Ice-VII-like Structure Observed By XRD in Water Confined in Silica Nanoholes

In advanced semiconductor manufacturing, deep hydrophilic nanoholes are found in various applications, which require a wet clean after patterning. However, wetting of high aspect ratio nanoholes was showed to be incomplete for non-settled reasons. In this study, X-ray diffraction (XRD) was used to characterize water confined in deep nanoholes with 20 nm diameter. Long XRD measurements were made possible by the anomalous capillary condensation occurring in these nanoholes, which was proved by Attenuated Total Reflection – Fourier Transformed Infra-Red measurements. Condensation occurred in nanoholes submitted to the clean-room air with a relative humidity (RH) of about 40%, while no condensation was observed under a N2 flow with a RH of about 30%. XRD measurements showed the presence of small peaks varying as a function of the XR incidence angle, which were not present in the Si and oxide references. These peaks gave evidence for structuring of water confined in nanoholes.