TDM Etch Process Control for ARDE Reduction
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Solution Overview
Problem
Aspect ratio dependent etching (ARDE) in time division multiplexed (TDM) plasma etching processes leads to inconsistent etch rates across features of different dimensions, causing vertical dimension discrepancies in MEMS device fabrication, which existing methods fail to adequately address without using expensive SOI or SOG wafers or impractical etching processes.
Innovation Solution
A method and apparatus that utilize real-time metrology, specifically a twin spot interferometric camera, to monitor and control the etch depth differences between features of varying sizes by adjusting process parameters such as deposition, removal, and etch times within a TDM process loop, ensuring equivalent etch depths across different sized features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If standard TDM etching process is used, then high aspect ratio structures can be etched at high etch rates, but aspect ratio dependent etching (ARDE) causes etch rate to decrease as feature depth increases
Solution Approach 1:
The patent implements real-time monitoring of etch depth using optical interference techniques and feeds this information back to the process control system. The system dynamically adjusts etch process parameters based on measured etch depth and ARDE characteristics, enabling closed-loop control that maintains consistent etch rates across features of varying aspect ratios while preserving high productivity
Solution Approach 2:
The patent dynamically modifies process parameters including RF power, gas flow rates, and pressure during the etching process based on real-time measurements. By changing these parameters in response to measured ARDE effects, the system compensates for etch rate degradation in deep features while maintaining high etch rates in shallower features, thus resolving the contradiction between productivity and precision
2Productivity
If features of different dimensions are etched simultaneously, then manufacturing efficiency is improved, but ARDE causes wider trenches to etch faster than narrower trenches
Solution Approach 1:
The real-time optical monitoring system measures etch depth in features of different dimensions simultaneously and provides feedback to the control system. The system uses this information to dynamically adjust process parameters for each feature type, compensating for the dimensional dependencies of ARDE and achieving uniform etch depths across all feature sizes while maintaining simultaneous processing efficiency
Solution Approach 2:
The patent applies different etch process conditions to different feature types based on their specific dimensional characteristics. By tailoring the etch parameters (such as RF power and gas flow) to the local requirements of each feature size, the system achieves uniform etch depths across diverse feature dimensions while maintaining overall manufacturing efficiency
3Length of moving object
If etch time is increased to achieve deeper etching, then feature depth increases, but ARDE causes etch rate to decrease over time
Solution Approach 1:
The patent dynamically adjusts process parameters during the etching process based on real-time depth measurements. As features become deeper and ARDE reduces the etch rate, the system increases RF power and/or gas flow rates to compensate for the rate degradation, enabling continued high-speed etching to greater depths without suffering from the natural etch rate decay associated with increased etch time
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 ARDE, achieving consistent etch depths across features of various sizes, thereby improving the reliability and compatibility of MEMS device fabrication without the need for expensive wafers or impractical etching processes, and allows for real-time process adjustments to maintain optimal etch rates.
Implementation Method 1
A method and apparatus that utilize real-time metrology, specifically a twin spot interferometric camera, to monitor and control the etch depth differences
Implementation Method 2
Dry etching using a reactive gas in the plasma state is one of the more commonly employed processes for silicon etching
Implementation Method 3
in a deposition step, C4F8 facilitates protective polymer passivation onto the sidewalls as well as the bottom of etched structures
Implementation Method 4
in an etch step, SF6 facilitates spontaneous and isotropic etching of silicon
Implementation Method 5
upon energetic and directional ion bombardment, the polymer film coated in the bottom of etched structures from the preceding deposition step will be removed
Data Source
AI summary
The present invention provides a method and an apparatus for reducing aspect ratio dependent etching that is observed when plasma etching deep trenches in a semiconductor substrate through an alternating deposition/etch process. A plurality of different sized features on the substrate are monitored in real time during the alternating deposition/etch process. Then, based on the information received from the monitor, at least one process parameter is adjusted in the alternating deposition/etch process to achieve equivalent etch depths of at least two different sized features on the substrate.