JP5834567B2 - Detection device and method for manufacturing spectroscopic device - Google Patents

Description

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

  Conventionally, most of diffraction gratings used in spectroscopic devices such as a Raman spectroscope are of a reflective type. As a reflection type diffraction grating, for example, there is a blazed grating whose cross section is formed in a sawtooth shape (for example, a diffraction grating described in Patent Document 1).

JP 2004-354176 A

  However, the reflective diffraction grating has a problem that it is difficult to improve both wavelength resolution and widen the wavelength band where high diffraction efficiency can be obtained. For example, in a blazed diffraction grating, the diffraction efficiency is improved because the cross-sectional shape is blazed. However, in a blazed diffraction grating, if the grating period is shortened in order to improve the wavelength resolution, the wavelength band where high diffraction efficiency can be obtained becomes extremely narrow.

  According to some aspects of the present invention, it is possible to provide a spectroscopic device, a detection device, a spectroscopic device manufacturing method, and the like using a transmission diffraction grating that can improve both wavelength resolution and diffraction efficiency and reduce reflection loss.

(1) One aspect of the present invention is
A spectroscopic device including a transmissive diffraction grating that transmits incident light,
The transmission diffraction grating has a plurality of protrusions that periodically protrude from the base material along the first direction, each of the plurality of protrusions has an inclined surface, and the inclined surface is formed on the base material. Tilted with respect to a vertical reference line,
When the incident angle of incident light to the transmission diffraction grating is an angle α with respect to the reference line, and the diffraction angle of the diffracted light is an angle β with respect to the reference line,
The incident angle α is an angle smaller than the Bragg angle θ with respect to the inclined surface,
The diffraction angle β is an angle larger than the Bragg angle θ,
Each of the plurality of protrusions has a different protrusion height from the base material reaching the interface between each of the plurality of protrusions and air as the distance in the first direction from the inclined surface differs. The present invention relates to a spectroscopic device having a prevention structure.

  According to one aspect of the present invention, the inclined surfaces of the protrusions are inclined with respect to the reference line and arranged. Then, incident light with respect to the transmissive diffraction grating is incident at an angle α smaller than the Bragg angle θ, and diffracted light by the transmissive diffraction grating is emitted at an angle β larger than the Bragg angle θ. Thereby, it becomes possible to improve the wavelength resolution and widen the wavelength band where high diffraction efficiency can be obtained.

  Furthermore, according to one aspect of the present invention, in the first direction, the change in the refractive index at the interface between the protrusion and the air becomes smooth, and a sharp refractive index difference does not occur. For this reason, the light incident on the protrusion reaches the protrusion almost without being reflected, and the reflection loss is reduced.

  (2) In one aspect of the present invention, the first antireflection structure can be formed at a free end of the protrusion. The reflection loss at the free end of the protrusion can be reduced as compared with the flat end of the protrusion.

  (3) In one aspect of the present invention, the first antireflection structure can also be formed at the base end of the protrusion. The reflection loss at the free end portion of the protrusion can be reduced as compared with the case where the base end portion (bottom portion between the protrusions) of the protrusion is made flat.

(4) In one aspect of the present invention, each of the plurality of protrusions is formed to extend from one side surface to the other side surface along a second direction orthogonal to the first direction.
Each of the plurality of projections has a second projection height different from the base material reaching the interface between each of the plurality of projections and air as the distance in the second direction from the one side surface is different. It can further have a prevention structure.

  In this way, even in the second direction, the change in the refractive index at the interface between the protrusion and air becomes smooth, and a sharp refractive index difference does not occur. For this reason, the reflection loss is further reduced.

  (5) 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 surface is arranged with a period P / cos φ in the first direction, and the incident light is Linearly polarized light parallel to a plane perpendicular to the reference line and perpendicular to the arrangement direction of the inclined surfaces can be obtained.

  In this way, the inclined surface is arranged at an angle φ with respect to the reference line, linearly polarized light parallel to the inclined surface and perpendicular to the reference line is incident on the transmission diffraction grating, and the diffracted light Can be obtained.

(6) Another aspect of the present invention is:
The spectroscopic device described above;
An optical system that causes scattered light or reflected light from a target to enter the spectroscopic device at the incident angle α smaller than the Bragg angle θ;
A detector for detecting diffracted light from the spectroscopic device;
It is related with the detection apparatus containing.

  According to such a detection apparatus, since the reflection loss at the diffraction grating is reduced, the amount of diffracted light can be increased to increase the signal level at the detector.

(7) Still another aspect of the present invention is
The first laser beam and the second laser beam are incident on the resist applied to the base material, and the resist is subjected to interference exposure.
Developing the interference exposed resist;
The present invention relates to a method of manufacturing a spectroscopic device that is inclined at an inclination angle φ with respect to a normal line that faces the plane of the base material and that forms a resist pattern without exposing the base material. With this manufacturing method, a diffraction grating having a first reflecting structure can be manufactured.

(8) Still another aspect of the present invention provides:
Laser interference exposure of the resist applied to the substrate,
The substrate is rotated 90 degrees to perform laser interference exposure,
Developing the interference exposed resist;
The present invention relates to a method of manufacturing a spectroscopic device that is inclined at an inclination angle φ with respect to a normal line that faces the plane of the base material and that forms a resist pattern without exposing the base material. With this manufacturing method, it is possible to manufacture a diffraction grating having a second reflecting structure.

It is a figure which shows the blazed diffraction grating which is a comparative example of this embodiment. It is a characteristic view of the wavelength resolution with respect to the diffraction angle in a comparative example. FIG. 3A is a cross-sectional view of a configuration example of a diffraction grating having an inclined structure according to the present embodiment, and FIG. 3B is an explanatory diagram of Bragg reflection by a periodic structure of an inclined surface. It is a characteristic view of the wavelength resolution with respect to the diffraction angle in this embodiment. FIG. 5A is a characteristic diagram of diffraction efficiency with respect to the incident angle when the tilt angle is 0 °, and FIG. 5B is a characteristic diagram of diffraction efficiency with respect to the incident angle in the present embodiment. 6A is a characteristic diagram of diffraction efficiency with respect to the wavelength λ when the tilt angle is 0 °, and FIG. 6B is a characteristic diagram of diffraction efficiency with respect to the wavelength λ in the present embodiment. 7A and 7B are explanatory diagrams of a diffraction grating in which an antireflection film is formed on the plane of the base material. 8A and 8B are explanatory diagrams of a diffraction grating having first and second antireflection structures. FIG. 9A to FIG. 9D are explanatory diagrams of a method for manufacturing a diffraction grating. 10A and 10B are diagrams illustrating a first configuration example of the detection device. FIG. 11A and FIG. 11B are diagrams illustrating a second configuration example of the detection device.

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

1. Comparative Example As described above, the blazed diffraction grating has a problem that it is difficult to achieve both wavelength resolution and diffraction efficiency. This point will be described with reference to FIGS.

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

  First, consider 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 grating period Pa should be reduced and the diffraction angle βa should be increased.

Δβ / Δλ = 1 / (Pa · cos βa) (1)
FIG. 2 is a characteristic example of the wavelength resolution Δβ / Δλ with respect to the diffraction angle βa when the wavelength λa = 633 nm and the grating period Pa = 333 nm in the above equation (1). In this example, the ratio between the wavelength and the grating 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, the diffraction efficiency will be considered. In the case of a reflective diffraction grating, the diffraction efficiency can be increased by blazing the cross-sectional shape. However, if the grating 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 blazed (the latest diffractive optical element technology, Technical Information Cooperation, p.107-). p.120 (2004)). As described above, it is difficult to achieve high wavelength resolution and high diffraction efficiency at the same time in a reflective diffraction grating such as a blazed diffraction grating.

  For example, in a spectroscopic device such as a Raman spectrometer, 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, scattered light from a sample is mainly Rayleigh scattered light and Raman scattered light (hereinafter, attention is paid to a Stokes component having a Raman scattered wavelength λray + Δλ with respect to a Rayleigh scattered wavelength λray). This Raman spectroscopy has several practical problems. First, the intensity of Raman scattered light is extremely weak compared to the intensity of Rayleigh scattered light. Next, when a substance is specified by Raman spectroscopy, it is necessary to separate Raman scattered light scattered from the sample with a wavelength resolution of about 0.5 nm. Further, the wavelength difference between the Rayleigh scattered light and the Raman scattered light is about 100 nm. Considering these points, a 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, high diffraction efficiency is required to be obtained in a wide wavelength band of about 100 nm.

2. In this embodiment, the tilt structure of the diffraction grating that obtains high diffraction efficiency in a wide wavelength band is tilted so that the diffraction angle is increased and the grating period is increased to increase the wavelength. Improve resolution and widen the diffraction efficiency. The transmission diffraction grating of this embodiment (hereinafter abbreviated as a diffraction grating) will be described with reference to FIGS. In the following, the dimensions and ratios of the respective constituent elements are appropriately changed from the actual ones in order to make each constituent element recognizable on the drawing.

  Here, the case where a 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 techniques.

  FIG. 3A shows a cross-sectional view of a configuration example of the transmission diffraction grating of the present embodiment. This diffraction grating is a surface uneven type diffraction grating. The base material 100 (substrate) made of a dielectric has a plurality of protrusions 110 that periodically protrude in the first direction X, and each of the plurality of protrusions 110 has an inclined surface 140 (or an inclined surface 141). In addition, the inclined surface 140 (or the inclined surface 141) is inclined with respect to the reference line 130 perpendicular to the substrate 100. The plurality of protrusions 110 extend in a second direction Y (a direction orthogonal to the paper surface) orthogonal to the first direction A. 3A is a cross-sectional view taken along a plane that is perpendicular to the plane of the substrate 100 and parallel to the direction in which the plurality of protrusions 110 are arranged.

  The base material 100 is formed of a dielectric such as a quartz glass substrate that transmits incident light, and is formed in a rectangular flat plate shape or a disc shape. Transmitting incident light includes not only the case of being transparent with respect to the wavelength (use wavelength) of the incident light but also the case of being translucent to transmit a part of the amount of incident light.

  The plurality of protrusions 110 are formed of a dielectric (for example, the same dielectric as the base material 100), and are arranged at a period P / cosφ (lattice interval) along a first direction X parallel to the plane of the base material 100. The plane of the base material 100 is a surface parallel to the surface 101 (first surface) of the base material 100 on the side where the plurality of protrusions 110 are formed, for example. The plurality of protrusions 110 are formed to be inclined with respect to the reference line 130 by an angle φ (φ> 0 °). More specifically, the plurality of protrusions 110 are formed with inclined surfaces 140 (or inclined surfaces 141) that are inclined at an angle φ with respect to the reference line 130. The reference line 130 is a reference line for the tilt angle φ, the incident angle α, and the diffraction angle β, and is, for example, a perpendicular (normal line) to the plane of the substrate 100. The inclined surface 140 has a period P in a direction perpendicular to the inclined surface 140, and diffracted light (Bragg reflected light) is generated by a periodic structure of this period P. Note that it is desirable that the operating wavelength λ and the grating period P satisfy 1.0 <λ / P <2.0. Moreover, it is desirable that the grating period P is 200 to 1100 nm and the height of the plurality of protrusions 110 is 500 to 3000 nm. Further, it is desirable that the inclination angle is φ <45 °.

  As shown in FIG. 3A, incident light having a wavelength λ is incident on the diffraction grating at an angle α, and the diffracted light is transmitted to the back surface 102 (second surface) side of the substrate 100 at an angle β. Here, the back surface 102 of the base material 100 is a surface on the side where the plurality of protrusions 110 are not formed. At this time, the wavelength resolution Δβ / Δλ of the diffraction grating tilted at the tilt angle φ is expressed by the following equation (2). When φ = 0 in the following equation (2), the above equation (1) is obtained, which represents the wavelength resolution when there is no inclination.

Δβ / Δλ = cosφ / (P · cosβ) (2)
Next, a method for improving the wavelength resolution and diffraction efficiency according to the present embodiment will be described. As shown in FIG. 3B, in this embodiment, Bragg reflection by the periodic structure of the inclined surface 140 (or inclined surface 141) is used. In FIG. 3B, the case where the tilt angle φ = 0 ° is considered for convenience. When the incident angle of the incident light causing the Bragg reflection is the Bragg angle θ, the Bragg condition is expressed by the following expression (3). The Bragg angle θ is an angle with respect to the inclined surface 140. N is the refractive index of air (medium in a broad sense).

2nPsinθ = λ (3)
As described in the comparative example, in order to increase the wavelength resolution Δβ / Δλ, it is necessary to increase the Bragg angle θ (diffraction angle). From the above equation (3), it is understood that when the Bragg angle θ is increased, P must be decreased. However, as described in the comparative example, when P is reduced, the wavelength band with high diffraction efficiency is narrowed. Therefore, in the present embodiment, the diffraction angle β is increased by inclining the plurality of protrusions 110 as shown in FIG. At this time, the incident angle α is approximately α = θ−φ, and the diffraction angle β is approximately β = θ + φ. As described above, since the Bragg angle θ can be made smaller than the diffraction angle β by inclining the plurality of protrusions 110, the wavelength resolution Δβ / Δλ is increased by the diffraction angle β, and the period is longer than that in the case where φ = 0 °. P can be set to a larger value.

  In this way, it is possible to simultaneously improve the wavelength resolution by increasing the diffraction angle β and increase the diffraction efficiency in a wide band by increasing the period P as much as possible within a range in which the necessary wavelength resolution can be obtained. As will be described later, strictly speaking, the incident angle α = θ−φ and the diffraction angle β = θ + φ are not always satisfied.

  FIG. 4 shows a characteristic example of the wavelength resolution Δβ / Δλ with respect to the diffraction angle β. FIG. 4 shows an example in which the wavelength λ = 633 nm, the grating period P = 366 nm, and the tilt angle φ = 10 °. The Bragg angle of the first-order transmitted diffracted light is θ = 59.9 °. The grating period P = 366 nm is 10% larger than the grating period Pa = 333 nm in the above-described comparative example. Further, from the above equation (2), the wavelength resolution of this diffraction grating is the same as the wavelength resolution of the diffraction grating without inclination with a period of P / cos φ = 366 / cos (10 °) = 372 nm.

  When φ = 0 ° with no protrusion inclination, the diffraction efficiency of the first-order diffracted light becomes maximum when the diffraction angle is in the vicinity of 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 protrusion is tilted by φ = 10 °, the diffraction angle extends to β = 73 °, so that the wavelength resolution is improved by about 1.8 times from the case of φ = 0 °, and Δβ / Δλ = 0. 009 or more. This is a wavelength resolution equivalent to that of the comparative example described above. Thus, by tilting the diffraction grating at an angle φ = 10 °, high diffraction efficiency is realized in the vicinity of the diffraction angle β = 73 °.

  5A and 5B show examples of the characteristics of diffraction efficiency with respect to the incident angle α. In this example, the wavelength λ is 633 nm, the grating period P is 366 nm, and the height of the protrusion is 745 nm. The base material (and the group of protrusions) of the protrusions is quartz glass, and the refractive index is 1.46. Incident light is linearly polarized light, and its polarization direction (polarization direction) is parallel to the groove of the protrusion.

  As shown by A1 in FIG. 5A, when φ = 0 ° without the tilt of the diffraction grating, a high diffraction efficiency is obtained when the incident angle α is in the vicinity of the Bragg angle 59.9 °. When the incident angle α is 59.9 °, the diffraction angle β is also 59.9 °. On the other hand, as shown by B1 in FIG. 5B, when the inclination of the diffraction grating is φ = 10 °, a high diffraction efficiency is 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 with reference to FIG. 4, the wavelength resolution Δβ / Δλ is improved by 1.8 times to about 0.009.

  Thus, by tilting the diffraction grating by 10 °, the wavelength resolution Δβ / Δλ can be increased to 0.009, which is equivalent to that of the comparative example, even under a condition where the grating period is 10% larger than that of the comparative example. This is because the diffraction angle β can be made sufficiently large by tilting the diffraction grating and shifting the Bragg angle.

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

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

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

  In a reflective diffraction grating such as a blazed grating, it is necessary to reduce the diffraction angle β and the period P in order to improve the wavelength resolution, so it is difficult to improve both the wavelength resolution and the bandwidth of the diffraction efficiency. There was a problem that there was.

  In this respect, the present embodiment is a transmission diffraction grating (spectrometer in a broad sense) that transmits incident light. As shown in FIG. 3A, the transmissive diffraction grating has an inclined surface 140 (or an inclined surface 141) formed of a 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 incident angle of incident light on the transmissive 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 <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> θ) larger than the Bragg angle θ.

  As a result, it is possible to improve the wavelength resolution and widen the band of high diffraction efficiency. Specifically, when the inclined surfaces 140 are arranged with a period P, a one-dimensional periodic dielectric constant distribution is formed in the diffraction grating. Then, as shown in FIG. 5B, the dielectric constant distribution is inclined, for example, by φ = 10 ° with respect to the grating surface, so that the incident angle α is greater than the Bragg angle θ = 59.9 ° when there is no inclination. = 43 ° is shallow, 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 tilting the dielectric constant 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, even when the period P of the diffraction grating is relatively large, the wavelength resolution Δβ / Δλ can be sufficiently increased. Thus, in this embodiment, high wavelength resolution (for example, FIG. 4) and high diffraction efficiency are simultaneously satisfied in a wide wavelength band (for example, FIG. 6B). For example, when this embodiment is applied to Raman spectroscopy, it becomes possible to guide weak Raman scattered light having a wide wavelength band to a photodetector with high efficiency.

  In addition, in terms of separating the signal light and the stray light, an effect that an expensive band-pass filter, which has been conventionally required, is unnecessary can be expected. That is, since a high wavelength resolution can be obtained, it is not necessary to use a filter that sufficiently separates Raman scattered light and Rayleigh scattered light and has a sharp cutoff characteristic. Moreover, since the diffraction grating of this embodiment is a transmission type, the freedom degree of arrangement | positioning of optical elements, such as a lens and a mirror, can be made high, and a spectroscopic apparatus can be reduced in size.

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

  In the present embodiment, the incident light with respect to the transmissive 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 grooves of the grating (periodic permittivity distribution) can be incident as incident light. Thereby, the diffraction efficiency characteristics as described above (for example, the characteristics indicated by B1 in FIG. 5B) can be realized. Note that the present embodiment is not limited to this case, and it is sufficient that the incident light includes a polarization component parallel to the inclined surface 140 and perpendicular to the reference line 130.

  In the present embodiment, as shown in FIG. 3A, the transmission diffraction grating is formed on the base material 100 having a plane (for example, the surface 101) perpendicular to the reference line 130 by the first dielectric. The plurality of protrusions 110 are arranged with a period P / cosφ along a direction parallel to the plane of the substrate 100. The plurality of protrusions 110 are formed with inclined surfaces 140 that are inclined with respect to the reference line 130 at an angle φ.

  In this way, by arranging the plurality of protrusions 110 periodically, the inclined surface 140 whose period in the direction perpendicular to the inclined surface 140 is P can be realized. Thereby, an inclined concavo-convex transmissive diffraction grating can be realized.

  In the present embodiment, the inclination angle φ is set so that adjacent projections of the plurality of projections 110 do not overlap in a plan view projected perpendicularly to the plane of the substrate 100.

  In this way, the height of the plurality of protrusions 110 is suppressed by setting the inclination angle φ at which the protrusions do not overlap, and the manufacture of the plurality of protrusions 110 can be facilitated. In addition, since simulation such as diffraction efficiency can be performed with high accuracy, a highly reliable design is possible.

  A diffraction grating 340 with an antireflection film will be described with reference to FIGS. In the arrangement example shown in FIG. 7A, incident light is incident from the concave and convex surface side of the diffraction grating 340 (the surface 101 side on which the plurality of gratings 110 are arranged). On the other hand, in the arrangement example of FIG. 7B, incident light enters from the back surface 102 side of the diffraction grating 340. In any arrangement example, an antireflection film 190 is formed on the back surface 102 side of the substrate 100. Since the reflection of diffracted light or incident light is suppressed by the antireflection film 190, high diffraction efficiency close to the theoretical value can be realized. In addition, since the wavelength dependency and angle dependency of the diffraction efficiency are slightly different depending on the incident direction of light, it is desirable to use the diffraction grating in an arrangement having more excellent characteristics in the above arrangement examples.

  In particular, if FIG. 7A is used, it can be suppressed that diffracted light having a large diffraction angle β is reflected by the back surface 102 of the substrate 100 and transmitted diffracted light toward the back surface 102 is reduced. Thereby, since the transmitted diffracted light can be extracted efficiently, highly sensitive sensing becomes possible. Further, since the incident light is incident on the inclined surface 140 without passing through the substrate 100, highly efficient diffracted light can be obtained.

3. Further, in the present embodiment, as shown in FIGS. 8A and 8B, a transmission type diffraction grating having the grating periodic structure shown in FIG. ) An antireflection structure different from the antireflection film of (B) is further added.

  FIG. 8A shows the first antireflection structures 150 and 160 having different protrusion heights to the interface between the protrusion 110 and the air as the distance from the inclined surface 140 in the first direction X is different. One first antireflection structure 150 is formed at the free end portion of the protrusion 110, and the free end portion of the protrusion 110 is formed in a tapered shape (tapered shape), for example, to reach the interface between the protrusion 110 and the air. The protruding height gradually changes in the X direction. The other first antireflection structure 160 is formed at the base end portion of the projection 110 (the bottom portion of the groove 115 between the projections 110). For example, the bottom portion of the groove 115 is rounded up to the interface between the projection 110 and air. The protrusion height (depth of the groove 115) gradually changes in the X direction.

  In this way, with respect to the height direction Z, the cross-sectional area of the XY plane gradually changes at the free end portion and the base end portion of the protrusion 110, so that in the first direction X, the protrusion 110 and the air The change in the refractive index at the interface with the surface becomes smooth, and a sharp refractive index difference does not occur. For this reason, the light incident on the protrusion 110 reaches the protrusion 110 with almost no reflection.

  In FIG. 8B, each of the plurality of protrusions 110 is formed to extend from one side surface 111 to the other side surface (not shown) along a second direction Y orthogonal to the first direction X. The second antireflection structures 170 and 180 having different protrusion heights to the interface between the protrusion 110 and the air as the distance in the second direction Y from the side surface 111 is different are shown.

  On the other hand, the second antireflection structure 170 is formed at the free end of the protrusion 110, and the top of the protrusion 110 is formed in a corrugated shape so that the protrusion height to the interface between the protrusion 110 and the air is in the Y direction. It is gradually changing. The other second antireflection structure 180 is formed at the base end portion of the projection 110 (the bottom portion of the groove 115 between the projections 110). For example, the deepest portion of the groove 115 is formed in a corrugated shape. The protrusion height to the interface (depth of the groove 115) gradually changes in the Y direction.

  In this way, in addition to the first antireflection structures 150 and 160, the cross-sectional area of the XY plane gradually changes at the free end and the base end of the protrusion 110 with respect to the height direction Z. Thereby, also in the second direction Y, the change in the refractive index at the interface between the protrusion 110 and the air becomes smooth, and a sharp refractive index difference does not occur. For this reason, the reflection of the light incident on the protrusion 110 is further reduced.

  In the present embodiment, as long as one of the first reflection structures 150 is provided, the other first reflection structure 160 and further the second reflection structure 170 or 180 may be arbitrarily added. . If the protrusion height (depth of the groove 115) to the interface between the protrusion 110 and the air in the first and second directions X and Y changes gradually, the first and second antireflection structures. Various modifications such as a random structure can be performed on the shapes of 150 to 180.

4). Manufacturing Method A manufacturing method of a transmission diffraction grating having the inclined protrusion 100 and the antireflection structure 150 (160, 170, 180) will be described with reference to FIGS. 9A to 9D.

  First, the formation of the resist pattern latent image in FIG. As shown in FIG. 9A, a resist 210 is applied on a quartz glass substrate 200 to a thickness larger than usual, for example, about 1.2 μm. Then, the laser beam LS1 having an incident angle θ1 and the laser beam LS2 having an incident angle θ2 are irradiated, and the resist 210 is subjected to laser interference exposure. At this time, exposure is performed with an exposure amount, for example, 30 seconds, so that the resist pattern does not bottom the substrate 200. This exposure amount of 30 seconds is the exposure amount that bottoms on the substrate 200 when the resist 210 has a film thickness of 0.8 μm. By increasing the film thickness to 1.2 μm, the substrate 200 is not bottomed, and the groove 115 The bottom is rounded and a latent image of the first antireflection structure 160 is formed. Further, by performing bias exposure (exposure not causing interference) for 5 seconds, for example, the free end portion of the protrusion 110 is tapered (tapered), and a latent image of the first antireflection structure 150 is formed. The above exposure is continuously performed to form a latent image of the resist pattern shown in FIG. The order of exposure does not matter. Note that the bias exposure can be performed, for example, by performing exposure without causing interference through only one path in FIG. 9A.

  Next, the formation of the resist pattern latent image in FIG. 8B will be described. As in FIG. 8A, as shown in FIG. 9A, a resist 210 is applied on the quartz glass substrate 200 to a thickness greater than usual, for example, about 1.2 μm. Then, the laser beam LS1 having an incident angle θ1 and the laser beam LS2 having an incident angle θ2 are irradiated, and the resist 210 is subjected to laser interference exposure. At this time, exposure is performed with an exposure amount, for example, 30 seconds, so that the resist pattern does not bottom the substrate 200. This exposure amount of 30 seconds is the exposure amount that bottoms on the substrate 200 when the resist 210 has a film thickness of 0.8 μm. By increasing the film thickness to 1.2 μm, the substrate 200 is not bottomed, and the groove 115 The bottom is rounded and a latent image of the first antireflection structure 160 is formed. Next, when the substrate 200 is rotated 90 degrees and subjected to interference exposure for 5 seconds, for example, the free end portion of the protrusion 110 is tapered (tapered), and a latent image of the second antireflection structure 170 is formed. In the second antireflection structure 170, the protrusion height to the interface between the protrusion 110 and the air gradually changes in the Y direction. Next, when the quartz substrate 200 is placed upside down and subjected to interference exposure for 5 seconds from the back side, for example, the second antireflection structure 180 is hidden in the base end of the protrusion 110 (the bottom of the groove 115 between the protrusions 110). An image is formed. In the second antireflection structure 180, the protrusion height (depth of the groove 115) to the interface between the protrusion 110 and air gradually changes in the Y direction. The above exposure is continuously performed to form a latent image of the resist pattern shown in FIG. The order of exposure does not matter.

The distance D between the interference fringes due to the interference exposure is expressed by the following expression (4). λs is the wavelength of the laser beams LS1 and LS2. Further, the inclination angle φ of the interference fringes in the resist is expressed by the following formula (5). n _r is the refractive index of the resist 210 with respect to the exposure wavelength λs. Further, θ2> θ1.

D = λs / (sin (θ1) + sin (θ2)) (4)
φ = (sin ⁻¹ (sin (θ2) / n _r ) −sin ⁻¹ (sin (θ1))) / 2
(5)
For example, the laser light source for interference exposure is a continuous wave He—Cd laser (wavelength λs = 325 nm), the resist 210 is a positive resist, and the resist film thickness is 1.2 μm. Further, for example, the incident angles of the laser light are θ1 = 9.1 ° and θ2 = 45.7 °, and the refractive index of the resist is n _r = 1.60. At this time, from the above equation (4), the interval between 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 manner, the interference angle with respect to the normal line of the substrate 200 is asymmetrical on the left and right sides (θ1 and θ2), and a latent image of inclined interference fringes is formed in the resist 210.

  Next, as shown in FIG. 9B, the exposed resist 210 is developed to obtain a one-dimensional resist pattern 220 inclined by 10 °. Here, the resist 210 remains below the resist pattern 220, and the first antireflection structures 150 and 160 of the protrusion 110 shown in FIG. 8A are provided at the free end and the base end of the resist pattern 220. A similar structure is formed.

Next, as shown in FIG. 9C, the quartz glass substrate is anisotropically dry etched from an oblique direction of 10 ° using the resist pattern 220 as a mask. For example, CF ₄ , CHF _3, or C ₂ F ₆ is used as the etching gas. FIG. 9C is in the middle of etching, and as shown in FIG. 9D, over etching is performed until the resist pattern disappears. The selection ratio can be controlled by changing the conditions such as the flow rate of the etching gas and the gas composition. When the selection ratio with respect to the substrate 200 and the resist 210 is 1: 1, a plurality of protrusions 240 having the same shape as the resist pattern 220 can be formed. Further, the resist pattern depth can be freely changed by appropriately changing the selection ratio. Furthermore, the etching conditions may be changed midway. If the etching pressure and the configuration of the etching gas are changed only by the etching processing of the free end portion and the base end portion of the protrusion 110, the inclination of the antireflection structures 150, 160, 170, and 180 can be controlled. In this manner, a one-dimensional transmissive diffraction grating in which a plurality of protrusions 240 inclined by 10 ° and having the first reflecting structures 250 and 260 are arranged on the surface of the base material 230 is formed.

  In addition, although the example which forms the some protrusion 240 by the quartz glass same as the base material 100 was demonstrated above, this embodiment is not limited to this. For example, the resist pattern 220 shown in FIG. 9B is filled with a resin (polymer), the resin is cured, and the resist pattern 220 is peeled to form a plurality of protrusions 240 using a material different from the substrate 100. May be. In addition, a mold can be produced from the resist pattern 220, and a plurality of protrusions 240 can be mass-produced by transferring a resin.

  Furthermore, although the first antireflection structures 150 and 160 shown in FIG. 8A and the second antireflection structures 170 and 180 shown in FIG. 8B have been described as periodic structures, they may be random structures.

Hereinafter, a method for producing a random structure will be described. When Ag is vapor-deposited on the resist pattern formed by the interference exposure, Ag islands having a diameter of several nanometers to several tens of nanometers are formed at the free end and the base end of the protrusion 110. Next, dry etching is performed using a gas such as CF ₄ by using the resist pattern with an Ag island as a mask. Then, the first antireflection structures 150 and 160 are randomly formed on the free ends of the protrusions 110. At this time, the film thickness of Ag is preferably 5 to 10 nm. When the thickness is about 5 nm, the Ag island functioning as a mask is appropriately retracted by the dry etching process, and the first antireflection structures 150 and 160 can be randomly formed on the free ends of the protrusions 110. Various shapes are possible by changing the etching conditions.

5. Detection Device FIGS. 10A and 10B show a first configuration example of a detection device to which the diffraction grating of the present embodiment is applied. This detection apparatus includes a Raman sensor 300 (sensor chip, optical device), a first concave mirror 310, a bandpass filter 320, a polarizing plate 330, a diffraction grating 340, a second concave mirror 350, and an array photodetector 360 (detector). , A light source 370 and an edge filter 380. This detection apparatus is a single spectroscopic apparatus in which one diffraction grating 340 and two concave mirrors 310 and 350 are arranged in a predetermined positional relationship. In the following, a detection apparatus for performing Raman spectroscopic measurement will be described. However, the diffraction grating of the present embodiment can also be applied to a detection apparatus using another spectroscopic technique.

  As shown in FIG. 10B, the laser light from the light source 370 is reflected by the edge filter 380 and irradiated on the sample 390 (target object) on the Raman sensor 300. For example, the light source 370 is a continuous oscillation 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 longer wavelength. That is, Rayleigh scattered light is reflected by the edge filter 380 and Raman scattered light is transmitted. The transmitted Raman scattered light is incident on the concave mirror 310 and converted into parallel light by the concave mirror 310.

  Next, as shown in FIG. 10A, the reflected light from the concave mirror 310 passes through the band-pass filter 320 and the polarizing plate 330 and enters the diffraction grating 340 at a predetermined incident angle α. The bandpass filter 320 further blocks Rayleigh scattered light and transmits only Raman scattered light. The polarizing plate 330 makes incident light on the diffraction grating 340 linearly polarized light and makes its polarization direction parallel to the grooves of the diffraction grating 340. Incident light on the diffraction grating 340 is transmitted and diffracted at a diffraction angle β and split. The spectrally scattered Raman scattered light has a slightly different diffraction angle for each wavelength, and is parallel light at each wavelength. The spectrally scattered Raman scattered light is incident on the concave mirror 350 and is collected on the array photodetector 360 by the concave mirror 350 to form a spectral distribution. The array photodetector 360 detects the spectral distribution of the Raman scattered light.

  Next, the wavelength resolution of this detection apparatus will be specifically described. If 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 expressed by the following equation (6). expressed. 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 condensing distance f of the concave mirror is short, the spectrum between the Raman scattered light and the Rayleigh scattered light can be widely dispersed. Therefore, by using the high-resolution diffraction grating of the present embodiment, the condensing distance f of the concave mirror 350 can be shortened, each component can be arranged compactly, and the spectrometer can be downsized.

  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 tilt angle is 10 °, and the wavelength resolution is 0.009 rad / nm. In this case, using a concave mirror with a focal length f = 10 mm, two scattered light components having a wavelength difference 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. Thus, by using the diffraction grating of this embodiment, sufficient resolution can be realized even with a concave mirror with a short condensing 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 at which Rayleigh scattered light and Raman scattered light can be sufficiently separated. Therefore, the load on the characteristics of the bandpass filter 320 for blocking Rayleigh scattered light is greatly reduced. For spectral applications where the detection accuracy may be relatively low, the bandpass filter 320 can be omitted.

  11A and 11B show a second configuration example of a detection apparatus to which the diffraction grating of the present embodiment is applied. This detection device 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. Note that the same components as those described in FIGS. 10A and 10B are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

  As shown in FIG. 11B, the laser light from the light source 370 is reflected by the edge filter 380 and irradiated onto the sample 390 (target object) 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 enters the lens 400 and is converted into parallel light by the lens 400.

  Next, as shown in FIG. 11A, 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 causes the scattered light from the sample 390 to enter the diffraction grating 340 as a parallel light beam having a high degree of parallelism, the diffraction grating 340 can sufficiently exhibit its wavelength resolution and can divide extremely weak light. Incident light on the diffraction grating 340 is transmitted and diffracted at a diffraction angle β and split. The spectrally scattered Raman scattered light is incident on the concave mirror 350, is condensed on the array photodetector 360 by the concave mirror 350, and the spectral distribution is detected by the array photodetector 360.

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

  Although the present embodiment has been described in detail as described above, it will be easily understood by those skilled in the art that many modifications can be made without departing from the novel matters and effects of the present invention. Accordingly, all such modifications are intended to be included in the scope of the present invention. For example, in the specification or drawings, terms (transmission diffraction gratings, Raman sensors, array photodetectors, etc.) described at least once together with different terms (diffraction gratings, sensor chips, detectors, etc.) having a broader meaning or the same meaning are used. The different terms can be used anywhere in the specification or drawings. 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 this embodiment, and various modifications can be made.

100 base material, 101 front surface of base material, 102 back surface of base material, 110 plural protrusions,
130 reference line, 140, 141 inclined surface, 150, 160 first reflective structure,
170,180 second reflection structure, 190 antireflection film, 200 quartz glass substrate,
210 resist, 220 resist pattern, 230 base material, 240 multiple 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 second laser light, θ1 incident angle of the first laser light,
θ2 Incident angle of the second laser beam, λs exposure wavelength, f focusing distance

Claims (7)

A spectroscopic device including a transmissive diffraction grating that transmits incident light ;
A light source that impinges light on the target;
An optical system for allowing Raman scattered light from the target to enter the spectroscopic device as the incident light;
A detector for detecting a spectrum of diffracted light obtained by diffracting the Raman scattered light by the spectroscopic device,
The transmission diffraction grating has a plurality of protrusions that periodically protrude from the base material along the first direction, each of the plurality of protrusions has an inclined surface, and the inclined surface is formed on the base material. Tilted with respect to a vertical reference line,
The ratio λ / P between the wavelength λ of the incident light and the period P of the inclined surface in the direction perpendicular to the inclined surface is 1.0 <λ / P <2.0.
The optical system enters the Raman scattered light into the transmission diffraction grating at an incident angle α with respect to the reference line, which is smaller than a Bragg angle θ with respect to the inclined surface ,
The detector detects a spectrum of the diffracted light diffracted at an incident angle β with respect to the reference line, which is larger than the Bragg angle θ ;
Each of the plurality of protrusions has a different protrusion height from the base material reaching the interface between each of the plurality of protrusions and air as the distance in the first direction from the inclined surface differs. A detection device having a prevention structure. In claim 1,
The detection apparatus, wherein the first antireflection structure is formed at a free end of the protrusion. In claim 2,
The detection device, wherein the first antireflection structure is also formed at a base end portion of the protrusion. In any one of Claims 1 thru | or 3,
Each of the plurality of protrusions is formed to extend from one side surface to the other side surface along a second direction orthogonal to the first direction,
Each of the plurality of projections has a second projection height different from the base material reaching the interface between each of the plurality of projections and air as the distance in the second direction from the one side surface is different. A detection device further comprising a prevention structure. In any one of Claims 1 thru | or 4,
When the inclination angle of the inclined surface with respect to the reference line is φ,
The inclined surfaces are arranged with a period P / cosφ in the first direction,
The detection apparatus according to claim 1, wherein the incident light is linearly polarized light parallel to a plane perpendicular to the reference line and perpendicular to an arrangement direction of the inclined surfaces. The first laser beam and the second laser beam are incident on the resist applied to the substrate,
Interference exposure of the resist;
Developing the interference exposed resist;
6. The spectroscopic device according to claim 1 , wherein a resist film that covers the base material without being exposed and a resist pattern that is inclined at an inclination angle φ with respect to a normal line that faces the plane of the base material are formed. Method. Laser interference exposure of the resist applied to the substrate,
The substrate is rotated 90 degrees to perform laser interference exposure,
Developing the interference exposed resist;
The method for manufacturing a spectroscopic device according to claim 4 , wherein a resist film that covers the base material without being exposed and a resist pattern that is inclined at an inclination angle φ with respect to a perpendicular line that extends toward a plane of the base material.

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