JP5056997B2 - Manufacturing method of diffraction grating - Google Patents

Description

The present invention relates to a method for manufacturing a diffraction grating, and more particularly to a method for manufacturing a concave diffraction grating having a blazed diffraction grating groove and having both functions of light spectroscopy and light collection.

There are two types of concave diffraction gratings currently available on the market: a “round” shape when the concave surface is viewed from above (planar shape) and a “square” shape that is square or rectangular. Among these, the rectangular concave diffraction grating has an advantage that the direction of the diffraction grating groove that cannot be confirmed with the naked eye can be easily confirmed from the planar shape.

The diffraction grating grooves can be roughly divided into two types: “blazed type” having a sawtooth cross-sectional shape and “laminar type” having a rectangular cross-sectional shape. A diffraction grating having a blazed groove is mainly used in a wavelength region from the ultraviolet region to the near infrared region (having a wavelength close to the visible region) having a wavelength of about 200 nm or more.

Hereinafter, an example of a method for manufacturing a concave diffraction grating having a blazed diffraction grating groove will be described with reference to FIG.
First, the upper surface 111 of the substrate 11 is processed into a concave surface by mechanical polishing (a), and a photosensitive layer 12 is formed by applying a photosensitive agent (b). Next, the photosensitive layer 12 is irradiated with coherent light 131 and 132 from two directions (c). Thereby, interference fringes by both coherent lights are formed on the photosensitive layer 12, and the photosensitive layer 12 is exposed according to the intensity of light in the interference fringes. Thereafter, when processed with a developing solution, a portion where the substrate 11 is exposed and a portion where the photosensitive agent remains are formed in a stripe shape according to the pattern of the interference fringes 15 (d). Such a method of forming a striped pattern on the photosensitive layer using interference fringes of coherent light is generally called “holographic exposure method”.

  Next, using the remaining striped photosensitive agent as a mask (12A), the surface thereof is irradiated with an ion beam to form a striped uneven pattern on the upper surface of the substrate 11 (e). At that time, the ion beam is incident on each point on the upper surface of the substrate 11 perpendicular to the stripe and at the same incident angle with respect to the contact surface (see Patent Document 1). As a result, a blazed concave diffraction grating 14 comprising a large number of diffraction grating grooves all having the same blaze angle can be formed (f).

JP-A-55-131730 (page 3, upper right column, line 9 to lower left column, line 2, Fig. 7)

Conventionally, a blazed concave diffraction grating used in a fluorescence analyzer has been designed to be optimized for light having a wavelength of about 400 to 470 nm, that is, to have the highest diffraction efficiency. In recent years, there is an increasing demand for analysis of light on a shorter wavelength side in a fluorescence analyzer. However, in such a conventional blazed concave diffraction grating, the diffraction efficiency at a wavelength of 200 to 250 nm is very low (for example, The diffraction efficiency at a wavelength of 200 nm is less than 10%).

In order to use with high diffraction efficiency up to the short wavelength side, it is generally necessary to reduce the blaze angle. The blaze angle can be controlled by adjusting the incident angle of the ion beam. However, if the blaze angle is reduced, the following problems occur.

2 (a) and 2 (b), a square concave diffraction grating 20 having a square planar shape and a round concave diffraction grating 25 having a circular planar shape whose area of the circle is equal to the square area are shown. The contour lines of the groove forming surface are shown. On the groove forming surface of the round concave diffraction grating 25, the outer edges are all the same height. On the other hand, on the groove forming surface of the rectangular concave diffraction grating 20, each side of the outer edge is the lowest at the midpoint, and becomes higher as the corners 231 to 234 are approached, and the gradient becomes larger. Further, the heights of the corner portions 231 to 234 are higher than the outer edge of the round concave diffraction grating 25.
When a diffraction grating groove is formed by irradiating an ion beam parallel to one of the four sides with respect to the groove forming surface of such a square concave diffraction grating 20, the following problem occurs. FIG. 2C shows ion beams 221, 222, and 223 irradiated to the points 211, 212, and 213 on the AA ′ cross section of FIG. As shown in FIG. 2 (c), at the point 212 where the gradient to the corner 231 increases near the corner 231 on the upstream side of the ion beam, the blaze angle is made smaller than before (that is, the ion beam is reduced). When the incident angle is increased), the ion beam 222 is blocked by the substrate 11 in the vicinity of the corner portion 231. Therefore, the ion beam 222 cannot be incident. Further, at a point 213 at a site where the gradient near the corner 232 on the downstream side of the ion beam is large, it is necessary to make the ion beam 223 incident from below the substrate 11, which is also blocked by the substrate 11. For this reason, when the blaze angle is made smaller than before, there is a problem that a portion where the diffraction grating groove is not formed is formed on the groove forming surface of the square concave diffraction grating.

On the other hand, the circular concave diffraction grating does not cause such a problem, but has a drawback that the direction of the groove cannot be easily confirmed from its planar shape.

The problem to be solved by the present invention is that a diffraction grating groove can be formed on the entire groove forming surface (upper surface, concave surface), and a method for manufacturing a blazed concave diffraction grating in which the direction of the groove can be easily confirmed Is to provide.

In order to solve the above problems, the present invention provides a method for manufacturing a blazed concave diffraction grating having a blazed diffraction grating groove and a groove forming surface being a concave surface. A substrate including one side having an obtuse angle and having a concave surface is formed on the surface, and a mask having grooves parallel to the one side is formed on the surface. The diffraction grating groove is formed by making an ion beam incident at a predetermined incident angle from the side.

In the method of manufacturing the blazed concave diffraction grating according to the present invention, the angle of the corners at both ends of one side parallel to the diffraction grating groove is obtuse, and the conventional square (rectangular) concave surface at those corners. The height can be made lower than that of the diffraction grating, and the gradient near the corner can be reduced. Therefore, when producing a blazed diffraction grating groove, it is perpendicular to the diffraction grating groove (that is, perpendicular to the one side) and has a large incident angle (angle from the normal to the surface) with respect to the groove formation surface. Even if the ion beam is incident on the groove forming surface, the ion beam can be prevented from being blocked by the substrate in the vicinity of the corners. Thereby, the diffraction grating groove can be formed even if the blaze angle is smaller than that of the conventional one.

  In addition, the blazed concave diffraction grating of the present invention has one side of the planar shape parallel to the diffraction grating groove, so that the direction of the diffraction grating groove can be easily changed from the direction of the one side during inspection after use or during use. Can be confirmed.

In other words, according to the present invention, a blazed blade having the advantages of a round concave diffraction grating that can form a diffraction grating groove without being blocked by an ion beam and the advantage of a square concave diffraction grating that allows easy confirmation of the groove direction. A mold concave diffraction grating can be obtained.

The effect of the present invention can be obtained by making the polygon more than a pentagon when compared with a conventional rectangular planar shape, but it is preferably an octagon. This is because, as shown in FIG. 3, the shape can be obtained simply by cutting off each corner of a conventional quadrangle, and the manufacturing is easy.

In a circular blazed concave diffraction grating having strings parallel to the groove, the planar shape is basically circular, so that a conventional diffraction groove can be formed without blocking the ion beam. The advantage of the diffraction grating can be obtained as it is, and since the direction of the diffraction grating groove can be confirmed by the string, the setting of the groove direction can be easily performed.

The longitudinal cross-sectional view which shows an example of the method of producing a concave diffraction grating by the holographic exposure method. The top view showing the contour lines of the groove forming surface (upper surface) of the square concave diffraction grating 20 (a) and the round concave diffraction grating 25 (b), and problems in manufacturing the square concave diffraction grating by the holographic exposure method The longitudinal cross-sectional view (c) shown. The top view which shows a response | compatibility of the planar shape of an octagonal concave diffraction grating and a square diffraction grating. FIG. 2 is a perspective view (a) and a top view (b) showing an octagonal blazed concave diffraction grating which is an embodiment of the blazed concave diffraction grating of the present invention. The perspective view and longitudinal cross-sectional view which show an example of the manufacturing method of the octagon blazed concave diffraction grating of this embodiment. The graph which shows the result of having measured the relative diffraction efficiency of the octagonal blazed concave diffraction grating of this embodiment, and the square concave diffraction grating of a comparative example. The top view which shows other embodiment of the blazed concave diffraction grating of this invention. The perspective view (a) and top view (b) which show the circular concave diffraction grating which has a string which is other embodiment of the blazed concave diffraction grating of this invention.

The blazed concave diffraction grating manufactured by the manufacturing method according to the present invention will be described with reference to FIG.
FIG. 4 is a perspective view (a) and a top view (b) of the blazed concave diffraction grating 30 manufactured by the manufacturing method according to the present invention . The blazed concave diffraction grating 30 has a regular octagonal planar shape, and one of the eight sides 331 (and the side 332 parallel to the side 331) is a straight line (reference number) shown in FIG. 32) parallel to the diffraction grating grooves extending in the direction of 32). In the concave diffraction grating 30 of this embodiment, since the planar shape is a regular octagon, the angles of the corner portions 341 and 342 at both ends of the side 331 are obtuse angles (135 °).

An example of the manufacturing method of the octagonal blazed concave diffraction grating 30 which is an embodiment of the manufacturing method according to the present invention will be described with reference to FIG. First, prepare the same square flat plate BK7 optical glass substrate 41 (length 54mm x width 54mm x thickness 10mm) as that used for the conventional square concave diffraction grating (a), and use a surface grinder to remove the four corners. By cutting (oblique line (a)), the planar shape is changed to a regular octagon ((b), optical glass substrate 41A). After chamfering each side and each corner of the upper surface, the upper surface 411 of the optical glass substrate 41A is polished (sanding polishing and pitch polishing) using the reference dish 42 having a radius of curvature of 134.85 mm (c), The upper surface 411 is formed into a concave shape ((d), the optical glass substrate 41B). Next, a photoresist 43 is applied on the upper surface 411, and a groove parallel to the side 331 is formed in the photoresist 43 at an interval of 900 lines / mm by a spherical wave holographic exposure method using a laser beam having a wavelength of 441.6 nm. 44 is formed (f).

Next, an ion beam is irradiated on the upper surface of the optical glass substrate 41B from the side 331 side at an incident angle of 80 ° perpendicular to the groove 44 of the photoresist 43 (g) until the photoresist 43 just disappears. The surface of the optical glass substrate 41B is etched. As a result, only the groove 44 of the photoresist 43 is etched, and a sawtooth diffraction grating groove 45 having a blaze angle of 7 ° is formed on the surface of the optical glass substrate 41B.

At this time, since the planar shape is a regular octagon, the height of each corner of the optical glass substrate 41B and the gradient near each corner are smaller than when the planar shape is a quadrangle (FIG. 3). Thereby (particularly because the height of the corners 341 and 342 on both sides of the ion beam incident side and the gradient in the vicinity thereof are small), the ion beam is not blocked by the optical glass substrate 41B, and the upper surface (groove An ion beam can be incident on the (forming surface).

Next, an octagonal concave master diffraction grating 47 is obtained by depositing Al46 with a thickness of 0.2 μm on the surface of the optical glass substrate 41B (i). Thereafter, a resin film 482 made of an epoxy resin coated on a convex float glass 481 having the same radius of curvature as that of the reference dish 42 was pressed onto the octagonal concave master diffraction grating 47 to cure the epoxy resin. Then, by separating from the octagonal concave master diffraction grating 47, a negative diffraction grating 48 having a regular octagonal planar shape is obtained (j). Further, a resin film 492 made of an epoxy resin applied on a concave float glass 491 having the same radius of curvature as that of the reference dish 42 is pressed onto the negative diffraction grating 48 (k), and the epoxy resin is cured. By separating from the octagonal concave negative diffraction grating 48, an octagonal concave replica diffraction grating 49 is obtained (l).

FIG. 6 shows the result of measuring the relative diffraction efficiency of the octagonal concave replica diffraction grating 49 manufactured by the above method. Here, in order to show the reproducibility of the experiment, two octagonal concave replica diffraction gratings 49 (one example) each produced from two octagonal concave master diffraction gratings 47 produced by the same method. , Blaze angle: 7 °). In addition, the measurement results of the relative diffraction efficiency of the conventional square (square) concave diffraction grating ("comparative example", blaze angle: 10 °) having the same surface area and concave curvature as the octagonal concave replica diffraction grating 49 are shown. . The relative diffraction efficiency is defined as a value obtained by dividing the ratio of the intensity of a certain order of diffracted light to the intensity of incident light (absolute diffraction efficiency) by the reflectance of the surface of the diffraction grating. The horizontal axis of FIG. 6A is the wavelength of the diffracted light.
Note that when a conventional rectangular concave diffraction grating is manufactured with the same curvature and blaze angle as in the present embodiment, a part of the ion beam is blocked by the corner of the upper surface, and there is a portion where the diffraction grating groove is not formed on the upper surface. End up. Therefore, in the comparative example, the diffraction grating groove was formed on the entire upper surface by making the blaze angle larger than that of the present example as described above.

As shown in FIG. 6, the relative diffraction efficiency of the comparative rectangular concave diffraction grating shows a wavelength dependency that has a peak near a wavelength of 400 nm on the longer wavelength side than the measurement range (maximum 360 nm). In this example, the wavelength dependence has a peak near the wavelength of 300 nm. This is because in this embodiment, the blaze angle can be made smaller than in the comparative example. Since the relative diffraction efficiency peak can be made shorter on the short wavelength side in this example, the present example is more than twice that of the comparative example at a wavelength of 250 nm or less (about 2 at a wavelength of 250 nm). Times, approximately 3 times the diffraction efficiency at a wavelength of 215 nm).

In addition to the octagonal blazed concave diffraction grating described so far, as shown in a top view in FIG. 7, a concave diffraction grating 501 (FIG. 7 (a)) having a pentagonal planar shape or a concave surface having a hexagonal shape. As in the diffraction grating 502 (FIG. 7B), etc., the planar shape can take various polygons such as a pentagon or more. In either case, one side 511 or 512 of the polygon is parallel to the groove direction 53 (shown by the direction in which the straight line extends in the figure), and the angle of the corners on both sides of the side is an obtuse angle.

The planar shape is not limited to a regular polygon such as a regular pentagon, a regular hexagon, and a regular octagon.

Moreover, a trapezoid as shown in FIG. In this case, since the angles of the corners 5231 and 5232 at both ends of the shorter base 513 are obtuse, the ion beam is blocked by the corners 5231 and 5232 by irradiating the ion beam from the direction of the base 513. Can be prevented.

The diffraction grating manufactured by the manufacturing method according to the present invention may be a circle having a string. An example is shown in FIG. The concave diffraction grating 60 of this embodiment is a circular diffraction grating provided with a string (orientation flat) 61. The string 61 is provided in parallel to the diffraction grating groove 62. Since the concave diffraction grating 60 of the present embodiment is basically circular, the ion beam can be prevented from being blocked. Further, since the user can know the direction of the diffraction grating groove by the string 61, the groove direction can be easily set.
Although an example in which only one string 61 is provided is shown here, two strings 61 may be provided in parallel.

11 ... Substrate 111, 31, 411 ... Upper surface of substrate (groove forming surface)
DESCRIPTION OF SYMBOLS 12 ... Photosensitive layer 12A ... Mask 131, 132 ... Coherent light 14 ... Diffraction grating 15 ... Interference fringe 20 ... Square concave diffraction grating 221-223 ... Ion beam 231-234 ... Square corner 25 ... Round concave diffraction grating 30 ... Octagonal concave diffraction gratings 32, 53, 62... Diffraction grating groove directions 331, 332, 511, 512, 513... Sides 41 parallel to the diffraction grating grooves. Optical glass substrate 41A. Optical glass substrate 41B ... Optical glass substrate 42 after concave processing ... Reference plate 43 ... Photoresist 44 ... Photoresist groove 45 ... Diffraction grating groove 46 ... Al layer 47 ... Octagonal concave master diffraction grating 48 ... Octagonal concave negative Diffraction gratings 481, 491 ... Float glass 482, 492 ... Resin film 49 ... Octagonal concave replica diffraction grating 501 ... Pentagonal concave diffraction grating 502 ... Concave diffraction grating 61 ... chords having a rectangular concave diffraction grating 503 ... trapezoidal concave diffraction grating 60 ... chords

Claims (1)

In a method of manufacturing a blazed concave diffraction grating having a blazed diffraction grating groove and having a concave groove forming surface,
A planar shape is a shape including one side where the angle of the corners at both ends is an obtuse angle, and the substrate has a concave surface,
Forming a mask having a groove parallel to the one side on the surface;
The method for producing a blazed concave diffraction grating, wherein the diffraction grating groove is formed by making an ion beam incident on the surface from the one side at a predetermined incident angle .

Images