Schott Lithotec is producing and developing the optical materials for the 248-nm, 193-nm and 157-nm lithography technology. 248-nm systems are in use already, the first 193-nm prototype system has been set up and the first 157-nm stepper system is expected to run in 2003. Schott Lithotec provides the Fused Silica and CaF₂ materials for these systems both in production and in development. In order to ensure the requirements on transmission and laser durability as well as on homogeneity and birefringence numerous metrology R&D activities have been performed. The requirements on the optical material quality concerning these materials are extremely high and continuously increasing. We present the status of R&D activities for the metrology, which is necessary to demonstrate the improvement of the optical material quality. Based on the forecasts of the semiconductor industry (ITRS, SIA and DATAQUEST Roadmaps), we will derive the needs for metrology in the future.

An absorptance measurement system has been developed for evaluation of the absorption loss of optical coatings at the wavelength of F2 laser(157nm). Calorimetry was adopted as measurement method because of its high reliability. In the system, the calorific values generated by irradiation has estimated by comparison with those generated by an electric heater in order to obtain the high accuracy of measurement. The repeatability of measurement has been attained so far to be +/- 0.02%. We have found out with the system that the absorptance is increased by measurement in the vacuum compared with in nitrogen and decreased by irradiation of F2 laser light due to its contamination cleaning effect. We have measured the absorptance of samples with anti-reflection coatings that several suppliers fabricated by their own methods.

A compact experimental setup, based on the laser induced deflection technique (LID), measures small absorption coefficients in fused silica upon 193-nm irradiation with high sensitivity and accuracy. For that, two probe laser beams are passed numerous times through a sample and are deflected by a refractive index gradient which is generated by the power absorbed within the material. The absorption coefficient of the sample is determined by applying a comfortable and precise electrical calibration procedure. The investigation of two equivalent fused silica samples of different thickness confirmed that the setup allows to exclusively measure the bulk absorption of the material without contributions from the irradiated surfaces. Furthermore, influences of irradiation parameters like repetition rate and pulse width on the absorption coefficient of fused silica at a fixed applied energy density have been investigated. The results confirm the complexity of the absorption mechanism present in fused silica upon laser irradiation. In order to separate linear and nonlinear absorption two fused silica samples have been irradiated with different energy densities keeping the repetition rate and the pulse width constant. The results show a nonlinear dependence of the absorption coefficient on the energy density which can qualitatively be explained by the two-step absorption mechanism in fused silica.

A new Coblentz type scatterometer is developed for evaluation of 157-nm optical coatings. The Coblentz hemisphere has ellipsoidal design for higher sensitivity and stability. The scatterometer works under nitrogen atmosphere keeping away from the organic contamination. Some kind of antireflective coatings are obtained from several Japanese suppliers and evaluated by the scatterometer. Results of the scatter measurement are almost equal except one sample that includes Na₃AlF₆ layer as low refractive index material. Its extremely high scatter loss could be ascribed degradation by reaction to the water in the air.

Spectroscopic ellipsometry has long been recognized as the technique of choice to characterize thin films and multilayers. In 1983, SOPRA has developed the first commercial spectroscopic ellipsometer for research and development. Since this date, the wavelength range has been extended from visible to near infrared (2 micrometers ), and far infrared up to 18 micrometers . For 193-nm microlithography, deep UV option down to 190 nm has also been developed and delivered more recently. Instrumentation for the next generation of VUV lithography at 157 nm requires special optical setup since O₂ and H₂O are extremely absorbing below 190 nm. A new system has been developed which works into a purged glove box to reduce the oxygen and water contamination in the part per million range. The optical setup includes a premonochromator in the polariser arm to avoid photobleaching. The wavelength range of the instrument is 140-700 nm. The system works in rotating analyser configuration to minimize the parasitic residual polarisation. Ellipsometric and photometric measurements versus wavelength and angle of incidence can be performed. Scatterometric measurements can also be made. In this wavelength range, the samples are extremely sensitive to any surface contamination and surface roughness. It is why a grazing x-ray option has been added on the same instrument to provide a better picture of the analyzed samples. This paper presents in detail the new system with its two measurement methods, and including experimental results on resist, antireflective coatings and gate dielectrics for use in the field of microlithography.

The in situ measurement capabilities and advantages of recently developed spectroscopic ellipsometry (SE) instrumentation, which covers wide spectral ranges (190-1700 nm, or 0.73-6.5 eV) and is based on rotating-compensator technology, are described. A technique which can quantitatively correct for window birefringence is presented. Current in situ SE deposition monitoring and control applications in the compound semiconductor, display, and optical coatings industries are also presented.

Infrared Spectroscopic Ellipsometry is presented as a feasible and novel technique for contactless and nondestructive measurement of free-carrier and crystal-structure properties in the characterization of complex semiconductor heterostructures for device applications. Infrared-active lattice modes and coupling of free-carrier plasmons to longitudinal-optical lattice phonon modes strongly affect the infrared-optical response of semiconductor materials. Analysis of ellipsometry data from 2 micrometers to 100 micrometers can provide precise information on phonon mode frequencies and broadening parameters, static dielectric constants, free-carrier concentration, and free-carrier mobility at optical frequencies of III-V compound semiconductors, even for films with thicknesses only a fraction of the probing wavelengths. Alloy composition, strain, crystal quality, and free-carrier properties of constituent layers in thin-film structures, designed for optoelectronic or electronic device applications, can be derived. We demonstrate the characterization of coherent and incoherent light emitter structures based on group-III-nitride materials, where information such as concentration and mobility of free carriers in n- and p-type regions, thickness, composition, and quality of device constituents are accessible.

Spectroscopic ellipsometry has long been recognized as a powerful technique to characterize thin films and multilayer structures. It is now routinely used for non-destructive on-line characterization of semiconductor process. SOPRA, leader in commercial spectroscopic ellipsometer for research and development, has already developed an infrared ellipsometer as an option on visible instrument to provide the largest wavelength range available up to now (from deep UV 190 nm to far infrared up to 18 micrometers ). A new design of the instrument is presented here which includes a small spot size to get ride of the problems of back face reflection on silicon wafers, and an improved signal /noise ratio to allow rapid measurements compatible with an industrial environment. Some examples of application concerning dopant density in epilayers and composition of low k dielectrics are presented.

For any industrial integrated metrology application three key issues must be addressed - feasibility, applicability and cost-effectiveness. This paper reports progress on the integration of spectroscopic ellipsometry (SE) in the cool-down chamber of an Applied Materials Epi Centura Cluster System. SE is capable of providing rapid information on layer thickness, composition, crystallinity, surface roughness, etc. However, major issues remain to be addressed for integration in commercial tools, including development of compact hardware with high stability and accuracy to fit in the accessible space, automatic alignment and movement systems, and calibration of chamber access windows. A novel SE instrument has been designed to interface to the cluster tool to demonstrate feasibility. The focused beam size allows measurements to be made in the scribe lines of patterned wafers using pattern recognition software, and linescans across a wafer radius are used to assess uniformity. Applicability of the technique is demonstrated on a series of complex structures based on thin Si and Si_1-xGe_x layers. Thickness and composition repeatability is estimated to be +/- 4 angstrom for 400 angstrom Si and Si_1-xGe_x layers, +/- 0.003 for x equals 0.12. Measurements may be made after each layer deposition and on the completed structure. The results are compared with off-line post-deposition characterization.

Attempts have been made over a number of years to scale laser induced damage threshold measurements across the boundaries of pulse length, spot size, wavelength and material differences. These efforts have been hampered by the absence of pertinent data, made under identical conditions, on the threshold results that have been published. The new ISO 11254-1, -2, -3 Standards for the Measurement of Laser Induced Damage and ISO11551 for Absorption have now been finalised and if accepted by the scientific fraternity will enable meaningful comparative results to be published. This paper will discuss the similarities and differences between 1- on- 1, S- on- 1 and R- on- 1, laser induced damage threshold, LIDT, measurements and damage assurance methodology and will show how differences in absorption can effect both the damage values and the damage morphology.

We report our investigations on interferometric precision measurements of fused silica for a required reproducibility of (sigma) ((Delta) (eta) )<EQ1x10^-7 with special focus on thermal environmental conditions. An analytical description is proposed for a qualitative consideration of the thermalization process; numerical results are given for a quantitative prediction of temperature induced measurement errors. Experiments and numerical calculations point to the fact, that, apart from the thermal conductivity, the heat transfer between sample surface and environment has to be taken into account for precise process analysis. Reducing the thickness of the sample, the heat exchange rate between air and glass becomes more important. An effective heat conductivity can be introduced to describe the thermalization process of the sample more easily. Temperature stability of interferometric systems, as well as accuracy and reproducibility of measurement results, were analyzed experimentally in order to study their correlation. The reduction of environmental fluctuations by one magnitude has shown remarkable improvements in the interferometer stability.

An automated, compact system for high-accuracy measurements of specular reflectivity at different laser wavelengths (633 nm, 822 nm) on the basis of lock-in technique and LabView has been developed. With a spatial resolution of less than 2 micrometers , a signal resolution of less than 10^-4 was obtained. Micro-optical components like microlenses with angular-compensating antireflection coatings, nonuniform micro-mirror arrays, broad-stripe diode laser facets and low-numerical-aperture graded-index microlenses have been characterized by two-dimensional reflectivity mapping. Errors caused by the angular spectrum of the focused polarized probe lasers were analysed.

Carbon coatings of thickness down to 2 nanometers are needed to increase the storage density in magnetic hard disks and reach the 100 Gbit/in² target. Methods to measure the properties of these ultrathin hard films still have to be developed. We show that combining Surface Brillouin Scattering (SBS) and x-ray reflectivity measurements the elastic constants of such films are accessible. Tetrahedral amorphous carbon films of thickness down to about 2 nm were deposited on Si by an S bend filtered cathodic vacuum arc, achieving a continuous coverage on large areas free of macroparticles. Film thickness and mass density are measured by x-ray reflectivity: densities about 3 g/cm³ are found, indicating a significant sp³ content. The dispersion relations of surface acoustic waves are measured by SBS. We show that for thicknesses above approximately 4 nm these waves can be described by a continuum elastic model based on a single homogeneous equivalent film. The elastic constants can then be obtained by fitting the dispersion relations, computed for given film properties, to the measured dispersion relations. For thicknesses of 3 nm or less qualitative differences among films are well measurable, but quantitative results are less reliable. We have thus shown that we can grow and characterise nanometer size tetrahedral amorphous carbon films, which maintain their high density and peculiar mechanical properties down to around 4-nm thickness, satisfying the requirements set for the hard disk coating material.

Defect detection and counting have been used to qualify silicon wafers for use in device production for several years. Defect sizing is attempted by comparing scatter signals, used for detection, to signals produced from spherical polystyrene latex spheres of known diameter. Real particles are neither spherical nor made of plastic, and scatter differently. This paper addresses the issue of spherical particle material identification through the measurement of scatter signals into several directions. The basic idea is that the average diameter and material constants comprising the complex index amount to three unknowns. The question is whether they can be estimated from three independent measurements. The results presented here are quite positive. The issue of particle shape is left for another paper.

Laser particle scanners are traditionally calibrated with polystyrene latex spheres, and these spheres are used to create a sizing scale in light scatter equivalents. Particle scatter signals can vary strongly with particle materials, thus concealing the true particle size. As previously reported, particle material identification in a laser scanner will allow true sizing of spherical particles through the application of accurate scatter models. This paper reports extending that work to non-spherical particles through the use of modeling scatter from ellipsoidal particles.

This paper reviews a light scatter technique used to size particle depositions of polystyrene latex spheres on silicon wafers. The technique has proved to provide accurate (approximately 1% uncertainty) sizing of PSL sphere depositions. Measurements were made of NIST Standard Reference Materials as a means of checking the technique and an uncertainty analysis was performed using the techniques prescribed by NIST. The technique has the advantage that measurements are made of PSL spheres depositions on a substrate, which is the way in which they are used to calibrate defect scanners. In addition to presenting the details of the sizing technique the paper also discusses implications for scanner calibration accuracy.

A major problem of in situ surface characterization with angle-resolved light scatter (ARS) measurements is the fast and accurate detection of surface defects with respect to industrial applications. The paper deals with a specific application - the angle resolved scatter measurements on PSL particles on Si wafers (spheres with a particle diameter 5 micrometers , 10 micrometers ) by using a calibrated CMOS photo detector array (CPDA). In the first part of the paper a short overview about the development of ARS sensors will be outlined. In the second part of the paper the experimental setup of the ARS sensor and its components will be discussed. The ARS sensor consists of a CPDA and a data acquisition system which allows ARS measurements in 32887 different angles, in an intensity range of 7 decades and an acquisition speed of up to 10 million angles per second. In the third part of the paper the PSL particle detection on Si- wafers will be considered. Experimental data will be presented and compared with simulated scatter data. In the last part of the paper the results will be summarized, the applicability of the ARS sensor will be discussed with respect to specific applications, and further design stages to improve the sensor performance will be outlined.

According to industry standards (SEMI M43, Guide for Reporting Wafer Nanotopography), Nanotopography is the non- planar deviation of the whole front wafer surface within a spatial wavelength range of approximately 0.2 to 20 mm and within the fixed quality area (FQA). The need for precision metrology of wafer nanotopography is being actively addressed by interferometric technology. In this paper we present an approach to mapping the whole wafer front surface nanotopography using an engineered coherence interferometer. The interferometer acquires a whole wafer raw topography map. The raw map is then filtered to remove the long spatial wavelength, high amplitude shape contributions and reveal the nanotopography in the filtered map. Filtered maps can be quantitatively analyzed in a variety of ways to enable statistical process control (SPC) of nanotopography parameters. The importance of tracking these parameters for CMOS gate level processes at 180-nm critical dimension, and below, is examined.

The Rapid Confocal Sensor delivers sub-micron depth and five-micron lateral resolutions over a 300-mm format. With some a priori knowledge of a sample, an analysis over the 300-mm field is completed in approximately 7 minutes. An overview of the optical system (sensor) is given. Application of this technology is made to rapid 3D process inspection of semiconductor samples, particularly die contact bumps. Results demonstrating performance from a commercially available system are presented.

A novel optoelectronic setup based on a quasi confocal, z- axis extended field, proprietary design has been developed for High Resolution Non Contact 3D Surface Metrology including roughness characterization and surface flaw detection.

We have developed a new noncontacting approach for obtaining the full aperture, absolute aspheric profile of optical surfaces. The approach has many advantages for a wide range of optics, including self-referencing and motion-insensitive operation; extremely high accuracy; compact size; and the ability to test concave, flat and convex optics over a wide range of spatial frequencies. In a separate paper, we describe the underlying theory of operation, a prototype instrument, preliminary measurement results, and projected accuracies. In this paper, we discuss the specific advantages that are especially relevant for Extreme Ultra Violet (EUV) lithography components. These mirrors are responsible for the fabulously accurate imaging of the reticle onto the wafer. They therefore have typical surface accuracy requirements of a fraction of a nanometer, with the need to characterize the errors over an enormous range of spatial frequencies. The need to provide diffraction-limited imaging at EUV wavelengths over large Fields Of View (FOVs) and Numerical Apertures (NAs) puts a premium on freedom in the optical design. Specifically, the use of aspheres and convex mirrors can be of great help. Therefore, performance, FOV, and NA all benefit from the most accurate and flexible metrology. All of these factors make this new profiling technique well suited to the unique requirements of EUV lithography mirrors.

It is a promising method for measuring steep aspheres and complex surfaces with nanometer and sub-nanometer accuracy to measure the curvature and to calculate the topography from it, since unlike slope and distance, the curvature is an intrinsic property of a surface and less insensitive to error influences. For the development of a measuring instrument based on the physical property of curvature, various topics have been investigated. The method described does not rely on external form references, and the errors of the scanning stages and the whole-body movement of the artifact have only little influence on the accuracy. In comparison to other measuring techniques, it is an advantageous feature of the curvature measuring technique that distance and angle between sensor and surface element can be controlled and kept constant during scanning as it is the curvature and not the distance or the slope which is the measurand. This leads to the result that, apart from the calibration of the curvature sensor, the whole system no longer suffers from first-and second-order errors. The uncertainty budget shows that nanometer accuracy is achievable.

Scanning Laser Microscopes (SLM) have been used to characterise the magnetic domain properties of various magnetic and magneto-optical materials. The SLM in our laboratory has been designed to enable both static and dynamic read-write operations to be performed on stationary media. In a conventional (static) SLM, data bits are recorded thermo-magnetically by focusing a pulse of laser light onto the sample surface. If the laser beam has a Gaussian intensity distribution (TEM00) then so will the focused laser spot. The resultant temperature profile will largely mirror the intensity distribution of the focused spot, and in the region where the temperature is sufficiently high for switching to occur, in the presence of bias field, a circular data bit will be recorded. However, in a real magneto-optical drive the bits are written onto non-stationary media, and the resultant bit will be non-circular. A versatile optical system has been developed to facilitate both recording and imaging of data bits. To simulate the action of a Magneto-Optical drive, the laser is pulsed via an Acousto-Optic Modulator, whilst being scanned across the sample using a galvanometer mounted mirror, thus imitating a storage medium rotating above a MO head with high relative velocity between the beam and medium. Static recording is simply achieved by disabling the galvanometer scan mirror. Polar magneto-optic Kerr effect images are acquired using multiple-segment photo-detectors for diffraction-limited scanned spot detection, with either specimen scanning for highest resolution or beam scanning for near real-time image acquisition. Results will be presented to illustrate the systems capabilities.

Scanning Probe Microscopy is a powerful tool in nanometrology. SPMs are now widely used in research institutions, and even in some branches of high-tech industry. However, there is a severe drawback: these instruments provide mainly images, not measurements of micro- and nano-objects. Therefore the European Commission decided to establish a network to investigate the possibility of calibration procedures traceable to the national standards of the partners involved. This paper deals with the objectives of the network, the partners, some round robin tests, the calibration structures used and the conclusions drawn from the work of the SPMet group. Consequently, it is a summary of the deliverables for the European Commission authored by the members of the network.

Atomic force microscopy (AFM) is usually the instrument of choice for the investigation of the surface roughness of thin films. Often a detailed image and roughness analysis is hindered by tip artifacts. Many of these artifacts arise from a spatial convolution or dilation of the actual tip and the shape of the surface features imaged. Therefore a careful tip evaluation and calibration is important for a reliable roughness evaluation. In this study about a process for the fabrication of self- assembled nanometer-sized surface structures using low- energy ion sputtering of semiconductor surfaces is reported. The dimension of these structures (typically between 10 and 100 nm), the distance between them and their shape can be tuned by the parameters of the sputter process. With the help of surfaces prepared by this way the influence of the actual AFM tip quality on the measured surface topography was evaluated. Furthermore, it is shown that the tip quality has a strong influence on the parameters extracted from first- and second-order statistics of the surface roughness. This applies particularly with regard to surfaces characterized by a low surface roughness (approximately 1 nm) as generally obtained by means of thin film technologies.

Solid Immersion Lenses (SILs) have an outstanding potential for applications in future generations of optical data storage systems. We report the realization of a diffractive Solid Immersion Lens (dSIL) which is the diffractive analog of the refractive hemispherical SIL. Here, inside the medium the propagation angles of the first order diffracted waves point in the same direction as the incident angles from outside the SIL. We realized two types of dSILs: binary phase elements were fabricated in a highly refracting glass (LaSF35) by direct 3-beam writing and successive reactive ion etching, and dSILs with a blazed profile were manufactured in photoresist by holographic lithography. The minimum distance between adjacent zones in the diffracting structure is in the range of one wavelength. Polarization dependencies and phase impacts have to be consideration in the design of an optical element with features this small. In comparison to the lithographically realized binary phase grating, the holographic elements have the advantage of high diffraction efficiency.

We have developed a rapid XRR system that is capable of acquiring the reflectivity data in the angular range of 0.1 - 1.6 degree in less than 20 sec. The data were analyzed to obtain the thickness, density and roughness of the film of interest in a few seconds. The system consisted of an x-ray source with a tungsten target and a Si monochromator, a sample stage, and a 1024-pixel photo-diode array. The system was used to characterize the multiple film stack of Ta/Al₂O₃/Ta/SiO₂/Si. The Ta and Al films were sputtered onto the SiO₂/Si substrate and the Al was oxidized to form the film of Al₂O₃. The thickness of the Ta layers was about 100 angstrom while the thickness of Al₂O₃ varied from 40 angstrom to 200 angstrom. The XRR sensitivity to parameters such as thickness, density, and roughness of the Ta and Al₂O₃ layer was also studied. We found that the XRR can measure the thickness and density of each layer with a standard deviation less than 0.5% and 1.5% of the target thickness and density, respectively. The roughness was found to have a standard deviation better than 1 angstrom. We also found that the density of the film of Al₂O₃ varied from 2.7 - 4.0 g/cm³, indicating that the stoichiometry of the Al₂O₃ films ranged from the non-oxidized pure Al to the fully oxidized Al₂O₃. The information of the thickness, density and roughness of each of the Ta and Al₂O₃ films from XRR is particularly useful to nondestructively monitor the thin film deposit conditions in real time.

The analysis of the roughness of B₄C films of different thickness as well as W/B₄C multilayer mirrors of different periods is performed basing on AFM and x-ray scattering (XRS) measurements. It is demonstrated that the linear model of a film growth is able to describe the whole set of experimental data including films at initial island stage of growth, if suppose the relaxation processes of a film surface to depend on the film thickness. New approach to the inverse problem of x-ray reflectometry consisting in inferring the dielectric constant profile from the reflectivity data is shortly discussed.

Sub-aperture stitching interferometry (SASI) is an appropriate method to measure either large optical plane surface topologies or aspheres with strong deviation from the flatness with standard interferometers. Using SASI the surface shape is measured with a higher lateral resolution by multiple adjacent sub-aperture measurements with a sufficient overlap of the neighboring areas. In a second step, the total surface shape is composed with the help of a computer code by stitching the sub-aperture areas together. The overlap areas allow fitting. By means of a regression analysis, tilt and vertical displacement of adjacent areas are calculated and minimized. A confidence band calculated using a MATLAB based code describes the accuracy of the composition. The variance of this estimation is inverse proportional to the peak to valley value (PV) of the measured area and decreases with a 10-3 scaling of the width of the overlapping area. A statistical experimental design method is used to minimize the number of sub-apertures to be measured. The accuracy of the stitched total surface measurement can be increased with the help of model calculations by optimizing (i) the position of the sub-aperture, which was regarded as a standard, and (ii) the sequence of the stitched adjacent areas.

Microstructure and laser damage resistance of dielectric optical thin-film coatings was determined by several experimental techniques. These are film growth and test parameters as well as thin-film characteristics, e.g. absorption, structure and reflective index. The oxide coatings (HfO₂, Nb₂O₅, Ta₂O₅, TiO₂, and ZrO₂) were prepared with varying technology parameters by reactive e-beam evaporation in Leybold A1100 batch coater. The structure of the films was found to be amorphous for very thin films with tendency to columnar growth for thicker films. X-ray diffraction (XRD) and reflectivity (GIXR) were used to determine the structural properties of the films. The surface morphology of oxide layers was determined using atomic force microscopy (AFM). The optical properties were investigated in UV-IR ranges by spectrophotometer measurements. The changes in the shape of absorption edge are found to be related to the structure of thin films. Laser damage threshold for the coatings was measured at wavelength of pulsed Nd:YAG laser. Correlation between the observed film properties and laser damage threshold is discussed.

Polarized light scattering by monodisperse copper and gold spheres, having diameters ranging from 96 nm to 205 nm, deposited on silicon substrates were measured using visible light. The results are compared to an exact theory for scattering by a sphere on a surface, originally developed by Bobbert and Vlieger. The results show that accurate calculation of the scattering of light by a metal sphere requires that the near-field interaction between the sphere and its image be included in a complete manner, that the normal incidence approximation does not suffice for this interaction, and that the existence of any thin oxide layer on the substrate must be included. The polarization of light scattered by these spheres on silicon substrates can be used to determine the size of those spheres. However, uncertainties in the thickness of the substrate oxide layer, roughness of the particles, and uncertainties in the optical properties of the particles may prevent them from being used as standard scatterers. The implementation of the theory, which requires special care when the spheres are metallic and the substrate is highly reflecting, is described in detail.