ELECTRON-SCATTERING OF LOW-Z HIGH-DENSITY MATERIALS IN X-RAY MASK PATTERNING

The scattering properties of low-Z high-density materials are discusse d, through Monte Carlo simulation, in view of their utilization as mem branes for X-ray masks. The interplay between low atomic number and hi gh atomic density is discussed and a comparison with silicon is carrie d out, both in case of bulk targets and membranes. The low Z causes sm aller proximity effects, but the decisive factor relative to silicon i s constituted by the higher mechanical stiffness, which, in principle, allows to greatly reduce membrane thickness. However, we show that, i n spite of the more favourable intrinsic scattering properties, the ch oice of these materials, in actual systems, is not always a real advan tage. In the analysis of the single-layer resist process for X-ray mas k fabrication, no significant difference relative to Si is found in th e two limits of low and high energy. On the contrary, the choice of lo w-Z high-density materials is found to be advantageous at intermediate energy. In particular, we demonstrate that, while in the case of low- Z high-density materials, 0.15 mum resolution is successfully obtained already at 30 keV, in case of Si, this same resolution is only reache d at e-beam energies of at least 40 keV.