ELLIPSOMETRIC STUDIES OF THERMALLY-INDUCED TRANSFORMATION PHENOMENA IN OXIDE-FILMS

Post deposition annealing of supported films not only can induce trans formation to a different phase but also can promote ion diffusion acro ss the film-substrate interface with subsequent chemical reaction at t hat interface. Such interfacial processes have been observed in zinc o xide films deposited on borosilicate glass or vitreous silica substrat es when heated to temperatures exceeding 675 K. Raman measurements acq uired as a function of temperature show gradual transformation to a zi nc berate or silicate phase with concomitant change in dielectric prop erties. Analogous reactions have been observed for zinc oxide films de posited on sapphire substrates. Spectroscopic ellipsometry and Raman s pectroscopy are used to characterize the film-substrate interaction at the buried interface for ZnO and doped ZnO films subjected to post de position annealing. Films studied are either amorphous, consist of ran domly oriented wurtzite crystalline grains, or are highly c-axis orien ted wurtzite, depending upon the deposition method. It is shown that a bove a critical temperature, not only substrate interactions occur, bu t resident cation dopants also can chemically react with the zinc oxid e matrix. Such reactivity can significantly limit the effects such dop ants have on the optical and conductivity properties of ZnO. (C) 1997 Elsevier Science S.A.