Growth and Nucleation of Hydrogenated Amorphous Silicon on Silicon (100) Surfaces

ABSTRACTA scanning tunneling microscope (STM) has been used to study the topology of the surfaces of a series of thin hydrogenated amorphous silicon (a-Si:H) films deposited by rf discharge from pure silane. The substrates were atomically flat, oxide-free, single-crystal Si (100). Films were grown in our laboratory and transferred to the STM with no air exposure between growth and measurement. A series of thin films between 1 and 50 nm in thickness reveals the initial growth stage of a-Si:H on Si (100). Initial nucleation and islanding can be seen on these films. The surface has a distribution of island sizes. The rms roughness and a surface lateral correlation length were measured as functions of film thickness. The rms roughness grows sublinearly with thickness from 0.3–0.5 nm as the film thickness is raised from 1 to 50 nm. The lateral size of the surface features also grows with film thickness. The growth of the roughness and correlation length can be compared with the dynamic scaling model. In addition, the topographs reveal occasional structures of larger size and low density on the film surface. These structures are nanoparticles of silicon deposited from the plasma during film growth. The frequency of these features scales with film thickness, and represents 10−510−4 of the total film volume.