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Copper Cu Notes


Copper (Cu) General Information

Copper is one of the most highly utilized elements in the world with evidence of its usage found during ancient times. It is reddish-orange in color with a melting point of 1,083°C, a density of 8.92 g/cc, and a vapor pressure of 10-4 Torr at 1,017°C. Two of the most popular alloys in the world, brass and bronze, contain copper. It is known to be an excellent conductor of heat and electricity and can be found in wire, coins, and electromagnets. The vacuum industry relies heavily on copper material for backing plates which are bonded to sputtering targets. Copper, along with its alloys and compounds, are evaporated under vacuum to form layers in the manufacture of semiconductors, sensors, and circuit devices.

Copper Cu Specifications

Material TypeCopper
SymbolCu
Atomic Weight63.546
Atomic Number29
Color/AppearanceCopper, Metallic
Thermal Conductivity400 W/m.K
Melting Point (°C)1,083
Coefficient of Thermal Expansion16.5 x 10-6/K
Theoretical Density (g/cc)8.92
SputterDC
Max Power Density
(Watts/Square Inch)
200*
Type of BondIndium, Elastomer
Z Ratio0.437
E-BeamExcellent
Thermal Evaporation Techniques Boat:  Mo, W
Coil:  W
Basket:  W
Crucible:  Al2O3, Mo, Ta
E-Beam Crucible Liner MaterialGraphite, Molybdenum
Temp. (°C) for Given Vap. Press. (Torr) 10-8:  727
10-6:  857
10-4:  1,017
CommentsAdhesion poor. Use interlayer (Cr). Evaporates using any source material.

* This is a recommendation based on our experience running these materials in KJLC guns. The ratings are based on unbonded targets and are material specific. Bonded targets should be run at lower powers to prevent bonding failures. Bonded targets should be run at 20 Watts/Square Inch or lower, depending on the material.

Z-Factors

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.