Contains reports on five research projects.DARPA/Naval Electronic Systems Command (Contract MDA-903-85-C-0215)Charles Stark Draper Laboratory (Contract DL-H-261827)U.S. Navy - Office of Naval Research (Contract N00014-84-K-0073)Nippon Telephone and TelegraphHitachi Central Research Laborator

Antoniadis, Dimitri A.

Barrett, J. L.

Dubner, Andrew D.

Jacobs, Jarvis B.

Lezec, Henri J.

Lowther, Rex E.

Mahoney, Leonard J.

Melngailis, John

Musil, Christian R.

Shedd, Gordon M.

Thompson, Carl V.

Thompson, W. B.

DSpace@MIT

Focused Ion Beam Fabrication3.0 Focused Ion Beam FabricationAcademic and Research StaffProf. D.A. Antoniadis, Dr. J. Melngailis, Prof. C.V. ThompsonCollaborating ScientistsL. Mahoney', R.E. Lowther2 , J.L. Bartlett 3, W.B. Thompson4Graduate StudentsA.D. Dubner, J.B. Jacobs, H. Lezec, C.R. Musil, G.M. Shedd, J. Ro3.1 Focused Ion Beam ProgramJohn MelngailisA focused ion beam system capable of mass separation and accurate submicronbeam writing on a wafer has been purchased from Ion Beam Systems Inc. as part of theMicrosystems Technology Program. So far the system has demonstrated 150kV oper-ation. It has exposed dots in PMMA of 0.1 am diameter and operated with the followingion species: Ga, Au, Si, Pd, B, As. The system will be delivered to M.I.T. in March 1987and is scheduled to be in operation in May 1987. We had access to the machine andhave carried out precision patterned doping of GaAs and Si.In addition we have purchased a 50kV non-mass separated column which has abeam diameter of 0.05 pm. This system is intended for ion milling and ion induceddeposition and etching. A DOD/University Instrumentation Grant has been received forthe construction of an ultrahigh vacuum chamber to be used with this column. In themeantime the system will be used with an ordinary vacuum chamber.3.2 Fabrication of Graded Channel FETs in GaAs and SiDARPA/Naval Electronic Systems Command (Contract MDA -903-85-C-0215)Henri Lezec, Leonard Mahoney,' Jarvis B. Jacobs, Rex E. Lowther, Christian R. Musil,Dimitri A. Antoniadis, and John Melngailis1 Lincoln Laboratory2 Visiting Scientist from Harris Semiconductor3 Hughes Research Laboratory4 IBS, Beverly, Mass.5 Lincoln LaboratoryFocused Ion Beam FabricationThe goals of this program are to use the focused ion beam system to fabricated fieldeffect transistors in GaAs and in Si with graded doping profiles and to model the be-havior of these novel device structures. Graded doping profiles, where the implanteddensity varies linearly from source to drain, have been successfully implanted in GaAs.These implants were aligned to existing features, and, in addition, alignment marks wereion milled into the surface to align the gate electrodes with the ion implants. Prelimi-nary results show an increase in transconductance in the graded devices as well asflatter ID vs. VD curves in the saturation region. Computer simulation of these structuresare being carried out. In silicon, we have used a Pd/B/As liquid metal ion source toimplant test structures. A mask has been designed for transistors which will have thechannel region implanted by focused ion beams. In silicon, device models have beendeveloped which include graded doping and the dependence of the mobility on thedistance from the surface.3.3 Ion Induced DepositionCharles Stark Draper Laboratory (Contract DL-H-261827)U.S. Navy - Office of Naval Research (Contract N00014-84-K-0073)Nippon Telephone and TelegraphGordon M. Shedd, Andrew D. Dubner, Henri Lezec, Carl V. Thompson, John MelngailisA focused ion beam can be used to induce material deposition with submicron re-solution if a local gas ambient is produced at the point of ion impact. The local gasambient is produced by aiming a miniature gas nozzle at the surface in close proximity.We have, used WF6 and deposited tungsten. However, because the deposition wascarried out in a background vacuum of 10-6 to 10- 7 torr, the film contains from 5 to 30%oxygen. We are building an ultrahigh vacuum chamber to eliminate the oxygen. In themeantime by choosing a less reactive material we have deposited gold from a gas ofdimethyl gold hexafluoro acetylacetonate. The ions used were either 15kV Ga+ from a0.5 m diameter focused beam, unfocused 70 keV Si+ ions from an implanter, or 0.75keV Ar+ from an ion miller. Deposition occurred in all cases with yields of between 5to 16 atoms deposited/incident ion. Except for the expected Ga other contaminantssuch as C or O are at levels below 5%. The resistivity of the film was measured to varybetween 20 and 500 /p2cm (bulk gold is 2.5 p.Qcm) depending on the depositionconditions. This is comparable to or better than polysilicon which is used as an ICinterconnect material. With the focused ion beam lines of 0.5 Pm width (equal to thebeam diameter) were deposited. Thus this is a promising technique for integrated cir-cuit rewiring, repair, or prototyping, and for repair of x-ray lithography masks.3.4 Focused Ion Beam Microsurgery for ElectronicsCharles Stark Draper Laboratory (Contract DL-H-261827)C.R. Musil, J.L. Barrett, 6 and John Melngailis6 Hughes Research Laboratory22 R.L.E. P.R. No. 129Focused Ion Beam FabricationThe modification of selected areas of an integrated circuit to alter its electrical func-tion has many potential applications. The simplest such application is the breaking ormaking of electrical connnections, which can lead to circuit diagnostics and debugging,to customization, and to defect avoidance. At present lasers are used in large integratedcircuit memories to cut conductors and excise faulty circuit elements and wire in re-dundant spares. However, lasers typically blast away the conductors leaving craters5-10 pm in diameter. The focused ion beam can perform such cutting in a much morecontrolled fashion with submicron resolution.We have demonstrated the cutting of conductors and also developed methods forelectrically connecting two overlapping conductors initially separated by oxide. Thecost of the increased resolution is the time taken to cut conductors. This can extendto minutes if a fine beam is simply scanned over an area to mill an opening in the con-ductor. To make connections we have developed a method which consists of millingtwo concentric square sided pits through a conductor-insulator-conductor sandwich.Deliberate redeposition on vertical sidewalls makes an electrical connection. The pitsranged in size from 3x3 ym to 0.5 x 0.5 pm. For the smallest pits a 4 to 8 Q connectioncan be made in 7 seconds. In addition, in many cases the breaking or making of con-nections can be verified by using the focused ion beam in the scanning ion microscopemode. Depending on the electrical connections parts of a circuit will charge up to dif-ferent voltages limiting the secondary electron emission and showing up on the screenwith different contrast. As circuit dimensions shrink and their complexity grows focusedion beam circuit restructuring, because of the increased control and precision, will be-come an increasingly useful technique.3.5 Measurement of Beam ProfileHitachi Central Research LaboratoryJohn Melngailis and W.B. Thompson7The focused ion beam profile is expected to be Gaussian. We have measured theprofile over five orders of magnitude in intensity and found that from about two ordersof magnitude below the peak, the profile has shoulders which make the beam broader.We also plan to investigate the relation between resolution in the imaging mode andbeam diameter, and the relation between beam diameter and the resolution of thedopant pattern implanted.PublicationsLowther, R.E., J.B. Jacobs, and D.A. Antoniadis, "Simulation of Implantation and Dif-fusion of Profiles Made with a Focused Ion-Beam Implanter," I.E.E.E. Trans.Electron Dev., ED-33, 1251 (1986).Melngailis, J., D.J. Ehrlich, S.W. Pang, J.N. Randal, "Cermet as an Inorganic Resist forIon Lithography," J. Vac. Sci. Tech. B 5, 379 (1987).7 IBS, Beverly, Mass.Focused Ion Beam FabricationMelngailis, J., "Focused Ion Beam Technology and Applications," a review, J. Vac. Sci.Tech., 469 (1987).Melngailis, J., G.J. Dunn, and W.B. Thompson, "Focused Ion Beam Induced Deposi-tion," Techical Proceedings of SEMICON/EAST 1986, Boston, Mass., 1986, pp.53-61.Melngailis, J., C.R. Musil, E.H. Stevens, M. Utlaut, E.M. Kellogg, R.J. Post, M. Geis,and R.W. Mountain, "The Focused Ion Beam as an Integrated Circuit RestructuringTool," J. Vac. Sci. Tech. B4, 176 (1986).Melngailis, J., "Focused-Ion-Beam Technology," I.E.E.E. Electrotech. Rev. (1986), p.58.Musil, C.R., J.L. Bartlett, and J. Melngailis, "Focused-lIon-BeamElectronics," I.E.E.E. Electron Devices Lett., EDL-7, 285 (1986).Microsurgery forMusil, C.R., J.L. Bartlett, and J. Melngailis, "Focused Ion Beam Microsurgery for Inte-grated Circuit Customization and Repair," Proceedings of the I.E.E.E. 1986 CustomIntegrated Circuits Conference, p. 591.Shedd, G.M., H. Lezec, A.D. Dubner, and J. Melngailis, "Focused Ion Beam InducedDeposition of Gold," Appl. Phys. Lett. 49, 1584 (1986).ThesisShedd, G.M., "Ion Assisted Deposition of Gold," M.S. Thesis, Dept. Nucl. Eng., M.I.T.,Cambridge, Mass., 1986.24 R.L.E. P.R. No. 129

Focused Ion Beam Fabrication

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