Contains reports on eight research projects.DARPA/Naval Electronics Systems Command (Contract MDA 903-85-C-0215)DARPA/U.S. Army Research Office (Contract DAAL03-88-K-0108)U.S. Army Research Office (Contract DAAL03-87-K-0126)Charles Stark Draper LaboratoryInternational Business Machines Corporation - Research Division, General Technologies DivisionU.S. Air ForceDARP

Antoniadis, Dimitri A.

Blauner, Patricia G.

Butt, Yousaf

Dubner, Andrew D.

Herndon, Terry O.

Ismail, Khalid

Lezec, Henri J.

Mahoney, Leonard J.

Melngailis, John

Murguia, James E.

Musil, Christian R.

Ro, Jaesang

Shepard, Mark I.

Thompson, Carl V., III

Wagner, Alan

Zamani, Susan

DSpace@MIT

Chapter 3. Focused Ion Beam FabricationChapter 3. Focused Ion Beam FabricationAcademic and Research StaffDr. John Melngailis, Professor Dimitri A. Antoniadis, Professor Carl V. Thompson III, Dr.Patricia G. Blauner, Mark I. ShepardCollaborating ScientistsLeonard J. Mahoney,1 Terry 0. Herndon,2 Dr. Alan Wagner3Graduate StudentsAndrew D. Dubner, Henry J. Lezec, James E. Murguia, Christian R. Musil, Jaesang Ro, KhalidIsmailUndergraduate StudentsYousaf Butt, Susan Zamani3.1 Focused Ion BeamProgramPrincipal InvestigatorDr. John MelngailisTwo types of machines are being used forresearch in focused ion beam applications.The first system has mass separation and canproduce beams of the dopants of Si andGaAs with diameters below 0.1 um. Thissystem, used for ion implantation and litho-graphy, operates at voltages up to 150 kV,has sophisticated pattern generation soft-ware, and accepts up to 5 inch substrates.The second, simpler, system, which does nothave mass separation, operates with Ga*ions, produces a beam of 0.06 ym diameterat voltages up to 50 kV, and is mainly usedfor ion induced deposition and milling.Because it is mounted on an ultrahighvacuum system, reactive materials such as Alor W can be deposited without oxidation.3.2 Development of FocusedIon Beam Lithography andPatterningSponsorsDAR PA/Naval Electronics SystemsCommand(Contract MDA 903-85-C-0215)DARPA/U.S. Army Research Office(Contract DAAL03-88-K-0108)Project StaffHenri J. Lezec, Mark I. Shepard, Christian R.Musil, James E. Murguia, Susan Zamani, Dr.John MelngailisTo be useful for both implantation and litho-graphy, the mass separated system must becapable of beam writing aligned to existingfeatures and high accuracy placement over a5 inch area. The ion beam can be electricallydeflected over a field 128 ym x 128 jim.Larger distances are covered by interferomet-rically controlled stage motion. Beamdeflection calibration routines have beendeveloped, and the stage motion distance1 MIT Lincoln Laboratory.2 MIT Lincoln Laboratory.3 I.B.M. Corporation, Yorktown Heights, New York.Chapter 3. Focused Ion Beam Fabricationcalibration and axis non-orthogonality hasbeen corrected using wafers with known,accurate patterns. Alignment to existing fea-tures on a wafer is carried out by imaging thefeatures in the scanning ion microscopemode and by accurately locating the featuresin the center of the deflection field by meansof stage displacement. Using Be++ ions of260 keV energy, 60 nm wide lines have beenexposed in PMMA 300 nm thick. Afterdevelopment, these lines, which have nearlyvertical sidewalls, have proven to be usefulfor the fabrication of ultrafine feature x-raylithography masks. See figure 1.Focused Ion Beam Lithography:Focused Ion Beam Lithography:Electroplated FeaturesIon BeamM //A P MA/Figure 1. Focused ion beam lithography and gold electroplating is used to fabricate gold features 50 nm wide and200 nm high. PMMA is spun over a thin gold plating base. After ion exposure with a beam of 280 KeV Be++ ionsto a dose of about 2.5 x 1013 ions/cm2, the PMMA is developed, and gold is electroplated up into the submicronfeatures. The PMMA is then dissolved leaving the structure shown. These structures, which will be used for x-raylithography masks, were fabricated in collaboration with W. Chu, A.T. Yen, K. Ismail, Y.C. Ku, J. Carter, and H.I.Smith.30 RLE Progress Report Number 131,-- GoldDevelop & PlateS0.3 imDissolve PMMAChapter 3. Focused Ion Beam Fabrication3.3 Frequency Tunable GunnDiodes Fabricated by FocusedIon Beam ImplantationSponsorsDARPA/Naval Electronics SystemsCommand(Contract MDA 903-85-C-0215)DARPA/U.S. Army Research Office(Contract DAAL03-88-K-01 08)Project StaffHenry J. Lezec, Khalid Ismail, Mark I.Shepard, Leonard J. Mahoney, ProfessorDimitri A. Antoniadis, Dr. John MelngailisGunn diodes have been fabricated byimplanting a gradient of doping along thesurface between the two contacts. Whenbias is applied, the electric field in the con-duction region varies as a function of dis-tance, and the distance that a Gunn domaincan travel is a function of bias. Thus theoscillation frequency can be tuned with bias.We have shown tunability from 6 to 23 GHzas the bias was changed by 12 volts. AGunn diode with uniform doping shows verylittle change in frequency as the bias isvaried. The device has been modelled todetermine the optimum lateral doping gra-dient profile which would yield the largestfrequency variation. These tunable Gunndiodes may prove to be useful in a number ofapplications including in collision avoidanceradar.3.4 Field-Effect Transistorswith Focused Ion BeamImplanted Channel RegionsSponsorsDARPA/Naval Electronics SystemsCommand(Contract MDA 903-85-C-0215)DARPA/U.S. Army Research Office(Contract DAAL03-88-K-0108)Project StaffJames E. Murguia, Christian R. Musil, HenryJ. Lezec, Professor Dimitri A. Antoniadis, Dr.John MelngailisPreliminary experiments in which GaAsMESFETs were focused-ion-beam implantedwith a lateral gradient of doping between thesource and drain showed asymmetrical char-acteristics with some marginal improvementsin performance in one direction compared touniformly doped control devices. Thesedevices had 1 ym gate lengths. Theimprovements are likely to be more signif-icant if the gate length is in thesubmicrometer regime. Since, as describedin 3.1, " Focused Ion Beam Program" onpage 29, our machine is now capable ofwriting with higher accuracy, we can fabri-cate submicron devices. In silicon, wafershave been prepared by conventional fabri-cation up to the point of channel implant.These implants will be carried out with thefocused ion beam with boron or arsenic ions.3.5 Microstructure andProperties of Gold FilmsProduced by Ion InducedDepositionSponsorsU.S. Army Research Office(Contract DAAL03-87-K-0126)Charles Stark Draper LaboratoryProject StaffJaesang Ro, Dr. Patricia G. Blauner, YousafButt, Professor Carl V. Thompson III, Dr.John MelngailisMaterial deposition can be produced byusing incident ions to break up adsorbed gasmolecules. If the gas is dimethyl goldhexafluoro acetylacetonate (C7 H7F60 2Au),gold is deposited. This form of deposition,when carried out with a focused ion beam, isuseful in repairing clear defects in photo andx-ray lithography masks and integrated cir-cuits. Using transmission electron micros-copy, we have examined the films grown bythis process. In the case of Ar ions from abroad beam generated by an ion implanterand Ga ions from a scanned focused ionbeam, the films grown at room temperatureconsist of isolated hemispherical islands of60-100 nm diameter. Auger analysis showsthe films to contain 30-50 percent carbon inChapter 3. Focused Ion Beam Fabricationaddition to the gold. Deposition at temper-atures above 100 degrees C yields films withless than 10 percent carbon and a connectedpolycrystalline structure. The resistivity ofthese films is near the bulk value for goldwhile the films deposited at room temper-ature have resistivities 200 to 500 timeshigher. The microstructure also depends onthe growth rate that is determined by localgas pressure and the ion current density.3.6 Focused Ion Beam InducedDepostion of SubmicrometerStructuresSponsorsU.S. Army Research Office(Contract DAAL03-87-K-01 26)Charles Stark Draper LaboratoryProject StaffDr. Patricia G. Blauner, Jaesang Ro, YousafButt, Professor Carl V. Thompson Ill, Dr.John MelngailisFocused ion beam induced deposition isbeing used for repairing clear defects incommercial photolithography masks. Thistechnique is expected to be used as well forrepairing x-ray lithography masks and alsofor repairing and local restructuring of inte-grated circuits. Using a scanned beam of 60nm diameter and a local gas ambient of(C7H7F60 2Au), lines of 0.1 pm width havebeen written. In addition, patches 3 x 3 pm,1 pm thick with steep side walls have beenproduced. Typical deposition times are20-100 sec. per 1 pm 3, depending on beamdiameter. Some of these features have beendeposited on actual x-ray lithography masksand replicated in resist at the FraunhoferInstitute in Berlin. The lines have beendeposited across metal contact fingers andthe resistivity has been measured as 500 to1000 p~)cm (bulk gold measures 2.5 p~ cm).Even at these values, however, local conduc-tors can be fabricated for integrated circuitrepair. We have installed a heated stagewhich is expected to permit deposition oflower resistivity films. Films of tungstenhave also been deposited from a gas of WF 6,and films of Al from organometallic gaseswill also be tried. In the past, films of thesereactive metals have proven to be highlyoxidized. Since our system is ultrahighvacuum, we expect to avoid this oxidation.3.7 In-Situ Measurement ofGas Adsorption and Ion InducedDepositionSponsorsInternational Business MachinesCorporation - Research Division,General Technologies DivisionProject StaffAndrew D. Dubner, Dr. Alan Wagner, Pro-fessor Carl V. Thompson III, Dr. JohnMelngailisA quartz crystal microbalance was mountedin a vacuum system where both a flux of gasand a flux of 0.1 to 10 keV ions can be inci-dent. The mass of films adsorbed or depos-ited on the quartz is measured by noting thechange in resonant frequency of the crystal.The number of molecules of dimethyl goldhexafluoro acetylacetonate (CH 7 F206Au)adsorbed as a function of pressure wasmeasured. The number of moleculesadsorbed was found to rise rapidly at lowpressure (below 1 mtorr), corresponding toapproximately a monolayer, to level off, andthen to begin to rise again approaching thevapor pressure of the compound (400 mtorrat room temperature). A flux of ions wasintroduced, and the deposition rate of goldfilm was measured. The yield of atomsdeposited per ion was found to increase withincreasing gas pressure and with decreasingtemperature. The cross section for decom-position was found to be 2 x 10- 13cm 2 for 5keV Ar+ ions. The deposition is a competi-tion between sputtering and gas moleculedecomposition. The sputtering rate wasmeasured simply by observing the film thick-ness decrease when the ion beam was kepton while the gas supply was turned off.32 RLE Progress Report Number 131Chapter 3. Focused Ion Beam Fabrication3.8 Planar Vias through Si3N4and SiO2 Fabricated by FocusedIon Beam ImplantationSponsorsU.S. Air ForceDARPAProject StaffDr. John Melngailis, Terry O. Herndon, MarkI. Shepard, Henry J. LezecImplantation of Si3N4 and SiO 2 at dosesabove 1017cm -2 has been shown (at LincolnLaboratory) to render the insulators con-ducting in some cases. This has been pro-posed as a means of making planar vias. Wehave used a focused ion beam to make theselevel-to-level interconnects in Si3N4, thusavoiding the need for resist or mask.Implants were carried out at a single energy,160 keV, using Si- ions, or at two energies,80 keV and 160 keV, using Si+ andSi " ions,respectively. Films of 0.25 y-thick Si3N4over Al metal were implanted. Then theupper layer was deposited, patterned, and thestructure was sintered at 425 degrees C for30 minutes. The dose threshold for con-duction was between 2 x 1017 and 5 x1017 cm - 2, and depended on whether the 160keV only or the two-energy implants werecarried out. Interconnects formed in areas1.6 x 1.6 .y had resistance as low as 0.15 Q,while the minimum dimension implants,made with an unscanned beam in 6 to 12 s,has resistances of 1.5 to 5 Q. Experimentsare planned for the implantation of SiO 2 withBe ions. Even with the present state of tech-nology, focused ion beam implantationappears to be a promising technique formaking level-to-level interconnects throughinsulators in limited, critical areas of devices.PublicationsBlauner, P.G., J.S.Thompson, and J. IVstructure of GoldFocused Ion BeamFall 1988 MaterialsProceedings 129 (toRo, Y. Butt, C.V.lelngailis, "The Micro-Films Written byInduced Deposition,"Research Symposiumbe published).Lezec, H.J., K. Ismail, L.J. Mahoney, M.I.Shepard, D.A. Antoniadis and J.Melngailis, "Tunable-Frequency GunnDiode Fabricated by Focused Ion BeamImplantation," IEEE Electron Device Lett.9:476 (1988).Melngailis, J., "Focused Ion Beam Microfab-rication," SPIE Conference on Electron-beam X-Ray and Ion Beam Technologies:Submicrometer Lithographies VII, 923:72(1988).Melngailis, J., A.D. Dubner, J.S. Ro, G.M.Shedd, H.J. Lezec, and C.V. Thompson,"Focused Ion Beam Induced Deposition,"In Emerging Technologies for In-Situ Pro-cessing, eds. B.J. Ehrlich and V.T.Nguyen, 153. Martinus Nijhoff, 1988.Melngailis, J., T.O. Herndon, M. Shepard,and H.J. Lezec, "Planar Vias ThroughSi3N4 Fabricated by Focused Ion BeamImplantation," J. Vac. Sci. Technol.B6:1022 (1988).Ro, J.S., A.D. Dubner, C.V. Thompson, andJ. Melngailis, "Ion Induced Deposition ofGold Films." J. Vac. Sci. Technol.B6:1043 (1988).Ro, J.S., A.D. Dubner, C.V. Thompson, andJ. Melngailis, "Microstructure of GoldFilms Grown by Ion Induced Deposition,"Materials Research Symposium Pro-ceedings, 101:255 (1988).Professor Sylvia T. Ceyer34 RLE Progress Report Number 131

Focused Ion Beam Fabrication

http://dspace.mit.edu/bitstream/1721.1/57076/1/RLE_PR_131_01_01s_03.pdf

Focused Ion Beam Fabrication

Abstract

Similar works

Full text

Available Versions

DSpace@MIT