KR101582357B1 - Apparatus and method for measuring thickness of film - Google Patents

Abstract

Model conversion unit (721A) is a theory according to the fitting portion updates the thickness (d ₁₎ of the first layer according to the parameter update instruction from the (722A) in sequence, and the thickness of the first layer after the update (d ₁₎ Thereby updating the function representing the reflectance. Further, the modeling unit 721A repeatedly calculates the theoretical reflectance (spectrum) at each wavelength in accordance with the updated function. By such a procedure, the film thickness d ₁ of the first layer is determined by the fitting. When the fitting has not converged within the prescribed number of times, the film thickness d ₁ of the first layer is determined using the Fourier transform.

A film thickness measuring device, a cut filter, an image-forming lens, a beam splitter, a collimate lens

Description

TECHNICAL FIELD [0001] The present invention relates to a film thickness measurement apparatus,

The present invention relates to a film thickness measuring apparatus and a film thickness measuring method, and more particularly to a configuration and a method for measuring a film thickness of a measured object on which a plurality of layers are formed on a substrate.

Recently, a substrate structure called SOI (Silicon on Insulator) has been attracting attention in order to achieve lower power consumption and higher speed in CMOS (Complementary Metal Oxide Semiconductor) circuits and the like. This SOI substrate is formed by disposing an insulating layer (BOX layer) such as SiO ₂ between two Si (silicon) substrates, and is formed between a PN junction formed on one Si layer and the other Si layer Parasitic diodes, stray capacitance, and the like can be reduced.

As a method of manufacturing such an SOI substrate, an oxide film is formed on the surface of a silicon wafer, another silicon wafer is sandwiched so as to sandwich the oxide film, and a silicon wafer on the side where circuit elements are formed is polished to a predetermined thickness Is known.

In order to control the thickness of the silicon wafer by the polishing process, it is necessary to continuously monitor the film thickness. As a method of measuring the film thickness in such a polishing step, a method using a Fourier transform infrared spectrophotometer (FTIR) is disclosed in Japanese Patent Application Laid-Open Nos. 05-306910 and 05-308096 . Japanese Patent Application Laid-Open No. 2005-19920 discloses a method of using a reflection spectrum measured by a dispersion type multi-channel spectroscope.

Japanese Patent Application Laid-Open No. Hei 10-125634 discloses a method of measuring the film thickness by irradiating an object to be polished with an infrared ray from an infrared light source through a polishing body and detecting the reflected light.

Japanese Unexamined Patent Publication (Kokai) No. 2002-228420 discloses a method of irradiating infrared rays having a wavelength of 0.9 탆 or more toward the surface of a silicon thin film to obtain a result of interference between light reflected by the surface of the silicon thin film and light reflected by the back surface of the silicon thin film A method of measuring a film thickness of a silicon thin film is disclosed.

In addition, Japanese Patent Application Laid-Open No. 2003-114107 discloses an apparatus for measuring an optical interfering film thickness using infrared light as measurement light.

However, in the measurement methods disclosed in Japanese Patent Application Laid-Open Nos. 05-306910 and 05-308096, it is only necessary to measure the relative value of the film thickness to the reference sample, The absolute value of the thickness can not be measured.

In the measurement method disclosed in Japanese Patent Application Laid-Open No. 2005-19920, the period is estimated by the autoregressive model, assuming that the refractive index is a fixed value that does not depend on the wavelength, but the actual refractive index is It has wavelength dependency, and an error due to such wavelength dependence can not be excluded. The same problem also occurs in the measuring method disclosed in Japanese Patent Application Laid-Open No. 2003-114107.

Further, in the measuring method disclosed in Japanese Patent Application Laid-Open No. 2002-228420, it is necessary to form a penetration portion in the sample to be measured, and the film thickness can not be continuously measured non-destructively.

An object of the present invention is to provide a film thickness measuring apparatus and a film thickness measuring method capable of measuring a film thickness with higher precision.

A film thickness measuring apparatus according to a certain aspect of the present invention includes a light source, a spectroscopic measurement unit, a first determining means, a converting means, an analyzing means, and a second determining means. The light source irradiates measurement light having a predetermined wavelength range to the object to be measured on which a plurality of layers are formed on the substrate. The object to be measured includes a first layer closest to the light source and a second layer adjacent to the first layer. The spectroscopic measurement unit acquires the wavelength distribution characteristics of the reflectance or transmittance based on the light reflected from the measured object or the light transmitted through the measured object. The first determining means determines the film thickness of at least the first layer by fitting the wavelength distribution characteristic using the model equation including the film thickness of each layer included in the measured object. The conversion means converts the correspondence between the wavelengths in the wavelength distribution characteristics and the reflectance or transmittance values at the wavelengths into the corresponding relationship of the wave number for each wavelength and the conversion value calculated in accordance with a predetermined relational expression, Create a property. The analyzing means acquires the amplitude value of each wave number component included in the wave number distribution characteristic. The second determining means determines at least the film thickness of the first layer based on a wavenumber component having an amplitude value included in the wavenumber distribution characteristic. Then, the first determining means and the second determining means are selectively validated.

Preferably, a value of the film thickness of the first layer determined by the second determination means is set in a model expression including the film thickness of each layer included in the measured object, and then fitting is performed on the wavelength distribution characteristic Thereby determining the film thickness of the second layer.

Preferably, the second determining means is validated when the fitting by the first determining means does not converge within the prescribed number of times.

Preferably, the model equation includes a function for the wavelength representing the refractive index.

Preferably, the predetermined wavelength range includes the wavelength of the infrared band.

Preferably, the analyzing means includes means for discrete Fourier transforming the wave number distribution characteristic.

Preferably, the analyzing means acquires amplitude values of the respective wave number components included in the wave number distribution characteristic by using the optimization method.

A film thickness measuring method according to another aspect of the present invention includes a step of irradiating measurement light having a predetermined wavelength range to an object to be measured on which a plurality of layers are formed on a substrate. The object to be measured includes a first layer in which measurement light is initially incident and a second layer adjacent to the first layer. The film thickness measuring method may further include the steps of obtaining a wavelength distribution characteristic of reflectance or transmittance based on light reflected from the measured object or light transmitted through the measured object; A first determining step of determining a film thickness of at least a first layer by fitting to a wavelength distribution characteristic by using a model equation including a wavelength distribution characteristic and a reflectance Or transmittance values of the respective wave number components included in the wave number distribution characteristic into the corresponding relationship of the wave number for each wavelength and the conversion value calculated according to a predetermined relational expression to generate a wave number distribution characteristic; A second determination step of determining at least a film thickness of the first layer based on a wavenumber component having an amplitude value included in a wavenumber distribution characteristic, And a and a step of selectively enabling the second determination step.

According to the present invention, the film thickness of the object to be measured can be measured with higher accuracy.

These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

According to the present invention, it is possible to provide a film thickness measuring apparatus and a film thickness measuring method capable of measuring a film thickness with higher accuracy.

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described in detail with reference to the drawings.

In the drawings, the same or equivalent portions are denoted by the same reference numerals and the description thereof will not be repeated.

<Device Configuration>

1 is a schematic block diagram of a film thickness measuring apparatus 100 according to an embodiment of the present invention.

The film thickness measuring apparatus 100 according to the present embodiment is capable of measuring the film thickness of each layer in an object to be measured having a single layer or a multilayer structure. Particularly, the film thickness measuring apparatus 100 according to the present embodiment is suitable for measuring the film thickness of a measured object including a relatively thick layer (typically 2 占 퐉 to 1000 占 퐉).

Specifically, the film thickness measuring apparatus 100 is a microscopic spectroscopic type measuring apparatus, which irradiates a light to a measured object and measures the wavelength distribution characteristic (hereinafter also referred to as &quot; spectrum &quot;) of the reflected light reflected from the measured object So that the film thickness of each layer constituting the measured object can be measured. Further, the measurement of the (absolute and relative) reflectance in each layer and the analysis of the layer structure are also possible. Instead of the spectrum of the reflected light, a spectrum (spectrum of transmitted light) of the light transmitted through the measured object may be used.

In the present specification, a case in which one or more layers are formed on a single substrate or a substrate is used as an object to be measured. Specific examples of the object to be measured include a substrate having a relatively large thickness such as an Si substrate, a glass substrate, and a sapphire substrate, a substrate having a multilayer structure such as an SOI (Silicon on Insulator) substrate, and the like. Particularly, the film thickness measuring apparatus 100 according to the present embodiment can measure the film thickness of the Si substrate after cutting, polishing, the Si layer (active layer) of the SOI substrate, the film thickness of the Si layer after the polishing (CMP: Chemical Mechanical Polishing) It is suitable for measurement of film thickness of Si substrate and the like.

1, the film thickness measuring apparatus 100 includes a light source for measurement 10, a collimator lens 12, a cut filter 14, imaging lenses 16 and 36, a diaphragm 18 The beam splitter 20, the observation light source 22, the optical fiber 24, the output section 26, the pinhole mirror 32, the axis conversion mirror 34, A display unit 39, an objective lens 40, a stage 50, a movable mechanism 51, a spectroscopic measurement unit 60, and a data processing unit 70 do.

The light source for measurement 10 is a light source for generating measurement light having a predetermined wavelength range in order to acquire a reflectance spectrum of the object to be measured. Particularly, a wavelength component (for example, 900 nm to 1600 nm or 1470 nm To 1600 nm) is used. As a light source for measurement 10, a halogen lamp is typically used.

The collimator lens 12, the cut filter 14, the image forming lens 16 and the diaphragm 18 are arranged on the optical axis AX2 connecting the measuring light source 10 and the beam splitter 30 Thereby optically adjusting the measurement light emitted from the measurement light source 10.

Specifically, the collimator lens 12 is an optical component to which the measurement light from the measurement light source 10 is first incident, and refracts the measurement light propagated as a diffused light to convert it into a parallel light beam. The measurement light having passed through the collimator lens 12 is incident on the cut filter 14. The cut filter 14 blocks unnecessary wavelength components included in the measurement light. Typically, the cut filter 14 is formed by a multilayer film deposited on a glass substrate or the like. The imaging lens 16 converts the measurement light passing through the cut filter 14 from a parallel light beam to a convergent light beam to adjust the beam diameter of the measurement light beam. The measurement light having passed through the imaging lens 16 is incident on the diaphragm 18. The diaphragm 18 adjusts the light amount of the measurement light to a predetermined amount and then outputs the light to the beam splitter 30. Preferably, the diaphragm 18 is arranged at the imaging position of the measurement light converted by the imaging lens 16. The adjustment amount of the diaphragm 18 is appropriately set in accordance with the depth of field of the measurement light incident on the object to be measured, 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 measurement object 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 object to be measured. The observation light source 22 is connected to the output section 26 through the optical fiber 24 and the observation light generated by the observation light source 22 propagates through the optical fiber 24 as the optical waveguide and then passes through the output section 26 To the beam splitter 20, as shown in Fig.

The output unit 26 includes a mask unit 26a for masking a part of the observation light generated by the observation light source 22 so that a predetermined observation reference image is projected onto the measured object. This observation reference image is intended to facilitate focusing even on an object to be measured (typically, a transparent glass substrate or the like) on which no shape (pattern) is formed on the surface. Further, the shape of the reticle may be any, but a circular pattern or a cross pattern may be used as an example.

That is, although the light intensity (amount of light) in the beam cross section of the observation light immediately after being generated by the observation light source 22 is substantially uniform, the mask part 26a masks (shields) a part of the observation light, (Shadow region) in which the light intensity is substantially zero in the beam cross section is formed. This shadow region is projected onto the measured object as an observation reference image.

The stage 50 is a sample stage for disposing the object to be measured, and its placement surface is formed flat. The stage 50 is freely driven in three directions (X direction, Y direction, and Z direction) by a mechanically connected movable mechanism 51 as an example. The movable mechanism 51 typically includes a three-axis servo motor and a servo driver for driving each servo motor. Then, the movable mechanism 51 drives the stage 50 in response to a stage position command from a user or a control device (not shown) or the like. By driving the stage 50, the positional relationship between the object to be measured and the objective lens 40 described later is changed.

The objective lens 40, the beam splitter 30 and the pinhole mirror 32 are disposed on the optical axis AX1 which extends in the 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 to convert the propagation direction of the measurement light to a downward paper surface of the optical axis AX1. Further, the beam splitter 30 transmits the reflected light from the object to be measured, which propagates the optical axis AX1 upward on the paper surface.

On the other hand, the beam splitter 20 reflects the observation light generated by the observation light source 22, thereby converting the propagation direction to the right side of the paper surface of the optical axis AX2. That is, the beam splitter 20 functions as a light injecting unit for injecting observation light at a predetermined position on the optical path from the measurement light source 10 to the objective lens 40 as the condensing optical system. The measurement light and the observation light synthesized by the beam splitter 20 are reflected by the beam splitter 30 and then enter the objective lens 40. [

In particular, since the measurement light includes the wavelength component of the infrared band and the observation light includes the wavelength component of the visible band, the beam splitters 20 and 30 all have the transmission / reflection characteristics ranging from the visible band to the infrared band to a desired value Which can be maintained.

The objective lens 40 is a condensing optical system for condensing the observation light and the measurement light propagating the optical axis AX1 downward on the paper surface. That is, the objective lens 40 converges the measurement light and the observation light so as to form an image at the object to be measured 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.). By using such a magnifying lens, the area where the optical characteristic of the measured object is measured can be made smaller than the beam cross section of the light incident on the objective lens 40. [

Further, the measurement light and the observation light incident on the object to be measured through the objective lens 40 are reflected by the object to be measured, and propagate upward on the optical axis AX1. The reflected light passes through the objective lens 40, then passes through the beam splitter 30 and reaches the pinhole mirror 32.

The pinhole mirror 32 functions as a light separating portion for separating the measurement reflected light and the observation reflected light from the reflected light generated in the measured object. Specifically, the pinhole mirror 32 includes a reflecting surface that reflects the reflected light from the object to be measured, which propagates the optical axis AX1 upwardly on the paper surface. The pinhole mirror 32 rotates about the intersection of the reflecting surface and the optical axis AX1 (Pin holes) 32a are formed in the outer circumferential surface. The size of the pinhole 32a is smaller than the beam diameter at the position of the pinhole mirror 32 of the measurement reflected light generated by the measurement light from the measurement light source 10 reflected from the object to be measured . The pinhole 32a is arranged so that the measurement light and the observation light are coincident with the imaging position of the measurement reflected light and the observation reflected light generated by being reflected from the measured object, respectively. With this configuration, the reflected light generated in the measured object passes through the pinhole 32a and enters the spectroscopic measurement unit 60. [ On the other hand, the remaining portion of the reflected light is converted in its propagation direction and is incident on the axis conversion mirror 34.

The spectroscopic measurement unit 60 measures the reflectance spectrum from the measurement reflected light passing 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 restricting a wavelength component outside the measurement range included in the measurement reflected light passing through the pinhole 32a and incident on the spectroscopic measurement unit 60. In particular, do. The shutter 68 is used to block light incident on the detection unit 64, for example, when the detection unit 64 is reset. The shutter 68 is typically made of a mechanical shutter driven by an electromagnetic force.

The diffraction grating 62 splits the measurement reflected light incident thereon, and then guides each of the split waves to the detection unit 64. Specifically, the diffraction grating 62 is a reflection-type diffraction grating, and is configured so that diffraction waves at predetermined wavelength intervals are reflected in corresponding angular directions. When the measured reflected wave is incident on the diffraction grating 62 having such a configuration, the included wavelength components are reflected in the corresponding directions and are incident on the predetermined detection area of the detection unit 64. Further, this wavelength interval corresponds to the wavelength resolution capability of the spectroscopic measurement unit 60. The diffraction grating 62 is typically made of a flat focus type spherical grating.

The detection unit 64 outputs an electric signal corresponding to the light intensity of each wavelength component included in the measurement reflected light that has been spectroscopically measured by the diffraction grating 62, in order to measure the reflectance spectrum of the measured object. The detection unit 64 is made of an InGaAs array or the like having sensitivity to an infrared band.

The data processing section 70 measures the film thickness of each layer constituting the measured object by performing the characteristic processing relating to the present invention on the reflectance spectrum acquired by the detecting section 64. [ The data processing section 70 can also analyze the reflectance and the layer structure of each layer of the measured object. Details of such processing will be described later. Then, the data processing section 70 outputs the optical characteristics including the film thickness of the measured object to be measured.

On the other hand, the observation reflected light reflected by the pinhole mirror 32 is propagated along the optical axis AX3, and is incident on 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 is incident on the observation camera 38.

The observation camera 38 is an imaging unit for acquiring a reflection image obtained by the observation reflected light, and typically includes a CCD (Charged Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) sensor. In addition, the observation camera 38 typically has a sensitivity in the visible band, and often has a sensitivity characteristic different from that of the detection unit 64 having sensitivity in a predetermined measurement range. Then, the observation camera 38 outputs a video signal according to the reflection image obtained by the observation reflected light to the display unit 39. The display unit 39 displays a reflection image on the screen based on the video signal from the observation camera 38. [ The user observes the reflected image displayed on the display unit 39 and performs focusing on the measured object and confirmation of the measurement position. The display unit 39 typically comprises a liquid crystal display (LCD) or the like. Instead of the observation camera 38 and the display unit 39, a finder that allows the user to directly observe the reflection image may be provided.

&Lt; Analytical Investigation of Reflected Light >

First, the reflected light observed when the measurement light is irradiated to the measured object is mathematically and physically examined.

2 is an example of a cross-sectional schematic diagram of an object to be measured OBJ to be measured by the film thickness measuring apparatus 100 according to the embodiment of the present invention.

Referring to Fig. 2, an SOI substrate is considered as a representative example of the object OBJ. That is, the object OBJ has a three-layer structure in which the SiO ₂ layer 2 (BOX layer) is disposed between the Si layer 1 and the base Si layer 3 (substrate layer). It is assumed that the irradiated light from the film thickness measuring apparatus 100 is incident on the measured object OBJ from above the paper surface. That is, it is assumed that the measurement light enters the Si layer 1 first.

For easy understanding, it is assumed that the measurement light incident on the object OBJ is reflected at the interface between the Si layer 1 and the SiO ₂ layer 2 and is reflected. In the following description, subscript i is used to represent each layer. The subscript "0" is the atmosphere layer such as air or vacuum, the subscript "1" is the Si layer 1 of the object to be measured (OBJ), and the subscript "2" is the SiO ₂ layer 2. The index of refraction in each layer is represented by the index i using the index _i .

Since the reflection of light occurs at the interfaces of the layers having different refractive indexes (n _i ), the amplitude reflectance r ^(P ) of the P polarization component and the S polarization component at each interface between the i layer and the i + ⁾ _i , _{i + 1} , r ^(S) _i , _{i + 1} can be expressed as follows.

Here,? _I is an incident angle in the i-th layer. This incident angle? _I can be calculated from the incident angle in the uppermost atmosphere layer (O layer) by the following Snell's law.

In the layer having a film thickness capable of interfering with light, the light reflected by the reflectance expressed by the above formula is reciprocated in the layer several times. As a result, the optical path lengths are different between the light directly reflected at the interface with the adjacent layer and the light after the multiple reflection in the layer, so that the phases become different from each other, Lt; / RTI &gt; In order to exhibit the interference effect of light in each layer as described above, the phase angle? _I of the light in the layer of the i-th layer can be introduced as follows.

Here, d _i represents the film thickness of the i-layer, and λ represents the wavelength of the incident light.

For simplicity, when light is irradiated perpendicularly to the object OBJ, that is, when the incident angle? _I = 0, there is no distinction between the P polarized light and the S polarized light, and the amplitude reflectance at the interface between the respective layers The phase angle? ₁ of the thin film is as follows.

The reflectance R of the three-layer object to be measured OBJ shown in Fig. 2 is as follows.

Considering the frequency transformation (Fourier transform) of the phase angle? ₁ in the above equation, cos2? _{1, which} is a phase factor, becomes non-linear with respect to the reflectance R. Therefore, conversion to a function having a linearity with respect to this phase factor cos ₂ ? ₁ is performed. As an example, the reflectance R is transformed as shown in the following expression to define the wave-form converted reflectance R 'as a unique parameter.

This wave-converted reflectance R 'becomes a linear expression with respect to the phase factor cos ₂ ? ₁ and becomes linear. Here, R _a in the equation is a slice in the wave number converted reflectance (R '), and R _b is a slope in the wave number converted reflectance (R'). That is, the wave-converted reflectance R 'is a function for linearizing the value of the reflectance R at each wavelength with respect to the phase factor cos ₂ ? ₁ concerning the frequency conversion. As a function for linearizing the phase factor, a function of 1 / (1 - R) may be used.

Therefore, the number of waves (K ₁ ) in the target Si layer 1 can be defined as follows.

Here, when the light velocity of the wavelength? In the Si layer 1 is s and the light velocity of the wavelength? In vacuum is c, the refractive index n ₁ is expressed as c / s. The electromagnetic wave E (x, t) generated by the light propagating in the x direction in the Si layer 1 can be obtained by using the wave number K ₁ , the angular frequency ω and the phase δ, E (x, t) = E ₀ exp [j (? T - K ₁ x +?)]. That is, the propagation characteristic of the electromagnetic wave in the Si layer 1 depends on the wave number (K ₁ ). From these relationships, it can be seen that the light having the wavelength? In a vacuum is reduced in the layer, so that the wavelength also increases from? To? / N ₁ . In consideration of such a wavelength dispersion phenomenon, the wave number conversion reflectance R 'is defined as follows.

From this relationship, when the wave-converted reflectance R 'is frequency-converted (Fourier transformed) with respect to the wave number K, a peak appears in the periodic component corresponding to the film thickness d ₁ , The film thickness d ₁ can be calculated.

That is, the correspondence relation between the reflectance spectrum measured from the measured object OBJ and the reflectance at each wavelength can be expressed as a corresponding relationship between the wave number calculated from each wavelength and the wave number converted reflectivity R 'calculated according to the above-mentioned relational expression (Wavenumber distribution characteristic), frequency conversion of the function of the wave number conversion reflectance R 'including the wave number K with respect to the wave number K, and based on the peak appearing in the characteristic after the frequency conversion, The film thickness of the Si layer 1 constituting the water OBJ can be calculated. This means that the amplitude value of each wavenumber component included in the wavenumber distribution characteristic is acquired, and the film thickness of the Si layer 1 is calculated based on the wavenumber component having a larger amplitude value. As described later, as a method for analyzing a wavenumber component having a large amplitude value from the wave number distribution characteristic, a method using a discrete Fourier transform such as an FFT (Fast Fourier Transform), a method using a maximum entropy method (Hereinafter, also referred to as &quot; MEM &quot;) method.

In the definition of the wave-converted reflectance (R '), R _a and R _b are values that are independent of the interference phenomenon in the layer, but are not limited to the interface between the layers including the refractive index (n ₁ ) of the Si layer Depends on the amplitude reflectance of the light source. Therefore, when the refractive index n ₁ has a wavelength 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. Thus, represents the Fourier transform to ⊃, R ', R _a, R _b, cos2K ₁ when the d ₁ to the wave number (K) the function of the power spectrum after a Fourier transform to the respective P, P _a, P _b, F, The following expression is established.

The component depending on the film thickness in P _a in the formula is relatively small and has a peak independent of the power spectrum F and does not affect the power spectrum F. [

On the other hand, P _b in the formula is being power spectrum (F) and the convolution, the thickness component in the P _b exert a modulated component of the power spectrum to the film thickness (F). However, since P _b is irrelevant to the interference phenomenon in the layer and is influenced only by the wavelength dependency of the refractive index in the adjacent two layers, the film thickness component of P _b with respect to the wave number K is the film thickness of F Which is negligibly small compared to the components. For example, if R _b is a periodic function of the film thickness q and P _b after the Fourier transformation modulates the film thickness component d of the power spectrum F by convolution, The peak is "d-q" or "d + q", but the influence on the peak position (d) is small since the value of q is very small.

When Fourier transform is performed, as described later, the maximum film thickness of the layer to be measured is taken into consideration, and a suitable sample interval for the wave number converted reflectance (R ') according to the Nyquist sampling theorem and Sampling is performed with the number of samples. Thus, for a sampling frequency converting reflectivity (R ') thickness resolution (r) of the power spectrum calculated based on the film thickness component (q) of P _b is more likely less than (q <r), the film It can be said that there is little influence on the measurement result of the thickness d.

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

In the above description, the reflectance spectrum is used, but the transmittance spectrum may be used. In this case, when the measured transmittance is T and the &quot; wavenumber conversion transmittance &quot; is T ', it is expressed by the following relational expression.

Even in the case of using the transmittance spectrum, the transmittance T becomes non-linear with respect to the phase factor cos ₂ ? ₁ . Hence, from the same reason as described above, the wave-converted transmittance T 'having linearity with respect to the phase factor cos ₂ ? ₁ is adopted. According to the above equation, the wave number converted transmittance T 'becomes a linear expression with respect to the phase factor cos ₂ ? 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-converted transmittance T 'is a function for linearizing the value of the transmittance T at each wavelength with respect to the phase factor cos ₂ ? ₁ related to frequency conversion.

2, reflection light generated by reflection at the interface between the SiO ₂ layer 2 and the base Si layer 3 is considered. When the refractive index of the Si layer 1 is n ₁ and the film thickness is d ₁ , the refractive index of the SiO ₂ layer 2 is n ₂ , and the film thickness is d ₂ , the wave number conversion reflectance R ' do.

Here, when the film thickness d ₁ of the Si layer 1 and the film thickness d _{2 of the} SiO ₂ layer ₂ are separately calculated, the number of wafers converted into the waveness (K ₁ , K ₂ ) The reflectance [R ₁ '(K ₁ ), R ₂ ' (K ₂ )] is used. Concretely, it is shown as follows.

In the these equations, d ₁ 'and d _2' is not a precise film thickness, frequency conversion reflectance _{[R 1 '(K 1)} ] the original thickness from the peak of the power spectrum corresponding to the second term of (d ₁ ), And the original film thickness d ₂ can be obtained from the peak in the power spectrum corresponding to the third term of the wave number conversion reflectance [R ₂ '(K ₂ )].

In reality, the refractive indexes of the Si layer 1 and the SiO ₂ (2) are close to each other, and the reflectance at the interface between them is relatively small in comparison with the reflectance at the other interface. As a result, as compared to R _b or R _d is included in the function of frequency conversion reflectance, the value of R _c is small, from the power spectrum corresponding to claim 3, wherein the frequency conversion reflectance _{[R 2 '(K 2)} ] It is often difficult to identify peaks. In this case, the frequency conversion reflectance [R ₂ and '(K _2)] of the peak position of the power spectrum (d ₁ corresponding to claim 4, wherein' + d _2), frequency conversion reflectance [R ₂ '(K ₂₎ , The film thickness d ₂ can be calculated by calculating the peak position d ₁ 'of the power spectrum corresponding to the second term of the equation ( ₁ ) and taking the difference therebetween.

<Regarding Wavelength Range and Wavelength Resolution>

Fig. 3 is a diagram showing the measurement result when the SOI substrate is measured using the film thickness measuring apparatus 100 according to the present embodiment. 3 shows a case in which a wavelength range of 900 to 1600 nm is used (FIG. 3A) and a wavelength range is 1340 to 1600 nm (FIG. 3B) For example. It is also possible to select the diffraction grating 62 having a suitable characteristic according to the measurement wavelength so that the number of detection points (the number of detection channels) in the detection unit 64 (FIG. 1) 512 channels). In other words, the narrower the wavelength range, the smaller the wavelength interval per detection point (i.e., the wavelength resolution).

According to the above analytical review, the measured reflectance will be periodically changed with respect to wavelength.

In the measurement results shown in Fig. 3 (a), there is an indication that the reflectance is periodically changed with respect to the wavelength, but sufficient accuracy for measuring the film thickness is not obtained.

On the other hand, in the measurement results shown in FIG. 3 (b), the peaks and valleys of the reflectance are clearly shown, so that it is possible to measure the change period of the reflectance. 3C shows a result of frequency conversion for the wave number K after converting the measurement result (reflectance spectrum) shown in FIG. 3B into a function of the wave number converted reflectivity R ' . A value corresponding to the main peak shown in FIG. 3 (c) can be determined as the film thickness of the Si layer 1.

4 and 5 show other measurement results of the SOI substrate.

4 is a view showing another measurement result of measuring the SOI substrate using the film thickness measurement apparatus 100 according to the present embodiment. 4 shows a measurement example in which the film thickness of the Si layer 1 is 10.0 占 퐉 (design value) and the film thickness of the SiO ₂ layer 2 is 0.3 占 퐉 (design value). 4A shows a case where a side light having a wavelength component of a visible band (330 to 1100 nm) is used and FIG. 4B shows a case where a wavelength component of an infrared band (900 to 1600 nm) Is used as the measurement light. Further, as described above, the number of detection points (the number of detection channels) in the detection unit 64 (FIG. 1) is all the same.

As shown in Fig. 4 (a), when the measuring light having the wavelength component of the visible band is used, the reflectance shows a periodic behavior in the wavelength range longer than about 860 nm, It can be seen that no periodic change has occurred. On the other hand, as shown in FIG. 4 (b), when the measurement light having the wavelength component of the infrared band is used, the periodic change of the reflectance is significant.

5 is a view showing still another measurement result of measuring the SOI substrate using the film thickness measurement apparatus 100 according to the present embodiment. 5 shows a measurement example in which the film thickness of the Si layer 1 is 80.0 占 퐉 (design value) and the film thickness of the SiO ₂ layer 2 is 0.1 占 퐉 (design value). 5A shows a case where measurement light having a wavelength component of infrared band (900 to 1600 nm) is used, and FIG. 5B shows a case where measurement light having a wavelength of narrower infrared band (1470 to 1600 nm) Is used as the measurement light. In addition, as described above, the number of detection points (the number of detection channels) in the detection unit 64 (Fig. 1) is all the same.

As shown in Fig. 5 (a), even when the measuring light having the wavelength component of the infrared band is used, it can be seen that no significant periodic change is observed in the measured reflectance. On the other hand, as shown in Fig. 5 (b), it can be seen that when the measurement light having a wavelength component of a narrower infrared band is used, the periodic change of the reflectance is significant.

According to the measurement example described above, it is necessary to appropriately set the wavelength range and the wavelength resolution of the measurement light in order to measure the film thickness of the relatively thick layer with high accuracy. This is because it is a measurement method using the optical interference phenomenon in the layer and that the wavelength resolution of the reflected light by the detection unit 64 is finite. By setting the wavelength of the appropriate measurement light by the procedure described below .

In the following examinations, the lower limit of the film thickness measuring range is d _min and the upper limit of the film thickness measuring range is d _max . The lower limit of the wavelength detection of the detection unit 64 is? _Min and the upper limit of the wavelength detection of the detection unit 64 is? _Max . The wavelength range of the measurement light irradiated by the measurement light source 10 (FIG. 1) may be any range as long as it includes the wavelength detection range of the detection unit 64. Further, the number of detection points (the number of detection channels) in the detection unit 64 (Fig. 1) is defined as S _p .

6 is a diagram for explaining the relationship between the film thickness measurement range according to the embodiment of the present invention, the detection wavelength range of the detection unit 64, and the number of detection points.

(1) Relationship between the lower limit value (d _min ) of the film thickness measuring range and the detection wavelength range

According to the film thickness measuring method described above, it is necessary to find a wavelength causing optical interference in the object to be measured of the object. Therefore, it is necessary for the detector 64 to have a wavelength range in which optical interference can occur. 6 (a), it is necessary that the reflectance waveform measured with respect to the measured object changes by one cycle or more in the detection wavelength range of the detection unit 64. [

This means that the optical distance generated by the change of the detection wavelength range of the detection unit 64 from the lower limit value (? _Min ) to the upper limit value? _Max needs to be changed by the reciprocation of the film thickness of the object to be measured. Therefore, it is necessary to satisfy the following conditional expression 1 as a relation between the lower limit value d _min of the film thickness measuring range and the wavelength range of the measuring light.

[Conditional expression 1]

(2) Relationship between the upper limit value (d _max ) of the film thickness measurement range and the number of detection points

As shown in Fig. 6 (b), the longer the wavelength of the measurement light, the longer the period of the reflectance waveform measured with respect to the measured object. The reflectance waveform shown in FIG. 6C is obtained by converting the reflectivity waveform shown in FIG. 6B into the coordinates of the wave number (1 / f). At this time, if each array element such as InGaAs is arranged at an equal interval with respect to the wavelength, it can be seen that the arrangement interval of each array element with respect to the wave number becomes wider as the wave number becomes smaller.

Therefore, in order to accurately sample the reflectance waveforms that change with a predetermined period with respect to the wave number, it is necessary that the arrangement interval (wavelength resolution (DELTA lambda)) of each array element satisfies Nyquist's sampling theorem, by the conditions in that meet, the film is determined by the upper limit value (d _max) of the thickness measuring range.

The wavelength resolving power DELTA lambda in the detecting unit 64 can be expressed by DELTA lambda = (lambda _max - lambda _min ) / S _p using the number of detected points (the number of detected channels) (S _p ).

(Peak or valley) occurs in the upper limit value (? _Max ) of the measurement light in the reflectivity waveform, the peak value of the reflectance waveform is set so that the extreme value adjacent to the peak When the wavelength for generating a valley) adjacent the peak or valley in which λ _1, a film needs to be met under the following conditions between the upper limit value (d _max) of the thickness measuring range.

Here, when the film thickness of the layer to be measured is relatively large, it can be regarded as n _max? N _1. Therefore, the above-described condition can be expressed by the following conditional expression 2.

[Conditional expression 2]

At this time, regarding the wavelength resolution (?), The following condition needs to be satisfied.

A relational expression of the above-described wavelength resolution (Δλ), by substituting the relation of the upper limit value (d _max) can be expressed as the conditional expression 3 as follows Eliminating the terms of λ _1,.

[Conditional expression 3]

When the film thickness measurement range (lower limit value (d _min ) to upper limit value (d _max )) required for the measured object is determined in advance as a result of the above-described examination, The lower limit value (d _min ) to the upper limit value (d _max )) and the number of detection points (S _p ).

<Calculation example>

An example in which calculation is performed with respect to the conditions required for measuring the film thickness of the Si layer 1 of the SOI substrate as shown in Fig. 2 is shown below.

In this calculation example, it is assumed that the upper limit d _max of the Si layer 1 of the SOI substrate is 100 μm, and the refractive index n is a constant (n = 3.5) that does not affect the wavelength. In this calculation example, the lower limit value d _min of the Si layer 1 of the SOI substrate is not considered.

Substituting the above values into the above-mentioned conditional expressions 2 and 3, the upper limit value? _Max = 1424.0 nm and the wavelength resolution? Lambda = 1.445375 nm are calculated. Therefore, when the 512-channel detector 64 is used to measure the film thickness of a measurement object having a film thickness of 100 mu m at the maximum, measurement light including a wavelength range of about 684-1424 nm is used, It is found that the detection unit 64 detects the reflected light in the range (wavelength resolution (DELTA lambda) = 1.4453125 nm).

However, the wavelength resolution (DELTA lambda) calculated by the above-described conditional formula describes the theoretical minimum specification, and in actual measurement, it is preferable to make the precision higher than the calculated wavelength resolution DELTA lambda. Further, it is more preferable to be several times (for example, 2 to 4 times). In addition, increasing the precision means setting the value of the wavelength resolution (DELTA lambda) to be smaller.

That is, in an actual film thickness measuring apparatus, the spectral accuracy may deteriorate depending on the influence of the incident angle of the measurement light on the measured object, the influence of the aperture angle when the lens condenser system is used, and the like. In such a case, the peak height on the power spectrum becomes small, making it difficult to calculate the film thickness. In addition, when FFT or the like for discrete frequency conversion is used by using finite number of sampling values, there may be a case where a conversion error such as a wavenesis conversion is largely affected by aliasing. In addition, there is also a possibility that the refractive index dispersion of the measurement object changes largely depending on the wavelength range of the measurement light, and there is a possibility that the refractive index dispersion partially does not match the condition.

Fig. 7 is a diagram showing the result of simulating the measurement result using a film thickness measuring apparatus having a wavelength resolution close to the theoretical value. Fig. Fig. 8 is a view showing the result of simulating the measurement result using a film thickness measuring apparatus having a wavelength resolution with doubling of the precision with respect to the theoretical value. Fig. In addition, the film thickness of the object to be measured was set at 100 mu m.

More specifically, FIG. 7A shows a result of measuring the reflectance spectrum (wavelength resolution (DELTA lambda) = 2.734375 nm) in the range of 900 nm to 1600 nm using the 512 channel detector 64 , And FIG. 7 (b) shows a power spectrum obtained by performing frequency conversion (FFT transform) on the reflectance spectrum shown in FIG. 7 (a). As shown in Fig. 7B, in this case, although a peak exists in the vicinity of 100 mu m, the level is small compared to the noise (ghost) on the thin film side, and it is sometimes difficult to determine the film thickness .

8A shows a measurement result when the wavelength range is set such that the accuracy of the wavelength resolution in the detection unit 64 is twice the theoretical value. Fig. 8B shows a measurement result in Fig. (Here, FFT-transformed) the reflectance spectrum shown in Fig. In this example, the number of detection points and the wavelength range are determined so that the wavelength resolution ?? of the detection unit 64 is 1.3671875 nm. As shown in Fig. 8 (b), in this case, a strong peak appears near the original film thickness of 100 m, which means that the film thickness of the measured object can be accurately measured.

<Outline of Film Thickness Calculation Process>

As described above, the film thickness of the object to be measured can be calculated based on the periodicity of the reflectance spectrum. That is, the power spectra can be obtained by frequency-converting the detected reflectance spectrum, and the film thickness can be calculated from the peak appearing in this power spectrum. Such a power spectrum is actually calculated by a discrete Fourier transform method such as FFT. However, in the FFT, a power spectrum sufficiently reflecting periodicity may not be obtained. Therefore, the film thickness measuring apparatus 100 according to the present embodiment is configured to be able to execute an optimization method such as MEM in addition to discrete Fourier transform such as FFT as a power spectrum calculating method. That is, the film thickness measuring apparatus 100 according to the present embodiment selectively or integrally executes the Fourier transform and the optimization method in accordance with the detected reflectance spectrum. Details of the processing of MEM are described in &quot; Microcomputer / Personal Computer Application Technology in Waveform Data Processing and Measurement System for Scientific Measurement &quot; by Minami Shigeo, edited by CQ Publishing Co., August 1, 1992 10 edition, and the like, so that it may be referred to.

Further, the film thickness measuring apparatus 100 according to the present embodiment may further include a method of calculating the film thickness from the physical model calculated from the measurement target, in addition to the method of analytically calculating the film thickness from the detected reflectance spectrum as described above A so-called fitting method is also practicable in which the optical property value of the measurement object is searched based on the deviation between the reflectance spectrum and the actually detected reflectance spectrum.

By the way, as the SOI substrate shown in FIG. 2, the second layer as compared to the film thickness of the SiO ₂ layer 2, the first for the large object to be measured is the thickness of two or more digits of the first layer Si layer (1) of , The film thickness of each layer can not be calculated with sufficient precision in the fitting method.

9 is a diagram showing a measurement result of a reflectance spectrum for an SOI substrate. 9 shows a measurement example in which the film thickness of the Si layer 1 of the first layer is 100 占 퐉 and the film thickness of the SiO2 layer _{2 of} the second layer is changed in the range of 0.48 to 0.52 占 퐉 to 0.1 占 퐉 pitch . As shown in FIG. 9, even when the film thickness of the SiO ₂ layer 2 as the second layer is changed, it can be seen that the measured reflectance spectrum does not change much. That is, in the reflectance spectrum measured from such a measured object, since the influence of the Si layer 1 of the first layer is dominant, even if the parameters of the SiO ₂ layer ₂ of the second layer are changed, It means nothing.

Therefore, the film thickness measuring apparatus 100 according to the present embodiment is a film thickness measuring apparatus according to the present embodiment, in which, for an object to be measured having a plurality of different layers such as an SOI substrate, the film thickness of each layer can be independently analyzed accurately, , The optimization method, and the fitting method, or a plurality of them, are appropriately combined and executed. Hereinafter, the details of the film thickness calculating process in the film thickness measuring apparatus 100 according to the present embodiment will be described. Such a film thickness calculating process is executed by the data processor 70 (Fig. 1).

<Configuration of Data Processing Unit>

10 is a schematic diagram showing a schematic hardware configuration of a data processing unit 70 according to an embodiment of the present invention.

10, the 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), a CPU 200 A hard disk unit (HDD: Hard Disk Drive) 210 for non-volatile storage of a program executed by the CPU 200. The memory unit 212 temporarily stores data necessary for executing the program in the CPU 200 do. A program for realizing a process to be described later is stored in the hard disk unit 210 in advance. The program is stored in the hard disk unit 210 by a flexible disk drive (FDD) 216 or a CD-ROM drive 214 Is read out from the flexible disk 216a or CD-ROM (Compact Disk-Read Only Memory) 214a or the like.

The CPU 200 receives an instruction from a user or the like through an input unit 208 such as a keyboard or a mouse and outputs a measurement result or the like measured by the execution of the program to the display unit 204. [ Each part is connected to each other via a bus 202.

&Lt; Operation processing structure >

The data processing section 70 according to the present embodiment can be applied to the type and number of unknown values in the parameters (material, film thickness, film thickness range, refractive index, extinction coefficient, etc.) Therefore, it is possible to select and execute any one of the following processing patterns 1 to 6. In the following description, the case where the film thicknesses of two laminated layers (referred to as "first layer" and "second layer", respectively) are independently calculated as in the case of the SOI substrate shown in FIG. 2 By the same procedure, it is possible to independently calculate the film thicknesses which are stacked more.

(1) Processing pattern 1

The treatment pattern 1 is a film thickness calculation process that can be executed when the refractive index and the extinction coefficient of the first layer and the second layer are known. In this processing pattern 1, the film thicknesses of the respective layers are all determined by the fitting method. As a fitting method, a case of using a least squares method is exemplified.

11 is a block diagram showing a control structure for executing the film thickness calculating process relating to the processing pattern 1 according to the embodiment of the present invention. The block diagram shown in Fig. 11 is realized by the CPU 200 reading a pre-stored program such as the hard disk unit 210 or the like in the memory unit 212 and executing it.

11, the data processing unit 70 (FIG. 1) includes a buffer unit 71, a modeling unit 721, and a fitting unit 722 as its functions.

The buffer unit 71 temporarily stores the actually measured reflectance spectrum R (?) Output from the spectroscopic measurement unit 60 (FIG. 1). More specifically, since the reflectance value is output from the spectroscopic measurement unit 60 for each predetermined wavelength resolution capability, the buffer unit 71 stores the wavelength and the reflectance at that wavelength in association with each other.

The modeling unit 721 receives the parameters related to the measured object, determines a model equation (function) showing the theoretical reflectance in the measured object based on the received parameters, and determines, based on the determined function, And the theoretical reflectance (spectrum) at each wavelength is calculated. The calculated theoretical reflectance at each wavelength is output to the fitting portion 722. [ More specifically, the modeling unit 721 receives the refractive index n ₁ and the extinction coefficient k _{1 of} the first layer, the refractive index n ₂ and the extinction coefficient k ₂ of the second layer, The initial value of the film thickness d ₁ of the first layer and the initial value of the film thickness d ₂ of the second layer are received. Although the user may input each parameter, parameters of a standard material may be previously stored as a file or the like, and read out as necessary. Further, the refractive index (n ₀ ) and the extinction coefficient (k ₀ ) of the atmosphere layer are also input, if necessary.

The model equation representing the theoretical reflectance is the same as the reflectance R in the three-layer object to be measured (OBJ), and therefore is a function including at least the value of the film thickness of each layer.

Further, the modeling unit 721 updates the function indicating the theoretical reflectance according to the parameter update command from the fitting unit 722, which will be described later, and calculates the theoretical reflectance (spectrum) at each wavelength in accordance with the updated function do. More specifically, the modeling unit 721 sequentially updates the film thickness d _{1 of} the first layer and the film thickness d ₂ of the second layer as parameters.

The fitting section 722 reads the measured value of the reflectance spectrum from the buffer section 71 and sequentially calculates the square deviation between the theoretical value of the reflectance spectrum output from the modeling section 721 and each wavelength. The fitting portion 722 calculates the residual from the deviation at each wavelength, and determines whether or not the residual is below a predetermined threshold value. That is, the fitting unit 722 determines whether or not convergence has been achieved with respect to the current parameter.

If the residual is not less than the predetermined threshold value, the fitting unit 722 gives a parameter update command to the modeling unit 721, and waits until the theoretical value of the reflectance spectrum is newly output. On the other hand, if the residual is less than or equal to the predetermined threshold value, the fitting portion 722 outputs the film thickness d ₁ of the first layer and the film thickness d ₂ of the second layer at the current point as the analytical value.

12 is a flowchart showing the procedure of the film thickness calculating process related to the processing pattern 1 according to the embodiment of the present invention.

Referring to Fig. 12, first, the user places the measured object (sample) on the stage 50 (Fig. 1) (step S100). Subsequently, when the user gives a measurement preparation command, the observation light source 22 (Fig. 1) starts irradiation of observation light. The user refers to the reflected image photographed by the observation camera 38 displayed on the display unit 39 and gives a stage position command to the movable mechanism 51 to adjust the measurement range and perform focusing (step S102).

When the user gives a measurement start command after adjustment of the measurement range or focusing is completed, the measurement light is started to be generated from the measurement light source 10 (Fig. 1). The spectroscopic measurement unit 60 receives the reflected light from the measured object, and outputs the reflectance spectrum based on the reflected light to the data processing unit 70 (step S104). Subsequently, the CPU 200 of the data processing unit 70 temporarily stores the reflectance spectrum detected by the spectroscopic measurement unit 60 in the memory unit 212 or the like (step S106). Thereafter, the CPU 200 of the data processing unit 70 executes the following film thickness calculating process.

The CPU 200 displays an input screen on the display unit 204 (Fig. 10) or the like and prompts the user to input parameters (step S108). The user inputs the refractive index n ₁ and the extinction coefficient k ₁ of the first layer and the refractive index n ₂ and the extinction coefficient k ₂ of the second layer of the object to be measured At the same time, an initial value of the film thickness d _{1 of} the first layer and the film thickness d ₂ of the second layer with respect to the object to be measured is inputted (step S110).

Further, the CPU 200 calculates the theoretical value of the reflectance spectrum based on the parameter inputted by the user (step S112). Subsequently, the CPU 200 sequentially calculates the square deviation between the measured value of the reflectance spectrum and the theoretical value of the reflectance spectrum stored in the memory unit 212 and the like, and calculates the residual between them (Step S114) . Further, the CPU 200 determines whether the calculated residual is equal to or less than a predetermined threshold value (step S116).

If the calculated residual is not less than the predetermined threshold value (in the case of 'No' in step S116), the CPU 200 determines whether or not the film thickness d _{1 of} the first layer and the film thickness d ₂ of the second layer The current value is changed (step S118). The degree to which the film thicknesses d ₁ and d ₃ are to be changed is determined according to the degree of occurrence of residuals. Then, the process returns to step S112.

On the other hand, when the calculated residual is less than or equal to the predetermined threshold (in the case of "YES" in step S116), the CPU 200 sets the film thickness d _{1 of} the first layer and the film thickness d ₂ As the film thickness (analysis value) of each layer of the object to be measured (step S120). Then, the process ends.

In the block diagram shown in Fig. 11, the configuration for inputting the fixed value as the refractive index (n ₁ , n ₂ ) and the extinction coefficient (k ₁ , k ₂ ) is exemplified. However, the refractive index and the extinction coefficient May be used. For example, as the refractive index and the extinction coefficient in consideration of wavelength dispersion, the following Cauchy model equation may be used.

When such an equation is used, an initial value or a known value is input in advance for each coefficient in the equation, and these coefficients also become fitting targets.

Alternatively, a Sellmeier model equation as shown below may be used.

(2) Processing pattern 2

The processing pattern 2 is an executable film thickness calculation processing when the refractive index and the extinction coefficient of the first layer and the second layer are known. In this processing pattern 2, the first layer having a large film thickness is determined by frequency conversion using discrete Fourier transform, the film thickness of the first layer is set to a fixed value, and the film thickness of the second layer is determined by fitting do. As a fitting method, a case of using a least squares method is exemplified.

13 is a block diagram showing a control structure for executing the film thickness calculating process relating to the processing pattern 2 according to the embodiment of the present invention. The block diagram shown in Fig. 13 is realized by the CPU 200 reading a pre-stored program such as the hard disk unit 210 and the like in the memory unit 212 and executing it.

13, the data processing section 70 (Fig. 1) includes a buffer section 71, a wavenumber conversion section 731, a buffer section 732, a Fourier transform section 733, 734, a modeling unit 735, and a fitting unit 736 as its functions.

The buffer unit 71 temporarily stores the actually measured reflectance spectrum R (?) Output from the spectroscopic measurement unit 60 (FIG. 1). Since details of the processing of the specific configuration have been described above, detailed description thereof will not be repeated.

The wave number conversion section 731 receives the parameters relating to the first layer (the refractive index n ₁ and the extinction coefficient k ₁ ), and stores the reflectance spectrum temporarily stored in the buffer section 71 based on the received parameters. (R) (?). That is, the wave number conversion section 731 converts the correspondence between each wavelength in the reflectance spectrum (R) (?) And the reflectance at that wavelength into the wave number (K ₁ ) (?) For each wavelength, Converted reflection ratio R ₁ 'calculated according to the relational expression. More specifically, the wave number conversion section 731 converts the wave number K ₁ (λ) and the wave number conversion reflectance R ₁ '(λ) {= R (λ) / [ 1 - R ([lambda])]}, and outputs it to the buffer unit 732.

The buffer unit 732 stores the wave number K ₁ (λ) sequentially output from the wave number conversion unit 731 and the wave number conversion reflectance R ₁ '(λ) in association with each other. That is, the wave number conversion reflectance R ₁ '(K ₁ ), which is the wavenumber distribution characteristic of the wave number conversion reflectance relating to the wave number (K ₁ ) (λ), is stored in the buffer unit 732.

Fourier transform unit 733 performs a Fourier transform on the frequency conversion reflectivity (R ₁₎ (K ₁₎ that is stored in the buffer unit 732 to the wave number (K _1), and calculates the power spectrum (P _1). As the Fourier transform method, fast Fourier transform (FFT) or discrete cosine transform (DCT) can be used.

The peak search section 734 searches for a peak appearing in the power spectrum P ₁ calculated by the Fourier transform section 733 and obtains the film thickness corresponding to the peak to obtain the film thickness d ₁ ).

The modeling unit 735 receives the parameters related to the measured object, determines a model expression (function) representing the theoretical reflectance in the measured object based on the received parameter, (Spectral) of the light beam. The calculated theoretical reflectance at each wavelength is output to the fitting portion 736. [ More specifically, the modeling unit 735 receives the film thickness d ₁ of the first layer output from the peak search unit 734, the refractive index n ₂ of the second layer, and the extinction coefficient k ₂ , And the initial value of the film thickness d ₂ of the second layer is received. Although the user may input each parameter, parameters of a standard material may be previously stored as a file or the like, and read out as necessary. The model equation representing the theoretical reflectance is the same as the reflectance R in the above-described three-layer object OBJ and is a function including at least the value of the film thickness of each layer.

The modeling unit 735 updates the function indicating the theoretical reflectance according to the parameter update command from the fitting unit 736 and again calculates the theoretical reflectance (spectrum) at each wavelength in accordance with the updated function . More specifically, the modeling unit 735 sequentially updates the film thickness d ₂ of the second layer as a parameter.

The fitting section 736 reads the measured value of the reflectance spectrum from the buffer section 71 and sequentially calculates the square deviation between the theoretical value of the reflectance spectrum outputted from the modeling section 735 and each wavelength. The fitting portion 736 calculates the residual from the square deviation at each wavelength and determines whether or not the residual is below a predetermined threshold value. That is, the fitting unit 736 determines whether or not convergence is taking place in the current parameter.

If the residual is not less than the predetermined threshold value, the fitting unit 736 gives a parameter update command to the modeling unit 735, and waits until the theoretical value of the reflectance spectrum is newly output. On the other hand, if the residual is less than or equal to the predetermined threshold value, the fitting portion 736 outputs the film thickness d ₁ of the first layer and the film thickness d ₂ of the second layer as the analytical values.

Fig. 14 is a flowchart showing a procedure of the film thickness calculating process relating to the processing pattern 2 according to the embodiment of the present invention. Among the steps of the flowchart shown in FIG. 14, the processes of steps S100 to S108 are the same as the steps of the flowchart shown in FIG. 12, and detailed description thereof will not be repeated. Hereinafter, the film thickness calculating process after step S132, which is different from the flowchart shown in Fig. 12, will be described.

In step S132, the user is the refractive index from the displayed input screen or the like, the first layer of the object to be measured (n ₁₎ and the extinction coefficient (k ₁₎ and the refractive index of the second layer of the object to be measured (n ₂₎ and an extinction coefficient ( k ₂ ) is inputted and the initial value of the film thickness d ₂ of the second layer is input.

Then, the CPU 200 waves-converts the reflectance spectrum stored in the memory unit 212 or the like based on the inputted refractive index n ₁ and the extinction coefficient k ₁ of the first layer (step S134). Then, the CPU 200 stores the wave-number-converted reflectance obtained by this wave number conversion into the memory unit 212 or the like (step S136). Further, the CPU 200 calculates the power spectrum by performing the Fourier transform on the wave number conversion reflectance with respect to the wave number (K ₁ ) (step S138). Further, the CPU 200 acquires the peak appearing in the calculated power spectrum and the film thickness corresponding to the peak as the film thickness d ₁ of the first layer (step S140).

Subsequently, the CPU 200 calculates the theoretical value of the reflectance spectrum based on the film thickness d ₁ of the first layer acquired in step S210 and the parameters relating to the second layer inputted by the user (step S142). Then, the CPU 200 sequentially calculates the square deviation between the measured value of the reflectance spectrum stored in the memory unit 212 and the theoretical value of the reflectance spectrum for each wavelength, and calculates the residual between them (Step S144) . Further, the CPU 200 determines whether the calculated residual is less than or equal to a predetermined threshold value (step S146).

If the calculated residual is not less than the predetermined threshold value (in the case of 'No' in step S146), the CPU 200 changes the current value of the film thickness d2 of the second layer (step S148). The direction in which the film thickness d ₂ is to be changed is determined according to the degree of occurrence of residuals. Then, the process returns to step S142.

On the other hand, if the calculated residual is less than or equal to the predetermined threshold value (YES in step S146), the CPU 200 calculates the thickness d ₁ of the first layer and the thickness d ₂ As the film thickness (analysis value) of each layer of the object to be measured (step S150). Then, the process ends.

Further, similarly to the above-described process pattern 1, a refractive index and an extinction coefficient in consideration of wavelength dispersion may be used. Since the detailed functions have been described above, detailed description thereof will not be repeated.

(3) Treatment pattern 3

The treatment pattern 3 is a film thickness calculation process that can be executed when the refractive index and the extinction coefficient of the first layer and the second layer are known. This processing pattern 3 differs from the above-described processing pattern 2 in that the optimization method other than the Fourier transformation is used in calculating the film thickness of the first layer. The other processing is the same as the processing pattern 2 described above.

Fig. 15 is a block diagram showing a control structure for executing the film thickness calculating process relating to the processing pattern 3 according to the embodiment of the present invention. The block diagram shown in Fig. 15 is realized by the CPU 200 reading a pre-stored program such as the hard disk unit 210 and the like in the memory unit 212 and executing it.

15, the data processing unit 70 (FIG. 1) includes a buffer unit 71, an optimization operation unit 741, a modeling unit 742, and a fitting unit 743 as its functions.

The buffer unit 71 temporarily stores the actually measured reflectance spectrum R (?) Output from the spectroscopic measurement unit 60 (FIG. 1). Since details of the processing of the specific configuration have been described above, detailed description thereof will not be repeated.

The optimization operation unit 741 analyzes the frequency component of the reflectance spectrum stored in the buffer unit 71 using the optimization method such as MEM to calculate the film thickness d ₁ of the first layer. More specifically, the optimization calculation unit 741 uses an autoregressive model to obtain an autocorrelation function for the measured value of the reflectance spectrum, and determines an autoregressive coefficient describing the autoregressive model from these values. The optimization calculation unit 741 acquires the film thickness corresponding to the wavelength of the main component obtained by performing the frequency analysis in this manner and outputs it as the film thickness d ₁ of the first layer. The optimization calculation unit 741 calculates the search range of the film thickness d ₁ of the first layer, the refractive index n ₁ and the extinction coefficient k _{1 of} the first layer, The refractive index n ₂ and the extinction coefficient k ₂ are accepted and a preliminary value of the film thickness d ₂ of the second layer is received. Although the user may input each parameter, parameters of a standard material may be previously stored as a file or the like, and read out as necessary.

The modeling unit 742 and the fitting unit 743 receive the film thickness d ₁ of the first layer and the parameters relating to the measured object calculated by the optimization calculation unit 741 and calculate the film thickness d ₂ ) is determined by fitting. The processing of the modeling unit 742 and the fitting unit 743 are the same as those of the modeling unit 735 and the fitting unit 736 of the above-described processing pattern 2, respectively, and therefore detailed description thereof will not be repeated.

16 is a flowchart showing the procedure of the film thickness calculating process relating to the processing pattern 3 according to the embodiment of the present invention. Among the steps of the flow chart shown in Fig. 16, the processes of steps S100 to S106 are the same as those of the steps denoted by the same reference numerals in the flowchart shown in Fig. 12, and therefore detailed description thereof will not be repeated. Hereinafter, the film thickness calculating process after step S162 different from the flowchart shown in Fig. 12 will be described.

In step S162, the user selects, from the displayed input screen or the like, the search range of the first layer thickness d ₁ of the measured object, the refractive index n ₁ of the first layer of the measured object and the extinction coefficient k ₁ (N ₂ ) and the extinction coefficient (k ₂ ) of the second layer of the object to be measured.

Then, the CPU 200 analyzes the frequency component of the reflectance spectrum stored in the memory unit 212 or the like using the optimization method, thereby calculating the film thickness d ₁ of the first layer (step S164) .

Subsequently, CPU (200) on the basis of the parameters relating to the cost and the film thickness (d ₁₎ of the first layer, the second layer the user input obtained at step S164 and calculates the theoretical value of the reflectivity spectrum (step S166). Then, the CPU 200 sequentially calculates the square deviation between the measured value of the reflectance spectrum and the theoretical value of the reflectance spectrum stored in the memory unit 212 and the like, and calculates the residual between them (step S168). Further, the CPU 200 determines whether the calculated residual is equal to or less than a predetermined threshold value (step S170).

If the calculated residual error is not the predetermined threshold or less (in the case of NO in step S170), the, CPU (200) modifies the value of the current thickness (d ₂₎ of the second layer (step S172). The direction in which the film thickness d ₂ is to be changed is determined according to the degree of occurrence of residuals. Then, the process returns to step S166.

On the other hand, if the calculated residual is less than or equal to the predetermined threshold value (YES in step S170), the CPU 200 determines whether or not the film thickness d _{1 of} the first layer and the film thickness d ₂ As the film thickness (analysis value) of each layer of the object to be measured (step S174). Then, the process ends.

As in the case of the above-described process pattern 1, a refractive index and an extinction coefficient in consideration of wavelength dispersion may be used. Since the detailed functions have been described above, detailed description thereof will not be repeated.

(4) Processing pattern 4

The processing pattern 4 is a method in which the processing pattern 1 is improved, and the convergence by the fitting is further ensured. That is, in an object to be measured in which the film thicknesses of the first layer and the second layer are greatly different from each other like an SOI substrate, an initial value for fitting the film thickness of each layer is important. Accordingly, in the processing pattern 4, the initial value of the film thickness of each layer is first determined by using the optimization method, and the film thicknesses of the first layer and the second layer are determined by the fitting method using these initial values.

17 is a block diagram showing a control structure for executing the film thickness calculating process relating to the processing pattern 4 according to the embodiment of the present invention. The block diagram shown in Fig. 17 is realized by the CPU 200 reading a pre-stored program such as the hard disk unit 210 and the like in the memory unit 212 and executing it.

The control structure relating to the processing value 4 shown in Fig. 17 is substantially the same as the control structure relating to the processing pattern 1 shown in Fig. 11, in which the optimization operation section 751 is added.

The optimization operation unit 751 analyzes the frequency components of the reflectance spectrum stored in the buffer unit 71 using the optimization method such as MEM to determine the film thickness d ₁ of the first layer and the film thickness of the second layer d ₂ , respectively. In particular, the optimization calculation unit 751 extracts two or more peaks obtained by frequency analysis of the actually measured reflectance spectra, and calculates the film thickness d ₁ of the first layer and the film thickness d _{1 of} the second layer from the film thickness corresponding to these peaks. And the thickness d ₂ are respectively calculated. The calculated film thickness d ₁ of the first layer and the film thickness d ₂ of the second layer are used as initial values of fitting, and no precise accuracy is required. Since the specific frequency analysis method in the optimization calculation unit 751 is the same as the above-described optimization calculation unit 741, detailed description thereof will not be repeated.

The modeling unit 721 and the fitting unit 722 are designed such that the film thickness d _{1 of} the first layer and the film thickness d ₂ of the second layer calculated by the optimization calculation unit 751 are used as initial values, The film thickness d _{1 of} the first layer and the film thickness d ₂ of the second layer are determined by fitting. Since details of processing of the modeling unit 721 and the fitting unit 722 have been described above, detailed description thereof will not be repeated.

18 is a flowchart showing the procedure of the film thickness calculating process related to the processing pattern 4 according to the embodiment of the present invention. The flow chart shown in Fig. 18 is similar to that of the steps shown in Fig. 12 except that steps S111A and S111B are provided instead of step S110, and the other steps are the same as those given with the same reference numerals. Do not repeat. Hereinafter, a process different from that of Fig. 12 will be described.

Referring to Fig. 18, after the execution of step S108, the processing of step S111A is executed. In step S111A, the user has a refractive index from the displayed input screen or the like, the first layer of the object to be measured (n ₁₎ and the extinction coefficient (k ₁₎ and the refractive index of the second layer of the object to be measured (n ₂₎ and an extinction coefficient (k ₂ ), and also inputs a search range of the film thickness d ₁ of the first layer and a search range of the film thickness d ₂ of the second layer. In the following step S111B, CPU (200) is by analyzing the frequency components by using, optimization method for the reflectance spectra stored in a memory or the like section 212, the thickness of the first layer (d ₁₎ and second layer (D &lt; ₂ &gt;). The film thickness d _{1 of} the first layer and the film thickness d ₂ of the second layer calculated in this step S111A are used as the initial values of the fitting. After this step S111B, the same processing as the processing after step S112 in Fig. 12 is executed.

Further, similarly to the above-described process pattern 1, a refractive index and an extinction coefficient in consideration of wavelength dispersion may be used. Since the detailed functions have been described above, detailed description thereof will not be repeated.

(5) Processing pattern 5

The processing pattern 5 is a modification of the above-described processing pattern 1, which is applied when the film thickness of one layer is known and only the film thickness of the other layer is analyzed. In the following description, a method in which the film thickness of the second layer of the measured object is known and the film thickness of the first layer is determined by fitting is exemplified.

Fig. 19 is a block diagram showing a control structure for executing the film thickness calculating process relating to the processing pattern 5 according to the embodiment of the present invention. Fig. The block diagram shown in Fig. 19 is realized by the CPU 200 reading a pre-stored program such as the hard disk unit 210 or the like in the memory unit 212 and executing it.

The control structure relating to the processing pattern 4 shown in Fig. 19 includes a modeling unit 721A instead of the modeling unit 721 in the control structure relating to the processing pattern 1 shown in Fig.

Model conversion unit (721A) is at the same time for receiving the refractive index (n ₁₎ and refractive index (n ₂₎ and an extinction coefficient (k ₂₎ of the extinction coefficient (k _1), the second layer of the first layer, the first layer layer receives the value (fixed value) of the base having a thickness (d ₁₎ a thickness (d ₂₎ of the initial value and the second layer. Although the user may input each parameter, parameters of a standard material may be previously stored as a file or the like, and read out as necessary. Further, the refractive index (n ₀ ) and the extinction coefficient (k ₀ ) of the atmosphere layer are also input, if necessary.

In addition, the model conversion unit (721A) is a fitting portion to update the thickness (d ₁₎ of the first layer according to the parameter update instructions from the 722 in sequence, and the thickness of the first layer after the update (d ₁₎ Therefore, the function representing the theoretical reflectance is updated. Further, the modeling unit 721A repeatedly calculates the theoretical reflectance (spectrum) at each wavelength in accordance with the updated function. By such a procedure, the film thickness d ₁ of the first layer is determined by the fitting.

Since other configurations are described above, detailed description thereof will not be repeated.

Fig. 20 is a flowchart showing the procedure of the film thickness calculating process relating to the processing pattern 5 according to the embodiment of the present invention. The flow chart shown in Fig. 20 is different from the flowchart shown in Fig. 12 in that steps S110A, S118A and S120A are provided instead of steps S110, S118 and S120, and the other steps are denoted by the same reference numerals As such, the detailed description is not repeated. Hereinafter, a process different from that of Fig. 12 will be described.

20, in step S110A, the user selects, from the displayed input screen or the like, the refractive index (n ₁ ) and the extinction coefficient (k ₁ ) of the first layer of the measured object and the refractive index n ₂₎ and an extinction coefficient (at the same time for inputting the k _2), and inputs the value of the base of the first layer thickness (d ₁₎ a thickness (d ₂₎ of the initial value and the second layer of the.

In step S118A, the CPU 200 changes the current value of the film thickness d ₁ of the first layer. That is, in the processing pattern 5, only the film thickness d ₁ of the first layer is to be fitted.

In step S120A, and CPU (200) is not more than the calculated residual error is the predetermined threshold value is outputted as the film thickness (d ₁₎ a thickness (haeseokchi) of each layer of the current measured value of the blood in the first layer.

As in the case of the above-described process pattern 1, a refractive index and an extinction coefficient in consideration of wavelength dispersion may be used. Since the detailed functions have been described above, detailed description thereof will not be repeated.

(6) Processing pattern 6

The processing pattern 6 is a modification of the above-described processing pattern 5, which is applied when the film thickness of one layer is known and only the film thickness of the other layer is analyzed. In the following description, the film thickness of the second layer of the measured object is known, and a method of determining the film thickness of the first layer by fitting or Fourier transform is exemplified.

21 is a block diagram showing a control structure for executing the film thickness calculating process relating to the processing pattern 6 according to the embodiment of the present invention. The block diagram shown in Fig. 21 is realized by the CPU 200 reading a pre-stored program such as the hard disk unit 210 or the like in the memory unit 212 and executing it.

The control structure relating to the processing pattern 4 shown in Fig. 21 is such that, in the control structure relating to the processing pattern 4 shown in Fig. 19, the fitting portion 722A is arranged instead of the fitting portion 722, A buffer unit 732, a Fourier transform unit 733, and a peak search unit 734 are further added.

That is, in this processing pattern, the film thickness d ₁ of the first layer of the object to be measured is determined by the fitting, but when the fitting does not converge within the specified number of times, the Fourier transform is used to change the film thickness d ₁ ) is determined.

The fitting section 722A reads the measured value of the reflectance spectrum from the buffer section 71 and outputs the measured value of the reflectance spectrum to the modeling section 721A so that the residual between the theoretical values of the reflectance spectrum output from the modeling section 721A becomes a predetermined threshold value or less And a parameter update command are sequentially given. The fitting section 722A may further include a wavenumber conversion section 731 to determine the film thickness d ₁ of the first layer by using Fourier transform when the residual is not equal to or smaller than a predetermined threshold value by a predetermined number of calculations, Quot;).

Since the wave number conversion section 731, the buffer section 732, the Fourier transform section 733 and the peak search section 734 have been described in the processing pattern 2 shown in Fig. 13, detailed description thereof will not be repeated .

22 is a flowchart showing the procedure of film thickness calculation processing with respect to the processing pattern 6 according to the embodiment of the present invention. The flowchart shown in Fig. 22 adds the processing of step S117 in the flowchart shown in Fig. 20 and adds the processing of steps S134 to S140 of the flowchart shown in Fig. The other processes are the same as the steps given the same reference numerals, and the detailed description thereof will not be repeated. Hereinafter, a process different from that shown in Figs. 14 and 20 will be described.

Referring to Fig. 22, in step S117, the CPU 200 determines whether or not the fitting process has been repeated more than the prescribed number of times. If the fitting process is not repeated more than the prescribed number of times (in the case of 'No' in step S117), the process returns to step S112 after the process of step S118 is executed. On the other hand, if the fitting process is repeated more than the prescribed number of times (YES in step S117), the process proceeds to step S134.

In steps S134 to S140, the film thickness d ₁ of the first layer is determined by using Fourier transform. Since the processing of each of these steps has been described above, detailed description thereof will not be repeated.

<Measurement example>

23 shows an example of a result of measurement of a film thickness of an SOI substrate using a film thickness measuring apparatus according to an embodiment of the present invention. Fig. 23 shows a power spectrum obtained by frequency-transforming (FFT-transforming) the reflectance spectrum.

23 (a) shows the result of measurement of an SOI substrate formed with a target that the Si layer as the first layer has a thickness of 22.0 m and the SiO2 layer as the _second layer has a thickness of 3.0 m. In Fig. 23 (a), frequency conversion was performed using components of 1470 to 1600 nm in the measured reflectance spectrum. As a result, the first peak occurs at a position corresponding to 21.8613 mu m.

Fig. 23B shows the result of measurement of an SOI substrate formed with a target that the Si layer as the first layer has a thickness of 32.0 mu m and the SiO2 layer as the _second layer has a thickness of 2.0 mu m. In Fig. 23 (b), frequency conversion was performed using the components of 1500 to 1600 nm in the measured reflectance spectrum. As a result, a first peak occurs at a position corresponding to 30.6269 mu m.

FIG. 23C shows the result of measurement of the SOI substrate formed with the aim that the Si layer as the first layer has a thickness of 16.0 μm and the SiO ₂ layer as the _second layer has a thickness of 1.3 μm. In (c) of FIG. 23, frequency conversion was performed using components of 1400 to 1600 nm in the measured reflectance spectrum. As a result, a first peak occurs at a position corresponding to 15.9069 占 퐉.

It can be seen that the measurement results are substantially good.

<Intervention of shielding member>

As described above, the film thickness measuring apparatus 100 according to the present embodiment mainly measures the film thickness of the measured object OBJ based on the reflectance spectrum in the infrared band. Therefore, the measurement light source 10 1) to the object to be measured (OBJ). That is, a member such as a polymer resin does not transmit light in the visible band, but can transmit light in the infrared band.

Fig. 24 is a schematic diagram showing a configuration in the case where an object to be measured (OBJ) on which an opaque pad is arranged is measured using the film thickness measuring apparatus 100 according to the embodiment of the present invention.

24, a planar object to be measured OBJ is mounted on a stage 50 via spacers, and a planar opaque pad 52 (a light source) is provided on the upper surface of the object OBJ . This opaque pad 52 corresponds to a polishing member or the like used in the polishing process, and is mainly made of a polymer resin or the like. Such a non-transparent pad 52 transmits light in an infrared band (for example, 900 to 1600 nm) though its transmission amount is small.

25 and 26 show the results of measurement of the SOI substrate on which the opaque pad 52 is disposed using the film thickness measuring apparatus according to the embodiment of the present invention. Fig. 25 shows the results when an enlargement lens having a magnification of 10 times is used as the objective lens 40 (Figs. 1 and 24), and Fig. 26 shows the result when the objective lens 40 (Figs. 1 and 24) Of the magnification of the zoom lens of the present invention.

25 and 26, the results in a state in which the opaque pad 52 is not disposed are overlapped and displayed for comparison. It should also be noted that the ranges (absolute values) of the respective reflectance spectra are different.

Fig. 27 shows the power spectrum obtained from the reflectance spectrum in a state in which the Pad 52 shown in Fig. 25 and Fig. 26 is not disposed, Fig. 28 shows the Pad 52 shown in Fig. 25 and Fig. 26 Shows a power spectrum obtained from the reflectance spectrum in a state where there is a state in which the light is reflected.

25, when a magnifying lens having a magnification of 10 times is used as the objective lens 40, the result when the opaque Pad 52 is present is the result when the opaque Pad 52 is not present The noise component is increased.

26, when a magnifying lens having a magnification of 2.83 is used as the objective lens 40, the result when the opaque pad 52 is present is the result when the opaque pad 52 is not present Almost the same as the result, the periodicity is sufficiently measured.

As shown in Figs. 27 and 28, it can be seen that almost the same power spectrum can be obtained irrespective of the presence or absence of opaque pads when an enlargement lens having a magnification of 2.83 times is used as the objective lens 40 .

On the other hand, it can be seen that when a magnifying lens having a magnification of 10 is used as the objective lens 40, a sufficient power spectrum can not be obtained. This is because the numerical aperture changes with the change of the magnification of the objective lens 40, and as a result, when a lens having a magnification of 10 times is used, it is considered that the diffused light increases and the noise component increases.

As described above, it was confirmed that it is possible to measure the film thickness of the measured object OBJ on which the opaque pad 52 is arranged by using the film thickness measuring apparatus 100 according to the present embodiment. However, it may be said that it is necessary to design the optical system for irradiating measurement light and the optical system for receiving reflected light so as to exclude the influence of diffused light.

[Modifications]

A Y-type fiber may be used as an optical system for irradiating the object to be measured (OBJ) with measurement light and receiving reflected light.

29 is a schematic diagram showing a structure of an optical system of a film thickness measuring apparatus 100 # according to a modification of the embodiment of the present invention.

29, the film thickness measuring device 100 # is a film thickness measuring device that guides measurement light from the measurement light source 10 (Fig. 1) to the object OBJ and also outputs reflected light from the object OBJ And a light projection and reception fiber 56 as an optical system for guiding the light to the detection unit 64 (FIG. 1).

The water-permeable optical fiber 56 is a Y-type fiber capable of coupling two light beams to one light beam and separating one light beam into two light beams. As a more specific example, the permeable optical fiber 56 is made of Ge-doped single-wire Y-type fiber.

The measurement light generated from the measurement light source 10 (FIG. 1) is incident on the measured object OBJ via the first branch fiber 56a and the reflected light generated by the reflected light from the measured object OBJ passes through the second branch fiber (56b).

Further, a pinhole optical system 54 functioning as a &quot; diaphragm &quot; is disposed between the water-permeable optical fiber 56 and the object OBJ.

By using the film thickness measuring apparatus 100 # shown in FIG. 29, even when the measured object OBJ is arranged in a solution such as a polishing liquid, the film thickness can be measured.

30 is a schematic diagram showing a mode for measuring a film thickness of a measured object OBJ in a solution by using a film thickness measuring apparatus 100 # according to a modification of the embodiment of the present invention.

Referring to Fig. 30, the object to be measured OBJ is arranged on a table 57 disposed in a container through a spacer, and the inside of the container is filled with a solution 58 such as an abrasive liquid. Then, a part of the water-permeable optical fiber 56 side of the water-permeable optical fiber 56 is immersed in the solution 58. With this configuration, the film thickness of the object to be measured OBJ in the solution can be measured.

In the case of using the solution 58 containing water as a solvent, it is preferable to use the above-mentioned infrared band (900 to 1600 nm) for measuring the film thickness except for the absorption wavelength of water. Specifically, since water absorbs in a wavelength band of about 1320 nm or more, it is preferable to use a reflected light spectrum in the range of 900 to 1320 nm for measuring the film thickness of the object to be measured (OBJ).

[Other Embodiments]

The program according to the present invention may be executed by calling necessary modules from a program module provided as a part of an operating system (OS) of a computer in a predetermined arrangement at a predetermined timing. In this case, the program itself does not include the module but is executed in cooperation with the OS. A program not including such a module may also be included in the program according to the present invention.

The program according to the present invention may be provided in a part of another program. In this case, the program itself does not include a module included in the other program, but executes processing in cooperation with another program. Such a program assembled into another program may also be included in the program according to the present invention.

The provided program product is installed and executed in a program storage unit such as a hard disk. The program product also includes a program itself and a storage medium in which the program is stored.

Furthermore, some or all of the functions realized by the program according to the present invention may be configured by dedicated hardware.

According to the embodiment of the present invention, when the film thicknesses of the respective layers constituting the measured object are independently calculated based on the reflectance spectrum (or the transmittance spectrum) obtained by irradiating the measurement object with the measurement light, 1) a method of determining a film thickness by calculating a main wavenumber component using a discrete Fourier transform such as FFT or an optimization method such as MEM, and (2) a method of determining a film thickness using a fitting using a model equation And can be selectively executed. This makes it possible to measure the film thickness of each layer more accurately, even when there are many layers constituting the measured object, or when there is a large difference in the film thickness of each layer.

Further, according to the embodiment of the present invention, the wavelength range (or the wavelength detection range) of the measurement light and the wavelength resolution of the detection unit can be appropriately set in accordance with the film thickness of each layer constituting the measurement target object Therefore, the film thickness of each layer can be measured more accurately.

While the invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, and the scope of the invention is to be construed according to the appended claims.

1 is a schematic structural view of a film thickness measuring apparatus according to an embodiment of the present invention;

2 is a view showing an example of a cross-sectional schematic diagram of a measured object to be measured by a film thickness measuring apparatus according to an embodiment of the present invention.

3 is a view showing a measurement result when an SOI substrate is measured by using the film thickness measuring apparatus according to the present embodiment.

4 is a view showing another measurement result in which an SOI substrate is measured using the film thickness measuring apparatus according to the present embodiment.

5 is a view showing another measurement result of the SOI substrate measured using the film thickness measuring apparatus according to the present embodiment.

6 is a diagram for explaining a relationship between a film thickness measuring range according to an embodiment of the present invention, a detection wavelength range of the detecting section, and the number of detection points.

7 is a view showing a result of a simulation performed using measurement results obtained by using a film thickness measuring apparatus having a wavelength resolution close to a theoretical value;

FIG. 8 is a view showing a result of simulation using measurement results obtained by using a film thickness measuring apparatus having a wavelength resolution with doubling of precision with respect to a theoretical value. FIG.

9 is a view showing a measurement result of a reflectance spectrum for an SOI substrate;

10 is a schematic diagram showing a schematic hardware configuration of a data processing unit according to an embodiment of the present invention;

11 is a block diagram showing a control structure for executing film thickness calculation processing relating to the processing pattern 1 according to the embodiment of the present invention.

12 is a flowchart showing the procedure of the film thickness calculating process relating to the processing pattern 1 according to the embodiment of the present invention.

13 is a block diagram showing a control structure for executing film thickness calculation processing relating to the processing pattern 2 according to the embodiment of the present invention.

14 is a flowchart showing the procedure of the film thickness calculating process relating to the processing pattern 2 according to the embodiment of the present invention.

15 is a block diagram showing a control structure for executing the film thickness calculating process relating to the processing pattern 3 according to the embodiment of the present invention.

16 is a flowchart showing the procedure of the film thickness calculating process according to the processing pattern 3 according to the embodiment of the present invention.

17 is a block diagram showing a control structure for executing the film thickness calculating process relating to the processing pattern 4 according to the embodiment of the present invention.

18 is a flowchart showing the procedure of the film thickness calculating process relating to the processing pattern 4 according to the embodiment of the present invention.

Fig. 19 is a block diagram showing a control structure for executing the film thickness calculating process relating to the processing pattern 5 according to the embodiment of the present invention. Fig.

20 is a flowchart showing the procedure of the film thickness calculating process relating to the processing pattern 5 according to the embodiment of the present invention.

21 is a block diagram showing a control structure for executing the film thickness calculating process relating to the processing pattern 6 according to the embodiment of the present invention.

22 is a flowchart showing the procedure of the film thickness calculating process relating to the processing pattern 6 according to the embodiment of the present invention.

23 is a view showing an example of a result of measuring a film thickness of an SOI substrate using a film thickness measuring apparatus according to an embodiment of the present invention.

24 is a schematic diagram showing a configuration in the case of measuring a surface of a measurement object on which an opaque pad is disposed using a film thickness measuring device according to an embodiment of the present invention.

25 is a view showing a result of measurement of an SOI substrate on which opaque pads are arranged using a film thickness measuring apparatus according to an embodiment of the present invention.

26 is a view showing another result of measuring an SOI substrate on which opaque pads are arranged using a film thickness measuring apparatus according to an embodiment of the present invention;

Fig. 27 is a diagram showing a power spectrum obtained from a reflectance spectrum in a state in which the opaque pad shown in Fig. 25 and Fig. 26 is not disposed; Fig.

28 is a diagram showing a power spectrum obtained from a reflectance spectrum in a state where the opaque pads shown in Figs. 25 and 26 are arranged; Fig.

29 is a schematic diagram showing a structure of an optical system of a film thickness measuring apparatus according to a modification of the embodiment of the present invention.

30 is a schematic diagram showing a mode of measuring a film thickness of a measurement object in a solution by using a film thickness measurement apparatus according to a modification of the embodiment of the present invention.

[Description of Symbols]

10: Light source for measurement

12: Collimate lens

14: Cut filter

16, 36: image forming lens

18:

20, 30: Beam splitter

22: Observation light source

24: Optical fiber

26:

26a:

32: Pin hole mirror

32a: pin hole

34: Axis conversion mirror

38: Observation camera

39:

40: Objective lens

50: stage

51:

52: Opaque Pad

54: Pinhole optical system

56: Perforated optical fiber

56a, 56b: branch fibers

57: Table

58: solution

60: Spectroscopic measuring unit

62: diffraction grating

64:

66: Cut filter

68: Shutter

70:

71, 732:

100, 100 #: Film thickness measuring device

200: CPU

202: bus

204:

208:

210: Hard disk unit (HDD)

212:

214: CD-ROM drive

214a: CD-ROM

216: Flexible disk drive (FDD)

216a: flexible disk

721, 721A, 735, 742:

722, 722A, 736, 743:

731: wave number conversion section

733: Fourier transform unit

734: Peak search section

741, 751:

OBJ: Measured object

Claims (8)

A film thickness measuring apparatus comprising: And a light source for irradiating a measurement object having a plurality of layers on the substrate with measurement light having a predetermined wavelength range, wherein the object to be measured includes a first layer closest to the light source and a second layer closest to the first layer The second layer comprising a first layer, A spectroscopic measurement unit for acquiring a wavelength distribution characteristic of reflectance or transmittance based on light reflected from the object to be measured or light transmitted through the object to be measured; A first determination for determining the film thicknesses of the first layer and the second layer, respectively, by fitting the wavelength distribution characteristic using a model equation including a film thickness of each layer included in the measured object, Sudan, By converting the correspondence between the respective wavelengths in the wavelength distribution characteristics and the reflectance or transmittance values at the wavelengths into the correspondence relationship between the wave number for each wavelength and the conversion value calculated in accordance with a predetermined relational expression, Conversion means for generating, An analyzing means for obtaining an amplitude value of each wave number component included in the wave number distribution characteristic, And a second determining means for determining at least a film thickness of the first layer based on a wavenumber component having a larger amplitude value included in the wave number distribution characteristic, Is not converged within the prescribed number of times, it is selectively validated, After setting a value of the film thickness of the first layer determined by the second determination means in a model expression including a film thickness of each layer included in the measured object, fitting is performed on the wavelength distribution characteristic And a third determination means for determining a film thickness of the second layer. 2. The wavelength conversion device according to claim 1, wherein the conversion means converts the respective wavelengths in the wavelength distribution characteristics and the reflectance or transmittance values at the wavelengths into the wave number for each wavelength and the wave number conversion reflectance To the corresponding relationship of the wave number for each wavelength and the wave number converted transmittance which is the reciprocal of the transmittance. 3. The film thickness measuring device according to claim 1 or 2, wherein the model equation includes a function for a wavelength representing a refractive index. The film thickness measurement device according to any one of claims 1 to 5, wherein the predetermined wavelength range includes a wavelength of an infrared band. 3. The film thickness measuring device according to claim 1 or 2, wherein the analyzing means includes means for discrete Fourier transforming the wave number distribution characteristic. 3. The film thickness measuring device according to claim 1 or 2, wherein the analyzing means acquires the amplitude value of each wave number component included in the wave number distribution characteristic by using the optimization method. A film thickness measuring method comprising: And a step of irradiating measurement light having a predetermined wavelength range to a measured object on which a plurality of layers are formed on a substrate, wherein the measured object includes a first layer in which the measurement light is initially incident, And a second layer adjacent to the layer, Acquiring a wavelength distribution characteristic of reflectance or transmittance based on light reflected from the measured object or light transmitted through the measured object; Wherein the first layer and the second layer are formed by fitting to the wavelength distribution characteristic using a model equation including a film thickness of each layer included in the measured object, A determination step, By converting the correspondence between the respective wavelengths in the wavelength distribution characteristics and the reflectance or transmittance values at the wavelengths into the correspondence relationship between the wave number for each wavelength and the conversion value calculated in accordance with a predetermined relational expression, A step of generating, Acquiring an amplitude value of each wave number component included in the wave number distribution characteristic; And a second determination step of determining at least a film thickness of the first layer based on a wave number component having a larger amplitude value included in the wave number distribution characteristic, If the fitting does not converge within the specified number of times, it is selectively validated, A value of a film thickness of the first layer determined in the second determination step is set to a model expression including a film thickness of each layer included in the measured object and then fitting is performed on the wavelength distribution characteristic And a third determination step of determining a film thickness of the second layer. delete

Images