Improved structural properties of sputtered hafnium dioxide on silicon and silicon oxide for semiconductor and sensor ap
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Improved structural properties of sputtered hafnium dioxide on silicon and silicon oxide for semiconductor and sensor applications H. Grüger, Ch. Kunath, E. Kurth, W. Pufe, S. Sorge Fraunhofer IPMS, Grenzstr. 28, 01109 Dresden, Germany Abstract 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. 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 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/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 amorphous bodies. High heating rates of about 50K/s and annealing temperatures ranging 800 to 1000°C 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. Introduction The crystal structure has an important influence on the properties of metal oxide thin films. This type of layer has been used for semiconductor devices and sensors, as well as protective coatings due to favorable electrical, mechanical and optical properties. Up to now silicon oxide or so called ONO-stacks (SiO2/Si3N4/SiO2) have been used typically. Other candidates are Al2O3 [1], ZrO2 [2,3], Y2O3 [4], MoO3 [5], TiO2 [6] or WO3 [7] for example. Our work was aimed at Ta2O5 and HfO2 [8]. This paper focuses on the structural properties of HfO2. The comprehension of he crystallization process and its control is essential for the layers application in mind. “As deposited”-layers are mostly amorphous. The crystallization starts above an threshold temperature. Rapid heating to high temperatures leads to small grains [9]. This means if small crystallite sizes are desired, high heating rates have to be applied. This can be achieved typically by rapid thermal annealing (RTA) only. The crystallite size can be estimated by TEM viewing the crystallites or by XRD by measuring the full width at half maximum (FWHM) of the peaks. R. f. sputtering of hafnium oxide has been used to deposit layer in a thickness range from 100 to 150 nm. Deposition took place on 150mm wafer
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