Particle Formation and Trapping Behavior in a TEOS/O₂ Plasma and Their Effects on Contamination of a Si Wafer

Particle formation and growth in a TEOS/O₂ radiofrequency (rf) plasma were studied by an in situ laser light scattering (LLS) technique and ex situ scanning electron microscopy (SEM). The particles, after being generated, were located around the sheath near the electrodes. Visualization using a high-resolution video camera shows that the particles are trapped around the sheath near the powered electrode (showerhead) and are ultimately located in localized regions between the showerhead holes. Particle-free regions are present immediately below the holes and their surroundings within a certain radius. The particles form a lump cloud when a low gas flow rate is used, change to a line shape when the flow rate is increased, and finally the LLS technique can no longer detect them when high flow rates are used. The particle trapping behavior described above clearly has an influence on particle contamination on the wafer. The particles appear to grow through coagulation as shown by the SEM images of particles taken from the trap regions. A high gas flow rate and high substrate temperature tend to suppress particle formation and growth. On the other hand, particle formation and growth are enhanced with increasing rf power.