Development of a magnetron sputtering system for in-situ deposition of thin multilayerscoatings.
M. Salhi1,*, S.E.K. Abaidia2
1Centre de Recherche Nucléaire de Birine, B.P. 180, Ain Oussera, Djelfa, Algérie.
2Unité de Recherche MPE, Faculté des Sciences de l’Ingénieur, Université M’hamed Bougarra de Boumerdes, Boumerdes, Algérie.
*e-mail adress:[email protected] Abstract—In house Physical Vapor Deposition-
Dual Magnetron Sputtering System (PVD-DMSS) was designed and manufactured based on basis criteria, relevant on R&D and industrial systems, and on the feedback experience acquired from operation of an old classical physical vapor deposition system of our laboratory. Its permit to elaborate in situ multilayer’s thin films without breaking vacuum and with varying several operation parameters, namely the inter-electrode distance, substrate rotation, polarization and the heating of substrate. The sputtering chamber of developed PVD-DMSS has a volume of about 10 liter; equipped with many accesses (for loading/unloading of samples, for the control of operation parameters and for the installation of diagnosis instruments). The PVD-DMSS is also equipped with two planar balanced magnetron cathodes providing magnetic field of 400mT, the cathodes can be powered by either a radiofrequency alternative current or continuous current, and connected to a high vacuum system. Monolayer’s and multilayer’s Nickel and Titanium thin films obtained and the results of plasma diagnosis make obvious that the PVD-DMSS developed allows a good level of operation flexibility as well as obtaining reproducible thin films and multilayer with a desired quality.
Keywords—PVD system design; magnetron sputtering; thin film; plasma diagnostic
I. INTRODUCTION
Given their promising properties compared to bulk materials, micro and nanostructures materials have found wide applications in various field of industry namely microelectronics, optics, mechanics, corrosion, magnetism, decoration… [1- 3]. Magnetron sputtering deposition technique is widely used for obtaining these kinds of materials in the form of thin layers. Basically, the technique consists to produce under high vacuum energetic positive ions, from ionization of inert plasma gas, which are bombarded a target (cathode) in order to extract superficial atoms to be condensed onto a substrate (anode) [4-6]. At low pressure the electric field (AC-generated by 13.56MHz or DC sources) between the two electrodes causes the ionization of
the residual inert gas which is in the sputtering chamber and gives rise to electrons, which are attracted by the anode, and positive ions will be attracted to the target. All particles which are formed between electrodes constitute the plasma.
The magnetic field lines generated by magnetron cathode confine electrons close to the target surface and enhance sputtering yield. Since 10 years ago, Unit Research- Material Environment and Processes of M’hamed Bouguerra Boumerdes University (UR-MPE/UMBB) with collaboration of Research Nuclear Center of Birine (CRNB/COMENA) were worked on the development of a magnetron sputtering system for the multilayer deposition to be used for different applications. The system [7] has been recently installed and commissioned at the unit research. In this paper, we give an overview of the design of main components of PVD-DMSS and some results about the commissioning of this system.
II. DESIGN BASIS
Dual source planar cathodes magnetron combined with rotating substrates placing them alternatively over both cathodes were used as solution to elaborate multilayer’s nanostructures without vacuum breaking. The inter-electrode distance is adjusted at when the pumping is in shutdown state. The functional dimensions of main components of the system were determined according the following criteria: Minimum time to reach the working vacuum, thickness homogeneity of thin films, confined plasma. Flexibility of the operation of the system was considered also as main design criteria especially for loading and unloading of samples in/from sputtering chamber.
Materials of the PVD system were chosen to satisfy vacuum requirement and to avoid any possible contamination, contamination from vacuum system must be avoided as possible.
III. Dual magnetron cathodes sputtering system
The PVD-DMSS (Fig.1 and Fig.2) is constituted of sputtering chamber, magnetron cathode, substrates holder, cooling system, vacuum system and control system.
Fig.1 PVD Dual magnetron cathodes sputtering system (UR-MPE/UMBB)
A. Sputtering chamber
The sputtering chamber is a cylindrical stainless steel chamber with dimensions of 220x250x5 mm, equipped with two upper and lower covers.
The chamber has two magnetron cathodes, an anode (substrate holder), and two diametrically opposed Quartz windows of 𝟏𝟐𝟎 𝐦𝐦 in diameter used for visual control of the plasma and for loading/unloading of samples. The magnetron cathodes are mounted from the top cover of the sputtering chamber. The pumping pipe is connected on the lower cover. The chamber has several sealed passages of different diameters intended for the introduction of gas (plasma and reactive), for instrumentation (spectroscopic and electrostatic probe, quartz balance), for vacuum measurement gauges for evacuation of air ...etc.
B. Magnetron cathode
In house planar balanced magnetron cathode was designed for the PVD system; the cathode can house a target of 50 mm in diameter. It is constitute of permanent magnets of 400 mT inserted in stainless steel container, iron plate is used as magnetic yoke to magnetic field lines. The heat generated in the target and the permanent magnets is removed by a cooling water circulation of a flow of 0.1 l/s under 1 bar of pressure. The cathode can feed either a DC current or an AC current of 13.56 MHz.
C. Substrates holder
The substrates holder is composed of a cache and a rotating disc. The substrates may be heated by thermal conduction with heating canes which are located just below the rotating disc. The anode may be biased by a 100 V voltage.
D. Cooling system
A cooling system was designed to remove heat generated in: magnetron cathodes of the PVD system, secondary vacuum turbo molecular pump, impedance matching box of magnetron cathode RF13.56 MHz power supply. The system is composed of centrifugal pump, heat exchanger, instruments, valves, pipes. The flow rate of each component to be cooled is adjusted by using a set of valves.
E. Vacuum system
The vacuum system is composed of: mechanical primary pump of pumping speed of 4.17 l/s, turbo molecular secondary pump of pumping speed of 220 l/s, throttle valve, electromagnetic valve, filters, standards valves and vacuum pipes. A vacuum of 𝟓 × 𝟏𝟎−𝟔𝐦𝐛𝐚𝐫 can be achieved in the sputtering chamber after approximately 3 hours of pumping.
The turbo-molecular pump is monitored and controlled by a PC; it is protected by a protection system that prevents any anomalies or wrong operations. A vacuum measuring gauges set, primary and secondary, and reading instruments are used to control the pressure inside the sputtering chamber.
Fig. 2 The general view of the sputtering chamber along with its components
IV. COMMISSIONING AND
QUALIFICATION OF PVD-DMSS The visual inspection during Nickel and Titanium deposition process show that plasmas are stable and well confined between the electrodes, the reflected power remain under 2 W during all deposition processes. (Ni, Ar) Plasma diagnosis by electrostatic Langmuir probe [8] and microstructure analysis of Titanium and Nickel thin films by GIXRD technique were the two preliminary tests which were used to qualify our PVD-DMSS. The I(V) characteristics obtained by Langmuir probe measurement at RF power of 40 W and 60 W (Fig.3) shows that both curves are not perturbed by RF interferences and noises and the deposition process is stable. The main plasma parameter calculated from the obtained I(V) curves [9] shows
that electron density of about 1010 /cm3 and the electron temperature of about 1.2 eV.
Fig. I(V) curves obtained by Langmuir probe at cathode power of 40W and 60 W.
V. CONCLUSION
Dual magnetron cathodes sputtering system is presently under operation in thin films laboratory of Unit Research-Materials Environment and Processes of M’hamed Bouguerra Boumerdes University (UR-MPE/UMBB). The first obtained results of preliminary commissioning shows that the design of the developed system is appropriate and meets the design criteria’s. Others tests and characterizations are provided in near future to in- depth assess the system under harsh operating conditions.
Acknowledgement
This work was supported by the UR-MPE of M’hamed Bouguerra University and Algerian Atomic Energy Commission. The authors are grateful for the financial support.
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