Method for manufacturing planar optical circuit and planar optical circuit

Abstract

A method for manufacturing a planar optical circuit is specified. A method for manufacturing a planar optical circuit, the method comprising: providing a substrate without a light generation region; providing a waveguide layer; providing a photostructurable mask on the waveguide layer; optically processing the photostructurable mask to remove the photostructurable mask in a plurality of regions; etching the waveguide layer in the plurality of regions such that a plurality of channels for confining a waveguide are generated in the waveguide layer; removing the photostructurable mask; and singulating the planar optical circuit. Further, the planar optical circuit is specified.

Description

Technical Field

[0001] Relates to a method for manufacturing a planar optical circuit and a planar optical circuit.

[0002] U.S. Patent Application No. 17 / 482,740 describes an optoelectronic semiconductor device having a semiconductor laser. The disclosure of this application is incorporated herein by reference.

[0003] An object is to provide an efficient method for manufacturing a planar optical circuit. Further, a planar optical circuit having improved characteristics is provided.

Summary of the Invention

[0004] Hereinafter, the planar optical circuit will be described as an optical waveguide circuit that combines a plurality of laser outputs. This is to distinguish it from the "waveguide combiner" structure in an augmented reality (AR) glasses that spreads image information on the surface of AR glasses that emphasize an eyebox.

[0005] According to at least one embodiment, a method for manufacturing a planar optical circuit includes providing a substrate. Specifically, the substrate is a substrate without a light generation region. In other words, the substrate is not designed to generate electromagnetic radiation. In some embodiments, the substrate is made of a material that is transparent to electromagnetic radiation in the visible light wavelength range.

[0006] For example, the substrate is formed as a wafer. Thereby, a plurality of planar optical circuits can be generated. In some embodiments, the substrate is coated with a transparent intermediate layer that is transparent to the visible light wavelength range. As a result, the substrate can be easily cut.

[0007] According to the method according to at least one embodiment, a waveguide layer is provided. Specifically, the waveguide layer is preferably provided directly on the substrate. The waveguide layer preferably consists of a material having a high refractive index, for example, a refractive index of 1.8 to 2.5, or contains such a material. It is particularly preferable that the refractive index of the material of the waveguide layer is higher than the refractive index of the material of the substrate. For example, the coefficient of thermal expansion of the material of the substrate is equivalent to the coefficient of thermal expansion of the material of the waveguide layer. For example, the coefficients of thermal expansion of the material of the substrate and the material of the waveguide layer differ by at most + / - 10%. The substrate preferably can mechanically stabilize the waveguide layer.

[0008] According to the method according to at least one embodiment, a photostructurable mask is provided on the waveguide layer. Specifically, the photostructurable mask changes its structure and / or composition when exposed to electromagnetic radiation.

[0009] According to the method according to at least one embodiment, the photostructurable mask is optically processed such that the photostructurable mask is removed in a plurality of regions. That is, it is preferable that the plurality of regions do not contain the photostructurable mask after optical processing. Specifically, during optical processing, the photostructurable mask is exposed to electromagnetic radiation, for example, UV light. After being exposed to the electromagnetic radiation, the photostructurable mask is developed with a developer reagent and removed in a plurality of regions. Specifically, in the regions where the photostructurable mask is removed, the waveguide layer is exposed.

[0010] The waveguide mask may be formed using other lithography methods such as electron beam lithography and nanoimprint lithography.

[0011] According to the method according to at least one embodiment, the waveguide layer is etched in a plurality of regions such that channels are generated within the waveguide layer. Specifically, the waveguide is confined by the channels. Each channel preferably directly adjoins the waveguide. The channels, for example, extend completely through the waveguide layer. That is, the bottom surface of the channel is formed by the substrate. For example, the etching rate of the photostructurable mask is lower than the etching rate of the waveguide layer.

[0012] In another manufacturing method of the planar optical circuit, everything except the waveguide layer is removed by etching. Since only the channels are generated within the waveguide layer by etching, as an effect, most of the waveguide layer remains on the substrate. For this reason, a more mechanically robust planar optical circuit can be manufactured, and etching artifacts can be prevented. The planar optical circuit described in this specification is also suitable for a flip-chip configuration in which regions outside the channels are metallized for soldering or bonding to the substrate.

[0013] According to the method according to at least one embodiment, the photostructurable mask is removed, particularly completely. The photostructurable mask is removed, for example, using an acid such as sulfuric acid.

[0014] According to the method according to at least one embodiment, the substrate provided with the waveguide layer is singulated into planar optical circuits. Specifically, the singulation is performed by cleavage, etching, mechanical dicing, or laser dicing.

[0015] According to at least one embodiment, a method for manufacturing a planar optical circuit includes providing a substrate without an optical generation region, providing a waveguide layer, providing a photostructurable mask on the waveguide layer, optically processing the photostructurable mask to remove the photostructurable mask in a plurality of regions, etching the waveguide layer in the plurality of regions such that a plurality of channels for confining a waveguide are generated in the waveguide layer, removing the photostructurable mask, and singulating the planar optical circuit. The above steps are preferably carried out in a given order.

[0016] By using a photostructurable mask to selectively etch channels into the waveguide layer, internal reflections that occur during optical processing and cause distortion and defects in the desired final structure are minimized as a result. Specifically, by minimizing defects, scattering is reduced in the waveguides of the planar optical circuits manufactured by this method. A small amount of scattering couples the initial modes excited by the laser diode field to most of the waveguide modes, so that the output of the waveguide is illuminated with a more uniform distribution regardless of the position of the input laser diode.

[0017] According to the method of at least one embodiment, the thickness of the photostructurable mask is such that the photostructurable mask is not completely etched away during the etching of the waveguide layer. Specifically, the etching rate of the photostructurable mask (Erate(mask)) is close to the etching rate of the waveguide layer (Erate(layer)). In this case, it is preferable that the thickness of the photostructurable mask (tmask) is greater than the thickness of the waveguide layer (tlayer). However, if the thickness of the photostructurable mask is too large, the fidelity of the etching may be lost. For example, the thickness of the photostructurable layer falls within the range defined by the following formula.

Number

[0018] According to the method according to at least one embodiment, SiN x , SiO x N y , GaN, HfO2, LiNbO3, Ta2O5, Nb2O5, HfO2, TiO2, Si, and mixtures thereof. In addition to, or instead of, this, other etchable materials having a high refractive index may be used in the waveguide layer. Si may be either epitaxial or amorphous. A waveguide layer made of Si is useful when using infrared light. However, due to the high refractive index of Si, the output may have a far-field distribution with a complete hemispherical shape. That is, the output of the waveguide may have an unacceptable high numerical aperture (NA).

[0019] Specifically, the waveguide layer includes SiN x or consists of SiN x . As an effect, SiN x is easily available, placed, and etchable. SiN x has a high refractive index, particularly a refractive index of 1.85 to 2.0, preferably 1.90 to 2.0. In some cases, by greatly changing the ratio of Si to N, a material having a refractive index less than 1.8 and greater than 3.0 can be obtained depending on the wavelength. Since SiN x has a high refractive index, it preferably has a high refractive index contrast with surrounding substances such as air and SiO2. Thereby, the confinement and the allowable number of modes for a given cross-sectional area can be increased. The increase in the allowable number of modes is advantageous for alleviating alignment problems and relaxing constraints regarding the input coupling structure design. This helps reduce spatial coherence. Furthermore, a planar optical circuit having a waveguide layer made of SiN x has high compatibility with low-cost complementary metal oxide semiconductor (CMOS)-based manufacturing.

[0020] The waveguide layer preferably includes low Si-SiN x or consists of low Si-SiN x . Specifically, low Si-SiN xIt is composed of a smaller number of Si-Si bonds compared to theoretical Si3N4. As a result, the absorption of visible light is reduced, and the optical quality of SiN x is improved. Specifically, the absorption band of SiN x shifts from the visible region to the ultraviolet region of the electromagnetic spectrum because of the smaller number of Si-Si bonds. The number of Si-Si bonds can be measured using IR spectroscopy. In addition to, or instead of, this, the composition of SiN x can be determined using the refractive index.

[0021] According to the method according to at least one embodiment, the waveguide layer is subjected to a surface plasma activation treatment, especially before providing a photostructurable mask. Specifically, oxygen and methane are used as reactants for the surface plasma activation treatment. This step improves the adhesion of the photostructurable mask on the waveguide layer.

[0022] According to the method according to at least one embodiment, the adhesion layer is provided on the waveguide layer before providing a photostructurable mask. The adhesion layer especially contains or consists of SiO2. The adhesion layer can improve the adhesion of the photostructurable mask on the waveguide layer. As a result, the plasma surface activation treatment of the waveguide layer can be omitted.

[0023] For example, the adhesion layer is provided using plasma enhanced chemical vapor deposition (PECVD). Specifically, the thickness of the adhesion layer is 5 nanometers to 20 nanometers, for example, about 10 nanometers.

[0024] According to the method according to at least one embodiment, an adhesion promoter is provided on the waveguide layer before providing the photostructurable mask layer. For example, hexamethyldisilazane (HMDS) is used as the adhesion promoter. Specifically, the adhesion promoter is applied after applying the adhesion layer. In other words, the adhesion promoter is applied on the adhesion layer. The adhesion promoter is applied, for example, by spin coating.

[0025] According to the method according to at least one embodiment, the waveguide layer is provided by plasma enhanced chemical vapor deposition (PECVD). In this coating method, a waveguide layer having a thickness of at least 500 nanometers can be provided on the substrate. Specifically, the waveguide layer coated by PECVD, preferably SiN x composed of shows low attenuation and / or compressive stress. The waveguide layer showing low attenuation has, as an effect, improved optical properties. Furthermore, due to the compressive stress, as an effect, a waveguide layer having a thickness of at least 500 nanometers can be obtained.

[0026] According to the method according to at least one embodiment, a low-frequency plasma source is used in plasma enhanced chemical vapor deposition. The low-frequency plasma source provides a waveguide layer with increased compressive stress in particular. The compressive stress cancels out the inherent tensile stress seen, for example, in a waveguide layer with a thickness of 500 nanometers or more provided by other methods. The compressive stress can be measured by a polarized light microscope.

[0027] Specifically, the time during which the low-frequency plasma source is turned on during PECVD is 20% to 50%, preferably 30% to 40%, for example about 35%. The time during which the high-frequency plasma source is turned on during PECVD is, in particular, between 50% and 80%, preferably between 60% and 70%, for example about 65%.

[0028] In particular, a high-quality waveguide layer can be provided by PECVD using a low-frequency plasma source. A low-quality waveguide layer is, for example, non-uniform and causes scattering especially at short wavelengths.

[0029] According to the method according to at least one embodiment, during PECVD, a flow of NH3 of 20 sccm to 60 sccm, in particular 30 sccm to 50 sccm, for example about 40 sccm was applied. In addition to or instead of this, during PECVD, a flow of Ar containing 5% SiH4 of 130 sccm to 190 sccm, in particular 140 sccm to 180 sccm, for example about 160 sccm may be applied.

[0030] SiN x As another aspect, the silicon content can be increased, but the waveguide layer may exhibit higher losses at visible light wavelengths.

[0031] According to the method according to at least one embodiment, the surface of the substrate is cleaned before providing the waveguide layer. Specifically, the surface of the substrate is cleaned by plasma cleaning. For example, N2O is used for cleaning the substrate.

[0032] According to the method according to at least one embodiment, the waveguide layer is etched by inductively coupled plasma etching. Inductively coupled plasma etching is a particularly highly selective etching method. In inductively coupled plasma etching, at least one of the process gases SF6, CHF3, C4F8, CF4, CH2F2, O2, Ar can be used. Combinations of CF4 / O2 and CH2F2 / O2, as well as CF4, CHF3 and Ar, may also be used. The combination of CF4 / O2 and CH2F2 / O2 results in a reduction in the polymerization of by-products.

[0033] According to the method according to at least one embodiment, the reaction chamber for inductively coupled plasma etching is cleaned before etching the waveguide layer. By cleaning the reaction chamber, the plasma can surely enter the waveguide layer, and the plasma can be prevented from disappearing during etching. Specifically, the reaction chamber is cleaned using at least one of the process gases O2, SF6, CHF3, C4F8, CF4, CH2F2.

[0034] According to the method according to at least one embodiment, after removing the photostructurable mask, a cladding is provided on the waveguide layer. By providing the cladding, as an effect, the sensitivity of the waveguide layer, particularly to dust in the waveguide, is reduced. Further, by providing the cladding, breakage of the waveguide during singulation can be prevented. Also, the cladding can enhance the efficiency of the planar optical circuit. And the cladding reduces the refractive index difference of the waveguide compared to air and reduces the numerical aperture, and thus is useful in many applications.

[0035] Specifically, the cladding is provided by PECVD. For example, the cladding is provided using at least one of the reactants of SiH4, CF4, and N2O. As an effect, CF4 enhances the compatibility of the cladding by reactive etch-back. That is, the cladding is etched simultaneously with being provided.

[0036] Furthermore, a planar optical circuit is specified. Specifically, the planar optical circuit is manufactured by the method described in this specification. Therefore, all the features and embodiments described in conjunction with this method are also applicable to the planar optical circuit, and vice versa.

[0037] According to at least one embodiment, the planar optical circuit includes a substrate without a light generation region and a waveguide layer on the substrate. Specifically, the waveguide layer includes a channel for confining the waveguide. For example, the waveguide is a ridge waveguide.

[0038] The waveguide layer is preferably transparent to electromagnetic radiation in the visible to infrared range of the electromagnetic spectrum. For example, the waveguide layer, and thus the waveguide, is transparent to electromagnetic radiation of 405 nanometers to 780 nanometers, preferably 450 nanometers to 650 nanometers. In other words, the planar optical circuit can be designed for use in the visible range of the electromagnetic spectrum.

[0039] According to the planar optical circuit according to at least one embodiment, the waveguide is a multimode waveguide. Specifically, by using a multimode waveguide, the alignment problem of the planar optical circuit by the coupled laser diode is alleviated as compared with a single-mode waveguide.

[0040] In other aspects of the planar optical circuit, it is assumed that the light emitting point is single-mode in order to avoid an undesirable speckle effect from the multimode waveguide. This means that the alignment of the laser diode to the single-mode waveguide is very difficult and requires positioning the light emitting point of the laser diode well below one wavelength. If the position is misaligned, the efficiency may be significantly reduced. Also, other planar optical circuits may have a low production yield because they are most sensitive to alignment. Furthermore, coupling a plurality of waveguides into a single waveguide may lead to significant efficiency losses when using a single-mode waveguide. For this reason, other planar optical circuits actually rarely combine waveguides for red, green, and blue electromagnetic radiation into a single waveguide, but only bring the outputs of the respective red, green, and blue waveguides closer to each other on the light emitting side. For this reason, in other planar optical circuits using a single-mode waveguide, a true single light emitting point is often not obtained. In other examples, the branching portion of the single-mode waveguide is joined in the planar optical circuit using various techniques such as an evanescent coupler or a multimode interference coupler. However, in such a configuration, attention must be paid to manufacturing tolerances and design.

[0041] In particular, the planar optical circuit having a multimode waveguide, as an effect, relaxes the limitation of the tolerance regarding the alignment of the laser diode, for example, the lateral alignment of the laser diode. In particular, the production yield and efficiency are improved.

[0042] According to the planar optical circuit according to at least one embodiment, the waveguide is a single-mode waveguide. A planar optical circuit having a single-mode waveguide can be used in applications where coherence and low optical loss are required. In this case, a resonator, a nonlinear structure, and an interferometer may be further provided.

[0043] According to the planar optical circuit according to at least one embodiment, the substrate includes a transparent or opaque inorganic substance selected from the group consisting of fused quartz, sapphire, YAG, MgF2, AlN, various glasses, and single crystal materials. Specifically, the single crystal semiconductor-based material is a low bandgap semiconductor-based material and / or is selected from the group consisting of GaN, AlGaN, SiC, Ge, GaAs, AlGaAs, InP, and silicon. The substrate preferably exhibits a strong absorbance to ultraviolet light, which is advantageous for optical processing of the photostructurable mask continuously disposed on the substrate. However, in the case of an absorptive substrate, the substrate also needs to include a transparent intermediate layer having a refractive index lower than that of the waveguide material.

[0044] A substrate containing fused silica is particularly transparent to visible light. Thereby, backside alignment can be performed with a visible light camera.

[0045] In the case of a substrate made of a semiconductor-based material with a lower bandgap, alignment is possible using an infrared optical system. As an effect, a substrate made of a semiconductor-based material is preferably easily cleaved for facet generation, has good thermal conductivity, and absorbs stray light and scattered light. Further, in a substrate made of a semiconductor-based material, for example, etching of precise alignment fiducials, trenches, and other features becomes possible, and alignment and incorporation of optical components such as laser diodes and collimating optical systems based on wafer-level refractive optics, diffractive optics, or meta-optics become easy. When the waveguide layer contains SiN x it is advantageous because the thermal expansion coefficient of the semiconductor-based material is close to that of SiN x

[0046] According to the planar optical circuit according to at least one embodiment, the substrate is opaque. Specifically, the substrate absorbs UV and / or visible light. For example, the substrate absorbs at least 90%, at least 95% or at least 99% of the UV and / or visible light incident on the substrate. For example, the opaque substrate is made of a single crystal semiconductor-based material.

[0047] According to the planar optical circuit according to at least one embodiment, the substrate includes an intermediate layer. The material of the intermediate layer is particularly selected from the group consisting of oxides and fluorides. For example, the material of the intermediate layer is selected from the group consisting of SiO2, Al2O3, MgF2, LiCaAlF6, SiO, GeO2. The intermediate layer preferably is transparent and / or has a low light absorption rate. Specifically, the thickness of the intermediate layer is 1 micrometer to 5 micrometers, particularly 1 micrometer to 3 micrometers. Such a thickness is preferable when the waveguide is used for visible electromagnetic radiation. More generally, the evanescent tail of the waveguide mode should not interact with the substrate. For example, the intermediate layer thickness λ inter needs to satisfy at least the following conditions.

Number

[0048] Here, λ is the free space wavelength, and n inter is the refractive index of the intermediate layer. When the substrate has even slight light absorption at the wavelength of the laser diode that can be coupled to the planar optical circuit, the substrate preferably includes an intermediate layer. In addition, as an effect, the intermediate layer can enhance the alignment between the thermal expansion coefficient of the substrate and the waveguide layer.

[0049] According to a planar optical circuit according to at least one embodiment, an adhesive layer is disposed on a waveguide layer. Specifically, the adhesive layer contains SiO2 or consists of SiO2. In addition to or instead of this, the adhesive layer is in direct physical contact with the waveguide layer. The adhesive layer can enhance the adhesiveness of a subsequent layer such as a cladding or a photostructurable mask to the waveguide layer.

[0050] According to a planar optical circuit according to at least one embodiment, a cladding is disposed on the waveguide layer. Specifically, the cladding is disposed on the adhesive layer.

[0051] According to a planar optical circuit according to at least one embodiment, the material of the cladding has a lower refractive index than the material of the waveguide layer. Specifically, the cladding is transparent to visible electromagnetic radiation. It is desirable that the cladding has a coefficient of thermal expansion that matches the coefficient of thermal expansion of the waveguide layer.

[0052] For example, by using a cladding material with a refractive index that is lower by a refractive index difference of 0.2 to 0.5, a large refractive index difference can be provided between the waveguide layer and its adjacent portion. Thereby, the number of modes available in the waveguide can be increased. Therefore, the alignment of the laser diode is simplified, the use of various input coupling structures becomes possible, and coherent artifacts due to a decrease in the lateral coherence of the multimode output can be suppressed.

[0053] According to the planar optical circuit according to at least one embodiment, the material of the cladding is selected from the group consisting of SiO2, Al2O3, HfO2, Y2O3, MgF2, CaF2, YLiF4, oxide and fluoride glasses, and transparent organic polymers. The transparent organic polymer is particularly selected from the group consisting of polysiloxane, silicone, poly(methyl methacrylate (PMMA), polyetheretherketone (PEEK), perfluoropolymers such as Cytop, and mixtures thereof. The material of the cladding is doped with, for example, fluorine. SiO2, Al2O3, HfO2, and oxide glasses constitute the refractive index in the region where the difference in refractive index between the waveguide layer and the cladding is large. As a result, the efficiency of the planar optical circuit is improved.

[0054] According to the planar optical circuit according to at least one embodiment, the cladding has a thickness of 1 micrometer to 5 micrometers, particularly 1 micrometer to 3 micrometers. If the thickness of the cladding is within this range, in particular, interference between the waveguide layer and various contaminants can be prevented. In many cases, the evanescent field is confined within the cladding layer.

[0055] According to the planar optical circuit according to at least one embodiment, the waveguide layer has a thickness of 50 nanometers or more and 5000 nanometers or less. Specifically, the thickness is 50 nanometers to 500 nanometers. This range of thickness is preferable when the waveguide is used in single-mode operation or is used in only a small number of modes. Alternatively, the thickness is 200 nanometers to 5000 nanometers. This range of thickness is preferable for multimode waveguides.

[0056] According to the planar optical circuit according to at least one embodiment, the side surface of the channel is perpendicular or substantially perpendicular to the main extension surface of the planar optical circuit. Alternatively, the side surface is inclined. Specifically, the side surface is curved. Thereby, a fillet can be formed. Such a fillet serves an auxiliary role when providing the cladding.

[0057] According to a planar optical circuit according to at least one embodiment, the waveguide includes at least two branch portions that merge into a single branch portion within at least one coupling region in a top view. For example, the coupling region is a branch. Specifically, each branch portion is confined by a channel in the waveguide layer. Each branch portion is preferably directly adjacent to two channels. For example, the waveguide includes three branch portions that merge into a single branch portion. In order to integrate the three branch portions into a single branch portion, the waveguide preferably includes one or two coupling regions.

[0058] According to a planar optical circuit according to at least one embodiment, at least one of the branch portions has a sigmoid shape or a shape of a tangent function in a top view. In addition to or instead of this, one of the branch portions is linear in a top view. Specifically, the branch portions and the coupling region are parameterized by a Bezier function.

[0059] Furthermore, a radiation emitting device is specified. Specifically, the planar optical circuit described herein is used in a radiation emitting device. For this reason, all features and embodiments described in conjunction with the planar optical circuit are also applicable to the radiation emitting device, and vice versa.

[0060] According to a radiation emitting device according to at least one embodiment, the planar optical circuit is used as a beam combiner. Specifically, the outputs of a plurality of laser diodes are combined within the planar optical circuit, for example, at a single emission point. The combined output can be used for projection, laser processing, AR / VR, and applications related thereto. The plurality of laser diodes are preferably of the same color or different colors. That is, the outputs of red, green, and blue laser diodes, or a plurality of laser diodes of one of these colors can be combined. For example, the planar optical circuit is used or configured to combine red, green, and blue electromagnetic radiation at a single emission point.

[0061] According to the radiation emitting device according to at least one embodiment, the planar optical circuit is used as a beam splitter. That is, the output of a single laser diode is split to obtain, for example, a plurality of coherent outputs or at least partially coherent outputs. The coherent output or at least partially coherent output can be used in various applications such as interferometers.

[0062] According to at least one embodiment, the radiation emitting device includes at least one laser diode and a planar optical circuit. The planar optical circuit is arranged following the at least one laser diode or vice versa.

[0063] Advantageous embodiments and modifications of the method for manufacturing a planar optical circuit, the planar optical circuit, and the radiation emitting device are illustrated by exemplary embodiments described with reference to the following drawings.

Brief Description of the Drawings

[0064]

Fig. 1A

Fig. 1B

Fig. 1C

Fig. 1D

Fig. 1E

Fig. 1F

Fig. 1G

Fig. 1H

Fig. 2

Fig. 3A

Fig. 3B

Fig. 4

Fig. 5

Fig. 6

Fig. 7

Fig. 8

Fig. 9

Fig. 10A

Fig. 10B

Fig. 10C

Fig. 11

Fig. 12

DETAILED DESCRIPTION OF THE INVENTION

[0065] In the exemplary embodiments and figures, components that act similarly or in a similar manner are given the same reference numerals. The elements shown in the figures and their relative sizes to one another should not be considered to be to scale. Further, individual elements may be shown in exaggerated sizes for ease of viewing and / or understanding.

[0066] As shown in FIG. 1A, a substrate 1 is provided by a method for manufacturing a planar optical circuit according to an exemplary embodiment. The substrate 1 is not provided with a light generation region. Here, the substrate 1 includes a substrate layer 2 and an intermediate layer 3. The substrate layer 2 contains silicon or consists of silicon, and the intermediate layer 3 contains wet thermal SiO2 or consists of wet thermal SiO2. The thickness of the intermediate layer 3 is about 2 micrometers. Alternatively, a substrate 1 containing fused silica or consisting of fused silica is provided. The substrate 1 is provided in wafer form.

[0067] The waveguide layer 4 is provided on the substrate 1 as shown in FIG. 1B. Before providing the waveguide layer 4, plasma cleaning using N2O is performed at 200 watts for about 5 minutes on the surface of the substrate 1, particularly on the surface of the intermediate layer 3. Here, the waveguide layer 4 contains low Si-SiN x or consists of low Si-SiN x The waveguide layer 4 is provided directly on the substrate 1, particularly on the intermediate layer 3 of the substrate 1. The waveguide layer 4 is provided by PECVD according to the parameters shown in Table 1.

[0068] [Table 1] The thickness of the waveguide layer 4 is here about 3 micrometers. Table 2 shows the attenuation coefficient of the waveguide layer 4 for each wavelength. Hereinafter, the attenuation coefficient should be understood as the parameter b in the formula I(x)=I0*exp(-b*x). I is the intensity that depends on the distance x along the waveguide.

[0069] [Table 2] After providing the waveguide layer 4, as shown in FIG. 1C, an adhesive layer 5 is provided on the waveguide layer 4. Here, the adhesive layer 5 contains or consists of SiO2. The thickness of the adhesive layer 5 is about 10 nanometers. The adhesive layer 5 is provided by PECVD according to the parameters shown in Table 3.

[0070]

Table 3

[0071]

Table 4

[0072]

Table 5

[0073] Before photolithography, the photostructurable mask 7 is rehydrated. For this purpose, the photostructurable mask 7 is left in air for about 30 minutes.

[0074] As shown in FIG. 1E, the photostructurable mask 7 is photo-processed so that the photostructurable mask 7 is removed within each region. In the photo-processing, the photostructurable mask 7 is exposed to electromagnetic radiation within the region. Here, UV ultraviolet rays are used. Table 6 shows detailed parameters regarding the exposure to electromagnetic radiation.

[0075]

Table 6

[0076] After the exposure to electromagnetic radiation, the photostructurable mask 7 is developed with a developer. Thereby, the photostructurable mask 7 is removed within the region. Here, a potassium-based buffered developer mixed with water is used as the developer. The ratio of water to the developer is 1:4. The development time is about 90 seconds.

[0077] In the method for manufacturing a planar optical circuit, in the next step, in the region without the photostructurable mask 7, the waveguide layer 4 is etched (FIG. 1F). Thereby, a channel 8 is formed in the waveguide layer 4. The channel 8 confines the waveguide 9. The channel 8 is directly adjacent to at least one waveguide 9. The channel 8 extends through the waveguide layer 4. That is, the waveguide layer 4 is completely removed in the region without the photostructurable mask 7 after the photo-processing. The bottom surface of the channel 8 is formed by the substrate 1, particularly the intermediate layer 3 of the substrate 1. The waveguide layer 4 is etched by inductively coupled plasma (ICP) etching using various fluorine and carbon-based gases.

[0078] Before etching the waveguide layer 4, the reaction chamber for inductively coupled plasma etching is cleaned. To clean the reaction chamber, the parameters shown in Table 7 are set. The cleaning time is, for example, about 10 minutes.

[0079] [Table 7] After cleaning the reaction chamber, the waveguide layer 4 is etched according to the parameters shown in Table 8. The etching time is about 12.5 minutes.

[0080] [Table 8] During the etching of the waveguide layer 4, the adhesive layer 4 is also removed in the regions without the photostructurable mask 7.

[0081] As shown in FIG. 1G, after etching the waveguide layer 4 to form the channel 8 in the waveguide layer 4, the photostructurable mask 7 is removed. Here, the photostructurable mask 7 is removed using a mixture of H2SO4 and H2O2 prepared from 4 parts of 70% H2SO4 and 1 part of 30% aqueous H2O2 solution. This mixture is also called a piranha solution. The photostructurable mask 7 is removed by immersing it in the mixture for less than 10 minutes. Then, the waveguide layer 4 is rinsed with deionized water.

[0082] As shown in FIG. 1H, a cladding 11 is provided on the waveguide layer 4 by PECVD. The cladding 11 suppresses scattering loss and insertion loss. The thickness of the cladding 11 is about 2 micrometers. In PECVD, the parameters shown in Table 9 are used.

[0083] [Table 9] The cladding 11 covers the waveguide layer 4. Specifically, the cladding 11 is in direct physical contact with the adhesive layer 5. The channel 8 is partially filled with the cladding 8. The bottom surface 20 and the side surface 21 of the channel 8 formed by the substrate 1 are covered by the cladding 11.

[0084] The planar optical circuit 10 is formed by singulating the wafer. For singulation, cleavage portions 12 are etched into the wafer. The planar optical circuit 10 is obtained by cleaving using pliers at the cleavage portions 12, 13, 14. The cleavage order is shown in FIG. 2. Cleavage is performed in the order of the first cleavage portion 12 (hash line), the second cleavage portion 13 (dotted line), and the third cleavage portion 14 (solid line).

[0085] In addition, the wafer is, specifically, diced, lapped, and polished. However, care must be taken to minimize chipping of the waveguide facets.

[0086] The planar optical circuit 10 shown in FIG. 2 each includes a waveguide 9 having three branch portions 15, 16. Here, the three branch portions 15, 16 merge into a single branch portion 18 in the coupling region 17. As shown in the top view of FIG. 2, the waveguide 9 has a symmetry axis extending parallel to the intermediate branch portion 16. The branch portion 15 has a curved shape.

[0087] FIGS. 3A and 3B are diagrams showing the results of ellipsometry measurements of the waveguide layer 4, respectively. According to the parameters shown in Table 1, a waveguide layer 4 containing low Si - SiN under compressive stress showing the measured values in FIG. 3B was generated. A waveguide layer 4 consisting of SiN close to stoichiometry showing the measured values in FIG. 3A was generated according to other parameters. x from which x was generated.

[0088] FIGS. 3A and 3B show the refractive index n and the attenuation coefficient k depending on the wavelength λ, respectively. The waveguide layer 4 containing low Si - SiN under compressive stress has a refractive index curve N2 and an attenuation coefficient curve K2. SiN close to stoichiometry x from which xThe waveguide layer 4 consisting of has a refractive index curve N1 and an attenuation coefficient curve K1. Both the curves N2 and K2 show a steeper gradient than the curves N1 and K1. Further, the refractive index of the waveguide layer 4 containing low Si - SiN under compressive stress is lower than that of the waveguide layer 4 consisting of stoichiometric SiN x The attenuation coefficient of the waveguide layer 4 containing low Si - SiN under compressive stress is hardly recognized as compared with that of the waveguide layer 4 consisting of stoichiometric SiN x from. The refractive index of the waveguide layer 4 containing low Si - SiN under compressive stress is lower than that of the waveguide layer 4 consisting of stoichiometric SiN x from. The attenuation coefficient of the waveguide layer 4 containing low Si - SiN under compressive stress is hardly recognized as compared with that of the waveguide layer 4 consisting of stoichiometric SiN x from.

[0089] FIG. 4 is a diagram showing a plot of the estimated N / Si ratio against the measured refractive index of the waveguide layer 4 containing SiN x at 900 nm. The N / Si ratio can be estimated from the following equation.

Equation

[0090] Here, n Si is the reflectivity of the waveguide layer 4 made of Si, and n Si3N4 is the reflectivity of the waveguide layer 4 made of stoichiometric SiN x , that is, the waveguide layer 4 made of the layer Si3N4, and n waveguidelayer is the reflectivity of the waveguide layer 4 made of non - stoichiometric SiN x . Here, n Si = 3.610 and n Si3N3 = 2.018.

[0091] According to the plot shown in FIG. 4, the N / Si ratio of the waveguide layer 4 as shown in the graph of FIG. 3A is about 0.94. That is, this waveguide layer 4 is made of SiN with a composition close to stoichiometry x . The N / Si of the waveguide layer 4 as shown in the graph of FIG. 3B is about 1.29. That is, the waveguide layer 4 in FIG. 3B has low Si.

[0092] The SEM image shown in FIG. 5 shows an intermediate stage of the etching of the waveguide layer 4. The waveguide layer 4 is provided on a substrate 1 including a substrate layer 2 containing silicon and an intermediate layer 3 containing SiO2. The waveguide layer 4 contains low Si-SiN x and. The photostructurable layer 7 is disposed on the waveguide layer 4. The channel 8 extends into the waveguide layer 4. Specifically, the bottom surface of the channel 8 is formed in the waveguide layer 4. In other words, the waveguide layer 4 shown in FIG. 4 is not completely etched. The two channels 8 confine the waveguide 9.

[0093] FIG. 6 is a diagram showing a top-view SEM image of a process of a method for manufacturing a planar optical circuit 10. Here, the photostructurable mask 7 has not yet been removed. By etching the waveguide layer 4, the photostructurable mask 7 is polymerized on its surface. The polymerization residue 19 of the photostructurable mask 7 is difficult to remove with a solvent such as acetone.

[0094] FIG. 7 is a diagram showing a top-view SEM image of a planar optical circuit 10 according to an exemplary embodiment. The planar optical circuit 10 includes a waveguide layer 4 having channels 8. The channels 8 extend through the waveguide layer 4 and confine the waveguide 9. Here, the waveguide 9 includes three branch portions 15, 16 that merge with each other at a single branch portion 18 in the coupling region 17. Each of the branch portions 15, 16 is confined by the channel 8.

[0095] FIG. 8 is a diagram showing a cross-sectional SEM image of a planar optical circuit 10 according to an exemplary embodiment. The planar optical circuit 10 includes a substrate 1 having a substrate layer 2 and an intermediate layer 3. The substrate layer 2 contains or consists of silicon, and the intermediate layer 3 contains or consists of SiO2. The waveguide layer 4 is disposed in physical direct contact with the intermediate layer 3. Here, the waveguide layer 4 contains low Si-SiN xIt consists of. Channel 8 confines waveguide 9 within the waveguide layer 4. Waveguide 9 is formed from the same material as the surrounding waveguide layer 4. In cross-sectional view, waveguide 9 is rectangular. Two faces of waveguide 9 are directly adjacent to channel 8. The other faces of waveguide 9 are directly adjacent to the intermediate layer 3.

[0096] The structure of the planar optical circuit 10 shown in Fig. 9 is the same as that shown in Fig. 8. However, channel 8, and thus waveguide 9, has a different shape, particularly in cross-sectional view. Here, the side surface 21 of channel 8 is not perpendicular to the main extension plane of the planar optical circuit 10. In this example, the side surface 21 is slightly inclined. For this reason, channel 8 has a substantially trapezoidal shape in cross-sectional view.

[0097] The planar optical circuit 10 whose cross-section is shown in Fig. 10A includes a cladding 11 on the waveguide layer 4. In top view, it is preferable that the cladding 11 completely covers the waveguide layer 4. Channel 8 is partially filled by the cladding 11. Specifically, the planar optical circuit 10 shown in Fig. 10A is manufactured by the method described in conjunction with Figs. 1A - 1H.

[0098] Specifically, the planar optical circuit 10 shown in Fig. 10B is the same as that shown in Fig. 10A. The waveguide layer 4 is disposed on a substrate 1 including a substrate layer 2 and an intermediate layer 3. The waveguide layer 4 is in direct physical contact with the intermediate layer 3. The substrate 1 here includes a substrate layer 2 made of silicon and an intermediate layer 3 made of SiO2. The waveguide layer 4 contains low Si - SiN x or consists of low Si - SiN x

[0099] Channel 8 penetrates the waveguide layer 4, and waveguide 9 is formed in the waveguide layer 4. Waveguide 9 is confined by two channels 8. For this reason, in cross-sectional view, channel 8 in the waveguide layer 4 and waveguide 9 has a rectangular shape.

[0100] ​A cladding 11 is disposed on the waveguide layer 4. The cladding 11 is provided so as to partially fill the channel 8 in the waveguide layer 4. Here, the cladding 11 contains fluorine-doped SiO2 or consists of fluorine-doped SiO2. In a cross-sectional view, the waveguide 9 surrounded by the cladding 11 has a substantially trapezoidal shape with two rounded corners. This shape is like the shape of a toast.

[0101] The bottom surface and side surfaces of the channel 8 are covered by the cladding 11. The thickness of the cladding 11 at the bottom surface 20 of the channel 8 is smaller than the thickness at the upper surface 22 of the waveguide 9 on the side opposite to the substrate 1. The thickness of the cladding 11 on the side surface 21 of the channel 8 decreases toward the bottom surface 20 of the channel 8. In other words, the cladding 11 has an undercut in the region of the channel 8. Outside the channel 8 in the waveguide layer 4, the distance of the cladding 11 is smaller than that inside the channel 8.

[0102] FIG. 10C is an enlarged view showing the planar optical circuit 10 of FIG. 10B. Further, the thicknesses of the cladding 11 and the waveguide 9 are shown. In the cross-sectional view of FIG. 10C, the height of the waveguide 9 is larger than its width. Specifically, the height of the waveguide 9 is perpendicular to the main extension plane of the planar optical circuit 10, and its width is parallel to the main extension plane of the planar optical circuit 10. Here, the waveguide 9 has a height of about 3.37 micrometers and a width of about 2.76 micrometers.

[0103] The thickness of the cladding 11 at the bottom surface 20 of the channel 8 is smaller than the thickness at the upper surface 22 of the waveguide 9. Here, the thickness of the cladding 11 is about 1.08 micrometers at the bottom surface 20, and about 2.45 micrometers at the upper surface 22 of the waveguide 9. The thickness of the cladding 11 at the side surface 21 is about 844 nanometers in the region of the bottom surface 20 of the channel 8. The thickness at the side surface 21 increases until it reaches about 1.09 micrometers in the region of the upper surface 22 of the waveguide 9. The cladding 11 surrounding the waveguide 9 has a maximum width of about 5.48 micrometers in the region above the upper surface 22 of the waveguide 9. The distance between the cladding 11 on the waveguide 9 and the cladding 11 on the surrounding waveguide layer 4 is about 550 nanometers at the narrowest point.

[0104] FIG. 11 is a top view image of a planar optical circuit 10 according to an exemplary embodiment. The planar optical circuit 10 includes a waveguide 9 having three branching portions 15, 16. The three branching portions 15, 16 merge into a single branching portion 18 at a coupling region 17. The waveguide 9 has a symmetry axis parallel to the intermediate branching portion 16. Here, the symmetry axis is an axis of reflection. The intermediate branching portion 16 becomes a single branching portion 18 without bending. That is, the intermediate branching portion 16 and the single branching portion 18 are arranged on the same virtual line. That is, the starting point of the intermediate branching portion 16 and the end point and / or starting point of the single branching portion 18 are on the same line.

[0105] The branching portion 15 has a curved shape in the top view. For example, the branching portion 15 has a Bézier, sigmoid, or tangent function shape. In the top view, the path of the branching portion 15 includes at least one inflection point. The starting points of the two branching portions 15 are equidistant to the starting point of the intermediate branching portion 16.

[0106] The efficiency of the planar optical circuit 10 was measured using both a lens-coupled laser diode and a butt-coupled laser diode. The obtained results are shown in Table 10. In the measurement, a high NA microscope objective lens (NA = 0.85) was used.

[0107]

Table 10

[0108] When light was coupled into the intermediate branching portion 16 of the planar optical circuit 10 using a green edge-emitting laser diode, an efficiency of 0.45 was obtained.

[0109] FIG. 12 is a diagram showing a radiation emitting device 23 according to an exemplary embodiment. Here, the radiation emitting device 23 includes N laser diodes 24. The laser diodes 24 emit electromagnetic radiation of different wavelengths. The laser diodes 24 can be operated in continuous wave (CW), modulation, pulse (including an alternating pulse pattern). The radiation emitting device 23 further includes a planar optical circuit 10 used as a beam combiner. The planar optical circuit 10 includes a waveguide 9 having N branching portions 15, 16. The branching portions 15, 16 merge into a single branching portion 18 at the coupling region 17. The N - 1 branching portions 15 have a curved shape and the branching portion 16 has a linear shape. The radiation emitting device 23 is used, for example, as a device for spectroscopy.

[0110] In the case of inline or imaging spectroscopy using the radiation emitting device 23, the laser diodes 24 are switched on sequentially (not in a specific order) such that the desired wavelengths appear at the source port of the spectroscopy system and the detector detects the currently applied excitation wavelengths. Further, a more advanced approach may be adopted so that all the laser diodes 24 can be pulsed or modulated simultaneously. For example, an orthogonal pulse sequence such as a Hadamard orthogonal set is used for modulation. Alternatively, each laser diode 24 can be modulated at a different frequency and individually detected using a lock-in method or a down-conversion method.

[0111] The features and exemplary embodiments described in connection with the figures can be combined with each other according to further exemplary embodiments even if not all combinations are explicitly described. Further, the exemplary embodiments described in connection with the figures may have alternative or additional features as described in the general part.

[0112] Cross-reference to related applications This patent application claims priority to non-provisional U.S. patent application Ser. No. 17 / 835,141, the disclosure of which is incorporated herein by reference.

[0113] The present invention is not limited to the exemplary embodiments by the description based on the above-described exemplary embodiments. Rather, the present invention includes any new features and any combination of features, particularly any combination of features in the claims and any combination of features in the exemplary embodiments even if such a feature or such a combination itself is not explicitly specified in the claims or the exemplary embodiments.

Description of reference numerals

[0114] 1 Substrate 2 Substrate layer 3 Intermediate layer 4 Waveguide layer 5 Adhesive layer 6 Adhesion promoter 7 Photo-structurable mask 8 Channel 9 Waveguide 10 Planar optical circuit 11 Cladding 12, 13, 14 Cleavage part 15 Branch part 16 Intermediate branch part 17 Coupling region 18 Single branch part 19 Overlay residue 20 Bottom surface 21 Side surface 22 Top surface 23 Radiation emitting device 24 Laser diode N1, N2 Refractive index curves K1, K2 Attenuation coefficient curves R Ratio

Claims

1. A method for manufacturing a planar optical circuit (10), comprising: providing a substrate (1) without a light generation region; providing a waveguide layer (4); applying a photostructurable mask (7) to the waveguide layer (4); optically processing the photostructurable mask (7) to remove the photostructurable mask (7) in a plurality of regions; etching the waveguide layer (4) in the plurality of regions such that a plurality of channels (8) for confining a waveguide (9) are formed in the waveguide layer (4); removing the photostructurable mask (7); and singulating the planar optical circuit (10). A method for manufacturing a planar optical circuit (10).

2. The waveguide layer (4) is SiN ｘ , SiO ｘ N ｙ , GaN, HfO ２ , LiNbO ３ , Ta ２ O ５ , Nb ２ O ５ , HfO ２ , TiO ２ and is made of a material selected from Si, and mixtures thereof The method for manufacturing a planar optical circuit (10) according to Claim 1.

3. Before applying the photostructurable mask (7), providing an adhesive layer (5) on the waveguide layer (4). The method for manufacturing a planar optical circuit (10) according to Claim 1 or 2.

4. Before applying the photostructurable mask (7), applying an adhesion promoter (6) on the waveguide layer (4). The method for manufacturing a planar optical circuit (10) according to any one of Claims 1 to 3.

5. The waveguide layer (4) is provided by plasma chemical vapor deposition. The method for manufacturing a planar optical circuit (10) according to any one of Claims 1 to 4.

6. In the plasma chemical vapor deposition method, using a low-frequency plasma source. The method for manufacturing a planar optical circuit (10) according to Claim 5.

7. The waveguide layer (4) is etched by inductively coupled plasma etching. The method for manufacturing a planar optical circuit (10) according to any one of Claims 1 to 6.

8. Before etching the waveguide layer, cleaning the reaction chamber for inductively coupled plasma etching. The method for manufacturing a planar optical circuit (10) according to Claim 7.

9. After removing the photostructurable mask (7), providing a cladding (11) on the waveguide layer (4). The method for manufacturing a planar optical circuit (10) according to any one of Claims 1 to 8.

10. A substrate (1) without a light generation region; and a waveguide layer (4) on the substrate (1), wherein the waveguide layer (4) includes channels (8) for confining a waveguide (9). A planar optical circuit (10).

11. The waveguide (9) is a multimode waveguide. The planar optical circuit (10) according to Claim 10.

12. The substrate (1) contains or consists of a transparent or opaque inorganic substance selected from the group consisting of fused quartz, sapphire, YAG, MgF ２ , AlN, various glasses, and single crystal materials, The planar optical circuit (10) according to claim 10 or 11.

13. The substrate (1) is opaque, The substrate (1) includes an intermediate layer (3), The intermediate layer (3) is transparent, The planar optical circuit (10) according to any one of claims 10 to 12.

14. An adhesive layer (5) is disposed on the waveguide layer (4), The planar optical circuit (10) according to any one of claims 10 to 13.

15. A cladding (11) is disposed on the waveguide layer (4), The material of the cladding (11) has a refractive index lower than that of the material of the waveguide layer (4), The planar optical circuit (10) according to any one of claims 10 to 14.

16. The clad (11) is made of a material selected from the group consisting of SiO ２ , Al ２ O ３ , HfO ２ , and oxide glass. The planar optical circuit (10) according to claim 15.

17. The thickness of the waveguide layer (4) is at least 500 nanometers, The planar optical circuit (10) according to any one of claims 10 to 16.

18. The waveguide (9) includes at least two branch portions (15) that merge with each other into a single branch portion (18) in at least one coupling region (17) in a top view, The planar optical circuit (10) according to any one of claims 10 to 17.

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