U.S. patent application number 11/610704 was filed with the patent office on 2007-06-21 for semiconductor device and manufacturing method of the same.
Invention is credited to Atsushi Fujiki, Yoshito Nakazawa, Hirokatsu Suzuki.
Application Number | 20070138566 11/610704 |
Document ID | / |
Family ID | 38172474 |
Filed Date | 2007-06-21 |
United States Patent
Application |
20070138566 |
Kind Code |
A1 |
Suzuki; Hirokatsu ; et
al. |
June 21, 2007 |
SEMICONDUCTOR DEVICE AND MANUFACTURING METHOD OF THE SAME
Abstract
A semiconductor device which combines reliability and the
guarantee of electrical characteristics is provided. A power MOSFET
and a protection circuit formed over the same semiconductor
substrate are provided. The power MOSFET is a trench gate vertical
type P-channel MOSFET and the conduction type of the gate electrode
is assumed to be P-type. The protection circuit includes a planar
gate horizontal type offset P-channel MOSFET and the conduction
type of the gate electrode is assumed to be N-type. These gate
electrode and gate electrode are formed in separate steps.
Inventors: |
Suzuki; Hirokatsu; (Tokyo,
JP) ; Fujiki; Atsushi; (Tokyo, JP) ; Nakazawa;
Yoshito; (Tokyo, JP) |
Correspondence
Address: |
MATTINGLY, STANGER, MALUR & BRUNDIDGE, P.C.
1800 DIAGONAL ROAD
SUITE 370
ALEXANDRIA
VA
22314
US
|
Family ID: |
38172474 |
Appl. No.: |
11/610704 |
Filed: |
December 14, 2006 |
Current U.S.
Class: |
257/369 ;
257/E21.427; 257/E21.618; 257/E21.623; 257/E21.629; 257/E27.06;
257/E27.062; 257/E29.064; 257/E29.268; 438/199 |
Current CPC
Class: |
H01L 29/7813 20130101;
H01L 29/66666 20130101; H01L 29/66696 20130101; H01L 29/66704
20130101; H01L 27/0248 20130101; H01L 29/1087 20130101; H01L 27/088
20130101; H01L 21/82345 20130101; H01L 29/7835 20130101; H01L
21/823412 20130101; H01L 29/66659 20130101; H01L 21/823487
20130101; H01L 29/7815 20130101 |
Class at
Publication: |
257/369 ;
438/199; 257/E27.062 |
International
Class: |
H01L 29/94 20060101
H01L029/94; H01L 21/8238 20060101 H01L021/8238 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 16, 2005 |
JP |
2005-363815 |
Claims
1. A semiconductor device comprising; a P-channel trench gate
MOSFET formed over a main face of a semiconductor substrate,
wherein a P-channel planar gate MOSFET is formed over the same main
face of the semiconductor substrate as the trench gate MOSFET.
2. The semiconductor device according to claim 1, wherein the
conduction type of the gate electrode of the trench gate MOSFET is
P-type, and wherein the conduction type of the gate electrode of
the planar gate MOSFET is N-type.
3. The semiconductor device according to claim 1, wherein the
trench gate MOSFET is a power MOSFET, and wherein the planer gate
MOSFET includes a protection circuit which protects the trench gate
MOSFET.
4. The semiconductor device according to claim 3, wherein the
planer gate MOSFET has an offset drain structure.
5. The semiconductor device according to claim 3, wherein the
protection circuit is a temperature detection overheat cutoff
circuit.
6. The semiconductor device according to claim 3, wherein the
protection circuit is an over-current limit circuit.
7. A manufacturing method of a semiconductor device in which a
P-channel trench gate MOSFET and a P-channel planer gate MOSFET are
formed over the same main face of a semiconductor substrate,
wherein a gate of the trench gate MOSFET and a gate of the planer
gate MOSFET are formed in separate steps.
8. The manufacturing method of a semiconductor device according to
claim 7, wherein the conduction type of the gate electrode of the
trench gate MOSFET is P-type, and wherein the conduction type of
the gate electrode of the planar gate MOSFET is N-type.
9. The manufacturing method of a semiconductor device according to
claim 7, wherein the trench gate MOSFET is a power MOSFET, and
wherein the planer gate MOSFET includes a protection circuit which
protects the trench gate MOSFET.
10. The manufacturing method of a semiconductor device according to
claim 9, wherein the planer gate MOSFET has an offset drain
structure.
11. The manufacturing method of a semiconductor device according to
claim 9, wherein the protection circuit is a temperature detection
overheat cutoff circuit.
12. The manufacturing method of a semiconductor device according to
claim 9, wherein the protection circuit is an over-current limit
circuit.
13. A manufacturing method of a semiconductor device in which a
P-channel trench gate MOSFET and a P-channel planer gate MOSFET are
formed over the same main face of a semiconductor substrate
comprising the steps of: (a) preparing the semiconductor substrate;
(b) forming a trench groove in a first region of the main face of
the semiconductor substrate; (c) forming a first gate insulator
film over the side wall in the trench groove; (d) forming a first
gate electrode over the first gate insulator film so as to be
buried inside the trench groove; (e) forming a second gate
insulator film in a second region of the main face of the
semiconductor substrate; and (f) forming a second gate electrode
over the second gate insulator film, wherein the step (d) and the
step (f) are separate steps.
14. The manufacturing method of a semiconductor device according to
claim 13, wherein the step (d) comprises the steps of: (d1) forming
a silicon film over the main face of the semiconductor substrate;
(d2) introducing an impurity to make the silicon film a P-type
conduction type; and (d3) removing a part of the silicon film and
forming the first gate electrode.
15. The manufacturing method of a semiconductor device according to
claim 14, wherein the impurity is boron.
16. The manufacturing method of a semiconductor device according to
claim 13, wherein the step (f) comprises the steps of: (f1) forming
a silicon film over the main face of the semiconductor substrate;
(f2) introducing an impurity to make the silicon film an N-type
conduction type; and (f3) removing a part of the silicon film and
forming the second gate electrode.
17. The manufacturing method of a semiconductor device according to
claim 16, wherein the impurity is arsenic.
18. The manufacturing method of a semiconductor device according to
claim 13, wherein the step (f) comprises the steps of: (f1) forming
a silicon film having an N-type conduction type over the main face
of the semiconductor substrate; and (f2) removing a part of the
silicon film and forming the second gate electrode.
19. The manufacturing method of a semiconductor device according to
claim 13, wherein a drain of the planer gate MOSFET includes a
first semiconductor region and a second semiconductor region formed
over the main face of the semiconductor substrate, wherein the
impurity concentration of the first semiconductor region is lower
than the impurity concentration of the second semiconductor region,
and wherein the first semiconductor region is formed between the
second gate electrode and the second semiconductor region.
20. The manufacturing method of a semiconductor device according to
claim 13, wherein the step (f) is carried out after the step
(d).
21. The manufacturing method of a semiconductor device according to
claim 20, wherein an insulator film is formed so as to cover the
first gate between the step (d) and the step (f).
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority from Japanese patent
application No. 2005-363815 filed on Dec. 16, 2005 the content of
which is hereby incorporated by reference into this
application.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a semiconductor device and
a manufacturing method thereof, specifically relates to an
effective technology for applying a semiconductor device where a
trench gate MOSFET (Metal Oxide Semiconductor Field Effect
Transistor) and a planer gate MOSFET are formed over the same
semiconductor substrate.
[0003] For instance, in an electronic control unit for automobiles,
a semiconductor device where a power MOSFET and a protection
circuit (protection element) thereof are combined in one unit is
applied for the purpose of making it smaller and highly reliable in
a high temperature environment.
[0004] Japanese Unexamined Patent Publication No. Show
63(1988)-229758 (patent document 1) discloses a technology relating
to a vertical type power MOS transistor having a self overheat
protection function.
[0005] Japanese Patent No. 3414569 (Patent document 2) discloses a
technology relating to a trench insulator gate (trench gate type)
semiconductor element and horizontal type insulator gate (planer
gate type) semiconductor element formed over the same chip.
[Patent document 1] Japanese Unexamined Patent Publication No. Show
63(1988)-229758
[Patent document 2] Japanese Patent No. 3414569
SUMMERY OF THE INVENTION
[0006] A semiconductor device where a power MOSFET which is applied
to the load side of electronic parts, etc. as a switching element
and a protection circuit thereof are combined in one unit makes it
possible to integrate electronic parts and reduce the manufacturing
cost by formation over the same semiconductor substrate
(integration) compared with structures where a power MOSFET and a
protection circuit are formed separately. Herein, a protection
circuit is a circuit for protecting a power MOSFET, for instance,
it is a temperature detection overheat cutoff circuit, etc.
[0007] For instance, it is assumed that grounding (short-circuit)
occurs in the case when a P-channel power MOSFET is applied to a
high side switch for automobiles as shown in FIG. 17. In the case
when no protection is applied to the power MOSFET, a large current
flows momentarily, resulting in the power MOSFET being broken.
Therefore, maintenance such as exchanging an electronic control
unit (board) where the power MOSFET is mounted becomes necessary.
Then, by using a protection circuit, it is thought that the power
MOSFET is prevented from ground breakdown (short-circuit
breakdown).
[0008] Herein, there are two methods, one is a method where a
protection circuit and a power MOSFET are constructed separately
(the protection circuit is not built in the power MOSFET) and
another is a method where a protection circuit is built in a power
MOSFET itself. However, because of a reduction in the number of
parts, cost reduction, and ease in handling, a power MOSFET where a
protection circuit is built-in (power MOSFET with a built-in
protection circuit) is effective. Specifically, in the
above-mentioned fields where high reliability is required, such as
in the aforementioned automobiles and industrial equipment, a power
MOSFET with a built-in protection circuit is effective. Moreover,
since a power MOSFET and a protection circuit are formed by
applying a semiconductor processing technique, a protection circuit
can be built in a power MOSFET over the same semiconductor
substrate.
[0009] Thus, integration of electronic parts can be achieved and
manufacturing costs can be reduced by forming a power MOSFET and a
protection circuit over the same semiconductor substrate. As a
semiconductor device which includes a power MOSFET and a protection
circuit formed over the same semiconductor substrate (power MOSFET
with build-in protection circuit), for instance, a planer gate type
N-channel vertical type MOSFET which is a planer gate is utilized
as a power MOSFET, and a planer gate type N-channel horizontal type
normal MOSFET which is a planer gate is utilized as a protection
circuit in the aforementioned patent document 1. Herein, normal
means that it is not an offset drain structure to be described
later.
[0010] In general, a low on resistance is demanded in order to
suppress the loss (heat) while switching to the aforementioned
power MOSFET. A decrease in the resistivity of the power MOSFET can
be designed by assuming the gate to be not a planer structure but a
trench structure. Since the trench gate is formed by burying a
conductive film in the groove through the gate insulator film, a
gate insulator film with high quality and high reliability is
necessary in order to maintain the gate breakdown voltage and
decrease gate leakage.
[0011] As a semiconductor device which includes a trench gate power
MOSFET and a protection circuit formed over the same semiconductor
substrate, for instance, a trench gate vertical type N-channel
MOSFET is applied to the power MOSFET and a planer gate horizontal
type offset N-channel MOSFET is applied as the protection circuit
in the aforementioned patent document 2. Herein, in the present
invention, offset means a structure which can maintain a high
breakdown voltage at, for instance, a shallow region (semiconductor
region) which is about several microns from the surface of the
semiconductor substrate. Moreover, the structure where only the
drain side has an offset structure is called an offset drain
structure.
[0012] For instance, in the case of a semiconductor device which
includes a trench MOSFET and an offset MOSFET as shown in FIG. 18,
the input voltage from the gate is applied to the gate of the
trench MOSFET and the drain of the offset MOSFET. In addition, as
mentioned above, in order to maintain the gate insulator film with
high quality and high reliability, voltage screening is performed
in order to remove initial faults in the gate insulator film.
Therefore, a screening voltage is applied to the drain in the
offset MOSFET during voltage screening, so that an offset drain
structure is required which has a breakdown voltage higher than at
least the screening voltage.
[0013] By the way, the power MOSFETs are applied to the load side
of electronic parts in automobiles, and the power MOSFET includes a
high side switch and a low side switch according to the car body
ground conditions of the battery. In the case when the high side
switch circuit includes an N-channel MOSFET (FIG. 19 (a)), a
step-up circuit (charge pump) is necessary for the gate drive. On
the other hand, in the case when it includes a P-channel MOSFET
(FIG. 19 (b)), a step-up circuit is not necessary. Therefore, as
shown in FIG. 20, the packing substrate area can be reduced to
about 1/3 when the high side switch includes a P-channel MOSFET
compared with the case when the high side switch includes an
N-channel MOSFET. That is, in the case when a P-channel power
MOSFET is used for the high side switch, the packing substrate area
can be reduced because a step-up circuit is not necessary.
[0014] As a P-channel power MOSFET constituting such a high side
switch circuit, for instance, since it is thought that a power
MOSFET having a protection circuit formed over the same
semiconductor substrate (power MOSFET with a built-in protection
circuit) can be applied, the inventors examined this point.
Although the aforementioned patent document 1 and patent document 2
describe a semiconductor device which includes a power MOSFET and a
protection circuit formed over the same semiconductor substrate,
there is no description of a P-channel power MOSFET including a
high side switch circuit.
[0015] It is assumed that a semiconductor device including a power
MOSFET and a protection circuit formed over the same semiconductor
substrate which was investigated by the inventors uses a trench
gate vertical type P-channel MOSFET for a power MOSFET and uses a
planer gate horizontal type offset P-channel MOSFET for a
protection circuit. Herein, in order to simplify the manufacturing
process, the trench gate MOSFET and the planer gate MOSFET were
formed in one step. Therefore, for instance, each gate electrode is
formed of arsenic (As) or phosphorus (P) doped polycrystalline
silicon, resulting in their becoming the same conduction type
(N-type).
[0016] On the other hand, in the power MOSFET with a built-in
protection circuit, a low on resistance is required for the power
MOSFET, and low characteristic fluctuation is required for the
planer MOSFET in order to prevent malfunctions.
[0017] In the case when the gate electrode of the P-channel MOSFET
is made to be N-type, Vth becomes about 1 V deeper than that of a
P-type because of the difference in the work functions. However,
the characteristic fluctuation becomes smaller due to bias
stress.
[0018] Therefore, in a trench P-channel MOSFET and an offset
P-channel MOSFET examined by the inventors, the characteristic
fluctuation of the offset P-channel MOSFET can be reduced when both
gate electrodes are made to be N-type. However, the Vth of the
trench P-channel MOSFET becomes deeper, so that a problem arises
that the "on" resistance increases under the condition where a
sufficient gate voltage is not provided.
[0019] Thus, a method for forming the channel layer (N-type layer)
of the P-channel MOSFET and the impurity layer of the opposite
conduction type (P-type) is generally known as a technology to
control the Vth at the shallower side. However, when this method is
applied, it is necessary to keep a sufficient effective channel
length. Because if this impurity layer is formed in the condition
where the effective channel length is short, punchthrough occurs
easily and the breakdown voltage is reduced. In the case of the
offset P-channel MOSFET, it is possible to make the Vth shallower
while preventing the punchthrough if the effective channel length
is controlled to be, for instance, 4 .mu.m or more. However, in the
power MOSFET, the channel resistance increases and the "on"
resistance increases when the effective channel length is made
longer. Therefore, a device in which punchthrough does not occur
and the "on" resistance is low is extremely difficult to make.
[0020] On the other hand, in a trench P-channel MOSFET and an
offset P-channel MOSFET examined by the inventors, the Vth of the
trench P-channel MOSFET becomes shallower when both gate electrodes
are made to be P-type. However, a problem arises where the
characteristic fluctuation of the offset P-channel MOSFET becomes
greater due to NBT (negative bias temperature).
[0021] Although the aforementioned patent document 1 and patent
document 2 describes a semiconductor device which includes a power
MOSFET and a protection circuit formed over the same semiconductor
substrate, there is no description of the problem where the Vth of
the power MOSFET increases when it is made to be an N-type gate and
the characteristic fluctuation of the MOSFET of the protection
circuit becomes greater when it is made to be a P-type gate.
Moreover, the gate of the power MOSFET and the gate of the MOSFET
of the protection circuit are examined only in the case when both
conduction types are the same.
[0022] In the case when a trench P-channel MOSFET and an offset
P-channel MOSFET (protection circuit) are simply combined, problems
with the thickness of the gate insulator film and the thickness of
the gate electrode arise in addition to the aforementioned problem
of the conduction type of the gate.
[0023] The problem of the thickness of the gate insulator film is
that the thickness of the gate insulator film of the offset MOSFET
becomes thicker when the gate insulator film is made thicker in
order to maintain the gate breakdown voltage of the P-channel
MOSFET. Therefore, the threshold voltage Vth of the P-channel
offset MOSFET has to be controlled by the well concentration.
Moreover, when an attempt is made to lower the well concentration
to decrease the threshold voltage Vth of the P-channel offset
MOSFET, the variation of the threshold voltage Vth becomes
greater.
[0024] The problem of the thickness of the gate electrode is that
thick polycrystalline silicon films have to be stacked for burying
the trench of the trench MOSFET and the gate electrode of the
offset MOSFET also has to be formed of a thick polycrystalline
silicon film. Therefore, the machining accuracy becomes worse,
resulting in the variation of the threshold voltage Vth of the
offset MOS becoming greater.
[0025] It is an objective of the present invention to provide a
highly reliable MOSFET with a built-in protection circuit.
[0026] Moreover, it is a further objective of the present invention
to provide a MOSFET with a built-in protection circuit having
excellent electrical characteristics.
[0027] The aforementioned and other objectives and new features of
the present invention will become apparent from the following
descriptions with reference to the accompanying drawings of this
specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a schematic plane drawing illustrating a
semiconductor device with a layout of the chip in the embodiment of
the present invention;
[0029] FIGS. 2(a) and 2(b) are schematic explanatory drawings
illustrating a semiconductor device in a power MOS region in the
embodiment, in which FIG. 2 (a) is a plane drawing and FIG. 2(b) a
cross-sectional drawing;
[0030] FIGS. 3(a) and 3(b) are schematic explanatory drawings
illustrating a semiconductor device in a protection circuit region
in the embodiment, in which FIG. 3 (a) is a plane drawing and FIG.
3(b) a cross-sectional drawing;
[0031] FIG. 4 is a circuit diagram from which a semiconductor
device in the embodiment is configured;
[0032] FIG. 5 is a main part cross-sectional drawing schematically
illustrating a semiconductor device in a manufacturing process in
the embodiment of the present invention;
[0033] FIG. 6 is a main part cross-sectional drawing schematically
illustrating a semiconductor device in a manufacturing process
following FIG. 5;
[0034] FIG. 7 is a main part cross-sectional drawing schematically
illustrating a semiconductor device in a manufacturing process
following FIG. 6;
[0035] FIG. 8 is a main part cross-sectional drawing schematically
illustrating a semiconductor device in a manufacturing process
following FIG. 7;
[0036] FIG. 9 is a main part cross-sectional drawing schematically
illustrating a semiconductor device in a manufacturing process
following FIG. 8;
[0037] FIG. 10 is a main part cross-sectional drawing schematically
illustrating a semiconductor device in a manufacturing process
following FIG. 9;
[0038] FIG. 11 is a main part cross-sectional drawing schematically
illustrating a semiconductor device in a manufacturing process
following FIG. 10;
[0039] FIG. 12 is a main part cross-sectional drawing schematically
illustrating a semiconductor device in a manufacturing process
following FIG. 11;
[0040] FIG. 13 is a main part cross-sectional drawing schematically
illustrating a semiconductor device in a manufacturing process
following FIG. 12;
[0041] FIG. 14 is a main part cross-sectional drawing schematically
illustrating a semiconductor device in a manufacturing process
following FIG. 13;
[0042] FIG. 15 is a main part cross-sectional drawing schematically
illustrating a semiconductor device in a manufacturing process
following FIG. 14;
[0043] FIG. 16 is a main part cross-sectional drawing schematically
illustrating a semiconductor device in a manufacturing process
following FIG. 15;
[0044] FIG. 17 is a circuit drawing of a high side switch circuit
where a power MOSFET is applied;
[0045] FIG. 18 is a circuit drawing illustrating a power MOSFET
with a built-in protection circuit;
[0046] FIGS. 19(a) and 19(b) are circuit drawings, in which FIG.
19(a) is one constituting a low side switch and FIG. 19(b) is one
constituting a high side switch; and
[0047] FIGS. 20(a) and 20(b) are schematic plane drawings
illustrating a semiconductor device constituting a high side
switch, in which FIG. 20(a) is the case constituted by an N-channel
MOS and FIG. 20(b) is the case constituted by a P-channel MOS.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0048] The outline of a typical one disclosed in the present
invention will be simply described as follows.
[0049] The semiconductor device of the present invention includes a
power MOSFET and a protection circuit formed over the same
semiconductor substrate, in which the power MOSFET is a trench gate
vertical-type P-channel MOSFET and the protection circuit is a
planer gate horizontal-type P-channel MOSFET. The conductivity of
the gate electrode of this trench gate vertical-type P-channel
MOSFET is P-type and the conductivity of the gate electrode of the
planer gate horizontal-type offset P-channel MOSFET is N-type.
[0050] The effects obtained by a typical one disclosed in the
present invention will be simply described as follows.
[0051] According to a semiconductor device of the present
invention, a MOSFET with a built-in protection circuit can be
supplied which secures both reliability and electrical
characteristics.
[0052] Before explaining the embodiments of the present invention,
terms in the present invention will be defined, especially in the
case where there are no explanations. "MOS" is an abbreviation of
MOSFET (Metal Oxide Semiconductor Field Effect Transistor);
"vertical type" is a structure where the current between source and
drain flows in the thickness direction of the semiconductor
substrate; "horizontal" is a structure where the current between
source and drain flows perpendicular to the thickness direction of
the semiconductor substrate. Moreover, "trench (trench gate)" will
be described later and is a structure where a gate electrode is
formed in a groove formed in the thickness direction of the
semiconductor substrate, and "planar (planar gate)" is a structure
where a gate electrode is formed on the main face of the
semiconductor substrate. Furthermore, "offset" is a structure which
maintains a high breakdown voltage at, for instance, a shallow
region (semiconductor region) which is about several microns from
the surface of the semiconductor substrate.
[0053] Hereinafter, the embodiments of this invention are described
in detail on the basis of the drawings as follows. In all the
figures to describe the embodiment, the same reference letters are
affixed to the same material as a rule, and repetitive explanations
are omitted.
[0054] A semiconductor device described in the embodiment of the
present invention includes a power MOSFET and a protection circuit.
This power MOSFET is a P-channel trench gate vertical-type MOSFET
(hereinafter, it is called a trench PMOS) and the protection
circuit is a P-channel planar gate horizontal-type offset MOSFET
(hereinafter, it is called an offset PMOS). Specifically, this
protection circuit is a control circuit which is intended to let
the trench PMOS not self-destruct and it includes an offset
PMOS.
[0055] FIG. 1 is a schematic plane drawing illustrating a
semiconductor device in a chip state in which a trench PMOS and an
offset PMOS are provided. FIGS. 2(a) and 2(b) are schematic
explanatory drawings illustrating the trench PMOS of FIG. 1, in
which FIG. 2 (a) is a main part plane drawing and FIG. 2(b) is a
main part cross-sectional drawing. FIGS. 3(a) and 3(b) are
schematic explanatory drawings illustrating the offset PMOS of FIG.
1, in which FIG. 3 (a) is a main part plane drawing and FIG. 3(b)
is a main part cross-sectional drawing. In FIG. 2(a), in order to
make the cell structure of the trench PMOS easy to understand, the
interconnect layer 21 shown in FIG. 2(b) is omitted.
[0056] The trench PMOS region, At, and the protection circuit
region (offset PMOS region), Ac, are shown in FIG. 1. As external
terminals, a gate pad (gate electrode) of the trench PMOS and a
source pad (source electrode) of the trench PMOS are arranged at
the chip surface; a drain electrode of the trench PMOS is arranged
at the chip rear surface; and the protection circuit has no
external terminal. That is, the protection circuit (offset PMOS) is
built into the trench PMOS.
[0057] These trench PMOS and protection circuits (offset PMOS) are
formed on one chip, and, as shown in FIG. 2 and FIG. 3, the trench
PMOS and the offset PMOS are formed on the main surface of the same
semiconductor substrate 1. This semiconductor substrate 1 is a
substrate where P+ type single crystalline silicon 1B in which an
impurity having P-type conduction type is doped is epitaxially
grown on the main face of a P++ type single crystalline silicon
substrate 1A having P-type conduction type (hereinafter, it is
simply called a substrate).
[0058] In the trench PMOS region At shown in FIG. 2, a gate
electrode 6 is formed by burying P-type poly-silicon in the groove
made in the thickness direction of the substrate 1. Specifically,
the conduction type of the gate electrode 6 of the trench PMOS is
p-type. The explanation of the structure of the trench PMOS except
for the gate electrode 6 will be described along with the
manufacturing method.
[0059] Thus, in the present invention, the threshold voltage (Vth)
is about 1 V shallower than the case of the N-type polysilicon
because of the difference of the work functions in the case when
P-type poly-silicon is applied to the gate electrode 6 of the
trench PMOS. Thus, "on" resistance can be decreased in a state
where the gate voltage is not sufficiently supplied. By applying
P-type poly-silicon, the characteristic fluctuation increases
compared with the case of N-type poly-silicon, but the advantage of
decreasing the "on" resistance is great because it does not need
the accuracy of the characteristics comparable to an offset
PMOS.
[0060] On the other hand, in the protection circuit region Ac shown
in FIG. 3, a gate electrode 10 composed of N-type poly-silicon is
formed over the main face of the substrate 1 in the direction
perpendicular to the thickness direction of the substrate 1. That
is, the conduction type of the gate electrode 10 of the offset PMOS
is N-type. This gate electrode 10 is electrically connected to the
gate interconnect G through the contact Cg. Moreover, the source
and drain of the offset PMOS are electrically connected to the
source interconnect S through the contact Cs and to the drain
interconnect D through the contact Cd.
[0061] In the case when the N-type polysilicon is applied to the
gate electrode of the offset PMOS as in the present invention, the
characteristic fluctuation can be suppressed and malfunctions of
the circuit can be prevented. The threshold voltage (Vth) becomes
deeper by using N-type poly-silicon. However, for instance, in an
MOS applied to an analogue circuit, it is necessary to set the
effective channel length longer in order to suppress variations in
the characteristics. However, when the effective channel length is
maintained at, for instance, 4 .mu.m or more, punchthrough does not
occur and the threshold voltage (Vth) can be controlled on the
shallow side even if an impurity layer which has a conduction type
(P-type) opposite that of the channel layer (V-type layer) is
formed over the channel surface.
[0062] Herein, the structure of the offset PMOS shown in FIG. 3
will be explained. This offset PMOS asymmetrically has a source
region and a drain region opposite the gate electrode 10.
Specifically, the drain region includes a P-type semiconductor
region (first semiconductor region) 12 and a P+ semiconductor
region (second semiconductor region) 14 and the source region
includes a P+ type semiconductor region (second semiconductor
region) 14, in which the impurity concentration of this P-type
semiconductor region 12 is lower than the impurity concentration of
the P+ type semiconductor region 14. Put another way, the offset
PMOS has an LDD (Lightly doped drain) which is a low concentration
region between the gate electrode 10 and the drain region. The high
breakdown voltage can be maintained by controlling the impurity
concentration in the LDD region and the length of the LDD region
along the surface of the substrate 1.
[0063] The offset structure is a structure which maintains a high
breakdown voltage at, for instance, a shallow region (semiconductor
region) which is about several microns from the surface of the
semiconductor substrate. The offset PMOS shown in the embodiment of
the present invention is an offset drain structure where only the
drain side has the offset structure and it is not one where both
source and drain are offset such as a CMOS (Complementary Metal
Oxide Semiconductor) of an LDD structure.
[0064] Next, a circuit including semiconductor device of the
embodiment is shown in FIG. 4. A protection circuit is electrically
connected between the gate and source of the trench PMOS which is a
power MOSFET (it is shown as Mo in FIG. 4). All of the MOSFETs
formed in this protection circuit are offset PMOS. A semiconductor
device of the embodiment includes a current sense trench MOS for a
control circuit (it is shown as Ms in FIG. 4) besides a trench PMOS
(it is shown as Mo in FIG. 4) and a protection circuit which are
power MOSFETs.
[0065] As mentioned above, the protection circuit including the
offset PMOS formed over the same substrate as the trench PMOS can
prevent the semiconductor device from self-destruction by
performing a circuit operation (overcurrent limit) so as not to let
a current flow higher than a certain amount into the trench PMOS
when a situation occurs in which an overcurrent flows to the trench
PMOS. Moreover, the protection circuit of the overcurrent limit
circuit controls the current flowing by the protection circuit in
order to avoid the current breakdown when a large current flows
into the device.
[0066] Moreover, the protection circuit detects a temperature of
150.degree. C. or more and performs an operation where the input
voltage from the gate is shut down (temperature detection overheat
shutdown), thereby, a current flowing between the drain and source
is self-shut down and self-destruction due to heat can be
prevented. Specifically, when heat of 150.degree. C. or more is
generated by self-heating caused by power loss while a large
current flows in the device, a built-in protection circuit works in
the protection circuit of the temperature detection overheat
shutdown circuit, resulting in the gate voltage of the trench PMOS
being self-shut down.
[0067] Next, a manufacturing method of a semiconductor device of
the present invention will be explained referring to FIGS. 5 to 16.
FIGS. 5 to 16 are schematic explanatory drawings illustrating
cross-sections of a semiconductor device during manufacturing, in
which a trench PMOS region At, an offset PMOS region Ac, and a
border region Ac-At between the trench PMOS region At and the
offset PMOS region Ac are shown.
[0068] First, as shown in FIG. 5, a semiconductor wafer to be a
semiconductor substrate (hereinafter, it is simply called a
substrate) 1 is ready, in which a P-type impurity doped P+ type
single crystalline silicon layer 1B is epitaxially grown over the
main face of the P++ type single crystalline silicon substrate 1A
having P-type conduction type. Next, after the surface (main face)
of the P+ type single crystalline silicon layer 1B is thermally
oxidized, a silicon nitride film (which is not shown in the figure)
is deposited over the entire surface of the substrate 1, N-type
impurity ions are injected thereto by using a silicon nitride mask
which was patterned for use as a selector by using photolithography
and etching techniques, and an N-type well 2 is formed by thermal
diffusion. Then, after the exposed surface of the substrate 1 is
oxidized, the element separation part 3 is formed by removing the
aforementioned silicon film.
[0069] As shown in FIG. 6, the substrate 1 is etched by using
photolithography and etching techniques, the groove 4 is formed,
and the silicon oxide film 5 is formed at the bottom part and the
side walls of the groove 4 by applying heat treatment to the
substrate 1. This silicon oxide film 5 becomes a gate insulator
film of the trench PMOS.
[0070] As shown in FIG. 7, a P-type impurity (for instance, boron)
doped polycrystalline silicon film is deposited over the silicon
oxide film 5 which includes the inside of the groove 4 and fills
the groove 4. Or, after non-doped polycrystalline silicon is
deposited over the silicon oxide film 5, which includes the inside
of the groove 4, to fill the groove 4, the polycrystalline silicon
may be made P-type by injecting P-type impurity ions (for instance,
boron) into the non-doped polycrystalline silicon. Next, the gate
electrode 6 of the trench PMOS is formed in the groove 4 by leaving
the polycrystalline silicon film in the groove 4 in the trench PMOS
region At using the photo-resist film patterned by using a
photolithography technique as a mask. Moreover, in the border
region Ac-At, the interconnect layer 6M which is electrically
connected to the gate electrode 6 is formed.
[0071] As shown in FIG. 8, after depositing a silicon oxide film 7
over the main face of the substrate 1, the silicon oxide film 7
which will be a channel of the offset PMOS channel is opened by
using photolithography and etching techniques and an implant layer
(which is not shown in the figure) is formed by injecting ions for
controlling the threshold voltage (Vth).
[0072] As shown in FIG. 9, after a silicon oxide film 8 of the
offset PMOS composed of a silicon oxide film is formed by using
photolithography and etching techniques, an N-type impurity (for
instance, arsenic or phosphorus) doped polycrystalline silicon film
9 is deposited to cover the silicon oxide film 8. Or, the
polycrystalline silicon film 9 may be made to be N-type by
injecting N-type impurity (for instance, arsenic or phosphorus)
after depositing a non-doped polycrystalline silicon film 9. After
that, a silicon oxide film (which is not shown in the figure) is
deposited over this polycrystalline silicon film 9.
[0073] As shown in FIG. 10, the polycrystalline silicon film 9 and
the silicon oxide film 8 are removed by using photolithography and
dry-etching techniques to form the gate electrode 10 and the gate
insulator film 11 of the offset PMOS.
[0074] As mentioned above, in the present invention, the gate
electrode 10 of the offset PMOS is manufactured in a separate step
from the gate electrode 6 of the trench PMOS which has been
previously formed. Moreover, the conduction type of the gate
electrode 10 of the offset PMOS is formed to be N-type and the
conduction type of the gate electrode 6 of the trench PMOS is
formed to be P-type.
[0075] As shown in FIG. 11, after removing the silicon oxide film 7
by using photolithography and dry-etching techniques, at the offset
PMOS region Ac, P-type impurity ions are injected into the P+ type
single crystalline silicon layer 1B using the photo-resist film
(which is not shown in the figure) patterned by using a
photolithography technique as a mask. Next, at the trench MOS
region At, N-type impurity ions are injected into the P+ type
single crystalline silicon layer 1B using the photo-resist film
(which is not shown in the figure) patterned by using a
photolithography technique as a mask. Then, those P-type and N-type
impurity ions are allowed to diffuse respectively by applying a
heat treatment to the substrate 1 to form the P-type semiconductor
region 12 and the N-type semiconductor region 13. This N-type
semiconductor region 13 will be a channel layer of the trench
PMOS.
[0076] Then, impurity ions having P-type conduction type are
introduced into the P+ type single crystalline silicon layer 1B
using the photo-resist film (which is not shown in the figure)
patterned by using a photolithography technique as a mask, thereby,
a P+ type semiconductor region 14 which has a higher impurity
concentration than the P- type semiconductor region 12 is formed in
the offset PMOS region Ac. Moreover, impurity ions having P-type
conduction type are introduced into the P+ type single crystalline
silicon layer 1B using the photo-resist film (which is not shown in
the figure) patterned by using a photolithography technique as a
mask, thereby, the P+ type semiconductor region 15 is formed in the
trench PMOS region At. According to the steps described above, a
trench PMOS can be applied, in which the P++ type single
crystalline silicon substrate 1A and the P+ type single crystalline
silicon layer 1B are used for the drain and the N-type
semiconductor region 13 is used for the source. Moreover, the P+
type semiconductor region 15 can be used for a punch through
stopper layer in the trench MOS.
[0077] As mentioned above, in the present invention, a P- type
semiconductor region 12 which has a lower impurity concentration
than the P+ type semiconductor layer 14 is formed between the P+
type semiconductor region 14 and the gate electrode 10 to be an
offset drain structure, which maintains a high breakdown voltage
at, for instance, a shallow region which is about several microns
from the surface of the semiconductor substrate 1.
[0078] As shown in FIG. 12, after depositing a silicon oxide film
over the substrate 1, a silicon nitride film is deposited over the
silicon oxide film and an insulator film 16 including the silicon
oxide film and the silicon nitride film is formed by using
photolithography and etching techniques.
[0079] As shown in FIG. 13, after depositing a PSG (Phospho
Silicate Glass) filmover the substrate 1, an SOG (Spin On Glass)
film is coated over the PSG film, resulting in an insulator film 17
being formed including the PSG film and the SOG film.
[0080] As shown in FIG. 14, after the insulator film 17 and the
substrate 1 are etched using a photo-resist film (which is not
shown in the figure) patterned by using a photolithography
technique as a mask, a contact groove 18 is formed by removing the
photo-resist film. This contact groove 18 is formed so as to
penetrate through the P+ type semiconductor region 15 which will be
a source of the trench PMOS between the adjoining gate electrodes
6.
[0081] By introducing N-type impurity ions from the bottom of the
contact groove 18, an N+ type semiconductor region 19 is formed at
the bottom of the contact groove 18. Thus, by forming the contact
groove 18, introducing impurity ions from the contact groove 18
using the insulator film 17 as a mask, and providing the N+ type
semiconductor region 19 self-epitaxially at the bottom of the
contact groove 18, the gap between the adjoining gate electrodes 6
can be made finer because, for instance, the mask adjustment margin
can be decreased. This N+ type semiconductor region 19 is one for
making ohmic contact with the interconnect layer 21 formed in the
following step with the N-type semiconductor region 13 at the
bottom of the contact groove 18.
[0082] As shown in FIG. 15, a contact groove 20 is formed by
etching the insulator film 17 using a photo-resist film (which is
not shown in the figure) patterned by using a photolithography
technique as a mask, and removing the photo-resist film. This
contact groove 20 is formed so as to expose the surface of the P+
type semiconductor region 14 at the offset PMOS region Ac.
Moreover, at the border region Ac-At, this contact groove 20 is
formed so as to expose the surface of the interconnect layer 6M
which is electrically connected to the gate electrode 6.
[0083] Next, as shown in FIG. 16, after a film composed of TiW
(tungsten titanium) (which is not shown in the figure) is thinly
deposited as a barrier conductor film by using, for instance, a
sputtering technique over the upper surface of the insulator film
17 which includes the inside of the contact grooves 18 and 20, a
heat treatment is applied to the substrate 1. After a conductive
film composed of Al (aluminum) having a lower resistivity than the
polycrystalline silicon film which forms the gate electrode 6 is
deposited over the TiW film by using a sputtering technique, an
interconnect layer 21 composed of Al is formed by using
photolithography and etching techniques. The conductive film is a
film mainly composed of Al and, for instance, Si (silicon) and Cu
(copper) may also be included. Moreover, the barrier conductor film
plays a role in preventing an undesired reaction layer from being
formed by contacting Al with the substrate 1.
[0084] After depositing the protection film (which is not shown in
the figure) to cover the insulator film 17 and the interconnect
layer 21, the surface of the interconnect layer 21 which will be a
surface electrode (electrode pad) is exposed by removing the
protection film at the predetermined area on the interconnect layer
21 by using photolithography and etching techniques. After that, by
depositing the rear electrode (which is not shown in the figure) at
the rear face of the substrate 1, a semiconductor device including
a trench PMOS with a built-in protection circuit (offset PMOS) is
almost completed.
[0085] As mentioned above, in this embodiment, the gate electrode 6
of the trench PMOS and the gate electrode 10 of the offset PMOS are
formed in separate steps and the trench PMOS and the offset PMOS
are formed over the main face of the same substrate. At this time,
after the gate electrode 6 of the trench PMOS is formed of boron
(B) doped P-type polycrystalline silicon, the gate electrode 10 of
the offset PMOS is formed of arsenic (As) or phosphorus (P) doped
N-type polycrystalline silicon. As a result, the threshold voltage
(Vth) fluctuation of the offset PMOS constituting the protection
circuit can be controlled without an increase in the threshold
voltage (Vth) of the trench PMOS.
[0086] The invention developed by the inventors was concretely
described on the basis of the embodiments, however it is to be
understood that the invention is not intended to be limited to the
specific embodiments, and variations may be made by one skilled in
the art without departing from the spirit and scope of the
invention.
[0087] For instance, in the aforementioned embodiment, as steps for
forming the P-type gate electrode of the trench PMOS and N-type
gate electrode of offset PMOS are formed, a case was described in
which the polycrystalline silicon to be the gate electrode of the
offset MOSFET was formed after forming the polycrystalline silicon
to be the gate electrode of the trench PMOS (polycrystalline
silicon 2-layer process). On the other hand, the polycrystalline
silicon to be the gate electrode of the trench PMOS and the offset
PMOS may be formed simultaneously (polycrystalline silicon 1-layer
process). For instance, gate insulator films of the trench PMOS and
the offset PMOS are formed independently and, at the same time,
non-doped polycrystalline silicon is deposited over these gate
insulator films. After that, the polycrystalline silicon at the
trench MOS formation region is made to be P-type by injecting boron
ions, and the polycrystalline silicon at the offset PMOS formation
region is made to be N-type by injecting phosphorus ions. According
to this, the threshold voltage (Vth) fluctuation of the offset PMOS
constituting the protection circuit can be controlled without an
increase in the threshold voltage (Vth) of the trench PMOS.
[0088] The present invention is widely used in manufacturing
businesses which produce semiconductor devices.
* * * * *