Dr. Warren W. Flack Profile

Dr. Warren W. Flack

Vice President, Applications at Veeco Instruments Inc

SPIE Involvement:

Author

Publications (46)

Proceedings Article | 26 March 2007 Paper

Development and characterization of a 300-mm dual-side alignment stepper

Warren Flack, Emily True, Robert Hsieh, Detlef Fuchs, Ray Ellis

Proceedings Volume 6520, 65202R (2007) https://doi.org/10.1117/12.711609

KEYWORDS: Semiconducting wafers, Optical alignment, Silicon, Packaging, Image sensors, Metrology, Overlay metrology, Lithography, Microelectromechanical systems, Wafer-level optics

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Proceedings Article | 29 March 2006 Paper

Highly re-entrant profiles in a thick photosensitive material for nanotechnology applications

Warren Flack, Ha-Ai Nguyen, Mark Shaw, Manny do Canto

Proceedings Volume 6153, 61534I (2006) https://doi.org/10.1117/12.655721

KEYWORDS: Photoresist materials, Lithography, Photosensitive materials, Scanning electron microscopy, Head, Semiconducting wafers, Photography, Nanotechnology, Photoresist processing, Photoresist developing

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Proceedings Article | 29 March 2006 Paper

A novel photosensitive material for redistribution and stress buffer reduction on 300mm wafers

Warren Flack, Ha-Ai Nguyen, Elliott Capsuto

Proceedings Volume 6153, 61534K (2006) https://doi.org/10.1117/12.655727

KEYWORDS: Semiconducting wafers, Photoresist materials, Scanning electron microscopy, Photography, Lithography, Silicon, Packaging, Sputter deposition, Photosensitive materials, Copper

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Proceedings Article | 10 May 2005 Paper

Dual side lithography measurement, precision, and accuracy

Daniel Schurz, Warren Flack, Robert Hsieh

Proceedings Volume 5752, (2005) https://doi.org/10.1117/12.598861

KEYWORDS: Semiconducting wafers, Metrology, Optical alignment, Lithography, Cameras, Manufacturing, Microelectromechanical systems, Image registration, Calibration, Precision measurement

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Proceedings Article | 4 May 2005 Paper

A comparison of new thick photoresists for solder bumping

Warren Flack, Ha-Ai Nguyen, Mark Neisser, Ernesto Sison, Ping Hung Lu, Bob Plass, Toshimichi Makii, Yoshio Murakami

Proceedings Volume 5753, (2005) https://doi.org/10.1117/12.598469

KEYWORDS: Photoresist materials, Semiconducting wafers, Electroplating, Chemistry, Photoresist developing, Lithography, Reticles, Scanning electron microscopy, Standards development, Packaging

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The performance requirements for ultra-thick photoresists are rapidly increasing with the dramatic growth in lithographic applications that require electroplating processes. Two of the main applications for ultra-thick photoresists are advanced packaging and nanotechnology (MEMS). Flipchip packaging has become widely adopted to address electrical device performance and chip form factor considerations. The growth in the nanotechnology market is driven by a wide range of products, which include accelerometers, ink jet print heads, biomedical sensors and optical switches. The requirements of thick photoresists for solder electroplating are significantly different from typical thin photoresists used in front end of line applications. As the photoresist becomes thicker, processing times increase for many process steps. Photospeed gets slower due to the requirements for more chemical reactions per area of coating. Coating uniformity and edge bead control also become more difficult as photoresist films get thicker and time delay issues between process steps can arise. This result has led to the requirement for special photoresist formulations for thick photoresist films. These are traditionally positive tone DNQ-Novolak materials such as AZ 50XT. Such materials can be designed to work for a particular range of thicknesses, but as the desired thicknesses increases the processing times can become very long for high volume manufacturing. Many new bumping schemes require photoresists in a 60 to 70 μm thickness range. While DNQ-Novolak chemistry can work, there is a desire for faster alternatives to improve total cost of ownership (COO) of the lithography cell. In order to have fast photospeeds and reasonable processing times a chemistry that is very photo efficient is needed. Negative tone cross linking chemistries, which can give tens of thousands of chemical events for one photochemical event, provide excellent photospeed and process times. Positive tone chemically amplified photoresist provide hundreds or thousands of chemical events per photochemical event. They are somewhat slower in photospeed than free radical materials, but still provide reasonable photospeeds. This paper compares the lithography and processing performance of these two newer types of thick film chemistries with the performance of a state of the art DNQ-Novolak thick film photoresist. The lithographic performance of these three ultra-thick positive photoresists were optimized to control critical dimensions (CD), sidewall angles and aspect ratios. The experimental results includes process latitude studies, electroplating performance and stripping performance. The general result is that negative free radical chemistry has the edge in photo-speed and processing times, but positive photoresist is better for stripping and perhaps for process integration.

Proceedings Article | 4 May 2005 Paper

Characterization of 100 micron thick positive photoresist on 300-mm wafers

Warren Flack, Ha-Ai Nguyen, Elliott Capsuto, Kelly Abreau

Proceedings Volume 5753, (2005) https://doi.org/10.1117/12.598208

KEYWORDS: Photoresist materials, Semiconducting wafers, Electroplating, Coating, Plating, Lithography, Packaging, Thin film coatings, Scanning electron microscopy, Photoresist developing

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The widespread adoption of advanced packaging techniques is driven by device performance and chip form factor considerations. Flip chip packaging is currently growing at a thirty percent compound annual rate and it is expected that in the near future over sixty percent of all 300 mm wafers will be bumped. To ensure optimal productivity and cost of ownership it is imperative to provide lithographic equipment and materials that are optimized for these applications. Due to the constantly shrinking bump pitch, it is critical to show excellent CD uniformity across the entire 300 mm wafer surface for feature sizes as small as 70 microns. Flip chip packaging as well as Nanotechnology (MEMS) applications frequently use one or more very thick photoresist layers for electroplating applications. The plating levels require a photosensitive polymer material capable of coating, exposing and electroplating with conventional equipment and standard ancillary process chemicals. Additionally the process times for coating, baking, exposure and development must be considered since these impacts the overall cost of ownership of the lithography cell. For thick photoresist layers the sidewall profile, plating resistance and postplating stripability are important characteristics. This study will characterize a novel single coat, positive tone photoresist (ShinEtsu SIPR 7120-20) used in electroplating levels up to 100 μm thick on 300 mm wafers exposed with the Ultratech Spectrum 300e² stepper and coated and developed with a Steag Hamatech Modutrack system. Process capability is determined by analyzing photoresist film thickness uniformity and critical dimension (CD) control across the wafer. Basic photoresist characterization techniques such as cross sectional SEM analysis are used to establish lithographic capabilities. This study shows excellent adhesion to copper with no surface treatment and no photoresist popping during exposure or post exposure bake (PEB). High aspect ratio, lead-free, solder structures were then electroplated using the optimized photoresist process to demonstrate photoresist durability and stripability.

Proceedings Article | 24 May 2004 Paper

Dual side wafer metrology for micromachining applications

Dan Schurz, Warren Flack, Doug Anberg

Proceedings Volume 5375, (2004) https://doi.org/10.1117/12.535928

KEYWORDS: Semiconducting wafers, Metrology, Optical alignment, Cameras, Lithography, Tolerancing, Calibration, Imaging systems, Image registration, Micromachining

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Proceedings Article | 14 May 2004 Paper

Contrast enhancement materials for thick photoresist applications

Warren Flack, Ha-Ai Nguyen, Jim Buchanan, Elliott Capsuto, Alan Marks

Proceedings Volume 5376, (2004) https://doi.org/10.1117/12.556842

KEYWORDS: Photoresist materials, Lithography, Semiconducting wafers, Packaging, Photoresist developing, Microelectromechanical systems, Scanning electron microscopy, Thin film coatings, Photomasks, Photography

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Proceedings Article | 17 December 2003 Paper

Defect printability for high-exposure dose advanced packaging applications

Max Mikles, Warren Flack, Ha-Ai Nguyen, Dan Schurz

Proceedings Volume 5256, (2003) https://doi.org/10.1117/12.518160

KEYWORDS: Photoresist materials, Pellicles, Packaging, Reticles, Semiconducting wafers, Lithography, Particles, Electroplating, Semiconductors, Saturn

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Pellicles are used in semiconductor lithography to minimize printable defects and reduce reticle cleaning frequency. However, there are a growing number of microlithography applications, such as advanced packaging and nanotechnology, where it is not clear that pellicles always offer a significant benefit. These applications have relatively large critical dimensions and require ultra thick photoresists with extremely high exposure doses. Given that the lithography is performed in Class 100 cleanroom conditions, it is possible that the risk of defects from contamination is sufficiently low that pellicles would not be required on certain process layer reticles. The elimination of the pellicle requirement would provide a cost reduction by saving the original pellicle cost and eliminating future pellicle replacement and repair costs. This study examines the imaging potential of defects with reticle patterns and processes typical for gold-bump and solder-bump advanced packaging lithography. The test reticle consists of 30 to 90 μm octagonal contact patterns representative of advanced packaging reticles. Programmed defects are added that represent the range of particle sizes (3 to 30 μm) normally protected by the pellicle and that are typical of advanced packaging lithography cleanrooms. The reticle is exposed using an Ultratech Saturn Spectrum 300e² 1X stepper on wafers coated with a variety of ultra thick (30 to 100 μm) positive and negative-acting photoresists commonly used in advanced packaging. The experimental results show that in many cases smaller particles continue to be yield issues for the feature size and density typical of advanced packaging processes. For the two negative photoresists studied it appears that a pellicle is not required for protection from defects smaller than 10 to 15 μm depending on the photoresist thickness. Thus the decision on pellicle usage for these materials would need to be made based on the device fabrication process and the cleanliness of a fabrication facility. For the two positive photoresists studied it appears that a pellicle is required to protect from defects down to 3 μm defects depending on the photoresist thickness. This suggests that a pellicle should always be used for these materials. Since a typical fabrication facility would use both positive and negative photoresists it may be advantageous to use pellicles on all reticles simply to avoid confusion. The cost savings of not using a pellicle could easily be outweighed by the yield benefits of using one.

Proceedings Article | 12 June 2003 Paper

Characterization of an ultra-thick positive photoresist for electroplating applications

Warren Flack, Ha-Ai Nguyen, Elliott Capsuto

Proceedings Volume 5039, (2003) https://doi.org/10.1117/12.483748

KEYWORDS: Photoresist materials, Copper, Electroplating, Scanning electron microscopy, Semiconducting wafers, Photography, Lithography, Packaging, Plating, Reticles

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Proceedings Article | 27 December 2002 Paper

Pellicle life-testing for high-exposure dose applications

Dan Schurz, Warren Flack

Proceedings Volume 4889, (2002) https://doi.org/10.1117/12.467758

KEYWORDS: Pellicles, Reticles, Photoresist materials, Mercury, Semiconducting wafers, Packaging, Lithography, Lithographic illumination, Glasses, Excimer lasers

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There are an increasing number of microlithography applications such as advanced packaging, nanotechnology and thin film head production that require the use of thick photoresist materials. The exposure dose requirements for these applications dramatically increase as the photoresist thickness increases. For example, some positive acting novolak photoresists require exposures in excess of 5000 mJoules/cm² for 100 μm thick films. When a single reticle is used to pattern many wafers, a significant amount of light and heat energy is transferred from the lithography tool illumination source to the pellicle protecting the reticle image. In high volume production environments, a pellicle can be subjected to accumulated dosages exceeding 500 kJoules/cm² within a matter of weeks. Because thick photoresist applications benefit from using 1X broadband steppers with high wafer plane irradiance, life-testing results were reviewed for broadband pellicles designed for maximum transmission at g, h and i-line wavelengths of Hg. Historically, pellicle lifetime testing was typically carried out only to approximately 500 kJoules/cm² . While this test limit may have been sufficient for thin photoresist applications used in semiconductor applications, longer lifetime studies are required to determine pellicle durability for thick photoresist applications. In this study, life testing was performed on multiple pellicle films designed for broadband illumination, including nitrocellulose, cellulose acetate, cellulose ester and fluoropolymer films. Spectroscopic transmission at g, h and i-line was first measured on unexposed pellicles. The pellicles were attached to test reticles and exposed to high-energy doses on an Ultratech broadband stepper, accumulating up to 3000 kJoules/cm² . Transmission was periodically re-measured and the pellicle films were visually inspected for color change and any apparent physical damage. Results were compared to the expected optical properties for each film type, and recommendations are provided for the most appropriate fil type for high-energy applications. Of the six pellicles tested, the two fluoropolymer films showed substantially better transmission stability than the cellulose based films. Discoloration occurred on the cellulose films over the chrome to glass transition area of the test reticle field suggesting that heat in the chrome surface affects the chemical structure of the pellicle films, thereby changing their transmission properties.

Proceedings Article | 24 July 2002 Paper

Characterization of a novel photoresist redistribution material for advanced packaging applications

Warren Flack, Ha-Ai Nguyen, Elliott Capsuto

Proceedings Volume 4690, (2002) https://doi.org/10.1117/12.474198

KEYWORDS: Photoresist materials, Scanning electron microscopy, Lithography, Semiconducting wafers, Packaging, Dielectrics, Reticles, Photography, Photomasks, Saturn

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Proceedings Article | 11 March 2002 Paper

Simulation study of reticle enhancement technology applications for 157-nm lithography

Dan Schurz, Warren Flack, Linard Karklin

Proceedings Volume 4562, (2002) https://doi.org/10.1117/12.458255

KEYWORDS: Lithography, Reticles, Resolution enhancement technologies, Optical proximity correction, Binary data, Phase shifting, Photomasks, Optical lithography, Photoresist materials, Manufacturing

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Proceedings Article | 14 September 2001 Paper

Process improvements for ultrathick photoresist using a broadband stepper

Warren Flack, Ha-Ai Nguyen, Elliott Capsuto

Proceedings Volume 4346, (2001) https://doi.org/10.1117/12.435796

KEYWORDS: Photoresist materials, Photoresist developing, Lithography, Semiconducting wafers, Packaging, Electroplating, Micromachining, Scanning electron microscopy, Reticles, Plating

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Proceedings Article | 14 September 2001 Paper

Characterization study of an aqueous developable photosensitive polyimide on 300-mm wafers

Warren Flack, Scott Kulas, Craig Franklin

Proceedings Volume 4346, (2001) https://doi.org/10.1117/12.435795

KEYWORDS: Semiconducting wafers, Photoresist materials, Scanning electron microscopy, Lithography, Photomasks, Reticles, Photoresist developing, Optical lithography, Metals, Etching

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The advent of 300 mm wafer processing for semiconductor manufacturing has had a great impact on the development of photolithographic materials, equipment and associated processes. At the same time advanced packaging techniques for these semiconductor devices are making strides for smaller, faster and lower cost parts with improved reliability. Photosensitive polyimides are used for passivation stress buffer relief and soft error protection on almost all memory devices such as DRAM as well as final passivation layers for subsequent interconnect bumping operations on most of today's advanced microprocessors. For processing simplicity and total cost of ownership, it is desirable to use an aqueous developable polyimide to maintain compatibility with standard photoresist processes. This study will investigate the feasibility of processing photosensitive polyimides on 300 mm wafers. The performance of a commercially available, positive acting, aqueous developable polyimide is examined at a thickness appropriate for logic devices. A broadband stepper is utilized since polyimides are highly aromatic polymers that strongly absorb UV light below 350 nm. This stepper exposes photosensitive films using mercury vapor spectrum output from 390 nm to 450 nm (g and h-line) and allows rapid exposure of both broadband as well as narrow spectral sensitive films. The system has been optimized for thick photoresists and polyimides and uses a combination of low numerical aperture with maximum wafer level intensity to achieve well formed images in thick films. Process capability for 300 mm wafers is determined by analyzing polyimide film thickness uniformity and critical dimension (CD) control across the wafer. Basic photoresist characterization techniques such as cross sectional SEM analysis, process linearity and process windows are also used to establish lithographic capabilities. The trade-offs for various process capability windows are reviewed to determine the optimum process conditions for different polyimide applications.

Proceedings Article | 22 January 2001 Paper

High-optical-density photomasks for large exposure applications

Dan Schurz, Warren Flack, Makoto Nakamura

Proceedings Volume 4186, (2001) https://doi.org/10.1117/12.410770

KEYWORDS: Reticles, Photoresist materials, Semiconducting wafers, Chromium, Photomasks, Absorption, Scanning electron microscopy, Ultraviolet radiation, Spectrophotometry, Absorbance

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Proceedings Article | 5 July 2000 Paper

Development of 157-nm small-field and mid-field microsteppers

Ron Miller, Paul Bischoff, Roger Sumner, Stephen Bowler, Warren Flack, Galen Fong

Proceedings Volume 4000, (2000) https://doi.org/10.1117/12.388998

KEYWORDS: Photoresist materials, Lithography, Photoresist developing, Reticles, Optical lithography, Silica, Objectives, Semiconducting wafers, Lens design, Photomasks

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Proceedings Article | 23 June 2000 Paper

Process characterization of an aqueous developable photosensitive polyimide on a broadband stepper

Warren Flack, Scott Kulas, Craig Franklin

Proceedings Volume 3999, (2000) https://doi.org/10.1117/12.388329

KEYWORDS: Semiconducting wafers, Photoresist materials, Lithography, Scanning electron microscopy, Reticles, Standards development, Manufacturing, Photomasks, Optical lithography, Photoresist developing

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The number of lithographic applications that require the use of photosensitive polyimides is rapidly increasing. The major applications for photosensitive polyimides include flip chip bumping, advanced packaging, passivation stress buffer relief and interlevel dielectric films. The thickness requirements for these applications can vary from less than 1 micron to more than 20 microns. For processing simplicity and total cost of ownership, it is desirable to use an aqueous developable polyimide to maintain compatibility with standard photoresist processes. Optical steppers offer significant advantages for processing thick photosensitive polyimides due to the tighter overlay and improved critical dimension (CD) control possible with these lithography tools versus contact printers or full wafer scanners. A stepper has an additional advantage with thick polyimide structures since the focus can be adjusted at various levels into the film, which will result in improved wall angles and enhanced aspect ratios. For this study the performance of a commercially available, positive acting, aqueous developable polyimide is examined over a range of thicknesses using a novel broadband exposure system. This stepper exposes photosensitive films using the full mercury vapor spectrum output from 350 nm to 450 nm (g, h and i line) and allows rapid exposure of both broadband as well as narrow spectral sensitive films. The system has been optimized for thick photoresists and polyimides and uses a combination of low numerical aperture with maximum wafer level intensity to achieve well formed images in thick films yet offers the advantages of tighter CD control and tight overlay inherent in projection optics. Basic photoresist characterization techniques established for thin films in IC manufacturing are applied to the photosensitive polyimide films. Cross sectional SEM analysis, process linearity and process windows are used to establish relative lithographic capabilities for different polyimide thicknesses and stepper exposure wavelengths. The trade-offs for each of the various process capability windows are reviewed to determine the optimum process conditions for different polyimide applications.

Proceedings Article | 23 June 2000 Paper

Process characterization of an ultrathick strippable photoresist using a broadband stepper

Warren Flack, Scott Kulas, David Minsek

Proceedings Volume 3999, (2000) https://doi.org/10.1117/12.388331

KEYWORDS: Photoresist materials, Semiconducting wafers, Lithography, Scanning electron microscopy, Photoresist developing, Saturn, Photomasks, Micromachining, Chemistry, Reticles

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Proceedings Article | 30 December 1999 Paper

Effects of mask error factor on process window capability

Dan Schurz, Warren Flack, Simon Cohen, Thomas Newman, Khiem Nguyen

Proceedings Volume 3873, (1999) https://doi.org/10.1117/12.373317

KEYWORDS: Critical dimension metrology, Reticles, Cadmium, Photomasks, Semiconducting wafers, Photoresist materials, Lithography, Computer aided design, Tolerancing, Scanning electron microscopy

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Proceedings Article | 30 August 1999 Paper

Thick photoresist imaging using a three-wavelength exposure stepper

Bradley Todd, Warren Flack, Sylvia White

Proceedings Volume 3874, (1999) https://doi.org/10.1117/12.361238

KEYWORDS: Photoresist materials, Semiconducting wafers, Reticles, Lithography, Scanning electron microscopy, Manufacturing, Photomasks, Photosensitive materials, Micromachining, Optical lithography

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Proceedings Article | 11 June 1999 Paper

Process characterization of 100-um-thick photoresist films

Warren Flack, Sylvia White, Bradley Todd

Proceedings Volume 3678, (1999) https://doi.org/10.1117/12.350230

KEYWORDS: Photoresist materials, Scanning electron microscopy, Semiconducting wafers, Lithography, Microelectromechanical systems, Manufacturing, Photoresist developing, Reticles, Photomasks, Saturn

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Proceedings Article | 18 December 1998 Paper

Characterization of OPC masks for thin-film head pole trimming applications

Warren Flack, Sylvia White, Calvin Ho, Dan Schurz, Fabio Consentino

Proceedings Volume 3546, (1998) https://doi.org/10.1117/12.332846

KEYWORDS: Photoresist materials, Optical proximity correction, Reticles, Head, Photomasks, Computer aided design, Manufacturing, Lithography, Thermal weapon sites, Semiconducting wafers

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Proceedings Article | 1 September 1998 Paper

Characterization of ultrathick photoresists for MEMS applications using a 1X stepper

Warren Flack, Warren Fan, Sylvia White

Proceedings Volume 3512, (1998) https://doi.org/10.1117/12.324073

KEYWORDS: Photoresist materials, Lithography, Microelectromechanical systems, Scanning electron microscopy, Semiconducting wafers, Photomasks, Saturn, Manufacturing, Reticles, Critical dimension metrology

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There is a growing interest in using optical steppers for Micromachining and Microfabrication (MEMS) applications due to the tighter overlay and improved critical dimension (CD) control possible with these lithography tools versus a contact printer or full wafer scanner. MEMS applications frequently require the use of ultra-thick photoresists which can easily exceed fifty microns. Extremely large structure heights and high aspect ratios are often required for micro- electrodeposition of mechanical components such as coils, cantilevers and valves. A stepper has an additional advantage with these structures since the focus can be adjusted at various levels into a thick photoresist, which will result in improved wall angles and enhanced aspect ratios. The patterning of high aspect ratio structures in these ultra- thick photoresist films is extremely challenging. The aspect ratios easily exceed those encountered in submicron lithography for standard integrated circuit (IC) manufacturing. In addition, the specific photoresist optical properties and develop characteristics degrade the CD control for these ultra-thick films. The bulk absorption effect of the photoresist reduces the effective dose at the bottom of the film. This effect is exacerbated by the isotropic wet development process, which produces sloped profiles. Unlike thin photoresist for IC manufacturing, lithography modeling and characterization tools are not available for ultra-thick photoresist films. For this study the performance of several commercially available positive and negative ultra-thick photoresists is examined at a thickness of fifty microns using both high throughput i-line and gh-line lithography systems optimized for thick photoresist processing. The photoresists used in this study are selected to represent the full range of available chemistries available from different suppliers. Basic photoresist characterization techniques created for thin films are applied to the ultra-thick photoresist films. Cross sectional SEM analysis, process linearity and Bossung plots are used to establish relative lithographic capabilities of each photoresist. The trade-offs between the various photoresist chemistries are reviewed and compared with the process requirements for high aspect ratio applications.

Proceedings Article | 29 June 1998 Paper

Optimization and characterization of ultrathick photoresist films

Warren Flack, Warren Fan, Sylvia White

Proceedings Volume 3333, (1998) https://doi.org/10.1117/12.312452

KEYWORDS: Photoresist materials, Lithography, Scanning electron microscopy, Reticles, Saturn, Semiconducting wafers, Microelectromechanical systems, Manufacturing, Critical dimension metrology, Photoresist developing

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There are in increasing number of advanced lithographic technologies that require photoresist film thickness in excess of twenty microns. For example, suppliers of microprocessors are migrating to flip chip packaging because of bond pad limitations. The flip chip application can require photoresist materials as thick as 125 micrometers for the bump-bonding step. Another application that requires ultra- thick photoresist films is micromachining. Extremely large structure heights are frequently required for micro- electrodeposition of the mechanical components such as coils, cantilevers and valves. These applications can require photoresist in excess of a hundred microns thickness. The patterning of high aspect ratio structures in these ultra-thick photoresist films is extremely challenging. The aspect ratios easily exceed those encountered in submicron lithography for standard integrated circuit (IC) manufacturing. In addition, the specific photoresist optical properties and develop characteristics degrade the critical dimension control for these ultra-thick films. The bulk absorption effect of the photoresist reduces the effective dose at the bottom of the film. This effect is exacerbated by the isotropic wet development process which produces sloped profiles. Unlike thin photoresist for IC manufacturing, lithography modeling and characterization are not readily available for ultra-thick photoresist films. The performance of several commercially available positive and negative ultra-thick photoresists is examined over a thickness range of 20 to 100 micrometers . This paper is primarily focused on the 25 micrometers film thickness using both high throughput i-line and gh-line lithography systems optimized for thick film processing. The various photoresists used in this study were selected to represent the full range of available chemistries from multiple suppliers. Basic photoresist characterization techniques for thin films are applied to the ultra-thick photoresist films. The cross sectional SEM analysis and Bossung plots were used to establish relative lithographic capabilities of each photoresist. The trade-offs between the various photoresist chemistries is reviewed and compared with the process requirements for the various applications. A future paper will discus the capabilities of these same photoresists at both 50 and 100 micrometers film thicknesses.

Proceedings Article | 8 June 1998 Paper

Reticle defect printability and photoresist modeling of contact structures

Warren Flack, Dan Schurz, Richard Lee, Calvin Ho

Proceedings Volume 3332, (1998) https://doi.org/10.1117/12.308773

KEYWORDS: Photoresist materials, Reticles, Opacity, Lithography, Semiconducting wafers, Computer aided design, Optical lithography, 3D modeling, Optical proximity correction, Standards development

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Proceedings Article | 7 July 1997 Paper

Advanced simulation techniques for thick photoresist lithography

Warren Flack, Gary Newman, Douglas Bernard, Juan Rey, Yuri Granik, Victor Boksha

Proceedings Volume 3049, (1997) https://doi.org/10.1117/12.275881

KEYWORDS: Photoresist materials, Photoresist developing, Lithography, Semiconducting wafers, Optical lithography, Thin films, Refractive index, Computer simulations, Critical dimension metrology, Energy coupling

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Proceedings Article | 7 July 1997 Paper

Simulation of subhalfmicron-mask defect printability at 1X reticle magnification

Warren Flack, Gary Newman, Dan Schurz

Proceedings Volume 3050, (1997) https://doi.org/10.1117/12.275910

KEYWORDS: Reticles, Opacity, Semiconducting wafers, Critical dimension metrology, Data modeling, Lithography, Optical proximity correction, 3D metrology, Optical simulations, Photoresist materials

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There has been considerable attention given to the printability of reticle defects and their impact on wafer yields. Over the last year the printability risk from small defects increased due to the wider application of optical proximity correction structures and the inclusion of more phase shifting retictles. There have been several simulation studies on the printability of sub-halfmicron defects using lens and illumination parameters of 5X reduction steppers. Since submicron 1X projection systems are being incorporated into numerous fabricant lines, there is a clear need to determine if these system show similar sensitivity to sub- halfmicron defects as reduction steppers. Earlier experimental work examined the printability of several classes of sub-halfmicron 25 micrometers defects on a submicron 1X stepper. To extend this work, a 3D optical lithography simulation tool has been employed to predict the printablity of various reticle defect scenarios. Experimental data was used to validate the 3D simulator by comparing modeling data to SEM measurements of wafers exposed with a reticle containing programmed clear pinhole and opaque pindot defects. A statistically designed simulation study was performed to quantify the critical dimension variation resulting from defects of varying size, proximity to a feature edge and variation in the pitch of the impacted line/space features. An additional statistically designed simulation was then use to predict the printability behavior of defects relative to different features sizes over a range of numerical aperture and partial coherence settings applicable to a 1X lens design. Finally, the impact of defect length and width on printability were characterized for rectangular defects over a range of sizes. Overall, this analysis enhances the understanding of the relationship between reticle defects and 1X projection optics and allows for determination of optical reticle defect specifications for cost effective lithography applications.

Proceedings Article | 12 February 1997 Paper

Printability of 1X reticle defects for submicron design rules

Dan Schurz, Warren Flack, Gary Newman

Proceedings Volume 3236, (1997) https://doi.org/10.1117/12.301217

KEYWORDS: Reticles, Opacity, Lithography, Semiconducting wafers, Scanning electron microscopy, Computer aided design, Critical dimension metrology, Photoresist materials, Optical lithography, Optical simulations

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As the push for improved resolution in wafer lithography intensifies and 0.18 micrometer devices are nearing production, the potential impact of subhalf micron reticle defects has become a growing concern. There have been several studies on the printability of subhalf-micron defects on high resolution reduction photolithography equipment. These studies have been extended to 1X lithography systems and more recently to advanced sub-micron 1X steppers. Previous studies have indicated that 0.20 micrometer opaque and 0.25 micrometer clear pinhole defects were at the margins of adversely impacting 0.65 micrometer lithography on a 1X stepper. However, due to the limited number of defects at these sizes on the reticle, definitive conclusions on printability could not be drawn. An additional study, using a three dimensional (3D) optical lithography simulation program, has shown defect size, proximity to an adjacent feature, and feature pitch to be significant factors contributing to reticle defect printability. Using the simulation findings as a guide, a new reticle was designed to contain an increased number of clear pinhole and opaque defects in the 0.15 to 0.30 micrometer range located in multiple pitches of both horizontal and vertical line/space pairs. Defect printability was determined using a 1X i-line projection stepper with focus and exposure optimized for nominal critical dimensions of 0.65 micrometer. The reticle and wafer defects were measured using low voltage SEM metrology. Simulation and experimental results have shown that pitch is the most significant contributor in the printability of clear pinhole, opaque, square and aspect ratio defects. In general, the impact of defect proximity to an adjacent feature is less extreme than the effect of pitch, but is more pronounced for clear pinhole defects. This study suggests that simulation can be a useful tool to help lithographers understand the behavior of reticle defects for particular layout design parameters. Consequently, simulation can be used to develop realistic reticle defect specifications with mask vendors, and improve cost-effectiveness. Defect printability simulation can also be used to predict the effect of known defects on existing reticles to determine if these reticles should be used for manufacturing.

Proceedings Article | 27 December 1996 Paper

Subhalf-micron mask defect detectability and printability at 1X reticle magnification

Dan Schurz, Warren Flack, Gary Newman

Proceedings Volume 2884, (1996) https://doi.org/10.1117/12.262801

KEYWORDS: Reticles, Semiconducting wafers, Computer aided design, Inspection, Opacity, Manufacturing, Scanning electron microscopy, Lithography, Photomasks, Defect detection

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Proceedings Article | 7 June 1996 Paper

Investigation of the properties of photosensitive polyimide films

Warren Flack, Gary Flores, Lorna Christensen, Gary Newman

Proceedings Volume 2726, (1996) https://doi.org/10.1117/12.240970

KEYWORDS: Lithography, Semiconducting wafers, Photoresist materials, Manufacturing, Chemistry, Scanning electron microscopy, Optical lithography, Photoresist developing, Critical dimension metrology, Process modeling

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Modem package designs generate a large amount of stress on the die which can be controlled using a thick film of polyimide over the passivation layer. Polyimide film thicknesses in excess of twenty microns at exposure are becoming common for very thin packages. The standard polyimide lithographic process frequently utilizes a trilayer film consisting of an adhesion layer, a polyimide film, and photoresist. A major advance in polyimide technology occurred with the introduction of photosensitive polyimide materials. These materials reduce the total number of process steps in the polyimide process. They also offer the opportunity to combine the passivation and polyimide lithography steps into one process level resulting in significant process simplification and manufacturing cost reduction. Consequently, there is a rapid increase in the use of photosensitive polyimides in the semiconductor industry. There are a number of important issues associated with photosensitive polyimide processing. Because most photosensitive polyimides are negative tone, residual film formation has a major impact on resolution and the usable process window. The high exposure doses required for thicker polyimide films exacerbates the residual film problem. Also, resolving small features such as fuse windows in DRAMs is frequently required in thick photosensitive polyimide layers. These small features result in polyimide height-to-linewidth aspect ratios that are comparable to many photoresist applications. Because of these requirements, photosensitive polyimide applications could benefit from detailed process characterization to enhance resolution and increase process latitude. Unfortunately, there is scant literature pertaining to lithographic performance and lithographic process modeling for photosensitive polyimide films. An extension of basic photoresist characterization techniques for thin films can be applied to thick photosensitive polyimide processes. The develop rate characteristics and lithographic performance for several commercial photosensitive polyimide products were studied at a thickness of 12 microns. Cross sectional SEM analysis, Bossung plots, and film retention plots are used to establish relative lithographic capabilities. These experimental results are used to study the effects of polyimide physical and chemical properties on lithographic performance.

Proceedings Article | 21 May 1996 Paper

Efficient overlay optimization of stepper correctables

Warren Flack, Susan Avlakeotes, David Chen, Gary Flores

Proceedings Volume 2725, (1996) https://doi.org/10.1117/12.240101

KEYWORDS: Data modeling, Overlay metrology, Semiconducting wafers, Diffractive optical elements, Systems modeling, Metrology, Error analysis, Statistical analysis, Statistical modeling, Lithography

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Proceedings Article | 26 May 1995 Paper

Application of pattern recognition in mix-and-match lithography

Warren Flack, Gary Flores, Thinh Tran

Proceedings Volume 2440, (1995) https://doi.org/10.1117/12.209317

KEYWORDS: Optical alignment, Semiconducting wafers, Lithography, Pattern recognition, Cameras, Reliability, Reticles, Manufacturing, Target recognition, CCD cameras

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Proceedings Article | 22 May 1995 Paper

Monitoring and diagnostic techniques for control of overlay in steppers

Gary Flores, Warren Flack, Susan Avlakeotes, Mark Merrill

Proceedings Volume 2439, (1995) https://doi.org/10.1117/12.209193

KEYWORDS: Semiconducting wafers, Overlay metrology, Lithography, Statistical analysis, Process control, Manufacturing, Diagnostics, Optical lithography, Metrology, Optical alignment

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Proceedings Article | 7 December 1994 Paper

Reticle correction technique to minimize lens distortion effects

Warren Flack, Gary Flores, Alan Walther, Manny Ferreira

Proceedings Volume 2322, (1994) https://doi.org/10.1117/12.195821

KEYWORDS: Reticles, Distortion, Overlay metrology, Lithography, Error analysis, Semiconducting wafers, Photomask technology, Manufacturing, Metrology, Photomasks

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Proceedings Article | 17 May 1994 Paper

Optimized registration model for 2:1 stepper field matching

Warren Flack, Gary Flores, Joseph Pellegrini, Mark Merrill

Proceedings Volume 2197, (1994) https://doi.org/10.1117/12.175465

KEYWORDS: Semiconducting wafers, Lithography, Overlay metrology, Data modeling, Systems modeling, Optical alignment, Error analysis, Composites, Algorithm development, Instrument modeling

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Proceedings Article | 16 May 1994 Paper

Investigation of the properties of thick photoresist films

Gary Flores, Warren Flack, Elizabeth Tai

Proceedings Volume 2195, (1994) https://doi.org/10.1117/12.175386

KEYWORDS: Photoresist materials, Photoresist developing, Lithography, Critical dimension metrology, Process modeling, Semiconductors, Photoresist processing, Absorption, Picture Archiving and Communication System, Systems modeling

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Proceedings Article | 8 August 1993 Paper

Photoresist thin-film effects on alignment process capability

Gary Flores, Warren Flack

Proceedings Volume 1927, (1993) https://doi.org/10.1117/12.150476

KEYWORDS: Optical alignment, Photoresist materials, Semiconducting wafers, Metals, Coating, Thin film coatings, Signal detection, Lithography, Error analysis, Optical lithography

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Proceedings Article | 8 August 1993 Paper

Lithographic performance of a new generation i-line optical system: a comparative analysis

Gary Flores, Warren Flack, Lynn Dwyer

Proceedings Volume 1927, (1993) https://doi.org/10.1117/12.150487

KEYWORDS: Lithography, Photoresist materials, Critical dimension metrology, Semiconducting wafers, Manufacturing, Thin films, Optical lithography, Lithographic illumination, Image processing, Optics manufacturing

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Proceedings Article | 8 August 1993 Paper

Overlay distortions in wafer-scale integration lithography

Warren Flack

Proceedings Volume 1927, (1993) https://doi.org/10.1117/12.150451

KEYWORDS: Lithography, Optical alignment, Semiconducting wafers, Error analysis, Optics manufacturing, Integrated circuits, Optical lithography, Overlay metrology, Electron beam lithography, Metals

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Proceedings Article | 26 March 1993 Paper

Chrome dry-etching for photomask fabrication

Warren Flack, Ken Tokunaga, Kenneth Edwards

Proceedings Volume 1809, (1993) https://doi.org/10.1117/12.142153

KEYWORDS: Etching, Photomasks, Dry etching, Semiconducting wafers, Reticles, Wet etching, Photoresist processing, Oxides, Lithography, Quartz

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Proceedings Article | 9 July 1992 Paper

Mix-and-match lithography in a manufacturing environment

Warren Flack, David Dameron, Valerie Alameda, Ghassan Malek

Proceedings Volume 1671, (1992) https://doi.org/10.1117/12.136008

KEYWORDS: Lithography, Distortion, Semiconducting wafers, Wafer-level optics, Optical alignment, Overlay metrology, Error analysis, Electron beam lithography, Reticles, Optics manufacturing

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Proceedings Article | 1 June 1992 Paper

Lithographic chip identification: meeting the failure analysis challenge

Lynn Perkins, Kevin Riddell, Warren Flack

Proceedings Volume 1673, (1992) https://doi.org/10.1117/12.59819

KEYWORDS: Reticles, Semiconducting wafers, Manufacturing, Process control, Integrated circuits, Optical alignment, Inspection, Failure analysis, Metrology, Lithography

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Proceedings Article | 1 June 1992 Paper

Characterization of mask fabrication for submicron geometries using a shaped vector electron-beam system

Warren Flack, David Dameron, Richard Mann, Valerie Alameda

Proceedings Volume 1674, (1992) https://doi.org/10.1117/12.130341

KEYWORDS: Reticles, Etching, Photomasks, Mask making, Phase shifting, Critical dimension metrology, Optical lithography, Dry etching, Optical alignment, Semiconducting wafers

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Proceedings Article | 1 August 1991 Paper

Mix-and-match lithography for half-micrometer technology

Warren Flack, David Dameron

Proceedings Volume 1465, (1991) https://doi.org/10.1117/12.47353

KEYWORDS: Lithography, Optical alignment, Semiconducting wafers, Distortion, Wafer-level optics, X-ray lithography, Electron beam lithography, Overlay metrology, Manufacturing, Reticles

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Proceedings Article | 1 June 1990 Paper

Evaluation of a silicon trench alignment target strategy

Gary Flores, Warren Flack

Proceedings Volume 1264, (1990) https://doi.org/10.1117/12.20191

KEYWORDS: Metals, Optical alignment, Silicon, Signal processing, Oxides, Reticles, Dielectrics, Silicon films, Composites, Optical lithography

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Showing 5 of 46 publications

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