Oxide Semiconductor Film Interface Engineering
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Solution Overview
Problem
Oxygen vacancies in oxide semiconductor films lead to the generation of localized levels, causing degradation of electrical characteristics in semiconductor devices, such as increased interface states, reduced field-effect mobility, and variations in threshold voltage, resulting in unreliable transistor performance.
Innovation Solution
A multilayer film structure is implemented, where an oxide film with a lower electron affinity than the oxide semiconductor film is used to reduce interface states, and an insulating film with higher oxygen content is provided to fill oxygen vacancies, ensuring stable electron flow and minimizing the impact of trap levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an oxide semiconductor film is used for transistor channel formation, then the transistor can be manufactured with simpler processes and lower costs, but oxygen vacancies are generated during manufacturing which cause localized levels and degrade electrical characteristics
Solution Approach 1:
An oxide film with lower electron affinity is introduced as an intermediary layer between the oxide semiconductor film and the insulating film. This intermediary oxide film prevents oxygen release from the oxide semiconductor film during manufacturing processes, thereby preventing oxygen vacancy formation and maintaining electrical characteristic stability while preserving manufacturing simplicity
Solution Approach 2:
The oxide film is formed beforehand to cushion or prevent the harmful effect of oxygen release. By having this protective oxide film in place before manufacturing processes that release oxygen, the oxide semiconductor film is protected from developing oxygen vacancies, thus preemptively preventing electrical characteristic degradation
2Device complexity
If the oxide semiconductor film is stacked with an insulating film, then device structure is formed, but interface states are generated at the interface which cause carrier scattering and reduce field-effect mobility
Solution Approach 1:
The oxide film serves as an intermediary buffer layer between the oxide semiconductor film and the insulating film. This intermediary layer reduces interface states at both interfaces (oxide semiconductor/oxide film and oxide film/insulating film), thereby minimizing carrier scattering and maintaining high field-effect mobility while preserving the necessary device structure
3Productivity
If oxygen is released during manufacturing process, then manufacturing is completed, but oxygen vacancies are formed which increase interface states and cause threshold voltage variation
Solution Approach 1:
The oxide film acts as an intermediary that absorbs or buffers the oxygen release during manufacturing processes. By having this oxide film present, oxygen is released into the oxide film rather than creating oxygen vacancies in the oxide semiconductor film, thus maintaining manufacturing productivity while achieving precise threshold voltage control
Solution Approach 2:
The oxygen release that would normally be harmful (creating oxygen vacancies) is converted into a beneficial effect by having the oxide film serve as an oxygen reservoir. The oxygen that is released during manufacturing fills into the oxide film instead of creating vacancies, thus converting a harmful process byproduct into a protective mechanism
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 configuration results in a semiconductor device with low localized level density, stable electrical characteristics, reduced variation in threshold voltage, and inhibited increase in off-state current, leading to a highly reliable transistor with improved mobility and reliability.
Implementation Method 1
an oxide film which contains one or more kinds of metal elements included in the oxide semiconductor film is formed in contact with the oxide semiconductor film
Implementation Method 2
an insulating film with higher oxygen content is provided to fill oxygen vacancies
Data Source
AI summary
A highly reliable semiconductor device having stable electrical characteristics is provided. Oxide films each containing one or more kinds of metal elements included in an oxide semiconductor film are formed in contact with an upper side and a lower side of the oxide semiconductor film where a channel is formed, whereby interface states are not easily generated at an upper interface and a lower interface of the oxide semiconductor film. A material which has a lower electron affinity than the oxide semiconductor film is used for the oxide films in contact with the oxide semiconductor film, whereby electrons flowing in the channel hardly move in the oxide films and mainly move in the oxide semiconductor film. Thus, even when an interface state exists between the oxide film and an insulating film formed on the outside of the oxide film, the state hardly influences the movement of electrons.