Germanium Epitaxial Image Sensor Near-Infrared Absorption
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Solution Overview
Problem
Silicon image sensors have low optical absorption efficiency for near-infrared wavelengths, limiting their effectiveness in time-of-flight applications where near-infrared light sources are used.
Innovation Solution
The method involves forming an epitaxial structure with a germanium-based light absorption material within a recess on a semiconductor substrate, followed by polish treatments to optimize the thickness and structure of the insulating and epitaxial layers for enhanced signal intensity, using techniques like chemical mechanical polishing and selective epitaxial growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon material is used in image sensor, then manufacturing process is mature and cost is low, but optical absorption efficiency for near-infrared wavelengths is low
Solution Approach 1:
The patent employs a composite structure combining silicon substrate with germanium-based epitaxial layers. The silicon substrate provides mature manufacturing benefits while the germanium-based epitaxial structure (including buffer layer, first epitaxial layer, and second epitaxial layer) enhances near-infrared optical absorption efficiency, thus resolving the contradiction between ease of manufacture and optical performance.
Solution Approach 2:
The patent applies local quality by introducing germanium-based materials specifically in the epitaxial regions where near-infrared absorption is needed, while maintaining silicon substrate elsewhere. This localized material substitution optimizes optical absorption in critical areas without requiring complete material replacement across the entire device, thereby managing manufacturing complexity.
2Reliability
If epitaxial structure with germanium-based material is formed, then near-infrared detection capability is improved, but manufacturing process complexity increases
Solution Approach 1:
The epitaxial structure is segmented into multiple functional layers: buffer layer, first epitaxial layer, and second epitaxial layer, each with specific germanium concentrations and thicknesses. This segmentation allows optimization of near-infrared detection capability in each layer while managing manufacturing complexity through systematic process design for each segment.
Solution Approach 2:
The patent utilizes parameter changes by varying germanium concentration across different epitaxial layers (e.g., higher germanium content in second epitaxial layer for enhanced near-IR absorption) and controlling layer thicknesses. These parameter optimizations improve detection capability while the systematic control of parameters keeps the manufacturing process manageable.
3Manufacturing precision
If multiple polish treatments are performed, then surface flatness and layer thickness precision are improved, but manufacturing time increases
Solution Approach 1:
The patent performs preliminary polish treatments during the manufacturing process to establish proper surface flatness and layer thickness before subsequent processing steps. By conducting polish operations at strategic intermediate stages rather than only at the end, the process achieves high precision while managing total manufacturing time through efficient scheduling of polishing operations.
Solution Approach 2:
The patent implements feedback control in the polishing process by measuring surface flatness and layer thickness after each polish treatment and using this information to adjust subsequent polishing parameters. This feedback mechanism ensures manufacturing precision is achieved while avoiding excessive polishing time by stopping when target specifications are met.
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 configuration enhances the image sensor's ability to detect near-infrared light, improving its performance in time-of-flight applications by increasing signal intensity and preventing defects, thereby improving depth information determination of three-dimensional objects.
Implementation Method 1
Silicon image sensors have low optical absorption efficiency for near-infrared wavelengths
Implementation Method 2
followed by polish treatments to optimize the thickness and structure of the insulating and epitaxial layers
Implementation Method 3
forming an epitaxial structure with a germanium-based light absorption material within a recess on a semiconductor substrate
Data Source
AI summary
A method for fabricating an image sensor is described which includes forming an insulating layer on a semiconductor substrate and forming a recess in the semiconductor substrate and the insulating layer. An epitaxial structure is grown in the recess. A first polish treatment is then performed to the insulating layer and the epitaxial structure. The insulating layer is detected to obtain a signal intensity, and the signal intensity increases as a thickness of the insulating layer decreases. The first polish treatment stops when the signal intensity reaches a target value.