Choosing the Right Source for Your Thermal Evaporation Process

The right source for your thermal evaporation process will depend on many factors. We offer a wide selection of evaporation sources through our catalog and website, as well as custom fabrication to meet you specific need. Most sources are available in tungsten, tantalum and molybdenum, and many are available with an alumina coating applied to the top surface to minimize migration and corrosion of materials. Standard Product information and technical information and publications are available on our website.

The diagram below illustrates the typical layout of a thermal evaporation system within a vacuum chamber:

Factors to Consider When Choosing a Source

A) What is minimum & maximum length of source that will fit in to your mounting scheme?
B) What is the throw distance? (source to substrate)
C) What material will you be evaporating?
D) Which source material is compatible with your evaporant? (see our Source Reference Guide)
E) What temperature will you be reaching?
F) How much power do you have to heat the source (amperage)?
G) What capacity will you need to achieve your desired thickness?
H) Are you evaporating in an upward, downward or sideways direction?

These are some of the factors that will help determine the right thermal evaporation source for your needs. If after determining the answers to the above factors, please give us a call if you need further assistance. Below is a compilation of evaporation tips that you may find useful if you are attempting to evaporate any of the following materials for the first time.

Aluminum Evaporation

Aluminum is a very popular material for evaporation. We have many different sources that can be used to successfully evaporate aluminum. However, there are a few common problems that occur when evaporating this material. One problem that you may be aware of that aluminum wets to most surfaces and does not stay in the evaporation area, we call this migration. The other, more significant problem is that molten aluminum is very corrosive and will corrode through most surfaces and cause the boat or box to break during the evaporation process. Spitting is not normally a problem. Tungsten is the most resilient of the materials to this corrosiveness

For small amounts of aluminum you can use a filament, basket or rod sources. For larger amount you may want to consider a boat, box or crucible with crucible heater.

Also, consider our new “Cool Lip Crucibles” (see below) which do a great job of controlling the wetting of the aluminum and minimize any migration of the aluminum out of the crucible. We offer these in ½” and 1” diameters to fit most of our crucible heaters.

Gold Evaporation

Gold can be successfully evaporated by a variety of methods. Boats, Baskets, crucibles, and filaments are the most common types of sources used. However, gold, when molten, has 2 issues:

1) It is corrosive and will corrode through the boat eventually and
2) Gold will try to migrate to cooler areas of the boat (where it is mounted).

Our alumina coated boats are ideal to solve these problems. For example, with the S21-AO-W, the entire dimple area is coated with alumina.

This prevents the gold from wetting to the tungsten thus eliminating migration and corrosion. However this boat takes about 30% more power than an uncoated boat due to the alumina coating. On the other hand, our S42B-AO-W barrier style boat solves the migration issue by letting the gold wet to the dimple area, but the AO coating prevents the gold from leaving the dimple area. The .010” thick tungsten is thick enough to withstand the corrosiveness for a few runs.

We also offer high purity gold pellets, wire and sputtering targets in a variety of sizes and quantities.

Nickel Evaporation

Nickel has two characteristics that occur during thermal evaporation that can complicate the deposition process. These difficulties are 1) Ni is very corrosive when molten and will eat through (alloy with) most materials and 2) Ni is very aggressive and will migrate out of the evaporation area. The good news is that there are a few ways to manage these difficulties that can result in a successful and repeatable evaporation process. For small amounts of Ni evaporation, you can consider using a tungsten basket made from stranded tungsten wire. These baskets are inexpensive, easy to use and only require low power (20-30 amps). The downside of these baskets is that they will have a limited lifetime. Another good choice would be to use our “alumina coated tungsten baskets”. These operate at the same low power levels, have a longer lifetime and help to control the behavior of the Ni. These parts were designed for the evaporation of Ni. This would be our first recommendation.