MRAM Top Electrode Contact Hole Taper for Uniform MTJ Landing
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Solution Overview
Problem
The Magnetic Tunnel Junction (MTJ) in existing MRAM technologies faces issues of poor performance and metal pollution due to over-etching during the formation of top electrode contact holes, leading to uncontrollable and non-uniform landing on the MTJ post.
Innovation Solution
A semiconductor structure and manufacturing method that involves forming a top electrode contact hole with a unique tapered design, where the radial width of the second portion in contact with the top electrode decreases with increasing depth, using a combination of dielectric layers and etching techniques to improve controllability and prevent over-etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional etching is used to form top electrode contact holes, then the contact holes can be formed quickly, but the radial width becomes uncontrollable leading to over-etching and metal pollution
Solution Approach 1:
The patent applies parameter changes by modifying the etching conditions through a tapered etching process. The etching parameters are changed progressively through multiple etching steps with different conditions, allowing the radial width to be controlled while maintaining etching efficiency. The tapered shape is achieved by adjusting etching depth and width parameters in a controlled sequence.
Solution Approach 2:
The etching process is segmented into multiple distinct steps: a first etching step to form an initial contact hole, and a second etching step to create the tapered portion. This segmentation allows each step to be optimized independently, with the first step focusing on penetration speed and the second step focusing on precision and taper formation, thereby resolving the contradiction between productivity and precision.
2Reliability
If over-etching is performed to ensure contact hole formation, then the contact holes can be formed completely, but metal pollution and performance degradation occur
Solution Approach 1:
The patent applies preliminary action by forming a tapered portion in the contact hole before completing the full etching process. This preliminary tapered structure serves as a guide and constraint for the subsequent etching, preventing the etching from proceeding too far and causing over-etching. The tapered portion is created in advance to control the final contact hole dimensions and prevent metal pollution.
Solution Approach 2:
The tapered etching process incorporates feedback control where the formation of the tapered portion provides visual and structural feedback on the etching progress. This feedback mechanism allows real-time monitoring and adjustment of the etching process, ensuring that the contact hole is formed completely without excessive etching that would cause metal pollution.
3Object-generated harmful factors
If the contact hole radial width is reduced to prevent over-etching, then metal pollution is reduced, but the dimensional tolerance and controllability are worsened
Solution Approach 1:
The patent applies asymmetry by creating a tapered contact hole with different radial widths at different depths. The contact hole has a larger radial width at the top and a smaller radial width at the bottom, forming an asymmetric tapered shape. This asymmetric structure provides dimensional tolerance at the top for alignment while maintaining precise control at the bottom to prevent metal pollution, thereby resolving the contradiction between tolerance and precision.
Data Source
AI summary
A semiconductor structure includes: a Magnetic Random Access Memory (MRAM) cell, including a bottom electrode, a Magnetic Tunnel Junction (MTJ) stack and a top electrode; an insulating layer covering a sidewall partially and a top surface of the MRAM cell; a first dielectric layer, a stop layer and a second dielectric layer sequentially stacked on the insulating layer; and a top electrode contact hole penetrating through the second dielectric layer, the stop layer, the first dielectric layer and the insulating layer, and extending to the top electrode, where the top electrode contact hole includes a first portion and a second portion connected with each other in the stop layer, and a radial width of the second portion in contact with the top electrode is gradually decreased with an increase in a depth of the top electrode contact hole. Method for manufacturing the structure and semiconductor memory are also provided.