Trench MOSFET Uniform Doping via Thermal Diffusion

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Solution Overview

Problem

Trench MOSFETs face limitations in achieving high withstand voltage and uniform doping distribution, leading to potential leakage and reduced process window due to non-uniform doped region thickness and doping concentration along the trench sidewalls and bottom, especially in high aspect ratio trenches.

Innovation Solution

A semiconductor device is fabricated using a thermal diffusion process to form a doped region with uniform thickness and doping concentration along the sidewalls and bottom of the trench, allowing for increased breakdown voltage and reduced leakage risk, while the polysilicon layer is used to fill the trench and enhance the device's performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Shape

If conventional doping methods are used in high aspect ratio trenches, then the trench gate structure can be formed, but the doped region thickness becomes non-uniform along the sidewalls and bottom

Engineering Contradiction:

Improvetrench gate structureVSAvoiddoped region thickness uniformity

Core Design Contradiction:

ShapeVSManufacturing precision

Solution Approach 1:

A liner layer is formed on the trench sidewalls and bottom before doping to establish a uniform thickness reference. This preliminary structure enables subsequent doping processes to achieve uniform doped region thickness by using the liner as a template, solving the non-uniformity problem in high aspect ratio trenches.

Inventive Principle:

Principle #10Preliminary action

2Strength

If doping concentration is increased to improve breakdown voltage, then withstand voltage capability increases, but leakage current increases due to non-uniform doping

Engineering Contradiction:

Improvebreakdown voltageVSAvoidleakage current

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The patent employs a thermal diffusion process where dopants diffuse through the liner layer into the semiconductor substrate. This diffusion mechanism, driven by thermal energy, ensures uniform dopant distribution and doped region thickness, achieving high breakdown voltage without the leakage issues associated with non-uniform doping from conventional methods.

Inventive Principle:

Principle #29Pneumatics and hydraulics

3Power

If the trench aspect ratio is increased to reduce on-resistance, then current handling capability improves, but the process window decreases due to manufacturing difficulties

Engineering Contradiction:

Improvecurrent handling capabilityVSAvoidprocess window

Core Design Contradiction:

PowerVSAdaptability or versatility

Solution Approach 1:

The liner layer is deposited as a preliminary structure before doping, providing a uniform thickness template that guides subsequent processing. This approach enables precise control of doped region geometry even in high aspect ratio trenches, expanding the feasible process window and allowing higher current handling capability without manufacturing compromise.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent replaces conventional mechanical or chemical vapor deposition doping methods with a thermal diffusion process. This substitution enables better control over dopant distribution in high aspect ratio structures, increasing the process window and allowing higher trench aspect ratios for improved current handling.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 thermal diffusion process ensures uniform doped region thickness and concentration, resulting in lower on-state resistance, higher breakdown voltage, and increased process window, reducing the risk of leakage and improving the versatility of the semiconductor device's layout.

Implementation Method 1

forming a doped region with uniform thickness and doping concentration along the sidewalls and bottom of the trench through a thermal diffusion process

Methodology Applied

Scientific EffectThermal diffusion: Diffusion

Data Source

PatentUS9525045B1Semiconductor devices and methods for forming the same

Publication Date: 2016.12.20 VANGUARD INTERNATIONAL SEMICONDUCTOR CORPORATION

AI summary

A semiconductor device and a method for forming the same are provided. The semiconductor device includes a substrate having a first conductive type and an epitaxial layer having the first conductive type disposed over the substrate, wherein a trench is formed in the epitaxial layer. The semiconductor device also includes a polysilicon layer having the first conductive type disposed in the trench. The semiconductor device further includes a doped region having a second conductive type disposed along a sidewall and a bottom of the trench in the epitaxial layer, wherein a thickness along the sidewall and the bottom of the trench is uniform, and wherein the thickness is a vertical distance between the outermost side of the trench to the sidewall or the bottom of the trench.