BSE Gradients at low mag

[Probeman]

We had been having a problem with BSE imaging especially at low mag where we would see a nasty "gradient" across the image as seen here:



Recently Edgar Chavez and our in house engineer Steve Wiemholt performed an adjustment of the BSE diodes and much improved this gradient issue as seen here:



So much improved but now a slight gradient from upper left to lower right. Steve wrote the following description of the process:

Hi John,
To solve the low magnification backscatter electron image brightness gradient problem the engineer from Cameca performed a DC voltage offset adjustment procedure. He actually followed a moderately lengthy procedure he had on file on his laptop.  It seems that an DC offset adjustment is done for all BSE detector channels, then another AC/DC potentiometer adjustment is done. This is followed by yet another pass at the DC offset adjustment. In our case, the brightness gradient was reduced somewhat, but the remaining gradient is now rotated.

Instead of a pure left to right, darker to brighter offset, we now have a NW to SE, brighter to darker gradient. So if we want this residual offset eliminated, the Cameca engineer can simply do another run through the procedure, with the residual gradient in mind, and restore the image to near zero brightness gradient.

Regards,
Steve

Just wanted to let others know that this issue can be fixed with help from Cameca.