RF biased substrate holder, water-cooled
General:
For many plasma and ion based processes in materials science and
technology it is often desirable to control the ion energy indepently from the plasma
generating mechanism. Usually this is done by applying a negative dc bias to the substrate
holder. The 13.56 MHz rf-biased and water cooled substrate holder RBS 150/100 provides an
efficient and powerful solution to meet these requirements. Substrates with diameters of
up to 6 inches (150 mm) can be accomodated.
RF biasing:
The standard dc-bias method is not applicable when electrically
non-conducting substrates are being processed or when insulating films such as SiO2 or
non-conductiong polymers are deposited at the substrate surface. Therefore, the RBS 150/100
is rf powered at a frequency of 13.56 MHz. In this case a negative "self bias" develops which is proportional to the rf power fed into the system
and the gas pressure, which can be exactly
controlled for conducting as well as non-conducting substrates.
Base plate:
The substrate is clamped to a water-cooled substrate base plate. Good
thermal contact to the substrate is achieved by a specially treated highly planar base
plate surface.
Clamping system:
A mechanical clamping system based on the bayonet
principle is used. The clamping ring is fixed with three screws to the rf biased base
plate. With different rings it is possible to fix substrates with a diameter of up to 150
mm (6 inch wafer).
Matching network:
To minimize the reflected power of the substrate holder, an impedance
matching is needed. Therfore, an optional compact gamma type matching network can be
included to the system. RF power coupling of up to 300 W is possible. Due to an optimized
substrate holder geometry and the corresponding tuning components (inductance L and
variable capacitors Cload and Ctune) the reflected power can be kept close to zero for
atomic and molecular gases (i.e. argon, oxygen, nitrogen, hydrogen) for a broad pressure
range.
Dark space shield:
To avoid the generation of unwanted plasma at the reverse of the
base plate and the connection rod a dark space shielding is used. This is mandatory for an
efficient use of the rf power for biasing the substrate holder.
Base plate position:
The connection rod length and thus the substrate position can be varied
continously by 100 mm (about 4") maximum. This can be done while the system is under
vacuum and the substrate holder is powered.
Technical data
maximum substrate diameter: 150 mm
vacuum flange: DN 250 ISO-K or larger, CF flange optionally
max. rf power: 300 W
Vmax (dc): 800 V
pressure range: 0.04 - 10 mbar
Application note: