Copper damascene electrodeposition and additives

Abstract

Copper via filling is one of the most recent nanoscale electrodeposition technologies used in semiconductor fabrication. Sub micrometer vias on silicon wafers serve as digital signal conductors, when filled with copper. The additives in the electrodeposition bath are critical to obtain vias free of voids and defects. Current–voltage curves show that different additives have either inhibition or acceleration effects. Polyethylene glycol (PEG) and Janus green B (JGB) additives are inhibitors. Scanning electron microscopy images indicate that PEG molecules of about 30 nm in diameter absorb preferentially at the edges of copper macrosteps and inhibit the lateral growth of copper electrodeposits. Rotating disk electrode (RDE) experiments show that higher rotation speeds produce lower deposition current with PEG and JGB additives. Through-mask cathodes to simulate via bottoms were used to simulate the via bottom surfaces so that the enhancement rates could be investigated. With bis(3-sulfopropyl) disulfide (SPS) in addition to chloride ions (Cl −), PEG and JGB, the current at the simulated via bottom cathode increases. This current also increases with an increase in SPS concentration. This accelerating effect of SPS was found with the typical combination of four additives (Cl −+PEG+JGB+SPS) used for via filling. The current increases with an increase in aspect ratios of the through-mask cathodes. With a higher aspect ratio of a deeper via, it is proposed that the via bottom accelerating Cu(I)thiolate complex is accumulated at the via bottom. From cross-sectional observations of the deposit thickness, the complex must form during electrolysis, and accumulate at the deeper via bottoms during electrolysis.