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8Second International Symposium «Safety and Economy of Hydrogen Transport»
IFSSEHT-2003
USE OF ION BEAM SPUTTERING METHOD FOR THE PRODUCTION OF SENSITIVE HYDROGEN SENSOR LAYERS
A. V. Sitnikov
Voronezh State Technical University (VSTU), 14 Moskovsky pr., Voronezh, 394026, Russia Phone: (0732) 46-66-47, fax: (0732) 46-32-77, e-mail: kalinin@ns1.vstu.ac.ru
To obtain sensitive layers of hydrogen sensors, various methods for solid body sputtering are used. This paper offers an ion beam sputtering method successfully used in VSTU for these purposes.
The sputtering system was designed based on the YBH-2M vacuum sputtering installation. After its modernization, three ion beam sputtering sources have been emplaced in the vacuum chamber of the sputtering system: two sources serve for sputtering the sensitive layers of hydrogen sensors and one source in combination with the electron source is used for the substrate cleaning. Since the ion source is not connected with the sputtering object (a target or a substrate), it allows to sputter magnetic and non-magnetic metals and alloys as well as dielectric materials (if a compensator is available).
To apply a high voltage to the ion beam sputtering source anodes, the BP-100 modernized power supply units are used. A substrate holder, that is fixed on the axle and can revolve at the speed up to 2 RPM, is located over the vacuum chamber perimeter. Six 200x200 mm2 substrates can be placed on the substrate holder. Sputtering dielectric materials uses a source of intensive electronic radiation (compensator) representing a tungsten wire 0.2 mm in diameter connected to a separate power supply unit to neutralize the positive potential occurring on the dielectric surface.
The plasma concentration in the area of the magnetic clearance of ion sources allows to avoid a significant heating of the substrates with sputtering even without use of forced cooling, which considerably simplifies the technology for producing amorphous alloys. The absence of forced cooling also simplifies the mechanism for alternating the substrate between sputtering, film application and ion cleaning positions. The use of a similar source types and their layout in the vacuum chamber of the YBH-2M installation allows to obtain sensitive layers of hydrogen sensors, both on a rotating substrate with mass sensor production and on a fixed substrate for research purposes.
For sputtering thin tin oxide films doped with silicon oxide, an alloyed target and a composite target are used. The doped target was manufactured from 99.98% pure tin by melting in vacuum using an induction furnace. The melt of the corresponding composition has
been poured into a specially prepared mould with the dimensions of270x70x14 mm in vacuum. The target has been subjected to polishing on both sides, soldered to the water-cooled base and installed into the sputtering position. The composite target has been an alloyed pure tin target with five quartz plates fixed on its surface with the thickness of ~ 2 mm and the width of ~ 9 mm, which spacing varied from 10 mm on one target end up to 44 mm on the other end.
Varying the number of silicon oxide plates and the spacing between them, one could change the volume ratio of the dielectric layers of tin and silicon oxides obtaining the continuous spectrum of gas-sensitive layer compositions during one process cycle, which allows to enhance the authenticity of subsequent investigations.
To sputter tin oxide, the ion beam reactive sputtering method is used. 99.992% pure argon with the served the working gas. The continuous change of argon in the chamber occurred during the sputtering because of its over-supply though a dosing valve into the ion source and pumping-out by means of a diffusion pump of the H 2500/350 type with the capacity of 1800 l/s. Preliminarily, the working chamber was pumped out approximately during one hour at least up to the pressure 1x10-5 Torr. To control the tin oxidation rate in the sputtering process, oxygen has been input to the operating gas (argon) in the vacuum chamber at various partial pressure values.
While operating, the optimal sputtering modes have been experimentally determined: the gas mixture pressure in the chamber — 7.0x10-4 Torr, the partial pressure of oxygen — 62%, the plasma current — 160 mA at ~ 3000 V. For given operating modes, the rate of deposition of the SnO + SiO composite onto a fixed sub-
n n *
strate has been not less than 1.0 mm/hour. The sputtering layer thickness was determined by the sputtering time. The glass-ceramic material plates with the area of 60x48 mm2 (during sputtering of samples for electrical resistance measurements), common salt monocrystals (for electronic translucent microscopy) were used as substrates.
The samples obtained by sputtering represent 0.15— 1.5 mm thick films. The film thickness was measured with the MII-4 interferometer.
The work was accomplished the ISTC financial support (Project No. 1580).
