Composite Work Function Layer for Ultrathin Gate Thickness Control
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Solution Overview
Problem
Conventional methods for forming metal work function layers in MOS devices, such as TiAlC, face challenges in achieving ultrathin thicknesses with controlled thicknesses of 10 angstroms or less due to deposition rate limitations, which affects the performance of n-type MOS devices.
Innovation Solution
The formation of work function layers involves using two or more deposition processes with different precursors for the same work function material, where the lower layer is formed with a precursor resulting in a higher aluminum percentage and greater per-cycle-thickness, and the upper layer with a lower aluminum percentage and smaller per-cycle-thickness, allowing for better control over the thickness and more aluminum at the interface with the high-k dielectric layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional deposition methods are used to form work function layers, then the deposition process is simple, but the thickness control precision deteriorates for ultrathin layers (10 angstroms or less)
Solution Approach 1:
The work function layer is divided into multiple sub-layers (first work function layer and second work function layer) deposited at different stages. The first layer is deposited before the high-k dielectric layer while the second layer is deposited after, allowing independent thickness control of each layer to achieve precise total thickness control for ultrathin structures
Solution Approach 2:
The first work function layer is deposited in advance before forming the high-k dielectric layer. This preliminary deposition establishes a foundation layer that can be precisely controlled in thickness before the main dielectric structure is built, enabling better overall thickness management
2Quantity of substance
If single precursor deposition is used, then the deposition process is fast, but the aluminum percentage at the interface with high-k dielectric deteriorates
Solution Approach 1:
Different regions of the work function layer are given different aluminum compositions. The first work function layer deposited before the high-k dielectric has a higher aluminum percentage to ensure optimal interface characteristics, while the second layer deposited after has different composition requirements, allowing local optimization of each region's properties
Solution Approach 2:
The aluminum percentage parameter is changed between different deposition stages. The first work function layer uses a higher aluminum percentage to maximize interface quality with the high-k dielectric, while subsequent layers can use adjusted aluminum percentages to balance interface quality with deposition efficiency and overall device performance
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 enables the formation of ultrathin work function layers with improved performance by ensuring a high aluminum atomic percentage at the interface, enhancing the device's characteristics and facilitating accurate thickness control.
Implementation Method 1
depositing a first aluminum-containing work function layer using a first aluminum-containing precursor, wherein the first aluminum-containing work function layer is over the gate dielectric layer; depositing a second aluminum-containing work function layer using a second aluminum-containing precursor different from the first aluminum-containing precursor
Data Source
AI summary
A method includes forming a gate dielectric layer on a semiconductor region, and depositing a first aluminum-containing work function layer using a first aluminum-containing precursor. The first aluminum-containing work function layer is over the gate dielectric layer. A second aluminum-containing work function layer is deposited using a second aluminum-containing precursor, which is different from the first aluminum-containing precursor. The second aluminum-containing work function layer is deposited over the first aluminum-containing work function layer. A conductive region is formed over the second aluminum-containing work function layer.