JP2006235379A - Thermo-optical phase modulator and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermo-optical phase modulator of low power consumption whose clad thickness is not so thick and which can realize a desired response speed without the need for machining with a high aspect ratio, and its manufacturing method. <P>SOLUTION: The thermo-optical phase modulator which has a core in a clad layer deposited on a substrate and also has a thin-film heater arranged on an over-clad right above the core is characterized in that a portion of the clad layer which includes the heater and core is enclosed with a heat insulating groove to prevent heat from the heater from being dissipated and a portion of the clad layer enclosed with the heat insulating groove is formed in hollow structure apart from the substrate to reduce the area of contact between the portion including the heater and core and the substrate. In addition, the connection portion where the clad and substrate come into contact with each other to support the hollow structure is provided on one side apart from the heater and placed in an overhang state, and the the cross section of the connection portion is made smaller than the cross section of the other clad. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a thermo-optic phase modulator, which is an optical waveguide circuit used in the field of optical communication, and a manufacturing method thereof. More specifically, the present invention relates to a technique for realizing low power consumption in a thermo-optic phase modulator using a thermo-optic effect.

  Thermo-optic phase modulators using planar optical circuit technology are key devices (main elements) in the broadband optical communication field using, for example, wavelength division multiplexing technology. In this thermo-optic phase modulator, the phase of the light is controlled by applying power to the thin film heater on the top of the waveguide to raise the temperature of the core. As the temperature of the core rises due to heating from the heater, the refractive index of the core increases, and the optical path length increases corresponding to the amount of change and the length of the refractive index, so that the phase of the output light at the exit end Is modulated.

  A typical application of a thermo-optic phase modulator using this planar optical circuit technology is in an optical switch. Light incident on the waveguide is branched by a 3 dB optical coupler, connected to a thermo-optic phase modulator provided with a heater on at least one of the branched waveguides, and output light from the thermo-optic phase modulator and the other branch An optical switch is realized by combining light with an optical coupler again. The phase difference corresponding to the half wavelength of the wavelength to be used while being branched is given to the signal light by the thermo-optic phase modulator, thereby switching the light at the output end of the circuit.

  The problem to be solved by the thermo-optic phase modulator using this planar optical circuit technology is power consumption. The power consumed by one thermo-optic phase modulator is about 450 mW in the conventional typical structure. If such a conventional thermo-optic phase modulator is used to realize a large-scale switch of 1 × 32, 16 × 16, etc., the power consumption of the entire circuit becomes very large. Thus, various approaches have been considered so far in order to reduce the power consumption of the thermo-optic phase modulator.

  As one of the approaches, it is known to form heat insulating grooves 409 and 409 on both sides of a thin film heater 407 as shown in FIG. 12A (Non-patent Document 1). The heat insulating grooves 409 and 409 prevent the heat applied from the thin film heater 407 from diffusing in the horizontal direction of the substrate 401 through the cladding around the core 405 and preventing power from being effectively consumed for the temperature rise of the core 405. There is work. According to Non-Patent Document 1, as the width of the ridge (ridge line, ridge line) delimited by the heat insulating grooves 409 and 409 becomes thinner, the power consumption becomes smaller, and a phase modulator corresponding to a half wavelength at 45 mW is realized. . Further, Non-Patent Document 1 shows that by reducing the ridge width, only the power consumption is reduced and the response speed is not deteriorated.

  In order to further reduce power consumption for further large-scale integration, it is effective to form the heat insulating grooves 409 and 409 and increase the distance between the substrate 401 and the core 405 having higher thermal conductivity than the underclad. It is known. This is because it is necessary to prevent the heat applied by the thin film heater 407 from escaping to the substrate 401 having a high thermal conductivity. Therefore, it is useful to increase the thickness of the undercladding and increase the distance between the core 405 and the substrate.

  Further, as a method of reducing power consumption, a thermo-optic phase modulator and a substrate provided with a heater 407 are removed by removing a portion of the clad or the substrate 401 below the core 405 as shown in FIG. Non-Patent Document 2 proposes a method of blocking the diffusion of heat to the substrate 401 by providing a gap 411 made of air between the substrate 401 and the substrate 401. The effect of the air gap 411 is ideally equivalent to the effect of the infinite thickness of the undercladding, and has a structure that can almost completely block the diffusion of heat to the substrate 401, and can reduce power consumption. Is expensive.

S.Sohma et al., “Low switching power silica-based super high data thermo-opticswitch with heat insulating grooves,” Electronics Lett., VOl.38, No.3, pp.88-89, January 2002 A. Sugita et al., “Bridge-suspended silica-waveguide thermo-optic phase shifterand its application to Mach-Zehnder type optical switch,” Trans. IEICE, Vol.E73, No.1, pp.105-109, January 1990

  In order to further reduce the power consumption according to the method presented so far (Non-Patent Document 1), it is necessary to make the ridge width defined by the heat insulating grooves 409 and 409 as narrow as possible and to increase the thickness of the underclad that forms the ridge. There is.

  However, if the undercladding is made too thick, not only does it take a long time to deposit the undercladding, but also warpage of the substrate 409 increases, which hinders subsequent processes such as photolithography, which is a process after the deposition. . In addition, it takes time to form the heat insulating grooves 409 and 409, and the burden on the machining process increases. Furthermore, a thick clad layer can cause cracks in the clad due to stress.

  Even if the undercladding can be made thick, processing with a high aspect ratio is required to narrow the ridge width defined by the heat insulating grooves 409 and 409 and form the heat insulating grooves 409 and 409 up to the substrate 401. For example, in order to achieve a ridge width of 20 μm and a power consumption that is half of the power consumption (45 mW) shown in Non-Patent Document 1, it is necessary to form the heat insulating grooves 409 and 409 in a clad having a thickness of approximately 140 μm. There is. Therefore, processing with an aspect ratio of 7 or more is required. In processing with an aspect ratio of 7 or more, it is difficult to control the pattern shift when forming the heat insulating grooves, not only reducing the yield, but also the in-plane distribution of the film thickness in the wafer, the in-plane distribution of etching, the heater, etc. Due to manufacturing errors such as alignment accuracy at the time of formation, it is difficult to make the power consumption of the thermo-optic phase modulator in the wafer constant.

  Furthermore, in the structure as shown in FIG. 12B in which a gap 411 made of air is provided between the lower clad of the heater 407 of the thermo-optic phase modulator proposed in Non-Patent Document 2 and the substrate 401, Since the heat insulation effect by the air layer is high, the effect of reducing the power consumption is large, and it can be understood that the power applied to the heater can be efficiently used to raise the temperature of the core. However, on the other hand, heat that is no longer necessary cannot be efficiently released to the substrate 401 side, resulting in extreme deterioration of response speed. In the conventional thermo-optic phase modulator using the planar optical circuit technology, the response speed is about 3 msec. In the structure of FIG. 12B, the response speed is about 50 msec, which is a single digit. The response speed also decreases as described above, and when the core and clad below the heater are completely cut off from the substrate 401 by the gap 411, the response speed may be 100 msec or more. Thus, although the thermo-optic phase modulator proposed in Non-Patent Document 2 can reduce power consumption, there is a problem that a practical response speed cannot be obtained.

  In order to achieve a practical response speed even at the expense of some reduction in power consumption, a space 411 is provided between the substrate or the lower layer of the heater with the substrate or the substrate 401 removed as described above. Instead, the substrate 401 or a portion of the cladding under the heater is left without being completely removed, and the cladding under the heater and the substrate 401 are connected with the remaining very narrow connecting portion. ing. FIG. 12C shows a structure in which a part of the clad is narrowed to form a connecting portion 413, and FIG. 12D shows a structure in which the upper portion of the Si substrate 401 is partially removed and a remaining portion is connected to the connecting portion 414. The structure is shown. The thermal resistance between the heater 407 and the substrate 401 is controlled by the remaining width of the connecting portions 413 and 414 to control power consumption and response time.

  Since the processing process for removing a part of the substrate 401 or the cladding under the heater is a processing process in the horizontal direction of the substrate, it is usually performed by isotropic dry etching or wet etching. However, in these processes, since the method for monitoring the progress of etching is scarce, it is very difficult to control the widths of the connecting portions 413 and 414. Therefore, in the structure in which the connecting portions 413 and 414 are provided in the gap portion made of air between the clad under the heater of the thermo-optic phase modulator provided with the heater 407 and the substrate 401, the connecting portions 413 and 413 are provided. The power consumption varies greatly depending on the width of 414, and there is a problem that a thermo-optic phase modulator cannot be manufactured stably and with a high yield.

  The present invention has been made in view of the above-mentioned problems, and its purpose is not to make the cladding deposited on the substrate so thick (as a result, the substrate warpage is small), and processing with a high aspect ratio is required. The object is to provide a thermo-optic phase modulator using a planar optical circuit technology with low power consumption capable of realizing a desired response speed, and a method for manufacturing the same.

  In order to achieve the above object, a thermo-optic phase modulator according to the present invention includes a clad layer deposited on a substrate, a core formed in the clad layer and having a higher refractive index than the clad layer, The thin film heater formed on the cladding layer, the first heat insulating groove formed in the cladding layer in the vicinity of the thin film heater, and the side having the first heat insulating groove across the thin film heater The clad extending in the same direction as the substrate surface, sandwiched between the second heat insulation groove and the second heat insulation groove formed in the clad layer away from the thin film heater in a direction A space that separates the layer from the substrate, and terminates the space adjacent to the second heat insulation groove, and is sandwiched between the first heat insulation groove and the second heat insulation groove to be the same as the substrate surface A substrate connecting portion for connecting the cladding layers extending in the direction; Characterized in that it has.

  Here, a distance between the substrate connecting portion and the thin film heater may be longer than a distance between the thin film heater and the substrate.

  In addition, the thickness of at least a part of the cladding layer including the upper part of the substrate connecting portion and sandwiched between the first heat insulating groove and the second heat insulating groove and extending in the same direction as the substrate surface is the core. It can be characterized by being thinner than the surrounding cladding layer.

  In addition, the second heat insulating groove on the substrate connecting part side may have a U shape or an inverted U shape.

  The length of the substrate connecting portion in the direction parallel to the waveguide may be shorter than the length of the cladding layer in the vicinity of the thin film heater in the direction parallel to the waveguide.

  The clad layer sandwiched between the first heat insulation grooves and the second heat insulation grooves and extending in the same direction as the substrate surface has an arrangement shape in which trapezoidal shapes are connected in multiple stages. be able to.

  The substrate may be an SOI substrate having an SOI layer.

  In order to achieve the above object, a manufacturing method of a thermo-optic phase modulator according to the present invention includes a cladding layer deposited on a substrate, a core formed in the cladding layer and having a higher refractive index than the cladding layer, In a manufacturing method of a thermo-optic phase modulator having a thin film heater formed on the clad layer above the core and a pair of heat insulating grooves respectively formed in the clad layers on both sides of the thin film heater, a substrate connecting portion later Removing the SOI layer on the substrate at the location, and depositing an underclad layer and a core layer on the substrate from which the location of the SOI layer has been removed, processing the core from the core layer, and overcoating the core A step of embedding in the clad, a step of forming the pair of heat insulation grooves, and selectively removing the SOI layer exposed by the heat insulation grooves, thereby sandwiching the pair of heat insulation grooves to form the substrate surface A step of isolating the clad layer extending in the same direction and the substrate, and simultaneously forming the substrate connecting portion that terminates the space and connects the substrate and the clad layer. .

  Here, the method may include a step of removing at least a part of the cladding layer extending in the same direction as the substrate surface including the upper portion of the substrate connecting portion.

  In addition, the step of removing the SOI layer on the substrate at the location that becomes the substrate connecting portion may be characterized by forming a groove that serves as an etching stopper when performing isotropic etching at the same time.

  Further, the groove serving as an etching stopper when the isotropic etching is performed may be filled with glass simultaneously in the step of depositing the under cladding.

  In the present invention, as described above, a part of the clad layer surrounded by the heat insulating groove is formed as a hollow structure separated from the substrate, and a substrate connecting portion supporting the hollow structure is provided on one side away from the heater, whereby the heat insulating groove is formed. It is characterized in that the entire cross section of the clad layer surrounded by is shaped like a cantilever (or overhang). With this characteristic configuration, the present invention has an effect that the thermal resistance between the substrate and the heater, which has been very difficult with the conventional structure, can be accurately adjusted using a planar processing process widely used in the semiconductor industry. It is done. Therefore, according to the present invention, the thickness of the clad deposited on the substrate is not so thick, and a low power consumption thermo-optic phase modulator capable of realizing a desired response speed without requiring a high aspect ratio processing is realized. it can.

  In addition, according to the present invention, the thermal resistance can be easily adjusted with high accuracy as described above, so that a small-sized thermo-optic phase modulator with low power consumption can be manufactured with high yield.

  Furthermore, by using the manufacturing method of the present invention, when performing processing in the horizontal direction of the substrate using isotropic etching, which has conventionally been difficult to control, processing can be performed with high accuracy. As a result, according to the present invention, it is possible to easily manufacture a thermo-optic phase modulator with high yield and uniform power consumption.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
1A is a bird's-eye view (perspective view) showing a configuration of a thermo-optic phase modulator according to the first embodiment of the present invention, and FIG. 1B is a view in FIG. A cross-sectional structure taken along the line AA ′ is shown. 2A to 2H are cross-sectional views taken along the line AA ′ of FIG. 1A in the order of the manufacturing method of the thermo-optic phase modulator according to this embodiment (on the right side of the drawing). ) And a top view (left of the drawing).

  In this embodiment, as shown in FIGS. 1A and 1B, a thin film heater 107 is formed on the overclad just above the core 105 formed in the clad layer 103 deposited on the substrate 101. The first heat insulating groove 109 is formed in the vicinity of the core 105, and the second heat insulating groove 115 is formed at an opposite position relatively far from the core 105. Then, the lower part of the clad layer 103 surrounded by the both heat insulating grooves 109 and 115 that is in contact with the substrate 101 is removed leaving the portion of the substrate connecting part 113, thereby comparing the air layer that isolates the clad layer 103 and the substrate 101. A wide gap 111 is formed. The substrate connecting portion 113 that supports the hollow structure composed of the gap 111 is formed in contact with the second heat insulating groove 115 away from the heater 107, whereby the entire cladding layer 103 surrounded by both heat insulating grooves 109, 115 is formed. The cross-sectional shape is a cantilever shape (or overhang shape). More simply, the ridge shape that extends perpendicularly to the conventional substrate 101 and is partitioned by the heat insulating grooves 109 and 115 is a cross-sectional structure that is bent in the horizontal direction by a clad below the core 105.

Such a structure can be easily manufactured by a process as shown in FIG. In this embodiment, an SOI substrate (silicon on insulating substrate) is used as the substrate 101. There is 3 μm of SiO ₂ on the Si serving as the substrate 101 (this layer is called a BOX layer 201), and there is a 3 μm single crystal Si layer on this (this layer is called an SOI layer 203), and a thin natural layer A substrate on which an oxide film is formed. However, the thickness of each layer is not limited to this. In this example, a commercially available SOI substrate is used. After depositing a glass layer corresponding to the BOX layer 201 on the substrate 101, an Si layer (amorphous Si, polycrystalline Si, etc.) corresponding to the SOI layer 203 is used. The substrate is not limited to the SOI substrate as long as the substrate includes a BOX layer or a layer of a substance having a large selection ratio when etched with the glass used for the cladding. Hereafter, the process of an Example is demonstrated.

  As step 1, first, the oxide film on the surface of the substrate was removed using a 5% hydrofluoric acid aqueous solution.

  Next, as step 2, the resist layer is applied to the portion 205 to be the substrate connecting portion later and the portion 205 to be the etching stopper, a resist is applied, and patterning is performed using a normal photolithography technique, and then ICP (induction) is performed. It was removed using a coupled plasma) etcher. At this time, the BOX layer 201 of the SOI substrate functions as an etching stop layer in the film thickness direction. Later, the SOI layer 203 having a width of 40 μm and a length of 2.2 mm as a bottom portion of the substrate connecting portion and the heat insulation groove and a width of 1.5 μm and a length of 2.2 mm as an etching stopper were previously removed. This etching only needs to remove the SOI layer 203 at a desired location, and a simple method such as wet etching or isotropic dry etching may be used.

  Next, as step 3, on the substrate on which etching of the desired SOI layer 203 was completed, the undercladding 209 and the glass serving as the core were deposited by a flame deposition method on the surface on which the SOI layer etching was performed, and transparency was performed. The thickness of the deposited underclad 209 was 10 μm, and the thickness of the core layer 211 was 4.5 μm. The relative refractive index difference of the core layer 211 was 1.5%.

Here, the flame deposition method is a method in which a chloride film such as SiCl ₄ is burned in an oxyhydrogen flame to form a glass film on the substrate at high speed, and is suitable for depositing a relatively thick film. In addition, since it has excellent embedding characteristics, it is a widely used method for manufacturing optical waveguides. Immediately after the deposition, since it is a collection of fine particles, white is shown due to the scattering of visible light, but a transparent film can be obtained by performing heat treatment. In general, in order to lower the transparent temperature, for example, glass to which an appropriate amount of P ₂ O ₅ , B ₂ O ₃ or the like is added is deposited, and GeO ₂ or the like is added to the core layer 211 in order to increase the refractive index.

  Further, in step 2 described above, the portion 205 where the gap Si is removed as the portion 205 to be the substrate connecting portion later and the portion 205 to be the etching stopper has a step (approximately 3 μm) corresponding to the thickness of the SOI layer 203. However, the surface level difference after glass deposition using the flame deposition method was only about 0.3 μm. Such a level difference does not cause any trouble in the subsequent processes, and does not cause a loss even if the waveguide crosses the portion.

  When the substrate 101 having a relatively thick SOI layer 203 of about 8 μm is used, a step of about 1 μm may occur on the surface of the glass layer deposited on the step. When a waveguide is formed on this, it may cause a loss. In such a case, the SOI layer 203 below the core is not removed in step 2, and etching is performed with a pattern as shown in FIG. It becomes possible to produce without generating.

  FIG. 3B shows a top view of the final shape. A portion indicated by an arc forms an arc shape by isotropic etching. Although this arc portion is difficult to control, there is no problem because it is located away from the heater 107. (For the heater 107 having a length of about 2 mm, the radius of the arc is about 100 μm.)

  Next, as step 4, the substrate 101 deposited up to the core layer 211 was processed into a desired waveguide circuit using a normal photolithography technique.

  Next, in step 5, the width of the core 105 was set to 5 μm so as to be a single mode waveguide. The core 105 was again embedded with a glass 213 having a thickness of 15 μm by using a flame deposition method.

  Thereafter, as step 6, heat insulating grooves 109 and 115 were formed at predetermined positions. At this time, the positions where the heat insulating grooves 109 and 115 are formed are slightly inside the etching stopper 215 provided in advance (on the side of the SOI layer to be removed later) in order to prevent the SOI layer 203 other than the SOI layer to be removed later from being etched. ).

  FIG. 4 shows an enlarged view of the etching stopper 215. The hatched portion in the figure indicates the location where the etching gas flows. By isolating the SOI layer 203 that does not need to be etched from the etching gas using the glass of the etching stopper 215, Si that does not need to be removed can be protected from the etching gas. By preventing the removal of the extra SOI layer, the mechanical strength can be maintained, and furthermore, the area occupied by the circuit board can be reduced as much as possible, which results in lowering the cost of the optical circuit.

  Further, at a location where the substrate connecting portion 113 is to be formed later, glass remains between the location where the SOI layer 203 has been removed in advance and the SOI layer 203 where the SOI layer 203 has not been removed, and the heat insulating groove 109 is located at a location where the etching stopper 215 is formed in the substrate horizontal direction. 115 are formed. In this embodiment, the case where a part of the Si removed portion as the substrate connecting portion 113 is used as the etching stopper 215 is shown. However, the present invention is not limited to this, and the etching stopper may be provided at another location. Good. FIG. 4 shows a cross-sectional view in a direction perpendicular to the waveguide through which light propagates. However, by providing this etching stopper 215 also in a direction parallel to the waveguide, unnecessary etching removal of the SOI layer 203 is performed. It is possible to prevent. When the step becomes a problem, the etching stopper 215 is not provided at a position located under the waveguide, and thus an arc as shown in FIG.

Next, in step 7, isotropic dry etching using SF ₆ as an etching gas is performed in a state where a part of the SOI layer 203 to be removed is exposed, and the SOI layer 203 is selectively removed, whereby the cladding 103. A space 111 was formed between the substrate 101 and the substrate 101. The selection ratio between glass and Si by SF ₆ is very large (> ˜70), and the cladding layer 103 is hardly affected by this etching.

  When the etching reaches the previously formed substrate connecting portion 113 and the etching stopper 215, the etching is stopped. Therefore, the area where the substrate 102 and the clad 103 are connected can be made the same at all locations in the wafer. The width of the connecting portion 113 formed by etching was 10 μm. The distance in the horizontal direction of the substrate between the center 113 of the connecting portion and the heater 107 was 100 μm.

  Finally, as step 8 of the final process, a heater 107 was formed of Cr over the Au electrode (not shown) and the core 105. The heater 107 has a width of 15 μm, a length of 2.0 mm, and a thickness of 0.5 μm. In the present embodiment, the wiring (not shown) and the heater 107 are manufactured after the processing steps of the heat insulating grooves 109 and 115. However, the same is true if a metal process is performed before the heat insulating grooves 109 and 115 are formed. Further, the metal to be used is not limited to Au / Cr, and is not limited to Au / Cr as long as it is a substance that can exhibit an equivalent function as the wiring and heater 107.

  The operation of the thermo-optic phase modulator manufactured by the process described above will be described. The distance in the substrate horizontal direction between the center of the connecting portion 113 of the manufactured thermo-optic phase modulator and the center of the heater 107 is 100 μm. The thickness of the cladding portion of the thermo-optic phase modulator is 25 μm, including the under cladding 209 and the over cladding 213. A conventional thermo-optic phase modulator corresponding to this has a clad thickness of 25 μm and a depth of 120 μm or more (including the thickness of the over clad 213) of the ridge portion partitioned by the heat insulating grooves 109 and 115. .

  For comparison, FIG. 5A shows a simulation result of a temperature gradient when power necessary for applying a phase change corresponding to a half wavelength is applied to the heater 407 in the conventional structure. Assuming that the substrate 401 is kept at room temperature, a boundary condition is given and calculation is performed. FIG. 5B shows the simulation result of the temperature gradient when the power necessary to give the phase change corresponding to the half wavelength is applied to the heater 107 in the structure of the first embodiment according to the present invention. Yes. The substrate 101 is assumed to be kept at room temperature, and the calculation is performed by giving boundary conditions. According to the results of these calculations, it was found that the conventional structure shown in FIG. 5A requires 25 mW of power to give the phase modulation corresponding to the half wavelength. Moreover, in the structure of this embodiment of (B) of FIG. 5, it turned out that the electric power of 18 mW which is less than that is sufficient. Therefore, according to the structure of this embodiment, a power reduction of about 30% is expected compared to the conventional structure.

  Although the structure of the present embodiment and the conventional structure have the same substrate-heater distance, the power of the structure of the present embodiment is significantly smaller than the power predicted by the conventional structure as described above. As shown in FIG. 5, in the structure of this embodiment, the cross-sectional area of the substrate bonding portion 113 is smaller than the cross-sectional area of the other cladding 103 that is continuous (that is, the width of the substrate bonding portion 113 is narrow). This is because the thermal resistance at the location of the substrate joint 113 is increased.

  In the conventional method, in order to increase the thermal resistance between the heater 407 and the substrate 401, a part of the ridge portion delimited by the heat insulating grooves 409 and 409 is narrowed (a structure as shown in FIG. 12C). The machining process was complicated and difficult to implement. For example, even if a part of the ridge portion can be narrowed, the controllability of the width of the ridge portion is lacking, and the power consumption within the wafer surface tends to vary. In contrast, in the structure of this embodiment, it is possible to easily adjust the substrate bonding area at the time of design, and by adjusting the thermal resistance, it is possible to easily produce a thermo-optic phase modulator with desired power consumption. There are advantages you can do.

  Based on the previous prediction, in order to actually compare the performance of the structure of this embodiment, an attempt was made to produce a thermo-optic phase modulator having a conventional structure with the dimensions described above. However, when a glass was formed and heat treatment was performed, cracks occurred and a circuit could not be produced. By depositing a thick underclad (approximately 90 μm), it is considered that a crack was applied due to stress due to the difference in thermal expansion coefficient from the substrate 401.

  In addition, when the electric power giving a phase difference corresponding to the half wavelength of the thermo-optic phase modulator manufactured according to the present embodiment was measured, it was 20 mW. A thermo-optic phase modulator with almost expected power consumption could be obtained.

  Conventionally, in order to reduce the power consumption, a structure in which the width of the ridge portion delimited by the heat insulating grooves 409 and 409 is narrowed and the undercladding is made thick to deposit the undercladding thickly, In addition, according to the present embodiment, the processing time required for forming the deep heat insulating grooves 409 and 409 can be greatly reduced. Further, according to the present embodiment, the problem of crack generation that tends to occur when the underclad is deposited thick can be avoided. Furthermore, according to the present embodiment, processing with a high aspect ratio, which is very difficult, can be avoided, and the yield can be improved. In addition, according to the present embodiment, it is difficult to manufacture with the conventional structure, and it is possible to increase the thermal resistance by narrowing a part between the substrate and the heater. It is possible to fabricate the wafer easily and with good uniformity within the wafer simply by changing the area, and the yield can be dramatically improved.

(Second Embodiment)
6A is a bird's-eye view showing a thermo-optic phase modulator according to the second embodiment of the present invention, and FIG. 6B is a cutting line AA ′ in FIG. The cross-sectional structure of is shown. In this embodiment, a structure in which power consumption is further reduced from the structure shown in the first embodiment will be described.

  As shown in FIG. 6B, the thermo-optic phase modulator according to the present embodiment further includes a clad that is parallel to the substrate 101 and further includes the upper portion of the substrate connecting portion 113 from the structure shown in the first embodiment. In this structure, at least a part of 103 is removed in the thickness direction. In the example shown in the figure, the cladding portion excluding the vicinity of the heater 107, the entire over cladding 213 above the substrate connecting portion 113, and a part of the under cladding 209 are cut off.

  Such a structure can be manufactured as follows. 2 can be produced by replacing the step 6 in FIG. 2 shown in the first embodiment with two steps, step 6-1 and step 6-2 shown in FIG.

  First, the upper portion of the substrate connecting portion 113 and a portion that becomes a clad parallel to the substrate 101 are etched in advance until a desired remaining thickness is obtained (step 6-1). Thereafter, the mask is again applied with a resist or the like, and only the portions to be the heat insulating grooves 109 and 115 are etched to the substrate 101 or the BOX layer 201 serving as a stop layer, thereby forming the heat insulating grooves 109 and 115. Subsequent steps 7 and 8 are the same as those in the first embodiment.

  In this embodiment, in Step 6-1, at least a part of the clad that is parallel to the substrate 101 including the upper portion of the substrate connecting portion 113 is etched thin, and at the same time, the portions of the heat insulating grooves 109 and 115 are also etched. . By doing so, since the etching amount at the time of forming the heat insulation grooves 109 and 115 in the next step 6-2 can be reduced, the process time can be shortened. Of course, the etching may be performed separately.

  Next, the effect of thinning the substrate 103 including the upper part of the substrate connecting portion 113 and the clad 103 that is horizontal will be described. FIG. 8 shows the relationship between the power consumption of the clad portion normalized by the power consumption when the thickness of the substrate 101 including the upper part of the substrate connecting portion 113 and the horizontal clad portion 103 is 25 μm and the power consumption. Results are shown. The thickness of the cladding is 25 μm based on the structure of the first embodiment.

  According to the graph of FIG. 8, it can be seen that the thickness of the clad portion is reduced and the power consumption is reduced. By reducing the thickness of the cladding part to 5 μm, it is expected that the power consumption will be reduced to about 30% compared to when the thickness is 25 μm. Considering that the power consumption required for the thermo-optic phase modulator manufactured with the structure of the first embodiment shown in FIG. 1 to give a phase difference corresponding to a half wavelength is 20 mW, the second The power consumption of this embodiment corresponds to a power consumption of about 7 mW.

  The reduction in the power consumption obtained in the second embodiment increases the thermal resistance between the substrate 101 and the heater 107 at a location where the cladding portion is thinned, so that a phase change can be given with less power. Because.

On the other hand, in the conventional structure as shown in FIG. 12, the thermal resistance between the substrate 401 and the heater 407 is similarly increased by narrowing a part of the clad (or substrate 401) closer to the substrate 401 than the core 405. Then, the processing difficulty that etching must be performed in the horizontal direction of the substrate occurs. Specifically, a part of the composition of the clad 403 (or substrate 401) may be changed, and the clad (or substrate) may be partially thinned due to a difference in etching rate. For example, a layer to which an additive (P ₂ O ₅ or the like) is added is prepared between the substrate 401 and a normal clad, soaked in an appropriate etching solution, and a specific location is determined from the difference in etching rate between the clad and the additive layer. It can be considered that the clad is narrowed ((C) in FIG. 12). Further, the Si substrate 401 is removed from the portions exposed from the heat insulating grooves 409, 409 by isotropic etching, and Si is removed from the substrate, and the etching is stopped while leaving the thickness of a predetermined bonding portion, so that the substrate is partially removed. There is a method of increasing the thermal resistance between 401 and the heater 407 ((D) of FIG. 12). As shown in FIG. 12B of the conventional example, the accuracy is not necessary to completely leave the gap 411, but the accuracy is not removed because of the problem that the response time is too slow as described above. There is a need to leave well.

  However, in these conventional methods, it is very difficult to narrow a desired portion with a fixed width, regardless of whether the gap 411 is completely opened between the substrate 401 and the clad. This is because these processes are performed in the horizontal direction of the substrate 401. Therefore, there is no appropriate method for monitoring how much etching should be performed in the middle of the etching, and in many cases, only the etching time obtained from the condition determination is used. This is because it becomes control.

  When a part of the clad 403 (or the substrate 401) is narrowed by a conventional method, the unevenness (unevenness) in processing due to etching is largely reflected in the power consumption unevenness of the thermo-optic phase modulator in the wafer, which becomes a problem. For example, in FIG. 8, when the thickness varies by 2.5 μm, a change of about 10% in power is observed. That is, the power consumption greatly increases and decreases due to the difference in the thickness of the narrowed portion. Therefore, using a conventional structure or a conventional processing method makes it difficult to manufacture a product with constant power consumption with a high yield.

  On the other hand, in the structure shown in the second embodiment of the present invention, the thickness of the clad including the upper portion of the substrate connecting portion 113 and the substrate parallel to the substrate can be accurately controlled. That is, according to this embodiment, it is possible to manufacture a thermo-optic phase modulator with a constant power consumption with a high yield. This is because, in the semiconductor process technology that is generally widely used, the processing accuracy in the thickness direction (substrate vertical direction) that is implemented in this embodiment is the lateral direction (substrate that is required in the prior art). This is because the accuracy is much higher than the processing accuracy in the horizontal direction). The processing in the film thickness direction performed in the present embodiment can be performed while always monitoring the processed film thickness or the residual film thickness with high accuracy during the etching. Many high-accuracy etching film thickness monitors such as a film thickness monitor using interference by a monochromatic laser beam and an interference film thickness monitor using a white light source are commercially available.

  As described above, it was difficult to adjust the thermal resistance by narrowing a portion of the clad (or substrate) between the core and the substrate of the ridge section separated by the conventional heat insulating grooves in the horizontal direction of the substrate. In this embodiment, the problem can be solved by replacing the processing in the thickness direction (vertical direction of the substrate). As a result, according to the present embodiment, it is possible to control the thermal resistance with high yield, that is, power consumption with high yield.

(Third embodiment)
FIG. 9A is a bird's-eye view showing the configuration of the thermo-optic phase modulator according to the third embodiment of the present invention. FIG. 9B is a top view of FIG. (C) shows a cross-sectional structure taken along a cutting line AA ′ in FIG. In this embodiment, a structure in which power consumption is further reduced from the structure shown in the second embodiment will be described.

  As shown in FIGS. 9A to 9C, the thermo-optic phase modulator according to this embodiment includes a substrate 101 including an upper portion of the substrate connecting portion 113 in addition to the structure shown in the second embodiment. At least a part of the horizontal clad 103 is removed so that the clad 103 becomes gradually thinner toward the substrate connecting portion 113 when viewed from above. In the configuration example of FIG. 9, the clad 103 sandwiched between the two heat insulating grooves 109 and 115 is processed into a trapezoidal shape as viewed from above. As a result, the area of the heat insulating groove 115 on the substrate connecting portion 113 side is larger than that of the second embodiment, but the shape of the heat insulating groove 115 is not limited to this.

  Of course, the trapezoidal structure of the present embodiment can be applied to the structure shown in the first embodiment to obtain the effect. Even if the structure is not thinned gradually, the effect can be obtained as long as at least a part is thinned.

  Further, in FIG. 9, the heater 107 portion is shown with a shortened length for easy understanding. In an actual circuit, the heater 107 has a length of about 2 to 3 mm, so that the trapezoidal structure is arranged in multiples as shown in FIG.

  Such a structure proposed in this embodiment can be manufactured by the same manufacturing method as described in the first embodiment and the second embodiment. When the heat insulation grooves 109 and 115 are formed, the structure of this embodiment is obtained by patterning and etching after resist application so as to become gradually thinner from the vicinity of the core 105 toward the substrate connecting portion 113. It is only necessary to change the shape of the mask used for the production at the time of designing, and there is no increase in the number of steps from the first embodiment and the second embodiment.

  As described above, the length of the substrate connecting portion 113 in the direction parallel to the waveguide is made shorter than the length of the clad layer 103 in the vicinity of the heater 107 (at least a part thereof is shortened). The resistance can be increased. As a result, power consumption can be further reduced.

  On the other hand, in the conventional structure shown in FIGS. 12C and 12D, a constriction (or substrate) is provided in part of the cladding (or substrate) in the direction perpendicular to the guided light traveling direction to increase the thermal resistance. The process could be difficult but possible. However, it can be said that it is almost impossible to provide a structure that increases the thermal resistance in the direction parallel to the guided light traveling direction as shown in this embodiment.

  As shown in FIG. 10, when the structure of this embodiment is arranged in multiples, the larger the number of trapezoids constituting the multiples, the smaller the circuit, which is desirable. The trapezoidal structure of the present embodiment is a structure in which the distance between the heater 107 through which heat flows and the substrate 101 changes depending on the waveguide direction, so that it is not a uniform overheating with a temperature distribution on the waveguide. . However, since the thermo-optic phase modulator originally only changes the phase, the problem is how much the optical path length can be changed in the entire modulator, and the temperature distribution during that time does not matter.

  When an optical switch is configured with the structure shown in the first and second embodiments, the circuit may be increased in some cases. FIGS. 11A and 11B show the structure of an optical switch having two 3 dB couplers 301 and two thermo-optic phase modulators. FIG. 11A shows a case where the structure of the first embodiment or the second embodiment is used. Even this will work as a sufficient circuit and low power consumption can be expected. Usually, the arm interval (the distance indicated by the arrow in the figure) of the optical switch in the figure is determined by the relative refractive index difference of the waveguide core 303 to be used and the waveguide bending radius. However, if the distance between the heater 107 and the board connecting portion 113 is too long in order to obtain a desired power consumption, the arm interval is determined by the distance, and the entire circuit becomes inappropriately large. Think about it. In particular, when the refractive index of the core 105 is sufficiently larger than that of the clad 103, the required distance between the heater 107 and the substrate connecting portion 113, although the size of the circuit itself can be considerably reduced. Therefore, it may be necessary to increase the size inappropriately.

  On the other hand, as shown in FIG. 11B, when the structure of this embodiment is used, if the thermal resistance can be adjusted by adjusting the area of the board connecting portion 113, the heater 107 and the board connecting portion. Even if the distance between 113 is not so long, a desired thermal resistance can be realized. As a result, the entire circuit can be reduced.

(Other embodiments)
In the above, the preferred embodiment of the present invention has been described by way of example. However, the embodiment of the present invention is not limited to the above-described example, and the constituent members thereof are within the scope of the claims. Various modifications such as replacement, change, addition, increase / decrease in number, change in shape design, etc. are all included in the embodiments of the present invention.

As described above, the present invention provides a low power consumption thermo-optic phase modulator that can realize a desired response speed without requiring a high aspect ratio processing without requiring a very thick clad deposited on a substrate. realizable. In addition, according to the present invention, it is possible to manufacture a small-sized thermo-optic phase modulator with low power consumption with high yield. Furthermore, according to the present invention, it is possible to easily produce a thermo-optic phase modulator with uniform yield and high power consumption. Therefore, the present invention is an extremely useful technique indispensable for manufacturing a more practical low power consumption, large-scale thermo-optic optical switch circuit, and integrated thermo-optic variable optical attenuator.

(A) is a bird's-eye view which shows the structure of the thermo-optic phase modulator which concerns on the 1st Embodiment of this invention, (B) is sectional drawing which follows the cutting line AA 'in (A). It is process drawing which shows the manufacturing method of the thermo-optic phase modulator which concerns on the 1st Embodiment of this invention in process order. In the manufacturing method of the thermo-optic phase modulator which concerns on the 1st Embodiment of this invention, it is a figure which shows the structure which does not produce a level | step difference in a waveguide core, (A) is a processing pattern of SOI layer, (B) is It is a top view which shows the shape after the last process. It is an enlarged view of the etching stopper part shown in FIG. (A) is a characteristic diagram showing normalized calculation results of temperature distribution of a thermo-optic phase modulator according to a conventional thermo-optic phase modulator, and (B) is a thermo-optic phase according to the first embodiment of the present invention. FIG. 6 is a characteristic diagram showing normalized calculation results of the temperature distribution of the modulator. (A) is a bird's-eye view which shows the structure of the thermo-optic phase modulator which concerns on the 2nd Embodiment of this invention, (B) is sectional drawing which follows the cutting line AA 'in (A). It is process drawing which shows the manufacturing method of the thermo-optic phase modulator which concerns on the 2nd Embodiment of this invention in process order. FIG. 6 is a characteristic diagram illustrating a relationship between cladding thickness and power consumption (standardization) for explaining the effect of the thermo-optic phase modulator according to the second embodiment of the present invention. (A) is a bird's-eye view showing a configuration of a thermo-optic phase modulator according to a third embodiment of the present invention, (B) is a top view thereof, and (C) is a cutting line AA ′ in (A). FIG. FIG. 10 is a top view showing a structure in which the structure of FIG. 9 is arranged in multiples in a thermo-optic phase modulator according to a third embodiment of the present invention. It is a top view which shows the structure of the thermo-optic switch using the thermo-optic phase modulator of this invention, (A) is a figure which shows the case where the structure shown in 1st, 2nd embodiment is used, (B ) Is a diagram showing a case where the structure shown in the third embodiment is used. It is a figure which shows the structure of the conventional thermo-optic phase modulator, (A) is a figure which shows the example which uses a heat insulation groove | channel, (B) is a figure which shows the example of a structure which provides a clearance gap between a clad and a board | substrate. (C) is a view showing an example of a structure in which a part of the cladding is narrowed and connected to the substrate in the structure of (B), and (D) is a portion where the substrate Si is not removed and the cladding. It is a figure which shows the example which is connected.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Substrate 103 Cladding layer 105 Core 107 Thin film heater 109 Heat insulation groove 111 Space, gap 113 Substrate connection part 115 Heat insulation groove 201 BOX layer 203 SOI layer 205 Substrate connection part, etching stopper 209 Under clad 211 Core layer 213 Over clad 215 Etching stopper 301 3 dB coupler 401 Substrate 405 Core 407 Thin film heater 409 Heat insulation groove 411 Space 413 Connection portion 415 Connection portion

Claims (11)

A cladding layer deposited on a substrate;
A core formed in the cladding layer and having a higher refractive index than the cladding layer;
A thin film heater formed on the cladding layer above the core;
A first heat insulating groove formed in the cladding layer in the vicinity of the thin film heater;
A second heat insulating groove formed in the clad layer away from the thin film heater in a direction opposite to the side where the first heat insulating groove is located across the thin film heater;
A space that is sandwiched between the first heat insulation groove and the second heat insulation groove and that extends in the same direction as the substrate surface and that separates the substrate from the substrate;
Substrate connection for terminating the space adjacent to the second heat insulation groove and connecting the clad layer sandwiched between the first heat insulation groove and the second heat insulation groove and extending in the same direction as the substrate surface And a thermo-optic phase modulator.   2. The thermo-optic phase modulator according to claim 1, wherein a distance between the substrate connecting portion and the thin film heater is longer than a distance between the thin film heater and the substrate.   The thickness of at least a part of the cladding layer including the upper part of the substrate connecting part and extending in the same direction as the substrate surface sandwiched between the first heat insulating groove and the second heat insulating groove is around the core. 3. The thermo-optic phase modulator according to claim 1, wherein the thermo-optic phase modulator is thinner than the clad layer.   The thermo-optic phase modulator according to any one of claims 1 to 3, wherein the second heat insulation groove on the substrate connecting portion side has a U-shape or an inverted U-shape. .   4. The length of the substrate connecting portion in the direction parallel to the waveguide is shorter than the length in the direction parallel to the waveguide of the clad layer near the thin film heater. 5. The thermo-optic phase modulator as described.   The clad layer sandwiched between the first heat insulation groove and the second heat insulation groove and extending in the same direction as the substrate surface has an arrangement shape in which trapezoidal shapes are connected in multiple stages. 5. The thermo-optic phase modulator according to 5.   4. The thermo-optic phase modulator according to claim 1, wherein the substrate is an SOI substrate having an SOI layer. A clad layer deposited on the substrate, a core formed in the clad layer and having a higher refractive index than the clad layer, a thin film heater formed on the clad layer above the core, and on both sides of the thin film heater In a method of manufacturing a thermo-optic phase modulator having a pair of heat insulating grooves formed in the cladding layer,
Removing the SOI layer on the substrate at a location to be a substrate connecting portion later;
On the substrate from which the portion of the SOI layer has been removed, an under clad and a core layer are sequentially deposited, a core is processed from the core layer, and the core is embedded with an over clad;
Forming the pair of heat insulating grooves;
By selectively removing the SOI layer exposed by the heat insulation groove, a space that is sandwiched between the pair of heat insulation grooves and extends in the same direction as the substrate surface is separated from the substrate, and the space And a step of simultaneously forming the substrate connecting portion for connecting the substrate and the clad layer by terminating the substrate.   9. The method of manufacturing a thermo-optic phase modulator according to claim 8, further comprising a step of removing at least a part of a clad layer extending in the same direction as the substrate surface including the upper portion of the substrate connecting portion.   9. The thermo-optic according to claim 8, wherein the step of removing the SOI layer on the substrate at a position to be the substrate connecting portion forms a groove that serves as an etching stopper when performing isotropic etching at the same time. A method of manufacturing a phase modulator. 11. The method of manufacturing a thermo-optic phase modulator according to claim 10, wherein a groove serving as an etching stopper when performing the isotropic etching is simultaneously filled with glass in a step of depositing an under clad.

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