Parameter Optimization of PVD Tungsten Interconnects for CMOS Using Magnetron Sputtering with Focus on Film Stress

Sammanfattning

Copper is widely used as the interconnect material in advanced CMOS technology due to its low resistivity. However, its applicability is limited in high-temperature environments, since copper exhibits poor resistance to electromigration and can diffuse into surrounding dielectrics. Tungsten, although having approximately twice the resistivity of copper, offers superior high-temperature stability, strong resistance to electromigration, and negligible diffusion through dielectrics. For this reason, tungsten is an attractive candidate for Complementary Metal-Oxide-Semiconductor (CMOS) technologies that must operate reliably above 250 °C. However, using tungsten as interconnect introduces its own challenges, and the main issue is the residual stress that it introduces. This thesis investigates the deposition via Physical Vapor Deposition (PVD) technique of tungsten interconnects for high temperature CMOS applications, focusing on film stress and resistivity. The experiment was divided into two phases, the first phase focused on systematically varying the deposition parameters to understand their influence on film stress and sheet resistance. In addition to the deposition parameters, stack composition and film thickness were varied to explore their effects on film properties. Three stack compositions were investigated: Si/W, Si/SiO2/W, and Si/SiO2 /TiW/W. The second phase focused on implementing a linear regression model based on the results from the first phase, and performing a second deposition round using deposition parameters that were estimated to provide a near stress free film. Results showed that the chamber pressure has the biggest impact on the stress in the film, where low pressure produces high compressive stress, while high pressure provides tensile stress. These findings contribute to a better understanding of stress management in tungsten interconnects, providing valuable insights into optimizing tungsten deposition.