SiC Trench Side Wall Orientation for Channel Mobility
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Solution Overview
Problem
Conventional silicon carbide semiconductor devices face challenges in achieving high channel mobility and minimizing channel length variation, particularly when forming trench side walls corresponding to semi-polar planes like {0-33-8}, which affects device performance.
Innovation Solution
A silicon carbide semiconductor device with a substrate having a main surface off-angle of 5° or smaller, where the silicon carbide layer is epitaxially formed with trench side walls corresponding to stable semi-polar planes such as {0-33-8}, {01-1-4}, or {100} planes, using a reactive gas containing oxygen and chlorine for etching, to enhance channel mobility and reduce channel length variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If isotropic etching is used to form gate trench side walls, then the breakdown voltage of the gate insulating film is improved, but the side walls cannot correspond to semi-polar planes such as {0-33-8}, making it difficult to sufficiently increase channel mobility
Solution Approach 1:
The patent changes the etching method from isotropic to anisotropic etching, which fundamentally alters the etching characteristics and enables the formation of side walls with specific crystallographic orientations. This parameter change in the etching process allows the side walls to correspond to semi-polar planes such as {0-33-8}, thereby achieving high channel mobility while maintaining adequate breakdown voltage through proper trench design
2Ease of manufacture
If conventional etching methods are used, then the gate trench can be formed, but the side walls cannot be made to correspond to semi-polar planes, resulting in insufficient channel mobility enhancement
Solution Approach 1:
The patent employs anisotropic etching instead of conventional isotropic etching, changing the etching parameters to achieve direction-dependent etching rates. This enables the side walls to be formed with precise crystallographic orientation corresponding to semi-polar planes, thereby achieving both ease of manufacture and high manufacturing precision in side wall orientation
Solution Approach 2:
The patent uses a composite approach combining anisotropic etching with specific mask patterns to achieve the desired side wall orientation. The combination of etching method and mask design creates the necessary conditions for forming side walls that correspond to semi-polar planes, achieving precise orientation control
3Ease of manufacture
If the main surface off angle is not controlled, then substrate preparation is simpler, but channel length variation increases, affecting device properties such as threshold values
Solution Approach 1:
The patent specifies controlling the main surface off angle to be within a particular range, which is a parameter change in the substrate preparation process. This controlled off angle ensures that the epitaxial growth and subsequent etching processes produce uniform channel lengths, thereby achieving both ease of manufacture and high manufacturing precision in channel length uniformity
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 increases channel mobility and suppresses channel length variation, leading to improved device performance with higher breakdown voltage and reduced leakage current.
Implementation Method 1
The silicon carbide layer is epitaxially formed on the main surface of the substrate
Implementation Method 2
using a reactive gas containing oxygen and chlorine for etching
Data Source
AI summary
A substrate is provided with a main surface having an off angle of 5° or smaller relative to a reference plane. The reference plane is a {000-1} plane in the case of hexagonal system and is a {111} plane in the case of cubic system. A silicon carbide layer is epitaxially formed on the main surface of the substrate. The silicon carbide layer is provided with a trench having first and second side walls opposite to each other. Each of the first and second side walls includes a channel region. Further, each of the first and second side walls substantially includes one of a {0-33-8} plane and a {01-1-4} plane in the case of the hexagonal system and substantially includes a {100} plane in the case of the cubic system.