With a high resolution electron microscope it is possible to image directly the atomic surface lattice of vapor-deposited Au(111) films. The contrast of the surface atoms can be either black or white relative to the background which is characteristic of close-packed planes of atoms in the stacking sequence ABCABC.... An analysis of these images was performed using multislice dynamical diffraction computations of 256 × 256 = 65 536 reciprocal space points and subsequent image simulations. The effects of top and bottom surface roughness, different termination layers and the contrast compared with single-atom imaging are considered.

The identification of atomic structure detail at incoherent double-position boundaries in these (111) films was also achieved. Surface layer terminations, variations in the choice of every third matching plane and the possibility that twinning planes produce boundaries with jogs were investigated. Multislice computer programs were designed to calculate the diffraction effects from these inclined boundaries using two-dimensional fast Fourier transform and shift techniques of the projected potential. This is the first time that inclined planar defects have been analyzed in this manner.

A tracer technique using radioactive 56Ni* was applied to investigate the growth mechanisms ofNi2Si, NiSi and NiSi2 on Si<100> and Si <111> wafers. A thin Ni* tracer layer initially at the Ni-Si interface was observed to migrate and spread during the growth of nickel silicides at 350, 450 and 800°C. These data are discussed, together with other results from 31Si* tracer work and xenon marker experiments. Ni appears to be the dominant moving species in all cases, diffusing both substitutionally and by grain boundary paths (in comparable amounts) for Ni2Si and substitutionally for NiSi and NiSi2.

It is well established that near-noble metals and refractory metals form two distinct classes of silicide contacts with silicon. Rare earth metals have been studied in the same manner and found to form a new class that is very distinct from the other two in terms of properties and characteristics. Some of these characteristics are the formation of a disilicide phase, as an apparently first and last phase, at a surprisingly low temperature (250–400°C). Marker motion study using implanted krypton and argon showed silicon to be the dominant diffusing species for ErSi2. The Schottky barrier height to n-Si is 0.40 ± 0.04 eV and to p-Si is 0.70 ± 0.04 eV for all six of the metals studied. The surface morphology after reaction indicates the formation of a tensile stress by the silicide reaction. Oxidation of the rare earth metals is a severe problem although a variety of passivation schemes have been shown to work.

It is proposed that interface reaction barriers in binary A/B diffusion couples lead to the absence of phases predicted by the equilibrium phase diagram, provided that the diffusion zones are sufficiently thin (“thin film case”). With increasing thickness of the diffusion zones the influence of interface reaction barriers decreases and the simultaneous existence of diffusion-controlled growth of all equilibrium phases is expected (“bulk case”). First-phase and different modes of second-phase formation in the diffusion zones as well as the influence of impurities are discussed with specific reference to silicide formation. For this discussion the concept of a critical thickness of the first forming phase is introduced, below which a second compound phase cannot grow simultaneously with the first one.

An in situ annealing X-ray study was applied to Cu-Al thin film couples over a wide range of copper-to-aluminum film ratios. This new technique, which has been previously described for a study on the Au-Al thin film system, enables us to make a temperature-dependent photographic X-ray analysis. The present study indicated that only a limited number of the wide variety of bulk phases form in the Cu-Al thin film interface, while some of these phases in the interface are transient. In the transient stages of the interface reaction, the f.c.c.-ordered phase β-Cu3A1 grows over the entire range of copper-to-aluminum film ratios after the first nucleation of CuA12, indicating a two-step nucleation reaction. On the aluminum-rich side, this phase transforms to a new ordered hexagonal phase β′. It could be interpreted as a superlattice of the metastable hexagonal ω phase occurring in zirconium-based alloys. The end phases are CuA1 and CuAl2.

Several recent transmission electron microscopy studies have shown that small voids and/or gas bubbles are present in various thin metallic films. The formation and growth of these voids have been studied as a function of the deposition and subsequent annealing conditions. From these studies, two conflicting views as to why these voids grow have emerged. Some investigators claim that the void growth occurs as a result of the precipitation of trapped gaseous impurities, whereas others believe that the growth is due to the annihilation of quenched-in excess vacancies at pre-existing voids. In this paper we present arguments with which we hope to resolve the present controversy.

A review of recent advances in polycrystalline thin film solar cells is presented. A comparison of the fundamental mechanisms and the performance of heterojunction, Schottky barrier, metal-insulator-semiconductor, inversion layer and p-n junction devices is given. The emphasis is placed on devices fabricated by low temperature processes, and the influence of grain boundaries on carrier recombination and transport is discussed.

Large-area platinum and palladium Schottky barrier solar cells with diode quality factors approaching unity have been fabricated on magnetron-sputterdeposited hydrogenated amorphous silicon (a-Si:H). Measured optical band gaps and barrier heights are comparable with those obtained on glow-dischargeproduced a-Si:H but open-circuit voltages are lower. High surface defect densities are suggested to be responsible for the decrease in Voc.

An electron-beam-induced voltage (EBIV) technique has been developed to measure the barrier height of Schottky diodes. The principle of this technique is described and is compared with the conventional electron-beam-induced current (EBIC) technique. Applications of both techniques are illustrated in a study of composite silicide Schottky diodes with mixed high and low barrier areas formed using bilayer and co-evaporated Pd-Ti and Pt-Ti films on silicon substrates. The difficulty of using EBIC for quantitative studies of diode characteristics is discussed and contrasted with the advantages of the EBIV technique. The extension of the EBIV technique to contactless measurements of barrier height variation with good lateral resolution is described.

Dynamic conductance measurements in metal-oxide-semiconductor (MOS) capacitors and the effects of bias-temperature stresses are considered together with noise measurements to determine the origin of 1/f noise in an MOS field effect transistor (MOSFET) operated either under subthreshold or above threshold conditions. The 1/f noise in a subthreshold MOSFET is shown to be due to the dispersion of dielectric loss of the interfacial oxide. The source of 1/f noise in the inversion regime is less certain. Both the number fluctuation model and the mobility fluctuation model are consistent with the data of the bias-temperature treatment effect on 1/f noise reported by Vandamme and Dik provided that the data are interpreted in the reconstructing interface states model. Further inference from conductance data tends to favor the mobility fluctuation model. It is also pointed out that there is only one microscopic model that provides a unified mechanism which gives not only the dispersive dielectric loss and the 1/f noise at subthreshold but also the mobility fluctuations at inversion.

The properties of PtSi-Si Schottky barrier contacts formed by a new technique employing multilayer metallization are compared with those of contacts prepared by the conventional single-layer metallization method. The multilayer technique permits the formation of very shallow contacts without any limitation being placed on the thickness of the PtSi layer. For a PtSi layer of given thickness the PtSi-Si contact interface obtained by this technique is more uniform than the interface formed by annealing a single layer of platinum on silicon. The interfacial uniformity is independent of PtSi thickness for shallow PtSi-Si contacts produced by the multilayer technique, while for conventional contacts the uniformity decreases with increasing PtSi thickness. Large-area (9.4 × 10−3 cm2) diodes utilizing shallow PtSi-Si contacts about 200 Å deep have been fabricated without guard rings. These diodes exhibit near-ideal forward current-voltage characteristics, low reverse leakage currents (less than 5 nA at −10 V) and high breakdown voltages (over −90 V). These characteristics are superior to those of diodes using conventional PtSi-Si contacts.

Resistivity and grain size measurements on thin films of co-sputtered WSi2 show that the resistivity in this material is dominated by grain boundary scattering. The reflection coefficient for the transport of charge carriers through the grain boundaries was determined to be approximately 0.9.

The structural defect properties of silicon on sapphire (SOS) are investigated with transmission electron microscopy and Rutherford backscattering. The results for as-grown SOS films are compared with SOS films which have been implanted with 1016 Si+ ions cm− 2 at an energy of 170 keV and annealed at 600°C (1 h) and 1000°C (18 h). The regrowth proceeds from the silicon surface even though it is noncrystalline as determined by reflection high energy electron diffraction. The structural defects consist of stacking faults, microtwins and dislocations. The stacking faults and microtwins show a dramatic reduction with processing. The nature of the structural defects at the interface after implantation and annealing is reported here for the first time. It is different from the bulk of the silicon film and consists of a layer of dislocation loops of various sizes and short dislocation lines which follow the interface and curve upwards. This behavior is analogous with the secondary defects generated in self-implanted bulk silicon. Suggestions, based on results from bulk silicon implantation, are made for optimizing the ion implantation furnace annealing process.

The advent of very-large-scale integration in microelectronics has been achieved by reduction in lithographic dimensions coupled with a corresponding decrease in vertical dimensions in properly scaled device structures. This development has placed severe demands upon interconnection technology. The practice of using semiconducting regions (diffusions or polycrystalline silicon) for interconnecting devices is no longer viable because of the high resistance associated with such regions (i.e. interconnections do not “scale” properly). One solution to this problem is the use of multilevel metallization, but this requires tens of thousands of small contacts to shallow diffusions. Refractory metals such as titanium are being explored as materials which provide the necessary stable low resistance contacts suitable for integrated circuit applications. Another solution to the problem is to develop a higher conductivity material to replace or supplement polycrystalline silicon. Refractory metal disilicides have been extensively investigated for this application -both as a direct replacement for polycrystalline silicon or in a silicide/polycrystalline silicon composite (polycide). A critical review of the present status in both these areas will be presented. Emphasis will be upon our experience gained in conjunction with the development of a 1 μm silicon gate metal/oxide/ semiconductor field effect transistor technology.

Progress in patterning technologies and computer-aided circuit designs have brought us to the threshold of very-large-scale integrated (VLSI) circuits with 100 000 or more devices to be integrated on a silicon chip. In this paper we review thin film applications in the fabrication of contacts and interconnects for VLSI circuits. Device structures suitable for both bipolar and metal/oxide/semiconductor (MOS) VLSI circuit applications tend to have shallow junction depths and contact areas (silicon-metal interfaces) in the 0.2–0.5 μm and 1–2μm2 ranges respectively; also some of the circuits require Schottky barrier diodes. Consumption of silicon in the contact windows needs to be minimized with the use of silicide layers for siliconmetal contacts. The formation and use of platinum silicide layers for bipolar applications are reviewed. Our observations indicate that the carbon and oxygen present in Czochralski-grown silicon crystals interfere in platinum silicide formationand affect the electrical characteristics of the contacts. The use of barrier layers in VLSI metallization is illustrated. The interdependence of film microstructure, electromigration-induced failures and VLSI interconnection reliability is examined. The integration of a large number of components on a VLSI chip with a single level of interconnections consumes more chip area. Long interconnection paths adversely affect circuit performance. Multilevel interconnections (conductor/insulator/conductor) offer an attractive solution to increase the packing density and circuit performance. The application of PtSi/(Ti: W)/(Al-Cu)/SiO2 /(Ti: W)/A1 film layers in the fabrication of a bipolar VLSI circuit with a minimum feature size of 1.25 μm is illustrated. As the complexity of VLSI circuits continues to grow with micron size device structures, three or more levels of interconnections compatible with shallow junctions on the substrates and complex packaging technologies are required. Areas of concern and desirable features in VLSI metallization are summarized.

The effect of both metal defects (nicks and scratches) and passivation defects (Griffith cracks or pinholes) was theoretically and experimentally investigated. Flux divergences due to temperature and stress gradients are considered. It was observed that failure near a severe metal defect or at a defect in the passivation layer can be a major contributor to electromigration-induced lifetime degradation.

TiN thin films have interesting applications in silicon device technology. We show that TiN is a very efficient barrier for silicon diffusion in metallizations to silicon and discuss implications for high-temperature-resistant and reliable contacts to silicon power devices. The barrier height of TiN on n-type silicon was found to be 0.49 V, allowing the fabrication of low barrier Schottky diodes on high resistivity material and good ohmic contacts to low resistivity n- and p-type material. Finally, we present results on the oxidation kinetics of TiN and the preparation of metaloxide- semiconductor capacitors and field effect transistors with TiN as the gate material.

A reduction in the effective barrier height in a PtSi-p-Si Schottky diode was achieved using low energy ion implantation to introduce a shallow p+ layer on a p-Si substrate. After the Schottky diode had been implanted with 3 keV 11B+ ions to a dose of 4 × 1012 ions cm−2, the barrier height was observed to decrease from 0.26 to 0.16eV. The reduction in barrier height correlated well with the boronconcentration found at or near the PtSi-Si interface.

An investigation of the formation of refractory metal (tungsten, molybdenum and tantalum) silicides by reaction of the metal with crystalline and polycrystalline silicon at temperatures above 900°C indicates that WSi2 formation can be inhibited by certain processing techniques. These techniques utilize the growth of an SiO2 diffusion barrier about 20 Å thick on crystalline silicon and the deposition of tungsten films in vacuum ambients that will ensure oxygen incorporation (P ≥ 2 × 10−7 Torr). The reactivity of vacuum-deposited tungsten films results in the formation of an isolating oxide between the deposited silicon and tungsten films and the maintenance of the stability of the SiO2 diffusion barrier between tungsten films and a crystalline silicon substrate. This barrier is effective up to 1050°C in hydrogen ambients containing 15–20 ppm H2O. These procedures, however, are ineffective in preventing the formation of MoSi2 or TaSi2 at or above 900°C. A possible explanation for these results is that the tungsten film contains some level of oxygen due to the gettering of residual oxygen in the vacuum. In addition, the outgassing of the silicon source may enhance the level of oxygen at the evaporated W-Si interface. When the composite layer is annealed at high temperatures in a hydrogen ambient, the oxygen diffuses readily out of the bulk of the tungsten film to the interface, probably forming Sio2 which is more stable than WO3.The resulting thin SiO2 film has sufficient integrity to prevent silicon diffusion into the tungsten, thereby preventing WSi2 formation. This property of tungsten makes it inherently useful for buried-metal films in silicon devices.