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Electron sensitive resists have been exposed on optical masks in a variably shaped spot electron beam lithography system, EL3, at 25 and 50 kV and beam current densities up to 50 A/cm2 to evaluate the effects of resist heating during electron exposure. Resist heating effects are primarily observed in dense patterns at high electron exposure dose. For the purpose of comparison resist heating effects are quantified in terms of the development rate change that is caused by the temperature rise in the resist during electron beam exposure. From an energy density point of view the maximum temperature rise in the resist during exposure is very similar for both 25 and 50 kV exposures. The area on the mask over which the temperature rise in the resist can change resist properties is significantly larger at 50 kV: up to 20 μm at 50 kV compared to ∼5 μm at 25 kV. Using sensitive electron beam resists requiring 1–5 μC/cm2 exposure dose no resist heating effects are observed at beam current densities up to 50 A/cm2.

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Articles you may be interested inMultiaxis and multibeam technology for high throughput maskless E-beam lithography J. Vac. Sci. Technol. B 30, 06FC01 (2012); 10.1116/1.4767275 Distributed axis electron beam technology for maskless lithography and defect inspection J. Vac. Sci. Technol. B 21, 2834 (2003); 10.1116/1.1629291High-throughput electron-beam lithography with a raster-scanned, variably shaped beam

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Calculations have been performed on the contrast available in thick specimens. Ten modes of operation have been considered, six in the conventional electron microscope (CEM) and four in the scanning transmission electron microscope (STEM). Electrons passing through the specimen fall into four categories, elastically scattered, inelastically scattered, unscattered, and those scattered both elastically and inelastically. For the various operation modes these groups are taken in combinations to form practical signal intensities. In the calculation of practical intensities, the angular distribution of plurally scattered electrons is considered. The fraction of each scattered group passing through the microscope aperture has been calculated for various types of illumination. The practical intensities are used to calculate the contrast available in stained and unstained specimens. For very thick specimens bright field offers the best combination of contrast and signal intensity. Other contrast modes show a reversal in the sign of contrast for thicknesses close to one mean free path for elastic scattering. The equations for signal intensity and contrast are quite general, and apply to all values of voltage and instrumental resolution.

Articles you may be interested inFacet and bulk heating of GaAs/AlGaAs high-power laser arrays studied in spatially resolved emission and micro-Raman experiments

The importance of mutual repulsion of beam electrons is investigated for conditions relevant to electron beam lithography. A Monte Carlo calculation has been performed which evaluates the spot size for a given beam current and column geometry. The results show that the beam broadening due to mutual repulsion significantly limits the current density obtainable. Experimental results are presented, and the agreement with theory is excellent. For a column 21.5 cm long operating with a 3 mrad aperture semi-angle, the spot size was measured as .14 μm at 100 nA, and .30 μm at 1 μA of beam current. The theory predicts that an optimum spot size exists that is proportional to the 1/4 power of the lens spherical aberration coefficient, and to the 3/4 power of the beam current.