JP3665548B2 - Schottky junction semiconductor devices - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrode structure of an SiC semiconductor device having advantages such as being able to operate stably and reliably even in a high temperature environment.
[0002]
[Prior art]
Currently, Si, GaAs, or the like is generally used as a semiconductor material, but Si has a forbidden band width of only 1.1 eV and is difficult to operate at high temperatures. Since GaAs is a material with a wide forbidden band, it can operate even at high temperatures, but it cannot withstand use at high power because heat conduction is only one-third that of Si. GaAs also contains 50% toxic arsenic. On the other hand, SiC has excellent physical properties such as about 3 times the forbidden band width, about 3 times the thermal conductivity, about 7 times the critical electric field strength, and about 2 times the saturated electron drift velocity, compared to Si. Contains no toxic elements. Both p-type and n-type conductive types important for semiconductor devices are possible, and SiC itself is a stable material up to 1500 ° C. or higher, so that it can operate as an electronic device even at a high temperature of about 500 ° C.
[0003]
The SiC material itself is stable, but in order to have reliability to withstand practical use as a high-temperature device, not only SiC but also the surrounding electrode material and insulating material are stable, and a reaction occurs at the interface between them and SiC. It is difficult and it is required that the device characteristics do not change.
To date, Ti, Ni, Pt, Cr, Mo, W, Al and alloys thereof are known as Schottky junction electrode materials for SiC (Japanese Patent Laid-Open Nos. 8-139051 and 2000-164528). ). However, when these metals are used as Schottky electrode materials, the device characteristics deteriorate with use, for example, the reaction between the electrode and SiC accompanying the use at high temperature proceeds rapidly and the leakage current increases. In particular, the device characteristics after heat treatment change and there is a problem in reliability.
[0004]
[Problems to be solved by the invention]
The present invention provides an electrode material that suppresses fluctuations in device characteristics even when used for a long time at a high temperature.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, the present invention firstly used (1) a stable and very slow reaction material as a Schottky electrode that is in direct contact with SiC. Further, (2) a compensation electrode is further laminated on the Schottky electrode so that the characteristics are hardly affected even if the Schottky electrode reacts. Forming a carbide layer of a metal selected from chromium, molybdenum, tungsten or an alloy thereof as a Schottky electrode, and forming a compensation layer of a metal selected from chromium, molybdenum, tungsten or an alloy thereof thereon Thus, it has a configuration characterized in that fluctuations in device characteristics are kept small.
In an actual device, Ni is laminated on Mo when solder-bonded to a lead frame, and Al is laminated when wire-bonded.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a cross-sectional view showing an embodiment of the present invention, in which molybdenum is used as a metal selected from chromium, molybdenum, tungsten or alloys thereof, 1 is an n-type SiC substrate, and 2 is a SiC epitaxial layer. 3 is an insulating layer, 4 is a molybdenum carbide Schottky electrode, 5 is a Mo compensation layer, and 6 is a back ohmic electrode. In this structure, a molybdenum carbide layer 4 is first deposited on the surface of the SiC epitaxial layer 2. As a deposition method, molybdenum carbide is laminated on SiC by a direct sputtering method. Molybdenum carbide has a minimum eutectic point (corresponding to the melting point) as high as 1220 ° C., and is sufficiently stable up to about 500 ° C., which is the operating temperature of the SiC device. Further, the Mo compensation layer 5 is laminated on the molybdenum carbide by the sputtering method.
[0007]
Mo and molybdenum carbide do not react in consideration of thermodynamics. The rate at which SiC and Mo react through the molybdenum carbide layer is very slow because of the molybdenum carbide present in the middle, and even if it reacts, molybdenum carbide is preferentially formed. The silicon remaining as a result of the generation of molybdenum carbide has a high solid solubility in Mo, so that it is difficult to form silicide. As a result, the molybdenum carbide layer stably exists as a Schottky electrode on the SiC surface even when heat is applied.
[0008]
FIG. 2 is a voltage-current characteristic diagram measured before and after heat treatment at 900 ° C. for the Schottky diode of the embodiment of the present invention compared with the conventional example. It is clear that there is almost no difference in characteristics before and after. On the other hand, in the conventional example, the characteristics are greatly changed as shown in the characteristics (b) (b ′).
[0009]
Incidentally, Table 1 shows the characteristic values before and after the heat treatment for the Schottky barrier rectifier of the embodiment of the present invention shown in FIG. The implementation of the present invention shows that there is no characteristic variation even when operating at high temperatures.
Table 1
Sample VF @ 100Acm-2 φBn n
Before heat treatment 1.55V 1.23eV 1.03
After heat treatment 1.53V 1.17eV 1.02
[0010]
Next, FIG. 3 shows the result of examining the phase existing after the heat treatment by X-ray diffraction in the Schottky barrier rectifier of the embodiment of the present invention shown in FIG. In the X-ray diffraction pattern, only a diffraction peak due to molybdenum carbide and Mo is detected, and a peak due to molybdenum silicide is not detected. It is clear that the electrode according to the present invention exists stably even at 900 ° C., which is much higher than the device operating temperature of 500 ° C.
[0011]
FIG. 4 shows the result of examining the element distribution in the depth direction by Auger electron spectroscopy for the Schottky barrier rectifier of one embodiment of the present invention. Before the heat treatment (a), a molybdenum carbide layer first exists on the SiC substrate, and a Mo compensation layer exists thereon. After the heat treatment (b), it has a similar laminated structure, but the molybdenum carbide layer grows thick, and it is clear that the electrode exists stably according to the mechanism described in the operation of the present invention.
[0012]
Although an example in which the present invention is applied to a Schottky diode has been described above, it can also be applied as a gate electrode of a MESFET.
[0013]
As an example of the present invention, an example in which a molybdenum carbide layer and a molybdenum compensation layer are applied is shown. However, a tungsten carbide layer and a molybdenum compensation layer, a molybdenum carbide layer and a chromium compensation layer, a chromium carbide layer and a tungsten compensation layer, a tungsten carbide layer, A combination of a molybdenum-chromium alloy compensation layer, a tungsten-molybdenum alloy carbide layer, and a chromium-tungsten alloy compensation layer can also be applied.
[0014]
【The invention's effect】
As is apparent from the above description, according to the present invention, a highly reliable semiconductor device capable of stable operation without deterioration of characteristics in a high temperature environment can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of the present invention.
FIG. 2 is a voltage-current characteristic diagram of an embodiment of the present invention compared with a conventional example.
FIG. 3 is an X-ray diffraction pattern after heat treatment in an example of the present invention.
FIG. 4 is an element distribution diagram in the depth direction obtained by Auger electron spectroscopy in an example of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 n-type SiC semiconductor substrate 2 Epitaxial SiC layer 3 Insulating layer 4 Schottky electrode 5 by the carbide layer of the metal selected from chromium, molybdenum, tungsten thru | or those alloys The metal selected from chromium, molybdenum, tungsten thru | or those alloys Compensation layer 6 Ohmic electrode 7 Ni
8 Solder 9 Al
10 Al wire

Claims (4)

The metal carbide layer formed by combining carbon and a metal selected from chromium, molybdenum, tungsten, or an alloy thereof in direct contact with the SiC substrate, and the selected layer formed by directly contacting the metal carbide layer. A Schottky junction type semiconductor device comprising a metal layer made of the same metal as the metal . Molybdenum carbide layer in direct contact on a SiC substrate, a Schottky junction type semiconductor device, characterized in that the is composed of molybdenum metal layer laminated in direct contact to the molybdenum carbide layer. 3. The Schottky junction semiconductor device according to claim 1, wherein the semiconductor device is a Schottky diode. 3. The Schottky junction semiconductor device according to claim 1, wherein the semiconductor device is a MESFET.

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