No abstract

A new Monte Carlo simulation of electron scattering has been achieved for extension to the low-energy region and to heavy elements such as Au. The Kanaya-Okayama equation, which includes adjustable parameters, is used for the calculation of energy loss instead of the Bethe equation. Further, the Mott equation, which is obtained from a more exact treatment for elastic scattering, is used instead of the screened Rutherford equation for angular scattering. The calculated results are compared with various kinds of experimental results such as the electron range, the backscattering coefficient, and the depth distribution of energy dissipation. The theoretical results are found to be in satisfactory agreement with the experimental results.

A computer program has been developed for the three-dimensional calculation of the absorbed energy density in polymer films on substrates in electron beam lithography. In this calculation the Monte Carlo results have been used for the radial energy intensity distribution for a point source electron beam. The program is based on the reciprocity principle proposed by Chang. Some exposure experiments have been conducted with an electron resist of PMMA (polymethyl methacrylate) for isolated patterns in the from of a line of finite length (8.1 µm) as well as of a rectangle (3.1×8.1 µm2) in order to check the reliability of the calculations. Operating beam voltages used for the investigation are 14 and 20 keV. The electron resist thickness is 8000 A. Relatively good agreement has been obtained between the calculated and the experimental results. This program is applicable to an arbitraty pattern, and therefore it will be useful for investigations of the proximity effect in electron beam lithography.

Uphill diffusion of boron or phosphorus in silicon due to high-temperature proton irradiation is explained by a proposed model in which a vancancy mechanism is assumed. The results calculated from the model show good agreement with the experimentally measured profiles, and some physical parameters can be estimated. A significant feature of the proposed model is that Fick’s law is included as a special case.

New Monte Carlo simulations of electron scattering based on the single scattering model have been performed in the low-energy region for an aluminum target, where two basic equations are required, namely the elastic scattering cross section and the energy-loss rate. We investigated the screened Rutherford equation and the Mott equation for two different atomic potentials for the former, and the Rao Sahib-Wittry equation (the modified Bethe equation) for the latter. The validity of each model is discussed in a comparison between Monte Carlo results and experimental results such as the electron range, electron backscattering, and electron transmission which have been reported by various authors. Consequently, it was found that a combination of the Mott cross section and the Rao Sahib-Wittry equation showed the best accuracy. However, the accuracy of a previous model with the screened Rutherford equation is not as bad as aniticipated because of the higher accuracy of the Born approximation for light elements such as Al, compared to Au.