JP2000101100A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain an electrode from acting on an SiC board so as to lessen a leakage current by a method, where the electrode is formed of an element such as iron, ruthenium, osmium, iridium, or rhodium or alloy of two or more metals selected from among them. SOLUTION: An N-type SiC layer 2 is grown epitaxially on an N-conductivity type SiC board 1, the SiC board 1 is cleaned, and then Fe is evaporated as a Schottky electrode 4 on the epitaxial layer 2 on the SiC board 1. Ni is evaporated as an ohmic electrode 3 on the rear of the SiC board 1. An Fe electrode is formed through a patterning process. Ruthenium, osmium, iridium, or rhodium may also be used in place of iron. As a result, an electrode is made hardly reacting with SiC, and a leakage current can be restrained from increasing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a 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 has a feature that high-speed switching can be performed because minority carriers in the semiconductor are not used. However, a Schottky diode using silicon has a problem that the withstand voltage is low. On the other hand, a Schottky diode using SiC has a feature that the breakdown voltage is high. Also, S
Since a Schottky diode using iC can operate even at a high temperature, it is only necessary to use no cooling means or use only a small cooling device for applications in which a large current flows.

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

On the other hand, when operating the Schottky diode, it is preferable to reduce the on-resistance to increase the on-current. In this case, the potential barrier between the semiconductor and the metal, that is, a 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]

As described above, when using, for example, titanium as a Schottky electrode, heat treatment at a high temperature causes a problem that titanium reacts with SiC and a leakage current at the time of reverse bias increases. Was.

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. However, the barrier height when Ti is used as the Schottky electrode is about 1 eV. And it was not always satisfactory.

SUMMARY OF THE INVENTION 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, a reaction between the SiC and the electrode is suppressed to reduce a leakage current. A first object is to reduce the voltage, and a second object is to reduce the barrier height between the semiconductor and the electrode to increase the on-current.

[0008]

According to the present invention, there is provided a semiconductor device in which a Schottky junction is formed between SiC and an electrode, wherein the electrode is selected from iron, ruthenium, osmium, iridium, rhodium and the like. In addition, an alloy of at least two metals is used.

The above-mentioned metals have little reaction with SiC, and by using these metals as Schottky electrodes,
Even if heat treatment is performed at a high temperature, it is possible to suppress an increase in leakage current at the time of reverse bias.

Further, according to the present invention, in a semiconductor device in which a Schottky junction is formed between SiC and an electrode, the electrode is a IIIa-group (Sc, Y, La or other lanthanum-based, actinium-based) semiconductor. 2. The metal and work function of 1.
It is characterized by using an alloy of 9 eV or more with a second metal.

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

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

As described above, even when the IVa group alloy is used as the Schottky electrode, the barrier height of the Schottky junction with SiC can be reduced.
The ON current can be increased.

[0014]

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 manufactured as follows, and the manufactured 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 provided on a SiC substrate 1 (0.2 mm thick) exhibiting n-type conduction at an impurity concentration of 10 ¹⁸ / cm ^3. A substrate on which 10 μm was epitaxially grown was prepared. The substrate is immersed in a mixed solution of aqueous ammonia and hydrogen peroxide, washed by immersing it in a dilute hydrofluoric acid aqueous solution or the like, and then Fe is deposited on the epitaxial layer 2 side as a Schottky electrode 4 to a thickness of 1 μm. Was deposited. Further, Ni is used as an ohmic electrode 3 on the back surface of the SiC substrate 1.
Was deposited in a thickness of 1 μm. Thereafter, a patterning process such as resist coating, exposure, development, and etching was performed to form a 0.1 mm-diameter Fe electrode (Schottky electrode 4). As a comparative example, a sample in which Ti was formed as a Schottky electrode was also manufactured.

Both samples prepared as described above were heat-treated at 700 ° C. in an argon atmosphere, and the leakage current in the reverse direction of the diode was measured. As a result, the leakage current at a voltage of −100 V was about 10 ⁻⁴ (A) when Ti was used as the Schottky electrode, but was 1 in the case of Fe.
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 each deposited in 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 almost no silicide was observed in Fe.

Thus, it is considered that the reason why the reaction between Fe and SiC is small is that the leak current is small. In other words, Fe has a heat of formation of silicide which is about the same as or larger than heat of formation of SiC, and is more stable when it is present as a metal than when it reacts with silicon in SiC to form silicide. Therefore, it is considered that the heat treatment hardly reacts with SiC, and thus an increase in leak current can be suppressed.

As for the sample in which Fe was formed to a thickness of 10 nm, and after annealing, Al was vapor-deposited at 1 μm, the leakage current was small as in the above. Also, the samples using ruthenium, osmium, iridium, and rhodium instead of iron had a small leak current similarly to the above.

(Embodiment 2) A Schottky diode as shown in FIG. 1 was manufactured by changing the type of the Schottky electrode as in the first embodiment, and the manufactured Schottky diode was evaluated.

In this embodiment, Ti silicide, specifically, Ti ₃ Si, TiSi and TiSi ₂ is formed as a Schottky electrode. As a forming method, Ti and Si
Were used as evaporation sources, and both were evaporated at the same time by an E-gun evaporation apparatus. The substrate temperature at this time is 250 ° C
And

After the heat treatment was performed on the manufactured sample in the same manner as in the first embodiment, the leak current was measured. As a result, in the case of Ti ₃ Si, the leakage current was of the order of 10 ⁻⁵ (A), but in the case of TiSi, it was 4 × 10 ⁻⁶ (A).
_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 peak other than the respective silicide was observed. In the case of Ti ₃ Si, it is considered that the leakage current is slightly higher and there is a slight reaction with SiC,
Good characteristics were obtained in other samples. Note that the crystallinity of silicide has been improved by annealing, which is also considered to have contributed to the improvement of characteristics.

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

Also, when heat treatment was similarly performed using a silicide of a metal other than Ti as a 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, in silicide containing Si at a predetermined ratio, it can be said that it is more thermally stable if the silicide remains as it is than it is to deprive SiC of Si 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 an increase in leakage current can be suppressed.

As the metal M forming 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,
Pd, Lu, Fe, Os, Ir, Co, Rh, and Pt are mentioned. 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
It is preferable to make the above.

Although the first and second embodiments have been described above, the thickness of the Schottky electrode is preferably about 10 nm or more. Other metals may be stacked as described.

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

(Embodiment 3) A Schottky diode as shown in FIG. 1 was manufactured as follows, and the manufactured 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 provided on a SiC substrate 1 (0.2 mm thick) exhibiting n-type conduction at an impurity concentration of 10 ¹⁸ / cm ^3. A substrate on which 10 μm was epitaxially grown was prepared. After cleaning by an ordinary cleaning method, an oxide film was formed at 1200 ° C. in dry oxygen. Thereafter, 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 an N-type ohmic electrode 3 is formed 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 secure ohmic properties. After that, the oxide film on the epitaxial layer 2 side is dissolved to remove the epitaxial layer 2.
Surface was exposed.

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 simultaneously deposited. The substrate temperature was set to 200 ° C. to facilitate formation of a solid solution of both metals. As a sample, Sc: Hf
Alternatively, ones having Sc: Zr ratios of 3: 2, 1: 1, and 9: 1 were produced. Thereafter, 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.

Although Sc used as the first metal easily forms silicide and carbide and has a sufficient adhesion to SiC, it has a small work function and therefore forms a Schottky barrier when bonded to SiC. Can not. Therefore, a Schottky diode having a low barrier height with respect to SiC is formed by increasing the work function of the solid solution by using Hf or Zr having a work function larger than Sc and easily forming a solid solution with Sc.

With respect to the sample manufactured as described above, the built-in voltage was obtained from the relationship between the voltage and the capacity, and the barrier height was obtained. As a comparative example, a device in which Ti was used as a Schottky electrode was similarly manufactured, and the barrier height was determined. As a result, the barrier height was 0.9 eV in the case of Ti.
It was in the range of 0.8 eV. Although there was some variation,
Rather, the smaller the ratio of Sc, the larger the value of the barrier height.

When the electrode was subjected to X-ray diffraction, the sample of this embodiment was a single phase. Also, no phenomenon such as peeling due to phase separation in annealing which is common in mixed phase electrodes was observed.

When an electrode is formed in a normal cleaning and vapor deposition process, a thin oxide film is easily formed at the interface, and a large barrier height may be observed due to the influence. Therefore,
When ion bombardment or the like was performed before vapor deposition to clean the interface, a stable interface could be obtained. Hereinafter, a specific description will be given.

He or Ar is deposited on a vapor deposition apparatus having an RF coil.
Plasma was generated by introducing a small amount of an inert gas such as hydrogen gas or a reducing gas such as hydrogen or hydrocarbon, and a DC voltage of about 100 V or less was applied to the plasma to collide with the surface of the SiC substrate. After performing such ion bombardment treatment, the barrier height of the Schottky electrode was evaluated. After annealing at 300 ° C., the barrier height without the ion bombardment treatment had a variation of about ± 0.2 eV, but the variation with the ion bombardment treatment was improved to within ± 0.1 eV. Was done.

In addition, under reduced pressure with hydrogen gas introduced, 60
Even when a heat treatment at 0 ° C. was performed and then a metal material to be a Schottky electrode was deposited at 200 ° C., the variation in barrier height was also within ± 0.1 eV.

(Embodiment 4) Hf is used as the first metal,
A Schottky diode was fabricated in the same manner as in the third embodiment, using Ti as the second metal and using a 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. Also, as in the first embodiment, there was no electrode peeling.

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

(Embodiment 5) La is used as the first metal,
Al was used as the second metal, and these were used at a substrate temperature of 200
At the same time, two kinds of Schottky diodes using La ₃ Al and LaAl ₂ as Schottky electrodes were produced in the same manner 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 was 0.4 eV for La ₃ Al and LaA
At l ₂ , it was 0.6 eV. Annealing was performed on a sample using LaAl ₂ for the electrode. 100 in the opposite direction
When a voltage of V is applied, annealing at 300 ° C.
^Although the leakage current was ^-4 (A), 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 no particular change was observed in the shape of the sample using LaAl ₂ for the electrode. (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, or the like is used as the second metal.
An alloy having a ratio of first metal / second metal of 0.3 to 3 was used as a Schottky electrode using Tl, Sn, Pb, Sb, Bi, Pt, and Au. The fabrication 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 was 0.3 to 0.8.
eV. Note that the barrier height was not significantly affected even when the second metal contained about 1% of the impurity element. Further, as the second metal, Ru, Ag, C
o, Zn, Cd, Hg, Ga, In, Tl, Sn, P
When b, Sb, Bi, Pt, and Au are used, 700
Even after annealing at ℃, there was no change in the electrodes and heat resistance was obtained.

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

[0044]

According to the present invention, by using a predetermined metal as an electrode material for forming a Schottky junction with SiC, it is possible to obtain an excellent semiconductor element having a small leak current even when a high-temperature heat treatment is performed. it can.

In the present invention, the barrier height of the Schottky junction can be reduced by using an alloy of a predetermined metal as the electrode material for forming the Schottky junction with SiC. Semiconductor element can be obtained.

[Brief description of the 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]

 DESCRIPTION OF REFERENCE NUMERALS 1: SiC substrate 2: SiC epitaxial layer 3: Ohmic electrode 4: Schottky electrode

Claims (4)

[Claims] 1. A semiconductor device in which a Schottky junction is formed between SiC and an electrode, wherein said electrode is iron, ruthenium, osmium, iridium, rhodium, or an alloy of at least two or more metals selected from these. A semiconductor device characterized by using: 2. A semiconductor device in which a Schottky junction is formed between SiC and an electrode, wherein said electrode is IIIa
A semiconductor device using an alloy of a first metal belonging to the group III and a second metal having a work function of 3.9 eV or more. 3. The method according to claim 1, wherein the first metal is scandium (S).
3. The semiconductor device according to claim 2, wherein c) uses a Group IVa metal as the second metal. 4. 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.