Plasma Etching Selectivity for CoFeB Magnetic Layers
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Solution Overview
Problem
The existing plasma processing methods for MRAM devices face challenges in achieving high etching selectivity between magnetic layers and insulating layers, particularly when using MgO as the insulating material, leading to potential leak currents and degraded device characteristics due to residue deposition on the side walls.
Innovation Solution
A plasma processing method and apparatus that uses a processing gas containing H2 and F or fluorine compounds to etch the second magnetic layer, improving selectivity and preventing residue deposition by reacting with CoFeB without affecting MgO, and includes a multi-step etching process to manage the modified layers and residues effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching methods are used to etch the magnetic layer, then the etching process can proceed, but residue containing conductive material is deposited on the side wall of the insulating layer causing leak current
Solution Approach 1:
The etching process is divided into multiple sequential steps with different processing gases. First, a fluorine-containing gas (SF6) is used to etch the magnetic layer with high selectivity. Then, a hydrogen-containing gas (H2) is used to remove residues from the side walls. This segmentation of the etching process allows each step to address a specific problem: the first step achieves precise etching while the second step cleans residues, thereby preventing leak current without compromising etching precision.
2Object-affected harmful factors
If the etching process is stopped on the top surface of the insulating layer to suppress residue deposition, then leak current is reduced, but etching selectivity between magnetic layer and insulating layer must be increased
Solution Approach 1:
The patent changes the chemical parameters of the processing gas to achieve high etching selectivity. By using fluorine-containing gas (SF6) for the first etching step, the process exploits the chemical reactivity difference between fluorine and magnesium oxide (the insulating layer material). Fluorine reacts readily with the magnetic layer materials (CoFeB, CoFe) but does not react with MgO, thereby achieving high selectivity without requiring the etching to be stopped on the insulating layer surface. This parameter change in gas composition resolves the contradiction between preventing leak current and maintaining etching selectivity.
3Reliability
If MgO is used as the insulating layer material to achieve high MR ratio, then device characteristics improve, but etching selectivity between magnetic layer and insulating layer becomes difficult to achieve
Solution Approach 1:
The patent addresses the etching selectivity problem with MgO insulating layer by changing the processing gas parameter from conventional chlorine-based gases to fluorine-based gases (SF6). Fluorine has high chemical reactivity with the magnetic layer materials (CoFeB, CoFe) forming volatile fluorides, while showing no reactivity with MgO due to the stability of Mg-O bonds. This parameter change in gas chemistry enables high etching selectivity (greater than 3:1) while maintaining the high MR ratio benefits of MgO insulating layers.
4Ease of manufacture
If metal mask is formed on the magnetic layer, then etching can be performed, but the top surface of the magnetic layer is modified forming a modified layer
Solution Approach 1:
The patent applies preliminary action by performing a pre-etching step before the main etching process. A fluorine-containing gas (SF6) is used in a preliminary etching step to remove the modified layer that forms on the magnetic layer surface during mask formation. This preliminary action restores the original magnetic layer surface composition and properties before the main etching proceeds, ensuring that the magnetic layer maintains its intended characteristics while still allowing metal mask formation for etching patterning.
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 enhances the verticality of the magnetic layers, suppresses leak currents, and improves the overall characteristics of the MRAM device by effectively stopping the etching process on the insulating layer surface, reducing residue dispersion, and allowing for efficient removal of residues.
Implementation Method 1
Since a F radical reacts with CoFeB contained in the second magnetic layer but does not react with MgO contained in the insulating layer, etching selectivity between the second magnetic layer containing CoFeB and the insulating layer containing MgO can be improved
Implementation Method 2
an apparatus described in Patent Document 1, when the multilayered object is etched
Data Source
AI summary
A plasma processing method is used to etch a multilayered material having a stacked structure, in which a first magnetic layer, an insulating layer, a second magnetic layer, and a mask material are stacked in sequence, in a plasma processing apparatus including a processing chamber that partitions a processing space where plasma is generated and a gas supply unit that supplies a processing gas into the processing space. The plasma processing method includes a mask forming process of forming a mask on the second magnetic layer by etching the mask material; an etching process of supplying the processing gas into the processing chamber to generate plasma, etching the second magnetic layer by the mask, and stopping the etching on a surface of the insulating layer. Further, the second magnetic layer contains CoFeB, the insulating layer contains MgO, and the processing gas contains H2 and F or a fluorine compound.