Design and analysis of a scanning beam interference lithography system for patterning gratings with nanometer-level distortions

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003.Includes bibliographical references (p. 353-364).This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.This thesis describes the design and analysis of a system for patterning large-area gratings with nanometer level phase distortions. The novel patterning method, termed scanning beam interference lithography (SBIL), uses the interference fringes between two coherent laser beams to define highly coherent gratings in photo resist. The substrate is step and scanned under the interference pattern to expose large gratings. Our experimental system, the "Nanoruler", employs interference lithography optics, an X-Y air bearing stage, column referencing displacement interferometry, refractometry, a grating length-scale reference, a beam alignment system, and acousto-optic fringe locking. Supporting systems also include an environmental enclosure, a beam steering system, and vibration isolation with feedforward. The system can pattern 300 mm diameter substrates. The errors are categorized and analyzed. The image-to-substrate motion during writing is comprised of "servo error", which is calculated from interferometric measurements, and unobservable error. The Nanoruler contains a built-in metrology capability where it can measure directly the image-to-substrate motions, which includes the unobservable error. In this special metrology mode, measurements can be performed at all substrate locations and on the fly - a capability possessed by no other patterning machine. This feature is used to assess the image-to-substrate motions. On-the-fly writing and metrology is further noted to be important because periodic errors in the interferometry can be eliminated. I control the fringe placement with a novel system of stage control and acousto-optic fringe locking. The experimentally verified system performance allows control of the servo error to the limits of quantization and latency.(cont.) The impacts of stage controller performance and vibration isolation feedforward performance on unobservable errors are modeled and verified. Extremely high resonant frequency metrology frames were designed that provided unusual insensitivity to disturbances. The vibration errors are estimated to be sub angstrom (0 to 100 Hz). Based on my results and modeling, it is concluded that SBIL is capable of satisfying sub nanometer placement requirements. In my work I have demonstrated long term (1 hour) fringe placement stability of 1.4 nm, 3 (0 to 1.4 Hz). Also, the short term placement stability is less than 4 nm, 3 (O to 5 kHz). When considering the integrated intensity of the scanned image traveling at 100 mm/s, the dose placement stability is 2.1 nm, 3. The wafer mapping repeatability was shown to be 2.9 nm, 3a while measuring a 100 mm substrate. The repeatability is consistent with error models. The index of air uniformity and the thermal stability of assemblies currently limit the repeatability. An improved system of thermal control, enclosed beam paths, and lower coefficient of thermal expansion components is critical for achieving sub nanometer placement error.by Paul Thomas Konkola.Ph.D

Development of a passive compliant mechanism for measurement of micro/nano-scale planar three DOF motions

This paper presents the design, optimization, and computational and experimental performance evaluations of a passively actuated, monolithic, compliant mechanism. The mechanism is designed to be mounted on or built into any precision positioning stage which produces three degree of freedom (DOF) planar motions. It transforms such movements into linear motions which can then be measured using laser interferometry based sensing and measurement techniques commonly used for translational axes. This methodology reduces the introduction of geometric errors into sensor measurements, and bypasses the need for increased complexity sensing systems. A computational technique is employed to optimize the mechanism’s performance, in particular to ensure the kinematic relationships match a set of desired relationships. Computational analysis is then employed to predict the performance of the mechanism throughout the workspace of a coupled positioning stage, and the errors are shown to vary linearly with the input position. This allows the errors to be corrected through calibration. A prototype is manufactured and experimentally tested, confirming the ability of the proposed mechanism to permit measurements of three DOF motions

Nanometer-precision electron-beam lithography with applications in integrated optics

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (p. 179-185).Scanning electron-beam lithography (SEBL) provides sub-10-nm resolution and arbitrary-pattern generation; however, SEBL's pattern-placement accuracy remains inadequate for future integrated-circuits and integrated-optical devices. Environmental disturbances, system imperfections, charging, and a variety of other factors contribute to pattern-placement inaccuracy. To overcome these limitations, spatial-phase locked electron-beam lithography (SPLEBL) monitors the beam location with respect to a reference grid on the substrate. Phase detection of the periodic grid signal provides feedback control of the beam position to within a fraction of the period. Using this technique we exposed patterns globally locked to a fiducial grid and reduced local field-stitching errors to a < 1.3 nm. Spatial-phase locking is particularly important for integrated-optical devices that require pattern-placement accuracy within a fraction of the wavelength of light. As an example, Bragg-grating based optical filters were fabricated in silicon-on-insulator waveguides using SPLEBL. The filters were designed to reflect a narrow-range of wavelengths within the communications band near 1550-nm. We patterned the devices in a single lithography step by placing the gratings in the waveguide sidewalls. This design allows apodization of the filter response by lithographically varying the grating depth. Measured transmission spectra show greatly reduced sidelobe levels for apodized devices compared to devices with uniform gratings.by Jeffrey Todd Hastings.Ph.D

Writing of holographic diffraction gratings of unrestricted length.

Available from British Library Document Supply Centre-DSC:DXN049851 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Toward nano-accuracy in scanning beam interference lithography

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (p. 213-217).Scanning beam interference lithography is a technique developed in our laboratory which uses interfering beams and a scanning stage to rapidly pattern gratings over large areas (300x300 mm2) with high precision. The repeatability of the system [approx.] ±3 nm is an important precursor for obtaining nanometer accuracy. The R&D award winning tool developed in our laboratory, referred to as the nanoruler, uses scanning beam interference lithography to pattern large gratings with periods on the order of 574 nm at velocities approaching 100 mm/s. In this thesis, I will present techniques which I developed to improve the accuracy of the nanoruler. These techniques include mirror mapping, which allows one to characterize the reference mirrors used for stage scanning. In addition, I will present characterization techniques which include translation and rotation tests to measure the distortion present in our system. In order to correct for the measured distortion, I have implemented an on the fly phase-lookup technique in which the phase of the interfering beams are modulated to correct for the system distortion. Several potential applications of this technology require not only high phase fidelity, but uniform linewidth as well.(cont.) Toward this end, I have presented a detailed analysis of the relationship between the exposure dose contrast, beam geometry, phase modulation, and stage scanning parameters. In addition, I have implemented novel scanning techniques which have allowed for patterning more general periodic structures. For example, a technique referred to as Doppler writing will allow one to scan the stage perpendicular to the interference fringes. This technique may be utilized to create several overlapping strips of grating, each with a different period, allowing one to obtain a chirp in a direction parallel to the interference fringes. Furthermore I developed a patterning technique referred to as beam-blanking. While conceptually simple, the challenges for implementing this writing strategy includes synchronization of high speed electronics with the stage motion to phase-lock the interfering beams to the stage at high stage velocities. By combining all of the latter techniques: namely the ability to phase-lock, turn off the writing beams, implement generalized scanning with phase-look up on the fly, several more generalized geometries of interest for applications including photonic Bragg devices, metrology, and X-Ray telescopes may be patterned at high speed, over large distances, with precision and accuracy.by Juan Montoya.Ph.D

Application of precision engineering for nanometre focussing of hard X-rays in synchrotron beam lines

This thesis was submitted for the degree of Master of Philosophy and awarded by Brunel University.Many modern synchrotron beamlines are able to focus X-rays to a few microns in size. Although the technology to achieve this is well established, performing routine experiments with such beams is still time consuming and requires careful set up. Furthermore there is a need to be able to carry out experiments using hard X-ray beams with even smaller beams of between 100nm and 10nm. There are focussing optics that are able to do this but integrating these optics into a stable and a usable experimental set up are challenging. Experiments can often take some hours and any change in position of the beam on the sample will adversely affect the quality of the results. Experiments will often require scanning of the beam across the sample and so mechanisms suitable for high resolution but stable scanning are required. Performing routine experiments with nanometre sized beams requires mechanical systems to be able to position the sample, focussing optics, detectors and diagnostics with significantly higher levels of stability and motion resolution than is required from so called micro focus beam lines. This dissertation critically reviews precision engineering and associated technologies that are relevant for building nano focus beamlines, and the following key issues are explored: • Long term position stability due to thermal effects • Short term position stability due to vibration • Position motion with nanometre incremental motion • Results of some tests are presented and recommendations given. Some test results are presented and guidance on designing nano focus beamlines presented.Diamond Light Sourc

Pattern-integrated interference lithography for two-dimensional and three-dimensional periodic-lattice-based microstructures

Two-dimensional (2D) and three-dimensional (3D) periodic-lattice-based microstructures have found multifaceted applications in photonics, microfluidics, tissue engineering, biomedical engineering, and mechanical metamaterials. To fabricate functional periodic microstructures, in particular in 3D, current available technologies have proven to be slow and thus, unsuitable for rapid prototyping or large-volume manufacturing. To address this shortcoming, the new innovative field of pattern-integrated interference lithography (PIIL) was introduced. PIIL enables the rapid, single-exposure fabrication of 2D and 3D custom-modified periodic microstructures through the non-intuitive combination of multi-beam interference lithography and photomask imaging. The research in this thesis aims at quantifying PIIL’s fundamental capabilities and limitations through modeling, simulations, prototype implementation, and experimental demonstrations. PIIL is first conceptualized as a progression from optical interference and holography. Then, a comprehensive PIIL vector model is derived to simulate the optical intensity distribution produced within a photoresist film during a PIIL exposure. Using this model, the fabrication of representative photonic-crystal devices by PIIL is simulated and the performance of the PIIL-produced devices is studied. Photomask optimization strategies for PIIL are also studied to mitigate distortions within the periodic lattice. The innovative field of 3D-PIIL is also introduced. Exposures of photomask-integrated, photomask-shaped, and microcavity-integrated 3D interference patterns are simulated to illustrate the richness and potential of 3D-PIIL. To demonstrate PIIL experimentally, a prototype pattern-integrated interference exposure system is designed, analyzed with the optical design program ZEMAX, and used to fabricate pattern-integrated 2D square- and hexagonal-lattice periodic microstructures. To validate the PIIL vector model, the proof-of-concept results are characterized by scanning-electron microscopy and atomic force microscopy and compared to simulated PIIL exposures. As numerous PIIL underpinnings remain unexplored, research avenues are finally proposed. Future research paths include the design of new PIIL systems, the development of photomask optimization strategies, the fabrication of functional devices, and the experimental demonstration of 3D-PIIL.Ph.D