Low-Temperature Atomic Layer Deposition of Copper Films Using Borane Dimethylamine as the Reducing Co-reagent

Abstract

The atomic layer deposition (ALD) of Cu metal films was carried out by a two-step process with Cu(OCHMeCH 2 NMe 2 ) 2 and BH 3 (NHMe 2 ) on Ru substrates and by a three-step process employing Cu(OCHMeCH 2 NMe 2 ) 2 , formic acid, and BH 3 (NHMe 2 ) on Pd and Pt substrates. The two-step process demonstrated self-limited ALD growth at 150 °C with Cu(OCHMeCH 2 NMe 2 ) 2 and BH 3 (NHMe 2 ) pulse lengths of ≥3.0 and ≥1.0 s, respectively. An ALD window was observed between 130 and 160 °C, with a growth rate of about 0.13 Å/cycle. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) revealed rough Cu films that likely originate from the Cu nanoparticle seed layer. The Cu films exhibited poor electrical conductivity because of their nanoparticulate natures. The three-step process showed self-limited ALD growth on Pd and Pt at 150 °C with Cu(OCHMeCH 2 NMe 2 ) 2 , formic acid, and BH 3 (NHMe 2 ) pulse lengths of ≥3.0, ≥ 0.3, and ≥1.0 s, respectively. ALD windows were observed between 135 and 165 °C on both Pd and Pt, with growth rates of 0.20 Å/cycle on both substrates. Plots of film thickness versus number of cycles showed linear growth behavior on Pd with a growth rate of 0.20 Å/cycle up to 2000 cycles. By contrast, a similar plot for growth on Pt revealed nonlinear growth behavior, with a growth rate of about 0.4 Å/cycle up to 500 cycles, and then a growth rate of about 0.03 Å/cycle between 500 and 2000 cycles. The large difference in growth behavior between Pd and Pt substrates is proposed to occur by formation of a Cu/Pd alloy film and continuous catalytic decomposition of the BH 3 (NHMe 2 ) by the surface Pd sites. By contrast, there is much less surface Pt in the growing Cu film, and catalytic decomposition of BH 3 (NHMe 2 ) by the diminishing surface Pt as the Cu film grows leads to a decreased growth rate beyond 500 cycles. X-ray photoelectron spectroscopy reveals the formation of high purity Cu metal for all depositions, with low levels of C, N, O, and B. The Cu films on Pd and Pt showed smooth, continuous films at all thicknesses and had low electrical resistivities.

Quantum Chemical Study of the Effect of Precursor Stereochemistry on Dissociative Chemisorption and Surface Redox Reactions During the Atomic Layer Deposition of the Transition Metal Copper

“…Cu(dmap) 2 has also been previously used in experiments due to its high decomposition temperatures, low non-volatile residue and high sublimation rate 52 ZnEt 2 is found to dissociate into a ZnEt fragment and Et on a bare copper surface. The…”

Kinetics and Coverage Dependent Reaction Mechanisms of the Copper Atomic Layer Deposition from Copper Dimethylamino-2-propoxide and Diethylzinc

“…It is extremely difficult to deposit continuous thin films of Cu at 2 nm thickness and instead formation of Cu islands with size of 10-90 nm tends to be more favourable. 9 Of these deposition approaches, ALD shows the most promise in surmounting the island growth problem as well as meeting future demands of device scaling. [10][11][12] Many copper organometallic compounds are used with H 2 or H 2 plasma in copper ALD experiments [13][14][15][16][17][18] .…”

“…6 Kalutarage et al compared twostep and three-step processes using the ALD reaction of Cu(dmap) 2 with BH 3 (NHMe 2 ) and separately with BH 3 (NHMe 2 ) and HCO 2 H. 9 They showed that the two-step process requires a Cu seed layer, and affords a growth rate of about 0.13 Å/cycle within the 130−160 °C ALD window.…”

Precursor Adsorption on Copper Surfaces as the First Step during the Deposition of Copper: A Density Functional Study with van der Waals Correction

“…13 In these cases, the Cu(dmap) 2 precursor is successful because of its relatively high vapor pressure and thermal stability. Given these promising developments, the reaction mechanism and surface chemistry of Cu(dmap) 2 precursor during Cu ALD should be carefully investigated in order to identify better precursors and design new ALD processes for Cu as well as other metals.…”