AVS 45th International Symposium
    Plasma Science and Technology Division Friday Sessions
       Session PS-FrM

Paper PS-FrM1
Large Enhancement of Silicon Etch Rate by Metal Contamination

Friday, November 6, 1998, 8:20 am, Room 318/319/320

Session: Plasma-Surface Interactions - II
Presenter: P.G.M. Sebel, Eindhoven University of Technology, The Netherlands
Authors: P.G.M. Sebel, Eindhoven University of Technology, The Netherlands
L.J.F. Hermans, Eindhoven University of Technology, The Netherlands
H.C.W. Beijerinck, Eindhoven University of Technology, The Netherlands
Correspondent: Click to Email
Given the ever decreasing dimensions of I.C.'s, it is essential to understand the various influences which affect the etching behaviour. We found a remarkably large enhancement of silicon etch rates by even small contamination with Ni and W. Our experiments indicate that the contamination migrates into the silicon due to vacancy production by ions. The experiments were performed in a molecular beam setup, where silicon is etched by XeF@sub 2@ and Ar@super +@ ions. The etch behaviour is monitored by a mass spectrometer using the SiF@sub 4@ signal. The effect of contamination appears very pronounced when the ion beam is switched off. With contamination, a temporary enhancement of the spontaneous etch rate is measured. With traces of contamination in the order of 0.01 ML the etch rate may be enhanced by a factor of 2 for W and somewhat less for Ni. It is concluded that the contamination moves into the silicon by diffusion to vacancies created by the Ar@super +@ ions, as proposed by Hart et. al. for Cu contamination.@footnote 1@ For 1 keV Ar@super +@ ions the contamination moves to a depth of 30 Å, equal to the penetration depth of the ions. As the effect of contamination disappears after etching of 170 Å, it is concluded that contamination has a catalytic effect on the silicon etch rate. Simulations, which describe the measured effect of contamination very well, indicate that only 3% of the contamination is removed after etching a monolayer silicon. Besides this catalytic effect, there are indications that the etch rate can be lowered under certain conditions, because of the formation of silicides. @FootnoteText@ @footnote 1@R.R. Hart, H.L. Dunlap and O.J. Marsh, J. Appl. Phys. 46, 1947 (1975).