Determination of the proximity parameters in electron beam lithography using doughnut-structures

In literature many different methods for the determination of the proximity parameters are described. They all have the inconvenience of difficult curve fitting formulae, because of their assymmetry. Moreover, some of these methods need in their evaluation, SEM metrology for linewidth measurements. A new method is proposed here, which is easier to use and at least as accurate as the existing methods. It applies a test pattern which is based on the radial symmetry of the proximity function. This method uses a test pattern consisting of a set of rings (DOUGHNUTS) with varriable inner radius and large but constant outer radius. The evaluation of the exposure after development can easily be done by optical microscope. The curve fitting formula belonging to this DOUGHNUT-method becomes much more simple because of its radial symmetry. A set of experimental data obtained with this method including the influence of beam current, resist thickness and substrate type on the parameters is also given. To show the validity of the parameters obtained with the DOUGHNUT-method a small resist pattern with and without error correction will be presented.