X-ray photoelectron spectroscopy and thermal desorption spectroscopy comparative studies of L-CVD SnO2 ultra thin films

In this paper we present the results of comparative studies of the chemical stability of L-CVD SnO2 ultra thin films (20 nm) deposited on the atomically clean Si(100) substrate after their subsequent in situ hydrogenation and oxidation, and then after air exposure. For the control of surface chemistry of these films we used in a comparative way the X-ray Photoemission Spectroscopy (XPS) combined with ion depth profiling (DP XPS) and Thermal Desorption Spectroscopy (TDS). Our XPS experiments showed that the L-CVD SnO2 ultrathin films after subsequent in situ hydrogenation and oxidation consist of strongly nonstoichiometric layer at the top of Si dioxide substrate. After subsequent air exposure they were covered with undesired 3 monolayers of C contamination and various forms of oxygen. During the TDS procedure a two-step desorption of molecular hydrogen (H2), water vapor (H2O), carbon dioxide (CO2) and atomic oxygen (O) at the temperatures of ~ 530 K and 600 K was observed, respectively. The TDS results were in a good correlation with evident decreasing of the relative concentration of C contaminations, as well as variation of nonstoichiometry of the L-CVD SnO2 ultra thin films as determined by XPS combined with ion depth profiling.