Forming Feedthroughs in Laser-Drilled Holes in Semiconductor Wafers by Double-Sided Sputtering

Electrical feedthroughs in semiconductor wafers were made by laser drilling an array of holes in a wafer and subsequently depositing a conductor on the walls of the holes by double-sided sputtering and through-hole electroplating. A maximum depth-to-diameter ratio of six for feedthrough holes through semiconductor wafers successfully implanted with a conductor by this method was determined from both experiments and theory. Two factors dictated this limit. First, the sputtered film thickness shows a very sharp decrease with distance down the hole. Second, the critical film thickness required for film coalescence and electrical continuity increases with distance down the hole because the incidence angle of sputtered material becomes more oblique with distance down the hole and increases the tendency of the film to grow as separate islands.