JPS63153820A - Projection exposure device - Google Patents

Abstract

PURPOSE:To bring illumination beams to a state of double foci by utilizing a Fresnel pattern or a polarizing lens (a double focus element), and to eliminate the need for a particular correction lens by using illumination beams having a wavelength different from exposure beams as beams for alignment. CONSTITUTION:Laser beams from a laser beam source 30 are reflected by a beam splitter 80, and projected to a mark section for alignment in a reticle 16 as mutually different polarized light components (P-polarized light and S- polarized light) through each of a scanner 83, a double focus lens 32, an objective (a telecentric one is preferable) 81 and a mirror 38. Each of the reflected beams of illumination beams applied to the reticle 16 and a wafer 24 by the characteristics of the double focus lens is transmitted through the beam splitter 80, beams having one polarized light characteristics is transmitted by a polarizing plate 87 and projected to a photodetector 66, and beams having the other polarized light characteristics are reflected and projected to a photodetector 52.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a projection exposure apparatus, and particularly relates to an improvement of an alignment method in the apparatus.

[Prior Art] Of the methods of aligning a mask or reticle to a square using a projection exposure apparatus, in a method that uses light of a wavelength different from the exposure wavelength, the reticle and the square align at the same wavelength as the exposure light. On the other hand, since they are in conjugate positions, the reticle and wafer are not necessarily in conjugate positions with respect to the wavelength of the alignment light.

For this reason, countermeasures have been taken such as inserting a correction lens or changing the optical path.

[Problems to be Solved by the Invention] However, with the above-mentioned measures, there is a problem that offset is likely to occur and the alignment position is fixed.

Furthermore, when light at the exposure wavelength is used as alignment light, there is a problem that the resist on the wafer is exposed to light during alignment, and the marks used for alignment cannot be used again.

In particular, when a dyed resist that absorbs exposure light and does not reflect it is used as the resist, there is a problem that alignment becomes difficult.

The present invention has been made in view of these points, and it is an object of the present invention to provide a projection exposure apparatus that can perform highly accurate and good alignment without alignment offset.

[Means for Solving the Problems] The present invention utilizes the fact that light transmitted or reflected through a Fresnel pattern or light transmitted through a lens with polarization characteristics (bifocal element) forms images at two positions. However, the technical point is that the illumination light is imaged on the reticle and the wafer by making the interval between the imaging positions correspond to the amount of chromatic aberration of the projection optical system.

[Function] According to the present invention, illumination light having a wavelength different from that of exposure light is used as alignment light. Therefore, the resist is not exposed. Since a Fresnel pattern or a polarizing lens (bifocal element) is utilized to bifocal the illumination light, there is no need to insert a special correction lens into the alignment optical path between the reticle and the square.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a first embodiment of a projection exposure apparatus according to the invention. In this figure, projection lens 10 is composed of lenses 12 and 14.

A reticle 16 is placed above the projection lens 10 and is held by a reticle stage 18 . A condenser lens 20 is disposed above the reticle 16, and the exposure light is incident on the reticle 16 through the condenser lens 20.

A wafer 24 is placed on a stage 22 below the projection lens 10, and a reference mark 26 is provided on the stage 22 at an appropriate position on its end side.

Next, laser light 28, which is alignment light having a wavelength different from that of the exposure light, is output from a laser light source 30.

The laser beam 28 is made to enter the alignment mark portion of the reticle 16 via a Fresnel pattern plate 32, a beam splitter 34, an objective lens 36, and a mirror 38, respectively.

Next, the laser beam 28 that has passed through the reticle 16 further passes through the projection lens 10, enters the wafer 24, is reflected there, returns to the outward path, and passes through the reticle 16 again, passing through the mirror 38 and the objective lens 36. The beam is made incident on the beam splitter 34.

Then, the laser beam 2 reflected by the beam splitter 34
The reflected light of 8 is incident on a half mirror 40, and one of the reflected lights is incident on a light receiving element 52 via a lens 42, an aperture 44, a lens 46, a spatial filter 48, and a lens 50, respectively.

The reflected light of the other laser beam 28 is reflected by the mirror 54 and the lens 5.
6, aperture 58, lens 60, spatial filter 62,
The light enters the light receiving element 66 through each lens 64.

Next, the light receiving element 52 and the light receiving element 66 are each connected to a signal processing section 68, and are connected to the Fresnel pattern plate 3 described above.
The second drive section 70 is also connected to the signal processing section 68. This signal processing section 68 is connected to a main controller 76 along with a drive section 72 of the stage 22 and an interferometer 74 that detects the position of the stage 22.

Among the above components, the Fresnel pattern plate 32 has a pattern as shown in FIG. 8, for example, and the laser beam 28 that passes through this is focused at two positions. In this example, the first focal point (the focal point of the first-order diffracted light)
is P, and the second focal point (the focal point of the second-order diffracted light) is Q.

The first focal point P is imaged on the reticle 16, as shown by the solid line in FIG.
is arranged to form an image on the wafer 24, as shown by the broken line.

That is, the first focus P is conjugate with the reticle 16, and the second focus Q is conjugate with the wafer 24.

Then, when the Fresnel pattern plate 32 is driven by the driving unit 70, each imaged pattern comes to vibrate on the reticle 16 or the wafer 24, and the reticle 16
Alternatively, optical information from a pattern (mark) on the wafer 24 is read by the light receiving element 52 or the light receiving element 66.

Next, the reflected light of the illumination light projected onto the reticle 16 and the wafer 24 by the action of the Fresnel pattern of the Fresnel pattern plate 32 is reflected by the beam splitter 34, and further split by 40, and sent to the light receiving elements 52 and 66.
The beams are made incident on each of them.

Among the above, the lens 42, the aperture 44, the lens 46, and the spatial filter 48 that make the reflected light enter the light receiving element 52
, the lens 50 transmits an image (diffraction, dark field image due to scattered light) of the reflected light from the reticle 16 to the light receiving element 5.
Its optical properties have been set so that it can be imaged on 2. In addition, the mirror 54, lens 56, aperture 58, lens 60, spatial filter 62, and lens 64 that make the reflected light enter the light receiving element 66 are used as a whole to form an image (diffraction, dark-field image due to scattered light) of the reflected light from the wafer 24. ) is set so that it can be imaged on the light receiving element 66. Further, the aperture 44 is connected to the reticle 16.
The aperture 58 is arranged conjugately with the pattern (or mark RM) of the wafer 24, that is, the point P, and the aperture 58 is arranged conjugately with the pattern (or mark WM) of the wafer 24, that is, the point Q.

Next, the signal processing unit 68 detects the positional deviation of the alignment mark from the detection outputs of the light receiving element 52 and the light receiving element 66, and outputs the result to the main controller 76.

The main controller 76 has a function of controlling the drive unit 70, grasping the position of the stage 22 based on the output of the interferometer 74, and controlling and adjusting the position of the stage 22 using the output of the signal processing unit 68. .

Next, the overall operation of the above embodiment will be explained with reference to FIGS. 2 to 7.

Note that FIG. 2 shows an example of alignment marks on the reticle 16, and has a configuration in which reticle marks RM+ and RM2 are formed within the window RW.

The illumination light SR of the reticle marks RMr and RM2 includes focused illumination light 5PR at the first focus (see the solid line) and unfocused illumination light 5QR at the second focus (see the broken line).

FIG. 3 shows the intensity distribution of the illumination lights SPR and SQR in the left-right direction in FIG. In the figure, (A) shows each distribution, and (B) shows the overall distribution. As shown in this figure, the illumination light SPR strongly illuminates a narrow area, whereas the illumination light SQR has a wide distribution.

Further, FIG. 4 shows an example of an alignment mark on the wafer 24, which corresponds to the wafer mark WM.

The figure also shows projected images of reticle marks RMI and RM2. The illumination light SW of the wafer mark WM includes unfocused illumination light spw at the first focus (see solid line) and focused illumination light 5QW at the second focus (see broken line). The intensity distribution of these illumination lights has a relationship opposite to that in FIG. 2.

First, by driving the Fresnel pattern plate 32 by the driving unit 70, the illumination light SR changes to the reticle marks RM, % R.
When M2 is scanned, light is strongly reflected (scattered) from the edge portion of the mark, and a photoelectric signal IR having a waveform as shown in FIG. 5 is obtained by the light receiving element 52. The center of the reticle marks RMI and RM2 is the beak X of the photoelectric signal IH.
Find the centers of A and XB and the centers of peaks XC and XD,
Next, the center between these centers may be further determined. Note that since the aperture 44 is not conjugate with the sea urchin surface, most of the light reflected from the sea urchin surface is blocked.

On the other hand, by driving the Fresnel pattern plate 32 described above,
When the illumination light SW scans over the wafer mark WM, the light is strongly reflected (scattered) from the edge portion of the mark, and a photoelectric signal IW having a waveform as shown in FIG. 6 is obtained by the light receiving element 66. The center of the wafer mark WM is the photoelectric signal IW.
It is determined from the center of the peaks XE and XF. Note that since the aperture 58 is not conjugate with the reticle surface, most of the reflected light from the reticle surface is blocked.

Photoelectric signal IR obtained as described above.

The IWs are each input to the signal processing unit 68, where they are added together to form an added signal as shown in FIG. 7, and the resulting signal is input to the main controller 76.

Then, the positional deviation d between the reticle 16 and the wafer 24 is determined by the method described above. For example, reticle mark RM,
, the positions of the peaks of the photoelectric signal IR generated at the edges of RM2 are A% B, C, D, and the positions of the peaks of the photoelectric signal IW generated at the edges of the wafer mark WM are ε, F, then d=(2 (FE) −(A+D) + (
B+C))/4.

Reticle 16 and wafer 24 obtained as above
The positional deviation of the stage 22 is fed back by the main controller 76, and the stage 22 is fed back by the main controller 76. ! ! Alignment will be performed under the order.

Next, Figure 9, ′! Another example of the Fresnel pattern board 32 will be described with reference to FIG. JJ10.

The one shown in Fig. 9 is a transmission type; of the illumination light LB that enters from the right side of the figure, the positive order light LBI is focused at the primary focus S1, and the negative order light LB2 is focused at the secondary focus S2. It comes into focus.

Therefore, the distance between the focal points S1 and S2 may be made to correspond to the amount of chromatic aberration of the projection lens 10.

Next, the one shown in FIG. 10 is a reflective type, and one of the positive order lights of the illumination light LB incident from above the figure.
The secondary light LJ1 is focused at the primary focus S4, and the secondary light LB2, for example, of the plus-order beams is focused at the secondary focus S3. Therefore, similarly, the distance between the focal points S3 and S4 may be made to correspond to the amount of chromatic aberration of the projection lens 10.

As explained above, according to this embodiment, the illumination light is focused or imaged at a plurality of positions using the Fresnel pattern plate 32, and the intervals between the positions are made to correspond to the amount of chromatic aberration of the projection lens 10. This makes it possible to effectively eliminate alignment offsets caused by laser shake and changes over time, and since light at a non-exposure wavelength is used, the mark can be protected and the same mark can be used multiple times. There is an effect that it can be done.

Note that the present invention is not limited to the above-mentioned embodiments. For example, if alignment is performed using the reference mark 26 fixedly formed on the stage 22, the baseline (wafer alignment microscope and This makes it possible to perform measurements such as distance from a TTL microscope, reticle alignment, etc. Further, the Fresnel effect by a lens system may be used instead of the Fresnel plate.

Next, a second embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 11 shows a second embodiment of the projection exposure apparatus according to the present invention. In this figure, bifocals P, Q
The configuration is the same as that of the first embodiment except for the light transmitting optical system for giving the light and the light receiving optical system for alignment.
The laser light from the laser light source 30, the explanation of which will be omitted, is transmitted to the beam splitter 8.
0 and is reflected by the scanner 83. bifocal lens 82.
Objective lens (preferably telecentric)
81. The polarized light components (P-polarized light and S-polarized light) that are different from each other are incident on the alignment mark portion of the reticle 16 via the mirrors 38 .

Next, the laser beam that has passed through the reticle 16 further passes through the projection lens 10, enters the wafer 24, is reflected there, returns to the forward path, and passes through the reticle 16 again to the mirror 3.
8. Objective lens 81° Bifocal lens 82. The light then enters the beam splitter 80 via a scanner 83 provided at a position that relays the pupil position of the projection lens 1o. (Note that the pupil position where the scanner 83 exists is common to P-polarized light and S-polarized light due to the above configuration.) The transmitted light of the laser light transmitted by the beam splitter 80 is conjugated with the lens 84, 85 and the pupil plane. The light enters a polarizing plate (polarizing beam splitter) 87 through a spatial filter (for example, for cutting specularly reflected light) 86 arranged in the . Then, one polarized light passes through the polarizing plate 87 and is transmitted through the lens 6.
4, the other polarized light is reflected by the polarizing plate 87, and passes through the lens 50 to the light receiving element 5.
It is designed to be incident on 2.

Next, the light receiving element 52 and the light receiving element 66 are each connected to a signal processing section 68, and the driving section 70 of the scanner 83 described above is also connected to the signal processing section 68.

Of the above-mentioned components, an enlarged view of the bifocal lens 82 and objective lens 81 is shown in FIG. It is a crystal that has a refractive index of no in ordinary rays (polarization plane parallel to the plane of the paper). The part without diagonal lines is ordinary glass with a refractive index of no, and extraordinary rays are refracted at the boundary surface according to its curvature, but ordinary rays travel straight. the result,
One polarized light is focused on a first focal point P by the objective lens 81, and the other polarized light is focused on a second focal point Q as shown by a broken line. That is, as in the first embodiment, the first focus P is conjugate with the reticle 16, and the second focus Q is conjugate with the wafer 24.

When the scanner 83 is vibrated by the drive unit 70,
Each of the two laser beams with different polarization components is placed on the reticle 1.
6 and the wafer 24, respectively, and vibrate. At this time, in order to make the spot light into a slit shape as in the first embodiment, a cylindrical lens or the like may be provided in the optical path between the laser light source 30 and the beam splitter 80. When this spot light scans a pattern (mark) on the reticle 16 or wafer 24, the light receiving element 52 or 66 receives optical information (scattered light or diffracted light) from the pattern. At this time, due to the characteristics of the bifocal lens, each of the reflected lights of the illumination light irradiated onto the reticle 16 and the wafer 24 is transmitted through the beam splitter 80, and the light having one polarization characteristic is further transmitted through the polarizing plate 87. The light that enters the light receiving element 66 and has the other polarization characteristic is reflected and enters the light receiving element 52.

Also, as in the first embodiment, the optical system such as the lens 50.64 converts the image (night vision image or Fourier image on the pupil plane) of the light reflected from the reticle and the lens onto the light receiving element 52.66. Optical characteristics are determined so that an image is formed on each light receiving surface. The detection section is almost the same as that in the first embodiment, so the explanation will be omitted.

In the second embodiment, the bifocal element and the objective lens constitute part of the light transmitting optical system of the present invention, but they also serve as part of the light receiving system. In addition, as a combination of a bifocal element and an objective lens, for example,
It is also possible to employ the method disclosed in Japanese Patent No. 9-42517.

Each embodiment of the present invention has been described above, but the illumination light for alignment only needs to have a sufficiently low sensitivity to the resist to be exposed, and does not necessarily have to be a light that does not expose the resist (for a long period of time). may be a sensitive light).

[Effects of the Invention] As explained above, according to the present invention, the occurrence of offset can be effectively prevented by using illumination light of a wavelength different from the exposure light without using any optical system for correction. In addition to being able to perform highly accurate alignment, it is also possible to protect marks, and furthermore, it is possible to achieve high throughput.

Furthermore, in the second embodiment, since the polarization characteristics of the first focus and the second focus are different, it is possible to separate the signal from the reticle mark and the signal from the reticle mark using a polarizing plate and receive the signal. This has the effect of improving the N ratio, improving alignment accuracy, and reducing loss of laser light (for light transmission).

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention,'! Figure J2 is an explanatory diagram showing an example of a reticle mark, Figure 3 is a line diagram showing an example of the intensity distribution of illumination light, Figure 4 is an explanatory diagram showing an example of a wafer mark, and Figure 5 is an explanatory diagram showing an example of a wafer mark. Fig. 6 is a line diagram showing an example of a photoelectric signal obtained by reflected light from a wafer mark, Fig. 7 is a line diagram showing an example of photoelectric signal processing, Fig. 8 9 and 10 are explanatory diagrams showing examples of linear Fresnel patterns.
The figure is an explanatory diagram showing another example of a Fresnel pattern board, No. 11.
This figure is a block diagram showing a second embodiment of the present invention, and FIG. 12 is an explanatory diagram showing an example of a lens having polarization characteristics. 10... Projection lens, 16... Reticle, 22...
・Stage, 24... Wafer, 28... Laser light,
32...Fresnel pattern plate, 52□, 66...light receiving element, 68...signal processing unit, 81...objective sink 4
82...21 focal length lens.

Claims (1)

[Scope of Claims] A mask is irradiated with exposure light having a wavelength capable of sensitizing a photoreceptor on a substrate, and the mask is arranged so as to be substantially conjugate with the mask through a projection optical system under the exposure light. In a projection exposure apparatus that projects a pattern of the mask onto a substrate, the illumination system outputs illumination light having a wavelength different from that of the exposure light and for illuminating alignment marks formed on the mask and the substrate, respectively. and a light transmission optical system that is disposed in the illumination light optical path between the illumination system and the mask and forms images of the illumination light at two locations separated by an interval corresponding to the amount of chromatic aberration of the projection optical system with respect to the illumination light. One of the imaging planes of the illumination light is located at a position substantially coincident with or approximately conjugate with the mask, and the other imaging plane of the illumination light is located at a position approximately conjugate with the substrate. projection exposure equipment.