Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Junction field effect transistor
Reexamination Certificate
1999-11-19
2001-05-01
Bowers, Charles (Department: 2813)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Junction field effect transistor
C257S284000, C257S282000, C257S283000
Reexamination Certificate
active
06225653
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to semiconductor components with at least one highly-doped diode, in particular with a Zener diode or a tunnel diode and at least one Schottky diode connected to it in parallel, having a low-doped epitaxial layer of the same type of doping on a highly-doped substrate of the first type of doping, with a zone of a second type of doping being diffused into the epitaxial layer and with a Schottky junction being formed between the epitaxial layer and a Schottky metal on the side of the epitaxial layer facing away from the substrate. In addition, this invention relates to methods of manufacturing such semiconductor components.
Zener diodes of the usual design have a high power loss because of the comparatively high voltage drop in the direction of flow. With so-called double Zener diodes implemented in the form of antiparallel pn junctions, the forward voltage of the other diode is added to the Zener voltage of the one diode. The forward voltage is subject to greater process fluctuations because of the bulk resistance, so that corresponding manufacturing tolerances also occur accordingly.
Japanese published patent application (kokai) JP 8-107 222 A describes a semiconductor component with a Zener diode, having a low-doped epitaxial layer of the same type of doping (N−) on a highly-doped substrate of a first type of doping (N+), with a zone of a second type of doping (P) being diffused into the epitaxial layer, and with a Schottky junction being formed between the epitaxial layer and a Schottky metal on the side of the epitaxial layer facing the substrate.
The layer structure of this semiconductor component is comparatively complicated, and accordingly, many diffusion processes and lithography steps are required, making manufacture of such components expensive. Thus, two metallizations are required for the Schottky junction and the Zener junction. In addition, guard rings around the Schottky junction must be produced in separate steps. Due to the position of the Zener junction within the epitaxial layer and the outer terminal contacting the substrate, the diode current flows through the epitaxial layer, which is a comparatively poor conductor, so there is an increased differential Zener resistance.
Japanese published patent application (kokai) JP 62-165 978 A describes a semiconductor component having a diffused area on a substrate with a Schottky junction there. Opposite types of conduction and double-diffused areas are arranged on the periphery of the Schottky electrode, and an ohmic electrode is provided in the outer area. A Zener diode is formed by the double-diffused areas. This design yields, on the one hand, a Schottky diode having a very short switching time and, on the other hand, a Zener diode connected in parallel, its Zener voltage being of a size such that the Schottky diode, which is sensitive to overvoltage in the reverse direction, is protected from voltage peaks.
The Zener junction formed by the double-diffused areas extends approximately at a right angle to the top side of the arrangement. Therefore, the diffusion concentration decreases uniformly for both areas from the surface toward the inside. Due to this concentration gradient, only a very narrow area near the surface is effective for the Zener junction, so that the Zener diode has only a very low current carrying capacity. Due to the asymmetrical layer arrangement, two photo-lithography steps are required, thus increasing the cost. In addition, two terminals are arranged side by side, resulting in a poor utilization of space by the semiconductor arrangement.
SUMMARY OF THE INVENTION
An object of the present invention is to create a semiconductor component with a Zener diode having improved electrical properties and, in particular, a low forward voltage and a reduced temperature coefficient, if necessary. In addition, a manufacturing method for such semiconductor components should be feasible at a low cost.
To achieve this object, it is proposed first with regard to the device that the zone of the second type of doping should be a highly-doped zone extending all the way to the substrate in the area of the interface between the substrate and the epitaxial layer to form a pn Zener junction, and the Schottky metal should cover the diffused zone at least partially.
By the Schottky junction, a Schottky diode is connected in parallel to the Zener diode and receives the current flow in the forward direction of the Zener diode. There is only a low voltage drop at the Schottky diode and, accordingly, also a low power loss. With this semiconductor component especially good electrical properties are achieved despite the very simple design. This is also true, in particular, of the current carrying capacity and the volume resistance, because on the one hand, the Zener junction can be adapted to the required current carrying capacity with no problem, and because furthermore, there are no layers to increase resistance in the current path. This also contributes to a low power loss.
A first method of producing such a semiconductor component provides for a low-doped epitaxial layer of the same type of doping to be applied to a highly-doped substrate of a first type of doping; then a highly-doped zone of a second type of doping is diffused into the epitaxial layer and extends as far as the substrate layer to form a pn Zener junction in the vicinity of the interface between the substrate and the epitaxial layer; and a Schottky metal at least partially covering the area of the diffused zone is applied to the side of the epitaxial layer facing away from the substrate to form a Schottky junction between the epitaxial layer and the Schottky metal.
This method can be carried out with a few lithography steps and diffusion processes. In particular, only a single metallization is necessary, and at the same time a guard ring for the Schottky junction is formed on diffusion of the highly-doped zone into the epitaxial layer to form the pn Zener junction, so that no separate process step is required for this. Thus, on the whole, the manufacturing cost can be reduced by approximately one-half in comparison with previous methods of producing such semiconductor components.
According to a second embodiment, which is independently worthy of protection, it is provided that a low-doped epitaxial layer of the same type of doping is applied to a highly-doped substrate of a first type of doping; then a highly-doped layer of a second type of doping is introduced into some areas of the highly-doped substrate of the first type of doping to form a pn Zener junction; a low-doped diffused area of the second type of doping extends from this highly-doped layer in the substrate into the epitaxial layer, as far as the surface of the epitaxial layer; and the Schottky metal at least partially covers the low-doped diffused area, forming another Schottky junction between this area and the Schottky metal and the Schottky junction between the Schottky metal and the epitaxial layer.
In this embodiment, a Zener diode with a low temperature coefficient is formed by the series connection of oppositely polarized Zener diode and Schottky diode, if the Zener diode has a positive temperature coefficient, which is the case at approximately 5.6 volt. In addition, a low forward voltage is achieved through the Schottky diode, which is connected in parallel to the series connection of the Zener diode and the first Schottky diode and is polarized in the forward direction of the Zener diode.
According to a refinement of the invention, there is also the possibility of the layer structures according to either of the above embodiments being applied side by side to a common substrate.
Combination with the features of the first embodiment above yields arrangements connected in antiparallel, with the two antiparallel-connected branches each having a Zener diode and a Schottky diode connected in parallel.
Combination with the features of the second embodiment above yields antiparallel-connected arrangements with a Zener diode a
Igel Gunter
Krumrey Joachim
Akin Gump Strauss Hauer & Feld L.L.P.
Bowers Charles
Micronas GmbH
Schillinger Laura M
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