Scientific, or research excimer lasers have been around since tl1e mid- 1970s, and in the past few years industrial excimer lasers have started to evolve. This paper will address the demands of manufacturing operations on high power excimer lasers, 100 to 200 Watts, operating three shifts a day, seven days a week. The issues of durability, reliability, serviceability, and cost will be addressed.
Krypton Fluoride exciTner laser-based wafer steppers are now expected to extend optical microlithography to sub-0. 5pra design rules in VLSI chip fabrication. The performance and operational requireraents for the excinter laser for this application are very stringent and different from conventional excimer lasers. For practical reasons the stepper requires that the spectral bandwidth of the laser be reduced to less than 3pm while the wavelength is stabilized to better than +/0. Spm. This paper will discuss these issues and the design features of such an excimer laser. This paper also addresses issues relating to the integration of this laser with a wafer stepper and operation in a wafer fabricatio''n environment
Virtually every materials processing application which uses an excimer laser requires a uniform beam at the surface of the workpiece. Producing a uniform beam is non-trivial requiring both a uniform discharge and an optimized optical resonator. This paper explores the conditions necessary to produce and maintain a uniform beam as well as various ways of measuring the uniformity. For some applications conditioning optics such as homogenizers are required to further improve the uniformity of the beam. Various types of homogenizers will be described along with techniques used to image the uniform beam onto the surface of the workpiece.
Various investigations in the field of material processing indicate that the characteristics of excimer lasers such as emission of radiation in the UV and short pulse duration in the range of some 10 ns with very high pulse intensities lead to several advantages for processing thermally sensitive workpieces. Nevertheless various questions regarding the complex interaction mechanism between radiation and solids cannot be answered sufficiently. This paper deals with an introduction to the absorption behaviour of brittle materials during laser irradiation. Furthermore this paper discusses experimental results which show the influence of different process parameters on the removal behaviour of ceramic materials. To determine energy losses due to plasma absorption or reflection losses different measurement methods are described to estimate the efficiency of the removal process. Finally some laser supported techniques are presented aimed at optimizing the removal result.
Laser photoablation of a variety of polymer films was observed at UV wavelengths. The etch curves do not fit Beer's law and the Srinavasan model but follow the trend of a multiphotonic process. Ablation occurs with minimal degradation in the remaining material. Linear absorption characteristics and chemical composition are not the only factors which contribute to the etching mechanism. Process parameters also include mechanical properties, sample purity and microstructure.
The precise control and high-resolution ablation capability inherent in excimer laser machining make it ideally suited for creating slots for passive alignment of optical fibers to planar channel waveguides as well as for direct waveguide-to-waveguide coupling. This paper describes KrF excimer laser generation of passive alignment coupling slots and the results achieved using this technique with Polyguid polymeric integrated optic system single and multimode waveguide coupling.
Excimer laser (248 rim) ablation has been used for rapid large area defmition of total internal reflection (TIR) mirrors in thick (50 tim) polymeric optical waveguides. The mitrors are capable of reflecting light into or out of the waveguide plane with a loss of less than 1 dB
The use of an excimer laser to process polymers for optical waveguide applications has several advantages in processing over conventional plasma etching. For multi level interconnects and resonant couplers this technique offers the only viable option for demanding geometries in acrylates and polyimides. In addition this process will added design flexibility over the current poled waveguide technique currently in ). Through proper choice of etch parameters waveguides have been formed with excellent sidewall definition in 2-3 micron geometries.
Due to its short wavelength and high peak power the excimer laser has become the de facto choice for Pulsed Laser Deposition (PLD) of ceramic superconductors as well as other complex chemical compounds. This paper will describe a unique excimer-based laser deposition system which is capable of producing thin films of a variety of oxide compounds or other materials over large areas (up to 46 cm2). Well over a dozen chemical compounds have been deposited with this system for a wide variety of electronic applications. Also the PLD technique has been adapted to grow thin films on the internal surface of cored cylindrical substrates in order to form resonant microwave cavity structures. The uniformity morphology and electrical properties of films grown on both planar and cylindrical substrates will be discussed.
Damage resistant optical coatings are needed for cost effective beam delivery systems for high energy laser applications. At excimer wavelengths the photon energy either exceeds or is comparable to bandgap energies of most materials and limits the materials suitable for optical coatings. Other constraints are imposed by limits on near specular scatter and fluorine resistance for selected components.
Excimer laser performance and operational efficiency can be enhanced by simultaneously applying several different approaches related to gas technology. Causes of laser beam power and profile decay, as well as degradation of laser cczriponents are detailed with special regard to laser gases. 4ethods for canbating these deleterious effects are then detailed. These include in—depth discussion of (1) initial gas purity, (2) gas handling between source and laser, (3) laser operating techniques, and (4) in—situ gas purification.
New Results on the trapping efficiency of cryogenic gas purifiers indicate that efficiencies of over 95 can be obtained. High power industrial excimer lasers operate at high buffer gas pressures and use large volume discharge vessels. A prototype gas purifier offering a circulation flow rate and operating pressure twice that of a conventional gas purifier has been developed. The performance and applicability of this device to industrial excimer lasers will be discussed.
The development of laser based diagnostics for a variety of media has been one of the most important applications of lasers. Techniques such as laser induced fluorescence are now capable of determining important parameters such as species concentration and temperature in combustion media and in other environments. In this talk we will discuss how some of the unique characteristics of excimer lasers have been exploited for these applications.
As a result of progress in deep UV resists lasers and optics exposures well below 50 pulses are becoming routine. To maintain the degree of dose control required for linewidth control some means of pulse energy modulation is necessary during the course of an exposure. It is possible to achieve 1 dose control for exposures using as few as 6 pulses by relatively simple means. This paper will present a statistical analysis of some dose control methods along with some results of the application of energy modulation in excimer laser steppers.
This paper describes a novel excimer laser beam delivery method for surface sculpting using a binary mask approach. This technique is useful for profiling a surface into arbitrary shapes and geometries with a high laser energy delivery efficiency. The binary mask technique is particularly attractive for deliver of a pulsed laser such as excimer lasers which are normally operated at a relatively low repetition rate but their output energies per pulse are high. This paper discusses the principle and the method of using the binary masks to regulate the laser energy distribution. An example is given in which a set of 8 binary masks each has 1 00 by 1 00 pixels over an area of 5mm in diameter is used for flattening the curvature of a spherical surface.
Numerous potential excimer laser processing applications have recently been reported in the literature but examples of large scale excimer laser use in an industrial environment are very rare. In this article we inform about the different techniques and also about one of the first processes in which excimer lasers are used in a production line: Via-holes with aspect ratios close to one used in a printed circuit board of a high density multi-chip module are generated by ablation of the dielectric layer in an extremely reliable and reproducible way. The important processing parameters will be discussed.