Lateral growth of focused ion beam deposited platinum for stencil mask repair

Focused ion beams can repair conventional lithography masks through milling and deposition. Repairs to stencil masks for ion projection lithography pr esent a greater challenge than conventional mask repair; as the standard mo del of ion induced deposition requires a surface for deposition to take pla ce. In a stencil mask, a bridge must be formed across the open area, anchor ed to the mask on either side of a slot. Focused ion beam deposition can in duce such horizontal growth of material. Ion-induced growth of platinum ove r slots up to 3 mu m wide in a 2.75 mu m silicon membrane is demonstrated f or an average beam current density of 7 mA/cm(2). The primary method used t o accomplish this is by scanning the focused ion beam in a rectangular patt ern that extends over the slot. Material is built up From the edges, and gr ows inwards to span the slot and form a bridge. The direction of gas. flow is an important consideration. When gas flow is perpendicular to the slot, the downstream side of the bridge will grow much faster than the upstream s ide. Gas flow parallel to the slot results in uniform growth from both side s. Platinum deposition was not found to be gas flow Limited within the depo sition parameters used. The horizontal growth as a unction of time was meas ured, and found linear. The slope of this line is the horizontal growth rat e, 23+/-0.05 nm/s. The x intercept of this Line yields the minimum time for deposition to begin, which is 5.96+/-0.11 s. Sample bridges were deposited , and trimmed of excess material and redeposited platinum. These are presen ted as examples that uniformly wide bridges may be obtained at submicron di mensions, both in simple spanning and zig-zag configurations. (C) 1999 Amer ican Vacuum Society. [S0734-211X(99)18306-9].