Oxide Semiconductor Transistor Electrode Design
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Solution Overview
Problem
The use of titanium, tungsten, or molybdenum for source and drain electrode layers in oxide semiconductor transistors can lead to the formation of titanium oxide, reduction of the oxide semiconductor film, oxygen vacancies, and shifts in threshold voltage, resulting in decreased on-state current due to high resistance components.
Innovation Solution
Employing a metal film with higher oxidation resistance than the oxide semiconductor film, such as copper, silver, or ruthenium, for the source and drain electrode layers, and using a conductive film like gold or platinum to reduce oxygen extraction and diffusion, thereby maintaining the integrity of the oxide semiconductor film and preventing resistance increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If titanium is used for source electrode layer and drain electrode layer which are provided in contact with an oxide semiconductor film, then good electrical contact is achieved, but titanium oxide is formed at the interface and the oxide semiconductor film is reduced causing threshold voltage shift
Solution Approach 1:
A metal oxide film is introduced as an intermediary layer between the source/drain electrode layers and the oxide semiconductor film. This metal oxide film acts as a buffer that prevents direct harmful interaction between the electrode material and the semiconductor film, thereby maintaining both good electrical contact and film composition stability.
Solution Approach 2:
The electrode structure is designed as a composite multi-layer system comprising a metal layer, a metal oxide film, and the oxide semiconductor film. This composite structure combines the advantages of different materials: the metal layer provides electrical conductivity while the metal oxide film protects the semiconductor film from reduction and oxygen extraction.
2Ease of manufacture
If high-temperature heat treatment is performed while oxide semiconductor film and tungsten or molybdenum layer are in contact, then processing is simplified, but the oxide semiconductor film is reduced causing threshold voltage shift
Solution Approach 1:
The metal oxide film serves as a protective intermediary that allows high-temperature heat treatment to be performed without causing reduction of the oxide semiconductor film. The metal oxide film is stable at the heat treatment temperature and prevents oxygen diffusion from the semiconductor film to the electrode material.
3Ease of manufacture
If high-temperature heat treatment is performed while oxide semiconductor film and tungsten or molybdenum layer are in contact, then processing is simplified, but oxygen diffuses to the electrode layer forming high resistance component
Solution Approach 1:
The metal oxide film acts as a diffusion barrier that prevents oxygen from the oxide semiconductor film from diffusing into the tungsten or molybdenum electrode layer during high-temperature heat treatment. This maintains low resistance in the electrode layers while allowing simplified processing.
4Stability of the object's composition
If metal film with higher oxidation resistance is used for source and drain electrode layers, then oxygen extraction from oxide semiconductor film is prevented, but material selection is limited
Solution Approach 1:
The electrode structure uses a composite of metal layer and metal oxide film, where the metal layer can be selected from various materials (titanium, tungsten, molybdenum, etc.) for electrical conductivity, while the metal oxide film provides the necessary protection against oxygen extraction. This composite approach maintains material selection flexibility while ensuring film stability.
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 effectively suppresses the shift of threshold voltage and reduces resistance in the transistor, maintaining high on-state current and reliability by preventing oxygen extraction and diffusion, thus enhancing the performance of the oxide semiconductor device.
Implementation Method 1
a metal film having a higher oxidation resistance than a metal element included in the oxide semiconductor film is used as a source electrode layer and a drain electrode layer which are in contact with the oxide semiconductor film
Implementation Method 2
oxygen might be diffused from the oxide semiconductor film to the tungsten layer or the molybdenum layer
Data Source
AI summary
A semiconductor device in which a shift of the threshold voltage of a transistor is suppressed is provided. A semiconductor device in which a decrease in the on-state current of a transistor is suppressed is provided. The semiconductor device is manufactured as follows: forming a gate electrode layer over a substrate; forming a gate insulating film over the gate electrode layer; forming an oxide semiconductor film over the gate insulating film; forming a metal oxide film having a higher reducing property than the oxide semiconductor film over the oxide semiconductor film; performing heat treatment while the metal oxide film and the oxide semiconductor film are in contact with each other, thereby the metal oxide film is reduced so that a metal film is formed; and processing the metal film to form a source electrode layer and a drain electrode layer.