Oxygen-Doped Si Diffusion Barrier for Superjunction Conduction Loss
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Solution Overview
Problem
In superjunction power MOSFETs, the out-diffusion of p-type dopant species from p-type pillars affects the conduction loss figure of merit and the thickness and number of epitaxial foundation layers, leading to reduced carrier mobility and increased costs, necessitating better control over dopant diffusion.
Innovation Solution
A diffusion barrier structure comprising alternating layers of Si and oxygen-doped Si, with a Si capping layer, is disposed along the sidewalls and bottom of the superjunction structure regions to control dopant interdiffusion, thereby improving dopant distribution and reducing conduction losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the impurity concentration of n-type pillar regions is increased to reduce conduction loss, then the conduction loss figure of merit is improved, but the out diffusion of p-type dopant species increases which defines the device pitch and reduces carrier mobility
Solution Approach 1:
The device structure is segmented into alternating n-type and p-type doped regions (pillars) within the drift zone, creating a superjunction structure. This segmentation allows independent control of dopant concentrations in each region, enabling high n-type doping for low conduction loss while containing p-type dopant diffusion through the alternating structure geometry.
Solution Approach 2:
An intermediate layer or interface is introduced between the n-type and p-type doped regions at the boundaries of the pillars. This intermediate structure acts as a barrier to dopant diffusion, preventing p-type dopants from migrating into the n-type regions while maintaining the electrical functionality of the superjunction device.
2Manufacturing precision
If multiple epitaxial foundation layers are used to form superjunction structure, then the dopant distribution can be controlled, but the fast-diffusing dopants act as background doping in non-intended zones and reduce carrier mobility
Solution Approach 1:
The doping concentration and type are made local to specific regions rather than uniform throughout the drift zone. Each pillar region has tailored dopant concentration (high n-type or p-type), while the alternating structure ensures that dopants remain confined to their intended zones. This local quality control prevents fast-diffusing dopants from acting as unwanted background doping in adjacent regions.
3Loss of energy
If the out diffusion of p-type dopant species is allowed to define the device pitch, then the conduction loss figure of merit is reduced, but the thickness and number of epitaxial foundation layers increase leading to higher costs
Solution Approach 1:
The alternating n-type and p-type doped regions are pre-formed during the epitaxial growth process itself, rather than requiring subsequent separate doping steps. This preliminary formation of the superjunction structure during growth reduces the number of processing steps and epitaxial layers needed, lowering manufacturing complexity and cost while maintaining the dopant distribution necessary for low conduction loss.
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
The diffusion barrier structure reduces conduction loss by 20% or more, allowing for smaller cell pitch and enabling the use of superjunction transistors in low voltage ranges while maintaining performance in high voltage applications.
Implementation Method 1
a diffusion barrier structure disposed along sidewalls of the regions of the second conductivity type of the superjunction structure, the diffusion barrier structure comprising alternating layers of Si and oxygen-doped Si
Data Source
AI summary
A semiconductor device includes a source region and a drain region of a first conductivity type, a body region of a second conductivity type between the source region and the drain region, a gate configured to control current through a channel of the body region, a drift zone of the first conductivity type between the body region and the drain region, a superjunction structure formed by a plurality of regions of the second conductivity type laterally spaced apart from one another by intervening regions of the drift zone, and a diffusion barrier structure disposed along sidewalls of the regions of the second conductivity type of the superjunction structure. The diffusion barrier structure includes alternating layers of Si and oxygen-doped Si and a Si capping layer on the alternating layers of Si and oxygen-doped Si.