LDMOS Structure With Segmented Buried Rings
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Solution Overview
Problem
Conventional high-voltage lateral diffused metal oxide semiconductor (LDMOS) devices face a trade-off between high breakdown voltage and low on-resistance, with the electrical field crowding effect reducing breakdown voltage and increasing on-resistance, necessitating a semiconductor structure and fabrication method that can enhance both characteristics.
Innovation Solution
The semiconductor structure incorporates a second conductivity type well region with first conductivity type buried rings arranged horizontally, dividing the well region into upper and lower drift regions, and a gate structure formed between the diffused source and drain, allowing for optimized doping profiles and dielectric layers to reduce on-resistance and increase breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the doping concentration of the N-type well is increased to reduce on-resistance, then the on-resistance decreases, but the breakdown voltage decreases due to electrical field crowding effect
Solution Approach 1:
The N-type well region is segmented into multiple regions by introducing P-type buried rings that divide it into upper and lower drift regions. This segmentation allows different portions of the N-type well to have different doping concentrations, enabling the lower region to maintain high doping for low on-resistance while the upper region has lower doping for high breakdown voltage.
Solution Approach 2:
Different regions within the N-type well are given different doping concentrations to optimize local performance. The lower drift region near the drain maintains high doping concentration for low on-resistance, while the upper drift region near the channel has lower doping concentration to reduce electrical field crowding and increase breakdown voltage.
2Reliability
If the doping concentration of the N-type well is decreased to increase breakdown voltage, then the breakdown voltage increases, but the on-resistance increases
Solution Approach 1:
The N-type well is divided into multiple drift regions by P-type buried rings, allowing the lower region to maintain high doping concentration for low on-resistance while the upper region has reduced doping for high breakdown voltage.
Solution Approach 2:
Different regions within the N-type well have different doping concentrations: the lower drift region near the drain maintains high doping for low on-resistance, while the upper drift region has lower doping to reduce electrical field crowding and increase breakdown voltage.
3Reliability
If a uniformly doped flat P-type region is used as RESURF layer, then the N-type well can be easily depleted, but electrical field crowding occurs around the N+-type drain reducing breakdown voltage
Solution Approach 1:
The P-type RESURF layer is segmented into multiple buried rings instead of a continuous uniform layer. This segmentation allows the P-type regions to be positioned strategically to deplete the N-type well while avoiding concentration of electrical fields at the drain region.
Solution Approach 2:
The P-type buried rings act as intermediary structures that facilitate depletion of the N-type well region while distributing the electrical field more uniformly. These buried rings mediate between the need for carrier depletion and the need to avoid electrical field crowding at the drain.
Data Source
AI summary
A semiconductor structure is provided. A second conductivity type well region is formed on a first conductivity type substrate. A second conductivity type diffused source and second conductivity type diffused drain are formed on the first conductivity type substrate. A gate structure is formed on the second conductivity type well region between the second conductivity type diffused source and the second conductivity type diffused drain. First conductivity type buried rings are arranged in a horizontal direction, and formed in the second conductivity type well region, and divide the second conductivity type well region into an upper drift region and a lower drift region.