The technology of x-ray lithography is not considered a front-runner in the next-generation lithography race, but a company called JMAR Technologies continues to make progress with x-ray lithographic technology. The company has now crafted .1 micron patterns using an x-ray source. JMAR used reticles made by IBM, and the x-ray source produced one nanometer x-ray light. Currently, most of JMAR's funding comes from DARPA and other military sources. Major semiconductor makers like Intel have devoted the preponderance of their R&D lithography budgets to Extreme UltraViolet Lithography, a technology which is increasingly behind schedule. Current estimates are for EUV to make its commercial debut around 2010, but even this late date now appears dicey. X-ray lithography may have certain cost advantages over EUV. JMAR claims that:
We believe that the high cost of EUV tools is a fundamental weakness in the approach. Tool costs exceeding $40 – 50 million are reported [for EUV]. JMAR believes that CPL [Collimated Plasma Lithography – JMAR's version of x-ray] represents a more robust, multigenerational solution to current and upcoming lithographic challenges. We believe that the industry should recognize the merit and success of the extensive R&D successes using proximity XRL and the superiority (practicality) of JMAR's CPL implementation. CPL has the potential to move lithography forward at a much reduced rate of increase in costs.
JMAR boasts that x-ray sources can etch 35 nm transistors, and notes that work is being done to see if x-rays can create even smaller features. If neither EUV nor x-ray lithography proves viable, the semiconductor industry will be forced to try to push 157 nm lithograpy, combined with immersion lithography, to the 35 nanometer node.
USER COMMENTS 27 comment(s)
|noble effort… (4:48pm EST Fri Dec 12 2003)
but hard to carry out large-scale. X-ray lithography requires difficult masks and get blurred by several mechanisms. Perhaps it could get revived by tabletop synchrotrons. – by fc
|Lets not forget… (5:27pm EST Fri Dec 12 2003)
That X-Ray tech is a “near-field” tech, in that it relies on carefully collimated beams to illuminate a series of 'partial masks' that when overlaid constitute the entire mask. The masks are only a few nanometers above (and typically contacting in spots) the chip surface. They tend to get “dirty” easily.
Masks themselves (due to the nature of x-rays) are made up of light, thermally stable, extremely flat, “optically transparent” low-atomic-weight materials, such as beryllium (which is absolutely the best, but costs like the GDP of Argentina) or even very thin silicon itself (since there is a whole industry of making large, remarkably flat wafers out there). The masking material needs to be “optically opaque”, which for the non-physicists out there, is simply any element (compounds make no difference) that has a big ol' honkin' nucleus. So, elements such as platinum, gold (nice 'cuz they don't oxidize, lousy 'cuz they're as soft as butter), or tungsten, or especially uranium (which has its own problems with oxidation) are the masking 'stuff'.
For reasons that completely elude me (now isn't that a first!), masking is done in partial-masking operations, where (as a simplistic example) all teh horizontal traces are done in “this pass”, and all the vertical in the “next pass”. Has something to do I recall with the inteference of the underlying silicon substrate with the near-field diffraction of the x-ray beams themselves (making them “fuzzy” in on direction, but nice and “clear” in the other). Or it is something else. Whatever.
In any case though, it is a “prefocussed” technology, where the X-ray source (which is either typically a point-source, or a 'line' geometry) is several dozen meters (!!!) from the target, and a series of gently carved multi-layerd “mirrors” bend the exit cone into a narrower or even collimated beam. In the newest systems, that beam is in turn focussed a second time to a 1.5 by 1.5 centimeter “spot”, to increase intensity, while retaining collimation.
The chief issue with the X-Ray technique is that the wavelength of radiation is SO small, that there are few organics that absorb an appreciable amount of it, making the resists terribly insensitive. Then, to counter that, either the beam intensity is increased, or exposure time increased, both of which tend to disrupt the underlying chip through intense X-ray exposure. Not optimal.
I'd therefore bet that JMAR has come up with some novel chemistry for the resists that incorporate some heavy reactive atoms in the mix. Again, uranium wouldn't surprise me, although there is a pretty big “stable” of 2nd tier lanthanides ripe for the pickin'.
Goats view? “Better than nano-imprinting (more general, and less geometrically constrained), probably better than EUV, has problems with mask wear-n-tear, but that should be resolvable”. Goatpunch: “Nasty sources, lousy reliability, who knows if practical resists are coming, and lots of damage to the underlying chip”
– by GoatGuy
|Re: let's not forget… (5:39pm EST Fri Dec 12 2003)
The two-pass exposure is new to me. It may be polarization-related as you hinted, or it could be because of the doughnut effect (can the membrane support an island).
Radioactive resists?! I'd think they'd self-expose!! – by fc
|Nah… (5:55pm EST Fri Dec 12 2003)
Depleted uranium is almost completely nonradioactive. What is it, something like a 4.5 billion year half life, and a 1 micron thick layer, 1.5 cm on a side would have some 2.5e15 atoms … which would be a 20 or so disintegrating per second.
But you're right — why bother, when there's nice heavies not far away, such as Bismuth.
– by GoatGuy
|Fundamental Problems (1:38am EST Sat Dec 13 2003)
Use of energy levels that affect the nucleus ultimately limits you to fairly trivial chip geometry.
Production CPUs already require a dozen layers of metal interconnects but even if you use non-metalic interconnects, the substrate is broken into many crystaline domains, severely compramiseing electron mobility in the completed chip.
And that's completely disregarding the problem of nuclear transmutation. When you're aiming for regions with only a handful of dopant atoms and a billion gates, it is a factor even with xrays.
High energy feature construction is the past, not the future of chip design.
|Ummmm….me?? (1:36pm EST Sat Dec 13 2003)
I care about all of this. I just switched majors from Chemical Engineering to Electrical Engineering, for the simple reason that my interests lie in exactly this type of conversation. This is my passion. And thanks to wonderful people like GoatGuy and MrX_TLO, I'm learning that my background in chemistry can really help me understand these new arising problems in the tech sector….if nothing else, I'm learning how to train my thinking when reading articles such as the BLURB above………so maybe you don't care, but I sure do…. – by thenewguy
|Wow. (3:58pm EST Sat Dec 13 2003)
More info here than you can shake a large periodic table at. Too bad I'm no physics guy. Computer networking on the burner? We'll talk. But nice to know you guys know what the heck you're doing, cause if it was up to me we'd still be trying to figure out how to make ENIAC smaller. – by InsaneX
|X-ray focus… (7:07pm EST Sat Dec 13 2003)
Hey Goat, those multilayer focusing elements you mentioned work for soft X-rays (like ~10 nm), but I don't think there is adequate multilayer technology for harder X-rays (like ~ 1 nm).
For focusing X-rays, the only mature technology I am familar with is the use of Fresnel zone plates. They are commonly used, though they do not focus 100% of the light (more like 10% in binary case).
The funny thing about JMAR's CPL source is it is not monochromatic (unlike synchrotrons). So you actually need to filter the radiation to get the band you want. Otherwise the longer wavelength included would blur the intended image. This has also plagued other EUV source development, as a significant throughput limiter.
All these NGL techniques depend critically on the resist. I am expecting more investigations in that direction. – by fc
|thick or thin resists? (7:36pm EST Sat Dec 13 2003)
The key issue of resists in my mind is the optimum thickness. Too thick, you cannot make too small a feature or it will topple over. Too thin, the graininess of the resist aggravates the line-edge roughness. Once the optimum thickness is settled, there is also the issue of how much radiation is absorbed. Again there is a tradeoff. Not enough absorption means less sensitivity and longer exposure time (as Goat has mentioned above). This arises with high-energy electrons and X-rays. Too much absorption (like for ions, low-energy electrons or EUV) means resist profiles are harder to control and actually limit the focus window.
So some more exploration will be required here, or else we will have to use something like nano-dipping. – by fc
|NEC/Tokuyama ebeam resist (4:18am EST Sun Dec 14 2003)
Here is a good example of work that's going on. LER down to 1 nm though this is still a large percentage of the resolution.
No sensitivity data here, but considering how many electrons to expose a 10 nm pixel, a really high dose is needed just to minimize statistical fluctuations (shot noise). – by fc
|that is one hellava post there Goat… (5:44pm EST Sun Dec 14 2003)
WOW!!! WE ARE BLESSED BY YOUR PLENTIFUL KNOWLEDGE TIME AND TIME AGAIN! THANK YOU! – by Silicon
|X-Ray Lithography (10:44pm EST Sun Dec 14 2003)
Doesn't IBM in East Fiskill NY have an X-ray lithography chip making faculty there? Don't know if its for R&D or production though. – by By RGK
|optical litho forever (8:02pm EST Mon Dec 15 2003)
IBM has such good optical lithography already, it would be a shame to throw it all away on X-rays. – by optical litho foreve
|Now that you mentioned IBM… (11:31pm EST Mon Dec 15 2003)
Haven't heard much about EPL (electron projection lithography) lately. That was a technique IBM was championing recently.
Would also use double stencil masks, by the way. – by fc
|JMAR (1:05am EST Wed Dec 17 2003)
was also in the running for developing a high-efficiency laser-driven EUV source. What happened there? – by X-ray eyes
|JMAR (8:43pm EST Wed Dec 17 2003)
JMAR intent is not necessarily (at least now) planning to overtake EUV but to fill a potentially very large niche for smaller and much less expensive chip production using X-ray lith– satisfying fab centers who need commercial chips for various reasons but can't afford the tooling of EUV. Darpa for example looking at JMAR for next generation military tasks (think weapons)where current needs and portability are more important than the delay expected with EUV until 2010 or beyond). CPL is a happening NOW event if JMAR is successful. – by PeeEye
|JMAR's CPL (10:02pm EST Wed Dec 17 2003)
Sorry, but you guys are so out on a limb speculating on how JMAR's xray litho technology works..
JMAR's form of xray litho uses an array of diode pumped solid state lasers to converge on a copper tape target and generate 1nm light. It is my understanding that they do get monchromatic light. I believe copper gives them the 1nm peak that is free of the other unwanted radiation. Some of that light is collected by a polycapillary collimator (made by XOS of New York), straightened out and directed to the mask. The distance from source to mask is at best a meter. The gap between mask and wafer is in the range of 10-15 microns, not nanometers. The lithography source, as with the synchrotron-based xray litho source, is a projection source, that does full fields (25×25+mm or so), not some serial or multipass process. The resist so far has been commercial resists same as that used by E-Beams. No exotic materials in any of this. The masks are an issue, in terms of getting someone to manufacture them in commercial quantities to get the price down. IBM has been supplying xray masks to JMAR from its mask shop in Vermont. Masks are particularly exotic either, but the main difficulty is xray litho is a 1:1 litho (as opposed to optical litho which uses optics and can be a 5:1 process, whereby you can have a mask 5 times larger than the intended features. (But that is in theory, because in industry they have to use expensive optical proximity correction and other “tricks” to avoid problematic effects and blurring that cause them to have to create some 1x features). So, with xray masks, you need to use an E-beam to create the mask features at the same size as the ultimate chip features, and when you are trying to get to 50nm or 35nm features (which is what Xray and EUV purport to be able to do), that makes for some tough mask-making. But it has been done in Japan and elsewhere. It just has to be made cost-effective.
More info on JMAR's website ( site (one of their subsidiries) for lots of good CPL/XRL info. – by RealTime
|JMAR CPL II (10:09pm EST Wed Dec 17 2003)
Also, to follow on someone else's question about IBM, IBM invested hundreds of millions in Xray litho in the 1980-90s, building an expensive synchrotron facility at East Fishkill, NY. They processed sub-100nm powerpc chips and other chips and developed a lot of the assoicated processes. IBM eventually shut down its program because of the expense and inflexibility of using a synchrtron as your chip-making source and the rest of the industry lost interest in XRL for similar reasons. JMAR's approach has been to build a compact source that is equivalent in size to current optical litho sources. Now, if JMAR can finalize a fully commercialized version, it might persuade the industry to take another look. Time will tell. – by RealTime
|Thanks.. (11:32pm EST Wed Dec 17 2003)
Good info, especially from the nanolitho link. The JMAR link info actually mentioned quite a broad spectrum from the source. Generally, with a plasma you can get a fairly significant peak above the background spectrum, but it's hardly as monochromatic as a laser. I mistakenly thought the synchrotron was monochromatic but it also has quite a spread. So no advantage there.
I also agree about the masks being difficult to make. There's the membrane and film stress, the feature profile, etc. – by fc
|goat guy (1:28pm EST Thu Dec 18 2003)
Why waste everyones time with incorrect information…..? – by KELLY
|All right, everybody study X-rays! (11:48pm EST Thu Dec 18 2003)
I highly recommend the work of Prof. Cerrina at U Wisconsin. – by X-ray Geek
|Re: X-ray focus (2:11am EST Sat Dec 27 2003)
Kirkpatrick-Baez mirror pairs are another way to focus X-rays. These work at grazing incidence. They can be made from multilayers but don't have to since reflection is high at such angles anyway. – by n' synch
|Re: n' synch (3:34am EST Sat Dec 27 2003)
Thanks for bringing that up. That's a good point. K-B mirrors are pretty prevalent as synchrotron beam collimators. However grazing incidence is not that simple since there is still finite loss in all materials.
For a wavelength of ~ 1 nm, the critical angle is quite small (about a few degrees or so), so you would have to use really small grazing angles (near parallel to the surface). Obviously your illumination spot will blow up in the longitudinal direction by more than 10x. This would increase the necessary mirror size.
As long as spot image quality doesn't make a difference, I wouldn't be concerned about controlling all the aberrations in the collimation. But for microscopy and lithography applications, it should make a difference. – by fc
|rthrhsxtsdrj (11:03am EST Sun Feb 29 2004) – by srtjhtfjty|
|a comedy or errors (4:54pm EST Thu Jun 03 2004)
From jmar to ibm to nsa to darpa to whoever…my god since the 1970's they can not get it right…this reminds me of the magnetic fusion program for energy production.
Dump Kelly at IBM and his crew…a real failure man…
concerning JMAR they are funny — they are like jack in the box producing jack chips..that's all we can say….In silence they rob…(it use to be serve. It is my …th birthday…and they still can not get it. – by thegoldenowl
|Look this up first… (12:16am EST Wed May 11 2005)
…then think really hard! – by NGL Geek
|x-ray lithography vs. ion beam lithography.. Which is better?? (9:51pm EST Tue Apr 18 2006)
Does anyone out there know which lithography process is better?? – by doubt