Lateral-Diffusion MOSFET Doping Gradient for Breakdown Voltage
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Solution Overview
Problem
Conventional LDMOS devices face limitations in achieving high breakdown voltage due to uniform doping concentration in deep n-wells, which affects the surrounding device structure and restricts the ability to increase breakdown voltage without compromising on-state resistance.
Innovation Solution
A method involving a semiconductor substrate with multiple regions of different doping concentrations, where a thermal process diffuses dopants to form deep wells with varying concentrations, and isolation structures are used to create a LDMOS device with a dual gate structure, allowing for a lower concentration difference at the PN junction, thereby enhancing breakdown voltage and reducing on-state resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the doping concentration of the deep n-well is lowered to achieve higher breakdown voltage, then the breakdown voltage is improved, but the concentration of the surrounding device is affected immediately, causing on-state resistance to increase
Solution Approach 1:
The patent applies local quality by creating a non-uniform doping concentration distribution within the deep n-well. The deep n-well has higher doping concentration at the edges (near the p-well) and lower doping concentration at the center, achieved through selective ion implantation processes. This gradient structure allows the edge regions to provide adequate carrier concentration for low on-state resistance while the center region provides the low doping concentration needed for high breakdown voltage, thus resolving the contradiction between these two parameters
Solution Approach 2:
The deep n-well is segmented into different doping concentration regions through multiple ion implantation steps with different doses and activation processes. The first ion implantation creates a base doping level, while subsequent implantations create concentrated dopant regions at specific locations. This segmentation allows different parts of the deep n-well to serve different functions: edge regions for conductivity and center regions for voltage withstand capability
2Reliability
If double diffuse drain (DDD) technology is applied to increase breakdown voltage, then the breakdown voltage is improved, but the hot electron effect is suppressed only partially and electrical breakdown under high operational voltages still occurs
Solution Approach 1:
The patent changes the doping concentration parameter within the deep n-well from uniform to non-uniform distribution. By implementing a doping gradient with higher concentrations at the edges and lower concentrations in the center, the electric field distribution is optimized. This parameter change reduces peak electric fields that cause hot electron effects while maintaining adequate carrier supply for conductivity, thereby improving both breakdown voltage and hot electron suppression
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 approach results in a LDMOS device with increased breakdown voltage from 50 volts to 70 volts and reduced on-state resistance from 138 ohms to 70 ohms, while maintaining efficient power switching performance.
Implementation Method 1
performing a thermal process to diffuse the dopants within the first deep well and the second deep well into the semiconductor substrate to form a third deep well
Data Source
AI summary
A method for fabricating a lateral-diffusion metal-oxide semiconductor (LDMOS) device is disclosed. The method includes the steps of: providing a semiconductor substrate; forming a first region and a second region both having a first conductive type in the semiconductor substrate, wherein the first region not contacting the second region; and performing a thermal process to diffuse the dopants within the first region and the second region into the semiconductor substrate to form a deep well, wherein the doping concentration of the deep well is less than the doping concentration of the first region and the second region.