LumArray, Inc. is developing a maskless photolithography system, the ZP-150, based on zone-plate-array lithography (ZPAL), a technology invented and developed initially in the NanoStructures Laboratory at MIT between 1999 and 2006. Figure 1 illustrates schematically the basic components and operating principle of the ZP-150.
Figure 1:Schematic of LumArray's implementation of zone-plate-array lithography (ZPAL) in its ZP-150 system. A CW laser illuminates a spatial-light modulator (SLM), each pixel of which controls the light level to one diffractive-optical microlens (e.g., pi-phase zone plates) of an array, adjusting the focal-spot intensity from zero to maximum quasi-continuously. By moving the stage under computer control, while modulating the focal spot intensities, complex patterns of arbitrary geometry can be written over an entire 150 mm-diameter substrate while maintaining long-range spatial-phase coherence. Eight-bit intensity modulation in the focal spots enables feature-size control to the sub-1nm level as well as proximity-effect correction.
LumArray's ZP-150 utilizes up to 1000 microlenses writing in parallel. This, combined with modern high-speed graphics-processing units, yields high throughput. Because patterns are written on substrates directly from data files, changes can be made as rapidly as on a word processor. During the research-and-development phases of a project such rapid turnaround enables cost-effective convergence to an optimal design. Multiple experimental designs can be implemented in parallel on the same substrate. The ZP-150 also provides economic manufacturing of small-volumes of customized products.
At present, the 405 nm wavelengthGaN source combined with 0.85 NA zone plates limits the resolution of the ZP-150 to about 200 nm in dense patterns. To achieve sub-100 nm resolution one can either employ a shorter wavelength source or a technique such as Absorbance Modulation Optical Lithography (AMOL); see references below.
Further details on the early development of ZPAL and LumArray’s ZP-150 can be found in the following references.
-  H.I. Smith, "A Proposal for Maskless, Zone-Plate-Array Nanolithography," J. Vac. Sci. Technol. B 14, 4318-4322 (1996).
-  D.J.D. Carter, D. Gil, R. Menon, M. Mondol and H. I. Smith, "Maskless, Parallel Patterning with Zone-Plate Array Lithography (ZPAL)," J. Vac. Sci. Technol. B 17(6) 3449-3452 (1999).
-  D. Gil, R. Menon, D. J. D. Carter and H. I. Smith, "Lithographic Patterning and Confocal Imaging with Zone Plates, "J. Vac. Sci. Technol. B 18(6), 2881-2885, (2000).
-  D. Gil, D.J.D. Carter, R. Menon, X. Tang and H. I. Smith, "Parallel maskless optical lithography for prototyping, low-volume production, and research", J. Vac. Sci. Technol. B 20(6), 2597-2601 (2002).
-  D. Gil, R. Menon, and H. I. Smith, "The Case for Diffractive Optics in Maskless Lithography", J. Vac. Sci. Technol. B 21(6), 2810-2814 (2003).
-  D. Gil, R. Menon and H. I. Smith, "Fabrication of High-Numerical-Aperture Phase Zone Plates with a Single Lithography Exposure and no Etching," J. Vac. Sci. Technol. B 21(6), 2956-2960 (2003).
-  R. Menon, A. Patel, E. E. Moon, and H. I. Smith, "Alpha-prototype system for zone-plate-array lithography," J. Vac. Sci. Technol. B 22(6), 3032-3037 (2004).
-  R. Menon, E. E. Moon, M. K. Mondol, F. J. Castano, and H.I. Smith, "Scanning-spatial-phase alignment for zone-plate-array lithography", J. Vac. Sci. Technol. B 22(6), pp. 3382-3385, Nov/Dec (2004).
-  R. Menon, A. Patel, D. Gil, and H. I. Smith, "Maskless lithography", Materials Today, pp. 26-33, February (2005).
-  R. Menon, D. Gil, and H. I. Smith "Experimental Characterization of Focusing by High-Numerical-Aperture Zone Plates", J. Opt. Soc. Amer., 23 (3), 567-571 (2006).
-  H. I. Smith, R. Menon, A. Patel, D. Chao, M. Walsh, and G. Barbastathis, "Zone-plate-array lithography: a low-cost complement or competitor to scanning-electron-beam lithography," Microelectronic Engineering, 83, 956-961 (2006).
-  Henry I. Smith, Michael E. Walsh, Feng Zhang, Juan Ferrera, Gavin Hourihan, Dan Smith, Robert Light and Martin Jaspan, "An innovative tool for fabricationg computer-generated holograms," J. Phys. Conf. Ser. 415, 012037 (2012),http://dx.doi.org/10.1088/1742-6596/415/1/012037
References to research on Absorbance Modulation Optical Litography (AMOL) and related techniques.
-  R. Menon and H. I. Smith, "Absorbance-modulation optical lithography," J. Opt. Soc. Amer. A 23, 2290-2294 (2006).
-  R. Menon, H.-Y. Tsai, and S.W. Thomas III, "Far-Field Generation of Localized Light Fields using Absorbance Modulation," Phys. Rev. Lett., 98, 043905 (2007).
-  H-Y. Tsai, G. M. Wallraff, and R. Menon, "Spatial-frequency multiplication via absorbance modulation," Appl. Phys. Lett., 91(9), 094103 (2007).
-  H-Y. Tsai, H. I. Smith, and R. Menon, "Reduction of focal-spot size using dichromats in absorbance modulation," Opt. Lett., 33(24), 2916 (2008).
- T. L. Andrew, H-Y. Tsai and R. Menon, "Confining light to deep sub-wavelength dimensions to enable optical nanopatterning," Science, 324, 917 (2009).
-  M. Fu-tai, p.9-11 (adult work).
- R. Menon, "Towards diffraction-unlimited optical nanopatterning," Optics and Photonics News, December 17, 2009.
-  R. Menon, P. Rogge, and H-Y. Tsai, "Design of Diffractive Lenses that Generate Optical Nulls without Phase Singularities," J. Opt. Soc. Am. A. 26(2), p.297-304 (2009).
-  H-Y. Tsai, S. W. Thomas, III and R. Menon, "Parallel scanning optical nanoscopy with optically confined probes," Opt. Exp. 18(15), 16015 (2010).
-  N. Brimhall, T. L. Andrew, R. V. Manthena and R. Menon, "Breaking the far-field diffraction limit in optical nanopatterning via repeated photochemical and electrochemical transitions in photochromic molecules," Phys. Rev. Lett. 107, 205501 (2011).
-  P. Cantu, N. Brimhall, T. L. Andrew, R. Castagna, C. Bertarelli and R. Menon, "Subwavelengthnanopatterning of photochromic diarylethene films," Appl. Phys. Lett. 100, 183103 (2012).
-  F. Masid, T. L. Andrew and R. Menon, "Optical patterning of features with spacing below the far-field diffraction limit using absorbance modulation," Opt. Exp. 21, 4 5209-5214 (2013).
-  G. Pariani, R. Castagna, R. Menon, C. Bertarelli and A. Bianco, "Modeling absorbance-modulation optical lithography in photochromic films," Opt. Lett. 38(16) 3024-3027 (2013).
-  P. Cantu, T. L. Andrew and R. Menon, "Nanopatterning of diarylethene films via selective dissolution of one photoisomer," Appl. Phys. Lett. 103, 173112 (2013).