TiAlN Gate Electrode Work Function Stability
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Solution Overview
Problem
Existing semiconductor technologies face challenges in achieving a stable and high effective work function for metal nitride films used in gate electrodes, particularly for P-type MOSFETs, due to variations in work function caused by diffusion and poor heat resistance, and lack optimal film composition and crystal orientation for high permittivity gate insulating films.
Innovation Solution
A metal nitride film with specific molar fractions of Ti, Al, and N, where (N/(Ti+Al+N)) is 0.53 or more, (Ti/(Ti+Al+N)) is 0.32 or less, and (Al/(Ti+Al+N)) is 0.15 or less, is used as the gate electrode, combined with a high permittivity insulating film, to maintain a high effective work function and improve thermal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal nitride film is used as gate electrode to achieve high work function, then the work function can be adjusted for P-type MOSFETs, but the work function varies due to cross reaction with gate insulating film or poly-silicon in heat treating process
Solution Approach 1:
The patent uses a laminate structure combining TiN and TaN metal nitride films. TiN provides high work function (4.8 eV or more) suitable for P-type MOSFETs, while TaN layer suppresses Si diffusion from poly-silicon to TiN during heat treatment. This composite structure maintains stable work function by preventing harmful cross-reactions between the gate electrode and gate insulating film.
Solution Approach 2:
The TaN film acts as an intermediary barrier layer between the TiN gate electrode and the poly-silicon gate insulating film. This intermediate layer prevents direct contact and cross-reactions, blocking Si diffusion from poly-silicon to TiN during thermal processes, thereby maintaining work function stability.
2Reliability
If TiN is formed by CVD method to achieve high work function, then work function of 4.8 eV or more can be obtained, but the number of processes increases and EOT varies due to oxygen hole formation in gate insulating film
Solution Approach 1:
The patent combines multiple functions into a single TaN layer: it serves as part of the gate electrode structure, provides diffusion barrier functionality, and prevents oxygen hole formation in the gate insulating film. This merging of functions reduces the total number of separate process steps while achieving the desired work function and EOT stability.
Solution Approach 2:
The patent converts the potential harm of heat treatment processes (which cause oxygen hole formation and EOT variation) into a benefit by using the TaN layer to protect the gate insulating film. The TaN barrier prevents oxygen diffusion and hole formation, turning a problematic thermal process into a controlled step that maintains EOT stability.
3Reliability
If TiAlN is used as gate electrode to achieve high work function, then work function can be increased by Al diffusion, but phase separation occurs and excessive Al diffuses into gate insulating film causing EOT variation
Solution Approach 1:
The patent extracts the Al diffusion function from the gate electrode structure itself and places it in a dedicated TaN barrier layer. By separating the work function provision (TiN) from the diffusion control (TaN), the invention prevents excessive Al diffusion into the gate insulating film while maintaining high work function, thus stabilizing EOT.
Solution Approach 2:
The patent changes the material parameters by selecting specific metal nitride films with appropriate properties: TiN for high work function and TaN for low Al diffusion. This parameter selection optimizes both work function enhancement and EOT stability by controlling the diffusion characteristics of each layer.
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 solution provides a metal nitride film with a high effective work function suitable for P-type channel MOSFETs, enhancing erasing characteristics and retention in nonvolatile elements while maintaining low leak current and EOT stability even after annealing.
Implementation Method 1
the work function of the gate electrode... it is necessary to use a material having a work function of the Si mid gap (4.6 eV) or less... for P-type MOSFETs, it is necessary to use a material having the work function of the Si mid gap (4.6 eV) or more
Implementation Method 2
gate leak current is reduced by thickening a physical film thickness using a high permittivity material as the gate insulating film
Implementation Method 3
the work function of the metal film varies by the cross reaction with the gate insulating film or the poly-silicon in a heat treating process
Data Source
AI summary
The present invention provides a metal nitride film that realizes an intended effective work function (for example, a high effective work function) and has EOT exhibiting no change or a reduced change, a semiconductor device using the metal nitride film, and a manufacturing method of the semiconductor device. The metal nitride film according to an embodiment of the present invention contains Ti, Al and N, wherein the metal nitride film has such molar fractions of Ti, Al and N as (N/(Ti+Al+N)) of 0.53 or more, (Ti/(Ti+Al+N)) of 0.32 or less, and (Al/(Ti+Al+N)) of 0.15 or less.