Tantalum (Ta) Pellets Evaporation Materials

Tantalum (Ta) Pellets Overview

We sell these pellets and pieces by unit weight for evaporation use in deposition processes. These approximate materials prices are published to provide budgetary guidelines. Actual prices can vary and may be higher or lower, as determined by availability and market fluctuations. To speak to someone directly about current pricing, please click here .

Tantalum (Ta) General Information

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

**** Suggestion based on previous experience but could vary by process. Contact local KJLC Sales Manager for further information

Z-Factors

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.

Thermal Evaporation of Tantalum (Ta)

Tantalum is nearly impossible to deposit by thermal evaporation due to the high power required for the material to evaporate. E-beam evaporation or magnetron sputtering are the recommended methods for tantalum deposition.

E-beam Evaporation of Tantalum (Ta)

Tantalum is rated 'excellent' for e-beam evaporation. However, the process can be difficult and should be monitored very closely.

Due to its high melting point (3,017°C), tantalum requires high powers in order to achieve an effective deposition rate. Typically, tantalum does not melt well to form a solid slug for evaporation. In other words, if the starting material is in pellet form, there is a high risk that even at high powers (>5kW), the pellets will not melt together uniformly which will increase the likelihood of the e-beam burning through the pellets and hitting the crucible. This can be evidenced by a sudden and steep fall-off of the deposition rate. It is then possible for the e-beam to drill a hole through the crucible liner and into the e-gun hearth. For these reasons, the e-beam evaporation of tantalum should be closely monitored through welder's shade 9 glass. Great care should be taken during the entire evaporation cycle due to the high degree of difficulty and risk of equipment damage.

We recommend using a pre-machined slug (or starter source) instead of pellets. The two main benefits of using a starter source are ease of use and handling as well as superior packing density. We have also found that using a rod for high temperature materials like tantalum helps to reduce the amount of power required for deposition. We machine a rod such that the outer diameter of the rod is not in contact with the cooled walls of the crucible liner. This allows higher temperatures to be achieved at lower powers and eliminates the problem of partially melted pellets. Tantalum will still require high power for evaporation even when using a starter source or rod, but less so than when using pellets.

KJLC® can produce these starter sources. Contact us by clicking here with your e-gun manufacturer, pocket size, and number of pockets in order for us to produce a quote.

We also recommend using a FABMATE® or graphite crucible liner or running tantalum directly from the hearth of the e-gun. Because not using a crucible liner is not always an option, especially in shared systems, some customers will use a copper crucible liner and place the starter source in the copper crucible liner instead of placing directly in the hearth.

A key process note is to consider the fill volume of the crucible liner. We find that the melt level of a material in the crucible directly affects the success of the crucible liner. Overfilling the crucible will cause the material to spill over and create an electrical short between the liner and the hearth. The outcome is cracking in the crucible liner. This is the most common cause of crucible liner failure. Placing too little material in the liner or evaporating too much material before refilling can be detrimental to the process as well. When the melt level is below 30%, the e-beam is likely to strike the bottom or walls of the crucible which immediately results in breakage. Our recommendation is to fill the crucible between 2/3 and 3/4 full to prevent these difficulties.

Crucible liners should be stored in a cool, dry place and always handled with gloves or forceps.