Closed-Loop Control of the "Z" Stage of a Wafer Prober
Original Publication Date: 1983-Dec-01
Included in the Prior Art Database: 2005-Feb-08
A feedback system has been installed on the "Z" stage of a wafer prober. Analog hardware has been installed on the probes which connect to the device's power supply pins. As the "Z" stage is moving upwards, its motion can be stopped by either of two methods. The first method is by the analog hardware sensing power supply current. As soon as the current exceeds a predetermined value (VREF), a signal is sent to stop the "Z" stage motor. For safety reasons a backup system must stop the "Z" stage if the analog signal fails to occur. A positioning signal on the "Z" stage is required for this. This could be obtained by counting the number of pulses on the output of a stepping motor controller or counting the pulses from an optical encoder disc on the "Z" stage.