Enhanced anisotropy in advanced semiconductor nanofabrication via ultralow electron temperature plasma for cryogenic etching

Cryogenic plasma etching enables the fabrication of high-aspect-ratio nanostructures, but its practical implementation is hindered by excessive plasma heat flux that necessitates extreme substrate cooling. Here, we demonstrate an ultralow electron temperature (ULET) plasma generated by a DC-biased grid in an inductively coupled plasma system, which effectively suppresses all major components of plasma heat flux. Compared to conventional plasmas, the electron temperature in ULET plasmas decreases by an order of magnitude, resulting in over 50 % reduction in substrate heating. Measurements of the ion energy distribution and substrate temperature reveal that high electron temperatures predominantly contribute to ion bombardment, UV radiation, and surface recombination heat flux. The lower plasma heat flux in ULET plasmas leads to enhanced etch anisotropy in high-aspect-ratio SiN/SiO₂/Si patterns, showing a sixfold improvement compared to conventional cryogenic plasma etching. Moreover, this high anisotropy is maintained even when the substrate temperature is increased by 100 K above typical cryogenic conditions. These results suggest that ULET plasmas enable energy-efficient, high-fidelity cryogenic etching, potentially reducing cooling costs while improving profile control for advanced semiconductor nanofabrication.