Diffusion barriers

The choice of the metallic film for the contact to a semiconductor device is discussed. One way to try to stabilize a contact is by interposing a thin film of a material that has low diffusivity for the atoms in question. This thin film application is known as a diffusion barrier. Three types of barriers can be distinguished. The stuffed barrier derives its low atomic diffusivity to impurities that concentrate along the extended defects of a polycrystalline layer. Sacrificial barriers exploit the fact that some (elemental) thin films react in a laterally uniform and reproducible fashion. Sacrificial barriers have the advantage that the point of their failure is predictable. Passive barriers are those most closely approximating an ideal barrier. The most-studied case is that of sputtered TiN films. Stuffed barriers may be viewed as passive barriers whose low diffusivity material extends along the defects of the polycrystalline host

Electrical characteristics of Al contact to NiSi using thin W layer as a barrier

We show that the thermal instability that is observed in Schottky diodes with an Al film on NiSi contact to can be removed by introducing a very thin (~250 Å) tungsten film between the Al and the NiSi layers. This structure can be formed by sequential evaporation of Ni, W, and Al and subsequent thermal annealing to form NiSi. Schottky barrier measurements show that the contact is thermally stable at 450 °C up to about 1-h annealing with very little change in the electronic barrier height. A model, derived from the electrical measurements, is proposed for the failure mode of the tungsten barrier after excessive annealing

Thermal oxidation of nickel disilicide

The thermal oxidation characteristics of nickel disilicide on Si substrates have been investigated in the temperature range of 700–900 °C in dry oxygen and wet oxygen. A surface layer of SiO2 grows parabolically in time. The growth rate is independent on the crystalline structure (epitaxial or polycrystalline) and thickness of the NiSi2 layer. We surmise that the oxidation mechanism is dominated by oxygen diffusion through the growing SiO2. Activation energies for the dry and wet oxidation are 1.0±0.1 eV and 1.5±0.1 eV, respectively. NiSi2 layers on SiO2 oxidize with the same rate—resulting with progressively Ni-rich NiSi2. Preliminary measurements of the oxide quality yield dielectric strength of 2.1×10^6 V cm^−1, and a pinhole density of about 100 per cm2. A survey of oxidation data for Si and other refractory metal silicides shows that their oxidation does not draw similar kinetics to that of NiSi2

Pure Space-Charge-Limited Electron Current in Silicon

Phosphorus diffusion on π‐type silicon is used to fabricate n^+πn^+ structures of base widths between 3 μ and 60 μ with π‐type resistivities of 300 Ω⋅cm and 8 kΩ⋅cm. The V‐I characteristics of the structures are measured at room temperature and at liquid‐nitrogen temperature. The change in current for constant applied voltage is also observed in that temperature range. The results are interpreted in terms of simple models based on the assumption that pure space‐charge‐limited current of electrons is present. The models describe well the characteristics measured on 300‐Ω⋅cm samples, except for the range of small biases on the thinnest samples. It is concluded that the drift velocity of electrons at 78°K tends towards saturation at 1.0×10^7 cm∕sec ± 10%. The current observed at this temperature actually reaches this value. The critical electric field at 78°K is 10^3 V∕cm±30% but the meaning of this concept for electrons in silicon is vague. The temperature dependence of the current at fixed bias voltages is in general agreement with the variation of the low field mobility. Results obtained on 8‐kΩ⋅cm samples need clarification. Effects of breakdown and trapping are not observed

Generation and recovery of strain in (28)Si-implanted pseudomorphic GeSi films on Si(100)

Effects of ion implantation of 320 keV Si-28 at room temperature in pseudomorphic metastable GexSi1-x (x almost-equal-to 0.04, 0.09, 0.13) layers approximately 170 nm thick grown on Si(100) wafers were characterized by x-ray double-crystal diffractometry and MeV He-4 channeling spectrometry. The damage induced by implantation produces additional compressive strain in the GexSi1-x layers, superimposed on the intrinsic compressive strain of the heterostructures. This strain rises with the dose proportionally for doses below several times 10(14) Si-28/cm2. Furthermore, for a given dose, the strain increases with the Ge content in the layer. Upon thermal processing, the damage anneals out and the strain recovers to the value before implantation. Amorphized samples (doses of greater than 2 x 10(15) Si-28/cm2) regrow poorly

Defects production and annealing in self-implanted Si

230-keV 28Si ions were implantated into Si(100) at room temperature with doses from 1014 to 1015/cm2. The samples were analyzed by x-ray double crystal diffractometry and 2-MeV 4He ion channeling spectrometry. The implanted layer has a parallel lattice spacing equal to that of the unimplanted substrate. The perpendicular lattice spacing is larger than that of the unimplanted substrate and is proportional to the defect concentration extracted from the channeling measurement. Both the perpendicular lattice spacing and the defect concentration increase nonlinearly with ion dose. The defect concentration initially increases slowly with dose until a critical value (~15%, at 4×1014/cm2), then rises rapidly, and finally a continuous amorphous layer forms. The initial sluggish increase of the damage is due to the considerable recombination of point defects at room temperature. The rapid growth of the defect concentration is attributed to the reduction of the threshold energy for atomic displacement in a predamaged crystal. The amorphization is envisioned as a cooperative process initiated by a spontaneous collapse of heavily damaged crystalline regions. The annealing behavior of the damaged layer reveals various stages of defect recovery, indicating that the damage consists of a hierarchy of various defect structures of vacancy and interstitial aggregates

Self-confined metallic interconnects for very large scale integration

A novel method to produce narrow metallic lines is presented. Lines of NiSi2 lithographically formed on SiO2 substrates are oxidized. The formed SiO2 layer consumes most of the Si from the silicide, leaving a metallic Ni line fully confined by SiO2. The associated problems together with the potential utilization are discussed

Defect production in Si(100) by 19F, 28Si, 40Ar, and 131Xe implantation at room temperature

We used x-ray double-crystal diffractometry and MeV 4He channeling spectrometry to study quantitatively the damage produced in Si(100) at room temperature by 230-keV 19F, 230-keV 28Si, 250-keV 40Ar, or 570-keV 131Xe implantation. The measured defect concentration and the perpendicular strain have the same depth profile, and both are depleted near the surface compared to the Frenkel pair concentration calculated from computer simulation. The perpendicular strain is proportional to the defect concentration with a coefficient of B~0.01 common to all implanted species. The maximum value of the perpendicular strain and of the defect concentration rises nonlinearly with the dose for all species. The damage produced by different implanted species depends on the dose in approximately the same way save for a scaling factor of the dose. In the regime of low damage, the strain and the defect concentration rise linearly with increasing dose. The slope of this rise with dose increases with the square of the Frenkel pairs produced per unit dose of incident ions, as calculated from computer simulations. This fact means that stable defects produced by room-temperature implantation in Si(100) cannot be predicted by a linear cascade model

Damage production and annealing in 28Si-implanted CoSi2/Sim(111) heterostructures

The damage in epitaxial CoSi2 films 500 nm thick grown on Si(111) produced by room-temperature implantation of 150 keV 28Si were investigated by 2-MeV 4He channeling spectrometry, double-crystal x-ray diffractometry, and electrical resistivity measurements. The damage in the films can be categorized into two types. In lightly (heavily) damaged CoSi2 the damage is in the form of point-like (extended) defects. The resistivity of lightly damaged CoSi2 films rises with the dose of implantation. Electrical defects correlate well with structural ones in lightly damaged films. The resistivity of heavily damaged films flattens off while the structural defects continue to rise with the dose, so that resistivity no longer correlates with structural defects. Upon thermal annealing, lightly damaged films can fully recover structurally and electrically, whereas heavily damaged films do so only electrically. A residual structural damage remains even after annealing at 800 °C for 60 min

Drift velocity of electrons in silicon at high electric fields from 4.2° to 300°K

The drift velocity of electrons in silicon at high electric fields is measured in the direction over the range of lattice temperatures from 4.2° to 300°K. It is established that in this range a limiting drift velocity exists. Its temperature dependence is measured. The samples used and the method of measurement are briefly described