Oxide Semiconductor Transistor Hydrogen Diffusion Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Oxide semiconductor transistors face challenges in maintaining stable electric characteristics due to hydrogen diffusion from gate insulating films, leading to degradation and variations in performance, particularly when used in large-sized glass substrates where heat treatment can cause impurity diffusion and shift the threshold voltage negatively.
Innovation Solution
A semiconductor device with a bottom-gate structure incorporating multiple gate insulating films, where a silicon nitride film and silicon oxynitride film are used to prevent hydrogen diffusion, and heat treatment at temperatures above 450°C is performed to reduce hydrogen concentration, combined with a high-density sputtering target and optimized deposition conditions to form a dense oxide semiconductor film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heat treatment is performed at high temperature (450°C or higher) to reduce hydrogen concentration in the oxide semiconductor film, then the electric characteristics stability is improved, but the hydrogen diffusion from the nitride insulating film may increase and cause degradation
Solution Approach 1:
Heat treatment is performed at a high temperature of 450°C or higher before forming the oxide semiconductor film to reduce the hydrogen concentration in the nitride insulating film in advance. This preliminary action prevents hydrogen diffusion into the oxide semiconductor film during subsequent processing, thereby maintaining electric characteristics stability without causing degradation.
Solution Approach 2:
The gate insulating film is divided into multiple layers: a nitride insulating film (first gate insulating film) and an oxide insulating film (second gate insulating film). This segmentation allows the nitride layer to be pre-treated to reduce hydrogen, while the oxide layer provides a protective barrier, thus resolving the contradiction between hydrogen reduction and preventing hydrogen diffusion.
2Reliability
If a nitride insulating film is used as the gate insulating film to provide good interface characteristics, then the transistor performance is improved, but hydrogen in the nitride film diffuses into the oxide semiconductor and causes threshold voltage shift and normally-on characteristics
Solution Approach 1:
The nitride insulating film undergoes heat treatment at 450°C or higher before the oxide semiconductor film is formed. This preliminary treatment removes or reduces hydrogen in the nitride film, preventing subsequent hydrogen diffusion into the oxide semiconductor that would cause threshold voltage shift and normally-on characteristics, while preserving the good interface characteristics.
Solution Approach 2:
An oxide insulating film is introduced as an intermediary layer between the nitride insulating film and the oxide semiconductor film. This oxide layer acts as a barrier that prevents hydrogen diffusion from the nitride film to the oxide semiconductor, while allowing the nitride film to maintain its beneficial interface characteristics.
3Reliability
If the oxide semiconductor film is formed after heat treatment at 450°C or higher, then hydrogen concentration is reduced and electric characteristics are stabilized, but the deposition process becomes more complex
Solution Approach 1:
The heat treatment step at 450°C or higher is merged with existing process steps (such as annealing or activation steps) to reduce hydrogen in the nitride insulating film. By combining multiple functions into a single heat treatment step, the process complexity is minimized while achieving the desired hydrogen reduction and electric characteristics stability.
Solution Approach 2:
The heat treatment at 450°C or higher serves multiple functions: it reduces hydrogen concentration in the nitride insulating film, improves the interface characteristics between insulating films, and stabilizes the oxide semiconductor film properties. This multi-functionality reduces the need for separate process steps, thereby managing complexity while achieving reliability.
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 results in a highly reliable semiconductor device with stable electric characteristics and reduced hydrogen-induced degradation, enabling the production of transistors with improved reliability and performance on large glass substrates.
Implementation Method 1
heat treatment is performed at a temperature of 450° C. or higher, preferably 650° C. or higher
Implementation Method 2
hydrogen is released from the nitride insulating film and diffuses into the oxide semiconductor film
Implementation Method 3
the hydrogen element bonds to oxygen in the oxide semiconductor film, so that H2O or the like formed in this manner is released
Implementation Method 4
it is preferable that a sputtering target which is polycrystalline and has a high relative density is used; the sputtering target is sufficiently cooled to room temperature
Data Source
AI summary
A highly reliable semiconductor device in which a transistor including an oxide semiconductor film has stable electric characteristics is manufactured. In the semiconductor device which includes an inverted-staggered transistor having a bottom-gate structure and being provided over a substrate having an insulating surface, at least a first gate insulating film and a second gate insulating film are provided between a gate electrode layer and an oxide semiconductor film, and heat treatment is performed at a temperature of 450° C. or higher, preferably 650° C. or higher, and then the oxide semiconductor film is formed. By the heat treatment at a temperature of 450° C. or higher before the formation of the oxide semiconductor film, diffusion of hydrogen elements into the oxide semiconductor film, which causes degradation or variations in electric characteristics of the transistor, can be reduced, so that the transistor can have stable electric characteristics.