Oxide Semiconductor Transistor Oxygen Vacancy Reduction
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Solution Overview
Problem
Transistors using oxide semiconductors face issues with oxygen vacancies leading to poor electrical characteristics, reliability concerns, and a tendency to be normally-on due to localized states, which affect the threshold voltage and off-state current.
Innovation Solution
A transistor structure is developed with a first and third oxide semiconductor film, where oxygen is added to reduce oxygen vacancies by heat treatment, and a second oxide semiconductor film is formed with In or Ga, reducing oxygen vacancies and improving electrical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oxygen is added to oxide semiconductor films through heat treatment, then oxygen vacancies are reduced and electrical characteristics improve, but the manufacturing process complexity increases
Solution Approach 1:
Oxygen is added to the first and third oxide semiconductor films before forming the second oxide semiconductor film. This preliminary oxygen addition ensures that oxygen is already present in the structure before the In-Ga-Zn oxide film is deposited, allowing oxygen diffusion to occur naturally during subsequent heat treatment without requiring complex external oxygen supply systems.
Solution Approach 2:
The first and third oxide semiconductor films act as oxygen reservoirs or intermediary layers that supply oxygen to the second oxide semiconductor film through heat treatment. This intermediary mechanism allows oxygen transfer without requiring direct external oxygen introduction during the heat treatment process, simplifying the manufacturing equipment requirements.
2Reliability
If a multi-layer oxide semiconductor structure is used to reduce oxygen vacancies, then transistor reliability improves, but device complexity increases
Solution Approach 1:
Different oxide semiconductor films are strategically positioned at different locations within the transistor structure. The first oxide semiconductor film is located between the gate electrode and the second oxide semiconductor film, while the third oxide semiconductor film is positioned between the second oxide semiconductor film and the source/drain electrodes. Each layer performs a specific function: the first layer prevents oxygen diffusion from the gate, the second layer provides the active channel with reduced oxygen vacancies, and the third layer prevents oxygen diffusion toward the electrodes.
Solution Approach 2:
The invention uses a composite structure combining multiple oxide semiconductor materials with different properties. The first and third oxide semiconductor films serve as protective barrier layers, while the second oxide semiconductor film (In-Ga-Zn-based oxide) serves as the active channel layer. This composite structure leverages the complementary properties of different oxide materials to achieve both structural stability and excellent electrical characteristics.
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 approach results in improved electrical characteristics, enhanced reliability, and a reduction in oxygen vacancies, stabilizing the threshold voltage and minimizing off-state current, achieving normally-off characteristics.
Implementation Method 1
the oxygen is diffused to the second oxide semiconductor film by heat treatment or the like, so that oxygen vacancies in the second oxide semiconductor film are reduced
Implementation Method 2
heat treatment is performed to transfer part of oxygen contained in the first oxide semiconductor film to the second oxide semiconductor film
Data Source
AI summary
The semiconductor device is manufactured by the following method. A first oxide semiconductor film is formed over a first gate electrode and a first insulating film, oxygen is added to the first oxide semiconductor film, and then a second oxide semiconductor film is formed over the first oxide semiconductor film. Then, heat treatment is performed. Next, part of the first insulating film, part of the first oxide semiconductor film, and part of the second oxide semiconductor film are etched to form a first gate insulating film having a projection. Next, a pair of electrodes is formed over the second oxide semiconductor film, and a third oxide semiconductor film is formed over the second oxide semiconductor film and the pair of electrodes. Then, a second gate insulating film is formed over the third oxide semiconductor film, and a second gate electrode is formed over the second gate insulating film.