JP2001267300A - Measuring method and apparatus of etching depth - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to decide a replacement time of an optical fiber correctly. SOLUTION: During measurement of etching depth, light from a light source 34 is conducted through an optical source optical fiber 35 and irradiated on an etching substrate 5 in the etching chamber 1. The reflected light from the etching substrate 5 is passed through a detecting optical fiber 36 and a spectroscope 37 and the etching depth is measured by a depth processing unit 38. When the deterioration of the optical fiber in ages is tested, a reflective body is mounted between the etching chamber and both optical fibers, and the reflected light from the reflective body is separated by the spectroscope into waveforms, such as a waveform with transmission coefficient decreasing as the optical fiber deteriorates in ages, and a waveform with a transmission coefficient without a decrease, regardless of the deterioration of the optical fiber. The replacement time of the optical fiber by deterioration is decided from the intensity of two separated waveforms and decision values of replacement.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etching depth measuring apparatus using an optical fiber and a measuring method thereof, and more particularly to an etching depth measuring apparatus having a function of inspecting an optical fiber for deterioration and a measuring method thereof.

[0002]

2. Description of the Related Art An etching depth measuring apparatus of this kind is a technique already known from a prior document (Japanese Patent Publication No. 8-8242).

FIG. 8 is an overall configuration diagram of an etching apparatus provided with an etching depth measuring apparatus proposed in the above-mentioned prior art document.

This prior art document includes an etching apparatus and an etching depth measuring apparatus, of which the etching apparatus has an etching chamber 1 in which an upper electrode 2 and a lower electrode 3 are opposed to each other. In addition, an etching gas serving as an etching processing medium is supplied. A high-frequency power supply 4 is connected to the lower electrode 3 and a substrate 5 to be etched is placed on the lower electrode 3. Further, an observation window 6 for observing the state of the etching process on the substrate 5 to be etched is provided at the upper part of the etching chamber 1.

On the other hand, the etching depth measuring device includes a light source 7
A light source optical fiber 8 for guiding light from the light source 7 to irradiate the substrate 5 to be etched;
A detection optical fiber 9 which takes in the reflected light from the optical fiber and guides it to a predetermined location, and is connected to the light emitting end side of the detection optical fiber 9 and splits the reflected light from the optical fiber 9 into a designated wavelength to obtain a spectral intensity. Spectrometer 10 that outputs an electric signal corresponding to the above, and a depth calculation device 11 that measures the etching depth based on the electric signal output from the spectroscope 10
It is constituted by.

When performing an etching process using the above-described etching apparatus, the inside of the etching chamber 1 is evacuated, and then an etching gas is supplied. Then, a high-frequency electric field is applied from the high-frequency power supply 4 to the upper electrode 2 or the lower electrode 3 to generate plasma in the chamber 1. When the plasma reaches the surface of the substrate 5 to be etched, a reaction occurs on the substrate surface by ions and radical particles in the plasma flow, and the substrate 5 to be etched is etched.

At the time of this etching process, the light output from the light source 7 is radiated from the light source optical fiber 8 to the substrate 5 to be etched through the observation window 6 in the upper part of the etching chamber 1, and the reflected diffraction light from the substrate 5 due to the irradiation is observed. It is taken out through the window 6. The detection optical fiber 9 guides the reflected diffracted light extracted from the observation window 6 to the photodetector 10, and the photodetector 10 outputs an electric signal corresponding to the intensity of the reflected diffracted light from the optical fiber 9, It is sent to the arithmetic unit 11. The depth calculation device 11 is a light detector 1
The etching depth is measured based on the phase change of the magnitude of the electric signal output from 0.

[0008]

By the way, the transmittance of the optical fibers 8 and 9 as described above deteriorates as shown in FIG. 9 due to the ultraviolet light of the plasma generated at the time of the etching process, and the transmittance at the wavelength in the ultraviolet region is reduced. There is a problem that the transmittance is greatly reduced. Incidentally, FIG. 9 is a diagram showing a decrease in the transmittance after a certain period elapses for each wavelength, that is, a deterioration state of the optical fibers 8 and 9, and the period varies depending on the material of the fiber, the intensity of the ultraviolet light and other factors.

Therefore, when the transmittance is reduced due to the deterioration of the optical fiber, the intensity of the reflected light from the substrate 5 to be etched, which is received by the photodetector, is attenuated. The peak position of the interference reflected light from the etching substrate 5 cannot be accurately determined, and a measurement error of the etching depth and a measurement accuracy of the etching depth become a problem.

Further, there is a problem that the spectral intensity distribution of the emitted plasma varies depending on the type of the etching processing medium, and further, the replacement time of the optical fibers 8 and 9 cannot be uniquely determined due to the optical fiber material and other various factors.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides an etching depth measuring apparatus and an etching depth measuring apparatus for appropriately determining a deterioration state of an optical fiber and, consequently, a replacement time, thereby measuring the etching depth with high accuracy. To provide.

[0012]

(1) In order to solve the above-mentioned problems, an etching depth measuring apparatus according to the present invention comprises:
A light source optical fiber for irradiating the substrate to be etched with light output from the light source, a light detecting unit for measuring the intensity of the reflected light from the substrate to be etched, and the reflected light from the substrate to be etched to the light detecting unit. In an etching depth measuring device for measuring the etching depth of the substrate to be etched from the light detecting means using a guiding optical fiber, the optical fiber is detachably attached to an optical path between the both optical fibers and the substrate to be etched. An optical path turning means for introducing light emitted from the light source optical fiber into the detection fiber, and an optical path of the optical fiber based on an output of the light detecting means according to the light intensity of the light guided by the optical path turning means. And a deterioration inspection means for inspecting deterioration.

[0013] The light detecting means may use a spectroscope that splits the light into a predetermined wavelength and outputs an electric signal corresponding to each spectral intensity.

(2) A substrate setting step of setting a reference mirror having a reference reflectance on a lower electrode in an etching chamber in which a substrate to be etched is placed before an etching processing step; And irradiating the reference mirror body with the light, the reflected light is taken in by the detection optical fiber, and the light is transmitted to the light detection means by the detection optical fiber, and the deterioration state of the optical fiber is determined based on the output of the light detection means. An etching depth measurement step comprising: a deterioration determination step for determining; and a depth measurement step for measuring an etching depth of the substrate to be etched by an etching process from an output of the light detecting means when the soundness is determined in the deterioration determination step. This is the method.

(3) The deterioration inspection means measures the spectral intensities of the first and second wavelengths output from the spectroscope, and determines the first optical fiber whose transmittance does not decrease due to deterioration of the optical fiber. Measure the intensity when normalized by wavelength and the intensity of the wavelength at which the transmittance of the optical fiber decreases due to the degradation of the optical fiber, and inspect the degradation of the optical fiber, or the transmittance of the optical fiber due to the degradation of the optical fiber This is to measure the spectral intensity at the wavelength at which the optical fiber decreases, and inspect the optical fiber for deterioration.

[0016]

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

(First Embodiment) FIG. 1 is a configuration diagram showing an embodiment of an etching depth measuring apparatus according to the present invention. In this figure, since the etching apparatus for performing the etching process on the substrate to be etched has the same configuration as that of FIG. 1, the same components are denoted by the same reference numerals 1 to 6, and the description thereof will be omitted. The configuration of an etching depth measuring apparatus that is a main part of the present invention will be described.

This measuring apparatus includes an etching chamber 1
A converging lens 31 that is arranged close to or parallel to the upper observation window 6 with a required interval and condenses reflected light from the substrate 5 to be etched, and the observation window 6 On the opposite side, there is provided an optical unit 33 having a reflecting mirror 32 provided with, for example, an Al (aluminum) film having an excellent reflectance of ultraviolet light, which is detachably disposed automatically or manually and is detachable.

The optical section 33 is provided with a light introduction / irradiation system for guiding light and irradiating the substrate 5 to be etched, and a light guiding / measuring system for guiding reflected light from the substrate 5 to be etched and measuring an etching depth. Have been.

This light introducing / irradiating system is constituted by a white light source 34 such as a Xe lamp which emits light from the ultraviolet region to the near infrared region, and a quartz optical fiber 35 for a light source for guiding the light output from the light source 34 to the optical unit 33. ing.

On the other hand, the light guiding and measuring system is a quartz optical fiber 3 for detection that takes in the reflected light reflected by the substrate 5 to be etched and collected by the condenser lens 31 and guides it to a predetermined location.
6. A light detecting means connected to the light emitting end side of the optical fiber 36 for detecting the intensity of the input reflected light, for example, a spectroscope 37 such as a monochromator capable of dispersing the reflected light and measuring the received light intensity of a designated wavelength. And a depth calculator 38 having a function of measuring an etching depth based on an electric signal corresponding to the received light intensity output from the spectroscope 37 and a function of determining fiber deterioration. Reflecting mirror 3
2 constitutes an optical path turning means for guiding the light emitted from the light source optical fiber 35 to the detection optical fiber 36.
In addition to the reflecting mirror 32, a corner cube or a U-shaped optical path connecting optical fiber may be used as the optical path turning means.

As shown in FIG. 2, the depth calculation device 38 includes a depth measurement program, a deterioration determination program, other calculation formula data, known data required for calculation, a deterioration determination value, and the like. A program memory 41 for storing,
An output port 42 for setting the spectroscope 37 for specifying and outputting the specific wavelength data, an input interface 43 for converting and outputting an electric signal corresponding to the received light intensity of the specified wavelength obtained from the spectroscope 37 into data that can be processed later, and a CPU. And a buffer memory 45 for storing data input from the input interface 43, data being processed, data of a processing result, and the like. In response to the optical fiber deterioration inspection, the depth measurement processing unit 44
The mirror drive output unit 46 for mounting the reflector 32, the display unit 47 for displaying the depth measurement result and the deterioration judgment result and other necessary information, and the instructions necessary for the measurement / deterioration inspection, etc. And an input unit 48 for inputting data.

Next, the operation of the measuring apparatus configured as described above will be described with reference to FIG.

When the operation of the apparatus is started, after initialization processing such as erasing unnecessary data in the buffer memory 45 and setting data necessary for calculation in the buffer memory 45 (S1), the optical fibers 35 and 37 are processed. It is determined whether or not to perform the deterioration inspection of (S2). Periodically (for example, at the start of the operation of the apparatus or at the end of a predetermined rod) or when the user inputs an inspection instruction from the input unit 48, it is determined that the deterioration inspection is to be performed. Then, the etching depth of the substrate 5 to be etched is measured according to the depth measuring program in the program memory 41 (S3). Then, when the substrate 5 to be etched reaches a predetermined etching depth (S4), the etching process is terminated. At this time, the reflecting mirror 32 of the optical unit 33 is in a state of being separated from the optical path.

On the other hand, when it is determined in step S2 that the optical fiber is to be inspected for deterioration, it is determined whether or not the reflecting mirror 32 is mounted on the optical path passing through the optical section 33 (S5). When the reflecting mirror 32 is not mounted, the mounting instruction is output manually or automatically through the reflecting mirror driving output unit 46 to mount the reflecting mirror 32 (S6). As a result, the first and second wavelengths, which are the designated wavelengths, are set to the spectroscope 37 via the output port 42 after it is determined that the reflector is mounted or during the initialization process (S1) (S1)
7).

Here, the first wavelength is the optical fiber 3
It means a wavelength at which a decrease in transmittance clearly appears due to the deterioration of 5 and 36, and becomes 250 nm or less as is clear from FIG. 9, but a wavelength of 219 nm is used as an example. On the other hand, the second
Means a wavelength at which the transmittance of the optical fiber does not decrease despite the deterioration of the optical fibers 35 and 36, and is also 250 nm or more as is clear from FIG.
As an example, 350 nm is used.

Therefore, in the above state, the light source 3
The light output from 4 enters the optical unit 33 through the light source optical fiber 35, is reflected by the reflecting mirror 32 before the condenser lens 31, and is guided to the spectroscope 37 through the detection optical fiber 36.

The spectroscope 37 converts the incident light reflected from the reflecting mirror 32 into a first wavelength of 219 nm and a second wavelength of 219 nm.
, And outputs electric signals A and B according to the reception intensity.

Then, the depth measurement processing section 44 fetches the electric signals A and B corresponding to the reception intensity of each designated wavelength via the input interface 43 and stores them in the buffer memory 45 (S8). Here, the relative intensity I ₂ at the first wavelength of 219 nm when normalized at the second wavelength of 350 nm is determined by the following equation (I ₂ = A / B) (1) (S9), and then the optical fiber 3
Since the relative intensity I ₁ already obtained at the time of the new installation immediately after the replacement of 5, 36 is obtained, these I ₂ / I ₁ are I ₂ / I ₁ <70% (2). _It is determined whether or not ₂ / I ₁ is equal to or less than an exchange determination value, for example, 70% (S10). This replacement determination value of 70% is considered as one replacement determination reference value that affects the etching depth measurement accuracy, but differs depending on the allowable range of the measurement accuracy.

In step S9, when I ₂ / I ₁ becomes equal to or less than the replacement determination value 70%, a warning is displayed on the display unit 47, or another replacement optical fiber is already provided along with the currently used optical fibers 35 and 36. If there is, the fiber is switched to the replacement fiber (S11), and after the warning confirmation or the completion of the fiber switching is confirmed (S12), the deterioration inspection is ended.

When I ₂ / I ₁ is not equal to or smaller than 70% in step S10, a normal etching depth measuring process is executed (S3).

Therefore, according to the above-described embodiment, the reflecting mirror 32 is mounted on the optical path at the time of measuring the etching depth, and the light from the optical fiber for light source 35 is reflected to be transmitted through the optical fiber for detection 36. The optical fiber replacement time is determined from the spectral intensity and the replacement determination value for the two different designated wavelengths, which are led to the spectroscope 37, so that the replacement time of each optical fiber can be clearly determined. The etching depth can be measured with high accuracy while the S / N ratio of the interference reflected light is always good.

Since the reflecting mirror 32 can be detachably set above the observation window 6, for example, the substrate 5 to be etched can be set.
Can be easily set during the preparation of etching, such as during the supply of an etching gas, during the supply of the etching gas, or immediately before the depth measurement, and has no influence on the conventional etching apparatus and the etching depth measurement. Without optical fiber 3
Deterioration of 5, 36 can be reliably determined.

Although the above embodiment has been applied to the etching apparatus shown in FIG. 1, the present invention is not particularly limited to the etching apparatus shown in FIG. 1. In short, the etching depth of the substrate to be etched is reduced by using an optical fiber. The present invention can be applied to all types of etching devices that can be measured.

(Second Embodiment) FIG. 4 is a view for explaining an embodiment of the etching depth measuring method according to the present invention. In this figure, the same parts as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In this embodiment, an optical fiber is inspected using a silicon substrate before a thin film is formed as a reference mirror having a reference reflectance before etching, and etching is performed simultaneously with etching when the measurement accuracy is not affected. This is a method of measuring depth.

This etching depth measuring method uses the optical unit 3
3, only the condenser lens 31 is installed, and the silicon substrate 51 before the thin film is formed
Is set, and the deterioration inspection of the optical fibers 35 and 36 is performed. The inspection is performed in the following procedure.

(1) Silicon substrate setting step: At the time of etching, the lower electrode 3 in the etching chamber 1
A silicon substrate 51 before forming a thin film, which is a substrate to be etched before etching, is set thereon. Since the silicon substrate 51 needs to reflect light, its surface needs to be mirror-finished.

(2) Light transmission processing step: After setting the silicon substrate 51 as described above, the light source 3
Light is output from 4 and enters the optical unit 33 through the light source optical fiber 35. The light incident on the optical unit 33 is converted into parallel light by the condenser lens 31, passes through the observation window 6, and is irradiated on the silicon substrate 51.

As a result, the mirror-finished silicon substrate 5
1 outputs a reflected light, and the reflected light is
And the light is condensed by the optical fiber 36 for detection.
7 is input. The spectroscope 37 converts the input reflected light into a designated first wavelength, for example, 219 nm and a second wavelength.
At a wavelength of, for example, 350 nm, and outputs electric signals A and B according to the received intensity.

At this stage, since the high frequency power supply 4 is not applied to the electrodes 2 or 3, it is not affected by the plasma light.

(3) Optical fiber deterioration determination step: When the depth calculator 38 receives the electric signals A and B according to the received light intensity for the designated wavelength from the spectroscope 37, the above equation (3) and (4) According to the formula, the optical fiber 35,
It is determined whether 36 is in a degraded state beyond the allowable range of the measurement accuracy, that is, whether it is time to replace the fiber.

(4) Replacement notification step: When it is determined in the above (3) that it is time to replace the fiber, an alarm for prompting the replacement of the optical fiber or, if a replacement optical fiber is already provided, switching to the replacement.

(5) Etching Depth Measuring Step: When it is determined in the above (3) that the optical fibers 35 and 36 are in a healthy state, the high frequency power supply 4 is applied according to the same procedure as in the prior art to start the etching process. With
The etching depth of the silicon substrate 51 which is the substrate to be etched is measured.

Therefore, according to the above embodiment, the deterioration of the optical fiber can be easily inspected only by placing the silicon substrate 51 before the thin film is formed on the lower electrode 3. In addition, the optical section 33 becomes smaller, and the etching chamber 1 becomes smaller.
Since the installation of the above components is facilitated, and the soundness is checked after the deterioration inspection of the optical fiber, the etching depth during the etching process is measured, so that the etching depth can be always accurately measured in a good state. Although the silicon substrate before thin film formation was used as the reference mirror surface, a reflection mirror having the reference reflectance was set on the lower electrode when replacing the wafer cassette managed in lot units, and after the optical fiber deterioration inspection, the reflection mirror was set. Can be avoided from within the etching chamber 1.

(Third Embodiment) FIG. 5 is a block diagram showing another embodiment of the etching depth measuring apparatus according to the present invention. In this figure, the same parts as those in FIG. 1 are denoted by the same reference numerals, detailed description thereof will be omitted, and only different parts will be described.

This embodiment is an example in which an optical fiber for a light source and an optical fiber for detection are optically connected to each other to inspect the deterioration of the optical fiber.

More specifically, the light output end of the optical fiber 35 and the light incident end of the optical fiber 36 are connected by the optical connection section 52 so that the light source optical fiber 35 and the detection optical fiber 36 can be reproduced at the same position. It is a configuration consisting of

Various optical connection methods are conceivable for the optical connection section 52. The optical connection section 52 is directly applied to a method of irradiating the substrate 5 in the etching chamber 1 with light and measuring the etching depth from the reflected light. In this case, for example, the following two methods are conceivable.

(1) When measuring the etching depth, a U-shaped optical fiber 52d is inserted between the light source optical fiber 35 and the detection optical fiber 36 as shown in FIG. 6, and the deterioration of the optical fiber is inspected.

(2) The etching depth measurement is stopped at another appropriate time after the completion of the etching process, and the light emitting end of the light source optical fiber 35 and the light incident end of the detecting optical fiber 36 are stopped as shown in FIG. May be directly connected by the optical connection unit 52 to inspect the deterioration state of the optical fibers 35 and 36.

The optical fibers 35 and 36 or the optical fibers 35 and 36 including the optical fibers 52b and 52c are used.
Is the same as that of the first embodiment, the description of the operation is given to the description of the first embodiment, and the description is omitted here.

Therefore, according to the above-described embodiment, since the two optical fibers 35 and 36 are simply connected by the optical connection section 52, the deterioration state of the optical fiber can be inspected with a very simple configuration.

(Fourth Embodiment) FIG. 7 is a block diagram showing another embodiment of the etching depth measuring apparatus according to the present invention.

This embodiment is an example in which a reflecting mirror is provided as an optical path turning means between the observation window at the upper part of the chamber and the optical part.

In the first embodiment, the optical fiber 3
Although the reflecting mirror 32 is detachably installed between the condenser lenses 5 and 36 and the condenser lens 31, for example, a necessary part is provided between the observation window 6 in the upper part of the chamber and the condenser lens 31 of the optical section 33 from the condenser lens 31. The reflecting mirror 32 may be detachably provided at a distance, may be detached from the optical path when measuring the etching depth, and may be mounted on the optical path when measuring the optical fiber deterioration.

The operation of such an apparatus is the same as that of the first embodiment, and thus will be described only in the first embodiment.

Therefore, also in this embodiment, the first
The same effect as that of the embodiment can be obtained.

(Other Embodiments) In the above embodiment, the spectroscope 37 is used. Instead of the spectroscope 37, the intensity of the wavelength at which the transmittance of the optical fiber decreases due to deterioration of the optical fibers 35 and 36 is detected. A possible photodetector is provided, and when the intensity of the wavelength at which the transmittance of the optical fibers 35 and 36 decreases falls below a certain value, the optical fiber 3
It is good also as exchange time of 5,36.

The spectrometer 37 is not limited to a monochromator, but may be a polychromator capable of simultaneously measuring from the ultraviolet region to the visible region. Further, the light source 34 is not limited to the Xe lamp, and may be any light source that can emit light from the ultraviolet region to the visible region. The reflecting mirror 32 is not limited to the Al film, and may be a reflector such as a dielectric multilayer film that reflects a wavelength at which the transmittance decreases due to the deterioration of the optical fiber and a wavelength at which the transmittance does not decrease despite the deterioration of the optical fiber. Should be fine. Further, the wavelength for inspecting the deterioration of the optical fiber is 219 nm, 350
The wavelength is not limited to nm, and may be any wavelength at which the transmittance decreases due to the deterioration of the optical fiber and any wavelength at which the transmittance does not decrease despite the deterioration of the optical fiber.

In addition, the present invention can be variously modified and implemented without departing from the gist thereof.

Further, a spare light source optical fiber and a detection optical fiber are provided, and the spare light source optical fiber and the detection optical fiber are alternately replaced at the time of the optical fiber deterioration determination step. The deterioration state may be detected individually.

[0063]

As described above, according to the present invention, the replacement time of the optical fiber can be easily determined, and the etching depth is always measured using the optical fiber in the best condition. The etching depth can be measured with high accuracy by increasing the S / N ratio of the reflected light.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of an etching depth measuring apparatus according to the present invention.

FIG. 2 is a diagram illustrating a configuration example of hardware of the depth calculation device illustrated in FIG. 1;

FIG. 3 is a flowchart illustrating the operation of the device of the present invention.

FIG. 4 is a configuration diagram illustrating an etching depth measuring method according to the present invention.

FIG. 5 is a configuration diagram showing another embodiment of the etching depth measuring apparatus according to the present invention.

FIG. 6 is a diagram illustrating a configuration example of an optical connection unit illustrated in FIG.

FIG. 7 is a configuration diagram showing another embodiment of the etching depth measuring apparatus according to the present invention.

FIG. 8 is a configuration diagram of a conventional etching depth measuring device.

FIG. 9 is a diagram illustrating a state of deterioration of an optical fiber due to ultraviolet light of plasma generated at the time of etching.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Etching chamber 2 ... Upper electrode 3 ... Lower electrode 4 ... High frequency power supply 5 ... Substrate to be etched 6 ... Observation window 31 ... Condensing lens 32 ... Reflecting mirror 33 ... Optical part 34 ... Light source 35 ... Optical fiber for light source 36 ... Detection Optical fiber 37 ... Spectroscope 38 ... Depth calculator 51 ... Silicon substrate before thin film formation 52 ... Optical connection

Continued on the front page F term (reference) 2F065 AA25 BB01 CC17 DD04 DD08 FF41 FF48 GG03 GG12 GG24 JJ01 KK01 LL02 LL12 LL67 QQ03 QQ23 QQ25 UU07 2G086 CC07 4M106 AA01 BA04 CA48 DB03 DB16 DB30 DH03 DH12 DH03 DH12 DH03

Claims (5)

[Claims] 1. An optical fiber for a light source for irradiating a substrate to be etched with light output from a light source, a light detecting unit for measuring the intensity of light reflected from the substrate to be etched, and the substrate for etching is provided on the light detecting unit. An optical fiber for detection that guides reflected light from the substrate, and an etching depth measuring apparatus that measures the etching depth of the substrate to be etched from the light detecting means, wherein an optical path between the two optical fibers and the substrate to be etched is provided. An optical path turning means which is detachably mounted and introduces light emitted from the light source optical fiber into the detection fiber; and an output of the light detecting means corresponding to the light intensity of the light guided by the optical path turning means. An etching depth measuring device for inspecting the deterioration of the optical fiber based on the inspection result. 2. An etching depth measuring apparatus according to claim 1, wherein said light detecting means uses a spectroscope which splits the light into a predetermined wavelength and outputs an electric signal corresponding to each of the spectral intensities. . 3. A substrate setting step of setting a reference mirror having a reference reflectance on a lower electrode in an etching chamber on which a substrate to be etched is placed before an etching processing step; Guiding the light to the reference mirror, irradiating the reflected light with a detection optical fiber, and guiding the reflected light to light detection means with a detection optical fiber; and determining a deterioration state of the optical fiber based on an output of the light detection means. And a depth measuring step of measuring an etching depth of the substrate to be etched by an etching process from an output of the light detecting means when it is determined that the substrate is sound in the deterioration determining step. Etching depth measurement method. 4. The deterioration inspection means measures spectral intensities of first and second wavelengths output from the spectroscope, and determines the first wavelength at which transmittance of the optical fiber does not decrease due to deterioration of the optical fiber. 2. The etching depth measurement according to claim 1, wherein the intensity at the wavelength at which the transmittance of the optical fiber decreases due to the deterioration of the optical fiber is measured, and the deterioration of the optical fiber is inspected. apparatus. 5. The etching method according to claim 1, wherein the deterioration inspection means measures the spectral intensity of a wavelength at which the transmittance of the optical fiber decreases due to the deterioration of the optical fiber, and inspects the deterioration of the optical fiber. Depth measuring device.