CN-122028532-A - Image sensor and method of forming the same

Abstract

The invention discloses a realization method for improving the optical performance of an image sensor, which comprises the steps of providing a substrate, etching the front surface of the substrate to form a groove, filling a first medium layer with a low refractive index at least at the bottom of the groove, and thinning the back surface of the substrate until part or all of the first medium layer with the low refractive index in the groove is exposed to form a light splitting structure so as to improve the optical performance of the image sensor.

Inventors

• HUANG KUN
• ZHAO LIXIN
• CHEN QINGYU
• TANG XIA

Assignees

• 格科微电子（上海）有限公司

Dates

Publication Date

20260512

Application Date

20241111

Claims (19)

1. 1. A method for improving the optical performance of an image sensor, comprising: Providing a substrate; Etching the front surface of the substrate to form a groove; Filling a first dielectric layer with low refractive index at least at the bottom of the groove; And thinning the back surface of the substrate until part or all of the first dielectric layer with the low refractive index in the groove is exposed, so as to form a light splitting structure, thereby improving the optical performance of the image sensor.
2. 2. The method of claim 1, wherein at least a portion of the low index first dielectric layer has a top portion that is higher than a back side substrate surface.
3. 3. The method of claim 1, wherein the low refractive index first dielectric layer fills the trench bottom or wherein a hollow gap structure is present in the low refractive index first dielectric layer.
4. 4. The method of claim 1, wherein thinning the back surface of the substrate to expose a portion or all of the low refractive index first dielectric layer in the trench, after forming the beam-splitting structure, further comprises: Forming an interface passivation layer and a second dielectric layer with high dielectric constant on the back surface of the substrate; The part of the second dielectric layer with high dielectric constant, which is positioned at the edge of the light splitting structure, is higher than the part of the second dielectric layer, which is positioned at the photosensitive center of the pixel unit of the image sensor.
5. 5. The method of claim 4, wherein thinning the back side of the substrate comprises: etching the back surface of the substrate to enable part or all of the surface of the substrate on the back surface to be lower than the top of the light-splitting structure, and forming a groove region between the light-splitting structures.
6. 6. The method of claim 5, further comprising chemical mechanical polishing the back surface of the substrate prior to etching the back surface of the substrate.
7. 7. The method of claim 5, further comprising, after forming a high dielectric constant second dielectric layer on the back side of the substrate: depositing a third dielectric layer on the second dielectric layer with high dielectric constant, and filling the groove area; and thinning the back surface of the substrate, and removing at least part of the third dielectric layer thinned to the top of the light splitting structure.
8. 8. The method of claim 1, wherein the trench is underfilled with a low refractive index first dielectric layer and the trench sidewalls form the low refractive index first dielectric layer.
9. 9. The method of claim 8, further comprising continuing to fill the trench fill material after the trench is underfilled with the low index first dielectric layer to complete the filling of the trench.
10. 10. The method of claim 9, wherein the trench fill material comprises one or more of polysilicon, a metallic material, and doped silicon oxide.
11. 11. The method of claim 9, wherein the trench fill material fills the remaining trench or wherein the trench fill material has a hollow gap structure.
12. 12. The method of claim 1, further comprising, after the trench is underfilled with the low refractive index first dielectric layer: And continuing to complete the complete filling of the grooves and forming all the front-side well structures and device structures of the image sensor.
13. 13. The method of claim 1, wherein the etching the substrate front surface to form a trench comprises: Etching the front surface of the substrate to form a first groove; forming a first epitaxial layer on the side surface of the first groove through epitaxy so as to reduce the width of the first groove; when the first epitaxial layer is etched back, at least part of the bottom of the first groove is further deepened to form a second groove; and the bottom of the second groove is filled with the first dielectric layer with low refractive index or a hollow gap structure exists at the bottom.
14. 14. The method of claim 11, further forming a second epitaxial layer by epitaxy, the second epitaxial layer closure region for forming a transistor, a floating diffusion, and/or a substrate contact of the pattern sensor.
15. 15. The method as recited in claim 7, further comprising: And continuing to form grids, optical filters and microlenses on the back surface of the substrate to form the image sensor.
16. 16. The method of claim 7, wherein the second dielectric layer of high dielectric constant has a dielectric constant greater than 5.0.
17. 17. The method of claim 7, wherein the material of the high dielectric constant second dielectric layer is one or more of aluminum oxide, tantalum oxide, hafnium oxide, zirconium oxide.
18. 18. The method of claim 1, wherein the low refractive index first dielectric layer has a refractive index of less than 1.7.
19. 19. An image sensor formed by the method of any one of claims 1 to 18.

Description

Image sensor and method of forming the same Technical Field The present disclosure relates to semiconductor technology, and more particularly, to an image sensor and a method for forming the same. Background A CMOS image sensor (CMOS Image Sensor, CIS) is a semiconductor device that converts an optical image into an electrical signal. The CIS includes a Photodiode (PD) for sensing light and a logic circuit for processing the sensed light into an electrical signal. Isolation of the photosensitive area of the CIS is common in the backside illuminated image sensor process. In a common method, a back thinning process of a substrate wafer is firstly carried out, then a pattern for isolating an image photosensitive region is formed on the surface of the wafer through a photoetching process, then a deep groove is formed on the back of the substrate through an etching process, and then a medium is filled in the deep groove to complete isolation of the image sensor photosensitive region. However, the conventional method still has the following problems that ① is easy to distort and deform the wafer substrate in the process of thinning the back surface of the wafer of the grinding substrate, the alignment error of photoetching per se also causes larger error between the groove pattern on the back surface of the wafer and the center of a pixel, so that the lateral isolation effect is influenced, the opening of the deep groove structure on the back surface of ② is large and small, incident light is easy to sink into the deep groove for multiple reflections in the process of entering from the back surface, optical crosstalk is generated, sensitivity is lost, plasmas used in the etching process of ③ damage the side wall, in the process of the back surface of the wafer, a high-temperature process cannot be born, so that the damage of the side wall is difficult to repair, and the line width difference exists between the patterns of the lateral isolation area and the diagonal cross area of two adjacent pixel units of ④, so that the depth difference between the lateral area and the diagonal cross area of adjacent pixel units is caused, and the isolation and noise effect is influenced. Disclosure of Invention Based on the problems existing in the prior art, the invention provides an implementation method for improving the optical performance of an image sensor, which comprises the steps of providing a substrate, etching the front surface of the substrate to form a groove, filling a first dielectric layer with a low refractive index at least at the bottom of the groove, and thinning the back surface of the substrate until part or all of the first dielectric layer with the low refractive index in the groove is exposed to form a light splitting structure so as to improve the optical performance of the image sensor. In some embodiments, at least a portion of the low index first dielectric layer has a top that is higher than the back substrate surface. In some embodiments, the low refractive index first dielectric layer fills the bottom of the trench, or the low refractive index first dielectric layer has a hollow gap structure. In some embodiments, the method further comprises forming an interface passivation layer and a second dielectric layer with high dielectric constant on the back surface of the substrate after the back surface of the substrate is thinned to expose part or all of the first dielectric layer with low refractive index in the groove to form the light splitting structure, wherein the part of the second dielectric layer with high dielectric constant at the edge of the light splitting structure is higher than the part of the second dielectric layer with high dielectric constant at the photosensitive center of the pixel unit of the image sensor. In some embodiments, thinning the back surface of the substrate includes etching the back surface of the substrate such that a portion or all of the substrate surface of the back surface is below the top of the beam-splitting structures and forming a recessed region between the beam-splitting structures. In some embodiments, the etching of the back surface of the substrate may further comprise chemical mechanical polishing of the back surface of the substrate. In some embodiments, after the second dielectric layer with high dielectric constant is formed on the back surface of the substrate, the method further comprises the steps of depositing a third dielectric layer on the second dielectric layer with high dielectric constant and filling the groove area, and thinning the back surface of the substrate until at least part of the third dielectric layer on the top of the light splitting structure is removed. In some embodiments, a low-refractive-index first dielectric layer is filled at the bottom of the groove and the side wall of the groove is used for forming the low-refractive-index first dielectric layer. In some embodiments, the method further comprises continuing to fill