Argon fluoride laser

The argon fluoride laser (ArF laser) is a particular type of excimer laser, which is sometimes (more correctly) called an exciplex laser. With its 193-nanometer wavelength, it is a deep ultraviolet laser, which is commonly used in the production of semiconductor integrated circuits, eye surgery, micromachining, and scientific research. "Excimer" is short for "excited dimer", while "exciplex" is short for "excited complex". An excimer laser typically uses a mixture of a noble gas (argon, krypton, or xenon) and a halogen gas (fluorine or chlorine), which under suitable conditions of electrical stimulation and high pressure, emits coherent stimulated radiation (laser light) in the ultraviolet range. ArF (and KrF) excimer lasers are widely used in high-resolution photolithography machines, a critical technology for microelectronic chip manufacturing. Excimer laser lithography has enabled transistor feature sizes to shrink from 800 nanometers in 1990 to 7 nanometers in 2018. Extreme ultraviolet lithography machines have replaced ArF photolithography machines in some cases as they enable even smaller feature sizes while increasing productivity, as EUV machines can provide sufficient resolution in fewer steps. The development of excimer laser lithography has been highlighted as one of the major milestones in the 50-year history of the laser. An argon fluoride laser absorbs energy from a source, causing the argon gas to react with the fluorine gas producing argon monofluoride, a temporary complex, in an excited energy state: 2 Ar + F2 → 2 ArF The complex can undergo spontaneous or stimulated emission, reducing its energy state to a metastable, but highly repulsive ground state. The ground state complex quickly dissociates into unbound atoms: 2 ArF → 2 Ar + F2 The result is an exciplex laser that radiates energy at 193 nm, which lies in the far ultraviolet portion of the spectrum, corresponding to an energy difference of 6.4 electron volts between the ground state and the excited state of the complex.