JP2019132905A - Transmission type diffraction element, laser oscillator, and laser beam machine - Google Patents

Abstract

To provide a transmission type diffraction element that reduces: in-plane variations of machined lattice shapes to have a high diffraction efficiency; and variations between lots to have high reproducibility with the high diffraction efficiency.SOLUTION: A transmission type diffraction element 100 is provided that includes: a substrate 40 having a front surface and a rear surface; an antireflection layer 20 that is formed on the surface of the substrate 40 and is made of a zirconium oxide; and a lattice part 10 that is formed on the antireflection layer 20 and has a periodic rugged pattern.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a transmissive diffraction element, a laser oscillator using the transmissive diffraction element, and laser processing.

  A diffraction element is used in an optical system such as an optical pickup device, a spectroscopic measuring device, an optical transmission module, and a laser oscillator. From the viewpoint of energy efficiency, it is desirable that the diffraction efficiency of the diffraction element in the wavelength band to be used is higher.

  In order to reduce the reflection of incident light by the transmissive diffractive element and improve the transmissive diffraction efficiency, an antireflection layer made of a material having a refractive index different (lower or higher) from the substrate material is provided on the surface of the element or the multilayer. Solutions are known for introduction into a part of the membrane. Patent Document 1 discloses a diffraction grating having a multilayer film including a zirconium oxide having a relatively high refractive index among optical materials. Patent Document 2 discloses a transmissive diffraction element having high diffraction efficiency and low polarization dependence over the entire wavelength band of incident light.

JP 2008-217954 A Japanese Patent Laid-Open No. 2017-4004

  However, the performance of the diffractive element varies depending on the material, size, shape, and the like of the uneven grating structure formed on the surface of the diffractive element by means such as dry etching. The diffraction grating of Patent Document 1 has a problem that the diffraction efficiency deteriorates due to in-plane variations in the processing depth and groove bottom shape caused by means such as dry etching for forming a grating structure, and the diffraction efficiency due to lot-to-lot variations. There is a problem that it is difficult to obtain reproducibility.

  In the transmission type diffraction grating of Patent Document 2, there is a problem in that in-plane variation (for example, under-etching and over-etching) occurs in the grating shape due to dry etching when forming a multilayer grating structure, and diffraction efficiency is lowered.

  The present invention has been made to solve the above-described problems, and has high diffraction efficiency by reducing in-plane variation of the lattice shape due to processing, and also improves diffraction efficiency by reducing variation between lots. An object of the present invention is to provide a transmissive diffraction element having high reproducibility.

  In order to solve the above problems, one embodiment of the present invention is formed on a substrate having a front surface and a back surface, an antireflection layer made of zirconium oxide formed on the surface of the substrate, and the antireflection layer. And a diffractive element including a grating portion having a periodic uneven pattern.

  According to the present invention, it is possible to obtain a transmission type diffractive element having high diffraction efficiency by reducing in-plane variation of the grating shape due to processing and having high reproducibility with high diffraction efficiency by reducing lot-to-lot variation.

1 is a schematic cross-sectional view of a transmissive diffraction element according to Embodiment 1 of the present invention. It is a schematic diagram which shows the relationship between the incident light and diffracted light of the transmissive | pervious diffraction element by Embodiment 1 of this invention. It is a schematic sectional drawing of the comparative example of a transmissive | pervious diffraction element. It is a graph which shows the diffraction efficiency of the transmission type diffraction element by Embodiment 1 of this invention, and the -1st order transmission diffracted light of a comparative example. It is a graph which shows the total value of the diffraction efficiency of 0th-order reflective diffracted light, and the diffraction efficiency of -1st-order reflected diffracted light in a target wavelength band. FIG. 2 is a schematic cross-sectional view showing a transmission type diffraction element according to Embodiment 1 of the present invention when overetching occurs. It is a schematic sectional drawing which shows the comparative example of a transmissive | pervious diffraction element when overetching arises. It is a graph which shows the fall amount of the diffraction efficiency of the -1st order transmitted light of a transmission type diffraction element when the depth of an overetching part changes. It is a graph which shows the relationship between the depth of the overetching part of an antireflection layer, and the diffraction efficiency of -1st order transmitted light about the transmission type diffraction element by Embodiment 1 of this invention. It is a graph which shows the relationship between the depth of the overetching part of a board | substrate, and the diffraction efficiency of -1st order transmitted light about the comparative example of a transmissive | pervious diffraction element. It is a schematic sectional drawing of the other specific example of the transmissive | pervious diffraction element by Embodiment 1 of this invention. It is the elements on larger scale of sectional drawing of FIG. It is a schematic sectional drawing of the transmissive | pervious diffraction element by Embodiment 2 of this invention. It is the elements on larger scale of sectional drawing of FIG. It is a schematic sectional drawing of the comparative example of a transmissive | pervious diffraction element. It is a graph which shows the diffraction efficiency of the transmission type diffraction element by Embodiment 2 of this invention, and the -1st order transmission diffracted light of a comparative example. It is a graph which shows the total value of the diffraction efficiency of 0th-order reflective diffracted light, and the diffraction efficiency of -1st-order reflected diffracted light in a target wavelength band. It is a schematic sectional drawing which shows the transmission type diffraction element by Embodiment 2 of this invention when overetching arises. It is a schematic sectional drawing which shows the comparative example of a transmissive | pervious diffraction element when overetching arises. It is a graph which shows the fall amount of the diffraction efficiency of the -1st order transmitted light of a transmission type diffraction element when the depth of an overetching part changes. It is a graph which shows the relationship between the depth of the overetching part of an antireflection layer, and the diffraction efficiency of -1st order transmitted light about the transmission type diffraction element by Embodiment 2 of this invention. It is a graph which shows the relationship between the depth of the overetching part of a board | substrate, and the diffraction efficiency of -1st order transmitted light about the comparative example of a transmissive | pervious diffraction element. It is a typical block diagram of the laser oscillator by Embodiment 3 of this invention. It is a typical block diagram of the laser beam machine by Embodiment 4 of this invention.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be specifically described below with reference to the drawings. In the following description, in order to facilitate understanding of the present invention, terms representing a specific direction such as up and down are used, but it should be understood that these terms limit the scope of the present invention. Not.

  FIG. 1 is a schematic cross-sectional view of a transmissive diffractive element (hereinafter, simply referred to as “diffractive element”) according to Embodiment 1 of the present invention, the whole being represented by 100. The diffraction element 100 includes a substrate 40 having a front surface and a back surface, an antireflection layer 20 formed on the surface of the substrate 40, and a grating portion 10 formed on the antireflection layer 20. The diffraction element 100 may further include a back surface antireflection layer 50 on the back surface of the substrate 40. The antireflection layer 20 and the grating portion 10 are collectively referred to as a diffraction grating 30.

  In this specification, the thickness direction of the substrate 40 is defined as the Z direction, and the plane perpendicular to the Z axis is defined as the XY plane. The front surface and the back surface of the substrate 40 are surfaces substantially parallel to the XY plane. A direction perpendicular to the paper surface of FIG. 1 is a Y direction, and a direction perpendicular to the Y axis and the Z axis is an X direction.

  The substrate 40 is, for example, a transparent substrate that is transparent with respect to the wavelength of incident light (for example, the wavelength of visible light to the wavelength of near infrared light). For example, the substrate 40 is made of quartz glass or synthetic quartz.

In the illustrated example, the antireflection layer 20 is a single layer film made of zirconium oxide. The antireflection layer 20 is formed on the surface of the substrate 40 by a thin film forming method such as a vacuum evaporation method or a sputtering method. D ₂₀ represents the thickness (height) of the antireflection layer 20.

In FIG. 1, which is a cross-sectional view, the lattice portion 10 is adjacent to a large number of convex portions (projections) 11 that are arranged periodically (with a period P) at intervals in the X direction on the antireflection layer 20. It consists of a recess (gap) 12 between the protrusions 11. The lattice unit 10 has a line and space structure having a uniform shape in the Y direction. That is, the cross-sectional shape of the diffraction element 100 cut perpendicularly to the Y-axis is substantially the same regardless of the Y position. Protrusion 11 has a width W in the X-axis direction and the height _{D G.}

  The convex portion 11 has a single-layer or multi-layer structure made of one or more materials selected from silicon oxide, silicon nitride, and silicon oxynitride. For example, the lattice portion 10 includes a step of depositing the material of the convex portion 11 on the antireflection layer 20 by a thin film forming method such as a vacuum evaporation method or a sputtering method, and known methods such as dry etching, wet etching, and nanoimprinting. And a step of processing the deposited material.

As described above, the material of the convex portion 11 containing silicon is typically processed by dry etching using a fluorocarbon gas (for example, CF ₄ ). Zirconium oxide has high etching resistance against fluorocarbon gas. Therefore, the etching rate of the material of the convex portion 11 is significantly different from the etching rate of the antireflection layer 20 made of zirconium oxide. Overetching can be suppressed by using the ratio of the relative etching rates (the etching rate of the processing target (material of the convex portion 11) / the etching rate of the non-processing target (antireflection layer 20)). That is, the antireflection layer 20 made of zirconium oxide functions as an etching stopper.

  The back surface antireflection layer 50 is formed on the back surface of the substrate 40 by a thin film forming method such as a vacuum evaporation method or a sputtering method. The back surface antireflection layer 50 is an optical multilayer film including a low refractive index material such as silicon oxide, silicon oxynitride, and magnesium fluoride, and a high refractive index material such as silicon nitride, titanium oxide, and tantalum pentoxide. Alternatively, the back surface antireflection layer 50 is selected from a low refractive index material made of one or more materials selected from silicon oxide, silicon oxynitride, and magnesium fluoride, and silicon nitride, titanium oxide, and tantalum pentoxide. And an optical multilayer film made of a high refractive index material made of one or more materials. The back surface antireflection layer 50 suppresses reflection loss of light when light exits from the substrate 40 into the air or enters the substrate 40 from the air.

FIG. 2 is a schematic diagram showing the relationship between incident light and diffracted light of the diffraction element 100. First, incident light 101 from a light source (not shown) is incident on the diffraction element 100 at an incident angle θ ₀ . The incident light 101 is diffracted by the grating portion 10 of the diffractive element 100 to generate 0th-order (diffraction order m = 0) reflected diffracted light 102 and −1st-order (m = −1) reflected diffracted light 103. . In general, the reflection diffraction angle θ _Rm of the m-th order reflected diffracted light satisfies the following formula (1).

  Here, P is the grating period and m is the diffraction order.

Accordingly, the diffraction angles θ _R0 and θ _R−1 of the reflected diffracted light beams 102 and 103 can be derived from the equation (1).

Further, FIG. 2 shows 0th-order (m = 0) transmitted diffracted light 104 and -1st-order (m = −1) transmitted diffracted light 105 transmitted through the diffraction element 100. The diffraction angles θ _T0 and θ _T−1 of the transmitted diffracted light 104 and 105 can be derived by replacing the reflection diffraction angle θ _Rm in the equation (1) with the transmission diffraction angle θ _Tm .

It is known that a higher diffraction efficiency can be obtained in an arrangement (Littrow arrangement) in which the absolute value of the incident angle θ ₀ is equal to the absolute value of the zero-order reflection diffraction angle θ _R0 (Littrow arrangement). In the Littrow arrangement, the following equation (2) is established.

  When light is incident on the diffractive element, higher-order diffracted light such as 0th order, ± 1st order, ± 2nd order, etc. is generated, thereby reducing the light utilization efficiency. In view of this, the incident light is incident on the surface of the diffractive element at an angle from the vertical direction so as not to generate higher-order diffracted light than the diffracted light used (in the present invention, -1st order transmitted diffracted light). It is preferable to make it.

  Next, the effect obtained by providing the antireflection layer 20 immediately below the lattice part 10 will be described. First, the effect of improving the diffraction efficiency will be described.

FIG. 3 shows a diffraction element 200 that does not include the antireflection layer 20 as a comparative example with respect to FIG. The diffraction efficiency of the diffraction element 100 of FIG. 1 and the diffraction element 200 of FIG. 3 will be compared. 4 shows the diffraction efficiency of -1st order transmitted diffracted light (hereinafter referred to as “transmitted diffraction efficiency”) η1 _T-1 (solid line) with respect to the wavelength of incident light as the horizontal axis. ) And −1st-order transmission diffraction efficiency η2 _T-1 (broken line) of the diffraction element 200 that does not include the antireflection layer 20. The value of the diffraction efficiency in FIG. 4 is obtained by simulation. For the simulation, an electromagnetic field simulator “DiffractMOD” (synopsys) based on the RCWA (Rigorous Coupled-Wave Analysis) method was used. The parameters used for the simulation are shown in Table 1 below.

  Here, the wavelength λ is the center wavelength of the wavelength band of incident light to be simulated. Δλ is a wavelength width, and the simulation was performed by changing the wavelength of incident light from λ−Δλ to λ + Δλ. This is a wavelength band used in a laser resonator, for example. The incident azimuth φ is an angle formed by the projection of the incident light 101 projected on the XY plane and the X axis. The deflection angle ψ is an angle formed by a projection obtained by projecting the electric field vibration direction of the incident light 101 on the XY plane and the X axis. When ψ = 90 °, it means that the polarized light is orthogonal to the light incident surface. The occupation rate F is defined by W / P using the period P and the width W of the convex portion 11. In order to facilitate the processing of the lattice portion 10, it is preferable that 0.2 ≦ F ≦ 0.8.

The height D _G , the occupation ratio F, and the thickness D ₂₀ of the antireflection layer 20 in Table 1 are optimized. Here, “optimization” refers to selecting parameter values so that the diffraction efficiency is maximized in the target wavelength band (λ−Δλ to λ + Δλ).

In the simulation, the refractive index of zirconium oxide (N ₂₀ = 2.208) was used as the refractive index N ₂₀ of the antireflection layer 20.

  It should be noted that the simulation for deriving the diffraction efficiency does not consider the back surface antireflection layer 50.

  As can be seen from FIG. 4, it is confirmed that the transmission diffraction efficiency is improved in the target wavelength band (0.94 μm to 1.03 μm) by introducing the antireflection layer 20.

FIG. 5 shows the total value of the diffraction efficiency of 0th-order reflected diffracted light (hereinafter referred to as “reflected diffraction efficiency”) η _R0 and −1st-order reflected diffraction efficiency η _{R-1 in} the target wavelength band (hereinafter referred to as “ It is referred to as “total reflection diffraction efficiency.”) Η _R is a graph. In FIG. 5, the horizontal axis represents the wavelength of incident light. The solid line indicates the total reflection diffraction efficiency η1 _R of the diffraction element 100 including the antireflection layer 20, and the broken line indicates the total reflection diffraction efficiency η2 _R of the diffraction element 200 not including the antireflection layer 20. FIG. 5 shows that the total reflection diffraction efficiency is reduced in the target wavelength band by introducing the antireflection layer 20.

  When there is no loss such as light absorption by the diffraction element 100 or 200, the following expression (3) holds.

To improve the transmission diffraction efficiency by the introduction of the anti-reflection layer 20 as described above, as in FIG. 5, is considered a total reflection diffraction efficiency eta _R is due to be reduced.

In the above description, the material of the substrate 40 and the convex portion 11 is both silicon dioxide (SiO ₂ ). That is, the simulation was performed by setting the refractive indexes N _S and _NG of the material of the substrate 40 and the convex portion 11 to 1.457 which is the refractive index of SiO ₂ . However, the present invention is not limited to this, and the material of the convex portion 11 may be silicon oxide, silicon nitride, or silicon oxynitride. It should be noted that if the material of the convex portion 11 is different, the optimum height D _G of the convex portion 11 and the thickness D _{20 of the} antireflection film may also vary.

  Next, the effect that the diffraction efficiency can be prevented from being deteriorated due to the influence of processing such as etching by providing the antireflection layer 20 immediately below the grating portion 10 will be described.

FIG. 6 is a schematic cross-sectional view showing the diffraction element 100 when overetching occurs in the dry etching process for forming the protrusions 11. A groove in the antireflection layer 20 generated by overetching is referred to as an overetched portion 60. In FIG. 6, D ₆₀ represents the depth of the overetched portion 60. In other words, D ₆₀ is the distance in the Z-axis direction from the bottom surface of the overetched portion 60 to the top surface of the antireflection layer 20.

FIG. 7 is a schematic cross-sectional view showing the diffraction element 200 when overetching occurs in the dry etching process for forming the protrusions 11. A groove in the substrate 40 generated by overetching is referred to as an overetched portion 70. In FIG. 7, D ₇₀ represents the depth of the overetched portion 70. The diffraction efficiencies of the diffraction element 100 and the diffraction element 200 in which over-etching has occurred are compared.

When fluorocarbon gas is used, the etching rate for zirconium oxide is known to be about 1/5 of the etching rate for SiO ₂ (eg, H.-S. Kim et al., The Use of Inductively Coupled CF ₄ / Ar Plasma to Improve the Etch Rate of ZrO2 Thin Films. TRANSACTIONS ON ELECTRICAL AND ELECTRONIC MATERIALS. 2013, 14 (1), pp.12-15 Therefore, the simulation was performed on the assumption that the etching speed of the diffraction element 100 with respect to the antireflection layer 20 was about 1/5 of the etching speed of the diffraction element 200 with respect to the substrate 40.

FIG. 8 is a graph showing the amount of decrease in the −1st order transmission diffraction efficiency η _T-1 of each of the diffraction elements 100 and 200 when the depths D ₆₀ and D _{70 of the} overetched portions ₆₀ and ₇₀ are changed. . The target wavelength band is, for example, a wavelength band (0.95 μm ≦ λ ≦ 1.01 μm) used for a laser resonator. FIG. 8 shows the amount of decrease in the −1st order transmission diffraction efficiency η _T-1 of each of the completed diffraction elements 100 and 200 when the overetching time is 0, T1, and T2. In other words, the horizontal axis represents the depth of the over-etched portions 60 and 70 normalized by the processing time.

8 on the horizontal axis in FIG. 8 means that the antireflection layer 20 or the substrate 40 of the processed diffraction elements 100 and 200 is not in an over-etched state or an under-etched state. In other words, 0 on the horizontal axis in FIG. 8 means that the depths D ₆₀ and D ₇₀ of the over-etched portions ₆₀ and ₇₀ are 0 nm.

T1 on the horizontal axis in FIG. 8 means that overetching has been performed for the time T1 after completion of appropriate etching. In this case, the simulation was performed by setting D ₆₀ = 5 nm and D ₇₀ = 25 nm. This value was determined considering that the etching rate for zirconium oxide was about 1/5 of the etching rate for SiO ₂ as described above.

T2 on the horizontal axis in FIG. 8 means that overetching has been performed for the time T2 after completion of appropriate etching. In this case, the simulation was performed by setting D ₆₀ = 10 nm and D ₇₀ = 50 nm.

From FIG. 8, when the overetching is performed for the same time, the decrease amount of the −1st-order transmission diffraction efficiency η _T-1 of the diffraction element 100 is remarkably small as compared with the diffraction element 200 without the antireflection layer 20. Recognize.

  Next, with reference to FIG. 9 and FIG. 10, the diffraction element 100 and the diffraction element 200 when over-etching occurs are compared in terms of the transmission diffraction efficiency reduction effect and the wavelength dependence of the transmission diffraction efficiency.

FIG. 9 is a graph showing the relationship between the depth D ₆₀ of the overetched portion 60 of the antireflection layer 20 and the −1st-order transmission diffraction efficiency η _T-1 for the diffraction element 100. The horizontal axis in FIG. 9 is the wavelength of incident light in the same range as in FIG. The solid line in FIG. 9, when the depth _D 60 = 0 nm overetch portion 60 (i.e., when the over etching does not occur), the broken _line, in the case of D 60 = 5 nm, the dotted _{line, D 60} = The transmission diffraction efficiency in the case of 10 nm is shown.

FIG. 10 is a graph showing the relationship between the depth D ₇₀ of the overetching portion 70 of the substrate 40 and the −1st-order transmission diffraction efficiency η _T-1 for the diffraction element 200. The solid line in FIG. 10, when the depth _D 70 = 0 nm in the over-etching portion 70 (i.e., when the over etching does not occur), the broken _line, in the case of D 70 = 25 nm, the dotted _{line, D 70} = The transmission diffraction efficiency in the case of 50 nm is shown.

As can be seen from FIG. 9, the diffraction efficiency of the diffraction element 100 having the antireflection layer 20 is only slightly reduced over a wide range of the target wavelength band even if overetching progresses. In contrast, in the diffraction element 200 that does not include the antireflection layer 20 of FIG. 10, when over-etching proceeds, the diffraction efficiency is significantly reduced, particularly in a relatively short wavelength band of the target wavelength band. This is for the diffraction element 100 with an anti-reflection layer 20, since the depth D ₆₀ of the over-etching portion 60 is suppressed relatively small, and the change in shape of contributing grating portion 10 in diffraction surface of the grating portion 10 This is considered to be because the internal variation can be kept small.

  In general, since the incident light has a wavelength width and the diffraction dimensions of the diffraction element vary in the manufacturing process, the diffraction element preferably has high diffraction efficiency over a wide wavelength band. From this viewpoint, the diffraction element 100 of the present invention is advantageous because high diffraction efficiency can be obtained over a wide wavelength band even when overetching occurs.

  When the lattice portion 10 is formed using dry etching, it is desirable that the etching rate (processing rate) is high in order to shorten the cycle time, but it becomes difficult to suppress overetching accordingly. However, as described above, by providing the antireflection layer 20 made of zirconium oxide immediately below the lattice portion 10, overetching can be suppressed relatively easily even if the etching rate is increased. Therefore, high diffraction efficiency can be ensured by reducing in-plane variation. Furthermore, by reducing the variation between lots, reproducibility with high diffraction efficiency can be obtained, and a high yield can be achieved in the manufacture of diffraction elements.

  As described above, in the diffraction element 100 of the present invention, the transmission diffraction efficiency is improved by providing the antireflection layer 20 to prevent reflection of incident light and reduce in-plane variation of the grating shape due to processing such as etching. To do. Furthermore, reproducibility with high diffraction efficiency can be obtained by reducing the variation between lots.

In addition, although the specific example whose cross-sectional shape of the convex part 11 is substantially rectangular was demonstrated above, the shape of the convex part 11 is not limited to this. FIG. 11 is a schematic cross-sectional view of another specific example of the transmissive diffraction element according to the first embodiment of the present invention, the whole being represented by 150. FIG. 12 is a partially enlarged view of the diffraction element 150 of FIG. 11 and shows a schematic enlarged view of the cross section of the convex portion 11. The convex part 11 has the substantially flat upper surface 11a and the opposing side wall 11b. 11 and 12, unlike FIG. 1, the side wall 11b is inclined. An angle formed by the Z axis and the side wall 11b is defined as an inclination angle S. That is, the cross-sectional shape of the convex portion 11 is a trapezoid, and this trapezoid has a top surface width W _T and a bottom surface width W _B. When the upper surface width W _T and the inclination angle S is determined, the value of the bottom surface width W _B is uniquely determined. Note that the tilt angle S can vary depending on the dry etching conditions.

Embodiment 2. FIG.
FIG. 13 is a schematic cross-sectional view of a transmissive diffractive element according to Embodiment 2 of the present invention, the whole of which is represented by 300. In FIG. 13, the same reference numerals as those in FIG. 1 denote the same or corresponding parts. Further, in the following description, as a general rule, differences from the first embodiment will be mainly described, and redundant description will be omitted for other portions. Similar to the diffraction element 100 of the first embodiment, the diffraction element 300 includes the substrate 40, the antireflection layer 20 formed on the surface of the substrate 40, and the grating portion 10 formed on the antireflection layer 20. Is provided. The diffraction element 300 may further include a back surface antireflection layer 50 on the back surface of the substrate 40. The antireflection layer 20 and the grating portion 10 are collectively referred to as a diffraction grating 30.

In the second embodiment, the convex portion 11 is formed on the first layer 15 in contact with the surface of the antireflection layer 20, the second layer 14 formed on the first layer 15, and the second layer 14, for example. The third layer 13 is formed. However, the convex portion 11 is not limited to a three-layer structure, and may have a two-layer structure or a laminated structure of four or more layers. The material of the first layer 15 is, for example, SiO ₂ (refractive index 1.457), the material of the second layer 14 is, for example, Si ₃ N ₄ (refractive index 2.023), and the material of the third layer 13 Is, for example, SiO ₂ .

FIG. 14 is a partially enlarged view of the diffraction element 300 of FIG. 13, and shows a schematic enlarged view of the cross section of the convex portion 11. The cross-sectional shape of the convex portion 11 is a trapezoid, and this trapezoid has a top surface width W _T and a bottom surface width W _B. When the upper surface width W _T and the inclination angle S is determined, the value of the bottom surface width W _B is uniquely determined. Note that the tilt angle S can vary depending on the dry etching conditions.

FIG. 15 shows a diffraction element 400 that does not include the antireflection layer 20, unlike FIG. 13. The diffraction efficiencies of the diffraction element 300 of FIG. 13 and the diffraction element 400 of FIG. 15 are compared. FIG. 16 shows the −1st-order transmission diffraction efficiency η1 _T-1 (solid line) of the diffraction element 300 and the −1st-order transmission diffraction efficiency η2 _T-1 (broken line) of the diffraction element 400 with the wavelength of incident light as the horizontal axis. ). The value of diffraction efficiency in FIG. 16 is obtained by simulation. The parameters used for the simulation are shown in Table 2 below.

  The wavelength λ, the wavelength width Δλ, the incident azimuth φ, the deflection angle ψ, and the diffraction order m were set to the same values as in Table 1.

FIG. 17 is a graph showing the total value (total reflection diffraction efficiency) η _R of the 0th-order reflection diffraction efficiency η _R0 and the −1st-order reflection diffraction efficiency η _{R-1 in} the target wavelength band. In FIG. 17, the horizontal axis indicates the wavelength of incident light. The solid line indicates the total reflection diffraction efficiency η1 _R of the diffraction element 300 including the antireflection layer 20, and the broken line indicates the total reflection diffraction efficiency η2 _R of the diffraction element 400 not including the antireflection layer 20. FIG. 17 shows that the total reflection diffraction efficiency is reduced by the introduction of the antireflection layer 20. As described above, it is considered that the transmission diffraction efficiency is improved by the introduction of the antireflection layer 20 as described above.

When FIG. 4 is compared with FIG. 16, in the second embodiment of the present invention, the convex portion 11 has a three-layer structure including Si ₃ N ₄ , so that the first-order transmission is compared with that in the first embodiment. It can be seen that the diffraction efficiency is improved. This is because Si ₃ N ₄ is a material having a higher refractive index than SiO ₂ .

  FIG. 18 is a schematic cross-sectional view showing the diffraction element 300 when overetching occurs in the dry etching process for forming the protrusions 11. FIG. 19 is a schematic cross-sectional view showing the diffraction element 400 when overetching occurs in the dry etching process for forming the protrusions 11.

FIG. 20 is a graph showing the amount of decrease in the −1st-order transmission diffraction efficiency η _T-1 of each of the diffraction elements 300 and 400 when the depths D ₆₀ and D _{70 of the} overetched portions ₆₀ and ₇₀ change. . The target wavelength band is, for example, a wavelength band (0.95 μm ≦ λ ≦ 1.01 μm) used for a laser resonator. FIG. 20 shows the amount of decrease in the −1st-order transmission diffraction efficiency η _T-1 of each of the completed diffraction elements 300 and 400 when the overetching time is 0, T1, and T2. In other words, the horizontal axis represents the depth of the over-etched portions 60 and 70 normalized by the processing time.

20 on the horizontal axis in FIG. 20 means that the antireflection layer 20 or the substrate 40 of the processed diffraction elements 300 and 400 is not in an over-etched state or an under-etched state. In other words, 0 on the horizontal axis in FIG. 20 means that the depths D ₆₀ and D _{70 of the} overetched portions ₆₀ and ₇₀ are 0 nm.

T1 on the horizontal axis in FIG. 20 means that overetching has been performed for the time T1 after completion of appropriate etching. In this case, the simulation was performed by setting D ₆₀ = 5 nm and D ₇₀ = 25 nm.

T2 on the horizontal axis in FIG. 20 means that overetching has been performed for the time T2 after completion of appropriate etching. In this case, the simulation was performed by setting D ₆₀ = 10 nm and D ₇₀ = 50 nm.

From FIG. 20, when the overetching is performed for the same time, the decrease amount of the −1st-order transmission diffraction efficiency η _T-1 of the diffraction element 400 that does not include the antireflection layer 20 is 0.022 on the average. Thus, it can be seen that the decrease amount of the −1st order transmission diffraction efficiency η _T-1 of the diffraction element 300 is only 0.001.

FIG. 21 is a graph showing the relationship between the depth D ₆₀ of the overetched portion 60 of the antireflection layer 20 and the −1st-order transmission diffraction efficiency η _T-1 for the diffraction element 300. The horizontal axis of FIG. 21 is the wavelength. The solid line in FIG. 21, when the depth _D 60 = 0 nm overetch portion 60 (i.e., if the overetching does not occur), the broken line in _the case of D 60 = 5 nm, the dotted _line, if the D 60 = 10 nm The transmission diffraction efficiency is shown.

FIG. 22 is a graph showing the relationship between the depth D ₇₀ of the overetching portion 70 of the substrate 40 and the −1st order transmission diffraction efficiency η _T-1 for the diffraction element 400. The solid line in FIG. 22, when the depth _D 70 = 0 nm in the over-etching portion 70 (i.e., if the overetching does not occur), the broken _line, if the D 70 = 25 nm, the dotted _line, if the D 70 = 50 nm The transmission diffraction efficiency is shown.

As can be seen from Figure 21, the diffraction element 300 with an anti-reflection layer 20, when the depth D ₆₀ of the over-etching portion 60 is increased, except for a part of the wavelength band, the diffraction efficiency decreases slightly. Compared with this, in the diffraction element 200 without the antireflection layer 20 of FIG. 22, the transmission diffraction efficiency is relatively greatly reduced except for a part of the wavelength band.

As described above, in the diffraction element 300 of the present invention, the transmission diffraction efficiency can be improved by making the convex portion 11 have a three-layer structure including Si ₃ N ₄ . Further, the antireflection layer 20 is provided to prevent the reflection of incident light and to reduce the in-plane variation of the lattice shape due to processing such as etching, thereby preventing the diffraction efficiency from deteriorating. Furthermore, reproducibility with high diffraction efficiency can be obtained by reducing the variation between lots.

Embodiment 3 FIG.
FIG. 23 is a schematic configuration diagram of the laser oscillator according to the third embodiment of the present invention, the whole being represented by 500. The laser oscillator 500 includes a plurality of laser light sources 501, 502, and 503 that emit laser light. Laser light sources 501, 502, and 503 emit laser beams 511, 512, and 513, respectively. The wavelengths of the laser beams 511, 512, and 513 may be different wavelengths. Although three laser light sources are shown in FIG. 23, the number of laser light sources of the present invention is not limited to this. The laser light sources 501, 502, and 503 are laser diodes (LD), for example.

  The laser oscillator 500 further includes mirrors 521, 522, and 523 that correspond to the laser beams 511, 512, and 513, respectively, and can change the traveling directions of these laser beams. The laser beams 511, 512, and 513 whose traveling directions have been changed by the mirrors 521, 522, and 523 are focused on one point. The diffractive element 100 of the first embodiment (or the diffractive element 300 of the second embodiment not shown in FIG. 23) is arranged at this focusing point. The laser beams 511, 512 and 513 diffracted and synthesized by the diffraction element 100 become a single synthesized laser beam 510. Preferably, the diffracted light utilized is −1st order transmitted diffracted light.

  The combined laser beam 510 then arrives at the partial reflection mirror 530. Alternatively, the combined laser beam 510 may arrive at the partial reflection mirror 530 after being guided in a desired direction by a mirror (not shown).

  The partial reflection mirror 530 has a function of reflecting a part of the combined laser beam 510 (for example, reflecting a laser beam corresponding to a part of the energy of the combined laser beam 510) and transmitting the rest. A part of the combined laser beam 510 reflected by the partial reflection mirror 530 returns to the diffraction element 100, and the number corresponding to the number of laser beams irradiated to the diffraction element 100 by the diffraction element 100 (three in FIG. 23). Are divided into laser beams. The divided laser beams are fed back to laser light sources 501, 502, and 503, respectively. Thereby, the diffraction element 100 and the partial reflection mirror 530 function as an external resonator. On the other hand, the remaining laser light that is not reflected by the partial reflection mirror 530 and passes through it is taken out as output light of the laser oscillator 500 (for example, laser light 601 in FIG. 24).

  The laser oscillator 500 further includes a housing (not shown). The diffraction element 100, the laser light sources 501, 502 and 503, the mirrors 521, 522 and 523, and the partial reflection mirror 530 are accommodated in this housing.

  The incident angles of the laser beams 511, 512, and 513 to the diffraction element 100 are adjusted so that the respective diffracted beams become one synthetic laser beam 510. Specifically, since the diffraction angle is determined by the wavelength and the incident angle as shown in Expression (1), the incident angle is adjusted by the mirrors 521, 522, and 523 in accordance with the wavelengths of the laser beams 511, 512, and 513.

  In the laser oscillator 500, a difference in diffraction efficiency on the order of 1% affects the system performance (influences on the photoelectric conversion efficiency and can also affect the maximum output), and thus a particularly high diffraction efficiency is required. In the third embodiment of the present invention, high diffraction efficiency is realized by the diffraction element 100, so that high system performance can be obtained for the laser oscillator 500.

Embodiment 4 FIG.
FIG. 24 is a schematic configuration diagram of the laser beam machine according to the fourth embodiment of the present invention, which is generally represented by 600. The laser processing machine 600 includes a laser oscillator 500 according to the third embodiment that emits a laser beam 601, a beam adjustment optical system 611 that adjusts and shapes the laser beam 601 to a desired beam diameter and profile, and a beam adjustment optical system 611. A mirror 612 that can change the traveling direction of the emitted laser light 601, a lens 613 that focuses the laser light 601 coming from the mirror 612 to a desired position (for example, the workpiece 622), and a workpiece 622 And a stage base 621 to be placed. The laser processing machine 600 may further include an optical fiber that transmits the laser light 601. The laser processing machine 600 is used, for example, for sheet metal processing.

  Thus, by using the laser oscillator 500 having high system performance, it is possible to obtain a laser processing machine 600 that can use high-power laser light and can perform high-speed processing.

  DESCRIPTION OF SYMBOLS 10 Grating part, 11 Convex part, 12 Concave part (gap part), 13 3rd layer, 14 2nd layer, 15 1st layer, 20 Antireflection layer, 30 Diffraction grating, 40 Substrate, 50 Back surface antireflection layer, 60, 70 Overetching part, 100, 200, 300, 400 Diffraction element, 500 Laser oscillator, 501, 502, 503 Laser light source, 521, 522, 523 Mirror, 530 Partial reflection mirror, 600 Laser processing machine, 611 Beam adjustment optical system, 612 mirror, 613 lens, 621 stage base, 622 Workpiece.

Claims (8)

A substrate having a front surface and a back surface;
An antireflection layer made of zirconium oxide formed on the surface of the substrate;
A grating portion formed on the antireflection layer and having a periodic uneven pattern;
A transmissive diffraction element.   The transmissive diffraction element according to claim 1, wherein the antireflection layer is a single layer.   The transmissive diffraction element according to claim 1, wherein the grating portion has a single-layer structure or a multi-layer structure made of one or more materials selected from silicon oxide, silicon nitride, and silicon oxynitride.   The transmissive diffraction element according to claim 1, wherein the substrate is made of quartz glass or synthetic quartz.   The transmissive | pervious diffraction element in any one of Claims 1-4 further equipped with the back surface antireflection layer which consists of a single layer or a multilayer optical material film | membrane on the said back surface of the said board | substrate. The transmissive diffraction element according to any one of claims 1 to 5,
One or more laser light sources for irradiating the transmissive diffraction element with laser light;
A laser oscillator comprising: A laser oscillator according to claim 6;
An optical component for condensing the diffracted light emitted from the laser oscillator at a processing point;
A laser processing machine.   The laser processing machine according to claim 7, wherein the diffracted light collected by the optical component is −1st order transmitted diffracted light.

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