G.F. Gomes

Application of a dc glow discharge source with controlled plasma potential in plasma immersion ion implantation

A dc glow discharge source with controlled plasma potential was developed for application in plasma immersion ion implantation processing of materials surfaces. This type of ion implantation system allows cost effective surface modification of workpieces with complex shapes. The effects of the nitrogen plasma etching during the plasma immersion ion implantation process was studied using Si wafers as monitors, as we varied the externally controlled plasma potential between 0 and 350 V. When the plasma potential is controlled below 70 V, the ion implantation is dominant, otherwise the etching overtakes. The nitrogen implanted silicon wafers were analyzed by high resolution x-ray diffraction and Auger electron spectroscopy which revealed successful implantation of ions with accumulated nitrogen dose of 1.5×1017 cm−2, for the low potential case.

Plasma immersion ion implantation experiments at the Instituto Nacional de Pesquisas Espaciais (INPE), Brazil

Abstract Historical perspective of the development of PIII devices at the Instituto Nacional de Pesquisas Espaciais (INPE) is given, together with the description of the present system under operation and our overall results on this three-dimensional implantation research. Starting with an ignitron switched pulser (1 pulse per 3 min) and an intermittent microwave plasma, we improved our PIII system developing a pulse forming network (PFN) based pulser (20 Hz), 2 years later. We also improved our plasma source towards a DC, highly stable, medium density glow discharge system. A much faster hard tube pulser was recently incorporated to our PIII system (670 Hz) allowing us to achieve good implantation results in different materials. Presently, we are testing a recently purchased RUP-4 commercial pulser to obtain arc prevented, 1.1 kHz, square pulses for new experiments in this active field of PIII research.

In-line nitrogen PIII/ion nitriding processing of metallic materials

Abstract Hybrid surface modification involving plasma immersion ion implantation (PIII) and ion nitriding has been attempted. DC cathode nitrogen glow discharges with 600–1000 V, 50–300 mA were typically obtained using the sample support as the cathode and the vacuum chamber as the anode. In this mode, sample temperatures of 500–600 °C can be reached easily while PIII at 10 kV, 50 μs and 400 Hz alone can provide about 300 °C heating. Combining these two highly conformal treatments and achieving high temperature, high efficiency three dimensional ion implantation is our objective. X-ray diffractions (XRD and high resolution XRD in the glancing mode) showed effects of ion nitriding in the AISI 304 stainless steel samples surface which indicate very thick nitrided layer, especially when operating the glow discharge in the low pressure but with high temperature nitriding mode. Auger electron spectroscopy and microhardness measurements confirmed nitriding in the sample surface. The hybrid treatment (PIII/ion nitriding) is expected to improve further these surfaces.

Alternated high- and low-pressure nitriding of austenitic stainless steel: Mechanisms and results

A combined surface modification treatment consisting of ion nitriding at high pressure and high temperature, followed by a cycle at low pressure, both cycles using a gas mixture of (N2/H2):(50/50) in pressure, was applied to stainless-steel AISI 304. In the first cycle, in a glow discharge at 4×10−1 mbar and temperatures of 400–450 °C, high-pressure nitriding was applied to the samples. In the second cycle, in a glow discharge at 8×10−4 mbar, low-pressure nitriding was applied to the samples. Applying this sequential hybrid treatment alternately, good nitriding was obtained. X-ray diffraction (XRD) measurements showed the effects of this hybrid ion nitriding in the AISI 304 surface, indicating thick nitrided layers, confirmed by Auger electron spectroscopy (AES). Conversion electron Mossbauer spectroscopy, combined with AES and XRD, showed phases and compounds induced by such treatments. Vickers hardness measurements showed great enhancement in the surface hardness. Applying other combinations of gas mixt...

Plasma immersion ion implantation using a glow discharge source with controlled plasma potential

Abstract A DC glow discharge plasma source was used in a plasma immersion ion implantation (PIII) experiment providing nitrogen plasmas with densities of 1–3 ×10 10 cm −3 and temperatures of 5–10 eV. Nitrogen ions were extracted from these plasmas and implanted in a variety of immersed samples (Al 5040, SS 304, Si) using repetitive high voltage pulses from two types of sources: PFN pulser and a hard tube pulser. Due to the high potential present in our plasma (350 V), a significant sputter etching of the samples surface occurred at long irradiation times. An electron shower source was used to lower this potential allowing its control from 0 to 350 V. Operating the plasma source at potentials below 70 V reduced the sputtering to negligible levels and a retained dose of 1.5×10 17 cm −2 was achieved in a silicon surface, after irradiation of 1500 min. For plasma with potential of 350 V (no electron shower), the retained doses in Al 5040 and SS 304 samples were smaller than 5×10 16 cm −2 , for same plasma and pulser conditions (but 2500 min irradiation), confirming the deleterious effects of sputtering measured in Si samples. Upon using the higher repetition rate pulser, the treatment time was reduced by a factor of 700, thus easing considerably the sputtering problem.