I had been searching for about 5.5hrs for the holes....
god d*** you, it is actually an easy task...however, luck was not by my side....may be I never been good for long time.... (must donate more for those earthquake victims)
4 holes of 0.02mm...on a single tiny+soft metal plate, what we called it objective aperture plate.
It was hold by an assembly which is installed inside the column of high vacuum.
Using very manual way, we gonna search for the center by determine the light at the leftmost and rightmost. then go to the center. Once settle for the X, we gonna adjust the Y to search for the coordinate of the hole.
Thanks god I was not giving after so many hours of trying! finally found it! the beam was shining brightly! A little bit more of patience (actually a lot, we put the new obj aperture, taken out; replaced the original one, taken out; putting in another new one.....in between need pump down chamber about 25min's time) At least, bo sia sui lahh..... smile :)
(I am talking about changing objective aperture plate for CDSEM, my job)