The advantages and applications of chalcogenide glass (ChG) thin film photoresists for grayscale lithography are demonstrated. It is shown that the ChG films can be used to make ultrathin (~600 nm), high-resolution grayscale patterns, which can find their application, for example, in IR optics. Unlike polymer photoresists, the IR transparent ChG patterns can be useful as such on the surface or can be used to transfer the etched pattern into silicon or other substrates. Even if the ChG is used as an etch mask for the silicon substrate, its greater hardness can achieve a greater etch selectivity than that obtained with organic photoresists. The suitability of ChG photoresists is demonstrated with inexpensive and reliable fabrication of ultrathin Fresnel lenses that are transparent in the visible as well as in the IR region. The optical functionality of the Fresnel lenses is confirmed. Application of silver photodissolution in grayscale lithography for microelectromechanical systems (MEMS) applications is also shown. A substrate to ChG/silver thickness etching ratio of ~10 is obtained for the transfer of patterns into silicon using reactive ion etching (RIE), more than a fivefold increase compared to traditional polymer photoresist.
The advantages and applications of chalcogenide glass (ChG) thin film photoresists for grayscale lithography are
demonstrated. It is shown that the ChG films can be used to make ultrathin (~600 nm), high-resolution grayscale
patterns, which can find their application, for example, in IR optics. Unlike polymer photoresists, the IR transparent
ChG patterns can be useful as such on the surface, or be used to transfer the etched pattern into silicon or other
substrates. Even if the ChG is used as an etch mask for the silicon substrate, its greater hardness can achieve a greater
transfer ratio than that obtained with organic photoresists. The suitability of ChG photoresists is demonstrated with
inexpensive and reliable fabrication of ultrathin Fresnel lenses that are transparent in the visible as well as in the IR
region. The optical functionality of the Fresnel lenses is confirmed. Application of silver photodissolution in grayscale
lithography for MEMS applications is also shown. The process consists of the following steps: ChG film deposition, Ag
film deposition, irradiation through a grayscale mask, removal of the excess Ag and the transfer of the pattern to Si by
dry etching. A substrate to ChG thickness etching ratio of ~ 10 is obtained for the transfer of patterns into silicon, more
than a five fold increase compared to traditional polymer photoresist.
A bond-conversion model for the photostructural changes in the photoluminescence and Raman spectra is proposed. The essential role in this model belongs to lone-pair electrons of chalcogen atoms, which are optically convert into bonding ones, leading to the structure reconstruction.
The present paper is concerned with investigations of photosensitive properties of As-S thin layers. Spectral dependence of the refraction index n of variously treated (virgin, exposed, annealed) samples was estimated from optical transmission in the spectral region 400 - 2500 nm. The n energy dependence of variously treated samples was fitted by the Wemple-DiDomenico dispersion relationship and used to estimate the single-oscillator model parameters. It was found, that exposure, as well as annealing leads to the increase in n values over the all investigated spectral region. Compositional dependencies of single-oscillator model parameter Ed (dispersion energy), optical dielectric constant ε(0) show maximum at stoichiometric composition As40-S60 and, possibly, weak maximum at As28.6S71.4 composition. Composition evolution of the intensity of bands in Raman spectra corresponding to the As rich and S rich molecular fragments is in agreement with compositional changes of Ed and optical dielectric constant. Changes of the parameters of the single-oscillator model induced by treatment are discussed on the base of photo- and thermally-induced structural changes and are consistent with topological models and models that claim a degree of chemical ordering. Such photoinduced structural changes provide good etching selectivity of As-S layers in amine based solvents. Surface relief patterns that were fabricated have good surface quality. Diffraction efficiency values of holographic diffraction gratings obtained on the base of As100-XSX layers consisted 60 - 70%.
The present paper is concerned with the investigation of imaging properties of As-S-Se media in application for fabrication of holographic optical security elements. Structural changes in such medica under the influence of external factors (exposure or annealing) were studied. Photo- and thermally induced structural changes were directly confirmed by Raman scattering measurements. Surface relief formation properties were investigated with the help of improved amine based solvents, which provided good surface quality. Various types of holographic security elements (HSE) were fabricated and their properties studied. Fabricated surface relief provided high values of diffraction efficiency. For example, diffraction efficiency of such elements as holographic diffraction gratings consisted up to 60 - 70% in non-polarized light. High quality polymer copies of the initial HSE were obtained.
The present paper deals with an investigation of the image formation properties of As40Se60 thin layers and their application for the production of diffractive optical elements. Thin layers (0.5 - 5 micrometers ) were deposited by the vacuum thermal evaporation and exposed by a Xe-lamp or annealed at 150 degree(s)C. The spectral dependence of the index of refraction, n, of variously treated samples was obtained using Swanepoel method and the single-oscillator model parameters ((epsilon) , Eo, Ed) were estimated. Photo- and thermally induced changes of n, (epsilon) , Eo and Ed induced by exposure or by annealing are discussed on the basis of photo- and thermally induced structural changes, which were directly confirmed by Raman spectroscopy. Such photostructural changes provide good etching selectivity of unexposed and exposed parts of As40Se60 layers in amine based solutions. This provides possibility for the fabrication of surface-relief patterns. The sensitivity of As40Se60 layers has been found to be approximately 10 cm2/J. Holographic diffraction gratings were produced by the Ar and/or HeNe laser exposure. Diffraction efficiency values of holographic gratings achieved approximately 90% for the polarized light. The results obtained show that As40Se60 inorganic resists can be used for the production of holographic diffraction gratings.
The present paper is concerned with an investigation of the image formation properties of As38S62 thin layers and their application in the surface relief formation. The spectral dependence of the index of refraction n of variously treated samples (virgin, exposed, annealed) was obtained from optical transmission in the spectral region 0.4 - 2.5 micrometers . The energy dependencies of n for variously treated samples were well fitted by the Wemple-DiDomenico dispersion relationship and were used for the estimation of the single-oscillator model parameters. It was found, that exposure as well as annealing causes an increase in refractive index n values over the all spectral region. The values of optical dielectric constant (epsilon) is also increasing. Changes of the single-oscillator model parameters induced by exposure and/or by annealing are discussed on the basis of photo- and thermally induced structural changes, which were directly confirmed by Raman spectroscopy. Such photostructural changes provide good etching selectivity of As32S62 layers in amine based etching solutions. This provided possibility for the fabrication of surface-relief patterns, in particular, diffraction gratings. The results obtained, show that As38S62 inorganic resists can be successfully used in holography and other optical applications.19
The results of investigations of photostimulated phenomena in As40S40Se20 thin films with the help of optical methods are presented in this paper. Raman spectra, optical constants in the transparency region of as- evaporated, exposed and annealed films were obtained. The As40S40Se20 thin films have shown good etching selectivity in amine based (in particular, nonaqueous solutions based on triethylamine) etching solutions.
Reversible changes of the Raman spectra by the cycle of band-gap laser irradiation and annealing (storing in the dark) has been observed for amorphous Ge20S80 thin films for the first time. The observed changes in the region of stretch vibrations of the chalcogenide atoms is direct evidence for the occurrence of gross structural changes in local bonding configuration cased by optical irradiation. It has been shown that under the laser irradiation the bonding tendency of the chalcogenide atoms is to form rings rather than chains, i.e. the cis-conformation is preferred over trans-conformation.
The present paper is concerned with investigations of image formation properties of As40S20Se40 thin layers. Spectral dependence of the refraction index n of variously treated samples was estimated from optical transmission in the spectral region 400-2500 nm. The n energy dependence of variously treated samples was fitted by the Wemple- DiDomenico dispersion relationship and used to estimate the single-oscillator model parameters. It was found, that exposure, as well as annealing leads to the increase in n values over the all investigated spectral region. Changes of the parameters of the single-oscillator model induced by treatment are discussed on the base of photo- and thermally- induced structural changes, which were directly confirmed by Raman scattering measurements. Such photoinduced structural changes provide good etching selectivity of As40S20Se40 layers in nonaqueous amine based solvents. The best obtained sensitivity values consisted of approximately 40 cm2/J. Surface relief patterns that were fabricated have good surface quality.Diffraction efficiency values of holographic diffraction gratings obtained on the base of As40S20Se40 layers consisted of 60-70 percent.
The kinetics of photo-induced solid state chemical reaction of silver with a As33S67 films in conventional sandwich structure was measured by monitoring the change in thickness of the undoped chalcogenide using a modified computer-controlled technique. The kinetic data obtained shows that there are two stages in the photo-induced reaction process. Rate coefficient and activation energies have been measured and a comparison of the composition and structure of reaction products detected by Rutherford backscattering spectroscopy (RBS) has been made. The RBS spectra obtained at different stages of the photo-induced reaction process show a step-like form of the Ag concentration profile during the course of the reaction and the homogeneous distribution of Ag in the final reaction products, e.g. 31 at percent Ag. The step-like form of the Ag concentration profile is discussed in the framework of the G-cAg diagram for the Ag-As33S67 system. On the basis of the RBS results, it is suggested model explaining the kinetics of the photo-induced reaction.
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