Industry Defining EUV Source

The three major subsystems of the source are the drive laser, the beam transport system (BTS) and the source vessel. The drive laser is a CO₂ laser with multiple stages of amplification to reach the required power level of up to ~40 kW. It is operated in pulsed mode at ~40-60kHz with radio-frequency (RF) pumping from generators operating at 13.56 MHz. The laser is typically installed in the sub-fab along with its RF generators and heat exchangers. The laser beam is expanded as it leaves the drive laser to lower the energy density on the BTS mirrors. Three turning mirrors are used to allow the beam to travel from the sub-fab to the fab through the waffle-slab floor with the needed flexibility for positioning the laser with respect to the source vessel (and scanner) on the floor above. The laser and BTS are completely enclosed and interlocked to meet laser class 1 requirements. The BTS delivers the beam to a focusing optic where the 10.6 micron wavelength light is focused to a minimum spot size defined by the numerical aperture of the focusing system. The focused beam propagates through a central aperture in the collector and strikes the droplet at the focus of the ellipsoidal collector mirror inside the vacuum space of the source vessel. The droplet generator delivers liquid tin droplets of 30 micron diameter to the same position at ~ 50 kHz repetition rate; both laser pulse and droplets are steered and timed to ensure proper targeting. The laser pulse vaporizes and heats the tin into a plasma of critical temperature. The EUV light emitted by the plasma is collected and reflected with the multi-layer coated ellipsoidal mirror to the IF where it passes through a small aperture into the scanner volume that houses the illumination optics.

• Class 1 high power/high repetition rate drive laser  
• Beam transport system  
• Source vessel  
• Normal Incidence Collector  
• Droplet Generator

• High Repetition Rate enables better dose control of the resulting EUV light.