Parallel Micro Manipulator for Effective Optical Spot Array Alignment

We focus our attention on complex lithographic pattern generation on a huge substrate with no manipulation of the light source shape for Digital Micromirror Device (DMD) based maskless lithography. To overcome the limitations of existing pattern generation methods developed upon the assessment of lithographic paths of the reflected beam spots rather than the recognition of patterns, we place our primary concern on the pattern. We consider pattern generation for maskless lithography using the DMD as a graphic recognition field problem. The pattern generation process is conceptualized as dual pattern recognition in two contrary views, which are the substrate’s view and the DMD’s view. For pattern recognition in the DMD’s view, a unique criterion, the area ratio, is devised for approval of the on/off reflection of the DMD mirror. The Region-based Pattern Generation (RPG) scheme based upon the area ratio is proposed. For verification, a prototype RPG system is implemented, and lithography using the system is performed to fabricate an actual Flat Panel Display (FPD) glass. The results verify that the RPG scheme is robust enough to generate lithographic patterns in any possible lithographic configuration and the RPG system is precise enough to attain the lithographic quality required by the FPD manufacturer.

The research work reported here is supported by the NSFC under Grant No. 59885006 and 50275129, 50905075 and Supported by the Self-determined Research Program of Jiangnan University under Grant No. JUSRP10908.

Analysis of the line pattern width and exposure efficiency in maskless lithography using a digital micromirror device

The aim of this study is to provide a simulation method for investigation of the intensity fluctuation caused by the inclined incident angle in DMD (digital micromirror device) maskless lithography. The simulation consists of eight main processes involving the simplification of the DMD aperture function and light propagation utilizing the non-parallel angular spectrum method. These processes provide a possibility of co-simulation in the spatial frequency domain, which combines the microlens array and DMD in the maskless lithography system. The simulation provided the spot shape and illumination distribution. These two parameters are crucial in determining the exposure dose in the existing maskless lithography system.

In this paper, we propose an effective method for optimizing mask design using an enhanced genetic algorithm (GA), significantly boosting digital micromirror device (DMD) maskless lithography performance. After a thorough evaluation of various optimization techniques, we determined that the simulated annealing-enhanced GA (SA-GA) offers superior improvements in lithography simulations, thus optimizing mask design more effectively. Our findings reveal that this method achieves up to 88% and 75% enhancement in simulation accuracy for circular and heart-shaped patterns, respectively, surpassing the results of conventional Hopkins lithography simulations. The remarkable effect of improved GA in enhancing the quality of DMD digital lithography shows that it will have great potential in micro-fabrication applications, and paves the way for the realization of high-fidelity and efficient DMD digital lithography technology, which has excellent versatility and adaptability in the field of microelectronics manufacturing.

Digital micromirror device (DMD) based maskless lithography has a number of advantages including process flexibility, no physical photomask requirement, fast turnaround time, cost effectiveness. It can be particularly useful in the development stage of microfluidic and bioMEMS applications. In this report, we describe the initial results of thick resist SU-8 patterning, soft lithography with polydimethylsiloxane (PDMS) and lift-off of Cr features using a modified DMD maskless system. Exposures of various patterns and microfluidic channels reveal that the system is well capable of printing 60 μm thick resist at a resolution as small as a single pixel (less than 13 μm) with an aspect ratio about 5:1. Both negatively and positively tapered sidewalls are achieved by projecting the UV light from front side of the SU-8 coated Si wafer and from the back side of the coated glass, respectively. The positive sidewall has an angle 88o which is ideal to serve as a mold for subsequent PDMS soft lithography. Both SU-8 and PDMS microfluidic devices for biomolecular synthesis were fabricated with this maskless system. In addition, a lift-off process was also developed with the intention to create built-in metal features such as electrodes and heaters.

As the use of Digital Micro Mirror Devices (DMDs) becomes more prevalent in optics research, the ability to precisely locate the Fourier “footprint” of an image beam at the Fourier plane becomes a pressing need. In this approach, Bayesian adaptive exploration techniques were employed to characterize the size and position of the beam on a DMD located at the Fourier plane. It couples a Bayesian inference engine with an inquiry engine to implement the search. The inquiry engine explores the DMD by engaging mirrors and recording light intensity values based on the maximization of the expected information gain. Using the data collected from this exploration, the Bayesian inference engine updates the posterior probability describing the beam’s characteristics. The process is iterated until the beam is located to within the desired precision. This methodology not only locates the center and radius of the beam with remarkable precision but accomplishes the task in far less time than a brute force search. The employed approach has applications to system alignment for both Fourier processing and coded aperture design.

Maskless lithography based on oblique scanning of point array with digital distortion correction

The <i>Infrared Multi-Object Spectrometer (IRMOS)</i> is a principle investigator-class instrument for the Kitt Peak National Observatory 2.1 m and Mayall 3.8 m telescopes. <i>IRMOS</i> is a near-IR (0.8-2.5 micron) spectrometer with low- to mid-resolving power (R = &#955;/&#916;&#955; = 300-3000). On the 3.8 m telescope, <i>IRMOS</i> produces simultaneous spectra of ~100 objects in its 2.8 x 2.0 arcmin field of view using a commercial micro electro-mechanical systems (MEMS) digital micro-mirror device (DMD) from Texas Instruments. The multi-mirror array DMD operates as a real-time programmable slit mask. The all-reflective optical design consists of two imaging subsystems. The focal reducer images the focal plane of the telescope onto the DMD field stop, and the spectrograph images the DMD onto a large-format detector. The instrument operates at ~90 K, cooled by a single electro-mechanical cryocooler. The bench and all components are made from aluminum 6061. There are three cryogenic mechanisms. We describe laboratory integration and test of <i>IRMOS</i> before shipment to Kitt Peak National Observatory. We give an overview of the optical alignment technique and integration of optical, mechanical, electrical and cryogenic subsystems. We compare optical test results to model predictions of point spread function size. We discuss some lessons learned and conclude with a prediction for performance on the telescope.

Digital micromirror devices (DMDs) are commercial micro-electromechanical systems, consisting of millions of mirrors which can be individually addressed and tilted into one of two states (+/-12deg). These devices were developed to create binary patterns in video projectors, in the visible range. Commercially available DMDs are hermetically sealed and extremely reliable. Recently, DMDs have been identified as an alternative to microshutter arrays for space-based multi-object spectrometers (MOS). Specifically, the MOS at the heart of the proposed Galactic Evolution Spectroscopic Explorer (GESE) uses the DMD as a reprogrammable slit mask. Unfortunately, the protective borosilicate windows limit the use of DMDs in the UV and IR regimes, where the glass has insufficient throughput. In this work, we present our efforts to replace standard DMD windows with custom windows made from UV-grade fused silica, low-absorption optical sapphire (LAOS) and magnesium fluoride (MgF2). We present transmission measurements of the antireflection coated windows and the reflectance of bare (window removed) DMDs. Furthermore, we investigated the long-term stability of the DMD reflectance and experiments for coating DMD active area with a layer of pure aluminum (Al) to boost reflectance performance in the UV spectral range (200400 nm).

We present the novel use of a digital micromirror device (DMD) as a digitally adjustable and programmable aperture for lens-free digital in-line holographic microscopy (LFDIHMY). The proposed micro-electro-mechanical system (MEMS) based DMD aperture can be used as a compact and inexpensive replacement for existing mechanical based aperture control methods required for many resolution enhancement methods. Simulation of the DMD aperture in an in-line holography setup is presented using a general DMD model from literature. A hardware prototype was successfully implemented and demonstrated. The resolution of both simulated and experimental holograms recorded with a conventional pinhole aperture and the proposed DMD aperture are compared using a 1951 USAF resolution test target. We show that a resolution of 2.46 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm { \mu {\textbf {m}}}$ </tex-math></inline-formula> , close to the sensor pixel limit, can be obtained with each aperture. This demonstrates that a DMD can be used as a programmable replacement for a pinhole aperture.

Two major research areas pertinent to microelectromechanical systems (MEMS) materials and material surfaces were explored and developed in this 5-year PECASE LDRD project carried out by Professor Roya Maboudian and her collaborators at the University of California at Berkeley. In the first research area, polycrystalline silicon carbide (poly-SiC) was developed as a structural material for MEMS. This material is potentially interesting for MEMS because compared to polycrystalline silicon (polysilicon), the structural material in Sandia National Laboratories' SUMMiTV process, it may exhibit high wear resistance, high temperature operation and a high Young's modulus to density ratio. Each of these characteristics may extend the usefulness of MEMS in Sandia National Laboratories' applications. For example, using polycrystalline silicon, wear is an important issue in microengines, temperature degradation is of concern in thermal actuators and the characteristics of resonators can be extended with the same lithography technology. Two methods of depositing poly-SiC from a 1,3-disilabutane source at 650 C to 800 C by low-pressure chemical vapor deposition (LPCVD) were demonstrated. These include a blanket method in which the material is made entirely out of poly-SiC and a method to coat previously released and fabricated polysilicon MEMS. This deposition method is much simpler to use than previous methods such as high temperature LPCVD and atmospheric CVD. Other major processing issues that were surmounted in this LDRD with the poly-SiC film include etching, doping, and residual strain control. SiC is inert and as such is notoriously difficult to etch. Here, an HBr-based chemistry was demonstrated for the first time to make highly selective etching of SiC at high etch rates. Nitrogen was incorporated from an NH3 gas source, resulting in high conductivity films. Residual strain and strain gradient were shown to depend on deposition parameters, and can be made negative or positive. The tribology of poly-SiC was also investigated. Much improved release stiction and in-use stiction performance relative to polysilicon MEMS was found. Furthermore, wear of poly-SiC-coated MEMS was much reduced relative to uncoated polysilicon MEMS. A prototype baseline process flow now exists to produce poly-SiC in the Berkeley Sensor and Actuator (BSAC) facility. In the second project, galvanic deposition of metals onto polysilicon surfaces has been developed. The possible applications include reflective and optical coatings for optical MEMS, microswitches and microrelays for radio frequency MEMS and catalytic surfaces for microchemical reactors. In contrast to electroless deposition, galvanic displacement deposition requires no prior activation of the surface and is truly selective to silicon surfaces. This approach was used to deposit copper, gold and rhodium onto polysilicon MEMS. A method to study the adhesion of these metals to polysilicon was developed. It was also shown that the surfaces could be rendered hydrophobic by applying thiol-based self-assembled monolayers. This procedure also lowered their surface energy to {approx}3 {micro}J/m{sup 2}, consistent with monolayer-coated polysilicon MEMS.

In maskless lithography, micromirrors in an array work like a mask to write patterns directly onto substrates. We focus our attention on lithographic data generation for digital micromirror device (DMD) based maskless lithography on a huge substrate, with no manipulation of the light source shape, with no adjustment of mirror tilting angles, and/or without grey imaging levels. To overcome the limitations of existing lithographic data generation methods developed upon the assessment of lithographic paths of the reflected beam spots, we place our primary concern on the pattern. To generate lithographic data for controlling the on/off reflection of millions of micromirrors, we devise a unique criterion, the occupancy limit. By comparing the actual occupancy of the pattern per unit micromirror to the occupancy limit, which is a value determined upon the lithography process condition by the user, binary reflections off micromirrors are approved. A strategy for the computation of the actual occupancy of the pattern per unit micromirror is devised upon the micromirror cell decomposition (MCD). The MCD algorithm for lithographic data generation is proposed. For verification, along with a lithography simulation, an actual lithography experiment is performed to fabricate a pattern on a wafer

A volume holographic optical element is designed and fabricated using photopolymer (PQ-PMMA) for super Gaussian beam. A Lee hologram and Digital Micro Mirror Device (DMD) are used for modulating the laser beam to a uniform one all over its beam diameter. The efficiency and uniformity of super Gaussian beams generated through volume holographic optical component is experimentally demonstrated with optimized parameters. Super Gaussian beam generated by volume holographic grating with unique diffractive properties are advantageous for variety of laser applications.

This paper presents our implementation of a multi-view autostereoscopic 3D display system by using time-multiplexing approach, digital micro-mirror devices (DMD), and the optical Wedgereg. The whole system consists of three major parts: high frame rate DMD projector, an active shutter, and an optical Wedgereg. This research investigates and develops the approaches to interface and control DMDs at very high bit rates and ultra-high frame rates to drive a novel flicker-free 3D flat panel device, with a wide viewing area and without need of special viewing glasses or head-tracking system. It needs to design a digital interface circuit capable of receiving video image data in a conventional format and translating it into a form appropriate for display on a DMD light modulator. This approach differs from existing ones in that it facilitates the modulation of the DMD to achieve much high frame rates, though with a trade-off in greyscale resolution. The outcomes of this research will have the great potential for commercialising the autostereoscopic display systems