Guy M. Burrow

Multi-Beam Interference Advances and Applications: Nano-Electronics, Photonic Crystals, Metamaterials, Subwavelength Structures, Optical Trapping, and Biomedical Structures

Research in recent years has greatly advanced the understanding and capabilities of multi-beam interference (MBI). With this technology it is now possible to generate a wide range of one-, two-, and three-dimensional periodic optical-intensity distributions at the micro- and nano-scale over a large length/area/volume. These patterns may be used directly or recorded in photo-sensitive materials using multi-beam interference lithography (MBIL) to accomplish subwavelength patterning. Advances in MBI and MBIL and a very wide range of applications areas including nano-electronics, photonic crystals, metamaterials, subwavelength structures, optical trapping, and biomedical structures are reviewed and put into a unified perspective.

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.

Three-beam interference lithography methodology

Three-beam interference lithography represents a technology capable of producing two-dimensional periodic structures for applications such as micro- and nanoelectronics, photonic crystal devices, metamaterial devices, biomedical structures, and subwavelength optical elements. In the present work, a systematic methodology for implementing optimized three-beam interference lithography is presented. To demonstrate this methodology, specific design and alignment parameters, along with the range of experimentally feasible lattice constants, are quantified for both hexagonal and square periodic lattice patterns. Using this information, example photonic crystal rodlike structures and holelike structures are fabricated by appropriately controlling the recording wavevector configuration along with the individual beam amplitudes and polarizations, and by changing between positive- or negative-type photoresists.

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.

Constrained Parametric Optimization of Point Geometries in Multi-Beam-Interference Lithography

Multi-beam-interference lithography parameters are systematically analyzed and optimized. High absolute contrast and a variety of point geometries ranging from elliptical to rectilinear or rhombic intensity profiles are demonstrated.

Interference Projection Exposure System

An interference projection exposure system is presented for single-exposure fabrication of low-spatial-frequency functional elements in a high-spatial-frequency, all-surrounding periodic pattern. Photonic crystal devices are demonstrated.

Parametric constraints in multi-beam interference

Abstract. Multi-beam interference (MBI) represents a method of producing one-, two-, and three-dimensional submicron periodic optical-intensity distributions for applications including micro- and nano-electronics, photonic crystals, metamaterial, biomedical structures, optical trapping, and numerous other subwavelength structures. Accordingly, numerous optical configurations have been developed to implement MBI. However, these configurations typically provide limited ability to condition the key parameters of each interfering beam. Constraints on individual beam amplitudes and polarizations are systematically considered to understand their effects on lithographically useful MBI periodic patterning possibilities. A method for analyzing parametric constraints is presented and used to compare the optimized optical-intensity distributions for representative constrained systems. Case studies are presented for both square and hexagonal-lattices produced via three-beam interference. Results demonstrate that constraints on individual-beam polarizations significantly impact patterning possibilities and must be included in the systematic design of an MBI system.

Pattern-Integrated Interference Lithography Demonstration

Pattern-integrated interference lithography (PIIL), a new method integrating superposed pattern imaging with interference lithography, is presented. A prototype system is used to demonstrate PIIL potential through the single-exposure fabrication of representative photonic crystal structures.