Showing papers on "Silicon published in 1971"

Studies of tunnel MOS diodes, I. Interface effects in silicon Schottky diodes

Abstract: A theoretical and experimental study has been made of silicon Schottky diodes in which the metal and semiconductor are separated by a thin interfacial film. A generalized approach is taken towards the interface states which considers their communication with both the metal and the semiconductor. Diodes were fabricated with interfacial films ranging from 8 to 26 A in thickness, and their characteristics are related to this model. The effects of reduced transmission coefficients together with fixed charge in the film are investigated. The interpretation of the current-voltage characteristics and the validity of the C−2-V method in the determination of diffusion potentials are discussed.

Structural model for amorphous silicon and germanium

Abstract: A model for amorphous germanium and silicon has been constructed using the random network concept. Each atom has a first coordination number of four, and only a small variation in the nearest neighbor distance is allowed. Non-crystallinity is due to variations in the tetrahedral bond angle and rotations about bonds. No difficulty was encountered in continuing to make the model larger and no difference in structure between the central and outer regions could be observed. The radial distribution function and the density of the model agree well with recent measurements.

Current transport in metal-semiconductor-metal (MSM) structures

Abstract: The current-voltage characteristics of a metal-semiconductor-metal structure (essentially two metal-semiconductor contacts connected back to back) have been studied based on the thermionic emission theory. When a uniformly doped semiconductor is thin enough that it can be completely depleted before avalanche breakdown occurs, the structure can exhibit many novel transport behaviors. Two outstanding features of the structure are that (1) a wide range of high-level injection of minority carriers can be achieved by varying the barrier heights of the two contacts and (2) the critical voltage at which the minority carrier injection increases rapidly can be varied by varying the semiconductor doping and thickness. Experimental silicon MSM structures of PtSi-Si-PtSi have been made from n-type silicon with doping of 4×1014 cm−3 and thickness of 12 μm. The critical voltage at room temperature is about 30 V. The current increases over five orders of magnitude with only 10 per cent increase of the voltage. The above results and other measurements over wide temperature range do substantiate the theoretical predictions.

Study of Silicon-Silicon Dioxide Structure by Electron Spin Resonance II

Abstract: Three kinds of paramagnetic centers named PA, PB and PC have been found in a silicon-silicon dioxide structure at liquid nitrogen temperature. PA (g=~2.000, ΔH=~4 Oe), and PB having anisotropic g-value (g=~2.000~2.010, ΔH=~6 Oe) are in the exide, while PC which also has anisotropic g-value (g=~2.06~2.07, ΔH=~9 Oe) is in the silicon near the Si-SiO2 interface. Distribution of PB is successfully determined that it has the maximum concentration within about 400A from the interface. PA and PB appear when the silicon is oxidized in dry oxidizing ambient or the Si-SiO2 is cooled from elevated temperatures to room temperature with a cooling speed of about 500°C/sec. PC appears when the Si-SiO2 is heated at elevated temperatures followed by rapid cooling to room temperature or is exposed to the ambient containing an appreciable amount of hydrogen at elevated temperatures such as 1000°C, for 10 min. PB is ascribed to a trivalent silicon \overset\shortmid\underset\shortmid-Si which has a nonbonding orbital electron in the Si-O network. The mechanisms for the various behaviors of the centers are also discussed in detail.

Characterization of Silicon Nitride Films

Abstract: Various "silicon nitride" films have been prepared from , N2, , and in an rf‐promoted glow discharge reaction. These films are described primarily through the use of infrared absorption. Aided by ultraviolet absorption, the inclusion of excess silicon or of oxygen in the films is readily followed. Changes in index of refraction, etch rates in HF acid, and electrical conductivity of the films are correlated with the optical absorption study. Comparisons of these films with those formed by pyrolysis or by reactive sputtering are made. Some reproducible physical properties of an amorphous film are stated.

Low‐temperature migration of silicon in thin layers of gold and platinum

Abstract: The backscattering method is employed to obtain microscopic information about solid‐solid reactions of Si with thin layers (500–2000 A) of both vacuum‐evaporated Au and sputtered Pt. A remarkable observation is the migration of Si atoms into Au and Pt at relatively low temperatures (150 and 350 °C, respectively). Migration of Si in Pt induces first the formation of Pt2Si‐like compounds and then PtSi. In the Au–Si system, on the other hand, Si moves through and accumulates on the Au surface in the form of SiO2 under an oxidizing heat‐treatment atmosphere.

FORMATION OF SiC IN SILICON BY ION IMPLANTATION

Abstract: The production of SiC in single‐crystal silicon by C12+ implantation to fluences of 1017/cm2‐side followed by annealing has been detected by the characteristic infrared absorption of the TO phonon of SiC. Immediately following room‐temperature implantation and after 20‐min isochronal anneals up to temperatures ≤ 825°C, a previously unreported broad absorption band centered at 700–725 cm−1 is observed. SiC is observed to form at temperatures ≈ 850°C. For anneals ≥ 850°C, most of the broad absorption band shifts into the SiC‐TO phonon absorption band. From the infrared absorption measurements together with the results of He+ backscattering, we conclude that about half of the implanted atoms are incorporated into microregions of SiC which are surrounded by bulk silicon.

Ionic Contamination and Transport of Mobile Ions in MOS Structures

Abstract: A fast, simple and very sensitive technique has been developed to determine the extent of ionic contamination of oxides in MOS capacitors. The method is capable of detecting better than 109 mobile ions/cm2 and is based on the measurement of the displacement current response to a slow linear ramp voltage at elevated temperatures. This yields an ionic displacement current peak whose area is proportional to the total mobile ionic space charge. The method is expected to be very useful for routine process and quality control applications. This technique has been used to study positive mobile charge behavior in silicon dioxide. The voltage dependence of the ionic displacement current indicates that trapping of ions occurs at the metal‐oxide interface and that ionic transport from the metal to the silicon interface is controlled by trap emission. Ion transport from the silicon to the metal interface is characterized by a single, bulk‐limited transport mechanism below 300°C with an activation energy that appears concentration dependent. Above 300°C an additional transport mechanism is observed which is slow in comparison to the primary transport mechanism.

Method of fabricating integrated circuits with oxidized isolation and the resulting structure

Abstract: A thin silicon epitaxial layer, formed on a silicon substrate, is subdivided into electrically isolated pockets by a grid of oxidized regions of epitaxial silicon material which extend through the epitaxial layer to a laterally extending PN junction.

Hydrides and Hydroxyls in Thin Silicon Dioxide Films

Abstract: Determinations of the hydroxyl content of anodically and thermally grown silicon dioxide films by internal reflection spectroscopy in the infrared show that hydroxyl and silicon hydride are already incorporated into these films during their formation. The concentration, as well as the distribution, of these compounds within freshly formed anodic and thermal films is given.

High‐Temperature Annealing of Oxidized Silicon Surfaces

Abstract: The densities of fixed charge and trapping centers on thermally oxidized silicon surfaces have been measured by the MOS capacitance technique upon annealing in O2, N2, He, and vacuum at various temperatures from 600° to 1100°C. These surface characteristics are always determined by the conditions of the final high‐temperature process, except for , which will never increase in neutral ambients. In all atmospheres, higher annealing temperatures yield lower values. It was also found that the values are very sensitive toward trace amounts of water in the high‐temperature ambient. They decrease for increasing water vapor pressure. Effects of other impurities were not observed in this study. Based on saturation values and kinetic data a discussion is given of some models for both types of centers.

Silicon-on-Sapphire Epitaxy by Vacuum Sublimation: LEED–Auger Studies and Electronic Properties of the Films

Abstract: Epitaxy of silicon on sapphire was studied by growing films up to 20 μ thick using high-temperature sublimation in 10−10 Torr vacuum on the (1012), (1123), (0001), and (1120) substrate surfaces. The surface structure and chemistry of both substrate and film could be monitored using LEED and Auger electron spectroscopy. The epitaxial relationships and the electrical properties were found to depend on deposit-substrate interactions, substrate temperature, and surface structure. A range of epitaxial temperatures could be defined for each substrate orientation within which the proper surface structure could be maintained during film growth. The behavior outside the epitaxial range was explored, revealing several causes for breakdown of optimum growth. The (1012) substrate was found to have the largest epitaxial temperature range. Silicon films of (100), (111), and, under special circumstances, the (110) orientations could be produced. Films thicker than 2 μ could be grown with essentially bulk values for carrier mobility (carrier concentration between 5×1015 and 8×1018/cm3). Film type (n or p), resistivity, and carrier concentration could be controlled by the choice of proper source material, and were reproducible within a factor of 2. Minority carrier lifetimes were about 10−9 sec; this short lifetime is probably due to the presence of defects, especially within the first micron of growth.

High Temperature Electronics.

Abstract: : The fabrication of a silicon carbide (SiC) junction field effect transistor (J-FET) was shown practicable. Several amplifier designs were breadboarded with silicon devices to study the required parameters. A simplified building block amplifier was constructed and tested. (Author)

Metallurgical properties and electrical characteristics of palladium silicide-silicon contacts

Abstract: The fabrication, metallurgical properties, and electrical characteristics of palladium silicide (Pd 2 Si) contacts to n -type Si have been investigated. Pd 2 Si/Si contacts are similar in electrical and metallurgical behavior to PtSi/Si contacts, but can be fabricated at much lower temperatures. Pd was found to react readily with Si at 200°C to form a silicide phase which was identified as Pd 2 Si from X-ray diffraction analysis. The electrical resistivity of the silicide is 40 × 10 −6 Ω cm as determined from sheet resistivity measurements. The barrier height at the Pd 2 Si/Si interface was determined from differential capacitance measurements to be 0.745±0.015 V. Current-voltage measurements and activation energy analysis gave barrier heights within this same range. Contact resistance measurements were made on contacts to Si surfaces with phosphorus doping levels of 2×10 20 /cm 3 . Resistance values obtained are comparable to both theoretical predictions and measurements reported on PtSi and Al contacts to Si.

Schottky barriers on p-type silicon

Abstract: Measurements have been made of the electrical characteristics of Schottky barriers made by evaporating films of various metals (Al, Pb, Ni, Au, Ag, Cu) onto p-type silicon. The barriers were generally lower than on n-type silicon, and in the case of Au the barrier was so low as to provide an effectively ohmic contact at room temperature. The truly exponential portion of the forward I–V characteristic was restricted to a comparatively small voltage range. Within this range ‘n’ values of about 1.10 were obtained. The reverse characteristics could be explained in terms of generation in the depletion region. The variation of barrier height with metal work-function indicates that the surface-state parameters (density of states and position of neutral level) are essentially the same for p-type as for n-type silicon. This is confirmed by the fact that, for a given metal, the sum of the barrier heights on n-type and p-type silicon is approximately equal to the band-gap.

Gallium Nitride Films

Abstract: The thermal decomposition of a gallium tribromide‐ammonia complex in an ammonia, argon, or nitrogen atmosphere has been used for the deposition of gallium nitride films on silicon and hexagonal silicon carbide substrates in a gas flow system. The substrate temperature and the nature of the ambient are the most important parameters of the deposition process. Adherent and transparent films of gallium nitride have been deposited at substrate temperatures up to about 600°C in an ammonia atmosphere and up to about 750°C in a nitrogen or argon ambient. At higher temperatures, the deposit became contaminated with gallium. The gallium nitride films deposited on {111} oriented silicon substrates at 600°–700°C were found to show a (110) fiber orientation. Epitaxial, single crystalline gallium nitride films have been grown successfully on the basal plane of hexagonal silicon carbide substrates at 520°–600°C. These films are of high resistivity indicating that the thermal decomposition of gallium nitride is negligible. Thus, the thermal decomposition of the gallium tribromide‐ammonia complex provides a new promising technique for the crystal growth of gallium nitride.

Localized conduction processes in amorphous germanium

Abstract: The current-voltage behaviour of amorphous germanium sandwich layers has been investigated in the temperature range 2°K to 79°K. The results obtained, in conjunction with those of Walley (1968) for the range 77°K to 300°K, are discussed in terms of a model for conduction in amorphous germanium. It is also shown that similar processes must be responsible for conduction in amorphous silicon.Following the analyses of Mott (1969) and Hill (1970) it is concluded that conduction in amorphous germanium (and silicon) is by hopping in the temperature range up to 300°K. The carriers are supplied by a large density of acceptor states (1018-1019 cm-3) near to the localized valence band. At low temperatures the current limiting process is field assisted emission from acceptors and this gives rise to power law (I ∝ V8) and exponential (I ∝ exp V½) behaviour in the current-voltage characteristics. Transport between the acceptors is via states in the localized part of the valence band. At higher temperatures the limiting...

Precipitation in high purity silicon single crystals.

Abstract: Precipitation in high‐purity Lopex (low‐oxygen dislocation‐free) silicon has been examined by x‐ray diffraction topography and transmission electron microscopy. It has been found that the impurity concentration in the as‐grown silicon crystals is sufficient to cause precipitation of a second phase if the specimens are annealed in the temperature range 700–1000°C, followed by a critical cooling rate. The precipitating phase has been tentatively identified as α Fe3Si. The precipitates appear in colonies. Each colony has a three‐dimensional starlike configuration, where the different arms are planar arrangements of precipitates enveloped by a dislocation loop. The precipitates have a blocky shape and the dislocation loops are of interstitial edge type and both 12−a 〈110〉 and a 〈100〉 Burgers vectors are involved. The nucleation of colonies is heterogeneous and the presence of small silica particles as nucleation centers is suggested.

Arsenic Clustering in Silicon

Abstract: Large decreases in the conductivity of arsenic‐doped silicon have been observed during 500–970°C heat treatments. The rate of conductivity change depends upon the prior quenching rate from diffusion temperature to room temperature. These conductivity changes are reversed by higher‐temperature treatments. The relationship between the electrically active arsenic, as calculated from the conductivity, and the total arsenic is shown to be consistent with a model of substitutional arsenic atoms being nonionized when in a cluster or in a complex involving one or more vacancies.

Carbide Contamination of Silicon Surfaces

Abstract: The techniques of grazing angle reflection high‐energy electron diffraction (RHEED), mass spectroscopy, and electron microscopy have been used to study carbide contamination of silicon samples heated in ultra‐high vacuum. The RHEED data showed that the surfaces of silicon crystals heated between 800°–1000°C were covered with β‐SiC crystallites well oriented with respect to the substrate. Heating between 1000°–1100°C formed a nonoriented β‐SiC phase, and further heating above 1100°C removed the surface carbide. CO and CO2 evolution was observed when samples were heated above 800°C. The carbide reappears with heating to 800°C if the carbide free surface is exposed to atmosphere or left in the vacuum environment for a sufficient time. Electron micrographs of platinum‐shadowed carbon replicas from samples contaminated with β‐SiC indicated that the carbide existed within protuberances at the surface. Data from samples heated to 950° and 1050°C showed particles ∼400 A in size, of cylindical shape and tapering towards the top; the surface density of the protuberances was observed to vary from 2×107 to 6×109/cm2. In all cases of carbide formation, the carbide results from the chemical reaction of a carbon‐containing adsorbate with the silicon surface. Although a gaseous origin for an adsorbate has been demonstrated, additional adsorption probably also results from chemical cleaning of the sample. Surface steps on the silicon are correlated with the presence of β‐SiC protuberances (or other artifacts) and appear to have been pinned by these particles.