Modulation Transfer Function (MTF) for the aerial image formation and Critical Modulation Transfer Function (CMTF)
from the image formation system are two most important parameters for the photolithography processes. In this paper,
we studied CMTF, or to be precise, we studied the contrast γ of the photoresist. γ is essential to the photolithography
processes. New method to measure contrast γ is proposed and studied on DNQ/novolac photoresist.
We provided the UV-vis absorption spectroscopic figures of the DNQ/novolac photoresist with sequentially increased
exposure energy. In the figures the exposure energy from the i-line (365 nm) contact aligner is from 100 mJ/cm<sup>2</sup> to 220
mJ/cm<sup>2</sup>. Higher amount of exposure dose was also applied to the resist. The UV-vis wavelength range is between 300
to 450 nm and 250 to 550 nm. Based on our UV-vis spectra, the contrast value for the resist is retrieved. We also
provided a table that does the contrast comparison of the photography science, the photolithography and our UV-vis
method. Our simplified CMTF measurement method yields the contrast of 1.11 and the CMTF of 0.8 for AZ 1500 at
365 nm. The CMTF measurement from the semiconductor fab requires 20-60 data points on one complete wafer to
achieve the contrast value and the process latitude. Here CMTF from UV-vis requires two complete spectra.
Because of the latent image, this new CMTF measurement is different from the old ways by applying UV-vis method.
In the table, we compared the new method with the existing method of the photography and the semiconductor
photolithography. Whether in the photography and the photolithography area, contrast is the baseline for the quality
With decreasing CD in semiconductor industry, the ability to detect smaller resist particles on wafers after
photolithography process becomes increasingly important for the advanced photolithography processes. It is important
to be able to detect the resist defect for the advanced photolithography processes. To be able to measure the resist,
defect after development process can give the indication and the early warning of the photoresist defect on the wafer.
The diazoquinone/novolak resist particles were collected after the development of several lots of wafers, while the wafer
critical dimension is 2μm. The particle size and its distribution after development process were obtained. The resist
particles were negatively stained before TEM. The TEM figures and the measurement data of the resist particle
diameters were reported. The size measurement data of TEM figures of diazoquinone/novolak resist particles after
photolithography development process was analyzed. The particle size mainly has dual separate distribution peaks:
>85% of particles have the diameters distributed around ~23 nm and 15% of bigger particles around 220 nm. Because
of the unique role of DNQ, which is both the photo-sensitizer and the development inhibitor before exposure, the
correlation of 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, polymer macromolecular weight and the polymer / PAC ratio.
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
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 Ag<sub>4</sub>
+ 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
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
The introduction of the hybrid sol-gel silica glass for direct semiconductor dielectric layer process involves three aspects of photolithography processes. First, the hybrid sol-gel silica glass is possible for the low k dielectric process. Second, it is also photosensitive and UV- patternable at 193 nm or shorter wavelength as the photoresists. Third, it can be used for direct dielectric process that can dramatically simplify the process flow and act as both dielectric materials and photoresist. To directly fabricate semiconductor dielectric layer by using spin-on and UV-patternable materials, to grow glass directly on the quartz, glass or even on the wafer substrate, to have photosensitive materials suitable for direct dielectric layer lithography process is in demand. With decreasing feature sizes, shorter wavelength for exposure is needed. At 193 nm wavelength, most of the materials are not transparent. Hybrid sol-gel silica glass in one of the UV- patternable materials for direct electronic device processing. It may be useful for reticle, DRAM, flat panel or even ASIC manufacturing. It can be 'formed' into intricate and precise 3D configuration. Exposure to DUV or 193 nm light result in a polymerization of the underlying sol-gel glass. the process alters the chemical properties within the bulk of the material as well as at the surface.
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<SUP>-13</SUP> cm<SUP>2</SUP>/s.
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<SUB>n</SUB> equals 13k, T<SUB>g</SUB> 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<SUB>t</SUB> - I<SUB>o</SUB>)/(I<SUB>(infinity</SUB> ) - I<SUB>o</SUB>) equals erfc [L/(Dt)<SUP>1/2</SUP>] 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<SUP>-10</SUP> cm<SUP>2</SUP>/s to 10<SUP>-12</SUP> cm<SUP>2</SUP>/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.