JPH06188170A - Method of projection exposure - Google Patents

Abstract

PURPOSE:To detect the projection of a wafer pattern by arranging an optical system that responds to wavelength-dependent changes of position where the image of the pattern is projected. CONSTITUTION:A pattern on a wafer 4 forms its image on a reticle through a reduction lens 3 at a wavelength of exposure light. The same image is formed on the reticle at a wavelength of green color if the wafer is lowered a given distance. An optical system for detection is arranged to respond to wavelength- dependent changes of position where the image is projected so that the projection of the pattern may be detected. This enables pattern detection at various wavelengths. Detection signals of good contrast can constantly be obtained if an appropriate wavelength is selected depending on the thickness of photoresist on the wafer, the material of photoresist, and the material of the wafer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pattern position detecting method and apparatus used for precise position measurement of a wafer or a mask in a mask aligner in a semiconductor manufacturing process.

[0002]

2. Description of the Related Art As an example of a pattern detection apparatus, a reduction projection exposure apparatus as shown in FIG. 1 (see Japanese Patent Laid-Open No. 55-16).
2227) will be described as an example.
In the reduction projection exposure apparatus, the circuit pattern of the reticle 2 to be newly formed is overprinted by the exposure condenser lens 1 and the reduction lens 3 on the circuit pattern on the wafer 4 which is usually formed in the previous step. Usually, this repeated baking is sequentially repeated for several reticles to form a desired circuit pattern on the wafer. At this time, the alignment of the two circuit patterns to be superposed is usually required to have a high accuracy of 1 μm or less. In the reduction projection exposure apparatus shown in FIG. 1, such alignment is performed by detecting the position of the alignment pattern on the wafer and relatively moving the reticule having a pattern to be newly formed so as to match the wafer. I am doing it.

That is, the alignment pattern (not shown) of the wafer 4 is locally illuminated by a light guide 10, and the reflected light is reciprocated through a reduction lens 3, a reticle 2, and a magnifying optical system 5 with a slit 6 mounted thereon. An enlarged image is formed on the moving surface of the movable table 7. Magnified image is slit 6
And the photoelectric conversion of the light and darkness of the light passing through the slit is carried out by the photomultiplier 9.
The position of the wafer can be obtained by the method described in JP-A-3-69063). That is, by using the arbitrary position X _i of the slit as a virtual center, 2 m pieces of data (Y _i ) on both sides thereof are superposed, To calculate. The point giving the minimum value of the Z values thus obtained is the center position of the wafer alignment pattern.

[0004]

In this apparatus, the center position of the alignment pattern on the wafer with respect to the center position of the reticle reference pattern or the origin sensor (not shown) provided on the reciprocating carriage 7 is determined, In accordance with the result, a new pattern is overlaid on the pattern on the wafer.

As described above, when the pattern position is detected via the reduction lens 3, since the reduction lens 3 is aberration-corrected with respect to the exposure wavelength, normally monochromatic light having only the exposure wavelength is used as the detection light wavelength. To do. Therefore, uniform thickness interference fringes are generated in the photoresist coated on the wafer, and the thickness of the photoresist leads to a decrease in the contrast of the detection signal, resulting in the deterioration of the pattern alignment accuracy. Further, since reflection from the wafer having the exposure wavelength hinders formation of a fine pattern, an antireflection film may be provided on the wafer, or a light absorber having the exposure wavelength may be mixed in the photoresist. In such a case, the intensity of the reflected light that is sufficient for detection cannot be obtained from the wafer by the detection using the exposure wavelength.

In order to solve the above drawbacks, it is necessary to detect a pattern with a wavelength different from the exposure wavelength. At this time, usually, a chromatic aberration correction lens is provided between the reduction lens 3 and the reticle 2, or a dedicated pattern detection optical system according to chromatic aberration is provided in advance to perform pattern detection only with a specific wavelength. Therefore, a pattern detection error occurs due to the reproduction error of the correction lens position, or the pattern detection optical system dedicated to different wavelengths cannot perform the pattern detection by changing the wavelength depending on the sample. That is, there is a defect that the pattern cannot be detected with an arbitrary wavelength.

[0007]

A reticle having a predetermined pattern, a reduction lens arranged below the reticle, an exposed substrate having marks arranged below the reduction lens, and a reticle from above. A light source for exposing a pattern on the reticle onto the exposed substrate through the reduction lens, an illumination light for illuminating a mark on the exposed substrate through the reduction lens, and the illumination light for illuminating the mark. A step of aligning the substrate to be exposed with a projection exposure apparatus comprising photoelectric conversion means for converting the reflected light from the mark into an electric signal and detecting the signal, and a pattern on the reticle to the substrate to be exposed. In the projection exposure method, which comprises the step of projecting onto and exposing to light, the step of aligning the exposed substrate includes As the light for illuminating the mark on the substrate to be exposed, using light having a wavelength different from that of the exposure light, and arranging the substrate to be exposed at a position of a height different from that at the time of exposure, and illuminating through the reduction lens, The exposure light includes a step of guiding light reflected by the mark due to light having a different wavelength to the photoelectric conversion means, and a step of converting the light to an electric signal by the photoelectric conversion means to align the substrate to be exposed.

[0008]

In order to solve the above drawbacks, it is necessary to detect a pattern with a wavelength different from the exposure wavelength. At this time, usually, a chromatic aberration correction lens is provided between the reduction lens 3 and the reticle 2, or a dedicated pattern detection optical system according to chromatic aberration is provided in advance to perform pattern detection only with a specific wavelength. Therefore, a pattern detection error occurs due to the reproduction error of the correction lens position, or the pattern detection optical system dedicated to different wavelengths cannot perform the pattern detection by changing the wavelength depending on the sample. That is, there is a defect that the pattern cannot be detected with an arbitrary wavelength.

An object of the present invention is to use monochromatic light of an arbitrary wavelength to effectively utilize the equal-thickness interference fringes generated in the photoresist on the wafer to improve the contrast of the pattern detection signal and improve the pattern alignment. It is to obtain high precision. In order to achieve the above object, in the present invention, the detection optical system corresponding to the variation of the image forming position of the pattern on the wafer according to the wavelength used in the detection optical system is configured to detect the projected image of the pattern on the wafer. To do.

[0010]

EXAMPLES The present invention will be described in detail below with reference to examples. First, the chromatic aberration of the reduction lens will be described with reference to FIG. In FIG. 2, the alignment pattern 4 ′ on the wafer 4 is magnified and imaged on the reticle 2 as indicated by the solid line 21 in the figure by the purple exposure wavelength. However, when a different wavelength, for example, green light is used, the image is not formed on the reticle 2 as shown by the dotted line 22 in the figure, and is enlarged above the reticle 2. Therefore, FIG. 3 shows one embodiment according to the present invention which has a detection optical system corresponding to each of the magnified image by the exposure wavelength and the magnified image by the green light. In the example of FIG. 3, the pattern on the wafer imaged on the reticle according to the wavelength of the exposure light is photoelectrically converted by the photomultiplier 9 through the magnifying optical system 5 and the slit 6. On the other hand, when detecting a wafer that does not have sufficient reflection at the exposure wavelength for detection, the magnified image formed above the reticle by green light is photoelectrically converted by the photo-maru 9'through the magnifying optical system 5'and the slit 6 '. As a result, a detection signal having a sufficient contrast for detection can be obtained. At this time, the wavelength can be designated by switching the optical filter at the entrance or the exit of the light guide or by switching a predetermined optical filter in the magnifying optical system 5 or 5 '. When the chromatic aberration of the reduction lens is large as in the present embodiment and the image forming position is different, only an enlarged image with a predetermined wavelength can be detected regardless of the presence or absence of an optical filter. In this embodiment, the objective lenses are installed in parallel, but it is also possible to have a structure in which they are stacked in two stages above the reticle, and the installation position may be arbitrary.

On the other hand, when the chromatic aberration of the reduction lens is large and the image formation position is different, the image formation position can be corrected by changing the distance between the wafer and the reduction lens. For example, move the wafer up and down according to the wavelength used,
It is also possible to form an image of the pattern on the wafer on the reticle regardless of the wavelength used. The outline of the optical system is shown in FIG. As shown in this figure, the green position of the wafer at which the pattern on the wafer is imaged on the reticle at the exposure wavelength is lowered by a predetermined amount for green light. Pattern is imaged. One embodiment of the present invention based on this principle is shown in FIG. In this embodiment, the wafer is mounted on each of the X, Y and Z moving bases and is movable in each direction. Further, an optical filter switching mechanism 11 is provided in the magnifying optical system. As a result, the pattern detection by the exposure wavelength is the same as the conventional one, but at the green light wavelength, the wafer is lowered by a predetermined amount, and the image formed on the reticle can be formed on the slit 6 through the green optical filter. In this case, it is not necessary to add new optical parts, etc. in the imaging optical system between the wafer and the reticle as the wavelength is switched.
No pattern detection error occurs due to the addition of optical components. In this example, the wafer was moved up and down to correct the chromatic aberration due to the change in wavelength.
It is also possible to raise the reticle, the pattern detection optical system and the like to form an image of the pattern on the wafer on the reticle. Further, when the chromatic aberration of the reduction lens is small and the variation of the image forming position is so small that it can be ignored, the present invention can be carried out by simply specifying the detection light wavelength by switching the optical filters.

[0012]

As described above, according to the present invention, it is possible to detect patterns at various wavelengths, and depending on the photoresist thickness on the wafer, the photoresist material, and the substrate material,
By selecting the detection wavelength, it is possible to always obtain a detection signal with good contrast. Further, at this time, since it is not necessary to insert an optical component such as a correction lens, it is possible to improve the accuracy of pattern detection.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of a reduction projection exposure apparatus including a conventional pattern detection device.

FIG. 2 is a conceptual diagram showing chromatic aberration of a reduction lens.

FIG. 3 is a diagram showing an embodiment of the present invention.

FIG. 4 is a conceptual explanatory diagram of chromatic aberration correction of a reduction lens by vertically moving a wafer.

FIG. 5 is a diagram showing another embodiment of the present invention.

[Explanation of symbols]

1 ... Focusing lens for pattern exposure, 2 ... Reticle, 3 ...
Reduction lens, 4 ... Wafer, 4 '... Positioning pattern on wafer, 5 ... Enlargement optical system by exposure wavelength, 5' ...
Enlarging optical system in detection optical system having different wavelengths, 6, 6 '... Slit, 7 ... Reciprocating stage, 8 ... Linear encoder, 9,
9 '... Photo Maru, 10 ... Light guide for pattern detection illumination, 11 ... Interference filter exchange mechanism, 12 ... X moving stand, 1
3 ... Y mobile base, 14 ... Z mobile base.

Front Page Continuation (72) Inventor Yoshio Kawamura 1-280 Higashi Koigokubo, Kokubunji, Tokyo Inside Hitachi Central Research Laboratory (72) Inventor Sumio Hosaka 1-280 Higashi Koikeku, Tokyo Kokubunji City Inside Hitachi Central Research Laboratory (72) Akihiro Takanashi 1-280 Higashi Koigokubo, Kokubunji City, Tokyo Metropolitan Research Center, Hitachi, Ltd.

Claims (3)

[Claims] 1. A reticle having a predetermined pattern, a reduction lens arranged below the reticle, an exposed substrate having a mark arranged below the reduction lens, and a reduction lens from above the reticle. A light source for exposing the pattern on the reticle to the exposed substrate, illumination light for illuminating the mark on the exposed substrate through the reduction lens, and illuminating the mark with the illumination light, Using a projection exposure apparatus comprising a photoelectric conversion means for converting the reflected light of the above into an electric signal and detecting the same, and using the step of aligning the above-mentioned substrate to be exposed, and projecting the pattern on the reticle onto the above-mentioned substrate to be exposed. In the projection exposure method, which comprises the step of exposing, as the step of aligning the substrate to be exposed, the substrate to be exposed is As the light for illuminating the upper mark, a light having a wavelength different from that of the exposure light is used, and the substrate to be exposed is arranged at a position having a height different from that at the time of exposure, and the illumination is performed through the reduction lens. The projection exposure is characterized in that it comprises a step of guiding the reflected light from the mark by light of different wavelengths to the photoelectric conversion means, and a step of converting the light into electric signals by the photoelectric conversion means and aligning the exposed substrate. Method. 2. The projection exposure method according to claim 1, wherein a plurality of lights having different wavelengths are switched and used as the illuminating light. 3. The projection exposure method according to claim 1, wherein, as the illuminating light, light having the same wavelength as the exposure light and light having a different wavelength from the exposure light are switched and used.