Cobalt Contact Plug Corrosion Protection in Semiconductor Devices
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Solution Overview
Problem
In semiconductor devices, the use of cobalt for contact-hole plugs, while reducing RC delay, is hindered by corrosion issues when tungsten is deposited using WF4 gas, which affects the performance and reliability of the interconnect structures.
Innovation Solution
A protective layer is formed over the cobalt layer to prevent corrosion from WF4 gas during tungsten deposition, ensuring the cobalt layer's integrity and facilitating the formation of reliable interconnects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cobalt is used for contact-hole plugs to reduce RC delay, then the electrical performance is improved, but the cobalt layer suffers corrosion when tungsten is deposited using WF4 gas
Solution Approach 1:
A protective layer is introduced as an intermediary between the cobalt layer and the WF4 gas environment. This protective layer acts as a barrier that prevents the corrosive WF4 gas from directly contacting the cobalt, thereby eliminating the corrosion issue while allowing the cobalt to maintain its low resistance properties for improved electrical performance.
Solution Approach 2:
The protective layer is formed over the cobalt layer before the tungsten deposition process begins. This preliminary protective action ensures that when WF4 gas is later introduced for tungsten deposition, the cobalt layer is already shielded and cannot be corroded, thus preserving the electrical performance benefits of cobalt throughout the subsequent processing steps.
2Reliability
If a protective layer is formed over the cobalt layer to prevent corrosion, then the cobalt layer integrity is maintained, but the device structure becomes more complex
Solution Approach 1:
The protective layer is applied locally and selectively only where the cobalt layer requires protection from corrosion, rather than uniformly across the entire device structure. This localized approach maintains cobalt layer integrity in critical areas while minimizing the overall structural complexity and avoiding unnecessary protective layers in areas where cobalt is not exposed to corrosive environments.
Data Source
AI summary
A method for forming a semiconductor device includes forming a gate structure on a substrate, and a doped source/drain region on each side of the gate structure; forming a first interlayer dielectric layer, the top surface of the first interlayer dielectric layer leveled with the top surface of the gate structure; forming a contact hole in the first interlayer dielectric layer on each side of the gate structure; forming a cobalt layer in the contact hole, the top surface of the cobalt layer lower than the top surface of the first interlayer dielectric layer; forming a protective layer to cover the cobalt layer, the top layer of the protective layer lower than the top surface of the first interlayer dielectric layer; and forming a second interlayer dielectric layer, the top surface of the second interlayer dielectric layer leveled with the top surface of the first interlayer dielectric layer.