Purifying Oxide Semiconductor Layer with Halogen for Low Off-State Current
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Solution Overview
Problem
Semiconductor devices using oxide semiconductors face issues with variations in threshold voltage and increased off-state current due to impurities like hydrogen, leading to reliability and power consumption concerns, and require high-purity oxide semiconductor layers to maintain low power consumption and high productivity.
Innovation Solution
The method involves adding a halogen element, such as fluorine, to the oxide semiconductor layer to break strong bonds with hydrogen, followed by heat treatment to remove impurities and achieve high purity, resulting in a semiconductor device with reduced off-state current and stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If heat treatment at high temperature is performed to remove impurities from the oxide semiconductor layer, then most impurities can be removed, but impurities strongly bonded to metal (hydrogen, hydroxyl groups) remain due to strong bonding force
Solution Approach 1:
A halogen element (fluorine, chlorine, bromine, or iodine) is introduced as an intermediary substance that selectively bonds to metal atoms in the oxide semiconductor layer. This intermediary action weakens the strong bonds between metal and hydrogen/hydroxyl groups, enabling removal of these strongly bonded impurities without requiring extreme heat treatment that would damage the substrate.
Solution Approach 2:
The bonding parameters of the oxide semiconductor layer are changed by introducing halogen elements. The halogen-metal bonds have different bond energies and lengths compared to metal-hydrogen bonds, fundamentally altering the chemical environment and enabling selective removal of hydrogen and hydroxyl groups through subsequent heat treatment at moderate temperatures.
2Area of stationary object
If amorphous silicon is used for transistors, then larger glass substrates can be used, but field effect mobility is low
Solution Approach 1:
The invention changes the material parameter from conventional amorphous silicon to purified oxide semiconductor, fundamentally altering the electrical properties. The oxide semiconductor provides high field effect mobility comparable to polycrystalline silicon while maintaining the ability to be deposited on large substrates using sputtering techniques.
3Speed
If polycrystalline silicon is used for transistors, then high field effect mobility is achieved, but crystallization steps such as laser annealing are required which are not suitable for larger glass substrates
Solution Approach 1:
The invention changes the material parameter from polycrystalline silicon to oxide semiconductor, eliminating the need for crystallization steps. The oxide semiconductor can be deposited as an amorphous film and then purified through heat treatment and halogen introduction, achieving high mobility without requiring laser annealing or other complex crystallization processes.
Solution Approach 2:
The invention extracts and removes the problematic crystallization step from the manufacturing process. By using oxide semiconductor instead of silicon-based materials, the entire crystallization sequence (laser annealing, rapid thermal annealing) is eliminated, simplifying the process for large substrate manufacturing.
4Ease of manufacture
If oxide semiconductor with impurities is used, then manufacturing is simpler, but threshold voltage variation increases and off-state current increases
Solution Approach 1:
The halogen element serves as an intermediary that selectively bonds to metal atoms, creating a chemical environment that facilitates the removal of hydrogen and hydroxyl impurities. This intermediary mechanism enables purification without compromising the simplicity of the sputtering deposition process.
Solution Approach 2:
The halogen introduction and heat treatment steps are performed as preliminary actions before final device fabrication. This preliminary purification ensures that the oxide semiconductor layer starts with minimal impurities, preventing threshold voltage shifts and low off-state current from the beginning rather than requiring corrective measures later.
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 reduces off-state current and maintains low power consumption, enhancing the reliability and productivity of semiconductor devices by purifying the oxide semiconductor layer, thereby minimizing variations in threshold voltage and improving device performance.
Implementation Method 1
a substance which can be strongly bonded to an impurity is added into the oxide semiconductor layer... The substance which can be strongly bonded to an impurity is preferably a substance including a halogen element... a bond between a metal of the oxide semiconductor and hydrogen, a bond between a metal and a hydroxyl group, or a bond between oxygen and hydrogen in a hydroxyl group that is bonded to a metal can be cut
Implementation Method 2
heat treatment is performed to remove a stable substance including hydrogen from the oxide semiconductor layer
Data Source
AI summary
An object of the present invention to provide a highly reliable semiconductor device. Another object is to provide a manufacturing method of a highly reliable semiconductor device. Still another object is to provide a semiconductor device having low power consumption. Yet another object is to provide a manufacturing method of a semiconductor device having low power consumption. Furthermore, another object is to provide a semiconductor device which can be manufactured with high mass productivity. Another object is to provide a manufacturing method of a semiconductor device which can be manufactured with high mass productivity. An impurity remaining in an oxide semiconductor layer is removed so that the oxide semiconductor layer is purified to have an extremely high purity. Specifically, after adding a halogen element into the oxide semiconductor layer, heat treatment is performed to remove an impurity from the oxide semiconductor layer. The halogen element is preferably fluorine.