Darkfield (DF) alignment signals are commonly obtained by scanning targets beneath a focused probe beam while integrating the light scattered outside a pupil stop, the latter serving to block specular reflections. Additional information pertaining to target position can be obtained by refocusing the collected light to form an instantaneous DF image that moves across the detector as the target is scanned through the focused illumination probe. A simple method to achieve a significantly sharper and more selective response to the target is to apply a confocal prefiltering to the instantaneous image before integrating it to read out the signal level, i.e., successive frames of the instantaneous image are multiplied by a template aperture corresponding to the image of a centered alignment mark. A fiducial scan is used to approximately center the template, providing a reference position. In the case of a test wafer so grainy that the conventional DF signal is significantly broadened and almost overwhelmed by random scatter, the signal obtained with a confocal filter modified to trigger on target symmetry and matched edge slopes is sharper by an order of magnitude and is virtually free of background.