JP6867316B2 - Optical device - Google Patents

Description

The present invention relates to an optical device that can be combined with a silicon electronic device.

In recent years, in order to improve the efficiency and reduce the cost of manufacturing optical devices, the technology for manufacturing optical devices using mature semiconductor electronic device manufacturing equipment has been advanced. In particular, an optical modulator that combines a silicon optical waveguide and an electronic device structure has been energetically developed (Non-Patent Document 1).

Further, it is also realized that such a semiconductor optical device and an electronic device are monolithically integrated on the same wafer. For example, there is a technique for consistently manufacturing and integrating an optical device and a drive / control electronic circuit by a wafer process (see Non-Patent Document 2). This is expected to simplify the post-process and reduce the manufacturing cost.

U.S. Patent Application Publication No. 2012/0280345

G. T. Reed et al., "Silicon optical modulators", Nature Photonics, vol. 4, pp. 518-526, 2010. B. Analui et al., "A Fully Integrated 20-Gb / s Optoelectronic Transceiver Implemented in a Standard 0.13-m CMOS SOI Technology", IEEE Journal of Solid-State Circuits, vol. 41, no. 12, pp. 2945- 2955, 2006.

However, there is a problem that the silicon optical device that realizes the operation such as optical modulation is larger than the general electronic device structure. For example, in the silicon optical waveguide type modulator shown in Non-Patent Document 1, the core width of the silicon (Si) optical waveguide constituting the optical phase shifter is generally several hundred nm, and the core height is also several hundred. It is nm. From the viewpoint of the manufacturing process, the Si core line width formed by lithography is an order of magnitude larger than the Si pattern line width of electronic devices such as transistor gates. Further, in the formation of the Si core by dry etching, there is a problem that processing that is not in the Si layer process process of the electronic device is required, and manufacturing equipment and manufacturing conditions that are significantly different from those of the electronic device are required.

Further, in the conventional Si waveguide type modulation, _{a clad made of SiO 2} having a low refractive index is generally arranged in the lower part of the Si core to a thickness of several μm in order to confine the light in the Si waveguide. It is also different from electronic devices in that respect. Therefore, in the conventional Si waveguide type modulation, a silicon-on-insulator (SOI) substrate having an embedded oxide film (BOX) layer having a thickness of several μm is used in manufacturing, and a thick box layer is used as a clad. On the other hand, in the manufacture of electronic devices, an SOI substrate having such a thick BOX layer is not used, and the manufacture of an optical modulator in the substrate is also significantly different from the manufacture of an electronic device.

The above-mentioned difference has been a major obstacle to the efficiency and cost reduction of optical device manufacturing by using the electronic device manufacturing equipment.

The present invention has been made to solve the above problems, and an object of the present invention is to enable more efficient and low-cost manufacturing of optical devices by using electronic device manufacturing equipment.

The optical device according to the present invention includes a gate electrode formed on a silicon layer via a gate insulating layer, a source region and a drain region formed on the silicon layer with a region on which the gate electrode is formed, and a drain region. A metal source electrode formed by connecting over the source region, a metal drain electrode formed by connecting over the drain region, and a metal VDD formed between the source region and the source electrode. The silicon layer is provided with a source contact layer made of the same material and a drain contact layer made of a metal silicide formed between the drain region and the drain electrode, and is sandwiched between the source contact layer and the drain contact layer in a silicon layer directly below the gate electrode. A plasmonic waveguide having a region of the formed channel as a core and a gate width direction as a waveguide direction is provided.

In the above optical device, the gate electrode further comprises a gate contact layer made of silicon and made of a metal silicide formed on the gate electrode.

In the above optical device, the gate insulating layer may be made of silicon nitride.

The optical device includes another plasmonic waveguide formed in a silicon layer continuously with the plasmonic waveguide.

In the above optical device, the silicon layer is a silicon substrate. Further, the silicon layer may be a surface silicon layer of the SOI substrate.

As described above, according to the present invention, a source contact layer made of metal silicide is provided between the source region and the source electrode, and a drain contact layer made of metal silicide is provided between the drain region and the drain electrode. Since a plasmonic waveguide having a channel region formed in the silicon layer directly below the gate electrode sandwiched between the source contact layer and the drain contact layer as the core is constructed, it is more efficient to use electronic device manufacturing equipment. The excellent effect of being able to manufacture optical devices at low cost can be obtained.

FIG. 1 is a cross-sectional view showing the configuration of an optical device according to the first embodiment of the present invention. FIG. 2 is a distribution diagram showing the results of calculating the electric field strength distribution in the plasmonic mode for the optical device according to the first embodiment by the two-dimensional finite element method. FIG. 3 is a cross-sectional view showing the configuration of the optical device according to the second embodiment of the present invention. FIG. 4 is a distribution diagram showing the results of calculating the electric field strength distribution in the plasmonic mode for the optical device according to the second embodiment by the two-dimensional finite element method.

Hereinafter, embodiments of the present invention will be described.

[Embodiment 1]
First, the optical device according to the first embodiment of the present invention will be described with reference to FIG. In this optical device, first, a gate electrode 103 formed on the silicon layer 101 via a gate insulating layer 102 and a source region 104 formed on the silicon layer 101 with a region on which the gate electrode 103 is formed are interposed. And a drain region 105. The silicon layer 101 may be, for example, a Si substrate. The gate electrode 103 may be made of polysilicon, for example. Further, p-type impurities are introduced into the silicon layer 101, and n-type impurities are introduced into the source region 104 and the drain region 105. These have the same configuration as the well-known n-channel MOSFET.

The optical device also includes a metal source electrode 106 formed by connecting over the source region 104 and a metal drain electrode 107 formed by connecting over the drain region 105.

Further, this optical device is formed between the source contact layer 108 made of metal silicide formed between the source region 104 and the source electrode 106 in the layer thickness direction, and between the drain region 105 and the drain electrode 107. A drain contact layer 109 made of metal silicide is provided. The source contact layer 108 and the drain contact layer 109 are, for example, regions formed by silicating the source region 104 and the drain region 105 from the surface side, respectively.

The source contact layer 108 and the drain contact layer 109 may be made of a material having a negative permittivity real part in the n-channel MOSFET, such as nickel silicide (NiSi), cobalt silicide (CoSi _{2), and tantalum silicide.} For example, by forming a metal layer such as Ni, Co, Ta in the source region 104 and the drain region 105 and forming an alloy of Si and a metal by heating, the source contact layer 108 made of the above-mentioned metal silicide is formed. The drain contact layer 109 can be formed. The source contact layer 108 and the drain contact layer 109 are arranged at the same position (height) in the layer thickness direction as the region 121 of the channel formed between the source region 104 and the drain region 105.

Further, the optical device according to the first embodiment guides the gate width direction with the channel region 121 formed in the silicon layer 101 directly below the gate electrode 103 sandwiched between the source contact layer 108 and the drain contact layer 109 as a core. It is equipped with a plasmonic waveguide in the wave direction. As described above, the plasmonic waveguide having a desired light intensity distribution can be formed by sandwiching the region 121 of the channel with the source contact layer 108 and the drain contact layer 109 having a predetermined thickness.

In the first embodiment, the gate electrode 103 is made of polysilicon, and the gate contact layer 110 made of metal silicide is provided on the gate electrode 103. The gate contact layer 110 may also be made of a material such as _{NiSi, CoSi 2, or tantalum Silicide.} For example, after forming the gate electrode 103, a metal layer such as Ni, Co, Ta is formed on the source region 104 and the drain region 105, and an alloy of Si and a metal is formed by heating. As a result, the gate contact layer 110 can be formed together with the source contact layer 108 and the drain contact layer 109.

Side walls 111 are formed on both sides of the gate electrode 103 and the gate contact layer 110. Further, the gate electrode 103, the gate contact layer 110, the side wall 111, the source electrode 106, and the drain electrode 107 are contained in the passivation film 112. A contact (not shown) connected to each electrode is formed on the passivation film 112, and is connected to a wiring (not shown) formed on the passivation film 112.

Here, the gate electrode 103 and the gate insulating layer 102 made of Si affect the plasmonic mode of the plasmonic waveguide having the channel region 121 as the core. Therefore, by arranging a layer of metal silicide also on the gate electrode 103 and appropriately setting the thickness of the gate electrode 103 and the gate insulating layer, the desired plasmonic mode in the above-mentioned plasmonic waveguide can be used. Can be adjusted to obtain.

In the optical device according to the first embodiment described above, a predetermined bias voltage is applied between the source electrode 106 and the drain electrode 107, and a gate voltage is applied to the gate electrode 103 to carrier the channel region 121. In the region 121 of the channel, the refractive index changes due to the carrier plasma effect. By this change in the refractive index, the above-mentioned plasmonic waveguide can be confined in the plasmonic mode, and intensity / phase modulation can be applied to the light that is guided.

By forming another plasmonic waveguide continuous with the above-mentioned plasmonic waveguide and forming another plasmonic waveguide on the silicon layer 101, an optical modulator using a Mach-Zehnder interferometer using the optical device of the first embodiment as a light intensity / phase shifter is realized. it can. For example, the optical device having the MOSFET structure of the first embodiment is formed with a predetermined gate width (waveguide length), and is composed of cores continuous from both ends in the gate width direction (waveguide direction) to the channel region 121. The plasmonic waveguide may be formed. For example, another plasmonic waveguide having no impurity introduction region serving as a gate electrode or a source / drain and having metal silicides formed on both sides of the core may be used. Further, by forming grooves on both sides of the core continuous to the channel region 121 from both ends in the gate width direction (waveguide direction) of the optical device and arranging a metal layer in the grooves, other plasmonic leads can be obtained. It may be used as a waveguide (see Patent Document 1). A basic Mach-Zehnder interferometer may be constructed by another plasmonic waveguide, and the optical device according to the first embodiment may be arranged on one of the arms.

In the intensity / phase modulation of the waveguide light in the region 121 of the channel described above, the shorter the channel length, the shorter the carrier travel time, which is desirable. On the other hand, since light is not trapped depending on the dielectric constant of the silicide material, the channel length is appropriately adjusted so that the plasmonic mode exists.

By the way, in an n-channel MOSFET, it is well known that by applying tensile strain to the channel region 121, the mobility of carriers increases and contributes to high speed. Since the improvement in mobility increases the carrier plasma effect and contributes to high-efficiency modulation, such distortion imparting is preferable. For example, as is well known, if the gate insulating layer 102 is formed by depositing silicon nitride, tensile strain can be applied to the region 121 of the channel.

Next, regarding the optical device according to the first embodiment, the result of calculating the electric field strength distribution in the plasmonic mode by the two-dimensional finite element method will be described with reference to FIG. The wavelength is 1550 nm. The source contact layer 108, the drain contact layer 109, and the gate contact layer 110 were made of CoSi ₂ (complex refractive index: N = 0.97 + i7.56) and had a thickness of 60 nm.

The gate electrode 103 is made of polysilicon and has a thickness of 100 nm. The gate length was 60 nm, the gate insulating layer 102 was SiO ₂ , and the thickness was 2 nm. The distance between the source contact layer 108 and the drain contact layer 109 (channel region 121) was set to 120 nm.

As shown in FIG. 2, it can be seen that light is confined in the region 121 of the channel between the source contact layer 108 and the drain contact layer 109.

As described above, according to the first embodiment, the optical modulator can be manufactured with the same element dimensions as that of a general MOSFET. Further, according to the first embodiment, unlike the prior art, the light intensity / phase shifter can be configured without the need for a lower clad made of _{SiO 2 or the like.} As a result, for example, an optical modulator can be manufactured using a low-cost bulk Si substrate widely used for manufacturing electronic circuits, without using an SOI substrate having a thick embedded insulating layer that is not generally used in manufacturing electronic devices. .. As described above, according to the first embodiment, it is possible to obtain an excellent effect that the optical device can be manufactured more efficiently and at low cost by using the electronic device manufacturing equipment.

The materials and dimensions shown in the first embodiment are examples. In a plasmonic waveguide whose core is the region 121 of the channel sandwiched between the source contact layer 108 and the drain contact layer 109, a MOSFET can be obtained so that a low-loss plasmonic mode can be obtained and optical modulation can be obtained with high efficiency. Adjust appropriately to obtain plasmonic mode confinement inside the channel.

[Embodiment 2]
Next, the optical device according to the second embodiment of the present invention will be described with reference to FIG. This optical device includes a gate insulating layer 102, a gate electrode 103, a source region 104, a drain region 105, a source electrode 106, a drain electrode 107, a source contact layer 108, a drain contact layer 109, a gate contact layer 110, a side wall 111, and a passivation. A film 112 is provided. These configurations are the same as those in the first embodiment described above.

In the second embodiment, the above-described configuration is formed on the silicon layer 201, which is a surface silicon layer of a well-known SOI (Silicon on Insulator) substrate, and on the silicon layer 201. The silicon layer 201 is arranged on the embedded insulating layer 211 of the SOI substrate. This SOI substrate is used in a completely empty MOSFET, and the thickness of the embedded insulating layer 211 is about 0.2 μm, which is not suitable for clad of an optical waveguide using a general Si core.

Next, regarding the optical device according to the second embodiment, the result of calculating the electric field strength distribution in the plasmonic mode by the two-dimensional finite element method will be described with reference to FIG. The wavelength is 1550 nm. The source contact layer 108, the drain contact layer 109, and the gate contact layer 110 were made of NiSi (complex refractive index: N = 1.54 + i4.73) and had a thickness of 60 nm. The thickness of the silicon layer 201 was set to 80 nm.

The gate electrode 103 is made of polysilicon and has a thickness of 100 nm. The gate length was 60 nm, the gate insulating layer 102 was SiO ₂ , and the thickness was 2 nm. The distance between the source contact layer 108 and the drain contact layer 109 (channel region 121) was set to 120 nm.

As shown in FIG. 4, it can be seen that also in the second embodiment, the light is confined in the region 121 of the channel between the source contact layer 108 and the drain contact layer 109.

As described above, also in the second embodiment, the optical modulator can be manufactured with the same element dimensions as that of a general MOSFET. As described above, according to the second embodiment, it is possible to obtain an excellent effect that the optical device can be manufactured more efficiently and at low cost by using the electronic device manufacturing equipment.

The materials and dimensions shown in the second embodiment are also examples. In a plasmonic waveguide whose core is the region 121 of the channel sandwiched between the source contact layer 108 and the drain contact layer 109, a MOSFET can be obtained so that a low-loss plasmonic mode can be obtained and optical modulation can be obtained with high efficiency. Adjust appropriately to obtain plasmonic mode confinement inside the channel.

As described above, according to the present invention, a source contact layer made of metal silicide is provided between the source region and the source electrode, and a drain contact layer made of metal silicide is provided between the drain region and the drain electrode. Since the plasmonic waveguide having the channel region formed in the silicon layer directly under the gate electrode sandwiched between the source contact layer and the drain contact layer as the core was constructed, it is more efficient to use the electronic device manufacturing equipment.・ It will be possible to manufacture optical devices at low cost.

The present invention is not limited to the embodiments described above, and many modifications and combinations can be carried out by a person having ordinary knowledge in the art within the technical idea of the present invention. That is clear.

101 ... Silicon layer, 102 ... Gate insulating layer, 103 ... Gate electrode, 104 ... Source region, 105 ... Drain region, 106 ... Source electrode, 107 ... Drain electrode, 108 ... Source contact layer, 109 ... Drain contact layer, 110 ... Gate contact layer, 111 ... side wall, 112 ... passivation film, 121 ... channel region.

Claims (6)

A gate electrode formed on the silicon layer via a gate insulating layer,
The source region and the drain region formed on the silicon layer with the region on which the gate electrode is formed are interposed therebetween.
A source electrode made of metal formed by connecting on the source region,
A drain electrode made of metal formed by connecting on the drain region,
A source contact layer made of a metal silicide formed between the source region and the source electrode,
A drain contact layer made of a metal silicide formed between the drain region and the drain electrode is provided.
A plasmonic waveguide having a channel region formed in the silicon layer immediately below the gate electrode sandwiched between the source contact layer and the drain contact layer as a core and a gate width direction as a waveguide direction is provided. A featured optical device. In the optical device according to claim 1,
The gate electrode is made of silicon.
An optical device further comprising a gate contact layer made of a metal silicide formed on the gate electrode. In the optical device according to claim 1 or 2.
An optical device characterized in that the gate insulating layer is made of silicon nitride. In the optical device according to any one of claims 1 to 3.
An optical device comprising the plasmonic waveguide continuous with another plasmonic waveguide formed in the silicon layer. In the optical device according to any one of claims 1 to 4.
An optical device in which the silicon layer is a silicon substrate. In the optical device according to any one of claims 1 to 4.
An optical device characterized in that the silicon layer is a surface silicon layer of an SOI substrate.

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