E. Grace, J. Beall, J. Bond, H. Cho, R. Datta, M. Devlin, R. Dünner , A. Fox, P. Gallardo, M. Hasselfield, S. Henderson, G. Hilton, A. Hincks, R. Hlozek, J. Hubmayr, K. Irwin, J. Klein, B. Koopman, D. Li, M. Lungu, L. Newburgh, Jo. Nibarger, M. Niemack, L. Maurin, J. McMahon, S. Naess, L. Page, C. Pappas, B. Schmitt, J. Sievers, S. Staggs, R. Thornton, J. Van Lanen, E. Wollack
ACTPol is the polarization-sensitive receiver on the Atacama Cosmology Telescope. ACTPol enables sensitive millimeter wavelength measurements of the temperature and polarization anisotropies of the Cosmic Microwave Background (CMB) at arcminute angular scales. These measurements are designed to explore the process of cosmic structure formation, constrain or determine the sum of the neutrino masses, probe dark energy, and provide a foundation for a host of other cosmological tests. We present an overview of the first season of ACTPol observations focusing on the optimization and calibration of the first detector array as well as detailing the on-sky performance.
The proposed application of holographically formed polymer dispersed liquid-crystal (H-PDLC) thin films is a real-time dynamically reconfigurable mask for the resist exposure step in the photolithographic process. An adaptable photomask has advantages over traditional binary masks that include multiple fabrication patterns using a single mask, reduction in realignment error between different masks, real-time correction and adjustment of fabricated structures, and the ability to alter the mask pattern during exposure. H-PDLC films, or thin periodic nanostructures of alternating layers of polymer and liquid crystal, have unique electro-optic properties, including the ability to modulate a particular wavelength as a function of bias applied to the film. Structures formed using the H-PDLC photomask device have been compared to similar structures formed with a static photomask using an optical profilometer. Features studied were decreasing lines with a maximum width of 121 µm to a minimum width of 84 µm. Edge width between structures formed using the H-PDLC mask and static photomask differ by <5%. Additionally, morphology studies have been performed on developed regions of glass and resist formed using a static and an H-PDLC mask to demonstrate that no structural defects exist due to formation under an H-PDLC grating.
In this paper, we demonstrate a silicon etching application of a holographically formed polymer dispersed liquid
crystal (H-PDLC) photomask. H-PDLC is a periodically nanostructured material consisting of stratified layers
of polymer and liquid crystal. Due to the natural random alignment of the liquid crystal axes with respect to
the polymer layers, an index of refraction mismatch exists and a reflection occurs. Application of bias across
the film aligns the liquid crystals and eliminates the index mismatch causing the film to become transparent.
H-PDLC films have been shown to sufficiently attenuate the UV exposure dose in the photolithographic process
when in the unbiased state, and can be electrically controlled to modulate the amount of UV transmission when
electric field is applied. We show etch depth profiles of patterns masked on a silicon substrate using the H-PDLC
photomask device compared with etch profiles of similar structures patterned with more conventional ink jet
printed photomasks and chrome on quartz glass photomasks. We investigate reactive ion etching technique and
potassium hydroxide wet etch technique.
The proposed application of holographically formed polymer dispersed liquid crystal (H-PDLC) thin films is a
real-time dynamically reconfigurable mask for the resist exposure step in the photolithographic process. H-PDLC
films, or thin periodic nanostructures of alternating layers of polymer and liquid crystal have unique electro-optic
properties including the ability to modulate a particular wavelength as a function of bias applied to the film.
The H-PDLC photomask device consists of patterned electrodes that form pixels with independent bias control
over each segment. This is achieved by etching the optically clear yet electrically conductive indium-tin-oxide
electrodes on the glass confining the H-PDLC film. This mask has been used to cure Shipley 1800 series positive
photoresist at its peak sensitivity wavelength of 440 nm. Structures formed using the H-PDLC photomask device
have been compared to similar structures formed with a static photomask using an optical profilometer. Near
vertical walls have been achieved using the H-PDLC photomask for structures with line width of 260 μm, and
more narrow structures have been fabricated with resolution nearing 100 μm. Line width between structures
formed using the H-PDLC mask and static photomask differ by less than 15%. Additionally, morphology studies
have been performed on developed regions of glass and resist formed using a static and an H-PDLC mask to
demonstrate that no structural defects exist due to formation under an H-PDLC grating.
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