High-k Gate Stack Plasma Tuning for Precise MOS Threshold Voltage
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Solution Overview
Problem
Conventional methods for forming Metal-Oxide-Semiconductor (MOS) devices, such as FinFETs, face challenges in accurately adjusting threshold voltages, requiring thermal anneal processes and work-function metal adjustments, which are inefficient and limited in precision.
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 through the trapping of charges in high-k dielectric layers, while protecting underlying metal layers from plasma effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional thermal anneal process with ammonia is used to change threshold voltage, 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 the nitrogen flow rate parameter in the plasma process, the patent achieves precise threshold voltage adjustment to intended values, resolving the imprecision of conventional thermal anneal while maintaining manufacturing feasibility
Solution Approach 2:
The patent substitutes the thermal chemical process (thermal anneal with ammonia) with a plasma-based process. This replacement enables more precise control over threshold voltage adjustment by leveraging plasma chemistry and nitrogen flow rate control, achieving the intended voltage values that were impossible with conventional thermal methods
2Productivity
If thermal anneal process is performed to adjust threshold voltage, then threshold voltage can be changed, but additional work-function metal adjustments are required
Solution Approach 1:
The patent merges multiple functions into a single plasma treatment process: it simultaneously adjusts the threshold voltage to intended values and modifies the high-k dielectric layer properties. This consolidation eliminates the need for separate work-function metal adjustments, reducing process complexity and improving manufacturing efficiency
Solution Approach 2:
The plasma treatment process with controlled nitrogen flow rates serves multiple purposes: it adjusts threshold voltage precisely, modifies dielectric layer composition, and optimizes device performance characteristics. This multi-functional approach replaces the need for multiple specialized process steps, including separate work-function metal adjustments
3Ease of manufacture
If conventional plasma ashing is used to remove etching mask, then mask removal is achieved, but underlying metal layers are oxidized
Solution Approach 1:
The patent employs plasma treatment in a nitrogen-dominated environment that creates an inert chemical atmosphere. This inert plasma environment effectively removes the etching mask through ashing while preventing oxidation of the underlying metal layers, as the nitrogen-based plasma does not promote oxidative reactions that would damage the metal
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 precise and independent adjustment of threshold voltages in MOS devices, reducing oxidation of metal layers and improving manufacturing efficiency by eliminating the need for thermal nitridation processes, thereby enhancing the control over device performance.
Implementation Method 1
The meta stable plasma may be generated by introducing a process gas including nitrogen and helium into a reaction chamber
Implementation Method 2
adjustment of the threshold voltage may be achieved by exposing the high-k dielectric layer to the meta stable plasma
Implementation Method 3
generating the meta stable plasma may include introducing a process gas including nitrogen and helium into a reaction chamber
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.