| Summary: | 碩士 === 國立清華大學 === 電子工程研究所 === 93 === Decreasing the temperature at which dielectrics are deposited without causing any deterioration of the dielectrics properties has become a priority in the thin film research area. Low-temperature deposition is needed, for example, for producing thin film transistors (TFTs) on ultra-thin, plastic substrates that can withstand temperatures of up to 100℃. Such flexible substrates may replace the glass screens in future displays due to several advantages, e.q., lower cost, lower power consumption, lower weight, and better flexibility.
The standard gate dielectric nowadays for amorphous TFTs is silicon nitride deposited by radio-frequency plasma enhanced chemical vapor deposition (rf-PECVD). However, the processing temperature of rf-PECVD is 300℃, which is too high for flexible displays. Furthermore, these layers exhibit high hydrogen contents of up to 20 atom % and low dielectric strength. In contrast, electron cyclotron resonance (ECR) PECVD Si3N4 layers with good material and electrical properties have been successfully deposited in recent years, at much lower temperatures. ECR plasma operates at a low pressure, has a low electron and ion energy, and a high degree of ionization. Because of the dense characteristics of the ECR plasma, the deposition temperature can be lowered, while reducing the concentration of unwanted hydrogen bonds through ion bombardment.
Our aim is to obtain layers with low hydrogen bonds at room temperature, without any annealing process. Helium is known to efficiently eliminate hydrogen in rf-PECVD layers. Hence silane diluted in helium was employed as a gas precursor in our deposition system.
In this thesis, the influences of the silane flow, the nitrogen flow, and two different microwave power on deposition rate, film composition, and capacitance-voltage (C-V) and I-V measurements were investigated in order to find the optimal deposition conditions. We focused on the electrical characteristic.
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