This PDF file contains the front matter associated with SPIE Proceedings Volume 8612, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

A holographic multiphoton fabrication technique is applied to the development of a microcantilever based analyte sensor. Holograms generated using a spatial light modulator (SLM) initiate the fabrication of sub-micron three-dimensional structures. Chemically functional microstructures are patterned onto the surface of commercially available piezoelectric microcantilevers using this holographic lithography technique. Controlling the form and location of the added structure enables the resonant frequency of the cantilever to be regulated with a higher accuracy than is currently available using bulk lithography techniques and without the inclusion of additional electronic feedback control components. A potential analyte sensor is then developed by patterning on an array of multiple piezoelectric microcantilevers, which are initially identical within manufacturing tolerances. The resonant frequency, was adjusted such that cantilevers, which were initially separated by 2.82 kHz, are tuned to be within 0.13 kHz of each other. Connecting the piezoelectric microcantilevers in series enables the response of each sensor element to be measured simultaneously using a single frequency based data acquisition system and allowing rapid data collection.

Bioelectronics involves interfacing functional biomolecules or living cells with electronic circuitry. Recent advances in electrically conductive inks and inkjet printing technologies have enabled bioelectronic devices to be fabricated on mechanically flexible polymers, paper and silk. In this research, non-conductive graphene-oxide (GO) inks are synthesized from inexpensive graphite powders. Once printed on the flexible substrate the electrical conductivity of the micro-circuitry can be restored through thermal reduction. Laser irradiation is one method being investigated for transforming the high resistance printed GO film into conductive oxygen reduced graphene-oxide (rGO). Direct laser writing is a precision fabrication process that enables the imprinting of conductive and resistive micro-features on the GO film. The mechanically flexible rGO microcircuits can be further biofunctionalized using molecular self-assembly techniques. Opportunities and challenges in exploiting these emerging technologies for developing biosensors and bioelectronic cicruits are briefly discussed.

Implementations of roll to roll contact lithography require new approaches towards manufacturing tooling, including stamps for roll to roll nanoimprint lithography (NIL) and soft lithography. Suitable roll based tools must have seamless micro- or nano-scale patterns and must be scalable to roll widths of one meter. The authors have developed a new centrifugal stamp casting process that can produce uniform cylindrical polymer stamps in a scalable manner. The pattern on the resulting polymer tool is replicated against a corresponding master pattern on the inner diameter of a centrifuge drum. This master pattern is created in photoresist using a UV laser direct write system. This paper discusses the design and implementation of a laser direct write system targeting the internal diameter of a rotating drum. The design uses flying optics to focus a laser beam along the axis of the centrifuge drum and to redirect the beam towards the drum surface. Experimental patterning results show uniform coatings of negative photoresist in the centrifuge drum that are effectively patterned with a 405 nm laser diode. Seamless patterns are shown to be replicated in a 50 mm diameter, 60 mm long cylindrical stamp made from polydimethylsiloxane (PDMS). Direct write results show gratings with line widths of 10 microns in negative photoresist. Using an FPGA, the laser can be accurately timed against the centrifuge encoder to create complex patterns.

Metal films on transparent substrates are widely applied for mask production in lithography, and lasers are frequently used for their patterning. Quality of the patterning is limited by fundamental phenomena taking place close to edges of the laser ablated area. We experimentally and numerically investigated transformations in metal films during their irradiation with the nanosecond laser beam with fluence above the ablation threshold. Ridges of the resolidified metal with non-uniform thickness were always formed on edges of the cleaned area. Instabilities during the ablation process forced the molten metal in the ridges to break up into droplets with the periodicity predicted by the Plateau–Rayleigh instability. The droplets on ridges were starting points for formation of self-organized lines of metal film by irradiation with partially overlapping laser pulses. The initial droplets and later the self-organized parallel lines of chromium metal were heat sinks that cooled down the metal in their close proximity. Temperature modulation along the laser irradiation spot was high enough to initiate the Marangoni effect which resulted in movement of the molten metal from hot to colder areas.

Utilizing the transparency of silicon at 2 μm, we are able to ablate the backside of 500-μm thick silicon wafers without causing any damage to the front surface using a novel nanosecond Tm:fiber laser system. We report on our high energy/high peak power nanosecond Tm:fiber laser and provide an initial description of the effects of laser parameters such as pulse duration and energy density on the ablation, and compare thresholds for front and backside machining. The ability to selectively machine the backside of silicon wafers without disturbing the front surface may lead to new processing techniques for advanced manufacturing in solar cell and microelectronics industries.

This work explores the combination of laser transfer and laser doping in a single process, as a way to produce highly defined, heavily doped volumes on semiconductors, to produce electronic devices. The process has been realized on mono and multicrystalline silicon by means of nanosecond laser pulses. The paper studies the mechanism of the process and the requirements in terms of beam shaping, energy levels and specific constrains of the setup to get proper dopant transfer and diffusion, as well as high compositional gradient. Bismuth is selected as n-dopant, and aluminum is used as an already well known solution for laser driven heavy p-doping on silicon. The suitability of laser transfer doping for direct writing of electronic devices is assessed in terms of transfer, melting and doping capability, and compared with other State-of-the-Art laser doping processes.

In this paper, we present the investigation results on doping to a BK7 glass sample ( OHARA, S-BSL7 ) by use of a CO2 laser. CO2 laser system generates CW ( continuous wave ) laser beam with a wavelength of 10.6 μm. Laser beam irradiated on a sample substrate ( 30 mm × 5 mm × 0.67 mm thick ). A surface of the glass was applied fluorescent material. The doped regions were created by translating the glass sample perpendicular to the laser axis with a distance of 2 mm and a scan speed of 1 mm/s. After processing, the cross section of sample was analyzed by energy dispersive X-ray analysis ( EDX ) in scanning electron microscope for revealing the contained elements in the glass. The results show that carbon was widely distributed in the doped regions although the original glass material did not contain carbon element.

Micro-system for biology is a growing market, especially for micro-fluidic applications (environment and health). Key part for the manufacturing of biology MEMS is the deep silicon etching by plasma to create microstructures. Usual etching process as an alternation of etching and passivation steps is a well-known method for MEMS fabrication, nowadays used in high volume production for devices like sensors and actuators. MEMS for biology applications are very different in design compared to more common micro-systems like accelerometers for instance. Indeed, their design includes on the same chip structures of very diverse size like narrow pillars, large trenches and wide cavities. This makes biology MEMS fabrication very challenging for DRIE, since each type of feature considered individually would require a specific etch process. Furthermore process parameters suited to match specifications on small size features (vertical profile, low sidewall roughness) induce issues and defects on bigger structures (undercut, micro-masking) and vice versa. Thus the process window is constrained leading to trade-offs in process development. In this paper process parameters such as source and platen powers, pressure, etching and passivation gas flows and steps duration were investigated to achieve all requirements. As well interactions between those different factors were characterized at different levels, from individual critical feature up to chip scale and to wafer scale. We will show the plasma process development and tuning to reach all these specifications. We also compared different chambers configurations of our ICP tool (source wafer distance, plasma diffusion) in order to obtain a good combination of hardware and process. With optimized etching we successfully fabricate micro-fluidic devices like micro-pumps.

This study focused on optimizing a vapor-phase hydrofluoric acid etching process to eliminate stiction occurrence during NEMS release. A dedicated lithography mask was designed to assess the performance of the HF vapor process from a stiction standpoint. This mask features all typical structures found in NEMS and MEMS devices (beams, combs, ground planes). For each structure type, representative dimensions vary (for instance: for a fixed beam width, length ranges from 1 to 200μm). Therefore, the release efficiency for a given process is the maximum size of a specific structure that is released without observing any stiction. Several design-of-experiments were successively carried out in order to compute different models representing the stiction occurrence for a given structure design as a function of process parameters (HF and IPA flowrates, temperature). The main output parameter in DOEs was the release efficiency on different beam designs, which is characterized on SOI wafers patterned with the mask described above. Though, for industrial considerations, etch rate and etch uniformity were also taken into account. Model accuracies were then tested experimentally and the best fit was found to be a second degree model including only the HF and IPA flowrates as factors, the temperature being held constant at 20°C. Thanks to this model, optimization was then carried out by targeting the highest release performance achievable. A new set of process parameters was figured out which improved release efficiency by 15% while the etch rate is four times faster than the former process used.

We developed a process for the fabrication of thin vertical mirrors as integrated structures of MEMS electrostatic actuators. The mirrors can be implemented as a vertical extension of the actuator sidewall, or can be positioned at any movable part of the actuator. The process involves the fabrication of a mesa structure on the handle layer of a silicon-oninsulator (SOI) wafer through deep reactive ion etching (DRIE). The etch/passivation cycles of the DRIE process were optimized to achieve vertical etch profiles with a depth of up to 200 μm with an aspect ratio of 10:1. The DRIE process introduced typical etch scallops with peak-to-valley and rms roughnesses on the order of 100 nm and 30 nm, respectively. A mask layer was used to pattern a 2.1 μm sacrificial oxide layer for the mesa structure. A second mask layer allowed us to define a large etch cavity for handle layer back-etch. The DRIE etched mesa structure was then etched with diluted potassium hydroxide (KOH) in isopropyl alcohol (IPA). Temperature and etch concentration were optimized for the removal of etch scallops without the formation of ⟨111⟩ etch facets. The etch scallops were almost completely removed and mirror quality surfaces were achieved. The developed mesa structures are suitable for integration into actuators that are patterned in the device layer. A third masking layer, aligned through infrared camera, was used to position the thin vertical mirror at the actuator sidewall. The process provides design flexibility in integrating vertical mirrors of adjustable dimensions to movable elements of MEMS structures.

A surface micromachining technique of LiNbO₃ substrates, based on an improved implantation-assisted wet etching process, will be presented and discussed. 2.3 μm high relief structures with optical quality surfaces were fabricated on LiNbO₃ by 5 MeV Cu ion implantation through an SU-8 10 μm thick photoresist masking layer patterned by a standard photolithographic process. The LiNbO₃ regions amorphized by implantation were etched in a 49% HF aqueous solution at a rate of 100 nm/s exploiting the high differential etching rate between damaged and undamaged LiNbO₃ (100 nm/s against 1 nm/s). The process can be repeated to obtain higher aspect ratios. In this work the results of both single and double step processes will be presented. The sidewalls morphology of the microstructures will be also discussed. Both the surface quality and features of the manufactured structures make this technology highly promising for integrated optics and acousto/opto-fluidics.

We found that the tip size of a tapered hollow micro-tube can affect the properties of an emitted Bessel light beam. In addition, the incident light polarization state was also found to influence the characteristics of the emitted light beam. From a lithography viewpoint, we looked at the correlation between an emitted Bessel light beam from a subwavelength annular aperture on metallic film and from a tapered hollow micro-tube. Intensity profiles were analyzed using finitedifference time-domain (FDTD) simulations and lithography experiments were undertaken. The approaches used to couple the incident light into the hollow micro-tube and to the subwavelength annular aperture are discussed. Effects from the waveguide mode were studied. Our results showed that the tube thickness of the tapered hollow micro-tube tip is an important factor in generating the Bessel light beam wavelength. We show that lithography can be used with a through-silicon-via (TSV) process in a far-field region while maintaining a near diffraction-limit spot size. Our tapered hollow tube design is useful for applications such as optical lithography, super resolution optical detection, and fabrication of high aspect ratio structures.

Diffractive optical elements (DOEs), with their thin profile and unique dispersion properties, have been studied and utilized in a number of optical systems, often yielding smaller and lighter systems. Despite the interest in and study of DOEs, the application of DOEs has been limited to narrow spectral bands. This is due to DOEs depths, which are optimized for optical path differences of only a single wavelength, consequently leading to rapid decline in efficiency as the working wavelength shifts away from the design wavelength. Various broadband DOE design methodologies have recently been developed that improve spectral diffraction efficiency and expand the working bandwidth of diffractive elements. Two such extended bandwidth diffractive designs have been modeled and fabricated. The diffraction efficiency test result for one broadband DOE design is presented.

This paper presents design, fabrication and measurements for single-axis piezoelectric MEMS micromirrors with 1 mm² apertures. These micromirrors, which feature thin-film PZT actuators and mechanical leverage amplification, are dedicated for laser projection and meet the requirements of high resonant frequency and large deflection angles. To identify the optimal micromirror geometries a parametric study by means of FEM simulations and analytic modeling has been performed. Characterization, related to the material qualities of PZT and the mechanical performance of the micromirrors, have verified the reliability of the process, the robustness and the performance of the fabricated prototypes. According to the measurements the fabricated micromirrors feature high Q-factor about 1570. The micromirror reaches the θ_opt·D product of 42.5 °·mm at 32 kHz driven by a low voltage of 7 V. Furthermore, new designs with larger apertures and deflections are currently being developed.

In the present work the technique of the high-pressure thermoelectric (TE) investigation has been developed for the phase transition recording at Si and the values of thermopower (S) for the different high pressure and metastable phases of Si have been obtained using the automated high-pressure set-up. The TE properties of various phases and states of Si were established which may be potentially used in Si-based nano-devices [1, 2]. The technique was shown also to be sensitive to the pre-treatments applied to a sample including annealing, doping, and irradiation by high-energy particles. The band structure calculations of the several phases of Si were carried out using linear muffin-tin orbital method (LMTO). The experimental values of thermoelectric power of various phases of Si up to 25 GPa are compared with the theoretical estimations basing on the band structure calculations performed. The theoretical calculations have confirmed the principal role of the contribution of d-band both in the forming of the electron states in the vicinity of Fermi level, as well as in the positive sign and the value of a thermoelectric power.

A method of generating arbitrary structures using spatial light modulator (SLM) based holograms with multiphoton absorption is presented. Current methodologies for designing 3D prototyping, such as G-code, are not ideally suited for holographic lithography and therefore limit its functionality or requires additional complex processing. The process outlined here allows a microstructure to be fabricated based on designs from commercially available CAD software. CAD software enables the microstructures to be designed and then realized using dynamic holographic lithography methods enabling designers a simple, quick, and robust method of fabricating novel microstructures. Holographic patterning routines such as raster scans of one or multiple focal points, holograms encoded with two or three dimensional spatial information, or a combination of both techniques may be utilized with this methodology. The process described allows for the development of complex structures that would be difficult to otherwise program using traditional methods. No limitations are placed on the form or function of the designed components, enabling undercut and interlocking features to be fabricated. This methodology also enables the location and orientation of the structures to be controlled dynamically simplifying the process of creating multi-scaled structures or complex arrays of arbitrary structures. As a proof of concept demonstration, a simple cantilever beam was modeled and fabricated.

Surface wettability depends on both physical surface structure and chemical material. In this report, we demonstrate super-hydrophobic surface of cast polymethyl methacrylate (PMMA) sheet by femtosecond laser fabrication. Twodimensional micro-array structures of square-typed pillars with various heights, widths, and intervals were fabricated on the PMMA surface by femtosecond laser irradiation and chemical etching. The Yb:KGW femtosecond laser processing system (λ=1030 nm) delivering 250 fs pulses at a repetition rate 100 kHz was employed for fabrication. The contact angle of PMMA changed 64° (hydrophilic plane) to 150° (super-hydrophobic structure). We also improved superhydrophobicity up to 170° contact angle by spin-coating PMMA surface with PDMS and fabricating regular microstructures including irregular nano-structures. We also coated the structured PMMA surface with a car ash spray material to use another combination of surface morphology and chemistry. All the experimental results were compared with those expected values by Cassie-Baxter model.