JP5600086B2 - Optical device and manufacturing method thereof - Google Patents

Description

  The present invention relates to an optical element using a rare earth compound and a method for manufacturing the same.

The research field of silicon photonics that aims to monolithically fabricate an optical waveguide, a light emitting element, and a light receiving element on a silicon substrate has greatly advanced (see Non-Patent Document 1). In this silicon photonics, when a silicon-based semiconductor is used as a light emitting element material on a silicon substrate, the problem is that the emission intensity is very weak compared to a direct transition type semiconductor material such as a compound semiconductor. In silicon photonics, thin silicon wires play an important role as optical waveguides (see Patent Documents 1 and 2). Since light having a wavelength of 1.1 μm or less is absorbed by silicon, silicon photonics requires light having a wavelength of 1.1 μm or more.

  Against this background, attempts have been made to add rare earth elements that emit light at 1.5 μm, such as erbium, to silicon. However, due to the solid solubility limit of erbium in silicon, sufficient intensity of light emission can be obtained. (See Non-Patent Document 2). Here, even if silicon-based relatively weak light emission can be added with an optical amplification function such as an erbium doped fiber amplifier (EDFA) realized by an optical fiber, excitation in silicon photonics is possible. There is a possibility that it can be sufficiently used as light or signal light.

However, in the case of EDFA, the fiber length for performing optical amplification usually requires several tens of meters, and it is physically impossible to mount on a silicon substrate. Usually, the gain of optical amplification is determined by the concentration (amount) of rare earth ions added to the glass. In the case of EDFA, about 10 ¹⁹ cm ^-3 erbium ions are added. This concentration is determined by the solid solution limit of erbium ions in the glass, and the concentration of erbium cannot be increased more than that described above.

  On the other hand, if the fiber length is further increased, the amount of erbium ions contributing to optical amplification can be increased, and the gain of optical amplification can be improved. However, further increasing the fiber length makes it more difficult to apply to silicon photonics. As described above, it is not practical to apply EDFA to silicon photonics due to physical restrictions (see Non-Patent Document 2).

  On the other hand, in the natural world, there are rare earth compounds containing a large amount of rare earth ions, for example. For example, erbium compounds exist. In particular, rare earth oxides and rare earth silicate materials have attracted much attention because of their high potential for application to silicon photonics (see Non-Patent Document 3).

The reason will be described below. For example, when erbium oxide and erbium silicate structures are taken as examples, erbium oxide and erbium silicate crystals naturally contain Er ³⁺ ions at a concentration of 10 ²² cm ⁻³ in the unit cell. This concentration corresponds to about 1000 times when compared with the case of EDFA, and when this is applied to EDFA, even if the length of EDFA is reduced to 1/1000, that is, to a length of several hundred nm, the same level of light amplification. It means that the performance of can be obtained.

  Therefore, if the rare earth compound as described above is used, the application to silicon photonics considering optical circuit design on silicon will be in the field of view. For example, erbium oxide and erbium silicate are the most promising material candidates for realizing a light amplification function on a silicon substrate.

  Under such a background, researches on the growth of erbium compounds on silicon substrates and the evaluation of optical properties of erbium compounds have been actively conducted recently (see Non-Patent Documents 4, 5, and 6). In silicon photonics, it is necessary to produce functions such as light emission, light reception, and resonator at desired positions on a silicon substrate, and the same applies to an optical amplifier. In other words, a technique for arranging erbium oxide or erbium silicate crystals at a desired position of a silicon wafer is important, and establishment of this technique is strongly demanded.

JP 2004-281972 A JP 2004-319668 A

Yoshihiko Kinmitsu and Satoshi Fukatsu, “Silicon Photonics”, Ohmsha, pages 89-118. A. J. Kenyon, "Erbium in silicon", Semicond. Sci. Technol., VOL.20, R65-R84, 2005. Edited by Shoichi Sudo, “Erbium-doped fiber amplifier”, Optronics, pages 3-22. C. P. Michael et al, "Growth, processing, and optical properties of epitaxial Er2O3 on silicon", OPTICS EXPRESS, Vol.16, No.24, pp.19649-19666, 2008. John B. Gruber et al., "Modeling optical transitions of Er3 + .4f11… in C2 and C3i sites in fused Y2O3", JOURNAL OF APPLIED PHYSICS, vol.104, 023101, 2008. H.ISSHIKI and T.KIMURA, "Toward Small Size Waveguide Amplifiers Based on Erbium Silicate for Silicon Photonics", IEICE TRANS. ELECTRON., Vol.E91.C, no.2, pp.138-144, 2008.

  As a technique described above, for example, in order to fabricate an optical resonator structure such as an optical waveguide and a microdisk, the following is generally performed. First, a rare earth oxide (for example, erbium oxide) is vapor-deposited on a silicon oxide film (refractive index n = about 1.5) having a film thickness of several hundreds nm on a silicon substrate to form a rare earth oxide layer. The silicon oxide film becomes the lower cladding layer. Next, the rare earth oxide layer is patterned by a known photolithography and etching technique to form a thin wire core of erbium oxide (refractive index n = 2.0) on the lower cladding layer made of a silicon oxide film. Thereafter, an oxide film or an epoxy resin is applied on the formed erbium oxide thin wire core to form an upper clad layer, thereby forming a waveguide structure.

  However, in this method, erbium oxide is formed as a film on the entire surface of the substrate, and most of it is removed by lithography and etching as described above. Thus, there is a problem that the rare earth compound material is wasted, resulting in an increase in material cost.

  The present invention has been made to solve the above problems, and an object of the present invention is to make it possible to manufacture an optical element using a rare earth compound without wasting materials.

  The optical device manufacturing method according to the present invention includes a step of forming a rare earth-containing layer made of a rare earth oxide on the lower silicon layer by physical vapor deposition, and a step of heating the rare earth-containing layer to form an optical functional layer. And at least.

In the method for manufacturing the optical element, comprising the step of forming a groove in the surface of the lower portion the silicon layer to form a rare earth-containing layer on the lower silicon layer to form a groove. By aggregating the groove by heating the rare-earth-containing layer that form a light function layer serving as a core of the optical waveguide.

Further, the optical element according to the present invention is an optical amplifier comprising an optical amplifying unit composed of an optical functional layer as a core.

  As described above, according to the present invention, an optical element using a rare earth compound can be manufactured without wasting materials.

FIG. 1A is a cross-sectional view showing a state in each step for explaining a method of manufacturing an optical element in Embodiment 1 of the present invention. FIG. 1B is a cross-sectional view showing a state in each step for explaining the method of manufacturing an optical element in the first embodiment of the present invention. FIG. 1C is a cross-sectional view showing a state in each step for explaining the method of manufacturing an optical element in the first embodiment of the present invention. FIG. 1D is a cross-sectional view showing a state in each step for explaining the method of manufacturing an optical element in the first embodiment of the present invention. FIG. 1E is a cross-sectional view showing a state in each step for explaining the method of manufacturing an optical element in the first embodiment of the present invention. FIG. 1F is a plan view showing a state in each step for explaining the method of manufacturing an optical element in the first embodiment of the present invention. FIG. 2A is a cross-sectional view showing a state in each step for explaining the method of manufacturing an optical element in the second embodiment of the present invention. FIG. 2B is a cross-sectional view showing a state in each step for explaining the method of manufacturing an optical element in the second embodiment of the present invention. FIG. 2C is a cross-sectional view showing a state in each step for explaining the method of manufacturing an optical element in the second embodiment of the present invention. FIG. 2D is a plan view showing a state in each step for explaining the method of manufacturing the optical element in the second embodiment of the present invention. FIG. 2E is a cross-sectional view showing a state in each step for explaining the method of manufacturing an optical element in the second embodiment of the present invention. FIG. 2F is a cross-sectional view showing a state in each step for explaining the method of manufacturing an optical element in the second embodiment of the present invention. FIG. 3A is a cross-sectional view showing a state in each step for explaining the method of manufacturing an optical element in the third embodiment of the present invention. FIG. 3B is a cross-sectional view showing a state in each step for explaining the method of manufacturing an optical element in the third embodiment of the present invention. FIG. 3C is a plan view showing a state in each step for explaining the method of manufacturing an optical element in the third embodiment of the present invention. FIG. 3D is a cross-sectional view showing a state in each step for explaining the method of manufacturing an optical element in the third embodiment of the present invention. FIG. 3E is a cross-sectional view showing a state in each step for explaining the method of manufacturing an optical element in the third embodiment of the present invention. FIG. 3F is a plan view showing a state in each step for explaining the method of manufacturing an optical element in the third embodiment of the present invention. FIG. 4A is a plan view showing a state in each step for explaining the method of manufacturing an optical element in the fourth embodiment of the present invention. FIG. 4B is a plan view showing a state in each step for explaining the method of manufacturing an optical element in the fourth embodiment of the present invention. FIG. 4C is a plan view showing a state in each step for explaining the method of manufacturing an optical element in the fourth embodiment of the present invention. FIG. 4D is a plan view showing a state in each step for explaining the method of manufacturing an optical element in the fourth embodiment of the present invention. FIG. 4E is a plan view showing a state in each step for explaining the method of manufacturing an optical element in the fourth embodiment of the present invention. FIG. 4F is a plan view showing a state in each step for explaining the method of manufacturing an optical element in the fourth embodiment of the present invention. FIG. 5 is a plan view showing a configuration example of the optical element in the embodiment of the present invention. FIG. 6 is a cross-sectional view showing a configuration example of the optical element in the embodiment of the present invention. FIG. 7 is a plan view showing a configuration example of the optical element in the embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Embodiment 1]
First, Embodiment 1 of the present invention will be described with reference to FIGS. 1A to 1F. 1A to 1F are a cross-sectional view and a plan view showing a state in each step for explaining a method of manufacturing an optical element in Embodiment 1 of the present invention. 1A to 1E are sectional views, and FIG. 1F is a plan view.

  First, as shown in FIG. 1A, a substrate including a silicon layer (lower silicon layer) 103 is prepared. The substrate is an SOI (Silicon On Insulator) substrate including a silicon base 101 and a buried insulating layer 102, and the surface silicon layer of the SOI substrate is a silicon layer 103.

  Next, as shown in FIG. 1B, a groove 104 is formed in the silicon layer 103. For example, the groove 104 may be formed by patterning the silicon layer 103 by a known photolithography and etching technique.

Next, as shown in FIG. 1C, a rare earth-containing layer 105 made of an oxide of erbium (rare earth) is formed. The rare earth-containing layer 105 is a layer of erbium oxide (Er ₂ O ₃ ), and is formed by a physical vapor deposition method such as a sputtering method without heating the substrate. Note that the rare earth-containing layer 105 may be formed by a vacuum evaporation method. The rare earth-containing layer 105 thus formed is in an amorphous state.

  Next, the rare earth-containing layer 105 is heated to, for example, 1000 ° C. to agglomerate the rare earth-containing layer 105 into the groove portion 104, and as shown in FIG. 1D, a rare earth core portion (optical functional layer) 106 made of erbium oxide crystals. Form. The rare earth oxide aggregates in the recess formed in the base by heating. In addition, since the amorphous erbium oxide is crystallized by this heating, the rare earth core portion 106 is composed of erbium oxide crystals. In other words, it is important that the temperature for aggregation is at least the temperature for crystallization. The dimension of the rare earth core portion 106, for example, the height of the cross-sectional shape is determined by the amount of the rare earth-containing layer 105.

Next, as shown in FIG. 1E, a silicon oxide layer 107 is formed on the silicon layer 103 on which the rare earth core portion 106 is formed. For example, the silicon oxide layer 107 can be formed by depositing silicon oxide by a sputtering method. As shown in the plan view of FIG. 1F, the planar shape of the rare earth core 106 is a rectangle that is long in the waveguide direction (the vertical direction on the paper surface). In the cross-sectional view of FIG. 1E, it has a core shape extending from the front to the back of the page. As a result, an optical amplifying element using the rare earth core portion 106 made of erbium oxide having an optical waveguide structure in which the buried insulating layer 102 is a lower cladding layer and the silicon oxide layer 107 is an upper cladding layer is obtained.

  In the optical waveguide structure formed by the manufacturing method described above, the dimensions of the cross-sectional shape of the rare earth core portion 106 are, for example, a height and a width of 1.5 μm or more. Moreover, the layer thickness of the silicon layer 103 should just be more than half of the thickness of the rare earth core part 106. FIG.

  As described above, according to the present embodiment, the rare earth core portion 106 can be formed without removing most of the deposited rare earth-containing layer 105 by etching or the like. The optical waveguide composed of the rare earth core portion 106 can be used as an optical modulator (optical element). Thus, according to the present embodiment, an optical element using a rare earth compound can be manufactured without wasting materials.

[Embodiment 2]
Next, Embodiment 2 of the present invention will be described with reference to FIGS. 2A to 2F. 2A to 2F are cross-sectional views and plan views showing states in respective steps for explaining the method of manufacturing an optical element in the second embodiment of the present invention. 2A to 2C, 2E, and 2F are cross-sectional views, and FIG. 2D is a plan view.

  First, as shown in FIG. 2A, a substrate provided with a silicon layer (lower silicon layer) 203 is prepared. The substrate is an SOI substrate including a silicon base 201 and a buried insulating layer 202, and the surface silicon layer of the SOI substrate is a silicon layer 203.

Next, as shown in FIG. 2B, a rare earth-containing layer 204 made of erbium oxide is formed on the silicon layer 203. The rare earth-containing layer 204 is an erbium oxide (Er ₂ O ₃ ) layer, and is formed by a physical vapor deposition method such as a sputtering method without heating the substrate. The rare earth-containing layer 204 thus formed is in an amorphous state.

Next, the rare earth-containing layer 204 is heated to, for example, 1000 ° C. to cause the rare earth-containing layer 204 and the silicon of the silicon layer 203 to react, and as shown in FIGS. 2C and 2D, a plurality of nanostructures made of erbium silicate 205 is formed. In the second embodiment, since the silicon layer 203 has no unevenness, the rare earth-containing layer 204 made of erbium oxide does not aggregate by heating, and reacts with the silicon of the lower silicon layer 203 to form silicate. To do. In the case of erbium, erbium silicate is produced by a chemical reaction of “Er ₂ O ₃ + O ₂ + Si → Er ₂ SiO ₅ ” or “Er ₂ O ₃ + 2O ₂ + 2Si → Er ₂ Si ₂ O ₇ ”.

  Next, as shown in FIG. 2E, a silicon layer (upper silicon layer) 206 is formed on the silicon layer 203 on which the nanostructure 205 is formed. Thereafter, as shown in FIG. 2F, the silicon layer 203 and the silicon layer 206 are patterned into a predetermined mesa structure, an electrode 207 is formed on the silicon layer 206, and an electrode 208 connected to the silicon layer 203 is formed. .

  In the above structure, when the silicon layer 203 is p-type and the silicon layer 206 is n-type, a light-emitting element having a plurality of nanostructures 205 sandwiched therebetween as a light-emitting layer can be obtained. Note that the silicon layer 203 may be n-type and the silicon layer 206 may be p-type.

[Embodiment 3]
Next, Embodiment 3 of the present invention will be described with reference to FIGS. 3A to 3F. 3A to 3F are cross-sectional views and plan views showing states in respective steps for explaining the method of manufacturing an optical element in the third embodiment of the present invention. 3A, 3B, 3D, and 3E are cross-sectional views, and FIGS. 3C and 3F are plan views.

  First, as shown in FIG. 3A, a substrate provided with a silicon layer (lower silicon layer) 303 is prepared. The substrate is an SOI substrate including a silicon base 301 and a buried insulating layer 302, and the surface silicon layer of the SOI substrate is a silicon layer 303.

Next, as shown in FIG. 3B, a groove 304 is formed in the silicon layer 303. For example, the groove 304 may be formed by patterning the silicon layer 303 by a known photolithography and etching technique. As shown in the plan view of FIG. 3C, the groove 304 is formed in a state of being arranged on each side of the quadrangle. The four grooves 304 arranged in this way are in a state in which these inner regions are enclosed.

Next, as shown in FIG. 3D, a rare earth-containing layer 305 made of erbium oxide is formed on the silicon layer 303. The rare earth-containing layer 305 is a layer of erbium oxide (Er ₂ O ₃ ) and is formed by heating a substrate by a physical vapor deposition method such as a sputtering method. The rare earth-containing layer 305 thus formed is in an amorphous state.

  Next, by heating the rare earth-containing layer 305 to, for example, 1000 ° C., as shown in FIGS. 3E and 3F, pattern portions 306 made of erbium oxide crystals are formed in the four groove portions 304, and the pattern portions 306 are formed on these grooves 304. A plurality of nanostructures 307 made of erbium silicate are formed on the silicon layer 303 in the enclosed region.

  In the four groove portions 304, the rare earth-containing layer 305 aggregates to form a pattern portion 306. On the other hand, in the flat region surrounded by the four groove portions 304, the silicate is formed by reacting with the silicon of the lower silicon layer 303 to form the nanostructure 307. As described above, the nanostructure 307 can be arranged in a specific region by the unevenness formed in the silicon layer 303. The thickness of the pattern portion 306 and the size of the nanostructure 307 can be controlled by the deposition amount of the rare earth-containing layer 305, the width of the groove portion 304, and the interval between the groove portions 304.

[Embodiment 4]
Next, Embodiment 4 of the present invention will be described with reference to FIGS. 4A to 4F. 4A to 4F are a cross-sectional view and a plan view showing a state in each step for explaining the method of manufacturing an optical element in the fourth embodiment of the present invention. 4A, 4B, and 4D to 4F are sectional views, and FIG. 4C is a plan view.

  First, as shown in FIG. 4A, a substrate provided with a silicon layer (lower silicon layer) 403 is prepared. The substrate is an SOI substrate including a silicon base 401 and a buried insulating layer 402, and the surface silicon layer of the SOI substrate is a silicon layer 403.

  Next, as shown in FIG. 4B, a mask pattern 404 is formed on the silicon layer 403. The mask pattern 404 includes a rectangular opening 405 as shown in the plan view of FIG. 4C. For example, the mask pattern 404 may be formed by patterning a photoresist layer applied on the silicon layer 403 by a known photolithography technique. In the opening 405, the silicon layer 403 is exposed.

Next, as shown in FIG. 4D, a rare earth-containing layer 406 made of erbium oxide is formed on the silicon layer 403 on which the mask pattern 404 is formed. The rare earth-containing layer 406 is a layer of erbium oxide (Er ₂ O ₃ ), and is formed by a physical vapor deposition method such as a sputtering method without heating the substrate. The rare earth-containing layer 406 thus formed is in an amorphous state.

  Next, by removing the mask pattern 404 and removing the rare earth-containing layer 406 formed on the mask pattern 404 other than the opening 405, a portion of the silicon layer 403 is formed on the silicon layer 403 as shown in FIG. 4E. In particular, the rare earth-containing layer 406 is arranged.

  Next, the rare earth-containing layer 406 is heated to, for example, 1000 ° C., and the rare earth-containing layer 406 and the silicon of the silicon layer 403 are reacted to form a specific region on the silicon layer 403 as shown in FIG. 4F. A plurality of nanostructures 407 made of erbium silicate are formed. In the fourth embodiment, the nanostructure 407 is arranged in a desired specific region by using the mask pattern 404.

  As described above, various optical elements can be formed by heating a rare earth-containing layer made of a rare earth oxide formed on a silicon layer by physical vapor deposition. For example, if unevenness is formed in the silicon layer, the rare earth-containing layer can be aggregated and crystallized in the recess. In this case, if the concave portion is formed in a thin line shape, a thin wire core (optical functional layer) made of a rare earth oxide crystal such as erbium oxide can be formed, and an optical amplification element can be configured by using this. In this structure, an electrode can be provided to function as a light-emitting element.

  Further, a nanostructure made of a rare earth silicate such as erbium silicate can be formed in the flat region of the silicon layer. A plurality of nanostructures made of rare earth silicate can be used as a light emitting material.

For example, as shown in the plan view of FIG. 5, the nanostructure forming part 511, the rare earth core part 512, and the silicon fine wire core 513 can be arranged and combined in the optical waveguide direction. The nanostructure forming portion 511 and the rare earth core portion 512 are formed on the silicon layer 501, and the silicon fine wire core 513 is formed on the buried insulating layer 504. Here, as shown in the cross-sectional view of FIG. 6, the formation region of the rare earth core portion 512 is formed in the concave portion of the silicon layer 501 , and the silicon oxide layer 502 is formed thereon. Although not shown, a silicon oxide layer 502 is also formed on the nanostructure forming portion 511 and the silicon thin wire core 513.

Under the silicon layer 501 , a buried insulating layer 504 and a silicon base 503 are disposed. The silicon base 503, the buried insulating layer 504, and the silicon layer 501 are SOI substrates. FIG. 6 shows a cross section taken along line XX ′ of FIG. In these configurations, the buried insulating layer 504 serves as a lower cladding layer, and the silicon oxide layer 502 serves as an upper cladding layer.

  Further, as shown in the plan view of FIG. 7, the nanostructure forming portion 511, the silicon fine wire core 513, and the rare earth core portion 512 may be arranged in this order in the waveguide direction.

  The nanostructure forming portion 511 and the rare earth core portion 512 form a rare earth-containing layer made of a rare earth oxide on the silicon layer 501 as is apparent from the description in the first to fourth embodiments. Can be formed by heating. Further, the silicon fine wire core 513 can be formed by patterning the silicon layer 501 by a known lithography and etching technique. As described above, each optical element can be easily combined with an optical waveguide made of the silicon fine wire core 513.

  Further, these can be formed by a generally used LSI integrated circuit manufacturing technique, and the positional accuracy with respect to the waveguide direction can be in units of sub-μm. Therefore, it is easy to align the nanostructure forming portion 511, the rare earth core portion 512, and the silicon fine wire core 513 in order to arrange them in the waveguide direction. In addition, at the stage where each configuration is formed, the optical axes are aligned, and there is no need to adjust the optical axes later.

The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious. For example, in the above, the rare earth-containing layer, a case has been described which is composed of mainly erbium oxide as an example, not limited thereto, europium oxide, neodymium oxide, thulium oxide, praseodymium oxide, hafnium oxide, The same applies to other rare earth oxides such as yttrium, gadolinium oxide, terbium oxide, and dysprosium oxide.

  The rare earth-containing layer may contain not only the rare earth oxide described above but also yttrium oxide, silicon oxide, titanium oxide, aluminum oxide, bismuth oxide, germanium oxide, and the like. These can be formed, for example, in the state of being included in the rare earth-containing layer by vapor deposition at the same time as the rare earth oxide. Note that since the crystallization temperature differs depending on the material, the temperature of the heat treatment is set appropriately. Even when a nanostructure made of silicide is formed, the heat treatment time is appropriately set in order to form a complete compound.

  In the above description, the SOI substrate is used. However, the present invention is not limited to this, and a silicon substrate, a germanium substrate, a GOI (Germanium on insulator) substrate, or an SGOI (Silicon germanium on insulator) substrate may be used. . Further, for example, the linear rare earth core 106 is formed by forming the groove 104 in a straight line, but the present invention is not limited to this, and a ring shape may be used. A resonator can be formed by forming it in a ring shape. By forming the resonator in this way, the resonator can be combined with the optical circuit described with reference to FIGS. Further, the intensity of excitation light can be enhanced by applying the resonator structure to a light emitting element.

  DESCRIPTION OF SYMBOLS 101 ... Silicon base part, 102 ... Embedded insulating layer, 103 ... Silicon layer (lower silicon layer), 104 ... Groove part, 105 ... Rare earth containing layer, 106 ... Rare earth core part (optical functional layer), 107 ... Silicon oxide layer.

Claims (2)

Forming a rare earth-containing layer made of a rare earth oxide on the lower silicon layer by physical vapor deposition;
And heating the rare earth-containing layer to form an optical functional layer ,
And a step of forming a groove on the surface of the lower silicon layer,
Forming the rare earth-containing layer on the lower silicon layer in which the groove is formed;
Method for manufacturing an optical element characterized that you form the optical functional layer by heating the rare-earth-containing layer becomes a core of the optical waveguide by aggregating the groove. An optical element manufactured by the method for manufacturing an optical element according to claim 1 ,
An optical element comprising an optical amplifying unit configured from the optical functional layer serving as the core.

Images