Substrate selectivity in the low temperature atomic layer deposition of cobalt metal films from bis(1,4-di-tert-butyl-1,3-diazadienyl)cobalt and formic acid

Abstract

The initial stages of cobalt metal growth by atomic layer deposition are described using the precursors bis(1,4-di-tert-butyl-1,3-diazadienyl)cobalt and formic acid. Ruthenium, platinum, copper, Si(100), Si-H, SiO, and carbon-doped oxide substrates were used with a growth temperature of 180 °C. On platinum and copper, plots of thickness versus number of growth cycles were linear between 25 and 250 cycles, with growth rates of 0.98 Å/cycle. By contrast, growth on ruthenium showed a delay of up to 250 cycles before a normal growth rate was obtained. No films were observed after 25 and 50 cycles. Between 100 and 150 cycles, a rapid growth rate of ∼1.6 Å/cycle was observed, which suggests that a chemical vapor deposition-like growth occurs until the ruthenium surface is covered with ∼10 nm of cobalt metal. Atomic force microscopy showed smooth, continuous cobalt metal films on platinum after 150 cycles, with an rms surface roughness of 0.6 nm. Films grown on copper gave rms surface roughnesses of 1.1-2.4 nm after 150 cycles. Films grown on ruthenium, platinum, and copper showed resistivities of <20 μΩ cm after 250 cycles and had values close to those of the uncoated substrates at ≤150 cycles. X-ray photoelectron spectroscopy of films grown with 150 cycles on a platinum substrate showed surface oxidation of the cobalt, with cobalt metal underneath. Analogous analysis of a film grown with 150 cycles on a copper substrate showed cobalt oxide throughout the film. No film growth was observed after 1000 cycles on Si(100), Si-H, and carbon-doped oxide substrates. Growth on thermal SiO substrates gave ∼35 nm thick layers of cobalt(ii) formate after ≥500 cycles. Inherently selective deposition of cobalt on metallic substrates over Si(100), Si-H, and carbon-doped oxide was observed from 160 °C to 200 °C. Particle deposition occurred on carbon-doped oxide substrates at 220 °C.

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).…”

Area Selective Chemical Vapor Deposition of Metallic Films using Plasma Electrons as Reducing Agents

“…Selectivity can also be afforded by utilizing different film growth or nucleation rates on different materials on the substrate [99], which can be further enhanced by adding etching steps to the deposition process [100]. Blocking areas of the substrate can also be achieved by applying a layer of masking materials such as polymers, which offers an inexpensive and simple way to achieve selective deposition on macro and micro/nanoscale dimensions [101,102].…”

Area Selective Deposition of Iron Films Using Temperature Sensitive Masking Materials and Plasma Electrons as Reducing Agents

“…[12][13][14][15] Competitive film growth rate, or nucleation rate, on different materials on the substrate can also be utilized for ASD, which can be further improved by additional etching. 16,17 Another approach is to block areas of the substrate by applying a layer of masking materials such as polymers. 18,19 The latter method offers a cheap and easy way to achieve selective deposition, not only on large areas but also on micro/nano dimensions.…”