Ion Beam Etching for MRAM Bottom Electrode Self-Alignment
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Solution Overview
Problem
Existing methods for fabricating magnetoresistive random access memory (MRAM) cells with magnetic tunnel junctions (MTJ) face challenges such as surface damage, re-deposition of conductive materials, and complexity in etching processes, particularly in achieving high density arrays due to issues with sidewall angles and material selectivity during etching.
Innovation Solution
The use of Ion Beam Etching (IBE) with adjustable incidence angles and wafer rotational profiles to etch the bottom electrode simultaneously with sidewall cleaning, eliminating the need for additional masks and reducing chemical damage, while utilizing reactive ion etching (RIE) for improved selectivity and minimizing top electrode thickness loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional reactive ion etching (RIE) is used for bottom electrode etching, then chemical etching selectivity is improved, but re-deposition of conductive material on sidewall occurs causing electrical shorts
Solution Approach 1:
A dielectric passivation layer is deposited over the MTJ stack before bottom electrode etching. This intermediary layer prevents conductive material from re-depositing on the sidewall during IBE, eliminating electrical shorts while allowing selective etching of the bottom electrode through the passivation layer's controlled removal or permeability.
Solution Approach 2:
The patent replaces conventional chemical RIE with physical Ion Beam Etching (IBE) for bottom electrode patterning. IBE uses directed ion bombardment instead of chemical reactions, which significantly reduces re-deposition of conductive material on sidewalls while maintaining adequate etching selectivity through physical sputtering mechanisms.
2Productivity
If vertical directional etching is used, then etching rate is improved, but top electrode thickness is excessively removed making downstream interconnect process difficult
Solution Approach 1:
The patent employs asymmetric angled etching (e.g., 45-degree incidence angle) instead of vertical etching. This asymmetric approach creates sloped sidewalls that protect the top electrode from excessive removal while maintaining high etching rates on the bottom electrode, reducing top electrode thickness loss to acceptable levels for downstream interconnect processes.
3Manufacturing precision
If additional masks are used for bottom electrode etching, then etching precision is improved, but device complexity and process steps increase
Solution Approach 1:
The patent implements self-aligned bottom electrode etching where the MTJ stack structure itself serves as the alignment reference. By using angled IBE with the MTJ stack as a shadow mask, the bottom electrode is automatically aligned to the MTJ without requiring additional photolithography masks, reducing process complexity while maintaining precise alignment.
Solution Approach 2:
The IBE process serves multiple functions simultaneously: it etches the bottom electrode, cleans sidewalls of damaged layers, and provides self-alignment all in a single step. This multi-functionality eliminates the need for separate masking and alignment steps, reducing overall device complexity while achieving high precision.
4Object-affected harmful factors
If shallow sidewall slope is used, then re-deposition is reduced, but MTJ size control and uniformity for scalability are compromised
Solution Approach 1:
The patent optimizes the IBE incidence angle parameter (e.g., 45 degrees) to achieve an optimal balance: this angle creates sufficient sidewall slope to minimize re-deposition while maintaining adequate lateral etching control for precise MTJ size definition. The angled parameter enables both reduced re-deposition and scalable MTJ uniformity across wafers.
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 enables self-aligned bottom electrode fabrication, reduces re-deposition, and simplifies the process flow, allowing for smaller cell sizes and higher density arrays by controlling sidewall angles and etch rates, thereby improving the scalability and efficiency of MRAM cell production.
Implementation Method 1
Ion Beam Etching (IBE) has been widely used in various industries for patterning thin films
Implementation Method 2
IBE with adjustable incidence angles and wafer rotational profiles to etch the bottom electrode simultaneously with sidewall cleaning
Implementation Method 3
utilizing reactive ion etching (RIE) for improved selectivity
Data Source
AI summary
Fabrication methods using Ion Beam Etching (IBE) for MRAM cell memory elements are described. In embodiments of the invention the top electrode and MTJ main body are etched with one mask using reactive etching such as RIE or magnetized inductively coupled plasma (MICP) for improved selectivity, then the bottom electrode is etched using IBE as specified in various alternative embodiments which include selection of incident angles, wafer rotational rate profiles and optional passivation layer deposited prior to the IBE. The IBE according to the invention etches the bottom electrode without the need for an additional mask by using the layer stack created by the first etching phase as the mask. This makes the bottom electrode self-aligned to MTJ. The IBE also achieves MTJ sidewall cleaning without the need for an additional step.