Optical techniques of measuring endpoint during the processing of material layers in an optically hostile environment

A method of determining an endpoint in a process of polishing a surface from a rough state into a smooth state, comprising the steps of:

• directing a radiation beam against said surface in a manner to be scattered thereby when in the rough state and reflected thereby when in the smooth state,
• positioning light gathering optics with respect to the surface and the radiation beam directed thereagainst in order to receive the beam reflected from the surface when the surface is in the smooth state,
• during the polishing process, monitoring as a function of time an intensity level of said received beam reflected from the surface, and
• determining from the intensity level of the received reflective beam as a function of time when the polishing has reached a desired level of completion.

A process of chemically and mechanically removing material from a layer of opaque material carried by a front side of a substrate in the form of either a semiconductor wafer or a flat panel display, wherein the substrate has a back side held by a carrier and the layer urged against a polishing block with an abrasive slurry therebetween while relative motion is imparted between the carrier and the polishing block, wherein the removal of material is monitored in real time by a method comprising:

• directing a beam of radiation through the carrier against the back side of the substrate, said radiation including a wavelength to which the substrate is transparent, said radiation thereby passing through said substrate to said layer,
• detecting a portion of said radiation that is reflected from the layer and travels back through the substrate and the carrier,
• monitoring the level of the detected radiation portion, thereby to monitor the material removal process as it is occurring, and
• identifying a characteristic of the monitored detected radiation portion that corresponds to the existence of a particular condition of the material removal process.

A process of chemically and mechanically removing material from a layer of transparent material carried by a front side of a substrate in the form of either a semiconductor wafer or a flat panel display, wherein the substrate has a back side held by a carrier and the layer urged against a polishing block with an abrasive slurry therebetween while at least the carrier is moved with respect to the polishing block, wherein the removal of material is monitored in real time by a method comprising:

• directing a beam of radiation through the carrier against the back side of the substrate, said radiation including a wavelength to which the substrate is transparent as well as said layer, said radiation thereby passing through said substrate to said layer and portions thereof being partially reflected from various interfaces and back through the substrate and the first member,
• detecting at least two of said reflected radiation portions, one of which is reflected from an exterior surface of the layer, said radiation detection occurring after the radiation has traveled from the layer back through the substrate and the first member,
• monitoring a resulting interference between the detected at least two of said reflected radiation portions, thereby to optically monitor progress of the removal of material from the layer, and
• identifying a characteristic of the monitored radiation interference that corresponds to the existence of a particular condition of the material removal process.

In a chemical-mechanical planarization apparatus that includes a carrier with a surface capable of holding a backside of a substrate thereagainst and which provides relative movement of a front side of the substrate against a polishing block with an abrasive slurry therebetween, a system that monitors removal of material from the front side of the substrate, said system comprising:

• a source of electromagnetic radiation,
• at least one optical element that is transparent to said radiation and which is embedded in the surface of said carrier in a position adjacent a backside of a substrate carried thereby,
• an optical system positioned to direct said radiation through the optical element and a substrate held against the carrier surface,
• a photodetector positioned to receive, through said at least one optical element, radiation that is reflected from a front side of said substrate, thereby to,generate an electrical signal related to the reflected radiation,
• means receiving the electrical signal for identifying a particular characteristic of the electrical signal that corresponds to a predefined condition of the wafer front side, and
• means responsive to an identification of the particular characteristic for changing some aspect of operation of the apparatus.

A method of planarizing an exterior surface having adjacent raised and depressed areas thereacross, said exterior surface being on a layer carried by a substrate, comprising:

• removing material from the exterior surface,
• directing electromagnetic radiation through boundary surfaces of said substrate and layer to said exterior surface in a manner to be partially reflected from both the boundary surfaces and a region of the exterior surface including both raised and depressed areas,
• detecting the radiation that is partially reflected from the boundary and exterior surfaces after said partially reflected radiation exits the substrate, and
• monitoring a component of the partially reflected radiation that varies in intensity, during removal of material from said exterior surface, as a result of interference between reflections from the exterior surface and at least one of the boundary surfaces, thereby to optically monitor progress of the exterior surface planarization.