Sidewall Spacer Masking for MTJ Etching Yield
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional methods for forming magnetic tunnel junctions (MTJ) features in MRAM integrated circuits face challenges with redeposition of etching byproducts, leading to reduced yield due to anisotropic etching and difficulties in achieving reproducible tapering of etched features.
Innovation Solution
The use of sidewall spacer features during processing, which create a tapered masking layer and encapsulate the film stack, allowing for controlled etching and reducing redeposition of etching byproducts, while also potentially serving as vertical contacts for higher metallization levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If reactive ion etching is used to pattern MTJ features, then anisotropic etching is achieved with preferential etching normal to the substrate, but redeposition of etching byproducts occurs on sidewalls leading to yield reduction
Solution Approach 1:
A spacer layer is deposited conformally on the sidewalls of trenches before the main etching process. This preliminary action creates a protective mask that prevents etching byproducts from redepositing on the sidewalls during subsequent etching steps, thereby solving the redeposition problem while maintaining anisotropic etching capability
Solution Approach 2:
The spacer layer acts as an intermediary protective layer between the etching environment and the MTJ film stack sidewalls. This intermediary structure absorbs or deflects etching byproducts, preventing their harmful redeposition on the sidewalls while allowing the anisotropic etching process to proceed effectively
2Manufacturing precision
If RIE chemistry is adjusted to balance sputtering, chemical etching, and byproduct redeposition, then etching control is improved, but the process becomes complex and highly sensitive to etch tool conditions
Solution Approach 1:
The etching process is segmented into distinct steps: first forming trenches with vertical sidewalls, then depositing a spacer layer, selectively removing spacer material to create tapered sidewalls, and finally performing the main etch. This segmentation simplifies each individual step while achieving the desired tapered profile, reducing overall process complexity and sensitivity to tool conditions
Solution Approach 2:
The sidewall angle is controlled by changing the geometry of the spacer layer rather than adjusting complex RIE chemistry parameters. By controlling spacer layer deposition thickness and pattern dimensions, the tapered profile is achieved through geometric parameters that are more stable and less sensitive to etch tool condition variations
3Shape
If a masking layer is physically sputtered to create taper, then tapered features are formed, but the underlying film stack may be damaged and lower reaches cannot be tapered sufficiently
Solution Approach 1:
The spacer layer serves as an intermediary protective mask during the main etching process. It protects the underlying film stack from direct ion bombardment and physical sputtering damage, allowing the formation of sufficient taper at lower reaches without compromising the integrity of the sensitive MTJ film stack
Solution Approach 2:
The spacer layer is deposited and patterned in advance before the main etching process. This preliminary preparation creates the tapered profile geometry that guides the subsequent etching, ensuring that sufficient taper is achieved at lower reaches without requiring aggressive physical sputtering that would damage the film stack
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 method enhances the reliability and reproducibility of MTJ feature formation, reducing redeposition issues and improving processing yield by achieving a tapered film stack profile and allowing for efficient integration with higher metallization levels.
Implementation Method 1
a spacer layer is deposited on the film stack
Implementation Method 2
They sputter the material from the surface, as well as chemically react with the material, thereby producing reaction products that are volatile and can be pumped away
Data Source
AI summary
Novel methods for reliably and reproducibly forming magnetic tunnel junctions in integrated circuits are described. In accordance with aspects of the invention, sidewall spacer features are utilized during the processing of the film stack. Advantageously, these sidewall spacer features create a tapered masking feature which helps to avoid byproduct redeposition during the etching of the MTJ film stack, thereby improving process yield. Moreover, the sidewall spacer features may be used as encapsulating layers during subsequent processing steps and as vertical contacts to higher levels of metallization.