電漿處理對奈米碳管合成及奈米碳管表面特性之影響

Abstract

近年來，在矽元件尺寸微小化的趨勢下，奈米碳管特別被期待應用在奈米電子元件上，此乃因奈米碳管具有極佳的特性。本論文試圖提出電漿處理運用於奈米碳管的研究，將實驗結果中包括前處理與成長特性、表面特性、電子傳輸能力、與機械特性作連貫性的探討。 在前處理與成長特性部分，氫電漿前處理，可促使微小顆粒產生聚集，依據對鎳層觸媒前處理產生之效應，證明週期時間、氫氣流量對於顆粒化有其對應的趨勢。經由拉曼光譜儀的量測，合成後的奈米碳管在適當條件下的氫電漿前處理可使非晶質碳與非序結構降低，進而提升奈米碳管之品質。此外，藉由奈米壓痕壓縮測試，從壓力控制模式，可發現到奈米顆粒之楊氏模數與硬度值皆比鎳層為低，因而證實前處理奈米顆粒的特性。 在表面特性上，經由四氟化碳與氧氣電漿後處理，奈米碳管表面非晶質碳明顯降低。由拉曼光譜儀顯示，短時間之後處理可提升品質比值，而長時間卻降低品質比值。此外，傅立葉光譜儀可證實表面存在碳氧與碳氟的鍵結。由熱脫附量測顯示出，奈米碳管表面氟氧鍵確實有脫附的現象。X光電子能譜亦印證出表面確實具有氟化之增益。 在電子傳輸研究中，以曝光顯影製作橫向之結構，讓奈米碳管連接於兩邊之電極。藉由四氟化碳與氧氣電漿後處理，證實電漿後處理確實具有修飾奈米碳管與增進電子傳輸之效益，而使得元件在室溫下可表現出蕭特基(Schottky)接觸特性。 至於機械特性部分，本論文選用奈米壓痕針頭對頂部奈米碳管薄膜作測試，可得到相對的韌性並展現出奈米碳管薄膜的特點。此外，利用拉曼光譜儀量，印證當增加施力所產生的裂痕越大，量測品質變化量(ID/IG)上升，由此可印證奈米碳管之非序結構確實提升。 整體實驗中，無論是觸媒的形成，奈米碳管的吸附能力，電性、機械方面的測試上，均可藉由實驗證實其特性。

In the semiconductor industry, silicon devices are being scaled down to smaller dimensions. Carbon nanotubes (CNT) are of particular interest for future nanoelectronic applications, because of their high aspect ratio, small radius of curvature, high chemical stability, and large mechanical strength. Plasma surface treatments are promising techniques in the design and development of new materials because surfaces can be modified without altering the bulk properties of the material. Accordingly, more sensitive surface analysis approaches are being used to obtain more precise information regarding the plasma-treated surface chemistry. An experiment was conducted to elucidated pretreatment, the adsorption (desorption) in plasma surface treatment, the electronic conduction property associated with surface treatments, and the mechanical characteristics of CNTs. In the pretreatment, CNTs were synthesized by microwave plasma chemical vapor deposition (MPCVD) on Ni/TiN/Si and Ni/TaN/Si systems. The effect of the pretreatment period and flow rate on the growing characteristics of the Ni catalyst layer and the properties of the CNTs was examined. The mechanical response of particle aggregates to the compression of substrates is emphasized. The improvement of the surface performance of the catalyst is using H2 plasma is suggested. Therefore, small agglomerates of catalyst nanoparticles formed on TiN buffer substrates, helping to elucidate the mechanical properties of relatively large pretreated nanoparticles. The deformation behavior of the agglomerates under loaded control-mode nanoindentation was investigated. Nanoparticle testing demonstrated a lower modulus (from 238.9±8.4 to 176.2±6.1 GPa) and hardness (from 17.2±1.6 to 11±0.8 GPa) than those of the Ni film. The effects of the H2 plasma flow rate during pretreatment on the synthesis of CNTs using an MPCVD system are also studied. Raman spectroscopy was employed with a change-coupled detector is used to elucidate the effect of the flow rate on the intensity ratio of G and D bands (ID/IG), which in turn yields the amounts of amorphous carbon and carbonaceous particles in the CNTs. The effect of CF4/O2 plasma on the surface performance of CNTs in the post-treatment is elucidated. SEM and TEM studies reveal changes in the surface morphologies of CNTs that were exposed to the CF4/O2 plasma. Additionally, the ID/IG ratios reveal that chemical treatment with CF4/O2 plasma for 2 min reduces the degree of disorder. After 10 min, however, the degree of disorder in CNTs is increased. FTIR absorption spectra include peaks that correspond to C-O and C-F stretching vibrations. The TDS results yield adsorption information. XPS datum reveals fluorination in CF4/O2 plasma-treated CNTs and the absence of a significant of physisorbtion on CNTs. This result shows that adding oxygen to the plasma increases the decomposition efficiency. A CNT bridge on SiO2 that is patterned photolithographically in an electronic device is described. The CNTs grow laterally to the substrate over a Ta vertical growth barrier and connect to the side of the electrode pad. The CF4/O2 post-treated has a higher current-voltage curve than the surface-modified. The typical Schottky contact characteristics at room temperature are discussed. The surface of the CNT interacts with the surrounding plasma, breaking C-C bonds and creating active sites to bond the functional groups (fluorination). C-F binding in the amorphous carbon can be reduced by modifying the CNTs. A CNT film was studied using nanoindentation equipment (Berkovitch indenter) by varying the loading force. CNT films exhibit features that are associated with toughening against cracks caused by indentation. The quantitative indentation force is utilized to determine the CNTs axial modulus, depending on the Raman shift. The ID/IG ratios of the CNTs films are associated with an increase in the force. Such features follow in part from the fact that CNTs films generally contain some disordered regions. The experiment on plasma treatments yields information on the formation of the catalyst, the adsorption (desorption) capacity, the electronic conduction and the mechanical behavior in CNTs.