JP2000106444A - Schottky electrode, formation thereof, semiconductor element and fabrication thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize excellent heat resistance by providing a semiconductor of SiC, and a Schottky electrode containing Ni formed thereon. SOLUTION: An n-type 4H-SiC substrate 1 is prepared and the surface thereof is subjected to cleaning where the surface of the substrate 1 is degreased, treated with mixture liquid of sulfuric acid and hydrogen peroxide water and then treated with HF solution in order to remove natural oxide from the surface. Subsequently, the n-type 4H-SiC substrate 1 is set on an Inconel substrate holder 4 placed in the chamber of a vacuum deposition system which is then evacuated. Thereafter, Schottky electrodes 3a-3d are formed of an Ni film on the n-type 4H-SiC substrate 1 through a metal mask by heating the substrate 1 by means of a heater 5 built in the substrate holder 4 keeping the high vacuum of 1×10-7 or below in the chamber. Temperature of the substrate 1 is measured by means of a thermocouple 6 buried in the substrate holder 4 on the surface side thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a Schottky electrode, a method for forming a Schottky electrode, a semiconductor device, and a method for manufacturing a semiconductor device.

[0002]

2. Description of the Related Art In recent years, semiconductor devices made of silicon carbide (SiC) have been actively researched and developed as environment-resistant devices and power devices. In particular, it is noted that this semiconductor element is an element having excellent heat resistance.

A typical example of such a silicon carbide semiconductor device is a MESFET (metal-semiconductor field effect semiconductor device). Since this MESFET is also made of SiC, high heat resistance is expected.

[0004]

SUMMARY OF THE INVENTION However, MES
In the case of an FET, the Schottky electrode and the S
The interface with iC is most affected by heat, and this determines the upper limit of the heat resistance of the device.

As a result, the heat resistance of MESFET is SiC
There is a problem that the heat resistance is inferior to the inherent heat resistance.
For example, the heat resistance temperature of a Schottky electrode made of Pt is about 500 ° C., which is lower than the heat resistance temperature of about 1000 ° C. which SiC originally has.

This problem also occurs in common with other semiconductor devices having a Schottky electrode other than the MESFET.

The present invention has been made in view of the above problems, and comprises a Schottky electrode having excellent heat resistance, a method of forming a Schottky electrode having excellent heat resistance, and a Schottky electrode having excellent heat resistance. It is an object to provide a semiconductor device and a method for manufacturing the same.

[0008]

According to the present invention, a Schottky electrode includes a semiconductor made of SiC and a Schottky electrode containing Ni formed on the semiconductor.

The Schottky electrode of the present invention can have high heat resistance. As a result, in a semiconductor device using this electrode, the heat resistance of this electrode is improved, so that the heat resistance of the device can be higher than before.

The Schottky electrode containing Ni may be, for example, an electrode substantially composed of Ni alone as a metal material.
Examples of the electrode include Ni as a main component.

The method of forming a Schottky electrode according to the present invention comprises:
A metal film serving as a Schottky electrode is formed over a heated semiconductor by a vapor deposition method.

When a metal film formed on a heated semiconductor by vapor phase epitaxy is subsequently heated, the temperature at which ohmic characteristics are exhibited while suppressing deterioration of the surface properties of the metal film increases. .

Therefore, a semiconductor device having a Schottky electrode formed by this method can have a higher heat-resistant temperature than conventional ones.

The metal film formed on a heated semiconductor by vapor phase growth may be a metal film formed on a semiconductor in a heated state by vapor phase growth.

Particularly, the heating is a high-temperature heating.

The higher the heating temperature of the semiconductor is, the more the Schottky electrode can maintain the Schottky characteristics even if the subsequent environmental temperature increases, and has high heat resistance.
High-temperature heating is preferred as long as the semiconductor characteristics are good.

Further, although the reason is unknown, even if the heating temperature of the semiconductor is increased, the surface deterioration when the environmental temperature is increased can be suppressed.

In particular, in order for the Schottky electrode to have good Schottky characteristics at a predetermined high environmental temperature, the heating temperature at the time of manufacturing the Schottky electrode is preferably a temperature close to or higher than a predetermined environmental temperature, preferably a predetermined temperature. The temperature may be higher than the ambient temperature.

The above-mentioned heating includes heating by a heating means in addition to heating when the source constituting the metal film is formed on the semiconductor by the vapor phase growth method. It does not mean only heating when formed on a semiconductor by vapor deposition.

In particular, the semiconductor is made of SiC.

As SiC, 4H-SiC is preferable from the viewpoint of device characteristics such as electron mobility and anisotropy, but other polycrystalline systems such as 6H-SiC and 3C-SiC may be used.
Further, it may be polycrystalline or amorphous.

Further, the metal film contains Ni (nickel).

Conventionally, Ni is used as a material for an ohmic electrode with respect to SiC, but in the present invention, on the contrary, it is used as a Schottky electrode material.

The following semiconductor device of the present invention uses the above-described Schottky electrode of the present invention, and the method of manufacturing a semiconductor device of the present invention uses the method of forming a Schottky electrode of the present invention.

The semiconductor device of the present invention is a semiconductor device having a Schottky electrode formed on a semiconductor, wherein the semiconductor is SiC and the Schottky electrode is an electrode containing Ni. I do.

In the present invention, the Schottky electrode can be made to have high heat resistance, so that the heat resistance of the element can be made higher than before.

The method of manufacturing a semiconductor device according to the present invention is a method of manufacturing a semiconductor device having a Schottky electrode formed on a semiconductor, wherein the Schottky electrode becomes a Schottky electrode on a heated semiconductor. The method is characterized in that the metal film is formed by a vapor deposition method.

When a metal film formed on a heated semiconductor by a vapor phase growth method is heated, the heating temperature at which ohmic characteristics are increased while suppressing deterioration of the surface properties of the metal film when heated.

Therefore, the semiconductor device of the present invention can have a higher heat-resistant temperature than before.

In the method of manufacturing a semiconductor device according to the present invention, an element is formed by an annealing process for obtaining ohmic characteristics when an ohmic electrode is present or an activation annealing process for activating an impurity when an impurity diffusion region is present. If the annealing temperature for the annealing is equal to or higher than the heat-resistant temperature of the Schottky electrode, the Schottky electrode is formed after the annealing process having a temperature higher than the heat-resistant temperature.

As the semiconductor device according to the present invention, MES
A semiconductor device having a Schottky electrode such as an FET or a Schottky diode can be used.

Further, the heating temperature at the time of producing the Schottky electrode is preferably from 500 ° C. to 800 ° C.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A Schottky electrode according to one embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows 4H-
It is a schematic block diagram which shows the Schottky electrode which consists of Ni formed on SiC.

In FIG. 1, reference numeral 1 denotes an n-type 4H-SiC substrate (dopant: nitrogen, carrier concentration: 4 × 10 ¹⁹ cm ⁻³ );
a to 3d represent Ni formed on the n-type 4H-SiC substrate 1.
A Schottky electrode composed of

Such a Schottky electrode is formed as follows.

First, an n-type 4H-SiC substrate 1 is prepared, and its surface (0001) is cleaned. In the cleaning treatment in the present embodiment, the surface of the substrate 1 is degreased using acetone and ethanol in this order, and then treated with a mixed solution of sulfuric acid and hydrogen peroxide (volume ratio 1: 1). Next, a natural oxide film on the surface is removed by treatment with an HF solution.

Subsequently, the n-type 4H-type is placed on the Inconel substrate folder 4 in the chamber of the vacuum evaporation apparatus shown in FIG.
After mounting the SiC substrate 1, vacuum is applied. Thereafter, while the substrate 1 is heated by the heater 5 built in the substrate folder 4, the Schottky electrodes 3a to 3d made of a Ni film are formed on the n-type 4H-SiC substrate 1 via a metal mask. At the time of this formation, the inside of the chamber is 1
A high vacuum of × 10 ⁻⁷ Torr or less has been achieved.

In the case of this embodiment, the temperature of the substrate 1 is
The temperature was measured by a thermocouple 6 embedded on the front side of the substrate folder 4.

3 to 5 show Schottky electrodes 3 formed while heating SiC substrate 1 (substrate temperature: 700 ° C.).
Immediately after film formation (as-deposition), electrical characteristics (IV characteristics) of samples annealed at a holding temperature of 700 ° C. and a holding temperature of 800 ° C. are shown by a three-terminal method. Here, in the annealing treatment, the above-mentioned holding temperature was held for 10 minutes in an Ar (argon) gas atmosphere at a flow rate of 2 l / min. In the figure, the current profile at the time of reverse bias is shown.
Is considered to be dependent on the measurement method.

FIG. 3 shows that the Schottky electrode 3 has good Schottky characteristics immediately after film formation.

FIG. 4 shows that the Schottky electrode 3 has good Schottky characteristics even after annealing at a holding temperature of 700 ° C. for 10 minutes.

FIG. 5 shows that the Schottky electrode 3 has characteristics close to ohmic characteristics after annealing at a holding temperature of 800 ° C. for 10 minutes.

6 to 8, immediately after the formation of the Schottky electrode 3 formed in a state where the substrate 1 is heated (substrate temperature: 200 ° C.) (as-deposition), a holding temperature 700
The electrical characteristics (IV characteristics) when annealing was performed at 800C and a holding temperature of 800C, respectively. Here, the annealing conditions are the same as in FIGS. 3 to 5 except for the holding temperature.

FIG. 6 shows that the Schottky electrode 3 has good Schottky characteristics immediately after the film formation.

FIG. 7 shows that the Schottky electrode 3 has characteristics close to ohmic characteristics after annealing at a holding temperature of 700 ° C. for 10 minutes.

FIG. 8 shows that the Schottky electrode 3 does not have Schottky characteristics after annealing at a holding temperature of 800 ° C. for 10 minutes and has good ohmic characteristics.

From FIG. 3 to FIG. 8, the Schottky electrode 3
As described above, if the substrate temperature at the time of film formation is high, the Schottky characteristics can be maintained even if the subsequent environmental temperature increases,
Has high heat resistance.

In particular, from FIGS. 3 to 5, since the Schottky electrode 3 has good Schottky characteristics at a predetermined high environmental temperature, the Schottky electrode 3 is at least at a predetermined environmental temperature and its vicinity at the time of film formation. It can be seen that the substrate temperature should be set to the following.

Further, a sample having a substrate temperature of 700 ° C.
Even when annealing was performed at 0 ° C. and 800 ° C., deterioration of the surface of the Schottky electrode 3 was small.

FIG. 9 shows the electrical characteristics (IV characteristics) of the Schottky electrode 3 formed in a state where the substrate 1 is heated at a substrate temperature of 800 ° C. immediately after the film formation (as-deposition).

From FIG. 9, when the substrate temperature is 800 ° C.,
Since the film has characteristics relatively close to the ohmic characteristics immediately after film formation, it is understood that the substrate temperature is preferably 800 ° C. or less.

When the substrate temperature is 500 ° C., the electrode 3
When the surface condition of the substrate is 200 ° C. and 700 ° C.
C., and a substrate temperature of 500.degree. C. or more is preferable in order to have higher heat resistance from the viewpoint of Schottky characteristics.

A MESFET according to one embodiment of the present invention will be described in detail with reference to the drawings. FIG. 9 shows the MES of this embodiment.
FIG. 2 is a schematic configuration diagram of an FET.

In FIG. 10, reference numeral 11 denotes an n-type 4H—SiC substrate (dopant: nitrogen, carrier concentration: 2 × 10 ¹⁸ c).
m ⁻³ ), 12 is 5 μm formed on the n-type SiC substrate 1
Thick p-type 4H-SiC epitaxial layer (dopant:
Al, carrier concentration: 7 × 10 ¹⁵ cm ⁻³ ), 13 is 0.5 μm formed on the p-type SiC epitaxial layer 12.
Thick n-type 4H-SiC epitaxial layer (dopant:
Nitrogen, carrier concentration: 2 × 10 ¹⁷ cm ⁻³ ), 14a, 1
Reference numeral 4b denotes an n ⁺ -type impurity-implanted region (carrier concentration: about 10 ¹⁹ cm ⁻³ ) formed as a 100-nm-thick contact region formed in the n-type SiC epitaxial layer 13 so as to be separated from each other.

Reference numerals 15a and 15b denote n ⁺ -type impurity implanted regions 1
800 nm thick N formed on each of 4a and 14b
An ohmic electrode 16 made of an i film and a Schottky electrode 16 made of a 400 nm thick Ni film formed on the n-type SiC epitaxial layer 13 are shown.

A method for manufacturing such a MESFET will be described with reference to FIG.

First, as shown in FIG.
On a H-SiC substrate 11, a p-type 4H-SiC epitaxial layer 12 and an n-type 4H-SiC epitaxial layer 13
Are epitaxially grown in this order by CVD (chemical vapor deposition).

Thereafter, the n-type 4H-SiC epitaxial
The area within layer 13 that is spaced apart from N⁺High ion
Activation of dopant after implantation by hot ion implantation
Annealing in Ar atmosphere at 1150 ° C for 30 minutes
To process. In addition, the implantation conditions are such that the substrate temperature is 400 to 100.
0 ° C., acceleration voltage 30 keV, dose 5 × 10^Fifteencm ^-2
It is.

Next, as shown in FIG. 11B, 800 nm thick N is deposited on the n ⁺ -type impurity implanted regions 14a and 14b in a state where the substrate is not heated (the substrate temperature before film formation is about 25 ° C.).
An i film is formed by a vacuum deposition method, and thereafter, annealing is performed at 1000 ° C. for 5 minutes to form ohmic electrodes 15a and 15b made of a Ni film.

Subsequently, as shown in FIG. 11 (c), the substrate temperature is set to 70 on the n-type 4H-SiC epitaxial layer 13.
At a temperature of 0 ° C., a Ni film is formed by a vacuum evaporation method.
The Schottky electrode 16 made of i is formed and completed.

In such a MESFET, since the Schottky electrode 16 for defining the upper limit temperature of heat resistance is made of Ni, high heat resistance is obtained.

In particular, the Schottky electrode 16 has a substrate temperature of 7
Since the film is formed at 00 ° C., sufficient Schottky characteristics can be maintained at an element environment temperature of 700 ° C. As a result, the element itself can operate at a higher temperature than before.

The above-mentioned MESFET may be configured so that the conduction type is the reverse conduction type.

The present invention can be applied to a semiconductor device such as a Schottky diode other than the MESFET.

[0065]

According to the present invention, a Schottky electrode having excellent heat resistance, a method for forming a Schottky electrode having excellent heat resistance,
A semiconductor element having a Schottky electrode having excellent heat resistance and a method for manufacturing the same can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a Schottky electrode according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a substrate holder of a vacuum evaporation apparatus for forming a Schottky electrode according to the embodiment.

FIG. 3 is a view showing electric characteristics of the Schottky electrode according to the embodiment.

FIG. 4 is a view showing electric characteristics of the Schottky electrode according to the embodiment.

FIG. 5 is a view showing electric characteristics of the Schottky electrode according to the embodiment.

FIG. 6 is a view showing electric characteristics of the Schottky electrode according to the embodiment.

FIG. 7 is a view showing electric characteristics of the Schottky electrode according to the embodiment.

FIG. 8 is a view showing electric characteristics of the Schottky electrode according to the embodiment.

FIG. 9 is a view showing electric characteristics of the Schottky electrode according to the embodiment.

FIG. 10 is a schematic configuration diagram of a MESFET according to an embodiment of the present invention.

FIG. 11 is a manufacturing process diagram of the MESFET.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 n-type SiC substrate 3 a to 3 d Schottky electrode 13 n-type SiC epitaxy layer 16 Schottky electrode

Claims (7)

[Claims] 1. A Schottky electrode comprising: a semiconductor made of SiC; and a Schottky electrode containing Ni formed on the semiconductor. 2. A method for forming a Schottky electrode, comprising forming a metal film to be a Schottky electrode on a heated semiconductor by a vapor deposition method. 3. The method according to claim 2, wherein the heating is high-temperature heating. 4. The method according to claim 2, wherein the semiconductor is made of SiC. 5. The method according to claim 4, wherein the metal film contains Ni. 6. A semiconductor device comprising a Schottky electrode formed on a semiconductor, wherein the semiconductor is SiC, and the Schottky electrode is an electrode containing Ni. 7. A method for manufacturing a semiconductor device having a Schottky electrode formed on a semiconductor, wherein the Schottky electrode is formed by forming a metal film to be a Schottky electrode on a heated semiconductor by a vapor deposition method. A method for manufacturing a semiconductor device, comprising: