Lateral DMOS Drift Region Segmentation for Hot Hole Suppression
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Solution Overview
Problem
LDMOS devices experience undesirable changes in on-state resistance and breakdown voltage due to avalanche-generated hot holes being injected into the gate oxide and spacer regions, leading to 'walk-out' phenomena at high voltage applications.
Innovation Solution
The semiconductor device features a vertically structured N-type drain region with varying doping concentrations and a P-type deep body region, formed by series of implants, which moves the avalanche hole generation point away from the surface, suppressing hot hole injection and trapping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the avalanche breakdown voltage is increased by allowing hot hole injection into gate oxide and spacer regions, then the breakdown voltage increases, but the on-state resistance changes undesirably and device performance becomes unstable
Solution Approach 1:
The drift region is divided into three sub-regions (upper, middle, lower) with different doping concentrations. The upper sub-drift region has lower doping concentration to reduce electric field and prevent hot hole injection, while the lower sub-drift region has higher doping concentration to maintain breakdown voltage. This local differentiation of doping quality resolves the contradiction between maintaining breakdown voltage and preventing performance instability.
Solution Approach 2:
The drift region is segmented into three distinct sub-regions with varying doping concentrations arranged vertically. This segmentation allows each sub-region to perform a specific function: the upper region protects against hot hole injection, the middle region transitions the electric field, and the lower region maintains the necessary breakdown characteristics, thereby stabilizing overall device performance.
2Strength
If hot holes are injected into gate oxide and spacer regions during avalanche breakdown, then breakdown voltage is achieved, but walk-out phenomenon occurs due to hole trapping
Solution Approach 1:
The upper sub-drift region is designed with lower doping concentration to create a softer electric field gradient that prevents hot hole generation and injection before they can cause walk-out. This preliminary protective structure counteracts the harmful effect of hot hole trapping in the gate oxide and spacer regions, eliminating the walk-out phenomenon while maintaining breakdown voltage.
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 configuration maintains stable breakdown voltage and reduces undesirable changes in on-state resistance by positioning the peak electric field and doping concentration gradient below the surface, preventing hot hole injection and associated performance changes.
Implementation Method 1
electron-hole pairs are typically nucleated in the area of high electric field impact ionization under the gate termination in the drift region
Implementation Method 2
electron-hole pairs are typically nucleated in the area of high electric field impact ionization
Implementation Method 3
forming an N-type well region in a layer grown on a semiconductor substrate by implanting a series of N-type dopants with varying doping concentration
Data Source
AI summary
A lateral DMOS device with peak electric field moved below a top surface of the device along a body-drain junction is introduced. The LDMOS has a deep body and a drift region formed by a series of P-type and N-type implants, respectively. The implant doses and depths are tuned so that the highest concentration gradient of the body-drift junction is formed below the surface, which suppresses the injection and trapping of hot holes in the device drain-gate oxide region vicinity, and the associated device performance changes, during operation in breakdown.