Spectroscopic instrument, detector, and method for manufacturing spectroscopic instrument

The present invention relates to a spectroscopic device, a detection device, a method for manufacturing the spectroscopic device, and the like.

Conventionally, most of the diffraction gratings used in spectroscopes such as Raman spectroscopes are reflective type. As a reflection type diffraction grating, for example, there is a blaze grating having a serrated cross section (for example, the diffraction grating described in Patent Document 1).

<p><patcit num="1"><text>Japanese Unexamined Patent Publication No. 2004-354176</text></patcit></p>

<p> However, the reflection type diffraction grating has a problem that it is difficult to achieve both improvement of wavelength resolution and widening of the wavelength band in which high diffraction efficiency can be obtained. For example, in a blazing diffraction grating, the diffraction efficiency is improved by blazing the cross-sectional shape. However, in a blaze diffraction grating, if the grating period is shortened in order to improve the wavelength resolution, the wavelength band in which high diffraction efficiency can be obtained becomes extremely narrow.</p><p> According to some aspects of the present invention, it is possible to provide a spectroscopic device, a detection device, a method for manufacturing the spectroscopic device, and the like, which can improve both wavelength resolution and diffraction efficiency.</p>

<p> One aspect of the present invention is a spectroscopic device including a transmission type diffraction grating that transmits incident light, and the transmission type diffraction grating has an inclined surface formed by a first dielectric, and the inclined surface is , The angle of incidence of the incident light on the transmission type diffraction grating is defined as the angle α with respect to the reference line, and the diffraction angle of the diffracted light is defined as the angle β with respect to the reference line. In this case, the incident angle α is an angle smaller than the Bragg angle θ with respect to the inclined surface, and the diffraction angle β is related to a spectroscopic device having an angle larger than the Bragg angle θ.</p><p> According to one aspect of the present invention, the inclined surfaces formed by the first dielectric are inclined and arranged with respect to the reference line. Then, the incident light on the transmission type diffraction grating is incident at an angle α smaller than the Bragg angle θ, and the diffracted light by the transmission type diffraction grating is emitted at an angle β larger than the Bragg angle θ. This makes it possible to improve the wavelength resolution and widen the wavelength band in which high diffraction efficiency can be obtained.</p><p> Further, in one aspect of the present invention, when the inclination angle of the inclined surface with respect to the reference line is φ, the inclined surfaces are arranged in a direction perpendicular to the reference line with a period P / cos φ, and the incident light. May be linear polarization parallel to the plane perpendicular to the reference line and perpendicular to the arrangement direction of the inclined surfaces.</p><p> In this way, the inclined surfaces are arranged so as to be inclined at an angle φ with respect to the reference line, and linear polarized light parallel to the inclined surface and perpendicular to the reference line is incident on the transmission type diffraction grating, and the diffracted light thereof. Can be obtained.</p><p> Further, in one aspect of the present invention, when the inclination angle of the inclined surface with respect to the reference line is φ, the transmission type diffraction grating is formed on a base material having a plane perpendicular to the reference line. The protrusions formed by the dielectric are arranged with a period P / cosφ along the direction parallel to the plane of the base material, and the protrusions have the angle φ with respect to the reference line. The inclined surface inclined with the above may be formed.</p><p> In this way, by periodically arranging the protrusions, it is possible to realize an inclined surface in which the period in the direction perpendicular to the inclined surface is P.</p><p> Further, in one aspect of the present invention, the inclination angle φ may be set so that adjacent protrusions of the protrusion group do not overlap in a plan view projected onto the plane of the base material.</p><p> In this way, the inclination angle φ can be set so that the adjacent protrusions do not overlap in the plan view projected on the plane of the base material. This makes it possible to improve the simulation accuracy and the like.</p><p> Further, in one aspect of the present invention, when the inclination angle of the inclined surface with respect to the reference line is φ, the transmission type diffraction lattice is formed on a substrate having a plane perpendicular to the reference line. The dielectric and the second dielectric having a different dielectric constant from the first dielectric are formed by alternately arranging them in a direction parallel to the plane of the base material with a period of P / cosφ. The inclined surface is a boundary surface between the first dielectric and the second dielectric, and may be formed by the boundary surface inclined at the angle φ with respect to the reference line.</p><p> In this way, by periodically arranging the first dielectric and the second dielectric, it is possible to realize an inclined surface in which the period in the direction perpendicular to the inclined surface is P. ..</p><p> Further, in one aspect of the present invention, in the transmission type diffraction grating, the inclined surface is formed on the first surface side of the base material on which the incident light is incident, and the diffracted light is emitted from the base material. An antireflection film may be formed on the two side surfaces.</p><p> In this way, the incident light can be incident on the inclined surface without passing through the base material. In addition, the antireflection film can suppress the reflection of diffracted light. This enables highly efficient spectroscopy.</p><p> In another aspect of the present invention, the spectroscope according to any one of the above and the scattered light or reflected light from the target are incident on the spectroscope at an incident angle α smaller than the Bragg angle θ. It relates to a detection device including an optical system and a detector that detects diffracted light from the spectroscopic device.</p><p> Further, in still another aspect of the present invention, the resist is subjected to interference exposure by injecting a first laser beam and a second laser light onto the resist coated on the substrate, and the resist is subjected to interference exposure. The present invention relates to the method for manufacturing a spectroscopic apparatus according to any one of the above, wherein a resist pattern is formed which is inclined at an inclination angle φ with respect to a perpendicular line toward a plane of the base material.</p>

<figref num="1">An example of a blaze diffraction grating which is a comparative example of this embodiment.</figref><figref num="2">An example of the characteristics of wavelength resolution with respect to the diffraction angle in the comparative example.</figref><figref num="3">FIG. 3A is a cross-sectional view of a configuration example of the diffraction grating of the present embodiment. Fig. 3 (B) is an explanatory diagram of Bragg reflection due to the periodic structure of the inclined surface.</figref><figref num="4">An example of the characteristic of wavelength resolution with respect to the diffraction angle in this embodiment.</figref><figref num="5">Fig. 5 (A) is an example of the characteristics of diffraction efficiency with respect to the incident angle when the inclination angle is 0 °. FIG. 5B is an example of the characteristic of diffraction efficiency with respect to the incident angle in this embodiment.</figref><figref num="6">Figure 6 (A) shows an example of the diffraction efficiency with respect to the wavelength λ when the tilt angle is 0 °. FIG. 6B is an example of the characteristic of diffraction efficiency with respect to the wavelength λ in this embodiment.</figref><figref num="7">7 (A) to 7 (D) are explanatory views of a method for manufacturing a diffraction grating.</figref><figref num="8">Sectional drawing of the 2nd structural example of a diffraction grating.</figref><figref num="9">9 (A) and 9 (B) are first configuration examples of the detection device.</figref><figref num="10">FIGS. 10 (A) and 10 (B) are a second configuration example of the detection device.</figref><figref num="11">11 (A) and 11 (B) are explanatory views of the incident direction of the incident light on the diffraction grating.</figref>

Hereinafter, preferred embodiments of the present invention will be described in detail. The present embodiment described below does not unreasonably limit the content of the present invention described in the claims, and all the configurations described in the present embodiment are indispensable as a means for solving the present invention. Not necessarily.

1. Comparative example As described above, the blaze diffraction grating has a problem that it is difficult to achieve both wavelength resolution and diffraction efficiency at the same time. This point will be described with reference to FIGS. 1 and 2.

FIG. 1 shows an example of a blaze diffraction grating as a comparative example of the present embodiment. As shown in FIG. 1, the lattice period of the blazing diffraction grating is Pa, the wavelength of the incident light is λa, the incident angle of the incident light is αa, and the diffraction angle of the diffracted light is βa.

First, consider the wavelength resolution. The wavelength resolution Δβ / Δλ of the diffraction grating is expressed by the following equation (1). From the following equation (1), it can be seen that in order to increase the wavelength resolution Δβ / Δλ, the lattice period Pa should be reduced and the diffraction angle βa should be increased.

Δβ / Δλ = 1 / (Pa cosβa) (1) FIG. 2 shows an example of the characteristics of the wavelength resolution Δβ / Δλ with respect to the diffraction angle βa when the wavelength λa = 633 nm and the lattice period Pa = 333 nm in the above equation (1). In this example, the ratio of wavelength to lattice period is λa / Pa = 1.9. At this time, as shown in FIG. 2, when the diffraction angle βa is 70 °, the wavelength resolution Δβ / Δλ is improved to about 0.009.

Next, consider the diffraction efficiency. In the case of a reflective diffraction grating, it is possible to improve the diffraction efficiency by blazing the cross-sectional shape of the grating. However, if the lattice period Pa is reduced in order to improve the wavelength resolution Δβ / Δλ, it is difficult to obtain high diffraction efficiency even if the cross-sectional shape is blurred (Latest Diffractive Optical Element Technology Complete Works, Technical Information Association, p.107- p.120 (2004)). As described above, in a reflection type diffraction grating such as a blaze diffraction grating, it becomes difficult to realize high wavelength resolution and high diffraction efficiency at the same time.

For example, in a spectroscope such as a Raman spectroscope, there is a demand for a diffraction grating that simultaneously satisfies high wavelength resolution and high diffraction efficiency in a wide wavelength range. In Raman spectroscopy, the scattered light from the sample is mainly Rayleigh scattered light and Raman scattered light (hereinafter, the Stokes component having a Raman scattering wavelength λray + Δλ with respect to the Rayleigh scattering wavelength λray is focused on). In this Raman spectroscopy, there are some practical problems. First, the intensity of Raman scattered light is extremely weak as compared with the intensity of Rayleigh scattered light. Next, when a substance is identified by Raman spectroscopy, it is necessary to disperse the Raman scattered light scattered from the sample with a wavelength resolution of about 0.5 nm. Furthermore, the wavelength difference between Rayleigh scattered light and Raman scattered light is about 100 nm. Considering these points, the diffraction grating used for Raman spectroscopy is required to obtain a high wavelength resolution of about 0.5 nm in the visible to near infrared (wavelength 400 nm to 1100 nm). In addition, it is required that high diffraction efficiency can be obtained in a wide wavelength band of about 100 nm.

2. Configuration example In the present embodiment, the wavelength resolution is improved and the diffraction efficiency is widened by inclining the periodic structure that causes Bragg reflection so that the diffraction angle can be increased and the lattice period can be increased. The transmission type diffraction grating of this embodiment (hereinafter abbreviated as a diffraction grating) will be described with reference to FIGS. 3 (A) to 6 (B). In the following, in order to make each component recognizable on the drawing, the dimensions and ratios of each component are appropriately different from the actual ones.

Here, the case where the diffraction grating is used for surface-enhanced Raman scattering spectroscopy will be described below, but the present embodiment is not limited to this case, and the diffraction grating can be used for various spectroscopic methods.

FIG. 3A shows a cross-sectional view of a configuration example of the diffraction grating of the present embodiment. This diffraction grating is a surface-concavo-convex type diffraction grating, and includes a base material 100 (substrate) and protrusions 110 (convex portions). Note that FIG. 3A is a cross-sectional view of the base material 100 in a plane perpendicular to the plane and parallel to the arrangement direction of the protrusions 110.

The base material 100 is formed of a dielectric material such as a quartz glass substrate that transmits incident light, and is formed in the shape of a quadrangular flat plate or a disk. The term "transmitting incident light" includes not only a case of being transparent to the wavelength of the incident light (wavelength used) but also a case of being translucent to transmit a part of the amount of incident light.

The protrusion group 110 is formed of a first dielectric (for example, the same dielectric as the base material 100), and is arranged with a period P / cosφ (lattice spacing) along a direction parallel to the plane of the base material 100. The plane of the base material 100 is, for example, a plane parallel to the surface 120 (first surface) of the base material 100 on the side where the protrusions 110 are formed. The protrusion group 110 is formed so as to be inclined by an angle φ (φ&gt; 0 °) with respect to the reference line 130. More specifically, each protrusion of the protrusion group 110 is formed with an inclined surface 140 (or an inclined surface 150) that is inclined at an angle φ with respect to the reference line 130. The reference line 130 is a line that serves as a reference for the inclination angle φ, the incident angle α, and the diffraction angle β, and is, for example, a perpendicular line (normal line) with respect to the plane of the base material 100. The inclined surface 140 has a period P in the direction perpendicular to the inclined surface 140, and diffracted light (Bragg reflected light) is generated by the periodic structure of this period P. It is desirable that the wavelength λ used and the lattice period P satisfy 1.0 &lt;λ / P &lt;2.0. Further, it is desirable that the lattice period P is 200 to 1100 nm and the height of the protrusion group 110 is 500 to 3000 nm. Further, it is desirable that the inclination angle is φ &lt;45 °.

As shown in FIG. 3A, incident light having a wavelength of λ is incident on the diffraction grating at an angle α, and the diffracted light is transmitted to the back surface 160 (second surface) side of the base material 100 at an angle β. Here, the back surface 160 of the base material 100 is the surface on the side where the protrusion group 110 is not formed. At this time, the wavelength resolution Δβ / Δλ of the diffraction grating that is inclined at the inclination angle φ is expressed by the following equation (2). If φ = 0 in the following equation (2), the above equation (1) is obtained, which is an equation expressing the wavelength resolution when there is no slope.

Δβ / Δλ = cosφ / (P cosβ) (2) Next, a method for improving the wavelength resolution and the diffraction efficiency according to the present embodiment will be described. As shown in FIG. 3 (B), in this embodiment, Bragg reflection due to the periodic structure of the inclined surface 140 (or the inclined surface 150) is used. In FIG. 3B, the case where the inclination angle φ = 0 ° is considered for convenience. Assuming that the incident angle of the incident light that causes Bragg reflection is the Bragg angle θ, the Bragg condition is expressed by the following equation (3). The Bragg angle θ is an angle with respect to the inclined surface 140. Further, n is the refractive index of air (in a broad sense, a medium).

2nPsinθ = λ (3) As explained in the comparative example, it is necessary to increase the Bragg angle θ (diffraction angle) in order to increase the wavelength resolution Δβ / Δλ. From the above equation (3), it can be seen that when the Bragg angle θ is increased, P must be decreased. However, as explained in the comparative example, if P is made small, the wavelength band having high diffraction efficiency becomes narrow. Therefore, in the present embodiment, the diffraction angle β is increased by inclining the protrusion group 110 as shown in FIG. 3 (A). At this time, the incident angle α is approximately α = θ-φ, and the diffraction angle β is approximately β = θ + φ. In this way, since the Bragg angle θ can be made smaller than the diffraction angle β by inclining the protrusion group 110, the wavelength resolution Δβ / Δλ can be increased by the diffraction angle β, and the period P can be increased as compared with the case of φ = 0 °. Can be a larger value.

In this way, it is possible to simultaneously increase the diffraction angle β to improve the wavelength resolution and increase the period P as much as possible within the range in which the required wavelength resolution can be obtained to widen the diffraction efficiency. Strictly speaking, as will be described later, the incident angle α = θ-φ and the diffraction angle β = θ + φ are not always satisfied.

3. Specific configuration example FIG. 4 shows an example of the characteristics of the wavelength resolution Δβ / Δλ with respect to the diffraction angle β. FIG. 4 shows an example when the wavelength is λ = 633 nm, the lattice period is P = 366 nm, and the inclination angle is φ = 10 °, and the Bragg angle of the first-order transmitted diffracted light is θ = 59.9 °. The lattice period P = 366 nm is a value 10% larger than the lattice period Pa = 333 nm in the above comparative example. Further, from the above equation (2), the wavelength resolution of this diffraction grating is the same as the wavelength resolution of the non-gradient diffraction grating having a period of P / cos φ = 366 / cos (10 °) = 372 nm.

When φ = 0 ° with no lattice inclination, the diffraction efficiency of the first-order diffracted light is maximized when the diffraction angle is near the Bragg angle θ = 59.9 °. At this time, as shown in FIG. 4, the wavelength resolution remains at Δβ / Δλ = 0.005. On the other hand, when the lattice is tilted by φ = 10 °, the diffraction angle expands to β = 73 °, so the wavelength resolution is improved by about 1.8 times from the case of φ = 0 ° to Δβ / Δλ = 0.009 or more. .. This has the same wavelength resolution as the above-mentioned comparative example. By inclining the diffraction grating at an angle φ = 10 ° in this way, high diffraction efficiency is realized in the vicinity of the diffraction angle β = 73 °.

Figures 5 (A) and 5 (B) show examples of the characteristics of diffraction efficiency with respect to the incident angle α. This example is a characteristic example when the wavelength is λ = 633 nm, the lattice period is P = 366 nm, and the lattice height is 745 nm. The base material (and protrusions) of the lattice is quartz glass, and its refractive index is 1.46. The incident light is linearly polarized light, and its polarization direction (polarization direction) is parallel to the groove of the lattice.

As shown in A1 of FIG. 5 (A), when the diffraction grating has no inclination of φ = 0 °, high diffraction efficiency can be obtained when the incident angle α is in the vicinity of the Bragg angle of 59.9 °. When the incident angle α is 59.9 °, the diffraction angle β is also 59.9 °. On the other hand, as shown in B1 of FIG. 5 (B), when the inclination of the diffraction grating is φ = 10 °, high diffraction efficiency can be obtained when the incident angle α is in the vicinity of 43 °. From this characteristic, for example, when the incident angle α is 46 °, the diffraction angle β is 73 °. At this time, as described above in FIG. 4, the wavelength resolution Δβ / Δλ is improved by 1.8 times to about 0.009.

By tilting the diffraction grating by 10 ° in this way, it is possible to increase the wavelength resolution Δβ / Δλ to 0.009, which is equivalent to that of the comparative example, even under the condition that the lattice period is 10% larger than that of the comparative example. This is because the diffraction angle β can be made sufficiently large by inclining the diffraction grating and shifting the Bragg angle.

Figures 6 (A) and 6 (B) show examples of the characteristics of diffraction efficiency with respect to the wavelength λ. This example is a characteristic example when the wavelength is λ = 633 nm, the lattice period is P = 333 nm (Fig. 6 (A)), and P = 366 nm (Fig. 6 (B)). Further, the incident light is linearly polarized light, and its polarization direction is parallel to the groove of the lattice.

As described above in the comparative example, if the lattice period P is relatively small, high wavelength resolution Δβ / Δλ can be expected without inclining the lattice. However, if the lattice period P is reduced, the wavelength band in which high diffraction efficiency can be obtained becomes narrow. Specifically, as shown in FIG. 6 (A), under the condition that the lattice period P is 333 nm, the wavelength band in which high diffraction efficiency of, for example, 0.8 or more can be obtained is as narrow as 560 nm to 640 nm, which is the wavelength band required for Raman spectroscopy. 100nm cannot be secured. This is because the long wavelength end of the wavelength band in which high diffraction efficiency can be obtained is close to the boundary between the diffraction region (for example, λ / P 2) and the non-diffraction region (λ / P&gt; 2).

On the other hand, as shown in FIG. 6B, under the condition that the lattice period P is 366 nm, the long wavelength end of the wavelength band in which high diffraction efficiency can be obtained is separated from the boundary between the diffraction region and the non-diffraction region. Therefore, the wavelength band in which a high diffraction efficiency of 0.8 or more can be obtained is widened to the long wavelength side to be 565 nm to 675 nm, and the wavelength band of 100 nm required for Raman spectroscopy can be secured.

By the way, in a reflection type diffraction grating such as a blaze grating, it is difficult to improve both the wavelength resolution and the bandwidth of the diffraction efficiency because it is necessary to reduce the diffraction angle β and the period P in order to improve the wavelength resolution. There was a problem that there was.

In this respect, the present embodiment is a transmission type diffraction grating (in a broad sense, a spectroscopic device) that transmits incident light. As shown in FIG. 3 (A), the transmissive diffraction grating has an inclined surface 140 (or inclined surface 150) formed by the first dielectric. The inclined surface 140 is inclined at an angle φ with respect to the reference line 130, and is arranged so that the period in the direction perpendicular to the inclined surface 140 is P. The angle of incidence of the incident light on the transmission type diffraction grating is an angle α with respect to the reference line 130, and the diffraction angle of the diffracted light is an angle β with respect to the reference line 130. In this case, the incident light is incident at an incident angle α (α &lt;θ) smaller than the Bragg angle θ determined by the period P of the inclined surface 140. The diffracted light is diffracted at a diffraction angle β (β&gt; θ) larger than the Bragg angle θ.

This makes it possible to improve the wavelength resolution and widen the band of high diffraction efficiency. Specifically, by arranging the inclined surfaces 140 with a period P, a one-dimensional periodic permittivity distribution is formed in the diffraction grating. Then, as shown in FIG. 5 (B), by inclining this dielectric constant distribution with respect to the lattice surface, for example, φ = 10 °, the incident angle α = 43 rather than the Bragg angle θ = 59.9 ° when there is no inclination. The ° can be made shallower, and the transmission diffraction angle β = 73 ° can be made deeper than the Bragg angle θ = 59.9 ° when there is no inclination. That is, by inclining the permittivity distribution, the light incident angle α at which the maximum diffraction efficiency is obtained is shifted from the Bragg angle θ to a shallow angle. As a result, the wavelength resolution Δβ / Δλ can be sufficiently increased even under the condition that the period P of the diffraction grating is relatively large. In this way, in the present embodiment, high wavelength resolution (for example, FIG. 4) and high diffraction efficiency are simultaneously satisfied in a wide wavelength band (for example, FIG. 6 (B)). For example, when this embodiment is applied to Raman spectroscopy, it is possible to efficiently guide weak Raman scattered light having a wide wavelength band to a photodetector.

Further, in terms of separating signal light and stray light, it can be expected that the expensive bandpass filter, which has been indispensable in the past, becomes unnecessary. That is, since high wavelength resolution can be obtained, Raman scattered light and Rayleigh scattered light are sufficiently separated, and it is not necessary to use a filter having steep blocking characteristics. Further, since the diffraction grating of the present embodiment is a transmission type, the degree of freedom in arranging optical elements such as a lens and a mirror can be increased, and the spectroscopic device can be miniaturized.

In the cross section shown in FIG. 3A, the incident angle α of the incident light is, for example, an angle in the first direction (counterclockwise, positive direction) with respect to the reference line 130. In this case, the inclination angle φ of the inclined surface 140 is an angle in the second direction (clockwise, negative direction) different from the first direction with respect to the reference line 130.

Further, in the present embodiment, the incident light on the transmission type diffraction grating is linearly polarized light parallel to the inclined surface 140 and perpendicular to the reference line 130.

In this way, linearly polarized light parallel to the groove (periodic permittivity distribution) of the lattice can be incident as incident light. As a result, the above-mentioned diffraction efficiency characteristics (for example, the characteristics shown in B1 of FIG. 5B) can be realized. In this embodiment, the present embodiment is not limited to this case, and the incident light may include a polarization component parallel to the inclined surface 140 and perpendicular to the reference line 130.

Further, in the present embodiment, as shown in FIG. 3A, the transmission type diffraction grating is formed by the first dielectric material on the base material 100 having a plane (for example, the surface 120) perpendicular to the reference line 130. The protrusions 110 are formed by arranging the protrusions 110 with a period of P / cosφ along a direction parallel to the plane of the base material 100. Then, the protrusion group 110 is formed with an inclined surface 140 that is inclined at an angle φ with respect to the reference line 130.

In this way, by periodically arranging the protrusions 110, it is possible to realize the inclined surface 140 whose period is P in the direction perpendicular to the inclined surface 140. As a result, an inclined uneven transmission type diffraction grating can be realized.

Further, in the present embodiment, the inclination angle φ is set so that adjacent protrusions of the protrusion group 110 do not overlap in a plan view projected perpendicularly to the plane of the base material 100.

By doing so, the height of the protrusion group 110 can be suppressed by setting the inclination angle φ so that the protrusions do not overlap, and the production of the protrusion group 110 can be facilitated. In addition, since simulation of diffraction efficiency and the like can be performed with high accuracy, highly reliable design becomes possible.

Further, in the present embodiment, as will be described later in FIG. 8, the transmission type diffraction lattice is formed on a base material 100 having a plane perpendicular to the reference line 130 with a first dielectric layer 170 (first dielectric). , The second dielectric layer 180 (second dielectric), which has a different dielectric constant (reflectivity) from the first dielectric layer 170, has a period P / along the direction parallel to the plane of the base material 100. It may be formed by alternately arranging them with cosφ. In this case, the inclined surface 140 (or the inclined surface 150) is formed by the boundary surface between the first dielectric layer 170 and the second dielectric layer 180.

In this way, the boundary surface between the first dielectric layer 170 and the second dielectric layer 180 is periodically arranged, and the boundary surface causes the period in the direction perpendicular to the inclined surface 140 to be P. The inclined surface 140 can be realized. As a result, a tilted refractive index modulation type transmission diffraction grating can be realized.

Further, in the present embodiment, as will be described later in FIG. 11A, in the transmission type diffraction grating, an inclined surface 140 is formed on the surface 120 (first surface) side of the base material 100 on which the incident light is incident. An antireflection film 190 is formed on the back surface 160 (second surface) side of the base material 100 from which diffracted light is emitted.

In this way, it is possible to prevent the diffracted light having a large diffraction angle β from being reflected by the back surface 160 of the base material 100 and reducing the transmitted diffracted light toward the back surface 160 side. As a result, the transmitted diffracted light can be efficiently extracted, and highly sensitive sensing becomes possible. Further, since the incident light is incident on the inclined surface 140 without passing through the base material 100, highly efficient diffracted light can be obtained.

4. Manufacturing method A method of manufacturing a transmission type diffraction grating having a group of inclined protrusions will be described with reference to FIGS. 7 (A) to 7 (D).

First, as shown in FIG. 7A, the resist 210 is applied onto the quartz glass substrate 200. Then, the laser beam LS1 having an incident angle θ1 and the laser beam LS2 having an incident angle θ2 are irradiated to expose the resist 210 by laser interference. The interval D of the interference fringes due to the interference exposure is expressed by the following equation (4). λs is the wavelength of the laser beams LS1 and LS2. The inclination angle φ of the interference fringes in the resist is expressed by the following equation (5). n_rIs the refractive index of the resist 210 with respect to the exposure wavelength λs. Also, let θ2&gt; θ1.

D = λs / (sin (θ1) + sin (θ2)) (4) φ = (sin^-1(sin (θ2) / n_r)-sin^-1(sin (θ1))) / 2 (Five) For example, the laser light source for interference exposure is a continuously oscillating He-Cd laser (wavelength λs = 325 nm), the resist 210 is a positive resist, and the resist film thickness is 1 μm. Further, for example, the incident angle of the laser beam is θ1 = 9.1 ° and θ1 = 45.7 °, and the refractive index of the resist is n._r= 1.60. At this time, from the above equation (4), the interval of the interference fringes in the direction parallel to the plane of the substrate 200 is D = 372 nm. Further, from the above equation (5), the inclination φ of the interference fringes is about 10 ° (φ = 10.4 °). The period of the interference fringes in the direction perpendicular to the inclination is D · cos φ = 366 nm. In this way, the interference angle of the substrate 200 with respect to the normal is made asymmetrical on the left and right (θ1 and θ2), and a latent image of inclined interference fringes is formed in the resist 210.

Next, as shown in FIG. 7B, the exposed resist 210 is developed to obtain a one-dimensional resist pattern 220 tilted by 10 °. Next, as shown in FIG. 7C, the quartz glass substrate is anisotropically dry-etched from an oblique direction of 10 ° using the resist pattern 220 as a mask. For etching gas, for example, CF₄And CHF₃Is used. The etching depth can be adjusted by the ultra-short etching time. Next, as shown in FIG. 7 (D), the resist remaining after etching is removed by oxygen plasma. In this way, a one-dimensional transmission diffraction grating in which the protrusions 240 inclined by 10 ° are arranged on the surface of the base material 230 is formed.

Although the example in which the protrusion group 240 is formed from the same quartz glass as the base material 100 has been described above, the present embodiment is not limited to this. For example, the resist pattern 220 shown in FIG. 7 (B) is filled with a resin (polymer), the resin is cured, and the resist pattern 220 is peeled off to form a protrusion group 240 with a material different from the base material 100. You may.

5. Second configuration example In the above embodiment, the diffraction grating that causes Bragg reflection due to the inclined surface of the protrusion group has been described, but in this embodiment, Bragg reflection may be generated by the inclined refractive index modulation structure.

FIG. 8 shows a cross-sectional view of a second configuration example of this embodiment. This transmission type diffraction grating includes a base material 100, a first dielectric layer 170, and a second dielectric layer 180. The first dielectric layer 170 is formed by a first dielectric having a first dielectric constant (first refractive index). The second dielectric layer 180 is formed by a second dielectric having a second dielectric constant (second refractive index) different from the first dielectric constant.

The first dielectric layer 170 and the second dielectric layer 180 are arranged alternately and periodically. Specifically, the first dielectric layer 170 is arranged with a period P / cosφ along a direction parallel to the plane of the base material. The second dielectric layer 180 is formed between the layers of the first dielectric layer 170. The interface between the first dielectric layer 170 and the second dielectric layer 180 forms an inclined surface 140 (or inclined surface 150) that is inclined at an angle φ with respect to the reference line 130. The arrangement period of the first dielectric layer 170 (or the second dielectric layer 180) in the direction perpendicular to the interface is period P.

For example, this transmission type diffraction grating is manufactured by the following steps. First, the resist pattern 220 shown in FIG. 7B is filled with a first resin (first polymer), the first resin is cured, the resist pattern 220 is peeled off, and the first dielectric layer is formed. Form 170. Next, a second resin (second polymer) is filled between the layers of the first dielectric layer 170, and the second resin is cured to form the second dielectric layer 180.

6. Detection device 9 (A) and 9 (B) show a first configuration example of the detection device to which the diffraction grating of the present embodiment is applied. This detector includes Raman sensor 300 (sensor chip, optical device), first concave mirror 310, bandpass filter 320, polarizing plate 330, diffraction grating 340, second concave mirror 350, array photodetector 360 (detector). , Light source 370, edge filter 380. This detection device is a single spectroscopic device in which one diffraction grating 340 and two concave mirrors 310 and 350 are arranged in a predetermined positional relationship. Although the detection device for performing Raman spectroscopic measurement will be described below, the diffraction grating of the present embodiment can also be applied to a detection device using another spectroscopic method.

As shown in FIG. 9B, the laser beam from the light source 370 is reflected by the edge filter 380 and irradiates the sample 390 (target) on the Raman sensor 300. For example, the light source 370 is a continuously oscillating He-Ne laser (wavelength 633 nm, output 20 mW). The sample 390 irradiated with the laser light generates Rayleigh scattered light and Raman scattered light by surface-enhanced Raman scattering by the Raman sensor 300. These scattered lights are incident on the edge filter 380. The edge filter 380 reflects light having a wavelength of laser light (633 nm) and transmits light having a wavelength longer than that. That is, the Rayleigh scattered light is reflected by the edge filter 380, and the Raman scattered light is transmitted. The transmitted Raman scattered light is incident on the concave mirror 310 and is made into parallel light by the concave mirror 310.

Next, as shown in FIG. 9A, the reflected light from the concave mirror 310 passes through the bandpass filter 320 and the polarizing plate 330, and is incident on the diffraction grating 340 at a predetermined angle of incidence α. The bandpass filter 320 further blocks Rayleigh scattered light and transmits only Raman scattered light. The polarizing plate 330 makes the light incident on the diffraction grating 340 linearly polarized, and makes the polarization direction parallel to the groove of the diffraction grating 340. The light incident on the diffraction grating 340 is transmitted and diffracted at the diffraction angle β and dispersed. The dispersed Raman scattered light has a slightly different diffraction angle for each wavelength, and is parallel light at each wavelength. The dispersed Raman scattered light is incident on the concave mirror 350 and condensed on the array photodetector 360 by the concave mirror 350 to form a spectral distribution. Then, the spectral distribution of Raman scattered light is detected by the array photodetector 360.

Next, the wavelength resolution of this detection device will be specifically described. Assuming that the position of Rayleigh scattered light on the array photodetector 360 is X (λ) and the position of Raman scattered light (Stokes light) is X (λ + Δλ), the distance between these positions is given by the following equation (6). ). Here, f is the focusing distance (focal length) of the concave mirror 350, and Δβ / Δλ is the wavelength resolution of the diffraction grating.

X (λ + Δλ) -X (λ) = f Δλ (Δβ / Δλ) (6) From the above equation (6), it can be seen that when the wavelength resolution Δβ / Δλ is sufficiently large, even if the focusing distance f of the concave mirror is short, it is possible to widely disperse between the Raman scattered light and the Rayleigh scattered light. Therefore, by using the high-resolution diffraction grating of the present embodiment, the focusing distance f of the concave mirror 350 can be shortened, and each component can be arranged compactly to reduce the size of the spectroscope.

For example, in the diffraction grating described in FIG. 3A and the like, the period of the diffraction grating is 366 nm (2700 lines / mm), the inclination angle is 10 °, and the wavelength resolution is 0.009 rad / nm. In this case, using a concave mirror with a focal length of f = 10 mm, two scattered light components with a wavelength difference of Δλ = 0.5 nm can be separated by 45 μm on the array photodetector 360. This distance is a distance that can be sufficiently resolved using a general array photodetector. As described above, by using the diffraction grating of the present embodiment, sufficient resolution can be realized even with a concave mirror having a short focusing distance. The distance from Rayleigh scattered light to Raman scattered light is about 45 μm × 100 / 0.5 = 9 mm. This distance is a distance that can sufficiently separate Rayleigh scattered light and Raman scattered light. Therefore, the load on the characteristics of the bandpass filter 320 for blocking Rayleigh scattered light is greatly reduced. The bandpass filter 320 can be omitted in spectroscopic applications where the detection accuracy may be relatively low.

10 (A) and 10 (B) show a second configuration example of the detection device to which the diffraction grating of the present embodiment is applied. The detector includes a Raman sensor 300, a bandpass filter 320, a polarizing plate 330, a diffraction grating 340, a concave mirror 350, an array photodetector 360, a light source 370, an edge filter 380, and a lens 400. This detection device is a single spectroscopic device in which one diffraction grating 340 and one concave mirror 350 are arranged in a predetermined positional relationship. The same components as those described in FIGS. 9 (A) and 9 (B) are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

As shown in FIG. 10 (B), the laser light from the light source 370 is reflected by the edge filter 380 and irradiates the sample 390 (target) on the Raman sensor 300. The scattered light from the sample 390 is incident on the edge filter 380, and the Raman scattered light is transmitted. The transmitted Raman scattered light is incident on the lens 400 and is made into parallel light by the lens 400.

Next, as shown in FIG. 10A, the parallel light from the lens 400 passes through the bandpass filter 320 and the polarizing plate 330, and is incident on the diffraction grating 340 at a predetermined incident angle α. Since the lens 400 makes the scattered light from the sample 390 into parallel light rays having high parallelism and causes them to enter the diffraction grating 340, the diffraction grating 340 can sufficiently exhibit its wavelength resolution and disperse extremely weak light. The light incident on the diffraction grating 340 is transmitted and diffracted at the diffraction angle β and dispersed. The dispersed Raman scattered light is incident on the concave mirror 350, condensed on the array photodetector 360 by the concave mirror 350, and the spectral distribution is detected by the array photodetector 360.

According to this second configuration example, as in the first configuration example, a concave mirror 350 with a short focusing distance (for example, f = 10 mm) can obtain sufficient resolution (for example, 45 μm / 0.5 nm) or bandpass. The load on the filter 320 can be reduced. Further, the volume occupied by the configuration of the detection device in the space can be made smaller than that of the first configuration example, and the detection device can be made compact. Further, in the second configuration example, since the parallel scattered light is incident on the edge filter 380, the wavelength selection action of the edge filter 380 can be used more effectively.

The incident direction of the incident light on the diffraction grating 340 will be described with reference to FIGS. 11 (A) and 11 (B). In the arrangement example shown in FIG. 11A, incident light is incident from the uneven surface side of the diffraction grating 340 (the surface 120 side where the protrusions 110 are arranged). On the other hand, in the arrangement example of FIG. 11B, incident light is incident from the back surface 160 side of the diffraction grating 340. In any of the arrangement examples, the antireflection film 190 is formed on the back surface 160 side of the base material 100. Since the antireflection film 190 suppresses the reflection of diffracted light or incident light, high diffraction efficiency close to the theoretical value can be realized. Since the wavelength dependence and angle dependence of the diffraction efficiency differ slightly depending on the incident direction of light, it is desirable to use the diffraction grating in an arrangement having more excellent characteristics among the above arrangement examples.

Although the present embodiment has been described in detail as described above, those skilled in the art will easily understand that many modifications that do not substantially deviate from the novel matters and effects of the present invention are possible. Therefore, all such modifications are included in the scope of the present invention. For example, in the specification or drawings, terms (transmission grating, Raman sensor, array photodetector, etc.) described at least once with different terms (diffraction grating, sensor chip, detector, etc.) in a broader sense or synonymous are used. , Wherever in the specification or drawings, can be replaced with the different term. Further, the configuration and operation of the diffraction grating, the spectroscopic device, the detection device, and the like are not limited to those described in the present embodiment, and various modifications can be performed.

100 base material, 110 protrusions, 120 base material surface, 130 reference line, 140,150 inclined surface, 160 back surface of base material, 170 first dielectric layer, 180 second dielectric layer, 190 anti-reflection coating, 200 quartz glass substrate, 210 resist, 220 resist pattern, 230 base material, 240 protrusions, 300 Raman sensor, 310 concave mirror, 320 bandpass filter, 330 polarizing plate, 340 diffraction grating, 350 concave mirror, 360 array photodetector, 370 light source, 380 edge filter, 390 sample, 400 lens, P period, φ tilt angle, α incident angle, β diffraction angle, θ Bragg angle, λ wavelength, Δβ / Δλ wavelength resolution, LS1 first laser beam, LS2 2nd laser beam, θ1 1st laser beam incident angle, θ2 Incident angle of the second laser beam, λs exposure wavelength, f focusing distance