JPH0340417A - Projection aligner - Google Patents

Abstract

PURPOSE:To accurately detect the inclination and height of the surface of the photoresist on the material to be exposed by a method wherein the light emitted from a source of coherent light is made to irradiate diagonally, and the grown interference fringes are measured. CONSTITUTION:The light emitted from the coherent light source 1 such as a semiconductor laser and the like is formed into a parallel illumination light 15 by a lens 11. This illumination light 15 is made to irradiate diagonally at the incidence angle theta on the exposure region of the projection optical system, consisting of an illumination system 81, an exposure and projection lens 8 and the like located on the surface of the photoresist on a wafer 4, through the intermediary of a beam splitter 10. The interference fringes, which are obtained by having the reference light 17 formed by splitting the light emitted from a light source 1 by a beam splitter 10 on a pattern detector 3 at the desired angle, is detected. The inclination and the height of the surface of the photoresist on the wafer 4 can be computed from the change of the pitch and phase of the above-mentioned interference fringes.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a projection exposure apparatus for fine patterns such as semiconductor circuit patterns, display device patterns such as liquid crystals, etc., and in particular, it is capable of exposing the entire exposure area with high resolution. The present invention relates to a projection exposure apparatus equipped with means for detecting the inclination and height of an object to be exposed.

[Prior art] Exposure of fine patterns of semiconductor integrated circuits or TF
T (Thin Film Transistor)
When exposing a 15°, 16°, and 17° drive circuit pattern, which is one of the large field-of-view patterns of display devices such as LCD televisions, it is necessary to expose a pattern that is faithful to the original image and has little variation in line width over the entire exposed area. be. Especially in the field of semiconductor integrated circuits, the future will be 0.
It is necessary to expose the entire area of nearly 15 areas with a line width pattern of 5 μm or less, but as the pattern becomes finer, the imaging range (depth of focus) becomes ±1 μm or less. For this reason, it is essential to accurately align the photoresist surface on the wafer with the pattern image formation surface. To achieve this, it is necessary to accurately detect the inclination and height of the exposed area of the wafer surface (photoresist surface).

In the first known example disclosed in Japanese Patent Laid-Open No. 63-7626, a semiconductor laser is focused on the wafer surface from an oblique direction, and the height is detected by detecting the focused position. . In addition, in this known example, multiple reflections due to the multilayer structure of the wafer are dealt with by using a three-wavelength semiconductor laser, and the light focusing position is changed to the oblique incident direction and the right angle direction, and the heights of different places on the wafer are determined. ing. This known example mainly detects the height, and it is also possible to detect the inclination by changing the measurement location in the oblique incident direction and the perpendicular direction, but it is also possible to detect the inclination.
It is difficult to obtain an accurate value of the inclination even if two locations in a narrow area of about 0 mm are measured. In order to achieve highly accurate height detection in this known example, it is necessary to sufficiently condense the light on the wafer, that is, to make the condensed diameter as small as possible. It is necessary to increase the condensing angle (the angle of the outermost ray of the condensed beam with respect to the principal ray), and as a result, the angle of incidence of the principal ray must be made small. When this angle is made smaller (the angle from a line perpendicular to the wafer surface becomes smaller), the influence of multiple interference associated with the multilayer structure of the wafer increases for reasons described later. In this known example, three wavelengths are used to solve this problem, but each wavelength is affected by interference, so it is not a fundamental over-solution.

In addition, as a conventional method of detecting inclination,
In the second known example shown in Publication No. 20, a tilt detection light different from the exposure wavelength is irradiated through a projection lens, one reflected light is collected, and the tilt is detected from the focused position. Since the light is incident perpendicularly or at a shallow angle, the influence of interference with light reflected from the base cannot be ignored for reasons described later, making accurate detection difficult.

Furthermore, in a third known example of a conventional height detection method for a multilayered object, disclosed in Japanese Patent Application Laid-Open No. 63-247741, the reflected light from the base film is separated separately. It is difficult to perform this method on thin films that appear in the process of creating semiconductor circuits.

[Problems to be Solved by the Invention] The above-mentioned conventional technology does not take into account the fact that information on the inclination and height within the exposure area can be accurately obtained for a multilayer structure such as a wafer having a semiconductor circuit pattern. Future 0.
There was a problem with the highly accurate tilt and height control required for circuit pattern exposure of 5 μm or less.

An object of the present invention is to solve the above-mentioned conventional problems, to accurately detect the inclination and height of the photoresist surface in the exposure area for any wafer in a semiconductor process, and to always keep the image on the image plane at or near the photoresist surface. An object of the present invention is to provide a projection exposure apparatus that exposes a high-resolution pattern with little variation in line width in an optimal position.

[Means to solve the problem]

In order to achieve the above object, the present invention uses parallel illumination light emitted from a coherent light source and irradiates the exposure area of the projection optical system on the photoresist surface on the wafer obliquely at an incident angle θ. , the reflected light and the reference light created by separating the light emitted from the light source are incident on a pattern detector at a desired angle to detect interference fringes.

From changes in the interference fringe pitch and phase, it is possible to determine changes in the inclination and height of the photoresist on the wafer and the surface. In addition, it is easy to set the incident angle to 85° or more in the present invention, which uses a parallel light beam, and because the incident angle is large, most of the reflection occurs on the photoresist surface, and the reflection on each layer of the underlying layer structure. As a result, the influence of interference that occurs becomes almost negligible. Furthermore, if the light incident on the photoresist is made into S-polarized light, the reflection on the surface will be further increased and the accuracy will be improved.

In addition, the light reflected on the photoresist surface is incident perpendicularly on a plane mirror, the reflected light is made incident on the photoresist surface again, and the reflected light is used as object light to obtain information on the interference pattern. It becomes possible to perform detection with twice the sensitivity, and even more accurate detection becomes possible.

In addition, by configuring the reference light to travel in substantially the same direction and pass through the same area as the photoresist irradiation light and object light (reflected light), each optical path is free from external disturbances such as air fluctuations. In the same way, it is possible to detect inclination and height that are less susceptible to changes in the surrounding environment.

In addition, if the information on the obtained interference fringes is subjected to fast Fourier transform and the slope Δθ and height Δh are calculated from the resulting information near the spectrum of the fringes, Δθ can be calculated at a high speed that can be considered as real time.
, Δh are found. At this time, if the photoresist irradiation position is in an optically conjugate (imaging) relationship with the light receiving surface of the array sensor, which is the pattern detection means, information on only the desired area on the wafer can be selected, and the inclination and height of that area can be selected. It becomes possible to seek the

Furthermore, when performing the above-mentioned interferometric measurement using light of one wavelength, the height is determined from the phase of the interference fringes obtained. Even if the phase changes from α to 2Ωπ + α (n: integer), n is cannot be identified, so a second coherent light with a different wavelength is used,
If the light of the first wavelength is guided to the same optical system (optical path), the two wavelengths are separated at the time of detection, and the height is determined using the two pieces of interference fringe information.

It becomes possible to precisely obtain height information over a wide range of height changes. In addition, by using other wafer height detection means such as air micro, the uncertainty factor in the height direction due to single wavelength detection can be removed, and height information can be precisely obtained over a wide range of height changes. It becomes possible.

[Effect]

Since the interference fringe information obtained by the above-mentioned pattern detector includes pitch and phase information, inclination and height information can be obtained at the same time. Moreover, when the incident angle is set to 85 degrees or more, the inclination and height of the photoresist surface can be determined accurately and simultaneously, as will be explained below. The angle of incidence, the polarization of the incident light, and the accuracy of detection will be explained below.

If the amplitude of light incident on the object to be measured is As and Ap for S-polarized light and P-polarized light, the amplitudes of light reflected and refracted on the surface of the object with refractive index n are Rs, Rp, and Ds.

Dρ is the incident angle θ, the refraction angle ψ (sinφ=sinθ/
n) is given by the following formula.

) 〉 ) ] For S-polarized light, the incident angle is from 0° to 60°; for P-polarized light, from 0° to 75°, the transmitted light is larger than the surface reflected light, and the surface reflection is due to the reflected light from the boundary of the underlying multilayer structure. Large-amplitude interference occurs with light. Although the amplitude of the surface reflected light becomes larger when the incident angle is about 85° from the above value, this is an insufficient condition to realize accurate measurement.

The reason is shown below. As shown in Figure 17, the angle of incidence O
Light with amplitude A that is incident at
It becomes Rb. Here, if the amplitude of the incident light A is 1, then D is the amplitude transmittance. Therefore, when the light reflected from the base passes through the surface, its amplitude becomes RbD'. Other swing @AC=1)
The incident light is reflected by the surface and its amplitude becomes R. Here, R and D indicate whether the polarization of the incident light is S or P, and Rs, Ds, and R
If expressed in PtDP, the above equations (1) to (4) hold 0
The light R8 reflected on the surface and the light R1 reflected on the underlayer overlap when the layer thickness d is small, resulting in a complex amplitude A1 expressed by the following equation.
It becomes the light of

However, here, λ is the wavelength of light used for measurement. It can be seen from equation (5) that the phase of A1 changes even when the thickness d of the film shown in FIG. 3 changes slightly (a change in length one digit below the wavelength). Therefore, the relationship between the incident angle θ and R and D is as shown in Figs. 5 and 6 for S and P polarized light, respectively, and to make it easier to understand from this graph, it becomes a noise component (
5) By finding the amplitude ratio RbD"/R of the second term to the first term in the equation, it is possible to evaluate the degree of error that will affect the measurement. Therefore, considering the case where Rb = 1 as the worst case, D" FIG. 7 shows /R determined for the incident angle θ and for the two polarized lights.

Since D''/R becomes a noise (error) component in various detection methods, it is clear that in order to keep this value below 5%, it is necessary to set the angle of incidence to 856 or more. It can be seen from FIG. 7 that the noise becomes even smaller.

As shown in Figure 3, the method of reflecting twice on the surface of the object to be measured is such that the 4α light is tilted with respect to the surface inclination α, and the detection sensitivity for tilt and height is doubled compared to the case of reflecting once. This enables highly accurate detection.

In addition, the reflected light from the underlying surface is superimposed on the interference pattern and disturbs the pitch and phase of the interference fringes, but by using 85' or more of incidence or by using S-polarized light, it is possible to almost eliminate this effect as mentioned above. Highly accurate detection becomes possible. Furthermore, by making the reference optical path used for this interference measurement almost the same optical path as the measurement light, stable and highly accurate measurement that is almost unaffected by the measurement environment such as air fluctuations can be realized.

In addition, the obtained interference fringe information is subjected to fast Fourier transform (FTT).
When the spectrum is detected by a program, the information on the spectrum corresponding to the frequency of the fringe represents the pitch and phase, so the slope and height can be determined at the same time from this value. Also FF
Since T is a matrix calculation, parallel calculation processing is possible, and if such a parallel calculation circuit is used, processing can be performed in less than 1 ms, and it is also easy to detect tilt and height and control in real time. .

In addition, in the case of interference detection, if a change of one pitch of interference fringes occurs, the detected interference fringes become exactly the same. Therefore, the amount obtained by adding or subtracting the movement amount of the integer pinch remains as an uncertain value of the detected value.

In the present invention, interference detection is performed using the second wavelength as the detection light in the same way as the first wavelength, and accurate height detection over a wide range is possible from the phase relationship between the first and second wavelengths. Allows for tilt and height control. Further, other wafer height detection means such as an air micro is used to detect an uncertain range when detecting one wavelength, thereby making it possible to accurately detect the height over a wide range.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

Exposure light emitted from the exposure illumination system 81 illuminates the reticle 9, and the transmitted light is projected by the reduction projection lens 8 onto the surface of the wafer 4 on the stage 7 as a reduced image of the pattern on the reticle. The relative position of the reticle 9 and the wafer 4 is detected by an alignment system 800, and by controlling either the reticle 9 or the wafer 4 by fine movement, overlapping exposure of patterns is performed. 100X is a system for detecting the tilt and height in the X direction, and a similar optical system exists for the tilt in the Y direction, although it is not shown. The detection system will be explained below.

Light emitted from coherent light 11 such as a semiconductor laser is converted into parallel light 15 by a lens 11. The parallel beam 15 is separated into parallel beams 16 and 17 by the beam splitter prism 10. The parallel light 16 is transmitted through a beam splitter 12 which is an irradiation means.
．． The light passes through the mirror 13 and enters the photoresist on the upper surface of the wafer 4, which is the object to be exposed, on the stage 7, which is equipped with a vertical and two-axis lifting mechanism, at an incident angle θ (88°). As mentioned above, almost all of the light is reflected by the photoresist surface, and this reflected object light 16' enters the plane boundary 14, which is the folding detection optical system, perpendicularly and traces the optical path of the 5 elements in the reverse direction, to reach the exposed object 4. reflected by mirror 1 as object light 26#
3° beam splitter 12, lens 21. Micro aperture plate 2
3, the lens 22, and then the pattern detection means 3.

On the other hand, the reference beam 17 separated by the beam splitter 10 is
The reference light travels in the same direction on almost the same optical path as the irradiation light 16 (but strictly speaking, at an angle of 92° with respect to the wafer normal), is reflected vertically by the plane mirror 14, and follows almost the same path as the object light 26'. 27″', and reaches the pattern detection means 3 via the wedge glass 24.The reference optical path differs from the object optical path in that it is not reflected by the object to be exposed 4, and it passes through the wedge glass 24.The lens 21 and 22 emits the incident light as parallel light, and the irradiation position of the irradiation light on the wafer, that is, the exposure area O, is almost imaged on the pattern detector.If there is no wedge glass, the wafer surface The intersection point A of the reference beam and the object light that has been reflected back from ), so that the two lights intersect on the light-receiving surface and an image is formed in the exposure area O.The micro-aperture plate 23 arranged in the folded detection optical system enters the lens 21. It is located at the focal point of the object beam, which is parallel light, and the reference target, and has a minute aperture at the focal point.This minute aperture plate is a lens, beam splitter, etc. that causes problems when using highly coherent laser beams. The generated back-reflected light is removed to prevent noise light from being superimposed on the light-receiving surface of the pattern detection means.The interference fringes detected by the pattern detection means 3 have an intensity distribution Ix as shown in FIG. The pattern detection means 3 is a one-dimensional array sensor, and intensity values are determined at the positions marked on the X axis in FIG. 2, and this data is transmitted to the processing circuit 5. When the image formation plane of the reticle 9 formed by the exposure and imaging system coincides with the image formation plane of the reticle 9 (4 in Fig. 3), interference fringes with a pitch P shown by the solid line in Fig. 2 are obtained.If the surface of the exposure area is When tilted by α as shown by the dotted line LL',
As is clear from FIG. 3, the first reflected light is tilted by 2α, and the second reflected light is tilted by 4α. As a result, the interference fringes obtained by the pattern detection means have a pitch P' as shown by the dotted line in FIG. The interference signal obtained by the detection means is input to the processing circuit 5 shown in FIG. 4 via a transmission line 31. The input signal is first A/D converted and input to the FF7 circuit at timings corresponding to the points marked on the horizontal axis in FIG. This FFT input signal is as shown in Figure 4(b),
The FFT result is obtained as a complex number C(k), and as shown in Figure 4 (C) (however, the vertical axis of this graph is Ic(k)I), the spectrum generally has peaks at =o and =m. . k=
o corresponds to the bias component of the sine wave, and k=m corresponds to the period of the sine wave. Although m corresponds to the pitch P, the output can only be obtained discretely, so in order to find the true spectral peak position, interpolation processing is performed from C(m) and its neighboring data to find the true peak position. By finding , the slope ΔφX can be found. Also, the phase (tan” (I m(
C(m) ) /Re (C(m) ) ) to height (
Information ΔZ of Z) is obtained. Δ obtained in this way
The top and bottom of the stage 7 and the The two-axis lifting mechanism is controlled to align the reticle imaging plane and the photoresist surface to a desired positional relationship.

FIG. 8 shows an embodiment of the present invention. The same numbers as in FIG. 1 are the same. Similarly to FIG. 1, the illustration of the y-direction tilt detection system is omitted. The wavelength of the semiconductor laser 1 is λ□, and the wavelength of the semiconductor laser 1' is λ, for example, λl = 8
10 nm, λ, = 750 nm, the light emitted by semiconductor lasers 1 and 1' is 11 and 11', respectively.
becomes parallel light, and is separated into 0th-order and 1st-order parallel light by the diffraction grating 18.18'.The four separated parallel beams are passed through the wavelength separation mirror 19, and the light of λ is transmitted, λ2
The light is reflected, and the four beams become mutually parallel parallel beams at the prism 110. Beams 16 with wavelengths λ1 and λ2.
16' passes through the same optical path, is reflected by mirror 13, and enters the wafer at 01, and the reflected light becomes object light and is reflected by mirror 2.
3. The light passes through a detection optical system consisting of lenses 21 and 22 and enters the pattern detection means 3. On the other hand, the beams 17 and 17' having wavelengths λ and λ2 pass through the same reference optical path and enter the pattern detection means 3 at a constant angle with the object light. The object optical path and the reference optical path pass through exactly the same optical components, except for reflection at the wafer surface. Processing mouth j! 5' is the semiconductor laser and 1
' blinks alternately, and the pattern detection means 3 detects λ□ and λ2.
Interference fringe information of wavelengths is received alternately. Figure 9 shows the difference in wavelength of λ received by the processing circuit. This is 5 stripe information. The solid line is at the best height position, and the dotted line is when the height changes by ΔZ. When there is no change in the slope of the rain detection signal, a phase difference Δφ2 shown by the following value is generated.

However, when determining ΔZ from the detected phase difference Δφ2, there is uncertainty as shown by the following equation.

Here n is an integer. For example, λ□=0.81 μm.

If it is 0.22 degrees, it has an uncertain value of true value + 11.6 nμm. In this embodiment, this problem is solved by measurement using the second wavelength λ2. Figure 10(a) shows the detection intensity 1z for the change in height of the wafer surface at the reference position (x=xo) when detected at a wavelength of λ□, and Figure 10(b) shows the detection intensity 1z when detected at a wavelength of λ2. It is in. The intensity of the detected pattern is expressed by the following equation.

(X, ΔZ; λi)=:a+bcos Here, X is the coordinate of the light receiving surface of the detection means, and M is the imaging magnification. Therefore I z = I (XotΔZ;λi)
becomes. The phase value detected at λ1 is Δ-1, and the height corresponding to this value is P-, as shown in Figure 10.
Assuming that they correspond to P-1t, p, p, , p, . . . , it is not known to which of these points ΔZ corresponds to the true value. If the phase value detected at λ2 is Δ-2, the corresponding ΔZ is...P-,
, P, , Pl, P, . . . .

The interval SiS between ΔZ=S, which has the same phase, and ΔZ=S, which has the same phase in FIGS. Then, the phase of λ□ becomes Δ only at one point Δz0, and the next Δ that satisfies this condition
The value of Z is the height given by the following equation.

ΔZ=ΔZ□+m5XSO=-(10) where m is an integer.

λ1=0.81 pm, λ2::0.75μm, l
: When iL=2', S1S is 145 μm. The height of the wafer surface does not vary over such a wide range;
If wafers of different thicknesses are used, no problem will occur because the values are known in advance.

In the embodiment shown in FIG. 1, a folding plane mirror is used to reflect the wafer twice, so the value corresponding to 5180 is half that of the embodiment shown in FIG. 8, which is 72.5μ.
m.

FIG. 11 shows an area 41 exposed on the wafer in one exposure.
In contrast, illumination lights 16 and 16 in the X direction and the y direction are shown. The location of the illumination light 16 on the wafer corresponds to the address of the array element on the light receiving surface 301 of the pattern detection means 3.

Among the addresses js"je corresponding to the entire illumination area, only a desired area is selected, for example, from Is to Ie in FIG.
In Figure 2, take out Is1 to Ie and Is2 to Is,
FFT can be easily performed using only this data. Since it is possible to specify any part in this way, for example, by specifying a part that includes a fine pattern as the detection area and excluding the coarse pattern part, the slope and height of the fine pattern part can be accurately determined. , it becomes possible to perform exposure at a position closer to the focal point.

FIG. 13 shows an embodiment of the present invention. The same numbers as in FIGS. 1 and 8 represent the same items. Light emitted from the semiconductor lasers 1 and 1 having wavelengths λ and λ2 becomes parallel light by the collimator lenses 11 and 11, and becomes the same optical path by the wavelength separation mirror 19. Cylindrical lenses 110 and 120
is used to widen the beam diameter in the y direction. FIG. 14 shows the expanded range of the irradiation light 16 (dotted line) with respect to the exposure area 41 on the wafer 4. As shown in FIG. The irradiated portion is pattern detecting means 3' and 3# consisting of two-dimensional array elements.
An image is formed on the light-receiving surface 302 of. Of the two-dimensionally obtained interference fringes of the irradiated area, only the information of the desired area 42.degree. 43 shown in FIG. 14 is processed. The inclination and height in the X direction are determined at each location 42 and 43, and the direction and height in the X+'j direction for the entire surface of 41 is determined.

FIG. 15 shows an embodiment of the present invention. This figure is a plan view, and the exposure optical system of the projection exposure apparatus is omitted. The stage can be slightly rotated wx and wy around a rotation axis 71 in the X-axis direction and a rotation axis 72 in the y-direction of the stage raising mechanism. Irradiation light for tilt and height detection is irradiated onto the exposure area 41 on the wafer 4 from a direction tilted by 45 degrees from the X axis (X direction), and the reflected light is returned vertically by the plane mirror 14 to detect the aforementioned tilt and height. The light is detected by the detection optical system 100. In this embodiment, the detection light has an inclination of 45° with respect to the two-axis lifting mechanism, and an interference pattern as shown in FIG. 16 is generated on the two-dimensional imaging surface of the pattern detection means. When the wafer surface remains horizontal, the interference pattern is a solid line, and when the wafer surface is tilted in the y direction, it is a dotted line. Therefore, if the pitch and phase in the X and y directions on the imaging plane are determined, the inclination and height in the X and y directions can be determined from one detection optical axis system. Further, in the embodiment shown in FIG. 15, the light beam may be divided into two just before the pattern detection means, and the X direction and the Y direction may be detected by separate pattern detection means.

FIG. 18 shows an embodiment of the present invention. The same number as the first engineering drawing represents the same item. The difference from FIG. 1 is the following point S. ■ A tube laser 101 typified by a He-Ne laser or the like is used as a laser source, and a pinhole plate 102 for selecting a part of the laser beam (the center of the Gaussian distribution) is provided at a position conjugate with the folding plane mirror 14. (1) The beam 15 passes through the beam splitter 12, is reflected by the mirror 14, and the number of reflections until it reaches the pattern detection means 3 is an even or odd number for both the reference optical path and the object optical path (■)
The pattern detection means 3 and the folding plane mirror 14 are in a conjugate relationship (
The parallel plane glass 201 is connected to the reference optical path 27 # (or the object optical path 26 “), ■Pattern detection means 3
A correction lens 204 is inserted just before the pattern detection means so that the object light and reference light incident on the pattern become plane waves,
(2) The air micro 82 is also used to detect the height of the wafer 4.

The light emitted from the lens 103 enters a minute opening of the pinhole plate 102 provided at a position conjugate with the folding plane [14] and selects the center of the Gaussian distribution.

Next, lenses 103 and 105 produce parallel light 1 of desired thickness.
5 and enters the beam splitter 106. Parallel light 1
5 is separated into parallel beams 16 and 17 by a beam splitter 106. Here, the parallel light 16 is transmitted to the beam splitter 106
is transmitted (the number of reflections is O), and the parallel light 17 is reflected twice within the beam splitter 106.

This is so that the beam 15 passes through the beam splitter 12, is reflected by the mirror 14, and the number of reflections until it reaches the pattern detection means 3 is an even or odd number for both the reference optical path and the object optical path. By aligning them, when the direction of the incident light 15 to the beam splitter 106 changes, the variation in the intersection angle between the reference light and the object light can be kept small, and as a result, there is almost no change in the interference fringe pitch, resulting in high precision. detection becomes possible. In the case of this embodiment, the number of reflections of the reference beam and the object beam after beam splitting by the beam splitter 106 before reaching the pattern detection means is six, which is an even number. The parallel light 16 emitted from the beam splitter 106 passes through the beam splitter 12° mirror 13 to the stage 7 which is equipped with a vertical and two-axis tilting mechanism.
Almost all the light is reflected by the photoresist surface on the upper surface of the wafer 4, which is the object to be exposed on the
is incident perpendicularly to . The parallel light 16 reflected by the folding plane mirror 14 reverses its original optical path again and becomes an object light 26'' through the mirror 13° beam splitter 12, lens 202, minute aperture plate 23° lens 203., 204, and pattern detection means. 3.

On the other hand, the parallel light 17 separated by the beam splitter 106 travels along almost the same optical path as the parallel light 16 and passes through the beam splitter 1.
2. After passing through the mirror 13 and directly entering the folding mirror 14 perpendicularly, the light beam returns along the original optical path again, and returns to the mirror 13. as the reference beam 27#. Beam splitter 12° parallel plane glass 201. Lens 202. Micro aperture plate 23° lens 203
．． It reaches the pattern detection means 3 via 204.

The reference optical path differs from the object optical path in that it is not reflected by the object to be exposed 4 and that it passes through the parallel plane glass 201. The lenses 202, 203, and 204 image a plane perpendicular to the optical axis between the reflective surface of the folding plane mirror 14 and the exposure center O onto the pattern detection means 3. This is because when detecting the tilt and height only from information on the part corresponding to the desired location of the exposed object, the correspondence between the position within the interference fringes and the position on the wafer must be clear. By employing the above configuration, the images of the wafer in the forward and return optical paths can be almost equally formed on the pattern detection means 3, and even if only a portion is detected, it can be detected with high accuracy. However, when a plane perpendicular to the optical axis between the reflective surface of the folding plane mirror 14 and the exposure center O is imaged on the pattern detection means 3, the exposure area and the intersection point A do not coincide, so the pattern cannot be detected as it is. Detection means 3
It is not possible to superimpose the reference light and the object light on the above, so the parallel plane glass 201 is inserted into the reference light N27' (or the object light 826'), and the reference light is translated in parallel to be referenced on the pattern detection means 3. I made the light and object light overlap. Lens 204 is the same as lenses 202 and 203
This lens is arranged immediately in front of the pattern detection means 3 to correct the spherical waves of the reference light and object light generated by the above into plane waves. By making both wavefronts plane waves, variations in the pitch of interference fringes can be eliminated and high detection accuracy can be obtained.

In this detection method, when detecting one wavelength, there is a problem of uncertainty in the wafer height as shown by equation (7). Although the solution using two wavelength illumination has been described above, it can also be solved by using other wafer height detection means in combination.

In this embodiment, this problem was solved by using the air micro 82 in combination. That is, the wafer height is positioned by the air micro to the range where the height can be reliably detected by the present detection method shown by equation (6), and this detection method is used within the range of phase change shown by equation (6). Alternatively, other detection means such as an air micrometer may be used to detect the height of the wafer, and the present detection method may be used to detect the inclination. FIG. 21 shows the principle of the air micro. Pressurized air is supplied from the air pressure source 821 to the air micro nozzle 822 and the reference air micro nozzle 823, and the air micro nozzle 82
The pressure difference between the back pressure 824 in the air micro nozzle 824 determined by the gap between the air micro nozzle 2 and the wafer 4 and the back pressure 825 of the reference air micro nozzle 823 is converted into an electrical signal by the differential pressure converter 826, and the height of the stage 7 is determined by the processing circuit 5. The pressure is controlled and stopped when the differential pressure reaches O.

Figures 19 and 20 are diagrams for explaining the effect of the method of selectively illuminating a part of the Gaussian distribution in this embodiment.
Figure 9 shows the illuminance distribution of the reference light (solid line) and object light (broken line) on the pattern detection means 3 when a part of the Gaussian distribution is not selected, and Figure 20 shows the illuminance distribution when a part of the Gaussian distribution is selected. It is something. The vertical axis shows the illuminance Ix, and the horizontal axis shows the detection position X of the pattern detection means 3. When the wafer is tilted, the object light moves on the pattern detection means 3, and the overlapping state (shaded area) of the reference light and object light changes. At this time, in the embodiment of FIG. 19 in which a part of the Gaussian distribution is not selected, the illuminance of the overlapping portion of the reference light and the object light changes greatly, and the interference intensity changes greatly. On the other hand, in the case of illumination in which a part of the Gaussian distribution shown in FIG. 20 is selected, the change in illuminance at the overlapping portion of the reference light and object light is small, and the fluctuation in interference intensity is also small. The smaller the variation in interference intensity, the smaller the error in the signal processing process, and the more accurate detection becomes possible. Since the signal processing of this embodiment has been described above, the explanation will be omitted.

FIG. 22 shows an embodiment of the present invention. In this embodiment, laser light is irradiated diagonally across the exposure area 41 of the wafer 4. 100x is a system that detects the tilt and height in the X direction, 1
00Y is a system for detecting the tilt and height in the y direction, and 14 is a folding plane mirror. FIG. 23 is an enlarged view of the exposure area 41, and is an example in which one exposure area has two circuit sections (memory, etc.). In the figure, 412 indicates the circuit section 4.
13 indicates a boundary, and laser light 411 irradiates the exposure area in a diagonal direction. Figure 24 is I of Figure 23.
-I cross section is shown, but generally the circuit portion 412 and the boundary portion 413
The heights are different. Therefore, if the laser beam is irradiated in a direction perpendicular or parallel to the sides of the exposed area, there is a risk that the inclination and height of the boundary part will be detected instead of the inclination and height of the circuit part that is originally desired to be detected. . Against this.

As shown in FIG. 23, by irradiating the laser beam in the diagonal direction of the exposure area and selecting an arbitrary detection range as necessary, it is possible to accurately determine the inclination and height of the circuit section.

In addition, when irradiating the laser beam in the diagonal direction of the exposure area,
It also has the effect of providing the longest irradiation range and allowing more accurate detection based on the slope and height of the exposed area.

In the embodiments shown above, a semiconductor exposure apparatus has been described, but the present invention can be similarly applied to exposure apparatuses for other display devices such as liquid crystal displays, and can exhibit great effects.

〔Effect of the invention〕

The present invention is constructed as described in one or more ways and provides the advantages described below.

(1) Inclination and height can be determined simultaneously by interferometric measurement.

(2) By configuring the reference light to pass through almost the same location as the irradiation and detection light, fluctuations in the air, etc. can be avoided.

Stable tilt and height detection is possible without being affected by disturbance factors.

(3) By setting the angle of incidence on the object to be exposed to 85° or more, and by making the incident light S-polarized, the inclination and height of the photoresist surface can be controlled by the underlying film structure. can be detected accurately.

(4) By vertically turning back the reflected light of the light obliquely irradiated onto the exposed object and irradiating it again onto the exposed object.

The accuracy of tilt and height detection can be doubled.

(5) By making the imaging surface of the pattern detection means conjugate with the beam irradiation position on the surface of the object to be exposed and detecting the inclination and height only from the information of the part corresponding to the desired location of the object to be exposed, especially precise You can focus where you need to focus.

As explained above, it is now possible to stably detect the inclination and height of the surface of the exposed object without being affected by the underlying surface, and especially for LSI equivalent focal depths with line widths of 0.5 μm or less. This contributes to a significant improvement in the yield of the exposure process for pattern exposure where there is little margin.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration of an embodiment of the present invention including a folded detection optical system, Fig. 2 is a diagram showing a detection pattern signal waveform, and Fig. 3 is for explaining the effect of the folded detection optical system. , FIG. 4 is a diagram showing an example of the processing circuit, FIGS. 5 to 7 are diagrams showing the relationship between the incident angle, reflection, and transmission complex amplitude, and characteristics of the noise component rate. FIG. 8 is a diagram showing the characteristics of the noise component rate. A diagram showing the configuration of an embodiment of the invention that uses two wavelengths, FIG. 9 is a diagram showing changes in the detection pattern signal due to height changes, and FIG. 11 and 12 are diagrams showing changes in the signal Iz at the point of interest due to the height change ΔZ.
The figure shows the irradiation light for the exposure area and the calculation processing area,
Fig. 13 is a diagram showing the configuration of an embodiment of the present invention that detects two-dimensionally at two wavelengths, Fig. 14 is a diagram showing the calculation processing area for the exposure area of the embodiment shown in Fig. 13, and Fig. 15. 16 is a diagram showing a detection system according to an embodiment of the present invention that detects inclinations in two directions, and FIG. 16 is a diagram showing its detection pattern.
Figure 17 is a diagram explaining the amplitude component of the irradiation detection light, Figure 18
The figure is a diagram showing the configuration of an embodiment of the present invention in which an air micro is used in combination and the optical system is further improved. Figures 19 and 20 are diagrams each illustrating the effects of the illumination method according to the present invention. , FIG. 21 is a diagram showing the principle of the air micro according to the present invention, and FIGS. 22 to 24 are explanatory diagrams of the case where laser light is irradiated in the diagonal direction of the exposure area according to the present invention. 1... Laser light source, 10.12... Beam splitter, 14... Folding plane mirror, 21.22... Lens, 23... Micro aperture plate, 24... Wedge glass, 3.
3', 3'... Pattern detection means, 4... Wafer, 5... Processing circuit, 7... Stage, 8
...Exposure projection lens, 81...Illumination system, 9.
...Reticle. 82...Air Micro. 1st Ward Diagram A (2) Shi-m- F f o-￥e Tapping om Haya Qc i y snow; f ■
Yukitto 0 Zaifue Qτ□゛Suui No. 8 Listen No. 0 En No. 1 Figure No.! 2 Figure 15 View 7g Figure 1θ0 Figure 77 Scale b 〆hen 4Z Figure 8 Figure rq Figure % 20 Section 2I must Figure 22 Figure ZJ Figure 24 View

Claims (1)

[Claims] 1. An exposure illumination system, a mask or reticle, a projection optical system, a stage that holds an object to be exposed and moves the object to be exposed in three orthogonal directions, the mask or reticle, and the object to be exposed. In a projection exposure apparatus, the light emitted from the coherent light source is used as parallel irradiation light, and the projection optical system on the surface of the object to be exposed is at least one irradiation means that irradiates the exposure area obliquely at an incident angle θ; at least one detection optical system that guides the object light reflected by the object to be exposed to the pattern detection means; and the light emitted from the coherent light source. at least a means for separating the reference light and generating a reference light, and a means for guiding the reference light to the pattern detecting means and superimposing it on the pattern detecting means at a desired angle with respect to the optical axis of the object light so as to cause interference. one reference light means, a processing circuit for obtaining information on at least one of the inclination or height of the object to be exposed from information on the interference pattern obtained by the pattern detection means; A projection exposure apparatus characterized by being equipped with a stage control system that controls at least one of the inclination in at least one direction or the height. 2. The projection exposure apparatus according to claim 1, wherein the irradiation light, the object light, and the reference light proceed in substantially the same direction and pass through the same area. 3. The projection exposure apparatus according to claim 1, wherein the incident angle θ is 85° or more. 4. The projection exposure apparatus according to claim 1, wherein the irradiation light is S-polarized light. 5. Arranging a folding plane mirror, the object light reflected by the object to be exposed is reflected almost perpendicularly by the folding plane mirror, travels the same optical path as the forward path in the opposite direction, is reflected by the object to be exposed again, and is sent to the pattern detecting means. 2. The projection exposure apparatus according to claim 1, further comprising a folded detection optical system for guiding the pattern, and causing the reference light to interfere with the pattern detection means. 6. The projection exposure apparatus according to claim 5, further comprising means configured such that the reference light passes through substantially the same direction and the same area as the object light. 7. The pattern detection means is an array sensor, and the pitch P and phase φ correspond to the inclination Δθ and height Δh of the exposed object.
7. The method of claim 1, wherein a sine wave signal having a value of A projection exposure apparatus according to any one of the above. 8. Claim 1, 5 or 6, wherein the irradiation position on the object to be exposed is in a substantially conjugate relationship (imaging relationship) with the pattern detection means by the detection optical system or folded detection optical system. The projection exposure apparatus described. 9. The projection exposure apparatus according to claim 1, wherein the object light and the reference light incident on the pattern detection means are effectively plane waves. 10. The pattern detection means is an array sensor, and the irradiation position on the object to be exposed is in a substantially conjugate relationship with the pattern detection means by the detection optical system or the folded detection optical system, and is not obtained by the array sensor. a processing circuit that selects only a desired region of the exposed information, performs a fast Fourier transform operation, and calculates at least one of the slope or the height of the desired region of the exposure region of the exposed object from the obtained spectral information. 7. A projection exposure apparatus according to claim 1, characterized in that: 11. In the optical path of the detection optical system or the folded reflection optical system and the reference light, a minute aperture is provided in the light converging portion of both optical paths to block noise light components reflected from the front and back surfaces of optical components in both optical paths. 7. A projection exposure apparatus according to claim 1, characterized in that: 12. A second coherent light source having a different wavelength from the coherent light source is provided, the light emitted from the second coherent light source is introduced into the irradiation means, and the optical path is approximately the same as that of the first coherent light source. A means for separating the second wavelength light from the first wavelength light is disposed in the detection optical system or the folded detection optical system, and the separated second wavelength light is separated from the first wavelength light. detecting the object light and the reference light with a second pattern detection means;
Claim 1: Uncertainty factors in the height direction are removed from the interference fringe information obtained by the first and second pattern detection means, thereby making it possible to detect accurate height information over a wide range.
Or the projection exposure apparatus according to 5 or 6. 13. The projection according to claim 1, 5 or 6, characterized in that the number of reflections of the reference light and the object light are made equal to even or odd numbers before one beam passes through the beam splitter and reaches the pattern detection means. Exposure equipment. 14. By using other wafer height detection means such as air micro, the uncertainty factor in the height direction due to single wavelength detection is removed, and accurate height information can be detected over a wide range. 7. A projection exposure apparatus according to claim 1, wherein said projection exposure apparatus comprises: 15. The projection exposure apparatus according to claim 1, 5 or 6, wherein the laser beam is irradiated in a substantially diagonal direction of the exposure area. 16. The projection exposure apparatus according to claim 1, further comprising a pinhole plate provided in the illumination optical path for selecting part of the laser beam. 17. Claim 16, characterized in that a pinhole plate for selecting part of the laser beam is provided at a position substantially conjugate to the exposure area.
The projection exposure apparatus described.