Vapour phase decomposition
Encyclopedia
Vapour phase decomposition (VPD) is a method used in the semiconductor industry to improve the sensitivity of total-reflection X-ray fluorescence spectroscopy by changing the contaminant from a thin layer (which has an angle-dependent fluorescence intensity in the TXRF-domain) to a granular residue, which has a more intense fluorescence signal in angles smaller than the isokinetic angle, improving the limits of detection. A related technique is VPD-DC (vapour phase decomposition-droplet collection), the wafer is scanned with a droplet that collects the metal ions that were dissolved in the decomposition step. This procedure affords better limits of detection when applying atomic absorption spectroscopy
(AAS) in order to detect metal impurities of very small concentrations on wafer
surfaces.
This can be achieved by enhancing the impurity concentration in the solution to be analyzed. In standard AAS, the impurity is dissolved together with the matrix element. In VPD, the surface of the wafer is exposed to hydrofluoric acid
vapour, which causes the surface oxide to dissolve together with the impurity metals. The acid droplets, condensed on the surface, are then analyzed using AAS.
The method has yielded good results for the detection and measurement of nickel
and iron
.
To improve the range of elemental impurities and lower detection limits, the acid droplets obtained from the silicon wafers are analyzed by ICP-MS (inductively coupled plasma-mass spectrometry). This technique, VPD ICP-MS provides accurate measurement of up to 60 elements and detection limits of in the range of 1E6-E10 atoms/sq.cm on the silicon wafer.
Atomic absorption spectroscopy
Atomic absorption spectroscopy is a spectroanalytical procedure for the qualitative and quantitative determination of chemical elements employing the absorption of optical radiation by free atoms in the gaseous state. In analytical chemistry the technique is used for determining the concentration...
(AAS) in order to detect metal impurities of very small concentrations on wafer
Wafer (electronics)
A wafer is a thin slice of semiconductor material, such as a silicon crystal, used in the fabrication of integrated circuits and other microdevices...
surfaces.
This can be achieved by enhancing the impurity concentration in the solution to be analyzed. In standard AAS, the impurity is dissolved together with the matrix element. In VPD, the surface of the wafer is exposed to hydrofluoric acid
Hydrofluoric acid
Hydrofluoric acid is a solution of hydrogen fluoride in water. It is a valued source of fluorine and is the precursor to numerous pharmaceuticals such as fluoxetine and diverse materials such as PTFE ....
vapour, which causes the surface oxide to dissolve together with the impurity metals. The acid droplets, condensed on the surface, are then analyzed using AAS.
The method has yielded good results for the detection and measurement of nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
and iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
.
To improve the range of elemental impurities and lower detection limits, the acid droplets obtained from the silicon wafers are analyzed by ICP-MS (inductively coupled plasma-mass spectrometry). This technique, VPD ICP-MS provides accurate measurement of up to 60 elements and detection limits of in the range of 1E6-E10 atoms/sq.cm on the silicon wafer.