The bottom-up filling capabilities of electroless copper plating bath with an addition of additives, such as poly- ethylene glycol （PEG）, polypropylene glycol （PPG） and triblock copolymers of PEG and PPG with ethylene oxide terminal blocks termed EPE, were investigated by the cross-sectional scanning electron microscopy （SEM） obser- vation of sub-micrometer trenches. Though three additives had inhibition for electroless copper deposition, the suppression degrees of three additives were different. EPE-2000 had the strongest suppression for electroless copper deposition, and the suppression of PEG-2000 was the weakest. The bottom-up filling capability of electroless copper was investigated in a plating bath containing different additives with the concentration of 2.0 mg/L. The cross-sectional SEM observation indicated the trenches with the width of 280 nm and the depth of 475 nm were all completely filled by the plating bath with an addition of EPE-2000, but the trenches were not completely filled by the plating bath with an addition of PEG-2000 or PPG-2000, and some voids appeared. Linear sweep voltammetry measurement indicated that three additives all inhibited the cathodic reduction reaction and the anodic oxidation reaction, and the inhibition of EPE-2000 was the strongest among three additives, which agreed with that of the deposition rate of electroless copper. Significant differences in surface roughness of deposited copper film were observed by UV-visible near-infrared for different suppressors, and the bright and smooth of deposited copper film were in accordance with the inhibition of three additives.
