Dr. Ping Zhang Profile

Dr. Ping Zhang

at Southeast Univ

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Author

Publications (6)

Proceedings Article | 21 November 2007 Paper

Study of critical modulation transfer function by UV-vis spectroscopy

Ping Linda Zhang, Song Hu, Lu Chuan Zhang, Zhong Yuan Jin, Hai Liang Yu, Le Wang, Yong Yang

Proc. SPIE. 6724, 3rd International Symposium on Advanced Optical Manufacturing and Testing Technologies: Design, Manufacturing, and Testing of Micro- and Nano-Optical Devices and Systems

KEYWORDS: Optical lithography, Spectroscopy, Photography, Photoresist materials, Absorbance, Modulation transfer functions, UV-Vis spectroscopy, Photoresist processing, Semiconducting wafers, Absorption

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Proceedings Article | 21 November 2007 Paper

Particle size study of diazonaphthoquinone/novolak

Ping Linda Zhang, Hai Liang Yu, Song Hu, Zhong Yuan Jin, Le Wang, Li Yu Liu, Lu Chuan Zhang, Yong Yang

Proc. SPIE. 6724, 3rd International Symposium on Advanced Optical Manufacturing and Testing Technologies: Design, Manufacturing, and Testing of Micro- and Nano-Optical Devices and Systems

KEYWORDS: Optical lithography, Polymers, Particles, Silver, Transmission electron microscopy, Photoresist materials, Photoresist processing, Semiconducting wafers, Photoresist developing, Picture Archiving and Communication System

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Proceedings Article | 11 January 2007 Paper

Application of diazonaphthoquinone/novolak photosensitive material for photography image formation

Ping Linda Zhang, Hai Liang Yu, Song Hu, Zhong Yuan Jin, Le Wang, Lu Chuan Zhang, Yong Yang

Proc. SPIE. 6279, 27th International Congress on High-Speed Photography and Photonics

KEYWORDS: Polymers, Particles, Silver, Photography, Transmission electron microscopy, Absorbance, Photoresist processing, Semiconducting wafers, Photoresist developing, Picture Archiving and Communication System

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Historically diazoquinone/novolak- the two-component photosensitive material (photoresist) was efficiently used in various industries. In the semiconductor industry it is used for the high contrast, high resolution binary image formation for the integrated circuitry. Comparing with the silver halide photosensitive system which has Ag₄ + cluster or T-grain sensitizing center that generates detailed gray scale (photographic density) black & white images, the diazoquinone / novolak resist for the gray scale image formation has not been investigated thoroughly in the past. Diazoquinone/novolak could be used in the photography field as one of the non-silver photosensitive materials and this passive photosensitive material also has its broad exposure-energy response towards the image formation. Here in this paper we provide this silver-halide supplement material to transfer our semiconductor photolithography binary process experience of that resist to its photography application. We also reported the TEM figures and the measurement data of the resist particle diameter after the photolithography development process. The thick photoresist was coated on the aluminum substrate. Using critical dimension, CD = 2μm photomask to process several lots of wafers, the resist particles were collected and the particle size and its distribution after the development process was obtained. Their size distribution mainly has dual separate distribution peaks: 85% of particles have the diameter distributed around 23±3 nm and the rest 15% of bigger particles around 220±50 nm. Here in the experiment we use the standard-equivalent projection reticle to substitute the standard contact mask to obtain 2μm CD latent images thereafter the corresponding particles throughout several lots. Because of the unique role of DNQ, which is both the photo-sensitizer and the development inhibitor before its exposure, the correlation of the resist particle size with respect to the developer concentration, the size of the radius of gyration, the "photosensitizing center" and the "development center" is speculated. Generally the particle size distribution is mainly correlated to the developer concentration, possibly also to the polymer resin molecular weight and the polymer / PAC ratio etc. We added our study of its photochemistry property (here specifically the UV-vis absorbance or optical density), provided its spectroscopic response figures with respect to the sequentially increased exposure of the resist on quartz (250 - 550 nm and 300 - 450 nm). The relationship of the photographic contrast and its photochemistry property of the resist was briefed.

Proceedings Article | 11 June 1999 Paper

Spinnable and UV-patternable hybrid sol-gel silica glass for direct semiconductor dielectric layer manufacturing

Mark Andrews, Ping Zhang, S. Iraj Najafi, Keith Chao, Nicholas Pasch

Proc. SPIE. 3678, Advances in Resist Technology and Processing XVI

KEYWORDS: Semiconductors, Thin films, FT-IR spectroscopy, Silica, Glasses, Dielectrics, Silicon, Manufacturing, Polymerization, Sol-gels

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Proceedings Article | 29 June 1998 Paper

Diffusion of photoacid generators by laser scanning confocal microscopy

Ping Zhang, Stephen Webber, J. Mendenhall, Jeff Byers, Keith Chao

Proc. SPIE. 3333, Advances in Resist Technology and Processing XV

KEYWORDS: Confocal microscopy, Microscopes, Polymers, Luminescence, Diffusion, Reflectivity, Laser scanners, Spatial resolution, Signal detection, Photoresist developing

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Diffusion of the photogenerated acid during the period of time between exposure and development can cause contrast loss and ultimately loss of the latent image. This is especially relevant for chemically amplified photoresists that require a post-exposure baking step, which in turn facilitates acid diffusion due to the high temperature normally employed. It is thus important to develop techniques with good spatial resolution to monitor the photogeneration of acid. More precisely, we need techniques that provide two distinct types of information: spatial resolution on various length scales within the surface layer and also sufficient depth resolution so that one can observe the transition from very surface layer to bulk structure in the polymer blend coated on silicon substrate. Herein laser scanning confocal microscopy is used to evaluate the resist for the first time. We report the use of the confocal microscopy to map the pag/dye distribution in PHS matrices, with both reflectance images and fluorescence images. A laser beam is focused onto a small 3D volume element, termed a voxel. It is typically 200 nm X 200 nm laterally and 800 nm axially. The illuminated voxel is viewed such that only signals emanating from this voxel are detected, i.e., signal from outside the probed voxel is not detected. By adjusting the vertical position of the laser focal point, the voxel can be moved to the designated lateral plane to produce an image. Contrast caused by topology difference between the exposed and unexposed area can be eliminated. Bis-p-butylphenyl iodonium triflat (7% of polyhydroxystyrene) is used as photoacid generators. 5% - 18% (by weight, PHS Mn equals 13 k) resist in PGMEA solution is spin cast onto the treated quartz disk with thickness of 1.4 micrometers , 5 micrometers space/10 micrometers pitch chrome mask is used to generate the pattern with mercury DUV illumination. Fluoresceinamine, the pH-sensitive dye, is also used to enhance the contrast of fluorescence image. The typical PEB temperature is 90 degree(s)C for 90 seconds. 488 nm is used as the excitation wavelength. Both reflectance and fluorescence images (> 510 nm) are processed by using Adobe Photoshop. It was found that the reflectance is more sensitive to the change of the refractive index of the resist while the fluorescence is more sensitive to the distribution of the PAG/dye. The NIH Image software is used for acid exchange rate calculation. Second Fick's Law is applied to analyze the image change. The diffusion coefficient for this PAG in PHS during PEB is smaller than 8.8 X 10^-13 cm²/s.

Proceedings Article | 7 July 1997 Paper

Acid diffusion through polymer films

Ping Zhang, Andrew Eckert, C. Grant Willson, Stephen Webber, Jeff Byers

Proc. SPIE. 3049, Advances in Resist Technology and Processing XIV

KEYWORDS: Sensors, Quartz, Polymers, In situ metrology, Luminescence, Diffusion, Photoresist materials, Critical dimension metrology, Polymer thin films, Data analysis

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In order to perform 0.2 micrometer processes, one needs to study the diffusion of photoacid generators within the photoresist system, since diffusion during post exposure bake time has an influence on the critical dimension (CD). We have developed a new method to study the diffusion of photoacid generators within a polymer film. This new method is based on monitoring the change of the fluorescence intensity of a pH- sensitive fluorescent dye caused by the reaction with photoacid. A simplified version of this experiment has been conducted by introducing acid vapor to quench the fluorescence intensity of this pH sensor. A thin polymer film is spin cast onto the sensor to create a barrier to the acid diffusion process. During the acid diffusion process, the fluorescence intensity of this pH sensor is measured in situ, using excitation and emission wavelengths at 466 nm and 516 nm, respectively. Fluoresceinamine, the pH sensitive fluorescent dye, is covalently bonded onto the treated quartz substrate to form a single dye layer. Poly(hydroxystyrene) (M_n equals 13k, T_g equals 180 degrees Celsius) in PGMEA (5% - 18% by weight) is spin cast onto this quartz substrate to form films with varying thickness. The soft bake time is 60 seconds at 90 degrees Celsius and a typical film has a thickness of 1.4 micrometers. Trifluoroacetic acid is introduced into a small chamber while the fluorescence from this quartz window is observed. Our study focuses on finding the diffusion constant of the vaporized acid (trifluoroacetic acid) in the poly(hydroxystyrene) polymer film. By applying the Fick's second law, (I_t - I_o)/(I_(infinity ) - I_o) equals erfc [L/(Dt)^1/2] is obtained. The change of fluorescence intensity with respect to the diffusion time is monitored. The above equation is used for the data analysis, where L represents the film thickness and t represents the average time for the acid to diffuse through the film. The diffusion constant is calculated to be at the order of 10^-10 cm²/s to 10^-12 cm²/s. All the experiments are conducted at room temperature and are valid only for acid vapor. With different film thickness, it was found that the acid diffuses through the film with a similar diffusion constant. The diffusion is faster with increased solvent residue in the film (controlled by spin coating speed). The theoretical computer modeling of the local acid concentration with respect to acid diffusion is also performed.

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