A photoacoustic 3D imaging system for animal experiments was made. This system is special because it has a hemispherical detector array. To test its performance, we used a chart from the field of optics as a sample. We checked the whole imaging range using the ISO 12233 chart, which is used to test digital camera images. We found that there was no distortion in the xy-plane and the system had high resolution. We also tested it using a high image quality mode with a different scanning sequence. In this study, live albino mice with white hairs were anesthetized and photographed. Using hair removal cream, we were able to visualize the vascular network throughout their bodies, including blood vessels in organs such as the liver and kidneys. The smallest vessels we were able to visualize were less than 0.1 mm in diameter. We used photoacoustic (PA) images to relatively estimate the oxygen saturation of the mice's blood at two different wavelengths, which we refer to as the S-factor. By analyzing the PA images, we were able to estimate the arterial and venous systems of the whole body, as well as the difference in S-factor between the two systems within the liver. When the mice were euthanized and examined post-mortem, we observed that the S-factor of the whole body decreased and the difference in S-factor between the two systems within the liver was lost.
Nanoimprint lithography (NIL) manufacturing equipment utilizes a patterning technology that involves the field-by-field deposition and exposures of a low-viscosity resist deposited by jetting technology onto the substrate. The technology faithfully reproduces patterns with a higher resolution and greater uniformity compared to those produced by photolithography equipment. Previous studies have demonstrated NIL resolution better than 10 nm, making the technology resolution suitable for the patterning of several generations of critical memory levels with a single mask.
Overlay is critical for advanced memory devices such as dynamic random-access memory and phase change memory. Both device types continue to scale, with expected half pitches down to 14 nm and beyond. Typical overlay budgets are on the order of 20% of the half pitch, meaning overlay requirements of <3 nm. Previously, we have employed systems (such as high-order distortion correction) to improve upon higher order distortion errors, thereby improving the overlay performance of our process.
Some process variables that are unique to NIL and that can be considered as process tunable variables include imprint force and tip/tilt of the imprint head relative to the wafer. These were identified to be significant variables to further improve the overlay and to achieve good overlay stability in a production run at throughput. We introduce these overlay tuning knobs for NIL and present the techniques and models to achieve stability of imprint force and tip/tilt in order to reduce both wafer to wafer variation as well as the field–field variation of these variables. Applying these techniques enables NIL to meet the overlay requirements for advanced memory device production.
The integration of a NIL into production for advanced memory devices will require compatibility with existing high-end optical lithography processes in order to meet the aggressive overlay performance specifications. To deliver such a demanding overlay specification, it is necessary for NIL to achieve reliable alignment and to expand its overlay error budget to include as many as higher-order error components along with their countermeasure options. In this paper, NIL overlay models have been developed to address alignment of full fields and partial fields.
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