Segmented Bottom Electrode for MRAM Stability
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Solution Overview
Problem
In the manufacturing of magnetoresistive random access memory (MRAM) devices, the stability of the bottom electrode is compromised due to tilting and bowing issues, especially as critical dimensions approach 20 nm, leading to partial metallic shorts and array yield loss.
Innovation Solution
A dielectric material structure is formed laterally adjacent to the bottom electrode, which is then trimmed to create a unitary construction with a wider lower portion and a narrower upper portion, preventing tilting and bowing by maintaining the stability of the bottom electrode, even at high aspect ratios greater than 2:1.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the bottom electrode is made smaller to increase switching efficiency, then the MTJ pillar size is reduced and switching efficiency increases, but partial metallic shorts occur due to resputtered metallic particles
Solution Approach 1:
The bottom electrode is segmented into two distinct portions: a lower portion with a first diameter and an upper portion with a second diameter that is greater than the first diameter. This segmentation allows the upper portion to be smaller for efficient switching while the lower portion provides a larger base for stability and resistance to metallic shorts.
2Manufacturing precision
If the bottom electrode height is increased to allow sufficient dielectric thickness for overetching and sidewall cleaning, then overetching capability improves, but the aspect ratio becomes excessively high causing tilting and bowing
Solution Approach 1:
Different portions of the bottom electrode are given different diameters to optimize local functions. The upper portion has a smaller diameter to accommodate the MTJ pillar and enable sidewall cleaning, while the lower portion has a larger diameter to provide structural stability and prevent tilting and bowing.
Solution Approach 2:
The bottom electrode transitions from a symmetric cylindrical shape to an asymmetric shape with varying diameter along its height. The asymmetric profile, with a larger lower portion and smaller upper portion, provides both the height needed for sidewall cleaning and the structural stability to prevent deformation.
3Productivity
If the bottom electrode is made with high aspect ratio to support scaled MTJ pillars, then device scaling is achieved, but tilting and bowing of the bottom electrode occurs
Solution Approach 1:
The diameter parameter of the bottom electrode is changed along its height, creating a gradient structure. The diameter transitions from a smaller value at the upper portion to a larger value at the lower portion, optimizing both scaling capability and structural stability.
Data Source
AI summary
A dielectric material structure is formed laterally adjacent to a bottom portion of a bottom electrode metal-containing portion that extends upward from an electrically conductive structure that is embedded in an interconnect dielectric material layer. The physically exposed top portion of the bottom electrode metal-containing portion is then trimmed to provide a bottom electrode of unitary construction (i.e., a single piece) that has a lower portion having a first diameter and an upper portion that has a second diameter that is greater than the first diameter. The presence of the dielectric material structure prevents tilting and/or bowing of the resultant bottom electrode. Thus, a stable bottom electrode is provided.