Abstract
Optical inspection of periodic nanostructures is a major challenge in the semiconductor industry due to constantly decreasing critical dimensions. In this paper we combine coherent Fourier scatterometry (CFS) with a sectioning mask for subwavelength grating parameter determination. By selecting only the most sensitive regions of the scattered light in the Fourier plane, one can retrieve grating parameters faster and with higher sensitivity than previous approaches. Moreover, the full process of CFS using focused light is explained and implemented in a subwavelength grating regime. The results of using transverse magnetic polarized input fields together with the proposed sectioning mask are presented and compared to the non-mask case.
Highlights
Optical scatterometry is a very commonly used measurement technique in the fields of photonics, optics, electronics, biology, and medicine, where non-destructive measurement methods are required [1,2]
Attention has been directed towards coherent Fourier scatterometry (CFS) which in a prior study [8] was reported as a method offering smaller uncertainty and higher
In order to analyse the most sensitive regions of the far field, computational simulations were performed by using rigorous coupled-wave analysis (RCWA) which solves Maxwell’s equations based on periodic conditions and computes the efficiency of the diffraction orders in the far field for each incident angle on the grating
Summary
Optical scatterometry is a very commonly used measurement technique in the fields of photonics, optics, electronics, biology, and medicine, where non-destructive measurement methods are required [1,2]. In recent approaches [9] it was reported that, by imaging the target through multiple focus positions, it is possible to reconstruct the scattered volume This method can be applied for the determination of the parameters of nanostructures. The structure is characterized based on the unique intensity pattern captured in the back focal plane, and in the case of subwavelength grating, without scanning. The goal of this research is to determine the most sensitive segments of the complex scattered field and to use them for more efficient retrieval of subwavelength grating parameters. We propose a sectioning mask which will help to analyse only the most sensitive segments of the light patterns in a Fourier plane In this way, due to data reduction it becomes a time saving tool for the retrieval of subwavelength grating parameters. These gratings are widely used in the fabrication of microchips and other electronic components
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