Gasonics for Descum -I would not

Ed Myers edmyers at
Mon Sep 14 08:01:00 PDT 2009


During my time doing training on the Gasonics  I would discourage 
anyone from using the tool for descum.  The tool is designed for 
massive photoresist removal and is not optimized for soft processes 
such as descum.   As Raja found, the uniformity of the resist removal 
is very poor.  The resist removal rate is very dependent on wafer 
temperature.  The purpose of step 0, is to increase the wafer 
temperature significantly high 300C or greater to get a rapid 
initiation of the carburization of the photoresist.  The process is 
exothermic, so we lower the lamps to assist in the continuation of 
the process once it has been initiated.  If you do not heat the 
wafer, then the carburization process is even more difficult to 
control.  Putting all this together you can see this is a very 
difficult tool to control a process such as descum.  One other 
critical point to note, is the resist removal is very isotropic.  In 
RIE systems the ion energy makes the descum process much more anisotropic.

I know there has been desire in the past to use the Gasonics for 
descum (or even the matrix).  From what I've learned about the 
Gasonics, I believe you will get a very poor descum process and I 
don't recommend it.


At 05:04 PM 9/13/2009, Raja Jain wrote:
>Fellow drytek2 users,
>For those of you customarily using drytek2 for descum, gasonics may be a
>reasonable backup based on the tests below (3um 220-3 on bare Si).  (Thanks
>to Jim McVittie for the recipe suggestions)
>Test #1: Gasonics 0A
>Resist removed from wafer center: 150A
>Test #2: Gasonics 0D
>Resist removed from wafer center: 4084A (likely due to strong heating
>Resist thicknesses were measured using the litho nanspec.
>-----Original Message-----
>From: John Shott [mailto:shott at]
>Sent: Friday, September 11, 2009 11:59 PM
>To: drytek2 at
>Subject: Tentative clear of shutdown ... but use with extreme caution!!!
>SNF Lab Members:
>I have just cleared the shutdown on drytek2 .... but want to make sure
>that you all read this very carefully before proceeding with any
>critical etching.
>As you know, this machine has been experiencing pump down and vacuum
>readout problems.  We have now replaced the main vacuum pump as well as
>the Capacitance Manometer with a brand new 1 Torr head. The other
>dryteks (1 and 4) use a 10 Torr head.
>This difference is why I am asking you to proceed with caution in any
>etching that you do with drytek2 this weekend.  While I believe that we
>are reading and controlling to a proper pressure .... that is, when it
>reads 150.0 it is actually 150 mTorr, there is a chance that that is not
>Why the confusion?  The 10 Torr heads on dryteks 1 and 4 produce a 0-10
>V output signal when the chamber pressure varies from 0 - 10 Torr ... so
>that a 150 mTorr vacuum should produce 0.150 V.  The 1 Torr head on
>drytek2, however, produces 0 - 10 V output as the pressure varies from
>0-1 torr that 150 mTorr vacuum produces 1.50 V.  I believe that I
>have properly set the pressure controller on drytek2 to accommodate this
>10X more sensitive capacitance monitor.
>In any event, I THINK that everything is set up properly .... but we
>have not had time to yet run test wafers or make corroborating pressure
>measurements.  As a result, if you have a critical etch for drytek2, I
>strongly suggest that you wait until Elmer and Nancy can perform
>additional machine tests and run test wafers, respectively, to make sure
>that I am not in error.  If, on the other hand, you have a non-critical
>usage, such as a descum, you may be willing to run some wafers this
>weekend,  I'd still recommend running test wafers just to be sure ....
>but I know that there may be some pent up demand for this tool, so I
>wanted to clear the shutdown so that you could use it .... but also warn
>you that while I believe we are controlling pressure correctly, that we
>may still have a pressure readout problem.
>Thanks for your continued support,

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