JP2016080668A - Device and method for monitoring surface treatment state - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface treatment state monitoring device capable of measuring the thickness of a measured layer changing by the minute in real time.SOLUTION: The device comprises: a light source emitting measurement light having wavelength width; an interference optical system having light, which is reflected by upper and lower faces of a measured layer, interfered; a spectroscopic part for performing wavelength dispersion of interference light; and a detection part for detecting light on which the wavelength dispersion is performed for each wavelength. The device further comprises: a storage unit in which a theoretical formula is stored, the formula including the first term which changes depending on a value of ratio between the product of the thickness of the measured layer by a refraction index and the wavelength and which corresponds to the intensity of interference light of light reflected by the upper face of the measured layer and light entering the measured layer and then reflected by the lower face, and a second term which corresponds to the intensity of interference light of the upper face reflected light and light entering the measured layer, reflected again thereinside and then emitted; and a thickness determination unit which determines a thickness of the measured layer so that a plurality of intensity values detected and a theoretical value of the intensity of the interference light match.SELECTED DRAWING: Figure 1

Description

  The present invention relates to the depth and level difference of fine holes formed in a semiconductor substrate or the like by etching processing, such as TSV (= Through Silicon Via: silicon through-hole), substrates or crystals whose surfaces are scraped by various polishing processes, etc. The present invention relates to a surface treatment status monitoring apparatus and a surface treatment status monitoring method for measuring in real time during processing a thickness or a film thickness when a film is formed on a substrate surface by CVD or the like.

  In a manufacturing process of a semiconductor integrated circuit, an etching process is performed to form fine holes and grooves in a semiconductor substrate such as a silicon wafer. Usually, in the etching process, etching is performed after masking with a resist film on the substrate, and the unmasked portion is selectively etched. Thereby, holes and grooves are formed in the substrate. Then, the resist film is removed after processing.

  In order to confirm the progress of surface treatment such as etching, the following has been proposed as a method for monitoring temporal changes in the thickness of a layer to be treated (such as an etching layer or a resist film).

  In Patent Document 1, in an SOI substrate in which an oxide film and an active layer are stacked on a supporting substrate, when the thickness of the active layer as a surface layer is polished to adjust the thickness, the change in the thickness of the active layer over time is disclosed. A method for monitoring is described. In this method, the SOI substrate is irradiated with white light (light source having a wide wavelength band), reflected from the surface of the active layer, reflected from the surface of the oxide film through the active layer, and the active layer. Then, the interference light passes through the oxide film and is reflected on the surface of the support substrate by the interference optical system, the interference light is wavelength-dispersed by the spectroscopic element, and detected by a CCD line sensor or the like to obtain the wavelength-intensity characteristics. Then, by utilizing the fact that the maximum value or the minimum value appears in the intensity of the interference light when the thickness of the active layer and the wavelength of the interference light satisfy a predetermined relationship, the period of the active layer is extracted by extracting the period. Monitor changes over time.

  Patent Document 2 describes a method of monitoring a temporal change in the depth of a groove formed by etching when etching a substrate whose surface is masked with a resist film. In this method, laser light is irradiated on the substrate to be processed and reflected by the surface of the resist film, light reflected by the surface of the substrate through the resist film, and the bottom surface of the trench formed by etching. Interference light obtained by interfering with reflected light is detected. Then, every time the trench depth changes by a quarter of the wavelength of the irradiated laser beam, the maximum value and the minimum value appear in the intensity of the interference light, and the temporal change in the trench depth is obtained. Monitor.

JP 2005-184013 A Japanese Patent Laid-Open No. 10-325708

In the method described in Patent Document 1, since interference light is obtained by irradiating light emitted from a white light source, the intensity of light detected after wavelength dispersion of the interference light is weak. Therefore, in order to obtain a sufficient intensity for extracting a periodic change of the interference light intensity with respect to the wavelength, a signal must be accumulated in the detector, which takes time for measurement. Therefore, it cannot be measured in real time.
In the method described in Patent Document 2, the intensity of interference light is continuously observed, and after confirming that the tendency of the change is reversed, the maximum value and the minimum value (hereinafter, these are collectively referred to as “ Cannot be determined. Therefore, a time lag occurs between the timing at which the extreme value actually appears and the timing at which the extreme value is determined. Further, after the extreme value is determined, the thickness of the layer to be measured cannot be determined until the next extreme value is determined.

  Thus, the conventionally proposed method has a problem that the thickness of the layer to be measured, which changes every moment, cannot be measured in real time.

  The problem to be solved by the present invention is to provide a surface treatment status monitoring apparatus and a surface treatment status monitoring method capable of measuring in real time the thickness of a layer to be measured that changes every moment during surface treatment processing. It is.

In order to solve the above-mentioned problems, a first invention is a surface treatment status monitoring apparatus for measuring a thickness of a layer to be measured that increases or decreases due to surface treatment on a sample having a layer structure, On the other hand, a light source that irradiates measurement light having a predetermined wavelength width, an interference optical system that interferes with light reflected from the upper surface and the lower surface of the layer to be measured, and a spectrum that disperses the interference light by the interference optical system. A surface treatment status monitoring apparatus comprising: a detection unit that detects, for each wavelength, the light wavelength-dispersed by the spectroscopic unit;
a) Upper surface reflected light that is light reflected from the upper surface of the measured layer, and first reflected light that is light emitted from the upper surface of the measured layer after entering the measured layer and reflected by the lower surface thereof The first term corresponding to the intensity of the first interference light that is interference light with the light, the upper surface reflected light, and the light entering the measured layer and reflected on the lower surface thereof, and then reflected on the upper surface of the measured layer A storage unit storing a theoretical expression including a second term corresponding to the intensity of the second interference light that is interference light with the second reflected light that is emitted after being reflected by the lower surface;
b) The thickness of the layer to be measured is adjusted so that the plurality of intensity values detected for each wavelength by the detection unit and the theoretical value of the interference light calculated for each wavelength by the theoretical formula are matched. A thickness determining unit to be determined;
It is characterized by providing.

The theoretical formula used in the surface treatment status monitoring apparatus according to the first invention is a formula including a first term corresponding to the intensity of the first interference light and a second term corresponding to the intensity of the second interference light. For example, the following formula (1) can be used. In this equation (1), the intensity for each wavelength of the light obtained by causing the light reflected from the upper and lower surfaces of the measured layer to interfere with each other at the thickness T (t) and the wavelength λ of the measured layer. It is expressed by a term that periodically changes in accordance with the ratio of the product of the refractive index n (λ) of the layer and the wavelength λ.

In equation (1), t is time, Rr (λ) is measured in advance, the intensity of reflected light from the surface of the layer under measurement (for example, the substrate), α ₁ is the top surface of the layer under measurement or the measurement Coefficients relating to the intensity of light reflected from the lower surface of the layer, α ₂ and α ₃ are coefficients relating to the intensity of interference light. The coefficients α ₁ , α _2, and α ₃ change with time in accordance with the state of the layer to be measured and the change in the thickness T (t).

  The reason why not only the first interference light but also the term corresponding to the intensity of the second interference light is included in the theoretical formula used in the surface treatment status monitoring apparatus according to the first invention will be described.

  As described above, when a white light source is used, the intensity of interference light or the like after wavelength separation is reduced, and therefore it is necessary to use a light source having a higher intensity than the white light source. Further, in order to capture a periodic change in the intensity of the interference light with respect to the wavelength, it is necessary to detect intensity values Sig (λ) at a plurality of wavelengths. Therefore, as the light source, there is a light source capable of emitting light having a higher intensity and a wavelength width than a white light source, for example, an SLD (= Super Luminescent Diode) light source having a full width at half maximum of about 15 nm. Used.

  However, when the layer to be measured is a thin layer such as a resist film, the period of change in the intensity of the interference light with respect to the wavelength becomes long. For this reason, even if interference light is detected for each wavelength within the wavelength range of about 15 nm using an SLD light source, the intensity value is not significantly different and the change in the intensity of the interference light cannot be captured. It may be difficult to accurately determine the thickness of the layer.

  The above equation (1) includes not only a cos function that changes at 2T (t) / λ, but also a cos function that changes at 4T (t) / λ. Therefore, the thickness determining unit substantially determines the thickness T (t) of the film layer so that the detected value Sig (λ) of the intensity for each wavelength matches the theoretical value Rm (λ, t). The wavelength band is doubled. In the surface treatment status monitoring apparatus according to the present invention, by using a theoretical formula including a term corresponding to the intensity of the second interference light, even when the layer to be measured is thin and the period of change in the intensity of the interference light with respect to the wavelength is long, The thickness T (t) of the layer to be measured can be accurately determined by capturing the intensity change.

When the interference light is wavelength-separated and the light after wavelength separation is detected by an array detector including a plurality of detection elements, the same intensity value Sig (λ) as the number of detection elements is obtained each time detection is performed. Then, the theoretical value Rm (λ, t) of the intensity at each of the plurality of wavelengths detected by the equation (1) is calculated, and the intensity value Sig (λ) and the theoretical value Rm (λ, t) are equal at each wavelength. As described above, the thickness T (t) of the layer to be measured and the coefficients α ₁ , α _2, and α ₃ are determined as parameters of the equation (1). Thereby, the thickness T (t) of the layer to be measured can be determined in real time. In determining the degree of coincidence between the theoretical value Rm (λ, t) and the detected intensity value Sig (λ), for example, the residual sum of squares σ shown in the following equation (2) is calculated for each value of T (t). Then, it is possible to use a method for determining that a combination of parameters having the smallest value σ has the highest degree of matching. The number of wavelengths that match the intensity value Sig (λ) and the theoretical value Rm (λ, t) is the number of parameters included in the theoretical formula (T (t), coefficient α ₁ , 4 or more of α ₂ and α ₃ suffice.

  The thickness determination unit compares the detected value of the intensity for each wavelength with the theoretical value, changes the value of the thickness T (t) included in the theoretical formula, and sets the thickness so that the detected value matches the theoretical value. Although the value of the thickness T (t) is determined, if the time required until the value of the thickness T (t) is determined becomes long, the real-time property of the measurement is lost. Therefore, it is preferable that a narrowing condition when the thickness determining unit determines the thickness of the layer to be measured is set in advance, and the thickness T (t) of the layer to be measured is determined within the range of the condition. By setting the narrowing conditions in this manner, the thickness determination unit can speed up determination of the thickness of the layer to be measured, and real-time measurement can be ensured. In this case, the initial thickness determination accuracy may not always be high, so when the thickness is determined for the second and subsequent times, the previous determination value is used as an initial value, and the value is updated. It is configured so that the accuracy of determination is high.

That is,
In the storage unit, an initial value of the thickness of the layer to be measured and a narrowing condition when determining the thickness of the layer to be measured by the thickness determination unit are stored,
The thickness determining unit determines the thickness of the measured layer based on the initial value and the narrowing condition when determining the initial thickness, and determines the previous determined value and the narrowing when determining the thickness after the second time. It is desirable to make an estimation based on the inclusion conditions.

Another aspect of the first invention is a surface treatment status monitoring method for measuring a thickness of a layer to be measured that increases or decreases due to surface treatment on a sample having a layer structure, and has a predetermined wavelength with respect to the sample. A light source that emits measurement light having a width; an interference optical system that interferes with light reflected from the upper surface and the lower surface of the layer to be measured; a spectroscopic unit that wavelength-disperses interference light from the interference optical system; In the surface treatment status monitoring method using the apparatus comprising: a detection unit that detects, for each wavelength, the light wavelength-dispersed by the unit,
a) Upper surface reflected light that is light reflected from the upper surface of the measured layer, and first reflected light that is light emitted from the upper surface of the measured layer after entering the measured layer and reflected by the lower surface thereof The first term corresponding to the intensity of the first interference light that is interference light with the light, the upper surface reflected light, and the light entering the measured layer and reflected on the lower surface thereof, and then reflected on the upper surface of the measured layer Further, the theoretical value of the intensity of the interference light is calculated by a theoretical formula including a second term corresponding to the intensity of the second interference light that is the interference light with the second reflected light that is emitted after being reflected from the lower surface. And
b) determining the thickness of the layer to be measured so that a plurality of intensity values detected for each wavelength by the detection unit and the theoretical value of the intensity respectively match.
It is characterized by that.

The second invention made to solve the problem is a surface treatment status monitoring device for measuring a thickness of a layer to be measured that increases or decreases by surface treatment on a sample having a layer structure, the sample being A light source that emits measurement light having a predetermined wavelength width, an interference optical system that interferes with light reflected from the upper surface and the lower surface of the measured layer, and wavelength dispersion of the interference light by the interference optical system In a surface treatment status monitoring apparatus comprising: a spectroscopic unit; and a detection unit that detects light wavelength-dispersed by the spectroscopic unit for each wavelength.
a) a spectrum acquisition unit that acquires an interference light spectrum based on the intensity of each wavelength detected by the detection unit at a plurality of time points;
b) a frequency component extraction unit for converting the interference light spectrum from a wavelength axis to a wave number axis and extracting the frequency component;
c) The change condition of the thickness of the measured layer set in advance is compared with the change of the frequency component extracted by the frequency component extraction unit, and the frequency component that matches the change condition is compared with the thickness of the measured layer. A frequency component determination unit to determine as
It is characterized by providing.

  In the second aspect of the invention, the intensity Rm (λ, t) of the interference light changes periodically with the thickness T (t) of the measured layer as a variable, for example, expressed by a cos function. Use. That is, the interference light spectrum obtained by wavelength-separating and detecting the interference light is Fourier-transformed to obtain the optical path difference of the reflected light related to the interference light, and the thickness T ( t) is measured in real time.

  The intensity of interference light generated by an arbitrary combination of reflected light at each interface of a sample having a layer structure is superimposed on the spectrum of interference light actually obtained. Therefore, for example, when this spectrum is subjected to Fourier transform, values of optical path length differences respectively corresponding to the plurality of interference lights are obtained. When the change in the plurality of optical path length differences is traced during the surface treatment, the change is reflected by reflecting the combination of reflected light that causes the optical path length difference. Therefore, in the surface treatment status monitoring apparatus according to the second aspect of the invention, for example, when measuring the remaining thickness of the layer to be etched, the frequency component determination unit changes at a speed corresponding to the etching speed set in the etching apparatus. By measuring the frequency component to be extracted, the thickness of the measured layer is measured in real time. That is, when measuring the remaining thickness of the layer to be etched, the change in the thickness of the layer to be measured described above is that the frequency component changes at a rate similar to the etching rate set in the etching apparatus. It becomes a condition. As a method for extracting frequency components, a maximum entropy method which is a stochastic method can be used in addition to the Fourier transform.

  When the measured layer is an etched layer whose thickness changes during the etching process, immediately after the start of etching, the optical path length of the reflected light from the bottom surface of the hole or the like formed by etching and the non-etched part of the etched layer Since the optical path lengths of the reflected light from the upper surface of the light are substantially the same, it is difficult to separate the frequency components of the interference light related to them. Also, just before the etching process is completed, the optical path length of the reflected light from the bottom surface of the hole or the like formed by etching is almost the same as the optical path length of the reflected light from the lower surface of the etched layer. It is difficult to separate frequency components.

Therefore, in the surface treatment status monitoring apparatus according to the second invention,
The surface treatment is an etching process, the measured layer is an etched layer,
d) a degree-of-separation determination unit that determines the degree of separation of a plurality of frequency components obtained by the frequency component extraction unit;
e) an etching depth measuring unit that measures the depth of the hole formed in the etched layer at the plurality of points;
f) Based on the value of the frequency component determined by the frequency component determination unit and the value of the depth of the hole at a plurality of time points when it is determined that the frequency component is separated by the separation degree determination unit. A thickness determining unit for determining the thickness of the measurement layer;
It is desirable to provide.

  In the aspect including the separation degree determination unit and the thickness determination unit, the value of the frequency component and the value of the depth of the etching hole at a plurality of time points obtained in a state where the target frequency component is separated from other frequency components. Based on the above, the thickness of the layer to be measured is determined. Thereby, even when it is difficult to separate the frequency component of the interference light, for example, just before the end of the etching process, the remaining thickness of the etching target layer can be accurately determined. In addition, the completion timing of etching of the etching target layer can be predicted.

Another aspect of the second invention is a surface treatment status monitoring device for measuring a thickness of a layer to be measured that increases or decreases due to surface treatment on a sample having a layer structure, and has a predetermined wavelength with respect to the sample. A light source that emits measurement light having a width; an interference optical system that interferes with light reflected from the upper surface and the lower surface of the layer to be measured; a spectroscopic unit that wavelength-disperses interference light from the interference optical system; A detection unit that detects, for each wavelength, the light wavelength-dispersed by the unit, and a surface treatment status monitoring method using an apparatus comprising:
a) At a plurality of times, an interference light spectrum is obtained based on the intensity for each wavelength detected by the detection unit,
b) converting the interference light spectrum from the wavelength axis to the wave number axis, and extracting the frequency component;
c) The change condition of the thickness of the measured layer set in advance is compared with the change of the extracted frequency component, and the frequency component that matches the change condition is determined as the thickness of the measured layer.
It is characterized by that.

Each of the surface treatment status monitoring apparatus and method according to the first and second aspects of the present invention includes a theoretical formula that expresses the intensity for each wavelength of the interference light as a function of the thickness of the layer to be measured, and the intensity for each wavelength of the interference light. Based on the technical idea of measuring in real time the change in dimension of the structure to be measured based on the detected value.
Using the surface treatment status monitoring apparatus or method according to the first invention, comparing the theoretical value of the intensity for each wavelength of the interference light and the detected value, and determining the thickness of the measured layer so as to match them Thus, the thickness of the layer to be measured can be measured in real time.
When using the surface treatment status monitoring apparatus or method according to the second invention, the interference light spectrum created from the detected value of the intensity of the interference light is Fourier-transformed to obtain the optical path length difference of the light related to the interference light. By extracting the one that matches the change condition of the layer to be measured, the thickness of the layer to be measured can be measured in real time.

1 is a main part configuration diagram of a surface treatment status monitoring apparatus according to Embodiment 1. FIG. The figure explaining the reflected light from the sample 50. FIG. 5 is a flowchart for explaining a surface treatment status monitoring method according to the first embodiment. FIG. 6 is a configuration diagram of a main part of a surface treatment status monitoring apparatus according to a second embodiment. FIG. 6 illustrates reflected light from a sample. 9 is a flowchart for explaining a surface treatment status monitoring method according to a second embodiment. 7 shows an example of an interference light spectrum in the second embodiment. The example which extracted the frequency component from the interference light spectrum. The graph which shows the relationship between a frequency component and etching depth. The figure explaining the isolation | separation state of the frequency component immediately after an etching start. The figure explaining the isolation | separation state of the frequency component just before completion | finish of an etching.

  Embodiments of a surface treatment status monitoring apparatus and method according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a surface treatment status monitoring apparatus according to a first embodiment. This surface treatment status monitoring device is a device for monitoring the resist thickness of the sample 50, the substrate thickness, and the like that change from moment to moment by processing in, for example, a plasma etching device or a substrate polishing device. The surface treatment status monitoring apparatus of this embodiment includes a light source 10, a measurement optical system 20, a spectroscopic unit 30, and a data processing unit 40. The light source 10 and the measurement optical system 20, and the measurement optical system 20 and the spectroscopic unit 30 are connected via an optical fiber.

  The light source 10 of this embodiment is an SLD light source having a center wavelength of 830 nm and a full width at half maximum of 15 nm. Measurement light emitted from the light source 10 is introduced into the incident side optical fiber 21 of the measurement optical system 20, travels through the optical fiber 23 via the fiber coupler 22, and exits from the tip of the optical fiber 23. The measurement light emitted from the end of the optical fiber 23 is irradiated onto the sample 50 through the collimator lens 24.

  The sample 50 of this example is obtained by applying a resist film 52 to the surface of a substrate 51 (see FIG. 2), and the thickness of the resist film 52 decreases with time as etching progresses. The sample 50 is not limited to this, as long as the thickness of the film formed on the surface of the substrate or the like changes every moment. For example, a film may be deposited on the surface of the substrate 51, that is, a film thickness may increase every moment.

  The reflected light 62 from the surface of the resist film 52 and the reflected light 61 that has passed through the resist film 52 and reflected by the surface of the substrate 51 follow the collimator lens 24 in the opposite direction to the time of light irradiation and enter the optical fiber 23. . Then, the light reaches the spectroscopic unit 30 via the fiber coupler 22. By passing through the optical fiber 23 and reaching the spectroscopic unit 30, the reflected light 61 and 62 interfere to become interference light. The reflected light 61 enters the resist film 52, is reflected at the interface with the substrate 51, and then enters the resist film 52 with the light 61 a emitted from the upper surface of the resist film 52, and has a thickness inside the resist film 52. And light 61b emitted from the upper surface of the resist film 52 after two reciprocations in the direction (see FIG. 2).

  In the spectroscopic unit 30, the interference light is wavelength-dispersed by the diffraction grating 31, and light having a plurality of wavelengths is simultaneously detected by the CCD line sensor 32. The signal corresponding to each wavelength detected by the CCD line sensor 32 is subjected to noise removal by a noise filter (not shown) and input to the data processing unit 40. The reason why the noise filter is used in this embodiment is to suppress the magnitude of noise included in the detection signal to a value smaller than the residual in the calculation of the residual sum of squares described later.

  In addition to the storage unit 41, the data processing unit 40 includes a spectrum acquisition unit 42 and a thickness determination unit 43 as functional blocks. The entity of the data processing unit 40 is a personal computer, and the function of the data processing unit 40 can be exhibited by executing data processing software installed in the computer in advance. An input unit 48 and a display unit 49 are connected to the computer.

  Hereinafter, the operation of the surface treatment status monitoring apparatus of the present embodiment will be described with reference to FIG. 1 and FIG. FIG. 3 is a flowchart of the operation of the surface treatment status monitoring apparatus of this embodiment.

さらに、記憶部４１には、膜厚モニタリングの継続または終了を決定するための終了条件が設定されている。本実施例の終了条件は、エッチング時間終了あるいはエッチング膜厚が所定値を下回ること、のいずれかであり、後者の場合には、図示しないエッチング装置に対してエッチング加工を終了させるための制御信号を出力するようになっている。 The storage unit 41 reads and stores the spectrum data R _r (λ) of the reflected light obtained in advance from the substrate surface not coated with the resist film 52 (step S1). The spectrum data R _r (λ) of the reflected light is obtained by subtracting the dark signal of the CCD line sensor 32 from the actually measured data of the reflected light. The storage unit 41 also includes the above-described theoretical formula (1) and parameters for calculating the interference light intensity using the formula (1) (the resist film thickness T (t) and the coefficient α _1. , Α ₂ , and α ₃ ) and the narrowing-down conditions are stored (step S2). Details of the narrowing conditions will be described later. Since it is difficult to grasp the thickness of the resist film formed during the etching process starts correctly, the initial thickness T ₀ of the thickness T (t) of the resist film, in the etching process beginning Estimated value is set.

Furthermore, the storage unit 41 is set with an end condition for determining whether to continue or end the film thickness monitoring. The end condition of this embodiment is either the end of the etching time or the etching film thickness being less than a predetermined value. In the latter case, the control signal for ending the etching process to an etching apparatus (not shown). Is output.

  After the etching process is started, when the intensity Sig (λ) of the interference light at a plurality of wavelengths is acquired under the control of the spectrum acquisition unit 42 (step S3), the thickness determination unit 43 determines the film thickness of the resist film as follows. Determine T (t).

When determining the initial film thickness T (t), all parameters included in the theoretical formula (1) are determined from initial values (T ₀ , α ₁₀ , α ₂₀ , α ₃₀ ) to predetermined values (ΔT, Δα ₁ , Δα ₂ , A predetermined number (2n _T +1, 2n ₁ +1, 2n ₂ +1, 2n ₃ +1) values separated by Δα ₃ ) are prepared. That is, the above-described narrowing conditions are the predetermined value and the predetermined number, and the following values are prepared for each parameter. Note that the number of values to be prepared for each parameter and the magnitude of the predetermined value are appropriately set in consideration of computer calculation time and the like.
Resist film thickness T (t) = T ₀ ± ΔT × n _T
Coefficient α ₁ = α ₁₀ ± Δα ₁ × n ₁
Coefficient α ₂ = α ₂₀ ± Δα ₂ × n ₂
Coefficient α ₃ = α ₃₀ ± Δα ₃ × n ₃

そして、残差平方和が最小となるパラメータセットを抽出し、その中に含まれるパラメータT(t)の値をレジスト膜の膜厚に決定する（ステップＳ６）。 Then, the values prepared for each parameter are extracted one by one and substituted into the theoretical formula (1), and the theoretical value Rm (λ, t) of the interference light intensity is calculated for each detection wavelength (step S4). Then, the theoretical value Rm () for each of the parameter sets of (2n _T +1) × (2n ₁ +1) × (2n ₂ +1) × (2n ₃ +1) which are all combinations of the prepared parameter values, respectively. When the calculation of λ, t) is completed (YES in step S5), a residual sum of squares σ, which is the sum of squares of the difference between the theoretical value and the detected value at each wavelength, is calculated for each parameter set. The residual sum of squares is calculated by the following equation (2).

A parameter set that minimizes the residual sum of squares is extracted, and the value of the parameter T (t) included therein is determined as the film thickness of the resist film (step S6).

  When the film thickness T (t) of the resist film is determined, it is confirmed whether or not the above-mentioned end condition is satisfied. And when not satisfy | filling completion | finish conditions (it is NO at step S7), step S3-step S6 mentioned above are repeated. However, when calculating the theoretical values for the second and subsequent times, not the initial values of each parameter, but a predetermined number of values separated from each other by a predetermined value with the most recently determined parameter value as the central value are prepared, and all combinations of these values are prepared. Use to calculate the theoretical value. Then, when the end condition is satisfied (YES in step S7), the resist film thickness monitoring is ended.

  Thus, in the surface treatment status monitoring apparatus according to the first embodiment, the detected value Sig (λ) of the intensity of interference light at a plurality of wavelengths and the theoretical value Rm (λ) of the intensity of interference light at the plurality of wavelengths are obtained. The film thickness T (t) included in the parameter set that minimizes the residual sum of squares is determined as the film thickness at that time. Therefore, the film thickness of the layer to be measured can be measured in real time.

Next, a surface treatment status monitoring apparatus according to the second embodiment will be described.
FIG. 4 is a schematic configuration diagram of the surface treatment status monitoring apparatus according to the second embodiment. Of the surface treatment status monitoring apparatus of the second embodiment, the light source 10, the measurement optical system 20, and the spectroscopic unit 30 are the same as those of the first embodiment.

  The surface treatment status monitoring apparatus according to the second embodiment monitors the remaining thickness of the etching target layer 152 of the sample 150 (see FIG. 5) in which the resist film 153 is formed on the substrate having the etching target layer 152 and the lower layer 151. Device.

  In addition to the storage unit 141, the data processing unit 140 includes a spectrum acquisition unit 142, a frequency component extraction unit 143, a frequency component determination unit 144, a separation degree determination unit 145, an initial thickness determination unit 146, and a remaining thickness determination as functional blocks. Part 147 is provided. As in the first embodiment, the data processing unit 140 is a personal computer, and functions as the data processing unit 140 are exhibited by executing data processing software installed in the computer in advance. Can do. An input unit 148 and a display unit 149 are connected to the computer.

  Hereinafter, the operation of the surface treatment status monitoring apparatus according to the second embodiment will be described with reference to FIGS. 4 and 6. FIG. 6 is a flowchart of the operation of the surface treatment status monitoring apparatus of this embodiment.

  After starting the etching process, first, interference light intensities Sig (λ) at a plurality of wavelengths are acquired under the control of the spectrum acquisition unit 142 to obtain an interference light spectrum (step S11). FIG. 7A shows an example of an interference light spectrum obtained simultaneously with the start of etching, and FIG. 7B shows an example of an interference light spectrum obtained at 300 seconds after the start of etching.

  When the interference light spectrum is obtained, the frequency component extraction unit 143 converts the interference light spectrum to the wavenumber axis, and then performs Fourier transform to extract the frequency component (step S12).

  As indicated by the above-described equation (1), the intensity of the interference light has a wavelength-intensity characteristic that periodically changes in accordance with the optical path difference between the two reflected lights constituting the interference light. Therefore, when the obtained interference light spectrum is converted into the wave number axis and Fourier-transformed, a frequency component corresponding to the optical path difference between the two reflected lights constituting the interference light can be extracted. The frequency component can be extracted not only by Fourier transform but also by a maximum entropy method that is a stochastic method.

Here, the interference light obtained from the sample 150 will be described with reference to FIG. Since the sample 150 of the present example has the above-described layer structure, the following reflected lights 1 to 5 are obtained from the sample 150, and the wavelength corresponding to the optical path difference by any combination thereof. -Interference light having intensity characteristics is generated.
Reflected light 1: reflected light 161 from the surface of the resist film 153
Reflected light 2: Reflected light 162 from the interface between the resist film 153 and the layer to be etched 152
Reflected light 3: Reflected light 163 from the bottom of the etched portion
Reflected light 4: Reflected light 165 from the interface between the etched layer 152 and the lower layer 151 in the non-etched portion.
Reflected light 5: Reflected light 164 from the interface between the etched layer 152 and the lower layer 151 in the etched portion

In the following description, the interference light formed by the combination of the reflected lights 1 to 5 will be described as follows.
Interference light A: Interference light between reflected light 1 and reflected light 2 Interference light B: Interference light between reflected light 1 and reflected light 3 Interference light C: Interference light between reflected light 1 and reflected light 4 Interference light D: Reflected light 2 Interference light E of reflected light 3 Interference light E: Interference light of reflected light 2 and reflected light 4 Interference light F: Interference light of reflected light 3 and reflected light 4 Interference light G: Interference light of reflected light 3 and reflected light 5

ここで、T_etchは非エッチング部における被エッチング層１５２の厚さ（エッチング部における被エッチング層１５２の初期厚さ）、D_etchはエッチング深さである。 The remaining thickness T _left of the etching target layer 152 monitored in this embodiment is expressed by the following formula (3).

Here, T _etch is the thickness of the layer to be etched 152 in the non-etched part (the initial thickness of the layer to be etched 152 in the etched part), and D _etch is the etching depth.

ここで、L_iは波長λ_iにおける測定光の強度、R₃₅は測定光に対する反射光３及び反射光５の強度の割合の積、N_etchは被エッチング層１５２の屈折率である。 The intensity L _G of the interference light G corresponding to T _left can be expressed by the following equation (4).

Here, L _i is the intensity of the measurement light at the wavelength λ _i , R ₃₅ is the product of the ratio of the intensity of the reflected light 3 and the reflected light 5 to the measurement light, and N _etch is the refractive index of the etched layer 152.

  In actual measurement, in addition to the interference light G, light including interference light corresponding to a combination of a plurality of reflected lights is detected, and when this is Fourier-transformed, frequency components respectively corresponding to the combinations of the plurality of reflected lights are obtained. can get. As an example, the frequency components of the interference lights A to G extracted from the interference light spectrums of FIGS. 7A and 7B are shown in FIGS. 8A and 8B, respectively.

  If frequency component extraction by the frequency component extraction unit 143 is the first time (YES in step S13), the process returns to step S11 to acquire the interference light spectrum, and the frequency component is extracted again in the same procedure as described above.

When the frequency component extraction unit 143 extracts the frequency component a plurality of times after the start of etching (NO in step S13), the change of each frequency component can be extracted. In the case of the present embodiment, the frequency component G _freq of the interference light G indicates a change according to the progress of the etching process, so the frequency component determination unit 144 extracts a frequency component that matches the condition, and the component is the frequency component. G _freq is determined (step S14). That is, the condition for changing the thickness of the layer to be measured in the present invention is that the frequency component is changed at a rate similar to the etching rate set in the etching apparatus in this embodiment. The frequency components of the interference lights A to G described in FIG. 8 are based on the result determined by the frequency component determination unit 144.

When the frequency component determination unit 144 determines the frequency component G _freq , the separation degree determination unit 145 determines the separation degree of the frequency component G _freq . The degree of separation can be determined by various methods. For example, the degree of separation is determined based on whether or not the extracted frequency component G _freq is a predetermined value or more away from other frequency components. If it is determined that the frequency component G _freq is separated from the other frequency components (YES in step S15), the remaining thickness determining unit 147 determines the remaining thickness T _left of the etching target layer 152 from the frequency component G _freq. Obtained (step S16). Further, the etching depth (depth of the hole in the etched portion) D _etch is determined (step S17). The etching depth D _etch can be obtained from frequency components of other interference light, for example.

As described above, if the frequency component G _freq is separated from other frequency components, the remaining thickness of the etched layer 152 can be obtained from the frequency component G _freq . However, immediately before the end of etching, the frequency component G _freq of the interference light G is mixed with the frequency components and DC components of other interference light, so that it is difficult to separate only the frequency component G _freq of the interference light G. Therefore, in the time period when the frequency component G _freq of the interference light G is separated from the other frequency components, the coefficient relating the etching depth D _etch of the etching portion and the frequency component G _freq of the interference light G as follows. _Ask for K _etch and O _etch .

The degree-of-separation determination unit 145 determines whether or not the frequency component G _freq separated from other frequency components has been acquired at a plurality of points in time, and if a plurality of frequency components have been acquired (YES in step S18), Go to step. If NO in step S15 or step S18, the process returns to step S11, and the above steps are executed again.

If there are a plurality of frequency components G _freq determined to be separated by the separation degree determination unit 145 (YES in step S16), the remaining thickness determination unit 147 determines the frequency based on the values of the plurality of frequency components G _freq. The component G _freq is related to the etching depth D _etch . This point will be described below.

When the vertical axis represents the frequency component G _freq and the horizontal axis represents the etching depth D _etch, and two sets of values of the frequency component G _freq and the etching depth D _etch are plotted, the graph shown in FIG. 9A is obtained. The relationship between the frequency component G _freq and the etching depth D _etch has a certain slope K _etch (exactly depending on the refractive index of the etched layer 152 and the wavelength of the incident light) and the intercept O _etch , This is expressed by equation (5).

When G _freq and D _etch are acquired at a plurality of time points (t1, t2), the initial thickness determining unit 146 obtains the slope K _etch and the intercept O from the following equations (6), (7) to (5). _Etch is obtained (step S19).

Since Equation (5) is a first order polynomial, K _{etch and} O _etch may be obtained by using a first order polynomial approximation by a least square method from G _freq and D _etch obtained at a plurality of time points.

The frequency component G _freq of the interference light G is proportional to the product of the remaining thickness T _left of the etched portion 152 and the refractive index N _etch of the etched portion 152. Therefore, the frequency component G _freq is expressed by the following equation (8) with a constant α.

From the equations (5) and (8), the following equations (9) and (10) are derived.

Further, from the equations (9) and (10), the initial thickness T _etch of the etched portion 152 is obtained by the following equation (11) (step S20).

The remaining thickness T _left of the etched portion 152 is a value obtained by subtracting the etching depth D _etch from the initial thickness T _etch , and is represented by the equation (12). Thereby, even if the frequency component G _freq of the interference light G is not separated from other frequency components, the remaining thickness T _left of the etching target layer 152 can be accurately obtained.

When the initial thickness T _etch of the etching target layer 152 is determined from the equation (11), the spectrum acquisition unit 142 acquires the interference light spectrum again (step S21). Then, the etching depth D _etch is obtained in the same manner as in step S17 (step S22). Then, the remaining thickness T _left of the etched layer 152 is determined from the equation (12) and the etching depth D _etch (step 23). When the frequency component G _freq of the interference light G obtained from the interference light spectrum data acquired in step S20 is separated from other frequency components, (etching depth D _etch , frequency component G _freqq ) is The values of K _etch and O _etch are sequentially updated by using the least square method or the like (FIG. 9B). As a result, noise of measurement of D _etch can be removed, and the accuracy of the values of K _etch and O _etch (that is, the value of the initial thickness T _etch of the etching target layer 152 obtained from these values) can be improved. it can. Each step in the acquisition of the interference light spectrum from (step S20) to determine the residual thickness T _left of the layer to be etched 152 is performed at predetermined time intervals, YES when the residual thickness T _left becomes a predetermined value (at step S24 ), The etching process for the etching target layer 152 is completed.

The values of K _etch and O _etch (that is, the value of the initial thickness T _etch of the etched layer 152 obtained from these values) are obtained at an arbitrary timing when the frequency component G _freqq is separated from other frequency components. be able to. However, the interference light G is reflected light at the bottom surface of the hole formed in the etched layer 152 by etching and reflected light at the lower layer interface, and the region where the reflected light contributing to the interference light G is generated is narrow. Therefore, the intensity of the interference light G is smaller than the intensity of the other interference light. Therefore, it is desirable to increase the accuracy of the values of K _etch and O _etch (that is, the value of the initial thickness T _etch of the etched layer 152 obtained from these values) when the etching depth D _etch is shallow. .

FIG. 10 shows an example of the state of each frequency component immediately after the start of etching. FIGS. 10A to 10D are obtained when 20 seconds, 200 seconds, 470 seconds, and 500 seconds have elapsed from the start of etching, respectively. As can be seen from FIG. 10, since the frequency component G _freq cannot be separated from other frequency components immediately after the etching is started, it is difficult to accurately determine the value of the frequency component G _freq (that is, the thickness of the layer to be etched). .
FIG. 11 shows an example of the state of each frequency component immediately before the end of etching. FIGS. 11A to 11D are obtained when the remaining thickness of the layer to be etched becomes 8.3 μm, 5.0 μm, 1.7 μm, and 0.17 μm, respectively. As can be seen from FIG. 11, it is difficult to separate the frequency component G _freq from other components immediately before the end of etching.
Even at a time other than immediately after the start of etching or immediately before the end, the frequency component G _freq cannot be separated in a time zone in which the thickness of the etched layer is approximately the same as the thickness of another layer.
In this embodiment, the values of the component G _freq and the etching depth D _etch are obtained at a plurality of times when the frequency component G _freq is separated from the other components, and based on this, the accurate initial thickness T of the etching target layer 152 is obtained. Determine _etch . Therefore, the remaining thickness T _{left of the} layer to be etched 152 can be accurately determined in real time even in a time zone immediately before the end of etching in which the frequency component G _freq is not separated from the other components. In addition, it is possible to accurately predict the timing at which the etching of the etching target layer is completed.

Examples 1 and 2 described above are merely examples, and can be appropriately changed in accordance with the spirit of the present invention. For example, a surface treatment status monitoring apparatus having the configurations of the first and second embodiments may be configured and the above steps may be performed in parallel.
Further, in the first embodiment, the film thickness of the resist film and the thickness of the etching target layer in Example 2 have been described as examples. However, the same applies to the case where the measurement target layer is another layer. The thickness of the layer can be monitored by the following procedure.

  In addition, the configurations of an SLD light source, a diffraction grating, a CCD line sensor, and the like given as an example can be replaced as long as they have equivalent functions, and are not limited to these. Further, in the above embodiment, the thickness of the film layer was monitored based on various specific mathematical formulas, but as described above, the technical idea of the present invention is the reflected light from the substrate surface that can be acquired in advance, The thickness of the film layer is measured in real time during the surface treatment based on the theoretical formula showing the relationship with the interference light spectrum obtained by actual measurement. Accordingly, theoretical formulas other than the formulas shown in the above embodiments can be used within the scope of this technical idea.

DESCRIPTION OF SYMBOLS 10 ... Light source 20 ... Measurement optical system 21 ... Incident side optical fiber 22 ... Fiber coupler 23 ... Optical fiber 24 ... Collimating lens 30 ... Spectrometer 31 ... Diffraction grating 32 ... CCD line sensor 40, 140 ... Data processing part 41, 141 ... Storage unit 42, 142 ... Spectrum acquisition unit 43 ... Thickness determination unit 140 ... Data processing unit 141 ... Storage unit 142 ... Spectrum acquisition unit 143 ... Frequency component extraction unit 144 ... Frequency component determination unit 145 ... Separation degree determination unit 146 ... Initial stage Thickness determining unit 147 ... Remaining thickness determining unit 48, 148 ... Input unit 49, 149 ... Display unit 50, 150 ... Sample 51 ... Substrate 52, 153 ... Resist film 151 ... Lower layer 152 ... Etched layer 152 ... Etched part 61 , 61a, 61b, 62, 161-165 ... reflected light

Claims (9)

A surface treatment status monitoring apparatus for measuring a thickness of a layer to be measured that increases or decreases due to surface treatment on a sample having a layer structure, the light source irradiating measurement light having a predetermined wavelength width to the sample; An interference optical system for interfering light reflected from the upper surface and the lower surface of the layer to be measured, a spectroscopic unit for wavelength-dispersing interference light from the interference optical system, and the wavelength-dispersed light by the spectroscopic unit for each wavelength In the surface treatment status monitoring device comprising:
a) Upper surface reflected light that is light reflected from the upper surface of the measured layer, and first reflected light that is light emitted from the upper surface of the measured layer after entering the measured layer and reflected by the lower surface thereof The first term corresponding to the intensity of the first interference light that is interference light with the light, the upper surface reflected light, and the light entering the measured layer and reflected on the lower surface thereof, and then reflected on the upper surface of the measured layer A storage unit storing a theoretical expression including a second term corresponding to the intensity of the second interference light that is interference light with the second reflected light that is emitted after being reflected by the lower surface;
b) The thickness of the layer to be measured so that the plurality of intensity values detected for each wavelength by the detection unit and the theoretical value of the intensity of interference light calculated for each wavelength by the theoretical formula are matched. A thickness determining unit for determining the thickness;
A surface treatment status monitoring device comprising: The theoretical value of the intensity of the interference light is Rm (λ, t), λ is the wavelength of the measurement light, t is time, Rr (λ) is the intensity of reflected light from the upper surface of the lower layer of the measured layer, α ₁ Is a coefficient related to the intensity of light reflected from the upper surface of the lower layer and the upper surface of the measured layer, α ₂ is a coefficient related to the first interference light, α ₃ is a coefficient related to the second interference light, T When (t) is the thickness of the measured layer at time t, the theoretical formula is

The surface treatment status monitoring apparatus according to claim 1, wherein: In the storage unit, an initial value of the thickness of the measured layer and a narrowing condition when determining the thickness of the measured layer by the thickness determining unit are stored,
The thickness determining unit determines the thickness of the measured layer based on the initial value and the narrowing condition when determining the initial thickness, and determines the previous determined value and the narrowing when determining the thickness after the second time. The surface treatment status monitoring apparatus according to claim 1, wherein the estimation is performed based on an insertion condition. A surface treatment status monitoring apparatus for measuring a thickness of a layer to be measured that increases or decreases due to surface treatment on a sample having a layer structure, the light source irradiating measurement light having a predetermined wavelength width to the sample; An interference optical system for interfering light reflected from the upper surface and the lower surface of the layer to be measured, a spectroscopic unit for wavelength-dispersing interference light from the interference optical system, and the wavelength-dispersed light by the spectroscopic unit for each wavelength A surface treatment status monitoring method using an apparatus comprising:
a) Upper surface reflected light that is light reflected from the upper surface of the measured layer, and first reflected light that is light emitted from the upper surface of the measured layer after entering the measured layer and reflected by the lower surface thereof The first term corresponding to the intensity of the first interference light that is interference light with the light, the upper surface reflected light, and the light entering the measured layer and reflected on the lower surface thereof, and then reflected on the upper surface of the measured layer Further, the theoretical value of the intensity of the interference light is calculated by a theoretical formula including a second term corresponding to the intensity of the second interference light that is the interference light with the second reflected light that is emitted after being reflected from the lower surface. And
b) determining the thickness of the layer to be measured so that a plurality of intensity values detected for each wavelength by the detection unit and the theoretical value of the intensity respectively match.
Surface treatment status monitoring method characterized by the above. A surface treatment status monitoring apparatus for measuring a thickness of a layer to be measured that increases or decreases due to surface treatment on a sample having a layer structure, the light source irradiating measurement light having a predetermined wavelength width to the sample; An interference optical system for interfering light reflected from the upper surface and the lower surface of the layer to be measured, a spectroscopic unit for wavelength-dispersing interference light from the interference optical system, and the wavelength-dispersed light by the spectroscopic unit for each wavelength In the surface treatment status monitoring device comprising:
a) a spectrum acquisition unit that acquires an interference light spectrum based on the intensity of each wavelength detected by the detection unit at a plurality of time points;
b) a frequency component extraction unit for converting the interference light spectrum from a wavelength axis to a wave number axis and extracting the frequency component;
c) The change condition of the thickness of the measured layer set in advance is compared with the change of the frequency component extracted by the frequency component extraction unit, and the frequency component that matches the change condition is compared with the thickness of the measured layer. A frequency component determination unit to determine as
A surface treatment status monitoring device comprising:   The surface treatment status monitoring apparatus according to claim 5, wherein the frequency component extraction unit extracts the frequency component by Fourier transform.   The surface treatment status monitoring apparatus according to claim 5, wherein the frequency component extraction unit extracts the frequency component by a maximum entropy method. The surface treatment is an etching process, the measured layer is an etched layer,
d) a degree-of-separation determination unit that determines the degree of separation of a plurality of frequency components obtained by the frequency component extraction unit;
e) an etching depth measuring unit that measures the depth of the hole formed in the etched layer at the plurality of points;
e) Based on the value of the frequency component determined by the frequency component determination unit and the value of the depth of the hole at a plurality of time points when it is determined that the frequency component is separated by the separation degree determination unit. An initial thickness determining unit for determining an initial thickness of the layer to be measured;
The surface treatment status monitoring device according to any one of claims 5 to 7, further comprising: A surface treatment status monitoring apparatus for measuring a thickness of a layer to be measured that increases or decreases due to surface treatment on a sample having a layer structure, the light source irradiating measurement light having a predetermined wavelength width to the sample; An interference optical system for interfering light reflected from the upper surface and the lower surface of the layer to be measured, a spectroscopic unit for wavelength-dispersing interference light from the interference optical system, and the wavelength-dispersed light by the spectroscopic unit for each wavelength A surface treatment status monitoring method using an apparatus comprising:
a) At a plurality of times, an interference light spectrum is obtained based on the intensity for each wavelength detected by the detection unit,
b) converting the interference light spectrum from the wavelength axis to the wavenumber axis, and extracting the frequency component;
c) The change condition of the thickness of the measured layer set in advance is compared with the change of the extracted frequency component, and the frequency component that matches the change condition is determined as the thickness of the measured layer.
Surface treatment status monitoring method characterized by the above.

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