High Current Implantation Research Articles

Applied high-current N-ion-beam surface engineering of metals and industrial tools at Chiang Mai University

A 150-kV, high-current, non-mass-analyzed ion implanter based on a modified duoplasmatron ion source and a completely computerized control has been developed for industrially applicable ion beam surface engineering at Chiang Mai University. High-current (∼mA) N-ion implantation in steels and alloys and other ion beam techniques such as single-ion-beam assisted deposition have been explored using the facility for modification of tribological properties. The ion implanter has been engaged in industrial service to local customers in implanting various practical objects. The ion implantation for both academic and applied purposes has proved to be successful in improving hardness and wear resistance as well as prolonging lifetime of the ion-beam-processed tools.

Pattern evolution ofNiSi2grown on a Si surface upon high-current pulsed Ni-ion implantation

Growth of surface fractal patterns of Ni disilicide was induced by high-current pulsed Ni ion implantation into Si wafers. By increasing the substrate temperature and the supplemental Ni deposited on Si wafers, the fractal dimensions were determined and found to increase from less than 1.64, corresponding to that of cluster-diffusion-limited aggregation, to beyond the percolation threshold of 1.88, and eventually up to 2.0 of a uniform ${\mathrm{NiSi}}_{2}$ layer on the Si surface with fine grains. The mechanism of fractal pattern evolution is discussed, based on the consideration of the dynamic process of high-current pulsed metal-ion implantation.

Thermal stability of nanoparticles in silica glass implanted with high-flux Cu− ions

Thermal stability of nanoparticles, fabricated by high-current negative ions, has been studied focusing on optical applications. Negative Cu ions of 60 keV were irradiated to silica glasses at high dose rates up to 50 μA/cm2, to a total dose of 3×1016ions/cm2. The high-current implantation caused a bimodal distribution of Cu nanoparticles. Thermal annealing at 773–1273 K for 1 h was applied to the specimens. For each step, optical absorption was measured in an energy range from 0.5 to 6.5 eV and nanoparticle morphology was evaluated by cross-sectional TEM. Depth profiles of Cu atoms were compared to those by RBS. Thermal annealing below 873 K gave no discernible changes in either nanoparticle morphology or absorption spectra. Above 1073 K, pronounced coarsening of Cu particles occurred, with enhancing the bimodal distribution. Around 1273 K, all the Cu particles disappeared, suggesting evaporation of Cu implants from the surface. The result indicates that the nanoparticle structure is thermally stable below about 873 K, and becomes unstable at higher temperatures.

Characteristics of CrSi 2 and Cr(Ni)Si 2 synthesis in MEVVA ion source implantation and post-annealing processes

We investigate the formation of silicide layers in (111) Si wafers with a high-current implanter. Cr ions form a disilicide layer of low sheet resistance. If the sample is also implanted with Ni, the total number of Cr atoms is reduced by sputtering, and the previously prepared CrSi 2 layer is disordered. However, a stable textured Cr 1− x Ni x Si 2 phase can be prepared by proper annealing. Above 1150°C the ternary phase segregates into CrSi 2 and NiSi 2. Thus the introduction of Ni can result in well-defined and stable Cr 1− x Ni x Si 2 alloys.

Formation of high-conductivity NiSi 2 layers on Si at zero-mismatch temperature by high-current Ni-ion implantation

and Si lattices at 380 °C, which was defined as zero-mismatch temperature. The implantation was conducted with a metal vapor vacuum arc (MEVVA) ion implanter at an extraction voltage of 45 kV. Based on a thermal conduction estimation, a temperature rise of 380 °C required the Ni-ion current density to be 35 μA/cm2. For the Si(111) wafers, the high conducting NiSi2 layers were indeed directly formed after Ni-ion implantation with this specific current density to a normal dose of 2×1017 ions/cm2 and the resistivity was as low as 9 μΩ cm. For the Si(111) wafers pre-covered with a 10-nm Ni overlayer, the resistivity of the NiSi2 layers obtained under the same conditions decreased down to about 6 μΩ cm. The superior electrical property of the NiSi2 was thought to be related to its formation temperature, i.e. at a zero-mismatch temperature of 380 °C, which resulted in minimizing the stress and stress-induced defects involved in its formation as well as cooling process.

Percolation network of PdGe phase formed on Ge surface by high-current Pd-ion implantation

High-current Pd-ion implantation technique was employed to synthesize Pd germanide on Ge wafers, using a metal vapour vacuum arc (MEVVA) ion source. The implantation was conducted with an extracted voltage of 34 kV, beam current densities of 17.7 and 53 A and at a fixed dose of ions . It was found that implantation with a current density of 17.7 could directly synthesize the equilibrium PdGe phase on the Ge surface and that the formed germanide loosely dispersed on the surface. Interesting, in the case of implantation with the current density of 53 , the formed PdGe grains organized themselves in a fractal pattern with a dimension close to the percolation threshold of 1.90, and the sheet resistivity was therefore significantly reduced down to 59 . The formation of the PdGe phase as well as the percolation network under MEVVA implantation is also discussed.

High current Ni-ion implantation to synthesize NiSi 2 layers on Si with very low resistivity

Metal Vapor Vacuum Arc (MEVVA) ion implantation was employed to synthesize NiSi 2 layers on Si(1 0 0) wafers and was conducted at a voltage of 45 kV with various current densities to a fixed dose of 2 × 10 17 ions/cm 2, required by the chemical stoichiometry. From a thermal expansion calculation, there would be no size mismatch between NiSi 2 and Si lattices at 380°C. A current density of 35 μA/cm 2 was required, according to an estimation, to heat the wafers to 380°C. Implanting with this selected current density, a unique NiSi 2 layer was indeed obtained with a resistivity as low as 14 ± 2 μΩ cm. Furthermore, a temperature dependence of the resistivity was observed and the NiSi 2 layers formed at temperatures deviated from the zero-mismatch temperature featured greater resistivities than that of the layer synthesized at 380°C. The experimental results are reported in detail together with a discussion of the observed temperature dependence.

Self-assembled two-dimensional distribution of nanoparticles with high-current Cu − implantation into insulators

High-current and low-energy implantation has been carried out with negative ions, alleviating specimen charging. Negative Cu ions of 60 keV were implanted into silica glasses over a wide dose-rate range up to 260 μA/cm 2 with a total dose at 3.0 × 10 16 ions/cm 2. Cross-sectional TEM was conducted to quantitatively evaluate the microstructures. At high dose rates, spherical Cu nanocrystals were created near the projected range of Cu ions. The nanoparticle morphology showed significant variations with the dose rate. Depth profile of the Cu atoms became narrower and shallower with increasing the dose rate. A surface sputtering process was concurrently promoted with the dose rate. At an optimum dose rate, a magnificent in-plane arrangement of nanocrystals occurred. A critical balance between the in-beam nanocrystal growth and the surface recession attained the self-assembled two-dimensional distribution.

Dose-rate dependence of negative copper ion implantation into silica glasses and effects on colloid formation

Although high-current implantation of negative ions, which alleviates charging, is potentially capable of efficient surface modification of insulators, the beam–solid interactions and material kinetics have not been well understood. We have studied the implantation of 60 keV negative Cu ions into silica glasses, at various current densities up to 260 μA/cm 2, at a fixed fluence of 3.0 × 10 16 ions/cm 2. A masking method was developed to dissipate the beam loading, and multi- or single-hole masks were alternatively applied to change the boundary condition. Optical properties were determined in the range of 1.4–6.2 eV and the microstructures were examined by TEM. A significant dose-rate effect occurred for optical absorption and reflection. There was an optimum dose-rate to obtain a certain absorbance. Changes in the mask shape resulted in different dose-rate dependence, which indicated that beam–solid interactions near the surface affected the implantation. At high dose rates, spherical Cu colloids with a pronounced bimodal distribution were produced. The surface morphology also changed and suggested significant atomic migration.

High duty factor nitrogen RFQ as a prototype high current implanter

High energy implanters have been proposed as surface modification facilities for e.g. steel. We have designed and built a 1.5 MeV accelerator for N +, working with beam currents up to 10 mA on duty factors of 25%. This paper describes the properties of the structure and possible applications, and discusses problems of high duty factor operation and experimental results.

High current Ni-ion implantation into Al films

The Al3Ni strengthening phase was formed by Ni-ion implantation into Al films using a Metal Vapor Vacuum Arc (MEVVA) ion source. The depth distribution of the volume fraction of Al3NiAl was found to depend on the ion current density as well as the Ni-ion dose. At a fixed dose of 3 × 1017cm−2 and implanting with a current density of 25 μA/cm2, most of the Al3Ni phase was grown in the near surface layer. While increasing the current density up to 89 μA/cm2, the Al3Ni phase distributed uniformly into a relatively deep region. When implanting with 89 μA/cm2 to a dose 6 × 1017cm−2, in addition to distributing into a deep region, the Al3Ni phase was also detected with a high content near the surface. The temperature rise during implantation caused by beam heating was responsible for the formation of the Al3Ni phase, which in turn modifies the surface mechanical properties of the Al films.

Surface hardening of Al by high current Fe-ion implantation

Surface modification of Al was studied by high current Fe-ion implantation using a metal vapor vacuum arc ion source. In the implantation process, two parameters were adjusted, that is, current density and ion dose, corresponding to varying the temperature and time for growing surface Fe-aluminide compound. The major hardening phase was identified to be Al13Fe4 and its depth profile was found to depend on the current density and dose. At a fixed dose of 3×1017 Fe/cm2, implanting with a low current density from 25 to 51 μA/cm2, the Al13Fe4 compound penetrated into a depth between 2500 and 4000 Å. Whereas implanting with a high current density up to 101 μA/cm2, the Al13Fe4 compound not only be situated in a 1000 Å surface layer, but also extended into a deep region when the dose was increased to 1×1018 Fe/cm2. Another dual implantation was conducted with two different current densities and it resulted in a modified region of 4500 Å thick with a high concentrated Al13Fe4 compound in a 1000 Å surface layer. Accordingly, the microhardness of the implantation treated Al films was considerably increased. The formation of the hardening phase of Al13Fe4 compound was responsible for the improvement of the surface mechanical property and was discussed in terms of temperature rise, irradiation time, and radiation-enhanced diffusion in the process of implantation.

TEM Analysis of Defects in Simox Silicon-On-Insulator Material

Abstract Silicon-on-Insulator is the leading technology for VLSI fast speed processors and low voltage applications. SIMOX (Separation by Implantation of Oxygen) is a subset of SOI with a high quality top silicon layer onto which VLSI circuitry is placed. SIMOX processing begins with a high energy, high current implantation of a large dose of O+ ions to penetrate the wafer’s surface to form the buried oxide and top silicon layers. This implantation creates numerous precipitates and a large damage region. Therefore a multi-step anneal is used to improve the quality of the top silicon layer by significantly reducing precipitate and dislocation densities, to create smooth interfaces, and to remove any ion residual damage. Using TEM, this study traces the defect formations through the various processing steps, with the objective to arrive at device quality. The SIMOX wafers were implanted with an oxygen ion implant dose of 5xl017cm−2, and then subjected to multiple implantation and anneal steps, bringing the final oxygen ion dose to 1.5xl018cm−2[1].

Negative copper ion implantation into silica glasses at high dose rates and the optical measurements

A technique of high-current implantation, with negative heavy ions, has been developed to attain efficient high-density implantation, especially for metal modification of dielectrics. The Cu − ions were implanted into silica glasses to study the dose rate dependence at a fixed dose of 3.0 × 10 16 ion/cm 2, up to a current density 260 μA/cm 2. To dissipate the heat load onto the substrate, a masking method was developed using a multi-hole Cu plate. Optical absorption and reflection in a wavelength range, λ = 200–900 nm, showed a surface plasmon peak of Cu colloids at λ = 560 nm and a broad band of E′ centers, etc. Although the spectral shapes were similar, irrespective of the dose rate, the absorbance and the reflectivity at the peak showed a dose rate dependence, i.e., a two-humped variation. For X-ray fluorescence, the dose rate dependence had a fair correlation with the Cu-L variation. Besides the dose rate dependent precipitation, the Cu amount retained in the substrates may be affected by the mass transport around the beam-solid interface.

The influence of ion energy on the nitriding behaviour of austenitic stainless steel

Recent work on austenitic stainless steels has indicated that low energy, high current density nitrogen implantation can result in nitrided layers several micrometers in depth and of considerable hardness. This work was initiated to examine the effects of ion energy during ion implantation at elevated temperatures.Three nitriding methods were considered: plasma immersion ion implantation (PI3), radio frequency (r.f.) plasma nitriding and ion beam nitriding.The structure and nitrogen profile of austenitic stainless steel were examined after the different treatments by a range of analytical techniques including glancing angle X-ray diffraction (GAXD), ultra microhardness indentations (UMIS), glow discharge optical spectroscopy (GDOS) and nuclear reaction analysis (NRA).It was found that similar surface structures can be formed by PI3 treatments at high energies and ion beam nitriding at low energies. The resultant microstructures, as determined by GAXD, consist primarily of an expanded austenite layer. It appears that the adherent oxide film present on stainless steel must be either removed by sputtering, at low ion energies, or passed through by implantation, at high energies. Subsequent diffusion at elevated temperatures allows the formation of a nitrided layer several micrometers thick in both cases.

Ion implanters for surface modification of metals

Extensive experience has now been gained with respect to the application of ion implantation for surface modification of metals. Some implanters have been specifically developed to serve in research and development as well as in service implantation work within this field. This paper gives an overview of available ion implanters for surface modification of metals and their different design philosophies. A special magnetic scanning and beam position control has been designed for our high-current implanter, capable of fast and efficient ion implantation of tools and components. Accurate magnetic steering of the ion beam by means of computer control allows high-current ion implantation to be performed on selected areas and patterns in the process chamber. In this way, only the important and relevant areas of the specimens are implanted. Thus, ion beam-induced heating of the specimens is decreased and the total process time is considerably reduced, making ion implantation a less costly commercial treatment for several tools and components. Finally, future trends in equipment and technology have been touched upon.

A comparative study of beam ion implantation, plasma ion implantation and nitriding of AISI 304 stainless steel

This paper presents the results of a comparative study using beam ion implantation (BII), plasma ion implantation (PII), ion nitriding and gas nitriding of AISI 304 stainless steel. We have demonstrated that under controlled conditions (the same treatment times of 30 and 60 min, and the same treatment temperature of 400 °C), the microstructures produced by all four techniques are similar, being mainly the formation of nitrogen in solid solution (γ N phase). However, the concentrations of nitrogen and the detectable depths of the nitrogen-enriched layers are significantly different, depending on the process. Both BII and PII produce thick nitrogen-enriched layers (greater than 1 μm) at high concentrations (20–30 at.%) compared with either ion nitriding or gas nitriding (layers less than 1 μm thick with low nitrogen concentrations). As a result, the load-bearing capacity after either BII or PII is much greater than after either ion or gas nitriding. It has also been found that high current density implantation is crucial for the formation of the thick N-enriched layers.

High Current Implantation of Negative Copper Ions into Silica Glasses

AbstractHigh- current implantation of Cu- ions into silica glasses has been demonstrated using mAclass negative ion beams at 60 keV. Negative ion implantation has an advantage to alleviate specimen charging for insulating substrates and has attained high dose rates, up to 260 μA/cm2. Spherical Cu colloids form in the silica glasses without additional thermal annealing. Optical absorption and reflection of the implanted specimens vary with the current density, even at a fixed dose level. A beam- induced surface plasma may affect the high current implantation.

Solid-state amorphization of a tool steel by high-current-density, low-energy nitrogen ion implantation

The influence of high-current density nitrogen implantation on the microstructure of α-iron and molybdenum type high speed steel was investigated. It has been demonstrated that ion beam treatment dramatically changes the microstructure of both materials. In the case of steel, ion treatment resulted in amorphization of the surface.

Charge neutralization in ion implanters

The control of wafer charging in high current implantation is the key to maintaining high yeild as gate oxide thicknesses decrease. The effectiveness of different charge neutralization techniques and different Faraday configurations have been evaluated using an in situ charge sensor in the Varian E1000 high current ion implanter. The in situ measurements also aid in understanding the charging process and underscore the plasma nature of the ion beam.