A. Robertsson

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...

Al induced crystallization of a‐Si

The crystallization of amorphous Si induced by Al during heat treatment has been investigated by cross section and plan view transmission electron microscopy. The lowest temperature of Al induced crystallization of amorphous Si was found to be 440 K. The crystallization temperature, however, depends on the thickness of Al layers in layered structures and on the concentration of Al in co‐deposited layers below 1‐nm‐layer thickness and 15 at.% of Al concentration, respectively. Al‐induced crystallization in layered structures starts at the Al/amorphous Si interfaces and is located close to them. The amount of crystallized Si depends on the quantity of Al and on the temperature and increases with them. The mechanism of crystallization involves intermixing of Al with Si and the formation of an alloy of high metal concentration in the amorphous/crystalline interface. When the formation of this alloy is not assured due to low Al concentration, then crystallization does not start or the process of crystallization stops. In Al induced crystallization the nucleation of polycrystalline Si grains rather than their crystal growth is affected.

Al‐doped and Sb‐doped polycrystalline silicon obtained by means of metal‐induced crystallization

Thin‐film multilayer structures of a‐Si/Al/a‐Si and a‐Si/Sb/a‐Si were deposited by electron‐beam evaporation. The microstructure and the electrical properties of as‐deposited and annealed (T<1370 K) thin films were determined. A p‐n junction was formed between polycrystalline silicon (poly‐Si) doped with Sb and a p‐type Si substrate. Al and Sb were found to induce crystallization of a‐Si at 600 and 700 K, respectively. After annealing to 1370 K for 60 min, the resistivities 7.0×10−3 Ω cm for the Al‐Si sample and 1.4×10−2 Ω cm for the Sb‐Si sample were obtained. Passivation of poly‐Si grain boundaries by Sb is proposed.

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.

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.

A metal-oxide-silicon field-effect transistor made by means of solid-phase doping

Solid‐phase doping has currently been receiving attention because of the demand for further decreasing geometrical dimensions in integrated circuits. In this paper, we report our implementation of a metal‐oxide‐silicon (MOS) field‐effect transistor using Sb‐doped polycrystalline silicon, which is obtained by annealing amorphous Si and Sb thin films, as a diffusion source and also as active elements. Good characteristics of the transistor are obtained, which confirms the applicability of using solid‐phase doping in making devices. The technique and the configuration of the device suggest the possibility of reducing the number of processing steps of MOS integrated circuits and achieving small dimension and high‐speed devices.

Simultaneous Sb doping and formation of self-aligned TiSi2 by codeposition of Ti and Sb

Thin Ti films containing Sb were deposited on silicon by electron‐beam evaporation. The films were annealed in three steps at different temperatures in order to achieve simultaneous Sb doping and self‐aligned TiSi2 formation. Sb behavior during the Ti silicide formation and silicide structures were investigated with Auger electron spectroscopy, transmission electron microscopy, and secondary ion mass spectroscopy. Shallow n+‐p junctions have been obtained by using a modified self‐aligned TiSi2 process.

Multilayer Metallization Structures in a Gate Array Device Shown by Cross-Sectional Transmission Microscopy

A multilayer metallization structure in a gate array circuit has been investigated by cross-sectional transmission electron microscopy. Microstructures of thin films, interfaces, contacts, dislocations and step coverage are revealed. Good step coverage was observed when polyimide was used as an insulator between two metal layers.

Sb-Doped Polycrystalline Si Obtained by Means of Sb and Si Thin-Film Reactions

We have grown Sb-doped poly-Si by thin-film reactions between Sb and amorphous Si (a-Si). The reactions and microstructures of the films were investigated by transmission electron microscopy (TEM) during in situ annealing and Auger electron spectroscopy (AES). The reactions either resulted in an amorphous Sb-Si (a-Sb-Si) alloy or caused crystallization of a-Si at low temperatures, depending on the film thickness of the a-Si layer as well as the heating rate. The electrical properties of the as-deposited and the annealed thin multi-layers deposited on SiO 2 layer were determined using Hall measurements. After annealing at 1375 K for 60 minutes, Sb-doped poly-Si with a resistivity of 1.4×10 −2 ohm-cm was obtained. A p-n junction was formed in a p-type Si substrate by using an a-Si/Sb/a-Si multi-layer as a diffusion source. The doping concentration in the Si substrate was obtained using secondary ion mass spectrometry (SIMS).