Multilayer chemical mechanical polishing pad with broad spectrum, endpoint detection window

A multilayer chemical mechanical polishing pad is provided, having: a polishing layer having a polishing surface, a counterbore opening, a polishing layer interfacial region parallel to the polishing surface; a porous subpad layer having a bottom surface and a porous subpad layer interfacial region parallel to the bottom surface; and, a broad spectrum, endpoint detection window block comprising a cyclic olefin addition polymer; wherein the window block exhibits a uniform chemical composition across its thickness; wherein the polishing layer interfacial region and the porous subpad layer interfacial region form a coextensive region; wherein the multilayer chemical mechanical polishing pad has a through opening that extends from the polishing surface to the bottom surface of the porous subpad layer; wherein the counterbore opening opens on the polishing surface, enlarges the through opening and forms a ledge; and, wherein the broad spectrum, endpoint detection window block is disposed within the counterbore ope