Tantalum and tantalum nitride films deposited by electron cyclotron resonance sputtering as barriers to copper diffusion

Abstract

Tantalum (Ta) and tantalum nitride (TaN) films deposited by electron cyclotron resonance (ECR) sputtering have been investigated as barriers to Cu diffusion in very large scale integrated interconnections. An ECR plasma source coupled with divided microwaves was used to deposit Ta and TaN films. The addition of N2 to Ar enabled the ECR TaN film to be easily deposited by using a Ta metal target at low temperature without external substrate heating. To investigate the barrier characteristics, sample with Cu/ECR–Ta/SiO2 and Cu/ECR–TaN/SiO2 structures were heat treated in Ar at 550 and 650 °C, respectively, and analyzed by secondary ion mass spectroscopy, which determined the Cu diffusion density. The normalized signal intensity ratio of Cu to Si at the interface between the barrier metal and SiO2 was 0.035 for the ECR TaN film and 0.087 for the ECR Ta film, but 0.26 for the rf-sputtered TaN film. ECR sputter deposited films had excellent characteristics for use as barriers to Cu diffusion.