Low Temperature, Selective Atomic Layer Deposition of Cobalt Metal Films Using Bis(1,4-di-tert-butyl-1,3-diazadienyl)cobalt and Alkylamine Precursors

Abstract

The atomic layer deposition (ALD) of cobalt metal films is described using the precursor bis­(1,4-di-tert-butyl-1,3-diazadienyl)­cobalt and tert-butylamine or diethylamine. Platinum, copper, ruthenium, Si(100) with native oxide, thermal SiO2, hydrogen-terminated silicon, and carbon-doped oxide substrates were used with growth temperatures between 160 and 220 °C. Plots of growth rate versus pulse lengths showed saturative, self-limited behavior at ≥3.0 s for bis­(1,4-di-tert-butyl-1,3-diazadienyl)cobalt and ≥0.1 s for tert-butylamine. An ALD window was observed between 170 and 200 °C, with a growth rate of 0.98 Å/cycle on platinum substrates. A plot of thickness versus the number of cycles at 200 °C on platinum substrates was linear between 25 and 1000 cycles, with a growth rate of 0.98 Å/cycle. A 98 nm thick film grown at 200 °C showed crystalline cobalt metal by X-ray diffraction. Atomic force microscopy of 10 and 98 nm thick cobalt metal films grown on platinum substrates at 200 °C showed rms roughness values that were ≤3.1% of the film thicknesses. X-ray photoelectron spectroscopy analyses were performed on 49 and 98 nm thick films grown on platinum substrates at 170 and 200 °C, respectively. Both samples showed oxidized cobalt on the film surface but revealed cobalt metal upon argon ion sputtering. The films showed >98% pure cobalt, with ≤0.9% each of oxygen, carbon, and nitrogen. On copper substrates, a plot of thickness versus the number of cycles was linear between 25 and 500 cycles, with a growth rate of 0.98 Å/cycle. In contrast, analogous growth studies on ruthenium substrates showed no films after 25 and 50 cycles, a small amount of growth at 100 cycles, and a growth rate of 0.98 Å/cycle at 200 and 500 cycles. No film growth was observed at 200 °C on Si(100) with native oxide, 100 nm thermal SiO2, hydrogen-terminated silicon, and carbon-doped oxide substrates after 500 cycles. Similarly, no growth was observed on these insulating substrates after 200 cycles at temperatures between 160 and 220 °C. Accordingly, this process affords inherently selective cobalt metal growth on metal substrates between 160 and 220 °C. Lower purity nitrogen carrier and purge gas (<99.9%) afforded a much lower growth rate, likely because of the formation of surface cobalt oxides and attendant reduced cobalt metal nucleation. A mechanism for cobalt metal growth is proposed in which 1 and tert-butylamine form an adduct, which then decomposes thermally to cobalt metal, 1,4-di-tert-butyl-1,3-diazadiene, and tert-butylamine.

Editors' Choice—Review—Cobalt Thin Films: Trends in Processing Technologies and Emerging Applications

“…Another emerging advantage of thermal Co ALD is its ability to enable or prevent area-specific or area-selective film growth, in what is commonly referred to as area-selective ALD. [59][60][61][62][63][64] Customized complexes (precursors) and surface assemblies or configurations can be made to react in a tightly controlled fashion so as to catalyze or inhibit Co deposition on specific areas of the underlying substrate surface, resulting in Co film formation only on the desired regions of the substrate. However, current ALD technologies suffer from high surface roughness and very limited growth rates (and thus low manufacturing throughput).…”

Chemical vapor deposition of metallic films using plasma electrons as reducing agents

“…[25][26][27] It can also be noticed that the level of carbon impurities far exceeds the amount of carbon reported in cobalt and nickel films deposited by thermal ALD using molecular reducing agents. 28,29 It should be noted that these films where deposited using a metal precursor with two bidentate diazadienyl ligands forming metal-nitrogen bonds instead of metallocene precursors as in this study.…”

A Rare Low‐Spin CoIV Bis(β‐silyldiamide) with High Thermal Stability: Steric Enforcement of a Doublet Configuration

“…To contextualize the performance of 1, we subjected two recently reported Co II precursors to thermal analysis: namely CoCl 2 (TMEDA) and Co(DAD) 2 (DAD= tert ‐butyldiazadienyl) (see the Supporting Inforamtion). We applied our recently developed “Figure of merit” σ that takes key parameters such as thermal range, vapor pressure, and extent of decomposition during TGA into account to quantitatively compare precursors (Table S2) .…”