規則性奈米平板鑽石沉積在高方向性(111)鑽石薄膜基板之研究

Abstract

本論文探討微波電漿化學氣相沉積對奈米平板鑽石形成的影響；分為兩個部份，首先探討氮氣對奈米平板鑽石的成長，其次是奈米平板鑽石的規則性。

在氮氣對奈米平板鑽石的影響這部份，將以平板鑽石的一次成長和二次成長分別作分析。在一次成長中，所使用的是一般載台，分別通入不同流量的氮氣當作對照並進行平板鑽石的大小尺寸比較。而二次成長則是在一次成長過後的平板鑽石上，再進行第二次的成長，研究在高密度電漿條件，氮氣對平板鑽石形成的效應。實驗結果顯示，高濃度的氮氣不利於平板鑽石的成長，但是少量的氮可以使平板鑽石之邊緣成為平整的形狀。

第二部份是利用微波化學氣相沉積法先行成長<111>晶向之鑽石薄膜，做為沉積奈米平板鑽石之基板；因<111>鑽石膜中之雙晶可以做為平板鑽石成長之位置，當以此鑽石膜作基板，可以進行奈米平板狀鑽石陣列的成長。因此，論文中探討具有規則性的板狀鑽石陣列成長之條件及其特徵。<111>晶向之鑽石薄膜是在以刮痕法做前處理過之Si(111)晶片上沉積。(111)面向的鑽石薄膜之晶粒尺寸約為2-3μm之間。在奈米平板狀鑽石的成長實驗中，探討甲烷濃度與沉積時間對形成較具規則性的平板狀鑽石陣列的影響。掃描式電子顯微鏡觀察發現，具有規則的平板鑽石陣列，大多數排列方式皆平行於(111)面鑽石晶粒基板的三個邊，隨著時間的增長，規則性將隨之變差。此外，在兩個相鄰的(111)面鑽石晶粒之間，其夾角處為(100)面向的凹槽，此凹槽面上的鑽石並不會成長平板狀鑽石，反而形成一平坦面。另外，在已經成長出平板鑽石的(111)面基板之晶粒邊緣區域，未發現平板鑽石，而有類似梯狀流(step-flow)方式之(111)面成長形式，表面相對平整。

This thesis studies the effect of processing conditions of microwave plasma chemical vapor deposition (MPCVD) on the formation of diamond nanoplatelets using gas mixture of hydrogen (H2) and methane (CH4). The experimental works consist of two parts: the first part focuses on the effect of nitrogen (N2) addition on the formation of nano-platelet diamonds, and the second part shows the formation of the array of nano-platelet diamonds on {111} diamond films. The morphology and size of deposited diamonds were characterized using scanning electron microscopy (SEM). For the effect of N2 gas, we deposited diamond nano-platelets in two- step growth conditions. In the first step, we used a flat holder to grow diamond nano-platelets at different N2 concentrations. The second growth step was to deposit diamond on the diamond nano-platelets formed in the first step using a cone-like holder which could increase the plasma density. It was found that the addition of nitrogen does not favor the formation of platelets. However, the smoothness of platelet edges was improved. For the array formation of diamond nano-platelets, {111} textured MPCVD diamond films on Si (111) were used as substrate in which the twins intersected with the surface can be the nucleation sites for platelets. Diamond nano-platelets deposited with different methane concentrations for various times were characterized in terms of the array characteristics. SEM observations showed that the arrays on 2-3μm sized {111} diamond grains of twins can aligned along triangular directions. However, the appearance of the arrays was gradually lost after long-time deposition with high methane concentrations. The nano-platelets were aligned along in the <110> directions parallel to the sides of {111} facets of the substrate. For those regions on {111} diamonds without twins, no nano-platelet was observed, instead (111) diamond growth in step-flow mode occurs.