High repetition rate excimer laser

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For many years, excimer laser are well established in industry as reliable UV light sources. For each application the beam characteristics have to fulfil different requirements and demands, in terms of technology and cost efficiency. One of the biggest advantages of the excimer laser is that it generates light at DUV-wavelengths and can produce high repetition rates at the same time. Many applications benefit from these characteristics. The trend toward smaller feature sizes in microlithography requires both a shift to shorter writing wavelengths, as well as the use of special techniques for photomask manufacture. These so-called Resolution Enhancement Techniques (RET) utilize more sophisticated mask making methods, thus increasing mask manufacturing costs. Furthermore, more advanced metrology methodologies must also be employed in order to inspect RET based masks, and this inspection much often be performed at the wavelength of use (193 nm) in order to accurately identify potential errors. Excimer lasers with high repetition rates and excellent beam characteristics are used for the detection and classification of mask defects in order to maximize yields during wafer fabrication. Excimer lasers are also used with spatial light modulators (SLM) to generate photomask patterns directly. This approach, as compared to conventional e-beam photo-mask writing technology, presents a way to manage the decreasing feature sizes with low operation cost. This technique also requires an excimer laser that delivers the high repetition rates necessary to sustain adequate process through put and extremely well stabilized energy output for writing accuracy. This paper reviews the performance and technology of high repetition rate excimer lasers specifically for use in photomask inspection and optical mask writing.