Vapour phase decomposition (VPD) is a method used in the

semiconductor industry The semiconductor industry is the aggregate of companies engaged in the design and fabrication of semiconductors and semiconductor devices, such as transistors and integrated circuits. It formed around 1960, once the fabrication of semiconduct ...

to improve the sensitivity of total-reflection

x-ray fluorescence X-ray fluorescence (XRF) is the emission of characteristic "secondary" (or fluorescent) X-rays from a material that has been excited by being bombarded with high-energy X-rays or gamma rays. The phenomenon is widely used for elemental analysis ...

spectroscopy Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...

by changing the contaminant from a thin layer (which has an angle-dependent fluorescence intensity in the TXRF-domain) to a granular residue. When using granular residue the limits of detection are improved because of a more intense fluorescence signal in angles smaller than the isokinetic angle.

Method

When using granular residue the limits of detection are improved because of a more intense fluorescence signal in angles smaller than the isokinetic angle. This can be achieved by enhancing the impurity concentration in the solution to be analyzed. In standard atomic absorption spectroscopy (AAS), the impurity is dissolved together with the matrix element. In VPD, the surface of the wafer is exposed to

hydrofluoric acid Hydrofluoric acid is a Solution (chemistry), solution of hydrogen fluoride (HF) in water. Solutions of HF are colourless, acidic and highly Corrosive substance, corrosive. It is used to make most fluorine-containing compounds; examples include th ...

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.

Advantages

The method has yielded good results for the detection and measurement of

nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to ...

and

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...

. 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 Inductively coupled plasma mass spectrometry (ICP-MS) is a type of mass spectrometry that uses an inductively coupled plasma to ionize the sample. It atomizes the sample and creates atomic and small polyatomic ions, which are then detected. It is ...

). 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.

Related Techniques

One related technique is VPD-DC (vapour phase decomposition-droplet collection), where 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 AAS in order to detect metal impurities of very small concentrations on

wafer A wafer is a crisp, often sweet, very thin, flat, light and dry biscuit, often used to decorate ice cream, and also used as a garnish on some sweet dishes. Wafers can also be made into cookies with cream flavoring sandwiched between them. They ...

surfaces.

References

Semiconductor device fabrication {{spectroscopy-stub