APPLICATIONS

     With high average powers (commonly over 100 W for many commercial lasers) and an output in the ultraviolet region of the spectrum, excimer lasers are useful for many applications, ranging from dye laser pumping to cutting and materials processing applications. The largest commercial application for excimers are use in eye surgery to correct the shape of the cornea to reduce the need for corrective lenses (commonly known as lasik surgery). For these applications ArF with an output wavelength of 193 nm and a pulse energy of under 0.5 J is used. The 193-nm wavelength is used since it is readily absorbed by tissue on the surface of the cornea, which is ablated without producing significant heat to damage surrounding tissue. Since the laser light is absorbed readily by tissue on the front of the eye, no laser energy is transmitted to the retina, sparing it damage. By 2003, over 2 million such corrective surgeries have been performed using the excimer laser.

        The largest current industrial use for excimer lasers is photolithography. When manufacturing integrated circuits, multiple layers of semiconductor material are “grown” onto a wafer of silicon by diffusion at high temperatures. Features (desired areas) are then produced on the layer by coating the wafer with photoresist, exposing the photosensitized wafer to UV light passed through a mask outlining features desired on that layer, developing the resist, and etching away unwanted silicon material with hydrofluoric acid. To expose the photoresist, UV light from a mercury lamp, the standard light source for such uses until the mid-1990s, is passed through a photographic mask. Whereas mercury lamps feature short-wavelength UV light, which allows for finer features to be resolved, the spectral linewidth is broad, leading to chromatic aberration in the lens system of cameras used to focus the image onto the photosensitized chip. The net effect is to defocus the image at the edge features on the mask. In contrast to this, excimer lasers have a relatively narrow linewidth, producing a sharper image (despite the fact that excimers have a much broader linewidth than do many lasers). The KrF laser has become the workhorse of the semiconductor industry for photolithography.

      Because of the extremely short wavelength, ArF excimers are also used for glass marking applications, since the beam is readily absorbed by glass (which is transparent to longer wavelengths). Along these lines, ArF (and sometimes KrF) is used to manufacture fiber Bragg gratings for optical fiber communications. During manufacture, a pattern is cut into a single-mode fiber using a phase grating. Other applications for excimer lasers include wire stripping (especially for ultra-fine wires used in the microelectronics industry), surface-mount component marking, drilling inkjet printer nozzle holes, and marking wires.