Dual-Depth STI Formation for CMOS Imaging Sensors
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Solution Overview
Problem
The existing methods for manufacturing CMOS imaging sensors with STI structures face challenges in achieving a suitable depth-to-width ratio for isolation trenches, leading to voids or gaps, and require complex processes with additional photomasks, increasing manufacturing costs.
Innovation Solution
A dual-depth STI formation method involving sequential deposition of layers, photoresist patterning, and etching processes to create trenches of different depths in pixel and peripheral circuit areas, simplifying the process and reducing costs by eliminating the need for repeated patterning and additional photomasks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the isolation trench depth is increased to improve signal-to-noise ratio, then the image quality is improved, but the depth-to-width ratio becomes too large causing void or gap formation
Solution Approach 1:
The patent applies different etching depths to different regions: pixel unit areas have shallower trenches while peripheral circuit areas have deeper trenches. This local differentiation allows each region to have optimal trench depth for its specific function, preventing void formation in pixel areas while maintaining signal-to-noise ratio in peripheral areas.
Solution Approach 2:
The substrate is divided into different regions (pixel unit areas and peripheral circuit areas) with different trench depth requirements. The etching process is segmented into multiple steps with different durations to create dual-depth trenches, allowing independent optimization of each region's trench characteristics.
2Reliability
If the pixel fill rate is increased to improve signal-to-noise ratio, then the image quality is improved, but the isolation trench size decreases causing large depth-to-width ratio and void formation
Solution Approach 1:
As pixel fill rate increases and trench width decreases, the patent makes the trench depth adjustment even more critical. By making pixel area trenches shallower and peripheral area trenches deeper, the patent compensates for the reduced trench width, maintaining adequate filling quality despite the smaller dimensions required by high pixel fill rate designs.
3Manufacturing precision
If repeated patterning process is used to control trench depth in different regions, then the trench depth precision is improved, but the process complexity and manufacturing cost increase
Solution Approach 1:
The patent combines multiple trench formation operations into a single etching process. By using a unified etching step with region-specific etch rates or selective masking, the patent achieves different trench depths in pixel and peripheral areas without requiring separate patterning and etching cycles for each region, thereby reducing process complexity.
Solution Approach 2:
The patent performs preliminary preparation of the substrate surface and masking layers before the etching process. By pre-configuring the masking structure that exposes different regions differently, the patent enables the subsequent etching process to automatically create the desired dual-depth trench structure in a single step, avoiding the need for repeated patterning operations.
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 effectively decreases the depth of isolation trenches in pixel unit areas while maintaining the required depth in peripheral circuit areas, reducing manufacturing complexity and costs, and preventing insufficient filling in trenches.
Implementation Method 1
coat a first photoresist layer on said poly-silicon layer and a first opening pattern is then formed in the first photoresist layer
Implementation Method 2
inject dopant to said second overlapping portion along said first opening pattern by using the first photoresist layer as a mask
Implementation Method 3
etch said thick mask layer portion, said poly-silicon layer and said first mask layer along said second opening pattern to form a first type trench
Data Source
AI summary
The present invention is related to the trench manufacturing field in semiconductor, especially a manufacturing method of STI structure with difference depth which is apply to the imaging sensor including forming a dielectric layer with different thickness on the substrate which includes a first region and a second region, then forming a first type trench in the thick dielectric layer and a second type trench in the thin dielectric layer, and etching the substrate of the first region and the substrate of the second region, and thus form a first STI and a second STI with different depth which are located in the substrate of the first region and the second region respectively.