The role of copper in the electronics industry as an interconnecting agent

Mendeleev to Periodic table: “Dear PT, according to you, which is the most boring element of them all?” PT: “My Lord, Maybe copper?” Mendeleev: “Why do you say this?” PT: “It gets very boring for me. Unlike the other transition elements, for example iron, nickel, cobalt, which show magnetism, copper has no choice but to settle with one spin. Such monotony in spin makes it quite boring, I think.” Mendeleev:- “Do you understand the beauty of copper? Do you know that it could change the modern electronics industry?” PT: “No, never thought of that.” Mendeleev: “Then listen to me carefully

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

Using quantum chemical calculations, we investigate surface reactions of copper precursors and diethylzinc as the reducing agent for effective Atomic Layer Deposition (ALD) of Cu. The adsorption of various commonly used Cu(II) precursors is explored. The precursors vary in the electronegativity and conjugation of the ligands and flexibility of the whole molecule. Our study shows that the overall stereochemistry of the precursor governs the adsorption onto its surface. Formation of different Cu(II)/Cu(I)/Cu(0) intermediate complexes from the respective Cu(II) compounds on the surface is also explored. The surface model is a (111) facet of a Cu55 cluster. Cu(I) compounds are found to cover the surface after the precursor pulse, irrespective of the precursor chosen. We provide new information about the surface chemistry of Cu(II) versus Cu(I) compounds. A pair of CuEt intermediates or the dimer Cu2Et2 reacts in order to deposit a new Cu atom and release gaseous butane. In this reaction, two electrons from the Et anions are donated to copper for reduction to metallic form. This indicates that a ligand exchange between the Cu and Zn is important for the success of this transmetalation reaction. The effect of the ligands in the precursor on the electron density before and after adsorption onto the surface has also been computed through population analysis. In the Cu(I) intermediate, charge is delocalized between the Cu precursor and the bare copper surface, indicating metallic bonding as the precursor densifies to the surface

Mechanism for the atomic layer deposition of copper using diethylzinc as the reducing agent – a density functional theory study using gas phase molecules as a model

We present theoretical studies based on first-principles density functional theory calculations for the possible gas-phase mechanism of the atomic layer deposition (ALD) of copper by transmetalation from common precursors such as Cu(acac)(2), Cu(hfac)(2), Cu(PyrIm(R))(2) with R = (i)Pr and Et, Cu(dmap)(2), and CuCl(2) where diethylzinc acts as the reducing agent. An effect on the geometry and reactivity of the precursors due to differences in electronegativity, steric hindrance, and conjugation present in the ligands was observed. Three reaction types, namely, disproportionation, ligand exchange, and reductive elimination, were considered that together comprise the mechanism for the formation of copper in its metallic state starting from the precursors. A parallel pathway for the formation of zinc in its metallic form was also considered. The model Cu(I) molecule Cu(2)L(2) was studied, as Cu(I) intermediates at the surface play an important role in copper deposition. Through our study, we found that accumulation of an LZnEt intermediate results in zinc contamination by the formation of either Zn(2)L(2) or metallic zinc. Ligand exchange between Cu(II) and Zn(II) should proceed through a Cu(I) intermediate, as otherwise, it would lead to a stable copper molecule rather than copper metal. Volatile ZnL(2) favors the ALD reaction, as it carries the reaction forward

Copper reduction and atomic layer deposition by oxidative decomposition of formate by hydrazine

We have used density functional theory (DFT) to study the mechanism of three step atomic layer deposition (ALD) of copper via formate and hydrazine. The technique holds promise for deposition of other transition metals

Copper(I) carbene hydride complexes acting both as reducing agent and precursor for Cu ALD: a study through density functional theory

We propose dual functional copper complexes that may act both as reducing agents and as Cu sources for prospective Cu atomic layer deposition. The example here is a CuH carbene complex, which can donate the H− anion to another Cu precursor forming neutral by-products and metallic Cu(0). We compute that such a reaction is thermodynamically possible because the Cu–H bond is weaker than that of Cu–C (from the carbene). Most other neutral ligands such as PPh3 and BEt3 show opposite order of bond strengths. We also find that substitution in the carbene by electronegative groups reduces the Cu–H bond strength. This further facilitates the donation of H− to the surface. The most promising copper carbene precursor is computed to be 1,3-diphenyl-4,5-imidazolidinedithione copper hydride (S-NHC)–CuH

Classification of processes for the atomic layer deposition of metals based on mechanistic information from density functional theory calculations

Reaction cycles for the atomic layer deposition (ALD) of metals are presented, based on the incomplete data that exist about their chemical mechanisms, particularly from density functional theory (DFT) calculations. ALD requires self-limiting adsorption of each precursor, which results from exhaustion of adsorbates from previous ALD pulses and possibly from inactivation of the substrate through adsorption itself. Where the latter reaction does not take place, an “abbreviated cycle” still gives self-limiting ALD, but at a much reduced rate of deposition. Here, for example, ALD growth rates are estimated for abbreviated cycles in H2-based ALD of metals. A wide variety of other processes for the ALD of metals are also outlined and then classified according to which a reagent supplies electrons for reduction of the metal. Detailed results on computing the mechanism of copper ALD by transmetallation are summarized and shown to be consistent with experimental growth rates. Potential routes to the ALD of other transition metals by using complexes of non-innocent diazadienyl ligands as metal sources are also evaluated using DFT

Deposition of copper by plasma-enhanced atomic layer deposition using a novel N-Heterocyclic carbene precursor

Two novel N-heterocyclic carbene (NHC)-containing copper(I) amides are reported as atomic layer deposition (ALD) precursors. 1,3-Diisopropyl-imidazolin-2-ylidene copper hexamethyldisilazide (1) and 4,5-dimethyl-1,3-diisopropyl-imidazol-2-ylidene copper hexamethyldisilazide (2) were synthesized and structurally characterized. The thermal behavior of both compounds was studied by thermogravimetric analysis (TGA), and they were both found to be reasonably volatile compounds. Compound 1 had no residual mass in the TGA and showed long-term stability at temperatures as high as 130 °C, while 2 had a residual mass of 7.4%. Copper metal with good resistivity was deposited using 1 by plasma-enhanced atomic layer deposition. The precursor demonstrated self-limiting behavior indicative of ALD, and gave a growth rate of 0.2 Å/cycle. Compound 2 was unsuccessful as an ALD precursor under similar conditions. Density functional theory calculations showed that both compounds adsorb dissociatively onto a growing copper film as long as there is some atomic roughness, via cleavage of the Cu-carbene bond

Atomic layer deposition of copper – study through density functional theory

The wonder of the last century has been the rapid development in technology. One of the sectors that it has touched immensely is the electronic industry. There has been exponential development in the field and scientists are pushing new horizons. There is an increased dependence in technology for every individual from different strata in the society. Atomic Layer Deposition (ALD) is a unique technique for growing thin films. It is widely used in the semiconductor industry. Films as thin as few nanometers can be deposited using this technique. Although this process has been explored for a variety of oxides, sulphides and nitrides, a proper method for deposition of many metals is missing. Metals are often used in the semiconductor industry and hence are of significant importance. A deficiency in understanding the basic chemistry at the nanoscale for possible reactions has delayed the improvement in metal ALD. In this thesis, we study the intrinsic chemistry involved for Cu ALD. This work reports computational study using Density Functional Theory as implemented in TURBOMOLE program. Both the gas phase and surface reactions are studied in most of the cases. The merits and demerits of a promising transmetallation reaction have been evaluated at the beginning of the study. Further improvements in the structure of precursors and coreagent have been proposed. This has led to the proposal of metallocenes as co-reagents and Cu(I) carbene compounds as new set of precursors. A three step process for Cu ALD that generates ligand free Cu layer after every ALD pulse has also been studied. Although the chemistry has been studied under the umbrella of Cu ALD the basic principles hold true for ALD of other metals (e.g. Co, Ni, Fe ) and also for other branches of science like thin film deposition other than ALD, electrochemical reactions, etc

Using a Vapor-Phase Surfactant to Control Gold Metal Plate Growth

Hexamethyldisilazide-1,3-diisopropylimidazolidine-2-ylidenegold(I) (1) is used to deposit gold microplates with (111) faces. In the absence of any secondary vapor-phase surfactant, these plates show secondary nucleation and growth of gold metal nanoparticles on the (111) faces. When tetrahydrothiophene (THT) is used as a secondary, vapor-phase surfactant, plate size increases, and secondary nucleation is controllable by temperature. Deposition of gold microplates at 370 °C using a 45 mTorr overpressure of THT shows the best experimental results, growing 20 μm2 plateaus with no apparent secondary nucleation. Computational modelling demonstrates that THT is a stronger surfactant than the carbene ligand (from the gold precursor) due to steric hindrance from the alkyl groups present in the carbene ligand