EUV generation using a droplet of a suspension including tin as a target of a high-efficiency LPP source for high volume production

Abstract

Technologies for materializing our cotton-cake like tin target scheme are being developed. With the scheme, we expect to achieve 4% conversion efficiency into 2π sr supported by our experimental data. In order to implement EUVL, EUV power exceeding 100 W is considered to be required to be sent to an illumination box. Large collection solid angle and high conversion efficiency are the mandatory requirements for a source for EUVL. A route to the goal is not yet clear. With our scheme, we can expect EUV exceeding 100 W at the entrance of an illuminator is obtained with a 15 kW YAG laser. Difficulties we encountered when we tried plasma production by shooting droplets of a SnO 2 suspension were preparation of a long life SnO 2 suspension and stable droplet generation with the suspension. In these few years our technologies are highly improved, and we are now able to supply the suspension for several hours without stop, and concentration of a suspension is now increased to as high as 40 wt %. EUV intensity dependence on concentration was studied by shooting a jet of a suspension. We found the EUV intensity saturated at around several at %, which corresponds to several tens wt%, and the EUV intensity comparable to that from a Sn plate was observed. By introducing active synchronization of laser pulses with droplets, we can now shoot droplets running at 10 kHz with a 10 Hz YAG laser with no miss shot. We are now ready to challenge formation of cotton-cake like tin target to demonstrate a very high CE.

Sharpening of the 6.8 nm peak in an Nd:YAG laser produced Gd plasma by using a pre-formed plasma

“…As discussed by Tomie et al, 25 the conversion efficiency (CE), which is defined as a ratio of the usable emission energy at one wavelength to the irradiating laser energy, is a product of the laser absorption efficiency by the plasma, η abs , the radiation efficiency, η rad , the spectral efficiency, η spec , and the collection efficiency of a radiation collector mirror, η col , i.e., CE = η abs η rad η spec η col . In order to achieve a high CE, all the efficiencies must be maximized.…”

Tin laser-produced plasma as the light source for extreme ultraviolet lithography high-volume manufacturing: history, ideal plasma, present status, and prospects

“…The author defined 21 spectral efficiency η S as the ratio of the usable energy emitted in 2% bandwidth to the total radiation energy.…”

“…Power of a radiation source into a solid angle of 2πsr is given by the following equation 21 when opacity of the source τ opa is well smaller than 1.…”

“…Total conversion efficiency η total is given by a product of four efficiencies: 21 energy deposition efficiency η abs , radiation efficiency η rad , spectral efficiency η S , and collection efficiency η G .…”

“…4, a jet of SnO 2 suspension was blown off by the high pressure of a plasma. 21 The bright spot in the picture is the visible emission from a plasma. If a droplet target is too close to a plasma, it is blocked to reach the position of laser focus by the pressure of the plasma created in the previous shot.…”