FinFET Gate Stack Plasma Ashing for Precise Threshold Voltage Tuning
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Solution Overview
Problem
Conventional methods for forming Metal-Oxide-Semiconductor (MOS) devices struggle to accurately adjust threshold voltages of FinFETs, requiring additional steps like thermal anneal and work-function metal adjustments, which are inefficient.
Innovation Solution
The use of meta stable plasma treatment during the ashing process to adjust threshold voltages by controlling the nitrogen flow rate, allowing for precise adjustment of flat-band and threshold voltages without affecting adjacent transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional thermal anneal process with ammonia is used to change threshold voltages, then threshold voltage can be changed, but it is impossible to adjust threshold voltages to intended values precisely
Solution Approach 1:
The patent changes the fundamental parameter of the treatment process from thermal anneal with ammonia to plasma treatment with controlled nitrogen flow rates. By adjusting plasma power, pressure, and nitrogen flow rate parameters, the threshold voltage can be precisely tuned to intended values without requiring additional process steps or multiple work-function metal layers.
Solution Approach 2:
The patent replaces the thermal chemical process (thermal anneal with ammonia) with a plasma-based process. This substitution enables more precise control over threshold voltage adjustment through electromagnetic field control in plasma, eliminating the limitations of conventional thermal methods.
2Manufacturing precision
If different work-function metals and thickness adjustments are adopted to achieve threshold voltage adjustment, then intended threshold voltages can be achieved, but the process complexity increases
Solution Approach 1:
The patent extracts the threshold voltage adjustment function from the work-function metal selection and thickness control approach. By using plasma treatment with nitrogen, the adjustment capability is separated from the metal layer structure, allowing threshold voltage tuning without changing the metal stack configuration.
Solution Approach 2:
The plasma treatment process with nitrogen serves multiple functions: it acts as both the primary gate dielectric formation method and the threshold voltage adjustment mechanism. This multi-functionality eliminates the need for separate work-function metal adjustments and simplifies the overall device structure.
3Ease of manufacture
If conventional plasma ashing is used to remove BARC, then BARC removal is achieved, but threshold voltage cannot be adjusted and metal layers may be oxidized
Solution Approach 1:
The patent merges the BARC removal function and the threshold voltage adjustment function into a single plasma treatment step. By introducing nitrogen during plasma ashing, the process simultaneously removes BARC and adjusts threshold voltage, eliminating the need for separate treatment steps.
Solution Approach 2:
Nitrogen acts as an intermediary substance in the plasma process. It serves as both the ashing agent for BARC removal and the medium for threshold voltage adjustment through nitrogen incorporation into the gate dielectric, protecting metal layers from oxidation while enabling precise voltage control.
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
Enables independent adjustment of threshold voltages in FinFETs with improved precision and reduced oxidation of metal layers, eliminating the need for thermal nitridation and maintaining stability across different ashing durations.
Implementation Method 1
The use of meta stable plasma treatment during the ashing process to adjust threshold voltages by controlling the nitrogen flow rate
Implementation Method 2
eliminating the need for thermal nitridation
Implementation Method 3
reduced oxidation of metal layers
Data Source
AI summary
A method includes forming a first high-k dielectric layer over a first semiconductor region, forming a second high-k dielectric layer over a second semiconductor region, forming a first metal layer comprising a first portion over the first high-k dielectric layer and a second portion over the second high-k dielectric layer, forming an etching mask over the second portion of the first metal layer, and etching the first portion of the first metal layer. The etching mask protects the second portion of the first metal layer. The etching mask is ashed using meta stable plasma. A second metal layer is then formed over the first high-k dielectric layer.