Non-Contact Microwave Evaluation of Oxide Semiconductor TFT Threshold Voltage
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Solution Overview
Problem
Conventional evaluation methods for oxide semiconductor thin films are insufficient for evaluating the electrical characteristics of thin-film transistors (TFTs) during the manufacturing process, as they do not account for changes in physical properties due to temperature distributions and layer formations, such as annealing treatments.
Innovation Solution
A method using the microwave photoconductive decay technique to measure the reflectance change of an oxide semiconductor layer in a TFT, calculating the decay period and determining the threshold voltage and resistance value, allowing for non-contact evaluation of the TFT's electrical characteristics, including the channel protection layer and interlayer insulating layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional evaluation methods targeting only oxide semiconductor thin films are used, then the measurement process is simple, but the evaluation is insufficient for oxide semiconductor TFTs due to physical property changes during manufacturing processes
Solution Approach 1:
The patent replaces conventional contact-based electrical measurement methods with a non-contact microwave photoconductive decay method. By using microwave radiation to probe the oxide semiconductor layer, the system can evaluate electrical characteristics without physical contact, thereby avoiding interference with the device structure while achieving accurate threshold voltage determination.
Solution Approach 2:
The patent utilizes changes in microwave reflectance parameters caused by photoexcitation to determine electrical characteristics. By measuring the decay of reflectance changes after light irradiation, the system extracts threshold voltage information without requiring direct electrical contact, thus resolving the contradiction between measurement accuracy and device complexity.
2Measurement precision
If non-contact microwave photoconductive decay method is used for oxide semiconductor TFT evaluation, then evaluation accuracy for TFT electrical characteristics is improved, but measurement complexity increases
Solution Approach 1:
The patent substitutes complex electrical contact measurements with a non-contact microwave optical measurement system. The microwave photoconductive decay method uses electromagnetic radiation interaction to probe electrical characteristics, replacing cumbersome electrical probes and contacts while achieving superior measurement accuracy for threshold voltage determination.
Solution Approach 2:
The microwave photoconductive decay method serves multiple functions simultaneously: it measures threshold voltage, evaluates carrier dynamics, and characterizes the oxide semiconductor layer properties all through a single non-contact measurement process, thereby reducing overall measurement complexity while improving comprehensive evaluation accuracy.
3Reliability
If evaluation is performed after stabilizing annealing processes, then the electrical characteristics reflect final TFT performance, but physical properties of oxide semiconductor may have varied due to temperature distributions
Solution Approach 1:
The patent performs microwave photoconductive decay measurements at multiple stages during the manufacturing process, including before and after stabilizing annealing. This preliminary and intermediate evaluation allows detection of uniformity variations early in the process, enabling corrective actions before final device completion, thus ensuring both reliability and manufacturing precision.
Solution Approach 2:
The patent implements a feedback mechanism where microwave measurement results are used to monitor and control the manufacturing process. By continuously measuring threshold voltage and electrical characteristics at various stages, the system provides feedback to adjust annealing parameters and other processing conditions, compensating for temperature distribution variations and ensuring uniform oxide semiconductor layer properties.
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
Enables effective evaluation and quality control of oxide semiconductor TFTs in high-volume manufacturing processes, ensuring the electrical characteristics fall within predetermined ranges, thereby identifying defective or non-defective products.
Implementation Method 1
measuring a change in a reflectance of an emitted microwave to the oxide semiconductor layer while the oxide semiconductor layer is irradiated with excitation light by pulse irradiation
Implementation Method 2
measuring a change in a reflectance of an emitted microwave to the oxide semiconductor layer while the oxide semiconductor layer is irradiated with excitation light by pulse irradiation; calculating a decay period which is a period of time taken for the reflectance to decay
Data Source
AI summary
A method of evaluating a thin-film transistor (TFT) which is disposed on a substrate, and includes at least: an oxide semiconductor layer which functions as a channel layer; and a channel protection layer disposed above the oxide semiconductor layer. The method includes: measuring a change in a reflectance of a microwave emitted to the oxide semiconductor layer while the oxide semiconductor layer is irradiated with excitation light by pulse irradiation; calculating a decay period which is a period of time taken for the reflectance to decay to 1/e or 1/e2, based on the change in the reflectance obtained in the measuring; and performing determination related to a threshold voltage of the oxide semiconductor layer, based on the decay period calculated in the calculating.