Active solid-state devices (e.g. – transistors – solid-state diode – Specified wide band gap semiconductor material other than... – Diamond or silicon carbide
Reexamination Certificate
2001-09-12
2004-08-03
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Specified wide band gap semiconductor material other than...
Diamond or silicon carbide
C257S107000, C257S113000, C257S114000
Reexamination Certificate
active
06770911
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to microelectronic devices and fabrication methods therefor, and more particularly to two electrical terminal silicon carbide devices, such as light activated silicon carbide thyristors, and manufacturing methods therefor.
BACKGROUND OF THE INVENTION
Silicon carbide thyristors are described, for example, in U.S. Pat. No. 5,539,217 (the '217 patent) the disclosure of which is incorporated herein by reference as if set forth fully. The thyristors described in the '217 patent are three terminal devices having a gate and one of an anode or a cathode on a first side of the device and the other of the anode and the cathode on the opposite side of the device. Such silicon carbide thyristors may exhibit improved power handling capabilities over similar silicon thyristors.
Light-activated thyristors having an integrated light source and a silicon carbide active layer have been described in U.S. Pat. No. 5,663,580. Such devices may include four terminal devices and include anode and cathode terminals for a light emitting diode which acts to trigger a thyristor having its own anode and cathode terminals.
Silicon thyristors which are light activated have been utilized in high power applications. For example, optically triggered parallel lateral thyristors are described in U.S. Pat. No. 4,779,126.
While silicon carbide thyristors may provide improved power handling capabilities over comparably sized silicon devices, it may be difficult to create large scale thyristors in silicon carbide. For example, in silicon a single thyristor may be made on a wafer such that the thyristor is substantially the same size as the wafer. However, manufacturing defect free silicon carbide wafers may be difficult, if not impossible. Thus, a device which consumes an entire wafer may have defects incorporated into the device which may limit its performance.
SUMMARY OF THE INVENTION
Embodiments of the present invention provide light-activated silicon carbide thyristors and methods of fabricating light-activated silicon carbide thyristors. In particular embodiments of the present invention, a first layer of silicon carbide having a second conductivity type is provided on a silicon carbide substrate having a first conductivity type. A first region of silicon carbide having the first conductivity type is provided on the first layer of silicon carbide opposite the substrate. A second region of silicon carbide having the second conductivity type is provided on the first region of silicon carbide opposite the first layer of silicon carbide and is configured to expose a portion of the first region of silicon carbide to light from a light source external to the silicon carbide thyristor so as to provide a light-activated gate region. A first electrode is provided on the second region of silicon carbide and a second electrode is provided on the silicon carbide substrate.
In further embodiments of the present invention, a second layer of silicon carbide is disposed between the silicon carbide substrate and the first layer of silicon carbide. The second layer of silicon carbide has the first conductivity type.
In additional embodiments of the present invention, a second layer of silicon carbide is disposed between the silicon carbide substrate and the first layer of silicon carbide. The second layer of silicon carbide is of the second conductivity type and has a carrier concentration greater than a carrier concentration of the first layer of silicon carbide.
In particular embodiments of the present invention, the first region of silicon carbide forms a mesa. In such embodiments, a third region of first conductivity type silicon carbide may be provided in the first layer of silicon carbide outside of the mesa formed by the first region of silicon carbide so as to provide a junction termination extension.
In still further embodiments of the present invention, a third region of silicon carbide having the first conductivity type is provided in the exposed portion of the first region of silicon carbide. Such a third region of silicon carbide may have a carrier concentration greater than a carrier concentration of the first region of silicon carbide.
Furthermore, the second region of silicon carbide may be configured to expose a pinwheel-shaped portion of the first region of silicon carbide to light from a light source external to the silicon carbide thyristor so as to provide a light-activated gate region having a pinwheel configuration. Alternatively, the second region of silicon carbide may be a plurality of fingers configured to expose a corresponding plurality of finger portions of the first region of silicon carbide to light from a light source external to the silicon carbide thyristor so as to provide a light-activated gate region interdigited with the second region of silicon carbide.
In further embodiments of the present invention, a silicon carbide thyristor, is provided having a silicon carbide substrate having a first conductivity type and a first layer of silicon carbide on the silicon carbide substrate and having a second conductivity type. A first region of silicon carbide having the first conductivity type is provided on the first layer of silicon carbide opposite the substrate. A second region of silicon carbide having the second conductivity type is also provided on the first region opposite the first layer. The first and second regions of silicon carbide are configured to expose a portion of the first layer of silicon carbide to light from a light source external to the silicon carbide thyristor so as to provide a light-activated gate region. A first electrode is provided on the second region of silicon carbide and a second electrode is also provided on the silicon carbide substrate.
In additional embodiments of the present invention, a second layer of silicon carbide is disposed between the silicon carbide substrate and the first layer of silicon carbide and having the first conductivity type. Furthermore, a third region of silicon carbide having the second conductivity type may be provided in the exposed portion of the first layer of silicon carbide and may have a carrier concentration greater than a carrier concentration of the first layer of silicon carbide.
In still further embodiments of the present invention, the first and second regions of silicon carbide are configured to expose a pinwheel-shaped portion of the first layer of silicon carbide to light from a light source external to the silicon carbide thyristor so as to provide a light-activated gate region having a pinwheel configuration. Alternatively, the first and second regions of silicon carbide may be a plurality of fingers configured to expose a corresponding plurality of finger portions of the first layer of silicon carbide to light from a light source external to the silicon carbide thyristor so as to provide a light-activated gate region interdigited with the first and second regions of silicon carbide.
In certain embodiments of the present invention, in the first conductivity type is n-type conductivity silicon carbide and the second conductivity type is p-type conductivity silicon carbide. In other embodiments of the present invention, the first conductivity type is p-type conductivity silicon carbide and the second conductivity type is n-type conductivity silicon carbide.
In additional embodiments of the present invention, a light-activated silicon carbide thyristor is provided by a plurality of light-activated silicon carbide thyristor cells on at least a portion of a silicon carbide wafer, the light-activated silicon carbide thyristor cells having corresponding gate regions at a first face of the silicon carbide wafer that are configured to be exposed to light from a light source external to the thyristor cells and first contacts on the first face of the silicon carbide wafer and a second contact on a second face of the silicon carbide wafer opposite the first face. A connecting plate electrically connects the first contacts of ones of the plurality of silicon carbide thyristor c
Agarwal Anant
Palmour John W.
Ryu Sei-Hyung
Cree Inc.
Flynn Nathan J.
Mondt Johannes
Myers Bigel Sibley & Sajovec P.A.
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