JP2007233283A - Reflection-type diffraction grating - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflection-type diffraction grating which reduces stray light caused by light infiltrating the inside of a substrate. <P>SOLUTION: An aluminum thin film 33 is formed by vapor deposition on the grating surface of a diffraction grating 20, which serves as a parent mold, and then a grating groove pattern of the diffraction grating 20 is reverse transferred on the surface of a replica substrate 31, together with the aluminum thin film 33, to form a replica diffraction grating 30. In this case, at least the back surface 31b (surface opposite to a surface on which the grating groove pattern is transferred) of the replica substrate 31 is made rough. Accordingly, even if there is an area which is not coated with the aluminum thin film 33, in a part of the grating surface of the replica diffraction grating, the reflectivity of light which intrudes into the inside of the substrate 31 from the area and is made incident into the back surface 31b is decreased to reduce stray light. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a reflective diffraction grating.

  A reflection type diffraction grating used in a spectroscope or the like is an optical element that performs wavelength dispersion using diffraction of light reflected by a grating surface. Such a reflective diffraction grating is generally manufactured by evaporating a metal such as aluminum on the surface of a translucent substrate such as glass having a number of grooves formed on the surface.

  However, such a reflective diffraction grating may have a portion where a metal thin film is not deposited on the grating surface depending on the shape of the groove. For example, in a ruled type (mechanical engraved type) diffraction grating, since the apex angle of the groove having a sawtooth cross section is almost a right angle, the entire surface of the groove can be uniformly coated with a metal thin film by vapor deposition. On the other hand, in the case of a blazed holographic type diffraction grating having a sawtooth groove in cross section, a sine half wave groove of photoresist is formed using holographic exposure, and then sawtooth is formed on the substrate by ion beam etching. In the process of forming the groove, the apex angle of the groove may become an acute angle. In this case, in the subsequent vapor deposition process, a part of the groove may be shaded, and a region not covered with the metal thin film may be generated.

  In addition, in order to reduce the cost by mass production and to reduce the variation in performance, a resin molded product based on the diffraction grating manufactured by the above procedure is used as a matrix. A replica diffraction grating is manufactured (see, for example, Patent Document 1). In the production of the replica diffraction grating, first, a metal thin film layer is formed on a diffraction grating to be a matrix, and a separately prepared substrate and the diffraction grating are bonded together via an adhesive such as an epoxy resin, By peeling, a negative mold in which the matrix groove pattern of the mother mold is reversely bonded to the substrate is produced. Next, a replica diffraction grating is manufactured by transferring the negative type grating groove pattern onto a desired substrate such as glass (referred to as a replica substrate) by the same procedure using the negative type as a mother die. At this time, float glass is generally used as a replica substrate, and the back surface of the replica substrate is used to make it easier to visually recognize bubbles that have entered the adhesive surface when the negative mold and the replica substrate are bonded together with an adhesive. The glossy surface of float glass is used as it is (the surface on the side where the grating groove pattern is not transferred).

JP 2005-157118 A

  As described above, when there is a region 43 that is not covered with the metal thin film 42 on the grating surface of the reflective diffraction grating, when the grating surface is irradiated with light, a part of the incident light is transferred from the region 43 to the substrate. It penetrates into the inside of 41 (FIG. 4). The light that has entered the substrate 41 in this way ("transmitted light" in the figure) is reflected by the back surface 41a of the substrate 41 and is emitted again from the region without the metal thin film 42 to the surface of the diffraction grating. Cause.

  Therefore, the problem to be solved by the present invention is to provide a reflection type diffraction grating capable of reducing stray light caused by light entering the inside of the substrate.

  The reflection type diffraction grating according to the present invention, which has been made to solve the above-mentioned problems, is a reflection type diffraction grating having a grating groove pattern coated with a metal thin film on one surface of a translucent substrate. It is characterized by the rough surface.

  In the reflective diffraction grating of the present invention, it is preferable that the peripheral surface of the translucent substrate is also a rough surface.

  According to the diffraction grating of the present invention having the above-described configuration, the back surface of the substrate (that is, the surface on which the grating groove pattern is not formed) is roughened (so-called a ground surface), and thus is covered with the metal film. It is possible to reduce the reflectance of light that enters the inside of the substrate from an area that is not present and enters the back surface, and scatters the entire surface to reduce stray light. Further, even for light that penetrates the metal coating and slightly enters the inside of the substrate, it is possible to prevent such light from being reflected on the back surface of the substrate and to suppress generation of stray light.

  Furthermore, when the peripheral surface of the substrate is roughened, stray light caused by light that enters the substrate and reflects off the peripheral surface can be prevented, and a higher stray light reduction effect can be achieved.

  Therefore, according to the present invention, since stray light generated due to the sharp groove shape can be reduced, high efficiency without impairing the characteristics of the holographic diffraction grating having a groove periodicity higher than that of the ruled type. In addition, a low stray light diffraction grating can be provided. For this reason, the diffraction grating of the present invention can be suitably used particularly for applications that handle weak light such as Raman spectroscopy. In addition, since the rear surface of the diffraction grating can be easily realized by changing the conventional glossy surface to a rough surface, it is possible to provide a diffraction grating with excellent performance at a low cost.

  Hereinafter, the best mode for carrying out the present invention will be described using embodiments.

  FIG. 1 shows a manufacturing process of a master diffraction grating as a matrix of a replica diffraction grating according to the present embodiment, FIG. 2 shows a process of manufacturing a negative diffraction grating from the master diffraction grating, and FIG. The process of producing a replica diffraction grating from a diffraction grating is shown.

<Manufacturing process of master diffraction grating>
First, the substrate 11 (about 60 mm × 60 mm × 11.3 mm) made of BK7 optical glass is optically polished, and then the surface is cleaned by ultrasonic cleaning. The substrate 11 may be of any type as long as it can be optically polished and can be coated with a photoresist. For example, in addition to the BK7, Pyrex (registered trademark) glass, quartz glass, or the like is used. Can do. Next, a photoresist layer 12 is formed on the surface of the substrate 11 (FIG. 1A). Any photoresist can be used as long as it can perform holographic exposure. For example, MP1800 series (manufactured by Shipley Co., Ltd.), OFPR5000 (manufactured by Tokyo Ohka Co., Ltd.), or the like can be used. In this embodiment, MP1805 is spin-coated at 3000 rpm for 40 seconds and then baked in a convection oven at 90 ° C. for 30 minutes to form a photoresist layer 12 having a thickness of 0.3 μm.

  The substrate 11 is set in a holographic exposure apparatus (for example, see Japanese Patent Laid-Open No. 06-034807), and 1200 is applied to the photoresist layer 12 by holographic exposure by two-beam interference of a He—Cd laser (λ = 441.6 nm). An interference fringe with a density of 1 book / mm is exposed. Then, after developing with exclusive developing solution MP303A (made by Shipley Co., Ltd.), the resist pattern 12 in which the diffraction grating pattern was formed is producible by performing pure water rinse sequentially. At this time, since the intensity distribution of the interference fringes of the two-beam interference is sinusoidal, the diffraction grating pattern of the sinusoidal half-wave photoresist 12 is produced on the surface of the substrate 11 by appropriately controlling the exposure time and the development time. (FIG. 1 (b)). In the present embodiment, the groove depth of the sine half-wave diffraction grating pattern is 0.1 μm.

Next, reactive ion beam etching is performed by irradiating the substrate 11 with an ion beam obliquely above the resist pattern forming surface and in a direction perpendicular to the arrangement direction of the lattice grooves of the resist pattern 12. At this time, a mixed gas of CF ₄ and Ar is used as an etching gas, the mixing ratio is Ar / (CF ₄ + Ar) = 60%, and the gas pressure is 2 × 10 ⁻² Pa. A diffraction grating pattern having a sawtooth cross-section is gradually formed on the BK7 glass substrate 11 until the resist 12 disappears and the resist diffraction grating groove pattern 12 is completely transferred to the glass substrate 11 for about 20 minutes. Etching is performed (FIG. 1C). As a result, a glass diffraction grating pattern having a blaze angle (grid groove inclination angle) of 7.6 ° is prepared. After the etching, the substrate 11 on which the grating grooves are engraved is washed, and the lattice grooves are formed by vacuum deposition. An aluminum thin film 13 having a film thickness of about 0.2 μm is formed on the surface (FIG. 1D). The master diffraction grating 10 is completed through the above steps.

<Negative diffraction grating fabrication process>
A release agent such as silicon grease is deposited on the master diffraction grating 10 completed through the above steps to form a release agent layer 14 (FIG. 2A), and then an aluminum thin film 23 is formed by vacuum deposition. (FIG. 2 (b)). This aluminum thin film 23 will later cover the grating surface of the negative diffraction grating, and here the film thickness is about 0.2 μm. Next, a float glass plate (about 60 mm × 60 mm × 11.3 mm) to be the negative substrate 21 is washed, and an adhesive (thermosetting epoxy resin) 22 is applied in a substantially uniform thickness (FIG. 2C). Then, the negative substrate 21 and the master diffraction grating 10 in the state shown in FIG. 2B are bonded to each other through the adhesive 22 and pressed with an appropriate pressure. As a result, the adhesive 22 spreads so as to fill a groove having a sawtooth cross section in the aluminum thin film 23 (FIG. 2D).

  This is held at 70 ° C. for 24 hours to cure the adhesive 22, and then the negative substrate 21 is peeled off from the master diffraction grating 10 with the release agent layer 14 as a boundary. Then, the aluminum thin film 23 formed into a sawtooth shape in cross section is peeled off in a state of being bonded to the negative substrate 21 via the adhesive 22 (FIG. 2 (e)). As a result, a negative diffraction grating 20 having a grating groove obtained by reversing and transferring the grating groove of the master diffraction grating 10 is obtained.

<Replica diffraction grating manufacturing process>
First, a float glass plate (about 60 mm × 60 mm × 11.3 mm) serving as a replica diffraction grating substrate (replica substrate) 31 is prepared (FIG. 3C), and abrasive grains having a mesh size of # 600 to # 1000 are prepared. The entire surface (surface on which the lattice groove pattern is transferred) 31a and side surface (circumferential surface) 31c of the substrate is roughened by the sanding process used (FIG. 3D). At this time, it is desirable that the center line average roughness of these surfaces be 4 μm to 20 μm. Note that the method of roughening the replica substrate is not limited to such sanding, and any method such as blasting or chemical treatment may be used.

  Next, the replica diffraction grating 30 is manufactured using the negative diffraction grating 20 described above as a matrix. The procedure is the same as that for producing the negative diffraction grating 20 described above, and the release agent layer 24 and the aluminum thin film 33 are formed on the surface of the grating groove of the negative diffraction grating 20 (FIGS. 3A and 3B). Then, the replica substrate 31 in the state of FIG. 3D is pasted with the adhesive 32 interposed therebetween (FIGS. 3E and 3F). Then, after the adhesive 32 is cured, the entire back surface 31b is roughened by sanding using abrasive grains having a mesh size of # 600 to # 1000 (FIG. 3 (g)). At this time, it is desirable that the center line average roughness of the back surface 31b be 4 μm to 20 μm. Thereafter, the replica substrate 31 is peeled off from the negative diffraction grating 20 with the release agent layer 24 as a boundary. As a result, the grating groove pattern of the negative diffraction grating 20 is inverted and transferred to the adhesive 32, and the surface thereof is covered with the aluminum thin film 33, so that a replica diffraction grating 30 as shown in FIG. Thereby, ideally, the shape of the diffraction grating groove of the replica diffraction grating 30 is the same as that of the master diffraction grating 10.

  In order to confirm the effect of the replica diffraction grating of the present embodiment, the replica diffraction grating is manufactured according to the steps of the above embodiment, and as a comparative example, only the surface side (side on which the grating groove pattern is formed) is roughened, The other surface is a replica substrate that remains a glossy surface, and other than that, replica diffraction gratings manufactured in the same manner as in the above embodiment are prepared, and the wavelength of 1.5 μm with respect to these replica diffraction gratings is prepared. Light was irradiated at an incident angle of -70 °. As a result, in the replica diffraction grating of this example, a significant reduction in stray light was confirmed compared to the replica diffraction grating of the comparative example.

  As described above, the best mode for carrying out the reflective diffraction grating according to the present invention has been described using examples. However, the numerical values and materials described in the above examples are merely examples, and the present invention is not limited thereto. It is not limited. In addition, it is apparent that other points can be appropriately changed or modified within the scope of the gist of the present invention.

  For example, the replica substrate is not necessarily required to have a rough surface on the entire surface (front surface, back surface, and side surface), and at least the back surface may be a rough surface.

  In addition, the present invention is not limited to a replica type diffraction grating produced by transferring a grating groove pattern from a master diffraction grating as in the above-described embodiment, and is applied to a substrate by a technique such as holographic exposure and ion beam etching The present invention can be similarly applied to a so-called original type diffraction grating manufactured by directly forming a grating groove. In this case, at least the back surface side of the substrate is roughened in advance, and the grating grooves and the metal thin film layer are formed by the same procedure as in the master diffraction grating manufacturing process.

  Furthermore, the reflection type diffraction grating of the present invention is similarly applied to a so-called concave diffraction grating having a curved grating surface in addition to a so-called planar diffraction grating having a planar grating surface as shown in FIGS. be able to.

Schematic explaining the manufacturing process of a master diffraction grating in preparation of the replica diffraction grating which concerns on one Example of this invention. Schematic explaining the process of producing a negative diffraction grating from the said master diffraction grating in the production process of the replica diffraction grating of the Example. Schematic explaining the process of producing a replica diffraction grating from the said negative diffraction grating in the production process of the replica diffraction grating of the Example. The figure explaining the problem of the conventional reflection type diffraction grating.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Master diffraction grating 11 ... Substrate 12 ... Photoresist 13 ... Aluminum thin film 14 ... Release agent layer 20 ... Negative diffraction grating 21 ... Negative substrate 22 ... Adhesive 23 ... Aluminum thin film 24 ... Release agent layer 30 ... Replica diffraction Lattice 31 ... Replica substrate 32 ... Adhesive 33 ... Aluminum thin film

Claims (5)

  A reflective diffraction grating having a grating groove pattern coated on one surface of a translucent substrate with a metal thin film, wherein the other surface of the substrate is a rough surface.   The reflective diffraction grating is a replica diffraction grating formed by transferring a grating groove pattern of a diffraction grating serving as a master to one surface of a translucent replica substrate, and the other surface of the replica substrate is a rough surface. The reflective optical element according to claim 1, wherein the optical element is a reflective optical element.   The reflective diffraction grating according to claim 1 or 2, wherein the peripheral surface of the substrate or the replica substrate is a rough surface.   The reflection type diffraction grating according to claim 1, wherein a center line average roughness of the rough surface is 4 μm to 20 μm. In a method of manufacturing a replica diffraction grating by transferring a grating groove pattern of a diffraction grating to be a master mold to one surface of a translucent replica substrate,
a) forming a metal thin film layer on a grating surface of a diffraction grating to be a matrix via a release agent layer;
b) roughening at least the surface of the replica substrate on which the lattice groove pattern is not transferred;
c) a step of separating the metal thin film layer and the replica substrate from each other with the release agent layer as a boundary after adhering the replica substrate through an adhesive;
A method of manufacturing a replica diffraction grating, comprising:

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