Laser Plasma

The range of temperatures, pressures, and electromagnetic fields in natural or laboratory plasmas (=ionized gases) covers many orders of magnitude, from the case of large astronomic systems, to lightnings, tokamaks or displays. The governing physics is basically unsteady fluid dynamics coupled with electromagnetic fields. In the last few decades the interest in plasmas has matured from a qualitative scientific attraction to quantitative technical solutions in a number of applications.

The use of plasmas as scalable radiation sources for lithography, i.e. for nano-chip manufacturing, is one such application. Indeed, the need for a powerful Extreme UV source (i.e., λ = 13.5 nm, P = 115 W) is likely to be solved only with plasma technology in lithography, because of its accessible cost-of-ownership compared to Synchrotron facilities or e-beams.

The Applied Laser Plasma Science (“ALPS”) research program, initiated in 2007, focuses on the engineering of a EUV lithography source collector module, and its  operation for space- & time-resolved parametric optimization. The plasma is ignited irradiating a fuel target (e.g. lithium, tin) with a powerful laser beam (I = 100 GW/cm2). The laser-induced breakdown expands hypersonically with initial electron temperatures of 25-30 eV. Such temperatures are necessary to induce spontaneous emission in the EUV. Concomitantly with the EUV emission, highly ionized fuel atoms (e.g. Sn+8 up to Sn+12) are accelerated up to a few keV’s. High kinetic energy particles that shower onto the EUV collection optics can erode the functional coatings, thereby rapidly degrading the reflectivity.