微波電漿氣相沉積鑽石膜結構與附著性改良之研究

Abstract

具有優選方位鑽石膜使用微波電漿化學氣相沉積法製作，其參數為: 1200 W的微波功率、腔體壓力為110 torr、甲烷與氫氣的比例為1/20、處理時間為0.5-4.0 h。在鑽石膜生長2.0-4.0 h後，鑽石膜表面形態呈現四方形結構且規則的堆疊，此形態從XRD數據顯示是{111}結構鑽石膜，但表面形態偏向生長出{110}優選方位的鑽石結構。此現象是在生長初期鑽石先由(111)矽晶片異質磊成長(heteroepitaxial growth)而生成球狀鑽石，到生長4.0 h後形成正方且堆疊的形態，由3.0 h沉積後的TEM明視野像得知堆疊層間距為200 nm。最後結果顯示在不同時間沉積成長的鑽石膜，具有球形與{110}四方形鑽石2個型態特徵。由 I-V曲線，可以知道在沉積4 h後的薄膜較符合歐姆接觸特性，因在此形態下鑽石膜表面粗糙度最小。 為了避免鈷造成負面效應，在含6 wt %鈷的碳化鎢(WC-6 % Co)底材上生長鑽石膜處理前，在基材表面上覆蓋鎢粉而增加鑽石膜附著度。鑽石沉積過程中，鎢粉會轉變成W2C 和WC，其WC可與碳原子形成鑽石膜，所以鎢粉會幫助抓取碳並在附近沉積成鑽石，使鑽石顆粒圍繞著鎢粉成核和生長。由洛氏硬度測試後的表面觀察，發現較小顆粒鎢粉的間距與空隙相對較小，所以較小鎢粉有較好附著性，故鎢粉間隙是影響附著性的因素之一。最後，再由拉曼、硬度與附著性測試知道使用2.0 μm鎢粉前處理碳化鎢試片，可以使鑽石膜有好品質、高硬度(可達27.78 GPa)與好的附著性。

The textured orientation of diamond films is elaborated by microwave plasma chemical vapor deposition (MPCVD) in 1200 W, 110 torr, CH4/H2=1/20, and 0.5-4.0 h deposition time. The special morphology revealed the rectangular structure stacked regularly on diamond films after growing 2.0-4.0 h. The {111} textured orientation of diamond films grew {110} preferred orientation on the surface that measured by XRD results. The formation of the diamond film epitaxial formed the textured octahedron on the ball-shape (or cauliflower-like) diamonds in an early duration 0.5 h, then the surface of diamond films extended to pile the rectangular structure at 4.0 h. And the width of the tier was about 200 nm in the 3.0 h deposition time by TEM images. The result revealed that textured diamond films in different deposition time had two morphology properties of typical ball-shape and rectangular diamonds in the growth period. The I-V characteristics of the oriented diamond films in 4.0 h deposition time was more conform to the ohmic contact. To increase the adhesion of diamond films and avoid the negative effects of using cobalt, previous treatments have employed tungsten particles to cover the surface of the 6 wt.% cobalt-cemented tungsten carbide (WC-Co) substrate. The surface of the tungsten particles is transformed into W2C and WC, which attracts and traps carbon. Through the process of nucleation, the carbon forms around the tungsten particles, thereby satisfying the conditions necessary for the formation of diamond film. Rockwell indentation tests indicate that addition of tungsten particles promotes the interfacial adhesion of diamond films with WC-Co substrates. We determined that using smaller tungsten particles decreased the number of gaps and cavities on the surface of the substrate, thereby enhancing the adhesion of the diamond film. Using Raman spectroscopy, we determined that diamond films of excellent quality with good adhesive properties and a hardness level as high as 27.78 GPa could be produced following pretreatment with 2.0 μm tungsten particles.