Extreme Ultraviolet Source Based on Microwave Discharge Produced Plasma Using Cavity Resonator

Abstract

A microwave discharged produced plasma (MDPP) source is used to generate 13.5 nm extreme ultra violet (EUV) radiation for applications in photolithography. The maximum power of the 2.45 GHz magnetron microwave source is 6 kW and it can be operated in a pulsed mode with repetition frequency up to 100 Hz. The working gas is Xenon at pressure in the range 0.5-1.2 Pa. Radiation in the visible and near UV range is removed with the help of a 100 nm Zr filter. The EUV radiation is reflected using two Mo/Si multilayer mirrors in order to attenuate the residual out of band radiation before measuring the in-band EUV using a silicon diode. The initial experiments were conducted at a reduced microwave power in order to avoid overheating the cavity in the absence of a fully operational cooling system. The experimental result shown that for microwave pulse from 1 ms to 10 ms, intensity was increased 6 times lager. For microwave power, time averaged intensity was increased rapidly 0 mV to 1.2 mV at microwave power of 50 W to 150 W. And it was observed that intensity was increased slowly 1.2 mV to 2 mV at 175 W to 475 W. It is anticipated that more EUV power is generated when the facility is operated at higher microwave input power after the installation of the cooling system.

Microwave discharge plasma production with resonant cavity for EUV mask inspection tool

“…Figure 5 shows the reflection meter system, which consisted of a Zr filter, two Mo=Si multi-layer reflection mirrors, two apertures of ϕ5 and ϕ10 mm, and a silicon photodiode (IRD,XUV). 7) Figure 6 shows the reflectivity of the Mo=Si mirror and the transmission of the Zr filter as functions of the wavelength. The Zr filter cuts out the visible light, but it has a wide bandwidth of about 6-20 nm.…”

“…To develop the inspection equipment for EUV radiation, a microwave DPP source was invented using a cavity resonator. 7) The attractive features of the microwave DPP are less debris, compactness, and continuous working (CW) operation. Xe is used as the working gas, although it has a lower conversion efficiency than that of Sn, to reduce contamination.…”