  Massive primordial halos exposed to moderate UV backgrounds are the potential
birthplaces of supermassive black holes. In such a halo, an initially
isothermal collapse will occur, leading to high accretion rates of
$\sim0.1$~M$_\odot$~yr$^{-1}$. During the collapse, the gas in the interior
will turn into a molecular state, and form an accretion disk due to the
conservation of angular momentum. We consider here the structure of such an
accretion disk and the role of viscous heating in the presence of high
accretion rates for a central star of $10$, $100$ and $10^4$~M$_\odot$. Our
results show that the temperature in the disk increases considerably due to
viscous heating, leading to a transition from the molecular to the atomic
cooling phase. We found that the atomic cooling regime may extend out to
several $100$~AU for a $10^4$~M$_\odot$ central star and provides substantial
support to stabilize the disk. It therefore favors the formation of a massive
central object. The comparison of clump migration and contraction time scales
shows that stellar feedback from these clumps may occur during the later stages
of the evolution. Overall, viscous heating provides an important pathway to
obtain an atomic gas phase within the center of the halo, and helps in the
formation of very massive objects. The latter may collapse to form a massive
black hole of about $\geq 10^4$~M$_\odot$.
