JPH07325016A - Reflectance measuring apparatus - Google Patents

Abstract

PURPOSE:To carry out measurement for an unknown specimen while the incident angle of luminous fluxes to be measured being set correctly by setting an optical axis correctly by using an adjusting mark having a small hole and a reflection standard mirror before the measurement. CONSTITUTION:An adjusting mark 24 having a small hole 25 is set at a prescribed position in a reflecting optical measuring system 10. At that time, positioning is so carried out by moving the whole body of the reflecting optical measuring system 10 as to make the luminous fluxes to be measured pass the small hole 25. Meanwhile, a reflection standard mirror 21 is set at a position at which a specimen is to be installed. That is, if the angle between the specimen standard face 14 and the impinging light is 30 degrees, the reflection angle of the reflection standard mirror 21 is set precisely at 30 degrees. If there is difference, the reflected light comes out of the impinging light route and impinges against a wall face of the adjusting mark 24 without passing the small hole 25. Consequently, the incident angle of the light to the specimen can be corrected precisely by positioning the reflecting optical measuring system 10 while observing the reflected light of the wall face of the adjusting mark 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring the optical reflectance of a sample, and more particularly to a reflectance measuring apparatus capable of calibrating the incident angle of a measuring light beam on the sample.

[0002]

2. Description of the Related Art Of the optical characteristics of a sample, especially a solid sample, the reflectance is measured not only for the performance evaluation and quality control of optical elements (mirrors, lenses, etc.), but also for samples such as semiconductor materials. In some cases, it is an important measurement method that can obtain useful physical property information from the reflectance measurement.

As a reflectance measuring device, in addition to a dedicated measuring device, as a method for measuring the spectral reflectance characteristic more simply and versatilely, a method in which a special accessory device is attached to a general-purpose spectrophotometer is used. is there.

The reflectance measurement includes a relative reflectance measurement for measuring the reflectance as a relative value with respect to a reference sample and an absolute reflectance measurement for measuring the absolute value of the reflectance without using the reference sample. Several methods are known for each.

FIG. 5 is a diagram showing a schematic configuration of a relative reflectance measuring apparatus. The measurement light flux from the external light source is the first mirror 1
1, the sample S is bent in the sample direction and applied to the sample S.
The reflected light from the sample S is introduced into the external photometric optical system by the second mirror 12. The measurement is performed by alternately measuring the reference mirror S0 prepared in advance and the unknown sample S, and determining the reflectance of the sample S as a relative value with respect to the reflectance of the reference mirror S0.

Another method of measuring reflectance is an absolute reflectance measuring device. The details of the configuration of this method / apparatus are also disclosed in the one already filed by the same inventor as the present application, but basically, in order to make the optical paths completely equivalent during sample measurement and reference measurement, The absolute reflectance of the sample is measured by switching the position and angle of each mirror of the reflectance measuring device without using the reference sample.

Whether the relative reflectance measurement or the absolute reflectance measurement, the reflectance of the sample changes depending on the incident angle of the measurement light beam to the sample. Generally, an angle device is prepared and used properly according to the purpose of measurement.

The reflectance characteristic of the sample is affected by the polarization state of the beam, especially when the angle of incidence of the beam on the sample increases. For this reason, it is general that the reflectance measuring device is provided with a polarizer for keeping the polarization state of the light flux constant.

[0009]

As described above, the reflectance characteristic of the sample depends on the incident angle of the measurement light beam on the sample, and the degree thereof generally increases as the incident angle increases. Further, in the actual reflectance measurement, for example, when the reflectance characteristic of the optical element is to be measured, it is desirable to be able to measure the reflectance in the actual usage state of the element.

Therefore, various angles of incidence on the sample are assumed, and the angle accuracy affects the accuracy of reflectance measurement itself.

However, in the conventional reflectance measuring apparatus, especially in the apparatus prepared as an auxiliary apparatus of the general-purpose spectrophotometer, there is a problem that it is extremely difficult to calibrate the incident angle of the measuring light beam on the sample. It was This is for the following reasons.

One reason is that it is extremely difficult to measure the angle of incidence / reflection of the light beam on the sample. That is, the optical adjustment of this type of device is generally performed by adjusting the position and angle of each mirror so that the center of each mirror or the like that configures the device coincides with the center of the measurement light beam. According to the method, although the entire apparatus can be adjusted, it is not possible to adjust the incident angle itself of the light flux to the sample of interest.

FIG. 6 shows a state in which the incident angle on the sample is deviated from a predetermined angle, although the angle is adjusted by this method as a whole. This example shows the case of a relative reflectance measuring device in which the incident angle of the measurement light beam on the sample is 30 degrees. FIG. 5 shows a state in which the first mirror 11 is deviated from the angle necessary for setting the incident angle of the measurement light beam on the sample to 30 degrees, that is, 60 degrees by 3 degrees.

The optical adjustment is set so that the center of the light beam coincides with the center of each of the first mirror 11, the second mirror 12 and the measurement reference surface 14 regardless of this error of the first mirror 11.

As a result, even if the apparent optical adjustment seems to be perfectly performed, the measurement reference plane 14 is actually shifted to the left by about 7.5 mm from the normal position, and
The incident angle of the measurement light is deviated from the predetermined angle of 30 degrees by about 0.4 degrees. Moreover, there is no method for detecting this deviation (however, the deviation value in this example is a value when the distance between the first mirror and the sample S is set to a predetermined value, and if the distance is further increased, the deviation is The value will be even larger).

Another more serious problem is that the reflectance measuring device is formed by using a reflection optical measuring system as an accessory to the main body device such as a spectrophotometer. Occurs when That is,
Even if the reflection optical measuring system of the reflectance measuring device is used alone, even if it is completely adjusted, when it is attached to a spectrophotometer, etc., the relative relationship between the reflection optical measuring system and the spectrophotometer is It may not be in the ideal state.
It is also conceivable that the optical adjustment on the spectrophotometer side is not perfect enough to meet the required angle accuracy of reflectance measurement.

In these cases, even if the reflection optical measuring system alone is accurately adjusted, the angle of incidence on the sample will deviate from the predetermined angle by mounting it on the spectrophotometer.

FIG. 7 shows a state in which the attached catoptric measurement system is set with the optical axis deviated from the spectrophotometer. This example also shows the case of the relative reflectance measuring apparatus in which the incident angle of the light flux on the sample is 30 degrees, as in FIG.

In the case of FIG. 7, it is assumed that the first mirror 11, the second mirror 12 and the measurement reference surface 14 of the catoptric optical measurement system are all mounted at the position angles as designed and are fixed in this state. As described above, even if the adjustment by the reflection optical measurement system alone is complete, the relative positional relationship between the light source and the reflection optical measurement system is displaced as shown in FIG. 7, and the incident angle on the first mirror 11 is changed. If is deviated by 1 degree with respect to a predetermined angle, an error of 1 degree (incident at 31 degrees, for example) will also occur in the incident angle of the measurement light beam on the sample.

In the conventional reflectance measuring apparatus as described above, in order to make the incident angle to the sample a predetermined value, the optical system of the reflectance measuring apparatus and the optical system of the spectrophotometer are used. In the case of an accessory device, a method of calibrating it including the relative positional relationship with the main body side is also conceivable. However, as a practical problem, it is impossible for the user to carry out the adjustment work, which is difficult even at the time of production at the manufacturer, during installation and measurement.

Therefore, conventionally, the calibration of the incident angle on the sample has been performed by measuring the sample with a known reflectance at a predetermined angle and adjusting the optical system of the apparatus so that the reflectance has a predetermined value. .

However, according to this method, if there is no sample of which reflectance is known at the required angle, adjustment becomes impossible, and the adjustment itself becomes a messy operation while performing the measurement, and it takes a lot of time and time. It took effort.

The present invention has been made in order to solve such a problem, and an object of the present invention is to provide a reflectance measuring apparatus capable of performing measurement in a state where the incident angle of a measurement light beam is correctly calibrated.

[0024]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, in which a light beam incident from a light source into a reflection measuring optical system is attached to a sample reference plane in the reflection measuring optical system. In a reflectance measuring device that is incident on the sample surface to be measured and introduces the reflected light from the sample surface to be measured into a photometric optical system, it is adjustable with a small aperture so that the light beam passes through this small aperture. Adjustable positioning means for attaching the adjustment to the reflection measurement optical system, and is attached according to the sample reference surface instead of the sample to be measured, and the angle formed with the sample reference surface is the incident angle of the incident light beam to the sample reference surface. A reflection reference mirror having a reflection surface set at the same angle, and a light beam passing through an adjustable small aperture attached to the adjustable positioning means passes through the small aperture and is reflected by the reflection surface of the reflection reference mirror. Made me Characterized in that so as to align the optical axis from the position of back the return light Seiteki.

The operation of the reflectance measuring apparatus of the present invention will be described below.

[0026]

In the reflectance measuring apparatus of the present invention, the optical axis of the reflectance measuring system is adjusted to the normal state by performing the optical axis alignment using the adjustable and reflecting reference mirrors having a small aperture before measuring the unknown sample. Set accurately. The optical axis alignment is performed as follows.

An adjuster having a small aperture is set at a predetermined position on the reflection optical measurement system, for example, an incident end position where the measurement light beam from the light source enters the reflection optical measurement system. At this time, the entire reflection optical measurement system is moved so that the measurement light beam from the light source passes through the small aperture for alignment.

On the other hand, the reflection reference mirror is set at the position where the sample is attached. The reflection surface of the reflection reference mirror is such that the light beam incident on the reflection reference mirror when the optical system is set to the ideal state is reflected by tracing the same optical path as the incident light path in the opposite direction. The angle formed by and (the reflection angle) is set. That is, if the angle formed by the sample reference surface and the incident light is, for example, 30 degrees, the reflection angle of the reflection reference mirror is also accurately set to 30 degrees.

When light is incident from the light source with the adjusting and reflection reference mirrors having small apertures attached, the incident light passes through the small adjustment apertures and is reflected by the reflecting surface of the reflection reference mirror. When the reflection measurement optical system is set correctly, the light beam reflected by the reflection reference mirror follows the same optical path as the incident light and passes through the small aperture for adjustment, but is reflected if there is a deviation. The light deviates from the incident light path and hits the adjustable wall without passing through the small aperture. At this time, even if the deviation of the incident angle is small, the deviation is amplified while the light flux travels back and forth in the optical path, so it is easy to know the deviation by observing the position of the reflected light that hits the adjustable wall surface. You can

Therefore, the incident angle to the sample can be accurately calibrated by aligning the reflection optical measurement system while observing the reflected light on the adjustable wall surface, and the reflectance measurement in the accurately calibrated state can be performed. The device can be easily obtained.

[0031]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a main part of a reflection measuring optical system of a reflectance measuring apparatus according to an embodiment of the present invention.
FIG. 2 is an overall view of the reflectance measuring apparatus when the reflection reference mirror and the adjustment are removed in FIG. 1. Also, FIG.
[Fig. 4] is a plan view (a) and a front view (b) showing a reflection reference mirror of the present invention, and Fig. 4 is a plan view (a) and a right side view (b) showing adjustment. The present embodiment described below is for a relative reflectance measuring device whose mechanism is simple and easy to explain, but basically the same configuration is also possible for an absolute reflectance measuring device.

In the figure, 10 is a reflection optical measuring system,
It is used in a state of being inserted between the light source 19 and the photometric optical system 20, and these constitute the reflectance measuring device 1.
The catoptric optical measurement system 10 mainly includes a first mirror 11, a second mirror 12, and a sample positioning portion 13, and the surface of the sample positioning portion 13 on which the sample is in contact is attached to the sample reference surface 14 (this surface). By making contact with the reflectance measurement surface of the sample to be measured, a surface is formed so that the incident light on the sample can be incident at a preset incident angle. As shown in the drawing, in this embodiment, as an example, the case of measuring the reflectance at an incident angle of 30 degrees is shown.

The reference sample 1 is aligned with the sample reference surface 14.
When 5 or the unknown sample 16 is brought into contact, the measurement light can be easily incident on the surface of the sample to be measured at a predetermined incident angle. The reference sample 15 or the unknown sample 16 as a sample to be measured is fixed by a sample pressing arm 17 biased by a spring or the like.

A well-known adjusting mechanism (for example, the center of the entrance / reflection center position) is used to rotate the sample positioning portion 13 at the light reflection position 26 when the sample to be measured is attached, that is, the center of the entrance / reflection. There is provided a structure in which the material positioning portion is supported by a rotation shaft capable of rotating in a plane perpendicular to the plane). Light source 1 of reflection measurement optical system 10
A positioning pin 18a for fixing an adjusting member 24 described later is provided near the end on the 9th side. The positioning pin 18a is
It suffices that the adjusting member 24 be positioned so as to block the optical path when the adjusting member 24 is attached, but for the present invention, it is more effective to provide the adjusting member 24 at a position as far as possible from the light reflection position 26 of the sample to be measured. Therefore, it is attached to the end portion on the light source 19 side.

The reflection reference mirror 21 has a reference surface 22 as shown in FIG. 3, and forms an angle of 30 degrees with respect to the reference surface 22 with a high angle accuracy of about 0.1 degree. The reflecting surface 23 is processed by using the optical element manufacturing technique. The reflection reference mirror 21 is attached so that the reference surface 22 of the reference sample 15 and the unknown sample 16 is brought into contact with the sample reference surface 14 of the positioning portion 13 by the sample pressing arm 17 instead of the reference sample 15 and the unknown sample 16 during the optical axis alignment. The surface 22 is flush with the sample reference surface 14 when mounted.

As shown in FIG. 4, the adjusting member 24 has a base portion,
On the other hand, a small vertical opening 25 is provided in the wall, and a positioning hole 18b is provided in the base.
Is provided. When aligning the optical axes, the positioning pin 18a of the reflective optical system is inserted and fixed in the positioning hole 18b. The small opening 25 of the adjustable 24 is set so that the light flux from the light source 19 passes through the small opening 25 with the adjustable 24 fixed by the positioning pin 18a and the positioning hole 18b.

The operation of the reflectance measuring device having the above structure will be described. First, when performing a normal measurement, the reference sample 15 or the unknown sample 16 is attached to the sample pressing arm 17
It contacts the sample positioning part 13. At this time, the adjuster 24 is removed, and the light flux from the light source 19 is reflected by the first mirror 11 (installed at an angle of 60 degrees with respect to the photometric light flux in this embodiment) as shown in FIG. The light enters the sample to be measured at 30 degrees, is reflected at the same angle, is bent by the second mirror 12 (installed at an angle of 60 degrees with respect to the photometric light beam in this embodiment), and is then sent to the photometric optical system 20. Then, the reference sample 15 and the unknown sample 16 are alternately measured, and the relative reflectance of the unknown sample to the reference sample can be measured from the ratio of these photometric values.

On the other hand, when a reflection measurement optical system, which has been removed from a predetermined position between the light source 19 and the photometric system 20, is newly attached, the optical axis is aligned before the measurement is started. In order to make the incident angle to the sample a predetermined value (30 degrees in this embodiment), the first mirror 11 and the second mirror 1 are set as described above.
2 is 60 degrees with respect to the measurement light beam, and the positioning unit 1
Not only the relative angle of the sample reference surface 14 of No. 3 is accurately determined, but also the relative angles of the light source 19 and the photometric unit 20 with the external optical system are accurately adjusted.

However, when considering the configuration of the reflectance measuring optical system, what is actually required is not all the adjustment of the relative angular relationship with the entire optical system and the optical system outside the device, but the reflection It is understood that the angle of incidence of the measurement light on the measurement sample is determined by the angle of the light beam 30 incident on the sample with respect to the sample reference surface 14, and it suffices that only this portion be adjusted accurately. Therefore, the optical axis alignment is performed as follows.

First, the positioning pin 1 is placed in the positioning hole 18b.
The adjusting member 24 is fixed to the reflection optical system 10 by fitting 8a. At this time, even if the center of the measurement light beam does not exactly coincide with the center of the small aperture, there is no problem because the adjustment will be performed later.

Further, the sample reference surface 1 of the sample positioning portion 13
The reflection reference mirror 21 is attached so that the reference surface 22 of the reflection reference mirror 21 abuts on the surface 4, and is fixed by the sample pressing arm 17. At this time, as shown in FIG. 1, the measurement light beam from the light source 19 strikes the reflection surface 23 of the reflection reference mirror 21.

The small aperture 25 of the adjusting device 24 is mounted at a designed position such that the measurement light beam from the light source 19 such as a spectroscope passes through its center. Due to an error and a relative positional deviation between the reflection measurement optical system 10 and the light source 19, the measurement light flux does not always match.

In this case, the entire reflection measuring optical system 10 is adjusted relative to the light source without adjusting the light source 19 side, and the measurement light beam passes through the center of the small opening 25 for adjustment. To do so.

After passing through the small aperture 25, the measurement light beam travels as shown by arrow A in FIG. 1, is reflected by the first mirror 11 of the reflection measurement optical system 10, travels along the optical path 30, and is reflected by the reflection reference mirror 21. Hit surface 23.

The reflection angle reference mirror 21 has the reference surface 22 (sample reference surface 14) of the reflection reference mirror 21 as described above.
Is processed at a high angle accuracy of 30 degrees with respect to the same surface), and the measurement light beam is reflected by the first mirror 11, but at this time, the measurement light beam is accurately 30 degrees with respect to the sample reference surface 14. If it is incident, this measurement light beam is reflected by the reflecting surface 23 of the reflection reference mirror 21 in the same direction as the incident direction, that is, in the direction of the arrow B, and follows the same path as at the time of incidence, and again for adjustment. The light is emitted from the small opening 25 of 24.

If the incident angle on the reflection reference mirror 21 deviates from a predetermined angle, that is, 30 degrees, the measurement light beam reflected by the reflection reference mirror 21 follows a path deviated from the path at the time of incidence. It returns to the direction for adjustment 24 and hits a position deviated from the center position of the small opening 25.

The degree of non-coincidence, that is, the deviation of the light flux in the horizontal direction is represented by C in FIG. 7. C is the error in the incident angle of the measurement light flux on the reflection reference mirror 21, the adjustment target 24 and the reflection reference mirror. The length is determined by the round-trip distance between the reflective surface 23 of 21 and the reflective surface 23. For example, in the case of a small angle error of 0.1 degree, simple visual measurement or calibration by a reflectance measurement value of a sample with a known reflectance at this angle is completely impossible, but according to the present invention. The reflection angle error is amplified (amplified as the optical path length becomes longer) by two processes, that is, from the adjustment to the reflection reference mirror 21 and back and forth between the incident light path A and the reflected light path B, so that it can be detected easily by visual measurement. Become.

That is, first, the incident angle error of 0.1 degree is
The incident / reflected light by the angle reference mirror 21 doubles to 0.2 degrees. Further, this angular error is multiplied by the round trip distance and further magnified when the size in the horizontal direction when returning to the adjusting 24 is set. For example, as shown in FIG. 1, the distance a + b between the adjustable 24 and the reflecting surface 23 is 10
If it is 0 mm, the horizontal dimension L on the 24 plane for adjustment corresponding to an angular error of 0.1 degree is 2 * (a + b) *.
It becomes tan (0.2 degree), that is, 0.7 mm. This value is large enough to be visually confirmed.

In this state, the sample reference surface 14 of the sample positioning section 13 is adjusted so as to rotate about the light reflection position 26 when the sample to be measured is attached, that is, the center of reflection and reflection. If the return light from the reflection reference mirror 21 is made to coincide with the center of the small opening 25 on the surface, the incident angle on the sample can be easily calibrated to a predetermined angle.

According to this method, the complicated optical adjustment of the reflection measurement optical system 10 is not performed, and even if the relative relationship between the reflection measurement optical system 10 and the external optical system such as the light source 19 is incorrect, By adjusting only the sample reference surface 14 of the reflection measurement optical system 10, the incident angle of the light beam on the sample to be measured can be calibrated to a predetermined angle.

In addition, the adjustment is extremely easy as compared with the conventional method because it has a clear goal of adjusting the reflected return light from the reference mirror 21 to the small aperture 25.

The measuring light flux from the light source for spectroscopic analysis such as a spectroscope generally has a certain spread and may not be suitable as the light source for adjustment of the present invention (the light flux shape on the small aperture 25 is not clear. , If the amount of misalignment cannot be visually confirmed, etc.). In this case, for example, a light source with high straightness such as a laser for adjustment may be installed as the light source 19, and the light source may be adjusted by this light source before switching to the actual measurement light source.

Further, in the present embodiment, the shape of the small opening 25 is a slit shape, but this is to calibrate the incident angle of the measurement light beam on the sample to be measured only within the entrance / reflection surface (uniaxial direction). If you want to calibrate in the plane vertical to the entrance / reflection surface, you can use a small circular aperture.

[0055]

As described above, in the reflectance measuring apparatus of the present invention, by using the adjustable and reflection reference mirrors having a small aperture, the measurement light flux which has an important influence on the accuracy of reflectance measurement is measured. Since the incident angle can be accurately calibrated, it is possible to provide a reflectance measuring device capable of highly accurate measurement.

In particular, in the reflection optical measurement system which is conventionally used by being attached as an accessory device of the spectrophotometer on the user side, the adjustment when combined with the spectrophotometer can be easily and accurately adjusted only by the user. It is a very easy-to-use reflectance measuring device.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a main part of a reflection measuring optical system of a reflectance measuring apparatus that is an embodiment of the present invention.

FIG. 2 is a configuration diagram showing an entire reflectance measuring apparatus which is an embodiment of the present invention.

FIG. 3 is a configuration diagram showing a reflection reference mirror of a reflectance measuring apparatus that is an embodiment of the present invention, FIG.
(B) is the front view.

4A and 4B are configuration diagrams showing the adjustability of a reflectance measuring apparatus according to an embodiment of the present invention, FIG. 4A is a plan view thereof, and FIG. 4B is a right side view thereof.

FIG. 5 is a diagram showing a schematic configuration of a relative reflectance measuring device.

FIG. 6 is a view showing a state in which the incident angle on the sample is deviated from a predetermined angle, although the reflectance is measured as a whole by the reflectance measuring apparatus.

FIG. 7 is a view showing a reflection optical measurement system attached to the spectrophotometer, showing a state when the spectrophotometer is set with its optical axis displaced.

[Explanation of symbols]

 1: Reflectance measuring device 10: Reflection measuring optical system 13: Sample positioning part 14: Sample reference surface 18a: Positioning pin 18b: Positioning hole 19: Light source 20: Photometric optical system 21: Reflection reference mirror 22: Reference surface 23: Reflection Surface 24: Adjustable 25: Small opening

Claims (1)

[Claims] 1. A light beam entering a reflection measurement optical system from a light source is made incident on a sample surface to be measured attached to a sample reference surface in the reflection measurement optical system to reflect light reflected from the sample surface to be measured. In a reflectance measuring device to be introduced into a photometric optical system for measurement, an adjusting device having a small aperture and an adjusting positioning means for attaching the adjusting device to the reflection measuring optical system so that a light beam passes through the small aperture, A reflection reference mirror having a reflection surface, which is attached to the sample reference surface instead of the sample to be measured, and whose angle formed with the sample reference surface is set to the same angle as the incident angle of the incident light beam on the sample reference surface, A light beam that has passed through an adjustable small aperture attached to the adjustable positioning means passes through the small aperture, is reflected by the reflection surface of the reflection reference mirror, and the optical axis is adjusted from the position of the return light that has returned after adjustment. What you did Reflectance measuring apparatus characterized.