Plasma Etching Selectivity via SiF4 Protective Deposit
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Solution Overview
Problem
In semiconductor manufacturing, the etching of silicon nitride films on silicon oxide films faces challenges with the reduction of the silicon oxide film thickness and the need for improved selectivity due to ion/assist reaction mechanisms, leading to reduced etching ratios and shape control issues during spacer structure formation in microminiaturized devices.
Innovation Solution
A plasma etching method using a mixed gas composition including CH3F, O2, and SiF4, where the etching gas components form a deposited film on the silicon oxide film, enhancing the etching ratio by controlling the etching speed and shape of the silicon nitride film without etching the silicon oxide film, thereby improving the selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high bias is applied to improve etching speed for silicon nitride film, then etching speed improves, but etching also progresses in silicon oxide film and selection ratio falls
Solution Approach 1:
The patent applies local quality by introducing SiF4 gas that specifically reacts with silicon oxide to form a protective deposited film on the silicon oxide film surface. This creates locally different properties: the silicon nitride film continues to etch at high speed while the silicon oxide film surface is protected by the deposited film, maintaining high selection ratio even with high bias applied.
Solution Approach 2:
The patent uses a composite etching gas system comprising CF4, CHF3, and SiF4 gases. The CF4 and CHF3 provide fluorine radicals for silicon nitride etching, while SiF4 provides silicon and oxygen components that deposit on the silicon oxide film surface. This composite gas system enables simultaneous achievement of high etching speed and high selection ratio.
2Length of moving object
If silicon oxide film thickness is reduced for microminiaturization, then device scaling improves, but etching selectivity control becomes more difficult
Solution Approach 1:
The patent applies preliminary action by forming a protective deposited film on the silicon oxide film surface before the main etching process progresses significantly. The SiF4 gas reacts with silicon oxide to create this protective layer in advance, which then prevents excessive etching during subsequent high-speed silicon nitride film etching, ensuring precise selectivity control even for ultra-thin silicon oxide films.
3Manufacturing precision
If fluorocarbon gas is used to increase selected etching ratio, then selection ratio improves, but etching speed may be limited
Solution Approach 1:
The patent applies parameter changes by optimizing the composition ratios and flow rates of CF4, CHF3, and SiF4 gases in the etching atmosphere. By adjusting these parameters, the patent achieves a balance where fluorine radicals from CF4 and CHF3 provide sufficient etching speed for silicon nitride, while SiF4 provides the necessary deposited film formation to maintain high selected etching ratio.
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 method significantly improves the etching ratio of silicon nitride to silicon oxide films, achieving the required selectivity for microminiaturized semiconductor devices by forming a thicker deposit with more Si—O bonding on the silicon oxide film, allowing precise control of etching speeds and shapes without damaging the silicon oxide film.
Implementation Method 1
a fluorocarbon deposited film is deposited on the silicon oxide film
Implementation Method 2
the silicon nitride film is etched on the basis of a radical reaction involving a fluorine radical (F*) as main etching species
Implementation Method 3
etching based on an ion/assist reaction mechanism mainly involving CF3 ions as main etching spices progresses
Data Source
AI summary
It is an object of the present invention to provide a plasma etching method that can improve a selection ratio of a film to be etched to a film different from the film to be etched than that in the related art. The present invention provides a plasma etching method for selectively etching a film to be etched with respect to another film different from the film to be etched, the plasma etching method including etching, using gas that can generate a deposited film containing components same as components of the another film different from the film to be etched, the film on which generation of the deposited film is suppressed.