M. N. Toropov

A source of a reference spherical wave based on a single mode optical fiber with a narrowed exit aperture

A new type of a reference spherical wave source (SWS) based on a single mode optical fiber with a narrowed down up to the submicrometer size exit aperture is proposed. It is intended for the precision point diffraction interferometers as a source of a reference wave. Systematic experimental errors which influence the measurement accuracy of the quality of the wave fronts generated by the SWSs are considered. Experimental data on wave front deformations are given. The combined root-mean-square (rms) wave deformation for a couple of the SWSs measured in a numerical aperture of NA=0.27 reaches the value of rms=0.36 nm that corresponds to rms=0.25 nm of a single SWS or about lambda2500 for the red He-Ne laser.

Problems in the application of a null lens for precise measurements of aspheric mirrors

Problems in the application of a null lens for surface shape measurements of aspherical mirrors are discussed using the example of manufacturing an aspherical concave mirror for the beyond extreme ultraviolet nanolithographer. A method for allowing measurement of the surface shape of a sample under study and the aberration of a null lens simultaneously, and for evaluating measurement accuracy, is described. Using this method, we made a mirror with an aspheric surface of the 6th order (i.e., the maximum deviation from the best-fit sphere is 6.6 μm) with the parameters of the deviations from the designed surface PV=5.3  nm and RMS=0.8  nm. An approximation of the surface shape was carried out using Zernike polynomials {Z(n)(m)(r,φ),m+n≤36}. The physical limitations of this technique are analyzed. It is shown that for aspheric measurements to an Angstrom accuracy, one needs to have a null lens with errors of less than 1 nm. For accurate measurements, it is necessary to establish compliance with the coordinates on the sample and on the interferogram.

Resolving capacity of the circular Zernike polynomials

Circular Zernike polynomials are often used for approximation and analysis of optical surfaces. In this paper, we analyse their lateral resolving capacity, illustrating the effects of a lack of approximation by a finite set of polynomials and answering the following questions: What is the minimum number of polynomials that is necessary to describe a local deformation of a certain size? What is the relationship between the number of approximating polynomials and the spatial spectrum of the approximation? What is the connection between the mean-square error of approximation and the number of polynomials? The main results of this work are the formulas for calculating the error of fitting the relief and the connection between the width of the spatial spectrum and the order of approximation.

Manufacturing and investigation of objective lens for ultrahigh resolution lithography facilities

Status of activities in field of manufacturing and investigation of objective lens for ultrahigh resolution lithography facilities carrying out in IPM RAS is reported. Some physical aspects of operation of interferometers with diffraction reference wave are considered. A scheme of a point diffraction interferometer developed in IPM is presented. Last experimental data on making high precision spherical substrates with NA=0.25 are presented. A problem of surface shape measurements of aspherical substrates with a help of a point diffraction interferometer is discussed. A scheme of measurements and experimental data of wave deformation of 6-lens objective are given.

A plane wave diffraction on a pin-hole in a film with a finite thickness and real electrodynamic properties

On a base of the Kirchhoff-Helmholtz method and using the Green function for a half-space which is covered by a film of any thickness and with arbitrary optical properties, amplitude-phase characteristics of diffracted on a pin-hole field were calculated. Analysis was carried out for some materials of the film at radiation wave-length λ0=633 nm using experimental values of the dielectric constants. The diffracted wave front has deformations which dependent on the film thickness and material electrodynamic characteristics, and the observation angle. The deformation determined by the film thickness essentially limits an accuracy provided by point diffraction interferometers.

Chemically amplified resists for high-resolution lithography

Chemically amplified resists based on methyl methacrylate ter-copolymers with methacrylic acid and isobornyl (met)acrylates, experiencing hydrolysis in the presence of photogenerated acid, responsible for pattern generation in resists, when they are exposed to the deep ultraviolet (254 nm), extreme ultraviolet (13.5 nm), and electron beam, are studied. The influence of the polymeric matrix, photoacid generator, and exposure conditions on quality of the chemically amplified image is evaluated.

Current status and development prospects for multilayer X-ray optics at the Institute for Physics of Microstructures, Russian Academy of Sciences

A real opportunity for applying traditional optical methods to soft X-ray and extreme UV (ultraviolet) radiation bands has appeared thanks to recent successes in the area of multilayer-mirror deposition and procedures for fabricating supersmooth and highly precise substrates of mirrors. The implementation of this opportunity opens up fundamentally new prospectss in the nanodiagnostics of substances, micro- and nanoelectronics, microbiology, solar astronomy and other applications. The main directions in multilayer X-ray optics developed at the Institute for the Physics of Microstructures, Russian Academy of Sciences, are presented and the aspects of the use thereof in science and technology are considered. The main problems arising during the fabrication of multilayer interference structures for the soft X-ray and extreme UV bands are discussed. The main results obtained recently in the scope of each direction of investigation are presented. Plans for the future development of these directions are discussed.

Effect of Polymer Matrix and Photoacid Generator on the Lithographic Properties of Chemically Amplified Photoresist

Resistive compositions based on ter-copolymers of isobornylacrylate with methylmethacrylate and (meth)acrylic acid, which are synthesized using the controlled radical polymerization with reversible chain transfer, as well as triphenylsulphoniumtriflate as a photo-sensitive catalyst are studied. The effect of the chain-transfer agent, as well as the composition and molecular weight of the copolymer on the sensitivity of the resists to UV radiation (222 nm), is determined. Using the ter-copolymer of tert-butoxycarbonyloxystyrene with methylmethacrylate and methacrylic acid, the dependence of the lithographic properties of the photoresist on the chemical composition of the photoacid generator is analyzed. The plasma-chemical stability of (co)polymer resists of methacrylic series in the plasma of Ar + SF6 is studied.

A double-stream Xe:He jet plasma emission in the vicinity of 6.7 nm

We present the results of investigations of extreme ultraviolet (EUV) light emission in the range from 5 to 10 nm. The light source was a pulsed “double-stream” Xe:He gas jet target irradiated by a laser beam with a power density of ∼1011 W/cm2. The radiation spectra were measured with a Czerny-Turner monochromator with a plane diffraction grating. The conversion efficiency of the laser energy into EUV radiation caused by Xe+14…+16 ion emission in the range of 6–8 nm was measured using a calibrated power meter. The conversion efficiency of the laser radiation into EUV in the vicinity of 6.7 nm was (2.17 ± 0.13)% in a 1 nm spectral band. In the spectral band of the real optical system (0.7% for La/B multilayer mirrors) emitted into the half-space, it was (0.1 ± 0.006)%. The results of this study provide an impetus for further research on laser plasma sources for maskless EUV lithography at a wavelength of 6.7 nm.

Principles of certification of aspherical mirrors for an EUV lithography lens at a wavelength of 13.5 nm

The study is devoted to modification of the lens of an EUV lithographer and the method of certification of the aspherical mirrors of the lens without using a wavefront corrector. A lens aberration pattern is reconstructed from the interference pattern of fronts that passed through the lens and the reference. This pattern contains information about the surface deformations of both aspherical mirrors. A procedure for determining the pattern of each mirrors by turning one of the mirrors and solving systems of linear equations is proposed.