JP2924485B2 - Overlay accuracy measuring machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superposition accuracy measuring device for measuring a deviation amount between a resist pattern and a base pattern formed in a photolithography process in a semiconductor device manufacturing process.

[0002]

2. Description of the Related Art Although not shown in the drawings, a conventional overlay accuracy measuring device includes an illumination light source, an optical system for guiding light from the illumination light source to a wafer as an object, and an optical system for capturing an image of the wafer. System and a camera, and an image processing unit for processing a video signal from the camera.

When measuring the displacement of a resist pattern formed on a wafer using such an overlay accuracy measuring device, first, an image of an overlay accuracy measurement mark on the wafer is captured by a camera. Next, the video signal is sent to an image processing unit, where processing such as averaging a certain range of the image signal is performed, edges in the pattern are detected from the signal waveform, and overlay accuracy is measured from the edge position.

[0004]

In the overlay accuracy measuring apparatus described above, if the optical axis is tilted with respect to the object, the image on the camera is affected and the image signal is deformed. Will cause an error. For this reason, the following method has conventionally been used to find and configure the inclination of the optical axis.

In this method, first, the overlay accuracy is measured using an erect image or an inverted image, and then the wafer is manually rotated by 180 degrees .
Each time it is reversed, superposition accuracy is performed. Soshi
Then, manually compare the data, verify the amount of optical axis tilt, adjust the optical axis tilt, confirm the optical axis tilt again by the same means, and by this trial and error, set the optical axis tilt to the allowable range I was adjusting. For this reason, it has taken a long time to check the optical axis inclination.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a superposition accuracy measuring device capable of measuring a pattern displacement without being affected by an inclination of an optical axis.

[0007]

SUMMARY OF THE INVENTION The present invention is characterized by a stage on which a wafer on which an overlay accuracy measuring mark is formed is mounted, an optical system for guiding light from an illumination light source to the wafer, An optical system and a camera for capturing the image of the mark, and an image processing unit for processing a video signal from the camera;
And a reversing optical system for rotating the image of the mark by 180 degrees when the mark is aligned.
The measured value of the relative displacement of the image is
By calculating the relative position shift measurement value of the image of the mark that has been inverted at a time , and averaging these relative position shift amounts,
This is a superposition accuracy measuring device for obtaining a displacement .

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a configuration of an overlay accuracy measuring device according to an embodiment of the present invention. As shown in FIG. 1, the overlay accuracy measuring device includes a wafer chuck 2 for holding a wafer 1, a movable stage on which the wafer chuck 2 is placed and which can move in a horizontal plane, and a light source 10 for emitting light. Surface light source and lens 1 having uniform intensity by dispersion plate 9
1, an illumination optical system for illuminating the wafer 1 via the aperture 8, the prism 7, the aperture 6, and the objective lens 5, and the image of the wafer to the CCD camera 15 via the objective lens 5, the aperture 6, the prism 7, and the lens 12. An optical system for forming an image is provided as well as the conventional one.

In this embodiment, an inverting optical system 13 that can move across the optical axis is provided in the optical path between the prism 7 and the objective lens 5. The reversing optical system 13 is shown in a retracted state in the drawing, but is movable in a horizontal plane perpendicular to the optical axis. The reversing optical system driving mechanism 14 controls the prism 7 and the objective lens 5. The center can be adjusted on the optical axis connecting.

[0011]

Next, a description will be given of a means for measuring a position shift by the overlay accuracy measuring device. First, an image of the overlay accuracy measurement mark on the wafer 1 is formed on the CCD camera 15 with the reversing optical system 13 retracted. As a result, the edge of the measurement mark is detected by the image signal detection circuit 16 and the shift amount is detected. Next, the shift amount is sent to the control circuit 17 and the amount is stored. Next, the reversing optical system 13 is positioned on the optical axis by the reversing optical system driving mechanism 14, and similarly, the amount of displacement in a state where the image is reversed is detected. Next, the two shift amounts are averaged to determine the shift amount.

By inverting the optical axis in this way and averaging the respective shift amounts, errors due to the inclination are canceled. Therefore, even in a state where the optical axis is inclined, it is possible to detect a good shift amount without being affected by the inclination.

[0014]

As described above, according to the present invention, the optical axis is set to one.
A reversing optical system for reversing the temperature by 80 ° C is provided. Even when the optical axis is inclined, the measured value when the overlay accuracy measurement is performed with an erect or inverted image and the illumination light of the wafer around the optical axis. By averaging the measured values when the overlay accuracy measurement is performed with the optical axis relatively inverted, errors due to the tilt of the optical axis can be canceled out, thus affecting the tilt of the optical axis. Therefore, there is an effect that a good overlay accuracy measurement can be performed without any problem.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of an overlay accuracy measuring apparatus according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Wafer 2 Wafer chuck 3 Moving stage 4 Base 5 Objective lens 6 Aperture 7 Prism 8 Aperture 9 Light scattering plate 10 Light source 11 Lens 12 Lens 13 Inverting optical system 14 Inverting optical system driving mechanism 15 CCD camera 16 Image signal detection circuit 17 Control circuit

Claims (1)

(57) [Claims] An optical system for guiding light from an illumination light source to the wafer; an optical system for capturing an image of the mark on the wafer; A camera, an image processing unit for processing a video signal from the camera, and moving the optical system and the camera.
When the optical axis of the camera coincides with the optical axis,
A reversing optical system for rotating 0 degrees , wherein the reversing optical system is
The measured value of the relative positional deviation of the image of the mark
Of the image of the mark inverted through 180 degrees
A superposition accuracy measuring device which obtains a relative position shift measurement value and obtains a position shift by averaging these relative position shift amounts .