I. Suni

Effects of electrically active impurities on the epitaxial regrowth rate of amorphized silicon and germanium

Abstract The influence of electrically active n-type ( 75 As) and p-type ( 11 B) impurities on the solid phase epitaxial regrowth of ion-implanted amorphized Si〈100〉 and Ge〈100〉 has been studied for low temperature furnace annealing. Both types of impurity increase the rate of regrowth of both silicon and germanium at a concentration level of 10 20 cm -3 . Above this level, 75 As retards regrowth in germanium. In compensated surface layers, the regrowth rate slows down to the values observed in self-implanted or intrinsic crystals for both silicon and germanium. The results can be qualitatively explained in terms of electrically induced generation of point defects at the amorphous-crystalline interface.

Stability of amorphous Fe-W alloys in multilayer metallizations on silicon

Abstract Co-sputtered amorphous Fe 0.37 W 0.63 alloys were investigated for applications as diffusion barriers in multilayer metallizations on silicon. Interface reactions and recrystallization during thermal annealing at 400–800°C were studied by back-scattering spectrometry and X-ray diffraction. On SiO 2 substrates the recrystallization of these films occurs at approximately 700°C. On silicon the recrystallization is accompanied by the formation of a silicide layer containing FeSi 2 and WSi 2 phases. No detectable reaction is observed when the alloy film is amorphous. In contact with an overlay metal such as aluminum, copper, nickel or platinum the amorphous Fe 0.37 W 0.63 layer prevents direct interaction between the silicon substrate and an overlay metal film 1000 A thick during thermal annealing for 30 min at 650°C. The lifetime of the barrier is limited by dissolution and compound formation at the interface and at grain boundaries of the overlay metal.

Titanium nitride as a diffusion barrier between nickel silicide and aluminum

The diffusion barrier properties of titanium nitride between nickel silicide and aluminum have been investigated in NiSi Schottky contacts on silicon for annealing temperatures of 400–600°C. No interaction between the metals of the contact structure was detected by backscattering spectrometry, even at 600°C. The electron barrier height of Schottky diodes stays constant at ϕBn = 0.67 ± 0.01 upon thermal annealing in vacuum at 500°C for 2 h . The ideality factor is n = 1.01. After 4 h, ϕ Bn decreases by about 10 mV and n rises to 1.0 6. The diodes degrade after annealing at 550°C or 600°C for 30 min.

Recrystallization of amorphous silicon layers on sapphire

Abstract Electrical conductance measurements, X-ray diffraction, optical microscopy with transmitted light, megaelectronvolt 4 He + backscattering and channeling techniques were used to investigate the recrystallization characteristics of amorphous silicon layers on sapphire obtained by ion implantation or vacuum evaporation. It was found that the electrical conductance characteristics strongly depend on the mode of recrystallization which in turn depends on the ability of the amorphous silicon layer to form an interconnecting network of crystalline silicon before or after the crystallites have grown vertically through the entire film. The limitations of using electrical conductance measurements to deduce growth rates are discussed. It is also shown that optical microscopy can be useful in monitoring the nucleation and growth process. The temperature range for growth rate determination can be extended to 800 °C or more if a lateral motion method is used. The growth rates determined by this method were found to be in agreement with those determined by channeling and reflectivity measurements.

Thermal oxidation of sputtered TiN diffusion barriers

The oxidation of thin (up to 3000 A) TiN layers was studied experimentally. It was found that the TiN layers transform into TiO2 with a rutile structure during heat treatment at temperatures around 500 °C in oxidizing ambient. The growth of the oxide layer has a dependence that follows the square root of time. Measurements of the optical properties of the oxide layers so formed indicate that they can be used as antireflecting coatings on solar cells.

Interdiffusion of thin bilayers of copper and nickel

Abstract The interdiffusion of vacuum-deposited Cu/Ni bilayers is investigated for annealing at temperatures from 500 to 800°C. Backscattering spectra, electrical sheet resistance data and X-ray analysis confirm independently that strong interdiffusion sets in at 400°C after annealing for 15 min. We conclude that thin nickel films will not perform as reliable diffusion barrier for copper in metallization schemes with silicon.

Finite metal-sheet-resistance in contact resistivity measurements: Application to Si/TiN contacts

Abstract The standard transmission line model cannot be applied to evaluate the contact resistivity of thin TiN layers on highly doped p + and n + substrates because the finite sheet resistance of the TiN must be accounted for. We present two ways to include this effect using existing analytical models. The results are shown to agree with measurements where the effect of the finite sheet resistance of TiN is eliminated with a metallic overlayer. With the help of these evaluation techniques, it is shown that the contact resistivity of TiN changes in opposite ways for p + and n + Si after vacuum annealing at 600°C for 15 min. This result is consistent with an increase of the barrier height φ Bn of the contact by ≅0.1 V to near midgap value.

GeSi heterostructures by crystallization of amorphous layers

Abstract Heterostructure of Ge x Si 100− x layers on Si〈100〉 substrates were fabricated by solid phase growth. The samples were analyzed by X-ray diffraction, transmission electron microscopy, megaelectronvolt backscattering spectrometry and four-point probe measurements before and after thermal annealing. The conditions at the interface between the amorphous layer and the substrate play an important role in controlling the crystalline structure of the grown layer. With increasing content of germanium in the alloy, the onset time (delay time) for crystallization is observed to decrease. A model is developed to rationalize the crystallization behavior observed on both single-crystal silicon and SiO 2 substrates.

Contact resistivities of sputtered TiN and TiTiN metallizations on solar-cell-type-silicon

Abstract Contact resistivities of TiN and TiTiN contacts on a shallow junction solar-cell-type silicon substrate have been investigated. The contact materials were sputter-deposited. The method of the transmission line model was applied for contact resistivity measurements. The contact resistivity of the n + SiTiN contact system was 2 × 10 −3 Ωcm 2 ± 50 per cent and remained constant after annealing up to 700°C for 30 min. For the n + SiTiTiN system, the contact resistivity of 9 × 10 −4 Ωcm 2 ± 50 per cent was measured. A heat treatment of 700°C. 30 min decreases this value by one order of magnitude and the interposed Ti fully reacts with Si and forms a TiSi 2 layer. The voltage drop caused by the n + SiTiN contact system in a standard non-concentrator solar cell is negligible. The n + SiTiSi 2 TiN contact system should be acceptable for Si solar cells used at up to 100 times solar concentration.

Phase transformations in ion‐irradiated silicides

The phase transformations in a number of ion‐implanted and subsequently annealed silicides have been investigated. The electrical resistance change as a function of 28Si+ ion implantation has been found to correlate with the presence of a disordered state in the silicide. Epitaxial silicides such as CoSi2 were found to regrow in a layer by layer manner when implanted such that the top region was amorphous but with a single‐crystal seed remaining at the bottom of the original layer. Recrystallization temperatures (defined as the temperature at which one half of the silicide has transformed) were determined by in situ electrical measurements as well as by x‐ray diffraction studies. Recrystallization temperatures were found to be approximately 1/3 of the silicide melting point. Both cosputtered and implanted refractory metal silicides were also found to be governed by this rule. Under the assumption that recrystallization can be described by the Avrami equation, it was found that n, the mode of transformatio...