Wetting of deep hydrophilic nanoholes by aqueous solutions

Abstract

In advanced semiconductor manufacturing, deep hydrophilic nanoholes are found in various applications, which require a wet clean after patterning. In this work, we use an in-situ ATR-FTIR spectroscopy technique to characterize the wetting of nanoholes in a silica matrix by UPW and electrolyte solutions. Besides, water structuring in the nanoholes was characterized by an analysis of the OH stretching peak, while monitoring the dissolution of CO2 in the wetted nanoholes allowed characterizing the diffusivity and the permittivity in the nano-confined solutions. The formation of gas pockets or nanobubbles upon wetting of nanoholes was evidenced by heating tests showing an hysteresis in plots of the OH stretching to bending ratio when temperature was decreased. This was accompanied by water structuring that was characterized by a large fraction of the OH stretching peak showing up at frequencies higherthan that of ice. Dissolution of CO2 in confined solutions showed a solubility higher by a factor up to about 50 compared to bulk UPW, indicating a decrease in permittivity. The wetting time decreased significantly by heating the solution, while the addition of NaI or CoCl2 at 1 M concentration, respectively a structure making or breaking salt, had no significant effect at room temperature. Finally, a slower diffusion, as measured with CO2, was most likely the cause of the surprisingly long lifetime of the nanobubbles formed upon wetting of the nanoholes.