Fundamentals of Focused Ion Beam Nanostructural Processing ...
Chapter 3. Focused Ion Beam Fabrication
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Chapter 3. Focused Ion Beam Fabrication Chapter 3. Focused Ion Beam Fabrication Academic and Research Staff Dr. John Melngailis, Professor Dimitri A. Antoniadis, Professor Carl V. Thompson III, Dr. Patricia G. Blauner, Mark I. Shepard Collaborating Scientists Leonard J. Mahoney, 1 Terry 0. Herndon, 2 Dr. Alan Wagner 3 Graduate Students Andrew D. Dubner, Henry J. Lezec, James E. Murguia, Christian R. Musil, Jaesang Ro, Khalid Ismail Undergraduate Students Yousaf Butt, Susan Zamani 3.1 Focused Ion Beam Program Principal Investigator Dr. John Melngailis Two types of machines are being used for research in focused ion beam applications. The first system has mass separation and can produce beams of the dopants of Si and GaAs with diameters below 0.1 um. This system, 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 not have mass separation, operates with Ga* ions, produces a beam of 0.06 ym diameter at voltages up to 50 kV, and is mainly used for ion induced deposition and milling. Because it is mounted on an ultrahigh vacuum system, reactive materials such as Al or W can be deposited without oxidation. 3.2 Development of Focused Ion Beam Lithography and Patterning Sponsors DAR PA/Naval Electronics Systems Command (Contract MDA 903-85-C-0215) DARPA/U.S. Army Research Office (Contract DAAL03-88-K-0108) Project Staff Henri J. Lezec, Mark I. Shepard, Christian R. Musil, James E. Murguia, Susan Zamani, Dr. John Melngailis To be useful for both implantation and litho- graphy, the mass separated system must be capable of beam writing aligned to existing features and high accuracy placement over a 5 inch area. The ion beam can be electrically deflected over a field 128 ym x 128 jim. Larger distances are covered by interferomet- rically controlled stage motion. Beam deflection calibration routines have been developed, and the stage motion distance 1 MIT Lincoln Laboratory. 2 MIT Lincoln Laboratory. 3 I.B.M. Corporation, Yorktown Heights, New York.
Transcript of Chapter 3. Focused Ion Beam Fabrication
Chapter 3. Focused Ion Beam Fabrication
Chapter 3. Focused Ion Beam Fabrication
Academic and Research Staff
Dr. John Melngailis, Professor Dimitri A. Antoniadis, Professor Carl V. Thompson III, Dr.Patricia G. Blauner, Mark I. Shepard
Collaborating Scientists
Leonard J. Mahoney,1 Terry 0. Herndon,2 Dr. Alan Wagner3
Graduate Students
Andrew D. Dubner, Henry J. Lezec, James E. Murguia, Christian R. Musil, Jaesang Ro, KhalidIsmail
Undergraduate Students
Yousaf Butt, Susan Zamani
3.1 Focused Ion BeamProgram
Principal Investigator
Dr. John Melngailis
Two 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 andPatterning
SponsorsDAR PA/Naval Electronics Systems
Command(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 Melngailis
To 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 distance
1 MIT Lincoln Laboratory.
2 MIT Lincoln Laboratory.
3 I.B.M. Corporation, Yorktown Heights, New York.
Chapter 3. Focused Ion Beam Fabrication
calibration 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 means
of 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 Features
Ion Beam
M //A PMMA/
Figure 1. Focused ion beam lithography and gold electroplating is used to fabricate gold features 50 nm wide and
200 nm high. PMMA is spun over a thin gold plating base. After ion exposure with a beam of 280 KeV Be++ ions
to a dose of about 2.5 x 1013 ions/cm 2, the PMMA is developed, and gold is electroplated up into the submicron
features. The PMMA is then dissolved leaving the structure shown. These structures, which will be used for x-ray
lithography masks, were fabricated in collaboration with W. Chu, A.T. Yen, K. Ismail, Y.C. Ku, J. Carter, and H.I.
Smith.
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,-- Gold
Develop & Plate
S0.3 im
Dissolve PMMA
Chapter 3. Focused Ion Beam Fabrication
3.3 Frequency Tunable GunnDiodes Fabricated by FocusedIon Beam Implantation
Sponsors
DARPA/Naval Electronics SystemsCommand(Contract MDA 903-85-C-0215)
DARPA/U.S. Army Research Office(Contract DAAL03-88-K-01 08)
Project Staff
Henry J. Lezec, Khalid Ismail, Mark I.Shepard, Leonard J. Mahoney, ProfessorDimitri A. Antoniadis, Dr. John Melngailis
Gunn 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 Regions
Sponsors
DARPA/Naval Electronics SystemsCommand(Contract MDA 903-85-C-0215)
DARPA/U.S. Army Research Office(Contract DAAL03-88-K-0108)
Project Staff
James E. Murguia, Christian R. Musil, HenryJ. Lezec, Professor Dimitri A. Antoniadis, Dr.John Melngailis
Preliminary 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 InducedDeposition
Sponsors
U.S. Army Research Office(Contract DAAL03-87-K-0126)
Charles Stark Draper Laboratory
Project Staff
Jaesang Ro, Dr. Patricia G. Blauner, YousafButt, Professor Carl V. Thompson III, Dr.John Melngailis
Material 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 in
Chapter 3. Focused Ion Beam Fabrication
addition 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 SubmicrometerStructures
SponsorsU.S. Army Research Office
(Contract DAAL03-87-K-01 26)Charles Stark Draper Laboratory
Project StaffDr. Patricia G. Blauner, Jaesang Ro, YousafButt, Professor Carl V. Thompson Ill, Dr.John Melngailis
Focused 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 tungsten
have 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 InducedDeposition
Sponsors
International Business MachinesCorporation - Research Division,General Technologies Division
Project Staff
Andrew D. Dubner, Dr. Alan Wagner, Pro-fessor Carl V. Thompson III, Dr. JohnMelngailis
A 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.
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Chapter 3. Focused Ion Beam Fabrication
3.8 Planar Vias through Si3N4and SiO2 Fabricated by FocusedIon Beam Implantation
Sponsors
U.S. Air ForceDARPA
Project StaffDr. John Melngailis, Terry O. Herndon, MarkI. Shepard, Henry J. Lezec
Implantation 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.
Publications
Blauner, P.G., J.S.Thompson, and J. IVstructure of GoldFocused Ion BeamFall 1988 MaterialsProceedings 129 (to
Ro, 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. Ceyer
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