U.S. patent application number 11/373488 was filed with the patent office on 2006-10-05 for semiconductor device and method of manufacturing the same.
This patent application is currently assigned to SANYO ELECTRIC CO., LTD.. Invention is credited to Hiroyasu Ishida, Kazunari Kushiyama, Makoto Oikawa, Tetsuya Okada, Yasuyuki Sayama.
Application Number | 20060220122 11/373488 |
Document ID | / |
Family ID | 37069295 |
Filed Date | 2006-10-05 |
United States Patent
Application |
20060220122 |
Kind Code |
A1 |
Sayama; Yasuyuki ; et
al. |
October 5, 2006 |
Semiconductor device and method of manufacturing the same
Abstract
An n type impurity region is provided below a gate electrode. By
setting a gate length to be less than a depth of a channel region,
a side surface of the channel region and a side surface of the n
type impurity region adjacent to the channel region form a
substantially perpendicular junction surface. Thus, since a
depletion layer widens uniformly in a depth direction of a
substrate, it is possible to secure a predetermined breakdown
voltage. Furthermore, since an interval between the channel
regions, above which the gate electrode is disposed, is uniform
from its surface to its bottom, it is possible to increase an
impurity concentration of the n type impurity region, resulting in
an achievement of a low on-resistance.
Inventors: |
Sayama; Yasuyuki; (Ota-city,
JP) ; Okada; Tetsuya; (Kumagaya-city, JP) ;
Oikawa; Makoto; (Ota-city, JP) ; Ishida;
Hiroyasu; (Ora-gun, JP) ; Kushiyama; Kazunari;
(Ora-gun, JP) |
Correspondence
Address: |
MORRISON & FOERSTER LLP
1650 TYSONS BOULEVARD
SUITE 300
MCLEAN
VA
22102
US
|
Assignee: |
SANYO ELECTRIC CO., LTD.
Osaka
JP
|
Family ID: |
37069295 |
Appl. No.: |
11/373488 |
Filed: |
March 13, 2006 |
Current U.S.
Class: |
257/341 ;
257/E21.418; 257/E29.134; 257/E29.136; 257/E29.257 |
Current CPC
Class: |
H01L 29/66712 20130101;
H01L 29/7802 20130101; H01L 29/42372 20130101; H01L 29/0878
20130101; H01L 29/4238 20130101 |
Class at
Publication: |
257/341 |
International
Class: |
H01L 29/76 20060101
H01L029/76 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 17, 2005 |
JP |
2005-077570 |
Feb 24, 2006 |
JP |
2006-048729 |
Claims
1. A semiconductor device comprising: a semiconductor substrate of
a first general conductivity type; a semiconductor layer of the
first general conductivity type disposed on a surface of the
semiconductor substrate so as to provide a drain region; two
channel regions of a second general conductivity type disposed on
the semiconductor layer; an impurity region of the first general
conductivity type disposed between the two channel regions, an
junction interface between the impurity region and one of the
channel regions being perpendicular to the surface of the
semiconductor substrate; an insulating film disposed on the
impurity region; a gate electrode disposed on the insulating film;
and a source region of the first general conductivity type formed
in a surface of each of the channel regions.
2. The semiconductor device of claim 1, wherein a bottom of the
impurity region and a bottom of each of the channel regions are at
a same level.
3. The semiconductor device of claim 1, wherein the gate electrode
comprises a first gate electrode portion and a second gate
electrode portion that are disposed on the impurity region between
the two channel regions, the first gate electrode portion is at
least partially separated from the second gate electrode portion,
and the first and second gate electrode portions are covered by
another insulating film.
4. The semiconductor device of claim 3, wherein a width of each of
the first and second gate electrode portions is equal to or less
than a depth of the channel regions.
5. The semiconductor device of claim 3, wherein a ratio of a
separation width between the first and second gate electrode
portions to the depth of the channel region is 0.15 or smaller.
6. The semiconductor device of claim 1, wherein the impurity region
is configured to be pinched off by depletion regions extending from
the channel regions when a the gate electrode and the source region
are at a same electrical potential and a reverse bias voltage is
applied between the source and drain regions.
7. A method of manufacturing a semiconductor device, comprising:
providing a device intermediate comprising a semiconductor
substrate of a first general conductivity type, a semiconductor
layer of the first general conductivity type disposed on the
semiconductor substrate and a first insulating film disposed on the
semiconductor layer; forming a gate electrode on the first
insulating film; forming an impurity region of the first general
conductivity type in the semiconductor layer under the gate
electrode after the formation of the gate electrode; forming two
channel regions of a second general conductivity type in the
semiconductor layer so that the impurity region connects the two
channel regions; forming a source region of the first general
conductivity type in each of the channel regions; and forming a
second insulating film covering the gate electrode.
8. A method of manufacturing a semiconductor device, comprising:
providing a device intermediate comprising a semiconductor
substrate of a first general conductivity type, a semiconductor
layer of the first general conductivity type disposed on a surface
of the semiconductor substrate and a first insulating film disposed
on the semiconductor layer; forming on the first insulation film a
gate electrode having an opening therein; implanting a first
impurity for the first general conductivity type into part of the
semiconductor layer through the opening of the gate electrode;
implanting a second impurity for the second general conductivity
type into part of the semiconductor layer that is outside the gate
electrode; heating the device intermediate so that the first and
second impurities are diffused so as to form an impurity region and
a channel region that have an junction interface perpendicular to
the surface of the semiconductor substrate; forming a source region
of the first general conductivity type in the channel region; and
forming a second insulating film covering the gate electrode.
9. The method of claim 8, wherein a width of the gate electrode
between the opening and an edge of the gate electrode is equal to
or less than a depth of the channel region.
10. The method of claim 7, wherein the impurity region and the
channel regions have an equal impurity concentration.
11. The method of claim 8, wherein the impurity region and the
channel region have an equal impurity concentration.
12. The method of claim 10, wherein the equal impurity
concentration is about 1.times.10.sup.17 cm.sup.-3.
13. The method of claim 11, wherein the equal impurity
concentration is about 1.times.10.sup.17 cm.sup.-3.
14. The method of claim 8, wherein the opening of the gate
electrodes creates a separation of two parallel portions of the
gate electrode, a ratio of a separation width between the two
parallel portions to a depth of the channel region is 0.15 or
smaller.
15. The method of claim 7, wherein a bottom of the impurity region
and a bottom of each of the channel regions are at a same
level.
16. The method of claim 8, wherein a bottom of the impurity region
and a bottom of the channel region are at a same level.
17. The method of claim 8, wherein the source region is formed by
an ion implantation and a diffusion.
18. A semiconductor device comprising: a semiconductor substrate of
a first general conductivity type; a semiconductor layer of the
first general conductivity type disposed on a surface of the
semiconductor substrate so as to provide a drain region; two
channel regions of a second general conductivity type disposed on
the semiconductor layer; an impurity region of the first general
conductivity type disposed between the two channel regions so as to
connect the two channel regions; an insulating film disposed on the
impurity region; a gate electrode disposed on the insulating film
and comprising a first gate electrode portion and a second gate
electrode portion that are disposed on the impurity region between
the two channel regions, the first gate electrode portion being at
least partially separated from the second gate electrode portion;
and a source region of the first general conductivity type formed
in a surface of each of the channel regions.
19. A semiconductor device comprising: a semiconductor substrate of
a first general conductivity type; a semiconductor layer of the
first general conductivity type disposed on a surface of the
semiconductor substrate so as to provide a drain region; two
channel regions of a second general conductivity type disposed on
the semiconductor layer, each of the channel regions being
elongated in a direction; an impurity region of the first general
conductivity type disposed between the two elongated channel
regions, the impurity region being elongated in the direction; an
insulating film disposed on the elongated impurity region and
channel regions; a gate electrode disposed on the insulating film
and having a slit elongated in the direction but not reaching an
edge portion of the gate electrode; and a source region of the
first general conductivity type formed in a surface of each of the
channel regions.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a semiconductor device and
a method of manufacturing the same. In particular, the present
invention relates to a semiconductor device whose drain-to-source
breakdown voltage, V.sub.DSS, is increased and a method of
manufacturing the same.
[0003] 2. Description of the Related Art
[0004] By referring to FIG. 10 and FIGS. 11A to 11C, a conventional
semiconductor device and a method of manufacturing the same will be
described by taking a MOSFET as an example.
[0005] As shown in FIG. 10, a drain region 20 is provided, for
example, by laminating an n type epitaxial layer 22 on an n+ type
silicon semiconductor substrate 21, and a plurality of p type
channel regions 24 are provided on a surface of the drain region
20. A gate electrode 33 is provided on a portion on the surface of
the n type epitaxial layer between the two p type channel regions
24 which are adjacent to each other, with a gate insulation film 31
interposed therebetween. Peripheries of the gate electrode 33 are
covered with an interlayer insulating film 36. Additionally, n+
type source regions 35, being formed in the surface of the channel
regions 24, are in contact with a source electrode 38.
[0006] As a technology for the above-mentioned MOSFET of a
so-called planar structure, one in which an n type impurity layer
40 having a higher impurity concentration than the epitaxial layer
22 is arranged on the surface of the n- type epitaxial layer 22
between the two adjacent p type channel regions 24 is also known.
In case of a MOSFET whose breakdown voltage is 600 V, it is
possible to increase the impurity concentration of the n type
impurity layer 40 to approximately 1.times.10.sup.16 cm.sup.-3.
This technology brings about an effect of reducing a
drain-to-source resistance when the MOSFET is in the ON state. This
technology is described, for instance, in Japanese Patent
Application Publication No. 2622378.
[0007] By referring to FIGS. 11A to 11C, the method of
manufacturing the above-mentioned MOSFET will be described.
[0008] A substrate, obtained, for example, by laminating the n-
type epitaxial layer 22 on the n+ type silicon semiconductor
substrate 21, forms the drain region 20. Ions of an n type impurity
(for example, phosphor: P) are implanted into an entire surface of
the n- type epitaxial layer (FIG. 11A). Thereafter, the gate oxide
film 31 and the gate electrode 33 are formed. Then, ions of a p
type impurity (for example, boron: B) are implanted, by using the
gate electrode 33 as a mask (FIG. 11B). Subsequently, by diffusing
the n type impurity and the p type impurity through a thermal
treatment, the n type impurity layer 40 and the channel regions 24
are formed. On the surface of the channel regions 24, the source
regions 35 are formed (FIG. 11C). Then, the gate electrode 33 is
covered with the interlayer insulating film and the source
electrode (not illustrated) is formed.
[0009] In the MOSFET shown in FIG. 10, when the MOSFET is in the ON
state, the drain region 20 below the gate electrode 33 works as a
region for causing an electric current to flow in a direction
perpendicular to the substrate. That is, the n type impurity layer
40 having a high impurity concentration is arranged in a portion
(hereinafter, referred to as a .pi. portion 45) on the surface of
the drain region 20 between each two adjacent ones of the channel
regions 24 because it is preferable that, when the MOSFET is in the
ON state, a resistance of the drain region 20 be low.
[0010] On the other hand, when the MOSFET is in the OFF state, a
drain-to-source voltage is applied and a reverse bias is generated.
As a result, a depletion layer 50 extends from pn junctions with
the channel region 24 and generates a depletion state, whereby the
breakdown voltage is increased. That is, it is preferable that the
impurity concentration of the .pi. portion 45 be higher in order to
allow the drain region 20 to have a lower resistance. However, if
the impurity concentration of the .pi.60 portion 45 increases more
than necessarily, the extension width of the depletion layer 50
becomes narrow as shown in the dotted line of FIG. 10, whereby
there arises a problem that a breakdown voltage is
deteriorated.
[0011] Additionally, because a curvature from a bottom to a side
surface becomes large in each of the channel regions 24 formed
through diffusion, the interval between the two adjacent ones of
the channel regions 24 becomes wide in vicinity of the bottoms
thereof. That is, the depletion layer 50 pinching off sufficiently
in vicinity of the top surface of the channel regions 24 does not
sufficiently pinch off in vicinity of the bottoms thereof, whereby
there arises a problem that a breakdown tends to occur in corner
portions (refer to a region "a" in FIG. 10) of each of the channel
regions 24.
[0012] Furthermore, because the ion implantation of the n type
impurity layer 40 is performed before the formation of the gate
electrode (refer to FIG. 11A), the n type impurity (for example,
phosphor) is diffused through a thermal treatment during the
formation of the gate electrode 33. Therefore, after the formation
of the channel regions 24, a depth of each of the channel regions
24 tends to be shallower than that of the .pi. portion 45, whereby
a reduced V.sub.DSS becomes a problem.
SUMMARY OF THE INVENTION
[0013] The present invention provides a semiconductor device that
includes a semiconductor substrate of a first general conductivity
type, a semiconductor layer of the first general conductivity type
disposed on a surface of the semiconductor substrate so as to
provide a drain region, two channel regions of a second general
conductivity type disposed on the semiconductor layer, an impurity
region of the first general conductivity type disposed between the
two channel regions, an junction interface between the impurity
region and one of the channel regions being perpendicular to the
surface of the semiconductor substrate, an insulating film disposed
on the impurity region, a gate electrode disposed on the insulating
film, and a source region of the first general conductivity type
formed in a surface of each of the channel regions.
[0014] The present invention also provides a method of
manufacturing a semiconductor device. The method includes providing
a device intermediate comprising a semiconductor substrate of a
first general conductivity type, a semiconductor layer of the first
general conductivity type disposed on the semiconductor substrate
and a first insulating film disposed on the semiconductor layer,
forming a gate electrode on the first insulating film, forming an
impurity region of the first general conductivity type in the
semiconductor layer under the gate electrode after the formation of
the gate electrode, forming two channel regions of a second general
conductivity type in the semiconductor layer so that the impurity
region connects the two channel regions, forming a source region of
the first general conductivity type in each of the channel regions,
and forming a second insulating film covering the gate
electrode.
[0015] The present invention further provides a method of
manufacturing a semiconductor device. The method includes providing
a device intermediate comprising a semiconductor substrate of a
first general conductivity type, a semiconductor layer of the first
general conductivity type disposed on a surface of the
semiconductor substrate and a first insulating film disposed on the
semiconductor layer, forming on the first insulation film a gate
electrode having an opening therein, implanting a first impurity
for the first general conductivity type into part of the
semiconductor layer through the opening of the gate electrode,
implanting a second impurity for the second general conductivity
type into part of the semiconductor layer that is outside the gate
electrode, heating the device intermediate so that the first and
second impurities are diffused so as to form an impurity region and
a channel region that have an junction interface perpendicular to
the surface of the semiconductor substrate, forming a source region
of the first general conductivity type in the channel region, and
forming a second insulating film covering the gate electrode.
[0016] The present invention further provides a semiconductor
device that includes a semiconductor substrate of a first general
conductivity type, a semiconductor layer of the first general
conductivity type disposed on a surface of the semiconductor
substrate so as to provide a drain region, two channel regions of a
second general conductivity type disposed on the semiconductor
layer, an impurity region of the first general conductivity type
disposed between the two channel regions so as to connect the two
channel regions, an insulating film disposed on the impurity
region, a gate electrode disposed on the insulating film and
comprising a first gate electrode portion and a second gate
electrode portion that are disposed on the impurity region between
the two channel regions, the first gate electrode portion being at
least partially separated from the second gate electrode portion,
and a source region of the first general conductivity type formed
in a surface of each of the channel regions.
[0017] The present invention further provides a semiconductor
device that includes a semiconductor substrate of a first general
conductivity type, a semiconductor layer of the first general
conductivity type disposed on a surface of the semiconductor
substrate so as to provide a drain region, two channel regions of a
second general conductivity type disposed on the semiconductor
layer, each of the channel regions being elongated in a direction,
an impurity region of the first general conductivity type disposed
between the two elongated channel regions, the impurity region
being elongated in the direction, an insulating film disposed on
the elongated impurity region and channel regions, a gate electrode
disposed on the insulating film and having a slit elongated in the
direction but not reaching an edge portion of the gate electrode,
and a source region of the first general conductivity type formed
in a surface of each of the channel regions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIGS. 1A and 1B are cross-sectional views and FIG. 1C is a
perspective view explaining a semiconductor device of a first and a
second embodiments of the invention.
[0019] FIG. 2 is a characteristic chart explaining the
semiconductor device of the first and the second embodiments of the
invention.
[0020] FIG. 3 is a cross-sectional view explaining a method of
manufacturing the semiconductor device of the first and the second
embodiments of the invention.
[0021] FIG. 4 is a cross-sectional view explaining the method of
manufacturing the semiconductor device of the first and the second
embodiments of the invention.
[0022] FIG. 5 is a cross-sectional view explaining the method of
manufacturing the semiconductor device of the first and the second
embodiments of the invention.
[0023] FIG. 6 is a cross-sectional view explaining the method of
manufacturing the semiconductor device of the first and the second
embodiments of the invention.
[0024] FIG. 7 is a cross-sectional view explaining the method of
manufacturing the semiconductor device of the first and the second
embodiments of the invention.
[0025] FIGS. 8A and 8B are cross-sectional views explaining the
method of manufacturing the semiconductor device of the first and
the second embodiments of the invention.
[0026] FIG. 9 is a cross-sectional view explaining the method of
manufacturing the semiconductor device of the first and the second
embodiments of the invention.
[0027] FIG. 10 is a cross-sectional view explaining a conventional
semiconductor device.
[0028] FIGS. 11A to 11C are cross-sectional views explaining a
method of manufacturing the conventional semiconductor device.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] An embodiment of the present invention will be described
with reference to FIGS. 1 to 9 by taking an n-channel MOSFET as an
example.
[0030] FIGS. 1A and 1B are cross-sectional views indicating a
structure of a MOSFET of a first embodiment of the invention. FIGS.
1A and 1B are cross-sectional views showing a single cell of the
MOSFET, and plural ones of the cells are arranged to constitute the
MOSFET. FIG. 1C shows a perspective view of the MOSFET cut at the
section shown in FIG. 1A.
[0031] The MOSFET includes a semiconductor substrate 1, a
semiconductor layer 2, channel regions 4, a one conductive type
impurity region 14, a gate electrode 13, a gate insulation film 11,
an interlayer insulating film 16, and source regions 15.
[0032] A substrate obtained, for example, by laminating the n type
epitaxial layer 2 on the n+ type silicon semiconductor substrate 1
is prepared, and thus a drain region 10 is provided. The p type
channel regions 4 are provided on the surface of the n- type
epitaxial layer 2. The channel regions 4 are a plurality of p type
impurity regions provided on the n- type epitaxial layer 2 through
an ion implantation and an ion diffusion. Note that, in some cases,
a low-resistance layer 1 is formed on the semiconductor layer 2 by
the impurity diffusion.
[0033] The gate oxide film 11 is provided on the surface of the n-
type epitaxial layer 2, and the gate electrode 13 is arranged on
the gate oxide film 11. The interlayer insulating film 16 is
provided over the gate electrode 13. Peripheries of the gate
electrode 13 are covered with the gate oxide film 11 and the
interlayer insulating film 16.
[0034] The cell shown in FIGS. 1A-1C includes the gate electrode 13
that has a separation hole 12 elongated in the longitudinal
direction of the gate electrode 13. The width of the separation is
L.sub.KT. In this embodiment, the separation hole 12 does not
completely separate the gate electrode 13, and both ends of the
gate electrode 13 are left intact. As a modification, one end of
the gate electrode 13 may be separated completely while another end
holds the separated portions of the gate electrode together. As a
further modification, the gate electrode may be completely
separated. In either embodiment, all the gate electrode 13 are
connected together outside the MOSFET element region on which the
cells are formed. As shown in FIG. 1C, the separated gate
electrodes 13a and 13b are covered by a single interlayer
insulating film 16. Both of the separated gate electrodes 13a and
13b have an equal width L.sub.g. As shown in FIG. 1C, the channel
region 4 also has an elongated form and is aligned with a
corresponding gate electrode.
[0035] The source regions 15 are highly concentrated n type
impurity region provided in the channel regions 4. Each of the
source region 15 is placed in a portion of a region, a part of
which is under the gate electrode 13, and the rest being outward
thereof. The source regions 15 are in contact with a source
electrode 18 through contact holes CH between the interlayer
insulating film 16.
[0036] In a region under the gate electrode 13 on the surface of
the n- type epitaxial layer 2, an n type impurity region 14 is
provided. Side surfaces of the n type impurity region 14 and side
surfaces of each of the channel region 4 adjacent thereto form a
substantially perpendicular junction surfaces. Additionally, a
bottom of the n type impurity region 14 and bottoms of the channel
regions 4 are located at a substantially equal depth by the
diffusion of the impurities.
[0037] The separated gate electrodes 13a and 13b are arranged
symmetrically with respect to the n type impurity region 14. That
is, a centerline of the separation hole 12 substantially coincides
with a centerline of the n type impurity region 14 as indicated by
an alternate long and short dash line. Additionally, the gate width
L.sub.g is not more than a depth X.sub.ch of the channel regions 4.
In this manner, the n type impurity region 14 having the side
surfaces forming the junction surface substantially perpendicular
to the channel regions 4, and having the equal depth to that of the
channel regions 4 is formed. Details thereof will be described
later. Additionally, a drain electrode is formed on a back surface
of the substrate 1 although an illustration thereof is omitted.
Note that, since the separated gate electrodes 13a and 13b are
identical, the following description will be given by using the
gate electrode 13a.
[0038] FIG. 1B is a cross-sectional view indicating a state of a
depletion layer 50 when drain-to-source voltage is applied in the
OFF state. Note that the interlayer insulating film 16 and the
source electrode 18 are omitted in FIG. 1B.
[0039] In this embodiment, the side surfaces of the n type impurity
region 14 respectively form the junction surfaces substantially
parallel to the side surfaces of the channel regions 4 adjacent
thereto, and the bottom of the n type impurity region 14 and the
bottoms of the channel regions 4 are located substantially at an
equal depth. That is, the channel regions 4 adjacent to each other
are apart from each other not in a manner that cross-sectional
shapes of edge portions of the respective channel regions 4 are in
curved shapes with the edge portions having curvatures, rather in a
manner that an equal distance between the channel regions 4 is kept
in vicinity of the top and in vicinity of the bottom. Additionally,
the n type impurity region 14 is provided with conditions allowing
the depletion layer 50, which extends from the channel regions 4 in
both sides thereof, to pinch off. Specifically, a ratio of the
separation width L.sub.KT of the gate electrode 13 to the depth
X.sub.ch of the channel regions 4 is set to 0.15 or less: 1.
[0040] In this manner, the depletion layer 50 inside the n type
impurity region 14 extends from the channel regions 4 in both sides
thereof and pinches off as indicated by dashed lines, and thereby
extends substantially evenly in a depth direction (vertical
direction) of the substrate.
[0041] Conventionally, the depletion layer does not sufficiently
pinch off in the corner portion (the region "a" in FIG. 10) of each
of the channel regions 24, whereby there arises a problem that a
breakdown tends to occur in the corner portion. However, in this
embodiment, it is possible to avoid this and to enhance a breakdown
voltage of the MOSFET.
[0042] Additionally, distances between the channel regions 4
arranged with the gate electrode 13 interposed therebetween are
uniform at the top surfaces thereof and at the bottoms thereof,
whereby the depletion layer 50 sufficiently pinches off.
Accordingly, it becomes possible to increase an impurity
concentration of the n type impurity region 14. That is,
on-resistance reduction is achieved in the ON state of the
MOSFET.
[0043] As described above, in this embodiment, the bottoms of the
channel regions 4 and the bottom of the n type impurity region 14
are formed in a substantially same plane. Then, when the
drain-to-source voltage is applied in the OFF state of the MOSFET,
the depletion layer 50 extending from the channel regions 4 in the
both sides thereof is allowed to pinch off in the n type impurity
region 14.
[0044] In the manner described above, it is possible to obtain a
semiconductor device ensuring a predetermined breakdown voltage and
having a low on-resistance in the ON state of the MOSFET.
[0045] Next, a second embodiment of the invention will be
described.
[0046] As shown in FIGS. 1A and 1B (the first embodiment),
respective junction surfaces of side surfaces of an n type impurity
region 14 and channel regions 4 can be formed to be substantially
perpendicular by setting the gate width L.sub.g to be not more than
the depth X.sub.ch of the channel regions 4. Additionally, by
allowing a depletion layer 50 to pinch off evenly inside the n type
impurity region 14 in the depth (vertical) direction of the
substrate, a predetermined breakdown voltage can be obtained.
[0047] In the second embodiment, more specifically, an MOSFET
capable of obtaining a predetermined breakdown voltage will be
described. Note that, because a structure thereof is the same as
the one shown in FIGS. 1A and 1B, the description will be given by
referring to FIGS. 1A and 1B.
[0048] In the second embodiment, a description will be given by
taking as an example a MOSFET to which a drain-to-source voltage
not less than 600 V can be applied, i.e., a MOFSET realizing a
breakdown voltage of 600 V or higher.
[0049] As in the case with the first embodiment, in order to make a
side surface of a n type impurity region 14 and a side surface of
each of a channel regions 4 form a substantially perpendicular
junction surface, a gate length L.sub.g is set to be not more than
the depth X.sub.ch of the channel regions 4. Additionally, in order
to equalize the depth of the channel regions 4 and the depth of the
n type impurity region 14, dose amounts of respective impurities
are at levels comparable to each other.
[0050] In the second embodiment, a ratio of a separation width
L.sub.KT of a gate electrode 13 to the depth X.sub.ch of the
channel region 4 (L.sub.KT: X.sub.ch) is set to 0.15 or less: 1. To
be more concrete, the separation width L.sub.KT is set to 0.6
.mu.m, and the depth X.sub.ch of the channel regions 4 is set to 4
.mu.m. Furthermore, a resistivity of an n- type epitaxial layer 2
is set to a range of 15 .OMEGA. cm to 20 .OMEGA. cm.
[0051] By adopting the above-described conditions for the
separation width L.sub.KT and the depth X.sub.ch of the channel
region 4, the depletion layer 50 is fully pinched off, and a pn
junction having a substantially perpendicular junction surface is
obtained. Therefore, it is possible to increase an impurity
concentration of the n type impurity region 14 to 1.times.10.sup.17
cm.sup..quadrature.3. Note that an impurity concentration of the
channel region 4 is also 1.times.10.sup.17 cm.sup..quadrature.3 in
this case.
[0052] Specifically, in the ON state of the MOSFET, since the
impurity concentration of the n type impurity region 14 which is a
region (the conventional .pi. portion) serving as a current path
just below the gate electrode 13, is high, it is possible to allow
a current through the current path with a low resistance, and hence
an on-resistance of the MOSFET can be reduced. On the other hand,
in the OFF state of the MOSFET, the depletion layer 50 can be
widened uniformly in the depth direction of the substrate
(vertically). Therefore, even in the case where a voltage of about
600 V is applied between the source and the drain, it is possible
to widen the depletion layer 50 uniformly in the depth direction of
(vertical direction to) the substrate. Specifically, the MOSFET
having a low on-resistance as well as a high breakdown voltage of
about 600 V can be provided.
[0053] FIG. 2 is a chart showing a relation between the separation
width L.sub.KT and V.sub.DSS. Under the condition that the n type
impurity region 14 is formed with a constant impurity
concentration, the breakdown voltage (V.sub.DSS) was evaluated
while the separation width L.sub.KT being varied. Note that a dose
amount of the n type impurity region 14 is 1.5.times.10.sup.13
cm.sup.-2.
[0054] According to the above-described structure, if the
separation width L.sub.KT is 0.6 .mu.m or less, the depletion layer
50 is fully pinched off. Therefore, it is proved that the n type
impurity region 14 with the breakdown voltage of 600 V is
obtained.
[0055] By referring to FIG. 3 to FIG. 9, a method of manufacturing
the MOSFET of these embodiments will be described by taking a case
of the second embodiment as an example.
[0056] A method of manufacturing the semiconductor device of this
embodiment comprises: a step of forming a drain region by
laminating a one conductivity type semiconductor layer on a one
conductivity semiconductor substrate and of forming a first
insulating film on the entire surface of the resultant structure; a
step of forming a plurality of gate electrodes on the first
insulating film, at least part of which are isolated from each
other with a predetermined separation width; a step of implanting
impurities of one conductivity type into a surface of the
semiconductor layer between the plurality of gate electrodes;
implanting impurities of an opposite conductivity type to one
conductivity type into a surface of the semiconductor layer outside
the plurality of gate electrodes; a step of performing a thermal
treatment, thus forming a plurality of channel regions and an
impurity region of one conductivity type having a junction surface
approximately perpendicular to a side surface of each of the
channel regions; a step of forming a source region of one
conductivity type in surfaces of the channel regions; and a step of
forming a second insulating film covering the plurality of gate
electrodes wholly.
[0057] A first step (see FIG. 3):
[0058] An n- type epitaxial layer 2 is laminated on an n+ type
silicon semiconductor substrate 1, thus preparing a substrate
serving as a drain region 10. An entire surface of the resultant
structure is thermally oxidized at a temperature of about
1000.degree. C., thus forming a gate oxide film 11 to a thickness
of, for example, about 1000 .ANG. in accordance with a threshold
value of the MOSFET.
[0059] A second step (see FIG. 4):
[0060] A non-doped polysilicon layer is deposited on an entire
surface of the gate oxide film 11, and phosphor (P), for example,
is implanted and diffused into the non-doped polysilicon layer at a
high concentration, thus making the non-doped polysilicon layer
highly conductive. By use of a photoresist film (not shown) having
a desired pattern as a mask, the polysilicon film is subjected to
dry etching, thus forming a gate electrode 13. One cell of the
MOSFET is composed of gate electrodes 13a and 13b, which have an
equal gate width L.sub.g and which are separated from each other at
last part of thereof by a separation hole 12. Specifically, the
separation hole 12 is formed simultaneously with a formation of a
pattern of the gate electrode 13, thus forming the separated gate
electrodes 13a and 13b. A width of the separation hole 12, which is
a separation width L.sub.KT, is equal to about 0.6 .mu.m, for
example. Note that the gate electrode 13 may be formed in a way
that an impurity doped polysilicon layer is deposited on the entire
surface of an insulating film 11 and then patterned. The patterning
of the gate electrode 13 and the formation of the separation hole
12 may be carried out in different steps. Since the separated gate
electrodes 13a and 13b, which are separated from each other, have
the same structure, the description of subsequent steps will be
made by use of the separated gate electrode 13a.
[0061] The gate width L.sub.g of the separated gate electrode 13a
is set to be not more than a depth of a channel region to be formed
afterward, which is, for example, about 2.0 .mu.m.
[0062] A third step (see FIG. 5):
[0063] A photoresist film PR is formed on an entire surface of the
resultant structure, and then patterned so that the separation hole
12 and a periphery of the separation hole 12 are exposed. N type
impurities, for example, phosphor P, are ion-implanted by use of
the photoresist film PR as a mask. For example, a dose amount is
about 1.0.times.10.sup.13 cm.sup.-2, and an acceleration energy is
120 KeV. The n type impurities are implanted from the separation
hole 12 into the surface of an n- type epitaxial layer 2 through
the gate oxidized film 11. Specifically, a surface region of the n-
type epitaxial layer 2 having a width approximately equal to the
separation width L.sub.KT, which is located just below the
separation hole 12, is an implantation region of the n type
impurities, as shown in FIG. 5.
[0064] A fourth step (see FIG. 6):
[0065] A photoresist film PR is formed again, and a portion in the
photoresist film PR covering at least the separation hole 12 is
left by use of a photolithography process. P type impurities, for
example, boron (B), are ion-implanted into the surface of the n-
type epitaxial layer 2 outside the gate electrode 13. Herein, a
dose amount of the p type impurities in the fourth step and the
dose amount of the n type impurities in the third step are
approximately equal. For example, in the case of the boron, the
boron impurities are ion-implanted under the condition that the
acceleration energy is 80 KeV and the dose amount is
2.times.10.sup.13 cm.sup.-2. The surface of the n- type epitaxial
layer 2 outside both sides of the gate electrode 13 is an
implantation region into which the p type impurities are
implanted.
[0066] A Fifth step (see FIG. 7):
[0067] A thermal treatment is carried out at a temperature of
1150.degree. C. for 180 minutes, whereby the n type impurities and
the p type impurities are diffused. Thus, channel regions 4 are
formed in portions of a surface of the epitaxial layer 2 disposed
on both sides of the gate electrode 13, and an n type impurity
region 14 is formed below the separation hole 12.
[0068] The n type impurities implanted from the separation hole 12
are diffused in a vertical direction with respect to the depth of
the substrate, and simultaneously are diffused in a lateral
(horizontal) direction with respect to the substrate. Specifically,
by setting the gate length L.sub.g of the separated gate electrode
13a to be equal to or less than the depth X.sub.ch of the channel
region 4, side surfaces of the n type impurity region 14 form
junction surfaces substantially parallel to the side surfaces of
the channel regions 4 adjacent thereto. Additionally, a bottom of
the n type impurity region 14 and bottoms of the channel regions 4
are located at depths substantially equal to each other by the
diffusion of the impurities under the conditions of the fourth
step.
[0069] Furthermore, a relation expressed by a ratio (the separation
width L.sub.KT: the depth X.sub.ch of the channel region 4, which
is equal to 0.15 or less: 1) is adopted. To be more concrete,
L.sub.KT is set to 0.6 .mu.m, and X.sub.ch is set to 4 .mu.m. Thus,
a depletion layer can be fully pinched off in the n type impurity
region 14.
[0070] Specifically, since it is possible to suppress a breakdown
in the vicinity of the bottoms of the channel regions 4, the
impurity concentration of the n type impurity region 14 can be
improved to be higher than that in the related arts. Accordingly,
it is possible to reduce a resistance of a current path in the ON
state of the MOSFET.
[0071] When the depth X.sub.ch of the channel region 4 is formed to
be further deeper depending on characteristics of the MOSFET, the
diffusion process is further carried out. Thus, though the width of
the n type impurity region 14 varies, there is no problem as long
as the width thereof is within a range where the MOSFET can pinch
off at the application of V.sub.DSS.
[0072] A sixth step (see FIGS. 8A and 8B):
[0073] A mask exposing a part of the channel region 4 is formed by
a new photoresist film PR, n+ type impurities, for example, arsenic
(As), are ion-implanted. An acceleration energy is set to 100 KeV,
and a dose amount is set to about 5.times.10.sup.15 cm.sup.-2 (see
FIG. 8A).
[0074] Thereafter, an insulating film 16' such as PSG (Phosphorus
Silicate Glass) serving as an interlayer insulating film is
deposited by a CVD method. The n+ type impurities are diffused by a
thermal treatment at the time when the insulating film 16' is
formed, thus forming a source region 15 (see FIG. 8A). The thermal
treatment is carried out at a temperature lower than 1000.degree.
C. for about 60 minutes.
[0075] A sixth step (FIG. 9):
[0076] The insulating film 16' is etched by use of a new
photoresist film (not shown) as a mask, and an interlayer
insulating film 16 is left, and simultaneously contact holes CH are
formed. The separated gate electrodes 13a and 13b above the n type
impurity region 14 are wholly covered with the interlayer
insulating film 16.
[0077] Thereafter, a barrier metal (not shown) is formed on the
entire surface of the resultant structure, and aluminum alloy is
sputtered so as to have a film thickness ranging from about 20000
.ANG. to 50000 .ANG.. An alloying and thermal treatment is
performed, thus forming a source electrode 18 patterned to a
desired pattern. Thus, a final structure shown in FIG. 1A is
obtained.
[0078] An n channel type MOSFET was described as the example in
this embodiment of the present invention, and a p channel type
MOSFET having an opposite conductive type to the n channel type
MOSFET can be similarly embodied. Preferred embodiments of the
present invention are not limited to these. Specifically, preferred
embodiments of the present invention can be similarly embodied and
the same effects can be achieved as long as the semiconductor
element is one of insulated gate type including an IGBT (Insulated
Gate Bipolar Transistor) which is an insulated gate type bipolar
transistor and in which a semiconductor layer having an opposite
conductivity type to the one conductivity type semiconductor
substrate 1 is disposed below the substrate 1.
[0079] According to preferred embodiments of the present invention,
first, the n type impurity region is provided, whereby the junction
surface in which the side surface of the channel region is
substantially perpendicular to the side surface of the n type
impurity region can be formed. Accordingly, a width of an interval
between the channel regions is constant from the surface of the
channel regions to the bottom thereof. Then, by forming the n type
impurity region under the condition that the depletion layer
extending from both sides of the channel regions is pinched off
(with a certain impurity concentration and a certain width), the
pinch-off of the depletion layer is sufficient even in the bottom
portion of the channel region. Thus, it is possible to avoid a
breakdown in corner portions of the channel regions (regions "a" of
FIG. 10).
[0080] To be more concrete, in the diffusion step of forming the
channel region, by setting the depth X.sub.ch of the channel region
to be not less than the gate length L.sub.g of the separated gate
electrodes of one cell, it is possible to provide the n type
impurity region having the junction surface perpendicular to the
side surface of the channel region and having the depth equal to
that of the channel region.
[0081] Furthermore, by adopting a relation expressed by a ratio
(the separation width L.sub.KT of the separated gate electrodes:
the depth X.sub.ch of the channel region, which is equal to or less
than 0.6:4), it is possible to form the n type impurity region
forming the junction surface perpendicular to the channel region,
and it is possible to make the width of the n type impurity region
equal to the width having a value for pinching off the depletion
layer in the n type impurity region. Thus, the drain-to-source
voltage V.sub.DSS of not less than 600 V can be obtained.
Furthermore, since the depletion layer is fully pinched off even in
the vicinity of the bottom portion of the channel region, it is
possible to increase the impurity concentration of the n type
impurity region up to 1.times.10.sup.17 cm.sup.-3. Hence, it is
possible to achieve a low resistance in the ON state of the MOSFET
and an increase of the breakdown voltage in the OFF state
thereof.
[0082] Secondly, performing the ion-implantation of n type impurity
region, after the formation of the gate electrode, the n type
impurity region is formed in the diffusion step for forming the
channel region. Thus, a control of the depth of the n type impurity
region is made easier without being influenced by the thermal
treatment during the formation of the gate electrode.
[0083] Furthermore, by controlling of the dose amount in the
channel region and the n type impurity region, it is possible to
form the bottoms thereof to be substantially uniform. For example,
boron is implanted into the channel region under the condition that
the acceleration energy is 80 KeV and the dose amount is
2.times.10.sup.13 cm.sup.-2, and phosphor is implanted into the n
type impurity region under condition that the acceleration energy
is 120 KeV and the dose amount is 1.times.10.sup.13 cm.sup.-2, and
then the thermal treatment is carried out at the temperature of
1150.degree. C. Thus, the channel region and the n type impurity
region have the substantially uniform depth. In this case, though
the n type impurity region has an impurity concentration, which is
about 1.times.10.sup.17 cm.sup.-3 and is higher than that in the
related art, the depletion layer is pinched off vertically in the
depth direction of the substrate. Thus, the predetermined breakdown
voltage is obtained. For example, in this embodiment, in the case
where the resistivity p of the n type epitaxial layer ranges from
15 .OMEGA. cm to 20 .OMEGA. cm, the drain-to-source breakdown
voltage of not less than 600 V can be obtained.
* * * * *