Oxide Semiconductor Doping Masking for Stable Normally-Off Transistors
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Solution Overview
Problem
Oxygen vacancies in the channel region of oxide semiconductor transistors lead to defects in electric characteristics, causing shifts in threshold voltage and normally-on characteristics, as well as instability under gate bias-temperature stress and light irradiation, affecting reliability and power consumption.
Innovation Solution
A method involving the formation of an insulating film over an oxide semiconductor film, with a buffer film and conductive film added to introduce oxygen and an impurity element, reducing oxygen vacancies and stabilizing the transistor characteristics by using the conductive film as a mask for impurity addition and heat treatment to move excess oxygen to the semiconductor film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oxygen is added to the oxide semiconductor film to reduce oxygen vacancies, then reliability and electric characteristic stability are improved, but additional process steps and device complexity increase
Solution Approach 1:
An insulating film containing excess oxygen is formed over the oxide semiconductor film before final transistor completion. This preliminary oxygen reservoir prevents oxygen vacancies during subsequent processing and operation, improving reliability without adding complex oxygen injection equipment.
Solution Approach 2:
The insulating film acts as an intermediary oxygen source between external oxygen supply and the oxide semiconductor film. It contains excess oxygen that can be supplied to the semiconductor film when needed, simplifying the overall device structure while ensuring oxygen availability.
2Ease of operation
If the channel region is kept free of impurity elements to maintain low resistance and normally-on characteristics, then ease of operation is improved, but manufacturing precision becomes more difficult due to the need to prevent impurity contamination
Solution Approach 1:
The insulating film is positioned specifically over the channel region to provide oxygen where needed, while impurity elements are intentionally added to source/drain regions. This local differentiation maintains low resistance where required while preventing channel degradation, balancing ease of operation with manufacturing precision.
Solution Approach 2:
The insulating film serves as a protective intermediary layer that prevents impurity contamination of the channel region during manufacturing processes. It acts as a barrier that allows oxygen diffusion to the channel while blocking harmful impurities, simplifying contamination control.
3Reliability
If a buffer film is formed over the insulating film to add oxygen, then oxygen vacancy reduction is improved, but device complexity and manufacturing steps increase
Solution Approach 1:
The insulating film performs multiple functions simultaneously: it serves as a gate insulator, an oxygen source to reduce vacancies, and a protective layer during processing. This multi-functionality eliminates the need for a separate buffer film, reducing device complexity while maintaining oxygen vacancy reduction benefits.
Solution Approach 2:
The oxygen supply function is extracted from a dedicated buffer film structure and integrated into the gate insulator itself. The insulating film contains excess oxygen that can be supplied to the semiconductor film, eliminating the need for additional buffer film layers while achieving the same oxygen vacancy reduction effect.
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 prevents variations in electric characteristics, improves reliability, and enables the manufacturing of semiconductor devices with low power consumption and stable normally-off characteristics by reducing oxygen vacancies and enhancing the channel region's stability.
Implementation Method 1
heat treatment to move excess oxygen to the semiconductor film
Implementation Method 2
excess oxygen in the insulating film is moved to the oxide semiconductor film
Data Source
AI summary
Provided is a method for manufacturing a semiconductor device whose electric characteristics are prevented from being varied and whose reliability is improved. In the method, an insulating film is formed over an oxide semiconductor film, a buffer film is formed over the insulating film, oxygen is added to the buffer film and the insulating film, a conductive film is formed over the buffer film to which oxygen is added, and an impurity element is added to the oxide semiconductor film using the conductive film as a mask. An insulating film containing hydrogen and overlapping with the oxide semiconductor film may be formed after the impurity element is added to the oxide semiconductor film.