Specific Process Knowledge/Characterization/XPS: Difference between revisions

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XPS-ThermoScientific

A X-ray Photoelectron Spectroscopy (XPS) system can be used at Danchip. The system is a Thermo K-Alpha system, placed in the basement of building 346.

The user manual(s), user APV(s), technical information and contact information can be found in LabManager:

XPS-ThermoScientific in LabManager

Elemental analysis

The XPS instrument can be used to do elemental analysis, chemical state analysis on the sample surface or deeper down by a depth profiling. A comparison about techniques and instruments used for elemental analysis at Danchip can be found on the page Element analysis.

More about the different possibilities with the XPS instrument is found here:

XPS technique

XPS is a surface sensitive and non destructive technique used for analysis of the elemental composition. Only the outermost atomic layers (some nanometers) are probed, but with an ion gun etch it is possible to probe deeper laying layers.

In the XPS spectrometer system the probed samples are irradiated by photons with a specific energy, and the photoelectrons that leaves the sample are detected. The energy levels of the electrons are elemental specific, and by measuring the energy of the outgoing electrons, it is possible to detect which elements that are present in a sample.

You can read further about the technique here: [1]

The technique can be used for different purposes:

Equipment performance of XPS-ThermoScientific

Purpose	Chemical analysis	Probing elemental composition Chemical state identification Non destructive technique Surface sensitive Depth profiling possible by ion beam etch of sample
Performance	Spot size	Can be set between 30µm - 400µm
	Probing depth	Depending on probed element. Max probe depth lies within 10-200 Å.
	Resolution	Dependent on probed elements. Concentrations down to about 0,5 atomic % can in some cases be detected.
	Charge compensation	Flood gun can be used for charge compensation of non conductive samples
	Finding structures	Choose measuring spot from camera image (magnified)
Depth profiling	Purpose	With ion beam etch the top layer of the material can be removed, to do a depth profiling
Depth profiling	Ion beam size	About 0,3x1 mm
Substrates	Substrate size	Max 60x60 mm
Substrates	Substrate thickness	Max height about 20 mm

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 The technique can be used for different purposes:
-===Depth profiling===
-[[Image:Stochiometry 20110510.JPG|425x425px|left|thumb|The composition of a NiCr as a function of film depth (etch time). The relationship between Cr and Ni is quite constant through the 70nm thick film. Measurements done with XPS-ThermoScientific. ]]
-The analysis is made on a chosen spot on the sample surface (chosen with the system camera). The technique is, as written above, very surface sensitive and probes only the top nanometers of the sample.
-With the ion beam gun on the system an etch of the sample can be done. The system measures the desired spectrum, does an etch step and measures again. A series of etch cycles can be set up, measuring the composition of the sample at different depths (for example at different depth of a film).
-'''Example: NiCr film'''
-As an illustration, a figure to the left, shows an elemental analysis through a metallic film consisting of Ni and Cr. The metallic layer was about 70 nm thick, and the atomic percentage of Ni and Cr was measured through the layer.
-In the graph, you see the atomic % as a function of etch depth, and it is possible to detect that the relationship between Ni and Cr is fairly constant through the metallic film.