Argon fluoride laser
Encyclopedia
The argon fluoride laser (ArF laser) is a particular type of excimer laser
Excimer laser
An excimer laser is a form of ultraviolet laser which is commonly used in the production of microelectronic devices , eye surgery, and micromachining....

, 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. The term 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
Photolithography
Photolithography is a process used in microfabrication to selectively remove parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical "photoresist", or simply "resist," on the substrate...

 machines, one of the critical technologies required for microelectronic chip manufacturing. Excimer laser lithography has enabled transistor feature sizes to shrink from 0.5 micrometer in 1990 to below 45 nanometers in 2010.

Theory

An argon fluoride laser absorbs energy from a source, causing the argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...

 gas to react with the fluorine
Fluorine
Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...

 gas producing argon fluoride, a temporary complex
Complex (chemistry)
In chemistry, a coordination complex or metal complex, is an atom or ion , bonded to a surrounding array of molecules or anions, that are in turn known as ligands or complexing agents...

, in an excited energy state:
2 Ar + → 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 +


The result is an exciplex laser
Excimer laser
An excimer laser is a form of ultraviolet laser which is commonly used in the production of microelectronic devices , eye surgery, and micromachining....

 that radiates energy at 193 nm, which lies in the near ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

 portion of the spectrum
Spectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...

, corresponding with the energy difference between the ground state and the excited state of the complex.

Applications

The most widespread industrial application of ArF excimer lasers has been in deep-ultraviolet photolithography
Photolithography
Photolithography is a process used in microfabrication to selectively remove parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical "photoresist", or simply "resist," on the substrate...

 for the manufacturing of microelectronic devices (i.e., semiconductor integrated circuits or “chips”). From the early 1960’s through the mid-1980’s, Hg-Xe lamps had been used for lithography at 436, 405 and 365 nm wavelengths. However, with the semiconductor industry’s need for both finer resolution (for denser and faster chips) and higher production throughput (for lower costs), the lamp-based lithography tools were no longer able to meet the industry’s requirements. This challenge was overcome when in a pioneering development in 1982, deep-UV excimer laser lithography was invented and demonstrated at I.B.M. by K. Jain. With phenomenal advances made in equipment technology in the last two decades, today semiconductor electronic devices fabricated using excimer laser lithography total $400 billion in annual production. As a result, it is the semiconductor industry view that excimer laser lithography (with both ArF and KrF lasers) has been a crucial factor in the continued advance of the so-called Moore’s law (that describes the doubling of the number of transistors in the densest chips every two years – a trend that is expected to continue into this decade, with the smallest device feature sizes approaching 10 nanometers). From an even broader scientific and technological perspective, since the invention of the laser in 1960, the development of excimer laser lithography has been highlighted as one of the major milestones in the 50-year history of the laser.

The UV light from an ArF laser is well absorbed by biological matter and organic compounds. Rather than burning or cutting material, the ArF laser dissociates the molecular bonds of the surface tissue, which disintegrates into the air in a tightly controlled manner through ablation rather than burning. Thus the ArF and other excimer lasers have the useful property that they can remove exceptionally fine layers of surface material with almost no heating or change to the remainder of the material which is left intact. These properties make such lasers well suited to precision micromachining organic materials (including certain polymers and plastics), and especially delicate surgeries such as eye surgery (e.g., LASIK).

Recently, through the use of a novel diffractive diffuse system composed of two microlens arrays, surface micromachining
Surface micromachining
Unlike Bulk micromachining, where a silicon substrate is selectively etched to produce structures, surface micromachining builds microstructures by deposition and etching of different structural layers on top of the substrate....

 by ArF laser on fused silica
Fused quartz
Fused quartz and fused silica are types of glass containing primarily silica in amorphous form. They are manufactured using several different processes...

 has been performed with submicrometer accuracy.

Safety

The light emitted by the ArF is invisible to the human eye, so additional safety precautions are necessary when working with this laser to avoid stray beams. Gloves are needed to protect the flesh from the potentially carcinogen
Carcinogen
A carcinogen is any substance, radionuclide, or radiation that is an agent directly involved in causing cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes...

ic properties of the UV beam, and UV goggles are needed to protect the eyes.
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