High Aspect Ratio Trench Fabrication via Angled RIE
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Solution Overview
Problem
Current methods for fabricating nanoscale features and doping profiles are limited by the difficulty in achieving high aspect ratio structures and precise control at the nanoscale, particularly in creating angled features using conventional lithography and reactive ion etching, which often result in shallow profiles and inadequate control over ion implantation.
Innovation Solution
A method involving a multi-layer structure with a photoresist and germanium layer, using electron beam lithography and low-pressure reactive ion etching to create high-aspect ratio trenches at arbitrary angles within the plasma dark space, allowing for precise control of ion implantation and doping profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional lithography and reactive ion etching are used to create angled features, then the fabrication process is simple and uses standard tools, but the resulting profiles are shallow and lack precise nanoscale control
Solution Approach 1:
The fabrication process is divided into multiple sequential steps: forming a first resist pattern, depositing a sacrificial layer, forming a second resist pattern at an angle, and performing selective etching. This segmentation allows each step to contribute specifically to achieving the final high aspect ratio angled structure with precise nanoscale control.
Solution Approach 2:
The sacrificial layer is deposited and prepared in advance before the angled etching step. The first resist pattern is formed beforehand to define the initial structure. These preliminary actions enable the subsequent angled reactive ion etching to create the high aspect ratio features with precise control over the final profile.
2Manufacturing precision
If high aspect ratio structures are etched at an angle to serve as implantation masks, then lateral ion straggle is reduced and implanted profiles become sharp, but the fabrication process becomes more complex and time-consuming
Solution Approach 1:
A sacrificial layer is introduced and then selectively removed through targeted etching steps. This extracted layer enables the formation of high aspect ratio angled structures that serve as effective implantation masks, achieving sharp implantation profiles while using standard fabrication tools.
Solution Approach 2:
The sacrificial layer acts as an intermediary material that facilitates the creation of the angled high aspect ratio structure. It is deposited, patterned, and selectively etched to enable the formation of the final mask structure, serving as a temporary mediator in the fabrication process.
3Shape
If standard lithography is used for step-edge junctions, then the process is economical and uses conventional tools, but the mask material erodes during ion milling resulting in shallow step-edge profiles
Solution Approach 1:
The invention transitions from planar lithographic patterns to three-dimensional high aspect ratio angled structures. By creating trenches with significant depth and angle, the mask structure gains vertical dimensionality that prevents erosion during ion milling and produces deep step-edge profiles suitable for SQUID fabrication.
Solution Approach 2:
The mask structure is formed as a composite of multiple materials: photoresist layers, sacrificial material, and the final mask material. This composite structure provides the mechanical strength and erosion resistance needed for deep step-edge formation while maintaining compatibility with conventional fabrication processes.
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
Enables the production of high-aspect ratio nanometer-scale angled features and doping profiles, facilitating the fabrication of complex devices like SQUIDs and MEMS, while utilizing existing RIE tools, thus overcoming the limitations of conventional lithography and etching techniques.
Implementation Method 1
forming a pattern in the masking layer to expose portions of the target material; positioning the substrate on an angle mount at a pre-determined angle relative to a cathode of a reactive ion etcher so that the target material is within a plasma dark space of the plasma etch gas; and etching the exposed portions of the target material using ballistic ions within the plasma dark space
Implementation Method 2
target material is removable using a reactive ion etch in a plasma etch gas
Implementation Method 3
forming a pattern in the masking layer to expose portions of the target material
Implementation Method 4
As the ballistic transport of ions in the dark space ensures a high directionality, a tilted surface located inside this dark space will continue to be etched perpendicular to the cathode
Implementation Method 5
etching the exposed portions of the target material using ballistic ions within the plasma dark space
Data Source
AI summary
A process for forming trenches in a target material includes forming a masking layer onto the target material, where the masking layer comprises a material having high selectivity to a plasma etch gas adapted for etching the target material. A pattern is formed in the masking layer to expose portions of the target material and the sample is placed on an angle mount at a pre-determined angle relative to a cathode of a reactive ion etcher so that the target material is within a plasma dark space of the plasma etch gas. Ballistic ions within the plasma dark space form a trench structure within the target material. The process may further include repeating the steps of positioning the sample and etching the exposed portions of the target material with the substrate at a different angle to define a triangular structure.