Superjunction MOSFET with Segmented Columnar Regions
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Solution Overview
Problem
Superjunction MOSFETs experience hard recovery of parasitic diodes, leading to rapid reverse recovery current changes and noise issues, particularly in inverter circuits driving inductive loads, due to the fast spreading of depletion layers and oscillations in reverse recovery characteristics.
Innovation Solution
A semiconductor device with a specific structure featuring a first conductive type base layer, second conductive type columnar regions, and collector layers arranged at distinct pitches, which reduces on-resistance and alleviates hard recovery by separating the columnar regions and optimizing the rear surface electrode configuration, thereby controlling the depletion layer spread and improving recovery characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If superjunction MOSFETs use conventional structures with p-type columnar regions extending from the p-type base layer towards the drain layer, then on-resistance is reduced and switching speed is improved, but hard recovery of the parasitic diode occurs causing rapid reverse recovery current changes and noise issues
Solution Approach 1:
The p-type columnar region is divided into two separate regions: a first p-type columnar region extending from the p-type base layer towards the drain layer, and a second p-type columnar region extending from the p-type base layer towards the drain layer at a different position. This segmentation allows independent optimization of each region's function, with the first region primarily reducing on-resistance and the second region helping to control depletion layer spread during reverse recovery, thereby reducing hard recovery characteristics.
Solution Approach 2:
Different regions of the semiconductor device are given different impurity concentrations and structural characteristics. The first p-type columnar region has specific impurity concentration characteristics optimized for reducing on-resistance, while the second p-type columnar region has different impurity concentration characteristics optimized for controlling reverse recovery behavior. This local quality differentiation allows simultaneous optimization of both on-resistance and soft recovery characteristics.
2Adaptability or versatility
If the chip size of MOSFET is increased to be compatible with both low voltage ranges and high voltage ranges, then versatility is improved, but manufacturing cost increases
Solution Approach 1:
The semiconductor device structure is designed to function effectively across both low voltage and high voltage ranges through the superjunction configuration with separated p-type columnar regions. The first p-type columnar region handles high voltage blocking while the second p-type columnar region assists in controlling reverse recovery, allowing a single device structure to serve multiple voltage range applications without requiring different chip sizes or additional components.
Solution Approach 2:
The device utilizes controlled changes in impurity concentration parameters across different regions and depths of the semiconductor structure. By varying the impurity concentration in the first and second p-type columnar regions, as well as in the n-type drift layer, the device can optimize its electrical characteristics for both low and high voltage operation within a compact form factor, avoiding the need for larger chip sizes.
3Reliability
If heavy particle irradiation is applied from the rear surface of the n-type drain layer, then reverse recovery characteristics are improved, but hard recovery characteristics are not sufficiently improved
Solution Approach 1:
The second p-type columnar region acts as an intermediary structure between the n-type drain layer and the external circuit. During reverse recovery, this second columnar region helps control and moderate the spread of the depletion layer, preventing the rapid current changes that cause hard recovery. This intermediary structure works in conjunction with heavy particle irradiation to achieve softer recovery characteristics without compromising the benefits of particle irradiation for reverse recovery improvement.
Data Source
AI summary
A semiconductor device that includes the following is manufactured: an n− base layer; a p-type base layer formed on the surface of the n− base layer; an n+ source layer formed in the inner area of the p-type base layer; a gate electrode formed so as to face a channel region across a gate insulating film; a plurality of p-type columnar regions that are formed in the n− base layer so as to continue from the p-type base layer and that are arranged at a first pitch; and a plurality of p+ collector layers that are selectively formed on the rear surface of the n− base layer and that are arranged at a second pitch larger than the first pitch.