Self-Aligned Corner Implant for Image Sensor STI
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Solution Overview
Problem
Existing methods for fabricating corner implants in shallow trench isolation regions of image sensors lead to increased surface dark current and silicon pitting, and require additional processing steps and photoresist masking, which are undesirable.
Innovation Solution
A method involving the formation of a first hard mask layer, patterning, and etching to create self-aligned corner implants without exposing the STI corner, followed by the deposition of a second hard mask layer to form sidewall spacers and etch a trench, allowing for the implantation of dopants into the substrate without creating silicon pits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If photoresist mask is formed and patterned to create corner implants, then corner implants can be formed to suppress surface dark current, but additional processing steps are created increasing manufacturing complexity
Solution Approach 1:
The method performs the corner implant formation as a preliminary action during the STI fabrication process itself, rather than as a separate subsequent step. The etch-stop layer is formed before the trench etching, and the corner implant is created automatically during the trench formation process through self-alignment, eliminating the need for separate photoresist masking and patterning steps.
Solution Approach 2:
The STI fabrication process itself serves to create the corner implant through self-alignment. The etch-stop layer automatically defines the corner implant region without requiring external masking, and the process aligns itself to create the implant at the correct location, making the system self-sufficient.
2Productivity
If hard mask is removed from sidewalls and corners to simultaneously implant sidewalls and corners, then implantation can be performed in one step, but silicon pits are created at corner implants during subsequent etching
Solution Approach 1:
The etch-stop layer acts as an intermediary protective layer during the trench etching process. It prevents the etchant from attacking the corner implant region, thereby avoiding silicon pit formation while still allowing the trench to be etched to the required depth. The etch-stop layer is selectively removed only after the trench formation is complete.
3Reliability
If conventional corner implant methods are used, then surface dark current is suppressed, but the STI is not self-aligned and additional photoresist masking is required
Solution Approach 1:
The STI fabrication process automatically creates the corner implant through self-alignment without requiring external photoresist masking. The etch-stop layer and the trench etching process work together to automatically position the corner implant at the correct location, making the system self-aligning and easier to manufacture.
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 reduces surface dark current and eliminates silicon pitting while providing a self-aligned shallow trench isolation, enhancing the manufacturing efficiency and performance of image sensors.
Implementation Method 1
forming a first hard mask layer of over an etch-stop layer on a semiconductor substrate and providing a photoresist mask over the hard mask layer. The photoresist mask is patterned to create an opening and the portion of the first hard mask layer exposed in the opening is etched down to the etch-stop layer
Implementation Method 2
A first dopant is then implanted into the semiconductor substrate through the exposed etch-stop layer
Data Source
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AI summary
A method for fabricating corner implants in the shallow trench isolation regions of an image sensor includes the steps of forming a photoresist layer on a first hard mask layer overlying an etch-stop layer on a semiconductor substrate. The photoresist mask is patterned to create an opening and the portion of the first hard mask layer exposed in the opening is etched down to the etch-stop layer. A first dopant is implanted into the semiconductor substrate through the exposed etch-stop layer. The photoresist mask is removed and a second hard mask layer is formed on the remaining structure and etched to create sidewall spacers along the side edges of the first hard mask layer. The etch stop layer and the semiconductor substrate positioned between the sidewall spacers are etched to create a trench and a second dopant implanted into the side and bottom walls of the trench.