L-Shaped Spacer for Vertical Transistor Gate Length Control
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Solution Overview
Problem
Conventional fabrication processes for vertical transistors result in significant variations in gate length, affecting device properties and performance.
Innovation Solution
The use of an L-shaped spacer is introduced to protect the gate region from subsequent etch and polish steps, ensuring precise control and repeatability in gate length by forming spacers with an L-shaped cross-section above the vertical channel fin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional fabrication processes are used for vertical transistors, then device scaling and transistor density are improved, but gate length variation increases
Solution Approach 1:
The spacer structure is formed in advance before the gate material deposition. The L-shaped spacer with its specific geometry (first portion extending from sidewall, second portion extending from top surface) is created as a preliminary structure that defines the eventual gate length boundaries. This preliminary action establishes precise dimensional constraints that guide subsequent gate formation processes, ensuring consistent gate length across devices while maintaining high transistor density.
2Reliability
If etch and polish steps are applied to the gate region, then device performance is improved, but gate length precision deteriorates
Solution Approach 1:
The L-shaped spacer structure is designed to preemptively counteract the harmful effects of etch and polish steps on gate length precision. The spacer's geometry (with portions extending from both sidewall and top surface) creates a protective framework that limits material removal during etching and polishing operations. This preliminary anti-action ensures that beneficial etch and polish steps improve device performance without compromising gate length precision.
3Reliability
If the gate stack extends beyond the channel fin base portion, then gate coverage is improved, but gate length control worsens
Solution Approach 1:
The spacer structure implements local quality by having different portions serve different functions: the first portion (extending from sidewall) provides lateral definition for gate length control, while the second portion (extending from top surface) ensures adequate gate coverage. This spatial differentiation of functions within the spacer structure allows simultaneous achievement of precise gate length control and sufficient gate coverage without compromise.
Data Source
AI summary
A transistor includes a vertical channel fin on a bottom source/drain region. The vertical channel fin includes a base portion and an upper portion. The base portion has a width greater than a width of the upper portion and a top surface height greater than a top surface height of the bottom source/drain region. A gate stack formed on sidewalls of the vertical channel fin. Spacers are formed above the gate stack, one above each sidewall of the vertical channel fin. A top source/drain region is formed between the spacers.