A new aluminum metallization process was developed for blanket Al chemical vapor deposition(CVD) used in ultralarge-scale integrated(ULSI) interconnections. This process involves deposition of Al/TiN multilayer. The key feature of this process is the periodic interruption of grain growth during Al chemical vapor deposition which results in enhanced surface smoothness and ease of patterning. The interruption of grain growth was done by TiN atomic layer deposition(ALD).
First, the surface morphology of Al films deposited by MOCVD on TiN has been observed as a function of deposition time by detecting reflected light intensity on the surface during Al growth. The behavior of the reflected light intensity with respect to the deposition time corresponds to the progress of Al growth as follows. The reflected light intensity, which decreases in the early stage, reveals scattering from Al nuclei. The subsequent increase shows an increase in Al coverage due to Al nuclei growth and coalescence. The maximum value shows that the deposited Al film has much smoother surface. The subsequent decrease with further deposition time indicates that scattering occurs due to rough surface morphology caused by grain growth.
To improve surface morphology of thick Al film, Al/TiN multilayer is fabricated as follows. Al is deposited on TiN until reflected light intensity has maximum value and very thin ALD-TiN film(~ 1.5 nm) is deposited on Al film without vacuum break. Then Al is deposited again. Al shows the progress of growth i.e. nucleation, growth, coalescence, smooth film formation, and surface roughening again on the ALD-TIN film. This means that ALD-TiN film acts as new nucleation sites and interrupts continuous Al grain growth. By repeating Al and ALD-TiN deposition, Al/TiN multilayer is fabricated. The deposited Al/TiN multilayer films have superior surface morphology compared to the Al films on the same thickness. Using this process, smooth and thick Al film can be fabricated successfully.
