摘要:
本文采用甚高频等离子体增强化学气相沉积技术制备了沉积速率系列不同生长阶段的微晶硅薄膜,通过椭圆偏振技术研究了生长过程中微晶硅薄膜表面粗糙度的演化.实验结果表明:沉积速率为0.08和0.24 nm/s的低速沉积时,硅薄膜表面粗糙度接近,生长指数分别为β=0.21和β=0.20,对应有限扩散生长模式,此时沉积速率对硅薄膜生长影响不大,原因是低速沉积时成膜先驱物有足够时间迁移到能量低的位置;当沉积速率增加到0.66 nm/s时,硅薄膜表面粗糙度明显增加,生长指数β=0.81,大于0.5,出现了异常标度行为,与低速沉积的生长模式明显不同,原因是高速沉积时成膜前驱物来不及扩散就被下一层前驱物覆盖,降低了成膜前驱物在薄膜表面的扩散,使表面粗糙度增加和生长指数β增大.β大于0.5的异常标度行为与阴影效应有关.
Abstract:
Three sets of hydrogenated mierocrystalline silicon (μc-Si:H) films for different deposition time were prepared by very high frequency-plasma enhanced chemical vapor deposition with different deposition rates. The surface roughness evolution of μc-Si : H has been investigated using spectroscopic ellipsometry. For films with the deposition rate of 0.08 nm/s and 0. 24 nm/s, the surface roughness of films changes a little, and the growth exponent β is about 0.20. Similar β values ascribed to the adatoms have enough time to move to the site with lower energy under lower deposition rate. However, when the deposition rate increases to 0.66 nm/s, the surface roughness of films increases obviously, and the exponent β is about 0. 81, which is much higher than 0. 5 for zero diffusion limit in the scaling theory. The growth mode of high-rate deposited μc-Si:H is clearly different from that of lower-rate deposited μc-Si: H. This is due to the fact that the adatoms have no enough time to diffuse before being covered by the radicals of the next layer under high deposition rate, which decreases the surface diffusion of the adatom, and therefore increases the film surface roughening which results in a larger β. The case of β > 0. 5 is related to the shadowing effect.
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