JP2001338871A - Projection aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a projection aligner that can accurately align a reticle and a wafer speedily. SOLUTION: In this projection aligner for allowing a pattern that is formed in a reticle that is illuminated with exposure light to project onto a wafer surface via a projection lens for exposure, a lattice-shaped mark that is provided on the wafer surface is illuminated with monochromatic light from a lighting means via the projection lens, reflection diffraction light from the lattice-shaped mark is passed through the projection lens and is led outside an exposure light path by a reflection member where a reflection surface is arranged at a position nearly conjugating with the lattice-shaped mark to the projection lens, ±nth-order light (n=1, 2, 3...) of the reflection diffraction light is selectively picked up by a stopper, an interference image is formed by the picked-up nth- order light, and information that is obtained by forming the interference image is used for detecting the position of the lattice-shaped mark, thus aligning the wafer to a specific position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus suitable for manufacturing a semiconductor device, and more particularly to a projection exposure apparatus which adjusts a relative position between a reticle having a conjugate relationship with a wafer and an imaging means synchronized (aligned) with the wafer. By using an interference image based on reflected diffraction light generated from periodic lattice marks (wafer mark, alignment mark) provided on the surface, it is possible to perform highly accurate and highly integrated semiconductor devices. It is suitable.

[0002]

2. Description of the Related Art Recent advances in semiconductor device manufacturing technology have been remarkable, and the accompanying fine processing technology has also advanced remarkably.
In particular, the optical processing technology has reached a fine processing technology having a submicron resolution since the manufacture of 1MDRAM semiconductor devices. As a means for improving the resolving power, a method in which the exposure wavelength is fixed and the NA (numerical aperture) of the optical system is increased has been used in many cases. However, recently, various attempts have been made to change the exposure wavelength from g-line to i-line and to improve the resolving power by an exposure method using an ultra-high pressure mercury lamp.

It is generally known that the depth of focus of a projection optical system (stepper) is inversely proportional to the square of NA. For this reason, when trying to obtain a submicron resolution, a problem arises in that the focus advance becomes shallower.

On the other hand, various methods have been proposed for improving the resolving power by using light of a shorter wavelength typified by an excimer laser. It is known that the effect of using light of a short wavelength generally has an effect inversely proportional to the wavelength, and the depth of focus becomes deeper as the wavelength is shortened.

On the other hand, with respect to the relative positioning of a wafer and a reticle in a conventional projection exposure apparatus, that is, so-called alignment, an alignment mark formed on a wafer surface is formed on an image pickup means surface with or without a projection lens, and the image is taken. This is performed by observing the alignment marks on the means surface and obtaining the position information of the wafer.

At this time, as an observation method of an alignment mark on a wafer surface for obtaining wafer position information,
Mainly, the following three methods are used. (A) A method that uses non-exposure light having a different wavelength from the exposure light and does not pass through the projection lens (OFF-AXIS method). (B) A method that uses light having the same wavelength as the exposure light and passes through the projection lens (exposure) (Light TTL method) (c) A method of using non-exposure light having a different wavelength from the exposure light and passing through a projection lens (non-exposure light TTL method) FIG. 12 shows the main part of the OFF-AXIS optical system of (A). It is a schematic diagram. In the figure, the alignment mark AM on the wafer W surface is illuminated by the non-exposure light from the light source 501 via the half mirror 502 and the detection lens system 503. Then, the alignment mark AM is imaged on the surface of the imaging means 504 via the half mirror 502 by the detection lens system 503.

FIG. 13 is a schematic view of a main part of an optical system of (b) the exposure light TTL system.

In FIG. 1, a half mirror 602 and a detection lens system 60 are sequentially arranged with a light beam having the same wavelength as the exposure light from the light source 601.
3, the mirror 604 illuminates the alignment mark AM on the surface of the wafer W via the projection lens 1. Then, the alignment mark AM is sequentially transferred to the projection lens 1 and the mirror 60.
4. An image is formed on the surface of the image pickup means 605 via the detection lens system 603.

FIG. 14 is a schematic view of a main part of the optical system of the non-exposure light TTL system shown in FIG. In the figure, a half mirror 702 and a correction lens system 703 are sequentially used with non-exposure light from a light source 701.
(Lens system for correcting aberration generated due to the difference with the wavelength of exposure light), and illuminates alignment mark AM on wafer W surface via mirror 704 projection lens 1. Then, an image of the alignment mark AM is formed on the surface of the imaging unit 705 via the projection lens 1, the mirror 704, the correction lens system 703, and the half mirror 702 in this order.

As described above, in the conventional method shown in FIGS. 12 to 14, the position information of the wafer W is obtained by detecting the position of the alignment mark AM formed on the image pickup means.

Means for specifically detecting the position of an alignment mark from image information obtained by each of the above-mentioned observation methods include, for example, a pattern matching detection method disclosed in Japanese Patent Application Laid-Open No. Kaihei 3-28
No. 2715 discloses a phase detection method using FFT.

[0012]

Recently, the miniaturization of semiconductor elements has been advanced, and the exposure wavelength of a projection exposure apparatus has been shortened in order to increase the degree of integration of these semiconductor elements. For this reason, the g-line (436 nm) of a high-pressure mercury lamp has been conventionally used as an exposure wavelength, but an i-line (365 nm) or an excimer laser, for example, a KrF laser (248 nm) has been increasingly used as an exposure light. ing. As the exposure wavelength becomes shorter as described above, at the same time, it becomes an important issue how to set the alignment method. This is because the aberration of the projection lens is generally corrected only for the exposure wavelength.

The OFF-AXIS method (a) is a method in which alignment light is transmitted without passing through a projection lens, and is not affected by the exposure wavelength of the projection lens. Therefore, there is a feature that the design of the observation optical system is relatively easy.

However, the OFF-AXIS method is
Due to the geometric constraints between the observation optical system and the projection lens, generally, the alignment position and the exposure position are significantly different,
After the alignment is completed, it is necessary to drive the XY stage to the exposure position.

There is no problem as long as the distance between the alignment position and the exposure position (hereinafter referred to as a base line) is always stable. Due to the influence of the aging effect).

[0016] Therefore, in the OFF-AXIS system, the baseline is generally measured and corrected at certain time intervals. As described above, since the OFF-AXIS method has an error factor of “baseline fluctuation over time”, there is a problem that it takes time to perform the measurement and correction, and the throughput is reduced.

Furthermore, since the OFF-AXIS method does not pass through the projection lens, it does not follow the behavior of the projection lens (for example, change in magnification and focus position due to exposure, change in magnification and focus position due to atmospheric pressure, etc.). There is.

On the other hand, the TTL system in which the alignment light is aligned through the projection lens is advantageous from the viewpoint of following the behavior of the projection lens, and does not cause the problem of the baseline. OFF-AX even if it occurs
Compared to the IS method, it is generally shorter by one digit or more and is less susceptible to environmental fluctuations.

However, the aberration of the projection lens is corrected so that the projection exposure is optimal with respect to the exposure wavelength. When a light beam having a wavelength other than the exposure wavelength is used as the alignment light, the aberration generated by the projection lens is very large. It becomes something.

According to the exposure light TTL method (b) described above,
Since the exposure light is used as the alignment light, the aberration of the projection lens is satisfactorily corrected, and a good observation optical system can be obtained.

However, in many cases, a photosensitive material (resist) to which an electronic circuit pattern is transferred is applied on the wafer surface. For this reason, when observing the alignment mark formed on the wafer surface, the resist usually absorbs much light at a short wavelength. For this reason, as the exposure wavelength becomes shorter as described above, it becomes difficult to detect the alignment mark on the wafer through the resist film at the exposure wavelength.

Further, when the alignment mark is observed with the exposure light, there is a problem that the resist is exposed to the exposure light and the detection of the alignment mark becomes unstable or impossible.

In the non-exposure light TTL method (c), as described above, since a light beam having a wavelength other than the exposure wavelength is used as the alignment light, a large amount of aberration occurs in the projection lens. For this reason, conventionally, when this non-exposure light TTL method is used, alignment is performed via a correction optical system for correcting aberrations generated in a projection lens as disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 3-61802. It is configured to detect a mark.

However, an excimer laser such as K
When an rF laser (248 nm) is used as the exposure light, the practical glass material constituting the projection lens is limited to quartz or fluorite due to the transmittance and the like. As a result, the non-exposure generated by the projection lens The aberration with respect to light becomes very large. For this reason, there has been a problem that it is difficult to satisfactorily correct the aberration generated in the projection lens using the correction optical system, and it is difficult to obtain a sufficient NA, and furthermore, it is impossible to configure a realistic correction system.

A pattern matching detection method or the like as a means for specifically detecting the position of an alignment mark from image information obtained by the above-described observation method uses an A / A for processing an electric signal obtained by an imaging means. The signal becomes a discrete series by the D conversion, and the position of the detected alignment mark also takes a discrete value.

Therefore, in order to achieve the desired accuracy, it is necessary to use some kind of interpolation means, and an error due to the approximation at that time becomes a factor of the detection error. Further, the image of the alignment mark may be distorted due to the influence of noise such as uneven coating of the resist applied thereon and uneven lighting.
There is a problem that the detection accuracy is lowered due to the deterioration of the N ratio.

On the other hand, the applicant of the present invention has disclosed in the prior art
A phase detection method using FFT disclosed in Japanese Patent No. 82715 is proposed to solve this problem.

However, a bright-field detection image of an alignment mark (hereinafter referred to as a wafer mark) formed on a wafer is shown in FIG.
In a configuration in which a wafer mark having a cross-sectional shape as shown in FIG. 5C is coated with a resist, the wafer mark image as shown in FIG. May be detected from the CCD, or a wafer mark image as shown in FIG. 15B may be detected from the CCD.

Therefore, when the phase detection method based on the FFT is used, the spatial frequency to be processed differs depending on the process conditions, so that the processing system can accurately perform the offset (the measured value for each spatial frequency) for a wide range of spatial frequencies. ) Is required. This imposes a heavy load on the processing system and is a factor that hinders high-precision processing for a certain fixed spatial frequency.

Further, in such a bright-field detection method, particularly in a low step process, the S / N ratio may be poor and detection may not be possible.

Further, by performing dark field observation of the detection optical system, the edges can be illuminated regardless of the process conditions.
It is possible to stably detect a wafer mark image as shown in FIG.

However, dark-field observation has a problem in scattering efficiency and requires a larger amount of light than bright-field observation, and similarly to the above-described bright-field detection, particularly in a low step process, the S / N ratio is so poor that detection becomes impossible. There was a problem that many occurred.

According to the present invention, for positioning (alignment) provided on a wafer surface by a configuration in which each element is appropriately set.
Is illuminated with monochromatic light having a wavelength different from the wavelength of the exposure light, an interference image based on the reflected and diffracted light generated at this time is formed on the imaging means surface, and a video signal obtained by the imaging means is used. Accordingly, an object of the present invention is to provide a positioning method capable of performing high-resolution projection exposure with high-speed and high-precision alignment between a reticle and a wafer and a projection exposure apparatus using the same.

[0034]

According to a first aspect of the present invention, there is provided a projection exposure apparatus for projecting a pattern formed on a reticle illuminated with exposure light onto a wafer surface through a projection lens. The lattice mark provided on the wafer surface is illuminated with monochromatic light from the illuminating means through the projection lens, and the reflected diffraction light from the lattice mark passes through the projection lens. The light is guided out of the exposure light path by a reflection member having a reflection surface disposed at a position substantially conjugate with the lattice mark, and ± n-order light (n = 1, 2, 2) of the reflected diffraction light
3) are selectively extracted by a stopper, and electrically or optically projected and integrated in one direction of two-dimensional coordinates obtained from an imaging signal of an interference image formed using the extracted n-order light. The obtained one-dimensional projection integrated signal is converted into a spatial frequency domain by orthogonal transformation, and a spatial frequency that appears uniquely in the spatial frequency domain from the one-dimensional projection integrated signal based on the interference image based on the periodicity of the lattice mark The wafer is positioned at a predetermined position by selecting a component and detecting the position of the lattice mark.

[0035]

FIG. 1 is a schematic view of a main part of a projection exposure apparatus as an example for explaining the present invention.

In FIG. 3, the electronic circuit pattern on the reticle R surface illuminated by the exposure light from the illumination device IL is reduced and projected by the projection lens 1 onto the surface of the wafer W mounted on the wafer stage ST. Exposure transfer of patterns is performed.

Next, each element of the positioning means of FIG. 1 will be described.

Reference numeral 53 denotes a detection optical system having a reference mark GS; 101, an image pickup device having the solid-state image pickup device 14;
Denotes a wafer mark (also referred to as a lattice mark or an alignment mark) provided on the wafer surface.

In FIG. 1, the relative positions of the reticle R with respect to the projection lens 1, the detection optical system 53, and the image pickup device 101 are obtained in advance by an appropriate detection system. And the detection optical system 5
The relative position between the reticle R and the wafer W is indirectly detected by detecting the position of the projection image of the reference mark GS in 3 and the wafer mark GW of the wafer W on the imaging surface of the imaging device 101.

Next, a method for detecting the position of the wafer mark GW on the surface of the wafer W and aligning the wafer W at a predetermined position will be described.

A light beam having a wavelength λ different from the wavelength of the exposure light radiated from the linearly polarized He-Ne laser-2 is made incident on an acousto-optic element (AO element) 3, and a lens is formed by the AO element 3. The amount of light going to 4 is controlled, for example, to completely block light in a certain state.

The light beam that has passed through the AO element 3 is condensed by a lens 4, and then, after a spatial illumination range is limited by a field stop SIL disposed on a plane optically conjugate with the wafer W, the polarization beam splitter 5 Is incident. Then, the light enters the polarization beam splitter 5. The light is reflected by the polarization beam splitter 5, and the λ / 4 plate 6, the lens 7, the mirror 8, the lens 19, and the projection lens 1 illuminate the wafer mark GW on the wafer W surface in the vertical direction.

At this time, the illumination light is projected on the pupil plane (the Fourier transform plane of the image plane which is the wafer W plane) of the optical system composed of the projection lens 1, the lens 7 and the lens 19 as shown in FIG. The light beam 41 is incident almost perpendicularly on the surface of the wafer W as shown in FIG. (V and w in FIG. 4A are coordinates of the pupil plane, and represent the distribution of the incident angle of the illumination light with respect to the wafer W surface). The wafer mark GW on the surface of the wafer W is formed of a so-called lattice mark composed of a diffraction grating having a pitch P as shown in FIG. In FIG. 4B, the hatched area and the other areas have different steps on the surface of the wafer W, different reflectances, different phases, and the like, thereby forming a diffraction grating.

The light beam reflected from the wafer mark GW passes through the projection lens 1 and then passes through the lens 19, the mirror 8, the lens 7, the λ / 4 plate 6, and the polarizing beam splitter 5 in order.
An aerial image of the wafer mark GW is formed at the position F through the lens 9 and the beam splitter 10.

The aerial image of the wafer mark GW formed at the position F is further passed through the Fourier transform lens 11 to the stopper 12.
Of the reflected diffracted light from the wafer mark GW, for example, only the reflected diffracted light beam whose angle on the wafer W corresponds to ± sin-1 (λ / P) is transmitted through the Fourier transform lens 13 and the imaging means. An interference image of the wafer mark GW is formed on the solid-state image pickup device 14 as shown in FIG.

This interference image has a pitch P illuminated with monochromatic light.
Since the image of the wafer mark GW forms the diffraction grating of the above, the signal light amount and the contrast are sufficiently higher and stable than a dark-field image using mere scattered light.

Here, the lens 19, the lens 7, and the lens 9
Constitutes a correction optical system 51, and corrects aberrations generated by the projection lens 1 with respect to the wavelength of the illumination light of the wafer mark GW, mainly, axial chromatic aberration, spherical aberration, and the like.

It is not necessary for the correction optical system 51 to perform aberration correction on all of the aperture light beams that are taken in. The correction optical system 51 only needs to perform aberration correction on only the reflected and diffracted light beams that pass through the stopper 12. It has a simple configuration.

When a so-called excimer stepper that uses light from an excimer laser as exposure light is used, the amount of aberration generated with respect to illumination light is smaller than that of a projection exposure apparatus using g-line or i-line light. It is very effective because it is much larger.

On the other hand, a light beam from a light source 15 such as an LED, which emits a wavelength different from the wavelength of the illumination light of the wafer mark GW, is condensed by a condenser lens 16 and the reference mask 17.
The reference mark GS formed on the surface is illuminated.
This reference mark GS is, for example, composed of a grid-like mark similar to the wafer mark GW as shown in FIG. 5. In FIG. 5, the hatched portion is a transparent region and the others are opaque regions.

The light beam transmitted through the reference mark GS is the lens 1
8, the light beam from the LED 15 is reflected, and the reference mark is formed on the F surface via the beam splitter 10 having an optical characteristic of transmitting the light beam from the He-Ne laser 2.
An aerial image of GS is formed.

Thereafter, the aerial image of the reference mark GS on the F plane is converted to a Fourier transform lens 11 like the wafer mark GW.
13 forms an image on a solid-state imaging device 14. The optical system 52 composed of the Fourier transform lenses 11 and 13 is well corrected for aberration at two wavelengths of illumination light for the reference mark GS and the wafer mark GW.

The wavelength of the light beam from the light source 15 may be the same as the wavelength of the illumination light of the wafer mark GW, and the optical path may be combined by changing the beam splitter 10 into a polarized beam splitter. At this time, the optical system 52 may perform aberration correction only for the illumination wavelength of the wafer mark GW.

The stopper 12 acts as a pupil plane filter for the intensity distribution of the reflected light from the wafer mark GW when the illumination light is incident on the wafer W surface. As a result, the light beam incident on the solid-state imaging device 14 is only the ± n-order diffracted light from the wafer mark GW. However, n = 1, 2, 3, ...
・ It is.

In this case, only the ± 1st-order diffracted light is used, and the wafer mark G as shown in FIG.
An interference image M of W is formed. The intensity distribution of the interference image M is a COS function having a period T represented by T = β · P / 2 (β is an imaging magnification), and corresponds to a positional deviation of the wafer mark GW on the wafer W from the optical axis. 5 shows an intensity distribution having the determined positional deviation amount.

This interference image M forms a desired intensity distribution as a COS function having a period T, no matter how the thickness of the resist covering the step or the surface of the wafer mark GW changes.

It is not necessary to limit the diffracted light selected by the stopper 12 to only ± 1st-order diffracted light, but ± nth-order diffracted light (N =
A pupil plane filter that transmits only (1, 2, 3...) May be used.

The fact that various orders can be selected also corresponds to changing the wavelength, and the detection rate of the wafer mark GW can be improved. For example, if the ± 1st-order diffracted light is small, the detection rate of the wafer mark GW can be improved by using the ± 2nd-order diffracted light.

At this time, the coordinate position of the pupil plane filter is a position where the angle on the wafer W is equivalent to ± sin-1 (nλ / P), and the image is formed on the solid-state image sensor 14 at the period T =
It becomes a COS function of β · P / (2n).

The image of the reference mark GS and the image of the wafer mark GW formed on the solid-state imaging device 14 are obtained by setting the pitches Q and P of the reference mark GS and the wafer mark GW in advance. By determining the pitch corresponding to the imaging magnification, the same pitch T is set. This allows the FF to be described next.
Analysis at a fixed frequency is always possible in the phase difference detection in the T processing.

In this apparatus, the projection lens 1, the detection optical system 53, and the solid-state
And the relative position of the reticle R with respect to the image pickup apparatus 101 is obtained.

Therefore, the positioning is performed by detecting the position of the image of the reference mark GS and the image of the wafer mark GW on the imaging surface of the imaging device 101 including the solid-state imaging device 14.

That is, the wafer mark GW on the wafer W surface
And a relative position between the reference mark GS on the surface of the reference mask 17 and the reticle R using data detected at this time and data on a relative position between the reference mark GS and the reticle R detected in advance. R and wafer W are aligned.

The image of the reference mark GS and the image of the wafer mark GW as detection mark images formed on the solid-state imaging device 14 are converted into two-dimensional electric signals. FIG. 2 is an explanatory diagram on an imaging surface including a detection mark image formed on the imaging device 101.

In FIG. 2, the interference image M is a detection mark, and when the direction for detecting the position of the pattern is the x direction in FIG. 2, the detection mark M has a period T in the x direction. The intensity distribution pattern becomes a COS function. By forming such a detection mark M, the cross section of the pattern in the x direction has symmetry with respect to the pattern center xc to be obtained.

The pattern image converted into a two-dimensional electric signal by the imaging device 101 is converted by the A / D converter 102 in FIG. 1 according to the optical magnification of the projection lens 1 and the detection optical system 53 and the pixel pitch of the imaging surface. At the determined sampling pitch Ps, the signal is converted into a two-dimensional discrete electric signal sequence corresponding to the address of the pixel on the two-dimensional device in the X and Y directions.

In FIG. 1, reference numeral 103 denotes an integrating device.
(A) After setting a predetermined two-dimensional window including a detection mark M shown in FIG. 2A, pixel integration is performed in the window 20 in the y direction shown in FIG. An electric signal sequence s (x) that is discrete in the x direction is output.

Reference numeral 104 in FIG. 1 denotes an FFT operation device, which performs a discrete Fourier transform on the input electric signal sequence s (x), converts the electric signal sequence s (x) into a spatial frequency domain, and calculates the Fourier coefficient thereof at high speed. Is what you do. The technique is known (for example, "Fast Fourier Transform", published by Science and Technology Publisher, E.I.
This is described in Chapter 10, Fast Fourier Transform, by ORAN BRIGHAM. This is based on the fast Fourier transform (FFT) of N points (N = 2r). When the sampling frequency is fs = 1, the complex Fourier coefficient X (k) of the frequency f (k) = k / N is

[0069]

(Equation 1) Becomes

At this time, the intensity E of the spatial frequency f (k)
(K) and Θ (k) are E (k) = ((Re (X (k))) 2 + (Im (X
(K)) 2)) 1/2 (2) Θ (k) = tan-1 (Im (X (k)) / Re
(X (k)))｝ (3) (where Re (X (k)) and Im (X (k)) represent a real part and an imaginary part of a complex number X (k)).

FIG. 3 (A) shows the spatial frequency intensity E (F) when the FFT is performed so as to include the entire detection mark using the vicinity xs of the center of the detection mark M obtained in advance by an appropriate detection means as a reference point. k) represents the distribution.

Due to the periodicity of the pattern, the pattern-specific spatial frequency f (h) = (Ps / T) · N that appears in the one-dimensional discrete signal S (x) of the pattern becomes large,
A peak occurs on the graph of FIG.

Reference numeral 105 in FIG. 1 denotes a frequency intensity detection device, and the spatial frequency f (h) unique to the pattern is obtained by the equation (4).
The peak position Pi and the peak frequency f (Pi) are detected in the range of α near. Pi = [k | max (E (k), f (h) · N-α <k <f (h) · N + α, k = 0, 1, 2, ..., N-1] (4 Here, α is a positive integer and is determined so that Pi becomes significant with respect to pattern pitch fluctuation.

On the other hand, if the optical magnification fluctuates from a predetermined value due to some reason such as the adjustment state of the optical system in the range of α, the frequency f (Pi) showing this peak is detected, and the pattern is obtained. It is possible to correct the variation of the optical magnification from the unique spatial frequency. Upon peak detection, interpolation means (for example,
The frequency resolution may be increased by using least square approximation, weighted averaging, or the like.

Reference numeral 106 in FIG. 1 is a phase detector which detects the phase of the spatial frequency intensity peak f (Pi) and the frequency component near the peak at the reference point xs according to the equation (3).

Reference numeral 107 in FIG. 1 denotes a shift amount detecting device.
From the phase, the shift amount Δk in the real space is calculated by the following equation (5) ΔK = (1 / 2π) · (N / K) · PS · ΘK (5)

FIG. 3B is a graph plotting the shift amount Δk in the vicinity of the frequency region unique to the pattern. Generally, as shown in FIG. 3 (B), the deviation Δk near the mark-specific frequency shows a constant stable value. , The deviation amount Δc from the reference point xs at the center of the pattern is detected according to the weighted averaging process (Equation (6)).

Δc = [Σ ｛E (k) · Δk｝] / [Σ ｛E (k)]] (6) f (Pi) · N−α <K <f (Pi) · N + αf ( P
i) · N−α <K <f (Pi) · N + α FIG. 3C is a diagram showing the result of the weighted averaging process. In this way, the shift amount Δc is detected while focusing on only the signal of the detection pattern while improving the S / N ratio, reducing the calculation amount, and stabilizing the detection by the weighted averaging process.

Up to now, FFT has been used to calculate the Fourier coefficients. However, taking advantage of the fact that the spatial frequency unique to the pattern does not fluctuate greatly, only the required Fourier coefficients of the frequency components are directly calculated from the equation (1). You may do it.

In this case, since the number of sampling points can be arbitrarily selected, the frequency component obtained by the discrete Fourier transform is closest to the frequency component to be obtained in consideration of the fact that the frequency component is represented by k / N. By optimally selecting the number N of sampling points as described above, it is possible to more accurately determine the spatial frequency unique to the pattern. Further, by reducing the frequency components used for detection, the amount of calculation can be reduced.

In this manner, the wafer mark on the wafer W surface
The relative position between the mark GW and the reference mark GS on the surface of the reference mask 17 is detected, and the detection data at this time and the relative position between the previously detected reference mark GS and the reticle R are detected. The reticle R and the wafer W are aligned using the position data.

Although the misalignment between the wafer mark GW and the reference mark GS has been detected, the reticle mark on the reticle R is connected to the solid-state imaging device 14 via an optical system instead of the reference mark GS. It is also possible to directly detect the positional deviation between the reticle mark and the wafer mark GW by imaging.

Further, instead of forming the reference mark GS on the solid-state image pickup device 14, a reference mark is virtually set on an image memory for recording a signal of the solid-state image pickup device 14, and the reference mark is set.
It may be used as a substitute for GS.

Also, grid marks provided on the object to be aligned are provided in the X and Y directions, respectively, and the respective positions in the X and Y directions are detected by separate optical systems. It may be formed so that the X and Y directions are detected simultaneously or by switching with one optical system. This can be similarly applied to each of the examples described below.

Next, a description will be given of a projection exposure apparatus as another example for describing the present invention. Here, stopper 1
2 capture NAs are specified.

In the configuration shown in FIG. 1, if the take-in NA (opening shape) of the stopper 12 is set to, for example, the opening 12b as shown in FIG. 6, the interference fringes formed on the surface of the imaging means 14 are evaluated and the alignment is performed. When having a relatively large NA in the direction orthogonal to the direction in which
Unnecessary image information in or around the lattice mark GW provided on the wafer W (object) is transmitted to the imaging unit 14 and
/ N ratio may be reduced.

More specifically, a random detection error occurs at the time of alignment in a process with a severe surface roughness, or a measurement error occurs when there is dust or a defect in or around the lattice mark GW. May come.

In addition, in order to reduce the influence of speckle noise generated by using a monochromatic light source as illumination light, a large amount of light is generally lost by setting some swinging means such as a diffusion plate. Often,
If the S / N ratio of the detection signal is lowered, or if the conditions are poor, such as a low step process or a low substrate reflectivity, the amount of illumination light may be insufficient to make detection impossible.

Further, when the input NA for the reflected diffracted light increases, the aberration generated in the projection lens with respect to the illumination wavelength of the non-exposure TTL type non-exposure light, especially when an excimer laser is used as the exposure light, The optical system becomes very large, and the optical system for correcting the aberration generated in the projection lens becomes complicated. In some cases, a realistic correction optical system cannot be formed.

The above-mentioned problems are solved by setting the opening conditions of the stopper 12 appropriately as follows, and high-precision alignment is realized.

In general, assuming that the capture angle of the stopper on the wafer side with respect to each reflected diffracted light is NA, the wavelength of the illumination light is λ, and the cutoff frequency of the optical system (the limit frequency that can be transmitted) is NC, NC is NC = 2 · It is represented by NA / λ.

On the other hand, the spatial frequency of the interference fringes formed on the imaging means 14 to be detected is represented by T,
When the absolute value of the optical magnification between 4 is β and this spatial frequency T is converted into a spatial frequency TW on the wafer W, it is expressed as TW = T · β.

Therefore, the cut-off frequency NC is changed to the spatial frequency T
If NA is set so as to be smaller than W, it is possible to obtain a form in which unnecessary image information in or around the lattice mark provided on the object is not transmitted to the imaging means.

Therefore, the take-in NA of the stopper 12 is set as 0 <NA <T · β · λ / 2.

FIG. 7 is a plan view of a main part of the stopper 12, and FIG.
FIG. 2 is an explanatory diagram of a main part in which the optical path of FIG. 1 when a stopper 12 is used is schematically developed. In FIG. 7, reference numeral 12a denotes an opening of the stopper 12.

The wavelength λ of the illumination light for illuminating the lattice mark GW provided on the wafer W (object) to be aligned with monochromatic light is λ = 633 nm, the absolute value of the optical magnification between the wafer W and the image pickup means 14. When β is β = 100 ×, and the spatial frequency T of the interference fringes formed on the imaging means 14 is T = 2, the capture NA derived from the above relational expression is NA <0.063.
Is satisfied, and at the same time, the capture NA on the wafer W side for each reflected diffracted light of the stopper 12 that selectively takes out the reflected diffracted light so that the ± 1st-order reflected diffracted light selected by the stopper 12 is sufficiently transmitted, NA is set to 0.03.

By configuring the taking-in NA of the stopper 12 so as to satisfy the above-mentioned conditional expression, unnecessary image information in or around the lattice mark GW provided on the wafer W (object) is transmitted to the imaging means 14. In addition, it is possible to prevent the S / N ratio from lowering, and at the same time, to eliminate the need for any oscillating means typified by a diffusion plate for eliminating the influence of speckle noise, thereby preventing the loss of light quantity.

Further, since the area for correcting the aberration generated by the projection lens is limited to only the NA section for taking in the signal light, a correction optical system is not required, and it can be realized with a very simple configuration such as a single lens. So that high S
/ N ratio always enables stable position measurement. In particular, in a projection exposure apparatus using an excimer laser as exposure light, a highly accurate alignment method using a non-exposure TTL method can be realized.

Next, Embodiment 1 of the projection exposure apparatus of the present invention will be described.

This embodiment is characterized in that the arrangement of the reflection member 8 for extracting the reflected diffraction light from the wafer mark GW passing through the projection lens 1 to the outside of the exposure optical path is specified.

In this embodiment, the reflected and diffracted light reflected and diffracted by the lattice mark GW provided on the wafer W (object) to be aligned passes through the projection lens 1 and is taken out of the exposure optical path by the reflecting member 8. I have. If a mirror or a prism as shown in FIGS. 9A and 9B is used as the reflecting member 8 at this time, the attitude of the mirror or the prism is such that the inclination component in the direction in which the position of the lattice mark GW is detected and the alignment is performed. When a change over time occurs due to the influence of the environment in which the device is placed (temperature, atmospheric pressure, or mechanical stability due to vibration of the device itself), the position measurement value changes.

As shown in FIG. 10, the degree of the influence is as follows.
Assuming that the distance of the lattice mark GW provided above to the conjugate plane CS is d and the absolute value of the optical magnification from the wafer to be aligned to the conjugate plane CS is β, the position detection error Δst
Is Δst = d · tanε / β.

For example, d = 100 mm, β = 5x, Δst
Is set to 0.02 μm, it is necessary to set the attitude holding accuracy of the mirror 8 to a very strict value of 0.2 seconds or less.

Therefore, in this embodiment, a reflecting member 8 for extracting the reflected diffracted light out of the exposure optical path of the projection lens 1 is used.
Is set in the vicinity of the position of the lattice mark GW and the conjugate position via the projection lens 1 so that the environment in which the device is placed (temperature, atmospheric pressure, or vibration of the device itself). Due to the effects of mechanical stability, etc.), the effect of a change over time is minimized.

Here, the vicinity of the conjugate position means a range in which even if the reflection member 8 is slightly inclined, the detection accuracy is not largely affected.

FIG. 11 is an explanatory diagram showing the optical action at this time.

FIG. 11 shows the operation when the position of the reflecting surface of the reflecting member 8 is set near a position conjugate with the position of the lattice mark GW. As shown by the broken line in the figure,
Even if the reflection member 8 tilts and the optical path shifts, the imaging unit 1
It is shown that the position of the interference image does not shift on the four surfaces.

As a result, in this embodiment, stable position measurement which is hardly affected by the environment and can be always performed can be performed. In particular, in a projection exposure apparatus using an excimer laser as exposure light, high-precision alignment by the non-exposure TTL method is used. Is possible. Also, in the present invention, all of the imaging means
A one-dimensional projection integrated signal is obtained by detecting a one-dimensional video signal and electrically integrating it in one direction. For example, a cylindrical lens is configured in front of an imaging unit to optically integrate in one direction. It is also possible to easily obtain a one-dimensional projection integrated signal by one-dimensional imaging means.

[0109]

According to the present invention, a grid mark for positioning (alignment) provided on the wafer surface by the configuration in which the respective elements are appropriately set as described above is monochromatic with a wavelength different from the wavelength of the exposure light. It is illuminated with light, an interference image based on the reflected diffracted light generated at this time is formed on the imaging means surface, and the alignment between the reticle and the wafer is performed at high speed by using the video signal obtained by the imaging means. Perform with high accuracy,
A positioning method capable of high-resolution projection exposure and a projection exposure apparatus using the same can be achieved.

In particular, according to the present invention, the position of the apparatus is set by setting the position of the reflecting surface of the reflecting member for extracting the reflected diffracted light out of the projection lens near a position substantially conjugate with the lattice mark position. Due to the influence of the environment (temperature, atmospheric pressure, mechanical stability due to the vibration of the device itself, etc.), the influence on the problem that changes with time occur is minimized, and stable position measurement is always possible.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of a projection exposure apparatus as an example for explaining the present invention.

FIG. 2 is an explanatory diagram relating to an interference image of a grid-like mark on an imaging means surface of FIG. 1;

FIG. 3 is an explanatory diagram relating to signal processing of an interference image.

FIG. 4 is an explanatory diagram of a pupil plane and a grid mark of the projection exposure apparatus.

FIG. 5 is an explanatory view of a fiducial mark.

FIG. 6 is an explanatory view showing an opening of a stopper.

FIG. 7 is an explanatory view of a stopper.

FIG. 8 is a developed schematic view of a part of an optical system of a projection exposure apparatus as another example for explaining the present invention.

FIG. 9 is an explanatory view of a reflecting member according to the present invention.

FIG. 10 is an explanatory view of a reflection member according to the present invention.

FIG. 11 is an explanatory view of a reflection member according to the present invention.

FIG. 12 is an explanatory view of a conventional OFF-AXIS type alignment device.

FIG. 13 is an explanatory diagram of a conventional exposure light TTL type alignment device.

FIG. 14 is an explanatory diagram of a conventional non-exposure light TTL type alignment device.

FIG. 15 is an explanatory diagram of a wafer mark image and a cross section of a wafer mark.

[Explanation of symbols]

 IL illuminator R reticle W wafer GW wafer mark (lattice mark) GS fiducial mark 1 projection lens 2 laser 3 AO element 4 lens 5 beam splitter 6 λ / 4 plate 7 lens 8 reflecting member 10 beam splitter 11, 13, 21 Fourier Conversion lens 12 Stopper 14,22 Group imaging device 51 Correction optical system 52 Optical system 53 Detection optical system

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/30 525R 525W

Claims (1)

[Claims] 1. A projection exposure apparatus for projecting and exposing a pattern formed on a reticle illuminated with exposure light onto a wafer surface via a projection lens. After illuminating with light through the projection lens and passing the diffracted light reflected from the lattice mark through the projection lens, a reflection surface is disposed at a position substantially conjugate with the lattice mark with respect to the projection lens. Is guided out of the exposure light path by the reflecting member, and ± n-order light (n = 1,
2, 3 ...) is selectively taken out by a stopper,
A one-dimensional projection integrated signal that is electrically or optically projected and integrated in one direction of two-dimensional coordinates, obtained from an imaging signal of an interference image formed using the extracted n-order light,
The spatial frequency component is converted into a spatial frequency domain by orthogonal transform, and a spatial frequency component that uniquely appears from the interference image based on the periodicity of the grid-like mark is selected from the one-dimensional projection integrated signal on the spatial frequency domain, and the spatial-frequency component of the grid-like mark is selected. A projection exposure apparatus wherein the wafer is aligned with a predetermined position by detecting the position.