Sidewall Etching with Compound Masks to Preserve Feature Height
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Solution Overview
Problem
Existing angled particle beam etching techniques fail to effectively preserve the original height of critical structures during the etching process, leading to undesirable changes in structure profile and potential device failure due to the use of hard masks that may not prevent artifact formation and height reduction.
Innovation Solution
A compound masking layer comprising a first masking layer with the same etch properties as the substrate features and a second masking layer with a lower etch rate is used to protect the features during etching, ensuring the original height is maintained by preventing etching of the first masking layer and allowing for selective removal of residual material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If angled particle beam etching is used to etch sidewalls, then lateral geometry changes are achieved, but the original height of the structures is reduced
Solution Approach 1:
The masking function is segmented into two distinct layers: a first masking layer that protects the structure top surface and a second masking layer that protects the first masking layer during etching. This segmentation allows each layer to be optimized for its specific protective function, preventing both lateral over-etching and height reduction simultaneously.
Solution Approach 2:
The solution transitions from a single-layer mask to a multi-layer mask structure, adding a vertical dimension to the masking approach. The first masking layer extends laterally to protect sidewalls, while the second masking layer extends vertically to protect the first layer, creating a stepped mask configuration that addresses both lateral and vertical protection needs.
2Length of moving object
If a hard mask is used to protect critical structures, then structure height is preserved, but artifacts form below the mask during etching
Solution Approach 1:
The first masking layer is designed with different local properties: it has the same etch properties as the substrate features in the exposed regions (allowing controlled etching), while providing protection in the masked regions. This local quality variation allows the mask to protect during etching without creating artifacts, as the etch process can proceed uniformly where exposed.
Solution Approach 2:
The first masking layer is made of material with the same etch properties as the substrate features, effectively creating a copy of the feature's etch response. This allows the mask and feature to be etched at the same rate where both are exposed, preventing artifact formation while maintaining height protection where the mask covers.
3Reliability
If a hard mask is used during etching, then some protection is provided, but undesirable changes in structure profile occur
Solution Approach 1:
The compound masking layer is applied and configured before the etching process begins, with the first masking layer already extending laterally to protect sidewalls and the second masking layer positioned to protect the first layer. This preliminary configuration ensures that the structure profile is protected from undesirable changes throughout the entire etching process, maintaining both vertical and lateral dimensions.
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 method ensures that features are left on the substrate with their original intended height, maintaining vertical sidewalls and preventing unwanted height reduction, thus enhancing the reliability and performance of semiconductor and microfabrication devices.
Implementation Method 1
One common technique used for etching these structures is angled particle beam etching. This process involves directing a beam of particles, such as ions, at an angle to the substrate surface, which results in the removal of material from the exposed areas of the substrate.
Data Source
Figure 1A~3C
Figure 4A~4C
AI summary
A method for etching sidewalls of features on a substrate is disclosed. The method comprises providing a compound masking layer on the features, which comprises a first masking layer and a second masking layer over the first masking layer. The compound masking layer masks at least part of the field regions and leaves the sidewalls unmasked. The method further comprises etching the sidewalls, where the second masking layer prevents etching of the first masking layer, maintaining the height of the features and the first masking layer with respect to the substrate. The first masking layer is then removed, along with any remaining part of the second masking layer.