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Aluminum Oxide Al2O3 Evaporation Process Notes

Aluminum oxide, or more commonly called alumina, is a chemical compound with a chemical formula of Al2O3. It is generally white or clear in appearance with a melting point of 2,072°C, a vapor pressure of 10-4 Torr at 1,550°C, and a density of 3.97 g/cc. It is most commonly found in nature as the mineral corundum, from which ruby and sapphire are derived. Aluminum oxide is used extensively as an abrasive and is utilized in various industrial applications. It can also be found in paint, cosmetics, and surgical implants. It is evaporated under vacuum to form dielectric films for the semiconductor industry and as a mirror-like protective layer for optical coatings.

Aluminum Oxide Al2O3 Specifications

Material TypeAluminum Oxide
Color/AppearanceWhite, Crystalline Solid
Melting Point (°C)2,072
Theoretical Density (g/cc)3.97
Max Power Density
(Watts/Square Inch)
Type of BondIndium, Elastomer
Z Ratio0.336
Thermal Evaporation Techniques Boat:  W
Basket:  W
E-Beam Crucible Liner MaterialFABMATE®, Tungsten
Temp. (°C) for Given Vap. Press. (Torr) 10-4:  1,550
CommentsSapphire excellent in E-beam; forms smooth, hard films.

* This is a recommendation based on our experience running these materials in KJLC guns. The ratings are based on unbonded targets and are material specific. Bonded targets should be run at lower powers to prevent bonding failures. Bonded targets should be run at 20 Watts/Square Inch or lower, depending on the material.


Empirical Determination of Z-Factor

Unfortunately, Z Factor and Shear Modulus are not readily available for many materials. In this case, the Z-Factor can also be determined empirically using the following method:

  • Deposit material until Crystal Life is near 50%, or near the end of life, whichever is sooner.
  • Place a new substrate adjacent to the used quartz sensor.
  • Set QCM Density to the calibrated value; Tooling to 100%
  • Zero thickness
  • Deposit approximately 1000 to 5000 A of material on the substrate.
  • Use a profilometer or interferometer to measure the actual substrate film thickness.
  • Adjust the Z Factor of the instrument until the correct thickness reading is shown.

Another alternative is to change crystals frequently and ignore the error. The graph below shows the % Error in Rate/Thickness from using the wrong Z Factor. For a crystal with 90% life, the error is negligible for even large errors in the programmed versus actual Z Factor.

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