Mr. Charles W. Bowers Profile

Charles W. Bowers

Applicaton Manager at Eco-Snow Systems

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Publications (9)

Proceedings Article | 17 October 2014 Paper

Qualification of local advanced cryogenic cleaning technology for 14nm photomask fabrication

Ralf Taumer, Thorsten Krome, Chuck Bowers, Ivin Varghese, Tyler Hopkins, Roy White, Martin Brunner, Daniel Yi

Proceedings Volume 9235, 923525 (2014) https://doi.org/10.1117/12.2074473

KEYWORDS: Carbon dioxide, Cryogenics, Diffractive optical elements, Raster graphics, Photomasks, Particles, Scanning electron microscopy, Contamination, SRAF, Mask cleaning

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Proceedings Article | 8 November 2012 Paper

A new approach in dry technology for non-degrading optical and EUV mask cleaning

Ivin Varghese, Ben Smith, Mehdi Balooch, Chuck Bowers

Proceedings Volume 8522, 852218 (2012) https://doi.org/10.1117/12.976889

KEYWORDS: Photomasks, Atmospheric particles, Carbon, Carbon dioxide, Extreme ultraviolet, Contamination, Pellicles, Particles, Silicon, EUV optics

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Proceedings Article | 14 October 2011 Paper

Extending CO2 cryogenic aerosol cleaning for advanced optical and EUV mask cleaning

Ivin Varghese, Charles Bowers, Mehdi Balooch

Proceedings Volume 8166, 816615 (2011) https://doi.org/10.1117/12.896962

KEYWORDS: Carbon dioxide, Photomasks, Extreme ultraviolet, Reflectivity, Aerosols, Pellicles, Ruthenium, EUV optics, Particles, Cryogenics

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Cryogenic CO₂ aerosol cleaning being a dry, chemically-inert and residue-free process is used in the production of optical lithography masks. It is an attractive cleaning option for the mask industry to achieve the requirement for removal of all printable soft defects and repair debris down to the 50nm printability specification. In the technique, CO₂ clusters are formed by sudden expansion of liquid from high to almost atmospheric pressure through an optimally designed nozzle orifice. They are then directed on to the soft defects or debris for momentum transfer and subsequent damage free removal from the mask substrate. Unlike aggressive acid based wet cleaning, there is no degradation of the mask after processing with CO₂, i.e., no critical dimension (CD) change, no transmission/phase losses, or chemical residue that leads to haze formation. Therefore no restriction on number of cleaning cycles is required to be imposed, unlike other cleaning methods. CO₂ aerosol cleaning has been implemented for several years as full mask final clean in production environments at several state of the art mask shops. Over the last two years our group reported successful removal of all soft defects without damage to the fragile SRAF features, zero adders (from the cleaning and handling mechanisms) down to a 50nm printability specification. In addition, CO₂ aerosol cleaning is being utilized to remove debris from Post-RAVE repair of hard defects in order to achieve the goal of no printable defects. It is expected that CO₂ aerosol cleaning can be extended to extreme ultraviolet (EUV) masks. In this paper, we report advances being made in nozzle design qualification for optimum snow properties (size, velocity and flux) using Phase Doppler Anemometry (PDA) technique. In addition the two new areas of focus for CO₂ aerosol cleaning i.e. pellicle glue residue removal on optical masks, and ruthenium (Ru) film on EUV masks are presented. Usually, the residue left over after the pellicle has been removed from returned masks (after long term usage/exposure in the wafer fab), requires a very aggressive SPM wet clean, that drastically reduces the available budget for mask properties (CD, phase/transmission). We show that CO₂aerosol cleaning can be utilized to remove the bulk of the glue residue effectively, while preserving the mask properties. This application required a differently designed nozzle to impart the required removal force for the sticky glue residue. A new nozzle was developed and qualified that resulted in PRE in the range of 92-98%. Results also include data on a patterned mask that was exposed in a lithography stepper in a wafer production environment. On EUV mask, our group has experimentally demonstrated that 50 CO₂ cleaning cycles of Ru film on the EUV Front-side resulted in no appreciable reflectivity change, implying that no degradation of the Ru film occurs.

Proceedings Article | 25 September 2010 Paper

Fundamentals and applications of dry CO2 cryogenic aerosol for photomask cleaning

Ivin Varghese, Mehdi Balooch, Charles Bowers

Proceedings Volume 7823, 78232Y (2010) https://doi.org/10.1117/12.877555

KEYWORDS: Carbon dioxide, Photomasks, Particles, SRAF, Aerosols, Cryogenics, Atmospheric particles, Mask cleaning, Personal digital assistants, Extreme ultraviolet

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Proceedings Article | 30 September 2009 Paper

Advances in CO2 cryogenic aerosol technology for photomask post AFM repair

Charles Bowers, Ivin Varghese, Mehdi Balooch, Jaime Rodriguez

Proceedings Volume 7488, 74881R (2009) https://doi.org/10.1117/12.829690

KEYWORDS: Carbon dioxide, Aerosols, SRAF, Cryogenics, Atmospheric particles, Photomasks, Personal digital assistants, Critical dimension metrology, Atomic force microscopy, Contamination

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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 FMA_CO2. 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.

Proceedings Article | 11 May 2009 Paper

Advances in post AFM repair cleaning of photomask with CO2 cryogenic aerosol technology

Charles Bowers, Ivin Varghese, Mehdi Balooch, Werner Brandt

Proceedings Volume 7379, 73791I (2009) https://doi.org/10.1117/12.824295

KEYWORDS: Aerosols, Carbon dioxide, Atmospheric particles, Cryogenics, SRAF, Control systems, Personal digital assistants, Atomic force microscopy, Photomasks, Mask cleaning

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As the mask technology matures, critical printing features and sub-resolution assist features (SRAF) shrink below 100 nm, forcing critical cleaning processes to face significant challenges. These challenges include use of new materials, oxidation, chemical contamination sensitivity, proportionally decreasing printable defect size, and a requirement for a damage-free clean. CO₂ cryogenic aerosol cleaning has the potential to offer a wide process window for meeting these new challenges, if residue adder issues and damage can be eliminated. Some key differentiations of CO₂ cryogenic aerosol cleaning are the non-oxidizing and non-etching properties compared to conventional chemical wet clean processes with or without megasonics. In prior work, the feasibility of CO₂ cryogenic aerosol in post AFM repair photomask cleaning was demonstrated. In this paper, recent advancements of CO₂ cryogenic aerosol cleaning technology are presented, focusing on the traditional problem areas of particle adders, electrostatic discharge (ESD), and mask damage mitigation. Key aspects of successful CO₂ cryogenic aerosol cleaning include the spray nozzle design, CO₂ liquid purity, and system design. The design of the nozzle directly controls the size, density, 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. Adder control can be achieved only through use of highly purified CO₂ and careful materials selection. 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 of adders. The previous damage threshold of 150 nm SRAF structures has been reduced to 70nm and data will be shown indicating 60 nm is possible in the near future. Data on CO₂ tribocharge mitigation, the main cause of ESD, will also be presented and application to current technology nodes discussed.

Proceedings Article | 5 November 2005 Paper

Characterization of photomask surface cleaning with cryogenic aerosol technique

S. Banerjee, C.C. Lin, S. Su, C. Bowers, H.F. Chung, W. Brandt, K. Tang

Proceedings Volume 5992, 59921H (2005) https://doi.org/10.1117/12.632226

KEYWORDS: Particles, Cryogenics, Carbon monoxide, Atmospheric particles, Photomasks, Semiconducting wafers, Aerosols, Silicon, Inspection, Air contamination

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Proceedings Article | 19 October 1994 Paper

Qualification of CO2 jet spray cleaning for use on magnesium-fluoride-protected aluminum coatings for the corrective optics space telescope axial replacement (COSTAR)

John Hagopian, Charles Fleetwood, Ritva Keski-Kuha, Douglas Leviton, Geraldine Wright, Charles Bowers

Proceedings Volume 2261, (1994) https://doi.org/10.1117/12.190154

KEYWORDS: Mirrors, Contamination, Optical coatings, Reflectivity, Carbon dioxide, Optical testing, Surface roughness, Particles, UV optics, Ultraviolet radiation

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Proceedings Article | 1 November 1990 Paper

Contamination removal by CO2 jet spray

Ronald Peterson, Charles Bowers

Proceedings Volume 1329, (1990) https://doi.org/10.1117/12.22599

KEYWORDS: Carbon dioxide, Contamination, Particles, Mirrors, Liquids, Bidirectional reflectance transmission function, Glasses, Contamination control, Control systems, Surface finishing

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