  We study star cluster formation in various environments with different
metallicities and column densities by performing a suite of three-dimensional
radiation hydrodynamics simulations. We find that the photoionization feedback
from massive stars controls the star formation efficiency (SFE) in a
star-forming cloud, and its impact sensitively depends on the gas metallicity
$Z$ and initial cloud surface density $\Sigma$. At $Z=1~Z_{\odot}$, SFE
increases as a power law from 0.03 at $\Sigma = 10~M_{\odot}{\rm pc^{-2}}$ to
0.3 at $\Sigma = 300~M_{\odot}{\rm pc^{-2}}$. In low-metallicity cases
$10^{-2}- 10^{-1} Z_{\odot}$, star clusters form from atomic warm gases because
the molecule formation time is not short enough with respect to the cooling or
dynamical time. In addition, the whole cloud is disrupted more easily by
expanding H{\sc ii} bubbles which have higher temperature owing to less
efficient cooling. With smaller dust attenuation, the ionizing radiation
feedback from nearby massive stars is stronger and terminate star formation in
dense clumps. These effects result in inefficient star formation in
low-metallicity environments: the SFE drops by a factor of $\sim 3$ at
$Z=10^{-2}~Z_{\odot}$ compared to the results for $Z=1~Z_{\odot}$, regardless
of $\Sigma$. Newborn star clusters are also gravitationally less bound. We
further develop a new semi-analytical model that can reproduce the simulation
results well, particularly the observed dependencies of the SFEs on the cloud
surface densities and metallicities.
