Plasma Etching for MRAM MTJ Devices
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing plasma etching methods for magnetic materials in magnetoresistive random access memory (MRAM) devices, such as those using high-frequency plasma with fluorocarbon compounds, often result in conductive magnetic films on the side walls of MTJ devices, leading to short-circuits and reduced magneto-resistance effects, and struggle to form vertical MTJ devices without deteriorating device characteristics.
Innovation Solution
A plasma etching method using a hard mask with laminated films of a magnetic film, a barrier layer, and an insulating barrier layer, employing a sequence of etching steps with N2 gas and mixed gases containing carbon elements, such as N2 and CH4, to achieve a vertically shaped MTJ device without short-circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If fluorocarbon compound gas is used for plasma etching of magnetic material film, then etching can be performed, but conductive magnetic film is formed on the side wall causing short-circuit between magnetic layers
Solution Approach 1:
The etching process is divided into multiple sequential steps with different gas compositions. The first step uses fluorocarbon compound gas for initial etching, followed by a second step using mixed gas (N2 + CO) to form an insulating film on the side wall, and optionally a third step to complete the etching. This segmentation allows the process to achieve both etching capability and prevention of short-circuits.
Solution Approach 2:
The gas composition parameter is changed between etching steps. The patent specifies using fluorocarbon compound gas (CF4, C2F6, or C3F8) in the first step, then switching to mixed gas containing N2 and CO in a specific ratio (3:1 to 1:3) in the second step. This parameter change transforms the side wall deposition from conductive magnetic film to insulating film, preventing short-circuits while maintaining etching effectiveness.
2Reliability
If nitrogen gas is used to increase electric resistance of re-deposit, then magnetic resistance effects are preserved, but the deposit on pattern side wall makes it difficult to form vertical MTJ device shape
Solution Approach 1:
The patent changes the gas composition parameters to achieve both vertical shape and preserved magnetic resistance effects. By using mixed gas of N2 and CO in specific ratios (3:1 to 1:3) in the second etching step, the process forms an insulating film on the side wall that maintains high electric resistance (preserving magnetic resistance effects) while the controlled deposition enables vertical MTJ device formation.
Solution Approach 2:
The etching process uses composite gas composition (N2 + CO mixed gas) rather than pure nitrogen gas. This composite approach creates a deposit with both insulating properties (from CO) and controlled morphology (from N2), achieving vertical sidewalls while maintaining high electric resistance to preserve magnetic resistance effects.
3Productivity
If high frequency plasma is used to generate plasma from reaction gas, then magnetic material film can be etched, but conductive magnetic film forms on side wall leading to short-circuit
Solution Approach 1:
The high frequency plasma etching process is segmented into multiple steps with different gas compositions. The first step uses fluorocarbon compound gas for efficient etching, followed by a second step using N2 + CO mixed gas to form an insulating film on the side wall. This segmentation maintains high etching efficiency while preventing short-circuits through controlled side wall deposition.
Solution Approach 2:
The gas composition parameter is changed between etching steps to resolve the contradiction. The patent specifies using fluorocarbon compound gas (CF4, C2F6, or C3F8) in the first step for efficient etching, then switching to mixed gas containing N2 and CO in a specific ratio (3:1 to 1:3) in the second step to form an insulating film, thereby maintaining both etching efficiency and device characteristics.
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 effectively prevents short-circuits between magnetic layers and maintains device characteristics by forming a vertically shaped MTJ device, improving the magnetic resistance effects and etching efficiency.
Implementation Method 1
plasma etching method for performing plasma etching on a sample
Implementation Method 2
a first step of etching the laminated films using N2 gas; and a second step of etching the laminated films after the first step using mixed gas of N2 gas and gas containing carbon elements
Implementation Method 3
performing plasma etching on a sample using a hard mask, the hard mask including at least one of a Ta film and a TiN film
Implementation Method 4
a second step of etching the laminated films after the first step using mixed gas of N2 gas and gas containing carbon elements
Data Source
AI summary
A plasma etching method performs plasma etching on a sample, which has laminated films containing a variable layer of a magnetic film, a barrier layer of an insulating material, and a fixed layer of a magnetic film, using a hard mask, which includes at least one of a Ta film and a TiN film. The plasma etching method includes a first step of etching the laminated films using N2 gas; and a second step of etching the laminated films after the first step using mixed gas of N2 gas and gas containing carbon elements.