U-Shaped Metal Gate Work Function Layer Fabrication
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Solution Overview
Problem
Conventional semiconductor devices with poly-silicon gates face performance issues due to boron penetration and depletion effects, leading to inferior device performance and complex process control challenges in dual metal gate technologies, particularly in gate last processes where high thermal budgets and material precision are required.
Innovation Solution
A method for manufacturing semiconductor devices with metal gates that involves forming U-shaped work function layers through an O2 ambient treatment, dry etching, and wet etching processes to improve layer quality and facilitate easy fabrication, including a hardening process for the work function layer and a pull back step to remove the upper portion, allowing for high-quality U-shaped structures and improved gap filling profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional poly-silicon gate is used, then process simplicity is maintained, but device performance deteriorates due to boron penetration and depletion effects
Solution Approach 1:
The patent changes the material parameter of the gate electrode from poly-silicon to metal (such as tungsten, titanium nitride, or tantalum nitride), fundamentally altering the electrical and thermal properties to eliminate boron penetration and depletion effects while maintaining process feasibility through the developed U-shaped structure formation method
2Reliability
If dual metal gate method is adopted, then device performance is improved, but process complexity increases
Solution Approach 1:
The patent segments the work function layer into two distinct parts: a first work function layer forming the U-shaped structure in the trench, and a second work function layer formed subsequently. This segmentation allows different regions to have optimized work functions for NMOS and PMOS devices while using a unified process flow, thereby reducing overall process complexity
Solution Approach 2:
The patent performs preliminary actions by forming the U-shaped first work function layer with specific etch selectivity characteristics before forming the second work function layer. The O2 ambient treatment and dry etching processes create a structure that is pre-configured for subsequent selective removal and replacement, simplifying the overall dual metal gate formation process
3Adaptability or versatility
If gate last process is used, then material choices are increased, but process integrity requirements become more stringent
Solution Approach 1:
The patent applies local quality by creating a U-shaped work function layer structure with specific spatial distribution - the first work function layer is positioned at the bottom and sides of the trench while the second work function layer fills the upper portion. This local structural differentiation enables precise control of electrical properties in different regions while maintaining overall process robustness
Solution Approach 2:
The patent introduces an intermediary approach by using a sacrificial layer or spacer structure during the formation of the U-shaped work function layer. This intermediary element facilitates the creation of the complex U-shaped profile through standard etching processes, reducing the need for highly specialized process steps and thereby improving process integrity
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 method enables the fabrication of high-quality U-shaped work function layers that are easier to produce and improve the integrity and reliability of metal gates, reducing void defects and simplifying the fabrication process compared to conventional methods.
Implementation Method 1
the O2 ambient treatment is performed to improve its quality
Implementation Method 2
the first work function layer is subjected to a dry etching process, so the upper portion thereof can be removed easily
Implementation Method 3
the first work function layer is subjected to a dry etching process
Implementation Method 4
so the upper portion thereof can be removed easily by a wet etching process
Data Source
AI summary
A method of manufacturing a semiconductor device having a metal gate is provided. A substrate having a first conductive type transistor and a second conductive type transistor formed thereon is provided. The first conductive type transistor has a first trench and the second conductive type transistor has a second trench. A first work function layer is formed in the first trench. A hardening process is performed for the first work function layer. A softening process is performed for a portion of the first work function layer. A pull back step is performed to remove the portion of the first work function layer. A second work function layer is formed in the second trench. A low resistive metal layer is formed in the first trench and the second trench.