Method for avoiding photoresist resist residue on semioconductor feature sidewalls

A method for blocking out diffusion of nitrogen containing photoresist contaminating species to improve trench patterning and etching in a dual damascene process comprising the steps of:

• providing a semiconductor wafer having a process surface including a via opening extending through a semiconductor wafer thickness portion including an uppermost DARC layer and at least a portion of an underlying dielectric insulating layer;
• blanket depositing a flowable polymeric resinous layer having an average molecular weight of from about 10,000 to about 90,000 over the DARC layer to include filling the via opening;
• curing the flowable polymeric resinous layer by exposing the polymeric resinous layer to at least one of thermal or photonic energy to initiate polymer cross linking;
• chemically mechanically polishing (CMP) the polymeric resinous layer according to an oxide CMP process to substantially remove the polymeric resinous layer thickness to expose the DARC layer and form a via plug substantially filling the via opening;
• providing a photolithographically patterned photoresist layer over the process surface for etching a trench line opening overlying and encompassing the via opening;
• etching the trench opening according to a plasma etching process to extend through the DARC layer and a thickness portion of the dielectric insulating layer while leaving the via plug in place;
• and,
• removing the photolithographically patterned photoresist layer and the via plug according to at least one of a plasma ashing process and a wet chemical stripping process.