Subject: report on service visit
From: Michael Kahl <michael_kahl@gmx.de>
Date: Wed, 2 Jul 2003 03:07:42 +0200 (MEST)
Wed, 2 Jul 2003 03:07:42 +0200 (MEST)
Hello Raith users at Stanford,

as James is not in his office at the moment, I would like to send you
directly a brief update on the status of the Raith 150 after the Raith service
visit.

1.) Problems that have been fixed:

1.a) The laser stage has been exchanged. Stitching tests resulted now in 30
nm stitching accuracy (mean = 3 sigma), and a write field rotation depending 
on the stage position was no longer observed. Thus, this kind of effect will
no longer cause any stitching errors.

1.b) We found that the gun had not been adjusted properly. The former setup
caused both a too low, unstable beam current, and high beam position drift.
Actually, this position drift might have caused some of the stitching errors
that were reported. Anyway, the gun recovered with new settings during the
last week and is stable now (beam current drift < 0.5% per hour, beam position
drift < 90 nm per hour). 

1.c) Some users reported that it is not possible to burn a contamination dot
 at high magnifcation. We found that an error on the electron optics board
caused this problem, and thus this board has been exchanged as well to fix the
problem.

2.) Outstanding points:
2.a) We found a new problem which could be described as sudden jumps in the
x-direction during SEM imaging (see attached image). We suspect a thermal or
contact problem in the column or on related boards as cause for this, because
this problem appears suddently and then disappears for most of the time.
This is probably also the reason why it has not been reported before. Anyway, we
could not yet solve it because we were not prepared for this. We will do
this as soon as possible, though. In the meantime, please use the system as
usual, as the scanning will be normal most of the time. However, in case you see
jumps as in the attached image, you should stop your work and wait until this
effect disappears, because it will also result in bad placement accuracy in
exposed patterns. Moreover, please report this error to James whenever it
comes up, so that I can track it together with him. Nevertheless, I hope that it
will not effect much of the work to be done, because the problem occured
only twice during the last 2 weeks (one time for 5 hours, the other time for
less than 1 hour).

2.b) The piezo elements for levelling are still missing, because we could
not get them in time. Therefore, the sample holder is put on Ti posts at the
moment. One disadvantage of this is that the sample holder is not well levelled
in the y-direction of the stage (3 mum change of working distance per 1 mm
travel in y-direction). Please take of this during your exposures. Focus
either close to the y position where the pattern is placed, or use the focus
control in the AdjustUV window. I expect that the piezos will be installed within
the next 6 weeks, and then this will be no longer an issue. 

Much success with your work!

Best regards,

Michael Kahl

Application scientist
Raith GmbH   

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