SOI Transistor High Field Regions via Nested Wells
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Solution Overview
Problem
Conventional methods for creating high field regions in thin film silicon-on-insulator (SOI) technology, such as surface lightly doped drain (LDD) devices and shallow trench isolation (STI) structures, are either sensitive to hot carrier injection or incompatible with thin film SOI technology, limiting the effective design of field-effect transistors (FETs).
Innovation Solution
A semiconductor device is designed with a N-well within a P-well in a silicon layer atop a buried oxide layer, featuring source and drain regions with a gate positioned atop the N-well, generating both lateral and vertical high field regions, allowing for the creation of high field regions suitable for FETs on SOI substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a surface lightly doped drain (LDD) device is used to handle high field, then the high field region is created, but the device becomes too sensitive to hot carrier injection
Solution Approach 1:
The patent applies local quality by creating distinct doped regions with different properties within the device structure. Specifically, it forms a first doped region (LDD) with lower doping concentration and a second doped region (extension) with higher doping concentration, each serving different functions: the LDD region handles the high field while the extension region provides hot carrier protection, thus resolving the contradiction between high field capability and hot carrier sensitivity
Solution Approach 2:
The patent implements nesting by placing the first doped region (LDD) and second doped region (extension) in a nested spatial relationship where the extension region is positioned adjacent to and overlapping with the LDD region. This nested configuration allows both regions to work together, with the extension region providing hot carrier protection while the LDD region maintains high field handling capability
2Reliability
If a shallow trench isolation (STI) structure is built to handle high field, then the high field region is created, but it cannot be built on a structure with thin film silicon-on-insulator technology
Solution Approach 1:
The patent applies parameter changes by modifying the doping concentration parameter to create different functional regions. Instead of using STI structures, it varies the doping concentration from the first doped region (lower concentration for high field handling) to the second doped region (higher concentration for hot carrier protection), achieving high field handling capability while maintaining compatibility with thin film SOI technology
Solution Approach 2:
The patent substitutes the mechanical/structural approach of STI (shallow trench isolation) with a doping-based approach. Instead of using physical isolation structures to handle high field, it uses doped regions with different concentrations to create the necessary electric field distribution, making the solution compatible with thin film SOI technology where STI cannot be implemented
Data Source
AI summary
A semiconductor device is disclosed. In an embodiment, a semiconductor device includes a N-well within a P-well in a silicon layer, the silicon layer positioned atop a buried oxide layer of a silicon-on-insulator (SOI) substrate; a first source region and a second source region within a portion of the P-well; a first drain region and a second drain region within a portion of the P-well and within a portion of the N-well; and a gate positioned atop the N-well, wherein a lateral high field region is generated between the N-well and the P-well and a vertical high field region is generated between the gate and the N-well. A related method is disclosed.