Quasiperiodic nanostructures in focused ion beam deposited tungsten at high angles of incidence

Abstract

As reported in our previous work, at high (near glancing) angles of incidence of the ion beam, a quasiperiodic, comb-blade-like metal structure can form in focused ion beam induced deposition, most typically in tungsten but also in gold, platinum, or copper depositions. This kind of discontinuity tends to increase the resistance if a metal link needs to be made across a rather deep and near-vertical wall. On the other hand, if controlled, it may find some useful applications in nanofabrication. We investigated this phenomenon by using ‘‘milling-and-deposition’’ on single crystal silicon and examining the correlation between the ‘‘period’’ and various experimental parameters. We found that there is no correlation between the period and step size of beam scanning. The average period depends on the beam incidence angle (relative to the surface normal), and especially on the ion beam energy. The average period is 55, 75, and 105 nm for the Ga+ energy at 10, 20, and 25 keV, respectively, when the beam incidence angle during deposition is around 75°. The thickness of the ‘‘comb blades’’ is about 75±25 nm. The period becomes larger as the beam energy and beam incidence angle increases.