The theory of image formation is formulated in terms of the coherence function in the object plane, the diffraction distribution function of the image-forming system and a function describing the structure of the object. There results a four-fold integral involving these functions, and the complex conjugate functions of the latter two. This integral is evaluated in terms of the Fourier transforms of the coherence function, the diffraction distribution function and its complex conjugate. In fact, these transforms are respectively the distribution of intensity in an 'effective source', and the complex transmission of the optical system-they are the data initially known and are generally of simple form. A generalized 'transmission factor' is found which reduces to the known results in the simple cases of perfect coherence and complete incoherence. The procedure may be varied in a manner more suited to non-periodic objects. The theory is applied to study inter alia the influence of the method of illumination on the images of simple periodic structures and of an isolated line.

On the diffraction theory of optical images

Precision positioning of an object relative to a reference point is a common task in many activities of production engineering. Sensor technologies for single axis measurement, either linear or rotary, which form the fundamentals of measurement technologies for precision positioning, are reviewed. Multi-axis coordinate measurement methods such as triangulation and multilateration, as well as Cartesian and polar systems for specifying the position in a plane or three-dimensional (3D) space are then presented, followed by a discussion on traceability and standards. Some advanced applications of measurement technologies for precision positioning in manufacturing industries are also demonstrated.

Measurement technologies for precision positioning

Wire grid polarizers (WGPs), periodic nano-optical metasurfaces, are convenient polarizing elements for many optical applications. However, they are still inadequate in the deep ultraviolet spectral range. It is shown that to achieve high performance ultraviolet WGPs a material with large absolute value of the complex permittivity and extinction coefficient at the wavelength of interest has to be utilized. This requirement is compared to refractive index models considering intraband and interband absorption processes. It is elucidated why the extinction ratio of metallic WGPs intrinsically humble in the deep ultraviolet, whereas wide bandgap semiconductors are superior material candidates in this spectral range. To demonstrate this, the design, fabrication, and optical characterization of a titanium dioxide WGP are presented. At a wavelength of 193 nm an unprecedented extinction ratio of 384 and a transmittance of 10% is achieved.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adom.201600250

Materials Pushing the Application Limits of Wire Grid Polarizers further into the Deep Ultraviolet Spectral Range

An illumination optical apparatus guides exposure light emitted from an exposure light source, to an illumination target object. The illumination optical apparatus has a plurality of spatial light modulation members arranged in an array form, and each spatial light modulation member is so configured that a plurality of reflecting optical elements each including a movable reflecting surface are arranged in an array form. At least one of the spatial light modulation members is arranged in an optical path of the light emitted from the light source.

Illumination optical apparatus, exposure apparatus, and device manufacturing method

Hybrid metrology apparatus (1000, 1100, 1200, 1300, 1400) measures a structure (T) manufactured by lithography. An EUV metrology apparatus (244, IL1/DET1) irradiates the structure with EUV radiation and detects a first spectrum from the structure. Another metrology apparatus (240, IL2/DET2) irradiates the structure with second radiation comprising EUV radiation or longer-wavelength radiation and detects a second spectrum. Using the detected first spectrum and the detected second spectrum together, a processor (MPU) determines a property (CD/OV) of the structure. The spectra can be combined in various ways. For example, the first detected spectrum can be used to control one or more parameters of illumination and/or detection used to capture the second spectrum, or vice versa. The first spectrum can be used to distinguish properties of different layers (T1, T2) in the structure. First and second radiation sources (SRC1, SRC2) may share a common drive laser (LAS).

Metrology methods, metrology apparatus and device manufacturing method

This paper reports on the current status of PROVE TM - a new photomask registration and overlay metrology system currently under development at Carl Zeiss The scope of the project is to design and build a photomask pattern placement metrology tool which is serving the 32 nm node Performance specifications of the tool are actually driven by double exposure/ double patterning approaches which will help to extend the 193 nm lithography platforms, while keeping the semiconductor industry conform to ITRS roadmap requirements A secondary requirement of pattern placement metrology tools is the CD meas urement option for design features of interest Combining both registration and CD measurement reduces the number of process operations a photomask has to encounter during manufacture Optical design considerations are discussed, which led to the tool being designed for 193 nm illumination corresponding to at-wavelength metrology for most current and future photomask applications The concept enables registration and CD metrology by transmitted or reflected light The short wave length together with a NA of 06 also provides sufficient resolution even at working distances compatible with the use of pellicles, hence enabling the tool for qualification of final, production ready masks Imaging simulations with a rigorous Maxwell solver prove our chosen optical concept to be adequate for the various mask types (eg COG, MoSi, EUV) commonly used today and presumably in the future The open concept does enable a higher NA for future, pellicle free applications Keywords: registration metrology, pattern placement, opti cal design, resolution, imaging performance

Photomask registration and overlay metrology by means of 193 nm optics

In order for the lithography world to continue on its path to ever smaller features, process solutions such as OPC assist
features and double patterning / exposure strategies put more and more focus on the quality of photomasks The
community roadmap requires for the 45nm/32nm node nominal mask features of 120 nm and 85 nm, respectively Small
feature sizes in combination with tight overlay budgets of only 48 nm or even 34 nm for the 32 nm node illustrate the
need for a registration metrology tool with high resolving power and yet unprecedented specifications on reproducibility
and accuracy Carl Zeiss reports on the concept and the project timeline of its new registration tool currently under
development Novel concepts such as the high resolution at-wavelength imaging optics, an integrated full-field autofocus
system, and a correlation algorithm for image analysis are presented as examples for the innovative approach to achieve
the very demanding goal

High-resolution and high-precision pattern placement metrology for the 45 nm node and beyond

Immersion lithography offers the semiconductor industry the opportunity to extend current ArF processes before switching to shorter wavelengths. As numerical apertures of scanners for hyper NA move above 1.0 with immersion lithography, increased attention must be paid to the photomask or reticle and its wafer printability. Feature sizes on the photomask become increasingly critical as they behave more like partial wire grid polarisers, as they become comparable to, or smaller than the wavelength. Besides challenges to address reticle polarisation effects, lithographers must also consider the polarisation state of the illumination and subsequently the contrast loss for light with a TM polarisation state. Such an effect, also called the vector effect, is caused by the increasing angle of incidence of the diffracted light for larger numerical apertures on the scanner. Therefore, for wafer printing using hyper NA scanners, the industry consensus is that TE polarised illumination must be used to meet the stringent requirements of imaging contrast. In this paper, initial results of measurements using the optical test stand and the alpha tool of a completely new AIMS™ 1 tool for the 45nm node will be presented. The system covers all aspects of immersion and polarisation lithographic emulation. Measurements have been made on binary and phase shift masks with different sizes of features and on programmed defects.

First results for hyper NA scanner emulation from AIMS 45-193i

During mask inspection it is necessary to identify defects which also occur during wafer exposure. Therefore, the aerial images generated in the resist and on the detector have to be as far as possible identical. In order to achieve an equivalent image generation, during mask inspection the illumination and, on the object side, the numerical aperture are adapted to the scanner used. The invention relates to a mask inspection microscope for variably setting the illumination. It serves for generating an image of the structure (150) of a reticle (145) arranged in an object plane in a field plane of the mask inspection microscope. It comprises a light source (5) that emits projection light, at least one illumination beam path (3, 87, 88), and a diaphragm for generating a resultant intensity distribution of the projection light in a pupil plane (135) of the illumination beam path (3, 87, 88) that is optically conjugate with respect to the object plane. According to the invention, the diaphragm is embodied in such a way that the resultant intensity distribution of the projection light has at least one further intensity value between a minimum and a maximum intensity value.

Mask inspection microscope with variable illumination setting

Bei der Maskeninspektion sind Defekte zu erkennen, die auch bei der Waferbelichtung auftreten. Deshalb mussen die im Resist und auf dem Detektor erzeugten Luftbilder moglichst identisch sein. Um eine aquivalente Bilderzeugung zu erreichen, werden bei der Maskeninspektion die Beleuchtung und objektseitig die numerische Apertur dem verwendeten Scanner angepasst. Die Erfindung betrifft ein Maskeninspektionsmikroskop zur variablen Einstellung der Beleuchtung. Es dient zur Erzeugung eines Bildes der Struktur (150) eines in einer Objektebene angeordneten Retikels (145) in einer Feldebene des Maskeninspektionsmikroskops. Es weist eine Projektionslicht emittierende Lichtquelle (5), zumindest einen Beleuchtungsstrahlengang (3, 87, 88) und eine Blende zur Erzeugung einer resultierenden Intensitatsverteilung des Projektionslichts in einer zur Objektebene optisch konjugierten Pupillenebene (135) des Beleuchtungsstrahlengangs (3, 87, 88) auf. Erfindungsgemas ist die Blende derart ausgebildet, dass die resultierende Intensitatsverteilung des Projektionslichts zwischen einem minimalen und einem maximalen Intensitatswert zumindest einen weiteren Intensitatswert aufweist.

Norbert Rosenkranz

Papers

Photomask registration and overlay metrology by means of 193 nm optics

High-resolution and high-precision pattern placement metrology for the 45 nm node and beyond

First results for hyper NA scanner emulation from AIMS 45-193i

Mask inspection microscope with variable illumination setting

Maskeninspektionsmikroskop mit variabler Beleuchtungseinstellung