Plasma Etching High-Aspect-Ratio Structures
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Solution Overview
Problem
Conventional plasma etching methods for high-aspect-ratio structures result in twisted trench profiles due to unbalanced ion distribution and concentration of etch and deposition gases, leading to non-qualified trenches that cause open or short circuits in stacked capacitors.
Innovation Solution
A plasma etching method where bias RF power is supplied discontinuously, allowing secondary electrons to neutralize positive ions by switching the bias RF power to the off state, thereby eliminating the sheath and ensuring straight high-aspect-ratio structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If continuous bias RF power is supplied to generate plasma for etching, then etching process continues, but positive ions accumulate at the trench bottom causing twisted profiles
Solution Approach 1:
The bias RF power is supplied in a periodic pulsed manner rather than continuously. During the on-time (Ton), plasma is generated for etching. During the off-time (Toff), the sheath disappears allowing secondary electrons to neutralize positive ions. This periodic action maintains etching productivity while preventing ion accumulation that causes twisted trench profiles.
2Quantity of substance
If DC power is supplied to induce secondary electron emission, then electron emission increases, but secondary electrons cannot reach the substrate due to high energy requirements
Solution Approach 1:
By periodically turning off the bias RF power, the plasma sheath that normally blocks secondary electrons from reaching the substrate is eliminated during the off-time. This allows secondary electrons generated during the on-time to effectively reach and neutralize positive ions at the trench bottom, solving the reliability issue without requiring excessive DC power.
Solution Approach 2:
The periodic pulsing creates a continuous cycle where secondary electrons are generated during the on-time and immediately utilized during the off-time for neutralization. This continuous useful action ensures that electrons effectively reach the substrate to neutralize ions, maintaining process reliability.
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 effectively neutralizes positive ions, resulting in straight high-aspect-ratio structures and preventing defects like twisted trenches, ensuring reliable connections in stacked capacitors.
Implementation Method 1
supplying a bias RF power to the lower electrode plate so as to generate a plasma in the processing chamber to etch the substrate
Implementation Method 2
secondary electrons pass through the bulk plasma and reach the substrate to neutralize to the positive ions
Data Source
AI summary
The present invention relates to a plasma etching method and apparatus for preparing high-aspect-ratio structures. The method includes the steps of placing the substrate into a plasma etching apparatus, wherein the plasma etching apparatus includes an upper electrode plate and a lower electrode plate; continuously supplying an upper source RF power and a DC power to the upper electrode plate; and discontinuously supplying a bias RF power to the lower electrode plate. When the bias RF power is switched to the off state, a large amount of secondary electrons pass through the bulk plasma and reach the substrate to neutralize the positive ions during the duration time of the off state (Toff).