JPH10107040A - Compound semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compound semiconductor device which is constituted in such a way that the resistance value fluctuation of a resistance element incorporated in a microwave monolithic IC can be reduced and the semiconductor device can be manufactured easily with a high yield. SOLUTION: A compound semiconductor device is constituted so that a heterojunction bipolar transistor 30 and a resistance element 31 can be formed on a semi-insulating compound semiconductor substrate. The element 31 is made of the same material 19 as that used for the sub-collector layer of the bipolar transistor 30 and the sub-collector layer has a thin transition layer 12A the composition of which changes from that of the sub-collector layer to that of a collector layer on its surface on the collector layer side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a compound semiconductor device and, more particularly, to a heterojunction bipolar transistor (HB).
The present invention relates to a microwave monolithic IC in which T) and a resistance element are mounted on a semi-insulating compound semiconductor substrate.

[0002]

2. Description of the Related Art In recent years, with the spread of devices operating in the ultra-high frequency band such as portable telephones, the development of high-power devices operating in the GHz band has been demanded. A heterojunction bipolar transistor (HBT) has, for example,
By using a dissimilar material junction such as lGaAs or GaInP / GaAs, the electron mobility is high and the band gap of the emitter is larger than the band gap of the base, so that the electron injection efficiency can be increased. For this reason, GHz
A high output characteristic of about several W is obtained in a band, and attention is paid to satisfying the above requirement.

For example, a document (IEEE ELECTRON DEVICE LET)
TERS, Vol 14, No10, October 1990 PP493-495), Japanese Patent No. 252280, and the like disclose an example of a heterojunction bipolar transistor using a compound semiconductor material. This is n +-on a semi-insulating GaAs substrate.
GaAs sub-collector layer, n-GaAs collector layer, p
+ -GaAs base layer, n-AlGaAs emitter layer,
An n + -GaAs emitter contact layer and the like are stacked.

By the way, there is a tendency that such a heterojunction bipolar transistor is also provided with a resistance element to be made into a monolithic IC. When a monolithic IC is formed, the sub-collector layer has a high impurity concentration,
Since ohmic contact can be easily made with a wiring metal such as Ge / Ni / Au, a sub-collector layer is patterned into a required dimension and used as a resistor as a resistor.
Further, since the impurity concentration of the subcollector layer can be easily controlled, the sheet resistance can be controlled to about several tens of Ω / □, and a resistor having an arbitrary resistance value can be formed by selecting a pattern shape.

FIG. 3 shows an example of a cross-sectional structure of a microwave monolithic IC in which such a conventional heterojunction bipolar transistor and a resistance element are integrated. A heterojunction bipolar transistor 30 and a resistance element 31 are formed on a semi-insulating GaAs substrate 11. In the heterojunction bipolar transistor 30, a collector layer 13 composed of an n-type GaAs layer is formed on a subcollector layer 12 composed of an n + -type GaAs layer, and a base layer 14 composed of a p-type GaAs layer is formed thereon. An emitter layer 1 composed of an n-type AlGaAs layer, which is a different material, is formed on the upper layer.
6 are formed. The electrodes 21 and 21 are extraction electrodes of the collector layer, the electrodes 22 and 22 are extraction electrodes of the base, and the electrode 23 is an extraction electrode of the emitter layer.

On the other hand, in the resistance element 31, a resistor 19 is formed using a layer made of the same material as the subcollector layer 12 of the heterojunction bipolar transistor, and the electrodes 24, 24 serve as extraction electrodes. In this figure, the connection wiring between the transistor and the resistance element is not shown.

FIG. 4 shows a compound semiconductor substrate before a heterojunction bipolar transistor and a resistance element are formed. This substrate comprises an n + -type GaAs layer 12 serving as a sub-collector layer, an n-type GaAs layer 13 serving as a collector layer, a p-type GaAs layer 14 serving as a base layer, and an emitter layer on a semi-insulating GaAs substrate 11 from below. N-type AlGaAs layers 16 and the like are stacked by epitaxial growth. FIG.
In the heterojunction bipolar transistor 30 and the resistive element 31 shown in FIG. 5, each epi-grown layer is patterned and etched stepwise by photolithography to form a mesa.

[0008]

However, in order to form the resistor 19 using the sub-collector layer of the hetero-junction bipolar transistor, the n-type GaAs layer 13 serving as the upper collector layer is removed by etching. There must be. However, both the collector layer 13 and the sub-collector layer 12 are made of the same n-type GaAs layer, and differ only in their concentration. For this reason, it is difficult to detect the end point of the etching, and when the overetching is performed, the thickness of the resistor 19 becomes too thin, which causes the resistance value to be changed. In the case of under-etching, the n-type GaAs layer remains, and the resistance extraction electrode 2
Ohmic contact between the resistors 4 and 24 and the resistor 19 cannot be obtained, and similarly, the resistance value may be deviated.

For this reason, in a conventional microwave monolithic IC in which a heterojunction bipolar transistor and a resistor are integrated, the resistance of the resistor has a large variation, which may deviate from the allowable range, and the manufacturing yield is reduced. Contributed to the decline.

The present invention has been made in view of the above circumstances, and in a microwave monolithic IC in which a heterojunction bipolar transistor and a resistive element are integrated, variations in the resistance value of the resistive element are reduced, and the manufacture thereof is facilitated. It is another object of the present invention to provide a structure of a compound semiconductor device that can be manufactured with a good manufacturing yield.

[0011]

According to the present invention, there is provided a compound semiconductor device comprising a heterojunction bipolar transistor and a resistor formed on a semi-insulating compound semiconductor substrate, wherein the heterojunction bipolar transistor has a collector. A sub-collector layer of the same conductivity type and a different material as the collector layer, wherein the resistance element is made of the same material as the sub-collector layer of the heterojunction bipolar transistor. On the collector layer side surface, a thin transition layer whose composition changes from the band gap or composition of the subcollector layer to the band gap or composition of the collector layer is provided.

According to the configuration of the present invention described above, since the subcollector layer of the transistor constituting the resistor is made of a material different from that of the upper collector layer, the etchant for etching the collector layer is a subcollector. Selectivity can be given so that a semiconductor layer included in the layer is not etched. Due to such selectivity of the etchant, the etching of the collector layer proceeds smoothly, but when the subcollector layer is exposed on the surface, this layer is not etched, so that the etching by the etchant can be terminated there. As a result, the resistance value of the resistor based on the sheet resistance originally possessed by the subcollector layer can be obtained without changing the thickness of the subcollector layer, that is, without changing the thickness of the resistor, leaving the collector layer remaining and causing poor contact. Can be

Further, the subcollector layer has a thin transition layer whose composition changes from the composition of the subcollector layer to the composition of the collector layer on the surface of the collector layer side, so that the bandgap of the collector layer is changed to the bandgap of the subcollector layer. Can be continuously changed smoothly for enlargement. If this transition layer is not provided, the collector layer and the sub-collector layer are made of different materials, so that a sharp change in the band gap occurs at this boundary. As a result, the electrons running in the drift electric field are braked, causing a problem that the collector resistance increases. By providing the above-described transition layer, such a problem is solved.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a sectional configuration of a compound semiconductor device according to an embodiment of the present invention. Semi-insulating GaAs substrate 11
The point on which the heterojunction bipolar transistor 30 and the resistance element 31 are mounted is the same as in the prior art. In the present invention, the heterojunction bipolar transistor 3
The 0 sub-collector layer and the resistor 19 of the resistance element 31 are made of GaInP or AlGaAs of a different material from the collector layer. This layer is an n + type 3 × 10 18 / cm
It has an impurity concentration of about 3 and a thickness of 10,000
About Å.

On the collector layer side surface of the subcollector layer 12, there is provided a thin transition layer 12A whose composition smoothly changes from the composition of the subcollector layer to the composition of the collector layer. The transition layer 12A is as thin as, for example, about 300 Å, and has a composition of the subcollector layer on the subcollector layer side, that is, Ga0.51In0.49P or Al0.
The composition of the collector layer on the collector layer side, that is, GaAs, is 25 Ga 0.75 As, and the composition changes smoothly and continuously in the middle.

The collector layer 13 and the base layer 14 are both made of GaAs.
000 ° and the base layer 14 is 1,000 °.
The collector layer has an n-type impurity concentration of 5 × 10 16 / cm 3, and the base layer has a p-type impurity concentration of 4 × 10 19 / cm 3.

The emitter layer 16 is a layer made of a different material forming a heterojunction with the base layer, and uses an AlGaAs layer having a band gap larger than that of GaAs of the base layer. Specifically, it is an Al 0.25 Ga 0.75 As n-type layer having an impurity concentration of about 4 × 10 17 / cm 3, and has transition layers 15 and 17 to GaAs on both sides thereof. The thickness of each transition layer 15, 17 is 300 mm,
It is about 500 °.

The uppermost layer of the emitter layer is the cap layer 18, the material is GaAs, and the impurity concentration is 5 × 10 18 / c.
It is an n + type of m3 and has a thickness of about 1,000 °.
This layer is made of an emitter electrode 2 made of AuGe / Ni / Au.
This is a layer for making ohmic contact with No. 3. Base layer 1
4 are base electrodes 22 and 22 made of Ti / Pt / Au.
Are arranged, and AuGe / Ni /
Extraction electrodes 21 and 21 of collector layer composed of Au
Is arranged. Both ends of the resistor 19 are also AuGe /
Extraction electrodes 24, 24 made of Ni / Au are arranged.

The original sheet resistance of the subcollector layer 19 can be controlled with an error of about 3% due to the progress of the epi growth technique. According to the above structure, the resistance value of the resistance element 31 is determined only by the sheet resistance value of the sub-collector layer 19 and the error of the photolithography in the lateral direction, so that the variation in the resistance value can be suppressed. Also, since the transistor 30 has a compound semiconductor heterojunction structure,
High output characteristics of about several W in the GHz band can be obtained.

Next, a method of manufacturing the compound semiconductor device will be described. First, a substrate is prepared by epitaxially growing various compound semiconductor materials on the semi-insulating substrate shown in FIG. This substrate is composed of a semi-insulating GaAs substrate 11 and a GaInP or AlGaAs layer serving as a subcollector layer 12.
A layer is epitaxially grown, an n-type GaAs layer serving as a collector layer 13 is further epitaxially grown thereon, and a p-type GaAs layer serving as a base layer 14 is further epitaxially grown thereon. GaInP or AlG to be the sub-collector layer 12
A thin transition layer 12A whose composition smoothly changes to GaAs is formed on the surface side of the aAs layer.

Further, a transition layer 15 from a GaAs layer to an AlGaAs layer is epitaxially grown on the base layer 14, and an n layer having a larger band gap than that of the base layer serving as the core of the heterojunction bipolar transistor is further formed thereon. A type AlGaAs layer is epitaxially grown, a transition layer 16 to GaAs is epitaxially grown thereon, and an n + type GaAs layer serving as a cap layer 18 is further epitaxially grown thereon.

Next, as shown in FIG. 2B, the layers 15, 16, 17, and 18 for forming an emitter region are subjected to mesa etching by patterning by photolithography. Next, as shown in FIG. 2C, the base layer 14 and the collector layer 13 are similarly patterned by photolithography, and a mesa etch is performed.

In this etching, GaAs which is a material of the base layer 14 and the collector layer 13 is etched, and InGaP or AlGaAs constituting the sub-collector layer 12 is etched.
Use a selective etchant that does not etch the layer. For example, as an etchant for etching GaAs and not for InGaP, a sulfuric acid-based or phosphoric acid-based etchant is preferable. In addition, GaAs
An etchant that etches but does not etch AlGaAs is a citric acid-based etchant.
By using an etchant having such selectivity, when the etching of the collector layer 13 is sufficiently completed,
Without etching the subcollector layer 12, the progress of the etching can be completely stopped there.

A transition layer 12A whose composition changes exists on the surface of the subcollector layer 12, and this transition layer 12A
Since the thickness is as small as about A ゜, the influence on the fluctuation of the resistance value of the resistor 19 is extremely small and can be ignored.

Next, mesa etching for forming the sub-collector layer 12 and the resistor 19 is performed. In this step, too, after resist application, patterning is performed by photolithography to obtain Ga
Mesa etching is performed using an etchant for etching a subcollector layer made of an InP layer or an AlGaAs layer.

Next, as shown in FIG. 1, electrodes such as an emitter electrode, a collector electrode and a resistance electrode are provided. In this method, after applying a photoresist, patterning is performed by photolithography, AuGe / Ni / Au is deposited, and predetermined electrodes 22, 23, and 24 are formed by lift-off. Then, the alloy ensures contact with the semiconductor layer. Next, the base electrode is attached. Similarly, after a predetermined pattern is formed on a resist by photolithography, Ti / Pt / A
u is vapor-deposited, a predetermined electrode 21 is formed by lift-off, and an alloy is used to ensure contact with the semiconductor layer.

Further, a SiN film, for example, of about 2,000 ° is deposited on the entire surface by CVD, and patterning for opening a contact portion by photolithography is performed. Further, similarly, after patterning the wiring pattern by photolithography, Ti / Pt / Au is deposited, and a wiring electrode, a bonding pad electrode and the like are formed by lift-off. As a result, wiring connection and the like between the heterojunction bipolar transistor and the resistance element are performed, and a microwave monolithic IC is completed.

In the above embodiment, Ga is used as the collector layer.
As is used, and InGaP or AlGa
Although an example using a different material made of As has been described,
The gist of the present invention is not limited to this. It is possible to use an etchant having selectivity that etches the material constituting the collector layer and does not etch the material constituting the subcollector layer, and can easily and reliably end the etching of the collector layer If so, it goes without saying that the gist of the present invention can be applied.
Thus, various modifications can be made without departing from the spirit of the present invention.

[0030]

According to the present invention, as described above, in a semiconductor device in which a heterojunction bipolar transistor and a resistance element are formed on a semi-insulating compound semiconductor substrate, the collector layer and the subcollector layer of the heterojunction bipolar transistor are formed of different materials. The material is used. Thus, when forming the resistance element using the subcollector layer, only the collector layer can be completely removed without etching the subcollector layer. Therefore, the sheet resistance of the resistor formed of the same material as that of the sub-collector layer can be suppressed from fluctuating, and a resistance element whose resistance value falls within an allowable range can be easily formed.

Further, since a thin transition layer whose composition smoothly changes to the composition of the collector layer is provided on the surface of the subcollector layer, it is possible to smoothly and continuously increase the band gap from the collector layer to the subcollector layer. it can. As a result, an increase in the collector resistance can be prevented, and deterioration of high-frequency characteristics due to joining of different materials having different band gaps can be prevented.

Therefore, a microwave monolithic IC having a heterojunction bipolar transistor having a power output of the order of watts in the GHz band and a resistance element can be easily manufactured with a good yield.

[Brief description of the drawings]

FIG. 1 is a sectional view of a compound semiconductor device according to one embodiment of the present invention.

FIG. 2 is an explanatory view showing a manufacturing process of the compound semiconductor device.

FIG. 3 is a cross-sectional view of a conventional compound semiconductor device.

FIG. 4 is an explanatory view of a conventional epi growth substrate.

Claims (1)

[Claims] In a compound semiconductor device in which a heterojunction bipolar transistor and a resistance element are formed on a semi-insulating compound semiconductor substrate, the heterojunction bipolar transistor has a collector layer and a different conductivity type than the collector layer. A subcollector layer of a material, wherein the resistance element is made of the same material as the subcollector layer of the heterojunction bipolar transistor, and the bandgap or composition of the subcollector layer is on the collector layer side surface. A compound semiconductor device comprising a thin transition layer that changes from the band gap or composition of the collector layer to the band gap or composition of the collector layer.