Super Junction MOSFET Trench Width Variation
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Solution Overview
Problem
Power MOSFETs with super junction structures face challenges in maintaining consistent withstand voltage due to manufacturing variations, which can lead to trench wall collapse and uneven impurity concentrations, resulting in fluctuating withstand voltage and increased on-resistance.
Innovation Solution
The semiconductor device features a drift layer with P-type and N-type columns arranged in a super junction structure, where the width of the embedded P-type columns changes continuously along the longitudinal direction, reducing the risk of trench wall collapse and stabilizing the charge balance, thereby minimizing withstand voltage fluctuations without the need for additional photolithography and etching processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the drift layer is made thicker to increase withstand voltage, then the withstand voltage is improved, but the on-resistance becomes higher
Solution Approach 1:
The drift layer is segmented into alternating P-type columns and N-type columns, creating a super junction structure. This segmentation allows the depletion layer to extend laterally across multiple columns under reverse bias, achieving high withstand voltage without requiring excessive drift layer thickness, thereby maintaining low on-resistance.
Solution Approach 2:
Different regions of the drift layer are given different conductivity types (P-type and N-type) to create localized properties. The P-type columns provide depletion regions that extend laterally, while the N-type columns maintain low resistance current paths, optimizing both withstand voltage and on-resistance locally throughout the structure.
2Manufacturing precision
If straight trenches are formed from one end to the other of the cell part, then the super junction structure is formed, but the wall surrounding the trench may collapse
Solution Approach 1:
The trench walls are formed with a curved profile rather than straight vertical walls. The curvature provides structural reinforcement to the trench walls, preventing collapse during the deep etching process while still achieving the required trench depth for the super junction structure.
3Reliability
If the impurity amount of P-type column and N-type region are made equal, then the maximum withstand voltage is obtained, but manufacturing variations cause withstand voltage fluctuations
Solution Approach 1:
The patent intentionally changes the impurity concentration parameters from the ideal equal-state to a deliberately unbalanced state. By making the P-type column impurity concentration higher than the N-type region impurity concentration, the design compensates for manufacturing variations, ensuring consistent withstand voltage performance across production batches.
4Manufacturing precision
If additional photolithography and etching processes are added to control impurity amount balance, then manufacturing precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The impurity concentration balance is predetermined during the epitaxial growth stage rather than requiring subsequent adjustment processes. By pre-setting the P-type column impurity concentration to be higher than the N-type region during crystal formation, the patent eliminates the need for additional photolithography and etching steps to correct imbalances, simplifying the overall manufacturing process.
Data Source
AI summary
The disclosure reduces the risk of collapse of the wall surrounding the trench and suppresses the withstand voltage fluctuation that accompanies the manufacturing variation for a semiconductor device having a super junction structure. The semiconductor device includes a drift layer of a first conductivity type and a plurality of embedded parts embedded in the drift layer. The embedded parts are of a second conductivity type different from the first conductivity type, and the embedded parts are arranged with a first direction as a longitudinal direction and spaced from each other along a second direction that intersects the first direction. A width of each of the embedded parts in the second direction changes continuously along the first direction.