富含矽奈米結構之氧化矽薄膜之成長與其特性研究; Investigation of Growth and Characteristics of Si Nanoclusters Embedded in Si Oxide Film

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/6704

Title:	富含矽奈米結構之氧化矽薄膜之成長與其特性研究;Investigation of Growth and Characteristics of Si Nanoclusters Embedded in Si Oxide Film
Authors:	林駿宏;Chun-Hung Lin
Contributors:	光電科學研究所
Keywords:	二氧化碳雷射;量子侷限效應;矽奈米結構;電漿增強型化學氣相沉積;CO2 laser;PECVD;quantum confinement effect;Si nanocluster
Date:	2005-06-25
Issue Date:	2009-09-22 10:26:17 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	在本論文中，吾人設計一新式的雷射輔助化學氣相沉積系統，來沉積含有矽奈米結構之氧化矽薄膜。此一雷射輔助化學氣相沉積系統乃是利用傳統的電漿增強式化學氣相沉積系統在結合一外加之二氧化碳雷射，並利用矽烷與笑氣作為反應氣體。由於矽烷氣體分子對波長10.6 μm的二氧化碳雷射光之光子有很強的吸收，所以吾人利用二氧化碳雷射的輔助來加強反應矽烷氣體分子的活化並矽烷氣體分子之分解，並使得所沉積的氧化矽薄膜中形成矽奈米結構。吾人利用不同功率（0-40 W）的二氧化碳雷射來輔助成長，並利用相分離的模式來說明矽奈米結構在薄膜形成的過程之中由氧化矽的基體中分離出來的情況。研究中發現，二氧化碳雷射的輔助使得氧化矽薄膜在沉積時發生相分離的情形，亦即分離出矽奈米結構與氧化矽的基體，且當二氧化碳雷射功率提升時，所形成之矽奈米結構的尺寸也愈大，使得量測到的光激發光譜有紅移的現象，並進一部透過矽奈米結構與氧化矽基體的混合物模型來計算並佐證此一項分離的現象。此外，調整矽烷氣體流量比（矽烷/總反應氣體之比例）為0.6~0.75的比例來沉積氧化矽薄膜，並利用無二氧化碳雷射輔助之電漿增強式化學氣相沉積系統所沉積之薄膜做為對照。所沉積的薄膜則分別利用傅氏轉換紅外線光譜、拉曼光譜、光激發光譜、能量散佈光譜與穿透式電子顯微鏡進行分析。吾人發現可以調變所形成之矽奈米結構的尺寸由3.7 nm減小至2.7 nm。透過熱處理，可以增強矽奈米結構從氧化矽基體分離的情況，使得氧化矽基體變成更趨近於二氧化矽，同時矽奈米結構顆粒的尺寸也增加。另外，吾人也發現光激發光譜的強度會隨著激發光源(氦鎘雷射)的照射時間會有衰退的現象，利用傅氏轉換紅外線光譜的定量與定性分析，得知氦鎘雷射的持續照射會造成矽氫鍵結的斷鍵，而形成非放射複合中心，因而使得光激發光譜的強度衰退。利用氫氣環境在400℃下進行5分鐘的熱處理，可以修補所形成之懸鍵，且利用氫氣熱處理，亦可修補薄膜中原先就存在的懸鍵，進而提昇光激發光之發光。 In this thesis, we present a novel laser-assisted chemical vapor deposition (LACVD) system for growing Si nanoclusters embedded in a Si oxide matrix at a room temperature. This LACVD system was constructed by combining a conventional plasma enhanced chemical vapor deposition (PECVD) system and a CO2-excited laser. A gaseous mixture of SiH4 and N2O was used for the reactants. In view of the point of a high absorption coefficient of a wavelength of 10.6 μm by SiH4, an external CO2 laser beam was guided into a conventional PECVD system. A CO2 laser with various powers was used in a conventional PECVD system to assist the decomposition of SiH4 molecules and also to separate the Si clusters from Si oxide matrix. The phase separation model was proposed to discuss the inconsistency between the calculated and actual composition of O/Si atomic ratio. The dependencies of the photoluminescence (PL) photon energy and intensity on the CO2 laser power were observed. The mixture model of both pure Si and pure oxide phases were also used for calculating the refractive indices of the matrix. These results have demonstrated the existence of laser-induced phase-separated Si nanoclusters and the relation between the sizes of Si nanoclusters and the CO2 laser power were also elucidated. Varying N2O gas ratio (defined as N2O/total gases) from 0.6 to 0.75 caused the observed PL light emission to vary from 1.65eV to 1.92eV without post-annealing. A phase-separated model and PL measurements were used to identify Si nanoclusters embedded in Si suboxides. Furthermore, the average dot sizes of the films grown by the LACVD system with XN2O=0.6, 0.67, 0.71, and 0.75 are identified by images of transmission electron microscope (TEM) as 3.7, 3.2, 3.0, and 2.7 nm, respectively. Further, the optical characteristics and annealing behaviors were also studied. The PL emission intensity increased with the annealing temperature until some temperature, then decreased as the annealing temperature increased. Since defect centers in Si suboxides would be gradually annihilated during thermal annealing process, the PL emission intensity originated from defect centers would be reduced with the annealing temperature. The quantum confinement effect is found as the dominant PL emission mechanism in Si nanoclusters embedded in Si suboxides. Si nanoclusters would be separated from the Si suboxide matrices due to the decomposition assistance of SiH4 by CO2 laser. Raman spectroscopy and photoluminescence measurements of the as-deposited and annealed films were used to identify the Si nanoclusters embedded in the Si suboxide matrices were identified. By studying the light emission behaviors, we deduce that the quantum confinement effect is the dominant mechanism. A degradation of PL intensity by irradiating the sample with helium-cadmium (He-Cd) laser was also observed. The dependence of PL degradation on long-term irradiation of He-Cd laser was investigated. We found that He-Cd laser induced breakage of Si-H related bonds resulted in Si dangling bonds such as D centers and Pb centers, which are known to reduce the PL intensity. The PL intensity of the He-Cd laser irradiated samples can be improved to the level of as-deposited samples after subjecting the samples to a H2 ambient at 400 °C for 5min. Post-annealing in H2 could also help to increase the PL intensity plays by passivating the defect centers in as-deposited samples.
Appears in Collections:	[Graduate Institute of Optics and Photonics] Electronic Thesis & Dissertation

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