This paper deals with the structure and the optical properties of thin
As40S60 − xSex
films doped with silver. The refractive index
n and the optical
band gap Egopt
were calculated from the transmittance and reflectance spectra. The results showed that
the photo-doping leads to increase in the refractive index by about 0.25–0.27. An effect of
thickness expansion was observed in the photo-doped layers. The non-linear refractive index,
γ, and the two-photon
absorption coefficient, β, were evaluated by applying a formula developed by Sheik-Bahae. Each of the films studied
exhibits a highly non-linear refractive index at the telecommunication wavelength, 70–850
times higher than that measured for fused silica. From the Raman spectra of thin
As40S30Se30
it might be concluded that under dissolution, the silver interacts with both sulfur
and selenium. The surface of the thin films was investigated by using a white
light interferometric profiler. It was found that the increase in the thickness of
the silver layer results in roughening of the surface of the photo-doped films.
The optical properties of single layers from As2Se3 and GeS2, double-layered stack and quarter-wave multilayer structure consisting of alternating layers from both materials are investigated. For modelling of multilayer coating the thickness dependence of the refractive index of single coatings from both materials is studied. The particularities and scope of application of different spectrophotometric methods for calculation of optical parameters of thin chalcogenide layers are discussed for film thickness, d, in the range λ/25–1.5λ (λ being the operating wavelength). Having acquired the knowledge of optical parameters (refractive index, n, and extinction coefficient, k) of the single layers, we designed and produced a one-dimensional photonic crystal with fundamental reflection band at λ = 850 nm. It was shown that the photoinduced changes of the refractive index of thin chalcogenide films can be used for enhancement of the optical contrast of both materials.
The surface and mechanical properties of thin Cr films play an essential role in microphotolithographic processes in which an inorganic photoresist based on vacuum-evaporated As,S, is used as a light-sensitive system. The present paper reports some XPS data about thin chromium layers obtained by thermal evaporation, high-frequency sputtering, electron beam evaporation and dc magnetron sputtering. A correlation is found between the surface elemental composition of the metal coating and the possibilities of obtaining good adhesion between the Cr and As& used as the inorganic photoresist. It is shown that the presence of pure Cr on the surface of the samples is a defining condition for photolithography in the submicron region.
I N T R O D U C T I O N EXPERIMENTALThe use of thin chromium films for the preparation of metal photomasks in photolithography has increased the interest in studying the main photochemical properties of such films.'-4 The surface and mechanical properties of the chromium coatings are very essential in microlithographic processes using an inorganic photoresist based on vacuum-deposited As2S3 as a lightsensitive ~y s t e m .~ The small thickness of the chalcogenide layer and its amorphous structure allow the reproduction of details with a line width down to 0.35 pm. However, this is possible only if the adhesion between the As2S3 layer and the metallized glass substrate is good. The surface and bulk properties of chromium samples have been of special interest in publications applying AES and XPS methods of analysis.'.6 A system of spectral characteristics of different standards containing Cr has been obtained and it has been shown that during deposition of Cr films by thermal evaporation the contamination of the layers with oxygen and carbon is lower at higher temperatures of the substrate. The reactive properties of thin chromium films obtained by vacuum evaporation have been comparatively well studied.'Regardless of the available information and the experiments performed to determine the elementary composition of the Cr coatings, the above investigations have been more or less methodological in character.The present paper reports some XPS data on thin chromium films obtained by thermal evaporation, highfrequency sputtering, electron beam evaporation and dc magnetron sputtering. The study is performed to explain the correlation between the adhesion of the vacuum-deposited As,S, layers used as inorganic photoresist and the properties of the metal films. The XPS studies were carried out in an Escalab Mk I1 (VG Scientific) electron spectrometer with base pressures in the preparation and analysis chamber of -2 x lo-* and -1 x lo-* Pa, respectively. The photoelectron spectra were excited with a twin-anode x-ray source (Mg Ka at 1253.6 eV and A1 Ka at 1486.6 eV). The instrumental resolution measured as the full width at half-maximum (FWHM) of the Ag 3d,,, photoelectron peak was 1.2 and 1.3 eV for the two sources, respectively. Experiments were carried out with Mg Ka exitation. The photoelectron lines...
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