Active solid-state devices (e.g. – transistors – solid-state diode – Schottky barrier
Reexamination Certificate
2002-10-11
2004-03-23
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Schottky barrier
C257S475000, C257S508000, C257S596000, C257S154000, C257S168000
Reexamination Certificate
active
06710418
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates in general to semiconductor technology and in particular to improved Schottky rectifier structures and methods of manufacturing the same.
Silicon-based power rectifiers are well known and have been used in power electronic systems for many decades. Silicon Schottky rectifiers have generally been used in applications operating at mid to low voltages due to their lower on-state voltage drop and faster switching speed. A conventional planar Schottky rectifier structure is shown in
FIG. 1A. A
top metal electrode forms a Schottky contact with the underlying semiconductor region
106
. The traditional method of optimizing this rectifier changes the Schottky contact metal to alter the barrier height. Although the on-state voltage drop can be reduced by decreasing the barrier height, the reverse leakage current increases exponentially leading to unstable operation at high temperatures. Attempts to improve upon this tradeoff between on-state and reverse blocking power losses has led to the development of the junction barrier controlled Schottky (JBS) structure shown in FIG.
1
B.
In
FIG. 1B
, closely-spaced p-type regions
114
are formed in n-type region
112
. A top metal electrode
113
forms a Schottky contact with the surface area of n-type region
112
between p-type regions
114
, and forms an ohmic contact with p-type regions
114
. The pn junction formed by p-type regions
114
and n-type region
112
forms a potential barrier below the Schottky contact, resulting in a lower electric field at the metal-semiconductor interface. The resulting suppression of the barrier height lowering responsible for the poor reverse leakage in these devices allowed some improvements in the power loss tradeoff. However, the Schottky contact area through which the on-state current flows is reduced due the lateral diffusion of p-type regions
114
, and the series resistance is increased by current constriction between the junctions.
Further performance improvements have been obtained by the incorporation of a trench MOS region under the Schottky contact to create the trench MOS-barrier Schottky (TMBS) rectifier structure shown in FIG.
1
C. The MOS structure greatly reduces the electric field under the Schottky contact while enabling the support of voltages far in excess of the parallel-plane breakdown voltage in mesa region
119
. This allows optimizing mesa region
119
to have a higher diping concentration thus reducing the rectifier's on state voltage drop A further improvement in the electric field distribution under the Schottky contact has been obtained by using a graded doping profile in the mesa region.
It has been observed however, that the TMBS structure suffers from high leakage due to phosphorous segregation at the oxide-silicon interface. The increased phosphorous concentration reduces the accumulation threshold on the mesa sidewalls and increases the leakage current. Further, the TMBS and JBS structures have higher capacitance due to the presence of MOS structures
118
in the TMBS structure and the presence of p-type regions
114
in the JBS structure.
Thus, Schottky rectifiers having a low forward voltage, high reverse breakdown voltage, and low capacitance which do not suffer from high leakage are desirable.
BRIEF SUMMARY OF THE INVENTION
In accordance with an embodiment of the present invention, a semiconductor rectifier includes an insulation-filled trench formed in a semiconductor region. Strips of resistive material extend along the trench sidewalls. The strips of resistive material have a conductivity type opposite that of the semiconductor region. A conductor extends over and in contact with the semiconductor region so that the conductor and the underlying semiconductor region form a Schottky contact.
In one embodiment, the semiconductor region is formed over a substrate, and the substrate and the semiconductor region have the same conductivity type.
In another embodiment, the strips of resistive material are discontinuous along the bottom of the insulation-filled trench.
In another embodiment, the strips of resistive material comprise doped silicon material.
In another embodiment, the conductor is in contact with the strips of resistive material.
In another embodiment, the strips of resistive material comprise silicon material having a doping concentration of about four to five times greater than a doping concentration of the semiconductor region.
In accordance with another embodiment of the present invention, a semiconductor rectifier is formed as follows. A trench is formed in a semiconductor region. Strips of resistive material are formed along the trench sidewalls. The strips of resistive material have a conductivity type opposite that of the semiconductor region. The trench is substantially filled with insulating material. A conductor is formed over and in contact with the semiconductor region so that the conductor and the underlying semiconductor region form a Schottky contact.
In another embodiment, the semiconductor region is formed over a substrate, and the substrate and the semiconductor region have the same conductivity type.
In another embodiment, the strips of resistive material are discontinuous along the bottom of the trench.
In another embodiment, the strips of resistive material comprise silicon material having a doping concentration of about four to five times greater than a doping concentration of the semiconductor region.
The following detailed description and the accompanying drawings provide a better understanding of the nature and advantages of the present invention.
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Fairchild Semiconductor Corporation
Flynn Nathan J.
Forde Remmon R.
Townsend and Townsend / and Crew LLP
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