Hydrogen implanted silicon oxidation

The oxidation rate and the oxide thickness of the hydrogen ion implanted silicon wafers were examined. It was observed that the native oxide thickness is higher for the H⁺ implanted Si(100) compared to the Si(111). Also the native oxide thickness depended on the implanted hydrogen distribution. The thickness increased with the hydrogen con-centration. The oxide thickness after wet oxidization of the H⁺ implanted Si(111) was higher than that of the unimplanted wafers. The oxide thickness also depended on the resistivity of the H⁺ implanted Si wafers. The suggested explanation is that in high energy H⁺ implanted Si the oxidation rate is higher as a result of the higher diffusion and reaction kinetics. All these measurements were done with the assumption that the implanted and the unimplanted samples have the same indices of refraction for the oxide as well as for the substrate.     

Electrical conduction in implanted polycrystalline silicon

Undoped polycrystalline silicon (poly-Si) films, 0.5 μm thick, have been prepared at 700‡C by chemical vapor deposition (CVD) onto thermally oxidized n⁺-Si substrates. The impurity concentration was varied by implanting with As, P, and Sb ions, accelerated to 30 keV; total doses ranged from 2×10¹¹ to 3×10¹⁵ ions/cm². Sheet resistance measurements, spanning 8 orders of magnitude, were made as a function of implantation dose. A reduction of 6 orders of magntiude in poly-Si sheet resistance took place within the implantation dose range between 10¹² and 10¹⁴ ions/cm². Some samples also exhibited large reductions in sheet resistance following the standard heat treatment for Al contact sintering and surface state reduction, which is normally at 450‡C for 0.5 hr in H₂. Sheet resistance measurements were also made as a function of temperature in the range 0 to 315‡C. The effective activation energy for electrical conduction depends upon implantation dose. At low doses (2×10¹¹cm₋₂) the poly-Si is intrinsic, withE _A = 0.65 eV. At a dose of 10¹⁵ cm⁻², electrical conduction is a weak function of temperature, withE _A = 0.027 eV.     

Diffusion of terbium in silicon

The diffusion of terbium in silicon in the temperature range of 1100–1250°C is studied using the direct radioisotope technique for the first time. The diffusion parameters of terbium in silicon are determined.     

Diffusion of europium in silicon

The diffusion of europium in silicon has been studied for the first time in the temperature range 1100–1250°C by the direct radioactive-tracer method. The diffusion parameters of europium impurity in silicon have been established.     

Diffusion of yittrium in silicon

The diffusion of yttrium in silicon is studied for the first time. The diffusion is performed in air or vacuum in the temperature range of 1100–1250°C. The temperature dependence of the diffusivity of yttrium in silicon is described by the relation D = 8 × 10^?3 exp(?2.9 eV/kT) cm² s^?1. The acceptor nature of yttrium in silicon is revealed.     

Diffusion of ytterbium in silicon

Diffusion of ytterbium in silicon is studied by the direct method of radioactive isotopes in the temperature range of 1100–1250°C. Diffusion coefficients of ytterbium impurity in silicon are determined.     

Growth oxygen-containing defects in silicon grown in a weak vertical magnetic field

Properties of silicon (M-Si) prepared by the Czochralski growth technique in a vertical magnetic field of 0.05 T applied to a melt are studied by measuring IR absorption spectra, microindentation, and selective etching. The effect of increasing the concentration of interstitial oxygen upon the thermal treatment of M-Si is found. It is shown that microhardness of M-Si is higher than that of silicon grown by the traditional Czochralski technique by ∼8%. The features in the behavior of M-Si are attributed to the formation of oxygen-containing defect-impurity complexes during the growth. Upon thermal treatment at 900°C in the hydrogen flow, these complexes decompose with the extraction of interstitial oxygen, which suppresses thermal hardening typical of the silicon single crystals grown by the traditional Czochralski technique.     

Radiation-thermal activation of silicon implanted in gallium arsenide

The layer density, density profile, and mobility of electrons in ²⁸Si-ion-doped layers of semiinsulating GaAs after radiation annealing with electron energy above and below the defect formation threshold and after thermal annealing in the temperature range T _a =590–830 °C are investigated. It is shown that for radiation annealing energy above the defect formation threshold ion-doped layers are formed with much lower annealing temperatures, and the degree of electrical activation of silicon in these layers is high and the density of electron mobility limiting defects is low. Fiz. Tekh. Poluprovodn. 33, 687–690 (June 1999)     

Capless annealing of silicon implanted gallium arsenide

Numerous commercially available semi-insulating GaAs substrates have been implanted with silicon ions and the post implantation annealing carried out using the technique of capless annealing in an arsine atmosphere. Results are presented on the implanted atomic silicon distribution along with carrier concentration and mobility profiles, Hall mobility and percentage activation figures for various implanted substrates. The phenomenon of thermally induced surface conduction layers in semi-insulating GaAs is discussed in the context of a capless annealing technique.     

Properties of silicon implanted with boron ions through thermal silicon dioxide

The properties of silicon implanted with boron ions through thermal SiO₂ films were studied using sheet resistivity measurements (corroborated by Hall data). Electrical properties for implants through 0.1 μm of SiO₂, as compared to bare silicon, showed no unusual behavior as a function of anneal temperature. Sheet resistivity measurements as a function of SiO₂ thickness for fixed ion energy, and as a function of energy for fixed oxide thickness were made after 525 and 925°C anneals, for boron doses of 10¹³, 10¹⁴ and 10¹⁵ ions/cm². The profile of boron ions in SiO₂ is near Gaussian for the energy range investigated and the stopping power is 0 to 20% lower than the theoretical value currently in the literature. Considerations for device manufacture are discussed in light of the results.     

Diffusion of interstitial magnesium in dislocation-free silicon

The diffusion of magnesium impurity in the temperature range T = 600–800°C in dislocation-free single-crystal silicon wafers of p-type conductivity is studied. The surface layer of the wafer doped with magnesium by the ion implantation technique serves as the diffusion source. Implantation is carried out at an ion energy of 150 keV at doses of 5 × 10¹⁴ and 2 × 10¹⁵ cm^–2. The diffusion coefficient of interstitial magnesium donor centers (D _i ) is determined by measuring the depth of the p–n junction, which is formed in the sample due to annealing during the time t at a given T. As a result of the study, the dependence D _i (T) is found for the first time. The data show that the diffusion process occurs mainly by the interstitial mechanism.     

Effects of dislocations in silicon transistors with implanted emitters

Silicon bipolar transistors have been made by substituting a shallow phosphorus implanation for the standard emitter deposition used in the manufacture of linear integrated circuits. The implantation was followed by a high temperature heat treatment (drive-in), which caused the implanted ions to diffuse deeper into the semiconductor to give emitter/base junction depths of typically 1.8 μm. When the high temperature heat treatment was performed in an oxidising atmosphere, the resulting transistors had lower gains and higher emitter/base leakages than the comparable standard diffused transistors. However, if an 1180°C drive-in, in an inert atmosphere, was performed prior to the oxidation drive-in, high gains and low emitter/base leakages were obtained. Alternatively, if the oxidation drive-in was omitted, and instead an inert drive-in performed at any temperature between 1000 and 1180°C, high gains and low emitter/base leakages were again obtained. Etching and TEM studies revealed that the low gains and high emitter/base leakages were again obtained. Etching and TEM studies revealed that the low gains and high emitter/base leakages were caused by emitter edge dislocations intersection the emitter/base junction around the perimeter of the emitter. A mechanism is suggested to describe the formation of the emitter edge dislocations.     

Bonding and thermal stability of implanted hydrogen in silicon

The behavior of implanted hydrogen in Si has been investigated by differential infrared transmittance measurements using multiple-internal-reflection (MIR) plates. Si-H bonding of implanted hydrogen is detected by seven absorption bands between 4.5 and 5.5 μm after implantation with 10¹⁶ H⁺/cm² at ion energies between 70 and 400 keV. The absorption bands are close in frequency to those for SiH stretching modes for silane, and they are produced only by hydrogen implantation. Implantation with deuterium gave absorption bands shifted to lower frequencies in accord with the square root of the reduced mass ratio for Si-H relative to Si-D. The multiplicity of hydrogen-associated bands is apparently a consequence of defects in the implanted layer. A dependence of the hydrogen-associated bands on the disorder is suggested by the annealing loss of five of the initial seven bands, and a growth of the other two, for the same temperatures (100–300°C) as those for annealing out the broad divacancy band at 1.8 μm. A disorder dependence of the Si-H vibrational frequencies is further demonstrated by a regeneration of the bands annealing below 300°C when a hydrogen-implanted MIR plate annealed at 300°C was subsequently bombarded with neon. In addition to the seven resolved bands after H⁺ implantation, five other bands in the same range of frequencies grow in and anneal out between 100 and 700°C. Annealing at 700°C eliminates all SiH bands, and they cannot be regenerated by bombardment with other ions. It is suggested that implanted hydrogen in Si is bonded at defect sites, and that a loss of an SiH band is caused by either a change in charge state of a defect or by the loss of a defect. This work was supported by the United States Atomic Energy Commission     

Effects of dislocations in silicon transistors with implanted bases

Silicon bipolar transistors have been made by substituting a shallow boron implantation for the standard base deposition used in the manufacture of integrated circuits. This was followed by a high-temperature oxidation drive-in, and the transistor structure completed with a standard phosphorus deposition and drive-in. The implantations were performed through oxides with thicknesses in the range 0.08–0.17 μm. For the 0.17 μm transistors, the electrical characteristics were comparable with standard diffused transistors, while for the 0.08 μm transistors low gains and high emitter/base and collector/base leakages were obtained. For the latter transistors, etching and TEM studies revealed a dislocation network in the emitter region with a small fraction (10^?3) of the dislocations looping down to intersect the emitter/base and collector/base junctions. The poor electrical characteristics are explained in terms of the looping dislocations, and a mechanism is suggested to describe how the dislocations form.     

Anomalous solubility of implanted nitrogen in heavily boron-doped silicon

It is established that an anomalously high electron concentration can be attained in heavily boron-doped silicon using ion implantation followed by implantation with nitrogen at an elevated temperature; the concentration of electrons can exceed that of boron. A model of this phenomenon is suggested that is based on the reaction of displacing boron atoms from the lattice sites by silicon self-interstitials with subsequent filling of the vacancies with nitrogen atoms (so that donor centers are formed).     

Ion beam annealed As+ implanted silicon

As+ and Ar+ ion beams have been used to anneal silicon implanted with 6 × 1015 As+/cm2 at 170 keV. Samples were annealed by (i) Ar+ incident on the back face or (ii) direct heating by the dopant ions. Those annealed by (i) exhibited good crystallinity, a low sheet resistivity of 24.0 ± 0 1?/? and no measurable change in the arsenic distribution.     

Defects in annealed 1.5 MeV boron implanted p-type silicon

Effects of temperature and dosage on the evolution of extended defects during annealing of MeV ion-implanted Czochralski (CZ) p-type (001) silicon have been studied using transmission electron microcopy. Excess interstitials generated in a 1 10¹⁵ cm⁻²/1.5 MeV B⁺ implanted Si have been found to transform into extended interstitial {311} defects upon rapid thermal annealing at 800°C for 15 sec. During prolonged furnace annealing at 960°C for 1 h, some of the {311} defects grow longer at the expense of the smaller ones, and the average width of the defects seems to decrease at the same time. Formation of stable dislocation loops appears to occur only above a certain threshold annealing temperature (∼1000°C). The leakage current in diodes fabricated on 1.5 MeV B⁺ implanted wafers was found to be higher for a dosage of 1 10¹⁴cm⁻² and less, as compared to those fabricated with a dosage of 5 10¹⁴ cm⁻² and more. The difference in the observed leakage current has been attributed to the presence of dislocations in the active device region of the wafers that were implanted with the lower dosage.     

CW laser annealing of boron implanted polycrystalline silicon

The electrical characteristics have been measured on CW laser annealed boron implanted polycrystalline silicon layers. It is shown, that a resistivity can be obtained, which is only about double that of a single crystalline layer doped to the same level. By appropriate choice of doping and laser annealing parameters, a temperature coefficient close to zero can be achieved. It is also shown that laser irradiation can be used to trim a furnace annealed polysilicon resistor to a desired resistance value.