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 microm) 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% H2 + 95% N2 atmosphere. The fabricated nanoparticles in high purity nitrogen atmosphere had spherical shape and were dispersed in the 1.5 microm 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% H2 + 95% N2 atmosphere, surface plasmon resonance from metallic Cu nanoparticle was enhanced. In the specimens cured in reducing atmosphere, 5% H2 + 95% N2, 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% H2 + 95% N2 atmosphere were metallic Cu. Thermal curing in reducing atmosphere produces nanoparticles of high density, and uniform dispersion in a relatively thick PI film.