Effects of Plasma Treatment on the Composition and Phase Changes of Sputter-Deposited SnOx Thin Films.

Abstract

This study examined the effects of the plasma treatment of CF₄ or SF6 on the properties of tin oxide (SnOx) thin films prepared at room temperature using a radio frequency sputtering technique. The properties of the samples were characterized by dynamic-secondary ion mass spectrometry, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Hall Effect measurements. All untreated samples showed Sn4+ and Sn2+ XPS peak area percentages of 57.6 and 34.6%, respectively, indicating a larger amount of SnO₂ phase in the samples than SnO. The samples treated with CF₄ plasma exhibited the maximum and minimum Sn4+ and Sn2+ peak areas, respectively, at a treatment time of 35 s. This was attributed to the maximum oxygen atomic percentage at 35 s and the injection of additional carbon and fluorine into the sample with increasing treatment time. On the other hand, in the case of samples treated with SF6 plasma, the Sn4+ peak area increased with increasing treatment time while the Sn2+ peak area decreased. This suggests that SnO₂ is a stronger phase for samples treated with SF6 plasma for a longer duration. Furthermore, the changes in the Sn4+ and Sn2+ peak areas of the samples treated with CF₄ plasma were much larger than those of the samples treated with SF6 plasma, which indicates that CF₄ plasma has a larger impact on the properties of the samples. This difference in impact showed a correlation with the sharper decrease in the number of oxygen vacancies for CF₄ plasma-treated samples. These results were attributed to the introduction of additional fluorine and carbon into CF₄ plasma-treated samples compared to the SF6 plasma-treated ones. In addition, XRD showed that the plasma treatment did not affect the amorphous phase in the samples.