JPH0785465B2 - Observation device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an observing device, and more particularly to an optical system for observing an object having a transparent thin film on its surface and detecting the information. A typical example of this type of optical system is an exposure apparatus that aligns a wafer coated with a photoresist with a reticle, such as a stepper.

[Problems to be Solved by Prior Art and Invention] The two basic performances of this type of exposure apparatus are resolution and overlay accuracy. The resolution is very simple to handle. This is because there are few parameters that determine the resolving power, and in a device called a stepper, the resolving power of the optical system can be easily inferred if only the wavelength used and the numerical aperture (NA) of the projection lens are known. In addition, even in the case of X-ray exposure, there are only limited parameters such as penumbra blurring due to the size of the light source.

Since the realization of one transistor of the memory cell, it has been the progress of lithography, that is, the fine line width printing technology and the progress of the process technology such as etching, which has played a role in the high integration of semiconductors. Regarding the resolving power, the optical system has been steadily improving, as can be understood by tracing the history of the stepper lens. The optical method breaks the wall of 1 μm, and lenses for the submicron era are being announced one after another.

On the other hand, in the process as well, new ideas have been realized with the idea of three-dimensional IC in combination with the low step and high step such as the trench digging method. Advances in resolution on the exposure equipment side and advances on the process side will find the greatest point of contact in the stage of superimposing patterns of each process. In that sense, it can be said that overlay accuracy is becoming more and more important in exposure equipment.

It is difficult to display overlay accuracy with simple parameters that deal with resolution. It shows the variety of wafer processes, but on the other hand, it can be said that it is due to the variety of configurations of alignment systems for overlaying. The reason why the wafer process factor is made more complicated is that the problem is not limited to one wafer substrate, and it is necessary to discuss the photoresist including the photoresist coated on the wafer. One of the clear directions of current semiconductors is the flow toward the three-dimensional construction of ICs. Among them, it is inevitable that the wafer surface has a high level difference, but this high level difference has a clear adverse effect on the coating state of the photoresist. Wafers are becoming larger and larger, from 6 inches to 8 inches and even 10 inches. When photoresist is applied to a large-diameter wafer by the spin method, it is obvious that the resist application situation is different between the central part and the peripheral part, and the difference may be more remarkable as the step difference on the wafer surface is larger. it is obvious. In fact, it is known that the alignment state changes under the influence of resist coating, and conversely, research has been conducted on how to perform uniform coating.

Another point to note in photoresists is the trend toward multilayering in the submicron era. Measures for improving the resolution, such as the multi-layer resist process and CEL, are inevitably adopted in some steps, and countermeasures against them are also necessary. It can be said that the exposure apparatus is forced to deal with these new wafer processes in the stage of overlaying.

On the other hand, the variety of alignment systems is a proof of the flexibility and difficulty of system configuration.
At present, no single alignment system has been proposed and implemented, and each system has its own advantages and disadvantages. For example
58-25638 “Exposure device” is one example. This system is one of the excellent configuration examples that realized the idea of TTL on Axis by using the telecentric optical system for both the reticle and the wafer as the projection optical system. Although the projection lens has been corrected for aberrations with respect to the g-line (436 nm), the same performance is also exhibited at the He-Cd laser wavelength (442 nm). In one embodiment disclosed in this patent application, a laser beam scanning method using a He-Cd laser is adopted as an alignment signal detection method, which results in TTL
It is possible to immediately start the exposure operation on the Axis, that is, in the aligned state. The TTL on Axis system has the least systematic error factor in the sense that there is only one alignment signal detection error as an exposure device, and it is close to the ideal system. The only drawback of this system is that it is vulnerable to processes such as multilayer resists that absorb wavelengths near the exposure wavelength.

On the other hand, on the other hand, a wavelength other than the exposure wavelength, specifically e
Many system configuration examples using longer wavelengths such as line (546 nm) and He-Ne laser (633 nm) have been proposed.
This system has the advantage of being robust against absorption-type processes such as multilayer resists, since wavelengths longer than the exposure wavelength are used. However, the image height for alignment is usually fixed with respect to the projection lens due to various color aberrations of the projection lens, and an error factor of moving the wafer to the exposure position after detecting the alignment is introduced. Become. Therefore, the alignment system with light other than the exposure wavelength is inevitably a TTL off Axis system.

However, in recent years, the requirement for overlay accuracy has become more and more strict, and even the detection error of the alignment signal, which is the error factor in the ideal system as shown in Japanese Patent Laid-Open No. 58-25638, can be put into a problem area. ing. The present invention is characterized by improving the alignment accuracy by analyzing the detection error component of the alignment signal based on the conventional example and removing the error factor.

According to the analysis of the detection error component of the alignment signal by the inventors of the present application, it has been found that most of the error component is mainly due to the photoresist coating problem. There are various causes of error due to the photoresist, and the largest of these is considered to be the following two factors.

The first is the effect of interference between the light reflected from the surface of the resist and the light that passes through the resist and strikes the wafer substrate and returns. In particular, as described above, the photoresist is not always uniformly applied within the wafer, and the applied state is often different between the center and the periphery. The wafer substrate itself also has a problem of uniformity in the wafer such as etching and sputtering. Therefore, the structure of the alignment mark of each shot in the wafer is different depending on the place when considering the resist and coating.
Therefore, the interference effect is also different. It is considered that the effect of this interference is the largest in causing the alignment error due to the influence of the resist coating.

The second factor is multiple reflection. The resist has a character as an optical waveguide. Therefore, a part of the light reflected by the wafer substrate is reflected by the interface between the resist and air, and returns to the wafer to be re-reflected. This effect is more remarkable as the reflectance of the substrate is higher, and this multiple reflected light eventually causes interference and deteriorates the alignment accuracy.

Other factors such as image shift due to refraction can be considered as factors of the resist, but these are only secondary factors, and it is possible to eliminate the two factors mentioned here, especially the first interference effect. As a result of the analysis, it was confirmed that it greatly contributes to the improvement of the accuracy of.

Therefore, it is an object of the present invention to provide a system that reduces interference effects and realizes higher alignment detection accuracy.

[Means for Solving the Problems] In order to achieve the above object, in the present invention, an apparatus for projecting and exposing a pattern drawn on a first object onto a second object coated with a resist via a projection optical system. In the observation device for observing the mark formed on the second object, the observation optical system for observing the mark via the projection optical system, and the light flux of the light flux that the observation optical system has on the second object. NA
In the case of sinA, the illumination light for illuminating the second object has a dark field illumination optical system that makes an angle with the optical axis of the observation optical system about A + 10 °.

In addition, the features of the present invention, such as various embodiments of the present invention, are described in the following examples.

[Embodiment] An embodiment of the present invention is shown in FIG. FIG. 1 is an example in which the present invention is applied to a stepper, that is, a reduction projection exposure apparatus.

In the figure, the reduction lens 3 serves to project and expose the pattern 2 on the reticle 1 onto the wafer 4. The reduction lens 3 is provided with the unevenness of the wafer to be printed,
Usually, the wafer side is usually telecentric so that the distortion and the magnification do not change due to focus fluctuations caused by measurement drive errors of the autofocus system arranged between the lens 3 and the wafer 4. is there. In addition, the place corresponding to 2 on the wafer corresponds to 5 in FIG.

The most important feature of the present invention resides in the illumination system arranged below the projection lens 3. It should be burned in Fig. 1,
The alignment mark 6 for the part 5 of the wafer is in this case illuminated obliquely by an illumination system which exists between the wafer 4 and the projection lens 3.

This is the most important part of the present invention.

As described above, the largest cause of the alignment signal detection error is interference between the surface reflection of the resist and the reflected light of the wafer substrate. There are several ways to eliminate this effect, but the most fundamental solution is to eliminate one. When observing the resist coating state with an SEM or an interference microscope, even if the wafer has a very large step structure, the slope of the resist surface coated on it is only about 5 ° at the maximum and steeper than that. It turns out that there is no slope. Due to the problem of step coverage, it is usual to apply a resist having a thickness larger than that to a large step, and as a result, a value of about 5 ° can be set. Therefore, the present invention is characterized in that the following conditions are added to the illumination light as shown in FIG. That is, (maximum angle A + 10 ° that the detection optical system has on the wafer) ≤ (incident angle B of the illumination light to the wafer) (1) In this way, the component of the illumination light reflected on the resist surface is detected. It does not enter the optical system and escapes to the outside (Fig. 2). Therefore, only the reflected light from the wafer substrate can be captured by the detection optical system. Since the light intensity detected by the detection optical system generally decreases as the incident angle of the illumination light on the wafer increases, the angle B formed by the illumination light with the optical axis of the observation optical system in the previous period is preferably about A + 10 °. . The detection optical system in FIG. 1 means the entire observation optical system of the wafer through the projection lens 3 and the alignment scope optical system 7 to the photoelectric conversion means 8 such as CCD. When the exposure wavelength and the observation wavelength are different, a correction optical system such as 9 may be inserted to enable simultaneous observation of the reticle and the wafer, or only the wafer is observed as shown in FIG. Therefore, an alignment scope optical system may be brought between the reticle and the projection lens. In the case of FIG. 3, the reticle is independently aligned by another alignment scope system, and the reference value calibration is performed so that the wafer system alignment reference and the reticle system alignment reference have a predetermined relationship.

The maximum angle A that the detection optical system has on the wafer is on the alignment scope side and coincides with the value determined by the NA of the projection lens unless a special aperture is set and the NA of the projection lens is restricted.
That is, if the lens has NA of 0.35, A = sin ^-1 0.35 =
Since it is 20.49 °, the incident angle B of the illumination system must be 30.49 ° or more. If there is a diaphragm on the alignment scope side and the NA of the projection lens is restricted,
The value of is smaller than the value determined by NA. All TTL methods that have been proposed for steppers so far are methods that illuminate incident light from above via an alignment scope. On the other hand, the present invention is a method of illuminating the wafer from the outside of the projection lens, and succeeds in removing the reflection on the resist surface by providing a regulation value of 10 °. Being able to disperse scattered and diffracted light from the wafer substrate at the bottom of the resist means directly improving the alignment accuracy.

In the present invention, since the scattered light and the diffracted light from the wafer substrate itself are thus taken, it is advantageous to enter the illumination light as P polarized light so that the loss of reflection on the resist surface is reduced. Since the surface polarization of P-polarized light is smaller than that of S-polarized light, more light reaches the substrate. Further, if the incident angle is set at Brewster's angle, surface reflection is minimized, which is advantageous. It is also possible to determine other degrees of freedom, such as the shape of the mark, so as to meet this condition. In FIG. 1, reference numeral 10 denotes a laser, and illumination light from the laser 10 illuminates an alignment mark 6 on the wafer 4 via a mirror 11 and a lens 12.

Another feature of the illumination system of FIG. 1 is that light is incident from a predetermined direction corresponding to the pattern direction which is known in advance. For this reason, it is desirable that the illumination light has a directionality such that it is incident from a direction orthogonal to the edge of the mark to be detected.

FIG. 4 shows how to enter the illumination light when the dot marks are used. Here, it is assumed that the center position C in the width direction of the mark composed of dots is to be obtained as an alignment signal. In the example of FIG. 4 (A), the illumination light is incident from a direction that illuminates the edges P and P'which are the directions showing the width of the grating. The incident direction is indicated by arrows D and D '. In this case, the image actually observed on the image plane is as shown in FIG. 5 (A), and the center position C can be obtained by receiving this image with a CCD or scanning it with a slit-shaped opening. it can. The way in which the edges P, P ′ shine corresponds to the incident directions D, D ′. However, the incident light from D does not always illuminate P, and P ′ may be brighter than P depending on the step amount of the substrate and the coating state of the resist. Although the asymmetry of P and P'is eased when the illumination light is introduced from two directions of D and D ', the symmetry of both is not particularly necessary when obtaining C. Fig. 5 (A) I understand more. Therefore, when considering the system configuration, it is not always necessary to insert D and D'symmetrically from two directions, and only one of them may be inserted, or even if they are inserted from both directions, an asymmetrical arrangement, that is, FIG. 4 (A) Α at
The position of C can be detected with sufficient accuracy without making the values of α ′ the same.

In the example of FIG. 4 (B), the illumination light is incident from the direction orthogonal to the direction of the illumination light in FIG. 4 (A). In the image observed in this case, as shown in FIG. 5 (B), an edge in the opposite direction to that in the case of FIG. 5 (A) is observed. Which direction of edges shown in (A) and (B) is illuminated depends on the signal processing method of the mark used. Further, the dot row is adopted in the description because it has edges in two directions as the mark, but needless to say, it is not limited to this example.

By adopting the above illumination method, it is possible to observe a bright image with a good S / N ratio even with monochromatic light without the influence of surface reflection. The mark portion 6 of the illuminated wafer is once focused on the position of the observation optical system 1 via the projection lens 3 and the correction optical system 9 in FIG. Then, it enters the alignment scope section and is captured as an image at position 8. As a method of shifting to the exposure operation after detecting the alignment state, various known system configurations such as a method of feeding a predetermined amount to the exposure position or retracting the correction optical system 9 out of the exposure light flux can be adopted. It is possible.

FIG. 3 is an example of a system for taking the wafer signal between the reticle and the projection lens in the system of FIG. The reticle 1 is separately aligned by a reticle alignment optical system (not shown). Although the laser 10 is also used for illumination, in this example, the beam is directly incident on the alignment mark 6 on the wafer by utilizing the directivity of the laser beam. The wafer signal is guided to 20 or less wafer observing optical systems via the projection lens 3. In the figure, 20 is an objective lens, 21 is an erector lens, and a galvanometer mirror 23 is disposed after the erector. The image of the wafer 6 is scanned by the galvanometer mirror 23, and the scanned image is guided to the photomultiplier 25 through the slit 24 placed on the image plane.
Accordingly, the auto alignment signal is detected. When the dark field illumination light and the exposure light have different wavelengths, it may be necessary to insert a correction optical system corresponding to 9 in FIG. 1 in front of 20 or in an optical system of 20 or less.

FIG. 6 is a modification of FIG. 3, but is characterized in that, in addition to 10, another 10 'laser beam having a different wavelength from 10 is incident. 10 is, for example, He-Ne laser (633 nm), 1
The 0 'A _r ⁺ ion laser (515nm) or green H
An e-Ne laser (543 nm) or the like is considered. The addition of the laser 10 'to the laser 10 depends on the step structure of the wafer.
This is because the scattered light from the 633 nm He-Ne laser may become extremely weak in some cases, and this has been dealt with. Since the weakening condition is closely related to the laser wavelength, when lasers of different wavelengths are made incident, their output characteristics become complementary and more stable measurement becomes possible. In this case, the wafer detection optical system is also separately provided in consideration of the difference in the chromatic aberration of the projection lens 3 depending on the wavelength. Further, it is efficient and advantageous to use a dichroic film for the beam splitter 13 for combining the two wavelengths.

Illuminating from outside the projection lens 3 so that the surface reflection of the resist does not enter the detection optical system is the conceptual diagram of the first, third,
This is shown in figure 6 briefly.

Conventionally, an autofocus function is provided between the projection lens 3 and the wafer 4 in the stepper era. As shown in the present invention, since the illumination method has not been positively defined, there has been no attempt to coexist both methods. However, since the condition satisfying the conditional expression (1) as in the gist of the present invention can be positively meaningful for the detection of the wafer information, coexistence of the both is considered,
It turned out that both can mechanically coexist. Also,
If the autofocus is performed by TTL, the autofocus mechanism between the projection lens wafers can be removed, so that this illumination method can be easily mounted between the projection lens wafers. Less than,
An example of the present invention on a specific implementation will be touched upon.

One of the most important problems in the dark field method of the present invention is the amount of light. Therefore, the present invention has consistently featured a combination of laser dark field illumination and a projection lens. The reason for this lies in the observation, which is different from the exposure wavelength, and the chromatic aberration of the projection exposure system 3 when a wavelength is used. Generally, the projection lens 3 is designed to exhibit the best performance at the exposure wavelength,
In many cases, performance at the observation wavelength is left unchecked. For example, a lens for g-line (436 nm) is designed with consideration given to the spectral width of the g-line, and as shown in FIG.
The wavelength vs. focus change is shown as if touched by a line. For this reason, when the observation wavelength is different, the coefficient of change due to the focus color becomes extremely large. For example, it is conceivable to use e-line (546 nm) of mercury as a dark-field illumination light source, but considering the spread of the spectrum of this e-line, a focus change of about 10 μm may occur. . This chromatic aberration is not the amount that can be completely corrected in the alignment optical system shown in FIG. As one measure, it may be possible to insert a bandpass filter with a narrow band, but in that case, the drop in light quantity cannot be ignored.
On the other hand, if the spectrum is not narrowed, there is a problem that the contrast is lowered due to the focus shift in the spectrum. The reason why a laser is used for dark-field illumination as in the present invention is that the spectral width of the laser is so small that it can be neglected, so that the laser can be freed due to such restrictions of the projection lens. In addition to the focus change, various aberrations occur depending on the color, which can also be corrected by utilizing the monochromaticity of the laser. 9 in FIG. 1 corresponds to this. Regarding the correction and the like, Japanese Patent Application Laid-Open No. 62-28
A detailed explanation is given in No. 1422 “Exposure Device”.

Since the light source itself of the laser has high brightness, it is very advantageous in terms of the amount of light. Also, as a countermeasure against disappearance due to interference of signals based on monochromaticity, as shown in FIG. You can also see it at. As for the incident angle here, the marks have a pitch as shown in FIG.
When illuminating from the direction as shown in FIG. 3A, it is preferable that the incident angle is such that the nth-order diffracted light emerges in parallel with the optical axis of the projection lens 3. Since a grating having such a pitch is a kind of grating, the well-known diffraction theory of grating is established. Generally (1)
In the case where the condition is satisfied, the detection system often detects considerably higher-order light such as third-order light or fourth-order light. Normally, the higher the order of diffracted light, the smaller the amount of light. Therefore, if the diffracted direction is predetermined, it is preferable to make the diffracted light of any order parallel to the optical axis of the projection lens 3. This is related to the fact that the projection lens 3 has a telecentric structure on the wafer side so that the distortion does not change due to the unevenness of the wafer and the accuracy of autofocus. That is, in the example of FIGS. 1, 3, and 6, the position observed by the detection optical system is outside the optical axis of the projection optical system 3, but because of the telecentricity, the chief ray at this observation point is also It is parallel to the optical axis and perpendicular to the wafer surface.

In the case of an ordinary silicon wafer, a sufficiently good S / N signal can be obtained by such a simple illumination method. However, it is also possible to adopt the illumination method as shown in FIG. 8 in order to further increase the S / N ratio and the detection rate.

FIG. 8A shows an example in which the illumination light emitted from the laser 10 is vibrated by the galvanometer mirror 31 to illuminate the alignment mark 6 on the wafer. In this example, the reflecting point of the vibrating mirror is placed at a position substantially conjugate with the mark 6, and the angle of incidence on the mark 6 is changed according to the rotation of the mirror. The change of the incident angle changes the scattering and diffraction condition of the edge of the alignment mark, so that the signal output changes. In particular, when the amount of step difference at the edge is matched with the wavelength of the laser and there is a condition for canceling signals, the effect of this change in the incident angle is great. The incident angle can be changed not only by the reflection type as shown in FIG. 8A but also by the transmission type as shown in FIG. 8B, and various modifications can be considered. When the incident angle is changed with time, it may be synchronized with the detection system. For example, in the example of FIG. 1, the detection is CCD, but in this case, it is synchronized with the timing of reading the CCD, or the change in the incident angle is made faster than the reading, and It is necessary not to have an influence.

As another means, it is of course possible to control the change of the incident angle at the most advantageous position of signal output.

The embodiment shown in FIG. 9 is an example in the case of illuminating with a fiber without directly going through a mirror or the like. Due to the space problem between the projection lens and the wafer, it is difficult to route the laser light, and it may be better to use a fiber as the illumination means. FIG. 9A shows an example in which Koehler illumination is performed using the fiber outlet 35 as a secondary light source. The lens 12 is not always necessary depending on the distance. In the present embodiment using the fiber bundle, a demerit of using the fiber, that is, speckle interference of laser light occurs on the wafer surface. In order to remove the influence of speckles, in this embodiment, the laser beam entering the fiber bundle is oscillated by the galvanometer mirror 31 and the motor 32 and temporally integrated, and as a result, speckles on the wafer surface are removed. Is used. The galvanometer mirror can be replaced with a rotary polygon mirror or an AO element, but the same thing as described with reference to FIG. 8 can be said in terms of the synchronous relationship with the detection system.

FIG. 9B shows an example of critical illumination. In this case, the exit 35 of the fiber is imaged on the mark 6 on the wafer surface by the lens 12 as the secondary light source. In such an example, the non-uniformity of illumination due to the core of the fiber may cause speckle. Therefore, in FIG. 9 (B), the galvanometer mirror is placed in the optical path on the way to perform scanning to remove the illumination unevenness. The relationship of synchronization with the detection system is the same as before.

Although the principle of the preferred embodiment has been mainly described with reference to FIGS. 7 to 9 in a two-dimensional sectional view, in actuality, the illumination system on the side of the apparatus must consider the correlation with the mark. For example, in the example of FIG. 9, the auto alignment mark 6 is a line extending in the direction perpendicular to the paper surface. It is sufficient that the alignment mark is formed only by the edges in this direction, but if there is a line orthogonal to this in the mark, the line will not be detected by the detection system at all (FIGS. 4 and 5). reference). For example, consider a case where the auto alignment mark 6 is composed of four rectangles as shown in FIG. 10 (A). If these four lines are observed in the embodiment of FIG. 1, for example, they will be as shown in FIG.
Alignment is achieved by sandwiching the reticle mark shown by the dotted line.

The mark in Fig. 10 is the line in Fig. 11 (A) because of its function.
It is divided into two areas U and L so as to be divided by 40. Then, when light is applied to each region in the direction indicated by the arrow in the figure, the edges for alignment appear to shine as shown in FIG. 11 (B). At this time, there is also a method in which light is incident from four directions at a time, but in the case where a rough surface wafer is the target, if the light in the vertical direction necessary for the U area is also applied to the L area, Then, it may become background noise and reduce the S / N ratio. Conversely, the same applies when the left-right light necessary for the L region is mixed in the U region. Therefore, the preferred embodiment of the present invention is characterized in that the illumination system has a field stop in accordance with the desired region of the mark to limit the irradiation area as shown in FIG. Reference numeral 41 in the figure denotes an illumination area limiting slit, and the illumination area is limited by projecting this slit onto the wafer mark through the imaging lens 12.

This figure shows the case of the illumination method using the fiber of FIG. 9 (A) type.

In order to more tightly limit the illumination area, it is difficult to understand in FIG. 12, but it is convenient to tilt the slit with respect to the optical axis so as to satisfy the tilting condition, as schematically shown in FIG.

In addition, FIG. 14 shows the directions in which the light is made incident on the U region and the L region.
A suitable mark is shown when the light is incident perpendicularly to the direction of the drawing.

The slit 41 provided in the illumination system has another effect. Since the feature of the present invention is that the surface reflection of the resist is removed, the wavelength is not limited to non-exposure light, and the same applies to exposure light. However, if the exposure light is illuminated without the slit 41,
The actual element mark near the alignment mark is exposed. Therefore, when the light for exposing the resist is used, this problem can be solved by installing a field stop for illuminating only a desired portion of the alignment mark in the illumination system.

In addition, although the field limiting slit 41 is used in FIG. 12, in the case of using a scanning system such as that used in FIG. 3 even in a system that simply switches the illumination direction, four fibers are synchronized with the scanning at the entrance. It is also possible to improve the S / N ratio similar to that of a field stop by turning the AO element on and off.

Various modifications between the projection lens 3 and the wafer 4 have been described above. In any case, the irradiation angle satisfies the expression (1), and the surface reflection of the resist can be removed, so that the wafer can be removed. The signal is captured correctly and the alignment accuracy is significantly improved.

On the other hand, although it is a detection system, even though the detection system may have a rough surface on the wafer or insertion of a correction optical system unless there is a particularly high step, the detection system will eventually become a normal microscope system. It is enough to connect. However, in the case of a rough surface, it is not possible to take out only the edge signal from the light scattered in the direction generated by the rough surface, and at high steps, the wraparound of light due to multiple reflection cannot be ignored.

For example, FIG. 15 shows the light quantity distribution at the pupil position of the detection system objective lens, but FIG. 15 (A) shows a rough surface which is uniformly spread over the entire pupil. On the other hand, FIG. 4B shows a diffracted light distribution from the alignment mark when light is applied to the dot pattern as shown in FIG. 4 as shown in FIG. In this case, three high-order diffracted lights are in the pupil. Therefore, when the spatial frequency filter as shown in FIG. 15 (C) is inserted in the objective lens, the S / N ratio is improved and the signal of the desired pattern can be extracted. This filter can have various shapes depending on the marks used. On the other hand, creating a filter corresponding to the alignment mark in this way can reduce the influence of multiple reflection.

[Effects of the Invention] As described above, according to the observation device of the present invention,
By using the illumination system and the detection system to flexibly take the measures described for various wafers, it becomes possible to observe only the wafer information without removing the influence of interference with the resist. This method is very effective not only for auto-alignment but also for auto-focusing such as auto-focusing for accurately extracting information on a wafer coated with a resist.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an observation apparatus according to an embodiment of the present invention, FIG. 2 is a diagram showing illumination light to a wafer and reflection components on a resist surface thereof, and FIG. 3 is a reticle. FIG. 4 is a diagram showing an example in which an alignment scope optical system is arranged between a projection lens and FIG. 4, FIG. 4 is a diagram showing an irradiation direction of illumination light when a dot mark is used, and FIG. FIG. 6 is a diagram showing an image actually observed on an image plane by illumination, FIG. 6 is a diagram showing an example in which two laser beams having different wavelengths are made incident, and FIG. 7 is illumination light on a wafer and scattering at a mark. FIG. 8 is a diagram showing diffracted light, FIG. 8 is a diagram showing an example of irradiating an alignment light on a wafer by vibrating the illumination light, and FIG. 9 is a diagram showing an example of illuminating with a fiber. Shows an example of the alignment mark. FIG. 11 shows the alignment mark shown in FIG. Fig. 12 is a diagram showing the direction of illumination light with respect to the ark, Fig. 12 is a diagram showing an example of an illumination system having an irradiation area limiting slit, and Fig. 13 is a diagram showing that the slit satisfies the tilting condition with respect to the optical axis. FIG. 14 is a diagram showing an example in which the mark is suitable for illumination from a direction orthogonal to the direction shown in FIG. 11, and FIG. 15 is a light amount distribution at the pupil position of the detection system objective lens. FIG. 16 is a graph showing wavelength vs. focus change. 1: reticle, 4: wafer, 6: alignment mark, 7: alignment scope optical system, 8: photoelectric conversion means, 9: correction optical system, 10, 10 ′: laser light source, 12: imaging lens, 23, 32: Galvano mirror, 35: fiber exit, 41: irradiation area limiting slit.

Claims (5)

[Claims] 1. A mark formed on a second object in an apparatus for projecting a pattern drawn on the first object onto a second object coated with a resist through a projection optical system, and observing the mark formed on the second object. In the observation device, an observation optical system for observing the mark via the projection optical system, and an NA of a light flux that the observation optical system has on the second object are sinA
And a dark field illumination optical system that makes an angle of illumination light for illuminating the second object with the optical axis of the observation optical system approximately A + 10 °. 2. The observation apparatus according to claim 1, wherein the illumination light is P-polarized light and is incident on the second object. 3. The observation device according to claim 1, wherein the illumination light is incident at a Brewster angle of the resist. 4. The observation device according to claim 1, 2 or 3, wherein the light source of the illumination light of the illumination optical system is a laser. 5. The observation apparatus according to claim 1, wherein a spatial frequency filter corresponding to the mark is arranged in the observation optical system.