The wave front sensor used in this paper is based on Makyoh method: the studied sample is illuminated by a collimated
light beam and the reflected beam is collected by a camera. Previously it was demonstrated that this method enables the
determination of surface flatness in the nanometer range. For this purpose the deformation of an initially planar wave
front is detected and evaluated using patterns projected on the surface. This paper demonstrates that the sensor can also
be used without patterns for characterization of surfaces flatness in the sub-micrometer and micrometer ranges. The
intensity distribution image obtained can be interpreted in terms of topography as follows: convex areas of the studied
surface defocus the beam (dark regions on the image) while the concave areas focus it (bright regions). The main result
of this work is the development of a new approach for the fast assessment of the surface quality. This approach estimates
the areas and the intensities of bright regions on the image and gives the value of the maximum concavity on the studied
surface. For evaluation of data a simulation of the reflected from the given profile was made. The setup parameters, e.g.
distances between the optical components, were optimized with the parameters obtained from the 2D simulation of the
wave front sensor. This paper demonstrates the feasibility of wave front sensing for the topography analysis of reflective
surfaces such as bare wafers' surfaces, metallic thin films, etc. used in semiconductor industry.
Wave front sensing allows determination of topography and flatness of reflecting surfaces. As there is no contact to the
surface, the method enables a contamination free and non-destructive surface analysis which meets the requirements of
semiconductor and optical industries. This paper demonstrates that the sensor is suitable for defect estimation on the
studied surface without topography reconstruction, where defect is considered as a dimple or a mound on the wafer
surface. Based on the development, it is possible to reduce the evaluation time for the measurements by the reduction of
both processing time for topography calculation and the number of acquired images. The method judges whether the
surface of the studied sample is defect-free. That is a key for fast and reliable inspection. The Makyoh image shows the
light distribution of the beam reflected from the surface. The images of bare wafers show unevenly alternate bright and
dark areas. These areas appear due to the focusing and defocusing of the wave front and are caused by the local surface
defects. The intensity changes are qualitatively interpreted with the help of the geometrical optics, and the maximum
curvature of the defects on the studied surface is roughly estimated. Furthermore, the measurements of the sample
rotated underneath the fixed sensor prove that the intensity changes are the result of the surface shape and not due to the
aberration in the optical system. According to the results the method is useful for characterization of both micro- and
nanometer scale surface flatness deviations.
Wave front sensing is an optical method allowing non-contacting topography measurements of flat surfaces.
Applications of the method are, for instance, the characterization of optical components, semiconductor surfaces, or subcomponents
used in semiconductor manufacturing equipment. The method developed here is covering the
characterization of flatness on mirror-like surfaces within three orders of magnitude from micro- to nanometer scale.
This is due to the high range of detectable surface slopes from very low to relatively high values. Therefore, the method
is applicable to both, micro- and nanometer scale height deviations on surfaces. The wave front sensing is capable of
studying the topography in a real-time operating mode. The technique enables vertical resolution of approximately 10 nm
at a lateral resolution of 0.6 mm on bare silicon wafer surfaces. Moreover, highly reflective surfaces with height
deviations of 10-15 μm could be easily resolved at a lateral resolution of 2.4 mm. In this study, we focused on the
application in semiconductor surfaces and manufacturing equipment: measurements were performed on bare wafers as
well as on the mirror-like surface of a wafer holder used for wafer polishing (a 'polishing head'). An obstacle for
measurements is a low reflectivity of surfaces. Both, metallic surfaces and silicon wafers, however, show high surface
reflectivity.
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