H. T. G. Hentzell

Mechanisms of reactive sputtering of titanium nitride and titanium carbide II: Morphology and structure

Titanium was reactively r.f. sputtered in mixed ArN2 and ArCH4 discharges onto substrates held at 775 K. The films obtained were characterized by scanning electron microscopy and X-ray diffraction and through measurements of the microhardness and electrical resistivity. The composition of the films was determined by Auger electron spectroscopy. The measurements show that the morphology of the deposits to a large extent influences the properties of the films obtained. For TiN coatings the electrical resistivity reaches the bulk resistivity only if coatings with the full bulk density are obtained. The difference observed in the lattice parameter for TiN thin film and bulk samples is explained using a grain boundary relaxation model. It is also shown that the heat of formation of the compounds plays an important role in the formation of carbide and nitride films. A high heat of formation promotes the development of large grains and dense structures.

Crystallization of amorphous silicon during thin‐film gold reaction

The crystallization of a‐Si in a‐Si (50‐nm) and Au (5‐nm) thin‐film bilayers has been investigated during heat treatment in a transmission electron microscope. When crystallization of a‐Si first begins at 130 °C, the Au‐Si alloy (Au and a precursor phase) reflections observed at lower temperatures vanish, and several new reflections from metastable Au‐Si compounds occur. Dendritically growing islands of poly‐Si are observed after heating at 175 °C. If the samples are held at a constant temperature of 175 °C for 10 min, the poly‐Si islands coalesce. The formation of poly‐Si depends on the diffusion of Au into a‐Si and the formation of metastable Au‐Si compounds, which act as transport phases for both Si and Au. After crystallization Au segregates to the front and back surfaces of the poly‐Si film. The result of this work and earlier diffraction investigations are interpreted in terms of superlattices based on a sublattice. A fundamental body‐centered‐cubic structure with a=5.52 A and composition Au4Si is s...

Adhesion of titanium nitride coatings on high‐speed steels

The adhesion is of vital importance for the performance of tools coated with titanium nitride. In view of this, we have studied the effects of substrate temperature and pretreatment on the adhesion of TiN coatings. Since high‐speed steels are among the most used substrate materials for tool applications we have chosen to deposit the films onto eight different high speed steels. The TiN coatings were deposited using reactive dc‐magnetron sputtering, and the adhesion was measured using the scratch test. In order to study the film–substrate interface Auger electron spectroscopy was used in combination with ion beam depth profiling. On most of the steels, the adhesion of the films increased with substrate temperature, reaching a maximum between 400 and 500 °C. The increased adhesion is associated with changes in the oxide layer on the steel substrate. As the temperature increases, Fe2O3 and F3O4 decompose to FeO. Sputter etching of the substrate prior to deposition improves the film adhesion even though a com...

Mechanisms of reactive sputtering of titanium nitride and titanium carbide III: Influence of substrate bias on composition and structure

Abstract Films of TiN and TiC were grown by reactive r.f. sputtering of titanium in mixed ArN2 and ArCH4 discharges on negatively biased substrates. The compositions of the films were measured using Auger electron spectroscopy and their structure and morphology studied using X-ray diffraction and scanning electron microscopy respectively. The composition was found to be strongly affected by the bias voltage. An increase in bias both the carbon and the nitrogen contents in substoichiometric films. However, when stoichiometric TiN is formed no further change in the composition occurs. For TiC films an increase in the carbon- to-titanium ratio above 1.0 is possible. The structure is also affected by the bias voltage. For example the grain size of TiN has a maximum at a bias of 200 V. A possible explanation is a double influence of the ion bombardment. At low voltages, the adatom mobility is enhanced and the grain size increases but as the bias increases resputtering of species from the growing film surface becomes increasingly important and the grain size decreases.

Formation of aluminum silicide between two layers of amorphous silicon

Thin‐film structures of amorphous Si/Al/amorphous Si were deposited consecutively without breaking the vacuum. During annealing to 440 K, Al reacts with Si to form a homogeneous compound layer between the two a‐Si layers. This compound has a unique and well‐defined structure, different from both Al and Si although some similarities exist. The Al silicide observed is stable up to 575 K, at which temperature it dissociates when a‐Si crystallizes.

Initial solid‐state reactions between crystalline Sb and amorphous Si thin films

Bilayers of Sb and Si thin films were deposited at room temperature on a thin (20–30 nm) Si3N4 film using electron‐beam evaporation. The solid‐state reactions in the bilayers were investigated using transmission electron microscope (TEM) during in situ annealing and Auger electron spectroscopy (AES). The reactions resulted in either an amorphous Sb‐Si (a‐Sb‐Si) alloy or caused crystallization of amorphous silicon (a‐Si) at low temperatures, depending on the film thickness of an a‐Si layer as well as the heating rate. As predicted from the phase diagram, no compounds between Sb and Si were observed. The initial intermixing of Sb and a‐Si was found to be anomalously fast.

Effects of Sb on phase transformations of amorphous TiSi2 thin films

Co‐deposited amorphous TiSi2 thin films with various Sb concentrations were prepared in order to study the effects of Sb on TiSi2 phase transformations. The crystallization behavior of the films was investigated by in situ annealing in a transmission electron microscope. The phase transformation from C49 TiSi2 to C54 TiSi2 in the films was examined with x‐ray diffraction. It was observed that incorporation of Sb resulted in a higher crystallization temperature of the amorphous TiSi2 film and a lower crystal growth rate. The activation energies for the crystal growth during the crystallization were determined to be 1.37, 1.62, 1.63, and 1.87 eV (±0.07 eV) for the films with 0, 0.3, 1.3, and 2.5 at. % Sb, respectively. For the C49→C54 transformation, it was, however, observed that the activation energy decreased when the Sb content increased. These indicate that the Sb incorporation in TiSi2 retards the crystallization of the amorphous TiSi2 film, but enhances the transformation from C49 TiSi2 to C54 TiSi2.

Thermodynamic investigations of solid-state Si-metal interactions. I, experimental and analytical studies of the Si-Ti binary system

An experimental study has been made on reactions in codeposited and multilayer films consisting of silicon and titanium deposited by electron beam evaporation. Transmission electron microscopy and Auger electron spectroscopy were used to determine structures and compositions. The experimental results from the codeposited films in the whole composition range (0%–100%) were compared with the predictions from the calculated free‐energy diagram of the Si‐Ti system. It is revealed that the phenomena of metal‐induced crystallization of amorphous silicon and formation of amorphous alloys appear in two different composition ranges in the binary system. Metal‐induced crystallization of amorphous silicon is attributed to lowering of bonding energy of SiSi bonds by titanium atoms in the Si‐rich composition range and the formation of an amorphous Si‐Ti alloy is attributed to the dominant SiTi bonding due to the largely negative heat of mixing between the two elements in a medium composition range.An experimental study has been made on reactions in codeposited and multilayer films consisting of silicon and titanium deposited by electron beam evaporation. Transmission electron microscopy and Auger electron spectroscopy were used to determine structures and compositions. The experimental results from the codeposited films in the whole composition range (0%–100%) were compared with the predictions from the calculated free‐energy diagram of the Si‐Ti system. It is revealed that the phenomena of metal‐induced crystallization of amorphous silicon and formation of amorphous alloys appear in two different composition ranges in the binary system. Metal‐induced crystallization of amorphous silicon is attributed to lowering of bonding energy of SiSi bonds by titanium atoms in the Si‐rich composition range and the formation of an amorphous Si‐Ti alloy is attributed to the dominant SiTi bonding due to the largely negative heat of mixing between the two elements in a medium composition range.

Metal induced crystallization of amorphous silicon

The reactions between a thin metal film of Al or Ag and a layer of amorphous Si have been investigated using transmission electron microscopy and Auger electron spectroscopy. The samples were analyzed after deposition and after different heat treatments. Al and Ag were found to reduce the crystallization temperature of amorphous Si. A crystallization temperature of 325 °C was observed for the Al–Si structure and of 525 °C for the Ag–Si structure. A new phase between Al and Si, which has not previously been reported, has been detected at a temperature of 150 °C. Some evidence for a formation of a metastable phase between Ag and Si during the crystallization process has also been found.

Initial growth of TiN on different phases of high speed steel

Abstract High speed steel is a complex substrate material consisting of various phases including metal carbides such as MC and M 6 C. The MC carbides, which mainly consists of VC 0.8 , have the same crystal structure as TiN (NaCl B1) and a similar lattice parameter (4.16 A) to that (4.24 A) for TiN. Different nucleation and growth modes can thus be expected on the various phases during growth of TiN thin films. For example, on the MC carbides a local epitaxial growth can be expected. Deposition of TiN layers 40–60 nm thick by d.c. magnetron sputtering was carried out onto electrolytically thinned steel substrates for transmission electron microscopy examination. The substrate temperature was varied between 310 and 920 K. Air-exposed substrates were deposited with and without sputter etching. Examination of the as-deposited films shows fine equiaxed grains of TiN on the substrate that was not sputter etched. On the sputter-etched substrate, TiN grew epitaxially on the MC carbides and with fine equiaxed grains on the surrounding steel matrix. The size and number of TiN grains per unit area were the same for the non-sputter-etched substrates and for the steel matrix in the sputter-etched substrates. The carbide grains are randomly oriented and distributed in the steel matrix. Epitaxial growth of TiN is observed on the six most densely packed lattice planes of the MC carbides.