STS2 Update Additions

[Jim McVittie]

STS2 Users,

I have some additions to my May 2 note. In particular, you also need to 
pay attention to the pressures, to monitor the forward and reflected coil 
powers and to remove your wafer from the chamber after every run or plasma 
test.

STS warns that pressures below 10 mT can lead to plasma instabilities, 
which could be causing some of out problems. They suggest that we either 
use the AUTO APC pressure mode or check our recipe pressures on a regular 
basis if we are using manual pressure mode. The reason for checking is 
that the turbo pump speed will change with time so the pressure you get 
for a given APC percent setting will change with time. For a repeatable 
process you want the same pressure during your dep and etch cycle during 
each run. For each of your recipes you should know what the optimal dep 
and etch pressures are. If you do not know these pressures, you can go 
back in the datalog files to a known good run for a given recipe and get 
the pressures. As an example, for Jim-Etch-Test1 (shallow) recipe the 
optimum pressures are 15 mT dep and 40  mT etch.

Another step, which may help reduce the intermittent high reflective power 
problem, is to move your wafer back to the carousel after every run or 
plasma strike. At this point, I have correlation that this helps.      

In my previous note, I forgot to say that you need to monitor the forward 
and reflective coil powers during your runs using the trace display on the 
process monitor screen.

Here is an undated list of items, which should be done, to minimize the 
dropout problem and to reduce stress on the coil generator:  

1. Run a 10 min O2 clean step before your run. 

2. Make sure your recipe starts with a 10s stabilization period so the gas
flows, pressure and matching network positions are stabilize before the 
plasma comes on. 

3. Your recipe should have the "Tolerance Recipe" box selected. This 
insures that the process will quickly fault out if there is a problem with 
excessive reflected power or other condition, which could damage tool or 
your wafer.

4. Do not start with a etch (SF6) step for a switched process. 

5. Check your tune and load matching network preset positions. I or some 
knowledgeable user can help you do this. A starting point for the switched 
dep/etch process is 42% for the coil load position and 37% for the tune 
position.
 
6. Make sure the pressure does not go below 10 mT during your run. If you 
use manual pressure control, you will need to change the percent setting 
over time to adjust for changes in the turbo pumping speed.

7. Remove your wafer from the chamber after each run (plasma strike). 

8. We still have not corrected the initial rf generator fault, which 
occurs each time the coil generator turns on after a new wafer has been 
loaded. You need to use the retry button at the bottom of the error page 
to continue with your run.

9. During your runs, use the TRACE mode on the Process Monitor screen to 
monition the forward and reflected powers. If you see more than a few 
power dropouts, you should abort the run. 

       Thanks,  Jim

--------------------------------------------------------------
James (Jim) P. McVittie, Ph.D.	        Sr. Research Scientist 
Paul G. Allen Building                  Electrical Engineering
Stanford Nanofabrication Facility       jmcvittie at stanford.edu
Stanford University             	Office: (650) 725-3640
Rm. 336X, 330 Serra Mall		Lab: (650) 721-6834
Stanford, CA 94305-4075			Fax: (650) 723-4659