磁控溅射ZnO薄膜的成核机制及表面形貌演化动力学研究

Study on nucleation and dynamic scaling of morphological evolution of ZnO film deposition by reactive magnetron sputtering

利用原子力显微镜分析了ZnO薄膜在具有本征氧化层的Si(100)和Si(111)基片上的表面形貌随沉积时间的演化.通过对薄膜生长形貌的动力学标度表征,研究了射频反应磁控溅射条件下,ZnO薄膜的成核过程及生长动力学行为.研究发现,ZnO在基片表面的成核过程可分为初期成核阶段、低速率成核阶段和二次成核阶段.对于Si(100)基片,三个成核阶段的生长指数分别为β1=1·04,β2=0·25±0·01,β3=0·74;对于Si(111)基片,β1=0·51,β2=0·08±0·02,β3=0·63.在初期成核阶段,ZnO薄膜的成核密度可能与Si基片表面的本征缺陷有关,薄膜的生长过程除扩散效应影响以外,还可能存在着比较强的晶粒择优生长和晶格错配应力粗化机制.在低速率成核阶段,薄膜的生长行为主要受沉积速率所支配,而扩散效应的影响相对弱化,错配应力得以进一步释放.在二次成核阶段,载能粒子对基片表面的轰击是导致ZnO薄膜再次成核的重要原因,同时阴影效应也可能对薄膜的生长有一定的影响.在薄膜生长后期的稳定生长阶段,薄膜的表面粗糙度明显降低,具有典型的柱状晶生长特征.

Atomic force microscopy has been applied to study the morphological evolution of ZnO film on Si（100） and Si（ 111 ） substrates with a native oxide layer. With dynamic scaling of the film morphology at different growth stages, the nucleation and growth behavior have been studied for ZnO films deposited by radio-frequency reactive magnetron sputtering. It is found that ZnO film has three nucleation stages, namely the stages of initial nucleation, low-rate nucleation, and secondary nucleation. The growth exponents of the three stages are β1 = 1.04,β2 = 0.25 ± 0.01 and β3 = 0.74 for ZnO film on Si（100） and β1 = 0.51, β2 = 0.08 ± 0.02 and β3 = 0.63 for ZnO film on Si（ 111）, respectively. In the initial nucleation stage, the intrinsic defects on Si substrates may be responsible for the surface roughening and the density of surface defects determines the nucleation density of ZnO films. The growth behavior of ZnO film is dominated by the diffusion effect and oriented growted mechanism, as well as the coarsening mechanism induced by the lattice mismatch stress. In the low-rate nucleation stage, few new ZnO islands are detected and the films are roughened slowly in morphology. The deposition rate plays a role of controlling the morphological evolution and the lattice mismatch stress may be released in this stage. The secondary nucleation of ZnO films may result from the bombardment of energetic ions or atoms on the surface of Si substrates. In the secondary nucleation stage, shadowing effect may influence the roughening of ZnO films. In the stage of steady growth, ZnO films have a roughness value much lower than the ones in nucleation stages and grow in the form of columnar grains.