U.S. patent application number 14/306071 was filed with the patent office on 2015-12-17 for optimized layer for semiconductor.
The applicant listed for this patent is Infineon Technologies AG. Invention is credited to Christian HECHT, Jens Peter KONRATH, Roland RUPP, Hans-Joachim SCHULZE.
Application Number | 20150364550 14/306071 |
Document ID | / |
Family ID | 54706949 |
Filed Date | 2015-12-17 |
United States Patent
Application |
20150364550 |
Kind Code |
A1 |
SCHULZE; Hans-Joachim ; et
al. |
December 17, 2015 |
OPTIMIZED LAYER FOR SEMICONDUCTOR
Abstract
Representative implementations of devices and techniques provide
an optimized layer for a semiconductor component. In an example, a
doped portion of a wafer, forming a substrate layer may be
transferred from the wafer to an acceptor, or handle wafer. A
component layer may be applied to the substrate layer. The acceptor
wafer is detached from the substrate layer. In some examples,
further processing may be executed with regard to the substrate
and/or component layers.
Inventors: |
SCHULZE; Hans-Joachim;
(Taufkirchen, DE) ; KONRATH; Jens Peter; (Villach,
AT) ; RUPP; Roland; (Lauf, DE) ; HECHT;
Christian; (Buckenhof, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Infineon Technologies AG |
Neubiberg |
|
DE |
|
|
Family ID: |
54706949 |
Appl. No.: |
14/306071 |
Filed: |
June 16, 2014 |
Current U.S.
Class: |
257/77 ;
438/518 |
Current CPC
Class: |
H01L 29/7395 20130101;
H01L 21/0465 20130101; H01L 21/76254 20130101; H01L 29/7827
20130101; H01L 21/762 20130101; H01L 21/26506 20130101; H01L
29/1608 20130101 |
International
Class: |
H01L 29/16 20060101
H01L029/16; H01L 21/02 20060101 H01L021/02 |
Claims
1. A semiconductor component, comprising: a substrate layer cut
from an initial wafer and bonded to an acceptor wafer, one or more
doping properties of the substrate layer tuned based on a type of
the semiconductor component; and a second layer formed on a surface
of the substrate layer, the second layer having a greater thickness
than the substrate layer and a lesser doping density than the
substrate layer.
2. The semiconductor component of claim 1, further comprising a
metallic layer formed on another surface of the substrate
layer.
3. The semiconductor component of claim 1, wherein at least one of
the substrate layer and the second layer comprises silicon carbide
(SiC).
4. The semiconductor component of claim 3, wherein the substrate
layer comprises a highly doped p-type substrate.
5. The semiconductor component of claim 1, wherein the substrate
layer is substantially homogeneously doped using epitaxy or
implantation at a doping density greater than or equal to 10.sup.20
cm.sup.-3.
6. The semiconductor component of claim 1, wherein the substrate
layer is comprised of a first portion having an n-type doping and
an adjacent second portion having a p-type doping.
7. The semiconductor component of claim 1, wherein the substrate
layer is comprised of a plurality of laterally oriented portions
alternately having an n-type doping and a p-type doping.
8. The semiconductor component of claim 1, wherein the substrate
layer is formed on the initial wafer and is transferred to the
acceptor wafer prior to forming the second layer.
9. The semiconductor component of claim 1, wherein the second layer
is epitaxially formed on the surface of the substrate layer.
10. A silicon carbide (SiC) semiconductor device, comprising: a
poly-silicon carbide acceptor wafer; a highly doped, low impedance
SiC substrate layer having a first thickness and having a tuned
doping characteristic, bonded at a first surface of the substrate
layer to a surface of the acceptor wafer; and a lightly doped SiC
component layer epitaxially formed on another surface of the
substrate layer and arranged to be doped to form a desired
component, the acceptor wafer being removed from the substrate
layer as part of forming the desired component.
11. The SiC semiconductor device of claim 10, further comprising an
insulating layer between the substrate layer and the acceptor
wafer, the insulating layer arranged to be removed from the
substrate layer as part of forming the desired component.
12. The SiC semiconductor device of claim 10, the substrate layer
further comprising one or more at least partially filled
trenches.
13. The SiC semiconductor device of claim 12, wherein the one or
more trenches are arranged with variations in spacing and/or
thickness.
14. The SiC semiconductor device of claim 12, wherein one or more
of the trenches are filled with a doping that is an opposite doping
type as the substrate layer.
15. The SiC semiconductor device of claim 12, wherein sidewalls of
the one or more trenches are implanted with a doping that is an
opposite doping type as the substrate layer.
16. A method, comprising: doping a semiconductor wafer to a desired
extent to form a substrate layer; transferring the substrate layer
of the semiconductor wafer to an acceptor wafer; forming a
component layer on a surface of the substrate layer; detaching the
acceptor wafer from the substrate layer.
17. The method of claim 16, further comprising doping the
semiconductor wafer substantially uniformly over an area of the
semiconductor wafer or doping the semiconductor wafer using a
masked implantation or a trench fill epitaxy process, to form the
substrate layer.
18. The method of claim 16, further comprising doping the
semiconductor wafer in alternating portions of n-type and p-type
doping, to form the substrate layer.
19. The method of claim 16, further comprising implanting the
semiconductor wafer with hydrogen ions to a desired depth and
cutting the substrate layer from the semiconductor wafer at the
desired depth to determine a thickness of the substrate layer.
20. The method of claim 16, further comprising bonding the
substrate layer to the acceptor wafer using an oxidic bonding
process.
21. The method of claim 16, further comprising forming an
insulating layer on a surface of the substrate layer prior to
transferring the substrate layer to the acceptor wafer.
22. The method of claim 21, further comprising removing the
insulating layer in addition to the acceptor wafer from the
substrate layer and doping an exposed surface of the substrate
layer.
23. The method of claim 16, further comprising forming the
component layer on the surface of the substrate layer using a
lighter doping density than a doping density of the substrate
layer.
24. The method of claim 16, further comprising applying and
annealing a metallization layer to a surface of the substrate layer
that is exposed by detaching the acceptor wafer from the substrate
layer.
25. The method of claim 16, further comprising coupling a
stabilizing layer to an exposed surface of the component layer
during processing and removing the stabilizing layer after
processing.
Description
BACKGROUND
[0001] Developments in semiconductor technologies include the use
of materials such as silicon carbide (SiC) in the production of
fast, high-temperature, high-voltage capacity semiconductor
devices. In many cases, n-type SiC substrates used in the
production of SiC devices are obtained by sawing off portions from
bulk crystals, then sanding, polishing, and so forth. This can be a
difficult and expensive process. Often the substrates have
inhomogeneous doping characteristics, and may be limited to a
doping concentration at or below 10.sup.19 cm.sup.3. Higher doping
concentrations can lead to mechanical instabilities of the SiC
wafer (e.g., warping or spontaneous cracking in high-temperature
process steps or mechanical stresses).
[0002] Generally, there are similar issues regarding the production
of p-type substrates. Additionally, there may be difficulties
growing sufficiently large p-type crystals in the desired doping
concentration, due to depletion of the p-type dopant (e.g.,
aluminum) during manufacturing, for example. This can make it
problematic to produce, for example, re-channel insulated-gate
bipolar transistors (IGBT), and the like.
[0003] In some cases, desired devices may be manufactured by
growing a thick n-type drift layer on a substrate, and then
grinding away the substrate afterwards. A highly doped p-type layer
may be formed on one surface of the drift layer, by epitaxy for
example. This process may be successful if the drift layer is
stable enough for handling after grinding away the substrate (e.g.,
if the thickness of the drift layer remains at least 100 microns or
greater). Thus, the mechanical stability of the drift layer may be
a limiting factor for the production of devices using this process.
Further, this process can be difficult and expensive, particularly
if a SiC substrate is used to grow the drift layer, and is ground
away afterwards.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The detailed description is set forth with reference to the
accompanying figures. In the figures, the left-most digit(s) of a
reference number identifies the figure in which the reference
number first appears. The use of the same reference numbers in
different figures indicates similar or identical items.
[0005] For this discussion, the devices and systems illustrated in
the figures are shown as having a multiplicity of components.
Various implementations of devices and/or systems, as described
herein, may include fewer components and remain within the scope of
the disclosure. Alternately, other implementations of devices
and/or systems may include additional components, or various
combinations of the described components, and remain within the
scope of the disclosure.
[0006] FIG. 1 is a cross-sectional profile view of a homogeneously
doped starting layer for semiconductor epitaxy, according to an
example.
[0007] FIG. 2 is a cross-sectional profile view of a structured
starting layer for semiconductor epitaxy, according to another
example.
[0008] FIG. 3 is a cross-sectional profile view of an example
structured starting layer, with the addition of implanted
side-walls in trenches of the substrate, according to an
implementation.
[0009] FIG. 4 is a cross-sectional profile view of an example
structured starting layer, including filled implantation in
trenches of the substrate, according to an implementation.
[0010] FIG. 5 is a cross-sectional profile view of an example
structured starting layer, showing variations in spacing,
thickness, and/or depth of implanted trenches, for example.
[0011] FIG. 6 is a flow diagram illustrating an example process for
producing an optimized layer for a semiconductor, according to an
implementation.
DETAILED DESCRIPTION
Overview
[0012] Representative implementations of devices and techniques
provide an optimized starting layer for a semiconductor component,
such as a silicon carbide (SiC) semiconductor component. In an
example, a wafer, such as a SiC wafer, may be doped to a desired
concentration to form a starting layer (i.e., substrate layer). The
doping properties of the starting layer may be "tuned" to form the
optimized starting layer for the semiconductor component. In
various implementations, the tuning may comprise one or more
processes, which may be performed either before or after
transferring the substrate layer to an acceptor wafer for forming
the semiconductor component.
[0013] In one implementation, the wafer is uniformly doped over the
area of the wafer, to form a homogeneously doped substrate wafer.
In another implementation, the wafer is doped in a pattern to form
a substrate layer having alternating doping. In various
implementations, the wafer may be masked, implanted, and/or
trenched to form a doped pattern on the wafer. For example, the
masked areas or trenches may be partially or fully filled using an
implantation or epitaxy process to form portions having an opposite
type of doping.
[0014] In an implementation, the substrate layer is transferred
from the wafer to an acceptor, or handle wafer, for processing, for
instance. In various implementations, the substrate layer is cut
from the wafer using ion implantation and in particular hydrogen
implantation, or the like. The substrate layer may be bonded to the
acceptor wafer using various bonding techniques.
[0015] In an implementation, a component layer is applied to a
surface of the substrate layer, using epitaxial Techniques for
instance. In various examples, the component layer may be
processed, including being doped, having metallization added, and
the like. In an implementation, the acceptor wafer is detached from
the substrate layer. In some examples, further processing may be
executed with regard to the substrate and/or component layers to
form a completed semiconductor device.
[0016] Various implementations and arrangements are discussed with
reference to electrical and electronics components and varied
materials. While specific materials (i.e., silicon carbide (SiC),
etc.) are mentioned, this is not intended to be limiting, and is
for ease of discussion and illustrative convenience. The techniques
and devices discussed with reference to SiC are applicable to any
type of semiconductor materials, such as silicon, other "wide
band-gap materials," or the like. Accordingly, the use of "SiC" in
the disclosure is intended to also apply to these other
materials.
[0017] Implementations are explained in more detail below using a
plurality of examples. Although various implementations and
examples are discussed here and below, further implementations and
examples may be possible by combining the features and elements of
individual implementations and examples.
Example Arrangement
[0018] FIG. 1 is a cross-sectional profile view of a semiconductor
arrangement 100 including a starting layer (e.g., carrier,
substrate, etc.) 102 for constructing a semiconductor component,
according to an example. The arrangement 100 represents an example
environment whereby the techniques and devices discussed herein may
be applied. For instance, a semiconductor component may be formed
by adding to the starting layer 102, epitaxial layers and in
particular in combination with implantation techniques and suitable
high-temperature processes for annealing and in-diffusion of the
dopants for example.
[0019] The techniques, components, and devices described herein
with respect to the semiconductor arrangement 100 are not limited
to the illustrations in FIGS. 1-5, and may be applied to other
designs, types, arrangements, and constructions without departing
from the scope of the disclosure. In some cases, alternative
components or materials may be used to implement the techniques
described herein. In various implementations, the arrangement 100
may be stand-alone, or it may be a portion of a system, component,
structure, or the like.
[0020] The illustration of FIG. 1 shows an example configuration of
the starting layer 102, in relation to other portions of the
semiconductor arrangement 100, according to one implementation. In
various implementations, other configurations, designs, and the
like, may also be used for the semiconductor arrangement 100.
[0021] In an implementation, as shown in FIG. 1, the semiconductor
arrangement 100 includes a substrate layer (i.e., structured
starting layer) 102 and a component layer 104. In one
implementation, the substrate layer 102 comprises a high doping
density relative to a much lower doping density of the component
layer 104. The doping density of the layer 104 is for example in
the range of 10.sup.14/cm.sup.3-10.sup.17/cm.sup.3, more typically
in the range 5*10.sup.14 cm.sup.3-10.sup.16/cm.sup.3. The layer 102
has a doping density of 10.sup.18/cm.sup.3-10.sup.20/cm.sup.3, more
typically 10.sup.19/cm.sup.3-5*10.sup.19/cm.sup.3. Further, in
various implementations, the thickness of the substrate layer 102
may be substantially less than the thickness of the component layer
104. The thickness of the layer 104 is for example in the range of
20 .mu.m-200 .mu.m, more typically in the range of 50 .mu.m-100
.mu.m. The layer 102 has a thickness of 5 .mu.m-20 .mu.m, more
typically 5 .mu.m-10 .mu.m.
[0022] In an implementation, the substrate layer 102 is formed by
doping a SiC wafer, for example, at a desired doping density. In
one implementation, the substrate layer 102 comprises a highly
doped p-type substrate. In an alternate implementation, the
substrate layer 102 comprises a highly doped n-type substrate.
[0023] In various implementations, one or more doping properties of
the substrate layer 102 are tuned based on a type of the
semiconductor component to be formed on the substrate layer 102.
For example, the doping properties or characteristics may be
deliberately tuned to be optimized for forming a desired device. In
some implementations, in the case of high n-type doping, the
substrate layer 102 may be tuned to form a low ohmic drain contact
for power MOSFETs, for example, as a rear-side contact zone for
Schottky diodes, bipolar diodes or power MOSFETs, or as an emitter
for a bipolar junction transistor (BJT). In the case of a p-type
doping, the substrate layer 102 may be optimized to serve as a rear
emitter (e.g., for an bipolar transistor, insulated-gate bipolar
transistor (IGBT), or thyristoretc.) or as a drain region or a
contact zone for power MOSFETs with a p-doped drift region, or the
like.
[0024] In various implementations, as shown in FIG. 1, the
substrate layer 102 is homogeneously doped using epitaxy or
implantation. In one implementation, the substrate layer 102 is
homogeneously doped at a doping concentration of 10.sup.20
cm.sup.-3, or greater. In other words, the substrate layer 102 is
tuned and has a uniform, high-density doping.
[0025] In another implementation, the substrate layer 102 may be
tuned to include adjacent p-type and n-type doping. For example,
the substrate layer 102 may be comprised of a first portion having
an n-type doping and an adjacent second portion having a p-type
doping. In other words, the substrate layer 102 may be composed of
adjacent portions with opposite types (n-type and p-type) of
doping. This may be advantageous in the formation of various
semiconductor devices, for example.
[0026] In one example implementation (as shown in FIG. 2), the
substrate layer 102 layer is comprised of a plurality of laterally
oriented portions alternately having an n-type doping and a p-type
doping. In various implementations, the alternating doping pattern
may be formed using a masked implantation in combination with
subsequent annealing or diffusion steps at high process
temperatures, a trench fill epitaxy, or the like. In example
implementations, a substrate layer 102 having alternating doping
can serve as a local emitter structure, for instance, without
extensive additional processing to the backside surface of the
substrate layer 102.
[0027] In various implementations, after tuned doping, the
substrate layer 102 is removed from the bulk SiC wafer, and is
transferred to an acceptor wafer (e.g., handle wafer, carrier,
etc.) 106. In one example, the substrate layer 102 is removed using
ion implantation, or the like. For instance, the bulk SiC wafer may
be implanted with hydrogen ions at a uniform desired depth, and
thermally treated. The uniform desired depth represents the desired
thickness of the substrate layer 102. The substrate layer 102 is
then cleaved or cut from the SiC wafer at the depth of the ion
implantation.
[0028] Once removed from the SiC wafer, the substrate layer 102 is
transferred and may be bonded to the acceptor wafer 106 for
semiconductor component processing. In one implementation, the
substrate layer 102 is bonded to the acceptor wafer 106 using an
oxidic bonding process, or the like. In various implementations,
the acceptor wafer 106 is comprised of a material that is
compatible with a SiC epitaxial process (e.g., tungsten,
poly-silicon carbide, SiC coated carbon, etc.). For example, the
acceptor wafer 106 may be comprised of a material capable of
withstanding a hydrogen atmosphere, and a temperature of 1500-1600
C, or the like. In other implementations, the acceptor wafer 106 is
comprised of a material that is compatible with an epitaxial
process (or other formation process) of an alternate material
(silicon, etc.) of the substrate layer 102.
[0029] In an implementation, the substrate layer 102 includes an
insulating layer 108 on the surface of the substrate layer 102 that
is bonded to the acceptor wafer 106. This insulating layer 108 may
be formed by oxidation, for example, on the surface of the
substrate layer 102 prior to transferring the substrate layer 102
to the acceptor wafer. For example, the insulating layer 108 may be
comprised of silicon dioxide (SiO.sub.2) or the like.
[0030] In various implementations, the insulating layer 108 is
located between the substrate layer 102 and the acceptor wafer 106,
and insulates the substrate layer 102 from the acceptor wafer 106
during the manufacturing process. In various implementations, as
shown in FIG. 1, the semiconductor arrangement 100 may also include
a protection layer 110. In one example, the protection layer 110
protects the oxide insulating layer 108 during the epitaxial
process. For example, based on the atmospheric conditions of the
epitaxial process, the oxide insulating layer 108 can be dissolved
without the protection of the protection layer 110. In some
implementations, the protection layer 110 is a sacrificial layer,
being dissolved in the epitaxial process instead of the oxide
insulating layer 108.
[0031] In an alternate implementation, a thin layer of the bulk SiC
wafer may be transferred to the acceptor wafer 106 prior to doping
(e.g., implantation, epitaxy, etc.) to form the substrate layer
102. In the implementation, the thin layer of the bulk SiC wafer
may be cut from the bulk SiC wafer using ion implantation, or the
like, as described above. After transferring the thin layer to the
acceptor wafer 106, the thin layer may be uniformly doped over the
surface of the thin layer, or it may be doped in an alternating
doping pattern, with a high doping density in either case.
Additionally or alternatively, the thin layer may be trench etched,
epitaxially filled, implanted, or the like, to form the substrate
layer 102.
[0032] In an alternate implementation the bonding process of the
hydrogen-implanted substrate layer to the acceptor wafer takes
place prior to the annealing step which induces the separation of
the layer 102 from the rest of the substrate layer.
[0033] In various implementations, the component layer 104 is
formed (e.g., by epitaxy, implantation, etc.) on a surface of the
substrate layer 102 after the substrate layer 102 is bonded to the
acceptor wafer 106. As described above, in the implementations, the
component layer 104 may be doped at a lesser density than the
substrate layer 102, may be thicker than the substrate layer 102,
and/or may have a greater impedance than the substrate layer
102.
[0034] In an implementation, the component layer 104 is comprised
of a lighter doped SiC layer. The component layer 104 may be grown
on the surface of the substrate layer 102 after the substrate layer
102 has been processed (e.g., implanted, annealed, trenched,
epitaxially filled, etc.) as described further below. Once the
component layer 104 is formed, the component layer 104 may be
processed also, including implantation, etching, filling,
metallization, edge passivation, and the like, to form a desired
semiconductor component.
[0035] In various implementations, the acceptor wafer 106 and the
insulating layer(s) 108, 110 are detached (i.e., removed) from the
substrate layer 102 to form the semiconductor component. In an
example, the acceptor wafer 106 is used for handling the substrate
layer 102 (and the component layer 104) during processing of the
substrate layer 102 and the component layer 104. The acceptor wafer
106 may be removed when "topside" processing (e.g., processing
involving the substrate layer 102 surface opposite the acceptor
wafer 106 and the component layer 104) is partially or fully
completed, for example.
[0036] In alternate implementations, the acceptor wafer 106 may be
detached using a mechanical process, a chemical process, laser
lift-off, a combination of these, or like process(es). In one
implementation, if the substrate layer 102 and component layer 104
are not stable enough for "backside" processing (e.g., processing
involving the substrate layer 102 surface formerly adjacent to the
acceptor wafer 106), a support wafer, or the like, may be coupled
temporarily to the component layer 104 during further processing.
The insulating layer 108 may serve as an etch-stop layer resulting
in a well-controlled and homogeneous adjustment of the final device
thickness.
[0037] In alternate implementations there is no insulating layer
108 on the substrate layer 102.
[0038] In various implementations, the "backside" processing may
include depositing and annealing backside metal (e.g., metallic
layer, metallization, etc.) to the backside surface of the
substrate layer 102, once the acceptor wafer 106 and insulating
layer(s) 108, 110 are removed from the backside surface.
Example Implementations
[0039] FIG. 2 illustrates an example of a semiconductor arrangement
100 having a substrate layer 102 with one or more trenches 212
etched, or otherwise cut, laterally into the substrate layer 102.
In the example implementation of FIG. 2, the trenches 212 may be
filled, using epitaxy for example, with the material comprising the
component layer 104. For example, the trenches 212 may be filled
with a lightly doped p-type SiC, when a lightly doped p-type SiC is
used for the component layer 104 and a heavily doped p-type SiC is
used for the substrate layer 102. Alternately, both the component
layer 104 and the trenches 212 may be filled with a lightly doped
n-type SiC, when the substrate layer 102 is comprised of a heavily
doped n-type SiC.
[0040] FIG. 3 is a cross-sectional profile view of a semiconductor
arrangement 100 having a substrate layer 102 with one or more
trenches 212 etched, or otherwise cut, laterally into the substrate
layer 102. In various implementations, as shown in FIG. 3, the
substrate layer 102 comprises one or more at least partially filled
trenches 212.
[0041] In the example implementation of FIG. 3, the trench 212
walls may be lined (302), using implantation or epitaxy for
example, with an n-type SiC, when a lightly doped p-type SiC is
used for the component layer 104 and a heavily doped p-type SiC is
used for the substrate layer 102. Alternately, the trench 212 walls
may be lined, using implantation or epitaxy for example, with a
p-type SiC, when the component layer 104 comprises a lightly doped
n-type SiC and the substrate layer 102 comprises a heavily doped
n-type SiC. In either case, the substrate layer 102 includes one or
more laterally alternating doping regions (e.g., lateral n-type
doping portion adjacent to lateral p-type doping portion).
[0042] FIG. 4 is a cross-sectional profile view of a semiconductor
arrangement 100 having a substrate layer 102 with one or more
laterally alternating doping regions (e.g., lateral n-type doping
portion adjacent to lateral p-type doping portion), according to
various implementations. For example, in one implementation, the
substrate layer 102 is masked and implanted to form the one or more
laterally alternating doping regions. For instance, a first mask
may be applied during an n-type doping implantation and a second
opposite mask may be applied during a p-type doping implantation.
The result of the masking and implanting can be the lateral
alternating doping pattern shown in FIG. 4, by the light and dark
shaded areas of the substrate layer 102.
[0043] In an alternate implementation, the substrate layer 102 may
be initially doped in a uniform manner, and then one or more
trenches 212 may be etched, or otherwise cut, laterally into the
substrate layer 102. In the alternate implementation of FIG. 4, the
trenches 212 may be filled (402), using implantation or epitaxy for
example, with an n-type SiC, when a lightly doped p-type SiC is
used for the component layer 104 and a heavily doped p-type SiC is
used for the substrate layer 102. Alternately, the trenches 212 may
be filled (402), using implantation or epitaxy for example, with a
p-type SiC, when the component layer 104 comprises a lightly doped
n-type SiC and the substrate layer 102 comprises a heavily doped
n-type SiC. In either case, the substrate layer 102 includes one or
more laterally alternating doping regions (e.g., lateral n-type
doping portion adjacent to lateral p-type doping portion).
[0044] FIG. 5 is a cross-sectional profile view of a semiconductor
arrangement 100 having a substrate layer 102 with one or more
laterally alternating doping regions (e.g., lateral n-type doping
portion adjacent to lateral p-type doping portion), according to
the various implementations as described relative to FIG. 4. The
illustration of FIG. 5 shows that the alternating doping pattern
may include variations (502) in spacing and/or thickness.
[0045] For example, as shown in FIG. 5, the laterally alternating
doping regions may not necessarily have regularity in spacing and
thickness across the area of the substrate layer 102. Instead, the
laterally alternating doping regions may be more concentrated at
one or more locations, and may be less concentrated at other
locations. This can be seen in FIG. 5 particularly with the darker
shaded lateral portions of the substrate layer 102. Further, the
thickness of a given lateral portion may be greater or lesser than
the thickness of another lateral portion of the same doping type
(n-type or p-type). This can be seen in FIG. 5 particularly with
the lighter shaded lateral portions of the substrate layer 102.
[0046] In various implementations, the laterally alternating doping
regions of the substrate layer 102 may allow for the production of
desired semiconductor devices, such as but not limited to power
MOSFETs, bipolar diodes, Schottky diodes, IGBTs, and the like.
Further, variations in the spacing and/or thickness of the
laterally alternating doping regions may allow for designing the
emitter efficiency of SiC-based IGBT devices and diodes and/or
including design techniques that reduce injection of free carriers
in the edge termination region of the chip or in the area of the
gate pad or gate feeders by a reduction of the effective backside
emitter area. Additionally, variations in the spacing and/or
thickness of the laterally alternating doping regions may allow for
variations in the lateral direction of injection of holes with
IGBTs or variations in the lateral direction of injection of
electrons from the wafer back side to realize fast switching
diodes.
[0047] Different configurations for an arrangement 100, including a
substrate layer 102 may be possible with different implementations.
In alternate implementations, various other combinations and
designs of the arrangement 100 and/or the substrate layer 102 are
also within the scope of the disclosure. The variations may have
fewer elements than illustrated in the examples shown in FIGS. 1-5,
or they may have more or alternative elements than those shown.
Representative Process
[0048] FIG. 6 illustrates a representative process 600 for
producing an optimized substrate layer (such as substrate layer
102, for example) for a semiconductor component, such as a silicon
carbide (SiC) semiconductor component, for example, according to
various implementations. In an implementation, the optimized
substrate layer is cut from a bulk wafer and bonded to a handle
wafer (such as acceptor wafer 106, for example). In various
implementations, one or more doping properties or characteristics
are tuned to optimize the substrate layer for forming the desired
semiconductor component. The process 600 is described with
reference to FIGS. 1-5.
[0049] The order in which the process is described is not intended
to be construed as a limitation, and any number of the described
process blocks can be combined in any order to implement the
process, or alternate processes. Additionally, individual blocks
may be deleted from the process without departing from the spirit
and scope of the subject matter described herein. Furthermore, the
process can be implemented in any suitable materials, or
combinations thereof, without departing from the scope of the
subject matter described herein.
[0050] At block 602, the process includes doping a semiconductor
wafer to a desired extent to form a substrate layer (such as
substrate layer 102, for example). In an implementation, the
process includes heavily doping the semiconductor wafer with n-type
or p-type dopant to form the substrate layer. In various
implementations, the semiconductor wafer is comprised of SiC.
[0051] In various implementations, one or more doping properties or
characteristics of the substrate layer are tuned to optimize the
substrate layer as an individualized starting layer for a
semiconductor device to be formed on it. In one implementation, the
process includes doping the semiconductor wafer substantially
uniformly over an area of the semiconductor wafer. In other words,
the area of the semiconductor wafer is homogeneously doped to a
desired density. In one example, the area of the semiconductor
wafer is homogeneously doped at a concentration at or greater than
10.sup.20 cm.sup.3.
[0052] In another implementation, the process includes doping the
semiconductor wafer in alternating portions of n-type and p-type
doping, to form the substrate layer. For example, in one
implementation, the process includes doping the semiconductor wafer
using a masked implantation to form a doped pattern over the area
of the semiconductor wafer. In the implementation, the masked
implantation creates the alternating doping pattern.
[0053] In another implementation the process includes using a
trench-fill epitaxy or implantation process to form the substrate
layer. For example, one or more trenches may be etched or otherwise
cut into the area of the semiconductor wafer (e.g., or into the
substrate layer). In an implementation, the trenches are arranged
laterally along the area of the semiconductor wafer. In various
implementations, the trenches may be partially or fully filled, by
implantation, epitaxy, or the like, with a doping that is the
opposite type of doping as the doped portion of the semiconductor
wafer or substrate layer that the trenches are cut into. In the
implementations, the partially or fully filled trenches create the
alternating doping pattern.
[0054] At block 604, the process includes transferring the
substrate layer of the semiconductor wafer to an acceptor wafer
(such as acceptor wafer 106, for example). In an implementation,
the process includes implanting the semiconductor wafer with
hydrogen ions to a desired depth and cutting the substrate layer
from the semiconductor wafer at the desired depth to determine a
thickness of the substrate layer. In the implementation, the cut
substrate layer is transferred to the acceptor wafer. In one
example, the process includes bonding the substrate layer to the
acceptor wafer using an oxidic bonding process, for example.
[0055] In various implementations, the acceptor wafer is comprised
of a material that is compatible with an epitaxial process
performed on the substrate layer. In some implementations, the
acceptor wafer is comprised of a poly-silicon carbide, tungsten,
SiC coated carbon, or like material.
[0056] In an implementation, the process includes forming an
insulating layer on a surface of the substrate layer prior to
transferring the substrate layer to the acceptor wafer. The
insulating layer may include an oxide, such as silicon dioxide, or
the like. In another implementation, the process includes forming a
protection layer over the insulating layer (e.g., such as when an
oxide material is used for the insulating layer). In the
implementation, the protection layer prevents the insulating layer
from dissolving in the atmosphere of the epitaxial process.
[0057] At block 606, the process includes forming a component layer
(such as component layer 104, for example) on a surface of the
substrate layer. For example, the component layer may be formed on
the surface of the substrate layer that is opposite the acceptor
wafer. In an implementation, the process includes forming the
component layer using a lighter doping density than a doping
density of the substrate layer. In another implementation, the
process includes forming the component layer such that it is
thicker than the substrate layer and/or such that it has a greater
impedance than the substrate layer.
[0058] In alternate implementations, the component layer may be
formed on a surface of the substrate layer prior to transferring
the substrate layer to the acceptor wafer, or after transferring
the substrate layer to the acceptor wafer.
[0059] In an implementation, the component layer is formed by
epitaxy on the surface of the substrate layer. In a further
implementation, the component layer is comprised of SiC, or the
like material. In various implementations, the component layer is
implanted, etched, filled, metallized, and/or the like, to form a
desired semiconductor device or component.
[0060] At block 608, the process includes detaching the acceptor
wafer from the substrate layer. In various implementations, the
acceptor wafer is detached from the substrate layer after
processing the component layer. For example, the acceptor wafer may
be detached from the substrate layer using mechanical, chemical,
laser lift-off, or other techniques. In one implementation, the
process includes removing the insulating layer in addition to the
acceptor wafer from the substrate layer and doping an exposed
surface of the substrate layer.
[0061] In an implementation, if the substrate layer with the
component layer are mechanically instable after removing the
acceptor wafer, the process includes coupling a stabilizing layer
to an exposed surface of the component layer during processing of
the opposite (e.g., exposed underside) surface of the substrate
layer, and removing the stabilizing layer after processing.
[0062] In various implementations, the process includes applying
(e.g., depositing, etc.) and annealing a metallization layer to a
surface of the substrate layer that is exposed by detaching the
acceptor wafer from the substrate layer. In other implementations,
other processes may be performed with regard to the exposed
underside (i.e., backside) surface of the substrate layer, such as
implanting, etching, filling, and the like.
[0063] In alternate implementations, other techniques may be
included in the process 600 in various combinations, and remain
within the scope of the disclosure.
CONCLUSION
[0064] Although the implementations of the disclosure have been
described in language specific to structural features and/or
methodological acts, it is to be understood that the
implementations are not necessarily limited to the specific
features or acts described. Rather, the specific features and acts
are disclosed as representative forms of implementing example
devices and techniques.
* * * * *