Highly-Conductive and Well-Adhered Cu Thin Film Fabricated on Quartz Glass by Heat Treatment of a Precursor Film Obtained Via Spray-Coating of an Aqueous Solution Involving Cu(II) Complexes

Philipus Hishimone,Mitsunobu Sato,Hiroki Nagai,Masato Morita,Tetsuo Sakamoto

doi:10.3390/coatings8100352

Abstract

A Cu thin film on a quartz glass substrate was fabricated by a wet process involving heat-treatment of a precursor film spray-coated with an aqueous ammonia solution containing Cu(HCOO)2∙4H2O and Cu(II) complex of ethylenediamine-N,N,N′N′-tetraacetic acid. The precursor film that formed on the substrate at 180 °C in air was heat-treated at 350 °C and post annealed at 400 °C by placing an identical-sized glass on top, under Ar gas flow in a tubular furnace. X-ray diffraction pattern of the resultant film showed only peaks of Cu. The resultant film of 100 nm thickness has an adhesion strength and electrical resistivity of 37(7) MPa and 3.8(6) × 10−5 Ω cm, respectively. The images of atomic force and field-emission scanning-electron microscopies revealed a film of well-connected Cu grains with an average surface roughness of 11 nm. The reflectance of the thin film is more than 90% in the far-infrared region. The film’s chemical composition was also examined by using Auger electron spectroscopy.

Highlights

Cu is an important metallic material due to its excellent electrical conductivity, only second to silver but more abundant and affordable
In our previous work [10], we reported the fabrication of a Cu thin film, whose reflectance approaching nearly 100% in the identical region, with a thickness of 100 nm and an electrical resistivity of
The fabrication of a Cu thin film was achieved by the use of an aqueous coating solution containing

Summary

Introduction

Cu is an important metallic material due to its excellent electrical conductivity, only second to silver but more abundant and affordable. Thin films of metallic Cu have been identified as promising conductive materials and extensively used in microelectronics [1]. Leading techniques, such as radio-frequency sputtering [2] and chemical vapor deposition [3], have been found to be capable of depositing Cu thin films of good quality. The use of inks containing Cu nanoparticles is a promising technique for fabricating Cu films, usually of several microns in thickness and this research area is very active [6,7,8]. The multiple steps required in preparing the Cu nanoparticles, protecting them against oxidation using capping agents and finding appropriate solvents to obtain suitable inks still remain as some of the challenging aspects

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Conclusion