Focused Ion Beam Induced Deposition

Abstract

Ion induced deposition is a novel method of thin film growth in which a local gas ambient is created near an ion bombarded surface. The ion bombardment causes the gas molecules to break up and some of the gas constituents to deposit on the surface. If a focused ion beam is used, then this becomes a technique for maskless, resistless, patterned deposition. Depositions of films from gases of Al(CH₃)₃, WF₆ and Ta(OC₂H₅)₂ have been reported. The films for the most part have contained high (approaching 50%) concentrations of impurities such as O or C, presumably due to the lack of ultrahigh vacuum conditions. Gold deposition has been observed from dimethyl gold hexa fluoroacetylacetonate (C₇ H₇F₆ O₂ Au), with both focused ion beams and broad beams. In many cases, the gold films are much purer (less than 5% C or O) and have exhibited resistivities from 20 to 1000µΩcm (Bulk gold resistivity is 2.5µΩcm.) Deposition yields (atoms deposited per incident ion) of 4 to 100 have been observed. But the higher yields correlate with higher resistivity and higher impurity content. Preliminary transmission electron microscope examination shows the gold films to start out as unconnected islands of 40 to 60nm dimensions. The mechanisms for the deposition is at present not well understood. Some hypotheses will be discussed. Ion-induced deposition appears to be a promising technique for in-situ deposition of metals or insulators with submicrometer resolution.