This work presents the applications of the method of the disappearing diffraction pattern for refractometric measurements and analysis of scattering media. The behavior of the refractive indices of different aqueous dispersions containing metal and polymer particles is studied theoretically and experimentally. Both metallic and latex solutions exhibit linear dependence of the refractive index on the concentration of particles. Values of the specific refractive index increment dn/dc for Co, Fe and Ag nano-dispersions are calculated. Poly(2-ethylhexyl) acrylate and poly(vinyl acetate) latexes with size of particles between 50 and 1300 nm and concentration up to the maximum possible are systematically studied with respect to the properties of the particles-concentration, diameter and refractive index. Empirical relationships are derived for the investigated latexes, describing the dependence of the refractive index of latexes on their properties and on the light wavelength. Such approach could be used to solve the inverse problem of calculating the concentration or the size of particles, measuring the refractive index. It is shown that the refractometry provides a simple, easy and accurate way to study and analyze properties of dense nano- and micro-dispersions.
For all kinds of laser applications is important to know the refractive indices of materials for the corresponding wavelength. Accurately measured RI value can be used for structural analysis, in many branches of the science and industry. However, commercial refractometers usually measure refractive index at the wavelength of one lamp's discrete line. That's why investigators sometimes have to design new or to modify standard refractometers to perform adequate experiment on the desired wavelength. This work reports the design of a simple automatic laser refractometer. The method of the disappearing diffraction pattern is used for the measurements. The device uses diode laser placed in a socket, which allows easy replacement of lasers and performing measurements at different wavelengths. The apparatus can measure RI of liquids with accuracy better than 1.10-3 in a range from 1.33 to 1.40.
A method was developed to separate and quantitatively characterize a contribution of resist heating and proximity effects into CD-variation in electron-beam lithography. An experimental and theoretical study of these two effects were done using a 30 kV variably shaped beam system. TEMPTATION software tool was used to simulate temperature rise during electron exposures. Good agreement of experimental results and simulated data was found. A method was developed to measure proximity function which is free of resist heating influence.
KEYWORDS: Electron beam lithography, Critical dimension metrology, Distortion, Laser scattering, Scattering, Computing systems, Lithography, Electron beams, 3D modeling, Software development
Distortion of critical dimension (CD) is an important problem in electron beam lithography. Two main reasons for the distortions are proximity effects and resist heating. The influence of both these factors is examined for a 30 kV variably shaped electron beam lithography system. A change of linewidth with exposure dose was experimentally measured at variable exposure conditions of a pattern. In this way, the influence of resist heating was varied while electron scattering was constant. A simulation method was developed that allows one to take into account the contribution of proximity effects and resist heating to a linewidth change. An advanced model of resist heating was used for simulation. This method can be used to predict CD change. A technique for determination of a heat-to-dose transfer coefficient was proposed.
The suitability of pattern transfer through multi-component chemically amplified resists (CARs) has been studied. We report on direct-write electron-beam lithographic and reactive ion etching (RIE) experiments with single-layer CARs used for the fabrication of silicon structures with sizes from micro- down to submicrometer scale and high aspect ratio. The 30 keV e-beam response of new types of CARs in thicker layers and the optimization possibilities of the exposure and etching conditions were investigated as well. We measured the basic characteristics of used resists and also the influence of proximity effects. The study includes the effects of resist process variations on the global 3D resist-relief structure. The resolved resist- relief structures at optimized process conditions have shown high aspect ratios with nearly vertical sidewalls. The paper will discuss the deep pattern transfer results into the underlying SiO2 and/or directly into Si-substrate by using RIE. The results show an etch that has excellent vertical sidewalls free of passivation, and is anisotropic.
Measurements of dose characteristics of PMMA were performed with various resist temperatures. The quantitative data shows sensitivity changes with the temperature increase. The model of resist heating effect is presented and a possible technique to correct distortions due to resist heating is discussed.
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