SiC Semiconductor Device Local Carrier Lifetime Control
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Solution Overview
Problem
Conventional silicon carbide semiconductor devices face challenges in managing the carrier lifetime of the n-type drift layer, particularly in ensuring that the locally controlled carrier lifetime is within the designed range, which affects the tradeoff between ON resistance and reverse recovery current, and can lead to defects in the edge termination structure due to the substitution of aluminum and vanadium at the same atomic sites.
Innovation Solution
A silicon carbide semiconductor device with a first-conductivity-type epitaxial layer and a second-conductivity-type epitaxial layer, where the first-conductivity-type layer is doped with nitrogen and vanadium to form a recombination center, positioned deeper than 5 μm from the pn junction surface, allowing for local control of carrier lifetime and separation from the pn junction surface to prevent adverse effects on the edge termination structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If vanadium is doped in the n-type drift layer to reduce carrier lifetime, then reverse recovery current is reduced, but defects occur in the edge termination structure due to substitution of aluminum and vanadium at the same atomic sites
Solution Approach 1:
The patent divides the n-type drift layer into multiple regions with different vanadium doping concentrations. The first region (edge termination region) has a first vanadium doping concentration, while the second region (drift region) has a second vanadium doping concentration that is higher than the first. This segmentation prevents vanadium-aluminum substitution at the pn junction while still achieving reverse recovery current reduction in the drift region.
Solution Approach 2:
The patent applies different vanadium doping concentrations to different regions of the n-type drift layer. The edge termination region receives a lower vanadium concentration to prevent defects, while the drift region receives a higher concentration to reduce carrier lifetime and reverse recovery current. This local quality approach optimizes both reliability and switching performance.
2Loss of energy
If carrier lifetime of the n-type drift layer is increased to reduce ON resistance, then ON resistance decreases, but reverse recovery current increases during switching
Solution Approach 1:
The patent implements local carrier lifetime control by doping only specific regions of the n-type drift layer with vanadium. The drift region has a shorter carrier lifetime due to higher vanadium concentration, reducing reverse recovery current, while the edge termination region maintains a longer carrier lifetime with lower vanadium concentration, preserving low ON resistance characteristics.
Solution Approach 2:
The n-type drift layer is segmented into functional regions with different carrier lifetimes. The drift region is segmented to have short carrier lifetime for low reverse recovery current, while the edge termination region is segmented to have long carrier lifetime for low ON resistance. This segmentation resolves the tradeoff between the two parameters.
3Object-generated harmful factors
If uniform vanadium doping is applied throughout the n-type drift layer, then reverse recovery current is reduced, but the edge termination structure develops defects due to aluminum-vanadium substitution
Solution Approach 1:
The patent segments the vanadium doping profile into at least two distinct regions: an edge termination region with lower vanadium concentration and a drift region with higher vanadium concentration. This prevents uniform doping from causing aluminum-vanadium substitution at the pn junction while maintaining reverse recovery current reduction in the drift region.
Solution Approach 2:
Different vanadium doping concentrations are applied locally to different regions. The edge termination region has low vanadium concentration to prevent substitution defects, while the drift region has high vanadium concentration to reduce reverse recovery current. This local quality differentiation resolves the contradiction between reducing harmful factors and maintaining manufacturing precision.
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 enables non-destructive evaluation of the carrier lifetime and improves the tradeoff between ON resistance reduction and reverse recovery current reduction during switching, while preventing defects in the edge termination structure, thus enhancing device performance and quality management.
Implementation Method 1
a first-conductivity-type layer selectively provided in the first first-conductivity-type epitaxial layer and separated from the pn junction surface, the first-conductivity-type layer containing, as impurities, the first element and a second element that forms a recombination center
Implementation Method 2
applying a predetermined voltage between both surfaces of the first first-conductivity-type epitaxial layer, causing a depletion layer in the first first-conductivity-type epitaxial layer to spread
Data Source
AI summary
During epitaxial growth of an n−-type drift layer having a uniform nitrogen concentration, vanadium is doped in addition to the nitrogen, whereby an n−-type lifetime reduced layer is selectively formed in the n−-type drift layer. The n−-type lifetime reduced layer is disposed at a depth that is more than 5 μm from a pn junction surface between a p-type anode layer and the n−-type drift layer in a direction toward a cathode side, and the n−-type lifetime reduced layer is disposed separated from the pn junction surface. Further, the n−-type lifetime reduced layer is disposed in a range from the pn junction surface to a depth that is ⅓ times a thickness of the n−-type drift layer. A vanadium concentration of the n−-type lifetime reduced layer is 1/100 to ⅕ of a nitrogen concentration of the n−-type lifetime reduced layer.