JP3934822B2 - Schottky diode and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a Schottky diode using SiC (silicon carbide) as a substrate and a manufacturing method thereof.
[0002]
[Prior art]
When selecting the electrode material for a semiconductor device, it is necessary to fully consider the type of semiconductor and the characteristics required for the electrode (device and process requirements such as adhesion to the semiconductor, heat resistance, and ease of wire bonding). There is. These metal materials can be broadly divided into (1) those that form stable compounds with all semiconductor constituent elements, (2) those that form compounds only with some of the semiconductor constituent elements, and (3) refractory metals. being classified.
[0003]
First, the metallic material (1) uniformly reacts with a compound semiconductor such as GaAs (gallium arsenide). As a well-known semiconductor device, there is Pt / GaAs using Pt (platinum) as an electrode material. In this semiconductor device, polycrystalline PtAs and PtGa are formed by heat treatment at 200 ° C. or higher. In this case, the bonding interface is sharp (the interface is clear), has good heat resistance, and oxides and dirt on the GaAs surface are removed along with the solid-phase reaction. Therefore, even if no special attention is paid to the surface treatment, n A Schottky electrode having a good factor (representing the characteristics of a Schottky diode, also referred to as an n value) can be obtained. However, since a compound of this metal material and a group V element generally has a large specific resistance, it is necessary to cover the upper surface with a metal having a small specific resistance to reduce the resistance of the entire circuit.
[0004]
The metal material (2) generally does not easily react with semiconductors. For example, for a compound semiconductor of III-V, a metal that forms a compound only with a V group having a high vapor pressure is particularly difficult to react and is excellent in heat resistance and reliability. As an example, there is Al which is often used as a gate electrode of GaAs. On the other hand, in a system that reacts only with group III, the vapor pressure of the group V element is large, so that it easily scatters from the electrode surface, and the reaction with the semiconductor proceeds even if the metal and group III compound formation energy is small. That is the Au / GaAs reaction.
[0005]
The metal material (3) has good heat resistance because W (tungsten), Mo (molybdenum), etc. have a low reaction rate with the compound semiconductor.
[0006]
By the way, as a compound semiconductor material, an SiC substrate has been commercially available, and research on the device has been actively conducted. This SiC has a thermal conductivity three times that of Si (silicon), a saturation electron drift velocity of about twice, and the forbidden band width of the hexagonal 6H-SiC reaches as large as 3.09 eV. .
[0007]
For this reason, the dielectric breakdown voltage is about 10 times higher than that of Si, the operable temperature reaches 500 ° C., and its conductivity type can be controlled to be either p-type or n-type. It has been expected as a material that operates in a harsh environment such as a power device and a radiation-resistant device.
[0008]
With regard to whether a stable ohmic electrode can be formed on such a SiC crystal, since SiC has a wide forbidden band and high chemical stability as described above, a relatively high temperature is required for alloying. However, various metals have been tried in ohmic junctions to n-type SiC.
[0009]
For example, in an example in which a Ni (nickel) electrode is ^{deposited on} a SiC substrate having a doping concentration of 5 × 10 ¹⁸ cm ⁻³ , a contact resistivity of 10 ⁻⁵ Ω · cm ² is obtained, and a higher doping is achieved. for SiC substrate concentration of 10 ^- and ^{6 Ω} · cm ² units, already low resistivity enough to be practical is obtained by application of the element (C.Aranodo, etc., Ins.Phys.Conf Ser. 142, P. 577, 1996).
[0010]
[Problems to be solved by the invention]
However, Ni and Ti (titanium) have been tried to form a good Schottky electrode on the SiC crystal, but the Schottky barrier is as large as 1.3 eV and 0.85 eV, and the same current flows. There is a problem in that the forward voltage required for this is increased.
[0011]
An object of the present invention is to provide a Schottky semiconductor device having a low forward voltage and a method for manufacturing the same.
[0012]
[Means for Solving the Problems]
In the Schottky diode of the first invention for solving the above-described problem, a ruthenium oxide film is formed as a Schottky electrode on a surface of an active layer of a silicon carbide substrate, and the ruthenium oxide film of the silicon carbide substrate is formed. An ohmic electrode was formed on the surface opposite to the opposite surface .
[0013]
According to a second invention, in the first invention, a pad electrode made of gold or aluminum is formed on the upper surface of the ruthenium oxide film.
[0014]
According to a third aspect of the present invention , there is provided a Schottky diode manufacturing method comprising a step of forming an ohmic electrode on a back surface of a silicon carbide substrate, and a reactive sputtering method, a vapor deposition method or a sol-gel method on the active layer surface of the silicon carbide substrate. And a step of etching the ruthenium oxide film to form an electrode having a predetermined shape .
[0015]
According to a fourth invention , in the method for manufacturing a Schottky diode according to the third invention , a step of forming a gold or aluminum pad electrode on the ruthenium oxide film is provided after the step of forming the ruthenium oxide film. Configured.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram showing a manufacturing process of a Schottky semiconductor device according to an embodiment of the present invention. In this embodiment, first, as shown in FIG. 1A, N (nitrogen) is formed on the upper surface of an n-type SiC substrate 1 doped with impurities at a high concentration (for example, 5 × 10 ¹⁸ cm ⁻³ ). A substrate is prepared by previously growing the epitaxial layer 2 having a thickness of 13 μm attached with 3.5 × 10 ¹⁸ cm ⁻³ as impurities.
[0019]
Next, as shown in FIG. 1B, a Ni layer 3 is deposited on the back surface of the substrate 1 by a predetermined thickness by vacuum vapor deposition, and heat treatment is performed at a temperature of 950 ° C. for 2 minutes. As a result, the Ni layer 3 is alloyed at the interface with the SiC substrate 1 and functions as an ohmic electrode having a contact resistivity of 10 ⁻⁵ Ω · cm ² .
[0020]
Next, as shown in FIG. 1C, a ruthenium oxide (RuO ₂ ) film 4A is formed by reactive sputtering. This reactive sputtering method is performed by supplying ruthenium as a target and supplying Ar (argon) for sputtering and O ₂ (oxygen) for oxidation. The conditions at this time are such that the pressure is, for example, 12 m Torr and the gas flow rate is such that Ar / O ₂ is 15/45 sccm, thereby forming a ruthenium oxide film 4A of about 200 nm. .
[0021]
Next, as shown in FIG. 1 (d), patterning of the resist 5 applied to the ruthenium oxide film 4A is performed by a well-known photolithography method. The ruthenium oxide film 4A is etched by etching to form a shape as the ruthenium oxide electrode 4 as shown in FIG. Ruthenium oxide can be etched with CF ₄ gas, and is processed at an etching rate of 12 nm / min when the pressure is 0.04 Torr, the flow rate of CF ₄ is 40 sccm, and the high-frequency power is 250 W.
[0022]
Finally, an Au (gold) or Al (aluminum) electrode 6 is formed by a vacuum deposition method to be a pad for connecting wirings or the like. This low resistance pad electrode 6 also reduces the resistance of the entire circuit.
[0023]
The Schottky diode formed as described above has a Schottky barrier height of 0.5 eV and a forward on-resistance of 4 mΩ · cm ² .
[0024]
The ruthenium oxide formed here has an electric resistivity of 4 × 10 ^-5 Ω · cm at room temperature, which is almost the same as platinum of 1 × 10 ^-5 Ω · cm, and this ruthenium oxide decomposes to 800 ° C. It is stable.
[0025]
Note that although the case where ruthenium is used as a target and oxygen is supplied to form a ruthenium oxide film by a reactive sputtering method is described here, sputtering can also be performed using ruthenium oxide as a target. Even in this case, reactive sputtering for supplying oxygen is preferable. In addition, the ruthenium oxide electrode can be formed by a vacuum vapor deposition method in which the ruthenium oxide is evaporated and deposited. In this case, it is preferable to supply oxygen. Furthermore, the ruthenium oxide electrode can also be formed by a sol-gel method (a method in which ruthenium oxide is formed into a sol or gel and applied onto the epitaxial film 2 and then dried and sintered to form an electrode) (S. Saito, etc., Jpn.J.Appl.Phy.31,1991 p.135).
[0026]
【The invention's effect】
As described above, according to the present invention, there is an advantage that the forward voltage required to pass the same current to the Schottky diode can be significantly reduced as compared with the case where Ni or Ti is used for the Schottky electrode.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a method for manufacturing a Schottky diode of the present invention.
[Explanation of symbols]
1: SiC substrate with high concentration of impurities 2: Epitaxial layer (active layer)
3: Ni layer (ohmic electrode)
4A: Ruthenium oxide film 4: Ruthenium oxide Schottky electrode 5: Resist 6: Pad electrode

Claims (4)

A ruthenium oxide film is formed as a Schottky electrode on the surface of the active layer of the silicon carbide substrate, and an ohmic electrode is formed on the surface of the silicon carbide substrate opposite to the surface on which the ruthenium oxide film is formed. Characteristic Schottky diode.   2. The Schottky diode according to claim 1, wherein a pad electrode made of gold or aluminum is formed on the upper surface of the ruthenium oxide film. Forming an ohmic electrode on the back surface of the silicon carbide substrate;
Forming a ruthenium oxide film on the surface of the active layer of the silicon carbide substrate by a reactive sputtering method, a vapor deposition method or a sol-gel method;
Etching the ruthenium oxide film to form an electrode having a predetermined shape;
A method for manufacturing a Schottky diode, comprising: 4. The method for manufacturing a Schottky diode according to claim 3, further comprising a step of forming a gold or aluminum pad electrode on the ruthenium oxide film after the step of forming the ruthenium oxide film .

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