MOSFET Dual-Well Doping for Punch-Through and Resistance
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Solution Overview
Problem
As semiconductor devices are scaled down, the short channel effects in MOSFETs lead to increased risk of punch-through failures and higher on resistance, which complicates maintaining performance in power applications.
Innovation Solution
The implementation of superimposed wells in MOS transistors with varying doping densities, where a second P-type well is embedded in a first P-type well, enhances the doping density near the source and reduces it near the drain, thereby improving the punch-through window and reducing body resistance without adding extra fabrication steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a shorter channel length is employed to reduce on resistance, then on resistance decreases, but punch-through failure risk increases
Solution Approach 1:
The patent applies local quality by implementing a dual-well structure where the first well and second well have different doping concentrations in different spatial regions. The first well has higher doping concentration near the source and lower near the drain, while the second well has the opposite distribution. This creates locally optimized doping profiles that prevent punch-through at the source end while maintaining low resistance at the drain end, resolving the contradiction between short channel length and punch-through reliability.
2Productivity
If a shorter channel length is employed, then device scaling is achieved, but short channel effects worsen
Solution Approach 1:
The patent changes the doping concentration parameters by implementing a dual-well structure with varying doping levels. The first well uses a first doping concentration and the second well uses a second doping concentration, with the doping profile changing along the channel length. This parameter variation allows the device to maintain effective channel control despite the shorter physical length, mitigating short channel effects while enabling further scaling and higher integration density.
3Reliability
If doping density is increased near the source, then punch-through window is improved, but body resistance increases
Solution Approach 1:
The patent applies asymmetry by creating an asymmetric doping distribution through the dual-well structure. The first well has higher doping concentration near the source region to improve punch-through window, while the second well has higher doping concentration near the drain region to reduce body resistance. This asymmetric arrangement of doping profiles in the two wells allows simultaneous optimization of both punch-through reliability and resistance characteristics.
Data Source
AI summary
A MOS transistor comprises a substrate of a first conductivity, a first region of the first conductivity formed over the substrate, a second region of the first conductivity formed in the first region, a first drain/source region of a second conductivity formed in the second region, a second drain/source region of the second conductivity and a body contact region of the first conductivity, wherein the body contact region and the first drain/source region are formed in an alternating manner from a top view.