Stage apparatus and lithographic apparatus comprising such stage apparatus

A stage apparatus to position an object, the stage apparatus including a table configured to hold the object, a support structure configured to support the table, the table being displaceable relative to the support structure, the support structure including one of a first data clock and a second data clock and the table including the other one of the first data clock and the second data clock; and a circuit configured to synchronize the first and second data clocks, the circuit including a transmitter and receiver, the transmitter configured to wirelessly transmit clock signal data from the first data clock to the second data clock, and a synchronization circuit configured to synchronize the second data clock with the first data clock from the wirelessly transmitted clock signal data received by the receiver.

FIELD

The present invention relates to a stage apparatus and to a lithographic apparatus comprising such stage apparatus.

BACKGROUND

In lithography, use is made of stages, such as a substrate stage or a patterning device stage that is movable so as to position the substrate respectively the patterning device, which stage is provided with a cable connection, e.g. to provide electric power to actuators (such as a short stroke motor), sensors (such as encoder measurement heads mounted on the stage), etc. The cable, due to its inherent properties such as its stiffness, may contribute to sources of mechanical disturbance when positioning/moving the stage with high accuracy and/or high speed. Therefore, it may be desirable to be able to provide a stage in which wired connections are omitted as much as possible.

Clock data may be transmitted to the stage. The clock data may for example be used to clock (i.e. to time) position measurements of the stage, e.g. during movement of the stage. In case the stage is equipped with encoder measurement heads, the measurements by the encoder measurement heads may for example be clocked. Given a range of movement of the stage, a wireless transmission of clock data to the stage would result in varying delay of the wireless transmission of the clock data: as a propagation path of the transmission would vary depending on a length of the transmission path. As a result, the clock data as received at the stage would exhibit a delay in dependency of the position of the stage. Given high speeds of movement of the stage and high positioning accuracy requirements, it may be desirable to determine a position of the stage—e.g. during a movement—with high accuracy in terms of the position itself, as well as in terms of the time at which that position is measured. Thereto, an accurate clock may be desirable.

SUMMARY

It is desirable to provide a wireless transmission of clock data to a movable stage, whereby a propagation delay dependency on a length of a propagation path is at least partly compensated.

According to an embodiment of the invention, there is provided a stage apparatus to position an object, the stage apparatus including a table to hold the object, a support structure to support the table, the table being displaceable relative to the support structure, wherein the support structure includes one of a first data clock and a second data clock and the table includes the other one of the first data clock and the second data clock, the stage apparatus including a circuit to synchronize the data clocks, the circuit including: a transmitter-receiver combination configured to wirelessly transmit clock signal data from the first data clock to the second data clock, and a synchronization circuit to synchronize the second data clock to the first data clock from the wirelessly transmitted clock signal data as received by the receiver.

In another embodiment of the invention, there is provided a lithographic apparatus including such stage apparatus.

DETAILED DESCRIPTION

The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, to direct, shape, or control radiation.

The lithographic apparatus may be of a type having two (dual stage) or more substrate tables or “substrate supports” (and/or two or more mask tables or “mask supports”). In such “multiple stage” machines the additional tables or supports may be used in parallel, or preparatory steps may be carried out on one or more tables or supports while one or more other tables or supports are being used for exposure.

FIG. 2highly schematically depicts a stage apparatus comprising a table TA which is movable in respect of a support structure STR. The table is, in this example movable in a direction of movement indicated by the arrow DM. The table may for example be formed by a substrate table or a mask table (i.e. a support) of a lithographic apparatus. The support structure may be formed by a reference frame (such as a metrology frame) or other stationary structure. The support structure may also be formed by a movable structure, such as a long stroke actuator: in such case, the direction of movement may be formed by a short stroke actuator direction of movement e.g. of the lithographic apparatus. The concept as explained with reference toFIGS. 2 and 3may be applied for example in situations wherein the table is movable is a single direction, such as the direction of movement DM. A first data clock C1is provided at the support structure STR: the first data clock may be generated at the support structure, or may be transmitted to the support structure via any suitable transmitter, such as a wired or wireless data clock signal, data clock bus, etc. A second data clock C2is provided at the table TA. The second data clock may be provided by a suitable data clock generator, such as a synchronisable data clock generator, and/or may be derived from the wirelessly transmitted clock signal data as explained below. As depicted inFIG. 2, the first data clock C1is transmitted to the table TA via dual (wireless) transmission paths: firstly, a transmission path CT1ais provided, and secondly a transmission path CT1bis provided. Thereto, corresponding transmitters are provided at the support structure STR and corresponding receivers are provided at the table TA. The table TA hence receives clock data from the first clock C1twice. The table TA may move along the direction of movement DM. Therefore, a length of the paths CT1aand CT1bmay vary. As a result, a delay via each of the paths CT1aand CT1bmay vary in dependency of the position of the table TA in respect of the support structure STR. The clock data as transmitted along the two transmission paths is thus received twice at the table TA. The more the table TA is moved along the direction DM to one side, the shorter one of the transmission paths (hence the shorter the delay via that transmission path), while the longer the other one of the transmission paths (thus the longer the delay via that transmission path), as the transmission paths extend oppositely directed along the direction of movement DM. Both the clock data as received via the wireless transmission paths are provided to a synchronization circuit SYN which is arranged to mix the clock data as received via both of the transmission paths and derive a synchronization for the second data clock C2there from. In an embodiment, the synchronization circuit may essentially synchronize the second data clock C2to an average of the delay via the transmission paths. In addition to such averaging, a constant (e.g. calibrated) delay may be added, so as to compensate for example for path length, delay of transmission-, reception-, and/or processing electronics.

It will be appreciated that in a causal system, negative delays that compensate for real world delays, may be impossible. However, as the data clocks provide a period signal, a delay of 360 phase shift effectively results in a zero delay, thus delays encountered in for example transmission-, reception-, and/or processing electronics, along the transmission paths, etc, may be compensated by a further delay so as to result in a substantially identical steady state behavior.

FIG. 3depicts a block schematic circuit to illustrate an embodiment of the synchronization circuit of the embodiment as described with reference toFIG. 2. The clock data as received via the transmission paths CT1aand CT1bis provided to a mixer MX. As both received clock data have a same frequency, however may differ in phase, the mixer at its output provides a signal component at substantially twice the data clock frequency and a substantially constant (DC-direct current) signal component. The signal component at twice the data clock frequency is selected by a high pass filter HPF, the remaining signal being divided e.g. by a factor 2 in frequency by a divider DIV. As the signal component at twice the frequency may be expressed as a sum of the clock frequencies as received along the two transmission paths and a sum of the phases as received along the two transmission paths, the sum of the phases will be constant, irrespective of the position of the table TA along the direction of movement DM. An output signal of the divider—which hence provides an accurate, constant phase shift independent of the position of the table TA, is further delayed by delay unit DLY in order to at least partially compensate for the delays encountered in for example transmission-, reception-, and/or processing electronics, along the transmission paths, etc.

The other signal component at the output of the mixer MX substantially corresponds to a difference in frequency and phase between the clock data from CT1aand CT1b. As the received frequencies may be substantially the same, a signal component which expresses a difference in phase remains. As the difference in phase is position dependent, position data POS representative of the position of the table TA may be derived from the output of low pass filter LPF.

FIG. 4depicts another embodiment which may be applied in case of a table TA having a range of movement extending in multiple directions. In order to enable this, the transmitter-receiver combination is further configured to transmit clock data from the second data clock (i.e. in this example the table) back to the first data clock (i.e. in this example the support structure STR). By sending the clock data to the second clock and back again to the first clock, information about the delays encountered with the transmission may be derived from the clock data as received back, e.g. by comparing the first data clock with the signal as twice transmitted. Thereto, in this embodiment, a control circuit or controller CON is provided to derive a synchronization from a comparison of the first data clock on the one hand and the clock data as transmitted to the second data clock (i.e. in this example the table TA) and transmitted back to the first data clock on the other hand. Adjustable (ie. variable) delay units TD are provided, which are under control of the control circuit CON. The adjustable delay units TD and the control circuit CON are comprised in synchronization circuit SYN. A first one of the delay units TD is provided in series with the transmission path from the first clock to the second clock. A second one of the delay units TD is provided in series with the transmission path from the second clock back to the first clock. In this embodiment, both delay units are provided at the side of the first clock, i.e. in this embodiment at the support structure STR. The control circuit is arranged to control the adjustable delay units TD such that a phase of the signal received at the first input thereof (namely the clock signal of the first data clock C1) equals in phase the signal received at the second input (namely the signal as transmitted forth and back and as delayed by both the delay units TD). In case of equal delay values of both adjustable delay units TD, a delay TA encountered by the wireless transmission to the second clock is compensated by the first one of the delay units TD, while the delay encountered by the transmission back to the first clock (ie. in this embodiment to the support structure STR) is compensated by the second one of the delay units TD. At the second clock (i.e. in this example at the table TA) the remaining delay caused by for example electronics, etc, may be compensated by a delay unit DLY which may for example be set to a calibrated delay value. The second clock C2may be synchronized to or derived from an output signal of the delay unit DLY.

An embodiment of the control circuit CON will now be explained with reference toFIG. 5. The clock data as received back (inFIG. 4andFIG. 5referred to as RCL) is delayed by a delay of 90 degrees phase delay. The first data clock C1and the 90 degrees phase delayed received signal are then mixed by a mixer MX. As a result, a signal component at twice the clock frequency and a substantially constant (Direct Current DC) signal is obtained. The latter depends on a phase difference between the clock C1and the received clock data RCL. This component is selected by low pass filtering using a low pass filter LPF, followed by integration by integrator INT and/or amplification by amplifier AMP so as to provide a control signal to control a delay of the adjustable delay units TD as depicted inFIG. 4, thereby being able to control the adjustable delay units td with sufficient loop gain and at a required accuracy.

The embodiments as described with reference toFIGS. 2-4provide examples of a stage apparatus to position an object, the stage apparatus including: a table to hold the object, a support structure to support the table, the table being displaceable relative to the support structure, wherein the support structure comprises one of a first data clock and a second data clock and the table comprises the other one of the first data clock and the second data clock, the stage apparatus comprising a circuit to synchronize the data clocks, the circuit including: a transmitter and receiver configured to wirelessly transmit clock signal data from the first data clock to the second data clock, and a synchronization circuit to synchronize the second data clock to the first data clock from the wirelessly transmitted clock signal data as received by the receiver. Thereby, an accurate clock timing may be enabled at the stage, while obviating a need for wired transmission of clock signal data to the stage.

The second data clock C2at the table may be applied to clock data acquisition (e.g. position measurement of the table position by position sensors such as encoders, interferometers, etc.), as well as to provide data to actuators/actuator controllers, etc.

The term data clock (also referred to as clock) may be understood as a circuit generating a repetitive signal that is intended for timing data operations, such as data acquisition, data processing, data storage, data communication, data output (e.g. to an actuator, driver etc), etc. Further, it is remarked that the term data clock may refer to the circuit that is configured to generate the repetitive signal, as well as to the repetitive signal itself.

The terms clock data and clock signal data are to be interpreted so as to include any kind of data clock related data: the repetitive clock signal itself, or any signal derived there from, related thereto, etc. In an embodiment, the clock data that is wirelessly transmitted comprises the repetitive clock signal itself (as such or modulated onto a carrier) so as to invoke no or little delays by conversion, processing etc.

The wireless transmission may include any type of wireless transmission, such as radio frequency, infrared, etc. The term circuit (circuit, synchronization circuit, etc) is to be understood as comprising any kind of electronic and/or electric circuit, including analogue and or digital electronics, discrete and/or integrated electronic and/or electric circuits, etc.

The stage as described may be applied in a lithographic apparatus and/or in other applications.