Recent Progress in High Frequency Electron Cyclotron Resonance ...

126 ( HEP & NP ) 31 an hexapolar magnetic configuration, magnetic fieldlines are such that they present a three branch starshape at each end of the plasma chamber. As electronsand consequently ions follow these field lines,there is some space in the plasma chamber withoutalmost any particles. A simple solution to be “powersaving” is to avoid the microwaves going into thisspace. This could be achieved by simple grids or bysome metallic pieces of course well cooled. In otherwords, an optimized plasma chamber would no longerbe simply cylindrical, but must correspond to theshape of the magnetic field lines. Moreover, if corrugated,such a star shape plasma chamber could stillserve as a multimode cavity; anyhow, the use of amovable biased disk would efficiently work as a piston.Finally, it is hard to take benefit of a broadbad frequency with a gyrotron, as with a TWT. Forexample, the tube utilized for SERSE 28GHz is at27.962GHz, which correspond to a resonance fieldat 0.9986T. And the use of several gyrotrons havingslightly different frequencies is costly not conceivable.The only solution is to tune the magnetic gradientaround the resonance with coils or iron plugs.4 Industrial applicationsIt is commonly known that ECRIS can advantageouslybeen used in ion implantation, however theuse of an ECR plasma as a light source still remainconfidential despite experiments performed atLBL and CEA. For example, Extreme UV lithographyneeds powerful photon source able to delivermore than 100W at 13.5nm. In addition, source lifetimemust be several months and it must not produceany debris that could pollute the wafer. Up tonow, gas discharge plasma (GDP) and laser produceplasmas (LPP) are best candidates, but their majordrawbacks are their lifetime and the debris they produce.ECR plasma could be an alternative as it hasseveral advantages: it works in CW during monthsand doesn’t produce any debris. However, 100Wof photon power corresponds to 6.7×10 18 photons,while the electron density of high frequency ECRISs isabout 10 13 e − /cm 3 . This means that an ion must undergoa lot of excitation/deexcitation processes duringits lifetime. Preliminary experiment showed thatan all-permanent magnet ECRIS can produce 6×10 15photons [8] . Therefore a possible powerful ECR photonsource could be a small plasma spot at 37GHzsurrounded by another plasma at 50GHz. This secondplasma would provide the electrons that are necessaryfor the excitation processes. In addition, ascompared with GDP or LPP, an ECR plasma has thecapability to use at the same time several elements ofthe periodic table known to give photons at 13.5nm(O 6+ , Xe 10+ , Sn 8+..10+ ). And then the photon sourceplasma could advantageously be a mixture of variouselements, metallic or not. Already utilized in todayEUV source, a mirror system Wolters type would beinstalled inside the plasma chamber to take photonsemitted by the 50GHz plasma and focus them in theso-called intermediate focus. Some other tricks usefulfor an efficient photon source are also presented inRefs. [9—12].5 ConclusionPowerful ECRISs not only require optimized magneticconfiguration but also optimized plasma chamberfor the use of minimum rf power as possible. Formore details, a complete review of recent progress inECRIS could be found in:Advances in Imaging and Electron Physics, Volume144. Edited by Peter Hawkes, Elesevier Science,ISSN 1076-5670/05.6 AcknowledgmentsThis review could not have been written withoutthe outstanding work done during tens of years bythe worldwide ECRIS community, to which I give mywarmest thanks for the real pleasure I had to workwith in this domain.

D. Hitz ECR 127References1 Apard P, Bliman S, Geller R et al. Physics Letters, 1973,A44: 432—4342 Bliman S, Dousson S, Fremion L et al. Nucl. Instrum. Methods,1978, 148: 213—2163 Hitz D, Delaunay M, Girard A et al. An All-PermanentMagnet ECR Ion Source for the ORNL MIRF UpgradeProject. Proceedings of the 16th ECRIS Workshop, AIPConference Proceedings, 2005, 49: 123—1264 Melin G, Nguyen T K, Farchi A. RF Waves and RF CouplingSystems in ECR Ion Source. Proceedings of 12thECRIS Workshop, 1995. 105—1095 ZHAO H W, SUN L T, ZHANG X Z et al. Rev. Sci. Instrum.,2006, 77: 03A3336 Lyneis C M, Leitner D, Abbott S R et al. Rev. Sci. Instrum.,2004, 75: 1389—13937 Hitz D, Cormier D, Mathonnet J M et al. Grenoble TestSource (GTS): a Multipurpose Room Temperature ECRIS.Proceedings of the 15th ECRIS Workshop, 2002. 53—558 Hitz D, Delaunay M, Quesnel E et al. All-Permanent MagnetECR Plasma for EUV Light. 3rd International Symposiumon EUV Light, Miyazaki, Japan (2004)9 Hitz D, Cormier D. Device for Controlling the ElectronicTemperature in an ECR Plasma. Patent #WO2005/04629610 Delaunay M, Hitz D. Photon Source Comprising anElectron Cyclotron Resonance Multicharged Ion PlasmaSource. Patent #FR055072411 Hitz D, Delaunay M. Photon Source Comprising an ECRSource with Pressure Gradient, Patent # FR055125612 Hitz D, Delaunay M, Vannuffel C et al. Photon SourceComprising an ECR Source Equipped with Mirrors. Patent# FR0503421