JP2007010475A - Thickness of membrane measuring device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thickness of membrane measuring device capable of measuring the thickness of a membrane with good precision on real time even regarding the membrane of uneven thickness and large grain growth accompanied by the thickness of the membrane. <P>SOLUTION: The method of measuring the thickness of the membrane attaching on the steel plate having largely different grain growth surface depending on the thickness of the membrane, comprises the following steps: the light projection process for projecting the linear polarization light having the parallel and vertical components of azimuth angle to the incident surface of the measurement surface; the light receiving process for receiving the light with the specular component of the reflection light from the measurement surface at the surface and inside of the membranes and three polarization angles by setting the elliptic polarized light changed by the reflection component of the dispersion/scattering on the surface and inside of the membrane to the angles of the major axis, minor axis and the intermediate angle between the major axis and the minor axis; and the thickness operation process using the multiple regression equation for estimating the thickness of the membrane, based on the received light amount in the light receiving process. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a film thickness measuring apparatus and method for measuring a film thickness by, for example, irradiating polarized light on a steel sheet surface and receiving polarized light reflected from a film adhering to the irradiated steel sheet.

  One of the polarization applied measurements is an ellipsometer film thickness measuring technique, which is a technique often used for measuring a thin film on a silicon wafer. When linearly polarized light is incident on the film, the light reflected from the film by reflection on the surface of the film and multiple reflection inside the film is reflected as elliptically polarized light. A method for measuring the ellipticity Δ of the elliptically polarized light, the azimuth angle ψ, and the complex refractive index of the measurement object that is known in advance to obtain the film thickness is called ellipso logic.

  As a conventional technique using this ellipso logic, for example, there is a technique disclosed in Patent Document 1. This technology measures a chromium oxide film on a chromium layer on a substrate, a linearly polarized light source, a splitting means for splitting elliptically polarized light reflected by the film into a plurality of partial constraints, and a partial luminous flux The means for measuring the intensity of each and the ellipticity Δ of elliptically polarized light is calculated from the intensity. From the discovery that the azimuth angle ψ is constant within a certain incident angle range peculiar to chromium oxide, the film thickness is calculated by measuring only the ellipticity Δ using the azimuth angle ψ known in advance.

  As another conventional technique, there is a technique disclosed in Patent Document 2. This is a film thickness measurement technique that measures the film thickness of the thin film applied to the substrate. By entering two different wavelength lights at the same incident angle and the same linear polarization angle, the ellipticity Δ and the azimuth angle ψ are obtained. This is a technique for calculating the film thickness and measuring the film thickness even when the complex refractive index of the base changes.

As another technique, for example, there is a method of measuring the amount of oxygen adhering to the surface of a steel sheet and converting the film thickness by using an ultra-low acceleration SEM method disclosed in Patent Document 3.
JP-A-2-263105 JP-A-63-36105 JP 2005-98923 A

  The techniques disclosed in Patent Document 1 and Patent Document 2 described above both receive linearly polarized light, measure the elliptically polarized light of the reflected light, determine the ellipticity Δ and azimuth angle ψ of the ellipsometer parameter, Furthermore, it is a technique for obtaining the film thickness by using ellipso logic by combining the complex refractive index of the surface. However, the oxide film adhering to the surface of the steel sheet to be measured by the present invention is not a uniform film, but a surface on which the crystal grows on the steel sheet, and becomes a film in which crystals and voids are mixed. Yes. For this reason, clean multiple reflection does not occur inside the film, scattering on the surface, scattering reflection on the inside occurs, the conventional ellipso logic does not hold, and the techniques disclosed in Patent Document 1 and Patent Document 2 described above, There was a problem that an accurate film thickness was not required.

  In addition, the technique using the ultra-low acceleration SEM method described above has a problem that it takes a very long measurement time because it is necessary to punch out a sample of about 1 cm for measurement and measure the sample in a vacuum. .

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a film thickness capable of measuring the film thickness accurately and in real time even for a film in which the film is not uniform and crystal growth increases depending on the film thickness. It is to provide a measuring device and method.

  The invention according to claim 1 of the present invention is a film thickness measuring apparatus for measuring a film thickness of a film having a surface on which a crystal grows greatly depending on the film thickness attached to the steel sheet, A linearly polarized light source having an azimuth angle component parallel to the incident surface and a perpendicular azimuth angle component; reflected light from the surface to be measured on the film surface and inside the film; and on the film surface and inside the film Light receiving means for receiving light at three polarization angles, wherein the elliptically polarized light changed by the scattering / diffuse reflection component of light is set to the major axis, the minor axis, and the intermediate angle between the major axis and the minor axis of the elliptically polarized light, and the light receiving means And a film thickness calculation processing device that estimates the film thickness by a multiple regression equation based on the amount of received light.

  The invention according to claim 2 of the present invention is the film thickness measuring device according to claim 1, wherein the film is an oxide film adhered to the surface of the steel sheet, and the network crystal is changed to a plate crystal depending on the film thickness. It is a film thickness measuring device characterized by being a film that grows greatly.

  The invention according to claim 3 of the present invention is a film thickness measuring method for measuring the film thickness of a film having a surface on which a crystal has grown that differs greatly depending on the film thickness attached to the steel sheet. Projecting the linearly polarized light having an azimuth angle component parallel to the incident surface and a perpendicular azimuth angle component to the surface to be measured, and reflecting light from the surface to be measured on the film surface and inside the film. Three polarization angles with elliptical polarized light changed by the reflection component and the scattering / diffuse reflection component on the film surface and inside the film set to the major axis and minor axis of the elliptical polarization and the angle between the major axis and minor axis A film thickness measuring method, comprising: a light receiving process for receiving light at a light receiving process; and a film thickness calculation processing process for estimating a film thickness by a multiple regression equation based on the amount of light received by the light receiving process.

  Furthermore, the invention according to claim 4 of the present invention is the film thickness measuring method according to claim 3, wherein the film is an oxide film adhering to the surface of the steel sheet, and from a network crystal to a plate crystal. The film thickness measuring method is characterized in that the film grows greatly.

  In the present invention, linearly polarized light is incident, and the film thickness is measured by luminance measurement of three detection angles of elliptically polarized light affected by scattering on the film surface, scattering inside the film, and the difference in crystal surface depending on the film thickness. Therefore, the film thickness can be measured with high accuracy in real time even for a film in which the film is not uniform and crystal growth increases with the film thickness.

  The best mode for carrying out the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing a configuration example of a film thickness measuring apparatus according to the present invention. In the figure, 1 is a rod-shaped light source unit, 2 is a polarizing plate, 3 is a light receiving polarizing plate, 4 is a line sensor camera, 5 is an A / D converter, 6 is a film thickness calculation processing device, and 7 is a film thickness output device. Each is shown. First, a rod-shaped light source for irradiating the surface to be measured as linear light is used as a light source for entering linearly polarized light. This light source is composed of a rod-shaped light source unit 1 for emitting linear light, a cylindrical lens (not shown) for condensing light attached in front of it, and a polarizing plate 2 placed in front of it. Composed.

  The installation angle of the polarizing plate 2 is set to 45 °, and 45 ° linearly polarized light is incident on the surface to be measured. The linearly polarized light is polarized light having an azimuth component parallel to the incident surface with respect to the surface to be measured and a vertical azimuth component. If this linear light source is a thin linear light source that can uniformly illuminate the steel sheet and sufficiently secure the amount of light, the light from the lamp was guided to both ends of a transparent light guide rod partially coated with diffuse reflection paint. A linear light source, a fiber light source in which light from a lamp is linearly guided by an optical fiber, or another linear light source may be used.

  Light from this polarized light source is irradiated linearly onto the surface to be measured at a projection angle of 60 °. Then, the line sensor camera 4 receives the regular reflection light having a light receiving angle of 60 ° through the light receiving polarizing plate 3 disposed in front of the camera. The angle of the light receiving polarizing plate 3 is the long axis angle of the elliptically polarized light of the reflected light (I3, mainly receiving the regular reflection light component) and the short axis angle (I2, mainly receiving the diffuse reflection component). A total of three light receiving polarization angles of an intermediate angle between the axis and the short axis (I1, including regular reflection light and diffuse reflection light components) are selected, and light is received using the three line sensor cameras 4. At this time, the optical axes of the three cameras are adjusted so as to see the same linear shape on the steel plate.

  In the measurement of the oxide film on the target steel plate, the projection angle of 60 ° was optimal. However, the optimum value of the correlation with the film thickness differs depending on the shape of the target oxide film and the crystal growth. It is necessary to set the incident angle.

  The polarization angle of the light receiving polarizing plate is the angle between the major axis of the elliptical polarized light reflected from the film surface, I3 = −45 °, the minor axis is I2 = 45 °, and the major axis / minor axis on the surface of the target oxide film. Although I1 was set to 0 °, the major axis and minor axis angles of the reflected elliptically polarized light differ depending on the crystal state and surface shape state of the oxide film to be measured. Therefore, it is necessary to select the optimum angles I1, I2, and I3.

  FIG. 2 is a diagram schematically showing the state of reflection on the surface due to the difference in measurement object. (A) shows the conventional uniform film structure in which multiple reflection of the ellipso logic is realized, and (b) shows the structure in which the plate-like crystal of the oxide film targeted by the present invention is grown. .

  As shown in FIG. 2 (b), the target surface is an oxide film grown on a steel plate in a plate shape and is a film in which crystals are uniformly dense. There are many. For this reason, the light entering the film cannot be subjected to clean multiple reflection like the conventional ellipsometer inside the film, and the ellipso logic does not hold.

  When light enters the target oxide film, a component that is regularly reflected on the surface of the film and a component that is partially scattered / diffuse reflected are generated. The light that has entered the film is scattered inside and part of the light is reflected in the regular reflection direction, and part of the light is reflected in the direction of the optical axis of the camera as scattered / diffuse reflected light. When the reflected light was measured, it was found that the incident linearly polarized light was reflected as elliptically polarized light under the influence of reflection including scattering on the surface and inside of the film.

  Therefore, by measuring the state of this elliptically polarized light and receiving polarized light having an angle between the major axis (I3) and minor axis (I2) and an angle between the major axis and minor axis (I1), the specular reflection component is received. The light is received at three polarization angles having the light of the above, the light of the diffuse reflection component, and the light of both the regular reflection diffuse reflection. The received light is output as an analog signal, and through the A / D converter 5, the film thickness calculation processing device 6 performs arithmetic processing to obtain the film thickness, and is output to the film thickness output device 7.

  The arithmetic processing in the film thickness arithmetic processing device 6 has a model for estimating the thickness of the target oxide film, and the creation of this film thickness model will be described below.

  To create a film thickness model, first, the amount of oxygen on the surface of the steel sheet is measured by the current extremely low acceleration SEM method, and the film thickness is converted to obtain the film thickness. Using this value as the correct value for the film thickness, multiple samples with different film thickness levels are prepared, and the film thickness is measured by the ultra-low acceleration SEM method. These film thickness measurement values and the data of the same pixels (positions) I1, I2 and I3 when measured on the steel sheet with the camera of the received light amount received at the three polarization angles of I1, I2 and I3 described above. Use the multiple regression to create a model formula for film thickness measurement.

In the oxide film targeted this time, a model of the film thickness X is constructed by, for example, the following equation (1).
X = A × I1 + B × I2 + C × I3 + D (1)
In the above equation (1), A, B, C, and D are constants, which are parameters that vary depending on the type of oxide film, physical properties, and the degree of crystal growth with respect to the film thickness. For this reason, it is necessary to obtain constants beforehand for the oxide film to be actually measured by the above-described model creation procedure.

  FIG. 3 is a diagram showing an example of a film thickness measurement result according to the present invention. The film thickness measured by the ultra-low acceleration SEM method is compared with the film thickness obtained from the polarization luminance information of I1, I2 and I3 measured by the optical system of the present invention. It was confirmed that the thickness can be measured with very high accuracy. According to the present invention, it has become possible to realize film thickness measurement of an oxide film having crystal growth on the surface, which could not be measured by conventional ellipso logic.

  In the present invention, since the line sensor camera is used and the film thickness calculation formula is simple, the apparatus configuration can be measured at a personal computer level in real time. In the present invention, the spot position can be measured in 100 msec or less where a very low acceleration SEM method has been required for measuring the spot position, and thus the film thickness can be measured over the entire width of the steel sheet in real time. The present invention makes it possible for the first time to perform online film thickness measurement and film thickness change detection.

It is a figure which shows the structural example of the film thickness measuring apparatus which concerns on this invention. It is the figure which showed typically the mode of reflection on the surface by the difference in a measuring object. It is a figure which shows an example of the film thickness measurement result by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bar-shaped light source part 2 Polarizing plate 3 Light-receiving polarizing plate 4 Line sensor camera 5 A / D converter 6 Film thickness calculation processing apparatus 7 Film thickness output apparatus

Claims (4)

A film thickness measuring device for measuring a film thickness of a film having a surface on which a crystal grows greatly depending on a film thickness attached on a steel sheet,
A linearly polarized light source having a component of an azimuth angle parallel to the incident surface with respect to the surface to be measured and a component of a perpendicular azimuth angle;
Reflected light from the surface to be measured is converted into specular reflection components on the film surface and inside the film, and elliptically polarized light changed by scattering / diffuse reflection components on the film surface and inside the film, A light receiving means for receiving light at three polarization angles set at an intermediate angle between the long axis and the short axis;
A film thickness measuring apparatus comprising: a film thickness calculation processing apparatus that estimates a film thickness by a multiple regression equation based on the amount of light received by the light receiving means. In the film thickness measuring device according to claim 1,
The film thickness measuring apparatus is characterized in that the film is an oxide film attached to the surface of a steel plate, and is a film in which plate crystals grow greatly from a network crystal according to the film thickness. A film thickness measuring method for measuring a film thickness of a film having a surface on which a crystal grows greatly depending on a film thickness attached on a steel sheet,
A light projecting step in which linearly polarized light having a component of an azimuth angle parallel to the incident surface with respect to the surface to be measured and a component of a perpendicular azimuth angle is incident on the surface to be measured;
Reflected light from the surface to be measured is converted into specular reflection components on the film surface and inside the film, and elliptically polarized light changed by scattering / diffuse reflection components on the film surface and inside the film, A light receiving step for receiving light at three polarization angles set at an intermediate angle between the long axis and the short axis;
A film thickness calculation method comprising: a film thickness calculation processing step of estimating a film thickness by a multiple regression equation based on the amount of received light received in the light receiving step. In the film thickness measuring method according to claim 3,
The film thickness measuring method characterized in that the film is an oxide film attached to the surface of a steel plate, and is a film in which plate crystals grow greatly from a network crystal according to the film thickness.