電漿輔助化學氣相沉積碳氮化矽薄膜之光學性質:探討前驅物與沈積條件之影響

Abstract

新穎的非晶相矽碳氮薄膜近年來持續成為極具吸引力的材料,原因為其優異的機械性質、光電性質。有些薄膜由於其在可見光和紫外光波段具有高穿透度和低反射率還有極優良的阻水性質，可應用於太陽能電池和有機發光元件(OLED)上。矽碳氮材料也可產生寬能隙而廣泛應用於光電元件中。 在本論文中,使用矽氮烷單一前驅物,並以射頻電漿輔助化學氣相沉積矽碳氮薄膜，而達到較好的組成變化以及較低的漏電流密度。具體來說，探討三種獨特的單一前驅物對矽碳氮薄膜之影響。三種分別為[(n-methyl-aza-2,2,4-trimethylsilacyclopentane (MTSCP) ， 1,3-divinyl-1,1,3,3-tetramethyl- disilazane (DVTMDS) ， 和 1,3,5-trimethyl-1,3,5-trivinyl-cyclotrisilazane (VSZ)] ，其各具有不同的碳矽比、碳氮比，和有無乙烯基的結構。 我們驗證前驅物的結構和不同沉積溫度對矽碳氮薄膜的影響。相比於MTSCP前驅物，具有乙烯基結構的DVTMDS 和VSZ，在電漿聚合中傾向於形成Si-(CH2)2-Si亞甲基橋交聯結構且保留下較多的碳氫結構，形成的薄膜具有較好的機械強度、熱穩定性和光學穿透度。DVTMDS and VSZ在400 oC下，其薄膜具有較好的光學穩定性且分別在可見光區維持在83%和65%的穿透度。相反的，在MTSCP分子中的N-CH3 和Si-CH2CH3結構容易在電漿中裂解，造成不同溫度下結構變化較大。隨著基板溫度提升至400℃, MTSCP薄膜在可見光範圍整體穿透度跌至50%。然而在低溫沉積下，三種前驅物所沉積出的矽碳氮薄膜皆具有高穿透度以及高的光學能矽。在這篇論文中對於MTSCP, DVTMDS and VSZ製程的矽碳氮薄膜同時對化學結構、光學能矽和反射率進行研究探討。

Novel amorphous SiCxNy coatings are becoming increasingly attractive because of their mechanical, optical and electronic properties. Such films show promising applications for solar cells and organic light-emitting diodes (OLEDs) applications owing to their high transmittance and reduced reflection in ultra-violet and visible range as well as their excellent moisture barrier properties. In addition, SiCxNy materials can be tailored and fabricated into a wide range of band-gap for optoelectronic devices applications. In this thesis, SiCxNy films are fabricated by radio frequency (RF) chemical vapor deposition (PECVD) using silazane single precursor at lower power density to achieve better compositional control and lower dielectric leakage. In specific, three unique single precursors: [(n-methyl-aza-2,2,4-trimethylsilacyclopentane (MTSCP), 1,3-divinyl-1,1,3,3-tetramethyl- disilazane (DVTMDS), and 1,3,5-trimethyl-1,3,5-trivinyl-cyclotrisilazane (VSZ)) of various C/Si and N/Si ratios, and with or without vinyl groups were studied. We examined the effects of the precursor chemical structure and deposition conditions such as substrate temperature on the optical properties of SiCxNy films. Compared to MTSCP, the vinyl groups of DVTMDS and VSZ readily formed the Si-(CH2)2-Si methylene bridge cross-linking in SiCxNy films, resulting in better mechanical strength, thermally stability, and optical transmittance. SiCxNy films prepared at 400 oC by using VSZ and DVTMDS possessed better optical stability and maintained at ~ 83% and ~65% transmittance in visible wavelength, respectively. In contrast, the N-CH3 and Si-CH2CH3 bondings of MTSCP could be easily broken into fragments under plasma deposition conditions, leading to less retained -CH2 or –CH3 bondings, i.e. more Si-N or Si-C bondings. When Ts was increased to 400℃, the transmittance of MTSCP thin films dropped to 50% in visible range. Nevertheless, at low deposition temperature, SiCxNy films prepared by these 3 precursors all exhibit high transmittance and high optical band gap. The chemical structures, optical band gap, and reflectance of SiCxNy films using VSZ, MTSCP, and DVTMDS were also examined and discussed in this thesis.