The rates are fairly easy to control at 1-5 Angstroms/sec. There is no interaction between the sublimating chromium and the tungsten boat. Using this boat, we sublimated chromium pieces with a standard 3.3V 375A KJLC ® power supply. We have reported success in the past using a thin width, thick gauge, high current tungsten boat such as our EVS20A015W. The second option is to evaporate the material from a refractory boat. 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. Sublimation occurs easily and quickly, compared with evaporating from a boat, and affords a potentially much lower thermal load on the chamber. Because the chromium is plated directly on the tungsten rod, heat transfer is by conduction. These electroplated rods are ideal for depositing very thin adhesion layers. The first option is to use chrome plated tungsten rods. There are two main recommendations for thermally evaporating chromium. Two, the heat transfer mechanism of solid chromium pieces is almost entirely by thermal radiation which means the heater must be much higher than 1,400☌. One, heating anything to 1,400☌ might generate an unacceptably high thermal load in the chamber. Since its melting point is higher (1,857☌), it will sublime from a solid phase. According to chromium's vapor pressure curve, the necessary temperature for this to occur is 1,400☌. This provides for good deposition rates in systems with "normal" source-to-substrate geometries. In order to perform thermal evaporation, a material's temperature must be raised to the point where its equilibrium vapor pressure is 1E -2 Torr. Chromium can be problematic to thermally evaporate because it will sublime under high temperatures.
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