MCsn+-SIMS: An Innovative Approach for Direct Compositional Analysis of Materials without Standards

Abstract

This review primarily deals with the compensation of ‘matrix effect’ in secondary ion mass spectrometry (SIMS) for direct quantitative analysis of materials using MCs+-SIMS approach. Emphasis has been given on exploring the formation mechanisms of MCsn+ (n = 1, 2,..) molecular ions (M denotes the element to be analyzed and Cs+ is the bombarding ion) emitted in the SIMS process. Following a brief introduction on SIMS, a study on MCsn+ molecular ions emitted from various metal targets under Cs+ primary bombardment has been discussed. These studies essentially concentrate on the secondary ion energy distributions of the emitted species under different bombarding energies and impact angles. We have discussed a systematic study on the effect of reactive species like oxygen and cesium on the emission of MCsn+ molecular ions. In all cases we have estimated the changes in local surface work function from the leading parts of the secondary ion energy distributions. The observations are explained in the light of surface work function changes at the sputtering sites. Formation mechanisms of MCsn+ molecular ions are explained in the framework of sputter-ion emission models. Suppression of matrix effects in the compositional analysis of molecular beam epitaxy (MBE) - grown SiGe alloy structures has been discussed in detail. We have essentially applied the MCs+-SIMS method for the minimization of ‘matrix effect’, which is routinely encountered in conventional SIMS analysis hindering quantification of materials. Under the impact of energetic Cs+ ions, both SiCs+ and GeCs+ ions have been monitored for SiGe alloy samples with Ge concentration between 0 and 72 at.%. Following optimization of various experimental parameters, we have shown that the matrix effects are practically suppressed for Ge content up to 72 at.% in SiGe samples. A procedure for the accurate quantification of Ge concentration in Si1−xGex alloys using this method has been presented. This novel methodology has successfully been applied in the depth profiling of Si/Ge multilayer structures grown by MBE technique.