BSI Image Sensor Metal Grid Formation for Uniform Thickness
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Solution Overview
Problem
Existing BSI image sensors and their manufacturing processes cannot meet the requirements for products with higher performance, particularly due to issues with metal grid formation such as uneven thickness and defects like pinholes and residual silicon nitride layers.
Innovation Solution
A method of forming a metal grid in BSI image sensors involves providing a substrate with a conductive component and a conductive pillar, depositing an etch stop layer and a metal material layer in geometric conformity, forming a bonding pad and dielectric cap layer, and etching these layers to form the metal grid, which results in improved thickness uniformity and reduced defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional methods are used to form metal grid in BSI image sensors, then the manufacturing process is simpler, but the metal grid thickness is uneven and defects like pinholes and residual silicon nitride layers occur
Solution Approach 1:
The patent segments the metal grid formation process into multiple controlled steps: depositing etch stop layer (first material layer), depositing metal material layer (second material layer), forming bonding pad, depositing dielectric cap layer, and selective etching. This segmentation allows precise control over each layer's thickness and composition, achieving uniform metal grid thickness while eliminating defects through systematic process control
Solution Approach 2:
The patent applies preliminary actions by depositing the etch stop layer before the metal material layer, and depositing the dielectric cap layer before etching. The etch stop layer prevents metal diffusion into the substrate in advance, and the dielectric cap layer is prepared beforehand to enable subsequent selective etching that removes residual silicon nitride and forms the final metal grid structure with uniform thickness
2Reliability
If existing manufacturing processes are used, then production is faster, but pinhole defects and residual silicon nitride layers remain in the metal grid
Solution Approach 1:
The patent introduces an etch stop layer made of a material that is neither silicon oxide nor silicon nitride as an intermediary between the substrate and the metal material layer. This intermediary layer prevents metal diffusion into the substrate and eliminates residual silicon nitride layers during etching, thereby eliminating pinhole defects and improving metal grid reliability without significantly impacting manufacturing efficiency
Solution Approach 2:
The patent changes the material parameter of the etch stop layer to a material that is neither silicon oxide nor silicon nitride, which fundamentally alters the etching behavior. This parameter change enables complete removal of residual silicon nitride layers during the etching process, eliminating pinhole defects and ensuring high reliability of the metal grid while maintaining production efficiency
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed method achieves improved thickness uniformity of the metal grid, reduces pinhole defects, and eliminates residual silicon nitride layers, leading to enhanced performance of the BSI image sensors.
Implementation Method 1
the etch stop layer may be made of a material that is neither silicon oxide nor silicon nitride and is able to prevent a metal from diffusing into the substrate from the metal material layer
Implementation Method 2
successively depositing an etch stop layer and a metal material layer in geometric conformity over surfaces of the substrate, the conductive pillar and the recess
Data Source
AI summary
The present invention provides a method of forming a metal grid, a backside illuminated (BSI) image sensor, and a method of forming the BSI image sensor. In the methods, an etch stop layer and a metal material layer are successively deposited in geometric conformity over a substrate already formed therein with a recess and a conductive pillar, followed by the formation of a bonding pad on the metal material layer in the recess. After that, a dielectric cap layer is deposited and etched together with the metal material layer and the etch stop layer to form the metal grid. According to the present invention, the deposited metal material layer has reduced surface roughness, which results in improved thickness uniformity of the resulting metal grid. The metal grid is overall easier to form, resulting in savings in cost and increased performance of the device being fabricated.