JPH10142492A - Focusing position detecting device and focusing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately and easily detect the focusing position of coherent light by providing a light quantity characteristic output means which outputs variation characteristics of a detected light quantity when a body is displaced relatively to an optical system as characteristics including at least a maximum or minimum value. SOLUTION: Laser light 2 as coherent light from a laser light source 1 is passed through a half-mirror 3, and converged by an objective 4 to t irradiate the surface of a sample 5. A sensor 6 detects the quantity of part of the laser light transmitted through the halfmirror 3. The signal from the sensor 6 is inputted to an arithmetic processor 13, which calculates variation characteristics of the detected light quantity. Its arithmetic output C is outputted from an output device 14 such as a display. When the height of the sample 5 is adjusted to the position (height) where the quantity of the laser light that the sensor 6 receives varies to the largest value, the laser light can accurately be converged on the surface of the sample 5. Namely, the laser light is in focus.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a focus position detecting device and a focusing method used to focus coherent light from a coherent light source and focus on a predetermined object plane.

[0002]

2. Description of the Related Art In an apparatus using coherent light such as laser light, it is often required to accurately focus on a desired position when converging the light. For example, a technique is known in which a light beam such as a laser beam is converged and irradiated on a sample surface to measure the thickness of a thin film provided on the sample surface (Japanese Patent Laid-Open No. 3-17505;
It may be called PR method (Beam Profile Reflectometry). ). The BPR method irradiates the thin film with a convergent light beam or a divergent light beam to irradiate light from various angles θ, and reflects light from the thin film (reflected light from the front and back surfaces of the thin film and scatters in the thin film). And the light intensity distribution (reflectance distribution) in the light beam of the light emitted from the surface after the irradiation is detected as the distribution related to the incident angle θ, and based on the detected distribution, the film thickness, the refractive index, and the attenuation coefficient of the thin film or the substrate. For example, by comparing the detected distribution with a theoretical distribution previously determined for each film thickness, and seeing which film thickness matches the distribution, it is possible to determine the optical characteristics by measuring the distribution. An optical characteristic value such as the film thickness of a certain thin film is calculated.

In such a measurement technique, the more accurately the focal position is adjusted to a desired position, the higher the measurement accuracy is, and the more accurately the film thickness of the thin film can be measured.

[0004] In addition to the technique for measuring the thickness of a thin film as described above, if the focus position for converging coherent light can be accurately and easily adjusted to a desired position, a technique useful in various fields is considered. Become.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to make it possible to accurately and easily detect the in-focus position of coherent light. Improve the accuracy of the measuring device,
Another object of the present invention is to provide a device using coherent light with desired performance or to further enhance the performance.

[0006]

In order to solve the above-mentioned problems, a focus position detecting apparatus according to the present invention comprises a coherent light source, a coherent light from the light source to a surface of an object and a reflection from the object surface. An optical system that makes at least a part of the light incident on the coherent light source, and a detecting unit that detects the amount of light emitted by the coherent light source of the coherent light source, and the object when the object is displaced relative to the optical system. A light quantity characteristic output means for outputting a change characteristic of the light quantity detected by the detection means as a characteristic including at least a maximum value or a minimum value is provided.

[0007] The light quantity characteristic output means may output, for example, the output A of the detection means when the object is absent or is located at a place away from the in-focus position so that the influence of the reflected light from the object is negligible. And a means for calculating and outputting the difference between the output B of the detection means and the power of the difference when the object is present. In this case, if the absolute value of the difference between the output A and the output B is taken, the output of the light amount characteristic output means can always be a positive value. By taking the power of the difference, the rate of change of the output signal can be increased, and the focus can be detected with higher sensitivity. Further, if the power of the difference is raised to the second power, the fourth power,... And the even power, the calculation result can always be a positive value.

The coherent light used in the above-mentioned in-focus position detecting device is not particularly limited, but laser light can be used as the most general coherent light. As the laser light source, a semiconductor laser light source can be used. The output of the used laser beam is preferably 30 mW or less.

The wavelength of the coherent light is preferably in the range of 400 nm to 850 nm which can cover the visible region.

Further, it is preferable that the amount of reflected light incident on the coherent light source, that is, the amount of return light is 0.1% or more and 25% or less of the output of the coherent light from the coherent light source. If the amount is significantly less than 0.1%, the change in the light emission amount of the coherent light source corresponding to the focal position due to the return light is too small. If the amount exceeds 25%, the influence on the coherent light source is too large and the stability may be impaired. There is. In a configuration in which the amount of reflected light is large, if the light reflectance greatly differs for each object, reproducibility and the like may be affected. As a result, the change in the output of the coherent light source caused by the reflected light appears remarkably above a certain level, and the above-described change characteristic of the detected light amount is detected with high accuracy.

Further, the in-focus position detecting apparatus according to the present invention as described above can be incorporated in a microscope using coherent light, for example. For example, BPR as described above
Microscope that enables the measurement of thin film thickness by the
It can be incorporated in a microscope having a light intensity distribution sensor for detecting the light intensity distribution in the light beam of the reflected light from the sample as the measurement object.

Further, the focusing method according to the present invention comprises:
When converging the coherent light from the coherent light source to irradiate the object surface, at least a part of the reflected light from the object surface is incident on the coherent light source, and detects the light emission amount of the coherent light of the coherent light source. A method of extracting a change characteristic of the detected light amount when displaced as a characteristic including at least a maximum value or a minimum value, and setting a position of the object surface exhibiting the maximum value or the minimum value as a focus position. .

In the focus position detecting device and the focusing method as described above, at least a part of the reflected light from the object surface returns (incidents) to the coherent light source, so that the output characteristic of the coherent light source changes. . This change is detected as a change in the amount of coherent light from the coherent light source. Since this change characteristic exhibits a maximum value or a minimum value at the in-focus position according to a principle described later, the position of the object plane corresponding to the maximum value or the minimum value can be accurately detected as the in-focus position.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. First, a basic principle of a focus detection function in a focus position detection device and a focus adjustment method according to the present invention will be described. FIG. 1 shows a case where a laser light source 1 (laser unit) is used as a coherent light source, and a laser light 2 as a coherent light from the light source 1.
Is focused (converged) by the objective lens 4 via the half mirror 3
Then, the output of the laser light source 1 is detected by irradiating the surface of the sample 5 as an object to be measured and detecting the light amount of a part of the laser light transmitted through the half mirror 3 with the sensor 6, FIG. 2 shows a configuration of a focus indicator modeled on a microscope, which can be photographed by an imaging camera 8 via a lens 7.

As shown in FIG. 1, a collimated laser beam 2 is incident on an optical system of a general-purpose microscope via a half mirror 3, and the sample surface is irradiated with the laser beam through an objective lens 4. The emitted light amount of the laser beam can be monitored.

At this time, the laser beam 2 emitted from the laser unit 1 returns to the emission section of the laser unit 1 through the objective lens 4 (see FIG. 2). Here, when the height of the sample is adjusted so that the laser light is most focused on the sample surface, that is, when the focus is adjusted on the sample surface, the reflected light from the sample surface follows the same path as the incident light. .

As a result, when return light from the surface of the sample enters the laser light emitting portion, a large change occurs in the characteristics within the laser resonator, and the output of the laser light changes.

When the sample 5 is at a height other than the height at which the laser light is most concentrated, the reflected light from the sample surface follows a different path from the incident light. Has almost no return light from the sample surface, and the output of the laser light hardly changes.

Accordingly, as shown in FIG. 3, the maximum between the output of the detected laser beam (the amount of light received by the sensor 6) and the position of the sample 4 (the height of the sample 4) is shown in FIG. There is a relation of a characteristic exhibiting a value or a minimum value. In this case, depending on how the characteristics (e.g., oscillation mode, carrier density, mode gain, etc.) in the laser resonator change, either the characteristic 9 exhibiting the maximum value or the characteristic 10 exhibiting the minimum value is obtained.

The present invention makes it possible to detect the position of the focal point by utilizing such properties.
That is, when the laser light is applied to the sample surface through the objective lens 4 and the height of the sample 5 is adjusted to a position (height) where the laser light amount received by the sensor 6 changes most, the laser light is accurately applied to the sample surface. Can be collected. That is, it is in focus.

The characteristic shown in FIG. 3 indicates the difference between the output A of the sensor 6 in the absence of the sample 5 and the output B of the sensor 6 in the presence of the sample 5 by the light amount characteristic output means of the present invention. It is obtained by calculating and outputting the power of the difference. In particular, the absolute value of the difference between the sensor output A when the sample 5 is not under the objective lens 4 (the sample height is sufficiently far) and the sensor output B when the sample 5 is under the objective lens 4, or By calculating the value C of the square of the difference, the fourth power,..., It is possible to obtain a characteristic curve having a maximum value as shown in FIG. C = | AB | or C = (AB) ⁿ , n = 2, 4, 6,...

In FIG. 4, when the height of the sample 6 is slightly changed, as indicated by a point X, if the value C increases, the in-focus position is located ahead of the moving direction. When the height of the sample 6 is slightly changed, as in the case of the point Y, if the value C becomes smaller, the in-focus position is in the direction opposite to the moving direction. Therefore, the direction of the region where the focus position exists can be easily grasped, and the focus position can be easily adjusted.

Further, by performing the nth power calculation as described above, the rate of change of the signal can be expanded, and the focus can be detected with high sensitivity. As described above, the moving direction for detecting the focal point can be easily found, and the point of the maximum value of the calculated value C can be easily and accurately detected as the focal point.

The signal processing circuit of the in-focus position detecting device according to the present invention using the above-described detection principle can be configured as shown in FIG. 5, for example.

In FIG. 5, the configuration of the focus indicator unit 11 and its surroundings is basically the same as the configuration shown in FIG. 1, so that the description is omitted by attaching the same reference numerals as in FIG. A signal from the light amount detection sensor 6 as a detecting means for detecting the amount of coherent light from the coherent light source is A / D (analog / digital).
The detection signal input to the converter 12 and converted to a digital signal is input to the arithmetic processing unit 13.

The arithmetic processor 13 calculates the change characteristic of the detected light amount as shown in FIG. Operation (calculation)
The output C is output from an output device 14 such as a display or a printer. Therefore, the arithmetic processing unit 13 and the output device 14 constitute a light amount characteristic output unit according to the present invention. From the output characteristics from the output device 14 as shown in FIG. 4, the in-focus position is very easily and accurately grasped, and the surface of the sample (object) is adjusted to the in-focus position with high accuracy.

Such an in-focus position detecting device can be incorporated in a general-purpose microscope as shown in FIG. 6, for example.
The A / D converter 12, the arithmetic processing unit 13 (for example, a microcomputer), and the output device 14 may be incorporated separately into the microscope main body, and may be electrically connected.

In FIG. 6, 31 is the whole microscope, 32 is a sample stage, 33 is a sample, 34 is a focus indicator unit, 35 is a microscope main body, 36 is an objective lens, 37 is an illumination light source, 38 is an imaging camera, and 39 is a contact lens. The glasses are each shown. This focus indicator unit 34
A configuration for measuring the thickness of a thin film based on the BPR method as described above, that is, a configuration having a light intensity distribution sensor for detecting the light intensity distribution in the light beam of the reflected light from the sample may be incorporated.

Further, it is needless to say that the in-focus position detecting apparatus and the focusing method according to the present invention can be applied not only to the above-mentioned microscope but also to any measuring apparatus using coherent light and any other apparatuses.

[0030]

As described above, according to the in-focus position detecting apparatus and the focusing method of the present invention, the output change characteristic of the coherent light source due to the reflected light from the target object surface includes the characteristic including the maximum value or the minimum value. As the focus position is grasped from the change characteristics, it is possible to easily and accurately adjust the focus position.

Further, since the in-focus position detecting device according to the present invention has no movable parts, the structure can be simple and inexpensive.
It can be easily incorporated into existing general-purpose microscopes and the like.
Further, since the detection of the focus position does not depend on the objective lens at all, it can be easily incorporated regardless of the specifications of the microscope.

Further, when a measuring head to which the BPR method is applied is provided, it can be easily incorporated in the same optical system.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a configuration of a focus indicator.

FIG. 2 is a schematic configuration diagram showing a path of a laser beam in the apparatus of FIG.

FIG. 3 is a diagram showing a relationship between a sample height and a sensor light reception amount in the apparatus of FIG. 1;

FIG. 4 is a relationship diagram between a sample height and a calculated value C.

FIG. 5 is a schematic configuration diagram of a focus position detection device according to an embodiment of the present invention.

6 is a schematic configuration diagram of a microscope to which the device of FIG. 5 is applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Laser unit as a coherent light source (laser light source) 2 Laser light as coherent light 3 Half mirror 4 Objective lens 5 Sample (target object) 6 Sensor (light amount detecting means) 7 Relay lens 8 Imaging camera 9 Characteristics having a maximum value 10 Characteristics having a minimum value 11 Focus indicator unit 12 A / D converter 13 Processing unit 14 Output device 31 Microscope 32 Sample table 33 Sample 34 Focus indicator unit 35 Microscope main body 36 Objective lens 37 Illumination light source 38 Imaging camera 39 Eyepiece

Claims (8)

[Claims] 1. A coherent light source, an optical system for guiding coherent light from the light source to a surface of an object and causing at least a part of light reflected from the object surface to enter the coherent light source, and emission of coherent light from the coherent light source Detecting means for detecting an amount, and outputting a change characteristic of a light amount detected by the detecting means when the object is displaced relative to the optical system as a characteristic including at least a maximum value or a minimum value. An in-focus position detecting device comprising light amount characteristic output means. 2. An output A of said detection means when said light quantity characteristic output means is located at a position away from a focus position such that said object is absent or an influence of reflected light from said object is negligible. The in-focus position detecting device according to claim 1, wherein the in-focus position detecting device calculates and outputs a difference or an exponent of the difference from an output B of the detecting unit when the object is present. 3. The in-focus position detecting device according to claim 1, wherein said coherent light source is a laser light source. 4. The wavelength of the coherent light is 400 nm.
The in-focus position detecting device according to claim 1, wherein the in-focus position detecting device is in a range from 850 nm to 850 nm. 5. The combination according to claim 1, wherein the amount of reflected light incident on the coherent light source is 0.1% or more and 25% or less of the output of the coherent light from the coherent light source. Focal position detector. 6. A microscope comprising the in-focus position detecting device according to claim 1. 7. The microscope according to claim 6, further comprising a light intensity distribution sensor for detecting a light intensity distribution in a light beam of a reflected light from a sample as an object to be measured. 8. When coherent light from a coherent light source is converged and irradiated onto an object surface, at least a part of light reflected from the object surface is incident on the coherent light source, and the amount of emitted coherent light from the coherent light source is detected. A change characteristic of the detected light amount when the object surface is displaced is extracted as a characteristic including at least a maximum value or a minimum value,
A focusing method, wherein a position of an object plane exhibiting the maximum value or the minimum value is set as a focus position.