Integration of metal masking and etching for deep submicron patterning

Although copper damascene interconnects offer many advantages over conventi onal subtractive etched Al alloys, the challenges and costs associated with converting to copper have combined to extend the useful life of Al alloy e tching into the deep submicron regime. As a result, metal masking and etchi ng are facing new challenges. Deep ultraviolet (DW) photolithography has re placed the conventional i-line technique for patterning fine metal pitches, but some DUV photoresists are less able to withstand the aggressive plasma environment than their i-line counterparts. Reflectivity increases at DUV wavelength, so dielectric antireflective films are added on top of the meta l stack. The mask-open process, where the dielectric film is plasma etched prior to etching the metal stack, alters the photoresist further and influe nces the subsequent metal etch. Aspect ratio dependent etch effects increas e when etching narrow spaces resulting from tightened metal Ditches, and ga s additives may be required to protect the metal sidewalls. These effects a re characterized and the challenges of deep submicron metal etch process de velopment are discussed. The option of true hardmasked etching of the metal stack is also investigated. (C) 2000 American Vacuum Society. [S0734-2101( 00)04104-X].