JP2006071316A - Film thickness acquiring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve correspondence for a system representing a color space unique to a light receiving device and to speedily acquire an in-plane distribution of the thickness of a film provided on a flat plate with a simple constitution in a film thickness acquiring method. <P>SOLUTION: Irradiation light from a light source of which wavelength distribution is broad is made incident on a film provided over a substrate to be measured. Interfering reflected light from the film is measured by a light receiving device. The color variation of the interfering light due to different film thickness where the intensity of the interfering light becomes maximal and minimal for every wavelength of the measured reflected light, is detected in reference with the hue defined by NTSC standard, thereby acquiring the thickness of the film. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a film thickness acquisition method. For example, when a thin film is applied on a flat plate in a manufacturing process of a liquid crystal display device or the like, the distribution of the applied thin film thickness can be obtained at high speed with a simple apparatus. The present invention relates to a method for obtaining a film thickness characteristic of the structure.

  In the manufacturing process of a liquid crystal display device or the like, a number of thin film forming processes such as a photoresist coating process or an antireflection film forming process are required. In such a thin film forming process, a thin film film is required. It is necessary to make the thickness uniform, and in particular, as the liquid crystal panel becomes larger, further in-plane uniformity is required to increase the manufacturing yield.

  Conventionally, as a method for measuring the thickness of such a thin film in a non-contact manner, a type using a change in polarization due to interference and a method using a change in spectral reflectance due to interference are known.

Among these types, an ellipsometer is a type that uses a change in polarization due to interference. This ellipsometer measures and analyzes changes in polarization of incident light and reflected light, and measures film thickness, optical constants, material properties, and the like. Device.
The data obtained by this measurement has various features such as the ability to measure a film having a complicated structure, but the apparatus is generally expensive.

On the other hand, the film thickness meter using the spectral reflectance, when white light is reflected by a thin film, provides a spectral reflectance whose reflection intensity varies depending on the wavelength due to interference.
The film thickness and optical constant can be measured by fitting with a waveform obtained by measuring this with a spectroscope or by maximal / minimal analysis.

A method for measuring the thickness of the color material layer using the chromaticity of reflected light has also been proposed (see, for example, Patent Document 1).
This proposal uses the fact that the color of the color material layer itself appears to change as the thickness increases.
JP 7-225119 A

  However, the conventional film thickness inspection technique described above has a problem that basically only a local film thickness can be measured at the same time. In order to measure the film thickness distribution in the substrate surface, There is a problem that it takes a lot of time.

  Also, whether it is an ellipsometer or a film thickness meter using a spectroscope, the measuring instrument part is expensive and large, so it is realistic to arrange the measuring instruments in an array and measure a wide area at the same time. It is difficult.

Therefore, in order to obtain a film thickness distribution over a wide area, it is necessary to scan the measuring instrument along the object to be measured. It will take a lot of time.
In particular, the time required for measurement greatly increases as the liquid crystal panel becomes larger.

  The proposal in the above-mentioned patent document 1 does not use coloring due to interference in a thin film, and is intended for measurement of a film thickness on the order of several tens of μm to several μm. The film thickness cannot be measured with an accuracy of several percent or more.

  Therefore, the present inventor makes the irradiation light from the light source having a wide wavelength distribution incident on the film provided on the substrate which is the measurement object, and measures the reflected light causing interference from the film by the light receiving device, The film thickness of the coating can be determined by detecting the change in the color of the interference light due to the difference in the thickness of the interference light having the maximum and minimum values for each measured reflected light wavelength, based on the chromaticity of the XYZ color system. It has been proposed to obtain (see Japanese Patent Application No. 2000-072222).

  However, R, G, and B acquired by a CCD camera or the like is a system that represents a color space unique to the camera, whereas the XYZ color system is a system that represents an actual color and is 1: 1 when converted. There is a problem that it is not easy to use.

  Therefore, the present invention improves the compatibility with the system representing the color space unique to the light receiving device and obtains the in-plane distribution of the film thickness of the thin film provided on the flat plate with a simple configuration at high speed. Objective.

FIG. 1 is a conceptual diagram showing the correlation between film thickness and hue representing the basic configuration of the present invention. Here, means for solving the problems in the present invention will be described with reference to FIG.
See FIG. 1. (1) In order to achieve the above object, according to the present invention, in the film thickness acquisition method, irradiation light from a light source having a wide wavelength distribution is incident on a film provided on a substrate as a measurement object. Then, the reflected light causing interference from the coating is measured by a light receiving device, and the color change of the interference light due to the difference in the thickness of the interference light is maximized and minimized for each wavelength of the measured reflected light. The film thickness of the film is obtained by detecting the hue defined by the standard as a reference.

  Instead of capturing the change in film thickness as a change in wavelength dependency or polarization state as in the past, the light receiving device detects the change in the hue of light by using the hue H based on the NTSC standard as a color change. Since only the acquisition is required, the apparatus configuration is simplified and the measurement speed can be increased.

  In this case, as shown in FIG. 1, the hue changes between 0 ° and 360 ° as the film thickness changes under the condition of a specific incident angle under a light source having a continuous wavelength. Can be converted into a film thickness.

  In addition, since the change in hue due to the change in the intensity of the interference light for each wavelength of reflected light in the thin film is used, it is possible to measure the thickness of the colorless film, and the thickness of the submicron order is several. % Accuracy can be measured.

  (2) Further, according to the present invention, in the film thickness acquisition method, the reflected light caused the interference from the coating by causing the irradiation light from the light source having a wide wavelength distribution to enter the coating provided on the substrate as the measurement object. The light is measured by the light receiving device, and the change in the color of the interference light due to the difference in the film thickness at which the intensity of the interference light is maximized and minimized for each wavelength of the reflected light is measured using the HSV color system, the HSL color system, Alternatively, it is characterized in that the film thickness of the coating is obtained by detecting the hue of any one of the HSB color schemes as a reference.

In this way, instead of the hue H based on the NTSC standard, the hue H of any one of the HSV color system, the HSL color system, or the HSB color system may be used as a reference.
Since the hue H in each method is substantially equivalent except that the colors arranged in the hue circle are different, the same accuracy can be obtained.

(3) Further, according to the present invention, in the method for obtaining a film thickness, the irradiation light from a light source having a wide wavelength distribution is incident on a film provided on a substrate as a measurement object, and the reflection caused interference from the film. The light is measured by the light receiving device, and the change in the color of the interference light due to the difference in the film thickness at which the intensity of the interference light is maximized and minimized for each wavelength of the measured reflected light is represented by u ′ and v ′ in the LUV color system. Alternatively, the film thickness of the coating is obtained by detecting a ^* and b ^* in the LAB color system.

As described above, instead of the hue H based on the NTSC standard, u ′ and v ′ of the LUV color system or a ^* and b ^* of the LAB color system may be used as a reference.
Since this LUV color system or LAB color system is a system representing an actual color, it is effective when a device such as a luminance meter or the like that directly measures the color is used as the light receiving device.

  (4) Moreover, the present invention is characterized in that, in any one of the above (1) to (3), a two-dimensional distribution of the film thickness of the thin film is obtained using an area sensor type image sensor as the light receiving device. To do.

Thus, by using an area sensor type image sensor as the light receiving device and using each pixel of the image sensor as an individual light receiving element, it is possible to obtain a large area two-dimensional film thickness distribution at high speed.
In this case, the image sensor may be any of a CCD type, a CMOS type, or a MOS type.

  (5) Further, in the above (4), the present invention is characterized in that an image for each of R, G, and B is acquired by the light receiving device.

In this way, by obtaining an image for each of R, G, and B by the light receiving device, the RGB value can be converted to the NTSC standard hue H, luminance Y, saturation S, or HSV color system or HSB color system color. H, saturation S, brightness V (Value) or B (Brightness) Y, or hue H, saturation S, brightness L (Lightness) of the HSL color system, or lightness L (Lightness) of the LUV color system , U ′, v ′, or lightness L (Lightness), a ^* (red-green axis), b ^* (yellow-blue axis) of the LAB color system, each hue being an index of hue H, u ′ and v ′, or a ^* and b ^* may be used.

  According to the present invention, using a general CCD type or CMOS type area sensor type image sensor, colors due to interference in a wide area are collectively acquired as RGB values, and an index representing hue such as hue of the NTSC standard. Since the film thickness is obtained from the film thickness-hue correlation, the correspondence with the RGB values acquired by the light receiving device is improved, and a special measuring instrument such as a spectroscope is required as in the past. Therefore, it is possible to perform measurement at high speed, which contributes to cost reduction and high display quality of a large liquid crystal display device.

  The present invention makes light irradiated from a light source with a wide wavelength distribution incident on a film such as a photoresist provided on a substrate as a measurement object, and receives reflected light that causes interference from the film, in particular, a light receiving device, Changes in the color of the interference light due to the difference in the thickness of the interference light intensity, which is measured with a CCD type or CMOS type area sensor image sensor, and the interference light intensity is maximized or minimized for each measured reflected light wavelength. Is converted into an index representing the hue such as hue H, and the correspondence between the index representing the converted hue and the film thickness is fitted to obtain the film thickness of the film.

Here, with reference to FIG. 2 thru | or FIG. 6, the film thickness acquisition method of embodiment of this invention is demonstrated.
FIG. 2 is a conceptual configuration diagram of a film thickness acquisition apparatus used in the embodiment of the present invention. An area sensor type color CCD camera 12 having a surface light source 11 and an imaging lens 15, and a measurement target. A measurement panel 13 on which a thin film is formed and a stage 14 on which the measurement panel 13 is horizontally placed and held are configured.

  Here, a normal fluorescent tube that emits light at a continuous wavelength is used as the surface light source 11, and the surface light source is sufficiently diffused on the surface of the surface light source so that there is no change in luminance and chromaticity depending on the prospective angle, or there is no practical problem. Use the one with little fluctuation.

  The color CCD camera 12 is a 3CCD color camera that acquires image signals for each of R, G, and B using three CCDs, and is installed at an angle of about 15 ° from the vertical direction.

  Since the image captured by the color CCD camera 12 is distorted due to the influence of the tilt of the camera and the aberration of the imaging lens 15, the distortion of the captured image is corrected, and the shape of the image on which measurement panel 13 is corrected. Also make sure the correct image is obtained.

  By taking an image of the measurement panel 13 with such a film thickness acquisition device, for each pixel of the CCD constituting the color CCD camera 12, a difference in hue due to a difference in film thickness of the thin film at a corresponding position of each pixel. Thus, outputs of different RGB values are obtained.

  It is assumed that the color CCD camera 12 used here is white balanced under the light source 11 for imaging so that the change in film thickness is efficiently reflected in the change in color.

At this time, the hue H in the NTSC standard is obtained from the RGB values of the image acquired using the color CCD camera 12.
First, RGB values are converted into luminance Y and color differences C ₁ and C ₂ by the following equations (1) to (3).
Y = 0.3R + 0.59G + 0.11B (1)
C ₁ = R−Y = 0.7R−0.59G−0.11B (2)
C ₂ = BY = −0.3R−0.59G + 0.89B (3)

Next, the hue H and the saturation S are obtained from the Y, C ₁ , and C ₂ values by the equations (4) and (5).
H = tan ⁻¹ (C ₁ / C ₂ ) (4)
S = (C ₁ ² + C ₂ ² ) ^−1/2 (5)

Next, a method for converting the obtained hue H to film thickness will be described.
As shown in FIG. 1, the hue H changes between 0 ° and 360 ° as the film thickness changes, and changes from 0 ° (color close to blue) → 90 ° (red) It circulates in the order of close color) → 180 ° (yellowish green) → 270 (blue green) → 360 ° (color close to blue).

At this time, the coordinates on which plane at which film thickness are obtained are based on the wavelength intensity distribution of the light source used, the refractive index and the extinction coefficient of the thin film and the substrate to be measured as shown in FIG. The film thickness is obtained by making a table by making a table of such fluctuations and fitting the hue obtained by actual measurement with this reference.
When the change in film thickness is large, as shown in FIG. 1, the same hue may be shown in a plurality of film thicknesses. However, considering that the film thickness changes continuously, the film thickness range is limited. It can be dealt with by the method of doing.

Based on the above, a specific film thickness acquisition method will be described with reference to FIGS. FIG. 3 is an explanatory diagram of the positional relationship between the color CCD camera and the measurement panel at the time of imaging. As a measurement target, a resist film 22 applied on a glass substrate 21 having a size of 1800 mm × 1500 mm used for a large liquid crystal panel. And
The refractive index n of this photoresist is n = 1.619 when λ = 550 nm.

Here, the height H from the surface of the glass substrate 21 provided with the resist film 22 to be measured to the principal point of the imaging lens 15 of the color CCD camera 12 is set to 440 mm.
At this time, if the focal length of the imaging lens 15 is 4 mm and the CCD size is a 1/3 inch type, the angle of view is approximately 61 ° × 48 °.

  The range of 48 ° from the height of 440 mm on the surface of the glass substrate 21 is about 400 mm, and the range of 61 ° is 760 mm. Therefore, in order to cover an area of 1800 mm × 1500 mm, the glass substrate 21 is 3 × It is necessary to divide the image into 4 and divide it into 12 parts.

Also, here, the film thickness of the photoresist film 22 is set to about 500 nm, and this is targeted to be able to detect a film thickness change of 3%.
3% of 500 nm is 15 nm, and if a safety factor is expected and 0.3% is targeted, it is necessary to detect a film thickness change of 1.5 nm.

See FIG. 4 FIG. 4 shows, as a conversion table, the result of simulating changes in hue associated with changes in the film thickness of a thin film when viewed from a viewing angle of 30 ° under a certain light source.
Here, the result of the sample which apply | coated the resist on BK7 board | substrate is shown.

See FIG. 5. The chromaticity curve shown in FIG. 5 was obtained by graphing the data shown in FIG.

  Next, the RGB values of the predetermined area are acquired at once using the color CCD camera 12, and the hue H of the area corresponding to each pixel is obtained from the above formulas (1) to (5). Fit to obtain film thickness.

At this time, when the hue H is corrected, if there is data of about 3 significant digits, it can be said that a film thickness difference of 1 nm can be detected.
Since the RGB values acquired by measurement are converted to hue H by linear conversion, it is considered that the significant figures at the time of the RGB values are almost preserved. Therefore, a CCD having a gradation of 10 bits for each of R, G, and B should be used. It will be good.

The RGB value acquired at the point P of the viewing angle θ = 30 ° of the measurement panel 13 by the color CCD camera 12 is
(R, G, B) = (196, 224, 184)
Suppose that

Next, by applying this to the above formulas (1) to (4),
H = 209.2
Is obtained.
Note that the saturation S is not used in the film thickness acquisition method of the present invention.

  When the hue H and the data of the conversion table shown in FIG. 4 are fitted to detect the film thickness with the smallest difference, the film thickness d at the point P is d = 406 nm.

  When the viewing angle of the point to be obtained is different from the point P, the film thickness distribution of the entire measurement panel can be obtained by creating and converting the same table as FIG. 4 for each viewing angle. .

Although the embodiments of the present invention have been described above, the present invention is not limited to the configurations described in the embodiments, and various modifications can be made.
For example, in the above embodiment, a 3CCD color area sensor is used as the light receiving device, but a color area sensor using a single CCD may be used.
Further, the system is not limited to the CCD system, and a CMOS type or MOS type area sensor may be used.

  In addition, the camera tilt angle, installation height H, and viewing angle for capturing images set in the first embodiment are merely examples, and can be appropriately changed according to the resolution of the camera used and the numerical aperture of the lens used. Needless to say.

  In the first embodiment, a film thickness-hue correlation conversion table is prepared in advance by simulation, and the film thickness is obtained by fitting with this table. Actually, various film thickness references are actually measured. Thus, a conversion table of film thickness-chromaticity correlation may be prepared, and the light source at this time is a light source having the same wavelength intensity distribution as that for measuring the film thickness of the thin film in the actual manufacturing process. Use it.

  For example, using a standard sample whose film thickness is known and changing stepwise, move it in steps for every predetermined moving distance Δ to obtain RGB values, and obtain the hue at each viewing angle θ. In addition, the correction coefficient for the position shifted in the horizontal direction (Y direction) from the center line can be obtained simultaneously.

  In the first embodiment, the hue H based on the NTSC standard is used as the hue standard. However, the hue H is not limited to the hue H based on the NTSC standard, and various colors or various colors are used. An index indicating the hue of the color system may be used.

For example, instead of the hue H based on the NTSC standard, the hue H of the HSV color system may be used as a reference.
This HSV color system is a system expressed using three elements of hue H, saturation S, and lightness V (Value). Hue H is 0 ° with respect to red, and clockwise, red → yellow → green → It is represented by a hue circle in which colors are arranged in 360 ° from blue to purple to red.

Since the hue H of the HSV color system is substantially equivalent to the hue H based on the NTSC standard except that the colors arranged in the hue circle are different, the same accuracy can be obtained.
Note that the saturation S is represented by 0 to 100%, and the lightness V is 100% for the lightest color for each hue and 0% for the darkest color, that is, black.

Alternatively, instead of the hue H based on the NTSC standard, the hue H of the HSB color system may be used as a reference.
This HSB color system is a system that uses three elements of hue H, saturation S, and lightness B (Brightness), and is the same as the HSV color system except for lightness B.

Alternatively, instead of the hue H based on the NTSC standard, the hue H of the HSL color system may be used as a reference.
This HSL color system is a system expressed using three elements of hue H, saturation S, and lightness L (Lightness), and the hue used for film thickness acquisition of the present invention is the same as the HSV color system.
The lightness B in this case is white with a maximum lightness of 100%, black with a minimum lightness of 0%, and the lightness of the purest color of each hue is 50%. The definition of lightness and saturation is HSV color specification. It is different from the method.

  The above color specification method is suitable for an image pickup apparatus that separates colors into RGB, such as a color CCD camera, etc. However, if a device such as a luminance meter that directly measures the color is used, it is equivalent. An LUV color system or a LAB color system standard, which is a typical color system of a color space (UCS: Uniform Color Space), may be used.

  This LUV color system is a system expressed using three elements of lightness L (Lightness), u ′, and v ′. As a standard regarding the hue used in the film thickness acquisition of the present invention, u ′ and v ′ are combined. Can be used.

This LAB color system is a system that uses three elements of lightness L (Lightness), a ^* (red-green axis), and b ^* (yellow-blue axis), and is used for film thickness acquisition of the present invention. As a reference for the above, a ^* and b ^* may be used together.

  In the first embodiment, the method for obtaining the film thickness of the resist film formed on the glass substrate constituting the liquid crystal panel is described. However, the method is not limited to the resist film, and various thin film films are used. It is applied to the measurement of thickness, and may be transparent or semi-transparent to the wavelength serving as the light source.

  The present invention is not limited to a liquid crystal panel, and is also applicable to a film forming process in another display device such as a plasma display device or various film forming steps in a manufacturing process of various devices such as a semiconductor device. It is what is done.

  Furthermore, the present invention is not limited to the film forming process of a specific apparatus, but can be applied to all film forming processes for forming a micron to submicron order thin film on a substrate having a flat surface.

In Embodiment 1 of the present invention, a normal fluorescent lamp is used as the light source, but a fluorescent lamp that is as close to white as possible is desirable.
In addition, the light source is not limited to white light, and may be a light source having a continuous wavelength intensity distribution in a certain wide wavelength range. In this case, color prediction is performed in consideration of the color deviation of the light source from the beginning. Just do it.

  As a practical example of the present invention, the film thickness measurement of each coating film in the manufacturing process of a large liquid crystal panel is typical, but it is not limited to a large liquid crystal panel, but various sizes of liquid crystal panels and organic EL The present invention is also applied to a film forming process in an electronic device such as a plasma display panel and a semiconductor device, and further applied to all processes for applying a thin film on a plate-like body.

It is a conceptual diagram which shows the correlation of the film thickness and hue which show the fundamental structure of this invention. It is a notional block diagram of the film thickness acquisition apparatus used for the Example of this invention. It is explanatory drawing of the positional relationship of the color CCD camera and measurement panel in Example 1 of this invention. It is a hue-film thickness conversion table in a film thickness range of d = 400 to 559 nm. It is a graph which shows the correspondence of the hue-film thickness in the range whose film thickness is d = 400-559 nm.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Surface light source 12 Color CCD camera 13 Measurement panel 14 Stage 15 Imaging lens 21 Glass substrate 22 Resist film

Claims (5)

Irradiation light from a light source with a wide wavelength distribution is incident on a coating provided on the substrate that is the object to be measured, the reflected light causing interference from the coating is measured by a light receiving device, and the wavelength of the measured reflected light The film thickness of the coating film is obtained by detecting the color change of the interference light due to the difference in the film thickness at which the intensity of the interference light is maximum and minimum for each time, based on the hue defined by the NTSC standard. A characteristic film thickness acquisition method. Irradiation light from a light source with a wide wavelength distribution is incident on a coating provided on the substrate that is the object to be measured, the reflected light causing interference from the coating is measured by a light receiving device, and the wavelength of the measured reflected light The color change of the interference light caused by the difference in film thickness at which the intensity of the interference light is maximized and minimized is different for each of the color schemes of the HSV color scheme, the HSL color scheme, and the HSB color scheme. A film thickness acquisition method, wherein the film thickness of the film is acquired by detecting the hue as a reference. Irradiation light from a light source with a wide wavelength distribution is incident on a coating provided on the substrate that is the object to be measured, the reflected light causing interference from the coating is measured by a light receiving device, and the wavelength of the measured reflected light The change in the color of the interference light due to the difference in the thickness of the interference light that is maximized and minimized for each, with reference to u ′ and v ′ of the LUV color system or a ^* and b ^* of the LAB color system. A film thickness acquisition method comprising acquiring the film thickness of the coating film by detection. 4. The film thickness acquisition method according to claim 1, wherein an area sensor type image sensor is used as the light receiving device to obtain a two-dimensional distribution of the film thickness of the thin film. The film thickness acquisition method according to claim 4, wherein an image for each of R, G, and B is acquired by the light receiving device.

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