JPH0864800A - Silicon carbide semiconductor device - Google Patents

Abstract

PURPOSE: To realize an ohmic electrode which has a low contact resistance and high reliability so as to obtain a silicon carbide semiconductor device which has a high operating voltage, large operating current, and is excellent in reliability by a method wherein a composite compound composed of low-resistance metal silicide, metal carbide, metal, silicon, and carbon is formed on a silicon carbide single crystal. CONSTITUTION: A mixed-phase layer 12 of titanium silicide and titanium carbide is formed on a silicon carbide single crystal 11, and furthermore a titanium layer 13 is laminated thereon to serve as an ohmic electrode. By this setup, an ohmic electrode of low contact resistance and high reliability can be obtained. Furthermore, as silicon carbide and the electrode have small thermal expansion coefficient, a silicon carbide semiconductor device which has a high operating voltage, large operating current, excellent in reliability at a high temperature, and equipped with an ohmic electrode of low contact resistance and high reliability can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon carbide semiconductor device.

[0002]

2. Description of the Related Art An ohmic electrode formed on a conventional silicon carbide (SiC) semiconductor is nickel (Ni) for n-type SiC,
Aluminum (Al) and silicon (S
After the vapor deposition of each material consisting of eutectic of i), heat treatment was performed to obtain ohmic bonding (J. Electrochem. Soc., vo
l. 135, p.359.). There are many crystal systems in SiC,
It has a band gap of 2.2 to 3.3 electron volts due to its crystal structure. Further, SiC is a material that is extremely stable thermally, chemically and mechanically, is rare as a wide-gap semiconductor, and stably exists in both p-type and n-type. Therefore, an element in which an electrode for electrically connecting to an external circuit is formed on a SiC single crystal is expected to be applied to a large power element, a high temperature operation element, a radiation resistant element, a photoelectric conversion element and various other electronic technical fields. .

[0003]

When forming electrodes on a SiC semiconductor as described above, Ni is not used for n-type SiC.
Is used. An ohmic bond can be formed by forming a compound of Si and Ni by heat treatment after vacuum deposition, but C has a small solid solution amount with respect to Ni, and C and Ni
Does not form a compound. Therefore, since C is mixed in the semiconductor / electrode interface, the contact resistance is high and it is difficult to use it as a semiconductor element. Also, C in Ni
Has a low diffusion coefficient and requires a high temperature of about 1100 ° C. to discharge C from the semiconductor / electrode interface. On the other hand, p-type Si
For C, Al and Al alloys are used as ohmic electrodes. Al and Al alloys have a problem in heat resistance during heat treatment. Further, during heat treatment, peeling of the electrode occurs due to the difference in expansion coefficient between Ni, Al and SiC. An object of the present invention is to provide a highly reliable ohmic electrode having a low contact resistance and to provide a highly reliable silicon carbide semiconductor element at high voltage, large current and high temperature.

[0004]

In order to form an ohmic electrode having low contact resistance and high reliability on a SiC single crystal, the present invention provides a metal silicide, a metal carbide and a metal, silicon on the surface of the silicon carbide single crystal. , A layer containing a plurality of kinds of composite compounds composed of carbon or a layer containing a plurality of kinds of composite compounds composed of metal silicide, metal carbide and metal, silicon, carbon on a surface of a silicon carbide single crystal and an arbitrary metal layer. It is laminated to form an ohmic electrode. In particular, the contact resistance is lowered by stacking a layer containing a plurality of kinds of metal silicide, metal carbide and a complex compound composed of metal, silicon and carbon on a silicon carbide single crystal having a high impurity concentration to form an ohmic electrode. . Also, even if a layer containing a plurality of kinds of metal silicides, metal carbides and composite compounds composed of metal, silicon, and carbon and an arbitrary metal layer are laminated on the surface of a high-concentration silicon carbide single crystal, an ohmic bond is obtained. The contact resistance is low.
The metals used here include Ti, V, Cr, Zr, Nb,
It is suitable to select an alloy containing at least one kind of metal from Mo, Hf, Ta and W. Ti, V, C
An alloy of one kind of metal selected from r, Zr, Nb, Mo, Hf, Ta and W, or an alloy by stacking a laminated film of one kind of metal on a silicon carbide single crystal and then heat-treating
At the semiconductor interface, metal silicide, metal carbide and metal, silicon,
It is also possible to form a layer containing a plurality of types of composite compounds made of carbon. Further, in order to prevent oxidation during heat treatment, a metal such as Au, Pt, Pd, Ni, Cu or the like which is difficult to oxidize on an alloy layer made of at least one of the above metals, or Ti-Al, Ni- It is also effective to perform heat treatment after laminating at least one layer of Al-based alloy or the like.
Also, for connection with an external circuit, A on the ohmic electrode
A low resistance metal such as 1, Au, Cu, or Ni may be laminated. Moreover, Ti, V, Cr,
After ion-implanting one kind of metal from Zr, Nb, Mo, Hf, Ta, and W, heat treatment is performed to form a layer containing a plurality of kinds of metal silicide, metal carbide, and a compound compound of metal, silicon, and carbon. It is also possible to form and obtain an ohmic electrode. In addition, a silicon carbide semiconductor element and a semiconductor circuit using the above electrode structure having a low contact resistance have a high voltage,
High reliability in high current and high temperature use.

[0005]

[Function] A low contact resistance can be obtained by forming a layer containing a low resistance metal silicide, metal carbide, and a plurality of kinds of composite compounds composed of metal, silicon, and carbon on a silicon carbide single crystal and using it as an ohmic electrode. I was asked. In addition, a layer containing a plurality of kinds of metal silicide, metal carbide, and a complex compound of metal, silicon, and carbon has an impurity concentration of 10 ¹⁸ / cm 3.
By stacking on a high-impurity concentration silicon carbide single crystal of ³ or more, an ohmic junction with a lower contact resistance was obtained due to the tunnel effect. In the case where any one kind of metal was laminated on the electrode structure, the ohmic contact with low contact resistance was similarly obtained. The metal element used for these electrode structures is T which exists as a stable phase in both silicide and carbide.
It is selected from among i, V, Cr, Zr, Nb, Mo, Hf, Ta and W. Further, a metal silicide, a metal carbide, and a composite compound composed of metal, silicon, and carbon, which have a low resistance, are obtained by stacking an alloy using at least one kind of metal on a silicon carbide single crystal and then applying a heat treatment. It is possible to form a layer containing a plurality of types of the above at the metal / semiconductor interface. Further, these layers containing a plurality of kinds of metal silicides, metal carbides, and composite compounds composed of metals, silicon, and carbon have a coefficient of thermal expansion close to that of silicon carbide, and therefore do not peel off from silicon carbide during heat treatment. Further, it does not deteriorate even when used at high temperatures. For the above reasons, by using a metal, an ohmic electrode having a low contact resistance can be surely obtained by heat treatment. Also, Ti, V, Cr, Zr, N
Since b, Mo, Hf, Ta, and W are active metals, a high resistance oxide layer may be formed on the electrode surface during heat treatment, but carbonization of an alloy containing at least one metal Au, P stacked on a silicon single crystal and resistant to oxidation
metals such as t, Pd, Ni, Cu, or Ti-Al,
By performing post-lamination heat treatment using at least one layer of a Ni-Al alloy as a cap metal, oxidation of the electrode surface is avoided and an ohmic electrode having a low contact resistance can be reliably obtained. Also, Ti, V, Cr, Zr, Nb, Mo, H
It is possible to form a layer containing multiple kinds of metal silicide, metal carbide, and a complex compound of metal, silicon, and carbon by performing heat treatment after ion implantation of one kind of metal from f, Ta, and W. Is. At this time, it is easy to control the thickness of the layer containing a plurality of kinds of metal silicide, metal carbide, and a composite compound of metal, silicon, and carbon by appropriately selecting the ion implantation conditions and controlling the implantation depth of the metal element. Was realized. Al, Cu, Au, N having a low electric resistance is formed on the electrode structure of the silicon carbide semiconductor formed by the above means.
It was possible to easily connect to an external circuit by stacking i and the like. In addition, these silicon carbide semiconductor devices having an electrode structure of low contact resistance are suitable for high voltage and large current, and show high reliability. In addition, circuits using these semiconductor elements also showed excellent reliability in high voltage and large current control.

[0006]

【Example】

(Embodiment 1) FIG. 2 shows one of the embodiments of the present invention. A layer 21 made of a mixed phase of tungsten silicide (WSix) and tungsten carbide (WCy) having a thickness of 200 nm was laminated on the silicon carbide single crystal 11 by a sputtering method, and then heat treatment was performed at 1000 ° C. in a vacuum atmosphere of 10 ⁻⁸ Torr. The electrode thus obtained exhibited ohmic properties as shown in FIG. FIG. 4 shows the contact resistance (Rc) with respect to the impurity concentration (N) of n-type SiC. In particular, a low resistance ohmic junction was obtained in the high impurity concentration region. As shown in FIG. 5, by stacking the Al layer 51 on the layer 21 composed of the mixed phase of 200 nm tungsten silicide and tungsten carbide, it was possible to easily connect to the external circuit by the Al wire 52.

(Example 2) As shown in FIG. 6 (a), a Ti layer 13 was formed on a silicon carbide single crystal 11 by vacuum evaporation to a thickness of 200
10 nm in a vacuum atmosphere of 10 ⁻⁸ Torr after stacking
Heat treatment was performed at 00 ° C. By heat treatment, as shown in FIG. 1B, silicon carbide single crystal 11, titanium silicide (TiSi
x), a layer 1 composed of a mixed phase of titanium carbide (TiCy)
2, a laminated structure of the Ti layer 13 was obtained. FIG. 7 shows the IV characteristics of the junction with respect to the heat treatment temperature. FIG. 8 shows changes in the contact resistance Rc depending on the heat treatment temperature Ta. An ohmic electrode having a low contact resistance was obtained because the layer 12 composed of a mixed phase of TiSix and TiCy was uniformly formed by the heat treatment at a high temperature. As shown in FIG. 9A, a Ti layer 13 having a thickness of 200 nm and a platinum Pt layer 91 having a thickness of 200 nm were laminated on the SiC single crystal 11 by vacuum deposition, and then heat treatment was performed in a vacuum atmosphere of 10 ⁻⁸ Torr and an Ar flow.
FIG. 10 shows changes in the apparent contact resistance Rc ′ obtained by adding the resistance of the electrode itself to the contact resistance Rc in each atmosphere with respect to the heat treatment temperature Ta. In an electrode in which only a Ti layer is laminated on SiC, Rc 'increases at high temperature due to oxidation of the electrode surface during Ar flow. On the other hand, an electrode in which a Pt layer as a cap metal was laminated on a Ti layer on SiC was able to realize an ohmic electrode with low resistance in each atmosphere.

(Embodiment 3) As shown in FIG. 11, tungsten-copper (W) is formed on a silicon carbide single crystal 11 by a sputtering method.
-Cu) alloy layer 111 is laminated to a thickness of 200 nm and then 10 ^-8
A heat treatment at 1000 ° C. was performed in a Torr vacuum atmosphere.
By heat treatment, as shown in FIG. 12, SiC single crystal 11, W
A layered structure of the layer 21 composed of the mixed phase of Six and WiCy and the W—Cu alloy layer 111 was obtained. This electrode exhibited low contact resistance and ohmic characteristics.

Example 4 As shown in FIG. 13, the surface of the n-type silicon oxide layer 121 was heat-treated at 1200 ° C. to form an oxide film 122, and then a pattern was formed by etching with hydrofluoric acid. Acceleration voltage 400k due to ion implantation
After implanting nitrogen at eV, heat treatment was performed at 1600 ° C. to recover and form an n + layer 123 having a high impurity concentration (FIG. 1).
4 (a)). The impurity concentration of the n + layer was 10 ¹⁹ / cm ³ . A titanium layer 13 having a thickness of 200 nm is deposited by vacuum evaporation, and then heat treatment is performed at 1000 ° C. to form a layer 12 made of a mixed phase of TiSix and TiCy at a metal / high impurity concentration semiconductor interface.
By forming the above-mentioned structure, it was possible to selectively obtain an ohmic electrode having a low contact resistance (FIG. 14 (b)).

(Example 5) As shown in FIG. 13, titanium was implanted into the surface of the SiC single crystal 11 at an acceleration voltage of 400 keV by an ion accelerator. 18 in a vacuum atmosphere of 10 ^-8 Torr
By heat treatment at 00 ° C., a layer 12 made of a mixed phase of TiSix and TiCy is formed on the surface of the SiC single crystal 11 as shown in FIG. After that, an Al layer 51 having a thickness of 200 nm was laminated to form an ohmic electrode having a low contact resistance. Further, as shown in the drawing, the ohmic electrode can be selectively formed by forming the oxide film on the SiC single crystal by heat treatment in an oxidizing atmosphere using the oxide film as a mask.

(Embodiment 6) FIG. 17 is a schematic sectional view of a silicon carbide MOS field effect transistor having an electrode structure according to the present invention. 1 silicon carbide is used for the silicon oxide layer 121.
A silicon oxide film formed by heat treatment in an oxidizing atmosphere at 200 ° C. was used. Further, another crystalline silicon carbide was used for the gate electrode 142.

[0012]

According to the present invention, a low resistance ohmic electrode can be formed by providing a layer containing a metal silicide, a metal carbide, or a composite compound on a silicon carbide single crystal. Further, since the difference in the coefficient of thermal expansion between silicon carbide and the electrode is small, it is possible to obtain a highly reliable silicon carbide semiconductor device equipped with a highly reliable ohmic electrode having a low contact resistance at high voltage, large current and high temperature. .

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an electrode structure of a silicon carbide semiconductor.

FIG. 2 is a cross-sectional view showing an electrode structure of a silicon carbide semiconductor.

3 is an IV of the electrode structure of the silicon carbide semiconductor shown in FIG.
Characteristic diagram.

FIG. 4 is an explanatory diagram of a change in contact resistance with respect to the impurity concentration of the silicon carbide single crystal of the electrode structure of the silicon carbide semiconductor shown in FIG.

FIG. 5 is an explanatory diagram of a method for forming an ohmic electrode of a silicon carbide semiconductor.

FIG. 6 is an explanatory diagram of a method for forming an ohmic electrode of a silicon carbide semiconductor.

FIG. 7 is an IV of the electrode structure of the silicon carbide semiconductor shown in FIG.
Explanatory drawing of heat treatment temperature dependence of a characteristic.

8 is an explanatory diagram of heat treatment temperature dependence of contact resistance of the electrode structure of the silicon carbide semiconductor shown in FIG.

FIG. 9 is an explanatory diagram of a method for forming an ohmic electrode of a silicon carbide semiconductor.

FIG. 10 is an explanatory diagram of heat treatment temperature dependency of apparent contact resistance in a heat treatment atmosphere of the electrode structure of the silicon carbide semiconductor shown in FIGS. 6 and 9.

FIG. 11 is an explanatory diagram of a method for forming an ohmic electrode of a silicon carbide semiconductor.

FIG. 12 is an explanatory diagram of a method for forming an ohmic electrode of a silicon carbide semiconductor.

FIG. 13 is an explanatory diagram of a method for forming an ohmic electrode of a silicon carbide semiconductor.

FIG. 14 is an explanatory diagram of a method for forming an ohmic electrode of a silicon carbide semiconductor.

FIG. 15 is an explanatory diagram of a method for forming an ohmic electrode of a silicon carbide semiconductor.

FIG. 16 is an explanatory diagram of a method for forming an ohmic electrode of a silicon carbide semiconductor.

FIG. 17 is a cross-sectional view of a field effect transistor having an electrode structure according to the present invention.

[Explanation of symbols]

11 ... Silicon carbide single crystal, 12 ... Layer composed of mixed phase of titanium silicide and titanium carbide, 13 ... Titanium layer 21 Layer composed of mixed phase of tungsten silicide and tungsten carbide,
51 ... Aluminum layer, 52 ... Aluminum wire, 91 ... Platinum layer,
111 ... Tungsten-copper alloy layer, 121 ... Silicon oxide layer, 131 ... N-type silicon carbide single crystal, 132 ... High concentration n-type silicon carbide single crystal, 141 ... P-type silicon carbide single crystal, 142
... gate electrode.

Front Page Continuation (72) Inventor Tsutomu Yao 7-1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory

Claims (12)

[Claims] 1. A silicon carbide semiconductor device characterized in that an ohmic electrode is formed by laminating a layer containing a plurality of kinds of a metal silicide, a metal carbide and a composite compound consisting of metal, silicon and carbon on a silicon carbide single crystal. . 2. An ohmic electrode is obtained by laminating a layer containing a plurality of kinds of a metal silicide, a metal carbide and a composite compound consisting of metal, silicon and carbon on a silicon carbide single crystal and an arbitrary metal layer. A silicon carbide semiconductor device. 3. A layer containing a plurality of kinds of metal silicides, metal carbides and composite compounds composed of metal, silicon and carbon and an arbitrary metal layer are laminated on a silicon carbide single crystal having an impurity concentration of 10 ¹⁸ / cm ³ or more. A silicon carbide semiconductor device characterized by being formed into an ohmic electrode. 4. A silicon carbide single crystal containing Ti, V, Cr, Zr,
A layer containing a plurality of kinds of metal silicides and metal carbides containing at least one kind of metal selected from Nb, Mo, Hf, Ta and W, and any one kind of metal layer. Alternatively, a silicon carbide semiconductor element is obtained by stacking alloy layers. 5. A silicon carbide single crystal containing Ti, V, Cr, Zr,
An alloy of one kind of metal among Nb, Mo, Hf, Ta and W, or a metal silicide, a metal carbide and a metal at the alloy / semiconductor interface by heat treatment after laminating a laminated film of one kind of metal, A silicon carbide semiconductor device characterized in that an ohmic electrode is formed by forming a layer containing a plurality of kinds of composite compounds composed of silicon and carbon. 6. A silicon carbide single crystal containing Ti, V, Cr, Zr,
An alloy of one kind of metal selected from Nb, Mo, Hf, Ta and W or one kind of metal is laminated, and then another metal layer or another metal alloy layer is laminated thereon, and then heat treated to form an alloy / A silicon carbide semiconductor device characterized in that an ohmic electrode is formed by forming a layer containing a plurality of kinds of a metal silicide, a metal carbide, and a composite compound composed of metal, silicon, and carbon on a semiconductor interface. 7. Ti, V, Cr, Z on the surface of a silicon carbide single crystal.
After ion-implanting one kind of metal selected from r, Nb, Mo, Hf, Ta, and W, a heat treatment is performed to form a layer containing a plurality of kinds of metal silicide, metal carbide, and a complex compound of metal, silicon, and carbon. A silicon carbide semiconductor device characterized by laminating one kind of metal after being formed. 8. A silicon carbide semiconductor device according to claim 1, 2, 3, 4, 5, 6 or 7, wherein Al or Au is laminated on the electrode structure of the silicon carbide semiconductor. 9. A diode comprising the electrode structure according to any one of claims 1 to 8. 10. A thyristor equipped with the electrode structure according to claim 1. Description: 11. A transistor comprising the electrode structure according to any one of claims 1 to 8. 12. An electric circuit comprising the semiconductor device according to any one of claims 1 to 11.