The Extreme Engineering of ASML’s EUV Light Source

after 20 plus years of development extreme ultraviolet lithography has become a commercial reality as i write these words multi-million dollar machines from asml use euv light to create impossibly small patterns in wafers this technological magic requires a powerful heart inside of it and indeed there is an amazing system driving asml's 150 million dollar lithography machine the euv light source in this video we're going to look at the lasers firing pulses at tin droplets to create the powerful 13.5 nanometer wavelength light for our latest greatest microprocessors but first i want to talk about the asianometry patreon if you like what this channel does you can support the work by joining the early access tier early access members get to see new videos and selected references for them before they are released to the public there is also general support tier signing up for that would be amazing too so head on over to the patreon page and take a look i deeply appreciate anything you'd be able to sign up for thank you and on with the show before we move on i have to note something this video will mostly focus on the euv approach taken by kymer an asml subsidiary there is another semiconductor laser company called gigaphoton a subsidiary of komatsu that is also attempting to reliably generate uv light with their own unique approach i think what they are doing is pretty cool too we can cover them in a future video but not in this one maybe if this video gets 20 000 likes or something like that every so often the best engineers across all the top semiconductor firms get together to try and decide what they might use to etch the next generation of chips they hash out the technical aspects of the candidates coordinate the necessary r d and then cooperate despite usually being rivals for a long time the industry was etching with light in the 193 nanometer wavelength this generation was getting long in the tooth but engineers kept finding ways to extend its usefulness in the industry for instance they realized that shooting the light through ultra pure water through to the wafer allowed them to focus more sharply and etch yet smaller features this technique is called immersion lithography then they started using techniques like double patterning this is where you use additional exposures to improve the feature density in other words kind of like doing a double pass through the machine these help the industry push ahead but at the end of the day they needed to move on from 193 nanometer an euv light would be the 13.5 nanometer 150 million dollar raft to take them there scientists and engineers identified two simple but big requirements for the next generation euv light source we have advanced far beyond simple light bulbs the first big requirement is that the source needed to have a high conversion efficiency that means it has to be able to generate enough euv light in the correct wavelength 13.5 nanometers furthermore the light needs to be emitted in the right direction backwards towards the light collector optics then the mirror roughly shaped like a headlamp can collect this light and send it towards the rest of the optic system and of course it needs to generate this light relatively efficiently you don't want to put an obscene amount of energy into this light source the second big requirement has to do with the debris firing lasers at things creates a lot of debris that stuff will find its way to the critical optic system and dampen their performance to meet cost of ownership requirements a way has to be found to mitigate this debris these two major issues are surprisingly simple to explain but they turned out to be incredibly difficult to overcome the euv laser story begins all the way back in 1986 japanese researcher hiro kunoshita began experimenting with new wavelengths of light essentially x-rays to etch transistors onto silicon his work allowed him to print 500 nanometer half-pitch patterns half-pitch meaning half the minimum distance spacing between lines bell labs soon followed with a 50 nanometer half pitch print in 1990 these early experiments were done with synchotron radiation a synchotron is a class of donut-shaped particle accelerator descended from the cyclotron it keeps a particle beam continuously circulating for many hours emitting radiation essentially a relative of the large hadron collider industrialists envision having one synchotron linked up to multiple lithography tools but researchers quickly realized that these light sources were not practical for the industry not because building an iron man style arc reactor to edge chips would cost too much or take up too much space tsmc would do it but because the synchrotron emitted uv light over too broad a field of view not enough of it would go into the collector mirror thus failing the first big requirement at the same time the goal post moved farther backwards euv had originally been scheduled for the 100 nanometer node which meant the light source and print resolution did not have to be all that powerful but then it got penciled in for the 70 nanometer node and then the 50 nanometer node later on it would fall even further as delays piled up this had cascading effects throughout the entire design the euv optics system painstakingly crafted by german optics maker carl zeiss needed to change to increase the print resolution zeiss had to add more mirrors into the projection and illumination optic systems each mirror even when perfectly made is only capable of reflecting at most around 70 percent of the euv light that hits it the rest gets absorbed these two factors together meant that for euv lithography to work on the shop floor asml needed a stronger singular is that a word more brilliant point of plasma light capable of at least 250 watts to be competitive with the current 193 nanometer laser technology something to note it's not just good enough for the technology to work anyone can slap together a bunch of lab equipment and shove it in front of the users it also has to be appreciably better than what is already on the market or else there is no point for it to be customer commercial requirements constantly set the bar for these engineering wonders thus another breakthrough in euv light generation was required before industry leaders could start to take it seriously researchers for a long time have been experimenting with something called laser produced plasma or lpp this is where you point a laser at a gold plate or wire target so to create plasma the plasma then presumably emits uv light in the proper wavelength required this might work but the prevailing issue everyone thought would be the deal breaker was debris bits and pieces of the target would fly off and contaminate the optic system degrading performance researchers tried a variety of different targets narrowing it down to three lithium tin and xenon at first the most promising targets seem to be rare xenon gas in either gaseous or ice form and yag lasers yag stands for yitrium aluminum garnet lasers they are powered by a crystal kind of reminds me of those things they use for lightsabers early experiments had researchers firing one kilowatt diag lasers at a jet of xenon at a rate of 10 000 cycles per second scientists at sandia laboratory were eventually able to suppress xenon ice particles from getting to the optics using a gas jet but the xenon ice plasma also emitted high energy ions that degraded the optics anyway nobody knew how to fix that that that last paragraph sounds like a line of dialogue from a star trek movie the second most plausible option was tin tin plasma certainly emits a lot of uv light in the required wavelength but the conversion efficiency you got from firing lasers at a tin plate was terrible more on that later furthermore using tin has an euv light source notoriously generates a lot of tin debris as i mentioned before a tin layer just 1.2 nanometers thick will cause a 20 percent decline in collector efficiency and a 10 decline in total tool output how are people going to deal with that thus tin did not seem to hold all that much promise regardless people continued experimenting various companies in the industry began tinkering with firing lasers at tin droplets rather than a tin plate with good results then in 2002 all the leading mines got together in dallas to talk about it they debated the future of the xenon laser option and realized that xenon did not offer a very promising technical future the xenon option had a fundamental roadblock the conversion efficiency was too low less than one percent it cannot generate more than several tens of watts of euv light the tin option would create a debris nightmare up ahead in the development roadmap but maybe with enough engineering this could be overcome there would be no fundamental physics issue ahead thus the industry made a massive turn and embarked on a journey towards tin plasma the original target material had been a tin plate however the conversion efficiency with the plate was rather low the reason for this is because of a low level of what is called spectral efficiency this refers to the ratio of 13.5 nanometer light as compared to the energy put into it with the tin plate the spectral efficiency was very low like around one percent the plasma made on a tin plate shape had too high in opacity which blocked 13.5 nanometer wavelength light from reaching the mirror so a new shape was proposed to increase the spectral efficiency one that is more concave rather than flat fire a laser onto this and it will create 13.5 nanometer light with far more intensity the overall spectral efficiency and thus overall conversion efficiency of the light source improves to an acceptable level on an entirely separate issue having a big plate of tin or even a tin wire as the target created too much debris or fast ions obviously we want to avoid this so you want the target to be as small as possible thus the droplets that companies had already started to experiment with engineers looked at this double challenge small as possible concave shaped and the double solution they eventually came up with was pretty wicked how do we get the shape we want but as small as humanly possible with two shots from two lasers hitting a falling bullseye not once but twice lasers akimbo one hundred thousand times a second the first shot comes from a low energy laser pulse called a pre-pulse hitting the tin droplet with this pre-pulse creates strong pressure waves that reshape the tint droplet from a sphere into a concave sheet the pre-pulse needs to hit the droplet at the exact right location if not the concave sheet tilts in the wrong direction and messes up the second shot furthermore it could reflect the second shot back at the laser machine damaging it but when done right it can properly and consistently set the table for what comes next the second shot is the main pulse generated by an amplified carbon dioxide laser operating in the 10 micrometer wavelength this more powerful blast again remakes the droplet into an acorn shape and vaporizes it creating the dense plasma from the liquid target this plasma is what emits the 13.5 nanometer like that we so desperately crave it is hotter and denser than the plasma created by lightning but it does fall short of the plasma created within the sun's core room for improvement i guess the pre-pulsed laser was the critical ingredient systems installed at customer sites as recently as 2010 struggled to get past the 10 watt uv power level adding the pre-pulse in 2016 along with drastically more powerful co2 lasers allowed asml and kymer to drastically scale up its euv light source power levels thereafter from 10 watts to 200 plus teams around the world studied and modeled the physics and dynamics of the tin droplet when struck by the two lasers there are papers and papers studying the expansion dynamics cavitation and fragmentation of a single falling tin droplet yet there remained so much more to know so we talked on the physics now how does the actual machine work the machine itself is rather simple and has a few main components the high powered co2 laser which includes a master oscillator and a power amplifier the latter two together are referred to as mopa the beam transport system which handles the laser's focusing and the beam positioning then there is the vacuum vessel filled with low pressure hydrogen gas it houses the droplet generator metrology modules for monitoring performance within the system and the euv collector mirror this collects the light and sends it on its merry little way there is a hole in the middle of this ellipsoid shaped mirror for the laser to fire through the co2 laser needs to reach a power level of over 20 kilowatts which requires a lot of amplification it is so big and bulky it typically has to be installed under the fab clean room floor the droplet generator shoots tin droplets into the vessel at a very high rate 50 kilohertz or 50 000 cycles a second despite the name they are not dropped but shot through the vessel at a surprisingly high speed 80 meters per second that is about 288 kilometers per hour the reason for this is because we want to have a large separation space between each 30 micrometer wide droplet about 1.6 millimeters this is to make sure that the tim plasma from one droplet does not interfere with another literally hitting 50 000 bullets a second with a laser twice the resulting final conversion efficiency from this setup six percent a massive leap forward from the one percent that we saw at the very start with those lightsaber yag lasers this finally allowed asml's euv machines to reach the stable 250 watt power level needed to achieve the 125 wafers per hour operation level that its clients desire there even exists a pathway towards 450 watts in the future when researchers industrialists embarked on the tin journey they realized that they needed to figure out some way to have the collector optics survive the over 100 billion pulses or 30 000 hours throughout its lifetime bilayer collector mirror is at threat not only from tin debris particles but also high energy ions and neutrals from the plasma what zeiss and asml eventually decided upon was to pump hydrogen into the vacuum chamber as a buffer gas the hydrogen gas would cool the plasma block a percentage of tin ions and etch layers of tin from the mirror surface i also briefly covered this in my previous video about carl zeiss's euv optics nikola tesla once said about his frenemy thomas edison edison was by far the most successful and probably the last exponent of the purely empirical method of investigation everything he achieved was the result of persistent trials and experiments often performed at random but with extraordinary vigor and resource this method was inefficient in the extreme for an immense ground had to be covered to get anything at all unless blind chance intervened a little theory and calculation would have saved him ninety percent of labor backhanded compliment if i ever ever heard of one but it demonstrates the difference between creating the argon fluoride lasers for 193 nanometer and the euv laser with the first two the most necessary basic technologies had already been developed the semiconductor industry merely had to grind through the many variations in a trial and error manner to find what worked not to say that the effort wasn't admirable it most certainly was but with euv such trial and error cannot be done now we are in green grass territory only a deep understanding of the physics and its fundamental dynamics can help uncover the best way to deal with the thorny energy efficiency and debris mitigation issues while achieving what is commercially needed in the industry they literally first calculated the exact opacity temperature droplet size ion density emission duration and such years ahead of time then they built a machine to achieve it in real life the modern day moon landing thus in other words one was edison the other was tesla alright that's it for tonight thanks for watching if you enjoyed the video consider subscribing the feed will show you a bunch of other videos from this channel that might fit your interest want to send me an email drop me a line at john asinometry.com i love reading your emails introduce yourself suggest a topic or more until next time i'll see you guys later

Channel: Asianometry

Views: 403,219

Keywords:

Id: 5Ge2RcvDlgw

Length: 17min 20sec (1040 seconds)

Published: Sun Dec 26 2021

Reddit Comments

[u/nismotigerwvu]

To be honest, I'm stunned that this tech ever panned out. Due to the insane complexity, it was "five years away" every year since the early 90's. It's as if a bone fide, practical flying car was released.

[u/NoobFace]

I knew it was tin droplets, I didn't realize they were being fired at 80mps spaced 1.1mm apart. This tech is even more impressive than I had understood.

[u/dankhorse25]

And this is just the light source.

[u/AbheekG]

Black magic wizardry. Amazing, mind-boggling that humans could conceptualize, and then create and then actually productize such technology. Who and how TF did someone discover that firing a laser onto a droplet of tin would cause it to release extreme ultraviolet light on account of it being liquified into plasma?? Like WTF?!!

[u/MiyaSugoi]

Even witches and wizards would be in awe of technology like this. Incredible.

[u/GarfsLatentPower]

fire is a light source :p

https://www.asml.com/en/news/press-releases/2022/fire-incident-at-asml-berlin

[u/nickstatus]

EUV tech blows my mind. I want to take the machine apart.

[u/cstar1996]

An interesting fact from when I interned there, the older DUV machines run the reticles at 14gs of acceleration almost constantly, and the EUV machines goes even faster. 14gs!!!! It’s insane!