JPH01227431A - Projection aligner - Google Patents

Abstract

PURPOSE:To detect a pattern in a wafer coated with a photoresist film positively, and to realize alignment having high accuracy by installing a light source lighting two waves or more of continuous spectral light, a recognizing section recognizing a position by projecting reflected light from an exposure object, and a chromatic aberration correcting lens mechanism. CONSTITUTION:A light source 8 lighting at least two wavelengths or more of continuous spectral light to a pattern formed onto an exposure object 5 through a projection reducing glass 5, a recognizing section 20, to which reflected light from the pattern is projected and which recognizes the position of the exposure object 5, and a chromatic aberration correcting lens mechanism 16 set up on the optical path of reflected light between the exposure object 5 and the recognizing section 20 are mounted on a projection exposure device aligning an original plate 4 in an exposure process and the exposure object 5. A light source 8 exclusive for detecting the pattern made independent of a light source 1 for exposure composed of a mercury lamp and constituted of a xenon lamp is used as said light source 8. An astigmatism correcting lens 17 is fitted together with said chromatic aberration correcting lens mechanism 16.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to alignment technology, and in particular to alignment of a semiconductor wafer (hereinafter simply referred to as "wafer") with respect to a mask in a reduction projection exposure process in the manufacture of semiconductor devices. Concerning techniques that are effective when applied to

[Conventional technology]

A technology that uses a reduction projection exposure system is common as a technology for transferring a circuit pattern formed with a light-shielding film on a mask such as a reticle onto a wafer. This is done, for example, as follows.

That is, illumination light is irradiated through a reduction projection lens to an alignment mark formed by uneven step shapes on the surface of the wafer, and reflected light from the alignment mark is made to enter a TV camera via a beam splitter or the like. By detecting an electrical signal based on this reflected light, the position of the alignment mark is determined,
This is to position the target exposure area of the sea urchin with respect to the mask. Such a positioning technique is generally called a through-the-lens (TTL> method).

By the way, a document pointing out future problems with the TTL method mentioned above is "Nikkei Micro Devices" published by Nikkei McGraw-Hill, December 1, 1986, P80-P81.
There is.

Here, we introduce the 7th TTL method alignment technology.
This will be explained using the system diagram shown in the figure.

That is, in FIG. 7, 71 is a wafer which is a non-exposure target, 72 is a reduction projection lens for exposure located directly above it, 73 is a reticle as an original, 74 is a TV camera as a recognition unit, and 75 is an exposure unit. It is a mercury lamp that serves as both a light source and an illumination light source.

A reflecting mirror 76, a relay lens 77, and a beam splitter 78 are arranged on the optical path between the reduction projection lens 72 and the TV camera 74, and the light transmitted by the beam splitter 78 is incident on the TV camera 74. It has a structure.

On the other hand, a bandpass filter 80 and a condenser lens 81 are respectively arranged between the mercury lamp 75 and the beam subrifter 78 to allow only the E-ray (546 nm) to pass among the wavelengths from the mercury lamp 75.

As described above, monochromatic E-line light is used as illumination light for pattern detection, and G-line (436 nm) exposure light is used during exposure.

The illumination light is irradiated onto the wafer 71 from the beam splitter 78 via the relay lens 77, the reflecting mirror 76, and the reduction projection lens 72, and this reflected light travels backward along the above path to the TV camera 7.
4, waveform detection is performed based on the recognized image of the TV camera 74, and the wafer 71 as shown in FIG.
The structure was such that the center position of the upper alignment mark 6 was calculated.

[Problem to be solved by the invention]

However, the inventors have discovered that the reduction projection exposure apparatus having the above structure has the following problems.

That is, the wafer, which is the exposure target, is provided to the reduction projection exposure apparatus in a state where the photoresist film 82 is applied, but the photoresist film 32 is applied by dropping the resist liquid while the wafer 71 is in a rotating state. This is done by utilizing the spread of the resist solution due to centrifugal force.

Therefore, due to the centrifugal force during the rotation, the coating thickness of the photoresist film 82 becomes unbalanced around the step of the alignment mark, and in particular, the deposited shape of the photoresist film 82 becomes asymmetrical with respect to the center of the step pattern. Here, as the illumination light for the above alignment, it is common to use the G-line (436 nm) used for exposure as a single wavelength long monochromatic light, so the light reflected from the original step pattern and the photo The interference fringes generated by the reflected light from the resist film 82 become asymmetrical, and the signal voltage waveform obtained from the interference fringes, which is an image recognized by the TV camera, also becomes asymmetrical and complicated. As a result, the step pattern of the alignment mark In some cases, detection was difficult.

Regarding this point, although several solutions have been introduced in the above literature, none of them can be said to provide a sufficient solution.

The present invention has been made in view of the above problems, and its purpose is to provide a technique that can reliably detect a pattern on a wafer coated with a photoresist film and realize highly accurate alignment.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means to solve the problem]

A brief overview of typical inventions disclosed in this application is as follows.

That is, a light source that illuminates an object to be exposed with continuous spectrum light of at least two wavelengths or more through a projection reduction lens, a recognition section that performs position recognition by receiving reflected light from the object to be exposed, and a recognition section that performs position recognition by receiving reflected light from the object to be exposed. The structure includes a chromatic aberration correction lens mechanism provided on the optical path of reflected light between the target object and the recognition unit.

[Effect]

According to the above means, by providing a chromatic aberration correction lens mechanism in the optical path of the illumination light and adjusting the focal length corresponding to each wavelength, continuous spectrum light of two or more wavelengths or more is used as the pattern illumination light. becomes possible. Therefore, for example, even if the photoresist film thickness is uneven and asymmetrical with respect to the alignment pattern of the detection area, it is possible to prevent detection failure due to asymmetrical interference fringes such as single wavelength light, and it is possible to prevent Accuracy can be increased.

〔Example〕

FIG. 1 is a perspective view of the main parts of a reduction projection exposure apparatus which is an embodiment of the present invention, FIG. 2 is a system diagram showing the optical system of this embodiment, and FIGS. 3(a) and 3) are respectively An explanatory diagram showing the chromatic aberration correction lens, FIG. 4 is a perspective view showing the astigmatism correction lens used in this example, and FIGS. 5(a) to (C) are
FIGS. 6(a), 6(b) are explanatory diagrams conceptually showing the principle of correction by the chromatic aberration correction lens in the embodiment. FIGS. .

The reduction projection exposure apparatus of this embodiment includes an exposure light source 1 made of a mercury lamp, a condenser lens 2 that focuses exposure light (not shown) emitted from the exposure light source 1, and a reduction projection lens 3.
It has an exposure optical system consisting of.

Between the condensing lens 2 and the reduction projection lens 3, a reticle (original plate) 4, which has an integrated circuit pattern formed on a transparent quartz glass substrate or the like with a light shielding film such as chromium (Cr), is removably arranged. There is.

On the other hand, a wafer (exposure target) 5 is placed below the reduction projection lens 3 and is movable in a horizontal plane on an XY stage (not shown). The wafer 5 has predetermined alignment marks 6 and the like as shown in FIG.
), it is formed in a stepped shape, and a photoresist film 7 is further deposited on its upper surface by a rotary coating technique. That is, in FIG. 1, the exposure light emitted from the exposure light if and transmitted through the reticle 4 is converted to a predetermined magnification (for example, 11
5) and is projected onto the wafer 5, thereby exposing the photoresist film 7 coated on the surface of the wafer 5 in a predetermined pattern.

An illumination light source 8 is provided in the vicinity of the exposure optical system, and the illumination light from the illumination light source 8 passes through a bandpass filter 10 and a condenser lens 1 provided on the optical path.
1 and enters a beam splitter 12 having a half-mirror structure.

In this embodiment, the illumination light source 8 is guided from the exposure light source 1 by a light guide means such as an optical fiber 13, and is constituted by a cylindrical mirror 14 attached to the tip thereof.

The bandpass filter 10 is configured to, for example, emit E-line (546 nm) among the emission wavelengths of a mercury lamp, which is the exposure light source 1.
The illumination light that has passed through the bandpass filter 10 is transmitted to the beam splitter 1 as continuous spectrum light in the visible light range.
2. On the optical axis of the beam splitter 12,
A relay lens 15, a chromatic aberration correction lens 16, and an astigmatism correction lens 1'7 are provided, respectively, and are structured to reach a reflecting mirror 18 provided on the side of the reduction projection lens 3.

On the other hand, on the optical axis of the beam splitter 12, a TV camera 20 serving as a recognition unit is arranged at a position symmetrical to the relay lens 15 through the relay lens 15.

Next, the chromatic aberration correction lens 16, which is a characteristic component of this embodiment, will be explained in detail.

Prior to the explanation, let us explain about chromatic aberration in Figures 8(a) and (
To explain based on c), a and b in the figure each indicate the distance from the lens 21 to the imaging position. Here, if the focal length of the lens 21 is f, then a, b
, f is - + -= - a b f △b= □△f The relational expression between the focal length f of 21 and the refractive index n is as follows.

f=□ (n-1> It shows the radius length.

From this equation (3), it can be seen that the change in refractive index Δn, The above formula (5) is [6] becomes.

From this equation (6), it can be understood that the imaging position also changes by Δb due to the change Δn in the refractive index. Here, since the wavelength of light and the refractive index n are inversely proportional, as the wavelength becomes longer, the imaging position shifts by Δb toward the lens 21. This is chromatic aberration. Generally, the reduction projection lens 3 used in a reduction projection exposure apparatus is designed to have optimal optical characteristics for the G-line, which is the exposure light. The focal length shift is not taken into account.

Therefore, when using continuous spectrum light consisting of E-rays and D-rays to prevent detection failure due to interference fringes, the short-wavelength E-rays are focused relatively close to the lens, and the long-wavelength rays are focused relatively close to the lens.
As a result, the line is imaged far from the lens, and according to the inventor's calculations, the TV of the same wavelength that has passed through the alignment optical system
The difference in image formation position in the camera 20 is about several tens of points.

In this embodiment, this problem is solved by using the chromatic aberration correcting lens 1G.

In other words, the chromatic aberration correction lens 16 has the function of maintaining the imaging position constant regardless of the magnitude of the incident wavelength, and reduces the imaging distance for light with a large incident wavelength, that is, a small refractive index. On the other hand, the imaging distance is adjusted to be large for light having a small incident wavelength, that is, a large refractive index.

This chromatic aberration correction lens 16 is, for example, as shown in FIG. 3(a).
As shown in (b), it is constructed by combining a concave lens 16a made of frigate glass and a convex lens 16b made of crown glass, and in this embodiment, a pair of chromatic aberration correcting lenses 16, 16 having the above structure are used. It is being Note that the combination shown in FIG. 2(b) may also be used. In this embodiment, the chromatic aberration correction lens 16 has a wavelength λ=500nm to 590nm as the chromatic aberration correction range.
It only needs to be able to correct inclusion, etc. in a wavelength band that includes the E-line and D-line of about m, and the chromatic aberration correctable range can be adjusted by changing the distance between the pair of chromatic aberration correction lenses 16. It is.

Figures 5 (a) to (C) conceptually illustrate the principle of the chromatic aberration correction lens 16 described above, and Figure 5 (a) shows the case where E-line monochromatic light is incident before chromatic aberration correction The imaging distance feS(b) to be opened is also the imaging distance fd, (C
) respectively indicate the imaging distance fs of the E-line and the D-line when the chromatic aberration correction lens 16 is placed on the optical path to correct the chromatic aberration. In the figure, the imaging distance fs is (a) and (b)
), i.e. approximately at the midpoint of the imaging distance with f s= (f
It is adjusted so that it becomes e+f d)/2. Therefore, when continuous spectrum light of E-line and D-line is used as illumination light, chromatic aberration can be suppressed and the imaging position can be kept constant. For this reason, E line or D line
It is possible to prevent the inability to detect a position due to the asymmetry of interference fringes that occurs when monochromatic light of only lines is used, and it becomes possible to detect an alignment pattern with high precision by the TV camera 20.

On the right, in this embodiment, an astigmatism correction lens 17 as shown in FIG. 4 is provided between a pair of chromatic aberration correction lenses 16 on the optical path. The astigmatism correction lens 17 is for correcting the XY force direction deviation of the detected image on the wafer 5 caused by the astigmatic ray bundle, that is, astigmatism, and is composed of a convex lens 17a made of a cylindrical lens and a concave lens. 17b. therefore,
According to this embodiment, illumination light whose chromatic aberration and astigmatism have been corrected is incident on the TV camera 20, so that position detection can be performed by highly accurate image recognition.

Next, the alignment method according to this embodiment will be explained.

First, by moving an
0. After passing through the condenser lens 11, the illumination light is refracted by the beam splitter 12, and the illumination light passes through the relay lens 15, the chromatic aberration correction lens 16, the astigmatism correction lens 17, the reflection mirror 18, and the reduction projection lens 3, and then reaches the wafer. 5 predetermined areas are irradiated. The reflected light from the wafer 5 travels backward along the above-mentioned path and reaches the beam splitter 12 via the reduction projection lens 3, the reflecting mirror 18, the chromatic aberration correction lens 16, and the astigmatism correction lens 17. Here, the reflected light passes through the beam splitter 12 and reaches the TV camera 20 via the relay lens 15. A signal processing section (not shown) is connected to the TV camera 20, and a signal waveform is detected from the image recognized by the TV camera 20.

FIG. 6(c) shows this signal detection waveform.

According to this embodiment, the chromatic aberration correction lens 1 is placed on the optical path of the illumination light.
6, even when continuous spectrum light of EIII and D lines is used as illumination light, chromatic aberration, that is, a shift in the imaging position is corrected. As a result, the illumination light i
1j! When monochromatic light is used for 8, the difficulty in detecting the alignment mark 6 due to the interference waveform caused by non-uniformity of the photoresist film thickness 7 can be avoided, and as shown in FIG. The corresponding detection signal can be reliably grasped, and the position of the alignment mark 6 can be accurately detected. Based on the position of the alignment mark 6 obtained in this way, the target part of the wafer 5 is accurately positioned on the exposure optical system, and then the exposure light is emitted from the exposure light source 1, the condenser lens 2, the reticle 4, The integrated circuit pattern on the reticle 4 is transferred onto the photoresist film 7 of the wafer 5 by exposure light (not shown) that has passed through the reduction projection lens 3 .

In the above description, a case has been described in which a mercury lamp, which is an exposure light source, is used as an illumination light source, but an independent xenon lamp may be used as a detection light source.

In this case, by using a xenon lamp that has relatively uniform light energy at each wavelength, continuous spectrum light can be selectively employed, and the correction rate of the chromatic aberration correction lens 16 can be adjusted to provide optimal correction. By setting the value, it is possible to prevent pattern detection from being impossible due to interference of reflected light, and it is possible to detect the pattern with high accuracy.

Although the invention made by the present inventor has been specifically explained based on Examples above, the present invention is not limited to the Examples (although it is possible to make various changes without departing from the gist of the invention). Not even.

For example, although a cylindrical mirror attached to the tip of an optical fiber is shown as an example of the illumination light source, the illumination light source is not limited to this and may be of any shape such as a polygonal column body or a polygonal conical cylinder body.

In the above explanation, the invention made by the present inventor is mainly applied to the field of application, which is alignment technology in so-called reduction projection exposure of wafers, but the invention is not limited to this, and is applicable to general reduction projection exposure. Widely applicable to alignment technology that depends on exposure.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows.

That is, according to the present invention, by providing a chromatic aberration correction lens mechanism in the optical path of the illumination light and adjusting the focal length in accordance with each wavelength, continuous spectrum light of two or more wavelengths or more is used as the pattern illumination light. becomes possible. Therefore, even if the photoresist film thickness is uneven and asymmetrical with respect to the alignment pattern of the detection area, for example, it is possible to prevent detection failure due to interference such as single wavelength light, and improve positioning accuracy during alignment. Can be done.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of essential parts showing a reduction projection exposure apparatus which is an embodiment of the present invention, Fig. 2 is a system diagram showing an optical system for pattern detection in this embodiment, and Fig. 3 (a) and 3). are explanatory views showing the chromatic aberration correction lens used in this example, FIG. 4 is a perspective view showing the astigmatism correction lens used in this example, and FIGS. 5(a) to (C) are explanatory views showing the astigmatism correction lens used in this example An explanatory diagram conceptually showing the principle of correction by a chromatic aberration correction lens, Fig. 6 (a)
) and Q)) are explanatory diagrams showing the relationship between the alignment marks formed on the wafer and the detected waveform in the example, FIG. 7 is a system diagram showing the optical system in pattern detection of the prior art, and FIG. ) and (b) are diagrams for explaining chromatic aberration. ■...Exposure light source, 2...Condensing lens, 3...Reducing projection lens, 4...Reticle (original plate), 5...Wafer (RI light object), 6...Alignment mark ,7
...Photoresist film, 8...Illumination light source, 10...
・Bandpass filter, 11・Fist-condenser lens,
12: ψ beam splitter, 13: optical fiber,
14...Cylindrical mirror, 15...Relay lens, 16...
Chromatic aberration correction lens, 16a...concave lens, 16b...
・Convex lens, 17... Astigmatism correction lens, 17a・
...Convex lens, 17b...Concave lens, 18...Reflector, 20...TV left camera 21...Lens, 22.
...Illumination light source (xen lamp), 71...Wafer, 7
2... Reduction projection lens, 73... Reticle (original version)
, 74...TV left camera recognition unit), 75...Mercury lamp (exposure light source, illumination light source), 76...Reflector, 77
...Relay lens, 78...Beam sub-lifter, 80
... Band pass filter, 81 ... Condenser lens, 82 ... Photoresist film. Agent Patent Attorney Daiwa Tsutsui Figure 1 Figure 2 Figure 3 (a) (b) Figure 4 Figure 5 Figure 6

Claims (1)

[Scope of Claims] 1. A projection exposure apparatus for positioning an original and an object to be exposed in an exposure process, which forms continuous spectrum light of at least two wavelengths or more on the object to be exposed through a projection reduction lens. a light source that illuminates the pattern, a recognition unit that recognizes the position of the exposure target by receiving reflected light from the pattern, and a light source on the optical path of the reflected light between the exposure target and the recognition unit. A projection exposure apparatus comprising: a chromatic aberration correcting lens mechanism; 2. The projection exposure apparatus according to claim 1, further comprising an astigmatism correction lens as well as a chromatic aberration correction lens mechanism. 3. The projection exposure apparatus according to claim 1, wherein the light source includes a light source dedicated to pattern detection that is independent of the exposure light source. 4. The projection exposure apparatus according to claim 3, wherein the light source for exposure is comprised of a mercury lamp, and the light source exclusively for pattern detection is comprised of a xenon lamp.