IGZO Thin Film Transistor Surface Modification via Fluorine Plasma Etching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing methods for manufacturing oxide semiconductor thin film transistors (TFTs) using IGZO films face challenges such as increased off-current due to oxygen deficit layers, difficulty in controlling doping for ohmic contact, and high process costs, particularly when using fluorine-based etching which leads to over-etching and low yield.
Innovation Solution
The solution involves forming a thin film device with a surface layer where the In3d peak in the XPS spectrum is shifted to a high energy side by chemically coupling indium and fluorine, and an interface layer where the In3d peak is shifted to a low energy side, using fluorine-based gas plasma etching with an inductive coupling plasma source, and placing the substrate on earth potential to suppress oxygen deficit layer formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If fluorine-based gas plasma etching is used to pattern source/drain electrode, then etching precision is improved, but oxygen deficit layer is formed on oxide semiconductor film surface causing off-current increase
Solution Approach 1:
The etching process is divided into two distinct stages: first using CF4-based plasma for precise pattern formation, then using SF6-based plasma to remove the oxygen deficit layer. This segmentation allows each etching step to optimize for its specific function without compromising the other.
Solution Approach 2:
The invention changes the chemical composition parameter of the etching gas from pure fluorine-based (CF4) to a two-step process involving CF4 followed by SF6. This parameter change enables the second step to specifically address oxygen deficit removal while maintaining the precision achieved in the first step.
2Object-generated harmful factors
If oxygen deficit layer is removed by hydrochloric acid etching, then off-current is reduced, but manufacturing process complexity and cost increase
Solution Approach 1:
The invention replaces the chemical wet etching method (hydrochloric acid) with a plasma-based dry etching method using SF6 gas. This substitution eliminates the need for liquid handling, rinsing, and drying steps associated with wet etching, thereby simplifying the manufacturing process while achieving the same goal of removing oxygen deficit layers.
3Productivity
If conventional etching is used without substrate potential control, then etching speed is maintained, but over-etching occurs reducing yield
Solution Approach 1:
The invention implements feedback control by monitoring the substrate potential during plasma etching and adjusting the process parameters accordingly. The substrate is biased at a specific negative potential (-100V to -300V) to control ion bombardment energy, providing real-time feedback that prevents over-etching while maintaining adequate etching speed.
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 suppresses oxygen depletion on the surface, achieving stable TFT characteristics with reduced off-current and enabling fine switching performance without etching the oxide semiconductor film, thus improving the on-off ratio and reducing costs.
Implementation Method 1
patterning the source/drain electrode metal film by using a plasma gas containing fluorine to form a source/drain electrode, wherein the plasma gas containing the fluorine is generated by an inductive coupling plasma source
Implementation Method 2
the plasma gas containing the fluorine is generated by an inductive coupling plasma source
Implementation Method 3
a peak position derived from an indium 3d orbital of an XPS spectrum in a surface layer in a part of the oxide semiconductor film where the source/drain electrode is not superimposed is shifted towards a high energy side than a peak position derived from an indium 3d orbital of an XPS spectrum in an oxide semiconductor region existing in a lower part of the surface layer
Implementation Method 4
placing the substrate on earth potential to suppress oxygen deficit layer formation
Data Source
AI summary
With a TFT using an oxide semiconductor film, there is such an issue that oxygen deficit is generated in a surface region of the oxide semiconductor film after performing plasma etching of a source/drain electrode, thereby increasing the off-current. Provided is a TFT which includes: a gate electrode on an insulating substrate; a gate insulating film on the gate electrode; an oxide semiconductor film containing indium on the gate insulating film; and a source/drain electrode on the oxide semiconductor film. Further, the peak position derived from an indium 3d orbital in the XPS spectrum of a surface layer in a part of the oxide semiconductor film where the source/drain electrode is not superimposed is shifted towards a high energy side than the peak position derived from the indium 3d orbital in the XPS spectrum of an oxide semiconductor region existing in a lower part of the surface layer.