Image Sensor Absorption Structure Mitigating Plasma Damage
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Solution Overview
Problem
CMOS image sensors face challenges in improving quantum efficiency due to plasma damage from dry etching processes, which leads to crystalline defects and increased dark current, degrading image quality.
Innovation Solution
A method involving a dry etching process followed by a wet etching process to form protrusions on the substrate, with absorption enhancement layers applied over and between the protrusions, reducing plasma damage and enhancing radiation absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dry etching process is used to form protrusions for absorption enhancement, then the quantum efficiency can be improved through increased light absorption, but plasma damage occurs causing crystalline defects and increased dark current
Solution Approach 1:
A sacrificial layer is introduced as an intermediary between the dry etching process and the substrate. This sacrificial layer absorbs the plasma damage that would otherwise directly affect the substrate, allowing the formation of protrusions while protecting the underlying crystal structure from harmful plasma effects
Solution Approach 2:
The protrusions are formed by first creating them in a sacrificial layer that replicates the desired geometry, then transferring this pattern to the substrate. This copying approach allows the complex protrusion structure to be formed without directly exposing the substrate to damaging plasma etching
2Reliability
If protrusions are formed to increase light absorption, then radiation absorption is enhanced, but crystalline defects increase due to plasma damage
Solution Approach 1:
The sacrificial layer serves as a mediator that enables the formation of light-absorbing protrusions while shielding the substrate from plasma-induced crystalline defects. The protrusions achieve enhanced radiation absorption without compromising crystal integrity
3Reliability
If dry etching is used to create absorption enhancement structures, then light absorption increases, but dark current increases due to plasma damage
Solution Approach 1:
The sacrificial layer acts as a protective intermediary during the etching process, preventing plasma-induced damage that would otherwise generate dark current. This allows the absorption enhancement structures to be formed while maintaining low dark current levels
Solution Approach 2:
The plasma process, which normally causes harm through damage and dark current generation, is redirected to etch the sacrificial layer instead. The harmful plasma energy is converted into a useful function by selectively removing the sacrificial material to form the desired protrusion pattern
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 method effectively reduces crystalline defects and improves quantum efficiency, leading to better image sensor performance by minimizing radiation reflection and increasing absorption of incident light.
Implementation Method 1
performing a dry etching process on the first side of the substrate according to the patterned masking layer to define a plurality of intermediate protrusions
Implementation Method 2
performing a wet etching process on the plurality of intermediate protrusions to form a plurality of protrusions
Implementation Method 3
forming one or more absorption enhancement layers over and between the plurality of protrusions
Data Source
AI summary
The present disclosure relates to an integrated chip. The integrated chip includes an image sensing element disposed within a substrate. The substrate has a plurality of protrusions disposed along a first side of the substrate over the image sensing element and a ridge disposed along the first side of the substrate. The ridge continuously extends around the plurality of protrusions.