Three-Layer Lithographic Stencil for Josephson Junction Fabrication
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Solution Overview
Problem
The existing double-angle shadow evaporation technique for fabricating Josephson junctions often results in distortion of the shape of features due to undesirable thinning of the top resist layer and narrowing of openings in the evaporation mask, leading to distorted geometries during the deposition process.
Innovation Solution
A three-layer lithographic stencil structure is employed, featuring a bottom resist layer, a middle resist layer with a bridge portion defining openings, and a top resist layer with a blocking portion that shields the openings from superconducting material deposition, preventing distortion and maintaining the integrity of the opening dimensions during the fabrication process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a two-layer lithographic resist structure is used for shadow evaporation, then the fabrication process is simpler and faster, but the top resist layer thins and openings narrow causing feature distortion
Solution Approach 1:
The lithographic stencil is divided into three separate resist layers instead of two, with each layer serving a specific function: the bottom layer defines the initial pattern, the middle layer maintains bridge thickness, and the top layer protects openings during deposition. This segmentation prevents the thinning and narrowing problems while maintaining fabrication efficiency.
Solution Approach 2:
The middle and top resist layers are deposited and patterned in advance to create a protective stencil structure before the shadow evaporation process begins. This preliminary action ensures that the openings maintain their intended dimensions throughout the deposition process, preventing feature distortion.
2Measurement precision
If electron beam dose is increased to develop the bottom resist layer, then the resist development is more complete, but the top resist layer experiences undesirable thinning
Solution Approach 1:
The resist structure is segmented into three layers with different material compositions and thicknesses. The bottom layer can be fully developed by electron beam without affecting the middle and top layers, which are designed to maintain their integrity during the process.
Solution Approach 2:
The middle resist layer acts as an intermediary protective barrier between the electron beam exposure of the bottom layer and the top resist layer. This intermediate layer absorbs the electron beam energy required for complete bottom layer development while protecting the top layer from thinning.
3Productivity
If openings in the evaporation mask are not shielded, then the deposition process is faster, but the deposited superconducting material distorts the opening shapes
Solution Approach 1:
The top resist layer is deposited and patterned in advance to create blocking portions that will shield the openings during deposition. This preliminary protective action allows fast deposition while preventing shape distortion.
Solution Approach 2:
The top resist layer serves as an intermediary shielding element between the deposited superconducting material and the openings. It allows the deposition to proceed rapidly while preventing the material from distorting the opening geometries.
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 three-layer lithographic stencil structure ensures the deposition of superconducting materials without distorting the shape of the features, enabling the fabrication of Josephson junctions with smooth and well-defined geometries, as demonstrated by the use of specific materials like polydimethylglutarimide, polymethylmethacrylate, and poly(methylmethacrylate/methacrylic acid) copolymer.
Implementation Method 1
a shadow mask technique to fabricate Josephson junctions
Data Source
AI summary
Techniques regarding lithographic processes for fabricating Josephson junctions are provided. For example, one or more embodiments described herein can comprise a method that can include depositing a first resist layer onto a second resist layer. The first resist layer can include a bridge portion that defines an opening for forming a Josephson junction. The method can also comprise depositing a third resist layer onto the bridge portion. The third resist layer can shield the opening from an angled deposition of a superconducting material during fabrication of the Josephson junction.