High-Temperature Plasma Etching for Reliable MEMS Devices
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Summary
Problems
Conventional etching processes for metal stacks in micro-electromechanical systems (MEMS) devices, such as auto-focus lenses, often result in electrical shorts due to the presence of stringers from titanium nitride residue, and fail to effectively prevent moisture ingress, which reduces the breakdown voltage and interferes with device operation.
Innovation solutions
A high-temperature isotropic plasma etching process using a gas mixture of tetrafluoromethane (CF4) and oxygen (O2) at temperatures above 200°C, with specific flow rates and RF power, to etch through titanium nitride and titanium layers, preventing stringers and oxide film formation while maintaining the integrity of the metal stack.
TRIZ Analysis
Specific contradictions:
General conflict description:
Principle concept:
If conventional etching processes are used for metal stacks, then the etching can be performed at lower temperatures with simpler processes, but stringers from titanium nitride residue form causing electrical shorts
Why choose this principle:
The patent applies parameter changes by raising the etching temperature to at least 200°C and using a dual-gas plasma process (CF4 and O2) to fundamentally alter the etching conditions. This resolves the contradiction by showing that changing temperature and gas composition parameters enables complete titanium nitride removal without stringer formation, achieving reliable electrical isolation while maintaining process control through defined parameters.
Principle concept:
If conventional etching processes are used for metal stacks, then the etching can be performed at lower temperatures with simpler processes, but stringers from titanium nitride residue form causing electrical shorts
Why choose this principle:
The patent uses a composite approach by combining two gases (CF4 and O2) in the plasma etching process. The CF4 provides fluorine for etching titanium nitride while O2 helps remove organic residues and prevents stringer formation. This composite gas system resolves the contradiction by achieving complete residue removal and electrical short prevention through the synergistic effect of multiple materials in the etching process.
Application Domain
Data Source
AI summary:
A high-temperature isotropic plasma etching process using a gas mixture of tetrafluoromethane (CF4) and oxygen (O2) at temperatures above 200°C, with specific flow rates and RF power, to etch through titanium nitride and titanium layers, preventing stringers and oxide film formation while maintaining the integrity of the metal stack.
Abstract
A method includes placing a device having a titanium nitride layer into a chamber. The device also has a mask that includes a photoresist material and an aluminum copper hardmask. The method also includes performing an ashing process on the mask using the chamber. The method further includes, after the ashing process, performing an etching process using the chamber to etch through portions of the titanium nitride layer. Performing the etching process includes flowing a gas mixture containing tetrafluoromethane (CF 4 ) and oxygen gas (O 2 ) into the chamber at a temperature of at least about 200° C.