The determination of the backward sputter rate for conventional focused ion beam milling has been studied in much detail both experimentally as well as theoretically. Thus, extensive knowledge regarding the dependence of the sputter yield on the respective materials being used, the temperature, and the sputter angle has been obtained.

 

In the case of forward sputtering, theoretical considerations exist. However, they are supported only by a small number of experimental investigations.

 

We present a general methodology for the direct determination of the forward sputtering rate and the angle dependent redeposition utilizing atomic force microscopy. Milling of thin membranes (50-200 nm thick) of silicon nitride showed initial backward sputtering which, with the thinning of the membrane, changed to a forward sputtering. The forward sputtering was found to be more efficient by about an order of magnitude as compared to backward sputtering. This ratio is similar to results found for sputtering various materials using fast neutrons [1], but much higher than was observed for sputtering of Gold using Argon ions [2].

 

Milling through the membrane into a silicon substrate positioned only a few microns away allowed for the direct determination of the angular distribution of redeposited ions. For normal incidence, a centrosymmetric redeposition was observed whereas milling under smaller angles led to oriented deposition in good agreement to simulation.

 

 

[1]        B. Ye, Y. Kasugai, Y. Ikeda, Y. Fan, J. Du, X. Zhou, R. Han, Measurement of backward sputtering yields induced by fast neutrons, J. Nucl. Mat. 281 (2000), 112-116

 

[2]        P. Sigmund, Theory of Sputtering. I. Sputtering yields of amorphous and polycrystalline targets, Phys. Rev. 184 (1969), 383-416

Bernhard Basnar*, Vienna University of Technology, Austria
Alois Lugstein, Vienna University of Technology, Austria
Markus Schinnerl, Vienna University of Technology, Austria
Gottfried Strasser, Vienna University of Technology, Austria
Emmerich Bertagnolli, Vienna University of Technology, Austria

*presenting author