Work Function Metal Patterning Using Isolation Pillars
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Solution Overview
Problem
In integrated circuits, the challenge lies in accurately patterning work function metals between adjacent active nanostructures, particularly when the distance between them is less than 45 nanometers, as conventional methods lead to overetching and mask edge placement errors, compromising the integrity of the devices.
Innovation Solution
The introduction of an isolation pillar between adjacent active nanostructures prevents overetching by creating a discontinuity in the metal layer, allowing for precise placement of the mask and ensuring that the work function metal on one active nanostructure is not removed during the etching process, while enabling the deposition of different work function metals for adjacent transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching methods are used to remove metal layers between adjacent active nanostructures, then the etching process can remove the metal layer, but overetching occurs that compromises the integrity of the devices when the distance between them is less than 45 nanometers
Solution Approach 1:
An isolation pillar is introduced as an intermediary structure between adjacent active nanostructures. This pillar acts as a physical barrier that prevents the etching process from over-removing metal layers and compromising device integrity. The isolation pillar is formed in the space between nanostructures and extends through the metal layers, creating a discontinuity that stops lateral etching propagation while allowing precise metal patterning on either side.
2Productivity
If the space between adjacent active nanostructures is reduced to increase device density, then more devices can be integrated, but mask edge placement errors increase making it difficult to accurately pattern different work function metals
Solution Approach 1:
The isolation pillar serves as a mediator that decouples the mask placement requirements from the narrow spacing between adjacent nanostructures. By providing a physical reference structure, the pillar allows masks to be accurately positioned relative to the pillar rather than requiring sub-45nm placement precision between nanostructures, thereby enabling different work function metals to be patterned even at reduced pitch.
Solution Approach 2:
The solution moves the reference framework from the horizontal plane (requiring precise lateral mask placement between nanostructures) to the vertical dimension (using the isolation pillar height as a reference). The mask can be placed relative to the pillar's vertical position rather than requiring precise horizontal alignment, effectively trading a difficult lateral placement problem for a more manageable vertical reference.
3Adaptability or versatility
If different work function metals are deposited for NFET and PFET devices, then the threshold voltage can be tuned correctly, but the etching process removes the first metal from the second active nanostructure instead of preserving it
Solution Approach 1:
The isolation pillar creates a segmentation or discontinuity in the metal layers between adjacent active nanostructures. This segmentation allows the first metal to be selectively removed from the second nanostructure's region while being preserved on the first nanostructure. The pillar divides the continuous metal layer into separate segments that can be independently processed, enabling selective removal based on lateral position rather than requiring the metal layer to be continuous across both devices.
Data Source
AI summary
A method includes forming an isolation pillar between first and second active nanostructures for adjacent FETs. A first WFM for one FET is deposited over the first active nanostructure, the pillar and the second active nanostructure. The first WFM is removed from a part of the pillar. The removing creates a discontinuity in the first WFM over the first active nano structure from the first WFM over the second active nanostructure but leaves the first WFM on sidewalls of the pillar. When the first WFM surrounding the second active nanostructure is removed, the pillar and the discontinuity in the first metal on the part of the pillar prevent the etching from reaching and removing the first WFM on the first active nanostructure. Depositing a second WFM surrounding the second active nanostructure and the isolation pillar forms part of the gate for the second FET and couples the FETs together.