JP4119968B2 - Electrode forming method for silicon carbide semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming an ohmic electrode having low contact resistance and high temperature stability on a silicon carbide semiconductor substrate.
[0002]
[Prior art]
Silicon carbide (SiC: silicon carbide) has a wide band gap of about 3 eV, and has about three times the thermal conductivity and about two times the electron saturation speed of silicon. Is expected as a material.
[0003]
As an electrode for a silicon carbide single crystal, ten kinds of metals such as Al, Au, Ni, Pt, Pd, Ti, W, Mo, Ta, Cr, Co, and Hf have been studied. Among them, as the n-type ohmic electrode, Ni heat-treated in Ar or vacuum at a temperature of 900 to 1100 ° C. for about 0.5 Ks is used, and as the p-type ohmic electrode, Al is laminated on Ti. And what was heat-processed at 950-1050 degreeC about 0.5 Ks etc. is used.
[0004]
[Problems to be solved by the invention]
However, in silicon carbide semiconductor devices, application of high-temperature operation devices is considered, and the above-described electrode material has insufficient high-temperature stability. In addition, in the formation of the various ohmic electrodes described above on the silicon carbide substrate, it has been reported that a contact resistance of 10 ⁻⁶ Ωcm ² is obtained when the doping concentration of impurities to the silicon carbide substrate is 10 ¹⁹ cm ⁻³ . However, further contact resistance reduction is desired from the standpoint of device development.
[0005]
An object of the present invention is to provide a method for forming an ohmic electrode having low contact resistance and high temperature stability in a silicon carbide semiconductor device.
[0006]
[Means for Solving the Problems]
The first invention for achieving the above object, to form an ion implanted region I implanting rows of first element which serves as a n-type or p-type impurity in the region for forming the ohmic electrodes on the silicon carbide substrate A first step, a second step of forming a first refractory metal compound electrode containing the first element on the upper surface of the ion implantation region, and a second step of containing carbon on the upper surface of the first refractory metal compound electrode. A third step of forming a melting point metal compound electrode; and a fourth step of annealing the substrate, the first refractory metal compound electrode, and the second refractory metal compound electrode, and the second refractory metal. The compound electrode was configured to be an ohmic electrode for wiring with another.
[0007]
According to a second invention, in the first invention, after the second step, the refractory metal thin film is deposited on the substrate and patterned to leave at least a portion covering the ion implantation region, and then the first element is formed. Is used to form the first refractory metal compound electrode by plasma treatment.
[0008]
According to a third invention, in the first invention, the second step comprises forming a first refractory metal compound thin film on the substrate by reactive sputtering in a gas atmosphere containing the first element with a refractory metal as a target. And then patterning so as to leave at least a portion covering the ion implantation region, thereby forming the first refractory metal compound electrode.
[0009]
According to a fourth invention, in the first invention, the first refractory metal compound thin film is formed on the substrate by a sputtering method in which the second step is performed in an inert gas using a refractory metal compound containing the first element as a target. And then patterning so as to leave at least a portion covering the ion implantation region, thereby forming the first refractory metal compound electrode.
[0010]
In a fifth aspect based on the first aspect, the third step covers a portion covering the first refractory metal compound electrode after the refractory metal thin film is deposited on the substrate and the first refractory metal compound electrode. Patterning was performed so as to leave, and thereafter, the second refractory metal compound electrode was formed by plasma treatment using the carbon .
[0011]
According to a sixth aspect, in any one invention of the first to fifth, wherein the first element is nitrogen, phosphorus, and configured to be a aluminum, or any boron.
[0012]
According to a seventh invention, in any one of the first to fifth inventions, the refractory metal of the first refractory metal compound electrode or the second refractory metal compound electrode is tungsten or molybdenum. Configured.
[0013]
According to an eighth aspect of the present invention, in any one of the first to seventh aspects, the fourth step is a step of locally heating at least a portion that substantially functions as an electrode with a laser beam. did.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
[First Embodiment]
FIG. 1 is a process diagram showing a manufacturing method according to a first embodiment of the present invention. First, as shown in FIG. 1A, a mask 2 is formed on the surface of a single crystal silicon carbide substrate 1 using photolithography so as to expose only a portion where an ohmic electrode is to be formed. By implanting nitrogen ions, a nitrogen implantation region 3 is formed at a position where the electrode is to be formed, and then the mask 2 is removed as shown in FIG.
[0015]
Next, as shown in FIG. 1C, a tungsten thin film 4 is deposited on the entire surface by sputtering.
[0016]
Then, as shown in FIG. 1D, a mask 5 is formed on the tungsten thin film 4 by photolithography, and RIE (reactive ion etching) using fluorine gas or chlorine gas is performed. As shown in FIG. 1E, the tungsten thin film 4 other than the region where the electrode is to be formed is removed by etching, and then the mask 5 is removed as shown in FIG.
[0017]
Next, as shown in FIG. 1F, a tungsten plasma electrode is obtained by nitriding the tungsten thin film 4 by supplying nitrogen or ammonia using a microwave plasma reactor.
[0018]
Next, as shown in FIG. 1G, a tungsten thin film 7 is deposited on the entire surface by sputtering.
[0019]
Next, as shown in FIG. 1 (h), the mask 8 is formed only in the region where the electrode is to be formed using photolithography, and the region other than the region where the electrode is formed by RIE using fluorine gas or chlorine gas. The tungsten thin film 7 is removed by etching, and then the mask 8 is removed as shown in FIG.
[0020]
Finally, as shown in FIG. 1 (j), the tungsten thin film 7 is carbonized by supplying carbon to the tungsten thin film 7 by using a microwave plasma reactor, and the tungsten carbide electrode 9 is obtained.
[0021]
Thereafter, annealing is performed at a high temperature (1500 ° C. to 1700 ° C.) to electrically activate nitrogen impurities in the nitrogen implantation region 3 and to recover crystal defects. Further, the substrate 1, tungsten nitride electrode 6, tungsten carbide electrode 9 An ohmic electrode is formed by forming an alloy layer at each interface.
[0022]
As described above, since annealing is performed after the entire surface of the region 3 into which nitrogen has been ion-implanted is covered with the tungsten nitride electrode 6, outward diffusion of nitrogen in the implantation region 3 is prevented, and reduction in impurity concentration is prevented. . Further, since nitrogen atoms decomposed from the tungsten nitride electrode 6 diffuse into the interface between the substrate 1 and the tungsten nitride electrode 6, the nitrogen impurity concentration in the implantation region 3 increases conversely. In particular, since tungsten has a large atomic radius, diffusion into the silicon carbide substrate 1 is negligibly small, and the tungsten nitride electrode 6 functions effectively as a nitrogen diffusion source while maintaining the tungsten nitride state. However, when the pressure generated by nitrogen separated from the tungsten nitride electrode 6 exceeds the equilibrium vapor pressure, the continuous decomposition of the tungsten nitride electrode 6 is suppressed. Further, since the tungsten carbide electrode 9 prevents the outward diffusion of nitrogen atoms decomposed from the tungsten nitride electrode 6, the impurity concentration in the implantation region 3 is also prevented from being reduced on this surface.
[0023]
As described above, the impurity concentration of the implantation region 3 in the silicon carbide substrate 1 is prevented from being reduced, and conversely, the concentration is increased, so that an ohmic electrode having a greatly reduced contact resistance can be realized.
[0024]
The tungsten carbide electrode 9 also serves as a protective film that prevents oxidation of the tungsten nitride electrode 6 because the tungsten nitride electrode 6 has a low melting point and reacts with oxygen at a high temperature.
[0025]
Further, since the silicon carbide substrate 1, the tungsten nitride electrode 6, and the tungsten carbide electrode 9 have substantially the same thermal expansion coefficient, the electrodes 6 and 9 are not peeled off or cracked.
[0026]
[Other embodiments]
In the above description, the case where nitrogen that is an n-type impurity is used as ions implanted into the silicon carbide substrate 1 has been described. However, it is also possible to use adjacent ions, and aluminum or boron can be used as a p-type impurity. .
[0027]
The tungsten nitride electrode 6 may be any tungsten compound electrode containing the same element as the element ion-implanted into the silicon carbide substrate 1.
[0028]
In addition, the tungsten nitride electrode 6 and the tungsten carbide electrode 9 do not have to have a double structure in all portions, and the tungsten nitride electrode 6 is formed as an extraction electrode only in a portion covering the implantation region 3, and the tungsten carbide electrode 9 is formed in other portions. It may be formed as a wiring electrode connected to the tungsten nitride electrode 6 formed in (1).
[0029]
As another method for obtaining the tungsten nitride electrode 6, the entire surface of the substrate 1 including the nitrogen implantation region 3 is formed by reactive sputtering using tungsten as a target in a gas atmosphere containing nitrogen, ammonia or a nitrogen element. It is also possible to employ a method of depositing a tungsten nitride thin film on the substrate and then etching away the tungsten nitride thin film other than the portion where the electrode 6 is to be formed by RIE.
[0030]
Further, as another method of obtaining the tungsten nitride electrode 6, a tungsten nitride thin film is deposited on the entire surface by sputtering using tungsten nitride as a target and in an inert gas atmosphere such as Ar, and then by RIE. A method of etching away the tungsten nitride thin film other than the portion where the electrode 6 is to be formed can also be employed.
[0031]
Further, when the final high temperature annealing is performed, if an annealing method in which the electrode forming region is locally heated by laser light is used, a high temperature heat treatment furnace is not required.
[0032]
In the above description, tungsten nitride and tungsten carbide are used as the electrode material. However, molybdenum nitride and molybdenum carbide can also be used, and other refractory metal compounds can be used. At this time, a molybdenum carbide electrode can be formed on the upper surface of the tungsten nitride electrode, or a tungsten carbide electrode can be formed on the upper surface of the molybdenum nitride electrode. That is, nitrides and carbides of different refractory metal thin films can be combined.
[0033]
【The invention's effect】
As described above, according to the present invention, since the refractory metal thin film is formed on the silicon carbide substrate having a high impurity concentration, there is an advantage that a silicon carbide semiconductor device having an ohmic electrode that is stable at a high temperature with a low contact resistance can be obtained. is there.
[Brief description of the drawings]
FIG. 1 is a process diagram of an electrode forming method according to a first embodiment of the present invention.
[Explanation of symbols]
1: silicon carbide substrate, 2: mask, 3: nitrogen implantation region, 4: tungsten thin film, 5: mask, 6: tungsten nitride electrode, 7: tungsten thin film, 8: mask, 9: tungsten carbide electrode.

Claims (8)

A first step of forming an ion implantation region I implanting rows of first element which serves as a n-type or p-type impurities to form the silicon carbide ohmic electrodes on the substrate region,
A second step of forming a first refractory metal compound electrode containing the first element on the upper surface of the ion implantation region;
A third step of forming a second refractory metal compound electrode containing carbon on the upper surface of the first refractory metal compound electrode;
And a fourth step of annealing the substrate, the first refractory metal compound electrode, and the second refractory metal compound electrode,
An electrode forming method for a silicon carbide semiconductor device, wherein the second refractory metal compound electrode is an ohmic electrode for wiring with another.   In the second step, after the refractory metal thin film is deposited on the substrate, patterning is performed so as to leave at least a portion covering the ion implantation region, and then the first refractory melting point is formed by plasma treatment using the first element. 2. The electrode forming method according to claim 1, which is a step of forming a metal compound electrode.   The second step deposits a first refractory metal compound thin film on the substrate by reactive sputtering in a gas atmosphere containing the first element with a refractory metal as a target, and then covers at least the ion implantation region. The electrode forming method according to claim 1, wherein the first refractory metal compound electrode is formed by patterning to leave a part.   In the second step, a first refractory metal compound thin film is deposited on the substrate by sputtering performed in an inert gas using the refractory metal compound containing the first element as a target, and at least the ion implantation region is then formed. The electrode forming method according to claim 1, wherein the first refractory metal compound electrode is formed by patterning so as to leave a covering portion. In the third step, after depositing a refractory metal thin film on the substrate and the first refractory metal compound electrode, patterning is performed so as to leave a portion covering the first refractory metal compound electrode, and then using the carbon. The electrode forming method according to claim 1, wherein the second refractory metal compound electrode is formed by plasma treatment. The first element is nitrogen, phosphorus, aluminum, or the electrode forming method according to any one of claims 1-5, characterized in that any one of boron. The manufacturing method according to any one of claims 1 to 5 , wherein the refractory metal of the first refractory metal compound electrode or the second refractory metal compound electrode is tungsten or molybdenum. The manufacturing method according to any one of claims 1 to 7 , wherein the fourth step is a step of locally heating at least a portion that substantially functions as an electrode with a laser beam.

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