Metallic contamination identification on AlN deposited at Berkeley Microlab

Chia-Fang Chiang cfchiang at stanford.edu
Thu Aug 7 14:38:07 PDT 2008


Hi Mary and SpecMat,

I am working on piezoelectric device. Aluminum nitride (AlN) is the piezoelectric film I am using, which is deposited at Berkeley Microlab. A few months ago, I have discussed with Mary on the process of AlN at SNF. (Please refer to the email below.) Mary suggested to identify metallic contamination beforehand if clean/semi-clean equipments are involved in my fabrication. After several email itinerancy, EAG conducted LEXES test on my sample and the results are attached along with this email. It has been shown that AlN film is free from platinum contamination. Given this fact, I would like to apply for using clean/semi-clean equipments at SNF.

Please let me know if you see any problems.

Thank you very much.

Cathy

>> a short quotation of the LEXES ANALYSIS REPORT -

Analytical Request:
One wafer was originally submitted for XRF analysis.  The wafers were described as a layered structure: AlN 2 microns/Si 50 microns/SiO2 4 microns/Si substrate.  The purpose of the analysis was to identify metallic contamination in the AlN layer.  Due to interference issues, XRF analysis was not an appropriate analytical method.  The AlN layer was analyzed for Pt using the LEXES technique.  Survey spectra were also acquired to determine possible metal contamination.

LEXES Results:
LEXES analysis for platinum of the AlN layer indicates that no platinum was measured above the detection limit.  The estimated detection limit for Pt is approximately 25 ppma.  Survey spectra were also acquired from the AlN layer.  These spectra indicate the presence of boron, carbon, nitrogen, oxygen, aluminum and argon in the AlN layer.  These peaks have been identified in the spectra.  No other elements were detected above the instrumental background.


----- "Mary Tang" <mtang at stanford.edu> wrote:

| Hi Cathy --
| 
| (some contents have been deleted)
| 
| I've contacted Sia Parsa, who's my counterpart at Berkeley.  He did
| not have a lot of specific information about processing of AlN and so 
| suggested contacting the researchers who use this film at Berkeley. 
| So, I think there are a couple of processing issues that you should check
| with your Berkeley counterparts:
| 
| 1.  The AlN etches somewhat in basic solutions, such as developer.  
| However, Sia did not know if wet etch patterning of AlN could be done.
| 
| If AlN can be appropriately patterned with wet etching, then this
| would be the easiest method.  However, you'd have to bias your mask if you 
| want to define 10 micron lines in 3 micron films.
| 
| 2.  Alternatively, AlN could be plasma etched in the p5000etch metal 
| chamber, if it can be demonstrated that the AlN is CMOS clean.  The 
| machine at Berkeley is considered by Sia to be CMOS clean, but they do
| not have data and processing is allowed on Pt-film coated wafers
| (which is not really CMOS clean.)  So, Sia could not say if the materials
| from this system could be considered clean for SNF.  If your counterparts 
| have any data on trace metal contamination on AlN films deposited in
| the Berkeley Microlab AMS, it would be greatly appreciated.  If not, then
| we would require that a study be made.  This could be done either at the
| SNL (Rich Chin or Ann Marshal would be the contacts there) or at Evans
| Analytical Group, a commercial provider of analytical services.  
| Typically, TXRF is used for contamination studies on surfaces, but a 
| bulk film technique might be more appropriate in this case.  Usually,
| these techniques will detect a spectrum of metal contaminants -- the 
| contaminants of interest would likely be Pt (since it is introduced to
| the system) and any likely contaminants from the chamber or deposition
| tool itself.  Please check out the Evans Analytical website, which has
| a lot of good information about different analytical methods.
| 
| (some contents have been deleted)
|
| Mary
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