TIDE Titanium Etching for High Aspect Ratio Microdevices
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Solution Overview
Problem
Existing methods for producing high aspect ratio micro and sub-micrometer features in titanium substrates are limited by low etch rates, residual stresses, and isotropic etching, which restrict the fabrication of robust and biocompatible titanium-based microdevices suitable for harsh environments and biological applications.
Innovation Solution
The development of monocyclic inductively coupled plasma etching processes using chlorine-based micromachining methods, known as the 'TIDE' process, which allows for rapid production of titanium microdevices with high aspect ratio features and smooth surfaces by varying parameters such as ICP source power, RF sample power, pressure, and gas composition, reducing undercutting and maintaining high etch rates and mask selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional plasma etching methods are used on titanium substrates, then micro features can be produced, but the etch rate is low and the process time is long
Solution Approach 1:
The patent employs cyclic plasma etching with alternating fluorocarbon-based and oxygen-based plasma steps. The fluorocarbon step deposits protective polymer layers on sidewalls to enable anisotropic etching, while the oxygen step removes deposited material and exposes fresh titanium surface. This periodic alternation maintains high etch rates by preventing mask undercutting and ensuring continuous vertical etching progress.
Solution Approach 2:
The patent systematically varies plasma process parameters including gas flow rates, RF power, pressure, and cycle timing to optimize etch rate. By adjusting these parameters across different cyclic steps, the process achieves maximum etch velocity while maintaining vertical sidewalls and preventing lateral undercutting of masks.
2Productivity
If high etch rates are achieved through aggressive plasma parameters, then productivity improves, but sidewall roughness and loss of verticality increase
Solution Approach 1:
The cyclic plasma process alternates between aggressive fluorocarbon etching steps that achieve high vertical etch rates and gentler oxygen cleaning steps that smooth sidewalls and remove rough deposits. This periodic refinement maintains manufacturing precision while sustaining overall high productivity through the cumulative etching effect.
Solution Approach 2:
Fluorocarbon-based plasma deposits polymer intermediaries on sidewalls during etching. These intermediary layers protect sidewalls from lateral attack, maintain vertical profiles, and can be subsequently removed by oxygen plasma steps. The intermediary deposits act as self-formed masks that preserve geometric fidelity.
3Device complexity
If isotropic etching is used to simplify the process, then manufacturing complexity reduces, but undercutting of masks occurs and aspect ratio control is lost
Solution Approach 1:
The cyclic alternation between fluorocarbon and oxygen plasma creates time-dependent anisotropic etching. During fluorocarbon steps, polymer deposits form directional protective layers that enable vertical etching. During oxygen steps, these deposits are removed and fresh surfaces are exposed. This temporal cycling enforces anisotropic etching behavior without requiring complex mask structures or additional process steps.
Solution Approach 2:
The cyclic process maintains continuous etching action by immediately following fluorocarbon deposition with oxygen cleaning and vice versa. This continuous cycling prevents idle time, ensures constant material removal progress, and maintains mask protection throughout the etching sequence, achieving high aspect ratio features with consistent verticality.
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 TIDE process enables the production of titanium microdevices with high fracture toughness, biocompatibility, and robustness, suitable for various applications, including microelectronics and biological uses, by achieving high etch rates and smooth surfaces with reduced undercutting and surface roughness.
Implementation Method 1
monocyclic inductively coupled plasma etching processes
Implementation Method 2
inductively coupled plasma
Implementation Method 3
chlorine-based micromachining methods
Data Source
AI summary
Monocyclic chlorine based inductively coupled plasma deep etching processes for the rapid micromachining of titanium substrates and titanium devices so produced are disclosed. The method parameters are adjustable to simultaneously vary etch rate, mask selectivity, and surface roughness and can be applied to titanium substrates having a wide variety of thicknesses to produce high aspect ratio features, smooth sidewalls, and smooth surfaces. The titanium microdevices so produced exhibit beneficially high fracture toughness, biocompatibility and are robust and able to withstand harsh environments making them useful in a wide variety of applications including microelectronics, micromechanical devices, MEMS, and biological devices that may be used in vivo.