초록 ▼

A method for automatically positioning a workpiece having at least one marking, specifically a wafer for integrated circuits which is to be processed in a charged-particle beam apparatus, relative to a scanning field or mask. In the method, a scanning beam scans the workpiece along the line and a ma

A method for automatically positioning a workpiece having at least one marking, specifically a wafer for integrated circuits which is to be processed in a charged-particle beam apparatus, relative to a scanning field or mask. In the method, a scanning beam scans the workpiece along the line and a marking signal is generated when the marking is reached by the beam. This marking signal controls a device which generates a control signal in response to the marking signal which is proportional to the deviation of the marking position from a reference position and which drives a device for correcting the position of the workpiece relative to the scanning field or mask. The improvement of the invention comprises the steps of scanning the beam across the workpiece successively in opposite directions at the same velocity through a forward sweep and a return sweep of the beam; integrating a positive reference voltage in an integrator during the forward sweep of the beam from the beginning of the line scanned until the marking on the workpiece is reached by the beam; integrating a negative reference voltage having the same magnitude as the positive reference voltage in the integrator during the return sweep of the beam from the end of the line scanned by the beam until the marking on the workpiece is reached by the beam; and generating an output control signal by means of the integrator after a full forward and return sweep of the scanning beam over the workpiece for correcting the position of the workpiece relative to the scanning field or mask. A method using digital scanning and apparatus for carrying out the methods are also disclosed.

대표청구항 ▼

In a method for automatically positioning a workpiece having at least one marking, specifically a wafer for integrated circuits which is to be processed in a charged-particle beam apparatus, relative to a scanning field or mask, in which a scanning beam scans the workpiece along a line and a marking

In a method for automatically positioning a workpiece having at least one marking, specifically a wafer for integrated circuits which is to be processed in a charged-particle beam apparatus, relative to a scanning field or mask, in which a scanning beam scans the workpiece along a line and a marking signal is generated when the marking is reached by the beam, said marking signal controlling a device which generates a control signal in response to the marking signal, said control signal being proportional to the deviation of the marking position from a reference position and driving a device for correcting the position of the workpiece relative to the scanning field or mask, the improvement comprising the steps of scanning the workpiece by the scanning beam successively in opposite directions at the same velocity through a forward sweep and a return sweep; integrating a positive reference voltage in an integrator during said forward sweep of said beam from the beginning of the line scanned until the marking on said workpiece is reached by said beam; integrating a negative reference voltage having the same magnitude as said positive reference voltage in said integrator during said return sweep of said beam from the end of the line scanned by said beam until the marking on said workpiece is reached by said beam; and generating an output control signal by means of said integrator after a full forward and return sweep of said scanning beam over said workpiece for correcting the position of said workpiece relative to said scanning field or mask. An apparatus for automatically positioning a workpiece having at least one marking, specifically a wafer for integrated circuits which is to be processed in a charged-particle beam apparatus, relative to a scanning field or mask, which workpiece is scanned by a scanning beam along a line and a marking signal is generated when the marking is reached by the beam, said marking signal controlling a device which generates a control signal in response to the marking signal, said control signal being proportional to the deviation of the marking position from a reference position and driving a device for correcting the position of the workpiece relative to the scanning field or mask, comprising a digital signal generator; a digital-to-analog converter coupled to said digital signal generator; a beam deflection system coupled to said digital-to-analog converter for deflecting said beam in a linear scan across said workpiece in equidistant steps; a square-wave signal generator coupled to said digital signal generator; a bidirectional counter, coupled to said square-wave signal generator and to said digital signal generator, for counting said scanning steps of said beam, said square wave generator controlling the direction and the start of counting by said bidirectional counter; a control device coupled to said square-wave signal generator, said digital signal generator, and said counter; switch means coupled to said counter and adapted to be controlled by said control device, said control device closing said switch means after a full forward and return sweep of said scanning beam; a storage control device, coupled to said switch means, the final count of said counter being transmitted to said storage device when said switch means is closed by said control device; a digital-to-analog converter, coupled to said storage control device, for generating an output control signal in response to said final count and correcting the position of said workpiece, said control device resetting said counter to zero after said final count of said counter is transmitted to said storage control device and restarting said digital signal generator for another sweep of said scanning beam; a detector for registering said marking signal; a preamplifier coupled to said detector; and a comparator coupled to said preamplifier and to said counter, said comparator being further coupled to means for setting a trigger threshold for said comparator including a reference voltage source and a voltage divider, said preamplifier and said comparator transforming said marking signal into a control signal for stopping said counter.