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Coulomb blockade devices can circumvent some of the problems that arise from the continuing miniaturization of conventional circuits. However, device miniaturization and higher circuit integration aggravate cross-coupling phenomena in Coulomb blockade circuits. As an example, a silicon-based bidirectional electron pump was electrically characterized with emphasis on cross-coupling arising from the clock signal driving the pump. The cross-coupling alters profoundly the expected device characteristics, and the experimental data are confirmed by Monte Carlo simulations.

We describe transport measurements on double quantum dot structures formed by trench isolation in a SiGe:Si heterostructure. Three different device geometries are described, and a number of phenomena are observed. Transport measurements at 4.2 K reveal a carrier energy filtering effect accompanying a period doubling in Coulomb oscillations, showing that tunnel barriers can be raised and lowered by application of a gate voltage. Peak splitting in Coulomb oscillations is also observed at 4.2 K, indicating interdot capacitive coupling. The stability diagram for a double dot is mapped out at dilution refrigerator temperatures. In another device, single hole electrometers are fabricated 50 nm away from a double quantum dot, and the ability to measure a single excess charge on the double dot is demonstrated at dilution refrigerator temperatures.

Electron transport in silicon nanopillars has been studied for pillars with zero, one, or two silicon nitride barrier layers of 2 nm thickness. Evidence of Coulomb blockade is presented and the role of the silicon nitride layers is discussed. Wide zero current regions are observed for some devices with two silicon nitride tunnel barriers and these are attributed to the formation of fully depleted quantum dots.

We describe the electrical characteristics of two multiple tunnel junction Coulomb blockade devices connected in series and separated by an island, which is large enough for Coulomb blockade phenomena in the island to be neglected. A sine wave rf signal applied to this island results in a current, which switches its polarity depending on the magnitude and sign of the gate voltages applied to the multiple tunnel junctions, even if the source drain voltage across the entire circuit is nonzero. We show that the transport mechanism responsible for this current is strongly related to the Coulomb blockade characteristics of the multiple tunnel junctions, which need to be asymmetric to achieve pump operation. The circuit characteristic can be explained theoretically by a bidirectional electron pump, which is therefore inherently different from conventional electron pumps driven by multiple ac signals.

The properties of the ruthenium nanocluster polymer of formula [Ru6C(CO)15P(C6H5)2CCP(C6H5)2]n are studied by atomic-force microscopy, Fourier-transform infrared spectroscopy, and electron microscopy as a function of electron-beam exposure. These properties are related to the electrical conductivity, which is measured at various temperatures and electric fields. A hopping correlation length of 240 nm is deduced and explained on the basis of the formation of ruthenium superclusters in an insulating matrix.

By applying a dithiol (1,6-hexanedithiol) treatment, it was observed that a submonolayer of gold colloidal particles deposited by using an aminosilane adhesion agent [i.e., 3-(2-aminoethylamino) propyltrimethoxysilane] transform themselves into chains consisting of a few gold colloidal particles. In those chains, gold colloidal particles are believed to be linked by alkane chains derived from the dithiol molecules. The particle chain was formed on a SiO2 substrate with source, drain, and gate metal electrodes defined by electron beam lithography. It was observed that the gold particle chain bridged a gap between the source and drain forming a single electron transistor with a multi-tunnel junction in the particle chain. The electron conduction through the chain exhibited a clear Coulomb staircase and the periodic conductance oscillation as a function of gate voltage. These measurement results corresponded closely to the results of a simulation based on the orthodox theory.

We have used the advantage of the high etch selectivity between metals in a wet etching process to develop an optimized technique for engineering magnetic materials. This method is based on electron beam lithography and optimized pattern transfer by a combination of dry and wet etching. The technique has been used in fabricating mesoscopic Ni80Fe20 dots and wires with lateral dimensions down to 0.2 μm. We have used scanning electron microscopy to verify the lateral sizes and edge acuity of the structures. The magnetic properties were characterized using magneto-optic Kerr effect and magnetoresistance measurements. A marked increase in the coercive field and the saturation field is seen as the width of the wire is decreased. The magnetoresistance change (∂R) is found to increase significantly as the width of the wire is decreased.

A three-way few-electron switch is implemented using bidirectional electron pumps in silicon-on-insulator material. The switch consists of three branches defined by single-electron transistors, connected to a central node. Any combination of two single-electron transistors forms a bidirectional electron pump. At 4.2K, each cycle of an rf signal applied to the central node pumps electron packets approximately ten electrons in size through the circuit. It is possible to switch the electron packets in any direction through the branches. The switch may be used for the precise transfer of electrons, and as the basic element in few-electron logic applications.

The magnetoresistance anomalies that are observed in multiprobe quantum wires (such as quenching of the Hall effect and negative bend resistance) have been investigated using a semiclassical billiard‐ball model that includes the effects of diffuse boundary scattering. This modeling predicts that two peaks are expected in the magnetoresistance of a quantum wire in which there is a significant amount of diffuse boundary scattering. One peak is due to diffuse boundary scattering in the wire and the other due to specular boundary scattering in the junctions at either end of the wire. The modeling also predicts that the well‐known quenching of the Hall effect and negative bend resistance anomalies are both expected to be enhanced by diffuse boundary scattering. This is explained in terms of the way in which diffuse boundary scattering affects the angular distribution of the electrons entering the junctions in the multiprobe wires. ‘‘Diffuse collimation’’ of the electron distribution occurs, increasing the prob...

Variable‐area resonant tunneling diodes have been fabricated using a process in which the lateral confinement is produced by an in‐plane implanted gate. The basic operation of such devices is discussed, and the lateral confinement shown by both measurements and numerical modeling to be very nearly symmetrical about the resonant tunneling diode (RTD) barriers. Fine structure has been observed near threshold for relatively large area devices and this has been attributed to single‐electron or few‐electron tunneling through donor states in the quantum well. Additional fine structure seen in the valley current of small‐area devices has been shown to be consistent with the effects of lateral quantization in the system. Finally, results are presented for strip devices in which the resonant tunneling peak breaks up into numerous subpeaks on application of the gate voltage, and this is attributed to pinning of the confining potential by donors close to the RTD barriers.

A single‐electron memory cell, in which one bit of information is represented by the excess or shortfall of a precise number of electrons, is described. An experimental memory circuit was fabricated using side‐gated constrictions in δ‐doped GaAs, and the basic operation was confirmed from 30 mK up to liquid‐helium temperature of 4.2 K. This memory can store information for longer than several hours. The intrinsic single‐electron memory characteristics in a regime where cotunneling is neglected are investigated, and the overall characteristics are explained by a semiclassical model.

This paper discusses the thermal and optical characteristics of a free‐standing microthermocouple with a view to its application as an infrared detector. This device is a radiation thermocouple in which the hot junction is thermally isolated from the substrate by making it free‐standing. When radiation is absorbed by the device, the free‐standing structure heats while the much larger cold junction, which is in physical and thermal contact with the substrate, remains at ambient temperature. Copper and constantan have been used as the thermocouple materials. Electrical and optical measurements have been performed for free‐standing wire lengths of 20, 40, and 60 μm and have been theoretically modeled. Thermal analysis shows that convective heat loss is significant and from the measurements a convection coefficient of 20 000 W m−2 K−1, for the free‐standing wires, has been deduced. The time constants of these devices were of the order of a few microseconds. The device output has been shown to depend on the po...

Time‐resolved reflectivity measurements have been used to investigate the morphology of an evolving amorphous‐crystalline interface during solid phase epitaxial regrowth of an ion‐implanted polycrystalline silicon film. Isothermal electron beam heating was used to produce partly regrown specimens for cross‐sectional transmission electron microscopy analysis, and this has enabled a direct correlation to be established between the interface shape and the observed reflectivity transients. Using a thin‐film optical model of an evolving rough interface, this correlation has enabled interface shapes to be inferred from the reflectivity at higher temperatures, where it is difficult to achieve partial regrowth. For undoped material, smaller grain sizes have been found to lead to rougher interfaces, with regrowth rates typically 20 times slower than for single crystal. At 620 °C, the presence of high concentrations of arsenic results in a smoother interface, but as the regrowth temperature is increased, the interf...

Channeled ions offer a means of patterning a wafer with a two‐dimensional electron gas (2DEG) buried deep below the surface. The implantation of 60–140 keV Si++ ions into a 580‐nm‐deep 2DEG formed at a GaAs/AlGaAs heterojunction has been characterized, with respect to ion energy, dose, and angle of incidence. Transverse electron focusing measurements have been used to investigate the roughness of the implanted boundary, leading to measured values for the specularity coefficient of about 0.5 at 1.7 and 4.2 K. Similar measurements at lower temperatures (120 mK) have shown fine structure in the magnetoresistance, in addition to the classical transverse electron focusing effect. The fine structure is attributed to electron interference effects at, or close to, the boundary. Channeled ion implantation has been used to define an in‐plane‐gated transistor which, at 300 mK, shows clear evidence of ballistic electron transport.

High-density silicon nanopillar cathodes were fabricated using a self-assembling colloidal gold etch mask. Scanning tunneling microscopy experiments were performed to locate individual nanopillars and to investigate their field emission properties. Emission characteristics were obtained over a range of fixed separations from the nanopillar apex, allowing the empirical determination of the geometric field enhancement factors from the resulting Fowler–Nordheim plots. The geometric enhancement factors were found to increase dramatically for decreasing anode–cathode separation and the rate of increase is dependent on the nanopillar geometry.

Two Coulomb blockade devices connected in series and separated by a main island to which a rf signal was applied, are characterized electrically. The main island is large enough so that Coulomb phenomena in it can be neglected. Although no source–drain voltage is applied, the rf signal causes a current. The polarity of this current depends on the dc gate voltages, which control the two Coulomb blockade devices. The experimental data correspond closely to the simulations. Furthermore, it is evident from theoretical considerations that the circuit can pump electron packets against an applied potential.

We have observed the splitting of Coulomb oscillation peaks in coupled Si0.9Ge0.1 double quantum dots at 4.2 K. The quantum dots are formed by trench isolation, which means that the dots can be made much smaller than possible with the surface-gated approach. A dot diameter of 50 nm or less increases the charging energy and, therefore, the operating temperature of the device compared to previous approaches. A simulation of the results using parameters calculated from the lithographic dimensions of the device shows that a good fit to the experimental data can be achieved with a realistic interdot capacitance value.

Single-electron effects have been observed up to 60 K in a side-gated point contact device fabricated in nanocrystalline silicon films. The films were phosphorus-doped and deposited at 300 °C by plasma enhanced chemical vapor deposition. Using transmission electron microscopy and Raman spectroscopy, the grain size, crystalline volume fraction, and grain boundary thickness are determined. The single-electron effects are associated with islands formed by crystalline silicon grains ∼4 nm in size, isolated by amorphous silicon regions ∼0.5 nm in thickness. The structural characteristics of the nc-Si film are correlated to the electrical behavior. The electrical transport mechanism at high temperatures is attributed to percolation conduction across a distribution of tunnel barriers with a maximum height of 40 meV.

We report far infrared (FIR) studies of plasmons in spatially modulated two‐dimensional electron gases (2DEGs) in AlGaAs/GaAs heterostructures using biased overlaid metal gratings, including interdigitated gratings, both as optical couplers and as spatially modulating gates. Comparison of the experimental results with the predictions of scattering matrix calculations of the FIR response of a modulated 2DEG in the presence of a perfectly conducting lamellar grating allow us to deduce the spatial variation of the number density distribution in the 2DEG as a function of grating bias. For the interdigitated grating gates, the 2DEG can be modulated at a period of twice that of the grating fingers by differentially biasing alternate fingers; 2D plasmon resonances have been observed at half‐integral values of the grating wave vector G, corresponding to the electrically induced periodicity of the 2DEG modulation itself acting as an optical coupler in addition to the metal grating. The observed G/2 plasmon frequencies decrease with increasing amplitude of the 2DEG number density modulation, in quantitative agreement with those obtained from scattering matrix calculations of the optical response of a modulated 2DEG under a perfectly conducting lamellar grating; calculations of the oscillating charge density profiles show that this occurs because, as the modulation amplitude increases, the oscillation becomes localized in regions of low 2DEG number density which are also under one of the sets of grating fingers, and is therefore better screened.

We report on measurements of hole transport through a double quantum dot structure formed by trench isolation from a SiGe:Si heterostructure. A period change in the Coulomb oscillations is observed upon changing a gate bias, which is attributed to the lowering of one of the tunnel barriers, effectively changing the device to a single quantum dot. Accompanying the period change is a significant change in the level of noise associated with the oscillations. This is explained by a carrier energy filtering effect in the double dot compared with the single dot, caused by the slight difference in energy level spacing in each quantum dot.

A polymer composed of ruthenium carbonyl and of the formula [Ru6C(CO)15Ph2PCCPPh2]n has been synthesized. It is found to behave as a negative electron-beam resist with a sensitivity of 400 C/m2. Upon exposure to the electron beam, the electrical conductivity of the patterned films is found to vary over seven orders of magnitude according to a power-law dependence on dose. Temperature dependence of the conductivity is studied, and the conduction is attributed to variable-range hopping between ruthenium superclusters in two dimensions.

Experiments have been carried out to determine the temperature distributions induced during swept‐line electron‐beam heating of silicon. In situ measurements of the reflectivity were used to determine the temperature rise, using as a basis the rise in reflectivity exhibited by silicon with increasing temperature. Sweep speeds between 10 and 60 cm/s were studied using line beams between 60 and 300 μm wide. The experimental results were compared with analytic one‐ and two‐dimensional models assuming constant thermal properties, and with a one‐dimensional (1D) numerical model which takes into account the variation of heat capacity and thermal conductivity with temperature. The analytic models were used to show the range of conditions over which the 1D approximation could be applied and to quantify the errors introduced as this approximation breaks down. The experimentally measured peak temperatures and those predicted by the numerical model were found to agree to within 5% for conditions where the heat flow ...

A nanoscale electron tube with a field-emission cathode and a control gate (nanotriode) has been fabricated and characterized. Electrons are field emitted from metal nanopillars with radii of about 1 nm into a vacuum nanochamber, collected at the anode, and controlled by a gate electrode. The nanochamber is sealed by an integrated anode and has vertical and horizontal dimensions of 100 nm. The turn-on voltage is less than 10 V and is independent of ambient temperature. Currents of 10 nA and transconductances of up to 6 nS per device have been observed; this would yield a transconductance of 60 S cm−2 at the maximum packing density of 1010 nanotriodes cm−2 for these devices. The emission stability is better than 3% at room temperature and improves to 0.1% at 20 K.

We have observed single-electron charging effects in heavily doped polycrystalline silicon nanowires at 4.2 K. Wires of approximately 20 nm by 30 nm active cross section were defined by electron-beam lithography and thermal oxidation in standard polycrystalline silicon material. We have measured a Coulomb staircase and periodic current oscillations with gate bias, attributed to localized carrier confinement resulting from a statistical variation in the intergrain tunnel barriers. A sharp change in the current oscillation period is seen and we speculate that it is due to electrostatic screening of the gate bias by grain boundary defect states.

Novel field emission devices with electron path lengths an order of magnitude less than the elastic mean free path of electrons in air have been fabricated and tested at atmospheric pressure. The nanoscale-tip field emission system consisted of multiple emitter tips of radii about 1 nm within an extractor aperture of diameter 50 nm. The extractor turn-on voltage was approximately 7.5 V; field-emitted currents of up to 10 nA were collected at extractor voltages of less than 10 V. Maximum current densities of over 1011 A m−2 have been observed, and the emission stability in air at atmospheric pressure is better than 3%.

We report the evolution of the magnetoresistance (MR) and magnetization behavior of Ni80Fe20 wire arrays as the width (w) is reduced from 200 to 0.3 μm. At around 1.5 μm width, the hysteretic behavior seen in continuous films shows the near reversible behavior characteristic of spin rotation processes. At low field (H Ms), the linear MR response to the in-plane perpendicular hard axis field suggests a bulklike transverse MR effect.

Isothermal electron beam heating combined with in situ optical measurements has been used to measure the temperature dependence of the spectral emissivity of lightly doped silicon in the range 345–723 °C for wavelengths between 1 and 9 μm. The absorption coefficient was deduced from the spectral emissivity and compared with the predictions of a model including phonon‐assisted processes involved in interband transitions, free‐carrier absorption, and lattice absorption. The experimental data agree well with the model’s results.

The Coulomb blockade region was measured directly in an experimental single‐electron memory device. The device was constructed with multiple‐tunnel junctions (MTJ) formed by making a sidegated constriction in δ‐doped GaAs. The Coulomb blockade region is defined by electron transfer rates of less than 10 electrons per second. At low values of sidegate voltages in the MTJ an enhancement of the Coulomb blockade is observed and explained by the formation of a nonuniform electrostatic potential in the semiconductor tunnel junctions.

We have studied focused electron beam induced deposition from W(CO)6 at beam primary energies between 20 and 0.06 keV. Submicrometer resolution with 4 nA beam current was maintained at very low primary energies using a retarding field configuration. Decomposition cross sections of W(CO)6 for primary energies below about 1 keV were found to be about a factor of 4 larger than those at 20 keV. Depending on the scan conditions, the resistivity of the deposits formed using low primary energies was found to be up to about a factor of 4 lower than at 20 keV implying a higher metallic content. These results form the basis of an improved method for repairing clear defects on x‐ray masks and for making conducting tracks on semiconducting materials.

We have fabricated constrictions in δ‐doped GaAs using implanted gates to provide the lateral confinement. Large conductance oscillations are observed when the gate voltage is varied. The drain‐source current‐voltage characteristics are highly nonlinear; as many as 30 peaks are present, and peak‐to‐valley ratios greater than 100 have been measured. These results are explained in terms of resonant tunneling through the random potential distribution in the point contact. Using a simple model for the potential distribution we are able to simulate qualitatively the structure in the conductance.

We report the fabrication of high aspect ratio, sub‐10 nm size, structures in silicon without involving any wet chemical etching. A 50 nm thick double layer of low and high molecular weight polymethylmethacrylate resist was exposed with an 80 kV electron beam of diameter smaller than 5 nm. After exposure the resist was developed in 3:7 cellusolve: methanol with ultrasonic agitation during development. A 5 nm thick AuPd film was deposited by ionized beam evaporation and a metal pattern was obtained by liftoff. Sub‐10 nm AuPd dots were recorded with a scanning electron microscope. The AuPd pattern was then used as a mask on the Si substrate which was etched with reactive ion etching. Silicon nanocolumns with diameters ranging from 5 to 7 nm and an aspect ratio of height to diameter of about 7:1 were obtained.

We studied the change in electrical conductivity of deposits from focused electron beam induced dissociation of W(CO)6 for different exposure conditions. Lines were deposited by scanning repeatedly to build up the same total electron dose; with different electron doses per scan, resistance differences of more than one order of magnitude resulted. The lines with lower deposited thicknesses also have lower resistances, and so cannot be explained in terms of constant resistivity and different cross‐sectional areas. A theoretical description involving an intermediate and a final product is proposed and compared to the experimental results.

We report on the fabrication and electron transport in a novel heterostructure in which layers of AlGaAs and GaAs have been grown after a submicron free‐standing GaAs wire has been formed. Electronic conduction at low temperatures in this material is shown to be consistent with three‐dimensional hopping conduction with a transition to one‐dimensional hopping at temperatures below 1 K.

Side‐gated point‐contact structures in delta (δ)‐doped layers have been used to form single‐electron tunnel junctions with variable resistance. Clear Coulomb‐blockade effects have been observed in the current‐voltage characteristics. The measured characteristics are described in terms of a series of single‐electron transistors formed by microsegments within the point contact. The effective tunnel capacitance and side‐gate capacitance are estimated to be 10 and 1 aF, respectively, which are both one order of magnitude smaller than the reported capacitance of tunnel junctions made from Al or GaAs/AlGaAs heterostructures.

We have carried out magnetoresistance measurements on a mesoscopic cross formed from two split gates on a GaAs/AlGaAs 2DEG and have observed anomalous peaks in the bend resistance before the electron collimation is finally destroyed by the magnetic field. We have considered two possible explanations for this effect, and have rejected the possibility of quantum mechanical effects in favor of a classical one in which we postulate the presence of an impurity close to the center of the active region.

We have studied the quantized conductance of a one‐dimensional ballistic channel in the two‐dimensional electron gas of a back‐gated GaAs/AlGaAs heterostructure. A standard Schottky split‐gate fabricated with electron‐beam lithography techniques is used to define the one‐dimensional channel, but we incorporate an epitaxially grownin situ back‐gate, situated ∼1 μm below the electron gas, to provide additional control of the carrier density. Quantized conductance steps can be induced by changing the bias on either gate, highlighting the self‐consistent nature of the electrostatics involved. We show that we can, in principle, achieve independent control of the one‐dimensional carrier density and channel width.

Beryllium implants have been used to form p‐n junctions which confine electrons laterally in a GaAs/AlGaAs heterostructure to make high‐mobility quasi‐one‐dimensional wires whose electrical width can be varied by biasing the implanted regions. Incorporation of an additional surface Schottky gate enables the electron density within the wires to be controlled independently. Magnetoresistance measurements have been performed at 1.7 K and the weak‐field boundary‐scattering maxima used to determine the width as a function of both the bias applied to the implanted regions and to the surface gate. The mobility is also calculated and is comparable to that reported for wires of similar dimensions fabricated using high energy ion damage.

Electron focusing has been observed in single‐ and double‐grid structures. The magnetoresistance shows strong maxima and minima with values both above and below the zero field resistance. These are interpreted in terms of electron trajectories which are either backscattered from or transmitted through the grids, with a good match between the measured and calculated magnetic field values for the position of these peaks. The difference in magnetoresistance between the two structures is explained by an internal scattering mechanism which is present only for the double‐grid system.

A novel microthermopile for CO2 laser radiation detection with a fast response time has been fabricated for the first time. The microthermopile is fabricated by high‐resolution e‐beam lithography and isotropic plasma etching of the substrate resulting in free‐standing hot junctions which are thermally isolated from the substrate. The good thermal isolation and small heat capacity of the hot junctions resulted in a responsivity of 60 V/W and a time constant of 20 μs. The device operates over the entire CO2 laser wavelength range from 9.4 to 10.6 μm. Detailed measurements are presented for 10.6 μm operation.

The field‐dependent magnetoresistance (MR) characteristic and magnetic hysteresis behavior has been studied in 300–500 A thickness Ni80Fe20 wires of variable width (w) in the range from 0.2 to 10 μm. As the width of the wire decreases, a marked increase in the easy axis coercive field is seen for fields applied along the wire axis and the form of the MR characteristic is markedly modified for the in‐plane perpendicular hard axis direction with a large field‐dependent MR response observed for applied field strengths exceeding the edge demagnetizing field. The low field hard axis results are discussed in terms of an inhomogeneous spin configuration across the width of the wires arising from the spatial variation of the demagnetizing field.

Silicon‐on‐sapphire films have been characterized by high‐resolution electron microscopy at 500 kV following silicon implantation and electron beam annealing. The effect of implantation with 1015 Si/cm2 at 190 keV was to amorphize most of the 0.3‐μm silicon layer, in particular breaking up the lattice defects originating from the interface. The remaining crystalline surface layer acted as a seed for the recrystallization of the film back to the interface. There was a substantial decrease in the number of lattice defects present in the silicon compared to the as‐grown films, although amorphous layers varying in thickness up to 50 A were formed at the interface. Rutherford backscattering spectrometry measurements of the film crystallinity showed good correlation with the observed microstructural changes.

An isothermal processing system using a 2‐kW electron beam is described. Processing of areas up to 4×4 in. is achieved by rapidly scanning the beam in the multiple scan mode. An analysis of this method and some typical heating cycles for silicon wafers are presented. There is good agreement between theoretically predicted and experimentally measured temperatures. Additionally, closed‐loop operation is demonstrated where an optical pyrometer is used to control the electron beam current. This machine can either process whole wafers, or can sequentially treat a large number of small chips. This enables, for example, the rapid assessment of the annealing behavior of a particular implant by processing chips, cut from the same wafer, under varying conditions. Heating cycles of a fraction of a second to tens of seconds or more, which are not possible with furnaces, at temperatures up to 1000°C or greater have found many applications in semiconductor processing. Two important uses are described in this paper illu...

The annealing characteristics of shallow (Rp

A recently developed time‐resolved reflectivity technique has been used to characterize the temperature distributions and molten zones induced in silicon‐on‐insulator structures by heating with scanned line‐shaped electron beams. Measured temperature distributions were compared to theoretical predictions from a one‐dimensional heat‐flow model, which assumes that the heat flow parallel to the surface can be ignored. The results from the experiments and the predictions from the numerical model were also compared to predictions from an analytical model for heating of a homogeneous material. The range of heating conditions for which the one‐dimensional approximation was suitable was determined, and it was found to be satisfactory for heating with line beams of more than 200‐μm width at sweep speeds greater than 5 cm/s. Conditions which produced melting of the silicon film were explored, and it was found that the numerical model did not adequately describe this phase transition. The discrepancy between the theoretical predictions and the observed results can be explained by the need to supercool the liquid silicon by approximately 155 °C before it freezes.A recently developed time‐resolved reflectivity technique has been used to characterize the temperature distributions and molten zones induced in silicon‐on‐insulator structures by heating with scanned line‐shaped electron beams. Measured temperature distributions were compared to theoretical predictions from a one‐dimensional heat‐flow model, which assumes that the heat flow parallel to the surface can be ignored. The results from the experiments and the predictions from the numerical model were also compared to predictions from an analytical model for heating of a homogeneous material. The range of heating conditions for which the one‐dimensional approximation was suitable was determined, and it was found to be satisfactory for heating with line beams of more than 200‐μm width at sweep speeds greater than 5 cm/s. Conditions which produced melting of the silicon film were explored, and it was found that the numerical model did not adequately describe this phase transition. The discrepancy between the the...

Seeded zone‐melt recrystallization using a dual electron beam system has been performed on silicon‐on‐insulator material, which was prepared with single‐crystal silicon filling of the seed windows by selective epitaxial growth. The crystal quality has been assessed by a variety of microscopic techniques, and it is shown that single‐crystal films 0.5–1.0 μm thick over 1.0 μm of isolating oxide may be prepared by this method. These films have considerably less lateral variation in thickness than standard material, in which the windows are not so filled. The filling method is suitable for both single‐ and multiple‐layer silicon‐on‐insulator, and gives the advantages of excellent layer uniformity after recrystallization and improved planarity of the whole chip structure. Experiments using various amounts of seed window filling have shown that the lateral variations of silicon film thickness seen in unplanarized material are due to stress relief in the cap oxide when the silicon film is molten, rather than the...

Silicon‐on‐insulator layers have been produced under conditions which are compatible with three‐dimensional device integration. The layers were formed by zone melting recrystallization of two types of seeded silicon films in a dual electron beam system. High‐resolution scanning electron microscopy was used to observe the starting materials and the stages of recrystallization from unseeded regrowth through seeded regrowth to under oxide melting. With the standard structure, which has an overall layer of polycrystalline silicon, good seeding requires melting into the bulk. However, when the silicon is deposited under conditions which give epitaxial growth in the seed windows, seeded recrystallization does not require melting in the substrate or even across the complete width of the window. A study of the silicon mass flow for the various stages is presented and the processing conditions for the minimum thickness variation of the silicon film are reported.

A time‐resolved reflectivity (TRR) technique has been developed for dynamic studies of swept beam heating of silicon‐on‐insulator (SOI) materials. The method exploits the temperature dependence of the reflectivity of SOI films to allow noncontact temperature measurement with high spatial and temporal resolution. This technique is of considerable practical importance for beam processing, since it allows the temperature distribution induced by a beam being scanned across a specimen to be determined. The temperature distribution produced by a line electron beam swept across a SOI specimen was experimentally measured and found to be consistent with a theoretical prediction. The TRR technique can also be used to study melting and will prove useful for characterizing zone melting recrystallization, where thermal modeling is often inadequate for the complex structures involved.

Shallow (Rp∼20 nm) As and B‐doped layers in (100) silicon, formed by low‐energy ion implantation, have been investigated using conventional and high resolution transmission electron microscopy before and after either electron beam or furnace annealing. After annealing residual defects were observed in the region beyond the original amorphous/crystalline interface for both As and B implants and the nature of these defects and their stability was found to be relatively insensitive to a variety of annealing conditions. Lattice images of 10‐keV As‐implanted material indicated that a continuous amorphous layer was formed after implantation which regrew into perfect single crystal following electron beam processing for 1 s with a peak temperature of 900 °C.

Micron‐sized loops of high‐mobility two‐dimensional electron gas have been made on GaAs‐AlGaAs heterostructures using a novel split‐gate technique. Aharonov–Bohm oscillations of amplitude up to 20% of the device resistance have been observed at very low temperatures (T

Fine structures can be fabricated in silicon dioxide layers by a two‐stage process in which localized ion implantation enhances the rate at which the oxide can be etched chemically. This process has been investigated as a technique for maskless microfabrication using a scanning ion beam lithography system.