Ion-beam-induced epitaxial crystallization and amorphization in silicon

Extensive experimental investigations have been reported on the ion-induced motion of the interface between the crystalline and amorphous phases of silicon. The crystal grows into the amorphous phase at low ion fluxes and high temperatures. The amorphous phase grows into the crystal at high ion fluxes and low temperatures. The experimental observations are shown to fit a model based on a single defect. The concentration of this defect decays by binary recombination, this is, two of the defects annihilate one another. The model accounts for the linear relationship between interface motion and reciprocal temperature, for the Arrhenius temperature dependence of the flux at which no interface motion occurs, and for the temperature independence of the crossover frequency observed in beam pulsing experiments. The defect on which this model is based has a motion energy of 1.2 eV. Assuming that the same defect is also responsible for thermal recrystallization of the amorphous phase gives a formation energy of 1.5 eV for the defect. The defect is believed to be a dangling bond in the amorphous phase.

A defect model for ion-induced crystallization and amorphization

Thin amorphous silicon layers can be produced in crystalline silicon substrates by ion-implantation. Subsequent ion-irradiation at elevated temperatures can induce such layers to either crystallize epitaxially or increase in thickness, layer by layer. This paper examines these processes and their dependence on substrate temperature and ion-irradiation parameters. It is shown that both processes, epitaxial crystallization and layer-by-layer amorphization, are controlled by ion-beam induced defect production at, or near, the crystalline/amorphous interface. The competition between defect production (determined by the ion flux and rate of nuclear energy deposition) and dynamic defect annealing (determined by the substrate temperature) is shown to play an important role in determining whether the layer crystallizes or amorphizes. Possible models for the observed behavior are discussed.

Ion-beam-induced crystallization and amorphization of silicon

The ion-bombardment-induced reversible movement of a planar amorphous/crystalline interface in silicon has been studied between 100 and 400 °C. The temperature dependence of the ion dose rate at which there is zero interface movement has an activation energy of 1.2 eV, the dissociation energy of divacancies. Scaling of this dose rate for different ion species exhibits a quadratic dependence on the density of displaced atoms in the collision cascade of individual ions, giving further evidence for divacancy control of the interface movement.

Divacancy control of the balance between ion-beam-induced epitaxial cyrstallization and amorphization in silicon

Kinetic electron emission from solid surfaces under ion bombardment

Ge (110) single crystals heated to a temperature of 228°C have been bombardment disordered by 40 keV ions at a dose rate of 6 × 1011 ions/cm2 sec. The enhanced annealing caused by 40 keV Ge ions at a dose rate of 6 × 1011ions/cm2 sec was studied as a function of dose by measuring the secondary electron yield. The depth distribution of damage was determined by the channeling technique using 500 keV He ions. It is shown that enhanced annealing occurs at the inner part of the damage region and proceeds outwards towards the crystal surface. The dose necessary to completely anneal a disordered layer is about 3.0 × 1015 ions/cm2. A model for the annealing process is discussed. The maximum path length of the secondary electrons emitted from Ge during the bombardment with 40 keV Ge ions has been determined to be equal to approximately 40 A.

A. Burén

Papers

Radiation enhanced annealing of radiation damage in Ge