Tantalum Ta Evaporation Process Notes
Tantalum is classified as a transition metal on the Periodic Table and is considered to be one of the refractory metals which are highly resistant to corrosion. Tantalum has a melting point of 3,017°C, a density of 16.6 g/cc, and a vapor pressure of 10-4 Torr at 2,590°C. It is metallic grey-blue in color with strikingly similar chemical properties to niobium. It is mainly used to make surgical implants due to its non-toxic nature. It is also used as a capacitor for electronics and may be alloyed with other metals to add strength and durability. Tantalum, along with its alloys and compounds, is evaporated under vacuum to make semiconductors, optical coatings, magnetic storage media, and wear and corrosion resistant coatings.
Tantalum Ta Specifications
|Color/Appearance||Gray Blue, Metallic|
|Thermal Conductivity||57 W/m.K|
|Melting Point (°C)||3,017|
|Coefficient of Thermal Expansion||6.3 x 10-6/K|
|Theoretical Density (g/cc)||16.6|
|Max Power Density|
|Type of Bond||Indium, Elastomer|
|E-Beam Crucible Liner Material||FABMATE®, Graphite|
|Temp. (°C) for Given Vap. Press. (Torr)||
|Comments||Forms good 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.