A compact long-wavelength infrared (LWIR) source, based on the combination of a high-pulse-rate, 1-μm-wavelength solid-state laser with rapid and broadly tunable tandem optical parametric oscillators (OPOs) was demonstrated. Nanosecond pulses with up to 100 μJ energy, tunable within the 8-11 μm LWIR range were achieved.
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.
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.
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.
Optical deep UV (DUV) lithography is aiming to reach feature sizes of below 100 nm. The likely choice of the exposure wavelength will be 157 nm, which is emitted by the F2 excimer laser. Experience with this laser type in a variety of applications has been gained at Lambda Physik for the past 20 years. A major breakthrough in performance, in particular laser efficiency and durability, was achieved with the introduction of our metal ceramic laser tube in 1996. In this paper, we report on the progress in the development of the F2 laser light source. A major advance in narrowing the bandwidth of a 10W laser is the achievement of output spectral width of about 1 pm. With a newly developed NovaTube based F2 discharge chamber we show more than 19 million pulses gas lifetime without any additional gas actions. The laser achieves up to 1 kHz repetition rate. Energy stability sigma is 1 percent, dose energy stability 0.5 percent. The performance characteristics as temporal and spatial beam profile and the suitability the laser for microlithography are discussed. Typical lifetimes of the key components and a projection of the present and future cost of operation are presented.
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