Gradient barrier layer for copper back-end-of-line technology

Abstract

The present invention is directed to a structure of a gradient barrier layer. The gradient barrier with a composite structure of metal/metal salt of different composition/metal such as Ta/TaN/TaN/TaN/Ta (tantalum/tantalumnitride/tantalum nitride/tantalumnitride/tantalum) is proposed to replace the conventional barrier for copper metallization. The gradient barrier can be formed in a chemical vapor deposition (CVD) process or a multi-target physical vapor deposition (PVD) process. For CVD process, using the characteristics of well-controlled reaction gas injection, the ratio of tantalum (Ta) and nitrogen (N) can be modulated gradually to form the gradient barrier. For the multi-target PVD process, the gradient barrier is formed by depositing multi-layers of different composition TaNfilms. After subsequent thermal cycle processes such as metal alloy, the inter-layer diffusion occurs and a more smooth distribution of Ta and N is achieved for the gradient barrier. The advantages of forming the gradient barrier include a well-controlled process, a strong adhesion between via and landing metal, more uniform step coverage, and less brittle to reduce crack.