The paper presents the results of the authors many year work in the field of ion&plasma sources development.
The families of DC and RF ion and plasma sources are described. The results of ion&plasma
sources utilization in materials surface modification technologies are discussed.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3540

Alexandrov, A.

Kralkina, E.

Nekliudova, P.

Pavlov, V.

Petrov, A.

Vavilin, K.

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 1 No 4, 04PITSE09(4pp) (2012)   2304-1862/2012/1(4)04PITSE09(4) 04PITSE09-1  2012 Sumy State University Advanced Ion and Plasma Sources for Materials Surface Engineering  A.F. Alexandrov, E.A. Kralkina, P.A. Nekludova, V.B. Pavlov, A.K. Petrov, K.V. Vavilin  Physical Faculty of MSU, 119991, GSP-2, Moscow, Vorobjevy Gory   (Received 20 June 2012; published online 24 August 2012)  The paper presents the results of the authors many year work in the field of ion&plasma sources de-velopment. The families of DC and RF ion and plasma sources are described. The results of ion&plasma sources utilization in materials surface modification technologies are discussed.  Keywords: Ion Source, Plasma Source, Surface Modification, Plasma, Ion Beam.   PACS number: 52.50.Dg.   1. INTRODUCTION  During last decades the trend became evident to utilize ion beam and plasma technologies in industrial applications [1]. The reason consists in wide possibili-ties and ecological compatibility of the ion beam and plasma processes. A lot of plasma sources models are known nowadays [1-13]. However the development of science and industrial technologies requires more flexi-ble, more energy efficient, more perfect plasma sources.  The paper presents the results of the authors many year work in the field of ion&plasma sources develop-ment as well as the results of their utilization in mate-rials surface modification technologies.  2. THE FAMILY OF DC IS  The distinguishing feature of the DC IS family (30, 50 and 100 mm in diameter) is the use of the glow dis-charge for electrons generation in the water cooled hol-low cathode (cold cathode). The absence of filament or “hot-hollow” cathode provides long life time of the IS even in case of reactive gases utilization.   2.1 The Construction of DC IS  The scheme of the DC IS is shown on Fig. 1.     Fig. 1 – Construction of the cold cathode ion source. 1, 2 –cathode and anode chambers; 3 – gas distributor, 4 -magnetic system; 5 - ion optic system; 6 – cone orifice  Cold cathode ion source (see Fig. 1) consists of cy-lindrical water cooled cathode 1, cylindrical anode 2, gas distributor 3, magnetic system 4 providing magnet-ic field in the cathode and anode chambers and ion ex-traction system (IOS) 5. Between cathode and anode chambers a cone orifice 6 is executed. It connects cath-ode and anode blocks.  2.2 Characterization of DC IS  Experiments showed that plasma potential meas-ured in the anode chamber was close to the anode one, electron energy distribution was highly enriched by the group of fast electrons. It should be also noted that spa-tial distribution of electrons is defined mainly by mag-netic field configuration and doesn't depend on diame-ter of the orifice connecting cathodic and anode cham-bers if its diameter doesn't exceed 5mm. Fig. 2 shows the extracted argon ion beam current ib versus the discharge current id. One can see that ion beam current is proportional to the discharge one in the wide range of id.     Fig. 2 – The extracted argon ion beam current versus the dis-charge current. Argon flow rate is equal to 2.5 cm3/min. Ion source diameter is 50 mm  DC IS (30, 50 and 100 mm in diameter) provide ion beam current density ranging from 0.5 to 4.5 mA/cm2, ion energy can be varied within 200-1500 eV. Fig. 3 represents radial dependence of the ion beam current density. The curve was obtained with flat elec-trodes of the IOS. The utilization of the profiled elec-trodes of the IOS leads to more homogeneous ib(r) dis-tribution however the ion beam current density be-comes lower.   3. DC RADICAL SOURCE   DC radical source (RS) is the modified DS IS. The construction of DC RS differs from the DC IS one by the absence of IOS. It is changed by the grounded per-forated electrode. The presence of fast electrons in the discharge leads to the high dissociation rate of the working molecular gas and gives the opportunity to obtain a flow of plasma enriched by the products of 0 200 400 600 800 1000 1200020406080100120i b (mA)id (mA)   A.F. ALEXANDROV, E.A. KRALKINA, P.A. NEKLUDOVA, ET AL. PROC. NAP 1, 04PITSE09 (2012)   04PITSE09-2 molecules dissociation at the exit of DS RS. The de-pendence of nitrogen and oxygen dissociation degree on discharge current is shown on Fig. 4.    Fig.3. Radial dependence of the ion beam current density near the exit of the 50mm in Diameter DC IS.    Fig. 4 – Dissociation rate versus discharge current.  4. RF GRIDDED ION SOURCE FAMILY  Since the last decade of the XX the systematic re-search of RF power absorption mechanism was con-ducted by the authors of the present paper [13]. The main attention was concentrated on revealing the con-ditions of efficient RF power input to plasma and high plasma density generation. It was shown that at pres-sure less than 10 mTorr the most efficient RF power absorption can be achieved under conditions of reso-nant helicons and oblique Langmuir waves excitation. That is the reason why inductive RF discharge located in an external magnetic field of certain vale, became a basic working process of the original family of RF grid-ded IS.  4.1 The construction of RF gridded IS  RF IS source consists of the dielectric gas-discharge chamber (GRC), magnetic and ion-optical systems. The magnetic system is based on electromagnets. The ion-optical system consists of three punched electrodes.  Cylindrical RF IS with diameter 100 and 200мм as well as linear RF IS with the IOS size 20  15cm are developed.  For ignitions and maintenance of the discharge the cooled spiral antenna located on a lateral or face exter-nal surface of GRC are used. The ends of the antenna are connected to the RF power supply through the matching system.    4.2 Characterization of RF gridded IS  Fig. 5 shows the dependences of ion beam current on the RF generator power. One can see that sources are efficient when using both inert, and chemically ac-tive gases.     Fig. 5 – Ion beam current versus RF generator power.   Spatial distribution of ion beam current density is of great interest for industrial applications. One of the most important factors influencing a profile of an ion current density is the value of an external magnetic field (see Fig.6). Fig.7 represents radial distribution of an ion beam current density measured at different dis-tances from the RF IS IOS. The magnetic field value corresponds to the best conditions of RF power absop-tion by plasma.    Fig. 6 – Radial dependencies of the normalized ion beam cur-rent density measured near IOS.    Fig. 7 – Radial dependencies of the ion beam current density measured at the different distances from IOS.   The ion beam energy can be changed from 50 to 1500 eV. Thus the IS provides possibilities for "soft" (at energy of ions about 50 eV), and "rigid" (at energy of ions of an order 1000 eV), impacts on samples. However the ion beam current density in the case of 50 eV ion energy is low.  ADVANCED ION AND PLASMA SOURCES … PROC. NAP 1, 04PITSE09 (2012)   04PITSE09-3 5. RF GRIDLESS ION SOURCE  In order to provide soft treatment of samples by of relatively high current ion beam the RF gridless IS was developed. The working process of the IS is also based on the inductive RF discharge located in the external mag-netic field which value corresponds to the resonant con-ditions of helicons and oblique Langmuir waves excita-tion.  5.1 The construction of RF gridless IS  The IS consists of cylindrical dielectric gas discharge  chamber with diameter 5cm and length  15cm (see Fig. 8). The working gas is supplied to the upper end of  the discharge  chamber while the other one ends with a Laval nozzle. The GDC is located in the external mag-netic field provided by the electromagnet.  The spiral antenna is assembled on the lateral side of the IS. An-tenna ends are connected to the RF power source through the matching system.      Fig. 8 – The laboratory model of RF gridless IS  5.2 Characterization of RF gridless IS  The ion energy distribution functions were meas-ured in dependence on gas flow rate, power input and magnetic field value. Measurements revealed the exist-ence of two groups of ions, i.e. slow (with energy about 30 eV) and fast ones (with energy 60-170 eV). The gas flow rate increase leads to the reduction of the high-energy ions number and enhancement of the slow ones quantity. Typical ion beam energy distribution function obtained at Ar flow rate 6cm3/min is shown on Fig. 9.     Fig. 9 –  Typical ion beam energy distribution 6. THE PROLONGED PLASMA SOURCE WORK-ING AT ATMOSPHERIC PRESSURE  6.1 The construction of atmospheric plasma source  The prolonged plasma source [14-16] (see Fig. 10) includes ignition and main electrodes, RF power input unit, gas distributor providing air or working gas flow. The discharge is ignited between the main electrode and the sample, placed on the grounded plane. The advantages of RF plasma source are the possibility of thick dielectric substrates processing and low ozone generation rate.     Fig. 10 – The scheme of the prolonged plasma source.  1 – ignition electrode, 2- grounded plate, 3 – main electrode,  4 – RF power input unit, 5 – RF power supply, 6 – sample  6.2 The properties of atmospheric plasma source  Fig. 11 demonstrates the distribution of nitrogen molecule and molecular ion radiation intensity in the gap between the main electrode and the grounded plane. If discharge occupies the whole gap the  maxima of radiation intensity can be observed near the elec-trodes. The appearance of the radiation maxima can be attributed to a formation of the spatial charge sheaths. A potential drop that accelerates ions towards elec-trodes is known to appear along the sheath. The sheath presence near the place where the samples are located indicates a significant role of the accelerated ions in the change of properties of processed materials as in the case of low pressure plasma.  Measurement of the radiation intensity in various points along the main electrode showed high uniformity of the discharge.    Fig. 11 – Nitrogen molecule (open circles) and molecular ion (filled squares) radiation intensity distribution in an interval between the main electrode and the grounded plane  A.F. ALEXANDROV, E.A. KRALKINA, P.A. NEKLUDOVA, ET AL. PROC. NAP 1, 04PITSE09 (2012)   04PITSE09-4 7. APPROBATION OF ION&PLASMA SOURCE IN SURFACE MODIFICATION TECHNOLOGIES  The developed ion&plasma sources were approved in modern surface modification technologies. The re-sults of PTFE surface modification are shown on Fig. 12. The irradiation of PTFE samples leads to sig-nificant improvement of its adhesion. The presence of oxygen especially enriched by radicals during the irra-diation of samples by argon is accompanied by further increase of the adhesive force. Irradiation of PTFE samples only by a flow of the oxygen enriched by radi-cals, leads to some improvement of adhesion but the result is much worse than in case of ion irradiation.      Fig. 12 – The PTFE adhesion force versus oxygen pressure. Dashed line  corresponds to adhesion force of the untreated PTFE. 1,2,3,4 correspond to the irradiation of PTFE only by Ar ions, by Ar ions in the presence of oxygen, by Ar ions in the presence of oxygen enriched by radicals, only by oxygen en-riched by radicals   Fig. 13 –  SEM pictures of PTFE surface: a) untreated PTFE, b) after ion beam irradiation, c) after treatment in atmospher-ic discharge   From all variety of the physical and chemical processes occur-ring on a PTFE surface [17] we will allocate two: the change of chemical properties of materials surface and change of the morphology of a surface. Experiments showed (see Fig.13) that irradiation of PTFE by the ion beam results in essential change of morphology of a surface, while the presence of chem-ically active particles, especially radicals, leads to the change of a chemical composition of a surface [18]. The treatment of PTFE by atmospheric discharge leads to smoothing and change in the chemical composition of its surface.   REFERENCES  1.  Handbook of plasma processing technology: fundamentals, etching,deposition, and surface interactions. (Edited by S.M. Rossnagel, J.J. Cuomo and W.D. Westwood), (Noyes Publications, 1990, 523p). 2. H.R. Kaufman and R.S. Robinson. Operation of broad-beam sources. (Commonwealth Scientific Corporation, Al-exandria, Virginia, 1987) 201p. 3. Handbook of plasma processing technology: fundamentals, etching, deposition, and surface interactions. (Edited by S.M. Rossnagel, J.J. Cuomo and W.D. Westwood), (Noyes Publications, 1990) 523. 4. H.R. Kaufman and R.S. Robinson. AIAA J. 20, 745 (1982). 5. Plasma accelerators and ion injectors (Ed. by N.P. Kozlov and Alexander Morozov), (Nauka, Moscow, 1984), 272. 6. S. Kadoma, S. Suzuki. Patent abstract of Japan 57011448 A. Jan. 21, (1982). 7. N. Gavrilov. Plasma emitted of ions. RU 2134921 C1, Nov.20, (1997). 8. N. 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