Trench Gate Oxide Uniformity at the Bottom Corner
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Solution Overview
Problem
Variation in the thickness of the gate insulating film near the bottom of the trench in semiconductor devices leads to localized low withstand voltage areas, reducing the reliability of power semiconductor elements and increasing inspection costs.
Innovation Solution
The semiconductor device features a trench structure with a flat shape near the bottom portion, achieved through a dry etching process using C4F8 and SF6 gases, ensuring the crystal plane is the (100) plane across the sidewall, corner, and bottom portions, which maintains uniformity in the gate insulating film thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a trench is formed using conventional etching processes, then the trench can be manufactured, but variation in gate insulating film thickness occurs near the bottom portion, reducing reliability
Solution Approach 1:
The patent applies parameter changes by modifying the etching process parameters - specifically using a two-step dry etching process with different gas compositions (first step: CF4-based gas; second step: CHF3-based gas) to control the trench shape. This parameter change ensures the trench bottom is positioned at the (100) crystal plane, which enables uniform gate insulating film thickness and improves both manufacturing precision and reliability
Solution Approach 2:
The patent implements preliminary action by pre-forming the trench with a specific shape (bottom at (100) crystal plane) before depositing the gate insulating film. This preliminary trench formation with controlled geometry ensures that subsequent gate insulating film deposition results in uniform thickness, preventing reliability issues before they occur
2Ease of manufacture
If the gate insulating film thickness varies near the trench bottom, then manufacturing is simpler, but localized low withstand voltage areas form, decreasing reliability
Solution Approach 1:
The patent changes the etching process parameters from a single-step to a two-step process with specific gas compositions and conditions. The first step uses CF4-based gas to etch to a certain depth, then the second step uses CHF3-based gas to finish etching at the (100) crystal plane. This parameter change achieves both ease of manufacture through automated process control and high reliability through uniform film thickness
3Device complexity
If conventional etching gases (Cl2 and O2) are used, then the etching process is straightforward, but the trench shape causes non-uniform gate insulating film thickness
Solution Approach 1:
The patent changes the etching gas parameters from conventional Cl2/O2 mix to a two-step process using CF4-based gas followed by CHF3-based gas. This parameter change modifies the etching chemistry to achieve a trench shape with the bottom at the (100) crystal plane, which ensures uniform gate insulating film thickness deposition while maintaining manageable process complexity
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 reliability of the semiconductor device by minimizing the occurrence of low withstand voltage areas, thereby improving yield and reducing inspection costs, as demonstrated by improved breakdown voltage and time-dependent deterioration lifetime.
Implementation Method 1
a dry etching process using C4F8 and SF6 gases
Data Source
AI summary
A semiconductor device includes an n-type semiconductor substrate, a trench, and a gate electrode formed in the trench via a gate insulating film. An absolute value of a difference between a thickness of the gate insulating film formed on a corner portion of the trench and a thickness of the gate insulating film formed on the bottom portion of the trench is smaller than an absolute value of a difference between the thickness of the gate insulating film formed on the corner portion of the trench and a thickness of the gate insulating film formed on the sidewall portion of the trench.