Fil-Tech, Inc.
How to Improve Crystal Performance
- Keep
the crystal surface clean. Avoid any physical contact with the center of the
crystal during handling and blow off any particulates using dry and filtered air or dry
nitrogen. Keeping the crystal surface clean lowers resistance and improves film
adhesion.
- Maintain
good electrical contact with the crystal. Keep cables in good condition and
snug to the sensor and feedthrough. Periodically inspect the finger spring contacts in
the sensor head and adjust or replace when necessary.
- Keep
the sensor head cap clean. Material buildup around the opening can cause
mechanical coupling and damping if it contacts the crystal.
- Maintain
the crystal sensor water temperature at a minimum of 25
°C. When using
a
ciruculating chiller with heating capability, run the sensor at 50
°C for high stress
coatings. The higher temperature reduces stress as the coating deposits and also
improves film/crystal adhesion.
- Use
Alloy or Longer Life Gold coated crystals in place of Gold for high stress material
depositions. Alloy and Longer Life Gold electrodes yield, dissipating film stress before
it reaches the crystal surface.
- Shield
the crystal from direct exposure to radiant heat sources or glow.
- Minimize
source “spitting” during evaporation. Large pieces of evaporant (“splatters”)
dramatically increase the resistance of the crystal and lead to erratic rate function or
early failure. Prevent crystal failure caused by material ejection during deposition with
proper source rate control, proper distance from the crystal to the source, and proper
type of source (e.g. Drumheller type for Silicon Monoxide).
- The SEM images
below show evaporatant splatter (images 1 and 2) and a fingerprint
(image 3) on the surface of a crystal. Evaporant splatter and fingerprints can result in
erratic (positive and/or negative) rate changes and even crystal failure.
The second SEM image below is magnified 2,000x, and shows the above
evaporatant splatter on
the surface of the crystal:
The image below shows a fingerpint on the surface of a crystal:
800-743-1743 www.filtech.com
617-742-0686
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