Semiconductor device manufacturing: process – Forming schottky junction
Reexamination Certificate
1999-05-17
2001-02-20
Chaudhuri, Olik (Department: 2814)
Semiconductor device manufacturing: process
Forming schottky junction
C438S092000
Reexamination Certificate
active
06191015
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a Schottky diode assembly including a Schottky contact formed on a semiconductor substrate and having a semiconductor region of a first conductivity type, a metal layer disposed adjacently on the semiconductor region, a protective structure constructed on a peripheral region of the Schottky contact, and a doped region constructed in the semiconductor substrate and having a second conductivity type of opposite polarity from the first conductivity type, the doped region extending from a main surface of the semiconductor substrate to a predetermined depth into the semiconductor substrate. The invention also relates to a method for producing such a Schottky diode assembly.
In order to improve the depletion properties of a Schottky diode, it is known to diffuse a guard ring, of opposite conductivity to the semiconductor region of the diode, at the peripheral region of the metal-to-substrate junction. That produces a graduated p-n junction at the diode edge, so that leakage currents can be reduced. In the case of an n-doped silicon epitaxial layer for the diode semiconductor region, the guard ring is p-type conductivity. As a result of that provision it is possible to successfully adjust the depletion currents of a Schottky diode uniformly over the production of the diode and at the lowest level for a particular diode type. In order to optimize the breakdown voltage for a predetermined diode type, the doping of the guard ring should be as low as possible and diffused as deeply as possible, yet should be located above the level of the epitaxial doping so that the p-n junction is effective. However, low doping of the guard ring at the boundary surface with the dielectric disposed adjacent the metal-to-substrate contact increases the danger of channeling at that boundary surface, which results in an increase in the depletion current of the diode and the capacitance.
Summary of the Invention
It is accordingly an object of the invention to provide a Schottky diode assembly and a production method, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and which improve a guard ring in a Schottky diode in such a way that the breakdown behavior of the diode is improved and at the same time the danger of channeling at a boundary surface with the dielectric of the guard ring can be effectively prevented.
With the foregoing and other objects in view there is provided, in accordance with the invention, a Schottky diode assembly, comprising a semiconductor substrate having a main surface, a semiconductor region of a first conductivity type and a metal layer disposed adjacently on the semiconductor region; and a Schottky contact disposed on the semiconductor substrate; the Schottky contact having a peripheral region, a protective structure on the peripheral region, the protective structure having a doped region in the semiconductor substrate with a second conductivity type of opposite polarity from the first conductivity type, the doped region extending from the main surface to a predetermined depth into the semiconductor substrate, the doped region having at least two different first and second doped portions disposed one below the other relative to the main surface, the first doped portion having a greater depth and a comparatively lesser doping, and the second doped portion having a comparatively higher doping and a lesser depth adjacent the main surface.
In accordance with another feature of the invention, the first doped portion is constructed by implantation of a dopant with a comparatively low implantation dose and deep diffusion, and the second doped portion is constructed by implantation of a dopant with a comparatively high implantation dose and shallow diffusion.
The invention contemplates at least a double implantation of the guard ring. A first implantation with a low dose but deep diffusion assures good breakdown behavior of the diode, while an ensuing second implantation with a high dose but shallow diffusion suppresses the danger of the development of a channel in the guard ring. Such channel development (known as “channeling”) is undesirable, since it leads to unfavorable yields as well as unstable tendencies of the diode. The high and simultaneously shallow doping in the depletion situation of the diode results in a lowering of the peak field intensity and thus overall a higher breakdown voltage of the diode. This doping is adjusted in such a way that the breakdown voltage in the guard ring is higher than in the actual Schottky diode, so that the breakdown voltage overall is determined solely by the Schottky diode.
In accordance with a further feature of the invention, the first doped portion extends to a depth of approximately one-third of the total depth of the semiconductor region of the first conductivity type, and the second doped portion extends from the main surface of the semiconductor substrate to a depth of one-fifth to one-tenth of the total thickness of the semiconductor region of the first conductivity type.
In accordance with an added feature of the invention, the total thickness of the semiconductor region of the first conductivity type is approximately 4-8 &mgr;m, the first doped portion extends to a depth of approximately 1-3 &mgr;m and the second doped portion extends to a depth of approximately 1 &mgr;m into the semiconductor substrate.
In accordance with an additional feature of the invention, the second doped portion at the main surface of the semiconductor substrate has a maximum doping of approximately 10
19
N·cm
−3
, and the first doped portion in a depth adjacent the second doped portion has a maximum doping of approximately 10
17
N·cm
−3
.
In accordance with yet another feature of the invention, the maximum doping of the second doped portion is greater by a factor of 100 than the maximum doping of the first doped portion.
In accordance with yet a further feature of the invention, the Schottky contact is radially symmetrical, and the protective structure on the peripheral region of the Schottky contact forms a guard ring.
In accordance with yet an added feature of the invention, the semiconductor substrate has silicon, and the semiconductor region is of the first conductivity type of the Schottky contact and represents an n-type conductivty epitaxial layer.
In accordance with yet an additional feature of the invention, the doped region of the protective structure is constructed by implantation of boron.
In accordance with again another feature of the invention, the Schottky contact has a breakdown voltage of approximately between 50 and 70 V.
With the objects of the invention in view, there is also provided a method for producing a Schottky diode assembly, which comprises forming a semiconductor substrate with a main surface, a semiconductor region having a first conductivity type and a metal layer disposed adjacently on the semiconductor region; forming a Schottky contact on the semiconductor substrate by providing the Schottky contact with a peripheral region, a protective structure on the peripheral region, and a doped region of the protective structure having a second conductivity type of opposite polarity from the first conductivity type and extending from the main surface to a predetermined depth into the semiconductor substrate; and forming the doped region with at least two different first and second doped portions disposed one below the other relative to the main surface by constructing the first doped portion at a greater depth and with a comparatively lesser doping and constructing the second doped portion with a comparatively higher doping and a lesser depth adjacent the main surface.
In accordance with another mode of the invention, there is provided a method which comprises forming the first doped portion by implantation of a dopant with a comparatively low implantation dose and deep diffusion, and forming the second doped portion by implantation of a dopant with a comparatively high im
Losehand Reinhard
Werthmann Hubert
Chaudhuri Olik
Greenberg Laurence A.
Lerner Herbert L.
Pham Hoai
Siemens Aktiengesellschaft
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