MRAM Top Electrode Structure for Low-Roughness MTJ Patterning
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Solution Overview
Problem
The existing etching processes for manufacturing magnetoresistive random-access memory (MRAM) devices, such as reactive ion etching and ion beam etching, often result in re-sputtering effects and high circular edge roughness due to the use of polycrystalline metal hard masks, leading to shorts between ferromagnetic layers and negatively impacting device performance.
Innovation Solution
The proposed solution involves forming a MRAM structure with a top electrode having distinct portions above and outside the second ferromagnetic layer, separated by a dielectric liner, and using anisotropic etching with amorphous dielectric hard masks to reduce circular edge roughness and prevent shorts, while also employing a method that includes forming a sacrificial dielectric layer and conducting material layers to create a structured top electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If reactive ion etching (RIE) and/or ion beam etching (IBE) processes are used to pattern the MTJ stack, then the vertical MTJ stack can be formed, but re-sputtering effect causes metal elements to be re-deposited onto sidewall surfaces, resulting in shorts between ferromagnetic layers
Solution Approach 1:
A dielectric liner is introduced as an intermediary layer between the ferromagnetic layers and the re-deposited metal elements. This liner prevents direct contact between conductive paths that would otherwise create shorts, while allowing the etching process to proceed. The dielectric material acts as a protective barrier during the RIE/IBE patterning process.
2Ease of manufacture
If polycrystalline metal hard masks are used in RIE and/or IBE etching processes, then the etching can be performed, but grain boundaries and defects in the polycrystalline metal are transferred into the MTJ stack, resulting in high circular edge roughness (CER)
Solution Approach 1:
The material state of the hard mask is changed from polycrystalline to amorphous. This parameter change eliminates grain boundaries and crystalline defects that cause edge roughness during etching. The amorphous hard mask provides a uniform structure that does not transfer defects to the MTJ stack, resulting in lower circular edge roughness while maintaining etching capability.
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 circular edge roughness and prevents shorts between ferromagnetic layers, enhancing the performance and reliability of MRAM devices by using a dielectric liner and amorphous hard masks in the etching process.
Implementation Method 1
such etching processes may sometimes come with re-sputtering effect, which causes metal elements from, for example, the blanket bottom electrode layer to be re-deposited onto sidewall surfaces of the ferromagnetic layers and/or the tunnel barrier layer
Implementation Method 2
grain boundaries and defects in the polycrystalline metal hard mask may be transferred into the MTJ stack during the patterning process
Data Source
AI summary
Embodiments of present invention provide a method of forming a MRAM structure. The method includes forming a sacrificial dielectric layer on top of a bottom contact; forming a stack of a first ferromagnetic layer, a tunnel barrier layer, a second ferromagnetic layer, and at least one hard mask on top of the sacrificial dielectric layer; forming an interlevel-dielectric (ILD) layer surrounding the stack; creating one or more via holes in the ILD layer to expose the sacrificial dielectric layer; selectively removing the sacrificial dielectric layer to create an opening underneath the first ferromagnetic layer; filling the opening with a first conductive material to form a bottom electrode; removing the at least one hard mask to expose the second ferromagnetic layer; and forming a top electrode of a second conductive material on top of the second ferromagnetic layer. An MRAM structure formed thereby is also provided.