Advantages of using PVD two-step titanium nitride barrier process and the impact of residual by-products from tungsten film deposition on process integration due to non-uniformity of the tungsten film

Device aspect ratios and dimensions at the contact and via levels for old and new technologies are driving PVD/WCVD-based metallization to its full limit at STMicroelectronics PF1 (Phoenix) site. Contact and via structures, while not posing the same rigorous dimensional problems or high aspect ratios, still suffer from problems associated with PVD sputtering of titanium (Ti) and titanium nitride (TiN) films and WCVD uniformity issues. These problems include poor barrier quality, which can lead to wormholes and volcanoes for tungsten plug technologies. Non-conformal step coverage leads to aluminum junction spiking for aluminum (Al) plugs due to poor TiN barrier quality. Bad tungsten uniformity leads to metal integration issues. Many types of metallization schemes were investigated for via structures in 0.9μm to 0.18μm technologies at the STMicroelectronics PF1 facility. One common strategy is simply to extend the existing PVD/WCVD-based solution to all technologies.; Aluminum plug technologies are still used for many different semiconductor device applications and are cost-effective processes. However, there are some disadvantages associated with them. The key disadvantage is aluminum junction spiking caused by aluminum diffusing down into the silicon substrate and silicon diffusing up into the aluminum plug, due to a poor titanium nitride (TiN) barrier. The tungsten plug process is mainly used for 0.5μm and smaller technologies. Titanium nitride barrier material plays an important role as an under layer for tungsten plugs to prevent the tungsten hexafluoride (WF ₆) from attacking the titanium (Ti) film. The role of the TiN barrier is to retard or prevent diffusion of the materials that the TiN layer separates. In this work, the TiN barrier film properties with respect to nitrogen flows at two different power set points and argon gas flows were investigated. Different experiments were performed to understand the properties of the TiN film with respect to process variables. Single-step and dual-step TiN barrier processes were studied for contact and via step coverage profiles used for aluminum and tungsten plug technologies.; Also the effects of residual by-products from a tungsten film deposition process and their impact on process integration due to the non-uniformity of the tungsten film were investigated in this work. The tungsten film deposition process involves three steps: nucleation, stabilization, and tungsten bulk fill. Many experiments were conducted in search for a solution to the problem. The resulting data suggest that excess nitrogen left in the chamber following the tungsten nucleation step, along with residual by-products, causes a shift in the tungsten film uniformity during the tungsten bulk fill process. Data reveal that, due to the residual by-products, an abnormal grain growth occurs causing a variation in the tungsten thickness across the wafer during the bulk fill step. Although several possible solutions were revealed by the experiments, potential integration problems limited the acceptable solutions to one. The solution chosen was the introduction of a 10 second pump down immediately following the nucleation step. This choice did not create any integration problems as confirmed by subsequent studies.