X-ray Photoelectron Spectroscopy Equipped with Gas Cluster Ion Beams for Evaluation of the Sputtering Behavior of Various Nanomaterials

The selection of ion-beam species and parameters for depth profiling requires experience to obtain accurate depth information and an efficient sputter rate on diverse samples. Sputter damage that causes changes in the chemical state and composition should be avoided. Monoatomic ion-beam sources are commonly utilized for the rapid sputtering of metals and inorganics, but sputter damage to highly oxidized metal oxides and organics is well-known. Cluster ion beams have become popular in recent years for soft materials because of their capability for low damage to organics, but sputter yields of metal and inorganic materials are very low. Currently, the material properties and structures of semiconductor devices have become more complicated because of rapid technical development. Thus, it is necessary to explore more sputtering methods for samples with hybrid architecture that contain metals/inorganics/organics together. Recently, gas cluster ion beams (GCIBs) with small cluster sizes were considered to be one of the methods with the advantages of both monatomic ion beams and conventional large-cluster GCIBs (>Ar2000+). A smaller-cluster GCIB results in higher energy per atom with a sputtering behavior similar to that of the monatomic ion beam and leads to enhancement of the sputter yield in metal and inorganic layers. However, the discussion of the cluster size selection for X-ray photoelectron spectroscopy (XPS) chemical state analysis during depth profiling is rather limited. In this work, a GCIB cluster measurement kit is developed and installed in an XPS system. The actual distribution of the cluster size of each GCIB setting can be measured before depth profiling. Depth profiling using GCIBs with a series of cluster sizes is performed to examine the sputter yield and evaluate the sputter effect on various organic, inorganic, and hybrid nanomaterials. The results also show the different sputtering behaviors of GCIBs with different cluster sizes (Ar500–2000+).