Naohiko Fujino

First Observations of 0.1 μm Size Particles on Si Wafers Using Atomic Force Microscopy and Optical Scattering

We have developed a new technique on the basis of an optical scattering phenomenon to link the coordinates of a commercially available wafer inspection system (WIS) to an analyzer with a high precision of ±0.1 μm. This new technique has been installed in a large sample atomic force microscope (AFM) capable of observing wafers of 8 in. size. One of the most remarkable features of this newly developed AFM is the ability to observe the same position on a wafer before and after certain processes. In this paper, we report on the results of the first observations of 0.10 μm size particles such as crystal-originated particles (COPs) and dusts on a polished (100) CZ-type Si wafer before and after SC1 cleaning by using the newly developed AFM. It was first found that the 0.10 μm size COPs are inherently juts before SC1 cleaning. After SC1 cleaning, these COPs turned into a deep crystalline pit. These pits run parallel to the axis of the wafer and have four facets with an angle of 54° with respect to the surface of the wafer. Second, the actual size of the dust particles were found to be much bigger than expected by using the WIS. The difference is considered to be attributed to the correction method used in the WIS by comparing with 0.10 μm in size polystyrene latex standard particles. These results show that the AFM combined with an optical scattering system is useful in the evaluation of 0.1 μm sized particles as well as in the wafer cleaning process.