JPH0612752B2 - Projection type alignment method and apparatus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection lens type alignment method and apparatus for semiconductor exposure, and particularly to a projection type method suitable for using alignment illumination light having a wavelength different from the exposure wavelength. The present invention relates to an alignment method and an apparatus therefor.

[Background of the Invention]

FIG. 1 shows a conventional example of an alignment apparatus of a reduction projection exposure apparatus using a reduction lens which is most often used in projection type semiconductor exposure apparatuses. In the reduction projection exposure apparatus, the pattern of the reticle 1 passes through the projection lens 2,
The exposure of the entire surface of the wafer is completed by exposing the wafer 3 by one or several chips at a time and by step-and-repeat driving the wafer stage 4, but it is necessary to align the reticle pattern with the wafer pattern. In this example, the reticle alignment optical system 5
After the reticle is set to the initial position by, the reticle pattern and the wafer pattern are aligned via the reduction lens 2 by the wafer alignment detection optical system. The wafer alignment detection optical system includes a mirror 6, a relay lens 7, a magnifying lens 8, a movable slit 9, a photomultiplier tube 10, and an optical fiber 11 which emits alignment illumination light. A window pattern 12 as shown in FIG. 2 is formed on the reticle, and a target mark 13 as shown in FIG. 3 is formed on the wafers. When these are irradiated with alignment illumination light having the same wavelength as the exposure light. , Movable slit 9
A wafer pattern enlarged image as shown in FIG. 4 is formed at the position of. 14 is an image of the window pattern, and 15 is an image of the target mark. When this image is detected by the photomultiplier tube 10 while scanning the movable slit 9, a waveform as shown by 16 in FIG. 5 is obtained. From this, the center 17 of the window pattern and the center 18 of the target mark are obtained. The deviation amount Δ is fed back to the reticle or wafer fine movement device to perform alignment.

However, as the semiconductor pattern becomes finer, the line width change due to the reflected light in the underlayer and the resolution limit due to the step difference in the underlayer pose problems, and multilayer resists and resists containing a light absorber have come to be used. In these resists, the light of the exposure wavelength (for example, i-line, h-line, g-line) does not reach the base, so that the target mark cannot be detected by the alignment method described above, and the wavelength of the alignment illumination light is changed ( For example, e-line and He-Ne line) became necessary.

FIG. 6 shows how the image formation position of the wafer pattern enlarged image changes due to chromatic aberration when the wafer side is fixed. Reference numeral 19 is an image forming position at the exposure wavelength, and 20 is an image forming position at the alignment illumination light having a wavelength different from the exposure wavelength. Usually, this difference in image forming position is several to several tens of millimeters, and in order to perform alignment with the conventional alignment detection optical system, the wafer side is lowered to the position 21 as shown in FIG. It is necessary to perform alignment of the reticle, return the wafer to the position of 22 again, and perform exposure, which causes a problem in alignment speed and accuracy.

In addition, in order to reduce the influence of chromatic aberration, there is an example in which mirrors 23 and 24 are inserted to correct the optical path length as shown in FIG. 8, but there is a problem that the accuracy of mirror attachment directly affects the alignment accuracy. Was.

[Object of the Invention]

The object of the present invention is to solve the above-mentioned problems of the prior art. A high-performance projection-type alignment capable of correcting the influence of chromatic aberration due to the wavelength difference between the exposure light and the alignment illumination light without deteriorating the alignment speed or accuracy. A method and an apparatus therefor are provided.

[Outline of Invention]

In order to achieve the above object, the present invention irradiates alignment marks formed on an exposed substrate installed on a substrate stage with alignment illumination light different from exposure light, and causes the substrate stage to emit light from the projection lens. X, Y perpendicular to the axis
The position of the alignment mark detected by the first light receiving means receiving the reflected light from the alignment mark by finely moving in the axial direction through the projection lens is aligned with the reference position, and on the aligned substrate to be exposed. In the projection type alignment method of exposing the circuit pattern formed on the mask by the exposure light by the projection lens, the circuit is provided on the substrate stage which is in an image formation relationship by the projection lens with respect to light having a wavelength substantially the same as the exposure light. The light of the target mark on the reference plate and the light of the alignment mark formed on the mask are received and detected by the second light receiving means, and the substrate stage or the mask stage on which the mask is mounted is projected by the projection. Arra on the mask detected by the second light receiving means by finely moving in the X and Y axis directions perpendicular to the optical axis of the lens. The alignment mark and the target mark are relatively aligned with each other, and in the aligned state, the alignment illumination light is illuminated on the target mark, and reflected light from the target mark is passed through the projection lens to form a first light beam. In the projection type alignment method, the position of the target mark received by the light receiving means and detected is extracted as the reference position. Further, according to the present invention, alignment illumination light different from exposure light is applied to an alignment mark formed on a substrate to be exposed installed on a substrate stage, and the substrate stage is X, Y perpendicular to the optical axis of the projection lens. The light reflected from the alignment mark is first moved through the projection lens by finely moving in the axial direction.
The position of the alignment mark detected by the light receiving means is aligned with the reference position, and the circuit pattern formed on the mask by the exposure light on the aligned substrate to be exposed is exposed by the projection lens. In the projection type alignment apparatus to be provided on the substrate stage,
And receiving the reference plate on which the target mark is formed, the light of the target mark and the light of the mark formed on the mask, which are in an image forming relationship by the projection lens in the light of the same wavelength as the exposure light. Second to detect
Of the light receiving means and the substrate stage or the mask stage on which the mask is mounted,
The mark on the mask detected by the second light receiving means and the target mark are relatively aligned by finely moving in the Y-axis direction, and in the state of alignment, the alignment illumination light is used for the target. Illuminate the mark,
A projection system comprising: a reference position extracting unit that extracts reflected light from the target mark through the projection lens by the first light receiving unit and extracts the position of the target mark detected as the reference position. It is an alignment device. Further, according to the present invention, in the projection type alignment apparatus, the first light receiving means and the second light receiving means are provided.
It is characterized in that it is constituted by different photoelectric conversion means arranged in an image forming relationship at the wavelength of each illumination light. Further, the present invention, in the projection type alignment apparatus, has optical path length changing means for arranging the first light receiving means and the second light receiving means in an image forming relationship at a wavelength of each illumination light, and the same photoelectric conversion means is provided. It is characterized in that it is constituted by a conversion means.

Embodiments of the Invention Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 9 is an embodiment showing the basic configuration of the present invention. Wavelength selection mirror 2 that reflects only the light of the wavelength of the alignment illumination light (for example, e-line He-Ne line) in the middle of the detection system
When reticle 1 is irradiated with light having the same wavelength (for example, g-line, h-line, i-line) as the exposure light from fiber 11 provided by reticle 1,
Pattern and the pattern of the reference plate 25 on the wafer stage 4, the mirror 6, the relay lens 7, the magnifying lens 8,
A detection optical system including a movable slit 9 which is reciprocally scanned as shown by an arrow and a photomultiplier tube 10 produces a detection waveform as shown in FIG. In this state, the reticle stage (not shown) on which the reticle 1 is mounted or the wafer stage 4 is finely moved, and the center of the image of the window pattern 12 on the reticle and the reference plate 25 as shown in FIG. Center the image of the target mark 37 of. Here, the illumination light is switched to the original alignment illumination light (e.g., e-line, He-Ne line), and the light is emitted from the fiber 31. Wavelength selection mirror 26
Via relay lens 27, magnifying lens 28, movable slit
29, the detection system of the photomultiplier tube 30 has an exposure wavelength (for example, g
Line, h line, i line) and the optical path length of the original illumination light for alignment different from that of the target mark 37 is formed on the movable slit 29. Therefore, the detection waveform of the photomultiplier tube 30 is , The window pattern of the reticle is defocused due to chromatic aberration and is not detected, and only the target mark 37 is detected, resulting in 32 signals shown in FIG. 32 is the detection waveform of the target mark 37, 33 is the defocused detection waveform 16 from the window pattern 12 of the reticle shown in FIG.
Is a superposition. 34 is the center position (virtual origin) of the target mark 37. This target mark 37
With the center position 34 of the virtual origin as the virtual origin, the subsequent alignment of the wafer during the actual exposure is performed by using the center position of the detected waveform detected from the alignment pattern of the wafer by the alignment illumination light as the virtual origin in the X and Y axis directions. Perform by adjusting to the reference position. FIG. 11 is an example of a reference plate provided on the wafer stage. The transparent glass 36 having the target mark 37 made by etching chrome or aluminum is placed on the black light-absorbing plate 35, but the light is reflected only at the target mark and the light is absorbed at other parts. It is like this. The center of the detected waveform is the symmetric pattern matching method (Japanese Patent Laid-Open No. 53-6906).
3), peak detection method, binarization center method, etc.

In the embodiment shown in FIG. 9, since the device becomes very large, it is necessary to integrate the two detection optical systems.
12 to 14 show an embodiment in which means having a function of correcting an optical path length difference for each wavelength is provided in the optical path of the detection optical system.

In FIG. 12, with the illumination light having the same wavelength as the exposure light emitted from the fiber 11 through the half mirror 39, the target mark on the reference plate on the wafer stage is aligned at the same 40 position as the window pattern on the reticle 1. Image. The image of the window pattern and the target mark is passed through the mirror 6 and the relay lens 7, and then passed through the optical path 47 for the exposure wavelength including the wavelength selection mirror 44, the mirror 45, and the wavelength selection mirror 46, and imaged again at the point 42. Then, the image is formed at the point 43 of the movable slit 9 via the magnifying lens 8 and the mirror 38, and the wavelength shown in FIG. 5 is obtained by detecting with a photomultiplier tube. The wavelength selection mirror 44 totally reflects only the original wavelength of the illumination light for alignment, while the wavelength selection mirror 46 totally reflects only the wavelength of the exposure light.

Now, when the window pattern of the reticle and the target mark on the reference plate are aligned in this way, the original illumination light for alignment is then reflected from the fiber 11. Due to the chromatic aberration of the projection lens (reduction projection lens), the image formation position of the target mark moves from point 40 to point 41.
Therefore, since the image forming position by the relay lens 7 is also shifted, it is branched by the wavelength selection mirror 44, and after the optical path difference is corrected by the mirror 48 and the optical path 50 through the filter 49 that absorbs the light of the exposure wavelength, the wavelength is corrected. With the selection mirror 46, when you return it to the original point
The image is formed on 42 and can be detected by the same detection optical system.

Also in FIG. 13, prisms 51 and 52 are used in place of the wavelength selection mirror, which is almost the same as in FIG. Figures 12 and 13
As shown in the figure, since the optical path length is corrected after the relay lens 7, the magnification of the detection optical system varies depending on the wavelength, but there is no problem if the zero loop closed loop control is performed until the alignment is adjusted to the virtual origin. .

FIG. 14 shows correction of the optical path length difference in front of the relay lens 7 and is most suitable when the chromatic aberration is large.

In the embodiment of FIGS. 9 to 14, the original alignment illumination was also performed from the reticle side. However, when the wavelength of the alignment illumination light and the exposure wavelength are different, the reticle illumination is not necessary. An oblique illumination system as shown may be used. 53 is a fiber and 54 is a condenser lens. In this case, the scattered light from the edge of the pattern is detected, so the detected waveform is as shown by 55 in FIG. 33 is a superposition of the detection waveforms of FIG.

As an alignment method, a method in which an alignment device is put under a reticle is also considered.

FIG. 17 shows an example of this system. On the reticle, as shown at 59 in FIG. 18, a light shielding pattern opposite to the window pattern is provided. The light from the reference plate on the wafer or the wafer stage 4 is reflected by the light shielding pattern. Reference pattern 58 on wafer stage 4
The structure of is shown in FIG. The reference plate comprises a transparent glass 36 and a target mark 37 made by etching chrome or aluminum. In determining the virtual origin at the exposure wavelength, the reflectance of the reticle's light-shielding pattern 59 is low, so in order to obtain a sufficient amount of light, as shown in FIG.
57 provides transillumination from under the reference plate. Since only the light that hits the light shielding pattern 59 is reflected and enters the detection optical system, the detection waveform is as shown in FIG.
In FIG. 17, 6 is a mirror, 7 is a relay lens, 8 is a magnifying lens, and 60 is a linear sensor provided in place of the movable slit and the photomultiplier tube. Reference numerals 51 and 52 are prisms for correcting the optical path length difference. After obtaining the virtual origin in this way, the original alignment illumination is performed by the fiber 53 and the condenser lens 54.

〔The invention's effect〕

According to the present invention, the reference position between the mask and the exposure light is extracted by using the target mark formed on the reference plate provided on the substrate stage on which the resist is not applied. The exposure wavelength (for example, g
Line, h line, i line) and an illumination light for alignment (for example, e line, He-Ne line) having a wavelength different from that of an alignment mark formed on a substrate to be exposed such as a wafer, and the alignment mark is passed through a projection lens. It is possible to realize the alignment of the exposed substrate at the reference position by detecting the mark, and it is possible to achieve the alignment of the exposed substrate through the projection lens at a very high speed and with high accuracy. .

[Brief description of drawings]

FIG. 1 is a perspective view showing a conventional alignment system, FIG. 2 is a view showing a reticle alignment pattern, FIG. 3 is a view showing a target mark on a wafer, and FIG. 4 is a view showing a movable slit position. FIG. 5 is a diagram showing an imaging pattern, FIG. 5 is a diagram showing detection signals detected from the pattern shown in FIG. 4, and FIGS. 6, 7, and 8 are optical systems each including an alignment system. FIG. 9 is a perspective view showing an alignment system according to the present invention, FIG. 10 is a detection signal waveform diagram according to the present invention, FIG. 11 is a perspective view showing a reference plate, and FIGS. FIG. 16 is a side view showing an optical system including an alignment system according to the present invention, FIG. 16 is a diagram showing detection signal waveforms when illuminated by the system shown in FIG. 15, and FIG. 17 is another diagram according to the present invention. Side view showing the optical system including the alignment system of FIG.
FIG. 19 is a diagram showing an alignment pattern on the reticle according to the present invention, FIG. 19 is a diagram showing a reference plate and its optical system, and FIG. 20 is a detection signal waveform when illuminated as shown in FIG. It is a figure. 1 …… Reticle 2 …… Projection lens 3 …… Wafer 4 …… Wafer stage 6 …… Mirror 7 …… Relay lens 8 …… Magnification lens 9,29 …… Movable slit 10,30 …… Photomultiplier tube 11, 31 …… Illumination fiber 36 …… Glass substrate 37 …… Target mark

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiko Tanaka, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Inside the Hitachi, Ltd. Institute of Industrial Science (72) Inventor Yukio Utsu, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Incorporated company Hitachi, Ltd.

Claims (4)

[Claims] 1. Alignment illumination light different from exposure light is applied to an alignment mark formed on a substrate to be exposed installed on a substrate stage, and the substrate stage is X, Y perpendicular to the optical axis of the projection lens. The position of the alignment mark detected by the first light receiving means receiving the reflected light from the alignment mark by finely moving in the axial direction through the projection lens is aligned with the reference position, and on the aligned substrate to be exposed. In the projection type alignment method of exposing the circuit pattern formed on the mask by the exposure light by the projection lens, the circuit is provided on the substrate stage which is in an image formation relationship by the projection lens with respect to light having a wavelength substantially the same as the exposure light. The light of the target mark on the reference plate and the light of the alignment mark formed on the mask. The mask detected by the second light receiving means by finely moving the substrate stage or the mask stage on which the mask is placed by the light receiving means to detect the light, and moving the substrate stage or the mask stage on which the mask is mounted in the X and Y directions perpendicular to the optical axis of the projection lens The upper alignment mark and the target mark are relatively aligned, the alignment illumination light is illuminated on the target mark in the aligned state, and the reflected light from the target mark is passed through the projection lens to a first position. The projection alignment method, wherein the position of the target mark detected by the first light receiving means is extracted as the reference position. 2. An alignment illumination light different from the exposure light is applied to an alignment mark formed on a substrate to be exposed installed on the substrate stage, and the substrate stage is X, Y perpendicular to the optical axis of the projection lens. The position of the alignment mark detected by the first light receiving means receiving the reflected light from the alignment mark by finely moving in the axial direction through the projection lens is aligned with the reference position, and on the aligned substrate to be exposed. In a projection type alignment apparatus for exposing a circuit pattern formed on a mask by the exposure light by the projection lens, a reference plate provided on the substrate stage and having a target mark formed thereon,
Second light receiving means for receiving and detecting the light of the target mark and the light of the mark formed on the mask, which are in an image forming relationship by the projection lens, in the light having substantially the same wavelength as the exposure light; The mark on the mask detected by the second light receiving means and the target mark are moved relative to each other by slightly moving the substrate stage or the mask stage on which the mask is mounted in the X and Y axis directions perpendicular to the optical axis of the projection lens. Position alignment is performed, and in the aligned state, the alignment illumination light is illuminated on the target mark, and reflected light from the target mark is received by the first light receiving means through the projection lens and detected. And a reference position extracting means for extracting the position of the target mark to be used as the reference position. 3. The first light receiving means and the second light receiving means are constituted by different photoelectric conversion means arranged in an image forming relationship at the wavelength of each illumination light. The projection type alignment apparatus according to item 2. 4. The first light receiving means and the second light receiving means are provided with an optical path length changing means so as to be arranged in an image forming relationship at the wavelength of each illumination light, and are constituted by the same photoelectric conversion means. The projection type alignment apparatus according to claim 2, characterized in that.