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Method for a photomask pellicle with an extended vent structure for rapid gas transfer

IP.com Disclosure Number: IPCOM000012550D
Publication Date: 2003-May-14
Document File: 6 page(s) / 76K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a photomask pellicle with an extended vent structure for rapid gas transfer. Benefits include improved performance and improved throughput.

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Method for a photomask pellicle with an extended vent structure for rapid gas transfer

Disclosed is a method for a photomask pellicle with an extended vent structure for rapid gas transfer.� Benefits include improved performance and improved throughput.

Background

        � � � � � For 157-nm lithography, all air must be purged from the pellicle cavity and replaced with nitrogen or some similar inert gas. If exposed to the high energies inherent at the exposure wavelength, air breaks down and yields reactive compounds, which attack and degrade pellicle materials. The result is a substantial negative impact on yield due to decreased transmission through the photomask and pellicle.

        � � � � � The process of purging air from the pellicle cavity is time consuming using the conventional method. The openings for air transfer are quite small and are further reduced by the presence of a high-efficiency particle filtering membrane completely covering each opening (see Figures 1-3).

        � � � � � The scalability of the conventional method is self-limited by the number of filter patches that can be placed on the side of the frame without overlapping. If overlapped, they cannot form a full seal and enable particles to enter the pellicle cavity.

        � � � � � One possible solution to increase the rate of air replacement beneath a pellicle, would be to provide a single or plurality of small holes drilled into the pellicle frame, each approximately 1.0 mm in diameter and covered with a gas permeable filter patch.

        � � � � � Other possible solutions include porous frames, which would allow air transfer directly through the frame material. However, these solutions are still in development and are not available for high volume production use.

General description

        � � � � � The disclosed method is a pellicle structure comprised of an extended frame and gas-permeable membrane coupled with large openings through the pellicle frame. This structure provides substantially increased rates of gaseous transfer to/from the pellicle cavity, providing greatly reduced N2 soak times prior to the 157-nm exposure.

        � � � � � The key elements of the method include:

•        � � � � Extensions of the pellicle frame, each defining a cavity adjacent to one edge of the pellicle frame, preferably the long edge

•        � � � � A gas permeable membrane attached to the top edge of each pellicle frame extension around the circumference of and fully enclosing the cavity defined by each pellicle frame extension

•        � � � � An open area or plurality of open areas defined in the pellicle frame between the cavity defined by each frame extension and the pellicle cavity, enabling free flow of gas between the cavity and the frame

Advantages

        � � � � � The disclosed method provides advantages, including:

•        � � � � Improved performance due to larger through-passages between the cavity and the frame, improving the free and rapid transfer of air in/out of the pellicle cavity

•        � � � � Improved throughput due to improved ga...