Shallow Trench Isolation Fabrication via Non-Plasma Dry Etching
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Solution Overview
Problem
Current shallow trench isolation (STI) fabrication processes face challenges in reducing current leakage, improving short channel effects, and minimizing surface divots as semiconductor devices shrink in size.
Innovation Solution
A method involving forming a trench in a substrate, creating a pad layer with silicon oxide and silicon nitride, using an in-situ steam generation process to form a liner, and performing a non-plasma dry etching process with hydrogen fluoride and ammonia gas to form a shallow trench isolation (STI) without wet etching, which avoids surface divots and enhances smoothness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional wet etching process is used to form STI, then the etching speed is fast, but surface divots are formed on the STI
Solution Approach 1:
The patent replaces the conventional wet etching process (chemical system) with a non-plasma dry etching process using hydrogen fluoride and ammonia gas. This substitution eliminates the formation of surface divots while maintaining etching effectiveness, resolving the contradiction between etching speed and surface smoothness.
Solution Approach 2:
The patent changes the etching parameters by using specific gas compositions (hydrogen fluoride and ammonia) and controlling the etching conditions to achieve smooth surfaces. The ammonia gas helps to passivate the silicon surface during etching, preventing divot formation while maintaining reasonable etching speed.
2Length of moving object
If STI size is reduced to isolate smaller devices, then device isolation is improved, but current leakage increases
Solution Approach 1:
The patent uses a composite pad layer structure with silicon oxide and silicon nitride layers. The silicon nitride layer provides better electrical isolation properties, reducing current leakage even when the STI size is reduced. This composite material approach allows smaller STI dimensions while maintaining effective current leakage prevention.
Solution Approach 2:
The pad layer acts as an intermediary between the substrate and the STI structure. The specific composition and structure of the pad layer help to control the electrical properties at the STI interface, reducing current leakage paths that would otherwise occur in smaller STI structures.
3Length of moving object
If STI size is reduced to isolate smaller devices, then device isolation is improved, but short channel effects worsen
Solution Approach 1:
The patent applies different materials and structures to different parts of the STI structure. The pad layer composition and the dielectric layer are optimized locally to provide better electrical characteristics. This local quality optimization helps to mitigate short channel effects in smaller STI structures by improving the electrical isolation and interface properties at critical locations.
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 effectively reduces current leakage, improves short channel effects, and minimizes surface divots, resulting in improved STI performance and device isolation without the formation of surface imperfections.
Implementation Method 1
forming a liner in the trench after forming the pad layer
Implementation Method 2
performing a dry etching process to remove the pad layer and part of the dielectric layer
Data Source
AI summary
A method for fabricating semiconductor device includes the steps of: forming a trench in a substrate; forming a pad layer adjacent to two sides of trench; forming a dielectric layer to fill the trench; and performing a dry etching process to remove the pad layer and part of the dielectric layer to form a shallow trench isolation (STI). Preferably, the dry etching process comprises a non-plasma etching process.