Photo-Definable C4-Ball Limiting Metallurgy Mask
Original Publication Date: 1989-May-01
Included in the Prior Art Database: 2005-Jan-27
Disclosed is a procedure for the deposition of terminal metallurgy in semiconductor back end of line (BEOL) processing using a thin layer (less than 1.0 um) of silicon nitride or titanium metal as in in situ mask for terminal metal deposition. Referring to the drawing, the thin layer of nitride or titanium is used as a mask to etch a relatively thick layer of uncured polyimide. Continued etching removes a previously deposited, cured polyimide layer at a slower rate than the uncured polyimide, thereby producing terminal vias. The etched, uncured polyimide then functions as a lift-off mask for terminal metallurgy since an overhang is formed due to undercutting of the nitride or titanium during the etch process.