OrbiSIMS depth profiling of semiconductor materials—Useful yield and depth resolution

OrbiSIMS is a secondary ion mass spectrometry method with dual mass analyzers: a time-of-flight (ToF) mass spectrometer for high-speed imaging and an Orbitrap^™ for high mass resolving power and mass accuracy. Originally developed for biological imaging, there is now growing interest in the application to semiconductor materials to resolve peak interferences that obfuscate analysis in traditional SIMS depth profiling experiments. We use a new method to calibrate the Orbitrap intensity scale to true counts, which allows comparison of the useful yield and duty cycle with a magnetic sector instrument and a time-of-flight instrument using an Sb implant in the silicon sample. The useful yield of the Orbitrap and magnetic sector instruments (for one detected peak) are similar. However, since the magnetic sector instrument has serial mass detection, its useful yield reduces as more peaks are analyzed. While the ToF instrument has parallel detection, it has a low duty cycle and the useful yield is two orders of magnitude lower for 1000 eV Cs⁺ sputtering. The depth resolution was also compared from the measurement of the downslope from depth profiles of an Sb delta multilayer. For 1000 eV Cs⁺ sputtering, the downslopes are 3.9, 2.3, and 2.7 nm/decade for Orbitrap, magnetic sector, and ToF instruments, respectively. Ion trajectory simulation shows that the poorer depth resolution of the OrbiSIMS is in part due to ion beam distortion at low energy.