Excimer lasers applications

Excimer lasers use gases, but because of their special properties are usually considered as a class of their own. Excimer is short for excited dimer, which consists of two elements, such as argon and fluorine, that can be chemically combined in an excited state only. These lasers typically emit radiation with veiy small wavelengths, in the ultraviolet region of the electromagnetic spectrum. This shorter wavelength is an enormous advantage for many applications. 

Rothe, E.W. and Andresen, R, Application of tunable excimer lasers to combustion diagnostics A review, Appl. Opt., 36,3971,1997. 

The capability to control an excimer laser beam also is exploited in the semiconductor industry, where these lasers are used to etch elaborate features during the fabrication of semiconductor chips. Neil Bartlett probably never dreamed that his explorations of the chemistry of xenon would lead to such exotic applications. 

Proceedings Excimer Lasers for Fusion and Industrial Applications (Abstracts Collection) Editors L. Cemoli and S. Martellucci. Publisher University of Rome Tor Vergata (to be... 

Exchanger design equation, 13 195 Exchange repulsion, 23 93 Excimer lamp technology, 19 107-108 Excimer lasers, 14 691-693 17 372 19 115 applications of, 14 693 species of, 14 692t... 

Azide-phenolic resin photoresists have been reported by workers at Hitachi. They are used for i-line (12) or for deep UV light (13), and the applications to KrF excimer laser lithography have not been demonstrated. 

It is confirmed that the polymer matrix around ablated area was also affected strongly by laser ablation. The change of the matrix properties are brought about over a few tens of pin. This type of information is basically important and indispensable for practical applications such as excimer laser lithography. The time-resolved fluorescence spectroscopy is one of the powerful characterization methods for ablated polymer matrix. 

Excimer lasers are of great importance for UV and vacuum UV (VUV) spectroscopy and photochemistry. They are also found in a wide range of applications. For example, they are used in micromachine medical devices, including refractive surgery, in photo-lithography for the microelectronics industry, for material processing, as optical pump sources for other type of lasers (dyes), and so on. More details about excimer lasers can be found in Rodhes (1979). 

Alternative dry etching techniques have recently been developed for the nitrides for low-damage applications. Photoassisted dry etching is set up analogously to CAIBE except that the ion beam source is replaced with an ultraviolet laser. Leonard and Bedair [25] reported on the photoassisted dry etching characteristics of GaN using HC1 gas and a 193 ran ArF excimer laser (1400 mJ/cm2) with the substrate... 

During the last decade, there has been considerable interest in studying the interaction between ultraviolet radiation and polymers by the use of pulsed excimer laser (1-41. In fact, some attractive applications in microelectronics and surgery have been successfully implemented (5.), and further informations about the different mechanisms (photochemistry, thermal effect...) involved at the polymer surface have been invoked in order to elucidate their relative contributions. More recently, the attention has been focused on this type of polymer surface modifications to improve some surface properties like the adhesion in metallized polymer structures. 

In addition, a novel generation of lamps with promising features for photochemical applications has been developed to industrial maturity over the last decade, the so-called incoherent excimer radiation sources (Eliasson et al., 1988). Note that these lamps are not laser sources. In contrast to well-known excimer lasers, excimer lamps are operated under different physical conditions and they emit incoherent electromagnetic radiation. Whereas pulsed laser radiation can reach very high irradiances, E up to 100 MW m , the irradiance E of excimer lamps is only in the range of 1000 W m . ... 

The time to measure spectra of this quality under high-pressure conditions has been about I min. The absolute time scale of the experiment depends on the method of initiation. In thermally initiated (spontaneous) polymerizations reaction time can be several hours or even days. In contrast, in excimer laser-initiated free radical polymerizations application of a few laser pulses each of about 20 ns duration can induce changes between subsequent spectra as on this figure. 

We have indicated that intensity dependent phenomena may be useful in at least two distinct ways. One is to obtain something approaching a "threshold detector" resist response. To obtain a threshold development response in typical positive resists is difficult, since the development rate is in general a smoothly varying function of the photochemical reaction progress. The application of a layer of polymer with the bleaching characteristics shown in Figure 5 provides a way to obtain such threshold response with conventional resists, provided an excimer laser is used in the illumination system. 

Another interesting source of DUV radiation for microlithography is excimer lasers (13). This relatively new class of very efficient and extremely powerful pulsed lasers became commercially available in 1978. They operate at several characteristic wavelengths ranging from less than 200 nm to greater than 400 nm. The output is typically 10-20-ns wide pulses with repetition rates from ten to several hundred Hertz. Jain (14) provided a recent review of laser application to microlithography. 

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