JPH11176838A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device which has a new heterojunction structure and is particularly useful as an HBT. SOLUTION: In a semiconductor device having a heterojunction structure A, where to the upper surface and the lower surface of an n-type or a p-type semiconductor layer, semiconductor layers having conductivity types opposite to that of the semiconductor layer are bonded, an n-type semiconductor layer 3 of the heterojunction structure A is composed of GaN-based compound semiconductor, and p-type semiconductor layers 2, 4 consists of diamond crystals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor device,
More specifically, the present invention relates to a semiconductor device which can operate at a high temperature and has an excellent high-output operation and is particularly useful as a high-performance heterobipolar transistor (HBT).

[0002]

2. Description of the Related Art An HBT is a transistor in which an emitter serving as a carrier supply source is formed of a semiconductor having a wide band gap. The basic structure of the HBT is such that the energy band at the junction between the emitter and the base is continuously inclined. There is a graded junction type and a step junction type in which the energy band changes discontinuously.
This HBT is a transistor that can obtain a very high current gain and can operate at high speed as compared with a homojunction transistor.

Conventionally, this HBT is usually manufactured using a GaAs compound semiconductor. An outline of an example of the manufacturing method will be described below. First, an n-type GaAs layer functioning as a collector, a p-type AlGaAs layer functioning as a base, and an n-type GaAs layer functioning as an emitter are formed on a semi-insulating GaAs substrate, for example, by MOCVD or MBE. Are laminated in this order to form a laminated structure. When the base is formed, a p-type impurity such as Be may be ion-implanted.

Accordingly, the formed laminated structure has an npn heterojunction structure in which an n-type layer is joined to the upper and lower surfaces of a middle p-type layer. Then, the surface of the laminated structure (on the emitter) is coated with SiO 2 by, for example, a plasma CVD method.
After forming an insulating film consisting of ₂ or SiNx, apply ordinary photolithography and etching to this,
The collector is loaded with a collector electrode made of, for example, Ti / Al / Ti, and the base and the emitter are made of, for example, Au.
An HBT is manufactured by loading a base electrode and an emitter electrode made of / Zn / Au, respectively.

[0005]

However, GaN and A
GaN-based compound semiconductors such as 1GaN, combined with their wide band gap, have been widely used in GaAs.
Since high-temperature operation is possible and high-power operation is superior to s-based compound semiconductors, these G
Attempts have been made to manufacture HBTs using aN-based compound semiconductors.

However, in the case of a GaN-based compound semiconductor, it is relatively easy to dope an n-type impurity to form a high-quality n-type layer, but dope a p-type impurity to reduce the carrier concentration to 1 ×. There is a problem that it is very difficult to form a low-resistance P-type layer by setting it to 10 ¹⁷ cm ⁻¹ or more. Therefore, when an HBT is manufactured using a GaN-based compound semiconductor, it is difficult to form a low-resistance p-type layer in an npn-junction structure or a pnp-junction structure with a GaN-based compound semiconductor. This means that HBT cannot be obtained.

An object of the present invention is to provide a semiconductor device having a novel heterojunction structure capable of solving the above-mentioned problems, particularly a semiconductor device useful as a high-performance HBT and a method of manufacturing the same.

[0008]

Means for Solving the Problems The present inventors have paid attention to the fact that the difficulty in manufacturing a high-performance HBT using a GaN-based compound semiconductor is derived from the fact that it is difficult to form a p-type layer in a heterojunction structure. did. If the p-type layer is formed of a semiconductor material having a lattice constant close to the lattice constant of an n-type GaN-based compound semiconductor located above and below it and having a band gap as wide as GaN, Have the idea that a heterojunction structure having the same performance as that of the heterojunction structure in which the layer of the GaN-based semiconductor compound is formed can be formed. Based on this idea, the inventor has
A study was made on a semiconductor material applicable to the p-type layer.

Attention was paid to diamond crystals, and their characteristic points were arranged as follows. (1) A perfect diamond crystal has a lattice constant of 3.5
67 °, which is close to the lattice constant of the hexagonal GaN crystal in the a-axis direction (3.189 °). (2) When growing a diamond crystal, it is difficult to grow an n-type one, but a p-type one can be grown relatively easily. Therefore, a p-type layer of a diamond crystal is formed by an epitaxial growth method. It is possible to do.

(3) The band gap of the p-type diamond crystal is 5.47 eV, and it is a semiconductor having a wide band gap like GaN. The electron mobility of the n-type diamond crystal is about 1800 cm ² / V · s, which is almost the same as that of the n-type GaN crystal.
Mobility in a diamond-type diamond crystal is 1600 cm ² /
V · s, indicating the highest electron mobility among p-type semiconductors.

(4) The diamond crystal has excellent heat resistance,
Its thermal conductivity shows a value of about 20.9 W / cm · deg, and this value is the largest among p-type semiconductors. From the above, we conclude that it is possible to join a p-type diamond crystal layer to an n-type GaN-based compound semiconductor by an epitaxial growth method, and that the obtained heterojunction structure enables high-speed operation and high-temperature operation. Hug,
As a result of further research, the semiconductor device of the present invention and a method for manufacturing the same have been developed.

That is, a semiconductor device according to the present invention is a semiconductor device having a heterojunction structure in which a semiconductor layer of the opposite conductivity type is bonded to an upper surface and a lower surface of an n-type or p-type semiconductor layer. The n-type semiconductor layer having the heterojunction structure is made of a GaN-based compound semiconductor, and the p-type semiconductor layer is made of a diamond crystal. In particular,
A semiconductor device is provided in which a thin film layer made of a C-doped GaN-based compound semiconductor is interposed between the n-type semiconductor layer and the p-type semiconductor layer.

[0013]

FIG. 1 shows an example of a heterojunction structure in a semiconductor device of the present invention used as an HBT. In FIG. 1, the heterojunction structure A has a laminated structure of a p-type diamond crystal layer 2, an n-type GaN layer 3, and a p-type diamond crystal layer 4. That is, the heterojunction structure A is a pnp junction structure in which the upper and lower surfaces of the n-type layer 3 are joined to the p-type layer of the opposite conductivity type to the n-type layer 3, and is entirely formed on the substrate 1. .

In this heterojunction structure A, the p-type diamond crystal layer 2 functions as a collector, and the n-type GaN
The layer 3 functions as a base, and the uppermost p-type diamond crystal layer 4 functions as an emitter. A buffer layer 5 composed of a diamond-like carbon thin film layer is provided between the substrate 1 and the p-type diamond crystal layer 2, and a C-doped Ga layer is provided between the p-type diamond crystal layer 2 and the n-type GaN layer 3.
A buffer layer 6 composed of an N thin film layer is interposed. Further, between the n-type GaN layer 3 and the uppermost p-type diamond crystal layer 4, a C-doped GaN thin film layer 7a formed on the n-type GaN layer 3 side and the p-type diamond crystal layer 4 A buffer layer 7 having a two-layered structure including a diamond-like carbon thin film layer 7b formed on the side is interposed.

Each of these buffer layers is formed by forming a p-type layer, an n-type layer, and a p-type layer on the substrate 1 in order by epitaxial growth described later. And at the same time, it is interposed to ensure good bonding between the lower layer and the upper layer. In addition, the diamond-like carbon mentioned here is a precursor of a diamond crystal, and its crystal structure is substantially a diamond type structure, but its physical and chemical properties are still the same as those of a perfect diamond crystal. Carbon that is not the same.

In the case of the semiconductor device shown in FIG. 1, an Si single crystal substrate is used as the substrate 1. This is because the above-described buffer layer 5 can be easily formed on the Si single crystal substrate, and thus the formation of the p-type diamond crystal layer 2 can be smoothly performed. By the way, FIG.
Is a pnp junction structure, but in the semiconductor device of the present invention, it may be an npn junction structure.

In this case, n-type GaN is
Layer, p-type diamond crystal layer, and n as the top layer
Type GaN layers are sequentially stacked by an epitaxial growth method.
At this time, the substrate 1 may be the lower Si single crystal substrate, or an amorphous GaN substrate may be formed on a sapphire substrate.
After forming a buffer layer such as AlN or AlN, the above-described n-type GaN layer 3 is laminated thereon.
A buffer layer 7 having a two-phase structure including the C-doped GaN thin film layer 7a and the diamond-like carbon thin film layer 7b is formed on the layer 3, and the p-type diamond crystal layer 2 is formed on the buffer layer. Is formed thereon, and the C-doped GaN thin film layer 6 is formed thereon, and then an n-type GaN layer may be formed thereon.

The semiconductor device of the present invention having the pnp heterojunction structure shown in FIG. 1 can be manufactured as follows. Using it as a substrate, an HB
The case of manufacturing T will be described. First, this pnp
The formation of the heterojunction structure is advanced using a gas source molecular beam epitaxial growth apparatus.

This apparatus has a C source nozzle for supplying hydrogen, which is a raw material for growing a diamond crystal layer, and a hydrocarbon such as methane gas into the apparatus.
At the tip of the nozzle, a heating filament made of W for activating a supply gas as a C source is disposed. Further, an N source nozzle for supplying an N source such as dimethylhydrazine or ammonia, and a Knudsen cell containing metal Ga, metal Al and metal In are also provided, and further, metal Si is stored. By providing Knudsen Cell and diborane supply device, respectively,
An n-type dopant source and a p-type dopant source are formed.

A single crystal Si substrate is set in this apparatus, and its surface is first cleaned. Then, the substrate is maintained at a predetermined temperature, a mixed gas of, for example, hydrogen and methane gas is supplied from a C source nozzle, the mixed gas is decomposed by a heating filament, activated, and irradiated on the surface of the substrate, A buffer layer 5 of diamond-like carbon having a desired thickness is formed on the substrate surface.

At this time, if a C monomolecular film is first formed on the surface of the Si single crystal substrate with a thickness of an atomic order, the C monomolecular film is easily bonded to Si constituting the substrate surface. Therefore, the bonding property between the two is improved, and the bonding property between the diamond-like carbon thin film layer formed thereon and the substrate is also improved. Thereafter, while the operation of the C source nozzle is continued, the diborane supply device is operated to supply diborane to the device at a predetermined flow rate, and the B-doped diamond crystal layer 2 (having a desired thickness on the diamond-like carbon buffer layer 5). (p-type layer).

Next, the supply gas from the C source nozzle is converted into a mixed gas of methane gas and N _2, and the mixed gas is decomposed by a heating filament to activate N, and at the same time, a Knudsen cell of metal Ga is formed. Upon operation, a C-doped GaN thin film layer 6 is formed on the p-type diamond crystal layer 2. In this case, in the initial stage of the growth of the C-doped GaN layer, the methane gas concentration of the mixed gas is increased to enhance the bonding property with the underlying p-type diamond crystal layer 2,
It is preferable to lower the methane gas concentration as the growth progresses, so as to enhance the bonding property with the n-type GaN layer formed next thereon.

Next, the operations of the C source nozzle and the diborane supply device are stopped, the N source nozzle and the Knudsen cell of metal Si are operated, and molecular beam epitaxial growth is advanced, and a predetermined thickness is formed on the C-doped GaN layer 6. Si-doped Ga
An N layer (n-type layer) 3 is formed. Next, on this Si-doped GaN layer 3, a C-doped G layer is formed in the same manner as described above.
An aN thin film layer 7a and a diamond-like carbon thin film layer 7b are sequentially laminated to form a buffer layer 7 having a two-phase structure, and B is formed on the diamond-like carbon thin film layer 7b in the same manner as described above. Doped diamond crystal layer 4 (p-type layer)
Is formed to obtain the laminated structure shown in FIG.

Then, for example, an SiO ₂ film is formed on the B-doped diamond crystal layer 4 by, for example, a plasma CVD method, and a known photolithography and etching process is performed thereon, and further, an electrode loading operation is performed. , FIG. 2
As shown in the figure, a collector electrode 8 made of Au is formed on the p-type diamond crystal layer 2 as a collector, a base electrode 9 made of Ti / Au is formed on the n-type GaN layer 3 as a base, and a p-type diamond crystal layer 4 as an emitter. HBTs each having an emitter electrode 10 made of Au are obtained.

[0025]

EXAMPLE The HBT shown in FIG. 2 was manufactured as follows. First, a Si single crystal substrate was set in a gas source molecular beam epitaxial growth apparatus, the substrate temperature was set to 950 ° C.,
Only hydrogen was supplied from the C source nozzle, the hydrogen was decomposed and activated by the heating filament, and the activated hydrogen was irradiated on the surface of the substrate to decompose and remove the oxide on the surface.

The substrate whose surface was cleaned was cooled to a temperature of 850 ° C. The temperature of the heating filament is set to 2500 ° C., and a mixture gas (30 Torr) consisting of 97% by volume of hydrogen and 3% by volume of methane gas is irradiated at a flow rate of 20 sccm from a C source nozzle to decompose and activate the filament. Irradiation. As a result, a thin film layer of diamond-like carbon having a thickness of 2000 mm was formed on the surface of the substrate.

While maintaining the substrate temperature at 850 ° C.,
Here, diborane was supplied at a flow rate of 2 sccm to form a 3000-nm thick B-doped diamond crystal layer on the thin film layer. Then, the supply gas from the C source nozzle was changed to nitrogen 98
The mixture is switched to a mixed gas of volume% and methane gas volume%, metal Ga (5 × 10 ⁻⁷ Torr) is supplied from the Knudsen cell, and molecular beam epitaxial growth is performed at a substrate temperature of 640 ° C., thereby obtaining the B-doped diamond crystal layer. A 200-nm thick C-doped GaN thin film layer was formed thereon.

In the initial stage of the growth of this thin film layer,
Doped C concentration is 1 × 10²⁰cm ^-3Mixed so that
Set the gas composition and as the epitaxial growth progresses
To change the composition of the mixed gas supplied so that the C concentration decreases.
Finally, C concentration is 5 × 10¹⁸cm^-3So that
The formation of the C-doped GaN layer was performed. Then, substrate temperature
Temperature to 850 ° C, C source nozzle, diborane feeder
Is stopped, and metal Ga from each Knudsen cell is removed.
(1 × 10^-6Torr), metal Si (5 × 10^-9Torr)
Ammonia from N source (5 × 10^-FiveMolecule using Torr)
Line epitaxial growth, the C-doped GaN layer
A 5000-nm thick Si-doped GaN layer (n-type layer)
Formed.

The operation of each Knudsen cell and the N source was stopped, and a 50 ° thick C-doped GaN thin film layer and a 50 ° thick diamond-like carbon thin film were deposited on the Si-doped GaN layer in the same manner as described above. The layers were sequentially stacked, and a B-doped diamond crystal layer (p-type layer) having a thickness of 3000 ° was formed thereon in the same manner as described above to obtain the stacked structure shown in FIG.

Then, the HBT shown in FIG. 2 was manufactured by processing the laminated structure according to a conventional method. The current and voltage were measured for this HBT. That is, the saturation characteristics of the collector current when the collector current was changed using the emitter current as a parameter were examined. As a result, when the emitter current was 5 mA, the characteristic that the collector current was saturated at 4 mA from the vicinity where the voltage between the collector and the base became 1 V was obtained. Furthermore current gain characteristic (dI _C / dI _B)
When the emitter current was 5 mA, 10
It was about ² .

Then, the HBT was heated to a temperature of 200 ° C., but there was no change in the current gain characteristics, and it was confirmed that the HBT could be operated at a high temperature. From these results, this HB
T was confirmed to function as a high-performance HBT.
In the above embodiment, dimethylhydrazine and ammonia are used as examples of the N source when the GaN layer is formed. However, plasma nitrogen, radical nitrogen, and the like can be used as the N source. The Ga source is not limited to metallic Ga, but may be an organic metallic Ga such as triethylgallium or trimethylgallium.

Further, although n-type GaN is shown as a base material, the present invention is not limited to this.
For example, S is added to InGaN, InGaAlN, and AlGaN.
Those in which i is doped as an n-type impurity can also be used.

[0033]

As is clear from the above description, the semiconductor device of the present invention has a novel heterojunction structure in which the n-type layer is made of a GaN-based compound semiconductor and the p-type layer is made of diamond crystal. When used as an HBT, the high-speed operation and the high-temperature operation are superior to the conventional mainstream GaAs-based HBT, and its industrial value is extremely large. This semiconductor device can also be applied to a thyristor having a pnpn junction structure and a field effect transistor.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a heterojunction structure in a semiconductor device of the present invention.

FIG. 2 is a cross-sectional view of a hetero bipolar transistor showing one example of the device of the present invention.

[Explanation of symbols]

Reference Signs List 1 substrate (Si single crystal substrate) 2 p-type diamond crystal layer (B-doped diamond crystal layer) 3 n-type GaN layer 4 p-type diamond crystal layer (B-doped diamond crystal layer) 5 diamond-like carbon thin film layer 6 buffer layer ( C-doped GaN layer) 7 Buffer layer 7a C-doped GaN thin film layer 7b Diamond-like carbon thin film layer 8 Collector electrode 9 Base electrode 10 Emitter electrode

Claims (3)

[Claims] 1. A semiconductor device having a heterojunction structure in which an n-type or p-type semiconductor layer has an upper surface and a lower surface joined to a semiconductor layer of the opposite conductivity type to the semiconductor layer. A semiconductor device, wherein the semiconductor layer is made of a GaN-based compound semiconductor, and the p-type semiconductor layer is made of a diamond crystal. 2. The semiconductor device according to claim 1, wherein a thin film layer made of a C-doped GaN-based compound semiconductor is interposed between said n-type semiconductor layer and said p-type semiconductor layer. 3. The n-type semiconductor layer is formed of AlGaN, GaN, InGaN, InGa doped with n-type impurities.
3. The semiconductor device according to claim 1, wherein the semiconductor device is made of AlN.