JP2013079921A - Film thickness measuring apparatus and film thickness measuring method - Google Patents

Abstract

A film thickness measuring apparatus and a film thickness measuring method capable of accurately measuring the film thickness of a dielectric thin film having an unknown refractive index are provided.
A film thickness measuring apparatus includes: a wavelength distribution generating unit that generates a first wavelength distribution and a second wavelength distribution for each of a first reflected interference light and a second reflected interference light; An optical path difference calculating unit 73 for obtaining a first optical path difference corresponding to the first incident angle and a second optical path difference corresponding to the second incident angle based on the wavelength distribution and the second wavelength distribution; Using the expression representing the optical path difference as a function of the angle, the film thickness, and the refractive index as variables, the first incident angle and the second incident angle, and the first optical path difference calculated by the optical path difference calculation unit 73 and A film thickness / refractive index calculator 74 for determining the film thickness and refractive index of the thin film by substituting the second optical path difference into the equation.
[Selection] Figure 4

Description

  Embodiments described herein relate generally to a film thickness measuring apparatus and a film thickness measuring method for measuring the film thickness of a dielectric thin film.

  The physical properties of the dielectric thin film vary depending on the film thickness and refractive index (or dielectric constant). For this reason, in order to give desired performance to the dielectric thin film, it is important to accurately measure the film thickness and the refractive index. As a method for measuring the film thickness, for example, reflectance spectroscopy, which is one of non-contact measurement methods that do not cause destruction of a sample, is known.

  Conventionally, as a technique for measuring the film thickness of a dielectric thin film using reflectance spectroscopy, for example, there is a technique disclosed in Japanese Unexamined Patent Application Publication No. 2010-2328 (Patent Document 1).

  The film thickness measuring device disclosed in Patent Document 1 obtains the correspondence between the wave number and the wave number conversion reflectance from the correspondence between the reflectance spectrum measured from the object to be measured and the reflectance at each wavelength. The reflectance is Fourier-transformed into frequency with respect to the wave number, and the film thickness of each layer can be obtained based on the obtained peak.

JP 2010-2328 A

  By the way, the filling factor (apparent filling factor) of the dielectric thin film varies depending on the manufacturing conditions. On the other hand, the refractive index of the thin film varies depending on the filling rate. For this reason, the refractive index of a thin film will change with manufacturing conditions.

  However, in the technique for obtaining the thickness of the dielectric thin film using the conventional reflectance spectroscopy, the refractive index is used as the initial parameter for obtaining the thickness of the thin film to be measured. Or the refraction index is assumed to be known. For this reason, when the refractive index of the standard sample is used, the film thickness is measured using a refractive index different from the actual refractive index of the thin film to be measured, resulting in a measurement error. In addition, when it is assumed that the refractive index is known, the refractive index of the thin film to be measured must be measured in a separate process in advance before measuring the film thickness.

  The present invention has been made in consideration of the above-described circumstances, and an object thereof is to provide a film thickness measuring apparatus and a film thickness measuring method capable of accurately measuring the film thickness of a dielectric thin film having an unknown refractive index. And

  In order to solve the above-described problem, a film thickness measuring apparatus according to an embodiment of the present invention is based on the wavelength distribution of reflected interference light generated by the optical path difference between the front surface reflected light and the back surface reflected light of the thin film. A film thickness measuring apparatus for measuring a film thickness, wherein irradiation light having a predetermined wavelength range is applied to a measured object having a thin film formed on a substrate surface, with a first incident angle and a first incident angle. Irradiating portions that irradiate at different second incident angles, and first reflected interference light and second reflected interference light from the thin film of light irradiated at the first incident angle and the second incident angle. Are received at a first reflection angle and a second reflection angle substantially equal to the first incident angle and the second incident angle, respectively, and the first reflected interference light and the second reflected interference A first wavelength distribution and a second wavelength distribution for each of the lights; And a first optical path difference corresponding to the first incident angle and a second incident angle, respectively, based on the formed wavelength distribution generating unit, the first wavelength distribution, and the second wavelength distribution. The first incident angle and the second incident angle are calculated using an optical path difference calculating unit for obtaining a second optical path difference and an expression representing the optical path difference as a function of the incident angle, the film thickness, and the refractive index as variables. And a film thickness refractive index calculation unit for obtaining a film thickness and a refractive index of the thin film by substituting the first optical path difference and the second optical path difference calculated in the optical path difference calculation unit into the equation, It is equipped with.

  According to the film thickness measuring apparatus and the film thickness measuring method according to the present invention, the film thickness of the dielectric thin film whose refractive index is unknown can be accurately measured.

1 is a schematic overall configuration diagram showing an example of a film thickness measuring apparatus according to an embodiment of the present invention. (A) is a y direction arrow view which shows an example in case a film thickness measuring apparatus has a 3rd irradiation unit and a 3rd light reception unit, (b) is a z direction arrow view, (c) is an x direction. Arrow view. Explanatory drawing which shows the relationship between the size of the irradiation light spot area which concerns on this embodiment, and the size of a light reception spot area. The schematic block diagram which shows the structural example of the function implementation part by CPU of a main control part. The figure for demonstrating the optical path difference of the surface reflected light and back surface reflected light of a thin film. The flowchart which shows the procedure at the time of measuring accurately the film thickness of the dielectric thin film whose refractive index is unknown by CPU of the main-control part shown in FIG. FIG. 6 is an explanatory diagram illustrating an example of a first wavelength distribution and a second wavelength distribution of a measurement target according to the first embodiment. Explanatory drawing which shows an example of the Fourier-analysis result using Formula (7a) and (7b) by the optical path difference calculation part in the example shown in FIG. Explanatory drawing which shows an example of the 1st wavelength distribution of the to-be-measured object which concerns on Example 2, and a 2nd wavelength distribution. Explanatory drawing which shows an example of the Fourier-analysis result using Formula (7a) and (7b) by the optical path difference calculation part in the example shown in FIG. Explanatory drawing which shows an example of the difference in wavelength distribution corresponding to the 2nd incident angle of 30 degree | times when using a halogen lamp as a light source and using a broadband laser light source with respect to the to-be-measured object which concerns on Example 3. FIG. Explanatory drawing which shows an example of the 1st wavelength distribution and 2nd wavelength distribution of the to-be-measured body which concerns on Example 3 in the case of using a broadband laser as a light source. Explanatory drawing which shows an example of the Fourier-analysis result using Formula (7a) and (7b) by the optical path difference calculation part in the example shown in FIG. The block diagram which shows the modification of an irradiation part and a light-receiving part. The figure which shows one structural example of the irradiation part for utilizing the incident angle of 0 degree | times in the modification of an irradiation part and a light-receiving part shown in FIG. The figure for demonstrating the calculation method of the optical path difference by the principle of the minimum effect | action in the thin film which has the refractive index ny in the thickness direction (Y direction), and the refractive index nx in a boundary parallel direction (X direction).

  Embodiments of a film thickness measuring apparatus and a film thickness measuring method according to the present invention will be described with reference to the accompanying drawings.

  A film thickness measuring apparatus according to an embodiment of the present invention makes irradiation light incident on the thin film at two different incident angles, and the front surface reflected light and the back surface reflected light of the thin film corresponding to the two types of incident light. The film thickness of the thin film is measured based on the wavelength distribution of the two types of reflected interference light generated by the optical path difference Y.

(1. Outline configuration)
FIG. 1 is a schematic overall configuration diagram showing an example of a film thickness measuring apparatus 10 according to an embodiment of the present invention. In the following description, an example in which the normal direction of the thin film is the Z axis and the directions perpendicular to the normal direction of the thin film are the X axis and the Y axis will be described.

  The film thickness measuring device 10 includes an irradiation unit 11, a light receiving unit 12, a spectroscopic unit 13, and an information processing device 14.

  The irradiation unit 11 includes a light source 20, a first irradiation unit 21, a second irradiation unit 22, and a beam splitter 23.

  The light source 20 is configured by a halogen lamp, a broadband laser, or the like, emits irradiation light having a predetermined wavelength range, and the illumination light is emitted from the first irradiation unit 21 via a light guide 24 configured by an optical fiber or the like. And to the second irradiation unit 22. Further, shutters 25 and 26 are provided on the light source side of the first irradiation unit 21 and the second irradiation unit 22, respectively.

  The shutters 25 and 26 are controlled by the information processing device 14, and the irradiation of the irradiation light to the measurement object 31 by the first irradiation unit 21 and the irradiation of the irradiation light to the measurement object 31 by the second irradiation unit 22 are performed simultaneously. The irradiation light is appropriately shielded so as not to be performed.

  The first irradiation unit 21 and the second irradiation unit 22 irradiate the measurement object 31 placed on the base 30 with irradiation light at a first incident angle and a second incident angle different from each other. The measured object 31 includes a substrate 32, and a thin film 33 made of a dielectric having a predetermined particle diameter is formed on the surface of the substrate 32.

  The light receiving unit 12 includes a first light receiving unit 41 and a second light receiving unit 42.

  The first light receiving unit 41 is disposed at a position facing the first irradiation unit 21 via the normal line of the surface of the thin film 33, and the thin film 33 is irradiated by the first irradiation unit 21 at a first incident angle. The first reflected interference light from the light thin film 33 is received at a first reflection angle substantially equal to the first incident angle. Further, the second light receiving unit 42 is disposed at a position facing the second irradiation unit 22 through the normal line of the surface of the thin film 33, and the second irradiation unit 22 forms the thin film 33 at a second incident angle. The first reflected interference light from the irradiated light thin film 33 is received at a second reflection angle substantially equal to the second incident angle.

  As shown in FIG. 1, when the first incident angle and the first reflection angle are set to 0 degrees, a beam splitter 23 may be used. At this time, the first light receiving unit 41 is not disposed at a position facing the first irradiation unit 21 via the normal line of the surface of the thin film 33, and for example, the first irradiation unit 21 and the first light receiving unit. One of 41 is arranged in parallel to the X axis, and the other is arranged on the normal line of the thin film 33. FIG. 1 shows an example in which the first irradiation unit 21 is arranged so as to emit irradiation light parallel to the X axis, and the first light receiving unit 41 is arranged on the normal line of the thin film 33. In this case, the irradiation light emitted from the first irradiation unit 21 in parallel to the X axis is reflected toward the thin film 33 through the beam splitter 23 in parallel to the Z axis (parallel to the normal line of the thin film 33). Thus, the thin film 33 is irradiated at an incident angle of 0 degree. The first reflected interference light is reflected at a reflection angle of 0 degree (parallel to the Z axis), passes through the beam splitter 23, and is received by the first light receiving unit 41.

2A is a view in the y direction showing an example of the case where the film thickness measuring apparatus 10 includes the third irradiation unit 51 and the third light receiving unit 52, and FIG. 2B is a view in the z direction. (C) is an arrow view in the x direction. FIG. 2 shows an example in which the first incident angle is 0 degree, the second incident angle is 20 degrees, and the third incident angle of the light irradiated by the third irradiation unit 51 is 30 degrees.
For convenience, the illustration of the third irradiation unit 51, the third light receiving unit 52, and the shutter 53 is omitted in FIG. 2A, and the illustration of the shutters 25, 26, and 53 is omitted in FIG. In (c), the second irradiation unit 22, the shutters 25 and 26, and the second light receiving unit 42 are not shown.

  As shown in FIG. 2, the number of irradiation units and light receiving units is not limited to two, and the number of incident angles of irradiation light on the thin film 33 can be easily increased by increasing the number of sets. Note that a shutter 53 controlled by the information processing device 14 may be provided on the light source 20 side of the third irradiation unit 51 in the same manner as the shutters 25 and 26.

  The spectroscopic unit 13 includes a general spectroscope, receives the first reflected interference light received by the first light receiving unit 41 via the light guide 43, and converts the first reflected interference light to a predetermined wavelength. Spectroscopy is performed at intervals, and information on the intensity of reflected interference light at each wavelength is given to the information processing device 14. Similarly, the spectroscopic unit 13 receives the second reflected interference light received by the second light receiving unit 42 via the light guide 43, splits the second reflected interference light at a predetermined wavelength interval, Information on the intensity of the reflected interference light at each wavelength is given to the information processing apparatus 14.

  The information processing apparatus 14 can be configured by, for example, a desktop type or notebook type personal computer or workstation. The information processing apparatus 14 includes an input unit 61, a display unit 62, a storage unit 63, and a main control unit 64.

  The input unit 61 includes a general input device such as a keyboard, a touch panel, and a numeric keypad, and outputs an operation input signal corresponding to a user operation to the main control unit 64. The display unit 62 is configured by a general display output device such as a liquid crystal display or an OLED (Organic Light Emitting Diode) display, and displays various types of information according to the control of the main control unit 64. The storage unit 63 is a storage medium that can be read and written by the CPU, and stores in advance an expression representing the optical path difference Y as a function with the incident angle, the film thickness, and the refractive index as variables.

  The main control unit 64 receives the spectral spectrum of the reflected interference light from the spectral unit 13, and based on the spectral spectrum, the first optical path difference and the second optical path difference corresponding to the first incident angle and the second incident angle. Ask for. Further, the main control unit 64 uses the formula stored in the storage unit 63 to substitute the first incident angle and the second incident angle, the first optical path difference, and the second optical path difference into the formula. The film thickness and refractive index of the thin film 33 are obtained. Details of the configuration and operation of the main control unit 64 will be described later.

(2. Increasing the intensity of reflected interference light)
When measuring the film thickness and dielectric constant (refractive index) of a dielectric thin film at high speed using reflectance spectroscopy, it is generally known that the interference signal between incident light and reflected light is weak. This is because (1) the reflected light from the surface of the dielectric thin film is weak due to scattering within the surface of the dielectric thin film, and (2) the surface of the substrate on which the dielectric thin film is applied and the inside thereof. The reflected light from the back surface of the dielectric thin film is weak due to scattering and interference, and (3) the reflected light from the substrate surface is weak due to scattering and interference inside the surface of the substrate on which the dielectric thin film or dielectric is applied and within it. (4) It is conceivable that the interference signal becomes small due to unevenness of the surface of the dielectric thin film or the surface of the substrate to which the dielectric thin film is applied.

  In order to increase the intensity of the reflected interference light, the film thickness measuring apparatus 10 according to this embodiment may be configured to satisfy the following conditions.

(2-1. Light source wavelength and incident angle according to particle size)
It is known that when light enters a dielectric, the phenomenon varies depending on the particle size of the particles constituting the dielectric. When the wavelength of light is sufficiently long relative to the constituent particles, a scattering phenomenon called Rayleigh scattering occurs, and the scattered light has a greater intensity as the wavelength is shorter. On the other hand, when the constituent particle diameter is on the order of almost equal to the wavelength, the state shifts to a state called Mie scattering. In this state, the intensity of forward scattering becomes very large, and there is a demerit that the intensity of error light increases for reflectance spectroscopy using reflected light (backscattered light).

  Therefore, for example, when the particle size of the dielectric is 200 nm or less, a wavelength of about 0.3-2 μm is used, and when the particle size is more than that, light having a longer wavelength (for example, when the particle size is 400 μm) It is preferable to use light having a lower limit of the wavelength region of 1.7 μm or more. When measuring a large particle size, an angle in a range in which the forward scattering region of the Mie scattering theory does not affect the back scattering region (reflected light region) (particle size of 400 nm or more, equivalent refractive index of 1.5 In this case, it is preferable to use an incident angle of 30 degrees or less.

(2-2. Light source wavelength considering the reflectance of the substrate 32)
Interference at the substrate 32 coated with the dielectric varies depending on the thickness and refractive index of the substrate 32. For this reason, it is possible to increase the interference signal by measuring the reflectance of only the substrate 32 in advance and using a measurement wavelength having a large reflectance from the result.
(2-3. Irradiation light area and light collection area)

  FIG. 3 is an explanatory diagram showing the relationship between the size of the irradiated light spot area A1 and the size of the light receiving spot area A2 according to the present embodiment.

  In order to efficiently collect the interference signal, it is preferable that the radius r2 of the light receiving spot area A2 is larger than the radius r1 of the irradiation light spot area A1. The radius r1 of the irradiation light spot area A1 can be controlled by adjusting the numerical aperture of the lenses constituting the irradiation units 21 and 22. The radius r2 of the light receiving spot area A2 can be controlled by adjusting the numerical aperture of the lenses constituting the light receiving units 41 and 42.

  In addition to the above conditions, it is possible to expect an increase in the strength of the interference signal by reducing the measurement area size of the thin film 33.

(3. Configuration of main control unit)
The main control unit 64 is configured by a storage medium such as a CPU, a RAM, and a ROM, and controls the operation of the film thickness measuring apparatus 10 according to a program stored in the storage medium.

  The CPU of the main control unit 64 loads a film thickness measurement program stored in a storage medium such as a ROM and data necessary for executing the program into the RAM, and in accordance with this program, a dielectric having an unknown refractive index. A process for accurately measuring the thickness of the body thin film is executed. The RAM of the main control unit 64 provides a work area for temporarily storing programs and data executed by the CPU. The storage medium such as the ROM of the main control unit 64 stores a startup program for the information processing apparatus 14, a film thickness measurement program, and various data necessary for executing these programs.

  A storage medium such as a ROM has a configuration including a recording medium readable by a CPU, such as a magnetic or optical recording medium or a semiconductor memory, and a part of programs and data in the storage medium. Or you may comprise so that all may be downloaded via an electronic network.

  FIG. 4 is a schematic block diagram illustrating a configuration example of the function realization unit by the CPU of the main control unit 64. In addition, this function realization part may be comprised by hardware logics, such as a circuit, without using CPU.

  As shown in FIG. 4, the CPU of the main control unit functions as at least an incident angle control unit 71, a wavelength distribution generation unit 72, an optical path difference calculation unit 73, and a film thickness refractive index calculation unit 74 by the film thickness measurement program. Each of the units 71 to 74 uses a required work area of the RAM as a temporary storage location for data.

  The incident angle control unit 71 is irradiated with the irradiation light with the one incident angle so as to prevent the adverse effect that the reflected interference light with the one incident angle is mixed with the reflected interference light with the other incident angle. After generating the wavelength distribution corresponding to this one incident angle, the irradiation light is irradiated at the next incident angle, and the wavelength distribution generating unit 72 generates the wavelength distribution corresponding to this next incident angle. Shutters 25, 26 and 53 are controlled.

  The wavelength distribution generation unit 72 is configured for each of the first reflected interference light and the second reflected interference light for each predetermined wavelength interval based on the intensity information of the reflected interference light at each wavelength generated by the spectroscopic unit 13. A discrete first wavelength distribution and second wavelength distribution consisting of the above data are generated. In addition, when the film thickness measuring apparatus 10 includes the third irradiation unit 51 and the third light receiving unit 52, the third reflected interference light corresponding to the third incident angle can be used. A third wavelength distribution is generated for the reflected interference light.

  The optical path difference calculation unit 73 treats the discrete first wavelength distribution and the second wavelength distribution composed of data for each predetermined wavelength interval as a function of the reciprocal of the wavelength, and unequal intervals corresponding to the predetermined wavelength interval. The first optical path difference and the second optical path difference are obtained by performing discrete Fourier transform by sampling at intervals of reciprocal wavelengths.

  The film thickness refractive index calculation unit 74 uses two types of incident angles (for example, a first incident angle and a second incident angle) and two types of incident angles corresponding to the respective incident angles, using the expressions stored in the storage unit 63. By substituting the optical path difference (for example, the first optical path difference and the second optical path difference) into the equation, the film thickness and the refractive index of the thin film 33 are obtained, and the results are displayed on the display unit 62.

(3-1. Optical path difference calculation method)
Here, a method of calculating the optical path length (more specifically, the optical path difference Y between the front surface reflected light and the back surface reflected light) by the optical path difference calculation unit 73 will be described in detail. In reflectance spectroscopy, first, the optical path difference Y is calculated using interference of reflected light at the front and back surfaces of the object to be measured and each of the interfaces in the case of a multilayer film. Conventionally, estimation using the wavelength of one or many sets of interference waveform peaks is often performed. However, in this estimation method, it is unclear which peak corresponds to which peak in the case of a multilayer film.

Therefore, in this embodiment, when light is expressed as a plane wave, the equation of light is

Use what you can write. Since the relationship between the wave number, wavelength and refractive index is k = 2π / (nλ) (where n is the refractive index and λ is the wavelength), the space-dependent part of the light equation (excluding the ωt term) )

  It becomes. Here, since the refractive index n is a constant, the optical path difference Y can be obtained by performing a discrete Fourier transform with φ being a function of the reciprocal of the wavelength. Moreover, due to the orthogonality of the basis function, the optical path difference Y due to the multilayer film reflection that cannot be separated when only the peak value is used can be separated.

  The discrete Fourier transform in this case is usually due to the use of equidistant measurement points for the wavelength to see the interference signal as a function of the reciprocal of the wavelength, so that the sampling of the data is relative to the reciprocal of the wavelength. Are not evenly spaced, and ordinary fast Fourier transform techniques cannot be used. However, since the accuracy of the discrete Fourier transform here is directly related to the accuracy of the optical path difference Y (and hence the accuracy of the film thickness and refractive index), it is not a simple trapezoidal formula, and is performed as follows to ensure accuracy.

First, the Fourier transform for φ (r) (for convenience, k = 1 / nλ)

Since the measurement data φ (k) is not a compact support (both sides of the measurement do not converge to zero), the window function W (k) often used in the discrete Fourier transform is used.

  And As the window function W (k), for example, a generalized Hamming window W (k) = a− (1−a) cos 2πk can be used.

  Here, φ (k) is not a continuous function but discrete observation data such as φ0, φ1,. For this reason, Formula (2) is discretized.

  In general, equation (4) is discretized using a trapezoidal formula. However, since the output of the spectroscopic unit 13 configured by a general spectroscope is equally spaced with respect to the wavelength, when the reciprocal of the wavelength is used, the intervals of k0, k1, k2,. It becomes. In addition, the accuracy of the equivalent optical path difference Y calculated using the equation (4) greatly depends on the accuracy of the film thickness and the refractive index. For this reason, in this embodiment, the trapezoid formula is not used, and discrete Fourier transform is performed by the following unique algorithm.

First, W (k) φ (k) (defined as ≡ψ (k)) and exp (−ikd) in Equation (4) are treated differently, and Equation (4) is separated into a real part and an imaginary part. To do.

式（７ａ）および（７ｂ）は、プログラム化を行った場合ループ処理を１回しか含まず、台形公式とそん色ない速度で計算が実行でき、しかも精度が良いアルゴリズムとなる。 It was replaced as Ψ _i = Ψ (k _i ). Since the integration of the equations (6a) and (6b) is feasible, the following equations (7a) and (7b) that do not include the integration can be finally obtained.

Expressions (7a) and (7b) include a loop process only once when programmed, can be executed at a speed comparable to the trapezoidal formula, and become a highly accurate algorithm.

  Therefore, the optical path difference calculation unit 73 performs a discrete Fourier transform using the equations (7a) and (7b) based on the discrete wavelength distribution and the second wavelength distribution made up of data for each predetermined wavelength interval. Thus, the optical path difference Y corresponding to each wavelength distribution is obtained.

(3-2. Calculation of film thickness and refractive index)
Next, a method for calculating the film thickness and refractive index of the thin film 33 by the film thickness refractive index calculation unit 74 will be described in detail.

  FIG. 5 is a diagram for explaining the optical path difference between the front surface reflected light and the back surface reflected light of the thin film 33.

  As shown in FIG. 5, the angle formed by the wavefront of incident light (dotted line portion with a vertical mark in the figure perpendicular to the incident light) and the thin film surface is θ1, and the incident angle in the film is θ2. At this time, the length of f in FIG. 5 is equal to the length of a multiplied by sin θ1 (f = a · sin θ1). On the other hand, if the length of the two-dot chain line is 2X, it can be written as a = 2X · sin θ2. Therefore, it can be expressed as f = 2X · sin θ1 · sin θ2.

Therefore, the optical path difference Y between the front surface reflected light and the back surface reflected light can be expressed as follows:
Y = n · 2X-f = 2X (n-sinθ1 · sinθ2) (8)

It becomes.
As apparent from FIG. 5, the length 2X of the two-dot chain line, the film thickness t, and the incident angle θ2 in the film satisfy the relationship of X = t / cos θ2. Using this relationship, when X and θ2 are eliminated from equation (8) and represented by t and n, the following equation (9) can be obtained.

  However, Y represents an optical path difference, θ1 represents an incident angle, θ2 represents an incident angle in the film, t represents a film thickness, and n represents a refractive index.

Therefore, it can be seen from the equation (9) that if the optical path difference Y at the two incident angles is obtained, the film thickness and the refractive index can be obtained. Expression (9) is stored in the storage unit 63 in advance. Note that Expression (9) may be stored in a storage medium such as the ROM of the main control unit 64.
(4. Operation)

  Next, an example of operation | movement of the film thickness measuring apparatus 10 which concerns on this embodiment is demonstrated.

  FIG. 6 is a flowchart showing a procedure for accurately measuring the film thickness of the dielectric thin film whose refractive index is unknown by the CPU of the main control unit 64 shown in FIG. In FIG. 6, reference numerals with numbers added to S indicate steps in the flowchart.

  This procedure starts when Equation (9) is stored in the storage unit 63.

  First, in step S <b> 1, the wavelength distribution generation unit 72 generates a plurality of wavelength distributions corresponding to each of a plurality of incident lights based on the information on the intensity of reflected interference light at each wavelength generated by the spectroscopic unit 13. .

  Next, in step S2, the optical path difference calculation unit 73 calculates a plurality of optical path differences Y corresponding to each of the plurality of wavelength distributions by using, for example, equations (7a) and (7b).

  Next, in step S <b> 3, the film thickness refractive index calculation unit 74 acquires Expression (9) from the storage unit 63.

  Next, in step S <b> 4, the film thickness refractive index calculation unit 74 substitutes at least two sets of the incident angle and the optical path difference Y into the equation (9) acquired from the storage unit 63.

  Next, in step S5, by combining at least two expressions obtained by substituting at least two sets of incident angles and optical path differences Y into Expression (9), the film thickness of the thin film 33 and Calculate the refractive index.

  By the above procedure, the film thickness of the dielectric thin film whose refractive index is unknown can be accurately measured.

  Since the film thickness measuring apparatus 10 according to the present embodiment irradiates the measurement object 31 with irradiation light at two different incident angles, at least one of the incident angles is different from 0 degrees. At this time, by using Expression (9), it is possible to accurately measure the film thickness of the dielectric thin film whose refractive index is unknown, and at the same time, the refractive index (dielectric constant) can be measured. For example, when three types of incident angles can be set (see FIG. 2), three types of film thickness and refractive index can be calculated from a group of three incident angles. In this case, the three calculated values may be averaged to obtain the final calculation result of the film thickness / refractive index of the thin film 33.

(5. Filling rate)
According to the film thickness refractive index calculation unit 74 according to the present embodiment, the refractive index of the thin film 33 can be measured. For this reason, by comparing the refractive index of the thin film 33 with the refractive index of the dielectric crystal constituting the thin film, the filling rate (apparent filling rate) of the dielectric thin film 33 constituting the thin film is obtained. be able to.

  For example, when the dielectric is titanium oxide, the content of titanium oxide in the titanium oxide thin film is a (%), and the apparent filling rate of the titanium oxide thin film is b (%) = 100−a (%). . Further, the refractive index of titanium oxide is N1, and the refractive index of another substance (for example, atmospheric gas such as air or resin) filling the space in the thin film is N2.

Now, it is assumed that the refractive index Na of the titanium oxide thin film is proportional to the content ratio of titanium oxide in the titanium oxide thin film and other substances filling the space in the thin film. This assumption is valid when the titanium oxide is homogeneous. At this time, the refractive index Na of the titanium oxide thin film is given by the following formula (10).
Na = N2 + (N1-N2) * a (10)

When the equation (10) is transformed, the following equation (11) is obtained.
a = (Na-N2) / (N1-N2) (11)

  Therefore, assuming that the refractive indexes N1 and N2 are known, the optical path difference Y calculated by the optical path difference Y calculated by the optical path difference calculation unit 73 using the expressions (7a) and (7b) is used as the expression (9). By substituting Na into the formula (11) for the refractive index obtained from the above, the titanium oxide content a can be obtained. From this a (%), the apparent filling factor b (%) of the titanium oxide thin film = 100−a (%) can be obtained.

(6. Example)
(6-1. Example 1)
As Example 1, when the first incident angle is 0 degree and the second incident angle is 30 degrees, a film of the measurement object 31 in which one layer of a titanium oxide thin film 33 as a dielectric thin film is applied to the substrate 32. Thickness and refractive index were measured. In the measurement with a laser confocal microscope, the film thickness of the thin film 33 was measured to be 12.0 μm.

  FIG. 7 is an explanatory diagram illustrating an example of the first wavelength distribution and the second wavelength distribution of the measurement target 31 according to the first embodiment. FIG. 8 is an explanatory diagram showing an example of a Fourier analysis result using the equations (7a) and (7b) by the optical path difference calculation unit 73 in the example shown in FIG.

  As shown in FIGS. 7 and 8, when the thin film 33 is a single layer, one peak is observed as a Fourier analysis result of the wavelength distribution corresponding to each incident angle. It should be noted that depending on the thickness and transmittance of the substrate 32, peaks due to the surface reflection and back surface reflection of the substrate 32 may be observed.

  In the example shown in FIGS. 7 and 8, the film thickness refractive index calculation unit 74 measured the film thickness as 11.66 μm and the refractive index as 1.60. This film thickness value can be said to be a value close to a measurement result of 12.0 μm by a laser confocal microscope. Further, since the refractive index of the used titanium oxide crystal was 2.52, it was possible to obtain 60.5% as an apparent filling rate from the equation (11).

(6-2. Example 2)
As Example 2, in the case where the first incident angle is 20 degrees and the second incident angle is 40 degrees, the film thickness of the measurement object 31 in which two layers of titanium oxide thin films as dielectric thin films are applied to the substrate 32. And the refractive index was measured. In the measurement with a laser confocal microscope, the total film thickness of the two layers was measured to be 9.6 μm.

  FIG. 9 is an explanatory diagram illustrating an example of the first wavelength distribution and the second wavelength distribution of the measurement target 31 according to the second embodiment. FIG. 10 is an explanatory diagram showing an example of a Fourier analysis result using the equations (7a) and (7b) by the optical path difference calculation unit 73 in the example shown in FIG.

  As shown in FIGS. 9 and 10, when the thin film 33 has two layers, at least two peaks are observed as Fourier analysis results of the wavelength distribution corresponding to each incident angle. As shown in FIG. 10, in this example, peaks due to the front surface reflection and the back surface reflection of the transparent electrode film formed on the substrate 32 are observed. In FIG. One peak can be confirmed.

  In the example shown in FIG. 9 and FIG. 10, the film thickness refractive index calculation unit 74 has a film thickness of 8.3 μm, a refractive index of 1.73, and a film thickness for each set of three peaks (a group surrounded by an ellipse). As a result, a film thickness of 5.2 μm and a refractive index of 1.40 were obtained.

  In addition, when there is a target film thickness in the multilayer film production stage in advance, the optical path difference Y estimated from the target film thickness can be predicted. In this case, the optical path difference calculation unit 73 may automatically extract a pair of peaks in the vicinity of the predicted optical path difference from the Fourier analysis result shown in FIG.

(6-3. Example 3)
As Example 3, in the case where the first incident angle is 10 degrees and the second incident angle is 30 degrees, the measurement object 31 is obtained by applying two thin films made of titanium oxide having a particle diameter of 400 nm to the substrate 32. The film thickness and refractive index were measured. In the measurement with a stylus, the film thickness was measured to be 15.6 μm.

  FIG. 11 shows an example of a difference in wavelength distribution corresponding to a second incident angle of 30 degrees when a halogen lamp is used as the light source 20 and a broadband laser light source is used for the measurement object 31 according to the third embodiment. It is explanatory drawing.

  As shown in FIG. 11, when a halogen lamp is used as the light source 20, the interference waveform is weak at a measurement wavelength of 1600 nm to 2100 nm for titanium oxide having a particle diameter of 400 nm. To increase the interference waveform, the measurement wavelength is increased. Alternatively, the interference waveform may be increased by using a broadband laser having high coherence instead of the halogen lamp as the light source 20.

  FIG. 12 is an explanatory diagram illustrating an example of the first wavelength distribution and the second wavelength distribution of the measurement target 31 according to the third embodiment when a broadband laser is used as the light source 20. FIG. 13 is an explanatory diagram showing an example of a Fourier analysis result using the equations (7a) and (7b) by the optical path difference calculation unit 73 in the example shown in FIG.

  In the example shown in FIG. 12 and FIG. 13, measurement was performed on a pair of peaks having the longest optical path difference. As a result, a film thickness of 15.1 μm and a refractive index of 1.68 were obtained.

(7. Modification of optical system)
FIG. 14 is a configuration diagram illustrating a modified example of the irradiation unit 11 and the light receiving unit 12.

  As shown in FIG. 14, the irradiation unit 11 may include a plano-convex lens 80 having an optical axis parallel to the normal line of the thin film 33 and arranged so that the flat side is the thin film 33 side. At this time, the irradiation unit 11 and the light receiving unit 12 may include one irradiation unit 81 and one light receiving unit 82, respectively.

  The irradiation unit 81 and the light receiving unit 82 are arranged on the convex side of the plano-convex lens 80, and are arranged so that the optical axes of the irradiation unit 81 and the light receiving unit 82 are parallel to the optical axis of the plano-convex lens 80.

  At this time, the incident angle control unit 71 controls the positions of the irradiation unit 81 and the light receiving unit 82 so that the positions of the optical axes of the irradiation unit 81 and the light receiving unit 82 are symmetrical with respect to the optical axis of the plano-convex lens 80. . By changing the distance from the optical axis of the irradiation unit 81 to the optical axis of the plano-convex lens 80 (equal to the distance from the optical axis of the light receiving unit 82 to the optical axis of the plano-convex lens 80), the incident angle of the irradiation light is changed. be able to.

  In the modification shown in FIG. 14, the irradiation unit 11 includes only one irradiation unit 81. For this reason, the shutters 25, 26, and 53 are unnecessary in the configuration shown in FIG.

  FIG. 15 is a diagram illustrating a configuration example of the irradiation unit 11 and the light receiving unit 12 for using an incident angle of 0 degrees in the modification of the irradiation unit 11 and the light receiving unit 12 illustrated in FIG. 14.

  In the configuration including one set of the irradiation unit 81 and the light receiving unit 82 as shown in FIG. 14, it is difficult to set the incident angle to 0 degrees. Therefore, when the incident angle of 0 degree is used in the modification shown in FIG. 14, the irradiation unit 84, the light receiving unit 85, and the beam splitter 86 for the incident angle of 0 degree are provided as in the configuration of the optical system shown in FIG. It is good to provide.

  In the configuration shown in FIG. 15, it is preferable to provide a shutter on the light source 20 side of each of the irradiation unit 81 and the irradiation unit 84.

(8. When the refractive index of the thin film 33 is anisotropic)
When the refractive index of the thin film 33 has anisotropy, the film thickness refractive index calculator 74 calculates the formula (9) corresponding to the anisotropy of the refractive index when calculating the film thickness and refractive index of the thin film 33. It is preferable to use an equation obtained by modifying.

  For example, it has been found that titanium oxide (titanium dioxide) may have refractive index anisotropy. When the size (particle size) of the particles is small, the randomness with respect to the direction of each particle is high, so it can be expected that the anisotropy is canceled as a whole. On the other hand, when the film thickness is thin and the particle size is large, anisotropy may remain as a result.

  Therefore, in the case where the thin film 33 has the refractive index ny in the thickness direction and the refractive index nx in the boundary parallel direction, a method for transforming the equation (9) corresponding to the anisotropy of the refractive index will be described below. In the following description, it is assumed that the thickness direction is the Y direction and the boundary parallel direction is the X direction.

The optical path difference Y between the front surface reflected light and the back surface reflected light can be written as in the following formula (12) using the refractive indexes nx and ny (see FIG. 5).

  In Expression (12), the refractive index in the Y direction is ny, and the refractive index in the X direction is nx. For this reason, in the relationship between sin θ1 and sin θ2, a general relational expression between sin θ and the refractive index n is not established. Therefore, in order to correctly solve the equation (12), the principle of minimum action must be used.

  FIG. 16 is a diagram for explaining a method of calculating an optical path difference based on the principle of minimum action in a thin film having a refractive index ny in the thickness direction (Y direction) and a refractive index nx in the boundary parallel direction (X direction).

The coordinate system is taken as shown in FIG. The light emitted from the point A (a, d) travels through the air layer, passes through the point X (x, 0), passes through the medium 1 (refractive index nx, ny), and reaches the point B (-a, -d). Shall. In general refraction theory

On the other hand, in order to obtain it using the principle of the minimum action, the time t for the light emitted from the point A to reach the point B via the point X is used, and X (x, 0) at which the time t is minimized. Is determined to be the path through which the actual light passes. In other words, if the speed of light is c,

And can be reduced to the problem of obtaining x where f (t) is a partial time differential f ′ (t) = 0.

On the other hand, when the refractive index is anisotropic as in this case, the action function f (t) is

Therefore, Equation (14) is solved. First, since x = α is the solution of equation (14),

Of these, it is necessary to obtain the thickness d, the refractive index, and the incident angle θ ₁ other than those.
First, the following equation is obtained from the previous two terms of equation (16).

Therefore, substituting these equations (18) and (19) into equation (17)

By substituting this into the equation (12) and arranging it, the following desired equation (21) can be obtained.

  In the equation (21), it can be seen that when nx = ny, it agrees with the equation (9).

  Therefore, when there is anisotropy in the refractive index of the thin film 33, the film thickness refractive index calculation unit 74 calculates the film thickness and refractive index of the thin film 33 using equation (21) instead of equation (9). Good.

  The anisotropy ratio ny / nx cannot be obtained only from the change in angle. For this reason, when using Formula (21), it is necessary to know the anisotropic ratio ny / nx in advance. The anisotropy ratio ny / nx may be experimentally obtained in advance by a method using a polarized wave or other methods, or information may be obtained in advance if it is determined from the manufacturing method.

  In addition, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 10 Film thickness measurement apparatus 11 Irradiation part 12 Light reception part 20 Light source 21 1st irradiation unit 22 2nd irradiation unit 25, 26, 53 Shutter 31 Measurement object 32 Substrate 33 Thin film 41 1st light reception unit 42 2nd light reception Unit 51 Third irradiation unit 52 Third light receiving unit 71 Incident angle control unit 72 Wavelength distribution generation unit 73 Optical path difference calculation unit 74 Film thickness refractive index calculation unit 80 Plano-convex lens

Claims (16)

A film thickness measuring device that measures the film thickness of the thin film based on the wavelength distribution of the reflected interference light generated by the optical path difference between the front surface reflected light and the back surface reflected light of the thin film,
An irradiating unit configured to irradiate the measurement target having the thin film formed on the substrate surface with irradiation light having a predetermined wavelength range at a first incident angle and a second incident angle different from the first incident angle; ,
First reflected interference light and second reflected interference light from the thin film of light irradiated at the first incident angle and the second incident angle are respectively converted into the first incident angle and the second incident light. A light receiving portion that receives light at a first reflection angle and a second reflection angle substantially equal to the angle;
A wavelength distribution generation unit that generates a first wavelength distribution and a second wavelength distribution for each of the first reflected interference light and the second reflected interference light;
An optical path for obtaining a first optical path difference corresponding to the first incident angle and a second optical path difference corresponding to the second incident angle based on the first wavelength distribution and the second wavelength distribution, respectively. A difference calculator;
The first incident angle, the second incident angle, and the first calculated by the optical path difference calculation unit are expressed using an expression representing the optical path difference as a function of the incident angle, the film thickness, and the refractive index as variables. Substituting the optical path difference and the second optical path difference into the above equation to obtain the film thickness and refractive index calculation unit for obtaining the film thickness and refractive index of the thin film;
A film thickness measuring device. The wavelength distribution generator is
For each of the first reflected interference light and the second reflected interference light, the discrete first wavelength distribution consisting of data for each predetermined wavelength interval and the first wavelength distribution are obtained by performing spectroscopy at a predetermined wavelength interval. Generate a second wavelength distribution;
The optical path difference calculation unit
Treating the discrete first wavelength distribution and the discrete second wavelength distribution as a function of the reciprocal of wavelength, for each non-equal interval of the reciprocal wavelength corresponding to the predetermined wavelength interval To obtain the first optical path difference and the second optical path difference by performing discrete Fourier transform
The film thickness measuring apparatus according to claim 1. The thin film is a multilayer film,
The wavelength distribution generated from each of the first reflected interference light and the second reflected interference light by the wavelength distribution generation unit depends on the optical path difference between the front surface reflected light and the back surface reflected light of each layer of the multilayer film. Has multiple peaks that occur,
The optical path difference calculation unit
Determining the first optical path difference and the second optical path difference for each of the peaks corresponding to the optical path difference of each layer;
The film thickness refractive index calculator is
Using the above formula, the first optical path difference and the second optical path difference for each peak of the respective layers calculated by the optical path difference calculation unit are calculated using the first incident angle and the second incident angle. By substituting into the equation, the film thickness and refractive index of each layer of the multilayer film are determined.
The film thickness measuring apparatus according to claim 2. The thin film is
An anisotropy having a first refractive index in the plane direction of the thin film and a second refractive index in the thickness direction of the thin film, and a ratio between the first refractive index and the second refractive index Sex ratio is known,
The film thickness refractive index calculator is
Calculation of the first incident angle, the second incident angle, and the optical path difference using an expression representing the optical path difference as a function of the incident angle, the film thickness, the first refractive index, and the anisotropy ratio as variables. From the first optical path difference and the second optical path difference calculated in the section and the known anisotropy ratio of the thin film, the thickness of the thin film, the first refractive index, and the second refractive index Seeking
The film thickness measuring apparatus according to any one of claims 1 to 3. The size of the light receiving spot area on the thin film of the optical system of the light receiving unit is
Larger than the size of the irradiation light spot area on the thin film of the optical system of the irradiation unit,
The film thickness measuring device according to any one of claims 1 to 4. The irradiation unit is
Setting the predetermined wavelength range of the irradiation light so that the lower limit wavelength of the predetermined wavelength range becomes a long wavelength according to the diameter of the particles constituting the thin film;
The film thickness measuring device according to any one of claims 1 to 5. The irradiation unit is
Having a broadband laser as a light source of the irradiation light,
The film thickness measuring device according to any one of claims 1 to 6. The irradiation unit is
A first irradiation unit for irradiating the measurement object with the irradiation light at the first incident angle; and irradiating the measurement object with the irradiation light at the second incident angle. A second irradiation unit of
The light receiving unit is
A first light-receiving unit disposed at a position facing the first irradiation unit via a normal line of the surface of the thin film and receiving the first reflected interference light; and the second light-receiving unit via the normal line A second light receiving unit that is disposed at a position facing the irradiation unit and receives the second reflected interference light,
The film thickness measuring device according to any one of claims 1 to 7. The irradiation unit is
A third irradiation unit for irradiating the measurement object with the irradiation light at a third incident angle;
The light receiving unit is
The third reflected interference light from the thin film of light incident at the third incident angle is disposed at a position facing the third irradiation unit via the normal line of the surface of the thin film, and A third light receiving unit for receiving light at a third reflection angle substantially equal to the incident angle of
The film thickness measuring apparatus according to claim 8. The irradiation unit is
A shutter provided on the optical path of the irradiation light;
After the irradiation light is irradiated at one incident angle and a wavelength distribution corresponding to the one irradiation angle is generated by the wavelength distribution generation unit, the irradiation light is irradiated at the next incident angle to generate the wavelength distribution. An incident angle control unit for controlling the shutter so that a wavelength distribution corresponding to the next irradiation angle is generated by the unit,
Further equipped with,
The film thickness measuring apparatus according to claim 8 or 9. The irradiation unit is
An irradiation unit having a variable position with respect to the measurement target so that an incident angle of the irradiation light with respect to the measurement target is variable;
The light receiving unit is
According to the position of the irradiation unit, the light receiving unit is disposed at a position facing the irradiation unit via the normal of the surface of the thin film, and the position relative to the measured object is variable.
An incident angle control unit for controlling the positions of the irradiation unit and the light receiving unit;
Further equipped with,
The film thickness measuring device according to any one of claims 1 to 7. The irradiation unit is
A plano-convex lens having an optical axis parallel to the normal line of the thin film and disposed so that a flat surface faces the thin film;
Further comprising
The irradiation unit and the light receiving unit are:
Arranged on the convex side of the plano-convex lens, and arranged so that the optical axes of the irradiation unit and the light receiving unit are parallel to the optical axis of the plano-convex lens,
The incident control unit includes:
The positions of the irradiation unit and the light receiving unit are controlled so that the positions of the optical axes of the irradiation unit and the light receiving unit are symmetrical with respect to the optical axis of the plano-convex lens. Changing the incident angle of the irradiation light by changing the distance to the optical axis of the convex lens;
The film thickness measuring apparatus according to claim 11. A film thickness measuring method for measuring the film thickness of the thin film based on the wavelength distribution of reflected interference light caused by the optical path difference between the front surface reflected light and the back surface reflected light of the thin film,
Irradiating the measurement object having the thin film formed on the substrate surface with irradiation light having a predetermined wavelength range at a first incident angle and a second incident angle different from the first incident angle;
First reflected interference light and second reflected interference light from the thin film of light irradiated at the first incident angle and the second incident angle are respectively converted into the first incident angle and the second incident light. Receiving at a first reflection angle and a second reflection angle approximately equal to the angle;
Generating a first wavelength distribution and a second wavelength distribution for each of the first reflected interference light and the second reflected interference light;
A step of obtaining a first optical path difference corresponding to the first incident angle and a second optical path difference corresponding to the second incident angle based on the first wavelength distribution and the second wavelength distribution, respectively. When,
The first incident angle, the second incident angle, and the first calculated by the optical path difference calculation unit are expressed using an expression representing the optical path difference as a function of the incident angle, the film thickness, and the refractive index as variables. Substituting the optical path difference and the second optical path difference into the equation to determine the film thickness and refractive index of the thin film;
A method for measuring a film thickness. Generating the first wavelength distribution and the second wavelength distribution;
For each of the first reflected interference light and the second reflected interference light, the discrete first wavelength distribution consisting of data for each predetermined wavelength interval and the first wavelength distribution are obtained by performing spectroscopy at a predetermined wavelength interval. Generating a second wavelength distribution;
Obtaining the first optical path difference and the second optical path difference;
Treating the discrete first wavelength distribution and the discrete second wavelength distribution as a function of the reciprocal of wavelength, for each non-equal interval of the reciprocal wavelength corresponding to the predetermined wavelength interval The first optical path difference and the second optical path difference are obtained by sampling and performing a discrete Fourier transform.
The film thickness measuring method according to claim 13. The thin film is a multilayer film,
The wavelength distribution generated from each of the first reflected interference light and the second reflected interference light has a plurality of peaks caused by the optical path difference between the front surface reflected light and the back surface reflected light of each layer of the multilayer film. And
Obtaining the first optical path difference and the second optical path difference;
Obtaining the first optical path difference and the second optical path difference for each of the peaks corresponding to the optical path difference of each layer;
The step of determining the thickness and refractive index of the thin film includes
Substituting the first optical path difference and the second optical path difference for each peak of the respective layers into the above formula using the formulas, the first incident angle and the second incident angle. The step of obtaining the thickness and refractive index of each layer of the multilayer film,
The film thickness measuring method according to claim 14. The thin film is
An anisotropy having a first refractive index in the plane direction of the thin film and a second refractive index in the thickness direction of the thin film, and a ratio between the first refractive index and the second refractive index Sex ratio is known,
The step of determining the thickness and refractive index of the thin film includes
Using the expression representing the optical path difference as a function of the incident angle, film thickness, first refractive index and anisotropy ratio as variables, the first incident angle, the second incident angle and the obtained Calculating the film thickness, the first refractive index, and the second refractive index of the thin film from the first optical path difference, the second optical path difference, and the known anisotropy ratio of the thin film. ,
The film thickness measuring method according to any one of claims 13 to 15.

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