R. Chowdhury

CHARACTERISTICS OF TITANIUM NITRIDE FILMS GROWN BY PULSED LASER DEPOSITION

Laser physical vapor deposition (LPVD) has been used to grow titanium nitride films on hydrogen-terminated silicon(100) substrates at deposition temperatures ranging from room temperature to 600 °C. A pulsed KrF excimer laser (λ = 248 nm, τ = 25 ns) was used with the deposition chamber maintained at a base pressure of 10 −7 Torr prior to deposition. Different properties of the films were investigated by x-ray diffraction, Auger electron spectroscopy, Raman spectroscopy, optical, scanning, and high resolution transmission electron microscopy, and measurement of electrical resistivity. When the substrate temperature was low (at and below 500 °C), oxygen atoms from the residual gases were incorporated in the films. The microstructures and resistivities of TiN films were found to be strongly dependent on the temperature of the silicon substrates. The TiN films deposited at 600 °C were oxygen-free, as observed from Auger analysis, and the room temperature resistivity was found to be 14–15 μΩ-cm. Raman spectroscopy of the films showed that the nitrogen-related optical phonon peak increased with deposition temperature in comparison with the titanium-related acoustic peak. Transmission electron microscopy and x-ray diffraction analyses showed that the films were polycrystalline at low temperature with grain size ranging from 300–600 A, depending on the temperature of the substrate. At 600 °C, the films were found to be single crystals with occasional presence of dislocation loops. The spacing of Moire fringes in TiN/Si samples deposited at 600 °C established the nearly periodic elastic strain field extending into the TiN and Si at the interface. Although there exists a large misfit between TiN and Si (24.6%), the epitaxial growth of TiN films on Si(100) substrates was explained by means of domain-matched epitaxy with a 4-to-3 match in unit cells for TiN/Si structure, giving rise to a residual lattice misfit of only 4%.

Pulsed laser deposition and characterization of epitaxial Cu/TiN/Si(100) heterostructures

Three‐dimensional epitaxial Cu/TiN/Si(100) heterostructures have been grown by pulsed laser deposition using a single chamber, in situ processing method. The epitaxial TiN layers on Si(100) were grown at 600 °C and epitaxial Cu layers on TiN/Si(100) in the temperature range 200–600 °C using optimized laser parameters. These structures were characterized using three‐axis x‐ray diffraction (Θ, Φ, Ψ scans) technique and high‐resolution transmission electron microscopy. The results clearly indicate cube‐on‐cube epitaxial alignment along the three axes, i.e., 〈100〉Cu∥〈100〉TiN∥〈100〉Si. The Cu/TiN and TiN/Si interfaces were found to be quite sharp without any indication of interfacial reaction. The growth mechanism of copper on TiN was found to be three dimensional, with the size of island varying from 0.3 to 1.5 μm. We discuss domain matching epitaxy as a mechanism of growth in these large lattice mismatch systems, where three lattice constants of Si(5.43 A) match with four of TiN(4.24 A) and seven units of Cu(...

Pulsed laser deposition of epitaxial Si/TiN/Si(100) heterostructures

We have successfully deposited multilayer Si/TiN/Si(100) epitaxial heterostructures using pulsed laser deposition technique. This silicon‐on‐conductor device configuration has potential applications in three‐dimensional integrated circuits and radiation hardened devices. The Si and TiN films were deposited by pulsed laser (KrF: λ=248 nm, τ =25 ns) physical vapor deposition technique at a substrate temperature of 600 °C in a chamber maintained at a vacuum of ∼10−7 Torr. The epitaxial nature of the films was characterized using x‐ray diffraction, Rutherford backscattering, and high resolution transmission electron microscopy techniques. The two interfaces (100)TiN/Si(100)substrate and (100)Si/(100)TiN layers were quite sharp without any indication of interfacial reaction between them. The epitaxial relationship was found to be 〈100〉Si∥〈100〉TiN∥〈100〉Si. In the plane, four unit cells of TiN matched with three unit cells of silicon with less than 4.0% misfit. This domain matching epitaxy provides a mechanism o...

Domain epitaxial growth of TiN/Si(001), TiN/GaAs(001), and Si/TiN/Si(001) heterostructures by laser physical vapor deposition: theory and experiment

We have successfully deposited epitaxial titanium nitride films on (001) silicon and (001) gallium arsenide substrates and multilayer Si/TiN/Si(001) epitaxial heterostructures using pulsed laser (KrF: λ = 248 nm, τ = 25 ns) physical vapor deposition. The deposition of TiN was carried out at a substrate temperature of 600°C on Si(001) and 400°C on GaAs(00l). The interfaces were sharp without any indication of interfacial reaction. The epitaxial relationships were found to be <001> TiN ‖<001> Si on the silicon substrate, <001> Si ‖<001> TiN ¦<001> Si on the heterostructure, and [1-10] TiN‖[110] GaAs and [001] TiN ‖[110] GaAs on the GaAs substrate. The growth in these large-mismatch systems is modeled and the various energy terms contributing to the growth of these films are determined. The domain matching epitaxy provides a mechanism of epitaxial growth in systems with large lattice mismatch.The epitaxial growth is characterized by domain epitaxial orientation relationships with m lattice constants of epilayer matching with n of the substrate and with a small residual domain mismatch present in the epilayer. This residual mismatch is responsible for a coherent strain energy. The magnitude of compression of Ti-N bond in the first atomic layer, contributing to the chemical free energy of the interface during the initial stages of growth, is found to be a very important factor in determining the orientation relationship. This result was used to explain the differences in the orientaion relationships between TiN/Si and TiN/GaAs systems. The various energy terms associated with the domain epitaxial growth are evaluated to illustrate that the domain epitaxial growth is energetically favorable compared to the lattice mismatched epitaxial growth. The results of this analysis illustrate that the observed variations in the epitaxial growth are consistent with the minimum energy configurations associated with the domain epitaxial growth.

Synthesis of Highly Dense β-SiC Pellet by Self Propagating High Temperature Synthesis

Abstract β-SiC has been synthesized using the process of self-propagating high temperature synthesis (SHS) (1). Ti was added as a binder and the effect of titanium addition on the reaction propagation has been studied. Temperature of combustion is considerably lowered by the addition of titanium and the incubation period leading to the melting of the silicon powders is reduced. The reaction propagated through the pellet faster and the product synthesized was dense and compact. The synthesized composite was characterized using X-ray, Raman spectroscopy, SEM and TEM. We proposed a model for the synthesis based on dissolution, diffusion and precipitation from the supersaturated solution. There was no indication of the formation of TiSi2, during synthesis. An attempt is made to explain this observation based on free energy considerations.

Growth of Continuous Diamond Film by Hot Filament C VD Technique on SiC/TiC Pellets, Synthesized Using Combustion Synthesis

Abstract β-SiC/TiC composites were synthesized using the process of self propagating-high temperature combustion synthesis (SHS). The heat released during the exothermic reaction between the metal and the carbon powder results in the melting of silicon and the titanium into which the carbon diffuses and then (3-SiC and TiC precipitates out from the supersaturated solution. The composite was characterized using X-ray diffraction techniques, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. An attempt was made to understand the mechanism of formation of the composite. A theory is proposed for the possible mechanism based on dissolution, diffusion and precipitation from the supersaturated solution. Diamond film was then grown on the pellet by hot filament CVD technique using methane and hydrogen gas as the reactants. The deposition was conducted for a period of four hours. A continuous film of diamond was found to grow on β-SiC/TiC composite using this technique. The diam...

Pulsed laser processing of epitaxial TiN/Si heterostructures

This paper reviews our recent work on laser processing and characterization of epitaxial TiN/Si heterostructures. Pulsed laser deposition (PLD) technique has been employed to grow TiN films on H- terminated Si(100) substrates at various temperatures in the range of 25 to 600 degree(s)C. A pulsed KrF excimer laser ((lambda) equals 248 nm, (tau) equals 25 X 10-9 sec) was used with the deposition chamber maintained at a base pressure of 10-7 Torr/. The films were characterized by x-ray diffraction technique, Auger electron spectroscopy, Raman spectroscopy, scanning and high resolution electron microscopy, Rutherford backscattering spectroscopy and four probe electrical resistivity. Auger and Raman spectroscopy revealed that the films were purely TiN and free from oxygen impurities. The x-ray diffraction and TEM results showed that the TiN films deposited at 600 degree(s)C were single crystal in nature with epitaxial relationship <100>TiN<100>Si. The RBS channeling yield for these films was found to be in the range of 10-13%. Four-point-probe electrical resistivity measurements showed characteristic metallic behavior of these films as a function of temperature with the lowest value of resistivity of about 15(mu) (Omega) -cm at room temperature. The epitaxial growth of TiN on Si(100) is rationalized in terms of domain matching epitaxy, where four unit cells of TiN match with three unit cells of Si with less than 4% misfit. This paper also describes the fundamental issues related to thin film growth, defect formation, atomic structure of defects and interfaces in semiconductor heterostructures.