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

O ₂ 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 O ₂ 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 O ₂ diffusion rate in Al-Cu when exposed to air. No O ₂ 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 O ₂ 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 O ₂ continue to diffuse through Al-Cu layer at lower rate until its surface is coated with photoresist. The O ₂ diffusion as analyzed by TEM-EDX method is a function of temperature and time. The higher the temperature, the faster the O ₂ diffusion while the longer the exposure time to air, the more the diffusion of O ₂ into Al-Cu.