Changes in defect production in a silicon single-crystal irradiated with nitrogen ions over an energy range of 1.7 to 16 MeV at depths less than the mean projected range have been studied. It is shown that the degree of damage to the subsurface region of a crystal is determined by the competition of two processes: the migration of defects from the depth to the crystal surface and their annealing due to an increase in the mobility of defect-forming atoms and vacancies. Depending on ion energy, the atomic number of the ion and the irradiation dose, both strong defect production and recovery of the crystal structure are observed.

Defect production and annealing due to high-energy ion implantation: I. Silicon

Silicon‐on‐insulator structures implanted by 200‐keV nitrogen with a dose of 7.5×1017 atoms/cm2 were studied by spectroscopic ellipsometry (SE). The SE measurements were carried out in the 300–700‐nm wavelength (4.13–1.78‐eV photon energy) range. For the analysis of the SE data we used the conventional method of assuming appropriate optical models and fitting the model parameters (layer thicknesses and compositions) by linear regression. Calculated data were in good agreement with measurements when a seven‐layer model, consisting of surface oxide layer, thick silicon layer, upper two interface layers, thick nitride layer, and lower two interface layers, was applied. Results obtained by SE were compared with those from Rutherford backscattering spectroscopy (RBS) and transmission electron microscopy. In contrast with RBS measurements, we found that the sensitivity of our optical model combined with the fitting technique was good enough to resolve the silicon‐rich transition layers at the upper and lower in...

/pdf/nondestructive-characterization-of-nitrogen-implanted-3229cgc411.pdf

Nondestructive characterization of nitrogen-implanted silicon-on-insulator structures by spectroscopic ellipsometry

The growth of thin nitride films of Si, MBE-grown Ge and Si x Ge 1− x alloys on Si by low energy ion beam nitridation (IBN)_has been investigated both theoretically and experimentally. This paper focuses on the modeling of the kinetics of IBN thin film growth. The model is based on our recent experimental results and includes the present understanding of atomic collisions at low energy and the thermal diffusivity and chemical reactivity of point defects generated by IBN. Three variables relevant to ion beam nitridation (IBN), ion energy, ion dose, and substrate temperature, are studied for their effect on the growth of nitride films and their resulting properties. These variables are shown to constitute attractive processing parameters to control nitride properties in a way that cannot be achieved thermally. The proposed model takes into account the range and range straggling of the ions, physical sputtering, desorption, chemical reaction and enhanced mobility of point defects created in the collision cascade. Based on this model, the film thickness and stoichiometry at any stage of IBN can be computed using finite differences calculation methods. Analytical expressions can also be derived for the two limiting cases of “low dose” or initial stage, and “high dose” which corresponds to growth saturation at steady state. Such modeling is shown to be useful in determining the chemical processes which govern the reactive growth of IBN nitride thin films. IBN is shown for instance to be a reaction of order greater than one. Diffusivity and reactivity are found to be competitive during IBN, quite the opposite of ion beam oxidation (IBO), where reactivity dominates over diffusivity.

Kinetics of ion beam nitridation (IBN) of Si and of MBE-grown Ge and SixGe1−x alloys: The role of ion energy, ion dose and substrate temperature

A thin Si 3 N 4 surface layer is formed by implantation of 60 keV 15 N nitrogen ions into single-crystalline silicon (100) with a fluence of 5.6 x10 17 ions/cm 2 and subsequent annealing (1295 °C, 15 min) under high vacuum conditions. The 15 N depth distribution is measured with the resonant nuclear reaction 15 N(p, αγ) 12 C. The formation of Si-N bonds is proven by Fourier transform infrared spectroscopy using samples implanted with 14 N ions and 15 N ions, respectively. The crystallinity of the Si 3 N 4 surface layer is studied by X-ray diffraction and transmission electron microscopy. The annealing process leads to the formation of a polycrystalline α-Si 3 N 4 surface layer with a thickness of 90 nm. The analysis of high resolution TEM micrographs shows that the layer is split into two sublayers both consisting of single α-Si 3 N 4 crystals with lateral extension up to 500 nm.

Ion Beam Synthesis and Characterization of Crystalline Si3N4 Surface Layers

Buried silicon nitride and oxynitride layers were formed in silicon by ion beam synthesis at 60 keV. In all cases monocrystalline silicon top layers were found already after implantation. Their defect density is reduced strongly after annealing at 1200°C which leads also to narrowing of the interregions silicon/compound layer. Silicon oxynitride remains amorphous after annealing. The electrical resistivity of the buried layer is in the range of 1015–1016 Ωcm. The quality of the layer systems with silicon oxynitride depends on the implantation sequence of the species. The long range order of polycrystalline silicon nitride may be strongly reduced by ion implantation.

Properties of buried insulating layers in silicon formed by high dose implantation at 60 keV

SOI (silicon on insulator)-structures were produced by implantation of 330 keV, 14N+-ions with doses ranging from 0.9 to 1.5 × 1018 cm−2 at a target temperature of 500°C into monocrystalline silicon to form buried silicon nitride layers. Post-implantation annealing was done at 1200°C up to 5 h. In this manner silicon nitride compounds with different stoichiometry and structure are produced. After implantation amorphous layers with Gaussian nitrogen profiles up to overstoichiometric concentrations are formed. Annealing leads to the transformation of the Gaussian profiles into rectangular ones if the maximum concentration of the as-implanted distribution does not exceed the value necessary for Si3N4 stoichiometry. In all cases the interfaces between the buried layer and the neighbouring silicon are steep and the structure of the silicon nitride is crystalline. For stoichiometric and overstoichiometric layers a high resistivity in the range of 1014 to 1016 Ω cm was found. After annealing monocrystalline silicon top layers of high quality are formed. A test is reported on the reamorphization of crystalline Si3N4. The results are promising.

U. Kreissig

Papers

Properties of ion beam synthesized buried silicon nitride layers with rectangular nitrogen profiles