Over the last decades, three-dimensional micro-manufacturing of fused silica via near-infrared ultrafast laser exposure combined with an etching step has become an established technique for producing complex three-dimensional components. Here, we explore the effect of ultraviolet exposure on process efficiency. Specifically, we demonstrate that shorter wavelengths not only enable enhanced resolution but also yield higher etching selectivity, with an order of magnitude lower pulse energy and significantly higher repetition rates than current practice. This result is obtained using an exposure regime where the laser beam alternates between regimes of self-focusing and defocusing in a stable manner, forming a localized filament. Using this principle, we demonstrate the fabrication of self-organized nano-channels with diameters as small as 120 nm after etching, reaching extreme aspect ratios, exceeding 1500.