Characteristics of Bias-enhanced Nucleation for Diamond Thin Films

• Main Authors: Chiang Ming Jeng, 江明政
• Other Authors: Hon Min Hsiung
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/50227469215395485502

博士 === 國立成功大學 === 材料科學及工程學系 === 89 === Diamond films were prepared by a microwave plasma chemical vapor deposition in a silica glass tube reaction chamber with a 2.45 GHz microwave generator. The substrates used were p-type (100) oriented single-crystal Si wafer of 1 cm in diameter. The surface pretreatments used included ultrasonic abrasion in a suspension of 1μm diamond powders in acetone, scratching with 1μm diamond paste, and applying negative or positive 100-300 dc bias. The changes of various species such as atomic hydrogen and carbonaceous radicals in the CH4-H2 plasma during positive dc bias have been identified using optical emission spectroscopy (OES). Diamond films grown by different surface pretreatments and selected intervals in bias-enhanced nucleation were analyzed for the surface compisition in the C1s and Si2p regions. Before diamond growth XPS analysis shows that the Si substrate surface was covered by a layer of SiO2 and carbonaceous residue. It was found that methods of surface pretreatment all introduced a substantial amount of carbon species on the substrate surface that was the primary reason for the enhancement of diamond nucleation. In negative biasing process, it reduced and suppressed the formation of oxide that further contributed to the enhanced nucleation density of diamond. And the presence of SiC in the initial stage of nucleation was observed due to the carbon interaction with the Si substrate. In positive biasing process, the effects of process parameters of bias voltage, methane content, bias time, working pressure and microwave power on the diamond nucleation were investigated. The nucleation density higher than 1010 cm-2 was achieved on an mirror-polished silicon substrate by positive dc biasing. With a bias voltage between the range of +200~ +300 V, it was found that high methane content was effective in the enhancement of diamond nucleation. It was also found that amorphous carbon was formed under the positive dc bias conditions. Uniform diamond films were obtained by combining the positive dc bias enhanced nucleation process for 5 min with subsequent growth under the usual MPCVD diamond deposition conditions. The effect of positive dc biasing on nucleation at high methane content to generate oriented diamond nuclei on (100) Si substrate was explored. Microstructures of positive/negative dc bias-enhanced diamond nucleation and growth by microwave plasma chemical vapor deposition on Si have been investigated by high resolution transmission electron microscopy (HRTEM). From cross section high resolution transmission electron microscopy analysis it was observed that an amorphous carbon interlayer was obtained between diamond-silicon interface after positive dc biasing and growth. In negative dc biasing, 5% CH4 was used to enhance nucleation and subsequent growth was conducted in a high quality diamond growth condition. It was found that no evidence of SiC phase or amorphous carbon phase was formed between diamond and silicon interface after negative dc biasing and growth. Emission lines from the Balmer series of atomic hydrogen, molecular hydrogen, CH, C2, and Ar were observed in the visible and ultraviolet ranges when CH4, H2, and Ar were used as the reactant gases. It was found that the concentrations of atomic hydrogen and hydrocarbon radicals increased with positive bias voltage applied. At 30 torr, raising Vb from 0 to +300 V increased the concentration of atomic hydrogen more than 25%. The effects of the process parameters of methane concentration and working pressure on the chemical species during positive dc biasing were also investigated.