blanking leakage - question

[James Conway]

Raith Users and Ofer Levi:

Let me make this very clear for everyone...  if you survived my Basic 
Users class you should all know this by memory:

Area Dose = Beam I * Dwell Time / Area Step **2

If you dwell upon an write field area for enough time to reach the dose 
to clear you will clear the exposed area.
This is true for when you intend to expose a pattern as well as for any 
emission coming through the column when you do not wish to expose a 
pattern. read: leakage of electrons from the column normally due to 
scattering events.
Again if the Blanker leakage emission when blanked multiplied by the 
dwell time you exposed a write field area for reaches the dose to clear 
you will have a cleared feature visible in your field when working in 
positive tone PMMA.

This could be a cleared area over or adjacent to your pattern normally 
coming from the upper right hand side of the write field.  The amount of 
typical leakage of the Raith ebeam Blanker is on the order of 0.0005 
nA.  This is typical for all electrostatic columns.  Recently the 
emission when blanked has been measured to be 0.0007 nA on the 30 um 
aperture and 0.0017 - 0.0023 nA on the 20 um aperture.  You can make 
this measurement yourself by moving to the faraday cup (FC) zooming to 
greater than 500 X magnification in order to confine the beam into the 
FC, then measuring your Beam Current with the blankers blanked and 
unblanked.

FOR ALL USERS working within a single write field for a long period of 
time, such as in Ofer's photonic crystal and others peoples waveguides 
and photonic devices AND whenever you idle the system over your sample 
for long enough dwell time to reach, or approach, the dose to clear you 
will obtain an exposure artifact of the blankers leakage emission 
profile, hence the 'trilliums' 'teardrops' and 'star' features users 
have been reporting.  The faster your resist in sensitivity the more 
apparent this problems will become.  It is plainly apparent under any 
optical microscope at any magnification over 10X.

Finally the problem will become even more acute when you do RIE etching 
pattern transfer on the sample with this feature.  As that it is thinner 
than the surrounding resist this are will clear first resulting a 
multiple stepped etched feature.

The only way I will be able to resolve this issue is to replace the 
FE-Gun tip and the aperture plate.  From their we can continue 
troubleshooting the RAITH  and LEO blanker assemblies and electronics if 
this problem still presents itself.
This is what RAITH USA has recommended and I have held them up this last 
month from performing this needed service to get your work completed on 
the system during our normally busy part of the term.

Your comments are invited.  Thread:  Blanking Leakage.

Thank you,

JWC





Ofer Levi wrote:

> Dear James,
> Please advise what do you mean.
> I write my whole patterns of 50x50 micron photonic crystal within one 
> write field and it takes ~ 21 minutes per structure. then I move 200 
> micron away and do it again. I use the 10 micron aperture.
> Please advise as I will not like to loose my samples due to these issues.
> Thanks,
> Ofer
>
>
> At 07:33 PM 11/16/2004, you wrote:
>
>> RAITH Blanker leakage issues continue. See report below or click 
>> here. 
>> <http://snf.stanford.edu/cgi-bin/ezmlm-cgi?2170:mss:257:200411:kbgfgjllpapbjgijnohi>
>>
>> Not so good for those people writing within one writefield for a long 
>> period of time.
>>
>> Time for the FE-gun replacement.
>>
>> more in the afternoon tomorrow!
>>
>> JWC
>>
>>
>> -------- Original Message --------
>> Subject: Problem raith SNF 2004-11-16 19:23:45: 20 um aperture 
>> blanking leakage has increased
>> Date: Tue., 16 Nov. 2004 19:23:45 -0800
>> From: jwc at snf.stanford.edu <mailto:jwc at snf.stanford.edu>
>> To: raith-pcs at snf.stanford.edu <mailto:raith-pcs at snf.stanford.edu>
>>
>>
>>
>>Greetings:
>>While on the 20 um aperture I observed that the RAITH blanker leakage has increased from 0.0005 nA to a average value of 0.0017 nA and is now out of RAITH specifications.
>>Emission and Secondary Electron features observed on stage moves when RAITH is blanked.  LEO blanker is fine and no problems.
>>JWC 11612004:1926 hours
>>    
>>
> ______________________________________________
>
> Ofer Levi,      Ph.D.
> Department of Electrical Engineering, Stanford University
> CIS-X Rm 310,  Stanford, CA 94305-4075
>
> Phone:                             (650)723-0464 or 725-6907
> Fax:                                              (650)723-4659
> Adm. Asst.: Gail Chun-Creech                  Ph:  (650)723-0983
> E-Mail:                          levi at snow.stanford.edu
> Web page:               http://snow.stanford.edu/~levi/
> <http://snow.stanford.edu/%7Elevi/>______________________________________________
>
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