Subject: Re: non-omogeneous PMMA?
From: James Conway <jwc@snf.stanford.edu>
Date: Wed, 16 Feb 2005 09:41:45 -0800
Wed, 16 Feb 2005 09:41:45 -0800
Gigi and Paul,

I looked into this with reference to the expired batch.   I track all 
lots of resist placed into the Cleanroom and here is from my inventory 
notes. This bottle was Bottle #4 of 4 250 ml bottles and was decanted on 
11-18-2003 from the stock bottle of LOT # 0304, manufactured on August 
2003. It was placed into the cleanroom solvent cabinet on 04-02-2004 I 
noted that this bottle was lost and listed as ' missing' from the 
Cleanroom on July 28, 2004. 

Note:  Thus far no other unusual reports of problems with the 2% 950K 
PMMA material. but few users note the bottle or lot numbers in their 
work. Since only a small amount of material remains in the bottle I am 
going to dispose of this material as waste

I then decanted the next batch of PMMA from the stock bottle on 
07-29-2004 from stock lot # 04030170 and placed bottle 1B into the lab 
on the same day. There remains some of this material in the lab and it 
appears to be fine.

Please go ahead and strip and repeat using material from bottle 1B -- or 
better yet move onto the new 2% 950K MW PMMA in Anisole. (coded in the 
bottles in the cleanroom as 2% 950K MW PMMA-A.

I have attached spin speed (f) Thickness curves from my data from last 
week.  For 100 nm thickness on silicon I found 1550 and 1580 RPM to be 
best. This data will be promptly posted on our process suite later this 
week. I am performing final dose determinations and contrast curves 
combined with users training sessions this week.


On the features you showed in your images.
I do not see the normal severe reticulation that I would expect to 
observe if the polymer had hydrolyzed due to contamination or exposure 
to water vapor. But I have seen similar results long before that were 
due to sample surface charging, typically the effect results in non 
uniformity of dot shots within a write field.  What I am not seeing in 
your images is if the sample is charging  is misplacement of shot dot 
position. In your images pitch and placement seem perfect.  My 
suggestion would be to strip and repeat again with the current bottle of 
PMMA material (1B).  I can provide you with a chip of my reference 
material as well with a measured thickness of 93 nm. Also be sure to 
ensure your sample clipped to the std. sample holder is properly 
grounded. I generally clip a sample down and give it a 1 -2 mm nudge to 
ensure the clip scrapes through the resist and to the substrate.  Was 
this one of the samples that have AL2O3 or GaN as a upper layer in your 
structure?

We will keep a close eye out and see if we have other similar reports.

James Conway


Luigi Scaccabarozzi wrote:

>Hi all,
>I wanted to report some bad patterns I wrote last week on PMMA 2%
>(microchem in chlorobenzene). I add that I used my standard recipe, dose,
>and even some pattern I have written already many times without problems.
>Most of my patterns appear deformed or heavily underexposed. The weird
>thing is that, in some of them, some areas are ok (I put a picture of a good area).
>It seems like that the PMMA was very non-omogeneous...
>I'd like to know if someone else had the same problem with this bottle of
>PMMA. In that case it's probably just the PMMA too old or contaminated and
>I will simply try again.
>Thanks to all
>Gigi
>Note: During the alignment I noticed that the PMMA was charging a bit more
>than usual, but I could do the Align Writefield without problems.
>
>  
>


Gigi and Paul,

I looked into this with reference to the expired batch.   I track all lots of resist placed into the Cleanroom and here is from my inventory notes. This bottle was Bottle #4 of 4 250 ml bottles and was decanted on 11-18-2003 from the stock bottle of LOT # 0304, manufactured on August 2003. It was placed into the cleanroom solvent cabinet on 04-02-2004 I noted that this bottle was lost and listed as ' missing' from the Cleanroom on July 28, 2004. 

Note:  Thus far no other unusual reports of problems with the 2% 950K PMMA material. but few users note the bottle or lot numbers in their work. Since only a small amount of material remains in the bottle I am going to dispose of this material as waste

I then decanted the next batch of PMMA from the stock bottle on 07-29-2004 from stock lot # 04030170 and placed bottle 1B into the lab on the same day. There remains some of this material in the lab and it appears to be fine.

Please go ahead and strip and repeat using material from bottle 1B -- or better yet move onto the new 2% 950K MW PMMA in Anisole. (coded in the bottles in the cleanroom as 2% 950K MW PMMA-A.

I have attached spin speed (f) Thickness curves from my data from last week.  For 100 nm thickness on silicon I found 1550 and 1580 RPM to be best. This data will be promptly posted on our process suite later this week. I am performing final dose determinations and contrast curves combined with users training sessions this week.


On the features you showed in your images.
I do not see the normal severe reticulation that I would expect to observe if the polymer had hydrolyzed due to contamination or exposure to water vapor. But I have seen similar results long before that were due to sample surface charging, typically the effect results in non uniformity of dot shots within a write field.  What I am not seeing in your images is if the sample is charging  is misplacement of shot dot position. In your images pitch and placement seem perfect.  My suggestion would be to strip and repeat again with the current bottle of PMMA material (1B).  I can provide you with a chip of my reference material as well with a measured thickness of 93 nm. Also be sure to ensure your sample clipped to the std. sample holder is properly grounded. I generally clip a sample down and give it a 1 -2 mm nudge to ensure the clip scrapes through the resist and to the substrate.  Was this one of the samples that have AL2O3 or GaN as a upper layer in your structure?

We will keep a close eye out and see if we have other similar reports.

James Conway


Luigi Scaccabarozzi wrote:
Hi all,
I wanted to report some bad patterns I wrote last week on PMMA 2%
(microchem in chlorobenzene). I add that I used my standard recipe, dose,
and even some pattern I have written already many times without problems.
Most of my patterns appear deformed or heavily underexposed. The weird
thing is that, in some of them, some areas are ok (I put a picture of a good area).
It seems like that the PMMA was very non-omogeneous...
I'd like to know if someone else had the same problem with this bottle of
PMMA. In that case it's probably just the PMMA too old or contaminated and
I will simply try again.
Thanks to all
Gigi
Note: During the alignment I noticed that the PMMA was charging a bit more
than usual, but I could do the Align Writefield without problems.

  

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