Staggered Column Superjunction for Power MOSFET Trade-Offs
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Solution Overview
Problem
Conventional power MOSFETs face a trade-off between low on-resistance (Rds-on) and high breakdown voltage (BV), with superjunction devices experiencing unstable Unclamped Inductive Switching (UIS) due to process variations and varying Rds-on and BV across a wafer, particularly in termination and corner regions.
Innovation Solution
A staggered column vertical superjunction semiconductor device is developed, featuring alternating P-type and N-type columns with different depths in active and termination regions, allowing for adjusted breakdown voltage and on-resistance characteristics, with deeper columns in termination regions for higher BV and shallower columns in active regions for lower Rds-on.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional lowly doped drift region is used to provide high breakdown voltage, then breakdown voltage is improved, but on-resistance increases dramatically
Solution Approach 1:
The drift region is segmented into alternating P-type and N-type doped columns (superjunctions) instead of a uniform lowly doped region. This segmentation allows the device to achieve high breakdown voltage through complete depletion of columns while maintaining lower on-resistance through the presence of highly doped column regions that provide conduction paths.
Solution Approach 2:
Different regions of the drift region are given different doping characteristics - P-type columns and N-type columns with specific doping concentrations and depths are created to optimize local electrical properties. The staggered column configuration creates local variations in depletion characteristics that improve overall device performance.
2Reliability
If superjunction devices are used to achieve low on-resistance and high breakdown voltage, then the trade-off between Rds-on and BV is improved, but UIS performance becomes unstable due to process variation
Solution Approach 1:
The invention changes the depth parameter of P-type columns in termination regions relative to active regions. By making P-type columns in termination regions deeper than those in active regions, the device compensates for process variations and ensures that termination regions do not break down before active cell regions during UIS conditions, thereby stabilizing UIS performance.
Solution Approach 2:
The invention introduces a vertical depth dimension differentiation between termination and active regions. By varying the P-type column depth in the vertical dimension across different device regions, the patent achieves region-specific breakdown voltage characteristics that stabilize overall UIS performance despite process variations.
3Ease of manufacture
If uniform P-type column depth is used across all regions, then manufacturing is simplified, but termination regions may break down before active cell regions during UIS
Solution Approach 1:
The invention applies different P-type column depths to different device regions - termination regions receive deeper P-type columns while active regions receive shallower columns. This local differentiation ensures that termination regions have higher breakdown voltage to prevent premature breakdown during UIS, while maintaining relatively simple manufacturing through region-specific processing steps.
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 stabilizes UIS performance by maintaining high breakdown voltage in termination regions while reducing on-resistance in active regions, effectively addressing the trade-off between BV and Rds-on, and minimizing damage from avalanche conditions.
Implementation Method 1
Dopants having a second conductivity type may be implanted through the openings to form first implanted regions
Implementation Method 2
A second semiconductor layer may be grown on top of the first semiconductor layer
Implementation Method 3
the dopants of second conductivity type may be diffused to form the columns of second conductivity type
Data Source
AI summary
A staggered column superjunction semiconductor device may include a cell region having one or more device cells. One or more device cells in the cell region include a semiconductor substrate configured to act as a drain and a semiconductor layer formed on the substrate. A first doped column may be formed in the semiconductor layer to a first depth and a second doped column may be formed in the semiconductor layer to a second depth. The first depth is greater than the second depth. The first and second columns are doped with dopants of a same second conductivity type and extend along a portion of a thickness of the semiconductor layer and are separated from each by a portion of the semiconductor layer.