INFICON STM-100/MF Thin Film Deposition Monitor - Manual (Page 73)

SYMPTOM CAUSE REMEDY
5. Thermal instability
(large changes in
thickness reading
during source
warm-up)
a. Poor crystal seating
Clean sensor
b. Poor or no water flow
Correct flow
c. Excessive heating due to secondary
electron formation in some
sputtering systems
Increase water flow
to sensor.
6. Poor thickness
reproducibility
a. Poor source emission pattern
Check source
move sensor
b. Material adhesion to sensor poor
New crystal
7. Computer interface
failure
a. Baud rate wrong
Correct cfgr
b. Format wrong
Correct cfgr
c. Device address bad
Correct cfgr
d. Cable connection
Check wiring
REPLACING A SENSOR CRYSTAL
The procedure for replacing the 6 MHz sensor crystal is the same for any
type sensor head. Use caution in handling the crystals as they are very
fragile. Chipped, cracked, dirty or stained crystals should not be used.
CAUTION Crystals should never be handled by bare hands! Always
use clean lab gloves and plastic tweezers to handle a
crystal. This will avoid surface contamination of the crystal
that might lead to poor electrical surface contact and
possible poor film adhesion.
Dielectric films sometimes do not adhere strongly to the crystal surface
and can cause erratic readings. Some dielectric will peel off the crystal when it
is exposed to air. This is caused by gas absorption greatly changing the film
stress characteristics. If peeling is observed, change to a new clean crystal.
Follow the procedures outlined below to change a sensor crystal.
1. Grip the sensor cap with a gloved hand and pull to unsnap the cap. The
sensor crystal is captured in the cap. Place the sensor cap on a flat
surface with the front face up and pop the crystal out by pressing gently
down on the coated crystal surface with clean plastic tweezers or a
similar type instrument. The crystal should come out easily. Take care not
to damage the cap aperture opening to the crystal. Turn the cap over and
place a new crystal with the fully coated surface towards the aperture
opening (this side receives the evaporant stream) in the sensor cap. Use
plastic tweezers to handle the new crystal.
2. Gently press the crystal into the finger spring holders using the plastic
tweezers. This operation does not require much force. The crystal
movement to become held by the finger springs is only about 25
thousandths of an inch. The sensor cap now holds the sensor crystal
firmly in place. The cap may now be snapped into the sensor body.
SECTION 6.2
MAINTENANCE Page 6 - 2