Variation in the critical dimension (CD) of a transistor is a primary concern for advanced lithography. Because variation from sources such as corner rounding or line edge roughness does not scale with CD, variability in transistor performance increases with scaling and may impact the timing or even the functionality of critical circuits such as static random access memories (SRAM) and ring oscillators. Spacer lithography is an attractive patterning method for future technology nodes, because its use of a very uniform and controllable chemical vapor deposition (CVD) step allows for the definition of very narrow lines with low variation and reduced pitch. In practice, however, the possible pitch reductions are limited by the need for conventional lithography to produce negative features (e.g., trenches and holes) and increasing CD variability with iterated spacer processing. In this work, an extension to spacer lithography is presented to overcome these limitations. Negative features down to 30 nm in width are fabricated using spacer-defined features. A multitiered hard mask process is also presented to enable eight-fold pitch reduction with no increase in CD variation. In combination, these processes enable ultradense circuit integration for regular layouts.
Photovoltaic solar cells are a route towards local, environmentally benign, sustainable and affordable energy solutions.
Antireflection coatings are necessary to input a high percentage of available light for photovoltaic conversion, and
therefore have been widely exploited for silicon solar cells. Multi-junction III-V semiconductor solar cells have achieved
the highest efficiencies of any photovoltaic technology, yielding up to 40% in the laboratory and 37% in commercial
devices under varying levels of concentrated light. These devices benefit from a wide absorption spectrum (300-
1800 nm), but this also introduces significant challenges for antireflection coating design. Each sub-cell junction is
electrically connected in series, limiting the overall device photocurrent by the lowest current-producing junction.
Therefore, antireflection coating optimization must maximize the current from the limiting sub-cells at the expense of
the others. Solar concentration, necessary for economical terrestrial deployment of multi-junction solar cells, introduces
an angular-dependent irradiance spectrum. Antireflection coatings are optimized for both direct normal incidence in air
and angular incidence in an Opel Mk-I concentrator, resulting in as little as 1-2% loss in photocurrent as compared to an
ideal zero-reflectance solar cell, showing a similar performance to antireflection coatings on silicon solar cells. A transparent conductive oxide layer has also been considered to replace the metallic-grid front electrode and for inclusion as part of a multi-layer antireflection coating. Optimization of the solar cell, antireflection coating, and concentrator system should be considered simultaneously to enable overall optimal device performance.
Variation in the critical dimension (CD) of a transistor is a primary concern for advanced lithography. Because
variation from sources such as corner rounding or line edge roughness does not scale with CD, variability in transistor
performance increases with scaling and may impact the timing or even the functionality of critical circuits such as static
random access memories (SRAM) and ring oscillators. Spacer lithography is an attractive patterning method for future
technology nodes, because its use of a very uniform and controllable chemical vapor deposition (CVD) step allows for
the definition of very narrow lines with low variation and reduced pitch1,2. In practice, however, the possible pitch
reductions are limited by the need for conventional lithography to produce negative features (e.g., trenches and holes)
and increasing CD variability with iterated spacer processing. In this work, an extension to spacer lithography is
presented to overcome these limitations. Negative features down to 30nm in width are fabricated using spacer-defined
features. A multi-tiered hard mask process is also presented to enable eight-fold pitch reduction with no increase in CD
variation. In combination, these processes enable ultra-dense circuit integration for regular layouts.
The Space Interferometry Mission (SIM) relies on interferometry and metrology capable of measuring the change in the optical path difference with picometer accuracy. For the last two years we designed and built the Micro-Arcsecond Metrology Testbed, the key technology demonstration for SIM. In a parallel effort the data analysis code was written. The interferometer was first used in a modified configuration; white light and light from a HeNe-laser was emerging from a fiber, collimated and split into the two arms with their respective delay lines. The recombined light was then dispersed onto the CCD camera. The tests done using this interferometer resulted in data on the effects that influence the accurate determination of the fringe phase delay: (1) alignment effects; (2) CCD camera parameters; (3) path length stability, and (4) analysis related inaccuracies. While offsetting the interferometer from equal arm length, the OPD was dithered using PZT-actuated mirrors. The white-light fringe was captured for each step. At the same time the (HeNe) laser light was monitored with two photo detectors--one serving as an intensity monitor, the second one monitoring the interfered laser light. This technique was used to accurately measure the path length changes by analyzing the linear parts of the HeNe sinusoidal interference signal normalized by the HeNe intensity signal. This simple metrology system is designed to determine the optical path length changes to about 100 pm.
The micro-arcsecond metrology testbed (MAM) is a high- precision long baseline interferometer inside a vibration- isolated vacuum tank. The instrument consists of an artificial star, a laser metrology system, and a single- baseline interferometer with a 1.8m baseline and a 5cm clear aperture. MAM's purpose is to demonstrate that the astrometric error budget specified for the Space Interferometry Mission can be met.
The Micro Arcsecond Metrology Testbed (MAM) is a laboratory- based, long baseline, white-light interferometer inside a vibration-isolated vacuum tank. The single baseline, high precision interferometer will be able to observe a translating, artificial star at a distance of 10.74 meters with 5 μ as accuracy. The MAM testbed consists of an artificial star, laser metrology and a high precision interferometer. This paper addresses the design and characteristics of the interferometer. The interferometer functions include both angle- and optical-path tracking. The optics are arranged to from dispersed fringes in a channeled spectrum on a charge coupled device and a true white-light fringe on an avalanche photodiode, while at the same time producing guide spots for angle tracking.
A new type of laser retroreflector has been developed for JPL's future Space Interferometry Mission. The retroreflector consists of an assembly of prisms of form multiple hollow cornercubes. This allows the limited field of view of about 60 degrees of a single corner can be overcome, to comply with the geometry of an optical truss. In addition, an innovative feature is that the retroreflector has common vertices, in order to define a single point optical fiducial necessary for point-to-point 3D laser metrology. The multiple cornercube provides better thermal stability and optical performance than spherical and hemispherical type retroreflectors. In manufacturing the prototype, the key technology of assembling prisms to the interferometric accuracy has been demonstrated. A non common vertex error of a few micrometers has been achieved.
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