Trench-Gated Switch P-Body Epitaxy for Precise Voltage Control
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Solution Overview
Problem
Existing insulated trench gate power devices face challenges in achieving precise control over dopant diffusion, leading to non-ideal net dopant concentrations and tradeoffs between turn-on voltage, breakdown voltage, and on-voltage.
Innovation Solution
The formation of a p-body by p-doping during epitaxial layer growth over the n-drift layer eliminates the need for a diffusion step, allowing for a more uniformly doped and defined p-body layer. This is followed by shallow p-dopant implantation and quick diffusion to form a thin, high p-concentration layer near the inversion channels, and subsequent n-dopant implantation and diffusion for the n+ source regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If p-doping is performed by implantation and diffusion into the n-drift layer to form the p-body, then the p-body can be formed, but the dopant diffusion takes a long time and results in non-ideal net dopant concentrations
Solution Approach 1:
The p-body layer is formed by incorporating p-type dopants during the epitaxial growth process itself, before subsequent device fabrication steps. This preliminary doping action during growth eliminates the need for separate, time-consuming diffusion steps that were previously required to form the p-body, thereby reducing total process time while achieving precise dopant concentration control
Solution Approach 2:
The patent replaces the thermal diffusion process (which relies on heat-driven dopant migration over extended periods) with an epitaxial growth process where dopants are incorporated during crystal formation. This substitution of the doping mechanism achieves the same p-body formation function with superior precision and significantly reduced time
2Reliability
If long diffusion time is used to form the p-body, then dopants can be distributed, but the control over doped region characteristics is poor
Solution Approach 1:
The desired p-body dopant concentration profile is established during the epitaxial growth stage, before any device-specific processing. This preliminary establishment of the doping profile ensures consistent, ideal net dopant concentrations that lead to predictable and reliable device performance characteristics
Solution Approach 2:
The patent changes the fundamental parameter of how doping is achieved - transitioning from post-growth diffusion (with uncontrolled concentration gradients) to in-growth doping during epitaxy. This parameter change enables precise control over dopant concentration and distribution, directly improving manufacturing precision and device reliability
3Adaptability or versatility
If p-dopant implantation and diffusion are used to form the p-body, then the p-body is created, but independent control of turn-on voltage, breakdown voltage, and on-voltage is not achieved
Solution Approach 1:
The patent segments the doping process into distinct stages: (1) p-type dopant incorporation during epitaxial growth to establish the base p-body concentration, and (2) subsequent selective shallow p-dopant implantation and quick diffusion to create a high-concentration layer near inversion channels. This segmentation enables independent optimization and control of different voltage parameters (turn-on voltage controlled by the high-concentration layer, breakdown voltage by the overall p-body structure, and on-voltage by the interface characteristics)
Solution Approach 2:
The patent implements local quality by creating a non-uniform p-body structure with a thin, high p-concentration layer positioned near the inversion channels, while the bulk p-body maintains a lower, uniformly distributed dopant concentration from epitaxial growth. This local differentiation allows independent control of voltage parameters - the high-concentration region influences turn-on voltage while the overall structure affects 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 approach enables faster diffusion times, better control over doped region characteristics, and independent control of turn-on voltage, breakdown voltage, and on-voltage, resulting in more predictable and repeatable device performance.
Implementation Method 1
The formation of a p-body by p-doping during epitaxial layer growth over the n-drift layer eliminates the need for a diffusion step
Implementation Method 2
followed by shallow p-dopant implantation and quick diffusion to form a thin, high p-concentration layer near the inversion channels
Implementation Method 3
followed by shallow p-dopant implantation and quick diffusion to form a thin, high p-concentration layer near the inversion channels
Implementation Method 4
subsequent n-dopant implantation and diffusion for the n+ source regions
Implementation Method 5
subsequent n-dopant implantation and diffusion for the n+ source regions
Data Source
AI summary
In a vertical switch having various doped layers, such as npnp or npn layers, and an array of trenched gates, a p-body layer is formed over an n-drift layer. A portion of the p-body layer is inverted by the voltage on the gate to form an n-channel to turn the device on. In a conventional device, the p-body layer is formed by implantation of p-dopants into the n-layer and then diffused. Since the p-body is fairly thick, diffusion takes a long time, resulting in the various layers having poor definition and imprecise characteristics. The device is improved by forming the p-body by epitaxial growth and varying the p-dopant concentration in the p-body to achieve the desired device characteristics. The top portion of the p-body may be enhanced by an implantation of additional p-dopants to achieve a desired turn-on voltage but not affecting the breakdown voltage of the device.