PHOTOCHEMICAL DRY STRIPPING OF SILICON-NITRIDE FILMS

UV photochemical processes have been developed for rapidly stripping f ilms of LPCYD Si3N4 in a dry reaction environment, free of plasma or p lasma effluents. These processes are carried out in a vacuum reactor w hich allows simultaneous exposure of a substrate wafer to a polyatomic halogen gas and UV radiation. Si3N4 stripping rates approaching 1000 Angstrom/min have been demonstrated for fluorine-based processes, whil e maintaining the bulk wafer temperature below 250 degrees C; It has b een shown that the mechanism for photochemical Si3N4 etching requires both photolytic production of gas-phase F atoms and direct photon expo sure of the etching surface. Selectivities between Si3N4 SiO2, and sil icon films are controlled through UV lamp exposure, substrate temperat ure, and with additions of N-2 diluent and various halogen-containing gases. Selectivities for Si3N4-to-SiO2 etching of greater than 30 can be achieved for the stripping of Si3N4 LOGOS mask layers in the presen ce of field oxide and pad oxide layers.