Abstract

We present a parameter retrieval method which incorporates prior knowledge about the object into ptychography. The proposed method is applied to two applications: (1) parameter retrieval of small particles from Fourier ptychographic dark field measurements; (2) parameter retrieval of a rectangular structure with real-space ptychography. The influence of Poisson noise is discussed in the second part of the paper. The Cramér Rao Lower Bound in both applications is computed and Monte Carlo analysis is used to verify the calculated lower bound. With the computation results we report the lower bound for various noise levels and analyze the correlation of particles in application 1. For application 2 the correlation of parameters of the rectangular structure is discussed.

Highlights

  • Ptychography [1,2,3,4,5,6] is a scanning coherent diffraction imaging method for reconstructing a complex valued object function from intensity measurements recorded in the Fraunhofer or Fresnel diffraction region

  • The proposed method is applied to two applications: (1) parameter retrieval of small particles from Fourier ptychographic dark field measurements; (2) parameter retrieval of a rectangular structure with realspace ptychography

  • With the computation results we report the lower bound for various noise levels and analyze the correlation of particles in application 1

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Summary

Introduction

Ptychography [1,2,3,4,5,6] is a scanning coherent diffraction imaging method for reconstructing a complex valued object function from intensity measurements recorded in the Fraunhofer or Fresnel diffraction region. For the case of real-space ptychography, the a priori knowledge is the exact information of the probe function and the set of relative positions Rj. The cost function is defined as the l2-distance between the modulus of the far field diffraction pattern || (Ψj ) (k′⟂)|| and the square root of the measured intensity Ijm(k′⟂): |. (1) Parameter retrieval of sub-wavelength particles using Fourier ptychography with dark field measurements only. (2) Parameter retrieval of rectangular objects using real-space ptychography This example comes from practical applications in semiconductor industry where we often want to measure the transmission, the width and the position of the rectangles on flat substrates [39,40]. 2. Application 1: parameter retrieval of sub-wavelength particles using fourier ptychography with dark field measurement

Description of the ’RapidNano 3’ particle scanner
Single dipole radiation
Dark field measurement from the particle scanner
Retrieving the parameters of the particles
Simulation
Single object embedded in constant surrounding
Retrieving the parameter of the rectangle
The CRLB analysis of the parameter retrieval scheme for Poisson noise
The Fisher information matrix for retrieval of the dipole
The CRLB of the dipole
The correlation between two dipoles
Fisher Information matrix for single rectangular object
The CRLB of the width and the position of the rectangle
Findings
Conclusion
Full Text
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