Honghui Tong

Steady-state direct-current plasma immersion ion implantation using an electron cyclotron resonance plasma source

We have developed a new direct-current (DC) plasma immersion ion implantation (PIII) technique by using a conducting grid positioned between the plasma source and sample chuck. In order to decrease the working gas pressure and increase the plasma density, an electron cyclotron resonance (ECR) plasma source was used in our experiments. In this paper, the experimental parameters and results pertaining to DC-PIII using an ECR plasma source are described. The uniformity of the ion dose and the energy monotonicity are discussed. Our experimental results indicate that DC-PIII is a novel and potentially useful technique for planar sample processing, particularly in microelectronics applications.

Effects of external magnetic field on propagation of electromagnetic wave in uniform magnetized plasma slabs

A simple method is proposed to describe the propagation of electromagnetic waves in magnetized uniform plasma slabs. Using this method, the reflection, absorption and transmission coefficients of such plasmas for right-hand circularly waves are studied and the effects of the continuously changing external magnetic field on the power of the electromagnetic waves propagated in magnetized plasma slabs with fixed parameters are presented. Our method enables more detailed numerical analyses which are useful in practical applications pertaining to the control of the reflection or absorption coefficients of electromagnetic wave through a uniform magnetized plasma slab by adjusting the external magnetic field.

Enhancement of implantation efficiency by grid biasing in radio-frequency inductively coupled plasma direct-current plasma immersion ion implantation

Direct-current plasma immersion ion implantation (dc-PIII) is an emerging method for the treatment of planar samples and particularly attractive as an efficient and economical technique to fabricate silicon-on-insulator. In this article, we report the use of grid biasing to enhance the implantation efficiency such as implantation current density. Experiments in argon plasma show that the implantation current density varies with the biased voltage (Vg), is higher at Vg⩾+30 V or Vg⩽−40 V than at Vg=0, and is saturated at Vg⩾+50 V or Vg⩽−50 V at a pressure of 0.2 mTorr. The implantation current density is always higher at Vg=+50 V than at Vg=0 at different pressure and radio-frequency (rf) power. Moreover, the implantation current density increases with the rf power and pressure at both 0 and +50 V biasing. The results of our particle-in-cell simulation and global model show that the observed phenomenon is partly due to the variation of the plasma density with the bias, and the variation in the shape of emit...

Effects of magnetic field on pulse wave forms in plasma immersion ion implantation in a radio-frequency, inductively coupled plasma

The time-dependent current wave forms measured using a pulse biased planar electrode in hydrogen radio-frequency (rf), inductively coupled plasma, plasma immersion ion implantation experiments are observed to vary in the presence of an external magnetic field B. Results further indicate that the magnitude of the pulse current is related to the strength and direction of the magnetic field, rf power, and pressure, but the pulse current curves can be primarily correlated with B. The plasma discharges are enhanced in all cases due to magnetic confinement of the electrons, enlargement of the plasma generation volume, and increase in the rf power absorbing efficiency. The plasma density diagnosed by Langmuir probe diminishes in front of the sample chuck with B, whereas the plasma is confined nearby the sidewall of the vacuum chamber at high magnetic field. The high degree of plasma density nonuniformity at high B in front of the sample chuck is not desirable for the processing of planar samples such as silicon ...

Steady-state direct-current plasma immersion ion implantation using a multipolar magnetic field electron cyclotron resonance plasma source

In semiconductor plasma immersion ion implantation (PIII) applications such as the synthesis of silicon-on-insulator by hydrogen PIII and ion cut, only ions arriving at the top surface of the sample stage are important. The ions implanted into the other surfaces of the sample chuck actually not only decrease the efficiency of the power supply and plasma source but also give rise to metallic contamination. In addition, low energy ions introduced by the initial plasma sheath propagation, pulse rise time, and pulse fall time introduce a large surface hydrogen concentration that creates surface damage and affects the wafer bonding efficacy. We have theoretically demonstrated direct-current PIII (DC-PIII) which retains the x–y immersion characteristic while simultaneously reducing this low energy ion component, obviating the need for the expensive power modulator, and extending the voltage ceiling that is no longer limited by the vacuum chamber and power modulator. In this article, we describe our hydrogen DC-...

Bioactivity and corrosion behavior of magnesium alloys treated by plasma electrolytic oxidation

Summary form only given. As a lightweight and nontoxic metal with mechanical properties similar to those of natural bones, magnesium based materials have attracted much interest in biomedical engineering. As the materials are both biocompatible and biodegradable, they can be used in many orthopedic and load-bearing applications. However, the poor corrosion resistance of magnesium-based biomedical implants in a physiological environment has hampered their use as substitutes for human hard tissues. Recently, plasma electrolytic oxidation (PEO) that is derived from anodic oxidation technology has been applied to treat valve-metals such as Al, Mg, Ti and their alloys. By utilizing micro-arc plasma discharges sustained at a high voltage in aqueous solutions, various oxide films can be formed on these metals to improve their surface properties such as wear and corrosion resistance as well as bioactivity. In this work, PEO treatments are conducted on magnesium alloys in different electrolytes and different voltage modes. The corrosion resistance is determined in simulated body fluids (SBF) based on the potentiodynamic polarization curves, and the surface bioactivity is investigated by monitoring the apatite inducing capability. The structure and chemistry of the plasma-formed surface oxide which exhibits a porous structure are evaluated. Our results show that the corrosion resistance and bioactivity of the PEO Mg alloys are much improved

Pulse current behavior in the presence of external magnetic field in radio frequency (RF)-inductively coupled plasma (ICP) quasi-direct current plasma immersion ion implantation

Summary form only given, as follows. In plasma immersion ion implantation (PIII) processes to fabricate silicon-on-insulator (SOI) materials such as separation by plasma implantation of oxygen (SPIMOX) and ion cut/wafer bonding, long-pulse PIII (or quasi-direct current PIII) has been shown to be more superior than conventional pulsed-mode PIII. The new process reduces the amount of the implanted ions in the near surface as well as the processing time. Our former experiments on quasi-DC and DC PIII utilize a grounded conducting grid above the sample holder to avoid plasma extinction as the plasma sheath expands. Recently, we have been successful in achieving stable operation in the long-pulse PIII mode by making the distance between the sample holder and plasma source long and the plasma density relatively high. In order to intensify the plasma discharge and produce one dominant ion species in the plasma, a weak external magnetic field (B) is generated using magnetic coils around the vacuum chamber. It is observed that the discharge is enhanced but the pulse current waveforms are significantly changed with the addition of B as well. Our results further indicate that the pulse current varies with the pressure and pulse voltage. We also observe that the magnitude of the pulse current is reduced as the pulse voltage increases in some pressure ranges. This can probably be attributed to the variation of the plasma generation volume and ion motion in the expanded sheath at different pulse voltages.