Reflexion Scanning Electron Diffraction from Growing Films

FOR thin films to be of use, in microelectronics, for example, they must be deposited on bulk substrates. Little is known, however, of the nucleation and structure of very thin films deposited in this way, because the usual methods of study, electron diffraction or microscopy in transmission are not applicable. If the film is polycrystalline and thinner than 100 A, reflexion electron diffraction can provide crystallographic information; if the film is a single crystal film then low energy electron diffraction is also possible. To study the film in the early stages of formation it must be deposited inside the diffraction camera. Rather few in situ studies by reflexion electron diffraction have been reported1,2, perhaps because conventional reflexion cameras suffer severe disadvantages compared with transmission cameras. The chief disadvantages are that (a) large numbers of secondary and loss electrons are produced which obscure the elastically scattered electrons carrying the erystallographic information; the total intensity of the loss electrons usually exceeds that of the elastically diffracted ones; (b) the effects of contamination are troublesome unless partial pressures of contaminant gases are below 5 × 10−9 torr; (c) the intensities are greatly affected by the surface condition of the specimen and by small changes of the angle of incidence of the electron beam.