Combined Physical Chemical Etch for MTJ Sidewall Damage Reduction
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Solution Overview
Problem
Current etch processes for MTJ stacks result in significant sidewall damage and redeposition of materials, leading to reduced yield and increased costs, particularly for devices with critical dimensions below 60 nm, as they fail to provide a single etch solution that maintains or improves magnetic properties like the magnetoresistive ratio.
Innovation Solution
A method involving a single etch step that combines physical and chemical components, using inert gases and specific chemicals like methanol, ethanol, or ammonia, to minimize sidewall damage and residue, with optional volatilization steps to convert non-volatile residues into volatile forms, allowing for the formation of MTJ nanopillars with improved magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional RIE with methanol is used for etching MTJ stack, then chemical damage and plasma damage occur on MTJ sidewalls, but if IBE is used, then redeposition of material occurs on sidewalls
Solution Approach 1:
The patent applies parameter changes by modifying the etch chemistry composition and process conditions. Specifically, it uses a mixed chemistry approach combining oxygen-based chemistries (to minimize redeposition) with fluorocarbon or chlorocarbon chemistries (to provide protective polymer layers on sidewalls). The patent also optimizes parameters such as RF power, pressure, and gas flow rates to balance physical sputtering and chemical etching components, thereby reducing both chemical/plasma damage and material redeposition on MTJ sidewalls.
Solution Approach 2:
The patent employs composite materials by combining multiple etch chemistries in a single process or in a sequence of processes. It uses mixed chemistry etchants that incorporate oxygen-containing compounds (like O2, CO, or oxygenated hydrocarbons) with fluorocarbon or chlorocarbon compounds. This composite approach leverages the benefits of each chemistry type: oxygen-based chemistries reduce redeposition while fluorocarbon/chlorocarbon chemistries provide sidewall protection, thereby resolving the contradiction between damage and redeposition.
2Manufacturing precision
If multiple etch steps are used to transfer pattern through MTJ stack, then etching accuracy improves, but manufacturing complexity and cost increase
Solution Approach 1:
The patent applies merging by combining multiple etch functions into a single integrated etch process. It uses a mixed chemistry etch recipe that simultaneously achieves pattern transfer through the hard mask and MTJ stack while minimizing sidewall damage and redeposition. This consolidation of multiple etch steps into one process maintains etching accuracy while reducing process complexity and manufacturing cost.
Solution Approach 2:
The patent employs universality by developing a single etch process that performs multiple functions: it transfers the pattern through the hard mask, etches through the MTJ stack layers (including magnetic layers and tunnel barrier), minimizes sidewall damage, and reduces material redeposition. This multi-functional etch process eliminates the need for separate specialized etch steps for each function, thereby simplifying the overall manufacturing process while maintaining precision.
3Object-affected harmful factors
If IBE is used for etching, then chemical damage is minimized, but throughput decreases due to multiple required steps
Solution Approach 1:
The patent applies continuity by implementing a single continuous etch process that maintains optimized conditions throughout the entire etch duration. The mixed chemistry etch recipe allows the process to proceed in one continuous step through the hard mask and MTJ stack without requiring interruption for intermediate cleaning or process changes. This continuous action maintains low chemical damage while achieving high throughput by eliminating step transitions.
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 significantly reduces sidewall damage and residue, enabling higher throughput and lower costs while maintaining or improving magnetic properties, particularly for MTJ nanopillars with critical dimensions ≤60 nm, by using a combined physical and chemical etching process that optimizes etch conditions to minimize sidewall damage and residue.
Implementation Method 1
a single etch process comprised of both physical and chemical components
Implementation Method 2
a single etch process comprised of both physical and chemical components
Implementation Method 3
a chemical treatment that converts non-volatile residue on MTJ sidewalls into volatile residue followed by a volatilization process
Data Source
AI summary
A process flow for forming magnetic tunnel junction (MTJ) nanopillars with minimal sidewall residue and minimal sidewall damage is disclosed wherein a pattern is first formed in a hard mask that is an uppermost MTJ layer. Thereafter, the hard mask sidewall is etch transferred through the remaining MTJ layers including a reference layer, free layer, and tunnel barrier between the free layer and reference layer. The etch transfer may be completed in a single RIE step that features a physical component involving inert gas ions or plasma, and a chemical component comprised of ions or plasma generated from one or more of methanol, ethanol, ammonia, and CO. In other embodiments, a chemical treatment with one of the aforementioned chemicals, and a volatilization at 50° C. to 450° C. may follow an etch transfer through the MTJ stack with an ion beam etch or plasma etch involving inert gas ions.