Monday, July 30, 2012

AuPd Coating Procedure Part 1: Setting Sample Height

As discussed in the AuPd Sputter Coater Calibration entry, the calibrated deposition rate of 0.015 nm/mA/s is dependent upon a fixed 25 mm target to sample distance.  In practice we don't measure to the actual target face which is reset somewhat inside the sputtering attachment.  It is much easier to just measure the distance between the sample surface and the top of the sputter chamber.  An easy way to do this is to place a straight edge across the top of the chamber and to measure the distance from the straight-edge to a representative SEM sample stub. Take great care in not bending the straight edge. Note that if one sets the distance between the sample platform and the top of the chamber to 25mm, the actual sample surface when stubs are placed inside will be roughly 10mm closer than intended.

If the stage height is not correct, remove the glass sputter chamber and put it in a safe place.  Note: with practice one will be able to do the sample platform height adjustment with the chamber in place.

Remove the sample platform as indicated by the green arrow.  The slot indicated by the red arrow can be used to screw the stage up and down with a flat standard screwdriver.  Replace the sample platform, replace the glass sputter chamber, and recheck the stage height as above.  This is a good point to inspect the O-ring sealing surfaces.  The blue arrow indicates particles on the O-ring surfaces that can prevent a good vacuum seal.  The bottom edge of the sputter chamber should also be checked for debris.  If vacuum grease is needed-- use sparingly.  More vacuum grease is not better!

When the sample stage is at the right height and the O-ring and glass chamber sealing surfaces are clean, replace the bell jar and install the samples.  Cluster samples around center of sample platform.

The last picture shows the working surface of the sputter head.  Blue arrows show particles on the O-ring surface which could cause a vacuum leak. Sputtered material often collects and flakes off the shutter shown by the red arrow.  As shown, the shutter is in the open position and the target is visible.  Flaking debris should be removed or it may migrate onto O-rings and cause a vacuum leak, or it may migrate into the target area and cause the target to short.  The green arrow indicates the high voltage electrode used to strike the Ar+ plasma.  It is spring loaded and can easily be removed.  Dusting around the target is very good to prevent the target from shorting to the electrode.

In summary:
  • Set sample platform height to 25 mm.
  • Make sure bottom O-ring surface and corresponding sealing surface of the glass chamber are clean.
  • Install samples, clustering them around the center of the sample platform.
  • Dust away any particles adhering to the sputter target shutter.
  • Remove the sputter electrode and dust around the target.
  • Replace the sputter electrode.
  • Make sure the top O-ring surface and corresponding sealing surface of the glass chamber are clean.
  • Close the sputter head on the chamber.
  • Continue to: AuPd Coating Procedure Part 2: Pumping.

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