In our semiconductor fab lab, we are depositing Cr-Pt-Au multi-metallic layers on Si (100) wafer using E-beam deposition instrument. We are using accelerating voltage 6 kV and required current values for Cr, Pt, Au are 10 mA, 130 mA and 280 mA respectively. The vacuum used is in the order of 10-7 mbar in the deposition chamber. Kindly explain why the power requirement for Au deposition is much higher than that of Pt which is much much higher than that of Cr. Is it a simple molten solid to vapor process that is being done by a high energy electron beam in e-beam metallization? But B.P. of Cr, Pt, Au are 2672, 3825 and 2700 degC respectively. Please explain and enlighten me on this aspect.
Hello Dr. Joy,
indeed, thermal properties like evaporation temperature and heat of sublimation hardly explain the differences for electrical current. Me seems the following explanation appropriate:
The metallic electrode (Au, Pt or Cr) is grounded. The energy of the electron beam is converted into heat with P = R*I2
with R as the metallic resistance.The power P necessary follows from the equilibrium of heat generation (P,R) and heat drain (determined by thermal conductivity). Thermal and electrical conductivity for gold are high what explains the high P for Au in comparision to Pt and Cr. The difference between Cr and Pt can only be explained if the differences in geometry of the electrodes (thickness, form) are taken into account.
Yours
R. Mitdank
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