New Design and Development of Size-Selected Gas Cluster SIMS

Abstract

A new cluster time-of-flight secondary ion mass spectrometry (TOF-SIMS) was developed using a size-selected gas cluster ion as a projectile. Since a large gas cluster ion can generate many low-energy constituent atoms in a collision with the surface, it causes multiple and ultra low energy sputtering. The mean kinetic energy of constituent atoms is provided by dividing the acceleration energy of the gas cluster ion by the number of constituent atoms. Therefore, the sputtering can be controlled to minimize the decomposition of sample molecules and substrate material by precisely adjusting the number of constituent atoms (the cluster size) and/or acceleration energy of the gas cluster ion. The cluster size was selected by the time-of-flight method using two ion deflectors attached along the ion-beam line. A high resolution of 11.7 was achieved for the cluster size/size width (m/Δm) of Ar-cluster ions. SIMS spectra of polymethyl methacrylate (PMMA) was measured using the size-selected gas cluster SIMS machine. As increasing the cluster size, large fragment ions emitted from PMMA were enhanced. This result suggested that the decomposition of the polymer structure was suppressed by the larger cluster ion projectile which decreased the kinetic energy per constituent atom of a cluster ion.