Localized ion plasma sputtering (LIPS)

Citation

(1999), "Localized ion plasma sputtering (LIPS)", Aircraft Engineering and Aerospace Technology, Vol. 71 No. 1. https://doi.org/10.1108/aeat.1999.12771aaf.001

Localized ion plasma sputtering (LIPS)

Localized ion plasma sputtering (LIPS)

Keywords Coatings, Plasma, Sputtering, Tabco

Localized ion plasma sputtering (LIPS) technology relates to the treatmentof materials in vacuum and can be used for high-efficient sputtering of the thin conductive, protective, antigalling, wear resistant and decorative coatings in the hard-to-reach places of various components for the electronic, automotive, aircraft industries, etc. ­ for example, for coating the interior surfaces of pipes with small diameters, various slots or the interior surface of the connective holes in printed circuit boards.

The coatings, by all metal and alloys, nitrides and carbides, are applied onto metals and alloys, ceramics and glasses, polymers and plastics (even such non-stick surfaces as teflon or new materials as AlSiC). In some cases, the coatings can be done at a low temperature (even at room temperature), thus avoiding damage to the substrate.

The coatings are stated to be completely adhesive, uniformly thick (between 0.2 and 800 micro inches) with extremely low porosity (about 0.07 vol.pct. of non-connected pores).

Tabco Technologies informs us that the area of coating can be controlled and this process allows coating inside tubing and holes as small as 0.08in. diameter.

Comparison of the LIPS process with other plasma sputtering processes

There are well-known contemporary methods of sputtering of materials in vacuum to obtain adhesive coatings on the different substrates to be coated: the method of cathode sputtering in the independent glow discharge and the high-efficient method of magnetron sputtering and its modifications.

The method of cathode sputtering

Cathode sputtering in the independent glow discharge is usually the system of two electrodes: cathode-target of the material to be sputtered and anode, where the substrate to be coated is located. The electrodes are placed in the vacuum chamber, which is pumped out continuously, and plasma-forming gas (for example argon) is fed into the chamber. When direct high voltage is applied to the electrode system the plasma forming gas is ionized and positive ions from the plasma bombard the cathode surface and sputter the cathode material. The atoms and electrically neutral block of atoms from the cathode travel to the anode and precipitate on its surface like a layer of coating. So, the substrate to be coated has to be placed near the anode or somewhere between the electrodes to obtain the coating on it.

This method and corresponding equipment ensure the possibility of sputtering of the flat cathode-targets of large areas, the obtaining of coatings on the rod disposed along the axis of a cylinder by use of sputtering on the inner surface of cylindrical cathode-target or the precipitation of coatings on the inner walls of tubes and cylinders by sputtering of the rod cathode-targets fastened in the center.

Tabco Technology believes that the main shortcoming of this method is low current density on the target, which does not exceed 10-20a per sq.m. That results in a very low productivity of sputtering system and low speed of coating the substrate. The increase of current density by raising the pressure of plasma forming gas in the vacuum chamber is possible, but only up to a definite value. This value is determined by the phenomenon of the back diffusion of the sputtered atoms on the cathode, when sputtered atoms travel back to the cathode having no energy to reach the substrate to be coated. It is known that the optimum pressure in the vacuum chamber for the cathode ion sputtering in the glow discharge is 5-6Pa.

It also believes that using this method is limited also when coatings have to be applied onto the inner surface of pipes and holes. When the distance between the surface to be coated and the surface of the cathode-target is less than the thickness of a dark cathode area, the glow discharge between the cathode and anode is not maintained at such a distance. The thickness of the area of the dark cathode space is usually 0.53in. (13mm) at the above-mentioned optimum gas pressure in the chamber equal to 6Pa. That means that the minimum possible inner diameter of pipes and holes which walls can be coated by the cathode sputtering method is not less than 1.22in. (30mm).

Some sputtering apparatus allows a gradual decrease of the plasma created gas pressure from the region near the target to the region near the substrate by special gas supply and gas withdrawal means, thus facilitating effective cathode sputtering.

It is very helpful to decrease resputtering phenomena for easy formation and good crystallitability of coatings. But this apparatus still uses the glow discharge cathode sputtering, so all shortcomings connected with this process ­ low current density on the target and big dark cathode space ­ are present.

The method of magnetron sputtering

The high-efficient method of magnetron sputtering and equipment for its realization are known in which the magnetic system of the loop field is mounted on the side opposite to the surface of the cathode-target to be sputtered. As a result of the interaction of the magnetic field of the indicated configuration and the electrical field above the cathode- target surface being sputtered, a localized tunnel zone of the working plasma with high ionization grade is formed. This stimulates the obtaining of a high current density on the cathode-target ­ up to 3,000sq.m.

Thus the minimum possible inner diameter of tubing and holes to be coated by this method is not less than 2.04in. (50mm).

Relatively new magnetron sputtering devices, known as "post magnetrons" use external magnets or coils instead of permanent magnets. They allow coating much smaller holes, but are said to be limited to a case where the substrate to be coated is not ferromagnetic.

LIPS process

According to Tabco Technologies, a lot of what it considers to be shortcomings in other processes can be eliminated by using the method of LIPS. This method of ion sputtering consists of sputtering of materials in vacuum using ions which have been supplied from the high plasma concentration local area and accelerated by an electric field. These ions bombard the cathode-target extracting atoms and and blocks of atoms. This method allows for control of the discharge power, current density as well as size of the intensive sputtering area on the cathode-target surface.

This technology is said to be capable of producing much higher current density to the cathode-target than magnetron sputtering ­ up to 10,000-15,000A/sq.m, which is four to five times higher current density ­ thus permitting a considerable increase of coating speed and productivity of unit.

It is is also said to be possible to regulate the size of sputtering sector of the cathode surface in wide variations: from 0.003sq.mm up to 100sq.mm. Owing to these advantages, the process of sputtering can be done in a very small space. The distance between the cathode and coated surfaces could be a minimum of several tenths of a millimeter which prevents the wasting of material to be sputtered and creates the new possibilities for component design.

The main advantage claimed of LIPS technology is a very effective coating by metals, different alloys, nitrides or carbides of internal surfaces of various components:

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  the interior surface of small diameter pipes or blind holes (through openings as small as 0.08in. (2mm);

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  inside surface of connective holes for printed circuit boards;

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  the interior of long (about 20in.) small ID tubes;

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  inside surface of small grooves and other complex-shapes; the interior surface of complex-shaped parts.

Technology can be provided for the precision ion treatment of work surfaces: piercing of micro size holes in foils, milling of grooves, adjustment of parameters of elements of electronic devices.

LIPS technology can reportedly be used for coating the central electrodes of spark plugs by such expensive metals as platinum or palladium. These coatings will provide extended life and better performance of the spark plug. The process may also be used for precise coating by copper or gold of electrical components. It also can be used to provide the initial coating on the ID of connective holes of printed circuit boards. Reflective or decorative coatings of plastic surfaces can also be obtained.

It is thought to be a very economical and material saving process for the group coating of small components, such as electrical contacts, etc.

For each actual application, Tabco Technologies proposes to produce an experimental lot of coated samples. We can develop the know-how for coating of your specific components and supply you with all the necessary equipment for mass production according to your technical requirements.

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  Patent of USA 4,412,906 11/1983 Y. Sato.

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  Patent of Germany No. 2729286, C 23 C15/00.

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  "Design and capabilities of novel cylindrical post magnetron sputtering source", D.W. Hoffman ­ Ford Motor Co.; paper presented 4/5/82 in San Diego.

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  Patent of Ukraine No. 7 111,2/95 D. Dudko et al., C23 C14/00,2.9. 1995.

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  Welding Design Fabrication, August 1988, p. 39.

Further details are available from Tabco Technologies Inc. Tel: +1 401 722 8888; Fax: +1 401 722 8937.