Dual Etch Stop Layers for MRAM Selector Elements
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Solution Overview
Problem
Ovonic threshold switch materials in MRAM devices are degraded by exposure to fluorine-containing plasma during anisotropic etch processes, leading to increased leakage current and damage.
Innovation Solution
The use of dual etch stop layers, comprising a ruthenium etch stop layer and a refractory metal-containing etch stop layer, to pattern ovonic threshold switch selector elements in MRAM devices, minimizing exposure to fluorine-containing plasma and preventing damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If fluorine-containing plasma is used for anisotropic etching of conductive material layer, then etching selectivity is improved, but ovonic threshold switch material is damaged and leakage current increases
Solution Approach 1:
A ruthenium etch stop layer is introduced as an intermediary between the conductive material layer and the ovonic threshold switch selector element. This ruthenium layer selectively withstands fluorine-containing plasma etching, allowing the conductive material to be etched with high selectivity while protecting the underlying selector element from plasma damage.
Solution Approach 2:
The ruthenium etch stop layer is deposited beforehand to cushion or absorb the harmful effects of fluorine-containing plasma. This layer acts as a sacrificial protective barrier that prevents direct contact between the damaging plasma and the sensitive ovonic threshold switch material during the etching process.
2Reliability
If dual etch stop layers are used to protect selector element, then selector element integrity is improved, but device structure complexity increases
Solution Approach 1:
The ruthenium etch stop layer serves multiple functions: it provides etch selectivity during conductive material patterning, protects the selector element from plasma damage, and acts as a diffusion barrier. By combining multiple functions in a single layer, the patent reduces the need for additional separate protective layers.
Solution Approach 2:
The patent utilizes the unique chemical properties of ruthenium, specifically its resistance to fluorine-containing plasma etching, to create a protective layer. By selecting a material with specific etching parameters that differ from both the conductive material above and the selector element below, the patent achieves protection without adding excessive structural complexity.
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 effectively reduces exposure to fluorine-containing plasma, thereby minimizing leakage current and maintaining the integrity of ovonic threshold switch selector elements in MRAM devices.
Implementation Method 1
performing a second anisotropic etch process having a second etch chemistry that etches ruthenium selective to a material of the refractory metal-containing etch stop layer; patterning the refractory metal-containing etch stop layer into refractory metal-containing etch stop plate by performing a third anisotropic etch process having a third etch chemistry that etches a material of the refractory metal-containing etch stop layer selective to a material of the upper electrode layer
Implementation Method 2
the third anisotropic etch process is a timed based etch process which employs a fluorine-based plasma which is timed to etch through the refractory metal-containing etch stop layer without etching all the way through the upper electrode layer, such that the ovonic threshold switch material is not exposed to the fluorine-based plasma
Data Source
Figure 1A~1C
Figure 2A~2C
Figure 3A~3C
AI summary
A refractory metal-containing etch stop layer, a ruthenium etch stop layer, and a conductive material layer can be sequentially formed over an electrode layer and a selector material layer. A sequence of anisotropic etch processes can be employed to etch the conductive material layer selective to the ruthenium etch stop layer, to etch the ruthenium etch stop layer selective to the refractory metal-containing etch stop layer, and to etch the refractory metal-containing etch stop layer within minimal overetch into the electrode layer. The selector material layer can be subsequently anisotropically etched without exposure to the plasma of etchant gases for etching the refractory metal-containing etch stop layer and the conductive material layer, which may include a fluorine-containing plasma that can damage the selector material.