UV curing-induced photoresist poisoning in advanced ULK BEOL integration schemes

Abstract

In today's advanced semiconductor technology, there are hundred of process steps that can significantly impact final yield and reliability performance. In our fabrication of advanced. BEOL Cu integration schemes based on porous ultra-low dielectric constant (ULK) interlevel dielectrics (ILD), we found missing pattern defects after via lithography, resulting in 70% drop in SRAM and via chain yields. In the current work, we investigated the root cause of missing via pattern (MVP) in advanced BEOL Cu interconnects using porous ULK ILD materials. While it is widely known that photoresist poisoning can be caused by diffusion of amine (NHx) based compounds coming from the underlying low-k SiCHN Cu passivation and etch-stop layer (ESL), we also found that the diffusion of amines is exacerbated by the use of the UV curing process, which is used to create porosity (for lower dielectric constant, k) and enhances matrix cross-linking of the ULK films. Experimental results suggest that UV-induced resist poisoning in ULK/Cu BEOL integration schemes using SiCHN Cu passivation layer can be prevented by an N-free SiC layer, optimized hardmask properties, or exposing the oxide hardmask surface to a special plasma treatment. © 2010 Materials Research Society.