JPH05256621A - Pattern position measuring device - Google Patents

Abstract

PURPOSE:To provide a pattern position measuring device capable of eliminating the measurement error caused by the abnormal attitude state of a sample due to the sticking of foreign objects such as refuse. CONSTITUTION:A pattern position measuring device is provided with a stage 5 mounted with a sample formed with the preset pattern on the surface and movable on the nearly horizontal plane, a height detecting means 11 detecting the height of the sample surface from the horizontal plane at multiple positions of the sample surface, and a comparing means 12 judging whether the difference between the height detected by the height detecting means and the preset reference height is within the preset allowable range or not.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pattern position measuring apparatus for detecting the position of a pattern formed on a sample such as a mask, a reticle or a wafer used in an exposure apparatus for manufacturing a semiconductor device or a liquid crystal device. The present invention relates to an improvement for reducing a measurement error caused by an abnormal posture state of a sample.

[0002]

2. Description of the Related Art In a semiconductor exposure apparatus or the like, a mask or reticle on which a predetermined circuit pattern is formed is exposed to light and the pattern is printed and transferred onto a wafer to form a semiconductor circuit. After manufacturing such a mask, reticle or wafer, the pattern position (coordinates) is measured by a pattern position measuring device in order to inspect the pattern forming accuracy and the like.

FIG. 6 shows the structure of a sample support portion of such a pattern position measuring device. (A) is a plan view, (b) is a sectional view, and (c) is an explanatory view of a sample supporting state. A sample 1 to be measured, such as a mask or a reticle, is mounted on four suction protrusions 3 provided on a holder 2. An adsorption port 4 connected to a vacuum device (not shown) is formed on the upper surface (adsorption surface) of each adsorption projection 3, and the four corners of the sample 1 are vacuum adsorbed and fixedly held. In this case, the sample 1 is in the state of the simple support beams at both ends, as shown in FIG. Normally, the pattern position measurement is performed in such a constant curved bending state.

[0004]

However, in the structure of the pattern position measuring apparatus, if foreign matter such as dust or scratches are present between the sample 1 and the suction projection 3, as shown in FIG. The posture changes from the normal bending state (reference posture) shown by a to the bending state in which the twist is added as shown by b. For this reason, the distance between the patterns to be measured (indicated by X) changes to Lb from what should have been La, causing an error in the measured value. As a result, the reliability of the measurement result, such as distinguishing a normal sample from a defective product and vice versa, decreases the reliability of the measurement result.

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and provides a pattern position measuring apparatus capable of reducing a measurement error caused by an abnormal posture state of a sample due to adhesion of foreign matter such as dust on the sample support portion. For the purpose of provision.

[0006]

To achieve the above object, a pattern position measuring apparatus according to the present invention comprises: a stage on which a sample having a predetermined pattern formed thereon is placed and which can move in a substantially horizontal plane; Height detection means for detecting the height of the sample surface from the horizontal plane at a plurality of positions on the sample surface; difference between the height detected by the height detection means and a preset reference height However, it has a comparison means for judging whether or not it is within a predetermined allowable range.

[0007]

[Function] The height from a predetermined horizontal plane is measured at a plurality of positions on the surface of the sample, and the measured value is compared with the height of a normal sample serving as a reference. If the difference exceeds an allowable range, the sample is set. Judge that the condition is abnormal.

[0008]

1 is a block diagram of a pattern position measuring apparatus according to an embodiment of the present invention. The sample (not shown) on which the pattern to be measured is formed is vacuum-sucked and fixedly held on the suction protrusion 3 of the holder 2 as described above. This holder 2
Is fixedly mounted on an XY stage 5 movable in the XY directions in a horizontal plane. The XY stage 5 is moved in each of the XY directions by an XY drive device 6 including an X-direction drive motor and a Y-direction drive motor, and moves the sample to a designated coordinate position. The XY drive device 6 is drive-controlled by the CPU 7. Holder 2 mounted on this XY stage 5
An optical system 8 for focus detection including an objective lens 9 is arranged above. The focus detection optical system 8 is, as described later,
It is for detecting the height from the XY plane at a plurality of points on the sample surface, and is drive-controlled by the CPU 7. The objective lens 9 can be moved up and down by a Z drive device 10 in the Z direction perpendicular to the XY plane, and this changes the focal position of the light beam with which the sample is irradiated. Z drive device 1
A height detector 11 is connected to 0 and detects the amount of movement of the Z drive device 10 to detect the height of the sample surface. The height detector 11 is connected to the comparison / discrimination circuit 12, and the measured height of the sample surface is compared with a predetermined reference value. Comparison discrimination circuit 12
Is connected to the CPU 7, and the CPU 7 determines the posture state of the sample according to the output of the comparison / determination circuit 12 and issues an alarm or the like if there is an abnormality.

A sample setting sequence of the pattern position measuring device having the above structure will be described with reference to the flowchart of FIG. First, the sample to be measured is mounted on the holder and fixed and held by vacuum suction as described above (step 13). Next, the three-dimensional posture (height of the sample surface from the XY plane) of the sample set using the focus detection optical system 8 is measured (step 14). At this time, the measurement points are instructed to be measured uniformly over the entire surface of the sample 1 at pitches Px and Py in each of the XY directions, as shown by the + mark in FIG. In the case of a holder supporting four points, the posture change of the sample due to the adhesion of foreign matter to the supporting points can be detected by measuring the vicinity of the four supporting points (suction protrusions 3). However, if the entire surface of the sample is measured uniformly, the entire shape can be observed with a three-dimensional graphic, and abnormalities of the supporting portion can be easily and reliably detected from the entire shape. Distribution is desirable. Further, depending on the sample, it may not be possible to use a holder supporting four points, so it is desirable to measure the entire surface of the sample uniformly and detect the abnormal portion from the overall shape.

Focusing is performed by the focus detection optical system 8 at each measurement point, and the focal length is read by the height detector 11 from the amount of movement of the Z drive device 10 and used as a measurement value of the height of each measurement point. Next, each measured value is compared with the value in the reference posture to obtain the difference (step 15). In this case, the height in the reference posture, which is the reference value, is statistically obtained by repeating the setting of the sample and the height measurement many times. Alternatively, the sample may be set with the suction protrusion of the holder and the lower surface of the sample completely cleaned, and the height at this time may be measured and used as a reference value. Such reference values are measured in advance corresponding to all the above-mentioned measurement points, and CP
It is stored in U7. Each measured value is the comparison / determination circuit 1
2, the difference from the reference value is calculated by performing subtraction processing between each measurement value and the reference value at the same measurement point.

Next, it is judged whether or not the result of this calculation is within the allowable range at the time of predetermined setting (step 16).
In this case, the allowable range varies depending on the type of sample, size, thickness and required accuracy of coordinate measurement. In order to determine this allowable range, the relationship between the difference between the measured value and the reference value and the coordinate measurement accuracy is statistically obtained, and the relationship is determined based on this relationship. Specifically, set the sample, measure the height at that time, further measure the coordinates to find the coordinate accuracy corresponding to the height, and repeat this many times to find the difference between the reference value and the measured value. The relationship between the difference between and the coordinate measurement accuracy is obtained. As a result, the difference between the measured value and the reference value corresponding to the required coordinate measurement accuracy is determined. An appropriate margin is added to the result determined in this way to make it an allowable range.

If the difference between the measured value and the reference value is within the permissible range in the judgment step 16, it is judged that the sample is mounted on the holder in a state satisfying the required coordinate measurement accuracy. The setting sequence is ended, and the sequence of steps for measuring the next pattern position is started. On the other hand, if the difference between the measured value and the reference value exceeds the permissible range in the discrimination step 16, foreign matter is present between the sample and its supporting portion (suction protrusion 3), and the posture of the sample has changed. Judge that
The CPU 7 gives some alarm to inform the operator of this abnormal condition. As a result, the operator cleans the contact portion between the sample and the holder to remove dust and the like (step 17). Then, the sample is set on the holder again (step 13), and the subsequent steps 14 to 1 are performed.
Repeat 6 If the difference between the measured value and the reference value exceeds the permissible range again in the second determination step 16, this sample deformation is not caused by the adhesion of dust or the like, and the sample itself is abnormally deformed. Judge and treat as a defective sample.

Next, the structure and operation of the focus detection optical system 8 in the above embodiment will be briefly described with reference to FIGS. 3 and 4. FIG. 3 shows the configuration of the automatic focus detection device. The beam diameter of the laser beam emitted from the laser light source 21 is expanded by the beam expander 22, passes through the beam splitter 23, is converged by the objective lens 24, and is converged and imaged on the surface of the sample 25 which is the object to be measured. The laser light that irradiates the sample in this way is reflected or scattered on the surface of the sample, and this reflected scattered light is again reflected by the objective lens 2.
After passing through 4, the beam is reflected by the beam splitter 23, focused on a spot by the condenser lens 26, and re-imaged. An aperture (or pinhole, slit, etc.) 32 is provided at this spot position (condensing image forming position). The aperture 32 is vibrated by the vibrator 27 in the optical axis direction. The optical signal passing through the vibrating aperture 32 is converted into an electric signal by the detector 28 including a photoelectric element. This electric signal is input to the synchronous detection circuit 30 via the preamplifier 29. A signal that drives the oscillator 27 is generated as a reference signal from the oscillator 31, and this reference signal is also input to the synchronous detection circuit 30. It is assumed that when the focus of the laser light is on the sample surface, the vibration center of the vibration aperture 32 is aligned with the re-imaging position of the spot of the laser light. The output of the synchronous detection circuit 30 at this time is zero volt.

When the distance between the objective lens 24 and the sample 25 changes, the synchronous detection output exhibits a characteristic called an S curve, depending on the amount of deviation from the focus, as shown in FIG.
Using the central portion of this S curve, the amount of irregularities on the sample surface can be measured, and the surface shape can be recognized. If there is a servo system that drives the objective lens in the direction of the optical axis, the synchronous detection output is fed back to this to make the amount of deviation from the focus zero and automatically perform focusing, or to move the objective lens. It is also possible to mechanically expand the amount and detect the unevenness of the sample surface from the amount of movement. That is, when detecting the height of the sample surface, the servo mechanism (Z drive device 1 of FIG.
0) etc., the objective lens (9 in FIG. 1) is moved to a position where the output of the S curve becomes zero, and the amount of this movement is detected by a height detector 11 using an encoder, for example, and the height from a predetermined initial value is detected. Change is calculated. The S curve of the broken line in FIG. 4 shows a state in which the center position of the aperture deviates from the optical axis, the amount of light decreases, and the slope of the curve decreases.

In the configuration of FIG. 1, the comparison / discrimination circuit 12 may be configured as a circuit in the CPU 7.

[0016]

As described above, in the present invention, when the sample for which the pattern position is to be measured is set on the holder, the posture of the sample is measured before starting the measurement of the pattern position, and the normal posture is measured. Error is detected, and based on this, the presence or absence of dust or scratches on the sample support is determined.If there is dust, the sequence is configured to remove it and then start measuring the pattern position. Therefore, the error in the pattern position measurement due to the abnormal posture state of the sample is reduced, and the reliability of the measurement result is improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a pattern position measuring device according to the present invention.

FIG. 2 is a flowchart showing a sample setting sequence of the pattern position measuring device according to the present invention.

FIG. 3 is a configuration diagram of an automatic focus detection device used in an embodiment of the present invention.

4 is an explanatory diagram of an S curve detected by the automatic focus detection device of FIG.

FIG. 5 is an explanatory diagram of a height detection position of a sample to be measured.

FIG. 6 is a posture explanatory view for explaining a bending state of a sample mounted on a holder.

FIG. 7 is an explanatory diagram of measurement error of the sample when the pattern position is measured in an abnormal posture state.

[Explanation of symbols]

1; sample, 2; holder, 3; adsorption protrusion, 4; adsorption port, 5; XY stage, 6; XY drive device, 7; CP
U, 8; optical system for focus detection, 9; objective lens, 10; Z
Drive device, 11; Height detector, 12, Comparison discrimination circuit.

Claims (1)

[Claims] 1. A stage on which a sample having a predetermined pattern formed thereon is placed and which can move in a substantially horizontal plane, and a height of the sample surface from the horizontal plane is detected at a plurality of positions on the sample surface. Height detecting means, and a comparing means for determining whether or not a difference between the height detected by the height detecting means and a preset reference height is within a predetermined allowable range. A pattern position measuring device characterized by: