Oxide Semiconductor Purification via Dehydration and Oxygen Supply
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Solution Overview
Problem
The challenge is to achieve stable electric characteristics in thin film transistors using oxide semiconductors by minimizing impurities such as hydrogen, moisture, and oxygen, which affect the conductivity and reliability of the devices.
Innovation Solution
The solution involves a method of heat treatment in a nitrogen atmosphere to dehydrate and dehydrogenate the oxide semiconductor layer, followed by cooling in an oxygen-rich atmosphere to purify the layer and reduce impurities, thereby achieving an intrinsic (i-type) oxide semiconductor with minimal hydrogen concentration and improved carrier mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If heat treatment is performed to remove impurities such as hydrogen and moisture from the oxide semiconductor layer, then the purity and electrical characteristics are improved, but oxygen deficiency occurs which degrades the semiconductor properties
Solution Approach 1:
Oxygen is supplied to the oxide semiconductor layer before the heat treatment step to prevent oxygen deficiency. The layer is subjected to oxygen plasma treatment or heating in an oxygen atmosphere prior to dehydration/dehydrogenation, ensuring oxygen is available to replenish any losses during subsequent high-temperature processing.
Solution Approach 2:
The heat treatment is performed in an inert gas atmosphere (nitrogen or rare gas) that has been pre-saturated with oxygen. This inert environment prevents contamination from atmospheric gases while the pre-introduced oxygen remains available in the oxide semiconductor layer to maintain stoichiometry during heating.
2Object-affected harmful factors
If the oxide semiconductor layer is heated to remove hydrogen and moisture, then impurity concentration is reduced, but thermal damage and structural degradation may occur
Solution Approach 1:
The heat treatment is conducted at controlled temperatures between 200-400°C, which is sufficient to remove hydrogen and moisture but below the threshold for significant thermal damage. The temperature, time, and atmosphere parameters are optimized to achieve impurity removal while preserving the oxide semiconductor crystal structure.
Solution Approach 2:
An inert gas atmosphere acts as an intermediary medium during heat treatment, providing a protective environment that prevents oxidation and structural degradation while allowing thermal energy to effectively remove impurities from the oxide semiconductor layer.
3Manufacturing precision
If multiple treatment steps are performed to achieve high purity, then the quality of the oxide semiconductor is improved, but the manufacturing process becomes more complex
Solution Approach 1:
Multiple treatment functions are combined into integrated process steps. For example, oxygen plasma treatment and dehydration are performed in sequence within the same chamber without breaking vacuum, and heat treatment for both oxygen supply and impurity removal is conducted in a single controlled step, reducing the total number of separate process steps.
Solution Approach 2:
The heat treatment step serves multiple functions simultaneously: it removes hydrogen, removes moisture, and can be performed in an oxygen-containing atmosphere to replenish oxygen. This multi-functionality reduces the need for separate dedicated steps for each treatment objective.
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 thin film transistors with reduced off-state current, enhanced reliability, and stable electric characteristics, enabling high-performance semiconductor devices that can be mass-produced.
Implementation Method 1
heat treatment in a nitrogen atmosphere or a rare gas atmosphere such as argon or helium or under reduced pressure
Implementation Method 2
heat treatment in a nitrogen atmosphere or a rare gas atmosphere such as argon or helium or under reduced pressure
Implementation Method 3
cooling treatment in an atmosphere of oxygen, an atmosphere of oxygen and nitrogen, or the air
Data Source
AI summary
An object is to provide a semiconductor device having stable electric characteristics in which an oxide semiconductor is used. An oxide semiconductor layer is subjected to heat treatment for dehydration or dehydrogenation treatment in a nitrogen gas or an inert gas atmosphere such as a rare gas (e.g., argon or helium) or under reduced pressure and to a cooling step for treatment for supplying oxygen in an atmosphere of oxygen, an atmosphere of oxygen and nitrogen, or the air (having a dew point of preferably lower than or equal to −40° C., still preferably lower than or equal to −50° C.) atmosphere. The oxide semiconductor layer is thus highly purified, whereby an i-type oxide semiconductor layer is formed. A semiconductor device including a thin film transistor having the oxide semiconductor layer is manufactured.