JPH102721A - Step-difference measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure an object to be measured having the step difference quickly and accurately with a simple constitution by providing the first and second light- detecting means, which output the signals, corresponding to the amount of the reflected light from a surface to be measured, and the third light-detecting means, which is vibrated vertically along an optical axis and outputs the measured step-difference signal of the object to be measured. SOLUTION: The reflected light from an object to be measured 2, which has been transmitted through a polarization beam splitter 4, is divided into two directions with a beam splitter 8 furthermore after the reflection from a beam splitter 7. One is applied into a photodetector 10, through a stop means 11, and the other is applied into a photodetector 12 through a stop means 11. Furthermore, the reflected light from the object to be measured 2 transmitted through the beam splitter 7, enters into a photodetector 21 through a stop means 20 of a light-detecting means 22, which is vibrated vertically, with respect to the optical axis. The signal output corresponding to the intensity of the reflected light from the object to be measured is transmitted to a signal processing means 13. In the signal processing means 13, the output signal of the photodetector undergoes differentiation operation, and the magnitude of the step difference of the object to be measured is measured by using the obtained differentiated signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a step measuring device provided with a light detecting sensor, and more particularly to a step measuring device for quickly and accurately measuring height information of a measurement object having a regular step. .

[0002]

2. Description of the Related Art In a conventional step measuring device, an object to be measured is placed on a stage, and the stage is moved while enlarging and observing a measuring point of the object to be measured through an objective lens by an image pickup device or the like. The step of the measurement object is measured by the focus detection means.

FIG. 7 is a diagram showing a schematic configuration of such a conventional step measuring device. As shown here, an object 2 to be measured is placed on a stage 1 and an object 2
Is illuminated by an illumination system (not shown). On the other hand, the laser beam emitted from the semiconductor laser 3 is reflected by the polarization beam splitter 4,
The light is radiated to the surface to be measured of the measurement object 2 via the 波長 wavelength plate 5 and the objective lens 6. Then, the reflected light from the surface to be measured again enters the polarization beam splitter 4 via the objective lens 6 and the quarter-wave plate 5. At this time, when the light incident on the polarizing beam splitter 4 passes through the quarter-wave plate 5, the polarization direction thereof is shifted by 90 °. Therefore, this incident light can pass through the polarizing beam splitter 4. Further, reflected light from the surface to be measured that has passed through the polarizing beam splitter 4 is transmitted to the first beam splitter 7.
After being reflected by the second beam splitter 8, the light is further divided into two directions. Here, one of the lights passes through the second beam splitter 8 and then enters the light receiving element 10 via the diaphragm means 9 arranged ahead of the converging point P. The other light is reflected by the second beam splitter 8, and then enters the light receiving element 12 through the diaphragm means 11 disposed behind the converging point P. The stop means 9 and the stop means 11 are arranged at the same distance in the forward and rearward directions with respect to the condensing point P, respectively.

Each of the light receiving elements 10 and 12 has a function of transmitting to the signal processing means 13 an electric signal corresponding to the amount of light reflected from the surface to be measured of the object 2 to be measured. FIG. 3A is a diagram showing the change characteristics of the output signals B and A output from the light receiving elements 10 and 12, respectively (F indicates the focal point of the objective lens 6, and the horizontal axis indicates the position of the object 2 to be measured). The position of the measurement surface is shown). The signal processing unit 13 performs a predetermined operation on the transmitted signals A and B, and generates a displacement signal J corresponding to the displacement of the surface of the measurement target 2 to be measured. FIG.
(B) shows the characteristic of the displacement signal J obtained as a result of performing the operation on the signals A and B in the signal processing means 13. Specifically, this displacement signal J
The calculation (AB) / (A + B) is executed on the basis of and is generated.

Next, a displacement signal J is transmitted from the signal processing means 13 to the Z-axis drive circuit 14 in order to focus the objective lens 6 on the surface of the object 2 to be measured. The Z-axis drive circuit 14 can move the objective lens 6 in the direction along the optical axis (the direction of arrow A in the figure) by operating the Z-axis drive means 15 based on the transmitted displacement signal J. Thereby, the relative distance between the stage 1 and the objective lens 6 can be changed. That is, the objective lens 6 can be focused on the measurement surface of the measurement object 2. The movement amount of the objective lens 6 is detected by the Z-axis scale 16 and can be counted by the Z-axis movement amount counter 17 based on the electric signal transmitted from the Z-axis scale 16. In the conventional apparatus, the magnitude of the step of the measurement target 2 is obtained by counting the amount of movement of the objective lens 6 by the Z-axis movement amount counter 17. The stage 1 on which the observation object 2 is placed is provided with a stage driving means 18 and a stage driving circuit 19, whereby the stage 1 can be moved in the direction of arrow B in the figure. .

Hereinafter, a method for measuring the size of the step of the measurement object 2 using the conventional step measuring apparatus having the above-described configuration will be specifically described. First, the stage 1 is moved in the direction of arrow B in the figure to position the surface to be measured, which is to be the reference of the measurement object 2, below the objective lens 6, and the objective lens 6 is moved in the direction along the optical axis. Thus, the focal position with respect to the measured surface is detected (the method of detecting the focal position at this time is as described above). Next, the stage 1 is moved again so that the surface to be measured of the object to be measured 2 having a height different from that of the surface to be measured is located below the objective lens 6, and the objective lens 6 is moved in a direction along the optical axis. Then, the focal position with respect to the measured surface is detected. Then, the movement amount of the objective lens 6 in this process is detected by the Z-axis scale 16, and based on the electric signal from the Z-axis scale 16,
By counting with the axis counter 17, the level difference of the measurement object 2 can be measured.

[0007]

However, when measuring an object having a regular step using the above-described conventional step measuring apparatus, there are the following problems.

FIG. 2 is a view showing a state in which the size of the step of the measuring object 2 is measured using a step measuring device.
At this time, the stage 1 is set for each measurement point of the measurement object 2.
Is stopped and fixed, and the objective lens 6 is moved in the optical axis direction, so that the operation of detecting the focal position at each measurement point of the measurement object 2 becomes necessary. It is not preferable to repeatedly perform such operations, which is very complicated and consumes a lot of time. Furthermore, if complicated operations are involved, the measurement accuracy may be reduced.

In view of the above-mentioned problems of the prior art, the present invention provides a step measuring apparatus capable of quickly and accurately measuring a measuring object having a regular step with a simple structure. The purpose is to provide.

[0010]

In order to achieve the above object, a step measuring device according to the present invention comprises a stage on which a measuring object is placed, and a light from a light source directed to a surface to be measured of the measuring object. An objective lens for irradiating and condensing light reflected from the surface to be measured, first and second light detecting means for outputting a signal corresponding to the amount of light reflected from the surface to be measured,
Signal processing means for outputting a signal for determining the position of the surface to be measured based on an output signal from the second light detection means; and a magnitude of a step of the measurement object vibrating up and down along an optical axis. And a third light detecting means for outputting a signal used to measure the light intensity. Further, in the step device according to the present invention, the third light detection means includes a stop means and a light receiving element arranged at a position where light reflected from the surface to be measured of the measurement object is condensed,
Further, the third light detecting means is provided with a driving means for vibrating the third light detecting means up and down along the optical axis.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to FIGS.

FIG. 1 is a diagram showing a schematic configuration of a step measuring device according to the present invention. The same members as those used in the conventional device shown in FIG. 7 are denoted by the same reference numerals. In the step measuring device of the present invention, in addition to the conventional device, a light detecting unit 22 including a diaphragm unit 20 and a light receiving element 21 is newly added.
A driving unit 23 for vibrating the light detecting unit 22 up and down along the optical axis, and a driving circuit 24 for driving the driving unit 23 are provided.

As shown in FIG. 1, in the apparatus of the present invention, an object 2 to be measured is placed on a stage 1, and a surface to be measured of the object 2 is illuminated by an illumination system (not shown). It has become. On the other hand, the laser beam emitted from the semiconductor laser 3 is reflected by the polarization beam splitter 4 and irradiates the measurement surface of the measurement object 2 via the quarter-wave plate 5 and the objective lens 6. Then, the reflected light from the surface to be measured again enters the polarization beam splitter 4 via the objective lens 6 and the quarter-wave plate 5. At this time, the light incident on the polarization beam splitter 4 is
, The polarization direction is shifted by 90 °. Therefore, this incident light can pass through the polarizing beam splitter 4. Further, the reflected light from the surface to be measured that has passed through the polarizing beam splitter 4 is reflected by the first beam splitter 7 and then further divided into two directions by the second beam splitter 8. Here, one light is
After passing through the second beam splitter 8, the light receiving element 10 is transmitted through a diaphragm 9 disposed in front of the focal point P.
Incident on. The other light is reflected by the second beam splitter 8, and then enters the light receiving element 12 through the diaphragm means 11 disposed behind the converging point P.

Each of the light receiving elements 10 and 12 has a function of sending an electric signal corresponding to the amount of reflected light from the measurement object 2 received to the signal processing means 13. FIG. 3A shows output signals B and A output from the light receiving elements 10 and 12, respectively.
(F indicates the focal point of the objective lens 6, and the horizontal axis indicates the position of the surface to be measured of the measurement object 2). In the signal processing means 13, each of the transmitted signals A, B
Is subjected to a predetermined calculation to generate a displacement signal J corresponding to the displacement of the surface to be measured of the measuring object 2. FIG. 3B shows the characteristic of the displacement signal J obtained as a result of performing the operation on the signals A and B. Specifically, the displacement signal J is calculated based on the signals A and B. (AB) / (A + B) is executed and generated.

Next, a displacement signal J is transmitted from the signal processing means 13 to the Z-axis driving circuit 14 in order to focus the objective lens 6 on the surface of the object 2 to be measured. The Z-axis drive circuit 14 generates a Z signal based on the transmitted displacement signal J.
By operating the shaft driving means 15, the objective lens 6
Can be moved in the direction along the optical axis (the direction of arrow A in the figure). Thereby, the relative distance between the stage 1 and the objective lens 6 can be changed, and the focus of the objective lens 6 can be adjusted on the surface to be measured of the object 2 to be measured. The stage 1 on which the observation object 2 is placed is provided with a stage driving means 18 and a stage driving circuit 19, whereby the stage 1 can be moved in the direction of arrow B in the figure. . The above configuration is the same as that of the conventional device.

On the other hand, the reflected light from the surface to be measured of the object to be measured 2 that has passed through the first beam splitter 7 is transmitted to the stop means 20 of the light detecting means 22 which can vibrate vertically along the optical axis.
Through the light receiving element 21. The light receiving element 21 has a function of transmitting an output signal C corresponding to the intensity of light reflected from the surface to be measured to the signal processing means 13. In the signal processing means 13, as shown in FIG. 5, the output signal C of the light receiving element 21 is subjected to differential operation processing, and the magnitude of the step of the measuring object 2 is measured using the differential signal C 'obtained thereby. You.

Hereinafter, a method of measuring the size of the step of the measuring object 2 having a regular step while moving the stage 1 in such a configuration will be described in detail with reference to FIG.

[0018] First, by driving the objective lens 6 on the basis of the displacement signal J from the signal processing system 13, focusing of the objective lens 6 in the S ₁ side of the object 2 (the state in FIG. 2 (i)).
At this time, since the value of the displacement signal J in S ₁ side is 0, the apparatus of the present invention, as shown in FIG. 3 (b), the origin of the graph is P, later this point P as the reference computation Is performed, the size of the step of the measurement object 2 is measured. Then, while maintaining the position of the objective lens 6 moves the stage 1 to the left in the drawing, to position the S ₂ side of the measurement object 2 on the lower side of the objective lens 6 (the state in FIG. 2 (ii) State). When moving from the state (i) to the state (ii), the light detecting means 22 vibrates up and down with respect to the optical axis by the driving means 23 and the driving circuit 24. In addition, the objective lens 6
Is always incident on the light receiving element 21 of the light detecting means 22, and the vibration speed of the light detecting means 22 is set to be higher than the moving speed of the stage 1.

FIG. 4 shows the light detecting means 2 in the state (ii).
FIG. 4 is a diagram showing the displacement of No. 2 and the manner in which detection light is incident on the light detection means 22. FIG. 5 is a graph showing a signal C output from the light detecting means 22 at this time and a state after the signal C is subjected to a differential operation. 4 and FIG. 5 respectively indicate that the output of the signal C in the state of .about. In FIG. 4 corresponds to the curve C in FIG. When measuring S ₂ side of the measurement object 2 (the state shown in FIG. 2 (ii)), the light detecting means 22 4
Vibrates vertically along the optical axis as in the state-shown, this time, the light receiving element 21 receives the reflected light from S ₂ side, the signal processing means output signal C as shown in FIG. 5 13 is output. When the output of the signal C is equal to or greater than the predetermined value f _th , the signal processing unit 13 performs a differential operation on the signal C. Further, as shown in FIG. 5, when the intensity of the differential signal C ′ of the signal C is within a predetermined value V _th (here, the predetermined value V _th is an absolute value of the differential signal C ′ based on 0). The signal processing means 13 outputs the displacement signal J shown in FIG. 3B, and the apparatus of the present invention measures based on this. The size of the step of the object 2 is obtained. For example, looking at the state in FIG. 5, the signal C is larger than the predetermined value f _th , and the differential signal C ′ of the signal C is within the predetermined value V _th . At this time,
In the apparatus of the present invention, the position of the S ₂ plane (that is, the point Q) corresponding to the displacement signal J shown in FIG. 3B is detected, and the position of the measurement object 2 Step size x
Is calculated.

In the step measuring device of the present invention, the signal processing means 13 obtains the value of (A + B) based on the output signals A and B from the light receiving elements 12 and 10, and sets a predetermined threshold value to this value. The focusing operation range of the apparatus is defined by applying T (see FIG. 6). By doing so, the step measurement range in the device of the present invention is defined, and erroneous detection is prevented.

As described above, when the step measuring device according to the present invention is used, the step measurement of the measuring object 2 can be accurately performed without stopping the stage 1 at each measurement point unlike the conventional device. Further, continuous measurement is possible without driving the objective lens 6 for each step.

[0022]

As described above, according to the present invention, a step measuring apparatus capable of quickly and accurately determining the size of a step of a measurement object having a regular step with a simple configuration. Can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a level difference measuring device according to the present invention.

FIG. 2 is a diagram for explaining a method for measuring a measurement target having a regular step using the step measurement device.

FIG. 3 is a diagram for explaining the operation of a light detection unit 22;

FIG. 4 is a graph for explaining a signal output from a light detection unit 22 and a processing method thereof.

5A is a graph showing characteristics of output signals B and A from the light receiving elements 10 and 12, and FIG. 5B is a graph showing characteristics of a displacement signal J generated based on the signals A and B;

FIG. 6 is a graph for explaining a method of defining a step measurement range and an erroneous detection in the apparatus of the present invention.

FIG. 7 is a diagram showing a schematic configuration of a conventional step measuring device.

[Explanation of symbols]

 Reference Signs List 1 stage 2 object to be measured 3 semiconductor laser 4 polarization beam splitter 5 quarter-wave plate 6 objective lens 7 first beam splitter 8 second beam splitter 9, 11, 20 aperture 10, 12, 21 light receiving element 13 signal processing Means 14 Z-axis drive circuit 15 Z-axis drive means 16 Z-axis scale 17 Z-axis movement counter 18 Stage drive circuit 19 Stage drive means 22 Light detection means 23 Light detection means drive means 24 Light detection means drive circuit

Claims (3)

[Claims] An object lens configured to irradiate light from a light source toward a surface to be measured of the object to collect light reflected from the surface to be measured; First and second light detecting means for outputting a signal corresponding to the amount of reflected light from the measured surface; and a position of the measured surface based on an output signal from the first and second light detecting means. Signal processing means for outputting a signal for determination, and third light detecting means for vibrating up and down along the optical axis and outputting a signal used for measuring the size of the step of the measurement object A step measuring device characterized by being performed. 2. The method according to claim 1, wherein the third light detecting means includes a diaphragm and a light receiving element arranged at a position where light reflected from the surface of the object to be measured is collected. The step measuring device according to claim 1. 3. The apparatus according to claim 1, wherein the third light detecting means includes a driving means for vibrating the third light detecting means up and down along the optical axis. The step measuring device according to the above.