A low-temperature thermal ALD process for nickel utilizing dichlorobis(triethylphosphine)nickel() and 1,4-bis(trimethylgermyl)-1,4-dihydropyrazine

• Published in: Dalton transactions : an international journal of inorganic chemistry 2022-07, Vol.51 (29), p.1898-198
• Main Authors: Vihervaara, Anton, Hatanpää, Timo, Mizohata, Kenichiro, Chundak, Mykhailo, Popov, Georgi, Ritala, Mikko
• Format: Article
• Language: English
• Subjects: Adducts; Atomic layer epitaxy; Chlorine; Halides; Low temperature; Nickel; Phosphines; Pinholes; Reducing agents; Substrates; Thermal stability
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/d2dt01347a

In this work, we developed a new ALD process for nickel metal from dichlorobis(triethylphosphine)nickel( ii ) (NiCl 2 (PEt 3 ) 2 ) and 1,4-bis(trimethylgermyl)-1,4-dihydropyrazine ((Me 3 Ge) 2 DHP). A series of phosphine adducts of nickel and cobalt halides were synthesized and characterized for their volatility and thermal stability. Also (Me 3 Ge) 2 DHP is a novel reducing agent in ALD. Smooth nickel films were deposited on different substrate materials at 110 °C, which is the lowest deposition temperature for Ni metal found in the literature. The growth rate is 0.2 Å per cycle when the film is not continuous and decreases to 0.1 Å per cycle after the film becomes pinhole-free. Besides a small amount (7 at%) of carbidic carbon, the films have only small amounts of impurities. Most notably, the chlorine content is below 0.2 at%, indicating efficient reduction. Furthermore, we think that (Me 3 Ge) 2 DHP can open new avenues for the ALD of other metals at low temperatures. Novel precursors enable the low-temperature ALD of metallic nickel thin films.