A new solid state laser based mask projection technique for micro-structuring materials is introduced and results obtained with a pilot system are shown. Details of the proposed architecture of production tools using the new technology are given. Advantages of the new method over conventional excimer laser based mask projection systems are summarized.
The demand on performance for displays and opto-electronics is ever increasing and the industry is looking for ways to produce large area microoptical films to help that cause. While conventional techniques are reaching their limits for large area structuring, earlier reports show that it is possible to structure a few m2 polymer film with microoptical features (>20 μm) by direct laser ablation. By employing the same optics and hardware studies were carried out to find the minimal feature size possible without compromising the area that can be processed. Looking at the sub-resolution ablation behaviour of Polycarbonate enables us to modify the so-called Synchronised Image Scanning (SIS) mask design to control shape and form of 3D-features only a few times bigger than the resolution limit of the laser ablation mask projection system. Results of optical 10μm and 5μm features are shown and discussed. The findings show that it is realistic to direct laser cut well defined optical 3D-features into polymer film with an unprecedented feature-area-ratio in excess of 1:1010.
We have used KrF excimer laser ablation in the fabrication of a novel MEMS power conversion device based on an axial-flow turbine with an integral axial-flux electromagnetic generator. The device has a sandwich structure, comprising a pair of silicon stators either side of an SU8 polymer rotor. The curved turbine rotor blades were fabricated by projection ablation of SU8 parts performed by conventional UV lithography. A variable aperture mask, implemented by stepping a moving aperture in front of a fixed one, was used to achieve the desired spatial variation in the ablated depth. An automatic process was set up on a commercial laser workstation, with the laser firing and mask motion being controlled by computer. High quality SU8 rotor parts with diameters of 13 mm and depths of 1 mm were produced at a fluence of 0.7 J/cm2, corresponding to a material removal rate of approximately 0.3 μm per pulse. A similar approach was used to form SU8 guide vane inserts for the stators.
Two new laser mask projection techniques Synchronized Image Scanning (SIS) and Bow Tie Scanning (BTS) have been developed for the efficient fabrication of dense arrays of repeating 3D microstructures on large area substrates. Details of these techniques are given and examples of key industrial applications are shown.
The use of ceramic cores of high dielectric constant is an essential part of a strategy to miniaturize GPS antennas for mobile telephones. The core reduces the guide wavelength of the conducting structures on the antenna, thereby creating a need for high-resolution imaging to maintain very accurate dimensions. It is for this principal reason that a novel laser imaging technology has been developed using a positive electrophoretic photoresist and UV excimer laser mask imaging to produce the conducting features on the surface of the antenna. Furthermore, a significant process challenge in producing this type of antenna concerns the reproducibility of the right-hand circular polarization performance and the bandwidth over which this can be achieved - which becomes progressively smaller as antenna size is reduce. It is therefore a vital requirement that the antennas have the point to be tuned by a laser trimming process at an automatic RF testing station. A galvanometer controlled Nd:YAG laser spot is used to trim the conductive pattern on the top of the antenna following an RF measurement to characterize the resonant frequencies of the four helical conductors. Results demonstrate the laser imaging and trimming techniques ensure a high-speed method of guaranteeing the antenna performance. The technique is appropriate for other antenna types such as GSM, Bluetooth and Wireless LAN.
With the aim of reducing the heat-affected zone to improve edge quality, we present results of drilling microholes using reshaped pulsed Gaussian laser beams. A diode-pumped, high repetition rate, nanosecond pulse duration 3rd harmonic Nd:YAG laser was reshaped such that the intensity gradient in the outer region of the focussed laser beam profile is increased. Compared to focussed Gaussian laser beams, such hard-edged intensity distributions produce smaller heat-affected zones. As a result there is less associated collateral damage, debris, remelt produced by the near-ablation threshold fluences. Specially designed spherically-aberrating Galilean telescopes are used to reshape the primary Gaussian laser beam into a quasi-tophat distribution at the mask plane. Gaussian illumination propagation simulations using Monte-Carlo ray tracing calculations compare well with measurements of reshaped distributions made with a beam profiler. Drilling trials in polymers and silicon nitride demonstrated improved edge quality, reduced debris and wall roughness and a significant reduction in the energy density required for drilling microholes of high aspect ratio.
Novel methods using pulsed laser ablation have been developed for the manufacture of micro-devices with axial symmetry in ceramic materials. Such techniques allow the prototyping and production of micro-parts that are very difficult or even impossible to process by other mechanical and/or chemical methods. To demonstrate these techniques we have manufactured small conical counter-electrodes for use in a Scanning Atom Probe (SAP) instrument. This paper details all the innovative steps developed to produce the double cone shaped electrode and demonstrates the potential for mass production of other devices of similar shapes and dimensions. Many different laser processing strategies for fabricating the cones have been tried in order to achieve a result with satisfactory accuracy and quality. High quality devices have finally been produced in quantity using a combination of excimer laser mask projection and UV Yag laser cutting. The laser methods developed allow micro-parts of an overall size down to 0.1mm and tolerances of a few microns to be manufactured directly in ceramics, glasses, or crystalline materials.
Excimer laser micromachining has developed into a mature production method and many industrial applications such as the drilling of ink-jet printer nozzles, production environments. The important concepts of excimer laser micromachining systems are described and the novel methods which have been developed in this area are presented. In particular, techniques for the production of complex, multi- level 3D microstructures are described and examples of such features are used to illustrate the relevant applications. Furthermore, some initial micromachining result from a sub- nanosecond, solid-state fiber laser are presented to highlight the rapidly-growing area of laser micro processing using ultra-short pulse lasers.
Micro-machining techniques using pulsed lasers are currently being applied world-wise in many diverse industrial application areas including biomedical devices, printers, flat-panel displays, semiconductors devices and telecommunication systems. In particular, the use of excimer lasers has been at the forefront of the new developments in the manufacture of complex micro-structures for the production of micro-optical-electro-mechanical-systems units such as nozzles, optical devices and sensors. This paper reviews the fundamentals of excimer laser micromachining techniques and details recent developments which have enhanced the capabilities of these approaches. Application areas where these techniques are of interest are highlighted.
In recent years, microfabrication techniques derived from existing expertise in the microelectronics industry have been applied to the fields of biotechnology and clinical diagnostics. In this work, 'Biofactory-on-a-chip' devices are being developed to demonstrate how these microfabrication techniques can be combined with electrokinetic phenomena to manipulate, separate and characterize biological material using non-uniform electric fields. Excimer laser ablation methods have been used to fabricate these devices. Key to the successful fabrication and functioning of 'Biofactory' devices is the ability to: machine microelectrodes with micrometer feature sizes over a large area; create via-holes in insulating layers to form electrical interconnects in multilayer structures; fabricate shaped microfluidic channels; and control alignment in the device production with micron accuracy.
Multilevel microelectrode structures have been produced using excimer laser ablation techniques to obtain devices for the electro-manipulation of bioparticles using traveling electric field dielectrophoresis effects. The system used to make these devices operates with a krypton fluoride excimer laser at a wavelength of 248 nm and with a repetition rate of 100 Hz. The laser illuminates a chrome-on-quartz mask which contains the patterns for the particular electrode structure being made. The mask is imaged by a high- resolution lens onto the sample. Large areas of the mask pattern are transferred to the sample by using synchronized scanning of the mask and workpiece with sub-micron precision. Electrode structures with typical sizes of approximately 10 micrometers are produced and a multi-level device is built up by ablation of electrode patterns and layered insulators. To produce a traveling electric field suitable for the manipulation of bioparticles, a linear array of 10 micrometers by 200 micrometers microelectrodes, placed at 20 micrometers intervals, is used. The electric field is created by energizing each electrode with a sinusoidal voltage 90 degree(s) out of phase with that applied to the adjacent electrode. On exposure to the traveling electric field, bioparticles become electrically polarized and experience a linear force and so move along the length of the linear electrode array. The speed and direction of the particles is controlled by the magnitude and frequency of the energizing signals. Such electromanipulation devices have potential uses in a wide range of biotechnological diagnostic and processing applications. Details of the overall laser projection system are presented together with data on the devices which have been manufactured so far.
Multi-level micro-electrode structures have been produced using excimer laser ablation techniques to obtain devices for the electro-manipulation of bioparticles using traveling electric field dielectrophoresis effects. The system sued to make these devices operates with a krypton fluoride excimer laser at a wavelength of 248 nm and with a repetition rate of 100Hz. The laser illuminates a chrome-on-quartz laser at a wavelength of 248nm and with a repetition rate of 100Hz. The laser illuminates a chrome-on-quartz mask which contains the patterns for the particular electrode structure being made. The masks then imaged by a high-resolution lens onto the sample. Large areas of the mask pattern are transferred to the sample by using synchronized scanning of the mask and workpiece with sub-micron precision. Electrode structures with typical sizes of approximately 10 micrometers are produced and a multi-level device is built up by ablation of electrode patterns and layering insulators. To produce a traveling electric field suitable for the manipulation of bioparticles, a linear array of 10 micrometers by 200 micrometers micro- electrodes, placed at 20 micrometers intervals, is used. The electric field is created by energizing each electrode with a sinusoidal voltage 90 degrees out of phase with that applied to the adjacent electrode. On exposure to the traveling electric field, bioparticles become electrically polarized and experience a linear force and so move along the length of the linear electrode array. The speed and direction of the particles is controlled by the magnitude and frequency of the energizing signals. Such electromanipulation devices have potential uses in a wide range of biotechnological diagnostic and processing applications.
New techniques for 3D micromachining by direct laser ablation of materials using excimer lasers have been developed. Basic to all of these techniques is the use of image projection in which the laser is used to illuminate an appropriate pattern on a chrome-on-quartz mask. The mask is then imaged by a high- resolution lens onto the sample. Non-repeating patterns with areas of up to 150 multiplied by 150 mm can be machined with sub-micron resolution and total accuracies of the order of a few microns by using synchronized scanning of the mask and workpiece. A combination of synchronized mask scanning and mask dragging techniques (in which the mask is held stationary and the workpiece moved during laser firing) enables patterns of up to 400 multiplied by 400 mm to be produced; the limiting feature being the travel and accuracy of the recision air- bearing stages used to support the workpiece. This talk describes the synchronized mask scanning and mask dragging techniques and illustrates their application by presenting details of novel micromachined structures and devices so produced. These include rapid prototyping of bioprocessor chips, fabrication of mechanical anti-reflection structures in CsI infra-red optical material, patterning films as frequency selective reflecting structures, laser-LIGA and high aspect ratio machining using lamination techniques to produce an optical methane detector.
Excimer laser projection methods have ben developed to directly create high resolution electrical circuits in both thin nd thick-film metallic layers in order to form robust, compact multi-chip module interconnection devices, miniature sensor elements, miniature flexible printed circuits, antennas etc at high sped and low cost. Patterning over small or large areas is possible at high speed using simple step and repeat or more complex synchronous mask and workpiece scanning methods. Ablation rates depend strongly upon the thickness of the metal layer varying from complete metal removal with 1 laser shot for thin films to multiple 10s of shots for films to a few J/cm2 for screen printed polymer thick films or thick sputtered films. Multiple layer interconnect circuits and complex advanced sensor devices have been successfully fabricated using these excimer laser metal film patterning methods together with laser via drilling and patterning of dielectric layers using a laser tool with appropriate level to level alignment and mask changing and scanning facilities.
An excimer laser microstepper, intended for R and D studies of 193nm lithography, is described. System details such as the laser performance, beam transport, wafer handling and photoresist processes are outlined.
Using advanced laser mask projection methods it is possible to manufacture miniature complex 3D structures in polymers and ceramics for sensor and micromechanical device prototyping or mass manufacture. Subtle movements of workpiece and mask (separately or together) during processing allow complex devices to be realized. Multilevel sensor structures can be constructed using lamination techniques. The full capabilities of laser micromachining techniques are explained in detail and an examples of novel 3D structures made by laser machining are shown.
A 193nm excimer laser microstepper has been developed for deep UV photolithography research at this wavelength. The system incorporates a x10, 0.5NA, 4mm field diameter, high-resolution imaging lens of either all-refractive or catadioptric design. An all-fused silica refractive lens has been used in the results reported here to carry out exposures in polymethylmethacrylate and polyvinylphenol photoresists. Well-resolved images of 0.2micrometers dense lines and spaces and 0.35micrometers diameter contact holes have been produced in PMMA and polyvinylphenol resists.
Excimer laser ablation provides the micromachining engineer with a unique tool for patterning, cutting, and structuring a wide variety of materials, including ceramics, glasses, and polymers. The short pulse (20 ns) ultra violet laser beam is used for nonthermal ablative material removal producing structures with a depth resolution of the order of 0.1 micrometers and spatial resolutions of the order of 1 micrometers or better. Careful control of laser dose (usually done using CNC systems) enables multi-level machining to be performed producing 3D microstructures which may be used directly, or as mold tools for laser-LIGA replication. This talk aims to illustrate both the possibilities, and limitations, of micormachining by excimer laser ablation, and will highlight some practical examples of structures and devices manufactured using this tool, many of which are currently in or near commercial production.
Efficient line-narrowing at 308, 248 and 193 nm is reported using intracavity etalons in commercial excimer lasers. With a single etalon the linewidth is reduced by a factor of X10 - 20 at each wavelength. The line-narrowing efficiency can then be as high as 60 - 75% of the broadband output and single pulse energies in the range of 200 - 300 mJ can be produced within a linewidth of approximately 20 pm. With two intracavity etalons the linewidth is restricted a further factor of approximately X10 with line-narrowing efficiencies of 15 - 25%. At all wavelengths single pulse energies of 60 - 100 mJ could readily be produced within 2 - 3 pm. Using an laser spectrometer with a 1-D diode array readout and PC interface, the wavelength of such a line-narrowed KrF laser has been actively locked to the stable line output from a HeNe laser.
Novel uses of excimer lasers for fabricating products such as biomedical probes and sensors, fenestrated contact lenses and microelectrode sensor arrays are described. With the suppliers of these products various types of excimer laser processing techniques have been developed-- from relatively straightforward micromachining of polymers to surface modification methods and holographic recording. Results that highlight the performances of various products are presented and the excimer laser methods employed in their production are discussed.
Fully integrated excimer laser mask macro and microprojectors and application workstations that produce on the workpiece illumination uniformities as low as +/-5% with overall energy throughput efficiencies of up to 70% are described.