Depth profile analysis by plasma profiling time of flight mass spectrometry

Abstract

Plasma profiling time of flight mass spectrometry (PP-TOFMS) provides direct measurement of the chemical composition of materials as a function of depth, with nanometre resolution and the capability to measure both thin and thick layers. It consists in a pulsed radio frequency (RF) glow discharge plasma source fed with pure Ar and created under a pulsed RF potential coupled to a time of flight mass spectrometer (TOFMS). There is a perfect fit between the fast erosion rate of the high density and low energy plasma and the ultra-fast detection and quasi-simultaneous acquisition of all mass ions of the TOFMS. Furthermore the separation between sputtering and ionisation processes makes this technique much less matrix dependent compared to SIMS. The orthogonal TOFMS configuration allows extraction of temporal plasma source characterisation. This is all the more important as signals are largely enhanced in the plasma extinction phase (once RF is turned off) in the so called afterglow region. Sample ion signals are then created through ionisation by Ar metastables called Penning Ionisation (Arm+M→M++e−+Ar0).Various applications will be presented ranging from thin film analysis for composition, contamination detection, surface area measurements and doping level to characterisation of diffusion mechanisms. Aspects of analytical performance with regards to sensitivity, quantification, repeatability and sample throughput will be discussed.