Ion assisted near-complete filling of high aspect ratio trenches for 3-D neutron detectors

Highlights: • Development of plasma enhanced chemical vapor deposition system. • Forward directed ions aid conformal filling of B_xC into high aspect ratio trench. • 94.25% fill factor and 88.25% conformal coverage ratio at 3:7 ar/he flow ratio. • Promising for fabrication of high efficiency neutron detector. A single-step process has been developed for the conformal deposition of boron carbide in high aspect ratio trenches fabricated in an n-type (111) silicon substrate. Plasma enhanced chemical vapor deposition was used to deposit boron carbide from ortho-carborane (OC₂B₁₀H₁₂) precursor mixed with helium and argon gas. The depositions were carried out under substrate self-bias conditions to achieve a high fill factor using forward-directed ions. Nearly complete filling of 25 µm deep trenches with high-aspect ratio (> 6:1) via conformal coating of side walls has been confirmed from cross-sectional scanning electron microscopy studies. The results presented in this article establish that the process technology developed for achieving conformal deposition of the neutron stopping layer is suitable for the fabrication of Silicon p-i-n based three-dimensional thermal neutron detectors with high neutron detection efficiency.