Showing papers on "Silicon published in 1977"

Auger coefficients for highly doped and highly excited silicon

Abstract: The recombination kinetics in highly doped p‐ and n‐type silicon has been investigated at 77, 300, and 400 K through the radiative band‐to‐band recombination. The minority‐carrier lifetime depends quadratically on the doping concentration as expected for Auger recombination. The Auger coefficients at 300 K for p‐ and n‐type silicon are found to be Cp=9.9×10−32 cm6 s−1 and Cn=2.8×10−31 cm6 s−1. They are nearly independent of temperature in the range investigated. The Auger coefficient in highly excited pure silicon at 4.2 K (electron‐hole drops) is essentially the same as in highly doped silicon.

Electrical and optical properties of amorphous silicon carbide, silicon nitride and germanium carbide prepared by the glow discharge technique

Abstract: Amorphous specimens of silicon carbide, silicon nitride and germanium carbide have been prepared by decomposition of suitable gaseous mixtures in a r.f. glow discharge. Substrates were held at a temperature T d between 400 and 800 K during deposition. In all three of the above materials the results of optical absorption and of d.c. conductivity measurements show a systematic variation with T d and with the volume ratio of the gases used. Electron microprobe results on silicon carbide specimens indicate that a wide range of film compositions can be prepared. The optical gap has a pronounced maximum at the composition Si00–32C0–68 where it is 2·8 eV for a sample deposited at T d = 500 K, but shifts to lower energies with increasing T d. The conductivity above about 400 K has a single activation energy approximately equal to half the optical gap and extended state conduction predominates if the silicon content exceeds 32%. If the latter is reduced, hopping transport takes over and it is suggested th...

A New Preferential Etch for Defects in Silicon Crystals

Abstract: A new preferential etch for (100) and (111) oriented, p‐ and n‐type silicon has been developed. Oxidation‐induced stacking faults, dislocations, swirl, and striations are clearly defined with minimum surface roughness or extraneous pitting. A relatively slow etch rate (∼1 μm per min) at room temperature provides etch control. The long shelf life of this etch allows the solution to be stored in large quantities.

Influence of 16O, 12C, 14N, and noble gases on the crystallization of amorphous Si layers

Abstract: Channeling effect measurements have been used to study the effect of impurities on the epitaxial regrowth of amorphous silicon layers on single‐crystal silicon. Implantation was used to form the amorphous layers and also to introduce the impurities 12C, 14N, 16O, 20Ne, 40A, and 84Kr. For 16O implants, the growth rate at 550 °C depended on the 16O concentration and at the level of 0.5 at.% the rate was reduced from about 90 to about 10 A/min. For similar atomic concentrations of 14N, the rate was comparable to the 16O case. For comparable concentrations of 12C, the regrowth rate was found to be three times higher than for that of the 16O case. Noble gas ions are also found to retard the growth rate of the amorphous layers. For 40Ar at about the 0.5‐at.% level, the regrowth rate is appreciably slower than even that for the 16O case.

Linear thermal expansion measurements on silicon from 6 to 340 K

Abstract: Linear thermal expansion measurements have been carried out from 6 to 340 K on a high‐purity silicon sample using a linear absolute capacitance dilatometer. The accuracy of the measurements varies from ±0.01×10−8 K−1 at the lowest temperatures to ±0.1×10−8 K−1 or 0.1%, whichever is greater, near room temperature, and is sufficient to establish silicon as a thermal expansion standard for these temperatures. The agreement with previous data is satisfactory at low temperatures and excellent above room temperature where laser‐interferometry data of comparable accuracy exist. Thermal expansions calculated from ultrasonic and heat‐capacity data are preferred below 13 K where experimental problems occurred.

Emission probability of hot electrons from silicon into silicon dioxide

Abstract: An experimental method is described for directly measuring the probability of electron emission from the silicon substrate into the SiO2 layer after the electron has fallen through a certain potential drop in traversing the depletion layer and reached the Si‐SiO2 interface. The method is based on optically induced hot‐electron injection in polysilicon‐SiO2‐silicon field‐effect‐transistor structures of reentrant geometry. The emission probability was studied as a function of substrate doping profile, substrate voltage, gate voltage, and lattice temperature. It was found that the hot electrons could be emitted by tunneling as well as by surmounting the Schottky‐lowered barrier. Over‐the‐barrier emission dominates at large substrate voltages, where the emission probability is high, and tunnel emission becomes appreciable and may even dominate at small substrate voltages where the emission probability is low. A simple model was developed based on the assumption that only those hot electrons lucky enough to escape collision with optical phonons were emitted. Using this model, we found that the expression P=A exp(−d/λ) described very well the dependence of the emission probability on doping profile, substrate voltage, and gate voltage. Here A=2.9 is a constant, λ is the optical‐phonon‐electron collision mean free path, d is the distance from the Si‐SiO2 interface where the potential energy is equal to the ’’corrected’’ barrier of (3.1 eV−βEOX1/2 −αEOX2/3ox), βEOX1/2 is the Schottky lowering of the barrier, and αEOX2/3 is a ’’barrier‐lowering’’ term introduced to account for the probability of tunneling. The temperature dependence of the collision mean free path was found to follow the theoretical relationship λ=λo tanh(ER/2kbT), with λo=108 A and ER=0.63 eV. This model is useful for evaluating potential hot‐electron‐related instability problems in IGFET and similar structures.

Defect energy levels in boron-doped silicon irradiated with 1-MeV electrons

Abstract: Using transient capacitance spectroscopy, we studied defect energy levels and their annealing behavior in boron-doped silicon of various resistivities irradiated with 1-MeV electrons at room temperature. Three levels located at ${E}_{v}+0.23$, ${E}_{v}+0.38$, and ${E}_{c}\ensuremath{-}0.27$ eV consistently appear in various samples, showing they are characteristic defects in boron-doped silicon. Many properties of the ${E}_{v}+0.23$-eV level and the divacancy are the same, according to the present study and others. We correlated the ${E}_{v}+0.38$-eV level to the vacancy-oxygen-carbon complex recently identified by Lee and Corbett using the EPR technique. The ${E}_{c}\ensuremath{-}0.27$-eV level could arise from an interstitial defect of oxygen and boron; and a new level at ${E}_{v}+0.30$ eV arising upon its disappearance could be a vacancy defect trapping an oxygen atom and a boron. Several additional defect levels are reported.

Optical and photoconductive properties of discharge‐produced amorphous silicon

Abstract: Optical and photoconductive properties of discharge‐produced amorphous silicon (a‐Si) of the type used in efficient thin‐film solar cells have been studied as a function of a wide range of deposition conditions The optical absorption, optical band gap, photoconductivity, hydrogen content, and the characteristics of the Si‐H vibrational mode in a‐Si were determined Both substrate temperature in the range ∼200–400 °C and the type of discharge used are found to be important factors in determining the measured optical and photoconductive properties of a‐Si For films produced at substrate temperatures near 200 °C, dihydride bonding occurs, and the optical band gap is about 17 eV As the substrate temerature increases, monohydride bonding is favored, the optical band gap decreases, the optical absorption increases, and the photoconductive properties improve These properties are, in part, associated with the presence of bonded hydrogen For substrate temperatures between 300 and 400 °C, the photoconductive

The dopant density and temperature dependence of electron mobility and resistivity in n-type silicon

Abstract: Traditional analysis of electron mobility in n -type silicon neglects the effect of electron-electron scattering in the mobility calculations. As a result, theory fails to conform with experiment when dopant density exceeds 2 × 10 16 cm −3 . In this work, an improved theoretical model for computing mobility and resistivity as functions of dopant density and temperature has been developed for n -type silicon. The model has been applied to phosphorus-doped silicon for dopant densities from 10 13 to 10 19 cm −3 , and temperatures between 100 and 500 K. The mobility was calculated analytically by appropriately combining lattice, ionized impurity and neutral impurity scattering contributions. The effect of electron-electron scattering was incorporated empirically for dopant densities greater than 2 × 10 16 cm −3 . Additionally, the anisotropic scattering effect was included in the mobility formulations. Resistivity measurements on seven phosphorus-doped silicon wafers with dopant densities from 1.2 × 10 14 to 2.5 × 10 18 cm −3 were carried out for temperatures from 100 to 500 K. Electron mobility at 300 K was deduced from resistivity and junction C-V measurements for dopant densities from 10 14 to 10 18 cm −3 . Agreement between theoretical calculations and experimental data for both electron mobility and resistivity of phosphorus-doped silicon was within ±7% in the range of dopant densities and temperatures studied.

Silicon nitride films on silicon for optical waveguides

Abstract: Silicon nitride (Si(3)N(4)) thin film optical waveguides with propagation losses of less than 0.1 dB/cm for the TE(0) mode at lambda(0) = 6328 A have been successfully grown by low-pressure chemical vapor deposition. Silicon wafers 5 cm in diameter were used as substrates, and the Si(3)N(4) was separated from the substrate by a steamoxide SiO(2) buffer layer. Propagation losses are examined for the various waveguide modes, and their dependence on waveguide parameters and wavelength are discussed and compared with exact calculations. Leakage into the silicon substrate is shown to be a major loss mechanism, especially at longer wavelengths and for higher mode numbers.

Ion‐surface interactions in plasma etching

Abstract: The surface chemistry and the etching behavior of silicon and oxidized silicon bombarded with a CF3+ ion beam (50–4000 eV) have been studied using Auger electron spectroscopy, and a quartz‐crystal microbalance. The conclusions of this study are as follows: (a) the etch rate of Si caused by CF3+ ion bombardment can be accounted for by physical sputtering; (b) the deposition and removal of carbon at the etched surface may be one of the most important phenomena affecting the operation of plasma‐etching systems; and (c) there is reason to believe that ion bombardment of the etched surface enhances the reaction rate of the neutral etching species which are most probably fluorine atoms and CF3 radicals.

Ink jet printing nozzle arrays etched in silicon

Abstract: Ink jet printing nozzle arrays in the form of truncated pyramidal holes anisotropically etched into a silicon substrate have been fabricated. Eight‐nozzle arrays dixplay excellent performance characteristics with regard to uniformity of direction (<± 1mra), velocity (<± 10 cm/sec) at 1000–3000 cm/sec), and drop formation.

Dependence of residual damage on temperature during Ar+ sputter cleaning of silicon

Abstract: It has been found that the kind and amount of damage produced in silicon following Ar+ ion bombardment at 1.0 keV and the annealing properties of the damage depend strongly on the temperature at which the sputtering is done in the range 25–800 °C. Some of these differences in damage are not evident with surface‐sensitive techniques such as LEED, RHEED, or AES, but have been revealed by transmission electron microscopy and by Rutherford ion backscattering. TEM examination of substrates annealed at 800 °C after being sputtered at temperatures in the range 25–800 °C shows an increase in the density and the size of crystal defects with increasing sputtering temperature. Rutherford ion backscattering shows an increase in silicon disorder and in retained argon with increasing sputtering temperature. These results are similar to observations reported for ion implantation at higher energies. Models for damage mechanisms are discussed briefly. It is concluded that for Ar+ ion sputter cleaning of silicon, the silic...

Method for forming isolated regions of silicon utilizing reactive ion etching

Abstract: A method for isolating regions of silicon involving the formation of openings that have a suitable taper in a block of silicon, thermally oxidizing the surfaces of the openings, and filling the openings with a dielectric material to isolate regions of silicon within the silicon block The method is particularly useful wherein the openings are made through a region of silicon having a layer of a high doping conductivity

High temperature amorphous semiconductor member and method of making the same

Abstract: An amorphous semiconductor member which is capable of withstanding high temperatures and of having good toughness characteristics comprises an amorphous semiconductor material including a composition of a plurality elements, at least one of which is a low atomic weight element comprising boron, carbon, nitrogen or oxygen, formed in a solid amorphous host matrix having structural configuration which have local rather than long range order and electronic configurations providing an energy gap and an electrical activation energy. It also includes a modifier material added to the amorphous host matrix, such as a transition metal or rare earth element, having orbitals which interact with the amorphous host matrix and form electronic states in the energy gap which modify substantially the electronic configurations of the amorphous host matrix at room temperature and above. The amorphous semiconductor member may also comprise an amorphous host matrix formed from boron, carbon, silicon or germanium having a modifier material of boron or carbon added thereto. The forming of the amorphous host matrix and the adding of the modifier material is preferably done by cosputtering or the like.

Optical fiber fabrication and resulting product

Abstract: A preform for fabrication of a glass fiber optical transmission line is prepared by chemical reaction of vapor ingredients within a glass tube. Reaction, which may be between chlorides or hydrides of, for example, silicon and germanium with oxygen, occurs preferentially within a constantly traversing hot zone. Flow rates and temperature are sufficient to result in glass formation in the form of particulate matter on the inner surface of the tube. This particulate matter deposits on the tube and is fused with each passage of the hot zone. Continuous rotation of the tube during processing permits attainment of higher temperatures within the heated zone without distortion of the tube.

A study of the optical emission from an rf plasma during semiconductor etching

Abstract: Spectroscopic analysis of optical emission during rf plasma etching of semiconductor materials has been used to gain a better understanding of the plasma chemistry involved in these systems. The emission was studied principally in CF4−O 2 gas mixtures, but other gases were observed as well. It is known that the addition of a relatively small percentage of O2 to CF4 yields a much faster etching rate for silicon and silicon nitride. With the addition of O2 to CF4 discharges we have studied emission from atomic O and molecular CO with a large increase in the emission of atomic F. When the plasma is actively etching silicon or silicon nitride, the emission intensities of both F and O atoms are significantly lower. The etching process can be monitored by observing the intensities of these lines. Analysis of the emission features has also been used to determine abnormal conditions which can adversely affect the etching process.

Defects in silicon substrates

Abstract: This paper reviews some defects of major importance in silicon substrates: their nature and geometrical distribution; the mechanism of formation; their interplays; and their implications. Topics discussed include swirl aggregates of point‐defect clusters and dislocation clusters; dislocations generated by thermal stresses; stacking faults generated by thermal oxidation both on the surface and in the bulk of substrates; and clustering and precipitation of oxygen.

Saturated electron drift velocity in 6H silicon carbide

Abstract: The saturated electron drift velocity has been measured in epitaxial 6H silicon carbide layers. The saturation occurs at an electric field of approximately 2×105 V/cm. The saturated drift velocity is 2×107 cm/s at room temperature, i.e., a factor of 2 higher than in silicon.

Dislocation pinning effect of oxygen atoms in silicon

Abstract: A definitive proof has now been obtained of the existence of a dislocation pinning effect by oxygen atoms in silicon. Ambiguities caused by uncertain material variables in different crystals or different parts of a crystal are avoided in this investigation by making oxygen out‐diffusion from a wafer, creating a continuous variation of oxygen concentration in a ∼60‐μm‐deep surface layer. Dislocation movement at different depths of this layer was studied using indentation dislocation rosettes (IDR) on a 2° beveled surface. The method of IDR is uniquely suitable for this study because microdislocation half‐loops are generated and confined to move within each ∼10‐μm‐deep layer in a series of precisely determined microregions down the bevel. The size of IDR increases steadily toward the sample surface, in good correlation with the steady decrease of oxygen concentration toward the same sample surface. The effect at the maximum oxygen concentration in this case increases the critical resolved shear stress in silicon by a factor of 4. This is a most beneficial effect in reducing thermal slip in the practical matter of silicon wafer processing.

Evidence for surface asperity mechanism of conductivity in oxide grown on polycrystalline silicon

Abstract: High conductivity observed in oxides grown on polycrystalline silicon has been previously speculated as being due to asperities on the silicon surface, which enhance the oxide field. Direct evidence of these asperities is shown here in SEM micrographs. The presence of the asperities is strongly correlated with the oxide conductivity (as controlled by the oxidation temperature).

Acceptor dopants in silicon molecular‐beam epitaxy

Abstract: Epitaxial silicon films have been grown on single‐crystal Si (100) substrates by evaporation from an e‐gun source in ultrahigh vacuum and have been doped with gallium and with aluminum from separate oven sources. Gallium doping profiles have been controlled accurately for substrate temperatures in the range 600–800 °C and for carrier densities in the range 1014–5×1017 cm−3. Examples are given of abrupt changes in doping level. Measured drift mobilities in the films are within 15% of values for bulk silicon. Crystallographic properties of the films are comparable to those of the substrates and are suitable for device applications. Films doped with aluminum exhibit comparable electrical and crystallographic properties, but good control of the doping profile has not been achieved for the range of parameters studied.

Thermal oxidation of silicon in various oxygen partial pressures diluted by nitrogen

Abstract: Oxide growth kinetics of SiO2 films grown on silicon at 950 to 1100 °C in an O2/N2 mixture is empirically studied. It is found that a linear‐parabolic law is in excellent agreement with the oxidation data under the oxygen partial pressure PO2 of 1 or 10−1 atm. However, a parabolic law is obtained at 10−2 atm, and an inverse‐logarithmic law at 10−3 atm. The Mott‐Cabrera oxidation rate equation is adapted to the thermal oxidation of silicon in the case of PO2≲10−2 atm. Finally, 43.9 kcal/mole is derived as the activation energy value of silicon atoms entering into the oxide.

Silicon Oxidation Studies: The Role of H 2 O

Abstract: The thermal oxidation of Si using and ambients has been studied with an automated ellipsometer which can observe the oxidationin situ. The oxidations were carried out in the temperature range of 780°–980°C on oriented single crystal Si. The resulting film growth data was analyzed according to a linear‐parabolic oxidation model. The parabolic rate constant was found to increase abruptly with small additions of to while the linear rate constant increased gradually over the range of added (0–2000 ppm). The over‐all increase in the rate of oxidation due to in was found to be greater than predicted based on the independent diffusion and reaction of and related oxidant species. These effects of were found to be reversible. Therefore, the kinetic role of on the oxidation of silicon is essentially twofold. The acts both as an additional source of oxidant and as an accelerator for the oxidation process involving. It is postulated that this latter effect occurs because the modifies the network thereby enhancing diffusion of the primary oxidant through the film.

Specific heat study of heavily P doped Si

Abstract: A framework for understanding plasma etching has been developed (using the CF4 plasma etching of silicon and silicon compounds as an example) which treats the discharge as a ’’pseudo‐black‐box’’ which is characterized by a dissociation rate G of the CF4 molecules and a recombination rate R at which CF4 and other inert molecules are re‐formed by recombination of the active fragments. Expressions based on the conservation of fluorine and carbon in the system have been derived which relate the concentration of the various species in the effluent gas to the etch rate. This approach provides a semiquantitative understanding of several aspects of plasma etching such as the effects of additive gases and the presence of a much larger ’’loading’’ effect for Si than for SiO2.

Plasma etching A ’’pseudo‐black‐box’’ approach

Abstract: A framework for understanding plasma etching has been developed (using the CF4 plasma etching of silicon and silicon compounds as an example) which treats the discharge as a ’’pseudo‐black‐box’’ which is characterized by a dissociation rate G of the CF4 molecules and a recombination rate R at which CF4 and other inert molecules are re‐formed by recombination of the active fragments. Expressions based on the conservation of fluorine and carbon in the system have been derived which relate the concentration of the various species in the effluent gas to the etch rate. This approach provides a semiquantitative understanding of several aspects of plasma etching such as the effects of additive gases and the presence of a much larger ’’loading’’ effect for Si than for SiO2.

Study of Encapsulants for Annealing GaAs

Abstract: Low temperature photoluminescence and Auger electron spectroscopy have been used to study chemical-vapor deposited SiO2 and SigN4 layers as en- capsulants for high temperature annealing of GaAs. Silicon dioxide or silicon oxynitride layers allow out-diffusion of Ga, while suitably prepared rf plasma deposited SisN4 layers can be used to anneal GaAs with negligible Ga out- diffusion. Ion implantation is a versatile method of doping semiconductors and is an established fabrication step for many silicon devices (1). Although the use of implantation in the III-V compounds is less wide- spread, important device applications have emerged. These include the fabrication of light emitting diodes (2), GaAs field-effect transistors, optical waveguid.es, and detectors (3). Because of the difficulties of selec- tively doping GaAs or other compound semiconductors by standard diffusion processes as compared with Si, it now appears that implantation will play an increas- ing role in future device applications of compound semiconductors. In view of the potential for this doping method, it is important to develop reliable procedures for im- plantation and annealing in these materials. Ion im- plantation produces considerable lattice damage which must be annealed out in order to restructure the lattice and activate the implanted impurities. While this pro- cedure is relatively straightforward in Si, annealing a compound semiconductor such as GaAs is more difficult. The incongruent evaporation of Ga and As from GaAs at temperatures ~ in excess of 600~ (4) makes it impossible to anneal bare GaAs samples without surface degradation. It is thus necessary to encapsulate the sample with a suitable dielectric layer or to perform the anneal in a carefully controlled ambient (5. 6). There have been numerous discussions of implantation and annealing in GaAs using encapsu- lants such as sputtered or chemical,vapor deposited SiO2 (7), thermally o r reactively deposited or sput- tered Si3N4 (8-10), or sputtered A1N (11). In the present work we have used low temperature photo- luminescence (PL) and Auger electron spectroscopy _(AES) to investigate the annealing-encapsulation properties of chemical vapor deposited SiO2 and rf plasma deposited Si.~N4 layers on GaAs. It is well known from diffusion experiments in Si that Ga has a very high diffusion coefficient in SiO2 (12). Gyulai et