High quality r.f. sputtered metal oxides (Ta2O5, HfO2 and their properties after annealing

Thin films of transition metal oxides have many applications like gate dielectrics in field effect transistors (FETs) and sensors, high-epsilon materials for capacitors or protective transparent coatings for photonic applications. Important are favorable electrical, optical and mechanical properties as well as high chemical inertness. Silicon oxide has been a standard material since the beginning of CMOS production. Tantalum pentoxide has been investigated for some years. Quite a new candidate in this area is hafnium oxide. Besides favorable properties, the material of choice must offer the possibility of reproduceable homogenous deposition at acceptable rates. The material properties should be adjustable, for example by thermal annealing, but must not change afterwards on a long term basis. Ta2O5 and HfO2 have been deposited by r.f. sputtering of high purity targets in Ar/O-2 mixtures. Due to the sensor application planned, thicknesses of 150 nm were deposited. The total thickness variation (TTV) across the whole 150 mm wafer was below +/-6%. After deposition, the layers were annealed with different methods. The mechanical stress can be adjusted through the annealing regime. The chemical inertness increases with the annealing temperature. All layers are insulating and transparent. Especially HfO2 annealed at 950 degreesC revealed favorable results: The layers are crystalline with a fine grained structure, smooth, dense and withstand NaOH as well as HF very well. It was verified, that these materials will be suitable for the applications desired, especially in contact with harsh environments. (C) 2003 Elsevier B.V. All rights reserved.