Friday, April 25, 2014

Ion Gun Raster Calibration

The sputtering yield is a function of current density, so rastering only the area required for one's application is desirable to optimize sputtering yield. This is particularly important when depth profiling to minimize the time required to do a depth profile.

To calibrate the rastering area, a thin layer of Au was sputtered onto a 304 stainless steel sample puck. Zalar rotation was turned on to produce a circular sputtering pattern since the sputtered area is actually a rectangle, the diagonal of which determines the diameter of the sputtered circle (presuming the gun is centered on the center of the puck). When the Au layer is sputtered through, a change in color is evident.

In this image the X & Y rastering was set to 15 mm and a sputtered circle of approximately 12 mm in diameter was produced. This experiment was repeated for 10 mm and 20 mm rastering sizes.

Fitting the estimated diameters vs the rastering size, the sputtered disk is approximately 85% of the set rastering size. Inverting the problem, one should set the rastering size to approximately 1.2X the the diameter of the sputtering region desired.

This was performed at 3 keV ion beam energy, but should apply to all energies. It was also performed at a stage height of 15.