Multiple Polysilicon Gate Layers for Image Sensor Noise Reduction
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Solution Overview
Problem
The challenge of forming reliable image sensor devices with decreasing feature sizes is exacerbated by the increasing complexity and difficulty of fabrication processes, which affects the performance and reliability of image sensor devices.
Innovation Solution
The use of multiple polysilicon layers in the gate electrode layer of image sensor devices, which reduces dark current and noise by limiting grain growth and increasing the number of interfaces, thereby improving the sensitivity and reliability of the devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If feature size is decreased to improve functional density, then the number of interconnected devices per chip area increases, but fabrication process complexity and difficulty increase
Solution Approach 1:
The gate electrode is segmented into multiple polysilicon layers (first polysilicon layer and second polysilicon layer) instead of using a single layer. This segmentation allows for better control of fabrication processes at smaller feature sizes, reducing the complexity associated with achieving uniform single-layer polysilicon gates at reduced dimensions while maintaining the required functional density.
2Productivity
If feature size is decreased to improve functional density, then more devices fit per chip area, but manufacturing reliability decreases
Solution Approach 1:
Dividing the gate electrode into multiple polysilicon layers improves manufacturing reliability at smaller feature sizes by making the fabrication process more robust and less sensitive to variations, thereby maintaining consistent device performance across the wafer even as feature dimensions are reduced to increase functional density.
Solution Approach 2:
The invention changes the structural parameter of the gate electrode from a single layer to multiple layers, which fundamentally alters the fabrication characteristics and improves reliability without sacrificing the ability to achieve smaller feature sizes for higher functional density.
3Device complexity
If single polysilicon layer is used in gate electrode, then device structure is simpler, but dark current and noise increase
Solution Approach 1:
The gate electrode is divided into multiple polysilicon layers with interfaces between them. These interfaces act as barriers that trap carriers and reduce dark current generation. The multiple layers also create additional grain boundaries that suppress noise, achieving better electrical performance with only moderate increase in structural complexity.
Solution Approach 2:
The gate electrode uses a composite structure of multiple polysilicon layers rather than a homogeneous single layer. This composite structure exploits the properties of interfaces and grain boundaries between layers to reduce dark current and noise, achieving superior electrical characteristics.
Data Source
AI summary
Embodiments of mechanisms for forming an image sensor device are provided. The image sensor device includes a semiconductor substrate and one photodetector formed in the semiconductor substrate. The image sensor device also includes one gate stack formed over the semiconductor substrate. The gate stack includes multiple polysilicon layers.