Substrate bias effect on amorphous diamond-like carbon films deposited by filtered cathodic arc system
研究生：徐耀斌 指導教授：陳家富 博士
提升儲存密度對於硬碟工業來說是一個非常重要的課題，為了要達到高的容量密度，磁頭和碟片磁性層之間的距離必須要減小。而減小保護膜的厚度可以很直接的達到這個目的。以 3 Gbit/in2的容量密度來說，磁頭和磁性層的距離必須小於50 nm，而保護膜的厚度則要求在10 nm，容量密度達到10-15 Gbit/in2的時候，上述的兩個數值則分別要求在25 nm 和5 nm以下。以目前生產硬碟的技術而言，大部份都選擇利用濺鍍法沈積含氫或含氮非晶質類鑽碳膜(a-C:H or a-C:N)以保護磁性層，當薄膜厚度要求越來越薄時，濺鍍法所沈積薄膜的性質已無法達到要求，這使得研究的重點轉而投向離子束沈積法和電子迴旋共振化學氣相沈積系統等其他方法。當薄膜厚度低到只有5-7 nm 的時候，上述兩種技術也會遇到薄膜機械強度不夠和抗腐蝕性太差的問題，為了解決這些問題，近年來的研究方向大多投入在過濾式陰極電弧沈積系統的技術發展。這篇論文簡要的描述了 45∘過濾式陰極電弧沈積系統的製程，並討論偏壓對陰極電弧沈積非晶質類鑽碳膜的影響和其微結構之間的關係。
實驗結果顯示，沈積後的非晶質類鑽碳膜經由拉曼光譜儀、歐傑電子能譜儀、紅外線光譜儀、毫微米壓痕器、和原子力顯微鏡的量測發現，薄膜最高的硬度分佈在基材偏壓為-50 V 到-100 V的範圍，而硬度則和拉曼光譜的 I(D)/I(G) 比沒有很直接的關係。當薄膜組成有高的sp3鍵結比例時會有較高的硬度。在摻雜氮氣時，氮含量會隨著負偏壓的增加而增加。摻雜氫氣時，氫含量則隨著負偏壓的增加而減少。實驗同時發現摻雜氮氣和氫氣都會使得薄膜較難以形成石墨化的小結晶顆粒。另外，越高的負偏壓和氫含量可得到較平整的薄膜表面型態，而氮含量則無此效應。
Substrate bias effect on amorphous diamond-like carbon films deposited by filtered cathodic arc system Student : Yew-Bin Shue Advisor : Dr. Chia-Fu Chen Institute of Materials Science and Engineering National Chiao Tung University Abstract In the field of the magnetic recording technology, there is a strong focus on increasing the storage capacity in computer disk drives. The areal density is predicted to reach 10 Gbit/in2 in the next few years. In order to reach this goal the spacing between the magnetic head (read/write transducer) and the magnetic media must reduced without the slider to actually come in to contact with the disk. One obvious way to reduce the magnetic spacing is to reduce the thickness of the protective overcoats. For example, an areal density of 3 Gbit/in2 needs no more than 50 nm magnetic spacing and 10 nm diamond like carbon (DLC) overcoat on both disk and slider, whereas for 10-15 Gbit/in2 recording density, magnetic spacing must be reduce to 25 nm, and overcoats no more than 5 nm. Present choice of carbon overcoat in the magnetic storage hard disk drive industry is sputter deposited. As overcoats get thinner, the performance/reliability of the sputtered carbon films becomes critical, In order to sustain the phenomenal growth rate in areal density, efforts are under way to develop alternative technology. Ion beam CVD, and electron-cyclotron-resonance chemical vapor deposition (ECR-CVD) are adopted to make 5-10 nm thick DLC films. As overcoat thickness reach 5-7 nm, the mechanical properties and corrosion protection become major challenge for DLC process development. Hydrogenated DLC films produced by Ion Beam CVD or ECR-CVD processes have 20-50 % hydrogen by atomic weight and 40-70 % of sp3 content. The films made by these processes may not meet film continuity, mechanical and corrosion requirements at the ultra-thin level (<10 nm). This motivated researchers to develop a new process to produce hydrogen-free, tetrahedral bonding dominated amorphous carbon films by cathodic arc deposition. In the present study, we briefly describe the 45-degree angle magnetic filter cathodic arc deposition process and investigate the influence of substrate bias on hardness of amorphous diamond-like carbon films. And try to correlate the microstructure, chemical composition, and chemical bonding states with hardness of the corresponding films. After deposition, the film properties were analyzed by Raman spectroscopy, Auger Electron Spectroscopy (AES), Fourier transform infrared spectroscopy (FTIR), Nanoindentation system (NIS). Film surface was examined Atomic force microscope (AFM). It was found that DLC films have highest hardness with substrate bias between –50 V to –100 V and the hardness doesn’t seems to have good correlation with Raman I (D)/I (G) ratio. Films have higher hardness when they have higher fraction of sp3 content. It was also found that nitrogen content increase with increasing substrate bias on nitrogen-doped amorphous carbon films and hydrogen content decrease with increasing substrate bias on hydrogen-doped amorphous carbon films. Nitrogen and hydrogen both has effect on the small graphitic crystalline grows. With examination by AFM, it was found that higher substrate bias and high hydrogen gas flow rate could produce smoother film.
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