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CN-122002925-A - Grid structure of image sensor and preparation method thereof

CN122002925ACN 122002925 ACN122002925 ACN 122002925ACN-122002925-A

Abstract

The invention relates to an optimization method of a low refractive index grid structure for a back-illuminated image sensor. By structural design of the isolation groove and the metal filling morphology on the back of the pixel region, a metal tungsten residual layer is reserved in the BDTI intersection region in the metal removing process, so that a local shielding structure is formed in the light path, optical crosstalk between adjacent pixels is effectively restrained, and imaging definition and signal to noise ratio are improved. Or by optimizing BDTI etching size, side wall morphology and buffer oxide layer deposition parameters, proper metal residues are formed in non-crossed linear regions, so that the uniformity of optical isolation and the uniformity of structures are realized. In addition, the scheme of the invention can synchronously remove the metal barrier layer when removing the metal tungsten, does not need to add extra etching steps, simplifies the process flow and reduces the manufacturing cost. The technical scheme has the advantages of optical performance and process manufacturability, and has obvious advantages in the aspects of optical isolation, etching uniformity and cost control.

Inventors

  • XU JIAN
  • ZOU WEN
  • ZENG TIAN
  • WANG CHUNLIN

Assignees

  • 格科半导体(上海)有限公司

Dates

Publication Date
20260508
Application Date
20251118

Claims (10)

  1. 1. The preparation method of the grid structure of the image sensor is characterized by comprising the following steps of: providing a substrate, and forming a groove array with an intersection area on a first surface of the substrate; filling a first dielectric layer in the groove, and forming a plurality of pits in the intersection area; Depositing a second dielectric layer on the first dielectric layer; depositing a metal layer on the second dielectric layer; removing at least part of the metal layer, retaining the metal layer in the pits, and forming a metal structure in the pit array; A grid structure is formed over the metal structure.
  2. 2. The method of claim 1, wherein, And when the first dielectric layer is filled in the groove, controlling one or more of the forming time of the groove array and/or the filling time, the reaction temperature, the precursor proportion and the deposition rate of the first dielectric layer to enable the non-crossing area to form a groove lower than the surface of the substrate.
  3. 3. The method of claim 2, wherein, While removing at least a portion of the metal layer, retaining the metal layer in the pit array while retaining a portion of the metal layer in the non-intersecting region.
  4. 4. The method of claim 1, wherein, An array of a plurality of photodiodes is formed between the trench arrays.
  5. 5. The method of claim 1, wherein, The first dielectric layer comprises one or more of silicon nitride, silicon oxide, silicon oxynitride, titanium nitride and titanium nitride.
  6. 6. The method of claim 1, wherein, The second dielectric layer is a metal barrier layer, and the material of the second dielectric layer is one or more of titanium nitride, tungsten nitride and aluminum oxide.
  7. 7. The method of claim 1, wherein, The process for removing the metal layer is dry etching and/or CMP.
  8. 8. The method of claim 1, wherein, The material of the grid structure is a material with a refractive index n lower than 1.6.
  9. 9. The method of claim 1, wherein, The metal layer material comprises tungsten and/or aluminum.
  10. 10. The method of claim 3, wherein, And removing the second dielectric layer simultaneously when removing part of the metal layer.

Description

Grid structure of image sensor and preparation method thereof Technical Field The invention relates to the field of semiconductor devices, in particular to an image sensor grid structure and a preparation method thereof. Background With the continuous improvement of resolution and optical performance of backside illuminated CMOS image sensors (BSI CIS), the optical structure and electrical structure design of the pixel area gradually tend to be complicated. In order to effectively suppress optical crosstalk between pixels and improve the utilization ratio of incident light, a low refractive index (Low refractive index, abbreviated as Ln) grid structure is commonly used in the pixel array region in recent years. Ln grids are typically located in the optical stack layers to form optically isolated channels between adjacent pixels to achieve effective control of the light path. However, during the process integration of the Ln grid, the underlying via structure and metal filling process often have a significant impact on the final structure quality and process stability. The formation of backside isolation trenches (BDTI) and BVIA (Blind Via) vias and metal filling are typically required to be completed in the pixel region before Ln grid formation. Typically, BVIA vias are filled with metal tungsten (W) and a metal barrier TiN is left at the bottom to ensure good conductivity and reliable electrical isolation. However, because of the large topography recess of the trench structure of the pixel region BDTI at the Cross (Cross) location, the deposition Thickness (THK) of the tungsten metal in this region is significantly higher than in the normal line-type region. The thickness non-uniformity makes the subsequent etching process for removing the redundant metal tungsten difficult to be obviously increased. In order to ensure complete removal of the tungsten layer at the Cross position, the etching selectivity of W to TiN can be improved only by increasing the Over etching amount (Over etching) of the dry etching or adjusting the etching atmosphere and parameters. However, these methods often present a risk of TiN damage to the metal barrier layer, further affecting the subsequent process window and device reliability. Therefore, how to optimize the metal removal process of the pixel region BVIA in the Ln grid structure, improve the problem of uneven etching caused by metal accumulation of the Cross region, and give consideration to the structural flatness and the electrical integrity while ensuring the optical isolation performance becomes a key problem in the process development of the current back-illuminated image sensor. Disclosure of Invention In order to solve the problems in the prior art, the invention provides an image sensor grid structure and a preparation method thereof, and the preparation method comprises the following steps of providing a substrate, and forming a groove array with an intersection area on a first surface of the substrate; filling a first dielectric layer in the groove, forming a plurality of pits in the crossing area, depositing a second dielectric layer on the first dielectric layer, depositing a metal layer on the second dielectric layer, removing at least part of the metal layer, retaining the metal layer in the pits, forming a metal structure in the pit array, and forming a grid structure on the metal structure. Further, when the first dielectric layer is filled in the groove, the non-crossing area is formed into the groove lower than the surface of the substrate by controlling one or more of the forming time of the groove array and/or the filling time, the reaction temperature, the precursor proportioning, the deposition rate and other technological parameters of the first dielectric layer. Further, when at least part of the metal layer is removed, the metal layer in the pit array is reserved, and meanwhile, part of the metal layer in the non-crossing area is reserved. Further, an array of a plurality of photodiodes is formed between the trench arrays. Further, the first dielectric layer comprises one or more of silicon nitride, silicon oxide, silicon oxynitride, titanium nitride and titanium nitride. Further, the second dielectric layer is a metal barrier layer, and the material of the second dielectric layer is one or more of titanium nitride, tungsten nitride and aluminum oxide. Further, the process of removing the metal layer is dry etching and/or CMP. Further, the material of the grid structure is a material with a refractive index n lower than 1.6. Further, the metal layer material comprises one or more of copper, tungsten and aluminum. Further, when part of the metal layer is removed, the second dielectric layer is removed at the same time. Furthermore, the invention also provides the image sensor prepared by the method. According to the invention, through optimizing design aiming at the characteristics of the isolation groove structure and the metal filling morphology