JP3361062B2 - Semiconductor device - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to silicon carbide (Si
The present invention relates to a semiconductor device using C).

[0002]

2. Description of the Related Art A Schottky diode having a structure using a Schottky electrode in which a metal and a semiconductor are in contact with each other is characterized in that high speed switching is possible because minority carriers in the semiconductor are not used. However, the Schottky diode using silicon has a problem of low breakdown voltage. On the other hand, the Schottky diode using SiC has a characteristic of high breakdown voltage. Also, S
Since the Schottky diode using iC can operate at high temperature, it is sufficient to use no cooling means or use a small cooling device for applications in which a large current flows.

Titanium (Ti), for example, is used as the Schottky electrode, but titanium has a problem that when it is heat-treated at a high temperature, it reacts with SiC to increase the leak current during reverse bias. Further, as a device, it is necessary to form an ohmic electrode in addition to the Schottky electrode.
Nickel is usually used as the ohmic electrode,
In order to produce a good ohmic property, it is necessary to perform heat treatment at a temperature of several hundreds of degrees. The heat treatment at this time causes an increase in the leak current as described above in the Schottky electrode. A method of forming a ohmic electrode, followed by heat treatment, and then forming a Schottky electrode is also conceivable. In this case, however, impurities in the annealing atmosphere contaminate the surface and conversely increase the leakage current. .

On the other hand, when operating the Schottky diode, it is preferable to lower the on-resistance and increase the on-current. In this case, the potential barrier between the semiconductor and the metal, that is, the so-called barrier height is required to be low. When Ti is used as the Schottky electrode, the barrier height is about 1 eV. However, it is desirable to further reduce the barrier height in order to obtain a large current.

[0005]

[0006]

As described above, in order to increase the ON current of the Schottky diode, it is necessary to lower the barrier height between the semiconductor and the metal, but Ti is used as the Schottky electrode. The barrier height when used was about 1 eV, which was not always satisfactory.

The present invention has been made to solve the above-mentioned conventional problems. In a semiconductor device in which a Schottky junction is formed between SiC and an electrode, the barrier height between the semiconductor and the electrode is lowered to turn on. Eye on increasing the current
It is the target.

[0008]

[0009]

[0010]

According to the present invention, in a semiconductor device in which a Schottky junction is formed between SiC and an electrode, a IIIa group (Sc, Y, or La) is used as the electrode.
And an alloy of a second metal having a work function of 3.9 eV or more and a lanthanum-based or actinium-based metal.

It is preferable that Sc is used as the first metal and a group IVa (Ti, Zr, Hf) metal is used as the second metal. Thus, the Group IIIa metal (Sc
Has a work function of 3.5 eV or less) and a work function of 3.9 e
By using an alloy with a metal of V or more as the Schottky electrode, it is possible to lower the barrier height of the Schottky junction with SiC (for example, the electron affinity of a crystal structure of 4H is about 3.7 eV). It is possible to increase the on-current.

The present invention is also characterized in that, in a semiconductor device in which a Schottky junction is formed between SiC and an electrode, an alloy of group IVa (Ti, Zr, Hf) is used as the electrode.

As described above, even when an alloy of IVa group is used as the Schottky electrode, the barrier height of the Schottky junction with SiC can be lowered.
It is possible to increase the on-current.

[0014]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) A Schottky diode as shown in FIG. 1 was produced as follows, and the produced Schottky diode was evaluated.

First, an n-type SiC layer (SiC epitaxial layer 2) having an impurity concentration of 5 × 10 ¹⁵ / cm ³ is formed on a SiC substrate 1 (thickness: 0.2 mm) which exhibits n-type conduction with an impurity concentration of 10 ¹⁸ / cm ^3. A substrate on which 10 μm was epitaxially grown was prepared. This substrate was dipped in a mixed solution of ammonia water and hydrogen peroxide solution, and further washed by dipping it in a dilute aqueous solution of hydrofluoric acid. Then, Fe was used as the Schottky electrode 4 on the epitaxial layer 2 side to have a thickness of 1 μm. It was deposited at. In addition, as the ohmic electrode 3 on the back surface of the SiC substrate 1, Ni is used.
Was evaporated to a thickness of 1 μm. Then, patterning processes such as resist coating, exposure, development and etching were performed to form a Fe electrode (Schottky electrode 4) having a diameter of 0.1 mm. Further, as a comparative example, a sample in which Ti was formed as a Schottky electrode was also prepared.

Both the samples produced as described above were heat-treated at 700 ° C. in an argon atmosphere, and the leak current in the reverse direction of the diode was measured. As a result, the leak current at a voltage of −100 V was about 10 ⁻⁴ (A) when Ti was used as the Schottky electrode, but was 1 when Fe was used.
It was as small as 0 ^-6 (A) or less. The ohmic electrode showed almost ohmic characteristics by the heat treatment.

To investigate the interface of the Schottky electrode, T
SiC in which i and Fe are evaporated to a thickness of 10 nm
The substrate was heat treated at 700 ° C. and X-ray diffraction was performed. In the case of Ti, a peak of silicide was observed, but in Fe, almost no silicide was observed.

Thus, it is considered that the small reaction between Fe and SiC is the reason for the small leak current. That is, Fe has a heat of formation of silicide equal to or larger than that of SiC, and it is more stable as a metal than reacting with silicon in SiC to form a silicide. Therefore, it is considered that the heat treatment does not easily react with SiC, so that the increase of the leak current can be suppressed.

The leak current of the sample in which Fe was formed to have a thickness of 10 nm and which was annealed and then 1 μm of Al was evaporated on Fe had a small leak current as in the above case. Further, the leak current was small in the samples using ruthenium, osmium, iridium, and rhodium instead of iron, similarly to the above.

(Embodiment 2) By changing the type of Schottky electrode, a Schottky diode as shown in FIG. 1 was produced in the same manner as in the first embodiment, and the produced Schottky diode was evaluated.

In this embodiment, Ti silicide, specifically, Ti ₃ Si, TiSi and TiSi ₂ is formed as the Schottky electrode. As a forming method, Ti and Si
Was used as an evaporation source, and both were simultaneously evaporated by an E gun vapor deposition device. The substrate temperature at this time is 250 ° C.
And

The produced sample was heat treated in the same manner as in the first embodiment, and then the leak current was measured. As a result, in the case of Ti ₃ Si, the leakage current was in the order of 10 ⁻⁵ (A), but in TiSi, it was 4 × 10 ⁻⁶ (A), and TiSi
_In ^No. ₂ , the leak current was 2 × 10 ⁻⁶ (A). Also,
X-ray diffraction at the interface was performed in the same manner as in the first embodiment. As a result, an unidentifiable peak was observed for Ti ₃ Si,
Other than that, no peaks other than the respective silicides were observed. In the case of Ti ₃ Si, the leak current is slightly high and it is considered that there is some reaction with SiC.
Good characteristics have been obtained in other samples. It should be noted that the crystallinity of silicide is improved by annealing, which is also considered to contribute to the improvement of characteristics.

Also, when Ti silicide was formed to a thickness of 100 nm and Ti was formed thereon to a thickness of 1 μm, the leak current could be reduced in the same manner as described above. In this case, as compared with the case where the Ti silicide was thick, it was possible to suppress the decrease in adhesion due to the heat treatment. Further, the effect was observed even when the thickness of Ti silicide was 20 nm.

Also, when a heat treatment was similarly performed using a silicide of a metal other than Ti for the Schottky electrode, the increase in leak current was small, and the leak current was 10 ^-5 (A) or less.

[0025] Metal silicide MSi _x (M is a metal) to the value of x is generated energy of the silicide becomes minimum in the vicinity of 1. Therefore, it can be said that in a silicide containing Si at a predetermined ratio, it is more thermally stable in the state as it is, rather than taking Si of SiC to form a compound having a larger x. Therefore, the use of silicide makes it difficult to react with SiC by heat treatment,
It is considered that the increase in leak current can be suppressed.

As the metal M forming the silicide, a metal having a work function of 5.2 or less has a small barrier height against SiC and can reduce the on-resistance. As the metal M, in addition to Ti, La, Zr, Hf, V, N
b, Ta, Cr, Mo, W, Mn, Re, Ni, Ru,
Examples thereof include Pd, Lu, Fe, Os, Ir, Co, Rh and Pt. Further, in view of suppressing the reaction between Si in SiC, the proportion of Si in the metal silicide MSi _x is given above, specifically, x is 0.3 or more, more preferably 1
The above is preferable.

Although the first and second embodiments have been described above, the thickness of the Schottky electrode is preferably about 10 nm or more, and in order to reduce the plane resistance or improve the bonding property, the examples are also used. Other metals may be stacked as described.

Although the Schottky diode has been described in the first and second embodiments, it can be used as the Schottky electrode of another semiconductor device such as MESFET.

(Embodiment 3) A Schottky diode as shown in FIG. 1 was manufactured in the following manner, and the Schottky diode manufactured was evaluated.

First, an n-type SiC layer (SiC epitaxial layer 2) having an impurity concentration of 5 × 10 ¹⁵ / cm ³ is formed on an SiC substrate 1 (thickness: 0.2 mm) showing an n-type conduction with an impurity concentration of 10 ¹⁸ / cm ^3. A substrate on which 10 μm was epitaxially grown was prepared. After cleaning by a normal cleaning method, an oxide film was formed at 1200 ° C. in dry oxygen. After that, the epitaxial layer 2 side was protected with a resist, and the oxide film on the opposite layer was dissolved with hydrofluoric acid. After removing the resist, cleaning is performed, and N is used as the ohmic electrode 3 on the back surface of the SiC substrate 1.
i was deposited to a thickness of 1 μm. Furthermore, annealing was performed at 950 ° C. to ensure ohmic properties. Then, the oxide film on the epitaxial layer 2 side is melted to form the epitaxial layer 2
Exposed the surface of.

Next, the substrate subjected to the above steps was set in a vapor deposition apparatus, and a metal material to be a Schottky electrode was vapor deposited. At this time, Sc was selected as the first metal and Hf or Zr was selected as the second metal, and the first metal and the second metal were vapor-deposited at the same time. The substrate temperature was 200 ° C. to facilitate the formation of a solid solution of both metals. As a sample, Sc: Hf
Alternatively, a Sc: Zr ratio of 3: 2, 1: 1, and 9: 1 was prepared. Then, patterning was performed to form a Schottky electrode 4 having a diameter of 100 μm. After patterning, annealing was performed at 300 ° C. for 1 hour in an argon atmosphere.

Sc used as the first metal is easy to form silicide or carbide and can obtain sufficient adhesion to SiC, but since it has a small work function, it should form a Schottky barrier when it is joined to SiC. I can't. Therefore, by using Hf or Zr, which has a work function larger than Sc and easily forms a solid solution with Sc, the work function of the solid solution is increased to form a Schottky diode having a low barrier height with respect to SiC.

With respect to the sample manufactured as described above, the built-in voltage was calculated from the relationship between the voltage and the capacitance, and the barrier height was calculated. As a comparative example, a Schottky electrode made of Ti was also prepared in the same manner, and the barrier height was obtained. As a result, in the case of Ti, the barrier height was 0.9 eV.
It was within the range of 0.8 eV. Although there were variations,
If anything, the smaller the proportion of Sc, the larger the barrier height value tended to be.

When the X-ray diffraction of the electrode was performed, the sample of this embodiment was in a single phase. In addition, there was no phenomenon such as peeling due to phase separation during annealing, which is likely to occur in mixed phase electrodes.

If an electrode is formed by a normal cleaning or vapor deposition process, a thin oxide film is likely to be formed on the interface, and a large barrier height may be observed due to the influence. Therefore,
Ion bombardment was performed before vapor deposition to clean the interface, and a stable interface could be obtained. The details will be described below.

He or Ar can be applied to a vapor deposition apparatus equipped with an RF coil.
A small amount of an inert gas such as hydrogen or a reducing gas such as hydrogen or hydrocarbon was introduced to generate plasma, and a DC voltage of about 100 V or less was applied to the plasma to collide with the surface of the SiC substrate. The barrier height of the Schottky electrode formed after the ion bombardment treatment was evaluated. After annealing at 300 ° C, the barrier height had a variation of about ± 0.2 eV without the ion bombardment treatment, but the variation was within ± 0.1 eV with the ion bombardment treatment. Was done.

Further, in a depressurized state in which hydrogen gas is introduced, 60
Even when the heat treatment was performed at 0 ° C. and then the metal material to be the Schottky electrode was vapor-deposited at 200 ° C., the variation in the barrier height was still within ± 0.1 eV.

(Embodiment 4) Hf is used as the first metal,
A Schottky diode was manufactured in the same manner as in the third embodiment, using Ti as the second metal and using the solid solution of both metals as the Schottky electrode. The Hf / Ti ratio was 9 to 0.1. As a result, the barrier height could be continuously changed from 0.3 to 0.7 eV. Further, as in the first embodiment, no electrode peeling occurred.

It is also effective to form a solid solution with Zr and Hf or Ti. In addition to the above Hf-Ti,
By using a solid solution of Hf-Zr or Zr-Ti, it is possible to lower the work function than Ti, and it is possible to obtain a Schottky junction with a low barrier height.

(Embodiment 5) La is used as the first metal.
Al is used as the second metal, and these are used at a substrate temperature of 200
Two types of Schottky diodes using La ₃ Al and LaAl ₂ as Schottky electrodes were simultaneously vapor-deposited at the same temperature as in the third embodiment. As a comparative example, a sample using La as a Schottky electrode was also manufactured.

As a result of the measurement, the barrier height of the Schottky junction with SiC is 0.4 eV for La ₃ Al and LaA.
It was 0.6 eV at l ₂ . Further, annealing was performed on the sample using LaAl ₂ for the electrode. 100 in the opposite direction
When a voltage of V is applied, 10 at annealing at 300 ° C.
The leak current was ^-4 (A), but it decreased to 10 ^-6 (A) by annealing at 800 ° C. In the sample using only La for the electrode, the electrode aggregated by annealing at 800 ° C., but the sample using LaAl ₂ for the electrode showed no particular change in shape. (Embodiment 6) Sc, Y or lanthanum based La, Ce, Gd, Nd is used as the first metal, and Ru, Ag, Co, Zn, Cd, Hg, Ga, In, as the second metal.
Tl, Sn, Pb, Sb, Bi, Pt, and Au were used, and an alloy having a ratio of the first metal / the second metal of 0.3 to 3 was used as the Schottky electrode. The manufacturing method was the same as in the third embodiment, and the barrier height was evaluated in the same manner.

As a result, the barrier height is 0.3 to 0.8.
It was within the range of eV. Even if the second metal contained an impurity element of about 1%, the barrier height was not significantly affected. Further, as the second metal, Ru, Ag, C
o, Zn, Cd, Hg, Ga, In, Tl, Sn, P
When b, Sb, Bi, Pt, Au is used, 700
Even if annealing was performed at ℃, the electrode did not change and heat resistance was obtained.

Although the respective embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications can be carried out without departing from the spirit of the present invention.

[0044]

[0045]

According to the present invention, the barrier height of a Schottky junction can be lowered by using an alloy of a predetermined metal as an electrode material forming a Schottky junction with SiC, which is excellent in a large on-current. It is possible to obtain an excellent semiconductor device.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a Schottky diode according to an embodiment of the present invention.

[Explanation of symbols]

1 ... SiC substrate 2 ... SiC epitaxial layer 3 ... Ohmic electrode 4 ... Schottky electrode

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 29/47 H01L 29/872

Claims (5)

(57) [Claims] 1. A semiconductor device having a Schottky junction formed between SiC and an electrode, wherein a scan electrode is used as the electrode.
An alloy of scandium (Sc) and hafnium (Hf) or scan
A semiconductor device comprising an alloy of zirconium (Zr) and zirconium (Sc) . 2. A Schottky junction is formed between SiC and an electrode.
In the formed semiconductor device, La _{3 is used} as the electrode.
Semiconductor device characterized by using Al or LaAl ₂
Place 3. A semiconductor device in which a Schottky junction is formed between SiC and an electrode, wherein an alloy of IVa group is used as the electrode. 4. The alloy used as the electrode is an alloy of hafnium (Hf) and titanium (Ti), hafnium (Hf).
And zirconium (Zr) alloy, or hafnium (H
The semiconductor device according to claim 3, which is an alloy of f), titanium (Ti), and zirconium (Zr). 5. The alloy used as the electrode is an alloy of hafnium (Hf) and titanium (Ti), and the Hf / Ti ratio is in the range of 9 to 0.1. The semiconductor device described.