed on the back side of the wafer. Since the wafer is flipped in step S120, with the patterned surface facing down, the markings on the patterned surface can be directly identified using the back-side alignment function of the SUSCH lithography machine. In step S130, photoresist has already been applied to the back side of the wafer; therefore, the patterned surface of the wafer is identified by the SUSCH lithography machine, and the identification pattern is exposed on the photoresist on the back side of the wafer.

[0058] Step S150: Develop, etch, and remove the resist from the back side of the carrier wafer.

[0059] After the identification pattern is exposed, it does not appear immediately. The wafer needs to be developed and etched to a depth of 0.2-2 micrometers to reveal the exposed pattern. After etching, the photoresist is removed, completing the identification pattern fabrication process.

[0060] According to some embodiments of the present invention, the identification pattern is a cross mark. The cross mark can be identified by a Suez lithography machine.

[0061] Understandably, other patterns that can be recognized by the lithography machine can also be used for pattern recognition.

[0062] According to some embodiments of the present invention, the thickness of the sensor wafer after thinning is 4-20 micrometers. Good performance can be maintained when the sensor wafer thickness is 4-20 micrometers.

[0063] According to some embodiments of the present invention, such as Figure 3 As shown, step S300 includes: S310, placing the sensor wafer above the carrier wafer, and applying adhesive to the surface of the sensor wafer; S320, feeding the sensor wafer and the carrier wafer into the Suez lithography machine, identifying the identification pattern on the carrier wafer through the Suez lithography machine, and exposing the pad pattern on the sensor wafer.

[0064] Step S310: Position the sensor wafer above the carrier wafer and apply adhesive to the surface of the sensor wafer.

[0065] After the sensor wafer and the carrier wafer are bonded together to form a single structure, the relative positions of the sensor wafer and the carrier wafer are adjusted so that the sensor wafer is above the carrier wafer. At this point, the identification pattern on the carrier wafer is located at the bottom of the single structure formed by the bonding of the carrier wafer and the sensor wafer. Photoresist is then applied to the surface of the sensor wafer.

[0066] It should be noted that before applying adhesive to the sensor wafer surface, the sensor wafer surface can be cleaned with deionized water or No. 1 cleaning solution.

[0067] Step S320: The sensor wafer and the carrier wafer are fed into the Suez lithography machine. The Suez lithography machine identifies the identification pattern on the carrier wafer and exposes the pad pattern on the sensor wafer.

[0068] The identification pattern of the carrier wafer is identified by the Suss lithography machine, and the pad pattern is exposed on the resist coating surface of the sensor wafer.

[0069] According to some embodiments of the present invention, the back-side alignment function of the Souss lithography machine is used to identify the identification pattern and expose the pad pattern on the back side of the sensor wafer. In step S310, the relative positions between the sensor wafer and the carrier wafer have been adjusted, and the identification pattern is located at the bottom of the integrated structure formed after the carrier wafer and the sensor wafer are bonded. The back-side alignment function of the Souss lithography machine can be used directly to identify the identification pattern and expose the pad pattern on the back side of the sensor wafer.

[0070] According to some embodiments of the present invention, step S400 includes: developing, etching and removing the resist from the sensor wafer.

[0071] After the pad pattern is exposed, it is not displayed. The sensor wafer needs to be developed and etched to reveal the exposed pad pattern. After etching, the photoresist is removed, completing the pad opening process.

[0072] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0073] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

[0074] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A backside illuminated image sensor pad opening method, characterized by, The method comprises the following steps: S100, providing a carrier wafer and a sensor wafer, identifying a lithography mark on a pattern surface of the carrier wafer by a suess lithography machine, and making an identification pattern on the back surface of the carrier wafer; in a subsequent process, a pad opening process is performed by identifying the identification pattern on the back surface of the carrier wafer; S200, bonding the carrier wafer and the sensor wafer into an integrated structure, and thinning the sensor wafer; S300, identifying the identification pattern by the back surface alignment function of the suess lithography machine and exposing the back surface of the sensor wafer, and the exposure pattern is a pad pattern; S400, post-processing the pad pattern to realize pad opening; comprising: coating, exposing, developing the sensor wafer, and etching the sensor wafer to make the exposed pad pattern visible; After etching, the photoresist is removed, and the pad opening process is completed.

2. The backside illumination image sensor pad opening method of claim 1, wherein, The step S100 comprises: S110, pasting a protective film on the pattern surface; S120, turning over the carrier wafer so that the back surface of the carrier wafer faces upward, and removing the back sealing structure of the carrier wafer; S130, coating the back surface of the carrier wafer; S140, transferring the carrier wafer into the suess lithography machine, identifying the pattern surface of the carrier wafer by the suess lithography machine, and exposing the identification pattern on the back surface of the carrier wafer; S150, developing, etching and removing the back surface of the carrier wafer.

3. The backside illuminated image sensor pad opening method of claim 2, wherein, The protective film is one of a blue film, a UV film or a high-temperature resistant film.

4. The backside illuminated image sensor pad opening method of claim 2, wherein, The step S120 comprises thinning and cleaning the back surface of the carrier wafer, and the thickness of the thinning is 3-80 microns.

5. The backside illuminated image sensor pad opening method of claim 4, wherein, The step 100 further comprises: after thinning and cleaning the back surface of the carrier wafer, depositing silicon dioxide on the back surface of the carrier wafer, and the deposition thickness is 0.2-2 microns.

6. The backside illumination image sensor pad opening method of claim 5, wherein, The identification pattern is a cross mark.

7. The backside illumination image sensor pad opening method of claim 1, wherein, The thickness of the sensor wafer after thinning is 4-20 microns.

8. The backside illumination image sensor pad opening method of claim 1, wherein, The step S300 comprises: S310, making the sensor wafer above the carrier wafer, and coating the surface of the sensor wafer; S320, transferring the sensor wafer and the carrier wafer into the suess lithography machine, identifying the identification pattern on the carrier wafer by the suess lithography machine, and exposing the pad pattern on the sensor wafer.

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