TEM-EDX Line Scan to Investigate O2 Diffusion across Physical Vapor Deposited Al-Cu Layer

O2 diffusion through Aluminium-Copper (Al-Cu) layer deposited by physical vapor deposition (PVD) process can be investigated using TEM (Transmission Electron Microscope) coupled with EDX (Energy Dispersive X-ray) line scan. During PVD process, the wafer is hot after Al-Cu deposition thus a cooling step is required before the wafer is unloaded (vacuum release). Higher amount of O2 diffusion was observed for sample with 30s cooling time compared to the one with longer cooling time which is 60s. This indicated that higher wafer temperature induce higher O2 diffusion rate in Al-Cu when exposed to air. No O2 diffusion within tungsten (W) layer was observed. Al-Cu exposure time to air before it is coated with photoresist is also studied. Wafer with 60s cooling time and 16 hours exposure time in air has O2 diffusion level is higher than the wafer with same cooling time but with 8 hours exposure time. The TEM-EDX line scan profile indicated that at room temperature, the O2 continue to diffuse through Al-Cu layer at lower rate until its surface is coated with photoresist. The O2 diffusion as analyzed by TEM-EDX method is a function of temperature and time. The higher the temperature, the faster the O2 diffusion while the longer the exposure time to air, the more the diffusion of O2 into Al-Cu.