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 sensorial applications under harsh environments. The material can be deposited using various techniques such as CVD or PVD in different thickness ranges. Thee 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 improve the layer properties with the sensorial application in mind, the deposition process and the post-processing need to be tightly controlled. Layers with thicknesses between 100 and 150nm have been deposited by r.f. sputtering of a high purity HfO2 target onto bare or oxidized silicon wafers under Ar- or Ar/O-2-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 amorphous bodies. High heating rates of about 50K/s and annealing temperatures ranging 800 to 1000degreesC in a rapid thermal annealing (RTA) chamber seem to be advantageous for the properties desired. The layer's structure such as grain size, crystal type and orientation was investigated using AFM, TEM and XRD. Layer tension was evaluated using laser deflection. The differences in structure found have been correlated to the chemical inertness obtained in measurements for layer applications.