Thermal management of EUV lithography masks using low-expansion glass substrates

Self Cite

Development of manufacturing infrastructure is required to ensure a commercial source of mask substrates for the timely introduction of EUVL. Improvements to the low thermal expansion materials that compose the substrate have been made, but need to be scaled to production quantities. We have been evaluating three challenging substrate characteristics to determine the state of the infrastructure for the finishing of substrates. First, surface roughness is on track and little risk is associated with achieving the roughness requirement as an independent specification. Second, with new flatnessmeasuring equipment just coming on line, the vendors are poised for improvement toward the SEMI P37 flatness specification. Third, significant acceleration is needed in the reduction of defect levels on substrates. The lack of highsensitivity defect metrology at the vendors' sites is limiting progress in developing substrates for EUVL.

Section: Methodsmentioning

confidence: 99%

Vendor capability for low-thermal-expansion mask substrates for EUV lithography

Blaedel

Taylor

Hector

et al. 2002

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“…This value is similar to values used in previous studies. 8 When a gas is used to fill the interstitial space, the average overall backside contact conductance will be considerably higher, depending on the gas heat transfer coefficient. For this study, the values ranged from 4.0 to 154.0 W/m 2 -K.…”

Section: Pressure [Kpa]mentioning

confidence: 99%

“…[1][2][3] Recently however, the research on thermal issues has spread to the reticle side of the manufacturing process. [4][5][6][7][8] One concern is that particles may become lodged between the chuck and reticle, inducing distortions once the reticle is chucked flat. With the advent and proliferation of the electrostatic chuck, backside particle contamination will have to be addressed by the lithographic community.…”

Section: Introductionmentioning

confidence: 99%

Thermomechanical modeling of the pin-chucked EUV reticle during exposure

Wei

Martin

Beckman

et al. 2002

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.

“…The mask absorbs a significant fraction of the incident EUV light, so it should be able to efficiently shed heat to the surrounding vacuum environment. 46 However, the mask will need to be actively cooled in the exposure tool, so maximizing emissivity is probably a low priority for material selection.…”

Section: Absorber and Buffer Layer Choicementioning

confidence: 99%

EUVL masks: requirements and potential solutions

Hector

2002

Self Cite

Extreme ultraviolet lithography (EUVL) is a leading next generation lithography technology. Significant progress has been made in developing mask fabrication processes for EUVL. The mask blank for EUVL consists of a low thermal expansion material substrate having a square photomask form factor that is coated with Mo/Si multilayers. A SEMI standard is now available for mask substrates. SEMI standards are also being developed for mask mounting, for mask blank multilayers and absorbers and for mask handling and storage. Several commercial suppliers are developing polishing processes for LTEM substrates, and they are progressing toward meeting the requirements for flatness, surface roughness, and defects defined in the SEMI standard.One of the challenges in implementing EUVL is to economically fabricate multilayer-coated mask blanks with no printable defects. Significant progress has been made in developing mask blank multilayer coating processes with low added defect density. Besides lowering added defect density, methods to reduce defect printability are being developed to effectively enable repair of many defect types. These repair processes might significantly increase yield of EUV mask blanks before defect density is lowered to production targets. Calculations of EUVL mask cost indicate that defect repair processes could allow the initial defect density targets for mask blanks to be relaxed.The mask patterning process for EUVL is nearly the same as that for conventional binary optical lithography masks. EUVL mask patterning efforts are focused on developing the EUV-specific aspects of the patterning process. Eight absorbers have been evaluated against the requirements for EUVL masks, and two absorbers-TaN and Cr--will probably meet the requirements after some further development.