Matthieu C. R. Leibovici

Pattern-integrated interference lithography: single-exposure fabrication of photonic-crystal structures

Multibeam interference represents an approach for producing one-, two-, and three-dimensional periodic optical-intensity distributions with submicrometer features and periodicities. Accordingly, interference lithography (IL) has been used in a wide variety of applications, typically requiring additional lithographic steps to modify the periodic interference pattern and create integrated functional elements. In the present work, pattern-integrated interference lithography (PIIL) is introduced. PIIL is the integration of superposed pattern imaging with IL. Then a pattern-integrated interference exposure system (PIIES) is presented that implements PIIL by incorporating a projection imaging capability in a novel three-beam interference configuration. The purpose of this system is to fabricate, in a single-exposure step, a two-dimensional periodic photonic-crystal lattice with nonperiodic functional elements integrated into the periodic pattern. The design of the basic system is presented along with a model that simulates the resulting optical-intensity distribution at the system sample plane where the three beams simultaneously interfere and integrate a superposed image of the projected mask pattern. Appropriate performance metrics are defined in order to quantify the characteristics of the resulting photonic-crystal structure. These intensity and lattice-vector metrics differ markedly from the metrics used to evaluate traditional photolithographic imaging systems. Simulation and experimental results are presented that demonstrate the fabrication of example photonic-crystal structures in a single-exposure step. Example well-defined photonic-crystal structures exhibiting favorable intensity and lattice-vector metrics demonstrate the potential of PIIL for fabricating dense integrated optical circuits.

Pattern-Integrated Interference Lithography: Prospects for Nano- and Microelectronics

In recent years, limitations in optical lithography have challenged the cost-effective manufacture of nano- and microelectronic chips. Spatially regular designs have been introduced to improve manufacturability. However, regular designed layouts typically require an interference step followed by a trim step. These multiple steps increase cost and reduce yield. In the present work, Pattern-Integrated Interference Lithography (PIIL) is introduced to address this problem. PIIL is the integration of interference lithography and superposed pattern mask imaging, combining the interference and the trim into a single-exposure step. Example PIIL implementations and experimental demonstrations are presented. The degrees of freedom associated with the source, pattern mask, and Fourier filter designs are described.

Pattern-integrated interference [Invited]

Pattern-integrated interference (PII) is described as a logical progression starting from the primary precursors of interference and holography. PII produces, in a single-exposure step, a periodic interference pattern with preselected periods absent. These blocked periods, for example, can form the nonperiodic functional elements of a photonic-crystal device or the circuit elements in a periodic-layout-design semiconductor chip. Various possible system configurations for PII are presented and compared. Example PII-produced intensity patterns for a photonic-crystal microresonator filter and an optical switch are simulated and discussed.

Pattern-integrated interference lithography instrumentation

Multi-beam interference (MBI) provides the ability to form a wide range of sub-micron periodic optical-intensity distributions with applications to a variety of areas, including photonic crystals (PCs), nanoelectronics, biomedical structures, optical trapping, metamaterials, and numerous subwavelength structures. Recently, pattern-integrated interference lithography (PIIL) was presented as a new lithographic method that integrates superposed pattern imaging with interference lithography in a single-exposure step. In the present work, the basic design and systematic implementation of a pattern-integrated interference exposure system (PIIES) is presented to realize PIIL by incorporating a projection imaging capability in a novel three-beam interference configuration. A fundamental optimization methodology is presented to model the system and predict MBI-patterning performance. To demonstrate the PIIL method, a prototype PIIES experimental configuration is presented, including detailed alignment techniques and experimental procedures. Examples of well-defined PC structures, fabricated with a PIIES prototype, are presented to demonstrate the potential of PIIL for fabricating dense integrated optical circuits, as well as numerous other subwavelength structures.

Pattern-integrated interference lithography: Vector modeling and 1D, 2D, and 3D device structures

Multibeam interference lithography (MBIL) represents a versatile, wafer-scale, rapid, and cost-effective fabrication technique for periodic-based microstructures. However, integrating arbitrary and nonperiodic functional elements within an MBIL-defined lattice typically requires an additional time-consuming step. To address this issue, the authors recently introduced pattern-integrated interference lithography (PIIL) that couples MBIL and imaging lithography simultaneously. In this work, the authors present a comprehensive multibeam high-numerical-aperture (NA) vector volume interference/image model for PIIL. This model accounts for the vector nature of light in a high-NA PIIL implementation, the beam propagation within a photoresist film, and the influence of the beam amplitudes and polarizations on the interference pattern. Using this model, PIIL capabilities are illustrated through examples of pattern-integrated one-, two-, and three-dimensional periodic microstructures.

Photonic-crystal waveguide structure by pattern-integrated interference lithography.

The pattern-integrated interference lithography (PIIL) technique combines multi-beam interference lithography (MBIL) and imaging to produce functional periodic-lattice-based microstructures in a rapid single-exposure step. A photonic-crystal waveguide structure with sub-micron resolution is designed, fabricated by PIIL, and characterized. Scanning electron and atomic force microscope images are found to be in good qualitative agreement with three-dimensional simulations of the developed photoresist.

Custom-modified three-dimensional periodic microstructures by pattern-integrated interference lithography

By combining interference lithography and projection photolithography concurrently, pattern-integrated interference lithography (PIIL) enables the wafer-scale, rapid, and single-exposure fabrication of multidimensional periodic microstructures that integrate arbitrary functional elements. To date, two-dimensional PIIL has been simulated and experimentally demonstrated. In this paper, we report new simulated results of PIIL exposures for various custom-modified three-dimensional (3D) periodic structures. These results were generated using custom PIIL comprehensive vector modeling. Simulations include mask-integrated and mask-shaped 3D periodic arrangements as well as microcavities on top of or fully embedded within 3D periodic structures. These results indicate PIIL is a viable method for making versatile 3D periodic microstructures.

Performance simulation of 2D photonic-crystal devices fabricated by pattern-integrated interference lithography

Pattern-integrated interference lithography (PIIL) has recently been proposed as a rapid, single-step, and wafer-scale fabrication technique for custom-modified one-, two- and three-dimensional periodic structures. Among these structures, photonic-crystal devices have significant potential applications. In this work, we simulate the fabrication of two-dimensional photonic-crystal devices by PIIL using a rigorous vector modeling and realistic photolithographic conditions. We also model the etched patterns in silicon and evaluate the photonic-crystal motif-area and motif-displacement errors. We further calculate the device intensity transmission spectra and show that the performance of PIIL-produced devices are comparable to, and in some cases are superior to, that of their idealized equivalents.

Simulation of Photonic-Crystal Devices Fabricated via Pattern-Integrated Interference Lithography

Pattern-Integrated Interference Lithography (PIIL) couples interference and imaging lithography to produce pattern-integrated periodic microstructures in a single exposure. Mask optimization mitigates lattice distortion. PIIL-produced devices exhibit promising performance.

Bicontinuity analysis of multibeam interference three-dimensional periodic structures: volume fractions and interface areas

Bicontinuous structures are an important subset of three-dimensional periodic structures. In multibeam interference structures, the conditions for bicontinuity depend on the beam parameters and the exposure dose. As described in the present work, these conditions can be applied to establish the range of bicontinuity for any multibeam-interference-produced structure. In addition to the bicontinuity range, the analysis yields the volume fraction of the constituent materials and the normalized interface areas. This analysis has been performed for rhombohedral and woodpile lattices as well as their cubic structure limiting cases. A sphere-at-each-lattice-site model for each of the cubic cases has also been developed for comparison. The multibeam interference structures were investigated for representative media and for various incident polarizations.