The effect of beam emittances on x-ray lithography exposure line resolution

Abstract

We have investigated in detail the effect of finite source size and beam divergence on the resolution of the exposure process for the case of an x-ray lithography proximity printing system with a synchrotron radiation source. An analytical expression for the exposure resolution is obtained and a connection between machine parameters and penumbral blur established. The effect of scanning the beam is included and is shown to have a profound effect on the resolution. Between the two cases of field exposure obtained by electron-beam wobbling or by a scanning mirror, we show that the first is preferable. Since such an approach is of difficult implementation in a multistation ring, we have analyzed in detail the effect of the scanning mirror. For this case we conclude that the divergence of the photon beam plays a dominant role in determining the broadening of the exposure. This is true for the vertical scanning direction, while we show that in horizontal the electron-beam divergence plays no role. This conclusion is very important for machine design. The expression for the broadening shows that is possible to keep broadenings well within tolerances of 25 nm (3σ) with machines of relatively large emittance and typical beamlines. Such an excellent definition can be used to advantage in the overall process tolerance budget to relax other parameters, for example, resist contrast. Conversely, if a tolerant process is available, the machine design requirements can be relaxed, leading to a more economical construction. We conclude that x-ray lithography based on storage rings can easily satisfy the strict linewidth control requirement of very large scale integrated processes with a machine of (relatively) modest performances.