Superjunction Charge Compensation for Trench Sidewall Angles
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Solution Overview
Problem
Conventional high-voltage semiconductor devices with superjunction structures face challenges in maintaining charge balance due to angled trench sidewalls, leading to reduced breakdown voltage and increased turn-on resistance.
Innovation Solution
The implementation of a charge compensation layer and plug with specific dopant concentrations and thicknesses to balance charges within the superjunction structure, regardless of the trench sidewall angle, ensuring consistent breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the concentration of impurities in the semiconductor body is increased to reduce turn-on resistance, then the turn-on resistance decreases, but the breakdown voltage is lowered due to increased space charges
Solution Approach 1:
The semiconductor body is divided into alternating N-type and P-type impurity regions (pillars) that extend vertically through the device. This segmentation allows the formation of a superjunction structure where charged regions provide low resistance paths while depleted regions maintain high breakdown voltage, resolving the contradiction between reducing turn-on resistance and maintaining breakdown voltage.
Solution Approach 2:
Different regions of the semiconductor body are assigned different impurity concentrations and conductivity types. The N-type and P-type pillars have high impurity concentrations to reduce turn-on resistance, while the depleted regions between them maintain low space charge to preserve breakdown voltage. This local differentiation allows simultaneous optimization of both parameters.
2Ease of manufacture
If conventional etching processes are used to form trenches for superjunction structures, then the manufacturing process is simple, but angled sidewalls cause charge imbalance and reduced breakdown voltage
Solution Approach 1:
A mandrel structure is formed first in the trench before etching, and the etching process is designed to create angled sidewalls that converge toward the mandrel. This preliminary positioning of the mandrel ensures that even with angled sidewalls, the impurity regions will be properly positioned and sized to achieve charge balance, compensating for the non-vertical geometry.
Solution Approach 2:
A mandrel structure serves as an intermediary element within the trench, providing a reference for positioning and sizing the impurity regions. The mandrel mediates between the angled trench sidewalls and the required charge balance, ensuring that the N-type and P-type pillars have appropriate dimensions and spacing to maintain equal and opposite charges despite the angled geometry.
Data Source
AI summary
A method of fabricating a high-voltage semiconductor device includes the following steps: providing a semiconductor layer; forming a plurality of trenches in the semiconductor layer to define a plurality of pillars of a first conductivity type in the semiconductor layer between adjacent trenches, wherein the trenches extend from a top surface of the semiconductor layer toward a bottom surface of the semiconductor layer; forming a charge compensation layer of a second conductivity type over at least sidewalls of each trench to a predetermined thickness thereby forming a groove in each trench; and substantially filling each groove with a charge compensation plug of the first conductivity type.