The haze nucleation and growth phenomenon on critical photomask surfaces has periodically gained
attention as it has significantly impacted wafer printability for different technology nodes over the
years. A number of process solutions have been shown to suppress or minimize the propensity for
haze formation, but none of these technologies has stopped every instance of haze. Additionally, the
management of photo-induced defects during lithography exposure is expensive, so some capability
will always be needed to remove haze on photomasks for long term maintenance over a mask's
A novel technology is reviewed here which uses a dry (no chemical effluents) removal system to
safely sweep the entire printable region of a pelliclized photomask to eliminate all removable haze.
This process is safe regardless of the mask substrate materials or the presence of small critical
patterns such as SRAF's that may represent damage problems for traditional cleaning methods.
Operational process techniques for this system and performance in removal will be shown for haze
located on the mask pattern surface. This paper will also discuss the theory of operation for the
system, including expected chemical reactions and address the reformation rate of haze crystals.
Data from tool acceptance and preliminary production use will also be reviewed including analysis
of process window through a focus-exposure matrix, repair durability, CD performance, and sort
Free space optical communications using 9-10 fs pulses was investigated through aerosol clouds
approaching 104 to 105 particles per cm3 in a 15 cm long tube containing aerosol particles 4-5 μm in
diameter. This small size is representative of the most difficult situation for the transmission of light
through the atmosphere. The ultra fast pulse transmission were compared to continuous wave (cw)
transmission through the exact same aerosols clouds and compared to the ultra short pulses. Results
indicate that there was increased transmission for the ultra short laser pulses, but was not as high as
expected. The results now can be explained by a recent paper demonstrating that deviation from the Beer
Lambert law does not occur until the ultra short pulse transverses a longer path length in water. Results
will be presented on the pulse dispersion in water and glass.
Inspired by previous theoretical work, experiments on diffraction of 10 femtosecond ultrashort pulses passing through a single slit have been performed. Fringes are dramatically reduced or even eliminated in the diffraction of 10 fs ultrashort pulsed laser in the near field compared with that of the continuous-wave laser. This can be explained in the frequency domain as a result of the broadband spectrum contained in ultrashort pulses. Simulations are performed for Fresnel diffraction for both 10 fs ultrashort pulsed and continuous-wave lasers and the results agree with the experimental observation. The results of this work have important implication in biomedical imaging and remote imaging applications to name only a few.
Steam laser cleaning of alumina and titanium carbide nanoparticles from silicon substrates is presented. A KrF excimer laser with a wavelength of 248 nm was used to irradiate the substrates in laser cleaning. A water layer of micrometer thickness was deposited on silicon substrates to improve the cleaning process. Cleaning efficiency was measured for different laser fluences ranging from 50 to 250 mJ/cm2 and pulse numbers from 1 to 100. Research work was carried out to address the factors governing steam laser cleaning, during which thickness of water thin film and lift-off velocities of water films from Si substrate surfaces were monitored. In addition, one-dimensional simulations were employed to estimate the temperature increase on the material surfaces upon laser irradiation. Water layer thickness was measured using Fourier Transform Infrared Spectroscopy. Monitoring of both lift-off velocities and water thin film removal time were carried out by optical probing approaches using He-Ne laser of 632.8 nm wavelength.
There is a need in many scientific and manufacturing processes to drill to small diameter holes with high aspect ratios in both brittle materials as well as metals. Femtosecond lasers operating at 795 nm or frequency doubled to 400 nm provide a unique tool for carrying out these processes. In this work, the femtosecond laser nanomachining facilities at the University of Nebraska is discussed to drill 1 micrometers holes in Si/SiO2 with aspect rations > 8. The quality of the cut and the small nanoparticles are discussed.
Microfabrication of sub-micron holes on 30 nm thick aluminum films on fused silica was investigated using pulse durations form 300 fs to 6 ns at 400 nm wavelength. Micromachined areas were investigate using atomic force microscopy for quality and size of features produced. Ablation diameters less than 400 nm was achieved with all pulse widths. Pulses less than 5 ps removed the films cleanly and left a flat- bottomed crater with no evidence of substrate melting over a wide fluence range.