Effects of thiols and their aging on copper electrodeposition for ULSI interconnects.

摘要

Six model thiols, Bis-(3-Sulfopropyl)-disulfide sodium salt (SPS), 3-Mercapto-1-propanesulfonic sodium salt (MPS), (O-Ethyldithiocarbonato)-s-(3-sulfoproplyl)-ester potassium salt (OPX), 3-S-Isothiuronium Propyl Sulfonate (UPS), N, N-Dimethyl-dithiocarbamylpropyl sulfonic sodium salt (DPS), and 3-(Benzothiazolyl-2-mercapto)-propyl-sulfonic sodium salt (ZPS) in an acid-copper plating bath containing chloride ions and polyethylene glycol (PEG) have been systematically evaluated and characterized by electrochemical method and by fill study. These thiols that all have a common thiol and disulfide group (-SCH₂CH₂CH₂SO ₃) that are commonly used for printed circuit board (PCB) plating baths were evaluated as potential accelerating elements for ULSI Cu plating.; The electrochemical analytical methods employed include linear sweep voltammetry (LSV), chronoamperometry (CA), and cyclic voltammetry (CV) on a rotating disk electrode. Examination of the i-E deposition characteristics of these electrolytes showed that in all cases an analysis of LSV, CA, and CV gives consistent estimates of thiol acceleration capability in an acid copper bath and supplements to one another. It revealed a hysteresis response associated with the acceleration capability of electrolytes containing SPS, OPX, DPS, and NIPS that can be employed to monitor and explore additive efficacy and consumption. In contrast, electrolyte containing UPS and ZPS showed no i-E hysteresis characteristics and retarded copper deposition. Superconformal electrodeposition was observed for a successful trench fill with electrolyte containing SPS.; Thiols are well known for their unstable nature in a plating bath. Examination of i-E characteristics of electrodeposition indicated that DPS and MPS degrade slower than other thiols. The accelerating characteristics of all these thiols disappeared in sixteen days.; Cu film microstructure can be influenced by many factors. This investigation showed organic additives have dominating influence on the film microstructure and self-annealing property. The films deposited from electrolyte containing SPS, UPS, OPX, and DPS exhibited spontaneous recrystallization at room temperature that resulted in a resistivity drop within a few hours of deposition. In contrast, film electrodeposited from ZPS bath showed little resistivity drop and had similar behavior as Cu film from Cl-PEG electrolyte. Microstructure of stabilized Cu films showed that the texture of electroplated Cu film was predominantly (111) oriented. Film roughness was strongly affected by the electrolyte additives, followed by plating current density.