High Purity Materials
Thin Film Substrates
Question: What is the proper fill rate of a material in an e-beam crucible liner?
Answer: Our recommendation of the crucible filling is between ⅔ and ¾ full. The melt level of a material in the crucible directly affects the success of the crucible liner. When the crucible is overfilling, the material will spill over and create an electrical short between the liner and the hearth, and caused crucible to crack. This is the most common reason to cause of crucible liner failure. If placing too little material in the crucible or evaporating too much material before refilling will be not good to the process as well. When the melt level of the crucible is below 30%, the e-beam has the risk to strike the bottom or walls of the crucible which immediately results the crucible breakage.
Question: What kind of crucibles should I use to thermally evaporate titanium?
Answer: Our recommendation is using a tall intermetallic crucible for titanium thermal evaporation, because the thin films of titanium can be evaporated from intermetallic crucibles. However, the film thickness may be limited to 500 angstroms, and the crucible may need to be replaced for each subsequent run. The Intermetallic crucibles are composed of titanium boride (TiB2) and boron nitride (BN). This material has good lubricious and electrically conductive characteristics, and the crucibles help prevent material spill-over and crucible cracking.
Question: What type of crucible should I use to thermally evaporate nickel/iron (81/19 wt%) alloys?
Answer: Nickel/iron alloys can be evaporated out of an aluminum oxide crucible. However, this method may not be the best choice. The crucible may only last for one run as the differences in the coefficients of expansion between the alloy and the aluminum oxide crucible when the melt cools. The material is at the bottom of the crucible, and the crucible’s bottom is cooler than its sides. Thus, the heater and crucible need to be heated to a much higher temperature to achieve evaporation. The heater may not able to get enough heat by a power supply. At 1,500°C, The vapor pressure of the aluminum oxide and possibly even the tungsten, may cause film contamination.
Question: Why is the tungsten boat breaking during thermal evaporation of nickel/iron (81/19 WT%) alloys?
Answer: Both nickel and iron can react with refractory metals when in liquid form, thus it is nearly impossible to evaporate out of a tungsten boat. Even when using a thin width and thick gauge tungsten boat, the nickel/iron alloy will vigorously attack the boat, and causing it to crack and break. Therefore, the boat may not even last one run. For another, a tungsten boat may not suitable for nickel/iron alloy evaporate because the materials may have the risk of alloying with the tungsten, changing the mechanical and electrical properties of the boat.
Answer: The Fabmate crucible liner is our recommended to e-beam evaporate tungsten is to use a rod in the crucible. Besides, tungsten can also be evaporated directly from the copper hearth of the e-gun. Some customers prefer to use a pre-machined slug which can directly place in the hearth pocket. Ease of use and handling excellent packing density are two main benefits of using a starter source.
Question: What is the best method to deposit samarium (Sm) thin films?
Answer: We recommend the samarium can be evaporated from a tantalum boat or an Al2O3 crucible with either a shielded tantalum box heater or a tungsten wire basket heater. Samarium begins to evaporate around 575 C (where its vapor pressure is 104 Torr). The deposition rate will be increased with higher temperatures, and DC sputtering is also an option. The pellets/target of Samarium will oxidize, and the deposited films should be protected from oxidation as much as possible by handling and storing it under inert gas like Ar. The material will be shipped in a mineral oil to protect the material from oxidation and that must be cleaned off before using. It is strongly advised to consult the MSDS prior to working with samarium.