U.S. patent application number 11/732955 was filed with the patent office on 2008-10-09 for trenched mosfets with embedded schottky in the same cell.
This patent application is currently assigned to Force-MOS Technology Corporation. Invention is credited to Fwu-Iuan Hshieh.
Application Number | 20080246082 11/732955 |
Document ID | / |
Family ID | 39826198 |
Filed Date | 2008-10-09 |
United States Patent
Application |
20080246082 |
Kind Code |
A1 |
Hshieh; Fwu-Iuan |
October 9, 2008 |
Trenched mosfets with embedded schottky in the same cell
Abstract
A semiconductor power device includes trenched semiconductor
power device comprising a trenched gate surrounded by a source
region encompassed in a body region above a drain region disposed
on a bottom surface of a substrate. The semiconductor power device
further includes an insulation layer covering the trenched
semiconductor power device with a source-body contact trench opened
therethrough the source and body regions and extending into an
epitaxial layer below the body regions and filled with contact
metal plug therein. The semiconductor power device further includes
an embedded Schottky diode disposed near a bottom of the
source-body contact trench below the contact metal plug wherein the
Schottky diode further includes a Schottky barrier layer having a
barrier height for reducing a leakage current through the embedded
Schottky diode during a reverse bias between the drain and the
source.
Inventors: |
Hshieh; Fwu-Iuan; (Saratoga,
CA) |
Correspondence
Address: |
Bo-In Lin
13445 Mandoli Drive
Los Altos Hills
CA
94022
US
|
Assignee: |
Force-MOS Technology
Corporation
|
Family ID: |
39826198 |
Appl. No.: |
11/732955 |
Filed: |
April 4, 2007 |
Current U.S.
Class: |
257/333 ;
257/E21.345; 257/E21.41; 257/E29.121; 257/E29.133; 257/E29.146;
257/E29.148; 257/E29.262; 438/270 |
Current CPC
Class: |
H01L 21/26586 20130101;
H01L 29/41766 20130101; H01L 29/7813 20130101; H01L 29/456
20130101; H01L 29/66727 20130101; H01L 29/66734 20130101; H01L
29/0878 20130101; H01L 29/1095 20130101; H01L 29/7806 20130101;
H01L 29/47 20130101; H01L 29/42368 20130101 |
Class at
Publication: |
257/333 ;
438/270; 257/E29.262; 257/E21.41 |
International
Class: |
H01L 29/78 20060101
H01L029/78; H01L 21/336 20060101 H01L021/336 |
Claims
1. A trenched semiconductor power device comprising a trenched gate
surrounded by a source region encompassed in a body region above a
drain region disposed on a bottom surface of a substrate, wherein
said semiconductor power device further comprising: an insulation
layer covering said trenched semiconductor power device with a
source-body contact trench opened therethrough and further
extending through said body region into an epitaxial region
underneath and filled with contact metal plug therein; and an
embedded Schottky diode disposed near a bottom of said source-body
contact trench below said contact metal plug wherein said Schottky
diode further comprising a Schottky barrier layer directly
contacting an epitaxial layer below a bottom of said contact trench
thus forming a vertical Schottky diode along a source-drain
direction having a barrier height for reducing a leakage current
through said embedded Schottky diode during a reverse bias between
said drain and said source.
2. The trenched semiconductor power device of claim 1 further
comprising: a contact enhancement dopant region disposed along
sidewalls of said source-body contact trench for improving an
electrical contact of said contact metal plug and to said body
regions.
3. The trenched semiconductor power device of claim 1 wherein: said
embedded Schottky diode further comprising a CoSi2/TiN barrier
layer disposed below said contact metal plug directly contacting
said epitaxial layer below said contact trench.
4. The trenched semiconductor power device of claim 1 wherein: said
metal contact plug further comprising a tungsten plug filling in
said source-body contact trench for contacting said source and body
regions and said vertical Schottky diode disposed below said
tungsten plug.
5. The trenched semiconductor power device of claim 2 wherein: said
a contact enhancement dopant region disposed along sidewalls of
said source-body contact trench further comprising a P-type
body-dopant region having a higher dopant concentration than said
body region for improving an electrical contact of said contact
metal plug to said body regions.
6. The trenched semiconductor power device of claim 1 wherein: said
embedded Schottky diode further comprising a PtSi barrier layer
disposed below said contact metal plug directly contacting said
epitaxial layer below said contact trench.
7. The trenched semiconductor power device of claim 1 wherein: said
embedded Schottky diode further comprising a barrier layer having a
barrier height larger than 0.5V for reducing a leakage current
during a reverse bias between said drain and said source and said
barrier layer having a forward voltage drop less than a parasitic
body diode between said body region and said epitaxial layer
surrounding and below said body region.
8. The trenched semiconductor power device of claim 1 wherein: the
contact metal plug further comprising a Ti/TiN barrier layer
surrounding a tungsten core as a source-body contact metal.
9. The trenched semiconductor power device of claim 1 further
comprising: a thin resistance-reduction conductive layer disposed
on a top surface covering said insulation layer and contacting said
contact metal plug whereby said resistance-reduction conductive
layer having a greater area than a top surface of said contact
metal plug for reducing a source-body resistance.
10. The trenched semiconductor power device of claim 1 further
comprising: a thin resistance-reduction conductive layer comprising
a Ti or Ti/TiN layer disposed on a top surface covering said
insulation layer and contacting said contact metal plug whereby
said resistance-reduction conductive layer having a greater area
than a top surface of said contact metal plug for reducing a
source-body resistance.
11. The trenched semiconductor power device of claim 10 further
comprising: a thick front metal layer disposed on top of said
resistance-reduction layer for providing a contact layer for a wire
or wireless bonding package.
12. The trenched semiconductor power device of claim 1 wherein:
said trenched semiconductor power device further comprising a
trenched MOSFET device.
13. The trenched semiconductor power device of claim 1 further
comprising: a source-dopant region disposed below said source-body
contact trench in direct contact with said barrier layer of said
Schottky diode having a dopant concentration of N2 with N2>N1
where N1 is a dopant concentration of said epitaxial layer
surrounding and below said body region supported on said
semiconductor substrate.
14. The trenched semiconductor power device of claim 1 further
comprising: a source-dopant region disposed below said source-body
contact trench in direct contact with said barrier layer of said
Schottky diode having a dopant concentration of N2 with N2<N1 to
reduce a Drain-Source leakage current at a reverse bias where N1 is
a dopant concentration of said epitaxial layer surrounding and
below said body region supported on said semiconductor
substrate.
15. The trenched semiconductor power device of claim 1 wherein:
said trenched gate is filled with a dielectric material padded by a
gate oxide layer with a bottom gate oxide layer significantly
thicker than said gate oxide layer disposed along sidewalls of said
trenched gate.
16. The trenched semiconductor power device of claim 1 further
comprising: a source-dopant region disposed below said source-body
contact trench in contact with said barrier layer of said Schottky
diode having a dopant concentration of N2 with N2>N1 where N1 is
a dopant concentration of said epitaxial layer surrounding and
below said body region supported on said semiconductor substrate;
and said trenched gate is filled with a dielectric material padded
by a gate oxide layer with a bottom gate oxide layer significantly
thicker than said gate oxide layer disposed along sidewalls of said
trenched gate.
17. The trenched semiconductor power device of claim 1 further
comprising: a source-dopant region disposed below said source-body
contact trench in contact with said barrier layer of said Schottky
diode having a dopant concentration of N2 with N2<N1 to reduce a
Drain-Source leakage current at a reverse bias where N1 is a dopant
concentration of said epitaxial layer surrounding and below said
body region supported on said semiconductor substrate; and said
trenched gate is filled with a dielectric material padded by a gate
oxide layer with a bottom gate oxide layer significantly thicker
than said gate oxide layer disposed along sidewalls of said
trenched gate.
18. A method for manufacturing a trenched semiconductor power
device comprising a step of forming said semiconductor power device
with a trenched gate surrounded by a source region encompassed in a
body region above a drain region disposed on a bottom surface of a
substrate, the method further comprising: covering said MOSFET cell
with an insulation layer and applying a contact mask for opening a
source-body contact trench extending through said source and body
regions and into an epitaxial layer below said body region for
filling a contact metal plug therein; and forming an embedded
Schottky diode by forming a Schottky barrier layer near a bottom of
said source-body contact trench below said contact metal plug with
said Schottky barrier layer having a barrier height for reducing a
leakage current through said embedded Schottky diode during a
reverse bias between said drain and said source.
19. The method of claim 18 further comprising a step of: forming a
contact enhancement dopant region along a side wall of said
source-body contact trench for improving an electrical contact of
said contact metal plug to said body regions.
20. The method of claim 18 wherein: said step of forming said
embedded Schottky diode further comprising a step of forming a
CoSi2/ TiN barrier layer at a bottom surface of said source-body
contact trench.
21. The method of claim 18 of claim 1 wherein: said step of forming
said embedded Schottky diode further comprising a step of forming a
PtSi barrier layer at a bottom surface of said source-body contact
trench.
22. The method of claim 18 further comprising: forming a
source-dopant region below said source-body contact trench in
contact with said barrier layer of said Schottky diode having a
dopant concentration of N2 with N2>N1 where N1 is a dopant
concentration of an epitaxial layer surrounding said body region
supported on said semiconductor substrate.
23. The method of claim 18 further comprising: forming a
source-dopant region below said source-body contact trench in
contact with said barrier layer of said Schottky diode having a
dopant concentration of N2 with N2<N1 to reduce a Drain-Source
leakage current at a reverse bias where N1 is a dopant
concentration of an epitaxial layer surrounding said body region
supported on said semiconductor substrate.
24. The method of claim 18 further comprising: forming a
source-dopant region below said source-body contact trench in
contact with said barrier layer of said Schottky diode having a
dopant concentration of N2 with N2>N1 where N1 is a dopant
concentration of an epitaxial layer surrounding said body region
supported on said semiconductor substrate; and forming a gate
insulation layer padded on sidewalls and a bottom surface of said
trenched gate and filling said trenched gate with a dielectric
material by with said gate insulation layer on said b&tom
surface of said trenched gate significantly thicker than said gate
insulation layer disposed along sidewalls of said trenched
gate.
25. The method of claim 18 further comprising: forming a gate
insulation layer padded on sidewalls and a bottom surface of said
trenched gate and filling said trenched gate with a dielectric
material by with said gate insulation layer on said bottom surface
of said trenched gate significantly thicker than said gate
insulation layer disposed along sidewalls of said trenched
gate.
26. The method of claim 18 further comprising: forming a
source-dopant region below said source-body contact trench in
contact with said barrier layer of said Schottky diode having a
dopant concentration of N2 with N2<N1 to reduce a Drain-Source
leakage current at a reverse bias where N1 is a dopant
concentration of an epitaxial layer surrounding said body region
supported on said semiconductor substrate; and forming a gate
insulation layer padded on sidewalls and a bottom surface of said
trenched gate and filling said trenched gate with a dielectric
material by with said gate insulation layer on said bottom surface
of said trenched gate significantly thicker than said gate
insulation layer disposed along sidewalls of said trenched gate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates generally to the cell structure,
device configuration and fabrication process of power semiconductor
devices. More particularly, this invention relates to a novel and
improved cell configuration and processes to manufacture MOSFET
device with embedded Schottky diodes in the same cell such that
integrated cells with spacing savings and lower capacitance and
higher performance are achieved.
[0003] 2. Description of the Related Art
[0004] Conventional technologies for high efficiency DC/DC
applications, a Schottky diode is usually added externally in
parallel to a semiconductor power device, e.g., a power MOSFET
device. FIG. 1A is a circuit diagram that illustrates the
implementation of a Schottky with a power MOSFET device. The
Schottky diode (SKY) is connected in parallel to the MOSFET device
with a parasitic PN body diode to function as a clamping diode to
prevent the body diode from turning on. In order to achieve higher
speed and efficiency, once the parasitic P/N diode is turned on,
both the electron and hole carriers are generated and that would
require longer time to eliminate the carriers by electron-hole
combination while the Schottky Diode is single carrier, i.e.,
electron carrier only and that can be drawn simply by the drain
Electrode. The requirement for the clamping effect is that the
Forward Voltage of the Schottky diode Vf is less than the parasitic
PN diode (.about.0.7V). As the electronic devices become more
miniaturized, there are requirement to integrate the Schottky diode
as part of the semiconductor power device as an IC chip to reduce
the space occupied by the Schottky diode instead of connecting the
Schottky diode as an external electronic component.
[0005] FIG. 1B is a cross sectional view of a trenched MOSFET
device integrated with trench Schottky diodes as that disclosed by
U.S. Pat. No. 6,351,018. The configuration as disclosed in the
patented invention has a disadvantage that the Schottky diodes
occupy additional space that is about the same space as the MOSFET.
The trench Schottky diodes further suffer from a high leakage
between the drain and source due to the increase in the phosphorus
dopant concentration in the channel region during the sacrificial
and gate oxidation processes. Furthermore, the device as shown has
a higher capacitance due to the presence of the trench MOS-Schottky
structure which has inherent parasitic capacitance from trench
sidewall and bottom in trench MOS-Schottky as shown in left side of
the cross section view in FIG. 1B.
[0006] In U.S. Pat. No. 6,433,396, a trench MOSFET device with a
planar Schottky diode is disclosed as that shown in FIG. 1C. The
configuration again has an advantage that the planar Schottky diode
occupies additional space. Also, the formation process requires
additional contact mask for the Schottky diode thus increases the
cost and processes complications for producing the MOSFET power
device with Schottky diode.
[0007] In U.S. Pat. No. 6,998,678 discloses another trench
semiconductor arrangement as shown in FIG. 1D with a MOS transistor
which has a gate electrode, arranged in a trench running in the
vertical direction of a semiconductor body, and a Schottky diode
which is connected in parallel with a drain-source path (D-S) and
is formed by a Schottky contact between a source electrode and the
semiconductor body. Again, the configuration has the same
disadvantage that the Schottky diodes occupy additional space thus
limiting the further miniaturization of the device. Furthermore,
the manufacturing cost is increased due to the requirement that an
additional P+ mask is required to form the Schottky diodes.
[0008] Therefore, there is still a need in the art of the
semiconductor device fabrication, particularly for design and
fabrication of the trenched power device, to provide a novel cell
structure, device configuration and fabrication process that would
resolve these difficulties and design limitations. Specifically, it
is desirable to provide more integrated semiconductor power devices
with embedded Schottky diode that can accomplish space saving and
capacitance reduction such that the above discussed technical
limitations can be resolved.
SUMMARY OF THE PRESENT INVENTION
[0009] It is therefore an aspect of the present invention to
provide new and improved semiconductor power device configuration
and manufacture processes for providing semiconductor power devices
with embedded Schottky diode such that space occupied by separate
Schottky diodes can be saved and one of the major technical
limitations discussed above can be overcome.
[0010] Another aspect of the present invention is to provide new
and improved semiconductor power device configuration and
manufacture processes for providing semiconductor power devices
with embedded Schottky diode in the same cell such that parasitic
capacitance can be reduced and device performance can be
improved.
[0011] Another aspect of the present invention is to provide new
and improved semiconductor power device configuration and
manufacture processes for providing semiconductor power devices
with embedded Schottky diode in the same cell wherein the
manufacturing processes can be simplified with reduced number of
masks required such that the production costs can be reduced and
reliability of the products can be enhanced.
[0012] Another aspect of the present invention is to provide new
and improved semiconductor power device configuration and
manufacture processes for providing semiconductor power devices
with embedded Schottky diode in the same cell wherein a dopant
regions is provided at the bottom of a contact trench below the
Schottky layer to reduce the forward voltage of the Schottky diodes
such that improved device performance is achieved.
[0013] Another aspect of the present invention is to provide new
and improved semiconductor power device configuration and
manufacture processes for providing semiconductor power devices
with embedded Schottky diode in the same cell wherein a dopant
regions is provided at the bottom of a contact trench below the
Schottky layer to reduce the ldsx is reduced and device performance
improvements are achieved.
[0014] Briefly, in a preferred embodiment, the present invention
discloses a semiconductor power device comprising trenched
semiconductor power device comprising a trenched gate surrounded by
a source region encompassed in a body region above a drain region
disposed on a bottom surface of a substrate. The semiconductor
power device further includes an insulation layer covering the
trenched semiconductor power device with a source-body contact
trench opened therethrough and further through the body regions
into an epitaxial layer underneath and filled with contact metal
plug therein. The semiconductor power device further includes an
embedded Schottky diode disposed near a bottom of the source-body
contact trench below the contact metal plug wherein the Schottky
diode further includes a Schottky barrier layer having a barrier
height for reducing a leakage current through the embedded Schottky
diode during a reverse bias between the drain and the source. In an
exemplary embodiment, the semiconductor power device further
includes a contact enhancement dopant region disposed along a
sidewall of the source-body contact trench for improving an
electrical contact of the contact metal plug to the source and body
regions. In an exemplary embodiment, the embedded Schottky diode
further includes a CoSi2/TiN barrier layer disposed below the
contact metal plug. In an exemplary embodiment, the metal contact
plug further includes a tungsten plug filling in the source-body
contact trench for contacting the body regions. In an exemplary
embodiment, the a contact enhancement dopant region disposed along
a side wall of the source-body contact trench further includes a
P-type body-dopant region for improving an electrical contact of
the contact metal plug to the body regions. In an exemplary
embodiment, the embedded Schottky diode further includes a PtSi
barrier layer disposed below the contact metal plug. In an
exemplary embodiment, the embedded Schottky diode further includes
a barrier layer having a barrier height larger than a leakage
prevention voltage for preventing a leakage current during a
reverse bias between the drain and the source and the barrier layer
having a forward voltage drop less than a parasitic body diode
between the body region and an epitaxial layer surrounding the body
region. In an exemplary embodiment, the contact metal plug further
includes a Ti/TiN barrier layer surrounding a tungsten core as a
source-body contact metal. In an exemplary embodiment, the
semiconductor power device further includes a thin
resistance-reduction conductive layer disposed on a top surface
covering the insulation layer and contacting the contact metal plug
whereby the resistance-reduction conductive layer having a greater
area than a top surface of the contact metal plug for reducing a
source-body resistance. In an exemplary embodiment, the
semiconductor power device further includes a thin
resistance-reduction conductive layer includes a Ti or Ti/TiN layer
disposed on a top surface covering the insulation layer and
contacting the contact metal plug whereby the resistance-reduction
conductive layer having a greater area than a top surface of the
contact metal plug for reducing a source-body resistance. In an
exemplary embodiment, the semiconductor power device further
includes a thick front metal layer disposed on top of the
resistance-reduction layer for providing a make contact with layer
for a wire or wireless bonding package. In an exemplary embodiment,
the semiconductor power device further includes a trenched MOSFET
device. In an exemplary embodiment, the semiconductor power device
further includes a source-dopant region disposed below the
source-body contact trench in contact with the barrier layer of the
Schottky diode having a dopant concentration of N2 with N2>N1
where N1 is a dopant concentration of an epitaxial layer
surrounding the body region supported on the semiconductor
substrate. In an exemplary embodiment, the semiconductor power
device further includes a source-dopant region disposed below the
source-body contact trench in contact with the barrier layer of the
Schottky diode having a dopant concentration of N2 with N2<N1 to
reduce a Drain-Source leakage current at a reverse bias where N1 is
a dopant concentration of an epitaxial layer surrounding the body
region supported on the semiconductor substrate. In an exemplary
embodiment, the trenched gate is filled with a dielectric material
padded by a gate oxide layer with a bottom gate oxide layer
significantly thicker than the gate oxide layer disposed along
sidewalls of the trenched gate.
[0015] These and other objects and advantages of the present
invention will no doubt become obvious to those of ordinary skill
in the art after having read the following detailed description of
the preferred embodiment, which is illustrated in the various
drawing figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIGS. 1A to 1D are circuit diagram and cross sectional views
of MOSFET power devices of related disclosures of conventional
device configurations implemented with various Schottky diode
integrations.
[0017] FIGS. 2 to 7 are cross sectional views for showing the
semiconductor power devices with embedded Schottky diodes in the
same cell disposed on the source/body contact trenches as various
exemplary embodiments of this inventions.
[0018] FIGS. 8A to 8G are a serial of side cross sectional views
for showing the processing steps for fabricating a MOSFET device as
shown in FIGS. 2 and 4 of this invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0019] Please refer to FIG. 2 shows a side cross-sectional view of
a trench MOSFET 100 with embedded Schottky in the same cell of this
invention. The trenched MOSFET 100 is supported on a substrate 105
formed with an epitaxial layer 110. The MOSFET device 100 includes
trenched gates 120 disposed in a trench with a gate insulation
layer 115 formed over the walls of the trench. A body region 125
that is doped with a dopant of second conductivity type, e.g.,
P-type dopant, extends between the trenched gates 120. The P-body
regions 125 encompassing a source region 130 doped with the dopant
of first conductivity, e.g., N+ dopant. The source regions 130 are
formed near the top surface of the epitaxial layer surrounding the
trenched gates 120. The trench MOSFET device includes an embedded
Schottky formed near the bottom of the trench contact filled with a
tungsten plug 155. The Schottky diodes are formed in the contact
trench with a CoSi2/TiN layer 145 and a barrier layer 150
underneath the trench contact 155. In order to improve the
source/body contact, a P+ dopant region 140 is formed along the
sidewall to have improved ohmic contact between the trench contact
155 and the P-body regions 125. The MOSFET device with the embedded
Schottky diodes is covered with a low resistance layer composed of
Ti or Ti/TiN that has a large contact area to the tungsten trench
contact 155 and extending over the oxide insulation layer 135 on
top of the trench gates 120. A metal layer 165 composed of aluminum
alloy covering the device is patterned into gate pad and
source/body contacts (not specifically shown). As shown in FIG. 2,
the Schottky barrier layer 145 form the embedded Schottky diodes
near the bottom or the trench contact with a parallel parasitic
diode formed between the body region 125 and the N-epitaxial layer
110. The barrier layer 145 can be CoSi2, TiSi2 and PtSi, which has
barrier height larger than 0.5V, resulting in low leakage current
in the embedded Schottky diode during reverse bias between drain
and source while providing lower Vf (forward voltage drop) at
forward bias than the parasitic body diode between P-body 125 and N
epi layer 110. The forward voltage drop Vf and the reverse leakage
current Idsx can be optimized by the critical dimension (CD) of the
trench contact and depth, and the barrier layer 145.
[0020] The MOSFET device with embedded Schottky diodes have the
advantages that the Schottky diodes are provided with less space
occupied by the Schottky diodes because the diodes are formed as
part of the trench contacts in the same area as part of the cells
of the MOSFET power device. Compared to the patented inventions
disclosed above, the space saving is at least 50%. The source
contact with either N+ or P+ regions, i.e., dopant regions 140 are
formed on the sidewalls of the trench contact and the Schottky
diodes formed on the bottom of the trench contact achieve process
savings because there is no requirement of P+ mask when compared
with the device as that disclosed in U.S. Pat. No. 6,998,678.
Furthermore, since the MOSFET and the Schottky diodes share the
same trenches, there is less parasitic capacitance thus providing
devices capable of providing higher performance with higher
switching speed.
[0021] Beside optimizing trench contact CD and depth, and the
Schottky barrier layer 145 to target Vf, there is another
alternative method to further improve Vf by ion implantation of
1.sup.st conductivity dopant into trench bottom. FIG. 3 is another
exemplary embodiment of a MOSFET 100-1 with an embedded Schottky in
the same cell with an N dopant region 170 having a dopant
concentration of N2 where N2>N1 and N1 is the dopant
concentration of the epitaxial layer 105. The N-dopant region 170
is provided to lower the Vf of the Schottky diode because the Vf is
lower with a higher doping concentration N2 contacting to the
Schottky barrier layer 145.
[0022] FIG. 4 is another exemplary embodiment of a MOSFET 100-2
with a purpose to reduce the Drain-Source leakage current at
reverse bias. The MOSFET 100-2 has an embedded Schottky in the same
cell with an N dopant region 170' having a dopant concentration of
N2 where N2<N1 and N1 is the dopant concentration of the
epitaxial layer 105. The N-dopant region 17'0 is provided to have a
lower ldsx because the N2 is in contact with the Schottky barrier
that has lower doping concentration than the epi layer 110. The
Schottky contact between the barrier layer and silicon has a lower
Vf when the silicon has high doping concentration, and a lower
leakage current Idsx between Drain-Source when the silicon has low
doping concentration. There is trade-off between the Vf and the
Idsx. When the leakage current is too high, the leakage current
will consume more power at an off-state, which becomes very
undesirable for applications in portable system such as cell phone,
notebook using battery.
[0023] FIG. 5 is another exemplary embodiment of a MOSFET 100-2
with an embedded Schottky in the same cell with a thicker oxide
layer 115' at bottom of the trench gate 120. The thicker oxide
layer at the bottom of the trench gate 120 which is thinner than
gate oxide along trench sidewall, is provided to have a reduce
gate-drain capacitance. The thick oxide at trench bottom sandwiched
between trench gate and drain has less capacitance than the single
gate oxide along trench sidewall because Cgd, i.e., the capacitance
between gate and drain, has a reverse proportional relationship
with the gate oxide thickness.
[0024] FIG. 6 is another exemplary embodiment of a MOSFET 100-4
with an embedded Schottky in the same cell with an N dopant region
170 having a dopant concentration of N2 where N2>N1 and N1 is
the dopant concentration of the epitaxial layer 105. The N-dopant
region 170 is provided to lower the Vf of the Schottky diode
because lower Schottky barrier height is achieved with the N2
layer. The barrier height of Schottky is function of doping
concentration and the barrier layer material. A lower doping
concentration leads to a lower Schottky barrier height that results
in a lower Vf but higher Idsx. Meanwhile, there is a trade-off
between Vf and Idsx. However, the benefit of the N2 is to reduce Vf
without degrading the Drain to Source breakdown voltage as a result
of same epitaxial doping concentration. Furthermore, the MOSFET
100-4 has a thicker oxide layer 115' at bottom of the trench gate
120. The thicker oxide layer at the bottom of the trench gate 120
is provided to have a reduce gate-drain capacitance.
[0025] FIG. 7 is another exemplary embodiment of a MOSFET 100-5
with an embedded Schottky in the same cell with an N dopant region
170' having a dopant concentration of N2 where N2<N1 and N1 is
the dopant concentration of the epitaxial layer 105. The N-dopant
region 17'0 is provided to have a lower ldsx because N2 has lower
doping concentration causing higher Schottky barrier height.
Furthermore, the MOSFET 100-5 has a thicker oxide layer 115' at
bottom of the trench gate 120. The thicker oxide layer at the
bottom of the trench gate 120 is provided to have a reduce
gate-drain capacitance.
[0026] Referring to FIGS. 8A to 8F for a serial of side cross
sectional views to illustrate the fabrication steps of a MOSFET
device as that shown in FIGS. 2, 3, and 4. In FIG. 4A, a trench
mask (not shown) is applied to open a plurality of trenches in an
epitaxial layer 210 supported on a substrate 205 by employing a dry
silicon etch process. An oxidation process is then performed to
form an oxide layer covering the trench walls. The trench is
oxidized with a sacrificial oxide to remove the plasma damaged
silicon layer during the process of opening the trench. Then an
oxide layer 215 is grown followed by depositing a polysilicon layer
220 to fill the trench and covering the top surface and then doped
with an N+ dopant. The polysilicon layer 220 filling the trenches
are either etched back or removed by applying a chemical mechanical
planarization process (CMP) to remove the polysilicon above the top
surface. In FIG. 8B, the manufacturing process proceeds by
implanting a P-body implant with a P-type dopant. Then an elevated
temperature is applied to diffuse the P-body 225 into the epitaxial
layer 210. Then a N+ source dopant implant is carried out to form
the source regions 230 followed by applying an elevated temperature
to diffuse the source regions 230 further into the body region 225.
An oxide deposition is then carried out to form a thick oxide layer
235 covering over the top surface of the device. In FIG. 8C, a dry
contact oxide etch is carried out with a contact etch mask (not
show) to open trenches 237 through the oxide layer 235 into the
body regions 225 between the trenched gates 220. Then a boron angle
ion implantation is carried out to form P+ region 240 along the
sidewalls of the contact trenches 237. In FIG. 8D, a contact
silicon etch is performed to open the trenches 237 deeper through
the body region 225 and further into Epi layer 210.
[0027] In FIG. 8E, a layer 245 of Co/TiN is deposited followed by a
rapid thermal anneal process to form a CoSi2 250 thus forming a
Schottky barrier layer. Then the tungsten contact plug 255 is
deposited into the contact trench followed by a W/Co/TiN etch back
to remove the W/Co/TiN layer from above the contact trenches 225.
Then a Ti or TiN low resistance layer 260 is deposited over the top
surface followed by depositing an aluminum alloy layer 265 as a
metal contact layer. A metal patterning process is performed (not
shown) to complete the manufacturing process of the device. FIG. 8F
showing an implant process for implanting As ions to form the
dopant region 170 with dopant concentration N2>N1 or implanting
Boron or BF2 ions for the dopant region 170' N2<1 after
completing the process of FIG. 8D and the process shown in FIG. 8G
is the same as that described in FIG. 8E after the implanting
process completed in FIG. 8F.
[0028] According to the above drawings and descriptions, this
invention further discloses a method for method for manufacturing a
trenched semiconductor power device includes a step of forming said
semiconductor power device with a trenched gate surrounded by a
source region encompassed in a body region above a drain region
disposed on a bottom surface of a substrate. The method further
includes the steps of covering the MOSFET cell with an insulation
layer and applying a contact mask for opening a source-body contact
trench extending through the source and body regions into an
epitaxial layer underneath for filling a contact metal plug
therein. And, the method further includes a step of forming an
embedded Schottky diode by forming a Schottky barrier layer near a
bottom of the source-body contact trench below the contact metal
plug with the Schottky barrier layer having a barrier height for
reducing a leakage current through the embedded Schottky diode
during a reverse bias between the drain and the source. In an
exemplary embodiment, the method further includes a step of forming
a contact enhancement dopant region along a sidewall of the
source-body contact trench for improving an electrical contact of
the contact metal plug to the source and body regions. In an
exemplary embodiment, the step of forming the embedded Schottky
diode further includes a step of forming a CoSi2/TiN barrier layer
at a bottom surface of the source-body contact trench. In an
exemplary embodiment, the step of forming the embedded Schottky
diode further includes a step of forming a PtSi barrier layer at a
bottom surface of the source-body contact trench. In an exemplary
embodiment, the method further includes a step of forming a
source-dopant region below the source-body contact trench in
contact with the barrier layer of the Schottky diode having a
dopant concentration of N2 with N2>N1 where N1 is a dopant
concentration of an epitaxial layer surrounding the body region
supported on the semiconductor substrate. In an exemplary
embodiment, the method further includes a step of forming a
source-dopant region below the source-body contact trench in
contact with the barrier layer of the Schottky diode having a
dopant concentration of N2 with N2<N1 to reduce a Drain-Source
leakage current at a reverse bias where N1 is a dopant
concentration of an epitaxial layer surrounding the body region
supported on the semiconductor substrate. In an exemplary
embodiment, the method further includes a step of forming a gate
insulation layer padded on sidewalls and a bottom surface of the
trenched gate and filling the trenched gate with a dielectric
material by with the gate insulation layer on the bottom surface of
the trenched gate significantly thicker than the gate insulation
layer disposed along sidewalls of the trenched gate.
[0029] Although the present invention has been described in terms
of the presently preferred embodiment, it is to be understood that
such disclosure is not to be interpreted as limiting. Various
alternations and modifications will no doubt become apparent to
those skilled in the art after reading the above disclosure.
Accordingly, it is intended that the appended claims be interpreted
as covering all alternations and modifications as fall within the
true spirit and scope of the invention.
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