Buried Diffusion Region in LDMOS for Breakdown Voltage
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Solution Overview
Problem
LDMOS transistors face a trade-off between achieving high breakdown voltage and low on-resistance, with existing methods either increasing on-resistance or decreasing breakdown voltage due to the concentration and length of the N-type drift region, which complicates production and affects reliability.
Innovation Solution
A semiconductor device with a buried diffusion region having projections from the body region into the drift region, discretely formed to separate electric field concentration, reducing avalanche current and improving on-breakdown voltage while maintaining low on-resistance and high off-breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the N-type drift region concentration is decreased or drift length is increased to achieve high breakdown voltage, then the breakdown voltage is improved, but the on-resistance increases
Solution Approach 1:
The drift region is segmented into multiple regions with different impurity concentrations along the current flow direction. A first drift region has a first concentration and a second drift region has a second concentration, creating a gradient structure that optimizes both breakdown voltage and on-resistance by distributing the electric field more effectively across the device structure.
Solution Approach 2:
Different regions of the drift structure are assigned different impurity concentrations tailored to their specific functional requirements. The first drift region near the body contact has one concentration optimized for field control, while the second drift region has another concentration optimized for current conduction, achieving local optimization of both breakdown and conduction characteristics.
2Reliability
If high-energy implantation is used to form the P-type embedded diffusion region, then the breakdown voltage is improved, but the manufacturing complexity increases
Solution Approach 1:
The formation of the P-type embedded diffusion region is merged with the existing field oxide formation process. The field oxide serves dual purposes as both an electrical isolation structure and a mask for the high-energy implantation, eliminating the need for separate masking steps and reducing overall manufacturing complexity while achieving the desired breakdown voltage enhancement.
Solution Approach 2:
The field oxide structure performs multiple functions: electrical isolation, process mask for implantation, and structural support. This multi-functionality reduces the total number of process steps required and simplifies the manufacturing sequence while maintaining the high breakdown voltage performance through the embedded diffusion region.
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
The solution effectively improves the trade-off relationship between breakdown voltages and on-resistance, enabling high breakdown voltage without increasing on-resistance, and simplifies the production process by stabilizing electric characteristics.
Implementation Method 1
a buried diffusion region having projections from the body region into the drift region, discretely formed to separate electric field concentration
Implementation Method 2
reducing avalanche current and improving on-breakdown voltage
Data Source
AI summary
A P type semiconductor substrate includes a P type body region, an N type drift region formed away from the P type body region in a direction parallel to a substrate surface, an N type drain region formed in a region separated by a field oxide film in the N type drift region so as to have a concentration higher than the N type drift region, an N type source region formed in the P type body region so as to have a concentration higher than the N type drift region. A P type buried diffusion region having a concentration higher than the N type drift region is formed of a plurality of parts each of which is connected to a part of the bottom surface of the P type body region and extends parallel to the substrate surface and its tip end reaches the inside of the drift region.