X-ray photon electron spectroscopy (XPS)

XPS is a surface sensitive method which provided information on the chemical composition of thin films, molecular layers or chemical surface modification. The sample is irradiated with monochromatic x-rays and photoelectrons close to the outer surface (~some nm) from core level shells are released. The binding energies information results from the measured kinetic energies of the electrons and are characteristically for specific chemical elements. Additionally, chemical bond states can be determined by chemical shifts in binding energies.

Multiprobe UHV-surface-analysis system (Omicron Nanotechnology)  

• X-ray source: DAR400 aluminium-anode 
• Quartz-crystal monochromator XM 500
• X-ray excitation energy: 1486,70eV (Al Kα1-line) 
• Monochromated x-ray line width (FWHM): 0.2 eV
• Energy analyzer: hemispherical analyzer, type EA 125 
• Signal-detection with pulse-counting channeltron (5 channels for count-rate enhancement) 
• Total energy resolution (x-ray source + hemispherical analyzer): 0.4eV for detailed scans at 10eV pass-energy (+ lifetime broadening of the electronic state) 
• Analyzed surface-area: around 1 mm in diameter
• Maximum sample size: (10 x 10) mm2 
• Information depth: between 2 and 5 nm inelastic photoelectron mean free path (depending on material and kinetic energy) 
• Charge-neutralization for non-conducting samples: electron-emissions-gun for low-energy electrons (0,1 – 500 eV): FG 15/40 (SPECS)
• Argon gun for surface modification and depth analysis
• ultraviolet radiation is at hand for UPS measurements

 A customers has issues on bonding dies from a specific batch of photo diodes onto a carrier substrate. Typically the surface modification with a self assembled monolayer enables this process. Using XPS the customer could identify that this batch of sample was wrongly processed and the SAM is absent which explains the problems during the bonding.  

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