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Method for dynamically controlling and reducing stress on photomasks during pellicalization using in-place monitoring sensors

IP.com Disclosure Number: IPCOM000020400D
Publication Date: 2003-Nov-19
Document File: 6 page(s) / 139K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for dynamically controlling and reducing stress on photomasks during pellicalization using in-situ monitoring sensors. Benefits include improved functionality, improved performance, and improved yield for photolithography.

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Method for dynamically controlling and reducing stress on photomasks during pellicalization using in-place monitoring sensors

Disclosed is a method for dynamically controlling and reducing stress on photomasks during pellicalization using in-situ monitoring sensors. Benefits include improved functionality, improved performance, and improved yield for photolithography.

Background

Conventional industry practice does not control reticle deformation in real-time in the pellicalization process. The severe strain experienced by the pellicle system and the reticle can cause image deformation. The conventional method, when applied to hard pellicles, does not monitor, adjust, or optimize strain distribution pellicle membranes and frames during pellicalization.

         The conventional technique of mounting a pellicle to a reticle has resulted in high local tilt and deformation on the hard pellicle and reticle. The pellicle surface flatness directly impacts the lithographic image quality and overlay, making pellicle flatness one of the most challenging areas in the development of fused silica pellicles. In spite of extensive effort from the industry to improve the pellicle-mounting process, high local tilt is the number one challenge for the technology’s success (see Figure 1).

Conventional pellicalization for polymer pellicles induces stress on the photomask and causes uncorrectable distortion patterning errors up to tens of nanometers. The ever tightening overlay budget in advanced lithography can no longer tolerate such large errors. However, reticle and pellicle stress is not characterized in realtime using pellicalization equipment.

For 157-nm lithography with thick, fused silica pellicles, stress on the hard pellicle membrane and frame during mounting is critical for pellicle flatness and the pattern fidelity of the photomasks. The conventional mounting equipment and process, when applied to hard pellicles, induces very high distortion for lithography resulting in very poor yields.

The conventional mounting technique is a combined mechanical and chemical adhesion process. A large amount of compression is applied to the adjoining parts with adhesive applied in the gap between them. To obtain a hermetical seal and reliable bonding, pressure as high as 27,000 kg/m2 has been commonly applied. Large uneven stress can build on the fused silica pellicle. The resulting tilt and deformation near the compressed locations add significant aberration to the optical path of the lithography tools.

No conventional technique exists for monitoring stress on photomasks or pellicles during pellicalization.

General description

         The disclosed method reduces stress on the patterned reticles during pellicalization by controlling the process and equipment based on in-situ strain sensor measurement. This technique improves pellicalization equipment for meeting extremely stringent distortion requirement in advanced lithography.

The disclosed method includes techniques to control...