Electrostatic capacitance sensor type measurement apparatus

A measurement apparatus which measures a distance between a sensor probe and a target to be measured by using an electrostatic capacitance sensor, comprises first and second sensor probes (101, 102) which are arranged at respective predetermined gaps to the target (4), and first and second sensor amplifiers (111, 112) which are connected respectively to the first and second sensor probes, wherein when the distance between the target and the first or second sensor probe is measured, said first amplifier supplies a first current with the first sensor probe and said second amplifier supplies a second current which is different phase and/or amplitude from the first current.

FIELD OF THE INVENTION

The present invention relates to an apparatus which measures, e.g., the position and shape of a target by using an electrostatic capacitance sensor. The measurement apparatus is suitably applied to an exposure system which transfers the pattern of a master (e.g., a mask or reticle) onto a substrate (e.g., a semiconductor wafer or glass plate) or a three-dimensional object.

BACKGROUND OF THE INVENTION

One of methods of precisely measuring the position and shape of a sample (target) uses an electrostatic capacitance sensor (e.g., see Japanese Patent Laid-Open No. 11-230704). According to this method, the magnitude or change amount of an electrostatic capacitance generated between a sensor probe (electrode) and a target is detected to measure the distance between the sensor probe and the target. The electrostatic capacitance is detected as an AC impedance.

FIGS. 22A and 22Bshow the arrangement of a measurement apparatus according to related art using an electrostatic capacitance sensor. More specifically, the measurement apparatus comprises first and second electrostatic capacitance sensors (sensor probes)101and102, first and second sensor amplifiers11and12which are electrically connected to the sensors101and102via connection cables103, a controller113which receives measurement values from the first and second sensor amplifiers11and12, and an oscillator114which outputs in-phase drive currents to the first and second sensor amplifiers11and12. Weak AC currents from terminals11aand12aof the sensor amplifiers11and12are supplied from the sensor probes101and102to a target104. A voltage drop by the impedance is measured to simultaneously measure distances “gap” between the sensor probes and the target at a plurality of measurement points on the target104.

Currents flowing from the first and second sensor probes101and102to the target104flow back to terminals11band12bof the sensor amplifiers via conductors which are set to almost the same potential as the housing ground of the apparatus.

In general, an electrostatic capacitance to be measured is a small value in pF order, and is readily influenced by the stray capacitance. The potential is generally so set as to reduce the influence of the stray capacitance on packaging from a sensor amplifier to a sensor probe and packaging from a target to a ground line.

The electrostatic capacitance sensor is ideally used by coupling a target sufficiently low in impedance to ground at low impedance. For this purpose, as shown inFIGS. 22A and 22B, a chuck105which chucks the target104is generally formed from a conductor such as a metal, and is grounded. In addition, a mount (base)106which supports the chuck105is insulated.

The sensor probes101and102are held by a holding member107extending from the surface of the chuck105such that the sensor probes101and102face the surface of the target104.

In the use of a plurality of electrostatic capacitance sensors, an electrostatic field interference must be prevented by, e.g., setting the distance between sensor probes large enough. If the target has a sufficiently low internal impedance and is grounded at sufficiently low impedance, the interference between the sensors can be substantially ignored.

When the measurement target of the electrostatic capacitance sensor is a semiconductor or the like, the target has a high internal impedance. The target may not be able to be grounded at low impedance. In this case, AC currents flow from a plurality of sensor probes into the internal impedance of the target and the ground impedance which are common impedances. Voltage drops at these portions produce errors in sensors (each sensor is comprised of a sensor amplifier and sensor probe).

In the electrostatic capacitance sensor ofFIG. 23, Z3and Z4function as impedances common to a plurality of sensors. The first and second sensors interfere with each other, and a voltage drop by a sensor current makes, appearing as a measurement error.

A measurement error by the sensor drive phase and ground impedance in the measurement apparatus of related art will be explained with reference toFIGS. 24A to 24F. The drive currents of the first and second sensor probes are in phase, and almost the sum of the two currents flows as a ground current into a common impedance, generating a voltage drop. The voltage drop appears between the terminals (between the terminals11aand11band the terminals between the terminals12aand12b) of the sensor amplifiers11and12, resulting in a measurement error in each sensor.

SUMMARY OF THE INVENTION

It is an object of the present invention to suppress an interference and error between sensors caused by the electrical characteristic of a target in measuring the target by using a plurality of electrostatic capacitance sensors.

It is another object of the present invention to prevent a measurement error which is generated by a common impedance or the electrostatic field interference between sensors in a measurement apparatus having a plurality of electrostatic capacitance sensors.

To solve the above problems, according to the present invention, there is provided a measurement apparatus which measures a distance between a sensor probe and a target to be measured by using an electrostatic capacitance sensor, comprising first and second sensor probes which are arranged at respective predetermined gaps to the target, and first and second sensor amplifiers which are connected respectively to the first and second sensor probes, wherein when the distance between the target and the first or second sensor probe is measured, said first amplifier supplies a first current with the first sensor probe and said second amplifier supplies a second current which is different phase and/or amplitude from the first current.

According to the present invention, there is provided a measurement apparatus which measures a distance between a sensor probe and a target to be measured by using an electrostatic capacitance sensor, comprising first, second and third sensor probes which are arranged at respective predetermined gaps to the target and a sensor amplifier which supplies a current to the sensor probes and output a measurement result, wherein the sensor amplifier supplies a firs current to the first sensor probe, a second current to the second sensor probe and a third current to the third sensor probe and the phases of the first, second and third current are set to be different by 120°.

As described above, the present invention can suppress the interference or error between sensors caused by the electrical characteristic of a target in measuring the target by using a plurality of electrostatic capacitance sensors.

In a measurement apparatus having a plurality of electrostatic capacitance sensors, a measurement error generated by a common impedance or the electrostatic field interference between the sensors can be prevented. This leads to, for example, a small line width, high line width control precision, high throughput, and a compact low-cost exposure apparatus in semiconductor exposure/transfer. The use of a plurality of measurement sensors can increase the throughput, providing a higher-productivity apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The first embodiment in which a measurement apparatus according to the present invention is applied to measurement of the position of a semiconductor wafer will be described.

FIGS. 1A and 1Bare views showing the arrangement of a measurement apparatus according to the first embodiment of the present invention. The same reference numerals as in the arrangement shown inFIGS. 22A and 22Bdenote the same parts. A description of the same parts as in the arrangement shown inFIGS. 22A and 22Bwill be omitted.

The measurement apparatus according to the first embodiment measures the surface level and inclination of a semiconductor wafer4serving as a target vacuum-chucked onto an SiC ceramic vacuum chuck5by using a plurality of (e.g., two) first and second sensor probes101and102fixed to a holding member107.

Intervals “gap” between the first and second sensor probes101and102and the target4will be referred to as measurement gaps. The setting of the measurement gap changes depending on the type of sensor probe. In the first embodiment, the measurement gap is set to about 300 μm or less, and preferably about 200 to 300 μm.

The sensor probes101and102are cylindrical, and have a three-layered structure of a central electrode, guard electrode, and external electrode concentrically from the center when viewed from a radial section. Electrodes used for measurement are the central electrodes, and the central electrodes are connected to central electrode terminals111aand112aof sensor amplifiers111and112. A sine-wave constant-amplitude current of several ten kHz is supplied from the sensor amplifiers111and112to the central electrodes. The current flows into housing ground GND via the target4capacitively coupled to the sensor probes101and102.

The housing ground GND is connected to ground terminals111band112bof the sensor amplifiers111and112, forming a closed circuit as a whole. The sensor amplifiers111and112detect voltages between the central electrode terminals111aand112aand the ground terminals111band112bto measure the impedance of the closed circuit including the capacitive impedance of the measurement gap.

FIG. 2is a circuit diagram showing the equivalent circuit of an electrostatic sensor measurement system in the measurement apparatus according to the first embodiment.

InFIG. 2, C1represents the measurement gap between the first sensor probe101and the semiconductor wafer4. C2represents the measurement gap between the second sensor probe102and the semiconductor wafer4. Z1represents the internal impedance of the semiconductor wafer4that acts as an independent impedance component in measurement by the sensor probe101. Z2represents the internal impedance of the semiconductor wafer4that acts as an independent impedance component in measurement by the sensor probe102. Z3represents the internal impedance of the semiconductor wafer4that acts as a common impedance component in the sensor probes110and102. Z4represents the impedances of the vacuum chuck5and a mount106that act as common impedance components in the sensor probes110and102.

Letting d be the measurement gap and S be the effective facing area between the sensor probe and the target, an electrostatic capacitance C of the measurement gap is given by
C=e0·S/d
where e0is the permittivity in vacuum. The permittivity in air is assumed to be almost equal to that in vacuum.

Letting ω be the angular frequency of an AC current supplied to the sensor probe and i be the current value, a voltage value e between the central electrode terminal and the ground terminal is given by
e=i/(ω·C)

From the two equations,
e=i·d/(ω·e0·S)
d=e·ω·e0·S/i
are derived. Assuming that i, ω, and S do not change, d proportional to e is obtained.

The guard electrode prevents an electric field generated by the central electrode from spreading to the periphery. The guard electrode is connected to the guard electrode terminal of the sensor amplifier. The guard electrode terminal is driven by a low-output-impedance driver at the same voltage as e. The sensor amplifier and sensor probe are connected using a coaxial cable. The central electrode is connected to the central wire of the coaxial cable, and the guard electrode is connected to the shield wire. This connection cancels the influence of the capacitance between two connection cables103.

The first and second sensor amplifiers111and112drive the sensor probes and measure voltages. The measured voltages are A/D-converted and transmitted to a controller13. For example, the controller13processes and displays measurement values. At this time, the offset, gain, nonlinearity, and the like may be corrected in the controller13.

The vacuum chuck5is formed from SiC ceramic in order to prevent deformation of the chuck upon a temperature change. The mount106of the chuck5is formed from ceramic.

Most of the structure on the lower surface side of the target4is formed from an insulator, and the target4is hardly expected to be coupled to the ground GND.

The controller13sets in advance the measurement timing of a measurement timing generation device14. The controller13receives the measurement values of the first and sensor amplifiers111and112, and externally displays the measurement values via a display or the like.

The measurement timing generation device14outputs the drive timing signals and measurement timing signals of the sensor probes101and102to the first and second sensor amplifiers111and112. The measurement timing generation device14also outputs the measurement timing signals to the controller13to provide measurement value reception timings.

The measurement timing will be explained with reference to the timing charts ofFIGS. 3A to 3F.

In the first embodiment, timings are so set as not to simultaneously supply drive currents (weak currents for measurement) to the first and second sensor probes101and102(e.g., the current or voltage of the second sensor probe102is set to 0 in measurement by the first sensor probe101). Alternatively, a change in a current or voltage applied to the second sensor probe102is set to 0 when a drive current is supplied to the first sensor probe101to enable measurement. Measurement by each sensor probe is performed a plurality of number of times, increasing the precision by the averaging effect.

That is, a slight time margin after the drive signal of the first sensor probe101is enabled, the measurement timing signal of the first sensor probe101is enabled a plurality of number of times to perform measurement a plurality of number of times. After the lapse of a predetermined time, the drive timing signal of the first sensor probe101is disabled, and after a slight time margin, the drive timing signal of the second sensor probe102is enabled. After a slight time margin, the measurement timing signal of the second sensor probe102is enabled a plurality of number of times to perform measurement a plurality of number of times. This processing is repetitively executed until a necessary number of measurement points are obtained.

Sensor probe drive currents inFIGS. 3A to 3Fare represented as constant-amplitude AC sine-wave currents actually supplied to the sensor probes101and102. The frequency of the sine wave inFIGS. 3A to 3Fis merely schematically expressed, and the relationship between the drive timing and the measurement timing is not limited toFIGS. 3A to 3F.

The first embodiment sets sufficient time margins for the drive timing signal and measurement timing signal. If a condition that one sensor is not driven during measurement by the other sensor, the throughput can be further increased.

In a conventional measurement apparatus using a plurality of electrostatic capacitance sensors, it is difficult to realize high precision owing to the interference between the sensors. However, the first embodiment can completely eliminate the influence of the interference.

The second embodiment in which a measurement apparatus according to the present invention is applied to an X-ray exposure apparatus for transferring a mask pattern onto a wafer by step & repeat will be described.

FIG. 4is a view showing the partial arrangement of an X-ray exposure apparatus including the measurement apparatus according to the second embodiment of the present invention.FIG. 4shows a part concerning an electrostatic capacitance sensor in the overall apparatus.

The X-ray exposure apparatus according to the second embodiment is a proximity gap equal-magnification X-ray exposure apparatus using a synchrotron ring light source. In an actual use environment, the part shown inFIG. 4is incorporated in a sealed chamber, and used in a high-purity helium atmosphere at 20 kPa.

In the second embodiment, exposure is done while a mask21and wafer22are held at a very small gap of 10 μm or less. High precision is required for measuring the levels of the wafer surface and mask surface. A set gap different from an assumed one results in serious influence on an exposure result such as degradation of the line width accuracy. To realize high throughput, the wafer is exposed by step & repeat while the exposure gap is maintained. At this time, low parallelism between the mask surface and the wafer surface leads to degradation of an exposure result and damage to the membrane due to the deformation of the mask membrane.

In the second embodiment, an X-ray emitted by a synchrotron ring light source (not shown) is guided in a direction S1inFIG. 4. In synchronism with this, exposure is done while both the mask21and wafer22are held vertically.

A mask frame23is formed from SiC with a diameter of 125 mm. A 4 inch mask substrate is bonded to the mask frame23. A membrane and absorber pattern are formed on the mask substrate. The mask substrate is etched back in the exposure area.

The mask is chucked by a mask chuck24shown inFIG. 4. The mask chuck24is mounted on a mask stage25, and has the degree of freedom around the Z, θ, ωx, and ωy axes.

InFIG. 4, the wafer22is vacuum-chucked to a wafer chuck26by a wafer transport system (not shown). The wafer chuck26is formed from SiC, and has many small pins on the chuck surface. The wafer chuck26is mounted on a SiC wafer stage27. The wafer stage27is mounted on an X stage28, and further mounted on a Y stage29. The Y stage29is clamped to a base30. The base30is set on a floor32via dampers31which cut off floor vibrations. The wafer stage27is driven by a linear motor or the like, and has the degree of freedom around the X, Y, Z, θ, ωx, and ωy axes. The positions of the mask21and wafer22are measured by an alignment measurement unit (not shown).

The arrangement and measurement of the measurement apparatus according to the second embodiment will be explained.

After the wafer22is chucked, the wafer stage27is driven to measure lattice points at a pitch of 20 mm on the wafer22serving as a target to be measured, by a plurality of (e.g., two) wafer measurement electrostatic capacitance sensor probes33and34. The wafer measurement electrostatic capacitance sensor probes33and34are attached to the mask frame23via a metal member35.

The wafer measurement electrostatic capacitance sensor probes33and34are fixed to the mask frame23. The wafer stage27is moved relatively to the wafer measurement electrostatic capacitance sensor probes33and34so as to measure all measurement points. In measurement, the wafer stage27need not be stopped, and a controller which drives and controls the wafer stage27can measure a measurement point while managing the measurement timing at the coordinate position.

The metal member35which holds the wafer measurement electrostatic capacitance sensor probes33and34also functions as a facing ground plate.

A mask measurement electrostatic capacitance sensor probe36is attached to a metal member37also functioning as a facing ground plate which is attached to the wafer stage27. Only one mask measurement electrostatic capacitance sensor probe36is arranged. The mask stage25is moved relatively to the mask measurement electrostatic capacitance sensor probe36so as to measure all measurement points, and a plurality of points on the mask21serving as a target to be measured (master bearing a transfer patter) are measured.

Both the metal members35and37are connected to the ground terminals of corresponding sensor amplifiers inFIG. 5by using conductors. The metal members35and37are set near corresponding targets with an area as large as possible in design so as to obtain capacitive coupling enough for facing ground plates.

It is difficult to ground without any mechanical influence a substrate (e.g., wafer) supported by an insulator (e.g., the mask frame23, wafer stage27, or base30) as described in the second embodiment. The ground impedance readily increases, and the substrate readily receives an interference from another sensor. To prevent this, the ground plates35and36facing the targets21and22are arranged to decrease the ground impedance by capacitive coupling.

Similar to the first embodiment, the sensor probes33,34, and36are cylindrical, and have a three-layered structure of a central electrode, guard electrode, and external electrode concentrically from the center when viewed from a radial section. Electrodes used for measurement are the central electrodes. The wafer measurement sensor probes33and34are connected to central electrode terminals55aand56aof sensor amplifiers55and56shown inFIG. 5. The mask measurement sensor probe36is connected to a central electrode terminal57aof a sensor amplifier57shown inFIG. 5. A sine-wave constant-amplitude current of several ten kHz is supplied from the sensor amplifiers55to57to the central electrodes. The current flows into the metal members35and37serving as facing ground plates via the sensor probes33,34, and36and the capacitively coupled targets (wafer measurement sensor probes33and34and wafer22, or mask measurement sensor probe36and mask21).

The metal member35is connected to ground terminals55band56bof the sensor amplifiers55and56, and the metal member37is connected to a ground terminal57bof the sensor amplifier57, forming a closed circuit as a whole. The sensor amplifiers55to57detect voltages between the central electrode terminals55ato57aand the ground terminals55bto57bto measure the impedance of the closed circuit including the capacitive impedance of the measurement gap.

FIG. 6is a circuit diagram showing the equivalent circuit of an electrostatic sensor measurement system in the measurement apparatus according to the second embodiment.

InFIG. 6, Cw1represents the measurement gap between the wafer measurement sensor probe33and the wafer22. Cw2represents the measurement gap between the wafer measurement sensor probe34and the wafer22. Zw1represents the internal impedance of the wafer22that acts as an independent impedance component in measurement by the wafer measurement sensor probe33. Zw2represents the internal impedance of the wafer22that acts as an independent impedance component in measurement by the wafer measurement sensor probe34. Zw3represents the internal impedance of the wafer22that acts as a common impedance component in the wafer measurement sensor probes33and34. Zw4represents the impedances of the wafer chuck26, wafer stage27, X stage28, and Y stage29that acts as a common impedance component in the wafer measurement sensor probes33and34. Cm1represents the measurement gap between the mask measurement electrostatic capacitance sensor probe36and the mask21. Zm represents the impedances of the mask21, mask chuck24, mask stage25, and mask frame23that concern measurement by the mask measurement electrostatic capacitance sensor probe36. Z5represents the impedance of the base30that acts as a common impedance component in the wafer measurement sensor probes33and34and mask measurement electrostatic capacitance sensor probe36.

The control block of the second embodiment will be described with reference toFIG. 5.

A console51controls the sequence of the whole exposure apparatus, and provides a user interface and network interface. A stage CPU52receives a sequence command from the console, and drives and controls the wafer stage27and mask stage25. In addition, the exposure apparatus comprises an alignment unit, transport unit, and illumination unit (none of them are shown). Each unit is controlled by a corresponding CPU. A stage DSP53performs driving control and positioning control of the wafer stage27and mask stage25. The stage DSP53executes digital control using a DSP capable of high-speed calculation.

The stage DSP53outputs driving control signals for the wafer stage27and mask stage25to a stage driver58for these stages on the basis of the measurement value of a stage interferometer60that is input via a stage interferometer I/F (interface)59.

The stage DSP53also receives the sensor drive timing signals, measurement timing signals, and measurement values of the electrostatic capacitance sensor probes33,34, and36which are the main point of the present invention. This is an arrangement necessary to perform measurement corresponding to the moving speed in measurement and the position coordinates according to the present invention.

A sensor I/F54transmits the sensor drive timing signals and measurement timing signals received from the stage DSP53to the wafer measurement sensor amplifiers55and56and mask measurement sensor amplifier57. The sensor amplifiers55to57control the presence/absence of currents to be supplied to the sensor probes33,34, and36in accordance with the sensor drive timing signals. The sensor amplifiers55to57receive measurement values and output them to the sensor I/F54in accordance with the measurement timing signals.

The measurement timing will be explained with reference to the timing charts ofFIGS. 7A to 7H.

In the exposure apparatus of the second embodiment, the wafer level is measured upon loading a wafer, and the mask level is measured upon loading a mask. The wafer level and mask level are not simultaneously measured because the wafer stage position changes. The drive currents (weak currents for measurement) of the wafer measurement sensor probes33and34are set to such timings as not to flow simultaneously (e.g., in measurement by the sensor probe33, the current or voltage of the sensor probe34is set to 0). Alternatively, when the drive current is supplied to the probe33to enable measurement, a change in a current or voltage applied to the sensor probe34is set to 0.

During the wafer measurement sequence, the stage DSP53instructs the sensor I/F54to enable the wafer measurement sensor drive timing signal and disable the mask measurement sensor drive timing signal. During the mask measurement sequence, the stage DSP53instructs the sensor I/F54to disable the wafer measurement sensor drive timing signal and enable the mask measurement sensor drive timing signal. This can prevent the interference between the wafer measurement sensor probes33and34and the mask measurement sensor probe36. The wafer measurement sensor probes33and34and mask measurement sensor probe36measure different targets, and hardly share the ground impedance. However, electrostatic fields face each other, and the wafer measurement sensor probes33and34and mask measurement sensor probe36readily electrostatically interfere with each other. It is therefore very effective to prevent any interference, like the second embodiment.

The operations of the wafer measurement sensor probes33and34in the wafer measurement sequence will be explained.

The stage DSP53designates not to simultaneously enable the sensor drive timing signals of the wafer measurement sensor probes33and34. This can prevent the interference between the sensors. Since these two sensors measure the same target, the electrostatic field interference and ground impedance interference readily occur. Hence, it is very effective to prevent any interference, like the second embodiment.

A predetermined time delay after the drive signal of the wafer measurement sensor33is enabled, the measurement timing signal of the wafer measurement sensor33is enabled a plurality of number of times. The predetermined time delay is set to ensure a time till stable measurement via a transient stage after supply of an AC current to the sensor probe starts. Measurement is done a plurality of number of times in order to increase the precision by the averaging effect.FIGS. 7A to 7Hmerely schematically express the drive currents of the sensor probes for descriptive convenience, and the relationship between the drive timing and the measurement timing is not limited toFIGS. 7A to 7H.

As a method of further increasing the measurement throughput in the second embodiment, the sensor drive timing signals of the wafer measurement sensor probes33and34may be enabled early. For example, the drive timing signal of the wafer measurement sensor probe34can be enabled immediately after the final measurement in S701ends. At this time, the drive timing signal of the wafer measurement sensor probe33is disabled by the time when the drive timing signal does not influence the first measurement in S703.

Control of synchronizing the wafer measurement sensor probes33and34and stage movement in the wafer measurement sequence will be explained.

The stage DSP53refers to the coordinate position of the wafer stage27in real time. The coordinate position of the wafer stage27and measurement values by the sensor probes can be associated with each other in consideration of a time delay till the time when the measurement timing signals of the sensor probes33and34are output or till actual measurement.

After measurement, the stage DSP53creates a table for the coordinate position of the wafer stage and the measurement values of the sensor probes, and transfers the table to the stage CPU52. The stage CPU52determines measurement data of a lattice point on the wafer by calculation from the table. The necessary interval of the lattice point is determined from the characteristics of the exposure apparatus, mask, and wafer. The lattice point interval in the second embodiment is, e.g., about 20 mm.

Measurement operation of the mask measurement sensor probe will be explained.

The mask stage25of the second embodiment does not have an X-Y stroke as large as that of the wafer stage27. The mask measurement sensor probe36is moved relatively to the mask21by the wafer stage27, or both the mask stage25and wafer stage27are relatively moved to measure a plurality of points on the mask21.

The mask21is exchanged not so frequently, compared to exchange of the wafer22. Even if exchange of the mask takes a long time, this hardly influences the throughput of the exposure apparatus. In the second embodiment, four points on the mask21are measured while the wafer stage27is stopped. The stage DSP53creates a table which associates the coordinate position of the wafer stage in measurement and the mask measurement value, and transfers the table to the stage CPU52. The stage CPU52obtains the mask level and inclination by calculation from the table.

The Z, ωx, and ωy coordinates of the wafer stage in wafer exposure are determined on the basis of the obtained measurement data at the lattice point on the wafer and the mask level and inclination.

The second embodiment uses two sensors for wafer measurement and one sensor for mask measurement. However, the present invention is not limited to these numbers in terms of the gist of the present invention (for example, the present invention can also be applied to an arrangement inFIG. 11to be described later).

According to the second embodiment, a system which executes measurement by relatively moving a target and electrostatic capacitance sensor can efficiently perform measurement in accordance with the position coordinates and/or moving speed. This results in a small line width, high line width control precision, high throughput, and a compact low-cost exposure apparatus in semiconductor exposure/transfer. The use of a plurality of measurement sensors can increase the throughput, providing a higher-productivity apparatus.

A measurement apparatus according to the third embodiment of the present invention will be described with reference toFIGS. 8A and 8B.FIGS. 8A and 8Bare views showing the arrangement of the measurement apparatus according to the third embodiment.FIG. 8Ais a perspective view showing the whole arrangement, andFIG. 8Bis a side view showing the main part. The same reference numerals as in the arrangement shown inFIGS. 1A and 1Bdenote the same parts. A description of the same parts as those in the arrangement shown inFIGS. 1A and 1Bwill be omitted.

In the third embodiment, a chuck5is set on a metal base17, and the metal base17is grounded.

A target4is grounded by capacitive coupling of a capacitance formed by sandwiching the chuck5between the target4and the metal base17. This arrangement is so designed as to satisfy the measurement precision in the use of only one sensor. However, the capacitive coupling portion exists as an impedance common to first and second sensor probes101and102.

InFIGS. 8A and 8B, a controller13sets the drive phase of each sensor in a phase control device18in advance. The controller13receives measurement values from first and second sensor amplifiers111and112, and externally displays the measurement values.

The phase control device18outputs sensor drive timing signals and sensor measurement timing signals to the first and second sensor amplifiers111and112. The sensor drive timing signal is 2 kHz. In the third embodiment, the sensor measurement timing signals of the first and second sensors are identical. The phase control device18also outputs the sensor measurement timing signals to the controller13to provide measurement value reception timings.

FIG. 9is a circuit diagram showing the equivalent circuit of an electrostatic sensor measurement system in the measurement apparatus according to the third embodiment. The feature of the third embodiment is to arrange a means for controlling the sensor drive phase for the first and second sensor amplifiers111and112, compared to the related art.

The sensor drive phase and measurement precision in the third embodiment will be explained with reference toFIGS. 10A to 10E.FIGS. 10A to 10Eare timing charts showing the drive current, ground current, and sensor measurement value of the sensor probe in the measurement apparatus according to the third embodiment.

In the third embodiment, the phase difference between the drive currents (weak currents for measurement) of the first and second sensors is set to 180°. This phase difference cancels currents flowing through a common impedance. The ground current inFIGS. 10A to 10Eis not completely 0. This is a residue generated because the ground currents of the first and second sensors do not completely coincide with each other. A measurement error whose value corresponds to the residue is generated, but the error can be greatly reduced from that of related art (seeFIGS. 24A to 24F).

The phase difference between sensors that is set by the controller13is not limited to 180°, and can be arbitrarily set. The phase difference can be set to one which maximizes the measurement precision. For example, attention can be given to the repetitive reproducibility of measurement. In this case, data is acquired for a set phase, and the controller13determines an optimal phase.

As another method, when the interference between sensors cannot be satisfactorily adjusted by only the phase, the current values of the sensors can be slightly increased/decreased to more accurately cancel the ground current. As still another method, not the phase but the current amplitude value may be changed between sensors to cancel the ground current.

In the third embodiment, the two, first and second sensors measure the same target. Even when sensors which measure different targets interfere with each other, the measurement precision can be increased by the same means as that of the third embodiment.

In a conventional measurement apparatus using a plurality of electrostatic capacitance sensors, it is difficult to realize high precision owing to the interference between the sensors. As described above, however, the third embodiment can reduce the influence of the interference.

An X-ray stepper which transfers a mask pattern to a wafer by step & repeat will be described as the fourth embodiment of the present invention.

FIG. 11is a view showing the partial arrangement of an X-ray exposure apparatus including a measurement apparatus according to the fourth embodiment of the present invention. The same reference numerals as in the arrangement shown inFIG. 4denote the same parts. A description of the same parts as in the arrangement shown inFIG. 4will be omitted.

As shown inFIG. 11, a circular wafer32having a diameter of 200 mm is a target in the fourth embodiment. Ten wafer measurement electrostatic capacitance sensor probes43are arranged in the Y direction. A wafer stage27is driven in the X direction so as to measure all measurement points serving as lattice points, and the measurement points are measured. The Y coordinate in measurement is a predetermined one. In measurement, the wafer stage27need not be stopped, and the controller of the wafer stage27can measure a measurement point while managing the measurement timing at the coordinate position and driving the wafer stage27.

The control block of the fourth embodiment will be described with reference toFIG. 12.FIG. 12is a block diagram showing the X-ray exposure apparatus according to the fourth embodiment. The same reference numerals as in the arrangement shown inFIG. 5denote the same parts. A description of the same parts as in the arrangement shown inFIG. 5will be omitted.

A stage DSP53receives the sensor drive phase instruction, measurement timing instruction, and measurement value of an electrostatic capacitance sensor as the main point of the fourth embodiment. A sensor I/F54outputs drive signals to first to 10th wafer electrostatic sensor amplifiers157ato157jand a mask electrostatic sensor amplifier158in accordance with a sensor drive phase instruction received from the stage DSP53. The sensor I/F54transmits measurement timing instructions to the electrostatic sensor amplifiers157ato157jand158. The electrostatic sensor amplifiers157ato157jand158control supply currents to first to 10th wafer sensor probes159ato159jand a mask sensor probe160in accordance with sensor drive signals. The electrostatic sensor amplifiers157ato157jand158receive measurement values and output them to the sensor I/F54in accordance with sensor measurement timing signals.

FIG. 13is a circuit diagram showing the equivalent circuit of an electrostatic sensor measurement system according to the fourth embodiment. Reference numerals601to610denote (10) sensor amplifiers corresponding to the first to 10th wafer measurement sensors. Reference numeral611denotes a sensor amplifier for the mask measurement sensor. Cw1to Cw10represent the electrostatic capacitances of measurement gaps corresponding to the first to 10th wafer measurement sensors. Cm represents the electrostatic capacitance of the measurement gap for the mask measurement sensor. Of impedances inside the wafer, Zw1to Zw10for the respective wafer sensors are independent terms, and Zw11is a common term. Zw12is a term common to the respective wafer sensors outside the wafer. The impedances of the wafer chuck, wafer stage, and anther capacitive coupling portion correspond to Zw12. Zm is an independent term for the mask sensor, and Z13is a term common to all the sensors. Z13is a substantially ignorable value. The most influential term is Zw12. Owing to Zw12, the first to 10th wafer sensors readily interfere with each other.

FIGS. 14A to 14Fand15A to15G show the relationship between the stage position and measurement.

The measurement phase relationship will be explained with reference toFIGS. 16A to 16J,17A to17F,18A to18E,19A to19J,20A to20F, and21A to21E.

FIGS. 16A to 16Jshow drive currents when all the sensors are used in the same phase in the arrangement of the fourth embodiment, similar to the related art. As a result of measurement in this case, the interference between the sensors appears by a change in ground current depending on the number of sensors facing the wafer, as shown inFIGS. 17A to 17Fand18A to18E.

When the sensors are driven in phases shown inFIGS. 19A to 19Jin the arrangement of the fourth embodiment, the ground current can always be canceled. Two sensors arranged symmetrical about a line parallel to the X-axis passing through the wafer center are paired. Sensor drive current phases shown inFIGS. 19A to 19Jare set opposite between the currents of each pair. This makes the ground current almost constant regardless of the number of sensors facing the wafer.FIGS. 20A to 20Fand21A to21E show measurement results in this case. The cause of generating a slight error in the measurement value inFIGS. 20A to 20Fand21A to21E is that the sensor currents of each pair are not completely canceled. This is because sensor current amplitudes do not coincide with each other and the phase difference cannot be completely set to 180°. These causes are mounting problems, and the error can be further reduced.

In the fourth embodiment, the fifth and sixth sensors having the largest measurement length are most readily influenced by the remaining sensors. When the remaining sensors pass over the wafer boundary, measurement values may be suddenly disturbed. To reduce such measurement error which is hardly corrected, the stage DSP53inFIG. 12is effectively equipped with the following phase setting means. That is, attention is given to the measurement value of a sensor (to be referred to as a sensor A) which suffers the most serious measurement error, and a sensor whose interference causes the above-mentioned sudden disturbance is estimated. More specifically, the disturbance is estimated to be generated under the influence of a sensor (to be referred to as a sensor B) which has passed over the wafer boundary at stage coordinates or time at which the measurement value has disturbed. The phase of the sensor B is slightly changed to perform measurement again, and a condition under which the measurement result of the sensor A is improved is determined. If another sensor suffering a measurement error exists under this condition, conditions are similarly searched for one under which all sensor precisions satisfy the requirement.

In the fourth embodiment, the sensor is fixed, and the wafer stage is driven to measure each point on the wafer. From the gist of the present invention, the same effects can also be achieved even if the sensor is mounted on a movable mechanism, measurement is done while changing the relative positions by moving the sensor or both the sensor and wafer, and points on the wafer are measured.

In the fourth embodiment, the number of sensors which simultaneously pass over the wafer boundary is two. When, for example, three sensors simultaneously pass over the wafer boundary, a phase difference of 120° is effective. The phases and/or current amplitude values of AC current signals supplied to a plurality of sensor probes simultaneously positioned at the target boundary are preferably so determined as to, when a plurality of sensor probes pass over the target boundary, minimize changes in the measurement values of the remaining sensors.

The controller in the fourth embodiment can determine the phases or/and current amplitude values of AC current signals supplied to the respective sensor probes in accordance with the layout of the sensor probes, the target shape, the position coordinates of the target stage or/and probe stage.

As described above, according to the fourth embodiment of the present invention, a system which executes measurement by relatively moving a target and electrostatic capacitance sensor can efficiently perform measurement in accordance with the position coordinates and/or moving speed.

The measurement apparatus according to each of the above embodiments can be adopted as a device manufacturing apparatus such as a semiconductor manufacturing apparatus or exposure apparatus by using a semiconductor wafer or transfer master as a target to be measured.

Accordingly, since the functions of the present invention are implemented by computer, the program code itself installed in the computer also implements the present invention. In other words, the claims of the present invention also cover a computer program for the purpose of implementing the functions of the present invention.

In this case, so long as the system or apparatus has the functions of the program, the program may be executed in any form, e.g., as object code, a program executed by an interpreter, or scrip data supplied to an operating system.