  We report on an ion implantation technique utilizing a screening mask made of
SiO$_2$ to control both the depth profile and the dose. By appropriately
selecting the thickness of the screening layer, this method fully suppresses
the ion channeling, brings the location of the highest NV density to the
surface, and effectively reduces the dose by more than three orders of
magnitude. With a standard ion implantation system operating at the energy of
10 keV and the dose of 10$^{11}$ cm$^2$ and without an additional etching
process, we create single NV centers close to the surface with coherence times
of a few tens of $\mu$s.
