| Summary: | 碩士 === 國立暨南國際大學 === 電機工程學系 === 92 === In this thesis, we investigated the application of low-dielectric-constant (low-k) hydrogen silsesquioxane (HSQ) for thin-film-transistor (TFT) arrary technology. The adoption of low-k HSQ for TFT passivation layer can effectively increase the aperture ratio of display matrix, reduce resistance-capacitance delay (RC delay), exhibiting high optical transparency (90% at 300-800nm), good planarization properties and excellent gap-filling capability. In this study we have investigated one of the promising candidates of low-k dielectrics, hydrogen silsesquioxane (HSQ), for TFT array technology application. The leakage current conduction mechanism in HSQ films after O2, H2/O2 plasma treatments and photo illumination will be discussed extensively.
In comparison with chemical vapor deposited (CVD) low-k materials, HSQ films can be deposited using spin-on process which is a simpler technique. The quality of the low-k HSQ film dependents on the residual quantity of the Si-H bonds in the film after curing. A low dielectric constant can be achieved if the Si-H bonds in the HSQ film outnumber the Si-OH bonds. For the investigation of photo-induced leakage current, we have found that dangling bonds are easy to be generated during the processing of the HSQ films; thereby, a small amount of photo-induced leakage current can be generated via these traps in HSQ films. Fortunately, the level of photo-induced leakage current is acceptable for TFT array applications. However, the leakage current of HSQ film is increased more than an order of magnitude after O2-plasma treatment during photoresist stripping, and the conduction mechanism for the leakage current transferring from Schottky emission to ionic conduction. In this work, we found that an hydrogen plasma treatment of the HSQ films can improve the films quality. The leakage current in HSQ films subjected to H2-plasma treatment is decreased. In this work, we have proposed a model to explain the role of the hydrogen in HSQ film. The hydrogen can effectively passivate the surface of HSQ film. If the surface is not passivaed by hydrogen, much of those dangling bonds will remain on the surface. Dangling bonds can easily absorb moisture and form Si-OH bonds, which will result in higher dielectric constant and leakage current. Hydrogen plasma provides hydrogen to passivate the surface and reduce the dangling bonds content and moisture uptake.
In conclusion, we have found that HSQ film is insensitive to light illumination; thereby, photo-induced leakage current of HSQ film is negligent under photo radiation. This indicates that HSQ has potential possibilities for being applied to the application in TFT display panel as the passivation layer.
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