Phase-modulation scatterometry

Abstract

Phase-modulation scatterometry is a metrology technique for determining, by means of a phase modulator as a key device, the parameters of gratings. The main source of error to be dealt with are the fluctuations of the phase-modulation amplitude. The grating zeroth-order reflectance modulated by the phase modulator is converted into a signal by the photodetector. The measurables are the direct term and the first two harmonics of the signal. For experimental data fitting, we used the ratio of the harmonics over the direct term because it significantly improves the accuracy. A sensitivity analysis was performed for two samples, one real and one theoretical, to find the measurement configuration that insures optimum determination precision for the grating parameters. For the real sample, comparison of the theoretical predictions for sensitivity with the actual values showed a good agreement. For both samples the sensitivity analysis indicated subnanometric precision for the critical dimension (grating linewidth).

Measurement configuration optimization for accurate grating reconstruction by Mueller matrix polarimetry

“…9 They further proposed to choose the measurement configuration with small parameter correlations and small estimated precision of the structural parameters. 10 It is also interesting to note from the previous works 4,5,10 that the accuracy of the extracted structural parameters varies greatly in different measurement configurations. Typical minimization of the parameter correlations and estimated precision may achieve an optimal configuration with a higher measurement precision, but cannot guarantee the final measurement accuracy.…”

“…Logofatu proposed a sensitivity analysis for fitting method by defining the sensitivity as the estimated precision of the structural parameters to optimize the measurement configuration for angle-resolved rotating-analyzer and angle-resolved phase-modulation scatterometers. 4,5 Littau et al investigated several optimal diffraction signature scan path selection techniques to improve scatterometry precision. 6 Gross et al proposed an algorithm to determine the optimal measurement data set by minimizing the condition number of the Jacobian matrix, whose elements are defined as the partial derivatives of the diffraction signature with respect to the structural parameters.…”

Dimensional characterization of biperiodic imprinted structures using optical scatterometry

“…This latter has been successfully employed for 1D gratings and imprinted structures [10][11][12][13][14], and rarely for 2D patterns [15,16]. To the best of our knowledge, optical scatterometry has not been applied yet for biperiodic imprinted structures characterization.…”

Measurement configuration optimization for grating reconstruction by Mueller matrix polarimetry

“…Logofatu proposed a SAF (Sensitivity Analysis for Fitting) method by defining the sensitivity as the estimated precision of the structural parameters to optimize the measurement configuration for angleresolved rotating-analyzer and angle-resolved phase-modulation scatterometers [13,14]. Littau et al investigated several optimal diffraction signature scan path selection techniques to improve scatterometry precision [15].…”

“…They further proposed to choose the measurement configuration with small correlations and small estimated precision of the structural parameters [19]. However, it can be also observed from the previous works [13,14,19] that the extracted structural parameter values vary greatly in different measurement configurations. Typical minimization of the parameter correlations and estimated precision may achieve an optimal configuration with higher measurement precision but cannot make sure the final measurement accuracy.…”