The Atomic Layer Deposition of Noble Metals for Microelectronics Applications

Kie Jin Park
Abstract & Cover

The purpose of this research has been to explore noble metals prepared using thermal atomic layer deposition (ALD) for gate electrode applications in CMOS technology. ALD Ruthenium and Rhodium metal films have been focused due to their high work function, low resistivity of their oxidation forms. Study includes 1) ALD Ru process, 2) ALD Ru nucleation behaviors, 3) area-selective ALD Ru process, 4) ALD Ru work function modification, 5) ALD Rh process and work function. For item 1), ALD Ru films were formed using ruthenocene and oxygen as precursors. ALD window was discovered within 310 to 340°C from ALD Ru growth rate dependence on deposition temperature. Self-limiting reaction behavior was shown from growth rate versus precursor dose time. ALD Ru resistivity was measured to about 20~30µΩ⋅cm and Auger spectroscopy result was consistent with metallic Ru. Foe item 2), ALD Ru was deposited on chemical SiO2, thermal SiO2, and H-terminated Si surfaces. From thickness vs. ALD cycle, growth rates of Ru on those substrates were similar while as initial nucleation periods were different. Contact angle values of initial substrates showed hydrophilicity was related to the incubation time difference between substrates. ALD Ru Nucleation behavior was investigated on H-terminated Si during incubation period and growth model was proposed. For item 3), extending ALD Ru nucleation study, area-selective ALD Ru process was demonstrated. Octadecyltrichlorosilane was used to make surface very hydrophobic inhibiting nucleation. Metal-oxide-semiconductor (MOS) capacitor was fabricated using selective deposition process and spectroscopic (XPS) and electrical (capacitance voltage) measurements of the capacitor confirmed the viability of selective deposition. For item 4), ALD Ru work functions on SiO2 and HfO2 was measured and it turned out that Ru work functions on high-k dielectrics are smaller than on SiO2 possibly due to dipole formation at metal/dielectric interface. Organic self-assembled monolayers were applied on high-k dielectric surfaces prior to ALD Ru deposition to modify the dipole at the interface. ALD Ru work functions increased with amine-terminated self-assembled monolayer and decreased with vinyl-terminated monolayer. For item 5), ALD Rh has rarely been studied even though Rh is a candidate material for PMOS gate electrode. We investigated and developed successful ALD Rh process using Rhodium acetylacetonate and oxygen as precursors. ALD window was found at 280 to 310°C. It was shown that ALD Rh resistivity decreased with deposition temperature having minimum (~10µΩ⋅cm) at 300°C. XPS result was consistent with metallic Rh.

Source of Information
Gregory Parsons
North Carolina State University
(Raleigh, North Carolina, USA)
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