JP4725547B2 - Diffraction grating pattern - Google Patents

Description

  The present invention relates to a pattern (multidot pattern) in which a plurality of minute cells (dots) made of diffraction gratings are arranged in a matrix on the surface of a substrate, and is expressed by a collection of them. The present invention relates to a diffraction grating pattern having a smooth outline defining the outer shape of (picture).

Many displays that are configured by arranging a plurality of minute dots made of a diffraction grating on the surface of a planar substrate are used.
As a method for producing such a display, a method exemplified in JP-A-60-156004 is known. In this method, a minute interference fringe (diffraction grating) due to two-beam interference of laser light is successively exposed on a photosensitive film while changing the pitch, direction, and light intensity.

On the other hand, an electron beam exposure apparatus is used instead of a laser, and an XY stage on which a planar substrate is placed is moved by computer control, so that a plurality of minute dots made of a diffraction grating are formed on the surface of the substrate. There has been proposed a method of manufacturing a display in which a diffraction grating pattern is formed by arranging the display.
The above method is disclosed in JP-A-2-72320 and US Pat. No. 5,058,992.
According to the method using an electron beam, since the diffraction grating (grating fringes) is drawn directly, the lattice spacing can be arbitrarily changed, or the diffraction grating (grating fringes) can be changed to a curved line or the like. Will improve dramatically.

  The above-mentioned display (hereinafter referred to as a diffraction grating pattern) exhibits gloss having directivity that cannot be expressed by ordinary printing, so that the display has an interesting visual effect (eye-catching effect) and prevents forgery. It is widely applied to the intended use as a security product.

By the way, in such a pattern, each minute dot having a unique diffraction grating is exposed (or drawn), so the contour line that defines the outer shape of the pattern (pattern) to be formed is the smallest structural unit. It depends on the shape of a certain cell (dot).
The dot due to the two-beam interference is generally circular because it depends on the cross-sectional shape of the laser beam, and it is impossible to close the adjacent dots closely and spread the diffraction grating without any gaps. The contour line to be defined has an arc.

In addition, since the cell by the method using the electron beam directly draws the internal lattice pattern, it can take any shape without being restricted by the shape.
When a diffraction grating cell is adopted as the minimum unit constituting a pattern, especially when a pattern is produced by computer control based on digital data, the cell shape is generally rectangular and the arrangement is generally a matrix arrangement. It is.
In this case, the outline that defines the outer shape of the pattern (picture) has a straight line that forms a rectangle.

  In order to smooth the contour line that defines the outer shape of the pattern (picture), the smaller the diffraction grating cell as a pixel, the closer it is to the target contour line. The number will be enormous and will require more time and effort to make.

If the diffraction grating cell is used as a structural unit of the pattern to the last, the influence of diffraction (due to the boundary line that determines the outline of the dot) at the junction between adjacent cells still remains.
For patterns in which diffraction gratings are arranged on a substrate in units of cells, it is inevitable that light scattering caused by the outer shape of the cell becomes a noise component, and this noise component varies depending on the design of the pattern, and can be captured quantitatively. Even if the same diffraction grating pattern fabrication method is used, depending on the type of diffraction grating used, there are some that have low noise components and high quality, and those that contain a large amount of noise components are not good. Sometimes there is a pattern. In the latter case, the saturation of the pattern decreases, and the whole image tends to be white.

  In particular, in a portion where a diffraction grating cell and a region without a diffraction grating (hereinafter sometimes referred to as a non-diffraction grating cell for convenience) are adjacent, diffracted light is not generated from the non-diffraction grating cell. The noise component resulting from the outer shape of the image will be remarkably observed.

  In addition, in the case of a diffraction grating pattern having rectangular pixels arranged in a matrix as a structural unit, a malicious person recognizing that may perform an analysis based on the pixel structure and perform imitation or forgery.

In the conventional diffraction grating pattern, a cell composed of a diffraction grating is used as a constituent unit, and each dot maintains its state in the entire pattern, and thus has the above-described problems.
The present invention provides a diffraction grating pattern in which the outline defining the outline is smooth and the saturation is not lowered by approximating the target outline without incurring a significant increase in production time and labor. With the goal.

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The diffraction grating pattern of claim 1 of the present invention is a diffraction grating pattern comprising a substrate and a diffraction grating composed of a number of grating lines on the substrate surface.
The diffraction grating includes a plurality of types of regions having different directions, spatial frequencies, and depths,
The shape of the end portion of the grating line is a diffraction grating pattern characterized in that it is a stepped shape including a line segment shorter than the width of the grating line at a boundary portion between the plurality of types of regions.

Diffraction grating pattern according to claim 2 of the present invention, the region where the diffraction grating is provided on the substrate, with the diffraction grating pattern according to claim 1, characterized in that it is surrounded by areas with no diffraction grating is there.

The diffraction grating pattern of the first different invention (other invention 1) not described in the claims is:
In a diffraction grating pattern in which a diffraction grating in which at least one of direction, spatial frequency, and depth is arbitrarily changed is arranged on the substrate surface,
The grating lines constituting the diffraction grating may have an arbitrary shape according to the outer shape of the region where the diffraction grating is formed.
The diffraction grating pattern of another invention 2 not described in the claims is:
The diffraction grating pattern according to another invention 1, wherein a line segment defining at least an end of a grating line constituting the diffraction grating has a side smaller than the grating line width.
The diffraction grating pattern of another invention 3 not described in the claims is:
For an area of a specific shape configured by adjacent sets of unit cells having the same diffraction grating, the outline of the area is defined, and a continuous diffraction grating with no phase shift inside the outline is not per unit cell. It is the structure formed for every said area | region, It is a diffraction grating pattern of another invention 1 or 2 characterized by the above-mentioned.
The diffraction grating pattern of another invention 4 which is not described in the claims is:
Another invention is characterized in that at the boundary between regions where the formed diffraction gratings are different, the outline of at least the end of the grating line is defined by a side smaller than the grating line width according to the boundary line. It is a diffraction grating pattern in any one of 1-3.
The diffraction grating pattern of another invention 5 which is not described in the claims is:
The diffraction grating pattern according to another invention 4 is characterized in that a relationship between a region having a diffraction grating and a region having no diffraction grating is included as a region where the formed diffraction grating is different.
The diffraction grating pattern of another invention 6 which is not described in the claims is:
6. The diffraction grating pattern according to any one of inventions 1 to 5, wherein 25,000 or more grating lines are formed per inch.
The diffraction grating pattern of another invention 7 which is not described in the claims is:
7. The diffraction grating pattern according to any one of inventions 1 to 6, wherein the outer shape of the grating line is defined by a cell structure of 1 μm square or less.

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The diffraction grating pattern according to the present invention does not have a cell in which the diffraction grating is formed as a constituent unit, but forms a pattern to be reproduced as a region for each diffraction grating, which is finer than the cell and has a grating line width or less. Since the outline of the region is defined based on the cell structure of the size, the following effects can be expected.
(1) Since the outer shape of the diffraction grating cell is so fine that it cannot be recognized, the information of the object read by the scanner and the information of the shape defined by the draw data are not impaired, and the image (appearance, atmosphere) of the object is not lost. It can be faithfully reproduced, and the difference from the counterfeit product can also be expressed clearly.

(2) Since the boundary between the diffraction grating cell that generates diffracted light and the cell that does not generate diffracted light is configured smoothly, the outer shape of the pattern is not blurred, the contrast between light and dark is high, and the S / N ratio is high. The image can be observed.

(3) When observing at the magnification level of the diffraction grating level, there is no diffraction grating cell with different spatial frequency and angle around the pattern expressed by the collection of diffraction grating cells, making it easy to recognize the pattern And can be done accurately.

(4) Although it is a diffraction grating pattern based on dot matrix data, it is difficult to determine the manufacturing method and the original data because the cell shape is not recognized even if observation is performed at a magnification of the diffraction grating level. It is extremely difficult to forge.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is an explanatory view showing an example of a conventional diffraction grating pattern.
As described above, when forming a pattern (pattern, pattern) by arranging a plurality of cells on a substrate with the cell as a structural unit, the outline of the pattern, pattern (in the figure, female The three areas of skin / clothes edge / clothes are composed of three types of diffraction gratings) can be considered smooth.

  However, as shown in the enlarged view in the figure, it is possible to recognize what the outer shape of the cell is in such a diffraction grating pattern, and the outer portion of the grid line cut out by the outer shape of this cell The diffracted light resulting from is scattered in a direction different from the original design direction (direction perpendicular to the grating lines), which causes the entire image of the diffraction grating pattern to become white.

  This will be described in detail with reference to FIG. 2. When cells are regularly arranged in a rectangular shape or the like, noise components due to diffraction and scattering that occur depending on the outer shape of the cells (in the figure, they are described as redundant diffracted light). ) Tends to appear strongly in the vertical direction and the horizontal direction, and when observing the diffraction grating pattern, some diffracted light is observed from a direction that is not normally visible, and this often causes a problem.

  In particular, as shown in FIG. 3, the noise component is strongly perceived from the contrast between the diffraction grating cell that generates the diffracted light and the non-diffraction grating cell that does not generate the diffraction grating cell and the non-diffraction grating cell adjacent to each other. The Rukoto.

  Such a noise component is likely to occur when the line segment that defines the outer portion of the cell is present at an angle different from the original grating direction at intervals larger than the pitch of the diffraction grating. If such a shape (line segment) is arranged at a smaller interval than that, the optical behavior is indefinite, and the noise component is not strongly recognized.

It is obvious that it is advantageous to make the diffraction grating cell as small as possible in order to further smooth the contour line in the pattern having the diffraction grating cell as a unit pixel. Consider a case in which the resolution of a digital image is improved) and the cell size is smaller than the grid line width.
Here, since the concept is different from a diffraction grating cell that is a pixel unit in which a diffraction grating is formed inside, a cell smaller than the grating line width is referred to as a “cell structure” to distinguish them.
If the cell structure exists in the pattern, is the cell structure buried in the grid line, does the cell structure not belong to the grid line at all, or is the cell structure placed on the outline of the grid line? This applies to either of the cases.

  In any case, if a cell structure of the same type exists alone, a pattern depending on the outer shape of the cell structure, which has nothing to do with the shape of the lattice line, is created. It is assumed that there are a sufficient number of groups of identical cell structures to configure, but by making the cell structure sufficiently smaller than the outline of the grid lines, the pitch of the grid lines is finer and optically smooth. It is possible to construct a grid line having an outer shape that can be regarded as.

FIG. 4 is an explanatory view showing an example in which the same diffraction grating pattern as that in FIG. 1 is produced based on the above idea.
As shown in the enlarged view in the figure, it is the same as in FIG. 1 in that three types of diffraction gratings (grating lines), which are left-down, right-down, and horizontal, are adopted, but in FIG. For a region of a specific shape configured as described above, the contour of the region is defined, and a continuous diffraction grating without a phase shift inside the contour is formed not for each cell but for each region. Yes.

The boundary where the lower right and horizontal diffraction gratings are adjacent to each other is further enlarged in FIG.
Since the line segment that defines the shape of the end of the grating line constituting the diffraction grating is defined by the above-mentioned “cell structure” having sides smaller than the grating line width, the end is stepped and smoother. A contour is realized.

  Even in this case, it is possible to suppress a phenomenon in which a noise component is strongly generated in a direction depending on the outer shape of the cell structure as a result of light diffraction and scattering depending on the outline of the lattice line.

  In general, the diffraction grating has a grating line of about 1000 lines / mm, and when the groove part (valley) is a grating line in a relief type diffraction grating, the effect of the present invention is expected by defining the outer shape of the grating line. For this, the size of the cell structure is desirably 1 μm square or less.

  The diffraction grating pattern defined based on such conditions can express a high-definition pattern because the outline of the grating line is smooth and the noise component is small.

As shown in FIG. 5, it is difficult to recognize a pattern if a specific pattern by the diffraction grating (the letter “TOP” in the figure) is present adjacent to another diffraction grating.
On the other hand, as shown in FIG. 6, if the non-diffraction grating cell is arranged around the character of the diffraction grating, the visual effect of the pattern can be further enhanced. This is because the outline can be easily recognized because the diffracted light from the diffraction gratings constituting the other patterns does not exist in the surroundings.

This high visual recognition effect can be expected similarly when observing the diffraction grating pattern with the naked eye or when magnifying the image using a microscope or the like.
In particular, a fine pattern such as a micro letter represented by a large diffraction grating cell so far cannot form a smooth outline, and the outer shape depends on the size of the diffraction grating cell.

  If such a micropattern is present adjacent to the surrounding diffraction grating cell, it is difficult to recognize the pattern, and at the same time, the difference from the counterfeit product cannot be clarified.

  By disposing a non-diffraction grating cell around a diffraction grating having a smooth outline according to the present invention, the effect of visually recognizing the shape of the pattern is high even under conditions where the diffraction grating does not shine, the pattern recognition is easy, and a high-definition pattern Can be obtained.

Explanatory drawing which shows an example of the conventional diffraction grating pattern. Explanatory drawing showing the noise component which generate | occur | produces in the external shape part of a diffraction grating cell. Explanatory drawing which shows the part which a diffraction grating cell and a non-diffraction grating cell adjoin. Explanatory drawing which shows an example of the diffraction grating pattern by this invention. Explanatory drawing which shows an example of a diffraction grating pattern. Explanatory drawing which shows an example of a diffraction grating pattern.

Claims (2)

In a diffraction grating pattern comprising a substrate and a diffraction grating composed of a large number of grating lines on the substrate surface,
The diffraction grating includes a plurality of types of regions having different directions, spatial frequencies, and depths,
The diffraction grating pattern is characterized in that the shape of the end portion of the grating line is a stepped shape consisting of a line segment shorter than the width of the grating line at a boundary portion between the plurality of types of regions. The diffraction grating pattern according to claim 1 , wherein the region where the diffraction grating is provided on the substrate is surrounded by a region without the diffraction grating.