Plasma Etching Method for Silicon Recess Formation
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Solution Overview
Problem
The existing plasma etching methods for forming recesses in silicon layers suffer from side-etching of intermediate layers, leading to increased leak current and inefficient throughput due to insufficient protection film deposition and chamber contamination.
Innovation Solution
A plasma etching method involving a three-step process: etching the intermediate silicon nitride layer, forming a protection film on the sidewalls using chlorine gas, and then etching the silicon layer with a sulfur and fluorine-containing gas to restrict side-etching and form a recess, while managing the attached matter to prevent chamber contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If CF gas is used to form a protection film on sidewalls, then side-etching of the intermediate layer is restricted, but the deposition efficiency becomes insufficient resulting in lower throughput
Solution Approach 1:
The patent changes the chemical composition parameters of the process gas from CF4-based to a mixed gas containing SF6, C4F8, and O2. This parameter change enables simultaneous achievement of high deposition efficiency (for throughput) and effective protection film formation (for side-etching restriction), resolving the contradiction between manufacturing precision and productivity
Solution Approach 2:
The patent uses a composite process gas mixture (SF6 + C4F8 + O2) instead of a single gas. The composite nature of the gas mixture allows multiple functions to be achieved simultaneously: SF6 provides etching capability, C4F8 provides deposition capability for protection film formation, and O2 enhances the protection film quality, thereby resolving the contradiction between deposition efficiency and side-etching prevention
2Manufacturing precision
If CF gas is used to form a protection film, then side-etching is restricted, but attached matter accumulates on the treatment chamber inner wall causing process adverse effects
Solution Approach 1:
The patent changes the gas composition parameters to include O2 and C4F8 in specific ratios, which modifies the chemical properties of the deposited matter. This parameter change reduces the adhesion and accumulation of attached matter on chamber walls while maintaining effective protection film formation on the substrate sidewalls, resolving the contradiction between side-etching restriction and chamber contamination
Solution Approach 2:
The patent converts the potentially harmful CFx byproducts into beneficial protection films on the substrate sidewalls by controlling the deposition process parameters. The same chemical reactions that could produce chamber contamination are directed to form protective layers on the substrate, transforming a harmful effect into a beneficial one
3Length of moving object
If the recess depth is increased to 100 μm, then three-dimensional device structures are achieved, but sidewall exposure to plasma causes intermediate layer side-etching and airspace formation
Solution Approach 1:
The patent applies preliminary action by forming the protection film on the intermediate layer sidewalls before the deep etching process. This pre-formed protection film prevents side-etching during the subsequent 100 μm deep etching, allowing achievement of the required recess depth without the harmful side-etching and airspace formation that would otherwise occur
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 method effectively restricts side-etching of the intermediate layer, maintaining device characteristics and preventing leak current increases by using the reaction product as a protection film, thereby enhancing throughput and reducing chamber contamination.
Implementation Method 1
supplying a chlorine gas to the substrate to cause a reaction product to attach onto sidewalls of opening portions of the resist mask and the intermediate layer
Implementation Method 2
etching a portion of the silicon layer corresponding to the opening portion of the intermediate layer using a process gas containing sulfur and fluorine to form a recess
Data Source
AI summary
There is provided a plasma etching method including a first process of etching an intermediate layer, which contains silicon and nitrogen and is positioned below a resist mask formed on a surface of a substrate, to cause a silicon layer positioned below the intermediate layer to be exposed through the resist mask and the intermediate layer, a second process of subsequently supplying a chlorine gas to the substrate to cause a reaction product to attach onto sidewalls of opening portions of the resist mask and the intermediate layer, and a third process of etching a portion of the silicon layer corresponding to the opening portion of the intermediate layer using a process gas containing sulfur and fluorine to form a recess in the silicon layer.