BSI Pixel Trench Barrier Layers for Ge Surface Uniformity
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Solution Overview
Problem
Backside illuminated (BSI) image sensors face challenges in reducing dark current due to surface non-uniformity of Ge or SiGe epitaxial structures, which is caused by high-temperature processing leading to lateral expansion and formation of recesses at trench edges, resulting in non-uniform interfaces and degraded sensor performance.
Innovation Solution
The formation of barrier layers, specifically using dielectric materials like silicon oxide, at the edges of trenches where Ge or SiGe epitaxial structures are formed, prevents lateral expansion and the growth of Ge or SiGe layers, thereby minimizing surface non-uniformity and reducing non-uniform interfaces between epitaxial structures and silicon capping layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high temperature processing is used to form Ge or SiGe epitaxial structures, then the pixel structures can be formed with desired material properties, but surface non-uniformity is induced leading to dark current
Solution Approach 1:
A barrier layer is formed on the substrate before forming the Ge or SiGe epitaxial structures. This preliminary barrier layer prevents lateral expansion of the epitaxial structures during high temperature processing, thereby preventing surface non-uniformity and dark current while allowing the desired material properties to be achieved.
Solution Approach 2:
The barrier layer acts as an intermediary between the substrate and the Ge or SiGe epitaxial structures. It mediates the interaction during high temperature processing by restraining lateral expansion of the epitaxial structures, thus preventing surface non-uniformity without interfering with the formation of desired material properties.
2Manufacturing precision
If barrier layers are added to prevent lateral expansion, then surface non-uniformity is reduced by 50% to 100%, but device complexity increases
Solution Approach 1:
The barrier layer is selectively formed only in specific regions where lateral expansion occurs, rather than uniformly across the entire substrate. This localized approach improves surface uniformity where needed while minimizing the overall complexity increase of the device structure.
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 reduces surface non-uniformity by 50% to 100% and enhances sensor performance by 40% to 60% compared to BSI image sensors without barrier layers, leading to improved accuracy in determining object distance.
Implementation Method 1
forming a barrier layer with first and second layer portions. The first layer portion is formed on a sidewall portion of the trench that is not covered by the epitaxial structure
Implementation Method 2
The barrier layer includes a dielectric material that inhibits growth of the Ge or SiGe layer at the trench edge
Data Source
AI summary
A semiconductor device with an image sensor and a method of fabricating the same are disclosed. The method includes depositing a dielectric layer on a substrate, forming a trench within the dielectric layer and the substrate, forming an epitaxial structure within the trench, and forming a barrier layer with first and second layer portions. The first layer portion is formed on a sidewall portion of the trench that is not covered by the epitaxial structure. The method further includes forming a capping layer on the epitaxial structure and adjacent to the barrier layer, selectively doping regions of the epitaxial structure and the capping layer, selectively forming a silicide layer on the doped regions, depositing an etch stop layer on the silicide layer, and forming conductive plugs on the silicide layer through the etch stop layer.