TWI454654B - Film thickness measuring device and method for measuring film thickness - Google Patents

Description

Film thickness measuring device and film thickness measuring method

The present invention relates to a film thickness measuring device and a film thickness measuring method, and more particularly to a film thickness measuring structure and method for forming a plurality of layers of a test object formed on a substrate.

In recent years, in order to achieve low power consumption and high speed in a complementary metal oxide semiconductor (CMOS) circuit and the like, a substrate structure of a silicon on insulator (SOI) on an insulating layer has been attracting attention. The SOI substrate is provided with an insulating layer (BOX layer) such as cerium oxide (SiO ₂ ) between two silicon (Si) substrates, so that a PN junction surface formed in one of the germanium layers and another germanium layer ( A parasitic diode (diode) and electrostatic capacitance generated between the substrates can be reduced.

Conventionally, the method for manufacturing the SOI substrate is to form an acidified film on the surface of a silicon wafer, and to adhere to other germanium wafers to sandwich the acidified film, and further, to form circuit components. The wafer is ground to a predetermined thickness.

According to this polishing process, in order to control the thickness of the germanium wafer, it is necessary to continuously monitor the film thickness. The method for measuring the film thickness of the polishing process, that is, the method using Fourier transform infrared spectroscopy (FTIR), is disclosed in Japanese Laid-Open Patent Publication No. Hei 05-306910 and No. Hei 05-308096. . In addition, Japanese Laid-Open Patent Publication No. 2005-19920 discloses a method of measuring a reflection spectrum using a distributed multi-channel spectroscope.

In addition, Japanese Laid-Open Patent Publication No. Hei 10-125634 discloses a measuring method in which an infrared ray from an infrared ray source is irradiated onto a polishing object through a polishing object to detect reflected light.

Further, in Japanese Laid-Open Patent Publication No. 2002-228420, it is disclosed that the infrared ray having a wavelength of 0.9 μm or more is irradiated toward the surface of the ruthenium film, and then the interference result of the reflected light on the surface of the ruthenium film and the reflected light in the ruthenium film is used as a basis. The method for measuring the film thickness of the film.

Further, Japanese Laid-Open Patent Publication No. 2003-114107 discloses an optical interference type film thickness measuring device using infrared rays as measurement light.

However, in the film thickness measuring method disclosed in Japanese Laid-Open Patent Publication No. Hei 05-306910 and No. Hei 05-308096, the film thickness relative value of the sample as a reference cannot be measured, and thus the absolute value of the film thickness cannot be measured. .

In the measurement method disclosed in Japanese Laid-Open Patent Publication No. 2005-19920, it is assumed that the refractive index is a fixed value without depending on the wavelength, and the cycle is estimated based on a self-regression model, however, the actual refraction The rate has a wavelength dependency, so the error due to this wavelength dependency cannot be ruled out. Further, the measurement method disclosed in Japanese Laid-Open Patent Publication No. 2003-114107 has the same problem.

In the measurement method disclosed in Japanese Laid-Open Patent Publication No. 2002-228420, it is necessary to form a through portion on the sample to be measured, and it is not possible to continuously measure the film thickness in a non-destructive manner.

In order to solve this problem, an object of the present invention is to provide a film thickness measuring device and a film thickness measuring method for measuring a film thickness having higher accuracy.

The film thickness measuring device of the present invention includes a light source, a spectrometry portion, a first determining unit, a converting unit, an analyzing unit, and a second determining unit. The light source irradiates the measurement light having a predetermined wavelength range to the object to be tested on which the plurality of layers are formed on the substrate. The object to be tested includes a first layer closest to the light source and a second layer adjacent to the first layer. The spectrometry portion is used to obtain the wavelength distribution characteristic of the reflectance or the transmittance according to the light reflected by the object to be tested or the light penetrating the object to be tested. The first determining unit performs a matching on the wavelength distribution characteristic by using the model formula to determine at least the film thickness of the first layer, and the model has a film thickness of each layer included in the object to be tested. The conversion unit converts the correspondence between the values of the reflectance or the transmittance of each wavelength and wavelength of the wavelength distribution characteristic into a correspondence relationship between the wave number of each wavelength and the converted value calculated according to the predetermined relational expression, and is used to generate Wavenumber distribution characteristics. The analyzing unit is configured to obtain an amplitude value of each wavenumber component included in the wave number distribution characteristic. The second determining unit determines at least the film thickness of the first layer based on the large wave number component of the amplitude value included in the wave number distribution characteristic. Thereafter, the first decision unit and the second decision unit are selectively enabled.

More preferably, the film thickness measuring device further includes a third determining unit that uses the value of the film thickness of the first layer determined by the second determining unit to set a model formula and performs matching on the wavelength distribution characteristic to determine The film thickness of the second layer, wherein the model has a film thickness of each layer included in the object to be tested.

Preferably, the second determining unit is enabled when the adaptation of the first determining unit does not converge within a predetermined number of times.

More preferably, the model includes a wavelength dependent function used to represent the refractive index.

More preferably, the predetermined wavelength range includes the wavelength of the infrared light domain.

More preferably, the parsing unit comprises a Fourier transform unit for performing discrete Fourier transform on the wavenumber distribution characteristics.

More preferably, the analysis unit utilizes an optimization method for obtaining amplitude values of respective wavenumber components included in the wave number distribution characteristic.

On the other hand, the film thickness measuring method of the present invention includes an irradiation step of irradiating the measurement light having a predetermined wavelength range to the object to be tested on which the plurality of layers are formed on the substrate, and the object to be tested includes the first layer closest to the light source. And adjacent to the second layer of the first layer. Further, the film thickness measuring method includes: a wavelength distribution characteristic obtaining step of obtaining a wavelength distribution characteristic of the reflectance or the transmittance according to the light reflected by the object to be tested or the light penetrating the object to be tested; Using a model, the wavelength distribution characteristic is adapted to at least determine the film thickness of the first layer, the model has a film thickness of each layer included in the object to be tested; and the generating step, the wavelength of the wavelength distribution characteristic and The correspondence relationship between the reflectance of the wavelength or the value of the transmittance is converted into a correspondence relationship between the wave number of each wavelength and the converted value calculated according to the predetermined relational expression, for generating the wave number distribution characteristic; the amplitude value obtaining step is used Obtaining an amplitude value of each wavenumber component included in the wave number distribution characteristic; and a second determining step of determining a film thickness of the first layer according to a large wave number component of the amplitude value included in the wave number distribution characteristic; An activation step for selectively making the first decision unit and the second decision unit valid.

According to the present invention, it is possible to measure the film thickness of the test object having higher accuracy.

The above described objects, features and advantages of the present invention will become more apparent from the description of the appended claims.

The preferred embodiments of the present invention are described below in conjunction with the drawings. In the following, the same or similar elements are denoted by the same or similar symbols, and the repeated description is omitted.

Device Architecture

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

The film thickness measuring apparatus 100 of the present embodiment can generally be used for measuring the film thickness of each layer of the test object of a single layer or a laminated structure. The film thickness measuring device 100 of the present embodiment is particularly suitable for film thickness measurement of a test object having a relatively large thickness (usually 2 μm to 1000 μm).

Specifically, the film thickness measuring device 100 is a micro-spectroscopic measuring device that irradiates light onto the object to be tested, and according to the wavelength distribution characteristic of the reflected light reflected by the object to be tested (hereinafter also referred to as "spectrum") It can be used to determine the film thickness constituting each layer of the test object. Furthermore, it is not limited to the measurement of the film thickness, and can also be used for the measurement of the reflectance of each layer (absolute and relative) and the analysis of the layer structure. Further, the spectrum of the light that penetrates the object to be tested (the spectrum of the transmitted light) may be used instead of the spectrum of the reflected light.

In the specification, a case is described in which a substrate or a substrate as a substrate to be tested is formed with one or more layers. In one embodiment, the object to be tested is a substrate having a laminated structure such as a thick substrate of a bismuth (Si) substrate, a glass substrate, and a sapphire substrate, and an SOI substrate. In particular, the film thickness measuring device 100 of the present embodiment is suitable for measuring the thickness of the germanium substrate after the cutting and polishing, the thickness of the germanium layer (active layer) of the SOI substrate, and the chemical mechanical polishing (CMP). Then the substrate film thickness and the like.

Referring to Fig. 1, a film thickness measuring apparatus 100 includes a measuring light source 10, a collimating lens 12, a cutting filter 14, imaging lenses 16 and 36, a diaphragm 18, and a beam splitter 20, and 30. Observation light source 22, optical fiber 24, injection portion 26, pinhole mirror 32, axis conversion mirror 34, observation camera 38, display portion 39, and data processing portion 70 .

In order to obtain the reflectance spectrum of the object to be tested, the measuring light source 10 is a light source for generating light having a predetermined wavelength range, and particularly has a wavelength component in the infrared light field (for example, 900 nm (nano) to 1600 nm, Or a light source of 1470 nm to 1600 nm). A halogen bulb (Halogen lamp) is usually used as the light source 10 for measurement.

The focus lens 12, the filter 14, the imaging lens 16, and the diaphragm 18 are disposed on the optical axis AX2 for connecting the measurement light source 10 and the beam splitter 30, and are optically adjusted to be emitted from the measurement light source 10. Measuring light.

Specifically, the focus lens 12 is an optical light at which the measurement light of the measurement light source 10 is initially incident, and the measurement light that propagates as the diffusion light is refracted into parallel light. The measurement light that has passed through the focus lens 12 is incident on the filter 14. The filter 14 is for blocking unwanted wavelength components in the measurement light. The filter 14 is usually formed of a multilayer film deposited on a glass substrate or the like. To adjust the beam diameter of the measurement light, the imaging lens 16 converts the measurement light that passes through the filter 14 from parallel rays to concentrated rays. The measurement light passing through the imaging lens 16 is incident on the diaphragm 18. The aperture 18 adjusts the amount of light of the measurement light to a predetermined amount for emission to the beam splitter 30. More preferably, the aperture 18 is configured in accordance with the measured light imaging position converted by the imaging lens 16. Further, the aperture amount of the aperture 18 is appropriately set to correspond to the measurement depth of field incident to the object to be tested, the necessary light intensity, and the like.

On the other hand, the observation light source 22 is a light source for generating observation light for focusing the object to be measured and confirming the measurement position. And the observation light generated by the observation light source 22 is selected to include the wavelength at which the object to be detected may be reflected. The observation light source 22 is connected to the emission portion 26 via the optical fiber 24, so that the observation light generated by the observation light source 22 is propagated through the optical fiber 24 as the optical waveguide, and then emitted from the emission portion 26 toward the beam splitter 20.

The emitting portion 26 includes a mask portion 26a for masking a portion of the observation light generated by the observation light source 22 to project a predetermined observation reference image onto the object to be tested. The observation reference image is also easy to focus on an object to be tested (generally a transparent glass substrate or the like) formed without any pattern on the surface. Further, a reticle of any shape can be used, such as a concentric circular shape and a cross-shaped pattern.

In other words, in the beam section of the observation light generated by the observation light source 22, the light intensity (the amount of light) is approximately the same, and a part of the observation light is masked (masked) by the mask portion 26a, which causes the observation light to be observed. An area where the light intensity is about zero (shaded area) is formed on the beam section. The shaded area is projected as an observation reference image on the object to be tested.

The stage 50 is a sample stage on which the object to be tested is placed, and its placement surface is flat. For example, the stage 50 is a mechanically coupled movable mechanism 51 that can be freely driven in three directions (X direction, Y direction, and Z direction). The movable mechanism 51 is generally constituted by a three-axis servo motor and a servo driver for driving each servo motor. Further, the movable mechanism 51 is driven by a user or a control device (not shown) or the like in response to an instruction of the position of the stage. According to the driving of the stage 50, the positional relationship between the object to be tested and the objective lens 40 to be described later is changed.

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

The dichroic mirror 30 reflects the measurement light generated by the measurement light source 10 to convert its propagation direction to the lower side of the paper surface toward the optical axis AX1. Further, the beam splitter 30 penetrates the reflected light of the object to be detected which propagates over the paper surface of the optical axis AX1.

On the other hand, the dichroic mirror 20 reflects the observation light generated by the observation light source 22, and converts the propagation direction to the right of the paper surface toward the optical axis AX2. That is, the beam splitter 30 has a function of a light injection portion for injecting observation light into a predetermined position from the optical source 10 for measurement to the optical path of the objective lens 40 of the light collecting optical system. The measurement light and the observation light synthesized by the beam splitter 20 are reflected by the spectroscope 30 and then incident on the objective lens 40.

In particular, since the measurement light has a wavelength component of the infrared light region and the observation light has a wavelength component of the visible light region, the spectroscopes 20 and 30 can maintain the transmission/reflection characteristics from the visible light region to the infrared region. Target value.

The objective lens 40 is a collecting optical system for collecting the measurement light and the observation light propagating downward under the plane of the optical axis AX1. That is, the objective lens 40 converges the measurement light and the observation light for imaging on the object to be tested or its adjacent position. Further, the objective lens 40 is a magnifying lens having a predetermined magnification (for example, 10 times, 20 times, 30 times, 40 times, etc.). Therefore, the magnifying lens can make the measurement area of the optical characteristics of the measuring light miniaturous compared to the beam cross section incident on the objective lens 40.

In addition, the measurement light and the observation light incident on the object to be tested by the objective lens 40 are reflected by the object to be detected, and propagate toward the upper side of the optical axis AX1. After the reflected light passes through the objective lens 40, it then passes through the beam splitter 30 to reach the pinhole mirror 32.

The pinhole mirror 32 has a function of a light separating portion, and separates the measured reflected light and the observed reflected light from the reflected light generated by the object to be tested. Specifically, the pinhole mirror 32 includes a reflecting surface for reflecting the reflected light from the object to be tested and propagating above the plane of the optical axis AX1, and forming a hole at the center of the intersection of the reflecting surface and the optical axis AX1. Part (pinhole) 32a. The measured reflected light generated after the measurement light of the measuring light source 10 is reflected by the object to be tested is smaller than the diameter of the beam at the position of the pinhole mirror 32, and the diameter of the pinhole 32a formed becomes smaller. . Further, the pinhole mirror 32 is disposed such that the measurement light and the observation light coincide with the imaging position of the measured reflected light and the observed reflected light generated by the object to be detected. In this configuration, the reflected light generated by the object to be tested is incident on the spectrometry portion 60 through the pinhole 32a. On the other hand, the propagation direction of the remaining reflected light is converted to be incident on the axis conversion mirror 34.

The spectrometry portion 60 is for measuring the reflectance spectrum of the reflected light measured by the pinhole mirror 32, and outputs the measurement result to the data processing portion 70. In more detail, the spectrometry portion 60 includes a diffraction grating 62, a detecting portion 64, a filter 66, and a shutter 68.

The filter 66, the shutter 68, and the diffraction grating 62 are disposed on the optical axis AX1. The filter 66 is an optical filter for measuring the reflected light incident on the spectrometry portion 60 through the pinhole 32a, and is used to limit the wavelength component outside the measurement range contained therein, particularly for blocking the measurement range. The wavelength component. The shutter 68 serves to block the light incident on the detecting portion 64 when the detecting portion 64 is reset or the like. Shutter 68 is typically comprised of a mechanically actuated mechanical shutter.

The diffraction grating 62 splits the incident measured reflected light, and then the respective optical waveguides are directed to the detecting portion 64. Specifically, the diffraction grating 62 is a reflective diffraction grating that reflects each of the diffracted waves to a corresponding direction at a predetermined wavelength interval. In the diffraction grating 62 having this configuration, when the reflected wave is incident, the respective wavelength components contained therein are reflected to the corresponding direction, and then incident into the predetermined detection region of the detecting portion 64. Furthermore, the wavelength interval corresponds to the wavelength resolution of the spectrometry portion 60. The diffraction grating 62 is typically composed of a flat focus type spherical grating.

In the measured reflected light split by the diffraction grating 62, an electronic signal corresponding to the light intensity of each wavelength component is outputted by the detecting portion 64 for measuring the reflectance spectrum of the object to be tested. The detecting portion 64 is composed of an indium gallium arsenide (InGaAs) array having infrared light field sensitivity.

The data processing section 70 performs a characteristic procedure relating to the present invention on the reflectance spectrum obtained by the detecting portion 64 for measuring the film thickness of each layer constituting the object to be tested. Furthermore, the data processing portion 70 can also be used to analyze the reflectivity and layer structure of each layer of the object to be tested. Further, the procedure will be described in detail below. Thereafter, the data processing section 70 outputs an optical characteristic including the film thickness of the object to be tested.

On the other hand, the observation reflected light reflected by the pinhole mirror 32 propagates along the optical axis AX1 and then enters the axis conversion mirror 34. The propagation of the reflected light is observed to be converted from the optical axis AX3 to the optical axis AX4. As a result, the reflected light is observed to propagate along the optical axis AX4 and then incident on the observation camera 38.

The observation camera 38 is an image capturing portion for obtaining a reflection image by observing reflected light, and is usually composed of a charge-coupled device (CCD) and a complementary metal oxide semiconductor (CMOS) sensor ( Sensor) composition. Further, the observation camera 38 generally has a visible light range sensitivity, and in many cases, the sensitivity characteristics are different from the detection portion 64 having a sensitivity of a predetermined measurement range. Next, after observing the reflected image obtained by the camera 38 from the reflected light, the corresponding video signal is output to the display portion 39. The display portion 39 displays the reflected image on the screen based on the video signal of the observation camera 38. After the user sees the reflected image displayed on the display portion 39, the focus of the object to be tested and the measurement position are confirmed. The display portion 39 is usually composed of a liquid crystal display (LCD). Furthermore, a finder can be provided to allow the user to directly view the reflected image instead of the observation camera 38 and the display portion 39.

Analytical inspection of reflected light

First, in the case where the measurement light is irradiated to the object to be tested, the observed and reflected light is subjected to physical and physical examination.

Fig. 2 is a cross-sectional view showing an object to be tested OBJ which is a measurement target of the film thickness measuring apparatus 100 according to the embodiment of the present invention.

Referring to Fig. 2, an SOI substrate is taken as a representative example of the object to be tested OBJ. That is, analyte OBJ arranged three-layer structure: silicon (Si) layer 1, the substrate (base) 3 silicon layer (substrate layer) of both the intermediate and the silicon dioxide (SiO ₂₎ layer 2 (BOX layer) . Further, the irradiation light of the film thickness measuring device 100 is incident from the upper side of the paper to the object to be tested OBJ. In other words, the measurement light is incident on the Si layer 1 at the beginning.

For the sake of easy understanding, the measurement light incident on the object to be tested OBJ is then considered to be reflected by the interface between the Si layer 1 and the SiO ₂ layer 2. In the following description, each layer is represented by i. That is, "0" indicates an atmosphere such as air and vacuum, and "1" indicates Si layer 1 of the object to be tested OBJ and SiO ₂ layer 2 indicates "2". In addition to this, the refractive index of each layer is expressed by i, that is, the refractive index n _i .

Since the reflection of light is generated at the interface of each layer having different refractive indices n _i , the amplitude of the P-polarized component and the S-polarized component can be reflected at each interface between the ith layer and the i+1th layer having different refractive indices. Rate (Frensnel coefficient) r ^{( P )} _{i , i +1} and r ^{( S )} _{i , i +1 are} expressed as follows:

Here, φ _i represents the incident angle of the i-th layer. According to the Snell rule described below, the incident angle φ _i can be calculated from the incident angle of the uppermost atmosphere (layer 0):

N ₀ sin φ ₀ = N _i sin φ _i

In the film thickness layer having optical interference, the light reflected by the reflectance shown by the above formula will be reciprocated multiple times in the layer. For this reason, the light directly reflected by the interface of the adjacent layer and the light after the multiple reflection in the layer are different in phase from each other due to the difference in the length of the optical path between the two, and light interference occurs on the surface of the Si layer 1. In order to express this light interference effect in each layer, the optical phase angle β _{i in} the i-th layer can be expressed as follows:

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

For more simplification, when the light is irradiated perpendicularly to the object to be tested OBJ, that is, when the incident angle φ _i =0, there is no difference between the P-polarized light and the S-polarized light, and the amplitude reflectance and the film phase angle of the interface between the layers are different. β _{1 is} as follows:

Further, in the three-layer system shown in Fig. 2, the reflectance R of the object to be tested OBJ is expressed as follows:

In the above formula, a frequency conversion on the phase angle β ₁ (Fourier transform), the phase factors (phase factor) cos2β ₁ in terms of reflectance R is nonlinear. Next, the phase factor cos2β _{1 is} converted into a linear function. In one embodiment, the reflectance R is converted by the following equation and defined as an independent variable "wavenumber converted reflectivity" R ':

among them, Represents the light (electromagnetic waves) in the material, i.e. the inner layer, a wave number K (propagation number) the time of transmission.

The wave number conversion reflectance R ' is a linear expression of the phase factor cos2β ₁ and is therefore linear. Here, R _a represents _a slice of the wave number conversion reflectance R ', and R _b represents a tilt angle of the wave number conversion reflectance R '. In other words, for the phase factor cos2β ₁ related to the frequency conversion, the wavenumber conversion reflectance R ' is a function for linearizing the value of the reflectance R in each wavelength. Furthermore, the function 1/(1- R ) can also be used as a function of the phase factor linearization.

Therefore, the wave number K ₁ in the Si layer 1 can be defined as follows:

Here, when the wavelength λ light velocity in the Si layer 1 is s and the wavelength λ light velocity in the vacuum is c, the refractive index is expressed as n ₁ = c / s . In addition, by using the wave number K ₁ , the angular frequency ω, and the phase δ, the electromagnetic wave E ( x , t ) generated by the light traveling in the x direction in the Si layer 1 can be expressed as E ( x , t ) = E ₀ exp [ ωt - K ₁ x +δ ] . In other words, the propagation characteristics of the electromagnetic waves in the Si layer 1 depend on the wave number K ₁ . Through these relationships, it is known that light having a wavelength λ in a vacuum is lengthened from λ to λ/ n ₁ because its light velocity falls within the layer. Considering this wavelength dispersion phenomenon, the wavenumber conversion reflectivity R ' can be defined as follows:

R ' ( K ₁ ) = R _a + R _b cos2 K ₁ d ₁

By this relationship, when the wave number conversion reflectance R ′ is subjected to frequency conversion (Fourier transformation) related to the wave number K , the peak appearing in the periodic component corresponding to the film thickness d ₁ is used to specify the peak The position of the peak is such that the film thickness d ₁ can be calculated.

In other words, the correspondence between the reflectance spectrum measured by the analyte OBJ and the reflectance of each wavelength is converted into the correspondence between the wave number calculated for each wavelength and the wave number conversion reflectance R ′ calculated by the above relational expression. after relationship, including the wave number of the wave number K of conversion reflectance R 'function associated with the wave number K of frequency conversion, then, according to the characteristics of the peaks that appear in the frequency conversion, it is possible to calculate the analyte configured OBJ The film thickness of the Si layer 1 is. This is because the amplitude value of each wavenumber component included in the wave number distribution characteristic is obtained, and then the film thickness of the Si layer 1 is calculated based on the large wavenumber component of the amplitude value. Furthermore, as described below, it is possible to use a method of discrete Fourier transform such as fast Fourier transform (FFT) or an optimization method using a maximum entropy method (hereinafter also referred to as "MEM"). For analyzing the large wavenumber component of the amplitude value from the wave number distribution characteristics.

In the definition of the wavenumber conversion reflectivity R ', R _a and R _b are the values of the interference phenomenon in the unrelated layer, but depend on the amplitude of the refractive index n ₁ of the Si layer 1 in the interface between the layers. Reflectivity. For this reason, when the refractive index n ₁ has a wavelength dispersion, the value is a function value depending on the wavelength (that is, the wave number K ), and therefore, it is related to the wave number K and cannot be a constant value. So, to In the Fourier transform, R ', R _a , R _b and cos2 K ₁ d ₁ are Fourier transformed with the wave number K , and the power spectrum as a function is set to P, P _a , P _b and F, then the following formula is established:

Where * indicates a convolution.

In the formula, the composition depending on the film thickness of P _a is relatively small, and the power spectrum F has independent peaks, so that it does not affect the power spectrum F.

On the other hand, since P _b in the formula is _decomposed with the power spectrum F, the film thickness component of P _b is modulated into the film thickness component of the power spectrum F. However, P _b is independent of the intra-layer interference phenomenon because it is only affected by the wavelength dependence of the refractive index in the adjacent two layers. For the wave number K, the film thickness component of P _b is thinner than the film thickness component of the power spectrum F. Can be ignored to a lesser extent. For example, R _{b is} used as a periodic function of the film thickness q, and the P _b after the Fourier transform is modulated into the film thickness component of the power spectrum F. Therefore, the peak displayed by the spectrum will be “dq”. 』 or 『d+q』, and since the q value is very small, the influence on the peak position d is small.

Further, when the Fourier transform is performed, the maximum film thickness of the measurement target layer is considered as follows, and the wave number conversion reflectance R ' is sampled at an appropriate sampling interval and number of samples according to the Nyquist sampling theorem. The wave-number converted reflectance R ′ sampled by this method is smaller than the film thickness resolution r of the calculated power spectrum, and the film thickness component q of P _b may be smaller (q<r), so that it can be said that it hardly It affects the measurement result of the film thickness d.

In this way, the calculated reflectance spectrum is converted to a function related to the wave number. Considering the wavelength dispersion of the film, the Fourier transform is performed, and the film thickness of the film can be accurately calculated.

Furthermore, in the above description, the reflectance spectrum is used, but the transmittance spectrum may also be utilized. Under this case, T represents the transmittance measured for T 'represents a "wave number conversion penetration", and the relationship is expressed as follows:

Even with the transmittance spectrum, the transmittance T is non-linear with respect to the phase factor cos2β ₁ . For this reason, for the above reasons, it is related to the phase factor cos2β ₁ and is a linear wave number conversion transmittance T '. According to the above formula, the number of wave conversion transmittance T 'is a phase factor cos2β ₁ of the formula, using the same manner as described above, it is possible to correct the film thickness of the film was calculated. That is, for the phase factor cos2β ₁ related to frequency conversion, the wavenumber conversion transmittance T ′ is a function for linearizing the transmittance values of the respective wavelengths.

Referring again to Fig. 2, the reflected light generated after the interface between the SiO ₂ layer 2 and the substrate 矽 layer 3 is reflected. When n ₁ represents the refractive index of the Si layer 1, d ₁ represents the film thickness, n ₂ represents the refractive index of the SiO ₂ layer 2, and d ₂ represents the film thickness, the wave number conversion reflectance R ' can be expressed as follows:

R '= Ra + Rb cos2 K ₁ d ₁ + Rc cos2 K ₂ d ₂ + Rd cos2 ( K ₁ d ₁ + K ₂ d ₂ ) + Re cos2 ( K ₁ d ₁ - K ₂ d ₂ )

Here, the wave number conversion reflectance converted by the wave numbers K ₁ and K ₂ , respectively, is used. ( K ₁ ) and (K _2), for separating and calculates the film thickness d of the thickness of the Si layer ₁₁ and SiO ₂ layer 2 of d _2. Specifically, as follows:

In these formulas, although Management Not the correct film thickness, however, wavenumber conversion reflectivity In the power spectrum corresponding to the second term of ( K ₁ ) , the original film thickness d ₁ can be obtained from the peak, and the wave number conversion reflectance In the power spectrum corresponding to the third term of ( K ₂ ) , the original film thickness d ₂ can be obtained from the peak.

Further, in actuality, the refractive indices of the Si layer 1 and the SiO ₂ layer 2 are similar, and in many cases, the reflectance at the interface is relatively small compared to the reflectance at other interfaces. As a result, the values of R _b and R _d and R _c included in the function of the wavenumber conversion reflectance are small, and therefore, in many cases, it is difficult to confirm the wave number conversion reflectance from the power spectrum. The peak corresponding to the third term of ( K ₂ ) . In this case, first calculate the wave number conversion reflectivity The peak position of the power spectrum corresponding to the fourth term of ( K ₂ ) ( + d ₂ ), and wave number conversion reflectivity The peak position of the power spectrum corresponding to the second term of ( K ₂ ) ( Then, after obtaining the difference between the two, the film thickness d ₂ can be calculated.

"About wavelength range and wavelength resolution"

Fig. 3 is a view showing the measurement results of the SOI substrate measured by the film thickness measuring apparatus 100 of the embodiment of the present invention. Further, in the measurement example shown in Fig. 3, in the case of the third (a) diagram, the wavelength of the measurement light is in the range of 900 nm to 1600 nm, and in the case of the third (b) diagram, the wavelength range is 1340 nm. 1600nm. Further, corresponding to the measurement wavelength, the diffraction grating 62 having an appropriate characteristic is selected such that the number of detection points (the number of detection channels) of the detection portion 64 are the same after the reflected light is incident on the detection portion 64 (for example, 512) Channels). In other words, the narrower the wavelength range, the smaller the wavelength interval (i.e., wavelength resolution) of each detected number of points.

According to the aforementioned analytical test, the measured reflectance should have a periodic change with respect to the wavelength.

In the measurement results shown in Fig. 3(a), although it can be seen that the reflectance has a periodic change with respect to the wavelength, a very accurate film thickness measurement cannot be obtained.

In this regard, in the measurement results shown in Fig. 3(b), the peaks and valleys of the reflectance are clearly displayed, and the period of change in the reflectance can also be measured. Fig. 3(c) is a diagram showing the measurement result (reflectance spectrum) shown in Fig. 3(b) converted to the function of the wave number conversion reflectance R ' to display the frequency associated with the wave number K. Conversion result. As shown in FIG. 3, the value corresponding to the main peak can be used as the film thickness of the Si layer 1.

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

Fig. 4 is a view showing another measurement result after the SOI substrate is measured by the film thickness measuring apparatus 100 of the embodiment of the present invention. In the measurement example of Fig. 4, the film thickness of the Si layer 1 was 10.0 μm (design value), and the film thickness of the SiO ₂ layer 2 was 0.3 μm (design value). Further, in the fourth (a) diagram, the measurement light having a wavelength component having a visible light range (330 nm to 1100 nm) is used, and in the fourth (b) diagram, the infrared light domain (900 nm to 1600 nm) is used. ) Measurement of wavelength components. Furthermore, as described above, the number of detection points (the number of detection channels) of the detection portion 64 (Fig. 1) is the same.

As shown in Fig. 4(a), when the measurement light having the wavelength component of the visible light region is used, the periodic variation of the reflectance is exhibited in the wavelength region larger than 860 nm, but in the shorter visible light region, It can be seen that there is no obvious cyclical change. On the other hand, as shown in Fig. 4(b), when the measurement light having the wavelength component of the infrared light region is used, it is known that a significant change in the periodicity of the reflectance occurs.

Fig. 5 is a view showing another measurement result after the SOI substrate is measured by the film thickness measuring apparatus 100 of the embodiment of the present invention. In the measurement example of Fig. 5, the film thickness of the Si layer 1 was 80.0 μm (design value), and the film thickness of the SiO ₂ layer 2 was 0.1 μm (design value). Further, in the fifth (a) diagram, measurement light having a wavelength component having an infrared light field (900 nm to 1600 nm) is used, and in the fifth (b) diagram, it is shown that a light source having a narrower infrared light is used ( 1470nm~1600nm) Measurement of wavelength components. Furthermore, as described above, the number of detection points (the number of detection channels) of the detection portion 64 (Fig. 1) is the same.

As shown in Fig. 5(a), even when the measurement light having the wavelength component of the infrared light region is used, the measured reflectance does not show a significant periodic change. In contrast, as shown in Fig. 5(b), when the measurement light having a narrower infrared wavelength region is used, it is known that a significant change in the periodicity of the reflectance occurs.

According to the above measurement examples, in order to measure the film thickness of the thick layer with high accuracy, it is necessary to appropriately set the wavelength range and wavelength resolution of the measurement light. Since this is a measurement method using the intra-layer light interference object, and the wavelength resolution of the detection portion 64 for the reflected light is limited, a more appropriate measurement light wavelength can be set according to the method described below.

In the following inspection, the lower limit of the wavelength detection of the detecting portion 64 is λ _min , and the upper limit of the wavelength detecting portion of the detecting portion 64 is λ _max . Further, the range of the measurement light wavelength to be irradiated by the measurement light source 10 (Fig. 1) may be any range if the wavelength detection range of the detection portion 64 is included. Further, the number of detection points (the number of detected channels) of the detection portion 64 (Fig. 1) is S _p .

Fig. 6 is a schematic view for explaining the film thickness measurement range and the detection wavelength range of the detecting portion 64 according to the embodiment of the present invention, and the relationship with the number of detection points.

(1) below the measurement range limit of the film thickness d _min relationship detection wavelength range.

According to the film thickness measuring method described above, since it is necessary to find the wavelength of the light interference generated in the object to be tested as the object, the detecting portion 64 is required to have a wavelength range capable of generating light interference. That is, as shown in Fig. 6(a), in the detection wavelength range of the detecting portion 64, the reflectance waveform measured by the object to be tested needs to have a change of more than one cycle.

This is because the detection wavelength range of the detecting portion 64 is changed from the lower limit value λ _{min to the} upper limit value λ _max , which means that the change in the generated optical distance is sufficient for the film thickness of the object to be tested to go back and forth.

Thus, the relationship between the wavelength measurement light value d _min and the film thickness under the scope of the measurement range must meet the following conditions of formula (1):

Wherein n _min represents the refractive index of the wavelength λ _min and n _max represents the refractive index of the wavelength λ _max .

(2) The relationship between the upper limit d _{max of the} film thickness measurement range and the number of detection points.

As shown in Fig. 6(b), the longer the wavelength of the measurement light is, the longer the period of the reflectance waveform measured by the object to be tested is. The reflectance waveform shown in Fig. 6(c) is a coordinate obtained by converting the reflectance waveform shown in Fig. 6(b) into a wave number (1/f). In this case, the array elements such as InGaAs are arranged at equal intervals for the wavelength. As a result, the smaller the wave number, the larger the arrangement interval of the array elements corresponding to the wave number is.

Therefore, in order to correctly sample the reflectance waveform corresponding to the wave number and change with a predetermined period, the arrangement interval (wavelength resolution Δλ) of each array element needs to satisfy the Nyquist sampling theorem, by satisfying the sampling theorem, The upper limit d _{max of the} film thickness measurement range is determined.

The detecting section 64 wavelength resolution △ λ, using detection points (detection channel number) S _p, can be expressed as _{△ λ = (λ max -λ min} ) / S p.

Since the longer the wavelength of the measurement light is, the shorter the period of the reflectance waveform is. Therefore, in the reflectance waveform, the extreme value (peak or valley) of the optical upper limit value λ _{max is} measured. when the wavelength of the generated extrema adjacent extreme value indicates the following conditions between the above, the film thickness measurement limit of the range d _max λ ₁ must satisfy:

Here, when the film thickness of the measurement target layer is large, n _max ≒ n ₁ can be assumed, and therefore, the above condition is expressed as the following conditional expression (2):

At this time, the wavelength resolution Δλ needs to satisfy the following conditions:

The relational expression of the upper limit value d _max is substituted into the relational expression of the above-described wavelength resolution Δλ, and after λ _{1 is} eliminated, the following conditional expression (3) can be expressed:

The above is the result of the inspection. If the film thickness measurement range (lower limit d _min to upper limit d _max ) required for the test object is to be determined in advance, it is necessary to determine the conditional expressions (1) and (2) above. The wavelength range of the light (lower limit value λ _min ~ upper limit value λ _max ) and the number of detection points S _{p are} measured.

Calculation Example

In the SOI substrate shown in Fig. 2, when the film thickness of the Si layer 1 is measured, the calculation of the necessary conditions will be described below.

In this calculation example, the upper limit d _max of the Si layer 1 of the SOI substrate was 100 μm, and the refractive index was constant (n=3.5) without depending on the wavelength. Furthermore, in this calculation example, the lower limit d _min of the Si layer 1 of the SOI substrate is not considered.

By substituting the above-mentioned set values into the above conditional expressions (2) and (3), the upper limit λ _max = 1424.0 nm can be calculated, and the wavelength resolution Δλ = 1.445375 nm. Therefore, when the detecting portion 64 having 512 channels is used for measuring the film thickness of the object to be tested having a maximum film thickness of 100 μm, if the measuring light used covers a wavelength range of about 684 to 1424 nm, the detecting portion can be used. Part 64 detects the reflected light in this range (wavelength resolution Δλ = 1.4453125 nm).

The wavelength resolution Δλ calculated based on the above conditional expression is used to explain the theoretical minimum specification. When actually measuring, it is better to improve the accuracy than the calculated wavelength resolution Δλ. degree. Furthermore, it is preferably several times (for example, 2 to 4 times). Furthermore, increasing the accuracy means setting the value of the wavelength resolution Δλ to be smaller.

That is to say, in the actual film thickness measuring device, the influence of the incident light angle of the object to be tested and the influence of the opening angle when using the lens collecting system cause a decrease in spectral accuracy. In this case, the peak height in the power spectrum becomes small, and it becomes difficult to calculate the film thickness. Furthermore, when a discrete frequency conversion is performed by a FFT or the like with a limited sampling value, the conversion error caused by the wave number conversion is also increased by the influence of aliasing. Further, the dispersion of the refractive index of the test object may also vary drastically due to the wavelength range of the measurement light, or some conditions may not be satisfied.

Fig. 7 is a view showing a simulation result of a measurement result using a film thickness measuring device having a wavelength resolution close to a theoretical value. Fig. 8 is a view showing a simulation result of a measurement result using a film thickness measuring device having a wavelength resolution and a precision higher than a theoretical value twice. Further, the film thickness of the object to be tested as a target was 100 μm.

More specifically, in the seventh (a) diagram, the result of measuring the reflectance spectrum (wavelength resolution Δλ=2.734375 nm) in the range of 900 nm to 1600 nm by the detecting portion 64 having 512 channels is shown. In Fig. 7(b), the power spectrum after frequency conversion of the reflectance spectrum shown in Fig. 7(a) (here, FFT conversion) is shown. As shown in Fig. 7(b), in this case, although a peak exists in the vicinity of 100 μm, the level is small compared with the noise (ghost) on the film side, and it is difficult to determine the film thickness.

On the other hand, in the eighth (a) diagram, the measurement result of the wavelength range of the detection portion 64 is determined to be twice the theoretical value, and in the eighth (b). In the figure, the power spectrum after frequency conversion of the reflectance spectrum shown in Fig. 8(a) (here, FFT conversion) is shown. In this embodiment, the number of detection points and the wavelength range are determined so that the wavelength resolution Δλ of the detecting portion 64 becomes 1.3671875 nm. As shown in Fig. 8(b), in this case, an extremely strong peak appears in the vicinity of the film thickness of 100 μm, which means that the film thickness of the test object can be accurately measured.

"Overview of the film thickness calculation program"

As described above, the film thickness of the object to be tested can be calculated from the periodicity of the reflectance spectrum. In other words, the detected reflectance spectrum is frequency-converted to obtain the power spectrum, and the peak appearing in the power spectrum can be used to calculate the film thickness. In fact, this power spectrum is obtained by a discrete Fourier transform method such as FFT. However, there is also a case where the FFT cannot be used to obtain a power spectrum that fully reflects the periodicity. For this reason, the film thickness measuring apparatus 100 of the present embodiment can perform a method of optimizing the MEM or the like as a method of calculating the power spectrum, in addition to discrete Fourier transform such as FFT. That is, the film thickness measuring apparatus 100 of the present embodiment performs a Fourier transform and optimization method selectively or in combination corresponding to the detected reflectance spectrum. Furthermore, the details of the MEM program are detailed in "Microcomputer/Personal Computer Usage Technology for Waveform Data Processing and Measurement System for Scientific Measurement" edited by Minami Shigeo, 10th edition, August 1992 Issued on the 1st, CQ Press, is hereby incorporated by reference.

Further, in the film thickness measuring apparatus 100 of the present embodiment, in addition to the film thickness is analytically calculated from the above-described detected reflectance spectrum, the reflection can be theoretically calculated by the physical model calculated by the measurement target. After the rate spectrum, the reflectance spectrum actually detected is compared, and the optical characteristic value of the measurement target is exploratoryly calculated based on the deviation value between the two, that is, a so-called fitting method is performed.

Further, in the SOI substrate shown in FIG. 2, the film thickness of the first Si layer 1 is two or more digits than that of the second SiO ₂ layer 2, and the object to be tested is used. It is also impossible to calculate the film thickness of each layer with sufficient accuracy by the fitting method.

Fig. 9 is a view showing the measurement results of the reflectance spectrum associated with the SOI substrate. In the measurement example of Fig. 9, the film thickness of the first Si layer 1 was 100 μm, and the film thickness of the second SiO ₂ layer 2 was 0.48 μm to 0.52 μm, and was changed at intervals of 0.1 μm. As shown in Fig. 9, even if the film thickness of the second SiO ₂ layer 2 is changed, the measured reflectance spectrum does not change too much. In other words, since the reflectance spectrum measured from this analyte is mainly affected by the first Si layer 1, it means that even if the parameters of the second SiO ₂ layer 2 are changed, it cannot be fully performed. Fit.

Next, for a sample having a different complex layer, such as an SOI substrate or the like, the film thickness measuring apparatus 100 of the present embodiment performs one of the above-described Fourier transform, optimization method, and fitting method, or appropriately combined, It is used to separate the thickness of each layer and can be correctly analyzed. Hereinafter, details of the film thickness calculation program of the film thickness measuring device 100 in the present embodiment will be described. Furthermore, the film thickness calculation program is executed by the data processing portion 70 (Fig. 1).

"Structure of Data Processing Part"

Figure 10 is a diagram showing a schematic hardware architecture of a data processing portion 70 in accordance with an embodiment of the present invention.

Referring to FIG. 10, a data processing portion 70 is generally implemented by a computer, including: a central processing unit (CPU) 200 for executing various programs including an operating system (OS); a memory portion 212 For temporarily storing the necessary data when the CPU 200 executes the program; and a hard disk drive (HDD) 210 for non-volatile storage of the program executed by the CPU 200. Further, in the hard disk portion 210, a program for realizing a program to be described later is stored in advance, and the program is respectively transmitted through a floppy disk drive (FDD) 216 or a CD-ROM drive 214. The floppy disk 216a or the compact disk-read only memory (CD-ROM) 214a is read.

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

Calculation Program Structure

The data processing part 70 of the embodiment corresponds to the type and quantity of unknown values in the parameters (material, film thickness, film thickness range, refractive index, de- fading coefficient, etc.) of the object to be tested, and the resolution precision, etc. Select one of the program patterns 1 to 6 shown below to execute. In the following description, the SOI substrate shown in Fig. 2 is an example in which the film thickness of each of the two layers is independently calculated. However, the same method can be used to independently calculate the film of each of the layers. thick.

(1) Program type 1

The program pattern 1 is a film thickness calculation program that can be performed when the refractive index and the attenuation coefficient of the first layer and the second layer are known. In this procedure 1, the film thickness of each layer was determined by the fitting method. Furthermore, in one embodiment, a least squares method can generally be utilized as the adaptation method.

Figure 11 is a block diagram showing the control structure for executing the film thickness calculation program associated with the program pattern 1 according to an embodiment of the present invention. In the block diagram shown in Fig. 11, the CPU 200 reads out the program previously stored in the hard disk portion 210 and the like to the memory portion 212, and then executes it.

Referring to Fig. 11, the data processing section 70 (Fig. 1) includes a buffer portion 71, a model portion 721, and a fitting portion 722.

The buffer portion 71 is configured to temporarily store the measured reflectance spectrum R(λ) output by the spectrometry portion 60. More specifically, the spectrometry portion 60 outputs the value of the reflectance according to each of the predetermined wavelength resolutions. Therefore, the buffer portion 71 stores the wavelength and the reflectance of the wavelength correspondingly.

The modeling portion 721 receives parameters related to the object to be tested, determines a model (function) for indicating the theoretical reflectance of the object to be tested according to the received parameters, and then calculates a theoretical reflection of each wavelength by using the determined function. Rate (spectrum). The calculated theoretical reflectance of each wavelength is output to the fitting portion 722. More specifically, the modeled portion 721 receives the refractive index n _{1 of the} first layer and the attenuation coefficient k ₁ , and the refractive index n ₂ and the attenuation coefficient k _{2 of} the second layer, and simultaneously receives the film thickness of the first layer. d ₁ initial value and film thickness d ₂ initial value of the second layer. Furthermore, the parameters may be input by the user, or the parameters of the standard material may be stored in advance as files, and then read if necessary. Further, if necessary, the refractive index n _{0 of the} atmosphere and the attenuation coefficient k ₀ may be input.

The model for displaying the theoretical reflectance is the same as the reflectance of the object to be tested OBJ of the above three-layer system, and is a function including at least the film thickness value of each layer.

Furthermore, the modeled portion 721 updates the function of displaying the theoretical reflectance according to the parameter update command of the matching portion 722 described below, and then calculates the theoretical reflectance of each wavelength according to the updated function ( Spectrum). More specifically, the modeled portion 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 adaptive portion 722 reads the measured value of the reflectance spectrum of the buffer portion 71, and then uses the theoretical value of the reflectance spectrum outputted by the modeled portion 721 to sequentially calculate the squared deviation value of each wavelength between the two. Next, the fitting portion 722 calculates a residual from the deviation value of each wavelength, and then determines whether the residual is below a predetermined critical value. That is, the matching portion 722 determines whether the current parameter is convergence.

When the residual is not below the predetermined threshold, the adaptation portion 722 transmits a parameter update command to the modeled portion 721 and then waits until the new reflectance spectrum is output. On the other hand, when the residual is below a predetermined critical 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 as analytical values.

Figure 12 is a flow chart showing the method of calculating the film thickness associated with the program type 1 according to the embodiment of the present invention.

Referring to Fig. 12, the user places the object to be tested (sample) on the stage 50 (Fig. 1) (step S100). Thereafter, when the user issues a measurement preparation command, the observation light source (Fig. 1) starts irradiation of the observation light. The user refers to the reflected image obtained by the observation camera 38 and displays it on the display portion 39, and issues the stage position command to the movable mechanism 51 for adjusting the measurement range and focusing (step S102).

After the adjustment of the measurement range and the focus are completed, the user issues a measurement start command, and the measurement light source 10 (Fig. 1) starts generating measurement light. The spectrometry portion 60 receives the reflected light of the object to be tested, and outputs a reflectance spectrum based on the reflected light to the data processing portion 70 (step S104). Next, the CPU 200 of the data processing section 70 temporarily stores the reflectance spectrum detected by the spectroscopic measurement section 60 in the spectrometry section 60 or the like (step S106). The CPU 200 of the data processing section 70 executes the film thickness calculation program described below.

The CPU 200 displays the input screen on the display portion 204 (Fig. 10) or the like, and requests the user to input parameters (step S108). The user inputs the refractive index n ₁ and the attenuation coefficient k ₁ of the first layer of the object to be tested, and the refractive index n ₂ and the attenuation coefficient k ₂ of the second layer of the object to be tested according to the input screen displayed, etc., The film thickness d _{1 of the} first layer and the film thickness d ₂ initial value of the second layer are input (step S110).

Further, the CPU 200 calculates a theoretical value of the reflectance spectrum based on the parameter input by the user (step S112). Next, for the measured value of the reflectance spectrum and the theoretical value of the reflectance spectrum stored in the memory portion 212 and the like, the CPU 200 sequentially calculates the squared deviation value of each wavelength between the two to calculate the residual between the two. Poor (step S114). Further, the CPU 200 determines whether or not the calculated residual is equal to or lower than a predetermined threshold (step S116).

When the calculated residual is not equal to or less than the predetermined threshold (in the case of NO in step S116), the CPU 200 changes the current value of the film thickness d _{1 of the} first layer and the film thickness d ₂ of the second layer (step S118). Further, the extent to which the film thickness d ₁ and the film thickness d _{2 are} to be changed depends on the degree of occurrence of the residual. After that, it returns to step S112 of the program.

In contrast, when the calculated residual in the case where the predetermined threshold value (the case of YES in step S116), CPU 200 the film thicknesses d of the first layer of the layers ₁ and d 2 to be used as the present value of ₂ The film thickness (analytical value) of each layer of the object is measured and output (step S120). After that, the program ends.

Furthermore, in the block diagram shown in FIG. 11, although the refractive indices n ₁ and n ₂ and the de-attenuation coefficients k ₁ and k ₂ are input at a fixed value, it is also possible to use a refractive index and a de-fading in consideration of wavelength dispersion. coefficient. For example, the following Cauchy model can be used as the refractive index and attenuation factor considering wavelength dispersion:

Where a , b , c , d , e , f represent the correlation coefficients in each layer.

When the formula is used, the coefficients in the formula can also be input with preset initial values or known values, and these coefficients can also be used as suitable objects.

Alternatively, you can use the Sellmeier model described below:

Where f , g , h are the Sellmeier coefficients and λ is the wavelength.

(2) Program type 2

The program pattern 2 is a film thickness calculation program that can be performed when the refractive index and the attenuation coefficient of the first layer and the second layer are known. In the procedure pattern 2, the film thickness of each layer was determined by a suitable method. Frequency conversion is performed by discrete Fourier transform to obtain a first layer having a large film thickness, and the film thickness of the first layer is a fixed value, and the film thickness of the second layer is determined by a fitting method. Furthermore, in one embodiment, a least squares method can generally be utilized as the adaptation method.

Figure 13 is a block diagram showing the control structure for executing the film thickness calculation program associated with the program pattern 2 according to an embodiment of the present invention. In the block diagram shown in Fig. 13, the CPU 200 reads out the program previously stored in the hard disk portion 210 and the like to the memory portion 212, and then executes it.

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

The buffer portion 71 is configured to temporarily store the measured reflectance spectrum R(λ) output by the spectrometry portion 60. Furthermore, the specific architecture and processing content have been described above in detail, and are not described herein.

The wave number conversion portion 731 receives the parameters of the first layer (the refractive index n ₁ and the attenuation coefficient k ₁ ), and waves the reflectance spectrum R(λ) temporarily stored in the buffer portion 71 based on the received parameters. Number conversion. In other words, the wave number conversion portion 731 converts the correspondence between each wavelength in the reflectance spectrum R(λ) and the reflectance of each wavelength into the wave number K ₁ (λ) associated with each wavelength and uses the above relationship Calculated wave number conversion reflectivity Correspondence. More specifically, for each wavelength stored in the buffer portion 71, the wave number conversion portion 731 sequentially calculates the wave number K ₁ (λ) and the wave number conversion reflectance. (λ) (= R (λ ) / (1- R (λ))), then the output part 732 to the buffer.

The buffer portion 732 outputs the wave number K ₁ (λ) and the wave number conversion reflectance sequentially in the wave number conversion portion 731. (λ) corresponds to storage. That is, the wave number conversion reflectance of the wave number conversion reflectance associated with the wave number K ₁ (λ), that is, the wave number conversion reflectance ( K ₁ ) is stored in the buffer portion 732.

The Fourier transform portion 733 converts the wavenumber converted reflectance stored in the buffer portion 732 ( K ₁ ) , a Fourier transform associated with the wave number K _{1 is} performed to calculate the power spectrum P ₁ . Furthermore, Fast Fourier Transform (FFT) and Discrete Cosine Transform (DCT) can be utilized as the method of Fourier transform.

The peak search portion 734 searches for the peak appearing in the power spectrum P ₁ calculated by the Fourier transform portion 733, and obtains the film thickness corresponding to the peak, and outputs it as the film thickness of the first layer.

The modeling part 735 receives parameters related to the object to be tested, determines a model (function) for expressing the theoretical reflectance of the object to be tested according to the received parameters, and then calculates a theoretical reflection of each wavelength by using the determined function. Rate (spectrum). The calculated theoretical reflectance of each wavelength is output to the fitting portion 736. More specifically, the modeling portion 735 receives the film thickness d _{1 of the} first layer and the refractive index n ₂ and the attenuation coefficient k _{2 of} the second layer output from the peak search portion 734, and receives the second layer. The film thickness d ₂ initial value. Furthermore, the parameters may be input by the user, or the parameters of the standard material may be stored in advance as files, and then read if necessary. The model for displaying the theoretical reflectance is the same as the reflectance of the object to be tested OBJ of the above three-layer system, and is a function including at least the film thickness value of each layer.

Furthermore, the modeling portion 735 updates the function of displaying the theoretical reflectance according to the parameter update instruction of the matching portion 736, and then calculates the theoretical reflectance (spectrum) of each wavelength according to the updated function. . More specifically, the modeled portion 735 sequentially updates the film thickness d ₂ of the second layer as a parameter.

The adaptive portion 736 reads the measured value of the reflectance spectrum of the buffer portion 71, and then uses the theoretical value of the reflectance spectrum outputted by the modeled portion 735 to sequentially calculate the squared deviation value of each wavelength between the two. Next, the fitting portion 736 calculates a residual from the deviation value of each wavelength, and then determines whether the residual is below a predetermined critical value. That is, the matching portion 736 determines whether the current parameter is convergence.

When the residual is not below the predetermined threshold, the adaptation portion 736 transmits a parameter update command to the modeled portion 735 and then waits until the new reflectance spectrum is output. On the other hand, when the residual is below a predetermined critical value, the fitting portion 736 outputs the film thickness d _{1 of the} first layer and the film thickness d _{2 of the} second layer as analytical values.

Figure 14 is a flow chart showing the method of calculating the film thickness associated with the program type 2 according to the embodiment of the present invention. In the steps of the flowchart shown in FIG. 14, the procedures of steps S100 to S108 and the flowcharts shown in FIG. 12 are denoted by the same reference numerals, and the detailed description thereof will not be repeated. Hereinafter, the film thickness calculation program after step S132 will be described with respect to the difference from the flowchart shown in Fig. 12.

In step S132, the user inputs the refractive index n ₁ and the attenuation coefficient k ₁ of the first layer of the object to be tested, and the refractive index n ₂ and the attenuation coefficient of the second layer of the object to be tested according to the displayed input screen or the like. k _2, while the thickness of the input layer 2 d ₂ of the second initial value.

Then, the CPU 200 performs wave number conversion on the reflectance spectrum stored in the memory portion 212 or the like based on the input refractive index n ₁ of the first layer and the attenuation coefficient k ₁ (step S134). Next, the wave number conversion reflectance obtained after the wave number conversion is stored in the memory portion 212 and the like (step S136). Further, the CPU 200 performs Fourier transform on the wave number conversion reflectance in association with the wave number K ₁ to calculate a power spectrum (step S138). Further, the CPU 200 obtains the peak appearing in the power spectrum and the film thickness corresponding to the peak, and outputs it as the film thickness d _{1 of the} first layer (step S140).

Next, the CPU 200 calculates a theoretical value of the reflectance spectrum based on the film thickness d ₁ of the first layer obtained in step S210 and the second layer parameter input by the user (step S142). Next, for the measured value of the reflectance spectrum and the theoretical value of the reflectance spectrum stored in the memory portion 212 and the like, the CPU 200 sequentially calculates the squared deviation value of each wavelength between the two to calculate the residual between the two. Poor (step S144). Further, the CPU 200 determines whether or not the calculated residual is equal to or lower than a predetermined threshold (step S146).

When the calculated residual is not below the predetermined threshold (in the case of NO in step S146), the CPU 200 changes the current value of the film thickness d ₂ of the second layer (step S148). Furthermore, the extent to which the film thickness d _{2 is} to be changed depends on the degree of occurrence of the residual. After that, it returns to step S142 of the program.

On the other hand, when the calculated residual is equal to or less than the predetermined threshold (in the case of YES in step S146), the CPU 200 treats the current value of the film thickness d _{1 of the} first layer and the film thickness d ₂ of the second layer as The film thickness (analytical value) of each layer of the object is measured and output (step S150). After that, the program ends.

Further, similarly to the above-described program pattern 1, it is also possible to use a refractive index and a decay coefficient in consideration of wavelength dispersion. The detailed function has been explained above and will not be described here.

(3) Program type 3

The program pattern 3 is a film thickness calculation program that can be performed when the refractive index and the attenuation coefficient of the first layer and the second layer are known. In the program pattern 3, the difference from the above-described program pattern 2 is that when the film thickness of the first layer is calculated, the Fourier transform is not performed, and the method of optimization is used. The other procedures are the same as the above-described program type 2.

Fig. 15 is a block diagram showing a control structure for executing a film thickness calculation program relating to the program pattern 3 according to an embodiment of the present invention. In the block diagram shown in Fig. 15, the CPU 200 reads out the program previously stored in the hard disk portion 210 and the like to the memory portion 212, and then executes it.

Referring to Fig. 15, the data processing section 70 (Fig. 1) includes a buffer section 71, an optimization calculation section 741, a modeling section 742, and an adaptation section 743.

The buffer portion 71 is configured to temporarily store the measured reflectance spectrum R(λ) output by the spectrometry portion 60. Furthermore, the specific architecture and processing content have been described above in detail, and are not described herein.

The optimization calculation section 741 analyzes the frequency component of the reflectance spectrum stored in the buffer section 71 by the optimization method of MEM or the like to calculate the film thickness d _{1 of the} first layer. More specifically, the optimization calculation section 741 utilizes a self-regression model for obtaining a self-correlation function relative to the measured value of the reflectance spectrum, and determines the self-regression coefficient used to describe the self-regression model from these values. The optimization calculation section 741 performs frequency analysis in this manner to obtain a film thickness corresponding to the wavelength of the principal component, and outputs it as the film thickness d _{1 of the} first layer. Further, before the method of optimizing is performed, the optimization calculation section 741 receives the search range of the film thickness d ₁ of the first layer, the refractive index n _{1 of the} first layer, the attenuation coefficient k ₁ , and the second The refractive index n _{2 of the} layer and the attenuation coefficient k _{2 are} simultaneously received at the film thickness d _{2 of} the second layer. Furthermore, the parameters may be input by the user, or the parameters of the standard material may be stored in advance as files, and then read if necessary.

The modeled portion 742 and the matching portion 743 receive the film thickness d ₁ of the first layer calculated by the optimization calculation portion 741 and the parameters related to the object to be tested, and determine the film of the second layer by using the fit. Thick d ₂ . The procedures of the modeled portion 742 and the fitting portion 743 are the same as those of the modeled portion 735 and the fitting portion 736 of the above-mentioned program type 2, and will not be further described herein.

Figure 16 is a flow chart showing the method of calculating the film thickness associated with the program type 3 according to the embodiment of the present invention. In the steps of the flowchart shown in FIG. 16, the procedures of steps S100 to S106 and the flowcharts shown in FIG. 12 are denoted by the same reference numerals, and the detailed description thereof will not be repeated. Hereinafter, the film thickness calculation program after step S162 will be described with respect to the difference from the flowchart shown in FIG.

In step S162, the user inputs a search range of the film thickness d ₁ of the first layer of the object to be tested, a refractive index n ₁ of the first layer of the object to be tested, and a decay coefficient k ₁ according to the displayed input screen or the like. The refractive index n ₂ of the second layer of the analyte and the attenuation coefficient k ₂ .

Then, the CPU 200 analyzes the frequency component of the reflectance spectrum stored in the buffer portion 212 by the optimization method to calculate the film thickness d _{1 of the} first layer (step S164).

Next, the CPU 200 calculates a theoretical value of the reflectance spectrum from the wave (step S166). Next, for the measured value of the reflectance spectrum and the theoretical value of the reflectance spectrum stored in the memory portion 212 and the like, the CPU 200 sequentially calculates the squared deviation value of each wavelength between the two to calculate the residual between the two. Poor (step S168). Further, the CPU 200 determines whether or not the calculated residual is equal to or lower than a predetermined threshold (step S170).

When the calculated residual is not below the predetermined threshold (in the case of NO in step S170), the CPU 200 changes the current value of the film thickness d ₂ of the second layer (step S172). Furthermore, the extent to which the film thickness d _{2 is} to be changed depends on the degree of occurrence of the residual. After that, it returns to step S166 of the program.

On the other hand, when the calculated residual is equal to or less than the predetermined threshold (in the case of YES in step S170), the CPU 200 treats the current value of the film thickness d _{1 of the} first layer and the film thickness d ₂ of the second layer as The film thickness (analytical value) of each layer of the object is measured and output (step S174). After that, the program ends.

Further, similarly to the above-described program pattern 1, it is also possible to use a refractive index and a decay coefficient in consideration of wavelength dispersion. The detailed function has been explained above and will not be described here.

(4) Program type 4

The program pattern 4 is a method for improving the program pattern 1 to converge more reliably according to the fit. In other words, in the case of the SOI substrate, for the test object having a large difference in film thickness between the first layer and the second layer, the initial value is important in order to fit the film thickness of each layer. Here, the program pattern 4 first determines the initial thickness of each layer by the method of optimization, and then determines the film thicknesses of the first layer and the second layer by using these initial values and the fit.

Figure 17 is a block diagram showing the control structure for executing the film thickness calculation program associated with the program pattern 4 according to an embodiment of the present invention. In the block diagram shown in Fig. 17, the CPU 200 reads out the program previously stored in the hard disk portion 210 and the like to the memory portion 212, and then executes it.

The control structure related to the program pattern 4 shown in Fig. 17 is substantially the same as the control structure associated with the program pattern 1 shown in Fig. 11 except that the optimization calculation section 751 is added.

The optimization calculation section 751 analyzes the frequency components of the reflectance spectrum stored in the buffer portion 71 by using an optimization method such as MEM to calculate the film thickness d ₁ and the second layer of the first layer, respectively. Film thickness d ₂ . In particular, the optimization calculation section 751 analyzes the frequency of the measured reflectance spectrum for extracting the obtained two or more peaks, and then the film thickness corresponding to the peaks, respectively, for calculating the first layer The film thickness d ₁ and the film thickness d _{2 of the} second layer. Further, 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 for the adaptation, so that strict precision is not required. Furthermore, the specific frequency analysis method of the optimization calculation section 751 is the same as the above-described optimization calculation section 741, and will not be described herein.

The modeled portion 721 and the matching portion 722 receive the film thickness d _{1 of the} first layer and the film thickness d _{2 of the} second layer calculated by the optimization calculation portion 751, and use the same as the initial value. The film thickness d _{1 of the} first layer and the film thickness d _{2 of the} second layer are determined. The program contents of the modeled portion 721 and the fitting portion 722 have been described above, and will not be described herein.

Figure 18 is a flow chart showing the method of calculating the film thickness associated with the program type 4 according to the embodiment of the present invention. In the flowchart shown in Fig. 18, the procedures of steps S111A and S111B are set in place of step S110 of the flowchart shown in Fig. 12. The same steps are denoted by the same reference numerals for the other procedures, and are not described herein. The following description differs from the program in Figure 12.

Referring to Fig. 18, after the execution of step S108, the routine of step S111A is executed. In step S111A, the user inputs the refractive index n ₁ and the attenuation coefficient k ₁ of the first layer of the object to be tested, and the refractive index n ₂ and the attenuation coefficient of the second layer of the object to be tested according to the displayed input screen or the like. k _2, at the same time, the film thickness of the first layer enter the film thickness d of the retrieval range of the layer of the second ₁ 2 d ₂ of the search range. In the next step S111B, the CPU 200 analyzes the frequency component of the reflectance spectrum stored in the buffer portion 212 by using the optimization method to calculate the film thickness d _{1 of the} first layer and the film of the second layer. Thick d ₂ . The film thickness d _{1 of the} first layer and the film thickness d _{2 of the} second layer calculated in the step S111A are used as initial values. Next, after step S111B, and after step S112 of Fig. 12, the same procedure is executed.

Further, similarly to the above-described program pattern 1, it is also possible to use a refractive index and a decay coefficient in consideration of wavelength dispersion. The detailed function has been explained above and will not be described here.

(5) Program type 5

The program pattern 5 is a modification in which the film thickness of one layer is known and only the film thickness of the other layer is analyzed. In the following description, the film thickness of the second layer of the test object is known, and the film thickness of the first layer is determined by the fitting method.

Figure 19 is a block diagram showing the control structure for executing the film thickness calculation program associated with the program pattern 5 according to an embodiment of the present invention. In the block diagram shown in Fig. 19, the CPU 200 reads out the program previously stored in the hard disk portion 210 and the like to the memory portion 212, and then executes it.

The control structure related to the program pattern 5 shown in Fig. 19 is a configuration modeling portion 721A for replacing the modeled portion 721 in the control structure related to the program pattern 1 shown in Fig. 11. .

The modeled portion 721A receives the refractive index n _{1 of the} first layer and the attenuation coefficient k ₁ , and the refractive index n ₂ and the attenuation coefficient k _{2 of} the second layer, and simultaneously receives the initial thickness of the film thickness d _{1 of the} first layer. And the film thickness d _{2 of the} second layer is a known value (known value). Furthermore, the parameters may be input by the user, or the parameters of the standard material may be stored in advance as files, and then read if necessary. Further, if necessary, the refractive index n _{0 of the} atmosphere and the attenuation coefficient k ₀ may be input.

Further, according to the model of the adapter portion 721A with portion 722 of the parameter update instruction for updating sequentially the thickness of the first layer D _1, D ₁ and then based on the thickness of the first layer after the update, display Theory The function of reflectivity is updated. Further, the modeled portion 721A calculates the theoretical reflectance (spectrum) of each wavelength based on the updated function. According to this aspect, the film thickness d ₁ of the first layer is determined by the fitting method.

Regarding other architectures, the above has been described in detail, and will not be described herein.

Figure 20 is a flow chart showing the method of calculating the film thickness associated with the program type 5 according to the embodiment of the present invention. In the flowchart shown in Fig. 20, the procedures of steps S110A, S118A, and S120A are set in place of steps S110, S118, and S120 of the flowchart shown in Fig. 12. The same steps are denoted by the same reference numerals for the other procedures, and are not described herein. The following description differs from the program in Figure 12.

Referring to FIG. 20, in step S110A, the user inputs the refractive index n ₁ and the attenuation coefficient k ₁ of the first layer of the object to be tested and the refractive index n of the second layer of the object to be tested according to the displayed input screen or the like. ₂ and the decay coefficient k ₂ , at the same time, the initial value of the film thickness d ₁ of the first layer and the known value of the film thickness d ₂ of the second layer are input.

In step S118A, the CPU 200 changes the current value of the film thickness d ₁ of the first layer. In other words, in the program pattern 5, only the film thickness d ₁ of the first layer is suitable for the object.

In step S120A, when the calculated residual is equal to or less than the predetermined threshold value, the CPU 200 outputs the current value of the film thickness d ₁ of the first layer as the film thickness (analytical value) of each layer of the object to be tested.

Further, similarly to the above-described program pattern 1, it is also possible to use a refractive index and a decay coefficient in consideration of wavelength dispersion. The detailed function has been explained above and will not be described here.

(6) Program type 6

The program pattern 6 is a modification in which the film thickness of one layer is known and only the film thickness of the other layer is analyzed, and is a modification of the above-described program pattern 5. In the following description, the film thickness of the second layer of the test object is known, and the film thickness of the first layer is determined by the fitting method or Fourier transform.

Figure 21 is a block diagram showing the control structure for executing the film thickness calculation program associated with the program pattern 6 in accordance with an embodiment of the present invention. In the block diagram shown in Fig. 21, the CPU 200 reads out the program previously stored in the hard disk portion 210 and the like to the memory portion 212, and then executes it.

The control structure related to the program pattern 4 shown in FIG. 21 is a configuration portion 722A for replacing the fitting portion 722 in the control structure related to the program pattern 4 shown in FIG. At the same time, the wave number conversion portion 731, the buffer portion 732, the Fourier transform portion 733, and the peak search portion 734 are further added.

In other words, this pattern program, the analyte of film thickness d ₁ of the first layer is determined by the fit method, however, in the case where the convergence frequency of the fit can not be in a predetermined, is determined using the Fourier transform of the first The film thickness of the layer is d ₁ .

The adaptive portion 722A reads the measured value of the reflectance spectrum of the buffer portion 71, and then transmits a parameter update command to the modeled portion 721A, so that the measured value and the theoretical value of the reflectance spectrum output by the modeled portion 721A are obtained. The residual between the two is below the established threshold. Further, even if the fitting portion 722A performs the calculation of the predetermined number of times and the residual cannot be below the predetermined threshold value, the switching command is transmitted to the wave number converting portion 731, and the film of the first layer is determined by Fourier transform. Thick d ₁ .

Further, the wave number conversion portion 731, the buffer portion 732, the Fourier transform portion 733, and the peak search portion 734 have been described above in conjunction with the program pattern 2 shown in Fig. 13, and will not be described herein.

Figure 22 is a flow chart showing the method of calculating the film thickness associated with the program type 6 in accordance with an embodiment of the present invention. In the flowchart shown in Fig. 22, the step S117 of the flowchart shown in Fig. 20 is added, and the steps S134 to S140 of the flowchart shown in Fig. 14 are added. The same steps are denoted by the same reference numerals for the other procedures, and are not described herein. The following description differs from the 14th and 20th programs.

Referring to Fig. 22, in step S117, the CPU 200 determines whether or not the fitting program has been repeated a predetermined number of times or more. When the fitting program is not repeated for a predetermined number of times or more (in the case of NO in step S117), after the program of step S118 is executed, the program returns to step S112. On the other hand, if the matching program has been repeated for a predetermined number of times or more (in the case of YES in step S117), the program proceeds to step S134.

In steps S134 to S140, the film thickness d _{1 of the} first layer is determined by Fourier transform. The procedures for these steps have been described above and will not be described herein.

"Measurement example"

Fig. 23 is a view showing the measurement results of measuring the film thickness of the SOI substrate by the film thickness measuring apparatus of the embodiment of the present invention. Furthermore, in Fig. 23, the power spectrum obtained after frequency conversion (FFT conversion) of the reflectance spectrum is shown.

Fig. 23(a) shows the measurement results of the SOI substrate in which the thickness of the first Si layer was 22.0 μm and the thickness of the second SiO ₂ layer was 3.0 μm. In Fig. 23(a), frequency conversion is performed using a composition of 1470 nm to 1600 nm in the measured reflectance spectrum. As a result, a maximum peak is generated at a position corresponding to 21.8613 μm.

Fig. 23(b) shows the measurement results of the SOI substrate in which the thickness of the first Si layer was 32.0 μm and the thickness of the second SiO ₂ layer was 2.0 μm. In Fig. 23(b), the frequency conversion is performed using a composition of 1500 nm to 1600 nm in the measured reflectance spectrum. As a result, a maximum peak is generated at a position corresponding to 30.6269 μm.

Fig. 23(c) shows the measurement results of the SOI substrate in which the film thickness of the first Si layer was 16.0 μm and the film thickness of the second SiO ₂ layer was 1.3 μm. In Fig. 23(c), frequency conversion is performed using a composition of 1400 nm to 1600 nm in the measured reflectance spectrum. As a result, a maximum peak was generated at a position corresponding to 15.9969 μm.

From this, it can be seen that the above test results are generally good.

"The existence of masking materials"

As described above, the film thickness measuring apparatus 100 of the present embodiment mainly measures the film thickness of the object to be detected OBJ based on the reflectance spectrum of the infrared light field. Therefore, the light source 10 for measurement (Fig. 1) to the object to be tested OBJ The path can be measured even if a masking material such as a polymer resin exists. In other words, although the light in the visible light region cannot penetrate the material of the polymer resin, the light in the infrared light region can penetrate.

Fig. 24 is a view showing the measurement of the object to be tested OBJ on which the opaque pad is placed by the film thickness measuring apparatus 100 of the embodiment of the present invention.

Referring to Fig. 24, the planar object to be tested OBJ is placed on the stage 50 via a spacer, and the planar opaque pad 52 is placed on the object to be tested OBJ (the side on which the light is irradiated). The opaque pad 52 is a polishing body used for polishing treatment and is mainly formed of a polymer resin. The opaque pad 52, although having a small amount of penetration, allows light in the infrared light field (for example, 900 to 1600 nm) to penetrate.

Figs. 25 and 26 show measurement results of an SOI substrate on which an opaque pad 52 is placed by using the film thickness measuring apparatus 100 of the embodiment of the present invention. Fig. 25 shows the result of using a magnifying lens having a magnification of 10 times as the objective lens 40 (Figs. 1 and 24), and Fig. 26 showing the use of a magnifying lens having a magnification of 2.83 times as the objective lens 40 ( Results of Figures 1 and 24).

In addition, in Figs. 25 and 26, for comparison, the results in the state in which the opaque pad 52 is not disposed are also shown. Furthermore, it should be noted that the range (absolute value) of the respective reflectance spectra is not the same.

Fig. 27 is a view showing the power spectrum obtained by transmitting the reflectance spectrum in the state where the pad 52 shown in Fig. 25 and Fig. 26 is not disposed. Fig. 28 is a view showing the power spectrum obtained by transmitting the reflectance spectrum in the state in which the pads 52 shown in Figs. 25 and 26 are arranged.

Referring to Fig. 25, in the case of using the magnifying lens having a magnification of 10 times as the objective lens 40, as a result of the presence of the opaque pad 52, the noise component is increased as compared with the case where the opaque pad 52 is not present.

On the other hand, referring to Fig. 26, in the case where the magnifying lens having a magnification of 2.83 is used as the objective lens 40, the result of the opaque pad 52 is substantially the same as that when the opaque pad 52 is absent. The periodicity is fully determined.

As shown in Figs. 27 and 28, in the case of using the magnifying lens having a magnification of 2.83 times as the objective lens 40, substantially the same power spectrum is obtained regardless of whether or not there is an opaque pad.

On the other hand, in the case of using the magnifying lens having a magnification of 10 times as the objective lens 40, it is understood that a power spectrum having sufficient accuracy cannot be obtained. This is because, as the objective lens 40 changes the magnification, the number of openings also changes, and in the case of using the magnifying lens 5 having a magnification of 10 times, the diffused light increases, and the noise component increases.

As described above, the film thickness of the object to be tested OBJ in which the opaque pad 52 is disposed can be measured by the film thickness measuring device 100 of the present embodiment. Among them, an optical system that illuminates the measuring light and an optical system that receives the reflected light need to have a design that can eliminate the influence of the diffused light.

"Modification"

It is also possible to use a Y-type optical fiber as an optical system for measuring the irradiation of the light and the reception of the reflected light by the object to be measured OBJ.

Fig. 29 is a view showing the configuration of an optical system of a film thickness measuring apparatus 100# according to another embodiment of the present invention.

Referring to Fig. 29, the film thickness measuring device 100# is an optical system in which the measuring light guide of the measuring light source 10 (Fig. 1) is guided to the object to be tested OBJ, and the reflected light of the object to be tested OBJ is guided to the detecting portion 64 ( Fig. 1), and has a light-receiving optical fiber 56.

The light-receiving optical fiber 56 is a Y-type optical fiber, which combines two light rays into a single light, and simultaneously separates a single light into two light rays. More specifically, in one embodiment, the light-receiving optical fiber 56 is formed of a germanium (Ge) doped single-line Y-type fiber.

The measurement light generated by the measurement light source 10 (Fig. 1) is incident on the object to be tested OBJ through the first branch fiber 56a, and the reflected light generated by the object OBJ is reflected by the second branch fiber 56b. Go to the detection section 64.

In addition to this, between the light-receiving optical fiber 56 and the object to be tested OBJ, a pinhole optical system 54 as an aperture is disposed.

According to the film thickness measuring apparatus 100# shown in FIG. 29, even if the object OBJ is placed in a solution such as a polishing liquid, the film thickness can be measured.

Fig. 30 is a view showing the film thickness of the object to be tested OBJ in the solution by using the film thickness measuring device 100# of another embodiment of the present invention.

Referring to Fig. 30, the table 57 is placed in a container, and then the object to be tested OBJ is placed on a table 57 via a spacer which is filled with a solution 58 of a polishing liquid or the like. Then, a portion of the light-receiving side of the light-receiving optical fiber 56 is immersed in the solution 58. With this structure, the film thickness of the analyte OBJ in the solution can be determined.

Further, when the solution 58 is made of water as a solvent, in the above-mentioned infrared light field (900 to 1600 nm), when measuring the film thickness, it is preferable to use the optical domain of the absorption wavelength of the removed water. Specifically, the water absorbs a wavelength region of about 1320 nm or more, and for the film thickness measurement of the object OBJ, it is preferable to use a spectrum of reflected light in the range of 900 to 1320 nm.

Other Embodiments

The program of the present invention is provided to the program module as part of the computer operating system (OS), and the necessary modules can be called in a predetermined arrangement and timing before executing the related program. In this case, the program itself does not include the above modules, but cooperates with the operating system to execute related programs. Programs that do not include such a module may also be included in the program of the present invention.

Further, the program of the present invention can also be programmed into one of the other programs. In this case, the modules included in the above other programs are not included in the program itself, but are executed in cooperation with other programs. Programs programmed into this other program may also be included in the program of the present invention.

The supplied program is executed by a program storage portion installed on a hard disk or the like. Furthermore, the program product includes the program itself and the memory medium of the memory program.

Further, some or all of the functions implemented in accordance with the program of the present invention may also be constructed of dedicated hardware.

According to an embodiment of the present invention, the reflectance spectrum (or the transmittance spectrum) obtained after the measurement light is irradiated on the object to be tested is used to independently calculate the film thickness of each layer constituting the object to be tested, (1) FFT, etc. Discrete Fourier transform, or a method using MEM or the like to calculate the main wavenumber component, and then determine the film thickness. (2) The method of determining the film thickness by the model formula can be selective. Execution. In this way, even when the number of layers constituting the object to be tested is large or the film thickness of each layer is large, the film thickness of each layer can be more accurately measured.

In addition, according to the embodiment of the present invention, the wavelength range (or wavelength detection range) of the measurement light and the detection can be appropriately set corresponding to the film thickness of each layer constituting the object to be tested in the object to be measured. The partial wavelength resolution allows the film thickness of each layer to be more accurately measured.

The present invention has been described in detail above, but the above description is only an example, and the present invention is not limited thereto, and the scope of the present invention is defined by the scope of the appended claims.

100. . . Film thickness measuring device

10. . . Measuring light source

12. . . Focusing lens

14, 66. . . Filter

16, 36. . . Imaging lens

18. . . aperture

20, 30. . . Beam splitter

twenty two. . . Observation light source

24, 56, 56a, 56b. . . optical fiber

26. . . Injection part

26a. . . Mask part

32. . . Pinhole mirror

32a. . . Pinhole

34. . . Axial conversion mirror

38. . . Observation camera

39. . . Display part

40. . . Mirror

50. . . Stage

51. . . Movable mechanism

60. . . Spectrometry

52. . . Solder pad

54. . . Pinhole optical system

57. . . table

58. . . Solution

62. . . Diffraction grating

64. . . Detection part

68. . . shutter

70. . . Data processing part

206. . . Interface part

204. . . Display part

200. . . CPU

208. . . Input part

216. . . Floppy disk player

216a. . . floppy disk

214. . . Optical disc drive

214a. . . Disc

210. . . Hard disk part

212. . . Memory part

731. . . Wavenumber conversion part

71,732. . . Buffer section

733. . . Fourier transform

734‧‧·Crest exploration part

721, 721A, 735, 742‧‧‧ modeled parts

722, 722A, 736, 749, 751‧‧ ‧ suitable parts

741‧‧‧Optimized calculations

AX1, AX2, AX3, AX4‧‧‧ optical axis

OBJ‧‧‧Test object

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

Fig. 2 is a cross-sectional view showing the object to be tested which is a measurement target of the film thickness measuring apparatus according to the embodiment of the present invention.

3(a) to 3(c) are views showing the measurement results of the SOI substrate after the film thickness measuring apparatus according to the embodiment of the present invention.

4(a) and 4(b) are views showing another measurement result after measuring the SOI substrate by using the film thickness measuring device of the embodiment of the present invention.

Fig. 5 (a) and (b) are views showing another measurement result after measuring the SOI substrate by using the film thickness measuring device of the embodiment of the present invention.

6(a) to (c) are schematic views for explaining the measurement range of the film thickness and the detection wavelength range of the detection portion according to the embodiment of the present invention, and the relationship with the number of detection points.

Fig. 7 (a) and (b) are diagrams showing simulation results of measurement results using a film thickness measuring device having a wavelength resolution close to a theoretical value.

Fig. 8(a) and (b) are diagrams showing the results of simulation of the measurement results using a film thickness measuring device having a wavelength resolution and a precision higher than twice the theoretical value.

Fig. 9 is a view showing the measurement results of the reflectance spectrum associated with the SOI substrate.

Figure 10 is a diagram showing a schematic hardware structure of a data processing portion in accordance with an embodiment of the present invention.

Figure 11 is a block diagram showing the control structure for executing the film thickness calculation program associated with the program pattern 1 according to an embodiment of the present invention.

Figure 12 is a flow chart showing the method of calculating the film thickness associated with the program type 1 according to the embodiment of the present invention.

Figure 13 is a block diagram showing the control structure for executing the film thickness calculation program associated with the program pattern 2 according to an embodiment of the present invention.

Figure 14 is a flow chart showing the method of calculating the film thickness associated with the program type 2 according to the embodiment of the present invention.

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

Figure 16 is a flow chart showing the method of calculating the film thickness associated with the program type 3 according to the embodiment of the present invention.

Figure 17 is a block diagram showing the control structure for executing the film thickness calculation program associated with the program pattern 4 according to an embodiment of the present invention.

Figure 18 is a flow chart showing the method of calculating the film thickness associated with the program type 4 according to the embodiment of the present invention.

Figure 19 is a block diagram showing the control structure for executing the film thickness calculation program associated with the program pattern 5 according to an embodiment of the present invention.

Figure 20 is a flow chart showing the method of calculating the film thickness associated with the program type 5 according to the embodiment of the present invention.

Figure 21 is a block diagram showing the control structure for executing the film thickness calculation program associated with the program pattern 6 in accordance with an embodiment of the present invention.

Figure 22 is a flow chart showing the method of calculating the film thickness associated with the program type 6 in accordance with an embodiment of the present invention.

23(a) to (c) show the measurement results of the film thickness of the SOI substrate measured by the film thickness measuring apparatus of the example of the present invention.

Fig. 24 is a view showing the measurement of the object to be tested on which the opaque pad is placed by using the film thickness measuring device of the embodiment of the present invention.

Fig. 25 is a view showing measurement results of an SOI substrate on which an opaque pad is placed by using a film thickness measuring apparatus according to an embodiment of the present invention.

Fig. 26 is a view showing measurement results of an SOI substrate on which an opaque pad is placed by using a film thickness measuring apparatus according to an embodiment of the present invention.

Fig. 27 is a view showing the power spectrum obtained by transmitting the reflectance spectrum in the state of the pad shown in Figs. 25 and 26 without being disposed.

Fig. 28 is a view showing the power spectrum obtained by transmitting the reflectance spectrum in the state in which the pads shown in Figs. 25 and 26 are arranged.

Figure 29 is a view showing the configuration of an optical system of a film thickness measuring device according to another embodiment of the present invention.

Fig. 30 is a view showing the film thickness of a sample to be measured in a solution by using a film thickness measuring device according to another embodiment of the present invention.

71. . . Buffer section

721. . . A modeled part

722A. . . Suitable part

731. . . Wavenumber conversion part

732. . . Buffer section

733. . . Fourier transform

734. . . Crest exploration part

Claims (6)

A film thickness measuring device comprising: a light source that irradiates measurement light having a predetermined wavelength range to an object to be tested formed on a substrate, the object to be tested comprising a first layer closest to the light source and adjacent to the object a second layer of the first layer; a spectroscopic portion, which is used to obtain a wavelength distribution characteristic of reflectance or transmittance according to the light reflected by the object to be tested or the light penetrating the object to be tested; And adapting the wavelength distribution characteristic to determine a film thickness of the first layer and the second layer respectively, wherein the model has a film thickness of each layer included in the object to be tested; and a conversion unit Converting the correspondence between the wavelengths of the wavelength distribution characteristics and the values of the reflectances or transmittances of the wavelengths into a correspondence relationship between the wavenumber conversion reflectances of the reciprocal of the wavenumbers and the reflectances of the respective wavelengths, or Is a correspondence between the wavenumber conversion transmittance converted to the reciprocal of the wave number and the transmittance of each wavelength to generate a wave number distribution characteristic; and an analyzing unit for obtaining each of the wave number distribution characteristics Wavenumber component An amplitude value; a second determining unit configured to determine at least a film thickness of the first layer according to a large wave number component of the amplitude value included in the wave number distribution characteristic, when the first determining unit is not adapted to a predetermined number of times Selecting the second decision unit to be effective when the inner convergence occurs; and the third determining unit, the value of the film thickness of the first layer determined by the second determining unit is used to set the model formula, and The wavelength distribution characteristic is adapted to determine a film thickness of the second layer, wherein the model has The film thickness of each layer included in the test object. The film thickness measuring device according to claim 1, wherein the model formula includes a wavelength correlation function for indicating a refractive index. The film thickness measuring device according to claim 1 or 2, wherein the predetermined wavelength range includes a wavelength of an infrared light domain. The film thickness measuring device according to claim 1 or 2, wherein the analyzing unit comprises: a Fourier transform unit for performing discrete Fourier transform on the wave number distribution characteristic. The film thickness measuring device according to claim 1 or 2, wherein the analyzing unit obtains an amplitude value of each wavenumber component included in the wave number distribution characteristic by an optimization method. A film thickness measuring method comprising: an illuminating step of irradiating a measuring light having a predetermined wavelength range to an object to be tested formed on a substrate, the object to be tested comprising a first layer closest to the light source and adjacent to a second layer of the first layer; a wavelength distribution characteristic obtaining step of obtaining a wavelength distribution characteristic of the reflectance or the transmittance according to the light reflected by the object to be tested or the light penetrating the object to be tested; Determining a step of performing, by using a model formula, the wavelength distribution characteristic to determine a film thickness of the first layer and the second layer, wherein the model has a film thickness of each layer included in the object to be tested; a generating step of converting a correspondence between each wavelength of the wavelength distribution characteristic and a value of a reflectance or a transmittance of the wavelength into a wavelength-dependent Correspondence between the wavenumber conversion reflectance of the reciprocal of the wave number and the reflectance, or the correspondence between the wavenumber conversion transmittance converted to the reciprocal of the wave number and the transmittance of each wavelength, to generate the wave number a distribution characteristic; an amplitude value obtaining step of obtaining amplitude values of respective wavenumber components included in the wave number distribution characteristic; and a second determining step of using a large wave number component in the amplitude value included in the wave number distribution characteristic Determining at least the film thickness of the first layer, wherein the second determining step is selectively made effective when the first determining step is not converged within a prescribed number of times; and the third determining step is to Determining the value of the film thickness of the first layer determined by the step, setting the model, and performing the matching on the wavelength distribution characteristic to determine the film thickness of the second layer, wherein the model has the The film thickness of each layer included in the test object.