U.S. patent application number 14/138167 was filed with the patent office on 2014-07-24 for method of producing a high-voltage-resistant semiconductor component having vertically conductive semiconductor body areas and a trench structure.
This patent application is currently assigned to Infineon Technologies AG. The applicant listed for this patent is Infineon Technologies AG. Invention is credited to Frank Pfirsch.
Application Number | 20140203349 14/138167 |
Document ID | / |
Family ID | 36061981 |
Filed Date | 2014-07-24 |
United States Patent
Application |
20140203349 |
Kind Code |
A1 |
Pfirsch; Frank |
July 24, 2014 |
METHOD OF PRODUCING A HIGH-VOLTAGE-RESISTANT SEMICONDUCTOR
COMPONENT HAVING VERTICALLY CONDUCTIVE SEMICONDUCTOR BODY AREAS AND
A TRENCH STRUCTURE
Abstract
A high-voltage-resistant semiconductor component (1) has
vertically conductive semiconductor areas (17) and a trench
structure (5). These vertically conductive semiconductor areas are
formed from semiconductor body areas (10) of a first conductivity
type and are surrounded by a trench structure (5) on the upper face
(6) of the semiconductor component. For this purpose the trench
structure has a base (7) and a wall area (8) and is filled with a
material (9) with a relatively high dielectric constant
(.epsilon..sub.r). The base area (7) of the trench structure (5) is
provided with a heavily doped semiconductor material (11) of the
same conductivity type as the lightly doped semiconductor body
areas (17), and/or having a metallically conductive material
Inventors: |
Pfirsch; Frank; (Munich,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Infineon Technologies AG |
Neubiberg |
|
DE |
|
|
Assignee: |
Infineon Technologies AG
Neubiberg
DE
|
Family ID: |
36061981 |
Appl. No.: |
14/138167 |
Filed: |
December 23, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11234585 |
Sep 23, 2005 |
8643085 |
|
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14138167 |
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Current U.S.
Class: |
257/328 ;
438/268 |
Current CPC
Class: |
H01L 29/7815 20130101;
H01L 29/0653 20130101; H01L 29/41766 20130101; H01L 29/7802
20130101; H01L 29/0878 20130101; H01L 29/66712 20130101; H01L 29/41
20130101 |
Class at
Publication: |
257/328 ;
438/268 |
International
Class: |
H01L 29/78 20060101
H01L029/78; H01L 29/66 20060101 H01L029/66 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 24, 2004 |
DE |
10 2004 046 697.1 |
Claims
1-25. (canceled)
26. A high-voltage-resistant semiconductor component comprising: a
vertical MOS channel area, comprising: lightly doped drift path
regions of a first conductivity type, and a trench structure
comprising a base area and a wall area, wherein a conductive buried
layer is arranged in the base area of the trench structure, a
material with a high relative dielectric constant is arranged on
the conductive buried layer and a gate electrode is arranged on the
material with a high relative dielectric constant.
27. The high-voltage-resistant semiconductor component according to
claim 26, further comprising an upper electrode arranged between
the gate electrode and the material with a high relative dielectric
constant.
28. The high-voltage-resistant semiconductor component according to
claim 27, further comprising a gate oxide arranged between the
upper electrode and the gate electrode.
29. The high-voltage-resistant semiconductor component according to
claim 27, wherein the upper electrode is coupled to a source.
30. The high-voltage-resistant semiconductor component according to
claim 26, wherein the wall area of the trench structure further
comprises an isolation layer.
31. The high-voltage-resistant semiconductor component according to
claim 30, wherein the isolation layer comprises one or more of an
oxide, a nitride, SiO.sub.2, Si.sub.3N.sub.4, TiO.sub.2, HfO.sub.2,
Ta.sub.2O.sub.5, Al.sub.2O.sub.3 and AlN.
32. The high-voltage-resistant semiconductor component according to
claim 26, wherein the conductive buried layer comprises a heavily
doped semiconductor material of the same conductivity type as the
lightly doped drift path regions.
33. The high-voltage-resistant semiconductor component according to
claim 32, wherein the heavily doped semiconductor material, has a
material whose impurity concentration is: N.gtoreq..epsilon..sub.r
.epsilon..sub.0(E.sub.crit).sup.2/E.sub.g where .epsilon..sub.r is
the relative dielectric constant, .epsilon..sub.0 is the absolute
dielectric constant of the vacuum, E.sub.crit is the critical field
strength, E.sub.g is the band gap.
34. The high-voltage-resistant semiconductor component according to
claim 32, wherein the heavily doped semiconductor material
comprises a crystalline silicon, polysilicon or silicon carbide
with an impurity concentration of: N.sub.D Or
N.sub.A.ltoreq.110.sup.18 cm.sup.-3
35. The high-voltage-resistant semiconductor component according to
claim 26, wherein the conductive buried layer comprises a
metallically conductive material.
36. The high-voltage-resistant semiconductor component according to
claim 35, wherein the metallically conductive material comprises
one of the group consisting of a silicide, a tungsten silicide, a
cobalt silicide and a material comprising titanium, hafnium,
tantalum or alloys thereof.
37. The high-voltage-resistant semiconductor component according to
claim 26, further comprising source electrodes arranged alternately
with the gate electrodes.
38. The high-voltage-resistant semiconductor component according to
claim 37, wherein the source electrodes contact heavily doped
regions of the first conductivity type.
39. The high-voltage-resistant semiconductor component according to
claim 38, further comprising a heavily doped zone of a second
conductivity type in direct contact with the source electrode.
40. The high-voltage-resistant semiconductor component according to
claim 39, further comprising a medium-doped channel zone of the
second conductivity type.
41. The high-voltage-resistant semiconductor component according to
claim 26, wherein the trench structure is embedded in a lightly
doped semiconductor body area of one conductivity type, which is
arranged on a heavily doped substrate of the same conductivity
type, with the filled trench structure surrounding a plurality of
semiconductor body areas of the lightly doped semiconductor body
area and the upper face areas of the semiconductor body areas
having an MOS structure with individual source electrodes and
individual gate electrodes, with a medium to heavily doped impurity
zone of the opposite conductivity type being arranged in the upper
face area of the semiconductor body areas, which impurity zone
contains a gate channel area, with the impurity zone having an
individual source electrode and with the plurality of individual
source electrodes in the semiconductor body areas being
electrically connected in parallel to form a common source
electrode, and being electrically connected to the trench
structure, while the gate channel area is covered by a gate oxide
and has an individual gate electrode, with the plurality of
individual gate electrodes in the semiconductor body areas being
interconnected to form a common gate electrode, and with the
heavily doped substrate of the same conductivity type as the
lightly doped semiconductor body area having a metal coating as a
large-area drain electrode on its lower face.
42. A method for production of a plurality of semiconductor chips
from a semiconductor wafer which has semiconductor chip positions
arranged in rows and columns, the method comprising: producing a
semiconductor wafer which is lightly doped with a first
conductivity type or of an epitaxial layer which is lightly doped
with the first conductivity type and is deposited on a
semiconductor wafer which is heavily doped with the first or second
conductivity type; introducing trench structures with a base area
and a wall area into a lightly doped semiconductor body area of the
semiconductor chip positions on the semiconductor wafer;
introducing heavy doping of the same conductivity type as the
lightly doped semiconductor body area into the base area of the
trench structures, or introducing a metallically conductive coating
into the base area of the trench structures; and introducing a
material with a high relative dielectric constant into the trench
structures.
43. The method as claimed in claim 42, wherein the heavy doping of
the same conductivity type as the lightly doped semiconductor body
areas is introduced into the base area of the trench structures by
means of ion implantation technology.
44. The method as claimed in claim 42, wherein the metallically
conductive coating is introduced to the base area of the trench
structures by means of physical sputtering, vapor-deposition, or
chemically by means of chemical gas-phase deposition or
electrolytic deposition.
45. The method as claimed in claim 42, wherein before the
introduction of the metallically conductive coating to the base
area of the trench structures, the wall area of the trench
structure and those surfaces of the semiconductor wafer which are
not to be coated are selectively provided with a protective layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 11/234,585 filed 23 Sep. 2005, which in turn claims
priority from German Patent Application No. 10 2004 046 697.1,
which was filed on Sep. 24, 2004, both of said applications
incorporated herein by reference in their entirety.
TECHNICAL FIELD
[0002] The invention relates to a high-voltage-resistant
semiconductor component having vertically conductive semiconductor
body areas and having a trench structure, and to a method for its
production.
BACKGROUND
[0003] In the case of conventional vertical MOSFETs, the maximum
donor concentration [N.sub.D] in an n.sup.--region and hence also
the electrical conductivity of the n.sup.--region is governed by
the required blocking capability, and vice versa. In the event of
an avalanche breakdown, the approximately 1.5.times.10.sup.12
cm.sup.-2 donors are ionized, and find their opposite charge in the
acceptor charge of the p-conductive region of the MOSFET structure,
if the aim is to allow a higher donor concentration, then opposite
charges for the donor atoms in the n.sup.--region must be found,
for example in the same conductor plane. In the case of MOS field
plate transistors with a trench structure, as are known from the
document U.S. Pat. No. 6,573,558 B2, this is achieved by means of
the charge carriers in the field plate. In the case of compensation
components, such as "CoolMOS", which have n.sup.--regions and
p-regions arranged alternatively in cells, this is achieved by
means of acceptors in the p-regions as opposite charges.
[0004] In this context, the expression an n.sup.--region or
p.sup.--region is understood as meaning an area of a semiconductor
component which is lightly doped and has an impurity concentration
[N.sub.D] or [N.sub.A] below
[0005] [N.sub.D] or[N.sub.A].ltoreq.5.times.10 cm.sup.-3,
respectively where [N.sub.D] is the donor concentration and
[N.sub.A]is the acceptor concentration. In compensation components
and components according to the
[0006] present invention, this area can also be extended up to
1.times.10.sup.17 cm.sup.-3. The expression an n-region or p-region
means an area of a semiconductor component with medium doping and
having an impurity concentration between 5.times.10.sup.15
cm.sup.-3.ltoreq.[N.sub.D] and [N.sub.A].ltoreq.1.times.10.sup.18
cm.sup.-3, respectively.
[0007] An n.sup.+-region or p.sup.+-region means an area of a
semiconductor component which is heavily doped and has an impurity
concentration above 1.times.10.sup.18 cm.sup.-3.ltoreq.[N.sub.D]
and [N.sub.A], respectively.
[0008] If the aim is to improve the electrical conductivity of an
n.sup.--region in the case of compensation components, such as
"CoolMOS", further, then the compensation level must be set ever
more accurately. This is now reaching the limits of technical
feasibility. The MOS field plate transistors which are known from
U.S. Pat. No. 6,573,558 B2 with a trench structure in contrast have
the disadvantage that the entire reverse voltage is dropped at the
drain-side end to the n.sup.--region, so that very thick isolation
layers are required. A continuous load of 600 V would require
SiO.sub.2 with a thickness of about 4-6 .mu.m, thus leading to a
relatively large structure grid and to considerable technological
problems.
[0009] Semiconductor devices with a trench structure are also known
from the documents U.S. Pat. No. 4,893,160 and U.S. Pat. No.
5,262,018. In these trench structures, avalanche breakdowns in the
lightly doped epitaxial area between a gate arrangement in the
trench structure and a drain area with a heavily doped substrate
are avoided by means of medium to heavily doped zones in the area
of the trench bases. Further semiconductor devices with a trench
structure are known from the document U.S. Pat. No. 6,608,350 B2.
Known trench structures such as these can be used to produce a
high-voltage transistor with a low forward resistance on an
n.sup.+-conductive semiconductor substrate with a lightly doped
semiconductor body area on the n.sup.+-conductive semiconductor
substrate, by defusing compensation regions out of the trench
structure into the lightly doped semiconductor body area. The
trench can be filled with a dielectric or with a highly resistive
material, as is also described in DE 19848828 C2.
[0010] The above forward resistance R.sub.onA and the breakdown
voltage of a high-voltage-resistant semiconductor component for a
power transistor are linked by the doping and length and the
thickness of a drift path, that is to say of the lightly doped
n.sup.--region which mainly provides the blocking voltage. High
doping and a short drift path mean a low forward resistance, but
also a low breakdown voltage. Conversely, light doping and a long
drift path are required for a high breakdown voltage, which results
in a high forward resistance R.sub.onA.
[0011] The German Patent Application DE 10 2004 007 197.7 describes
a semiconductor device in which significantly higher drift path
doping is made possible by means of layers which are arranged
parallel to the drift path and are composed of a material with a
high dielectric constant, which is referred to in the following
text as a high-k material (high dielectric constant material), thus
resulting in a considerably lower forward resistance. With typical
trench widths and widths of the n.sup.--region in the region of a
few micrometers, forward resistance values R.sub.onA which are
nowadays better than in the case of "CoolMOS" by a factor of at
least 3 can be achieved for 600 V components. A transition from a
material with a high dielectric constant to a material with a low
dielectric constant such as silicon is located on the lower face of
the high-k material layers. This is associated with a corresponding
sudden change in the normal component of the electrical field
strength E, because this field component is described by:
.epsilon..sub.hk E.sub.hk=.epsilon..sub.Si E.sub.Si,
where .epsilon..sub.hk is the high dielectric constant of the
trench material or of the high-k material, E.sub.hk is the field
strength at the boundary surface in the material with the high
dielectric constant, .epsilon..sub.Si is the dielectric constant of
the silicon and E.sub.Si is the field strength in the adjacent
silicon. Since the field strength E.sub.hk in the high-k region
typically in its own right amounts to half the breakdown field
strength of the semiconductor material, the field strength E.sub.Si
in the semiconductor located underneath this also rises, with a
relative dielectric constant of the high-k region of even only 50
to well above the breakdown field strength of the silicon as the
semiconductor material, so that the desired blocking capability
cannot be achieved in the proposed structures unless the region
which is filled with a high-k material, or the filled trench,
achieves the transition to the heavily doped n.sup.+-region of the
heavily doped substrate very precisely, which is technologically
scarcely feasible, but has been found to be disadvantageous in the
previous technology.
[0012] Another critical case of such high-voltage-resistant
semiconductor component structures occurs when the high-k region
extends too far into the heavily doped n.sup.+-semiconductor region
of the substrate. This results in a field strength peak at the
transition from the n.sup.--doped drift path to the heavily doped
region, and this likewise reduces the blocking capability. These
high-voltage-resistant semiconductor components are therefore
subject to the problem that the high-k region must end as precisely
as possible at a heavily doped region of the semiconductor
substrate, which, in technological terms, is an object which can be
achieved only with difficulty, not least because the trench
structures for the high-k regions are incorporated using
technologies such as laser ablation or plasma etching, which are
not suitable for the removal of material being stopped between
lightly doped epitaxial layer areas and heavily doped substrate
areas.
SUMMARY
[0013] One objective of the invention is to reduce as much as
possible the field strength peaks at the trench base of a high-k
region, which disadvantageously reduce the breakdown withstand
voltage of power semiconductor components in the prior art, despite
the trench structures being incorporated less accurately in a
semiconductor epitaxial layer. At the same time, another object of
the invention is to improve the breakdown withstand voltage for
semiconductor components such as these.
[0014] This object is achieved by the independent claims.
Advantageous developments of the invention are specified in the
dependent claims.
[0015] The invention specifies a high-voltage-resistant
semiconductor component having vertically conductive, lightly doped
semiconductor body areas as drift path regions of a first
conductivity type, and having a trench structure on its upper face.
In this case, the trench structure at least partially surrounds the
vertically conductive lightly doped semiconductor body areas, and
has a base area and a wall area. The trench structure is filled
with a material with a high relative dielectric constant, a
so-called "high-k material", with the base area of the trench
structure having a heavily doped semiconductor material of the same
conductivity type as the lightly doped semiconductor body areas,
and/or having a metallically conductive material.
[0016] This semiconductor component has the advantage that the
heavily doped semiconductor material of the same conductivity type
as the lightly doped semiconductor body areas and the metallically
conductive material in the base area of the trench structure make
it possible to reduce field strength peaks such as those which
occur when the heavily doped n.sup.+-semi conductor region of the
substrate is not reached, within a very short distance of a few
nanometers in this n.sup.+-conductive base area or metallic base
area. To do this, the introduction of the trench structures is
interrupted even before the heavily doped substrate is reached, and
the layer according to the invention is introduced in the base area
of the trench structure.
[0017] These high-voltage-resistant semiconductor components
furthermore have the advantage that the waste during manufacture is
considerably reduced, not least because a wider tolerance band is
now possible for the depth of the trench structure in the lightly
doped epitaxial layer of the semiconductor structure. The range of
depth scatter above a semiconductor wafer is also in consequence
therefore no longer as critical as in the case of the semiconductor
structures which are known from the Patent Application DE 10 2004
007 197.7.
[0018] In one preferred embodiment of the invention, the lightly
doped semiconductor body areas are arranged in the form of plates
alternately with corresponding trench structures in the form of
plates on the upper face of the semiconductor component. In this
case, the trench structures which are in the form of plates are
formed from the high-k material. The width of the trench structures
which are in the form of plates or the width of the lightly doped
semiconductor body areas governs the blocking capability of the
semiconductor components. If a critical width of the lightly doped
semiconductor body areas which are in the form of plates is
exceeded, then complete blocking of the n.sup.--conductive drift
zone is not ensured.
[0019] In a further embodiment of the invention, the lightly doped
semiconductor body areas are arranged in the form of columns with a
circular, square or other polygonal, preferably hexagonal, cross
section on the upper face of the semiconductor component and are
surrounded by the trench structure: In the case of an arrangement
in the form of a column such as this with a surrounding trench
structure, the trench structure is introduced by means of laser
ablation or by means of plasma etching. Both methods can represent
an anisotropic process or anisotropic etching, with the material
removal rate or the etching rate in the direction of the depth of
the trench structure being considerably greater than the removal
rate from the side wall structures of the trenches.
[0020] The wall area of the trench structure in one further
preferred embodiment of the invention has an isolation layer as a
protective layer, with the isolation layer having an oxide or a
nitride from the group of insulating materials such as SiO.sub.2,
Si.sub.3N.sub.4, TiO.sub.2, HfO.sub.2, Ta.sub.2O.sub.5,
Al.sub.2O.sub.3 or AlN, or mixtures thereof. An insulating wall
structure such as this- can at the same time protect the walls
during the filling of the trench structure, in particular during
the introduction of heavily doped semiconductor material or
metallically conductive material into the base area of the trench
structure.
[0021] During the process of etching such conductive layers, which
can be applied in the base of the trench, from the wall structure,
the protective layers which have been mentioned above and are
composed of oxides or nitrides can act as etching stop layers. On
the other hand, it is also possible to provide the wall area of the
trench structure with a-wall layer composed of semiconductor
material, of the opposite conductivity type to the first
conductivity type of the lightly doped area. This creates a space
charge zone, which improves the breakdown strength of the
semiconductor device.
[0022] In a further preferred embodiment of the invention, the base
area of the trench structure, as a heavily doped semiconductor
material, has a material whose impurity concentration is
N.gtoreq..epsilon..sub.r
.epsilon..sub.0(E.sub.crit).sup.2/E.sub.g
where .epsilon.r is the relative dielectric constant,
.epsilon..sub.0 is the absolute dielectric constant of a vacuum,
E.sub.crit is the critical field strength and E.sub.g is the band
gap of the semiconductor material. A heavily doped layer such as
this in the base area of the trench reduces the field strength peak
which occurs without such a layer when the trench is not
sufficiently deep or when the trench is introduced too deeply. This
improves the withstand voltage of the power transistor.
[0023] The base area of the trench structure preferably has a
crystalline silicon, polysilicon or silicon carbide with an
impurity concentration of
110.sup.18 cm.sup.-3.ltoreq.N.sub.D or
N.sub.A.ltoreq.510.sup.20
as the heavily doped semiconductor material. This heavy doping
makes it possible to reduce the voltage peaks which would otherwise
occur in the base area and to improve the breakdown withstand
voltage of the component in such a way that no avalanche affect can
occur.
[0024] Silicides, preferably tungsten or cobalt silicide, have been
proven as metallically conductive materials in the base area.
Silicides such as these are not only metallically conductive but
are also temperature-resistant, so that high power losses do not
adversely affect the functionality of the metallically conductive
materials arranged in the base area.
[0025] In a further preferred embodiment to the invention, metals
including titanium, hafnium, tantalum or alloys thereof are used as
the metallically conductive materials. These materials cannot,
however, be subject to indefinitely high temperature loads. On the
other hand, it is also possible to use nitrides of titanium,
hafnium or zirconium as conductive layers in the base area of the
trench structure, which are themselves electrically conductive and
likewise have good temperature resistance.
[0026] A highly conductive or metallic contact can be arranged on
the upper face of the filled trench structure, and is electrically
connected to a source electrode of a high-voltage-resistant MOS
power transistor or to an emitter diode of a high-voltage-resistant
IGBT power transistor. An embodiment of the invention such as this
has the advantage that the upper face of the trench structure, in
particular of the high-k material, is at the same potential as the
source electrode and the emitter electrode. The contact can
alternatively also be connected to another fixed potential or to
the gate electrode. It is possible for the lightly doped
semiconductor body areas to have different gate structures on their
upper faces. While a gate structure is arranged planar and flat on
the semiconductor body area, a gate structure can also be buried
vertically in the upper face of the lightly doped semiconductor
body area, and leads to a vertical gate channel which requires less
surface area than that which can be achieved by a planar or flat
gate structure. The vertical gate can be arranged in the same
trench as the high-k material.
[0027] A further aspect of the present invention relates to a
semiconductor device having a semiconductor component based on the
structure described above. In a first embodiment of the invention,
this semiconductor device has a Schottky diode material. In this
case, the trench structure which is filled with a high-k material
surrounds semiconductor body areas of a lightly doped semiconductor
body area of a first conductivity type, which has the Schottky
diode structure on its upper face. A layer of heavily doped
semiconductor material or a metal layer is arranged in the base
area of the trench structure. The lightly doped semiconductor body
area of the first conductivity type is arranged on a heavily doped
substrate of the same conductivity type. The upper faces of the
semiconductor body areas have a metal coating of a Schottky contact
material, which forms an individual electrode of a Schottky diode.
The individual electrodes of the plurality of semiconductor body
areas are electrically connected in parallel to form an overall
electrode, while the opposite electrode is formed by the heavily
doped substrate of the same conductivity type as the lightly doped
semiconductor body area. For this purpose, the heavily doped
substrate has a metal coating, which forms the opposite electrode,
on its rear face.
[0028] In a further preferred embodiment of the semiconductor
device, this semiconductor device has a high-voltage-resistant PIN
or NIP diode structure. This high-voltage-resistant diode structure
has a trench structure which is filled with a high-k material and
has a layer composed of heavily doped semiconductor material or a
metal layer in the base area of the trench structure, in order to
ensure the resistance to high voltage. The trench structure
surrounds a lightly doped semiconductor body area of a first
conductivity type. This semiconductor body area is arranged on a
heavily doped substrate of the same conductivity type as the
lightly doped semiconductor body area.
[0029] The filled trench structure surrounds a plurality of
semiconductor body areas of the lightly doped semiconductor body
area and the upper face areas of the semiconductor body areas have
a medium to heavily doped diffusion zone of the opposite
conductivity type, which is coated with an individual metal
electrode. The plurality of individual metal electrodes in the
semiconductor body areas are electrically connected in parallel to
form an overall electrode, and are electrically connected to the
filled trench structure on the upper face of the semiconductor body
area. The opposite electrode of the high-voltage-resistant PIN or
NIP diode is formed by a heavily doped substrate of the same
conductivity type as the lightly doped semiconductor body area. For
this purpose, the lower face of the semiconductor device has a
metal layer which is conductively connected to the heavily doped
substrate, and forms an opposite electrode for the upper face of
the semiconductor device.
[0030] Provision is also made for the high-k material and the
heavily doped base area of the trench structure or the metal layer
in the base area of the trench, structure to form a
high-voltage-resistant MOS power transistor structure. In this MOS
power transistor structure, the trench structure is composed of a
high-k material, which surrounds a lightly doped semiconductor body
area of a first conductivity type. This lightly doped semiconductor
body area is arranged on a heavily doped semiconductor substrate,
which is of the same conductivity type as the lightly doped
epitaxial layer with the trench structure.
[0031] The upper face areas of the semiconductor body areas are
equipped with an MOS structure with individual source electrodes
and individual gate electrodes. For this purpose, a medium to
heavily doped impurity zone of the opposite conductivity type is
provided for the semiconductor body areas in the surface area, and
forms a gate channel area towards the edge area of the
semiconductor body area. The impurity zone has a source electrode,
and the plurality of source electrodes in the semiconductor body
areas are electrically connected in parallel to form a common
source electrode, and are electrically connected to the trench
structure. The gate channel area of the medium to heavily doped
region in the edge area of the semiconductor body areas is covered
by a gate oxide. A gate electrode is arranged on the gate oxide,
with the plurality of individual gate electrodes in the
semiconductor body areas being interconnected to form a common gate
electrode above the upper face of the lightly doped semiconductor
body area. The heavily doped substrate material, which is of the
same conductivity type as the lightly doped semiconductor body
area, has a metal coating on its lower face, and this is used as a
large-area drain electrode.
[0032] An MOS power structure such as this has the advantage (when
a metallically conductive or heavily doped material is arranged in
the trench structure with the high-k material in the base area)
that the field strength peaks in the lightly doped semiconductor
body area, adjacent to the base area of the trench structure which
is filled with the high-k material, are reduced, and the full
breakdown withstand voltage can be achieved for devices such as
these. A semiconductor device with a high-voltage-resistant IGBT
(Insulated Gate Bipolar Transistor) is designed in a similar way to
the MOS transistor, but the heavily doped substrate is of the
opposite conductivity type to the lightly doped semiconductor body
area.
[0033] This high-voltage-resistant IGBT is a bipolar transistor
with an insulated gate connection. The structure of this power
transistor differs from the structure of a high-voltage-resistant
MOS power transistor only in that the trench structure is embedded
with a conductive layer on the trench base in a lightly doped
semiconductor body area of one conductivity type, which is arranged
on a heavily doped substrate of the opposite conductivity type.
This results in a bipolar transistor of the pnp type or of the npn
type, depending on the conductivity type and the combination of the
regions. The substrates of the components described above, such as
the Schottky diode, the PIN diode, the MOSFET or the IGBT, can been
made to be virtually indefinitely thin.
[0034] A method for production of a plurality of semiconductor
chips from a semiconductor wafer which has semiconductor chip
positions arranged in rows and columns is described by the
following method steps. First of all, a lightly doped semiconductor
wafer of a first conductivity type or an epitaxial layer which is
lightly doped with the first conductivity type and is deposited on
a semiconductor wafer which is heavily doped with the first
conductivity type is produced. Trench structures with a base and a
wall area are then introduced into the lightly doped surface area
of the semiconductor chip positions on the semiconductor wafer.
After this, heavy doping of the same conductivity type as the
lightly doped areas can be introduced into the base area of the
trench structure, or a metallically conductive coating is
introduced in the base area of the trench structure. When
introducing a layer into the base area, care should be taken to
ensure that the walls of the trench structure do not themselves
have any conductive coating. This can preferably be ensured by
means of anisotropic deposition of the conductive layer in the
trench structure with subsequent isotropic etching, with a metallic
coating being removed from the wall area. The trench structure is
then filled with a high-k material.
[0035] The advantage of this method is that the introduction of
heavy doping or of a metallically conductive coating on the base of
the trench structure decreases the field strength peaks which can
occur either at the side or underneath the trench structure at the
transition between the trench structure and a lightly doped
semiconductor region, by means of the metallically conductive or
heavily doped layer on the base of the trench, so that the full
theoretically feasible breakdown voltage over the drift path then
becomes possible.
[0036] The base area of the trench structure can be doped by means
of a directed ion implantation technique. For this purpose, the
upper face of the semiconductor component is protected by a
photoresist layer except for the trench structure itself, and the
ion beams do not pass through this photoresist layer. If the ion
beams are aligned orthogonally with respect to the surface of the
semiconductor wafer, it is possible to achieve very precise doping
of the base area of the semiconductor wafer. In order to minimize
the risk of doping of the side walls, they can be covered in
advance with an oxide layer or nitride layer of silicon or
aluminum. Tantalum oxides and hafnium oxides can also be used to
protect the side walls against the ingress of the dopant. On the
other hand, if the side walls have been loaded with dopant, the
thin layer loaded with dopant can be removed by isotropic
etching.
[0037] Physical methods such as sputtering, vapor deposition or
chemical methods such as chemical gas-phase deposition or
electrolytic deposition are advantageously used for application of
a metallically conductive layer in the area of the trench base,
preferably composed of a silicide such as tungsten silicide and/or
cobalt silicide. In this case as well, it is advantageous to
protect the wall areas of the trench structure by means of an
effective protective layer before the introduction of the metallic
layers on the trench base. After the production of the filled
trench structure, for which purpose the trench structure is filled
with a material with a high relative dielectric constant, a
so-called high-k material, manufacturing steps are carried out to
produce functional semiconductor chips on the semiconductor wafer,
and the semiconductor wafer is then cut up into individual
semiconductor chips. Once the semiconductor chips have been
manufactured, these chips are processed to form corresponding
high-voltage-resistant semiconductor devices, based on the device
variants described above.
[0038] In summary, it can be stated that a heavily doped or
metallically conductive region in the base area of the trench
structure makes it possible to reduce the high field strength peaks
at the transition from the high-k material to a lightly doped
semiconductor body area over a very short distance. For example, a
field of 10.sup.6 V/cm. in silicon with a doping of 10.sup.19
cm.sup.-3 is dissipated over a distance of only 6 nm. In this case,
a voltage of only just 0.3 V is dropped across, this distance, so
that the charge carriers cannot absorb sufficient energy in this
case to generate new charge carriers by impact ionization. No
avalanches are thus generated so that the breakdown voltage remains
uninfluenced by the high field strength peak which occurs in this
area. However, if the doping were to be only 10.sup.16 cm.sup.-3,
then the breakdown voltage would in contrast fall from 600 V to
only 200 V, which is associated with a high field strength peak in
the transition area, which could lead to an avalanche
breakdown.
[0039] In addition to the heavy doping of the semiconductor
material in the transition area, it is also possible to introduce a
metallic layer composed of a silicide at the base of the trench
underneath the high-k region. This layer acts as a lower electrode
of the high-k region and prevents the strong electrical field from
entering the lightly doped semiconductor material located
underneath it. The invention thus advantageously means that the
electrical field underneath the high-k regions is dissipated over
short distances by heavily doped material or by metallic material.
Furthermore, the invention advantageously means that the trench
structure is self-adjusting, and a heavily doped coating or
metallic coating can be introduced very easily in the depth of the
high-k region in this case.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] The invention will now be explained in more detail with
reference to the attached figures.
[0041] FIG. 1 shows the principle of the profile of the electrical
field strength E in a high-voltage-resistant semiconductor
component with a filled trench structure in a lightly doped
semiconductor body area without any buried conductive layers
according to the invention in the trench base area, as a function
of the vertical position coordinate d.
[0042] FIG. 2 shows the principle of the profile of the electrical
field strength E in a high-voltage-resistant semiconductor
component with a filled trench structure with a trench base area
which is arranged within a heavily doped semiconductor substrate
area (without the conductive layer according to the invention in
the trench base area), as a function of the vertical position
coordinate d.
[0043] FIG. 3 shows a schematic cross section through a
high-voltage-resistant semiconductor component with a filled trench
structure according to a first embodiment of the invention.
[0044] FIG. 4 shows a schematic cross section through a
high-voltage-resistant semiconductor component with a filled trench
structure according to a second embodiment of the invention.
[0045] FIG. 5 shows a schematic cross section through a
high-voltage-resistant semiconductor component with a filled trench
structure according to a third embodiment of the invention.
[0046] FIG. 6 shows a schematic cross section through a
high-voltage-resistant semiconductor component with a vertical MOS
channel area and a filled trench structure according to a fourth
embodiment of the invention.
[0047] FIG. 7, which includes FIGS. 7A-7C, illustrates a top view
of a high-voltage-resistant semiconductor component having
differently shaped cross sections on the upper face of the
semiconductor component according to an embodiment of the
invention.
DETAILED DESCRIPTION
[0048] FIG. 1 shows the principle of the profile of the electrical
field strength E as a function of the vertical position coordinate
d in a high-voltage-resistant semiconductor component 1 with a
filled trench structure 5, whose trench base area 7 is arranged in
a lightly doped semiconductor body area 17. The trench structure 5
is filled with a material 9 with a high relative dielectric
constant .epsilon..sub.r This structure does not yet have the
conductive buried layer according to the invention in the trench
base area 7. The field strength B is initially at its highest on
the upper face 14 of the trench structure 5, with E.sub.o, and
decreases to E.sub.s towards the base area 7 of the trench
structure 5. However, a field strength peak E.sub.s is formed
within the buffer layer 26 at the transition from the base area 7
to the lightly doped semiconductor body area 17, before then being
completely dissipated in the heavily doped substrate area 18.
[0049] This field strength peak E.sub.s in the buffer layer 26 can
lead to avalanche effects, thus reducing the breakdown voltage of
the semiconductor component 1, and hence the breakdown withstand
voltage of the semiconductor chip, and hence also of the power
unit. This field strength peak E.sub.s is suppressed only if the
trench structure extends with its base area 7 to the area of the
heavily doped substrate 18. However, if the trench structure is
continued deeper than to the heavily doped substrate area 18, then
field strength peaks which reduce the breakdown voltage are also
formed there. This is illustrated in the next FIG., FIG. 2.
[0050] FIG. 2 shows the principle of the profile of the electrical
field strength E as a function of the vertical position coordinate
d in a high-voltage-resistant semiconductor component 1 with a
filled trench structure 5, whose trench base area 7 is arranged
within a heavily doped substrate area 18 (without the conductive
buried layer according to the invention in the trench area). The
high field strength E.sub.o on the upper face 14 of the trench
structure 5 initially decreases as the depth d of the trench
structure increases, but now forms a field strength peak ED around
the trench structure to the adjacent lightly doped semiconductor
body area 17 at the transition to the substrate doping. This
therefore results in the requirement that the introduction of the
trench structure is extremely critical with respect to the trench
depth do both in the situation in FIG. 1 in which the trench
structure is not introduced sufficiently deeply, so that it does
not reach the heavily doped substrate area 18, and in the situation
shown in FIG. 2, in which the trench depth d.sub.G is too deep, and
the trench which is filled with a material having a high relative
dielectric constant .epsilon..sub.r projects too far into the
heavily doped substrate area 18, so that field strength peaks occur
in the transition area, and disadvantageously affect the breakdown
voltage of the semiconductor component 1.
[0051] FIG. 3 shows a schematic cross section through a
semiconductor component 1 of a high-voltage-resistant semiconductor
device 20 with a filled trench structure 5 according to a first
embodiment of the invention. The trench structure 5 still ends
before the heavily doped substrate area 18, and has a heavily doped
semiconductor material layer 11 in its base area 7. This heavily
doped semiconductor material layer 11 dissipates the field strength
peak, which is still present in FIG. 1, within the heavily doped
layer area 11, thus preventing any avalanche breakdown.
[0052] It is thus possible to use this semiconductor component to
provide a high-voltage-resistant MOS power transistor with a planar
gate arrangement without the trench structure having to reach the
heavily doped substrate area 18. This considerably widens the
previously narrow manufacturing tolerances relating to the trench
depth.
[0053] This high-voltage-resistant . semiconductor component 1, of
which only two MOS semiconductor body areas 10 are shown, has a
high-k material as the filling in the trench structure. This high-k
material bounds individual MOS semiconductor body areas 10 of width
b of a lightly doped semiconductor body area 17.
[0054] In this embodiment of the invention, the lightly doped
semiconductor body area 17 is formed by an n.sup.--region. An MOS
structure which in this embodiment forms two channel areas 21 is
arranged on the upper face 6 of the semiconductor component, and
thus on the upper face 16 of the semiconductor body area 10, with a
gate oxide 23 being arranged between the gate electrode G.sub.1 and
the upper face 16 of the semiconductor body area. The channel area,
with its channel length a, is formed by a medium-doped p-region 21,
which has been diffused from the upper face 16 of the semiconductor
body area 10 and is bounded on one side by a heavily doped
n.sup.+-region. The other boundary of the channel length a is
formed by the lightly doped semiconductor body area 17.
[0055] The individual source electrodes S.sub.1 make contact with
the trench structure at the same time via a metallic contact 15 and
are connected to one another via a common source electrode S.sub.G.
The individual gate electrodes G.sub.1 are also connected in
parallel by a common gate electrode, which is not shown in this
illustration. While the channel region 21 is produced by diffusion
of impurities into the lightly doped semiconductor body area 17
from the upper face 16 of the semiconductor body area 10, the
source region is produced by n.sup.+-doping by ion implantation and
subsequent recrystallization, with the polysilicon gate electrode
G.sub.1 forming the masking. The channel length a is in this case
achieved by means of a planar technology and thus cannot be
indefinitely reduced in size.
[0056] The entire structure comprising the buried layers and the
lightly doped semiconductor body area 17 is introduced into a
lightly doped epitaxial layer 25. Widely differing techniques such
as laser ablation and/or plasma etching can be used to produce the
trench structure. In this case, photoresist techniques and
diffusion methods as well as implantation methods are used for the
structuring of the surface of each semiconductor body area 10. The
filling of the trenches with a high-k material can also be modified
by introducing a film capacitor into the trenches, instead of a
homogeneous high-k material.
[0057] However, one critical factor for the present invention is
that a heavily doped semiconductor area 11 is in this embodiment
incorporated in the base area 7 of the trench structure 5 in order
to reduce field strength peaks. The introduction of this heavily
doped base area into the trench structure can likewise be carried
out by ion implantation, to be precise at the same time as the
doping of the n.sup.+-source regions, provided that the trench
structure has been incorporated in advance. In order to protect the
wall areas 8 against the ingress of impurities and against contact
with the high-k material, the wall faces 8 can be covered by a
protective layer before the heavy doping is introduced into the
trench base area 7. On the other hand, it is also possible to use
an isotropic etching process to etch any heavy doping away from the
trench walls 8 again after anisotropic introduction of the heavily
doped layer 11 into the base area 7 and into the n.sup.+-source
areas. The heavily doped n.sup.+-substrate, is covered on the lower
face 24 by a metal coating 19, which forms the drain electrode of
the MOS power transistor structure 22.
[0058] FIG. 4 shows a schematic cross section through a
high-voltage-resistant semiconductor component 2 based on a second
embodiment of the invention, with a filled trench structure 5,
whose trench base 7 is arranged in a lightly doped semiconductor
area 17, and is provided with a buried layer 11 according to the
invention, in the trench base area 7. Components with the same
functions as those in FIG. 3 are identified by the same reference
symbols, and will not be explained again.
[0059] The difference from the embodiment shown in FIG. 3 is that
the heavily doped layer 11 has been incorporated deep in the trench
base area 7 in such a way that it extends as far as the heavily
doped substrate area 18. Once again, this embodiment of the
invention reduces or avoids any field strength peaks in the
transitional area from the base area 7 to the heavily doped
substrate area 18. The level of the n.sup.+-doping under the high-k
region of the trench structure 5 should be at least 10.sup.18
cm.sup.-3, preferably at least 1019 cm.sup.-3, for silicon. In
general, the minimum n.sup.+-doping level is governed by the
semiconductor characteristics, on the basis of the quotient:
.epsilon..sub.R.times..epsilon..sub.0(E.sub.crit).sup.2/E.sub.g
[0060] In this case, E.sub.g is the band gap of the semiconductor
material, E.sub.crit is the breakdown field strength for a doping
level of 10.sup.16 cm.sup.-3, .epsilon..sub.R is the relative
dielectric constant of the semiconductor, and .epsilon..sub.0 is
the absolute dielectric constant of a vacuum. E.sub.crit for
silicon is about 410.sup.5 V/cm, E.sub.g is 1.1 eV and
.epsilon..sub.r is 11.7. This results in the value of at least
10.sup.18 cm.sup.-3, as already required above, for the
concentration of impurities in the heavily doped n.sup.+-region in
the base area 7 of the trench structure 5.
[0061] Suitable semiconductor materials for such components include
not only silicon but also silicon carbide and other, preferably
III-V, semiconductor materials. As shown in FIG. 4 here, it is
normally possible for these heavily doped areas of the trench base
7 to extend as far as the heavily doped substrate material 18. On
the other hand, the field strength peaks are likewise decreased
when the heavily doped material in the trench base area 7 does not
extend as far as the heavily doped substrate 18.
High-voltage-resistant semiconductor devices such as these can thus
be produced more easily and more reliably than by using
conventional technology, in which the trench structures must
exactly reach the boundary area to the heavily doped substrate
18.
[0062] Instead of the heavily doped n.sup.+-regions in the trench
base area 7, it is also possible to use a metallic layer, as is
shown in a third embodiment of the invention in FIG. 5.
[0063] FIG. 5 shows a schematic cross section through a
high-voltage-resistant semiconductor component 3 with a filled
trench structure 5 based on a third embodiment of the invention.
The trench base 7 is arranged in a lightly doped semiconductor body
area 17, with the trench base 7 having a metallic coating 12. This
metallic coating 12 in this embodiment of the invention is a
silicide such as a tungsten silicide or cobalt silicide, which is
introduced under the high-k region, with this layer 12 being used
as the lower electrode of the high-k region and preventing the
electrical field from entering the lightly doped semiconductor body
area 17 located underneath it. The layer 12 can also make direct
contact with the heavily doped substrate material 18.
[0064] FIG. 6 shows a schematic cross section through a
high-voltage-resistant semiconductor component 4 based on a fourth
embodiment of the invention with a vertical MOS channel area 27 and
a trench structure 5 based on a fourth embodiment of the invention.
The trench structure surrounds a lightly doped semiconductor body
area 17 with the trench base area 7 having a metallic layer 12. The
MOS structure on the upper face 6 of the semiconductor component
and on the upper face 16 differs considerably from the MOS
structure as is known from the previous embodiments. Where
components of the semiconductor component 4 have the same function
as in the previous figures, they are identified by the same
reference symbols, and will not be explained again.
[0065] Gate electrodes G.sub.1 and individual source electrodes
S.sub.1 are arranged alternately alongside one another on the upper
face 6 of the semiconductor component 4, with the source electrodes
S.sub.1 making contact with a source region with n.sup.+-doping.
This is then followed, staggered in the depth direction, by a
heavily doped p.sup.+-zone, which surrounds the source electrode
S.sub.1. This p.sup.+-region is followed by a medium-doped channel
zone 21 of the conductivity type p, which is controlled by a
vertically arranged gate G.sub.1 ; The- channel length a in this
embodiment of the invention is arranged vertically and thus has a
very small size, which makes the switching speed of the devices
higher than that of the planar-arranged gate structures. This is
because the channel length a corresponds to the diffusion depth of
the p-regions.
[0066] The gate function is provided with the aid of gate
electrodes G.sub.1 and a gate oxide 23 in the vertical direction,
together with the trench structure 5 for a material with a high
relative dielectric constant .epsilon..sub.r, by first of all
producing the trench structure and by then applying the gate oxide
23 to the walls 8 of the trench structure as an isolation layer 13
at this time. Once the trench structure has been protected by a
gate oxide in this way, the metallic layer 12 composed of silicides
can be incorporated in the base area 7 in order to reduce field
strength peaks. The high-k material is then incorporated above this
metallic layer 12 in the trench base area 7, and is likewise sealed
by an upper electrode 28 on the upper face 14 of the high-k
material.
[0067] The side boundary formed by the gate oxide at the same time
provides protection against metallic short circuits in the wall
area 8. This upper electrode 28 is covered by an oxide, and the
remainder is filled with a gate electrode G.sub.1, up to the upper
face 6 of the semiconductor component 4. Instead of introducing the
gate oxide 23 in the vertical direction on the trench walls 8, this
gate oxide 23 can also be introduced into the upper area of the
trench structure 5 shortly before the introduction of the gate
electrode metal.
[0068] The advantage of this semiconductor device is not just that
the field strength peaks are decreased by the metallic layer 12,
but also that the trench structure 5 is at the same time used to
represent a vertical channel region. This has considerable
manufacturing advantages, and short channel lengths a can also be
achieved as a result of the shallow diffusion depth of the channel
region p.
[0069] The overlap between the n.sup.+-source region and the
metallic gate electrode G.sub.1 is small and is restricted just to
the depth of the n.sup.+-source regions, which has a thickness of
only a few tens of nanometers, which cannot be achieved with planar
structuring of channel lengths, despite ion implantation and
self-masking, by the conductive gate material, as disclosed in the
other embodiments. In particular, the gate structure requires only
a very small surface area.
[0070] The heavily doped p.sup.+-region which surrounds the source
metal of the source electrode S.sub.1 is introduced in order to
avoid a Schottky effect at the metal transition between the source
electrode S.sub.1 and the channel area 21, and thus to ensure a low
contact resistance as well as high hole conductivity. The drain
electrode of this MOS power transistor is provided by metallization
on the lower face of the semiconductor component, so that the
n.sup.+-substrate 18 forms a drain electrode D.sub.g, which is
shared by all the MOS body areas 10.
[0071] (New paragraph) As referenced previously in the
specification, a further embodiment of the invention is shown in
FIGS. 7A-7C. FIGS. 7A-7C illustrate that the lightly doped
semiconductor body areas 17 can be arranged in the form of columns
with a circular, square or other polygonal preferably
* * * * *