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In proximity mask aligner photolithography, diffraction of light at the mask pattern is the predominant source for image shape distortions such as line end shortening and corner rounding. One established method to mitigate the impact of diffraction is optical proximity correction. This method relies on a deliberate sub-resolution modification of photomask features to counteract such shape distortions, with the goal to improve pattern fidelity and uniformity of printed features. While previously considered for masks featuring only rectangular shapes in horizontal or vertical orientation, called Manhattan geometries, we demonstrate here the capabilities of computational mask aligner lithography by extending optical proximity correction to non-Manhattan geometries. We combine a rigorous simulation method for light propagation with a particle-swarm optimization to identify suitable mask patterns adapt to each occurring feature in the mask. The improvement in pattern quality is demonstrated in experimental prints. Our method extends the use of proximity lithography in optical manufacturing, as required in a multitude of micro-optical devices. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

The wafer-level production of Fused Silica microlens arrays is limited by systematic process non-uniformities. The common molten resist-reflow process with subsequent dry-etching allows for manufacturing of microlens arrays on 200 mm wafers. A thorough process review yielded one free parameter. By switching from the geometrical lens description via radius of curvature and conic constant to a functional assessment via the optical design figure of merit we can describe microlens via their optical quality for the intended application with one parameter for a wide variety of cases. Leveraging these points we show improvements on the uniformity of microlens arrays by a factor of 2 for Fused Silica microlens arrays bigger than 100 mm by 100 mm.

The uniformity of large microlens arrays in Fused Silica is governed by the production process. It comprises photolithographic patterning of a spin-coated layer of photoresist on a 200mm wafer with a molten resist reflow process and subsequent dry etching. By investigating systematic influences throughout the production process we show how to steer the lens production process with a single degree of freedom to improve the uniformity of the final microlens array. To enable this we describe the optical performance of microlenses with only one parameter: the principal aberration component. It is the result of principal component analysis of the chosen optical merit function. We present the case of manufactured microlens arrays with element sizes > 100 mm x 100 mm where uniformity was improved by a factor of 2. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

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 7×7 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.

We introduce a novel industrial grade 193nm continuous-wave laser light source for proximity mask-aligner lithography. A diode seed laser in master-oscillator power-amplification configuration is frequency-quadrupled using lithiumtriborate and potassium-uoro-beryllo-borate non-linear crystals. The large coherence-length of this monomodal laser is controlled by static and rotating shaped random diffusers. Beam shaping with imaging and non-imaging homogenizers realized with diffractive and refractive micro-optical elements is compared in simulation and measurement. We demonstrate resolution patterns offering resolutions

We present a mask-aligner lithographic system operated with a frequency-quadrupled continuous-wave diode laser emitting at 193 nm. For this purpose, a 772 nm diode laser is amplified by a tapered amplifier in the master-oscillator power-amplifier configuration. The emission wavelength is upconverted twice, using LBO and KBBF nonlinear crystals in second-harmonic generation enhancement cavities. An optical output power of 10 mW is achieved. As uniform exposure field illumination is crucial in mask-aligner lithography, beam shaping is realized with optical elements made from fused silica and CaF2 featuring a diffractive non-imaging homogenizer. A tandem setup of shaped random diffusers, one static and one rotating, is used to control speckle formation. We demonstrate first experimental soft contact and proximity prints for a field size of 1 cm2 with a standard binary photomask and proximity prints with a two-level phase mask, both printed into 120 nm layers of photoresist on unstructured silicon substrates.

We present and discuss Talbot mask-aligner lithography, relying on a continuous wave laser emitting at 193nm for the illumination. In this source, a diode laser at 772nm is amplified by a tapered amplifier in master-oscillator power-amplifier configuration and frequency-quadrupled in two subsequent enhancement cavities using lithium triborate and potassium fluoro-beryllo-borate nonlinear crystals to generate the emission at 193 nm. The high coherence and brilliance of such an illumination source is predestined for plane wave mask-aligner illumination, crucial in particular for high-resolution lithographic techniques such as Talbot lithography and phase-shift masks. Talbot lithography takes advantage of the diffraction effect to image periodic mask features via self-replication in multiples of the Talbot distance behind the photomask when exposed by a plane wave. By placing a photoresistcoated wafer in one of the Talbot planes, the mask pattern is replicated in the resist. Periodic patterns with diverse shapes are required for wire grid polarizers, diffraction gratings, and hole arrays in photonic applications as well as for filters and membranes. Using an amplitude mask with periodic structures, we demonstrate here with such a technique sub-micron feature sizes for various designs at a proximity gap of 20 µm.

The application of laser light sources for illumination tasks like in mask aligner lithography relies on non-imaging optical systems with multi-aperture elements for beam shaping. When simulating such systems, the traditional approach is to separate the beam-shaping part (incoherent simulation) from dealing with coherence properties of the illuminating laser light source (diffraction theory with statistical treatment). We present an approach using Gaussian beam decomposition to include coherence simulation into ray tracing, combining these two parts, to get a complete picture in one simulation. We discuss source definition for such simulations, and verify our assumptions on a well-known system. We then apply our approach to an imaging beam shaping setup with microoptical multi-aperture elements. We compare the simulation to measurements of a similar beam-shaping setup with a 193 nm continuous-wave laser in a mask-aligner configuration.

In this paper we present chromatic confocal distance sensors for the parallelized evaluation at several lateral positions. The multi-point measurements are performed using either one- or two-dimensional detector arrays. The first sensor combines the concepts of confocal matrix sensing and snapshot hyperspectral imaging to image a two-dimensional array of laterally separated points with one single shot. In contrast to chromatic confocal matrix sensors which use an RGB detector our system works independently from the spectral reflectivity of the surface under test and requires no object-specific calibration. Our discussion of this sensor principle is supported by experimental results. The second sensor is a multipoint line sensor aimed at high speed applications with frame rates of several thousand frames per second. To reach this evaluation speed a one-dimensional detector is employed. We use spectral multiplexing to transfer the information from different measurement points through a single fiber and evaluate the spectral distribution with a conventional spectrometer. The working principle of the second sensor type is demonstrated for the example of a three-point sensor.

Dispersion causes the focal lengths of refractive and diffractive optical elements to vary with wavelength. In our contribution we show how it can be used for chromatic encoding and decoding of optical signals. We specifically discuss how these concepts can be applied for the implementation of systems with applications in the growing fields of hyperspectral imaging and chromatic distance coding. Refractive systems as well as hybrid combinations of diffractive and refractive elements are used to create specific chromatic aberrations of the sensors. Our design approach enables the tailoring of the sensor properties to the measurement problem and assists designers in finding optimized solutions for industrial applications. The focus of our research is on parallelized imaging systems that cover extended objects. In comparison to point sensors, such systems promise reduced image acquisition times and an increased overall performance. Concepts for three-dimensional profilometry with chromatic confocal sensor systems as well as spectrally resolved imaging of object scenes are discussed.

Speckle fields are formed when quasi-monochromatic light is scattered by an optically rough surface. These fields are usually described by reference to their first and second order statistical properties. In this paper we review and extend some of these fundamental properties and propose a novel technique for estimating the refractive index of a smooth sample. Theoretical and experimental results are presented. Separately, we also report on a preliminary experiment to determine some characteristics of speckle fields formed in free space by a rotating compound diffuser. Some initial measurements are made where we examine how the speckle intensity pattern in the output plane changes as a function of the relative rotation angle.

The statistical properties of speckles in paraxial optical systems depend on the system parameters. In particular, the speckle orientation and the lateral dependence (x and y) of the longitudinal speckle size can vary significantly. For example, the off-axis longitudinal correlation length remains equal to the on-axis size for speckles in a Fourier transform system, while it decreases dramatically as the observation position moves off axis in a Fresnel system. In this paper, we review the speckle correlation function in general linear canonical transform (LCT) systems, clearly demonstrating that speckle properties can be controlled by introducing different optical components, i.e., lenses and sections of free space. Using a series of numerical simulations, we examine how the correlation function changes for some typical LCT systems. The integrating effect of the camera pixel and the impact this has on the measured first- and second-order statistics of the speckle intensities is also examined theoretically. A series of experimental results are then presented to confirm several of these predictions. First, the effect the pixel size has on the measured first-order speckle statistics is demonstrated, and second, the orientation of speckles in a Fourier transform system is measured, showing that the speckles lie parallel to the optical axis. Author has checked copyright DG 18/10/2012

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.

We present a novel industrial-grade prototype version of a continuous-wave 193 nm laser system entirely based on solid state pump laser technology. Deep-ultraviolet emission is realized by frequency-quadrupling an amplified diode laser and up to 20 mW of optical power were generated using the nonlinear crystal KBBF. We demonstrate the lifetime of the laser system for different output power levels and environmental conditions. The high stability of our setup was proven in > 500 h measurements on a single spot, a crystal shifter multiplies the lifetime to match industrial requirements. This laser improves the relative intensity noise, brilliance, wall-plug efficiency and maintenance cost significantly. We discuss first lithographic experiments making use of this improvement in photon efficiency.

A high-power LED-based illumination system has been developed as a replacement for the mercury arc lamps used in mask-aligner lithography. LEDs are arranged in a grid array and placed in the entrance aperture of individual reflectors. Those reflectors decrease the angular extent of the light. With this multisource approach, different groups of LEDs can be switched on independently. The illumination patterns created determine the illumination angles and the spatial coherence in the mask plane. The spatial coherence is measured in the mask plane by using a circular double slits approach. The interference pattern for different illumination patterns are measured, showing the effect of the asymmetry and size of the angular extent of the illumination light. The effect of the different illumination patterns on the quality of the prints are also illustrated with print tests.