Optics: measuring and testing – By polarized light examination – Of surface reflection
Reexamination Certificate
2001-03-23
2002-11-26
Mack, Ricky (Department: 2877)
Optics: measuring and testing
By polarized light examination
Of surface reflection
Reexamination Certificate
active
06486951
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of evaluating a thin film having optical anisotropy, such as a crystal oriented film for providing crystal particles with an initial orientation.
As a method of evaluating the anisotropic thin film, there is known a method using a reflected light, which is disclosed in such as Japanese Unexamined Patent Publications (JP-A) Nos. 3-65637 (first prior art), 9-218133 (second prior art), 7-151640 (third prior art), and 5-5699 (fourth prior art).
The first prior art discloses a method of measuring anisotropy on the basis of an incident angle and dependency of an incident direction of the reflected light intensity. The second prior art discloses a method of determining dielectric constant, film thickness, and a direction of a main dielectric constant coordinate of an oriented area, and dielectric constant and film thickness of unoriented area. The third prior art discloses a method of measuring the anisotropy in accordance with two color differences by using of a infrared radiation. The fourth prior art discloses a method of measuring the anisotropy by changing the incident angle by using of a visible ray.
As the anisotropic thin film, there is known a crystal oriented film which is subjected to an orientation treatment for use in a liquid crystal display component. A method of evaluating such a film is disclosed in Japanese Unexamined Patent Publication (JP-A) 4-95845 (fifth prior art). Particularly, the fifth prior art discloses a method of evaluating the anisotropy by measuring reflected light intensity which is generated when a linear polarization is projected in the film.
In an inorganic material having high-level crystalline, a relation between crystal structure and optical anisotropy of a thin film has been clarified. Therefore, it is possible by the methods of the first through the third prior arts to quantitatively evaluate the crystal orientation equal to a particle orientation. However, there is a problem in each of the methods that dimensions to be measured at a one time becomes narrow or it takes more time for measuring.
On the other hand, there is known a method for evaluating the anisotropy of a film by projecting a P polarized light into a thin film sample at an angle of polarization of a substrate, and measuring an intensity of S polarization component of a reflected light (see JP-A 2000-121496). With this method, it becomes possible to make the intensity of P polarization component in the reflected light minimum by projecting the P polarized light at an angle of polarization. So that, there is increased accuracy of measuring the intensity of the light having S polarization component which is generated by the anisotropy of the film. In a case where the anisotropic film is directly formed on the substrate, it is possible to make the P polarization component in the reflected light minimum by projecting the P polarized light at an angle of polarization on the substrate. Generally, however, when a sample having a multifilm structure such as the liquid crystal display component is used, it can not be possible to define with accuracy the angle of polarization which lacks of P polarization component of the reflected light so that it becomes difficult to apply this method.
Furthermore, S polarization component is included in the reflected light generated in response to the incidence of the P polarization. The S polarization component has an amount which depends on a degree of the optical anisotropy and a thickness of the area having the optical anisotropy of the sample. Particularly, the amount becomes small as the anisotropy is smaller or the thickness becomes thinner. As a result, limitation of detecting the optical anisotropy is determined by the intensity of the light source and sensitivity of a detector. Therefore, it is difficult to improve the detecting sensitivity.
The fourth prior art discloses a method of evaluating liquid crystal orientation of the oriented film by using an amount of the reflected light on a surface of the oriented film when the linear polarization is projected on the surface of the oriented film. However, the intensity of the reflected light generated in response to the incidence of the linear polarization having an arbitrary vibrating direction depends on not only the refractive index of the film but the thickness of the film. Therefore, in the fourth prior art, it is difficult to detect the anisotropy of the refractive index from the intensity of the reflected light.
Additionally, as disclosed in the fifth prior art, when the linear polarization is projected on the surface of the sample in perpendicular, the incident light and the reflected light pass through the same optical path. However, it is impossible to arrange the light source and the photo-intensity detector on the same optical path, and it is also impossible to carry out the perpendicular incidence.
When a beam splitter is used, it is unnecessary to arrange the light source and the photo-intensity detector on the same optical path. However, this beam splitter is not for maintaining the polarized state of the reflected light and a transparent light, so that it becomes impossible to carry out the perpendicular incidence.
In the fifth prior art, the light is projected into the surface of the film not in perpendicular but at an inclined angle. In this case, the incident light and the reflected light have two components. One of the components is S polarization component as a vibration component parallel to the sample surface. Another of the components is P polarization component as a vibration component perpendicular to both of the through direction of the light and the S polarization component. When the sample has same optical direction, the P polarization component and the S polarization component have different refractive indexes each other. When the light is projected into the sample surface at a predetermined angle, the polarized state of the incident light is specified as S polarization.
It is to be noted the P polarization component does not have the vibration direction parallel to or perpendicular to the film surface. In order to project the light of vibration direction parallel to a rubbing direction, namely, the direction of the orientation treatment, it is necessary to project the S polarized light into the sample in a direction perpendicular to the rubbing direction. On the other hand, in order to project the light of the vibration direction perpendicular to the rubbing direction, it is necessary to project the S polarized light in the direction in parallel with the rubbing direction.
In particular, in the case of using the liquid crystal oriented film which is subjected with the orientation treatment by rubbing the film surface with a cloth, a grooved anisotropic irregularity is produced on the film surface almost in parallel with the rubbing direction. Since the intensity of the reflected light becomes different according to the incident direction because of its anisotropic surface state, it is impossible to measure in accurate the optical anisotropy of the film by the method disclosed in the fifth prior art. Furthermore, when a sample of which orientation direction is unknown is used, the light is not projected so that S polarization direction becomes parallel to or perpendicular to the orientation direction.
As mentioned above, according to the fifth prior art, it is impossible to measure in accurate the anisotropy of the film on the basis of the result of measuring the intensity of the reflected light generated when the linear polarization is projected in the sample surface.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method of evaluating an anisotropic thin film, which is capable of evaluating an inplane distribution of an optical anisotropy of the thin film material in high speed and accurate.
It is another object of the present invention to provide an evaluating apparatus, which is capable of evaluating the inplane distribution of the optical anisotropy of the th
Hirosawa Ichiro
Tanooka Daisuke
Hayes & Soloway P.C.
Mack Ricky
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