JP2001284323A - Etching depth detecting apparatus, etching apparatus, etching depth detecting method, etching method and method of manufacturing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an etching depth detecting method for accurately detecting etching depth, even if a material of small reflection rate is etched. SOLUTION: In an etching depth detecting method, a substrate is irradiated with light and reflected interference light is received, and the etching depth of a part to be etched is detected, based on information on reflected interference light. The reflection rate of a mask is calculated, based on the film thickness of the mask, information on reflected interference light is corrected based on the reflectance of the mask, and etching depth is calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an etching depth detecting device, an etching device, an etching depth detecting method, an etching method, and a semiconductor device manufacturing method.

[0002]

2. Description of the Related Art Semiconductor device manufacturing processes include an etching process for forming holes and grooves in a substrate such as a silicon wafer. This etching step is performed by performing masking and etching on portions of the substrate where holes and grooves are not formed. By performing etching in this way,
Only the unmasked portion can be selectively processed. At the time of this etching, the processing depth is measured during the etching so that the hole or groove to be formed has a predetermined depth. The measurement of the processing depth is disclosed in Japanese Patent Application Laid-Open No. 10-325708. As shown in FIG. 13, this measuring method is performed by detecting the interference light of the reflected light R1 from the mask 101 and the reflected light R2 from the portion to be processed by the photodetector 102. The intensity of the interference light of R1 and R2 changes periodically as the portion to be processed becomes deeper. When the intensity of the interference light changes by one period, the depth of the processed portion is の of the wavelength of the irradiated light. Therefore, the depth of the portion to be processed can be measured by detecting the interference light of R1 and R2 with the photodetector 102 and counting how many periods the interference light intensity has changed. Then, when the processing proceeds to a predetermined depth, the etching can be stopped and the processing can be performed to the predetermined depth.

[0003]

However, in the semiconductor manufacturing process, the material of the workpiece may be a dielectric such as a photoresist. In these cases,
The reflected light R2 from the portion to be processed becomes very weak. As R2 becomes weaker, the interference light between R1 and R2 also becomes weaker,
It becomes difficult to detect the intensity change of the interference light. Therefore, the working depth cannot be measured with sufficient accuracy.
Therefore, an object of the present invention is to provide an etching depth detection device and a detection method that can accurately detect an etching depth even when a substance having a small reflectance is etched. It is another object of the present invention to provide an etching apparatus and an etching method capable of performing accurate etching using the etching depth detection method. It is another object of the present invention to provide a method for manufacturing a semiconductor device, which enables highly accurate processing.

[0004]

According to the present invention, a first irradiation for irradiating a substrate having a mask forming portion on which a mask is formed and a portion to be etched without a mask with a first light is performed. Means for receiving interference light of the first light reflected from the mask forming portion and reflected light of the first light from the portion to be etched, and converting the interference light into a first electric signal A second irradiation unit that irradiates the mask forming unit with a second light, a unit that receives reflected light of the second light from the mask forming unit, and converts the reflected light into a second electric signal;
Detecting means for detecting a depth of the portion to be etched based on the first electric signal and the second electric signal;
An etching depth detecting apparatus comprising: Further, in the etching depth detection device, the detection unit includes a correction value calculation unit configured to calculate a correction value of the first electric signal based on the second electric signal, and the correction unit calculates the correction value based on the correction value. 1. An etching depth, comprising: a correction unit that corrects a first electrical signal; and a depth detection unit that calculates a depth of the portion to be etched based on the corrected first electrical signal. It is a detection device. Further, in the etching depth detecting apparatus, the detecting unit calculates a film thickness of the mask based on the second electric signal, and corrects the first electric signal based on the film thickness. Correction value calculating means for determining a value, correction means for correcting the first electric signal based on the correction value, and depth of the portion to be etched based on the corrected first electric signal. And a depth detecting means for calculating the etching depth.

[0005] Further, an etching means for etching the substrate is added to the etching depth detecting device, and the etching depth by the etching means is detected by the etching depth detecting device.
An etching apparatus characterized by the following. An irradiation step of irradiating a substrate having a mask forming portion on which a mask is formed and an etched portion on which the mask is not formed with first light; and reflection of the first light from the mask forming portion. A step of receiving interference light of light and a reflection of the first light from the portion to be etched, converting the light into a first electric signal, and an irradiation step of irradiating the mask forming unit with a second light Receiving the reflected light of the second light from the mask forming portion and converting the reflected light into a second electric signal; and detecting the light based on the first electric signal and the second electric signal. A detecting step of detecting a depth of the etched portion. Further, in the etching depth detecting method, the detecting step includes a correction value calculating step of calculating a correction value of the first electric signal based on the second electric signal, and the detecting step based on the correction value. (1) a correction step of correcting the electric signal of (1), and a depth detection step of calculating a depth of the portion to be etched based on the corrected first electric signal. It is a detection method.

[0006] In the etching depth detecting method, the detecting step may be performed based on the second electric signal.
Calculating the film thickness of the mask, correcting the first electric signal based on the film thickness, and correcting the first electric signal based on the corrected value. An etching depth detection method, comprising: a correction step; and a depth detection step of calculating a depth of the etched portion based on the corrected first electric signal. Further, in an etching method including an etching step of etching a substrate and a detection step of detecting the etching depth, the detection step performs detection using the etching depth detection method, Is an etching method. In addition, a semiconductor device includes a step of forming a mask on a predetermined portion of a semiconductor wafer, and a processing step of etching the semiconductor wafer while detecting depth and processing a portion not covered with the mask. In the manufacturing method, the processing step includes irradiating a substrate having an etching step of etching the semiconductor wafer and a substrate having a mask forming portion on which the mask is formed and a portion to be etched not covered with the mask with first light. Receiving an interference light between the reflected light of the first light from the mask forming portion and the reflected light of the first light from the portion to be etched, and converts the interference light into a first electric signal. Performing a step of irradiating the mask forming unit with a second light; receiving reflected light of the second light from the mask forming unit and converting the reflected light into a second electric signal; No. And electrical signals, on the basis of the second electrical signal, said a semiconductor device manufacturing method characterized by comprising: a detection step of detecting a depth of the etched portion.

An irradiation step of irradiating a substrate having a mask forming portion on which a mask is formed and a portion to be etched not forming the mask with first light; Receiving the interference light between the reflected light from the substrate and the reflected light of the first light from the portion to be etched, and converting the interference light into a first electric signal; A detecting step of detecting a depth of the portion to be etched based on film thickness information.

[0008]

(First Embodiment) FIG. 1 shows a configuration diagram of an etching depth detecting apparatus according to the present invention. This detection device is roughly classified into a chamber 1 of an etching device.
And an etching depth detecting means 2 'for detecting an etching depth based on a signal measured by the measuring head 2. The etching depth detecting means 2 ′ includes a mask thickness calculating section 3, a mask reflectance calculating section 4, a signal correction value calculating section 5, and a signal correcting section 6.
And a depth detection unit 7. Hereinafter, each component will be described. The measuring head 2 is connected to the upper surface of an observation window 41 made of quartz glass provided at the upper part of the chamber. The measuring head 2 includes a film thickness measuring unit 8 and a depth measuring unit 9 as shown in FIG. The depth measuring unit 9 includes a mercury lamp 14, an optical fiber 15, a lens 16,
It comprises an interference filter (not shown), a photodetector 17, and an automatic XY stage 19. The mercury lamp 14, which is the first irradiation means, emits ultraviolet light as the first light. The ultraviolet light passes through the optical fiber 15 and is collimated into parallel light by the lens 16, and irradiates the surface of the workpiece W vertically through the observation window 41. The reflected light from the workpiece W travels in the same optical path as the irradiation light in the opposite direction, and
5 and enter the interference filter.

The interference filter transmits only light of a specific wavelength, and the transmitted light is input to the photodetector 17. The photodetector 17 is configured to output an electric signal corresponding to the intensity of the received reflected light. Further, the irradiation position of the ultraviolet light to the workpiece W can be positioned by the automatic XY stage 19. The film thickness measuring unit 8 includes a tungsten lamp 10, an optical fiber 11, a lens 12, a spectroscope 13, and an automatic XY stage 18.
The tungsten lamp 10, which is the second irradiating means, emits the second light, that is, the light for film thickness measurement. The light for measuring the film thickness passes through the optical fiber 11 and is further focused on the surface of the workpiece W in the chamber 1 by the lens 12. The reflected light from the workpiece W due to the irradiation sequentially travels in the same optical path as the irradiation light in the reverse direction, and the spectroscope 13 serving as the second light receiving means.
To enter. The spectroscope 13 converts the input light into a spectrum and outputs it as an electric signal. Further, the irradiation position of the light for measuring the film thickness on the workpiece W can be positioned by the automatic XY stage 18. The mask film thickness calculation unit 3 has a function of calculating the film thickness of the mask 20 based on an electric signal output from the spectroscope 13 of the film thickness measurement unit 8. The calculated film thickness is output to the mask reflectance calculator.

The mask reflectance calculator 4 calculates the reflectance of the mask 20 based on the film thickness. The calculated reflectance is output to the signal correction value calculation unit. Signal correction value calculator 5
Calculates a correction value for correcting the electric signal output from the photodetector 17 based on the reflectance. This correction value is output to the signal correction unit 6. Signal correction unit 6
Performs correction of the electric signal output from the photodetector 17 based on the correction value. The depth detection unit 7 has a function of detecting the etching depth based on the signal corrected by the signal correction unit 6. Next, the operation of these configurations will be described. FIG. 3 shows a flowchart of the etching depth measurement. First, the workpiece W is set on the processing stage (S1). The workpiece W is a silicon wafer,
As shown in FIG. 4, a mask 20 made of silicon nitride is formed on the surface. The portions to be etched that are not covered with the mask 20 are filled with a photoresist 21. Subsequently, the irradiation positions of the first and second lights are positioned by the automatic XY stages 18 and 19 in FIG. The irradiation position of the light for measuring the depth, which is the first light, is positioned such that the aperture ratio between the mask forming portion on which the mask 20 is formed and the portion to be etched is, for example, 1: 1. On the other hand, the irradiation position of the light for measuring the film thickness, which is the second light, is also determined so as to irradiate only the mask forming portion (S2).

Next, the mask 20 is irradiated with light from the tungsten lamp 10, the reflected light is made incident on the spectroscope 13, and the spectrum obtained as an electric signal from the spectroscope 13 is calculated by the film thickness calculation unit 3. Then, the thickness of the mask is calculated as follows (S3). The film thickness measurement was performed as shown in FIG.
This is performed by comparing a curve between a spectral spectrum signal waveform detected by the spectroscope 13 and a theoretical waveform stored in a database in advance. Curve fitting is performed between a theoretical waveform corresponding to various film thicknesses and a spectral spectrum signal waveform, and a theoretical waveform curve that minimizes the difference between the two waveforms is selected. Then, the film thickness at which the theoretical waveform curve is obtained is regarded as the film thickness of the mask 20. The film thickness thus obtained is output to the reflectance calculator 4. In the reflectance calculating section 4, the reflectance of the light for measuring the depth, which is reflected from the mask 20, is calculated (S4). The calculation principle is shown below. As shown in FIG. 6, the light reflected from the mask 20 is interference light between the light reflected on the surface of the mask 20 and the light reflected from the workpiece W. Therefore, the reflectance R of the mask 20
2 is a reflectance R3 on the surface of the mask 20, a reflectance R4 on the surface of the workpiece W, a refractive index N of the mask 20, a film thickness T of the mask 20, and a wavelength 照射 of irradiated light. Is represented by the following equation.

[0012]

(Equation 1) The reflectance R3 on the surface of the mask 20 and the refractive index N of the mask 20
Is substituted by a value obtained from the physical properties of the mask 20. As the reflectance R4 on the surface of the workpiece W, a value obtained from the physical properties of the silicon wafer as the workpiece W is substituted. Further, Λ is substituted for the measurement wavelength of the ultraviolet light as the first light. In addition, the film thickness obtained by the film thickness calculation unit 3 is substituted for the film thickness T. Therefore, the reflectance R2 is calculated. Next, the signal correction value calculation unit 5 calculates an offset value and a gain value (S5). First, the offset value is calculated as follows. The intensity I detected by the photodetector 17 is expressed by the following equation using the reflectance R1 of the photoresist, the reflectance R2 of the mask 20, the measurement wavelength 外 of the ultraviolet light, and the depth D of the processed portion. .

[0013]

(Equation 2) A value determined from the physical properties of the photoresist is substituted for the reflectance R1 of the photoresist. Further, Λ is substituted with the measurement wavelength of the ultraviolet light. Further, the value calculated by the mask reflectance calculator is substituted for R2. Therefore, the signal strength I
Offset value which is a DC component of R1 × R1 + R2 × R
2 is calculated. Thereafter, the gain value is set so that the signal strength I from which the offset value has been removed becomes a value suitable for measurement. The setting of the gain value is set from the offset value and the measurement condition. As described above, the offset value and the gain value are calculated. After the initial setting described above, etching is started (S6). During the etching, as shown in FIG. 7, the portion to be etched and the mask 20 are irradiated with light for measuring the depth. Then, the photodetector 17 receives the reflected light of this light and converts it into an electric signal (S7). This electric signal is corrected by the signal correction unit 6 (S8). That is, after the offset is corrected based on the offset value obtained in advance by the signal correction value calculation unit, the gain is corrected based on the gain value obtained by the signal correction value calculation unit.
The electric signal after the gain correction is transmitted to the depth detection unit 7 as an intensity signal.

The depth detector 7 receives the intensity signal at predetermined time intervals, and calculates the etching depth as described below (S9). The intensity signal with respect to time becomes a periodic graph as shown in FIG. The depth detector 7 detects the etching depth based on this graph. The etching depth is obtained as follows. The distance processed from the time T1 at which the first pole S1 is detected to the time T3 at which the third pole S3 is detected is equal to a half wavelength of light. Therefore, the etching rate E is obtained by dividing the half wavelength of light by this time. In addition, the distance processed during the time until the pole is detected is a quarter of the light.
Wavelength. Therefore, for example, as shown in FIG.
T at which one extreme was detected and the fourth extreme was detected
Assuming that machining has been performed by ΔT from 4, the machining distance at this time is calculated as T1 × E + 3 × Λ / 4 + ΔT × E. As described above, the etching depth is calculated every predetermined time, and when the etching depth reaches the predetermined etching depth, the etching is completed (S10). With the above operation, the etching depth was detected. The etched portion is irradiated with light, and the reflected light is detected to detect the etching depth. At this time, by irradiating the mask with light, the reflected light is detected, and correction is performed based on a signal obtained from the reflected light, so that accurate depth detection is performed even when etching a substance having a low reflectance. It becomes possible.

The material of the portion to be processed is not limited to photoresist, and the effect of the present invention is great even with a dielectric such as a silicon oxide film. Further, in the case of processing a workpiece whose variation in the thickness of the mask is small, a correction value is calculated based on a previously input thickness without using the second irradiation unit, and the etching depth is calculated. May be detected. Also,
In this embodiment, the case where the aperture ratio between the mask forming portion and the portion to be etched is 1: 1 has been described, but the aperture ratio may be arbitrary. In addition, the present embodiment can be variously modified for the same purpose. (Second Embodiment) FIG. 9 shows a microwave plasma etching apparatus according to the present invention. Components having the same configuration and function as those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted. The microwave plasma etching apparatus includes a chamber 30, gas supply means 31 for supplying a reaction gas to the chamber 30, a vacuum pump 32 for reducing the pressure in the chamber 30, and a microwave for generating plasma. A generating unit 33, a measuring head 2 for detecting an etching depth, a mask film thickness calculating unit 3, a mask reflectance calculating unit 4, a signal correction value calculating unit 5, a signal correcting unit 6,
And a depth detector 7. The reaction gas is supplied from a gas supply pipe provided on the side wall of the chamber. The chamber 30 and the vacuum pump 32 are connected by an exhaust pipe. The microwave output from the micro generator 33 is
It is introduced into the chamber 30 by the waveguide 40. Also,
An observation window 41 made of quartz glass is provided on the ceiling of the chamber, and the operation of the above configuration in which the measuring head 2 is connected to the upper surface of the observation window 41 will be described.

First, the processing table 42 in the chamber 30
Then, a substrate 43 as a workpiece is set. This substrate 43 has an opening as shown in FIG.
The portion other than the opening is covered with the mask 44. Also,
The inside of the opening is filled with a photoresist 45. After setting the substrate 43, the vacuum pump 32 is activated,
The gas pressure in the chamber 30 is maintained at about 10-3 Pascal. In this state, the reaction gas is supplied from the gas supply pipe. On the other hand, the portion where the mask 44 is formed is irradiated with light for film thickness measurement from the tungsten lamp 10. The reflected light of this light is received by the spectroscope 13, and the film thickness of the mask 44 is calculated as in the first embodiment. Then, based on this film thickness, the offset value and the gain value are
The correction value is calculated by the correction value calculator 5. Etching is started based on the above initial values. Waveguide 4 in chamber 30
Microwaves of a predetermined wavelength guided by 0 are introduced through a quartz window, and the reaction gas in the chamber 30 is ionized to generate active particles. The opening of the substrate 43 is etched by these active particles. On the other hand, the substrate 43 is irradiated with light for depth measurement from the depth measurement unit 9 of the measurement head. Interference light between the reflected light from the mask 44 and the reflected light from the etched photoresist 45 is detected by the photodetector 17 and converted into an electric signal. This electric signal is corrected by the signal correction unit 6 and then transmitted to the etching depth detection unit 7. In the etching depth detector 7, the first
The etching depth is detected as in the embodiment. When the photoresist 45 is processed to a predetermined depth, a control signal is transmitted from the etching depth detection unit 7 to the gas supply unit 31 and the microwave generation unit 33, and the etching ends.

The etching was performed by the above operation.
The mask is irradiated with light, a signal correction value is calculated based on information of the reflected light, and a signal is corrected based on the signal correction value to detect an etching depth. Therefore, even when the intensity of the reflected light is low, it is possible to perform the processing with high accuracy. Third Embodiment The third embodiment relates to a method for manufacturing a semiconductor device. FIG. 11 shows a process of forming a trench fill, which is one process of manufacturing a DRAM. FIG.
(A) shows the structure before the trench fill is formed.
A mask 51 made of silicon nitride is formed on a silicon substrate 50 having a trench. The inside of the trench is filled with a fill 52 made of a photoresist. Further, silicon nitride (not shown) is formed on the boundary between the fill 52 and the inside of the trench. Under such a structure, the fill 52 is processed by chemical dry etching. The etching depth at this time is the first
It is measured using the etching depth measuring device shown in the embodiment. Specifically, first, only the mask 51 is irradiated with light, the reflected light is received, and a correction value is calculated. Then, while performing the etching, as shown in FIG. 12, the fill 52 and the mask 51 are irradiated with light, and the signal value obtained from the reflected light is corrected based on a correction value obtained in advance. . The etching depth is detected from the corrected signal value.

When the etching is completed to a predetermined depth, the etching is completed. FIG. 11B shows a cross-sectional view after processing. After that, predetermined processing is performed, and DRAM
Is manufactured. To operate the DRAM normally,
The trench fill needs to be accurately etched to a predetermined depth. By using the etching depth measuring method described in the first embodiment, the trench fill is processed to a predetermined depth, and as a result, the yield of DRAM can be improved. Note that the present embodiment is not limited to a DRAM, but can be applied to a semiconductor device manufacturing process including a step requiring an accurate etching depth. Various other modifications are possible for the same purpose.

[0019]

According to the present invention, when the interference light between the portion to be etched and the light reflected from the mask is received and the etching depth is measured based on the obtained signal, the mask is irradiated with light and the reflected light is received. The signal of the interference light was corrected based on the signal obtained as a result, so that it was possible to accurately measure the etching depth even when etching a substance having a low reflectance. Further, an etching apparatus and an etching method capable of performing accurate etching by using this etching method can be provided. Further, a method of manufacturing a semiconductor device with a high yield can be provided by using this etching method.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an etching depth detection device according to a first embodiment.

FIG. 2 is a configuration diagram of a measuring head according to the first embodiment.

FIG. 3 is a flowchart of etching depth measurement according to the first embodiment.

FIG. 4 is a diagram showing a structure of a workpiece in the first embodiment.

FIG. 5 is a diagram showing a principle of measuring a film thickness in the first embodiment.

FIG. 6 is a diagram showing light reflected on a mask surface and light reflected from a workpiece in the first embodiment.

FIG. 7 is a diagram illustrating a state in which light applied to a substrate is reflected from a hole and a mask in the first embodiment.

FIG. 8 is a diagram illustrating an intensity signal for each time according to the first embodiment;

FIG. 9 is a configuration diagram of a microwave plasma etching apparatus according to a second embodiment.

FIG. 10 is a diagram in which openings are filled with a photoresist in the second embodiment.

FIG. 11 is a view showing a state where a trench fill is formed in a manufacturing process of the semiconductor device according to the third embodiment.

FIG. 12 is a diagram showing reflected light from a fill and reflected light from a mask in a manufacturing process of a semiconductor device according to a third embodiment.

FIG. 13 is a diagram showing a state of detection of a conventional etching depth.

[Explanation of symbols]

2 measurement head, 3 mask thickness calculation section, 4 mask reflectance calculation section, 5 correction value calculation section, 6 signal correction section, 7
Etching depth detection control unit, 10 tungsten lamp, 13 spectroscope, 14 halogen lamp, 17 light detector.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2F065 AA25 AA30 CC19 CC31 CC32 FF41 FF52 GG02 GG03 GG23 LL02 LL22 LL67 PP12 QQ25 RR06 TT02 4M106 AB16 BA07 CA48 DH03 DH31 DH37 DH38 DJ04 DJ17 DJ18 DJ20 CB20 CB5F004 EB04 EB05

Claims (11)

[Claims] A first irradiating means for irradiating a substrate having a mask forming portion on which a mask is formed and an etched portion on which no mask is formed, with a first light; Means for receiving interference light between the reflected light from the mask forming portion and the reflected light of the first light from the portion to be etched, and converting the interference light into a first electric signal; A second irradiating means for irradiating the second light, a means for receiving reflected light of the second light from the mask forming portion, and converting the reflected light into a second electric signal; An etching depth detecting apparatus, comprising: detecting means for detecting the depth of the portion to be etched based on an electric signal. 2. The correction unit according to claim 1, wherein the detection unit calculates a correction value of the first electric signal based on the second electric signal, and calculates a correction value of the first electric signal based on the correction value. 2. The etching depth according to claim 1, further comprising: a correction unit configured to perform correction; and a depth detection unit configured to calculate a depth of the portion to be etched based on the corrected first electric signal. 3. Detection device. 3. The method according to claim 1, wherein the detecting unit calculates a film thickness of the mask based on the second electric signal, and a correction value for obtaining a correction value of the first electric signal based on the film thickness. Calculation means; correction means for correcting the first electric signal based on the correction value; and depth for calculating the depth of the portion to be etched based on the corrected first electric signal. The etching depth detecting apparatus according to claim 1, further comprising: detecting means. 4. An apparatus according to claim 1, wherein an etching means for etching said substrate is added, and an etching depth by said etching means is detected by said etching depth detecting device. The etching apparatus according to any one of the above. 5. An irradiating step of irradiating a substrate having a mask forming portion on which a mask is formed and an etched portion not having a mask formed thereon with a first light; and the mask forming portion of the first light. Receiving interfering light between the light reflected from the substrate and the reflected light of the first light from the portion to be etched, and converting the light into a first electric signal; and irradiating the mask forming portion with second light Irradiating; receiving the reflected light of the second light from the mask forming unit and converting the reflected light into a second electric signal; based on the first electric signal and the second electric signal ,
A detecting step of detecting a depth of the portion to be etched. 6. The etching depth detecting method according to claim 5, wherein the detecting step calculates a correction value of the first electric signal based on the second electric signal; A correction step of correcting the first electric signal based on a correction value; and a depth detection step of calculating a depth of the portion to be etched based on the corrected first electric signal. A method for detecting an etching depth, characterized in that: 7. The detecting step includes: calculating a film thickness of the mask based on the second electric signal; and a correction value for obtaining a correction value of the first electric signal based on the film thickness. A calculating step, a correcting step of correcting the first electric signal based on the correction value, and a depth of calculating a depth of the portion to be etched based on the corrected first electric signal. The method according to claim 5, further comprising a detecting step. 8. A substrate having a mask forming portion on which a mask is formed and an etched portion on which no mask is formed is irradiated with light to receive reflected interference light, and based on information of the reflected interference light. In the etching depth detecting method for detecting the etching depth of the portion to be etched, the reflectance of the mask is calculated based on the thickness of the mask, and the information of the reflected interference light is calculated based on the reflectance of the mask. And calculating the etching depth by correcting the etching depth. 9. An irradiation step of irradiating a first light to a substrate having a mask forming portion on which a mask is formed and an etched portion having no mask formed thereon; and the mask forming portion of the first light. Receiving interference light between reflected light from the substrate and reflected light of the first light from the portion to be etched, and converting the interference light into a first electric signal; and a film thickness of the first electric signal and the mask. A detecting step of detecting a depth of the portion to be etched based on information. 10. An etching method comprising: an etching step of etching a substrate; and a detecting step of detecting the etching depth, wherein the detecting step includes the etching depth according to claim 5 or 6. An etching method characterized in that detection is performed using a detection method. 11. A step of forming a mask on a predetermined portion of a semiconductor wafer, and a processing step of performing etching on the semiconductor wafer while detecting depth to process a portion not covered by the mask. In the method of manufacturing a semiconductor device, the processing step includes: an etching step of etching the semiconductor wafer; and a first light beam on a substrate having a mask forming portion on which the mask is formed and a portion to be etched not covered by the mask. Irradiating light, and receiving an interference light between the reflected light of the first light from the mask forming portion and the reflected light of the first light from the portion to be etched, and a first electric signal. A step of irradiating the mask forming section with a second light; and a step of receiving reflected light of the second light from the mask forming section and converting the reflected light into a second electric signal. When, wherein the first electrical signal based on the second electrical signal, the semiconductor device manufacturing method characterized by comprising: a detection step of detecting a depth of the etched portion.