Image Sensor Capping Structure for Low-Dark-Current Ge Interfaces
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Solution Overview
Problem
CMOS image sensors face performance degradation due to dark current, which occurs at the interface between germanium epitaxial structures and silicon capping structures, leading to inaccurate electrical signal generation even in the absence of incident radiation, particularly affecting time-of-flight sensors.
Innovation Solution
A second capping structure is introduced between the first capping structure and the epitaxial structure, comprising a group IV chemical element and a second chemical element with a different energy band gap, reducing the conduction and valence band discontinuities and thereby minimizing dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a silicon capping structure is used to cover the germanium epitaxial structure, then the manufacturing process is simplified and structural integrity is maintained, but dark current increases at the interface due to conduction and valence band discontinuities
Solution Approach 1:
An intermediate capping structure comprising a group IV chemical element and a second chemical element is introduced between the silicon capping structure and the germanium epitaxial structure. This intermediate layer acts as a mediator that reduces the conduction and valence band discontinuities at the interface, thereby minimizing dark current while maintaining the structural and manufacturing advantages of the silicon capping structure.
Solution Approach 2:
The capping structure is designed as a composite system with multiple layers: an outer silicon capping structure for structural integrity and manufacturing simplicity, and an inner intermediate capping structure comprising a group IV chemical element and a second chemical element with different energy band gap characteristics. This composite approach allows simultaneous optimization of manufacturing ease and dark current reduction.
2Measurement precision
If germanium epitaxial structures are used to enhance light absorption, then sensor sensitivity improves, but dark current generation increases at the silicon-germanium interface
Solution Approach 1:
The intermediate capping structure serves as a mediator between the germanium epitaxial structure and silicon capping structure, reducing the energy band discontinuities that cause dark current. This allows the germanium epitaxial structure to maintain its high light absorption capability and signal generation accuracy while the intermediate layer suppresses dark current at the interface.
Solution Approach 2:
The solution applies local quality modification by introducing an intermediate capping structure specifically at the interface region where dark current is generated, while maintaining the bulk properties of both the germanium epitaxial structure (for light absorption) and silicon capping structure (for structural integrity). The intermediate layer has tailored composition and energy band characteristics optimized for reducing interface dark current.
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 reduced dark current improves the performance of CMOS image sensors by ensuring more accurate signal generation, enabling reliable time-of-flight measurements with dark current levels below 0.5 nanoamps, suitable for precise distance determination.
Implementation Method 1
comprising a group IV chemical element and a second chemical element with a different energy band gap, reducing the conduction and valence band discontinuities and thereby minimizing dark current
Data Source
AI summary
In some embodiments, a semiconductor device is provided. The semiconductor device includes an epitaxial structure having a group IV chemical element disposed in a semiconductor substrate, where the epitaxial structure extends into the semiconductor substrate from a first side of the semiconductor substrate. A photodetector is at least partially arranged in the epitaxial structure. A first capping structure having a first capping structure chemical element that is different than the first group IV chemical element covers the epitaxial structure on the first side of the semiconductor substrate. A second capping structure is arranged between the first capping structure and the epitaxial structure, where the second capping structure includes the group IV chemical element and the first capping structure chemical element.