CMOS Image Sensor Pixel Light-Shielding Wall Structure
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Solution Overview
Problem
The increased storage time in 5T CMOS image sensors leads to significant parasitic light irradiation on the floating diffusion region, affecting its capacitance and deteriorating sensor performance.
Innovation Solution
A pixel structure with a light-shielding wall formed in the interlayer dielectric layer surrounds the floating diffusion region, effectively blocking obliquely incident parasitic light, and a light-shielding layer covers the region omnidirectionally to reduce light pollution, using metallic tungsten for superior light-shielding properties compatible with semiconductor processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If the storage time is increased to ms level in 5T structure CMOS image sensor, then the optical signal storage capability is improved, but the parasitic light irradiation on floating diffusion region significantly increases causing performance deterioration
Solution Approach 1:
A light-shielding wall is introduced as an intermediary structure between the floating diffusion region and the parasitic light sources. This wall, formed in the interlayer dielectric layer, acts as a physical barrier that blocks oblique parasitic light from reaching the floating diffusion region, thereby resolving the contradiction between extended storage time and parasitic light interference.
Solution Approach 2:
The solution addresses the light shielding problem by adding a vertical dimension element (the light-shielding wall extending into the interlayer dielectric layer) rather than only horizontal plane coverage. This three-dimensional approach effectively blocks oblique light paths that would otherwise reach the floating diffusion region during extended storage periods.
2Reliability
If a light-shielding wall is added to block parasitic light, then the performance is improved, but the device complexity increases
Solution Approach 1:
The light-shielding wall is integrated into the existing interlayer dielectric layer structure, serving both as an electrical isolation layer and a light-shielding barrier. This multi-functional approach improves sensor performance without proportionally increasing device complexity, as the wall utilizes the existing dielectric layer rather than adding a completely separate structure.
Solution Approach 2:
The light-shielding function is merged with the interlayer dielectric layer formation process. By forming the light-shielding wall within the interlayer dielectric layer during the same fabrication sequence, the patent combines two functions (electrical isolation and light shielding) into a single integrated structure, thereby minimizing the increase in device complexity.
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 solution effectively shields parasitic light, minimizing its impact on the capacitance of the floating diffusion region, thereby enhancing the performance and reducing noise in CMOS image sensors.
Implementation Method 1
a light-shielding wall formed in the interlayer dielectric layer, wherein a projection of the light-shielding wall in the height direction of the substrate surrounds a projection of the floating diffusion region in the height direction of the substrate
Data Source
AI summary
The present invention provides a pixel structure for a CMOS image sensor and a manufacturing method therefor, the pixel structure comprising: a substrate; a floating diffusion region formed in the substrate; an interlayer dielectric layer formed on an upper surface of the substrate and covering the pixel structure; and a light-shielding wall formed in the interlayer dielectric layer, wherein a projection of the light-shielding wall in the height direction of the substrate surrounds a projection of the floating diffusion region in the height direction of the substrate. The present invention further provides a manufacturing method for manufacturing the pixel structure. The pixel structure manufactured by means of the manufacturing method provided in the present invention can shield the irradiation of incident light on the floating diffusion region of the global CMOS image sensor, thereby reducing interference signals.