Impacts of Ionization Potentials and Megasonic Dispersion

It has been shown that megasonics can accelerate strip processes such as doped and plasma treated photoresist [1]. However, applied megasonic energy can also damage sensitive semiconductor devices. It was shown that adding a solvent such as IPA or lowering the temperature helps to control cavitation in semi-aqueous fluids [2]. Sonochemical reactions have been observed in various industries, however, there are no published observations in semiconductor cleaning. Ions may form in megasonic driven bubble collapse impacted by the characteristics of a gas or liquid that enters the bubble from the bulk liquid. Lower ionization potential gases or liquids may form ions earlier in the bubble collapse, so as to use up some of the total available energy through sonochemical reactions and possibly reducing the cavitations implosive energy. Here, tests are conducted to vary the liquid and gas type based on ionization potential to look into the impact this would have on cleaning and damage. It is shown that lower ionization or liquid additives lower the device damage.