JP5910214B2 - Semiconductor light modulation device and manufacturing method of semiconductor light modulation device - Google Patents

Description

The present invention relates to a semiconductor light modulation device and a method for manufacturing the semiconductor light modulation device .

  With the increase in information communication in recent years, studies on ultra-high speed and large capacity in optical communication and optical transmission have been made, and various optical modulators, optical switches, etc. are used for such optical communication. ing. As one of such optical modulators, there is a Mach-Zehnder (MZ) type optical modulator corresponding to input light having a broad wavelength. (For example, Patent Document 1)

  FIG. 1 shows a structure of an optical waveguide portion in which phase modulation of propagating light is performed in a Mach-Zehnder type optical modulator. 2A is a cross-sectional view taken along the alternate long and short dash line 1A-1B in FIG. 1, and FIG. 2B is a cross-sectional view taken along the alternate long and short dash line 1C-1D in FIG.

  This optical modulator has an optical waveguide 910 formed of a semiconductor material through which light propagates. The optical waveguide 910 includes, for example, a straight optical waveguide 910a formed on the light incident side, an optical modulation waveguide 920 that is phase-modulated, and a straight optical waveguide 910b formed on the light emission side. Have. Thus, light incident from the end of the straight optical waveguide 910a propagates in order through the straight optical waveguide 910a, the light modulation waveguide 920, and the straight optical waveguide 910b, and then exits from the end of the straight optical waveguide 910b. On the side surface of the light modulation waveguide 920, a connection structure portion 921 is provided on one side, and a connection structure portion 922 is provided on the other side. The connection structure portion 921 is provided with an n-type region 921a, and the connection structure portion 921 is connected to the common electrode 930 in the n-type region 921a. Similarly, a p-type region 922a is provided in the connection structure portion 922, and the connection structure portion 922 is connected to the signal electrode 931 in the p-type region 922a. In the portion where the light modulation waveguide 920 is formed, the shape formed by the light modulation waveguide 920 and the connection structure portions 921 and 922 is a lattice shape. Light propagates locally in the light modulation waveguide 920.

In the optical modulator having such a structure, by changing the voltage applied between the common electrode 930 and the signal electrode 931, free electrons and holes can be reduced between the n-type region 921a and the p-type region 922a. The carrier concentration can be changed. As a result, the refractive index in the light modulation waveguide 920 that is the core layer changes due to the free carrier plasma effect, so that the phase of light propagating through the light modulation waveguide 920 can be modulated. (For example, Non-Patent Document 1)
Incidentally, in such an optical modulator, for example, as shown in FIG. 2, the optical waveguide 910 is formed on an oxide film layer 902 formed on a substrate 901. Specifically, the substrate 901 is formed of silicon, the oxide film layer 902 is formed of a silicon oxide layer, and the optical waveguide 910 is formed of a silicon layer. Therefore, it can be formed using an SOI (Silicon on Insulator) substrate. In this case, the optical waveguide 910 is formed of an SOI layer, and the oxide film layer 902 is formed of a BOX (buried oxide) layer.

  Further, an upper oxide film layer 940 also called an over clad layer is formed on the straight optical waveguide 910a, the light modulation waveguide 920, and the straight optical waveguide 910b forming the optical waveguide 910. Since the upper oxide film layer 940 is made of silicon oxide, and the oxide film layer 902 becomes a lower oxide film layer, the optical waveguide 910 has an oxide film layer 902 that is a lower oxide film layer in the vertical direction. And the upper oxide film layer 940.

US Pat. No. 7,251,408

S. Akiyama, “12.5-Gb / s Operation of Efficient Silicon Mach-Zehnder Modulator Using Side-Wall Grating Waveguide,” (WA4) in proceeding of 8th IEEE International Conference on Group IV Photonics (GFP 2011). T. Tanabe et al, “Low power and fast electro-optic silicon modulator with lateral p-i-n embedded photonic crystalnanocavity,” Optics express, 17, 22505 (2009). Y A. Vlasov et al, “Activecontrol of slow light on a chip with photonic crystal waveguides,” nature, 438,65 (2005).

  By the way, in the optical modulator having the structure shown in FIG. 1 and FIG. 2, the propagation light spreads to the n-type region 921a in the connection structure portion 921, the p-type region 922a in the connection structure portion 922, and the like. large. For this reason, the thing of the structure which made the whole optical waveguide 910 completely hollow is disclosed (for example, patent documents 2 and 3). However, such a structure has a large mode mismatch, and part of the light propagating through the optical waveguide 910 is reflected between the light modulation waveguide 920 and the straight optical waveguide 910b, so that the optical loss increases. . This is because the connection structure portions 921 and 922 are formed on the side surface of the light modulation waveguide 920, but those corresponding to the connection structure portions 921 and 922 are not formed on the side surface of the straight optical waveguide 910b. This is probably due to this. Further, such a structure has low mechanical strength and low reliability.

  Therefore, there is a need for a semiconductor light modulation device with high reliability and low light loss and a method for manufacturing the semiconductor light modulation device.

According to one aspect of the present embodiment, each of the light modulation waveguides that are formed of a semiconductor material and on both sides of the side surface of the light modulation waveguide that the incident light propagates are provided. A connection structure portion formed of a semiconductor material connected to a side surface; an upper oxide film layer formed above the light modulation waveguide and the connection structure portion; and the connection structure portion in the upper oxide film layer An opening formed in a part or all of the substrate, a lower oxide film layer formed below the light modulation waveguide and the connection structure, and a lower oxide film in contact with the connection structure wherein in which the space portion is more formed to remove a portion, have a, which is formed on the lower side of the upper oxide layer is formed on the upper side of the light modulation waveguide and the light modulation waveguide The lower oxide layer is not removed and the optical modulation waveguide is sandwiched between them. And wherein the Idei Rukoto.

  Further, according to another aspect of the present embodiment, it is formed of a semiconductor material, and is formed on both sides of a light modulation waveguide through which incident light propagates, and a side surface of the light modulation waveguide, A connection structure formed of a semiconductor material connected to a side surface of the light modulation waveguide; an upper oxide film layer formed on the light modulation waveguide and the connection structure; and the upper oxide film layer And an opening formed in a part or all of the connection structure portion.

  According to another aspect of the present embodiment, a lower oxide film layer is formed on a substrate, and a semiconductor layer is formed on the lower oxide film layer. Forming a connection structure part connected on both sides of the side surface of the light modulation waveguide and the light modulation waveguide by removing a part; and forming on one side of the side surface of the light modulation waveguide A region of the first conductivity type is formed in all or part of the other connection structure portion, and a region of the second conductivity type is formed in all or part of the other connection structure portion formed on the other side. Forming an upper oxide layer on the light modulation waveguide and the connection structure, and removing all or part of the upper oxide layer on the connection structure A step of forming an opening, and a portion corresponding to the opening In the lower oxide layer, and having a step of forming a space by removing a portion of the lower oxide layer in contact with the connecting structure.

  According to the disclosed semiconductor light modulation device and semiconductor light modulation device manufacturing method, a semiconductor light modulation device with high reliability and low optical loss can be obtained.

Explanatory drawing of a conventional semiconductor light modulator (1) Explanatory drawing of a conventional semiconductor light modulator (2) Top view of the semiconductor light modulation device in the first embodiment Explanatory drawing of the semiconductor optical modulation element in 1st Embodiment Sectional drawing of the semiconductor optical modulation element in 1st Embodiment Explanatory drawing of model in simulation of semiconductor light modulator (1) Relationship diagram between position and energy density in optical waveguide (1) Explanatory drawing of model in simulation of semiconductor light modulator (2) Relationship between position and energy density in optical waveguide (2) Process drawing (1) of the manufacturing method of the semiconductor optical modulation element in the first embodiment Process drawing (2) of the manufacturing method of the semiconductor optical modulation element in the first embodiment Process drawing (3) of the manufacturing method of the semiconductor light modulation device in the first embodiment Process drawing (4) of the manufacturing method of the semiconductor optical modulation element in the first embodiment Process drawing (5) of the manufacturing method of the semiconductor optical modulation element in the first embodiment Process drawing (6) of the manufacturing method of the semiconductor optical modulation element in the first embodiment Process drawing (7) of the manufacturing method of the semiconductor light modulation device in the first embodiment Process drawing (8) of the manufacturing method of the semiconductor optical modulation element in the first embodiment Process drawing (9) of the manufacturing method of the semiconductor light modulation device in the first embodiment Explanatory drawing of the semiconductor optical modulation element in 2nd Embodiment Explanatory drawing of the semiconductor optical modulation element in 3rd Embodiment Sectional drawing of the semiconductor optical modulation element in 3rd Embodiment Process drawing (1) of the manufacturing method of the semiconductor optical modulation element in 3rd Embodiment Process drawing (2) of the manufacturing method of the semiconductor optical modulation element in the third embodiment Process drawing (3) of the manufacturing method of the semiconductor light modulation device in the third embodiment Process drawing (4) of the manufacturing method of the semiconductor optical modulation element in 3rd Embodiment Process drawing of the manufacturing method of the semiconductor light modulation element in the third embodiment (5) Process drawing (6) of the manufacturing method of the semiconductor optical modulation element in 3rd Embodiment Process drawing (7) of the manufacturing method of the semiconductor optical modulation element in 3rd Embodiment Process drawing (8) of the manufacturing method of the semiconductor light modulation device in the third embodiment. Process drawing (9) of the manufacturing method of the semiconductor light modulation device in the third embodiment. Process drawing (10) of the manufacturing method of the semiconductor light modulation device in the third embodiment. Explanatory drawing of the semiconductor optical modulation element in 4th Embodiment Sectional drawing of the semiconductor optical modulation element in 4th Embodiment Explanatory drawing of model in simulation of semiconductor light modulation element (3) Mode distribution diagram in an optical waveguide obtained by simulation Process drawing (1) of the manufacturing method of the semiconductor optical modulation element in 4th Embodiment Process drawing (2) of the manufacturing method of the semiconductor optical modulation element in 4th Embodiment Process drawing (3) of the manufacturing method of the semiconductor optical modulation element in 4th Embodiment

  The form for implementing is demonstrated below. In addition, about the same member etc., the same code | symbol is attached | subjected and description is abbreviate | omitted.

[First Embodiment]
(Semiconductor light modulator)
The semiconductor light modulation device in the first embodiment will be described with reference to FIGS. FIG. 3 is a top view of a Mach-Zehnder type optical modulator that is a semiconductor optical modulation element according to the present embodiment, and FIG. 4 is an enlarged view of a region surrounded by an alternate long and short dash line 3A in FIG. 5A is a cross-sectional view taken along the alternate long and short dash line 4A-4B in FIG. 4, and FIG. 5A is a cross-sectional view taken along the alternate long and short dash line 4C-4D in FIG. FIG.5 (c) is sectional drawing cut | disconnected by the dashed-dotted line 4E-4F in FIG.

  The Mach-Zehnder type optical modulator shown in FIG. 3 has a structure in which modulated light is emitted from an output-side optical waveguide 10b by allowing continuous light to enter the incident-side optical waveguide 10a. This semiconductor optical modulation element has a first optical waveguide 11 and a second optical waveguide 12, and the light incident side of both the first optical waveguide 11 and the second optical waveguide 12 is incident. The side from which light is emitted is connected to the optical waveguide 10b on the emission side. Therefore, the continuous light incident on the incident-side optical waveguide 10a is branched into light propagating through the first optical waveguide 11 and light propagating through the second optical waveguide 12, and is emitted after desired modulation or the like. Merges in the optical waveguide 10b on the side and is emitted as modulated light.

  The semiconductor optical modulation element in the present embodiment includes a common electrode 30, a first signal electrode 31, and a second signal electrode 32. The common electrode 30 includes the first optical waveguide 11 and the second optical signal. It is formed between the waveguide 12. The first optical waveguide 11 is sandwiched between the common electrode 30 and the first signal electrode 31, and the second optical waveguide 12 is interposed between the common electrode 30 and the second signal electrode 32. It is sandwiched between.

  In the present embodiment, the first optical waveguide 11 serving as the core layer is provided with the light modulation waveguide 20 or the like, and the straight optical waveguide 11a is provided on the light incident side of the light modulation waveguide 20 or the like. A straight optical waveguide 11b is provided on the emission side. Further, a plurality of rod-shaped connection structures 21 and 22 extending from the side surfaces on both sides of the light modulation waveguide 20 are formed on the side surfaces on both sides of the light modulation waveguide 20 by removing a part of the semiconductor layer. ing. Thus, one connection structure portion 21 is formed at a predetermined interval on one side of the side surface of the light modulation waveguide 20, and the other connection structure portion 22 is formed at a predetermined interval on the other side of the side surface. It is formed with. The same applies to the second optical waveguide 12. In the semiconductor device according to the present embodiment, the first optical waveguide 11 and the second optical waveguide 12 are formed in a semiconductor layer. The semiconductor layer is formed on a substrate 60 such as a Si substrate. The oxide film layer 61 is formed on the oxide film layer 61. Therefore, the semiconductor light modulation element in this embodiment can be manufactured using an SOI substrate.

  In the present embodiment, the width W1 of the first optical waveguide 11 or the like serving as the core layer is formed to be about 440 nm. In addition, the distance D1 between the light modulation waveguide 20 and the common electrode 30 and between the light modulation waveguide 20 and the first signal electrode 31 in the first optical waveguide 11 is formed to be about 2 μm. The distance D1 is equal to the length of the connection structures 21 and 22. The connection structures 21 and 22 are formed so as to extend in a direction substantially perpendicular to the light propagation direction in the light modulation waveguide 20 and the like, and the formed connection structures 21 and 22 have a width K1 of about 60 to 60. 80 nm and the pitch P1 is about 285 nm. The width K1 of the connection structures 21 and 22 and the like is a predetermined width, specifically, light so that light propagating through the light modulation waveguide 20 or the like does not leak from the light modulation waveguide 20 or the like. The modulation waveguide 20 or the like is formed to be narrower than the width W1. In the present embodiment, the first optical waveguide 11 and the like and the connection structures 21 and 22 are formed with substantially the same thickness, and the height H1 is about 220 nm.

  In the semiconductor optical modulation element according to the present embodiment, one connection structure portion 21 is provided with an n-type region 21a, and the connection structure portion 21 and the common electrode 30 are connected in the n-type region 21a. . The other connection structure portion 22 is provided with a p-type region 22a, and the connection structure portion 22 and the first signal electrode 31 are connected in the p-type region 22a.

In the present embodiment, P (phosphorus) is ion-implanted as an impurity element in n-type region 21a so that the impurity concentration is about 1 × 10 ²⁰ cm ⁻³ . Further, B (boron) is ion-implanted as an impurity element in the p-type region 22a so that the impurity concentration is about 1 × 10 ²⁰ cm ⁻³ . In the present embodiment, As or the like can be used in addition to P as the impurity element for forming the n-type region 21a, and B as the impurity element for forming the p-type region 22a. In addition, Al or the like can be used. In the present embodiment, the n-type is described as the first conductivity type and the p-type is described as the second conductivity type, but these relationships may be reversed.

  In the semiconductor light modulation device in the present embodiment, an upper oxide film layer 40 is formed on the first optical waveguide 11 and the like. The upper oxide film layer 40 is made of silicon oxide, and the first optical waveguide 11 or the like, which is the core layer, includes an oxide film layer 61 and an upper oxide film which are lower oxide film layers formed on the substrate 60. The upper and lower sides are sandwiched between layers 40.

  In the semiconductor light modulation device having this structure, the voltage signal source 70 changes the voltage applied between the common electrode 30 and the first signal electrode 31 to thereby change between the n-type region 21a and the p-type region 22a. It is possible to change the concentration of free carriers of electrons and holes. Thereby, the refractive index in the optical modulation waveguide 20 or the like, which is the core layer, is changed by the free carrier plasma effect, and the phase of light propagating in the optical modulation waveguide 20 or the like can be modulated.

  In addition, in the semiconductor light modulation element in the present embodiment, in the regions on both sides of the light modulation waveguide 20, a part of the oxide film layer 61 in the lower portion of the connection structure portions 21 and 22 is removed, whereby the space portion 62 is formed. Similarly, an upper oxide film layer 40 having an opening 41 is formed above the connection structures 21 and 22 in the same region. Thus, by forming the space 62 and the opening 41, it is possible to further prevent light propagating through the light modulation waveguide 20 from leaking to the connection structures 21 and 22, and the light modulation waveguide. The localization of the light inside 20 can be enhanced. In this way, by increasing the localization of light in the light modulation waveguide 20, reflection between the light modulation waveguide 20 and the straight optical waveguide 11b can be reduced, and the loss of propagating light is suppressed. be able to. The closer the space 62 and the opening 41 are to the light modulation waveguide 20, the more the propagation light can be suppressed from leaking to the connection structures 21 and 22, and the light 62 propagates through the light modulation waveguide 20. Light loss can be reduced. Further, in FIG. 5, the space portion 62 has a structure formed by removing a part of the surface portion of the oxide film layer 61, but the space portion 62 is an oxide film until the surface of the substrate 60 is exposed. It may have a structure in which the layer 61 is removed.

  In the present embodiment, the light modulation waveguide 20 is connected to the connection structures 21 and 22, and the connection structures 21 and 22 are in contact with the oxide film layer 61 and the upper oxide film layer 40. Compared to the hollow one, the mechanical strength is relatively high and the reliability is high.

(Simulation result in optical waveguide)
Next, a description will be given of the result of a simulation of the energy density distribution in the conventional semiconductor light modulation device and the semiconductor light modulation device in the present embodiment. Specifically, the structure of the semiconductor light modulation element in the present embodiment is assumed to have the structure shown in FIG. 6, and the structure of the conventional semiconductor light modulation element is assumed to have the structure shown in FIG. did. The simulation was performed by three-dimensional electromagnetic field calculation. As described later, the height H1 of the light modulation waveguide 20 is 220 nm, and the height of the light modulation waveguide 920 is also the same height.

  The structure shown in FIG. 6 is the semiconductor light modulation element in the present embodiment, and connection structure portions 21 and 22 are formed on the side surface of the light modulation waveguide 20. In addition, an oxide film layer 61 and an upper oxide film layer 40 are formed below and above the light modulation waveguide 20 and the connection structures 21 and 22, but regions where the connection structures 21 and 22 are formed. In FIG. 3, the oxide film layer 61 and a part of the upper oxide film layer 40 are removed. Specifically, the width W1 of the light modulation waveguide 20 is 440 nm, the connection structures 21 and 22 have a width K1 of 60 nm and a length L1 of 1 μm, and the pitch of the connection structures 21 and 22 to be formed. P1 is 285 nm. Further, the width S1 of the upper oxide film layer 40 and the oxide film layer 61 to be formed is 600 nm, and the light modulation waveguide 20 and the connection structures 21 and 22 are made of silicon. The film layer 40 is made of silicon oxide. 6A is a top view of the structure, and FIG. 6B is a cross-sectional view taken along the alternate long and short dash line 6A-6B in FIG. 6A.

  FIG. 2 shows a conventional semiconductor light modulation device. As described above, the connection structures 921 and 922 are formed on the side surface of the light modulation waveguide 920. Also, an oxide film layer 902 and an upper oxide film layer 940 are formed below and above the light modulation waveguide 920 and the connection structure portions 921 and 922, and in the region where the connection structure portions 921 and 922 are formed. The oxide film layer 61 and the upper oxide film layer 40 are formed without being removed. Specifically, the width of the light modulation waveguide 920 is 440 nm, the connection structures 921 and 922 have a width of 60 nm and a length of 1 μm, and the pitch of the connection structures 921 and 922 to be formed is 285 nm. It is. Further, the light modulation waveguide 920 and the connection structures 921 and 922 are formed of silicon, and the oxide film layer 902 and the upper oxide film layer 940 are formed of silicon oxide.

  FIG. 7 shows the results obtained by calculation regarding the relationship between the position from the center of the optical waveguide 960 and the light modulation waveguide 20 and the energy density. In FIG. 7, in the semiconductor optical modulation device in the present embodiment shown in FIG. 6, the distribution of energy density in the portion of the dashed line 6A-6B in FIG. In addition, in the conventional semiconductor light modulation device shown in FIG. 2, the distribution of energy density in a portion corresponding to the same portion is shown in 7B. The distribution of energy density of the semiconductor light modulation device in the present embodiment shown in FIG. 7A is compared with the distribution of energy density of the semiconductor light modulation device having the conventional structure shown in FIG. 7B. The energy density in the central part (position is 0 μm) is high. Further, less light leaks to a region outside the optical waveguide such as the light modulation waveguide 20 (the absolute value of the position is about 0.3 μm). Therefore, since the semiconductor light modulation element in the present embodiment shown in 7A can suppress light leaking out of the optical waveguide such as the light modulation waveguide 20, the propagating light is the light modulation waveguide. It can be localized inside the optical waveguide such as 20.

  Next, the result of simulation in another energy density distribution will be described. Specifically, the model of the semiconductor optical modulation element in the present embodiment is assumed to have the structure shown in FIG. 8A, and the model of the structure of the conventional semiconductor optical modulation element is shown in FIG. The structure shown is assumed. FIG. 8B is a model of a structure in which no oxide film layer is formed, and FIG. 8D is a model in the straight optical waveguide 11b. The simulation was performed by three-dimensional electromagnetic field calculation, and the heights of the light modulation waveguides 20 and 920 and the straight optical waveguide 11b described later are 220 nm.

  In the structure shown in FIG. 8A, connection structure portions 21 and 22 are formed on the side surface of the light modulation waveguide 20, and the light modulation waveguide 20 and the connection structure portions 21 and 22 are formed. An upper oxide film layer 40 and an oxide film layer 61 are formed in part of the region. Specifically, the width W1 of the light modulation waveguide 20 is 440 nm, the connection structures 21 and 22 have a width K1 of 60 nm, a length L1 of 1 μm, and the pitch P1 of the connection structures 21 and 22 is 285 nm. belongs to. Further, the width S1 of the upper oxide film layer 40 and the oxide film layer 61 is 600 nm, the optical modulation waveguide 20 and the connection structures 21 and 22 are formed of silicon, and the upper oxide film layer 40 and the oxide film layer 61 are formed. Is formed of silicon oxide.

  In the structure shown in FIG. 8B, connection structure portions 21 and 22 are formed on the side surface of the light modulation waveguide 20, and an oxide film layer is formed on the upper and lower portions. There is nothing. Specifically, the width W2 of the light modulation waveguide 20 is 440 nm, the connection structures 21 and 22 have a width K2 of 60 nm, a length L2 of 1 μm, and the pitch P2 of the connection structures 21 and 22 is 285 nm. belongs to. Further, the light modulation waveguide 20 and the connection structures 21 and 22 are made of silicon.

  In the structure shown in FIG. 8C, the connection structure portions 921 and 922 are formed on the side surface of the light modulation waveguide 920, and the light modulation waveguide 920 and the connection structure portions 921 and 922 are formed. The upper oxide film layer 940 and the oxide film layer 902 are formed in the region. Specifically, the width W3 of the light modulation waveguide 920 is 440 nm, the connection structures 921 and 922 have a width K3 of 60 nm, a length L3 of 1 μm, and the pitch P3 of the connection structures 921 and 922 is 285 nm. belongs to. The light modulation waveguide 920 and the connection structures 921 and 922 are formed of silicon, and the upper oxide film layer 940 and the oxide film layer 902 are formed of silicon oxide.

  In the structure shown in FIG. 8D, the straight optical waveguide 11b is formed on the oxide film layer 61, and the upper oxide film layer 40 is further formed on the straight optical waveguide 11b. Of the structure. Specifically, the width W4 of the straight optical waveguide 11b is 440 nm, the straight optical waveguide 11b is made of silicon, and the oxide film layer 61 and the upper oxide film 40 are made of silicon oxide.

  FIG. 9 shows a result obtained by calculation regarding the relationship between the position from the center of the light modulation waveguides 20 and 920 and the straight optical waveguide 11b and the energy density. In FIG. 9, 9A indicates the energy density of the portion of the structure shown in FIG. 8 (a) along the alternate long and short dash line 8A-8B, and 9B indicates the portion of the structure shown in FIG. 8 (b) along the alternate long and short dashed line 8C-8D. The energy density of 9C indicates the energy density of the portion of the structure shown in FIG. 8 (c) along the alternate long and short dash line 8E-8F, and 9D indicates the energy density of the portion of the structure shown in FIG. 8 (d) along the dashed dotted line 8G-8H. Show. In FIG. 9, the light modulation waveguides 20 and 920 and the straight optical waveguide 11b are described as waveguide cores.

  In FIG. 9, the light shown in 9B can most suppress the light leaking out of the light modulation waveguide 20, but has the lowest mode matching with that shown in 9D. In the case shown in 9C, light leaks most out of the light modulation waveguide 920, and the mode matching property with that shown in 9D is low. In addition, the mode shown in 9A in the present embodiment has the highest mode matching with that shown in 9D, and moreover than the one shown in 9C, it is outside the optical waveguide such as the light modulation waveguide 20 or the like. The light that leaks out is low.

  As described above, the light modulation waveguide 20 in the present embodiment in which the energy distribution shown in 9A is obtained has high mode matching with the straight optical waveguide 11b in which the energy distribution shown in 9D is obtained. Therefore, it is considered that the optical loss of propagating light can be most suppressed.

(Manufacturing method of semiconductor light modulator)
Next, a method for manufacturing a semiconductor light modulation device in the present embodiment will be described with reference to FIGS. 10 to 18, the straight optical waveguides 11a and 11b are omitted for convenience.

  First, as shown in FIG. 10, an SOI (silicon on insulator) substrate is prepared. In the SOI substrate, an oxide film layer 61 called a BOX (buried oxide) layer and a semiconductor layer 50 called an SOI layer are formed on the oxide film layer 61 on a substrate 60 such as Si. . In the present embodiment, silicon oxide having a thickness of 1 to 3 μm is formed as the oxide film layer 61 and crystalline silicon having a thickness of about 220 nm is formed as the semiconductor layer 50 in the SOI substrate. 10 is a cross-sectional view in this step, FIG. 10 (a) is a cross-sectional view of a portion corresponding to the one-dot chain line 4A-4B in FIG. 4, and FIG. 10 (b) is a single point in FIG. It is sectional drawing of the part corresponded to chain line 4C-4D.

Next, as shown in FIG. 11, using the semiconductor layer 50, the optical modulation waveguide 20, the connection structures 21 and 22, and the straight optical waveguides 11a and 11b are formed. Specifically, by applying a photoresist on the surface of the semiconductor layer 50 and performing exposure and development by an exposure apparatus, the light modulation waveguide 20, the connection structures 21 and 22, and the straight optical waveguides 11a and 11b are formed. A resist pattern (not shown) is formed on the region to be formed. After this, RIE (Reactive
By removing the semiconductor layer 50 in a region where the resist pattern is not formed by Ion Etching or the like, the light modulation waveguide 20, the connection structures 21 and 22, and the straight optical waveguides 11a and 11b can be formed. Thereafter, a resist pattern (not shown) is removed with an organic solvent or the like. 11 is a cross-sectional view in this step, FIG. 11 (a) is a cross-sectional view of a portion corresponding to the one-dot chain line 4A-4B in FIG. 4, and FIG. 11 (b) is a single point in FIG. It is sectional drawing of the part corresponded to chain line 4C-4D.

  Next, as shown in FIG. 12, the n-type region 21 a is formed in the connection structure portion 21, and the p-type region 22 a is formed in the connection structure portion 22. Specifically, a photoresist is applied to the surface of the semiconductor layer 50, and exposure and development are performed by an exposure apparatus, thereby forming a resist pattern (not shown) having an opening in a region where the n-type region 21a is formed. . Thereafter, phosphorus (P) ions are implanted to form the n-type region 21a, and the resist pattern (not shown) is removed with an organic solvent or the like. Next, a photoresist is applied again to the surface of the semiconductor layer 50, and exposure and development are performed by an exposure apparatus, thereby forming a resist pattern (not shown) having an opening in a region where the p-type region 22a is formed. . Thereafter, boron (B) ions are implanted to form the p-type region 22a, and a resist pattern (not shown) is removed with an organic solvent or the like. Thereby, the n-type region 21 a can be formed in the connection structure portion 21, and the p-type region 22 a can be formed in the connection structure portion 22. At this time, in the semiconductor layer 50, an n-type region 21a and a p-type region 22a are also formed in a region where a common electrode 30 and a first signal electrode 31 described later are formed. 12 is a cross-sectional view in this step, FIG. 12 (a) is a cross-sectional view of a portion corresponding to the one-dot chain line 4A-4B in FIG. 4, and FIG. 12 (b) is a single point in FIG. It is sectional drawing of the part corresponded to chain line 4C-4D.

Next, as shown in FIG. 13, the upper oxide film layer 40 is formed on the light modulation waveguide 20, the connection structures 21 and 22, and the straight optical waveguides 11a and 11b. Specifically, it is formed by depositing silicon oxide (SiO ₂ ) by CVD (Chemical Vapor Deposition). 13 is a cross-sectional view in this step, FIG. 13 (a) is a cross-sectional view of a portion corresponding to the one-dot chain line 4A-4B in FIG. 4, and FIG. 13 (b) is a single point in FIG. It is sectional drawing of the part corresponded to chain line 4C-4D.

  Next, as shown in FIG. 14, a contact hole 42 for connecting to the common electrode 30, the first signal electrode 31, and the like is formed. The contact hole 42 is for connecting an n-type region 21a in the connection structure 21 and a common electrode 30 to be described later, a p-type region 22a in the connection structure 22 and the first signal electrode 31 and the like. Specifically, a photoresist is applied on the upper oxide film layer 40, and exposure and development are performed by an exposure apparatus to form a resist pattern (not shown) having an opening in a region where the contact hole 42 is to be formed. To do. Thereafter, the upper oxide film layer 40 in the region where the resist pattern is not formed is removed by dry etching such as RIE, and the contact hole 42 is formed. Thereafter, the resist pattern (not shown) is removed with an organic solvent or the like. 14 is a cross-sectional view in this step, FIG. 14 (a) is a cross-sectional view of a portion corresponding to the one-dot chain line 4A-4B in FIG. 4, and FIG. 14 (b) is a single point in FIG. It is sectional drawing of the part corresponded to chain line 4C-4D.

  Next, as shown in FIG. 15, a metal film 35 is formed on the upper oxide film layer 40. Specifically, the metal film 35 is formed by forming an Al film on the upper oxide film layer 40 by sputtering. The metal film 35 is for forming a common electrode 30, a first signal electrode 31, and the like, which will be described later, and is formed in contact with the n-type region 21a and the p-type region 22a exposed in the contact hole 42. . 15 is a cross-sectional view in this step, FIG. 15A is a cross-sectional view of a portion corresponding to the one-dot chain line 4A-4B in FIG. 4, and FIG. 15B is a cross-sectional view in FIG. It is sectional drawing of the part corresponded to chain line 4C-4D.

  Next, as shown in FIG. 16, an opening 41 is formed in the upper oxide film layer 40. Specifically, a photoresist is applied on the metal film 35, and exposure and development are performed by an exposure apparatus, thereby forming a resist pattern (not shown) having an opening in a region where the opening 41 is formed. Thereafter, the opening 41 is formed by removing the metal film 35 and the upper oxide film layer 40 in the region where the resist pattern is not formed by dry etching. 16 is a cross-sectional view in this step, FIG. 16 (a) is a cross-sectional view of a portion corresponding to the one-dot chain line 4A-4B in FIG. 4, and FIG. 16 (b) is a single point in FIG. It is sectional drawing of the part corresponded to chain line 4C-4D.

  Next, as shown in FIG. 17, a space 62 is formed in the oxide film layer 61. Specifically, the oxide film layer 61 is etched from the opening 41 by etching using hydrofluoric acid in a gas phase state. In the etching using the hydrofluoric acid in the gas phase, the hydrofluoric acid in the gas phase wraps around and etches the oxide film. Therefore, in the opening 41, below the portion where the connection structures 21 and 22 are formed. The oxide film layer 61 can be removed by etching. In this manner, the space portion 62 is formed by removing the oxide film layer 61 in contact with the portion where the connection structure portions 21 and 22 are formed in the opening portion 41. Thereafter, a resist pattern (not shown) is removed. 17 is a cross-sectional view in this step, FIG. 17A is a cross-sectional view of a portion corresponding to the one-dot chain line 4A-4B in FIG. 4, and FIG. 17B is a single point in FIG. It is sectional drawing of the part corresponded to chain line 4C-4D.

  Next, as shown in FIG. 18, the unnecessary metal film 35 is removed to form the common electrode 30, the first signal electrode 31, and the like with the remaining metal film 35. Specifically, a photoresist is applied on the metal film 35, and exposure and development are performed by an exposure apparatus, thereby forming a resist pattern (not shown) having an opening in a region where the metal film 35 is removed. Next, the metal film 35 exposed at the opening of the resist pattern is removed by wet etching using acid or the like. Thereby, the common electrode 30 connected to the n-type region 21a, the first signal electrode 31 connected to the p-type region 22a, and the like are formed. Thereafter, the resist pattern (not shown) is removed with an organic solvent or the like. 18 is a cross-sectional view in this step, FIG. 18 (a) is a cross-sectional view of a portion corresponding to the one-dot chain line 4A-4B in FIG. 4, and FIG. 18 (b) is a single point in FIG. It is sectional drawing of the part corresponded to chain line 4C-4D.

  With the above manufacturing method, the semiconductor light modulation device in this embodiment can be manufactured.

[Second Embodiment]
Next, a second embodiment will be described. In the present embodiment, a photonic crystal is formed instead of the connection structures 21 and 22. Based on FIG. 19, the semiconductor light modulation device in the present embodiment will be described. FIG. 19A is a top view of the semiconductor light modulation device in the present embodiment, and FIG. 19B is a cross-sectional view taken along the alternate long and short dash line 19A-19B in FIG. The semiconductor light modulation device according to the present embodiment includes both sides of the light modulation waveguide 120 serving as a core layer, that is, between the light modulation waveguide 120 and the common electrode 30, and between the light modulation waveguide 120 and the first signal electrode. Photonic crystal regions 121 and 122 are formed between them and the like. In the photonic crystal regions 121 and 122, cylindrical holes 123 having a diameter of 215 nm are formed in a two-dimensional cycle with a pitch of 400 nm, and the photonic crystal is formed by the holes 123 formed in the two-dimensional cycle. Is formed. On the other hand, in the light modulation waveguide 120, since such a hole 123 is not formed, light can be propagated. In such a semiconductor device in this embodiment, a highly efficient phase shifter using the slow light effect of a two-dimensional photonic crystal can be obtained. Even when the slow light effect is used, the absorption loss due to the spread of the propagation light becomes a problem. However, in the semiconductor light modulation device in the present embodiment, a part of the upper upper oxide film layer 40 in the photonic crystal regions 121 and 122 is removed to form the opening 41, and the lower oxide film layer 61 is formed. Is removed to form a space 62. Thereby, optical loss due to mode mismatch or the like can be reduced.

  In the semiconductor optical modulation element in the present embodiment, the holes 123 are formed by the same process as the process of forming the connection structures 21 and 22 shown in FIG. 11 in the manufacturing method in the first embodiment. Can be produced. In the semiconductor light modulation device in the present embodiment, the photonic crystal regions 121 and 122 can be formed by such holes 123. Further, in the etching using hydrofluoric acid in the gas phase, since the hydrofluoric acid in the gas phase enters from the holes 123, the space 62 is formed as in the case shown in FIG. 17 in the first embodiment. Is possible.

  The contents other than the above are the same as in the first embodiment.

[Third Embodiment]
(Semiconductor light modulator)
Next, a third embodiment will be described. The semiconductor light modulation element in the present embodiment has a structure in which a low refractive index material layer is formed in a portion corresponding to the space 62 of the semiconductor light modulation element in the first embodiment.

  Based on FIG. 20 and FIG. 21, the semiconductor optical modulation element in the present embodiment will be described. FIG. 20 is a top view of the semiconductor light modulation device in the present embodiment. FIG. 21A is a cross-sectional view taken along the alternate long and short dash line 20A-20B, FIG. 21B is a cross-sectional view taken along the alternate long and short dash line 20C-20D, and FIG. It is sectional drawing cut | disconnected in the dashed line 20E-20F.

  As described above, the semiconductor light modulation element in the present embodiment has a structure in which the low refractive index material layer 262 is formed in a portion corresponding to the space 62 of the semiconductor light modulation element in the first embodiment. . Like the semiconductor light modulation element in the first embodiment, when the space 62 is air, vacuum, or the like, the refractive index is the lowest, which is preferable in terms of characteristics. However, even when the low refractive index material layer 262 is formed in a portion corresponding to the space portion 62 of the semiconductor optical modulation element in the first embodiment as in the present embodiment, the first embodiment has the same structure. The same effects as those can be obtained. In the present embodiment, since the portion corresponding to the space 62 is filled with the low refractive index material layer 262, the mechanical strength is further increased, which is preferable in terms of reliability and the like.

As a material for forming the low refractive index material layer 262, a material having a refractive index lower than that of silicon oxide is preferable, and examples thereof include magnesium fluoride (MgF ₂ ).

(Manufacturing method of semiconductor light modulator)
Next, a method for manufacturing the semiconductor light modulation device in the present embodiment will be described with reference to FIGS. 22 to 31, the straight optical waveguides 11a and 11b are omitted for convenience.

  First, as shown in FIG. 22, an SOI substrate is prepared. The SOI substrate is obtained by forming an oxide film layer 61 called a BOX layer on a substrate 60 such as Si and a semiconductor layer 50 called an SOI layer on the oxide film layer 61. In the present embodiment, silicon oxide having a thickness of 1 to 3 μm is formed as the oxide film layer 61 and crystalline silicon having a thickness of about 220 nm is formed as the semiconductor layer 50 in the SOI substrate. 22 is a cross-sectional view in this step, FIG. 22 (a) is a cross-sectional view of a portion corresponding to the alternate long and short dash line 20A-20B in FIG. 20, and FIG. 22 (b) is a single point in FIG. It is sectional drawing of the part corresponded to chain line 20C-20D.

  Next, as shown in FIG. 23, the optical modulation waveguide 20, the connection structures 21 and 22, and the straight optical waveguides 11 a and 11 b are formed using the semiconductor layer 50. Specifically, by applying a photoresist on the surface of the semiconductor layer 50 and performing exposure and development by an exposure apparatus, the light modulation waveguide 20, the connection structures 21 and 22, and the straight optical waveguides 11a and 11b are formed. A resist pattern (not shown) is formed on the region to be formed. Thereafter, the semiconductor layer 50 in the region where the resist pattern is not formed is removed by RIE or the like, thereby forming the light modulation waveguide 20, the connection structures 21 and 22, and the straight optical waveguides 11a and 11b. Thereafter, a resist pattern (not shown) is removed with an organic solvent or the like. 23 is a cross-sectional view in this step, FIG. 23 (a) is a cross-sectional view of a portion corresponding to the alternate long and short dash line 20A-20B in FIG. 20, and FIG. 23 (b) is a single point in FIG. It is sectional drawing of the part corresponded to chain line 20C-20D.

  Next, as shown in FIG. 24, the n-type region 21 a is formed in the connection structure portion 21, and the p-type region 22 a is formed in the connection structure portion 22. Specifically, a photoresist is applied to the surface of the semiconductor layer 50, and exposure and development are performed by an exposure apparatus, thereby forming a resist pattern (not shown) having an opening in a region where the n-type region 21a is formed. . Thereafter, phosphorus (P) ions are implanted to form the n-type region 21a, and the resist pattern (not shown) is removed with an organic solvent or the like. Next, a photoresist is applied again to the surface of the semiconductor layer 50, and exposure and development are performed by an exposure apparatus, thereby forming a resist pattern (not shown) having an opening in a region where the p-type region 22a is formed. . Thereafter, boron (B) ions are implanted to form the p-type region 22a, and a resist pattern (not shown) is removed with an organic solvent or the like. Thereby, the n-type region 21 a can be formed in the connection structure portion 21, and the p-type region 22 a can be formed in the connection structure portion 22. At this time, in the semiconductor layer 50, an n-type region 21a and a p-type region 22a are also formed in a region where a common electrode 30 and a first signal electrode 31 described later are formed. 24 is a cross-sectional view in this step, FIG. 24 (a) is a cross-sectional view of a portion corresponding to the alternate long and short dash line 20A-20B in FIG. 20, and FIG. 24 (b) is a single point in FIG. It is sectional drawing of the part corresponded to chain line 20C-20D.

Next, as shown in FIG. 25, an upper oxide film layer 40 is formed on the light modulation waveguide 20, the connection structures 21 and 22, and the straight optical waveguides 11a and 11b. Specifically, it is formed by depositing silicon oxide (SiO ₂ ) by CVD. 25 is a cross-sectional view in this step, FIG. 25 (a) is a cross-sectional view of a portion corresponding to the alternate long and short dash line 20A-20B in FIG. 20, and FIG. 25 (b) is a single point in FIG. It is sectional drawing of the part corresponded to chain line 20C-20D.

  Next, as shown in FIG. 26, a contact hole 42 for connecting to the common electrode 30, the first signal electrode 31, and the like is formed. The contact hole 42 is for connecting an n-type region 21a in the connection structure 21 and a common electrode 30 to be described later, a p-type region 22a in the connection structure 22 and the first signal electrode 31 and the like. Specifically, a photoresist is applied on the upper oxide film layer 40, and exposure and development are performed by an exposure apparatus to form a resist pattern (not shown) having an opening in a region where the contact hole 42 is to be formed. To do. Thereafter, the upper oxide film layer 40 in the region where the resist pattern is not formed is removed by dry etching such as RIE, and the contact hole 42 is formed. Thereafter, the resist pattern (not shown) is removed with an organic solvent or the like. 26 is a cross-sectional view in this step, FIG. 26 (a) is a cross-sectional view of a portion corresponding to the alternate long and short dash line 20A-20B in FIG. 20, and FIG. 26 (b) is a single point in FIG. It is sectional drawing of the part corresponded to chain line 20C-20D.

  Next, as shown in FIG. 27, a metal film 35 is formed on the upper oxide film layer 40. Specifically, the metal film 35 is formed by forming an Al film on the upper oxide film layer 40 by sputtering. The metal film 35 is for forming a common electrode 30, a first signal electrode 31, and the like, which will be described later, and is formed in contact with the n-type region 21a and the p-type region 22a exposed in the contact hole 42. . 27 is a cross-sectional view in this step, FIG. 27A is a cross-sectional view of a portion corresponding to the alternate long and short dash line 20A-20B in FIG. 20, and FIG. 27B is a cross-sectional view in FIG. It is sectional drawing of the part corresponded to chain line 20C-20D.

  Next, as shown in FIG. 28, an opening 41 is formed in the upper oxide film layer 40. Specifically, a photoresist is applied on the metal film 35, and exposure and development are performed by an exposure apparatus, thereby forming a resist pattern (not shown) having an opening in a region where the opening 41 is formed. Thereafter, the opening 41 is formed by removing the metal film 35 and the upper oxide film layer 40 in the region where the resist pattern is not formed by dry etching. 28 is a cross-sectional view in this step, FIG. 28 (a) is a cross-sectional view of a portion corresponding to the alternate long and short dash line 20A-20B in FIG. 20, and FIG. 28 (b) is a single point in FIG. It is sectional drawing of the part corresponded to chain line 20C-20D.

  Next, as shown in FIG. 29, a space 62 is formed in the oxide film layer 61. Specifically, the oxide film layer 61 is etched from the opening 41 by etching using hydrofluoric acid in a gas phase state. In the etching using the hydrofluoric acid in the gas phase, the hydrofluoric acid in the gas phase wraps around and etches the oxide film. Therefore, in the opening 41, below the portion where the connection structures 21 and 22 are formed. The oxide film layer 61 can be removed by etching. In this manner, the space portion 62 is formed by removing the oxide film layer 61 in contact with the portion where the connection structure portions 21 and 22 are formed in the opening portion 41. Thereafter, a resist pattern (not shown) is removed. 29 is a cross-sectional view in this step, FIG. 29A is a cross-sectional view of a portion corresponding to the alternate long and short dash line 20A-20B in FIG. 20, and FIG. 29B is a single point in FIG. It is sectional drawing of the part corresponded to chain line 20C-20D.

  Next, as shown in FIG. 30, a low refractive index material layer 262 is formed in the space 62 formed in the oxide film layer 61 and the opening 41 formed in the upper oxide film layer 40. The low refractive index material layer 262 is made of a material having a lower refractive index than silicon oxide such as magnesium fluoride, and can be formed by a vacuum film formation method such as sputtering. 30 is a cross-sectional view in this step, FIG. 30 (a) is a cross-sectional view of a portion corresponding to the alternate long and short dash line 20A-20B in FIG. 20, and FIG. 30 (b) is a single point in FIG. It is sectional drawing of the part corresponded to chain line 20C-20D.

  Next, as shown in FIG. 31, the unnecessary metal film 35 is removed to form the common electrode 30, the first signal electrode 31, and the like with the remaining metal film 35. Specifically, a photoresist is applied on the metal film 35, and exposure and development are performed by an exposure apparatus, thereby forming a resist pattern (not shown) having an opening in a region where the metal film 35 is removed. Next, the metal film 35 exposed at the opening of the resist pattern is removed by wet etching using acid or the like. Thereby, the common electrode 30 connected to the n-type region 21a, the first signal electrode 31 connected to the p-type region 22a, and the like can be formed. Thereafter, the resist pattern (not shown) is removed with an organic solvent or the like. 31 is a cross-sectional view in this step, FIG. 31 (a) is a cross-sectional view of a portion corresponding to the alternate long and short dash line 20A-20B in FIG. 20, and FIG. 31 (b) is a single point in FIG. It is sectional drawing of the part corresponded to chain line 20C-20D.

  Through the above-described steps, the semiconductor light modulation device in the present embodiment can be manufactured.

  The contents other than the above are the same as those in the first embodiment. In addition, this embodiment can be applied to the semiconductor light modulation element in the second embodiment.

[Fourth Embodiment]
(Semiconductor light modulator)
A semiconductor light modulation device in the fourth embodiment will be described with reference to FIGS. 32 and 33. FIG. 32 is an enlarged view of a region surrounded by the alternate long and short dash line 3A in FIG. 3 described in the first embodiment in the semiconductor light modulation device in the present embodiment. FIG. 33A is a cross-sectional view taken along one-dot chain line 32A-32B in FIG. Fig.33 (a) is sectional drawing cut | disconnected by the dashed-dotted line 32C-32D in FIG. FIG. 33C is a cross-sectional view taken along the alternate long and short dash line 32E-32F in FIG.

  In the present embodiment, the first optical waveguide 11 and the second optical waveguide 12 serving as the core layer are provided with a light modulation waveguide 320 or the like, and light enters the light modulation waveguide 320 or the like. Straight optical waveguides 11a and 11b are provided on the side and the exit side. Further, on both sides of the side surface of the light modulation waveguide 320, slab layers 321 and 322 are formed by partially removing the surface of the semiconductor layer and reducing the thickness of the semiconductor layer. Note that the slab layers 321 and 322 in this embodiment may be described as a connection structure portion.

  In the present embodiment, the width W5 of the light modulation waveguide 320 serving as the core layer is formed to be about 440 nm, and the light modulation waveguide 320 and the common electrode 30 or the first signal electrode 31 The interval D5 is formed to be about 1 μm. The height H5 of the light modulation waveguide 320 is about 220 nm, and the height HS5 of the slab layers 321 and 322 is such that light propagating through the light modulation waveguide 320 etc. leaks from the light modulation waveguide 320 etc. It is formed to be about 50 nm so as not to be emitted.

  In the semiconductor light modulation device in the present embodiment, one slab layer 321 is provided with an n-type region 321a, and the slab layer 321 and the common electrode 30 are connected in the n-type region 321a. The other slab layer 322 is provided with a p-type region 322a, and the slab layer 322 and the first signal electrode 31 are connected in the p-type region 322a.

In the present embodiment, P (phosphorus) is ion-implanted as an impurity element in n-type region 321a so that the impurity concentration is about 1 × 10 ²⁰ cm ⁻³ . Also, B (boron) is ion-implanted as an impurity element in the p-type region 222a so that the impurity concentration is about 1 × 10 ²⁰ cm ⁻³ . In the present embodiment, As or the like can be used in addition to P as the impurity element for forming the n-type region 221a, and B as the impurity element for forming the p-type region 222a. In addition, Al or the like can be used. In the present embodiment, the n-type is described as the first conductivity type and the p-type is described as the second conductivity type, but these relationships may be reversed.

  In the semiconductor light modulation device in the present embodiment, an upper oxide film layer 340 is formed on the light modulation waveguide 320 or the like. The upper oxide film layer 340 is formed of silicon oxide, and the optical modulation waveguide 320 or the like that is a core layer includes an oxide film layer 61 and an upper oxide film layer that are lower oxide films formed on the substrate 60. The upper and lower sides are sandwiched by 340.

  In the semiconductor light modulation device having such a structure, by changing the voltage applied between the common electrode 30 and the first signal electrode 31, electrons and holes are formed between the n-type region 321a and the p-type region 322a. The concentration of free carriers can be changed. Thereby, the refractive index in the light modulation waveguide 320 which is the core layer is changed by the free carrier plasma effect, and the phase of light propagating in the light modulation waveguide 320 can be modulated.

  Further, in the semiconductor light modulation device in the present embodiment, in the regions on both sides of the light modulation waveguide 320, the opening 341 is removed by removing a part of the upper oxide film layer 340 in the upper portions of the slab layers 321 and 322. Is formed.

  Thus, by forming the opening 341 in the upper oxide film layer 340, light propagating through the light modulation waveguide 320 can be further prevented from leaking into the slab layers 321 and 322, and the light modulation guide can be prevented. The localization of light inside the waveguide 320 can be enhanced. Thus, by increasing the localization of light in the light modulation waveguide 320, reflection between the light modulation waveguide 320 and the straight optical waveguide 11b can be reduced, and the loss of propagating light is suppressed. be able to. Note that the closer the opening 341 is to the light modulation waveguide 320, the more the propagation light can be prevented from leaking into the slab layers 321 and 322, and the loss of light propagating through the light modulation waveguide 320 can be further reduced. , Can be reduced.

  Next, based on FIG. 34 and FIG. 35, the result of having performed simulation about the energy density distribution in an optical waveguide is demonstrated. FIG. 34 (a) corresponds to the semiconductor optical modulation element in the present embodiment. Specifically, the light modulation waveguide 320 and the slab layers 321 and 322 are formed on the oxide film layer 61, and the upper oxide film layer 340 is formed on the light modulation waveguide 320. The upper oxide layer 340 is not formed on the layers 321 and 322. The light modulation waveguide 320 is formed so that the width W5 is 440 nm and the height H5 is 220 nm, and the slab layers 321 and 322 are formed so that the height HS5 is 50 nm.

  FIG. 34 (b) corresponds to a conventional semiconductor light modulation device. Specifically, a light modulation waveguide 950 and slab layers 951 and 952 are formed on the oxide film layer 971, and an upper oxide film layer 972 is formed on the light modulation waveguide 950 and slab layers 951 and 952. The structure is formed. The light modulation waveguide 950 has a width W6 of 440 nm and a height H6 of 220 nm, and the height HS6 of the slab layers 951 and 952 is 50 nm.

  FIG. 34C shows an optical waveguide 310 corresponding to the straight optical waveguides 11a and 11b. The optical waveguide 310 is formed on the oxide film layer 61, and an upper oxide film 340 is formed on the optical waveguide 310 so as to cover the entire optical waveguide 310. The optical waveguide 310 is formed so that the width W7 is 440 nm and the height H7 is 220 nm.

FIG. 35 shows the energy density distribution of these structures. Specifically, FIG. 35A shows the energy density distribution of the structure shown in FIG. 34A, and the effective refractive index n _eff of this structure is 2.448. FIG. 35B shows the energy density distribution of the structure shown in FIG. 34B, and the effective refractive index n _eff of this structure is 2.491. FIG. 35C shows the energy density distribution of the structure shown in FIG. 34C, and the effective refractive index n _eff of this structure is 2.441.

From the above, the effective refractive index n _eff of the structure shown in FIG. 34 (a) is more effective than that of the structure shown in FIG. 34 (b). It is close to the value of the rate n _eff . That is, the difference in effective refractive index n _eff between the structure shown in FIG. 34 (a) and that shown in FIG. 34 (c) is about 0.007, whereas FIG. The difference in effective refractive index n _eff between the structure shown in FIG. 34 and the structure shown in FIG. 34C is about 0.05. Therefore, the structure shown in FIG. 34 (a) has higher mode matching with the structure shown in FIG. 34 (c) than the structure shown in FIG. 34 (b). There is little optical loss when entering the structure shown in 34 (c). That is, the light loss when entering the straight optical waveguide 11b is smaller in the structure shown in FIG. 34A than in the structure shown in FIG.

(Manufacturing method of semiconductor light modulator)
Next, a method for manufacturing the semiconductor light modulation device in the present embodiment will be described with reference to FIGS. 36 to 38 are cross-sectional views in respective steps of a portion corresponding to the alternate long and short dash line 32A-32B in FIG. 36 to 38, the straight optical waveguides 11a and 11b are omitted for convenience.

  First, as shown in FIG. 36A, an SOI substrate is prepared. The SOI substrate is obtained by forming an oxide film layer 61 called a BOX layer on a substrate 60 such as Si and a semiconductor layer 350 called an SOI layer on the oxide film layer 61. In this embodiment mode, silicon oxide having a thickness of 1 to 3 μm is formed as the oxide film layer 61 and crystalline silicon having a thickness of about 220 nm is formed as the semiconductor layer 350 in the SOI substrate.

  Next, as illustrated in FIG. 36B, the light modulation waveguide 320 and the slab layers 321 and 322 are formed using the semiconductor layer 350. Specifically, a photoresist is applied to the surface of the semiconductor layer 350, and exposure and development are performed by an exposure apparatus, thereby forming a resist pattern (not shown) having openings in regions where the slab layers 321 and 322 are formed. . Thereafter, in the region where the resist pattern is not formed, the exposed semiconductor layer 350 is removed by dry etching such as RIE until the thickness becomes about 50 nm, whereby the light modulation waveguide 320 and the slab layer 321 are removed. And 322 are formed. Thereafter, the resist pattern (not shown) is removed with an organic solvent or the like.

  Next, as shown in FIG. 36C, an n-type region 321a is formed in the slab layer 321 and a p-type region 322a is formed in the slab layer 322. Specifically, a photoresist is applied to the surface of the semiconductor layer 350, and exposure and development are performed by an exposure apparatus, thereby forming a resist pattern (not shown) having an opening in a region where the n-type region 321a is formed. . Thereafter, phosphorus (P) ions are implanted to form an n-type region 321a, and a resist pattern (not shown) is removed with an organic solvent or the like. Next, a photoresist is applied to the surface of the semiconductor layer 350 again, and exposure and development are performed by an exposure apparatus, thereby forming a resist pattern (not shown) having an opening in a region where the p-type region 322a is formed. . Thereafter, boron (B) ions are implanted to form a p-type region 322a, and a resist pattern (not shown) is removed with an organic solvent or the like. Accordingly, the n-type region 321a can be formed in the slab layer 321 and the p-type region 322a can be formed in the slab layer 322. At this time, in the semiconductor layer 350, an n-type region 321a and a p-type region 322a are also formed in a region where a common electrode 30 and a first signal electrode 31, which will be described later, are formed.

Next, as shown in FIG. 37A, an upper oxide film layer 340 is formed on the light modulation waveguide 320, the slab layers 321 and 322, and the like. Specifically, it is formed by depositing silicon oxide (SiO ₂ ) by CVD.

  Next, as shown in FIG. 37B, a contact hole 342 for connecting to the common electrode 30, the first signal electrode 31, and the like is formed in the upper oxide film layer 340. The contact hole 42 is for connecting an n-type region 321a in the slab layer 321 and a common electrode 30 described later, a p-type region 322a in the slab layer 322, the first signal electrode 31, and the like. Specifically, a photoresist is applied on the upper oxide film layer 340, and exposure and development are performed by an exposure apparatus, thereby forming a resist pattern (not shown) having an opening in a region where the contact hole 342 is formed. To do. Thereafter, the upper oxide film layer 340 in the region where the resist pattern is not formed is removed by dry etching such as RIE, and a contact hole 342 is formed. Thereafter, the resist pattern (not shown) is removed with an organic solvent or the like.

  Next, as shown in FIG. 37C, a metal film 335 is formed on the upper oxide film layer 340. Specifically, the metal film 335 is formed by forming an Al film on the upper oxide film layer 340 by sputtering. The metal film 335 is used to form a common electrode 30, a first signal electrode 31, and the like, which will be described later, and is formed in contact with the n-type region 321a and the p-type region 322a exposed in the contact hole 342. .

  Next, as shown in FIG. 38A, an opening 341 is formed in the upper oxide film layer 340. Specifically, a photoresist is applied on the metal film 335, and exposure and development are performed by an exposure apparatus, thereby forming a resist pattern (not shown) having an opening in a region where the opening 341 is formed. Thereafter, the opening 341 is formed by removing the metal film 335 and the upper oxide film layer 340 in the region where the resist pattern is not formed by dry etching.

  Next, as shown in FIG. 38B, the unnecessary metal film 335 is removed, thereby forming the common electrode 30, the first signal electrode 31, and the like from the remaining metal film 335. Specifically, a photoresist is applied on the metal film 335, and exposure and development are performed by an exposure apparatus, thereby forming a resist pattern (not shown) having an opening in a region where the metal film 335 is removed. Next, the metal film 335 exposed at the opening of the resist pattern is removed by wet etching using acid or the like. Thereby, the common electrode 30 connected to the n-type region 321a, the first signal electrode 31 connected to the p-type region 322a, and the like can be formed. Thereafter, the resist pattern (not shown) is removed with an organic solvent or the like.

  Through the above-described steps, the semiconductor light modulation device in the present embodiment can be manufactured. The contents other than the above are the same as those in the first embodiment.

  Although the embodiment has been described in detail above, it is not limited to the specific embodiment, and various modifications and changes can be made within the scope described in the claims.

In addition to the above description, the following additional notes are disclosed.
(Appendix 1)
An optical modulation waveguide made of a semiconductor material through which incident light propagates;
On both sides of the side surface of the light modulation waveguide, a connection structure portion formed of a semiconductor material connected to each side surface of the light modulation waveguide;
A lower oxide film layer formed below the light modulation waveguide and the connection structure;
A space formed by removing a part of the lower oxide film layer in contact with the connection structure;
A semiconductor light modulation device comprising:
(Appendix 2)
An upper oxide film layer formed above the light modulation waveguide and the connection structure;
In the upper oxide film layer, an opening formed in a part or all of the connection structure portion;
2. The semiconductor light modulation device according to appendix 1, wherein:
(Appendix 3)
3. The semiconductor light modulation device according to appendix 1 or 2, wherein a low refractive index material layer is formed in the space portion from a material having a lower refractive index than the lower oxide film layer.
(Appendix 4)
4. The semiconductor light modulation device according to appendix 3, wherein the space portion and the opening portion are formed in corresponding regions via the connection structure portion.
(Appendix 5)
The connection structure is formed by a plurality of rod-shaped members extending from the side surface of the light modulation waveguide,
The semiconductor light modulation device according to any one of appendices 1 to 4, wherein the light modulation waveguide and the connection structure portion are formed with substantially the same thickness.
(Appendix 6)
The semiconductor optical modulation device according to any one of appendices 1 to 4, wherein the connection structure portion is formed of a photonic crystal.
(Appendix 7)
An optical modulation waveguide made of a semiconductor material through which incident light propagates;
A connection structure formed of a semiconductor material formed on both sides of the side surface of the light modulation waveguide, and connected to the side surface of the light modulation waveguide;
An upper oxide film layer formed above the light modulation waveguide and the connection structure;
In the upper oxide film layer, an opening formed in a part or all of the connection structure portion;
A semiconductor light modulation device comprising:
(Appendix 8)
The semiconductor light modulation device according to appendix 7, wherein the connection structure portion is thinner than the light modulation waveguide.
(Appendix 9)
9. The semiconductor light modulation device according to any one of appendices 1 to 8, further comprising an optical waveguide formed on a light emitting side of the light modulation waveguide.
(Appendix 10)
10. The semiconductor light modulation device according to any one of appendices 1 to 9, further comprising an optical waveguide formed on a light incident side of the light modulation waveguide.
(Appendix 11)
One connection structure formed on one side of the side surface of the light modulation waveguide has a region of the first conductivity type,
11. The semiconductor according to any one of appendices 1 to 10, wherein the other connection structure formed on the other side of the side surface of the light modulation waveguide has a second conductivity type region. Light modulation element.
(Appendix 12)
The semiconductor light modulation device according to appendix 11, wherein the first conductivity type is n-type and the second conductivity type is p-type.
(Appendix 13)
The region of the first conductivity type in the one connection structure portion is connected to a common electrode,
13. The semiconductor optical modulation element according to appendix 11 or 12, wherein the second conductivity type region in the other connection structure portion is connected to a signal electrode.
(Appendix 14)
The light modulation waveguide and the connection structure are formed of a common semiconductor layer,
14. The semiconductor light modulation device according to any one of appendices 1 to 13, wherein the semiconductor layer is formed on a lower oxide film layer formed on a substrate.
(Appendix 15)
15. The semiconductor light modulation element according to any one of appendices 1 to 14, wherein the semiconductor material contains silicon.
(Appendix 16)
16. The semiconductor light modulation device according to any one of appendices 1 to 15, wherein the oxide film layer and the upper oxide film layer contain silicon oxide.
(Appendix 17)
A lower oxide film layer is formed on a substrate, and a semiconductor layer is formed on the lower oxide film layer. By removing a part of the semiconductor layer, an optical modulation waveguide and the light Forming a connection structure connected on both sides of the side surface of the modulation waveguide;
A region of the first conductivity type is formed on all or part of one connection structure formed on one side of the side surface of the light modulation waveguide, and the other connection structure formed on the other side. Forming a region of the second conductivity type in all or part of
Forming an upper oxide film layer on the light modulation waveguide and the connection structure;
Forming an opening by removing all or part of the upper oxide film layer on the connection structure;
Forming a space portion by removing a part of the lower oxide film layer in contact with the connection structure portion in the lower oxide film layer corresponding to the opening; and
A method for manufacturing a semiconductor light modulation device, comprising:
(Appendix 18)
18. The method of manufacturing a semiconductor light modulation device according to appendix 17, wherein the space portion is formed by removing a part of the lower oxide film layer with hydrofluoric acid in a gas phase state.
(Appendix 19)
19. The method for manufacturing a semiconductor light modulation device according to appendix 18, wherein the space portion includes a step of forming a low refractive index material layer with a material having a lower refractive index than the lower oxide film layer.
(Appendix 20)
Forming a common electrode connected to a first conductivity type region of the one connection structure portion and a signal electrode connected to a second conductivity type region of the other connection structure portion. 20. A method for manufacturing a semiconductor light modulation device according to any one of appendices 17 to 19.

10a Optical waveguide (incident side)
10b Optical waveguide (outgoing side)
11 first optical waveguide 11a connection structure 11b connection structure 12 second optical waveguide 20 light modulation waveguide 21 connection structure 21a n-type region 22 connection structure 22a p-type region 30 common electrode 31 first signal electrode 32 Second signal electrode 40 Upper oxide film layer 41 Opening 50 Semiconductor layer 60 Substrate 61 Oxide film layer (lower oxide film layer)
62 Space 70 Voltage signal source

Claims (8)

An optical modulation waveguide made of a semiconductor material through which incident light propagates;
On both sides of the side surface of the light modulation waveguide, a connection structure portion formed of a semiconductor material connected to each side surface of the light modulation waveguide;
An upper oxide film layer formed above the light modulation waveguide and the connection structure;
In the upper oxide film layer, an opening formed in a part or all of the connection structure portion;
A lower oxide film layer formed below the light modulation waveguide and the connection structure;
A space portion that is more formed to remove a portion of the lower oxide layer in contact with the connection unit,
I have a,
Rukoto not across the optical modulation waveguides without the lower oxide film layer formed on the lower side of the upper oxide layer and the light modulation waveguide formed on an upper side of the light modulation waveguide is removed A semiconductor light modulation device. In the space portion, the semiconductor optical modulator according to claim 1, characterized in that the low refractive index material layer is formed of a material having a lower refractive index than the lower oxide layer. The connection structure is formed by a plurality of rod-shaped members extending from the side surface of the light modulation waveguide,
3. The semiconductor light modulation device according to claim 1, wherein the light modulation waveguide and the connection structure portion are formed with substantially the same thickness. The connection unit includes a semiconductor optical modulation device according to claim 1 or 2, characterized in that formed by the photonic crystal. The optical modulator device according to any one of the four claims 1, characterized in that it comprises an optical waveguide formed on the side where light is emitted in the light modulation waveguide. One connection structure formed on one side of the side surface of the light modulation waveguide has a region of the first conductivity type,
The other connection unit formed on the other side of the side surface of the light modulation waveguide, according to any one of claims 1 to 5, characterized in that it has a region of the second conductivity type Semiconductor light modulation device . A lower oxide film layer is formed on a substrate, and a semiconductor layer is formed on the lower oxide film layer. By removing a part of the semiconductor layer, an optical modulation waveguide and the light Forming a connection structure connected on both sides of the side surface of the modulation waveguide;
A region of the first conductivity type is formed on all or part of one connection structure formed on one side of the side surface of the light modulation waveguide, and the other connection structure formed on the other side. Forming a region of the second conductivity type in all or part of
Forming an upper oxide film layer on the light modulation waveguide and the connection structure;
Forming an opening by removing all or part of the upper oxide film layer on the connection structure;
Forming a space portion by removing a part of the lower oxide film layer in contact with the connection structure portion in the lower oxide film layer corresponding to the opening; and
A method for manufacturing a semiconductor light modulation device, comprising: 8. The method of manufacturing a semiconductor light modulation device according to claim 7 , wherein the space portion is formed by removing a part of the lower oxide film layer with hydrofluoric acid in a gas phase state. .