KR20090132537A - Apparatus and method for measuring thickness of film - Google Patents

Abstract

PURPOSE: A device and a method for measuring film thickness are provided to continuously measure the film thickness in a non-destructive mode by forming no penetration part in a measured sample. CONSTITUTION: A measurement light source(10) obtains a reflectance spectrum of a measured object. A collimate lens(12) inputs measurement light received from the measurement light source. A cut filter(14) blocks an unnecessary wavelength component included in the measurement light. The measurement light output from the measurement light source is optically adjusted. Imaging lenses(16,36) adjust a beam diameter of the measurement light. An iris part(18) adjusts and irradiates the quantity of light of the measurement light to a beam splitter(30). The collimate lens, the cut filter, the imaging lenses, and iris part are arranged on an optical axis connecting the measurement light source and the beam splitter.

Description

Film thickness measuring device and film thickness measuring method {APPARATUS AND METHOD FOR MEASURING THICKNESS OF FILM}

TECHNICAL FIELD The present invention relates to a film thickness measuring apparatus and a film thickness measuring method, and more particularly, to a structure and a method for measuring the film thickness of an object under test in which a plurality of layers are formed on a substrate.

In recent years, a substrate structure called a silicon on insulator (SOI) has been attracting attention for low power consumption and high speed of a complementary metal oxide semiconductor (CMOS) circuit. In this SOI substrate, an insulating layer (BOX layer) such as SiO ₂ is disposed between two Si (silicon) substrates, and is formed between a PN junction formed in one Si layer and the other Si layer (substrate). Parasitic diodes, stray capacitances, etc. can be reduced.

In such a method of manufacturing an SOI substrate, after forming an oxide film on the surface of a silicon wafer, other silicon wafers are faced to sandwich the oxide film, and the silicon wafer on the side where the circuit element is formed is polished to have a predetermined thickness. Known methods are known.

As described above, in order to control the thickness of the silicon wafer by the polishing step, it is necessary to continuously monitor the film thickness. As a measuring method of the film thickness in such a grinding | polishing process, Unexamined-Japanese-Patent No. 05-306910 and Unexamined-Japanese-Patent No. 05-308096 disclose the method using a Fourier transform infrared spectrophotometer (FTIR). It is. In addition, Japanese Patent Application Laid-Open No. 2005-19920 discloses a method of using a reflection spectrum measured by a distributed multi-channel spectrometer.

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

In addition, Japanese Patent Application Laid-Open No. 2002-228420 discloses an infrared ray having a wavelength of 0.9 µm or more toward the surface of a silicon thin film, and reflects the result of interference between reflected light by the surface of the silicon thin film and reflected light by the back surface of the silicon thin film. On the basis of this, a method of measuring the film thickness of a silicon thin film is disclosed.

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

However, in the measurement methods disclosed in Japanese Patent Application Laid-Open No. 05-306910 and Japanese Patent Application Laid-Open No. 05-308096, only the relative value of the film thickness with respect to the reference sample can be measured. The absolute value of the thickness cannot be measured.

In addition, in the measurement method disclosed in Japanese Patent Application Laid-Open No. 2005-19920, for example, assuming that the refractive index is a fixed value that does not depend on the wavelength, period estimation is performed by a self-regression model. It has wavelength dependency and cannot exclude the error resulting from such wavelength dependency. Moreover, the same problem is included also in the measuring method disclosed in Unexamined-Japanese-Patent No. 2003-114107.

In addition, in the measuring method disclosed in Japanese Patent Application Laid-Open No. 2002-228420, it is necessary to form a penetrating portion in the sample to be measured, and the film thickness cannot be continuously measured nondestructively.

This invention is made | formed in order to solve such a problem, The objective is to provide the film thickness measuring apparatus and film thickness measuring method which can measure a film with higher precision.

The film thickness measuring apparatus which concerns on one aspect of this invention contains a light source, a spectroscopic measuring part, a 1st determination means, a conversion means, an analysis means, and a 2nd determination means. The light source irradiates the measurement light having a predetermined wavelength range to the object to be measured in 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 measuring unit acquires the wavelength distribution characteristic 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 at least the film thickness of the first layer by fitting to the wavelength distribution characteristics by using a model formula including the film thickness of each layer included in the measurement object. The conversion means converts the correspondence between each wavelength in the wavelength distribution characteristic and the value of the reflectance or transmittance at the wavelength into a correspondence relationship between the wave number for each wavelength and the conversion value calculated according to the predetermined relational expression. Create a characteristic. The analyzing means acquires the amplitude value of each wave component included in the wave number distribution characteristic. The second determining means determines at least the film thickness of the first layer based on the wave component having a large amplitude value included in the wave number distribution characteristic. Then, the first determining means and the second determining means are selectively validated.

Preferably, after setting the value of the film thickness of the first layer determined by the second determining means in the model formula including the film thickness of each layer included in the measurement object, fitting is performed on the wavelength distribution characteristic. This further includes third determining means for 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 formula includes a function of the wavelength representing the refractive index.

Preferably, the predetermined wavelength range includes wavelengths in the infrared band.

Preferably, the analyzing means comprises means for discretely Fourier transforming the wavenumber distribution characteristic.

Preferably, the analyzing means obtains an amplitude value of each wave component included in the wave number distribution characteristic by using an optimization method.

A film thickness measuring method according to another aspect of the present invention includes a step of irradiating a measurement light having a predetermined wavelength range to an object to be measured in which a plurality of layers are formed on a substrate. The object to be measured includes a first layer in which measurement light is first incident and a second layer adjacent to the first layer. The film thickness measuring method further includes obtaining a wavelength distribution characteristic of reflectance or transmittance based on the light reflected from the measured object or the light transmitted through the measured object, and the film thickness of each layer included in the measured object. By fitting to the wavelength distribution characteristic using a model formula including the first determination step of determining the film thickness of at least the first layer, each wavelength in the wavelength distribution characteristic and the reflectance at the wavelength Alternatively, by converting the correspondence of the values of the transmittance into the correspondence between the wave number for each wavelength and the conversion value calculated according to the predetermined relational expression, the step of generating a wave distribution characteristic and the wave component of each wave component included in the wave distribution characteristic. A step for obtaining an amplitude value, a second determination step for determining at least a film thickness of the first layer based on a wave component having a large amplitude value included in the wave number distribution characteristic, and a first crystal 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 apparent from the following detailed description of the invention which is understood in connection 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 the film thickness with higher accuracy.

EMBODIMENT OF THE INVENTION Embodiment of this invention is described in detail, referring drawings.

In addition, about the same or equivalent part in drawing, the same code | symbol is attached | subjected and the description is not repeated.

<Device configuration>

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

The film thickness measuring apparatus 100 which concerns on this embodiment can measure the film thickness of each layer in the to-be-measured object of a single layer or laminated structure typically. In particular, the film thickness measuring apparatus 100 according to the present embodiment is suitable for measuring the film thickness of a measurement target including a relatively large layer (typically from 2 μm to 1000 μm).

Specifically, the film thickness measuring apparatus 100 is a microscopic spectroscopic measuring apparatus, and irradiates light onto a measurement target and is based on wavelength distribution characteristics (hereinafter referred to as "spectrum") of the reflected light reflected from the measurement target. Thus, the film thickness of each layer constituting the object to be measured can be measured. In addition, not only the measurement of the film thickness but also the measurement of the reflectance (absolute and relative) in each layer and the analysis of the layer structure are possible. In addition, you may use the spectrum (the spectrum of transmitted light) of the light which permeate | transmitted the to-be-measured object instead of the spectrum of reflected light.

In this specification, a case where the object to be measured is one in which one or more layers are formed on a substrate or a substrate is exemplified. As a specific example of a to-be-measured object, the board | substrate of comparatively thick bodies, such as a Si substrate, a glass substrate, and a sapphire substrate, a board | substrate of a laminated structure like a silicon on insulator (SOI) substrate, etc. are mentioned. In particular, the film thickness measuring apparatus 100 according to the present embodiment is characterized in that the film thickness of the Si substrate after cutting and polishing, the film thickness of the Si layer (active layer) of the SOI substrate, and the chemical mechanical polishing (CMP) process are used. It is suitable for the measurement of the film thickness of a Si substrate.

Referring to FIG. 1, the film thickness measuring apparatus 100 includes a light source 10 for measurement, a collimated lens 12, a cut filter 14, an imaging lens 16 and 36, and an aperture 18. ), Beam splitters 20, 30, observation light source 22, optical fiber 24, output unit 26, pinhole mirror 32, axis conversion mirror 34, , The observation camera 38, the display unit 39, the objective lens 40, the stage 50, the movable mechanism 51, the spectroscopic measuring unit 60, and the data processing unit 70. do.

The measurement light source 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, and particularly a wavelength component (for example, 900 nm to 1600 nm or 1470 nm in the infrared band). To 1600 nm) is used. As the light source 10 for a measurement, a halogen lamp is used typically.

The collimated lens 12, the cut filter 14, the imaging lens 16, and the aperture 18 are disposed on an optical axis AX2 connecting the light source 10 for measurement and the beam splitter 30. Then, the measurement light emitted from the measurement light source 10 is optically adjusted.

Specifically, the collimated lens 12 is an optical component to which the measurement light from the measurement light source 10 first enters, and refracts the measurement light propagated as diffuse light and converts it into parallel light. The measurement light passing through the collimated 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 the parallel light beam to the convergent light beam in order to adjust the beam diameter of the measurement light beam. The measurement light passing through the imaging lens 16 is incident on the aperture 18. The aperture unit 18 emits the light to the beam splitter 30 after adjusting the light amount of the measurement light to a predetermined amount. Preferably, the diaphragm 18 is disposed at an imaging position of the measurement light converted by the imaging lens 16. In addition, the adjustment amount of the diaphragm 18 is appropriately set according to the depth of field, required light intensity, and the like of the measurement light incident on the object under test.

On the other hand, the observation light source 22 is a light source for generating observation light used for focusing on the object under test or confirming the measurement position. And the observation light which the observation light source 22 generate | occur | produces is selected so that it may include the wavelength which can be reflected in a to-be-measured object. The observation light source 22 is connected to the output unit 26 through the optical fiber 24, and the observation light generated by the observation light source 22 propagates the optical fiber 24, which is an optical waveguide, and then exits the output unit 26. Is emitted toward the beam splitter 20.

The emission section 26 includes a mask section 26a that masks a part of the observation light generated by the observation light source 22 so that a predetermined observation reference image is projected onto the object to be measured. This observation criterion is for facilitating focusing even on a measurement object (typically, a transparent glass substrate or the like) in which no shape (pattern) is formed on the surface thereof. In addition, although the shape of a reticle form may be sufficient, as an example, a concentric pattern, a cross-shaped pattern, etc. can be used.

That is, although the light intensity (light quantity) in the beam cross section of the observation light immediately after being generated by the observation light source 22 is substantially uniform, the mask part 26a masks (shields) a part of this observation light, and the observation light becomes In the beam cross section, an area (shadow area) having a light intensity of approximately zero is formed. This shadow area is projected onto the measurement object as an observation standard.

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

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

The beam splitter 30 reflects the measurement light generated by the light source 10 for measurement, thereby converting its propagation direction downward on the paper plane of the optical axis AX1. In addition, the beam splitter 30 transmits the reflected light from the object under test that propagates the optical axis AX1 upward on the paper plane.

On the other hand, the beam splitter 20 reflects the observation light generated by the observation light source 22, thereby converting its propagation direction to the paper plane right side of the optical axis AX2. That is, the beam splitter 20 functions as a light injection unit for injecting observation light at a predetermined position on the optical path from the measurement light source 10 to the objective lens 40 which is 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, both the beam splitters 20 and 30 have their transmission / reflection characteristics at a desired value from the visible band to the infrared band. What can be maintained is adopted.

The objective lens 40 is a condensing optical system for condensing measurement light and observation light which propagate the optical axis AX1 downward on the paper plane. 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 in the vicinity thereof. The objective lens 40 is an enlarged lens having a predetermined magnification (for example, 10 times, 20 times, 30 times, 40 times, etc.). By using such an enlarged lens, the area where the optical characteristics of the object to be measured is measured can be made smaller compared to the beam cross section of the light incident on the objective lens 40.

In addition, the measurement light and the observation light incident on the object under test through the objective lens 40 are reflected by the object under test, and propagate the optical axis AX1 on the paper surface upward. The reflected light passes through the objective lens 40 and then passes through the beam splitter 30 to reach the pinhole mirror 32.

The pinhole mirror 32 functions as a light separation unit that separates the measured reflected light and the observed reflected light among the reflected light generated in the object to be measured. Specifically, the pinhole mirror 32 includes a reflecting surface that reflects the reflected light from the object under test, which propagates the optical axis AX1 upward on the paper plane, and focuses on the intersection of the reflecting surface and the optical axis AX1. The hole part (pin hole) 32a to be formed is formed. The size of this pinhole 32a is small compared with the beam diameter in the position of the pinhole mirror 32 of the measurement reflection light which the measurement light from the measurement light source 10 reflects in the to-be-measured object. It is formed to lose. In addition, the pinhole 32a is disposed so as to coincide with the imaging positions of the measured reflected light and the observed reflected light generated by the measurement light and the observation light reflected from the object under test. With such a configuration, the reflected light generated in the measurement object passes through the pinhole 32a and enters the spectroscopic measuring unit 60. On the other hand, the remaining portion of the reflected light is converted into the propagation direction and enters the axis conversion mirror 34.

The spectroscopic measuring unit 60 measures the reflectance spectrum from the measured reflected light passing through the pinhole mirror 32, and outputs the measurement result to the data processing unit 70. More specifically, the spectrometer 60 includes a diffraction grating (grating) 62, a detector 64, a cut filter 66, and a shutter 68.

The cut filter 66, the shutter 68, and the diffraction grating 62 are disposed on the optical axis AX1. The cut filter 66 is an optical filter for limiting wavelength components outside the measurement range, which is included in the measured reflected light passing through the pinhole 32a and incident on the spectroscopic measuring unit 60, and particularly blocks the wavelength components outside the measurement range. do. The shutter 68 is used to block light incident on the detector 64 when the detector 64 is reset. The shutter 68 is typically made of a mechanical shutter driven by electromagnetic force.

The diffraction grating 62 speculates the incident reflected reflected light, and then guides each spectral wave to the detector 64. Specifically, the diffraction grating 62 is a reflective diffraction grating, and is configured such that diffraction waves at predetermined wavelength intervals are reflected in corresponding directions. When the measured reflected wave enters the diffraction grating 62 having such a configuration, each wavelength component included is reflected in the corresponding direction and enters a predetermined detection area of the detection unit 64. This wavelength interval corresponds to the wavelength resolution in the spectroscopic measuring unit 60. The diffraction grating 62 typically consists of a flat focus spherical grating.

The detector 64 outputs an electrical signal corresponding to the light intensity of each wavelength component included in the measured reflected light spectroscopically measured by the diffraction grating 62 to measure the reflectance spectrum of the object to be measured. The detection unit 64 is formed of an InGaAs array or the like having sensitivity in the infrared band.

The data processing part 70 measures the film thickness of each layer which comprises a to-be-measured object by performing the characteristic process which concerns on this invention with respect to the reflectance spectrum acquired by the detection part 64. FIG. The data processing unit 70 can also analyze the reflectance and the layer structure of each layer of the object to be measured. In addition, the detail of such a process is mentioned later. And the data processing part 70 outputs optical characteristics including the film thickness of the measured object.

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

The observation camera 38 is an imaging unit which acquires a reflection image obtained by observation reflected light, and is typically made of a Charged Coupled Device (CCD), a Complementary Metal Oxide Semiconductor (CMOS) sensor, or the like. In addition, the observation camera 38 typically has sensitivity in the visible band and often has different sensitivity characteristics from the detection unit 64 having sensitivity in a predetermined measurement range. And the observation camera 38 outputs the video signal according to the reflection image obtained by observation reflection light to the display part 39. FIG. The display unit 39 displays the reflection image on the screen based on the video signal from the observation camera 38. The user visually sees the reflection image displayed on the display unit 39 and performs focusing on the object under test, confirmation of the measurement position, or the like. The display unit 39 typically consists of a liquid crystal display (LCD) or the like. In addition, instead of the observation camera 38 and the display part 39, you may provide the finder in which a user can directly see a reflection image.

<Analytical Review of Reflective Light>

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

2: is an example of the cross-sectional schematic diagram of the to-be-measured object OBJ which the film thickness measuring apparatus 100 which concerns on embodiment of this invention makes a measurement object.

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 an SiO ₂ layer 2 (BOX layer) is disposed between the Si layer 1 and the base Si layer 3 (substrate layer). The irradiation light from the film thickness measuring apparatus 100 is incident on the measurement object OBJ from above the paper surface. In other words, the measurement light first enters the Si layer 1.

For easy understanding, the reflected light generated by the measurement light incident on the object OBJ is reflected at the interface between the Si layer 1 and the SiO ₂ layer 2. In the following description, the subscript i is used to represent each layer. That is, subscript "0" is used for the atmosphere layer such as air or vacuum, the subscript "1" for the Si layer 1 of the object (OBJ), and the subscript "2" for the SiO ₂ layer 2 are used. In addition, the refractive index in each layer represents the refractive index n _i using the subscript i.

Since reflection of light occurs at the interface of the layers having different refractive indices n _i , the amplitude reflectances (Fresnel coefficients) of the P polarization component and the S polarization component at each interface between the i layer and the i + 1 layer having different refractive indices r ^{(P _{) i, i + 1, r}} (S) i, i + 1 can be expressed as:

Wherein, ø _i is the incident angle of the i-layer. This incidence angle ø _i can be calculated from the incidence angle in the atmosphere layer (O layer) of the uppermost layer by Snell's law as follows.

In a layer having a film thickness where light can interfere, light reflected at a reflectance expressed by the above formula reciprocates several times in the layer. Therefore, since the optical path lengths differ between the light directly reflected at the interface with the adjacent layer and the light after multiple reflection in the layer, the phases are different from each other, and the interference of light on the surface of the Si layer 1 is caused. This happens. In order to show such an interference effect of light in each layer, when the phase angle (beta) _i of light in the layer of i layer is introduce | transduced, it can show as follows.

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

If in order to simplify, that the light irradiated vertically to the object to be measured (OBJ), that is, if the incidence angle ø _i = 0, the amplitude reflectance of the P polarization and the distinction is the interface disappears, each of layers of the S-polarized light and The phase angle β ₁ of the thin film is as follows.

In addition, the reflectance R in the to-be-measured object OBJ of the three-layer system shown in FIG. 2 becomes as follows.

In the above equation, the phase Given the frequency transformation (Fourier transform) for each (β _1), the phase factor cos2β ₁ (Phase Factor) is a non-linear to the reflectivity (R). Therefore, the phase factor cos2β ₁ is converted into a function having linearity. As an example, this reflectance R is converted as in the following formula to define the &quot; wavelength converted reflectance &quot; (R ') which is an original variable.

This wavenumber conversion reflectance R 'becomes a linear equation with respect to the phase factor cos2β ₁ and has linearity. Here, "a fragment of the, R _b is a frequency converting reflectivity (R _a R wave number is converted reflectance (R)" in the formula is the slope of the). In other words, the wavenumber conversion reflectance R 'is a function for linearizing the value of the reflectivity R at each wavelength with respect to the phase factor cos2β ₁ related to the frequency conversion. In addition, you may use the function of 1 / (1-R) as a function for linearizing about such a phase factor.

Therefore, the wave number K _{1 in the} target Si layer 1 can be defined as follows.

Here, when the optical speed of the wavelength λ in the Si layer 1 is s and the optical speed of the wavelength λ in vacuum is c, the refractive index n ₁ = c / s is expressed. In addition, the electromagnetic waves E (x, t) generated by light propagating in the Si layer 1 in the x direction use the wave number K ₁ , the respective frequencies ω, and the phase δ. E (x, t) = E ₀ exp [j (ωt-K ₁ x + δ)]. That is, the propagation characteristics of the electromagnetic waves in the Si layer 1 depend on the wave number K ₁ . From these relations, it is understood that the light having the wavelength? In the vacuum has a low light speed in the layer, so that the wavelength also extends from? To? / N ₁ . In consideration of such wavelength dispersion phenomenon, the wavenumber conversion reflectance R 'is defined as follows.

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

That is, the correspondence relationship between the reflectance spectrum measured from the measurement target object OBJ and the reflectance at each wavelength is the correspondence relationship between the wave number calculated from each wavelength and the wavenumber conversion reflectance R 'calculated according to the above-described relational expression. (Wavelength distribution characteristic), the frequency-converted reflectance R 'including the wave number K is frequency-converted with respect to the wave number K, and the measurement is performed based on the peaks 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 wave component included in the wave number distribution characteristic is obtained, and the film thickness of the Si layer 1 is calculated based on the wave component of which the amplitude value is large. In addition, as will be described later, as a method of analyzing a wave component having a large amplitude value from the wave number distribution characteristic, a method using discrete Fourier transform such as FFT (Fast Fourier Transform) and a maximum entropy method (Maximum Entropy) Method (hereinafter, also referred to as "MEM") may be adopted by any method using an optimization method such as "MEM".

In the definition of the wave-conversion reflectance (R '), R _a and R _b are values independent of interference phenomena in the layer, but at the interface between each layer including the refractive index n ₁ of the Si layer 1. Depends on the amplitude reflectance. Therefore, when the refractive index n ₁ has wavelength dispersion, the value becomes a function value depending on the wavelength (that is, the wave number K) and does not become a constant value with respect to the wave number K. Therefore, when the Fourier transform is represented by, and the power spectrum after the Fourier transform of R ', R _a , R _b , and cos2K ₁ d ₁ with the wave number (K) is P, P _a , P _b , and F, respectively, The following formula holds.

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 thus does not affect the power spectrum (F).

On the other hand, P _b in the formula is convolved with the power spectrum F so that the film thickness component in P _b modulates the film thickness component of the power spectrum F. However, since P _b is irrelevant to the interference phenomenon in the layer and only depends on the wavelength dependence of the refractive index in two adjacent layers, the film thickness component of P _b with respect to the wave number K is the film thickness of F. Small enough to be negligible compared to the ingredients. For example, if R _b is a periodic function of the film thickness q and P _b after the Fourier transform modulates the film thickness component d of the power spectrum F by convolution, it appears as a spectrum. The peak becomes "d-q" or "d + q", but since the value of q is very small, the influence on the peak position d is small.

Further, when performing Fourier transform, in consideration of the maximum film thickness of the layer to be measured as described below, the sample interval appropriate for the wavenumber conversion reflectance R 'according to the sampling theorem of the Nyquist and Sampling is performed with the number of samples. With respect to the film thickness resolution r of the power spectrum calculated based on the sampled wavenumber conversion reflectance R 'thus sampled, the film thickness component q of P _b is likely to be smaller (q <r). It can be said that it hardly affects the measurement result of the thickness d.

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

In the above description, the case where the reflectance spectrum is used is illustrated, but the transmittance spectrum may be used. In this case, when the measured transmittance is T and the "wavelength conversion transmittance" is T ', it is represented by the following relationship.

Even when using the transmittance spectrum, the transmittance T becomes nonlinear with respect to the phase factor cos2β ₁ . Therefore, for the same reason as described above, the wavenumber conversion transmittance T 'having linearity with respect to the phase factor cos2β ₁ is adopted. According to the above formula, the wavenumber conversion transmittance T 'becomes a first-order formula for the phase factor cos2β ₁ , and according to the same procedure as described above, the film thickness of the thin film can be accurately calculated. That is, the wavenumber conversion transmittance T 'is a function for linearizing the value of the transmittance T at each wavelength with respect to the phase factor cos2β ₁ related to the frequency conversion.

Again, with reference to FIG, think about the reflected light generated is reflected by the interface between the SiO ₂ layer 2 and the Si base layer (3). When the refractive index of the Si layer 1 is n ₁ , the film thickness is d ₁ , and the refractive index of the SiO ₂ layer 2 is n ₂ , and the film thickness is d ₂ , the wavenumber conversion reflectance R ′ is as follows. do.

Here, the respective converted to the case of calculation by removing the membrane thickness (d ₂₎ of the thickness (d ₁₎ and a SiO ₂ layer (2) of the Si layer (1), wave number (K _1, K ₂₎ frequency conversion Reflectances [R ₁ '(K ₁ ), R ₂ ' (K ₂ )] are used. Specifically, it shows as follows.

In these equations, d ₁ ′ and d ₂ ′ are not exact film thicknesses, but the original film thickness d ₁ from the peak in the power spectrum corresponding to claim 2 of the wavenumber conversion reflectance [R ₁ ′ (K 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 wavenumber conversion reflectance [R ₂ '(K ₂ )].

Also, in practice, it is Si, and layer (1) and SiO _{2 (2)} is approximated that the refractive index, the reflectance at the interface of both in many cases be small relatively, compared to the reflectivity of the other surface. As a result, the value of R _c becomes smaller compared to R _b or R _d included in the function of the wave-conversion reflectivity, which corresponds to the third term of the wave-conversion reflectance [R ₂ '(K ₂ )] from the power spectrum. 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₎ After calculating the peak position d ₁ ′ of the power spectrum corresponding to the second term of], the film thickness d ₂ can be calculated by taking the difference between them.

<Wavelength range and wavelength resolution>

3 is a diagram illustrating a measurement result when the SOI substrate is measured using the film thickness measuring apparatus 100 according to the present embodiment. In addition, in FIG. 3, as a measurement light, when the thing whose wavelength range is 900-1600 nm is used [FIG. 3 (a)] and when the thing whose wavelength range is 1340-1600 nm is used [FIG. 3 (b)] For example. In addition, by selecting the diffraction grating 62 having appropriate characteristics in accordance with the measurement wavelength, the number of detection points (number of detection channels) in the detection unit 64 (FIG. 1) to which the reflected light is incident is the same (for example, 512 channels). In other words, the narrower the wavelength range, the smaller the wavelength spacing (ie wavelength resolution) per detection point.

According to the analytical review described above, the measured reflectance will change periodically with respect to the wavelength.

In the measurement result shown to Fig.3 (a), although the indication which the reflectance changes periodically with respect to a wavelength is seen, sufficient precision for measuring a film thickness is not acquired.

On the other hand, in the measurement result shown in FIG.3 (b), the peak and valley of a reflectance are shown clearly, and the measurement of the change period of a reflectance is also possible. (C) of FIG. 3 shows the result of performing frequency conversion with respect to the wave number K after converting the measurement result (reflectance spectrum) shown in FIG. 3 (b) as a function of the above-described wavenumber conversion reflectance R '. . A value corresponding to the main peak shown in FIG. 3C 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 diagram illustrating another measurement result obtained by measuring the SOI substrate using the film thickness measurement apparatus 100 according to the present embodiment. 4 shows a measurement example when the film thickness of the Si layer 1 is 10.0 µm (design value), and the film thickness of the SiO ₂ layer 2 is 0.3 µm (design value). FIG. 4A illustrates a case where measurement of light having a wavelength component in the visible band (330 to 1100 nm) is used, and in FIG. 4B, a wavelength component in the infrared band (900 to 1600 nm) is used. The case where the measuring light which has is used is shown. As described above, the number of detection points (number of detection channels) in the detection unit 64 (Fig. 1) are all the same.

As shown in Fig. 4A, when the measurement light having the wavelength component of the visible band is used, the reflectance exhibits periodic behavior in the wavelength region longer than about 860 nm, but is significant in the shorter visible band. It can be seen that no periodic change occurs. On the other hand, as shown in FIG.4 (b), when using the measurement light which has a wavelength component of an infrared band, it turns out that the periodic change of a reflectance is shown significantly.

5 is a figure which shows the further measurement result which measured the SOI board | substrate using the film thickness measuring apparatus 100 which concerns on this embodiment. FIG. 5 shows a measurement example in which the film thickness of the Si layer 1 is 80.0 µm (design value), and the film thickness of the SiO ₂ layer 2 is 0.1 µm (design value). 5A shows a case where measurement light having a wavelength component of an infrared band (900 to 1600 nm) is used, and FIG. 5B shows a wavelength of a narrower infrared band (1470 to 1600 nm). The case where the measurement light which has a component is used is shown. As described above, the number of detection points (number of detection channels) in the detection unit 64 (Fig. 1) are all the same.

As shown in Fig. 5A, even when the measurement 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 the periodic change in reflectance is significantly shown when the measurement light having a narrower infrared band wavelength component is used.

According to the above measurement example, in order to measure the film thickness of a comparatively thick layer with high precision, it can be said that it is necessary to set the wavelength range and wavelength resolution of a measurement light suitably. This is due to the measurement method using the optical interference phenomenon in the layer and the finite resolution of the reflected light by the detection unit 64. The wavelength of the appropriate measurement light is set by the procedure described below. It is desirable to.

In the following examination, the lower limit of the film thickness measurement range is d _min , and the upper limit of the film thickness measurement range is d _max . In addition, the lower limit of wavelength detection of the detection unit 64 is λ _min , and the upper limit of wavelength detection of the detection unit 64 is λ _max . In addition, as long as the wavelength range of the measurement light irradiated by the measurement light source 10 (FIG. 1) includes the wavelength detection range of the detection part 64, what kind of range may be sufficient as it. Further, the number of detection points (the number of detection channels) on the detector 64 (FIG. 1) to S _p.

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

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

According to the above-mentioned measuring method of the film thickness, since it is necessary to find the wavelength which generate | occur | produces optical interference in the to-be-measured object, it is necessary for the detection part 64 to have a wavelength range which can generate optical interference. That is, as shown in Fig. 6A, the reflectance waveform measured with respect to the object to be measured needs to be changed by one or more cycles in the detection wavelength range of the detection unit 64.

This means that the optical distance generated when the detection wavelength range of the detection unit 64 changes from the lower limit value λ _min to the upper limit value λ _max needs to be changed by more than a reciprocation of the film thickness of the object under test. Therefore, as a relationship between the lower limit d _min of the film thickness measurement range and the wavelength range of the measurement light, it is necessary to satisfy the following Conditional Expression 1.

[Condition 1]

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

As shown in Fig. 6B, the longer the wavelength of the measurement light, the longer the period of the reflectance waveform measured for the object under test. The reflectance waveform shown in Fig. 6C is obtained by converting the reflectance 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 arrange | positioned at equal intervals with respect to a wavelength, it turns out that the arrangement | interval interval of each array element with respect to a wave number becomes wider as a wave number becomes smaller.

Therefore, in order to accurately sample the reflectance waveform that changes at a predetermined period with respect to the wave number, the arrangement interval (wavelength resolution Δλ) of each array element needs to satisfy the Nyquist sampling theorem. By the condition to be satisfied, the upper limit d _max of the film thickness measurement range is determined.

The wavelength resolution Δλ in the detection unit 64 can be represented by Δλ = (λ _max −λ _min ) / S _p using the number of detection points (number of detection channels) S _p .

The longer the wavelength of the measurement light becomes, the shorter the period of the reflectance waveform is. Therefore, when an extreme value (peak or valley) occurs at the upper limit value λ _max of the measurement light in the reflectance waveform, an extreme value adjacent to the extreme value (adjacent to the peak) When the wavelength for generating the peak or the valley adjacent to the valley) is λ ₁ , the following conditions must be satisfied between the upper limit value d _max of the film thickness measurement range.

Here, when the film thickness of the layer to be measured is relatively large, it can be regarded as n _{max ≒} n ₁ , and the above-described conditions can be expressed as Conditional Expression 2 as follows.

[Condition Formula 2]

At this time, the following conditions need to be satisfied for the wavelength resolution Δλ.

When the term λ ₁ is eliminated by substituting the relational expression of the upper limit value d _max in the relational expression of the wavelength resolution Δλ described above, it can be expressed as the following Conditional Expression 3.

[Condition 3]

As a result of the above examination, when the film thickness measurement range (lower limit (d _min ) to upper limit (d _max )) required for the measurement target object is determined in advance, the wavelength range of the measurement light is satisfied so as to satisfy the conditional expressions 1 and 2 described above. Lower limit (d _min ) to upper limit (d _max )] and the number of detection points (S _p ) need to be determined.

Calculation example

An example calculated about the conditions required when 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, the upper limit value d _max of the Si layer 1 of the SOI substrate was 100 μm, and the refractive index n was a constant value (n = 3.5) regardless of the wavelength. In this calculation example, the lower limit d _min of the Si layer 1 of the SOI substrate is not considered.

Substituting the above prerequisite values into each of the above Conditional Expressions 2 and 3 yields an upper limit value of lambda _max = 1424.0 nm and a wavelength resolution of lambda lambda = 1.445375 nm. Therefore, in the case of using the detection unit 64 of 512 channels in order to measure the film thickness of the measured object having a film thickness of up to 100 μm, using the measurement light including the wavelength range of about 684 to 1424 nm, It can be seen that the detection unit 64 detects the reflected light in the range (wavelength resolution (Δλ) = 1.4453125 nm).

However, the wavelength resolution (Δλ) calculated by the above conditional expression describes the theoretical minimum specification. When the measurement is actually performed, it is preferable to make the accuracy higher than the calculated wavelength resolution (Δλ). Moreover, it is good to set it as about several times (for example, 2 to 4 times) more preferably. In addition, increasing the precision means setting the value of the wavelength resolution Δλ smaller.

That is, in an actual film thickness measuring apparatus, spectral precision may deteriorate according to the influence of the incident angle of the measurement light to a to-be-measured object, the influence of the aperture angle when a lens concentrator is used, etc. In such a case, the peak height on the power spectrum becomes small, and calculation of the film thickness becomes difficult. In addition, when an FFT or the like which discretely performs frequency conversion using a finite sampling value is used, there is a case where a conversion error at the time of wavenumber conversion is largely affected by aliasing. In addition, the refractive index dispersion of the object to be measured largely varies depending on the wavelength range of the measurement light, and there is a possibility that it does not partially meet the conditions.

7 is a diagram showing a result of simulating a result measured using a film thickness measuring apparatus having a wavelength resolution close to a theoretical value. FIG. 8 is a diagram showing a result of simulating a measurement result using a film thickness measurement apparatus having a wavelength resolution at which the precision is doubled with respect to a theoretical value. In addition, the film thickness of the to-be-measured object was 100 micrometers.

More specifically, Fig. 7A shows a result of measuring the reflectance spectrum (wavelength resolution (Δλ) = 2.734375 nm) in the range of 900 nm to 1600 nm using the detection unit 64 of 512 channels. FIG. 7B shows a power spectrum obtained by frequency converting (here, FFT transformed) the reflectance spectrum shown in FIG. 7A. As shown in Fig. 7B, in this case, a peak exists in the vicinity of 100 mu m, but the level is small compared to the noise (ghost) on the thin film side, and it may be difficult to determine the film thickness. .

On the other hand, Fig. 8A shows measurement results when the wavelength range is determined so that the precision of the wavelength resolution in the detection unit 64 is twice the theoretical value. ) Shows a power spectrum obtained by frequency conversion (here, FFT conversion) of the reflectance spectrum. In this example, the number of detection points and the wavelength range are determined so that the wavelength resolution Δλ of the detection unit 64 is 1.3671875 nm. As shown in Fig. 8B, in this case, a strong peak appears in the vicinity of 100 mu m, which is the original film thickness, which means that the film thickness of the measurement object can be measured accurately.

<Summary of film thickness calculation processing>

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 spectrum can be obtained by frequency-converting the detected reflectance spectrum, and the film thickness can be calculated from the peaks appearing in this power spectrum. Such a power spectrum is calculated by discrete Fourier transform methods such as FFT in reality. However, in some cases, the FFT cannot obtain a power spectrum sufficiently reflecting periodicity. Therefore, the film thickness measuring apparatus 100 which concerns on this embodiment is comprised by the method of calculating a power spectrum, and can implement optimization methods, such as MEM, in addition to the discrete Fourier transform, such as FFT. That is, the film thickness measuring apparatus 100 according to the present embodiment selectively or collectively performs Fourier transform and optimization in accordance with the detected reflectance spectrum. In addition, about the details of the processing of MEM, "the microcomputer / personal computer utilization technique in the waveform data processing measurement system for scientific measurement", Minami Shigeo edited, CQ publishing company, August 1, 1992 product Since it is described in detail in issuance of ten editions and the like, it may be referred to.

Moreover, the film thickness measuring apparatus 100 which concerns on this embodiment is theoretically computed from the physical model computed from a measurement object in addition to the method of calculating film thickness analytically from the detected reflectance spectrum as mentioned above. A method called so-called fitting, which exploratoryly calculates optical characteristic values of a measurement object based on the deviation between the reflectance spectrum and the actually detected reflectance spectrum, is also executable.

By the way, as with the SOI substrate shown in FIG. 2, about the to-be-measured object whose film thickness of the Si layer 1 of a 1st layer is 2 or more digits compared with the film thickness of the SiO2 layer 2 which is a _2nd layer. In the fitting method, the film thickness of each layer may not be calculated with sufficient precision.

9 shows measurement results of reflectance spectra for an SOI substrate. In FIG. 9, the film thickness of the Si layer 1 of a 1st layer is 100 micrometers, and the measurement example when the film thickness of the SiO2 layer 2 which is a _2nd layer was changed to 0.1 micrometer pitch in the range of 0.48 to 0.52 micrometers. Indicates. As shown in FIG. 9, even if the film thickness of the SiO2 layer 2 which is a _2nd layer changes, it turns out that not a big change generate | occur | produced in the measured reflectance spectrum. That is, in the reflectance spectrum measured from such an object to be measured, since the influence of the Si layer 1 of a 1st layer is principally, even if the parameter of the SiO ₂ layer 2 of a _2nd layer is changed, it can fully fit. It means no.

Therefore, the film thickness measurement apparatus 100 according to the present embodiment can perform the Fourier transform described above so that the film thickness of each layer can be independently and accurately analyzed for an object having a plurality of different layers, such as an SOI substrate. , An optimization method, a fitting method, or a combination of a plurality thereof is appropriately executed. Hereinafter, the detail of the film thickness calculation process in the film thickness measuring apparatus 100 which concerns on this embodiment is demonstrated. In addition, such a film thickness calculation process is performed by the data processing part 70 (FIG. 1).

<Configuration of Data Processing Unit>

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

Referring to FIG. 10, the data processing unit 70 is typically realized by a computer, and includes a CPU (Central Processing Unit) 200 and a CPU 200 that execute various programs including an operating system (OS). A memory unit 212 temporarily storing data necessary for the execution of the program in the memory card), and a hard disk drive (HDD: Hard Disk Drive (210) 210) for nonvolatile storage of the program executed in the CPU 200. do. In addition, a program for realizing the processes described below is stored in the hard disk unit 210 in advance, and such a program is stored by the flexible disk drive (FDD) 216 or the CD-ROM drive 214, respectively. It is read from the flexible disk 216a, the compact disk-read only memory (CD-ROM) 214a, and the like.

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

<Operation processing structure>

The data processing unit 70 according to the present embodiment includes an unknown type, number, analysis accuracy, and the like among parameters (material, film thickness, film thickness range, refractive index, extinction coefficient, etc.) of each layer of the object to be measured. Therefore, it is possible to select and execute any one of the process patterns 1-6 shown below. In addition, in the following description, it demonstrates about the case where the film thickness of two laminated | stacked layers (referred to also as a "first layer" and a "second layer") is computed independently like the SOI substrate shown in FIG. 2, respectively. However, by the same procedure, it is possible to independently calculate the film thicknesses laminated more.

(1) processing pattern 1

Processing 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, all the film thicknesses of each layer are determined by the fitting method. In addition, as a fitting method, the case where the least square method is used typically is illustrated.

11 is a block diagram showing a control structure for executing a film thickness calculation process according 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 and the like into the memory unit 212 and executing it.

With reference to FIG. 11, the data processing part 70 (FIG. 1) includes the buffer part 71, the modeling part 721, and the fitting part 722 as its function.

The buffer unit 71 temporarily stores the measured reflectance spectrum R (λ) output from the spectroscopic measuring unit 60 (Fig. 1). More specifically, since the reflectance value is output from the spectroscopic measurement unit 60 for each predetermined wavelength resolution, the buffer unit 71 stores the wavelength and the reflectance at the wavelength correspondingly.

The modeling unit 721 receives a parameter relating to the object under measurement, determines a model equation (function) showing the theoretical reflectance in the object under measurement based on the received parameter, and according to the determined function, The theoretical reflectance (spectrum) in each wavelength is computed. The theoretical reflectance in each of these calculated wavelengths is output to the fitting part 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 accepted. In addition, although a user may input each parameter, the parameter of a standard material may be previously stored as a file, and may be read as needed. In addition, as necessary, the refractive index n ₀ and the extinction coefficient k ₀ of the atmosphere layer are also input.

About the model expression which shows a theoretical reflectance, since it is the same as the reflectance R in the object OBJ of the three-layer system mentioned above, it becomes a function containing the value of the film thickness of each layer at least.

In addition, the modeling unit 721 updates a function indicating the theoretical reflectance according to the parameter update command from the fitting unit 722 described later, and calculates the theoretical reflectance (spectrum) at each wavelength according to the function after the update. 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 unit 722 reads the actual value of the reflectance spectrum from the buffer unit 71 and sequentially calculates the square deviation between the theoretical value of the reflectance spectrum output from the modeling unit 721 for each wavelength. And the fitting part 722 calculates a residual from the deviation in each wavelength, and determines whether this residual is below a predetermined threshold. In other words, the fitting portion 722 determines whether or not the fitting is converged in the current parameter.

If the residual is not less than or equal to the predetermined threshold, the fitting unit 722 gives a parameter update command to the modeling unit 721 and waits until a new theoretical value of the reflectance spectrum is output. On the other hand, when 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 present time as an analysis value.

It is a flowchart which shows the procedure of the film thickness calculation process which concerns on the process pattern 1 which concerns on embodiment of this invention.

Referring to FIG. 12, first, a user arranges a measurement object (sample) on the stage 50 (FIG. 1) (step S100). Subsequently, when a user gives a measurement preparation instruction, irradiation of observation light is started from the observation light source 22 (FIG. 1). The user gives a stage position command to the movable mechanism 51 while referring to the reflection image picked up by the observation camera 38 displayed on the display unit 39 to adjust or focus the measurement range (step S102).

After the adjustment of the measurement range or the completion of focusing, if a user gives a measurement start command, generation of measurement light is started from the measurement light source 10 (FIG. 1). The spectroscopic measuring unit 60 receives the reflected light from the measured object and outputs a 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 film thickness calculation process shown below.

The CPU 200 displays an input screen on the display unit 204 (FIG. 10) or the like and prompts the user to input a parameter (step S108). The user can adjust the refractive index n ₁ and extinction coefficient k ₁ of the first layer of the object under test, the refractive index n ₂ and the extinction coefficient k ₂ of the second layer of the object from the displayed input screen or the like. At the same time, the initial values of the film thickness d _{1 of} the first layer and the film thickness d ₂ of the second layer relating to the object to be measured are input (step S110).

The CPU 200 also calculates a theoretical value of the reflectance spectrum based on the parameter input by the user (step S112). Subsequently, the CPU 200 sequentially calculates the square deviation between the actual value of the reflectance spectrum and the theoretical value of the reflectance spectrum stored in the memory unit 212 and the like for each wavelength to calculate a residual between them (step S114). . In addition, the CPU 200 determines whether the calculated residual is equal to or less than a predetermined threshold (step S116).

If the calculated residual is not less than or equal to the predetermined threshold (NO in step S116), the CPU 200 determines the film thickness d _{1 of} the first layer and the film thickness d ₂ of the second layer. The present value is changed (step S118). In addition, how and in which direction the film thicknesses d ₁ and d ₃ are changed is determined according to the degree of occurrence of the residual. The process then returns to Step S112.

On the other hand, when the calculated residual is less than or equal to the predetermined threshold (YES in step S116), the CPU 200 determines the film thickness d _{1 of} the first layer and the film thickness d ₂ of the second layer. ) Is output as the film thickness (interpreted value) of each layer to be measured (step S120). The process then ends.

In the block diagram shown in Figure 11, refractive index (n _1, n _2), and although illustrated for a configuration to input a fixed value as the extinction coefficient (k _1, k _2), the refractive index and extinction coefficient for taking into account the wavelength dispersion You may use it. For example, as the refractive index and extinction coefficient which considered wavelength dispersion, you may use the formula of the Cauchy model shown below.

When using such an expression, the initial value or a known value is previously input also about each coefficient in a formula, and it becomes a fitting object also about these coefficients.

Or you may use the Sellmeier model formula shown below.

(2) processing pattern 2

Processing pattern 2 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 2, the first layer having a large film thickness is obtained by frequency conversion using a discrete Fourier transform, the film thickness of the first layer is fixed to be fixed, and the film thickness of the second layer is determined by the fitting method. do. In addition, as a fitting method, the case where the least square method is used typically is illustrated.

FIG. 13 is a block diagram showing a control structure for executing the film thickness calculation process according to the processing pattern 2 according to the embodiment of the present invention. FIG. 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 into the memory unit 212 and executing it.

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

The buffer unit 71 temporarily stores the measured reflectance spectrum R (λ) output from the spectroscopic measuring unit 60 (Fig. 1). In addition, since the process content of the specific structure was mentioned above, detailed description is not repeated.

The wavenumber converter 731 receives the parameters (refractive index n ₁ and extinction coefficient k ₁ ) relating to the first layer, and reflectance spectra are temporarily stored in the buffer unit 71 based on the received parameters. (R) (λ) is frequency-converted. That is, the wavenumber converting unit 731 has described the correspondence relationship between each wavelength in the reflectance spectrum R (λ) and the reflectance in the wavelength and the wave number K ₁ (λ) for each wavelength described above. The conversion is performed to the corresponding relationship of the corresponding wavenumber conversion reflectance R ₁ ′ calculated according to the relational expression. More specifically, the wavenumber converting portion 731 has a wavenumber K ₁ (λ) and a wavenumber conversion reflectance R ₁ ′ (λ) for each wavelength stored in the buffer portion 71 {= R (λ) / [ 1-R ([lambda])]} are sequentially calculated and output to the buffer unit 732.

The buffer unit 732 associates and stores the wave number K ₁ (λ) sequentially output from the wave number conversion unit 731 with the wave rate conversion reflectance R ₁ ′ (λ). That is, the buffer unit 732 stores the wavenumber conversion reflectance R ₁ ′ (K ₁ ), which is a wave shape distribution characteristic of the wavenumber conversion reflectance with respect to the wave number K ₁ (λ).

The Fourier transform unit 733 calculates the power spectrum P ₁ by performing Fourier transform on the wavenumber conversion reflectance R ₁ (K ₁ ) stored in the buffer unit 732 with respect to the wave number K ₁ . In addition, as a method of Fourier transform, a fast Fourier transform (FFT), a discrete cosine transform (DCT), or the like can be used.

The peak search unit 734 searches the peaks appearing in the power spectrum P ₁ calculated by the Fourier transform unit 733, acquires the film thickness corresponding to the peaks, and obtains the film thickness d ₁ of the first layer. Output as

The modeling unit 735 accepts a parameter relating to an object to be measured, determines a model equation (function) representing a theoretical reflectance in the object to be measured based on the received parameter, and according to the determined function, each wavelength The theoretical reflectance (spectrum) in is computed. The theoretical reflectance in each of these calculated wavelengths is output to the fitting part 736. More specifically, the modeling unit 735 receives the film thickness d _{1 of} the first layer, the refractive index n ₂ , and the extinction coefficient k ₂ of the second layer output from the peak search unit 734. At the same time, the initial value of the film thickness d ₂ of the second layer is accepted. In addition, although a user may input each parameter, the parameter of a standard material may be previously stored as a file, and may be read as needed. About the model expression which shows a theoretical reflectance, it is the same as the reflectance R in the object OBJ of the three-layer system mentioned above, and it becomes a function containing the value of the film thickness of each layer at least.

In addition, the modeling unit 735 updates the function representing the theoretical reflectance in accordance with the parameter update command from the fitting unit 736, and 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 unit 736 reads the actual value of the reflectance spectrum from the buffer unit 71 and sequentially calculates the square deviation between the theoretical value of the reflectance spectrum output from the modeling unit 735 for each wavelength. And the fitting part 736 calculates a residual from the square deviation in each wavelength, and determines whether this residual is below a predetermined threshold. That is, the fitting portion 736 determines whether or not the current convergence in the parameter.

If the residual is not less than or equal to the predetermined threshold, the fitting unit 736 gives a parameter update command to the modeling unit 735, and waits until a new theoretical value of the reflectance spectrum is output. On the other hand, when 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 at the present time as an analysis value.

It is a flowchart which shows the procedure of the film thickness calculation process which concerns on the process pattern 2 which concerns on embodiment of this invention. Since the process of step S100-S108 is the same as each step which attach | subjected the same code | symbol of the flowchart shown in FIG. 12 among the steps of the flowchart shown in FIG. 14, detailed description is not repeated. Hereinafter, the film thickness calculation process after step S132 differs from the flowchart shown in FIG. 12.

In step S132, the user selects the refractive index n ₁ and extinction coefficient k ₁ of the first layer of the measurement object and the refractive index n ₂ and extinction coefficient of the second layer of the measurement object, such as on the displayed input screen. k ₂ ) is input and the initial value of the film thickness d ₂ of the second layer is input.

Then, the CPU 200 converts the reflectance spectrum stored in the memory unit 212 or the like based on the input refractive index n ₁ and the extinction coefficient k ₁ of the first layer (step S134). The CPU 200 then stores the wavenumber conversion reflectance obtained by the wavenumber conversion in the memory unit 212 or the like (step S136). In addition, the CPU 200 performs Fourier transform on the wavenumber conversion reflectance on the wave number K ₁ to calculate a power spectrum (step S138). In addition, 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 obtained in step S210 and the parameters relating to the user input second layer (step S142). Then, the CPU 200 sequentially calculates the square deviation between the actual 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). . The CPU 200 also determines whether the calculated residual is equal to or less than a predetermined threshold (step S146).

If the calculated residual is not equal to or less than the predetermined threshold (NO in step S146), the CPU 200 changes the present value of the film thickness d2 of the second layer (step S148). For the addition, whether to some extent change the film thickness (d ₂₎ in any direction, it is determined according to the degree of occurrence of residual. The process then returns to Step S142.

In contrast, when the calculated residual is equal to or less than a predetermined threshold (YES in step S146), the CPU 200 determines the film thickness d _{1 of} the first layer and the film thickness d ₂ of the second layer. ) Is output as the film thickness (interpreted value) of each layer to be measured (step S150). The process then ends.

In addition, like the processing pattern 1 mentioned above, you may use the refractive index and extinction coefficient which considered wavelength dispersion. Since the detailed function has been described above, the detailed description will not be repeated.

(3) processing pattern 3

Processing 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 processing pattern 2 described above by using an optimization method other than the Fourier transform in calculating the film thickness of the first layer. About other processing, it is the same as that of the process pattern 2 mentioned above.

15 is a block diagram showing a control structure for executing a film thickness calculation process according 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 into the memory unit 212 and executing it.

Referring to FIG. 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 measured reflectance spectrum R (λ) output from the spectroscopic measuring unit 60 (Fig. 1). In addition, since the process content of the specific structure was mentioned above, detailed description is not repeated.

The optimization operation unit 741 analyzes the frequency component of the reflectance spectrum stored in the buffer unit 71 by using an optimization method such as MEM to calculate the film thickness d ₁ of the first layer. More specifically, the optimization operation unit 741 obtains an autocorrelation function for the actual value of the reflectance spectrum using the autoregressive model, and determines autoregressive coefficients describing the autoregressive model from these values. The optimization calculation unit 741 obtains the film thickness corresponding to the wavelength of the main component obtained by performing the frequency analysis in this way, and outputs it as the film thickness d ₁ of the first layer. In addition, the optimization calculation unit 741 may search for the film thickness d ₁ of the first layer, the refractive index n ₁ and the extinction coefficient k _{1 of} the first layer, and the second layer before the execution of the optimization method. The refractive index n ₂ and the extinction coefficient k ₂ are accepted, and a provisional value of the film thickness d ₂ of the second layer is received. In addition, although a user may input each parameter, the parameter of a standard material may be previously stored as a file, and may be read as needed.

The modeling unit 742 and the fitting unit 743 receive the film thickness d ₁ of the first layer calculated by the optimization calculating unit 741 and parameters related to the measured object, and the film thickness d of the second layer. ₂ ) is determined by fitting. Since the processing of the modeling unit 742 and the fitting unit 743 is the same as that of the modeling unit 735 and the fitting unit 736 of the above-described processing pattern 2, the detailed description is not repeated.

It is a flowchart which shows the procedure of the film thickness calculation process which concerns on the process pattern 3 which concerns on embodiment of this invention. In each step of the flowchart shown in FIG. 16, the processing in steps S100 to S106 is the same as each step denoted by the same reference numerals in the flowchart shown in FIG. 12, and thus detailed description thereof will not be repeated. Hereinafter, the film thickness calculation process after step S162 different from the flowchart shown in FIG. 12 will be described.

In step S162, the user searches for the film thickness d ₁ of the first layer of the measurement object, the refractive index n ₁ and the extinction coefficient k ₁ of the first layer of the measurement object, on the displayed input screen or the like. ) And the refractive index (n ₂ ) and extinction coefficient (k ₂ ) of the second layer of the measurement object.

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

Subsequently, the CPU 200 calculates the theoretical value of the reflectance spectrum based on the film thickness d ₁ of the first layer obtained in step S164 and the parameters relating to the user input second layer (step S166). The CPU 200 sequentially calculates the square deviation between the actual value of the reflectance spectrum and the theoretical value of the reflectance spectrum stored in the memory unit 212 and the like for each wavelength, and calculates the residual between them (step S168). In addition, the CPU 200 determines whether the calculated residual is less than or equal to a predetermined threshold (step S170).

If the calculated residual is not less than or equal to the predetermined threshold (NO in step S170), the CPU 200 changes the present value of the film thickness d ₂ of the second layer (step S172). For the addition, whether to some extent change the film thickness (d ₂₎ in any direction, it is determined according to the degree of occurrence of residual. The process then returns to Step S166.

In contrast, when the calculated residual is equal to or less than a predetermined threshold (YES in step S170), the CPU 200 determines the film thickness d _{1 of} the first layer and the film thickness d ₂ of the second layer. ) Is output as the film thickness (interpreted value) of each layer to be measured (step S174). The process then ends.

In addition, like the processing pattern 1 mentioned above, you may use the refractive index and extinction coefficient which considered wavelength dispersion. Since the detailed function has been described above, the detailed description will not be repeated.

(4) processing pattern 4

The process pattern 4 is an improved method of the process pattern 1, which ensures convergence by fitting more reliably. That is, in an object to be measured in which the film thicknesses of the first layer and the second layer are greatly different, such as an SOI substrate, an initial value for fitting the film thickness of each layer is important. Therefore, in the processing pattern 4, the initial value of the film thickness of each layer is first determined using an optimization method, and the film thickness of a 1st layer and a 2nd layer is determined by a fitting method using these initial values.

17 is a block diagram showing a control structure for executing a film thickness calculation process according 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 into the memory unit 212 and executing it.

The control structure of the processing pattern 4 shown in FIG. 17 is substantially the same as the addition of the optimization calculating unit 751 to the control structure of the processing pattern 1 shown in FIG.

The optimization operation unit 751 analyzes the frequency component of the reflectance spectrum stored in the buffer unit 71 by using an optimization method such as MEM, so that the film thickness d ₁ of the first layer and the film thickness of the second layer ( d ₂ ) are respectively calculated. In particular, the optimization calculation unit 751 extracts two or more peaks obtained by frequency analysis of the measured reflectance spectrum, and the film thickness d ₁ of the first layer and the film of the second layer from the film thicknesses corresponding to these peaks. The thickness d ₂ is respectively calculated. Note that 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 the fitting, and no precise precision is required. In addition, since the specific frequency analysis method in the optimization calculating part 751 is the same as that of the optimization calculating part 741 mentioned above, detailed description is not repeated.

The modeling unit 721 and the fitting unit 722 use the original thickness based on the film thickness d _{1 of} the first layer and the film thickness d ₂ of the second layer calculated by the optimization calculating unit 751. The film thickness d ₁ of one layer and the film thickness d ₂ of the second layer are determined by fitting. Since the processing contents of the modeling unit 721 and the fitting unit 722 have been described above, the detailed description thereof will not be repeated.

18 is a flowchart showing a procedure of film thickness calculation processing according to processing pattern 4 according to the embodiment of the present invention. The flowchart shown in FIG. 18 is the process of step S111A and S111B instead of step S110 in the flowchart shown in FIG. 12, and it is the same as each step which attaches | subjects the same code | symbol about other processes, and the detailed description is Do not repeat Hereinafter, the process different from FIG. 12 is demonstrated.

Referring to FIG. 18, after the execution of step S108, the process of step S111A is executed. In step S111A, the user checks the refractive index n ₁ and extinction coefficient k ₁ of the first layer of the measurement object, the refractive index n ₂ and extinction coefficient of the second layer of the measurement object, on the displayed input screen or the like. (k ₂ ) is input, and the search range of the film thickness d ₁ of the first layer and the film thickness d ₂ of the second layer are input. In subsequent step S111B, the CPU 200 analyzes the frequency component of the reflectance spectrum stored in the memory unit 212 or the like using an optimization method, whereby the film thickness d ₁ of the first layer and the second layer are analyzed. The film thickness d ₂ of is calculated. 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 initial values of the fitting. And after this step S111B, the same process as the process after step S112 of FIG. 12 is performed.

In addition, like the processing pattern 1 mentioned above, you may use the refractive index and extinction coefficient which considered wavelength dispersion. Since the detailed function has been described above, the detailed description will not be repeated.

(5) processing pattern 5

The processing pattern 5 is a method applied to the case where the film thickness of one layer is known and only the film thickness of the other layer is analyzed. The processing pattern 1 is modified. In the following description, the film thickness of the 2nd layer of a to-be-measured object is known, and the method of determining the film thickness of a 1st layer by fitting is illustrated.

19 is a block diagram showing a control structure for executing a film thickness calculation process according to the processing pattern 5 according to the embodiment of the present invention. 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 and the like into the memory unit 212 and executing it.

In the control structure according to the processing pattern 4 shown in FIG. 19, in the control structure according to the processing pattern 1 shown in FIG. 11, the modeling unit 721A is disposed instead of the modeling unit 721.

The modeling unit 721A receives 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. 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. In addition, although a user may input each parameter, the parameter of a standard material may be previously stored as a file, and may be read as needed. In addition, as necessary, the refractive index n ₀ and the extinction coefficient k ₀ of the atmosphere layer are also input.

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, we update the function that represents the theoretical reflectance. In addition, the modeling unit 721A repeatedly calculates the theoretical reflectance (spectrum) at each wavelength in accordance with the function after the update. By such a procedure, the film thickness d ₁ of the first layer is determined by fitting.

Since other configurations have been described above, the detailed description will not be repeated.

20 is a flowchart showing a procedure of film thickness calculation processing according to processing pattern 5 according to the embodiment of the present invention. The flowchart shown in FIG. 20 is provided with the process of step S110A, S118A, and S120A instead of step S110, S118, and S120 in the flowchart shown in FIG. Since it is the same, detailed description is not repeated. Hereinafter, the process different from FIG. 12 is demonstrated.

Referring to FIG. 20, in step S110A, the user can check the refractive index n ₁ and extinction coefficient k ₁ of the first layer of the measurement object, and the refractive index of the second layer of the measurement object from the displayed input screen or the like. n ₂ ) and the extinction coefficient k ₂ are input, and a known value of the initial value of the film thickness d ₁ of the first layer and the film thickness d ₂ of the second layer is input.

In step S118A, the CPU 200 changes the present value of the film thickness d ₁ of the first layer. That is, in the process pattern 5, only the film thickness d ₁ of a 1st layer becomes a fitting object.

In step S120A, the CPU 200 outputs the present value of the film thickness d ₁ of the _first layer as the film thickness (interpreted value) of each layer to be measured when the calculated residual is less than or equal to a predetermined threshold.

In addition, like the processing pattern 1 mentioned above, you may use the refractive index and extinction coefficient which considered wavelength dispersion. Since the detailed function has been described above, the detailed description will not be repeated.

(6) processing pattern 6

The processing pattern 6 is a method applied to the case where the film thickness of one layer is known and only the film thickness of the other layer is analyzed. The processing pattern 5 is modified. In the following description, the film thickness of the 2nd layer of a to-be-tested object is known, and the method of determining the film thickness of a 1st layer by fitting or a Fourier transform is illustrated.

21 is a block diagram showing a control structure for executing a film thickness calculation process according 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 and the like into the memory unit 212 and executing it.

In the control structure according to the processing pattern 4 shown in FIG. 21, in the control structure according to the processing pattern 4 shown in FIG. 19, instead of the fitting portion 722, the fitting portion 722A is disposed, and the wave number converting portion is arranged. 731, the buffer part 732, the Fourier transform part 733, and the peak search part 734 are corresponded.

That is, in the present processing pattern, when the film thickness d ₁ of the first layer of the measurement object is determined by the fitting, but the fitting has not converged within the prescribed number of times, the film thickness of the first layer is determined by using a Fourier transform. d ₁ ) is determined.

The fitting portion 722A reads the measured value of the reflectance spectrum from the buffer portion 71, and the modeling portion 721A so that the residual between the theoretical values of the reflectance spectrum output from the modeling portion 721A is equal to or less than a predetermined threshold value. Parameter update command is given sequentially. In addition, the fitting part 722A uses the Fourier transform to determine the film thickness d ₁ of the first layer when the residual does not fall below a predetermined threshold even after a predetermined number of calculations. ) Is given a switching command.

The wavenumber converting 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, and thus detailed description thereof will not be repeated. .

22 is a flowchart showing a procedure of film thickness calculation processing according to processing pattern 6 according to the embodiment of the present invention. The flowchart shown in FIG. 22 adds the process of step S117 in the flowchart shown in FIG. 20, and adds the process of steps S134-S140 of the flowchart shown in FIG. The rest of the processing is the same as that of each step denoted by the same reference numeral, and thus, detailed description thereof will not be repeated. Hereinafter, the process different from FIG. 14 and FIG. 20 is demonstrated.

Referring to Fig. 22, in step S117, the CPU 200 determines whether or not the fitting process is repeated more than the prescribed number of times. If the fitting process is not repeated more than the specified number of times (NO in step S117), the process returns to step S112 after the process of step S118 is executed. On the other hand, when 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 using a Fourier transform. Since the processing of each of these steps has been described above, the detailed description will not be repeated.

Measurement Example

23 shows examples of results obtained by measuring the film thickness of an SOI substrate using the film thickness measuring device according to the embodiment of the present invention. 23 shows a power spectrum obtained by frequency conversion (FFT conversion) of the reflectance spectrum.

FIG. 23A shows the result of measuring the SOI substrate formed with the aim of forming the film thickness of the Si layer as the first layer at 22.0 μm and the film thickness of the SiO ₂ layer as the _second layer at 3.0 μm. In FIG. 23A, frequency conversion was performed using components of 1470 to 1600 nm in the measured reflectance spectra. As a result, the first peak is generated at a position corresponding to 21.8613 µm.

FIG. 23B shows the result of measuring the SOI substrate formed with the aim of forming the film thickness of the Si layer as the first layer to be 32.0 µm and the film thickness of the SiO ₂ layer as the _second layer to 2.0 µm. In FIG. 23B, frequency conversion was performed using components of 1500 to 1600 nm in the measured reflectance spectra. As a result, the first peak is generated at a position corresponding to 30.6269 µm.

FIG. 23C shows the result of measuring the SOI substrate formed with the aim of forming the film thickness of the Si layer as the first layer at 16.0 μm and the film thickness of the SiO ₂ layer as the _second layer at 1.3 μm. In FIG. 23C, frequency conversion was performed using components of 1400 to 1600 nm in the measured reflectance spectra. As a result, the first peak is generated at a position corresponding to 15.9069 µm.

About any measurement result, it turns out that it is substantially favorable.

<Intervention of shield member>

As described above, the film thickness measuring apparatus 100 according to the present embodiment mainly measures the film thickness of the object OBJ based on the reflectance spectrum in the infrared band, so that the light source 10 for measurement (Fig. The measurement can be performed even if a shielding member such as a polymer resin is present on the path from 1) to the object OBJ. That is, a member such as a polymer resin does not transmit light in the visible band, but may transmit light in the infrared band.

FIG. 24: is a schematic diagram which shows the structure at the time of measuring the to-be-measured object (OBJ) image in which the opaque pad was arrange | positioned at the upper surface using the film thickness measuring apparatus 100 which concerns on embodiment of this invention.

Referring to FIG. 24, a planar object OBJ is loaded on the stage 50 through a spacer, and a planar opaque pad 52 is formed on the upper surface (irradiation side of the measurement light) of the object OBJ. ) Is arranged. This opaque pad 52 is corresponded to the grinding | polishing body etc. which are used at a grinding | polishing process, and consists mainly of polymeric resins. Such an opaque Pad 52 transmits light of an infrared band (for example, 900 to 1600 nm) although its transmittance is small.

25 and 26 show the results of measuring 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 result of using an magnifying lens having a magnification of 10 times as the objective lens 40 (FIGS. 1 and 24), and FIG. 26 shows 2.83 times as the objective lens 40 (FIGS. 1 and 24). The result when the magnifying lens which has a magnification of is used is shown.

In addition, in FIG. 25 and FIG. 26, the result in the state in which the opaque Pad 52 is not arrange | positioned is superimposed for comparison. It should also be noted that the range (absolute value) of each reflectance spectrum is different.

FIG. 27 shows a power spectrum obtained from the reflectance spectrum in a state where the pads 52 shown in FIGS. 25 and 26 are not arranged, and FIG. 28 shows the pads 52 shown in FIGS. 25 and 26. The power spectrum obtained from the reflectance spectrum of the state in which it exists is shown.

Referring to FIG. 25, when the 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 based on the result when the opaque Pad 52 is not present. In comparison, the noise component is increased.

On the other hand, referring to Fig. 26, when the magnifying lens having a magnification of 2.83 times is used as the objective lens 40, the result when the opaque Pad 52 is present is when the opaque Pad 52 is not present. Almost like the results, the periodicity is sufficiently measured.

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

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

As mentioned above, it was confirmed that it is possible to measure the film thickness of the to-be-measured object OBJ by which the opaque Pad 52 was arrange | positioned using the film thickness measuring apparatus 100 which concerns on this embodiment. However, it can be said that it is necessary to design the optical system for irradiating the measurement light and the optical system for receiving the reflected light so as to exclude the influence of diffused light.

[Modification]

As an optical system for irradiating the measurement light to the object to be measured OBJ and receiving the reflected light, a Y-type fiber may be used.

FIG. 29: is a schematic diagram which shows the structure of the optical system of the film thickness measuring apparatus 100 # which concerns on the modification of embodiment of this invention.

Referring to FIG. 29, the film thickness measuring apparatus 100 # guides the measurement light from the measurement light source 10 (FIG. 1) to the object OBJ, and also reflects light from the object OBJ. Is an optical system that guides the light to the detection unit 64 (FIG. 1), and includes a light projection and reception fiber 56.

The transmitted light fiber 56 is a Y-type fiber capable of combining two light beams into one light beam and simultaneously separating one light beam into two light beams. As a more specific example, the transmitted light fiber 56 is made of Ge-doped single-wire Y-type fiber.

Measurement light generated from the measurement light source 10 (FIG. 1) enters the object OBJ through the first branch fiber 56a, and the reflected light reflected from the object OBJ is generated in the second branch fiber. It is led to the detection part 64 through 56b.

Moreover, the pinhole optical system 54 which functions as an "aperture" is arrange | positioned between the light transmission light 56 and the object OBJ.

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

It is a schematic diagram which shows the form which measures the film thickness of the to-be-measured object OBJ in solution using the film thickness measuring apparatus 100 # which concerns on the modification of embodiment of this invention.

Referring to Fig. 30, the object to be measured OBJ is disposed on the table 57 disposed in the container via a spacer, and the container is filled with a solution 58 such as a polishing liquid. And a part of the permeation | transmission light bulb side of the light transmission optical fiber 56 is immersed in the solution 58. As shown in FIG. With such a configuration, the film thickness of the object under test (OBJ) in the solution can be measured.

In addition, when using the solution 58 which uses water as a solvent, it is preferable to use the band except the absorption wavelength of water among the infrared bands (900-1600 nm) mentioned above for film thickness measurement. Specifically, since water has absorption 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 thickness of the object OBJ.

[Other Embodiments]

The program according to the present invention may execute a process by calling necessary modules in a predetermined arrangement, at predetermined timing, from among program modules provided as part of an operating system (OS) of the computer. In that case, the program itself does not contain the module and the processing is executed in cooperation with the OS. Programs that do not include such modules may also be included in the program of the present invention.

In addition, the program which concerns on this invention may be provided integrated in one part of another program. Even in that case, the program itself does not include a module included in the other program, and the processing is executed in cooperation with the other program. Programs assembled with such other programs can also be included in the program of 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 the program itself and a storage medium in which the program is stored.

In addition, 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 calculating the film thickness of each layer constituting the object to be measured independently based on the reflectance spectrum (or transmittance spectrum) obtained by irradiating the measurement light to the object to be measured, ( 1) Determine the film thickness by calculating the main wave components using discrete Fourier transform such as FFT or optimization method such as MEM, and (2) Determination of film thickness using fitting using model formula. You can optionally run it. Thereby, even if there are many layers which comprise a to-be-measured object, or even if there is a big difference in the film thickness of each layer, the film thickness of each layer can be measured more correctly.

Moreover, according to embodiment of this invention, the wavelength range (or wavelength detection range) of a measurement light and the wavelength resolution of a detection part can be set suitably according to the film thickness of each layer which comprises the to-be-measured object to measure. Therefore, the film thickness of each layer can be measured more accurately.

While the invention has been shown and described in detail, it is for the purpose of illustration only and not of limitation, and the scope of the invention will be apparently interpreted by the appended claims.

1 is a schematic configuration diagram of a film thickness measurement apparatus according to an embodiment of the present invention.

It is a figure which shows an example of the cross-sectional schematic diagram of the to-be-measured object made into the film thickness measuring apparatus which concerns on embodiment of this invention.

3 shows measurement results when the SOI substrate is measured using the film thickness measurement apparatus according to the present embodiment.

4 shows another measurement result of measuring an SOI substrate using the film thickness measurement apparatus according to the present embodiment.

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

Fig. 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, and the number of detection points.

FIG. 7 is a diagram showing the results of simulations using the results measured using a film thickness measurement apparatus having a wavelength resolution close to a theoretical value. FIG.

FIG. 8 is a diagram showing the results of simulations using the results measured using a film thickness measuring apparatus having a wavelength resolution at which the precision is doubled with respect to a theoretical value. FIG.

9 shows measurement results of reflectance spectra for an SOI substrate.

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

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

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

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

14 is a flowchart illustrating a procedure of a film thickness calculation process according to Process Pattern 2 according to the embodiment of the present invention.

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

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

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

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

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

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

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

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

The figure which shows the example of the result of having measured the film thickness of an SOI substrate using the film thickness measuring apparatus which concerns on embodiment of this invention.

It is a schematic diagram which shows the structure at the time of measuring the to-be-measured object image which the opaque pad was arrange | positioned at the upper surface using the film thickness measuring apparatus which concerns on embodiment of this invention.

FIG. 25 is a view showing a result of measuring an SOI substrate on which an opaque pad is disposed using the film thickness measuring apparatus according to the embodiment of the present invention. FIG.

Fig. 26 shows another result of measuring an SOI substrate on which an opaque pad is disposed using the film thickness measuring apparatus according to the embodiment of the present invention.

FIG. 27 is a diagram showing a power spectrum obtained from reflectance spectra in a state where the opaque pads shown in FIGS. 25 and 26 are not disposed.

FIG. 28 is a diagram showing a power spectrum obtained from the reflectance spectrum in a state where the opaque pads shown in FIGS. 25 and 26 are disposed;

The schematic diagram which shows the structure of the optical system of the film thickness measuring apparatus which concerns on the modification of embodiment of this invention.

It is a schematic diagram which shows the form which measures the film thickness of the to-be-measured object in a solution using the film thickness measuring apparatus which concerns on the modification of embodiment of this invention.

[Description of the code]

10: light source for measurement

12: collimated lens

14: cut filter

16, 36: imaging lens

18: aperture part

20, 30: beam splitter

22: light source for observation

24: optical fiber

26: exit section

26a: mask portion

32: pinhole mirror

32a: pinhole

34: axis conversion mirror

38: observation camera

39: display unit

40: objective lens

50: stage

51: movable mechanism

52: Opaque Pad

54: pinhole optical system

56: floodlight fiber

56a, 56b: branch fiber

57: table

58: solution

60: spectrometer

62: diffraction grating

64: detector

66: cut filter

68: shutter

70: data processing unit

71,732: Buffer part

100, 100 #: film thickness measuring device

200: CPU

202: the bus

204: display unit

208: input unit

210: hard disk unit (HDD)

212: memory

214: CD-ROM Drive

214a: CD-ROM

216: Flexible Disk Drive (FDD)

216a: Flexible Disk

721, 721A, 735, 742: modeling unit

722, 722A, 736, 743: fitting part

731: frequency conversion unit

733: Fourier transform

734: peak search unit

741, 751: optimization calculation unit

OBJ: Object to be measured

Claims (8)

Film thickness measuring device, And a light source for irradiating measurement light having a predetermined wavelength range to the object to be measured having a plurality of layers formed on the substrate, wherein the object to be measured is adjacent to the first layer and the first layer closest to the light source. Including a second layer, A spectroscopic measuring unit for acquiring a wavelength distribution characteristic of reflectance or transmittance based on the light reflected from the measured object or the light transmitted through the measured object; First determination means for determining at least the film thickness of the first layer by fitting to the wavelength distribution characteristic using a model formula including the film thickness of each layer included in the measurement object; By converting the correspondence between the wavelengths in the wavelength distribution characteristic and the value of the reflectance or transmittance in the wavelengths into the correspondence relationship between the wave number for each wavelength and the conversion value calculated according to a predetermined relational expression, the wave number distribution characteristic is changed. Conversion means to generate, Analysis means for acquiring an amplitude value of each wave component included in the wave number distribution characteristic; Second determining means for determining at least the film thickness of the first layer based on a wave component having a large amplitude value included in the wave number distribution characteristic, And the first determining means and the second determining means are selectively validated. The wavelength distribution according to claim 1, wherein a value of the film thickness of the first layer determined by the second determining means is set in a model formula including the film thickness of each layer included in the object to be measured. The film thickness measuring apparatus further equipped with the 3rd determination means which determines the film thickness of the said 2nd layer by fitting to a characteristic. The film thickness measuring apparatus according to claim 1, wherein the second determining means is validated when the fitting by the first determining means does not converge within a prescribed number of times. The film thickness measuring apparatus according to any one of claims 1 to 3, wherein the model formula includes a function of a wavelength representing a refractive index. The film thickness measuring apparatus according to any one of claims 1 to 3, wherein the predetermined wavelength range includes a wavelength of an infrared band. The film thickness measuring apparatus according to any one of claims 1 to 3, wherein the analyzing means includes means for discretely Fourier transforming the wave number distribution characteristic. The film thickness measuring apparatus according to any one of claims 1 to 3, wherein the analyzing means obtains an amplitude value of each wave component included in the wave number distribution characteristic by using an optimization method. Film thickness measurement method, And irradiating the measurement light having a predetermined wavelength range to the measurement object having a plurality of layers formed on the substrate, wherein the measurement object includes a first layer and the first layer to which the measurement light first enters. A second layer adjacent to, Acquiring 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 determination step of determining at least the film thickness of the first layer by fitting to the wavelength distribution characteristic using a model formula including the film thickness of each layer included in the measurement object; The wave number distribution characteristic is converted by converting the correspondence between each wavelength in the wavelength distribution characteristic and the value of the reflectance or transmittance at the wavelength into a correspondence relationship between the wave number for each wavelength and the conversion value calculated according to the predetermined relational expression. The steps to create, Obtaining an amplitude value of each wave component included in the wave number distribution characteristic; A second determination step of determining at least the film thickness of the first layer based on a wave component having a large amplitude value included in the wave number distribution characteristic; And a step for selectively validating the first determination step and the second determination step.

Images