Stacked Oxide Semiconductor Vertical Transistor
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Solution Overview
Problem
The commercialization of semiconductor devices using silicon carbide is hindered by its difficulty in melting and the presence of defects like micropipes, which limits its productivity and introduces defects, making it challenging to achieve high power application characteristics such as high withstand voltage and low power loss.
Innovation Solution
A semiconductor device utilizing a novel oxide semiconductor material with a polycrystalline structure is formed by stacking oxide semiconductor films with crystallinity, where the first film acts as a seed crystal for the second film, allowing for epitaxial growth and achieving high field-effect mobility and low hydrogen concentration, thereby enhancing the semiconductor's properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon carbide is used as semiconductor material to improve withstand voltage and reduce power loss, then high power application characteristics are improved, but manufacturing difficulty increases due to inability to melt and presence of micropipe defects
Solution Approach 1:
The patent changes the semiconductor material from silicon carbide to oxide semiconductor, fundamentally altering the material parameters to achieve both high withstand voltage and ease of manufacture. The oxide semiconductor is formed at lower temperatures and does not exhibit micropipe defects, resolving the manufacturing difficulty while maintaining reliability.
Solution Approach 2:
The patent uses a composite structure with stacked oxide semiconductor films having different crystal orientations. The c-axis aligned film provides high withstand voltage, while the a-axis aligned film provides ease of manufacture, combining the advantages of different crystal orientations to resolve the technical contradiction.
2Loss of energy
If silicon carbide is used to improve power conversion efficiency, then power loss is reduced, but productivity decreases due to manufacturing challenges
Solution Approach 1:
The patent changes the material system from silicon carbide to oxide semiconductor, enabling formation at lower temperatures and simpler processes. This dramatically improves productivity while maintaining low power loss characteristics through the oxide semiconductor's inherent electrical properties.
Solution Approach 2:
The patent employs a simpler, more accessible manufacturing approach using oxide semiconductor that can be processed with conventional equipment, replacing the complex silicon carbide manufacturing process. This enables higher productivity and commercialization while achieving comparable or superior electrical characteristics.
3Reliability
If oxide semiconductor films are stacked with crystallinity to improve field-effect mobility, then electrical characteristics are enhanced, but manufacturing process complexity increases
Solution Approach 1:
The patent applies local quality by creating regions with different crystal orientations (c-axis and a-axis) in specific locations within the oxide semiconductor structure. The c-axis aligned region provides high field-effect mobility where needed, while the a-axis aligned region simplifies manufacturing, achieving both goals through spatial differentiation.
Solution Approach 2:
The patent introduces crystal orientation as an additional dimension of control in the oxide semiconductor structure. By stacking films with different crystal orientations rather than varying only thickness or composition, the patent achieves enhanced field-effect mobility while maintaining relatively simple manufacturing processes.
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 a semiconductor device with improved withstand voltage, reduced power loss, and high on-off ratio, suitable for high power applications, while also simplifying the manufacturing process by avoiding the challenges associated with silicon carbide.
Implementation Method 1
crystal growth is caused from a surface to the inside portion of the first oxide semiconductor film by performing heat treatment at a temperature higher than or equal to 450° C. and lower than or equal to 850° C.
Implementation Method 2
a second oxide semiconductor film having crystallinity is stacked over the first oxide semiconductor film having crystallinity... the first oxide semiconductor film having crystallinity has a function of a seed crystal for the second oxide semiconductor film
Implementation Method 3
heat treatment at a temperature higher than or equal to 450° C. and lower than or equal to 850° C., preferably higher than or equal to 550° C. and lower than or equal to 750° C.
Data Source
AI summary
Objects are to provide a semiconductor device for high power application in which a novel semiconductor material having high productivity is used and to provide a semiconductor device having a novel structure in which a novel semiconductor material is used. The present invention is a vertical transistor and a vertical diode each of which has a stacked body of an oxide semiconductor in which a first oxide semiconductor film having crystallinity and a second oxide semiconductor film having crystallinity are stacked. An impurity serving as an electron donor (donor) which is contained in the stacked body of an oxide semiconductor is removed in a step of crystal growth; therefore, the stacked body of an oxide semiconductor is highly purified and is an intrinsic semiconductor or a substantially intrinsic semiconductor whose carrier density is low. The stacked body of an oxide semiconductor has a wider band gap than a silicon semiconductor.