JP3265031B2 - Surface shape detection method and projection exposure apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting the surface shape of a flat substrate such as a semiconductor wafer and a projection exposure apparatus, and more particularly to a method for calculating the surface shape of a resist from optical interference fringe information by FFT. The present invention relates to a surface shape detection method for obtaining a surface inclination, a height, and the like, and a projection exposure apparatus that performs focusing by the method.

[0002]

2. Description of the Related Art In a pattern exposure process for a miniaturized semiconductor integrated circuit or a liquid crystal display, etc., it is necessary to accurately detect the inclination and height of the surface of a wafer or a substrate and accurately align the exposure surface. is there. For example, when exposing a pattern with a line width of 0.5 μm using a mercury lamp i-line in a semiconductor integrated circuit, the depth of focus is set to ± 1 μm or less in consideration of the warpage of the wafer and the unevenness of the surface. About 10μra
d. The height of the wafer surface needs to be 0.1 μm or less.

[0003] Japanese Patent Application No. Hei.
A method is disclosed in which the height, inclination, and the like of the resist surface are detected from interference fringes obtained by obliquely incident the S-polarized light on the wafer surface and causing the reflected light to interfere with the reference light. That is, the inclination of the wafer surface is obtained from the pitch of the interference fringes, and the height of the wafer surface is obtained from the phase of the interference fringes.

In this method, the beam size of the laser beam can be made extremely small, so that it is not necessary to increase the convergence angle. Further, since interference fringes are used, the spot diameter on the sensor due to the use of a condensing lens is reduced. Since no spread occurs, the incident angle of the incident light is set to 85 ° or more, for example, 88 °, etc., so that the amount of light entering the photoresist can be reduced.

Further, the reflected light from the wafer is reflected by a mirror and re-enters the wafer surface so as to enlarge the phase difference between the reflected light and the reference light so that the intensity distribution of the interference fringes can be accurately determined. It was made possible to detect.

[0006]

However, Japanese Patent Application No. Hei.
In the method disclosed in Japanese Patent Application Laid-Open No. -100026, it is necessary to maintain a conjugate positional relationship between the wafer surface and the interference fringe detection position. However, at the second incidence, the mirror has a conjugate positional relationship with the interference fringe detection position. There has been a problem that the wafer surface and the interference fringe detection position cannot be maintained in a conjugate positional relationship. For this reason, the second incident light defocuses on the wafer surface to generate an offset, and it is necessary to correct this offset each time measurement is performed.

FIG. 8 is a diagram for explaining the conventional interference fringe detecting method. FIG. 8A shows the case where the incident light is reflected once on the wafer surface, and FIG. 8B shows the case where the incident light is reflected twice.
It is assumed that the wafer surface 41 has a projection as shown with respect to the reference surface 40. The coherent laser light is divided into two parts, and one of them is used as detection illumination light 16 for the wafer surface 4.
1 and the other is used as reference light 17.

In FIG. 8A, the detection illumination light 16 is reflected by the wafer surface 41, and the reflected light 46 is reflected by the reference light 1 on the surface x.
7, interference fringes are generated as shown by the solid line in FIG. On the other hand, when there is no protrusion, the detection illumination light 16 is reflected by the wafer surface 41 as shown by a dotted line, and therefore overlaps with the reference light 17 at a position deviated from the above x and is shown by a dotted line in FIG. Such interference fringes are generated.

Since the phase difference φ between the solid line and the dotted line in FIG. 1C is derived as shown in equation (1), the phase difference φ between the interference fringe from the reference surface 40 and the interference fringe from the wafer surface is measured. Thus, the height z (y) of the protrusion on the wafer surface 41 can be obtained. φ = 4πm · cos θ · z (y) / λ (1) where m is the number of reflections and is 1 in the case of FIG.
θ is the incident angle of the detection illumination light 16 and λ is the same wavelength.

When m is 1, the phase difference φ is too small and the measurement accuracy is low, so that as shown in FIG.
Is returned to the original optical path by the mirror 40 and is reflected again on the wafer surface, and the second reflected light is superimposed on the reference light 17 on the surface x to generate an interference fringe.
M becomes 2 and the phase difference φ can be doubled, so that the measurement accuracy can be doubled.

However, the position of the reflection surface of the wafer surface 41 and the surface x
If the optical system can be configured to be conjugate, the height of each reflecting surface position of the wafer can be associated with the interference fringe information, and the tilt of the wafer can be detected accurately. Since the conjugate positional relationship with the interference fringe detection position is obtained, the wafer surface and the surface x deviate from the conjugate positional relationship,
Thus, there has been a problem that the height of the reflection surface position cannot be accurately detected.

That is, as shown in FIG. 9, the phase of the interference fringe intensity corresponds to the rapid change in the height of the wafer surface shown in FIG. (C), the phase change becomes gradual due to the shift of the conjugate relationship as shown in FIG. 7 (c), and the height of the wafer surface calculated from this is as shown in FIG. It was a gentle thing. SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for detecting the surface shape of a wafer which can solve the above-mentioned problem, and a projection exposure apparatus which can control the height and inclination of the exposure apparatus based on this information.

[0013]

In order to solve the above problem, an optical beam of a coherent monochromatic light source shaped into a predetermined shape is divided into two, and one of the optical beams (object light) is separated. A surface shape detection method for detecting the inclination, height, etc. of the sample surface from interference fringe information obtained by superimposing the reflected light obtained by irradiating the sample surface with the other light beam (reference light). ,
The reflected light from the sample surface is imaged at a position conjugate with the sample surface, and the imaged light is again irradiated on the sample surface, and the reflected light is provided at a position conjugate with the sample. The light is guided to a detector, and the inclination, height, and the like of the sample surface are detected from interference fringe information obtained by being superimposed on the reference light on the photodetector.

Therefore, an image forming optical system for forming an image of the reflected light from the sample surface at a position conjugate with the sample surface, and a reflection for re-irradiating the image forming light of the image forming optical system onto the sample surface. Means, a detection optical system for guiding reflected light of the re-irradiated light on the sample surface to a photodetector provided at a position conjugate with the sample, and reflected light for guiding the reference light to the photodetector surface And a signal processing circuit for detecting the inclination, height, etc. of the sample surface from the interference fringe information detected by the photodetector, and the inclination of the sample surface is determined by the output of the signal processing circuit. The position of the sample surface is appropriately corrected by means for controlling the height and the like.

Further, the imaging optical system comprises at least first and second lenses having a focal length of f ₁ and f ₂ , respectively, and the first lens is arranged at a distance f ₁ from the sample surface. , The distance of the second lens from the first lens (f
₁ + f ₂ ), and the reflecting means is connected to the second
To be arranged away from the lens by a distance f _2.
Further, at least a focal length of the imaging optical system is constituted by a lens is f _1, a distance the lens from the sample surface f
Only ₁ apart place, the reflecting means so as to spaced apart by a distance f ₁ from the lens. Further, means for adjusting a crossing angle between the object light and the reference light on the photodetector is provided.

[0016]

The reflected light from the sample surface forms an image at a position conjugate with the sample surface, and then is re-irradiated on the sample surface. The reflected light is guided to a photodetector located at a position conjugate to the sample. To form an interference fringe pattern having no phase error. The photodetector detects this interference fringe pattern, and the signal processing circuit calculates the inclination, height, etc. of the sample surface from the output signal of the photodetector, and corrects the inclination, height, etc. of the sample surface. Also, the lens system of the imaging optical system forms an image of the reflected light from the sample surface at a position conjugate to the sample surface, and the reflecting means reflects the image and reflects the image through the lens system. Image.

[0017]

FIG. 1 is a block diagram showing an embodiment of a reduction projection exposure apparatus according to the present invention. The reticle 9 is illuminated by the exposure illumination system 81, and its circuit pattern is imaged on the surface of the wafer (test object) 4 on the stage 7 by the reduction lens 8, and the surface detection system 2 detects the surface shape information of the wafer. And process. In the present invention, for example, the line width of the circuit pattern on the wafer 4 is 0.35.
In the case of μm, the depth of focus on the wafer is set to ± 1 μm or less, and the inclination and height of the wafer 4 are set to 5 μrad and 0.0 μm, respectively.
Control to 5 μm. Although FIG. 1 shows only one axis of wafer tilt detection, there is actually a system for detecting a wafer tilt in a direction perpendicular to the paper surface.

Light emitted from a laser (coherent light source) 1 passes through a shutter 5, and its s-polarized (linearly polarized) component is polarized beam.
The beam is extracted by the beam splitter 6, the beam diameter is expanded by the lenses 10 and 12, and the beam is separated by the prism 13 into two parallel beams. The opening 11 is located at a position conjugate with the reflection surface of the wafer 4 and its shape determines the spot shape on the wafer surface. The prism 15 gives a predetermined angle to each of the two parallel beams. One of the light beams emitted from the prism 15 is irradiated on the wafer 4 as object light 16,
The other becomes the reference light 17.

The object light 16 irradiates the wafer 4 at an incident angle of 88 ° (88 ° with respect to the perpendicular to the wafer 4), and the reflected light and reference light 17 are reflected by the mirror 19 and
The light is re-reflected by the mirror 22 via the optical path 0, 21 and travels backward in the original optical path.
It is reflected in the 3 'direction. The prisms 23 and 23 'extend the distance between the beams and simultaneously enter the lens 24 at a predetermined angle. Two beams emitted from the lens 24
The beam intersects with the reflection surface of the wafer 4 at a conjugate position A and interferes there.

A stop 25 is provided at the position A, and the light passing therethrough is compressed in one direction by a cylindrical lens 27 via a lens 26 to form interference fringes on the surface of the CCD sensor 28. In the conventional device, the lens 2
0, 21 and the mirror 22 are omitted, and the reflected light from the wafer 4 is reflected by the mirror 19 whose mounting angle is changed in principle and re-enters the wafer 4, and the reflected light is similarly reflected at another angle. It is configured to interfere with the reference light incident from the. However, in the present invention, since the image of the wafer 4 is formed on the mirror 22 and reflected, the mirror 22 can be set at a position conjugate to the reflection surface of the wafer 4.

FIG. 2 shows the wafer 4 and lenses 20, 21;
FIG. 7 is a diagram showing a positional relationship between the mirror 22 and the mirror 22. FIG.
As shown in (a), the focal lengths of the lenses 20 and 21 are respectively f ₁ and f ₂ , the distance between the wafer 4 and the lens 20 is f ₁ , and the distance between the lens 20 and the lens 21 is (f ₁ + f
₂₎ setting the distance between the lens 21 and the mirror -22 to f _2.

FIG. 2B shows a case where the wafer 4 is inclined by an angle ψ. The object light 16 is reflected by the wafer 4 at an angle of 2 ° as compared with the case of FIG. The reflected light 162 is reflected by the lens 20 as the reflected light 1 in the case of FIG.
(A) of the mirror 22 becomes parallel to the lens 61 and the lens 21.
The reflected light 163 becomes parallel to the light 161 and is reflected by the lens 20 at the same reflection position as the reflected light 162 on the wafer 4. As a result,
The reflection position of the wafer 4 with respect to the second reflected light 164 can be a conjugate position.

The reflected light 164 is inclined at an angle of 4 ° with respect to the incident light 16, so that the crossing angle with the reference light 17 is also 4 °.
Only ψ changes. The change in the cross angle is obtained from the change in the period of the interference fringes, and the inclination angle ψ of the wafer 4 can be calculated from the change in the cross angle. FIG. 2C shows a case where the height of the wafer 4 changes by d. The reflected light 165 for the object light 16 travels in parallel with the reflected light 161 in FIG.
1 and is reflected by the lens 21 so that the reflected light 16
1 again becomes parallel and is reflected by mirror-21. This reflected light travels backward on the same optical path as 165 and is reflected by the wafer 4. Therefore, the second reflected light 166 travels backward on the same optical path as the object light 16.

The optical path difference due to the height change d is 4 ds.
in θ, and the phase of the interference fringes changes accordingly, so that the change in height d can be calculated to calculate the cross-sectional profile of the wafer. If the inclination angle exists in addition to the height change d, the height change d is first derived after correcting the inclination angle 変 化. FIG.
(D) is a development view of the imaging relationship in (a) to (c) above. Since the right wafer image is inverted on the mirror 22 by the lenses 20 and 21, it is equivalently formed as a left wafer image.

Further, the left wafer image reflected by the mirror 22 is inverted at the same position on the wafer 4 by the lenses 21 and 20, so that the second reflected image becomes the same as the first reflected image. Therefore, the wafer image can be detected by detecting the second reflection image.

In FIG. 1, the reference light 17 is applied to the second reflected light shown in FIG. 2 to form interference fringes.
The waveform is detected by the CCD sensor 28 and the signal processing circuit 3
A / D conversion is performed, and the digital signal is converted into a digital signal. The height / tilt control unit 50 calculates the height, tilt, and the like of the chip based on the surface shape information, controls the stage 7, and controls the height tilt of the wafer 4. Should match the focal plane. The shape of the object light 16 on the wafer surface is given by the opening 11.

FIG. 3 shows an example of the shape of the object light 16 on the wafer surface. When the shape of the opening 11 is circular, oblique irradiation results in elliptical light 32 extending on the wafer 4 in the illumination direction on the wafer 4 as shown in FIG. When the chip 33 and the exposure area 34 on the wafer 4 are as shown in the figure, the elliptical light 32 is irradiated in a diagonal direction of the chip 33. In this case, the adjustment of the optical system becomes easy because of the small circular beam.

FIG. 3B shows a case in which the opening 11 is an elongated rectangle. The wafer 4 is illuminated with rectangular light 35 extending in a direction perpendicular to the illumination direction. In this case, since the depth of focus can be reduced, the lateral resolution of the surface shape can be increased. FIG. 3C shows a case where the opening 11 is rectangular. This light becomes rectangular light 36 spread on the wafer 4 and can be applied to the entire surface of the exposure area 34.
The surface shape of the chip 33 can be detected by the sensor 28.

FIG. 4 is a block diagram of another embodiment of the projection exposure apparatus according to the present invention. 4, the lens 20 shown in FIG.
21, mirror 22 and the like, lens 29, corner cube 3
0, replaced by Mira-31. The object light 16 reflected by the wafer 4 is reflected by the mirror 19 and forms a wafer image on the reflection surface of the corner cube 30 at a position conjugate with the reflection surface of the wafer 4 via the lens 29. I do. Corner cut
The reflected light from the probe 30 turns back on the optical path, forms an image again on the reflection position of the wafer on the wafer, and is reflected again. The reference light 17 is reflected by the return mirror 31 and travels backward in the original optical path.

FIG. 5 shows the wafer 4 and the lens 2 in FIG.
9 is a diagram showing a positional relationship between a corner cube 30 and a mirror 31. FIG. They set the focal length f ₁ of FIG. 5 (a), the both lens 29 a distance to the reflecting surface and the prism 30 of the wafer 4 to the lens 29.
FIG. 5B shows a case where the angle of the wafer 4 is inclined by ψ. The light 162 reflected by the wafer 4 is converted by the lens 29 into light 162 that travels in parallel with the reflected light 161 in the drawing (a), and is reflected by the corner cube 31. The reflected light 163 also travels in parallel with the light 161 and is reflected by the lens 29 at the same reflection position as the object light 16 on the wafer 4. As a result, the reflection position of the wafer 4 with respect to the second reflected light 164 can be set as a conjugate position.

Since the angle of the reflected light 164 is inclined by 4 ° with respect to the incident light 16, the crossing angle with the reference light 17 is also 4 °.
Only ψ changes. The change in the crossing angle is obtained from the change in the period of the interference fringes, and the inclination angle の of the wafer 4 can be calculated from the change. FIG. 5C shows a case where the height of the wafer 4 changes by d. The reflected light 165 for the object light 16 travels in parallel with the reflected light 161 in FIG. 9A and is imaged on the corner cube 31, and the reflected light 166 travels back on the original optical path.

At this time, the optical path difference caused by the height change d is 4 dsin θ, and the phase of the interference fringe changes accordingly. From this, the cross-sectional profile of the wafer can be calculated by calculating the height change d. When the inclination angle exists in addition to the height change d, first,
After the correction of the inclination angle ψ, the height change d is derived.

FIG. 5D is a developed view of the imaging relationship in the above (a) to (c). The wafer image on the right is lens 29
Is inverted on the corner cube 31 to form an equivalently left wafer image. Further, since the left wafer image is reflected at the same position on the wafer 4 by the lens 29, the second reflection image becomes the same as the first reflection image. Therefore, the wafer image can be detected by detecting the second reflection image.

FIG. 6 is an explanatory diagram of an algorithm for calculating the surface shape of the wafer. The interference fringe waveform shown in (a) is subjected to a fast Fourier transform (FFT) to obtain a spectrum shown in (b). At this time, the spectrum near the frequency f = 0 corresponds to the DC component b (x) of the interference fringe waveform, and the spectrum at the positions f ₀ and −f ₀ indicates the phase fluctuation φ (x) and the amplitude a ( x).

As shown in (c), after the spectrum corresponding to the above f ₀ is moved to the frequency origin, and the inverse FFT is applied, the waveform of (d) is obtained. The absolute value of p (x) is the amplitude a (x) of the interference fringe, and the phase is the fluctuation of the phase of the interference fringe φ
(X). Since this phase has an uncertainty of π unit and further has a tilt offset corresponding to (f ₀ −f ₁ ), this phase is first tracked along x and the phase is connected.

Next, since the above f ₀ is determined by the intersection angle between the reflected light and the reference light 17, the tilt offset is corrected to obtain the phase fluctuation φ (x) shown in (f). This φ
By substituting (x) into equation (1), the sectional profile z (y) of the wafer 4 can be obtained as shown in equation (2). z (y) = λφ (x) / 4πm cosθ (2) The coordinates x on the CCD 28 correspond to the coordinates y on the wafer.

The fluctuation of the interference fringe phase caused by the wavefront aberration of the optical system is caused by the φ
(X) Data is stored, and this is stored in the φ
Correction is made by subtracting from (x). Thus, the inclination correction amounts at the time of wavefront aberration measurement and wafer surface measurement are the same, so that the inclination correction processing performed in FIGS. 6E and 6F can be omitted. As shown in FIG. 7, data for one cycle of the interference waveform s (x) is converted into a sine wave (a ₀ + a ₁ s).
The above φ (x) can also be calculated by matching with inω ₀ t + a ₂ cosω ₀ t) by the least square method. The inclination and height of the wafer surface are obtained from the surface shape data calculated as described above, and the stage mechanism 7 is controlled so that the wafer surface coincides with the focal plane. Further, focusing can be performed accurately and functionally by selecting the surface shape information.

[0038]

According to the present invention, the accuracy of detecting the inclination, unevenness, etc. of the surface of a semiconductor wafer in a projection exposure apparatus can be improved. As a result, the wafer stage can be controlled to accurately fit the wafer surface within the focus margin of the projection lens, and the depth of focus of the light beam irradiating the wafer surface will be reduced due to future miniaturization of the pattern. It can cope with becoming shallow. Also, referring to the design data and the pattern density of the reticle, it focuses on the fine area of the pattern to be exposed, and excludes the area where the detected value of the surface shape is unstable. The height and the like can be obtained and corrected.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of a projection exposure apparatus according to the present invention.

FIG. 2 is an explanatory diagram of an optical system in FIG.

FIG. 3 is a diagram for explaining a relationship between a beam shape of object light irradiated on a wafer and a spot shape on the wafer.

FIG. 4 is a configuration diagram of another embodiment of a projection exposure apparatus according to the present invention.

FIG. 5 is an explanatory diagram of the optical system in FIG. 4;

6 and 7 are explanatory diagrams of a surface shape calculation method according to the present invention.

FIG. 8 is an explanatory diagram of an interference fringe detection method in a conventional device.

FIG. 9 is a waveform diagram illustrating a problem of interference fringes detected by a conventional device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser, 2 ... Surface detection system, 3 ... Signal processing circuit, 4 ...
Wafer, 5 ... shutter, 6 ... deflection beam splitter, 7
... Stage, 8 ... Reduction lens, 9 ... Reticle, ... 11 ...
Apertures 13, 15, 23 ... Prism, 14 ... Beam splitter, 16 ... Object light, 17 ... Reference light, 18, 19,2
2, 31, 40 ... mirror, 20, 21, 29 ... lens,
25 ... stop, 27 ... cylindrical lens, 28 ... CC
D sensor, 30: corner cube, 40: reference plane, 41
... wafer surface, 50 ... height / tilt control unit.

──────────────────────────────────────────────────続 き Continued on the front page (72) Minoru Yoshida 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside Production Technology Research Laboratory, Hitachi, Ltd. (56) References JP-A-5-259031 (JP, A) JP-A-3-40417 (JP, A) JP-A-3-255902 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01L 21/027 G03F 7/207

Claims (7)

(57) [Claims] 1. An optical beam of a coherent monochromatic light source shaped into a predetermined shape is divided into two, and one of them is an optical beam (object light).
The reflected light obtained by irradiating the sample surface with
In the surface shape detection method for detecting the inclination, height, and the like of the sample surface from interference fringe information obtained by superimposing a beam (reference light), reflected light from the sample surface is positioned at a position conjugate with the sample surface. To form an image, irradiate the image forming light again to the sample surface, guide the reflected light to a photodetector provided at a position conjugate to the sample, and, on the photodetector, the reference light and the reference light. A method for detecting a surface shape, wherein the inclination, height, and the like of the sample surface are detected from interference fringe information obtained by superimposition. 2. A light beam of a coherent monochromatic light source shaped into a predetermined shape is divided into two, and one of the light beams (object light) is divided.
The reflected light obtained by irradiating the sample surface with
In the projection exposure apparatus, the inclination and height of the sample surface are detected from interference fringe information obtained by superimposing the sample surface (reference light) to correct the inclination and height of the sample. An imaging optical system that forms an image of the reflected light from the sample surface at a position conjugate with the sample surface, a reflection unit that re-irradiates the image-forming light of the imaging optical system onto the sample surface, A detection optical system that guides the reflected light on the sample surface to the photodetector provided at a position conjugate with the sample, a reference optical system that superimposes the reference light on the reflected light guided to the photodetector surface, A signal processing circuit for detecting the inclination, height, etc. of the sample surface from the interference fringe information detected by the photodetector; and a means for controlling the inclination, height, etc., of the sample surface by the output of the signal processing circuit. A projection exposure apparatus characterized by the above-mentioned. 3. The imaging optical system according to claim 2, wherein the imaging optical system comprises at least first and second lenses having a focal length of f ₁ and f ₂ , respectively, and the first lens has a distance f ₁ from the sample surface. , The second lens is arranged at a distance (f ₁ + f ₂ ) from the first lens, and the reflecting means is arranged at a distance f ₂ from the second lens. A projection exposure apparatus characterized by the above-mentioned. 4. The method of claim 2, said image formation at least the focal length of the optical system is constituted by a lens is f _1, a lens was spaced apart by a distance f ₁ from the specimen surface, the lens said reflecting means projection exposure apparatus being characterized in that so as to spaced apart by a distance f ₁ from. 5. The projection exposure apparatus according to claim 2, further comprising means for adjusting an intersection angle between the object light and the reference light on the photodetector. 6. A projection exposure apparatus for projecting and exposing a circuit pattern formed on a mask onto a substrate by a projection lens, wherein a beam substantially parallel to a side between the projection lens and the substrate is formed on the substrate. Irradiating means for irradiating the substrate with a desired shape, and an imaging optical system for imaging the reflected object light from the substrate irradiated by the irradiating means at a position conjugate with the substrate surface,
A detector that receives the light image formed by the imaging optical system and converts the light image into a signal, and detects a surface shape of the substrate based on a signal detected from the detector to determine the inclination or height of the substrate. Control means for controlling the surface of the substrate to substantially match the image forming plane of the projection lens. 7. A projection exposure apparatus for projecting and exposing a circuit pattern formed on a mask onto a substrate by a projection lens, wherein a beam substantially parallel to a side between the projection lens and the substrate is formed on the substrate. Irradiates the object light in a desired shape on the substrate, forms an image of the reflected object light from the irradiated substrate at a position conjugate with the substrate surface, receives the formed light image with a detector, and converts it into a signal. And detecting the surface shape of the substrate based on the signal and controlling the inclination or height of the substrate to substantially match the surface of the substrate with the image plane of the projection lens.