The traditional bottom-up filling of electroless copper usually depends on inhibiting the surface deposition or accelerating the bottom deposition to achieve a relatively high deposition rate of electroless copper in the bottom of trenches. In this paper, a complete bottom-up filling of electroless copper, in which the deposition rates of electroless copper were inhibited at the surface of the substrate and accelerated in the bottom of the trenches, was designed and achieved in a plating bath containing glyoxylic acid as a reducing agent with an addition of bis(3-sulfopropyl)disulfide (SPS) and poly(ethylene glycol) (PEG). When SPS concentration was 0.5 mg L-1, the deposition rate of electroless copper was decreased from 9.6 to 1.9 mu m h(-1) with PEG-4000 concentration from 0 to 1 mg L-1. The cross-section scanning electron microscopy observation indicated that all trenches with different widths ranging from 100 to 590 nm were filled completely by electroless copper and no void was found. This was attributed to the synergistic effect of three factors, the acceleration of SPS only, strong suppression of bath SPS and PEG-4000, and low diffusion coefficient of PEG-4000, which resulted in a concentration gradient of PEG-4000 in the trenches. The effects of PEG-4000 and SPS on the cathodic and anodic reaction were studied by linear sweep voltammetry method. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3479191] All rights reserved.