Thin Film Substrate
Question: What is the proper fill rate of a material in an e-beam crucible liner?
Answer: Our recommendation is to fill the crucible between ⅔ and ¾ full. 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. This is the most common cause of crucible liner failure. Placing too little material in the crucible 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.
Question: What crucible should I use to thermally evaporate titanium?
Answer: We recommend using a tall, intermetallic crucible for thermal evaporation. Thin films of titanium can be evaporated from intermetallic crucibles. However, film thickness may be limited to 500 angstroms, and the crucible may need to be replaced for each subsequent run. Intermetallic crucibles are composed of titanium boride (TiB2) and boron nitride (BN). This material combination works well because the material is both lubricious and electrically conductive. The crucible is both strong and conductive, yet its lubricious properties 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 be unsuccessful. The crucible may only last for one run due to differences in the coefficients of expansion between the alloy and the aluminum oxide crucible as the melt cools. Because the material rests at the bottom of the crucible and, typically, the crucible’s bottom is cooler than its sides, the heater and crucible must be heated to a much higher temperature to achieve evaporation. A power supply may not be capable of getting the heater hot enough. Also, at 1,500°C, the vapor pressure of the aluminum oxide and, possibly even the tungsten, may cause film contamination.
Question: Why is my tungsten boat breaking during thermal evaporation of nickel/iron (81/19 WT%) alloys?
Answer: Both nickel and iron react with refractory metals when in liquid form, thus evaporating out of a tungsten boat is nearly impossible. Even when using a thin width, thick gauge tungsten boat such as our EVS20A015W, the alloy will vigorously attack the boat, causing it to crack and break. Therefore, the boat may not even last one run. Also, a tungsten boat may not work because there is risk that the materials may alloy with the tungsten, changing the mechanical and electrical properties of the boat.
Question: Should I use chrome plated tungsten rods or evaporate from a boat?
Answer: There are two main recommendations for thermally evaporating chromium. The first option is to use chrome plated tungsten rods. These electroplated rods are ideal for depositing very thin adhesion layers. Because the chromium is plated directly on the tungsten rod, heat transfer is by conduction. Sublimation occurs easily and quickly, compared with evaporating from a boat, and affords a potentially much lower thermal load on the chamber. The main disadvantages of these rods are the limited amount of chromium available from each rod and the fact that they are one-time use sources.The second option is to evaporate the material from a refractory boat. We have reported success in the past using a thin width, thick gauge, high current tungsten boat. There is no interaction between the sublimating chromium and tungsten boat. The rates are fairly easy to control at 1-5 Angstoms/sec. It is important to note that while the power supply is capable of 1,200W, a lower power was used during sublimation. Using a boat will allow for more material to be loaded per run.
Question: What type of crucible liner material should I use to e-beam evaporate tungsten?
Answer: Our recommended approach to e-beam evaporate tungsten is to use a rod in a Fabmate® crucible liner. Tungsten can also be evaporated directly from the copper hearth of the e-gun. Because of this, some customers prefer to use a pre-machined slug (or starter source) that is directly placed in the hearth pocket. The two main benefits of using a starter source are ease of use and handling as well as superior packing density.
Question: What is the best approach to deposit samarium (Sm) thin films?
Answer: 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). Higher temperatures will increase the deposition rate. DC sputtering is also an option.Samarium does oxidize so both the pellets/target and the deposited films should be protected from oxidation as much as possible by handling and storing it under inert gas like Ar. We ship the material in a mineral oil to protect the material from oxidation and that must be cleaned off prior to use. It is strongly advised to consult the MSDS prior to working with samarium. 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 evaporates around 575 deg C (where its vapor pressure is 104 Torr). Higher temperatures will increase the deposition rate. DC sputtering is also an option.