Stress Evolution in Electrodeposited Copper Metallization during Room-Temperature Aging

Abstract

Stress changes in electrodeposited copper films during room temperature aging were monitored by measuring the bending of the substrate using an optical fiber displacement sensor. Electrodeposition was carried out galvanostatically on evaporated copper films on borosilicate glass substrates in a stirred acidic copper sulphate bath at room temperature. It was observed that stress increases rapidly in the tensile direction reaching a plateau after ~1 hour of room temperature aging. The magnitude of the change was observed to increase with increasing current density but to decrease with increasing film thickness. The effect of additives to the bath was investigated. Films deposited in the presence of added chloride ions subsequently showed an increased change in stress during room-temperature aging but the effect did not increase significantly with concentration. Films deposited with BTA as an additive also showed an increased change in stress during aging and the effect increased significantly with increasing concentration. The effect of added PEG was small while the addition of thiourea had a significant and complex effect.