A. Ya. Lopatin

Multilayer Zr/Si filters for EUV lithography and for radiation source metrology

The technique for fabrication of thin film filters with high mechanical strength, capable of withstanding the prolonged heat load of 1 W/cm2, has been developed. Freestanding multilayer Zr/Si filters of size 20×150 mm2 with high transparency of 76% at wavelength λ = 13 nm were manufactured for EUV lithography tool. We have also developed and fabricated various designs of filters (freestanding or mesh supported) with lower transparency of 40-50% for experiments with intensive EUV sources. The tests of differential pressure withstandability and heat-resistance of filter samples were fulfilled. In order to model the influence on the filter of intensive radiation of the lithography source we have tested Zr/Si film samples by the Joule heating in vacuum at residual pressure of 10-8 Torr. The testing consisted in continuous heating of Zr/Si films at the electrical power per area unit from 0.5 W/cm2 to 6 W/cm2 during long period of time (up to 2 months). The influence of the long-term heat load on the transparency of samples at λ = 13 nm and within wavelength region 0.3 - 2 μm was investigated.

Soft X-rays generated by the electron-cyclotron resonance discharge in heavy gases sustained by a high-power microwave beam in a magnetic trap

The soft X-ray line emission from a pulsed electron-cyclotron resonance discharge in argon, maintained by a high-power millimeter-wavelength beam in a magnetic mirror trap, was studied using a multilayer mirror X-ray monochromator. The X-ray spectrum was measured, and the absolute spectral intensity of emission was determined in a 6–17 nm wavelength range. The discharge can be used as an effective source of soft X-rays with an efficiency of the microwave to X-ray power conversion on a level of 10% and a maximum spectral power density of 7.3 kW/nm at a wavelength of 9 nm.

Multilayer thin-film filters of extreme ultraviolet and soft X-ray spectral regions

Multilayer thin-film filters from different materi al pairs with spectral windows within the wavelength range 7n < 60 nm were developed. Optical characteristics of samples in the extreme ultraviolet, visible, and IR spectrum ranges were studied. Ultrathin freestanding Zr/Si large-aperture filters with transparencies up to 76% at 7n = 13 nm were manufactured for projection lithography test benches; variations in their properties during long-term thermal loads were studied.

Thin film multilayer filters for solar EUV telescopes

Al, with a passband in the wavelength range of 17-60 nm, and Zr, with a passband in the wavelength range of 6.5-17 nm, thin films on a support grid or support membrane are frequently used as UV, visible, and near-IR blocking filters in solar observatories. Although they possess acceptable optical performance, these filters also have some shortcomings such as low mechanical strength and low resistance to oxidation. These shortcomings hinder meeting the requirements for filters of future telescopes. We propose multilayer thin film filters on the basis of Al, Zr, and other materials with improved characteristics. It was demonstrated that stretched multilayer films on a support grid with a mesh size up to 5 mm can withstand vibration loads occurring during spacecraft launch. A large mesh size is preferable for filters of high-resolution solar telescopes, since it allows image distortion caused by light diffraction on the support grid to be avoided. We have investigated the thermal stability of Al/Si and Zr/Si multilayers assuming their possible application as filters in the Intergelioprobe project, in which the observation of coronal plasma will take place close to the Sun. Zr/Si films show high thermal stability and may be used as blocking filters in the wavelength range of 12.5-17 nm. Al/Si films show lower thermal stability: a significant decrease in the films transmission in the EUV spectral range and an increase in the visible spectrum have been observed. We suppose that the low thermal stability of Al/Si films restricts their application in the Intergelioprobe project. Thus, there is a lack of filters for the wavelength range of λ>17  nm. Be/Si and Cr/Si filters have been proposed for the wavelength range near 30.4 nm. Although these filters have lower transparency than Al/Si, they are superior in thermal stability. Multilayer Sc/Al filters with relatively high transmission at a wavelength of 58.4 nm (HeI line) and simultaneously sufficient rejection in the wavelength range near 30.4 nm (HeII line) have been fabricated. They are planned to be used in the project KORTES, whose telescopes will have an EUV channel at 58.4 nm.

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.

Spectral calibration of filters and detectors of solar telescope at a wavelength of 13.2 nm for the TESIS project

The telescope at a wavelength of 13.2 nm of the TESIS device of the CORONAS-PHOTON satellite is intended for imaging hot plasma (T ∼ 10 MK) of the solar corona. In this paper, calibration of optical elements of the telescope is described. The transmittance of multilayer Zr/Si filters and the sensitivity and radiation resistance of the CCD-array-based detector were measured. The transmittance of filters in the operating wavelength range was 40–50% (for filters of various thicknesses); the spectral dependence of the transmittance was close to the calculated one. The transmittance of filters in the visible region was (1–2) × 10−6. The detector sensitivity was 0.01–0.1 analog-to-digital units per photon (adu/photon), the radiation resistance was better than 109 rad.

The influence of the photoacid-generator structure on chemical amplification in a resist

The effect of structure of a photoacid generator (triarylsulfonium and diaryliodonium salts) on the trends of image formation in a chemically amplified resist based on a methyl methacrylate copolymer with methacrylic acid and ethoxyethyl methacrylate was studied. It was shown that the type and quality of image in the resist depend on the structure of the Bronsted acid produced upon UV irradiation, on postexposure bake temperature, and on exposure radiation energy.

Influence of the Chemical Structure of (Co)Polymer Resists on Their Sensitivity to Radiation

Resists operating via two mechanisms, i.e., disruption of the main chain and hydrolysis of side functional groups occurring upon EUV and electron beam irradiation, are studied as a function of the chemical composition of a polymer substrate. We show that the latter, belonging to the group of chemically amplified resists, are an order of magnitude more sensitive to radiation and possess outstanding contrast, as compared with disruptive type resists.

Mo-based EUV multilayer filters with enhanced thermal stability

New Mo-based multilayer structures are proposed, and sample free-standing filters 160 mm in diameter with a transparency of 71% at a wavelength of λ = 13.5 nm are described. The enhanced thermo-oxidative stability of filters with Mo layers is demonstrated as opposed to Zr-based films. It is shown in particular that Mo-based filters can withstand vacuum heat annealing at 800°C for three hours without any optical and structural changes.

Evolution of elemental distribution in free-standing structures of Zr/ZrSi2 with MoSi2 and ZrSi2 protective coatings under annealing

An analysis of the in-depth distribution of elements in annealed samples of multilayer Zr/ZrSi2 EUV filters with protective layers of MoSi2 and ZrSi2 was performed by secondary ion mass spectrometry (SIMS). The vacuum annealing of the samples was performed at temperatures of up to 720–950°C for 3–7 h and at a residual pressure of ∼10−7 torr. It was demonstrated that MoSi2 coatings effectively inhibit the accumulation of oxygen by the heated film, which is the process that determines the optical degradation of the filter.