Generation of positively charged particles at an anode and transport to device wafers in a real radio frequency plasma etching chamber for tungsten etch-back process

The transport path of particles, that have flaked off a grounded anode of a real parallel-plate radio frequency (rf) plasma etching equipment for tungsten etch-back processing to device wafers on the cathode, is measured by using an in situ monitoring system that measures laser light scattered by the particles. A few particles appear constantly only near the grounded anode while rf power is being supplied. These particles have parabolic trajectories that open upward. Few particles are observed near the wafer. On the other hand, at the timing of the turning off of rf power, many particles appear near the anode. Their trajectories from the anode to the chamber wall are sharply curved. Near the wafer, which has a negative self-bias voltage, almost all the particles’ trajectories are from the chamber wall to the wafer. Therefore, the particles move from the anode to the device wafer on the cathode and keep away from the after-glow plasma as well as from the bulk plasma. These particles are then attracted to the wafer by its negative self-bias voltage. These phenomena indicate that the particles generated at the anode have positive charges.