U.S. patent application number 14/048166 was filed with the patent office on 2014-02-06 for carbosilane precursors for low temperature film deposition.
The applicant listed for this patent is Todd Schroeder, Timothy W. Weidman. Invention is credited to Todd Schroeder, Timothy W. Weidman.
Application Number | 20140038427 14/048166 |
Document ID | / |
Family ID | 47830222 |
Filed Date | 2014-02-06 |
United States Patent
Application |
20140038427 |
Kind Code |
A1 |
Weidman; Timothy W. ; et
al. |
February 6, 2014 |
Carbosilane Precursors For Low Temperature Film Deposition
Abstract
Provided are processes for the low temperature deposition of
silicon-containing films using carbosilane precursors containing a
carbon atom bridging at least two silicon atoms. Certain methods
comprise providing a substrate; in a PECVD process, exposing the
substrate surface to a carbosilane precursor containing at least
one carbon atom bridging at least two silicon atoms; exposing the
carbosilane precursor to a low-powered energy sourcedirect plasma
to provide a carbosilane at the substrate surface; and densifying
the carbosilanestripping away at least some of the hydrogen atoms
to provide a film comprising SiC. The SiC film may be exposed to
the carbosilane surface to a nitrogen source to provide a film
comprising SiCN.
Inventors: |
Weidman; Timothy W.;
(Sunnyvale, CA) ; Schroeder; Todd; (Toledo,
OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Weidman; Timothy W.
Schroeder; Todd |
Sunnyvale
Toledo |
CA
OH |
US
US |
|
|
Family ID: |
47830222 |
Appl. No.: |
14/048166 |
Filed: |
October 8, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13609867 |
Sep 11, 2012 |
8575033 |
|
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14048166 |
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13288157 |
Nov 3, 2011 |
8440571 |
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13609867 |
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61534122 |
Sep 13, 2011 |
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Current U.S.
Class: |
438/778 |
Current CPC
Class: |
C23C 16/36 20130101;
H01L 21/02126 20130101; H01L 21/0262 20130101; H01L 21/02274
20130101; C23C 16/5096 20130101; H01L 21/02447 20130101; C23C
16/325 20130101; H01L 21/02211 20130101; H01L 21/02167 20130101;
H01L 21/02529 20130101; C23C 16/4554 20130101; H01L 21/0228
20130101 |
Class at
Publication: |
438/778 |
International
Class: |
H01L 21/02 20060101
H01L021/02 |
Claims
1. A method of forming a layer on a substrate surface, the method
comprising: providing a substrate; in a PECVD process, exposing the
substrate surface to a carbosilane precursor containing at least
one carbon atom bridging at least two silicon atoms; exposing the
carbosilane precursor to a low-powered energy source to provide a
carbosilane at the substrate surface; and stripping away at least
some of the hydrogen atoms to provide a film comprising SiC.
2. The method of claim 1, wherein stripping away at least some of
the hydrogen atoms comprises exposing the substrate surface to a
plasma containing one or more of He, Ar and H.sub.2.
3. The method of claim 1, wherein the film comprising SiC has a
ratio of Si:C approximately matching that of the carbosilane
precursor.
4. The method of claim 3, wherein the carbosilane precursor is one
or more of 1,3,5-trisilapentane, 1,3-disilapropane,
1,3-disilabutane, 1,3-disilacyclobutane and
1,3,5-trisilacyclohexane.
5. The method of claim 4, wherein the carbosilane precursor
comprises 1,3,5-trisilapentane.
6. The method of claim 4, wherein the carbosilane precursor
comprises 1,3-disilapropane.
7. The method of claim 5, wherein the SiC film has a ratio of Si:C
of about 3:2.
8. The method of claim 4, wherein the carbosilane precursor
comprises 1,3-disilabutane.
9. The method of claim 1, wherein exposing the carbosilane
precursor to a direct plasma results in polymerization of the
carbosilane.
10. The method of claim 1 wherein the low-powered plasma has an RF
value of about 50 W to about 500 W.
11. The method of claim 1, wherein the substrate surface has a
temperature of about 100 and about 400.degree. C.
12. The method of claim 1, wherein the SiC film is suitable as a
low k dielectric film.
13. A method of forming a layer on a substrate surface, the method
comprising: providing a substrate; exposing the substrate surface
to a carbosilane precursor 1,3-disilapropane, 1,3,5-trisilapentane,
1,3-disilabutane, 1,3-disilacyclobutane and
1,3,5-trisilacyclohexane; exposing the carbosilane precursor to a
low-powered plasma to provide a carbosilane at the substrate
surface; exposing the carbosilane to a plasma comprising H.sub.2.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. Non-Provisional
application Ser. No. 13/609,867, filed Sep. 11, 2012, which claims
priority to U.S. Provisional Application No. 61/534,122, filed Sep.
13, 2011, and is a continuation-in-part of U.S. Non-Provisional
application Ser. No. 13/288,157, filed Nov. 3, 2011, the contents
of both of which are hereby incorporated by reference in their
entirety.
TECHNICAL FIELD
[0002] Embodiments of the present invention generally relate to the
field of film deposition, and specifically to precursors for low
temperature deposition of films containing silicon, carbon and
nitrogen.
BACKGROUND
[0003] In the manufacture of electronic devices such as integrated
circuits, a target substrate, such as a semiconductor wafer, is
subjected to various processes, such as film formation, etching,
oxidation, diffusion, reformation, annealing, and natural oxide
film removal. Silicon-containing films are an important part of
many of these processes.
[0004] Silicon-containing films are used for a wide variety of
applications in the semiconductor industry. Examples of
silicon-containing films include epitaxial silicon, polycrystalline
silicon (poly-Si), and amorphous silicon, epitaxial silicon
germanium (SiGe), silicon germanium carbide (SiGeC), silicon
carbide (SiC), silicon nitride (SiN), silicon carbonitride (SiCN),
and silicon carboxide (SiCO). As circuit geometries shrink to
smaller feature sizes, lower deposition temperatures for
Si-containing films are preferred, for example, to reduce thermal
budgets.
[0005] Silicon nitride films have very good oxidation resistance
and insulating qualities. Accordingly, these films have been used
in many applications, including oxide/nitride/oxide stacks, etch
stops, oxygen diffusion barriers, and gate insulation layers, among
others. Several methods are known for forming a silicon nitride
film on the surface of a semiconductor wafer by Chemical Vapor
Deposition (CVD). In thermal CVD, a silane gas, such as monosilane
(SiH.sub.4) or polysilanes, is used as a silicon source gas.
[0006] SiN film formation has also been carried out via atomic
layer deposition using halosilane and ammonia. However, this
process requires high temperatures, in excess of 500.degree. C., to
effect clean conversion and eliminate NH.sub.4X byproducts. In
device manufacturing, processes that can be performed at lower
temperatures are generally desired for thermal budget and other
reasons.
SUMMARY
[0007] One aspect of the invention relates to a method of forming a
layer on a substrate surface. The method comprises: providing a
substrate; in a PECVD process, exposing the substrate surface to a
carbosilane precursor containing at least one carbon atom bridging
at least two silicon atoms; exposing the carbosilane precursor to a
low-powered energy source (e.g., direct plasma) to provide a
carbosilane at the substrate surface; and stripping away at least
some of the hydrogen atoms to provide a film comprising SiC.
[0008] Another aspect of the invention relates to a method of
forming a layer on a substrate surface, the method comprising:
providing a substrate; in a PECVD process exposing the substrate
surface to a carbosilane precursor containing at least one
methylene bridging two silicon atoms; exposing the carbosilane
precursor to a direct plasma to provide a carbosilane at the
substrate surface; stripping away at least some of the hydrogen
atoms; and exposing the carbosilane surface to a nitrogen source to
provide a film comprising SiCN suitable as a low k dielectric
film.
[0009] Various embodiments are listed below. It will be understood
that the embodiments listed below may be combined not only as
listed below, but in other suitable combinations in accordance with
the scope of the invention.
[0010] In one or more embodiments of either aspect, stripping away
at least some of the hydrogen atoms comprises exposing the
substrate surface to a plasma containing one or more of He, Ar and
H.sub.2. In some embodiments of either aspect, the film comprising
SiC has a ratio of Si:C approximately matching that of the
carbosilane precursor.
[0011] In some embodiments of either aspect, the carbosilane
precursor is one or more of 1,3,5-trisilapentane, 1,3-disilabutane,
1,3-disilacyclobutane and 1,3,5-trisilacyclohexane. In further
embodiments, the carbosilane precursor comprises
1,3,5-trisilapentane. In even further embodiments, the SiC film has
a ratio of Si:C of about 3:2. In an alternative embodiment, the
carbosilane precursor comprises 1,3-disilabutane.
[0012] The process conditions may be varied. In one or more
embodiments of either aspect, exposing the carbosilane precursor to
a low-powered plasma results in polymerization of the carbosilane.
In some embodiments of either aspect, the low-powered plasma has an
RF value of about 50 W to about 500 W. In some embodiments, the
low-powered plasma has a value of about 10 W to about 200 W. In one
or more embodiments of either aspect, the carbosilane precursor is
exposed to the low-powered plasma for between 0.10 seconds and 5.0
seconds. In some embodiments of either aspect, the substrate
surface has a temperature of about 100 and about 400.degree. C.
[0013] In one or more embodiments of either aspect, exposing the
carbosilane to a nitrogen source comprises exposing the
carbosiliane to a plasma containing nitrogen. In some embodiments,
exposing the carbosiliane to a plasma containing nitrogen results
in the formation of N--H bonds that promote irreversible attachment
of a monolayer of the carbosilane to the substrate surface. In some
embodiments, exposing the carbosilane to a nitrogen source
comprises flowing ammonia or nitrogen gas.
[0014] In some embodiment, the SiC or SiCN film is suitable as a
low k dielectric film.
[0015] A third aspect of the invention relates to a method of
forming a layer on a substrate surface, the method comprising:
providing a substrate; exposing the substrate surface to a
carbosilane precursor 1,3,5-trisilapentane, 1,3-disilabutane,
1,3-disilacyclobutane and 1,3,5-trisilacyclohexane; exposing the
carbosilane precursor to a low-powered plasma to provide a
carbosilane at the substrate surface; and exposing the carbosilane
to a plasma comprising H.sub.2. Any of the above embodiments may
also be used with this aspect.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIGS. 1A-C are Fourier transform infrared spectra of three
SiCN films formed in accordance with an embodiment of the
invention;
[0017] FIG. 2 is a Fourier transform infrared spectra of a SiCN
film formed in accordance with an embodiment of the invention;
[0018] FIG. 3 is a Fourier transform infrared spectra of a SiCN
film formed in accordance with an embodiment of the invention;
and
[0019] FIG. 4 is a Fourier transform infrared spectra of a SiCN
film formed in accordance with an embodiment of the invention.
DETAILED DESCRIPTION
[0020] Before describing several exemplary embodiments of the
invention, it is to be understood that the invention is not limited
to the details of construction or process steps set forth in the
following description. The invention is capable of other
embodiments and of being practiced or being carried out in various
ways.
[0021] A "substrate surface" as used herein, refers to any
substrate or material surface formed on a substrate upon which film
processing is performed during a fabrication process. For example,
a substrate surface on which processing can be performed include
materials such as silicon, silicon oxide, strained silicon, silicon
on insulator (SOI), carbon doped silicon oxides, silicon nitride,
doped silicon, germanium, gallium arsenide, glass, sapphire, and
any other materials such as metals, metal nitrides, metal alloys,
and other conductive materials, depending on the application.
Substrates include, without limitation, glass sheets, ceramic
substrates and semiconductor wafers. Substrates may be exposed to a
pretreatment process to polish, etch, reduce, oxidize, hydroxylate,
anneal and/or bake the substrate surface. In addition to film
processing directly on the surface of the substrate itself, in the
present invention any of the film processing steps disclosed may
also be performed on an underlayer formed on the substrate as
disclosed in more detail below, and the term "substrate surface" is
intended to include such underlayer as the context indicates.
[0022] As used herein, an "SiH-containing precursor" refers to a
precursor molecule that contains a plurality of Si--H bonds.
SiH-containing precursors include silanes and carbosilanes. The
term "silanes" refers to compounds which contain silicon and
hydrogen atoms, including silicon-to-hydrogen bonds. The term
"carbosilanes," which may be used interchangeably with
"organosilanes," refers to compounds that contain silicon, hydrogen
and carbon atoms, and contain at least one carbon-to-silicon
covalent bond. Thus, a "halogenated Si--H-rich precursor" or
"halogenated silane" or "halogenated carbosilane" refers to a
precursor molecule where at least one of the hydrogen atoms bonded
to a silicon atom is replaced with a halogen. By extension, a
"cyanated Si--H-rich precursor" or "cyanated silane" or "cyanated
carbosilane" refers to a precursor molecule where at least one of
the hydrogen atoms bonded to a silicon atom is replaced with a
cyano (CN) group.
[0023] As used herein, "containing at least one carbon atom
bridging at least two silicon atoms" refers to a carbosilane that
contains an Si--C--Si component. The carbon may have two hydrogens,
which would constitute a methylene group and result in a
Si--CH.sub.2--Si component. The silicon atoms may have a wide
variety of substituents, including, but not limited to, hydrogen or
additional silicon and/or carbon atoms. In some cases, the carbon
atom may bridge three or four silicon atoms.
[0024] As used herein, "low temperature" refers to processes that
are conducted at less than 400.degree. C. In specific embodiments,
low temperature refers to less than 300.degree. C., and in more
specific embodiments, less than 200.degree. C. and in highly
specific embodiments, less than 100.degree. C.
[0025] As used herein, "low-powered energy source" refers to a
source of energy that will not damage carbosilane precursor
deposited at a substrate surface. For example, where the source of
energy is a plasma, the RF value is less than about 200 W.
[0026] One aspect of the invention relates to a method of forming a
layer on a substrate surface, the method comprising providing a
substrate, exposing the substrate surface to a carbosilane
precursor containing at least one carbon atom bridging at least two
silicon atoms, exposing the carbosilane precursor to a low-powered
energy source to provide a carbosilane at the substrate surface,
densifying the carbosilane, and exposing the carbosilane surface to
a nitrogen source. The process then may be repeated to add
additional layers.
[0027] Described herein are PECVD processes to deposit SiC and SiCN
films. Accordingly, one aspect of the invention relates to a method
of forming a layer on a substrate surface, the method comprising:
providing a substrate; in a PECVD process, exposing the substrate
surface to a carbosilane precursor containing at least one carbon
atom bridging at least two silicon atoms; exposing the carbosilane
precursor to a low powered energy source to provide a carbosilane
at the substrate surface; and stripping away at least some of the
hydrogen atoms to provide a film comprising SiC. In one or more
embodiments, the low powered energy source comprises a direct
plasma.
[0028] In specific embodiments, carbosilane precursors containing
at least one carbon atom bridging at least two silicon atoms are
used to produce thin films of SiC. In some embodiments, these thin
films of SiC can then be converted to SiCN by displacing some of
the carbon atoms from the SiC. Carbosilane precursors, as described
herein, are used to deposit a thin layer of a silicon-containing
film. While not wishing to be bound by any particular theory, it is
thought that the carbosilane is polymerized at the substrate
surface after exposure to a low-powered energy source. The
carbosilane precursor is exposed to a low-powered energy source,
which forms a layer of the precursor on the substrate surface. In
one embodiment, exposing the carbosilane precursor to a low-powered
energy source comprises exposing the carbosilane precursor to an
electron beam. In another embodiment, exposing the carbosilane
precursor to a low-powered energy source comprises exposing the
carbosilane precursor to a low-powered plasma. In a specific
embodiment, the low-powered plasma has a value of about 10 W to
about 200 W or about 50 W to about 500 W. In some embodiments, the
RF value of the plasma ranges from about 10, 20, 30, 40, 50, 60 70,
80 or 90 W to about 175, 200, 225, 250, 275 or 300 W. In another
embodiment, the precursor is exposed to the low-powered plasma for
between about 0.10 seconds and about 5.0 seconds.
[0029] Carbosilane precursors have been demonstrated to undergo
efficient densification/dehydrogenation to silicon-rich SiC. Thus,
according to various embodiment, carbosilane precursor at the
substrate surface is at least partially densified/dehydrogenated.
In one embodiment, densification/dehydrogenation is plasma-induced.
A helium, argon and/or hydrogen-containing plasma may be used for
dehydrogenation. In specific embodiments, dehydrogenation involves
the use of plasma containing H.sub.2.
[0030] In addition to densification/dehydrogenation, nitrogen may
be introduced into the SiC layer by nitridation to form SiCN. This
occurs by exposing the carbosilane surface to nitrogen source. In
one embodiment, this comprises flowing ammonia or nitrogen gas. In
an alternative embodiment, nitridation occurs via exposure to a
nitriding plasma. In a more specific embodiment, this nitriding
plasma comprises N.sub.2. In a further embodiment, around 5% of the
plasma comprises N.sub.2. In yet another alternative embodiment,
nitridation does not occur.
[0031] These deposition processes can be accomplished using
relatively low RF power conditions and at temperatures lower than
previously available. In previous methods, higher temperatures of
more than 500.degree. C. were necessary. In specific embodiments,
substrate temperature during deposition can be lower than about
400, 350, 300, 250, 200, 150 or 100.degree. C.
[0032] Precursors are based on carbosilanes. Carbosilanes,
sometimes also referred to as organosilanes, are compounds
containing carbon-to-silicon covalent bonds. According to certain
embodiments, the carbosilane precursors should be chosen such that
there is reduced fragmenting in deposited films. Fragmentation of
the film to volatile fragments prevents densification, and causes
shrinking and cracking in flowable applications.
[0033] Carbosilanes may be linear, branched or cyclic. A
particularly suitable type of carbosilane is one that contains a
bridging methylene groups between at least two silicon atoms, such
that the carbon in the methylene group is bonded to the at least
two silicon atoms. In a further embodiment, the methylene group
bridges two silicon atoms. Either one, both, or neither of the two
silicon atoms may be halogenated or pseudohalogenated. Higher
carbosilanes with an extended Si--C--Si backbone are particularly
suitable as they tend towards dehydrogenative densification
reactions, instead of fragmentation. In another embodiment, the
carbosilane contains a bridging CH.sub.2 group or simple C atom
between three or four silicon atoms respectively. Precursors
without such bridging methylene groups, such as those initially
containing only terminal methyl substituents may undergo
rearrangements on plasma excitation to form methylene bridged
carbosilanes and are thus also suitable, though in this case there
may also be substantial cleavage of the Si--C bond of the
Si--CH.sub.3 substituent.
[0034] Polycarbosilanes containing more extended backbones of
alternating Si--C--Si--C--Si bonds, such as 1,3,5-trisilapentane,
are particularly preferable. Examples of suitable carbosilane
precursors include, but are not limited to 1,3,5-trisilapentane,
1,3,5-trisilacyclohexane, 1,3-disilabutane, 1,3-disilapropane and
1,3-disilacyclobutane. In a particular embodiment, the carbosilane
precursor is 1,3-disilabutane. In another particular embodiment,
the carbosilane precursor is 1,3,5-trisilapentane. Where a desired
level of carbon is desired and the precursor contains only terminal
methyl substituents, it is generally necessary to begin with
precursors possessing at least twice the Si:C ratio desired in the
final film.
[0035] In some cases, the conformality of films deposited using
such low power plasma steps may be sufficiently conformal such that
even after subsequent densification they may provide "ALD-like"
conformality. A useful way to enhance such conformality is to
employ a plasma activation step at the end of the activation
sequence--such as one resulting in the formation of N--H
bonds--that promotes the irreversible attachment of the first
monolayer of precursor deposited in a low power plasma step, while
subsequently deposited materials are bound reversibly, and may
re-enter the gas phase and be purged away during a subsequent purge
step. Accordingly, in one embodiment, exposing the carbosilane to a
plasma containing nitrogen results in the formation of N--H bonds
that promote irreversible attachment of a monolayer of the
carbosilane to the substrate surface. While the final surface
activation, applied immediately prior to the introduction of
precursor but after a plasma densification, may be a step involving
nitrogen plasma, it may also involve a non plasma step such as
simple exposure of the surface to a flow of ammonia (NH.sub.3).
[0036] Generally, exposure of "seed" films containing Si, C, and H
to N containing plasmas is effective for generating films
exhibiting N--H functionality as detectable by growth of a
characteristic absorption between about 3200-3600 cm.sup.-1 in the
FTIR. Typical conditions entail pressures in the range of 0.5 Torr
to 20 Torr and RF power levels (13.56 MHz, direct plasma) of
between 25 W and 500 W, for example 100 W for a duration of 2 sec
at a total pressure of 4 Torr and partial pressure of nitrogen
between about 1 Ton and 3 Torr, the balance being He or Ar. In
cases where the film being treated contains very little H (for
example if a plasma process has already been performed to remove H)
a small amount of hydrogen may also be added to the plasma mixture
to promote the generation of more N--H bonding.
[0037] The ratio of silicon to carbon in the film may be adjusted,
depending on the plasma power, exposure time and temperature. For
example, the ratio of Si:C can readily be reduced in a SiCN
composition by replacing carbon with nitrogen atoms using
post-treatment plasmas. The ratio of C to Si may be increased by
utilizing precursors containing a higher initial ratio. In one or
more embodiments, the ratio of Si:C is approximately the same as
that of the precursor. Thus, for example, in one or more
embodiments, if 1,3,5-trisilapentane is used as the precursor, the
Si:C ratio of the film may be about 3:2. Generally, carbosilane
precursors containing carbon in a bridging position between two
silicon atoms can be consolidated to carbide-type ceramics with
efficient retention of carbon. On the other hand, carbon is not
retained to such extent where the precursor does not contain a
bridging carbon atom. For example, precursors based on
methylsilanes undergo consolidation with substantial loss of
carbon.
[0038] Another aspect of the invention relates to exposure of the
substrate surface to plasma as part of the process of forming the
film or layer. The surface with bound precursor is exposed to a
densification/dehydrogenation plasma. Suitable dehydrogenation
plasmas include, but are not limited to, H.sub.2, He and Ar. The
surface is then exposed to a nitriding plasma. Suitable nitriding
plasmas include, but are not limited to N.sub.2 and ammonia.
Exposure to the plasmas may be done substantially simultaneously or
sequentially. Substantially simultaneous means that the substrate
surface is exposed to both plasmas at the same time, with little
exposure time to one plasma at a time. When done sequentially, the
dehydrogenating plasma may first be applied, followed by the
nitriding plasma. Any number of sequences may be used. In one
embodiment, plasma exposure may occur in every step of the process.
In another embodiment, plasma exposure may occur every other
sequence. Subsequent exposure to a nitriding plasma results in
conversion of the SiC film to SiCN.
[0039] In one embodiment of this aspect, dehydrogenation and
nitridation occur substantially simultaneously. By contrast, in
another embodiment, dehydrogenation and nitridation occur
sequentially.
[0040] Accordingly, in a second aspect of the invention, the
invention relates to a method of forming a layer on a substrate
surface, the method comprising providing a substrate, exposing the
substrate surface to a carbosilane precursor containing at least
one methylene bridging two silicon atoms, exposing the carbosilane
precursor to a low-powered plasma to provide a carbosilane at the
substrate surface, densifying the carbosilane, and exposing the
carbosilane surface to a nitrogen source. Such a SiCN may be
suitable for use as a low k dielectric film. In one embodiment of
this aspect, the low-powered plasma has a value of about 10 W to
about 200 W. In a different embodiment of this aspect, the
carbosilane precursor is exposed to the low-powered plasma for
between 0.10 seconds and 5.0 seconds.
[0041] In a different embodiment, the carbosilane precursor is one
or more of 1,3,5-trisilapentane, 1,3-disilabutane,
1,3-disilacyclobutane and 1,3,5-trisilacyclohexane. In a more
specific variant of this embodiment, the carbosilane precursor is
1,3,5-trisilapentane.
[0042] A third aspect of the invention relates to a method of
forming a layer on a substrate surface, the method comprising:
providing a substrate; exposing the substrate surface to a
carbosilane precursor 1,3,5-trisilapentane, 1,3-disilabutane,
1,3-disilacyclobutane and 1,3,5-trisilacyclohexane; exposing the
carbosilane precursor to a low-powered plasma to provide a
carbosilane at the substrate surface; and exposing the carbosilane
to a plasma comprising H.sub.2
[0043] In some embodiments, one or more layers may be formed during
a plasma enhanced chemical vapor deposition (PECVD) process. In
some processes, the use of plasma provides sufficient energy to
promote a species into the excited state where surface reactions
become favorable and likely. Introducing the plasma into the
process can be continuous or pulsed. In some embodiments,
sequential pulses of precursors (or reactive gases) and plasma are
used to process a layer. In some embodiments, the reagents may be
ionized either locally (i.e., within the processing area) or
remotely (i.e., outside the processing area). In some embodiments,
remote ionization can occur upstream of the deposition chamber such
that ions or other energetic or light emitting species are not in
direct contact with the depositing film. In some PECVD processes,
the plasma is generated external from the processing chamber, such
as by a remote plasma generator system. The plasma may be generated
via any suitable plasma generation process or technique known to
those skilled in the art. For example, plasma may be generated by
one or more of a microwave (MW) frequency generator or a radio
frequency (RF) generator. The frequency of the plasma may be tuned
depending on the specific reactive species being used. Suitable
frequencies include, but are not limited to, 2 MHz, 13.56 MHz, 40
MHz, 60 MHz and 100 MHz. Although plasmas may be used during the
deposition processes disclosed herein, it should be noted that
plasmas may not required. Indeed, other embodiments relate to
deposition processes under very mild conditions without a
plasma.
[0044] According to one or more embodiments, the substrate is
subjected to processing prior to and/or after forming the layer.
This processing can be performed in the same chamber or in one or
more separate processing chambers. In some embodiments, the
substrate is moved from the first chamber to a separate, second
chamber for further processing. The substrate can be moved directly
from the first chamber to the separate processing chamber, or it
can be moved from the first chamber to one or more transfer
chambers, and then moved to the desired separate processing
chamber. Accordingly, the processing apparatus may comprise
multiple chambers in communication with a transfer station. An
apparatus of this sort may be referred to as a "cluster tool" or
"clustered system", and the like.
[0045] Generally, a cluster tool is a modular system comprising
multiple chambers which perform various functions including
substrate center-finding and orientation, degassing, annealing,
deposition and/or etching. According to one or more embodiments, a
cluster tool includes at least a first chamber and a central
transfer chamber. The central transfer chamber may house a robot
that can shuttle substrates between and among processing chambers
and load lock chambers. The transfer chamber is typically
maintained at a vacuum condition and provides an intermediate stage
for shuttling substrates from one chamber to another and/or to a
load lock chamber positioned at a front end of the cluster tool.
Two well-known cluster tools which may be adapted for the present
invention are the Centura.RTM. and the Endura.RTM., both available
from Applied Materials, Inc., of Santa Clara, Calif. The details of
one such staged-vacuum substrate processing apparatus is disclosed
in U.S. Pat. No. 5,186,718, entitled "Staged-Vacuum Wafer
Processing Apparatus and Method," Tepman et al., issued on Feb. 16,
1993. However, the exact arrangement and combination of chambers
may be altered for purposes of performing specific steps of a
process as described herein. Other processing chambers which may be
used include, but are not limited to, cyclical layer deposition
(CLD), atomic layer deposition (ALD), chemical vapor deposition
(CVD), physical vapor deposition (PVD), etch, pre-clean, chemical
clean, thermal treatment such as RTP, plasma nitridation, degas,
orientation, hydroxylation and other substrate processes. By
carrying out processes in a chamber on a cluster tool, surface
contamination of the substrate with atmospheric impurities can be
avoided without oxidation prior to depositing a subsequent
film.
[0046] According to one or more embodiments, the substrate is
continuously under vacuum or "load lock" conditions, and is not
exposed to ambient air when being moved from one chamber to the
next. The transfer chambers are thus under vacuum and are "pumped
down" under vacuum pressure. Inert gases may be present in the
processing chambers or the transfer chambers. In some embodiments,
an inert gas is used as a purge gas to remove some or all of the
reactants after forming the silicon layer on the surface of the
substrate. According to one or more embodiments, a purge gas is
injected at the exit of the deposition chamber to prevent reactants
from moving from the deposition chamber to the transfer chamber
and/or additional processing chamber. Thus, the flow of inert gas
forms a curtain at the exit of the chamber.
[0047] The substrate can be processed in single substrate
deposition chambers, where a single substrate is loaded, processed
and unloaded before another substrate is processed. The substrate
can also be processed in a continuous manner, like a conveyer
system, in which multiple substrate are individually loaded into a
first part of the chamber, move through the chamber and are
unloaded from a second part of the chamber. The shape of the
chamber and associated conveyer system can form a straight path or
curved path. Additionally, the processing chamber may be a carousel
in which multiple substrates are moved about a central axis and are
exposed to deposition, etch, annealing, cleaning, etc. processes
throughout the carousel path.
[0048] During processing, the substrate can be heated or cooled.
Such heating or cooling can be accomplished by any suitable means
including, but not limited to, changing the temperature of the
substrate support and flowing heated or cooled gases to the
substrate surface. In some embodiments, the substrate support
includes a heater/cooler which can be controlled to change the
substrate temperature conductively. In one or more embodiments, the
gases (either reactive gases or inert gases) being employed are
heated or cooled to locally change the substrate temperature. In
some embodiments, a heater/cooler is positioned within the chamber
adjacent the substrate surface to convectively change the substrate
temperature.
[0049] The substrate can also be stationary or rotated during
processing. A rotating substrate can be rotated continuously or in
discreet steps. For example, a substrate may be rotated throughout
the entire process, or the substrate can be rotated by a small
amount between exposure to different reactive or purge gases.
Rotating the substrate during processing (either continuously or in
steps) may help produce a more uniform deposition or etch by
minimizing the effect of, for example, local variability in gas
flow geometries.
[0050] The approaches of low temperature atomic layer deposition of
SiCN and SiC films described above may also be used for the
deposition of extremely thin, defect-free and conformal films for
applications outside of the electronics industry. Such applications
include for the preparation of barrier and passivation layers.
Additionally, the low temperature reactivity would make the
processes applicable to the coating of organic substrates,
including plant- and animal-derived tissues and materials. In some
embodiments, the films described herein are used in low k
dielectric barrier applications. In one or more embodiments, the
deposited films are highly etch resistant and have a refractive
index (RI's) of between about 1.7 and 2.2.
EXAMPLES
Example 1
[0051] Three SiCN films were deposited using 1,3,5-trisilapentane
using the conditions listed in the Table 1. Films 1, 2, and 3 were
formed using multistep PECVD deposition and treatment-type
sequences, with very low powers (20 W) and short times (0.25 sec)
used in the first step. This very low power and short exposure time
formed 3-4 A of a "seed" layer per cycle. Upon completion of this
first step, the flow of the 1,3,5-trisilapentane precursor was
turned off. A flow of inert gases was continued until residual
traces of the precursor were purged from the process chamber. Once
purge was completed, gas flows were readjusted and stabilized at
the values selected for the first plasma treatment step and again
for a second plasma treatment step as indicated in Table 1. After
completion of the full sequence, the entire cycle was then repeated
until a desired film thickness was reached, for which the
measurements reported here was at least 100 A and more generally
200 A thick.
[0052] Films 1, 2, and 3 differed in respect to the plasma
densification and nitrogenation steps employed. Film 2 was
deposited in the same manner as Film 1, but also featured exposure
to a He/Ar plasma. Film 3 was deposited in the same manner as Film
2, but featured a nitrogen plasma at 100 W, instead of the 200 W
used for Films 1 and 2. Table 1 also shows the elemental
composition of all three films deposited at the various conditions
determined using Rutherford backscattering. It should be noted that
in this particular case analysis of the films for hydrogen content
was not performed, though there was likely residual hydrogen
remaining behind in the films. Most relevant for comparisons to
data on films derived from the precursor HMDS described in Example
2 are C:Si and N:Si ratios which can be calculated independent of
the H content. Because 1,3,5-trisilapentane contains no nitrogen,
all of the nitrogen incorporated into films derived from
1,3,5-trisilapentane can be attributed to the presence of nitrogen
gas added during the plasma treatments. The selection of specific
treatment conditions provides some means for adjusting the final
film composition.
TABLE-US-00001 TABLE 1 Elemental Content of Deposited Films BULK
Films Film 2 Film 3 Film 1: Deposition: Deposition: Deposition:
0.25 sec/20 Watt dep .25 sec/20 Watt dep, 0.25 sec/20 Watt dep
Treatments: Treatments Treatments: 1.5 sec H.sub.2 plasma at 100 W
1.5 sec H.sub.2 plasma at 100 W 1.5 sec H.sub.2 plasma at 100 W,
2.5 sec He/Ar at 150 W 2.5 s He/Ar Plasma at 150 W Element 2.10 sec
N.sub.2 Plasma at 200 W 3.5 sec N.sub.2 Plasma at 200 W 3.2 sec
N.sub.2 Plasma at 100 W Si 29 33 33 C 11 12 19 N 56 55 47 O 4 0 0
Ar 0.3 0.3 1 Approximate (average) thickness of film removed by 5
min exposure to dilute HF and etch raters based on 5 min etch time
30 Ang total 20 Ang total No significant etch 6 Ang/min 4 Ang/min
<1 Ang/min
[0053] Etch behavior was determined to be non-linear and, while not
wishing to be bound to any particular theory, appears to involve
the relatively rapid removal of a thin oxidized surface layer,
after which subsequent extended exposure to the etchant has little
effect. However, for consistency in comparing results to those of
Example 2, rates are reported based on a 5 min etch time in 100:1
HF. Similar behavior was observed using 6:1 BOE (6 parts
concentrated NH.sub.4F/1 part concentrated HF).
[0054] FIGS. 1A-C are graphical representations of Fourier
transform infrared (FTIR) spectra of the SiCN films of Example 1.
Film 1, which is a typical baseline process condition, is
represented in FIG. 1C. Film 2 is represented in FIG. 1B. Film 3 is
represented in FIG. 1A. Each of the three datasets was normalized.
The peak at about 3300 cm.sup.-1 corresponds to N--H bonding. The
peak at about 2300 cm.sup.-1 corresponds to CO.sub.2 present in
ambient air. The broad peak centered at around 900 cm.sup.-1
corresponds to SiCN and the shift seen from Film 1. The shift seen
from films 1 to Film 3 is attributable to increasing carbon
content, which also corresponds to their increasing resistance to
wet HF etch chemistries.
Example 2
[0055] Additional SiCN films 4 through 6 were deposited using the
precursor hexamethyldisilazane (HMDS) which has the formula
[(CH.sub.3).sub.3Si].sub.2NH. Accordingly, HMDS does not contain a
carbon atom bridging at least two silicon atoms. HMDS has a 3:1
carbon to silicon ratio, with each silicon atom bound to three
methyl substituents and one nitrogen. A series of cyclic
depositions analogous used in depositing Films 1 through 3 were
employed for the deposition of Films 4, 5, and 6, with results
listed in Table 2 below. In each case, a "seed" layer was deposited
at 20 W RF, 6 Torr, delivering HMDS from a pressure controlled
vapor draw ampoule using Ar carrier gas analogous to conditions
employed for 1,3,5-trisilapentane in Example 1. The deposition rate
was determined to be approximately linear with total plasma on
time/cycle and the initial step followed by a long inert gas purge
to remove residual precursor from the chamber. Film 4 was deposited
using only a hydrogen plasma treatment cycle. Film 5 was deposited
with an H.sub.2 plasma followed by a N.sub.2 plasma. Film 6 was
deposited using plasma comprising a mixture of H.sub.2 and
N.sub.2.
[0056] Table 2 also shows the elemental content of Films 4 through
6, as determined by Rutherford backscattering, as well as 100:1 wet
HF etch rates. It should be noted that unlike in Films 1 through 3,
Rutherford backscattering analysis for Films 4 through 6 included a
determination of hydrogen content in the films. Accordingly, direct
comparisons between Films 1 through 3 and Films 4 through 6 are
limited to ratios of carbon to silicon or nitrogen to silicon.
TABLE-US-00002 TABLE 2 Elemental Content of Deposited Films
Treatment Film 5 Film 4 1.10 sec H.sub.2 Plasma at 300 W Film 6
Element 10 sec H.sub.2 Plasma at 300 W 2.2 sec N.sub.2 Plasma at
100 W 7 sec H.sub.2 + N.sub.2 Plasma at 200 W Si 25.50% 26.50%
32.50% C 34% 19% 0% N 18.50% 38.50% 47.50% O 0% 3% 9% H 22% 13% 11%
100:1 <1 Ang/min >20 Ang./min (complete loss >20 Ang./min.
(complete loss DHF or >100 A thick film in 5 min. of >100 A
thick film in 5 min. Etch Rate
[0057] FIGS. 2-4 are graphical representations of Fourier transform
infrared (FTIR) spectra of the Films 4 through 6, respectively. The
results in FIG. 2 represent deposition followed by the use of an
using an H.sub.2 plasma only. The results in FIG. 3 represent
deposition using an H.sub.2 plasma followed by an N.sub.2 (in
sequence) plasma treatment analogous to that applied in Examples 1.
The results in FIG. 4 represent deposition using a plasma
comprising a mixture of H.sub.2 and N.sub.2, and result in complete
removal of carbon from the film.
[0058] In contrast to the work with 1,3,5-trisilapentane, the
conditions necessary to reduce C--H absorptions in the IR spectra
and induce growth in the SiCN region at about 800-1000 cm.sup.-1,
were found to result in substantial removal of carbon. In fact,
without any additional treatment the C:Si ratio, as determined by
RBS, dropped from the initial value of 3:1 to only 1.3:1 While Film
4 was removed slowly in 100:1 HF, the application of additional
steps involving a short N.sub.2 plasma step (as seen in Film 5 and
analogous to those employed in Example 1 films), or an alternative
process which combined H.sub.2 and N.sub.2 plasmas into a single
step (as seen in Film 6), underwent significantly higher carbon
loss and exhibited low resistance to etching by 100:1 HF.
[0059] Interestingly, the N.sub.2 plasma step added to each cycle
of the process used for Film 4 process to give Film 5 resulted in
the C:Si ratio decreasing from 1.3:1 to 0.72:1, with the result
still being higher than the ratios between 0.38:1 and 0.58:1
measured for the 1,3,5-trisilapentane-derived Films 1-3. Yet it was
the 1,3,5-trisilapentane-derived films which exhibited superior
etch resistance.
[0060] While not wishing to be bound by any particular theory,
these results suggest the bridging carbon atoms present in
precursors (and low power seed films derived therefrom) are more
effectively retained and converted to etch resistant carbides than
carbon originally present in the form of terminal methyl groups.
Furthermore, it should be noted that higher RF power levels and
longer H.sub.2 and/or inert gas plasma treatment times were
necessary to promote condensation of HMDS derived seeds to a level
approximating the properties of a 1,3,5-trisilapentane-derived
films. All the films of Example 1 were prepared using a final
Nitrogen plasma step (required for their conversion to SiCN--after
which they were shown to still exhibit reasonably high (and useful)
resistance to wet HF etch processes. However, applying a similar
process in the preparation of Film 5 (derived from the precursor
HMDS) resulted in its loss of HF etch resistance--even though the
final C:Si ratio remained higher (0.75) than measured in any of the
1,3,5-trisilapentane derived films. It may be concluded that carbon
originally present as "bridging" methylenes between Si atoms
converts to a form exerting a much greater impact on etch behavior
than can be estimated using compositional analysis alone. In the
case of the 1,3,5 trisilapenetane, the addition of a nitrogen
plasma step can effectively incorporate nitrogen without exerting a
large effect on the C:Si ratio (dropping from the value of 0.67:1
calculated from the ratio in the precursor to 0.53:1 in the case of
Film 3). Adding an analogous Nitrogen plasma step at the end of the
densification process used for the HMDS Film 4 resulted in a much
more significant impact on carbon content (1.3 dropping to 0.72
together with a severe degradation of etch resistance) suggesting
the bonding of the retained carbon in each case is significantly
different.
[0061] While it may indeed be possible to achieve a process with
more classic, self-limiting reactivity by incorporating an active
leaving group onto the HMDS molecule (by replacing one of the
methyl substituents with a halide or cyanide), the stability of
such a precursor may be severely compromised by the potentially
reactive, albeit somewhat hindered, N--H bond already present. For
this reason precursors possessing both bridging carbon and reactive
Si--H bonds (such as 1,3,5-trisilapentane) are particularly well
suited as SiCN precursors, since carbon is efficiently retained
while still permitting the introduction of Nitrogen (for example by
inserting into Si--H bonds or Si--Si bonds). This results in the
creation of reactive functionality not initially present in the
precursor itself, thereby enabling use of schemes employing the
various "activated" derivatives described herein, most or all of
which would not be expected to be viable with an N--H functionality
already present in the molecule, as would be the case with a
material derived from HMDS.
[0062] Therefore, the films of Example 2 show that compositions
exhibiting desirable etch properties required much longer and more
aggressive H.sub.2/inert plasma based densifications steps, after
which films were still insufficiently stable to permit use of a
nitrogen plasma activation step without significant loss of carbon
and etch resistance. This demonstrates the superiority of Example 1
films, deposited according to various embodiments of the
invention.
[0063] Thus, there is an apparent advantage of precursors such as
1,3,5-trisilapentane (which incorporate carbon in bridging
positions between Si atoms) relative to more common precursors
possessing non-bridging carbon substituents such as methyl
(--CH.sub.3), which is particularly evident when targeting
applications requiring that the films exhibit high wet etch
resistance to chemistries such as HF (100:1 H.sub.2O/concentrated
HF), or mixtures such as buffered oxide etch (a mixture on 6:1
concentrated NH4F to concentrated HF) designed to rapidly etch
SiO.sub.2.
[0064] Reference throughout this specification to "one embodiment,"
"certain embodiments," "one or more embodiments" or "an embodiment"
means that a particular feature, structure, material, or
characteristic described in connection with the embodiment is
included in at least one embodiment of the invention. Thus, the
appearances of the phrases such as "in one or more embodiments,"
"in certain embodiments," "in one embodiment" or "in an embodiment"
in various places throughout this specification are not necessarily
referring to the same embodiment of the invention. Furthermore, the
particular features, structures, materials, or characteristics may
be combined in any suitable manner in one or more embodiments.
[0065] Although the invention herein has been described with
reference to specific embodiments, it is to be understood that
these embodiments are merely illustrative of the principles and
applications of the present invention. It will be apparent to those
skilled in the art that various modifications and variations can be
made to the method and apparatus of the present invention without
departing from the spirit and scope of the invention. Thus, it is
intended that the present invention include modifications and
variations that are within the scope of the appended claims and
their equivalents.
* * * * *