JPH07111949B2 - Reduction projection type alignment method and apparatus thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a reduction projection type alignment method and apparatus used for manufacturing semiconductors, bubble memories, thin film transistors, etc., and particularly, the transmittance of visible light is extremely low. The present invention relates to a reduction projection type exposure method using an excimer laser beam as an exposure light having a reduction projection lens, and an apparatus therefor in which a substrate can be aligned at an exposure position with respect to a reticle. .

[Conventional technology]

As a conventional reduction projection exposure apparatus, TTL (Throngh The L
exposure position alignment method of Japanese Patent Laid-Open No. 52-109875
And JP-A-55-41739.

[Problems to be Solved by the Invention]

Even if the above conventional technique is applied to a reduction projection exposure apparatus that uses an excimer laser that is a narrow band laser as exposure light, the projection lens has a coating that allows the excimer laser to sufficiently pass therethrough. The light transmittance was extremely low, and it was difficult to align the exposure device through the projection lens.

In order to solve the above problems, an object of the present invention is to provide a reduction projection type exposure method and apparatus for performing reduction projection exposure of a circuit pattern on a reticle onto a substrate using a reduction projection lens by using an excimer laser beam as exposure light. It is an object of the present invention to provide a reduction projection type alignment method and an apparatus therefor capable of aligning a substrate with respect to a reticle at an exposure position without using a projection lens.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the present invention is a reduction projection alignment in which a substrate is aligned with respect to a reticle, and an excimer laser is used as exposure light to reduce and project a circuit pattern on the reticle onto a substrate by a reduction projection lens. In the method, the alignment mark of the linear diffraction pattern formed on the substrate is laterally provided between the reduction projection lens and the substrate, and the linear diffraction pattern is irradiated with light having a plurality of wavelengths from an oblique direction. Diffracted light based on a plurality of wavelengths from the alignment mark of the pattern is reflected by a mirror toward the side between the reduction projection lens and the substrate and condensed by an objective lens. The diffracted light based on the wavelength is diffracted by a diffraction grating provided near the position of the real image to be condensed and imaged, and is enlarged or reduced by a lens to form an image. The diffracted light having a plurality of wavelengths is received by the photoelectric conversion element and converted into a video signal, and the position of the alignment mark of the linear diffraction pattern is detected based on the converted video signal to detect the substrate by the reticle. Is a reduction projection type alignment method characterized by performing alignment with respect to.

Further, the present invention is characterized in that, in the reduction projection type alignment method, the light to be irradiated is P-polarized light.

Further, the present invention provides a reduction projection type alignment apparatus for aligning a substrate with respect to a reticle and using a excimer laser beam as exposure light to reduce and project a circuit pattern on the reticle onto a substrate by a reduction projection lens. An illumination optical system that irradiates light having a plurality of wavelengths from an oblique direction with respect to the alignment mark of the linear diffraction pattern formed on the substrate from the side between the lens and the substrate, and the linear diffraction pattern. Diffracted light based on a plurality of wavelengths from the alignment mark is reflected by a mirror toward the side between the reduction projection lens and the substrate and condensed by an objective lens. The diffracted light based on this is diffracted by a diffraction grating provided in the vicinity of the position of the real image to be condensed and imaged, and is enlarged or reduced by a lens to form an image. A detection optical system that receives diffracted light based on the wavelength of the photoelectric conversion element and converts it into a video signal, and aligns the linear diffraction pattern based on the video signal converted by the photoelectric conversion element of the detection optical system. A reduction projection type alignment apparatus characterized in that the position of a mark is detected to align the substrate with respect to the reticle.

Further, the present invention is characterized in that, in the illumination optical system in the reduction projection type alignment apparatus, there is provided a combining optical system for combining lights of different wavelengths emitted from the respective optical sources into the same optical path and irradiating them.

Further, the present invention is, in the illumination optical system in the reduction projection type alignment apparatus, a spectroscope for splitting light emitted from a light source into a plurality of different wavelengths, and combining the split light of different wavelengths in the same optical path. And a synthetic optical system for irradiating the light.

That is, the illumination angle θ (angle between the normal line of the sample and the illumination light) is 75 ° (30 ° to 85 °) with respect to the substrate of the P-polarized laser of four wavelengths.
°, most preferably 65 ° to 85 °. ) And illuminate it to obtain a diffracted light by using a linear dot pattern that causes diffraction as a registration mark, condense the diffracted light with an objective lens, and form a real image of this on a diffraction grating in a P-polarized state. The diffracted light is further focused by an intermediate lens to form a second real image, which is converted into a video signal by a photoelectric conversion element, and the position of the alignment mark is detected at the exposure position and aligned at a fixed position. I have made it possible.

Further, in the reduction projection exposure apparatus, the present invention provides the reduction projection lens with a light having a wavelength substantially equal to that of an excimer laser light on a registration mark on a detection substrate placed on a table and not coated with a resist. A illuminating means for illuminating through the image, a back projection image of the alignment mark on the detection substrate formed on the reticle through the reduction projection lens, and an image of the alignment pattern formed on the reticle are detected to produce a video signal. Based on the detector to be converted and the image signal obtained from the detector, the table is finely moved based on the alignment pattern on the reticle to position the alignment mark on the substrate. The position is detected by the detecting means, and the detecting means is finely moved to position the detecting means at a fixed position.

[Action]

By irradiating the alignment mark on the substrate with light of multiple wavelengths obliquely from the side of the gap between the reduction projection lens and the substrate (wafer), the diffracted light generated from the alignment mark is detected by the detector. Even if there is unevenness in the thickness of the resist applied on the substrate, the exposure position alignment is realized without using the reduction projection lens. In particular, in an apparatus that projects and exposes a circuit pattern on a reticle onto a substrate (wafer) with an excimer laser exposure light of approximately 248.5 nm, the alignment formed on the substrate via the reduction projection lens using the excimer laser light. When trying to detect the position of the mark,
Actually, a resist is applied on the alignment mark, and the resist absorbs the excimer laser light to reduce the reflected light from the uneven alignment mark formed on the lower surface of the resist, resulting in a weak detection signal and detection. It is difficult to do. Further, when light other than the excimer laser light, which is close to visible light, is used, the coating of the reduction projection lens causes the light to be attenuated as shown in FIG. 7, and similarly becomes a weak detection signal. Further, when the wavelength of the position detection light greatly differs from the wavelength of the excimer laser light, it is difficult to obtain an image of the alignment mark due to the chromatic aberration of the reduction projection lens. Therefore, in the present invention, the position of the alignment mark on the substrate (wafer) is detected at the exposure position without using the reduction projection lens. The position detection optical system of the substrate alignment mark and the position of the reticle are aligned with each other via the reduction projection lens when the reticle is installed.

[Embodiment] An embodiment of the present invention will be described below with reference to FIG. The reticle 1 is illuminated by an excimer laser 101 having a wavelength of about 248.5 nm, and the circuit pattern of the reticle is exposed on the substrate (wafer) 4 by the reduction projection lens 3 to form a chip 102.
As shown in FIGS. 3 and 4, a diffractive alignment mark 65 formed of a linear dot pattern is provided in the scribe area 60 around the chip 102, and this is illuminated with a laser.
The laser light from the Ar laser 103 that simultaneously oscillates wavelengths of 458 nm, 488 nm, and 515 nm is once dispersed by the spectroscope 104, and the filters 105a, 105b, and 105c for adjusting the intensity are inserted in the optical paths of the respective wavelengths to make them identical To the strength of. After that, the mirror 106 and the dichroic mirrors 107a and 107b combine lights of respective wavelengths into the same optical path. On the other hand, a He-Ne laser that oscillates a wavelength of 543 nm 1
Filter the light from 08 105d, dichroic mirror 107c
In addition to the optical paths of the light of the above three wavelengths, an optical path 109 of the light of four wavelengths is set through.

The P-polarized laser light is focused by the illumination lens 110 and focused on the diffraction type alignment mark 65. A reflective optical system is provided between them to set θi to about 75 °. Since the second-order diffracted light of the diffractive alignment mark 65 has a θo of 50 °, the mirror 11 is provided so as not to block the excimer laser for exposure.
The light is reflected by 1 and condensed by the objective lens 112 to form a real image 113. Diffraction grating 1 with 2000 grooves parallel to the real image 1mm
When 14 is provided, the first-order diffracted light from here proceeds almost vertically upward. When this is further magnified by the magnifying lens 115, a second real image 116 is obtained. Since this extends in the left-right direction, if the cylindrical lens 117 is provided in the middle of the magnifying optical system and the real image is compressed in the left-right direction, the second real image becomes 118, and the width ω
Is the same as the real image 116, but the horizontal length is shortened,
Illuminance is improved. As a result, the real image 118 becomes a photoelectric conversion element 119.
Can be detected clearly.

With the above optical system, the position of the alignment mark 65 in the y direction (direction perpendicular to the paper surface) can be obtained. To detect the position in the x direction (direction parallel to the paper surface), it is necessary to detect another alignment mark 120 provided in the y direction as shown in FIG. 2, and another illumination / detection optical system 121 is used. It is necessary to provide.

Since the positions of the alignment mark in the x and y directions are obtained by the above two detection optical systems, the stage 122 is moved so that the alignment mark comes to a predetermined position to position the wafer.

To incorporate the alignment mark detection optical system under the reduction projection lens 3 as described in the above embodiment, the illumination angle θ is set to
30 to 85 ° range (most preferably 65 ° based on 75 °
It is ゜ ~ 85 ゜. However, when the alignment mark 65 is detected from the direction of 75 °, the alignment mark 65 becomes long in the front-back direction of the optical axis and the resolution of the real image is extremely lowered.
Therefore, θ on the detection side is made small, and the alignment mark is detected in a state as vertical as possible.

Therefore, the alignment mark 65 is provided in the dicing line 60 of the substrate 4 in the X and Y directions in FIG. Its shape is the fourth
As shown in the figure, g ₁ = 1.5 μm, g ₂ = 3.5 μm, p = g ₁ + g ₂ = 5
It is formed by exposure and etching on the substrate with μm, h = 6 μm. The total length l ₀ of this alignment mark is preferably 40 μm or more. As shown in FIG. 5, the wavelength λ
_{When the 0} light 61 is illuminated at an angle θi, in addition to the specularly reflected light 62, A large number of diffracted lights 63 are generated in the direction of θ ₀ given by. As an example, if λ ₀ = 0.5 μm, p = 5 μm, θi = 75 °, then θo
Diffracted light is generated in the directions of = 60 °, 50 °, 42 ° .... The intensity of diffracted light decreases as θo decreases, such as 60 °, 50 °, 42 ° .... Therefore, it is necessary to select an appropriate angle.

Actually, as shown in FIG. 6, since the photoresist 12 is coated on the alignment mark 65, the diffraction situation slightly changes, but it is apparently the same as the value explained in FIG. It is important to note here that P-polarized light is used for illumination.
Is to use 109. This allows photoresist 12
The specular reflection light on the surface of the
Can be guided to the alignment mark 65 below. Θ as an example
If the diffracted light of o = 50 ° is detected, the alignment mark 65 can be detected from the direction of 50 °, and a good real image can be obtained as compared with the case of detecting from the direction of 75 °.

Next, a laser is used for illumination, but in the case of a single laser, the diffracted light causes multiple interference inside the photoresist 12 to generate interference fringes. Photoresist on alignment mark 65
No. 12 generally has coating unevenness, and when regular reflection light is detected, bright and dark interference fringes are irregularly generated as shown in FIG.
The alignment mark 65 cannot be detected. Since the same phenomenon occurs when detecting diffracted light, it is necessary to use lasers of two or more wavelengths for illumination. However, the angle θo of the diffracted light
(See FIG. 5) changes depending on the wavelength λ ₀ as described in the equation (1), and therefore the objective lens that collects this diffracted light is used.
As 112, a sufficiently large NA (numerical aperture) is used, and it is necessary to collect diffracted light of all wavelengths used for illumination.

Next, the image of the alignment mark 65 detected obliquely is used as the diffraction grating 114.
A method of reconstructing an image perpendicular to the optical axis by using will be described. In principle, as shown in FIG. 9, when the diffractive alignment mark 65 on the sample 4 is illuminated with laser light and the diffracted light 62 is condensed by the objective lens 112, the real image 113 is tilted with respect to the optical axis 67. To be If the diffraction grating 114 is provided on this, the diffracted light 69 travels vertically upward, and therefore it may be detected by enlarging it with the lens 115.

As shown in FIG. 10 (a), the diffracted light 62 is reflected almost horizontally by the tip mirror 111, and the objective lens 112 is cut off to the side surface.
Then, a real image 113 is formed through the intermediate mirror 73, and a diffraction grating 114 is provided in parallel with the real image 113. A view of the objective lens 112 seen from above is shown in FIG. Since scattered light from the diffractive alignment mark 65 spreads left and right like scattered light 74 in this plane, the objective lens 112 is not shaved in this plane in order to improve detection resolution. Actually, the shape of the objective lens 112 is made up of a holder 75 and a lens 76, and the upper and lower parts are scraped off as shown in FIG.

What should be noted here is that i becomes about 80 ° in FIG. 10 (a). When i is thus large, the intensity of the diffracted light 69 is greatly affected by the polarization. Since this phenomenon is not well known, the intensity of P-polarized light is about 20 times higher than that of S-polarized light (linearly polarized before and after the paper surface). Therefore, in the present invention, it is extremely important to provide the illumination, the objective lens, and the diffraction grating on the same optical axis so that all the P-polarized light can be transmitted and detected. As the light to be radiated in this way, light having a plurality of wavelengths of P-polarized light having high spatial point coherence (white light may be used) is radiated, and a spectroscope is provided at the detection optical system and diffracted light other than the 0th order is used. Obviously, it may be detected.

Another embodiment of the present invention will be described with reference to FIG. XY
The position detecting wafer 60 on which the resist 12 is not applied is set on the stage 22. This is provided with a registration mark 65 'having an uneven pattern on which the resist 12 is not applied as shown in FIG. On the other hand, the reticle 1 has a 13th
As shown in the drawing, a window 48 is provided, and excimer laser light 101 is irradiated from above, and the light passing through the window 48 illuminates the alignment mark 65 'on the position detecting wafer. Since the back projection image of the alignment mark 65 'is formed on the reticle 1, the calibration detector 70 including the half mirror 62, the objective lens 63, and the photoelectric element 64 is used.
To detect light that has passed through the window 48 on the reticle from the bottom to the top.

The output of the photoelectric element 64 at this time will be described with reference to FIG.
Since the alignment mark 65 'on the position detecting wafer on which the resist 12 is not applied is formed in a concavo-convex pattern, when the light is applied from above, the light is scattered at the step portion and the light returning upward is reduced. . When the output of the photoelectric element 64 is measured while sending the alignment mark 65 'in the y direction (direction perpendicular to the paper surface), the reflected light decreases when the alignment mark 65' enters the alignment mark 48 of the reticle, so the photoelectric element The output 65 of 64 is also reduced. If the center position 66 is obtained from this signal, this is the position that coincides with the center position of the window 48 on the reticle. Therefore, next, the XY stage 22 is moved to move the position detecting wafer to -y.
When the wafer reaches the position of the point 66, the XY stage 22 is stopped and the position detecting wafer 60 is stopped.

Next, the alignment mark detector 67 (comprising the illumination system 67a and the detection system 67b) provided between the reduction projection lens 3 and the position detection wafer 60 is moved in the xy direction to detect the alignment mark 65 '. As described above with reference to FIG. 1, it is optimal to illuminate the laser obliquely and detect the diffracted light from the alignment mark 65 'to obtain the position in the y direction, and this is used. The detector 67 is fixed when the measured value of the position in the y direction reaches a predetermined value.

After that, if the calibration detector 70 (consisting of 62, 63 and 64) is retracted, the exposure optical system and the above-mentioned oblique detection optical system are completely aligned. Note that here the alignment mark on the wafer
The relationship between the width Ww of 65 'and the width Wr of the alignment mark 48 on the reticle is preferably set as follows.

Wr ≧ Ww As a result, the signal 65 has one trough and the central position 66
Is easily required.

Although the position detection method in the y direction (direction perpendicular to the paper surface) has been described above with reference to FIG. 12, in practical use, another detection system is provided in the direction perpendicular to the x direction (direction parallel to the paper surface). It is necessary to detect the position.

By using the substrate (wafer) having the alignment mark 65 to which the ordinary resist is not applied, the alignment mark detector 67 for detecting the alignment mark of the substrate is aligned with the reticle. Can be aligned relative to the reticle at the exposure position.

〔The invention's effect〕

According to the present invention, the position of the substrate with respect to the reticle at the exposure position without using the reduction projection lens, the detection error of 0.05.
It is possible to project and expose the circuit pattern on the reticle onto the substrate by the reduction projection lens by using the excimer laser light as the exposure light by aligning it with high sensitivity by reducing it to less than μm and by using the excimer laser light. High integration
It is possible to realize the exposure of the LSI pattern.

In addition, the reduction projection lens for the excimer laser has a very low transmittance of the visible laser for detecting the alignment mark, so that non-TTL
There is no choice but to adopt the (detection method that does not pass through a reduction projection lens) method. The biggest problem at this time is the relative alignment between the non-TTL alignment mark detector and the exposure optical system.

In the present invention, the substrate for position calibration is set on the XY stage, the reflected light from the substrate is detected by the detector through the reference pattern provided on the reticle, and the substrate is positioned based on this. . Further, the alignment of the detection means is realized by detecting the alignment mark on the substrate, which is characterized in that the alignment is possible without changing the skeleton of the conventional reduction exposure apparatus. By applying the present invention, the alignment mark on the substrate can be detected with an error of ± 0.05 μm or less and can be positioned with an error of ± 0.1 μm (3σ) or less, and an LSI having a line width of 0.5 to 0.3 μm can be used.
Exposure became possible.

[Brief description of drawings]

FIG. 1 is a front view showing an embodiment of the present invention, and FIG.
FIG. 3 is a three-dimensional view of the principle of the drawing, FIG. 3 is a layout of alignment marks on a substrate, FIG. 4 is a view showing the shape of alignment marks used in the present invention, and FIG. 5 is shown in FIG. FIG. 6 shows the diffracted light of the alignment mark, FIG. 6 shows the diffracted light when resist is applied to the alignment mark shown in FIG. 4, and FIG. 7 shows the spectral transmittance of the reduction projection lens for excimer laser light. FIG. 8 is a diagram showing a video signal waveform obtained when the alignment mark is illuminated with a single laser beam, FIG. 9 is a diagram showing the principle of the oblique detection method according to the present invention, and FIG. FIG. 11 shows the principle of the detection method of the present invention, FIG. 11 is a perspective view showing the shape of an objective lens used in the present invention, FIG. 12 is a front view showing another embodiment of the present invention, and FIG. FIG. 13 is a diagram for explaining the processing of the video signal obtained in the device shown in FIG. 1 ... Reticle, 3 ... Reduction projection lens, 4 ... Substrate, 65 ... Registration mark, 12 ... Photoresist, 22 ... XY stage, 114 ... Diffraction grating, 103 ... Ar laser oscillator, 108 ... He-Ne laser oscillator, 101 ... Excimer laser light, 102 ... Chip, 112 ... Objective lens, 114 ... Diffraction grating, 115 ... Magnifying lens, 117 ... Cylindrical lens.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H01L 21/68 F

Claims (5)

[Claims] 1. A reduction projection alignment method in which a substrate is aligned with respect to a reticle, and a circuit pattern on the reticle is reduced and projected onto a substrate by a reduction projection lens by using an excimer laser beam as exposure light. Irradiating light having a plurality of wavelengths obliquely to the alignment mark of the linear diffraction pattern formed on the substrate from the side between the lens and the substrate, from the alignment mark of the linear diffraction pattern Diffracted light based on a plurality of wavelengths is reflected by a mirror toward the side between the reduction projection lens and the substrate and condensed by an objective lens. , Diffracted by a diffraction grating provided in the vicinity of the position of a real image to be focused and focused, and enlarged or reduced by a lens to form an image. The folding light is received by a photoelectric conversion element and converted into a video signal, and the position of the alignment mark of the linear diffraction pattern is detected based on the converted video signal to align the substrate with the reticle. A feature of the reduced projection type alignment method. 2. The reduction projection type alignment method according to claim 1, wherein the illuminating light is P-polarized light. 3. A reduction projection type alignment apparatus for aligning a substrate with respect to a reticle and using a excimer laser beam as exposure light for reducing and exposing a circuit pattern on the reticle onto a substrate by a reduction projection lens. An illumination optical system that irradiates light having a plurality of wavelengths from an oblique direction with respect to the alignment mark of the linear diffraction pattern formed on the substrate from the side between the lens and the substrate,
Diffracted light based on a plurality of wavelengths from the alignment mark of the linear diffraction pattern is reflected by a mirror toward the side between the reduction projection lens and the substrate and condensed by an objective lens. The diffracted light based on the plurality of wavelengths thus formed is diffracted by a diffraction grating provided in the vicinity of the position of a real image to be condensed and formed, and enlarged or reduced by a lens to form an image. A detection optical system that receives diffracted light based on a wavelength by a photoelectric conversion element and converts it into a video signal, and the alignment mark of the linear diffraction pattern based on the video signal converted by the photoelectric conversion element of the detection optical system. Is arranged to detect the position of the substrate and align the substrate with the reticle. 4. The reduction projection type alignment apparatus according to claim 3, wherein the illumination optical system comprises a combining optical system for combining lights of different wavelengths emitted from the respective light sources and irradiating them on the same optical path. . 5. In the illumination optical system, a spectroscope for separating light emitted from a light source into a plurality of different wavelengths, and a combining optical system for combining and irradiating the separated light of different wavelengths on the same optical path. The reduction projection type alignment apparatus according to claim 3, further comprising: