Experimental Investigations on Particle Contamination of Masks Without Protective Pellicles During Vibration or Shipping of Mask Carriers

Abstract

Extreme ultraviolet lithography (EUVL) is considered the next generation lithography to produce 32-nm feature-size or smaller. The challenge is that conventional pellicles are unavailable for protecting the EUVL masks against contaminant particles, because the EUV beam is easily absorbed by most solid materials. The masks are usually transported or stored in mask carriers. Without the protective pellicles, particles generated inside the mask carrier may deposit on the critical surface of the mask. It is therefore important to identify where the particles are generated inside the mask carrier during shipping. In this paper, two shipping carrier models of different mask holder designs were used. The mask carriers with quartz mask blanks inside were shaken manually, vibrated with a computer-controlled vibration table, or shipped via air freight. In order to simulate the EUVL mask shipping, no pellicles were used. Several online and offline particle detection techniques were employed to investigate particle generation inside the mask carrier during vibration or shipping. It was shown that particles were mostly generated at the contact points between the mask surface and the carrier element. The design of the mask-holding element in the mask carrier played an important role in reducing particle generation.

Deposition Velocity onto an Inverted Flat Surface in a Laminar Parallel Flow

“…Since the pellicles cannot be used in the EUVL technology, photomasks are vulnerable to particulate contamination (Yook et al 2007a). The control of particulate contamination is therefore getting critical in enhancing the product yield in semiconductor manufacturing, as the feature size shrinks.…”

Particle deposition velocity onto a face-up flat surface in a laminar parallel flow considering Brownian diffusion and gravitational settling

“…An EUVL photomask is vulnerable to particulate contamination, due to the unavailability of pellicles in the EUVL technology (Asbach, Fissan, Kim, Yook, & Pui, 2006;Yook et al, 2007c). Since the equation suggested by Liu and Ahn (1987) to predict deposition velocity in a parallel flow is limited to a wafer, i.e., a circular flat surface, Computational Fluid Dynamics (CFD) simulation needs to be performed and convective diffusion equation should be numerically solved to estimate the deposition velocity onto a square photomask surface in a parallel flow.…”

Investigation of particulate contamination of heated wafers contained in a closed environment

“…According to Yook et al (2007b), particles were mostly generated at the contact points between the mask surface and the carrier element, and the particles were able to contaminate the mask surface during vibration or shipping of mask carriers. Based on the results of Yook et al (2007b), this study assumed that the particles could mostly be generated in the FOUP due to the friction between the wafer and the FOUP part.…”