Halogen Plasma Treatment for Oxide Semiconductor Impurity Removal
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Solution Overview
Problem
The variation in electric characteristics of thin film transistors using oxide semiconductors is affected by impurities such as hydrogen, moisture, and hydroxyl, which form O—H bonds, leading to instability in the devices.
Innovation Solution
The introduction of a halogen element like fluorine or chlorine is used to reduce impurity concentrations in the oxide semiconductor layer by diffusing impurities into the gate insulating or oxide insulating layers, which contain defects and high binding energy, thereby stabilizing the device characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional thin film formation process is used, then the oxide semiconductor layer can be formed, but impurities such as hydrogen and moisture enter the layer forming O—H bonds that serve as electron donors, changing electrical conductivity and causing variation in device characteristics
Solution Approach 1:
The patent applies preliminary action by performing plasma treatment with a halogen-containing gas (CF4, SF6, or NF3) on the oxide semiconductor layer before subsequent processing steps. This pre-treatment introduces halogen atoms that bind to hydrogen impurities, preventing them from forming harmful O—H bonds later during thin film formation. The halogen acts as a protective agent in advance, reducing impurity effects before they can cause electrical conductivity variations.
Solution Approach 2:
The halogen element (fluorine, chlorine, bromine, or iodine) serves as an intermediary substance that mediates between the hydrogen impurities and the oxide semiconductor layer. The halogen atoms bind to hydrogen to form halogen-hydrogen bonds, preventing direct interaction between hydrogen and oxygen in the semiconductor lattice. This intermediary mechanism effectively removes the harmful effect of hydrogen without requiring direct removal of the impurity.
2Reliability
If the oxide semiconductor layer is highly purified to reduce impurity concentration, then electrical characteristic stability improves, but additional processing steps are required increasing manufacturing complexity
Solution Approach 1:
The patent merges the impurity reduction function with existing plasma treatment steps in the manufacturing process. Instead of adding a separate purification step, the plasma treatment with halogen-containing gas is integrated into the conventional process flow, combining cleaning/passivation functions in a single operation. This reduces process complexity while achieving high purification效果.
Solution Approach 2:
The patent changes the chemical composition parameter of the plasma treatment gas from conventional inert gases (Ar, N2) to halogen-containing gases (CF4, SF6, NF3). This parameter change transforms the plasma treatment function from simple surface cleaning to active impurity binding and removal, achieving enhanced purification without requiring additional process steps.
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 impurity concentrations in the oxide semiconductor layer, enhancing the stability and reliability of thin film transistors by suppressing parasitic channel formation and improving electrical performance.
Implementation Method 1
an impurity such as hydrogen or moisture (e.g., a hydrogen atom or a compound containing a hydrogen atom such as H2O) is diffused into the gate insulating layer and/or the oxide insulating layer with use of a halogen element
Implementation Method 2
An impurity such as hydrogen or moisture (e.g., a hydrogen atom or a compound containing a hydrogen atom such as H2O) is eliminated from the oxide semiconductor layer with use of a halogen element
Data Source
AI summary
An object is to provide a semiconductor device with stable electric characteristics in which an oxide semiconductor is used. An impurity such as hydrogen or moisture (e.g., a hydrogen atom or a compound containing a hydrogen atom such as H2O) is eliminated from an oxide semiconductor layer with use of a halogen element typified by fluorine or chlorine, so that the impurity concentration in the oxide semiconductor layer is reduced. A gate insulating layer and/or an insulating layer provided in contact with the oxide semiconductor layer can be formed to contain a halogen element. In addition, a halogen element may be attached to the oxide semiconductor layer through plasma treatment under an atmosphere of a gas containing a halogen element.