Oxide Semiconductor TFT Crystallization Control via Silicon Oxide Barrier
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Solution Overview
Problem
The challenge is to develop a semiconductor device using an oxide semiconductor that maintains amorphous structure during heat treatment to prevent surface unevenness and electrical characteristic variations, while ensuring high field effect mobility and reliability for applications in display devices.
Innovation Solution
A method involving the formation of an oxide semiconductor layer with a gate electrode, covered by a first insulating film, and then a second insulating film including silicon oxide with specific hydrogen and nitrogen densities, followed by heat treatment at 300°C or higher, to suppress crystallization and enhance TFT characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heat treatment is performed on the oxide semiconductor layer to improve TFT characteristics, then field effect mobility is enhanced, but crystallization occurs causing surface unevenness and electrical characteristic variations
Solution Approach 1:
A silicon oxide layer is introduced as an intermediary between the oxide semiconductor layer and the heat treatment process. This silicon oxide layer acts as a protective barrier that prevents direct heat-induced crystallization of the oxide semiconductor while still allowing heat treatment to proceed at temperatures of 300°C or higher to improve TFT characteristics and field effect mobility.
Solution Approach 2:
The silicon oxide layer is formed on the oxide semiconductor layer before heat treatment is applied. This preliminary formation of the protective layer ensures that when subsequent heat treatment is performed, the oxide semiconductor layer is already protected from crystallization, allowing the heat treatment to enhance electrical characteristics without causing structural degradation.
2Reliability
If the oxide semiconductor layer is heated to improve conductivity, then field effect mobility increases, but surface unevenness develops due to crystallization
Solution Approach 1:
The silicon oxide layer serves as a mediator that allows heat to be applied for improving conductivity while preventing the harmful crystallization effect. This intermediary layer enables the beneficial thermal effect (improved conductivity) while blocking the harmful effect (crystallization-induced surface unevenness).
3Reliability
If heat treatment temperature is increased to enhance TFT performance, then field effect mobility improves, but crystallization is more likely to occur
Solution Approach 1:
The presence of the silicon oxide layer changes the thermal parameter environment for the oxide semiconductor layer. It allows the heat treatment temperature to be increased to 300°C or higher (parameter change) to enhance TFT performance, while the silicon oxide layer prevents the parameter change from causing crystallization, thus maintaining structural control.
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 stable and uniform electrical characteristics for thin film transistors, reducing variations and maintaining high conductivity, suitable for display devices like liquid crystal displays and electronic paper.
Implementation Method 1
heat treatment is performed at 300° C. or higher, so that crystallization of the oxide semiconductor layer can be suppressed
Implementation Method 2
heat treatment is performed at 300° C. or higher
Data Source
AI summary
If an oxide semiconductor layer is crystallized by heat treatment without being covered with an inorganic insulating film, surface unevenness and the like are formed due to the crystallization, which may cause variation in electrical characteristics. Steps are performed in the following order: a second insulating film is formed on an oxide semiconductor layer over a substrate and then heat treatment is performed, instead of performing heat treatment during a period immediately after formation of the oxide semiconductor layer and immediately before formation of an inorganic insulating film including silicon oxide on the oxide semiconductor layer. The density of hydrogen included in the inorganic insulating film including silicon oxide is 5×1020/cm3 or more, and the density of nitrogen is 1×1019/cm3 or more.