Active solid-state devices (e.g. – transistors – solid-state diode – Schottky barrier – With means to prevent edge breakdown
Reexamination Certificate
2001-03-28
2003-06-24
Eckert, George (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Schottky barrier
With means to prevent edge breakdown
C257S471000, C257S481000, C257S483000
Reexamination Certificate
active
06583485
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a semiconductor device provided with a semiconductor substrate with a dopant of a first doping type with a doping concentration n
1
on which an epitaxial layer with a dopant of a first doping type with a doping concentration n
2
is provided, whereon an insulator layer with an opening is deposited, with a Schottky metal layer covering the epitaxial layer lying below said opening, with an annular semiconductor region lying in the epitaxial layer and comprising a dopant of a second doping type with a doping concentration n
3
which adjoins the insulating layer and the Schottky metal layer in a region surrounding the metal-insulator transition, and to a method of manufacturing such a semiconductor device.
BACKGROUND OF THE INVENTION
Schottky diodes are semiconductor devices which have a metal-semiconductor transition as their basic structure and whose basic electronic properties are defined by this transition. A Schottky diode is formed from a semiconductor-metal combination which is chosen such that a depletion zone arises at the boundary surface. The current-voltage characteristic of this arrangement depends on the polarity of the applied voltage.
Although the operating principle of the metal-semiconductor transition in a Schottky diode differs essentially from that of a pn junction, the characteristic curves of a pn diode and a Schottky diode are similar. Compared with a pn diode, a Schottky diode has a lower threshold voltage and a substantially smaller, but strongly temperature-dependent saturation current. In addition, a Schottky diode has a barrier layer capacitance and no diffusion capacitance, which results in shorter switching times. Furthermore, the breakdown characteristic in the blocked state is partly very marked, so that the achievable breakdown voltages are considerably lower than in the case of pn diodes.
To improve and indeed achieve a defined breakdown behavior of a Schottky diode, DE 197 05 728 A1 describes a guard ring of a second doping tape which is diffused into the epitaxial layer of a first doping type. This guard ring achieves that the reverse bias voltage, which is low in the case of a normal Schottky diode, is substantially increased in comparison therewith. This effect is achieved in that the gradient of the field lines of the edge field of the metal electrode, i.e. the Schottky metal layer, is linearized through the fact that it ends at least partly in the ring-shaped semiconductor region of the second doping type.
The properties of a semiconductor device laid down in a specification are determined by the materials used, the design of the semiconductor device, and the doping profiles.
After a semiconductor device has been manufactured, a wide variety of, for example, growing, implantation, and diffusion processes may be carried out. The design of a semiconductor device is defined by a set of masks which depends on the specification. Each additional manufacturing step or masking step, however, is very expensive because it increases the processing time of the wafers in manufacture and leads to a higher personnel and machine expenditure.
SUMMARY OF THE INVENTION
The invention has for its object to provide an improved semiconductor device which can be manufactured with simple processes and the lowest possible number of process steps.
This object is achieved by means of a semiconductor device provided with a semiconductor substrate with a dopant of a first doping type with a doping concentration n
1
on which an epitaxial layer with a dopant of a first doping type with a doping concentration n
2
is provided, whereon an insulator layer with an opening is deposited, with a Schottky metal layer covering the epitaxial layer lying below said opening, with an annular semiconductor region lying in the epitaxial layer and comprising a dopant of a second doping type with a doping concentration n
3
which adjoins the insulating layer and the Schottky metal layer in a region surrounding the metal-insulator transition, with a doping region present in the epitaxial layer and comprising a dopant of a first doping type with a doping concentration n
4
and the dopant of a second doping type with a doping concentration n
3
along the outer contour of the semiconductor device, and with an oxide layer which is present on the epitaxial layer, which adjoins the insulating layer, and which extends along the outer contour of the semiconductor device.
Such a semiconductor device comprises not only a guard ring but also a doping region along the outer contour of the diode. This doping region, also referred to as channel, is advantageous in preventing so-called channel currents. These channel currents flow between the guard ring and the separation lane, when the semiconductor device is biased in reverse direction.
A further advantageous embodiment is formed by the oxide layer along the outer contour of the diode. The outer contour at the same time represents the separation lane which delimits the individual semiconductor devices on the wafer. The oxide layer in the separation lane prevents the crystal from showing excessive fractures at the edge and being damaged during sawing.
It is preferred that the doping concentrations n
1
and n
4
are higher than the doping concentration n
2
.
It is furthermore preferred that the doping concentration n
4
is higher than the doping concentration n
3
.
A doping region, the channel, is obtained in the epitaxial layer which prevents a breakdown of the semiconductor device at low voltages already, thanks to the different doping concentrations.
It is preferred that the material for the semiconductor substrate and the epitaxial layer comprises silicon.
Silicon has higher admissible operational temperatures than other semiconductor materials such as, for example, germanium.
It is furthermore preferred that the dopant of the first doping type is chosen from the group comprising P, As, and Sb.
It is furthermore preferred that the dopant of the second doping type is chosen from the group comprising B, Al, and Ga.
The different doping profiles render possible the manufacture of a wide range of semiconductor devices with non-linear current-voltage characteristics.
It is advantageous when the insulating layer and the oxide layer comprise SiO
2
.
SiO
2
has a high chemical resistance, a low thermal conductivity, and a high coefficient of thermal expansion.
It is preferred that the Schottky metal layer comprises a material chosen from the group Al, Mo, W, Pt, Pd, Ag, Au, Ti, Ni, NiFe, and combinations of these materials.
Mo, W, Pt, Pd, Ag, Au, Ni, and Ti are metals with a high work function which do not diffuse into the semiconductor material. Although aluminum is not a metal with a high work function, it does present advantages as a Schottky metal layer at high voltages.
It is preferred that a protective layer is provided on the insulating layer and the oxide layer.
The protective layer protects the subjacent layers against mechanical loads and corrosion by moisture.
It is particularly preferred that the semiconductor device is a Schottky diode.
The semiconductor device is a so-called Schottky hybrid diode, because it has a guard ring.
The invention further relates to a method of manufacturing a semiconductor device provided with a semiconductor substrate with a dopant of a first doping type with a doping concentration n
1
on which an epitaxial layer with a dopant of a first doping type with a doping concentration n
2
is provided, whereon an insulator layer with an opening is deposited, with a Schottky metal layer covering the epitaxial layer lying below said opening, with an annular semiconductor region lying in the epitaxial layer and comprising a dopant of a second doping type with a doping concentration n
3
which adjoins the insulating layer and the Schottky metal layer in a region surrounding the metal-insulator transition, which method comprises at least the steps of:
generating an epitaxial layer with a dopant of a first doping type with a doping concentration n
2
on a semiconductor substrate
Biren Steven R.
Eckert George
Koninklijke Philips Electronics , N.V.
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