  Donor spins in silicon-28 ($^{28}$Si) are among the most performant qubits in
the solid state, offering record coherence times and gate fidelities above 99%.
Donor spin qubits can be fabricated using the semiconductor-industry compatible
method of deterministic ion implantation. Here we show that the precision of
this fabrication method can be boosted by implanting molecule ions instead of
single atoms. The bystander ions, co-implanted with the dopant of interest,
carry additional kinetic energy and thus increase the detection confidence of
deterministic donor implantation employing single ion detectors to signal the
induced electron-hole pairs. This allows the placement uncertainty of donor
qubits to be minimised without compromising on detection confidence. We
investigate the suitability of phosphorus difluoride (PF$_2^+$) molecule ions
to produce high quality P donor qubits. Since $^{19}$F nuclei have a spin of $I
= 1/2$, it is imperative to ensure that they do not hyperfine couple to P donor
electrons as they would cause decoherence by adding magnetic noise. Using
secondary ion mass spectrometry, we confirm that F diffuses away from the
active region of qubit devices while the P donors remain close to their
original location during a donor activation anneal. PF$_2$-implanted qubit
devices were then fabricated and electron spin resonance (ESR) measurements
were performed on the P donor electron. A pure dephasing time of $T_2^* = 20.5
\pm 0.5$ $\mu$s and a coherence time of $T_2^{Hahn} = 424 \pm 5$ $\mu$s were
extracted for the P donor electron-values comparable to those found in previous
P-implanted qubit devices. Closer investigation of the P donor ESR spectrum
revealed that no $^{19}$F nuclear spins were found in the vicinity of the P
donor. Molecule ions therefore show great promise for producing high-precision
deterministically-implanted arrays of long-lived donor spin qubits.
