JP2017211670A - Blazed diffraction grating and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a blazed diffraction grating having a blaze angle smaller than conventional blazed angles, and a manufacturing method for the same.SOLUTION: A substrate having a surface having a saw tooth-shaped cross-section comprising base blaze surfaces and base step surfaces alternately arranged in one direction is prepared, and a resin layer is formed directly on the surface of the substrate such that the thickness thereof changes monotonously in the one direction to form a metallic coating film covering the resin layer surface. The thickness of the resin layer can be monotonously changed either by means of difference in volatilization volume or by means of centrifugal force after coating the substrate with a solvent resin.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a blazed diffraction grating that is a wavelength separation / selection element used in a spectroscope, a demultiplexer, and the like, and a method for manufacturing a blazed diffraction grating.

  Although there are various types of diffraction gratings, a diffraction grating with a sawtooth cross-sectional shape of a groove is called a blazed diffraction grating and exhibits high diffraction efficiency for light of a specific wavelength in the ultraviolet to visible light region. Therefore, it is often used for a visible / ultraviolet spectroscope (see Patent Document 1).

  As a method for manufacturing a blazed diffraction grating, there are known an ion beam etching method in which an ion beam is incident at a predetermined incident angle using a photoresist as a mask and the substrate is cut, and a mechanical cutting method in which grooves are processed one by one by a ruling engine. . In the mechanical cutting method, the accuracy of the groove interval is low, and there are cases where uncut pieces that cause stray light are generated at the processed end portion. Therefore, the ion beam etching method is often used in manufacturing a diffraction grating that requires high accuracy.

  A method for manufacturing a blazed diffraction grating by ion beam etching will be described with reference to FIG. First, a photoresist is applied to the surface of a flat substrate 1 such as quartz or glass to form a photoresist layer 2 (FIG. 1A). The photoresist layer 2 is exposed and developed with interference fringes due to two-beam interference to form a parallel line resist pattern 3 as shown in FIG. 1B (holographic exposure). Then, using this resist pattern 3 as a mask, etching with an ion beam is performed from an obliquely upward direction so that a desired blaze angle θB is formed on the substrate 1 until the resist pattern 3 disappears. The lattice grooves 4 are formed (FIGS. 1C to 1E). Thereafter, as shown in FIG. 1F, a metal film 5 such as aluminum or gold is coated on the surface of the grating groove 4 to complete a blazed diffraction grating.

  In general, in the above-described etching process, the etching rate for the substrate 1 is higher than the etching rate for the resist pattern 3, that is, the selectivity (= etching rate for the substrate material (eg, glass) / etching rate for the photoresist) is 1. Ion beam etching is performed using a larger etching gas.

  Thereby, a master blazed diffraction grating is manufactured. A release agent layer is formed on the grating surface of the master diffraction grating, and a metal thin film is formed thereon. Subsequently, a glass substrate is bonded onto the metal thin film via an adhesive, and after the adhesive is cured, the glass substrate is peeled from the master diffraction grating. Thereby, the metal thin film in which the grating grooves are formed moves to the glass substrate side in an inverted state, and a replica diffraction grating is obtained. Using this replica diffraction grating as a matrix, a diffraction grating as a product is manufactured (see Patent Document 1).

  The wavelength of light diffracted by a diffraction grating is becoming shorter and shorter with the expansion of analysis objects in a spectroscopic analyzer. In order to shorten the diffraction wavelength, it is necessary to shorten the grating interval and the blaze angle.

  In order to manufacture a blazed diffraction grating having a small blazed angle using the above-described ion beam etching method, it is necessary to increase the incident angle α of the ion beam. At this time, as shown in FIG. 2, the step surface 12 between one blaze surface 11 and the adjacent blaze surface 11 is deeply etched, and the step surface 12 enters under the blaze surface 11 (that is, the blaze surface 11). An angle β between the surface 11 and the step surface becomes an acute angle), and an eave-like shape is formed such that the end of the blazed surface 11 covers the adjacent blazed surface 11 (this is called an overhang). A replica diffraction grating cannot be manufactured from a master diffraction grating in which such an overhang has occurred.

  Further, when the diffraction grating is a concave diffraction grating, when the incident angle α of the ion beam is reduced, a portion that is not etched is generated in the periphery. For example, in the case of a concave diffraction grating having a radius of curvature R, assuming that the diameter of the substrate is D, the edge of the substrate is warped from the horizontal direction by an angle θ = sin−1 (D / 2R) as shown in FIG. Therefore, when the incident angle α of the ion beam becomes (90−θ) ° or more, a portion where the ion beam does not enter (shadow portion) is generated on the substrate surface, and etching cannot be performed.

JP 2009-92687 A

  The problem to be solved by the present invention is to provide a blazed diffraction grating having a blazed angle smaller than an existing blazed angle and a method for manufacturing the same.

  The blazed diffraction grating according to the present invention, which has been made to solve the above-mentioned problems, is a) a cross-sectional shape of a sawtooth, and a support formed by alternately arranging a basic blazed surface and a basic stepped surface in one direction; B) a resin layer covering the basic blazed surface and the basic stepped surface of the support, the thickness of which is monotonously changed in the one direction on the basic blazed surface; and c) a metal coating covering the surface of the resin layer. And a membrane.

  In the blazed diffraction grating according to the present invention, as shown in FIG. 4, the thickness of the resin layer monotonously changes in the one direction on the “resin layer blazed surface” of the resin layer covering the basic blazed surface of the support. Therefore, regardless of the blaze angle θB1 of the basic blazed surface of the support, the blaze angle θB2 of the resin layer blazed surface can be arbitrarily determined. For example, as shown in FIG. 4, the thickness t1 of the resin layer is increased in the valley of the support (the deep side of the basic blaze surface), and the resin layer is formed in the direction of the support (the shallow side of the basic blaze surface). By reducing the thickness t2, the blaze angle θB2 of the resin layer blazed surface can be made smaller than the blaze angle θB1 of the basic blazed surface. On the contrary, by setting t1 <t2, a blazed diffraction grating having a blaze angle larger than the blaze angle θB1 of the basic blaze surface can be obtained. The metal coating film is a thin film that does not affect the thickness of the resin layer.

  In addition, a method for manufacturing a blazed diffraction grating according to the present invention, which has been made to solve the above-mentioned problems, includes the following: a) The cross-sectional shape is serrated, and the basic blazed surface and the basic step surface are alternately and repeatedly arranged in one direction. B) providing a resin layer covering the basic blazed surface and the basic stepped surface on the support so that the thickness monotonously changes in the one direction on the basic blazed surface. And c) forming a metal coating film covering the surface of the resin layer.

  As a method of forming the resin layer so that the thickness monotonously changes in the one direction on the basic blazed surface, there are two methods, a method using volatilization of a volatile solvent and a method using external force. .

  The method of utilizing the volatilization of the volatile solvent is that the resin constituting the resin layer is dissolved in the volatile solvent to prepare a solvent resin, and the surface of the solvent resin after applying the solvent resin is flat on the support. It is a method of forming a resin layer through a step of volatilizing a volatile solvent and solidifying the resin after coating. In a state where the solvent resin is applied on the support and the outermost surface is a flat surface, the depth from the flat surface to the basic blazed surface is different in each part of the basic blazed surface. Therefore, the volatilization amount of the solvent from the solvent resin is also different, and after the resin is solidified, a resin layer blazed surface having a blaze angle different from the basic blazed surface is obtained.

  In the method using an external force, when the liquid resin constituting the resin layer is coated on the support, the thickness of the resin layer coated on the basic blazed surface is monotonously changed by applying an external force in the one direction. Is. Examples of the external force used here include centrifugal force, gravity caused by tilting the support, and wind force applied by blowing air or the like on the surface. Here, in addition to adjusting the strength of the external force, the blaze angle of the blazed diffraction grating to be manufactured can also be adjusted by adjusting the viscosity of the solvent resin.

  When the method for producing a blazed diffraction grating according to the present invention is used, the cross-sectional shape is a sawtooth shape, and the basic blazed surface is formed on a support formed by alternately arranging a basic blazed surface and a basic stepped surface in one direction. By a simple manufacturing method of forming the resin layer covering the basic step surface so that the thickness monotonously changes in the one direction on the basic blaze surface, and forming a metal coating film covering the surface of the resin layer A blazed diffraction grating having an arbitrary blaze angle can be manufactured. Therefore, it is possible to produce a blazed diffraction grating having a smaller blaze angle than that of an existing blazed diffraction grating.

The cross-sectional schematic diagram explaining the procedure of the manufacturing method of a blazed diffraction grating. The figure explaining overhang. The figure explaining the curvature of the board | substrate edge part in the case of a concave-surface diffraction grating. The figure explaining the change of a blaze angle. The cross-sectional schematic diagram after solvent resin application | coating in the case of apply | coating the solvent resin which mixed the volatile solvent by dip coating on the blazed diffraction grating. The cross-sectional schematic diagram after volatilization of a volatile solvent in the case of apply | coating the solvent resin which mixed the volatile solvent by dip coating on the blazed diffraction grating. The schematic diagram of the unit which applies a centrifugal force. The cross-sectional schematic diagram of liquid resin on a blazed diffraction grating at the time of applying the centrifugal force.

  Hereinafter, the form for implementing this invention is demonstrated using an Example.

  A first embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a schematic cross-sectional view after application of the solvent resin when a solvent resin mixed with a volatile solvent is applied onto the blazed diffraction grating by dip coating. FIG. 6 is a schematic cross-sectional view after the volatile solvent is volatilized when a solvent resin mixed with a volatile solvent is applied on the blazed diffraction grating by dip coating.

  The first example is an example in which a method using volatilization of a volatile solvent is used as a method of forming the resin layer so that the thickness monotonously changes in one direction on the basic blazed surface.

In the first embodiment, a blazed diffraction grating 20 having a first blaze angle is used as a support. As an example, the blazed diffraction grating 20 has 900 grooves / mm and a groove depth of 0.30 μm.
A master diffraction grating having a first blaze angle of 14 ° and manufactured by an ion beam etching method is used.

  A resin (solvent resin) dissolved in a volatile solvent is applied to a surface having a plurality of grooves formed by the basic blazed surface 21 and the basic step surface 22 of the blazed diffraction grating 20. The solvent resin is applied by a dip coating method so that the resin surface after application is flat as shown in FIG. Here, the thickness of the resin layer 26 is about 1/2 to 3 times the groove depth of the blazed diffraction grating 20 at the thinnest portion (groove crest portion). Note that the thickness of the resin layer 26 also depends on the ratio of the solvent in the solvent resin. In the case of the blazed diffraction grating 20, it is applied so that the solvent resin after application is thickest at about 1 μm.

  Any photocurable resin or thermosetting resin can be used as the resin in the present invention. In addition, any volatile organic solvent such as ethanol, benzene, and acetone can be used as the volatile solvent in the present invention as long as it does not react with these resins. In this embodiment, ethanol is used as the volatile organic solvent.

  Next, ethanol in the solvent resin is volatilized. In order to promote volatilization, the entire blazed diffraction grating 20 coated with a solvent resin may be heated, or may wait for the volatile solvent to volatilize naturally over time. As ethanol in the solvent resin volatilizes as indicated by arrows in FIG. 6, the thickness of the solvent resin is reduced and the surface of the solvent resin has irregularities reflecting the shape of the grooves of the blazed diffraction grating 20. Become.

  Thereafter, when the resin is solidified by a predetermined method, a resin layer 36 having irregularities reflecting the shape of the groove of the blazed diffraction grating 20 is formed on the surface of the blazed diffraction grating 20 as shown in FIG. However, the thickness of the resin layer 36 is not uniform, changes monotonously in one direction on the basic blazed surface 21, and is the thickness above the peak (uneven convex portion) of the blazed diffraction grating 20 (t 2 in FIG. 4). Is smaller than the thickness (t1 in FIG. 4) above the valley (uneven recess) of the blazed diffraction grating 20. As a result, the groove of the resin layer 36 is shallower than the groove of the blazed diffraction grating 20. In the above example, the thickness of the resin layer 36 is about 100 nm to 200 nm at the thinnest place.

  The reason why the thickness of the resin layer 36 is not uniform and the thickness of the top of the blazed diffraction grating 20 is smaller than the thickness of the top of the blazed diffraction grating 20 is considered as follows. As shown in FIG. 5, in the dip coating method in which the coated resin surface is flattened, the thickness of the solvent resin after coating is thin on the top of the blazed diffraction grating 20 and the blazed diffraction grating 20 Thicker over the valley. Since the proportion of the volatile solvent contained in the solvent resin is equal, assuming that a certain proportion (for example, half) of the thickness of the solvent resin immediately after application of the solvent resin is volatilized, the relationship of the thickness of the solvent resin after application described above The film thickness is reduced by a certain rate while maintaining the above. As a result, the thickness of the resin layer 36 is not uniform, and the thickness of the top of the blazed diffraction grating 20 is smaller than the thickness of the top of the blazed diffraction grating 20.

  Thereafter, although not shown, in order to protect the surface of the resin layer 36, a metal coating film such as aluminum is formed by using a vacuum deposition method, a sputtering method, or the like, thereby completing the manufacture of the blazed diffraction grating. The thickness of the metal coating film is about several tens of nm and does not affect the shape of the surface of the resin layer 36.

  The resin layer 36 has a blazed surface 31 on the basic blazed surface 21 and a stepped surface 32 on the basic stepped surface 22, and the inclinations of the blazed surface 31 and the stepped surface 32 are the basic blazed surface 21 and the basic stepped surface 22, respectively. It has become more gradual. Therefore, the angle γ 1 between the blaze surface 31 and the step surface 32 is larger than the angle β ′ 1 between the basic blaze surface 21 and the basic step surface 22. The blaze angle (second blaze angle) of the blazed diffraction grating thus manufactured is smaller than the blaze angle (first blaze angle) of the blazed diffraction grating 20. In the above example, a blazed diffraction grating having 900 grooves / mm, a groove depth of 0.15 μm, and a second blaze angle of 7 ° is obtained.

  A blazed diffraction grating in which the resin layer is a support by utilizing the fact that the thickness of the residual resin layer becomes non-uniform due to the uniform volatilization of the solvent from the solvent resin with non-uniform thickness as in this example. The blazed material manufactured by forming monotonically changing in one direction on the basic blazed surface of 20 and making the thickness of the resin layer above the peak of the diffraction grating 20 smaller than the thickness above the valley of the blazed diffraction grating 20. The blaze angle of the diffraction grating can be made smaller than that of the blazed diffraction grating 20 used as a support. Therefore, it is possible to manufacture a blazed diffraction grating having a small blaze angle, which has been difficult with the conventional method for manufacturing a diffraction grating.

  Moreover, when the blaze angle of the manufactured blazed diffraction grating is not a desired angle, the formed resin layer may be peeled off and the resin layer may be formed again. Therefore, even if the processing fails, it is not necessary to discard the material to be processed, and the manufacturing cost can be reduced.

  A second embodiment of the present invention will be described with reference to FIGS. FIG. 7 is a schematic diagram of a unit that applies centrifugal force. FIG. 8 is a schematic cross-sectional view of the liquid resin on the blazed diffraction grating 40 when a centrifugal force is applied. In the following description of the second embodiment, a liquid resin is used. However, a resin liquefied with the same volatile solvent as in the first embodiment may be used. In the following, description that repeats the first embodiment will be omitted, and the description will focus on differences from the first embodiment.

  The second embodiment is an example in which a method using an external force is used as a method for forming the resin layer so that the thickness monotonously changes in one direction on the basic blazed surface, and centrifugal force is used as the external force. This is an example.

  In the second embodiment, a liquid resin is applied on the surface of a blazed diffraction grating 40 having a plurality of grooves formed by a basic blazed surface 41 and a basic stepped surface 42 as a support. The application method of the liquid resin is arbitrary, and may be a dipping method or a centrifugal method (spin coating). However, in the case of spin coating, the coating thickness is made sufficiently large without increasing the spin speed.

  The blazed diffraction grating 40 is set in the centrifuge so that a centrifugal force is applied to the blazed diffraction grating 40 coated with a liquid resin on the surface in the blaze direction (direction perpendicular to the groove). Specifically, as shown in FIG. 7, the blazed diffraction grating 40 is fixed to a peripheral edge as far as possible from the center of the disk-shaped rotating plate 60. At that time, the blazed diffraction grating 40 is fixed so that the blazed direction coincides with the radial direction of the rotating plate 60. When it is desired to form a resin layer having a blaze angle smaller than the blaze angle of the basic blazed surface 41, the blazed diffraction grating 40 is fixed so that the basic blazed surface 41 faces the outside of the rotating plate 60. Conversely, when it is desired to form a resin layer having a blaze angle larger than the blaze angle of the basic blazed surface 41, the basic blazed surface 41 faces the center of the rotating plate 60. For fixing, it is desirable to use a conductive adhesive or tape (for example, copper tape) in order to release the static electricity to the rotating plate 60 when the blazed diffraction grating 40 is charged.

  Next, the rotating plate 60 is rotated at a high speed of several thousand rpm, and a force (centrifugal force) is applied to the liquid resin on the surface of the blazed diffraction grating 40 in the blaze direction (arrow in FIG. 8). As a result, the liquid resin flows on the basic blazed surface 41. As described above, when the basic blazed surface 41 faces outward, the blaze angle of the resin layer 56 becomes smaller than that of the basic blazed surface 41, When the blazed surface 41 faces the center side, the blaze angle of the resin layer 56 is larger than the blaze angle of the basic blazed surface 41.

  Although the liquid resin is naturally solidified by such high speed rotation, solidification may be further promoted by irradiating the rotating surface with light or heating the rotating plate 60.

  By such a process, the liquid resin is solidified while applying a centrifugal force to the liquid resin, thereby reflecting the shape of the groove of the blazed diffraction grating 40 on the surface of the support, and the resin layer 56 having a blaze angle different from that. It is formed.

  Thereafter, although not shown in the drawing, as a metal coating film covering the surface of the resin layer 56, aluminum is maintained by using a vacuum deposition method, a sputtering method, or the like so as to maintain the blaze shape of the resin layer 56 (for example, a thickness of several tens of nm) To complete the blazed diffraction grating.

  In FIG. 8, the resin layer 56 has a blazed surface 51 on the basic blazed surface 41 and a stepped surface 52 on the basic stepped surface 42, and the inclinations of the blazed surface 51 and the stepped surface 52 are the basic blazed surface 41 and the stepped surface 52, respectively. It is gentler than the base step surface 42. Therefore, the angle γ 2 between the blaze surface 51 and the step surface 52 is larger than the angle β ′ 2 between the basic blaze surface 41 and the basic step surface 42.

  As in this embodiment, the resin layer monotonously changes in one direction on the basic blazed surface of the blazed diffraction grating 40 as a support, and the thickness of the resin layer on the top of the blazed diffraction grating 40 (t2 in FIG. 4) is By forming the blazed diffraction grating 40 so as to be smaller than the thickness above the valley (t1 in FIG. 4), the blazed angle of the blazed diffraction grating 40 used as a support is larger than the blazed angle of the blazed diffraction grating 40 used as a support. Can be small. Therefore, it is possible to manufacture a blazed diffraction grating having a small blaze angle, which has been difficult with the conventional method for manufacturing a diffraction grating.

  Moreover, when the blaze angle of the manufactured blazed diffraction grating is not a desired angle, the formed resin layer may be peeled off and the resin layer may be formed again. Therefore, even if the processing fails, it is not necessary to discard the material to be processed, and the manufacturing cost can be reduced.

  If this embodiment is used, the blaze angle of the blazed diffraction grating to be manufactured can be adjusted by adjusting the rotation speed of the rotating plate 60 and the viscosity of the liquid resin to be applied. The liquid resin may be mixed with the volatile solvent described in Example 1 to adjust the viscosity. Therefore, there is a high degree of freedom in adjusting parameters at the stage of manufacturing a blazed diffraction grating.

  In this embodiment, an example in which centrifugal force is used as an external force applied to the liquid resin has been shown, but the present invention is not limited to this. As an example, the support on which the liquid resin is applied may be inclined so that gravity is applied in the direction indicated by the arrow in FIG. Further, wind force may be used as an external force by blowing an inert gas such as nitrogen gas or air in a direction indicated by an arrow in FIG.

  In the above embodiment, the master diffraction grating is used as the blazed diffraction grating used for the support. However, the present invention is not limited to this. A replica diffraction grating may be used as the blazed diffraction grating used for the support. A replica diffraction grating can also be manufactured from the blazed diffraction grating manufactured in the above embodiment.

DESCRIPTION OF SYMBOLS 1 ... Board | substrate 2 ... Photoresist layer 3 ... Resist pattern 4 ... Grating groove 5 ... Metal film 20, 40 ... Blaze diffraction grating 21, 41 ... Base blazed surface 11, 31, 51 ... Blaze surface 22, 42 ... Base step surface 12, 32, 52 ... Stepped surfaces 26, 36, 56 ... Resin layer 60 ... Rotating plate

Claims (4)

a) a support having a sawtooth shape in cross section and a base blazed surface and a base step surface alternately arranged in one direction;
b) covering the basic blazed surface and the basic stepped surface of the support, and a resin layer whose thickness monotonously changes in the one direction on the basic blazed surface;
c) A blazed diffraction grating comprising a metal coating film covering the surface of the resin layer.   The blazed diffraction grating according to claim 1, wherein a blaze angle of the resin layer on the basic blazed surface is smaller than a blaze angle of the basic blazed surface. a) a step of preparing a support having a sawtooth cross-sectional shape and a base blazed surface and a base stepped surface alternately arranged in one direction;
b) forming a resin layer covering the basic blazed surface and the basic stepped surface on the support so that the thickness monotonously changes in the one direction on the basic blazed surface;
c) forming a metal coating film covering the surface of the resin layer;
A method for producing a blazed diffraction grating comprising: Forming the resin layer so as to monotonously change in the one direction,
d) dissolving the resin constituting the resin layer in a volatile solvent to create a solvent resin;
e) applying the solvent resin on the support so that the surface of the solvent resin after application is flat; and
f) after coating, volatilizing the volatile solvent, solidifying the resin;
The manufacturing method of the blazed diffraction grating of Claim 3 containing this.

Images