The quality of polycrystalline diamond films grown by chemical vapor deposition is dependent on the growth time, pressure, carbon-to-hydrogen ratio, bias, and nucleation mechanism involved. In this study, reaction gases, methane (CH4) and hydrogen (H2), were used to grow polycrystalline diamond on a p-type (111) silicon substrate with a microwave plasma-enhanced chemical vapor deposition system. In addition to the conventional etching, bias-en-hanced nucleation, and growth steps, the growth step was further divided into two stages. The first stage (growth Ⅰ) was carried out at low pressure and the second (growth Ⅱ) was carried out at high pressure. Results clearly indicate that the use of the growth Ⅰ stage can considerably improve the quality of the diamond film. In the growth Ⅰ stage, well-faceted grains with lower contents of graphite and carbide, and fewer defects are obtained. Therefore, the conductivity is drasti-cally decreased by nearly two orders of magnitude and the diamond film exhibits the semi-insulating characteristics of in-trinsic diamond. The improvement is caused solely by the addition of the low-pressure growth Ⅰ stage. Application of bi-as in the growth Ⅰand/or growth Ⅱ stages can only degrade the synthesized polycrystalline diamond film.%以化学气相沉积法成长多晶金刚石薄膜时,薄膜的品质会受到成长时间、成长压力、反应气体比例、偏压与否及成核的机制等因素影响.研究采用微波电浆辅助化学气相沉积(MPECVD)法,以甲烷(CH4)和氢气(H2)作为反应气体原料,在P型(111)硅基板沉积多晶金刚石薄膜.典型沉积多晶金刚石薄膜的制程可分为四个阶段:抛蚀表面阶段、渗碳阶段、偏压增强成核(BEN)阶段及成长阶段.研究将成长阶段划分为两个阶段,第一阶段压力较低(成长Ⅰ阶段),第二阶段压力较高(成长Ⅱ阶段).结果表明:第一阶段可大大改善金刚石薄膜的品质,所获多晶金刚石薄膜的晶粒具有明确的颗粒边界、较低的碳化物或缺陷,电导率急剧降低,显现出本徵金刚石半绝缘的性质.可以认为金刚石薄膜品质的改善完全为低压成长所致.实验发现在成长Ⅰ阶段或成长Ⅱ阶段施加偏压时,只会降低多晶金刚石薄膜的品质.
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