Microtopography of Ion Beam Etched NiP Films
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MICROTOPOGRAPHY OF ION BEAM ETCHED NiP FILMS. KAZUHIKO NOGUCHI, RYUZI UEDA, YOSHITAKA MAEYAMA, SHIGEO SASAKI, AND KAZUMICHI MACHIDA Manufacturing Development Laboratory, Mitsubishi Electric Corp., Amagasaki, Hyogo, Japan ABSTRACT The microtopography of NiP films ( P content, 8.7-12wt.% ; thickness, 40-50 lim) prepared by electroless plating on 18-8 stainless steel plates for molds and etched with a 10 keV Ar* ion beam was studied both by SEM observations and Talystep surface profile measurements. films containing less than 9.6wt.%P, which is supposed to have With a transient structure between the supersaturated solid solution and the amorphous solid, smooth surfaces were obtained down to a few micrometers of etch depth and after that craters were formed. As for the mechanism of crater formation, it is considered that Ni crystallites locally precipitate by ion bombardment and then are etched selectively. With amorphous films containing 1O.6wt.%P, microcavities less than 0.02 pmRmax instead of craters were observed regardless of the etch depth. The ion beam etching of NiP films has been found to be very promising for the preparation of precision molds of various grades, e.g. for plastic lenses used in opto-electronics, by selecting P content according to the desired surface roughness and etch depth of a particular application. INTRODUCTION Ultra precision processing with a high dimensional accuracy has been demanded for the preparation of precision molds for plastic lenses used in opto-electronics. Widely applied ultra precision turning sometimes induces figure errors by edge waviness of diamond tools. Machining of any figures with smaller size than the nose radius of the tool and free curved surfaces is difficult with the turning. Moreover, figure errors of very small size and complex contours can't be corrected by conventional polishing. Therefore we investigated the possibility of precision machining or finishing by ion beam etching which is generally used for microfabrication of semiconductors. Neither single- nor poly-crystalline materials are suitable for the preparation of precision molds, since the former is expensive and the latter induces the discontinuities at grain boundaries. There is a possibility, however, of obtaining smooth surfaces from amorphous materials which have no order in atomic arrangement and thus no grain boundaries. by In this study, NiP films of various compositions prepared electroless plating were given heat-treatment to change solid structures. These films were then etched with an Ar+ ion beam to study etching characteristics as a first step for the development of a new micro-machining technique. EXPERIMENTAL METHOD NiP films with 40-50 pm thickness containing 8.7-12wt.% of phosphorus were prepared by electroless plating from various kinds of plating solutions on finely polished surfaces of 18-8 stainless steel plates (1Ox1Ox2 mm). of room They were then heat-treated in a vacuum at temperatures temperature(R.T.) to 400'C for one hour. Phosphorus content (wt.%P) in the Analysis films w
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