Abstract: An electroless plating bath for filling high aspect ratio features with copper metal comprises water, a water soluble copper containing compound having an initial concentration of 0.5 to 50 g/L, a catalyst reducing agent having an initial concentration of 0.02 to 1.5 g/L, a bulk reducing agent having an initial concentration of 2.37 to 29.7 g/L, a buffering agent having an initial concentration of 25 to 100 g/L, a grain refining additive having an initial concentration of 0.25 to 5.0 g/L, a bath stabilizing agent having an initial concentration of 0.02 to 0.1 g/L, and a rate controlling additive having an initial concentration of 0.01 to 0.5 g/L. The catalyst reducing agent may comprise glyoxylic acid and the bulk reducing agent may comprise glycolic acid or hypophosphite.