Krypton fluoride laser

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The electra laser at NRL is a KrF laser that demonstrated over 90,000 shots in 10 hours. Electra Laser System NRL 2013.png
The electra laser at NRL is a KrF laser that demonstrated over 90,000 shots in 10 hours.

A krypton fluoride laser (KrF laser) is a particular type of excimer laser, [1] 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 circuits, 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 in the ultraviolet range.

Contents

KrF and ArF excimer lasers are widely incorporated into high-resolution photolithography machines, one of the critical tools required for microelectronic chip manufacturing in nanometer dimensions. Excimer laser lithography [2] [3] has enabled transistor feature sizes to shrink from 800 nanometers in 1990 to 10 nanometers in 2016. [4] [5]

Theory

A krypton fluoride laser absorbs energy from a source, causing the krypton gas to react with the fluorine gas producing the exciplex krypton fluoride, a temporary complex in an excited energy state:

2 Kr + F
2
→ 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 + F
2

The result is an exciplex laser which radiates energy at 248 nm, near the ultraviolet portion of the spectrum, 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: [6]

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 lipids, nucleic acids and proteins, 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 photolithography [2] [3] for the manufacturing of microelectronic devices (i.e., semiconductor integrated circuits 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. [2] [3] [11] 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 [4] that excimer laser lithography (with both KrF and ArF lasers) has been a crucial factor in the predictive power of Moore's law. 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. [12] [13] [14]

Fusion Research

The KrF laser has been used in nuclear fusion energy research since the 1980s. This laser offers several advantages: [7]

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

See also

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<span class="mw-page-title-main">Noble gas</span> Group of low-reactive, gaseous chemical elements

The noble gases are the naturally occurring members of group 18 of the periodic table: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). Under standard conditions, these elements are odorless, colorless, monatomic gases with very low chemical reactivity and cryogenic boiling points.

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<span class="mw-page-title-main">Krypton difluoride</span> Chemical compound

Krypton difluoride, KrF2 is a chemical compound of krypton and fluorine. It was the first compound of krypton discovered. It is a volatile, colourless solid at room temperature. The structure of the KrF2 molecule is linear, with Kr−F distances of 188.9 pm. It reacts with strong Lewis acids to form salts of the KrF+ and Kr
2
F+
3
cations.

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The argon fluoride laser is a particular type of excimer laser, which is sometimes 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 and a halogen gas, which under suitable conditions of electrical stimulation and high pressure, emits coherent stimulated radiation in the ultraviolet range.

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References

  1. Basting, D. and Marowsky,G., Eds., Excimer Laser Technology, Springer, 2005.
  2. 1 2 3 Jain, K.; Willson, C.G.; Lin, B.J. (1982). "Ultrafast deep UV Lithography with excimer lasers". IEEE Electron Device Letters. 3 (3): 53–55. Bibcode:1982IEDL....3...53J. doi:10.1109/EDL.1982.25476. S2CID   43335574.
  3. 1 2 3 Jain, K. "Excimer Laser Lithography", SPIE Press, Bellingham, WA, 1990.
  4. 1 2 La Fontaine, B., "Lasers and Moore's Law", SPIE Professional, Oct. 2010, p. 20.
  5. 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
  6. "Proceedings of the 4th international workshop on KrF laser technology" Annapolls Maryland, May 2, 1994 to May 5th 1994
  7. 1 2 Obenschain, Stephen, et al. "High-energy krypton fluoride lasers for inertial fusion." Applied optics 54.31 (2015): F103-F122.
  8. Divall, E. J., et al. "Titania—a 1020 W cm− 2 ultraviolet laser." Journal of modern optics 43.5 (1996): 1025-1033.
  9. Okuda, I., et al. "Performance of theSuper-ASHURA'main amplifier." Fusion engineering and design 44.1-4 (1999): 377-381.
  10. https://lasers.llnl.gov/multimedia/publications/pdfs/etr/1979_06.pdf [ bare URL PDF ]
  11. Basting, D., et al., "Historical Review of Excimer Laser Development," in Excimer Laser Technology, D. Basting and G. Marowsky, Eds., Springer, 2005.
  12. American Physical Society / Lasers / History / Timeline
  13. SPIE / Advancing the Laser / 50 Years and into the Future
  14. U.K. Engineering & Physical Sciences Research Council / Lasers in Our Lives / 50 Years of Impact Archived 2011-09-13 at the Wayback Machine