A study of pattern transfer fidelity during metal hard-mask open

Trench-first-metal-hard-mask (TFMHM) approach has been widely utilized for copper interconnect formation since 45nm CMOS technology node [1-3]. Trench patterns are defined by MHM etch. These trench patterns not only control final Cu line shape and location, but also will affect the subsequent via patterning because via pattern is self-aligned (at least partially) to trench pattern [4,5]. With continuously shrinking feature size and more complexity in Cu interconnects design, the requirement for pattern transfer fidelity is much higher than before. Pattern distortion happens in specific design, such as small hole, U-shape line, the entry of isolated Cu line into dense area, etc. These phenomena are largely unpredictable and cannot be compensated by OPC (Optical Proximity Correction). The distortion tolerance is much smaller in advanced technology. Weak point like copper short and/or via misplacement easily occurs, thus impacting chip yield. This work shows PR margin is the one of keys to improve the pattern fidelity. PR pre-treatment, material change and pulsing plasma etch technique can provide great improvement.