PREVAIL - An e-beam stepper with Variable Axis Immersion Lenses

Physical limits of silicon transistors and circuits

“…However, high throughput demands parallelism by simultaneous exposure of a considerable area rather than by a scanning beam. Projection exposures with masks and an electron source are not impossible and have been demonstrated (Berger 1991, Pfeiffer andStickel 1995) but they have not yet met the requirements of high throughput processing.…”

Electron caustic lithography

“…Simply increasing beam current to increase throughput creates the issue of space-charge effects which tend to blur image features. 6,8,9 However, ECL is a parallel illumination method which can simultaneously illuminate large areas of the resist, ameliorating the requirements for large beam currents. 8,10 In addition, dual beam LEEM methods have been shown to reduce the effect of the electron beam on the mirror itself, which causes some mirror surfaces to change potential and distort the outgoing electron beam.…”

“…6,8,9 However, ECL is a parallel illumination method which can simultaneously illuminate large areas of the resist, ameliorating the requirements for large beam currents. 8,10 In addition, dual beam LEEM methods have been shown to reduce the effect of the electron beam on the mirror itself, which causes some mirror surfaces to change potential and distort the outgoing electron beam. 10 ECL is entirely compatible with a multiple column architecture which can, in principle, reduce the required beam current in any one column, and realise several tens of wafers per hour.…”

“…Caustics are commonly produced when focusing an optical beam, and they are typically stable to perturbations 19 such as imperfections on the mirror surface, and aberrations in the optical system including an electron energy spread. 3,8,12 Thus a variety of caustics should be readily formed from a vast range of mirror surfaces, including curved lines and junctions, with contributions from both surface topography and potential variations, such as differences in material work function. Caustic features can typically be focused to finer dimensions than the surface structures or variations producing them, improving resolution of lithographic patterns.…”

“…This has led to innovative approaches such as SCALPEL which utilises the angular scattering properties of electrons, rather than absorption in the mask, to create intensity variations across a resist. 2,8,9,11 In addition there has been a development of maskless approaches, including the use of multiple beams, 14,15 low energy electron microscopy, 10 and reflective electron beam lithography (REBL) wherein the electron beam is reflected by an array of electrostatic mirrors. 12,13 In this letter we describe a complementary approach to REBL and electron projection lithography which is based on the formation of intense electron caustics which can be subsequently projected onto a resist by suitable electron optics.…”