Active solid-state devices (e.g. – transistors – solid-state diode – Schottky barrier
Reexamination Certificate
2001-10-15
2003-12-30
Zarabian, Amir (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Schottky barrier
C257S055000, C257S077000, C257S267000, C257S280000
Reexamination Certificate
active
06670687
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device basically made of silicon carbide and a module device incorporating the semiconductor device. In this specification, the present invention is discussed, taking a case of high-voltage semiconductor device as an example, but the present invention is not limited to such an application and can be applied to semiconductor devices for various uses.
2. Description of the Background Art
As well known, a current inverter needs voltage blocking capability of reverse direction. Therefore, a current inverter which has a switching element without voltage blocking capability of reverse direction (e.g., IGBT and power MOSFET) generally uses a diode connected in series to the switching element.
FIG. 7
is a vertical cross section showing a background-art module element used for a current inverter. As shown in
FIG. 7
, a switching device
601
and a diode
602
both of which are basically made of silicon are provided in an encapsulating container
617
.
The switching device
601
has a cathode electrode
603
and a control electrode
604
formed on a surface thereof and an anode electrode
605
formed on a back surface thereof. The diode
602
has an anode electrode
606
formed on a surface thereof and a cathode electrode
607
formed on a back surface thereof. The anode electrode
605
of the switching device
601
and the cathode electrode
607
of the diode
602
are both soldered onto a conducting board
608
. Therefore, these electrodes
605
and
607
are electrically connected to each other with a solder layer
609
and the conducting board
608
interposed therebetween. Contrary to this, the cathode electrode
603
and the control electrode
604
of the switching device
601
are connected to a cathode conducting bar
610
and a control conducting bar
611
with bonding wires
613
, respectively. The anode electrode
606
of the diode
602
is connected to an anode conducting bar
612
with a bonding wire
613
.
On the other hand, the conducting board
608
is connected to a metal body
615
comprising a hollow trench
616
with an insulating substrate
614
interposed therebetween. In the trench
616
, a cooling medium such as water is circulated. With such a structure, heat generated by loss of the switching device
601
and the diode
602
is radiated through the electrodes
605
and
607
, the solder layer
609
, the conducting board
608
, the insulating substrate
614
, the metal body
615
and the cooling medium which are formed on the back surfaces thereof.
Silicon carbide, which has larger energy gap between bands than silicon, is highly thermally stable. Therefore, a device using silicon carbide is operable even at a high temperature up to 1000 Kelvin. Moreover, since silicon carbide has larger thermal conductivity than silicon, silicon carbide devices can be arranged at high densities. Further, silicon carbide, which has breakdown voltage about ten times as large as silicon, is suitable to be used as a base material for a device which operates under a condition that high voltage may be generated in a blocking state of the device. In other words, the thickness of a silicon carbide device needed to maintain a certain level of voltage may be significantly thinner than that of a device whose base material is silicon, and therefore it is expected that the silicon carbide device can resolve an antinomic relation between a switching loss and a steady-state loss.
Since silicon carbide has breakdown voltage about ten times as large as silicon, in a silicon carbide device, the width of a depletion layer needed for a certain level of voltage blocking capability is very small. Therefore, the distance between an anode electrode and a cathode electrode is short and accordingly the voltage drop in a current-carrying state which is almost proportional to the electrode distance becomes small. In other words, use of silicon carbide as a base material makes it possible to reduce the steady-state loss caused in the current-carrying state. With this effect, a switching device or a diode using silicon carbide has an advantage of significantly resolving the antinomic relation between the switching loss and the steady-state loss as compared with a switching device or a diode using silicon.
Further, the silicon carbide device, which can operate at a high temperature, has an advantage of simplifying a device cooling system such as a heat sink.
Forming a pn junction in silicon carbide, however, needs heat treatment of much higher temperature than forming a pn junction in silicon and can not disadvantageously use an existing manufacturing facility for silicon.
Furthermore, when a wire is ultrasonically bonded onto an electrode formed on a surface of silicon carbide, a stress generated depending on the conditions such as a load in bonding is applied to the electrode and this changes a condition of junction between the silicon carbide and the electrode, thereby disadvantageously not producing an expected performance.
Moreover, in a silicon carbide device having a conducting board which is in electrical contact with silicon carbide, when there is difference in thermal expansion coefficient between the silicon carbide and the conducting board, a stress caused by heat cycle changes the performance of the device.
SUMMARY OF THE INVENTION
The present invention is directed to a semiconductor device. According to a first aspect of the present invention, the semiconductor device comprises: a silicon carbide layer of predetermined conductivity type comprising a surface having a first region, a second region and a third region sandwiched between the first region and the second region; an anode electrode having a Schottky contact with the first region; a cathode electrode having an ohmic contact with the second region; and a control electrode having a Schottky contact with the third region.
According to a second aspect of the present invention, in the semiconductor device of the first aspect, at least one Schottky barrier electrode out of the anode electrode and the control electrode has a thickness of not less than 5 &mgr;m.
According to a third aspect of the present invention, in the semiconductor device of the first aspect, the silicon carbide layer further comprises a back surface opposite to the surface, and the semiconductor device of the third aspect further comprises: a semi-insulation substrate formed on the back surface of the silicon carbide layer; and a metal layer formed on a surface of the semi-insulation substrate.
The present invention is also directed to a module device. According to a fourth aspect of the present invention, the module device comprises: a conducting board; the semiconductor device as defined in the third aspect having the metal layer formed on a surface of the conducting board with a solder layer interposed therebetween; and an encapsulating container for encapsulating the conducting board and the semiconductor device, and in the module device of the fourth aspect, only the semiconductor device is formed on the surface of the conducting board.
The present invention is still directed to a semiconductor device. According to a fifth aspect of the present invention, the semiconductor device comprises: a silicon carbide layer of predetermined conductivity type; and a Schottky barrier electrode having a Schottky contact with a predetermined region on a surface of the silicon carbide layer, and in the semiconductor device of the fifth aspect, the Schottky barrier electrode has a thickness of not less than 5 &mgr;m.
According to a sixth aspect of the present invention, the semiconductor device comprises: a silicon carbide layer of predetermined conductivity type; a plurality of electrodes formed on a surface of the silicon carbide layer; and a substrate being brought into electrical contact with at least one electrode out of the plurality of electrodes by an external pressure, and in the semiconductor device of the sixth aspect, the substrate is basically made of any one of carb
Ishizawa Shinichi
Satoh Katsumi
Mitsubishi Denki & Kabushiki Kaisha
Soward Ida M.
Zarabian Amir
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