Even if particles are removed still a residue or "footprint" is left behind. Such a footprint may in itself be large enough to
become a printable defect. Footprint of silica and PSL particles with diameters of 100 nm which were deposited on Si
surface and were stored at different environments was measured by atomic force microscope. Their particle removal
forces also were measured. Footprint of silica and PSL particles and their particle removal forces represented that silica
particles as an inorganic type particle were very sensitive humidity and it needs high removal force when the silica
particle aged at higher humidity level and longer storage time. On the other hand, PSL particles as an organic type
particle were not sensitive humidity, but footprints were observed even at low humidity condition and short storage time.
This study could help to improve the understanding of particle adhesion on EUV mask and might help to improve mask
life time longer.
In this paper, we suggest an optimal attenuated phase shift mask (PSM) structure for extreme ultra violet lithography
(EUVL) to minimize mask shadowing effect without loss of image contrast. The attenuated PSM proposed in this study
is based on Fabry-Perot structure that consists of tantalum nitride (TaN) attenuator, Al2O3 spacer, and molybdenum (Mo)
phase shifter. Deep ultra violet (DUV) reflectivity can be lowered down to 5% at 257nm for higher efficiency in DUV
inspection process through the optimal thickness combination of TaN and Al2O3. Since the thickness variation of Mo
dose not affect the DUV reflectivity, the phase shift effect can be controlled by Mo thickness only. As a result,
attenuated PSM with phase shift of 180±6° and absorber reflectivity of 9.5% could be obtained. The total thickness of
absorber stack is only 52nm. The analysis of aerial image was performed using SOLID-EUV simulation tool. The
attenuated PSM showed steeper edge profile and higher image contrast compared to binary mask. Imaging properties
including horizontal-vertical (H-V) critical dimension (CD) bias and pattern shift depending on both pattern size and
process condition were compared to the binary mask using aerial image simulation. Attenuated PSM showed less H-V
CD bias compared to that of binary mask. The 32nm dense pattern shows larger H-V CD bias than 45nm one due to
larger shadowing of smaller pattern size. Especially, 32nm dense pattern at binary mask has very large H-V CD bias. The
H-V CD bias was also affected by the change of focus. However, the H-V bias variation with defocus was below 1nm
within the process latitude. We also obtained the result that the pattern shift is less sensitive than H-V CD bias with the
optical property of absorber in EUVL.
Integration and optimization of the absorber stack has become a critical issue with the progress of the extreme ultraviolet lithography development because it influences many issues such as throughput, pattern fidelity, and mask yield. Simulation works to optimize an absorber stack were carried out and the results were empirically confirmed. TaN showed a great potential as an extreme ultraviolet absorber property but it did not meet the requirement for deep ultraviolet reflectivity for inspection. According to the simulation, Al2O3 was selected as an anti-reflection coating for DUV wavelength. Al2O3 ARC with optimum thickness reduces the DUV reflectivity from 42.5 to 4.4 % at 248 nm while maintaining the other properties. A novel absorber stack consisted of TaN absorber, Ru capping, and Al2O3 ARC is proposed, and the total thickness of the stack is only 47 nm and the EUV and DUV reflectivities are 0.97 % at 13.5 nm and 4.4 % at 248 nm, respectively.
Depth detection and image recovery of a target from its complex hologram have recently been proposed in optical remote sensing applications. The proposed technique involves synthesizing the so-called real-only spectrum hologram from the complex hologram. The resulting spectrum hologram contains the real-only information of the target's spectrum and carries the target's depth information. By digital processing of the spectrum hologram, we can extract the target's depth. Once the depth is obtained, we can recover the image of the target from its complex hologram. We report an experimental verification of the technique by optical acquisition of the complex hologram of the remote target and subsequently extract the target's depth. The image of the target at its depth location is subsequently recovered digitally. The novelty of this remote sensing technique is that by performing a single 2-D scan, we can acquire simultaneously the target's depth information and its image for possible subsequent optical correlation applications.
Short-period GaAs quantum wire (QWR) array was grown by metalorganic chemical vapor deposition on submicron gratings. And a new lithography technique to fabricate submicron current-blocking layer on the short-period QWR array without any external masks was developed. The methods include the followings. The photoresist was coated on the nonplanar top of the laser diode structure. The photoresist stripes were designed to remain over each QWR with a flood exposure and a develop technique. The GaAs contact layers on the parts of the (111)A and all the (100) top quantum wells were removed by employing the photoresist remaining on the top valley as masks. The submicron current-blocking layer was produced all over the regions except QWR's, by sputtering SiO2 film followed by lift-off and metal evaporation. It must help a majority of current pass into QWR active region.