Bottom-Up Fill for Submicrometer Copper Via Holes of ULSIs by Electroless Plating

Abstract

The bottom-up fill of copper in fine via holes is reported in electroless copper plating with the addition of bis(3-sulfopropyl) disulfide (SPS). When the concentration of SPS in the plating bath was varied from 0.05 to 0.5 mg/L with a plating time of 10 min, the ratio of the Cu thickness at the bottom of the hole to that at the surface called the bottom-up ratio, increased from 1.05 to 2.8 for a ⊘ 1.0 μm hole. The bottom-up ratio increases with SPS concentration and decreases with an increase in hole diameter. X-ray diffraction structure analyses and cross-sectional transmission electron microscopy observations indicated that the grain size of Cu film was reduced by the SPS addition, but Cu(111) texture was enhanced by the SPS addition. Bottom-up fill may be attributed to a higher SPS concentration at the surface than at the bottom of the holes due to SPS incorporation in the Cu film and diffusion-limited flux of SPS molecules into fine holes. © 2004 The Electrochemical Society. All rights reserved.