Contact metallization in large-scale semiconductor devices such as logic, memory, MEMS, and SoC using 2.5D and 3D interposers requires a high quality and conductivity metal barrier/seed layer for subsequent metal electroplating. Ruthenium metal has a bulk resistivity of 7.1 μΩ cm, a work function of 4.7 eV, and a low solid solubility with strong adhesion to Cu, making Ru an attractive contact metal barrier metal or seed layer for Cu electroplating. There have been numerous reports of Ru ALD using a variety of precursors. However, technical challenges remain including the need for high growth temperature, very long nucleation delay, and the use of plasma that limits Ru conformality in high aspect ratio features. Currently, there is a strong desire and demand for 3D-devices where high quality, uniform, and conformal metal growth on high aspect ratio structures for ultra largescale integration (ULSI) process flow including for 2.5D and 3D interposer substrates creation.
Here we have developed a low temperature (200oC) Ru atomic layer deposition process using Ru(DMBD)(CO)3 and O2 precursors. To enhance the Ru nucleation and growth, especially at low temperature, we performed low temperature Pt ALD using Pt(MeCp)Me3 and O2 to deposit a sub-monolayer Pt seed layer that greatly accelerates the subsequent Ru nucleation. High quality Ru films were deposited on a variety of substrates including Si(100), fused silica, Al2O3 and TiN. The ALD Ru films were uniform across the 18” deposition zone of our tubular ALD reactor. Thin Ru films were characterized by XPS, SEM, TEM, four point IV measurements, XRD and XRF. We have also performed Cu electroplating on the ALD Ru layers and found that the Ru films deposited using the Pt seed layer exhibited excellent Cu electroplating. Here we will present details of the Ru ALD and Cu electroplating.