JPH07104131B2 - Method and device for separating diffracted light - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention uses, in an exposure apparatus for manufacturing an LSI, for example, a positional deviation between a mask and a wafer by using a diffraction grating formed on the mask and the wafer. TECHNICAL FIELD The present invention relates to an optical system used when detecting by means of, for example, a separation method and a separation device for separating and extracting diffracted light from each diffraction grating.

[Conventional technology]

Along with the miniaturization of LSIs, it is required to align a mask and a wafer with each other with high accuracy in an exposure apparatus that transfers a mask pattern onto a wafer. Particularly, in the X-ray exposure apparatus, it is necessary to align the mask and the wafer with the mask and the wafer maintained at a gear gap of several tens of μm.

As a method for that purpose, the applicant has previously filed Japanese Patent Application No. Sho 61-1041.
In No.86, we proposed a registration method using optical heterodyne interferometry. This method will be described with reference to FIG.

In FIG. 3, the light emitted from the two-wavelength orthogonal polarization laser light source 1 becomes an elliptical beam through the mirror 2 and the cylindrical lens 3, and the beam has only a horizontal component or a vertical component by the polarization beam splitter 4. It is split into two linearly polarized lights having two different wavelengths. Each separated light is a mirror
The light enters the reflective diffraction grating 7 formed on the mask 6 and the reflective diffraction grating 9 formed on the wafer 8 at a desired incident angle via 5a and 5b (incident angle adjusting means). In the example of FIG.
The reflection type diffraction gratings 7 and 9 are displaced in the grating line direction, respectively, and are arranged in the same elliptical beam of incident light of two wavelengths. Further, the diffraction grating pitches of the reflection type diffraction gratings 7 and 9 are set to be equal. The diffracted light obtained from the diffraction grating 7 and the diffracted light obtained from the diffraction grating 9 through the window 10 provided in the mask 6 are mirror 5c (light combining means), prismatic mirror 11 (light separating means), polarizing plates 12a, 12b, The light is guided to the photodetectors 14a and 14b via the condenser lenses 13a and 13b, respectively,
The diffracted light beat signal is processed by the signal processing control unit 15.

The signal processing control unit 15 detects the phase difference between both beat signals by using one of the beat signals of the diffracted light obtained from the reflection type diffraction gratings 7 and 9 as a reference beat signal, and the phase difference is detected. Mask stage 16, so that it becomes 0 °
Alternatively, the wafer stage 17 is relatively moved, and the mask 6 and the wafer 8 are precisely aligned so that the pattern on the mask surface can be accurately overlapped and exposed at a predetermined position on the wafer surface.

[Problems to be solved by the invention]

In the optical system shown in FIG. 3, the diffracted light obtained from the reflection type diffraction gratings 7 and 9 is reflected by both surfaces constituting the tip edge of the prismatic mirror 11 and received by the photodetectors 14a and 14b. . At this time, the edge of the prism is usually rounded, while the diffracted light beam also has a size (diameter) of several 100 μm. Therefore, in order to separate and detect the diffracted light independently, see FIG. As shown, it is necessary to separate the reflective diffraction gratings 7 and 9 in the grating line direction by a distance l of about 1 mm. Therefore, both diffraction gratings should have the same beam spot 21.
In order to enter inside, the major axis of the elliptical laser beam that constitutes the incident light (only one of which is shown in FIG. 4) 22 must be increased, and if the output of the laser light source 1 is the same, There is a problem in that the average irradiation intensity of the laser light incident on the diffraction grating is reduced, the intensity of the diffracted light 23, 24 obtained is also reduced, and as a result, the detection accuracy is also reduced.

Further, the diffraction grating 7 provided on the wafer surface or the mask surface,
Either one of them must be placed at least about 1 mm away from the exposure areas (device areas) 25, 26 such as LSI patterns, and a wide alignment mark area is required.

[Means for solving problems]

The method for separating diffracted light according to the present invention uses convergent light or divergent light so that the diffracted light from each diffraction grating can be separated and detected as the light with which the diffraction grating is irradiated.

The diffracted light separation device according to the present invention includes means for converging or diverging the light from the light source device, in addition to the light source device and the means for detecting the diffracted light.

[Action]

The diffracted light obtained by irradiating the diffraction grating with divergent light becomes divergent light, and the diffracted light from both diffraction gratings is separated as the distance from the diffraction grating increases. When the convergent light is applied, the diffracted light converges and then diverges, so that the diffracted lights from both diffraction gratings are separated as described above.

〔Example〕

FIG. 1 is a schematic configuration diagram showing an embodiment in which the present invention is applied to an X-ray exposure apparatus. The same parts as those in FIG. 3 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 1, 31a and 31b are condenser lenses, which condense only the major axis direction of the elliptical beam. At this time, since each focusing lens 31a, 31b is arranged in a so-called front pin state so that its focal point is located in front of the reflection type diffraction gratings 7, 9, the light is incident on the reflection type diffraction gratings 7, 9. The light 32, 33 enters as divergent light. As a result, the diffracted light from each diffraction grating 34,3
5 becomes divergent light, and is separated as it moves away from the diffraction gratings 7 and 9. Therefore, even if the two reflection type diffraction gratings 7 and 9 are arranged close to each other, the respective diffracted lights can be easily separated and separated.
Can be detected independently. At this time, since the spot diameter of the elliptical laser beam applied to both diffraction gratings may be small, the diffracted light intensity can be increased and the S / N of the detection signal can be increased.
The ratio can be improved.

In this embodiment, the condenser lenses 31a and 31b are arranged so that their focal points are in front of the reflection type diffraction gratings 7 and 9, but conversely,
You may arrange | position so that a focus position may come to the back of both diffraction gratings 7 and 9, and may be in what is called a back pin state. In that case, as shown in FIG. 2, incident light (only one of which is shown in FIG. 2) 36 is incident on the reflection type diffraction gratings 7 and 9 as converged light. 37 is the beam spot at that time. For this reason, the diffracted lights 38 and 39 converge and then diverge.
Therefore, both diffracted lights can be easily separated and independently detected as in the case of FIG. 1 in which divergent light is incident.

In FIG. 1, the condenser lenses 31a and 31b are the mirrors 5a and
Although it is arranged between 5b and the mask 6, it may be inserted between the polarized beam splitter 4 and the mirrors 5a and 5b.

Each diffraction grating may be either an absorption type or a reflection type, and is not limited to a binary diffraction grating,
Various combinations such as a sinusoidal diffraction grating and a phrase diffraction grating are possible.

Further, in the above-mentioned embodiment, the opening was provided on the mask substrate as a monochromatic light incident / diffracted light extraction window, but in the case of a transparent thin film window through which incident light and diffracted light can pass without providing an opening. Can also obtain the same effect.

The description has been given above centering on the case of using for position alignment, but the present invention can also be applied to an apparatus for measuring a minute displacement of an object, a coordinate position detection or control apparatus, or the like.

〔The invention's effect〕

According to the present invention, by making the light irradiating the diffraction grating be convergent light or divergent light, it is possible to easily separate the diffracted light from the diffraction grating arranged in close proximity. Since the beam can be emitted with a narrow beam diameter, the intensity of the diffracted light obtained for the same light source output also increases, improving the S / N ratio, and improving the accuracy when used for alignment etc. it can. In addition, for example, when it is applied to an X-ray exposure apparatus, the alignment mark area can be small, so that there is an advantage that the original exposure pattern area can be made large.

[Brief description of drawings]

1 and 2 are views showing an embodiment of the present invention, FIG. 1 is a schematic configuration diagram, FIG. 2 is a detailed diagram of a diffraction grating portion, and FIG. 3 is a schematic configuration diagram showing a conventional example, FIG. 4 is a detailed view of the diffraction grating portion. 1 …… 2-wavelength orthogonal polarization laser light source, 7,9 …… diffraction grating, 11 …… prism mirror, 14a, 14b …… photodetector, 3
1a, 31b …… Condensing lens, 32,33,36 …… Incoming light, 34,35,3
8,39 ... Diffracted light, 37 ... Beam spot.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01L 21/027 21/68 F G02B 6/12 A

Claims (2)

[Claims] 1. A plurality of diffraction gratings arranged such that their grating lines are parallel to each other, the convergent light or divergent light for separating and detecting the diffracted light from each diffraction grating is the same for each diffraction grating. A method for separating diffracted light, which comprises irradiating the light so that it enters the spot and independently extracting the diffracted light obtained from each diffraction grating. 2. A light source device for emitting spot light and a means for converging or diverging the light emitted from this light source device and irradiating a plurality of diffraction gratings so that each diffraction grating enters the same spot. And a device for detecting diffracted light obtained from each diffraction grating, respectively.