A tunable and wavelength stabilized KrF excimer laser has been developed. Two Fabry-Perot etalons of 2.4 THz and 170 GHz FSR are placed inside of the laser cavity to reduce the lasing bandwidth to 0.003 nm (3 pm). The wavelength was found to be tunable over a range from 248.1 nm to 248.6 nm. Within this tuning range, a stable wavelength setting to ±0.5 pm was achieved with a feedback system composed of a wavelength detector and a controlling mechanism. This wavelength-stabilized tunable KrF excimer laser will find its applications in optical microlithography, plasma diagnostics and photochemical reactions.

The availability of reliable excimer lasers and the unique light-materials interactions at far UV wavelengths (308, 248, and 193 nm) have brought about demanding requirements for an optical beam delivery system for micromachining. An optical system is described which uses a split-lens Kohler illuminator in conjunction with a reflecting Schwarzchild objective to deliver a uniform (± 5%) beam with a fluence up to 12 J/cm² into a target area of up to 200 x 200 μm. Design and construction of the illuminator is described, as well as examples of results demonstrating beam uniformity, fluence, and resolution.

Excimer laser marking, profiling and drilling are usually not performed at the focal region of a lens. It is usually more economical to optimize a process at a relatively low energy density and process larger areas at an image plane of a lens system. Internal(within the resonator, i.e. intracavity) methods as well as external methods are used to achieve goal.

Excimer lasers are proving to be a unique and versatile tool in any materials processing applications. This paper reviews briefly. some of the fundamental aspects of excimer laser processing, and describes a general purpose excimer laser workstation. Examples of several relevant application areas are also discussed.

Lanthanum hexaboride has traditionally been used as a high-temperature thermionic emitter of electrons. This material, whose work function for a sintered multicrystalline composition is nominally 2.6 eV, appears to be a reasonably good photoemitter when irradiated by UV light. A quantum efficiency of 10^-3 was recorded for photoemission at a 193 nm (ArF) incident wavelength. At least 20 A/cm² were observed at 193 nm, 248 nm (KrF) and 308 (XeC1). Beam brightness appears to be a minimum of 4 x 10⁵ A/cm²-rad² at 248 nm.

This paper provides an overview of color center generation mechanisms in fused silica. Recent results obtained at Bell Laboratories, and elsewhere, proving the existence of excimer laser induced color centers are summarized. The impact of color centers on emerging DUV technologies are discussed, with regard to possible system power restrictions for acceptable optical lifetimes.

A simple optical imaging system has been designed and built for printing sub-half-micron lithographic images at 248 nm. The following discusses the design considerations of producing a system that can achieve the optical and mechanical criteria of microlithography while still maintaining the simplicity and versatility for a research and development instrument. Also, discussed are designs of lenses that perform at other UV wavelengths and mount in the same mechanical system as the 248 nm lens.

Optimum performance of a laser beam delivery system can generally be achieved only if key parameters are well known and controlled in real time or, at least, quasi-real time. Parameters of importance in typical applications of excimer lasers include energy delivered per pulse, size and shape of the beam, distribution of intensity over the beam's cross section, and the instantaneous and average location of the beam with respect to a target. The stability of each of these parameters over time is also of great importance. To maximize repeatability and uniformity of the laser system's performance, diagnostic measurement equipment should be integrated into the laser and beam delivery system itself. To maximize reliability of the measurement, it should be traceable to NBS standards. In this paper, selected techniques for accomplishing the desired diagnostic measurements are described briefly and hardware implications of incorporating diagnostic subsystems into typical beam delivery systems are discussed.

The results of current microscopic investigations show that during the process of athermal photoablation the material surrounding the target is thermally stressed. In order to get more information of the target's thermal behaviour during light interaction and, furthermore, about the process itself, we developed a microthermocouple device with high spatial (um) and temporal (us) resolution. So far temperature measurements were carried out during excimer laser (351nm) irradiation with 250 to 1600 mJ/cm² in single and repetition pulse mode. The measurements in polymers and in biological material gave the following results: 1) typical thermal effects like melting zones at polymer crater walls and tissue discoloration and smoke generation in biologic material. 2) In polymers as well as in biological materials the surface temperature increases with increasing energy density in single laser mode once the removal threshold is reached or exceeded. 3) The removal threshold depends on the heat capacity of the samples. The results indicate that photoablation of polymers and biological material (obtained with 351 nm short pulsed laser light wavelength of nearly 1000 mJ/cm²) is predominantly a photothermal process.

Evidence is presented, that the formation of conical structures on the surface of polyi-mide etched at low laser fluences is caused by shielding of the underlying polymer by particulate debris. The results show that with increasing diameter of the etched zone, higher laser fluences are required to achieve a smooth surface. XeCl ablation of polyimide in an atmosphere of oxygen at 0.2 J/cm² results in oxidation of nearly 90% of ablated carbon to CO₂ and CO, but does not eliminate the deposition of debris on the perimeter of the etched zone.

An excimer pumped dye laser Raman/fluorescence spectrometer is described and is evaluated for spectroscopic investigations of various base polymers and cured paints. The system is designed to achieve high signal-to-noise ratio for minimum detection time and to be adapted for both laboratory analyses and remote sensing applications. Some preliminary laboratory measurements are evaluated for the range of application in analytical studies and remote sensing.

UV excimer etching could be an alternative method to classical lithography for the conversion of MOT planar waveguides into strip waveguides. Some preliminary results are given, which concern HgCdTe photoablation by ArF excimer laser emitting at 193 nm, under inert or chemically active surrounding gas conditions.

Various industrial microprocessing applications of excimer lasers will be reviewed as well as the requirement and suitability of excimer lasers for each application.

Excimer lasers are finding increasing use in the area of laser materials processing. Of particular importance is the fact that excimers can remove material through ablation rather than by any purely thermal mechanism such as those associated with YAG or C0₂ processing. This paper reviews briefly the basic mechanisms associated with excimer laser ablation and presents several examples of practical applications of this new technique.

Excimer laser induced etching of silicon with chlorine exhibits distinct differences for 308 nm and 248 nm radiation. Photodissociation of chlorine occurs with high efficiency at 308 nm. The etch rates are strongly affected by chlorine gas pressure and gas flow. While at 248 nm these gas parameters are of minor importance, the photon energy suffices to directly break Si-Si and Si-Cl bonds of the solid surface. Higher etch rates are observed at 248 nm for a given laser fluence. Therefore, considering possible applications of excimer laser induced chemical etching of silicon 248 nm radiation appears to be more useful. An increase of the laser pulse repetition rate enhances the thermal contribution to the etch process which modifies the etch rate dependence on laser fluence. With xenondifluoride the spontaneous isotropic etch rate of silicon can be anisotropically enhanced by the laser radiation.

The use of the excimer laser as a source of energy for photo-assisted curing of industrial polymeric coatings was investigated. Presently, UV lamps are sometimes used to excite a photoinitiating molecule mixed with the starting monomers and oligomers of a coating. The resulting polymeric chain reaction multiplies the effect of the initial photons, making economical use of the light source. The high cost of laser photons may thus be justifiable if lasers provide advantages over lamps. A series of visibly transparent 7 μm coatings (a typical thickness for 'slick' magazine coatings) with various photoinitiators, monomers, and oligomers was illuminated with excimer laser light of various wavelengths, fluences, and pulse repetition rates. For the optimum parameters, it was found that the laser had large advantages in curing speed over existing UV lamp processes, due to its monochromaticity. Pigmented coatings (20 μm TiO₂ mixtures typical of appliance or automotive finishes) are not easily cured with UV lamps due to the inability of light to penetrate the absorbing and scattering pigmented layer. However, economically-viable cure rates were achieved with certain photoinitiators using a tunable excimer-pumped dye laser. A prototype of such a laser suitable for factory use was built and used to cure these coatings. Results are scaled to a factory situation, and costs are calculated to show the advantages of the laser method over currently used processes.

Focussed excimer laser micropatterning techniques are proving indispensable to researchers because of their ability to selectively perform ablation processes in highly localized areas without a mask. A typical system includes an excimer source operating at 193, 248, or 308 nm and an optical delivery system which simultaneously focusses the excimer laser light and permits real time viewing of the ablation process. The addition of a programmable stage allows a sample to be moved across the focussed beam for the generation of a variety of patterns covering areas as small as a few square microns to entire substrates. The importance and usefulness of this technique has been reported in such diverse fields as microelectronics packaging, semiconductor technology, optoelectronics, and high temperature superconductor research. Examples show how this micropatterning technique can be used in packaging to selectively remove either dielectric or metallic materials with no damage and to produce novel structures in a single processing step. The repair of electrical shorts and opens in complex microprocessors is discussed as well as applications to failure analysis. Finally several results are described showing the microfabrication of features as small as 1 μm in Hi-Tc superconductors to custom transmission lines.

The frequencies of surface acoustic wave resonators (SAWRs) sealed in novel all quartz packages have been accurately set using laser-induced forward transfer (LIFT) of aluminum-oxide thin films. This technique allows accurate frequency adjustment of SAWRs over -40 parts per million (PPM) with a resolution of better than ±1 PPM. This technique does not significantly degrade relevant electrical SAWR device characteristics and provides the user with substantial cost and time savings when setting a SAWR oscillator to frequency. However, some degradation in the long-term stability of oscillators driven by laser-trimmed SAWR devices has been measured. The quality of the LIFT-deposited oxide film plays an important role in both the frequency sensitivity and long-term stability of laser-trimmed SAWR devices.