CVD of Conducting Ultrathin Copper Films

Abstract

Miniaturization of electronic devices imposes challenges in terms of materials and production methods, and advances in the chemical vapor deposition ͑CVD͒ of metals are a key prerequisite toward reliable interconnects that are essential for their functionality. Electrically conducting ultrathin films of pure copper were grown on glass and silicon substrates starting at a temperature of 195°C. The growth kinetics does not exhibit any measurable nucleation time enabling early stage coalescence and high electrical conductivity. In situ monitoring of the CVD process using synchrotron-based mass spectrometry shows that the enhanced dehydrogenation of alcohols by copper II acetylacetonate precursor drives the Cu 0 deposition, which is kinetically favorable already at low temperature.The development of microelectronic devices faces several challenges regarding miniaturization and increased degree of integration, which is in part limited by the metal interconnects. 1 Copper remains a subject of intense development as an interconnect material 2-4 because of its remarkably low bulk electrical resistivity and resistance to electromigration. A highly conformal process, such as chemical vapor deposition ͑CVD͒, is particularly well adapted to overcome the deficiency in conformality of physical vapor deposition. However, CVD features are perceived to include complex nucleation kinetics on semiconducting surfaces and lack of morphology control for ultrathin films, in addition to the toxicity, limited availability, and laborious handling of successful precursors. These limitations are approached either by influencing the surface chemistry via the introduction of other families of CVD and atomic layer deposition ͑ALD͒ precursors 5 or by the development of deposition techniques, such as chemical fluid deposition ͑CFD͒. 6 Also, a two-step CVD process 4 was proposed to overcome the high readiness of copper atoms to diffuse on the surface, an effect which was demonstrated by ab initio molecular dynamics simulation. 3 Our recent efforts, taking advantage of pulsed liquid delivery ͓pulsed-spray evaporation-chemical vapor deposition ͑PSE-CVD͔͒ of the reactants, show that the use of alcohol as a unique coreactant is more efficient and attractive than the hydrogen reduction route for several transition metals. 7-10 Indeed, the utilization of alcohol as an additive in the CVD process was reported to enhance the growth kinetics, 11-13 yet the presence of hydrogen as a reducing agent was considered necessary. In contrast to CVD, the presence of hydrogen in addition to alcohol was not required to attain metallic thin films by CFD. 14 However, Cu-CFD requires the presence of catalytic surfaces ͑cobalt and nickel͒, and deposition temperatures are 100°C higher than those needed with H 2 reduction and thus less attractive.Our previous work on the growth of copper by CVD, which was performed using copper acetylacetonate ͓Cu͑acac͒ 2 ͔ and methanol, shows that smooth and polycrystalline copper films can be grown above 280°C. 9,15 In the present paper...

A comparative study of copper thin films deposited using magnetron sputtering and supercritical fluid deposition techniques

“…Bahlawane et al [47] also showed that the copper film resistivity increases with decreasing thickness for film prepared by CVD. Without specifying the crystallite size, some authors [22,48] announced that a chemical/supercritical fluid chemical deposition (CFD/SFCD) process, which enables precursor concentration far above ranges in CVD, yielded 50 nm thick films, exhibiting near-bulk resistivity.…”

Metal-based Inkjet Inks for Printed Electronics

“…The addition of ethanol in the MOCVD of (hfac)Ag(COD) (hexafluoroacetylacetonato)silver(I)(1,5 -cyclooctadiene) is one such example, where Bahlawane et al [187] identified the surface dehydrogenation of ethanol as the mechanism responsible for faster precursor conversion. Under the same conditions, AgNO 3 forms pure silver films at growth rates up to 18.5 nm min -1 with resistivities of <2 μ cm for 400 nm thick films grown at 573 K. The same methodology was also extended to Cu precursors with similarly positive results of near bulk resistivity copper films [188,189].…”

Efficient Process for Direct Atomic Layer Deposition of Metallic Cu Thin Films Based on an Organic Reductant

“…12,13 There is research going on towards finding new precursors [14][15][16] and new variants of the CVD technique, [17][18][19][20] but common to most of these processes is that hydrogen is used as the reducing agent in order to obtain a metallic film 21,22 As an alternative, few works have reported the use of alkyl alcohols as co-reactants/solvents to enhance the film growth, where dehydrogenation of alcohols produces hydrogen radicals that reduce copper oxides to pure metal. [23][24][25][26][27][28] With its self-limiting and sequential surface reactions, the stateof-the-art thin-film technique, i.e. atomic layer deposition (ALD), would in principle be a viable alternative for high-quality conformal copper thin film deposition.…”