Lateral Overflow Drain Fabrication in Image Sensors
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Solution Overview
Problem
Existing methods for forming lateral overflow drains in image sensors often result in damage to underlying layers, leading to contamination and defects due to double-etching of the nitride layer, which can cause charge carriers to spill over and affect image quality.
Innovation Solution
A double mask layer process is used to form lateral overflow drains and channel stops, where a hard mask layer is patterned to create openings, and dopants of opposite conductivity type are implanted to form lateral overflow drains, with a second mask layer aligning edges for precise formation without damaging underlying layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single mask layer process is used to form lateral overflow drains, then the fabrication process is simpler, but the alignment precision between lateral overflow drains and channel stops deteriorates
Solution Approach 1:
The fabrication process is divided into two separate mask layer steps: a first mask layer process to form channel stops, and a second mask layer process to form lateral overflow drains. This segmentation allows each structure to be formed with independent precision control, resolving the alignment precision issue while maintaining reasonable process complexity through systematic division of steps.
2Reliability
If the nitride layer is over-etched to accommodate thickness variations, then the lateral overflow drain formation is more robust, but the underlying insulating layer and substrate are damaged
Solution Approach 1:
A first insulating layer is formed beforehand to serve as a protective cushion layer between the nitride layer and the substrate. This cushioning layer prevents damage to the substrate and underlying structures during subsequent over-etching operations, allowing robust lateral overflow drain formation without harmful substrate exposure.
3Ease of manufacture
If the top surface of substrate is exposed during processing, then the lateral overflow drain can be formed, but the substrate surface is damaged and contamination occurs
Solution Approach 1:
The first insulating layer is deposited beforehand as a protective barrier that prevents substrate surface exposure and damage during lateral overflow drain formation. This cushioning approach enables easy manufacture of lateral overflow drains while maintaining substrate surface integrity and preventing contamination.
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 method allows for accurate and repeatable fabrication of lateral overflow drains and channel stops with minimal feature sizes, preventing damage to underlying layers and improving image sensor resolution.
Implementation Method 1
A dopant is then implanted through each second opening and into the substrate, layer, or well to form one or more lateral overflow drains
Data Source
AI summary
A lateral overflow drain and a channel stop are fabricated using a double mask process. Each lateral overflow drain is formed within a respective channel stop. Due to the use of two mask layers, one edge of each lateral overflow drain is aligned, or substantially aligned, with an edge of a respective channel stop.