A recently introduced novel concept ellipsometry, characterized by its unique derivation process of directly extracting the polarization information from the hologram image on pupil plane, has been evaluated experimentally targeting for the application to OCD and overlay tools. With an improvement of splitting the hologram on the pupil, this self-interferometric pupil ellipsometry (SIPE) has gained the capability of measuring all of Stokes parameters (S0-S3) throughout the incident angle of 0 to 72 degrees with omnidirectional orientation. A prototype system incorporating SIPE technology has been fabricated to conduct the performance test with patterned test samples for overlay and CD evaluation, the result of which exhibits the sufficient sensitivity to dimension variation and superior repeatability for practical use. The measurement of thousands of ellipsometric data on pupil only takes tens of milliseconds at the most, realized by leveraging the advantages of self-interferometry that does not have any rotating elements in optics. The experimental result demonstrates the consistency with the simulation results based on TEM data within entire pupil. In the front-line of advanced semiconductor manufacturing, the main obstacles to OCD application, low sensitivity and parameter coupling, have been evaluated, which indicates good prospects with SIPE technology.
An innovative self-interferometric pupil ellipsometry (SIPE) technique has been demonstrated to overcome the accuracy and throughput limitations raised from the conventional spectroscopic ellipsometry (SE) tools to precisely measure the optical critical dimensions (OCD) in the advanced semiconductor devices. The proposed SIPE technique will be extremely powerful, because key ellipsometric parameters, Ψ and Δ, from all possible incident angles can be obtained simultaneously from the single measurement, while the conventional SE technique needs to collect several hundreds of measurements to get the identical information. By employing a Nomarski prism, one can angularly separate the reflected light from the wafer into two orthogonally polarized lights. Then, the self-interference pupil ellipsometer could interfere those two beams without an additional reference beam path. The interfered fringe includes rich ellipsometric information at incident angles from -70º to 70º with 0-360º azimuthal directions, where those Ψ and Δ information can be extracted by the novel holographic algorithm we proposed. To verify the usefulness of SIPE system and the algorithms, both experimental and theoretical validation have been performed for the patterned wafers. In short, the proposed system and algorithms, which are completely new concept, show a capability to overcome current metrology challenges by breaking multiple parameter correlations between various structural parameters, eventually resulting in the improved metrology sensitivity and precision. Based on the results presented here, we strongly believe the SIPE is a promising metrology solution that can be eventually replacing the traditional OCD tools.
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