JP2009092454A - Device and method for analyzing multilayer film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer film analyzer and a multilayer film analyzing method capable of measuring the thickness of a multilayer film sample having wavelength dependence with higher accuracy. <P>SOLUTION: A wavenumber conversion section 721 calculates a wavenumber K<SB>1</SB>(λ) and a wavenumber-converted reflectivity R<SB>1</SB>'(λ)(=R(λ)/(1-R(λ))) successively for each wavelength stored in a buffer section 71, and outputs them to a buffer section 731. The buffer section 731 stores those wavenumbers K<SB>1</SB>(λ) and reflectivities R<SB>1</SB>'(λ) output successively from the conversion section 721, while associating them with each other. A Fourier conversion section 741 applies Fourier conversion to a wavenumber-converted reflectivity R<SB>1</SB>'(K<SB>1</SB>) stored in the buffer section 731 as to the wavenumber K<SB>1</SB>to calculate a power spectrum P<SB>1</SB>. A peak search section 751 searches for peaks appearing in the power spectrum P<SB>1</SB>calculated by the conversion section 741, and acquires a film thickness corresponding to each peak position. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a multilayer film analysis apparatus and a multilayer film analysis method, and more specifically to a technique for measuring a film thickness with higher accuracy.

  Conventionally, a method using a reflectance spectrum is known as a method for measuring the film thickness of a multilayer film sample such as a functional resin film or a semiconductor substrate. More specifically, first, the multilayer film sample is irradiated with white light, and the reflectance spectrum of the reflected light is acquired. And after performing a zero filling process, a filter process, etc. with respect to the data of the acquired reflectance spectrum, a power spectrum is acquired using a Fourier transform. Further, the optical film thickness nd (where n is the refractive index of the film and d is the film thickness) is calculated from the peak appearing in the power spectrum, and this optical film thickness nd is divided by the known refractive index n. The geometric film thickness d is calculated. Such film thickness measuring methods are disclosed in, for example, JP-A-2005-308394 (Patent Document 1), JP-A-2005-37315 (Patent Document 2), JP-A-07-294220 (Patent Document 3), It describes in Unexamined-Japanese-Patent No. 10-311708 (patent document 4), Unexamined-Japanese-Patent No. 2003-130614 (patent document 5), etc.

  In general, a substance constituting a thin film (for example, a dielectric) has wavelength dependency on its refractive index. However, in the method disclosed in the above prior art, the power spectrum is calculated on the assumption that the refractive index of the thin film constituting the multilayer film sample does not have wavelength dependency. Therefore, when measuring a multilayer film sample having a wavelength dependency on the refractive index, an error due to the refractive index occurs.

On the other hand, Japanese Patent Laid-Open No. 2001-227916 (Patent Document 6) corrects the optical film thickness nd calculated based on the power spectrum in consideration of the wavelength dependence of the refractive index n. A method of performing is disclosed.
JP 2005-308394 A JP 2005-37315 A JP 07-294220 A Japanese Patent Laid-Open No. 10-311708 JP 2003-130614 A JP 2001-227916 A

However, even in the method disclosed in Japanese Patent Laid-Open No. 2001-227916 (Patent Document 6), some terms appearing in the equation (for example, refractive index n ₂ , dn _f / dk, k = 2π / λ, etc.) ) Still has wavelength dependency, and there is a problem that errors due to wavelength dependency cannot be completely removed.

  The present invention has been made to solve such problems, and its purpose is to analyze a multilayer film that can measure the film thickness of a multilayer film sample having wavelength dependency with higher accuracy. An apparatus and a multilayer analysis method are provided.

  A multilayer film analyzer according to an aspect of the present invention includes a light source that irradiates measurement light having a predetermined wavelength range to a sample in which at least one film is formed on a substrate, and light or sample reflected by the sample. Based on the transmitted light, the spectroscopic unit that acquires the reflectance or transmittance wavelength distribution characteristic, the correspondence between each wavelength in the wavelength distribution characteristic and the value at that wavelength, the wave number for each wavelength and a predetermined relational expression A wave number characteristic converting means for converting to a corresponding relationship with a conversion value calculated according to the above, a frequency converting means for converting the frequency of the wave number with respect to the wave number distribution characteristic having a corresponding relationship converted by the wave number characteristic converting means, and a frequency And a film thickness calculating means for calculating the film thickness of the sample based on the peak appearing in the wave number distribution characteristics after the conversion.

  Preferably, the wave number characteristic conversion means calculates the wave number based on the refractive index of the film included in the sample inputted in advance and the corresponding wavelength.

  Preferably, the relational expression is a function for linearizing the value of reflectance or transmittance at each wavelength with respect to a phase factor related to frequency conversion in the frequency conversion means.

  More preferably, the wavelength distribution characteristic is a wavelength distribution characteristic of the reflectance R acquired based on the light reflected by the sample, and the relational expression is R / (1-R).

  Preferably, the wave number characteristic conversion unit calculates the wave number distribution characteristic for each of the plurality of films when the sample has a plurality of films, and the film thickness calculation unit calculates the frequency after frequency conversion for the plurality of films. Based on the peak appearing in each of the wave number distribution characteristics, the thickness of each of the plurality of films is calculated.

  Preferably, at least one layer structure candidate is sequentially selected based on at least one layer structure information out of the plurality of layer structure information, and a layer structure storage means for storing a plurality of layer structure information in which at least a refractive index and a film thickness are defined. From the selection means, the wavelength distribution characteristic calculating means for calculating the wavelength distribution characteristic of the reflectance or transmittance in the layer structure candidate based on the layer structure information corresponding to the layer structure candidate, and the wave number from the wavelength distribution characteristic of the layer structure candidate Wave number distribution characteristic calculation means for calculating the wave number distribution characteristic after frequency conversion by the same processing as the characteristic conversion means and frequency conversion means, the wave number distribution characteristic after frequency conversion calculated from the actually measured wavelength distribution characteristic, and the wave number distribution Correlation value calculation means for calculating a correlation value between the frequency distribution characteristics after frequency conversion calculated by the characteristic calculation means, and the selection means sequentially selects based on the correlation value. Further comprising determination means for determining the closest match to the measured value of the layer structure candidates.

  A multilayer film analysis method according to another aspect of the present invention includes a step of irradiating a sample having at least one film formed on a substrate with measurement light having a predetermined wavelength range, and light reflected from the sample or the sample. The step of obtaining the wavelength distribution characteristic of reflectance or transmittance based on the light transmitted through the light, the correspondence between each wavelength in the wavelength distribution characteristic and the value at that wavelength, the wave number for each wavelength and a predetermined relational expression Converting to the corresponding relationship with the conversion value calculated in accordance with the step, the step of converting the frequency of the wave number with respect to the wave number distribution characteristic composed of the corresponding relationship converted in the step of converting to the corresponding relationship, Calculating the film thickness of the sample based on the peak appearing in the wave number distribution characteristics.

  According to this invention, it is possible to measure the film thickness of a multilayer film sample having wavelength dependency with higher accuracy.

  Embodiments of the present invention will be described in detail with reference to the drawings. Note that the same or corresponding parts in the drawings are denoted by the same reference numerals and description thereof will not be repeated.

FIG. 1 is a schematic configuration diagram of a multilayer film analyzing apparatus 100 according to an embodiment of the present invention.
Multilayer film analysis apparatus 100 according to the present embodiment typically has a film thickness of each layer in the multilayer film sample based on the wavelength distribution characteristics (hereinafter also referred to as “spectrum”) of the reflected light reflected by the multilayer film sample. Perform measurement and analysis of layer structure. Instead of the spectrum of the reflected light, the spectrum of the light transmitted through the multilayer film sample (transmitted light spectrum) may be used.

  In this specification, a multilayer film sample means a sample in which at least one film is formed on a substrate. Typical multilayer film samples include a multilayer thin film in which a thin film is formed (coated) on the surface of a semiconductor substrate, a glass substrate, a sapphire substrate, a quartz substrate, a film, or the like. More specifically, the thin-film-formed glass substrate is used as a display part of a flat panel display (FPD) such as a liquid crystal display (LCD) or a plasma display panel (PDP). Is done. The thin-film sapphire substrate is used as a nitride semiconductor (GaN: Gallium Nitride) LED (Light Emitting Diode) or LD (Laser Diode). The quartz substrate formed with a thin film is used for various optical filters, optical components, projection liquid crystals, and the like. Hereinafter, the multilayer film sample is also simply referred to as “sample”.

  Referring to FIG. 1, the multilayer film analyzing apparatus 100 includes a measurement light source 10, a collimating lens 12, a cut filter 14, imaging lenses 16 and 36, a diaphragm unit 18, beam splitters 20 and 30, Observation light source 22, optical fiber 24, emitting section 26, pinhole mirror 32, axis conversion mirror 34, observation camera 38, display section 39, objective lens 40, stage 50, and movable mechanism 52. And a spectroscopic measurement unit 60 and a data processing unit 70.

The measurement light source 10 is a light source that generates measurement light having a predetermined wavelength range in order to acquire a spectrum of reflected light from the multilayer film sample, and a white light source having a relatively wide wavelength range is used. Typically, the measurement light source 10 is composed of a deuterium lamp (D ₂ lamp) or a tungsten lamp or a combination thereof.

  The collimating lens 12, the cut filter 14, the imaging lens 16, and the aperture unit 18 are arranged on the optical axis AX <b> 2 connecting the measurement light source 10 and the beam splitter 30, and are measured from the measurement light source 10. Adjust light optically.

  Specifically, the collimating lens 12 is an optical component on which the measurement light from the measurement light source 10 first enters, and refracts the measurement light propagating as a diffused light and converts it into parallel light. The measurement light that has passed through the collimating lens 12 enters the cut filter 14. The cut filter 14 blocks unnecessary wavelength components included in the measurement light. Typically, the cut filter 14 is formed of a multilayer film deposited on a glass substrate or the like. The imaging lens 16 converts the measurement light that has passed through the cut filter 14 from parallel light into convergent light in order to adjust the beam diameter of the measurement light. The measurement light that has passed through the imaging lens 16 is incident on the diaphragm 18. The diaphragm 18 adjusts the amount of measurement light to a predetermined amount and then emits the light to the beam splitter 30. Preferably, the diaphragm unit 18 is disposed at the imaging position of the measurement light converted by the imaging lens 16. The diaphragm amount of the diaphragm unit 18 is appropriately set according to the depth of field of the measurement light incident on the sample, the required light intensity, and the like.

  On the other hand, the observation light source 22 is a light source that generates observation light used for focusing on a sample and confirming a measurement position. The observation light generated by the observation light source 22 is selected so as to include a wavelength that can be reflected by the sample. The observation light source 22 is connected to the emission unit 26 via the optical fiber 24, and the observation light generated by the observation light source 22 propagates through the optical fiber 24, which is an optical waveguide, and then travels from the emission unit 26 to the beam splitter. It is emitted toward 20.

  The emission unit 26 includes a mask unit 26a that masks a part of the observation light generated by the observation light source 22 so that a predetermined observation reference image is projected onto the sample. This observation reference image is for facilitating user focusing even on a sample (typically a transparent glass substrate or the like) on which no pattern is formed. . Note that the shape of the reticle image may be any, but as an example, a concentric or cruciform pattern may be used.

  That is, the light intensity (light quantity) in the beam cross section of the observation light immediately after being generated by the observation light source 22 is substantially uniform, but the mask portion 26a masks (shields) a part of the observation light, thereby observing. The light has a region (shadow region) where the light intensity is substantially zero in the beam cross section. This shadow region is projected onto the sample as an observation reference image.

  The stage 50 is a sample stage for arranging samples, and the arrangement surface thereof is formed flat. The stage 50 is freely driven in three directions (X direction, Y direction, and Z direction) by a movable mechanism 52 that is mechanically coupled as an example. The movable mechanism 52 typically includes a servo motor for three axes and a servo driver for driving each servo motor. The movable mechanism 52 drives the stage 50 in response to a stage position command from a user or a control device (not shown). The positional relationship between the sample and an objective lens 40 described later is changed by driving the stage 50.

  The objective lens 40, the beam splitter 20, the beam splitter 30, and the pinhole mirror 32 are disposed on the optical axis AX1 that extends in a direction perpendicular to the flat surface of the stage 50.

  The beam splitter 30 reflects the measurement light generated by the measurement light source 10, thereby converting the propagation direction of the optical axis AX1 downward in the drawing. The beam splitter 30 transmits the reflected light from the sample propagating along the optical axis AX1 upward in the drawing. Typically, the beam splitter 30 is composed of a half mirror.

  On the other hand, the beam splitter 20 reflects the observation light generated by the observation light source 22, thereby converting the propagation direction of the optical axis AX <b> 1 downward in the drawing. At the same time, the beam splitter 20 transmits the measurement light reflected by the beam splitter 30 that propagates along the optical axis AX1 downward in the drawing. That is, the beam splitter 20 functions as a light injection unit that injects observation light at a predetermined position on the optical path from the measurement light source 10 to the objective lens 40 that is a condensing optical system. The measurement light and the observation light synthesized by the beam splitter 20 enter the objective lens 40. The beam splitter 20 transmits the reflected light from the sample propagating along the optical axis AX1 upward in the drawing. Typically, the beam splitter 20 is composed of a half mirror.

  The objective lens 40 is a condensing optical system for condensing measurement light and observation light that propagates along the optical axis AX1 downward in the drawing. That is, the objective lens 40 converges the measurement light and the observation light so as to form an image at the sample or a position close thereto. The objective lens 40 is a magnifying lens having a predetermined magnification (for example, 10 times, 20 times, 30 times, 40 times, etc.), and a region for measuring the optical characteristics of the sample is incident on the objective lens 40. Compared to the beam cross section, it can be further miniaturized.

  Further, the measurement light and observation light incident on the sample from the objective lens 40 are reflected by the sample and propagate upward on the optical axis AX1. The reflected light passes through the objective lens 40 and then passes through the beam splitters 20 and 30 to reach the pinhole mirror 32.

  The pinhole mirror 32 functions as a light separation unit that separates measurement reflected light and observation reflected light among the reflected light generated in the sample. Specifically, the pinhole mirror 32 includes a reflective surface that reflects the reflected light from the sample propagating along the optical axis AX1 upward in the drawing, and has a hole with a center at the intersection of the reflective surface and the optical axis AX1. (Pinhole) 32a is formed. The size of the pinhole 32a is formed so as to be smaller than the beam diameter at the position of the pinhole mirror 32 of the measurement reflected light generated when the measurement light from the measurement light source 10 is reflected by the sample. Further, the pinhole 32a is disposed so as to coincide with the imaging positions of the measurement reflected light and the observation reflected light generated by reflecting the measurement light and the observation light on the sample, respectively. With such a configuration, the reflected light generated in the sample passes through the pinhole 32a and enters the spectroscopic measurement unit 60. On the other hand, the remaining part of the reflected light is converted in its propagation direction and enters the axis conversion mirror 34.

  The spectroscopic measurement unit 60 measures the spectrum of the reflected measurement light that has passed through the pinhole mirror 32 and outputs the measurement result to the data processing unit 70. More specifically, the spectroscopic measurement unit 60 includes a diffraction grating (grating) 62, a detection unit 64, a cut filter 66, and a shutter 68.

  The cut filter 66, the shutter 68, and the diffraction grating 62 are disposed on the optical axis AX1. The cut filter 66 is an optical filter for limiting a wavelength component outside the measurement range included in the measurement reflected light that passes through the pinhole and enters the spectroscopic measurement unit 60, and particularly blocks the wavelength component outside the measurement range. . The shutter 68 is used to block light incident on the detection unit 64 when the detection unit 64 is reset. The shutter 68 is typically a mechanical shutter that is driven by electromagnetic force.

  The diffraction grating 62 separates the incident measurement reflected light and guides each spectral wave to the detection unit 64. Specifically, the diffraction grating 62 is a reflection type diffraction grating, and is configured so that a diffracted wave for each predetermined wavelength interval is reflected in each corresponding direction. When the measurement reflected wave is incident on the diffraction grating 62 having such a configuration, each wavelength component included is reflected in a corresponding direction and is incident on a predetermined detection region of the detection unit 64. The diffraction grating 62 is typically composed of a flat focus type spherical grating.

  The detection unit 64 outputs an electrical signal corresponding to the light intensity of each wavelength component included in the measurement reflected light that has been dispersed by the diffraction grating 62 in order to measure the reflectance spectrum of the sample. The detection unit 64 typically includes a photodiode array in which detection elements such as photodiodes are arranged in an array, a CCD (Charged Coupled Device) arranged in a matrix, and the like.

  The diffraction grating 62 and the detection unit 64 are appropriately designed according to the measurement wavelength range and the measurement wavelength interval of the optical characteristics.

  The data processing unit 70 measures the film thickness of the sample by performing characteristic processing according to the present invention on the reflectance spectrum acquired by the detection unit 64. Furthermore, the data processing unit 70 can also analyze the layer structure of the sample. A method for measuring the film thickness and a method for analyzing the layer structure will be described later. Then, the data processing unit 70 outputs the measured film thickness and layer structure of the sample as optical characteristics.

  On the other hand, the observation reflected light reflected by the pinhole mirror 32 propagates along the optical axis AX3 and enters the axis conversion mirror 34. The axis conversion mirror 34 converts the propagation direction of the observation reflected light from the optical axis AX3 to the optical axis AX4. Then, the observation reflected light propagates along the optical axis AX4 and enters the observation camera 38.

  The observation camera 38 is an imaging unit that acquires a reflected image obtained by the observation reflected light, and typically includes a CCD (Charged Coupled Device), a CMOS (Complementary Metal Oxide Semiconductor) sensor, or the like. Note that the observation camera 38 typically has sensitivity in the visible band, and often has sensitivity characteristics different from those of the detection unit 64 having sensitivity in a predetermined measurement range. Then, the observation camera 38 outputs a video signal corresponding to the reflected image obtained by the observation reflected light to the display unit 39. The display unit 39 displays a reflected image on the screen based on the video signal from the observation camera 38. The user visually observes the reflected image displayed on the display unit 39 to perform focusing on the sample and confirmation of the measurement position. The display unit 39 typically includes a liquid crystal display (LCD). Instead of the observation camera 38 and the display unit 39, a finder that allows the user to directly view the reflected image may be provided.

(Thickness measurement process 1)
Below, the process which measures the film thickness of the sample in the data processing part 70 is demonstrated.

FIG. 2 is a schematic cross-sectional view of a typical multilayer film sample.
In order to simplify the explanation, from the three layers shown in FIG. 2, an atmosphere layer such as air or vacuum (subscript 0), a thin film to be measured (subscript 1), and a substrate layer (subscript 2). Consider a typical multilayer film sample. With index i the refractive index of each layer, expressed as the refractive index n _i. Since reflection of light occurs at the interface between layers having different refractive indexes, the amplitude reflectance (Fresnel coefficient) of the P-polarized component and the S-polarized component at each interface between the i layer and i + 1 layer having different refractive indexes. Can be expressed as:

Here, φ _i is an incident angle in the i layer. This incident angle φ _i can be calculated from the incident angle in the uppermost atmosphere layer (0 layer) according to Snell's law as follows.

N ₀ sinφ ₀ = N _i sinφ _i
In a thin film having a thickness that allows light to interfere, the light reflected at the reflectance expressed by the above formula reciprocates in the thin film many times. For this reason, the light path length is different between the light directly reflected on the surface and the light after multiple reflection in the thin film, so that the phases are different from each other, and light interference occurs on the thin film surface. In order to show the light interference effect in each thin film, when the phase angle β _i of light in the i-layer thin film is introduced, it can be expressed as follows.

Here, d _i represents the thickness of the i layer, and λ represents the wavelength of incident light.
For further simplification, when light is irradiated perpendicularly to the multilayer film sample, that is, when the incident angle φ _i = 0, there is no distinction between P-polarized light and S-polarized light, and the amplitude reflectance at the interface of each layer The phase angle β _{1 of the} thin film is as follows.

  Further, the reflectance R in the three-layer multilayer film sample shown in FIG. 2 is as follows.

In the above equation, when considering the Fourier transform for the phase angle β ₁ , the phase factor cos 2β ₁ is non-linear with respect to the reflectance R. Therefore, to convert to a function having a linearity for the phase factor cos2β _1. As an example, the reflectance R is converted as shown in the following equation, and a unique variable “wave number conversion reflectance” R ′ is defined.

This wave number conversion reflectance R ′ is a linear expression for the phase factor cos 2β ₁ and has linearity. Here, R _a in the equation is an intercept in the wave number conversion reflectance R ′, and R _b is an inclination in the wave number conversion reflectance R ′. That is, the wave number conversion reflectance R ′ is a function for linearizing the value of the reflectance R at each wavelength with respect to the phase factor cos 2β ₁ related to frequency conversion. As a function for linearizing such a phase factor, a function 1 / (1-R) may be used.

Therefore, the wave number K ₁ in the thin film of interest can be defined as follows.

Here, when the light velocity of the wavelength λ in the thin film is s and the light velocity of the wavelength λ in the vacuum is c, the refractive index is represented by n ₁ = c / s. An electromagnetic wave E (x, t) generated by light traveling in the x direction in the thin film uses E (x, t) = E ₀ exp [j (ωt) using the wave number K ₁ , the angular frequency ω, and the phase δ. −K ₁ x + δ)]. That is, the propagation characteristic of the electromagnetic wave in the thin film depends on the wave number K. From these relationships, it can be seen that light having a wavelength λ in a vacuum has a longer wavelength from λ to λ / n ₁ because the speed of light decreases in the thin film. In consideration of such a wavelength dispersion phenomenon, the wave number conversion reflectance R ′ is defined as follows.

From this relationship, when the wave number conversion reflectance R 'Fourier transform wave number K, by the peaks appearing in the period component corresponding to the film thickness d _1, by identifying the peak position and calculates the film thickness d ₁ be able to.

  That is, multilayer analysis apparatus 100 according to the present embodiment determines the correspondence between each wavelength in the measured reflectance spectrum and the reflectance value at that wavelength according to the wave number calculated from each wavelength and the above-described relational expression. Conversion is made to a correspondence relationship with the calculated wave number conversion reflectance R ′. Then, the wave number K is frequency-converted with respect to the function of the wave number conversion reflectance R ′ including the wave number K, and the film thickness of the target sample is calculated based on the peak appearing in the characteristics after the frequency conversion.

Here, R _a and R _b are values irrelevant to the interference phenomenon in the thin film, but depend on the amplitude reflectivity at the interface of each layer including the refractive index n _{1 of the} thin film. Therefore, when the refractive index has chromatic dispersion, the value is a function value depending on the wavelength (that is, the wave number K), and does not become a constant value with respect to the wave number K. Therefore, when Fourier transform is represented by ⊃, and R ′, R _a , R _b , and cos 2K ₁ d ₁ are subjected to Fourier transform with a wave number K, the power spectra as functions are respectively represented by P, P _a , P _b , and F, respectively. The following equation holds.

Component dependent on the film thickness at P _a in the formula is relatively small, and since the power spectrum F with separated peaks, does not affect the power spectrum F.

On the other hand, P _b in the equation is convolved with the power spectrum F, so that the film thickness component in P _b modulates the film thickness component of the power spectrum F. However, P _b is independent of the interference phenomena in the film, since it is affected only in the wavelength dependence of the refractive index in the two adjacent layers, the thickness component of P _b for the wavenumber K is the thickness component of the F Is negligibly small compared to For example, _assuming that R _b is a periodic function of the film thickness q and P _b after the Fourier transform is modulated on the film thickness component d of the power spectrum F by convolution, the peak appearing as the spectrum is “d− q ”or“ d + q ”, but since the value of q is very small, the influence on the peak position d is small.

Further, when performing Fourier transform, sampling is performed at an appropriate sample interval and number of samples with respect to the wave number conversion reflectivity R ′ according to the Nyquist sampling theorem in consideration of the maximum film thickness of the thin film to be measured. . Thus for a film thickness resolution r of the power spectrum calculated based on the sampled-wavenumber conversion reflectance R ', thickness component q of P _b is high is less than possibility (q <r), film It can be said that the measurement result of the thickness d is hardly affected.

  Thus, the film thickness of the thin film can be accurately calculated by performing Fourier transform after converting the calculated reflectance spectrum into a function with respect to the wave number in consideration of wavelength dispersion in the thin film.

  In the above description, the case where the reflectance spectrum is used is exemplified, but the transmittance spectrum may be used. In this case, when the measured transmittance is T, and the “wave number conversion transmittance” is T ′, the following relational expression is obtained.

In the case of using the transmission spectra, the transmittance T becomes non-linear with respect to the phase factor cos2β _1. Therefore, for the same reason as described above, the wave number conversion transmittance T ′ having linearity with respect to the phase factor cos 2β ₁ is adopted. According to the above equation, the wave number conversion transmittance T ′ is a linear equation for the phase factor cos 2β ₁ , and the film thickness of the thin film can be accurately calculated according to the same procedure as described above. That is, the wave number conversion transmittance T ′ is a function for linearizing the value of the transmittance T at each wavelength with respect to the phase factor cos 2β ₁ related to frequency conversion.

(Measurement Example 1)
FIG. 3 is a diagram illustrating an example of a reflectance spectrum measured from the sample of Measurement Example 1. The sample shown in FIG. 3 is obtained by forming a 5.0 μm silicon nitride film on a quartz substrate.

  FIG. 4 is a diagram showing the results when the film thickness is calculated from the reflectance spectrum shown in FIG. 3 using a conventional method.

  FIG. 5 is a diagram showing the results when the film thickness is calculated from the reflectance spectrum shown in FIG. 3 using the method according to the present embodiment.

  Referring to FIG. 4, in the conventional method, the power spectrum is calculated by Fourier transform after pre-processing such as zero filling processing and filter processing is performed on the reflectance spectrum shown in FIG. In this measurement example 1, Fourier transform was performed using Fast Fourier Transform (FFT). Thus, the power spectrum obtained by directly Fourier-transforming the reflectance spectrum is a function with respect to the optical distance. Then, the optical distance corresponding to the peak position in the power spectrum is read, and this optical distance is divided by the apparent refractive index (for example, the average refractive index in the measurement wavelength range) of the silicon nitride that is the sample to be measured. Thus, the film thickness of the thin film to be measured was calculated. As shown in FIG. 4, when the conventional method is used, the value that should be 5.0 μm is calculated as “5.237 μm” with relatively many errors.

  On the other hand, referring to FIG. 5, in the method according to the present embodiment, the reflectance spectrum shown in FIG. 3 is converted into a wavenumber-converted reflectance spectrum, and then the power spectrum is obtained by Fourier transform as in the conventional method. Was calculated. The power spectrum obtained by Fourier transforming this wave number conversion reflectance spectrum is a function of the geometric thickness of the thin film. Therefore, the film thickness of the thin film can be directly obtained by specifying the peak position appearing in the power spectrum shown in FIG. As shown in FIG. 5, when the method according to the present embodiment is used, it is understood that “5.0 μm”, which is the original film thickness of the thin film, is calculated.

  Thus, comparing FIG. 4 with FIG. 5, it can be seen that the film thickness can be measured with higher accuracy than the conventional method according to the method according to the present embodiment.

(Thickness measurement process 2)
In the above description, the case where the thin film to be measured is a single layer has been exemplified, but each film thickness can be measured in the same procedure even when a plurality of thin films are present.

As an example, consider a sample in which two thin film layers as shown in FIG. 6 are formed. When the refractive index of the first layer is n ₁ , the film thickness is d ₁ , the refractive index of the second layer is n ₂₁ , and the film thickness is d ₂ , the wavenumber conversion reflectance R ′ is expressed as follows.

Here, when calculating the film thicknesses d ₁ and d ₂ of the first layer and the second layer, wave number conversion reflectances R ₁ ′ (K ₁ ) and R ₂ ′ converted by the wave numbers K ₁ and K ₂ , respectively. (K ₂ ) is used. Specifically, it is expressed as follows.

In these equations, d ₁ ′ and d ₂ ′ are not correct film thickness values, but the original film thickness from the peak in the power spectrum corresponding to the second term of the wave number conversion reflectance R ₁ ′ (K ₁ ). d ₁ is obtained, and the original film thickness d ₂ is obtained from the peak in the power spectrum corresponding to the third term of the wave number conversion reflectance R ₂ ′ (K ₂ ).

Actually, the refractive index of the first layer and the second layer is often approximate, and the reflectance at the interface between the two is relatively smaller than the reflectance at the other interface. There are many cases. As a result, the value of R _c becomes smaller than R _b and R _d included in the function of wave number conversion reflectivity, and the third term of the wave number conversion reflectivity R ₂ ′ (K ₂ ) is obtained from the power spectrum. Often it is difficult to identify the corresponding peak. In such a case, 'the peak position of the power spectrum corresponding to the fourth term of the _{(K 2) (d 1'} wavenumber conversion reflectance _{R 2} and + _{d 2),} wavenumber conversion reflectance _{R 2 '(K} 2) After calculating the peak position (d ₁ ′) of the power spectrum corresponding to the second term, the film thickness d ₂ can be calculated by taking the difference between the _two .

(Measurement example 2)
FIG. 7 is a diagram illustrating an example of the reflectance spectrum measured from the sample of Measurement Example 2. The sample shown in FIG. 7 is obtained by depositing a 3.0 μm thin film (first layer) and a 2.0 μm thin film (second layer) on a substrate. FIG. 7 also shows the transmittance of each thin film and substrate.

FIG. 8 is a power spectrum for the wave number conversion reflectance R ₁ ′ (K ₁ ) of the first layer converted from the reflectance spectrum shown in FIG. FIG. 9 is a power spectrum for the wave number conversion reflectance R ₂ ′ (K ₂ ) according to the second layer converted from the reflectance spectrum shown in FIG.

Referring to FIG. 8, four peaks corresponding to each term of wave number conversion reflectance R ₁ ′ (K ₁ ) should be observed, but as described above, the reflectance between thin films is Considering the relatively low value and the noise cut threshold value in the Fourier transform process, two peaks derived mainly from the second and fourth terms of the wave number transform reflectivity R ₁ ′ (K ₁ ) It is thought that it is appearing. Of the two peaks, it is possible to obtain a film thickness corresponding to the peak located at a smaller thickness as the thickness d ₁ of the first layer. That is, as shown in FIG. 8, a peak exists at a position where the film thickness is 3 μm, and from this, it can be determined that the film thickness d ₁ of the first layer is 3 μm.

Next, with reference to FIG. 9, 'even in the power spectra for (K _2), similarly to FIG. 8, mainly wavenumber conversion reflectance R _2' wavenumber conversion reflectance R ₂ the second term of (K ₂₎ And only two peaks from the fourth term appear. Here, after shifting the power spectrum of the wave number conversion reflectance R ₂ ′ (K ₂ ) by d ₁ ′ corresponding to the film thickness of the first layer calculated from the power spectrum shown in FIG. The film thickness corresponding to the peak derived from the fourth term of the conversion reflectance R ₂ ′ (K ₂ ) can be obtained as the film thickness d ₂ of the second layer. That is, as shown in FIG. 9, the peak derived from the fourth term after the shift exists at a position of 2 μm, and from this, the film thickness d ₂ of the second layer can be obtained as 2 μm.

Calculate the film thickness of each layer without being affected by the wavelength dependence of the refractive index using the wave number conversion reflectance or wave number conversion transmittance for a multilayer film sample of three or more layers by the same procedure as described above. Can do.
(Configuration of data processing unit)
FIG. 10 is a schematic diagram showing a schematic hardware configuration of data processing unit 70 according to the embodiment of the present invention.

  Referring to FIG. 10, data processing unit 70 is typically realized by a computer, and includes a CPU (Central Processing Unit) 200 that executes various programs including an operating system (OS), and a program executed by CPU 200. A memory unit 212 that temporarily stores data necessary for execution and a hard disk unit (HDD: Hard Disk Drive) 210 that stores a program executed by the CPU 200 in a nonvolatile manner are included. The hard disk unit 210 stores a program for realizing processing as will be described later, and such a program is stored in the flexible disk 216a or the CD-ROM by the FDD drive 216 or the CD-ROM drive 214, respectively. It is read from a ROM (Compact Disk-Read Only Memory) 214a or the like.

  The CPU 200 receives an instruction from a user or the like via the input unit 208 including a keyboard and a mouse, and outputs a measurement result measured by executing the program to the display unit 204.

(Control structure)
FIG. 11 is a block diagram showing a control structure for realizing a film thickness measurement process according to the embodiment of the present invention. The block diagram shown in FIG. 11 is realized by the CPU 200 reading a program stored in advance such as the hard disk unit 210 into the memory unit 212 and executing the program.

  11, data processing unit 70 (FIG. 1) includes buffer unit 71, wave number conversion units 721, 722,..., 72m, buffer units 731, 732,. , 74m, peak search units 751, 752,..., 75m, and a total calculation unit 76 are included as functions. FIG. 10 shows a general-purpose configuration for measuring the thickness of each layer in a sample in which m layers of thin films are formed.

  The buffer unit 71 temporarily stores the reflectance spectrum R (λ) output from the spectroscopic measurement unit 60. More specifically, since the reflectance value is output from the spectroscopic measurement unit 60 for each predetermined wavelength resolution, the buffer unit 71 stores the wavelength and the reflectance at that wavelength in association with each other.

The wave number conversion unit 721 performs wave number conversion on the reflectance spectrum temporarily stored in the buffer unit 71 based on the refractive index n1 of the first layer among thin films input in advance by a user or the like. That is, the wave number conversion unit 721 determines the correspondence between each wavelength in the reflectance spectrum and the reflectance at that wavelength, and the corresponding wave number conversion reflectance R ₁ calculated according to the wave number K ₁ for each wavelength and the above relational expression. Convert to a correspondence with '. More specifically, the wave number conversion unit 721 generates a wave number K ₁ (λ) and a wave number conversion reflectance R ₁ ′ (λ) (= R (λ) / (1−) for each wavelength stored in the buffer unit 71. R (λ))) are sequentially calculated and output to the buffer unit 731.

The buffer unit 731 stores the wave number K ₁ (λ) and the wave number conversion reflectance R ₁ ′ (λ) sequentially output from the wave number conversion unit 721 in association with each other. That is, the buffer unit 731 stores the wave number conversion reflectance R ₁ ′ (K ₁ ) that is the wave number distribution characteristic of the wave number conversion reflectance with respect to the wave number K ₁ (λ).

The Fourier transform unit 741 calculates the power spectrum P ₁ by performing a Fourier transform on the wave number conversion reflectance R ₁ ′ (K ₁ ) stored in the buffer unit 731 with respect to the wave number K ₁ . In addition, as a method of Fourier transform, fast Fourier transform (FFT), discrete cosine transform (DCT: Discrete Cosine Transform), etc. can be used.

Peak search unit 751 searches for a peak appearing in the power spectrum P ₁ calculated by Fourier transform unit 741, it acquires a thickness corresponding to the peak position.

  As described above, the wave number conversion unit 721, the buffer unit 731, the Fourier transform unit 741, and the peak search unit 751 acquire the film thickness corresponding to the peak appearing in the power spectrum caused by the thin film of the first layer. .

  Similarly, the wave number conversion unit 722, the buffer unit 732, the Fourier transform unit 742, and the peak search unit 752 acquire the film thickness corresponding to the peak appearing in the power spectrum caused by the thin film of the second layer. Furthermore, the wave number converting unit 72m, the buffer unit 73m, the Fourier transforming unit 74m, and the peak searching unit 75m acquire the film thickness corresponding to the peak appearing in the power spectrum caused by the m-th layer thin film.

  The total calculation unit 76 calculates the film thickness of each thin film based on the film thickness corresponding to the peak appearing in each power spectrum output from the peak search units 751, 752,. More specifically, as shown in FIG. 8 and FIG. 9, first, the film thickness of the first layer is determined based on the film thickness corresponding to the peak output from the peak search unit 751. The film thickness of the second layer is determined based on the film thickness and the film thickness corresponding to the peak output from the peak search unit 752. In the same manner, the thickness of each layer is sequentially calculated. Then, the total calculation unit 76 outputs the calculated measurement results of the thicknesses of the respective layers to the user, a host computer (not shown), or the like.

  11, the wave number conversion units 721, 722,..., 72m correspond to “wave number characteristic conversion means”, and the Fourier conversion units 741, 742,. The total calculation unit 76 corresponds to “conversion means” and “film thickness calculation means”.

(Processing procedure)
FIG. 12 is a flowchart showing a processing procedure related to film thickness measurement according to the embodiment of the present invention.

  Referring to FIG. 12, first, the user places a sample to be measured on stage 50 (FIG. 1) (step S100). In addition, the user inputs the refractive index of the thin film constituting the sample to be measured to the data processing unit 70 (step S102). In response to the input of the refractive index of the thin film by the user, the CPU 200 of the data processing unit 70 stores these values in the memory unit 212 or the like.

  Here, irradiation of observation light is started from the observation light source 22, and the user gives a stage position command to the movable mechanism 52 while referring to the reflection image taken by the observation camera 38 displayed on the display unit 39. Then, adjustment and focus adjustment of the area to be measured are performed (step S104).

  Thereafter, when the user gives a measurement start command, generation of measurement light from the measurement light source 10 is started, and the spectroscopic measurement unit 60 outputs the reflectance spectrum acquired from the reflected light from the sample to the data processing unit 70. (Step S106).

  The CPU 200 of the data processing unit 70 temporarily stores the reflectance spectrum from the spectroscopic measurement unit 60 in the memory unit 212 or the like (step S108). CPU 200 performs wave number conversion on the reflectance spectrum based on one of the input refractive indexes (step S110). Then, the CPU 200 stores the wave number conversion reflectance calculated by the wave number conversion in the memory unit 212 or the like (step S112). Further, the CPU 200 performs a Fourier transform on the calculated wave number conversion reflectivity to calculate a power spectrum (step S114). Thereafter, the CPU 200 acquires the peak appearing in the calculated power spectrum and the film thickness corresponding to the peak (step S116).

  Thereafter, the CPU 200 determines whether or not the peak and the film thickness acquisition process corresponding to the peak have been executed for all input refractive indexes (step S118). If the processing for obtaining the peak and the film thickness corresponding to the peak has not been executed for all input refractive indexes (NO in step S118), the processing from step S110 onward is repeated for one of the remaining reflectances. Executed.

  On the other hand, if the processing for obtaining the peak and the film thickness corresponding to the peak has been executed for all input refractive indexes (YES in step S118), CPU 200 calculates the peak calculated for each refractive index and the peak. Based on the film thickness corresponding to, the film thickness in each thin film is calculated (step S120). Then, the CPU 200 outputs the calculated film thickness of each thin film to a host computer (not shown) or the like via the display unit 204 or the interface unit 206 (step S122).

The film thickness of each layer of the multilayer film sample can be measured according to the series of processes as described above.
(Layer structure identification process)
As described above, a peak corresponding to the layer structure of the multilayer film sample appears in the power spectrum obtained by Fourier transforming the reflectance spectrum. However, in the calculation process, the calculated power spectrum is affected by the generation of pseudo-peaks such as pre-processing such as various filter processing, truncation processing, and apodization processing, and DC offset peak associated with the baseline setting. . Also, an optical phenomenon can occur between the layers. Therefore, in the power spectrum, one peak does not appear from one layer, but a plurality of peaks appear according to the combination of layers. For this reason, even when the layer structure is known in advance, it is often difficult to determine from which spectrum the peak that appears in the power spectrum is due to the interference of which layer. If the layer structure is unknown, it is difficult to identify the layer structure from the shape of the spectrum.

  Therefore, the multilayer analysis apparatus according to the present embodiment has a function of identifying the layer structure of the target sample. The function of identifying this layer structure is typically implemented in the data processing unit 70. Specifically, a virtual layer structure is set by extracting a predetermined number from a plurality of predefined layer structures, and a reflectance spectrum (theoretical value) is calculated from the virtual layer structure. The power spectrum is calculated by Fourier transforming the reflectance spectrum. At the same time, a power spectrum is calculated from the reflectance spectrum of the actually measured value by Fourier transform in the same processing procedure. Then, a correlation coefficient is calculated between these power spectra, and the virtual layer structure is sequentially changed based on the calculated correlation coefficient, and the combination with the highest correlation coefficient is selected as the sample. Determined as the layer structure.

  FIG. 13 is a block diagram showing a control structure for realizing the layer structure identification process according to the embodiment of the present invention. The block diagram shown in FIG. 13 is realized by the CPU 200 reading a program stored in advance such as the hard disk unit 210 into the memory unit 212 and executing the program.

  Referring to FIG. 13, the data processing unit 70 includes a layer structure database 300, a combination unit 304, a reflectance calculation unit 306, a theoretical spectrum calculation unit 308, power spectrum calculation units 310 and 320, and a buffer unit 318. And a correlation coefficient calculation unit 330 and a layer structure determination unit 332 as functions thereof.

  The layer structure database 300 stores a plurality of layer structure information 302 in advance. Each of the layer structure information 302 includes at least information of refractive index and film thickness for each layer. The layer structure information can be arbitrarily set by the user based on the film thickness calculated by the above-described film thickness measurement process, the known refractive index, and the like.

  The combination unit 304 selects a candidate layer structure by combining a predetermined number of layer structure information 302 among the plurality of layer structure information 302 stored in the layer structure database 300. Note that the number of layers to be combined by the combining unit 304 may be set in advance by the user.

  Based on the layer structure information (film thickness and refractive index) corresponding to the candidates combined by the combination unit 304, the reflectance calculation unit 306 analytically calculates the reflectance in the layer structure. Note that the absolute transmittance may be calculated instead of the reflectance.

  In calculating the reflectivity (or refractive index), as described above, the Fresnel coefficient at the adjacent layer interface and the phase angle due to interference of each layer are sequentially calculated, and reflection is repeated infinitely within the thin film. As a result, the reflectance (or absolute transmittance) can be analytically calculated as the convergence value (square) of an infinite geometric series.

  The theoretical spectrum calculation unit 308 sequentially calculates the intensity value at each wavelength based on the calculation formula of the reflectance of the candidate layer structure calculated by the reflectance calculation unit 306, and reflects the reflectance in the candidate layer structure. A spectrum (theoretical value) is calculated. The wavelength resolution of the reflectance spectrum is preferably the same as the resolution of the measured reflectance spectrum.

  The power spectrum calculation unit 310 performs Fourier transform on the reflectance spectrum (theoretical value) calculated by the theoretical spectrum calculation unit 308 to calculate a power spectrum (theoretical value). Here, the power spectrum calculation unit 310 executes the same processing as the power spectrum calculation processing performed by the wave number conversion unit 721, the buffer unit 731, and the Fourier transform unit 741 in FIG. 11. This is because the power spectrum calculated from the actually measured reflectance spectrum and the theoretically calculated power spectrum are compared under the same conditions.

  On the other hand, the buffer unit 318 temporarily stores the reflectance spectrum actually measured by the spectroscopic measurement unit 60. Then, the power spectrum calculation unit 320 calculates the power spectrum (measured value) from the reflectance spectrum (measured value) by the same power spectrum calculation process as that of the power spectrum calculation unit 310 described above.

The correlation coefficient calculation unit 330 calculates a correlation coefficient between the power spectrum (theoretical value) calculated by the power spectrum calculation unit 310 and the power spectrum (actual measurement value) calculated by the power spectrum calculation unit 320. . As an example of calculation of such a correlation coefficient, when the power spectrum (actual value) is R _m (K) and the power spectrum (theoretical value) is R _c (K), the cross-correlation function of the two power spectra It can be calculated according to C _mc = <R _m (K) R _c (K + κ)>. Alternatively, Pearson's linear correlation coefficient may be calculated.

  The layer structure determination unit 332 stores the correlation coefficient calculated by the correlation coefficient calculation unit 330 in association with the candidate layer structure at that time, and the calculation of correlation coefficients for all combinations is completed. Later, the combination with the highest correlation coefficient is determined as the layer structure in the sample.

  FIG. 14 is a flowchart showing a processing procedure related to the layer structure identification processing according to the embodiment of the present invention.

  Referring to FIG. 14, first, the user follows a procedure similar to steps S100 to S106 of the processing procedure relating to the film thickness measurement shown in FIG. 12 on the basis of the reflectance spectrum (measured value) based on the reflected light from the sample. Obtain (step S200). When the reflectance spectrum is input to the data processing unit 70, the CPU 200 of the data processing unit 70 temporarily stores the reflectance spectrum in the memory unit 212 or the like (step S202). Then, the CPU 200 calculates a power spectrum from the reflectance spectrum (actual measurement value) according to the same procedure as steps S110 to S114 of the processing procedure relating to the film thickness measurement shown in FIG. 12 (step S204).

  On the other hand, the CPU 200 selects a candidate layer structure by combining a predetermined number of layer structure information 302 among the plurality of layer structure information 302 stored in the hard disk unit 210 (layer structure database 300) (step S206). . Then, the CPU 200 analytically calculates the reflectance in the selected layer structure based on the layer structure information (film thickness and refractive index) corresponding to the candidate layer structure (step S208). Further, the CPU 200 calculates the reflectance spectrum (theoretical value) in the selected layer structure based on the calculation formula of the reflectance of the candidate layer structure (step S210). Further, the CPU 200 calculates a power spectrum from the reflectance spectrum (theoretical value) according to a procedure similar to steps S110 to S114 of the processing procedure relating to film thickness measurement shown in FIG. 12 (step S212).

  Thereafter, the CPU 200 calculates a correlation coefficient between the power spectrum (theoretical value) and the power spectrum (actual measurement value) (step S214), and the calculated correlation coefficient and the selected layer structure (combination). Are associated with each other and stored in the memory unit 212 or the like (step S216). Then, the CPU 200 determines whether or not an unselected combination exists for the plurality of layer structure information 302 stored in the hard disk unit 210 (layer structure database 300) (step S218). If there is an unselected combination (YES in step S218), the processes in and after step S206 are repeated.

  On the other hand, when there is no unselected combination (NO in step S218), the CPU 200 targets the layer structure corresponding to the highest one of the correlation coefficients stored in the memory unit 212. The layer structure is determined at (step S220). Then, the CPU 200 outputs the determined layer structure to an upper computer (not shown) or the like via the display unit 204 or the interface unit 206 (step S222).

The layer structure can be identified according to the series of processes as described above.
FIG. 15 is a measurement example showing a reflectance spectrum measured for an arbitrary sample.

  FIG. 16 shows an example of the result of identification for the reflectance spectrum shown in FIG. 15 using the layer structure identification process according to the embodiment of the present invention.

  As shown in FIGS. 15 and 16, according to the layer structure identification process according to the present embodiment, the film structure of the multilayer film sample can be identified with high accuracy.

  According to the embodiment of the present invention, in the process of calculating the power spectrum from the reflectance spectrum measured from the multilayer film sample, the wave number conversion that is a function of the wave number is considered in consideration of the chromatic dispersion of each wavelength in the multilayer film sample. Introduce reflectance. The power spectrum is calculated by performing a Fourier transform on the wave number with respect to the function of the wave number conversion reflectance. Further, the film thickness of the target sample is calculated based on the peak appearing in the power spectrum. In this way, in the process of calculating the power spectrum, by adopting a unique function that takes into account the chromatic dispersion of each wavelength, the influence of the wavelength dependency of the refractive index is eliminated, and the film of the multilayer film sample with higher accuracy. Thickness can be measured.

  Further, according to the embodiment of the present invention, a candidate layer structure is sequentially selected from a plurality of predetermined layer structure information, and a reflectance spectrum (theoretical value) in the candidate layer structure is calculated. Further, a power spectrum (theoretical value) is calculated from the reflectance spectrum. The most probable layer structure is determined based on the correlation coefficient between the power spectrum (measured value) calculated from the actually measured reflectance spectrum and the power spectrum (theoretical value). Thereby, even if it is a multilayer film sample in which many layers were laminated, the layer structure can be specified more correctly.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 is a schematic configuration diagram of a multilayer film analysis apparatus according to an embodiment of the present invention. It is a cross-sectional schematic diagram of a typical multilayer film sample. It is a figure which shows an example of the reflectance spectrum measured from the sample of the measurement example 1. FIG. It is a figure which shows the result at the time of calculating a film thickness using the conventional method from the reflectance spectrum shown in FIG. It is a figure which shows the result at the time of calculating a film thickness from the reflectance spectrum shown in FIG. 3 using the method according to this Embodiment. It is a cross-sectional schematic diagram of the multilayer film sample in which the two thin film layers were formed. It is a figure which shows an example of the reflectance spectrum measured from the sample of the measurement example 2. FIG. It is a power spectrum about the wave number conversion reflectance which concerns on the 1st layer converted from the reflectance spectrum shown in FIG. It is a power spectrum about the wave number conversion reflectance which concerns on the 2nd layer converted from the reflectance spectrum shown in FIG. It is a schematic diagram which shows the schematic hardware constitutions of the data processing part according to embodiment of this invention. It is a block diagram which shows the control structure for implement | achieving the film thickness measurement process according to embodiment of this invention. It is a flowchart which shows the process sequence which concerns on the film thickness measurement according to embodiment of this invention. It is a block diagram which shows the control structure for implement | achieving the layer structure identification process according to embodiment of this invention. It is a flowchart which shows the process sequence which concerns on the layer structure identification process according to embodiment of this invention. It is a measurement example which shows the reflectance spectrum measured with respect to arbitrary samples. It is a figure which shows an example of the result identified with respect to the reflectance spectrum shown in FIG. 15 using the layer structure identification process according to embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Measurement light source, 12 Collimate lens, 14,66 Cut filter, 16,36 Imaging lens, 18 Aperture part, 20, 30 Beam splitter, 22 Observation light source, 24 Optical fiber, 26 Output part, 26a Mask part, 32 Pinhole mirror, 32a Pinhole, 34 axis conversion mirror, 38 Observation camera, 39 Display unit, 40 Objective lens, 50 Stage, 52 Movable mechanism, 60 Spectrometer, 62 Diffraction grating, 64 Detector, 68 Shutter, 70 Data processing unit 71,731,732, ..., 73m Buffer unit, 741,742, ..., 74m Fourier transform unit, 751,752, ..., 75m Peak search unit, 76 Total calculation unit, 100 Multi-layer film analysis device, 204 Display unit, 206 interface unit, 208 input unit, 210 Hard disk unit (HDD), 212 memory unit, 214 CD-ROM drive, 214a CD-ROM, 216 FDD drive, 216a flexible disk, 300 layer structure database, 302 layer structure information, 304 combination unit, 306 reflectance calculation unit, 308 Theoretical spectrum calculation unit, 310, 320 Power spectrum calculation unit, 318 buffer unit, 330 correlation coefficient calculation unit, 332 layer structure determination unit.

Claims (7)

A light source that emits measurement light having a predetermined wavelength range to a sample having at least one film formed on a substrate;
A spectroscopic unit that acquires reflectance or transmittance wavelength distribution characteristics based on light reflected by the sample or light transmitted through the sample;
Wave number characteristic conversion for converting the correspondence between each wavelength in the wavelength distribution characteristic and the value of reflectance or transmittance at that wavelength into the correspondence between the wave number for each wavelength and the conversion value calculated according to a predetermined relational expression Means,
Frequency conversion means for frequency-converting the wave number with respect to the wave number distribution characteristics each having a corresponding relationship converted by the wave number characteristic conversion means;
A multilayer film analysis apparatus comprising: a film thickness calculation unit configured to calculate a film thickness of the sample based on a peak appearing in a wave number distribution characteristic after frequency conversion.   The multilayer film analyzer according to claim 1, wherein the wave number characteristic conversion unit calculates the wave number based on a refractive index of a film included in the sample input in advance and a corresponding wavelength.   3. The multilayer film according to claim 1, wherein the relational expression is a function for linearizing a reflectance or transmittance value at each wavelength with respect to a phase factor related to frequency conversion by the frequency conversion unit. Analysis device. The wavelength distribution characteristic is a wavelength distribution characteristic of reflectance R acquired based on light reflected by the sample,
The multilayer analysis apparatus according to claim 3, wherein the relational expression is R / (1-R). The wave number characteristic conversion means calculates the wave number distribution characteristic for each of the plurality of films when a plurality of films are formed on the sample,
The film thickness calculation means calculates the film thickness of each of the plurality of films based on a peak appearing in each of the wave number distribution characteristics after frequency conversion for the plurality of films. The multilayer film analysis apparatus according to any one of the above. Layer structure storage means for storing a plurality of layer structure information in which at least the refractive index and the film thickness are defined,
Selection means for sequentially selecting layer structure candidates based on at least one layer structure information among the plurality of layer structure information;
Based on the layer structure information corresponding to the layer structure candidate, wavelength distribution characteristic calculating means for calculating a wavelength distribution characteristic of reflectance or transmittance in the layer structure candidate;
From the wavelength distribution characteristic of the layer structure candidate, a wave number distribution characteristic calculating means for calculating a wave number distribution characteristic after frequency conversion by the same processing as the wave number characteristic converting means and the frequency converting means,
Correlation value calculating means for calculating a correlation value between the wave number distribution characteristic after frequency conversion calculated from the actually measured wavelength distribution characteristic and the wave number distribution characteristic after frequency conversion calculated by the wave number distribution characteristic calculating means. When,
6. The multilayer film according to claim 1, further comprising: a determination unit that determines a layer structure candidate that is sequentially selected by the selection unit based on the correlation value, and that determines the closest layer to the actual measurement value. Analysis device. Irradiating a sample having at least one film formed on a substrate with measurement light having a predetermined wavelength range;
Obtaining a reflectance or transmittance wavelength distribution characteristic based on light reflected by the sample or transmitted through the sample;
Converting the correspondence between each wavelength in the wavelength distribution characteristic and the value at that wavelength into a correspondence between the wave number for each wavelength and a conversion value calculated according to a predetermined relational expression;
For the wave number distribution characteristic consisting of the corresponding relationship converted in the step of converting into the corresponding relationship, frequency converting the wave number;
And a step of calculating a film thickness of the sample based on a peak appearing in a wave number distribution characteristic after frequency conversion.

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