Metal Gate Transistor Contact Plug Alignment via Etch Stop
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Solution Overview
Problem
Existing methods for fabricating contact plugs in metal gate transistors face challenges such as low product yield due to alignment accuracy issues and increased process costs, particularly in scaling down MOSFET devices, where short circuits between the metal gate and contact plugs are common, and improving alignment precision exacerbates these problems.
Innovation Solution
The method involves forming a dummy gate structure and etch stop sidewalls on a semiconductor substrate, followed by removing the dummy gate to create a trench, which is then filled with a high-k dielectric layer, work function layer, and metal gate, with an etch stop layer and contact plug formed to electrically connect to source/drain regions, reducing the need for precise alignment and increasing yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the size of the via and the overlay offset are reduced to improve device yield, then device yield is improved, but process cost increases
Solution Approach 1:
The patent introduces an intermediary layer (mandrel structure) between the contact plug formation process and the metal gate structure. This mandrel structure serves as a mediator that defines the contact plug position independently of the metal gate alignment, thereby improving device yield without requiring reduced via size or overlay offset that would increase process cost.
2Reliability
If precise alignment is used to prevent short circuits between metal gate and contact plug, then device yield is improved, but manufacturing complexity increases
Solution Approach 1:
The patent segments the alignment function into two independent parts: the mandrel structure defines contact plug position, and the metal gate structure is formed separately. This segmentation eliminates the need for precise alignment between contact plugs and metal gate, reducing manufacturing complexity while maintaining device yield.
Solution Approach 2:
The mandrel structure is formed in advance as a preliminary structure that pre-defines the contact plug position. This preliminary action allows subsequent contact plug formation to be performed without requiring precise alignment to the metal gate, thereby reducing alignment precision requirements and manufacturing complexity.
Data Source
AI summary
A metal gate transistor is provided. The metal gate transistor includes a semiconductor substrate; a metal gate structure formed on the semiconductor substrate; source/drain regions formed in the semiconductor substrate on sides of the metal gate structure; an etch stop layer formed on a top surface of the metal gate structure with a top surface leveled with a top surface of the first dielectric layer; an etch stop sidewall formed on each side of the metal gate structure with a top surface leveled with the top surface of the first dielectric layer; and a contact plug formed in the first dielectric layer to electrically connect to each source/drain region formed in the semiconductor substrate.