Self-Aligned BSI Image Sensor Grids Without Silicon-Damaging Etching
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Solution Overview
Problem
The fabrication of back side illumination (BSI) image sensors faces challenges such as silicon damage from dry etching processes and misalignment of metal grids with trench isolation grids, which affect optical isolation and performance.
Innovation Solution
A method is developed to self-align the metal grid with the trench isolation grid, eliminating the need for silicon-damaging dry etching by forming the metal grid without an intervening buffer layer, ensuring direct contact and alignment with the trench isolation grid, thereby enhancing optical performance and reducing substrate damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If dry etching process is used to form metal grid, then metal grid can be formed, but silicon damage occurs
Solution Approach 1:
The patent removes the buffer layer that was previously used in the fabrication process. By taking out this intermediate layer, the metal grid is formed in direct contact with the trench isolation grid, eliminating the need for dry etching through the buffer layer and thereby preventing silicon damage while still achieving proper metal grid formation
2Manufacturing precision
If buffer layer is used between metal grid and trench isolation grid, then misalignment is reduced, but optical isolation is degraded
Solution Approach 1:
The patent extracts/removes the buffer layer that was causing optical isolation degradation. By eliminating this intermediate layer, the metal grid achieves direct contact with the trench isolation grid, improving optical isolation while maintaining alignment through the self-aligned fabrication process
3Object-affected harmful factors
If direct contact between metal grid and trench isolation grid is achieved, then optical isolation is improved, but alignment precision may be compromised
Solution Approach 1:
The patent uses a self-aligned fabrication process where the trench isolation grid is formed first, and then the metal grid is deposited directly onto it. This preliminary formation of the trench isolation grid provides a reference structure that ensures precise alignment of the metal grid, achieving both direct contact for optimal optical isolation and precise alignment
Data Source
AI summary
A method of fabricating self-aligned grids in a BSI image sensor is provided. The method includes depositing a first dielectric layer over a back surface of a substrate that has a plurality of photodiodes formed therein, forming a grid of trenches, and filling in the trenches with dielectric material to create a trench isolation grid. Here, a trench passes through the first dielectric layer and extends into the substrate. The method further includes etching back dielectric material in the trenches to a level that is below an upper surface of the first dielectric layer to form recesses overlaying the trench isolation grid, and filling in the recesses with metallic material to create a metallic grid that is aligned with the trench isolation grid.