LINEAR, SELF-CLEANING PLASMA ENHANCED CHEMICAL VAPOUR DEPOSITION SOURCE
The deposition of thin ceramic or polymer layers at high deposition rates is undoubtedly advantageous from an economic viewpoint. However, it has one inherent drawback: Not only the substrates are coated at a high rate but also the inside surfaces of the tools.
Thin coatings usually adhere well on any surface but when they grow thicker the intrinsic stress will eventually exceed the adhesive force, leading to cracking and delamination. In the worst case fragments will land on substrate surfaces jeopardizing production yield. Therefore, the insides of coatings tools need to be cleaned sufficiently often.
Thus, a simple rule applies: The higher the deposition rates the shorter the production cycles. Down-times for vacuum coating systems will increases costs. Tool cleaning means: cool down time, venting, cleaning, pump down and heat up before a production re-start. All these steps can amount to several hours and to repeat the procedure every two to three days does not appear to be economical. W&L Coating Systems GmbH has developed a linear microwave PECVD source which does not have to be cleaned more often than magnetron sputter tools.
|Length:||currently 700 mm (lab tool) with one single microwave generator, can be extended to 3,500 mm theoretically|
|Operating frequency:||2.45 GHz c/w or pulsed, can be operated at RF and acoustic frequency insymmetrical electrode arrangement|
|Consumables:||gases and vapours in heated and adjustable supply line (100°C), a second supply line for plasma gas, lower gas inlet can be moved under vacuum conditons|
|Operating pressure:||10-4 mbar to 10 mbar, depending on precursors, device is equipped with adjustable, linear magnetic plasma confinement|
|Features:||“waist” is electrically insulated, plasma bias possible|
By forming a „waist“ two hollow cylinders seperate the plasma volume from the coating volume. The reactive gas or energy carrier gas is injected beyond the plasma source (Gas inlet 1). The film forming gas is injected between the plasma source and the substrate level by means of either one or both hollow cylinders (Gas inlet 2). Hence, the undesired self-coating mainly happens on the surface of the hollow cylinders. Subsequently, the outside surfaces of the two hollow cylinders can be cleaned mechanically as necessary from time to time by pivotable rotating brushes without venting the vacuum system. The magnet bars and the gas inlet 2 can be rotated under vacuum conditions for purposes of process optimisation
Mechanical cleaning of hollow cylinders
- Thin films showing surface energies of > 70 mN/m (very wettable)
- Thin films showing surface energies of < 20 mN/m (not wettable)
FT-IR spectrum of a thin acrylic layser on a organically modified thick quartz layer on polycarbonate. Vibrational modes, typical for acrylic acid, are clearly visable (marked in blue, measured by Nico Dams)
Mass spectrum taken in the exhaust line. The precursor molecule hexamethyldisiloxane experiences strong fragmentation even in the remote oxygen plasma process (measured by Nico Dams)