JPS62160761A - Semiconductor device - Google Patents

Abstract

PURPOSE:To reduce parasitic capacitance and to reduce base resistance, by depositing an SiC film, whose band gap becomes large with respect to silicon, on a region, which is to become an emitter, coating the surface of the film with an SiO2 film, and forming a polysilicon film, which is contacted with a base region formed on a P<+> type based substrate, as a base lead-out electrode. CONSTITUTION:An SiC film 16, which is to become an emitter, is formed in the state where the entire part is contacted with the upper part of a base region. Therefore, the distance between a base and the emitter is reduced to a large extent. A P<+> type doped polysilicon film 18, which is no become a base-electrode lead-out part, covers the SiC film 16 through an SiO2 film 17, which insulates the SiC film 16. The film 18 is contacted with the entire surface of the base region 15. The contact area between the polysilicon film 18 and the base region 15 is an area obtained by subtracting the areas of the SiC film 16 and the SiO2 film 17 thereon from the area of the base region. Since the SiC film 16 is formed in a small size, the base resistance is suppressed to a small value. The parasitic capacitance between a collector and a base can be suppressed to a small value. Thus the frequency characteristics of a transistor can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] This is a semiconductor device in which a base lead electrode extends over at least a portion of a wide gap emitter with an insulator interposed therebetween.

[Industrial application field]

The present invention relates to a semiconductor device, and more specifically, to a heterojunction bipolar transistor having a wide gap emitter with a small collector-base capacitance (Ccβ) and excellent high frequency characteristics.

[Conventional technology]

Conventional bipolar transistors have a homo-junction on a silicon substrate.
Made by forming 'N. Figure 2 shows the band structure of such a junction, with an N-type bandgap E
Since g is made of the same material, it is equal to the P-type band gap Eg. Therefore, the current amplification factor (t+p&) is gained by utilizing the fact that the emitter concentration N4 is larger than the base concentration P- in the difference in impurity concentration.

Therefore, a bipolar transistor with a heterojunction at the emitter/base was proposed. The band structure of the heterojunction is shown in Figure 3, where the emitter has a wide gap, i.e. Eg1'> E
When we bring a material such that g2, electrons flow across the barrier qVn as shown by the arrow ■, and holes flow as shown by the arrow ■, but a barrier of size qvp exists against the hole. . This barrier QVI
) is larger than qVn, so it becomes difficult for the Behole current to flow compared to the electron current. In other words, the emitter efficiency increases. In this way, Ip can be reduced and hFG can be increased. In other words, even if the base concentration is higher than the emitter concentration in terms of concentration difference, it is difficult for hole current to flow because the bandgap for holes is large (
Therefore, there is no problem even if the base concentration is high. Therefore, in a heterojunction, the base concentration can be increased, unlike in a homojunction, where the base concentration must be kept low in order to obtain hfε.

Here, when the base concentration is lowered, the base resistance increases, and when the concentration is lowered, the depletion layer spreads more and bunch-through is more likely to occur, so there is a limit to reducing the base width (or narrowing it). be.

On the other hand, when a heterojunction is used, the base concentration can be increased, so the base resistance is reduced, and the spread of the depletion layer is small, making it resistant to bunch-through. As a result, even if the base width is narrowed, it can be sufficiently accommodated.

This means that a transistor with a small base resistance and a narrow base width can be obtained, and the frequency characteristics (1 d) and delay characteristics (tpd) are improved.

To summarize the above, in the emitter and base junction,
If a bipolar transistor is made of a material with a large emitter bandgap, a transistor with low base resistance, high cutoff frequency, and high speed can be obtained.

Conventionally, GaA has been used as a wide gap emitter material.
GaAlAs has been used as a compound semiconductor called s, but no suitable material with a large band gap compared to silicon (Si) has been found. However, recently S
Silicon carbide (SiC) or 5IPO5 (Semi-I
nsulating Polycrystalline
A method has been developed to grow 5ili-con) on Si.

[Problem that the invention seeks to solve]

FIG. 4 shows a cross-sectional view of a conventional example using SiC, in which 31 is a silicon substrate on which an N+ type buried layer and an N-type epitaxial layer (not shown) are formed, 32 is a base region, and 33 is a 5i02 The film 34 is a SiC film constituting a wide-gap emitter, and in the overcast structure, a wide-gap material is deposited in a planar manner on a base region to constitute the emitter.

Although such a transistor has the advantages of the heterojunction described above, the area of the base region is large;
Parasitic capacitance occurs in the area surrounded by arrows in the figure, and the collector
The base capacitance fft (CaI2) is increased to reduce the switching speed of the transistor, and the base resistance (R
There is a problem that bb') increases as the base area increases.

The present invention was created in view of these points.
It is an object of the present invention to provide a method for manufacturing a bipolar transistor having a wide gap emitter made of C, in which conventional parasitic capacitance is reduced and base resistance is kept low.

[Means for solving problems]

FIG. 1(a) and crest) are a cross-sectional view and a plan view of an embodiment of the present invention, in which 11 is a P-type silicon substrate, 12 is an N+ type buried layer, 13 is an N-type epitaxial layer, 14 is a base region, 15 is a field oxide film, 16 is a SiC film, 17 is 5i021R', 18 is a P+ type doped polysilicon film, 19 is a 5i02 film, 20 is a base electrode window, and 21 is an emitter electrode window. .

In the semiconductor device of the present invention, a SiC film 15 having a larger band gap than silicon (Si) is deposited on a region that will become an emitter, and its surface is covered with a SiO+ film 16.
A polysilicon film 17 doped with P1 type and in contact with a base region 14 formed on the substrate is formed thereon as a base extraction electrode.

[Effect]

The above-described heterojunction bipolar transistor has the above-described advantages, and furthermore, the base region 14
The base lead-out electrode is formed to cover the 5iCIA16 constituting the emitter, so the distance between the emitter and the base can be reduced, and the base lead-out part is formed by covering the SiC film and SiO2 film due to the expansion of the base region. Since the base region is in contact with the other parts, the base region can also be significantly reduced, and as a result, CC[l can be reduced, frequency characteristics can be improved, and base resistance can be reduced.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

Referring to the cross-sectional view and plan view of FIG. As is clear from the comparison with , the distance between the base and emitter has been significantly reduced.

On the other hand, the P+ type doped polysilicon film 18 that serves as the base electrode lead-out portion is a 5i0 polysilicon film 18 that insulates the SiC film 16.
The base region 1 covers the SiC film 16 through the two films 17.
It is in contact with the entire surface of 5. The contact area between the polysilicon film 18 and the base region 15 is the area of the base region minus the spread of the SiC film 16 and the 5iOz film 17 thereon. Since it is formed smaller than the conventional example, the base resistance can be kept small. Further, the base region may be formed sufficiently smaller than the conventional example, since the base electrode extension portion made of the polysilicon film 18 contacts the base region as described above. As a result, it becomes possible to suppress the collector-base capacitance ccn to a small value, and the frequency characteristics of the transistor are improved.

In order to improve the contact between the base and the polysilicon film 18, which will become the base electrode lead-out portion, and to compensate for the base contact, boron ions may be implanted into the substrate surface.

In the above example, a 5i02 film was used to insulate the top and side portions of the SiC film 16 serving as the emitter, but a silicon nitride film may be grown instead.

In order to reduce the resistance, P" type doped polysilicon is coated on the base electrode lead-out portion, but other metals or silicide may be used instead.

Next, a method for manufacturing an embodiment of the present invention will be described.

An N+ type buried layer 1 is formed on a P type silicon substrate 11 using a normal technique.
2. Grow an epitaxial layer 13, form a field oxide film 14 for device isolation (it may be a U-groove), and implant boron ions, for example, to form a base region 15.
form.

Next, the n-type doped SiC (or 5IPO3'
), and then a SiO+ film is formed on the entire surface, and it is buttered as shown in Figure 1(b) to form a SiO+ film.
A SiC film 16 whose surface is covered with O2 is prepared.

Next, 5iO2 (or silicon nitride film) is applied to the entire surface again.
When the SiC film 16 is grown and reactive ion etching is performed until the SiO2 on the substrate surface is removed, only the upper and side parts of the SiC film 16 become SiO2, as shown in FIG.
The base region 15 is covered with two films 17, and the surface of the base region 15 is exposed.

Next, P+ type doped polysilicon is grown over the entire surface and patterned as shown in FIG. 1(b).

Finally, a SiO2 film 19 is formed as a protective film, a base electrode window 20 and an emitter electrode window 21 are opened thereon, and then a normal wiring process is performed. SiC film 16 is 5iOz film 1
The emitter electrode window 21 is formed at the position shown in FIG.

〔Effect of the invention〕

As described above, according to the present invention, in a heterojunction bipolar transistor, the emitter
The carriers between bases can be significantly reduced, the base area can be reduced, parasitic capacitance and base resistance can be reduced, and an element with excellent high frequency characteristics can be provided.

[Brief explanation of drawings]

FIGS. 1(a) and (bl are a sectional view and a plan view of an embodiment of the present invention,
FIGS. 2 and 3 are diagrams showing the band structures of a homojunction and a heterojunction, respectively, and FIG. 4 is a sectional view of a conventional example. In FIG. 1, 11 is a silicon substrate, 12 is a buried layer, 13 is an epitaxial layer, 14 is a base region, 15 is a field oxide film, 16 is a SiC film, 17 is a SiO2 film, 18 is a polysilicon film, and 19 is a polysilicon film. 5i02 film, 20 is a base electrode window, and 21 is an emitter electrode window. Figure 2 Figure 3 Wandering column Ch view Figure 4

Claims (1)

[Claims] A heterojunction is formed by providing a material film (16) with a large bandgap relative to silicon on a base region (15) of the same conductivity type of a semiconductor substrate (11) of one conductivity type.
In the bipolar transistor, a base electrode extension portion (18) is provided on the film (16) via the insulating film (17).
) extends in contact with a base region (15).