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Copper metallization in microelectronics using filtered vacuum arc deposition. Principles and technological development
Continuous efforts to further increase the performance of microelectronic circuits challenge all of the involved process modules including thin film deposition, lithographic masking and etching. Specifically, the recent trend of introducing copper as the wiring material required a change in the conventional backend process sequence that transfers the interconnect pattern. Whereas conventionally flat-deposited aluminum is masked and subsequently etched to generate metal lines, copper technology requires the filling of narrow vias and trenches etched into the dielectric interlayer. Established techniques such as thermal evaporation or sputtering have shown substantial difficulties in fully metallizing the prepared patterns. Typical failures are large voids in the volume of the resulting metal lines. In response to the requirements for next generation devices, research on plasma vapor deposition PVD processes continues to further improve film properties and reliability. Duringrecent years, evaporation techniques that generate significantly higher ionized metal plasmas than conventional sputtering have shown their potential to suppress the formation of voids. Several pulsed magnetron sputtering methods have been investigated as possible alternatives. So far, vacuum arc plasma sources have not been considered by the suppliers of the microelectronics as an alternative although they generate the highest plasma ionization very effectively. A major concern is the deposition of microscopic droplets of the cathode material that are inevitably generated during the arc discharge. Current demands, e.g. for ultra-thin and dense carbon coatings on computer hard disks or the copper metallization in CMOS structures have stimulated new developments of more compact and higher productive filtered arc sources. In Section 1, the present paper describes the current problems of metallization in microelectronics and the needs for a higher activated PVD tech niques. Vacuumarc evaporation is introduced as a process having the potential, to solve some actual problems, provided that the droplets can be eliminated. A short historical outline of the development and current stage of filtered arc technology is given in the following. Focusing on copper metallization and barrier coatings e.g. TaN in microelectronics, the paper evaluates and summarizes the current stage of filtered arc technology achieved by groups in the USA, East Asia, Australia and Europe