a void is defined between adjacent wiring lines to minimize rc coupling . the void has a low dielectric value approaching 1 . 0 . for one approach , hollow silicon spheres define the void . the spheres are fabricated to a known inner diameter , wall thickness and outer diameter . the spheres are rigid enough to withstand the mechanical processes occurring during semiconductor fabrication . the spheres withstand elevated temperatures up to a prescribed temperature range . at or above a desired temperature , the sphere walls disintegrate leaving the void in place . for an alternative approach , adjacent wiring lines are “ t - topped ” . dielectric fill is deposited in the spacing between lines . as the dielectric material accumulates on the line and substrate walls , the t - tops grow toward each other . eventually , the t - tops meet sealing off an internal void .