Low-Temperature Atomic Layer Deposition of Low-Resistivity Copper Thin Films Using Cu(dmap)₂ and Tertiary Butyl Hydrazine

Herein, we describe a process for the low-temperature atomic layer deposition of copper using Cu­(dmap)₂ (dmap = dimethylamino-2-propoxide). The use of tertiary butyl hydrazine (TBH) as the reducing agent was found to have a significant improvement on the purity and the resistivity of the Cu films compared to previous processes. Our process was studied at low temperatures of 80–140 °C on native oxide terminated Si. At 120 °C, self-limiting Cu deposition was demonstrated with respect to both Cu­(dmap)₂ and TBH pulse lengths. During the initial stages of the deposition (125–1000 cycles), a growth rate of 0.17 Å/cycle was measured. Once the substrate surface was completely covered, deposition proceeded with a more moderate growth rate of 0.05 Å/cycle. According to X-ray diffraction, the films were crystalline cubic Cu with a slight preference toward (111) orientation. Based on scanning electron micrographs, the Cu films were relatively smooth with the roughness increasing as a function of both increasing temperature and thickness. A 54 nm film deposited at the low temperature of 120 °C exhibited a low resistivity of 1.9 μΩ·cm. Composition analysis on this film showed a remarkably high purity of approximately 99.4 at.%, with the rest being hydrogen and oxygen. The films could be deposited also on hydrogen terminated Si, glass, Al₂O₃, TiN, and Ru, extending the suitability of the process to a wide range of applications