Niobium disilicide formation by rapid thermal processing: Resistivity-grain growth correlation and the role of native oxide

Abstract

The formation of NbSi2 from Nb/Si(100) is studied using rf sputtering and rapid thermal processing. For a long sputter-etching time (10 min) of the Si substrate, NbSi2 is first formed at 720 °C. The lowest resistivity attained is 38 μΩ cm, one of the best for refractory metal silicides. The variation of the sheet resistance versus annealing temperature is correlated to grain growth. The grain size is deduced from the x-ray coherence length of the NbSi2(111) peak which sharpens and increases in intensity for T≳720 °C. For shorter sputter etching time (5 min), NbSi2 only forms above 895 °C. This is attributed to the native oxide at the Si interface. An estimated ternary phase diagram of Nb-Si-O shows that Nb and SiO2 coexist at this temperature. Unlike other refractory metal silicides, oxygen in the Nb film is expelled as the silicide is formed.