In this design study a new design is proposed for an in situ surface inspection tool that can rapidly detect micrometer sized water droplets on a silicon wafer. This surface inspection tool is part of a proposed redesign of the thermal conditioning stage of VDL-ETGs atmospheric wafer handler. A meticulous requirements study was performed, and the most important results were the following: 1) droplets with diameters larger than 35 μm should be measured, 2) the size, shape and location of the droplets is not relevant, 3) the wafer is not allowed to heat up by more than 3 mk as a result of the inspection, 4) the entire wafer surface should be inspected in less than 2 seconds and 5) only one droplet may pass undetected in every 6200 wafers. Several concepts were generated and after comparing them the synchronous dark-field flying spot scanner was selected, mainly for its high signal strength, and the low amount of signal fluctuation for different droplet locations. The design contains several parameters, the combination of which influence the system performance in a non-trivial way. A parametric design tool has been developed that takes in the design parameters as inputs, and outputs the system performance values and important design dimensions. This design tool was used to find design parameters that yield the desired performance. A simplified version of the design was built as an experimental setup for validation. For the experimental setup, a small spot size was chosen. This allowed us to better characterize the scattering behavior, however as a consequence this also prevented us from directly comparing the experimental results to the system performance yielding from the design tool. The experimental results were the following: 1) A very small part of the droplet surface is responsible for the large majority of the measured scattering, 2) the peaks are narrower in the cross-scan direction than in the scan direction, most likely due to the droplets being flat. 3) The measured noise is much higher than the predicted noise, this is likely due to poor grounding, poor shielding or a lack of filtering out high frequencies. Although the experimental setup yielded interesting results, the setup was not sufficient to fully validate the design – further experimentation is required to determine 1) if the predicted signal amplitude is correct, 2) if the signal amplitude scales with the square of the diameter of a droplet, 3) if the optical components remain as clean as we expect during operation of the dry unit, and 4) if the noise levels can be reduced to the desired level. Additionally, to improve the design further we suggest looking into ways of reducing the wafer warp and wobble. ... Read more

To assist in the fast alignment of tiny components, Prodrive Technologies has developed a type of camera system called the Component Alignment Sensor (CAS) that is used on a pick-and-place machine. The system uses an optical target as the reference during its assembly and final testing steps. Two main components of the target are a glass reticle and a stainless steel carrier that are bonded together. These two components need to be precisely aligned w.r.t. each other. Till now, the alignment between the reticle and carrier has been performed manually by relative movement between them created by hand. However, this method has some limitations, including, but not limited to, an increase in the alignment time and sensitivity to external jerks or disturbances. Accordingly, the thesis objective is to create a (detailed) design of an alignment mechanism to perform the 3-DOF in-plane alignment in µm and sub-mrad level. The research starts with the formulation of design requirements, followed by concept design, evaluation and selection, and finally a detailed design of the mechanism. A flexure-based alignment mechanism was proposed and designed that uses fine screws for actuation. Various design principles were applied to construct a stiff and compact mechanism that uses a limited number of adjustment steps for the alignment. The process was supported by calculations and analyses that contributed to decision making. Besides, the assembly and alignment procedures of the alignment mechanism were described. The thesis is concluded with a plan to verify if the matured design meets the set requirements. ... Read more

Industry-wide there is an interest in chemical composition sensing of materials, which requires no sample preparation and can be implemented in real-time. Laser-Induced Breakdown Spectroscopy, or LIBS, is a measurement tool able to achieve this by exciting material, creating an analytical plasma followed by observing its atomic emission of light. Wavelengths characteristic for the elements present in the material can be identified and used for quantitative measurements. This thesis focuses on how an instrument utilizing LIBS can be designed such that deformations of the instrument due to environmental loads do not influence the creation, and especially, the observation of the plasma. Experiments done showed the calibrated algorithm to misestimate the chemical composition if the plasma is partly observed. The proposed design of the instrument is realized and put to the test for thermal and mechanical loads individually, which verified its performance to stably create and observe the analytical plasma while enduring these. ... Read more

Use of earth observation satellites have grown at a very high rate over the past few decades. On a closer observation of things around, most of them uses satellites, directly or indirectly. Satellites are being used in the day-to-day life without being aware of its application. Satellites are used for small things like weather report, communication to very large things like internet of things (IOT) and earth observation. Some CubeSats are also used for interplanetary missions. For the purpose of earth observation missions, the satellites are installed with an optical payload which is a camera. The cameras used for space are different from the regular camera and have special specifications in terms of the materials, components and the design which make them suitable for space missions. The optical payload which is to be launched has to be made sure that it can survive the launch and in orbit environment. This research focuses on the testing of these CubeSats and check if they are suitable for launch. The research starts with reviewing the testing procedure that is followed before the satellite is launched. A setup is provided for checking the performance of the camera mounted on the CubeSat and its suitability for launch. To investigate the performance of the camera, MTF and correlation techniques are used on different images to come to a conclusion. ... Read more

The ever-growing demand for smaller microchip feature sizes and thus more powerful chips, has fuelled innovation in photolithography machines for decades. Currently, within this context, one possibility that is explored at ASML involves an increase in the number of alignment markers on a wafer, for a more accurate mapping of local wafer deformations. The current alignment marker metrology system consists of a diffraction-based sensor that is space consuming and measures the markers one-by-one. To prevent a longer total measurement time due to a larger number of markers, parallel read-out is pursued by miniaturisation of the sensor. The technology that is explored for this miniaturisation is integrated optics, in which classical optical components are replaced by their waveguide-based equivalent structures on a chip-sized sensor. Contributing to the feasibility study of integrated optics for ASML’s wafer metrology, this work focuses on the design, construction and verification of an experimental setup for photonic integrated circuit (PIC) alignment sensors. The setup is capable of characterizing the output beams of grating couplers, important PIC components, by imaging their intensity profiles at different locations along their propagation direction. Spots of 40µm can be imaged with a spatial resolution of 0.3µm and an expected Z-position accuracy of 6µm. The setup is also able to scan alignment marks with a PIC alignment sensor, with an expected repeatability of 1.1nm. Anticipating completion of the first PIC alignment sensor designed by the TU Eindhoven, measurements on an alternative PIC containing elementary structures were conducted. Successful coupling between angle polished fibers and 15x15µm grating couplers was achieved, with a verified coupling efficiency of 21.4±3.6%, compared to a coupling efficiency of 28% with the conventional flat end-face fiber coupling method. ... Read more

With PLATO the European Space Agency (ESA) will launch its third medium-class mission in its Cosmic Vision program. The PLATO satellite consists of 26 optical refractive telescopes where 24 identical wide field cameras form composed images.

Each individual camera must be tested and characterized before being integrated in the satellite. At SRON (Netherlands Institute for Space Research) a thermal vacuum (TV) test facility will mimic the operating conditions of the camera during flight while a star will be simulated by a collimated beam filling the full entrance pupil of the camera.

The aim of this project is to design, build and validate a 150 mm diameter collimator with a λ/4 wavefront error at 700 nm to be used in the PLATO camera thermal vacuum (TV) test facility at SRON.

A requirement breakdown has been made to further determine the collimator design parameters. Multiple design concepts have been generated for distinct parts of the collimator. After choosing the final concepts, a detailed opto- echatranical design has been made. In parallel, an alignment procedure was developed.

The designed components have been manufactured, assembled, aligned, and validated. Result after final alignment is a of λ/5.2 wavefront error at 700 nm over a 150 mm diameter beam, well within the requirement for optical performance.

As the final step of the integration, the collimator has been installed in the TV test facility at SRON where it is now fully operational. ... Read more

There are strict tolerances on the placement of optical components in high performance optical systems. Compliant alignment mechanisms can be used to meet these tolerances. Conventional manufacturing techniques, such as milling and spark erosion, have been used to produce an extensive library of alignment solutions but are limited in the geometries they can produce. Metal 3D printing (SLM) is a newer manufacturing method that can produce complex geometries in a large design space with unique limitations but has no extensive library of solutions. A design method is proposed to construct building blocks for concept generation as a foundation for this library. The method aims at achieving this by reducing the size of the solution space, dividing it into separate constraint combinations. These constraint combinations and tools to develop them into building blocks are presented as tables with geometries and a flowchart describing their use. The design method is demonstrated by applying it towards the development of a compact, low-mass mechanism with three independent alignment stages. FEM analysis and a prototype in Ti6Al4V are used to explore some of the properties and manufacturability of this demonstration case. ... Read more

With climate change being a prime source of concern around the world, air pollution is a topic that requires special attention. Therefore, it is of utmost importance to track and measure the emissions in our environment for detecting the sources and understating the climate change so as to figure out possible solutions. Despite ongoing development, the current LEO and GEO satellite instruments have a long prolonged global survey, revealing the pollution trends at a broad scale, but there is still a lack of high-resolution data to pinpoint pollution sources.

For this, John Hopkins University (Applied physics lab) and NASA are now developing a new earth atmospheric monitoring mission called Compact Hyperspectral Air Pollution Sensor (CHAPS) to address it at a local scale. Presently, TNO is carrying out the design study for this system by employing both freeform optics and additive manufactured mechanics. The mission objective is to perform targeted local measurements of the atmosphere on a daily basis by providing high spatial and temporal resolution possible in UV-VIS wavelength range.

In order to characterize, quantify, and monitor emissions from urban areas, power plants, and other anthropogenic activities, it is important to collect accurate and precise data and calibrate the optical instrument. But the data often received from the sensor is not reliable due to the operational and the non-operational conditions leading to cross-sensitivity, change in the trajectory, and optomechanical errors. For this, an on-board calibration system is developed to perform continuous calibration of the science product, that is compatible with both the instrument and the satellite platform and is robust to the variable operating conditions. This requires a stable system that achieves a good performance that is insensitive to thermal and mechanical disturbances, in order to meet the strict specifications.

As opposed to conventional methods, additive manufacturing, enables new possibilities for developing Optomechanical structures because of the layer-wise manufacturing technique. This manufacturing process is widely touted as a foundation for the next industrial revolution as it offers profound advantages like shorter lead time, lower wastage of materials, and higher geometric complexity that can be useful for multi-functional and multi-material structures. It can also facilitate good strength, significant mass reduction, and better dimensional homogeneity and stability. At the same time, additive manufacturing is not an easy process and requires new design strategies and solutions for overcoming the existing constraints.

The prime research objective is to investigate the optomechanical design of the spectral calibration module applying a kinematic approach. The second research objective is to investigate design and the potential improvements when applying additive manufacturing. The present case study demonstrates and evaluates the preliminary phase of the calibration module design study, thus providing the key ingredients for the realisation of the full system. ... Read more

A wavelength modulated interferometer is presented, based on a telecom laser source. A solution for the target distance dependency of wavelength modulated interferometers is presented. With the introduction of a delay line, the modulation depth variation is reduced. A method and a sensor head for the reduction of the thermal dependency of this delay line are presented. The resulting interferometer has sub-nanometer non linearity errors and a thermal dependency of below 3 nmK¡1 with a working range of 1meter. ... Read more

The packaging of a microchip affects its size, performance and cost. With advanced packaging, more efficient and smaller microchips can be produced. For this, advanced packaging stepper systems are used, which are lithography machines with a highly optimized projection lens system, that use a powerful light source. The projection lens system for lithography machines are highly accurate optical assemblies with stringent optical requirements, such as a small wavefront error. These requirements need to be fulfilled, while also dealing with a high throughput. Due to the high throughput and the powerful light source, some of the light passing the projection lens system gets absorbed by the lenses. This causes local lens heating, which degrades the optical performance. Local lens heating causes thermal gradients to arise in the lenses, which cause refractive index gradients. Due to thermal expansion, the lenses will also deform, therefore changing the geometry of the optical surfaces. To analyze the lens heating effects, a Structural, Thermal and Optical Performance (STOP) analysis is performed. A multiphysics Finite Element Method (FEM) analysis model is build in COMSOL, which couples the structural, thermal and optical physics in a single model, which can model both steady-state and transient behaviour. ... Read more

The manufacturer of an electron beam lithography machine pushes a better understanding and higher performance of the optical column to provide a better product with each iteration. At the heart of the column is the source of electrons: the gun lens. It holds the field emitter from which the electrons originate and accelerates the beam to a first crossover. The main work in this thesis was concerned with development of a new and better gun lens design. Consideration of several physical phenomena is required in order for the gun lens to be more robust and with a more stable beam. It was found that the heating transient plays a large role in the operation of the gun lens. By defining the requirements clearly including by ray-tracing the optical geometry to find optical sensitivities, the main challenges of the project became evident. A new concept design is presented where the heat transport inside the gun lens is improved and thermal drift is greatly diminished. By using the ceramic insulators as flexures the short- and long-term stability of the lenses are improved and the thermal transient settling time is reduced from 26 hours to below 6 hours. By opening up the geometry inside the gun lens the local vacuum at the emitter is much better, which increases its lifetime. The electrostatic fields are made much more robust by burying the triple junction, which required using a new insulator shape. The final result is a gun lens concept design which improves in all aspects while remaining simple in construction. ... Read more

There is an increasingly demand for higher performing e-beam lithography machines. An important user requirement is the beam stability, this is dened for the short and long term. This thesis focuses on improving the beam stability with the use of a new metrology design. The e-beam machine has the potential to real-time correct for all correctly measured mechanical displacements, which makes the metrology a powerful tool in ensuring high beam stability. In the current system the main contributors to displacement measurement errors are vibrations and thermal drift present on/in the metrology system. These measurement errors decrease the beam stability. The proposed metrology design makes use of a differential displacement measurement between the electron optical column and the stage. This makes the displacement measurement almost insensitive to vibrations and thermal drift. The short term beam stability is improved from <5 nm to <3.5 nm and the long term stability is improved from <50 nm to <9 nm. ... Read more

As the world becomes more connected, smarter, and more eco-friendly, computer microchips represent both the limitation and the heart of the process. To keep up with this growth, ASML creates machines that areable to produce computer-chips that are increasingly powerful & energy efficient. State of the art machines are converting CO2 laser light into Extreme Ultra Violet (EUV) light that is crucial for the process. However, the conversion efficiency depends a lot on the beam quality of the CO2 laser light. This beam quality depends, among other things, on the optics (mirrors) and their associated surface deformations. Many examples exist in Opto-Mechanical oriented literature about mounting mirrors. However, many of them are tailored to the specific circumstances. In order to present and use existing knowledge, a literature study is conducted that summarises and elaborates on current technology. The purpose of this thesis is to present an existing Opto-Mechanical error in current design of a subsystem of the EUV machine, and thereby propose a new design, tailored to the requirements. The research follows the well known V-model, beginning with derivation of clear requirements leading to a verificationtable that analyse those specifications. This conceptual design has shown to have up to a 4X improvement in terms of astigmatism which mainly occurred due to the temperature variations during transport. ... Read more

Production and manipulation of microdroplets is an active are of research. The demand for finding new ways to produce microdroplets has resulted in a challenge to characterize these droplets. The problem becomes especially difficult for microdroplets which are placed on a transparent hydrophilic substrate. Ink-jet printing, Digital microfluidics, DNA synthesis are some of the applications which need topography measurements of low contact angle microdroplets. One application which is of interest is the sample preparation for Cryo Electron Microscopy (cryo-EM). A recent development in the search for efficient sample preparation for cryo-EM is to use hollow microcantilevers (HMC). HMCs can isolate even a single sub-cellular component and help prepare samples confined in a femtoliter droplet. These droplets are dispensed on a hydrophilic Electron Microscopy grid (EM-grid). By controlling the thickness of the water layer on the EM-grid through evaporation, it is possible to make the HMC technology more reliable by reducing sample wastage. However, such a control loop is absent. A real-time topography measurement of such droplets can serve as a control signal which can be used as feedback for a control loop. The objective of this project is to investigate the feasibility of optical methods to measure the topography information of a low contact angle microdroplet. The scope of this project is limited to develop a tool for a droplet which is supported by a glass slide (droplet-on-glass). In a subsequent study, the tool will be tested for droplets supported on grid (droplet-on-grid). An optical interferometry setup is proposed as a solution. A Mach-Zehnder interferometer is built to obtain the experimental fringes. A Single Frame Fourier Transform technique was used to analyze the data and obtain the results. Droplets of glycerol were dispensed on a glow discharged glass slide. Topography of the droplet was obtained until complete evaporation and a detection limit of 165nm was achieved. The accuracy of the method was found by comparing the results obtained with a Bruker White Light Interferometer (Bruker-WLI) in Phase Shifting Interferometry mode. An accuracy of 23\% was observed. The proposed setup had a repeatability of 14.7nm. To measure the reproducibility of the setup, a 3d printed structure which had the same size and shape as that of a droplet was used. The reproducibility of the setup was found to be 19.8nm over three days. Simulations were performed to analyze the effect of filter shape, filter width and the carrier frequency. Based on these findings, steps to measure a droplet-on-grid system with the proposed setup is explained. Further, to test the capabilities of the instrument the evaporation of a large water droplet on a EM-grid was observed using the proposed setup. It was found that the motion of fringe pattern as the droplet evaporates could give a good indication to control the evaporation time of even conventional machines, which do not employ hollow microcantilevers to dispense small droplets. However, final validation of the proposed setup with the cryo-EM is yet to be performed due to time constraints. As a recommendation for future work, new ways of dispensing samples on the EM-grid are explored. The necessary steps required to validate the setup with a cryo-EM are explained. Further, some ways in which the analysis time could be reduced are explored. This will be helpful in developing a software necessary to implement a real-time solution. ... Read more

The average worldwide internet traffic demand in 2022 is projected to be over 1200 Terabits per second. A fifth of this data would be transmitted using mobile networks. One of the technologies used for this is radio frequency (RF) telecommunication, but this technology is reaching its limits. Despite ongoing development, typical data rates are still in the order of Gigabits per second per link.

TNO is working on a telecommunication link (called TOmCAT) that can reach data transfer rates of a Terabit per second. The high data rate is achieved using a very promising alternative to RF telecommunication: optical telecommunication, which is also known as laser communication.

In order to reach the intended data rates, the data needs to be spread over multiple optical frequencies. These signals need to be combined into one transmitted beam using a free-space optical bulk multiplexer.

The laser beams that are transmitted by their collimators need to be aligned with respect to each other in order to reach the satellite as one beam. The footprint available for the required alignment mechanisms is very limited. Furthermore, the system needs to achieve a good thermal and mechanical stability in order to meet the strict specifications.

The aim of this thesis is two-fold: to show the need for achieving state-of-the-art alignment specifications with strict footprint constraints, and to defend the steps taken to achieve these requirements. The research spans the entire design process of the alignment assembly: from higher/system level trade-offs and calculations, to the derivation of the design specifications, to the conceptual and detailed design, and concluding with the manufacturing and testing of the first prototype.
... Read more