The characteristics of aluminum (A1) films prepared by the atomic layer deposition (ALD) technique using trimethylaluminum (TMA) and a hydrogen plasma were examined for use as a wetting layer for the two-step cold/warm Al deposition. The most important role of a hydrogen plasma was to act as a reducing agent for TMA. The growth rate was saturated at 0.15 nm/cycle, demonstrating that the thickness can be precisely controlled by the number of cycles. Initial layer-by-layer growth was observed and this continued for up to 50 cycles (similar to7.5 nm). The root-mean-square thickness variation of an Al film deposited in five cycles (similar to0.75 nm) was found to be 0.188 nm. As the P-H2/P-TMA injection ratio was increased to 10 at a buffer line, the carbon concentration decreased to 1-3 at. %. The resistivity of a 100-nm-thick Al film was 10 muOmega cm and this film was polycrystalline in nature. ALD Al films also had good step coverage on high aspect ratio trenches.