Thermomechanical modeling of the pin-chucked EUV reticle during exposure

Abstract

Extreme ultraviolet (EUV) lithography has emerged as the forerunner in the selection process to become the industry's choice as the technology for next-generation lithography (NGL). An advantageous characteristic of the EUV reticle is that it is reflective, so it can be chucked across the entirety of its backside. This chucking will aid in meeting flatness requirements as well enhancing the heat removal ability of the chuck when compared to the mounts used for optical reticles. The EUV exposure process occurs in a vacuum environment, which precludes the use of vacuum chucks; therefore, electrostatic chucks are the favored choice. One concern is that particles may become lodged between the chuck and reticle, causing distortions to occur once the reticle is chucked flat. To counter this effect, electrostatic pin chucks have been proposed. However, because of the lower heat transfer ability of the pin chuck due to the interstitial gap, thermal issues may arise. A predominant pin-chuck configuration has yet to emerge, and there is no set of standards to facilitate new designs. The intent of this paper is to provide general guidelines to assist in preliminary designs. Parameters that were seen as potentially important factors in pin chuck performance were chosen and the results are presented.

Analytical treatment of the deformation behavior of EUVL masks during electrostatic chucking

“…However, the pins on the chuck will distort the mask, an issue which has been partially examined in the literature via the finite element method. 7,8 The effect will be even higher in the case of thin wafer chucking 10 which has also been observed experimentally. 11,12 We will use our analytical model and directly correlate the pin-pitch, chucking pressure and pin-size to the mask OPD/IPD on the front-side.…”

“…Typical electro-static chucks feature a bed of pins on the clamping surface which will facilitate the declamping of the mask. Moreover, unpredictable particulate contamination will be less likely distort the mask 7,8 (effects on the mask deformation due to particles entrapped between the mask and the chuck are discussed elsewhere 9 ). However, the pins on the chuck will distort the mask, an issue which has been partially examined in the literature via the finite element method.…”