JPH065620A - Semiconductor device - Google Patents

Abstract

(57) [Abstract] [Purpose] It is an object of the present invention to provide an excellent semiconductor for high frequency power, which has good heat dissipation characteristics and a small resistance component. [Structure] On the main surface side of a semi-insulating GaAs substrate 1, semiconductor active layers serving as a collector 3, a base 4, and an emitter 5 of a bipolar transistor are continuously laminated. A back surface electrode 12 is formed through a groove 11 formed from the opposite main surface of the semi-insulating GaAs substrate 1 reaching the semiconductor active layer located at the lowest position of the stacked semiconductor active layers. Electrodes are drawn from the main surface side of the semi-insulating GaAs substrate 1 to the other stacked semiconductor active layers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device for high frequency power, particularly a semiconductor device such as a bipolar transistor.

[0002]

2. Description of the Related Art Since semiconductors for high frequency power use a large amount of power, it is necessary to take special measures for heat dissipation. Usually, the thickness of the semiconductor substrate is reduced from about 30 to 150 microns by polishing from the back side, and gold is deposited on the polished back side by about 30 microns to reduce the thermal resistance of the semiconductor substrate. In particular, when a semi-insulating GaAs substrate is used, the thermal resistance is about three times as high as that of silicon, so attention must be paid to the problem of heat dissipation.

On the other hand, since the bipolar transistor has a larger power density (output power per unit area) than a field effect transistor (hereinafter abbreviated as FET), heat generation causes a decrease in electrical characteristics such as output power with time. There was also a problem. Active 3 such as bipolar transistor
When the terminal element is formed on a semi-insulating GaAs substrate, measures against heat generation are especially important. Furthermore, when a bipolar transistor, which is an active three-terminal element, is formed on a semi-insulating GaAs substrate, the emitter, base, and collector electrodes have conventionally been drawn out on the surface. Since the semiconductor layer was used, resistance was added, and the original performance of the bipolar transistor could not be brought out to the outside.

In recent years, a bipolar transistor having a heterojunction formed on a semi-insulating GaAs substrate has a high-frequency characteristic improved to 100 GHz or more and is very promising as a small signal element, but a heat dissipation problem is a large power element. And the resistance is added by the high-concentration semiconductor layer used for extracting the electrode.
There was a major obstacle to further improving the high frequency characteristics above GHz.

FIG. 3 is a sectional view of a conventional bipolar transistor. A bipolar transistor having a heterojunction formed on a GaAs substrate which is a compound semiconductor will be described as an example. The collector contact layer 2, the collector layer 3, the base layer 4, the emitter layer 5, and the emitter contact layer 6 are continuously formed on the entire main surface of the semi-insulating GaAs substrate 1 by molecular beam epitaxy (hereinafter abbreviated as MBE), etc. Grow in the way.

The collector contact layer 2 is a region having a higher impurity concentration than the collector layer 3, and the collector contact layer 2 is laterally drawn out to form a collector electrode 9. As a matter of course, the collector electrode 9 is formed after the other film located on the surface is removed by etching.
A base electrode 8 is added to the base layer 4 and an emitter electrode 7 is added to the emitter contact layer 6 so that they can be electrically connected to the outside. Here, the emitter contact layer 6 is important for forming a stable ohmic electrode in a region having a higher impurity concentration than the emitter layer 5, as in the case of the collector.

Further, for the purpose of element isolation, hydrogen ions are implanted to form the ion implantation layer 10, and the conductive layer is converted into an insulating layer. This achieves isolation from other areas.

In the conventional bipolar transistor described in FIG. 3, since the semi-insulating GaAs substrate 1 has a low thermal conductivity, the element temperature rises, the output power decreases temporally, and finally the element is heated. It was destroyed and there was a big problem in reliability. This is because the bipolar transistor, in particular, has a high power density and therefore generates a lot of heat. Semi-insulating GaA
There is also a method of reducing the thermal resistance by thinning the s substrate 1, but a substrate thickness of about 50 to 100 microns is a thinness that can be processed in the process, which is a major obstacle to the reduction of the thermal resistance. Further, since the collector electrode 9 is formed by being laterally drawn out via the collector contact layer 2, there is a resistance and the gain and high frequency characteristics are sacrificed.

[0009]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention As shown in FIG.
In a conventional bipolar transistor, semi-insulating Ga
Since the thermal conductivity of the As substrate is low, the element temperature rises, the output power decreases temporally, and the element finally breaks, causing a serious reliability problem. Also, the collector electrode 9
Is formed by being laterally drawn out via the collector contact layer 2, there is a resistance and the gain and high frequency characteristics are sacrificed.

The present invention has been made in view of the above points, and can significantly reduce the thermal resistance without polishing the semi-insulating GaAs substrate to the maximum extent, and reduce the excess resistance to improve the high frequency characteristics. An object is to provide an excellent semiconductor device that can be improved.

[0011]

In order to solve the above-mentioned problems, the present invention successively stacks semiconductor active layers serving as collectors, bases, and emitters of bipolar transistors on the main surface side of a semi-insulating GaAs substrate, The back surface electrode is formed through the groove formed from the opposite main surface of the semi-insulating GaAs substrate reaching the semiconductor active layer located at the bottom of the stacked semiconductor active layers, and other stacked semiconductor active layers are formed. In this case, the electrode is drawn out from the main surface side of the semi-insulating GaAs substrate.

In order to solve the above-mentioned problems, the present invention continuously stacks a selective etching semiconductor layer and a semiconductor active layer serving as a collector, a base and an emitter of a bipolar transistor on the main surface side of a semi-insulating GaAs substrate. , Semi-insulating GaA reaching the semiconductor active layer located at the lowest position of the stacked semiconductor active layers penetrating the selective etching semiconductor layer
The back electrode is formed through the groove formed from the opposite main surface of the s substrate, and the electrode is drawn from the main surface side of the semi-insulating GaAs substrate to the other stacked semiconductor active layers.

[0013]

According to the present invention, as described above, the back surface electrode is formed through the groove formed from the opposite main surface of the substrate, which reaches the semiconductor active layer located at the bottom of the continuously stacked semiconductor active layers. Therefore, the heat generated in the semiconductor active layer of the bipolar transistor escapes directly to the package in which the device is mounted through the back electrode, and the problem of heat radiation is remarkably reduced. As a result, the bipolar transistor formed on the semi-insulating GaAs substrate becomes thermally stable and the output power does not change. Further, since the back surface electrode is directly connected to the semiconductor active layer located at the lowest position of the bipolar transistor, there is no region for drawing out in the lateral direction, the resistance component is reduced, and the gain and high frequency characteristics can be improved.

Further, according to the present invention, as described above, the selective etching semiconductor layer and the semiconductor active layer serving as the collector, the base and the emitter of the bipolar transistor are continuously laminated, and the semiconductor active layer laminated through the selective etching semiconductor layer is laminated. Since the back surface electrode is formed through the groove formed from the opposite main surface of the substrate that reaches the semiconductor active layer located at the bottom of the layer, heat generated in the semiconductor active layer is also mounted on the element through the back surface electrode. Since it escapes directly to the package, the problem of heat dissipation is solved and the back surface electrode is directly connected to the semiconductor active layer, so the resistance component decreases,
The gain and high frequency characteristics can be improved. Furthermore, by positioning the selective etching semiconductor layer below the semiconductor active layer, the groove formed by wet etching from the back surface of the semi-insulating GaAs substrate is selectively stopped at this selective etching semiconductor layer, and again by dry etching. Since the selective etching semiconductor layer can be penetrated, the controllability of the electrode formation through the groove is improved, the film thickness of the lowermost layer of the semiconductor active layer can be formed thinner, and the resistance can be further reduced, and the gain and High frequency characteristics can be improved.

[0015]

1 is a cross-sectional view of a bipolar transistor of the first invention. In the following description of the present invention, the parts equivalent to those in the drawings already described will be denoted by the same reference numerals. Similarly, as a semiconductor chip, a bipolar transistor using a semi-insulating GaAs substrate which is a compound semiconductor will be described as an example.

In FIG. 1, the collector contact layer 2 located at the bottom of the grown semiconductor active layer is reached by the back surface groove portion 11 from the back surface of the semi-insulating GaAs substrate 1 by a method such as wet etching, and then the back surface. The collector electrode 12 is formed on the entire back surface and functions as a collector electrode. Since the back surface groove portion 11 is automatically filled with solder by using solder or the like when mounting a semiconductor element in a package, all heat generated in the semiconductor active layer of the bipolar transistor is generated in the back surface groove portion 1.
1 to a package or the like.
Therefore, the problem of heat radiation due to the conventional semi-insulating GaAs substrate being located under the semiconductor active layer of the bipolar transistor is significantly reduced. Electrodes are drawn out to the other emitter portion and the base portion on the front surface side of the substrate as in the conventional case. Further, as shown in FIG. 1, according to the present invention, it is not necessary to arrange the semiconductor layer for drawing the collector electrode to the surface, which is conventionally necessary, and the collector contact layer 2 and the back surface collector electrode can be directly connected, which is unnecessary. The resistance component can be removed, and the gain and high frequency characteristics can be improved.

FIG. 2 is a sectional view of the bipolar transistor of the second invention. In FIG. 2, a selective etching semiconductor layer 13 is grown below the collector contact layer 2 before formation of semiconductor active layers such as collectors, bases, and emitters of bipolar transistors. This selective etching semiconductor layer 13 has a large etching selection ratio with respect to the semi-insulating GaAs substrate 1 when a groove is formed from the back surface of the semi-insulating GaAs substrate 1 by wet etching or the like. Etching will stop automatically. Specifically, the selective etching semiconductor layer 13 can be formed by using an AlGaAs semiconductor layer. As shown in FIG. 3, it is necessary to form a groove that penetrates the selective etching semiconductor layer 13 and reaches the collector contact layer 2. For this purpose, dry etching is used to force the selective etching semiconductor layer 13 to the selective etching semiconductor layer 13. Scraped off, collector contact layer 2
Exposed, and the backside collector electrode 12 is made of semi-insulating GaAs.
The collector contact layer 2 is deposited on the entire back surface of the substrate 1 by vapor deposition.
An electrode is formed on. In the second invention shown in FIG. 3,
Similar to the first invention shown in FIG. 1, the problem of heat radiation is remarkably alleviated, and since the back surface collector electrode 12 can be directly connected to the collector contact layer 2, unnecessary resistance components can be reduced and gain and high frequency characteristics are improved. It can be done. Furthermore, the introduction of the selective etching semiconductor layer 13 stabilizes the control of the depth of the back surface groove portion 11 and enables the thickness of the collector contact layer 2 to be made thinner, so that the resistance component in the vertical direction can be further reduced. It is possible to improve gain and high frequency characteristics.

In the description of the present invention, semi-insulating GaA is used.
Although the description is given by taking the structure in which the collector is the bottom growth layer of the bipolar transistor formed on the s substrate as an example, the same effect can be obtained by using the structure in which the emitter is the bottom growth layer. Is clear.

[0019]

As described above, the present invention brings the following effects.

1) Since the back surface electrode is formed through the groove formed from the opposite main surface of the substrate, the heat generated in the semiconductor active layer of the bipolar transistor escapes directly to the package in which the device is mounted through the back surface electrode. Therefore, the problem of heat radiation is solved, and it becomes thermally stable and the output power does not change. Further, since the back surface electrode is directly connected to the semiconductor active layer located at the lowest position of the bipolar transistor, there is no region for drawing out in the lateral direction, the resistance component is reduced, and the gain and high frequency characteristics can be improved.

2) Selective etching By introducing the semiconductor layer and forming the back surface electrode through the groove formed from the opposite main surface of the substrate, heat dissipation is remarkably improved and the controllability of the electrode formation through the groove is improved. It is possible to improve the thickness of the lowermost layer of the semiconductor active layer, reduce the resistance of the semiconductor active layer in the vertical direction, and improve the gain and high frequency characteristics.

[Brief description of drawings]

FIG. 1 is a sectional view of a bipolar transistor of the first invention.

FIG. 2 is a sectional view of a bipolar transistor of the second invention.

FIG. 3 is a sectional view of a conventional bipolar transistor.

[Explanation of symbols]

 1 Semi-Insulating GaAs Substrate 2 Collector Contact Layer 3 Collector Layer 4 Base Layer 5 Emitter Layer 6 Emitter Contact Layer 7 Emitter Electrode 8 Base Electrode 9 Collector Electrode 10 Ion Implantation Layer 11 Back Side Groove 12 Back Side Collector Electrode 13 Selective Etching Semiconductor Layer

Claims (2)

[Claims] 1. A semiconductor active layer serving as a collector, a base, and an emitter of a bipolar transistor is continuously stacked on the main surface side of a semi-insulating GaAs substrate, and the semiconductor active layer is located at the lowest position of the stacked semiconductor active layers. The back surface electrode is formed through the groove formed from the opposite main surface of the semi-insulating GaAs substrate reaching the semiconductor active layer, and the main surface side of the semi-insulating GaAs substrate is formed in the other stacked semiconductor active layers. A semiconductor device characterized in that an electrode is pulled out from the semiconductor device. 2. A semi-insulating GaAs substrate has a main surface side on which a selective etching semiconductor layer and semiconductor active layers serving as collectors, bases, and emitters of a bipolar transistor are continuously laminated, and penetrates the selective etching semiconductor layer. Then, the back surface electrode is formed through the groove formed from the opposite main surface of the semi-insulating GaAs substrate reaching the semiconductor active layer located at the bottom of the stacked semiconductor active layers, and other stacked semiconductor active layers are formed. The semiconductor device is characterized in that electrodes are drawn out from the main surface side of the semi-insulating GaAs substrate to the layer.