A systematic analysis of defects in ion-implanted silicon

A classification scheme for the different forms of implant-related damage which arise upon annealing consisting of five categories is presented. Category I damage is subthreshold damage or that which results prior to the formation of an amorphous layer. If the dose is increased sufficiently to result in the formation of an amorphous layer then the defects which form beyond the amorphous/crystalline (a/c) interface are classified as category II (end of range) damage. Category III defects are associated with the solid phase epitaxial growth of the amorphous layer. The most common forms of this damage are microtwins, hairpin dislocations and segregation related defects. It is possible to produce a buried amorphous layer upon implantation, If this occurs, then the defects which form when the two a/c interfaces meet are termed category IV (clamshell, zipper) defects. Finally, category V defects arise from exceeding the solid solubility of the implanted species in the substrate at the annealing temperature. These defects are most often precipitates or dislocation loops.In addition to presenting examples of this classification scheme, new results emphasizing category II, IV, and V defects will be presented. For category II defects, the source, dose and mass dependence as well as the influence of pre- and post-amorphization is discussed. The category IV defects which arise from buried amorphous layers in {100} oriented As implanted samples is presented. Half loop dislocations which arise during annealing of high dose As implants, are shown to originate in the category V defects and grow upon dissolution of As clusters and precipitates.     

Front and back surface cw CO2-laser annealing of arsenic ion-implanted silicon

The annealing behavior of arsenic-implanted silicon under scanned cw CO₂-laser irradiation from front and back surfaces is investigated. Ellipsometry, Hall effect, Rutherford backscattering measurements and neutron activation analysis indicate an enhancement of annealing efficiency by laser irradiation from the back surface, which provides complete recovery of crystal damage, high substitutionality and electrical activation of implanted arsenic atoms without redistribution of concentration profile. The enhancement of annealing efficiency under back-surface irradiation is explained by the difference in laser reflection from the front and back surface of silicon wafers. No differences in the results are found for scanned and static annealing.     

Quantitative Auger analysis using integration techniques

Problems encountered in electron-excited Auger analysis resulting from chemical alteration of the shapes of the characteristic features can be virtually eliminated by integration techniques. In addition, these techniques recover the signal strength lost by taking data derivative modes.     

Monovacancy and interstitial migration in ion-implanted silicon

The migration of monovacancies (V0) and self-interstitials (I) has been observed in ion-implanted low-doped float-zone silicon by variable-energy positron annihilation spectroscopy. V0 and I were created by the in situ implantation of approximately 20 keV helium ions below 50 K. Monitoring the time evolution of the vacancy response during isothermal heating enabled the measurement of activation energies for I and V(0) [corrected] migration of 0.078(7) and 0.46(28) eV, respectively. In highly As-doped Si, partial V annihilation occurs via free I migration, with a second stage of annealing, probably associated with V-As complexes, above room temperature.     

An orientation-dependent defect in ion-implanted silicon

A new EPR spectrum is resolved in the N⁺-implanted silicon, and this center can be produced only by the 〈110〉 channeling ions in the region underneath the amorphous layer.     

Electrical characteristics of ion-implanted laser-annealed silicon

The present paper summarizes recent experiments at the JRC, aiming to determine the relative damage effects produced in a-SiO2 by particles of different mass and energy, so as to correlate typical defects with specific production mechanisms. By systematic analysis of optical absorption spectra, the main colour centres that are currently associated with primary irradiation effects were characterized. Centres responsible for the B₂-band (5.04 eV) and E'-band (5.78 eV) were quantitatively investigated with respect to particle type, production yield and saturation behaviour. Arguments taken from energy loss and dpa seem to suggest that the E' centre is based on a stable structural substrate, which is not reconciled with simple ideas of a broken bond. The B₂ centre is confirmed to be associated with atomic defects produced by collisions. New determinations in the vacuum u.v., performed on heavy-ion irradiated samples, seem to put this centre in quantitative relationship to a centre responsible for a 7.15 eV absorption.     

Quantitative Auger spectroscopic analysis of segregation of phosphorus in iron

The segregation of phosphorus to a clean iron surface has been studied by Auger spectroscopy in an Fe-0.063 wt % P alloy, as a function of temperature. It is shown that with certain plausible assumptions and the help of the Crank diffusion equation for strongly adsorbed elements, a calibration of the relative surface concentrations of iron and phosphorus can be achieved. The empirical proportionality factor so derived agrees closely with the factor derived theoretically on the basis of relative ionization cross-sections, with the inclusion of Coster-Kronig contributions to ionization.     

X-ray study of lateral strains in ion-implanted silicon

Lateral strains induced by 80 keV argon ion implants into silicon have been studied using X-ray interferometry and X-ray diffraction topography. The stressed state is described by the expansion of a thin surface layer, and it is shown, how it will affect the dilatational moiré patterns observed in the interferograms. The integrated stress acting in the damaged layer has been studied as a function of the bombardment dose. A maximum is reached at a dose of about 2×10¹⁴ ions/cm². The maximum local stress is of the order of 1×10⁹ dyn/cm².     

Stresses in silicon crystals from ion-implanted amorphous regions

The plane elasticity problem of the interaction between an edge dislocation and an elliptical inhomogeneity is solved, and the image glide-force on dislocation is computed. Contour plots of the force exterted by either an elliptic hole (crack) or a rigid elliptical inhomogeneity show that force is stronger for more elongated shapes, and that in some cases dislocation trapping effects undergo drastic changes even for slight shape variations. The general case is investigated by means of angular plots of force. They show increasing oscillatory angular depence on increasing both elongation and shear moduli difference.     

Auger electron spectroscopy of silicon surfaces

The measurements of the spectra of Auger electrons of the silicon surfaces performed at the pressure of (2–5)×10^?7 Torr are described. In this pressure range rapid oxidation and carbonization of the uppermost layers take place. The changes of characteristic energies in Auger and loss spectra are related to the change of chemical composition of the surface. The combination of the characteristic loss spectroscopy with Auger electron spectroscopy makes possible the determination of the chemical shifts. The measurements of the chemical shifts of the individual energy levels of the silicon atoms in both the pure and contaminated silicon surfaces, in quartz and Fe∶Si alloy are given. Finally, the possibilities and limitations of the heating for the silicon surface cleaning are examined.     

Sheet resistance and noise properties of ion-implanted silicon structures

Experimental-study results are presented on the sheet resistance and low-frequency current-noise spectra in silicon layers that have been implanted by phosphorous and boron ions as functions of the conditions of implantation and post-implantation heat treatment. Results of evaluation of the Pearson implantation profiles are presented to explain the obtained dependences, and data in the literature on defects in ion-implanted silicon are cited. The noise spectra are analyzed using Hooge's empirical formula.Presented at All-Union Coordinating Conference Low-Frequency Noise in Semiconductor Devices (Chernogolovka, Moscow Region, June, 1991).Institute of Microelectronics, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 12, pp. 1136–1142, December, 1993.     

Quantitative Auger analysis of gold-copper-oxygen and gold-nickel-oxygen surfaces using relative sensitivity factors

Quantitative Auger analysis is becoming routine for unoxidized binary allowys. Many specimens of technological importance, however, contain large amounts of oxygen, which can complicate quantitative analysis by changing (a) peak shapes (e.g. ] ne widths, δ), (b) energy position of the peaks, (c) Auger currents, and (d) the sputtering correction factor (R). This paper describes quantitative Auger analysis of the gold- copper-oxygen and gold-nickel-oxygen systems, based on relative sensitivity factors before (P_rel) and after (P^s_rel) sputtering. The relative sensitivity factors, (P^s_rel) were found to be independent of the gold and oxygen concentrations for both systems. In the gold-copper-oxygen system this is attributed to the sharpness of the 920 eV (LMM) copper transition compared to the energy resolution (0.6%) of the CMA analyzer used. For the gold-nickel-oxygen system it is ascribed to a fortuitous cancellation of two effects (1) increased line width, δ, hence a decreased 848 eV (LMM) peak height upon oxidation, and (2) increased Auger emission of the 848 eV peak due to oxidation. A single crystal standard of Cu₂O was used to confirm the 2 : 1 ratio of Cu to O in the ternary samples. The sputtering correction factors were found to be R(O, Cu) = 1.0 for the composition of Cu₂O and R(O, Ni) = 0.72 for the composition NiO. The variation in R with Au concentration is negligible. The major limitation on the quantitative Auger analysis of these ternary systems has been found to be uncertainty in the sputtering correction Factor R. Nomographs for calculating concentrations for constant C_o/C_Cu and C_O/C_Ni using (P^s_rel) are also presented.     

Preparation of ion-implanted silicon for transmission electron microscopy

This paper deals with the preparation technique of thin foils (below 5000 Å) for the transmission electron microscopy from silicon implanted by N⁺ ions. Mechanical and chemical thinning and anodic oxidation techniques are discussed and selective etching of the surface of silicon for the purposes of the replica technique is noted. Compositions of etching solutions and other experimental parameters are mentioned. The results are demonstrated on electron micrographs showing the radiation damage due to ion implantation in silicon.     

Repolarization studies in amorphous and polycrystalline silicon

A procedure has been developed to extract qualitative and quantitative information on the muonium fractions, in particular the Mu^* fraction, in polycrystalline and amorphous materials from their longitudinal field repolarization curves. Preliminary results for amorphous silicon suggests that both the Mu^* and Mu^* fractions here are generally lower than in crystalline silicon at temperatures below 200K, but the Mu^* fraction may survive to room temperature in this disordered host.     

Carrier frequency-dependent intrinsic parameters in an ion-implanted silicon photo-MESFET

Carrier frequency-dependent intrinsic parameters of an ion-implanted silicon photo-MESFET have been analysed theoretically. The internal gate source capacitanceC _gs is found to increase with increasing carrier frequency under the normally OFF condition and the change is small under the normally ON condition. Also, the internal drain-source resistanceR _ds increases with frequency at a fixed flux density and wavelength of operation. The ion-implanted photo-MESFET could become useful as optically controlled switching device in digital circuits.