Oxide Semiconductor Transistor Hydrogen Barrier
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Solution Overview
Problem
Transistors using oxide semiconductors face reliability issues due to fluctuations in threshold voltage and tend to have normally-on characteristics, making it difficult to achieve stable logic circuits, especially in driver circuits.
Innovation Solution
A semiconductor device with a base insulating layer that reduces hydrogen concentration at the interface with the substrate, using heat treatments to eliminate hydrogen and supply oxygen to the oxide semiconductor layer, thereby stabilizing the threshold voltage and achieving normally-off characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a transistor is formed using an oxide semiconductor layer, then the transistor can operate at higher speed and be manufactured more easily, but the threshold voltage fluctuates and reliability is low
Solution Approach 1:
The patent applies preliminary action by performing heat treatment on the substrate before forming the oxide semiconductor layer to eliminate hydrogen from the substrate. This pre-treatment prevents hydrogen from diffusing into the oxide semiconductor layer during subsequent manufacturing steps, thereby preventing threshold voltage fluctuations and improving reliability while maintaining the ease of manufacture and high-speed operation characteristics of oxide semiconductors
2Ease of manufacture
If an oxide semiconductor layer is used, then manufacturing is easier compared to polycrystalline silicon, but the transistor exhibits normally-on characteristics making it difficult to provide proper logic circuits
Solution Approach 1:
The patent performs heat treatment on the substrate before forming the oxide semiconductor layer to eliminate hydrogen in advance. This preliminary action prevents hydrogen from causing normally-on characteristics, enabling the transistor to achieve proper normally-off behavior required for logic circuit operation while maintaining the manufacturing ease advantage of oxide semiconductors over polycrystalline silicon
3Ease of manufacture
If hydrogen is present in the substrate or base insulating layer, then the manufacturing process is simpler, but hydrogen diffuses into the oxide semiconductor layer causing negative shift of threshold voltage
Solution Approach 1:
The patent applies preliminary action by performing heat treatment on the substrate before forming the oxide semiconductor layer to eliminate hydrogen in advance. This prevents hydrogen from diffusing into the oxide semiconductor layer and causing threshold voltage negative shift, thereby improving threshold voltage control precision while maintaining relatively simple manufacturing processes
Solution Approach 2:
The patent introduces a base insulating layer with low hydrogen concentration as an intermediary between the substrate and the oxide semiconductor layer. This intermediary layer acts as a barrier to hydrogen diffusion, preventing hydrogen from reaching the oxide semiconductor layer and causing threshold voltage shifts, while allowing the manufacturing process to remain relatively simple
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 solution significantly reduces threshold voltage fluctuations, enhances reliability, and allows for the production of transistors with stable normally-off characteristics, improving the performance and functionality of oxide semiconductor devices.
Implementation Method 1
first heat treatment is performed on a substrate; a base insulating layer is formed over the substrate; an oxide semiconductor layer is formed over the base insulating layer
Implementation Method 2
the adverse effect of hydrogen diffused into an oxide semiconductor layer from a substrate through a base insulating layer is reduced
Implementation Method 3
supply oxygen to the oxide semiconductor layer, thereby stabilizing the threshold voltage
Data Source
AI summary
It is an object to manufacture a semiconductor device in which a transistor including an oxide semiconductor has normally-off characteristics, small fluctuation in electric characteristics, and high reliability. First, first heat treatment is performed on a substrate, a base insulating layer is formed over the substrate, an oxide semiconductor layer is formed over the base insulating layer, and the step of performing the first heat treatment to the step of forming the oxide semiconductor layer are performed without exposure to the air. Next, after the oxide semiconductor layer is formed, second heat treatment is performed. An insulating layer from which oxygen is released by heating is used as the base insulating layer.