Did you know excimer lasers have been key in making microelectronic devices since the 1960s? They are powerful ultraviolet lasers. They help in making high-resolution photolithography, a key tech in today’s electronics.
Excimer lasers are not just for electronics. They are also used in eye surgery and micromachining. Their ability to work in many areas is amazing.
Key Takeaways
- Excimer lasers are a form of ultraviolet laser, commonly used in microelectronic device production, eye surgery, and micromachining.
- The term “excimer” is short for “excited dimer”, while “exciplex” is short for “excited complex”.
- Excimer lasers have been widely used in high-resolution photolithography machines since the 1960s, enabling the production of modern electronics.
- These lasers operate in the ultraviolet spectrum, with wavelengths ranging from 157 nm to 351 nm, depending on the type of excimer laser.
- Excimer lasers can deliver pulse energies between 10 mJ and 1 J, with repetition rates from 10 Hz to 1 kHz or more.
What is an Excimer Laser?
Definition and Terminology
An excimer laser is a special kind of ultraviolet laser. It uses a noble gas like argon and a reactive gas like fluorine. Together, they form a pseudo-molecule called an excimer or exciplex.
When electrically stimulated and under high pressure, this pseudo-molecule creates laser light in the ultraviolet range. The term ‘excimer’ means ‘excited dimer’, and ‘exciplex’ means ‘excited complex’.
The excimer laser definition highlights its ability to produce high-energy ultraviolet light. This light is used in many areas, including medical procedures, photolithography, and fusion research. The excimer laser terminology also differentiates it from the excimer vs exciplex laser. The latter uses a different molecular structure to produce laser light.
- Excimer lasers use a combination of noble gases and reactive gases to create a pseudo-molecule called an excimer or exciplex.
- These pseudo-molecules can be electrically stimulated to produce high-energy ultraviolet laser light.
- The term ‘excimer’ is short for ‘excited dimer’, while ‘exciplex’ stands for ‘excited complex’.
- Excimer lasers have a wide range of applications, including medical procedures, photolithography, and fusion research.
- The terminology distinguishes between excimer and exciplex lasers, which utilise different molecular structures to generate ultraviolet laser light.
“Excimer lasers have revolutionised various industries, from medical treatments to cutting-edge research, by providing a reliable and precise source of ultraviolet light.”
History and Development
The story of the excimer laser started in 1960, when Fritz Houtermans first suggested it. The real work and discoveries began in the following years.
Early Discoveries and Pioneering Work
In 1971, a team at the Lebedev Physical Institute in Moscow made a key find. Nikolai Basov, V. A. Danilychev, and Yu. M. Popov saw a spectral line narrowing at 176 nm. They used liquid xenon dimer (Xe2) excited by an electron beam.
This find led to more research. In 1972, H.A. Koehler et al. showed more evidence of stimulated emission. They used high-pressure xenon gas.
In March 1973, Mani Lal Bhaumik of Northrop Corporation, Los Angeles, made a big breakthrough. He showed the first xenon excimer laser action at 173 nm. This was a major step in the excimer laser history and excimer laser development.
After these early excimer laser discoveries, researchers kept pushing forward. In 1975, noble gas halides (originally Xe Br) were developed. These efforts set the stage for the many uses of excimer lasers in the future.
| Year | Milestone |
|---|---|
| 1960 | Fritz Houtermans proposed the excimer laser |
| 1971 | Observation of a spectral line narrowing at 176 nm by Nikolai Basov, V. A. Danilychev, and Yu. M. Popov |
| 1972 | H.A. Koehler et al. presented a better substantiation of stimulated emission using high-pressure xenon gas |
| 1973 | Mani Lal Bhaumik presented the first xenon excimer laser action using high-pressure gas |
| 1975 | Development of noble gas halides (originally Xe Br) by various groups |
The early excimer laser pioneers set the stage for the many advancements and uses of this technology.
Laser Construction and Operation
An excimer laser uses a mix of noble gases (argon, krypton, or xenon) and reactive gases (fluorine or chlorine). When electrically stimulated and under high pressure, it creates an excimer molecule. This molecule can only exist in an energized state and emits light in the ultraviolet range.
Laser action in an excimer molecule occurs because it has a bound (associative) excited state, but a repulsive (dissociative) ground state. The molecule releases its energy through spontaneous or stimulated emission. This results in a molecule that quickly breaks down into two atoms.
Excimer lasers have higher pulse energy and average power than other UV lasers. They can operate from a single shot to a few kilohertz. Their beam has a large, rectangular shape, about 8 x 20 mm.
| Laser Type | Energy Source |
|---|---|
| Excimer Laser | Chemical Reactions |
| Helium Laser | Electric Discharges |
| Nd:YAG Laser | Light Focused from Diode Lasers |
| Ruby Laser | Ruby Crystal and Xenon Discharge Tube |
| Helium-Neon Laser | Neon and Radio Frequency Generator |
Excimer lasers have unique benefits in many fields. They interact differently with solid materials than longer wavelength lasers. Improvements in their design have made them more reliable and easier to maintain.
Some excimer lasers have closed-loop microprocessor control for consistent output. Gas circulation and filtration systems also help extend their lifespan and reduce maintenance needs.
“In stimulated emission, each electron emits two photons while falling to the ground state.”
The laser medium can be solid, liquid, or gaseous. The optical resonators have two mirrors, one fully reflective and the other partially reflective. Stimulated emission is the process of electrons producing light in the laser medium.
Wavelength Determination
The wavelength of an excimer laser depends on the molecules it’s made of. These lasers work in the ultraviolet part of the spectrum. They include Ar2* (126 nm), Kr2* (146 nm), F2* (157 nm), and others.
Excimer lasers, like XeF and KrF, can be tuned slightly. This is done with special prism and grating setups. It lets us adjust the excimer laser wavelength and excimer laser spectrum for different needs.
These lasers are great for pulsed laser ablation because of their UV light. They don’t need to be doubled in frequency. This makes them useful for many tasks.
| Excimer Laser System | Lasing Wavelength (nm) |
|---|---|
| F2 | 157 |
| ArF | 193 |
| KrCl | 222 |
| KrF | 248 |
| XeCl | 308 |
| XeF | 351 |
Being able to control the excimer laser wavelength and excimer laser spectrum is key. It lets us use these lasers for things like making microchips and in eye surgery.
“Excimer lasers are commonly used in Lasik surgery and in the production of microchips for creating smaller features on semiconductor wafers.”
Pulse Repetition Rate
The pulse repetition rate of an excimer laser is how many pulses it can fire per second. This rate is key for its use in different fields. Electron-beam pumped lasers can make high-energy pulses but with long gaps, often in minutes.
The Electra system was an exception, designed for fusion studies. It could fire 10 pulses of 500 J each in just 10 seconds.
On the other hand, discharge-pumped lasers can fire pulses continuously. They have a higher excimer laser pulse rate and excimer laser repetition rate. This makes them perfect for most uses.
Industrial lasers can keep firing at 300 pulses per second, or 300 Hz. This is thanks to their sustained energy of 1 J per pulse.
| Laser Type | Pulse Repetition Rate | Pulse Energy |
|---|---|---|
| Electron-beam pumped excimer laser | Low (minutes between pulses) | High (e.g. 500 J) |
| Discharge-pumped excimer laser | High (up to 300 Hz) | Moderate (e.g. 1 J) |
Discharge-pumped lasers are great for tasks like photolithography. They need a steady flow of high-repetition-rate pulses for efficient work.
“Excessive thermal damage can occur with repetition rates higher than 60 Hz, prompting modern devices to limit repetition rates in any specific location to under 40 Hz.”
Applications in Photolithography
Since the 1960s, excimer lasers have been key in deep-ultraviolet photolithography. This is a vital tech for making microelectronic devices. Before, mercury-xenon lamps were used for their light at 436, 405, and 365 nm wavelengths.
But, the need for better resolution and speed outgrew what these lamps could do. This led to a new solution.
In 1982, Kanti Jain at IBM showed deep-UV excimer laser photolithography could work. Now, most tools use light from KrF and ArF excimer lasers. These have wavelengths of 248 and 193 nanometers. This has made transistor sizes as small as 7 nanometres possible.
The growth of excimer laser tech has been huge for the semiconductor world. It has led to smaller, more efficient electronic devices. This is thanks to advances in excimer laser semiconductor fabrication and microelectronics.
| Laser Type | Wavelength (nm) | Applications |
|---|---|---|
| KrF | 248 | Photolithography, Materials processing |
| ArF | 193 | Photolithography, Materials processing |
| F2 | 157 | Photolithography, Materials processing |
Excimer laser photolithography has changed the game in semiconductors. It has made it possible to create more complex and tiny integrated circuits. This tech is at the heart of progress in semiconductor fabrication, microelectronics, and integrated circuits.
Applications in Fusion Research
The excimer laser has a big role in fusion research. It’s used in excimer laser fusion research, inertial confinement fusion, fusion energy, and fusion experiments.
In the late 1970s and early 1980s, the Naval Research Laboratory worked on two systems. They used the Krypton fluoride laser (248 nm) and the Argon fluoride laser (193 nm). These were the Electra and Nike laser systems.
Unlike solid-state lasers, excimer lasers don’t heat up. This is because they are gas-based. The Electra system showed its power by doing 90,000 shots in 10 hours. This proves excimer lasers are good for Inertial fusion power plants.
| Statistic | Value |
|---|---|
| Demand for high-temperature superconducting (HTS) tape is expected to increase | by a factor of ten between now and 2027 |
| Coherent’s “LEAP” excimer lasers are anticipated to play a key role in increasing HTS manufacturing capacity | – |
| Excimer lasers emitting at 193 nm, 248 nm, and 308 nm are used in various industrial applications | including organic LED and microLED display production |
| The deal with Mitsubishi Electric and Denso will see each company taking a 12.5 per cent stake in Coherent’s silicon carbide (SiC) wafer business | resulting in a $1 billion agreement |
The market for HTS tape is growing fast. It’s seeing double-digit annual percentage growth. This growth is thanks to uses beyond fusion reactors, like in zero-carbon aviation and advanced spaceships.
“In the late 1970s and early 1980s, the laser energy per pulse for inertial confinement fusion experiments increased from a few joules to tens of kilojoules.”
Medical Applications
Laser Eye Surgery
The excimer laser is widely used in medicine, especially in laser eye surgery. It uses ultraviolet light that is absorbed by living tissues. This allows for precise removal of corneal tissue without causing damage.
Laser eye surgeries like LASIK and PRK use the excimer laser to reshape the cornea. This corrects vision problems. The surgeon makes a flap in the cornea, applies the laser treatment, and then closes the flap. This method can fix myopia, hypermetropia, and astigmatism by changing the cornea’s shape.
Research shows excimer laser eye surgery works well. A study by Seiler and McDonnell (1995) looked at 118 patients and found good results. Another study by Dr. Manche et al. (1998) reviewed 470 patients, showing the technology’s success in correcting vision.
Excimer laser eye surgery has many benefits. Patients often recover faster than with old methods. The success rate is high for those who are good candidates. But, it’s important to check if someone is a good candidate before the surgery.
The excimer laser is a key tool in ophthalmology, changing how we treat vision problems. As it gets better, it will help more people see clearly and reliably.
Conclusion
Excimer lasers are a game-changer in many fields. They use special gases to create ultraviolet light. This light is key in making smaller transistors and in eye surgery.
These lasers are changing how we work and heal. They help make tiny electronics and fix eyes without hurting them. This shows how important they are in our world.
Excimer lasers are getting better and will help us even more. They can control light and speed, making them vital in many areas. Their future looks bright, promising new discoveries and improvements.
The versatility and adaptability of excimer lasers make them crucial today. As they keep getting better, they will shape our future in science and industry.
FAQ
What is an excimer laser?
An excimer laser is a special type of ultraviolet laser. It uses a mix of a noble gas and a reactive gas. This mix creates a pseudo-molecule called an excimer or exciplex. This molecule can emit light in the ultraviolet range.
What is the difference between an excimer and an exciplex?
‘Excimer’ means ‘excited dimer’, while ‘exciplex’ means ‘excited complex’. Most excimer lasers are actually exciplexes, not dimer. They are made from noble gases and halides.
What is the history and development of excimer lasers?
The idea of the excimer laser was first suggested in 1960 by Fritz Houtermans. The first steps were seen in 1971 with spectral line narrowing at 176 nm. The 1970s saw more progress, leading to the first clear evidence of excimer laser action in 1973.
How do excimer lasers work?
Excimer lasers mix a noble gas (like argon, krypton, or xenon) with a reactive gas (like fluorine or chlorine). When electrically stimulated and under high pressure, they create an excimer or exciplex. This can produce laser light in the ultraviolet range.
What wavelengths can excimer lasers produce?
The wavelength of an excimer laser varies based on the molecules used. It’s usually in the ultraviolet range. Some common wavelengths include: Ar2* (126 nm), Kr2* (146 nm), F2* (157 nm), and others.
What is the pulse repetition rate of excimer lasers?
Electron-beam pumped lasers can produce high pulses but with long gaps. Discharge-pumped lasers, however, can fire pulses more quickly. They are better for many applications because of their higher repetition rate and smaller size.
How are excimer lasers used in photolithography?
Excimer lasers, especially KrF and ArF, are key in deep-ultraviolet photolithography. This technology is vital for making microelectronic devices. Their deep-UV light has helped shrink transistor sizes to 7 nanometers.
What are the medical applications of excimer lasers?
Excimer lasers’ ultraviolet light is absorbed well by biological matter. This allows for precise material removal without heat damage. They are used in laser eye surgery to correct vision by reshaping the cornea.
