The special features of atomic layer deposition (ALD): easy control of layer thickness also in ultra thin films and conformal coating with extreme aspect ratios can be utilized in microelectronics in MOSFET gate oxides and trench capacitors in DRAM technology, respectively. In both application dielectrics with permittivities greater than that of SiO2 are required to continue downward dimensional scaling of the devices. In gate dielectrics ZrO2 and HfO2 are the most often studied alternative materials whereas in DRAM capacitors very high k-materials or ferroelectrics like BST (barium strontium titanate) and SBT (strontium bismuth tantalate) are examined. In this presentation the deposition of these materials by ALD is described.
In ALD the choice of precursors is extremely important. Most of the ALD studies on ZrO2 and HfO2 films have been dealing with one process, tetrachloride plus water. We have studied several alternative metal precursors such as iodides, alkoxides, aminoalkoxides, alkylamides and hydroxylamides. All precursors have their own impact to the electric properties of the ZrO2 and HfO2 films. The deposition of ternary oxide films by ALD is not very straightforward and totally new processes had to be developed. These processes are based on metalorganic compounds as metal source and water as oxygen source. In the presentation the growth processes will be discussed in more detail.