Carbon Diffusion Barrier for Power Device Dopant Control
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Solution Overview
Problem
In power field effect transistors (FETs), dopant out-diffusion from heavy body and source regions leads to increased contact resistance and altered threshold voltage, limiting transistor performance and device density due to lateral diffusion caused by temperature cycles during manufacturing.
Innovation Solution
The implementation of diffusion barrier regions, primarily composed of carbon, surrounding or extending between the heavy body and source regions to inhibit lateral dopant diffusion, thereby reducing out-diffusion and maintaining dopant concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If temperature cycles are used to drive heavy body dopants to desired depth, then dopant depth is improved, but lateral diffusion of dopants increases causing threshold voltage alteration and increased contact resistance
Solution Approach 1:
A carbon-based diffusion barrier layer is introduced as an intermediary between the heavy body dopant source and the channel region. This barrier layer selectively blocks lateral diffusion of dopants while permitting vertical diffusion to the desired depth, thus decoupling the depth control function from the lateral diffusion control function. The carbon layer acts as a mediator that allows the temperature cycling process to achieve proper dopant depth without suffering from the harmful lateral diffusion side effect.
2Manufacturing precision
If cell pitch is increased to avoid lateral diffusion effects, then manufacturing precision is improved, but device density decreases and drain-to-source on resistance increases
Solution Approach 1:
The carbon diffusion barrier layer serves as a localized intermediary that enables tight cell pitch by preventing dopant interference between adjacent devices. Instead of increasing pitch to avoid diffusion overlap, the barrier layer actively manages the diffusion process, allowing devices to be placed closer together while maintaining electrical performance specifications.
3Reliability
If heavy body dopant concentration is increased to improve ruggedness, then reliability is improved, but lateral diffusion interference with active channel increases
Solution Approach 1:
The carbon diffusion barrier layer creates a localized quality change in the semiconductor structure. The barrier is positioned specifically at the interface where lateral diffusion would harm the channel, while allowing heavy body doping in the bulk region to proceed at high concentrations for improved ruggedness. This local intervention enables high dopant concentration where needed (in the heavy body region) while protecting the channel region from diffusion interference.
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 contact resistance, stabilizes threshold voltage, and increases device density by preventing dopant diffusion into the channel area, enhancing transistor performance without affecting conventional manufacturing processes.
Implementation Method 1
A first diffusion barrier region at least partially surrounds the heavy body region... configured to minimize lateral diffusion of dopants from the heavy body region
Data Source
AI summary
A semiconductor structure comprises a drift region of a first conductivity type in a semiconductor region. A well region of a second conductivity type is over the drift region. A source region of the first conductivity type is in an upper portion of the well region. A heavy body region of the second conductivity type extends in the well region. The heavy body region has a higher doping concentration than the well region. A first diffusion barrier region at least partially surrounds the heavy body region. A gate electrode is insulated from the semiconductor region by a gate dielectric.