JPH0791920A - Optical device for light intensity monitoring - Google Patents

Abstract

PURPOSE:To provide an optical device for monitoring light intensity which lowers optical noise components generated inside the device and reduce the shading of reflection light due to the inclination of processed body. CONSTITUTION:Measuring light emitted out of a light outlet 33a of an optical fiber 33 for light emission passes through a first lens 34 and a half mirror 35, is bundled to be a parallel beam through a second lens 36 and cast on the sample surface of a substrate G for a liquid crystal indicator. The path of the reflection light from the sample surface having passed through the second lens 36 is changed at the half mirror 35, and the light is condensed by a third lens 37, received by a light receiver element 38 and the intensity is detected. The first lens 34 has a diameter satisfying the numerical aperture of the light outlet 33a of the optical fiber 3 for light emission and the second lens 36 has its convex surface on the first lens 34 side. A sample surface and light reception element 38 are arranged in a position conjugate to the second lens 36 and the third lens 37.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to, for example, the end point of surface treatment (for example, development or etching) for removing the surface layer of an object to be processed having a surface layer formed on a substrate. The present invention relates to a light amount monitor optical device used for a surface treatment end point detection device or the like that detects the amount of reflected light from the sample surface with respect to the measurement light irradiated on the sample surface.

[0002]

2. Description of the Related Art For example, a surface treatment for removing a surface layer of an object to be treated having a surface layer formed on a substrate supplies a predetermined treatment liquid to the surface layer while rotating or reciprocating the object to be treated. However, this treatment liquid is uniformly distributed over the entire surface layer. The end point of the surface treatment performed in this way is detected based on the optical measurement result. One of the detection methods is a reflectance measurement method.

As is well known, this reflectance measuring method irradiates a surface layer of a substrate with light containing a wavelength component that can be transmitted through the surface layer and reflects the light at the surface layer or at the interface between the surface layer and the substrate. The amount of reflected light is measured, and the end point of the surface treatment is detected based on the measurement result. That is, the film thickness of the surface layer decreases as the surface treatment progresses, and the light amount of the reflected light changes with the change of the film thickness. Therefore, the end point of the surface treatment is detected based on the change of the light amount of the reflected light. To do.

For example, as shown in FIG. 11A, a surface layer 2 is formed on the main surface of a substrate 1, and a resist layer 3 having a desired pattern is formed on the upper surface of the surface layer 2. The case of detecting the end point of the etching process on the etching region 4 of the processing object X will be specifically described. In the figure, reference numeral 5 is a region (mask region) which is not etched.

As shown in FIG. 1, when a measurement light L _t is applied to the upper surface of the object to be processed X from a light projector (not shown), the measurement light L _t in the etching region 4 is the upper surface and the surface of the surface layer 2. It is reflected on the interface between the layer 2 and the substrate 1, the lower surface of the substrate 1, and in the mask region 5, the upper surface of the resist layer 3, the interface between the resist layer 3 and the surface layer 2, the interface between the surface layer 2 and the substrate 1. And, it is reflected on the lower surface of the substrate 1. Then, the interference light L _RB of each reflected light in the etching region 4 and the interference light L _RA of each reflected light in the mask region 5 are received by a light receiving element (not shown).

By the etching process, as shown in FIG. 11B, the thickness of the surface layer 2 is reduced from the state of the dotted line to the state of the chain double-dashed line. At this time, interference from the mask region 5 occurs. The light L _RA is constant. On the other hand, etching area 4
As shown in FIG. 12, the amount of the interference light L _RB from the etching progresses, that is, the etching region 4 of the surface film 2 advances.
Changes with the decrease in the film thickness.

In FIG. 12, the horizontal axis represents time, and the vertical axis represents the amount of reflected light received by the light receiving element, showing the change in the amount of reflected light with the progress of etching of the surface layer 2. Is. In the figure, symbol A is the amplitude of the vibration formed by the interference light L _RB from the etching region 4, and a is the vibration center thereof. As shown in the figure, the amount of reflected light during the etching of the surface layer 2 is in progress, repeated vibration amplitude A at a substantially constant period, after t _f time, i.e., after the etching is completed The light amount S _f becomes constant. This is because the film thickness of the etching region 4 becomes constant due to the completion of the etching of the surface layer 2.

The end point of the etching process can be detected by detecting the stable time t _f with the light amount S _f based on the above optical characteristics.

An apparatus for detecting the end point of the surface treatment by such a reflectance measuring method generally irradiates the sample surface of the object to be measured with measuring light and detects the light quantity of the reflected light from the sample surface. An optical device for monitoring the amount of light for output,
And an arithmetic processing unit that performs arithmetic for detecting the end point of the surface treatment based on the change in the amount of light output from the optical device for monitoring the amount of light. In addition, the optical device for light quantity monitoring is a projector for emitting measurement light, a light receiving element that receives reflected light from the object to be processed and outputs a detection signal according to the light quantity, and collects measurement light and reflected light. It is configured to include optical parts such as a lens for the like.

[0010]

However, the conventional example having such a structure has the following problems. First, there is a problem that the detection signal output from the light receiving element includes noise generated inside the optical device for light quantity monitoring. For example, the measurement light emitted from the light projector may be reflected by the surface of an optical part or the like, and the reflected light may enter the light receiving element. All the light other than the reflected light from the sample surface becomes a noise component and reduces the S / N ratio of the detection signal output from the light receiving element. When the S / N ratio of the detection signal decreases, it becomes difficult to accurately detect the change in the amount of light, so that post-processing such as detection of the end point of the surface processing cannot be performed accurately.

Secondly, there is a problem that due to the inclination of the object to be processed during the surface treatment, vignetting of reflected light occurs, and the amount of reflected light cannot be accurately measured by the light receiving element. For example, in an etching apparatus, an object to be processed swings as it is rotated or reciprocally moved during the etching process, but at that time, the object to be processed may tilt. When the object to be processed is tilted, the direction of reflected light changes. At this time, a phenomenon occurs in which a part of the reflected light is blocked by an optical part for guiding the reflected light to the light receiving element, or does not enter the light receiving surface of the light receiving element (such a phenomenon is referred to as vignetting). When such vignetting occurs, the amount of reflected light cannot be accurately detected, and thus post-processing such as end point detection of surface treatment performed based on changes in the amount of light cannot be performed accurately.

The present invention has been made in view of the above circumstances, and reduces the optical noise component generated inside the optical device for light quantity monitoring to reduce the S of the detection signal itself.
An object of the present invention is to provide an optical device for light amount monitoring, which improves the / N ratio and reduces vignetting of reflected light due to the inclination of an object to be processed.

[0013]

The present invention has the following constitution in order to achieve such an object. That is, the invention according to claim 1 is a light amount monitor optical device for detecting the light amount of the reflected light from the sample surface with respect to the measurement light with which the sample surface of the object to be measured is irradiated. And a first lens that collects the measurement light from the light projection means, and a measurement light that has a convex surface on the first lens side and that has passed through the first lens. A parallel light beam or a state close to a parallel light beam, and a second lens that irradiates the sample surface, and a light beam that has passed through the second lens is reflected by the sample surface and then reflected by the second lens again. And a light receiving means for receiving the reflected light beam condensed by the third lens and outputting a detection signal corresponding to the amount of the light beam. The sample surface of the measurement object and the light receiving means, In which it is disposed a conjugate position with respect to the serial second lens and said third lens.

The invention according to claim 2 is an optical device for a light amount monitor for detecting the light amount of the reflected light from the sample surface with respect to the measuring light irradiated on the sample surface of the object to be measured. A projection means for emitting the measurement light, a first lens for collecting the measurement light from the projection means, a convex surface on the side of the first lens, and a passage through the first lens A second lens for irradiating the sample surface with the measured light made into a parallel light beam or a state close to a parallel light beam;
An aperture stop arranged at or near the focal point of the second lens, and a light flux that has passed through the second lens and passed through the aperture stop is reflected by the sample surface, and then reflected again through the second lens. And a light receiving means for receiving the reflected light beam condensed by the third lens and outputting a detection signal corresponding to the amount of the light beam. The sample surface of the object to be measured and the light receiving means are arranged at positions conjugate with the second lens and the third lens.

Further, in the invention described in Item 3, in the optical device for monitoring the light amount according to Item 1, the first aperture stop is provided near the first lens, and the first aperture stop is provided near the third lens. Two aperture stops are provided, and the first aperture stop and the second aperture stop are arranged at a position conjugate with the second lens.

According to a fourth aspect of the present invention, there is provided a third aspect of the optical device for monitoring a light amount according to the second aspect.
Second aperture stop is provided in the vicinity of the second lens, and the aperture stop and the second aperture stop arranged at or near the focal position of the second lens are conjugate positions with respect to the second lens. It is arranged in.

Further, in the invention described in claim 5, in the optical device for monitoring the light amount according to claim 1 or 2, the second lens is a plano-convex lens, and the plane side thereof is to be measured. It is arranged toward the sample surface of the object.

[0018]

The operation of the invention described in claim 1 is as follows. The measurement light from the light projecting means passes through the first lens, passes through the second lens, and becomes a parallel light beam or a light beam in a state close to the parallel light beam, and is irradiated onto the sample surface of the object to be measured.
The reflected light from the sample surface of the object to be measured again passes through the second lens, is condensed by the third lens, and is received by the light receiving means. The sample surface may be the upper surface of the measured object or the opposite surface (lower surface of the measured object).

Since the second lens has a convex surface on the side of the first lens, even if the measuring light passing through the first lens is reflected by the convex surface of the second lens, the reflected light is Spread. Therefore, most of the reflected light in which the measurement light emitted from the light projecting means is reflected by the surface of the second lens (on the side of the first lens) is not guided to the light receiving means, and from the sample surface received by the light receiving means. It is possible to reduce the noise component of the light amount of the reflected light.

Further, the measurement light applied to the sample surface is
When the light beam is in a state of being largely deviated from the parallel light beam, the diameter of the reflected light beam from the sample surface becomes large, and when the object to be processed is inclined during the surface treatment and the direction of the reflected light beam is changed,
Part of the reflected light beam may not enter the third lens,
Vignetting that does not enter the light receiving means is likely to occur. On the other hand, the second lens is configured to irradiate the sample surface of the object to be measured with the measurement light that has passed through the first lens in a parallel light flux or in a state close to the parallel light flux. Since the diameter of the reflected light beam from can be reduced, the vignetting described above is less likely to occur.

Further, since the sample surface of the object to be measured and the light receiving means are arranged at positions conjugate with the second lens and the third lens, the reflected light beam from the sample surface is The light is incident on the light receiving means in a state of being condensed with the minimum diameter. The diameter of the reflected light beam upon incidence and the position of incidence do not change even when the object to be processed is tilted. Therefore, even when the object to be processed is inclined, vignetting of the reflected light beam on the light receiving means can be eliminated.

The operation of the invention described in claim 2 is as follows. That is, the measurement light from the light projecting means passes through the first lens and the aperture stop, passes through the second lens, and becomes a parallel light flux or a light flux in a state close to the parallel light flux, and irradiates the sample surface of the object to be measured. To be done. The reflected light from the sample surface of the object to be measured again passes through the second lens, is condensed by the third lens, and is received by the light receiving means.

The aperture stop is arranged at or near the focal position of the second lens. That is, this claim 2
In the invention, the optical system until the measurement light from the light projecting means is irradiated to the sample surface is configured to be a telecentric optical system or a state close thereto, and the principal ray of the measurement light with respect to the optical axis of the second lens. Then, the measurement light is irradiated onto the sample surface in a parallel or nearly parallel state.

The second lens is constructed so as to have a convex surface on the side of the first lens, the parallel light flux or a light flux in a state close to the parallel light flux is applied to the sample surface, The function of arranging the sample surface of the object and the light receiving means at positions conjugate with the second lens and the third lens is the same as that of the invention described in claim 1 described above.

Further, according to the invention described in claim 3,
In the invention described in claim 1, the first aperture stop is provided near the first lens, the second aperture stop is provided near the third lens, and the first aperture stop and the second aperture stop are provided. By disposing the diaphragm and the conjugate position with respect to the second lens, the size of the light beam irradiated to the sample surface by moving the light projecting means closer to or further from the sample surface ( Even when the size of the irradiation area is changed, the reflected light beam from the sample surface is not eclipsed by the third lens. This is because the first aperture stop and the second aperture stop are arranged at positions conjugate with the second lens, so that the luminous flux of the measurement light focused by the first aperture stop is: This is because it always passes through the second aperture stop. Therefore, it is possible to adjust the size of the irradiation area simply by moving the light projecting means closer to or farther from the sample surface without causing vignetting due to the third lens.

According to the invention of claim 4, the first aperture stop in the invention of claim 3 is:
It is also used as the aperture stop used to construct the telecentric optical system.

Further, the operation of the invention described in claim 5 is as follows. For example, when the shape of the second lens on the sample surface side is a lens shape, when the refractive index of the medium (for example, the etching solution in the etching process) between the second lens and the sample surface changes, Since the power of the lens changes and the direction of the reflected light beam changes, the conjugate positional relationship (imaging relationship) between the sample surface and the light receiving means is broken,
Vignetting occurs in the third lens and the light receiving means, and accurate light amount measurement cannot be performed by the light receiving means. Therefore, in order to accurately measure the amount of light, it is necessary to adjust the light receiving means or the entire optical device according to the refractive index of the medium between the second lens and the sample surface.

On the other hand, in the fifth aspect of the present invention, the second lens is formed of a plano-convex lens, and the plane side thereof is arranged so as to face the sample surface of the object to be measured. Even if the refractive index of the medium between the lens and the sample surface changes, the power of the second lens is always the same, and the direction of the reflected light beam does not change. Therefore, the connection between the sample surface and the light receiving means is not changed. The image relationship is not broken, and the light amount can be accurately measured by the light receiving means. That is, it is not necessary to adjust the light receiving means or the entire optical device according to the refractive index of the medium between the second lens and the sample surface.

Further, since the second lens has a convex surface on the first lens side, as described in the invention of claim 1 described above, the second lens (on the first lens side ) It is also prevented that the S / N ratio of the detection signal output from the light receiving means is lowered by the reflected light reflected by the surface.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a diagram showing a schematic configuration of the entire surface treatment apparatus used in the embodiment of the present invention. The apparatus shown in FIG. 2 is configured as an etching apparatus that performs an etching process on a liquid crystal display substrate G as an object to be processed. In the following, a case of detecting an end point in the etching process of the liquid crystal display substrate G will be taken as an example. Take and explain.

As shown in FIG. 3, the liquid crystal display substrate G has ITO (Indium-Thin-Ox) on the main surface of the glass substrate 11.
ide) film 12 is formed, and a resist layer 13 having a desired pattern is formed on the upper surface of the ITO film 12. Then, in this etching apparatus, the resist layer 13
The ITO film 12 in the etching region 14 where the
Is being removed. In the figure, reference numeral 15 is a region (mask region) which is not etched.

The liquid crystal display substrate G includes rollers 21a and 2a.
It is sandwiched by 1b, 22a and 22b. During the etching process, the rollers 21a and 22a are rotationally driven in synchronization with the forward and reverse directions by a motor (not shown), and the liquid crystal display substrate G supported by the operation is horizontally reciprocated. Further, the drive control of the motor is performed by the control arithmetic unit 2
It is performed by the control unit 27a in the computer 7. On the other hand, the reciprocating liquid crystal display substrate G includes rollers 21a, 21
Since it is sandwiched between b, 22a, and 22b, the movement in the vertical direction is suppressed.

An etching liquid E is prepared in the tank 25, and the etching liquid E is pumped up by a pump P and supplied by a nozzle 26 to the surface of the reciprocating liquid crystal display substrate G. Nozzle 26
Is swung by the motor M as shown by the arrow. That is, the nozzle 26 oscillates to supply the etching solution E to the surface of the liquid crystal display substrate G, and the etching solution E is supplied.
Is uniformly distributed over the entire surface of the liquid crystal display substrate G by the reciprocating movement of the liquid crystal display substrate G, and etching proceeds. The drive control of the pump P and the motor M is also performed by the control unit 27a.

The light quantity monitoring optical device 30 is an essential part of the present invention, and the details thereof will be described later. While the liquid crystal display substrate G is being etched, a parallel light flux is generated by the liquid crystal display substrate G.
The sample light is irradiated perpendicularly to the sample surface, the reflected light reflected by the sample surface is received, and a detection signal corresponding to the amount of the reflected light is supplied to the arithmetic processing unit 27b in the control arithmetic unit 27. Arithmetic processing unit 2 to which a detection signal corresponding to the amount of reflected light is supplied
7b detects the end point of etching based on the detection signal as described in the conventional example.

The control arithmetic unit 27 is composed of a microcomputer including a CPU, RAM, ROM and the like (not shown). Further, the ROM stores in advance a control procedure for each member performed by the control unit 27a, a processing procedure (program) for detecting an end point performed by the arithmetic processing unit 27b, and the CPU controls each member according to the program. Then, the end point is detected based on the detection signal. In addition, based on the detection signal supplied from the light amount monitoring optical device 30, when processing other than the end point detection, for example, the processing state during etching processing is monitored or a specific state during etching processing is detected. For example, the end point detection program stored in the ROM may be changed to a desired processing program.

The structure of the light quantity monitoring optical device 30 will be described below in detail with reference to FIG. FIG. 1 is a view showing the arrangement of a light quantity monitoring optical device according to the first embodiment of the present invention. In this embodiment, the sample surface is made of ITO.
The upper surface of the membrane 12 constitutes the device.

The light quantity monitoring optical device 30 includes a light source 3
1, condenser lens 32, light projecting optical fiber 33, first lens 34, half mirror 35, second lens 36
And a reflected light receiving optical system including a second lens 36, a half mirror 35, a third lens 37, and a light receiving element 38, and a treatment liquid curtain forming mechanism 40. There is. The configuration of each unit will be described in detail below.

First, the structure of the measuring light irradiation optical system will be described. The light source 31 is composed of, for example, a halogen lamp or the like, and the white light emitted from the light source 31 is condensed by the condenser lens 32 and guided to the light projecting optical fiber 33. It is configured to be emitted from the light projecting port 33a. Also,
The white light emitted from the light projecting port 33a is emitted from the first lens 3
4. After passing through the half mirror 35, it is collimated by the second lens 36, and is irradiated onto the sample surface of the liquid crystal display substrate G.

The first lens 34 is used for the projection optical fiber 3
3 has a diameter satisfying the numerical aperture of the light projecting port 33a, that is, all the measurement light emitted from the light projecting port 33a of the projecting optical fiber 33 passes through the effective diameter of the first lens 34. , The half mirror 35, the second lens 36, and the sample surface of the liquid crystal display substrate G. For example, when the first lens 34 is arranged at a position close to the light projecting port 33a of the light projecting optical fiber 33, the diameter of the first lens 34 may be small, and the first lens 34 projects light. The diameter of the first lens 34 must be increased as the optical fiber 33 is placed away from the light projecting port 33a. That is, the first lens 34 has a diameter that satisfies the numerical aperture of the light projecting port 33a of the light projecting optical fiber 33, depending on the arrangement position of the light projecting optical fiber 33 with respect to the light projecting port 33a and the diameter thereof. Is adjusted.

The condenser lens 32 is used as the light source 31.
Is configured to have a diameter that satisfies the numerical aperture of.

The second lens 36 is composed of a plano-convex lens and is arranged with its convex surface facing the first lens 34 and its flat surface facing the sample surface. The second lens 36 is configured to convert the light passing through the first lens 34 and the half mirror 35 into a parallel light flux, but is not limited to the parallel light flux, and is a lens that converts the light flux into a light flux in a state close to the parallel light flux. It may be.

The light source 31 and the condenser lens 32,
The light projecting optical fiber 33 corresponds to the light projecting means in the present invention. Further, in this embodiment, the light projecting optical fiber 33 (and the condenser lens 32) is used to guide the light from the light source 31 to the vicinity of the sample surface, but the present invention is not limited to this, and only the light source 31 is used. Then, the light projecting means may be configured.
In this case, the first lens 34 is configured to have a diameter that satisfies the numerical aperture of the light source 31.

It should be noted that the irradiation area of the parallel light flux irradiated on the sample surface is, for example, 5 mm to 10 mm in diameter, and the diameter of the light projecting port 33a of the light projecting optical fiber 33 and the light projecting optical fiber. From the light projecting port 33a of 33 to the first lens 3
The distance to 4 etc. has been adjusted. In this way, the measurement light is converted into a light flux and a predetermined irradiation area is taken, so that the reflected light can be measured in a relatively wide area, and the detection signals are averaged over the entire sample surface. It is possible to detect the situation more accurately and improve the detection accuracy of the end point.

Next, the structure of the reflected light receiving optical system will be described. The parallel light flux applied to the sample surface of the liquid crystal display substrate G is reflected by the sample surface. The reflected light beam is
After passing through the second lens 36, the optical path is changed by the half mirror 35 toward the third lens 37, and the third lens 37
It is configured so that the light is condensed by and is incident on the light receiving element 38.

The sample surface of the liquid crystal display substrate G and the light receiving element 38 are arranged at positions conjugate with the second lens 36 and the third lens 37.

The light receiving element 38 is for outputting a detection signal corresponding to the light quantity of the incident reflected light beam and corresponds to the light receiving means in the present invention. The detection signal output from the light receiving element 38 is configured to be supplied to the arithmetic processing unit 27b.

The measurement light irradiation optical system and the reflected light reception optical system are covered with a housing 39. The inner peripheral surface of the housing 39 is made of an absorbing paper such as black Racha paper that does not reflect or scatter light.

Next, the structure of the treatment liquid curtain forming mechanism 40 will be described. In this treatment liquid curtain forming mechanism 40, two concentric cylinders are combined so that a large cylinder has an outer wall 4
1. A tank 43 in which a small cylinder serves as the inner wall 42. The upper surfaces of the outer wall 41 and the inner wall 42 are sealed, and the space between the outer wall 41 and the inner wall 42 is
The same liquid as the treatment liquid used for the surface treatment (the etching liquid E in this embodiment) is prepared, and the etching liquid E is introduced from a pipe 44 communicating with a tank (not shown). It flows out from the lower surface of the space between the liquid crystal display panel 42 and the upper surface to the upper surface of the liquid crystal display substrate G. The etching solution E that has flowed out in this manner is used as the second lens 36.
And the upper surface of the liquid crystal display substrate G. The inflow control of the etching liquid E is performed by the control unit 27a. The lower surface of the tank 43 and the upper surface of the liquid crystal display substrate G are spaced so that the etching liquid E flowing out from the lower surface of the tank 43 is filled between the upper surface of the liquid crystal display substrate G and the lower surface of the tank 43. If shown, 1mm-3mm
It is kept to a degree.

During the etching process, the etching solution E is supplied to the surface (sample surface) of the liquid crystal display substrate G.
Causes a pulsating flow or bubbles along with the reciprocating movement of the liquid crystal display substrate G. When the pulsating flow or bubbles occur in the irradiation region of the measurement light flux, the reflected light reflected by the pulsating flow or bubbles is generated. , Becomes scattered light and is not guided to the light receiving element 38. Therefore, in the treatment liquid curtain forming mechanism 40, the second lens 3
6 and the upper surface of the liquid crystal display substrate G between the etching liquid E
By satisfying the above condition, such pulsating flow and air bubbles are prevented from entering between the second lens 36 and the upper surface of the liquid crystal display substrate G.

In the present embodiment, the etching liquid E is sprayed from the nozzle 26 and is supplied to the surface of the liquid crystal display substrate G, so that the pulsating flow as described above and Bubbles may be generated, and the treatment liquid curtain forming mechanism 40 is provided to cope with the occurrence. However, for example, in the apparatus for performing the etching process by immersing the liquid crystal display substrate G in the etching liquid, the second
Since the space between the lens 36 and the upper surface of the liquid crystal display substrate G is always filled with the etching liquid, in the case of such an etching apparatus, the processing liquid curtain forming mechanism 4 is used.
It is not necessary to set 0.

Next, the operation of the apparatus of this embodiment will be described with reference to FIGS. FIG. 4 is a diagram in which the measurement light irradiation optical system in the apparatus of the first embodiment is extracted, and shows a state in which the light flux emitted from the light projecting port of the projecting optical fiber is irradiated to the sample surface. . Further, FIG. 5 is a diagram for explaining the difference in action between the case where the parallel flat plate glass is used for the window portion of the light quantity monitoring optical device and the case where the second lens is used. Further, FIG. 6 is a diagram showing an image formation state in the apparatus of the first embodiment. 4 to 6 are shown in FIG.
Is illustrated in a simplified manner, and the housing and the processing liquid curtain forming mechanism are omitted.

The measuring light emitted from the light projecting port 33 a of the light projecting optical fiber 33 passes through the first lens 34. As described above, the first lens 34 has a diameter that satisfies the numerical aperture of the light projecting port 33a of the light projecting optical fiber 33. That is, as shown in FIG.
All the measurement light emitted from the light projecting port 33a of No. 3 passes through the first lens 34, and is guided to the sample surface of the liquid crystal display substrate G through the half mirror 35 and the second lens 36. . That is, since a part of the light emitted from the light projecting port 33a of the light projecting optical fiber 33 is prevented from entering the light receiving element 38 as leakage light, the light projecting port of the light projecting optical fiber 33 is prevented. The disadvantage that the S / N ratio of the detection signal output from the light receiving element 38 due to the leaked light emitted from 33a is reduced can be avoided. The lens that satisfies the numerical aperture of the light projecting port 33a of the light projecting optical fiber 33 is
If it cannot be used as the lens 34, the diaphragm may be arranged in the vicinity of the light projecting port 33a in order to prevent leakage of light from the light projecting port 33a of the light projecting optical fiber 33.

The amount of the reflected light from the sample surface received by the light receiving element 38 is proportional to the amount of the measurement light irradiated on the sample surface, but the optical fiber 33 for projecting light is used.
Since all the measuring light emitted from the light projecting port 33a of the
The measurement light emitted from the light projecting port 33a of No. 3 can be efficiently used. In particular, when the reflectance of the sample surface is low, the light amount of the measurement light with which the sample surface is irradiated must be increased in order for the light receiving element 38 to receive a sufficient amount of light. Since the measurement light is efficiently used, the light projecting port 33a of the light projecting optical fiber 33 is used.
A light source 31 having a smaller amount of emitted light can be used as compared with an apparatus including an optical system in which all the measurement light emitted from is not guided to the sample surface.

Further, the second lens 36 is configured so that the measurement light that has passed through the first lens 34 is made into a parallel light beam (or a state close to a parallel light beam) and is irradiated onto the sample surface. Such actions and effects can be obtained. That is, when the measurement light applied to the sample surface is a light beam that is largely deviated from the parallel light beam, the diameter of the reflected light beam from the sample surface becomes large, so the object to be processed tilts during the etching process, When the direction of the reflected light beam is changed, part of the reflected light beam is partially reflected by the half mirror 35 or the third lens 3.
The phenomenon that the light does not enter 7 or does not enter the light receiving surface of the light receiving element 38, that is, vignetting easily occurs.
On the other hand, in the second lens 36, the first lens 34
Since the measurement light that has passed through is converted into a parallel light beam (or a state close to a parallel light beam) and is irradiated onto the sample surface, the diameter of the reflected light light beam from the sample surface can be reduced. Is hard to get up.

Since the diameter of the reflected light beam from the sample surface can be reduced, the liquid crystal display substrate G tilts,
Even when the direction of the reflected light flux changes,
Second lens 36, half mirror 35, third lens 3
The range of variation within each optical part when entering 7 becomes narrow. Therefore, the second lens 36 and the third lens 37 are prevented while preventing vignetting due to the inclination of the liquid crystal display substrate G.
With a small diameter, the half mirror 35
Since the one having a small area can be used, the light quantity monitoring optical device 30 can be made compact.

In order to detect the end point of the etching process, the etching state is observed in real time.
At this time, it is necessary to keep the light quantity monitoring optical device 30 close to the liquid crystal display substrate G at all times during the etching process. However, if the light quantity monitoring optical device 30 is large,
Since the etching liquid sprayed from the nozzle 26 is blocked and uneven etching is caused, it is preferable that the light quantity monitoring optical device 30 is small,
As described above, since the light quantity monitoring optical device 30 can be configured in a small size, it is possible to obtain an effect that etching unevenness can be reduced.

Further, since the second lens 36 is a plano-convex lens and the convex surface thereof is arranged on the first lens 34 side and the flat surface side is arranged on the sample surface side, the following actions and effects are obtained. can get. The second lens 36 serves as a window for irradiating the sample surface with the measurement light from the light quantity monitor optical device 30 and for taking in the reflected light from the sample surface. Conventionally, a parallel flat plate glass is generally used for such a window portion. However, when a parallel flat plate glass is used for the window portion, the measurement light L _t is parallel as shown in FIG. 5A. When the reflected light L _R is specularly reflected by the surface of the flat glass M by about 4 to 5% and enters the light receiving element 38, it becomes a noise component, and the S / N ratio of the detection signal decreases. On the other hand, the change in the reflectance with the change in the film thickness of the ITO film 12 is about 10% or more, so that it is 4
When the detection signal includes a light amount corresponding to about 5% as a noise component, it is not possible to accurately detect a change in reflectance due to a change in the thickness of the ITO film 12.

On the other hand, as in the apparatus of this embodiment, the window portion is constituted by the second lens 36, and the convex surface of this second lens is arranged so as to face the first lens side. 5
As shown in (b), the measurement light L _t is emitted from the second lens 36.
Even if it is reflected by the convex surface of, the reflected light L _R will be diffused. Therefore, the reflected light L _R obtained by reflecting the measurement light L _t on the surface of the second lens 36 (on the side of the first lens 34) is less likely to be guided to the light receiving element 38, and is reflected from the sample surface received by the light receiving element 38. It is possible to reduce the noise component of the amount of reflected light.

Although the surface of the second lens 36 on the sample surface side is a flat surface, the etching liquid is filled between the second lens 36 and the sample surface during the etching process. Since the difference in refractive index between the second lens 3 and
Since the surface of No. 6 on the sample surface side does not easily reflect, the noise component due to the reflected light reflected by the surface of the second lens 36 on the sample surface side is small.

By the way, when the surface of the second lens 36 on the sample surface side has a lens shape, for example, the kind of the etching liquid is changed, and the refraction of the medium between the second lens 36 and the sample surface is performed. When the ratio changes, the power of the second lens 36 changes, and the direction of the reflected light beam changes, so that the conjugate positional relationship (imaging relationship) between the sample surface and the light receiving element 38 collapses, and the third lens 37 changes. Also, vignetting may occur in the light receiving element 38, and accurate light amount measurement may not be performed in the light receiving element 38. Therefore, in order to perform accurate light quantity measurement, it is necessary to adjust the light receiving element 38 or the entire optical device 30 according to the refractive index of the medium between the second lens 36 and the sample surface. Become.

On the other hand, in the apparatus of this embodiment, since the plane side of the second lens 36 is disposed so as to face the sample surface, the refractive index of the medium between the second lens 36 and the sample surface is increased. , The power of the second lens 36 is always the same, and the direction of the reflected light beam does not change. Therefore, the image formation relationship between the sample surface and the light receiving element 38 is not broken,
The light receiving element 38 can always perform accurate light amount measurement. That is, depending on the refractive index of the medium between the second lens 36 and the sample surface, the light receiving element 38 or the optical device 3
There is no need to adjust the entire zero.

Assembling of the light quantity monitoring optical device 30 (each lens 32, 34, 36, 37 and half mirror 3).
The adjustment of the optical parts such as 5 and the arrangement of each member such as the light receiving element 38) is usually performed in an air environment, that is, in a state where air is present between the second lens 36 and the sample surface. The refractive index of air is different from that of the etching solution. At this time, if the surface of the second lens 36 on the side of the sample surface has a lens shape, even if each member is adjusted in an air environment, the adjustment does not allow the second lens 36 and the sample to be moved during the etching process. Since the refractive index of the medium is different from that of the surface, the light receiving element 38 during the etching process.
Therefore, it may not be possible to accurately measure the amount of light.

On the other hand, as in the apparatus of this embodiment, if the second lens 36 is arranged so that the plane side thereof faces the sample surface, even if each member is adjusted in an air environment, etching is performed. During the processing, the light receiving element 38 can accurately measure the amount of light. In other words, since the device can be assembled in the air environment, the device assembling work can be facilitated.

In addition, the sample surface of the liquid crystal display substrate G and the light receiving element 38 are composed of the second lens 36 and the third lens 3.
Since it is arranged at a position conjugate with 7 (in an image forming state), as shown in FIG. 6, the reflected light beam from the sample surface is condensed with a minimum diameter. Light receiving element 3
It is incident on 8. The diameter of the reflected light beam incident on the light receiving element 38 changes according to the magnification of the relationship between the second lens 36 and the light receiving element 38. For example, if the irradiation area on the sample surface is 5 mm in diameter and the magnification is ⅕, the diameter of the reflected light beam incident on the light receiving element 38 is 1 mm in diameter. Light receiving element 3
The incident position of the reflected light beam on 8 does not change even when the liquid crystal display substrate G is tilted. Therefore, even when the liquid crystal display substrate G is tilted, vignetting of the reflected light beam on the light receiving element 38 can be eliminated.

Further, the reflected light beam from the sample surface is incident on the light receiving element 38 in a state of being condensed with the minimum diameter, and even when the liquid crystal display substrate G is tilted, the reflected light beam at the time of incidence is Since the size of the diameter and the incident position do not change, a small light receiving element 38 can be used. Therefore, also in this respect, it is possible to contribute to downsizing of the device.

That is, according to the apparatus of this embodiment, it is possible to reduce the optical noise component generated inside the light quantity monitoring optical device 30 and improve the S / N ratio of the detection signal output from the light receiving element 38. In addition, vignetting of reflected light due to the inclination of the liquid crystal display substrate G can be reduced.

Although the second lens 36 is a plano-convex lens in the first embodiment, the second lens 36 is
May be composed of a biconvex lens. At this time, the surface of the second lens 36 on the sample surface side is also a convex surface (lens shape), and as described above, the refractive index of the medium between the second lens 36 and the sample surface changes, Light receiving element 3
In some cases, the amount of light cannot be accurately received at 8. Therefore, in order to avoid such an inconvenience, when the second lens 36 is composed of a biconvex lens, the device is set in an environment in which the refractive index of the medium between the second lens 36 and the sample surface does not change. It is preferable to operate.

In order to make the refractive index of the medium between the second lens 36 and the sample surface when assembling the device equal to the refractive index of the etching solution at the time of measurement, for example, the second lens is used. The device may be assembled by disposing a medium having a refractive index similar to that of the etching liquid at the time of measurement between the sample surface 36 and the sample surface, or etching between the second lens 36 and the sample surface. The device may be assembled while submerged in the liquid. Further, the arrangement position of each member may be calculated by optical calculation, and the device may be assembled based on the result.

Next, a modification of the above-described first embodiment device will be described with reference to FIG. FIG. 7 is a diagram showing a configuration of a modified example of the first embodiment device. In addition, in FIG. 7, the portions denoted by the same reference numerals as those in FIG. 1 have the same configuration as the above-described first embodiment apparatus, and the arrangement relationship of each member is also the same as that of the first embodiment apparatus. Detailed description is omitted. However,
1 is a simplified drawing of FIG. 1. For example, the housing is drawn only in the vicinity of the second lens in FIG.
Similar to the device of the first embodiment, the measuring light irradiation optical system and the reflected light receiving optical system are covered.

As shown in FIG. 7, in this modification, the measurement light is applied to the lower surface side of the liquid crystal display substrate G, and the reflected light from the surface is received by the light receiving element 38. The device 30 is configured. That is, in the above-described first embodiment device, the sample surface is used as the liquid crystal display substrate G.
This modification is characterized in that the sample surface is set on the lower surface side of the liquid crystal display substrate G, which is the opposite surface.

By setting the sample surface on the lower surface side of the liquid crystal display substrate G, it is not necessary to fill the etching liquid between the second lens 36 and the sample surface.
In this modification, the treatment liquid curtain forming mechanism 40 is not provided, but instead, an air blowing nozzle 50 is provided.

The structure of the air blowing nozzle 50 will be described below. One of the air blowing nozzles 50 communicates with an air supply source (not shown), and the other end has a cylindrical air blowing port 51 attached thereto. The air blowing port 51 is attached so that its cylindrical port is perpendicular to the air blowing direction of the air blowing nozzle 50. The mouth of the air blowing port 51 is directed toward the irradiation area on the sample surface of the liquid crystal display substrate G and the second lens 36, and is attached so that the measurement light and the reflected light pass through the inside of the cylinder. Has been. The air blown from the air blowing nozzle 50 hits the inner wall of the air blowing port 51, and is blown from the cylindrical port to the irradiation area of the sample surface of the liquid crystal display substrate G and the second lens 36. The control of the air blowing is performed by the controller 27a.

By blowing air from the air blowing nozzle 50 during the etching process, even when the etching liquid flows from the upper surface of the liquid crystal display substrate G into the irradiation area of the measurement light on the sample surface side, the air blows by the air. Since the etching liquid flowing into the irradiation region is blown off, it is possible to prevent the generation of scattered light due to the pulsating flow of the etching liquid and the bubbles on the sample surface.

In this modification, as in the first embodiment, the second lens 36 may be a biconvex lens instead of a plano-convex lens. At this time, in this modification, since the sample surface is set on the lower surface side of the liquid crystal display substrate G, air always exists between the second lens 36 and the sample surface. Regardless of the refractive index of the liquid, the light receiving element 38 can always accurately receive the amount of light. Also, the assembly of the device can be performed in an air environment.

The modified implementation of the first embodiment can be similarly implemented in the following embodiments.

Next, the configuration of the second embodiment device of the present invention will be described with reference to FIG. FIG. 8 is a diagram showing a schematic configuration of the second embodiment device. However, FIG. 8 is drawn by simplifying FIG. 1, and a housing for covering the measuring light irradiation optical system and the reflected light receiving optical system, a processing liquid curtain forming mechanism, and the like are omitted. In addition, the drawings of the following embodiments are also drawn in the same manner.

In this second embodiment apparatus, the first lens 34 of the first embodiment described above is provided with the first aperture stop 61, and
A second aperture stop 62 is provided on the third lens 37, and the first aperture stop 61 and the second aperture stop 62 are arranged at a position conjugate with the second lens 36. Characterize. Since the other configurations are the same as those of the above-described first embodiment, detailed description thereof will be omitted here.

By moving the light projecting port 33a of the light projecting optical fiber 33 closer to or farther from the first lens 34, the size of the light beam irradiated on the sample surface (size of the irradiation region) is changed. be able to. At this time, when the light flux irradiated to the sample surface is reduced, the diameter of the light flux reflected from the sample surface is reduced, and the third lens 3
Although there is no vignetting in 7, the diameter of the reflected light flux from the sample surface becomes large when the light flux irradiated to the sample surface is increased, and vignetting may occur in the third lens 37. On the other hand, by arranging the first aperture stop 61 and the second aperture stop 62 at positions conjugate with the second lens 36, the measurement performed by the first aperture stop 61 is stopped. Since the light flux of light always passes through the second aperture stop 62, the reflected light flux from the sample surface is prevented from being vignetted by the third lens 63. Therefore, the third lens 37 can be formed simply by moving the light projecting port 33a of the light projecting optical fiber 33 closer to or further from the sample surface.
The size of the irradiation region can be adjusted without causing vignetting.

The first aperture stop 61 may be arranged behind the first lens 34 as shown in FIG. 8 or may be arranged in front of the first lens 34.
In addition, the second aperture stop 62 has the second lens 36 with respect to the arrangement position according to the arrangement of the first aperture stop 61.
As long as the position is conjugate with, it may be located behind or in front of the third lens 37.

Next, the configuration of the third embodiment device of the present invention will be described with reference to FIG. FIG. 9 is a diagram showing a schematic configuration of the third embodiment device. In the third embodiment, the aperture stop 71 is provided on the first lens 34, and the aperture stop 71 is
It is characterized in that it is arranged at or near the focal position of the second lens 36 (the focal point of the second lens 36 is f). That is, in this third embodiment apparatus, the measurement light irradiation optical system of the first embodiment apparatus is constituted by a telecentric optical system, and the principal ray of the measurement light is secondly parallel to the optical axis of the lens 36 (aperture). When the diaphragm 71 is arranged at the focal position of the second lens 36) or in a state close to parallel (aperture diaphragm 7
1 is arranged in the vicinity of the focal position of the second lens 36), and the measurement light is applied to the sample surface. The other structure is the same as that of the first embodiment device.

When the measuring light irradiation optical system is not composed of a telecentric optical system, the principal ray of the measuring light does not enter the sample surface perpendicularly, so that part of the reflected light beam from the sample surface is the second light beam. In some cases, the light does not enter the lens 36. Therefore, the light amount of the reflected light beam received by the light receiving element 38 may decrease. On the other hand, if the measurement light irradiation optical system is composed of a telecentric optical system,
As described above, the principal ray of the measuring light becomes parallel or almost parallel to the optical axis of the second lens 36, and the principal ray of the measuring light is incident on the sample surface vertically or almost vertically. It For this reason, most of the reflected light beam from the sample surface is incident on the second lens 36, so that the reduction in the amount of the reflected light beam received by the light receiving element 38 is reduced.

Further, the diameter of the first lens 34 is configured so as to satisfy the numerical aperture of the light projecting port 33a of the light projecting optical fiber 33, and the second lens 36 is replaced by the first lens 34.
A convex surface on the side, a parallel light beam or a light beam in a state close to a parallel light beam is applied to the sample surface, and the sample surface of the liquid crystal display substrate G and the light receiving element 38 are Lens 36 and third lens 37
The effect of arranging it at a position conjugate with and is
Since it is the same as the case of the apparatus of the first embodiment described above, description thereof is omitted here.

Next, the structure of the apparatus of the fourth embodiment of the present invention will be described with reference to FIG. In this fourth embodiment device, a second aperture stop 62 is provided on the third lens 37 of the above-mentioned third embodiment device, and the second aperture stop 62 and the measuring light irradiation optical system are telecentric optical systems. The aperture stop 71 used for the above construction is arranged at a position conjugate with the second lens 36.

That is, in the above-described second embodiment, the first aperture stop 61 and the second aperture stop 61 are based on the device of the first embodiment.
The aperture stop 62 and the aperture stop 62 are attached, but in the fourth embodiment device, based on the above-mentioned third embodiment device,
The first aperture stop 61 in the second embodiment device is also used as the aperture stop 71 used in the third embodiment device to configure the measuring light irradiation optical system into a telecentric optical system.

Therefore, also in the device of the fourth embodiment,
Similar to the device of the second embodiment, the light projecting port 33a of the light projecting optical fiber 33 is simply moved closer to or farther from the sample surface, and the third lens 37 does not cause vignetting. The effect that the size can be adjusted is obtained.

In each of the above-described embodiments, the case where the substrate G for liquid crystal display is used as the object to be processed and the etching process is performed while the substrate G for liquid crystal display is reciprocally moved has been described as an example. A device for detecting a processing state (for example, an end point) of a surface treatment (for example, development), an object to be processed other than the liquid crystal display substrate G (for example, a silicon oxide film, a polysilicon layer on the main surface of a silicon wafer). , A device for detecting a processing state with respect to a surface treatment such as etching a polysilicon layer while rotating a substrate on which a resist layer having a predetermined pattern is formed),
Furthermore, even for an apparatus other than the surface treatment apparatus, for an apparatus or the like that performs a predetermined process based on the amount of reflected light from the sample surface with respect to the measurement light irradiated on the sample surface of the object to be measured, The optical device for light quantity monitoring according to the embodiment can be applied.

[0087]

As is apparent from the above description, according to the first aspect of the invention, the reflected light reflected by the second lens surface becomes difficult to be received by the light receiving means, so that the reflected light is reflected. The noise component due to light is reduced from being included in the detection signal from the light receiving means. That is, it is possible to reduce the noise component due to the reflected light reflected on the surface of the optical part, and to reduce the optical noise component generated inside the light quantity monitoring optical device to improve the S / N ratio of the detection signal. It is possible.

Even when the object to be processed is tilted, the vignetting of the reflected light from the sample surface is less likely to occur, and the light amount of the reflected light from the sample surface can be accurately detected by the light receiving means.

According to the invention described in claim 2, in addition to the effect of the invention described in claim 1,
Since almost all the reflected light flux from the sample surface is incident on the second lens, it is possible to reduce the decrease in the amount of the reflected light flux received by the light receiving means.

Further, according to the invention described in claim 3, in the light quantity monitoring optical device according to claim 1, the light projecting means can be moved closer to or farther from the sample surface. Without causing vignetting by the lens,
It is possible to adjust the size of the irradiation area.

According to the invention described in claim 4, in the optical device for monitoring the light amount according to claim 2, the light projecting means is moved closer to or farther from the sample surface. Without causing vignetting by the lens,
It is possible to adjust the size of the irradiation area.

Further, according to the invention of claim 5,
The optical device for monitoring light quantity according to claim 1 or 2, wherein even when the refractive index of the medium between the second lens and the sample surface of the object to be processed changes, the sample surface of the object to be measured and the light receiving The reflected light from the sample surface can always be accurately detected by the light receiving means without losing the conjugate positional relationship with the means.

[0093]

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an optical device for monitoring a light amount according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration of an entire surface treatment apparatus used in an embodiment of the present invention.

FIG. 3 is a diagram showing a schematic configuration of a liquid crystal display substrate.

FIG. 4 is a diagram showing a state of a light beam emitted from a light projecting port of a light projecting optical fiber to a sample surface in an optical system for irradiating measurement light in the apparatus of the first embodiment.

FIG. 5 is a diagram for explaining a difference in operation between a case where a parallel flat plate glass is used for a window portion of a light quantity monitoring optical device and a case where a second lens is used.

FIG. 6 is a diagram showing an image formation state in the apparatus of the first embodiment.

FIG. 7 is a diagram showing a schematic configuration of a modified example of the first embodiment device.

FIG. 8 is a diagram showing a schematic configuration of a second embodiment device.

FIG. 9 is a diagram showing a schematic configuration of a third embodiment device.

FIG. 10 is a diagram showing a schematic configuration of a device of a fourth embodiment.

FIG. 11 is a diagram for explaining detection of the end point of the etching process.

FIG. 12 is a diagram for explaining detection of the end point of the etching process.

[Explanation of symbols]

 30 ... Optical device for light quantity monitor 31 ... Light source 32 ... Condenser lens 33 ... Projection optical fiber 33a ... Projection port of projection optical fiber 34 ... First lens 36 ... Second lens 37 ... Third lens 38 ... Light receiving element 61 ... First aperture stop 62 ... Second aperture stop 71 ... Aperture stop G ... Liquid crystal display substrate (processing object)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naruaki Fujiwara No. 1 at Tenjin Kitamachi, 4-chome Tenjin Kitamachi, Kami-ku, Kyoto, Japan

Claims (5)

[Claims] 1. An optical device for monitoring a light amount for detecting a light amount of a reflected light from the sample surface with respect to the measured light irradiated on the sample surface of the object to be measured, wherein the light projecting means emits the measuring light. A first lens that collects the measurement light from the light projecting means; and a parallel light beam or a parallel light beam that has the convex surface on the first lens side and that passes the measurement light through the first lens. A second lens that irradiates the sample surface in a state close to the above, and the light flux that has passed through the second lens is reflected by the sample surface, and the reflected light flux that has passed through the second lens is condensed again. A third lens; and a light receiving unit that receives the reflected light beam condensed by the third lens and outputs a detection signal corresponding to the amount of light, and a sample surface of the object to be measured. The light receiving means is the second lens and An optical device for monitoring a light amount, which is arranged at a position conjugate with the third lens. 2. A light quantity monitor optical device for detecting the quantity of light reflected from the sample surface with respect to the measurement light applied to the sample surface of the object to be measured, wherein the light projecting means emits the measurement light. A first lens that collects the measurement light from the light projecting means; and a parallel light beam or a parallel light beam that has the convex surface on the first lens side and that passes the measurement light through the first lens. A second lens for irradiating the sample surface in a state close to the above, an aperture stop arranged at or near the focal position of the second lens, and passed through the second lens through the aperture stop. A third lens that collects the reflected light beam that is reflected by the sample surface and that has passed through the second lens again, and the reflected light beam that is collected by the third lens is received and Receiver that outputs the corresponding detection signal A step, and the sample surface of the object to be measured and the light receiving means are arranged at a position conjugate with the second lens and the third lens. Optical device for monitoring light intensity. 3. The optical device for light quantity monitor according to claim 1, wherein a first aperture stop is provided near the first lens and a second aperture stop is provided near the third lens, and the first aperture stop is provided. The aperture stop and the second aperture stop are arranged at positions conjugate with the second lens. 4. The optical device for monitoring light quantity according to claim 2, wherein a second aperture stop is provided near the third lens, and the aperture stop is provided at or near the focal position of the second lens. And the second aperture stop is arranged at a position conjugate with the second lens. 5. The optical device for monitoring light amount according to claim 1 or 2, wherein the second lens is a plano-convex lens, and the plane side of the second lens faces the sample surface of the object to be measured. An optical device for light quantity monitor characterized by.