Patent ID: 8760626
Filing Date: 2014-06-24
Classification: G03F

Abstract:
1. A focus detection apparatus for a projection lithography machine, comprising: a laser configured to emit a laser beam; a focus optical unit configured to focus the emitted laser beam; a force detection unit configured to receive the focused laser beam at the backside of the force detection unit and reflect the received laser beam; a position detection unit configured to detect variations in position of a light spot formed by the reflected laser beam so as to obtain information about the topography of an object, and to detect and output a strength signal indicating the strength of an interaction force between the force detection unit and the object under detection disposed on a wafer, the wafer being carried on a stage of the projection lithography machine; a differential amplifier configured to have one of its two input connected to the output of the position detection unit to receive the strength signal, and the other input connected to receive a reference signal, and to perform differential calculation between the strength signal and the reference signal to obtain and output a Z-direction differential signal; a Z-direction feedback control unit configured to perform feedback control such that a spacing between the force detection unit and the object is maintained within a specified range, wherein the Z-direction feedback control unit has one of its two inputs connected to the output of the differential amplifier to receive the Z-direction differential signal, and the other input connected to receive a predetermined gain signal, and the Z-direction feedback control unit outputs a Z scan drive signal for controlling the movement of the stage in the Z direction; and a scan signal generator configured to connect to the stage and output to the stage a XY 2D scan drive signal for controlling the movement of the stage in the XY plane, the Z direction being perpendicular to the XY plane.