We have developed a surface analysis system that allows us to analyse the elemental composition of a sample with three-dimensional spatial resolution.
The neutral material sputtered from a sample surface by Ga+ ion impact is post-ionized by non-resonant multiphoton ionization with an ArF
excimer laser at 193 nm. The photoions are selected by time-of-flight mass spectrometry. Lateral resolution is achieved by scanning the surface with
the tightly focused primary ion beam. The depth analysis is achieved by sequentially removing layers of material and sweeping the unfocused ion beam
over the sample surface, interleaved with raster scanning the ion beam.
We tested the performance of the apparatus by analysing the surface of a pixel detector for x-ray imaging. The sample consists of an array of Ti/Al
Schottky contacts grown on a GaAs substrate. We measured the distributions of elements Al, Ti, Ga and As in three dimensions over a lateral area of
150 x 150 μm2. The depth resolution was 20 nm and the lateral resolution was 3 μ, which does not yet approach the limitations
of the apparatus. This demonstrates for the first time that three-dimensional imaging of the element distribution of a large area sample is feasible
with high spatial and depth resolution by laser post-ionization of sputtered neutrals. © 1999 John Wiley & Sons, Ltd.