Tonghe Zhang

Surface modification of steel by high-dose pulse-ion implantation of titanium, tungsten, molybdenum and carbon

Ions of Ti, Mo W, and C, produced by a pulsed metal (MEVVA) ion source were implanted into H13 steel. Energies were from 25–50 keV. Hardnesses were increased by as much as 40% and wear resistances were improved by factors of 3 to 5 by the implantations. Rutherford backscattering (RBS) measurements demonstrated that implanted Mo can penetrate to depths of 1400 A into steel during the implantation period of 25 min for the fluence of 1 × 1017/cm2. This depth is greater than the calculated range. The average doping concentration was greater than 15 at.% for the various implants. It was observed by X-ray diffraction and by transmission electron microscopy that intermetallic compounds such as FeTi, Fe2Ti and FeMo were formed. It was concluded that the MEVVA type of ion source shows promise for metal-ion implantations into steel components for industrial application.

Foreign atom incorporation during metal silicide formation by ion beam synthesis

Depth distributions were measured of foreign atoms incorporated during the formation of thin silicide surface layers by ion beam synthesis. Si (111) wafers were implanted with Co and V ions using a pulsed Metal Vapour Vacuum Arc (MEVVA) ion source operated at 40 kV extraction voltage. Post-implantation analysis was carried out using Time of Flight-Energy dispersive Elastic Recoil Detection Analysis (ToF-E ERDA) with 60 MeV 127I10+. The results showed that addition to the metal ions, carbon and oxygen were incorporated at at.% levels, with distributions that were peaked at the surface and extended into the implanted layer. The findings suggest that incorporation of C and O is significantly influenced by the degree of silicide formation, with more continuous and stoichiometric silicides corresponding to a lower incorporation of foreign atoms.

Influence of post-implantation annealing on the oxidation behavior of Nb implanted γ-TiAl based alloy

Abstract The influence of post-implantation annealing on the isothermal oxidation behavior of Nb implanted (3×10 17 ions/cm 2 ) Ti–48 at.%Al was investigated. The kinetics of isothermal oxidation at 900°C for 100 h in air revealed that appropriate post-implantation annealing (800°C/5 h) could remarkably further improve the oxidation resistance of the as-implanted alloy; possible mechanisms were discussed considering the results of element distribution, oxidation product and its surface morphology examined by Auger electron spectra (AES), X-ray diffraction (XRD) and scanning electron microscope (SEM). It indicated that both the eliminating of the lattice damage induced by ion implantation and element redistribution in the implanted region caused by post-implantation annealing might be responsible for the further decrease of the oxidation rate.

Characterization of GeSi layers formed by high dose Ge implantation into Si

High dose Ge implantation into p-type Si wafers at 150 keV has been performed at doses of 3.6 × 1016, 6.7 × 1016 and 9.0 × 1016 cm−2. The Ge distribution and the crystal quality of the implanted layer before and after annealing at various temperatures have been studied by RBS and channeling experiments. It is found for the medium and high dose samples before annealing, more than 90% of the Ge atoms are interstitial sites and after annealing at 1000°C, more than 50% of the Ge atoms have become substitutional. The situation is better for the low dose sample where less than 70% of the Ge atoms are in interstitial sites before annealing and about 80% of them become substitutional after annealing at 1000°C. The ESR spectra of these samples are of Lorentzian shape with a g-value of about 2.007 and a spin density of about 6 × 1016 cm−3. The ESR signals of these samples have been inferred to be mainly due to Si-dangling bonds in the GeSi alloy layer and can be eliminated by annealing at 1000°C for 2 min. Electrical characterization of the GeSi layer by spreading resistance profiling technique shows that the implantation damage has been extanded deep into the substrate before annealing. After annealing at 1000°C, these defects are removed but the spreading resistance of the surface GeSi layer is found to remain higher than that of the substrate.

THE INFLUENCE OF HIGH-DOSE AND ELEVATED-TEMPERATURE IMPLANTATION ON PN-JUNCTION LEAKAGE CURRENT DURING RAPID THERMAL ANNEALING

The electrical properties of the pn junction formed by As implantation and rapid thermal annealing (RTA) have been studied in this article. It is found that the behavior of the pn junction formed by As implantation at elevated temperature (573 K) after RTA is better than that of room-temperature (RT) implantation. The changes of density of residual defects and motion of the defects for different annealing time were observed by TEM. The results of implanting at 5 × 1015 or 1.0 × 1016 cm−2 show that the density of residual defects for elevated-temperature (ET) implantation is lower than that of RT implantation. The carrier concentration profiles for different annealing times were measured by a spreading resistance probe (SRP). It is shown that the carrier concentration profile of elevated-temperature implantation is broader than that of RT implantation. The leakage current decreases with increasing RTA time and temperature. The depth of the pn junction (0.6 μm) for elevated-temperature implantation is larger than that of RT implantation (0.4 μm). The pn-junction leakage current of elevated-temperature implantation is several times lower than that of RT implantation. The influence of change of defect density on the leakage current of the pn junction was analyzed using these results. If the dose is as high as 5 × 1016 cm−2 for implantation, the result is different from that for a dose of 5 × 1015 cm−2, except for elevated-temperature implantation. The results from channeling measurements show that the lattice stress increases with increasing RTA time. Therefore the leakage current of the pn junction also increases with increasing RTA time. The minimum leakage current is obtained for RTA during 5 s.

A study on implanted impurity activation in silicon and in situ observation of residual defects in high voltage TEM

Abstract A convenient formula for the activation energy is obtained from the differential equation for the restoration of damaged lattice during thermal annealing. The dynamics of the restoration of damaged lattice was studied for different implantation conditions and annealing methods. The target temperature during implantation is room temperature (RT), low temperature (liquid nitrogen), or 300 ° C. Annealing temperature region is from 380 ° C to 1067 ° C. It is found that the activation energy is low when a low dose is used for implantation in Si. For example, when a dose of 2 × 10 14 cm 2 is used, the activation energy is only 0.028 eV. But when the As is implanted to a dose of 1 × 10 15 cm 2 , two kinds of activation energy appear. The activation energy at low temperatures is smaller than that at high temperatures. When a dose of 5 × 10 15 cm 2 is used, an amorphous layer appears, therefore there are three kinds of annealing temperature region in the annealing process: the epitaxial regrowth of amorphous layer, the transition region and the high activation energy region. When a dose of 2 × 10 16 cm 2 As is used to implant in Si at low temperature, there are four kinds of annealing temperature region in the annealing process. It is the same as mentioned above but there are two high activation energies in the activation energy region. When As is implanted to a dose of 1 × 10 16 cm 2 at 300 ° C, only three kinds of activation energy region appear. When a high dose is used to implant in Si, after rapid thermal annealing (RTA), the activation energy is greater than that for low dose implantation. The activation energy of B implantation in Si is different from As implantation. Only one activation energy is obtained for low dose B (or P) implantation in Si during RTA. But two activation energies appear for As implantation to a dose of 1 × 10 15 cm 2 in Si during RTA. So, the different activation energy correlates with the different process of damaged lattice restoration. The thermal annealing process of residual defects is observed in TEM.