JP2654962B2 - Defocus detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary of the Invention] The present invention relates to a method for detecting a focus shift that may occur at the time of image focusing performed before exposure in a semiconductor exposure apparatus. A light-emitting unit that irradiates a detection light to each position of an object to be measured with the object of providing a focus shift detection method capable of detecting a shift in advance,
A detector for detecting the reflected light from the object to be measured, a polarizing plate disposed on an optical path between the light emitting unit and the detector, and an angle detector for detecting a tilt of the polarizing plate are used. 14a to 14d) measuring the height at each position of the object to be measured according to the inclination, comparing the result with height data obtained by a focus mechanism, and detecting the flatness of the object to be measured (16). And a method of detecting a focus shift characterized by the following.

[Industrial applications]

The present invention relates to a method for detecting a focus shift that may occur at the time of image focusing performed before exposure by a semiconductor exposure apparatus.

[Conventional technology]

2. Description of the Related Art Conventionally, in the manufacture of semiconductor devices, for example, in order to expose a fine pattern on a wafer or the like, a projection exposure apparatus that repeatedly exposes a wafer to a reticle image on which a pattern such as an integrated circuit is formed has been used.

In such a projection exposure apparatus, a reticle image is reduced by a reduction projection lens to form a pattern on a wafer surface. An automatic focus detection mechanism is provided to automatically detect the focus of the pattern.

FIG. 5 is a schematic configuration diagram showing an example of a conventional autofocus mechanism. In the figure, light from a light emitting diode LED 1 as a light source is narrowed down into a beam by a slit 2, modulated by a diaphragm 3, and passed through a lens 4 at the same position as the focal position of a reduction projection lens 6 on the surface of a wafer 5. Illuminated and focused. This focal light is reflected and detected by the detector 8 through the lens 7. Based on the detection result of the detector 8, the stage 9 moves up and down so as to be focused.

[Problems to be solved by the invention]

In the conventional semiconductor exposure apparatus, the focus is detected at one location (one point) on the surface of the wafer 5,
It was impossible to detect a partial focus shift due to poor flatness such as inclination or unevenness of the wafer 5. Therefore, partial focus shift cannot be detected prior to exposure, and may be found after exposure. in this way,
If a partial focus shift is found after the exposure, the image is reproduced, which requires a lot of time and steps, and has a problem that a great deal of damage is caused.

2. Description of the Related Art In a semiconductor exposure apparatus, partial defocusing due to unevenness of a wafer has become remarkable with recent miniaturization of devices and increase in chips, and it is required to find out in advance.

Therefore, an object of the present invention is to provide a method of detecting a focus shift that can detect a partial focus shift in advance before exposure.

[Means to solve the problem]

The above-described problem is caused by a light emitting unit (11a, 11b) for irradiating each position of the device under test (16) with light for detection, and a detector (12a, 12b) for detecting reflected light from the device under test (16). A polarizing plate (13a to 13d) disposed on an optical path between the light emitting unit (11a, 11b) and the detector (12a, 12b); and the polarizing plate (13a to 13d).
Focusing at an arbitrary point on the surface of the device under test (16) by using the angle detectors (14a to 14d) for detecting the inclination of the object, and then the inclination of the angle detectors (14a to 14d). The height of the object to be measured (16) at a plurality of different positions is measured, the result is compared with the height data obtained in the focusing step, and the flatness of the object to be measured (16) is detected. The method can be performed by providing a method of detecting defocus having the steps of:

[Action]

FIG. 1 is a diagram illustrating the principle of the present invention. In the figure, 11
a and 11b are light emitting units used for focus detection 2
LEDs, 12a and 12b are two detectors for receiving the reflected light from the object to be measured, 13a to 13d are polarizing plates for putting light from the object to be detected into the detectors 12a and 12db, and 14a to 14d are Angle detectors for relatively detecting the height of the object to be measured by the inclinations of the polarizing plates 13a to 13d. A) lens. The polarizers 13a to 13d can be changed in angle and operate until light can enter the respective detectors 12a and 12b. This is because, as shown in FIG. 2, when the height of the object to be measured is different, the reflected optical axis shifts (in FIG. 2, the solid line shows no deviation and the dotted line shows a deviation). The light of the LEDs 11a and 11b is applied to predetermined four places (four points exposed in one shot shown in (a) to (d) in FIG. 1) of the wafer 16 which is an object to be measured. Height is an angle detector
Detected as the angle of the polarizing plates 13a to 13d by 14a to 14b,
The inclination is determined as the height of the measured object. That is, in the present invention, after focusing is performed by the conventional focusing mechanism, first, the LED 11a is caused to emit light,
The points (a) of the object to be measured are determined by the polarizing plates 13a and 13b.
The height of (b) is measured. Next, the LED 11b emits light, and the points (c) and (d) of the measured object are measured by the polarizing plates 13c and 13d.
Measure the height. Thereafter, the angles of the polarizing plates 13a to 13d are read by the angle detectors 14a to 14d. Next, the conventional focus value is compared with the values of the angle detectors 14a to 14d to determine whether there is any abnormal value. If a far apart value is found, an instruction is issued to a central processing unit or the like of the exposure apparatus to issue an alarm. Therefore, since detection is performed at four points, partial focus shift can be detected.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to an embodiment shown in the drawings.

FIG. 3 is a block diagram of a semiconductor exposure apparatus according to the embodiment of the present invention. Parts corresponding to FIG. 1 are denoted by the same reference numerals.
In FIG. 1, a reduction projection lens 17 constituting a semiconductor exposure apparatus is arranged on a wafer 16. On the side of the reduction projection lens 17, an LED 18 as a light source, lenses 19 and 20, a detector 21, and the like are arranged as a conventional autofocus mechanism. Further, on the other side of the reduction projection lens 17, LEDs 11a and 11b used for focus detection, detectors 12a and 12b receiving reflected light from the wafer 16, and polarization for entering light from the wafer 16 into the detectors 12a and 12b. Boards 13a-13
d, angle detectors 14a to 14d for relatively detecting the height of the wafer 16 by the inclination of the polarizing plates 13a to 13d, respectively,
Lenses 15a to 15d for irradiating 16 with a beam (or for receiving from an object to be measured) are arranged. The detection outputs of the detector 21 of the conventional autofocus mechanism and the angle detectors 14a to 14d are determined by a comparator 22 as to whether or not there is a defocus (defocus). To a central processing unit (CPU) (not shown).

Next, a method of detecting a focus shift by the above configuration will be described.

FIG. 4 is a flowchart showing a method of detecting a focus shift according to the embodiment of the present invention.

First, the LE that constitutes the conventional autofocus detection mechanism
Focusing is performed by D18, lenses 19 and 20, detector 21, and the like (step ST1).

Next, the LED 11a, the detector 12a, and the polarizing plates 13a and 13b
And the angle detectors 14a and 14b measure the heights of the points (a) and (b) on the wafer 16 (step ST2).
Also, an LED 11b, a detector 12b, polarizing plates 13c and 13d,
The heights of points (c) and (d) on the wafer 16 are measured by the angle detectors 14c and 14d (step ST3).

Next, the comparator 22 compares the measurement results of the points (a) to (d) with the measurement result of the conventional detector 21 (step ST4). Then, based on the comparison result, it is determined whether or not there is defocus (defocus) (step ST5). If there is, an instruction is given to the central processing unit, and if not, exposure is performed. In this manner, exposure is performed by detecting a focus shift for each shot. When there is a focus shift, the central processing unit performs measures such as stopping the exposure and notifying an alarm, or storing the position and proceeding to the next exposure.

By the above method, it is possible to detect partial focus shift due to poor flatness such as inclination or unevenness of the wafer 16 prior to exposure, and reproduction due to partial focus shift after exposure is eliminated.

In another embodiment, a detector is used in the above exposure apparatus.
12a and 12b are installed in pairs.

In this way, in the above-described embodiment, the height measurement is performed twice by the LED 11a and the detector 12a and the LED 11b and the detector 12b, but the height can be measured simultaneously (see FIG. 4). Step ST2 and step ST3 are made one step). Therefore, work efficiency can be improved.

In the present invention, light is emitted from a light emitting unit such as the LEDs 11a and 11b to each position on an object to be measured such as the wafer 16, and the reflected light is detected by the detectors 12a and 12b, and the polarizing plate 13a on the optical path is detected. It is only necessary to detect angles from 13 to 13d by the angle detectors 14a to 14d and measure the height at each position. Compare the height at each position with the height data of the focus mechanism,
If the values are far apart, it indicates that the measured object is not flat, and this value can be set to an arbitrary value depending on the measurement accuracy of the measured object.

〔The invention's effect〕

According to the present invention described above, after focusing is performed by a conventional focusing mechanism, by measuring the height of another point of the object to be measured, it is possible to detect partial unevenness of the wafer prior to exposure. Reproduction due to discovery after exposure is greatly reduced.

[Brief description of the drawings]

FIG. 1 is a view for explaining the principle of the present invention, FIG. 2 is a view showing the deviation of the reflected optical axis in FIG. 1, FIG. 3 is a structural view of an embodiment of the present invention, and FIG. FIG. 5 is a schematic diagram showing a conventional auto-focus mechanism. In the figure, 11, 11a and 11b are LEDs, 12, 12a and 12b are detectors, 13a to 13d are polarizing plates, 14a to 14d are angle detectors, 15a to 15d are lenses, 16 is a wafer, 17 is a reduction projection lens, Reference numeral 18 denotes an LED, reference numerals 19 and 20 denote lenses, reference numeral 21 denotes a detector, and reference numeral 22 denotes a comparator 22.

Claims (1)

(57) [Claims] A light emitting section (11a, 11b) for irradiating each position of a measured object (16) with light for detection, and a detector (12) for detecting reflected light from the measured object (16).
a, 12b), a polarizing plate (13a to 13d) disposed on an optical path of the light emitting section (11a, 11b) and the detector (12a, 12b), and an inclination of the polarizing plate (13a to 13d) is detected. Angle detector (14
a to 14d) to perform focusing at an arbitrary point on the surface of the DUT (16), and then, the inclination of the angle detectors (14a to 14d) causes the DUT (16) to move relative to each other. Measuring heights at a plurality of different positions, comparing the result with height data obtained in the focusing step, and detecting flatness of the object to be measured (16). Method.