Malcolm C. Gower

Microstructuring by excimer laser

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.

New techniques for laser micromachining MEMS devices

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.

Novel applications of excimer lasers for fabricating biomedical and sensor products

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.

Laser micromachining for manufacturing MEMS devices

Applications of laser micromachining to the manufacture and prototyping of MEMS and MOEMS devices are presented. Examples of microturbines, biofactory on a chip, microfluidic components and microoptical elements manufactured by laser micromachining are described.

Excimer laser projector for microelectronics applications

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.

Manufacture of miniature bioparticle electromanipulators by excimer laser ablation

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.

Experimental testing of integral truncation algorithms for the calculation of beam widths by proposed ISO standard methods

The experimental testing of baseline clipping algorithms was carried out on a purposely constructed test bench. Three different lasers were used for the tests including HeNe and collimated laserdiode. The beam profile intensity distribution was measured using a CCD camera at various distances from a reference lens. Results were analyzed on an 486 PC running custom developed software written in Turbo Pascal. This allows very fast evaluation of the algorithms to be performed at rates of several times per second depending upon computational load. Tables of beam width data were created and then analyzed using Mathematica to see if the data confirmed ABCD propagation laws. Values for the beam waist location, size, and propagation constant were calculated.

Practical implementation of test methods for the characterization of laser beam power and energy density distribution

This paper presents recent results on the experimental testing of characterization methods for laser beam power and energy density distribution as described in draft ISO standards ISO 11146 and 13694. The tests were carried out using various laboratory and industrial laser sources. The accurate and repeatable measurement of distributions is of particular concern. Attention has been paid to background compensation and noise reduction methods. Tests were made to calculate beam uniformity, goodness of fit, beam size and the higher order moments of beam profile data derived from various CCD array detectors. These methods are evaluated in the context of their usefulness for on line monitoring, final laser test, and laser R&D.

193-nm imaging using a small-field high-resolution imaging resist exposure tool

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.

Efficient line narrowing and wavelength stabilization of excimer lasers

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.