  This paper reports on the fabrication and characterization of a high purity
monocrystalline diamond detector with buried electrodes realized by the
selective damage induced by a focused 6 MeV carbon ion beam scanned over a
pattern defined at the micrometric scale. A suitable variable-thickness mask
was deposited on the diamond surface in order to modulate the penetration depth
of the ions and to shallow the damage profile toward the surface. After the
irradiation, the sample was annealed at high temperature in order to promote
the conversion to the graphitic phase of the end-of-range regions which
experienced an ion-induced damage exceeding the damage threshold, while
recovering the sub-threshold damaged regions to the highly resistive diamond
phase. This process provided conductive graphitic electrodes embedded in the
insulating diamond matrix; the presence of the variable-thickness mask made the
terminations of the channels emerging at the diamond surface and available to
be connected to an external electronic circuit. In order to evaluate the
quality of this novel microfabrication procedure based on direct ion writing,
we performed frontal Ion Beam Induced Charge (IBIC) measurements by raster
scanning focused MeV ion beams onto the diamond surface. Charge collection
efficiency (CCE) maps were measured at different bias voltages. The
interpretation of such maps was based on the Shockley-Ramo-Gunn formalism.
