CVD Diamond IR Optics Enable EUV Lithography

For more than 40 years, the well-known Moore's Law has been behind the optical lithography industry's push toward more powerful and energy-efficient computer chips. One of the key approaches to producing ever-smaller transistors is to take advantage of ever-shorter wavelengths of light in optical lithography. The latest transition is from deep-ultraviolet (DUV) light at 193 or 248 nm to extreme-ultraviolet (EUV) light at only 13.5 nm.1 There are limited ways of producing this light efficiently, with the frontrunner being emission from tin-based laser-produced plasma (LPP) pumped by carbon dioxide (CO2) lasers.

While many fundamental engineering issues have been resolved, these plasmas emit at the required wavelengths with low efficiency; in addition, once the light is emitted it is hard to manipulate without high system losses. This creates a challenge in introducing sufficient power into the plasma to enable rapid wafer processing rates—the average input IR pump power into the system must typically be higher than 20 kW, with pulse energies of up to 1 J at pulse durations of down to 10 ns—levels that have rarely been required in more-traditional laser applications.

Some CO2 lasers with appropriate average-power outputs are available; however, they need to be switched to produce the desired pulse shapes, leading to further inefficiencies. In practice, multiplexing of two or more high-power outputs is required for LPP extreme UV (EUV) systems. One challenge with the sort of laser powers being used is that traditional material solutions for the optics are either entirely insufficient or have short lifetimes. In addition, the environment around the plasma has significant debris, which further limits the performance of traditional materials.

http://www.laserfocusworld.com/articles/print/volume-49/issue-11/features/mid-infrared-optics-cvd-diamond-ir-optics-enable-euv-lithography.html