JP3811728B2 - Film thickness acquisition method - Google Patents

Description

なお、（１）式におけるＡはカラーフィルタの特性を表す３行３列の変換行列である。
【００２９】
次いで、（２）式によって、ＸＹＺ値を色度ｘ，ｙに変換すれば良い。
【数２】

【００３０】
次いで、得られた色度ｘ，ｙから膜厚への変換方法を説明する。
上述の図１に示したように、薄膜の膜厚が変化するにつれて、色度はｘ−ｙ平面上を移動する。
【００３１】
このとき、どの膜厚の時に、どの平面上のどの座標になるかを、使用する光源の波長強度分布、測定対象となる薄膜の屈折率を基にして図１のような変動をテーブル化してリファレンスとし、実測によって得られた色度座標をこのリファレンスとフィッティングすることによって膜厚を求める。
なお、膜厚の変化が大きい場合、異なる膜厚の時にも色度が近い値をとることがあるが、その場合は膜厚範囲を限定するなどの方法で対処すれば良い。
【００３２】
以上を前提として、次に、図３乃至図６を参照して、具体的膜厚取得方法を説明する。
図３参照
図３は、撮像時のカラーＣＣＤカメラと測定パネルの位置関係の説明図であり、測定対象として、大型液晶パネルに用いる１８００ｍｍ×１５００ｍｍのサイズのガラス基板２１上に設けたＳｉＯ₂ 膜２２とする。
なお、ＳｉＯ₂ の屈折率ｎは、λ＝６３２．８ｎｍの時に、ｎ＝１．４５となる。
【００３３】
ここでは、測定対象のＳｉＯ₂ 膜２２を設けたガラス基板２１の表面から、カラーＣＣＤカメラ１２の撮像用レンズ１５の主点までの高さＨを４４０ｍｍに設定する。
このとき、撮像用レンズ１５の焦点距離を４ｍｍ、ＣＣＤのサイズを１／３インチタイプとすると、画角は約６１°×４８°となる。
【００３４】
ガラス基板２１表面における４４０ｍｍの高さから４８°の範囲は約４００ｍｍであり、また、６１°の範囲は７６０ｍｍとなるので、１８００ｍｍ×１５００ｍｍの面積をカバーするためには、ガラス基板２１を３×４に１２分割して撮像する必要がある。
【００３５】
また、ここではＳｉＯ₂ 膜２２の膜厚は、およそ４００ｎｍ程度とし、これを、3 ％の膜厚変化を検出可能にすることを目標とする。
４００ｎｍの３％は１２ｎｍで、安全率を見込んで０．３％を目標とすると、１．２ｎｍの膜厚変化を検出する必要がある。
【００３６】
図４及び図５参照
図４及び図５は、ある光源のもとで、視野角３０°から見た時の薄膜の膜厚の変化に伴う色度の変化をシミュレーションした結果を変換テーブルとして示したものである。
【００３７】
図６参照
上記の図４及び図５に示したデータをグラフすることによって、図６に示した色度曲線が得られた。
【００３８】
ついで、カラーＣＣＤカメラ１２を用いて所定領域のＲＧＢ値を一括して取得し、上記の式（１）及び（２）から、各ピクセルに対応する領域の色度座標（ｘ，ｙ）を求め、予め取得したデータとフィッティングして膜厚を求める。
【００３９】
このとき、色度に直した時点で、有効数字３桁程度のデータがあれば、１ｎｍの膜厚差を検出できると言える。
測定により取得したＲＧＢ値から線形変換によってＸＹＺに変換するため、ほぼＲＧＢ値の時点の有効数字は保存されると考えられるので、Ｒ，Ｇ，Ｂそれぞれについて１０ｂｉｔの諧調を持つＣＣＤを使用すれば良いことになる。
【００４０】
使用するＲ，Ｇ，Ｂのそれぞれについて１０ビットの諧調を持つＣＣＤカメラについて、ＲＧＢ値からＸＹＺ表色系のＸＹＺ値に変換する具体的式が、下記の式（３）で表すことができるとする。
【数３】

【００４１】
カラーＣＣＤカメラ１２で測定パネル１３の視野角θ＝３０°の点Ｐにおいて取得したＲＧＢ値が、下記の（４）式である。
【数４】

【００４２】
次いで、これを上記の（１）式で線形変換し、さらに上記（２）式により、
ｘ＝０．３０８
ｙ＝０．３６５
の色度座標が得られる。
【００４３】
この色度座標（ｘ，ｙ）と、図４及び図５に示した変換テーブルのデータとをフィッティングして、最も差が小さくなる膜厚を検出したところ、点Ｐの膜厚ｄは、ｄ＝３８８ｎｍとなる。
【００４４】
なお、求める点の視野角が、点Ｐとは異なる場合は、それぞれの視野角ごとに図４及び図５と同様なテーブルを作成して変換することで、測定パネル全体の膜厚分布を求めることができる。
【００４５】
以上、本発明の実施の形態を説明してきたが、本発明は実施の形態に記載した構成に限られるものではなく、各種の変更が可能である。
例えば、上記の実施の形態においては受光装置として３ＣＣＤ型のカラーエリアセンサを用いているが、１枚のＣＣＤを用いたカラーエリアセンサを用いてもよい。
また、方式はＣＣＤ方式に限られるものではなく、ＣＭＯＳ型或いはＭＯＳ型のエリアセンサを用いても良いものである。
【００４６】
また、上記の実施の形態において設定したカメラの傾斜角、設置高さＨ、画像を取り込む視野角は単なる一例であり、使用するカメラの解像度や、使用するレンズの開口数に応じて適宜変更可能であることは言うまでもない。
【００４７】
また、上記実施の形態においては、予めシミュレーションにより膜厚−色度相関の変換テーブルを作成し、このテーブルとフィッティングすることによって膜厚を求めているが、実際にさまざまな膜厚のリファレンスを測定して、膜厚−色度相関の変換テーブルを作成しておいても良いものであり、この時の光源は実際の製造工程における薄膜の膜厚を測定するときと同じ波長強度分布を有する光源を用いることが望ましい。
【００４８】
例えば、膜厚が既知で且つステップ的に変化する標準試料を用いて、所定の移動距離Δ毎ステップ的に移動させて撮像してＲＧＢ値を得て、各視野角θにおける色度座標を取得すれば良く、また、中心線から横方向（Ｙ方向）にずれた位置に対する補正係数も同時に求めることができる。
【００４９】
また、上記の実施の形態においては、液晶パネルを構成するガラス基板に成膜したＳｉＯ₂ 膜の膜厚の取得方法として説明しているが、ＳｉＯ₂ 膜に限られるものではなく、各種の薄膜の膜厚の測定に適用されるものであり、光源となる波長に対して透明或いは半透明であれば良い。
【００５０】
また、本発明は、液晶パネルに限られるものではなく、プラズマ表示装置等の他の表示装置における成膜工程、或いは、半導体装置等の各種のデバイスの製造工程における各種の成膜工程にも適用されるものである。
【００５１】
さらには、本発明は特定の装置の成膜工程に限られるものではなく、表面が平坦な基板にミクロン〜サブミクロンオーダの薄膜を成膜する全ての成膜工程に適用されるものである。
【００５２】
また、本発明の実施の形態においては、光源として通常の蛍光灯を用いているが、できるだけ白色に近い蛍光灯が望ましい。
さらに、白色光に限られるものではなく、ある程度の広範囲の波長領域において連続的な波長強度分布を有する光源でも良く、この場合には、予め膜厚が既知の標準試料を用いて白色からのずれを測定して変換テーブルを補正すれば良い。
【００５３】
【発明の効果】
本発明によれば、一般的なＣＣＤ型やＣＭＯＳ型のエリアセンサ型のイメージセンサを用いて広い面積における干渉による色をＲＧＢ値として一括して取得し、ＸＹＺ表色系に線形変換して色度座標を求めて、膜厚−色度相関から膜厚を求めているので、従来のように分光器などの特殊な測定器を必要とせずに、高速で測定することが可能になり、ひいては、大型液晶表示装置等の低コスト化、高表示品質化に寄与するところが大きい。
【図面の簡単な説明】
【図１】本発明の原理的構成を表す膜厚と色度の相関を示す概念図である。
【図２】本発明の実施の形態に用いる膜厚取得装置の概念的構成図である。
【図３】本発明の実施の形態におけるカラーＣＣＤカメラと測定パネルの位置関係の説明図である。
【図４】膜厚がｄ＝３５０〜４０９ｎｍの範囲における色度座標の変換テーブルである。
【図５】膜厚がｄ＝４１０〜４５０ｎｍの範囲における色度座標の変換テーブルである。
【図６】色度曲線の説明図である。
【符号の説明】
１１ 面光源
１２ カラーＣＣＤカメラ
１３ 測定パネル
１４ ステージ
１５ 撮像用レンズ
２１ ガラス基板
２２ ＳｉＯ₂ 膜[0001]
BACKGROUND OF THE INVENTION
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.
[0002]
[Prior art]
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.
[0003]
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.
[0004]
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.
[0005]
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.
[0006]
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.
[0007]
[Patent Document 1]
JP-A-7-225119
[Problems to be solved by the invention]
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.
[0009]
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.
[0010]
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.
[0011]
Further, 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 μm to several μm. The film thickness cannot be measured with an accuracy of several percent or more.
[0012]
Accordingly, an object of the present invention is to obtain an in-plane distribution of the film thickness of a thin film provided on a flat plate with a simple configuration at high speed.
[0013]
[Means for Solving the Problems]
FIG. 1 is a conceptual diagram showing the correlation between film thickness and chromaticity representing the fundamental 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. The reflected light causing interference from the film is acquired as an image for each of R, G, and B by a light receiving device composed of an area sensor type image sensor , and the chromaticity based on the XYZ color system obtained from each acquired image is obtained. As a reference for the color of the interference light, the film thickness of the coating is obtained by detecting 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 measured. It is characterized by that.
[0014]
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 comprising an area sensor type image sensor detects the change in light shade as R. , G, and B need only be acquired as images, the apparatus configuration is simplified, and the measurement speed can be increased.
[0015]
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.
[0017]
In this case, as a reference for the color of the interference light, chromaticity x, y, and z based on the color matching functions of X, Y, and Z in the XYZ color system, which is the color standard defined by the CIE, are used . As shown in FIG. 1, since the coordinates in the xy chromaticity plane of the film film differ depending on the film thickness, the film thickness can be converted by obtaining the chromaticity x, y.
[0019]
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.
[0020]
( 2 ) Further, the present invention is characterized in that, in the above ( 1 ), the light receiving device is an area sensor type image sensor in which the RGB function of the color filter satisfies a router condition .
[0022]
DETAILED DESCRIPTION OF THE INVENTION
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 block 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.
[0023]
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.
[0024]
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.
[0025]
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.
[0026]
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.
[0027]
Note that the color CCD camera 12 used here is one in which the RGB function of the color filter satisfies the router condition.
The router condition is that the RGB function of the color CCD camera 12 for colorimetry is a linear conversion of the color matching function. The color matching function is an international color standard defined by CIE. X, Y, Z color matching functions of the XYZ color system are used.
[0028]
At this time, the RGB value of the image acquired using the color CCD camera 12 is converted into chromaticity x, y as follows.
First, RGB values are converted into XYZ values according to equation (1).
[Expression 1]

In the equation (1), A is a 3 × 3 conversion matrix representing the characteristics of the color filter.
[0029]
Next, the XYZ value may be converted into chromaticity x, y by equation (2).
[Expression 2]

[0030]
Next, a method for converting the obtained chromaticity x, y into a film thickness will be described.
As shown in FIG. 1 described above, the chromaticity moves on the xy plane as the film thickness changes.
[0031]
At this time, the coordinates as to which coordinate on which plane at which film thickness is obtained are tabulated on the fluctuation as shown in FIG. 1 based on the wavelength intensity distribution of the light source used and the refractive index of the thin film to be measured. The film thickness is obtained by fitting a chromaticity coordinate obtained by actual measurement with this reference as a reference.
Note that when the change in film thickness is large, the chromaticity may take a value close to that at different film thicknesses. In such a case, it may be dealt with by a method such as limiting the film thickness range.
[0032]
Based on the above, a specific film thickness acquisition method will now be described with reference to FIGS.
3. FIG. 3 is an explanatory view of the positional relationship between the color CCD camera and the measurement panel at the time of imaging, and an SiO ₂ film provided on a glass substrate 21 having a size of 1800 mm × 1500 mm used for a large liquid crystal panel as a measurement target. 22
The refractive index n of SiO ₂ is n = 1.45 when λ = 632.8 nm.
[0033]
Here, the height H from the surface of the glass substrate 21 provided with the SiO ₂ 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 °.
[0034]
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.
[0035]
Here, the film thickness of the SiO ₂ film 22 is set to about 400 nm, and this is targeted to be able to detect a film thickness change of 3%.
If 3% of 400 nm is 12 nm and the safety factor is expected to be 0.3%, it is necessary to detect a film thickness change of 1.2 nm.
[0036]
4 and FIG. 5 FIG. 4 and FIG. 5 show, as a conversion table, the result of simulating the change in chromaticity associated with the change in film thickness when viewed from a viewing angle of 30 ° under a certain light source. It is a thing.
[0037]
See FIG. 6. By plotting the data shown in FIGS. 4 and 5 above, the chromaticity curve shown in FIG. 6 was obtained.
[0038]
Next, RGB values of a predetermined area are acquired at once using the color CCD camera 12, and the chromaticity coordinates (x, y) of the area corresponding to each pixel are obtained from the above equations (1) and (2). The film thickness is obtained by fitting with previously acquired data.
[0039]
At this time, it can be said that when the chromaticity is corrected, a film thickness difference of 1 nm can be detected if there is data of about three significant digits.
Since the RGB values acquired by measurement are converted into XYZ by linear conversion, it is considered that the significant figures at the time of the RGB values are almost preserved. Therefore, if a CCD having a gradation of 10 bits for each of R, G, and B is used. It will be good.
[0040]
For a CCD camera having a 10-bit gradation for each of R, G, and B to be used, a specific expression for converting RGB values into XYZ values of the XYZ color system can be expressed by the following expression (3): To do.
[Equation 3]

[0041]
The RGB value acquired by the color CCD camera 12 at the point P at the viewing angle θ = 30 ° of the measurement panel 13 is the following equation (4).
[Expression 4]

[0042]
Next, this is linearly transformed by the above equation (1), and further by the above equation (2),
x = 0.308
y = 0.365
Can be obtained.
[0043]
This chromaticity coordinates (x, y), and Fitting I ing a data conversion table shown in FIGS. 4 and 5, where the most difference is detected the film thickness decreases, the film thickness d of the point P D = 388 nm.
[0044]
In addition, 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 is obtained by creating and converting the same table as in FIGS. 4 and 5 for each viewing angle. be able to.
[0045]
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 type color area sensor is used as the light receiving device, but a color area sensor using one 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.
[0046]
In addition, the camera tilt angle, installation height H, and viewing angle for capturing images set in the above 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.
[0047]
In the above embodiment, a film thickness-chromaticity correlation conversion table is created in advance by simulation, and the film thickness is obtained by fitting with this table. Actually, various film thickness references are measured. Then, a conversion table of film thickness-chromaticity correlation may be created, 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 a thin film in an actual manufacturing process. It is desirable to use
[0048]
For example, using a standard sample whose film thickness is known and changing in steps, move it in steps by a predetermined movement distance Δ to obtain RGB values and obtain chromaticity coordinates at each viewing angle θ In addition, a correction coefficient for a position shifted from the center line in the horizontal direction (Y direction) can be obtained at the same time.
[0049]
In the above embodiment, the method for obtaining the film thickness of the SiO ₂ film formed on the glass substrate constituting the liquid crystal panel has been described. However, the present invention is not limited to the SiO ₂ film, and various thin films It is applicable to the measurement of the film thickness of the light source and may be transparent or semi-transparent to the wavelength serving as the light source.
[0050]
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.
[0051]
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.
[0052]
In the embodiment 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.
Further, 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, a deviation from white using a standard sample whose thickness is known in advance may be used. To correct the conversion table.
[0053]
【The invention's effect】
According to the present invention, a general CCD type or CMOS type area sensor type image sensor is used to collectively obtain colors due to interference in a wide area as RGB values, and linearly converted into an XYZ color system to perform color conversion. Since the degree coordinate is obtained and the film thickness is obtained from the film thickness-chromaticity correlation, it becomes possible to measure at high speed without requiring a special measuring instrument such as a spectroscope as in the past. In addition, it greatly contributes to cost reduction and high display quality of large liquid crystal display devices.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing the correlation between film thickness and chromaticity representing the basic configuration of the present invention.
FIG. 2 is a conceptual configuration diagram of a film thickness acquisition apparatus used in an embodiment of the present invention.
FIG. 3 is an explanatory diagram of a positional relationship between a color CCD camera and a measurement panel in the embodiment of the present invention.
FIG. 4 is a conversion table of chromaticity coordinates in a film thickness range of d = 350 to 409 nm.
FIG. 5 is a chromaticity coordinate conversion table in a film thickness range of d = 410 to 450 nm.
FIG. 6 is an explanatory diagram of a chromaticity curve.
[Explanation of symbols]
11 surface light source 12 color CCD camera 13 measurement panel 14 stage 15 imaging lens 21 glass substrate 22 SiO ₂ film

Claims (2)

Is incident on the coating provided on the substrate with irradiation light that is the measuring object from a light source over a wide range distribution of wavelength, R by the light receiving device comprising a reflection light caused the interference from the coating from the image sensor of the area sensor type The intensity of the interference light is maximum for each wavelength of the reflected light measured using the chromaticity based on the XYZ color system obtained from each of the acquired images as a reference for the hue of the interference light. A film thickness acquisition method comprising: acquiring a film thickness of the coating film by detecting a change in color of interference light caused by a difference in minimum film thickness. 2. The film thickness acquisition method according to claim 1, wherein the light receiving device is an area sensor type image sensor in which an RGB function of a color filter satisfies a router condition.

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