JP2554091B2 - Exposure equipment - Google Patents

Description

The present invention relates to an exposure apparatus capable of accurately aligning a mask pattern with a resist on a semiconductor wafer.

[Conventional technology]

The conventional exposure apparatus is the IEE Transactions on Electron Devices (IEEE
TRANSACTIONS ON ELECTRON DEVICES) VOL.ED-26, No.
As described in 4, April, 1979, p723, it has the structure shown in FIG. In the above apparatus, the light from the first light source, that is, the exposure light, passes through the condenser lens 30 and enters the mask 31. The light transmitted through the mask 31 passes through the projection lenses 32 and 33 and reaches the wafer 34, and an image of the mask 31 is formed on the wafer 34. The light source system is a so-called telecentric optical system on both the object, that is, the mask 31 side and the wafer 34 side, and the principal ray in the light beam for image formation is the wafer 34 and the mask 31 on both the wafer side and the mask side. Is vertically incident on each of.
The light for alignment is the laser light 35 as the second light source.
The laser light 35 reflected by the small mirrors 36 in the projection lenses 33 and 32 is incident on a lattice pattern as a wafer mark. Of the reflected light from the grating pattern, only the ± 1st order diffracted light is selected by the spatial filter 37 in the projection lens and forms an image on the mask 31. A lattice pattern as a mask mark is arranged on the mask 31, the pattern from the wafer mark and the pattern of the mask mark are matched, and the positional deviation between the wafer 34 and the mask 31 is detected.

Further, as shown by 38 in FIG. 8, by using a polarizer, a diffraction image from the wafer mark is laterally shifted to form a double image, and each image is electrically taken out alternately by the Faraday element. , Attempts have been made to improve the alignment accuracy. However, in the above method, it is necessary to accurately shift each of the double images generated by the amount of laterally shifting the diffraction image to the right and left, so that the optical parts to be used can be created with high precision and economically. The structure must be such that no misalignment occurs.

[Problems to be solved by the invention]

The above-mentioned conventional technique has limitations and has drawbacks in the following points. That is, when the wavelength of the exposure light serving as the first light source and the wavelength of the alignment laser light serving as the second light source are widely separated, the chromatic aberration of the projection lens is not sufficiently corrected, and The reflected light does not form an image on the mask, and the above-mentioned conventional technique cannot be used. Further, in the optical system shown in FIG. 8, since the lattice pitch direction of the wafer mark is perpendicular to the line segment direction connecting the intersection point with the optical axis of the wafer and the wafer mark, ± 1 next time from the wafer mark The position of the pattern on which the folding light forms an image on the mask is deviated due to the chromatic aberration of the projection lens, and there is a drawback that the image formation position by the exposure light and the position detection position by the alignment laser light are deviated. Further, the filter for extracting the ± first-order diffracted light from the wafer mark is in the projection lens, and it partially blocks the exposure light for transferring the mask pattern onto the wafer, which is not preferable.

[Means for solving problems]

In order to solve the above problems, in the present invention, a grating pattern is provided in an exposure apparatus in which light from a first light source is applied as exposure light to a mask, a projection lens forms an image to expose a photosensitive material on a wafer. Is a wafer mark, and the wafer mark is arranged so that the direction perpendicular to the grating pitch direction of the wafer mark faces the optical axis direction passing through the center of the projection lens, and has a wavelength different from that of the first light source or a wavelength different from the first wavelength. In addition, the light from the second light source, which is emitted with wavelengths having different polarization states, is applied to the wafer mark, and ± 1st order diffracted light of the reflected light from the wafer mark is laterally shifted on the mask. The reflected light from the wafer mark is formed into an image on the photodetector by the second optical system, and the ± 1st-order diffracted light of the reflected light is formed on the Fourier plane of the second optical system. Is A filter for picking up the beam is mounted for alignment, or a filter that transmits the ± 1st-order diffracted lights so that they have different wavelengths is installed, and the frequency ν ₁ − generated by the interference of the ± 1st-order diffracted lights is attached.
By comparing the phase of the photodetection signal with respect to ν _{2 with} the reference signal of the second light source, high alignment accuracy can be realized.

[Action]

The principle of the present invention will be described with reference to FIGS. 9 to 13. As shown in FIG. 9, an IC pattern 5 and a wafer mark 4 composed of a lattice pattern for aligning the wafer are formed on the wafer 3. The mask pattern on the mask 1 is exposed to the exposure light 8
Then, an image is formed using the projection lens 2, and the IC pattern 5 formed on the wafer 3 is accurately aligned and overlapped. The present invention provides an apparatus for accurately aligning the wafer 3 and the mask 1 as described above. First, the principle of aligning the position of the wafer 3 with the position of the mask 1 using the wafer mark 4 will be described. FIG. 10 is a view for explaining the xz or yz section of the optical system with respect to the exposure light 8. The exposure light 8 has a wavelength of 248.
A 4 nm KrF laser beam is used and the focal length is used as the projection lens 2.
A synthetic quartz glass having a refractive index of 1.50831 and a wavelength of 80 nm is used, which has a magnification of 1/5 for reducing and projecting the mask 1. When the telecentric arrangement is used in which the diaphragm 6 is placed at the focus position on the mask side of the projection lens 2, the distance a between the projection lens 2 and the wafer 3 becomes
96 mm, the distance b between the projection lens 2 and the mask 1 is 480 mm. FIG. 11 is an explanatory diagram of an optical system for the alignment laser light. As a positioning laser, H with a wavelength of 632.8 nm
If an e-Ne laser is used, the refractive index of synthetic quartz, which is the lens material of the projection lens 2, is 1.4571, so the focal length of the projection lens 2 also changes significantly from 80 mm to 89 mm, and the mask corresponding to the surface of the wafer 3 is used. Image position b'on the 1st side is also 480m
This is a large deviation from the position of the mask 1 from m to 1214 mm. FIG. 11 (a) shows the reflected light from the wafer mark 4 as x
FIG. 11 (b) shows a shaded view on the yz section. Wafer mark 4 to observe
Is on the x-axis, and the direction perpendicular to the grating pitch is generally oriented to the x-axis, that is, the direction of the intersection d of the optical axis of the projection lens 2 and the wafer 3. The wafer mark 4 grid is
As shown in Fig. 12, if the concavo-convex grating with the pitch p is used and the angle between the incident laser light and the diffracted light is θ, then psinθ = m
There is a relationship of λ. Here, m is the order of diffraction, and λ is the wavelength of light. Now, the pitch p is 8 μm, λ = 0.6328 μ
m, the diffraction angle of the ± 1st order diffracted light is ± 4.537 ° (0.079
Radians). FIG. 11 (b) shows ± first-order diffracted light. The ± first-order diffracted light intersects the projection lens 2 at a position b ′, and forms an interference pattern at that position. By the way, at the position of the mask 1 (position at a distance b from the projection lens), the ± first-order diffracted lights are separated as shown in FIG. 11 (b). If this distant position is e, And e is 9.17 mm in the above example. Mask 1
To make a pattern with ± 1st order diffracted light at
As shown in FIGS. 13 (a) and 13 (b), the ± first-order diffracted lights are so arranged that they partially overlap each other at the position of the mask 1 while being laterally offset by e. That is, e <g in FIG. 13 (b)
To be set. g is the diameter of the ± first-order diffracted light beams at the mask position. An interference fringe corresponding to the wafer mark 4 is formed at a place where the ± first-order diffracted lights are overlapped. In FIG. 13 (a), the lattice pitch of the wafer mark 4 is in the y direction, and the wafer mark 4 is located at the center of the optical axis of the projection lens 2 in the oblique view of the yz plane.
Since the interference fringes in the vicinity of the plane are parallel to the xz plane and arranged in the y direction, even if the observation point of the interference fringe moves from a position away from the projection lens 2 to a position away from the projection lens 2, the interference fringes are displaced. Instead, the position of the wafer 3 can be accurately detected even on the surface of the mask 1.

Further, the case where the frequencies of the ± first-order light diffracted by the wafer mark 4 are different and are ν ₁ and ν ₂ and interfere with each other on the surface of the mask 1 will be described with reference to FIG. This is basically an application of the optical heterodyne technology. The ± first-order diffracted lights 7-1 and 7-2 are respectively Is represented by The interference pattern on the surface of the mask 1 can be calculated by the following equation.

Where c is the speed of light, t is time, λ is the wavelength of light, and Δ is
ν = ν ₁ −ν ₂ .

Therefore, the position y on the mask 1 is measured as follows. The reference signal 23 generated from the light detection signal of the laser light output at the frequencies of ν ₁ and ν ₂ is cos (2πΔνt) as schematically shown in FIG. 15, and at the position y on the mask 1. The generated interference pattern signal 24 is δ = 2ysinα /
The phase is shifted from the reference signal by (λΔν). By accurately measuring the phase difference δ, the position y of the mask 1 is
Ask for. The phase difference δ can be obtained by the phase comparator shown in FIG. If the phase difference δ is obtained with an accuracy of 1/1000 of the signal period 1 / Δν, the position y of the mask 1 can be obtained with a high accuracy of λ / 158.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings. First
FIG. 1 is a configuration diagram showing a first embodiment of an exposure apparatus according to the present invention,
2 (a) and 2 (b) are views showing the mask mark of the above embodiment, respectively, and FIGS. 3 (a) and 3 (b) are views showing the filter of the above embodiment, respectively, and FIG. 4 (a). (B) is a diagram showing two examples of the wafer mark of the above embodiment, FIGS. 5 (a), (b), and (c) are diagrams for explaining the operation of each embodiment, and FIG. 6 is the present invention. 2 is a configuration diagram showing a second embodiment of the present invention, and FIGS. 7 (a) to 7 (d) are explanatory views showing a filter in the above embodiment.

In FIG. 1 showing the first embodiment of the present invention, the exposure light 8 from the excimer laser passes through the condenser lens 21 and transfers the pattern on the mask 1 onto the wafer 3. The alignment of is performed as follows. He-Ne laser as a positioning laser
Use 10. The light from the He-Ne laser 10 is reflected by the semi-transparent mirror 14, passes through the lenses 15-2 and 15-1, and is reflected by the reflecting mirror portion of the mask mark 9 on the mask 1 (see FIGS. ) 9-
It is reflected by 3), passes through the projection lens 2 and enters the wafer mark 4. The light diffracted by the wafer mark 4 traces the incident optical path in the opposite direction, and after passing through the semitransparent mirror 14, only the ± first-order diffracted light passes through the filter 12 and reaches the two-dimensional photodetector 13. The lens systems 15-1, 15-2 and 15-3, 15-4 are designed so that the optical pattern on the mask mark 9 is imaged on the two-dimensional photodetector 13. The light source 11 is for detecting the position of the mask 1,
Illuminate 9-1 or 9-2 of the mask mark 9 shown in FIG. The mask mark 9-1 or 9-2
Is an optical system including lenses 15-1 to 15-4 and forms an image on the two-dimensional photodetector 13. At this time, since the filter 12 is unnecessary, it is taken out of the optical system as indicated by the arrow 22.
2A and 2B show different examples of the mask mark 9, 9-3 is the reflecting mirror portion of the mask mark 9 as described above, and 9-1 and 9-2 are the mask 1
This is a mark used for aligning. The shape of the mark 9-2 is similar to the shape of the mark 9-1, but a grating is formed inside, and even if the mask alignment light source 11 is sufficiently distant from the space through which the exposure light 8 passes, It is possible to allow the reflected light from the grating to sufficiently enter the optical systems 15-1 to 15-4, and the exposure light is not interrupted by an obstacle such as the light source 11 during exposure. FIGS. 3A and 3B show two examples of the filter 12, and FIG. 3A shows a hole through which ± 1st order diffracted light can pass.
12-1 is provided, and (b) shows that the place 12-2 through which the ± 1st-order diffracted light passes and the other place 12-3 are made of different polarizers, and the directions of the passing polarizations are 90 ° to each other. It is like this. In this case, the diffracted light reflected from the wafer 3 has a polarization direction orthogonal to the polarization direction of 12-3 so that it is blocked by 12-3. Further, the light from the mask alignment light source 11 is non-polarized or has a polarization that forms 45 ° with the polarization directions of 12-2 and 12-3, or is circularly polarized so that the image formation is not deteriorated by the filter 12. Or set to either. This eliminates the need to take the filter 12 in and out of the optical system, as shown in FIG.

FIGS. 4A and 4B are views showing two examples of the wafer mark 4. An example in which an optical pattern from the wafer mark 4 in FIG. 4 (a) is detected by a two-dimensional photodetector 13 and the photodetection signal is monitored by a synchroscope is shown in a curve 16 in FIG. A curve 17 shows an example in which the signal from the mark 9-1 is detected by the two-dimensional photodetector 13. By aligning the respective photodetection signals 16 and 17, the positions of the mask 1 and the wafer 3 can be precisely aligned. FIG. 5B shows the wafer marks 4-1 and 4-2 and the mask mark 9-1 shown in FIG. 4B.
It is a figure which shows the example which detected the signal from. The light detection signals based on the wafer marks 4-1 and 4-2 become curves 18 and 19 shown in FIG. 5 (b), respectively.
Are 180 ° out of phase with each other. Light detection signal 18, 1
Differential amplification of 9 has the advantage of reducing the DC component, noise, etc. of each signal. A curve 20 shown in FIG. 5 (c) represents a signal obtained by differentially amplifying the signals 18 and 19 shown in (b), and compares the signal with the signal 17 from the mask mark 9-1 or 9-2. By this, accurate alignment can be performed.

FIG. 6 is a block diagram showing a second embodiment of the present invention, and the alignment of the wafer 3 with respect to the mask 1 is performed as follows. As the wafer alignment laser 10, a so-called Zeeman laser to which the Zeeman effect is applied is used. That is, when a magnetic field is applied in the axial direction of the He-Ne laser tube, the frequencies differ by about 1.8 MHz separated by the Zeeman effect. Left and right circularly polarized light having two oscillation frequencies are output. By passing the λ / 4 plate 28 and the λ / 2 plate 29, the laser light becomes two kinds of linearly polarized light having mutually orthogonal polarization planes and different frequencies. The laser light is reflected by the semitransparent mirror 14, passes through the lenses 15-1 and 15-2, and is reflected by the reflecting mirror portion of the mask mark 9 of the mask 1 (see 9-3 in FIGS. 2A and 2B). It is reflected, passes through the projection lens 2, and is incident on the wafer mark 4 shown in FIG. The light diffracted by the wafer mark 4 traces the incident light path in the opposite direction, passes through the semi-transparent mirror 14, and only the ± 1st-order diffracted light is transmitted by the filter 12, and the slit 26
To reach the photodetector 13 via. Lens system 15-1 to 15-4
Is designed so that the optical pattern on the mask mark 9 is imaged on the photodetector 13. ± as shown in Fig. 7 (a)
The 1st-order diffracted lights 7-1 and 7-2 are set by the λ / 2 plate 29 so that their respective polarization components are directed in the arrow directions, and have frequencies ν ₁ and ν ₂ as shown in the figure, respectively. There is. Seventh
The filter 12 shown in FIGS. (B), (c), and (d) is (b)
12-1 and 12-2 shown in FIG. 2 are filters for passing only the polarized light in the fringe direction, 12-1 is the light of the ν ₁ component of the diffracted light 7-1 and 12-2 is the ν _{2 of the} diffracted light 7-2. Allow only the component light to pass. Reference numeral 12-3 shown in (c) is for passing only the polarization component in the direction orthogonal to the separation direction of the ± 1st order diffracted light so that the light of each frequency component interferes on the photodetector 13. , 12d for blocking the 0th order light and the high order diffracted light, and the ± 1st order diffracted light beams are passed by the slit 12-5 and guided to the photodetector 13.

The slit 26 in FIG. 6 is scanned as shown by the arrow 27,
The light detection signal at each scanning position is detected by the light detector 13. A part of the light emitted from the wafer alignment laser 10 is guided to the photodetector 31 by the semi-transparent mirror 30, and this photodetection signal is used as a reference signal shown by 23 in FIG.
It has been entered in 25. The light detection signal at each scanning position of the slit 26 is also input to the phase comparator 25, and as described above, the phase difference δ between these signals is calculated by the phase comparator 25.
Can be obtained by The phase difference δ is directly related to the position of the wafer mark 4, which means that the wafer position is obtained.

The light source 11 is for detecting the mask position and illuminates the mask mark 9-1 or 9-2 shown in FIGS. 2 (a) and 2 (b). The mask mark 9 is an optical system 15-1 to 15
An image is formed on the photodetector 13 at -4. The mask mark 9
At the time of detection of the
It is taken out of 15-1 to 15-4.

Although the second embodiment has shown the example in which the Zeeman laser is used as the wafer alignment light source 10, an apparatus for generating two types of light having different polarization states and frequencies due to the acousto-optic effect may be used.

In each of the above embodiments, the optical system in which the reflected light from the wafer mark 4 is reflected by the mask 1 is shown, but the present invention is not limited to this, and an optical system that transmits the mask 1 may be used.

〔The invention's effect〕

As described above, the exposure apparatus according to the present invention irradiates the mask with light from the first light source, forms an image on the wafer with the first optical system including the projection lens, and exposes the photosensitive material to light. A wafer mark made of a grating pattern on the wafer is arranged so that a direction perpendicular to the grating pitch direction faces an intersection of the optical axis passing through the center of the projection lens and the wafer, and a wavelength different from that of the first light source, Or, the light from the second light source that emits light of two wavelengths having different wavelengths and different wavelengths from that of the first light source is applied to the wafer mark, and ± 1 of the reflected light from the wafer mark Folded light partially overlaps on the mask in a laterally shifted state, reflected light from the wafer mark is imaged on a photodetector by a second optical system, and a Fourier plane of the second optical system is ± 1st order diffracted light of the reflected light Only the filter that takes out only the ± 1st-order diffracted light and the filter that transmits the ± 1st-order diffracted light so that the ± 1st-order diffracted lights have different wavelengths is mounted, thereby performing precise alignment based on the light detection signal. It is also possible to use light of two wavelengths having different polarization states as the second light source, and to determine the phase of the photodetection signal with respect to the frequency generated by the interference of the ± first-order diffracted light as the reference signal of the second light source. Since the alignment can be performed by comparing with, it is possible to realize the alignment of the mask and the wafer with high accuracy.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of an exposure apparatus according to the present invention, FIGS. 2 (a) and 2 (b) are views showing mask marks of the above-mentioned embodiment, respectively, and FIGS. 3 (a) and 3 (b). ) Is a diagram showing the filter of the above embodiment, FIGS. 4 (a) and 4 (b) are diagrams showing two examples of the wafer mark of the above embodiment, FIGS. 5 (a), 5 (b) and 5 (b), respectively. c) is a diagram for explaining the operation of the above embodiment, FIG. 6 is a configuration diagram showing a second embodiment of the present invention, and FIG. 7A is a diagram showing respective polarization components of ± first-order diffracted light. , (B), (c), and (d) each show a filter, FIG. 8 shows a configuration of a conventional exposure apparatus, FIG. 9 is an explanatory view of a positioning principle in the exposure apparatus, and FIG. Is an illustration of the optical system for exposure light,
FIG. 11 (a) is a diagram in which the reflected light from the wafer mark is shaded in the xz section, FIG. 11 (b) is a diagram in which the above reflected light is shaded in the yz section, FIG. Figures (a) and (b) are explanatory views for creating a pattern of ± first-order diffracted light at the mask position, and FIG. 14 is a diagram illustrating interference of ± first-order diffracted light,
FIG. 15 is an explanatory diagram of phase comparison, and FIG. 16 is a diagram illustrating a phase difference between the reference signal and the interference pattern signal. 1 ... Mask, 2 ... Projection lens 3 ... Wafer, 4 ... Wafer mark 8 ... Light of first light source, 10 ... Second light source 12 ... Filter, 13 ... Photodetector

Claims (6)

(57) [Claims] 1. An exposure apparatus in which light from a first light source is applied to a mask, a first optical system including a projection lens forms an image on the wafer, and a photosensitive material is exposed to light. Is arranged so that the direction perpendicular to the grating pitch direction is directed to the intersection of the wafer and the optical axis passing through the center of the projection lens, and the second light source having a wavelength different from that of the first light source is used. The wafer mark is irradiated with light so that ± 1st-order diffracted light of the reflected light from the wafer mark partially overlaps on the mask in a laterally shifted state, and the reflected light from the wafer mark is reflected by the second optical system. An exposure apparatus in which a filter for picking up only ± 1st-order diffracted light of the reflected light is attached to the Fourier plane of the second optical system so as to form an image on a photodetector. 2. The exposure according to claim 1, wherein the second optical system has a means for taking out the filter so that the light from the mask mark is imaged. apparatus. 3. The filter according to claim 1, wherein a polarizer having a polarization direction orthogonal to the polarization of the reflected light from the wafer mark is arranged in a place other than the optical path of the ± first-order diffracted light. The exposure apparatus according to item 1. 4. The wafer mark is provided with two or more grating patterns displaced from each other, and means for obtaining a difference in photodetection signal by each grating pattern detected by the photodetector is provided. An exposure apparatus according to claim 1, wherein: 5. The second light source emits light of two wavelengths having different polarization states, and extracts only the ± 1st order diffracted light of the reflected light from the wafer mark on the Fourier plane of the second optical system. The exposure apparatus according to claim 1, further comprising a filter that transmits the ± 1st-order diffracted lights so that they have different wavelengths. 6. The second optical system comprises means for comparing the phase of a light detection signal having a frequency ν ₁ -ν ₂ generated by the interference of the ± 1st-order diffracted light with the phase of a reference signal. The exposure apparatus according to claim 5.