Generally, cleaning phenomenon is considered as abrasive nano-particle behaviors, which are removed from a wafer surface and occasionally reattach to the surface or still stay on the surface to be a residual contamination. However, these contaminations on a wafer surface are usually inspected before and after cleaning process, not during the cleaning process. Hence, we have been duplicated experimental cleaning process of thin film material on a silica glass surface, and have also been proposing a real time observing method to inspect the removal of abrasive nano-particle behaviors during the cleaning process.
Because these behaviors occur in a few hundred nm range from the wafer surface. Therefore, an evanescent light that localizes on the surface being cleaned in range of a few hundred nm can be applied to limitedly optically illuminate to observe either abrasive nano-particle behaviors or PVA brush movement. By this optical illumination, the contaminated nano-particles and/or PVA brush existing in an evanescent field will scatter their evanescent field to be the propagating light, which can reach to a camera in a microscopy to visualize the brush scrubbing cleaning phenomenon (figure(a)).
However, both scattering lights from PVA brush and nano-particles are same wavelength of illuminated laser. In this paper, 100±20 nm fluorescence silica-nano-particles were employed to identify the contaminated silica particles by fluorescent wavelength (λ=600 nm) that different from the illuminated laser wavelength (λ=450 nm).
A typical result of optical method is shown in figure(b). A silica particle that was already adhered on a glass surface was removed by sliding of PVA brush in pure water. Evidently, fluorescence scattering light (red light intensity : λ=600 nm) and PVA brush scattering light (blue light intensity : λ=450 nm) could be distinguished in the recorded phenomenon in rate of 120 frame per second by a RGB color camera.
Before coming of PVA brush, 100 nm silica particle already adhered on a glass surface. Next, PVA brush moved with a sliding speed of 2.5 mm per second by a rotation motor. Where the sliding speed was calculated by distance of PVA brush movement during 1/120 s (≈8.3 ms). Then, 100 nm silica particle was removed from surface after 33.3 ms as quantitatively shown in figure(c). These results imply that nano-particle was removing away at the same time during the attachment of PVA brush to the nano-particle or the approach near to the nano-particle. By using evanescent field and fluorescent nano-particle, we can observe nanoscale cleaning phenomenon during PVA brush scrubbing in real time.