JPH05241077A - Light measuring instrument - Google Patents

Abstract

PURPOSE:To provide the light measuring instrument which removes a flare generated by an optical system and facilitates the alignment of optical elements. CONSTITUTION:The light from a light source 12 is made incident on a condenser lens 16 through a condenser lens 14 and converged on a sample 18. The light passed through the sample 18 is made incident on an objective 20 and converged. Light passed through a pinhole 22 arranged on an intermediate image plane is made incident on a light quantity detection part 24 and its quantity is measured. A black plate 26 for flare light measurement and a black plate 28 for light measurement are arranged selectively at the visual field stop position of the condenser lens 16. The black plate 26 for flare light measurement has a black part 26a with a diameter d2 in its center and also has a light shield part 26b having a circular opening which is concentric with the black part 26a and has a diameter d3=d2X(5-10). Further, the black plate 28 for light measurement has only a light shield part 28a having a circular opening which has a diameter d3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photometric device for detecting the light quantity of an optical microscope.

[0002]

2. Description of the Related Art This photometric device is a device for performing spectrophotometric measurement using a spectral grating and a line sensor placed after a pinhole, and processing the data to measure the film thickness of a thin film on a sample surface and identify a thin film substance. Used in devices, etc.

The optical system of the photometric device, as shown in FIG.
The illumination light emitted from the light source 112 is condensed by the condenser lens 114, passes through the pinhole 116 arranged at the field stop position of the condenser lens 120, and then the shutter 1
It is incident on the condenser lens 120 via 18 and the sample 1
It is focused on 22. The light that has passed through the sample 122 is condensed by the objective lens 124, enters the light amount detection unit 128 through the pinhole 126 arranged on the intermediate image plane, and the light amount is detected. In such a photometric device, a small hole Naoryo type in which an optical aberration is removed by using the same condenser lens as the measuring objective lens is famous. In addition, most commonly used field diaphragms for condenser lenses do not have pinholes.

For photometry, first, the shutter provided in the illumination optical path is closed, and the dark current of the detection system (light receiving element or amplifier circuit) and the light reflected by the sample are passed through the objective lens. The current (disturbance noise) generated by entering the detection system is stored in memory, and this value is subtracted from the value obtained by photometry with the shutter open.

Next, the photometric performance of the type having no pinhole in the field stop will be described. Since the sample is illuminated by the condenser lens over the entire field of view of the objective lens, the image on the intermediate image plane has many flares. This flare was 0.5-3% as measured by the inventor.

In the case of transmission, the measuring method is 1
A glass with a / 10 black part is placed on the sample surface, and a pinhole ⅕ of the black part image is placed on the intermediate image surface to measure the light quantity. F = (light quantity when the black plate is inserted) /
It is calculated by the formula of (amount of light when black plate is removed) × 100 [%]. In the case of incident light, a light absorption box is placed instead of the glass provided with the black portion, the light amount is measured, and the same calculation is performed.

Regarding the relationship between the field stop and flare, the flare becomes smaller as the field stop is narrowed down by the inventor's measurement. This is because the field of view becomes smaller each time the diaphragm is narrowed down without changing the size of the black portion, that is, the illumination field area which is a flare source becomes smaller.

Therefore, it is necessary to keep the illumination field constant for the measurement of flare. Further, in order to measure the flare accurately, the size of the black portion needs to be sufficiently smaller than the illumination field. This is because, of course, there is no black portion at the time of measurement, and the flare is reduced accordingly. Therefore, at Nikko Optics Research Association and ANSI, black diameter / territory diameter = 1/5 to 1
/ 20 is set so that the decrease in flare due to the black portion can be ignored. Also, the ratio of the photometric diameter to the black diameter is such that the lens aberration does not enter the photometric section, so the photometric diameter / black diameter = 1 /
4 to 1/5, the above organization proposes.

Next, flare in the small hole straight-through method will be described. In principle, this method is ideal because it irradiates only the necessary portion and only the light that passes through the necessary portion can be captured. However, in reality, it is difficult to accurately align the pinhole image with the pinhole, and the amount of flare light and aberration light generated by the optical system on the photometric side after passing through the sample is the subject of photometry. 2, the pinhole 126 must be larger than the image of the pinhole 116. That is, the pinhole 126 has a photometric diameter (d) larger than the irradiation spot diameter (s) on the sample surface. Therefore, if there is any light in the zone a in the figure, or the ring zone between the photometric diameter d and the irradiation diameter s, this will be picked up and an error will occur. The light illuminating the part a is not only the light in the room but also the light reflected by the condenser lens or the objective lens on the photometric side as shown in FIG. 3 or transmitted photometrically when the sample is placed on the glass plate or the color of the LCD substrate. For a filter such as a filter on which a filter is printed, there is double reflection of the glass as shown in FIG. Further, in epi-photometry, the photometric objective also serves as the irradiation condenser, so flare is large. Therefore, it is better for the irradiation spot and the photometric diameter to be as close to the same diameter as possible for a small hole. The flare component generated by the lens cannot be measured.

[0010] In addition, Naora Otoga has the drawbacks that it requires the accuracy of light projection measurement and the alignment of the optical axis of the lens on the light measurement side and the accuracy of focusing, which requires time and effort for measurement and complicates the apparatus.

For example, when changing the magnification of the objective lens, the revolver is rotated to change the objective lens, and
Accordingly, the condenser lens must be changed to have the same magnification. By the way, since the click accuracy of the revolver is about 5 μm to 1 μm and the accuracy of the mounting screw of the condenser lens is also about 5 μm to 1 μm, it is necessary to align the centers of both. Further, when the focal depth of the 50 × objective lens is 1 μm, the focusing between the objective lens and the condenser is also in μm unit.

Further, in the measurement such as a color filter coated on the surface of glass, it is necessary when a condenser lens having a long WD in which aberration due to the thickness of glass is corrected is transparent.

[0013]

As described above, in the conventional photometry device of the type having no pinhole, a large amount of flare is added to the photometry value. Even with the improved small hole straight type, the flare is added to the photometric value and the adjustment of the optical alignment is complicated, though not so much as the type without the pinhole.

It is an object of the present invention to provide a photometric device which can remove flare generated in an optical system and can easily adjust alignment of optical elements.

[0015]

A photometric device of the present invention is a device for photometrically measuring light passing through a pinhole arranged at an intermediate image plane position of a microscope, and is a condenser lens for converging illumination light on a sample. A removable black plate having a black portion that forms an image larger than the pinhole on the intermediate image plane is provided at the field stop position of, and when the black plate is arranged from the light amount when the black plate is not arranged, The flare is removed from the measured value by subtracting the light amount of.

[0016]

In the photometric device of the present invention, first, the black plate is inserted into the field stop position of the condenser lens to perform photometry, and the noise component consisting of the dark current and the flare current is measured and stored. Next, photometry is performed with the black plate removed. The value of the noise component stored in memory is subtracted from this measured value. As a result, photometric measurement is performed with flare removed.

[0017]

FIG. 1 shows an optical system of an embodiment of the photometric device of the present invention.
Shown in. A halogen lamp or the like is used as the light source 12 and is driven by a stabilized power supply. The light from the light source 12 enters the condenser lens 16 via the condenser lens 14,
It is focused on the sample 18. The light that has passed through the sample 18 enters the objective lens 20 and is condensed. The light passing through the pinhole 22 arranged on the intermediate image plane is incident on the light quantity detection unit 24 and the light quantity is measured. A flare photometric black plate 26 and a photometric black plate 28 are selectively arranged between the condenser lens 14 and the condenser lens 16 at the field stop position of the condenser lens 16. The flare photometric black plate 26 has a black portion 26a having a diameter d2 at the center thereof. The diameter d2 is given by the following equation, where d1 is the diameter of the pinhole 22.

D2 = d1 × {condenser magnification / photometric objective magnification} × (2 ^{1/2 to} 5) (1) where, condenser magnification = (diameter of black plate of diaphragm) / (diameter of image on sample) is there. Furthermore, the black plate for flare measurement 26
Is concentric with the black portion 26a and its diameter d3 is d3 = d2 × (5
10 to 10) has a light shielding portion 26b having a circular opening. The black portion 26a and the light-shielding portion 26b are made of glass B
It is made by forming a Cr film by vapor deposition. Further, the black plate for photometry 28 is almost the same as the black plate for photometry 26 for flare, except that it has only the light-shielding portion 28a having a circular opening with a diameter d3 and does not have a central black portion. The value of 2 ^{1/2 in} the equation (1) was obtained by an experiment so that the aberration of the optical system can be removed and the flare measurement is not significantly affected.

Next, the procedure of photometry will be described. First,
The black plate 26 for flare photometry is inserted in the field stop position, and dark current and flare (flare including room light around the objective lens)
Measure and store the amount of noise light (current) composed of current. Next, the flare photometric black plate 26 is removed, and instead the photometric black plate 28 is inserted to perform photometry. The previously stored value is subtracted from the measured value. In this way, the light entering the pinhole 22 from the illumination field other than the photometry section is the same whether the black section 26a is present or not, as long as the illumination field diameter is sufficiently large with respect to the area of the black section 26a. To be done.

Although the light from the photometric unit that does not enter the pinhole 22 due to aberrations and the light from the photometric unit that does not enter the middle pinhole of the flare caused by the photometric optical system cannot be photometered. Since the objective lens has almost no aberration in the vicinity of the optical axis by design, there is no problem because the light from the photometric unit and the light entering the pinhole 22 from other than the photometric unit are canceled. Further, flare can be considered in the same manner.

Such an optical system is more accurate than a system that does not use a pinhole. In addition, accurate alignment of the illumination spot and photometric pinhole, such as Naora Otome, is not required unless the pattern of the sample changes once flare is measured.

Even if the condenser lens moves up and down with respect to the sample, the state of the illuminating light beam does not substantially change. Therefore, the focusing of the condenser lens and the objective lens may be rough except during flare measurement.

[0023]

In the photometric device of the present invention, noise (flare) generated in the optical system can be removed, and dark current can be removed by the same operation. Further, it does not require accurate alignment as in the small hole straight-through method, and is easy to operate.

[Brief description of drawings]

FIG. 1 shows an optical system of an embodiment of a photometric device of the present invention.

FIG. 2 shows an optical system of a conventional photometric device.

FIG. 3 is a diagram illustrating a problem that occurs in a conventional device.

FIG. 4 shows a light amount distribution on a sample in the state of FIG.

[Explanation of Codes] 14 ... Condensing lens, 16 ... Condenser lens, 20 ... Objective lens, 26 ... Black plate for flare photometry.

Claims (1)

[Claims] 1. A photometric device for photometrically measuring light passing through a pinhole arranged at an intermediate image plane position of a microscope, wherein a field stop position of a condenser lens for converging illumination light on a sample is located on the intermediate image plane. A black plate with a black portion that forms an image larger than the pinhole is detachably provided, and the light amount when the black plate is placed is subtracted from the light amount when the black plate is not placed A photometric device characterized in that the flare component of is removed.