KR100503877B1 - Differential interferometer system and lithographic step-and-scan device with it - Google Patents

Abstract

The present invention relates to a differential interferometer system for measuring the movement and mutual position of a first object (WH) and a second object (MH), the system comprising a first interferometer unit having a first measuring reflector (RW) And second interferometer units 5, 6, 7, 8, having 1,2,3,4 and a second measuring reflector RM. Since the measuring beam bm passes through both the first and second interferometer units and is reflected by both the first and second measuring reflectors, the measuring beam and the reference beam br are between at least two interferometer units. Because they traverse the same path, precise measurements can be made very quickly. The interferometer system can be used with excellent advantages for step-and-scan lithographic apparatus.

Description

Differential Interferometer System and Lithographic Step-and-Scan Device with the System

The present invention relates to an interferometer system for measuring the movement and mutual position of a first and a second object in one or more directions, the system for one or more all possible mutual movements,

A first interferometer unit having a first beam splitter, a first measuring reflector and a plurality of first reflectors and associated with the first object,

A second interferometer unit having a second beam splitter, a second measuring reflector and a plurality of second reflectors and combined with a second object.

The invention also relates to a lithographic apparatus for projecting a mask pattern onto a substrate in accordance with the step-and-scan principle.

Known as step-and-scan devices, in particular such devices used in the manufacture of integrated circuits or ICs are known in particular in US Pat. No. 5,194,893.

Because of the need to increase the number of electronic components inside the IC, details called the line width must be drawn even smaller by the projection apparatus in all areas on the substrate where the IC is to be formed. The region is referred to herein as an IC region or " die. &Quot; Moreover, it is also desirable for the IC area to be enlarged so that the number of parts per IC can also be increased in this manner. In a projection lens system, this means that the resolution, and hence the numerical aperture, must be increased, and the image field must be enlarged.

To date, finding an optimal state between the two contrasting needs of a projection lens system has been a problem and costly. As an example, a projection lens system having a numerical aperture of 0.6 and an image field of 22 mm in a stepping apparatus known as a wafer stepper has been used to manufacture a 64 Mbit type IC. A line width of 0.35 mu m can be drawn on the substrate by this projection lens system. Although still fabricated, the projection lens system, which is not well suited for use, has reached practical limits. If very small details are to be drawn, i.e. very small line widths must be formed on the substrate, in other words, if the projection lens system must have a very large numerical aperture, this is only achieved at the expense of the drawing field size. .

Breaking out of this dilemma is possible by converting the stepping projection apparatus into the step-and-scan apparatus described in US Pat. No. 5,194,893. In the stepping projection apparatus, the entire mask pattern is exposed and drawn in the IC region on the substrate at one time. Subsequently, a step is performed, i.e., when the second IC region is disposed opposite the mask pattern and inside the drawing field of the projection lens system, the substrate is moved relative to the projection lens system and the mask pattern. The second image of the mask pattern is formed in the area. Subsequently, a step is again performed until the image of the mask pattern is formed in the entire IC region, such as being performed and drawn for the third IC region. The same stepping movement is performed in the step-and-scan apparatus, but only a small portion of the mask pattern is drawn on the corresponding partial area of the substrate each time. An image of the entire mask pattern is obtained on the IC region by drawing a continuous portion of the mask pattern on the continuous partial region of the IC. For this reason, the mask pattern is exposed, for example, to the projection beam having a small cross section of a rectangular or arch section, and the mask pattern and the substrate table are scanned with respect to the projection lens system and the projection beam. And a movement speed of the substrate table is M times the movement speed of the mask table. M is an enlargement ratio in which the mask pattern is drawn. Typical values of M are generally 1/4, but other values, such as 1, are also possible.

The projection beam cross section has a maximum dimension in the direction transverse to the scanning direction. This dimension may be equal to the width of the mask pattern so that the pattern is drawn in one scan movement. Alternatively, however, it is also possible that the dimension is half or smaller than the dimension of the mask pattern. In this case, the entire mask pattern is drawn with two or more opposing scan movements. At that time, it must be ensured that the movement of the mask and the substrate is synchronized very precisely. In other words, the speed v of the mask should always be M times the speed of the substrate.

Step-and-scan compared to a stepping projection device in which the mask pattern is already precisely aligned with respect to the IC area on the substrate, the projection lens system must be precisely focused on the substrate and the substrate table must be precisely inspected. In the projection apparatus, the condition of the velocity must additionally be measured. That is, it should be measured whether the substrate and the mask pattern are said to be stationary with respect to each other in the scan-drawing of the substrate and the mask pattern, so to speak. Based on the measurement, the speed of one of the tables can be adjusted to the speed of the other table.

In the projection apparatus disclosed in US Pat. No. 5,194,893, two interferometer systems are used to check the condition of the speed. The measuring reflector of the first interferometer system is fixed to the substrate table so that displacement of the substrate table in the scanning direction, hereinafter referred to as the X-direction, can be measured with this system. The measuring reflector of the second interferometer system is fixed to the mask table so that the displacement of this table in the scanning direction can be measured with this system. Output signals from the two interferometer systems are provided to an electrical processing unit, for example a microcomputer, where the signals are subtracted from each other and processed into actuators for the tables or control signals for the drive.

Due to the high speed of the table required since the substrate requires some large feed-through ratio through the device, the interferometer signal has a high frequency or bitrate. Compared to the high frequency signal, the speed of the processing electronics is a limiting factor. Thus, the delay time, i.e. the time that elapses between the moment the measurement is made and the moment the measurement result is available will play a large role. In a closed servoloop consisting of the measuring system and an actuator or drive for the tables, the delay time difference in the electrical signal processing causes an unwanted offset between the mask table and the substrate table. . Moreover, the tables will thus have a limited maximum speed.

1 and 2 show two embodiments of an interferometer system for a device according to the invention wherein the magnification is M = 1/4;

3 and 4 show two embodiments of an interferometer system for a device according to the invention wherein the magnification is M = 1;

5 shows the difference between an interferometer measurement in a device according to the invention and in a known device,

6 shows the mutual position of the substrate and the mask after being aligned in the apparatus;

7 shows an alternative to the embodiment shown in FIG. 2, FIG.

8 and 9 show an embodiment of a special interferometer for measuring the inclination of the substrate holder;

10 shows the calculation of the position of the projection lens with which the lens can be tilted around it without offset of the image;

11 shows an interferometer system with separate measurement of the position of the projection lens,

12 shows a differential interferometer system in which the measurement of the position of the projection lens is integrated (adjusted) at one point;

13 shows a differential interferometer system in which the measurement of the position of the projection lens is integrated (adjusted) at two points;

14 is a view showing mutual offsets of a reference beam and a measurement beam when the substrate holder is rotated;

15 and 16 show special reflector units that can be placed near the mask interferometer to eliminate the effects of offsets,

17 illustrates an embodiment of a differential interferometer system with projection lens position measurement with the effect of tilting or rotation of the substrate holder removed;

18 shows a mask interferometer sub-system used in this embodiment,

19 illustrates an embodiment of a differential interferometer system in which the effect of tilting or rotating the substrate holder is eliminated;

20-22 illustrate another embodiment of a mask interferometer sub-system for use in the embodiment of FIG. 19;

23 and 24 show two other embodiments of a differential interferometer system in which the effect of tilting or rotating the substrate holder is eliminated;

FIG. 25 shows the effect of tilt or rotation of a substrate holder on an interferometer signal with or without offset correction; FIG.

26A-C illustrate a single interferometer system in which the beam offset due to the tilt or rotation of the substrate holder is corrected.

The present invention provides a new concept for a step-and-scan projection apparatus that avoids the above problem. This new concept has a number of features that can be used individually or in combination.

According to a first aspect of the invention the interferometer system is characterized in that in the operating plane the measuring beam passes through both the first and second interferometer units and is reflected more than once by both the first and second measuring reflectors, The first and second interferometer units have a common radiation-sensitive detector, and the reference beam in combination with the measurement beam traverses the same path as the measurement beam between the first and second interferometer units. It is characterized by.

The position signals of the two tables are no longer electrically compared or subtracted from each other, but optically and in the interferometer system itself. In a controlled system, i.e., a closed servoloop, the frequency of the interferometer signal is always independent of the speed of the table and, therefore, is no longer a limiting factor.

An interferometer system having first and second measuring reflectors and first and second beam splitters is described in the English abstract of Japanese Patent Application No. 3-199,905, wherein the measuring beam of the interferometer system of the patent application is Used to cross the second beam splitter. However in the known system the measuring beam is reflected by only one measuring mirror, while the other measuring mirror reflects the reference beam. Moreover, the known system is not used to measure the mutual movement of two objects in one direction, but only for the measurement of the relative displacement of the X table relative to the Y table.

In one embodiment of the differential interferometer system suitable for a lithographic apparatus, the mask-pattern is drawn to a reduced size, with the number of reflections of the measuring beam reflected by the measuring reflector associated with the first object and the measuring reflector associated with the second object. It is further characterized in that the ratio between the number of reflections of the measuring beam reflected by it is equal to the ratio between the velocity of the second object and the velocity of the first object.

The interferometer system is further characterized in that the second interferometer unit is applied in such a way that the measuring beam arriving from the first interferometer unit is reflected by the number of m + 1 reflections in the second interferometer unit before returning to the first interferometer unit. It is preferable to set it as. Where m is an even number greater than 2.

This measurement prevents the rotation or tilt of the first object from affecting the interferometer signal.

The invention also relates to an apparatus for drawing a mask pattern on a substrate several times in accordance with the step-and-scan principle, the apparatus comprising: a mask holder disposed on a mask table and a substrate holder disposed on a substrate table and the mask table And a projection system disposed between the substrate table. The apparatus features the above-described interferometer system for measuring the mutual position of the mask and the substrate constituting the first and second objects.

The use of the present invention is not limited to step-and-scan projection apparatus. The present invention can generally be used in environments and devices where two objects must be moved quickly and very-accurately with respect to each other.

If a mask pattern with magnification M is drawn on the substrate in this projection device, then the number of reflections of the measurement beam reflected by the measurement reflector associated with the substrate and the reflection of the measurement beam reflected by the measurement reflector associated with the mask It is further characterized by the fact that the ratio between the recovery is equal to 1 / M.

According to another feature of the invention the device is further characterized in that the measuring reflector associated with the substrate and the measuring reflector associated with the mask are each constituted by the reflecting sides of the substrate holder and the mask holder.

The reflective side is understood as a means by which the side itself is reflectable or on which the reflector is fixed on the side.

Since the measuring reflector is rigidly connected to the substrate and the mask, it is not considered in the known apparatus and includes the movement resulting from the movement of the mask table elements relative to each other and the movement of the substrate table elements relative to each other. The movement of the component itself is measured directly and thus reliably.

For the manner in which an interferometer system, hereinafter referred to as a substrate interferometer, can be configured to measure the linear disp1accement and the tilt and rotation of the substrate and how it can be mounted in a lithographic apparatus, two-axis reference is made to US Pat. Nos. 4,251,160 and 4,737,283, which describe interferometer systems and 3-axis interferometer systems, respectively. Another embodiment of a substrate interferometer system is described in European Patent Application No. 0498 499.

The apparatus according to the invention is further characterized in that the interferometer system comprises a projection system interferometer unit for measuring the position of the projection system at a location, and the projection system further comprises a measuring reflector at the location.

The position of the projection system can be measured independently of the possible tilt of the system.

Another embodiment of the apparatus is further characterized in that the projection system comprises two additional measuring reflectors at positions close to the mask holder and at positions close to the substrate holder, respectively, wherein the reference beam is reflected by both measuring reflectors. do.

These and other features of the invention will be described and become apparent with reference to the embodiments described below.

1 shows a first embodiment of an interferometer system according to the invention for use in a projection apparatus in which the mask pattern is drawn to a size reduced by one quarter, and thus M = 1/4. This figure and other figures of the projection apparatus only show components cooperating with the differential interferometer system, namely the substrate holder WH with the reflector RW and the mask holder MH with the reflector RM. The measurement beam bm and the reference beam br emitted from the radiation source (not shown) are shown in solid and dashed lines, respectively. Since these beams are, for example, two mutually polarized components having different frequencies of radiation beams emitted by a Zeenan laser, the measurement is based on phase measurement. The directions of the measuring beam and the reference beam are shown by arrows.

The embodiment shown in FIG. 1 in the position of the substrate holder WH with a reflector RW is a polarization-sensitive splitter 1 and a quarter-wavelength lambda / 4 plate 2. And two retroreflectors 3, 4. In addition, the polarization-sensitive beam splitter 5, the λ / 4 plate 8 and two retroreflectors 6,7 are present at the position of the mask holder MH with the reflector RM. In addition, the stationary reflector MI is in place. The beam splitters 1, 5 pass a first component having a first direction of the beam polarization from a radiation source and a second component having a second direction of polarization perpendicular to the first direction of the beam polarization, and It has a polarizing-photosensitive interface 9, 10 that reflects or vice versa. In the illustrated embodiment, the beam component passed is the reference beam br and the reflected beam component is the measurement beam bm. The quarter-wave plates 2,8 having a polarization direction of 45 ° angle to the polarization of the beam component cause the direction of polarization of the beam component to rotate by 90 ° if the beam component passes through this plate twice.

The measuring beam bm passed by the interface 9 traverses the λ / 4 plate 2 and impinges on the reflector RW at position P1. The reflected beam crosses the [lambda] / 4 plate a second time so that the direction of the polarization is rotated by 90 [deg.] Relative to the direction of the original polarization and then passed by the interface 9 towards the retroreflector 3. Via the reflection on the inclined surface of the reflector the measuring beam enters the beam splitter 1 again and is then passed by the beam splitter to impinge on the reflector RW at the position P2 a second time. . The measuring beam from the position P2 is reflected by the boundary surface 9 towards the boundary surface 10 of the beam splitter 5 disposed proximate to the mask holder. Subsequently, the boundary surface 10 reflects the measurement beam to the mask holder reflector RM through which the measurement beam is incident at position P3 via the λ / 4 plate 18. The measuring beam reflected by the reflector RM crosses the [lambda] / 4 plate a second time, and the direction of polarization is again rotated by 90 [deg.], And is passed toward the retroreflector 6 by the interface. Via the reflection on the inclined surface of this reflector and the passage of the interface 10 and the λ / 4 plate, the beam reaches the reflector MI at position P4. The beam reflected by the reflector MI again traverses the [lambda] / 4 plate 8 and its polarization direction is rotated 90 [deg.] Again and the beam is reflected by the interface 10 towards the interface 9. The measuring beam is then sent back to the substrate reflector RW to be incident and reflected continuously at positions P5 and P6, similarly as described at positions P1 and P2. The beam reflected at position P6 is reflected from the interferometer system towards the detector (not shown) by the interface 9.

The reference beam br passed by the interface 9 also traverses the entire system, but the reflectors RW, RM, MI bypass. The beam is only reflected by the sides of the retroreflectors 4, 7 and always passed by the interface 9, 10 of the beam splitter 1, 5. The mutually polarized beams (bm, br) generated from the system pass through a spectrometer (not shown) having a polarization direction extending at an angle of 45 ° with respect to the polarization direction of the beams on the way to the detector, and mutual interference Pass two components of the beam where possible. The phase difference between the beam components depends on the mutual position of the mirrors RM, RW, and therefore on the extent to which the mirror and hence the mask and the substrate move in synchronization with consideration of magnification M. do. In a lithographic apparatus, a projection lens system (not shown in FIG. 1) is disposed between the mask holder MH and the substrate holder WH. In the embodiment of the interferometer system shown in FIG. 1, the measurement beam is reflected four times on the substrate reflector and once on the mask reflector, which has a magnification of 1/4.

FIG. 2 shows a second embodiment of a differential interferometer system for use in a projection device with an enlargement ratio M of 1/4. This embodiment omits the first retroreflector 3, in which two special reflectors 15, 16 are combined and combined with the first beam splitter 1, in the second beam splitter the two retroreflectors of FIG. 1. (6,7) is distinguished from the embodiment of FIG. 1 in that it is replaced by retroreflectors 18,19. In this embodiment the measuring beam bm coming from the left side is initially reflected twice by the substrate reflector RW via the beam splitter 1 and the λ / 4 plate at positions P1 and P2. The reflectors 15 and 16 reflect the measuring beam reflected at the position P2 to the fixed reflector MI. The measuring beam reflected by this reflector at position P3 is reflected by retrograde reflector 19 by interface 10. Via the reflection on the inclined plane of the reflector, the measuring beam is returned to the boundary plane 10 which is reflected to the position P4 on the mask reflector RM. From this reflector the measuring beam moves to position P5 on substrate reflector RW via reflection on reflectors 16 and 15. There the measuring beam is reflected again and successively the beam reflects the substrate reflector via the reflection on the interface 9, on the two inclined surfaces of the retroreflector 14 and again on the interface 9. Go to position P6 on (RW). The measurement beam bm reflected there reaches a detector (not shown) via the λ / 4 plate 2 and the beam splitter 1.

The reference beam br is continuously connected to the boundary surface 9, the two inclined surfaces of the retroreflector 4, the boundary surface 9, the reflectors 15 and 16, the boundary surface 10, and the reflector 18. On two inclined planes, the reflectors 15 and 16, the interface 9 and the two inclined planes of the reflector 4 to pass through the system and finally on the interface 9 as a beam br '. Via reflection it is sent to the same detector as in the case of the measuring beam bm '. The reference beam br therefore bypasses all reflectors RW, RM, MI.

3 shows an embodiment of a differential interferometer system for use with a projection device with magnification M = 1. In this embodiment without the fixed reflector MI, but having the same structure as shown in Fig. 1, the measuring beam bm is first reflected twice at positions P1 and P2 successively by the substrate reflector. The measuring beam emerging from position P2 is reflected at position P3 on mask reflector RM via reflection on boundary surfaces 9 and 10. The reflected measuring beam then goes to position P4 on the mask reflector RM which is reflected back to the interface 10 via reflection on the inclined plane of the retroreflector 6. This interface reflects the measurement beam b'm to a detector (not shown).

The reference beam br passes through the beam splitters 1 and 5 and is only reflected by the inclined surfaces of the retroreflectors 4 and 7. This beam bypasses the reflectors RW, RM.

4 shows a second embodiment of a differential interferometer system using a projection device with a magnification M = 1. This embodiment differs from the embodiment shown in FIG. 3 in that the redundant λ / 4 tube 20 is arranged below the first beam splitter 1 and the retroreflector 3 is omitted. The measuring beam bm introduced at the left is initially reflected by the substrate mirror RW at position P1. The measuring beam then goes to position P2 on the mask reflector RM via reflection on the interface 9, 10. The measuring beam reflected by this reflector is reflected by the inclined surface of the retro reflector 6 to the position P3 on the mask reflector RM. Via the reflection on the interfaces 10 and 9 the measuring beam returns to the substrate reflector RW which is reflected toward the detector (not shown) at position P4 with beam b'm.

The [lambda] / 4 plate 20 is arranged in the path of the reference beam br only, and this beam, first reflected by the interface 9, is then reflected on the inclined plane of the retroreflector 4 by the interface 9,10 after reflection. Pass towards retroreflector (7). The reference beam is returned to the retroreflector 4 via the reflection on the two inclined planes of the reflector. The interface 9 is finally the beam br 'and the reference beam coming out of the reflector is measured by the measuring beam bm. ') Is also sent to the receiving detector.

The differential interferometer system according to the present invention is not only used for step-and-scan projection devices with magnification M = 1/4 or M = 1, but also for example for devices with magnification M = 1/2 and the like. The differential interferometer system may have the same structure as shown in FIGS. 1 and 2 while the fixed reflector MI is removed to be applied to. In general, the differential interferometer system can be used in a projection device with a magnification M, where the system reflects the number of reflections of the measurement beam reflected by the substrate reflector and the mask reflector without changing the overall optical path length for the measurement beam. It can be configured in such a way that the ratio between the number of reflections of the measuring beam reflected by 1 / M is 1 / M. Also, if the latter condition is not met, the bit rate of the interferometer signal can be significantly reduced for known systems when using the idea of the present invention to reflect the measurement beam on both the substrate reflector and the mask reflector. . In the interferometer system according to the invention, it is important that the measurement beam and the reference beam follow the same path as possible. This is particularly important in lithographic devices because the distance between the mask holder and the substrate holder in such a device can be large.

1 to 4 schematically show only the substrate holder WH and the mask holder MH of the lithographic projection apparatus. Projection lens systems, such as US Pat. No. 5,194,893, described above, are disposed between these holders. Moreover, the substrate holder and the mask holder respectively form part of a substrate table (stage) and a mask table, whereby the substrate and the mask can be disposed and replaced relative to each other. This movement is performed under the control of the interferometer system. In more conventional step-and-scan apparatus the position of the mask as well as the substrate is measured relative to the apparatus reference. However, vibrations and other instability of the device have an unstable effect on the positioning of the substrate and the mask. Since the mutual position of the mask and the substrate is the most important factor for a clear scanning operation, it is better to measure the mutual position directly as already proposed in US Pat. No. 5,194,893. As already mentioned above, the magnification of the projection lens system as well as the Z position of the system, ie the position along the Z axis of the coordinate system of the device, must be taken into account. The scanning direction shown by horizontal lines in FIGS. 1 to 4 is, for example, the X direction of this coordinate system.

The mask and the substrate are well maintained and aligned with respect to one another in the X and Y directions, for example, with an accuracy of about 10 nm.

In initial or overall X and Y alignment, the apparatus comprises a separate alignment system, for example the system described in US Pat. No. 4,251,160, which aligns a particular mask alignment mark with a particular substrate alignment mark. Both the mask and the substrate in the Z direction must be precisely positioned relative to the projection lens system. The Z position of the substrate relative to the projection lens system can be precisely adjusted by a focus and leveling system, for example as described in US Pat. No. 5,191,200. The first incorrect Z position of the mask generates an error. To avoid this error, the spacing between the mask and the projection lens system must be adjusted to a precision of, for example, 1 占 퐉 and kept in the adjusted state. This can be realized by sufficient air bearing between the mask and the projection lens system.

The X and Y mutual positions of the mask and the substrate must also be measured. Furthermore, as described in EP 0 489 499, the inclinations φ x and φ y with respect to the X and Y axes of the substrate can be measured to prevent Abbe errors, and An interferometer system with five measuring axes can be used for the substrate. Five parameters, namely the X position, the Y position, the inclination φ x for the X axis, the inclination φ y for the Y axis, and the rotation φ z for the Z axis, can be determined from a combination of the signals of the measuring axis.

The measuring axis is shown in Fig. 5a. In this very schematic drawing, the substrate is shown as W, the mask as MA and the substrate holder as WH. Reference numerals RR1 and RR2 denote fixed reference reflectors, with which the orientation and position of the substrate reflectors RW1 and RW2 are measured. The interferometer system consists of two units, the first of which has two measuring axes in cooperation with the reflector RW1 and the second of which has three measuring axes in cooperation with the reflector RW2. The X position of the substrate is measured by the first interferometer unit along the X measurement axis. The unit has a second measuring axis shown by φ y and the second measuring axis extends in the X direction but is offset in the Z direction with respect to the first measuring axis. The slope φ y with respect to the Y axis can be determined from the difference between the signals reached from the first and second X measurement axes. The second interferometer unit has a first Y measurement axis, shown as Y1, from which the Y position of the substrate can be determined. The inclination λ x with respect to the X axis can be determined from the combination of the signal of this measurement axis and the signal offset for Y 1 in the Z direction and shown in φ x. The rotation φ z about the Z axis of the substrate can be determined from a combination of the measurement axis Y1 and Y2 signals offset relative to each other in the X axis direction. For a separate determination of the orientation and position of the mask, i.e. an interferometer system with three measuring axes to determine the X and Y positions and the rotation about the Z axis is required. As shown in FIG. 5B, the number of measuring axes of the entire interferometer system can be reduced from eight to five by differential measurements. As indicated by the X measurement axis dx, the relative position of the mask with respect to the substrate is now measured. In addition, as indicated by the measuring axes dy1 and dy2, the relative Y position of the mask with respect to the substrate and the relative rotation φ z with respect to the Z axis of the substrate and the mask with respect to each other are measured. Also, the inclination with respect to the Y axis and the inclination with respect to the X axis of the substrate must be measured, which is realized by the second X measuring axis φ y and the second Y measuring axis φ x with respect to the substrate. For the differential measuring side dx, dy1, dy2, an interferometer system described with reference to FIGS. 1 to 4 and further described below may be used.

Since only the relative position of the mask is measured relative to the substrate, a special procedure is necessarily used when the substrate and the mask are introduced into a lithographic apparatus. How the introduction procedure can be performed is described with reference to FIG. Initially, the mask table MT and the substrate table WT are moved to a fixed zero or reset position by a stop device in the form of, for example, Tesa feelers. The interferometer is set to zero. Subsequently, the mask table is placed above the projection lens system by a scanning servo loop. Because of the coupling via the differential interferometer system, the substrate table follows this movement. Then, the mask MA with the alignment marks M1, M2 is disposed in the holder of the mask table. Subsequently, the mask is held and the substrate table is moved to a position where the substrate is placed in a holder of the mask table. The substrate table is then displaced again in such a way that the substrate lies underneath the mask and the projection lens system. Subsequently, the substrate is aligned with respect to the mask by an alignment system present in the apparatus, and the mask marks M1, M2 and similar alignment marks in the substrate are drawn together and whether these marks are correctly positioned with respect to each other. It is determined. At this time, the situation shown in FIG. 6 is achieved. The X and Y positions of the substrate mark relative to the two-dimensional coordinate system, fixed by the X and Y interferometers, are also known. This coordinate system performs a stepping movement of the substrate table, i.e. the table so that the mask pattern is drawn on one IC region (die) of the substrate and then brings the complete IC region under the mask and the projection lens system. It is also used to move. After the substrate and the mask are aligned with respect to each other, the substrate table performs a first stepping movement so that the first IC region is under the mask while maintaining the found dy1-dy2 value, i. . Subsequently, the mask and the substrate perform synchronous movement while considering the magnification of the projection lens system and the projection beam while the projection beam is switched on. That is, the mask is drawn on the first IC region by the scanning movement. When the drawing operation is completed, the projection beam is switched off and the substrate table moves one step so that the accompanying IC region of the substrate is placed under the mask. Thereafter, the scanning operation is performed again so that the mask pattern is drawn on the second IC region. This step-and-scan procedure continues until an image of the mast pattern is formed on all IC regions of the substrate.

The relative positions (dx, dy1, dy2 shown in FIG. 6) can be measured with the differential interferometer system shown in FIG. A simpler embodiment of such an interferometer system is shown in FIG. This system is similar to the system shown in FIG. 2 except that the retroreflector 22 is disposed on a mask table or mask holder and there is no lambda / 4 plate 8 and no retroreflector 19.

Similar to the embodiment shown in FIG. 2, in the embodiment of FIG. 7 the first incoming beam of measurement bm impinges on the substrate reflector RW at position P1 and then at position P2. Then traverses to the mask via the reflectors 15, 16. There, it continuously collides at the positions P3 and P4 on the mask reflector which consists of the retroreflector 22. As shown in FIG. The measuring beam reflected at this position is passed to the positions P5 and P6 of the substrate reflector RW successively similar to FIG. 2 and finally reflected from the system to the measuring beam b'm. The reference beam br moves in the same path as in FIG. 2.

The interferometer system described consists of two interferometer units arranged in series. 1, 2 and 7 the distance to the substrate reflector RW of one interferometer unit traverses eight times and the distance to the mask reflector of the other unit traverses twice. The conclusion is that the measurement of the substrate position is four times more sensitive than the measurement of the mask position. Since the measurement beam and the reference beam travel the same path between the substrate interferometer and the mask interferometer, the measurement is insensitive to air turbulence and other irregularities, for example. In principle, numerous sensitivities related to the magnification of the projection lens system can be realized by choosing the right combination of interferometer units.

If the mask and the substrate exhibit the desired synchronized movement during scanning in the X direction in a lithographic apparatus with an enlargement ratio M, then the condition satisfies Equation 1, where XM and XW are the mask and X position of the substrate.

[Equation 1]

XM + (1 / M) XW = constant

At that time, the length of the optical path of the measuring beam bm is kept constant and the detector for the measuring beam bm 'does not detect any frequency shift. This means that the measuring frequency is always the same as the frequency of the radiation source that supplies the measuring beam, for example, if it is a frequency that is often used as the radiation source of an interferometer, but is identical to the frequency do. The measurement frequency during scanning is independent of the speed of the mask and the substrate. In fact the X position of the mask and the substrate is optically summed and no longer electrically summed, as is done when two separate interferometers are used. Thus, the problem due to the detection signal processing electronics and the difference in delay time occurring when a separate interferometer is used can be prevented.

In Equation (1), the + signal is applied to the embodiment of FIGS. 1 to 4 and 7 in which the measuring beam contacts the substrate reflector RW as well as the mask reflector RM. If the measuring beam only measures the position of one of the substrate reflector and the mask reflector, and if the reference beam measures the position of the other of the reflector, the + signal of equation (1) should be replaced with the minus signal. do.

The embodiment shown in FIG. 7 with a retroreflector on a mask holder is insensitive to the tilt of this holder. In this embodiment, however, the holder cannot be moved in the direction perpendicular to the measurement direction in the measurement. For example, if two opposite movements in the X axis must be performed to form a mask pattern image on the IC region, and displacement displacement of the mask and the mask in the Y direction is required between these vertical directions, Is essential. 1 to 4, the mask reflector is a flat reflector and may move perpendicular to the mask rk measurement direction.

In practice, because the substrate may have a wedge shape to some extent, and since the substrate lies on the back side of the substrate holder, the inclination of the substrate holder with respect to the X and / or Y axis may be necessary. However, the interferometer measurement may then be affected by Abbe errors. It is essential that these (s) slope (s) be measured to correct this error. As described in EP 0 498 499, an interferometer system extended in a manner with five measuring axes offers the possibility of measuring this tilt. When a differential interferometer system is used in a lithographic projection apparatus, it may be easier to use a separate interferometer for this tilt measurement. Such an interferometer must be sensitive to the inclination of the substrate holder as well as the position of the substrate holder.

8 shows a first embodiment of an interferometer for measuring the inclination of the substrate with respect to the Y axis of the substrate. This interferometer comprises a polarization-sensitive beam splitter 23 with three lambda / 4 plates 24, 25 and 26 disposed around it. Moreover, the interferometer includes a retroreflector 29 and two reflective prisms 28, 29. The measuring beam bm coming from the left side hits the substrate reflector RW at position A1 and is subsequently reflected to the prism 27 by the interface 23a of the beamsplitter. This prism sends the measuring beam bm to the retroreflector 29 which reflects the measuring beam back to the interface 23a via reflection on its inclined plane. This interface now reflects the measurement beam into the prism 28. The inclined surface of the prism continuously reflects the measuring beam to the boundary surface 23a, and the boundary surface reflects the measuring beam back to the retroreflector 29. This reflector sends the measuring beam back to the prism 27 and the prism reflects the beam to the interface 23a. This interface now reflects the measurement beam to the substrate reflector RW where the measurement beam is incident at position A2. The measuring beam reflected at this position passes through the interface 23a to finally reach a detector (not shown).

The reference beam br is first reflected by the interface 23a to the retroreflector 29 and subsequently reflected by the retroreflector to the prism 27 by which the prism goes to the interface and this interface To position A3 on the substrate reflector. The reference beam reflected at this position is sent back to the substrate reflector RW by the prism 28 and is incident therein to position A4. The reference beam reflected at this point is reflected to the prism 27 by the boundary surface 23a, and subsequently goes to the retroreflector 29 by this prism and back to the boundary surface by this reflector. This interface finally reflects the reference beam br 'to the detector.

In the interferometer shown in FIG. 8, both the measuring beam bm and the reference beam br measure the X position of the substrate reflector RW. However, this measurement is carried out at two different positions A1, A3 and A2, A4. Thus, the interferometer is only sensitive to the difference in the X distance of these two positions relative to the stationary element of the interferometer and is not sensitive to the X distance of this detector.

9 shows a second embodiment of an interferometer system for measuring the tilt φ y of the substrate reflector RW relative to the Y axis. This embodiment differs from the embodiment of FIG. 8 in that the reflective prism 27 is replaced by a flat reflector M2. This reflector reflects on itself the measuring beam bm and the reference beam br which are incident vertically. In FIG. 9, the reference beam and the measurement beam contact the substrate reflector RW, the reflector M2, the retroreflector 29, and the prism 28 in FIG. 8. 27) and the order of contact with the retroreflector 29 and the prism 28 are the same.

Differential interferometer systems for use in lithographic devices can be further improved by measuring such that instability in the device does not affect the measurement of the mutual position of the mask and the substrate. For this reason, the influence of the inclination and the position of the projection lens system, which will be omitted below and referred to as a projection lens, must be eliminated.

In this projection lens a point around the lens that can be tilted without changing the position of the image formed by this lens can be indicated. This point is point C in FIG. 10. In this figure, v and b are the object length and the image length, respectively, and OP and IP are the object plane and the image plane, respectively. The point C is between two nodes of the lens. When the medium is the same on both sides of the lens, for example air, the node coincides with the main points A and B of the projection lens. H and H 'represent the main plane of this lens. The lens must satisfy the condition of equation (2).

[Equation 2]

BN '/ AN = b / v = M

As a result

[Equation 3]

Bc = M / (M + 1) AB

to be.

because,

[Equation 4]

v = f / M + f

And,

[Equation 5]

f = f (M + f)

Because it is

The distance between the main surfaces

[Equation 6]

AB = L-2 · f-M · f-f / M

And,

[Equation 7]

OC = M / (M + 1) L

to be.

This indicates that the position of the point C is independent of all kinds of lens parameters, such as the length of the focal length and the position of the main surface, but is only affected by the distance and magnification between the object plane and the image plane. This means that the position of the point C is generally the same for all projection lenses. Projection lenses commonly used in stepping lithographic projection apparatus are, for example, magnifications M = 0.2, object-image lengths L = 600 mm and OC = 100 mm. Possible projection lenses for the step-and-scan apparatus may, for example, have a magnification of M = 0.25 and an object-image length of L = 120 mm. In such a lens, OC = 120mm.

If the position of the projection lens is measured to be able to correct the influence on the position of the image formed by the lens, it is preferable to perform the projection lens position measurement at the position of the point C. In fact the measurement is insensitive to the inclination of the projection lens. With reference to FIG. 11, the result can be shown, for example, as the horizontal displacement dC of the projection lens in the X direction. This figure shows the mask holder MH, the projection lens PL and the r1 plate holder WH. The X positions of the components are shown as XM, XL and XW, respectively. INT1, INT2 and INT3 are interferometers that can be used to measure the position of the substrate, mask and projection lens. The relationship between the displacement dC of the lens and the virtual displacement dV of the object, ie, the mask, is applied by the following equation.

[Equation 8]

dV / dC = L / OC = (M + 1) / M

In addition, the displacement (dB) of the image of the mask pattern on the substrate is as follows.

[Equation 9]

dB = MdV = (M + 1) dC

For example, if the magnification is M = 0.25, Equation 8 is as follows.

[Equation 10]

dV = 5dC

This means that the position of the projection lens can be measured five times more sensitive than the position of the mask. In order to eliminate the influence of the lens position when the mask is well positioned with respect to the substrate, the following conditions must be satisfied for the example.

[Equation 11]

XM + 4 XW-5 XL = constant

Or more generally,

[Equation 12]

XM + 1 / M (XW-(M + 1) XL) = constant

Five times greater measurement sensitivity to the lens position can be obtained by adding the sensitivity of the substrate measurement and the sensitivity of the mask measurement, which means that the interferometers INT1 and INT2 must be placed in series.

The interferometer system in this case is schematically shown in FIG. In this figure, the measurement beam bm is shown in solid lines and the reference beam br is shown in dashed lines, similar to the preceding or following figures. If the reference beam br is used for the measurement of the projection lens position XL, the-sign is applied in equations (11) and (12). For this reason, the system shown in FIG. 12 has an extra reflector M5. The measuring beam bm is used to measure the mutual position of the mask and the substrate. In the system of FIG. 12 the position XM of the mask is measured twice, the position XW of the substrate is measured eight sides and the position XL of the projection lens is measured ten times. Since the measuring paths of the measuring beam and the reference beam are partially different, it should be ensured that air turbulence and other irregularities do not occur in the radiation path.

An interferometer system insensitive to air turbulence and the like is schematically illustrated in FIG. 13. In this system the measurement of the projection lens position is split into two measurements of the lens position at different heights. The first lens position measurement is performed in the vicinity of the mask, which measurement has a sensitivity of the mask position measurement. The second lens position measurement is performed in the vicinity of the substrate, which measurement has a sensitivity of the substrate position measurement. The condition now is that the distance between the respective measuring positions XL.2 and XL.1 and the point C is the same ratio as the magnification M of the projection lens. For the synchronized movement of the mask and the substrate during the drawing scan operation, the condition of Equation 13 must be satisfied if the magnification M of the projection lens is 0.25.

[Equation 13]

XM + 4 XW-4 XL, 1-XL, 2 = constant

Under this condition, the point where the mask position is measured and the upper point where the lens position is measured are tied together. The same applies to the point where the substrate position is measured and the lower point where the lens position is measured.

Advantages of the interferometer system of FIG. 13 are as follows.

There is a correction for both the tilt and the displacement of the projection lens.

The measurement is independent of the irregularity of the radiation path between INT1 and INT2

The position of INT1 and INT2 is not critical, so the measurement is independent of vibration and instability of the device. Only the slope of INT1 and INT2 affects. In order to eliminate this influence, it is preferable that 5 占 is equal to L.

An important condition for precisely measuring the mutual position of the mask and the substrate, and therefore dX, dY1, dY2, is that these measurements are not affected by rotation about the Z axis and inclination about the X and Y axes. It is desirable to make the differential interferometer itself insensitive to the rotation and tilt so that no extreme necessary conditions are imposed on the bearing of the mask and substrate. If the mask holder moves only in the X direction and the other direction is fixed by the air bearing, the rotation φ z of the substrate holder is initially important.

14 shows the influence of the rotation φ z on the Z axis. This figure shows the elements of the lower part of FIG. 2. As described with reference to FIG. 2, the measurement beam bm is first reflected twice at the positions P1 and P2 by the substrate reflector RW, and the mask reflector RM in which the beam is continuously reflected. Is then returned to the substrate reflector to be continuously reflected at positions P3 and P4, and goes to a detector (not shown) with beam b'm. This is the state when the measuring beam is incident vertically on the substrate reflector, and thus when φ z = 0. This measuring beam is shown in bm. When φ z is not zero, the measuring beam crosses the path shown by the dotted line. The measuring beam is then first reflected again at position P1, but no longer vertical. This measuring beam is shown in bm.a. Via the position 100-103 of the boundary surface 9 of the beam splitter 1 and the reflection in the retroreflector 19, the beam bm.a changes the position P2 'of the substrate reflector. Are sent to. The reflected beam bm.a is then again parallel to the beam bm and thereby also parallel to the reference beam (not shown in FIG. 14), but offset through the distance δ. There is no further offset between the measurement beam bm.a and the reference beam on the way from or to the mask reflector. As can be inferred from FIG. 2, the offset between the measurement beam bm.a from the mask reflector and the reference beam is relative to the offset between the measurement beam bm.a going to the mask reflector and the reference beam. Point-mirror. The measuring beam bm.a from the mask reflector first impinges on the substrate reflector at position P5 '. The measurement beam reflected there then goes to position P6 'via reflection on points 105-108, where it is reflected back to the detector as beam b'm.a. The offset between the measurement beam and the reference beam is doubled on the second path of the measurement beam bm.a through the substrate interferometer. Because of this double sensitivity, the differential interferometer is also twice as sensitive to the rotation of the substrate.

Due to the offset 2δ between the measuring beam and the reference beam, the overlap between the measuring beam and the reference beam becomes smaller at the position of the detector, and thus, of the mutual position of the mask reflector and the substrate reflector. The signal, which is a sample, becomes smaller. For example, when a standard interferometer with a 5 mm diameter beam is used, this means that it can have an inclination of ± 2 mrad or less with respect to the substrate reflector, for example. This margin can be increased by increasing the diameter of the beam. But for this purpose, an extra beam-widening optical system is needed. However, this has a very big drawback that the optical component must be increased so that vignetting of the beam on the component does not occur. This component can be very expensive because it must have very good optical quality. As will be discussed below, the deleterious effects of measuring reflector rotation or tilt or the tilt sensitivity of the differential interferometer can be eliminated in accordance with additional features of the present invention.

For this reason, mirror symmetry of the mask interferometer can be applied as shown in FIGS. 15 and 16. FIG. 15 shows the mask interferometer and therefore shows part of a differential interferometer system disposed in the proximity of the projection lens reflector RL and the mask reflector RM used in the embodiment of FIG. 13. The mask interferometer comprises a polarization-sensitive beam splitter 5 having an interface 10, two reflective prisms 111, 112 and two λ / 4 plates 113, 114. The measurement beam bm going to the mask reflector and the reference beam br going to the lens reflector RL2 are shown in solid and dashed lines, respectively. Arrows perpendicular to the measurement beam and dotted lines perpendicular to the reference beam in this and the subsequent figures show how the e-beam is reflected in its path through the interferometer system. In FIG. 15 the measuring beam bm is reflected five times and the reference beam is reflected three times, which means that they maintain a relatively same orientation and that no possible offset between the incoming beams is reflected.

As described above, the reference beam and the measurement beam bm that arrive from the mask interferometer traverse the substrate interferometer twice. When a first offset occurs between the measurement beam and the reference beam on the first path through the substrate interferometer, a similar second offset occurs on the second path through the substrate interferometer. Since the first offset on the path through the mask interferometer does not change, the second offset compensates for the first offset. A solution consisting of an odd number of reflections within the mask interferometer for the problem of tilt and rotational sensitivity of the differential interferometer may alternatively be realized by arranging a special reflector between the substrate interferometer and the mask interferometer. An embodiment of this reflector unit is shown in FIG. 16. For example, this unit, which may be arranged at the position of the reflector 16 in FIG. 2, consists of a prism 37 and a penta-prism 40. The incident measurement beam bm traverses the prism 37 and is subsequently reflected by the side surfaces 38 and 39 of the penta prism and subsequently passes through the prism 37 towards the mask reflector.

FIG. 17 shows an embodiment of a differential interferometer system according to the principle of FIG. 13 in which this reflecting unit is incorporated. This figure shows a polarization-sensitive beam splitter 1 as well as a second interferometer unit or mask having a polarization-sensitive beam splitter 5, a retroreflector 19, a λ / 4 plate 8 and a reflector MI. And a first interferometer unit or substrate having a retroreflector 4 and a λ / 4 plate. Moreover, the system of FIG. 17 includes a split mirror 30 and a coupling-out prism 32. The projection lens PL of the projection apparatus in which the mask pattern is drawn on the substrate is disposed between the mask holder MH and the substrate holder WH. The projection lens has two extra reflectors RL1 and RL2, which reflectors constitute a reference reflector for the second and first interferometer units, respectively. The reflector 33, the λ / 4 plate 35 and the reflector 35 are disposed in close proximity to the lens reflector RL1, and the reflector 31 is disposed in close proximity to the lens reflector RL2. Similar to the previous figures, the measurement beam of FIG. 17 is also shown in solid lines and the reference beam is shown in dashed lines. Arrows in these lines show the path and the measuring beam through the system is reflected on the mask reflector RM via two initial reflections on the substrate reflector RW, reflected on the reflector MI, and the system The path of the reference beam through is reflected on lens reflector RL1 via two initial reflections on lens reflector RL2 and reflected on reflector 35 and via two additional reflections on lens reflector RL2.

A reflector unit comprising the penta prism 40 with an interface 41 and a prism 37 are disposed adjacent to the mask interferometer. 18 shows how the measurement and reference beams arriving from the substrate interferometer pass through a subsystem consisting of a reflector unit and a second mask interferometer. This subsystem includes an additional reflector 45 and a quarter wave plate 46. Arrows in the beam show the path of the measuring beam through the subsystem via continuous reflections at positions q1 to q9.

The sensitivity of the differential interferometer system to rotation about the Z axis of the substrate is as described above. The method described above for the removal of this sensitivity can of course also be used to remove possible sensitivity to tilt, with respect to the X and / or Y axis of the substrate or mask of the differential interferometer system.

FIG. 19 shows a further embodiment of a differential interferometer system for a projection device in which the magnification of which the tilt or rotation of the substrate reflector is compensated for is M = 1/4. The substrate interferometer unit includes a polarization-sensitive beam splitter 1 and a λ / 4 plate 2, as well as an additional λ / 4 plate 50 and a reflector 52 and retroreflector 51 for the reference beam. Include. The dotted line again shows the path of the reference beam which is not the same as the path of the measuring beam. This beam is first reflected twice by the substrate reflector RW at positions r1 and r2, and the reference beam is first reflected twice on the reference reflector 52. These beams then go to the mask interferometer unit 60 and the mask reflector RM. In FIG. 20, the mask interferometer unit 60 is shown in an enlarged size. This unit not only includes a polarization-sensitive beam splitter 5 and a λ / 4 plate 8, but also an additional λ / 4 plate 53, a reflector 57 and a retroreflector 54, 55 and 56 for the reference beam. It includes. The arrows in the measuring beam bm and the reference beam br show the unit pass path of these beams. The measuring beam is continuously reflected at positions r3 to r9 and then returns to the substrate reflector and substrate interferometer unit which reflects the beam twice again at positions r10 and r11 before sending the beam to the detector.

21 illustrates another embodiment of a subsystem including a mask interferometer and a reflector unit. The unit includes a first prism 60 having a reflecting surface 61 and a second prism 65 having reflecting surfaces 66, 67. By using this reflector unit the measuring beam and the reference beam on the subsystem passage path are not reversed, i.e., the left and right parts of the beams are not interchangeable. This is illustrated by the arrow perpendicular to the beam. The measuring beam, shown in solid lines, is continuously reflected at positions s1 to s7, in particular in a way that is reflected once by the mask reflector RM and once by the reflector MI. In addition, the reference beam shown in dashed lines is in particular reflected twice by the reflector 45 and seven times in total.

FIG. 22 shows an embodiment similar to the embodiment shown in FIG. 21 except that prisms 60 and 65 have been replaced by trapezoidal prism 70 with reflective surfaces 71, 72 and 73. do. Further, in this embodiment, the measuring beam is reflected seven times at the positions t1 to t7 as with the reference beam. The beam may have a width of 1/4 · a in this embodiment, whereas the beam may have a width of 1/2 · a in the embodiment shown in FIG. 21, where a is the width of the beam splitter 5. Height.

FIG. 23 shows a further embodiment of the differential interferometer system in which the measurement beam bm is reflected an odd number of times in the path through the mask interferometer sub-system to compensate for the rotation of the substrate reflector RW. The figure also shows a desired radiation source 80, for example HeNe but a laser (HeNe Zeeman laser), and two lenses 82,83 constituting a beam expanding optical system. The substrate interferometer has the same structure as that shown in FIG. The mask interferometer differs from the interferometer shown in FIG. 1 and a retroreflector 87 instead of the reflector MI of FIG. 1 disposed between the λ / 4 plate 8 and the substrate reflector RM. Moreover, the path of the reference beam is combined with the λ / 4 plate 46 and an extra reflector 88 is arranged above the re reflector 7. The measuring beam bm arriving from the position P2 on the substrate reflector is reflected by the retroreflector 87 by the interface 10 of the beam splitter 5. The measurement beam is sent to the retroreflector 6 via the reflection on the inclined surface of the reflector. This reflector continuously sends the measuring beam to the mask reflector RM. The measuring beam reflected at position P4 of this reflector is reflected by the interface 10 to the substrate interferometer system. After being continuously reflected by the substrate reflector at positions P5 and P6, the measuring beam b'm is sent to the detector 90 via reflectors 86 and 85. The reference beam br, which has arrived from the substrate interferometer system, goes through the interface 10 to the retroreflector 7 and is reflected back to the interface 10 by the retroreflector. This interface then reflects the reference beam to the retroreflector 6 and the retroreflector 6 reflects the reference beam back to the interface 10. This interface continuously reflects the reference beam to the reflector 88. The reference beam reflected by the reflector 88 then goes through the interface towards the substrate interferometer.

FIG. 24 shows an alternative embodiment to the embodiment shown in FIG. 23, in which retroreflectors 7, 87 are replaced with penta-prism 92 and reflector MI in the mask interferometer. . The measuring beam bm arriving from the substrate interferometer system is reflected by the interface 10 to the reflector MI, which reflects the measuring beam to the unit 92. This unit reflects the measurement beam to position P4 on the mask reflector RM. The measuring beam reached from the position P4 is reflected by the interface 10 towards the substrate interferometer. The reference beam br, which has arrived from the substrate interferometer, is directed through the interface 10 towards the reflector 88, which reflects the beam back to the interface. This interface then reflects the reference beam to unit 92, which sends the reference beam back to the interface. This interface continuously reflects the beam to the reflector 88, which directs the beam to the substrate interferometer via the interface.

25 shows the effect of the compensation described above by being reflected an odd number of times in the mask interferometer. The figure shows the contrast of the interferometer signal as a function of the rotation in mrad of the substrate reflector. Curve 95 applies when there is no compensation and curve 96 applies when compensation is used.

The above compensation of substrate reflector tilt or rotation can be used in a single system as well as in a differential interferometer system. That is, it may be used in an interferometer system having only one interferometer unit, for example, used in a stepping lithographic projection apparatus, wherein the apparatus only measures the movement and position of the substrate holder with the interferometer system. 26A-C illustrate embodiments of the interferometer system with different cross sections.

The incident measuring beam as shown in FIG. 26B first goes to the substrate reflector RW via reflection u1 on the interface 9 of the beam splitter 1, where the beam is located at position u2. Is reflected from. Subsequently, the measuring beam traverses the beam splitter 1 via reflection at positions u3 and u4 of the retroreflector 4 and is subsequently reflected at position u5 by the substrate reflector The beam splitter then exits the beam splitter via reflection on interface 9. The reference beam is continuously reflected at positions u7, u3, u4, u6, u8, and in particular, is reflected twice on the reference reflector 130 via the λ / 4 plate 131. The measurement beam and the reference beam reached from the beam splitter 1 are continuously reflected at positions u9, u10 and u11 by the surfaces 126, 127 and 121 of the prism 125 and 120, respectively, as shown in FIG. These beams enter the beam splitter 1 again. As shown in FIG. 26C, the measuring beam is continuously reflected at positions u13 and u14 of the substrate reflector. The measuring beam and the reference beam arriving from the beam splitter thus undergo three reflections before they enter the beam splitter again.

From the foregoing, it can be inferred that the position of the mask and the substrate can be measured only in one direction in the scanning direction or the X direction. As described in EP 0 498 499, a substrate interferometer system with five measuring axes can be used in a stepping lithographic projection apparatus and can measure not only the X position but also the Y position and the optical axis or Z axis. The rotation of the substrate and the inclination of the substrate with respect to the X and Y axes can be measured. For example, then two interferometer units are used, one with three measuring axes and the other with two measuring axes. In addition, the differential interferometer system can extend to five measurement axes, the system then having, for example, five measurement axes at the position of the substrate and the position of the mask, the differential measurement being for example this axis Wash everything along.

When the above-described differential interferometer system is used in a step-and-scan lithographic apparatus, the following advantages can be obtained.

-Interferometer measurements can be obtained independent of device instability,

The measurement is a measurement independent of the positional instability of the projection lens,

The measurement is insensitive to disturbances between the mask interferometer and the substrate interferometer such as air turbulence,

No electrical delay problem occurs during the scan-drawing of the mask pattern,

The measurement is insensitive to the tilt or rotation of the substrate holder,

The resolution of the measurement is increased, and

The number of interferometers required is reduced.

The present invention is described with reference to an example of use used in a step-and-scan drawing apparatus of a mask pattern on a substrate for manufacturing a collecting circuit. However, it can also be used in integrated optical systems, two-dimensional optical systems, devices for manufacturing induction and detection patterns for magnetic region storage devices, liquid crystal image display panels, and the like. The projection apparatus is not only used for photolithographic apparatus in which the projection beam is a beam of electromagnetic radiation such as deep UV radiation and the lens system is an optical projection lens system, but the projection radiation is electron radiation, ion radiation, ray Charged-particle radiation, such as X-ray radiation, may also be used in devices in which projection systems such as, for example, electronic lens systems are used.

Claims (9)

An interferometer system for measuring the movement and mutual position of a first and a second object in at least one direction, For one or more all possible directions of mutual movement, A first interferometer unit having a first beam splitter, a first measuring reflector and a plurality of first reflectors and combined with the first object; And An interferometer system comprising a second interferometer unit having a second beam splitter, a second measuring reflector and a plurality of second reflectors and combined with the second object, In operation a measuring beam passes through both the first and second interferometer units and is reflected more than once by both the first and second measuring reflectors, The first and second interferometer units have a common radiation-sensitive detector, A reference beam in combination with the measuring beam traverses in the same path as the measuring beam between the first and second interferometer units. The method of claim 1, Measure the mutual position of the first object moving at speed v and the second object moving at speed n · v, The ratio between the number of reflections of the measuring beam reflected by the measuring reflector in combination with the first object and the number of reflections of the measuring beam reflected by the measuring reflector in combination with the second object is n, where n Is an integer. The method according to claim 1 or 2, In order to eliminate the influence of the tilt or rotation of the first object on the interferometer signal, the second interferometer unit may be configured such that the measuring beam arriving from the first interferometer unit is returned to the first interferometer unit. Interferometer system, characterized in that m + one reflection in the interferometer unit, where m is an even number greater than two. An apparatus for multi-imaging a mask pattern on a substrate in accordance with a step-and-scan principle, A mask holder disposed on a mask table, a substrate holder disposed on a substrate table and a projection system disposed between the mask table and the substrate table, An apparatus for multiplexing a mask pattern, characterized in that the interferometer system described in claims 1 or 2 for measuring the mutual position of the mask and the substrate constituting the first and second objects. The method of claim 4, wherein Between the number of reflections of the measurement beam reflected by the measurement reflector combined with the mask and the number of reflections of the measurement beam reflected by the measurement reflector combined with the mask, with the mask pattern being drawn on the substrate at magnification M A mask pattern multi-drawing apparatus, characterized in that the ratio of 1 / M. The method of claim 4, wherein And the measuring reflector in combination with the substrate and the measuring reflector in combination with the mask are respectively constituted by reflecting surfaces of the substrate holder and the mask holder. The method of claim 4, wherein And the interferometer system comprises a projection system interferometer unit for measuring the position of the projection system at a location, the projection system having an extra measurement reflector at the location. The method of claim 7, wherein And said projection system interferometer unit is traversed by said measuring beam. The method of claim 4, wherein And said projection system has two additional measuring reflectors, respectively, in positions proximate said mask holder and said substrate holder, and said reference beam is reflected by both measuring reflectors.