基板温度对PVD薄膜分维的影响

Effects of Substrate Temperature on Fractal of PVD Thin Film

采用动态蒙特卡罗(KMC)方法研究物理气相沉积(PVD)制备薄膜过程中基板温度对薄膜微观结构的影响,并用分维理论研究薄膜表面的复杂程度。该KMC模型中既包括入射原子与表面之间的碰撞,又包括被吸附原子的扩散。模拟中用动量机制确定被吸附原子在表面上的初始构型,用分子稳态计算(MS)方法计算扩散模型中跃迁原子的激活能,用红黑树选择跃迁路径并更新系统跃迁机率。研究结果表明:基板温度大于500K时,薄膜表面分维均小于2.04,表面光滑,而当基板温度小于500K时薄膜分维随基板温度降低而增大,表面随基板温度升高变得越来越粗糙,直到基板温度降到250K时,分维达到最大的稳定值2.32,表面情况非常复杂,具有细致的皱褶和缺陷。分维与基板温度之间的关系说明高基板温度有利于分维小、表面光滑薄膜的制备,而低基板温度使薄膜分维增大、表面结构更加复杂。该研究结果与基板温度对PVD薄膜表面粗糙度影响的研究结果趋势上一致,分维能更细致地评价薄膜表面的复杂程度。

Kinetic Monte Carlo method was applied to simulate the relationship between substrate temperature and the microstructure of the thin film fabricated by means of physical vapor deposition （PVD）, and its surface topography was studied by fractal theory. Two phenomena were incorporated in the KMC model： adatom-surface collision and adatom diffusion. In the KMC simulation, Momentum Scheme was used to locate the initial location of adatom, activation energy was calculated by molecular statics （MS） calculations, and the algorithm was carried out by red-black tree. The results reveal that the fractal of thin film is less than 2.04 and thin film surface is smooth when substrate temperature is higher than 500 K. However, thin film fractal increases and surface become more and more rough with decreasing of substrate temperature when substrate temperature is lower than 500 K. When substrate temperature is 250 K thin film fractal is 2.32 and rough surface, fine rugosity and defect were achieved. The relationships between thin film fractal and substrate temperature indicate that higher substrate temperature is helpful to smooth film preparation with small fractal, however, thin film fractal is large and surface structure is complex when substrate temperature is lower. The study results agree with the study of substrate temperature and surface roughness factor, which reveal that fractal is a way to evaluate thin film surface topography.