$SiO2$ etching in magnetic neutral loop discharge plasma

Neutral loop discharge (NLD) plasma, which has attractive characteristics in both plasma production and spatial controllability, was successfully applied to large-wafer etching process, yielding satisfactory uniformity. Comparison of the etching characteristics in the NLD plasma with those in the inductively coupled plasma (ICP) plasma which was generated without magnetic field in the same device was made. $SiO2$ etch rate and selectivity to photoresist and Si in the NLD plasma were remarkably improved, comparing with those in the ICP plasma in a pressure range of 0.1–1 Pa. In the application of $SiO2$ etching process using the NLD plasma, a hole pattern of a high aspect ratio, 0.35 μm diameter and 2 μm depth, was successfully fabricated with a resist mask in an Ar (90%) +$C4F8$ (10%) plasma at 0.4 Pa. The selectivity to Si at the hole bottom was higher than 30. The etched profile was almost vertical (89°–90°) and the deviation of the $SiO2$ etch rate was within 3% on 200 mm wafer.