Nitrided High-k Gate Insulator for MIS Transistor Leakage
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Solution Overview
Problem
In semiconductor devices with MIS transistors, the use of high-k gate insulators faces challenges such as increased leakage current and reduced reliability due to thin gate insulators, especially when the gate length is 10 nm or less, where the presence of a process-induced oxide film affects the equivalent silicon oxide thickness and transistor characteristics.
Innovation Solution
A gate insulator structure is implemented with a silicon oxide film and a high-k film, where the high-k film contains more nitrogen at the lateral sides and upper surfaces, forming a nitrided region that prevents the formation of a process-induced oxide film, thereby enhancing the reliability and characteristics of the MIS transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the gate insulator is made thinner to improve transistor scaling, then the device size is reduced, but leakage current increases due to direct tunneling
Solution Approach 1:
The gate insulator uses a composite structure combining silicon oxide film and high-k film (such as HfO2, HfAlO3, or HfSiO3). This composite material approach allows the physical thickness to be increased while maintaining a low equivalent oxide thickness (EOT), thereby reducing direct tunneling leakage current while still achieving thin effective insulation.
Solution Approach 2:
The invention changes the dielectric constant parameter by introducing high-k materials with dielectric constants significantly higher than silicon oxide. This allows the physical thickness to be increased by a factor of 2-5 times while maintaining the same EOT, thus reducing leakage current without sacrificing gate control.
2Length of moving object
If the gate insulator thickness is reduced to improve transistor performance, then the ON current is improved, but depletion in the gate electrode near interfaces becomes more apparent
Solution Approach 1:
The composite gate insulator structure with high-k film provides sufficient physical thickness to reduce interface depletion effects while maintaining low EOT for good gate control. This resolves the contradiction between thin effective thickness for performance and thick physical thickness for reducing depletion.
3Ease of manufacture
If a process-induced oxide film is present at the gate insulator interface, then the manufacturing process is simplified, but the equivalent silicon oxide thickness increases and transistor characteristics deteriorate
Solution Approach 1:
The high-k film is deposited directly on the silicon oxide film before any gate electrode formation. This preliminary action prevents process-induced oxide formation at the critical interface during subsequent processing steps, maintaining precise EOT control while simplifying the overall process by avoiding additional interface treatment steps.
4Length of moving object
If the gate length is reduced to 10 nm or less to improve device scaling, then the transistor density is increased, but short-channel effects become more significant
Solution Approach 1:
The high-k gate insulator provides strong gate control over the channel even at 10 nm or less gate length. The high dielectric constant enables sufficient electric field penetration and control, suppressing short-channel effects while allowing aggressive scaling for high device density.
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 improves the reliability and characteristics of MIS transistors by reducing the equivalent oxide thickness, suppressing short-channel effects, and increasing the on/off current ratio, while maintaining high mobility and reducing power consumption.
Implementation Method 1
using materials having high permittivity for gate insulator is studied... an insulating film having higher permittivity obtained by adding nitride to a silicon oxide film... a high dielectric film which is so-called high-k film
Implementation Method 2
the high-k film contains more nitrogen at the lateral sides and upper surfaces, forming a nitrided region that prevents the formation of a process-induced oxide film
Data Source
AI summary
In a MIS transistor of which gate length is 10 nm or less, a gate insulator comprising a silicon oxide film formed on a silicon substrate and a high-k film formed on the silicon oxide film has a nitrided region including more nitrogen at the lateral side than at the central side in the gate-length direction, and including more nitrogen at the upper side than at the lower side in the film thickness direction. The reliability and characteristics of a MIS transistor using a gate insulator including a high-k (high dielectric constant) film is enhanced.