(685a) Process – Structure Relationships of Al2O3 and Hfo2 Composite Films on Silicon

In order to continue the pace of transistor scaling predicted by Moore's law, alternative high-k materials are sought to replace SiO₂ as gate dielectric material. HfO₂ and Al₂O₃ are among the most promising replacement materials. Each of these materials has different advantages and disadvantages for gate dielectric applications. HfO₂ has a relatively high dielectric constant (~25) but crystallizes at temperatures as low as 600 ^oC; while Al₂O₃ has a much lower dielectric constant (~9) but can remain amorphous up to about 1000 ^oC. Therefore, a more promising film may be a compositional mixture or nanolaminated structure of these two materials where the both the dielectric constant is higher than that of Al₂O₃ and the crystallization temperature higher than that of HfO₂. The optimal characteristics of such a film depend not only on its overall composition but its nanolaminated structure which can be customized using atomic layer deposition.

In this work, the Al₂O₃ and HfO₂ components in these compositional films are deposited using tetrakis(diethylamino)hafnium and tris(diethylamino)aluminum precursors sequentially with water as the oxidizer in an atomic layer deposition reactor. The metal oxide composition in the film is varied using one deposition cycle of Al₂O₂ and variable number of subsequent deposition cycles of HfO₂ and then vice versa. This provides homogenous films with variable composition. After deposition, these films are annealed at temperatures between 600 - 1000 ^oC in Ar. We find, for example, that films with one deposition cycle of Al₂O₃ and 10 of HfO₂ remained amorphous up to annealing temperatures of 600 ^oC, while films with one deposition cycle of Al₂O₃ and 7 of HfO₂ remained amorphous up to annealing temperatures of 800 ^oC. Films deposited with two cycles of Al₂O₃ and one of HfO₂ were found to be amorphous up to 1000 ^oC.

To examine the film structure relationship, different nanolaminated structures with same overall composition were also investigated. For example, a nanolaminate film generated from alternating one cycle of Al₂O₃ and one cycle of HfO₂ will have the same overall composition as a film generated from two cycles of Al₂O₃ and two cycles of HfO₂. While the overall composition of the film is the same in this case, the nanolaminate structure is different. Crystallization temperature of such nanolaminate structured films are analyzed using x-ray diffraction, Fourier transformed infrared spectroscopy, and transmission electron microscopy. The overall composition of the films is measured using Rutherford backscattering spectrometry. Electrical characterization of the resulting films will also be discussed.