Solid-State Imaging Device Antireflection Films Light Leakage
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Solution Overview
Problem
In solid-state imaging devices, particularly CMOS image sensors, the sensitivity is hindered by circuit elements and wiring on the front surface, leading to difficulties in improving image quality due to light shielding and reflection, and the occurrence of dark current at the photoelectric conversion interface.
Innovation Solution
A solid-state imaging device configuration with a semiconductor layer featuring photodiodes, a first antireflection film, a second antireflection film, and a light shielding layer, where the light shielding layer is positioned on the first antireflection film, and the antireflection films are made of high dielectric materials like hafnium oxide to suppress dark current and enhance sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If light shielding structures are added to block light between pixels, then light leakage is reduced, but device complexity increases
Solution Approach 1:
The light shielding layer is divided into multiple segments corresponding to different pixel regions, with each segment positioned to shield light between adjacent pixels while leaving light reception areas exposed. This segmentation approach effectively blocks light leakage between pixels without requiring a complete continuous shielding structure, thereby reducing overall device complexity.
Solution Approach 2:
The light shielding layer is selectively positioned only in regions where light leakage needs to be suppressed, rather than covering the entire substrate. The shielding structures are locally placed at pixel boundaries and interfaces, allowing light to pass through photodiode regions while blocking stray light between pixels, thus minimizing added complexity.
2Reliability
If antireflection films are applied to improve light sensitivity, then sensitivity increases, but manufacturing precision requirements increase
Solution Approach 1:
The antireflection film is formed using composite material structures, specifically utilizing silicon oxide and silicon nitride layers in combination. This composite approach provides effective antireflection properties across a broader wavelength range and reduces sensitivity to precise film thickness control, thereby lowering manufacturing precision requirements while maintaining high light sensitivity.
Solution Approach 2:
The antireflection film structure employs parameter optimization where the thickness and refractive index of each layer are carefully selected to achieve destructive interference of reflected light. By adjusting these parameters within specific ranges rather than requiring exact values, the system achieves high sensitivity while tolerating normal manufacturing variations.
3Productivity
If photodiodes are arranged closely to increase pixel density, then productivity increases, but dark current occurrence increases
Solution Approach 1:
Light shielding structures are introduced as intermediary elements positioned between adjacent photodiodes. These shielding structures act as mediators that block stray light and reduce optical interference between closely spaced pixels, thereby suppressing dark current generation while allowing the photodiodes to maintain high density arrangement for improved productivity.
Solution Approach 2:
The solution addresses the dark current problem by adding structures in the vertical dimension (light shielding layer above photodiodes) rather than increasing horizontal spacing between pixels. This dimensional approach allows photodiodes to remain closely spaced in the plane for high density while using overhead shielding structures to prevent optical interference that causes 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
This configuration improves image quality by reducing light leakage between pixels and effectively suppressing dark current, leading to enhanced color reproducibility and sensitivity in captured images.
Implementation Method 1
The photoelectric conversion portion is, for example, a photo diode, and creates a signal electric charge by receiving an incident light by a light sensing surface to perform the photoelectric conversion
Implementation Method 2
a first antireflection film located over a first surface of the semiconductor layer, a second antireflection film located over the first antireflection film
Implementation Method 3
a light shielding layer having side surfaces which are adjacent to at least one of first and the second antireflection film
Data Source
AI summary
A solid state imaging device including a semiconductor layer comprising a plurality of photodiodes, a first antireflection film located over a first surface of the semiconductor layer, a second antireflection film located over the first antireflection film, a light shielding layer having side surfaces which are adjacent to at least one of first and the second antireflection film.