Surface Roughening During Plasma-Enhanced Chemical-Vapor Deposition of Hydrogenated Amorphous Silicon on Crystal Silicon Substrates

The morphology of a series of thin films of hydrogenated amorphous silicon (a-Si:H) grown by plasma-enhanced chemical-vapor deposition (PECVD) is studied using scanning tunneling microscopy. The substrates were atomically flat, oxide-free, single-crystal silicon. Films were grown in a PECVD chamber directly connected to a surface analysis chamber with no air exposure between growth andmeasurement. The homogeneous roughness of the films increases with film thickness. The quantification of this roughening is achieved by calcullation of both rms roughness and lateral correlation lengths of the a-Si:H film surface from the height difference correlation functions of the measured topographs. Homogeneous roughening occurs over the film surface due to the collective baehavior of theflux of depositing radical species and their interactions with the growth surface.