TiAl Work Function Layer Gradient for Low-Leakage Gate Stacks
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Solution Overview
Problem
As transistors in semiconductor integrated circuits (ICs) shrink in size, it becomes challenging to reduce the threshold voltage without increasing gate leakage current and degrading carrier mobility, especially when using aluminum-containing metal alloy layers in the gate stack.
Innovation Solution
The solution involves forming an N-type transistor with a gate dielectric layer and a gate electrode, where the work function layer of the gate electrode includes a titanium aluminum (TiAl) metal alloy layer with a non-uniform aluminum concentration that increases from the bottom to the top surface, thereby modulating the threshold voltage and reducing aluminum diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If aluminum-containing metal alloy layers are used in the gate stack to reduce threshold voltage, then the threshold voltage is reduced, but gate leakage current increases
Solution Approach 1:
The patent applies local quality by creating a work function layer with non-uniform aluminum concentration distribution. The aluminum concentration is higher at the top surface and lower at the bottom surface in contact with the channel. This gradient structure allows the top portion to provide strong threshold voltage reduction while the bottom portion minimizes aluminum diffusion into the channel and reduces gate leakage current, thus resolving the contradiction between threshold voltage reduction and leakage current control.
Solution Approach 2:
The patent changes the concentration parameter of aluminum within the work function layer to resolve the contradiction. By adjusting the aluminum concentration profile from uniform to non-uniform (higher at top, lower at bottom), the patent optimizes both threshold voltage reduction and gate leakage current minimization simultaneously.
2Power
If aluminum-containing metal alloy layers are used in the gate stack to reduce threshold voltage, then the threshold voltage is reduced, but carrier mobility degrades
Solution Approach 1:
The patent uses local quality by implementing a non-uniform aluminum concentration profile where the bottom portion of the work function layer has lower aluminum concentration. This reduces aluminum diffusion into the channel region, thereby minimizing carrier mobility degradation while the top portion with higher aluminum concentration maintains effective threshold voltage reduction.
Solution Approach 2:
The patent changes the aluminum concentration parameter within the work function layer, creating a gradient where concentration increases from bottom to top. This parameter modification allows simultaneous optimization of threshold voltage and carrier mobility by controlling aluminum distribution.
3Ease of manufacture
If uniform aluminum concentration is used in the work function layer, then manufacturing is simplified, but aluminum diffusion into the channel increases
Solution Approach 1:
The patent applies local quality by creating spatial variation in aluminum concentration within the work function layer. The bottom portion has lower aluminum concentration to prevent diffusion into the channel, while the top portion has higher concentration for effective threshold voltage control. This non-uniform distribution is achieved through controlled deposition processes.
Solution Approach 2:
The patent implements preliminary action by pre-establishing the non-uniform aluminum concentration profile during work function layer formation. By controlling the deposition process to create the gradient structure before device operation, the patent prevents aluminum diffusion issues from the outset while maintaining manufacturing feasibility.
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 effectively reduces the threshold voltage of transistors while minimizing gate leakage current and enhancing carrier mobility, thus improving the overall performance of semiconductor devices.
Implementation Method 1
the work function layer of the gate electrode includes a metal alloy layer containing aluminum... modulating the threshold voltage
Implementation Method 2
a concentration of aluminum in a first portion of the aluminum-containing work function layer is different than the concentration of aluminum in a second portion... reducing aluminum diffusion
Data Source
AI summary
Semiconductor structures and methods are provided. An exemplary method according to the present disclosure includes forming a dielectric layer over a portion of a substrate, forming an aluminum-containing work function layer over the dielectric layer, where a concentration of aluminum in a first portion of the aluminum-containing work function layer is different than the concentration of aluminum in a second portion of the aluminum-containing work function layer, and forming a metal layer over the aluminum-containing work function layer.