Methods and tools for controlling the removal of material from microfeature workpieces

Methods and apparatus for controlling the removal of material from microfeature workpieces in abrasive removal processes. An embodiment of such a method comprises irradiating a periodic structure of the workpiece and obtaining an intensity distribution of radiation returning from the periodic structure. The workpiece can be irradiated with a wide spectrum of wavelengths (e.g., white light), or the workpiece can be irradiated with a laser or lamp at specific wavelengths. The intensity distribution can be an image or other signal from which a dimension or other physical parameter of the periodic structure can be determined. For example, the intensity distribution can be an intensity signal of radiation returning from the workpiece in a selected bandwidth (e.g., 200 nm-900 nm) or an image of a diffraction pattern of radiation that has been scattered by the periodic structure. The method further includes outputting a control signal based on the obtained intensity distribution. For example, the control signal can be an endpoint signal indicating the actual endpoint of the abrasive removal process.