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Proceedings Paper

Advances in CO2 cryogenic aerosol technology for photomask post AFM repair
Author(s): Charles Bowers; Ivin Varghese; Mehdi Balooch; Jaime Rodriguez
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Paper Abstract

As the mask technology moves towards production of 36 nm and 22 nm DRAM half pitch nodes, printing features and sub-resolution assist features (SRAF) shrink below 80 nm. These narrow features become more fragile and place new demands on cleaning processes for a physically non damaging solution. These challenges include compatibility with new materials, oxidation, chemical contamination sensitivity, proportionally decreasing printable defect size, and a requirement for a damage-free clean. CO2 cryogenic aerosol cleaning has, for many years, shown potential to offer a wide process window for meeting some of these new challenges. CO2 cryogenic aerosol cleaning for post AFM repair debris cleaning has been used for many years on masks greater than 90 nm DRAM half pitch nodes. Until recently, CO2 purity and delivery hardware issues resulted in foreign material adder (FMACO2) contamination and SRAF damage below 150 nm critical feature size. Some key desirable properties of CO2 cryogenic aerosol cleaning are the non-oxidizing and non-etching properties when compared to current chemical wet clean processes. In this paper, recent advancements of CO2 cryogenic aerosol cleaning technology are presented, highlighting improvements in the areas of FMACO2 reduction, lowering the critical feature size without damage, and electrostatic discharge (ESD) mitigation. Key aspects of successful CO2 cryogenic aerosol cleaning include the spray nozzle design, CO2 liquid purity, and integrated system design. The design of the nozzle directly controls the size, flux, and velocity of the CO2 snow particles. Methodology and measurements of the solid CO2 particle size and velocity distributions will be presented, and their responses to various control parameters will be discussed. FMACO2 mitigation can be achieved only through use of highly purified CO2 and careful materials selection of the delivery hardware. Recent advances in CO2 purity will be discussed and data shown. The mask cleaning efficiency by CO2 cryogenic aerosol and damage control is essentially an optimization of the momentum of the solid CO2 particles and elimination FMACO2. Data on CO2 tribocharge mitigation, the main cause of ESD, will be presented and application to current technology nodes discussed. The previous damage threshold of 150 nm SRAF structures have been reduced below 60 nm and data will be shown indicating sub-50 nm is possible. The tool capability has been improved from previously doing local cleaning of AFM repair sites to a full mask clean with prospects of replacing certain wet clean steps where phase and transmission are degraded.

Paper Details

Date Published: 30 September 2009
PDF: 17 pages
Proc. SPIE 7488, Photomask Technology 2009, 74881R (30 September 2009); doi: 10.1117/12.829690
Show Author Affiliations
Charles Bowers, Eco-Snow Systems LLC (United States)
Ivin Varghese, Eco-Snow Systems LLC (United States)
Mehdi Balooch, Eco-Snow Systems LLC (United States)
Jaime Rodriguez, Eco-Snow Systems LLC (United States)

Published in SPIE Proceedings Vol. 7488:
Photomask Technology 2009
Larry S. Zurbrick; M. Warren Montgomery, Editor(s)

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