JPH05190424A - Alignment scope provided with focus detection means - Google Patents

Abstract

PURPOSE:To make a light flux incident on a measuring region in such a way that reflection conditions form the measuring region are individually nearly equal and to position a wafer at high speed by a method wherein one measuring region out of a plurality of measuring regions on the face of a second object is irradiated, from the oblique direction, with the light flux from a light source and a change in the light path of a reflected light flux from the measuring region is detected. CONSTITUTION:An opening shape 14a in a field disphragm 14 used to irradiate a wafer 5 is set in such a way that it is situated as a measuring region IF inside a scribing line SL when an alignment mark AM is moved to the observation position of an alignment scope 1. When the opening shape 14a in the irradiating field diaphragmg 14 is set in this manner, conditions such as the pattern shape of an irradiation position and the like can be kept nearly the same when the wafer is aligned by driving an X-Y stage 6a and by detecting an alignment mark for another shot. That is to say, reflection conditions from a plurality of measuring regions on the face of the wafer 5 become individually nearly equal. Thereby, a focus can be detected at high speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alignment having a focus detecting means for detecting a relative positional relationship between a mask (reticle) and a wafer in a reduction type projection exposure apparatus (stepper) for manufacturing a semiconductor device. Regarding the scope, in particular, each exposed region of the semiconductor wafer mounted on the wafer stage is focused on the focal plane of the alignment scope at high speed, and the relative alignment between the mask and the wafer can be performed at high speed and with high accuracy. It was done like this.

[0002]

2. Description of the Related Art In recent years, a reduction type projection exposure apparatus (so-called stepper) has been used as an apparatus for exposing and transferring a fine circuit pattern.
Have been used in many production sites of semiconductor devices such as ICs and LSIs. This reduction type projection exposure apparatus reduces an image of a circuit pattern drawn on a reticle (mask) by a projection optical system to expose a layer of photoresist (photosensitive agent) on a semiconductor wafer.

In such a projection exposure apparatus for manufacturing a semiconductor, relative alignment between the mask and the wafer is an important factor for improving the performance. Particularly, in alignment in a recent projection exposure apparatus, an alignment scope having alignment accuracy of, for example, submicron or less is required for high integration of semiconductor elements.

At this time, in the alignment scope for performing relative alignment between the mask and the wafer, in order to observe the marks on the wafer surface and perform highly accurate alignment, the wafer is accurately positioned at the focus position of the alignment scope. It becomes important to let them do it. That is, it becomes important to detect the focus position of the alignment scope with high accuracy.

A focus detection method of the alignment scope is a detection optical system in which a light beam is obliquely incident on the wafer surface and the positional deviation of the reflection point of the reflected light from the wafer surface is detected as the positional deviation of the reflected light on the sensor. By using a system to detect the position of the wafer surface (hereinafter referred to as “grazing incidence AF”) and by processing the mark image formed on the wafer surface through an image pickup tube, a solid-state image sensor (CCD), etc. There is a method of detecting the position of the wafer surface (hereinafter referred to as "image AF") and the like.

[0006]

Among the conventional methods for detecting the position of the wafer surface, the oblique incidence AF method has a feature that position detection can be performed at high speed.

However, since a substantially optically transparent resist film exists on the wafer surface which is the projection target substrate, it is affected by the surface reflection of the resist film and the interference of the reflected light from the substrate surface (wafer surface). There were cases.

Further, the optical path of the detection light may change depending on the pattern formed on the substrate (wafer). That is, there is a problem that the measured value changes depending on the film thickness of the resist film, the refractive index, the reflectance of the substrate, the shape, and the like.

Further, the image AF method has a feature that the surface position of the substrate (wafer) can be accurately detected by detecting the contrast of the projected image, for example. However, there is a problem that the signal processing time of the image information becomes long and the throughput decreases when it is repeatedly used.

According to the present invention, by appropriately utilizing the oblique incidence AF method, the detection error based on the surface reflection of the resist film applied on the wafer surface and the reflected light from the wafer surface (substrate surface) by the oblique incidence AF method is eliminated. It is an object of the present invention to provide an alignment scope having a focus detection means suitable for manufacturing a semiconductor device, which can prevent the generation of the wafer and position the wafer on the optimum image plane of the alignment scope at high speed and with high accuracy.

[0011]

An alignment scope having a focus detecting means of the present invention is a first scope for projecting and exposing a pattern on a first object plane onto a second object plane via a projection optical system. An alignment scope for detecting a relative positional relationship between an object and a second object, wherein a light beam from a light source means is obliquely applied to one measurement area of a plurality of measurement areas on the second object plane. By detecting the change in the optical path of the reflected light flux from the measurement region, when detecting the focus position of the projection optical system in the measurement region, the reflection conditions from the plurality of measurement regions are set to be substantially equal to each other. It is characterized in that the luminous flux from the light source means is made incident on the measurement region.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a perspective view of an essential part of a first embodiment of the present invention, and FIGS. 2 and 3 are explanatory views of a part of FIG.

In FIG. 1, reference numeral 2 denotes a reduction type projection lens system (projection optical system), the optical axis of which is indicated by AX1 in the figure. A reticle (first object) 4 has an electronic circuit pattern formed on its surface. An illumination system 3 uniformly illuminates the surface of the reticle 4.

The projection lens system 2 reduces the circuit pattern of the reticle 4 by a factor of, for example, 1/5 and projects it to form a circuit pattern image on its focal plane. The optical axis AX1 is parallel to the z-axis direction in the figure. Reference numeral 5 denotes a wafer (second object) whose surface is coated with a resist, and has a large number of exposed regions (shots) in which the same patterns are formed in the previous exposure process.

Reference numeral 6 is a wafer stage on which a wafer is placed. The wafer 5 is adsorbed and fixed to a wafer chuck (not shown) of the Z stage 6b of the wafer stage 6. The wafer stage 6 is composed of an XY stage 6a which moves in the x-axis direction and the y-axis direction, and a Z stage 6b which is rotated by a motor 22 around an axis parallel to the z-axis direction and the x, y, z-axis directions. There is.

The x, y and z axes are set to be orthogonal to each other. Therefore, by driving the wafer stage 6, the position of the surface of the wafer 5 is changed to the projection lens system 2
Is adjusted in the optical axis AX1 direction and a direction along a plane orthogonal to the optical axis AX1, and the tilt with respect to the focal plane, that is, the circuit pattern image is also adjusted.

The XY stage 6a detects its position information by a laser interference device (not shown) and adjusts its position.

Reference numeral 21 denotes a control circuit, which drives and controls the motor 22. Reference numeral 1 denotes an alignment scope, which observes an alignment mark AM on the surface of the wafer 5 to perform relative alignment between the reticle 4 and the wafer 5.
Reference numeral 101 denotes a focus detection unit that uses the oblique incidence AF method, detects the focal plane of the alignment scope 1 (imaging lens 7), and positions the wafer 5 at that position. Reference numeral 8 is a lens for illumination, and 9 is a light source for illumination.

The luminous flux from the light source 9 is condensed by the illumination lens 8, reflected by the half mirror 19, and illuminates the alignment mark AM on the surface of the wafer 5 through the imaging lens 7. 10 is a CCD camera. The image forming lens 7 forms an image of the alignment mark AM on the surface of the wafer 5 on the surface of the CCD camera 10 via the half mirrors 19 and 18. An image processing circuit 20 obtains the positional relationship between the reticle 4 and the wafer 5 from the positional information of the alignment mark AM on the surface of the wafer 5 imaged on the surface of the CCD camera 10.

The control circuit 21 drives the motor 22 based on the signal from the image processing circuit 20 to adjust the position of the Z stage 5 in the optical axis AX2 direction.

Next, the oblique incidence AF type focus detection means 101
Each element of will be described.

A light beam from a light source 15 composed of an LED or the like passes through a field stop 14 having an opening 14a shown in FIG. 2, is condensed by a second lens 13, and the aperture stop 12 limits the passing light beam.

The light flux from the aperture stop 12 is the first lens 11
Then, the measurement area IF on the scribe line SL on the surface of the wafer 5 is obliquely illuminated by the imaging lens 7 via the half mirrors 18 and 19 as shown in FIG. At this time, the image 14a extending in the longitudinal direction of the scribe line SL of the field stop 14 is formed so that the alignment mark AM is included in the scribe line SL on the surface of the wafer 5 so as to be included in the illumination area. still,
In FIG. 3, RS indicates an area where the circuit pattern of the actual element is to be projected and exposed.

The reflected light flux from the measurement area IF of the wafer 5 is sequentially detected by the imaging lens 7, the half mirrors 19 and 18, the first lens 11, the third lens 16 and the rotatable plane parallel plate 23. The light is guided to the surface 17 and the image (spot light) of the field stop 14 is re-imaged on the surface.

The position information of the wafer 5 in the direction of the optical axis AX2 is obtained by detecting the position of the spot light formed on the surface of the detector 17. That is, alignment scope 1
The focal plane of is detected.

Next, the operation of this embodiment will be described.

In this embodiment, the focus detection means 1 is used when the reticle 4 and the wafer 5 are aligned with each other.
By 01, the focus of the alignment mark AM (position in the optical axis AX1 direction) is always detected so that alignment can be performed in the best focus state, and as a result, high-speed and high-precision alignment is realized.

First, the position of the alignment mark AM to be observed by moving the XY stage 6a is directly below the alignment scope 1, that is, the optical axis AX of the imaging lens 7.
Move to position 2.

Next, the Z stage 6b is sequentially moved in the direction of the optical axis AX2, and at the same time, the image signal of the alignment mark AM is taken in by the CCD camera 10 and the image contrast is evaluated by the image processing device 20. This evaluation value is the largest. The Z stage 6b is driven and set at a certain position.

Next, the light source 15 of the focus detecting means 101 is operated to rotate the plane-parallel plate 23 so that the output signal from the detector 17 is at the zero position.

By performing the above operation (hereinafter referred to as "calibration by image focus"), the zero position of the oblique incidence AF system is set to be the best focus position of the wafer 5 for alignment.

Further, the aperture shape 14a of the field stop 14 for projecting light onto the wafer 5 by the oblique incidence AF method is set as shown in FIG. As shown in FIG. 3, when the alignment mark AM is moved to the observation position of the alignment scope 1, the opening shape 14a is set in the measurement area I within the scribe line SL.
It is set so that it is set to F. When the aperture shape 14a of the field stop 14 for projecting light is set in this way, X
When the Y stage 6a is driven to detect the alignment mark of another shot and align the wafer, the conditions such as the pattern shape of the projection position by the oblique incidence AF method are kept substantially the same.

That is, the reflection conditions from the plurality of measurement areas on the surface of the wafer 5 are made substantially equal to each other. As a result, it is possible to use the oblique incidence AF method, which enables high-speed focus detection, for each alignment without having to use the image AF method having a long signal processing time for each alignment.

As a result, it is necessary to perform the calibration operation by the image focus method only once when the state of the projection position by the oblique incidence AF method changes (for example, when the process changes). All that is required is high speed, and all other alignments are performed at high-speed oblique incidence A
The F method ensures that alignment can always be performed in the best focus state. Thereby, in this embodiment, the alignment accuracy is improved without reducing the throughput.

[0035]

According to the present invention, as described above, the oblique incidence A
By properly using the F method, it is possible to prevent the occurrence of a detection error due to the surface reflection of the resist film applied on the wafer surface and the reflected light from the wafer surface (substrate surface) by the oblique incidence AF method, and It is possible to achieve an alignment scope having a focus detection means suitable for manufacturing a semiconductor device, which is capable of positioning a wafer on an optimum image plane at high speed and with high accuracy.

Particularly, in the present invention, the alignment is performed by setting the position and range of the reflecting surface on which the light rays obliquely applied to each measurement area of the projection target substrate (wafer) are reflected so that the measurement areas have substantially the same conditions. It has features such as high-speed and stable focus detection of marks, and high-speed and high-precision alignment.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is an explanatory view of a part of FIG.

FIG. 3 is an explanatory view of a part of FIG.

[Explanation of symbols]

 1 Alignment Scope 2 Projection Optical System 3 Illumination System 4 Reticle 5 Wafer 6 Stage 7 Imaging Lens 8 Illumination Lens 9 Light Source 10 CCD Camera 11 First Lens 12 Aperture Stop 13 Second Lens 14 Field Stop 15 Light Source 16 Third Lens 17 Detector 18, 19 Half mirror 20 Image processing circuit 21 Control circuit 22 Motor AM Alignment mark SL Scribe line IF measurement area 101 Focus detection means

Claims (1)

[Claims] 1. An alignment scope for detecting a relative positional relationship between a first object and a second object when projecting and exposing a pattern on the first object surface onto a second object surface through a projection optical system. Therefore, the measurement is performed by irradiating one measurement area of the plurality of measurement areas on the second object surface from a diagonal direction with the light flux from the light source means and detecting a change in the optical path of the reflected light flux from the measurement area. When detecting the focal position of the projection optical system in a region, the light flux from the light source means is made incident on the measurement region so that the reflection conditions from the plurality of measurement regions are substantially equal to each other. An alignment scope having focus detection means.