Rev 37 Operator’s Manual OM-610-1002-1
page 20 SECTION 5 OPERATION PDS-2010
WARNING: The pyrolysis zone has been preheated to approximately 690°C and the
probe cold trap has been pre-cooled to less than -90°C. The vacuum pump is running and
continuously pumping the system throughout the coating cycle.
4. Once system base pressure has been reached in step three, the vaporizer zone is heated to 120-
180°C. The vaporizer heater is cycled On/Off by the chamber pressure controller in order to
maintain the pressure in the chamber. As the pressure reaches the chamber pressure set point, the
power to the vaporizer heater is reduced to prevent the chamber pressure from overshooting. The
vaporizer heater is then maintained at a temperature where the chamber pressure is at the pressure
set point. This causes the solid Parylene dimer to slowly vaporize/sublime (go directly from a
solid to gas).
5. The pumping action of the vacuum pump causes the dimer gas to flow "downstream" through the
pyrolysis zone. The high temperature pyrolysis furnace cleaves the dimer gas to form the
Parylene monomer gas. The monomer is very reactive at this point and upon exiting the pyrolysis
zone will immediately seek a place to deposit and polymerize.
6. As the reactive monomer gas exits the pyrolysis zone and enters the chamber containing the
substrate material, deposition takes place. The monomer will deposit and polymerize on all
the
ambient temperature surfaces within the deposition chamber; this includes the loaded substrate,
fixturing, chamber walls, baffles, and any other extraneous surface within the deposition
chamber.
7. It is important to note that as the monomer gas flows into the deposition chamber, the additional
gas causes the pressure in the chamber to rise. Typically, the desired pressure rise is 15-30
milliTorr above base pressure for Parylene C The growth rate of the Parylene film in the
deposition chamber is proportional to the partial pressure of monomer gas. In practice, a feedback
control system is used to maintain the desired pressure within the deposition chamber by
controlling the rate at which dimer is vaporized.
8. Because of the gas flow dynamics associated with the vacuum pump, any monomer gas that flows
into the deposition chamber that does not deposit there will tend to flow through the cold trap and
toward the vacuum pump. However, because the cold trap is maintained at a sufficiently cold
temperature, any monomer gas that enters the cold trap will condense and deposit on the chilled probe
surface and not flow into the vacuum pump.
9. When the dimer has been completely vaporized, the pressure in the deposition chamber will decrease
and approach the base pressure that was observed in step 3 (before heat was applied to the vaporizer
zone). At this point, the deposition cycle is complete; the system can be brought back to atmospheric
pressure and the substrate can be removed.
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