The Preparation Of Ultra-fine Copper Powder And Its Application In Microelectronic Industry

The copper thick-film systems make of ultra-fine copper powders has excellentconductivity, low sheet resistances and good peel strength, and has importantapplications in the microelectronics industry. Copper powders with particle size lessthan5μm, spherical shape, narrow size distribution, well crystalline and very lowoxygen content（high purity） are required for application in microelectronics industrywhere high electrical conductivity is of primary consideration.In this work, a unique approach is presented for preparing ultra-fine copperpowders which can meet the requirements of the microelectronics using a wetchemical reaction, and its application in wafer capacitance is discussed in this paper.Then conclusions were got as following:（1） Non-agglomerated spherical ultra-fine copper powders, which has a narrowsize distribution about0.8-3.2μm, a high apparent density about3.6g/cm³, and wellcrystalline, were synthesized by glucose pre-reduction-hydrazine two step reductionmethod. The optimal process and formula conditions were as follows: concentrationof sulfate pentahydrate is2mol/L, concentration of sodium hydroxide is4mol/L,concentration of glucose is2.5mol/L, temperature of pre-reduction is60℃, beforesynthesizing of copper powders,2g of polymer A as dispersant are additive, theadditive proportion of hydrazine in the two steps is1:3, the reaction temperature is60℃. Appropriate amount of polymer A could effectively avoid the agglomerationphenomena of copper particles and tended to make the copper powder kind ofspherical shape. The mechanism of ultra-fine copper powder preparation shows that,effectively distinguishing between copper crystal nucleation and growth process, isthe critical factor to make the copper crystal slowly growing up, then getting uniformparticle size of ultra-fine copper powders.（2） Copper sulfate pentahydrate as10kg,20kg class in a pilot process on thebasis of the small test. The copper powder made from20Kg trial stage is spherical,uniform particle size distribution, particle size distribution is narrow, D₅₀ is1.95μm, the particle size distribution of1.1-4.1μm, a tap density of3.5g/cm³.（3） Surface treating of the copper powder deposited by the above method byoleic, gelatin, stearic, polyaniline or benzotriazole, the oxidation resistance of copperpowder was improved. After sintering the copper paste prepared by copper powderstreating by gelatin and stearic acid, the adhesion of copper electrode is greater than25N/4mm², solderability>90%, the capacitance loss less than0.01, meeting the wafercopper electrode capacitance current actual using requirement.（4） A copper paste using in wafer capacitance was prepared with7%of thelead-oxide-free glass material,79%of the above-mentioned which treated by gelatinand14%organic phases. The copper paste was printed on ceramic substrates wasdried at150℃for5min, then was fired at850℃for10min in a nitrogen atmosphereto obtain copper electrode. After fired, a color of fuchsia copper electrode was got.The copper electrode has good electrical and adherence properties, with the peelstrength is33.1N/4mm², solder ability is90%, and the capacitance loss is0.007. Theperformance of the above-mentioned copper paste reach the silver paste using now.