U.S. Philips Corporation

Henricus E Beekman

Jan Van Eijk

Hendrikus H Cox

Fransiscus Mathijs Jacobs

Gerard Van Engelen

A device for positioning a body (5) by means of at least two electromagnets (13, 15). A position sensor (29) measures the size of an air gap (23) between one of the electromagnets (13, 15) and a guide beam (1). An output signal of the position sensor (29) is applied to a linear electronic control unit (35) which passes a control current through the electromagnets (13, 15) in dependence on a difference between the measured and a desired size of the air gap (23). An electronic root extractor (37) is connected between the control unit (35) and the two electromagnets (13, 15). An output signal of the root extractor (37) has a value equal to the square root of a control signal coming from the control unit (35). In this way a force exerted by the electromagnets (13, 15) on the guide beam (1) is proportional to the value of the control signal, so that a control is obtained with the linear control unit ( 35) in which the stiffness and bandwidth are independent of the value of the control current. Since the electrical resistance losses in the electromagnets (13, 15) in such a device are low, the device is particularly suitable for use as an electromagnetic bearing in an optical lithographical device for the irradiation of semiconductor substrates, or in other precision machines.

Electromagnetic support with current-independent characteristics

An optical lithographic device having a machine frame (1) to which is fastened a lens system (11) having a vertical optical main axis (13). Below the lens system (11), a positioning device (35) is fastened on a support member (3) of the machine frame (1), by means of which device an object table (27) is displaceable relative to the lens system (11) over a guide surface (5) of the support member (3) extending perpendicular to the optical main axis (13). The device is provided with a force actuator system (67) fastened to a reference frame (83) and controlled by a feedforward control system (95). The force actuator system (67) exerts a compensatory force on the support member (3) with a direction opposite to a direction of a reaction force simultaneously exerted by the positioning device (35) on the support member (3), and with a value which is substantially equal to a value of the said reaction force. The control system (95) further comprises a negative acceleration feedback (107), whereby the force actuator system (67) exerts a control force on the support member (3) which is determined by an acceleration of the support member (3) measured by an acceleration transducer (111, 113, 115). The use of the force actuator system (67) prevents undesirable movements of the support member (3) under the influence of a reaction force exerted by the positioning device (35) on the support member (3) and under the influence of external forces. The optical lithographic device can be used inter alia for illuminating semiconductor substrates, where a semiconductor pattern provided on a mask (17) is imaged on a semiconductor substrate (25), which is positioned on the object table (27), by means of the lens system (11).

Growing community of inventors

Eindhoven, Netherlands

Henricus E Beekman