$Al_2O_3$ is considered as the most promising alternative to $SiO_2$ for a gate dielectric materials in future Si-based integrated circuits owing to its high dielectric constant and low leakage current.
In this study, amorphous $Al_2O_3$ films on p-Si(100) at 250 ℃ have been successfully grown by atomic layer deposition (ALD) using $Al(CH_3)_3$ [trimethylaluminum: TMA] and $C_3H_8O$ [isopropylalcohol: IPA]. TMA is a conventional Al precursor but IPA isn't conventional O precursor. Even though $H_2O$ is a conventional oxygen precursor to deposit $Al_2O_3$ using ALD, in this thesis, IPA was used to oxygen precursor. The main reason of IPA selection will be discussed in later.
The film growth kinetics were studied using the concept of ALD and also excellent film characteristics were confirmed. The ALD temperature range for $Al_2O_3$ using TMA and IPA was between 230 ℃ ∼ 290 ℃.
In order to acquire the best ALD condition for $Al_2O_3$ deposition using TMA and IPA at 250 ℃, $P_{TMA}$=0.01 torr, $P_{IPA}$=0.1 torr, the behaviors of deposition thickness/cycle with TMA pulse time and deposition thickness/cycle with IPA pulse time have been investigated. The set of minimum pulse times to get the fully saturated deposition thickness/cycle was (TMA pulse =2s,IPA pulse = 1s) and also, at the optimal condition, the fully saturated deposition thickness/cycle was around 0.8 Å/cycle, which corresponds to 0.37 ML (monolayer)/cycle. Also, refractive index of $Al_2O_3$ films has 1.61 ∼ 1.62. The refractive index of $Al_2O_3$ films were affected by IPA pulse time but not affected by TMA pulse time. Also, an ideal linear relationship between the number of cycles and the film thickness was confirmed.
The compositions of deposited films were investigated by x-ray photoelectron spectroscopy (XPS) and also, the carbon incorporations into the films were analyzed by secondary ion mass spectroscopy (SIMS). The results of these studies shows almost stoichiometric $Al_2O_3$ films with slightly oxygen rich phase $(Al_2O_{3.1})$ and also there were no carbon incorporations into the films, i.e. SIMS results showed the detection limits values.
Structure of $Al_2O_3$ films were studied by x-ray diffraction (XRD) method. The results showed us that all films have amorphous structure regardless of annealing treatments.
Surface morphology was also investigated by atomic force microscopy (AFM). Surface morphology of ALD $Al_2O_3$ films was as smooth as RMS roughness values of a few Å regardless of annealing treatments. These smooth surface of $Al_2O_3$ films indicated that the ALD process is the best choice to deposit ultra-thin layer with smooth surface.
The analysis of interfacial regions of $Al_2O_3$/Si was studied by XPS and transmission electron microscopy (TEM). For the as-deposited $Al_2O_3$ film, there was no parasitic $SiO_2$ at the interfacial regions of $Al_2O_3$/Si even though there were parasitic $SiO_2$ at the interfacial regions of $Al_2O_3$/Si for the cases of the annealed $Al_2O_3$ films.
The electrical properties of $Al_2O_3$ films were investigated by I-V, C-V measurements. The leakage current values of $Al_2O_3$ films were as low as $10^{-8}A/cm^2$. This low leakage value is desirable for sub-0.2 ㎛ design rule applications. Also, the dielectric constants of $Al_2O_3$ films were as high as 9.66, 10.29 for the O2-annealed and the Ar-annealed $Al_2O_3$ films, respectively. These high dielectric constant values correspond to the equivalent oxide thicknesses of 31.9 Å and 29.9 Å, for 80 Å-thick films, respectively. In general, since the equivalent oxide thickness required in sub-0.2 ㎛ design rule applications is about 26 Å, if $Al_2O_3$ film with thickness less than 70 Å is fabricated, $Al_2O_3$ film will be adopted in sub-0.2 ㎛ design rule applications.
$Al_2O_3$ film prepared by ALD using TMA and IPA gave us possibility to use $Al_2O_3$ film as a dielectric material for sub-0.2 ㎛ design rule applications.'
