Abstract: Metalization is widely used in integrated circuit devices to connect millions of devices together. The success of metallization depends strongly on diffusion barrier technology, due to the interactions of metals with surrounding materials. As device dimension further shrinks, diffusion barrier technology is facing more challenges and opening up new opportunities, particularly for chemical vapor deposition (CVD) process technology. CVD is attracting increased attention in advanced metallization mainly due to its capability in producing conformal thin films. In this review, we will focus our discussion on CVD processes for three most important classes of diffusion barriers: Ti, W and Ta-based diffusion banters. Examples from current literature will be examined.