Alexander O. Wiessner

High peak power solid-state laser for micromachining of hard materials

Laser micromachining has become a key enabling technology in the ever-continuing trend of miniaturization in microelectronics, micro-optics, and micromechanics. New applications have become commercially viable due to the emergence of innovative laser sources, such as diode pumped solid-state lasers (DPSSL), and the progress in processing technology. Examples of industrial applications are laser-drilled micro-injection nozzles for highly efficient automobile engines, or manufacturing of complex spinnerets for production of synthetic fibers. The unique advantages of laser-based techniques stem from their ability to produce high aspect ratio holes, while yielding low heat affected zones with exceptional surface quality, roundness and taper tolerances. Additionally, the ability to drill blind holes and slots in very hard materials such as diamond, silicon, sapphire, ceramics and steel is of great interest for many applications in microelectronics, semiconductor and automotive industry. This kind of high quality, high aspect ratio micromachining requires high peak power and short pulse durations.

High-throughput micromachining of steel and ceramics with solid state UV laser

Performance limits of 10 kHz, 15 nsec-pulse diode-pumped solid- state laser in microdrilling of metals and ceramics were studied. Average drilling rates approaching 1 cm/sec with micrometer-range accuracy of micro-holes are achievable in steel and ceramic samples up to 1 mm thick. We found that shielding effects of plasma plume can be minimized by proper selection of laser intensity. In samples 1 mm and thicker, using third harmonic output allows drilling of high aspect ratio holes at almost an order of magnitude higher ablation rates as compared to IR laser output.

High-accuracy microdrilling of steel with solid state UV laser at a rate of 10 mm/sec

We investigated wavelength- and intensity-dependence of ablation rate achievable with a diode-pumped Q-switched Nd:YAG laser with frequency doubling and tripling. The laser produced 15 ns-long pulses at a repetition rate of 10 kHz and output power of 28 W in the fundamental beam, and 15 W and 10 W in the second and third harmonics, respectively. We found that in thin stainless and carbon steel foils, fast ablation starts at the laser fluence level of 10 J/cm2. The ablation rate remains close to 1 micrometers per pulse with very little change as the laser fluence increases by more than order of magnitude above this threshold exit of the hole. This attenuation is strongly dependent on the laser wavelength. Particularly, using third harmonic output, we were able to sustain average drilling speed of more than 1 micrometers per pulse in samples up to 1 mm thick. At the same time, removal rate at fundamental wavelength decreased by almost an order of magnitude.

Novel results of laser precision microfabrication with excimer lasers and solid state lasers

Over the last decades laser technology has found the way into various industries. For microfabrication specifically excimer lasers have developed to powerful manufacturing tools because of their short UV wavelengths as well as the progress in excimer laser technology. More recently the development of pulsed medium-power diode-pumped solid-state lasers has opened the way to new micromachining applications related to the available superior beam quality. Here we review technological achievements in boh industrialized excimer lasers and diode-pumped Nd:YAG lasers for microfabrication. Data are presented for industrial 308 nm excimer lasers with energy stability better than 1 % (sigma) at 300 W average power. Using the latest technology in 157 nm excimer lasers applications of processing of difficult materials are presented. Finally we review results on studies of microdrilling of metals and ceramics using a newly developed 10 kHz diode-pumped solid-state laser at wavelengths 1064 nm, 532 nm and 355 nm.

Effect of the wavelength on high-aspect ratio microdrilling of steel with an all-solid-state laser

Summary form only given.We investigated wavelength and intensity dependences of the ablation rate in steel using a 10 kHz diode-pumped laser source. We present practical examples of trepanning of 100 /spl mu/m-diameter holes in up to 1 mm-thick steel with roundness and taper errors within a few micrometers. Additionally, by using 10 W UV output of the laser, we demonstrated percussion-drilling of 30 /spl mu/m-diameter holes in 1.5 mm-thick steel with aspect ratio of 50 and taper not exceeding 15%.

Sub-0.25-pm 50-W amplified excimer laser system for 193-nm lithography

We report performance parameters of a robust, 50 W, high repetition rate amplified ArF excimer laser system with FWHM bandwidth of less than 0.25 pm, 95% energy content bandwidth of less than 0.55 pm, and ultra-low ASE level. Proprietary design solutions enable stable operation with a substantial reliability margin at this high power level. We report on characterization of all the key parameters of importance for the next generation microlithography tools, such as spectrum and dose control stability, in various operating modes.

Fast drilling of high accuracy micro holes in stainless steel with DPSS laser

Summary form only given. Investigating the ablation rate of steel using a diode pumped Q-switched Nd:YAG laser at a repetition rate of 10 kHz we could demonstrate ablation rates up to more than 10 mm per second for 1.5 mm thick steel samples. Using 15 nsec laser pulses the threshold for fast material removal in thin foils was found to be 10 J/cm/sup 2/. Drilling through thicker materials the absorption of laser light in the plasma generated becomes more important, leading to higher energy thresholds.

Efficient high average power Ce:LiCAF laser with 5-pm spectral linewidth

We report on a simple and efficient Ce:LiCAF laser operating at 1-kHz repetition rate and delivering in excess of 180 mW when pumped by 1.8 W of fourth-harmonic radiation of a diode-pumped Nd:YAG laser. High conversion efficiency (up to 10%) of the laser is complemented by broad tunability range (281-301 nm) and a spectral linewidth of less than 5 pm, as well as compact all-solid-state construction, which comprises a unique combination.