The deposition mechanism and characteristics of Al films using dimethylethylamine alane (DMEAA) source were investigated. Al films were deposited by the pyrolysis of DMEAA on Si, $SiO_2$ and TiN substrates with and without carrier gases. When the Al film was deposited on Si and $SiO_2$ substrates below 160℃, the incubation time increased from 1 min to 11 min as the substrate temperature decreased. But no incubation time was observed on TiN substrate. The nucleation activation energies of Al on Si and $SiO_2$ were 0.71 and 0.79 eV, respectively. The growth rate increased as the substrate temperature increased to 160℃ and then it decreased with further increase in the substrate temperature. The maximum growth rate of 600 nm/min was observed on TiN substrate. Below 160℃, the growth activation energies of Al on Si, $SiO_2$, and TiN substrates were 0.23, 0.34, and 0.1 eV, respectively. The difference in the growth rate and activation energy might be related to substrate conductivity (Fermi level). In other words, the substrate with higher conductivity seemed to easily transfer electrons to DMEAA source gas and break H atom from DMEAA gas, resulting in the enhanced adsorption of DMEAA on the substrate surface. The texture of Al film was affected by TiN orientation and Al thickness. Al film with low resistivity was denser than that with high resistivity.
The growth rate of DMEAA ranged from 20 to 140 nm/min and the maximum rate of 140 nm/min existed between 155 and 170℃ in 0.1 Torr. The impurity concentration of Al films might affect the electrical property such as resistivity. AES results revealed that the carbon and oxygen concentrations were below 1 at.% int the Al film deposited by DMEAA. The resistivity of Al film was 3.5 μΩcm around 155℃. The value is higher than the 2.7 μΩcm bulk resistivity, but they are much lower than the resistivity of the CVD W. The Al morphology was dense in the range of 155 to 170℃ and the Al resistivity depended on the Al morphology. The resistivity of Al film was improved by in-situ annealing.
The step coverage of Al film deposited at 170℃ in 0.1 Torr was 23% at 0.45 μm diameter holes with a 2.5 aspect ratio. Theoritical step coverage is 25% when mass tranasport reaction occurs. So, the measured step coverage is very similar compared with calculated step coverage. To improve step coverage, we used the substrate-type difference of incubation time for selective growth of Al within contact hole. When selectively deposited on TiN/$SiO_2$, the holes with diameter 0.45 μm, aspect ratio 2 were fully filled with Al at 155℃.
Below 160℃, the Al deposition rate of DMEAA in a $H_2$ carrier gas was larger than that of DMEAA in an Ar carrier gas. Without carrier gas, the $H_2$ gas pre-treatment below 155℃ increased the Al deposition rate compared with Ar and He pre-treatments. At 220℃, however, the Al deposition rate was not changed regardless of pre-treatment gases.
To investigate the enhancement of Al deposition by hydrogen, the surfaces of TiN and $SiO_2$ substrates were exposed in a hydrogen plasma before Al depositon. The depostion rate of Al film on the TiN substrate was not changed regardless of various surface pre-treatment. The hydrogen plasma pre-treatment on $SiO_2$ substrate reduced the incubation time and made a denser Al film compared with Ar plasma pre-treatment or without plasma pre-treatment. To understand how the adsorbed hydrogen enhances Al deposition, the surface of $SiO_2$ substrate with $H_2$ plasma treatment was either chemically cleaned or thermally annealed. The morphology of the Al film deposited on the $SiO_2$ substrate which was $H_2$ plasma exposed and etched in HF : $H_2O$ = 1 : 50 solution was similar to that without plasma treatment. The nucleation density of Al films on the $H_2$ plasma pre-treated $SiO_2$ was still high despite of annealing. The result indicated that the surface chemistry of the $SiO_2$ substrate was not significantly changed after 600℃ annealing. It is known that no Si-H bond exists on Si surface after heat treatment at 600℃. FTIR analysis indicated that the concentration of OH radicals at the $SiO_2$ surface was increased by hydrogen plasma treatment. A continuous and dense film can be obtained on $SiO_2$ substrate by this treatment. We suggest that the reason of the decrease of Al incubation time is the enhanced reaction between DMEAA source gas and the adsorbed H from OH radicals formed at the $SiO_2$ surface.
The texture of Al film deposited on Si substrate was affected by substrate orientation due to the lattice mismatch. The deposition rate and texture of Al film on the TiN substrate was not changed regardless of various applying bias. However, the texture of Al film on the Si substrate was changed by applying bias. When the Si substrate was biased at +10V in a $H_2$ atmosphere, the degree of Al (111) texture was increased. When the Si substrate was biased at +100V, the degree of Al (111) texture was greatly improved. It is belived that the most stable (111) plane grows when the Fermi level of substrate is low.
