Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Charge transfer device
Reexamination Certificate
2000-09-22
2002-05-28
Abraham, Fetsum (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Charge transfer device
C257S244000, C257S513000, C257S520000, C257S397000, C257S332000, C257S329000, C257S510000
Reexamination Certificate
active
06396090
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to a semiconductor device, specifically, to a novel termination structure for trench MOS devices so as to prevent leakage current.
BACKGROUND OF THE INVENTION
Doubled diffused metal-oxide-semiconductor field effect transistor (DMOSFET), insulated gate bipolar transistor (IGBT), and Schottky diode are important power devices and use extensively as output rectifiers in switching-mode power supplies and in other high-speed power switching applications. For example, the applications include motor drives, switching of communication device, industry automation and electronic automation. The power devices are usually required carrying large forward current, high reverse-biased blocking voltage, such as above 30 volt, and minimizing the reverse-biased leakage current. There are several reports that trench DMOS, trench IGBT and trench Schottky diode are superior to those of with planar structure.
For power transistors are concerned, apart from the device in the active region for carrying large current, there is still required a termination structure design in the periphery of the active region usually at an edge of a die so as to prevent voltage breakdown phenomena from premature. Conventional termination structures include local oxidation of silicon (LOCOS), field plate, guard ring, or the combination thereof. The LOCOS is generally known to have bird beak characteristic. In the bird beak, electric field crowding phenomena is readily to occur, which is due to high impact ionization rate. As a result, leakage current is increased and electrical properties of the active region are deteriorated.
For example, please refer to
FIG. 1
, a semiconductor substrate with trench MOS structure for Schottky diodes, and a trench termination structure formed therein. The substrate is a heavily doped n+ substrate
10
and an epitaxial layer
20
formed thereon. A plurality of trench MOS
15
formed in the epitaxial layer
20
. The trench MOS devices including epitaxial layer
20
/gate oxide layer
25
/polysilicon layer
30
are formed in the active region
5
. The boundary of the active region
5
to the edge of the die is a LOCOS region of about 6000 Å in thick formed by conventional method.
For the purpose of lessening the electric field crowding issue, a p+-doping region
50
beneath LOCOS region is formed through ion implantation. The p+-doping region
50
is as a guard ring for reverse-biased blocking voltage enhancement. The anode (a metal layer)
55
is formed on the active region
5
and extends over p+ doping region
50
of LOCOS region. The object is to make the bending region of the depletion boundary far away from the active region
5
. Although guard ring
50
can alleviate the electrical field crowding and relax the bending magnitude occurred near the active region, the adjacent region between p+ region
50
and beneath the bottom of the trench MOS device, as arrow indicated denoted by
60
, is not a smooth curve. It will increase the leakage current and decrease the reverse-biased blocking capability. A similar situation occurred for field plate combines with guard ring. Furthermore, aforementioned prior art demanded more photo masks (at least four) to fabricate, and the processes are rather complicated. Still high cost for forming such structure is another inferior.
As forgoing several conventional termination structures can not solve the problems thoroughly. An object of the present invention thus proposes a novel termination structure. The new termination structure made the bending region of the depletion region far away from the active region, and depletion boundary is flatter than forgoing prior art. The manufacturing method provided by the present invention is even simpler than those prior arts. Since the termination structure and trench are formed simultaneously, it requires only three photo masks, low complicated processes and low cost.
SUMMARY OF THE INVENTION
The present invention discloses a novel termination structure, which can be formed with trench MOS devices simultaneously. The MOS devices can be Schottky diode, DMOS or IGBT depending on what kinds of the semiconductor substrate are prepared. The termination structure and trench MOS devices comprising: a semiconductor substrate having a plurality of first trenches spaced each other and formed in an active region and having a second trench formed from a boundary of the active region to an edge of the semiconductor substrate; a first-type MOS gate formed in each of the first trenches, and a second MOS gate formed on a sidewall of the second trench; a termination structure oxide layer formed in the second trench to cover a portion of the spacer-like MOS gate and to cover a bottom of the second trench; and a first electrode and a second electrode are, respectively, formed on a bottom surface and upper surface of the semiconductor substrate. The second electrode is located to cover the region from the active region through the spacer-like MOS gate and extended to a portion of the termination structure oxide layer so that a bending portion of the depletion region are distant from the active region.
REFERENCES:
patent: 5929482 (1999-07-01), Kawakami et al.
patent: 6020600 (2000-02-01), Miyajima et al.
patent: 6180966 (2002-01-01), Kohno et al.
Hsu Chih-Wei
Kao Ming-Che
Kung Pu-Ju
Liu Chung-Min
Tsai Ming-Jinn
Abraham Fetsum
Blakely , Sokoloff, Taylor & Zafman LLP
Industrial Technology Research Institute
LandOfFree
Trench MOS device and termination structure does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Trench MOS device and termination structure, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Trench MOS device and termination structure will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2875158