A. G. Liu

PLASMA IMMERSION ION IMPLANTATION OF THE INTERIOR SURFACE OF A LARGE CYLINDRICAL BORE USING AN AUXILIARY ELECTRODE

A model utilizing cold, unmagnetized, and collisionless fluid ions as well as Boltzmann electrons is used to comprehensively investigate the sheath expansion into a translationally invariant large bore in the presence of an auxiliary electrode during plasma immersion ion implantation (PIII) of a cylindrical bore sample. The governing equation of ion continuity, ion motion, and Poisson’s equation are solved by using a numerical finite difference method for different cylindrical bore radii, auxiliary electrode radii, and voltage rise times. The ion density and ion impact energy at the cylindrical inner surface, as well as the ion energy distribution, maximum ion impact energy, and average ion impact energy for the various cases are obtained. Our results show a dramatic improvement in the impact energy when an auxiliary electrode is used and the recommended normalized auxiliary electrode radius is in the range of 0.1–0.3.

Effects of the auxiliary electrode radius during plasma immersion ion implantation of a small cylindrical bore

The temporal evolution of the plasma sheath in a small cylindrical bore in the presence of an auxiliary electrode is determined for different electrode radii. The ion density, velocity, flux, dose, ion energy distribution, and average impact energy are calculated by solving Poisson’s Equation and the equations of ion motion and continuity using finite difference methods. The particle-in-cell method is also used to confirm the validity of the data. Our results indicate that more ions will attain high impact energy when the auxiliary electrode radius is increased, but the dose will decrease. Our results suggest that the normalized auxiliary electrode radius should range from 0.10 to 0.30 in order to maximize the dose and produce a larger number of ions with higher impact energy.

Dose and energy uniformity over inner surface in plasma immersion ion implantation

The absence of the line-of-sight restriction makes plasma immersion ion implantation an excellent interior surface treatment technique. In our experiments, we implanted both the outside and inside surfaces of a set of hollow cylindrical samples with and without a grounded conductive electrode positioned along the center of the bores to evaluate the impact energy as well as dose uniformity along the specimens. Our experimental results show that the use of the coaxial electrode increases the impact energy by 43% and retained dose by 71%. The nonuniformity is 20% to 30% and is worse with larger bore length.

Plasma-immersion ion implantation of the interior surface of a small cylindrical bore using an auxiliary electrode for finite rise-time voltage pulses

Plasma-immersion ion implantation (PIII) can be used to process the interior surfaces of odd-shape specimens such as a cylindrical bore. The temporal evolution of the plasma sheath in a small cylindrical bore in the presence of a grounded coaxial auxiliary electrode is derived for voltage pulses of different rise times by solving Poissons equation and the equations of ion continuity, and motion numerically using the appropriate boundary conditions. It is found that the maximum ion impact energy and the average impact energy are improved for finite rise-time voltage pulses, and shorter rise times yield better results. Our results allow the selection of a suitable auxiliary electrode radius to improve the average impact energy for a given rise time.

Corrosion protection of titanium by deposition of niobium thin films

Abstract Titanium is a promising material for medical implants, replacing bones and teeth. However, at pH values below 2, which occur in the dental environment, the corrosion resistance is compromised. The deposition of niobium layers onto titanium is a possibility to increase the corrosion resistance, as measured in 5 N HCl solution.

Inner surface ion implantation using deflecting electric field

Abstract Because of its non line-of-sight nature, researchers have recently focused on plasma immersion ion implantation (PIII) to enhance the properties of inner surfaces of industrial components to combat wear and corrosion. However, theoretical simulation has shown a relatively dim prospect because of the limitation on impact energy and retained dose. In this paper, we describe a procedure to improve the efficiency of inner surface implantation by using a symmetrical experimental setup and deflecting electric field. Improvements of 43% and 71% are observed for the implantation depth and retained dose, respectively. Since a large portion of the ions implanted into the interior surface originate from outside of the bore, a longer pulse-width will be more beneficial.

Pulsed sheath dynamics in a small cylindrical bore with an auxiliary electrode for plasma immersion ion implantation

The temporal evolution of the plasma sheath in a small cylindrical bore with an auxiliary electrode is calculated for zero-rise-time voltage pulses. The ion density, flux, dose, ion energy distribu-tion, and electric field are determined by solving Poisson’s equation and the equations of ion motion and continuity using finite difference methods. Our results indicate that the implantation time is about halved and slightly more than 50% of the ions possess impact energy higher than the maximum achieved when an auxiliary electrode is absent. The resulting ion flux, ion current, as well as ion energy distribution, are also determined.

Simulation of dose uniformity for different pulse durations during inner surface plasma immersion ion implantation

Without the line-of-sight limitation, plasma immersion ion implantation (PIII) emulates conventional beam-line ion implantation in inner surface modification of industrial components. However, dose uniformity on the inner surface is critical. Inner surface PIII of a cylindrical bore is modeled using a two-dimensional fluid model. It is found that the retained dose is not uniformly distributed on the inner surface and the maximum dose is observed away from the edge. The exact location of the maximum dose, which varies with the implant pulse duration, is closer to the center when the pulse width is longer. The maximum relative difference of the retained dose along the interior also depends on the implant pulse duration. It is smaller for a longer pulse duration after a threshold value has been exceeded.

A novel distributed system for plasma immersion ion implanter control and automation

The high voltage and electromagnetic field environment poses a big challenge to a control system for plasma immersion ion implantation (PIII). The automation process must be immune to electric field interference produced by the high voltage power supply, modulator, radio-frequency or microwave plasma generator, MEVVA plasma sources, and so on. We have recently designed and installed a distributed control system, PIIIDCS, to automate the operation of our PIII facility. Programmable logic controllers are used as the field control stations because of their good anti-interference ability and good real time response. A DH-485 network is used as the communication link between the field controllers and the management station in order to improve the robustness and reliability of the system. The newly developed interface is designed to work in a graphic mode in Microsoft Windows 95. Test runs have shown that the system is reliable, flexible, and easy to operate. The development of this novel control system will expedite the development of commercial PIII instrumentation.The high voltage and electromagnetic field environment poses a big challenge to a control system for plasma immersion ion implantation (PIII). The automation process must be immune to electric field interference produced by the high voltage power supply, modulator, radio-frequency or microwave plasma generator, MEVVA plasma sources, and so on. We have recently designed and installed a distributed control system, PIIIDCS, to automate the operation of our PIII facility. Programmable logic controllers are used as the field control stations because of their good anti-interference ability and good real time response. A DH-485 network is used as the communication link between the field controllers and the management station in order to improve the robustness and reliability of the system. The newly developed interface is designed to work in a graphic mode in Microsoft Windows 95. Test runs have shown that the system is reliable, flexible, and easy to operate. The development of this novel control system will ex...

Transient sheath in a small cylindrical bore with an auxiliary electrode for finite-rise-time voltage pulses

Summary form only given. Previous work concentrated on the determination of the ion-matrix sheath and the temporal evolution of the plasma sheath in a small cylindrical bore for zero-rise-time voltage pulses during plasma immersion ion implantation (PIII). Because realistic voltage pulses have a finite rise time, this paper addresses the temporal evolution of the plasma sheath in a small cylindrical bore with an auxiliary electrode for different rise times by solving Poissons equation and the equations of ion continuity and motion numerically using the appropriate boundary conditions. The ion density, flux, dose, energy, energy distribution, and average impact energy on the surface of the target for different rise times are determined and compared to the case when the auxiliary electrode is absent. Our results predict a substantial improvement of the impact energy during PIII of a cylindrical bore when an auxiliary electrode is employed even for finite-rise-time voltage pulses.