Edge termination for silicon power devices

Details Edge termination for silicon power devices Edge termination for silicon power devices

2002-12-20

2004-07-06

Cao, Phat X. (Department: 2814)

Active solid-state devices (e.g., transistors, solid-state diode

Field effect device

Having insulated electrode

C257S077000, C257S508000

Reexamination Certificate

active

06759719

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to silicon power semiconductor devices and, more particularly, to a silicon semiconductor die having an efficient and reliable edge termination zone.
BACKGROUND OF THE INVENTION
PN junctions within semiconductor devices are not infinite, terminating at the edge zones of a die. This edge effect limits the device breakdown voltage below the ideal value, V
brpp
, that is set by the infinite parallel plane junction. Care must be taken to ensure proper and efficient termination of the junction at the edge of the die; if the junction is poorly terminated, the device breakdown voltage can be as low as 10-20% of the ideal case. Such severe degradation in breakdown voltage can seriously compromise device design and lead to reduced current rating as well. In addition, an inefficient edge termination makes a device unstable and unreliable if the device is operated in a harsh environment or over a long period of time.
Various edge termination techniques have been developed, including, for example, field plate (FP), described in F. Conti and M. Conti, “Surface breakdown in silicon planar diodes equipped with field plate,”
Solid State Electronics
, Vol. 15, pp 93-105, the disclosure of which is incorporated herein by reference. Another edge termination approach is field limiting rings (FLR), described in Kao and Wolley, “High voltage planar p-n junctions,”
Proc. IEEE
, 1965, Vol. 55, pp 1409-1414, the disclosure of which is incorporated herein by reference. Further edge termination structures utilized variable lateral doping concentration (VLD), described in R. Stengl et al., “Variation of lateral doping as a field terminator for high-voltage power devices”,
IEEE Trans. Electron Devices
, 1986, Vol. ED-33, No. 3, pp 426-428, and junction termination extension (JTE), described in V. A. K. Temple, “Junction termination extension, a new technique for increasing avalanche breakdown voltage and controlling surface electric field in p-n junction,”
IEEE International Electron Devices Meeting Digest
, 1977 Abstract 20.4, pp 423-426, the disclosures of which are incorporated herein by reference.
The purpose of all these various techniques is to reduce electron-hole avalanche generation by lowering the peak electric field strength along the semiconductor surface and thereby shifting the avalanche breakdown location into the bulk of the device. To achieve this goal, the width of the edge termination zone (L
edge
) has to be several times higher than the depletion width (W
pp
) of the parallel-plane portion of the PN junction. For example, if L
edge
=2.98W
pp
, 98.7% of V
brpp
can be achieved when an “ideal edge termination,” as described in Drabe and Sittig, “Theoretical investigation of plane junction termination,”
Solid State Electronics
, 1996, Vol. 3, No. 3, pp 323-328, the disclosure of which is incorporated herein by reference, is used. In practice, a longer Ledge than the theoretical value should be used to guarantee device reliability. However, it is very important to point out that, even with very efficient edge termination, electron-hole impact generation at a rate of about 1×10
18
pairs/cm
3
.s, still exists along the semiconductor surface.
SUMMARY OF THE INVENTION
A silicon semiconductor die of the present invention comprises a heavily doped silicon substrate and an upper layer comprising doped silicon of a first conduction type disposed on the substrate. The upper layer comprises a well region of a second, opposite conduction type adjacent an edge termination zone that comprises a layer of a material having a higher critical electric field than silicon. Both the well region and adjacent edge termination zone are disposed at an upper surface of the upper layer, and an oxide layer overlies the upper layer and the edge termination zone.
Further in accordance with the present invention is a process for forming a silicon die having improved edge termination. The process comprises forming an upper layer comprising doped silicon of a first conduction type on a heavily doped silicon substrate, and forming an edge termination zone that comprises a layer of a material having a higher critical electric field than silicon at an upper surface of the upper layer. A well region of a second, opposite conduction type is formed at the upper surface of the upper layer adjacent the edge termination zone, and an oxide layer is formed over the upper layer and edge termination zone.


REFERENCES:
patent: 5914500 (1999-06-01), Bakowski et al.
patent: 6242784 (2001-06-01), Zeng et al.
patent: 2317054 (1998-03-01), None
patent: WO 9603774 (1996-02-01), None
Conti F et al., “Surface Breakdown in Silicon Planar Diodes Equipped with Field Plate”, Solid State Electron, vol. 15, pp. 93-105, 1972.
Drabe T et al., “Theoretical Investigation of Planar Junction Termination”, Solid State Electronics, Elsevier Science Publishers, Barking, GB, vol. 39, No. 3, pp. 323-328, 1996.
Kao Y. et al, “High Voltage Planer p-n Junctions”, Proc. IEEE, vol. 55, pp. 1409-1414, 1967.
Madapura S. et al, “Heteroepitaxial Growth of SiC on Si(100) and (111) by Chemical Vapor Deposition Using Trimethylsilane”; Electrochemical Society, Manchester, New Hampshire, US vol. 146, No. 3, pp. 1197-1202, 1999.
Stengl, R. et al., “Variation of Lateral Doping—A New Concept to Avoid High Voltage Breakdown of Planar Junctions”, International Electron Devices Meeting. Washington IEEE, Washington, Dec. 1-4, US, 1985.
Temple, VAK, “Junction Termination Extensions, A New Technique for Increasing Avalanche Breakdown Voltage and Controlling Surface Electric Field in p-n Junction”, IEEE International Electron Devices Meeting Digest, Abstract 20,4, pp. 423-426, 1977.

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