JP2005201634A - Film thickness measuring method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a noncontact film thickness measuring method and an apparatus, capable of high accuracy measurement of the film thickness of multi-layer films in a short time. <P>SOLUTION: A two-layer film 8 includes both one layer having a film thickness close at least to the overall thickness of the multi-layer film and the other layer having a thin film thickness; light is irradiated to the two-layer film, to measure reflected light or transmitted light; and a temporary initial value of the one layer having a film thickness close to the overall film thickness of the two-layer film, is determined by an calculation part 5 on the basis of measured values, to arbitrarily determine the positive initial value of the other film thickness. The theoretical value in a film thickness in the vicinity of the temporary initial value is determined by the calculation part 5, to determine errors between the measured values and the theoretical value. A film thickness having minimum error is taken as the positive initial value of the film thickness of the one layer close to the overall film thickness of the two-layer film, to compute each film thickness of the two-layer film, on the basis of the positive initial value of each film thickness of the two-layer film. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a film thickness measuring method and apparatus for measuring the film thickness of a thin film in a non-contact manner by spectral interference.

  Conventionally, non-contact film thickness measurement by spectral interferometry is used for transparent films, and is used for film thickness measurement of various thin films. The non-contact film thickness measurement by the spectral interference method irradiates the film with light, and the reflected light from the film surface and the light that passes through the film and is reflected at the interface between the film and the substrate are captured by the spectrometer. The interference caused by the phase difference between the light and the latter is measured. Since the phase difference changes when the film thickness changes and the optical distance between the two changes, the film thickness is calculated from the refractive index of the film.

As a method for measuring the film thickness of the multilayer film, a method of calculating the film thickness of the multilayer film by a curve fit method using an optical simulation called a matrix method is used. In the curve fitting method, the theoretical values of reflectance and transmittance at the initial value of the multilayer film thickness are calculated by the matrix method, and the initial values are changed so that the error from the measured values is minimized, and the actual values are measured. The film thickness optimal for curve fitting to the reflectance and transmittance is calculated. (For example, refer to Patent Document 1).
JP 07-004922 A

  However, when calculating the film thickness using the curve fitting method, if the refractive index of the film to be measured differs greatly between the upper and lower parts of the film, the curve fitting error does not converge or the convergence error is too large. There is a problem of reduced accuracy. Further, as one of the problems in the curve fitting method, there is a case where the error function does not converge to a value at which the error is minimized depending on the initial value setting condition but converges to another minimum value of the error function. In order to avoid this, it takes a very long time to calculate an optimal solution, such as searching for a true minimum value by setting all initial values, and may not be applicable to actual product inspections.

  The present invention has been made paying attention to the above circumstances, and an object of the present invention is to provide a film thickness measuring method and apparatus capable of performing a highly accurate film thickness measurement of a multilayer film in a non-contact and short time. There is to do.

  The present invention solves such a problem, and the invention of claim 1 is a film thickness measuring method for measuring each film thickness of a multilayer film formed on a substrate, wherein the multilayer film is at least a multilayer film. Including one layer having a film thickness close to the entire film thickness and one thin layer having another film thickness, irradiating the multilayer film with light and measuring reflected or transmitted light; and A step of obtaining a temporary initial value of the thickness of one layer close to the thickness by calculation from the measured value obtained by the measurement, and a step of arbitrarily determining a positive initial value of the thickness of another thin layer Determining a theoretical value of the film thickness in the vicinity of the temporary initial value obtained by the calculation, obtaining an error between the measured value and the theoretical value, and setting a film thickness that minimizes the error to a film thickness of the entire multilayer film. A step of setting a positive initial value of the film thickness of the nearest one layer, and a positive initial value of the film thickness of each of the multilayer films A film thickness measuring method comprising the steps of calculating the respective film thicknesses of the multilayer film based.

  Therefore, in the invention of claim 1, when measuring each film thickness of the multilayer film formed on the substrate, the multilayer film includes at least one layer having a film thickness close to the film thickness of the entire multilayer film, One thin layer is included, and the reflected light or transmitted light is measured by irradiating the multilayer film with light. Then, a temporary initial value of the film thickness of one layer close to the film thickness of the entire multilayer film is obtained by calculation from the measured value obtained by measuring, and the positive initial value of the film thickness of the other thin film layer is arbitrary. The theoretical value of the film thickness in the vicinity of the temporary initial value obtained by calculation is obtained, and the error between the measured value and the theoretical value is obtained. The film thickness that minimizes the error is the positive initial value of the film thickness of one layer close to the film thickness of the entire multilayer film, and each film thickness of the two-layer film is based on the positive initial value of the film thickness of each multilayer film. Is calculated. For this reason, measurement accuracy can be improved and measurement time can be shortened.

  The invention according to claim 2 is the film thickness measuring method, wherein in the step of measuring the reflected light or transmitted light, the wavelength of the irradiated light is 400 to 750 nm.

  Therefore, in the invention of claim 2, when measuring the reflected light or transmitted light, the wavelength of light to be irradiated is set to 400 to 750 nm. For this reason, measurement accuracy can be improved and measurement time can be shortened.

  The invention of claim 3 is a film thickness measuring device for measuring each film thickness of the multilayer film formed on the substrate, and the multilayer film has a film thickness at least close to the film thickness of the entire multilayer film. One layer and one thin layer having another thickness, a measuring means for irradiating the multilayer film with light and measuring reflected light or transmitted light, and a single layer thickness close to the entire multilayer film thickness A temporary initial value calculating means for calculating the temporary initial value of the film from the measured value obtained by the measurement, and a positive initial value calculating means for arbitrarily determining a positive initial value of the film thickness of another thin film layer; , Calculating a theoretical value of the film thickness in the vicinity of the temporary initial value obtained by the calculation, calculating an error between the measured value and the theoretical value, and determining a film thickness that minimizes the error as a film thickness of the entire multilayer film And a positive initial value determining means for setting the positive initial value of the film thickness of one layer close to the positive initial value of the film thickness of each of the multilayer films. A film thickness measuring device comprising a film thickness calculation means for calculating the respective film thicknesses of the multilayer film Te.

  Therefore, in the invention of claim 3, when measuring each film thickness of the multilayer film formed on the substrate, the multilayer film includes at least one layer having a film thickness close to the film thickness of the entire multilayer film, and other layers. One thin layer is included, and the reflected light or transmitted light is measured by irradiating the multilayer film with light. Then, a temporary initial value of the film thickness of one layer close to the film thickness of the entire multilayer film is obtained by calculation from the measured value obtained by measuring, and the positive initial value of the film thickness of the other thin film layer is arbitrary. The theoretical value of the film thickness in the vicinity of the temporary initial value obtained by calculation is obtained, and the error between the measured value and the theoretical value is obtained. The film thickness that minimizes the error is the positive initial value of the film thickness of one layer close to the film thickness of the entire multilayer film, and each film thickness of the two-layer film is based on the positive initial value of the film thickness of each multilayer film. Is calculated. For this reason, measurement accuracy can be improved and measurement time can be shortened.

  Further, the invention of claim 4 is the film thickness measuring apparatus according to the measuring means, wherein the wavelength of light to be irradiated is 400 to 750 nm.

  Therefore, in the invention of claim 4, the wavelength of the irradiated light is 400 to 750 nm. For this reason, the film thickness can be accurately measured in a short time.

  According to the film thickness measuring method and apparatus of the present invention, since the initial value of the film thickness of one layer close to the film thickness of the entire multilayer film is obtained in two stages, the measurement accuracy is improved and each film thickness of the multilayer film is improved. Measurement time can be shortened compared to the conventional method.

  Next, the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration diagram showing an embodiment of a film thickness measuring apparatus according to the present invention.

  As shown in FIG. 1, the film thickness measuring device according to the present invention includes a light source unit 1, a branching fiber 2, an objective lens 3, a spectroscope 4, and a calculation unit 5.

  The light source unit 1 includes a light bulb 10 and a cut filter 9. For example, a halogen bulb having a large amount of visible light is used as the bulb 10. In the bifurcated fiber 2, a portion connected to the light source unit 1 is for light projection, and a portion connected to the spectroscope 4 is for light reception. Each of them is, for example, a bundle of several hundred optical fibers, and they are combined into one on the way. Among these bundles, each of the light projecting and receiving optical fibers is bundled together so that both optical fibers are evenly arranged on the surface connected to the objective lens 3. . The objective lens 3 condenses incident light on a PS film on a substrate to be measured, such as a liquid crystal display substrate (for example, a PS (photo spacer) film and an ITO (transparent conductive) film) 8. . The spectroscope 4 includes a spectroscope unit 6 including a diffraction grating, a linear array, and the like, and a control unit 7 that controls the spectroscope unit 6 and digitally converts signals. The calculation unit 5 includes a personal computer, a keyboard, a mouse, a display monitor, and the like, and performs calculation to calculate a film thickness value. In addition, the spectroscope 4 is controlled and user interface processing is performed.

  Next, a film thickness measuring method to which the film thickness measuring apparatus according to the present invention is applied will be described with reference to the flowchart of FIG. This is a film thickness measurement method that measures each film thickness of a multilayer film formed on a substrate. This multilayer film is composed of one layer having a film thickness close to the film thickness of the entire multilayer film and another film. This can be applied when the thickness is a very thin layer.

  First, light from a light source is applied to the multilayer film (step S1).

  Next, reflected light or transmitted light from the substrate is measured with a spectroscope (step S2).

  Next, the multilayer film is regarded as a single-layer film close to the entire multilayer film thickness, and a method for determining the film thickness of the single-layer film such as the PV method from the measured value obtained in step S2 is used. The value obtained by the calculation is used as a temporary initial value of the thickness of one layer close to the entire thickness of the multilayer film, and a positive initial value of the thickness of a very thin layer is arbitrarily determined (step S3). .

  Next, a theoretical value for the film thickness in the vicinity of the temporary initial value obtained in step S3 is obtained by a matrix method, and an error between the measured value and the theoretical value is obtained (step S4).

  Next, the film thickness that minimizes the error between the calculated theoretical value and the measured value is set as the positive initial value of the film thickness of one layer close to the film thickness of the entire multilayer film (step S5).

  Next, based on the positive initial value of the film thickness of each multilayer film, each film thickness of the multilayer film is calculated using an optimization method such as a least square method (step S6).

  Subsequently, a specific example in the case where the multilayer film is a two-layer film will be described using the case where the film thicknesses of the PS film and the ITO film of the substrate for a liquid crystal display device are measured.

  In step S1, incident light that is output from the light source unit 1 and passes through the objective lens 3 is condensed on the liquid crystal display substrate 8 that is an object to be measured. In step S 2, the incident light is reflected on the liquid crystal display substrate 8, and the reflected light enters the spectroscope 4 via the objective lens 3 and the two-branch fiber 2. In addition, although the wavelength to be used for the spectroscope 4 is determined by the combination of the diffraction grating and the linear array element, it is sufficient to use a wavelength range of about 400 nm to 750 nm which is a visible light region. In step S3, the calculation unit 5 regards the two-layer film of the PS film and the ITO film as a single-layer film of the PS film, measures the film thickness using the PV method, and sets it as a temporary initial value. Further, a positive initial value of the ITO film thickness is arbitrarily determined. In step S4, a theoretical value in the film thickness near the temporary initial value of the PS film thickness is obtained, and an error between the measured value and the theoretical value is obtained. In step S5, the calculation unit 5 sets the film thickness that minimizes the error as a positive initial value of the film thickness of the two-layer PS film. In step S6, the calculation unit 5 calculates the film thickness of each of the two-layer films based on the two positive initial values using, for example, the least square method.

  Thus, according to the present invention, the PS film thickness measurement apparatus uses a halogen bulb with a large amount of light in the visible light region as a light source, and thus is not affected by the change in refractive index between the upper and lower portions in the ITO film. The film thickness can be calculated in a wide wavelength range.

  Next, the reason why the wavelength range of about 400 nm to 750 nm, which is the visible light region, has been used as the measurement light when measuring the film thicknesses of the PS film and the ITO film will be described. FIG. 3 shows the change in the refractive index between the upper and lower portions in the ITO film for Sample 1 and Sample 2. The change in the refractive index is clearly smaller in the visible light region than in the near infrared region. Therefore, the calculation error resulting from the curve fitting method in the visible light wavelength range is significantly smaller than the result of the curve fitting method processing in the near infrared wavelength region. Is shown in

  These results are the results of applying the curve fitting method using the optimal initial values described later, and are the problems of the physical properties of the ITO film that have nothing to do with the superiority or inferiority of the processing method. It was found that this could be solved.

  Subsequently, an initial value setting method of the curve fitting method applied in the present embodiment will be described. In the curve fitting method, the setting of the initial value is an extremely important factor, and the accuracy of the film thickness calculation can be good or bad depending on the setting. FIG. 5 shows the result of a simulation of the difference in the convergence result of the film thickness calculation according to the initial value setting conditions of the curve fitting method, and the comparison. In this simulation, a PS film of 4500 nm and an ITO film of 160 nm were used. The left side of the figure is the initial value of each of the PS film and the ITO film, and the right side is the convergence value of each.

  It should be noted in the above results that there are two variables of initial film thickness, ITO film thickness and PS film thickness. As apparent from the results shown in FIG. 5, the initial value of the PS film is very close to the true value (4500 nm), but only the correct value (4500 nm) is converged. The initial value is set to the correct value (160 nm) even if it is not so close to the true value (160 nm).

  Furthermore, in the measurement of ITO film thickness, it is possible to control the film thickness within the range of about 130 nm to 190 nm for manufacturing, and within this range, any value can be used as the initial value for curve fitting. It can be seen that there is no significant influence on the film thickness calculation by the method.

  However, in the measurement of the PS film thickness, it is difficult to control the film thickness for forming the PS film in production, and the measurement requires a range of about 2000 nm to 6000 μm. If any value is set as the initial value within this range, depending on the value, it will not converge to the correct value, and the performance of the inspection apparatus cannot be satisfied.

  When this cause is verified using FIG. 10 (a diagram plotting the error amount with respect to the PS film thickness displacement when the ITO film thickness is constant), the ITO film thickness is made constant and the PS film thickness is changed. In the case of the error function, the waveform is periodic, and there are many local minimum values in the range necessary for PS film thickness measurement. It is necessary to set the initial value of the PS film thickness within a range of about plus or minus 50 nm. On the other hand, in the error function when the thickness of the ITO film is changed and the thickness of the ITO film is changed, although not shown, there is only one minimum value in the range necessary for measuring the thickness of the ITO film. It can be seen that if the initial value of the ITO film thickness is set in the range of about 130 nm to 190 nm, the film thickness will converge to the correct film thickness.

  In consideration of manufacturing problems in the measurement of the PS film on the liquid crystal display substrate 8, the ITO film thickness is set to an initial value within a controllable range, and the PS film thickness is determined by some method. It is necessary to calculate the correct film thickness by applying the curve fitting method after setting the initial value within a range of about ± 50 nm of the true film thickness.

  From the above, it can be seen that the method for setting the initial value of the PS film thickness should be cleared. In this embodiment, the initial value is set using the film thickness measurement method using the PV method, which has a well-established measurement of the single layer film, for the measurement of the PS film. The method will be described in more detail below.

  The film thickness measurement method using the PV method is a measurement method that is strong against noise and has high accuracy, but its strict theory applies only to a single layer film, and is fundamental for estimation of a multilayer film. Not applicable to. However, the film thickness of the ITO film formed on the substrate 8 for the liquid crystal display device is thin. Even if the PS film formed on the ITO film is further measured by ignoring the thickness, the measurement error is about 3%. Measurement is possible. In this embodiment, first, an approximate measurement of the PS film is performed by this PV method, and a temporary initial value is calculated.

  A plurality of PS film samples were measured by applying the PV method, and the results are shown in FIG. As described above, the PS film thickness is measured by the PV method. As can be seen from the results of FIG. 6, it is found that the calculation cannot be performed with the accuracy of plus or minus 50 nm described above (accuracy with the contact method within 50 nm). did. Let the initial value measured here be a temporary initial value.

  Then, further, for example, the range of plus or minus 400 nm of the film thickness corresponding to the temporary initial value obtained by the PV method is operated at an interval of 25 nm, and the point where the error calculated by the matrix method is the smallest is determined. Is used as the initial value (positive initial value).

  The accuracy of the film thickness measurement calculated by applying the curve fitting method using the initial value (positive initial value) determined as described above is high. Since the curve fitting method is a well-known method, detailed description thereof is omitted here. Further, in the present invention, the PV method is described as a method for obtaining the temporary initial value, but any measurement method that can know the approximate film thickness (for obtaining the temporary initial value) can be used. Such a method may be used.

  Hereinafter, the present invention will be described in more detail using specific embodiments of the present invention.

  In the present embodiment, an embodiment of a method for measuring a film composed of two layers of an ITO film and a PS film formed on the liquid crystal display device substrate 8 and obtaining the PS film thickness with high accuracy will be described. In addition, the spectroscope used for the measurement uses the reflection type measuring instrument made from Matsushita Inter-Techno Co., Ltd., and the wavelength to be used shall be 450 nm-700 nm, for example. In addition, the personal computer as the arithmetic unit used was a CPU equipped with Pentium 3 and a memory equipped with 128 MB.

  The film thickness is measured based on the above conditions, and compared with the measured value of the contact-type film thickness measuring apparatus, the film thickness measuring apparatus applying the PS film thickness measuring method according to the present invention is evaluated. .

  First, the spectral reflectance of the PS film on the liquid crystal display substrate 8 is measured with a measuring apparatus having the same configuration as in FIG. (Initial value) is calculated. The actually measured spectral reflectance is as shown in FIG. 7, and the PS film thickness calculated by the PV method is as follows.

PV method calculation (tentative initial value) = 3657 nm
In this way, using the PS film thickness obtained by the PV method as a temporary initial value, the range of this value, for example, plus or minus 400 nm is operated at 25 nm intervals, and the error is calculated by the matrix method. The ITO film thickness was constant at 160 nm.

The calculation method is as follows.

The error calculated by the matrix method is as shown in FIG.

  Since the PS film thickness at the minimum of the errors in FIG. 8 is 3482 nm, this is determined as the initial value, and the film thickness using the curve fit method is combined with the initial value of the ITO film thickness of 160 nm. Is calculated. As a result of comparing the film thickness measured by the PS film measuring apparatus according to the present invention with the measured value of the contact type film thickness measuring apparatus, the measured value of the PS film thickness according to the present invention is 3476 nm, and the PS film thickness measured by the contact type is measured. The value was 3453 nm and the film thickness difference was 0.67%.

The measured value of the ITO film thickness according to the present invention was 157 nm.

  Moreover, the result of having implemented this with the sample of several PS film | membrane is FIG. 9, and the error of film thickness was 0.36-1.60%.

  As described above, by using the PS film thickness measuring method and the PS film thickness measuring apparatus of the present invention, it becomes possible to measure the PS film thickness with higher accuracy than the conventional method. In addition, in order to avoid calculation convergence with incorrect values of the disadvantages of the curve fit method, “the tentative initial value is set by the PV method” and “the tentative initial value is calculated in detail, and errors due to the matrix method are calculated. By adopting a two-step method of “setting the point where the calculated value is minimized” to the initial value, all the points of 2000 nm to 6000 nm necessary for the measurement of the PS film thickness are used as the initial values to introduce errors. Compared with the method that calculates and finds the minimum value, the calculation time is greatly reduced. This shortening of the calculation time is very important in the measurement of the PS film thickness in the manufacturing process, and the inspection on the production line is also possible by using the film thickness measuring apparatus and the film thickness measuring method of the present invention. Further, by adopting a curve fitting method using a theoretical matrix method for obtaining the optical characteristics of the multilayer film, reliability in actual operation can be obtained.

  In this apparatus, an example of measuring by reflectance is given. However, transmittance can be measured by changing the optical system. In that case, the equation of the matrix method is also an equation for obtaining the transmittance.

It is a lineblock diagram showing one embodiment of a film thickness measuring device concerning an embodiment of the present invention. It is a flowchart of the film thickness measuring method concerning embodiment of this invention. It is the figure which showed the refractive index of the upper part and lower part of the ITO film | membrane concerning embodiment of this invention. It is the figure which showed the comparison by the simulation by the curve fit method concerning embodiment of this invention, and the reflectance of an actual measurement value in the wavelength range of a near infrared region and a visible light region. It is a figure which shows the result of having simulated the difference of the convergence result of the film thickness calculation by the setting conditions of the initial value of the curve fitting method concerning embodiment of this invention, and compared. It is a figure which shows the result of having measured the film thickness of the several sample of PS film | membrane concerning embodiment of this invention by applying PV method. It is a figure which shows the spectral reflectance concerning embodiment of this invention. It is a figure which shows the error computed by the matrix method concerning embodiment of this invention. It is a figure which shows the comparison result of the measured value of PS film | membrane concerning the embodiment of this invention, and the measured value by a contact type. It is a figure which shows the plot of the error amount with respect to PS film thickness displacement when the ITO film thickness concerning embodiment of this invention is made constant.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light source part, 2 ... 2 branch fiber, 3 ... Objective lens, 4 ... Spectroscope, 5 ... Calculation part, 6 ... Spectroscope part, 7 ... Control part , 8 ... Substrate for liquid crystal display device, 9 ... Cut filter, 10 · · Light bulb

Claims (4)

A film thickness measuring method for measuring each film thickness of a multilayer film formed on a substrate, wherein the multilayer film has at least one film thickness close to the film thickness of the entire multilayer film and other film thicknesses. Including one thin layer,
Irradiating the multilayer film with light to measure reflected light or transmitted light;
Obtaining a temporary initial value of the film thickness of one layer close to the film thickness of the entire multilayer film by calculation from the measured value obtained by the measurement;
A step of arbitrarily determining a positive initial value of the thickness of another thin layer;
Obtaining a theoretical value of the film thickness in the vicinity of the temporary initial value obtained by the calculation, and obtaining an error between the measured value and the theoretical value;
Setting the film thickness at which the error is minimized to a positive initial value of the film thickness of one layer close to the film thickness of the entire multilayer film;
Calculating each film thickness of the multilayer film based on the positive initial value of the film thickness of each multilayer film;
A film thickness measuring method including: The film thickness measuring method according to claim 1, wherein the wavelength of light applied in the step of measuring the reflected light or transmitted light is 400 to 750 nm. A film thickness measuring device for measuring each film thickness of a multilayer film formed on a substrate, wherein the multilayer film includes at least one film having a film thickness close to the film thickness of the entire multilayer film and other film thicknesses. Including one thin layer,
Measuring means for irradiating the multilayer film with light and measuring reflected light or transmitted light;
A temporary initial value calculating means for calculating a temporary initial value of the film thickness of one layer close to the film thickness of the entire multilayer film by calculation from the measured value obtained by the measurement;
Positive initial value calculating means for arbitrarily determining the positive initial value of the film thickness of other thin layers;
An error calculation means for obtaining a theoretical value in a film thickness in the vicinity of the temporary initial value obtained by the calculation, and obtaining an error between the measured value and the theoretical value;
A positive initial value determining means for setting the film thickness at which the error is minimized to a positive initial value of a film thickness of one layer close to the film thickness of the entire multilayer film;
Film thickness calculation means for calculating each film thickness of the multilayer film based on the positive initial value of the film thickness of each multilayer film,
A film thickness measuring device including The film thickness measuring apparatus according to claim 3, wherein in the measuring means, the wavelength of light to be irradiated is 400 to 750 nm.

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