thermionics laboratory, inc
3kW Rod fed e-gun manual Page 2
Safety Instructions
DANGER: HIGH VOLTAGE
A. Before servicing or operating this equipment, read this manual and the associated e-Gun
power supply manual paying special attention to
ALL SAFETY PRECAUTIONS
.
B. The high voltage used by these evaporation sources can be
INSTANTLY FATAL
.
Furthermore, due to internal capacitance in the power supply,
THIS LETHAL VOLTAGE
CAN PERSIST EVEN AFTER THE POWER SUPPLY HAS BEEN TURNED OFF
. Before
entering the chamber make sure that the power supply is off and then use a grounding
hook on the high voltage leads from the e-gun. Do not touch the high voltage leads
unless the power supply is turned off and the grounding hook is attached to the part to be
serviced. All grounding hooks are supplied with Thermionics brand power supplies.
C. E-gun systems must be clean. Use lint free gloves when handling vacuum components.
As the e-gun source is operated coating will build up in the vacuum system and in time
create particulates (“flaking of the coating”). A periodic cleaning procedure should be
employed to prevent shorting and/or contamination of the e-gun source. Aluminum foil is
a popular way of shielding the vacuum system from unwanted coating build up with an
inexpensive, disposable material.
D.
Operation of an e-gun source without proper water-cooling
WILL
result in failure of the
source. A water flow interlock switch should always be used to assure proper water flow.
THEORY OF OPERATION
An electron beam evaporation source uses a beam of focused electrons to vaporize
material in a high vacuum environment. The vaporized material then condenses on an
object (called a substrate) in the same high vacuum chamber to form a thin film of
material. The material, which is evaporated to create the film, can be anything that is solid
in the vacuum environment, such as gold, silicon dioxide, or some mixture of substances,
depending on the specific application. The vapor emitted from an e-gun source can be
roughly calculated using cosine distribution as a model. Small deviations do exist from
this model due to the e-guns magnetic field and the ability of many materials to become
ionized during the evaporation process.
To evaporate a material with an e-gun source, a load (or “charge”) of material is placed in
a water-cooled copper crucible inside a vacuum chamber. Then a substrate is placed
above the crucible to receive the vapor (normally 10 to 14 inches for a 3kW source). The
chamber is evacuated. A filament, held in a
cathode assembly is given a high negative
potential relative to the grounded crucible. The filament is heated to the point of
thermionic emission by an electric current. The liberated electrons are then accelerated
away from the filament by a grounded anode plate placed just outside of the cathode
assembly. The accelerated electrons are injected into a permanent magnetic field that
directs and focuses the electrons to the water-cooled crucible. The accelerated electrons
kinetic energy is transformed to thermal energy as they impact the evaporant material
placed in the crucible. Temperature in excess of 3500 degrees Celsius can be easily
achieved allowing the direct evaporation of virtually any material.
