Backside-Illuminated Image Sensor Contact Hole Formation
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Solution Overview
Problem
In the manufacturing of backside-illuminated image sensors, the formation of normal contact holes is challenging due to the small diameter and increased depth requirements, leading to potential defects in conductive material filling and reduced manufacturing yield.
Innovation Solution
Forming the normal contact holes before the super contact hole and shielding layer, with a separate step for exposing the gate and active region, and using a shielding layer on the sidewalls and bottom of the contact holes to prevent depth increase and ensure proper filling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the light receiving area is minimized to increase the number of pixels, then the number of pixels increases, but the stack height cannot be reduced and light interference from metal wiring occurs
Solution Approach 1:
The patent inverts the conventional front-side illumination approach by implementing backside illumination. The light receiving area is formed on the back surface of the semiconductor substrate, allowing light to enter without passing through metal wiring layers. This inversion eliminates light interference from metal wiring and enables minimal light receiving area design while maintaining high pixel density.
2Ease of manufacture
If normal contact holes are formed after super contact hole and shielding layer, then the manufacturing process follows conventional sequence, but the depth increases and defective filling occurs
Solution Approach 1:
The patent applies preliminary action by forming normal contact holes through the inter-layer dielectric layer before forming the super contact hole and shielding layer. This sequence ensures that normal contact holes have controlled depth and proper exposure of gate and active region, preventing defective filling while maintaining ease of manufacture through systematic process reorganization.
Solution Approach 2:
The patent segments the contact hole formation process into distinct stages: first forming normal contact holes with controlled depth to expose gate and active region, then subsequently forming super contact holes and shielding layer. This segmentation allows independent optimization of each contact type and prevents the depth and filling issues that occur when forming all contacts simultaneously in the conventional sequence.
3Area of moving object
If the diameter of normal contact hole is small to reduce chip size, then the chip size decreases, but the depth increases and proper formation becomes difficult
Solution Approach 1:
The patent applies local quality by creating different contact hole characteristics in different regions. Normal contact holes are formed with specific depth control to expose gate and active region, while super contact holes are formed subsequently with different depth requirements. This localized quality control allows small diameter normal contact holes to be properly formed without compromising manufacturing precision, enabling chip size reduction while maintaining contact hole formation quality.
Data Source
AI summary
A method of forming a contact includes forming an inter-layer dielectric layer to cover a gate formed on a semiconductor substrate; and forming a first hole which passes through the inter-layer dielectric layer to expose the gate, a second hole which exposes an active region of the semiconductor substrate, and a third hole which exposes the semiconductor substrate at a preset depth. Further, the method includes forming a shielding layer on the semiconductor substrate including the bottom and sidewalls of the first hole, the second hole, and the third hole; and removing the shielding layer at the bottom of the first hole and the second hole to expose the gate and the active region. Furthermore, the method includes filling the first hole, the second hole, and the third hole with a conductive material.