Confocal Scanning Optical Microscopy and Related Imaging Systems (eBook)

Timothy R. Corle, Gordon S. Kino (Autoren)

eBook Download: EPUB

1996 | 1. Auflage
335 Seiten
Elsevier Science (Verlag)
978-0-08-052978-3 (ISBN)

Infos

This book provides a comprehensive introduction to the field of scanning optical microscopy for scientists and engineers. The book concentrates mainly on two instruments: the Confocal Scanning Optical Microscope (CSOM), and the Optical Interference Microscope (OIM). A comprehensive discussion of the theory and design of the Near-Field Scanning Optical Microscope (NSOM) is also given.
The text discusses the practical aspects of building a confocal scanning optical microscope or optical interference microscope, and the applications of these microscopes to phase imaging, biological imaging, and semiconductor inspection and metrology.A comprehensive theoretical discussion of the depth and transverse resolution is given with emphasis placed on the practical results of the theoretical calculations and how these can be used to help understand the operation of these microscopes.

Key Features
* Provides a comprehensive introduction to the field of scanning optical microscopy for scientists and engineers
* Explains many practical applications of scanning optical and interference microscopy in such diverse fields as biology and semiconductor metrology
* Discusses in theoretical terms the origin of the improved depth and transverse resolution of scanning optical and interference microscopes with emphasis on the practical results of the theoretical calculations
* Considers the practical aspects of building a confocal scanning or interference microscope and explores some of the design tradeoffs made for microscopes used in various applications
* Discusses the theory and design of near-field optical microscopes
* Explains phase imaging in the scanning optical and interference microscopes

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This book provides a comprehensive introduction to the field of scanning optical microscopy for scientists and engineers. The book concentrates mainly on two instruments: the Confocal Scanning Optical Microscope (CSOM), and the Optical Interference Microscope (OIM). A comprehensive discussion of the theory and design of the Near-Field Scanning Optical Microscope (NSOM) is also given. The text discusses the practical aspects of building a confocal scanning optical microscope or optical interference microscope, and the applications of these microscopes to phase imaging, biological imaging, and semiconductor inspection and metrology.A comprehensive theoretical discussion of the depth and transverse resolution is given with emphasis placed on the practical results of the theoretical calculations and how these can be used to help understand the operation of these microscopes. - Provides a comprehensive introduction to the field of scanning optical microscopy for scientists and engineers- Explains many practical applications of scanning optical and interference microscopy in such diverse fields as biology and semiconductor metrology- Discusses in theoretical terms the origin of the improved depth and transverse resolution of scanning optical and interference microscopes with emphasis on the practical results of the theoretical calculations- Considers the practical aspects of building a confocal scanning or interference microscope and explores some of the design tradeoffs made for microscopes used in various applications- Discusses the theory and design of near-field optical microscopes- Explains phase imaging in the scanning optical and interference microscopes

Inhalt

Cover 1
Contents 8
Preface 14
Chapter 1. Introduction 18
1.1 Confocal and Interferometric Microscopy 18
1.2 The Standard Optical Microscope 24
1.3 The Confocal Microscope 48
1.4 Optical Interference Microscopes 61
1.5 Comparison of Scanning Optical Microscopes with Other Types of Scanning Microscopes 73
References 80
Chapter 2. Instruments 84
2.1 Introduction 84
2.2 The Confocal Scanning Laser Microscope 85
2.3 Nipkow Disk Scanning Microscopes 101
2.4 Slit Microscopes 114
2.5 Confocal Transmission Microscopes 121
2.6 Alternative Imaging Configurations 125
2.7 Interference Microscopes 127
2.8 Near-Field Microscopy 137
2.9 Conclusion 155
References 156
Chapter 3. Depth and Transverse Resolution 164
3.1 Introduction 164
3.2 Depth Response of the Confocal Microscope with Infinitesimal Pinholes and Slits 166
3.3 Depth Response of the Confocal Microscope with Finite-Sized Pinholes 182
3.4 Transverse Response of the Confocal Microscope 192
3.5 Depth and Transverse Resolution of the Interferometric Microscope 206
3.6 The Near-Field Scanning Optical Microscope (NSOM) 223
3.7 The Solid Immersion Microscope (SIM) 229
3.8 Conclusion 237
References 237
Chapter 4. Phase Imaging 242
4.1 Introduction 242
4.2 Phase-Contrast Imaging in Conventional Microscopes 243
4.3 Phase-Contrast Imaging in the CSOM 246
4.4 Differential Interference Contrast Imaging 264
4.5 Phase Imaging with an Interference Microscope 283
4.6 Conclusion 289
References 289
Chapter 5. Applications 294
5.1 Introduction 294
5.2 Semiconductor Metrology 295
5.3 Film Thickness Measurements 317
5.4 Biological Imaging 325
5.5 Conclusion 333
References 334
Appendix A: Vector Field Theory for Depth and Transverse Resolution of a CSOM 340
A.1 The Depth Response 340
A.2 Transverse Response 343
References 347
Index 348

Textauszug

CHAPTER 1

Introduction

1.1 Confocal and Interferometric Microscopy

Optical microscopes have a ubiquitous presence in modern society. Virtually everyone has used one at some point in their life, if only to dissect a frog in school or observe the life hidden in a drop of pond water. They are used in laboratories and health clinics around the world. They have been developed into powerful measurement and observational tools with applications in geology, medicine, and manufacturing, to name a few areas. In the last few years, new types of optical microscopes have emerged. These microscopes enable researchers to visualize submicron structures, determine their surface profiles, and observe selected cross sections of transparent materials without cutting the sample into thin slices. In biology, fluorescence imaging has become increasingly important because biological activity can be traced by the fluorescence of markers associated with particular atomic or molecular species as they move through a cell. Application of microscopy principles in other fields, such as optical storage on compact disks, has also become important.

This book will concentrate on mainly two new types of optical microscopes: the confocal scanning optical microscope (CSOM) and the optical interference microscope (OIM). These instruments differ from the standard optical microscope because they have a shallow depth of focus and hence are capable of accurate height and thickness measurements and of obtaining cross-sectional images. There will also be a discussion of the near-field scanning optical microscope (NSOM), which is capable of obtaining definition well below the normal diffraction limits of optics.

In a standard optical microscope, when an image is defocused, its features blur so that the edges become less sharp, but the average light intensity does not change. With the CSOM, some types of OIMs, and NSOMs, on the other hand, a defocused image disappears rather than blurring. Put another way, the image intensity decreases as the image is defocused. This property enables structures which differ in height by as little as one optical wavelength to be independently imaged by these microscopes. As a result, quantitative measurements of height, surface profiles, and three-dimensional image reconstructions can be made.1,2 The resulting images also tend to have more contrast, leading to better edge definition, than those obtained using a standard microscope.

Confocal Microscopy The basic principle of the confocal microscope, illustrated in Fig. 1.1(a), is to illuminate only one spot on the sample at a time through a pinhole. The light reflected from the sample is imaged by the objective back to the pinhole. By scanning the spot or the sample in a raster pattern a complete image can be formed. If the sample moves out of focus, as shown in Fig. 1.1(b), the reflected light is defocused at the pinhole and hence does not pass through it to a detector located on the other side. The result is that the image of the defocused plane disappears. The signal output from a detector located behind the pinhole as the sample is moved in the focus direction is illustrated in Fig. 1.1(c).

Figure 1.1 Simplified schematic of a confocal scanning optical microscope showing the sample (a) in the focal plane of the objective and (b) out of focus. (c) The form of the signal output from the detector as a function of sample defocus.

Figure 1.2 shows three images of an integrated circuit taken at three different focus levels. Only the layers of the circuit which are within approximately ±0.25 μm of the focal plane appear in each of the photographs. For comparison, a conventional microscope image of the same sample is shown in Fig. 1.3(a). When the microscope is badly defocused, as in Fig. 1.3(b), the image blurs rather than disappearing.

Figure 1.2 Three images of an integrated circuit taken at three different focus positions: (a) substrate (0 μm); (b) 1.2 μm defocused; (c) 2.4 μm defocused.

Figure 1.3 A standard microscope image of an integrated circuit: (a) when the sample is in focus; (b) when it is defocused by 2 μm.

Interference Microscopy Interference microscopes form an interference pattern with light reflected by the sample and a reference surface. If the reference surface is kept in a fixed position, as in the Michelson interferometer system illustrated in Fig. 1.4, interference fringes of each pixel in the image are formed as the reflecting sample is moved through focus. The contrast of the interference fringes falls off rapidly as the object is defocused.

Figure 1.4 Simplified schematic of an interferometric microscope based on a Michelson interferometer.

By electronically processing the stored interference pattern, the envelope of the interference pattern for each pixel is determined. The shape of this envelope is very similar to the depth response of the confocal microscope. The cross-sectional images produced by the interference microscope are also very similar to those taken with the CSOM. Electronic processing of the fringe pattern allows measurement of not only the amplitude but also the phase of the reflected light. Since phase can be measured to an accuracy of a few degrees, it is possible to measure height or surface roughness to accuracies of a small fraction of an optical wavelength.

Near-Field Microscopy In this book, we will also discuss the NSOM. This device passes light through a small pinhole at the end of an optical fiber or a tapered aperture to illuminate or receive light from the sample, Fig. 1.5. If the pinhole is placed sufficiently close to the sample, the resolution is determined by the size of the pinhole rather than the wavelength of the light. Since the definition is not limited by diffraction as in other types of optical microscopes, it can be a very small fraction of a wavelength. An image is formed by scanning the pinhole in a raster pattern.3,4,5 The microscope is called a near-field microscope because the evanescent fields just outside of the pinhole that are used for imaging require a close spacing between the sample and the probe.

Figure 1.5 Simplified schematic of a near-field scanning optical microscope.

A related type of near-field microscope, the solid immersion microscope (SIM), focuses the light from a standard or confocal microscope beam onto the lower surface of a high-refractive-index solid transparent material, called a solid immersion lens (SIL), shown in Fig. 1.6. This additional lens element reduces the effective wavelength by the refractive index of the lens material improving the definition of the microscope.6 Because of total internal reflection of rays making a large angle to the axis, this enhanced definition can be obtained only if the sample is placed close to the SIL. Therefore, the device is also a near-field microscope.

Figure 1.6 Basic component of a solid immersion microscope.

In order to put the performance of these microscopes into the proper context, we will discuss the operating principles of the standard optical microscope in the next section. Much of the basic mathematical theory is covered in the texts by Hecht and Zajac7 and Born and Wolf.8 We will not rederive all the results here but will quote from them in order to give a basis of comparison for the principles of the confocal and interferometric microscopes.

Section 1.2 will also introduce definitions and notation which will be used throughout this book. This introduction is followed by a discussion of the different imaging techniques commonly used in a standard optical microscope. These imaging techniques are also available for use with the CSOM and thus form an important foundation for many of the later chapters in the book. Following the section on the standard optical microscope, the CSOM and the optical interference microscope will be described, with emphasis on the CSOM because of its simplicity of use and its wide range of applications. Chapter 1 concludes with a discussion comparing scanning optical microscopes with other types of scanning microscopes, such as the tunneling and force microscopes, the scanning electron microscope, and the scanning acoustic microscope. Our purpose is to illustrate the benefits and drawbacks of optical microscopy relative to other non-optical microscopy techniques.

1.2 The Standard Optical Microscope

1.2.1 Principle of Operation

Many of the design principles of the CSOM and interference microscopes are based on the standard microscope. A simplified form of a standard optical reflection microscope is shown schematically in Fig. 1.7. In this instrument, the sample is uniformly illuminated through the objective lens by a filament lamp or other bright incoherent light source such as a mercury vapor lamp. The objective lens forms a real inverted image of the object at the intermediate image plane of the microscope. The distance of the intermediate image plane from the back focal plane of the objective is called the tube...

Produkt-Details

• Erscheint lt. Verlag: 18.9.1996
• Sprache: englisch
• Themenwelt: Medizin / Pharmazie
• Themenwelt: Naturwissenschaften ► Biologie
• Themenwelt: Naturwissenschaften ► Physik / Astronomie ► Festkörperphysik
• Themenwelt: Naturwissenschaften ► Physik / Astronomie ► Optik
• Themenwelt: Technik ► Maschinenbau
• ISBN-10: 0-08-052978-X / 008052978X
• ISBN-13: 978-0-08-052978-3 / 9780080529783