Analysis on Copper Photocorrosion Induced by Illuminance in Chemical Mechanical Planarization Equipment Using Photodiode and Quartz Crystal Microbalance

Abstract

Photoassisted corrosion of copper (Cu) was evaluated using a photodiode and a quartz crystal microbalance (QCM). A chip-type silicon (Si) photodiode with a large junction area was used in place of actual Si devices. When the illuminated photodiode was connected to the anode and cathode electrodes in an electrolyte, it worked as a voltage source between the two electrodes, and the corrosion rate was governed by the current between the electrodes. The corrosion rate is nearly proportional to the illuminance at less than 100 lx, and corrosion initiates at an illuminance as low as 1 lx. In the geometrical aspect of the photoassisted corrosion system, the corrosion rate is proportional to the square root of the area ratio of a P-connected Cu line to an N line, and is proportional to the illuminated area of the junction in a photodiode. The wavelength of the illuminating light markedly affects the photoassisted corrosion.