Showing papers on "Silicon published in 1978"

Anisotropic etching of silicon

Abstract: Anisotropic etching of silicon has become an important technology in silicon semiconductor processing during the past ten years. It will continue to gain stature and acceptance as standard processing technology in the next few years. Anisotropic etching of

C.M.O.S. devices fabricated on buried SiO2 layers formed by oxygen implantation into silicon

Abstract: Buried SiO2, layers were formed by oxygen-ion (14O+) implantation into silicon. The impurity distribution of the oxygen-implanted silicon substrate was analysed by auger spectroscopy. The epitaxially-grown silicon layer on this substrate showed a good monocrystalline structure, and a 19-stage c.m.o.s. ring oscillator exhibited high performance in operation.

Plasma etching of Si and SiO2—The effect of oxygen additions to CF4 plasmas

Abstract: The plasma etching of silicon and silicon dioxide in CF4‐O2 mixtures has been studied as a function of feed‐gas composition in a 13.56‐MHz plasmagenerated in a radial‐flow reactor at 200 W and 0.35 Torr. Conversion of CF4 to stable products (CO, CO2, COF2, and SiF4) and the concentration of free F atoms ([F]) in the plasma were measured using a number of different diagnostics. The rate of etching, the concentration of F atoms, and the intensity of emission from electronically excited F atoms (3s 2 P–3p 2 P° transition at 703.7 nm) each exhibit a maximum value as a function of feed‐gas composition ([O2]); these respective maxima occur at distinct oxygen concentrations. For SiO2, the variation in etching rate with [O2] is accounted for by a proportional variation in [F], the active etchant. The etching of silicon also occurs by a reaction with F atoms, but oxygen competes with F for active surface sites. A quantitative model which takes oxygen adsorption into account is used to relate the etch rate to [F]. The initial increase of [F] with [O2] is accounted for by a sequence of reactions initiating with the production of CF3 radicals by electron impact and followed by a reaction of CF3 with oxygen. When [O2] exceeds ∼23% (under the present discharge conditions), [F] decreases due, probably, to a decrease in electron energy with an increase of oxygen in the feed gas.

α ′-Sialon ceramics

Abstract: OUR previous report1 on Si–Al–O–N ceramics stated that expanded α-silicon ‘nitride’ structures had been obtained by reaction of lithium–silicon nitride, LiSi2N3, with alumina. The unit-cell dimensions of one example (a, 7.822; c, 5.677A) gave a cell volume about 3% greater than that of α-silicon nitride. Subsequent work2 showed a variation in dimensions for the α′-lithium sialon when lithium aluminate, LiAlO2, was reacted in different proportions with Si3N4. However, other phases, such as β′-sialon and nitrogen–eucryptite, were always present and the product never contained more than ∼30% of the α′ material. αν-Sialons were also found in the Mg–Si–Al–O–N system3 but again never pure, and were observed by Masaki et al.4 during the nitriding of silicon with A1N and A12O3 additions. A recent claim by Mitomo5 of α′ solid solutions of Si3N4–Al2O3 and/or Si3N4–Y2O3 occurring during the sintering of Si3N4 at 1,700–1,800 °C with Al2O3–Y2O3 mixtures prompted this report of the preparation and characterisation of pure α′-phases in M–Si–Al–O–N systems where M is Li, Ca or Y. Such phases also occur, but have not so far been prepared in a pure form, in magnesium and other sialon systems.

Time‐resolved reflectivity of ion‐implanted silicon during laser annealing

Abstract: The time‐resolved reflectivity at 0.63 μm from arsenic‐implanted silicon crystals has been measured during annealing by a 1.06‐μm laser pulse of 50‐ns duration. The reflectivity was observed to change abruptly to the value consistent with liquid silicon and to remain at that value for a period of time which ranged from a few tens of nanoseconds to several hundreds of nanoseconds, depending on the annealing pulse intensity. Concurrently, the transmission of the primary annealing beam dropped abruptly. These observations confirm the formation of a metallic liquid phase at the crystal surface during the annealing process.

Crystalline to amorphous transformation in ion-implanted silicon: a composite model

Abstract: The transformation of silicon to the amorphous state by implanted ions was studied both experimentally and theoretically. Experimentally, the amount of transformed silicon and the critical ion dose necessary to amorphize the entire implanted layer were determined by ESR. How the critical dose varies with ion mass (Li, N, Ne, Ar, and Kr), ion energy (20–180 keV), and implant temperature (77–475 K) was determined. Theoretically, several phenomenological models were used to analyze these data. The overlap‐damage model was used to determine the critical dose from the data, the size of the amorphous region around the ion track, and the degree of overlap damage required for amorphization. For all implants, the first ion created only predamage, while the second or third ion into the same region caused the amorphous transformation. The critical‐energy‐density model was in good agreement with the measured critical doses. This model assumed that a region would become amorphous if the energy density deposited into atomic processes by the ions exceeded the critical energy density of 6×1023 eV/cm3. For high‐temperature implantations, out‐diffusion models can explain the temperature dependence of the critical dose. Although the analysis is not completely definitive, the critical‐energy‐density model may also be valid at high temperature if diffusion of the damage energy is taken into account. This out‐diffusion of energy from around the ion track occurs via a thermally activated process. Probably, the energy moves with the out‐diffusion of the vacancies from the ion track.

Luminescence studies of plasma-deposited hydrogenated silicon

Abstract: The photoluminescence of plasma-deposited amorphous silicon is investigated. The luminescence intensity and spectral line shape are shown to be sensitive to many deposition variables, in particular the power coupled into the discharge, the concentration of silane in the gas stream, and the deposition substrate temperature. Maximum intensity is obtained in samples deposited with low power (\ensuremath{\sim}1 W), a silane concentration of \ensuremath{\gtrsim} 10% and a deposition temperature of 200-300\ifmmode^\circ\else\textdegree\fi{}C. ESR studies show that the luminescence intensity is determined by competing nonradiative transitions to localized defect states whose density varies with deposition conditions. The presence of defect states is related to the way hydrogen is incorporated into the samples, but the details of the defect structure are not yet clear. Oxygen impurities are observed to give a broad, weak luminescence peak centered near 1.1 eV. It is suggested that the active oxygen centers are similar to the charged defects postulated for chalcogenide glasses.

A SIMS analysis of deuterium diffusion in hydrogenated amorphous silicon

Abstract: Secondary ion mass spectroscopy (SIMS) has been used to measure the diffusion of deuterium in hydrogenated amorphous silicon. For a film deposited in a dc glow discharge in SiH4 at a substrate temperature of 315 °C, the diffusion data fits D (T) =1.17×10−2 exp(−1.53 eV/kT) cm2/s. This result implies that degradation of these films due to hydrogen out‐diffusion at 100 °C will not be significant until after more than 104 years.

Explanation of the large spin-dependent recombination effect in semiconductors

Abstract: Previous theories to explain the variation of photoconductivity upon saturation of electron spin resonance, as observed by Lepine in silicon, predict an effect 10 to 100 times smaller than experiment. In the present model we show that, due to the shorter lifetime of electron-hole pairs in singlet configuration, the steady state spin distribution shows a surplus of triplet pairs. Saturation of resonance restores the random distribution, resulting in a shortening of the recombination time. The relative variation can be as large as 10 %, and is field independent as confirmed by experiment.

Grain Growth Mechanism of Heavily Phosphorus‐Implanted Polycrystalline Silicon

Abstract: Grain growth phenomena of heavily phosphorus‐implanted polycrystalline silicon films owing to high temperature annealing are investigated by transmission electron microscope. Phosphorus doping in excess of is found to enhance grain growth. This growth is broken down into primary and secondary recrystallization. Isochronal annealing reveals the activation energies for these as 2.4 and 1.0 eV, respectively. The driving force of the primary recrystallization is found to be the interface energy. Therefore, the elementary process behind the primary recrystallization is attributed to silicon diffusion across the grain boundary region.

Effect of silicon on manganese tolerance of bean plants ( Phaseolus vulgaris L.)

Abstract: The effect of silicon on manganese tolerance of bean plants (Phaseolus vulgaris L var ‘Red Kidney’) grown in water culture was studied at different levels of manganese supply Without silicon, growth depression and toxicity symptoms occurred already at 5 × 10−4 mM Mn in the nutrient solution After addition of Aerosil (075 ppm Si), the plants tolerated 5 × 10−3 mM Mn and, at a higher silicon supply of 40 ppm, as much as 10−2 mM Mn in the nutrient solution without any growth depression This increase in manganese tolerance was not caused by a depressing effect of silicon on uptake or translocation of manganese but rather by an increase in the manganese tolerance of the leaf tissue In absence of silicon, 100 ppm Mn was already toxic for the leaf tissue, whereas with a supply of 40 ppm Si, this ‘critical level’ in the leaves was increased to more than 1000 ppm Mn At lower manganese levels in the leaf tissue, a molar ratio Si/Mn of 6 within the tissue was sufficient to prevent manganese toxicity Above 1000 ppm Mn, however, even a much wider Si/Mn ratio (> 20) could not prevent growth depression by manganese toxicity With54Mn and autoradiographic studies, it could be demonstrated that, in absence of silicon, even at optimal manganese supply (10−4 mM), the distribution of manganese within the leaf blades was inhomogeneous and characterized by spot-like accumulations In presence of silicon, however, the manganese distribution was homogeneous in the lower concentration range of manganese and still fairly homogeneous in the high concentration range This effect of silicon on manganese distribution on the tissue level was also reflected on the cellular level In the presence of silicon, a higher proportion of the leaf manganese could be found in the press sap,ie, had been transported into the vacuoles, than in the absence of silicon The increase in manganese tolerance of bean leaves by silicon therefore seems to be primarily caused by the prevention of local manganese accumulation within the leaf tissue which leads to local disorders of the metabolism and, correspondingly, growth depression

Laser annealing of boron-implanted silicon

Abstract: The properties of boron‐implanted silicon annealed by high‐power Q‐switched ruby laser radiation are compared with results obtained by conventional thermal annealing. Laser annealing of the implanted layer results in significantly increased electrical activity, as compared to thermally annealed implanted silicon. This correlates well with transmission electron microscopy and ion‐channeling measurements which show a dramatic removal of displacement damage as a result of laser annealing. A substantial redistribution of the implanted boron concentration profile occurs after laser annealing which cannot be explained by thermal diffusion in the solid.

Free carrier absorption in silicon

Abstract: Free carrier absorption in heavily doped layers reduces the useful photon flux in the photoconductive region of extrinsic Si infrared detectors. A simple theory is developed which predicts the transmissivity of such layers as a function of their sheet resistance and the wavelength of the radiation. Experimental data over the 2.5-20 µm wavelength and 5-500 Ω/square sheet resistance range are given for both diffused and ion-implanted layers and also for polysilicon gases. The temperature dependence of both transmissivity and sheet resistance is investigated from 20 to 300 K.

Method of manufacturing a semiconductor device

Abstract: PHN 9829 7 An undoped polycrystalline silicon layer is provided on an electrically insulating layer at the surface of a semiconductor body and a metal layer, for example of molybdenum, is provided on the silicon layer. After heating to convert part of the silicon layer into a metal silicide layer a dopant, for example phosphorus, is introduced into the polycrystalline layer through the silicide layer. This method can be used to make an insulated gate field effect device where the gate comprises a double layer structure of metal silicide on polycrystalline silicon.

Self-Consistent Green's-Function Calculation of the Ideal Si Vacancy

Abstract: We have developed a method for solving the Green's-function equations describing an isolated localized defect in an otherwise perfect crystal. It yields a charge density in sufficinet detail to allow recalculation of the potential and iteration to self-consistency. The method is applied to the ideal (unrelaxed) vacancy in silicon, in the ionic-pseudopotential, local-exchange-correlation approximation.

Reactive Plasma Deposited Si‐N Films for MOS‐LSI Passivation

Abstract: Amorphous Si‐N films have been synthesized from and by reactive plasma deposition at 275°C in an improved radial flow reactor. With appropriate control of machine and process variables, films have been made with Si/N ratio of 0.75–1.5, density of 2.8‐2.2g cm−3, refractive index of 1.9–2.3, stress of compressive to tensile, and electrical resistivity at of 1020‐104 Ω‐cm. The process is MOS compatible and it produces relatively thick (1 μm) crack‐resistant Si‐N films (at 450°–500°C) having excellent step coverage and good adhesion to both Au and Al metallization. This paper describes the deposition technique, effect of deposition parameters on various film properties, and the advantages these films offer in silicon integrated circuit technology.

The crystal structure of η-Cu3Si precipitates in silicon

Abstract: The crystal structure of Cu-Si precipitates in silicon has been studied by means of transmission electron diffraction and microscopy. The precipitates are shown to be of the equilibrium Cu3Si phase, probably of the low-temperature η” form. Consistent with earlier X-ray diffraction data for this phase, the crystal structure of the precipitates is determined to be based on a trigonally distorted b.c.c. arrangement. The lattice is orthorhombic (C), and is a two-dimensional long-period superlattice, which it is suggested is based on the intermediate-temperature η' phase; lattice parameters aη” = 76.76, bη” = 7.00, cη” = 21.94 A. On the basis of the diffraction data for the precipitates, it is suggested that the ηand η' phases are both trigonal, space groups R{\bar 3}m and R{\bar 3} respectively, with lattice parameters aη = 2.47 A, αη = 109.74° and aη' = 4.72 A, αη' = 95.72°.

Structure and Stability of Low Pressure Chemically Vapor‐Deposited Silicon Films

Abstract: The structure of silicon films deposited by low pressure, chemical vapor deposition in the 600°C temperature range has been investigated by x‐ray diffraction and transmission electron microscopy. There is a critical temperature near 600°C, above which the deposited films are polycrystalline and below which amorphous films are obtained. This temperature is close to that used to deposit films for integrated circuit applications. When the films are polycrystalline, the texture dominates. The polycrystalline films are reasonably stable upon annealing to temperatures up to approximately 1100°C. The initially amorphous films, however, easily crystallize. Crystallization has been observed to be well advanced after annealing at 800°C. Large stresses are built into the amorphous films, while the stresses in the polycrystalline films are lower.

Free Carrier Absorption in Silicon

Abstract: Free carrier absorption in heavily doped layers reduces the useful photon flux in the photoconductive region of extrinsic Si infrared detectors. A simple theory is developed which predicts the transmissivity of such layers as a function of their sheet resistance and the wavelength of the radiation. Experimental data over the 2.5-20 /spl mu/m wavelength and 5-500 Omega/square sheet resistance range are given for both diffused and ion-implanted layers and also for polysilicon gates. The temperature dependence of both transmissivity and sheet resistance is investigated from 20 to 300 K.

Interactions of ion beams with surfaces. Reactions of nitrogen with silicon and its oxides

Abstract: Ion beam studies of chemical reactions between nitrogen and surfaces of silicon and its oxides are reported. A spectrometer system designed for these studies which combines the techniques of x‐ray and uv photoelectron spectroscopy, Auger electron spectroscopy, secondary ion mass spectroscopy, low energy electron diffraction, and ion bombardment is described. This work employs XPS and UPS to examine the products induced by 500 eV N+2 beams on targets of elemental Si, SiO, and SiO2. The N+2 ions undergo charge exchange and dissociation at the surface of the target to form hot N atoms. Reaction with Si, produces nitrides which are similar to those of the type Si3N4. Reaction with SiO and SiO2 forms nitrides, with no evidence of nitrate or nitrite formation. The chemical nature of the reaction is suggested by identification of the reaction products through XPS and UPS and energy level shifts. The thickness of the silicon nitride layer on Si(111) formed by 500 eV N+2 bombardment has been determined to be ∼19 A thick by using the film/bulk Si XPS intensity ratio. Estimates obtained by depth‐concentration profiling with 1 keV Ar+ and by using LSS projected ion range calculations agree with this approximate thickness.

Hydrogen bonding in silicon-hydrogen alloys

Abstract: Infra-red and Raman spectra have been obtained from thin films of silicon-hydrogen and silicon-hydrogen-deuterium alloys deposited from low pressure, r.f. excited plasmas in mixtures of SiH4/Ar and SiH4/D2/Ar respectively. The spectra are analysed using a valence-force-field model based on effective force constants determined from SiH4. For alloys deposited onto substrates held at 25°C it is concluded that the structure is best described as a pseudobinary alloy of the form (Si)x(Si2H4)1_ x . In contrast, for material deposited on to a substrate at a temperature T s⩾250°C, the hydrogen is incorporated onto Si-sites containing predominantlv one H-atom.

Photo‐induced vibrational predissociation of the van der Waals molecule (N2O)2

Abstract: An apparatus is described in which a supersonic beam of nitrous oxide in helium impinges upon a 2 °K silicon bolometer, or alternatively, is detected by a mass spectrometer. Laser excitation of the beam in the vicinity of ν3 of nitrous oxide decreases the flux of the van der Waal’s molecule (N2O)2 reaching the bolometer. Thus, excitation of ν3 is followed by vibrational predissociation of the van der Waal’s bond.

Physical and electrical properties of laser‐annealed ion‐implanted silicon

Abstract: The use of a laser as a tool for annealing of ion‐implantation damage is described. The principal results obtained are as follows: (1) electrical measurements show that activity comparable to that of a 1000 °C 30‐min anneal can be obtained; (2) TEM measurements show that complete recrystallization of the damaged layer occurs during the laser anneal; (3) impurity profiles obtained from SIMS measurments show that the dopant atoms remain in the LSS profile during annealing. Simple diodes were fabricated to examine the feasibility of the method for device fabrication.

Spatially controlled crystal regrowth of ion‐implanted silicon by laser irradiation

Abstract: We demonstrate the unique capability of a repetitively pulsed laser to ’’write’’ a monocrystalline pattern in ion‐implanted amorphous silicon layers. Ion‐channeling data, from the samples scanned with a focused beam of a Q‐switched Nd : YAG laser, show a continuity of the single‐crystal layer produced with spatially overlapping laser pulses, at 60–80 MW cm−2. Scattering yields indicate very high substitutionality of the implanted ions and an interdependence between the laser power density and the depth redistribution of the implants. Finally, similar recrystallization was obtained with a CO2 laser at 10.6 μm.

Hot-electron emission from silicon into silicon dioxide

Abstract: Recent progress in the study of hot-electron emission from silicon into silicon dioxide is discussed. Experimental techniques include avalanche injection using gated diodes and MOS capacitors, nonavalanche injection using IGFET structures with an underlying supply p - n junction, and optically induced injection using silicon-gate IGFET structures. IGFET structures allow the fields in the SiO2 layer and in the silicon depletion region to be varied independently. In addition, IGFET structures of reentrant geometry allow absolute emission probabilities of the hot electrons to be determined. Such absolute emission characteristics are useful not only for designing silicon devices but also for quantitative testing of theoretical models of the emission process. Several mechanisms of importance in the emission process have been identified. These are the Schottky lowering of the emission barrier, the scattering of hot electrons in the image-force potential well in the SiO2 layer, the tunneling of hot electrons, and the effect of lattice temperature on electron heating. There is also experimental evidence of the dependence of the hot-electron distribution on electric field gradient. At present, only phenomenological models based on the lucky-electron concept have been developed to the point where quantitative comparison with experimental results is possible. The essential features of these models are discussed.

The operation of the semiconductor‐insulator‐semiconductor (SIS) solar cell: Theory

Abstract: Recently 12% efficient indium tin oxide (ITO) on silicon solar cells have been reported. Experiments indicate the presence of a thin interfacial insulating layer. Thus, these devices appear to belong to a class of semiconductor‐insulator‐semiconductor (SIS) solar cells where one of the semiconductors is a degenerate wide‐band‐gap oxide. We have developed a theory in terms of minority‐carrier tunnel current transport through the interfacial layer where one semiconductor is in a nonequilibrium mode. The wide‐band‐gap semiconductor serves to block band‐to‐band majority‐carrier current and thus, in principle, give better device performance than with an MIS solar cell. The effects of interfacial layer thickness, substrate doping level, surface states and interface charge, temperature on the performance of SIS solar cells have been calculated. These indicate that real‐world ITO on silicon cells should be able to achieve 20% efficiency under AMl illumination. Other combinations of semiconductors would yield even...

Periodic regrowth phenomena produced by laser annealing of ion‐implanted silicon

Abstract: We have discovered that interference effects extant during pulsed laser irradiation annealing of ion‐implanted silicon produce periodic property variations in the annealed material that mimic the interference pattern. These are manifest at near‐annealing threshold power densities as surface ripple and at higher power densities may be revealed by etching. The surface ripple observed at low power densities is correlated with the occurrence of polycrystalline silicon regions in the annealed material. Our observations suggest that surface melting and epitaxial regrowth are responsible for the annealing effect.

Determination of boron and phosphorus concentration in silicon by photoluminescence analysis

Abstract: A novel method to obtain boron and phosphorus concentration in silicon crystals by photoluminescent (PL) analysis at liquid‐helium temperature is reported. The intensity ratio between intrinsic and extrinsic components in the PL spectra reflects the impurity concentration. The tentative calibration curves for boron and phosphorus for our method are obtained by comparison with the results of the resistivity measurement. The detection limit of this method is estimated to be as low as 1×1011 cm−3 for boron and 5×1011 cm−3 for phosphorus. The degree of compensation can be estimated also. The PL method makes it possible to determine nondestructively the concentration of small amount of impurities in a small region of a specimen.

Crystallographic study of semi‐insulating polycrystalline silicon (SIPOS) doped with oxygen atoms

Abstract: Thermally deposited silicon films doped with oxygen atoms and used as passivation films on silicon devices have been studied with transmission electron microscopy, x‐ray diffraction, and ESCA. The films contain at least two phases, silicon microcrystals and silicon oxide. The size of the microcrystals in as‐deposited films was dependent both on the deposition temperature and on the oxygen concentration. Heat treatment caused crystal growth which depended mainly on the annealing temperature and weakly on the annealing time. The lattice constant of the microcrystals was directly related to their size. The silicon oxide phase in as‐deposited films was found to be SiO1.4. The results suggest ’’mosaic’’ model of the films which are amorphous when the diameter of the silicon microcrystals was less than 10 A.

Measurements of the mechanical Q of single-crystal silicon at low temperatures

Abstract: Measurements of the mechanical quality factor Q in a single crystal of silicon vs. temperature have been made. A value of 2 × 109 has been measured at T = 3.5K.