  The nitrogen-vacancy center (NV) in diamond, with its exceptional spin
coherence and convenience in optical spin initialization and readout, is
increasingly used both as a quantum sensor and as a building block for quantum
networks. Employing photonic structures for maximizing the photon collection
efficiency in these applications typically leads to broadened optical
linewidths for the emitters, which are commonly created via nitrogen ion
implantation. With studies showing that only native nitrogen atoms contribute
to optically coherent NVs, a natural conclusion is to either avoid implantation
completely, or substitute nitrogen implantation by an alternative approach to
vacancy creation. Here, we demonstrate that implantation of carbon ions yields
a comparable density of NVs as implantation of nitrogen ions, and that it
results in NV populations with narrow optical linewidths and low charge-noise
levels even in thin diamond microstructures. We measure a median NV linewidth
of 150 MHz for structures thinner than 5 $\mu$m, with no trend of increasing
linewidths down to the thinnest measured structure of 1.9 $\mu$m. We propose a
modified NV creation procedure in which the implantation is carried out after
instead of before the diamond fabrication processes, and confirm our results in
multiple samples implanted with different ion energies and fluences.
