Dual damascene processing for back end of the line (BEOL) layers can employ bilayer film stack approaches for lithographic patterning. These bilayer resist systems are more prevalent for KrF layers and have many unique characteristics, including silicon-containing photoresists and gap fill underlayer material that must also act as a bottom anti-reflective coating (BARC). Bilayer resists pattern for copper deposition; as such, defect levels are a critical concern, as any post-patterning bridging or residue defects can often times render an entire die inoperable due to electrical shorts or breaks. Here, two such defect types were found: missing resist patterns and resist residue. Through several experiments and with process optimization, the defect origins were elucidated and the defects themselves significantly reduced. This work will detail the examination, root causes and eventual elimination of these significant bilayer resist defects.
Advancing technology nodes in semiconductor manufacturing require more demanding lithographic performance for patterning. The advent of 45 nm development necessitated dual damascene lithography moving from a KrF-based bilayer approach to one that includes an ArF photoresist for higher resolution. There are multiple methods for an ArF dual damascene (via first, trench last) system, including bilayer, trilayer and hard mask approaches. Flash manufacturing demands are sensitive to process cost of ownership, so more complex approaches such as trilayer and hard mask film stacks were not as attractive. One method examined as an ArF dual damascene solution was a so-called "modified bilayer" approach, which is a combination of both KrF and ArF resist materials; in particular, this film stack allows for the use of ArF silicon-containing resists along with a variety of anti-reflective and gap fill underlayer materials. The modified bilayer approach afforded many advantages, including chemical compatibility, etch performance and process robustness. The modified bilayer approach represents a culmination of learning that has enabled 45 nm back end of the line (BEOL) dual damascene processing with ArF silicon-containing photoresists.
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