Deep Silicon Etching via Gas Pulsing for Smooth Profiles
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Solution Overview
Problem
Time-multiplexed etching processes in the semiconductor industry result in scalloping of sidewalls, leading to profile non-uniformities and degraded electrical performance, while one-step processes face aspect ratio and depth limitations when etching high aspect ratio features.
Innovation Solution
A continuous gas pulsing process using alternating chemistries, comprising a passivation/oxidizing chemistry with silicon, oxygen, and a halogen, and an etch chemistry with a halogen-containing gas and fluorocarbon, is employed to etch deep silicon features, maintaining high etch rates and smooth profiles without residual polymer build-up.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If time-multiplexed etching processes (Bosch process) are used to etch high aspect ratio features, then the etching depth and aspect ratio are improved, but the sidewall profile exhibits scalloping and non-uniformities
Solution Approach 1:
The patent applies periodic action by cyclically alternating between etching gas flow and passivation gas flow during the etching process. This periodic gas switching enables continuous etching with intermittent sidewall passivation, achieving deep etching without the scalloping effect caused by repeated deposition cycles in traditional Bosch processes
Solution Approach 2:
The patent maintains continuity of useful action by performing etching continuously without stopping, while integrating passivation during the same continuous process through gas flow alternation. This eliminates the stop-start nature of time-multiplexed processes and prevents scalloping while maintaining high etching rates throughout the entire etch depth
2Manufacturing precision
If one-step continuous etching processes are used, then the sidewall profile is smooth without scalloping, but the aspect ratio and etching depth are limited
Solution Approach 1:
The patent uses periodic alternation between etching and passivation gas flows to overcome the depth limitation of continuous etching. The periodic passivation provides continuous sidewall protection that enables etching to proceed much deeper without profile degradation, while maintaining the smooth sidewall characteristic of continuous processes
Solution Approach 2:
The patent introduces a passivation gas as an intermediary that deposits protective material on sidewalls during continuous etching. This intermediary layer prevents sidewall damage and enables continuous etching to achieve high aspect ratios and deep etching depths that would otherwise be impossible
3Length of stationary object
If time-multiplexed etching with alternate deposition and etch steps is used, then deep etching is achieved, but residual polymer build-up occurs on sidewalls
Solution Approach 1:
The patent changes the chemical parameters by using oxygen-based passivation instead of fluorocarbon-based passivation. This parameter change fundamentally alters the passivation mechanism to produce oxide layers that do not leave residual polymer build-up, while still providing effective sidewall protection for deep etching
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 continuous gas pulsing process achieves faster etch rates, reduces undercut, and provides good mask selectivity, resulting in smooth sidewalls and high aspect ratio features without the scalloping issues of time-multiplexed processes.
Implementation Method 1
Plasma is formed from the first process gas mixture and from the second process gas mixture such that the silicon surface, through the patterned mask layer, is exposed to the plasma
Data Source
AI summary
Techniques disclosed herein include methods for etching deep silicon features using a continuous gas pulsing process that etches high aspect ratio features having a relatively smooth profile. Such methods provide an etch rate faster than time-multiplexed etch-deposition processes. Techniques include using a continuous process that comprises a cyclic gas-pulsing process of alternating chemistries. One process gas mixture includes a halogen-containing silicon gas and oxygen that creates an oxide layer. A second process gas mixture includes a halogen-containing gas and a fluorocarbon gas that etches oxide and silicon.