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Indium In Evaporation Process Notes

Indium (In) General Information

Indium is a post-transition metal with properties similar to gallium. It is soft and metallic-gray in color. It has a density of 7.3 g/cc, a melting point of 157°C, and a vapor pressure of 10-4 Torr at 742°C. One of its notable characteristics is its ability to cling to glass and other similar surfaces. Indium compounds are evaporated under vacuum to form thin films in the production of electronics and photovoltaic cells. Pure indium is utilized as a film layer in semiconductors.

Indium In Specifications

Material TypeIndium
Atomic Weight114.818
Atomic Number49
Color/AppearanceSilvery Lustrous Gray, Metallic
Thermal Conductivity82 W/m.K
Melting Point (°C)157
Coefficient of Thermal Expansion32.1 x 10-6/K
Theoretical Density (g/cc)7.3
Type of BondElastomer
Z Ratio0.841
Thermal Evaporation Techniques Boat:  W, Mo
Basket:  W
Crucible:  Gr, Al2O3
E-Beam Crucible Liner MaterialFABMATE®, Graphite, Molybdenum
Temp. (°C) for Given Vap. Press. (Torr) 10-8:  487
10-6:  597
10-4:  742
CommentsWets W and Cu. Use Mo liner. Low Melting Point materials not ideal for sputtering.


Empirical Determination of Z-Factor

Unfortunately, Z Factor and Shear Modulus are not readily available for many materials. In this case, the Z-Factor can also be determined empirically using the following method:

  • Deposit material until Crystal Life is near 50%, or near the end of life, whichever is sooner.
  • Place a new substrate adjacent to the used quartz sensor.
  • Set QCM Density to the calibrated value; Tooling to 100%
  • Zero thickness
  • Deposit approximately 1000 to 5000 A of material on the substrate.
  • Use a profilometer or interferometer to measure the actual substrate film thickness.
  • Adjust the Z Factor of the instrument until the correct thickness reading is shown.

Another alternative is to change crystals frequently and ignore the error. The graph below shows the % Error in Rate/Thickness from using the wrong Z Factor. For a crystal with 90% life, the error is negligible for even large errors in the programmed versus actual Z Factor.

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