Using ellipsometric analysis, the complex index of refraction of lowenergy, hydrogen ion bombarded, [100] single-crystal silicon was measured as a function of distance from the bombarded surface. The bombardment conditions were a 1600 eV hydrogen beam produced by a Kaufman ion source, 1.4 mA/cm2 flux, 2 × 1018 ions/cm2 fluence and 275°C bulk silicon temperature. These conditions are comparable to the conditions generally reported to result in a substantial increase in the electrical conductivity of polycrystalline silicon solar cell material. The results of this study indicate that the real and imaginary parts of the refractive index of the ion bombarded surface region approach that of the unbombarded substrate at a depth of 50 nm. The refractive index of about the first 10 nm of ion bombarded material is strongly dependent on the bombardment conditions. Variations in the imaginary part of the refractive index indicate that approximately 10% of incident radiation is absorbed by the first 50 nm of modified material.

We have Investigated the layer formed on Si surfaces passivated by a Kaufman Ion source using mixtures of hydrogen and hydrocarbons. Chemical, optical, and electronic techniques were employed to characterize this layer and Its effect on passivation of defects in the Si. The evidence Indicates that the layer Is a dielectric and probably has the formula Six C(1-x) (H). It does not appear to Impede the passivation of polycrystalline Si, but it does affect the reflectivity of the Si material, and also the barrier height In Schottky junctions. We suggest that a similar layer may be formed during other hydrogen/hydrocarbon plasma treatments of SI.

Use of N doping, N gas ambients and N implantation in Si processing has stimulated study of the incorporation and behaviour of N in Si. Studies of N-implanted Si and comparisons with melt-doped Si have shown that N pairing is the dominant mode for bonding of N into crystalline Si for a wide range of processing conditions. Studies have also shown that laser annealing quenches a small percentage of implanted N into a substitutional site. Nitrogen diffusion and aggregation have been shown to occur in N-implanted Si upon furnace annealing at temperatures >700°C and there is a simultaneous formation of shallow donors. Interactions between N and other impurities occur in both as-grown and ion-implanted Si. Additional studies are needed to describe more fully the electrical and structural consequences of N-N, Nimpurity and N-defect interactions in Si.

Nitrogen atoms exist in silicon as non-reactive nitrogen molecules. This is concluded from two I-R absorption experiments: one is the nitrogen isotope effects on N- N pairs and the other is silicon isotope shifts at 10 K. Intrinsic resistivities (over 20 K ohm-cm) are obtained by annealing at 1000°C, 1 min. in N2 in both p- and n-type nitrogen doped thin wafers. Resistivity increases are due to deep- level generations: 0.66 eV above the valence band for p-type and mainly 0.44 eV below the conduction band for n-type material. These deep levels are considered to be formed by nitrogen pairs and divacancies which are incorporated during growth. Since divacancies are easy to out diffuse to the wafers surface, the deep levels are also irreversibly removed. Diffusion coefficient of Si intersititialswici'ch are annihilated with divacancies in the lattice are calculated as 6×10−6cm2/s and 2×10−6cm2/s at 900°C and 1000°C respectively. Migration energy of Si interstitials is about 4.5 eV.

We report five photoluminescence lines N1 through N5 in silicon which emerge after sequential nitrogen and carbon implantation. Studied is in particular the 0.7456 eV (N1) electronic-vibronic spectrum. Single nitrogen and carbon atoms in the defect are identified by isotope shifts of the no-phonon transition and of a local mode satellite with vibration quantum energy ħω= 122.9 meV. Uniaxial stress or Zeeman measurements yield monoclinic I (C1h) or trigonal (C3v) symmetry, respectively, of the optical defect. Comparing the energy of the local mode and its isotope effects with recent literature data on the nitrogen 963 cm−1 IR vibrational absorption line we discuss a defect model involving a substitutional nitrogen atom modified by an interstitial carbon atom.

The pseudo Jahn-Teller effect and chemical rebonding are both considered as mechanisms that drive substitutional atoms, such as N in Si, off-center. By use of an effective Hamiltonian technique, impurities forming very deep levels, such as Si:N, are found to be susceptible to off-center displacement by the pseudo Jahn-Teller effect. Using a Hartree-Fock technique, we find two classes of N displacements which depend on the relaxation of the nearest-neighbor Si atom “cage”. For outward relaxation of the four nearest neighbors, the N displaces by 0.05 Å in the [111] direction and retains sp3 bonding; this mechanism appears equivalent to the pseudo Jahn-Teller effect. For inward relaxation of the “cage” by 0.45 Å the N displaces by 0.75 Å in the [1 1 1] direction and forms a trigonal sp2 bond; this is a chemical rebonding mechanism. Additional cluster calculations suggest that inward relaxation of the “cage” is likely. Similar calculations for 0 revealed a <100> displacement of approximately 1.1Å.

Current IC technology uses SiO2 almost exclusively; however, several technological and reliability problems warrant the search for an alternative dielectric. Proposed alternatives are silicon nitride and nitrided SiO2. This paper reviews the work on thermal nitridation of Si and SiO2. Several of the experimental thermal nitridation processes used to achieve good thin dielectrics are discussed. At this time a clear mechanism for the nitridation of Si is not available. The two theoretical attempts to model this process are reviewed. Innovative processes to accomplish the nitridation, such as plasma growth, etc., are presented. Finally, the influence of nitridation on stacking faults and diffusions is also reviewed.