GAA Transistor Work Function Layer Layout for Threshold Voltage Control
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Solution Overview
Problem
Existing GAA transistors face challenges in achieving desired threshold voltages due to difficulties in removing hard-to-remove work function layers between channel members, leading to incomplete removal and decreased performance.
Innovation Solution
The introduction of a sacrificial layer between channel members prevents the deposition of hard-to-remove work function layers, allowing for easy removal and enabling the formation of GAA transistors with specific threshold voltages by controlling the deposition of work function layers around each channel member.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If work function layers are deposited around channel members to control threshold voltage, then threshold voltage uniformity is improved, but removal difficulty increases and complete removal becomes challenging
Solution Approach 1:
The patent introduces a sacrificial layer that segments the space around channel members, creating distinct regions: areas where the work function layer can fully wrap around channel members (for uniform threshold voltage control) and areas where the sacrificial layer prevents deposition (for easy removal). This segmentation allows the work function layer to be deposited uniformly where needed while remaining removable where not needed.
Solution Approach 2:
The sacrificial layer acts as an intermediary element between the work function layer and the channel members. It mediates the deposition process by selectively blocking work function layer material from entering certain regions, thereby enabling controlled deposition patterns that achieve both uniformity and removability without direct conflict between these requirements.
2Reliability
If over-etching is used to remove work function layers completely, then removal completeness is improved, but damage to adjacent structures occurs
Solution Approach 1:
The sacrificial layer is deposited beforehand to pre-determine the final configuration of the work function layer. By performing this preliminary action, the patent eliminates the need for over-etching later, as the work function layer is already prevented from depositing in areas where it should not remain. This preliminary structuring ensures complete removal where needed without requiring aggressive etching that could damage adjacent structures.
Solution Approach 2:
The patent converts the potential harm of incomplete removal into a benefit by using the sacrificial layer to pre-control deposition. Instead of relying on aggressive removal processes that cause damage, the sacrificial layer ensures that the work function layer is never deposited in regions where it would need to be removed, thereby transforming the removal challenge into a controlled deposition pattern that is inherently complete and non-damaging.
3Reliability
If threshold voltage control is achieved through work function layer deposition, then device performance is improved, but process complexity increases due to multiple deposition and removal steps
Solution Approach 1:
The sacrificial layer serves as a process mediator that simplifies the overall fabrication sequence. By introducing this intermediate element, the patent converts a complex multi-step process involving deposition and aggressive removal into a more straightforward sequence where the sacrificial layer guides the deposition process itself, reducing the need for subsequent complex removal operations.
Solution Approach 2:
The process is segmented into distinct functional regions through the sacrificial layer, allowing different deposition outcomes in different areas. This segmentation enables a single deposition step to achieve both wrapped and non-wrapped configurations, thereby reducing process complexity compared to attempting uniform deposition followed by selective removal across the entire structure.
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
This approach facilitates the formation of GAA transistors with lower threshold voltages and improved threshold voltage uniformity, reducing the need for over-etching and enhancing yield by ensuring complete removal of work function layers without damaging adjacent structures.
Implementation Method 1
The introduction of a sacrificial layer between channel members prevents the deposition of hard-to-remove work function layers
Implementation Method 2
controlling the deposition of work function layers around each channel member
Data Source
AI summary
A semiconductor having a first gate-all-around (GAA) transistor, a second GAA transistor, and a third GAA transistor is provided. The first (GAA) transistor includes a first plurality of channel members, a gate dielectric layer over the first plurality of channel members, a first work function layer over the gate dielectric layer, and a glue layer over the first work function layer. The second GAA transistor include a second plurality of channel members, the gate dielectric layer over the second plurality of channel members, and a second work function layer over the gate dielectric layer, the first work function layer over and in contact with the second work function layer, and the glue layer over the first work function layer. The third GAA transistor includes a third plurality of channel members, the gate dielectric layer over the third plurality of channel members, and the glue layer over the gate dielectric layer.