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

Atomic force microscopy has been applied to study the morphological evolution o f ZnO film on Si(100) and Si(111) substrates with a native oxide layer. With dyn amic scaling of the film morphology at different growth stages, the nucleation a nd growth behavior have been studied for ZnO films deposited by radio-frequency reactive magnetron sputtering. It is found that ZnO film has three nucleation st ages, namely the stages of initial nucleation, low-rate nucleation, and seconda ry 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 f ilm on Si(111), respectively. In the initial nucleation stage, the intrinsic def ects on Si substrates may be responsible for the surface roughening and the dens ity of surface defects determines the nucleation density of ZnO films. The growt h behavior of ZnO film is dominated by the diffusion effect and oriented growth mechanism, as well as the coarsening mechanism induced by the lattice mismatch s tress. In the low-rate nucleation stage, few new ZnO islands are detected and t he 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 th e bombardment of energetic ions or atoms on the surface of Si substrates. In the secondary nucleation stage, shadowing effect may influence the roughening of Z nO films. In the stage of steady growth, ZnO films have a roughness value much l ower than the ones in nucleation stages and grow in the form of columnar grains.