Sergei V. Govorkov

Blue and green optically pumped semiconductor lasers for display

We discuss a compact RGB source with ouput power of several watts per color consisting of a red (638 nm) diode and OPS lasers with blue (460 nm) and green (530) nm output. Suitability for display applications is shown by replacing the lamp of a standard Rear Projection TV.

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.

Excimer laser for 157-nm lithography

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.

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.

20 Watt CW TEM00 intracavity doubled optically pumped semiconductor laser at 532 nm

Optically-pumped semiconductor (OPS) lasers are power-scalable, wavelength-flexible, infrared brightness converters. Adding intra-cavity frequency doubling turns them into efficient, low noise, high power visible laser sources. We report on a laser combining an InGaAs gain medium with an LBO nonlinear crystal to produce more than 20 Watt CW in single transverse mode at 532 nm. Efficient cooling of the single gain chip using advanced mounting techniques is the key to making the laser reliable at high CW powers. A rugged and compact package withstands significant environmental excursions. The lasers low noise makes it suitable for demanding Ti:Sapphire pumping applications.

Al-glass kW fibre laser end-pumped by MCCP-cooled diode stacks

High power industrial fibre lasers are typically pumped by single emitter diodes, with pump power aggregation and the fibre laser cavity being achieved in a monolithic “all-bibre” architecture comprising fused fiber bundles, fiber Bragg grating reflectors and numerous splices. [1]. The gain fiber utilizes a low index polymer coating to provide the wave-guiding for the multimode pump as well as for compatibility with the NA increase (typically 0.22–0.45) which occurs in the fused taper combiners. While this all fibre approach has been shown to be viable, it is not trivial to implement at power levels in excess of several hundred watts Issues include polymer coating degradation, transverse mode-coupling induced instability at splices or FBGs, grating walk-off, and modal instability, [2]. The latter issue arises because these fiber laser designs are focused on single-transverse-mode operation, [3.4], even though the fibres themselves are multimode to avoid nonlinear impairments. This is despite the face that most cutting and welding applications actually utilize a multimode fibre for delivery to the cutting head. The BBP of such systems is typically 2.5mm.mRad at a wavelength around 1080nm. However, single mode operation allows power scaling by incoherently combining several lower power fiber lasers into a single beam with that BPP.

Advanced F2 lasers for microlithography

According to the SIA-Roadmap, the 157 nm wavelength of the F2 laser emission will be used for chip production with critical dimensions of 100 nm down tot eh 70 nm node. Currently al basic technologies for 157 nm lithography are under investigation and development at material suppliers, coating manufacturers, laser suppliers, lens and tool manufacturers, mask houses, pellicle manufacturers, and resist suppliers.

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.

Lasers Solutions for Annealing

The application of lasers for annealing of wafer-based and thin-film microelectronic devices is steadily increasing. Excellent control of material characteristics (for example, dopant activation profile) can be achieved through proper selection of laser parameters, such as wavelength, pulse duration and fluence, which directly influence the laser material interaction. In this paper, we present several lasers and optical systems from Coherent that have proven to be useful for annealing in both microelectronic and macroelectronic applications. These laser systems include Excimer Lasers in the ultraviolet and our unique high-power continuous-wave laser system that delivers scalable output power of multiple hundreds of Watts in the visible wavelength range. We will present results from recent work involving dopant activation, and will present several application examples from Flat Panel Display annealing and crystallization, which we propose are directly applicable to wafer-based microelectronics as well.