Showing papers on "Silicon published in 1975"

The electrical properties of polycrystalline silicon films

Abstract: Boron doses of 1×1012–5×1015/cm2 were implanted at 60 keV into 1‐μm‐thick polysilicon films. After annealing at 1100 °C for 30 min, Hall and resistivity measurements were made over a temperature range −50–250 °C. It was found that as a function of doping concentration, the Hall mobility showed a minimum at about 2×1018/cm3 doping. The electrical activation energy was found to be about half the energy gap value of single‐crystalline silicon for lightly doped samples and decreased to less than 0.025 eV at a doping of 1×1019/cm3. The carrier concentration was very small at doping levels below 5×1017/cm3 and increased rapidly as the doping concentration was increased. At 1×1019/cm3 doping, the carrier concentration was about 90% of the doping concentration. A grain‐boundary model including the trapping states was proposed. Carrier concentration and mobility as a function of doping concentration and the mobility and resistivity as a function of temperature were calculated from the model. The theoretical and ex...

Picosecond optoelectronic switching and gating in silicon

Abstract: Quasimetallic photoconductivity produced by the absorption of picosecond optical pulses in silicon transmission line structures has been used to devise electronic switches and gates which can be turned on and off in a few picoseconds. Electrical signals as large as 100 V can be switched by a few microjoules of optical energy. The switching speed was measured by correlating the response of two transmission gates in tandem, each having an aperture time of 15 psec.

States in the gap and recombination in amorphous semiconductors

Abstract: The paper examines states in the gap in amorphous silicon and chalcogenides and their effect on photoconductivity, luminescence and drift mobility. It is supposed that carriers in an ‘ideal’ glassy semiconductor without defects would move by hopping at the band edge at low temperatures and by excitation to a mobility edge at high temperatures, and that the carriers do not form polarons; the results of Spear and co-workers (e.g. Spear 1974 a) for glow-discharge-deposited silicon and of Nagels, Callearts and Denayer (1974) for quenched As2Te3 containing silicon are considered. The effectively zero value of the Hall coefficient in the hopping regime is discussed. States in the gap are supposed to be due to dangling bonds which may form pairs at divacancies; if the concentration is high, these may have a predominating effect on the conductivity and in this case polaron-type hopping could occur, both for chalcogenides and for silicon. For the chalcogenides (in contrast to silicon), it is proposed, ada...

Electron mean escape depths from x−ray photoelectron spectra of thermally oxidized silicon dioxide films on silicon

Abstract: The mean escape depths of Si 1s, Si 2p, and O 1s photoelectrons from silicon−silicon dioxide structures were determined over a wide kinetic−energy range with magnesium, aluminum, and chromium x−ray sources. Variations in photoelectron line intensity were measured as a function of oxide film thickness. Film thicknesses were determined from ellipsometric data assuming an index of refraction of 1.47 for the oxide. Discrepancies in fitting intensity data to an escape−depth curve for films <20−A thick are associated with nonstoichiometry of the oxide film near the interface. The incompletely oxidized interfacial region is identified by variations in linewidth and in binding energies of the spectral lines as well as by the deviations from predicted intensity data.

Defects in irradiated silicon: EPR and electron-nuclear double resonance of interstitial boron

Abstract: An EPR spectrum, labeled Si-$G28$, is identified as arising from neutral interstitial boron in silicon. It is produced by 1.5-MeV electron irradiation at 20.4\ifmmode^\circ\else\textdegree\fi{}K, presumably when a substitutional boron atom traps a mobile interstitial silicon atom which is produced in the original damage event. Three possible models are discussed which are consistent with the EPR and electron-nuclear double-resonance results: (a) a bent Si-B-Si bonded interstitialcy; (b) a similar Si-Si-B interstitialcy; or (c) a Jahn-Teller distortion of the boron from the hexagonal interstitial site in the silicon lattice. Uniaxial stress in the presence of light at low temperatures produces alignment in one of the distortional degrees of freedom for the defect. This is interpreted as stress alteration of the capture matrix elements for electrons into the differently distorted configurations. Polarized light is also found to produce alignment in the absence of stress into a second degree of freedom for the defect. Thermally activated recovery from this alignment reveals an activation energy for reorientation of 0.6 eV. Interstitial boron is unstable at room temperature, disappearing in \ensuremath{\sim} 30 min with an activation energy also of \ensuremath{\sim} 0.6 eV. It is suggested that annealing may result from long-range migration of the interstitial boron with the one-jump diffusional process being identical to the 0.6-eV reorientational process. This is a natural consequence of models (a) or (c). The reorientation stimulated by light at 4.2\ifmmode^\circ\else\textdegree\fi{}K, therefore, indicates that athermal migration may be induced by the light. An attempt to test this using 1.06-\ensuremath{\mu}m YAIG:Nd laser illumination was inconclusive.

Heavy‐ion sputtering yields of gold: Further evidence of nonlinear effects

Abstract: The sputtering yield of vacuum‐deposited gold targets has been measured with 18 different 45‐keV ions throughout the periodic system. The results are compared with previously reported results obtained with copper, silicon, and silver targets and with the predictions of the Sigmund theory. The variation in the yield with projectile atomic number is found to be consistent with theory although rather large deviations are found for both heavy and light projectiles. The large experimental yields for heavy projectiles as well as the maximum in the energy dependence of the yield, which is more pronounced than predicted by theory, are explained by nonlinear effects in very dense collision cascades. This interpretation is supported by data obtained from irradiation with atomic and molecular ions of the same elements. The deviations for light projectiles are considered mainly to be due to the lack of a surface correction term in the theory.

Formation and Properties of Porous Silicon and Its Application

Abstract: Preparation, properties, and applications of porous silicon film were investigated. Silicon single crystal is converted into porous silicon film by anodization in concentrated hydrofluoric acid at currents below the critical current density. When an n‐type silicon was anodized, the silicon surface was illuminated to generate holes which were necessary for this anodic reaction. The growth rate of the film, from n‐type silicon, was larger than that from p‐type silicon in this experimental condition. The crystalline structure was the same as that of silicon single crystal. A new isolation technique for bipolar integrated circuits was proposed by making use of the properties of the film such that it can be formed several microns thick and oxidized easily to form an insulator. The main feature of the technique is that it provides a means to form thick insulating film inlaid through the n‐type epitaxial layer without prolonged heat‐treatment. A preliminary experiment was carried out to test the practical usage of the technique.

On etching very narrow grooves in silicon

Abstract: The etch rate on the {110} is shown to be at least 400 times faster than that on the {111} using 44% KOH : H2O at a temperature of 85 °C and below. A model is presented which attributes essentially all the etching on the near {111} planes to the misorientation ledges. Grooves of 0.6−μm width and 44−μm depth have been produced. Such grooves have been used to make high−value SiO2 capacitors and vertical multijunction solar cells.

Silicon nitride trap properties as revealed by charge−centroid measurements on MNOS devices

Abstract: Previous charge−centroid studies of MNOS devices have shown that electrons injected into the insulator structure from the silicon are trapped not solely at the dielectric interface, but can be distributed over nearly the entire nitride thickness. In this paper, results of charge−centroid measurements on thin−oxide MNOS devices are interpreted with a charge trapping model, leading to values for the nitride trap density, capture cross section, and average trapping distance of 6×1018/cm3, 5×10−13 cm2, and 35 A, respectively.

Laser photoelectron spectrometry of the negative ions of silicon and its hydrides

Abstract: Fixed−frequency laser photoelectron spectrometry has been utilized to study the ions Si−, SiH−, and SiH−2. In each case, the photodetached electron energy spectrum consists primarily of sharp, easily assignable peaks. The electron affinities of Si, SiH, and SiH2 have been determined to be (1.385±0.005) eV, (1.277±0.009) eV, and (1.124±0.020) eV, respectively. Two bound excited states attributed to 2D and 2P terms have been observed for Si−, and their binding energies determined. Similarly, two bound excited states, assigned to 1Δ and 1Σ+ symmetry, have been discovered in SiH−. The internuclear distance re in the ground state of SiH− has been determined by a Franck−Condon factor analysis to be (1.474±0.004) A. In addition, spectroscopic constants of the excited states have been deduced. Transitions from the ground state of SiH− to both the 1A1 and 3B1 states of SiH2 have been observed; unlike the case of CH2, the 1A1 state is the lower in energy.

Thermal Oxidation of Silicon In Situ Measurement of the Growth Rate Using Ellipsometry

Abstract: The formation of oxide films on resistively heated silicon in dry oxygen was followed in situ using a computer controlled ellipsometer. For (111) silicon surfaces two distinct growth regions were observed. Our results on the growth above 300A were found to agree with previous investigations. For films 200A or less (for which little previous data exist) the kinetics did not obey any existing model of the growth process. The rate of growth of the oxide on (111) surfaces in the 20–200A region was investigated from 700° to 950°C and at oxygen pressures between 50 and 1200 Torr. A possible explanation of the thin film kinetics is given and its relation to the thick film data is discussed.

Accurate lattice constants from multiple reflection measurements. II. Lattice constants of germanium silicon, and diamond

Abstract: The lattice constants of a diamond platelet and of large single, undoped, crystals of silicon and germanium have been determined from measurements of multiple diffraction patterns by the method described in Part I [Post (1975). J. Appl. Cryst. 8, 452–456]. The mean values, based on measurements of eight to twelve reflections, and their standard deviations are: diamond a = 3.566986 A, Aa/a = 2.6 × 10−6; silicon a = 5.430941 A, Aa/a = 2 × 10−6; germanium a = 5.657820 A, Δa/a = 1.6 × 10−6.

The role of the interfacial layer in metal−semiconductor solar cells

Abstract: Recent work has been reported on metal−semiconductor (Schottky barrier) solar cells in which efficiencies comparable to silicon p−n devices have been achieved. In these devices, the interfacial layer is believed to play an important role. In this discussion the nature of that role is examined. It is shown that the interfacial layer can enhance performance, and an outline for optimizing that enhancement is presented. The results are presented assuming n−type semiconductor material; however, the conclusions are equally valid for structures using p−type material.

Chemisorption of atomic hydrogen on the silicon (111) 7 × 7 surface

Abstract: The chemisorption of atomic hydrogen on the silicon (111) 7 \ifmmode\times\else\texttimes\fi{} 7 surface has been studied using ionneutralization spectroscopy and ultraviolet-photoemission spectroscopy with the help of low-energy electron diffraction and work-function measurement. Both spectroscopies showed that the dangling-bond surface state disappears when the clean surface is exposed to atomic hydrogen. Chemisorbed hydrogen produces two sharp peaks in the surface density of states at approximately -10 and -12 eV from the vacuum level. These results are in good quantitative agreement with the recent theoretical works by Appelbaum and Hamann and by Pandey.

Anomalous temperature effect of oxidation stacking faults in silicon

Abstract: We observed an anomalous temperature effect in the growth of oxidation stacking faults in silicon. For a given oxidation time, the size of stacking faults first increases with temperature following an Arrhenius relation, reaches a peak at some temperature, and then decreases with temperature rather sharply until, finally, the faults totally vanish. The temperature above which the oxidation stacking faults vanish is dependent on the crystal surface orientation as well as on the oxidation ambients. In dry oxygen, this temperature is ∼1240 °C for {100} surfaces, ∼1220 °C for {111} surfaces, and ∼1175 °C for {1,0,11} surfaces (5° off {100}). Thus, the size‐versus‐temperature curve of the growth of oxidation stacking faults can be divided into two regions, which may be called the growth and the retrogrowth regions. In the growth region the growth follows a power law of (size) ∝ (time)0.8; in the retrogrowth region, the power law breaks down. The activation energy in the growth region is 2.3 eV for all surface orientations and oxidation ambients. A more complete picture of the growth of stacking faults emerges, in which the reported ’’immunity to stacking faults’’ of certain vicinal {100} surfaces is merely a point far out in the retrogrowth region.

The chemical polishing of semiconductors

Abstract: The review first considers the types of reaction which occur when a semiconductor is chemically polished, taking the dissolution of silicon in nitric acid solutions as an example. Most initial reactions are of the oxidation-reduction type, which can be separated into their anodic and cathodic components. It is shown that electrons and holes can take part in both parts of the reaction, so chemical polishing can interfere with the carrier concentrations close to the surface being polished. In general, the products of the initial reaction are not soluble, so it is necessary to include a component in the polishing solution which will react to give soluble material, which can then be removed from the surface. The factors controlling the dissolution rate are then outlined. It is shown that polishing processes are conveniently divided into two main groups: (1) those for which the rate-limiting process is some aspect of the chemical reaction, and (2) those for which diffusion of atoms to or from the surface controls the rate. Crystallographic effects are discussed. It is shown that different surface orientations are etched at different rates, and possible reasons for this are outlined. The various types of surface features that can be observed under the microscope after polishing are then described, and their origins are discussed. A review of some of the more extensive investigations is then given, followed by an Appendix containing lists of chemical polishes that have been used for semiconductors of groups IV, III–V and II–VI.

Direct comparison of ion−damage gettering and phosphorus−diffusion gettering of Au in Si

Abstract: The residual disorder caused by different implanted ions after annealing at elevated temperatures (850−1150 °C) is dependent upon the ion species. The gettering of Au by damaged layers produced by Ar, O, P, Si, As, and B has been quantitatively compared to gettering by phosphorus diffusion. Each individual comparison was made between opposite surfaces of a Si sample by use of Rutherford backscattering. The damage disorder was quantitatively measured by backscattering and structurally studied using electron microscopy. Typically, an ion dose of 1016/cm2 and ion energy of 200 keV were used for implantations. The Au was present in the Si at ’’moderate’’ levels so that solubility in the phosphorus diffused layers was not exceeded. Ar ion−damaged layers were more effective for gettering Au than were phosphorus−diffused layers below ∼1000 °C and equally effective up to 1150 °C. The relative gettering efficiency of the damage produced by other ions studied was less than that of phosphorus diffusion at 1000 °C and was ranked in the order Ar≳O≳P≳Si≳As≳B. In general, the relative gettering efficiency of ion−damaged layers was related to the amount and type disorder after annealing. The initial disorder was of an amorphous nature for 1016 heavy ions/cm2 (As, Si, P, Ar, or O), and the final disorder state was different for different implanted ions after annealing. It is suggested that the disorder (and gettering efficiency) was influenced by size effects of the implanted ion during annealing.

Solar wind heavy ion abundances

Abstract: During periods in 1969–1971 when interplanetary flow conditions were quiet, 17 determinations of the solar wind Fe and Si abundances and 7 of the O abundance were made. On the average 〈N(Fe)/N(H)〉 = 5.3 × 10-5, 〈N(Si)/N(H)〉 = 7.6 × 10-5 and 〈N(O)/N(H)〉 = 5.2 × 10-4. Variations from the averages over a total range of factors of ∼4 for O, ∼4 for Si, and ∼ 10 for Fe have have observed. Although Fe and Si abundance variations appear to be correlated, no other element correlation pairs are unambiguously discernible from the present data set.

Optimization of the Hydrazine‐Water Solution for Anisotropic Etching of Silicon in Integrated Circuit Technology

Abstract: Anisotropic etching of silicon with the hydrazine‐water mixture is studied and characterized for its practical use in integrated circuit technology. The solution is applied to {100} wafers where the etch presents a v‐shaped cross section limited at the side‐walls by {111} planes and at the bottom by a {100} plane. The etching process is evaluated in terms of the etch rate of the {100} plane, quality of side‐walls and bottom surface, and corner rounding. It is shown that the results are both concentration and temperature dependent. The optimal temperature for the etching process is found to be 100°C for both simple temperature control and high quality etching. It is also shown that the optimal mixture concentration must be choesn according to the particular use of the anisotropic etching. The optimal volume concentrations of hydrazine for the various applications are: 65% for VMOS devices and for v‐groove isolation rings, 70–80% for two‐level structures with flat bottom surface, and for electrode and sensor fabrication.

Surface states from photoemission threshold measurements on a clean, cleaved, Si (111) surface

Abstract: Very accurate measurements of the photoemission yield were performed on the (111) face of Si as a function of photon energy in the threshold region down to the 10/sup -10/ range. By using a set of differently doped samples cleaved in ultrahigh vacuum, one can distinguish between surface- and bulk-state photoelectrons. (WDM)