阅读说明：本技术 一种增强近红外量子效率的背照式ccd及其制作方法 (Back-illuminated CCD (charge coupled device) for enhancing near-infrared quantum efficiency and manufacturing method thereof ) 是由 江海波 李睿智 杨修伟 黄建 曲鹏程 雷仁方 于 2020-06-24 设计创作，主要内容包括：本发明涉及CCD技术,涉及一种增强近红外量子效率的背照式CCD及其制作方法；所述制作方法包括在背照式CCD晶圆的正面上淀积低温二氧化硅；采用二氧化硅化学机械抛光工艺,平坦化CCD晶圆的表面,并去除一定厚度的低温二氧化硅；在低温二氧化硅光刻出多个圆形的微结构图形；采用二氧化硅各项同性干法刻蚀,在微结构图形上刻蚀出坡面,形成半球形微结构；采用磁控溅射法在半球形微结构表面淀积金属铝反射层；在其表面涂覆键合胶后,与载体片完成键合工艺制作；本发明采用刻蚀方法,刻蚀出半球形微结构淀积铝膜,从而形成铝反射镜,增强对入射光反射并形成全反射,提升了硅对入射光的吸收,提升尤其是近红外波段量子效率。(The invention relates to a CCD technology, in particular to a back-illuminated CCD for enhancing near-infrared quantum efficiency and a manufacturing method thereof; the manufacturing method comprises the steps of depositing low-temperature silicon dioxide on the front surface of a back-illuminated CCD wafer; flattening the surface of the CCD wafer by adopting a silicon dioxide chemical mechanical polishing process, and removing low-temperature silicon dioxide with a certain thickness; photoetching a plurality of circular microstructure patterns on low-temperature silicon dioxide; etching a slope on the microstructure pattern by adopting isotropic dry etching of silicon dioxide to form a hemispherical microstructure; depositing a metal aluminum reflecting layer on the surface of the hemispherical microstructure by adopting a magnetron sputtering method; after coating bonding glue on the surface of the carrier sheet, completing the manufacturing of a bonding process with the carrier sheet; according to the invention, the deposited aluminum film of the hemispherical microstructure is etched by adopting an etching method, so that an aluminum reflecting mirror is formed, the reflection of incident light is enhanced, the total reflection is formed, the absorption of silicon to the incident light is promoted, and especially the near-infrared band quantum efficiency is promoted.)

1. A back-illuminated CCD manufacturing method for enhancing near-infrared quantum efficiency is characterized by comprising the following steps:

depositing 2-3 mu m low-temperature silicon dioxide on the front surface of the back-illuminated CCD wafer, wherein the deposition temperature is 260-320 ℃;

flattening the surface of the CCD wafer by adopting a silicon dioxide chemical mechanical polishing process, and removing low-temperature silicon dioxide with the thickness of 0.5-1.5 mu m on the surface of the CCD wafer;

photoetching on low-temperature silicon dioxide to form a plurality of circular microstructure patterns;

etching a slope angle on the microstructure pattern by adopting isotropic dry etching of silicon dioxide, and forming a hemispherical microstructure;

depositing a metal aluminum reflecting layer on the surface of the hemispherical microstructure by adopting a magnetron sputtering method or an evaporation method;

and coating bonding glue on the surface of the metal aluminum reflecting layer, and then completing the bonding process with the carrier sheet.

2. The method of claim 1, further comprising, after completing the bonding process, the steps of:

thinning and polishing the back of the CCD wafer, and forming a passivation layer on the back of the thinned CCD wafer;

depositing an antireflection film on the upper surface of the passivation layer to enhance light absorption;

growing metal on the back of the CCD wafer, and photoetching to form shading aluminum on the back; and forming a pressure welding point on the back of the CCD wafer.

3. The method for manufacturing the back-illuminated CCD for enhancing the near-infrared quantum efficiency according to claim 1, wherein the conditions for dry etching the hemispherical microstructure by using isotropic silicon dioxide comprise a NF (NF) with a chamber pressure of 500-2000 mt and an etching atmosphere of 30-300 mL/min₃And He of 40-700 mL/min; NF₃And the He gas ratio is 3: 4-7, the radio frequency power is 500-800W, and the etching time is 40-90 s.

4. The method of claim 1, wherein the slope angle is greater than 36 °.

5. A back-illuminated CCD for enhancing near-infrared quantum efficiency comprises a CCD wafer and a carrier sheet; the front surface of the CCD wafer is connected with the carrier sheet through bonding; the CCD wafer comprises a dielectric layer, polycrystalline silicon and an epitaxial layer, a gate oxide dielectric layer grows on the epitaxial layer, and a polycrystalline silicon electrode and the dielectric layer are formed above the gate oxide dielectric layer; forming a potential well on the epitaxial layer by ion implantation; depositing low-temperature silicon dioxide above a dielectric layer of a CCD wafer, wherein a plurality of microstructure patterns are etched on the low-temperature silicon dioxide, and each microstructure pattern has a certain slope angle, so as to form a hemispherical microstructure; a metal aluminum reflecting layer is deposited on the outer surface of the hemispherical microstructure and is bonded with the carrier sheet through bonding glue; forming a passivation layer on the other surface, namely the back surface, of the epitaxial layer, forming an antireflection film on the surface of the passivation layer, growing metal aluminum, and photoetching to form shading aluminum; and finally, etching silicon to form a pressure welding point.

6. The back-illuminated CCD of claim 5, wherein the diameter of the microstructure patterns is 0.5-0.7 μm, and the center-to-center distance of each microstructure pattern is 1.3-1.7 μm.

7. The back-illuminated CCD for enhancing the near-infrared quantum efficiency of claim 5, wherein the etching depth of the hemispherical microstructure is 0.7-0.8 μm.

8. The back-illuminated CCD of enhanced near-infrared quantum efficiency according to claim 5, wherein the slope angle is greater than 36 °.

9. The back-illuminated CCD of claim 5, wherein the thickness of the metallic aluminum reflective layer on the surface of the microstructure is 0.8-1.2 μm.

Technical Field

The invention relates to a manufacturing technology of a Charge Coupled Device (CCD), in particular to a back-illuminated CCD for enhancing near-infrared quantum efficiency and a manufacturing method thereof.

Background

A back-illuminated charge-coupled device (CCD) generally adopts a back-incident imaging mode, so that the absorption and reflection of a CCD surface dielectric layer and a polycrystalline silicon electrode on incident light are avoided, and the quantum efficiency can reach 90% in a visible light wave band by combining a back antireflection film.

A typical back-illuminated CCD structure is shown in fig. 1, and a conventional back-illuminated CCD includes a CCD wafer and a carrier sheet; the front surface of the CCD wafer is connected with the carrier sheet through bonding; the CCD wafer comprises a dielectric layer (generally BPSG boron phosphorus silicon glass is adopted as the dielectric layer), polycrystalline silicon and an epitaxial layer, a gate oxide layer dielectric is grown on the epitaxial layer, and a polycrystalline silicon electrode and the dielectric layer are formed above the gate oxide layer dielectric; forming a potential well on the epitaxial layer by ion implantation; depositing low-temperature silicon dioxide on the dielectric layer of the CCD wafer, and bonding the CCD wafer and the carrier plate through bonding glue; and a passivation layer is formed on the back surface of the epitaxial layer, and an antireflection film is formed on the surface of the passivation layer.

The back side of the wafer is mainly processed as shown in FIG. 2, and mainly comprises depositing silicon dioxide on a corresponding CCD wafer, and connecting the wafer with a carrier plate in a bonding manner; thinning the back of the CCD wafer; cleaning the back surface of the substrate, forming a passivation layer on the back surface, depositing an antireflection film, growing metal aluminum, photoetching and etching to form back surface shading aluminum, and preparing the pressure welding points.

For the CCD and the preparation method thereof, the photoelectric conversion capability of the CCD can be quantified through quantum efficiency; the quantum efficiency is an important parameter for describing the photoelectric conversion capability of the photoelectric device, and refers to the ratio of the photocurrent generated by unit photon number to the incident photocurrent; the back-illuminated CCD quantum efficiency is given by the following equation:

wherein C is the charge collection efficiency, R is the reflectivity, x is the thickness of the silicon epitaxial layer, and L is the absorption depth. For a back-illuminated CCD with a specific epitaxial layer thickness, an antireflection film is deposited on an incident surface, so that the incident light reflectivity can be reduced, the quantum efficiency is improved, and in a visible light waveband, a silicon epitaxial layer with the thickness of about 15 mu m can fully absorb the incident light, so that the quantum efficiency is high and can reach 90%. The incident wavelength and absorption depth curve is shown in fig. 3, and the full absorption is realized in the near infrared band, and the absorption depth is more than 100 μm. For a back-illuminated CCD with the epitaxial layer thickness of 15 microns, only a small part of incident light is absorbed by the epitaxial layer, and most of the incident light penetrates through the epitaxial layer and is not absorbed by the silicon epitaxial layer, so that the quantum efficiency is not high, the average quantum efficiency is lower than 8% in the wave band of 1000 nm-1060 nm, and the requirement of CCD near-infrared detection imaging is not met.

Disclosure of Invention

In order to improve the near-infrared band quantum efficiency of the back-illuminated CCD, the invention provides a novel back-illuminated CCD for enhancing the near-infrared band quantum efficiency and a manufacturing method thereof, which are beneficial to improving the near-infrared band quantum efficiency.

In a first aspect of the present invention, the present invention provides a method for fabricating a back-illuminated CCD for enhancing near-infrared quantum efficiency, the method comprising:

depositing 2-3 mu m low-temperature silicon dioxide on the front surface of the back-illuminated CCD wafer, wherein the deposition temperature is 260-320 ℃;

flattening the surface of the CCD wafer by adopting a silicon dioxide chemical mechanical polishing process, and removing low-temperature silicon dioxide with the thickness of 0.5-1.5 mu m on the surface of the CCD wafer;

photoetching on low-temperature silicon dioxide to form a plurality of circular microstructure patterns;

and etching a slope microstructure with a certain angle on the microstructure pattern by adopting silicon dioxide isotropic dry etching.

Preferably, when the slope angle is greater than 36 °, the near-infrared band quantum efficiency of the CCD is optimal.

Depositing a metal aluminum reflecting layer on the surface of the hemispherical microstructure by adopting a magnetron sputtering method or an evaporation method and the like;

and coating bonding glue on the surface of the metal aluminum reflecting layer, and then completing the bonding process with the carrier sheet.

Optionally, after the bonding process is completed, the method further includes:

thinning and polishing the back of the CCD wafer, and forming a passivation layer on the back of the thinned CCD wafer;

depositing an antireflection film on the upper surface of the passivation layer, growing metal, and photoetching to form shading aluminum; and forming a pressure welding point on the back of the CCD wafer.

Preferably, the conditions for etching the hemispherical microstructure by adopting the silicon dioxide isotropic dry method comprise NF with the chamber pressure of 500-2000 mt and the etching atmosphere of 30-300 mL/min₃And He of 40-700 mL/min; NF₃And the He gas ratio is 3: 4-7, the radio frequency power is 500-800W, and the etching time is 40-90 s.

In a second aspect of the present invention, on the basis of the first aspect of the present invention, there is provided a back-illuminated CCD for enhancing near-infrared quantum efficiency, the back-illuminated CCD comprising a CCD wafer and a carrier sheet; the front surface of the CCD wafer is connected with the carrier sheet through bonding; the CCD wafer comprises a dielectric layer, polycrystalline silicon and an epitaxial layer, a gate oxide layer dielectric is grown on the epitaxial layer, and a polycrystalline silicon electrode and the dielectric layer are formed above the gate oxide layer dielectric; forming a potential well on the epitaxial layer by ion implantation; depositing low-temperature silicon dioxide above a dielectric layer of the CCD wafer, etching a plurality of microstructure patterns on the low-temperature silicon dioxide, and etching a slope surface with a certain angle on each microstructure pattern to form a hemispherical microstructure; a metal aluminum reflecting layer grows on the outer surface of the hemispherical microstructure and is bonded with the carrier sheet through bonding glue; a passivation layer is formed on the other surface, namely the back surface, of the epitaxial layer, and an antireflection film is formed on the surface of the passivation layer.

Further, the diameter of the microstructure pattern is 0.5 to 0.7 μm, and the center distance of each microstructure pattern is 1.3 to 1.7 μm.

Preferably, the diameter of the microstructure pattern is 0.8 μm; and the center-to-center distance of each microstructure pattern was 1.5 μm.

Furthermore, the etching depth of the hemispherical microstructure is 0.7-0.8 μm.

Preferably, the etching depth of the hemispherical microstructure is 0.75 μm, and the hemispherical microstructure with a slope angle larger than 36 ° is formed.

Furthermore, the thickness of the metal aluminum reflecting layer on the surface of the microstructure is 0.8-1.2 μm.

Preferably, the thickness of the metallic aluminum reflecting layer is 1.0 μm.

The invention has the beneficial effects that:

compared with the traditional process, the average quantum efficiency of the back-illuminated CCD based on the invention in the wave band of 1000-1060 nm can be greatly improved, and can be improved from 8% to 15%.

According to the silicon dioxide CMP process, deposited low-temperature silicon dioxide is subjected to CMP treatment, about 1 micron is removed by polishing, a flattened surface is obtained, the uniformity and consistency of the subsequent microstructure preparation process can be effectively improved, and the consistency of CCD output imaging is ensured;

the invention relates to a microstructure preparation process, which adopts an etching method to etch a hemispherical microstructure as a concave lens and deposit an aluminum film on the concave lens so as to form an aluminum reflecting mirror, enhance the reflection of incident light and form total reflection.

The process is integrated on the front side of the back-illuminated CCD chip, so that on one hand, the design and the manufacture of an antireflection film on the light incident surface of the back-illuminated CCD are not influenced, and an ideal antireflection film can be designed to improve the quantum efficiency of a visible light wave band; on the other hand, the total reflection of incident light is realized through the microstructure, so that the absorption of silicon to the incident light is improved, and the quantum efficiency of the near-infrared band is improved; the preparation process has the advantages of good stability, strong operability, larger process window, compatibility with the existing process and suitability for back-illuminated CCD process integration.

Drawings

FIG. 1 is a schematic diagram of a conventional back-illuminated CCD structure;

FIG. 2 is a flow chart of a method for fabricating a conventional backside illuminated CCD structure;

FIG. 3 is a graph of wavelength versus silicon absorption depth;

FIG. 4 is a schematic structural diagram of a back-illuminated CCD of the present invention;

FIG. 5 is a microstructure pattern shown in the present invention;

fig. 6 is a flowchart of a method for fabricating a back-illuminated CCD structure according to the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

FIG. 4 is a back-illuminated CCD with enhanced near-infrared quantum efficiency according to the present invention, the back-illuminated CCD includes a CCD wafer and a carrier sheet; the front surface of the CCD wafer is connected with the carrier sheet through bonding; the CCD wafer comprises a dielectric layer, polycrystalline silicon and an epitaxial layer, a gate oxide dielectric layer grows on the epitaxial layer, and a polycrystalline silicon electrode and the dielectric layer are formed above the gate oxide dielectric layer; forming a potential well on the epitaxial layer by ion implantation; depositing low-temperature silicon dioxide above a dielectric layer of a CCD wafer, etching a plurality of microstructure patterns on the low-temperature silicon dioxide, etching a slope microstructure with a certain angle on each microstructure pattern, optimally depositing a metal aluminum reflecting layer on the outer surface of the hemispherical microstructure when the slope angle is greater than 36 degrees, and bonding the metal aluminum reflecting layer with the carrier plate through bonding glue; a passivation layer is formed on the other surface, namely the back surface, of the epitaxial layer, and an antireflection film is formed on the surface of the passivation layer.

In the back-illuminated CCD structure, a hemispherical microstructure is prepared by photoetching and etching, and an aluminum reflecting layer is deposited on the surface of the hemispherical microstructure; and the hemispherical microstructure has a certain slope, so that the reflection effect of incident light is enhanced conveniently, and the total reflection of the incident light can be realized under a certain condition, so that the absorption length of the incident light in the epitaxial layer is enhanced, and the near-infrared band quantum efficiency is improved.

On the basis of the above embodiments, in the present embodiment, it is considered that in actual production, due to process reasons, structural parameters of each component have a certain error more or less, so that the effect of enhancing the near-infrared quantum efficiency is not optimal, and therefore, the inventor considers that negative effects caused by process errors are offset by changing the structural parameters on the device, for this reason, according to material characteristics, temperature characteristics and the like of etched silicon dioxide, when the slope angle is greater than 36 °, the reflection effect of the metal aluminum reflection layer is optimal, total reflection of incident light can be achieved, the absorption length of the incident light in the epitaxial layer is enhanced, and at this time, the manufactured back-illuminated CCD has the optimal near-infrared quantum efficiency.

In one embodiment, in order to achieve stability of the reflection effect of the hemispherical microstructures and reduce mutual interference of the hemispherical microstructures with incident light, the present invention is implemented by arranging the array microstructure pattern shown in fig. 5, and each of the remaining microstructure patterns and the adjacent microstructure patterns keep the same distance except for the microstructure pattern on the edge, and the size of each microstructure pattern is consistent.

In one embodiment, the diameter of the microstructure pattern is 0.5 μm to 0.7 μm, and the center distance of each microstructure pattern is 1.3 μm to 1.7 μm.

In one embodiment, the etching depth of the hemispherical microstructure is 0.7-0.8 μm.

In one embodiment, the thickness of the metallic aluminum reflecting layer on the surface of the microstructure is 0.8-1.2 μm.

It can be understood that no matter how the parameters of the structure are set, the near infrared enhancement can be realized as long as the microstructure is ensured to have a certain slope, and the total reflection of incident light can be realized when the inclination angle is more than 36 degrees, so that the absorption of silicon on the incident light is further improved, and especially the quantum efficiency of the near infrared band is improved.

Based on the above structure, the present invention also provides a method for manufacturing a back-illuminated CCD for enhancing near-infrared quantum efficiency, as shown in fig. 6, the method includes:

depositing 2-3 mu m low-temperature silicon dioxide on the front surface of the back-illuminated CCD wafer, wherein the deposition temperature is 260-320 ℃;

flattening the surface of the CCD wafer by adopting a silicon dioxide chemical mechanical polishing process, and removing low-temperature silicon dioxide with the thickness of 0.5-1.5 mu m on the surface of the CCD wafer;

photoetching on low-temperature silicon dioxide to form a plurality of circular microstructure patterns;

etching a hemispherical microstructure with a slope angle larger than 36 degrees on the microstructure pattern by adopting silicon dioxide isotropic dry etching;

depositing a metal aluminum reflecting layer on the surface of the hemispherical microstructure by adopting a magnetron sputtering method or an evaporation method and the like;

and coating bonding glue on the surface of the metal aluminum reflecting layer, and then completing the bonding process with the carrier sheet.

Optionally, after the bonding process is completed, the method further includes:

thinning and polishing the back of the CCD wafer, and forming a passivation layer on the back of the thinned CCD wafer;

an antireflection film is deposited on the upper surface of the passivation layer to enhance light absorption;

growing metal, such as aluminum, on the back of the CCD wafer, and photoetching to form shading aluminum; and forming a pressure welding point on the back of the CCD wafer.

The conditions for etching the hemispherical microstructure by adopting the silicon dioxide isotropic dry method comprise NF (nitrogen-nitrogen) with the chamber pressure of 500-2000 mt and the etching atmosphere of 30-300 mL/min₃And He of 40-700 mL/min; NF₃And the He gas ratio is 3: 4-7, the radio frequency power is 500-800W, and the etching time is 40-90 s.

It can be understood that the core improvement of the CCD manufacturing method of the invention is that a microstructure is prepared and an aluminum reflecting layer is deposited by photoetching and etching between the silicon dioxide deposition and the bonding process; when the microstructure has a certain slope angle, the reflection of incident light can be realized, the near infrared absorption is enhanced, and when the slope inclination angle is more than 36 degrees, the total reflection of the incident light can be realized, so that the absorption length of the incident light in the epitaxial layer is enhanced, and the near infrared band quantum efficiency is improved.

Based on the invention, the quantum efficiency of the near infrared band (1000 nm-1060 nm) can be improved.

Some characteristics of the back-illuminated CCD for enhancing near-infrared quantum efficiency and the manufacturing method thereof can be cited, and the invention is not repeated.

In the description of the present invention, it is to be understood that the terms "coaxial", "bottom", "one end", "top", "middle", "other end", "upper", "one side", "top", "inner", "outer", "front", "center", "both ends", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention.

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "disposed," "connected," "fixed," "rotated," and the like are to be construed broadly, e.g., as meaning fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; the terms may be directly connected or indirectly connected through an intermediate, and may be communication between two elements or interaction relationship between two elements, unless otherwise specifically limited, and the specific meaning of the terms in the present invention will be understood by those skilled in the art according to specific situations.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.