Optical view port for chemical mechanical planarization endpoint detection

A system for planarizing the surface of a workpiece, wherein said system comprises a planarizing device including process chamber which houses a rotating platen with a polishing pad disposed on the platen surface, a polishing head for holding the workpiece over the surface of the polishing pad, a platen drive spindle which rotates the platen about its center, said device further comprising:

• a recess in the platen located radially displaced from the center of the platen, said recess having a bottom surface within the platen;
• an aperture in the polishing pad, said aperture overlying the recess in the platen;
• an optical viewport assembly housed within the recess in the platen, said optical viewport assembly comprising a support member, a window casing, a window pane, and an optical fiber array, said support member resting on the bottom surface of the recess and supporting the optical fiber array, said window casing is disposed over the optical fiber array and is provided with an aperture disposed over the fiber array, said window casing being supported relative to the platen with at least one set screw which can be adjusted to raise and lower the window casing relative to the platen, at least one fastener for locking the window casing in place relative to the platen, said optical viewport extending from the platen into the aperture of the polishing pad, and said window pane being flush with the surface of the polishing pad;
• an optical fiber bundle communicating from the optical fiber array, radially inward toward the center of the platen, and then through the platen drive spool to a rotary optical coupling;
• said rotary optical coupling communicating with a laser interferometer capable of transmitting and receiving laser beams to the rotary optical coupling, said laser interferometer being located outside the process chamber.