Contains reports on ten research projects.U.S. Army Research Office Contract DAAL03-88-K-0108Hughes Research Laboratories FellowshipSEMATECHCharles S. Draper Laboratory Contract DL-H-261827U.S. Army Research Office Contract DAAL03-87-K-0126IBM General Technologies DivisionIBM Research Divisio

Blauner, Patricia G.

Butt, Yousaf

Dubner, Andrew D.

Huh, Jeung-Soo

Ismail, Khalid

Kaesz, Herbert D.

Lezec, Henri J.

Mahoney, Leonard J.

Melngailis, John

Murguia, James E.

Musil, Christian R.

Ro, Jaesang

Shepard, Mark I.

Swain, Herbert H.

Tao, Tao

Thompson, Carl V.

Wagner, Alfred

Xue, Ziling

Zamani, Susan

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Chapter 3. Focused Ion Beam FabricationChapter 3. Focused Ion Beam FabricationAcademic and Research StaffDr. John Melngailis, Dr. Patricia G. Blauner, Dr. Tao Tao, Mark I. ShepardVisiting Scientists and Research AffiliatesDr. Khalid Ismail,' Professor Herbert D. Kaesz,Ziling Xue2Graduate StudentsAndrew D. Dubner, Jeung-Soo Huh,Jaesang RoUndergraduate StudentsYousaf Butt, Susan ZamaniTechnical and Support StaffDonna Martinez3.1 Focused Ion BeamFabricationResearch in focused ion beam applications isbeing conducted on two types of machines.The first system has mass separation and canproduce beams of the dopants of Si andGaAs with diameters below 0.1 ym. Thissystem, which is used for ion implantationand lithography, operates at voltages up to150 kV, has sophisticated pattern generationsoftware, and can accept up to five inchsubstrates. The second, simpler system hasno mass separation and is operated with Gaions at energies up to 50 keV and minimumbeam diameters of 0.06 pm. It is mountedon an ultrahigh vacuum system and has asample stage which can be heated. Thissystem is mainly used for ion induced depo-sition and milling.,2 Leonard J. Mahoney,3 Dr. Alfred Wagner,'Henri J. Lezec, James E. Murguia, Christian R. Musil,3.2 Development of FocusedIon Beam Implantation andLithographySponsorU.S. Army Research OfficeContract DAAL03-88-K-0108Project StaffJames E. Murguia, Mark I. Shepard, Christian R.Musil, Henri J. Lezec, Susan Zamani, Dr. JohnMelngailisTo apply ion beam implantation and litho-graphy to integrated circuit fabrication, onemust align the pattern to be written toexisting features on the wafer. One mustalso generate this pattern from computeraided design. Accordingly, we have devel-oped and refined the capability to transferthe patterns of any given level of an inte-grated circuit layout from the computer-aideddesign software in use at MIT, called1 IBM Research Division, Yorktown Heights, New York.2 University of California, Los Angeles.3 MIT Lincoln Laboratory.Chapter 3. Focused Ion Beam FabricationMAGIC, to the focused ion beam system.Different ion doses or dose gradients can beassigned to each rectangle of the design.This permits a wafer to be processed to agiven step in the standard integrated circuitsfacility, transferred to the focused ion beamfor implantation or for ultrafine lithography,and then transferred back to complete thefabrication.Alignment is carried out by imaging align-ment marks on the wafer using the scanningion microscope mode. In addition, beamdeflection routines have been developedwhich calibrate beam deflection, stagemotion, and correct for axis non-orthogonality. We have placed features on awafer aligned to + 0.1 pm. The overall capa-bility that we have developed is essential toour implantation and lithography projects.3.3 Frequency Tunable GunnDiodes Fabricated by FocusedIon Beam ImplantationSponsorU.S. Army Research OfficeContract DAAL03-88-K-0108Project StaffHenri J. Lezec, Dr. Khalid Ismail, Mark I. Shepard,Leonard J. Mahoney, Professor Dimitri A.Antoniadis, Dr. John MeingailisWe have developed frequency tunable Gunndiodes which consist of two contacts on aGaAs surface. A conducting channel, whichhas a gradient of doping in the direction ofcurrent flow, runs between the two contacts.The frequency can be tuned from 6 to 23GHz by varying the bias voltage by about 12V. The power output of the devices is in the-3 to -4 dBm range. A Gunn diode withuniform doping shows very little variation offrequency with bias. Many gradients ofdoping were implanted by programming thefocused ion beam system appropriately. Inaddition, measurements were made of thepercent of activation as a function ofimplanted dose. Since this percentagedecreases with increasing dose, a linear gra-dient of dose does not imply a linear gradientof doping or of resistivity. The devices havebeen modeled using a computer programbased on the Bolzmann transport equation.The tunable Gunn diodes may prove usefulfor special radars such as those used in colli-sion avoidance.3.4 NMOS Transistors withFocused Ion Beam ImplantedChannel RegionsSponsorU.S. Army Research OfficeContract DAAL03-88-K-0108Project StaffJames E. Murguia, Mark I. Shepard, Christian R.Musil, Professor Dimitri A. Antoniadis, Dr. JohnMelngailisNMOS transistors with gate lengths from 1.6pm to 10 pm were fabricated in the inte-grated circuits facility. Focused ion beamimplantation was substituted for the thres-hold and punch-through control implants.Both boron and arsenic were implanted andboth the geometry of the implant and thedose were varied. A total of 1,920 combina-tions of variables were fabricated in duplicateon the wafer. Four wafers were processed toverify reproductibility. NMOS transistorswith a line implant (0.1 to 0.2 pm wide)adjacent to the source were compared todevices with no implant. A small increase intransconductance and a large increase inoutput conductance were observed. Thisresulted in a factor of twenty increase inopen circuit gain. This result demonstratesthe use of the focused ion beam to econom-ically explore novel device concepts over awide range of variables.30 RLE Progress Report Number 132Chapter 3. Focused Ion Beam Fabrication3.5 GaAs MESFETs Fabricatedwith Focused Ion BeamChannel ImplantsSponsorsHughes Research Laboratories FellowshipU.S. Army Research OfficeContract DAAL03-88-K-01 08Project StaffChristian R. Musil, Leonard J. Mahoney, Mark I.Shepard, Dr. John MelngailisWe expect GaAs MESFETs with a gradient ofdoping from source to drain to showimproved performance. This is of particularinterest for short gates. We have designedand fabricated a mask set to explore a widevariety of transistor structures. The contactsand longer gates will be fabricated by con-ventional optical lithography using thesemasks. Ultra short gates (below 0.1 jm) willbe fabricated using the focused ion beam toexpose the resist. The penetration of ionsinto the substrate during the resist exposureis an undesirable side effect. A technique toovercome this has been developed and testedusing a film of Si3N4 on the GaAs substrateunder the resist. The film prevents ion pene-tration and damage, yet can be etched toapply the contact.3.6 Focused Ion BeamExposure of ResistsSponsorSEMATECHProject StaffJeung-Soo Huh, James E. Murguia, ProfessorHerbert H. Sawin, Dr. John MelngailisThe goal of this program is to generateknown resist profiles for the purpose ofstudying their effect on plasma etched fea-tures. Optical lithography can be used downto about 1 jm. Below that, focused ionbeam lithography will be used. So far, wehave exposed features down to 0.05 jm inPMMA in 0.3 jm thick resist with verticalsidewalls. These were made into x-ray litho-graphy masks in collaboration with the MITSubmicron Structures Laboratory. We areseeking other focused ion beam resistsbesides PMMA. We have used Shipley SAL601 negative resist to also expose featuresdown to 0.1 ym. However, this is less desir-able since profile control in negative resists isdifficult. Microport 2400 which is a positivee-beam resist was also tried but was foundto have a small exposure window, i.e., lessthan a factor of two between threshold expo-sure and cross linking. Other candidates arebeing considered. The profile developmentwill be modelled using TRIM programs forion penetration and SAMPLE for resistdisolution.3.7 Focused Ion Beam InducedDeposition of Low ResistivityGold StructuresSponsorsCharles S. Draper LaboratoryContract DL-H-261827U.S. Army Research OfficeContract DAAL03-87-K-0126Project StaffDr. Patricia G. Blauner, Jaesang Ro, Yousaf Butt,Professor Carl V. Thompson, Dr. John MelngailisA local gas ambient is created in vacuum ona sample surface by aiming a gas feedcapillary tube at the surface in close prox-imity. For gold depositions we use a gas ofC7 H7F6O2Au. Deposition occurs when afocused ion beam is scanned on the surfacein the area of the gas ambient. Ion induceddeposition permits fabrication of depositedfeatures at dimensions much finer than thoseachieved by laser induced deposition. Ioninduced deposition is already in commercialuse for repair of photolithography masks. Ifconducting films can be deposited, thisprocess will be used for local repair andrestructuring of integrated circuits. Also, ifhigh aspect ratio structures (thick with steepside walls) can be deposited, the repair ofx-ray lithography mask will become possible.We have deposited gold lines down to 0.1ym width and patches 3 x 3 jm of 1 imthickness with steep side walls. The micro-structure of the gold films has been studiedby transmission electron microscopy. TheChapter 3. Focused Ion Beam Fabricationfilms grow in discontinuous, ball-like struc-tures at the early stages and in columns asthey thicken. Some features have beendeposited on actual x-ray lithography masksand tested at the Fraunhofer Institute inBerlin. In spite of the structure, the x-rayopacity of films 0.8 ym thick was found to besufficient for normal mask exposure.When the substrate is heated to about120'C, the structure of the deposited films isobserved to change. In addition, theresistivity is found to drop from a value of~ 1000 U~cm to a value below 10 /cm,i.e., near the bulk value for gold of 2.4 IQacm.This is the first deposition of low resistivitymetal film by this process. Low resistivity isneeded for application of focused ion beaminduced deposition to integrated circuitrestructuring and repair.3.8 Fundamental Properties ofIon Induced DepositionSponsorsCharles S. Draper LaboratoryContract DL-H-261827U.S. Army Research OfficeContract DAAL03-87-K-0126Project StaffJaesang Ro, Professor Carl V. Thompson, Dr. JohnMelngailisThe ion induced deposition of gold fromdimenthylgold hexafluoro acetylacetonatehas been studied using noble gas ions froman implanter. Although the instantaneouscurrent density in a focused ion beam isabout five orders of magnitude higher thanthat from a broad implanter beam, the funda-mental principles of the process are the same.In the case of a focused ion beam, the beamis usually scanned rapidly over a given areaso that the average current density is morenearly comparable. In going from Ne to Xe,the yield (atoms deposited/incident ion) isfound to increase. The yield correlates betterwith nuclear stopping power than with elec-tronic stopping power. In addition, the sput-tering yield for each ion species wasmeasured.The mechanism by which the ion transfersenergy to a molecule adsorbed on the surfaceis not clear. It is not direct ion-moleculeimpact because the cross section is too large.The substrate must participate. We areattempting to model the process using theTRIM program to calculate the energy dis-tribution of surface atoms as a function ofdistance from the point of ion impact. Theyield measurements are being carried out atroom temperature, where the films are knownto contain carbon, as well as at 120'C(where the films are much purer and theirresistivities are nearly equal to the bulk goldvalues).3.9 In-Situ Measurement ofGas Adsorption and Ion InducedDepositionSponsorsIBM General Technologies DivisionIBM Research DivisionProject StaffAndrew D. Dubner, Dr. Alfred Wagner, ProfessorCarl V. Thompson, Dr. John MelngailisWe have constructed a special apparatus tomeasure gas adsorption and ion induceddeposition. The apparatus consists of anultrahigh vacuum chamber with an ion gunhaving energies from 0.1 to 10 keV. Thesample is a quartz crystal microbalancewhich can measure the gas adsorption aswell as the film growth during ion induceddeposition. The gas used is dimethylgoldhexafluro acetylacetonate (C,7HF 60 2Au) anda monolayer is found to be adsorbed above 1mTorr pressure. If the sample is cooledbelow room temperature and the gas pres-sure is raised above 100 mTorr, then a thickerlayer of adsorbate is formed. The yield ofatoms deposited per incident ion can berapidly measured. The cross section fordecomposition was found to be 2 x 10- 13 cm 2for 5 keV Ar* ions. The deposition is a com-petition between sputtering and gas mole-cule decomposition. Contrary to ourobservations of ion induced deposition withhigh energy beams (30-100 keV) at theselower energies, relatively pure gold films canbe deposited even at room temperature.32 RLE Progress Report Number 132Chapter 3. Focused Ion Beam Fabrication3.10 Focused Ion Beam InducedDeposition of PlatinumSponsorsCharles S. Draper LaboratoryContract DL-H-261827U.S. Army Research OfficeContract DAAL03-87-K-0126Project StaffDr. Tao Tao, Ziling Xue, Professor Herbert D.Kaesz, Dr. John MelngailisFocused ion beam induced deposition ofplatinum from a precursor gas of(Methylcyclopentadienyl) - Platinumtrimetylhas been demonstrated. This organometallicis solid at room temperature with a vaporpressure of 0.06 Torr. A Ga ion beam at 35keV has been used. The resistivity and com-position of the film and the deposition yieldhave been studied as a function of ioncurrent density, line dose, substrate temper-ature, geometry, and supplementaryhydrogen pressure. Yield varied from 0.2 to30, and resistivity varied from 70 to700 ,Qucm depending on the conditions. Thelowest resistivity was observed at the highestcurrent density: 0.22 nA at 500 cm/sec scanspeed repeated over a 350 ym long line. Theminimum linewidth observed so far is 0.3 m,and the deposited platinum is found to besmooth. Auger analysis showed the films tocontain carbon. The addition of hydrogengas supplied to the same area by a secondnozzle was found to have little effect on yieldor resistivity. Although the deposition ofgold from an organometallic precursor on aheated substrate results in low resistivityfilms, in the case of platinum this is notobserved; in fact deposition yield drops tozero as the temperature is raised.Deposition was also carried out in a focusedion beam milled groove 0.65 ym deep. Theyield was found to be 34 at the bottom ofthe groove and decreased as the groove wasfilled in.Focused ion beams induced deposition ofplatinum is of interest for circuit restructuringand repair because (1) the films have thelowest resistivity reported so far for deposi-tion at room temperature and (2) platinum,unlike gold, is compatible with silicon devicefabrication. Platinum deposition is alsoexpected to be useful for x-ray lithographymask repair because the x-ray absorption ofplatinum is slightly higher than that of goldor tungsten.PublicationsBlauner, P.G., J.S. Ro, Y. Butt, C.V.Thompson, and J. Meingailis. "TheMicrostructure of Gold Films Written byFocused Ion Beam Induced Deposition."Mat. Res. Soc. Symp. Proc. 129 (1989).Blauner, P.G., J.S. Ro, Y. Butt, and J.Melngailis. "Focused Ion Beam Fabri-cation of Submicron Gold Structures." J.Vac. Sci. Technol. B 7: 609 (1989).Blauner, P.G., Y. Butt, J.S. Ro, C.V.Thompson, and J. Melngailis. "FocusedIon Beam Induced Deposition of LowResistivity Gold Films." J. Vac. Sci.Technol. B 7: 1816 (1989).Chu, W., A. Yen, K. Ismail, M.I. Shepard,H.J. Lezec, C.R. Musil, J. Melngailis, Y.C.Ku, J.M. Carter, and H.I. Smith."Sub-100 nm X-Ray Mask TechnologyUsing Focused-Ion-Beam Lithography." J.Vac. Sci. Technol. B 7: 1583 (1989).Dubner, A.D., and A. Wagner. "In-SituMeasurement of Ion Beam Induced Depo-sition of Gold." Mat. Res. Soc. Symp.Proc. 147: 155 (1989).Dubner, A.D., and A. Wagner. "In-SituMeasurement of Ion Beam Induced Depo-sition of Gold." J. Appl. Phys. 65(9):3636 (1989).Dubner, A.D., and A. Wagner. "The Role ofGas Adsorption in Ion-Beam-InducedDeposition of Gold." J. Appl. Phys.66(2): 870 (1989).Dubner, A.D., and A. Wagner. "Mechanismof Ion Beam Deposition of Gold." J. Vac.Sci. Technol. B7: 1950 (1989).Ismail, K., W. Chu, R.T. Tiberio, A. Yen, H.J.Lezec, M.I. Shepard, C.R. Musil, J.Melngailis, D.A. Antoniadis, and H.I.Smith. "Resonant Tunneling Across andChapter 3. Focused Ion Beam FabricationMobility Modulation Along Surface-Structured Quantum Wells." J. Vac. Sci.Technol. B 7: 2025 (1989).Melngailis, J. "Focused Ion Beam Litho-graphy and Implantation." Proceedings of8th Biennial University/-Government/Industry MicroelectronicsSymposium. June 1989.Melngailis, J. and P.G. Blauner. "FocusedIon Beam Induced Deposition." Mat. Res.Soc. Symp. Proc. 147 (1989) (Pro-ceedings of Spring Meeting San Diego,Symposium on Ion Beam Processing ofAdvanced Electronic Materials, April1989).34 RLE Progress Report Number 132

Focused Ion Beam Fabrication

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