LDMOS Drain Well Multi-Zone Doping for Kirk Effect Resistance
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Solution Overview
Problem
LDMOS devices face challenges with the Kirk effect, leading to reduced breakdown voltage and increased switching time due to base pushout, especially as device dimensions shrink, necessitating improved dopant concentration zones and separation to maintain performance.
Innovation Solution
The implementation of a drain well with multiple concentration zones of dopants, where each zone has a specific depth and width, and strategic implant angles to create a gradient that prevents carrier saturation and maintains high breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If device dimensions are shrunk to improve integration density, then productivity is improved, but breakdown voltage decreases and Kirk effect becomes more severe
Solution Approach 1:
The drain well is segmented into multiple zones with different dopant concentrations (first zone with concentration Nd1, second zone with concentration Nd2 where Nd1 < Nd2). This segmentation allows each zone to perform different functions: the lower concentration zone reduces Kirk effect and base pushout, while the higher concentration zone maintains breakdown voltage, thereby resolving the contradiction between device scaling and voltage maintenance.
Solution Approach 2:
Different regions of the drain well are assigned different dopant concentrations tailored to local requirements. The first zone (closer to drift region) has lower concentration to minimize Kirk effect in that critical area, while the second zone has higher concentration to maintain overall breakdown voltage. This local quality differentiation allows the device to achieve both high integration density and reliable voltage characteristics.
2Reliability
If dopant concentration is increased to maintain breakdown voltage, then reliability is improved, but Kirk effect and base pushout increase
Solution Approach 1:
The drain well is divided into zones with graded dopant concentrations. The first zone has lower concentration (Nd1) to suppress Kirk effect and base pushout, while the second zone has higher concentration (Nd2) to maintain breakdown voltage. This spatial segmentation of dopant concentrations allows simultaneous optimization of both voltage characteristics and Kirk effect resistance.
Solution Approach 2:
The dopant concentration parameter is varied spatially within the drain well structure. By changing the concentration from Nd1 in the first zone to Nd2 in the second zone, the patent optimizes the balance between breakdown voltage (requiring higher concentration) and Kirk effect suppression (requiring lower concentration), thereby resolving the contradiction.
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 approach enhances the LDMOS device's resistance to the Kirk effect, allowing it to handle higher currents without carrier saturation, thereby increasing carrier transit time and maintaining high breakdown voltage.
Implementation Method 1
Manufacturing techniques for LDMOS devices include multiple implant processes into P-type silicon substrates or P-type epitaxial layers
Data Source
AI summary
An integrated circuit includes a drift region in a substrate, a drain in the substrate which includes a doped drain well, the doped drain well including a first zone, having a first concentration of a first dopant, and a second zone, having a second concentration of the first dopant, where the first concentration is smaller than the second concentration, and a gate electrode over the drift region and being separated from the doped drain well in a direction parallel to a top surface of the substrate by a distance greater than 0.