Xia Lifang

Effect of pulse waveform on plasma sheath expansion in plasma-based ion implantation

Abstract In this paper, the effect of the pulse waveform on plasma sheath evolution around a diamond-shaped target has been simulated using fluid dynamic model in the context of plasma-based ion implantation (PBII). The implanted parameters of ions such as ion-implanted energy, impact angle and impact current have also been studied under different pulse shapes. Understandably, the longer pulse rise time would result in the lower ion impact energy, and less sheath expanding extent. By comparing the sheath structure under different pulse rise time, we found that long pulse rise time would enhance the conformation of the sheath to the target at the earlier stage of the pulse and would reduce the tendency of the ion depletion in the plasma sheath. Accordingly increase the ion impact current at the later stage of the pulse, which is quite important for the PBII process, when the ions have been accelerated adequately.

XPS of Ti+TiN+(N,C) multilayer films deposited by filtered cathodic arc deposition with controlled feed gas flow rate

Abstract Ti+TiN+Ti(N,C) films are deposited in a filtered vacuum arc deposition system by controlling the gas inlet order and gas flow rate, with a steady increase of C 2 H 2 and a steady decrease of N 2 flow rate. X-ray photoelectron spectroscopy (XPS) has been used to analysis the element depth profile. The C1s, N1s and Ti2p spectra are discussed.

Effect of plasma density on the distribution of incident ions and depth profile in plasma-based ion implanted layers

Abstract The retained dose and compositional depth profile were studied in the context of cylindrical target with different plasma density treated by plasma-based ion implantation (PBII). Nitrogen was implanted into silicon wafer clamped on the samples in order to acquire high quality profiles. Auger electron spectroscopy (AES) was used to acquire the nitrogen depth profile at the middle of Si wafer. A method, that combined fluid dynamic model to simulate plasma sheath expansion during high voltage pulse and TRIM code to simulate incident ion distribution in the solid was presented to simulate the experimental results. Both retained dose and N depth profile were compared with the results of theoretical simulation. The agreement between them for all three cases is good; that is, the model can give a good prediction and explanation to the experimental results. The retained dose for cylinder increases with increasing plasma density. The continuously distributed energy of incident ions and low N + /N 2 ratio in the plasma shift the N depth profile nearer to the surface and reduce the range significantly.

Simulation of a diamond-shaped target with different sizes in plasma based ion implantation

In this paper, plasma based ion implantation of a diamond-shaped target was simulated using a fluid dynamic model for three different sizes. The effects of the target size on plasma sheath evolution and the implanted ion parameters have been studied. It was found that a larger sized target would result in a faster sheath expansion, and better conformity between the sheath and the target. For all three cases, the ion implanting dose peaked near the corner and decreased at the corner, reminiscent of the sheath characteristic around an independent corner.

Simulation of the distribution of incident ions and depth profile in plasma-based ion implanted layers with different pulse width

The implantation dose and compositional depth profile were studied in the context of cylindrical target with different pulses treated by plasma-based ion implantation. Nitrogen was implanted into silicon wafer clamped on the samples in order to acquire high-quality profile. Auger electron spectroscopy was used to acquire the compositional depth profile at the middle of the Si wafer. The measured results, both implantation dose and depth profile, were compared with the results of theoretical simulation. A method, that combined fluid dynamic model to simulate the sheath expansion and TRIM code to simulate incident ion distribution in the solid was presented. The agreement between the measured results and theoretical calculations for all three cases is good. The implantation dose for the cylinder is increased with increase in pulse width, which is consistent with theoretical prediction. The continuously distributed energy of incident ions and N2+/N+ ratio in the plasma shift the depth profile nearer to the surface and reduce the projected range significantly.

Tribological behavior of aluminum alloys implanted with nitrogen, titanium then acetylene

The composition depth profiles, structure and ball-on-disk frictional characteristics of aluminum alloys 2024 plasma-based ion implanted with nitrogen, titanium and nitrogen then acetylene were investigated. The layers implanted with nitrogen then with nitrogen and titanium and finally with acetylene included three zones: a top DLC (diamond-like carbon) zone, a C, Ti and N coexisting intermediate zone which undergoes chemical changes forming TiC, Ti(C,N), TiN, (Ti, Al)N and AlN second phases, and the bottom zone of the substrate. The micro-hardness and nano-hardness of these layers are HK7.8 GPa and 22 GPa, respectively. The layers showed lower friction coefficient and higher wear resistance. The Raman spectra for worn tracks after sliding for different numbers of cycles showed that when the loading was 1 N after sliding 10,000 cycles, a slight graphitization phenomenon of the DLC film is found. If the loading was 20 N, the graphitization phenomenon of the DLC film is more obvious after sliding 2000 cycles. The SEM morphologies of the wear tracks showed that when the load was 1 N, after sliding 7200 cycles the wear is from rubbing and abrasive wear. When the load was 20 N, after sliding 2000 cycles, delamination wear is dominant. Scheduled for Presentation at the 58th Annual Meeting in New York City April 28–May 1, 2003

Measured and calculated retained dose with different process parameters in plasma based ion implantation

This paper reports the research that systematically studied the effect of the adjustable process parameters on the retained dose in plasma based ion implantation with an aim to provide a method for optimizing the implantation process. Nitrogen was implanted in a silicon wafer clamped on a cylindrical sample holder while varying parameters such as implantation voltage, radio frequency (RF) power, pulse width and target size. Auger electron spectroscopy was used to execute sputter depth profiling and to obtain the retained dose at the middle of the silicon wafer. The retained dose on the wafer was also predicted using fluid dynamic model, which simulates the sheath dynamic mode with consideration of the sputtering effect of the implanted ions. The measured results were compared with theoretical calculations, and the agreement for all the samples was good. The implantation dose for the cylinder will increase with increasing implantation voltage, pulse width or the RF power. A larger sample will result in a decreased dose, although the large ion reception area will push the sheath edge to a further position from the substrate.

Modelling and experiment of plasma-based ion-implanted two-dimensional target

A prismoidal-shaped target with trapezoidal section containing four different convex corners was implanted with nitrogen using plasma-based ion implantation (PBII) in order to study the effect of target shape on the retained dose and its distribution with depth. Nitrogen was implanted into a silicon wafer clamped on the side wall of the sample holder, and Auger electron spectroscopy was employed to obtain the nitrogen depth distribution and the retained dose. Both a former simulation and the present experimental analysis exhibit dependence of the dose on the target shape but with a reversed trend. A method that combines a fluid dynamic model to simulate plasma sheath expansion during a high voltage pulse and the Monte Carlo method of the TRIM code to simulate the incident ion distribution in the solid was presented to predict the concentration depth profile after PBII. When establishing the model, the mechanism of the resulting lower retained dose near the corner with the higher density of ion impact flux was discussed. It was found that the oblique impact of the ion flux reduces the retained dose of the modified layer in three ways and changes the form of the profile remarkably. The continuous distribution of ion impact energy and the low N+/N2 ratio in the plasma shift the N depth profile nearer to the surface, which reduces the implantation depth significantly. In addition, the oblique impact near the edge of the convex corner decreases the reduction in ion range and retained dose and should account for the gradient in the retained dose distribution on the target surface. The model presented can give a good prediction and explanation for the experimental results.

An Investigation of the Reason for the Intergranular Fracture Appearing at the Great Quantity of Retained Austenite Zone in the Ion Carbonitrided Layers of Steel 20Cr2Ni4A

ABSTRACT In this paper, the reason for forming intergranular fracture at the great quantity of retained austenitic zone in the ion carbonitrided layers of steel 20Cr2Ni4A is studied. Observation the impact fracture by scanning electron microscopy shows that the impact fracture of ion carbonitrided layers will form intergranular fracture in the zones corresponding to the great quantity of retained austenite in microstructure, if the treating is introduced at higher temperature and the content of carbon and nitrogen are higher in austenite. The analysis results by X-ray diffractometer, wavelength dispersive spectrometer and Auger electron spectrometer showed that the carbon and nitrogen and other elements such as sulphur and phosphorus gather on the austenite grain boundary for austenite containing higher carbon and nitrogen content, this makes the austenite grain boundary weakness and accelerats the intergranular fracture appearing at the great quantity of retained austenitic zone.