異質基板塗覆金剛烷及鑽石沉積之研究

Abstract

由於鑽石有許多優異的物理和化學性質，故其應用範圍相當廣泛。微波電漿氣相沉積法是最常用來合成高品質鑽石的方法，然而在非平整光滑的異質基材表面上沉積鑽石極為不易。若要得到高方向性和磊晶的鑽石薄膜，提高成核密度是主要關鍵之一。傳統的強化成核方法難以用在非導體的基板之上，特別是在光學應用上常見的非導電之氧化物和氮化物基板上。本論文主要是以一種新的浸塗方式將金剛烷塗覆於矽、藍寶石、氮化鋁(AlN)/藍寶石等異質基板上，並探討微波電漿氣相沉積鑽石過程中金剛烷在這些基板上輔助成核情形及鑽石成長狀況。 論文第一部分主要是藉由浸塗方式將金剛烷塗覆於矽基板，探討浸塗過程中金剛烷和兩種不同醇類溶劑之化學溶液對鑽石成核階段的影響，即乙二醇和二乙二醇兩種。由掃描式電子顯微鏡(SEM)、拉曼光譜及X光繞射(XRD)結果可知金剛烷有助於鑽石成核，而二醇溶劑更有助於金剛烷附著於基板，幫助後續鑽石成核，從穿透式電子顯微鏡(TEM)觀察及擇區電子繞射(SAD)分析直接成長在矽晶片上之鑽石具有<110>diamond // <110>Si 和{002}diamond //{002}Si之磊晶成長關係。 論文第二部分則是將此方法應用於非導電的氧化物藍寶石基板，金剛烷以浸塗方式塗覆在c面藍寶石基板上之後，微波電漿氣相沉積之鑽石藉由SEM、XRD、拉曼光譜等分析為<111>方向鑽石連續膜，從TEM觀察發現鑽石可直接成長於藍寶石上而無中間層形成，SAD分析得到鑽石與藍寶石基板可具有的磊晶關係為<110>diamond //<2 0>sapphire和{111}diamond //{0001}sapphire或{111}diamond //{0 14}sapphire。 論文的第三部分是將此方法應用於氮化鋁/藍寶石基板，探討將金剛烷塗覆與鑽石成長，其中AlN是以微波電漿方式將c面藍寶石基板進行氮化，形成於藍寶石基板上之AlN從XRD分析確認為磊晶層。經由SEM觀察磊晶層與X光電子能譜儀(XPS)分析化學組成，發現以H2/N2電漿進行氮化可於30分鐘後藍寶石基板得~ 270 nm厚之AlN薄膜，而以純N2電漿進行氮化30分鐘後可得~ 90 nm厚且含有氧的AlN薄膜。藉由浸塗方式將金剛烷塗覆於AlN磊晶層上所成長出鑽石，經由TEM的觀察發現鑽石亦可直接在AlN磊晶層上成長，擇區繞射(SAD)分析可得出鑽石/氮化鋁/藍寶石之磊晶關係為<110>diamond // <0 1 0>AlN // <2 0>sapphire和{1 1}diamond // {0002}AlN // {0006}sapphire。

Abstract

Diamond has a wide range of applications owing to its excellent physical and chemical properties. Microwave plasma chemical vapor deposition (MPCVD) is the most widely used method to grow high-quality diamond. However, the diamond nucleation is critical for growth on the smooth surface of a heterosubstrate. To obtain a highly oriented diamond film and a heteroepitaxial film, it is necessary to enhance the nucleation density. The conventional methods for enhanced nucleation on heterosubstrates are difficult to be applied onto the insulting substrates of oxide and nitrides for optical applications. Adamantane which can be treated as diamond nucleus is used in this work, and a dip coating method as pretreatment of adamantane seeding is developed for enhancement of diamond nucleation on Si, sapphire, and aluminum nitride/sapphire substrates in MPCVD diamond growth. In the first part of the thesis, the chemical solutions of adamantane in the solvents of ethylene glycol and diethylene glycol were used for dip coating on mirror-polished Si substrate. Comparisons have been made for their effects on diamond nucleation and the subsequent growth in MPCVD. The results from scanning electron microscopy (SEM), Raman spectroscopy, and x-ray diffraction (XRD) show that the dip coating of adamantane with glycol significantly assists the diamond nucleation, and the nucleation density is higher with diethylene glycol than ethylene glycol. Based on transmission electron microscopy (TEM) observations with selected-area diffraction (SAD) in cross-section view, the orientation relationship of diamond with Si is found to be <110>diamond //<110>Si and {002}diamond //{002}Si for diamonds directly grown on Si (100). In the second part of the thesis, the dip coating method using adamantane and diethylene glycol was applied onto sapphire substrate. The SEM, Raman spectroscopy, and XRD results show that a continuous <111> oriented diamond film can be synthesized on the c-plane sapphire. Cross-sectional TEM observations with SAD show that diamond can be directly grown on sapphire without formation of an interlayer, and the diamond/sapphire orientation relationship is found to be <110>diamond // <2 0>sapphire and {111}diamond // {0001}sapphire or {111}diamond // {0 14}sapphire. In the third part of the thesis, the same dip coating pretreatment was also used for the enhancement of diamond nucleation on AlN/sapphire. The AlN films were prepared by microwave plasma nitridation of c-plane sapphire. From the results of SEM, XRD, and XPS, a ~ 270 nm thick AlN layer can form epitaxially on sapphire after 30 min exposure to the nitrogen/hydrogen plasma, whereas the nitridation by pure nitrogen plasma for 30 min forms a ~ 90nm thick AlN layer containing oxygen. Diamond growth on adamantane-coated AlN/sapphire by MPCVD can be succeeded with the orientation relationship of <110>diamond // <0 10>AlN // <2 0>sapphire and {1 1}diamond //{0002}AlN // {0006}sapphire.