Self-Aligned Bottom Electrode Fabrication for Phase Change Memory
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Solution Overview
Problem
In the fabrication of semiconductor memory devices, the removal of sacrificial layers can lead to increased contact resistance and set fails due to direct contact between the access device and the lower electrode, resulting from the loss of conductive layers during the patterning process.
Innovation Solution
A protection layer is formed on the edge of the first conductive layer to a predetermined thickness, which is not removed during the sacrificial layer removal process, maintaining the underlying structure and ensuring stable electric contact between the access device and the lower electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the sacrificial layer is removed to enable lower electrode formation, then the lower electrode can be formed in a self-aligned manner, but the conductive layer is lost and contact resistance increases
Solution Approach 1:
The conductive layer is segmented into two functional parts: a first conductive layer that remains as the final contact layer, and a second conductive layer that serves as a sacrificial element. This segmentation allows the second layer to be selectively removed while preserving the first layer, thereby maintaining both self-alignment precision and low contact resistance.
Solution Approach 2:
The first conductive layer acts as an intermediary protective element between the access device and the lower electrode. It preserves the conductive path during the sacrificial layer removal process, preventing direct contact between the access device and lower electrode that would otherwise cause high contact resistance.
2Ease of manufacture
If the sacrificial layer is removed using phosphoric acid, then the sacrificial layer can be selectively removed, but the first conductive layer is thinned and lost in some cells
Solution Approach 1:
Different regions of the conductive structure are given different qualities: the first conductive layer is designed with phosphoric acid resistance to protect it during removal, while the second conductive layer is designed to be selectively removable. This local differentiation in chemical resistance enables selective removal without compromising the first layer's integrity.
Solution Approach 2:
The first conductive layer is formed and positioned in advance before the sacrificial layer removal process. This preliminary action ensures that the protective conductive layer is already in place to prevent direct contact and maintain alignment, and its phosphoric acid resistance is established beforehand to prevent thinning during removal.
3Device complexity
If the access device and lower electrode are formed in a self-aligned manner, then manufacturing complexity is reduced, but conductive layer loss occurs during patterning
Solution Approach 1:
The second conductive layer is designed as a disposable sacrificial element that is intentionally removed during manufacturing. It serves its purpose of maintaining alignment and structure during processing, then is selectively removed to complete the self-aligned structure without causing conductive layer loss.
Solution Approach 2:
The conductive system is segmented into permanent (first conductive layer) and temporary (second conductive layer) components. This segmentation allows the temporary component to be used for alignment during patterning without risking loss of the permanent conductive material, as the two are chemically differentiated.
Data Source
AI summary
A semiconductor memory device and a fabrication method thereof capable of improving electric contact characteristic between an access device and a lower electrode are provided. The semiconductor memory device includes an access device formed in a pillar shape on a semiconductor substrate, a first conductive layer formed over the access device, a protection layer formed on an edge of the first conductive layer to a predetermined thickness, and a lower electrode connected to the first conductive layer.