Monday, July 30, 2012

AuPd Sputter Coater Calibration

In coating for SEM applications, the first choice is materials. AuPd is the ideal choice for imaging, because of the small AuPd grains. For spectroscopic applications, the high density of AuPd will attenuate X-rays--particularly low-energy X-rays. In such applications a flash coating of graphite is desirable.

AuPd coating is done according to recipe. The target thickness is 10-25 nm depending upon the topography of the samples. Thicker coatings are desirable for samples with more topographic contrast to guarantee a continuous film across topographical features. Since the sputter coater does not have a deposition rate monitor-- many of coaters for SEM sample preparation do not-- deposition under fixed conditions is used to guarantee target film thickness.

The following parameters are considered fixed in the recipes that follow:
  • Sample-Target Distance = 25 mm.
  • Ar Partial Pressure = 5x10-2 mbar.
The calibrated AuPd thickness is 0.015 nm/mA/s.

For practical applications, for a very smooth insulating sample with very little topgraphic relief, a thin AuPd layer of ~ 15 nm would be desirable.  Assuming a 30 mA emission current this would require a 33 s deposition time. For a sample with larger topographic relief a ~ 25 nm AuPd film thickness would be desirable. Again assuming a 30 mA emission current this would require a 55 s deposition time.

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