Near-infrared enhanced CCD (Charge Coupled Device) process manufacturing method

Abstract

The invention belongs to the field of solid image sensors, and relates to a near-infrared enhanced CCD (Charge Coupled Device) process manufacturing method, which comprises the following steps of: temporarily bonding a glass slide and the front side of a front-side CCD wafer to support a subsequent process; carrying out mechanical thinning and acid liquor corrosion on the back surface to remove a damaged layer; a transition region is removed through the CMP process, and dark current is reduced; a hard mask is deposited through PECVD, and a periodic arrangement hole structure is photoetched; etching and exposing the epitaxial layer, and preparing a light trapping structure; a passivation layer is grown through ALD, and the interface state density is reduced; depositing a metal aluminum reflecting mirror through PVD (physical vapor deposition); depositing a flat layer by PECVD (plasma enhanced chemical vapor deposition); and after permanent bonding, de-bonding is carried out, and the front electrode is exposed. According to the invention, the quantum efficiency of the CCD in the wave band of 800nm-1000nm is improved, and the method is suitable for low-illumination and all-weather imaging systems.

Description

Technical Field

[0001] The invention belongs to the field of solid image sensors and relates to a near-infrared enhanced CCD process manufacturing method. Background Art

[0002] The front structure of a traditional front-illuminated CCD image sensor consists of polysilicon, a dielectric film, and metal electrodes. Light incident on the CCD is absorbed and reflected, resulting in a peak quantum efficiency of less than 40%. Furthermore, the absorption rate of near-infrared light with a wavelength greater than 1000nm is low, resulting in poor imaging quality. However, near-infrared-enhanced CCD image sensors significantly enhance the sensitivity to wavelengths greater than 1000nm, improving imaging quality, and can broaden the response spectral range at a low cost. The development of near-infrared-enhanced CCD image sensors has significant application value, improving the performance of imaging systems in low-light conditions and enhancing their all-weather capabilities, both day and night, and in adverse weather conditions.

[0003] Currently, the main technologies for realizing near-infrared enhanced CCD image sensors include thick epitaxial technology, wet-process suede structure preparation, dry etching technology, and femtosecond laser black silicon preparation technology. Among them, thick epitaxial technology uses high-resistivity (>10000Ω.cm) thick epitaxial material (epitaxial layer thickness 100μm~200μm) for back-illuminated CCD process, and enhances the absorption of near-infrared band (800nm~1000nm) by increasing the depth of the depletion region. The disadvantage of this technology is that the defects of the high-resistance material (>0.1Ω.cm) of the substrate are difficult to control, which will increase the dark current of the device. The thinning technology of the back-illuminated process is also one of the difficulties. The high-resistivity substrate material cannot undergo self-stop etching process, and it is impossible to achieve low imaging defects.

[0004] The wet method for preparing the velvet structure generally uses acid or alkaline solution for velvet preparation. The velvet structure prepared by acid consumes 5μm to 6μm of silicon material, and only on this basis can the velvet structure be formed. Its structural characteristics are irregular, and the corrosive liquid has no selectivity for corroding the substrate silicon material and the epitaxial silicon material, which also causes a lot of damage to the epitaxial layer. In addition, due to the fast corrosion rate, the uniformity is difficult to control, and the near-infrared anti-reflection film is difficult to design.

[0005] Black silicon structures can also be prepared by using etching gases such as CF4 and SF6 for silicon etching. Dry etching requires plasma bombardment. Although it will form a regular pyramid structure, under long-term and high RF power, the CCD will be damaged by plasma and the dark current of the device will increase abnormally.

[0006] Femtosecond laser preparation of black silicon is also one of the current hot topics. Its principle is to use femtosecond laser to ablate silicon materials in a gas atmosphere such as SF6, producing a pyramid-like microstructure on the silicon surface. Since a high temperature of thousands of degrees is generated on the silicon surface in a short time, SF6 can be doped into the silicon material in the form of S atoms. By introducing shallow energy levels in the silicon band gap, the absorption and photoelectric conversion of light with a wavelength of 800nm ​​to 1000nm can be achieved, thereby improving the quantum efficiency of the 800nm ​​to 1000nm band. However, the difficulty of this technology lies in the fact that the defects generated by femtosecond laser ablation of silicon materials are difficult to suppress, which will also lead to CCD imaging defects, increased dark current and other problems. The engineering application of this technology is relatively difficult. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a near-infrared enhanced CCD process manufacturing method to solve the shortcomings of existing near-infrared enhanced CCD technology such as many imaging defects, large dark current and low quantum efficiency.

[0008] To achieve the above object, the present invention provides the following technical solution: a method for manufacturing a near-infrared enhanced CCD, comprising the following steps:

[0009] S1. Use a glass slide to perform high-temperature temporary bonding on the front side of the positive-illuminated CCD wafer to provide support for subsequent thinning, etching, photolithography, and other processes.

[0010] S2. Mechanically thinning the back side of the temporarily bonded CCD wafer to a thickness of 550 μm to 600 μm;

[0011] S3. Acid etching is performed on the back of the wafer to a thickness of 50 μm to 60 μm, from the back of the CCD to the epitaxial layer to remove the damaged layer after mechanical thinning of the wafer;

[0012] S4. Use CMP to remove the transition region from the CCD's highly doped substrate to the low-doped epitaxial layer, removing a thickness of 3 μm to 5 μm to reduce the CCD's dark current.

[0013] S5. Etch the silicon dioxide hard mask using an etcher to a thickness of 300nm to 1000nm, exposing the light-trapping areas that require alkali etching.

[0014] S6. Photolithographically forming a periodically arranged hole structure on the hard mask, with a hole diameter of 0.5 μm to 0.9 μm and a hole spacing of 0.6 μm to 1 μm, and exposing the epitaxial layer by etching;

[0015] S7. Use ALD-grown SiO2 and Al2O3 to perform surface passivation, reducing the interface state density on the epitaxial silicon surface, forming a surface passivation layer, and reducing the CCD surface dark current;

[0016] S8. Using a PVD process, deposit aluminum metal to a thickness of 800 nm to 1000 nm as a reflector for the light-trapping structure.

[0017] S9. Deposit SiO2 by PECVD process to a thickness of 2000 nm as a planar layer before bonding;

[0018] S10. Using permanent bonding adhesive and a carrier sheet, permanently bond the back side of the temporarily bonded CCD wafer.

[0019] S11. Use a laser debonder to debond, remove the glass slide, and use a temporary bonding adhesive cleaner to remove the temporary bonding adhesive, exposing the CCD front electrode to facilitate wire bonding for chip packaging.

[0020] Optionally, in step S3, a PECVD process is used to deposit a silicon dioxide hard mask with a thickness of 300 nm to 1000 nm to prevent the alkaline etching solution from corroding a large area of ​​the epitaxial layer surface.

[0021] Optionally, in step S4, periodically arranged holes are designed, the hole size is 0.5 μm to 0.9 μm, and the interval is 0.6 μm to 1 μm, and the wafer is exposed and developed.

[0022] Optionally, in step S6, the light trapping structure has a height of 700 nm to 1000 nm and an angle of 40° to 50°.

[0023] Optionally, in step S7, the thickness of SiO2 is 1 nm to 3 nm, and the thickness of Al2O3 is 20 nm to 30 nm.

[0024] The beneficial effects of the present invention are as follows: a near-infrared enhanced CCD manufacturing method of the present invention adopts a combination of a temporary bonding process and a permanent bonding process. The temporary bonding method is used for back-illumination process, a light-trapping structure is prepared on the surface of the epitaxial layer on the back of the CCD, the surface of the CCD light-trapping structure is permanently bonded, and finally the temporary bonded surface is debonded, exposing the front of the CCD. Light enters from the front of the CCD, and the optical path of the incident light is enhanced through absorption and reflection by the light-trapping structure on the back of the CCD epitaxial layer, thereby improving the quantum efficiency in the 800nm ​​to 1000nm band.

[0025] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings, in which:

[0027] Figure 1 Schematic diagram of the light trapping structure of the present invention;

[0028] Figure 2 This is a schematic diagram of temporary wafer bonding of the present invention;

[0029] Figure 3 Schematic diagram of mechanical thinning of the wafer backside according to the present invention;

[0030] Figure 4 A schematic diagram of wafer self-stop etching according to the present invention;

[0031] Figure 5 Schematic diagram of SiO2 deposition by the PECVD process of the present invention;

[0032] Figure 6 A schematic diagram of the light trapping structure lithography of the present invention;

[0033] Figure 7 Schematic diagram of etching the light trapping structure crystal mask of the present invention;

[0034] Figure 8 Schematic diagram of the fabrication of the light trapping structure passivation layer, reflector and flat layer of the present invention;

[0035] Figure 9 This is a schematic diagram of permanent wafer bonding of the present invention;

[0036] Figure 10 Schematic diagram of laser debonding of the present invention. DETAILED DESCRIPTION

[0037] The following describes the embodiments of the present invention by means of specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0038] Among them, the accompanying drawings are only for illustrative purposes and represent only schematic diagrams rather than actual pictures, and should not be understood as limiting the present invention. In order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the accompanying drawings.

[0039] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc. indicating directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0040] Example 1,

[0041] See also Figures 1 to 10 This embodiment aims to solve the problems of low absorption efficiency, large dark current and many imaging defects of traditional CCDs in the near-infrared band through an optimized near-infrared enhanced CCD process manufacturing method, improve the quantum efficiency of CCDs in the 800nm ​​to 1000nm band, and is suitable for low-illumination and all-weather imaging systems.

[0042] Implementation steps:

[0043] 1. Temporary bonding: Use a glass carrier to perform high-temperature resistant temporary bonding with the positive-illuminated CCD wafer that has completed the front-side process to ensure the stability and support of subsequent processes.

[0044] 2. Backside thinning: Mechanically thin the backside of the temporarily bonded CCD wafer, with the thinning thickness precisely controlled between 550μm and 600μm to improve thinning efficiency and reduce damage.

[0045] 3. Acid etching and self-stop etching: Acid etching is performed on the back of the thinned wafer with an etching thickness of 50μm to 60μm. The self-stop etching technology is used to etch the back of the CCD to the epitaxial layer to remove the damaged layer after mechanical thinning.

[0046] 4. CMP process: Chemical mechanical polishing (CMP) is used to remove the transition area from the CCD high-doped substrate to the low-doped epitaxial layer, removing a thickness of 3μm to 5μm, effectively reducing the CCD dark current.

[0047] 5. Hard mask deposition and photolithography: A silicon dioxide hard mask with a thickness of 300nm to 1000nm is deposited through the PECVD process. Subsequently, a periodically arranged pore structure with a pore diameter of 0.5μm to 0.9μm and a pore spacing of 0.6μm to 1μm is designed and photolithographically formed to prepare for subsequent etching.

[0048] 6. Preparation of light-trapping structure: Use an etcher to etch the hard mask to expose the light-trapping area that requires alkaline solution etching. Then use a solution such as tetramethylammonium hydroxide to etch the epitaxial layer to prepare a light-trapping structure with a height of 700nm to 1000nm and an angle of 40° to 50°.

[0049] 7. Surface passivation and reflector fabrication: A composite dielectric film of SiO2 (1nm-3nm) and Al2O3 (20nm-30nm) is grown using ALD technology for surface passivation, reducing the interface state density on the epitaxial silicon surface. PVD is then used to deposit aluminum metal as a reflector, with a thickness of 800nm-1000nm.

[0050] 8. Flat layer deposition and permanent bonding: A 2000nm thick SiO2 layer is deposited by PECVD process as a flat layer before bonding, and then a permanent bonding adhesive is used to permanently bond it to the carrier sheet.

[0051] 9. Debonding and cleaning: Use a laser debonder to remove the glass slide and thoroughly clean it with a temporary bonding adhesive cleaner to expose the CCD front electrode for subsequent chip packaging.

[0052] Implementation effect: This embodiment significantly improves the quantum efficiency of CCD in the 800nm ​​to 1000nm band by optimizing each process step, reduces dark current, and reduces imaging defects, making it suitable for low-illumination and all-weather imaging systems.

[0053] Example 2 is similar to Example 1, but with some parameters adjusted, and includes the following steps:

[0054] S1. Temporarily bond the front side of the completed positive-view CCD wafer to the glass slide in a high-temperature resistant manner.

[0055] S2. Thin the back side of the CCD wafer after temporary bonding to a thickness of (610±10) μm;

[0056] S3. Perform a back-side self-stop process on the thinned CCD wafer to remove the epitaxial silicon highly doped silicon substrate;

[0057] S4. Performing a silicon CMP process on the wafer after the self-stop etching to remove the transition zone (2 to 4 μm) where the highly doped silicon material diffuses into the low-doped silicon material;

[0058] S5. The wafer after silicon CMP is coated with photoresist (3μm to 5μm), and the anti-mark area is photolithographically processed and developed;

[0059] S6. Performing PECVD silicon dioxide deposition on the wafer after silicon CMP to form a hard mask for etching the light-trapping structure;

[0060] S7. Expose and develop the light-trap structure of the wafer after the SiO2 hard mask is completed;

[0061] S8. Hard grinding and etching the wafer having the light trapping structure completed;

[0062] S9. The wafer after hard grinding and etching is subjected to light trapping structure etching;

[0063] S10. The wafer having the light trapping structure is subjected to ALD growth of SiO2 and Al2O3 surface passivation;

[0064] S11. The surface passivated wafer is processed into a reflector;

[0065] S12. The wafer on which the reflector is made is subjected to PECVD deposition of SiO2;

[0066] S13. Apply bonding adhesive to the positive-illuminated CCD wafer and the carrier to a thickness of (3.5±0.2) μm and cure;

[0067] S14. Align the CCD wafer with the silicon carrier after the front-side process is completed, and use a double-sided photolithography machine to achieve the alignment of the CCD wafer and the silicon carrier.

[0068] S15. The aligned CCD wafer and the silicon carrier are permanently bonded on a bonding machine by applying a pressure of 1500N to 2000N.

[0069] S16. Using a laser debonder to perform a debonding process to remove the temporarily bonded glass slide;

[0070] S17. Debonding and cleaning the wafer after laser debonding.

[0071] This embodiment achieves rapid production of near-infrared enhanced CCDs by optimizing process parameters and processes while maintaining or improving their performance, and is suitable for scenarios with higher requirements for production efficiency.

[0072] In summary, a temporary bonding process is used for back-illuminated fabrication. A low-damage light-trapping structure is fabricated on the back of the CCD epitaxial layer. A SiO2 and Al2O3 composite dielectric film is deposited using ALD thermal growth to passivate the surface of the light-trapping structure. This further reduces the number of suspended components on the epitaxial layer, forming surface field-effect passivation and reducing the CCD's dark current. The CCD that has completed the back-illuminated process is permanently bonded, and the light-trapping structure is buried between the carrier and the CCD wafer. Laser debonding is used to remove the temporarily bonded glass carrier. The device finally receives light from the front. Incident light in the 800nm ​​to 1064nm band that is not fully absorbed by the absorption layer is reflected by the light-trapping structure on the back of the CCD epitaxial layer and absorbed again. Compared to traditional near-infrared enhancement technology, the absorption optical path is doubled, and the quantum efficiency of the CCD for 800nm ​​to 1064nm is increased by approximately 50%.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. 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 solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A near-infrared enhanced CCD process manufacturing method, characterized in that: The following steps are involved: S1. Use a glass slide to perform high-temperature temporary bonding on the front side of the positive-illuminated CCD wafer to provide support for subsequent thinning, etching, photolithography, and other processes. S2. Mechanically thinning the back side of the temporarily bonded CCD wafer to a thickness of 550 μm to 600 μm; S3. Acid etching is performed on the back of the wafer to a thickness of 50 μm to 60 μm, and the back of the CCD is etched from the self-stopping etching to the epitaxial layer to remove the damaged layer after mechanical thinning of the wafer; S4. Use CMP to remove the transition region from the CCD's highly doped substrate to the low-doped epitaxial layer, removing a thickness of 3 μm to 5 μm to reduce the CCD's dark current. S5. Etch the silicon dioxide hard mask using an etcher to a thickness of 300nm to 1000nm, exposing the light-trapping areas that require alkali etching. S6. Photolithographically forming a periodically arranged hole structure on the hard mask, with a hole diameter of 0.5 μm to 0.9 μm and a hole spacing of 0.6 μm to 1 μm, and exposing the epitaxial layer by etching; S7. Use ALD-grown SiO2 and Al2O3 to perform surface passivation, reducing the interface state density on the epitaxial silicon surface, forming a surface passivation layer, and reducing the CCD surface dark current; S8. Using a PVD process, deposit aluminum metal to a thickness of 800 nm to 1000 nm as a reflector for the light-trapping structure. S9. Deposit SiO2 by PECVD to a thickness of 2000 nm as a planar layer before bonding; S10. Using permanent bonding adhesive and a carrier sheet, permanently bond the back side of the temporarily bonded CCD wafer. S11. Use a laser debonder to debond, remove the glass slide, and use a temporary bonding adhesive cleaner to remove the temporary bonding adhesive, exposing the CCD front electrode to facilitate wire bonding for chip packaging.

2. The method for manufacturing a near-infrared enhanced CCD according to claim 1, wherein: In step S3, a PECVD process is used to deposit a silicon dioxide hard mask with a thickness of 300 nm to 1000 nm to prevent the alkaline etching solution from corroding a large area of ​​the epitaxial layer surface.

3. The method for manufacturing a near-infrared enhanced CCD according to claim 1, wherein: In step S4, periodically arranged holes are designed with a size of 0.5 μm to 0.9 μm and a spacing of 0.6 μm to 1 μm, and the wafer is exposed and developed.

4. The method for manufacturing a near-infrared enhanced CCD according to claim 1, wherein: In step S6, the light trapping structure has a height of 700 nm to 1000 nm and an angle of 40° to 50°.

5. The method for manufacturing a near-infrared enhanced CCD according to claim 1, wherein: In step S7, the thickness of SiO2 is 1nm to 3nm, and the thickness of Al2O3 is 20nm to 30nm.

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