MTJ Etch Using Methanol Oxidant Gas Mixture
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Solution Overview
Problem
Current etch processes for magnetic tunnel junction (MTJ) stacks result in sidewall damage and residue, leading to electrical shunts and reduced magnetic properties, particularly in devices with critical dimensions less than 60 nm, where a single etch solution is lacking and additional steps are required for sidewall repair, increasing cost and reducing yield.
Innovation Solution
A method involving a single etch step using a gas mixture of oxygen and a noble gas, such as argon, with optional chemical oxidants like methanol, to minimize sidewall damage and residue, combined with a chemical treatment and volatilization process to convert non-volatile residues into volatile forms for removal, optimizing etch conditions to maintain or improve magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional methanol-based RIE is used for etching MTJ stack, then etch transfer is achieved, but chemical and plasma damage occurs on MTJ sidewalls
Solution Approach 1:
The patent changes the chemical composition parameters of the etch gas mixture by introducing oxidants (oxygen, nitrogen dioxide, ammonia, hydrogen peroxide, or their combinations) to the methanol-based RIE process. This parameter modification transforms the chemical environment to reduce sidewall damage while maintaining etch transfer efficiency, directly resolving the contradiction between productivity and harmful effects.
Solution Approach 2:
The patent introduces oxidant substances as intermediary agents that mediate between the methanol etchant and the MTJ sidewalls. These oxidants act as protective intermediaries that prevent direct chemical and plasma damage to the sidewalls during etching, thereby reducing harmful effects without sacrificing etch transfer capability.
2Object-affected harmful factors
If ion beam etch (IBE) is used for etching MTJ stack, then minimal chemical and plasma damage is produced, but high degree of redeposited material occurs on MTJ sidewalls
Solution Approach 1:
The patent modifies the physical-chemical parameters of the etch environment by adding oxidants to the methanol-based RIE process. This changes the volatility and reactivity parameters of the etched materials, preventing redeposition on sidewalls while maintaining minimal chemical and plasma damage characteristics similar to IBE.
3Productivity
If single etch process is used to transfer pattern through entire MTJ stack, then throughput is improved, but sidewall residue and damage increase
Solution Approach 1:
The patent optimizes the chemical composition parameters of the single etch process by incorporating oxidants into the methanol-based RIE gas mixture. This parameter change enables the single etch process to simultaneously achieve pattern transfer through the entire MTJ stack and maintain clean sidewalls with minimal residue, resolving the contradiction between throughput 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 significantly reduces sidewall damage and residue, enhancing the magnetoresistive ratio (DRR) and decreasing the low tail population in MTJ arrays, thereby improving device performance and throughput while maintaining or improving magnetic properties.
Implementation Method 1
a single etch process comprised of a gas flow that includes at least oxygen and a second oxidant such as methanol
Implementation Method 2
RIE with a gas flow that includes a noble gas, oxygen, and a chemical oxidant such as methanol, ethanol, ammonia, or a combination of CO and NH3
Implementation Method 3
oxygen and a chemical oxidant such as methanol, ethanol, ammonia, or a combination of CO and NH3
Implementation Method 4
A first process flow comprises an IBE step and then a separate chemical treatment to convert non-volatile residue on MTJ sidewalls into a volatile residue
Implementation Method 5
Next, an optional IBE step, plasma sputter etch step, or thermal treatment is employed to remove the volatile residue
Implementation Method 6
an optional IBE step, plasma sputter etch step, or thermal treatment is employed to remove the volatile residue
Implementation Method 7
The magnetoresistive ratio is expressed by dR/R (or DRR) where dR is the difference in resistance between the two magnetic states (RAP−RP) when a current is passed through the MTJ
Data Source
AI summary
A process flow for forming magnetic tunnel junctions (MTJs) with minimal sidewall residue and reduced low tail population is disclosed wherein a pattern is first formed in a hard mask that is an uppermost MTJ layer. Thereafter, the hard mask pattern is etch transferred through the underlying MTJ layers including a reference layer/tunnel barrier/free layer stack. The etch transfer may be completed in a single RIE step based on a first flow rate of O2 and a second flow rate of an oxidant such as CH3OH where the CH3OH/O2 ratio is at least 7.5:1. The RIE may also include a flow rate of a noble gas. In other embodiments, a chemical treatment with an oxidant such as CH3OH, and a volatilization at 50° C. to 450° C. may follow an etch transfer through the MTJ stack when the ion beam etch or plasma etch involves noble gas ions.