Oxide Semiconductor TFT Conductivity Control via Oxygen Plasma
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Solution Overview
Problem
Oxide semiconductor channel layers in microelectronic devices, such as thin film transistors (TFTs), exhibit increased conductivity after photolithographic patterning, making it difficult to turn off the TFTs effectively, which is a challenge in achieving controlled conductivity and on-to-off ratios.
Innovation Solution
Incorporating an oxygen-containing plasma treatment step following photolithographic patterning of the oxide semiconductor channel layer, which reduces conductivity and allows for better control over the turn-on voltage by annealing the device in air at 175°C and exposing it to oxygen plasma, resulting in a channel conductance of effectively zero at turn-on voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If photolithographic patterning is performed on oxide semiconductor channel layer, then device fabrication is enabled, but channel conductivity increases making TFT difficult to turn off
Solution Approach 1:
The patent applies preliminary action by performing oxygen plasma treatment immediately after photolithographic patterning to prevent the unwanted conductivity increase. The plasma treatment is applied as a corrective step right after the harmful effect occurs, restoring the channel layer's electrical properties before subsequent processing steps.
Solution Approach 2:
The patent converts the harmful effect of photolithographic patterning (increased channel conductivity) into a beneficial process by using oxygen plasma treatment. The plasma exposure, which initially causes conductivity increase, is followed by a controlled plasma treatment that restores and even improves the channel layer quality, turning the harmful side effect into an opportunity for enhanced device performance.
2Reliability
If oxygen plasma treatment is applied to reduce channel conductivity, then TFT on-to-off ratio improves, but additional process steps are required
Solution Approach 1:
The patent merges the oxygen plasma treatment step with the existing photolithographic processing sequence, combining two previously separate processes into an integrated workflow. The plasma treatment is performed using the same plasma equipment and process infrastructure already present in the fabrication line, reducing overall process complexity despite adding a treatment step.
Solution Approach 2:
The patent utilizes parameter changes by adjusting plasma treatment conditions (power, gas flow, duration) to optimize the conductivity reduction effect. By carefully controlling these parameters, the process achieves the desired electrical properties improvement while minimizing the impact of adding an extra process step to the fabrication sequence.
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
The oxygen-containing plasma treatment effectively reduces high channel conductivity, enhancing on-to-off ratios and allowing for precise control of the turn-on voltage, achieving a channel sheet resistance greater than or equal to 10^8 Ohms/square and improving device performance by reducing hysteresis and increasing mobility.
Implementation Method 1
exposing it to oxygen plasma
Implementation Method 2
oxygen-containing plasma treatment
Implementation Method 3
annealing the device in air at 175°C
Data Source
AI summary
A thin film transistor is manufactured by a process including forming an oxide semiconductor channel, patterning the oxide semiconductor channel with a photolithographic process, and exposing the patterned oxide semiconductor channel to an oxygen containing plasma.