Development and Plasma Characteristics Measurement of Planar-Type Magnetic Neutral Loop Discharge Etcher

A low-pressure and high-density plasma source, called a planar-type magnetic neutral loop discharge (NLD), has been developed for a single-wafer etching process, employing a pair of permanent magnet rings and a single-turn RF antenna on the quartz plate. First, the plasma characteristics of planar-type NLD were compared with those of a planar-type inductively coupled plasma (ICP) using the prototype etcher with a large magnetic neutral loop (MNL) of 230 mm diameter. The results of probe measurements in Ar plasmas have revealed that a planar-type NLD can be sustained at low pressures of 0.1–10 mTorr with higher plasma density and lower electron energy than a planar-type ICP. The depletion of high-energy electrons in NLD was revealed by the direct measurement of electron energy distribution function (EEDF) and optical emission spectroscopy. Next, for the purpose of uniform and large-diameter NLD generation, effects of magnetic field strength and the gap between an antenna and a wafer stage on the plasma uniformity have been investigated. By reducing the magnetic field strength that suppresses plasma diffusion, an ion current uniformity within ±2.5% and a high ion current density of 13 mA/cm 2 was obtained over a 240 mm diameter in the downstream Ar plasma. As for C 4 F 8 +90%Ar plasmas, preferable gas phase chemistry of ion and neutral species for highly selective SiO 2 /Si etching was attained due to relatively low electron energy, and a uniformity within ±2% was also achieved over a diameter of 240 mm.