Sn-containing composite thin films by plasma deposition of tetramethyltin

The time scale of the plasma on- and off-time is important for the control of the film composition in pulsed plasma process. Using low plasma on-times for the preparation of Sn-containing thin films with tetramethyltin (TMT) as precursor, significantly different results about the film chemistry and surface morphology were obtained, in contrast to the findings obtained at high plasma on-times in the literature. Upon changing the plasma on-times from 10 to 1 ms with the off-times below 520 ms and holding the other parameters constant, the surface morphology of the deposited films appeared from round particles of 100 nm at 10/330 through 40 nm at 10/510 in diameter to a tight smooth surface at 1/321 by atomic force microscope (AFM), while a stable particle size was reported at 10 ms on-time and 500-2000 ms off-times by other author. Detailed analysis of Fourier Transform Infrared Spectroscopy (FTIR) revealed that the content of the metal element Sn increased with plasma duty cycle or plasma on-time, in accord to the 'usual' plasma deposition mechanism. X-ray reflectometry was used to detect the aging effects under ambient condition on the film smoothness, density and thickness, while changes in film composition were observed by FTIR. In agreement with the morphology observation by AFM, a low roughness was found for the films deposited at low duty cycles. The film thickness increased by 3.6% after exposure to air, while a slight decrease in density was found. Higher density of the deposited substance attributed to higher Sn content was detected under higher plasma duty cycle, which was consistent with the FTIR results. Different deposition/ablation balance and weak Sn-C bond were attributed to the discrepancies.