Front-Side Substrate Contact Formation on SOI Wafers
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Solution Overview
Problem
Existing methods for forming substrate contacts on silicon-on-insulator (SOI) wafers are inadequate for advanced packaging technologies like flip chip and die stacking, as they require additional wafer processing and are not suitable for grounding or biasing the bottom substrate effectively, especially when creating contacts through the backside is prohibitive.
Innovation Solution
A method involving a SOI wafer with a mask layer, where an isolation region is formed through the mask and silicon layers, a contact opening is created to expose the underlying substrate, and a conductive plug is formed to electrically contact the substrate, surrounded by the insulating and buried insulating layers, allowing for front-side substrate contact integration with the SOI device process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a contact trench is etched through the SOI layers to the substrate before device processing, then substrate contact is achieved, but the process complexity increases and additional wafer processing is required
Solution Approach 1:
The contact opening is formed through the isolation region and buried oxide layer after device processing steps are completed, rather than before. This preliminary action allows the substrate contact to be created at the optimal stage of the process, avoiding the need to maintain and re-open trenches during subsequent device processing steps.
Solution Approach 2:
The substrate contact formation is segmented into distinct stages: first forming the isolation region through mask and silicon layers, then creating the contact opening through the isolation region and buried oxide, and finally forming the conductive plug. This segmentation allows each step to be optimized independently and integrated seamlessly with the overall device process.
2Reliability
If the bottom substrate is left without contact, then static charge build-up occurs causing back channel disturbance, but creating backside contact requires additional wafer processing
Solution Approach 1:
Instead of creating substrate contact through the backside of the wafer (traditional approach), the invention creates the contact through the front side by forming an opening through the isolation region and buried oxide layer. This dimensional change allows substrate contact to be achieved without additional wafer processing steps and is compatible with advanced packaging technologies like flip chip and die stacking.
Solution Approach 2:
The isolation region serves multiple functions: it provides electrical isolation for the device structures and simultaneously serves as the medium through which the substrate contact is formed. This multi-functionality eliminates the need for separate contact formation steps and integrates substrate biasing capability into the existing isolation structure.
3Reliability
If a trench is maintained during device processing and opened during source/drain implantation, then substrate contact can be made, but the process steps and time increase
Solution Approach 1:
The contact opening is formed through the isolation region and buried oxide layer after device processing steps are completed, rather than before. This preliminary action allows the substrate contact to be created at the optimal stage of the process, avoiding the need to maintain and re-open trenches during subsequent device processing steps.
Data Source
AI summary
A method for forming a substrate contact on a silicon-on-insulator (SOI) wafer is provided that can be integrated with a process for fabricating SOI devices without additional processing after wafer dicing. The method is applicable in many of the more advanced packaging technologies, e.g., such as flip chip and die stacking, directly creating a contact to silicon substrate via the front of the diced SOI wafer.