BSI Image Sensor Backside Metal Shield and Buffer Oxide Uniformity
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Solution Overview
Problem
Conventional BSI image sensor manufacturing processes result in non-uniform buffer oxide thickness over sensor array areas, leading to suboptimal performance in quantum efficiency, signal-to-noise ratio, and light mean uniformity due to the etching process that removes either part or all of the buffer oxide layer.
Innovation Solution
A method involving the formation of a bottom antireflective coating (BARC) layer, a buffer oxide layer, and a metal shield over the semiconductor substrate, followed by a selective etch process to remove the metal shield and buffer oxide from the sensor array area, and subsequent re-deposition of a uniform dielectric layer to maintain oxide thickness uniformity across the sensor array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional etch process is used to remove metal shield from sensor array areas, then metal shield removal is achieved, but buffer oxide thickness becomes non-uniform or completely removed
Solution Approach 1:
The patent segments the buffer oxide layer into two distinct layers: a first buffer oxide layer that is selectively removed during etching, and a second buffer oxide layer that remains to provide uniform thickness. This segmentation allows the metal shield to be removed while preserving the necessary oxide thickness for sensor performance.
Solution Approach 2:
The patent forms the multi-layer buffer oxide structure before the metal shield removal process. By preparing the oxide layers in advance with different thicknesses and removal characteristics, the process ensures that when etching occurs, the first layer is removed while the second layer remains intact, preventing the non-uniformity problem.
2Ease of operation
If buffer oxide layer is completely removed to expose sensor array, then metal shield access is improved, but quantum efficiency and signal-to-noise ratio deteriorate
Solution Approach 1:
The buffer oxide is divided into functional segments: the first layer serves the mechanical/access function of allowing metal shield removal, while the second layer serves the optical function of maintaining quantum efficiency and signal-to-noise ratio. This functional segmentation resolves the contradiction between access and performance.
Solution Approach 2:
Different portions of the buffer oxide structure serve different purposes: the first layer is designed for removal to provide access, while the second layer is designed to remain for optical performance. This local differentiation of quality and function allows simultaneous achievement of access and performance requirements.
3Ease of operation
If selective etch removes metal shield and first buffer oxide, then sensor array accessibility is improved, but light mean uniformity deteriorates
Solution Approach 1:
The oxide layer segmentation ensures that the remaining second buffer oxide layer provides a uniform base that maintains light mean uniformity across the sensor array, even after selective removal of the first oxide layer and metal shield.
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
This approach ensures uniform dielectric layer thickness, enhancing quantum efficiency, signal-to-noise ratio, and light mean uniformity, allowing for fine-tuning of the light path and color light mean value, thereby improving overall image sensor performance.
Implementation Method 1
forming a bottom antireflective coating (BARC) layer
Implementation Method 2
a selective etch process to remove the metal shield and buffer oxide from the sensor array area
Implementation Method 3
subsequent re-deposition of a uniform dielectric layer
Data Source
AI summary
A back side image sensor and method of manufacture are provided. In an embodiment a bottom anti-reflective coating is formed over a substrate, and a metal shield layer is formed over the bottom anti-reflective coating. The metal shield layer is patterned to form a grid pattern over a sensor array region of the substrate, and a first dielectric layer and a second dielectric layer are formed to at least partially fill in openings within the grid pattern.