Embodiments of inductively coupled plasma (ICP) reactors are provided herein. In some embodiments, a dielectric window for an inductively coupled plasma reactor includes: a body including a first side, a second side opposite the first side, an edge, and a center, wherein the dielectric window has a dielectric coefficient that varies spatially. In some embodiments, an apparatus for processing a substrate includes: a process chamber having a processing volume disposed beneath a lid of the process chamber; and one or more inductive coils disposed above the lid to inductively couple RF energy into and to form a plasma in the processing volume above a substrate support disposed within the processing volume; wherein the lid is a dielectric window comprising a first side and an opposing second side that faces the processing volume, and wherein the lid has a dielectric coefficient that spatially varies to provide a varied power coupling of RF energy from the one or more inductive coils to the processing volume.