PK
P. Kruit
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1
A critical-dimension scanning electron microscope (CD-SEM) is widely used for measuring the most important semiconductor device pattern geometries, known as critical dimensions (CDs). Radiation damage by the electron beam to patterns of materials, such as an extreme ultraviolet lithography (EUVL) resist, is a serious issue. A low-voltage SEM (LV-SEM) provides a gentler metrology tool for patterns. However, both spherical and chromatic aberrations of the objective lens increase, and thus the beam spot size becomes larger for lower landing energy beam. Aberration correction is necessary to improve the resolution of LV-SEMs. One of the typical corrector is an electron mirror with a large angle bending magnet, typically bending the beam over 90 degrees. Such large-angle deflection causes significant deflection aberrations. As a result, special complicated designs and precise machining and assembly have been implemented to suppress these aberrations. The technology of micro-electro-mechanical systems (MEMS) has advanced considerably. MEMS technology should, therefore, make it possible to realize miniature-scale mirrors as well. It will be possible to reduce the deflection angle of the electron beam further, sufficiently suppressing undesirable aberrations. This would drastically reduce not only manufacturing costs but also the size of the corrector unit. The goal of this dissertation is to suggest a conceptual design of a low-voltage aberration-corrected scanning electron microscope using a novel miniature electron mirror corrector and small-angle deflectors. By referring to prior research, we start by investigating perturbation theory for mirrors and deflectors to derive formulae for aberration coefficients.
First, we derive the aberration theory of electron mirrors. For the electron mirror, the incident electron must be reflected by the electrostatic field, and the slope of the trajectory, with respect to the optic axis, becomes divergent. To avoid it, time is taken as a parameter. Integral aberration formulae for both on- and off-axis path deviation and aberration coefficients up to second rank and third order for the system of rotationally symmetric electrostatic and magnetic fields, which overlap with each other, are derived.
Second, we derive the deflection aberration theory for standard lenses and deflectors. By applying perturbation theory to a system of round symmetric electrostatic and magnetic lenses and electrostatic and magnetic deflectors, relativistic deflection trajectory formulae and aberration coefficient formulae for deflection up to second rank and third order are derived for two independent deflectors in three types of configurations.
Third, we derive the deflection aberration theory for systems that include electron mirrors. A non-relativistic time-dependent deflection theory is developed based on the consideration of non-relativistic time-dependent aberration theory for round symmetric electrostatic and magnetic fields and on the deflection aberration theory of standard electron optics. The time-dependent deflection theory of mirrors and small angle deflectors up to second rank and third order is derived.
Forth, we propose a miniature aberration corrector consisting of double magnetic deflectors and double electrostatic mirrors, named the S-corrector. The optical properties of an SEM equipped with the proposed S-corrector with 50-mrad magnetic deflection are analyzed. Design examples of miniature mirrors and deflectors, as well as a possible configuration for an SEM with the post-deflection S-corrector, with a deflection angle of 50 mrad, are presented. Numerical calculations of aberration properties for a miniature electron mirror and double deflectors are performed using the formulae derived. The estimation method for higher-rank combination aberrations up to fourth rank and fifth order was considered. The estimated results of deflection aberrations and combination aberrations are, at their largest, 0.2 nm, which is negligible compared with target spot sizes of 1 nm for a landing voltage of 1000 V and 1.5 nm for a landing voltage of 100 V, except for fourth-rank chromatic spherical aberration and fifth-order spherical aberration. Numerical calculations based on wave optics are performed, accounting for all combination aberrations and residual deflection aberrations. The calculated spot sizes are 0.976 nm and 1.367 nm for landing voltages of 1000 V and 100 V, respectively. The potential of an aberration-corrected LV-SEM by miniature mirrors with small angle deflectors is demonstrated. ...
First, we derive the aberration theory of electron mirrors. For the electron mirror, the incident electron must be reflected by the electrostatic field, and the slope of the trajectory, with respect to the optic axis, becomes divergent. To avoid it, time is taken as a parameter. Integral aberration formulae for both on- and off-axis path deviation and aberration coefficients up to second rank and third order for the system of rotationally symmetric electrostatic and magnetic fields, which overlap with each other, are derived.
Second, we derive the deflection aberration theory for standard lenses and deflectors. By applying perturbation theory to a system of round symmetric electrostatic and magnetic lenses and electrostatic and magnetic deflectors, relativistic deflection trajectory formulae and aberration coefficient formulae for deflection up to second rank and third order are derived for two independent deflectors in three types of configurations.
Third, we derive the deflection aberration theory for systems that include electron mirrors. A non-relativistic time-dependent deflection theory is developed based on the consideration of non-relativistic time-dependent aberration theory for round symmetric electrostatic and magnetic fields and on the deflection aberration theory of standard electron optics. The time-dependent deflection theory of mirrors and small angle deflectors up to second rank and third order is derived.
Forth, we propose a miniature aberration corrector consisting of double magnetic deflectors and double electrostatic mirrors, named the S-corrector. The optical properties of an SEM equipped with the proposed S-corrector with 50-mrad magnetic deflection are analyzed. Design examples of miniature mirrors and deflectors, as well as a possible configuration for an SEM with the post-deflection S-corrector, with a deflection angle of 50 mrad, are presented. Numerical calculations of aberration properties for a miniature electron mirror and double deflectors are performed using the formulae derived. The estimation method for higher-rank combination aberrations up to fourth rank and fifth order was considered. The estimated results of deflection aberrations and combination aberrations are, at their largest, 0.2 nm, which is negligible compared with target spot sizes of 1 nm for a landing voltage of 1000 V and 1.5 nm for a landing voltage of 100 V, except for fourth-rank chromatic spherical aberration and fifth-order spherical aberration. Numerical calculations based on wave optics are performed, accounting for all combination aberrations and residual deflection aberrations. The calculated spot sizes are 0.976 nm and 1.367 nm for landing voltages of 1000 V and 100 V, respectively. The potential of an aberration-corrected LV-SEM by miniature mirrors with small angle deflectors is demonstrated. ...
A critical-dimension scanning electron microscope (CD-SEM) is widely used for measuring the most important semiconductor device pattern geometries, known as critical dimensions (CDs). Radiation damage by the electron beam to patterns of materials, such as an extreme ultraviolet lithography (EUVL) resist, is a serious issue. A low-voltage SEM (LV-SEM) provides a gentler metrology tool for patterns. However, both spherical and chromatic aberrations of the objective lens increase, and thus the beam spot size becomes larger for lower landing energy beam. Aberration correction is necessary to improve the resolution of LV-SEMs. One of the typical corrector is an electron mirror with a large angle bending magnet, typically bending the beam over 90 degrees. Such large-angle deflection causes significant deflection aberrations. As a result, special complicated designs and precise machining and assembly have been implemented to suppress these aberrations. The technology of micro-electro-mechanical systems (MEMS) has advanced considerably. MEMS technology should, therefore, make it possible to realize miniature-scale mirrors as well. It will be possible to reduce the deflection angle of the electron beam further, sufficiently suppressing undesirable aberrations. This would drastically reduce not only manufacturing costs but also the size of the corrector unit. The goal of this dissertation is to suggest a conceptual design of a low-voltage aberration-corrected scanning electron microscope using a novel miniature electron mirror corrector and small-angle deflectors. By referring to prior research, we start by investigating perturbation theory for mirrors and deflectors to derive formulae for aberration coefficients.
First, we derive the aberration theory of electron mirrors. For the electron mirror, the incident electron must be reflected by the electrostatic field, and the slope of the trajectory, with respect to the optic axis, becomes divergent. To avoid it, time is taken as a parameter. Integral aberration formulae for both on- and off-axis path deviation and aberration coefficients up to second rank and third order for the system of rotationally symmetric electrostatic and magnetic fields, which overlap with each other, are derived.
Second, we derive the deflection aberration theory for standard lenses and deflectors. By applying perturbation theory to a system of round symmetric electrostatic and magnetic lenses and electrostatic and magnetic deflectors, relativistic deflection trajectory formulae and aberration coefficient formulae for deflection up to second rank and third order are derived for two independent deflectors in three types of configurations.
Third, we derive the deflection aberration theory for systems that include electron mirrors. A non-relativistic time-dependent deflection theory is developed based on the consideration of non-relativistic time-dependent aberration theory for round symmetric electrostatic and magnetic fields and on the deflection aberration theory of standard electron optics. The time-dependent deflection theory of mirrors and small angle deflectors up to second rank and third order is derived.
Forth, we propose a miniature aberration corrector consisting of double magnetic deflectors and double electrostatic mirrors, named the S-corrector. The optical properties of an SEM equipped with the proposed S-corrector with 50-mrad magnetic deflection are analyzed. Design examples of miniature mirrors and deflectors, as well as a possible configuration for an SEM with the post-deflection S-corrector, with a deflection angle of 50 mrad, are presented. Numerical calculations of aberration properties for a miniature electron mirror and double deflectors are performed using the formulae derived. The estimation method for higher-rank combination aberrations up to fourth rank and fifth order was considered. The estimated results of deflection aberrations and combination aberrations are, at their largest, 0.2 nm, which is negligible compared with target spot sizes of 1 nm for a landing voltage of 1000 V and 1.5 nm for a landing voltage of 100 V, except for fourth-rank chromatic spherical aberration and fifth-order spherical aberration. Numerical calculations based on wave optics are performed, accounting for all combination aberrations and residual deflection aberrations. The calculated spot sizes are 0.976 nm and 1.367 nm for landing voltages of 1000 V and 100 V, respectively. The potential of an aberration-corrected LV-SEM by miniature mirrors with small angle deflectors is demonstrated.
First, we derive the aberration theory of electron mirrors. For the electron mirror, the incident electron must be reflected by the electrostatic field, and the slope of the trajectory, with respect to the optic axis, becomes divergent. To avoid it, time is taken as a parameter. Integral aberration formulae for both on- and off-axis path deviation and aberration coefficients up to second rank and third order for the system of rotationally symmetric electrostatic and magnetic fields, which overlap with each other, are derived.
Second, we derive the deflection aberration theory for standard lenses and deflectors. By applying perturbation theory to a system of round symmetric electrostatic and magnetic lenses and electrostatic and magnetic deflectors, relativistic deflection trajectory formulae and aberration coefficient formulae for deflection up to second rank and third order are derived for two independent deflectors in three types of configurations.
Third, we derive the deflection aberration theory for systems that include electron mirrors. A non-relativistic time-dependent deflection theory is developed based on the consideration of non-relativistic time-dependent aberration theory for round symmetric electrostatic and magnetic fields and on the deflection aberration theory of standard electron optics. The time-dependent deflection theory of mirrors and small angle deflectors up to second rank and third order is derived.
Forth, we propose a miniature aberration corrector consisting of double magnetic deflectors and double electrostatic mirrors, named the S-corrector. The optical properties of an SEM equipped with the proposed S-corrector with 50-mrad magnetic deflection are analyzed. Design examples of miniature mirrors and deflectors, as well as a possible configuration for an SEM with the post-deflection S-corrector, with a deflection angle of 50 mrad, are presented. Numerical calculations of aberration properties for a miniature electron mirror and double deflectors are performed using the formulae derived. The estimation method for higher-rank combination aberrations up to fourth rank and fifth order was considered. The estimated results of deflection aberrations and combination aberrations are, at their largest, 0.2 nm, which is negligible compared with target spot sizes of 1 nm for a landing voltage of 1000 V and 1.5 nm for a landing voltage of 100 V, except for fourth-rank chromatic spherical aberration and fifth-order spherical aberration. Numerical calculations based on wave optics are performed, accounting for all combination aberrations and residual deflection aberrations. The calculated spot sizes are 0.976 nm and 1.367 nm for landing voltages of 1000 V and 100 V, respectively. The potential of an aberration-corrected LV-SEM by miniature mirrors with small angle deflectors is demonstrated.
In this thesis, the author investigates the extended Schottky source for the application in a multi-beam source (MBS). The work has been done in both theoretical work and experimental work.
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In this thesis, the author investigates the extended Schottky source for the application in a multi-beam source (MBS). The work has been done in both theoretical work and experimental work.
The work described in the doctoral thesis aims to enhance the functionality of a scanning electron microscope (SEM) by integrating miniaturized versions of cleanroom tools used in microfabrication. The thesis presents the integration of substrate heating, in-situ thermal atomic layer deposition (ALD), sputtering, and thermal evaporation within the SEM. These techniques are expected to enable fast and efficient fabrication of proof-of-concept devices with minimal resources. The thesis also discusses the challenges, limitations, and future work of the integrated cleanroom processes in SEM.
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The work described in the doctoral thesis aims to enhance the functionality of a scanning electron microscope (SEM) by integrating miniaturized versions of cleanroom tools used in microfabrication. The thesis presents the integration of substrate heating, in-situ thermal atomic layer deposition (ALD), sputtering, and thermal evaporation within the SEM. These techniques are expected to enable fast and efficient fabrication of proof-of-concept devices with minimal resources. The thesis also discusses the challenges, limitations, and future work of the integrated cleanroom processes in SEM.
Focussed Electron Beam Induced Processing is a high resolution direct-write nanopatterning technique. Its ability to fabricate sub-10 nm structures together with its versatility and ease of use, in that it is resist-free and implementable inside a Scanning Electron Microscope, make it attractive for a variety of applications in nanofabrication. FEBIP comprises two complementary techniques: Electron Beam Induced Deposition and Electron Beam Induced Etching. In EBID (EBIE), the electron beam is scanned in the presence of a precursor gas that has been let into the chamber of the SEM. The precursor molecules adsorbed onto the sample surface are dissociated by the electron beam, as well as by secondary and backscattered electrons that are generated at the surface by the interaction of the electron beam with the sample. The nonvolatile dissociation product forms a deposit (etch) on the surface, while the volatile products are pumped out. A pattern can thus be deposited (etched) by merely scanning the beam in the presence of the precursor. As the secondary electrons are lower in energy (< 50 eV), they contribute more significantly to the dissociation than the higher energy backscattered or primary electrons. At the outset therefore, the resolution in EBID is limited by the emission radius of the secondary electrons, which can be as low as a few nanometres. The fabrication of lines as little as 3 nm wide on bulk silicon attests to the high resolution patterning capability of EBID, which in turn makes it potentially attractive for lithography. The development of a laboratory nanofabrication technique into a viable alternative for lithography, however, requires several criteria to be met.
...
Focussed Electron Beam Induced Processing is a high resolution direct-write nanopatterning technique. Its ability to fabricate sub-10 nm structures together with its versatility and ease of use, in that it is resist-free and implementable inside a Scanning Electron Microscope, make it attractive for a variety of applications in nanofabrication. FEBIP comprises two complementary techniques: Electron Beam Induced Deposition and Electron Beam Induced Etching. In EBID (EBIE), the electron beam is scanned in the presence of a precursor gas that has been let into the chamber of the SEM. The precursor molecules adsorbed onto the sample surface are dissociated by the electron beam, as well as by secondary and backscattered electrons that are generated at the surface by the interaction of the electron beam with the sample. The nonvolatile dissociation product forms a deposit (etch) on the surface, while the volatile products are pumped out. A pattern can thus be deposited (etched) by merely scanning the beam in the presence of the precursor. As the secondary electrons are lower in energy (< 50 eV), they contribute more significantly to the dissociation than the higher energy backscattered or primary electrons. At the outset therefore, the resolution in EBID is limited by the emission radius of the secondary electrons, which can be as low as a few nanometres. The fabrication of lines as little as 3 nm wide on bulk silicon attests to the high resolution patterning capability of EBID, which in turn makes it potentially attractive for lithography. The development of a laboratory nanofabrication technique into a viable alternative for lithography, however, requires several criteria to be met.
The goal of this Ph.D. research is to develop imaging systems for the multiple beam scanning electron microscope (MBSEM) built in Delft University of Technology. This thesis includes two imaging systems, transmission electron (TE) imaging system, and secondary electron (SE) imaging system. The major conclusions, key results and some suggestions for future improvements are highlighted in this chapter.
...
The goal of this Ph.D. research is to develop imaging systems for the multiple beam scanning electron microscope (MBSEM) built in Delft University of Technology. This thesis includes two imaging systems, transmission electron (TE) imaging system, and secondary electron (SE) imaging system. The major conclusions, key results and some suggestions for future improvements are highlighted in this chapter.
Doctoral thesis
(2015)
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DN ter Weele, Pieter Dorenbos, Dennis Schaart, H. Wieczorek, P. Fischer, H van der Graaf, Laurens Siebbeles, Pieter Kruit