Super-junction semiconductor device

Details Super-junction semiconductor device Super-junction semiconductor device

2001-02-09

2004-04-20

Loke, Steven (Department: 2811)

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

Field effect device

Having insulated electrode

C257S339000, C257S342000, C257S490000

Reexamination Certificate

active

06724042

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to vertical power semiconductor devices that facilitate a high breakdown voltage and a high current capacity, such as MOSFET (insulated gate field effect transistors), IGBT (conductivity-modulation-type MOSFET), bipolar transistors and diodes. The present invention relates also to the method of manufacturing such semiconductor devices.
DESCRIPTION OF RELATED ART
Semiconductor devices may be roughly classified as lateral devices that arrange electrodes on a major surface, or vertical devices that distribute electrodes on both major surfaces facing opposite to each other. When a vertical semiconductor device is ON, a drift current flows in the thickness direction of the semiconductor chip (vertical direction). When the vertical semiconductor device is OFF, the depletion layers caused by applying a reverse bias voltage expand also in the vertical direction.
FIG. 28
is a cross sectional view of a conventional planar-type n-channel vertical MOSFET. Referring to
FIG. 28
, the vertical MOSFET includes an n
+
-type drain layer
11
with low electrical resistance, a drain electrode
18
in electrical contact with n
+
-type drain layer
11
, a highly resistive n
−
-type drain drift layer
12
on n
+
drain layer
11
, p-type base regions
13
formed selectively in the surface portion of n
−
-type drain drift layer
12
, a heavily doped n
+
-type source region
14
formed selectively in p-type base region
13
, a heavily doped p
+
-type contact region
19
formed selectively in p-type base region
13
, a gate insulation film
15
on the extended portion of p-type base region
13
extended between n
+
-type source region
14
and n-type drain drift layer
12
, a gate electrode layer
16
on gate insulation film
15
, and a source electrode
17
in electrical contact commonly with n
+
-type source regions
14
and p
+
-type contact regions
19
.
In the vertical semiconductor device shown in
FIG. 28
, highly resistive n
−
-type drain drift layer
12
works as a region for making a drift current flow vertically when the MOSFET is in the ON-state. In the OFF-state of the MOSFET, n-type drain drift layer
12
is depleted by the depletion layers expanding from the pn-junctions between drain drift layer
12
and p-type base regions
13
to obtain a high breakdown voltage. Thinning highly resistive n
−
-type drain drift layer
12
, that is shortening the drift current path, is effective for substantially reducing the on-resistance (resistance between the drain and the source) of the MOSFET, since the drift resistance is lowered in the ON-state of the device. However, when the drift current path in n
−
-type drain drift layer
12
is shortened, the space between the drain and the source, into that the depletion layers expand from the pn-junctions between p-type base regions
13
and n-type drain drift layer
12
in the OFF-state of the device, is narrowed and the electric field strength in the depletion layers soon reaches the maximum (critical) value for silicon. Therefore, breakdown is caused before the voltage between the drain and the source reaches the designed breakdown voltage of the device.
A high breakdown voltage is obtained by thickening n
−
-type drain drift layer
12
. However, a thick n
−
-type drain drift layer
12
inevitably causes high on-resistance and loss increase. In short, there exists a tradeoff relation between the on-resistance (current capacity) and the breakdown voltage of the MOSFET. The tradeoff relation exists in other semiconductor devices, such as IGBT, bipolar transistors and diodes, which include a drift layer.
European Patent 0 053 854, U.S. Pat. Nos. 5,216,275, 5,438,215, Japanese Unexamined Laid Open Patent Application H09(1997)-266311 and Japanese Unexamined Laid Open Patent Application H10(1998)-223896 disclose semiconductor devices, which include an alternating conductivity type drift layer formed of heavily doped vertical n-type regions and vertical p-type regions alternately laminated horizontally with each other.
FIG. 29
is a cross sectional view of the vertical MOSFET disclosed in U.S. Pat. No. 5,216,275. Referring to
FIG. 29
, the vertical MOSFET of
FIG. 29
is different from the vertical MOSFET of
FIG. 28
in that the vertical MOSFET of
FIG. 29
includes an alternating conductivity type drain drift layer
22
, that is not a single-layered one but formed of n drift current path regions
22
a
and p partition regions
22
b
alternately laminated horizontally with each other. Even when the impurity concentrations in the alternating conductivity type layer are high, the alternating conductivity type layer facilitates obtaining a high breakdown voltage, since depletion layers expand laterally from the pn-junctions extending vertically across the alternating conductivity type layer in the OFF-state of the device, completely depleting drain drift layer
22
.
Hereinafter, the semiconductor device including an alternating conductivity type drain drift layer will be referred to as the super-junction semiconductor device.
In the super-junction semiconductor device, a high breakdown voltage is obtained in the alternating conductivity type drain drift layer beneath p-type base regions
13
(an active region of the device) formed in the surface portion of the semiconductor chip. However, the electric field strength in the depletion layers soon reaches the maximum (critical) value for silicon in the circumferential region of the alternating conductivity type drain drift layer (the peripheral region of the device), since the depletion layers from the pn-junction between drain drift layer
22
and the outermost p-type base region
13
does not completely expand outward nor to the bottom of the semiconductor chip. Therefore, the local breakdown voltage in the peripheral region of drain drift layer
22
, that is the local breakdown voltage in the peripheral region of the device, is not high enough.
The conventional guard ring formed for controlling the depletion electric field on the peripheral surface portion of the device or the conventional field plate structure formed for controlling the depletion electric field on the insulation film may be used to obtain a high local breakdown voltage in the peripheral region of the device adjacent to the outermost p-type base region
13
. It is difficult, however, to optimize the integral structure integrating the alternating conductivity type drain drift layer
22
for obtaining a higher breakdown voltage and the conventional guard ring or the conventional field plate for obtaining a certain local breakdown voltage in the peripheral region of the device. In other words, it is difficult to correct the depletion electric field by an external means added from outside such as the integral structures described above. The reliability of semiconductor device having such an external means for correcting depletion electric field is not high. Since the deep portion of the device spaced apart from the guard ring is not depleted, the local breakdown voltage in the peripheral region of the device is not so high as the breakdown voltage in the drain drift layer
22
. Therefore, the conventional guard ring or the conventional field plate is not effective to provide the entire device structure with a high breakdown voltage nor to fully utilize the functions of the alternating conductivity type drain drift layer. It is also necessary to employ the steps of forming masks for realizing the integral structure, implanting impurity, driving the implanted impurity atoms, depositing metal films, patterning the deposited metal films and such additional steps for manufacturing the super-junction semiconductor device.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a super-junction semiconductor device that facilitates providing the peripheral region thereof with a breakdown voltage higher than the breakdown voltage in the drain drift layer without employing a guard ring or field plate

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