JP2009200397A - High-frequency semiconductor apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a high output even at a high operating voltage. <P>SOLUTION: A high-frequency semiconductor apparatus includes: a field effect transistor having a semiconductor film 3 formed on a substrate 2, a source electrode 10 and a drain electrode 12 remotely formed on a first region to be served as the transistor active-portion forming region of the semiconductor film, and a gate electrode 14 formed on the first region between the source electrode and the drain electrode; insulating films 8, 16 formed in the shape of covering the semiconductor film, the source electrode, the gate electrode, and the drain electrode; a heat-dissipating plate 18 connected to the source electrode, and formed on the insulating film so as to extend to the upper portion of the gate electrode to cover it; and heat dissipators 22, 24 formed on the heat-dissipation plate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a high-power high-frequency semiconductor device.

  High-output high-frequency semiconductor devices are key devices for realizing communication systems, radar systems, high-frequency heating devices, etc., and increasing output power density (per unit size) to reduce system size and weight. Higher output) is desired. A field effect transistor made of a nitride semiconductor has a higher operating voltage and a higher current density than a high-frequency semiconductor device using a conventional semiconductor, and can realize an element with a high output power density at a high frequency. However, it is difficult to extract all the electric power input to the field effect transistor as high-frequency electric power, and a part is consumed as heat inside the element. Increasing the output power density leads to a higher heat generation density (higher heat generation per unit size) and causes a problem due to an increase in element temperature, that is, a decrease in output power and a decrease in reliability.

  Nitride semiconductor field effect transistors have addressed this problem by using a SiC substrate with high thermal conductivity as the substrate under the nitride semiconductor layer. The thermal conductivity of the SiC substrate is comparable to that of metal. Until now, a method has been adopted in which a heat dissipation member is connected to the surface of the SiC substrate opposite to the semiconductor layer forming the field effect transistor, and heat is diffused widely on the back surface of the substrate to avoid an increase in element temperature. It was. With this method, sufficiently high output characteristics and high reliability were obtained up to an operating voltage of about 50V. However, if the operating voltage is further increased to increase the power density in the future, the element temperature will rise, resulting in a problem that high output and high reliability cannot be obtained.

A nitride semiconductor field effect transistor may use a sapphire substrate in addition to a SiC substrate excellent in heat dissipation. In the case of a sapphire substrate, the thermal conductivity is lower than that of an SiC substrate, so that it is difficult to dissipate heat, and a structure aimed at measures against the heat dissipation and miniaturization of a high-frequency circuit has been proposed (see Patent Document 1). . These structures include a structure in which a nitride semiconductor field effect transistor is formed on a sapphire substrate, the substrate is then peeled off, and a thick Au plating for the source electrode is added to the upper part of the electrode (FIG. 1 of Patent Document 1). It has a structure for joining SiC substrates (FIG. 3 of Patent Document 1). However, it is very difficult to peel off the substrate, and this structure is not easy to realize. As for the heat dissipation effect, it has a mechanism to dissipate heat through the source and drain electrodes and the wiring formed on these electrodes, but the main point of heat generation inside the field effect transistor Since the electric field strength of the current path is high, that is, in the vicinity of the drain end of the gate, in these configurations, there is a problem that the heat dissipation path becomes long and a sufficient effect cannot be obtained.
JP 2007-142144 A

  As described above, in the conventional high-frequency semiconductor device, when the operating voltage is increased, the heat dissipation is insufficient and a high output cannot be obtained.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a high-frequency semiconductor device capable of obtaining a high output even when the operating voltage is increased.

  A high-frequency semiconductor device according to an aspect of the present invention includes a semiconductor film formed over a substrate, a source electrode and a drain electrode formed separately on a first region that is a transistor active portion formation region of the semiconductor film, A field effect transistor having a gate electrode formed on the first region between the source electrode and the drain electrode; and covering the semiconductor film, the source electrode, the gate electrode, and the drain electrode. An insulating film formed on the insulating film, connected to the source electrode, and extended above the gate electrode so as to cover the gate electrode; and And a heat dissipating part formed on the surface.

  According to the present invention, a high output can be obtained even if the operating voltage is increased.

  Hereinafter, embodiments of the present invention will be described in detail.

(One embodiment)
1 to 3 show a high-frequency semiconductor device according to an embodiment of the present invention. 1 is a plan view of the high-frequency semiconductor device according to the present embodiment, FIG. 2 is a cross-sectional view taken along a cutting line AA ′ shown in FIG. 1, and FIG. 3 is a cross-sectional view taken along a cutting line BB ′ shown in FIG. FIG. In addition, FIG. 1 has shown the top view just before the heat radiating device mentioned later and a heat radiating device connection part are formed.

  In the high-frequency semiconductor device according to the present embodiment, a nitride semiconductor film 3 is formed on a substrate 2, for example, a SiC substrate 2, as shown in FIG. The nitride semiconductor film 3 has a laminated structure in which, for example, a GaN layer 4 and an AlGaN layer 5 are sequentially laminated, and two-dimensional electrons are accumulated at the interface between the two layers. An insulating film 8 is formed on the nitride semiconductor film 3. The insulating film 8 is provided with a plurality of openings leading to the transistor active portion formation region of the nitride semiconductor film 3, and the source electrode 10, the drain electrode 12, and the gate electrode 14 are formed so as to fill these openings. Yes. Therefore, the source electrode 10, the drain electrode 12, and the gate electrode 14 are formed on the transistor active portion formation region of the nitride semiconductor film 3, and the source electrode 10, the drain electrode 12, and the gate electrode 14 are formed on the insulating film 8. Is electrically insulated by. The source electrode 10 and the drain electrode 12 have a laminated structure in which, for example, Ti layer / Al layer / Ti layer / Au layer are laminated in this order. The gate electrode has a stacked structure in which, for example, a Ni layer / Au layer is stacked in this order. As shown in FIG. 1, the source electrodes 10 and the drain electrodes 12 are alternately arranged in a line, and a gate electrode 14 is formed between the source electrode 10 and the drain electrode 12. That is, a plurality of source electrodes 10, drain electrodes 12, and gate electrodes 14 are provided. The plurality of drain electrodes 12 are commonly connected to the lead wiring 13, and the plurality of gate electrodes 14 are commonly connected to the lead wiring 15. That is, the high-frequency semiconductor device of this embodiment has a configuration in which a plurality of field effect transistors are arranged in a line so as to share the source electrode 10 or the drain electrode 12.

  In addition, as shown in FIG. 1, the gate electrode is connected to the second region adjacent to the first region in which the source electrode 10, the drain electrode 12, and the gate electrode 14 are arranged in a line through a lead wiring 15. 14, an input unit 26 for inputting an RF signal is provided on the insulating film 8. Unlike the first region, the second region has a structure in which two-dimensional electrons are not accumulated by performing ion implantation or removing the AlGaN layer 5. As shown in FIG. 3, the input portion 26 is connected to the insulating film 8, the nitride semiconductor film 3, and a contact 30 made of, for example, metal embedded in a through hole provided in the substrate 2. The contact 30 is connected to an input pad 32 provided on the back surface of the substrate 2 (surface opposite to the nitride semiconductor film 3). That is, the input unit 26 is connected to the input pad 32 via the contact 30. An RF signal is input to the input pad 32 from the outside of the high-frequency semiconductor device.

  In addition, as shown in FIG. 1, with respect to the region where the source electrode 10, the drain electrode 12, and the gate electrode 14 are arranged in a row, the region opposite to the region where the input unit 26 is provided is led out. An output unit 28 that outputs an RF signal and is connected to the drain electrode 12 through the wiring 13 is provided. Similar to the input unit 26, the output unit 28 has contacts (not shown) made of, for example, metal embedded in the insulating film 8, the nitride semiconductor film 3, and through holes (not shown) provided in the substrate 2. Connected). This contact is connected to an output pad (not shown) provided on the back surface of the substrate 2 (surface opposite to the nitride semiconductor film 3). That is, the output unit 28 is connected to the output pad through the contact. The output of the high-frequency semiconductor device is output from the output pad. The input unit 26 and the output unit 28 are formed in a region other than the transistor active unit formation region.

  In the high-frequency semiconductor device of this embodiment, as shown in FIG. 2, an interlayer insulating film 16 is further formed so as to cover the source electrode 10, the drain electrode 12, and the gate electrode 14. An opening leading to the source electrode 10 is formed in the interlayer insulating film 16, and a heat radiating plate 18 made of metal (for example, Au) is formed so as to fill the opening. Further, as shown in FIG. 3, in the region where the input part 26 and the output part 28 are formed, an opening through which the insulating film 8 is exposed is formed in the interlayer insulating film 16 on the bottom surface. A ground connection portion 19 is formed. The heat radiating plate 18 is connected to the ground connection portion 19 as shown in FIG. The ground connection portion 19 is connected to an external ground power source. Therefore, the source electrode 10 is connected to the ground power supply via the heat radiating plate 18 and the ground connection portion 19. In addition, it is preferable to form the heat radiating plate 18 and the ground connection portion 19 at the same time so that the upper surfaces thereof are the same surface. Note that an interlayer insulating film 16 exists between the gate electrode 14 and the heat dissipation plate 18.

  As shown in FIGS. 1 and 2, the heat radiating plate 18 extends from the source electrode 10 so as to cover the gate electrode 14, but does not cover the drain electrode 12. This is for preventing dielectric breakdown between the heat radiation plate 18 and the drain electrode 12 and preventing an increase in parasitic capacitance. Further, as shown in FIG. 1, the ground connection portion 19 is formed so as not to cover the input portion 26 and the output portion 28. This is also for preventing a dielectric breakdown between the ground connection portion 19 and the input portion 26 and the output portion 28 and preventing an increase in parasitic capacitance.

An interlayer insulating film 20 made of, for example, SiO ₂ is formed on the entire surface so as to cover the heat radiating plate 18 and the ground connection portion 19, and the interlayer insulating film 20 is flattened until the upper surfaces of the heat radiating plate 18 and the ground connection portion 19 are exposed. Turn into. As a result, the upper surfaces of the heat radiating plate 18 and the ground connection portion 19 and the upper surface of the interlayer insulating film 20 are substantially flush. Then, on the heat radiating plate 18 and the ground connecting portion 19 and the interlayer insulating film 20, a heat radiating device connecting portion made of a material having high thermal conductivity (for example, a plurality of layers including a metal or a package member and an adhesive layer). 22 is formed. A heat dissipation device 24 is formed on the heat dissipation device connection portion 22. The heat radiating device connecting portion 22 and the heat radiating device 24 constitute a heat radiating portion. The heat radiating portion has a function of releasing heat generated inside the semiconductor device to the outside of the semiconductor device.

  In addition, when the heat radiating devices 22 and 24 are provided on the side on which the heat radiating plate 18 is formed as in the present embodiment, this is connected to the outside on the same side for inputting or outputting high-frequency signals. Becomes difficult. Therefore, in the present embodiment, as shown in FIG. 3, a pad 32 for inputting / outputting a high frequency signal is formed on the back surface of the surface on which the field effect transistor is formed, and the pad 32 and the upper surface of the insulating film 8 are formed. The high frequency signal input / output portions 26 and 28 of the element formed in the above are connected by a contact 30 made of a metal that penetrates the substrate 2, the nitride semiconductor film 3, and the insulating film 8.

  In the present embodiment configured as described above, the heat radiation plate 18 and the ground connection portion 19 connected to the source electrode 10 are the same as those of the high-frequency semiconductor device except for the region where the drain electrode 12, the input portion 26, and the output portion 28 are formed. Since the heat radiating device formed of the high thermal conductive film 22 and the heat radiating film 24 connected to the heat radiating plate 18 and the ground connection portion 19 is formed on almost the entire surface of the high-frequency semiconductor device. The heat generated from the field effect transistor can be efficiently radiated. This will be described with reference to the simulation results shown in FIGS.

  The effect of heat dissipation of the heat radiating plate 18 could be confirmed by device simulation. This calculation uses a model that simultaneously solves the Poisson equation, the continuous current equation of electrons and holes, and the continuous equation of heat flow. The structure of the field effect transistor as a model of this embodiment is a HEMT (High Electron Mobility Transistor) made of GaN having a heat dissipation plate 18 as in this embodiment formed on a SiC substrate, and the SiC substrate is polished to 100 μm. Assuming that The heat radiating plate 18 was formed up to an intermediate point between the gate electrode 14 and the drain electrode 12. In this model, the ground connection portion 19 connected to the heat radiating plate 18 as shown in FIG. 3 is not provided.

  Further, as a model of the comparative example, unlike the present embodiment, a field effect transistor in which a heat radiating member is provided on the back side of the substrate without providing a heat radiating plate connected to the source electrode is provided. The field effect transistor of the model according to the present embodiment and the comparative example has the same configuration except for the heat dissipation plate and the heat dissipation member.

  The simulation of the temperature distribution inside the field effect transistor of this embodiment and the comparative example was performed under the same voltage condition, and the results are shown in FIGS. 4 (a) and 4 (b), respectively. When the heat is radiated from the back surface of the SiC substrate, the maximum temperature inside the element is 455 K (Kelvin) (see FIG. 4A), whereas when the heat is radiated from the upper surface of the heat radiating plate, the temperature is only 320 K (FIG. 4 ( b)), indicating that the temperature rise inside the device can be significantly suppressed.

  As can be seen from the simulation results, in this embodiment, the temperature inside the element can be lowered by about 130 degrees as compared with a comparative example in which a heat radiation member is provided on the back side of the substrate and heat is radiated from the back side. Due to the suppression of this temperature rise, the calculated value of the drain current per 1 mm of the gate width is 1.5 times, 1.1 A in this embodiment, compared to 0.7 A in the comparative example. Due to this increase in drain current, the high-frequency output power can be expected to be 1.5 times that of the comparative example by adopting the configuration of this embodiment.

  Further, in the simulation, the ground connection portion 19 connected to the heat radiating plate 18 shown in FIGS. 1 and 3 was not taken into consideration. In the present embodiment, the ground connection portion 19 formed simultaneously with the heat radiating plate 18 is formed so as not to cover the input portion 26 and the output portion 28 except for the region where the field effect transistor is formed. For this reason, since the heat radiation area is wider than in the case of the model considered in the simulation, the heat radiation effect becomes higher.

  In general, in a high-frequency semiconductor device composed of a field effect transistor, a positive high potential is applied to the drain electrode, an RF signal having an amplitude centered on a negative voltage is applied to the gate electrode, and the source electrode is Connected to ground power. Therefore, a high electric field is generated at the end of the gate electrode on the drain electrode side, and the field effect transistor may be destroyed. However, in the present embodiment configured as described above, the heat radiating plate 18 made of metal (for example, Au) is formed so as to extend from the source electrode 10 and cover the gate electrode 14 and is connected to the source electrode 10. Therefore, the high electric field generated at the end of the gate electrode 14 on the drain electrode 12 side can be relaxed by the heat radiating plate 18 and the withstand voltage can be improved. As a result, the operating voltage can be increased.

  Next, an increase in the gate-source capacitance Cgs when the heat dissipation plate 18 connected to the source electrode 10 is formed so as to cover the gate electrode 14 as in the present embodiment will be considered.

The gate-source capacitance Cgs of the genuine part of the field effect transistor is proportional to ε / d, where d is the depth from the gate electrode 14 to the channel and ε is the dielectric constant of the material therebetween. On the other hand, is added in the present embodiment, a parasitic capacitance due to the heat dissipation plate 18 which covers the gate electrode 14, a distance d _p from the gate electrode 14 to the heat radiating plate _18, when the dielectric constant epsilon _p therebetween substances, epsilon proportional to _p / _{d p.} In the case of the present embodiment, d _p is 3 times or more of d, and conversely, ε _p is as small as about 60% of ε. Therefore, the increase in gate-source capacitance Cgs due to parasitic capacitance is 20% or less of the true part. Become. Due to this increase in parasitic capacitance, characteristics such as the cut-off frequency and cut-off frequency of the element are slightly reduced. However, the gate element is generally formed using a gate formation process that can be realized at the present time, and operates on the order of GHz. There is no problem in forming an element to be used.

  As described above, according to the present embodiment, it is possible to effectively dissipate the heat generated inside the element, and thus it is possible to increase the high-frequency output power while suppressing the temperature rise inside the element. . Further, the breakdown voltage of the element can be improved, and the operating voltage can be increased.

(First modification)
In the high-frequency semiconductor device of this embodiment, the connection for grounding the field effect transistor is formed by forming a metal film 19 formed simultaneously with the heat dissipation plate 18 on the surface on which the field effect transistor is formed. However, as in the modification of the present embodiment shown in FIG. 5, a metal film to be a pad 36 for grounding is formed on the surface opposite to the surface on which the field effect transistor is formed (the back surface of the substrate 2). Then, the ground connection portion 19 of the field effect transistor or the back surface of the source electrode may be connected to the contact 34 made of a metal embedded in an opening penetrating the substrate 2 and the nitride semiconductor film 3. 5 is a cross-sectional view taken along the cutting line BB ′ shown in FIG.

  This first modification can also obtain the same effects as in the present embodiment.

(Second modification)
A plan view of a high-frequency semiconductor device according to a second modification of the present embodiment is shown in FIG. The high-frequency semiconductor device of this modification is configured such that the electrode length of the drain electrode 12 is shorter than the electrode length of the source electrode 10 as compared with the high-frequency semiconductor device of the present embodiment shown in FIG. By adopting such a configuration, the area of the heat radiating plate 18 can be made wider than that of the present embodiment shown in FIG. 1, and the heat radiating effect can be further enhanced. Note that reference numeral 34 shown in FIG. 6 is the contact described in FIG.

  This second modification can also obtain the same effect as that of the present embodiment.

  Although the nitride semiconductor field effect transistor has been described in the above-described embodiment and its modifications, the same effect can be expected from other semiconductors.

  Moreover, although the SiC substrate was used as the substrate, the same effect can be obtained by using other substrates such as a sapphire substrate and a Si substrate.

  In addition to GaN or AlGaN, AlN, InN, InAlN, InGaN, or the like can be used as the nitride semiconductor layer constituting the nitride semiconductor film.

  In the above-described embodiment, the nitride semiconductor film 3 has been described as an example of a structure in which two nitride semiconductor layers are stacked. However, the nitride semiconductor film 3 is a nitride semiconductor film in which three or more nitride semiconductor layers are stacked. However, the same effect can be obtained. Further, the present invention can be applied to a structure in which a thin insulating film is sandwiched between a gate electrode and a nitride semiconductor film.

  As described above, according to one embodiment of the present invention and its modification, it is possible to effectively dissipate the heat generated inside the element, so that the temperature rise inside the element can be suppressed and high frequency output can be achieved. The power can be increased. Further, the breakdown voltage of the element can be improved, and the operating voltage can be increased.

The top view of the high frequency semiconductor device by one embodiment of the present invention. Sectional drawing cut | disconnected by the cutting line A-A 'shown in FIG. Sectional drawing cut | disconnected by the cutting line B-B 'shown in FIG. The figure which shows the simulation result regarding the thermal radiation effect of the thermal radiation plate which concerns on one Embodiment of this invention. Sectional drawing of the high frequency semiconductor device by a 1st modification. The top view of the high frequency semiconductor device by the 2nd modification.

Explanation of symbols

2 Substrate
3 Nitride Semiconductor Film 4 GaN Layer 5 AlGaN Layer 8 Insulating Film 10 Source Electrode 12 Drain Electrode 13 Leading Wire 14 Gate Electrode 15 Leading Wire 16 Interlayer Insulating Film 18 Heat Dissipation Plate 19 Ground Connection 20 Interlayer Insulating Film 22 Heat Dissipating Device Connection 24 Radiator 26 RF signal input section 28 Output section 30 Contact 32 Input pad 34 Contact 36 Pad (for grounding)

Claims (6)

A semiconductor film formed on the substrate;
A source electrode and a drain electrode that are formed apart from each other in a first region to be a transistor active portion forming region of the semiconductor film;
A field effect transistor having a gate electrode formed on the first region between the source electrode and the drain electrode;
An insulating film formed to cover the semiconductor film, the source electrode, the gate electrode, and the drain electrode;
A heat dissipation plate connected to the source electrode and formed on the insulating film so as to extend above the gate electrode so as to cover the gate electrode;
A heat dissipating part formed on the heat dissipating plate;
A high-frequency semiconductor device comprising: An input portion formed on a second region different from the first region of the semiconductor film and connected to the gate electrode;
An output part formed on the second region and connected to the drain electrode;
An input contact and an output contact formed to penetrate from the upper surface of the semiconductor film to a surface of the substrate opposite to the semiconductor film, and connected to the input unit and the output unit, respectively,
An input pad and an output pad formed on a surface of the substrate opposite to the semiconductor film and connected to the input contact and the output contact;
The high-frequency semiconductor device according to claim 1, comprising: A ground connection part that is formed in the second region other than the region where the input part and the output part are formed and is connected to the heat dissipation plate;
A grounding contact that is formed so as to penetrate from the upper surface of the semiconductor film to a surface of the substrate opposite to the semiconductor film, and connected to the ground connection portion;
A grounding pad formed on a surface of the substrate opposite to the semiconductor film and connected to the grounding contact;
The high-frequency semiconductor device according to claim 2, further comprising:   4. The high-frequency semiconductor device according to claim 1, wherein an electrode length of the source electrode of the field effect transistor is longer than an electrode length of the drain electrode.   2. The field effect transistor according to claim 1, wherein there are a plurality of field effect transistors, and the field effect transistors are arranged in a line so as to share the source electrode or the drain electrode. 5. The high-frequency semiconductor device according to any one of 4   The high-frequency semiconductor device according to claim 1, wherein the semiconductor film is a nitride semiconductor.

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