Reactive Ion Etching High Aspect Ratio Features
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The Deep Reactive Ion Etching (DRIE) process suffers from Aspect Ratio Dependent Etching (ARDE), leading to 'footing' and loss of dimensional control, particularly in MEMS sensors, where achieving high aspect ratios results in larger device sizes due to RIE lag, and current compensation methods reduce etch rates.
Innovation Solution
A method involving an additional masking step where a second, inert mask material covers low aspect ratio features during initial etching, allowing high aspect ratio features to receive a head start, then both are etched simultaneously until the desired depth is reached, reducing RIE lag and maintaining uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If DRIE process is used to etch features with high aspect ratios, then the depth to width ratio is improved, but RIE lag occurs causing smaller features to be shallower than larger features
Solution Approach 1:
The patent applies a second mask material selectively to certain regions before the etching process begins. This preliminary masking action creates different etching conditions for different features from the start, allowing high aspect ratio features to be etched to full depth while low aspect ratio features are protected and etched less, thereby compensating for RIE lag and achieving uniform depth across all features.
2Manufacturing precision
If over etching is applied to wider features to compensate for RIE lag, then depth uniformity is improved, but footing and notching occur
Solution Approach 1:
The patent implements local quality by applying a second mask material selectively to specific regions corresponding to low aspect ratio features. This creates locally different etching conditions: high aspect ratio features receive full etching while low aspect ratio features are protected during portions of the etching process. This localized control prevents over-etching effects like footing and notching while maintaining depth uniformity.
3Volume of moving object
If device size is reduced to maintain compact MEMS sensors, then miniaturization is achieved, but RIE lag and footing problems worsen
Solution Approach 1:
By applying the second mask material before etching begins, the patent enables precise control of feature depths in miniaturized devices. This preliminary action allows high aspect ratio features to be etched completely while protecting low aspect ratio features, maintaining dimensional control and preventing footing even in compact device geometries where these problems are most severe.
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 enables higher aspect ratios without increasing device size, ensuring uniform depth and reducing the variation in width of features, thereby enhancing the precision and performance of MEMS sensors.
Implementation Method 1
a silicon plasma etching step (typically using SF6)
Implementation Method 2
ion assisted plasma etching is used preferentially to remove the fluoropolymer from the bottom of an etched feature
Implementation Method 3
a passivation step including a fluoropolymer (typically C4F8). During the passivation step, the fluoropolymer is deposited on all of the sample surfaces
Data Source
Figure 1~2
Figure 3A~3C
Figure 3D~3F
AI summary
A method of reactive ion etching a substrate 46 to form at least a first and a second etched feature (42, 44) is disclosed. The first etched feature (42) has a greater aspect ratio (depth:width) than the second etched feature (44). In a first etching stage the substrate (46) is etched so as to etch only said first feature (42) to a predetermined depth. Thereafter in a second etching stage, the substrate (46) is etched so as to etch both said first and said second features (42, 44) to a respective depth. A mask (40) may be applied to define apertures corresponding in shape to the features (42, 44). The region of the substrate (46) in which the second etched feature (44) is to be produced is selectively masked with a second maskant (50) during the first etching stage. The second maskant (50) is then removed prior to the second etching stage.