(685a) Process – Structure Relationships of Al2O3 and Hfo2 Composite Films on Silicon
AIChE Annual Meeting
2006 Annual Meeting
Materials Engineering and Sciences Division
Atomic Layer Deposition
Friday, November 17, 2006 - 3:15pm to 3:35pm
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.