Flow Z-Pinch EUV Light Source for Lithography

Abstract

Summary form only given. The next-generation of lithography will use extreme ultraviolet (EUV) light with 13.5 nm wavelength. The candidate light sources are plasma-based concepts due to the required high temperature for generation and vacuum for transmission. The leading candidates are either gas discharge-produced plasmas (GDPPs) or laser-produced plasmas (LPPs) using either xenon or tin as the working element. These sources produce short pulses of 13.5 nm light, less than a few hundred nanoseconds in length, from a plasma volume of approximately one cubic centimeter. The limitations are either power or stability. The sources are repetitively pulsed at a few kHz to produce effective power levels of 10 W (for LPPs) to 20 W (for GDPPs) at the entrance of the photolithography illuminator system or "intermediate focus" (IF). The power level required by high volume manufacturing (HVM) facilities is 180 W at the IF. Many challenges remain in extending these devices to the required power levels. A new method to produce stable plasmas at high temperature and density has been developed with the ZaP Flow Z-pinch experiment at the University of Washington. The novel concept forms long-lived, large-volume plasmas with lifetimes thousands times longer than the lifetimes of pinch/dense plasma focus methods of GDPP-based EUV sources under development. EUV output power is directly proportional to plasma lifetime at a fixed pulse frequency. Furthermore, the plasma volume is approximately 300 times larger. The flow Z-pinch plasma operating as a long-duration EUV light source has the potential to dramatically increase the per-pulse delivered energy at 13.5 nm. Such a technology breakthrough would greatly improve the economic and throughput performance of EUV lithography in semiconductor manufacturing. The ZaP concept uses a novel method of formation to embed a sheared axial flow in the plasma, mitigating the classical plasma instabilities (kink and sausage instabilities). (The same instabilities that limit the duration of the EUV emission phase in GDPPs.) Recent experiments on the ZaP Flow Z-Pinch at the University of Washington have been conducted using xenon as the working plasma and measuring the EUV light production. Diagnostic instruments measure many plasma parameters (for example magnetic fields, plasma density, flow velocities, and temperatures). A filtered photodiode instrument is constructed that admits a narrow wavelength bandwidth about 13.5 nm. Experimental results of the plasma behavior and EUV light production will be presented.