* Ion-Stimulated Processes * Transmutation Doping of Semiconductors by Charged Particles * Doping of Semiconductors Using Radiation Defects * Formation of Buried Porous and Damaged Layers

Radiation defect engineering

Single crystal n-type silicon samples were implanted at room temperature sequentially by molecular oxygen (16O2+) and nitrogen (14N2+) in different proportions to high fluence levels ranging from 5 × 1016 to 1 × 1018 ions cm−2 to synthesize silicon oxynitride layers of various compositions. Rapid thermal annealing (RTA) of some samples was carried out at different temperatures in nitrogen ambient. Fourier transform infrared (FTIR) measurements were performed on as-implanted and on annealed samples. The FTIR studies show that the structure of ion-beam synthesized oxynitride layers are strongly dependent on total ion-fluence as well as on the ratio of implanted oxygen and nitrogen. The SixOyNz structures formed at lower fluence levels are homogeneous, at intermediate fluence levels are composed of separate phases of oxide, nitride and some complexes of O, N and Si and at higher fluence levels seem to have again homogeneous silicon oxynitride complex structures (SixOyNz) due to sputter limited profile of implanted ions. RTA studies show pronounced structural changes of the ion-beam synthesized layers on heat treatment at different temperatures. The spectra of annealed samples showed shift of the peak towards higher wave number. The ESR signal of silicon samples implanted to different fluence levels exhibited an isotropic g-value of 2.0045 corresponding to D-center with line width 8 G. The spin density was found to decrease with increase in ion-fluence.

Synthesis of silicon oxynitride layers by dual ion-implantation and their annealing behaviour

Silicon oxynitride (SixOyNz) buried insulating layers were synthesized by SIMNOX (separation by implanted nitrogen–oxygen) process by 14N+ and 16O+ ion implantation to high fluence levels 1 × 1017, 2.5 × 1017 and 5 × 1017 ions cm−2 sequentially in the ratio 1:1 at 150 keV into p-type (1 0 0) silicon wafers. The identification of structures and defects in the ion beam synthesized buried layers were carried out by FTIR, XRD and ESR measurements before and after RTA treatments at different temperatures in nitrogen ambient. The FTIR spectra show single broad absorption band in the wavenumber range 1250–600 cm−1 confirming the formation of silicon oxynitride. The integrated absorption band intensity is found to increase with increasing ion fluence and on annealing indicating gradual chemical transformation of the ion implanted layer into silicon oxynitride. The XRD data of the implanted samples show the formation of Si2N2O (O) phase of silicon oxynitride. On annealing the samples, SiO2 (H)/Si3N4 (H) phases are also formed in addition to Si2N2O (O) phase. The concentration of the formed phases is found to increase with increase in the ion fluence as well as the annealing temperature. The ESR studies both at room temperature and at low temperatures reveal the presence of a defect center associated with silicon dangling bonds. The increase in ion fluence gives rise to small variations in g-values and increase in the spin density. The spin density decreases in general with increasing the annealing temperature.

Synthesis of buried silicon oxynitride layers by ion implantation for silicon-on-insulator (SOI) structures

Silicon oxynitride (Si x O y N z ) buried layers were synthesized by high fluence (≥ 1 × 10 17 ions-cm − 2 ) ion implantation of O + and N + sequentially into single crystal silicon at 150 keV to produce silicon-on-insulator (SOI) structures. The structures of the SOI devices were analyzed by FTIR and XRD measurements and the surface modification by using atomic force microscopy (AFM). The FTIR measurements on the implanted samples (≤ 1 × 10 18 ion-cm − 2 ) show a single absorption band in the wavenumber range 1300–750 cm − 1 attributed to the formation of silicon oxynitride bonds in silicon. The integrated absorption band intensity is found to increase with increase in the fluence. The samples with nitrogen–oxygen sequence of implantation showed nitrogen-rich oxynitride formation whereas samples with oxygen–nitrogen sequence resulted in oxygen-rich oxynitride. The formation of separate phases of Si–O and Si–N bonds was observed at high fluence level (≅ 2 × 10 18 ions-cm − 2 ). The XRD studies show the formation of mixed phases of Si 2 N 2 O and SiO 2 in the sample. The structures of the ion beam synthesized silicon oxynitride layers are found to be strongly dependent on the sequence of implantation. The surface roughness is observed to be very small at lower fluences and it increases as we go to high fluence levels due to heavy damage caused by implantation. The conical hill like structures on the silicon surface is seen due to heavy surface swelling and sputtering phenomena.

Study of structure and surface modification of silicon-on-insulator (SOI) devices synthesized by dual ion implantation

The application of silicon-on-insulator (SOI) substrates to high-power integrated circuits is hampered by self-heating effects due to the poor thermal conductivity of the buried SiO2 layer. We propose to replace the buried SiO2 layer in SOI with a plasma synthesized AlN thin film to mitigate the self-heating penalty. The AlN films synthesized on silicon by metal plasma immersion ion implantation and deposition exhibit outstanding surface topography and excellent insulating characteristics. Using a modified direct bonding process in conjunction with hydrogen-induced layer transfer, a silicon-on-AlN structure has been successfully fabricated. Cross-sectional high-resolution transmission electron microscopy, x-ray photoelectron spectroscopy, and spreading resistance profiling results reveal a uniform buried AlN layer beneath a single crystal Si overlayer. The interfaces between the top Si layer, buried AlN layer, and Si substrate are smooth and sharp. Moreover, the use of relatively thick buried AlN layer bo...

Formation of silicon on plasma synthesized aluminum nitride structure by ion cutting

The synthesis of silicon oxynitride buried layers, using the sequential implantation of substoichiometric doses of oxygen and nitrogen ions, has been studied. By using cross-sectional transmission electron microscopy (XTEM), secondary ion mass spectroscopy (SIMS) and infrared transmission spectroscopy we have shown that there is an interrelation between the structure of synthesized layer and the oxygen to nitrogen dose ratio. It has been found that for the chosen implantation and annealing regimes the synthesized structure: consists of buried dielectric, structurally dense, layers which have thicknesses of between 0.12 and 0.185 μm. When the nitrogen to oxygen dose ratio is 3.5, the whole buried layer is amorphous and the interfaces of the buried layer are perfect.

Peculiarities of buried silicon oxynitride layer synthesis by sequential oxygen and nitrogen ion implantation in silicon

Behavior of Implanted Nitrogen in Si with the Buried Layer of SiO2 Precipitates

Ion beam synthesis was performed by implantation of 150 keV N+ ions into silicon. The redistribution of nitrogen implanted at a dose of 1.2×1017 cm−2 was studied by SIMS as a function of annealing temperature (850, 1000, 1100, or 1200°C). In case of sequential ion beam synthesis the total implantation dose was 5.7, 7.6, and 9.5 × 1017 cm−2. Three series of specimens were annealed upon each increase of the implantation dose at temperatures of 850, 1100, and 1200°C. The final annealing was carried out for 2 h at 1200°C. Thus obtained specimens were studied by the XTEM technique. It has been established that during annealing the implanted nitrogen atoms move to the region of the concentration profile maximum. Such nitrogen redistribution depends on the annealing temperature in a nonmonotonical way. At annealing temperatures of 1000 and 1100°C an intermediate peak of nitrogen concentration is formed in the Si layer. In the sequential synthesis, the buried Si3N4 layer shows a porous region at implantation doses of 7.6 and 9.5×1017 cm−2. The highest degree of structural perfection in the buried Si3N4 layer and the upper Si layer was observed for specimens obtained upon intermediate annealing at 1100°C.

Sequential ion beam synthesis of buried Si3N4 layers in silicon

O+ and N+ ions were sequentially implanted at 150 keV atom−1 and water temperature of 650°C. The total implantation dose was 7.5 × 10 10 17 cm −2 . The O+ and N+ dose ratio has been chosen as 3:1 and 7:1. The implanted wafers were annealed in a nitrogen flow furnace at 1200°C for 2 h. The two sets of samples were analysed by cross-sectional transmission electron microscopy and X-ray diffractometry. In addition, the samples with a dose ratio of 3:1 were analysed by Auger spectroscopy. It has been shown that the structures obtained are characterized by a highly defective superficial silicon layer, heterogeneity of the chemical composition of the buried layer and the porous region inside this layer. A qualitative model providing an explanation of results obtained has been proposed.

Features of buried dielectric layers: ion beam synthesis in silicon by a high temperature sequential oxygen and nitrogen implantation with substoichiometric doses

A.F. Petrov

Papers

Peculiarities of buried silicon oxynitride layer synthesis by sequential oxygen and nitrogen ion implantation in silicon

Behavior of Implanted Nitrogen in Si with the Buried Layer of SiO2 Precipitates

Sequential ion beam synthesis of buried Si3N4 layers in silicon

Features of buried dielectric layers: ion beam synthesis in silicon by a high temperature sequential oxygen and nitrogen implantation with substoichiometric doses