News › Fraun­ho­fer IOF · Full EUV power on a small labo­ra­tory scale

The future has a color: it is extre­mely ultra­vio­let. Light in this par­ti­cu­larly short-wave spec­tral range, so-cal­led EUV light, can be used, for exam­ple, to pro­duce smal­ler and more powerful micro­chips than ever before. But fur­ther rese­arch faces a pro­blem: Expe­ri­ments with laser-like EUV light can so far usually only be con­duc­ted at expen­sive large-scale rese­arch faci­li­ties. Jena rese­ar­cher Robert Klas wants to change that. He has deve­lo­ped a com­pact EUV laser module that can be used to gene­rate this spe­cial light much more easily and cost-effec­tively. Par­ti­cu­lar poten­tial appli­ca­ti­ons are con­ceiva­ble in semi­con­duc­tor manu­fac­tu­ring and micro­scopy. Robert Klas has now been awarded the Hugo Gei­ger Prize for this work.

© Fraun­ho­fer IOF Robert Klas is the win­ner of the Hugo Gei­ger Prize 2023.

Rese­ar­cher Robert Klas from Jena has deve­lo­ped a com­pact module for gene­ra­ting laser-like EUV light as part of his doc­to­ral the­sis. Where rese­arch faci­li­ties the size of an entire house have been neces­sary until now, so-cal­led syn­chro­trons, Klas now pres­ents with his dis­ser­ta­tion a new and effi­ci­ent method to gene­rate laser-like EUV light in a faci­lity the size of a labo­ra­tory table.

Klas‹ doc­to­ral the­sis, which is the result of coope­ra­tion bet­ween Fried­rich Schil­ler Uni­ver­sity Jena, the Helm­holtz Insti­tute Jena and the Fraun­ho­fer Insti­tute for Applied Optics and Pre­cis­ion Engi­nee­ring IOF, pro­vi­des the most powerful laser-like EUV source on a labo­ra­tory scale to date, with an average power of 10 mil­li­watts – a hundred times more power than was com­mon in com­pa­ra­ble sys­tems when he began his doc­to­rate. This will make EUV rese­arch inde­pen­dent of a few large-scale faci­li­ties that are cos­tly to main­tain. What’s more, the com­pact setup costs only a fraction.

EUV source on a labo­ra­tory scale with a hundred times more power

Klas‹ work addres­ses a key chall­enge in laser optics. An important prin­ci­ple in this field is that the shorter the wave­length, the har­der it is to gene­rate laser radia­tion. In his work, the phy­si­cist is working in the wave­length range from 10 to 50 nano­me­ters. One nano­me­ter cor­re­sponds to one mil­lionth of a mil­li­me­ter. In short, extreme ultra­vio­let light is extre­mely dif­fi­cult to gene­rate as laser light.

To solve the pro­blem, Klas uses modern high-power ultra­fast lasers. These are con­ver­ted into EUV light by means of the pro­cess of gene­ra­ting high har­mo­nic radia­tion. To do this, Klas first focu­ses the high-power laser in a noble gas. In this pro­cess, elec­trons are acce­le­ra­ted within a few 100 atto­se­conds. An atto­se­cond is one tril­lionth of a second. Robert Klas illus­tra­tes this order of magni­tude with a com­pa­ri­son: »An atto­se­cond rela­tes to a second like a second rela­tes to our world age,« he explains. The elec­trons acce­le­ra­ted in this uni­ma­gi­n­ably short time sub­se­quently pro­duce the pre­cious EUV radia­tion by recom­bi­ning with their parent ion.

The great chall­enge here is to coher­ently super­im­pose the released radia­tion, i.e., to con­trol it in such a way that its so-cal­led wave crests in the extreme ultra­vio­let spec­trum add up and can be bund­led into a laser beam at the end. Through the cor­rect choice of laser para­me­ters as well as gas den­sity, he has suc­cee­ded in gene­ra­ting EUV radia­tion with laser-like para­me­ters in a highly effi­ci­ent man­ner. Which, in com­bi­na­tion with high-power dri­ver lasers, led to a signi­fi­cant increase in EUV performance.

High-power EUV source crea­tes novelty in high-reso­lu­tion microscopy

The sci­en­tist is con­vin­ced that his work will signi­fi­cantly faci­li­tate fur­ther rese­arch as well as appli­ca­tion of EUV light: »In the future, it is expec­ted that the results of my doc­to­ral the­sis will drive deve­lo­p­ment in many important areas such as the energy and sto­rage effi­ci­ency of chips, bio­logy as well as medicine.«

In the pro­cess, Klas has alre­ady tes­ted the first poten­tial appli­ca­ti­ons for his novel EUV source on a labo­ra­tory scale during his rese­arch. In par­ti­cu­lar, he has tur­ned his atten­tion to micro­scopy – spe­ci­fi­cally ima­ging in the tiny nano­me­ter range – in exch­ange with other rese­ar­chers. »With an expo­sure wave­length of 13.5 nano­me­ters, we have rea­li­zed a reso­lu­tion of 18 nano­me­ters,« he reports. By com­pa­ri­son, con­ven­tio­nal light micro­sco­pes only manage a reso­lu­tion of just under 500 nano­me­ters. Klas uses ano­ther exam­ple to illus­trate the incre­di­ble detail of the micro­scopy made pos­si­ble by EUV light: »In one expe­ri­ment, we achie­ved a so-cal­led field of view mea­su­ring 100 x 100 micro­me­ters. That means we can com­pa­ra­tively cover the size of a soc­cer field within an image and find a one-euro coin in it.«

Ano­ther inno­va­tion: With EUV-based micro­scopy, colo­red images can be crea­ted of a sam­ple under inves­ti­ga­tion. In this way, rese­ar­chers can »look inside a cell« and distin­gu­ish dif­fe­rent ele­ments or pro­por­ti­ons of dif­fe­rent sub­s­tances such as car­bon, lipids, etc. – »a novelty at such a high reso­lu­tion,« Klas empha­si­zes. »With our tech­no­logy, we can use it to advance bio­lo­gi­cal and medi­cal stu­dies in the future and hop­efully study dif­fe­rent types of viru­ses. At some point, we also want to be able to image DNA with a dia­me­ter of about two nano­me­ters using this method,« he says.

Qua­lity assu­rance in semi­con­duc­tor manu­fac­tu­ring using EUV lithography

The tech­no­logy deve­lo­ped by Klas has ano­ther spe­cial poten­tial appli­ca­tion in EUV litho­gra­phy. Here, tiny micro­chips are pro­du­ced with the help of extreme ultra­vio­let light. The semi­con­duc­tor indus­try alre­ady uses this pro­cess to apply more than ten bil­lion tran­sis­tors to a chip the size of a fin­ger­nail. A rese­arch team from TRUMPF, ZEISS and Fraun­ho­fer was awarded the Ger­man Future Prize in 2020 for the deve­lo­p­ment of EUV lithography.

Klas‹ rese­arch opens up a new pos­si­bi­lity for qua­lity assu­rance in this con­text. This is because the out­stan­ding micro­sco­pic pro­per­ties of his sys­tem can also be applied to an expo­sure mask. This is used in semi­con­duc­tor manu­fac­tu­ring to pro­duce the tiny EUV chips. If defects are hid­den in this mask, they are pas­sed on to the chips manu­fac­tu­red with it. EUV micro­scopy can be used to examine the mask for such defects. Detec­ting weak spots in the EUV mask early on and thus avo­i­ding fur­ther errors in pro­duc­tion saves time and money. »This pro­cess can reduce scrap and thus lead to more sus­tainable pro­duc­tion,« says Klas, explai­ning the bene­fits of this method.

Awarded the Hugo Gei­ger Prize

Robert Klas has now been awarded the »Hugo Gei­ger Prize for Young Sci­en­tists« for his ground­brea­king rese­arch work. The award is pre­sen­ted by the Free State of Bava­ria and the Fraun­ho­fer-Gesell­schaft to out­stan­ding young rese­ar­chers. The award cerem­ony took place on March 21 in Munich. A total of three sci­en­tists from Munich, Frei­burg and Jena were hono­red. Fur­ther infor­ma­tion on the award and the other prize win­ners can be found in the press release of the Fraunhofer-Gesellschaft.

EUV light – the light for the digi­tal age

Light in the extreme ultra­vio­let range, or EUV light for short, is a very spe­cial light. Due to its par­ti­cu­larly short wave­length, it can be used to pro­duce tiny struc­tures. This is important in semi­con­duc­tor manu­fac­tu­ring, for exam­ple: Here, EUV light can be used to pro­duce ultra-fine cir­cuits on micro­chips. In this way, semi­con­duc­tors can be made smal­ler and at the same time more powerful than ever before. And it is pre­cis­ely these mini-chips that we urgen­tly need, because wit­hout them, pro­gress in arti­fi­cial intel­li­gence and auto­no­mous dri­ving, for exam­ple, would be vir­tually inconceivable.

Until now, the gene­ra­tion of laser-like EUV light has only been pos­si­ble in expen­sive and com­plex large-scale faci­li­ties. Rese­ar­chers have to visit spe­cial rese­arch cen­ters, so-cal­led syn­chro­trons, to use these faci­li­ties. Sci­en­tists often wait for years for a place here, only to end up being able to expe­ri­ment for a few weeks or even days. Rese­arch and fur­ther tech­no­lo­gi­cal pro­gress, which EUV light pro­mi­ses espe­ci­ally in the digi­tal age, are thus mas­si­vely ham­pe­red. Klas intends to remedy this situa­tion in the future with its new, com­pact EUV source.


Roberts Klas
Fraun­ho­fer IOF
Albert-Ein­stein-Str. 7
07745 Jena
Phone +49 3641 807–640
Mail ed.refohnuarf.foi@salk.strebor