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DF: Fachverband Dielektrische Festkörper

DF 12: Dielectric and ferroelectric thin films and nanostructures II

DF 12.7: Vortrag

Donnerstag, 28. Februar 2008, 12:20–12:40, EB 107

Transition metal oxide based NVM for IHPs 0.13 micron BiCMOS technology — •Rakesh Sohal, Christian Walczyk, Ioan Costina, Peter Zauseil, Alexander Fox, and Thomas Schroeder — IHP Microelectronics, Im Technologiepark 25, 15236 Frankfurt (Oder), Germany

This Research is targeted to increase the functionality of IHP's 0.13 micron BiCMOS technology by integrating innovative embedded NVM cell concepts. The material of our interest is the tungsten oxide as insulator in metal-insulator-metal (MIM) structure to develop so called back-end-of-line (BEOL) integrated OxRAM cells. In this study, we report on the investigation of the tungsten oxidation process under BEOL constraints (<450°C) by using XPS, XRD, XRR and SEM.

The CVD prepared tungsten layers on TiN covered silicon wafers are thermally oxidised in oxygen environment (with 200 sccm O2 flow rate) in the temperature range of 300-450°C for 15-75 minutes. The tungsten oxide layer thickness estimated by XRR was in the range of 6 nm to 80 nm. The tungsten oxide was in WO3 stoichiometry as confirmed by XPS. The tungsten oxide prepared at higher temperatures (>350°C) show a small shoulder at lower binding energy which corresponds to tungsten sub-oxides. The tungsten oxide starts to crystallise in monoclinic phase at 350°C when it is oxidised for 30 minutes. A (001) oriented growth texture becomes dominant at higher temperatures (>400°C). The tungsten oxide surface was uniform for the layers prepared below 400°C. The tungsten oxide layers were also characterised by analysing the dielectric behaviour (i.e. leakage current).