JP2006201040A - Method of measuring film thickness - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of measuring film thickness which enables the measurement of each film thickness of a multilayer film formed on a substrate by using an ultrasonic wave, and can measure each film thickness of the multilayer film non-destructively or measure it safely, inexpensively, simply and precisely in a film forming process. <P>SOLUTION: In the method, the ultrasonic wave 5 is brought to impinge obliquely at an incident angle θ on the surface of the multilayer film 8 formed on the substrate 1, and the reflectivity of a reflection wave 7 is measured, and the thickness of one film in the multilayer film 8 is measured by using a frequency (intensity minimum frequency) as an index at which the intensity of the reflectivity becomes minimum. For measuring the film thickness, a higher mode of the intensity minimum frequency is used. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a film thickness measuring method for measuring each film thickness of a multilayer film formed on a substrate using ultrasonic waves.

  Conventionally, a method of measuring the thickness of a film formed on a substrate using ultrasonic waves is known (see Patent Document 1 and Patent Document 2).

  The case where the thickness of the copper foil on a printed circuit board is measured is demonstrated as a specific example of the film thickness measuring method using an ultrasonic wave. When an ultrasonic pulse is projected onto the printed circuit board through water at an incident angle θ, a surface wave is excited in the upper copper foil at a specific frequency f. Therefore, when looking at the spectrum of the reflected wave, a dip point (minimum portion) appears at the frequency f. The value obtained by multiplying the minimum frequency f by the thickness d of the copper foil is specific to the material to be measured. If the incident angle θ and the surface wave mode are determined, the relationship of f · d = c (constant) is obtained. To establish. This c is called the fd value, and the minimum frequency f of the standard sample whose film thickness d is known is obtained to determine the fd value. The thickness of the copper foil to be obtained is obtained from d = (fd value) / f.

However, conventionally, the thickness of a film formed on a substrate using ultrasonic waves can be obtained only by measuring the thickness of a single layer film. When this method is applied to a multilayer film, the film thickness cannot be uniquely measured in principle. Therefore, each film thickness of the multilayer film could not be measured.
Japanese Patent Publication No. 6-13964 JP 7-49225 A

  The problem to be solved is to provide a film thickness measuring method capable of measuring each film thickness of a multilayer film formed on a substrate using ultrasonic waves. It is an object to provide a film thickness measurement method that can be measured non-destructively or safely, inexpensively, easily and with high accuracy in a film formation process.

  In order to solve the above-mentioned problems, the present invention is a film thickness measuring method for measuring each film thickness of a multilayer film formed on a substrate using ultrasonic waves. A mode is used.

  Further, it is a film thickness measuring method for measuring each film thickness of a multilayer film formed on a substrate using ultrasonic waves, and uses a high-order mode of an intensity minimum frequency for film thickness measurement, and a higher order with respect to the film thickness in advance. A mode minimum intensity frequency is obtained in advance, and a film thickness is obtained by measuring the intensity minimum frequency of a higher-order mode at the time of film thickness measurement.

  Further, the reflectance when the ultrasonic wave is obliquely incident on the surface of the multilayer film formed on the substrate is measured, and the frequency at which the intensity of the reflectance is minimized (intensity minimal frequency) is used as an index. A film thickness measuring method for measuring the film thickness of one of the films, characterized in that a high-order mode with a minimum intensity frequency is used for film thickness measurement.

  Further, the reflectance when the ultrasonic wave is obliquely incident on the surface of the multilayer film formed on the substrate is measured, and the frequency at which the intensity of the reflectance is minimized (intensity minimal frequency) is used as an index. A film thickness measuring method for measuring the film thickness of one of the films, using a high-order mode of an intensity minimum frequency for film thickness measurement, and obtaining an intensity minimum frequency of a higher-order mode relative to the film thickness in advance. When measuring the thickness, the intensity minimum frequency of the higher order mode is measured to obtain the film thickness.

  The film thickness measurement method of the present invention is a film thickness measurement method for measuring each film thickness of a multilayer film formed on a substrate using ultrasonic waves, and uses a higher-order mode with a minimum intensity frequency for the film thickness measurement. Thus, it is possible to provide a film thickness measuring method capable of measuring each film thickness of the multilayer film formed on the substrate using ultrasonic waves, and nondestructively each film thickness of the multilayer film. Alternatively, it is possible to provide a film thickness measuring method that can be measured safely, inexpensively, easily, and with high accuracy in the film forming process.

  The film thickness measurement method of the present invention measures the reflectivity when ultrasonic waves are obliquely incident on the surface of a multilayer film formed on a substrate, and indicates the frequency at which the intensity of the reflectivity is minimized (intensity minimum frequency). As a film thickness measurement method for measuring the film thickness of one of the multilayer films, a high-order mode having a minimum intensity frequency is used for the film thickness measurement. By doing so, it is possible to provide a film thickness measuring method capable of measuring each film thickness of the multilayer film formed on the substrate using ultrasonic waves. It is possible to provide a film thickness measuring method that can be measured safely, inexpensively, easily, and with high accuracy in a non-destructive manner or in a film forming process.

  FIG. 1 is an explanatory diagram showing a measurement concept according to an embodiment of the present invention.

  In the present invention, the reflectance of the reflected wave 7 is measured when the ultrasonic wave 5 is obliquely incident on the surface of the multilayer film 8 formed on the substrate 1 at an incident angle θ, and the frequency at which the intensity of the reflectance is minimized ( A film thickness measuring method for measuring the film thickness of one of the multilayer films 8 using the intensity minimum frequency) as an index, and using a higher-order mode of the intensity minimum frequency for the film thickness measurement. An example will be described below including experimental results.

  As an example, a case where bismuth (Bi) 2 and silver (Ag) 3 are formed in two layers on a copper (Cu) alloy substrate 1 will be described. On the copper alloy substrate 1, silver 3 was coated at 4.8 μm, and bismuth 2 was coated at 7.4 μm. First, the influence of the film thickness on the ultrasonic reflectance of the coating material was examined.

  FIG. 2 shows the intensity of ultrasonic reflectance of the coating material when water 4 is used as a medium, as a function of the ultrasonic incident angle and frequency. It can be seen that the intensity locally decreases when the incident angle θ is around 29 degrees and the frequency is around 30 MHz. Such a behavior of the reflectance intensity of the reflected wave 7 is caused by excitation of the surface wave, and is closely related to the coating film thickness. Therefore, it is determined that the film thickness can be evaluated using the minimum position (intensity minimum frequency) f of the reflectance intensity as an index.

  Therefore, FIG. 3 shows the results of examining the film thickness dependence using the intensity minimum frequency f at an incident angle θ of 30 degrees as an index. FIG. 3 shows not only the relationship between the intensity minimum frequency f and the film thickness of bismuth (Bi) 2 but also the influence of the film thickness of silver (Ag) 3. In addition, the behavior of the high-order mode (second-order mode and third-order mode are shown) of the intensity minimum frequency f is also shown. From this result, it can be seen that the intensity minimum frequency f changes significantly depending on the film thickness, and the film thickness can be measured by using the intensity minimum frequency f as an index.

  However, in the basic mode of the intensity minimum frequency f, the intensity minimum frequency f is influenced not only by the film thickness of bismuth (Bi) 2 but also by the film thickness of silver (Ag) 3. It may be difficult to determine the thickness uniquely. On the other hand, in the higher order mode (second order mode and third order mode) of the intensity minimum frequency f, it can be seen that the intensity minimum frequency f is hardly affected by the film thickness of silver (Ag) 3. Therefore, in the high-order mode of the intensity minimum frequency f, the film thickness of bismuth (Bi) 2 can be measured with high accuracy.

  FIG. 2 shows the result of theoretical calculation, and the actual measurement result is shown in FIG. In the actual measurement, bismuth (Bi) 2 and silver (Ag) 3 were formed in two layers on the copper (Cu) alloy substrate 1 as in the case of theoretical calculation. On the copper alloy substrate 1, silver 3 was coated at 4.8 μm, and bismuth 2 was coated at 7.4 μm. The ultrasonic reflectance was measured using the broadband pulsed ultrasonic wave 5 in the range of the incident angle θ of 20 ° to 40 °, and the frequency spectrum was obtained. The result shown in FIG. 4 is in good agreement with the theoretical calculation result shown in FIG. 2, and a clear intensity minimum frequency f is observed. There is a slight difference in the intensity minimum frequency f between the calculation result and the experimental result, which is considered to be due to the uncertainty of the material property value used in the calculation.

  Specifically, when the silver alloy 3 having an arbitrary film thickness is coated on the copper alloy substrate 1 and the bismuth 2 having an arbitrary film thickness is coated thereon, when it is desired to know the film thickness of the bismuth 2, for example, If the intensity minimum frequency f of the secondary mode of the intensity minimum frequency f at an incident angle θ of 30 degrees is measured and this measured value is, for example, 300 MHz, the film thickness of the bismuth 2 is about 4 μm from the data of FIG. It can be seen that it is.

  In the above description, the case where a two-layer film is formed on a substrate has been described. However, in the present invention, even when three or more films are formed on a substrate, the film thickness of each layer is set to the above-described two layers. It can be measured in the same manner as in the case of the layer film.

  In the above description, the higher-order mode is described for the second-order mode and the third-order mode, but a higher-order mode higher than the fourth-order mode can be used as necessary.

  As described above, the film thickness measurement method of the present invention measures the reflectance when the ultrasonic wave 5 is obliquely incident on the surface of the multilayer film 8 formed on the substrate 1, and the intensity of the reflectance is minimized. This is a film thickness measurement method for measuring the film thickness of one of the multilayer films 8 using the frequency (minimum intensity frequency) as an index, and uses a higher-order mode of an intensity minimum frequency for the film thickness measurement. By doing so, it is possible to provide a film thickness measuring method capable of measuring each film thickness of the multilayer film formed on the substrate using ultrasonic waves. It is possible to provide a film thickness measuring method that can be measured safely, inexpensively, easily, and with high accuracy in a non-destructive manner or in a film forming process.

It is explanatory drawing which shows the measurement concept concerning one Example of this invention. It is explanatory drawing which shows the theoretical calculation result concerning one Example of this invention. It is explanatory drawing which shows the result of having investigated the film thickness dependence concerning one Example of this invention. It is explanatory drawing which shows the experimental result concerning one Example of this invention.

Explanation of symbols

1 Substrate 5 Ultrasound 7 Reflected Wave 8 Multilayer Film θ Incident Angle

Claims (4)

A film thickness measurement method for measuring each film thickness of a multilayer film formed on a substrate using ultrasonic waves, wherein the film thickness measurement method uses a high-order mode of an intensity minimum frequency for film thickness measurement. . A film thickness measurement method for measuring each film thickness of a multilayer film formed on a substrate using an ultrasonic wave, using a high-order mode of an intensity minimum frequency for film thickness measurement, A film thickness measuring method characterized in that an intensity minimum frequency is obtained, and a film thickness is obtained by measuring an intensity minimum frequency of a higher-order mode at the time of film thickness measurement. The reflectance when ultrasonic waves are obliquely incident on the surface of the multilayer film formed on the substrate is measured, and the frequency (intensity minimum frequency) at which the intensity of the reflectance is minimized is used as an index. A film thickness measuring method for measuring a film thickness of one film, wherein a high-order mode having a minimum intensity frequency is used for the film thickness measurement. The reflectance when ultrasonic waves are obliquely incident on the surface of the multilayer film formed on the substrate is measured, and the frequency (intensity minimum frequency) at which the intensity of the reflectance is minimized is used as an index. A film thickness measurement method for measuring the film thickness of a single film, using a high-order mode with a minimum intensity frequency for film thickness measurement, and obtaining a minimum intensity frequency of a higher-order mode with respect to the film thickness in advance. A method for measuring a film thickness, characterized in that the film thickness is sometimes obtained by measuring an intensity minimum frequency of a higher mode.

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