JPS62149129A - Reducing projection-type alignment system - Google Patents

Abstract

PURPOSE:To perform mutual alignment between a reticle and a wafer, by detecting an interference pattern and an alignment pattern on the reticle by means of alignment optical system to determine an alignment amount from a center position of the two patterns. CONSTITUTION:Before exposure of a circuit pattern on a reticle 1 is performed on a wafer 3 through a reducing projections lens 2, the reticle 1 and the wafer 3 are aligned. At this time, an alignment pattern 48 on the wafer 3, and a semitransparent mirror arranged in a position except the upper of the wafer 3 are illuminated by interference-capable alignment-illuminating light. Reflected light from the alignment pattern 48 on the wafer 1 through the reducing lens 2 and that from the semitransparent mirror are optically interfered. The pattern obtained by the interference and the alignment pattern on the reticle 1 are detected by means of an alignment optical system. Hence, mutual alignment between the reticle 1 and the wafer 3 can be performed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention aligns the circuit pattern on a reticle with the wafer with high precision before exposing the circuit pattern on the reticle onto the wafer through a reduction projection lens. The present invention relates to a reduced projection alignment method.

[Conventional technology]

As the miniaturization of semiconductor integrated circuits progresses, the current situation is that higher and higher alignment precision between a reticle and a wafer is required during exposure using a reduction projection exposure apparatus. Therefore, it is possible to deal with errors in the arrangement of chips within a wafer by performing alignment for each chip. It is believed that the TTL alignment method using a reduction projection lens will become mainstream in the production of highly integrated circuits in the future.

FIG. 13 shows an example of the TTL alignment method. According to this, the circuit pattern of the reticle 1 is exposed through the reduction projection lens 2 on the wafer 3 placed on the wafer stage 4 in units of 16 chips or several chips. Reticle initial setting pattern 15 by reticle alignment optical system 5, 5'
．． By detecting the position of 15', reticle 1
is set to the initial position. Next, on the wafer 3, the alignment pattern 14.14' near the chip 16 is imaged onto the alignment pattern (window pattern) 13.13' on the reticle 1 through the reduction projection lens 2, and both patterns are It is now detected by the system. The wafer alignment detection optical system includes a mirror 6.6', a relay lens 7.7', and a magnifying lens 8,8.
', a movable slit 9.9', a photomultiplier 10.10', and an optical fiber 11.11' that emits alignment illumination light of the same wavelength as the exposure light.
It is now composed of such things as optical fiber 11
．． Illumination light from 11' is a half mirror, relay lens 7
．． 7', mirror 6°6', the alignment pattern 13.13' is illuminated, while the reflected light from them is transmitted to mirror 6.6', relay lens 7.7', and half mirror 1.
The light is detected by a photomultiplier tube 10, 10' via magnifying lenses 8, 8', mirrors, and movable slits 9, 9'.

Now, if the detected wafer alignment pattern 14.14' and reticle alignment pattern 13.1
3', the wafer stage 4 on which the wafer 3 is mounted is moved in the X direction or the Y direction depending on the direction and amount of deviation, so that both patterns 14.
The positions of 14', 13 and 13' are made to match. After the alignment is completed in this manner, the exposure system 12 irradiates the reticle 1 with exposure light.

Note that, for example, Japanese Patent Application Laid-Open No. 55-41739 is related to this type of alignment method.

[Problem that the invention seeks to solve]

By the way, in this TTL alignment method, a problem that has been pointed out in the past but has not yet been solved is a decrease in alignment accuracy due to uneven coating of photoresist on a wafer (1). This problem has become extremely serious in recent years as semiconductor circuits become more highly integrated.

Here, to explain the method of applying photoresist to a wafer, as shown in FIG. 3 1-2 μm on the entire surface
(in the case of a single layer resist). In this case, the direction in which the photoresist flows is arrow A,
As shown by B, C, and D, the directions extend radially from the center of the wafer 3, and FIG. 15 shows an enlarged view of the X-direction alignment pattern 19 near the chip 17.

The normal alignment pattern is as shown in Figure 15.
There is a concave or convex step pattern on the i-board 21 5L02
constituted by being formed by layer 22,
Further, the film thickness of the photoresist 23 applied thereon is designed to draw a gentle curve depending on the shape of the step.

In this way, the alignment pattern> is the Si substrate 21.
As shown in FIG. 14, one problem is that the X-direction alignment pattern 19 near the chip 17 is parallel to the resist flow direction B, but for example, the X-direction alignment pattern 20 near the chip 18 is parallel to the resist flow direction B. The flow direction C is substantially perpendicular to the flow direction C. As a result, as shown in FIG.
The photoresist film thickness distribution in the pattern width direction at the alignment pattern 9 is symmetrical, but as shown in FIG. This means that the left and right sides are asymmetrical.

Now, these alignment patterns 19 and 20 are illuminated by pattern illumination lights 24a and 25a, but the reflected light from the patterns is approximately equal to the reflected light 24b and 25b from the photoresist surface, and the Si substrate 21 also has L<1tsio.

The light is obtained as interference light with reflected light 24c and 25c from the surface of the layer 22. That is, as can be seen from the interference intensity curve 28 shown in FIG. 18, the interference intensity curve periodically changes depending on the film thickness d of the photoresist 23. From the above, the reflected light intensity distribution 26 from the alignment pattern 19 is symmetrical as shown in FIG. 17(a), but the reflected light intensity distribution 27 from the alignment pattern 20 is symmetrical as shown in FIG. It is asymmetrical. Therefore, in the conventional Align Run 1 system, which utilizes the symmetry of the detection signal waveform and sets the center of symmetry of the waveform as the center position of the alignment pattern, as shown in FIG. may be regarded as the pattern center position, and an error ex may occur, resulting in an unavoidable drop in alignment accuracy. Furthermore, in the conventional TTL alignment method, it has been pointed out that not only the coating unevenness but also the contrast of the pattern detection signal changes greatly depending on the coating thickness of the photoresist has been pointed out.

Therefore, in view of the above-mentioned problems of the prior art, it is an object of the present invention to reduce the thickness and unevenness of the photoresist coating so that it can be stabilized without being affected by the coating thickness, and that can align the reticle and wafer with good accuracy. A projection alignment method is provided.

[Means for solving problems]

For this purpose, the present invention illuminates the alignment pattern on the wafer with coherent alignment illumination light and a semi-transparent mirror provided at a position other than the wafer, while illuminating the alignment pattern on the wafer obtained through a reduction projection lens. The alignment optical system optically interferes the reflected light from the alignment pattern with the reflected light from the semi-transparent mirror, and combines the interference pattern obtained by the interference with the alignment pattern on the reticle illuminated by the alignment illumination light. By detecting this, the alignment amount is determined from the center position of one pattern, and the reticle and wafer are relatively aligned.

[Effect]

The reflected light from the photoresist surface and the reflected light from the interface between the step pattern of the Si substrate and the photoresist interfere with each other with the reflected light from the semi-transparent mirror, so that an interference pattern is obtained. In this interference pattern, the influence of interference between the light reflected from the interface between the step pattern and the photoresist and the light reflected from the semi-transparent mirror is the strongest, and the phase changes at the step portion of the alignment pattern by the depth of the step. As a result, the interference pattern is obtained as having large signal changes. That is, the influence of interference caused by the thickness of the photoresist is reduced. Therefore, if this interference pattern and the alignment pattern on the reticle are detected by an alignment optical system and the amount of alignment is determined from the center position of both patterns, it is possible to relatively align the reticle and the wafer. It is what it is.

〔Example〕

The present invention will be explained below with reference to FIGS. 1 to 12.

First, before explaining the present invention in detail, the logical background thereof will be explained as follows.

That is, the present invention was originally developed by focusing on the fact that the reflectance at the interface between the photoresist and the step pattern constituting the wafer alignment pattern is higher than the reflectance at the interface between the photoresist coated on the wafer and the air. be.

Assuming a Si step pattern as the alignment pattern, the reflectance at the photoresist/air interface is usually 5.5.
% (Refractive index of air 1.0. Refractive index of photoresist 1.6
1 (for a wavelength of 514 nm)), whereas
The reflectance at the interface between photoresist 1 and the alignment pattern (step pattern) is as high as 24% (refractive index of Si: 4.75 (wavelength: 514 nm)). Therefore, an optical system as shown in FIG. 1 was devised. As shown in FIG. 1, illumination light 41 from a coherent light source 40 such as a laser light source is separated into two directions by a beam splitter 42, one of which is the alignment illumination light 41.
3, the alignment pattern 48 on the wafer is illuminated through the reduction projection lens 2. The alignment pattern 48 is formed as a step pattern on the Si substrate 45, and a photoresist 46 is applied thereon. On the other hand, the other side is made to be incident on a semi-transparent mirror (transmittance 0 in this case) 51, and the optical path length Qr from the beam splitter 42 to the semi-transparent mirror (reflecting mirror) 51 is also When the optical path length to the surface is made almost equal to the optical path length aV(X) and the optical path length difference is set within the coherent distance of the coherent light source 40, the reflected light 49 from the surface of the photoreceptor 1-46 and S
The reflected light 50 from the interface 47 between the step pattern of the i-substrate 45 and the photoresist 46 interferes with the reflected light 52 from the semi-transparent mirror 51, resulting in an interference pattern 53. Details of this will be described later, but considering the reflectance at each interface, this interference pattern 53 mainly uses reflected light 50 from the interface 47 between the step pattern and the photoresist 46, and the reflected light 50 from the semi-transparent mirror 5.
The influence of interference with the reflected light 52 from the alignment pattern 48 is the strongest, and the interference pattern 53 is obtained as having a large signal change due to the phase change by the step depth e at the step portion of the alignment pattern 48. It has become. That is, the relative film thickness d(x) of the photoresist 46
This means that the influence of interference caused by is reduced. This interference pattern 53 and an alignment pattern (not shown) on the reticle are detected by an alignment optical system (not shown) equipped with a magnifying lens and an imaging device, and the alignment amount is determined from the center position of both patterns. If determined, it becomes possible to align the reticle and wafer with relatively good accuracy. Note that FIG. 2 shows the incident state of the illumination light 43 made of a parallel beam incident on the alignment pattern 48.

By the way, the semi-transparent mirror into which the illumination light is incident is a mirror in a broad sense, and includes cases where the transmittance is 0 as in the optical system shown in FIG. This semi-transparent mirror can be provided outside the on-wafer alignment pattern illumination optical path including the reduction projection lens, or can be provided within the illumination optical path as will be described later. Further, preferably, a wavefront correction optical system is provided in the optical path provided with the semi-transparent mirror. Furthermore, the light from the coherent light source is temporally and spatially coherent.

Now, to explain in detail the interference pattern mentioned above, in the optical system shown in FIG. 1, the photoresist 46
If the intensity of the reflected light 49 from the surface is 12, the intensity of the reflected light 50 from the interface 47 between the step pattern of the Si substrate 45 and the photoresist 46 is 12, and the intensity of the reflected light 52 from the semi-transparent mirror 51 is Ir, then , the intensity distribution I(x) of the interference pattern 53 due to these three reflected lights is approximately expressed by equation (1).

I (x) = (If + 'I 2 + Ir)...
(1) where λ is the wavelength of the alignment illumination light, na is the refractive index of air, and nr is the refractive index of the photoresist.

The first term in this equation (1) gives the DC component of the interference intensity, the second term gives the modulation component of the interference intensity between the reflected light 49 and the reflected light 50, and the third term gives the reflected light 49. The fourth term gives a modulation component of the interference intensity between the reflected light 50 and the reflected light 52, and the fourth term gives a modulation component of the interference intensity between the reflected light 50 and the reflected light 52.

Here, the intensity of the illumination light 41 is set to 1, and the intensity of the beam splitter 42 is set to 1.
The ratio of reflectance to transmittance at is 1, n1==1.

nr = 1.6 (λ = 436 nm), the reflectance of the semi-transparent mirror 51 is 95%, the reflectance of the photoresist 46/air interface is 5.5%, and the reflectance of the stepped pattern/photoresist 46 interface 47 is 24%. Then, the first term in equation (1) is shown as a straight line 60 in FIG. 3, the second term is shown as a curve 61, the third term is shown as a curve 62, and the fourth term is shown as a curve 6.
3, respectively. This third
From the figure, the intensity distribution of the interference pattern 53 is the fourth term in equation (1), that is, the step pattern photoresist 46
It can be seen that the influence of interference between the reflected light 50 from the interface 47 and the reflected light 52 from the semi-transparent mirror 51 appears most strongly. As a result, the interference pattern 53 is obtained as having a large signal change because the phase changes by the step depth e at the step portion of the alignment pattern 48.

This is because the reflectance at the interface 47 is higher than the reflectance at the photoresist 46 surface. From now on.

The influence of interference (second and third terms in equation (1)) caused by the film thickness d (x) of the photoresist 46 is relatively small.

Therefore, as shown in FIG. 4(a), when the film thickness distribution of the photoresist 46 is asymmetrical at the stepped portion of the alignment pattern 48, the interference light intensity shown in FIG. As is clear from the curve, the reflected light intensity distribution 64 from the alignment pattern 48 is asymmetrical as shown in FIG. 4(b), and Xd is regarded as the pattern center position with respect to the true pattern center position XV. 'A detection error eX had occurred. However, according to the present invention, the reflected light intensity distribution 65 has good symmetry without being affected by the film thickness distribution of the photoresist 46, and has a high contrast, as shown in FIG. obtained as.

Ideally, the true pattern center position XW can be detected. As a result, deterioration in alignment accuracy caused by photoresist film thickness and coating unevenness can be eliminated.

In addition, in the present invention, the alignment pattern is as shown in FIG.
It is also applicable to cases in which transparent layers of 7, Si, and N46g are formed. This means that for the incident light 74, the reflected light from the photoresist 69 surface and each layer interface 72, 71, 70 is 75°, 76, 7
The one with the highest strength among 7 and 78 is the underlying SL board 6
This is because it is the reflected light 78 from the interface 70 between 6, Sin, and 67. Therefore, the resulting interference intensity distribution is SL
Since the thickness of the photoresist 69 changes greatly at the step portion of the substrate 66, the thickness of the photoresist 69 is not so affected and the same effect as in the previous case can be obtained.

Now, to explain the present invention in detail, FIG. 6 shows an alignment optical system in a first embodiment of the system according to the present invention. The alignment optical system in this case is composed of an alignment illumination system, an alignment pattern detection optical system, a reference optical path, and an alignment pattern detection signal processing system. In this case, Ar laser (wavelength 514.5 nm) is used as a coherent light source.
A laser beam 81 from 80 passes through a beam splitter 82,
2 by the beam splitter 84 via the relay lens 83
The system is separated into beams 86 and 87. Among them, the beam 87 is guided to a reference optical path consisting of mirrors 85b to 85f, a wavefront correction optical system 88, and a reflecting mirror 89, and is reflected by the reflecting mirror 89.
8, the beam 87 is subjected to beam diameter adjustment and wavefront phase adjustment corresponding to the imaging characteristics of the reduction projection lens. The other beam 86 is sequentially reflected by the mirror 85a and the mirror 1m surface on the reticle 1, and then enters the center of the entrance pupil 2p in the reduction projection lens 2, illuminating the alignment pattern 48 on the wafer 3. It becomes. FIG. 7 shows an enlarged view of the illumination state in this case. The beam 86 is a parallel beam and functions as alignment illumination light.

Here, the optical path length difference between the optical path length from the beam splitter 84 to the reflecting mirror 89 and the optical path length from the beam splitter 84 to the alignment pattern 48 on the wafer 3 is calculated by slightly moving the reflecting mirror 89 in the optical axis direction. When the beam is set within the coherence distance of the Ar laser 80, the reflected light from the reflecting mirror 89 and the reflected light from the alignment pattern 48 interfere with each other, just as in the Twyman-Green interferometer, and the beam splitter 84 This allows an interference pattern to be obtained. This interference pattern is sequentially passed through the relay lens 83, the beam splitter 82, the mirror 85g, and the magnifying lens 90, and is imaged by the two-dimensional surface image sensor. Thereafter, a preprocessing circuit 92 removes noise and performs AD conversion, and a vertical compression circuit 93 electrically compresses the signal in a direction perpendicular to the alignment pattern detection direction.

The center position of the alignment pattern 48 is determined by the computer 94 processing the signal converted into one-dimensional information by this compression in a predetermined manner.

The processing by the computer 94 at this time will be explained as follows.
FIGS. 8(a) and 8(b) show examples of interference patterns captured by the solid-state image sensor 91, respectively. The detection area 95 of the alignment run 1 to the optical system for the alignment run 1 to the pattern 48 is as shown in the figure. First, Figure 8 (a
), this shows a case where the reflecting mirror 89 and the alignment pattern 48 are relatively inclined in the direction of the arrow, and thin interference fringes 96 are generated depending on the magnitude and direction of the inclination. ing. In such a case, a one-dimensional signal 98 obtained by compression has a low contrast as shown in FIG. 9(a). Therefore, it is necessary to set in advance so that the reflecting mirror 89 and the alignment pattern 48, that is, the wafer, are completely parallel to each other. Incidentally, if the size of one chip on a wafer is 20 mm x 20 nm, the inclination of the wafer within one chip is approximately 1 μm at most.
Once the reflector 89 is finely adjusted, there is no need to constantly monitor it.

Next, referring to FIG. 8(b), this is the reflecting mirror 8.
This shows an interference pattern when 9 and the wafer are completely parallel, and an image 97 whose intensity changes greatly at the step portion of the alignment pattern is obtained. A one-dimensional signal 99 shown in FIG. 9(b) can also be obtained with a correspondingly high contrast. The computer 94 uses the one-dimensional signal 99 to determine the center position @XW (center position in the X direction) of the alignment pattern on the wafer by utilizing the symmetry of the waveform. The alignment amount Δ and the alignment direction are determined from the positional deviation between this and the center position Xr of the alignment pattern (not shown) on the reticle obtained separately. Based on this alignment amount Δ and the alignment direction, the stage 4 is slightly moved in the X direction, and the y
The situation is exactly the same regarding alignment in the direction. Once the alignment is completed in this manner, the circuit pattern on the reticle 1 is printed onto the chip on the wafer 3 by irradiating exposure light from an exposure system (not shown). By repeating the above alignment and printing operations for each chip, reduction projection exposure on the wafer 3 is performed.

Now, according to the embodiment described above, an alignment pattern detection signal can be obtained with good symmetry without being affected by the photoresist film thickness distribution as described above, and alignment accuracy caused by uneven coating of the photoresist can be obtained. This means that the decrease in Furthermore, in the case of the conventional alignment method, the contrast of the alignment pattern detection signal changes greatly not only due to coating unevenness but also due to the coating film thickness of the photoresist, but according to this embodiment, the reflector 89 is moved in the optical axis direction. By making slight movements, the interference intensity can always be set on the slope of the curve 63 shown in FIG. 3, making it possible to maintain high signal contrast.

Next, another embodiment will be described. FIG. 10 shows an optical system in that embodiment.

In this alignment optical system, the reference optical path is removed from the alignment optical system shown in FIG. 6, and a translucent filoo as a dichroic mirror is installed at the lower end of the reduction projection lens 2.
The difference is that the alignment illumination optical path itself is used as the reference optical path. As in the previous embodiment, the beam 81 from the Ar laser 80 is first reflected by the beam splitter 82, the relay lens 83, the mirror 85a, and the mirror 1m surface on the reticle 1, and then reflected by the entrance pupil 2p of the reduction projection lens 2. is incident on the center of the semi-transparent mirror lOO
After passing through the alignment pattern 48 on the wafer 3
It is designed to be incident as illumination light. Now, in this case, the upper surface of the semi-transparent mirror 100 is coated with an anti-reflection film (wavelength 51
4.5 nm), and its lower surface 101 is coated with a thin film having the reflectance/transmittance spectral characteristics shown in FIG.
When setting the optical path length up to 8 within the coherence distance of the Ar laser 80 by slightly moving the translucent mirror 100 in the optical axis direction, use the same principle as the Fizeau interferometer to set the optical path length of the semitransparent mirror 1 to within the coherence distance of the Ar laser 80.
The reflected light from the lower surface 101 of 00 and the reflected light from the alignment pattern 48 interfere to obtain an interference pattern. This interference pattern follows the same optical path in reverse through the reduction projection lens 2, and then is imaged by the two-dimensional surface image sensor 91 via the beam splitter 82, mirror 85g, and magnifying lens 90. Subsequent signal processing and alignment The procedure will be carried out in exactly the same manner as in the previous embodiment.

The thin film coated on the lower surface 101 of the semi-transparent mirror 100 has an exposure wavelength of 436 mm, as shown in FIG.
It exhibits an extremely high transmittance for wavelengths of 30 nm (g-line of a mercury lamp), and no particular problems occur during exposure. Further, reference numeral 111 indicates the imaging position of the interference pattern.

Here, to briefly explain the fine movement mechanism of the semi-transparent mirror 100, FIGS. 11(a) and 11(b) show the fine movement mechanism of the semi-transparent mirror 100. The semi-transparent mirror lOO is supported by a plate spring or the like (not shown) with respect to the reduction projection lens 2, and the fine movement mechanism 1, for example,
Three wedge-shaped bases 102a fixed to the top surface of 00
, 103a, and 104a by independently slightly moving the wedge-shaped movable spacers 102b, 103b, and 104b using three piezo elements 102c, 103c, and 104c, respectively. Piezo element 102
c, 103c.

One end of 104c is a wedge-shaped movable spacer 102b, 1
03b.

104b, and the other end is fixed to the reduction projection lens 2. Therefore, the piezo element 10
When a voltage signal is applied to 2c, 103c, and 104c, they expand and contract according to the voltage signal, and as a result, the translucent fi 100 can move slightly in the vertical direction.

Therefore, according to this embodiment, not only can the same effect as in the optical embodiment be obtained, but also the alignment optical path itself is used as the reference optical path, so that disturbances in the reference optical path or effects of the reduction projection lens can be avoided. At the same time, the influence of the image characteristics themselves on the interference pattern is removed.
Moreover, the effect that the alignment optical system is simplified can also be obtained.

[Effects of the Invention] As explained above, the alignment method according to the present invention solves problems in TTL alignment that have been pointed out in the past but still remain unsolved, and which are becoming serious problems as semiconductor circuits become more highly integrated. Deterioration in alignment accuracy caused by coating thickness and coating unevenness of a certain photoresist can be eliminated, stable and highly accurate alignment can be achieved, and high productivity and reliability can be obtained. In addition, with this method, a throughput comparable to that of conventional chip alignment can be obtained, and compared to the conventional method,
In addition to improved accuracy, the effect of having high overall performance can also be obtained at the same time.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an optical system for explaining the present invention in detail, Fig. 2 is a diagram showing the incident state of illumination light to the alignment pattern, and Fig. 3 is a diagram showing the difference in optical path length and interference intensity. Figure 4 (a) is a cross-sectional view of the alignment pattern showing the state of uneven coating of photoresist, and Figures (b) and (c) are diagrams showing the relationship between the conventional method and the present alignment method. A diagram for explaining the difference in reflected light intensity distribution, FIG. 5 is a diagram showing a cross section of an alignment pattern section having another transparent layer to which the present invention is applicable, and FIG. 6 is a diagram showing a method according to the present invention. FIG. 7 is a diagram showing the alignment optical system in the first embodiment, and FIGS. 8(a) and 8(b) are diagrams showing the state of incidence of illumination light on the alignment pattern in that case.
9(a) and 9(b) are diagrams showing examples of imaged interference patterns, respectively, and FIGS.
10 is a diagram showing the compressed one-dimensional signal waveform of the interference pattern shown in b), and FIG. 11 is a diagram showing the alignment optical system in the second embodiment of the method according to the present invention.
), (b) is a diagram showing the fine movement mechanism of the semi-transparent mirror in the optical system and a part of it, and Figure 12 is a diagram showing the reflectance/transmittance spectral characteristics of the thin film coated on the lower surface of the semi-transparent mirror. , FIG. 13 is a diagram showing an example of a conventional TTL alignment method. FIG. 14 is a diagram showing a method of applying photoresist to a wafer, FIG. 15 is a diagram showing an enlarged wafer alignment pattern, and FIGS. Figures 17(a) and 17(b) show differences in the intensity distribution of reflected light from the alignment pattern due to differences in thickness distribution, and Figure 18 shows interference with photoresist film thickness. It is a figure showing the relationship with strength. 1... Reticle, 2... Reduction projection lens, 3... Wafer, 4... Wafer stage, 40... Coherent light source, 42°82, 84... Beam splitter, 48... Alignment no. Turn, 51.100...Semi-transparent mirror, 5
3...Interference) (turn, 80...Ar laser, 88
...Wavefront correction optical system, 89...Reflector, 91...
Two-dimensional solid-state image sensor.

Claims (1)

[Claims] 1. In a method of aligning a reticle and a wafer before exposing a circuit pattern on a reticle onto a wafer through a reduction projection lens, the alignment pattern on the wafer is aligned using coherent alignment illumination light. and a semi-transparent mirror provided at a position other than the wafer, while optically combining the reflected light from the alignment pattern on the wafer obtained through the reduction projection lens and the reflected light from the semi-transparent mirror. The alignment optical system detects the interference pattern obtained by the interference and the alignment pattern on the reticle illuminated by the alignment illumination light, and then calculates the amount of alignment from the center position of both patterns, and then aligns the reticle and wafer. This is a reduction projection alignment method that is characterized by relatively aligning the . 2. The reduction projection alignment method according to claim 1, wherein the semi-transparent mirror includes one having zero transmittance. 3. The reduction projection alignment method according to claim 1, wherein the semi-transparent mirror is provided outside the optical path for illuminating the on-wafer alignment pattern that includes the reduction projection lens. 4. The reduction projection alignment method according to claim 1, wherein the semi-transparent mirror is provided in an optical path for illuminating an on-wafer alignment pattern that includes a reduction projection lens. 5. Coherent alignment The reduction projection alignment method according to claim 1, wherein the illumination light is temporally and spatially coherent. 6. The reduction projection alignment method according to claim 3, wherein a wavefront correction optical system is provided in the optical path provided with the semi-transparent mirror.