JP2636811B2 - Bipolar transistor and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bipolar transistor and a method of manufacturing the same, and more particularly, to a high-power bipolar transistor having a ballast resistor and a method of manufacturing the same.

[0002]

2. Description of the Related Art Bipolar transistors are characterized by being superior in power density and breakdown voltage as compared with field effect transistors. For this reason, research and development of microwave or millimeter-wave high-output power amplifiers using heterojunction bipolar transistors (hereinafter abbreviated as "HBTs") using compound semiconductors as well as silicon have been actively conducted. .

Meanwhile, a high-output HBT generally has a multi-finger configuration in which a plurality of transistors are arranged in parallel. However, in this configuration, a temperature rise occurs in the central transistor during operation, and as a result, current concentrates on the central transistor, and the temperature of this portion further increases, resulting in “positive feedback type thermal runaway”.
Has the disadvantage of causing

As a means for solving the above drawback, there is known a method of connecting a resistor called a "ballast resistor" in series to the emitter of each transistor.

[0005] The ballast resistor functions even if it is made of "a material whose resistance value does not change even if a temperature change occurs". However, it is more effective to use a material having a high resistance value at a high temperature (i.e., a material having a positive temperature coefficient) .For example, Japanese Patent Laid-Open No. 3-46334 discloses such a positive temperature coefficient. As an example of the ballast resistance, an "example using a semiconductor layer having a low impurity concentration" is disclosed.

Here, a conventional high-output HBT will be described.
This will be described with reference to FIG. FIG. 5 is a cross-sectional view of a semiconductor chip for explaining a conventional high-output HBT. This semiconductor chip has a semi-insulating property as shown in FIG.
GaAs substrate 1, collector contact layer 2 of n-type GaAs, collector layer 3 of n-type GaAs, base layer 4 of p-type GaAs, emitter layer 5 of n-type AlGaAs, low-concentration n-type GaAs Ballast resistor 18, high concentration n-type GaAs
And a source electrode 8, the collector electrode 9 made of AuGeNi, the insulating region 13, SiO ₂ sidewalls 15 - emitter contact layer 19, an emitter electrode 20 made of AuGe / Au, consisting AuMn base which composed of.

[0007]

SUMMARY OF THE INVENTION The above conventional high output type H
In the BT, the ballast resistor 18 is formed of n-type GaAs. Therefore, when changing the resistance value or the temperature characteristics, the impurity concentration (or film thickness) must be changed, and the transport characteristics of the intrinsic portion of the transistor are changed. Also has the disadvantage of complicating the design.

Further, in order to use a low-concentration n-type GaAs layer as a resistor, its thickness is required to be about 400 nm. As a result, the height of the emitter mesa is about 750 nm, which is 2% of that of a transistor having no ballast resistance. About double. For this reason,
There is a problem that the reduction in the cross-sectional area of the transistor due to side etching during the formation of the mesa becomes remarkable. In addition, an increase in the height of the mesa causes a problem that flattening during the wiring process becomes difficult.

The present invention has been made in view of the above-described problems, and has as its object to easily improve the temperature characteristics of a ballast resistor without affecting the transport characteristics of an intrinsic portion of a transistor. An object of the present invention is to provide a high-output type bipolar transistor that can be changed and a method of manufacturing the same.

[0010]

The present invention is characterized in that a sintered body containing barium metatitanate as a main component is used as a material of the ballast resistor. It is possible to easily change the temperature characteristics of the ballast resistor without providing the same. "

That is, the bipolar transistor according to the present invention comprises a first semiconductor layer of the first conductivity type, a second semiconductor layer of the second conductivity type, and a third semiconductor layer of the first conductivity type on the substrate. A high-output bipolar transistor having layers sequentially formed and having a ballast resistor between an emitter electrode and a ground terminal, wherein the ballast resistor is a sintered body containing barium metatitanate as a main component. A bipolar transistor. "

Further, the method of manufacturing a bipolar transistor according to the present invention includes the steps of "(1) forming a first conductive type first semiconductor layer, a second conductive type second semiconductor layer and a first conductive type on a substrate. A step of sequentially depositing and forming a third semiconductor layer of a mold; (2) a step of forming a sintered thin film containing barium metatitanate as a main component; and (3) a ballast by etching the sintered thin film. And a step of forming a resistor. A method for manufacturing a bipolar transistor. "

Hereinafter, the material of the "ballast resistor", which is a feature of the present invention, will be described in detail along with its operation. In the present invention, as described above, the ballast resistor is formed of a sintered body containing barium metatitanate as a main component. For example, a small amount of strontium, lead, manganese may be used in barium metatitanate. A sintered body obtained by adding an oxide or a rare earth element and sintering can be used.

The temperature characteristics of the ballast resistor made of the sintered body will be described with reference to FIG. Barium metatitanate with small amounts of strontium, lead, manganese oxide,
When a rare earth element is added and sintered, the resistivity of the obtained sintered body sharply increases at a certain transition temperature as shown in FIG.

When a ballast resistor is formed of such a sintered body, when current concentration occurs in a transistor in the multi-finger configuration and a certain temperature is reached, the resistance value of the ballast resistor of the transistor sharply increases. Since the current increases and the current flowing through the transistor decreases, thermal runaway can be prevented.

The transition temperature at which the resistivity changes abruptly can be changed by the type and amount of the element added to barium metatitanate. For example, by changing the amount of lead added from 0% to 40% with respect to barium, the transition temperature can be changed from about 100 ° C to about 300 ° C. In addition, this fact is, for example, `` Andrich (EA
ndrich), “Philips Technical Review (Philli
ps Technical Reviews) ", Volume 3 (1969), 170-177
Page ".

As described above, by using the above-mentioned “sintered body containing barium metatitanate as a main component” as the material of the ballast resistor, the temperature characteristic of the ballast resistor can be obtained without affecting the transport characteristics of the intrinsic portion of the transistor. Can be easily changed.

[0018]

Next, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and various modifications may be made without departing from the gist of the present invention. Can be changed.

(Embodiment 1) FIG. 1 is a sectional view of a semiconductor chip for explaining a bipolar transistor according to a first embodiment (Embodiment 1) of the present invention.

As shown in FIG. 1, the semiconductor chip according to the first embodiment has a semi-insulating GaAs substrate 1, a collector contact layer 2 made of n-type GaAs, a collector layer 3 made of n-type GaAs, and a p-type GaAs. Base layer 4, an emitter layer 5 of n-type AlGaAs, an emitter cap layer 6 of n-type InGaAs, an emitter electrode 7 of WSi, a base electrode 8 of AuMn, a collector electrode 9 of AuGeNi, insulating Region 13,
It is composed of a ballast resistor 14 made of a (Ba _{1 -X} Pb _X ) TiO ₃ sintered body and SiO ₂ side walls 15.

Next, a method of manufacturing the semiconductor chip according to the first embodiment will be described with reference to FIG. Note that FIG.
FIG. 3 is a view for explaining a manufacturing example of the semiconductor chip of FIG.

First, as shown in FIG.
An n-type Ga layer is formed on a GaAs substrate 1 by epitaxial growth.
As collector contact layer 2, n-type GaAs collector layer 3, p
-Type GaAs base layer 4, n-type AlGaAs emitter layer 5, n-type InGa
After sequentially growing the As emitter cap layer 6, the unnecessary portions of these layers are increased in resistance by proton ion implantation,
An insulating region 13 is formed. Next, on the front surface of the substrate 1, a WSi film 16 as a refractory metal film and a resistor thin film (Ba1 _- XP
b _X ) A TiO ₃ sintered body film 17 is formed by a sputtering method (see step A in FIG. 2).

In order to prevent thermal runaway, the temperature at which the resistance of the resistor rapidly rises (hereinafter referred to as “transition temperature”) is 15 °.
The temperature is suitably from about 0 ° C. to 200 ° C., but in order to show such a transition temperature, the Pb composition ratio may be in the range of 5 to 20%.

Therefore, in the (Ba _{1 -X} Pb _x ) TiO ₃ sintered body used as the resistor in the first embodiment, it is preferable that x is in the range of 0.05 to 0.20. In order to obtain a transition temperature of about 150 ° C., as an element added to barium metatitanate,
In addition to Pb, lanthanoids such as Sm, Sr, Mn and the like can be used, and a sintered body containing these elements is also included in the present invention.

Next, as shown in step B of FIG. 2, using a photoresist (not shown) as a mask, reactive ion etching (RIE) using SF ₆ gas is performed to (Ba _{1 -X} Pb _X ) TiO 2 ₍₃₎ Pattern the sintered body film 17 and WSi film 16 to obtain (Ba _1-X Pb _X ) T
A ballast resistor 14 made of an iO ₃ sintered body and an emitter electrode 7 made of WSi are formed.

Further, as shown in FIG. 2C, the n-type InGaAs emitter cap layer 6 and the n-type AlGaAs emitter layer 5 are successively removed by using the same mask (not shown) to form a reactive ion beam by chlorine plasma. By etching
Etching is performed to the surface of the type GaAs base layer 4 to form an emitter mesa.

Next, as shown in FIG. 2D, after forming an SiO ₂ film on the entire surface of the wafer, anisotropic etching by reactive ion etching using CF ₄ gas is performed to form SiO ₂ side walls 15. I do. Subsequently, as shown in step E of FIG. 2, an Au-based alloy (for example, AuMn) is formed on the entire surface of the wafer by a vacuum deposition method, and is patterned by an ion milling method using a photoresist as a mask. Forming the source electrode 8;

After that, the photoresist film is removed by washing with an organic solvent. Then, although not shown in FIG. 2, a new photoresist having a predetermined pattern is used as a mask.
The p-type GaAs base layer 4 and the n-type GaAs collector layer 3 are sequentially etched and removed with a mixture of phosphoric acid, hydrogen peroxide and water to expose the surface of the n-type GaAs collector contact layer 2, A collector electrode 9 made of AuGeNi is formed by a lift-off method to manufacture a semiconductor chip having the structure shown in FIG. 1 described above.

(Embodiment 2) FIG. 3 is a view for explaining a bipolar transistor according to a second embodiment (Embodiment 2) of the present invention, and FIG. FIG. 3B is a plan view of the chip, and FIG. 3B is a sectional view taken along line AA of FIG.

The semiconductor chip according to the second embodiment differs from the semiconductor chip according to the first embodiment in that, as shown in FIGS. 3A and 3B, a ballast resistor 14 is provided not directly above the emitter electrode 7. This is an example in which the transistor is arranged at a location away from the transistor.

That is, the semiconductor chip according to the second embodiment is
As shown in FIGS. 3A and 3B, the semi-insulating GaAs substrate 1, n
-Type GaAs collector contact layer 2, n-type GaAs collector layer 3, p-type GaAs base layer 4, n-type AlGaAs emitter layer 5, n
Emitter cap layer 6 of type InGaAs, emitter electrode 7 of WSi, base electrode 8 of AuMn, collector electrode 9 of AuGeNi, interlayer insulating film 10, through hole 1
1, a wiring 12, an insulating region 13, a ballast resistor 14 made of a (Ba _1-X Pb _X ) TiO ₃ sintered body, and a SiO ₂ side wall 15.

As in the second embodiment, the ballast resistor 14 is
The function of the ballast resistor 14 does not change at all even if the ballast resistor 14 is arranged not at the position directly above the emitter electrode 7 but at a place away from the transistor. The bipolar transistor having the structure shown in FIG.
The same effect as that of the first embodiment can be obtained.

In the first and second embodiments, the base layer 4 is made of GaAs. However, the present invention is not limited to this. For example, a p-type AlGaAs composition gradient layer or a p-type An InGaAs composition gradient layer of the n-type can be used as the base layer 4, and an emitter layer 5 using n-type InGaP can be used. Thus, the material system is variously changed. Bipolar transistors can be applied in the same manner and produce similar effects, and all of them are included in the present invention.

[0034]

According to the present invention, as described in detail above, the ballast resistor conventionally formed of low-concentration n-type GaAs is formed by "a sintered body containing barium metatitanate as a main component". The remarkable effect that "the temperature characteristics of the ballast resistor can be easily changed without affecting the transport characteristics of the intrinsic portion of the transistor" is produced.

[Brief description of the drawings]

FIG. 1 is a sectional view of a semiconductor chip for explaining a bipolar transistor according to a first embodiment (embodiment 1) of the present invention;

FIG. 2 is a view for explaining a manufacturing example of the semiconductor chip of FIG. 1 and is a cross-sectional view in the order of manufacturing steps including steps A to E;

FIG. 3 is a diagram for explaining a bipolar transistor according to a second embodiment (Embodiment 2) of the present invention;
Is a plan view of the semiconductor chip, and (B) is AA of (A).
Line cross section

FIG. 4 is a diagram showing temperature dependence of resistivity for explaining temperature characteristics of a ballast resistor used in the present invention.

FIG. 5 is a sectional view of a semiconductor chip for explaining a conventional bipolar transistor.

[Explanation of symbols]

Reference Signs List 1 semi-insulating GaAs substrate 2 n-type GaAs collector contact layer 3 n-type GaAs collector layer 4 p-type GaAs base layer 5 n-type AlGaAs emitter layer 6 n-type InGaAs emitter cap layer 7 emitter electrode 8 base electrode 9 collector Electrode 10 Interlayer insulating film 11 Through-hole 12 Wiring 13 Insulating region 14 Ballast resistor 15 SiO ₂ side wall 16 WSi film 17 (Ba _{1 -X} Pb _X ) TiO ₃ sintered thin film 18 Low concentration n-type GaAs ballast resistor 19 High concentration n-type GaAs emitter contact layer 20 AuGe / Au emitter electrode

Claims (3)

(57) [Claims] A first semiconductor layer of a first conductivity type on a substrate;
A second semiconductor layer of the second conductivity type and a third semiconductor layer of the first conductivity type are sequentially formed, and a high-power bipolar transistor having a ballast resistance element between the emitter electrode and the ground terminal. Wherein the ballast resistor element is a sintered body containing barium metatitanate as a main component. 2. The sintered body containing barium metatitanate as a main component is represented by the formula: (Ba ₁ -x Pb _x ) TiO ₃ [where x
= 0.05 to 0.20]. 2. The bipolar transistor according to claim 1, wherein: 3. A first semiconductor layer of a first conductivity type on a substrate,
A step of sequentially depositing and forming a second semiconductor layer of the second conductivity type and a third semiconductor layer of the first conductivity type, and a step of forming a sintered thin film containing barium metatitanate as a main component, Etching the sintered thin film to form a ballast resistor.