SiGe Epitaxial Layer for Near-Infrared Image Sensor Substrate
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Solution Overview
Problem
Image sensors of the 'front face' type have low sensitivity in the near infrared range due to the decreasing absorption coefficient of monocrystalline silicon, which limits their ability to capture photons effectively in wavelengths between 700 nm and 3 μm.
Innovation Solution
A substrate for image sensors is developed using a monocrystalline silicon-germanium (SiGe) active layer with a controlled germanium content and thickness, optimized through epitaxial growth to enhance absorption in the near infrared while maintaining compatibility with microelectronics processes and minimizing crystal defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a monocrystalline silicon active layer is used, then the crystalline quality and compatibility with microelectronics processes are maintained, but the absorption coefficient in the near infrared range decreases sharply
Solution Approach 1:
The patent changes the material composition parameter by introducing germanium into the silicon lattice to form SiGe alloy. This compositional change increases the absorption coefficient in the near infrared range while maintaining monocrystalline structure through controlled epitaxial growth, thus resolving the contradiction between crystalline quality and light absorption capability
Solution Approach 2:
The patent creates a composite material system by forming a SiGe active layer on a silicon support substrate. The SiGe layer combines the advantages of both materials: enhanced near-infrared absorption from germanium and good crystalline quality from silicon, while the epitaxial growth ensures lattice compatibility and minimizes defects
2Use of energy by moving object
If the germanium content in the SiGe layer is increased, then the absorption coefficient in the near infrared increases, but the number of dislocations increases
Solution Approach 1:
The patent applies local quality by creating a gradient in germanium content across the active layer thickness. The germanium concentration varies from 0% to a maximum value and then decreases to 0%, with the peak concentration optimized to balance absorption enhancement and dislocation minimization. This localized optimization of composition resolves the contradiction between high absorption and low defect density
3Use of energy by moving object
If a thick active layer is used, then the absorption of light in the near infrared is increased, but the crystal quality deteriorates due to increased dislocations
Solution Approach 1:
The patent changes the compositional parameter along the thickness direction to resolve the contradiction. By implementing a germanium concentration profile that peaks at an intermediate position rather than being uniform or increasing monotonically, the patent achieves both sufficient thickness for light absorption and controlled dislocation density, maintaining crystal quality while enhancing near-infrared response
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 SiGe active layer significantly increases photon absorption in the near infrared, achieving three to four times higher absorption coefficients compared to silicon, while minimizing dislocations and maintaining the crystalline quality necessary for the image sensor's functionality.
Implementation Method 1
The SiGe active layer significantly increases photon absorption in the near infrared, achieving three to four times higher absorption coefficients compared to silicon
Implementation Method 2
optimized through epitaxial growth to enhance absorption in the near infrared while maintaining compatibility with microelectronics processes and minimizing crystal defects
Data Source
Figure 1~3
Figure 4~6A
Figure 6B~6D
AI summary
The invention relates to a substrate for a front-side-type image sensor, comprising, successively, a supporting semiconductor substrate (1), an electrically insulating layer (2), and a semiconductor layer (3), known as the active layer, characterised in that the active layer (3) is an epitaxial layer of silicon-germanium having a germanium content of less than 10%. The invention also relates to a method for the production of such a substrate.