KR20230109640A - Mirror spot position calibration method, lithographic apparatus, and device manufacturing method - Google Patents

Abstract

A method of calibrating the position of a spot on a mirror of an interferometry system comprising at least two pairs of interferometry systems to provide a redundant measurement of the rotational position of an object about an axis of rotation comprising: a. rotating the object; b. measuring a change in a rotational position of the object about a rotational axis using each of the at least two pairs of interferometers; c. In the change in rotational position measured by one of the at least two pairs of interferometers, the deviation compared to the change in rotational position measured by the other pair of the at least two pairs of interferometers or two or more pairs of interferometry systems. determining the deviation compared to the average change in rotational position measured by and d. and obtaining information about a spot position on the mirror of the one pair of the at least two pairs of interferometers, based on the determined deviation.

Description

Mirror spot position calibration method, lithographic apparatus, and device manufacturing method

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims priority to EP Application No. 20209976.8, filed on November 26, 2020, the entire contents of which are incorporated herein by reference.

The present invention relates to a method for calibrating the position of a spot on a mirror of an interferometry system. The present invention also relates to a lithographic apparatus and a device manufacturing method.

A lithographic apparatus is a machine configured to apply a desired pattern to a substrate. A lithographic apparatus may be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus projects, for example, a pattern (also called a "design layout" or "design") of a patterning device (eg a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate (eg a wafer). can make it

As semiconductor manufacturing processes continue to evolve, the amount of circuit elements such as transistors per device continues to increase over several decades following a trend commonly referred to as "Moore's Law", while the dimensions of functional elements has continued to decrease. To ensure that Moore's Law continues, the semiconductor industry is seeking technologies that enable the creation of increasingly smaller features. To project a pattern onto a substrate, a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features patterned on the substrate. Common wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm and 13.5 nm. A lithographic apparatus using extreme ultraviolet (EUV) radiation having a wavelength in the range of 4 nm to 20 nm, for example 6.7 nm or 13.5 nm, is a lithographic apparatus using electromagnetic radiation having a wavelength of, for example, 193 nm. It can be used to form smaller features on a substrate.

Typically, a lithographic apparatus includes a positioning system for positioning an object, wherein an interferometry system configured to measure the object's position is used. In such an interferometry system, one or more light beams are directed to a mirror on an object to determine the optical path length difference of the one or more light beams compared to a reference optical path length. The position of an interferometry light beam incident on a mirror-like surface is indicated by a spot of light on that surface. In order to increase the optical path length difference caused by the motion of the object, the light beam may be directed towards the mirror and reflected more than once. Examples are a so-called two-pass interferometry system in which a light beam is directed twice towards the object so that two spots can be distinguished on each mirror, and a light beam is directed four times towards the object so that two spots can be distinguished on the mirror. are 4-pass interferometers directed at

Mirrors on objects generally do not have perfectly flat mirror surfaces and/or do not extend perfectly in the intended direction. For applications where accurate measurements of the object's position are required, imperfect mirrors may prevent making such accurate measurements, or may appear to be a disturbance to each of the individual position signals. Therefore, it may be desirable to calibrate the mirror and use the calibration, eg in the form of a mirror map, to compensate for the position signal for the imperfect mirror.

When compensating the position signal for an imperfect mirror, this compensation depends on the position of the light beam on the mirror, ie the spot position. Prior art compensation techniques use the intended spot location and ignore the spot location error.

In view of the foregoing, it is an object of the present invention to provide a method for compensating the position of a spot on a mirror of an interferometry system.

According to one embodiment of the present invention, a method for calibrating the position of a spot on a mirror of an interferometry system comprising at least two pairs of interferometers to provide a redundant measurement of the rotational position of an object about an axis of rotation. As,

a. rotating the object;

b. measuring a change in a rotational position of the object around the rotational axis using each of the at least two pairs of interferometers;

c. In the change in rotational position measured by one of the at least two pairs of interferometers, the deviation compared to the change in rotational position measured by the other pair of the at least two pairs of interferometers or two or more pairs of interferometry systems. determining the deviation compared to the average change in rotational position measured by and

d. Based on the determined deviation, acquiring information about a spot position on the mirror of the one pair of the at least two pairs of interferometers.

A method for calibrating the position of a mirror spot is provided.

According to another embodiment of the present invention, a lithographic apparatus comprising:

- a positioned object;

- an actuator system to position the object;

- a measurement system comprising the interferometry system, the interferometry system comprising at least two pairs of interferometry systems for providing redundant measurements of the rotational position of the object about a rotation axis; and

- a control system for driving the actuator system based on the output of the measurement system;

including,

A lithographic apparatus is provided, wherein the control system is configured to perform the method according to the present invention.

According to another embodiment of the present invention, a device manufacturing method in which a lithographic apparatus according to the present invention is used is provided.

Embodiments of the present invention will now be described only in an illustrative manner with reference to the accompanying schematic drawings:
- Figure 1 shows a schematic overview of a lithographic apparatus;
- Figure 2 shows a detailed view of a part of the lithographic apparatus of Figure 1;
- Figure 3 schematically depicts a position control system;
- Figure 4 schematically shows a top view of an interferometry system;
- Fig. 5 schematically shows the position of a spot on a mirror of the interferometry system of Fig. 4;
- Fig. 6 schematically shows a side view of the object of Fig. 4 after rotation of the object around the Y-axis;
- Fig. 7a schematically shows a simplified top view of the interferometry system of Fig. 4 in a first rotational position about an axis parallel to the Z-axis; and
- Fig. 7b schematically shows a simplified top view of the interferometry system of Fig. 4 in a second rotational position about an axis parallel to the Z-axis;

As used herein, the terms “radiation” and “beam” refer to ultraviolet radiation (e.g. radiation having a wavelength of 365, 248, 193, 157 or 126 nm) and EUV (e.g. wavelengths in the range of about 5-100 nm). It is used to cover all types of electromagnetic radiation including extreme ultraviolet radiation).

The terms "reticle", "mask" or "patterning device", when employed herein, are general patterning devices that can be used to impart an incoming beam of radiation with a patterned cross-section corresponding to a pattern to be created in a target portion of a substrate. It can be broadly interpreted as referring to a device. The term "light valve" may also be used in this context. Besides traditional masks (transmissive or reflective; binary, phase-shift, hybrid, etc.), examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays.

1 schematically depicts a lithographic apparatus LA. Lithographic apparatus LA comprises an illumination system (also called illuminator IL) configured to condition a radiation beam B (eg UV radiation or DUV radiation or EUV radiation), a patterning device (eg a mask) A mask (e.g., a mask table) (MT) connected to a first positioner (PM) configured to support the (MA) and configured to precisely position the patterning device (MA) according to certain parameters, a substrate ( A substrate support (e.g., wafer table) (WT) and patterning device (MA) configured to project the pattern imparted to the radiation beam (B) onto a target portion (C) (e.g. comprising one or more dies) of a substrate (W). and a projection system (eg, a refractive projection lens system) PS.

In operation, illumination system IL receives a radiation beam from radiation source SO via beam delivery system BD. The illumination system IL includes various types of optical components for directing, shaping, or controlling radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic and/or other types of optical components, and/or or any combination thereof. An illuminator IL may be used to steer the radiation beam B to have a desired spatial and angular intensity distribution in its cross section on the plane of the patterning device MA.

As used herein, the term "projection system (PS)" is suitable for the exposure radiation being used or other factors such as the use of an immersion liquid or the use of a vacuum. , refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic, and/or electrostatic optical systems, and/or any combination thereof. should be interpreted broadly to include All uses of the term “projection lens” herein may be considered synonymous with the more general term “projection system (PS)”.

The lithographic apparatus LA may be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, such as water, to fill a space between the projection system PS and the substrate W, which is immersion lithography. Also called More information on the immersion technique is provided in US6952253, incorporated herein by reference.

The lithographic apparatus LA may also be of the type having two or more substrate supports WT (also called "dual stage"). In such "multiple stage" machines, the substrate supports WT may be used in parallel, and/or steps preparing the substrate W for subsequent exposure may be located on one of the substrate supports WT, while In this case, another substrate W on another substrate support WT is being used to expose a pattern on the other substrate W.

In addition to the substrate support WT, the lithographic apparatus LA may include a measurement stage. The measuring stage is configured to hold the sensor and/or cleaning device. The sensor may be configured to measure a property of the projection system PS or a property of the radiation beam B. The measuring stage can hold multiple sensors. The cleaning device may be configured to clean a portion of the lithographic apparatus, for example a portion of the projection system PS or a portion of a system providing an immersion liquid. The measuring stage is movable under the projection system PS when the substrate support WT moves away from the projection system PS.

In operation, the radiation beam B is incident on a patterning device, for example a mask MA held on a support structure MT, and is guided by a pattern (design layout) on the patterning device MA. patterned. Traversing the patterning device MA, the radiation beam B passes through a projection system PS that focuses the beam onto a target portion C of the substrate W. With the help of the second positioner PW and the position measurement system IF, for example to position the different target parts C in the path of the radiation beam B to a focused and aligned position, The substrate support WT can be accurately moved. Similarly, the first positioning device PM and possibly another position sensor (not explicitly depicted in FIG. 1 ) is used to accurately position the patterning device MA with respect to the path of the radiation beam B. can be used for Patterning device MA and substrate W may be aligned using mask alignment marks M1 and M2 and substrate alignment marks P1 and P2. Although the substrate alignment marks P1 and P2 as shown occupy dedicated target portions, they may be located in the space between the target portions. The substrate alignment marks P1 and P2 are known as scribe lane alignment marks when positioned between the target portions C.

To clarify the present invention, a Cartesian coordinate system is used. A Cartesian coordinate system has three axes: x-axis, y-axis and z-axis. Each of the three axes is orthogonal to the other two axes. Rotation around the x-axis is called Rx-rotation. Rotation around the y-axis is called Ry-rotation. Rotation around the z-axis is called Rz-rotation. The x-axis and y-axis define the horizontal plane while the z-axis is the vertical direction. The Cartesian coordinate system is not intended to limit the present invention and is used only for clarity. Alternatively, other coordinate systems, such as cylindrical coordinate systems, may be used to clarify the present invention. The orientation of the Cartesian coordinate system can be different, for example the z-axis can have a component parallel to the horizontal plane.

FIG. 2 shows a detailed view of a portion of the lithographic apparatus LA of FIG. 1 . The lithographic apparatus LA may be provided with a base frame BF, a balance mass (BM), a metrology frame MF and a vibration isolation system IS. Measurement frame MF supports projection system PS. Additionally, the metrology frame MF may support a part of the positioning system PMS. The measurement frame MF is supported by the base frame BF via the vibration isolation system IS. The vibration isolation system IS is arranged to prevent or reduce vibration propagating from the base frame BF to the metrology frame MF.

The second positioner PW is arranged to accelerate the substrate support WT by providing a driving force between the substrate support WT and the balance mass BM. The driving force accelerates the substrate support WT in a desired direction. Since momentum is conserved, a driving force is also applied to the equilibrium mass BM of equal magnitude but in a direction opposite to the desired one. Typically, the mass of the equilibrium body BM is substantially greater than the mass of the moving part of the second positioner PW and the substrate support WT.

In one embodiment, the second positioner (PW) is supported by the equilibrium mass (BM). For example, the second positioner PW includes a planar motor for levitating the substrate support WT above the balance mass BM. In another embodiment, the second positioner PW is supported by the base frame BF. For example, the second positioner PW includes a linear motor, and the second positioner PW uses a bearing, such as a gas bearing, for lifting the substrate support WT above the base frame BF. include

The position measurement system (PMS) may include any type of sensor suitable for determining the position of the substrate support (WT). The position measurement system PMS may include any type of sensor suitable for determining the position of the mask support MT. The sensor may be an optical sensor such as an interferometer or encoder. A position measurement system (PMS) may include a combined system of an interferometer and an encoder. The sensor may be another type of sensor, such as a magnetic sensor, a capacitive sensor or an inductive sensor. The position measurement system PMS can determine the position relative to a reference, eg metrology frame MF or projection system PS. The position measurement system (PMS) may determine the position of the substrate table (WT) and/or mask support (MT) by measuring position or by measuring a time derivative of position, such as velocity or acceleration.

A position measurement system (PMS) may include an encoder system. An encoder system is known, for example, from United States patent application US 2007/0058173A1, filed September 7, 2006 and incorporated herein by reference. The encoder system includes an encoder head, a grating and a sensor. An encoder system can receive a primary radiation beam and a secondary radiation beam. Both the primary radiation beam and the secondary radiation beam are derived from the same radiation beam, ie the original radiation beam. At least one of the primary radiation beam and the secondary radiation beam is produced by diffracting the original radiation beam with a grating. If both the primary radiation beam and the secondary radiation beam are generated by diffracting the original radiation beam into a grating, the primary radiation beam needs to have a different diffraction order than the secondary radiation beam. The different diffraction orders are, for example, +1st, -1st, +2nd and -2nd order. An encoder system optically combines the primary and secondary radiation beams to produce a combined radiation beam. A sensor in the encoder head determines the phase or phase difference of the combined radiation beam. The sensor generates a signal based on phase or phase difference. This signal represents the position of the encoder head relative to the grating. One of the encoder head and grating may be disposed on the substrate structure WT. The other one of the encoder head and grating may be placed on the measurement frame (MF) or the base frame (BF). For example, a plurality of encoder heads are disposed on the metrology frame MF while a grating is disposed on the top surface of the substrate support WT. In another example, the grating is disposed on the bottom surface of the substrate support WT, and the encoder head is disposed below the substrate support WT.

A positioning system (PMS) may include an interferometry system. Interferometry systems are known, for example, from US patent US 6,020,964, filed July 13, 1998, incorporated herein by reference. An interferometry system may include beam splitters, mirrors, reference mirrors and sensors. A beam of radiation is split into a reference beam and a measurement beam by a beam splitter. The measuring beam is propagated to a mirror and is reflected by the mirror back to the beam splitter. The reference beam propagates to the reference mirror and is reflected back to the beam splitter by the reference mirror. In the beam splitter, the measurement and reference beams are combined to form a combined radiation beam. The combined radiation beam is incident on the sensor. A sensor determines the phase or frequency of the combined radiation beam. Sensors generate signals based on phase or frequency. The signal represents the displacement of the mirror. In one embodiment, the mirror is connected to the substrate support WT. The reference mirror may be connected to the measurement frame MF. In one embodiment, the measurement and reference beams are combined into a combined radiation beam by an additional optical component instead of a beam splitter.

The first position setter (PM) may include a long-stroke module and a short-stroke module. The short-stroke module is arranged to move the mask support MT relative to the long-stroke module over a small movement range with high accuracy. The long-stroke module is arranged to move the short-stroke module relative to the projection system PS over a large range of motion with low accuracy. Combining the long-stroke module and the short-stroke module, the first positioner PM can move the mask support MT relative to the projection system PS over a large movement range with high accuracy. Similarly, the second positioner PW may include a long-stroke module and a short-stroke module. The short-stroke module is arranged to move the mask support WT relative to the long-stroke module over a small range of motion with high accuracy. The long-stroke module is arranged to move the short-stroke module relative to the projection system PS over a large range of motion with low precision. Combining the long-stroke module and the short-stroke module, the second positioner PW can move the substrate support WT relative to the projection system PS over a large range of motion with high accuracy.

Actuators for individually moving the mask supporter MT and the substrate supporter WT are provided in each of the first positioner PM and the second positioner PW. The actuator may be a linear actuator for providing a driving force along a single axis, for example the y-axis. Multiple linear actuators may be applied to provide driving forces along multiple axes. The actuators may be planar actuators for providing driving forces along multiple axes. For example, a planar actuator may be arranged to move the substrate support WT in six degrees of freedom. The actuator may be an electromagnetic actuator comprising at least one coil and at least one magnet. The actuator is arranged to move the at least one coil relative to the at least one magnet by applying a current to the at least one coil. The actuator may be a moving-magnet type actuator, which has at least one magnet coupled to a substrate support (WT) and a mask support (MT), respectively. The actuator may be a moving-coil type actuator, which has at least one coil coupled to a substrate support (WT) and a mask support (MT), respectively. The actuator may be a voice-coil actuator, a reluctance actuator, a Lorentz-actuator or a piezo-actuator, or any other suitable actuator.

The lithographic apparatus LA includes a position control system PCS schematically shown in FIG. 3 . The position control system (PCS) includes a setpoint generator (SP), a feedforward controller (FF) and a feedback controller (FB). The position control system (PCS) provides a drive signal to the actuator (ACT). The actuator ACT may be an actuator of the first position setter PM or the second position setter PW. The actuator ACT drives the plant P, which may include a substrate support WT or a mask support MT. The output of the plant P is a position quantity such as position or velocity or acceleration. The position amount is measured with a position measurement system (PMS). The position measurement system (PMS) generates a signal that is a position signal representing the position amount of the plant (P). The setpoint generator (SP) generates a signal that is a reference signal representing the desired position amount of the plant (P). For example, the reference signal represents the desired trajectory of the substrate support WT. The difference between the reference signal and the position signal forms the input to the feedback controller FB. Based on these inputs, the feedback controller FB provides at least part of the drive signal for the actuator ACT. The reference signal may form an input for a feed forward controller (FF). Based on these inputs, the feedforward controller FF provides at least part of the drive signal for the actuator ACT. Feedforward (FF) may use information about the dynamic characteristics of the plant (P), such as mass, stiffness, resonance mode and natural frequency.

Figure 4 schematically shows a practical embodiment of an interferometry system, eg part of a position measuring system (PMS), configured to measure the position of an object OB, which is eg a substrate support (WT). ) or a mask support (MT).

The interferometry system includes a plurality of pairs of interferometers, among which three pairs of interferometry systems are shown in the top view of FIG. 4 . Although only these three pairs of interferometers will be used herein, it will be clear that other interferometry systems may be provided even though they are omitted for clarity.

The first pair of interferometers includes a first interferometer (IF1) and a second interferometer (IF2). The first interferometry system (IF1) directs the first measuring beam (MB1) onto the first mirror (FM) to provide a first position signal (PS1) representing the position of the object (OB) in the X-direction. are placed The second interferometer IF2 directs the second measuring beam MB2 onto the first mirror FM to provide a second position signal PS2 representing the position of the object OB in the X-direction. are placed

The second pair of interferometers includes a third interferometer (IF3) and a fourth interferometer (IF4). The third interferometer IF3 is arranged to provide a third position signal PS3 indicative of the position of the object OB in the Y-direction by directing the third measuring beam MB3 onto the second mirror SM. do. The fourth interferometry system IF4 is arranged to provide a fourth position signal PS4 indicative of the position of the object OB in the Y-direction by directing the fourth measuring beam MB4 onto the second mirror SM. do.

The third pair of interferometers includes a fifth interferometer (IF5) and a sixth interferometer (IF6). The fifth interferometer IF5 is arranged to provide a fifth position signal PS5 indicative of the position of the object OB in the X-direction by directing the fifth measuring beam MB5 onto the third mirror TM. do. The sixth interferometer IF6 is arranged to provide a sixth position signal PS6 indicative of the position of the object OB in the X-direction by directing the sixth measuring beam MB6 onto the third mirror TM. do.

The first mirror FM and the third mirror TM are disposed on both sides of the object OB and extend mainly in the Y-direction. The second mirror SM is disposed on one side of the object OB and mainly extends in the X-direction.

As mentioned above, although not shown in this Figure 4, the interferometry system is arranged to provide a position signal indicative of the position of the object OB in the Z-direction, the Z-direction being the X-direction and the Y-direction. It is perpendicular to both directions and is thus perpendicular to the plane of FIG. 4 by directing the measuring beam onto the mirror.

The interferometry may be a single-pass interferometry in which each measurement beam is directed only to the corresponding mirror and reflected back to interfere with the reference beam. However, as in this example, one or more, but preferably all interferometers may be multi-pass interferometers in which each measuring beam is directed more than once to a corresponding mirror. An example of one mirror is shown schematically in FIG. 5 .

Although FIG. 5 schematically shows the third mirror TM, the same content may be applied to the first mirror and/or the second mirror FM and SM with only necessary portions slightly modified. In this example, the fifth measuring beam MB5 is initially directed towards the third mirror TM by the fifth interferometer IF5 to determine the fifth interference from the third mirror TM at spot location SP5a. It is reflected back toward the measuring system IF5. The fifth interferometer IF5 directs the fifth measuring beam MB5 secondly towards the third mirror TM so that the fifth interferometer IF5 is measured from the third mirror TM at the spot position SP5b. It is configured so that it is reflected back towards.

Furthermore, the sixth measuring beam MB6 is initially directed towards the third mirror TM by the sixth interferometer IF6, so that the sixth interferometer is measured from the third mirror TM at spot position SP6a. (IF6). The sixth interferometer IF6 directs the sixth measuring beam MB6 secondly towards the third mirror TM so that the sixth interferometer IF6 is measured from the third mirror TM at the spot position SP6b. It is configured so that it is reflected back towards.

Actual spot locations are indicated using solid circles. Corresponding intended spot locations where each spot was designed to be are indicated using dotted circles. In the prior art, the spots are assumed to be at the intended location, but in practice there is an error in spot location compared to the intended spot location, due to, for example, misalignment introduced during assembly.

In this example, spot location SP5a has a spot location error only in the Y-direction, while spot location SP5b has a spot location error in both the Y-direction and the Z-direction. Further, the spot position SP6a has a spot position error only in the Z-direction, whereas the spot position SP6b has a spot position error in both the Y-direction and the Z-direction.

Each of the beam portions directed to and reflected from the third mirror TM has a contribution to the position signal of the corresponding interferometry system. However, since only the total contribution is determined within the interferometry system, it is impossible to determine which portion can contribute to which beam portion. The same applies to spot position error. Each spot location error has a contribution to the total error, but it has to determine that a portion of the error comes from a particular spot location error. As a result, multi-pass interferometers can be simplified with a single beam having an average spot location, which is the geometric center of the spot location. Except for FIG. 5, this simplified representation is used in FIGS. 1, 4, 6, 7a and 7b. In FIG. 5 this is indicated using the intended spot center (IC5 and IC6), which is the average spot location of each of the dotted line spot locations, and the actual spot center (AC5 and AC6), which are the average spot location of each of the solid line spot locations. Note that the intended spot centers (IC5 and IC6) are at the same level in the Z-direction, although this is not necessary for the present invention. Further, although the simplified representation of the multi-pass interferometry here relates to the multi-beam reflection of the mirror per interferometer, it also illustrates that the present invention can be readily applied to single-pass interferometry systems as well. .

Referring again to FIG. 4 , the first, second and third pairs of interferometers are all centered on an axis of rotation parallel to the Z-direction perpendicular to the X- and Y-directions, here referred to as Rz. OB) orientation can be measured. Therefore, two of the three Rz measurements are redundant, which can be used to obtain information of the actual spot center (AC5 and AC6) center as described in more detail below.

6 depicts a side view of the object OB along the Z-X plane. As indicated above, for brevity, the measuring beam is shown as a single beam impinging on each mirror at the actual spot center of each interferometry's spot location on object OB. As can be seen in FIG. 5 , the actual spot center AC5 is at a higher level in the Z-direction than the actual spot center AC6 , which is the fifth measuring beam above the sixth measuring beam MB6 in FIG. 6 . (MB5). Similarly, the first measurement beam MB1 is above the second measurement beam MB2, and the third measurement beam MB3 is above the fourth measurement beam MB4.

According to the method according to the invention, the object OB is rotated about an axis parallel to the Y-direction, in this example perpendicular to the plane of the drawing, and thus perpendicular to both the X-direction and the Y-direction. This direction of rotation will be called Ry. For brevity, the first, second and third mirrors (FM, SM, TM) will be considered perfectly flat and aligned mirrors unless otherwise indicated.

Rotating the object OB, as indicated, about an axis extending in the Y-direction while the second mirror SM extends in the X- and Z-directions affects the Rz measurement of the second pair of interferometers. will not be given, because the third and fourth measurement beams MB3 and MB4 will not experience a change in optical path length. This is because the rotation Ry causes the second mirror SM to rotate in plane and independently of the actual spot center of the third and fourth interferometers IF3 and IF4 on the second mirror SM.

The Rz measurement of the first and second pair of interferometers can be affected by this rotation, but only if the corresponding actual spot centers are not at the same level in the Z-direction as shown in FIG. 6 . Since the levels of the measurement beams MB1 and MB5 are different from those of the measurement beams MB2 and MB6, respectively, the optical path length difference caused by the optical path length difference of the first and third mirrors FM and TM is different. As a result, the position signals PS1 and PS2 will change differently, thus resulting in a change in the Rz measurement even if the object OB is not rotated about an axis extending in the Z-direction. The same applies to the position signals PS5 and PS5, which will also change differently and will therefore also change the Rz measurement. Changes in the Rz measurement provide information about the distance between the actual spot centers in the Z-direction. Therefore, if the actual spot center was at the same level in the Z-direction, the Rz measurement would not have changed.

In summary, by rotating the object OB about an axis parallel to the measuring beam of one of the pairs of interferometers (parallel to the second pair of interferometers in the example of FIG. 6 ), the distance between the actual spot centers is Information about the distance can be obtained in a direction perpendicular to the axis of rotation and perpendicular to the measuring beam of another pair of interferometers. Therefore, in the example of FIG. 6, information about the spot position of the second pair of interferometers is not obtained. However, the above can be repeated for rotation about the axis extending in the X-direction, so that no Rz measurement change will be observed using the first and third pair of interferometers, but the change is the actual spot centers may occur in the Rz measurement of the second pair of interferometers due to the non-zero distance between them (as is the case in Fig. 6).

FIG. 7A shows a simplified top view of the interferometry system of FIG. 4, displaying the object OB and all measuring beams MB1-MB6. As mentioned earlier, every pair of interferometers is determined due to the distance between the real spot centers in the Y-direction for the first and third pair of interferometers and for the second pair of interferometers in the X-direction. Due to the distance between the actual spot centers in the direction can provide an Rz measurement.

FIG. 7B shows the top view of FIG. 7A after rotating the object OB about an axis extending in the Z-direction. The Rz measurement of every pair of interferometers will change with rotation, but will change depending on the actual distance between each actual spot center, which may differ from the distance between the intended spot centers. Therefore, the change in the Rz measurement due to rotation provides information about the distance between the actual spot centers. Although it is possible to determine the difference between the actual change in the Rz measurement and the expected change in the Rz measurement, it is not possible to use the Rz measurement alone to determine the reference Rz, and to determine the difference between the actual change in the Rz measurement and the change in the reference Rz. It is also possible. In the example of FIGS. 7A and 7B where there are three pairs of interferometers, the following options are available as reference Rz:

i. Rz measurement provided by the first pair of interferometers;

ii. Rz measurement provided by the second pair of interferometers;

iii. Rz measurement provided by the third pair of interferometers;

iv. an average of the Rz measurement provided by the first pair of interferometers and the Rz measurement provided by the second pair of interferometers;

v. an average of the Rz measurement provided by the first pair of interferometers and the Rz measurement provided by the third pair of interferometers;

vi. an average of the Rz measurement provided by the second pair of interferometers and the Rz measurement provided by the third pair of interferometers; and

vii. Average of the Rz measurement provided by the first pair of interferometers, the Rz measurement provided by the second pair of interferometry systems, and the Rz measurement provided by the third pair of interferometers.

Therefore, in order to obtain information about the distance between the actual spot centers in the X-direction or the Y-direction, the deviation in the change in rotational position measured by one of the at least two pairs of interferometry systems is Average change in rotational position measured by two or more pairs of interferometry systems (option iv . to vii.).

Because the methods described in the examples of FIGS. 6 and 7A and 7B provide information about the location of the actual spot center in different directions, these methods can be combined to complement each other.

Furthermore, the methods described in the examples of FIG. 6 and FIGS. 7A and 7B can be repeated for other rotations to obtain more information about the actual spot center to improve accuracy.

In the case of the example of FIG. 6 , the rotation after rotating the object OB about Ry and indicated using a solid line may be referred to as the first rotated orientation, whereas the object OB is indicated by a dotted line in FIG. 6 . It may further have a neutral orientation. In this example, the neutral orientation corresponds to alignment in the X-, Y-, and Z-directions, which is usually provided by a support structure that restricts motion of the object in the X-, Y-, and Z-directions. usually determined Therefore, this method was performed by rotating the object OB from a neutral orientation to a first rotated orientation. It is possible to repeat this method for a second rotated orientation different from the first rotated orientation and different from the neutral orientation. The second rotated orientation may be obtained by rotating the object OB in an opposite direction starting from the neutral orientation compared to the required rotation when rotating the object OB from the neutral orientation to the first rotated orientation. In other words, the first rotated orientation and the second rotated orientation may be disposed on either side of the neutral orientation.

For the example of FIGS. 7A and 7B , the orientation of the object OB after rotating it about Rz is shown in FIG. 7B and may be referred to as the first rotated orientation, while the object OB is It may further have a neutral orientation as shown in FIG. 7A. Neutral orientation in this instance also corresponds to alignment in the X-, Y-, and Z-directions, which are usually determined by the support structure defining motion of the object in the X-, Y-, and Z-directions. do. Therefore, this method was performed by rotating the object OB from a neutral orientation to a first rotated orientation. It is possible to repeat this method for a second rotated orientation different from the first rotated orientation and different from the neutral orientation. The second rotated orientation may be obtained by rotating the object OB in an opposite direction starting from the neutral orientation compared to the required rotation when rotating the object OB from the neutral orientation to the first rotated orientation. In other words, the first rotated orientation and the second rotated orientation may be disposed on either side of the neutral orientation.

Although the preceding examples have been described assuming that the mirror is perfect, this may not be possible in practice. Since rotation of the object OB can cause the measurement beam, and therefore the spot, to move over the mirror, any deviation from the perfect mirror shape will cause a change in the Rz measurement that is not caused by a deviation in the location of the spot. can contribute to In order to distinguish the different contributions, the method according to the invention can be combined with a method for at least partially calibrating the mirrors of an interferometer.

In one embodiment, referring back to FIG. 6 , rotation of object OB as indicated causes both measuring beams MB1 and MB2 and measuring beams MB5 and MB6 to be rotated to the first and third mirrors FM, TM. ) will be moved above each. Adjust the method so that by translating the object in the Z-direction one pair of measuring beams (MB1, MB2 or MB5, MB6) can be positioned substantially in a position on the mirror as in the case of a neutral orientation of the object OB. It is possible. Additionally, this method can be repeated for the same rotation, but with another pair of measurement beams held in substantially the same position on the mirror. This additional measurement may allow to distinguish deviations caused by spot position deviations from deviations caused by imperfect mirrors and spot movement over the mirrors.

In another embodiment, referring again to FIGS. 7A and 7B , rotation of the object OB as indicated will move all measurement beams MB1 to MB6 above the respective mirrors FM, SM, TM. By translating the object in the X-direction and/or in the Y-direction, at least one pair of measuring beams, possibly two pairs of measuring beams, is positioned substantially in a position on the mirror as in the case of a neutral orientation of the object OB. It is possible to adjust the method so that Further, this method can be repeated for the same rotation, but with another pair of measurement beams or combination of measurement beam pairs held in substantially the same position on the mirror. This additional measurement may allow to distinguish deviations caused by spot position deviations from deviations caused by imperfect mirrors and spot movement over the mirrors.

Although the examples show the use of three pairs of interferometers, the present invention can be used with only two pairs of interferometers. For example, the example of FIG. 6 can be used even if the first or third pair of interferometers are omitted. Furthermore, the example of FIG. 7 can be used even if any one of the pair of interferometers is omitted.

Although the examples are primarily multi-pass interferometry and deal with the case where the actual spot center is the average of the spot locations, the present invention uses single-pass interferometry where the actual spot center coincides with the spot location and is no longer the average location. can also be applied. However, the same principle still applies.

Although specific reference may be made herein to the use of a lithographic apparatus in the field of manufacturing ICs, it should be understood that the lithographic apparatus described herein may have other applications. Other possible applications include the fabrication of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, and the like.

Although specific reference is made herein to embodiments of the present invention in the context of a lithographic apparatus, embodiments of the present invention may be used in other apparatuses as well. Embodiments of the present invention may be part of a mask inspection device, metrology device, or any device that measures or processes an object such as a wafer (or other substrate) or mask (or other patterning device). Such an apparatus may be generally referred to as a lithography tool. Such lithography tools may use vacuum conditions or ambient (non-vacuum) conditions.

Although specific reference has been made above to the use of embodiments of the invention in the context of optical lithography, the invention is not limited to optical lithography, where the context permits, but in other applications, such as imprint lithography. It will be appreciated that it may be used.

Where the context permits, embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (eg, a computing device). For example, machine-readable media may include read only memory (ROM); random access memory (RAM); magnetic media; optical storage media; flash memory devices; electrical, optical, acoustic or other forms of propagated signals (eg, carrier waves, infrared signals, digital signals, etc.), and others. Furthermore, firmware, software, routines, or instructions may be described herein as performing particular operations. However, it should be noted that these descriptions are for convenience only and that these operations may in fact result from a computing device, processor, controller, or other device executing firmware, software, routines, instructions, etc., of which an actuator or other device It should be acknowledged that they may interact with

Although specific embodiments of the invention have been described above, it will be understood that the invention may be practiced otherwise than as described. The above description is intended to be illustrative rather than limiting. Accordingly, it will be apparent to those skilled in the art that changes may be made to the invention as described without departing from the scope of the claims set forth below. Various aspects of the invention are set forth as in the following numbered sections.

1. A method of calibrating the position of a spot on a mirror of an interferometry system comprising at least two pairs of interferometers to provide a redundant measurement of the rotational position of an object about an axis of rotation, comprising:

a. rotating the object;

b. measuring a change in a rotational position of the object around the rotational axis using each of the at least two pairs of interferometers;

c. In the change in rotational position measured by one of the at least two pairs of interferometers, the deviation compared to the change in rotational position measured by the other pair of the at least two pairs of interferometers or two or more pairs of interferometry systems. determining the deviation compared to the average change in rotational position measured by and

d. Based on the determined deviation, acquiring information about a spot position on the mirror of the one pair of the at least two pairs of interferometers.

Including, mirror spot position calibration method.

2. In Section 1,

In step a, the object is rotated about the axis of rotation.

3. In Section 1,

The at least two pairs of interferometers may include a first pair of interferometers configured to measure the position of the object in a first direction perpendicular to the axis of rotation and a second direction perpendicular to the axis of rotation and the first direction. a second pair of interferometers configured to measure a position of the object;

In step a, the object is rotated about an axis parallel to the first direction,

step c comprises determining a deviation in a change in rotational position measured by the second pair of interferometers compared to a change in rotational position measured by the first pair of interferometers;

In step d, information about a spot position on a mirror of the second pair of interferometers is obtained.

4. In any one of Sections 1 to 3,

In step a the object is rotated from a neutral orientation to a first rotated orientation;

Steps b to d are repeated after rotating the object to a second rotated orientation;

wherein the first rotated orientation and the second rotated orientation are disposed on opposite sides of the neutral orientation.

5. In Section 2,

In step d, the obtained information provides information about a spot position on the mirror in a direction perpendicular to the axis of rotation.

6. In Section 3,

in step d, the obtained information provides information about a spot position on the mirror in a direction parallel to the axis of rotation.

7. In any one of Sections 1 to 6,

wherein the interferometers are multi-pass interferometers.

8. In any one of Sections 1 to 7,

wherein the object is translated to maintain a spot position on each mirror of the at least one pair of interferometers the same before and after rotating the object.

9. A lithographic apparatus,

- a positioned object;

- an actuator system to position the object;

- a measurement system comprising the interferometry system, the interferometry system comprising at least two pairs of interferometry systems for providing redundant measurements of the rotational position of the object about a rotation axis; and

- a control system for driving the actuator system based on the output of the measurement system;

including,

A lithographic apparatus, wherein the control system is configured to perform a method according to any one of claims 1 to 8.

10. In Section 9,

The lithography apparatus,

- an illumination system configured to modulate the radiation beam;

- a support structure configured to support a patterning device, wherein the patterning device is capable of imparting the radiation with a pattern in its cross-section to form a patterned radiation beam;

- a substrate table configured to hold a substrate; and

- A projection system configured to project the patterned beam of radiation onto a target portion of the substrate.

Including more,

The lithographic apparatus, wherein the object is the support or the substrate table.

11. A device manufacturing method in which the lithographic apparatus according to clause 9 or 10 is used.

Claims (11)

A method of calibrating the position of a spot on a mirror of an interferometry system comprising at least two pairs of interferometry systems to provide a redundant measurement of the rotational position of an object about an axis of rotation, comprising:
a. rotating the object;
b. measuring a change in a rotational position of the object around the rotational axis using each of the at least two pairs of interferometers;
c. In the change in rotational position measured by one of the at least two pairs of interferometers, the deviation compared to the change in rotational position measured by the other pair of the at least two pairs of interferometers or two or more pairs of interferometry systems. determining the deviation compared to the average change in rotational position measured by and
d. Based on the determined deviation, acquiring information about a spot position on the mirror of the one pair of the at least two pairs of interferometers.
Including, mirror spot position calibration method. According to claim 1,
In step a, the object is rotated about the axis of rotation. According to claim 1,
The at least two pairs of interferometers may include a first pair of interferometers configured to measure the position of the object in a first direction perpendicular to the axis of rotation and a second direction perpendicular to the axis of rotation and the first direction. a second pair of interferometers configured to measure a position of the object;
In step a, the object is rotated about an axis parallel to the first direction,
step c comprises determining a deviation in a change in rotational position measured by the second pair of interferometers compared to a change in rotational position measured by the first pair of interferometers;
In step d, information about a spot position on a mirror of the second pair of interferometers is obtained. According to any one of claims 1 to 3,
In step a the object is rotated from a neutral orientation to a first rotated orientation;
Steps b to d are repeated after rotating the object to a second rotated orientation;
wherein the first rotated orientation and the second rotated orientation are disposed on opposite sides of the neutral orientation. According to claim 2,
In step d, the obtained information provides information about a spot position on the mirror in a direction perpendicular to the axis of rotation. According to claim 3,
in step d, the obtained information provides information about a spot position on the mirror in a direction parallel to the axis of rotation. According to any one of claims 1 to 6,
wherein the interferometers are multi-pass interferometers. According to any one of claims 1 to 7,
wherein the object is translated to maintain a spot position on each mirror of the at least one pair of interferometers the same before and after rotating the object. As a lithographic apparatus,
- the positioned object;
- an actuator system to position the object;
- a measurement system comprising the interferometry system, the interferometry system comprising at least two pairs of interferometry systems for providing redundant measurements of the rotational position of the object about a rotation axis; and
- a control system for driving the actuator system based on the output of the measurement system;
including,
A lithographic apparatus, wherein the control system is configured to perform a method according to any one of claims 1 to 8. According to claim 9,
The lithography apparatus,
- an illumination system configured to modulate the radiation beam;
- a support structure configured to support a patterning device, wherein the patterning device is capable of imparting the radiation with a pattern in its cross-section to form a patterned radiation beam;
- a substrate table configured to hold a substrate; and
- a projection system configured to project the patterned radiation beam onto a target portion of the substrate
Including more,
The lithographic apparatus, wherein the object is the support or the substrate table. A device manufacturing method in which a lithographic apparatus according to claim 9 or 10 is used.