This paper reports the deep reactive ion etching of femtosecond laser machined highaspect graphitic channels through diamond. To begin, two chemical vapor deposition-grown diamond plates, one single-crystal and the other polycrystalline, are processed using the bulk microstructural modification technique of femtosecond-pulsed laser machining. Multiple laser parameters are varied in processing the polycrystalline sample, including laser pulse frequency, pulse energy, and number of pulses per micron step size between the back and the front of the diamond, whereas a constrained set of parameters is used with the single-crystal sample. Over the range of parameters evaluated for the polycrystalline diamond, Raman analysis exhibits photoluminescence from defects created near the surface through the laser machining process, but little, if any, graphite-like features. However, a Raman signal from graphite-like material is observed on the surface of the graphitic channels for the single-crystal diamond, from which it is determined that greater diamond to graphite-like phase conversion is obtained with a larger number of pulses per translation step and with a higher laser pulse energy. Further, a larger number of pulses per step results in strong luminescence, observed during Raman investigation. Subsequent deep reactive ion etching of the samples reveals that the laser-treated channels etch considerably faster near the surface than the surrounding diamond, and that a high relative etch rate is obtained even when graphite-like features are absent from the Raman spectra. The highest relative etch rate of the single-crystal sample was 1.61 µm/min.
A fabrication technique to create 3D diamond detectors is presented. Deep reactive ion etching was used to create an array of through-diamond vias (TDVs) in a 2 × 2 × 0.15 mm3 electronic grade single crystal diamond detector. The diameter of the TDVs was nominally 30 μm with a pitch of 100 μm between them. The TDVs were filled with chromium using hexavalent chromium electroplating to create 3D electrodes, which were connected electrically by interdigitated electrodes. The fabricated 3D diamond detector responded to both alpha particles and X-rays, exhibiting a charge collection efficiency of 52.3% at 200 V. Comparing to a diamond detector with the same interdigitated electrodes, but no 3D electrodes, confirms that the 3D electrodes are electrically active within the device. The average resistivity of the 3D electrodes is 2.89 ± 0.03 × 10−5 Ω cm, near that of bulk chromium. These results indicate that this fabrication technique is a potential option for 3D diamond detector fabrication.
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