Improved structural properties of sputtered hafnium dioxide on silicon and silicon oxide for semiconductor and sensor applications

Hafnium dioxide HfO2 is a candidate with promising properties for semiconductor industries as well as for optical and sensorical applications under harsh environments. The material can be deposited using various techniques such as CVD or PVD, some of them are suitable for replacement of silicon dioxide SiO2 and other gate dielectrics in MOS devices. The chemical inertness of HfO2 and the high band gap draw the attention of this paper towards application in optics as active and protective layer at the same time, chemical and physical sensors, such as moisture sensors and thin film capacities. In order to achieve optimized layer properties for the sensorical application in mind, the deposition process and the post-processing need to be tightly controlled. So, dense layers with a low amount of voids and a suitable grain structure can result. This way the layers feature the high inertness of HfO2 to the environment as well as to the underlayer. Layers with thicknesses between 25 and 150nm have been deposited by R.F. sputtering of high purity targets onto bare or oxidized silicon wafers under Ar- or Ar/O2-athmospheres. Initially the HfO2 has a mainly amorphous structure. Subsequent annealing controls the growth of recrystallized areas characterized by grain size and ratio between crystals and amourphous bodies. High heating rates (RTA) of about 50K/s and annealing temperatures ranging 800 to 1000°C seem to be advantegous for the area of interest. The layer's structure such as grain size, crystal type and transparency was investigated using AFM, TEM, XPS, SEM, XRD and ellipsometry. Layer tension was evaluated using laser deflection. The differences in structure found have been correlated to the results obtained in layer applications. The results are also discussed in comparision to SiO2 and tantalum-(V)-oxide Ta2O5.