ESR studies of thermally oxidized silicon wafers

We have performed ESR measurements on oxidized (111) silicon wafers and found two ESR centers. One, the previously known P_b center,was found to be a two level interface trap by corona bias studies. The other one, previously known as “damaged silicon” center was found to be a silicon center, probably related to the oxide growth process.     

Ordering in thermally oxidized silicon

We present new evidence and a model for residual ordering of silicon atoms within the oxide of thermally oxidized silicon wafers. X-ray scattering is used to observe the residual order in thermally grown SiO2 on Si(001), (011), and (111) surfaces with thicknesses of 60 to 1000 A, for both on-axis and miscut surfaces. In every case, the scattering position can be predicted using a model which expands the silicon lattice during oxidation without completely disordering it. The amount of expansion and disorder is dependent on the type of oxidation process employed.     

Theory of surface polaritons in n-type silicon in the presence of a DC current

A theoretical investigation has been carried out on the effect of a drift current on surface polaritons in n-type silicon. The current direction is taken to be parallel to the direction of propagation of the surface polaritons. From the dispersion curves, there is evidence that an interaction takes place between the current and the polaritons which gives rise to polariton instability or amplification for certain frequency ranges. These instabilities are believed to be due to the presence of the surface.     

Theory of the effect of a dc current on surface polaritons in n-type silicon

A theoretical investigation has been made of the effect of a drift current on surface polaritons in n-type silicon. The current direction is taken to be the same as the propagation direction of the surface polaritons. Retardation is included, but damping is neglected. In obtaining the dispersion relation, the specular-reflection/mirror-image technique of Kliewer and Fuchs is used to handle the boundary conditions. The results indicate that an interaction takes place between the current and polaritons which gives rise to polariton instabilities for certain frequency ranges. These instabilities are a consequence of the presence of the surface.     

Non-equilibrium surface state properties at clean cleaved silicon surface as measured by surface photovoltage

Surface photovoltage transients were measured at clean cleaved silicon (111) faces in ultrahigh vacuum. The temperature and doping of the samples, the intensity of the stimulating light pulses (energy less than band gap), and the surface coverage (clean and adsorbed water vapor) were varied systematically. The results yield information on the charge transfer at the surface and on surface recombination. The calculation of the surface photovoltage (using only the generation rates into and out of the surface states and data of thermal equilibrium) shows, that only one bulk band (conduction band for n-doped samples and valence band for p-doped samples) controls completely signal height and its relaxation via charge transfer to the surface states. The determined surface state parameters are: relaxation time constants, capture cross-sections for photons and transition probabilities. On the basis of the model all decay curves can be reproduced quantitatively.     

Combined frequency- and time-domain photocarrier radiometry characterization of ion-implanted and thermally annealed silicon wafers

A combined frequency-swept and quasi-time-domain photocarrier radiometry (PCR) technique was developed to characterize thermally annealed silicon wafers with B+ , P+ , and As+ ion implantation at doses ranging from 1 × 1011 cm-2 to 1 × 1016 cm-2 . The implantation dose dependence of the PCR amplitude, the frequency dependencies of the PCR amplitude and phase, as well as the quasi-time-domain PCR waveforms were simultaneously employed to analyze all the ion-implanted silicon samples. The dependence of the effective lifetime on the implantation dose has been investigated and shown to be related to the trap density and the lifetime extracted from the transient PCR signals.     

Radiation breakdown in silicon wafers

Radiation breakdown in silicon slabs is observed and studied as revealed in anomalous behavior of the dose characteristics of their radiation defects when the radiative intensity is varied. A theory is constructed for reversible radiation breakdown due to the bistability which develops in a gas of radiation vacancies when the gas can be regarded as quasi-two-dimensional. In order to explain the exponential saturation of the dose characteristics as the irradiation intensity is increased, scenarios are proposed in which different forms of the constituent radiation defects develop. Some parameters of the bistable gas of primary vacancies are estimated, including diffusion coefficients, dimensions of inhomogeneity regions, and the rate of movement of the stratification line. On the whole, satisfactory agreement with experiment is obtained. Discrepancies between the diffusion coefficient for neutral vacancies obtained here and in the literature are attributed to the role of interband recombination accompanying radiation defect formation during electron bombardment. Zh. éksp. Teor. Fiz. 114, 1067–1078 (September 1998)     

A SIMS study of ion beam induced migration of nitrogen in thermally oxidized silicon

The potential use of thin silicon nitroxide films as gate dielectrics in VLSI MOS devices has motivated much recent work. The present study shows that positive ion bombardment, as encountered in sputter depth profiling or ion implantation, can induce considerable movement of nitrogen in thin thermal oxide films on silicon. Low energy N⁺₂ implants are performed in-situ in a SIMS apparatus and are subsequently depth profiled. The effect of implant dose and oxide thickness are examined and comparisons are made to films prepared by rapid thermal nitridation and LPCVD. Profiles obtained under O⁺₂, O^-, and Cs⁺ bombardment are also compared. SIMS depth profiles of implanted 200 Å oxides using positive ion bombardment show a depletion of nitrogen near the surface, a shoulder in the nitrogen concentration near the Si-SiO₂ interface, and a peak in this concentration at the interface. Negative ion bombardment did not induce a shoulder-peak structure at the interface. The implications of these results are discussed.     

Hydrophobic and antireflective characteristics of thermally oxidized periodic Si surface nanostructures

We reported the antireflective properties of periodic silicon (Si) subwavelength gratings and flat substrates in combination with thermal oxidation for an effective surface passivation. Moreover, theoretical calculations and analysis based on rigorous coupled-wave analysis simulation were performed. For thermally oxidized Si subwavelength grating structures, the reflectance was significantly reduced compared to that of the thermally oxidized flat Si substrates in wide ranges of wavelengths and angles of incidence. As the oxidation time increased, the reflectance became lower with increasing SiO _x thickness on Si subwavelength gratings due to the more graded effective refractive index profile from air to the Si via the thermally oxidized Si subwavelength gratings with increased height. By incorporating a thermal oxidation process into the Si subwavelength gratings, a more hydrophobic surface with good surface passivation was obtained.     

Interaction of iron atoms with the oxidized silicon surface

The room-temperature interaction of iron atoms with the oxidized Si(100)2×1 surface at a coverage from a submonolayer to four monolayers is studied by core-level photoelectron spectroscopy using synchrotron radiation. Computer simulation of the Si 2p core electron spectra demonstrates that iron atoms penetrate beneath the silicon oxide even at room temperature. This process causes the initial silicon phases at the SiO_x/Si interface to disappear; gives rise to a complex ternary phase involving Fe, O, and Si atoms; and favors the formation of a Fe-Si solid solution at the interface.     

Theory of surface polaritons in n-type silicon in the presence of a dc current,including the electron thermal pressure gradient

A theoretical investigation has been made of the effect of a drift current, including the electron thermal pressure gradient, on surface polaritons in n-type Si. The polariton propagation and drift current directions are taken to be either parallel or antiparallel. Retardation is included, but damping is neglected. The specular reflection approach of Kliewer and Fuchs is used to obtain the polariton dispersion relation. The results show that the drift current and surface polaritons interact, leading to evanescent waves for certain frequencies. However, no wave amplification is obtained.     

Phonons in surface photovoltage of GaAs

Oscillatory surface photovoltage is reported in GaAs at 4.2°K, characterized by two series of minima. Dominating series is attributed to the capture of photoexcited electrons by surface states with emission of phonons. Second, weak series coincides with oscillations in photoconductivity.     

Anisotropic Voigt effect in n-type silicon

Donovan and Webster have studied the free-carrier Voigt effect, valid for all frequencies and magnetic-field strengths, taking into account multiple reflections in n-type germanium semiconductors. This theory is now extended to the case of n-type silicon. The high-frequency magneto-conductivity tensors are derived for a nondegenerate system of electrons, considering lattice scattering only. Theoretical calculations for Voigt rotation are carried out for a typical non-degenerate specimen of n-type silicon having d.c. conductivity α₀ = 1.8 × 10¹¹ e.s.u. (at 300 K).     

Positron annihilation in boron-implanted n-type silicon

The ion damaged effect and subsequent isothermal annealing in boron-implanted Si was studied by positron annihilation lifetime measurements. The mean positron lifetime in preimplanted n-type Si is 243 psec. The variation of mean lifetime is detectable when the implanted boron dose is greater than 1.0x10¹⁵/cm². The saturated mean positron lifetime (247 psec) occurs when the implantation dose reaches 2.5x10¹⁵/cm². The mean electron density of the positron sensitive defects is estimated to be about 85% less than that in the perfect parts of the crystal. Isothermal annealing was held in every 5-minute step at 1000°C. In the first step, the positron lifetime in the implanted sample increases slightly and then decreases completely to its initial state in the 3rd step. Sheet resistance of the sample monitored by 4-point probe method has been found closely related to the positron lifetime.     

Slip on the surface of silicon wafers under laser irradiation:Scale effect

The slip mechanism on the surface of silicon wafers under laser irradiation was studied by numerical simulations and experiments. Firstly, the slip was explained by an analysis of the generalized stacking fault energy and the associated restoring forces. Activation of unexpected {110} slip planes was predicted to be a surface phenomenon. Experimentally,{110} slip planes were activated by changing doping concentrations of wafers and laser parameters respectively. Slip planes were {110} when slipping started within several atomic layers under the surface and turned into {111} with deeper slip.The scale effect was shown to be an intrinsic property of silicon.     

Resonant four wave mixing in n-type silicon

We observe a strong resonance in the third order nonlinear optical susceptibility of n-type silicon corresponding to the valley orbit splitting of the 1s-states of phoshorous and antimony donors. Cross-sections for valley orbit Raman scattering near 10 μm obtained from our data agree with calculations based on an intraband model. The expression for the cross-section resulting from this model is equivalent to that of Jain et al.     

Optical properties of the clean and slowly oxidized surface of silicon

The optical absorption of an UHV cleaved (111) surface of Si has been investigated as a function of the exposure to oxygen. Data concerning the disappearing of surface states with oxidation are reported. The sticking coefficient for oxygen of a clean surface of Si is calculated from optical absorption data.     

Acoustoelectric current fluctuations in n-type CdS

Acoustoelectric current fluctuations in n-type CdS are measured under pulsed bias conditions. The experimental data are interpreted in terms of a model where electrons are trapped in potential troughs associated with spontaneously generated and acoustoelectrically amplified waves.