The electrical characteristics of power MOSFETs additionally implanted with nitrogen ions have been studied. Ion implantation of nitrogen was carried out through a protective oxide of 23 nm thickness with energies of 20 and 40 keV and doses of 1 ⋅ 1013‒5 ⋅ 1014 cm–2. Rapid thermal annealing was carried out at temperature of 900 or 1000 °C for 15 s. It has been established that nitridisation of the gate dielectric makes it possible to reduce the noise of the gate leakage currents and their dispersion. In the direct order of heat treatment (first rapid thermal annealing, and then the removal of the protective oxide), for samples prepared with an additional operation of nitrogen ion implantation, there is an increase in the threshold voltage compared to control samples. The capacitance of the gate dielectric in the case of implantation of nitrogen ions in the direct order of heat treatment is less than for control samples. It has been established that in the direct order of rapid thermal annealing, the doses of nitrogen ion implantation do not cause significant changes in the maximum value of the current-voltage slope. At the same time, in all studied cases, there is a shift in the maximum value of the current-voltage slope towards higher gate voltages. In the reverse order of heat treatment (first the removal of the protective oxide, and then rapid thermal annealing), there are no significant differences in the value of the threshold voltage for the samples created with additional nitrogen implantation and the control ones. The maximum value of the current-voltage slope also does not experience significant changes. It is shown that in the voltage range from – 0.15 to 0 V, the drain current of nitrogen-implanted samples manufactured using the direct order of heat treatment is higher than for control samples, and the drain current of nitrogen-implanted samples obtained with the reverse order of heat treatment it is lower compared to control samples. Results are explained by a decrease in the density of surface states at the Si – SiO2 interface in MOS-structures created using an additional operation of nitrogen ion implantation in the direct order of heat treatment.
Power MOS-transistors with vertical structure are investigated. Additionally, in some devices, ion implantation of nitrogen with energies of 20 and 40 keV was carried out in a dose range of 1 ⋅1013–5 ⋅ 1014 cm –2 through a sacrificial oxide 20 nm thick. For one group of wafers, rapid thermal annealing was first carried out, then oxide removal (forward order), for the other group – in the opposite sequence (reverse order). It was found that with the additional doping of nitrogen ions in doses of 1⋅1013–5 ⋅ 1013 cm –2 with energy of 20 keV, an increasing of gate dielectric charge to breakdown for both types of annealing is observed. The maximum effect occurred for the samples at a dose of nitrogen ions of 1⋅1013 cm –2 with the forward heat treatment order. This is due to the interaction of nitrogen atoms with dangling bonds of the Si – SiO2 interface during annealing, as a result of which strong chemical bonds are formed that prevent charge accumulation on the surface of the Si – SiO2 interface. It is assumed that the main contribution to the gate leakage current is made by the tunneling of charge carriers through traps.
Diazoquinone-novolac photoresist films implanted with B+ ions were studied by the method of attenuated total reflection (ATR). Films of positive photoresist FP9120 with a thickness h of 1.0 and 2.5 mm were deposited by centrifuging on p-type silicon plates with (111) orientation. Implantation with 60 keV B+ions in the dose range of 1015–1016 cm–2 in the constant ion current mode (current density 4 mA/cm2 ) was carried out at room temperature in a residual vacuum not worse than 10–5 Pa using the «Vesuvius-6» ion beam accelerator. The attenuated total reflection spectra were recorded in the range 400 – 4000 cm–1 by ALPHA spectrophotometer (Bruker Optik GmbH, Germany) at room temperature. It was shown that ion implantation leads to intensive transformation of the photoresist beyond the range of ions, which is characterized by the appearance in the spectrum of intense bands with peaks at 2151 and 2115 cm–1, due to stretching vibrations of double cumulative bonds, in particular С——С——О. In the implanted samples, a shift to the low-energy region of the maxima of the stretching vibrations of C—H bonds, plane deformation vibrations of O—H bonds and pulsating vibrations of the carbon skeleton of aromatic rings as well as the redistribution of intensities between closely spaced maxima, were observed.
Studies have been carried out by time-of-flight mass spectroscopy of secondary ions of subcutaneous silicon oxides, nitridation by ion implantation (II) or nitrided by high-temperature annealing in an atmosphere of N2. Nitrogen AI was produced with an energy of 40 keV, implantation doses of 2,5×1014 and 1×1015 cm-2. High-temperature annealing was carried out at a temperature of 1200 C for 2 hours or at 1100 C for 30 minutes. It is established that at the Si–SiO2 interface, after nitriding by II or high-temperature annealing, a maximum with a high concentration of nitrogen atoms is observed. It is shown that after conducting nitrogen AI with a dose of 2,5 ×1014 cm-2 through a protective SiO2 with a thickness of 23 nm and RTA at 1000 C for 15 seconds, the main maximum of nitrogen distribution (1×1019 cm-3) is observed at the Si–SiO2 interface, which indicates the presence of a saturation concentration of the Si–SiO2 interface. A charge-based one-dimensional Fermi model is proposed to describe the accelerated diffusion of nitrogen atoms. The main mechanism is the diffusion of interstitial atoms, which can occur with the preliminary displacement of nodal nitrogen atoms by their own embedding atoms. It is shown that nitrogen atoms can act as annihilation centers of point defects in the silicon crystal lattice.
The possibility of adjusting the operational parameters of industrial solar cells produced by the company Suniva based on monocrystalline silicon by means of additional diffusion doping with nickel in the temperature range 700–1200 °C has been investigated. It is shown that the optimal temperature of nickel diffusion is Tdiff = 800–850 °C. In this case the value of the maximum power Pmax increases by 20–28 % in relation to the parameters of the original industrial photocell. At diffusion temperatures Tdiff > 1000 °C, a sharp decrease in Pmax occurs, which is associated with an increase in the depth of the p–n-junction due to the distillation of phosphorus atoms during high-temperature diffusion of nickel. The positive effect of diffusion alloying with nickel on the electrophysical parameters of photocells is greatest in the case when the nickel impurity clusters are in the region of the p–n-junction, i. e. with diffusion alloying to the front side of the plate. The action of electrically neutral nickel clusters is less pronounced when they are located in the region of the isotypic p–p+ transition; in case of diffusion alloying with nickel in the opposite side of the plate.
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