Magnetically neutral loop discharged plasma sources and system

The magnetically neutral loop discharged (NLD) plasma was applied first for a processing use with a machine composed of three steady current coils and an alternating induction coil. This demonstrated the NLD plasma is much more useful than the inductive coupling plasma for Si/SiO2 etching processes using Ar, C3F8, C4F8, and H2 gases. A remarkable feature of the NLD plasma method is that a high density plasma with a doughnut-shaped distribution in any size on both radii of the major and minor axes can be generated at any distance apart from wafer. Second, the NLD high density plasma is generated at a rather low gas pressure range of 10−2 Pa with the characteristic that thermalization of the electrons is easier when the stronger alternating induction power is supplied. Sufficiently high etching rates with high selectivity were realized in a uniform manner by control of the characteristics on the NLD plasma. Furthermore, anisotropic etching was also achieved. The NLD is based on an unusual mechanism of power absorption that is effective in low pressure regime. In the NL region, an electron shows so called meandering motion, when an alternating electric field is applied. The meandering motion becomes chaotic, and effective heating occurs. The theory predicts that the effective resistance becomes 10–102 times larger than the classical collisional resistance. Under an appropriately selected set of parameters, the effective collision induced by the chaos is comparable to that in a gas of 0.1 Pa. These estimates are consistent with the experimental data. In conclusion, the NLD system opens a new region of plasma processing because of its versatile capability for being used to advantage in the age of 12 in. φ substrates.