JP5015762B2 - Semiconductor device - Google Patents

Description

  The present invention relates to a semiconductor device, and more particularly to a structure suitable for application to a power MOSFET, IGBT, or the like.

  In a MOSFET (horizontal type), for example, a gate electrode is provided via a gate oxide film between a source and drain diffusion layer (n + region) on the surface of a p-type substrate. When a predetermined gate voltage is applied, electrons in the substrate are It is attracted to the gate electrode by Coulomb force, a channel region is formed, and current flows. The on-resistance is determined by the gate voltage (gate-source voltage). The MOSFET performs on / off control of the device using an electrostatic field. Known devices using an electrostatic field include JFET (Junction Gate Field Effect Transistor), MESFET (Metal Semiconductor Field Effect Transistor), IGBT (Insulated Gate Bipolar Transistor), and the like.

  In the power MOSFET (vertical type), the drain terminal is provided on the bottom surface of the n− substrate, for example, and the source terminal connected to the n + region in the p region of the n− epitaxial layer and the gate terminal are attached on the upper side. The gate electrode is provided on the n− epitaxial layer via an insulating film. When a positive potential is applied to the gate electrode, electrons are attracted to the substrate side, so that the n-epitaxial layer and the source are conducted through the p region, and finally the electrons flow to the drain. The on-resistance is lowered by making the gate small and disposing it over the entire top surface of the substrate. A vertical MOSFET can pass a larger current than a lateral MOSFET, but the substrate becomes large in order to pass a large current. In this case, since the gate capacitance increases, switching at a high frequency becomes difficult.

  In an IGBT (Insulated Gate Bipolar Transistor) used for high power control, the collector is on the bottom of the p-type substrate, the emitter and the gate are connected to the diffusion layer of the epitaxial layer, and the top of the epitaxial layer. It is extracted from a gate electrode provided through an insulating film. The difference from the MOSFET (vertical type) is that a p region is set on the lower side. As a result, the carrier density is increased, so that the on-resistance is lowered, which is suitable for high power. Switch control is a unipolar type, and control power can be reduced. The on-resistance is bipolar. The turn-off time is longer than that of the MOSFET, and the switching time is longer.

  FIG. 10 is a diagram showing the structure of the IGBT and the carrier flow during the ON operation (the drawing of Non-Patent Document 1 is cited as it is). Holes flow upward from the collector side, and electrons flow downward from the emitter side. For this reason, carrier recombination occurs in the intermediate portion. Further, as shown in the figure, since a parasitic npn transistor is formed, when a large current flows, the conduction state is maintained and the turn-off function may be lost. The current path is relatively long. Therefore, a trench type IGBT (TIGBT) has been developed to reduce the on-resistance.

  FIG. 11 is a diagram illustrating an example of a trench IGBT (a diagram directly quoted from Mitsubishi Electric HP). The gate electrode is vertical and extends to the n− region. This shortens the current path and reduces the on-resistance. As the trench type IGBT, for example, CSTBT (Carrier Stored Trench gate Bipolar Transistor) is known. The CSTBT has a carrier stored n layer as compared with a normal TIGBT. The trench type electrode structure is also used in a lateral MOSFET or the like, and has been used in a DRAM or the like before the IGBT or power MOSFET or the like, and is a general means for reducing resistance. Although one unit is shown in FIG. 5, a plurality of units are usually provided on the same chip.

  FIG. 12 is a diagram for explaining the on-resistance of the power MOSFET, and is directly cited from the drawing of Non-Patent Document 1. The source resistance Rs and the drain resistance Rd are determined by the voltages of the source electrode and the drain electrode, respectively, and are relatively low. The on-resistance of the device is determined by Rch and Repi. Rch (channel resistance) is a resistance when flowing through the charge portion attracted by the gate, and since the channel current path is thin, it becomes a large resistance. In addition, Repi is a resistance when flowing through the epitaxial layer, and in IGBT or the like, the carrier density is high, so the resistance value is low.

  FIG. 13 shows the collector-emitter voltage (VCE) of an IGBT or a bipolar junction transistor (BJT), and the drain-source voltage (drain-to-source voltage) and output in the case of a MOSFET. It is a figure which shows the general relationship of an electric current, and was quoted as it is from the drawing of nonpatent literature 1. In the bipolar device, the current rapidly increases as the voltage increases, but eventually saturates. On the other hand, the MOSFET tends to monotonously increase in current as the voltage is increased.

Published by Hiroshi Yamazaki, “Introduction to Power MOSFET / IGBT”, published by Nikkan Kogyo Shimbun, July 2002 IEEE Photonics Technology Letters, Vol.16, No 1, p117, 2004

  An object of the present invention is to provide a semiconductor device that reduces the channel resistance of power elements such as power MOSFETs and IGBTs.

  The invention disclosed in the present application is generally configured as follows.

  The present invention includes a light source that irradiates light to a channel region in which carriers travel, and turns on the light source to flow a channel current.

  According to the present invention, a light source for irradiating light toward a gate portion is provided in a semiconductor device, and the light source is on / off controlled.

  The semiconductor device of the present invention includes a lateral MOSFET.

  The semiconductor device of the present invention includes a vertical MOSFET.

  The semiconductor device of the present invention includes an IGBT (Insulated Gate Bipolar Transistor). In this invention, it is good also as a structure provided with the light reflection board in the trench bottom part of the trench gate electrode of IGBT.

  In the present invention, the gate electrode and the gate oxide film are made of a conductive member that transmits the light.

  In the present invention, an insulating resin that transmits the light is filled between the gate electrode and the light source.

  In the present invention, the light source is provided in a space between the gate electrode and the side of the vertical MOSFET facing the source electrode.

  In the present invention, an opening is provided in the source electrode of the vertical MOSFET, one end of the opening is opposed to the gate electrode, and the other end of the opening is provided with the light source.

  In the present invention, an insulating resin that transmits the light is filled between the gate electrode and the light source.

  In the present invention, the emitter electrode of the IGBT is provided with an opening, one end of the opening is opposed to the gate electrode, the other end of the opening is opposed to the light source, and other than the opening of the light source. A light reflection plate is provided on the side opposite to the end.

  In the present invention, an optical waveguide that guides light from the light source may be provided.

  In the present invention, as the light source, a surface light emitting element is disposed to face a surface on which the gate electrode of the semiconductor device is disposed.

  In the present invention, a light source is disposed as the light source so as to face a surface on which the gate electrode of the semiconductor device is disposed, a light diffusion layer is disposed between the light source and the semiconductor device, A light emitting element including a light reflecting plate is provided on the side opposite to the side facing the light diffusion layer.

  In the present invention, an insulating resin covering the gate electrode transmits light from the light source.

  In the present invention, the light source includes an LED (Light Emitting Diode).

  In the present invention, a light-shielding film is provided at a portion that shields light on a joint surface between the semiconductor device and the light-emitting element.

  According to the present invention, the on-resistance is reduced because the channel current is controlled by the application of the gate voltage and the light irradiation.

The present invention will be described in detail below with reference to the accompanying drawings. FIG. 1A is a diagram illustrating the principle of a MOSFET according to an embodiment of the present invention. An n + region (source diffusion layer) 102 and an n + region (drain diffusion layer) 103 are formed on the surface of the p substrate 101, and electrodes 104 and 105, which respectively become a source electrode and a drain electrode, are provided. The electrodes 104 and 105 are disposed in accordance with a well-known semiconductor manufacturing process, and aluminum or copper is used. The gate electrode 107 (transparent electrode) is disposed on the p-type substrate 101 via the gate insulating film 106. The gate insulating film 106 is made of silicon dioxide (SiO ₂ ) when the p-type substrate 101 is silicon or SiC. Although not particularly limited, the film thickness is, for example, about 1 μm. As is well known, silicon dioxide (SiO ₂ ) is optically transparent and transmits light from the infrared to the visible and ultraviolet regions.

  The gate electrode 107 is made of, for example, ITO (indium tin oxide) or ZnO zinc oxide as an optically transparent conductive material. Alternatively, an organic material or the like may be used.

  In this embodiment, in order to pass a current (channel current) between the source and the drain, not only a gate voltage is applied to the transparent gate electrode 107 but also light is irradiated from behind. Since a potential is applied to the gate electrode 107, electrons serving as carriers are attracted as in the MOSFET, a channel region is formed between the source 102 and the drain 103, and a current flows between the source 102 and the drain 103. FIG. 1B is an equivalent circuit of FIG. When light is irradiated from behind, it is turned on even with a reverse voltage based on the same principle as a photodiode. Then, the light enters the substrate 101 by appropriately selecting the wavelength of the light. The channel current region is widened and the on-resistance is reduced. Such a device structure is called “Optical MOSFET” for convenience. A gate structure that reduces channel resistance by light irradiation is also referred to as an “optical gate”. Although not particularly limited, in this embodiment, an LED (Light Emitting Diode) is used as a light source.

  In a MOSFET, a leakage current (for example, a source-drain current that flows when the gate voltage falls below a threshold value) increases due to light irradiation. Therefore, the semiconductor substrate is usually packaged and shielded from light.

  On the other hand, in this embodiment, the on / off of the MOSFET is controlled using light to reduce the on-resistance. When a channel is formed by applying a gate voltage and electrostatically attracting electrons, the thickness of the channel region is about 1 μm (micrometer).

  In this embodiment, in order to turn on the MOSFET by light absorption, the energy of light to be irradiated needs to be higher than the band gap. Although the reach depth of light depends on the absorption coefficient, conduction between the source and the drain is ensured by reaching the channel region. In a silicon substrate, the reaching depth is in the visible light region, for example, about several tens of um to 100 μm, and reaches the channel region on the substrate surface.

  Thus, in this embodiment, the channel resistance is reduced as compared with the case where only the electrostatic method (application of gate voltage) is used.

  Further, according to the present embodiment, the same effect can be obtained without using a trench electrode. That is, the on-resistance can be reduced and a large current can flow without forming a trench in the semiconductor substrate.

In a device that is turned on / off by a gate voltage, when switching is performed at a high frequency, the gate size is reduced, the gate is divided, etc. in order to reduce the gate capacitance.
In the present embodiment, the LED of the light source emits light at an applied voltage of about 2V. When LEDs are connected in parallel for irradiation, the transistor can be turned on with a low gate voltage. Moreover, even if the power consumption of the LED is estimated, the power consumption of the entire device may be reduced. The switching frequency of a small LED is on the order of GHz, and when the present invention is applied to an IGBT or a MOSFET, the switching frequency is higher than that of a conventional device.

  In this embodiment mode, light from a light source (LED) is used for on / off control of a transistor to improve the switching frequency of the transistor, which is one of the features of the present invention. Examples of the present invention will be described.

<Example 1>
FIG. 2 is a diagram showing the configuration of the first exemplary embodiment of the present invention. In FIG. 2, a vertical MOSFET has an “Optical Gate” configuration, and light is irradiated from above the device. The gate insulating film 209 is made of a transparent insulating film, and the gate electrode 210 is made of a transparent conductive film, and transmits the irradiation light. Current flows from the n + regions 205 and 206 forming the source and drain diffusion layers through the p layers (p-type wells) 203 and 204 through the n− epitaxial layer 202. A current path is secured according to the light absorption. Since light is also introduced into the n-epitaxial layer 202, the resistance of the n-epitaxial layer 202 can also be reduced. This is an example of a photoconductive effect. FIG. 9 shows the configuration of the vertical MOSFET, but the present invention can be similarly applied to the IGBT.

  If light is used, the electron density in the n + layer 205 bonded to the source electrode 207 can be set low. This improves the dielectric strength characteristics and the like. Although not particularly limited, the gate electrode (transparent electrode) 210 is formed in a dimension of about several um.

<Example 2>
FIG. 3 shows an embodiment in which the present invention is applied to a trench IGBT, which has an “Optical Gate” structure and irradiates light from above. The gate insulating film 309 and the gate electrode 310 transmit irradiation light. The n + regions 205 and 306 pass through the p base layer 304 and pass through the n− epitaxial layer 303, the n + buffer layer 302, and the p + substrate 301, thereby securing a current path. Since light is also introduced into the n-epitaxial layer 303, the resistance of the n-epitaxial layer 303 can also be reduced. If light of different wavelengths is used, the distance absorbed in the material from which the device is made will be different, and the current channel can be controlled accordingly. You may utilize the LED light source from which a wavelength differs.

  A trench 311 is formed directly between the n + regions 305 and 306 forming the source and drain diffusion layers immediately under the gate, the inner wall of the trench is covered with an insulating film 311, and a conical light reflector having a protruding tip at the bottom of the trench. 314, a conductive member 313 is buried above the light reflection plate 314 in the trench, and the upper end of the conductive member 313 is in contact with the bottom surface of the gate electrode 310 to constitute a trench type gate electrode. The light reflecting plate 314 in the trench makes it easy to ensure the formation of the channel region along the trench-like gate electrode.

<Comparative example>
FIG. 4 is a diagram showing an example of a source and gate side electrode structure of a conventional MOSFET (vertical type) as a comparative example (cited from Non-Patent Document 1). Since a large current flows through the source 301, electrodes are attached to almost the entire main surface (front surface) to reduce resistance and further reduce heat generation by a heat dissipation action. Since a very large current does not flow through the gate 402, the gate electrode is extended and bundled at the end portion to form the gate of the element.

<Example 3>
An example in which the present invention is applied to a device having the configuration shown in FIG. 4 will be described. There are two methods for attaching a light source (LED) and irradiating light from the light source to the gate portion.

  In the case of a MOSFET, an LED is installed inside a source electrode (emitter electrode in IGBT). The light emitting part of the LED is about 0.1 mm square.

  FIG. 5 is a diagram showing a configuration of the third embodiment of the present invention, in which an LED 510 is arranged inside a source electrode 509 connected to a source diffusion layer (n + regions 505 and 506). In the space between the source electrode 509 and the substrate surface and between the gate electrode 507, an insulating layer (interlayer insulating film) (not shown) is deposited. The LED 510 is smaller than the size of the gate electrode 507. Note that the gate electrode 507 extends in a direction perpendicular to the paper surface.

  As a wiring form to the LED 510, one end is connected to the gate electrode 507 and the other end is connected to the source electrode 509. When the gate voltage is set to about 10 V, for example, the LED has a high voltage, and therefore the LEDs may be connected in series.

  Since the source electrode 509 (an emitter electrode in the case of IGBT) is made of a metal member, the inner surface exposed to light may be plated with aluminum, silver, or the like. The interlayer insulating film between the LED 510 and the gate electrode 507 is filled with a transparent resin (plastic) or the like.

  Instead of mounting the LED 510 for each finely processed gate electrode 507, an opening may be provided in the source electrode 509, and light may be applied to the gate from the opening. Alternatively, the opening may be filled with a transparent electrode material.

<Example 4>
FIG. 6 is a diagram showing the configuration of the fourth embodiment of the present invention, and shows an application example to the IGBT. An LED 610 is mounted above the emitter electrode 609. An opening 613 is provided in the emitter electrode 609 in order to guide light to a channel formation region immediately below the gate electrode. The emitter electrode 609 on the gate portion may be cut in the direction in which the gate electrode 608 is disposed to form a groove. In this case, light diffraction hardly occurs at a gate size of about several microns to 10 microns.

  Further, a light reflection plate 611 is provided on the side facing the upper surface of the emitter electrode 609 with the LED 610 interposed therebetween. The light reflecting plate 611 may be coated on the surface with a reflecting material or may be plated. In the emitter electrode 609, the region that receives light from the LED light source may be coated with a reflective material on the surface or may be plated.

  In addition, an insulating transparent resin (not shown) is embedded in the opening 613 through which light from the LED 610 passes. Also in this mounting example, a plurality of LEDs may be mounted. The wavelength may be selected in consideration of transmission of light to the semiconductor substrate.

  In order to irradiate the entire IBGT or MOSFET with an LED, a light diffusing plate is disposed between the LED and the emitter electrode in order to diffuse the light out of the LED and then guide it to the channel formation region directly under the gate. Also good.

<Reference example of optical waveguide>
FIG. 7 is taken directly from Non-Patent Document 2 (IEEE Photonics Technology Letters, Vol. 16, No 1, p117, 2004). (The inventor of the present application is not involved in the research conducted in Non-Patent Document 2 shown in FIG. 7.) The purpose of quoting the drawing of Non-Patent Document 2 in the present specification is merely an image of a waveguide. This is to support the understanding of The micro optical waveguide (FIGS. 7A and 7B), its socket (FIG. 7D) and the optical computer portion (FIG. 7C) are shown. FIG. 7A is an optical waveguide for guiding a large number of lights, and FIG. 7B is a partial enlarged view thereof. The optical waveguide is cylindrical and has a diameter of about 5 μm.

  The size of the gate is the same as that of the IGBT or power MOSFET described above. An optical waveguide is fixed through the socket part of FIG. 7C to form an optical circuit, and trial production of sockets arranged in a row or a matrix-like socket has been reported (Non-Patent Document 2).

<Example 5>
By using an optical waveguide and a socket as shown in FIG. 7, light can be guided to a necessary portion of the semiconductor device. That is, light may be emitted from the light source to the gate region of the element through the optical waveguide and the socket.

  As is well known, an organic EL (Electro Luminescence) display is a surface light emitting element, a fine structure element, light emission intensity is adjustable, and light of various wavelengths can be emitted. Have. The LED has a light emitting element size of about 0.1 mm square to about 0.3 mm square, and the size of the semiconductor substrate of the IGBT or power MOSFET is about 10 mm square. You need a way to do it.

<Example 6>
When a surface light emitting element is used as a light source having an “Optical Gate” structure, such a structure is unnecessary and can be switched by light. An IGBT or power MOSFET whose gate electrode is made of a transparent electrode material is manufactured, and for example, as shown in FIG. 6, an emitter electrode is provided with an opening, and then a surface light emitting element is attached to the gate side to complete the element. To do. Thereafter, sealing is performed with a resin or the like for light shielding. In addition, since the light source for displays has a relatively low frequency response, it is not suitable for high-speed switching.

  FIG. 8 shows an example in which a surface light emitting element (organic EL) 815 is mounted on an IGBT. Light is incident substantially perpendicularly to the gate side of the IGBT. The emitter electrode 809 and the gate electrode 808 extend in the direction perpendicular to the plane of the drawing, and are joined at end portions (not shown).

  On the IGBT side, a region below the bonding surface 812 is filled with an insulating film 810 such as a transparent resin, and transmits light. If necessary, for example, a light shielding member (light shielding film) 814 may be disposed at a position corresponding to the n + regions 805, 806, and the like. The surface light emitting element 815 in FIG. 8 is thin.

<Example 7>
FIG. 9 is a diagram schematically showing a cross-sectional configuration of the seventh embodiment of the present invention. A point light source composed of an LED 913 and a light diffusion layer (light diffusion plate) 916 are provided. A light reflection plate 915 is disposed on the opposite side of the light diffusion layer (light diffusion plate) 916 of the LED 913 from the opposite surface. The light diffusion layer 916 has a function of diffusing light from the LED 913 that is a point light source, so that the light reaches the light irradiation destination such as a gate portion evenly. Further, similarly to FIG. 8, a light shielding film 914 may be provided at a predetermined portion of the bonding surface 912. A transparent insulating resin 910 is deposited on the IGBT and then joined to the light emitting portion 917. Since the LED 916 has higher luminous efficiency and higher frequency characteristics than an organic EL or the like, the switching frequency can be increased.

  In this embodiment, an example using a point light source and a light diffusion layer has been described. However, in the case of using a point light source, an optical fiber may be used in addition to this, or an optical material may be appropriately selected. The light may be intensively applied to a necessary portion by selecting or controlling the refractive index and transmittance of the optical material.

  It is also possible to reduce the surface roughness of the boundary surface between the transparent gate electrode and the transparent gate insulating film and diffuse light. Or it is good also as a structure provided with the non-reflective coating film in the interface of a gate electrode and a gate insulating film.

In this embodiment, the light source for irradiating the gate portion may be constituted by a semiconductor laser.
In this embodiment, the semiconductor laser may be a silicon semiconductor laser (silicon laser).
In this embodiment, the light source may be composed of a silicon semiconductor laser formed on the same silicon wafer as the switching element.
In this embodiment, the silicon semiconductor laser is disposed next to the gate portion so that the light from the silicon semiconductor laser irradiates the gate portion of the switching element, and the emitted light from the silicon semiconductor laser is It is good also as a structure guided so that the upper part of a gate part may be irradiated. In the present embodiment, a configuration may be provided that includes a mirror that reflects light emitted from the silicon semiconductor laser and irradiates the reflected light on the upper portion of the gate portion.

  Although the present invention has been described with reference to the above-described embodiments, the present invention is not limited to the configurations of the above-described embodiments, and various modifications that can be made by those skilled in the art within the scope of the present invention. Of course, including modifications.

It is a figure which shows typically schematic structure of one embodiment of this invention. It is a figure which shows typically schematic structure of the 1st Example of this invention. It is a figure which shows typically schematic structure of the 2nd Example of this invention. It is a disassembled perspective view which shows typically schematic structure of a well-known semiconductor device. It is a figure which shows typically schematic structure of the 3rd Example of this invention. It is a figure which shows typically schematic structure of the 4th Example of this invention. It is a figure which shows typically schematic structure of the 5th Example of this invention. It is a figure which shows typically schematic structure of the 6th Example of this invention. It is a figure which shows typically schematic structure of the 7th Example of this invention. It is a figure which shows the flow of the carrier at the time of IGBT operation | movement (cited as it is from the nonpatent literature 1). It is a figure (it quotes as it is from Mitsubishi Electric's HP) explaining the structure of trench type IGBT. It is a figure explaining the on-resistance of power MOSFET (cited as it is from nonpatent literature 1). It is a figure explaining the voltage-current characteristic of on-resistance of power MOSFET (cited as it is from nonpatent literature 1).

Explanation of symbols

101 P substrate 102 n + region (source diffusion layer)
103 n + region (drain diffusion layer)
201 n + substrate 202 n− epitaxial layer 203, 204 p layer (p well)
205 n + region (source diffusion layer)
206 n + region (drain diffusion layer)
207 Source electrode 208 Drain electrode 209 Gate insulating film 210 Gate electrode 301 p + substrate 302 n + buffer layer 303 n− epitaxial layer 304 p base layer 305 n + region (source diffusion layer)
306 n + region (drain diffusion layer)
307 Source electrode 308 Drain electrode 309 Gate insulating film 310 Gate electrode 311 Trench 312 Insulating film 313 Conductive member (gate electrode)
314 Light Reflector 315 Collector Electrode 401 Source 402 Gate 403 Drain 501 n + Substrate 502 n−Epitaxial Layers 503 and 504 p Layer (P Well)
505 n + region (source diffusion layer)
506 n + region (drain diffusion layer)
507 Gate insulating film 508 Gate electrode 509 Source electrode 510 LED
511 Drain electrode 601 p + substrate 602 n- epitaxial layer 603, 604 p layer (p well)
605 n + region (source diffusion layer)
606 n + region (drain diffusion layer)
607 Gate insulating film 608 Gate electrode 609 Emitter electrode 610 LED
611 Light reflection plate 612 Collector electrode 801 p + substrate 802 n− epitaxial layer 803, 804 p layer (p well)
805 n + region (source diffusion layer)
806 n + region (drain diffusion layer)
807 Gate insulating film 808 Gate electrode 809 Emitter electrode 810 Transparent insulating resin 811 Collector electrode 812 Bonding surface 813 Light-emitting layer 814 Light-shielding film 815 Surface light-emitting element 901 p + substrate 902 n-epitaxial layers 903 and 904 p-layer (p-well)
905 n + region (source diffusion layer)
906 n + region (drain diffusion layer)
907 Gate insulating film 908 Gate electrode 909 Emitter electrode 910 Transparent insulating resin 911 Collector electrode 912 Bonding surface 913 LED (point light source)
914 Light-shielding film 915 Light reflection plate 916 Light diffusion layer 917 Optical element

Claims (14)

A power MOSFET and a light source that irradiates light in the vicinity of the channel region where the carrier travels,
The light source includes a light emitting element disposed to face a surface on which the gate electrode of the power MOSFET is disposed,
The gate electrode is made of a conductive member that transmits the light, and the gate insulating film is made of an insulating member that transmits the light,
In the bonding surface between the semiconductor device and the light emitting element, a light shielding member is provided at a predetermined portion ,
A semiconductor device, wherein the light source is turned on and a channel current is passed through the power MOSFET . The semiconductor device according to claim 1, characterized in that it comprises an optical waveguide for guiding light from the light source. Comprising a light diffusion layer on the optical waveguide for guiding light from the light source, the semiconductor device according to claim 1, wherein the diffusing light from the light source. As the light source, a light source is disposed facing a surface on which the gate electrode of the semiconductor device is disposed, a light diffusion layer is disposed between the light source and the semiconductor device, and the light diffusion layer of the light source the semiconductor device of claim 1, further comprising a light-emitting device having a light reflecting plate, it is characterized in the side opposed to the side opposite to. Includes a relatively lower region of the surface roughness at the interface of the gate insulating film and the gate electrode, it diffuses the light, the semiconductor device according to claim 1, characterized in that. The boundary surface of the gate electrode and the gate insulating film comprises an antireflection coating film, a semiconductor device according to claim 1, characterized in that. The semiconductor device according to claim 1 , wherein the light source includes an LED (Light Emitting Diode). The semiconductor device according to claim 1 , wherein the light source includes an LED (Light Emitting Diode), and one or a plurality of LEDs are connected between a source electrode and the gate electrode. Wherein the junction surface of the semiconductor device and the light emitting element, a semiconductor device according to claim 1, characterized in that it comprises a light blocking member at the predetermined site. The light emitting element, a semiconductor device according to claim 1, comprising an organic EL (Electro Luminescence) element. The semiconductor device according to claim 1, characterized in that said light source comprises a semiconductor laser. The semiconductor device according to claim 11 , wherein the semiconductor laser is a silicon semiconductor laser. The silicon semiconductor laser is disposed next to the gate so that the light from the silicon semiconductor laser irradiates the gate portion of the switching element, and the emitted light from the silicon semiconductor laser irradiates the upper portion of the gate portion. The semiconductor device according to claim 12 , wherein the semiconductor device is guided as follows. 14. The semiconductor device according to claim 13 , further comprising a mirror that reflects light emitted from the silicon semiconductor laser and irradiates an upper part of the gate portion with the reflected light.

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