To achieve high accuracy and precision in optical metrology for advanced semiconductors, it is crucial to identify and compensate for errors from optical components and environmental perturbations. In this study, we investigated the sources of the errors in the interferometric ellipsometer developed for next-generation OCD. The objective lens and beam splitters, the critical optical components of the system, are intensively investigated. The system errors induced by temperature fluctuation, wavelength inaccuracy, and defocus were quantitatively examined. We also proposed methods for compensating individual errors and analyzed the effect of the compensation. As a result of error compensation, the accuracy and precision of the system is improved by 6.9 times and 2.3 times, respectively. Although the investigation was conducted based on our interferometric ellipsometry system, the finding is not limited to this system, as these errors are commonly found in most optical metrology systems. The proposed method for error compensation will be essential strategies for various ellipsometry systems suffering from a low level of accuracy and precision.
We present advanced application of novel ellipsometry technique, referred to as self-interference pupil ellipsometry (SIPE), integrating self-interference and pupil microscopy to overcome the sensitivity limitations raised from the conventional spectroscopic ellipsometry. We investigated various samples including a SiO2 monolayer, grating patterned wafers, and DRAM wafers to demonstrate outstanding capability of SIPE for metrology. The angular range corresponds to approximately 5,000 acquisition of conventional ellipsometry tools with 2º angular step scanning. From the experimental results and simulation, we expect the sensitivity of SIPE for structure metrology is at least 0.15 nm at a single wavelength and even better for multispectral measurements.
An innovative self-interferometric pupil ellipsometry(SIPE) has been demonstrated to overcome the spectral sensitivity and throughput limitations for optical critical dimensions (OCD) metrology in the advanced semiconductor devices. The two orthogonally polarized lights from the target structure on wafer were combined through suitably devised polarization state analyzer to generate an interferometric fringe pattern on the pupil surface of the SIPE optical system. The measured fringe pattern was processed with our novel holographic reconstruction algorithm to extract the ellipsometric information (Ψ and Δ) with the entire incident angles 0 to 70º and azimuthal angle 0 to 360º separately. In contrast to conventional ellipsometry tools, no mechanical movements were required to obtain the multi-angular information. To verify the usefulness of SIPE system and the algorithms, both experimental and theoretical validation have been performed for patterned wafers as well as for SiO2 mono-layered wafers. We first measured the non-patterned wafers of various different thicknesses, and found that the obtained values from SIPE, commercial ellipsometry tool, and theoretical simulation present a good agreement for wide spectral and angular ranges. Furthermore, we show that the large amount of angle resolved information from SIPE technique can greatly enhance the ability to overcome the OCD ellipsometry’s recent challenges such as spectral sensitivity issues, parameter correlation and structural asymmetry problems, etc. In short, the proposed system and algorithms, which are completely new approaches, show a capability to overcome current metrology challenges and we strongly believe that the SIPE is a promising metrology solution that can be eventually replacing the traditional OCD metrology tools..
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