Effect of cleaning chemistry on MegaSonic damage

Abstract

Acoustic energy applied through the cleaning media results into two kinds of cavitation effects; namely stable and transient cavitation. A uniformly pulsating bubble transforms into stable cavitation behavior whereas a bubble implosion implies transient cavitation. Pattern damage of sensitive features on advanced masks as well as Ru pitting on EUVL reticles is mostly the result of transient cavitation. Stable cavitation on the other hand produces a very narrowly controlled energy distribution which allows cleaning without damage. Stable cavitation can be achieved by suitably tailoring physical, chemical and thermodynamic properties of the liquid and gas media. In this paper we investigate a new cleaning chemistry that has favorable physical and thermodynamic properties to produce stable MegaSonic cavitation. The cavitation created in this chemistry is characterized by measuring acoustic energy as well as by pattern damage and particle removal efficiency on mask level. The chemical properties (pH and zeta potential) of this chemistry are compared with conventional cleaning chemistries. Its effects on CD shift as well as phase and transmission loss are also studied.