Tapered Metal Gate Structure for Void-Free Deposition
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Solution Overview
Problem
In the fabrication of metal gate structures for integrated circuits, particularly in the 'gate last' process, voiding occurs due to difficulties in depositing metal into shrinking trenches, leading to incomplete filling and performance degradation as transistor gate lengths decrease.
Innovation Solution
Modifying the trench profile to have a wider top portion than bottom portion, allowing for a tapered metal gate electrode formation that facilitates easier deposition and reduces void formation during the metal gate formation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the trench size is reduced to accommodate smaller gate lengths, then the device scaling is improved, but the metal deposition becomes increasingly difficult and void formation increases
Solution Approach 1:
The patent applies asymmetry by modifying the trench profile from a symmetric rectangular shape to an asymmetric tapered shape. The trench has a wider opening at the top and a narrower bottom, creating an asymmetric geometry that facilitates metal deposition. This asymmetric profile allows metal atoms to reach the trench bottom more easily during deposition, preventing void formation while maintaining scaled-down gate dimensions.
Solution Approach 2:
The patent changes the geometric parameters of the trench by introducing a tapered profile with specific angle constraints (between 5-45 degrees). This parameter modification transforms the trench from a vertical-walled structure to a tapered structure, fundamentally altering the deposition dynamics and enabling complete metal filling even at reduced gate lengths.
2Area of moving object
If the trench width is reduced for smaller transistors, then the device density is improved, but the metal gate filling becomes incomplete due to voiding
Solution Approach 1:
The asymmetric tapered profile widens the trench opening relative to the bottom width, creating a funnel-like structure. This asymmetry allows metal to be deposited from the wider top opening and gradually fill the trench without forming voids, ensuring complete filling even when the overall trench dimensions are reduced for higher device density.
Solution Approach 2:
The tapered trench profile introduces curvature to the trench walls, transitioning from vertical straight lines to angled surfaces. This curved geometry facilitates metal atom trajectories during deposition, allowing metal to conformally coat the trench walls and bottom without creating voids, thereby maintaining gate structure integrity.
3Device complexity
If a vertical trench profile is used for simplicity, then the fabrication process is simplified, but voiding occurs during metal deposition into the trench
Solution Approach 1:
While the tapered profile adds some geometric complexity, it resolves the metal deposition problem by creating an asymmetric funnel shape. The additional complexity in profile formation is offset by the elimination of void-related rework and the ability to use simpler deposition parameters, ultimately simplifying the overall fabrication process.
Solution Approach 2:
The trench profile is pre-formed with a tapered geometry before metal deposition begins. This preliminary action of creating the asymmetric profile ensures that subsequent metal deposition proceeds without void formation, eliminating the need for complex deposition control or post-deposition void repair processes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The modified trench profile enables complete filling of the trench with metal, minimizing voids and maintaining stress and performance of the transistor, thus improving the reliability of the gate structure.
Implementation Method 1
depositing a metal layer into the trench
Data Source
AI summary
A device having a gate where the profile of the gate provides a first width at a top region and a second width at a bottom region is described. The gate may include tapered sidewalls. The gate may be a metal gate structure.