Miniature Image Sensor Using (110) Silicon Substrate
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Solution Overview
Problem
Current techniques for forming insulating walls in image sensors with small pixel dimensions and deep depth are limited by the thickness of resin masks, which restrict the width of the walls to around 0.7 μm, making it difficult to achieve a large shape factor, and result in reduced active surface area for pixels.
Innovation Solution
The use of a silicon substrate with crystal orientation (110) allows for dopant implantation perpendicular to the surface, utilizing channeling effects to achieve insulating walls with depths greater than 2 μm and widths less than 0.5 μm, using lower implantation powers and thinner masks, and employing N-type doping with phosphorus, arsenic, or antimony atoms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional dopant implantation techniques are used with resin masks, then insulating walls can be formed, but the mask thickness restricts the wall width to around 0.7 μm, preventing achievement of large shape factor
Solution Approach 1:
The patent changes the crystal orientation parameter of the silicon substrate from conventional (100) to (110), which fundamentally alters the dopant implantation behavior. This parameter change enables the formation of insulating walls with width less than 0.5 μm and depth greater than 2 μm, achieving a large shape factor without being constrained by thick resin masks
Solution Approach 2:
Instead of trying to work around the mask thickness limitation by adjusting other parameters, the patent inverts the approach by changing the fundamental substrate orientation. This inversion of the conventional approach allows dopant channeling to occur perpendicular to the surface, enabling precise control of wall dimensions independent of mask thickness
2Manufacturing precision
If insulating wall width is reduced to increase shape factor, then pixel efficiency improves, but active surface area for pixels is reduced
Solution Approach 1:
By changing the substrate crystal orientation to (110), the patent enables formation of insulating walls with width less than 0.5 μm, significantly increasing the shape factor (depth/width ratio). This parameter change allows the walls to be narrower without requiring proportionally deeper etching, thereby preserving more active surface area for pixels while achieving high shape factor
3Object-affected harmful factors
If deep insulating walls are formed to separate pixels, then crosstalk is reduced, but manufacturing complexity increases due to precision requirements
Solution Approach 1:
The patent utilizes the natural dopant channeling effect in (110) oriented silicon substrates to self-align and self-limit the dopant penetration depth and lateral spread. This self-service mechanism eliminates the need for complex precision control systems, as the crystal structure itself guides the dopant atoms to form walls with precise dimensions (width < 0.5 μm, depth > 2 μm) without requiring external intervention
Solution Approach 2:
The patent replaces mechanical precision control systems with a physics-based solution using dopant channeling effects. Instead of relying on mechanical positioning and thickness control of masks, the solution uses the inherent directional properties of dopant diffusion in (110) silicon to automatically achieve the required wall dimensions, reducing manufacturing complexity
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 approach enables the formation of image sensors with pixels of decreased lateral dimensions and large shape factor insulating walls, improving pixel efficiency and reducing crosstalk while maintaining deep absorption areas for light, and allows for the formation of high-speed transistors in a secondary substrate of orientation (100).
Implementation Method 1
utilizing channeling effects to achieve insulating walls with depths greater than 2 μm and widths less than 0.5 μm
Implementation Method 2
The photosensitive cell comprises a photodiode D having its anode connected to a source of a reference voltage GND
Data Source
AI summary
An image sensor including at least one photodiode and at least one transistor formed in and on a silicon substrate, the assembly of the photodiode and of the transistor being surrounded with a heavily-doped insulating wall, wherein the silicon substrate has a crystal orientation (110).