A krypton fluoride laser (KrF laser) is a particular type of

excimer laser An excimer laser, sometimes more correctly called an exciplex laser, is a form of ultraviolet laser which is commonly used in the production of microelectronic devices, semiconductor based integrated circuits or "chips", eye surgery, and micro ...

, which is sometimes (more correctly) called an exciplex laser. With its 248 nanometer wavelength, it is a deep ultraviolet laser which is commonly used in the production of semiconductor

integrated circuit An integrated circuit (IC), also known as a microchip or simply chip, is a set of electronic circuits, consisting of various electronic components (such as transistors, resistors, and capacitors) and their interconnections. These components a ...

s, industrial micromachining, and scientific research. The term excimer is short for 'excited dimer', while exciplex is short for 'excited complex'. An excimer laser typically contains a mixture of: a noble gas such as argon, krypton, or xenon; and a halogen gas such as fluorine or chlorine. Under suitably intense conditions of electromagnetic stimulation and pressure, the mixture emits a beam of coherent stimulated radiation as

laser light A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word ''laser'' originated as an acronym for light amplification by stimulated emission of radi ...

in the ultraviolet range. KrF and ArF excimer lasers are widely incorporated into high-resolution

photolithography Photolithography (also known as optical lithography) is a process used in the manufacturing of integrated circuits. It involves using light to transfer a pattern onto a substrate, typically a silicon wafer. The process begins with a photosensiti ...

machines, one of the critical tools required for

microelectronic Microelectronics is a subfield of electronics. As the name suggests, microelectronics relates to the study and manufacture (or microfabrication) of very small electronic designs and components. Usually, but not always, this means micrometre- ...

chip manufacturing in nanometer dimensions. Excimer laser lithographyJain, K. "Excimer Laser Lithography", SPIE Press, Bellingham, WA, 1990. has enabled transistor feature sizes to shrink from 800 nanometers in 1990 to 10 nanometers in 2016.La Fontaine, B.
"Lasers and Moore's Law"
SPIE Professional, Oct. 2010, p. 20.Samsung Starts Industry's First Mass Production of System-on-Chip with 10-Nanometer FinFET Technology; https://news.samsung.com/global/samsung-starts-industrys-first-mass-production-of-system-on-chip-with-10-nanometer-finfet-technology

Theory

A krypton fluoride laser absorbs energy from a source, causing the

krypton Krypton (from 'the hidden one') is a chemical element; it has symbol (chemistry), symbol Kr and atomic number 36. It is a colorless, odorless noble gas that occurs in trace element, trace amounts in the Earth's atmosphere, atmosphere and is of ...

gas to react with the

fluorine Fluorine is a chemical element; it has Chemical symbol, symbol F and atomic number 9. It is the lightest halogen and exists at Standard temperature and pressure, standard conditions as pale yellow Diatomic molecule, diatomic gas. Fluorine is extre ...

gas producing the exciplex krypton fluoride, a temporary

complex Complex commonly refers to: * Complexity, the behaviour of a system whose components interact in multiple ways so possible interactions are difficult to describe ** Complex system, a system composed of many components which may interact with each ...

in an excited energy state: :2 Kr + → 2 KrF 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 KrF → 2 Kr + The result is an exciplex laser which radiates energy at 248 nm, near the

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

portion of the

spectrum A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...

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

Example Systems

There have been several of these lasers built for ICF experiments; examples include: * Los Alamos built a KrF laser in 1985 to prove test firing of beam with an energy level of 1.0 × 10⁴

joule The joule ( , or ; symbol: J) is the unit of energy in the International System of Units (SI). In terms of SI base units, one joule corresponds to one kilogram- metre squared per second squared One joule is equal to the amount of work d ...

s. This was part of the larger Aurora laser research effort that looked at lasers and other systems. * Nike Laser. The Laser Plasma Branch of the

Naval Research Laboratory The United States Naval Research Laboratory (NRL) is the corporate research laboratory for the United States Navy and the United States Marine Corps. Located in Washington, DC, it was founded in 1923 and conducts basic scientific research, appl ...

completed a KrF laser called the Nike laser that can produce about 4.5 × 10³ joules of UV energy output in a 4

nanosecond A nanosecond (ns) is a unit of time in the International System of Units (SI) equal to one billionth of a second, that is, of a second, or seconds. The term combines the SI prefix ''nano-'' indicating a 1 billionth submultiple of an SI unit (e ...

pulse. The NIKE laser was switched to an Argon fluoride laser after 2013 to show the impact of going to shorter (193 nm) wavelengths. *

built the Electra laser and Nike to prove out both KrF and ArF lasers for ICF approaches. In 2013, Electra demonstrated 90,000 shots over 10 hours of operation.Obenschain, Stephen, et al. "High-energy krypton fluoride lasers for inertial fusion." Applied optics 54.31 (2015): F103-F122. * Rutherford Appleton Laboratory built the Sprite and Titania KrF lasers * Japan's Electrotechnical Laboratory built the Ashura and Super Ashura KrF lasers. * China Institute for Atomic Energy had a laser before the middle-1990's * Livermore National Laboratory developed a KrF laser and amplifier known as a Raman Amplifier Pumped by Intensified Excimer Radiation (RAPIER) system.

Applications

This laser has also been used to produce soft X-ray emission from a plasma, through irradiation by brief pulses of this laser light. Other important applications include manipulating of various materials such as plastic, glass, crystal, composite materials and living tissue. The light from this UV laser is strongly absorbed by

lipid Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...

nucleic acid Nucleic acids are large biomolecules that are crucial in all cells and viruses. They are composed of nucleotides, which are the monomer components: a pentose, 5-carbon sugar, a phosphate group and a nitrogenous base. The two main classes of nuclei ...

s and

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

s, making it useful for applications in medical therapy and surgery.

Microelectronics

The most widespread industrial application of KrF excimer lasers has been in deep-ultraviolet

for the manufacturing of

devices (i.e., semiconductor

s or "chips"). From the early 1960s through the mid-1980s, 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 demonstrated at IBM by K. Jain. With phenomenal advances made in equipment and technology in the last two decades, modern semiconductor electronic devices fabricated using excimer laser lithography now total more than $400 billion in annual production. As a result, it is the semiconductor industry view that excimer laser lithography (with both KrF and ArF lasers) has been a crucial factor in the predictive power of

Moore's law Moore's law is the observation that the Transistor count, number of transistors in an integrated circuit (IC) doubles about every two years. Moore's law is an observation and Forecasting, projection of a historical trend. Rather than a law of ...

. 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.U.K. Engineering & Physical Sciences Research Council / Lasers in Our Lives / 50 Years of Impact

Fusion Research

The KrF laser has been used in

nuclear fusion Nuclear fusion is a nuclear reaction, reaction in which two or more atomic nuclei combine to form a larger nuclei, nuclei/neutrons, neutron by-products. The difference in mass between the reactants and products is manifested as either the rele ...

energy research since the 1980s. This laser offers several advantages: * High rate repetition shots - because the KrF is made using gas it does not heat up, allowing for higher shot rates. * Higher beam uniformity * Relatively shorter wavelength for improved ICF compression.

Safety

The light emitted by the KrF 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 skin from the potentially

carcinogen A carcinogen () is any agent that promotes the development of cancer. Carcinogens can include synthetic chemicals, naturally occurring substances, physical agents such as ionizing and non-ionizing radiation, and biologic agents such as viruse ...

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

References

External links

Laser fusion energy
{{Excimer lasers Excimer lasers Krypton Fluorine