JPH05346306A - Pattern-position measuring apparatus - Google Patents

Abstract

PURPOSE:To obtain a pattern-position measuring apparatus, which can accurately detect the deflecting shape of the surface of a sample when the deflection of the position of a pattern is corrected. CONSTITUTION:Height measuring means 11, 12 and 20, which measure the heights of the surface of a sample 10, whose pattern is formed on the upper surface of a substrate, at a specified interval, are provided. Sample-surface discriminating means 11, 12 and 20, which judge whether the height measuring point is on the upper surface of the substrate or on the upper surface of the pattern, are provided. A height correcting means 20, which corrects the height of the surface of the sample based on the outputs of the sample-surface discriminating means, is provided. Furthermore, the following means are provided. A deflected-shape detecting means 20 detects the surface of the sample based on the corrected height of the surface of the sample. A gradient computing means 20 computes the gradient of the surface of the sample at the position of the pattern based on the detected deflected shape. A pattern-position correcting means 20 corrects the position of the pattern based on the computed gradient.

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 device for measuring the position of a pattern formed on the upper surface of a substrate of a sample such as a mask or reticle, and more particularly to correction of deflection of the pattern measuring position.

[0002]

2. Description of the Related Art Conventionally, when measuring the position of a pattern on the surface of a sample such as a mask or reticle placed on a stage, the measurement error of the position of the pattern due to the bending of the sample has been corrected. For example, JP-A-4-6561
In the pattern position measuring device disclosed in No. 9, the height of the sample surface placed on the stage is measured at predetermined intervals, and the bending shape of the sample surface is detected in advance from the measured height of the sample surface. Then, the gradient of the sample surface at the position of the edge of the pattern is obtained from the previously detected bending shape, and the correction amount is calculated based on the gradient to correct the position of the pattern to the state without bending. Was there.

[0003]

In the prior art as described above, when measuring the height of the sample surface, the height of the sample surface was measured without distinguishing between the upper surface of the substrate and the upper surface of the pattern. The bending shape of the sample surface detected from the measured height of the sample surface includes an error corresponding to the thickness of the pattern, so that there is a problem that the accurate bending shape of the sample surface cannot be detected.

The present invention has been made in view of the above conventional problems, and an object of the present invention is to provide a pattern position measuring apparatus capable of accurately detecting the bending shape of the sample surface.

[0005]

In order to solve the above problems, a sample having a precision pattern of a predetermined thickness formed on the upper surface of a substrate is placed on a stage, and the edge of the pattern is detected to detect the pattern. The pattern position measuring apparatus of the present invention for determining the position of a pattern includes height measuring means 11, 12, 20 for measuring the height of the sample surface at predetermined intervals, and the height measuring point is the upper surface of the substrate or the pattern. Sample surface determination means 11, 12, 20 for determining whether the surface is an upper surface, and height correction means 20 for correcting the height of the sample surface measured by the height measurement means based on the output of the sample surface determination means. A bending shape detecting means 20 for detecting a bending shape of the sample surface from the height of the sample surface corrected by the height correcting means; and a bending shape detected from the bending shape detecting means to a position of an edge of the pattern. Oh Wherein a gradient calculating means 20 for calculating the gradient of the sample surface, and a pattern position correction means 20 for correcting the position of the pattern on the basis of an output of the gradient calculation unit that.

[0006]

In the present invention, when the height of the sample surface is measured at predetermined intervals, it is determined whether the height measurement point is the upper surface of the substrate or the upper surface of the pattern, and the height of the sample surface measured by this determination result. Is corrected based on the thickness of the pattern, and the bending shape of the sample surface is detected from the corrected height of the sample surface.Therefore, an error corresponding to the thickness of the pattern is not included, and the bending shape of the sample surface is accurately determined. Can be detected.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a perspective view of a pattern position measuring device according to an embodiment of the present invention. The sample 10 on which a predetermined precision pattern is formed is placed on the XY stage 15, and the pattern image is enlarged by the objective lens 11 and imaged at a predetermined position in the optical device 12. A laser light source is provided in the optical device 12, and a laser spot is projected onto the sample 10 via the objective lens 11. Generally, the pattern of a mask or reticle has edges of minute unevenness, and therefore, when spot light is relatively scanned, scattered light or diffracted light is generated at the edge portion. The four light receiving elements 50a, 50b, 51a, 51b provided around the objective lens 11 are
It functions as an edge detecting unit that receives the scattered light and the like. For details of this edge detection method, see Japanese Patent Publication No. 56-25
Since it is disclosed in No. 964, its explanation is omitted. Also,
The optical device 12 is provided with a focus detection means (autofocus) capable of automatically focusing by moving the objective lens 11 up and down in the Z direction. As the focus detecting means, for example, the means described in Japanese Utility Model Publication No. 57-44325 can be used, and the height of the surface of the sample 10 can also be detected.
Here, the detection of the in-focus position by the focus detection means will be briefly described. First, the above-mentioned laser light is imaged on the sample 10 through the objective lens 11 in a spot shape (or slit shape), and the reflected light from the sample 10 is re-imaged through the objective lens 11. The objective lens 11 is moved up and down by a few microns, and the position of the pinhole (or slit) is simply oscillated in the optical axis direction (Z direction) about a predetermined focusing surface, and further the transmitted light of the pinhole (or slit) is transmitted. The output signal obtained by receiving the light is synchronously detected (synchronous rectification) at a single vibration frequency. As a result, an S-shaped curve in which the voltage value with respect to the position in the Z direction changes in an S shape as shown in FIG. 3 is obtained.

[0008] The S-curve signal and the defocus amount d and the voltage value V has a linearity before and after the small section of the focus position d _0, and the voltage value V in-focus position d ₀ is zero Since it has characteristics, the height of the sample 10 in the Z direction with respect to the in-focus position d ₀ can be easily obtained based on the S-shaped curve signal, that is, the sample 1
It is possible to detect the distance between the ideal moving horizontal plane of the XY stage 15 which is mounted 0 and moves two-dimensionally, and the surface of the sample 10.

Further, the S-shaped curve signal has a characteristic that the magnitude of the peak-to-peak voltage varies depending on the reflectance of the surface of the sample 10. Sample 10 has a chrome pattern formed on the upper surface of a glass substrate, and the reflectance is higher on the upper surface of the pattern than on the upper surface of the substrate, and the peak-to-peak voltage is large. Therefore, it is possible to determine whether the imaging position on the sample 10 is the upper surface of the substrate or the upper surface of the pattern from the magnitude of the peak-to-peak voltage.

The XY stage 15 on which the sample 10 is placed is two-dimensionally moved on the XY plane (reference plane) by a driving device 150 having a motor or the like. The X-axis and Y-axis interferometer systems 14a and 14b irradiate the reflecting surfaces of the movable mirrors 13a and 13b fixed to the upper end portions of the XY stage 15 with a laser beam for measuring the length, and the Position, that is, XY of the surface of the sample 10 on the optical axis of the objective lens 11.
A position (coordinate value) on the plane is detected, and a position signal indicating the detected coordinate value is input to main controller 20.

The main controller 20 receives signals from the focus detecting means of the optical system 12 according to the in-focus state, position signals from the X-axis and Y-axis interferometer systems 14a and 14b, and the light receiving element 50a. , 50b, 51a, and 51b are input, and control signals are output to the drive device 150 and the display device 21. The main controller 20 has the following six functions.

The first function is the X-axis interferometer system 14
While monitoring the X-axis and Y-axis position signals from the a and Y-axis interferometer system 14b, a control signal is input to the driving device 150 to two-dimensionally move the XY stage 15 at predetermined intervals. , At each stop position of the XY stage 15, the output signal (the output before the autofocus operation) of the focus detection means of the optical device 12 is read, and due to the deviation from the in-focus position d ₀ (zero voltage value), it is moved to the optical axis. The height of the surface of a certain sample 10 in the Z direction is detected, and the coordinate values indicated by the position signals from the interferometer systems 14a and 14b (these coordinate values correspond to the position on the optical axis of the objective lens 11 on the surface of the sample 10). The height detection function of the surface of the sample 10 is stored together with the above.

The second function is to obtain an S-shaped curve signal by moving the objective lens 11 of the optical device 12 up and down by about several microns at each stop position, and determine whether each height measurement point is the upper surface of the substrate or the upper surface of the pattern. It is a sample surface discrimination function that discriminates whether or not it is by comparing the peak-to-peak voltage magnitude of the S-curve signal obtained at each stop position with a threshold value stored in advance.

A third function is, when the height measurement point is determined to be the upper surface of the pattern, the thickness d ₁ of the pattern stored in advance from the height of the sample surface measured by the first function. When the height measurement point is determined to be the upper surface of the substrate by subtraction, the height measured by the first function is used as the corrected height of the sample surface. The fourth function complements a predetermined interval (between height measurement points) from the relationship between the height of the sample surface corrected by the third function and the coordinate value of the height measurement point to bend the sample surface. This is a flexure shape detection function that detects the shape and stores it together with the position of the XY stage 15.

The fifth function is a gradient calculation function for calculating the gradient of the sample surface at the position of the edge of the pattern from the bending shape of the sample surface detected by the fourth function.
The sixth function is a pattern position correction function that calculates the correction amount based on the gradient calculated by the fifth function and corrects the position of the edge of the pattern. The operation of the pattern position measuring device according to the embodiment of FIG. 1 configured as described above will be described with reference to the flowchart of the main controller 20 shown in FIG.

The main controller 20 monitors the position signals from the X-axis and Y-axis interferometer systems 14a and 14b in response to a measurement start command from an input device (not shown), and the XY stage 15 is initialized. A drive command is issued to the drive device 150 so that the drive device 150 comes to the position (step 101). As a result, the height measurement point 31a shown in FIG. 4 comes on the optical axis of the objective lens 11 of the optical device 12. The main controller 20 measures the height of the surface of the sample 10 at the height measurement point 31a by reading the output voltage before the autofocus of the focus detection means of the optical device 12 works (step 10).
2). Further, the objective lens 11 of the optical device 12 is moved up and down by about several microns to obtain the S curve signal at the height measurement point 31a. The peak-to-peak voltage magnitude of this S-curve signal is compared with a predetermined threshold value to determine whether the surface of the sample 10 at the height measurement point 31a is the substrate upper surface or the pattern upper surface. Sample 10 at height measurement point 31a
When the surface is discriminated as the pattern upper surface, the height d is corrected by subtracting the pattern thickness d ₁ from the measured height.
When the sample surface at the height measurement point 31a is determined to be the upper surface of the substrate, height correction is not performed, and the measured height is set as the corrected sample surface height (step 103). Main controller 20 stores the height of the surface of sample 10 after the height correction together with the coordinate values indicated by the position signals of interferometer systems 14a and 14b at this time.

Further, the main controller 20 sequentially moves the XY stage 15 in steps to set height measurement points 31b to 31.
The height of the surface of the sample 10 at z (see FIG. 4) is measured. Then, similarly to the case of the height measurement point 31a, it is determined whether each height measurement point is the pattern upper surface or the substrate upper surface, and the height of the surface of the sample 10 after the height correction is obtained according to the determination result. , The height measurement points are stored together with the coordinate values indicated by the position signals of the interferometer systems 14a and 14b when the height measurement points are on the optical axis of the objective lens 11.

Next, the main controller 20 determines the height of the sample 10 surface after the height correction at the height measuring points 31a to 31e (see FIG. 4) arranged in the X direction from the relationship between the height and the coordinate value of the surface of the sample 10. The bending shape on the line 32a in the X direction (see FIG. 3) is approximated by a quartic equation of z = a ₁ X ⁴ + a ₂ X ³ + a ₃ X ² + a ₄ X + a ₅ . z, unknowns a ₁ ~a against the five data X ₅ is the quartic because among 5 uniquely determined.

In this way, the height measuring points 31f to 31j in the X direction and the height measuring points 31k to 31 in the X direction are sequentially performed.
For the height measurement points 31q to 31u in the p and X directions and the height measurement points 31v to 31z in the X direction, a fourth-order approximation formula of the flexure shape is obtained. Further, the height measurement points 31a arranged in the Y direction
Similarly, for 31v, the bending shape of the line 32b (see FIG. 4) in the Y direction is approximated by a quartic equation of z = a ₁ Y ⁴ + a ₂ Y ³ + a ₃ Y ² + a ₄ Y + a ₅ .

In the same manner, the height measuring points 31b to 31w in the Y direction and the height measuring points 31c to 31 in the Y direction are sequentially performed.
For the height measurement points 31d to 31y in the x and Y directions and the height measurement points 31e to 31z in the Y direction, the quaternary equation of the bending shape is obtained. As a result, as shown in FIG. 5, the bent shape of the surface of the sample 10 is obtained (step 104).

Next, the main controller 20 operates the XY stage 1
After returning 5 to the initial position, control the drive device 150,
The XY stage 15 is sequentially moved from the initial position. When the spot light from the optical device 12 is relatively scanned, an edge detection signal is output from the light receiving elements 50a, 50b, 51a, 51b (step 105). The main controller 20 controls the interferometer system 14 when the edge of the pattern is detected.
The position of the XY stage 15 when the edge detection signal is output is read from the position signals of a and 14b (step 106).

For example, assume that edge detection signals are output at the pattern edge positions 33a and 33b in FIG. Coordinate values corresponding to the positions of the pattern edge positions 33a and 33b are read from the interferometer systems 14a and 14b and stored. The main controller 20 has an X coordinate value equal to the X coordinate value of the pattern edge position 33a, and the pattern edge position 33a of the previously calculated quaternary approximation formula
Then, gradients _{X X3} and θ _X4 in the X direction at the height measurement points 33c and 33d on the approximate expression adjacent to are calculated. This gradient θ _X3 ,
θ _X4 can be obtained by differentiating the previously calculated fourth-order approximation formula and substituting the X coordinate value.

If the positional relationship between the pattern edge position 33a and the height measurement points 33c and 33d is as shown in FIG. 4, the gradient θ _X1 in the X direction at the pattern edge position 33a is obtained.
Is proportional to θ _X1 = (l ₂ θ _X3 + l ₁ θ _X4 ) /
It is calculated as (l ₁ + l ₂ ). The gradient θ _X2 in the X direction at the other pattern edge position 33b is similarly calculated.

Further, the gradients Y _Y1 and θ _{Y2 in the} Y direction are calculated in the same manner. Then, the pattern edge position 33
correction amounts (tθ _X1 / 2), (tθ _Y1 /
2), (tθ _X2 / 2), (tθ _Y2 / 2) are calculated. However, t is the thickness of the sample 10 (see FIG. 6). Then, the positions of the pattern edges detected by the interferometer systems 14a and 14b are corrected by this correction amount. Here, the bending shape in the line 32c in the X direction where the pattern edge positions 33a and 33b are located is considered to be an arc shape with the point O as the center, as shown in FIG.

The correction amount is such that the neutral surface 10 'does not expand or contract,
Since the dimensional change amount of the sample 10 due to the deformation of the neutral surface 10 'is very small, it can be ignored and can be immediately obtained from the gradient. The distance between the pattern edge positions 33a and 33b includes an error of t (θ _X1 −θ _X2 ) / 2 as compared with the case where the sample 10 is placed on the ideal plane. However, as shown in Fig. 6, θ _X1 and θ _X2 are for sample 1
When the slope of 0 is rising to the right, it is positive, and when it is rising to the left, it is negative. In this case, the pattern edge positions 33a and 33b
The distance between and is measured long if the gradient difference (θ _X1 −θ _X2 ) is positive, and short if (θ _X1 −θ _X2 ) is negative. Even if the sample 10 is tilted with respect to the horizontal plane, the error is calculated from the difference between θ _X1 and θ _X2 , so the tilt is canceled. The same applies to the correction value of the coordinate in the Y direction.

The coordinate values corrected in this manner are used for the sample 1
0 It is very close to the coordinate value when the surface is not deflected. Therefore, the main controller 20 includes the light receiving element 50a,
Based on the coordinate values corrected by the above-described coordinate values indicated by the position signals of the interferometer systems 14a, 14b when the edge detection signals of 50b, 51a, 51b are generated, the edge interval and the like are obtained and displayed on the display device 21. ..

In the present embodiment, the distance between the reference plane and the virtual sample surface (pattern upper surface) is detected at 25, but the number of positions to be detected is not limited to this, and it is desired to reduce the approximation error of bending. You can increase the number. In this case, it is necessary to increase the order of the approximate expression. Further, the approximate expression of the flexure shape is not limited to the high-order expression, and any expression can be used. Further, as a method of approximating the bending shape, a curved surface may be approximated by an appropriate function of z = f (x, y). In this case, no matter where the position of the pattern edge is, it is not necessary to use proportional distribution as in the embodiment, but the gradient can be immediately obtained by differentiating the function and substituting the XY coordinate values. ..

In this embodiment, the height of the surface of the sample 10 is detected based on the signal output from the focus detecting means, but the present invention is not limited to this. For example, the vertical movement amount of the objective lens 11 may be read by a means such as an encoder, an interferometer, or a potentiometer. Further, not only the vertical movement amount of the objective lens 11 but also a Z stage that vertically moves in the Z direction may be provided on the XY stage 15, and the vertical movement amount of the Z stage may be read.

It is needless to say that a photoelectric microscope for scanning the image of the pattern edge formed by the objective lens 11 using a vibrating slit or the like can be used as another edge detecting means. Furthermore, it goes without saying that the bending of the sample to be measured is not limited to the arcuate shape shown in the embodiment, and the position of the pattern can be corrected even if it is deformed in any shape.

In the present embodiment, it is determined whether the height measurement point is the upper surface of the substrate or the upper surface of the pattern based on the magnitude of the peak-to-peak voltage of the S curve signal. You may make it discriminate | determine from a board | substrate upper surface or a pattern upper surface from the information of the obtained video signal. Further, when the height measurement point is determined to be the pattern upper surface, the pattern thickness d ₁ is subtracted from the height of the pattern upper surface, and when the height measurement point is determined to be the substrate upper surface, the measured height is measured. The height is corrected as the height of the sample surface after correction, but the height correction method is not limited to this, and the correction amount can be arbitrarily determined based on the pattern thickness. Needless to say.

[0031]

As described above, the pattern position measuring apparatus of the present invention measures the height of the sample surface, determines whether the height measurement point is the substrate upper surface or the pattern upper surface, and responds to this determination result. The height of the sample surface measured by the correction is corrected based on the thickness of the pattern, and the deflection shape of the sample surface is detected from the corrected height of the sample surface. A bending shape detection error can be eliminated, and an accurate bending shape can be detected.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment of a pattern position measuring device according to the present invention.

FIG. 2 is a flowchart of a main controller 20 used in FIG.

FIG. 3 is a diagram showing an example of an S-shaped curve signal.

FIG. 4 is a diagram illustrating a procedure for obtaining a deflection measurement position on the sample surface and a gradient on the sample surface.

FIG. 5 is a diagram showing an example of a bent shape of the sample surface obtained by approximation.

FIG. 6 is an explanatory diagram showing an example of bending of a sample.

[Explanation of symbols]

 11 Objective Lens 12 Optical Devices 14a, 14b Interferometer System 20 Main Controllers 31a-31z Height Measurement Points 50a, 50b, 51a, 51b Light-Receiving Element

Claims (1)

[Claims] 1. A pattern position measuring apparatus, wherein a sample having a precision pattern of a predetermined thickness formed on a top surface of a substrate is placed on a stage, and an edge of the pattern is detected to obtain a position of the pattern. Height measuring means for measuring the height of the surface at predetermined intervals, sample surface determining means for determining whether the height measuring point is the substrate upper surface or the pattern upper surface, and based on the output of the sample surface determining means A height correcting means for correcting the height of the sample surface measured by the height measuring means, and a bending shape for detecting a bending shape of the sample surface from the height of the sample surface corrected by the height correcting means Detecting means, gradient calculating means for calculating the gradient of the sample surface at the edge position of the pattern from the bending shape detected by the bending shape detecting means, and based on the output of the gradient calculating means And a pattern position correcting means for correcting the position of the pattern.