JP2002217404A - Bipolar transistor and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provided a bipolar transistor which can improve maximum oscillation frequency, without making a current cutoff frequency and a current gain lowered. SOLUTION: A collector layer 130 and a base layer 140 are stacked sequentially, and an emitter layer 150 and a base electrode layer 200 are formed on the surface of the base layer 140. In this case, the base layer 140 is provided with a trench groove 132 crossing in the direction of thickness, so that the total area ratio of the base layer to the emitter layer can be made smaller than heretofore. Therefore, this bipolar transistor can improve a maximum oscillation frequency, without lowering the current cutoff frequency and current gain.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bipolar transistor used for mobile communication equipment and the like.
The present invention relates to a technique for improving the high frequency characteristics.

[0002]

2. Description of the Related Art In recent years, with the advancement of an information-oriented society, the aim of practical use of multimedia and information superhighways has been rapidly increasing the frequency at which many lines and channels can be secured. Is being actively conducted in many companies and research institutions. Bipolar transistors are also used as such high-frequency devices, and among them, heterobipolar transistors (He
tero Bipolar Transistor, hereinafter referred to as "HBT". ) Is known as having a high maximum oscillating frequency fmax and excellent high-frequency characteristics.

FIG. 6 is a schematic diagram for explaining the structure of a conventional HBT. FIG. 6A is a plan view of the HBT, and FIG.
(B) shows a sectional view. As shown in both figures, the HBT is
The semiconductor device includes a semi-insulating substrate 11, a collector contact layer 12, a collector layer 13, a base layer 14, an emitter layer 15, an emitter contact layer 16, an emitter electrode layer 18, a collector electrode layer 19, a base electrode layer 20, and the like.

A semi-insulating substrate 11 made of GaAs or the like
A collector contact layer 1 made of n ⁺ -GaAs
2 is formed on the entire surface, and a collector layer 13 made of n-GaAs is laminated thereon. The collector layer 13 is separated from the collector layers 13a and 13b by two grooves 13c reaching the collector contact layer 12, and a collector electrode layer 19 made of AuGe / Au is linearly formed on the surface of the collector contact layer 12 in the groove 13c. It is arranged in.

A base layer 14 made of p ⁺ -GaAs is laminated on the collector layer 13b, and a linear emitter layer 15 (n-InGaP) and an emitter contact layer 16 (n -GaAs / n ⁺ -InGaAs) and an emitter electrode layer 18 (WSi). A base electrode layer 20 made of Ti / Pt / Au is linearly arranged on the base layer 14.

In an HBT having such a configuration,
Is the material constituting the base layer 14 and the emitter layer 15.
Each p⁺-GaAs and n-InGaP
It has a so-called hetero junction. This emitter layer 15
The n-InGaP of the base layer 14 ⁺Larger van than -GaAs
With a band gap, so-called band offset effect
Of the base layer 14 to the emitter layer 15 depending on the result.
And the hole density of the base layer 14 is high.
Round.

Therefore, the HBT has a very high frequency characteristic because it can lower the sheet resistance of the base layer 14 and increase the maximum oscillating frequency fmax.

[0008]

However, in recent years, higher frequency devices are generally required to be used in the field of mobile communication equipment and the like, and further higher frequency characteristics are required for bipolar transistors. ing. Further, in the case of a bipolar transistor, if the overall size is changed to improve the high-frequency characteristics, the high-frequency characteristics may fluctuate greatly, and there is a demand to maintain the current size as much as possible.

In view of the above problems, an object of the present invention is to provide a bipolar transistor having excellent high frequency characteristics while maintaining the current size, and a method of manufacturing the same.

[0010]

In order to solve the above-mentioned problems, a bipolar transistor according to the present invention comprises a collector layer formed on a substrate, a base layer formed on the collector layer, and a base layer formed on the collector layer. And a base electrode layer formed on the base layer and at a peripheral portion of the trench portion, and formed on the base layer and at a peripheral portion of the base electrode layer. And an emitter layer.

By providing the trench portion in the base layer, the parasitic capacitance between the base layer and the collector layer can be reduced by the amount of the trench portion without changing the size of the entire transistor. The maximum oscillating frequency can be improved without reducing the cutoff frequency and the current gain. Note that the term "trench portion formed in the base layer" refers to a structure having a trench-shaped concave portion such as a trench or a hole.

In this case, the trench portion only needs to cross the base layer in the thickness direction, and the bottom portion is formed so as to reach the collector layer, or is formed so as to cross the collector layer in the thickness direction. Preferably. In the bipolar transistor according to the present invention, a collector electrode layer is provided on the collector layer via a collector contact layer, and an emitter electrode layer is provided on the emitter layer via an emitter contact layer. It has such a configuration.

Specifically, the base electrode layer, the emitter electrode layer, and the collector electrode layer are linearly arranged, or are formed in a ring shape or a C-shape in which the start and end are close to each other. It can be. In addition, if the semiconductor material forming the emitter layer is a hetero-bipolar transistor having a larger bandgap than the semiconductor material forming the base layer, the high-frequency characteristics are further improved.

[0014]

[First Embodiment]

(1) Configuration of HBT FIG. 1 is a schematic diagram of an HBT according to the first embodiment of the present invention, FIG. 1 (a) is a plan view, and FIG. 1 (b) is a cross-sectional view. The figure shows an example of the dimensions of each electrode layer and the like.

As shown in both figures, this HBT is composed of a semi-insulating substrate 110, a collector contact layer 120, a collector layer 130, a base layer 140, an emitter layer 150, an emitter contact layer 160, an emitter electrode layer 180, and a collector electrode layer. 190, a base electrode layer 200, and the like. Semi-insulating substrate 110 made of GaAs
A collector contact layer 1 made of n ⁺ -GaAs
20 is formed on one surface, and a collector layer 130 made of n-GaAs is laminated thereon.

The collector layer 130 is formed by two grooves 131 reaching the collector contact layer 120. The collector layer 130a at both ends of the substrate and the collector layer 130b at the center of the substrate.
And are separated into On the surface of the collector contact layer 120 in each of the grooves 131, a collector electrode layer 190 (width 10 × length 30 μm) made of AuGe / Au is linearly arranged.

On the outermost surface of the collector layer 130b, p ⁺ -G
A base layer 140 (width 4 × length 30 μm) made of aAs is laminated, and a line-shaped emitter layer 150 (n-InGaP), an emitter contact layer 1
60 (n-GaAs / n ⁺ -InGaAs, width 3 × length 30 μm) and an emitter electrode layer 180 (WSi) are sequentially stacked. Here, the collector layer 130b and the base layer 1
40, a trench 132 (width 3 × length 30 μ) extending transversely to the thickness direction and extending in the short side direction of the substrate 110.
m) is formed. This trench groove 132 only needs to cross at least the base layer 140 in the thickness direction, and the depth is such that the base metal 201 coated on the bottom of the trench groove 132 does not contact the base layer 140. Is preferred.

The base electrode layer 20 made of Ti / Pt / Au is formed at the edge of the trench 132 in the base layer 140.
0s are arranged linearly. (2) Effect of Providing Trench Groove 132 As described above, the HBT according to the present invention has the base layer 14
0 has a trench groove 132 crossing the thickness direction. The effect of having the trench 132 on the high-frequency characteristics of the HBT will be described below.

As an index indicating the performance of the HBT, a maximum oscillating frequency fmax, a current cutoff frequency ft, and a current gain β are generally known. Each of these figures of merit is expressed by the following equation.

[0020]

(Equation 1)

[0021]

(Equation 2)

[0022]

(Equation 3)

Where Rb is the base resistance and Cbc is the base resistance.
The collector-to-collector capacitance, τb, τc, represent the base of the carrier and the collector transit time, Wb represents the thickness of the base layer, and Lb represents the diffusion length in the base layer. From the above equation, in order to improve the high-frequency characteristics of the HBT, that is, the maximum oscillating frequency fmax, the base resistance Rb and the base-collector capacitance
It can be seen that it is necessary to reduce Cbc. The base resistance Rb can be reduced by increasing the thickness of the base layer.
As a result, the current cutoff frequency ft and the current gain β decrease, so that it is necessary to reduce the base-collector capacitance Cbc in order to increase the frequency of the HBT.

Here, the base-collector capacitance cbc per unit area and the base-collector capacitance Cbc are expressed by the following equations, respectively, assuming that the dopant concentration of the base layer is sufficiently higher than the dopant concentration of the collector layer. You.

[0025]

(Equation 4)

[0026]

(Equation 5)

Here, εs is a dielectric constant, W is a depletion layer thickness, q is a unit charge, Nd is a collector dopant concentration, Vbi is a built-in voltage, Vcb is a collector-emitter applied voltage, Sb
Indicates the total area of the base layer. The base layer total area Sb indicates the total area where the base layer and the contact layer are in contact. As can be seen from the equation and the formula, in order to reduce the base-collector capacitance Cbc, it is necessary to reduce the collector dopant concentration Nd or the total area Sb of the base layer. However, the collector dopant concentration Nd cannot be reduced too much in order to keep the maximum value of the collector current high.

In recent HBT configurations, if the size of the HBT is changed in order to improve the high-frequency characteristics, the high-frequency characteristics may fluctuate greatly, and the emitter width is changed within the limited size. It is difficult to consider that, and given that the emitter width is constant,
The base resistance Rb is almost inversely proportional to the emitter length, that is, the total area Se of the emitter layer (the total area where the emitter layer and the emitter collector layer are in contact).

That is, the total area Se of the emitter layer and the base resistance
Rb becomes an inversely proportional relationship, and the relationship with the following formula is derived from the relationship with the formula. CbcRb∝Sb / Se… From this relationship, the base layer / emitter layer total area ratio
The smaller the Sb / Se, the higher the maximum oscillating frequency f
It can be said that it has a maximum and has excellent high frequency performance.

From these, the conventional HBT and the first HBT
Base-emitter area ratio Sb of the HBT according to the embodiment of FIG.
Consider / Se. (1) Conventional HBT Emitter layer total area Se: The area of the emitter layer 15 in FIG. 6 indicates the total contact area between the emitter layer 15 and the emitter contact layer 16.

Therefore, Se = width (11−8) / 2 × length 3
0 × number 2 = 90 μm ² . Base layer total area Sb: The total area of the base layer 14 in FIG. 6 indicates the total contact area between the base layer 14 and the collector contact layer 13. Therefore, Sb = width 11 × length 30 = 33
0 μm ² .

Therefore, the total area ratio Sb / Se of the base layer / emitter layer is 3.666. (2) In the case of the HBT according to the first embodiment Emitter layer total area Se: emitter layer 150 in FIG.
Indicates the total contact area between the emitter layer 150 and the emitter contact layer 160. Therefore, Se = width (11−
8) / 2 × length 30 × number 2 = 90 μm ²

Base layer total area Sb: The total area of the base layer 140 in FIG. 1 indicates the total contact area between the base layer 140 and the collector contact layer 130. Therefore, Sb = width (11-3) / 2 × length 30 × number 2 = 240 μm ² . Therefore, the total area ratio Sb / S
e becomes 2.666.

From these results, it can be seen that the total area ratio Sb / Se of the base layer / emitter layer is reduced from 3.666 of the related art to 2.666, which is about 28% smaller than that of the related art. This is because the HBT according to the present invention has the base layer 140
Is considered to be because the base layer total area Sb is reduced by having the structure having the trench groove 132 crossing in the thickness direction. As a result, the base layer / collector interlayer capacitance Cbc as a parasitic capacitance can be reduced without changing the size of the entire HBT, and the maximum oscillating frequency fmax of the HBT is considered to be improved accordingly.

As described above, the provision of the trench 132 crossing the base layer 140 in the thickness direction without changing the size of the HBT allows the current cutoff frequency f
Since the maximum oscillating frequency fmax of the HBT can be improved without lowering the t and the current gain β, an HBT excellent in high-frequency characteristics can be realized. (3) Manufacturing Method of HBT Next, the manufacturing method of the HBT will be described with reference to FIGS.

FIGS. 2 (a) to 2 (d), 3 (a) to 3 (e)
FIG. 4 is a cross-sectional view in each manufacturing step of the HBT. First,
On a semi-insulating GaAs substrate 110, a collector contact layer 120 made of n ⁺ -GaAs, a collector layer 130 made of n-GaAs, a base layer 140 made of p ⁺ -GaAs, n-InG
An emitter layer 150 made of aP and an emitter contact layer 160 made of n-GaAs / n ⁺ -InGaAs are epitaxially grown. Then, as shown in FIG. 2A, a film made of WSi, which is a refractory metal film, is formed on the emitter contact layer 160 by using a sputtering method, and an emitter electrode layer 180 is formed.

After a resist is patterned on the emitter electrode layer 180, reactive dry etching is performed to form the emitter electrode layer 1 as shown in FIG.
Etching is performed so that 80 has a predetermined rectangular shape in plan view. Using this emitter electrode layer 180 as a mask, a mixed solution of sulfuric acid, hydrogen peroxide solution, and water is used.
After the emitter contact layer 160 composed of n-GaAs / n ⁺ -InGaAs is etched, a mixed solution of hydrochloric acid and water is used.
By etching the emitter layer 150 made of n-InGaP, a shape as shown in FIG. 2C is formed.

Subsequently, the base layer 14 made of p ⁺ -GaAs is formed by using a mixed solution of sulfuric acid, hydrogen peroxide and water.
0 and collector layer 130 composed of n-GaAs
Is etched halfway to form a shape as shown in FIG. Using the rectangular opening resist pattern as a mask, the emitter electrode layer 180 is formed into a rectangular shape by reactive dry etching. Using the emitter electrode layer 180 as a mask, the emitter contact layer 160 composed of n-GaAs / n ⁺ -InGaAs is etched using a mixture of sulfuric acid, hydrogen peroxide and water, and then mixed with hydrochloric acid and water. By etching the emitter layer 150 made of n-InGaP using a liquid, a shape as shown in FIG. 3A is formed.

Next, in order to form a groove 131, a resist pattern is formed on the collector layer 130, and then a collector layer 130 composed of n-GaAs is formed using a mixed solution of sulfuric acid, hydrogen peroxide and water. Etch. The collector contact layer 120 at the bottom of the groove 131 thus formed is formed.
On the surface, a collector electrode layer 190 composed of AuGe / Au as shown in FIG. 3B is formed by a lift-off method. Thereafter, the entire substrate is heat-treated at about 450 ° C., so that the collector electrode layer 190 exhibits good ohmic characteristics.

Next, in order to form a trench 132 crossing the base layer 140 in the thickness direction, a resist pattern is formed, and the emitter layer 150 made of n-InGaP is etched using a mixed solution of hydrochloric acid and water. And the base layer 140
Is partially exposed. Subsequently, as shown in FIG. 3 (c), the entirety of the base layer 140 composed of p ⁺ -GaAs and the collector layer composed of n-GaAs using a mixed solution of sulfuric acid, hydrogen peroxide and water. Etching is performed halfway through 130 or halfway through collector contact layer 120 made of n-GaAs. Thus, a trench 132 that crosses the base layer 140 in the thickness direction can be formed.

Thereafter, the resist above the trench 132 is side-etched, and the etched resist is used as a mask to form a Ti / Ti as shown in FIG.
A base electrode layer 200 composed of Pt / Au is deposited.
Finally, the resist is removed using hydrofluoric acid to complete an HBT having a trench 132 as shown in FIG. At this time, as shown in FIG.
At the bottom of the trench 132, the base electrode layer 200
The Ti / Pt / Au layer 201 may be left. However, if the trench 132 is formed sufficiently deep in the middle of the collector layer 130 or the collector contact layer 120, a short circuit with the base layer 140 may occur. Since it disappears, the characteristics of the HBT are not affected at all.

[Second Embodiment] In the first embodiment, the emitter electrode layer 180, the collector electrode layer 190, and the base electrode layer 200 are formed linearly. However, they are formed in a ring shape. In this case as well, the high-frequency characteristics of the HBT can be improved as in the first embodiment.

FIG. 4 is a sectional view schematically showing an HBT according to a second embodiment of the present invention and a partial plan view showing the shape of each electrode layer. The HBT according to the second embodiment is different from the HBT according to the first embodiment.
The only difference is that the shape of each emitter, collector, base layer, electrode layer, etc. is annular.
Mainly, the shape will be described. The drawing shows an example of the dimensions of the electrode layer and the like.

As shown in the figure, this HBT is composed of a semi-insulating substrate 210, a collector contact layer 220, a collector layer 230, a base layer 240, an emitter layer 250, an emitter contact layer 260, an emitter electrode layer 280, and a collector electrode layer. 290, the base electrode layer 300, and the like. Here, the semi-insulating substrate 210 is circular,
A collector contact layer 220 is formed on the entire surface.

The collector layer 230, the base layer 240, the emitter layer 250, the emitter contact layer 260, the emitter electrode layer 280, the collector electrode layer 290, and the base electrode layer 300 are made of the same material as in the first embodiment. However, they are not formed in a straight line but in an annular shape in plan view. At substantially the center of the semi-insulating substrate 210, a trench hole 232 is formed up to the collector layer 230 crossing the base layer 240 in the thickness direction. By this trench hole 232, similarly to the first embodiment, the total area ratio Sb / Se of the base layer / emitter layer can be reduced as compared with the case where no trench hole is provided. Can be improved.

Actually, the total area ratio of the base layer / emitter layer Sb / Se
The following is a comparison of the values. Emitter layer total area Se: emitter layer 250 in FIG.
Area of the emitter layer 250 and the emitter contact layer 2
Shows the total area of contact with 60. Therefore, Se = π × ｛(11
/ 2) ² − (8/2) ² ｝ = 44.768 μm ² .

Base layer total area Sb: The total area of the base layer 240 in FIG. 4 indicates the total contact area between the base layer 240 and the collector contact layer 230. Therefore, Sb = π ×
{(11/2) ^2- (3/2) ² } = 87.645 μm
It becomes ² . Therefore, base layer / emitter layer total area ratio S
b / Se is 1.965. On the other hand, when the trench hole is not formed, the total area Sb of the base layer is as follows.

Sb = π × (11/2) ² = 95.0331
μm ² . Since the total area of the emitter layer is the same as that of the second embodiment, the total area ratio Sb / Se of the base layer and the emitter layer is 2.123. Accordingly, the total area ratio Sb / Se of the base layer and the emitter layer is reduced by about 8% due to the trench holes 232 crossing the base layer 240 in the thickness direction, and it is considered that the maximum oscillating frequency fmax is improved accordingly.

As described above, the provision of the trench hole 232 crossing the base layer 240 in the thickness direction improves the HBT maximum oscillating frequency fmax without lowering the current cutoff frequency ft and the current gain β. Therefore, an HBT having excellent high frequency characteristics can be realized. In the second embodiment, each of the electrode layers 280, 290, 300 and the like is formed in an annular shape in plan view, but may be an elliptical shape, a polygonal shape, or the like. Due to the partial loss, the linear electrode layer may have a C-shape in plan view in which the start and end of the linear electrode layer are close to each other. In the case of such a C-shape, it becomes possible to arrange wiring in the missing portion.

(Modifications of First and Second Embodiments) In the first and second embodiments, the bottom of the trench 132 and the bottom of the trench 232 are located in the middle of the collector layers 130 and 230. 5, the trench 133 may cross the collector layer 130c in the thickness direction, and the bottom of the trench 133 may be formed in the collector contact layer 121. Even if the trench 133 is formed in this manner, there is no significant difference from the HBT in the first and second embodiments, and the maximum oscillating frequency fmax can be improved.

In each of the above embodiments, the dimensions of each electrode layer are shown as shown in FIGS. 1 and 4. However, the present invention is not limited to this, and the present invention can be implemented with any desired dimensions. In each of the above embodiments,
Although the HBT has been described as an example, the present invention can be implemented in a normal bipolar transistor without a heterojunction.

[0052]

As described above, according to the bipolar transistor of the present invention, the collector layer formed on the substrate, the base layer formed on the collector layer, and the base layer formed on the base layer are formed. A trench portion, a base electrode layer formed on the base layer and around the trench portion, and an emitter layer formed on the base layer and around the base electrode layer. Therefore, the total area ratio Sb / Se of the base layer / emitter layer becomes smaller than that of the conventional one by the amount of the trench portion without changing the size of the entire transistor, and the current cutoff frequency ft and the current gain β are reduced. The maximum oscillating frequency fmax can be improved without lowering.

The method of manufacturing a bipolar transistor according to the present invention includes a first step of sequentially laminating a collector layer, a base layer, and an emitter layer on a substrate, and removing the base layer by removing a part of the emitter layer. Expose the second
A third step of forming a trench portion crossing the base layer in the thickness direction by etching the base layer exposed in the second step. Accordingly, a bipolar transistor having excellent high-frequency characteristics can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an HBT according to a first embodiment of the present invention, where (a) is a plan view and (b) is a cross-sectional view.

FIG. 2 is a process chart showing a method for manufacturing the HBT.

FIG. 3 is a process chart showing a method for manufacturing the HBT.

FIG. 4 is a schematic configuration diagram of an HBT according to a second embodiment of the present invention, where (a) is a plan view and (b) is a cross-sectional view.

FIG. 5 is a cross-sectional view showing a modification of the first and second embodiments of the present invention.

FIG. 6 is a schematic sectional view showing a configuration of a conventional HBT.

[Explanation of symbols]

 110, 210 Semi-insulating GaAs substrate 120, 220 Collector contact layer 130, 230 Collector layer 131 Groove 132 Trench groove 140, 240 Base layer 150, 250 Emitter layer 160, 260 Emitter contact layer 180, 280 Emitter electrode layer 190, 290 Collector Electrode layer 200, 300 Base electrode layer 232 Trench hole

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takeshi Tanaka 1-1, Komachi, Takatsuki-shi, Osaka Matsushita Electronics Co., Ltd. F-term (reference) 5F003 BB09 BC02 BF06 BH07 BH99 BM02 BM03

Claims (9)

[Claims] A collector layer formed on the substrate; a base layer formed on the collector layer; a trench formed on the base layer; and a trench formed on the base layer. A bipolar transistor, comprising: a base electrode layer formed in a peripheral portion; and an emitter layer formed on the base layer and in a peripheral portion of the base electrode layer. 2. The bipolar transistor according to claim 1, wherein the trench section crosses the base layer in a thickness direction. 3. The bipolar transistor according to claim 2, wherein the trench portion is formed so as to cross the base layer in a thickness direction and a bottom portion thereof reaches the collector layer. 4. The bipolar transistor according to claim 1, wherein said trench portion crosses said base layer and said collector layer in a thickness direction. 5. The collector layer is provided with a collector electrode layer via a collector contact layer, and the emitter layer is provided with an emitter electrode layer via an emitter contact layer. Claims 1-4
The bipolar transistor according to any one of the above. 6. The bipolar transistor according to claim 5, wherein the base electrode layer, the emitter electrode layer, and the collector electrode layer are arranged linearly. 7. The bipolar transistor according to claim 5, wherein the base electrode layer, the emitter electrode layer, and the collector electrode layer are arranged in a ring shape or a C-shape in which a start end and an end are close to each other. 8. The bipolar transistor according to claim 1, wherein a semiconductor material forming the emitter layer has a larger bandgap than a semiconductor material forming the base layer. 9. A bipolar process comprising: a first step of sequentially stacking a collector layer, a base layer, and an emitter layer on a substrate; and a second step of exposing the base layer by removing a part of the emitter layer. A method of manufacturing a transistor, comprising a third step of etching a base layer exposed in the second step to form a trench portion crossing the base layer in a thickness direction. A method for manufacturing a bipolar transistor.