Oxide Semiconductor Transistor with Mixed Phase Structure
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Solution Overview
Problem
Oxide semiconductor transistors face issues with parasitic channel formation and threshold voltage shift due to oxygen vacancies and hydrogen impurities, leading to instability in electrical characteristics and increased off-state current.
Innovation Solution
The solution involves creating a semiconductor device with an oxide semiconductor film that has a mixed crystal-amorphous phase structure, where the region near the source and drain electrodes is amorphous and the rest is crystalline, with a higher concentration of gallium stabilizers on the back channel side and indium on the channel side to reduce oxygen vacancies and hydrogen impurities, and using a stacked structure with an oxygen-excess oxide insulating film to inhibit parasitic channel formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If an oxide semiconductor film is used to form a transistor channel, then field-effect mobility can be improved, but oxygen vacancies and hydrogen impurities cause parasitic channel formation and threshold voltage shift
Solution Approach 1:
The oxide semiconductor film is structured with different crystallinity in different regions: a first region with lower crystal part proportion (more amorphous) near source/drain electrodes to prevent parasitic channels, and a second region with higher crystal part proportion (more crystalline) in the channel formation region for high mobility. This local quality differentiation resolves the contradiction between mobility and stability.
2Speed
If the oxide semiconductor film is made entirely crystalline to improve mobility, then field-effect mobility increases, but parasitic channel formation due to oxygen vacancies cannot be suppressed
Solution Approach 1:
Different regions of the oxide semiconductor film have different crystal part proportions tailored to their functional requirements. The channel formation region has high crystallinity for mobility, while the source/drain interface region has lower crystallinity (more amorphous) to suppress parasitic channel formation from oxygen vacancies.
Solution Approach 2:
The oxide semiconductor film comprises a composite structure of crystalline and amorphous phases within the same film. This composite structure allows simultaneous exploitation of high mobility from crystalline regions and parasitic channel suppression from amorphous regions.
3Reliability
If stabilizers like gallium are increased to reduce oxygen vacancies, then off-state current decreases, but manufacturing complexity increases
Solution Approach 1:
The patent specifies precise atomic ratio ranges for stabilizers (Ga: 0.01-5 atomic%, Zn: 0.01-5 atomic%) to achieve the desired balance between off-state current control and manufacturing feasibility. These parameter optimizations resolve the contradiction by finding the optimal compromise point.
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 results in a highly reliable transistor with improved field-effect mobility, reduced off-state current, and stable electrical characteristics by minimizing parasitic channel formation and threshold voltage variation.
Implementation Method 1
In an oxide semiconductor, oxygen vacancies and hydrogen partly serve as a donor to generate electrons that are carriers
Implementation Method 2
parts of a top surface and a side edge portion of an oxide semiconductor film in which carriers are stored are removed... a mixed crystal-amorphous phase structure
Data Source
AI summary
To provide a highly reliable semiconductor device by giving stable electrical characteristics to a transistor including an oxide semiconductor film. A gate electrode layer is formed over a substrate, a gate insulating film is formed over the gate electrode layer, an oxide semiconductor film is formed over the gate insulating film, a conductive film is formed over the oxide semiconductor film, so that a region in vicinity of an interface with the oxide semiconductor film in contact with the conductive film is made amorphous, heat treatment is performed, the conductive film is then processed to form a source electrode layer and a drain electrode layer, and a part of the amorphous region in the oxide semiconductor film which is exposed by formation of the source electrode layer and the drain electrode layer is removed.