计算机模拟在薄膜外延生长中的应用

计算机模拟是计算机技术的一个重要应用领域,具有高效、快捷、经济等多种特点.以Cu膜为例用Monte Carlo算法模拟了薄膜生长的随机过程,并提出了更加完善的模型.在合理选择原子间相互作用计算方法的基础上,考虑了原子的吸附、在生长表面的迁移及迁移所引起的近邻原子连带效应、从生长表面的脱附等过程.利用自行编写的4个软件模拟计算了薄膜的早期成核情况以及表征薄膜生长表面状况的粗糙度和表征薄膜内部晶格完整性的相对密度.结果表明,随着衬底温度的升高或入射率的降低,沉积在衬底上的原子逐步由众多各自独立的离散型分布向聚集状态过渡形成一些岛核,并且逐步由二维岛核向三维岛核过渡.在一定的原子入射率下,存在3个优化温度,成核率最高时的最大成核温度Tn,薄膜的表面粗糙度最低时的生长转变温度Tr,相对密度趋近于1时的相对密度饱和温度Td.三者均随入射率的对数形式近似线性增大,并且基本重合.这说明在一定入射率下这3个优化温度近似相等.这一现象的原因在于三者的形成机理都是基于原子的热运动.这一结论使探索工艺条件时不仅可以采用计算机模拟的方法,而且可以从早期最大成核条件预计沉积较厚薄膜的最佳生长工艺.同时发现,随着入射率的增大,相对密度不断减小.可是在不同温度区域入射率对早期成核率和表面粗糙度的影响不同.当温度较低时,随着入射率的增大,最大成核率基本不变,表面粗糙度不断增大;当温度较高时,随着入射率的增大,最大成核率不断增大,但表面粗糙度不断减小.

A computer simulation of island nucleation and growth in thin-film epitaxy

Computer simulation technique plays a very important role in the field of computer application. A three-dimensional kinetic Monte Carlo technique has been developed to simulate the growth of thin Cu films and the model involves incident atom attachments, diffusion of the atoms on the growing surface and detachment of the atoms from the growing surface. The related effect from surface atom diffusion was taken into account. A great improvement was made on the calculation of the activation energy for atom diffusion based on a reasonable assumption of interaction potential between atoms. The formation nucleation rate at the early stage, the surface roughness and the relative density of the films were simulated as functions of growth substrate temperature and deposition rate. The results showed that there exist three optimum growth temperatures at a given deposition rate, namely Tn at which the formation nucleation rate is maximum, Tr at which the surface roughness minimizes and Td at which the relative density approaches saturation. They all increase with an increment of the substrate temperature and the relations almost superpose, which means they are close to being equal at a given deposition rate. The simulation results also showed that the relative density decreases with the increase in the deposition rate. But the formation nucleation rate is close to being steady under a lower temperature while it increases at a higher temperature. The surface roughness increases at a lower temperature while decreasing at a higher temperature.