PREPARATION OF FINE, SPHERICAL COPPER PARTICLES BY SPRAY-PYROLYSIS TECHNIQUE

The objective of this paper is the preparation of fine, spherical Cu particles by spray-pyrolysis technique. Effects of reaction conditions on prppertie of Cu particles and the conductive properties of thick films made from the Cu particles were investigated. Cu(NO3)2 aqueous solution was atomized by ultrasonic vibration and heated under reductive atmosphere, H2-N2, by use of an electric furnace. Cu particles free from the oxides were produced above 600°C when H2 was above 6.2 vol% which was about 3 times of the equilibrium concentration (Table 1). Two morphological types of Cu particles, spherical and irregular-shaped, were observed (Fig. 4). This morphological difference was attributed to the melting of Cu. Spherical Cu particles were formed when the particles were heated above m. p. of Cu for about 0.1 s or more (Fig. 11), The number median diameter of spherical Cu particles varied from 0.3 to 1.3 pm in proportion to a cube root of Cu(MO3)2 concentration of the atomizing solutions (Fig. 6), suggesting the formation of one Cu particle from one droplet of atomized solution. When the atomized solution was heated above ca. 2000°C in rf-plasma flame consisting of H2-Ar, ultrafine Cu particles was produced, presumably from Cu vapor, in addition to the particles similar to these produced by furnace heating (Fig. 7). From the above results, the formation routes for Cu particles were classified into three (Fig. 10). Cu films prepared from the spherical Cu particles produced in the present study showed a low resistivity of 2.5μΩcm (Fig. 9). © 1990, The Chemical Society of Japan. All rights reserved.