Quantification of the Pt Concentration in a NiSi(Pt)-NiSi2 Semiconductor Structure

This application example shows EDS data from the epitaxial growth of a Pt alloyed NiSi thin film and the quantification of a few at% of Pt alloyed in NiSi. NiSi is used for nm-sized metallization structures in semiconductor devices like MOSFETs. Pt alloying of NiSi is applied to stabilize the metallic NiSi at elevated temperatures and to avoid its transformation into the less conductive NiSi2 phase. Pt is soluble in NiSi substituting Ni but it is not soluble in NiSi2. 

Ni and Pt were deposited on HF-cleaned (001) Si wafers by magnetron sputtering. The amount of Pt sputtered from a single Pt target was optimized to deposit a few at% Pt. The film was rapidly annealed for 30 s at 700 °C in N2 atmosphere, producing a mixture of NiSi and NiSi2. The more dense NiSi appears brighter in Z (atomic number)-contrast of the high angle annular dark field image (HAADF). The Pt content is difficult to quantify by EELS due to the delayed Pt edge. 

In the EDS map overlaid with the HAADF image and acquired within 7 minutes however, the Pt is clearly visible. A 0.12sr, 22° take-off angle SDD on a conventional STEM was used for the EDS-data acquisition. The preferred solution of Pt in NiSi was confirmed by this EDS experiment. Quantification of the Pt content in NiSi using theoretical Cliff-Lorimer factors delivers the expected 2 at% within an error range of ±1 at%, shown in the quantified map and extracted line scan. Both confirm that Pt is more or less uniformly distributed in the NiSi at 2 at%.