Printing sub-micron structures using Talbot mask-aligner lithography with a 193 nm CW laser light source

A continuous improvement of resolution in mask-aligner lithography is sought after to meet the requirements of an ever decreasing minimum feature size in back-end processes. For periodic structures, utilizing the Talbot effect for lithography has emerged as a viable path. Here, by combining the Talbot effect with a continuous wave laser source emitting at 193 nm, we demonstrate successfully the fabrication of periodic arrays in silicon substrates with sub-micron feature sizes. The excellent coherence and the superior brilliance of this light source, compared to more traditional mercury lamps and excimer lasers as light source, enables the efficient beam shaping and a reduced minimum feature size at a fixed gap of 20 μm. We present a comprehensive study of proximity printing with this system, including simulations and selected experimental results of prints in up to the fourth Talbot plane. This printing technology can be used to manufacture optical metasurfaces, bio-sensor arrays, membranes, or microchannel plates

Improved calibration of vertical scanning optical profilometers for spherical profiles measurements

A new method for calibrating optical scanning profilometers is presented. Especially adapted to spherical and aspherical profile measurements, it shows an increase of accuracy bigger than one order of magnitude for radius of curvature measurements. Calibration of vertical scaling is obtained with a reduction of its uncertainty by a factor larger than 2, which also demonstrates the advantage of this method for any surface measurements. Using commercially available reference balls, this method is easily implementabl

High power modular LED-based illumination system for lithography applications

Mask-aligner lithography is a technology used to transfer patterns with critical dimensions in the micrometer range from below 1 micron for contact printing to a dozen of microns in proximity printing. This technology is widely used in the fabrication of MEMS, micro-optical components, and similar fields. Traditionally, the light sources used for mask-aligners are high-pressure mercury arc lamps, which emit in the UV rang of the spectrum with peaks at 365 nm, 405 nm and 435 nm, respectively the g-, h- and i- lines. These lamps suffer from several disadvantages (inefficient, bulky, dangerous), which makes alternatives interesting. In recent years, high power UV LEDs at the same wavelengths appeared on the market, opening the door to new illumination systems for mask-aligners. We have developed a modular 250 W LED-based illumination system, which can advantageously replace a 1 kW mercury arc lamp illumination. LEDs, arranged in a 7x7 grid array, are placed in the entrance apertures of individual reflectors, which collimate the individual irradiation to an output angle of 10◦. A subsequent fly’s eye integrator homogenizes the illumination in the mask plane. It is followed by a Fourier lens, superimposing the individual channels in the mask plane, and a field lens to ensure telecentric illumination. This multisource approach allows the shaping of the source by switching individual illumination channels, determining the illumination angles and the spatial coherence in the mask plane. This concept can be used, for example, to do source-mask optimization. Compared to mercury arc lamp illumination, our system is simultaneously more efficient, compact, versatile, economic and sustainable. In our contribution, we present the design of the system as well as lithographic test prints done with different illumination patterns

Design and fabrication of a circular Digital Variable Optical Attenuator

The second generation circular digital variable optical attenuator (CDVOA) with an effective area of 1500 μm diameter has been designed and fabricated based on SOI technology. C-band incoming Gaussian light can be reflected to an outgoing fiber from a shiny circular area, which is divided into sectors that can be individually tilted and addressed electrostatically to achieve variable light attenuation. Using a delay mask process, each movable component i) has an underlying ridge frame to maintain flatness, ii) is suspended by two micro beams at a bridge structure that connects to a handle where aluminum electrode is located underneath, and iii) is separated by wall structures at the handle area to reduce crosstalk from adjacent electrodes. Critical fabrication processes including the mirror and chip release are performed using a HF vapor phase etcher. Fluidic pressure and chip-dicing shocks are avoided. Initial results show that a mirror sector suspended by two 345 μm long beams with a cross-section of about 5×5 μm2 can be tilted to 2.8° at about 18 V driving voltage. Initial interferometric measurement gives estimated individual mirror flatness after metallic reflective coating to be about λ/15. The assembled chips are ready for further testing and characterization

Assessing microlens quality based on 3D irradiance measurement at the focal spot area

During the fabrication process of microlenses, characterization is essential for two purposes: evaluate the optical quality of the element and provide surface information feedback for process optimization. However, no technique can fulfill these two objectives at the same time. Interferometry is used for quality evaluation and optical profilometry for process optimization. In order to address this problem, we propose to use a high resolution interference microscope to characterize microlenses. The focusing capacity can be directly measured by recording the field near the focal spot at different wavelengths. Information about the microlens surface can also be retrieved. All this is illustrated for the front focus of a fused-silica microlens

Printing sub-micron structures using Talbot mask-aligner lithography with a 193 nm CW laser light source

A continuous improvement of resolution in mask-aligner lithography is sought after to meet the requirements of an ever decreasing minimum feature size in back-end processes. For periodic structures, utilizing the Talbot effect for lithography has emerged as a viable path. Here, by combining the Talbot effect with a continuous wave laser source emitting at 193 nm, we demonstrate successfully the fabrication of periodic arrays in silicon substrates with sub-micron feature sizes. The excellent coherence and the superior brilliance of this light source, compared to more traditional mercury lamps and excimer lasers as light source, enables the efficient beam shaping and a reduced minimum feature size at a fixed gap of 20 µm. We present a comprehensive study of proximity printing with this system, including simulations and selected experimental results of prints in up to the fourth Talbot plane. This printing technology can be used to manufacture optical metasurfaces, bio-sensor arrays, membranes, or microchannel plates