In industrial laser micro processing, throughput is as important as process quality. Treating large areas in minimum time is pivotal in achieving reduced unit costs in high-volume production. Excimer lasers meet the requirements for clean and precise structuring and enable the smallest structures in an efficient way. The latest technical developments in high power excimer lasers is bound to take cost-efficient UV-laser micro processing to the next level and bridges the gap between achievable precision and achievable throughput. New excimer laser developments and beam concepts together with latest performance data for upscaling both UV power and UV pulse energy will be the topic of this paper against the background of upcoming market trends and high volume applications.
Ongoing progress in mass analysis applications such as laser ablation inductively coupled mass spectrometry of solid samples and ultraviolet photoionization mediated sequencing of peptides and proteins is to a large extent driven by ultrashort wavelength excimer lasers at 193 nm. This paper will introduce the latest improvements achieved in the development of compact high repetition rate excimer lasers and elaborate on the impact on mass spectrometry instrumentation. Various performance and lifetime measurements obtained in a long-term endurance test over the course of 18 months will be shown and discussed in view of the laser source requirements of different mass spectrometry tasks. These sampling type applications are served by excimer lasers delivering pulsed 193 nm output of several mJ as well as fast repetition rates which are already approaching one Kilohertz. In order to open up the pathway from the laboratory to broader market industrial use, sufficient component lifetimes and long-term stable performance behavior have to be ensured. The obtained long-term results which will be presented are based on diverse 193 nm excimer laser tube improvements aiming at e.g. optimizing the gas flow dynamics and have extended the operational life the laser tube for the first time over several billion pulses even under high duty-cycle conditions.
Average power scaling of 308nm excimer lasers has followed an evolutionary path over the last two decades driven by
diverse industrial UV laser microprocessing markets. Recently, a new dual-oscillator and beam management concept for
high-average power upscaling of excimer lasers has been realized, for the first time enabling as much as 1.2kW of
stabilized UV-laser average output power at a UV wavelength of 308nm. The new dual-oscillator concept enables low
temperature polysilicon (LTPS) fabrication to be extended to generation six glass substrates. This is essential in terms of
a more economic high-volume manufacturing of flat panel displays for the soaring smartphone and tablet PC markets.
Similarly, the cost-effective production of flexible displays is driven by 308nm excimer laser power scaling. Flexible
displays have enormous commercial potential and can largely use the same production equipment as is used for rigid
display manufacturing. Moreover, higher average output power of 308nm excimer lasers aids reducing measurement
time and improving the signal-to-noise ratio in the worldwide network of high altitude Raman lidar stations. The
availability of kW-class 308nm excimer lasers has the potential to take LIDAR backscattering signal strength and
achievable altitude to new levels.
Super-hard functional coatings are obtained by high power excimer laser based PLD. Diamond-like,
tetrahedral amorphous carbon (ta-C) is grown on substrates moderately heated to below 90°C inside a
vacuum chamber upon ablating a graphite target by means of a high pulse energy excimer laser at a
wavelength of 248 nm. The fast evaporation of the target material induced by the high photon energy of 5
eV, the short temporal width of 30 ns and the high fluence of the excimer laser pulses generates plume
species with a high degree of ionisation and high kinetic energies. As a consequence, the kinetic energies
resulting from excimer based PLD are significantly higher than those associated with the thermal
evaporation and the ion sputtering deposition methods. In fact, the mean kinetic energy of the atoms and
ions in the plume are in the range of 30 eV to 80 eV for fluencies of 5 J/cm2 to 20 J/cm2. Such large ontarget
UV fluences are easily provided by high energy excimer lasers such as the Coherent LPXpro and by
LSX laser models which can operate at output energies up to 1 J and average output powers up to 540 W.
High energy excimer lasers lend maximum flexibility to laser microprocessing, since virtually every
material is amenable to accurate, high resolution material ablation without subsequent post treatment. Due
to the UV photons provided with no up-conversion required as direct output by excimer lasers, output
powers of many hundred watts are easily achievable and are key to high throughput, and up-scaling
capability of manufacturing processes. In particular, the large flat-top excimer laser profile is well-suited
for most efficient parallel processing of two and three dimensional microstructures. Compact
micromachining concepts particularly suited for material ablation and surface activation will be
Stable, high energy excimer lasers providing pulsed output energies ranging from 100 mJ up to over 1000 mJ in the ultraviolet region with photon energies as high as 5 eV (248 nm), 6.3 eV (193 nm) or 7.9 eV (157 nm) lend maximum flexibility to laser microprocessing, since virtually every material is amenable to accurate, high resolution material ablation without subsequent cleaning. Due to the UV photons provided with no up-conversion required as direct output by excimer lasers, output powers of many hundred watts are easily achievable and are key to high throughput, and up-scaling capability of manufacturing processes. Most important for reproducible production results is a temporally and spatially stable behavior of consecutive laser pulses as well as utmost lateral homogeneity of the on-sample energy density (fluence). These requirements constitute the superiority of excimer lasers over other pulsed UV laser sources such as lamp-pumped Nd:YAG lasers. Pulse-to-pulse stabilities of less than 1 %, rms as easily provided by excimer laser systems which cannot be achieved with frequency converted Nd:YAG. Laser systems. In particular, the large flat-top excimer laser profile is well-suited for most efficient parallel processing of two and three dimensional microstructures. Spectral properties, temporal pulse and laser beam parameters of state of the art UV excimer lasers and beam delivery systems will be compared with frequency converted, flash-lamp pumped Nd:YAG lasers.
Reproducible and sensitive elemental analysis of solid samples is a crucial task in areas of geology (e.g. microanalysis of
fluid inclusions), material sciences, industrial quality control as well as in environmental, forensic and biological studies.
To date the most versatile detection method is mass-spectroscopic multi-element analysis. In order to obtain reproducible
results, this requires transferring the solid sample into the gas-phase while preserving the sample's stoichiometric
Laser ablation in combination with Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) is a proven powerful
technique to meet the requirements for reliable solid sample analysis. The sample is laser ablated in an air-tight cell and
the aerosol is carried by an inert gas to a micro-wave induced plasma where its constituents are atomized and ionized
prior to mass analysis.
The 193 nm excimer laser ablation, in particular, provides athermal sample ablation with very precise lateral ablation and
controlled depth profiling. The high photon energy and beam homogeneity of the 193 nm excimer laser system avoids
elemental fractionation and permits clean ablation of even transmissive solid materials such as carbonates, fluorites and
Excimer lasers are unique ultraviolet laser sources ideally suited for a wide range of applications driving innovations in almost every branch of industry including microsystem manufacturing, flat panel display production and dense wavelength division and multiplexing to name a few. The success of fiber Bragg gratings in the last years is based on their unique properties which make them extremely valuable for numerous applications in optical telecommunication networks. Expectations for the continued growth of demand for internet services and more bandwidth show a promising future also for passive optical components. Components which serve not only one but several purposes have a good possibility to participate in this success proportionally. Excimer laser written fiber Bragg gratings (FBGs) stabilize the frequency of laser diodes, flatten the non-linear gain of fiber amplifiers, compensate for the fiber's dispersion and filter
communication channels. Developments and optimization of 248 nm excimer laser systems for mass production environments are ongoing.
Ongoing progress in material research and processing industry is fueled to a large extent by the technique of pulsed laser deposition (PLD). With this powerful and versatile deposition method, multi-component target materials can be ablated and deposited onto a substrate to form functional layers with tailored physical properties. Monitoring of growth parameters such as thickness and surface roughness is mostly performed in-situ via electron diffraction or other diagnostic tools. High pulse energy excimer lasers with photon energies as high as 7.9 eV lend maximum flexibility to the technique of pulsed laser deposition since virtually every target material is amenable to excimer laser ablation and its subsequent stoichiometric transfer to a substrat. Spectral properties as well as recent technical advances in excimer lasers for thin film applications are shown in this paper.
As the most efficient UV laser sources excimer lasers are unique tools for the various fields of material processing. Essentially, the tight process windows fuel the need for better dose control during laser illumination and hence the demand for high repetition rate excimer lasers operating at comparably low pulse energies of only some 10 mJ. Compact, flexible excimer lasers offering high repetition rate-low energy and low cost of ownership pave the way to efficient mask writing and wafer inspection systems for chip manufacturing as well as to efficient testing of optical materials. Utilizing micro-mirror arrays, high-repetition rate-low energy excimer lasers are ideal for flexible direct-write material processing approaches e.g., in laser marking or cleaning. Moreover, medical applications such as refractive eye surgery currently using up to 200 Hz repetition rate will benefit from high-repetition rate excimer lasers offering reduced treatment times with excimer laser based systems with 500 Hz and even 1000 Hz in the near future.
Today the molecular fluorine (F2) laser emitting at a wavelength of 157 nm represents the strongest commercially available coherent light source in the vacuum-ultraviolet spectral range. Lambda Physik produces a broad variety of F2-Lasers which cover a wide range of output power (from less than 1 W to more than 20 W), repetition rate (from less than 100 Hz to more than 4 kHz) and single pulse energy (from less than 1 mJ to more than 30 mJ). The parameters of each of these kinds of F2-lasers are designed and suitable for specific fields of application. In the paper we will review the main parameters of these different types of F2-lasers, compare their special features and discuss the principle applications they are used for. The low energy, medium repetition rate is basically used for metrology and calibration tasks, the high energy or high repetition rate and high power F2-laser systems are mainly used for material investigations and in a growing extent for 157 nm-micromachining. Lithography tools use the high repetition rate, high power single-line F2-laser systems. All of these scientific or industrial applications take advantage of the unique properties of the 157 nm radiation, i.e. the ultra-short wavelength of emission and the very high photon energy of nearly 8 eV. Thus, very precise and fine microstructuring in the micrometer range is possible and the 157 nm optical lithography is on target for critical dimensions of integrated circuits below 70 nm. The short pulse duration and high photon energy also enables efficient and exactly located icroscopic ablation of most critical materials without thermal impact on the surrounding area. In the last part of the paper some recent results on F2-laser development and an outlook on future products will be given.