Characteristics of a mixed-gas cluster ion beam for time-of-flight secondary ion mass spectrometry

The gas cluster ion beam (GCIB) is a valuable tool for surface analysis, providing new 3D mass analysis equipment possibilities. The main feature of the GCIB is that many particles are involved during the collision of the cluster ion beam with a sample surface. Studying the characteristics of the GCIB is essential for improving the performance of the analysis equipment. We evaluated the efficiency of the GCIB using a mixed-gas of Ar and CO₂ as a primary ion beam for time-of-flight secondary ion mass spectrometry. We measured the characteristic factors and composition of the cluster ion beam depending on the mole fraction ratio of CO₂/Ar. We measured that the CO₂ composition of the output cluster ion beam rapidly increases to over 95% when the mole fraction ratio of CO₂ increases by more than 10% in the injected mixed gas. Nevertheless, the optimal ratio of the CO₂/Ar mole fraction (%) to increase the secondary ion efficiency was 96% CO₂, which more than doubled the secondary ion efficiency over that of pure Ar clusters. The beam spot size began rapidly decreasing from 95% CO₂, and it was reduced by up to 0.67 times at 100% CO₂. According to the mixed-gas ratio, the sputtering yield of the Si wafer was 8 times lower than that of pure Ar clusters.