[Detection of weak scatterers in a digital holographic mirror-pinhole microscope system]

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ACKNOWLEDGEMENT

I would take this opportunity to thank my research supervisor, family and friends for their support and guidance without which this research would not have been possible.

DECLARATION

I, [type your full first names and surname here], declare that the contents of this dissertation/thesis represent my own unaided work, and that the dissertation/thesis has not previously been submitted for academic examination towards any qualification. Furthermore, it represents my own opinions and not necessarily those of the University.

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ABSTRACT

Reflection configured digital holographic microscopy (DHM) can perform accurate optical topography measurements of reflecting objects, such as MEMs, MOEMs, and semiconductor wafer. It can provide non-destructive quantitative measurements of surface roughness and geometric pattern characterization with nanometric axial resolution in real-time. However, the measurement results may be affected by an additional phase curvature introduced by the microscope objective (MO) used in DHM. It needs to be removed either by numerical compensation or by physical compensation. We present a method of physical spherical phase compensation for reflection DHM in the Michelson configuration. In the object arm, collimated light is used for illumination. Due to the use of the MO, the object wavefront may have a spherical phase curvature. In the reference arm, a lens and mirror combination is used to generate a spherical recording reference wave in order to physically compensate the spherical phase curvature of the object wavefront. By controlling the position of the mirror and the sample stage, the compensation process has been demonstrated. The relative positions of the test specimen and the reference mirror must be fixed for the physical spherical phase to be totally compensated. A numerical plane reference wave is preferred for the numerical reconstruction of the phase introduced by the test specimen. Experimental results on wafer pattern recognition are also given. The phase reconstruction in a digital in-line holographic microscopy is compared using two numerical reconstruction methods. The first method uses one Fourier transform and second one uses three Fourier transforms. It is shown that the latter method gives improved object phase reconstruction as compared to the former.

TABLE OF CONTENTS

ACKNOWLEDGEMENT2

DECLARATION3

ABSTRACT4

TABLE OF CONTENTS5

CHAPTER 1: INTRODUCTION6

CHAPTER 2: LITERATURE REVIEW9

CHAPTER 3: EXPERIMENTAL DESIGN12

Digital in-line holographic microscopy12

CHAPTER 4: RESULTS AND DISCUSSION17

Principle of physical spherical phase compensated digital holography20

Two spherical wave interference22

Experimental Analysis24

Changing the positions of the sample stage24

Changing the positions of the reference mirror25

Measurement results26

CHAPTER 5: CONCLUSIONS29

REFERENCES30

CHAPTER 1: INTRODUCTION

The numerical reconstruction of electronically detected holograms fills the gap between physical holographic experiment and its analytical approach. This gives a new perspective to the Gabor's [2] holography and microscopy principle. The strength of the digital holographic microscopy lies in its ability to provide accurate and quantitative phase reconstruction of the sample in addition to the intensity information on a nearly real-time basis. Both off-axis and in-line digital holographic schemes have been used for imaging three-dimensional objects. Lensless in-line holography using a spherical reference beam, referred to in the literature as digital in-line holographic microscopy (DIHM), has been used for high-resolution microscopic ...