Temperature-Controlled Depth Profiling of Poly(methyl methacrylate) Using Cluster Secondary Ion Mass Spectrometry. 1. Investigation of Depth Profile Characteristics

Secondary ion mass spectrometry employing an SF5 + polyatomic primary ion source was used to depth profile poly(methyl methacrylate) (PMMA) at a series of temperatures ranging from −75 °C to 125 °C, where the primary glass transition for PMMA occurs at 105 °C. The depth profile characteristics (e.g., interface widths, sputter rates, damage accumulation factors, normalized intensities, and overall secondary ion stability or constancy) were monitored as a function of temperature. It was found that, at low temperatures, the quality of the depth profiles improved considerably, having decreased damage accumulation, higher normalized intensities, and decreased interface widths, particularly at −75 °C. Higher temperatures were correlated with increased sputter rates. However, the improvements in interfacial widths and decreased damage accumulation were not as prevalent as observed at low temperatures. The importance of glass transition temperature (T g) on the depth profile characteristics was also apparent. The resulting PMMA depth profile characteristics were compared with that of poly(lactic acid) (PLA), considered to be one of the more successful cases of polymer depth profiling (very low damage accumulation, high sputter rates, small interface widths). The measured interface widths and damage accumulation factors in PMMA characterized at low temperatures were comparable to PLA at room temperature. These results indicate that temperature is an important parameter in the sputtering of polymeric materials and should be optimized.