Effects of the temperature and beam parameters on depth profiles in X-ray photoelectron spectrometry and secondary ion mass spectrometry under C60+–Ar+ cosputtering

Abstract

Polymethylmethacrylate (PMMA) is widely used in various fields, including the semiconductor, biomaterial and microelectronic fields. Obtaining the correct depth profiles of PMMA is essential, especially when it is used as a thin-film. There have been many studies that have used earlier generation of cluster ion (SF5+) as the sputtering source to profile PMMA films, but few reports have discussed the use of the more recently developed C60+ in the PMMA sputtering process. In this study, X-ray photoelectron spectroscopy (XPS) and dynamic secondary ion mass spectroscopy (D-SIMS) were used concurrently to monitor the depth profiles of PMMA under C60+ bombardment. Additionally, the cosputtering technique (C60+ sputtering with auxiliary, low-kinetic-energy Ar+) was introduced to improve the analytical results. The proper cosputtering conditions could eliminate the signal enhancement near the interface that occurred with C60+ sputtering and enhance the sputtering yield of the characteristic signals. Atomic force microscopy (AFM) was also used to measure the ion-induced topography. Furthermore, the effect of the specimen temperature on the PMMA depth profile was also examined. At higher temperatures (+120°C), the depolymerization reaction that corresponded to main-chain scission dominated the sputtering process. At lower temperatures (−120°C), the cross-linking mechanism was retarded significantly due to the immobilization of free radicals. Both the higher and lower sample temperatures were found to further improve the resulting depth profiles.