JP2000164528A - Silicon carbide semiconductor device provided with schottky junction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen a silicon carbide semiconductor device in forward threshold voltage by a method wherein an alloy layer formed by reacting metal contained in a Schottky electrode on a silicon carbide semiconductor is formed on the silicon carbide semiconductor, and a Schottky junction is reduced in barrier height. SOLUTION: A SiC semiconductor Schottky diode is formed of a wafer that comprises an N-type 6H-S-iC (0001) substrate 1 of carrier concentration 3×1018 cm-3 and an N-type epitaxial layer 2 which is off by an angle of 3.5 deg. in a <11-20> direction, 3 μm in thickness, of carrier concentration 1×1018 cm-3, and formed on the substrate 1. An Ni film is deposited on the rear of the SiC substrate 1 to serve as an ohmic electrode 3, and the ohmic electrode 3 is brought into ohmic contact with the substrate 1 by a thermal treatment. Then, a film of metal selected out of Ti, Au, Pd and the like is evaporated on the surface of the epitaxial layer 2, and the metal film is patterned into a Schottky electrode 4. This Schottky junction is thermally treated at a temperature of 500 to 900 deg.C, so that an alloy layer 5 of Schottky electrode metal and SiC semiconductor is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a silicon carbide (Si)
C) The present invention relates to a semiconductor device having a Schottky junction using a semiconductor and using a high melting point metal such as a Schottky diode and a MESFET as a Schottky electrode.

[0002]

2. Description of the Related Art Silicon carbide (SiC) semiconductors are thermally and chemically stable and have excellent radiation resistance.
It is attracting attention as a material for environment-resistant devices and high-power devices.

[0003] SiC semiconductors are being developed as high-frequency semiconductor device materials because their electron mobility is about two to three times greater than that of GaAs semiconductors. In particular, SiC semiconductors are largely characterized by low on-resistance and high switching speed.

In the case of an n-type semiconductor, the barrier height between the Schottky electrode and the semiconductor is given by the difference between the work function inherent to the metal and the electron affinity of the semiconductor. The barrier height also depends on the carrier concentration of the semiconductor and changes with temperature. Generally, a metal having a small work function has a low barrier height. As for the forward characteristics at the time of switching, the loss at the time of switching is smaller as the series resistance of the diode is smaller and as the barrier height (rising voltage) is lower.

In an n-type SiC semiconductor, Ni, T
Metals such as i, Au, and Pt are used. Among them, Mg having a small work function has a low start-up voltage.

[0006]

When the Schottky barrier height is reduced, it is effective as a switching element, but there is a problem that the reverse leakage current increases.

Although Mg has a low barrier height of 0.2 V, there is a problem that Mg metal itself has high reactivity and is difficult to handle.

The present invention has been made in view of the above-mentioned problems, and provides a semiconductor device in which the height of the Schottky barrier is reduced and the forward rise voltage is reduced by using a metal which is easy to handle. The purpose is to:

[0009]

The present invention relates to a silicon carbide semiconductor device having a Schottky junction provided on a silicon carbide semiconductor using a high melting point metal as a Schottky electrode, wherein the metal of the Schottky electrode reacts with the silicon carbide semiconductor. The present invention is characterized in that a barrier height of a Schottky junction is reduced by forming an alloy layer having a reduced thickness.

[0010] As the metal for the Schottky electrode, it is preferable to use a metal that retains diode characteristics against high-temperature heat treatment.

When the silicon carbide semiconductor is an n-type semiconductor, the refractory metal for a Schottky electrode is Au,
Ag, Pd, Cr, Co, Ti, W, Pt, Al, N
It is preferable to select from i, Mo, Cs, and Mn.

When the silicon carbide semiconductor is a p-type semiconductor, the refractory metal for a Schottky electrode is Au,
It is preferable to select from Ag, Co, Ni, Pd, Ti, Al, and Cs. .

As described above, an n-type SiC semiconductor or p-type
As the Schottky electrode of the type SiC semiconductor, a metal material whose diode characteristics do not change even when heat treatment is performed is used. By performing heat treatment in an inert gas, metal and SiC
The reaction at the interface of the semiconductor proceeds to form an alloy layer. As a result, the Schottky barrier is reduced, and the rise voltage can be reduced.

As described above, by the heat treatment of the Schottky electrode, the height of the Schottky barrier is reduced, the forward resistance component at the time of switching is reduced, and the switching loss is reduced.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view showing a Schottky diode using an SiC semiconductor according to an embodiment of the present invention.

Carrier concentration 3 × 10¹⁸cm^-3N-type 6H
-<11-20> on the main surface of the SiC (0001) substrate 1
3 × carrier thickness 1 × turned off 3.5 ° in the direction
10 ¹⁸cm^-3N-type epitaxial layer 2 is formed
Using a wafer.

On the back surface of the SiC substrate 1, a Ni film is deposited as an ohmic electrode 3 by depositing 4,000 angstroms, and heat treatment is performed to make ohmic contact. This heat treatment is performed at a temperature of 950 ° C. for about 10 minutes at an Ar flow rate of 1 l / min and a pressure of 1 kg / cm ² . By this heat treatment,
An ohmic electrode 3 is formed.

Next, on the surface of the epitaxial layer 2, Ti,
One metal film is formed from a high melting point metal such as Au or Pd by 40
Deposit 00 angstrom. This metal film is patterned to form the Schottky electrode 4.

In the present invention, a heat treatment at a high temperature of about 500 to 900 ° C. is performed to lower the barrier height of the Schottky junction, thereby forming an alloy layer 5 of the metal for the Schottky electrode and the SiC semiconductor. The depth of the alloy layer 5 depends on the temperature and time of the heat treatment, and can be set to a target depth by controlling the temperature and time. In this embodiment, the depth of the alloy layer 5 is controlled to be 0.1 to 0.2 μm.

For example, when Au or Pd is used as the Schottky electrode 4, the same atmosphere as when the ohmic electrode 3 is formed, that is, an Ar flow rate of 1 l / min and a pressure of 1 kg is used.
The alloy layer 5 was formed by performing a heat treatment at a temperature of 900 ° C./cm ² for 5 minutes. Also, as the Schottky electrode 4, Ti
Was used, a heat treatment was performed at a temperature of 500 ° C. for 5 minutes under the same atmosphere conditions to form the alloy layer 5. Regardless of which metal is used, heat treatment is performed at a temperature and for a time that can maintain the diode characteristics.

An embodiment of the present invention in which a heat treatment is performed after the formation of the Schottky electrode 4 and a Schottky diode formed under the same conditions as the present invention except that no heat treatment is performed are prepared. FIG. 2 shows the measurement result of the rising voltage. FIG. 2A is an IV characteristic diagram of the embodiment without heat treatment, and FIG. 2B is an IV characteristic diagram of the embodiment with heat treatment. The metal of the Schottky electrode 4 was Ti.

As can be seen from FIG. 2, the forward rising voltage (1 μA current range) is from 0.95 V to 0.3
V.

Similarly, as the Schottky electrode 4, A
Each using u and Pd was prepared, and the rising voltage in the forward direction in the 1 μA current range was measured.

As a result, the forward rising voltage (1 μm)
A current range) is 0.7 V to 0.
In the case of 35V and Pd, they decreased from 0.7V to 0.5V, respectively.

As described above, by the heat treatment of the Schottky electrode, the height of the Schottky barrier decreases, the forward resistance component during switching decreases, and the switching loss can be reduced.

In the above embodiment, the case where Au, Pd, and Ti are used as the refractory metal of the Schottky electrode 4 has been described.
Any metal that can maintain the junction (rectification) characteristics between the metal and the SiC semiconductor even after the alloying of the iC semiconductor may be used.
o, W, Pt, Al, Ni, Mo, Cs, and Mn can be used.

In the above embodiment, the n-type S
Although an iC semiconductor is used, a similar configuration can be made using a p-type SiC semiconductor. At this time, the refractory metal for the Schottky electrode is Au, Ag, Co, Ni, Pd, Ti, Al, Cs.
You can choose from

When the above metals are used, conditions such as heat treatment temperature and time suitable for each metal may be selected.

In the above-described embodiment, the 6H type is used as the SiC semiconductor.
Similar effects can be obtained with a mold.

In the above embodiment, the Schottky diode has been described.
The present invention is also applicable to a MESFET using a Schottky electrode.

[0031]

As described above, according to the present invention, the heat treatment can lower the rising voltage of the Schottky diode and reduce the switching loss.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a Schottky diode using a SiC semiconductor according to an embodiment of the present invention.

FIGS. 2A and 2B are IV characteristic diagrams obtained by measuring a forward rising voltage in a Schottky diode. FIG. 2A shows a case where heat treatment is not performed, and FIG. Show.

[Explanation of symbols]

 Reference Signs List 1 n-type SiC semiconductor substrate 2 epitaxial layer 3 ohmic electrode 4 Schottky electrode 5 alloy layer

Claims (4)

[Claims] 1. A silicon carbide semiconductor device having a Schottky junction provided on a silicon carbide semiconductor using a refractory metal as a Schottky electrode, wherein an alloy layer in which a metal of the Schottky electrode has reacted with the silicon carbide semiconductor is formed. A silicon carbide semiconductor device having a Schottky junction, wherein a barrier height of the junction is reduced. 2. The silicon carbide semiconductor device having a Schottky junction according to claim 1, wherein the metal for a Schottky electrode is a metal that retains diode characteristics against high-temperature heat treatment. 3. The silicon carbide semiconductor is an n-type semiconductor, and the refractory metal for a Schottky electrode is Au, Ag,
Pd, Cr, Co, Ti, W, Pt, Al, Ni, M
The silicon carbide semiconductor device having a Schottky junction according to claim 1, wherein the silicon carbide semiconductor device is selected from o, Cs, and Mn. 4. The silicon carbide semiconductor is a p-type semiconductor, and the refractory metal for a Schottky electrode is Au, Ag,
The silicon carbide semiconductor device having a Schottky junction according to claim 1, wherein the device is selected from Co, Ni, Pd, Ti, Al, and Cs.