Two-Step Etching for Magnetoresistive Top Electrode Definition
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Solution Overview
Problem
The manufacturing of magnetoresistive devices, such as magnetic tunnel junctions, faces challenges in achieving precise electrode definition and high device density due to issues like oxidation and sidewall roughness caused by reactive spacer layers and etching chemistries, which can lead to operational deviations and reduced performance.
Innovation Solution
The use of a two-step etching process with varying isotropy and selective etching chemistries for electrode formation, combined with non-reactive photoresist stripping using water vapor or non-oxidizing gases to prevent oxidation and maintain precise physical definition, and the option of omitting reactive spacer layers to prevent sidewall roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If reactive spacer layers and etching chemistries are used, then etching performance is improved, but oxidation and sidewall roughness occur leading to reduced manufacturing precision
Solution Approach 1:
The etching process is divided into two distinct steps: a first etching step using reactive chemistry to achieve high etching performance, followed by a second etching step using non-reactive chemistry to remove remaining material without causing oxidation or sidewall roughness. This segmentation allows each step to be optimized for its specific function, resolving the contradiction between etching performance and manufacturing precision.
Solution Approach 2:
A non-reactive etching chemistry is introduced as an intermediary step between the reactive etching process and the final electrode formation. This intermediary step removes residual material and prevents oxidation without compromising the electrode definition, thereby maintaining high manufacturing precision while preserving the benefits of reactive etching.
2Strength
If reactive materials are used for spacer layers, then structural integrity is improved, but sidewall roughness and oxidation occur reducing device reliability
Solution Approach 1:
The spacer layer formation process is segmented into multiple stages with different material requirements. The lower spacer layer uses reactive materials for structural integrity, while the upper spacer layer uses non-reactive materials to prevent sidewall roughness and oxidation. This segmentation allows both structural integrity and device reliability to be optimized simultaneously.
Solution Approach 2:
Different regions of the spacer layer structure are assigned different material properties: the lower portion near the magnetic tunnel junction uses reactive materials with high structural integrity, while the upper portion exposed to etching chemistries uses non-reactive materials resistant to oxidation and sidewall roughness. This local quality differentiation resolves the contradiction between strength and reliability.
3Device complexity
If conventional single-step etching is used, then process complexity is reduced, but electrode feature sharpness and device density are compromised
Solution Approach 1:
The etching process is segmented into two steps with distinct chemistries: a first step using reactive chemistry for material removal and a second step using non-reactive chemistry for precise feature definition. Although this increases process complexity, it enables sharp electrode features and high device density by preventing oxidation and sidewall roughness that would otherwise limit manufacturing precision.
Solution Approach 2:
The etching process parameters are changed between two steps: the first step uses reactive chemistry with parameters optimized for high etch rates, while the second step uses non-reactive chemistry with parameters optimized for precise feature definition. This parameter change allows the process to achieve both efficient material removal and sharp electrode features, resolving the contradiction between process complexity and manufacturing precision.
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 sharper electrode features, reduced operational deviations, and higher device densities by minimizing oxidation and maintaining precise layer definitions, thereby improving the reliability and performance of magnetoresistive devices.
Implementation Method 1
subsequent photoresist stripping using water vapor or other non-oxidizing gases, which can also provide passivation
Implementation Method 2
a first portion of the electrically conductive layer is etched using a first plasma etch
Data Source
AI summary
A two-step etching process is used to form the top electrode for a magnetoresistive device. The etching chemistries are different for each of the two etching steps. The first chemistry used to etch the top portion of the electrode is more selective with respect to the conductive material of the top electrode, thereby reducing unwanted erosion of the photoresist and hard mask layers. The second chemistry is less corrosive than the first chemistry and does not damage the layers underlying the top electrode, such as those included in the magnetic tunnel junction.