JP2000056236A - Focusing device, focusing method, optical constant measuring instrument and microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently and automatically perform focusing operation by provid ing a means for outputting a focusing signal based on the spreading of photodetecting area of reflected light. SOLUTION: One part of reflected light from the surface of a sample 3 is transmitted through a half mirror 9 and such a part is reflected on a half mirror 11, guided through a condenser lens 12 to a beam splitter 13 and guided from there to an A sensor 14 and a B sensor 15 constituting of array sensors. On the opposite side of a light source 8 of the half mirror 9, a sensor 16 (I sensor) is provided as a light quantity detecting means for detecting the quantity of light in proportion to the total emitted light quantity of coherent light from the light source 8. The quantity of coherent light from the light source 8 detected by the I sensor 16 is remarkably changed at a focusing position or extremely nearby position. By grasping this change, the focusing position can be exactly detected. The control of a motor is performed while using a computer based on signals from these A and B sensors 14 and 15 and I sensor 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focusing device and a focusing method used for focusing light from a light source to focus on an object surface, and an optical constant of a sample by measuring reflected light from the sample. The present invention relates to an optical constant measuring device for determining an optical constant of a thin film formed on a sample surface, and a microscope using the same.

[0002]

2. Description of the Related Art In an apparatus using light from a light source, for example, coherent light such as laser light, it is often required to accurately focus on a desired position when converging the light. For example, there is known a technique in which a light beam such as a laser beam is converged and irradiated on a sample surface to measure the thickness of a single-layer or multi-layer thin film provided on the sample surface (Japanese Patent Laid-Open No. 17505/1991). Hereinafter, the BPR method (Beam
Profile Reflectometry). ). This BPR method irradiates light from various angles θ by irradiating the thin film with a convergent light beam or a divergent light beam,
The light intensity distribution (reflectance distribution) in the light beam of the reflected light from the thin film (reflected light from the front and back surfaces of the thin film and light emitted from the front surface after being scattered in the thin film) is detected as a distribution related to the incident angle θ. In a method of obtaining optical characteristic values such as a film thickness, a refractive index, and an attenuation coefficient of a thin film or a substrate based on a detected distribution, for example, the detected distribution is calculated based on a theoretical value at a predetermined film thickness of a specific film. The optical characteristics such as the film thickness of the thin film to be measured are calculated by comparing the above distribution with the distribution at which film thickness is matched.

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. Therefore, first, it is required that the in-focus position is accurately adjusted to a desired position.

In addition to the thin film thickness measuring technique as described above, in a measuring technique that requires focusing, if the focus position can be easily, quickly and accurately adjusted to a desired position, various methods can be used. This is a useful technique in the field of

Further, a measurement technique using an objective lens,
In particular, in a technique of measuring using a specific objective lens from among a plurality of objective lenses according to a measurement target, it is extremely convenient to be able to automatically and automatically detect which lens is currently used. Often.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to make it possible to accurately, easily and quickly focus light, and to precisely adjust a focus to a desired position. Accordingly, it is an object of the present invention to further improve the accuracy of various measuring devices, to allow various devices using coherent light to exhibit desired performance, or to further enhance performance.

Another object of the present invention is to enable the above-mentioned focusing operation to be performed efficiently and automatically.

Another object of the present invention is to make it possible to accurately and automatically grasp the type of an objective lens used in a measuring apparatus using the objective lens by utilizing the method according to the present invention. It is to make.

[0009]

In order to solve the above-mentioned problems, a focusing apparatus according to the present invention comprises a light source, and a light source for guiding light from the light source to a surface of an object and at least one of reflected light from the object surface. A first optical system that guides a portion to light detection means, and a focus signal based on the spread of a light detection area of the reflected light in the light detection means when the object is relatively displaced with respect to the first optical system. And a first focus signal output unit for outputting the first focus signal.

In this focusing apparatus, for example, the light source outputs coherent light, the coherent light from the light source is guided to the surface of an object, and at least a part of light reflected from the object surface is converted to the light source. A second optical system that is incident on the light source, a light amount detecting unit that detects an amount of emitted coherent light from the light source, and a light amount that is detected by the light amount detecting unit when the object is relatively displaced with respect to the second optical system. And a second focus signal output unit that outputs a focus signal based on the second focus signal.

Further, the focusing device has an actuator for relatively displacing the object with respect to at least the first optical system, and the operation of the actuator is performed by the first optical system.
It is preferable to be linked with the output of the focusing signal output means. By having such an actuator,
Focusing operation can be easily automated.

When the distance between the object and the first optical system is sufficiently larger than the in-focus state, the actuator is operated at a first operating speed in a direction to reduce the distance, and It is preferable that the operating speed is switched to a second operating speed lower than the first operating speed based on a change in the output of the focusing signal output means.
By performing such control of the operation speed, the operation is quickly performed at the first operation speed to a position very close to the focal point, the operation time for focusing is reduced, and the second operation is performed at a slower speed. It is operated at the speed and adjusted to the in-focus position with high accuracy. That is, both efficient focusing operation and accurate adjustment to the focused position are achieved.

Further, in the focusing method according to the present invention, the first optical system guides light from the light source to the surface of the object and guides at least a part of the light reflected from the object surface to the light detecting means. A focus position is determined based on a spread of a light detection area of the reflected light in the light detection means when the object is relatively displaced with respect to the first optical system.

Further, the optical constant measuring apparatus according to the present invention comprises an irradiation optical system for irradiating convergent light or divergent light to the surface of the sample, a light receiving optical system for guiding the convergent light or divergent light reflected from the sample, and a light receiving optical system. A measuring head having a light intensity distribution sensor for detecting a light intensity distribution in a light beam of the reflected light guided by the light receiving optical system, and the light intensity distribution sensor when the sample is displaced relative to the measuring head. First focus signal output means for outputting a focus signal based on the spread of the light detection area of the reflected light; and an optical constant of the sample based on the light intensity distribution in the light beam detected by the light intensity distribution sensor. Alternatively, an optical constant calculating device for calculating an optical constant of the thin film formed on the surface of the sample is provided.

The microscope according to the present invention comprises a focusing device or an optical constant measuring device as described above.

Further, the optical device provided with the objective lens according to the present invention provides a light source, and guides light from the light source to a surface of an object via the objective lens and transmits at least a part of reflected light from the object surface. An optical system for guiding the light to the light detecting means via the objective lens; and an objective lens determining means for determining the type of the objective lens based on the spread of the reflected light from the exit pupil of the objective lens on the light detecting means. It is characterized by having.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with preferred embodiments. FIG. 1 shows a basic device configuration of an optical device incorporating a focusing device according to an embodiment of the present invention, and FIG. 2 shows a configuration of a main part of the optical system.

1 and 2, reference numeral 1 denotes an entire optical device such as a microscope, which focuses on a surface of a sample 3 as an object placed on a stage (sample stage) 2. . The stage 2 is moved up and down by a motor 4 as an actuator, and the driving of the motor 4 is controlled by a motor controller 6 via a motor driver 5. That is, the motor 4 as an actuator displaces the sample 3 relatively to the optical system described below.

The optical system (first optical system) 7 has a light source 8 (for example, a laser light source that outputs a laser beam as coherent light). A part of the light reflected from the surface of the sample 3 is guided through the half mirror 9 and partly reflected by the half mirror 11, and is condensed by the condenser lens. The light is guided to a beam splitter 13 via the reference numeral 12, and then guided to an A sensor 14 and an B sensor 15, which are array sensors. The A sensor 14 and the B sensor 15 each constitute light detecting means, each of which is a one-dimensional sensor. By arranging the sensors in directions different from each other, preferably in directions substantially orthogonal to each other, two directions are provided. Is configured to be able to measure the distribution of the amount of light at.

In this embodiment, the half mirror 9
On the opposite side of the light source 8, a sensor 16 (hereinafter, also referred to as an I sensor) is provided as a light amount detecting means for detecting a light amount proportional to the total light emission amount of the coherent light from the light source 8. The light amount of the coherent light from the light source 8 detected by the I sensor 16 greatly changes at the in-focus position or a position very close to the in-focus position according to a principle described later. Therefore, by grasping this change, the in-focus position can be accurately detected. However, this change occurs only at the in-focus position or a position very close to the in-focus position. The motor 4 is controlled by the AB sensors 14 and 15
And using the computer 17 based on the signal from the I-sensor 16.

Now, the focusing apparatus and method according to the present invention use the above-described apparatus and utilize the principle described below. That is, the light reflected by the surface of the sample 3 again passes through the objective lens 10, the half mirror 11, the condenser lens 12, and the beam splitter 13 and strikes the two array sensors (A sensor 14 and B sensor 15).
In such an optical system, when the distance between the sample 3 and the objective lens 10 changes, the A sensor 14 surface and the B sensor 15
The spread (magnitude) of the laser reflected light hitting the surface changes. This change can be known by examining the output signal from the sensor which light receiving element on the array sensor is being irradiated with light. Each light receiving element has an output signal when light is applied, and has no output signal when light is not applied. In practice, an appropriate threshold value is set in advance, and when the output signal value is larger than that value, there is often a signal, otherwise, there is no signal.

The change in such an array sensor is
With respect to the position of the Z-axis (the axis in the direction in which the sample 3 and the objective lens 10 approach and separate from each other), the measurement result is shown as a change in the size (expansion) (indicated by the width) of the light detection area received by the array sensor. 3 is shown. As shown in FIG. 3, for all samples, the magnitude D of the reflected light captured by the sensor
The (spread) is substantially on the curve shown with respect to the shift amount Δ from the focal position of the sample.

By monitoring such a change, the distance between the sample 3 and the objective lens 10 can be reduced to at least the vicinity of the focal point. Then, when the focus can be adjusted to the vicinity of the focal point, the focal point can be detected by monitoring the change amount of the laser light output, which will be described later.

The basic principle of focus detection according to the present invention is schematically shown in FIG. As shown in FIG. 4, when the position of the objective lens 10 is far (for example, 1 mm or more) from the position of the focal point, there is almost no signal output from the array sensor (state A in FIG. 4). There is no signal change of the I sensor 16 with respect to the position change (state a in FIG. 3).

When the objective lens 10 approaches the position of the focal point (for example, 1 mm to about 20 μm), a signal output gradually starts to change with a change in the position of the lens, and the signal output changes with a change in the position of the lens. (State B in the figure). The spread (magnitude) of the signal output due to the reflected light detected by each light receiving element of the array sensor initially appears small (while the objective lens 10 is relatively far from the focal point), As the position changes and the lens approaches the focal point, the spread of this signal output increases (state C in the figure). In the present invention, the extent (change) of the spread of the light detection area in this array sensor is detected.
However, also at this time, the signal has not yet reached the focal point and is separated by a small distance from the focal point, so that there is no change in the signal of the I sensor 16 (the state of b in the figure).

When shifting from the state A to the state B and further to the state C, the magnitude (change) of the spread of the light detection area in the array sensor is detected as follows. . As shown in FIG. 5, assuming that the arrangement of pixels in the array sensor is 1, 2,... I,... J, the output signal of the sensor from the first pixel is examined. At this time, the position of the pixel which first exceeds the noise level or the predetermined threshold level is the i-th position, the position of the last pixel is the j-th position, and the position between the i-th pixel position and the j-th pixel position is By calculating the distance (size) X, the extent of the spread of the light detection area in the array sensor can be detected.

In this example, the size of the spread of the light detection area is determined by the number of pixels having an output exceeding the noise level using the array sensor, but this size is determined by the sensor having a single pixel. Sometimes you can. For example, in FIG. 5, when the total number of pixels of the array sensor is 256 and the output of the 100th to 156th pixels around the 128th pixel (the pixel located on the optical axis) is higher than the noise level, the required value is obtained. Assuming that the best focus state is obtained when the focus state is obtained and the above output is obtained at the 98th to 158th pixels, a single sensor is provided at the position of the 100th or 156th pixel. If the output of this sensor is higher than the noise level, it can be detected that the required in-focus state has been obtained. If a sensor of a single pixel is provided at the positions of the 98th to 158th pixels, Similarly, it can be detected whether or not the best focus state has been obtained. In this manner, the extent of the spread of the light detection area can be achieved by using one or more sensors capable of detecting whether or not the amount of light at a predetermined position away from the optical axis has exceeded a predetermined value. sell.

In the above state, although the position of the focal point has not been accurately reached, it has reached a position very close to the focal point. Up to this position, the objective lens 10 can be brought very close to the focal point based on the spread of the light detection area in the array sensor.

Then, from the above state, fine adjustment is performed to accurately adjust the position of the focal point. That is, in the immediate vicinity of the focal point (for example, about 20
When the position of the lens changes, the signal output of the array sensor greatly changes (for example, the state changes from C in FIG. 4 to D in FIG. 4). At this time, the output signal of the I sensor 16 greatly changes with respect to the change in the position of the lens.
When the change shows a maximum value or a minimum value, it can be determined that the focal point has been reached (state of c in FIG. 4). The fine adjustment to the in-focus position based on the change of the output signal of the I sensor 16 will be described later.

The focusing operation can be performed, for example, as described below by utilizing the change of the output signal of each sensor as described above, whereby the automation can be easily performed. Further, as described below, the operation speed (first operation speed) of the actuator (motor) up to the state of C in FIG. 4 is set relatively high, and the actuator (motor) is moved from the state of C to the in-focus position. By setting the operation speed of the actuator (motor) up to the operation speed (second operation speed) lower than the first operation speed, the adjustment up to the substantially in-focus position can be performed very quickly and easily. And then can be accurately adjusted to the in-focus position. That is, as a whole, the adjustment operation can be accurately performed to the in-focus position while ensuring quickness and easiness.

To exemplify such a series of operations, first, a sample is set, and a start button of a focusing operation is pressed. In response to the operation start command, the stage of the sample is started to move at a constant speed (for example, 0.5 to 1 mm / sec) by the motor in the Z-axis direction while monitoring the signals of the A and B array sensors, and the position of the sample is continuously changed. I will raise it. When the signal near the center of the array sensor starts to increase rapidly (about 0.5 to 1 mm before the focal point), the speed is reduced (for example, 0.2 to 0.3 mm / sec), and the array sensor Measure the spread width of the reflected light to be captured, and refer to Fig. 3 to determine how far to move to reach the in-focus position from the change in width, and to a position slightly before the in-focus position (about 20 µm). Move. If the output signal of the I sensor has not changed, the position of the sample is raised until the signal changes. In the vicinity of the in-focus position, the output signal of the I sensor has a low speed (for example, 0.02
(0.03 mm / sec), and that position is determined as the in-focus position. When the in-focus position is reached, the motor is held and an operation completion signal is sent. By controlling such a series of operations, the focus position can be adjusted accurately, quickly, and efficiently.

In the above, I near the in-focus position
About the focusing operation using the change of the output signal of the sensor,
In particular, the basic principle will be described with reference to FIGS.

FIG. 6 shows a case where a laser light source 21 (laser unit) is used as a coherent light source, and a laser light 22 as a coherent light from the light source 21 is reflected by a half mirror 23.
Is condensed (converged) by the objective lens 24, irradiates the surface of the sample 25 as an object to be measured, and detects the amount of partial laser light transmitted through the half mirror 23 by the I sensor 26. The output of the laser light source 21 is detected by the
8 shows a configuration of a focus indicator modeled on a microscope, which can be photographed at 8.

As shown in FIG. 6, the collimated laser beam 22 enters the optical system of the general-purpose microscope via the half mirror 23, irradiates the sample surface with the laser beam through the objective lens 24, and the I sensor 26 Thus, the amount of emitted laser light can be monitored.

At this time, the laser light 22 emitted from the laser unit 21 returns to the emission part of the laser unit 21 through the objective lens 24 (see FIG. 7). 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,
Light reflected from the sample surface follows the same path as 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 25 is at a height other than the height at which the laser beam 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, the output of the detected laser beam (the amount of light received by the sensor 26) and the position of the sample 25 (the sample 25)
As shown in FIG. 8, there is a characteristic relationship that exhibits a maximum value or a minimum value at the in-focus position. 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 29 having the maximum value or the characteristic 30 having the minimum value is obtained.

By utilizing such properties, the position of the focal point can be detected. That is, when the laser light is applied to the sample surface through the objective lens 24 and the height of the sample 25 is adjusted to a position (height) where the laser light amount received by the sensor 26 changes most, the laser light is accurately applied to the sample surface. Can be collected. That is, it is in focus.

The characteristic as shown in FIG. 8 indicates the difference between the output A of the sensor 26 in the absence of the sample 25 and the output B of the sensor 26 in the presence of the sample 25 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 25 is not under the objective lens 24 (the sample height is sufficiently far) and the sensor output B when the sample 25 is below the objective lens 24, or By calculating the value C of the square of the difference, the fourth power,..., A characteristic curve exhibiting a local maximum value as shown in FIG. 9 can be obtained. C = | AB | or C = (AB) ⁿ , n = 2, 4, 6,...

In FIG. 9, when the height of the sample 25 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. Further, when the height of the sample 25 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 n-th 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.

A signal processing circuit of a focusing position detecting device using the I sensor 26 according to the present invention using the above-described detection principle can be configured as shown in FIG. 10, for example.

In FIG. 10, the configuration of the focus indicator unit 31 and its surroundings is basically the same as the configuration shown in FIG. 6, so that the description is omitted by attaching the same reference numerals as in FIG. A signal from a light amount detection sensor 26 (I sensor) as a detecting means for detecting the light amount of coherent light from a coherent light source is input to an A / D (analog / digital) converter 32 and converted into a digital signal. The signal is input to the arithmetic processing unit 33.

The arithmetic processor 33 calculates the change characteristic of the detected light amount as shown in FIG. Operation (calculation)
The output C is output from an output device 34 such as a display or a printer. From the output characteristics of the output device 34 as shown in FIG. 9, 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.

As described above, the focus position detecting structure using the I sensor as the light amount detecting means uses the A and B array sensors as the first focus signal output means as shown in FIG. By being incorporated together with the optical system (first optical system), a quick, accurate, and efficient focusing operation as described above can be performed. In the configuration shown in FIG. 2, the first optical system and the second optical system using the I sensor
They are configured substantially simultaneously.

In the present invention, the optical constant of the sample or the optical constant of the thin film formed on the sample surface having the configuration using the A and B array sensors as the first focusing signal output means as described above is used. An optical constant measuring device to be obtained can also be configured. Since the configuration and operation of the focusing device using the first focusing signal output means have already been described, the remaining part of the optical constant measuring device will be described with reference to the drawings.

FIG. 11 shows a partial schematic configuration of an optical constant measuring apparatus according to an embodiment of the present invention. In the figure, reference numeral 41 denotes the entire optical constant measuring device, and the optical constant measuring device 41 includes a measuring head 42 and an optical constant calculating device 43. The combination configuration with the configuration having the I sensor is shown in an embodiment of FIG. 20 described later.

The measuring head 42 applies the light 4 to the surface of the sample 44.
5, a light receiving optical system 48 for guiding reflected light 47 of the light 45 from the sample 44, and the light receiving optical system 4.
A light intensity distribution sensor 49 for detecting the light intensity distribution in the light beam of the reflected light 47 guided by 8 is provided.

FIG. 11 shows a sample 44 to be measured, in which a thin film 44b is formed on a substrate 44a. However, a multilayer film composed of a plurality of thin films may be formed. It may be a sample consisting of only the sample. The optical constant in the present invention refers to the refractive index or extinction coefficient when the object to be measured is a substrate, and refers to the refractive index, extinction coefficient or film thickness when the object is a thin film.

The irradiation optical system 46 is directed toward the surface of the sample 44.
Is irradiated. In this embodiment, the laser light source 4
0 (for example, a semiconductor laser light source) is reflected by the half mirror 51, and then a convex lens (condensing lens)
The light is condensed at 52 and irradiated on the sample 44.

In FIG. 11, the irradiated light 45 is
Although the focus light is drawn just on the surface of the sample 44, as shown in FIG. 12, the light may be in the form of a convergent light 45a irradiated on the surface of the sample 44 before reaching the focus. Further, as shown in FIG. 13, after passing through the focal point, the surface of the sample 44 may be irradiated substantially in the form of divergent light 45b. In short, it is sufficient that the light is not parallel light but light that enters the surface of the sample 44 at various angles θ (shown in FIG. 11). However, it is preferable to use the focusing apparatus according to the present invention because the measurement accuracy is higher when the deviation from the in-focus position is accurately grasped.

The light 45 applied to the sample 44 is
Reflected from The reflected light from the sample 44 includes reflected light on the front surface and the back surface of the sample and reflected light after scattering inside the sample. For example, when the optical constant of the thin film 44b formed on the substrate 44a is a measurement target, the reflection of the irradiated light 45 becomes as shown in FIG.
It is performed in the form of multiple reflections.

In FIG. 14, t is the thickness of the thin film 44b,
n ₀ , n ₁ and n ₂ are air, thin film 44b, substrate 4
4a is the refractive index, and r ₁ and r ₂ are the reflectances of light at the boundary between air and the thin film and at the boundary between the thin film and the substrate. The reflectance of this light is P
The following (1) to (4) are different between polarized light and s-polarized light.
It is expressed by an equation.

R _1S = (n ₁ cos θ ₁ −n ₀ cos θ ₀ ) / (n ₁ cos θ ₁ + n ₀ cos θ ₀ ) (1) r _1P = (n ₁ cos θ ₀ −n ₀ cos θ ₁ ) / (N ₁ cos θ ₀ + n ₀ cos θ ₁ ) (2) r _2S = (n ₂ cos θ ₂ −n ₁ cos θ ₁ ) / (n ₂ cos θ ₂ + n ₁ cos θ ₁ ) (3) r _2P = (n ₂ cos θ ₁ −n ₁ cos θ ₂ ) / (n ₂ cos θ ₁ + n ₁ cos θ ₂ ) (4) where the subscripts of S and P mean S-polarized light and P-polarized light, respectively. I do. Θ ₀ , θ ₁ , and θ ₂ are angles with respect to the normal line of the sample surface when light passes through each medium.

Since r ₁ and r ₂ are not generally 0, multiple reflection of light occurs as shown in FIG. In the case of coherent light such as laser light, the total reflectance R in consideration of interference among the multiple reflected light beams a, b, c,... Is expressed by the following equation (5). R = (r ₁ + r ₂ e ^id ) / (1 + r ₁ r ₂ e ^id ) (5) where d is d = (2π / λ) n ₁ t cos θ ₁ (6), t is the thickness of the thin film, λ is the wavelength of light. (5)
When the change of the reflectance with respect to the incident angle θ _{0 in the} equation is plotted, for example, profiles (theoretical reflectance distribution) as shown in FIGS. 15 and 16 are obtained. The distribution of the reflectance with respect to the incident angle θ ₀ changes as the film thickness t changes.

Now, referring again to FIG.
Is reflected by the light receiving optical system 48 to the light intensity distribution sensor 49. In the present embodiment, the light receiving optical system 48 has a lens 52, a half mirror 51, and components and light paths common to the irradiation optical system 46, but is configured by a light path different from the irradiation optical system 46. You may.

The light intensity distribution sensor 49 includes a light receiving optical system 48
Is detected in the light beam of the reflected light 47 that has been guided. That is, it refers to an optical sensor that can measure at least one-dimensional distribution of light intensity, such as an array sensor such as a one-dimensional or two-dimensional CCD or an image intensifier in the cross-sectional direction of the light beam. In addition to the one in which the small single light receiving portion is arranged at least one-dimensionally, the one in which the small single light receiving portion moves in the beam with time is included.

As described above, since the light 45 irradiated on the sample 44 is incident at various angles θ, the light intensity distribution sensor 49 determines the distribution of the light intensity in the light beam with respect to the incident angle θ, and hence the reflectance. Is detected as a distribution.

Based on the detected light intensity distribution in the light beam (for example, reflectance distribution), more specifically, the detected light intensity distribution (reflectance distribution) is compared with the theoretical reflectance distribution described above. Then, the optical constant of the target sample is calculated. This calculation is performed by the optical constant calculation device 43. The optical constant calculation device 43 is composed of, for example, a microcomputer.

In the optical constant calculator 43, FIG.
As shown conceptually in FIG.
For the thin film 44b formed above, the reflectance R with respect to the incident angle θ is theoretically calculated for each film thickness t in advance from the physical model 60 of the thin film 44b as described above. According to this theoretical formula, for example, as shown in a model 61, various reflectance characteristics (characteristic curves) are used with the film thickness t as a parameter.
Is found. Then, as an actual measurement value of the sensor 49, an actual measurement characteristic of the reflectance R with respect to the incident angle θ as shown in the model 62 is detected. Fitting with nonlinear least squares method (curve fitting 63)
, It is possible to calculate (estimate 64) each parameter such as the film thickness. According to this method, even if the thin film is a multilayer film, it can be measured if a physical model and a theoretical curve are obtained.

The present invention relates to an optical constant measuring device 4 having a measuring head 42 and an optical constant calculating device 43 as described above.
1 is configured as one integrated device. From the calculation by the curve fitting, it is possible to obtain the refractive index and the extinction coefficient when the measurement target is a substrate based on the above-described equations (5) and (6). Can determine its refractive index, extinction coefficient or film thickness.

Based on the above-described measurement principle, the above-described measurement head can be incorporated in a microscope. That is, as shown in FIG. 18, the microscope 71 includes a sample stage 72 and
An irradiation optical system for irradiating the surface of the sample 73 mounted on the sample table 72 with the above convergent light or divergent light, a light receiving optical system for guiding the convergent light or divergent light reflected from the sample 73, and the light receiving device The measuring head 74 includes a light intensity distribution sensor that detects a light intensity distribution in the light beam of the reflected light guided by the optical system, and a microscope main body 75 to which the measuring head 74 is attached. The measuring head 74 is configured to be detachable from the microscope main body 75.

Parts other than the measuring head 74 have basically the same configuration as a commercially available microscope. In this embodiment, the objective lens 76, the illumination light source 77 (for example, a white light source), the CCD Imaging camera 7 including a camera and the like
8. An eyepiece 79 is provided.

A more specific structure can be realized, for example, as shown in FIG. In FIG. 19, parts having the same functions as those shown in FIG. 18 are denoted by the same reference numerals as in FIG.

The inside of the microscope 71 is, for example, shown in FIG.
It has a configuration as shown in FIG. In FIG. 20, the measuring head 74 includes a laser light source 80 that emits laser light as light emitted toward the sample 73. After the laser light 81 from the laser light source 80 is reflected by the half mirror 82, Then, the light is condensed by the objective lens 76 and irradiated on the surface of the sample 73. The I sensor 100 described above is provided at a position of the half mirror 82 opposite to the laser light source 80.

In this embodiment, the reflected light from the sample 73 passes through a light receiving optical system having a partly the same optical path as the irradiation optical system.
After passing through the half mirror 82, it is reflected by the half mirror 83, condensed by the condenser lens 84,
After passing through 5, the light intensity distribution in the light beam is detected as a P-polarized component and an S-polarized component by the array sensors 87 and 88 via the beam splitter 86.

In the present embodiment, the detected signal of the light intensity distribution in the light beam is sent to the optical constant calculating device 89, and the optical constant calculating device 89 calculates the signal based on the detected light intensity distribution in the light beam. Therefore, the sample 7
An optical constant of 3 is calculated.

The optical constant calculation device 89 includes a microscope 71
, Or as a set of devices. Therefore, as a microscope device including the optical constant calculation device 89, the optical constant of the sample 73 can be measured based on the above-described measurement principle.

It is also possible to prepare various standard samples whose optical constants are known in advance, and to calibrate with the standard samples to determine the optical constants of the sample 73 to be measured.

Since the measuring head 74 has a compact structure detachable from the microscope main body 75, the measuring head 74 can be easily modified by simply modifying a commercially available microscope.
It is possible to incorporate.

In the embodiment shown in FIG. 11, a white light source 9 is used as an illumination light source, similarly to a conventionally known microscope.
0, a condenser lens 91, a half mirror 92, a CCD camera 93 as an imaging camera, and a relay lens 94 are incorporated.

Further, when viewed with the naked eye with the eyepiece 79, it is not preferable for the laser light to reach the inside of the eyepiece. Therefore, it is preferable to weaken the reaching laser light or to select only the laser light. It is preferable to cut it. As means for selectively cutting only laser light, for example, there is a notch filter (not shown) that reflects or absorbs only light in a wavelength range included in the laser light, and is inserted between the half mirror 83 and the half mirror 92, for example. Then, only the laser beam may be cut by the notch filter so as to be viewed through the eyepiece.

As described above, in the microscope according to the present invention, the small measuring head 74 having the above-described functions is incorporated, that is, the small measuring head 74 is provided in the middle of the optical system of the general-purpose microscope. By inserting, the optical constant of the sample 73 can be measured very conveniently.

As described above, the array sensors 87, 8
8 as the first focus signal output means, and the I sensor 10
By using 0 as the second focus signal output means,
A focus signal can be output quickly and accurately.

In an optical device such as the one described above, for example, a microscope, when measuring the thickness of a sample, for example, an array sensor detects a reflected light intensity distribution pattern captured by a predetermined objective lens. At this time, if the objective lens is different, an erroneous measurement result will result. Therefore, when the array sensor detects the reflected light intensity distribution pattern, it is necessary to check that the pattern is from a predetermined objective lens. In order to realize this, it is easy to attach a mark (silver paper, etc.) to a predetermined objective lens attached to the microscope, detect it (with a photo sensor, etc.) and confirm that it is the predetermined objective lens. Can be considered. However, in such a method, a new detection mechanism is added, leading to an increase in cost, and a malfunction may be caused due to a misplacement of a mark or dirt or peeling due to long-term use.

The present invention also focuses on such a problem and provides an optical device that can easily and reliably detect a predetermined objective lens by utilizing an optical difference between objective lenses. That is, a light source, and an optical system that guides light from the light source to an object surface via an objective lens and guides at least a portion of reflected light from the object surface to light detection means via the objective lens. An optical apparatus comprising: an objective lens determination unit configured to determine a type of the objective lens based on a spread of the reflected light from an exit pupil of the objective lens on a light detection unit.

Specifically, when the collimated light is incident on the objective lens and focused on the sample surface, that is, when focused, the reflected light from the sample surface returns to the objective lens again, and And exits from the exit pupil of the objective lens. At this time, utilizing the fact that the pupil diameter of a commercially available objective lens varies depending on the magnification, the objective lens is identified by examining the size (spread) of the pupil image.

In an optical device having an array sensor as described above, the image of the exit pupil of the objective lens is projected onto the array sensor surface using a lens, and the pupil image is projected from the reflected light intensity distribution pattern detected by the array sensor. The size (spread) can be checked.

For example, FIGS. 21 and 22 show the configuration of an optical system in which an objective lens 111 having a magnification A and an objective lens 121 having a magnification B are set. Light from a light source 112 (for example, a laser unit) Is focused by the objective lens 111 or the objective lens 121 via the objective lens 111 and is irradiated to the surface of the sample 114 in a focused state, and the reflected light is again passed through the objective lens 111 or the objective lens 121 via the half mirror 115 and the lens 116 to the array sensor 11.
7, the size (spread) of the pupil image can be checked from the reflected light intensity distribution pattern detected by the array sensor 117.

At this time, the size (spread) of the pupil image detected by the array sensor 117 depends on, for example, the objective lens 111 of magnification A and the objective lens 121 of magnification B.
23 and 24 respectively. That is, the objective lenses 111 and 121 having different magnifications
Are detected as pupil images having different sizes, and the type of the objective lens is easily and accurately determined from the detection results.

An array sensor 117 for detecting the size of the pupil image used for determining the type of the objective lens includes:
The array sensor constituting the first focusing signal output means can be used as it is. The method of checking the size (spread) of the pupil image in the array sensor is the same as the method shown in FIG.

[0083]

As described above, according to the focusing apparatus and method of the present invention, the first focusing signal based on the spread of the light detection area of the reflected light in the light detecting means is output.
By having the focusing signal output means, it is possible to accurately, easily and quickly focus light. By providing a second optical system, a light amount detecting means for detecting the light emission amount of the coherent light of the light source, and a second focusing signal output means for outputting a focusing signal based on the light amount detected by the light amount detecting means. Further, accuracy can be given to an efficient focusing operation. Further, such a focusing operation can be easily automated.

Further, according to the optical constant measuring apparatus according to the present invention, the position of the focal point can be accurately and quickly set to a desired position when obtaining the optical constant of the sample or the optical constant of the thin film formed on the sample surface. In addition, the efficiency of measurement can be improved and the accuracy of measurement can be improved.

Further, according to the optical device of the present invention,
The type of the objective lens can be accurately confirmed optically, and a malfunction in the measurement can be prevented to improve the reliability and accuracy of the measurement.

A microscope using such an apparatus according to the present invention has good operability, can perform measurement quickly, and has high measurement accuracy and reliability.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a focusing device according to an embodiment of the present invention.

FIG. 2 is a partial configuration diagram of an optical system of the apparatus of FIG.

FIG. 3 is a characteristic diagram showing test results of A and B array sensors in the optical system of FIG. 2;

FIG. 4 is an explanatory diagram showing a change in an output signal of an array sensor and a change in an output signal of an I sensor.

FIG. 5 is an explanatory diagram showing an example of a method for detecting the spread of a light detection area in an array sensor.

FIG. 6 is a schematic configuration diagram showing a configuration of a focus indicator.

FIG. 7 is a schematic configuration diagram showing a path of a laser beam in the apparatus of FIG.

8 is a diagram showing the relationship between the sample height and the amount of light received by a sensor in the apparatus shown in FIG. 6;

FIG. 9 is a relationship diagram between a sample height and a calculated value C.

FIG. 10 is a schematic configuration diagram of a focusing device according to an embodiment of the present invention.

FIG. 11 is a schematic configuration diagram of an optical constant measurement device according to an embodiment of the present invention.

FIG. 12 is a schematic configuration diagram illustrating an example of convergent light applied to a sample.

FIG. 13 is a schematic configuration diagram illustrating an example of divergent light applied to a sample.

FIG. 14 is an explanatory diagram showing a state of multiple reflection on a sample.

FIG. 15 is a characteristic diagram showing an example of S-polarized light reflectance with respect to an incident angle.

FIG. 16 is a characteristic diagram illustrating an example of P-polarized light reflectance with respect to an incident angle.

FIG. 17 is an explanatory diagram illustrating a processing example in the optical constant calculation device.

FIG. 18 is a schematic configuration diagram of a microscope according to an embodiment of the present invention.

FIG. 19 is a configuration diagram showing a more specific external configuration of a microscope according to an embodiment of the present invention.

FIG. 20 is a schematic configuration diagram showing an example of the internal configuration of the microscope of the present invention.

FIG. 21 is a partial configuration diagram of an optical system when an objective lens having a magnification A is attached in the optical device according to an embodiment of the present invention.

22 is a partial configuration diagram of an optical system in a case where an objective lens having a magnification B is attached to the optical device in FIG. 21;

FIG. 23 is a characteristic diagram of a pupil image in the array sensor in the case of FIG. 21;

24 is a characteristic diagram of a pupil image in the array sensor in the case of FIG.

[Explanation of symbols]

Reference Signs List 1 optical device 2 stage (sample stage) 3 sample 4 motor as actuator 5 motor driver 6 motor controller 7 first optical system 8 light source 9, 11 half mirror 10 objective lens 12 condenser lens 13 beam splitter 14 array sensor (A sensor) 15) Array sensor (B sensor) 16 I sensor as light amount detecting means 17 Computer 21 Laser unit (laser light source) as coherent light source 22 Laser light as coherent light 23 Half mirror 24 Objective lens 25 Sample (target object) 26 Sensor (Light Amount Detecting Means) 27 Relay Lens 28 Imaging Camera 29 Characteristics with Local Maximum 30 Characteristics with Local Minimum 31 Focus Indicator Unit 32 A / D Converter 33 Arithmetic Processor 34 Output Device 41 Optical Constant Measurement Constant device 42 measuring head 43 optical constant calculating device 44 sample 44a substrate 44b thin film 45 irradiated light 45a convergent light 45b divergent light 46 irradiation optical system 47 reflected light 48 light receiving optical system 49 light intensity distribution sensor 50 laser light source 51 half mirror 52 Objective lens 71 Microscope 72 Sample table 73 Sample 74 Measurement head 75 Microscope main body 76 Objective lens 77 Illumination light source 78 Imaging camera 79 Eyepiece 80 Laser light source 81 Laser light 82, 83, 92 Half mirror 84 Condenser lens 85 Pinhole 86 Beam splitter 87 , 88 Array sensor 89 Optical constant calculation device 90 White light source 91 Condensing lens 93 CCD camera 94 Relay lens 100 I sensor 111 Objective lens of magnification A 112 Light source 113, 115 Half mirror 114 Sample 1 6 lens 117 array sensor 121 magnification B objective lens

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F065 AA06 AA61 BB22 CC22 DD06 FF04 FF41 GG04 HH04 JJ02 JJ03 JJ05 JJ25 LL04 QQ29 QQ31 2F112 AB07 AB10 CA07 DA09 DA25 DA32 2H051 AA11 AA15 BA52 BA57 CA06 DC02 CB02 AB21 AC18 AC27 AC34 AD05 AD09 AD16 AD34 AD37 AF02 AF14

Claims (10)

[Claims] A light source; a first optical system that guides light from the light source to a surface of an object and guides at least a part of light reflected from the object surface to light detection means; Focusing means for outputting a focus signal based on the expansion of the light detection area of the reflected light in the light detection means when the light detection means is displaced relative to the optical system. apparatus. 2. A light source for outputting coherent light, wherein the second light source guides the coherent light from the light source to a surface of an object and causes at least a part of light reflected from the object surface to enter the light source. An optical system, a light amount detecting means for detecting the light emission amount of the coherent light of the light source, and a focusing signal based on the light amount detected by the light amount detecting means when the object is displaced relative to the second optical system. 2. The focusing device according to claim 1, further comprising a second focus signal output unit for outputting. 3. An apparatus according to claim 1, further comprising an actuator for relatively displacing said object with respect to at least said first optical system, wherein an operation of said actuator is interlocked with an output of said first focusing signal output means. Or 2 focusing devices. 4. The actuator according to claim 1, wherein the actuator is operated at a first operating speed in a direction to reduce the distance when a distance between the object and the first optical system is sufficiently larger than a focused state. 4. The focusing device according to claim 3, wherein the operating speed is switched to a second operating speed lower than the first operating speed based on a change in the output of the first focusing signal output means. 5. A focusing device according to claim 1, wherein said light detecting means comprises a one-dimensional or two-dimensional array sensor. 6. A first optical system that guides light from a light source to a surface of an object and guides at least a portion of light reflected from the object surface to light detection means, and converts the object to the first optical system. A focus position is determined based on a spread of a light detection area of the reflected light in the light detection unit when the light detection unit is displaced relative to the focusing light. 7. An irradiation optical system for irradiating convergent light or divergent light to the surface of a sample, a light receiving optical system for guiding reflected light of the convergent light or divergent light from the sample, and a light receiving optical system for guiding reflected light guided by the light receiving optical system. A measurement head having a light intensity distribution sensor for detecting a light intensity distribution in a light beam, and the spread of the light detection area of the reflected light in the light intensity distribution sensor when the sample is displaced relative to the measurement head. First focusing signal output means for outputting a focusing signal based on the optical constant of the sample or a thin film formed on the surface of the sample based on the light intensity distribution in the light beam detected by the light intensity distribution sensor. An optical constant measurement device comprising: an optical constant calculation device that calculates an optical constant. 8. A microscope having the focusing device according to claim 1. 9. A microscope having the optical constant measuring device according to claim 7. 10. A light source, and an optical system for guiding light from the light source to an object surface via an objective lens and guiding at least a part of light reflected from the object surface to light detection means via the objective lens. And an objective lens determining means for determining the type of the objective lens based on the spread of the reflected light from the exit pupil of the objective lens on the light detecting means.