Vacuum plasma processor having coil with small magnetic field in its center

摘要

A substantially planar coil of a vacuum plasma processor has plural turns for exciting gas in the processor to a plasma state in response to r.f. coil energization. The coil is located outside the processor and surrounded by a shield tending to cause magnetic flux coupled from peripheral portions of the coil to the gas to be less than magnetic flux coupled from interior portions of the coil to the gas. The coil is arranged so magnetic flux derived from a center portion of an area circumscribed by the coil is less than the magnetic flux derived from all other areas circumscribed by the coil. The magnetic flux is such that the density of the plasma in the processor on a processed substrate is relatively uniform even though the coil exhibits transmission line properties so there are substantial peak-to-peak current variations along the length of the coil.