JP5109112B2 - Ellipsometry system - Google Patents

Description

  The present invention relates to a polarization analysis system that applies the diffraction characteristics of a polarization diffraction element and does not include a mechanical drive such as a rotation mechanism of a polarizer in a system that measures and analyzes the polarization of light waves.

  As the performance of optical information processing increases, optical devices and systems that use polarized light, which is one of the parameters of light waves, have become popular. For example, in the magneto-optical recording system, the recording pit is detected by detecting the rotation of the polarization plane of the light wave due to the magnetic Kerr effect of the magneto-optical recording material. The concept of polarization multiplexing has also been proposed for hologram recording, which is a next-generation high-density recording method. In ellipsometry used for surface analysis and optical thin film analysis, the thickness and refractive index of the thin film are determined by detecting the polarization state of the reflected light from the surface. In order to make various applications using such “polarized light” more sophisticated, a simple polarization state analysis system is necessary, and its importance will increase in the future.

The light wave is an electromagnetic wave, and the electric field vector of the light wave is always orthogonal to the wave traveling direction (referred to as the z-axis) (transverse wave). Electric field vector is proceed while oscillating temporally with the progress of the wave, the temporal trajectory of the vector, two field components E _x, the amplitude A _x of E _y, A _y and determined by the phase difference Δ Is given by the following equation (1).

  Polarization is defined by the temporal trajectory of the electric field vector given by equation (1), and its shape is generally given by an ellipse as shown in FIG. Performing ellipsometry determines the ellipticity of the ellipse and the inclination of the ellipse. Commonly used linearly polarized light and circularly polarized light correspond to the special case of this ellipse.

  Conventionally, in order to determine the ellipticity and inclination described above, at least two analyzers such as a quarter wave plate and a Glan-Thompson prism are required, and by a measuring method such as a quenching method or a rotating analyzer method, 1 / The four-wavelength plate and the Glan-Thompson prism need to be measured by mechanical rotation, and the analysis speed is slow, and an expensive waveplate and analyzer are required.

Japanese Patent Laid-Open No. 2004-341024

  Conventionally, the ellipsometry system used has been to detect the extinction position by combining a wave plate having a rotating mechanism and a polarizer. In order to realize a high-speed measurement and a compact analysis system and to apply it to a high-density optical recording system and a high-speed ellipsometry, an ellipsometry system that does not use such a mechanical rotation mechanism is expected.

  The gist of the present invention will be described with reference to the accompanying drawings.

A diffraction grating element comprising a polymer layer having a periodically varying the immobilized molecular orientation structure, a polarization analysis system comprising a detector device for measuring the intensity of diffracted light from the diffraction grating element, the diffraction The grating element consists of a diffraction grating having a lattice vector in which the molecular orientation direction formed by intensity-modulated exposure is constant and the orientation order degree is periodically modulated, and the molecular orientation direction formed by polarization-modulated exposure is periodically modulated. A diffraction grating having a grating vector formed, and measuring an intensity of diffracted light from the diffraction grating formed by the intensity modulation exposure to determine an azimuth angle of incident polarized light, and forming the polarization modulation exposure. The present invention relates to a polarization analysis system configured to measure the intensity of diffracted light from a diffraction grating and determine the ellipticity of incident polarized light .

  Since the present invention is configured as described above, it includes a diffraction grating element including a polymerized layer having a periodically changed molecular orientation structure and a detection element for measuring the intensity of diffracted light from the diffraction grating element. Provides an ellipsometric system that does not require a mechanical drive.

Furthermore, in the present invention, by having a lattice vector molecular alignment direction orientational order parameter constant is periodically modulated, the diffraction grating element comprising a grating vector that molecular orientation direction is periodically modulated, the machine An ellipsometric system that does not require a drive is provided .

  Embodiments of the present invention that are considered suitable (how to carry out the invention) will be briefly described with reference to the drawings, illustrating the operation of the present invention.

  As described above, the polarization of the light wave is defined by the shape of the temporal trajectory of the electric field vector of the light wave, and generally draws an elliptical trajectory as shown in FIG. In order to determine the shape of an ellipse, it is necessary to measure the amplitude of a light wave in an arbitrary direction of 360 degrees on a two-dimensional plane. Conventionally, a polarizer that transmits only a light wave in a specific direction is used. A method of measuring the transmitted light intensity at each angle by mechanical rotation has been performed.

  In order to provide an ellipsometry system that does not require an expensive polarizer and a mechanical driving unit for driving the polarizer, the present invention provides a diffraction grating including a polymerization layer having a periodically changed molecular orientation structure. Use elements. When such a diffraction grating element is fabricated on an optical design, it is possible to form a diffraction grating element having anisotropy with different diffraction efficiency depending on the direction of the electric field vector of the light wave. We have found that an arbitrary polarization state can be identified by combining the characteristics of anisotropic diffraction gratings having different properties, and measuring and analyzing the intensity ratio of each diffracted light of the two-dimensional diffracted light. .

  A diffraction grating element is widely used as an optical element for demultiplexing light. As a typical method for manufacturing such a diffraction grating element, a method using a photoresist used for manufacturing a semiconductor integrated circuit or the like can be given. A substrate coated with a photoresist is exposed to ultraviolet light whose intensity is periodically modulated by a photomask or interferometry, thereby forming a diffraction grating having irregularities on the surface, from which a mold can be produced and replicated. it can. Since the diffractive element formed in this way does not have optical anisotropy, it cannot be used for the ellipsometry system proposed in the present invention.

  In order to use the diffraction grating element in the ellipsometry system, it is necessary to have a function that the diffraction efficiency varies depending on the incident polarized light. We have already proposed that a diffraction grating element (polarization diffraction element) having such polarization dependence can be formed by fixing the periodic molecular orientation structure of organic molecules [Japanese Patent Application 2003]. -134355 (Japanese Patent Laid-Open No. 2004-341024)]. As a result of diligent efforts based on the results of the present invention, the present invention eliminates the need for the mechanical drive unit of the present invention by using a system that combines an optically designed two-dimensional polarization diffraction element and an element for detecting the intensity of the diffracted light. This led to the provision of an ellipsometry system.

  In order to form the polarization diffraction element as described above, it is necessary to have a structure in which optical anisotropy is highly controlled and periodic. In order to achieve such an object, for example, it is conceivable to cause optical anisotropy at the same time when a refractive index change is caused by a photochemical reaction.

  For example, polyvinyl cinnamate (PVCi), which is a negative photoresist, is known as a material capable of such a purpose. When the polyvinyl cinnamate film is irradiated with linearly polarized ultraviolet light, when the -C = C- bond of the cinnamic acid portion is parallel to the direction of the electric field of polarized light, light is selectively absorbed and dimerized. The refractive index of decreases. By utilizing this fact, it is possible to periodically control the optical anisotropy, but the induced refractive index anisotropy is as small as 0.01 or less, so that it is not practical.

  As other representative materials, use of a polymer material containing azobenzene has been studied. The azobenzene molecule undergoes an isomerization reaction between the cis- and trans-forms by external stimuli such as light and heat, and this can be used to control the molecular orientation, and periodic molecular orientation control is also possible. It can be done by irradiation. However, polymer materials containing azobenzene, which have been studied in the past, not only have a very high optical anisotropy, but also change their properties due to the influence of external fields such as heat and light, or in the visible region. Therefore, it is difficult to apply to passive optical devices that require high stability.

  In view of the above situation, in the present invention, by using an optically transparent polymer layer having a periodic molecular alignment structure, and further using a photoreactive polymer liquid crystal, a large refractive index anisotropy associated with mesogen alignment is obtained. A polarization analysis system according to the present invention is provided by applying high performance and high heat resistance due to the property.

  Examples of a method for forming an optically designed two-dimensional molecular alignment pattern include a mask exposure method, a laser beam drawing method, an interference exposure method, and the like, and are not particularly limited in the present invention. In order to form various two-dimensional molecular alignment patterns, it is desirable to use an interference exposure method. Examples of the method for forming a two-dimensional molecular orientation pattern by the interference exposure method include a method in which a diffraction grating is overwritten in a two-wave interference exposure and a method by multi-beam interference exposure with three or more light waves. Not.

  The intensity distribution and the polarization distribution of the interference light strongly depend on the polarization state of the two light waves as summarized in FIG. 2 (δ in FIG. 2 represents the phase difference of the two light waves). When considering the interference of two light waves, when the polarization states of the two light waves are equal to each other, the polarization state is constant and the intensity is modulated (intensity modulation). When the polarization states of the two light waves are orthogonal to each other, the intensity is constant and the polarization state is modulated (polarization modulation). When a functional material that induces molecular orientation with respect to the polarized light is irradiated with such interference light, a structure in which the orientation state is spatially modulated can be formed. Specifically, when intensity-modulated exposure is performed, a lattice vector in which the molecular orientation direction is constant and the orientation order is periodically modulated is formed. When polarization-modulated exposure is performed, the molecular orientation direction is periodically modulated. A lattice vector is formed.

  Now, suppose that a diffraction grating is formed by interference light described in PP in FIG. The Jones matrix representing the transmission of the diffraction grating formed by such exposure is given by the following equation (2).

である。但し、ｄは格子の厚さ、Δｎは誘起された複屈折の大きさ、λは波長をあらわしている。（１）式を級数展開して１次の成分を取り出すと、（４）式のようになる。 here,

It is. Where d is the thickness of the grating, Δn is the magnitude of the induced birefringence, and λ is the wavelength. When the primary component is extracted by expanding the series of the formula (1), the formula (4) is obtained.

  Now, assuming linearly polarized light as incident light and writing the azimuth angle of the polarization direction as θ, the Jones vector of the light emitted from the diffraction grating is given by equation (5).

  From equation (5), the diffraction efficiency is given by equation (6).

  Next, it is assumed that the diffraction grating is formed by the interference light described in OC of FIG. The Jones matrix representing the transmission of the diffraction grating formed by such exposure is given by the following equation (7).

  When the primary component is extracted from the equation (7), the equation (8) is obtained.

  The diffraction efficiency determined by the equation (8) does not depend on the azimuth angle of the incident polarized light but depends on the ellipticity of the polarized light. The elliptically polarized light is expressed by the following equation (9).

  Accordingly, the diffraction efficiency is expressed by the following equation (10).

  As can be seen from the equation (6), the diffraction efficiency of the diffraction grating formed by PP exposure strongly depends on the azimuth angle of incident polarized light. The dependency is shown in FIG. Further, as can be seen from the equation (10), the diffraction efficiency of the diffraction grating formed by the OC exposure does not depend on the azimuth angle of the incident polarized light but depends on the ellipticity. The dependency is shown in FIG. 3 and 4, the diffraction grating formed by PP exposure (having a lattice vector in which the molecular orientation direction is constant and the orientation order is periodically modulated) and the diffraction grating formed by OC exposure (molecular orientation). By measuring the diffracted light intensity from a grating vector whose direction is periodically modulated, it is possible to determine both the ellipticity and azimuth of the incident polarization.

  The polymer material that forms the diffraction grating may be any material that exhibits optical transparency, sufficient molecular orientation, and optical anisotropy. By using a polymer liquid crystal having a mesogen in the side chain, the material By utilizing the liquid crystallinity, a highly oriented state can be formed and a large optical anisotropy can be expressed. More preferably, the polymer layer is a polymer liquid crystal having a photocrosslinkable mesogen in the side chain and having a photoreactive group at the mesogen end, so that a fine periodic alignment structure is obtained by a molecular alignment process using polarized light. In addition to forming a cross-linked structure, it is possible to ensure the heat resistance necessary for application as an optical element by adopting a crosslinked structure.

  As a method of manufacturing a diffraction element, a liquid obtained by dissolving the above-mentioned photoreactive polymer liquid crystal in a solvent is thinly applied on a transparent substrate and then dried, and specific polarization and / or intensity is periodically modulated. There are a method of exposing and curing by light wave, and then performing reorientation by heat treatment, and a method of exposing and curing by light wave in which specific polarized light and / or intensity are periodically modulated while applying heat to the thinly coated layer. Though conceivable, a method of performing a heat treatment after exposure is preferable in that the apparatus structure is simple.

  The solvent, concentration and dissolution method for dissolving the above-mentioned photoreactive polymer liquid crystal are not particularly limited, and are appropriately selected depending on the substrate used, the drying time, and the like. As a method for uniformly applying the solution, a spin coating method, a gravure coating method, a comma coating method, and the like can be considered, but the method is not particularly limited and is appropriately selected depending on the required area, substrate shape, accuracy, and the like. The The substrate is not particularly limited as long as it is a transparent substrate, but a transparent substrate material having a small intrinsic birefringence is preferable in order to maximize the function of the functional polymer layer. Examples of transparent substrate materials having such properties include inorganic materials such as various types of glass and quartz, and organic materials such as polymethyl methacrylate, polycarbonate, norbornene-based polymers, cellulose-based polymers, and polyester-based polymers. . The form of a board | substrate is not specifically limited, A plate shape, a film form, etc. can be suitably selected according to a use.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited by these examples.

  Specific embodiments of the present invention will be described with reference to the drawings.

A photoreactive polymer liquid crystal having a chemical structural formula of the above formula (11) and having a photoreactive group directly bonded to a mesogen [liquid crystal temperature range: from 116 ° C. to 300 ° C. or higher (decomposes at about 300 ° C.) ] Was dissolved in chloroform at a concentration of 1% by weight and applied on a quartz substrate to a thickness of about 0.3 μm using a spin coater. In this example, diffraction grating elements having four types of grating vectors A, B, C, and D as shown in FIG. 5A were formed. The angles formed by the four types of lattice vectors were 45 degrees. He-Cd laser (wavelength: 325 nm) is divided into two by the beam splitter the light, first light waves (PP interference) obtained by interference as perpendicular to the optical bench of the polarization states of two light waves was 95mJ / cm ² irradiation A Next, the film was rotated 45 degrees to form a B grating, and further rotated 45 degrees to form a C grating. Next, after further rotating the film by 45 degrees, a light wave (OC interference) that interferes with the polarization state of the two light waves as clockwise circularly polarized light on one side and counterclockwise circularly polarized light on the other is irradiated at 95 mJ / cm ² A lattice was formed. Furthermore, heat treatment was performed at 150 ° C. for 15 minutes to produce a two-dimensional polarization diffraction element. Since the produced diffraction grating element has different grating vectors in four directions, eight first-order diffracted lights were generated as shown in FIG. These diffracted light intensities can be measured with a photodiode and analyzed according to the flow shown in FIG. 6 to determine the polarization state. In order to prove this, polarization analysis was performed on light having any three kinds of polarization states. The result is shown in FIG. The results described with the symbols in FIG. 7 are the results of observation with the Glan-Thompson prism rotated as before, and the curves are the results of the polarization analysis performed according to the present invention. As shown in FIG. 7, according to the present invention, it is understood that the polarization analysis equivalent to the conventional one can be performed without requiring a mechanical drive unit.

  Note that the present invention is not limited to the embodiments, and the specific configuration of each component can be designed as appropriate.

It is explanatory drawing which shows the locus | trajectory of the electric field vector of elliptically polarized light. It is explanatory drawing which represented typically the result of having interfered with the polarization state of two light waves. It is a graph which shows the calculation result of the relationship between the diffraction efficiency of the diffraction grating element formed by PP interference, and the azimuth angle of incident linearly polarized light. It is a graph which shows the calculation result of the relationship between the diffraction efficiency of the diffraction grating element formed by OC interference, and the phase difference of incident elliptically polarized light. It is explanatory drawing of the two-dimensional diffraction grating produced in the present Example, (a) represents the concept of four grating vectors, (b) is a schematic of the diffraction image from the formed diffraction grating element. It represents. It is a flow of the ellipsometry of a present Example. It is explanatory drawing which shows the result of the polarization analysis by a present Example, Comprising: A symbol is an analysis result by a prior art, and a curve is a result in a present Example.

Claims (1)

A diffraction grating element comprising a polymer layer having a periodically varying the immobilized molecular orientation structure, a polarization analysis system comprising a detector device for measuring the intensity of diffracted light from the diffraction grating element, the diffraction The grating element consists of a diffraction grating having a lattice vector in which the molecular orientation direction formed by intensity-modulated exposure is constant and the orientation order degree is periodically modulated, and the molecular orientation direction formed by polarization-modulated exposure is periodically modulated. A diffraction grating having a grating vector formed, and measuring an intensity of diffracted light from the diffraction grating formed by the intensity modulation exposure to determine an azimuth angle of incident polarized light, and forming the polarization modulation exposure. An ellipsometric system characterized in that the ellipticity of incident polarized light is determined by measuring the intensity of diffracted light from the diffraction grating .

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