Dr. Qiang Wu Profile

Dr. Qiang Wu

Development Staff Engineer at IBM Corp

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Publications (7)

Proceedings Article | 28 May 2004 Paper

Effect of the effective resist diffusion length to the photolithography at 65- and 45-nm nodes: a study with simple and accurate analytical equations

Qiang Wu, Scott Halle, Zengqin Zhao

Proceedings Volume 5377, (2004) https://doi.org/10.1117/12.544255

KEYWORDS: Diffusion, Photomasks, Optical lithography, Semiconducting wafers, Lithography, Phase shifting, Critical dimension metrology, Image processing, Photoresist processing, Diffraction

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As the current photolithography moves toward the 65 and 45 nm nodes, resist blur, which is now around 50 to 90 nm full width at half maximum (FWHM), starts to limit the printability of narrow pitches by lowering image contrast, increasing mask error factor (MEF), and changing critical dimension (CD) through pitch behavior. Since such resist blur is known to originate from acid and base diffusion, which is an important process for chemical amplification, the reduction of such blur may affect the resist performance. Therefore, knowing how much diffusion can be tolerated at any given lithographic condition is critical to the success of photolithography at the 65 and 45 nm nodes. In this paper, we present a systematic study of the effect of the resist diffusion with a series of simple and accurate analytic equations and experimental data for the 193 nm lithography. We also extend our predictions to the 193 nm immersion lithography. We first show a simple way to accurately measure the effective resist diffusion length through the regular wafer exposure method for many typical resists. We then show a method to accurately quantify the contrast reduction due to such resist diffusion for both alternating phase shifting masks (Alt-PSM) and attenuated phase shifting masks (Att-PSM). We conclude that the contrast reduction is very significant with typical 193 nm resists, which have diffusion lengths of around 30 to 40 nm. In the study, we found that the mask error factor (MEF), though dependent on the illumination condition, is a strong function of the resist diffusion length at any given illumination condition. For example, in the alt-PSM case, the MEF is almost entirely determined by the resist diffusion. In the att-PSM case, however, the MEF is only partially dependent on the resist diffusion length, about 50%. In fact, a short diffusion length of less than 20 nm will be required to extend its litho-worthiness to the 45 nm node with contrast levels comparable to the current ones. Plots of the contrast and MEF through pitch for both alt-PSM and att-PSM for various diffusion lengths under typical lithographic conditions will be presented. Experimental verification of the above analytical equations will be presented.

Proceedings Article | 28 May 2004 Paper

BEOL lithography for early development at the 65-nm node

Ronald DellaGuardia, Ranee Kwong, Wenjie Li, Peggy Lawson, Martin Burkhardt, Ioana Grauer, Qiang Wu, M. Angyal, H. Hichri, Ian Melville, K. Kumar, Y. Lin, Steven Holmes, R. Varanasi, T. Spooner, D. McHerron

Proceedings Volume 5377, (2004) https://doi.org/10.1117/12.544238

KEYWORDS: Lithography, Etching, Photomasks, Semiconducting wafers, Metals, Critical dimension metrology, Silicon, Image processing, Back end of line, Finite element methods

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Proceedings Article | 26 June 2003 Paper

Scaling rules of phase error control for the manufacturing of alternating phase-shifting masks for 193-nm photolithography and beyond

Qiang Wu, Scott Halle, Scott Bukofsky, Shahid Butt, Michael Hibbs

Proceedings Volume 5040, (2003) https://doi.org/10.1117/12.485504

KEYWORDS: Photomasks, Critical dimension metrology, Diffraction, Lithography, Error control coding, Phase shifting, Control systems, Tolerancing, Optical lithography, Phase shifts

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The use of alternating phase shifting masks (alt-PSM) can significantly improve lithographic process windows. However, the existence of phase error between the nominal 0 and 180 degree phase regions can cause printed lines to shift laterally toward each other in pairs at image planes away from the best focus. Such asymmetry, especially evident with small ground rules, challenges both overlay and critical dimension (CD) control. To minimize such effect, tight control in phase angle has been implemented, which contributes to the higher fabrication cost for an alt-PSM. Since the effect of the phase error varies with different lithographic conditions, knowing how much phase control is necessary for a given lithographic situation becomes essential to the reduction of the mask fabrication cost. Although this phenomenon has been studied in the past with a number of simulations and experiments, a systematic understanding of its mechanism, especially its interaction with CD and numerical aperture has not been reported. This paper explores the theoretical relationship between phase error and important parameters of photolithographic processes, such as CD, numerical apertures (NA), and overlay tolerance. A simple equation of the phase error is developed, which indicates that the effect of the phase error is inversely proportional to both phase error and defocus. We have compared the predictions of this theory to our first experimental results from a test mask and a good agreement is found. Based on this theory, we develop the quantity “tolerable phase error” relating the effect of the phase error to the CD, pitch, and depth of focus of the imaging system. We have found that for a system with depth of focus of +/- 300 nm, a phase error control about 2 degrees is necessary to realize a line shift control of less than 2.5% of the CD for the most aggressive feature size at any NA. We also note that the control of phase error can be relaxed at high NA. Calculations for 193 nm as well as 157 nm lithography are presented.

Proceedings Article | 16 July 2002 Paper

Ultrafast wafer alignment simulation based on thin film theory

Qiang Wu, Gary Williams, Byeong Kim, Jay Strane, Timothy Wiltshire, Eric Lehner, Hiroyuki Akatsu

Proceedings Volume 4689, (2002) https://doi.org/10.1117/12.473475

KEYWORDS: Optical alignment, Imaging systems, Signal processing, Photomasks, Thin films, Semiconducting wafers, Diffraction, Image segmentation, Lithography, Light scattering

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Proceedings Article | 22 August 2001 Paper

Optimization of segmented alignment marks for advanced semidonductor fabrication processes

Qiang Wu, Zhijian Lu, Gary Williams, Franz Zach, Bernhard Liegl

Proceedings Volume 4344, (2001) https://doi.org/10.1117/12.436746

KEYWORDS: Optical alignment, Image segmentation, Silicon, Scattering, Light scattering, Metals, Lithography, Computer simulations, Semiconductors, Tolerancing

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Proceedings Article | 25 June 1999 Paper

Evaluation of photoacid generators in chemically amplified resists for x-ray lithography using an on-wafer photoacid determination technique

Bing Lu, Paul Dentinger, James Taylor, Gilbert Feke, Dan Hessman, Qiang Wu, Robert Grober

Proceedings Volume 3676, (1999) https://doi.org/10.1117/12.351121

KEYWORDS: Luminescence, Lithography, Semiconducting wafers, Chemically amplified resists, Hydrogen, Halogens, X-ray lithography, X-rays, FT-IR spectroscopy, Nondestructive evaluation

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Proceedings Article | 3 October 1996 Paper

Novel optical filter for improvement in contrast of images

Guangyin Zhang, Jingjun Xu, Qian Sun, Simin Liu, Qiang Wu

Proceedings Volume 2897, (1996) https://doi.org/10.1117/12.252964

KEYWORDS: Optical filters, Absorption, Polymers, Sun, Transistors, Photonic devices, Electronic components, Polymethylmethacrylate, Physics

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Showing 5 of 7 publications

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