Device for detecting an end point in polishing operations

摘要

The present invention relates to an apparatus for remotely detecting impedance adapted for use on a polishing machine wherein the end point of polishing for removing a surface layer during the processing of semiconductor substrates is detected. A first stationary coil having a high permeability core is wound having an air gap and an AC voltage is applied to the stationary coil to provide a magnetic flux in the air gap. A second coil is mounted for rotation on the polishing table, in a position to periodically pass through the air gap of the stationary coil as the table rotates. The second coil is connected at its opposite ends to contacts which are embedded in the surface of the polishing wheel. The contacts are positioned to engage the surface of the substrate being polished and provide a load on the second rotating coil when it is in the air gap of the stationary coil, will perturb the flux field therein as a function of the resistance of the load caused by the contacts contacting either a conducting surface or a non-conducting surface. This perturbance of the flux field is measured as a change in the induced voltage in the stationary coil which is converted to a signal processed to indicate the end point of polishing, the end point being when a metallic layer has been removed to expose a dielectric layer or when a dielectric layer has been removed to expose a metallic layer.