JPH01196873A - Silicon carbide semiconductor device - Google Patents

Abstract

PURPOSE:To prevent leakage currents even under severe conditions such as a high temperature, large power, etc., by forming a first electrode onto the surface of an silicon carbide semiconductor layer shaped onto one surface of a substrate, a second electrode onto the other surface of the substrate and a third electrode onto the side face of the silicon carbide semiconductor layer. CONSTITUTION:A nickel film formed onto the rear of an silicon substrate 1 is used as a drain electrode 7, and a titanium-aluminum film shaped onto the projecting end face of an silicon carbide growth layer 2 having mesa structure is employed as a source electrode 6. Currents flowing between the source electrode 6 and the drain electrode 7 are controlled by fluctuating voltage applied to gate electrodes 8 and changing the width of depletion layers 9 spreading in the silicon carbide growth layer 2. Accordingly, an silicon carbide semiconductor device, in which leakage currents are not generated even under severe conditions such as a high temperature, large power, etc., and which has excellent characteristics, can be acquired.

Description

[Detailed description of the invention] (Technical field) The present invention relates to a silicon carbide semiconductor device.

(Prior art) In addition to silicon (St) semiconductors, gallium arsenide (Ga
Diodes, transistors, IC1LSI, etc. using compound semiconductor materials such as As) and gallium phosphide (GaP),
Semiconductor devices such as light emitting diodes, semiconductor lasers, and CCDs are widely used in various fields of electronics. On the other hand, silicon carbide semiconductors have a wider forbidden band width (2.2 to 3.3 eV) than these semiconductor materials, are extremely stable thermally, chemically, and mechanically, and are resistant to radiation damage. There is. Therefore, semiconductor devices using silicon carbide can be used under harsh conditions such as high temperatures, high power, and radiation exposure, which are difficult to use with devices using other semiconductor materials, and exhibit high reliability and stability. The device is expected to be applied in a wide range of fields.

Although silicon carbide semiconductor devices are expected to have a wide range of applications, their practical application is still hindered because of the high quality and large area silicon carbide required for mass production on an industrial scale with productivity in mind. This is because the establishment of crystal growth technology for obtaining single crystals has been delayed. Conventionally, on a laboratory scale, silicon carbide single crystals grown by sublimation recrystallization method (also called Rayleigh method) are used, or epitaxial growth is performed on this single crystal by vapor phase growth method or liquid phase growth method. Attempts have been made to fabricate diodes and I-transistors using silicon carbide single crystal films.

This technique was developed by R.B.Campbell and It.
-C,Chang+“5ilicon Carbid
e Junction Devices”, in”
Sem1 conductors and Semime
tals”, eds, R,K.

Willardson and A.C.Beer
(Academic Press, New York,
1971), vol 7, Pa5t B
Chap 9. It is described in P625 to P683.

However, with the above method, silicon carbide single crystals can only be obtained with a small area, and it is difficult to control the size and shape of the silicon carbide single crystals. It is not easy to control the impurity concentration, so using the silicon carbide single crystal produced in this way,
Semiconductor devices cannot be manufactured on an industrial scale.

Recently, the present inventors have established a method for growing high-quality, large-area silicon carbide single crystals on silicon single crystal substrates by using a vapor phase growth method (CVD method).
The application has been filed under No. 8-76842.

This method is a technique in which a silicon carbide thin film is formed on a silicon single crystal substrate by a low-temperature CVD method, and then a silicon carbide single crystal is grown by a CVD method while raising the temperature. According to this method, it is possible to supply a large-area, high-quality silicon carbide single-crystal film with controlled crystal polymorphism, impurity concentration, size, shape, etc. using a cheap and easy-to-handle silicon single-crystal substrate. This manufacturing method is suitable for mass production, and is expected to have high productivity. Furthermore, patent applications have been filed for methods of manufacturing various semiconductor devices including diodes and transistors using silicon carbide films on silicon substrates, which has been made possible by the above invention (Japanese Patent Application No. 58-246511, No. 58-249981, No. 58-252157).

Conventionally, as field effect transistors using silicon carbide, MrS type field effect transistors, Schottky gate type field effect transistors, etc. have been manufactured as shown in FIGS. 4(a) and 4(b).

, the old S-type field effect transistor shown in FIG. 4(a) is
An n-type silicon carbide growth layer 32 and an n-type silicon carbide growth layer 33 (channel layer) formed on the surface of a p-type silicon single crystal substrate 31, an insulating layer 34 formed on the surface of the silicon carbide growth layer 33, and Gate electrode 38 , n-type impurity implantation layer 35 and drain electrode 37 formed on the surface of silicon carbide growth layer 33 with gate electrode 38 in between, and n-type impurity implantation layer 39
and a source electrode 36.

The Schottky gate field effect transistor shown in FIG. 4(b) also includes a P-type silicon carbide growth layer 42 and an n-type silicon carbide growth layer 43 (channel layer) formed on the surface of an n-type silicon single crystal substrate 41. ), a gate electrode 48 formed on the surface of the n-type silicon carbide growth N43, and the gate electrode 48
It has a drain electrode 47 and a source electrode 46 formed on the surface of n-type silicon carbide growth layer 43 sandwiching them therebetween.

In the field effect transistor having the above structure, the width of the depletion layer extending within the channel layer 33, 43 is changed by changing the voltage applied to both the gate electrodes 38, 48, and the width of the depletion layer extending from the source electrode 36, 46 to the drain electrode 37, . 47 can be controlled.

(Problems to be Solved by the Invention) However, such a conventional field effect transistor has a planar structure and has the following problems.

(2) In field effect transistors of either structure, electrical insulation separation between channel layer 33.43 and silicon substrate 31.41 is achieved by a pn junction formed in a silicon carbide growth layer. However, the silicon carbide p'n junction obtained by current crystal growth technology does not exhibit sufficient rectification properties under harsh conditions such as high temperatures; The leakage current flowing through the growth layers 32 and 42 increases.

■In order to use transistors under conditions of large current and large output, it is desirable to connect multiple elements in parallel. However, in the conventional planar structure field effect transistor,
Such a structure would complicate the structure, making it impossible to connect multiple elements in parallel.

(Means for Solving the Problems) The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide a structure that exhibits good characteristics even under severe conditions such as high temperature and high power. An object of the present invention is to provide a silicon carbide semiconductor device in which a plurality of elements can be connected in parallel without complication.

(Means for Solving the Problems) A silicon carbide semiconductor device of the present invention includes a silicon carbide semiconductor layer provided on one surface of a substrate, a first electrode provided on the surface of the silicon carbide semiconductor layer, The semiconductor device includes a second electrode provided on the other surface of the substrate and a third electrode provided on the side surface of the silicon carbide semiconductor layer, thereby achieving the above object.

(Function) A first layer is formed on the surface of the silicon carbide semiconductor layer provided on one side of the substrate.
A second electrode is provided on the other surface of the substrate so that a current flows in the thickness direction of the silicon carbide semiconductor layer, and a second electrode is provided on the side surface of the silicon carbide semiconductor layer. By configuring the current to be controlled by the voltage applied to the electrode No. 3, the current flows only through the channel layer formed of this silicon carbide semiconductor,
No leakage current occurs. Furthermore, since a plurality of elements can be provided in parallel on a substrate and one side of the substrate can be used as a common electrode, a plurality of elements can be connected in parallel without complicating the element structure.

(Example) As an example of the present invention, the structure of a vertical field effect transistor using a silicon carbide semiconductor grown on a silicon substrate and its manufacturing method will be described below.

As for the method of forming a silicon carbide single crystal film on a silicon substrate, any of the above-mentioned methods can be adopted. Alternatively, a selective growth technique may be used to partially form silicon carbide on a silicon substrate, or a silicon carbide single crystal film may be selectively grown after forming a silicon carbide single crystal film on the entire surface of the silicon substrate. It may be removed by etching.

The selective growth technique described above involves forming a silicon oxide film or silicon nitride film partially on a silicon substrate, then forming silicon carbide on the entire surface, and then peeling off the silicon oxide film or silicon nitride film. This is a technique for partially forming silicon carbide on a silicon substrate by peeling off the film and simultaneously peeling off the silicon carbide on the film surface.

Vertical silicon carbide old S-type field effect transistor This vertical silicon carbide old S-type field effect transistor is manufactured as follows.

As shown in FIG. 2(a), a silicon carbide growth layer 2 made of a silicon carbide single crystal is formed on a part of the surface of an n-type silicon single crystal substrate l.
The film was made to a thickness of approximately 5 cm using chemical vapor deposition (CVD) using monosilane (Sil14) and propane (C,H,).
μm is formed. This silicon carbide growth layer 2 is formed without adding impurities, and the conductivity type of the formed growth layer 2 is n-type. Next, an aluminum layer 3 is vacuum-deposited in a circular shape (about 2 μm in diameter) on a part of the surface of the silicon carbide growth layer 2 (FIG. 2(b) and peaks).

Next, using this aluminum layer 3 as a mask, reactive ion etching is performed, as shown in FIG. 2(C).
A silicon carbide growth layer 2 having a mesa structure as shown in FIG. Next, after removing the aluminum layer 3 formed on the surface of the grown layer 2, the aluminum layer 3 was etched in an oxygen atmosphere.
By heat treatment at 0°C for 16 hours, an insulating thermal oxide film (SiO□
) form 4.

The thickness of oxide film 4 formed on the surface of silicon carbide growth layer 2 is approximately 50 nm (FIG. 2(d)). Next, the oxide film 4 formed on the surface of the silicon carbide growth layer 2 is removed by etching using photolithography, and the photoresist 5 is removed by etching the oxide film 4 formed on the surface of the silicon substrate 1 as shown in FIG. 4 and the periphery of the protruding end surface 2 a of the silicon carbide growth layer 2 and between the oxide film 4 formed on the corner surface of the protruding end of the silicon carbide growth layer 2 .

Next, titanium-aluminum a is vacuum-deposited on the entire surface of such a laminate (FIG. 2(f)), and then the photoresist 5 is removed. The titanium-aluminum film formed on the surface of photoresist 50 is removed at the same time as photoresist 5 is removed, and source electrode 6 is formed on the protruding end surface of silicon carbide growth layer 2 and gate electrode 8 is formed on the side surface of growth layer 2. . Thereafter, nickel is vacuum-deposited as an ohmic electrode on the entire surface of the silicon substrate to form a drain electrode 7, thereby obtaining a silicon carbide semiconductor device having the structure shown in FIGS. 1(a) and 2(g).

The silicon carbide semiconductor device manufactured in this way uses the nickel film formed on the back surface of silicon substrate 1 as drain electrode 7, and the titanium-aluminum film formed on the protruding end surface of silicon carbide growth layer 2 having a mesa structure. can be used as the source electrode 6, and the current flowing between the source electrode 6 and the drain electrode 7 can be controlled by changing the voltage applied to the gate electrode 8 and changing the width of the depletion layer 9 that spreads in the silicon carbide growth N2. It is a field effect transistor.

Note that in the above embodiment, an insulating film (thermal oxide film SiO□
) 4 was formed by heat treating silicon carbide growth layer 2 and silicon substrate 1, but this insulating film 4 was formed by sputtering,
It may also be formed directly on the silicon carbide growth layer 2 and the surface of the silicon substrate 1 by other methods such as the CVD method.

Vertical Silicon Carbide Schottky Gate Field Effect Transistor This vertical silicon carbide Schottky gate field effect transistor is manufactured as follows.

As shown in FIG. 3(a), an n-type silicon I'n crystal substrate 1
An n-type silicon carbide growth layer L2a using a nitrogen donor is formed on the surface of 1 by chemical vapor deposition (CVD) using monosilane (S i II a ) and propane (c:l II 8 ). Grow to a thickness of 0.1 μm. Next, CVD is performed without adding impurities to the surface of the growth layer 12a.
An n-type silicon carbide growth layer 12b is grown to a thickness of 5 μm using the method, and an n°-type silicon carbide growth layer 12c using a nitrogen donor is grown to a thickness of 0.1 μm on the surface thereof. next,
As shown in FIG. 3(b), n on the surface of the substrate with the growth layer
A plurality of aluminum films 13 are formed by vacuum-depositing aluminum in a circular shape (diameter 3 μm) on the surface of the shaped silicon growth layer 12c. Next, those aluminum films 13
By performing reactive ion etching using as a mask, silicon carbide growth layers 12 (12a, 12b, 12c) having a mesa structure as shown in FIG. 3(C) are obtained. Next, after etching and removing the aluminum film 13 on this silicon carbide growth layer 12, this laminate is heat-treated at 1050°C for 16 hours in an oxygen atmosphere.
An insulating thermal oxide film (SiO□
) 14 (Fig. 3(d)). Next, only the oxide film 14 formed on the protruding end face of the silicon carbide growth layer 12 is removed, and nickel is vacuum-deposited thereon as an ohmic electrode to form a source electrode 16 (FIG. 3(e)).

Next, oxide film 14 on the side surface of silicon carbide growth layer 12 is removed,
Next, as shown in FIG. 3(f), photoresist 15 is formed from source electrode 16 to the upper end of the side surface of silicon carbide growth layer 12 so as to cover them. Next, platinum is vacuum-deposited over the entire surface of the laminate to form a platinum film 18, and then the photoresist 15 and the platinum film 18 on the surface of the photoresist 15 are removed. After that, silicon substrate 1
A drain electrode 17 is formed as an ohmic electrode by vacuum-depositing nickel on the back surface, and a silicon carbide semiconductor device having the structure shown in FIG. 1(b) and FIG. 3(8) is obtained.

In the silicon carbide semiconductor device obtained as described above, similarly to Example 1, the nickel film formed on the back surface of silicon substrate 11 and the nickel film formed on the top of mesa-structured silicon carbide growth layer 12 are used as drain electrodes, respectively. 17 and source electrode 1
By changing the voltage applied to the platinum gate electrode 18 forming a Schottky junction with the silicon carbide growth layer 12, the current flowing between the source and drain electrodes 16 and 17 is applied to the silicon carbide growth layer I2. Depletion layer 1 spreads over
9. This is a vertical Schottky gate field effect transistor whose width can be controlled by changing it.

Moreover, according to the manufacturing process shown in this embodiment, the nickel film 17 formed on the surface of the silicon substrate 11 is used as a common drain electrode for each of the plurality of elements arranged in parallel on the substrate 11 as described above. Furthermore, since the platinum gate electrodes 18 formed on each element are continuous, a plurality of elements can be easily connected in parallel by connecting the source electrodes 16 of each element.

In addition, in the above example, platinum was used as the electrode material for the Schottky gate, but the electrode material was gold (Au).
Other materials that can form a Schottky junction with silicon carbide may also be used.

The field effect transistors manufactured in Examples 1 and 2 above exhibited the following favorable characteristics compared to conventional planar transistors even at room temperature.

The mutual conductance value of a conventional transistor is a planar MIS field effect transistor (Fig. 4(a)).
) was 0.8 mS/mm, and the Schottky gate field effect transistor (shown in FIG. 4(b)) was 1.7 mS/mm. However, in the case of the vertical type of the present invention, the value of mutual conductance is 2 mS/m in the old S-type field effect transistor (shown in Fig. 1(a)).
m, and 2.5 mS/mm for a Schottky gate field effect transistor (shown in FIG. 1(b)).

Further, the transistor of the present invention showed little characteristic deterioration even at a high temperature of 400°C. In other words, the value of transconductance at 400'C is 0.05m5/nun for a conventional S-type field effect transistor with a planar structure.
, 0.1 for Schottky gate field effect transistor
The characteristics deteriorate to 5m5/mm. However, in the case of the vertical type of the present invention, the value of mutual conductance at 400°C is 1.5 ms/mm for the old S-type field effect transistor.
, 2. Schottky gate field effect transistor.
It was 3mS/mm. It was also confirmed that the parallel connected element according to Example 2 was capable of large current operation.

(Effects of the Invention) As described above, according to the present invention, it is possible to obtain a silicon carbide semiconductor device with excellent characteristics that does not generate leakage current even under severe conditions such as high temperature and high power. Moreover, since the silicon substrate can be used as a common electrode, it is also possible to connect a plurality of elements in parallel. Therefore, it is possible to provide a silicon carbide semiconductor device with a simple structure that can be used under conditions of high power and high output, which have not been possible with conventional semiconductor devices.

↓-Plate■MomehenkuRikofatigue Figure 1 shows an embodiment of the vertical silicon carbide field effect transistor according to the present invention, and Figure 1 (a) is a cross-sectional view of the old S-type field effect transistor. (b) is a cross-sectional view of a Schottky gate field effect transistor;
(to) is a cross-sectional view showing an example of the manufacturing process of the old S-type vertical silicon carbide field effect transistor according to the present invention, FIG. 2(h) is a plan view of FIG. 2(b), and FIG. (a) to ((a) are cross-sectional views showing an example of the manufacturing process of a Schottky gate type vertical silicon carbide field effect transistor according to the present invention, and FIG. 4(a) is a conventional S-type electric field effect transistor. A cross-sectional view of an effect transistor, FIG. 4(b) is a cross-sectional view of a conventional Schottky gate type field effect transistor.

1, 11...Silicon substrate, 2.12...Silicon carbide growth layer, 6.16...Source electrode (first electrode), 7.1
7... Drain electrode (second electrode), 8.18...
Gate electrode (third electrode).

that's all

Claims (1)

[Claims] 1. A silicon carbide semiconductor layer provided on one surface of the substrate;
a first electrode provided on the surface of the silicon carbide semiconductor layer;
A silicon carbide semiconductor device comprising a second electrode provided on the other surface of the substrate and a third electrode provided on the side surface of the silicon carbide semiconductor layer.