Specific Process Knowledge/Characterization/XPS/Processing/ALDSandwich1/3scanned: Difference between revisions
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=Processing of high resolution scanned spectra = | =Processing of high resolution scanned spectra = | ||
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We start with the Al2p scan. Below is shown the etch level 23. Click 'Peak Fit' and select 'Add doublet' (''Not 'Add Single Peak' ''). In the tab 'Fit Peaks' of the 'Peak Fitting' panel click 'Fit All Levels'. | We start with the Al2p scan. Below is shown the etch level 23. Click 'Peak Fit' and select 'Add doublet' (''Not 'Add Single Peak' ''). In the tab 'Fit Peaks' of the 'Peak Fitting' panel click 'Fit All Levels'. | ||
[[File:ALD-Sandwich- | [[File:ALD-Sandwich-40b.jpg|700px]] | ||
So far we did not add any constraints at all. That means the Al2p spin orbit doublet is free to move anywhere to find a minimum error. | So far we did not add any constraints at all. That means the Al2p spin orbit doublet is free to move anywhere to find a minimum error. | ||
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== The Ti2p peak == | == The Ti2p peak == | ||
The titanium Ti2p peak is notoriously difficult to fit. | The titanium Ti2p peak is notoriously difficult to fit. Let us first look for some clues in [[Specific Process Knowledge/Characterization/XPS/Processing/XPSknowledgeview |XPS Knowledge view]]. The section below is a copy of the content in XPS Knowledge View (Avantage version 5.986). | ||
=== XPS Knowledge on the fitting of the Ti2p peak === | |||
'''''Binding energies of common chemical states''''' | |||
{| class="wikitable" | |||
|- | |||
! ''Chemical state'' !!'' Binding energy Ti2p<sub>3/2</sub>/eV'' | |||
|- | |||
| ''Ti metal'' || ''454.1'' | |||
|- | |||
| ''TiN'' || 454.9 | |||
|- | |||
| ''TiO<sub>2</sub>'' || ''458.5'' | |||
|- | |||
| ''SrTiO<sub>2</sub>'' || ''458.4'' | |||
|- | |||
|} | |||
'''''Interpretations of XPS spectra''''' | |||
*'' Ti metal gives asymmetric Ti2p peak shapes'' | *'' Ti metal gives asymmetric Ti2p peak shapes'' | ||
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*** ''Causes difficulty in accurately peak fitting Ti2p region with multiple chemical states.'''' | *** ''Causes difficulty in accurately peak fitting Ti2p region with multiple chemical states.'''' | ||
[[File:Ti ref 2.PNG|450px]] | [[File:Ti ref 2.PNG|450px]] | ||
''' ''General comments'' ''' | |||
* ''Metal is readily oxidized.'' | * ''Metal is readily oxidized.'' | ||
**''Titanium is used as a getter material for oxygen.'' | **''Titanium is used as a getter material for oxygen.'' | ||
* ''TiO<sub>2</sub> is readily reduced by argon monomer sputtering'' | * ''TiO<sub>2</sub> is readily reduced by argon monomer sputtering'' | ||
** ''Sub-oxides and/or metal may be formed during sputtering of the oxide.'' | ** ''Sub-oxides and/or metal may be formed during sputtering of the oxide.'' | ||
=== The fitting of the Ti2p peak === | |||
'''Please note that clicking on any of the two spectra above when using XPS Knowledge View in Avantage will generate a new processing grid with this particular set of data, peak table etc. It may be quite convenient to investigate what constraints have been added - obviously also for any other element.''' | |||
The only challenge we are missing from this cocktail of asymmetric peak shapes, differences in spin-orbit splitting, reduction of fully oxidized Ti2p to sub-oxides and satellite features is the presence of TiN. | |||
First, let us find some reasonable parameters for the Ti2p metallic peak. For that purpose, we analyse an old data set acquired on pure Ti. | |||
[[File:Ti 2p highres 1.jpg|700px]] | |||
In the red square it is seen that the constraints on some of the peak parameters are changed compared to the fittings of the Al2p and Hf4f peaks: | |||
* The FWHM are no longer required to be equal. This will open up for the broadening of the Ti2p<sub>1/2</sub> peak. In the previous fittings, the correct ratio between the two peaks in the the spin-orbit couples was maintained by the requirements that the FWHM were identical and the Height CPS had a specific ratio (hence the area ratio would be correct, see for instance the Al2p fitting parameters in the top image on this page). This constraint is gone now. However, with the addition of the asymmetry parameters (see below), the area requirement would be difficult to maintain anyway. | |||
* The Lorentzian-to-Gaussian ratio is freed. Before, it was set to 100. | |||
* The three asymmetry parameters 'Tail Mix', 'Tail Height' and 'Tail Exponent' are also free to find a minimum within some restricted range on the condition that the parameters of the two peaks be the same. | |||
An optimum fit is produced and accepted. In this case the outcome of the fitting is irrelevant for us - the interesting part is the the Peak table. To save it, click the upper 'Save Peak Table' button shown in the green square and save as *.vgt file. To load the peak table into our Ti2p fitting, click the lower 'Load Peak Table' in the green square. | |||