Excimer Leverages Litho Lessons for kHz Micromachining

Coherent, Santa Clara, California

Ultraviolet lasers currently are used in a very diverse range of industries and applications. This is because their high-energy photons directly can break inter-atomic bonds in many materials, and the short wavelength enables a high degree of spatial resolution (see Figure 1). Amongst ultraviolet lasers, excimers are unique in their ability to deliver a combination of high pulse energy and high average power. Because of these advantages, excimers are used in applications as diverse as ophthalmic corrective procedures, low-temperature silicon annealing for flat-panel displays, drilling inkjet nozzles, and treating the cylinder liners of diesel engines for greener automobile performance.

Figure 1. The deep UV output wavelengths and short pulse duration of Excimer Lasers allow these powerful lasers to micromachine objects as small and delicate as this human hair.

In recent years, there have been dramatic advances in component lifetime and excimer laser reliability, which have lowered their cost per photon. Now, an increase in pulse repetition rate is expected to spur further growth in manufacturing applications by enabling faster throughput and thus lower production costs.

Figure 2. An embolic filter is a small parachute-like device that crosses the lesion area before an angioplasty procedure is performed. When open, it acts as a trap with holes large enough to allow blood flow, but small enough to catch any potentially dangerous debris. These polymer filters are Laser-Drilled with 248-nm or 193-nm excimer lasers. (Photo courtesy of Resonetics)

Excimers are gas lasers typically filled with argon, krypton, or xenon combined with a halogen, such as fluorine or chlorine. The lasers operate by rapidly discharging a large capacitative power supply at tens of kilovolts between parallel electrodes running the length of a laser tube. This creates a massive transient population of excited species (e.g., ArF, KrF, XeCl) leading to a pulse of laser radiation, lasting from a few nanoseconds to tens of nanoseconds, depending on the laser design. After a recovery period, the process is then repeated.

Faster repetition-rate lasers have been developed for microlithography, but these are complex systems that are not cost effective for general commercial applications. Coherent is one company transferring some of those microlithographic lessons to conventional excimer lasers, including all metal-ceramic tube construction, efficient gas filtration and circulation systems, and all-solid-state circuit designs. The use of these technologies has enabled the development of the ExciStar-S Industrial excimer laser with a repetition rate of 1 kHz at a fraction of the cost of million-dollar microlithographic excimer sources.

This new design has a tube lifetime up to 10-billion pulses of steady operation, which reduces total cost of ownership. The compact Exci-Star Industrial laser also delivers stabilized pulse energies in the range of 8-12 mJ/pulse, pulse-to-pulse energy stability, and output powers of about 10 W.

The kilohertz repetition rate of this laser enables increased process speed for a number of micromachining applications, including drilling inkjet nozzles, inspection of semiconductor photomasks, and micromachining medical devices such as catheters, stents, and embolic filters (see Figure 2).

This article was written by Hans-Gerd Esser of Coherent’s Goettingen, Germany, facility. For more information, contact Mr. Esser at This email address is being protected from spambots. You need JavaScript enabled to view it..