Showing papers in "Journal of Vacuum Science & Technology B in 1993"

Novel scheme for the preparation of transmission electron microscopy specimens with a focused ion beam

Abstract: A novel scheme is presented for the preparation of cross‐section transmission electron microscopy (TEM) specimens, with a focused ion beam (FIB). This scheme is particularly suitable for highly structured substrates, such as integrated circuits. The specimen is made by cutting a thin slice of material from the substrate by sputtering with the FIB. The position of the specimen can be selected with submicron resolution. The specimen is subsequently removed from the substrate and transported to a standard TEM‐specimen holder. A specimen, ready for TEM inspection, can be prepared within 2 hs. The samples are of excellent quality as is illustrated with cross‐section TEM images of FIB‐made specimens of an electrically programmable read‐only memory.

Phenomenological modeling of ion‐enhanced surface kinetics in fluorine‐based plasma etching

Abstract: A multiple beam apparatus has been constructed to facilitate the study of ion‐enhanced fluorine chemistry on undoped polysilicon and silicon dioxide surfaces by allowing the fluxes of fluorine (F) atoms and argon (Ar+) ions to be independently varied over several orders of magnitude. The chemical nature of the etching surfaces has been investigated following the vacuum transfer of the sample dies to an adjoining x‐ray photoelectron spectroscopy facility. The etching ‘‘enhancement’’ effect of normally incident Ar+ ions has been quantified over a wide range of ion energy through the use of Kaufman and electron cyclotron resonance‐type ion sources. The increase in per ion etching yield of fluorine saturated silicon and silicon dioxide surfaces with increasing ion energy (Eion) was found to scale as (Eion1/2−Eth1/2), where Eth is the etching threshold energy for the process. Simple near‐surface site occupation models have been proposed for the quantification of the ion‐enhanced etching kinetics in these syste...

Self‐limiting oxidation of Si nanowires

Abstract: Achieving tolerances of the order of 1 nm for sub‐10 nm structures is both challenging and necessary for controlled experiments on such structures. Here the use of a self‐limiting oxidation reaction to yield silicon (Si) wires of less than 10 nm diam with a tolerance of ±1 nm over 0.5 μm. The final self‐limiting diameters were found to be controlled by oxidation temperature. For 30 nm initial Si column diameters, the asymptotic diameters were found to be 11 and 6 nm for dry oxidation at 800 and 850 °C, respectively. The mechanism of the self‐limiting reaction is not yet fully understood but the tiny radius of curvature is obviously a factor. In addition, there appears to be an anomalous loss of Si; this may be due to sublimation of SiO.

Generation and applications of compressive stress induced by low energy ion beam bombardment

Abstract: Compressive stress is a widespread phenomenon in films subjected to ion beam bombardment. A thermodynamic treatment of materials under a general stress is used to show that preferred orientation will occur as a result of free energy minimization in a biaxial stress field. The equilibrium between structural phases of materials is also affected by stress. Thermodynamics is used to calculate the equilibrium between graphite and diamond under biaxial stress. Recent molecular dynamics studies of the mechanism of compressive stress generation are reviewed in which the phenomena of focused collision sequences and thermal spikes are studied. Experimental work shows compressive stress is linked to preferred orientation in hexagonal boron nitride films and to stabilization of high pressure phases such as cubic BN and tetrahedral amorphous carbon films, in agreement with the thermodynamic analysis.

Multiple‐exposure interferometric lithography

Abstract: Interference effects between two coherent laser beams have long been used to create simple grating patterns in photoresist. With the addition of multiple exposures with variations in period, phase, and orientation, in the same level of photoresist, highly complex one‐ and two‐dimensional patterns of potential interest for device application are demonstrated. The spatial scale of the lines forming these patterns is ∼1/4 of the writing wavelength λ (period to λ/2 and line to space ratio of 1:1) and is in the extreme submicron range, ∼0.1 μm, for readily available laser sources, such as an Ar+‐ion laser operating at 364 nm. Importantly, the depth‐of‐focus for these pairwise exposures is unlimited on the scale of typical semiconductor device topographies and large area, uniform exposures to scales much larger than projected integrated circuit die sizes (e.g., to 30×30 cm2) are easily achieved. These patterns are closely related to moire interference patterns; relationships are illustrated. Diffractive readout is shown to be a powerful and intuitive technique for monitoring these structures. Additional flexibility in pattern fabrication is provided with conventional lithography to define areas on a larger scale and by the use of aperture and phase masks to isolate areas. An example is the fabrication of an interdigitated structure with submicron spaces over a large area.

Self‐assembled monolayer electron‐beam resists on GaAs and SiO2

Abstract: It was demonstrated that self‐assembled monolayers of n‐octadecanethiol [ODT; CH3(CH2)17SH] on GaAs and n‐octadecyltrichlorosilane [OTS; CH3(CH2)17SiCl3] on SiO2 act as self‐developing positive electron beam resists with electron‐beam sensitivities of ∼100–200 μC/cm2. For the OTS monolayer on a silicon native oxide, atomic force microscopy (AFM) images of the exposed layer before etching demonstrate the removal of all or part of the layer upon electron‐beam exposure. Features as small as 25 nm were resolvable in a 50 nm period grating. A resist contrast curve for OTS was obtained from AFM depth measurements as a function of dose. An ammonium hydroxide water etch was used to transfer patterns into the GaAs to a depth of at least 30 nm and buffered HF was used for pattern transfer into the SiO2 to a depth of at least 50 nm.

Active neural network control of wafer attributes in a plasma etch process

Abstract: The present invention is predicated upon the fact that an emission trace from a plasma glow used in fabricating integrated circuits contains information about phenoma which cause variations in the fabrication process such as age of the plasma reactor, densities of the wafers exposed to the plasma, chemistry of the plasma, and concentration of the remaining material. In accordance with the present invention, a method for using neural networks to determine plasma etch end-point times in an integrated circuit fabrication process is disclosed. The end-point time is based on in-situ monitoring of the optical emission trace. The back-propagation method is used to train the network. More generally, a neural network can be used to regulate control variables and materials in a manufacturing process to yield an output product with desired quality attributes. An identified process signature which reflects the relation between the quality attribute and the process may be used to train the neural network.

Lithographic patterning of self‐assembled films

Abstract: This article discusses a new, general approach for fabricating surfaces with precise positional control of chemical functionalities utilizing direct patterning of self‐assembled (SA) or‐ ganosilane monolayer films with lithographic exposure tools, including deep ultraviolet, x‐ray, and e‐beam sources. Lithographically patterned one‐ and two‐component SA films have been used to selectively deposit or attach a wide variety of materials to surfaces, including catalysts, electroless metal films, proteins, cells, and organic moieties. Selectively metallized, patterned SA films have been employed to fabricate functioning Si metal–oxide–semiconductor field effect transistor test structures. The utility of patterned SA films for microelectronics, sensors, and other applications is discussed.

New selective molecular‐beam epitaxial growth method for direct formation of GaAs quantum dots

Abstract: Numerous GaAs epitaxial microcrystals having an average base size of 700 A×700 A surrounded mainly by (111) and (110) facets were fabricated on a sulfer‐terminated (S‐terminated) GaAs (001) substrate by sequentially supplying Ga and As molecular beams. The S‐terminated GaAs (001) surface was produced by exposing the surface to a sulfur vapor in the molecular‐beam epitaxy system immediately after obtaining a Ga‐stabilized surface. The growth of GaAs microcrystals on the S‐terminated substrate is caused by a vapor–liquid–solid mechanism. The process consists of forming Ga droplets on the inert surface and reacting the droplets with As to produce GaAs microcrystals. This method termed droplet epitaxy is thought to be a promising growth method for fabricating the GaAs quantum dots.

Comparison of mobility‐limiting mechanisms in high‐mobility Si1−xGex heterostructures

Abstract: Relaxed Si1−xGex buffers on Si have yielded record low‐temperature mobilities for both electrons and holes in the Si–Ge system. We analyze various limitations on this mobility, including scattering from remote dopants, background impurities, interface roughness, alloy fluctuations, and the specific strain, morphology, and threading dislocations expected for relaxed alloy buffers. Comparison with experiments eliminates all but the first four as potential limitations on the mobility.

Fabrication of sub‐10 nm structures by lift‐off and by etching after electron‐beam exposure of poly(methylmethacrylate) resist on solid substrates

Abstract: Sub‐10 nm structures were fabricated by lift‐off and by etching following electron‐beam exposure of poly(methylmethacrylate) (PMMA) resist on solid semiconductor substrates. Electron beam lithography at 80 kV with a beam diameter smaller than 5 nm was used to expose PMMA resist on either Si or GaAs substrates. The exposed resist was developed with a 3:7 cellosolve:methanol mixture in an ultrasonic bath for 5 s followed by rinsing in IPA and blown dry with pure nitrogen. Ultrasonic agitation during development was found to be essential for forming sub‐10 nm structures in PMMA. The patterned PMMA resist was used either as a lift‐off mask or an etching mask and successful transfer of the pattern to the substrates was achieved. For lift‐off an ionized beam deposition method, which gives smaller grain size and better adhesion of the metal film to the substrate, was used to deposit a layer of AuPd. Metal dots with sub‐10 nm diam and metal structures with sub‐10 nm gaps were fabricated. For sub‐10 nm etched structures reactive ion etching was used to transfer either the PMMA pattern or the lift‐off metal pattern to either Si or GaAs substrates. Etched lines and pillars with dimensions smaller than 10 nm were obtained.

Selective and blanket copper chemical vapor deposition for ultra‐large‐scale integration

Abstract: Selective and conformal chemical vapor deposition (CVD) of copper from (hfac)Cu(VTMS), where hfac=1,1,1,5,5,5‐hexafluoroacetylacetonate, VTMS=vinyltrimethylsilane, has been studied. The compounds (hfac)CuL, L=VTMS, 1,5‐COD, and 2‐butyne, deposited copper on both SiO2 and W, nonselectively, under the conditions employed. Selective CVD onto W in the presence of SiO2 was obtained by passivating SiO2 surface hydroxyl groups via reaction with Me3SiCl in the liquid phase. However, selective deposition was maintained only for short periods (1 min), and loss of selectivity was attributed to the desorption of hydrogen‐bonded Me3SiCl groups which exposed the reactive SiO2 surface sites (hydroxyl groups). To avoid this problem, gaseous (CH3)2SiCl2 was introduced during Cu CVD and resulted in selective deposition for longer periods at respectable rates (≳2500 A/min at 170 °C). Highly conformal deposition was demonstrated on test structures with keyhole geometries and trenches with widths of 2.8–0.45 μm and aspect rat...

Theory of electron emission in high fields from atomically sharp emitters: Validity of the Fowler–Nordheim equation

Abstract: Field emission from metallic emitters is generally described by the Fowler–Nordheim (FN) theory, which is based on a planar model of the tip with a classical image correction. Within the free‐electron model and the Wentzel–Kramers–Brillouin approximation, the planar tip model leads to the well‐known FN equation. The form of this equation predicts that a plot of log J/F2 versus 1/F, where J is the current density and F is the field, should be a straight line within the rather narrow region of field strengths of typical field emission experiments, 3–5 V/nm. This has been experimentally confirmed for conventional emitters, (i.e., electrolytically etched tips with radii ≳50 nm). However, field emitters fabricated with today’s new techniques are much sharper with radii of curvature of the order of nanometers or even the size of a single atom. Hence, the local geometry of the tip may become an important factor in the electron emission process. To investigate the effects of the shape and/or size on emission, the authors, in a recent series of papers, studied the dependence of the current–voltage characteristics on the local geometry of pointed emitters. It was found that the calculated results, plotted as log J/V2 versus 1/V, do not exhibit the straight line behavior predicted by the FN theory. In addition, there is a dramatic increase in the tunneling current for a fixed external bias, V, relative to the FN result for a planar model of the tip with the same bias voltage. Using the exact current integral additional results have been obtained exhibiting the effects of emitter curvature on electron emission in high fields and temperatures. These results continue to differ with the predictions of the β‐modified FN equation. Therefore, the adequacy of a β factor in the conventional planar model FN equation to account for emitter curvature is examined. It is demonstrated that even the use of β‐modified FN equation is not valid when applied to sharp emitters (rt≤10 nm) and will lead to spurious results when extracting information such as field values or emitting area from experimental FN curves. The explanation for this is discussed.

Field‐emitter‐array development for high‐frequency operation

Abstract: Power amplification at high frequencies is one of many applications under investigation using vacuum microelectronics technology. The results of an ongoing program to develop a gigahertz amplifier using Spindt‐type field‐emitter arrays are reported. The maximum frequency at which a field‐emission source in the form of a Spindt‐type cathode array can be operated is determined by the capacitance of the structure and the transconductance of the array. It has been shown that by fabricating arrays with high emitter‐tip packing densities and small total areas it should be possible to achieve operation in the gigahertz range. Structures having a capacitance in the range of 0.1 pF have been fabricated, and total emission currents of 25 mA with current densities of 1000 A/cm2 have been demonstrated with a 0.1 pF structure having 625 emitter tips (40 μA/tip). The transconductance under these operating conditions was 500 μs or 0.8 μS/tip. Simultaneous experiments with our standard low‐frequency Spindt‐type cathode geometry have shown that average emitter tip loadings of 200 μA/tip and transconductances of 5 μS/tip can be achieved. A 625‐tip, 0.1‐pF array with transconductance of 5 μS/tip would have a cutoff frequency of about 5 GHz. The factors determining the capacitance and transconductance of the device and methods for improving performance are discussed.

Ultrasharp tips for field emission applications prepared by the vapor–liquid–solid growth technique

Abstract: A technique for preparation of ultrasharp tips, preferentially of silicon, useful for field‐emission research and applications is described. Regular arrays of tips, as well as triodelike microstructures (‘‘Spindt cathodes’’), can be prepared in such a way. In addition, high‐aspect‐ratio tips suitable for field‐ion microscopy and field‐electron microscopy can be prepared by this technique. Finally, a version of the technique allowing to prepare special‐shape probes for scanning tunneling microscopes and related instruments is given.

Nanofabrication of photonic lattice structures in GaAs/AlGaAs

Abstract: The nanofabrication of two‐dimensional photonic lattice structures in GaAs/AlGaAs is reported. The nanofabrication procedure combines direct‐write electron‐beam lithography and reactive‐ion‐beam etching to achieve etched features as small as 50 nm. The lattice comprises a hexagonal array of air cylinders etched into a semiconductor surface with a refractive index contrast of 3.54. A range of air volume fractions from 14% to 84% was investigated. The lithographic, masking, and etching processes necessary to fabricate the lattice are described along with practical limitations to achieving a lattice of arbitrary air volume fraction. Initial results from optical characterization of the lattice are also presented.

Fixed and trapped charges at oxide–nitride–oxide heterostructure interfaces formed by remote plasma enhanced chemical vapor deposition

Abstract: This article discusses the preparation of device‐quality oxide–nitride–oxide (ONO) structures by a sequence of low‐temperature plasma‐assisted processes. The emphasis is on the relationship between (i) the chemical bonding (a) within the nitride film and (b) at the internal interfaces of a metal–insulator–semiconductor (MIS) structure, and (ii) the electrical properties of these devices with an ONO gate dielectric. In a MIS device, the flatband voltage is shifted from its ideal value by fixed positive charge primarily at the two internal oxide–nitride (O/N) interfaces. The amount of fixed charge is relatively insensitive to the source gas mixture for nitride deposition, and can be reduced by a rapid thermal annealing (RTA) process. Charge trapping at the SiO2/Si interface is increased by N‐atom migration to this interface that occurs during the nitride deposition, and is more sensitive to the source gas mixture, but also is decreased by a high‐temperature RTA.

Semiconductor substrate temperature measurement by diffuse reflectance spectroscopy in molecular beam epitaxy

Abstract: The temperature of semiconductor substrates used in molecular beam epitaxy is determined from the diffuse reflection spectrum (DRS) of the substrates, measured with an external light source. The relative sensitivity of the technique is better than 1 °C. The absolute calibration of the DRS technique for substrates of different thickness, conductivity and back surface texture, is described. The DRS technique is also sensitive to changes in front surface roughness as demonstrated by the increase in the diffuse reflectance at short wavelengths when the oxide desorbs.

Schottky barrier height—do we really understand what we measure?

Abstract: Most measurement techniques of the Schottky barrier height (SBH) contain an inherent assumption of homogeneity. The vast majority of electrical characteristics experimentally obtained from SB junctions actually display clear evidence for inhomogeneities, contradicting the concept of a unique Fermi‐level position which is an essential part of Fermi‐level pinning models. It is also shown that many other basic assumptions of the pinning models are not born out by recent theoretical calculations. A large body of experimental data from well‐characterized epitaxial metal–semiconductor interfaces has firmly established the critical dependence of the SBH on local structure. Thus, understanding the formation of interface structure is likely a prerequisite of any predictive SB theory.

Water soluble conducting polyanilines: Applications in lithography

Abstract: A new class of water soluble conducting polyanilines has been developed This is accomplished by oxidatively polymerizing aniline monomers on a template such as a polymeric acid The resulting polyanilines readily dissolve in water These materials can be applied as removable discharge layers for electron‐beam lithography and for mask inspection by scanning electron microscopy They can be spin‐applied directly on top of resists without any interfacial problems Image distortion as a result of charging during resist exposure is not observed with these materials After exposure the polyaniline is readily and cleanly removed during the resist develop By incorporating cross‐linkable functionality on the polyaniline backbone, water soluble polyanilines that are radiation curable are attained Upon irradiation these materials cross‐link and become insoluble and thus can be utilized as permanent conducting coatings for electrostatic discharge applications In addition, the cross‐linkable polyanilines can be us

PROXECCO—Proximity effect correction by convolution

Abstract: In electron‐beam lithography the proximity effect limits achieved resolution. A possible approach for proximity effect correction is the transform based method which uses deconvolution. This method requires high computing power and data reduction algorithms because of the small grid size. The fine grid is mainly needed for preserving pattern, not for the resolution of the correction. The new method called PROXECCO avoids this disadvantage by separating the calculation into correction related and pattern related steps. The grid size is spatially independent from pattern and can be as coarse as needed for correction. This results in a quadratical gain in computing time for the transformation. The pattern dimensions are kept exactly maintained and data reduction is not needed anymore.

Characteristics of gas‐assisted focused ion beam etching

Abstract: Gas‐assisted etching with a finely focused ion beam has been studied. The presence of a reactive gas, in this case Cl2, results in an enhanced etch rate compared to the rate for sputtering for many materials, including Si, Al, and GaAs. Other advantages over sputtering are the absence of redeposited material and the high etch selectivity possible with some material combinations, which has been exploited in the etching of microstructures. In some applications of this technique, a protective layer of low etch rate material is used over the substrate to improve the quality of the etched structure. The characteristics of the etching process have been studied with variation in the scan speed, gas flux, and current density into the scanned area. In general, a high scan speed, high gas flux, and low current density were found to give the maximum enhancement in the etch rate over sputtering. The application of these results to etching over a wide range of experimental conditions is discussed, to give a basis for estimating the etching results that would occur under other conditions.

Resolution limits in electron-beam induced tungsten deposition

Abstract: Electron‐beam induced deposition of tungsten from the precursor gas W(CO)6 was investigated with the aim of determining the resolution limiting parameters. By exploring the effect of the beam energy and current, the resolution was found to correlate to the expected behavior of the beam diameter. To achieve a more accurate description of the deposition process, the time dependence of the needle height and diameter at the base was determined for deposition times ranging from 5 to 180 s. The measurements enabled a mathematical description of the needle surface as a function of time, and, therefore, the determination of the surface growth. The results exhibit that electron scattering cannot explain the observed growth. For that reason, the surface growth was correlated to the number of secondary electrons (SE) emitted by the primary e beam from the needle surface considering the Gaussian intensity distribution of the e beam and the angle dependence of the SE yield. These assumptions result in a good agreement of the number of SE with the surface growth and demonstrate that the beam diameter mainly limits the deposit resolution. As a consequence, by using a proper e‐beam system, a resolution of 1 μm high needles in the order of 50 nm is obtainable.

Thin film properties of low‐pressure chemical vapor deposition TiN barrier for ultra‐large‐scale integration applications

Abstract: Titanium nitride films deposited by low‐pressure chemical vapor deposition (LPCVD) on Si(100) using TiCl4 and NH3 as reactants, were investigated as a function of deposition temperature between 400 and 700 °C. LPCVD TiN depositions were carried out in a rapid thermal chemical vapor deposition system with a total deposition pressure of 155 mTorr. Stoichiometric TiN films were formed regardless of the deposition temperature and composition was uniform across the entire film. Depending on deposition temperature, varying amounts of chlorine (Cl) and oxygen (O) impurities are found in the TiN films. Films deposited at lower temperatures (400 and 550 °C) contained more than 5 at. % Cl, while the films produced at 700 °C contained as little as 1 at. % Cl. For the films deposited at 650 and 700 °C, the bulk of the TiN films is oxygen‐free. LPCVD TiN deposition rates of 400 A/min with no appreciable incubation time were routinely achieved. The LPCVD TiN deposition process is surface reaction controlled with an act...

Constructive three-dimensional lithography with electron-beam induced deposition for quantum effect devices

Abstract: Two‐ and three‐dimensional patterns and structures can be grown by electron‐beam induced deposition from organic and metalorganic precursors. Using a very fine electron beam in a dedicated field emission scanning electron microscope produces nanometer size deposits which extend from surfaces to heights in the micrometer range. The material is fed to the sample through a nozzle which presents a small leakage flux to the specimen chamber. Having an image processor attached to the microscope allows two‐ and three‐dimensional deposition of material to be controlled. Selecting special speed rates for the motion of the beam generates inclined deposits even at a 90° beam landing angle. Combining a tilted sample and the two‐dimensional way of structuring yield three‐dimensional structures. These nanostructures have very special characteristics with respect to resistivity and shape. Selecting dimethyl‐ gold‐trifluoro‐acetylacetonate as precursor, a current of 1 nA, and a low electron energy of 10 keV for the depos...

Influences of gases on the field emission

Abstract: Influences of gases on the field emission were measured using the specimens of Spindt‐type Mo field emitter array. Gases were introduced into a vacuum chamber where the specimens were driven with pulse and dc voltages to emit electrons. In case of pulse drive, effects of N2 , H2 , Ar, or CO2 on emitter arrays could hardly be observed until the vacuum level reduced to 5×10−6 Torr. When the vacuum level was recovered to the background level, emission showed the recovery to be almost the same value as that before gas introduction. When pulse driven, a small amount of H2 gas reduced the work function of the emitter surface and increase the emission characteristics of emission array. In case of dc drive, on the other hand, emission began decreasing at 10−7 Torr. The introduction of SO2 led to the decrease of emission to ∼70% of the initial value at 5×10−6 Torr because of the contamination of emitter tips caused by SO2 when pulse driven. It was also clarified that CH4 , H2 , and CO adsorbed to emitters to reduc...

Physical basis for applying the Fowler–Nordheim J–E relationship to experimental I–V data

Abstract: The purpose of this work is to show that the Fowler–Nordheim (FN) current–voltage (I–V) plot [log(I/V2) as a function of 1/V] must be treated, on principle, as nonlinear. The cause of this behavior is outlined to be the fact that the electric field and current density are not constant over the emitter’s surface. Traditional approach of the FN I–V plot as being linear may lead to physical contradictions. These contradictions are brought into light. A field emitter model is then developed, which allows to express in closed analytical equations the above statements. Expressions for field enhancement factor, area factor and also for the I–V relationship are obtained. The FN I–V plot nonlinearities are shown to be greater for smaller voltages. Within this model, the FN I–V plot can be taken as quasilinear, under some assumptions. Suggestions for technological parameter extraction from I–V data through nonlinear or linear least‐squares optimization techniques are done.

GaAs surface control during metalorganic vapor phase epitaxy by reflectance anisotropy spectroscopy

Abstract: GaAs(001) surfaces are studied during metalorganic vapor phase epitaxy by reflectance anisotropy spectroscopy (RAS). In analogy to RAS spectra measured from GaAs(001) surfaces under ultrahigh vacuum conditions which were simultaneously controlled by reflection high‐energy electron diffraction or low‐energy electron diffraction certain surface reconstructions can be assigned to specific RAS spectra. Arsenic‐rich disordered (4×4), centered (4×4), and (2×4) like surfaces are identified during deoxidation of the substrate at pregrowth heating. After starting growth the RAS signal shows oscillations the period of which corresponds to the growth of 1 ML of GaAs. This is verified by postgrowth layer thickness measurements. A (4×4) reconstructed surface before growth turns out to be the necessary condition for the appearance of these monolayer oscillations in the RAS signal.

Emission characteristics of metal-oxide-semiconductor electron tunneling cathode

Abstract: We have fabricated a metal–oxide–semiconductor (MOS) electron tunneling cathode with ultrathin SiO2 and examined the emission characteristics. We found that the emission occurred from an entire gate area by electron tunneling through the potential barrier in the MOS diode and the emission current was 0.7% of the total current flowing through the diode. The emission was also found to be nearly independent of pressure.

Focused‐ion beam induced deposition of copper

Abstract: As the dimensions of integrated circuits (ICs) decrease into the submicron range, the problems of circuit delay and interconnect reliability become more urgent. Due to its low resistivity (1.67 μΩ cm) and high electromigration resistance, copper has received attention as a candidate metal for the ICs of the future. In addition, the focused‐ion beam (FIB), with its capability for milling and deposition at linewidths of 0.1 μm or below, has proved useful as a tool for integrated IC ‘‘microsurgery.’’ FIB induced deposition of copper from a novel organometallic precursor compound, Cu(hfac)TMVS, has been achieved using 25–35 keV Ga+ ions from a liquid metal ion source. Submicron copper lines deposited at room temperature from this precursor exhibit resistivities as low as 50 μΩ cm; a sharp drop in these values is noted for deposition above 67 °C, and deposition on a substrate heated above ∼100 °C yields resistivities near those of pure bulk copper. Composition analysis by Auger electron spectroscopy shows the ...