Formation of Copper Based Nanoparticles Embedded in a Relatively Thick Polyimide Film by Thermal Curing in Reducing Atmosphere

Abstract

We investigated the formation of nanoparticles in a relatively thick polyimide (PI) film (>1 mu m) in controlled atmospheres and optical properties of these nanoparticles. Polyamic acid of 10 wt% BPDA-PDA was spin-coated on the 25 nm Cu thin film and thermally cured at 350 degrees C in high purity nitrogen or 5% H-2 + 95% N-2 atmosphere. The fabricated nanoparticles in high purity nitrogen atmosphere had spherical shape and were dispersed in the 1.5 mu m thick PI film. Its phase was revealed as Cu and Cuprous Oxide by X-ray diffraction (XRD). Its size and optical absorption depended on deposited metal thin film thickness. After post heat-treatment in 5% H-2 + 95% N-2 atmosphere, surface plasmon resonance from metallic Cu nanoparticle was enhanced. In the specimens cured in reducing atmosphere, 5% H-2 + 95% N-2, highly dense and 3.5 nm size nanoparticles were well dispersed in an entire PI film. XRD results and optical data revealed that nanoparticles fabricated in 5% H-2 + 95% N-2 atmosphere were metallic Cu. Thermal curing in reducing atmosphere produces nanoparticles of high density, and uniform dispersion in a relatively thick PI film.