U.S. patent application number 10/397993 was filed with the patent office on 2003-11-06 for low dielectric constant fluorine and carbon-containing silicon oxide dielectric material characterized by improved resistance to oxidation.
Invention is credited to Aronowitz, Sheldon, Zubkov, Vladimir.
Application Number | 20030207750 10/397993 |
Document ID | / |
Family ID | 25157722 |
Filed Date | 2003-11-06 |
United States Patent
Application |
20030207750 |
Kind Code |
A1 |
Zubkov, Vladimir ; et
al. |
November 6, 2003 |
Low dielectric constant fluorine and carbon-containing silicon
oxide dielectric material characterized by improved resistance to
oxidation
Abstract
A process is provided for forming a low k fluorine and
carbon-containing silicon oxide dielectric material by reacting
with an oxidizing agent one or more silanes including one or more
organofluoro silanes characterized by the absence of aliphatic C--H
bonds. In one embodiment, the process is carried out using a mild
oxidizing agent. Also provided is a low dielectric constant
fluorine and carbon-containing silicon oxide dielectric material
for use in an integrated circuit structure containing silicon atoms
bonded to oxygen atoms, silicon atoms bonded to carbon atoms, and
carbon atoms bonded to fluorine atoms, where the dielectric
material is characterized by the absence of aliphatic C--H bonds
and where the dielectric material has a ratio of carbon atoms to
silicon atoms of C:Si greater than about 1:3.
Inventors: |
Zubkov, Vladimir; (Mountain
View, CA) ; Aronowitz, Sheldon; (San Jose,
CA) |
Correspondence
Address: |
LSI LOGIC CORPORATION
1621 BARBER LANE
MS: D-106 LEGAL
MILPITAS
CA
95035
US
|
Family ID: |
25157722 |
Appl. No.: |
10/397993 |
Filed: |
March 25, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10397993 |
Mar 25, 2003 |
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09792683 |
Feb 23, 2001 |
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6572925 |
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Current U.S.
Class: |
501/133 ;
257/E21.261; 257/E21.264; 257/E21.276; 423/342; 501/151;
501/87 |
Current CPC
Class: |
C23C 16/401 20130101;
H01L 21/02211 20130101; H01L 21/31629 20130101; H01L 21/3122
20130101; H01L 21/02271 20130101; H01L 21/02131 20130101; H01L
21/3127 20130101 |
Class at
Publication: |
501/133 ; 501/87;
501/151; 423/342 |
International
Class: |
C04B 035/14; C04B
035/571; C01B 033/08 |
Claims
Having thus described the invention, what is claimed is:
1. A process for forming a low k fluorine and carbon-containing
silicon oxide dielectric material comprising reacting with an
oxidizing agent one or more silanes including one or more
organofluoro silanes characterized by the absence of aliphatic C--H
bonds.
2. The process of claim 1 wherein said oxidizing agent is a mild
oxidizing agent.
3. The process of claim 2 wherein said mild oxidizing agent is
hydrogen peroxide (H.sub.2O.sub.2).
4. The oxidizing agent of claim 1 wherein said oxidizing agent is
more reactive than hydrogen peroxide.
5. The process of claim 1 wherein said oxidizing agent is selected
from the group consisting of ozone (O.sub.3), oxygen (O.sub.2),
oxides of nitrogen (N.sub.2O, NO, NO.sub.2), and mixtures
thereof.
6. The process of claim 1, wherein said one or more organofluoro
silanes has the formula: (H).sub.ySi(C.sub.xF.sub.2x+1).sub.4-y,
where y=1 to 3 and x=1 to 5.
7. The process of claim 6 wherein said one or more organofluoro
silanes has the formula: (H).sub.3Si(CF.sub.m)(CF.sub.3).sub.n
where m=0 to 3, and n=3-m.
8. The process of claim 1 herein said one or more organofluoro
silanes has the formula: R.sub.1((R.sub.2)Si(L)).sub.nSi(R.sub.3)
where R.sub.1.dbd.(H) or (C.sub.xF.sub.2x+1), R.sub.2.dbd.(H).sub.2
or (C.sub.xF.sub.2x+1)(H), R.sub.3.dbd.(H).sub.3 or
(C.sub.xF.sub.2x+1)(H).s- ub.2, L=--(O)-- or
--(C(R.sub.4).sub.2).sub.m--, n=0 to 5, x=1 to 5, m=1 to 4, and
each R.sub.4 is independently F or (C.sub.xF.sub.2x+1).
9. The process of claim 8 wherein n is at least 1.
10. The process of claim 9 wherein said one or more organofluoro
silanes has the formula: (R.sub.4)Si(CF.sub.2)Si(R.sub.5) where
R.sub.4.dbd.(H).sub.3 or (CF.sub.3)(H).sub.2 and
R.sub.5.dbd.(H).sub.3 or (CF.sub.3) (H).sub.2.
11. The process of claim 1 wherein said one or more organofluoro
silanes has the formula:
((C.sub.xF.sub.2x+1).sub.pSi(H).sub.2-p(L)).sub.q where L=--(O)--
or --(C(R).sub.2).sub.r--; each R is independently F or
(C.sub.xF.sub.2x+1), p=1 to 2, q=3 to 6, r=1 to 4, and x=1 to
5.
12. The process of claim 1 wherein said one or more organofluoro
silanes are characterized by the presence of Si--H bonds.
13. The process of claim 1 wherein said one or more silanes further
include SiH.sub.4.
14. The process of claim 1 wherein said one or more organofluoro
silanes include CF.sub.3SiH.sub.3.
15. The process of claim 1 wherein said reacting is carried out at
low temperature.
16. A process for forming a low k fluorine and carbon-containing
silicon oxide dielectric material comprising reacting with a mild
oxidizing agent one or more silanes including one or more
organofluoro silanes characterized by the absence of aliphatic C--H
bonds.
17. The process of claim 16 wherein said one or more silanes
consist essentially of one or more organofluoro silanes.
18. The process of claim 16 wherein said mild oxidizing agent is
hydrogen peroxide.
19. The process of claim 16 wherein said one or more organofluoro
silanes include trifluorosilane (CF.sub.3SiH.sub.3).
20. The process of claim 16 wherein said reacting is carried out at
low temperature.
21. A low dielectric constant fluorine and carbon-containing
silicon oxide dielectric material for use in an integrated circuit
structure comprising silicon atoms bonded to oxygen atoms, silicon
atoms bonded to carbon atoms, and carbon atoms bonded to fluorine
atoms, wherein said dielectric material is characterized by the
absence of aliphatic C--H bonds and wherein said dielectric
material has a ratio of carbon atoms to silicon atoms of C:Si
greater than about 1:3.
22. The dielectric material of claim 21 further characterized by
the presence of C--C bonds.
23. The dielectric material of claim 21 consisting essentially of
silicon atoms, carbon atoms, fluorine atoms, and oxygen atoms.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The subject matter of this application relates to the
subject matter of copending application docket number 00-446,
entitled "A PROCESS FOR FORMING A LOW DIELECTRIC CONSTANT FLUORINE
AND CARBON-CONTAINING SILICON OXIDE DIELECTRIC MATERIAL
CHARACTERIZED BY IMPROVED RESISTANCE TO OXIDATION", assigned to the
assignee of this application, and filed on the same date as this
application.
[0002] The subject matter of this application relates to the
subject matter of copending application docket number 00-643,
entitled "A PROCESS FOR FORMING A LOW DIELECTRIC CONSTANT FLUORINE
AND CARBON-CONTAINING SILICON OXIDE DIELECTRIC MATERIAL
CHARACTERIZED BY IMPROVED RESISTANCE TO OXIDATION", assigned to the
assignee of this application, and filed on the same date as this
application.
[0003] The subject matter of this application relates to the
subject matter of copending U.S. patent application Ser. No.
09/590,310, filed on Jun. 7, 2000, entitled "A LOW TEMPERATURE
PROCESS FOR FORMING A LOW DIELECTRIC CONSTANT FLUORINE AND
CARBON-CONTAINING SILICON OXIDE DIELECTRIC MATERIAL CHARACTERIZED
BY IMPROVED RESISTANCE TO OXIDATION AND GOOD GAP-FILLING
CAPABILITIES", and assigned to the assignee of this
application.
BACKGROUND OF THE INVENTION
[0004] 1. Field of the Invention
[0005] This invention relates to integrated circuit structures.
More particularly this invention relates to the low temperature
formation of a low dielectric constant (k) fluorine and
carbon-containing silicon oxide dielectric material for use in the
formation of integrated circuit structures.
[0006] 2. Description of the Related Art
[0007] The shrinking of integrated circuits has resulted in levels
of electrically conductive interconnects being placed closer
together vertically, as well as reduction of the horizontal spacing
between the electrically conductive interconnects, such as metal
lines, on any particular level of such interconnects. As a result,
capacitance has increased between such conductive portions,
resulting in loss of speed and increased cross-talk. One proposed
approach to solving this problem of high capacitance is to replace
the conventional silicon oxide (SiO.sub.2) dielectric material,
having a dielectric constant (k) of about 4.0, with another
insulation material having a lower dielectric constant to thereby
lower the capacitance.
[0008] Dobson et al., in an article entitled "Advanced SiO.sub.2
Planarization Using Silane and H.sub.2O.sub.2", published in
Semiconductor International, December 1994, at pages 85-88,
describe the low temperature formation of SiO.sub.2 by reaction of
silane (SiH.sub.4) with hydrogen peroxide (H.sub.2O.sub.2) to
produce a silicon oxide which flows like a liquid and thus exhibits
good gap fill characteristics.
[0009] In an article by L. Peters, entitled "Pursuing the Perfect
Low-K Dielectric", published in Semiconductor International, Volume
21, No. 10, September 1998, at pages 64-74, a number of alternate
dielectric materials are disclosed and discussed. Included in these
dielectric materials is a description of a low k dielectric
material having a dielectric constant of about 3.0 formed using a
Flowfill chemical vapor deposition (CVD) process developed by
Trikon Technologies of Newport, Gwent, U.K. The process is said to
react methyl silane (CH.sub.3--SiH.sub.3) with hydrogen peroxide
(H.sub.2O.sub.2) to form monosilicic acid which condenses on a cool
wafer and is converted into an amorphous methyl-doped silicon oxide
which is annealed at 400.degree. C. to remove moisture. The article
goes on to state that beyond methyl silane, studies show a possible
k of 2.75 using dimethyl silane in the Flowfill process.
[0010] An article by S. McClatchie et al. entitled "Low Dielectric
Constant Oxide Films Deposited Using CVD Techniques", published in
the 1998 Proceedings of the Fourth International Dielectrics For
ULSI Multilevel Interconnection Conference (Dumic) held on Feb.
16-17, 1998 at Santa Clara, Calif., at pages 311-318, also
describes the formation of methyl-doped silicon oxide by the low-k
Flowfill process of reacting methyl silane with H.sub.2O.sub.2 to
achieve a dielectric constant of .about.2.9.
[0011] The incorporation of such carbon-doped silicon oxide
dielectric material into interconnect architecture has been very
attractive not only because of the low k properties, but also
because of the compatibility with conventional silicon process
technologies. Generally these materials remain stable upon
annealing at temperatures of up to 500.degree. C. The carbon doped
silicon oxide materials are characterized by the structure of
amorphous silicon oxide with incorporated methyl groups and
hydrogen species, and are also characterized by a reduced density
in comparison with conventional silicon oxide that can be explained
by the formation of microporosity surrounding the incorporated
methyl groups. Furthermore, such hydrocarbon-modified silicon oxide
dielectric materials deposited by CVD techniques are also
characterized by strong adhesion.
[0012] While such carbon-doped silicon oxide dielectric materials
do exhibit the desired low k (i.e., dielectric constants below
about 3.0), resulting in reduced capacitance of the dielectric
material, a major problem of such carbon-doped silicon oxide is a
low resistance to oxidation that results in a destruction of the
incorporated hydrocarbons and a resulting increase in the overall
dielectric constant of the dielectric material. The sensitivity to
oxidation is thought to be due to the reactivity of the C--H bonds
of the methyl group bonded to silicon. The removal of the methyl
group results in a more hydrophilic surface that may be responsible
for a so-called "via poisoning" which is observed after via etch
and photoresist strip with oxygen-containing plasma, and is related
to suppression of the surface nucleation in subsequent via liner
deposition steps.
[0013] More recently, Sugahara et al., in an article entitled
"Chemical Vapor Deposition of CF.sub.3-Incorporated Silica Films
for Interlayer Dielectric Applications", published in the 1999
Joint International Meeting, Electrochemical Society Meeting
Abstracts, volume 99-2, Abstract 746, 1999, described the reaction
of trimethyl-fluoromethyl-silane (CF.sub.3Si(CH.sub.3).sub.3) with
an ozone oxidizer at an elevated temperature. Sugahara et al.
stated that the low reactivity of Si--alkyl bonds required the
deposition to be carried at elevated temperatures
(.about.350.degree. C.). The material demonstrated resistance to
oxidation by oxygen plasma. However, it is known that dielectric
films produced by high temperature ozone processes are
characterized by poor gap-fill, while continuous shrinkage in
feature size of integrated circuit structure demands an increased
gap-fill capability. Further, the presence of C--H bonds in the
compound used by Sugahara may yield oxidation-sensitive dielectric
materials due to the presence of C--H bonds in the precursor silane
compound.
[0014] It would, therefore, be desirable to provide a low k silicon
oxide dielectric material which exhibits properties of better
resistance to oxidation during deposition and subsequent processing
steps. It would also be desirable to provide, in at least one
embodiment, a low k silicon oxide dielectric material which
exhibits the gap-fill properties and film adherence properties of
CVD-formed low k carbon doped silicon oxide dielectric materials
such as discussed by the Dobson et al., Peters, and McClatchie et
al. articles discussed above, while also maintaining a low
formation temperature to conserve the thermal budget of the
integrated circuit structure. This invention provides these
characteristics and provides additional advantages as well.
SUMMARY OF THE INVENTION
[0015] The invention provides a process for forming a low k
fluorine and carbon-containing silicon oxide dielectric material by
reacting with an oxidizing agent one or more silanes including one
or more organofluoro silanes characterized by the absence of
aliphatic C--H bonds. In one embodiment of the invention, the
oxidizing agent is a mild oxidizing agent.
[0016] The invention further provides a low dielectric constant
fluorine and carbon-containing silicon oxide dielectric material
for use in an integrated circuit structure containing silicon atoms
bonded to oxygen atoms, silicon atoms bonded to carbon atoms, and
carbon atoms bonded to fluorine atoms, where the dielectric
material is characterized by the absence of aliphatic C--H bonds
and where the dielectric material has a ratio of carbon atoms to
silicon atoms of C:Si greater than about 1:3.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The sole drawing is a flowsheet illustrating one embodiment
of the process of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The invention provides a process for forming a low
dielectric constant (k) fluorine and carbon-containing silicon
oxide dielectric material which includes reacting with an oxidizing
agent one or more silanes including one or more organofluoro
silanes characterized by the absence of aliphatic C--H bonds.
[0019] The low k fluorine and carbon-containing silicon oxide
dielectric material formed in the method of the invention will have
a resultant low dielectric constant relative to silicon oxide or
silicon nitride dielectric materials, and will have an increased
resistance to oxidation relative to organo-containing silicon oxide
dielectric materials, which contain oxidant-sensitive aliphatic
C--H bonds.
[0020] As used herein, an "organofluoro silane" is a compound that
contains at least one silicon atom bonded to at least one carbon
atom, at least one carbon atom bonded to at least one fluorine
atom, and, optionally, one or more silicon atoms bonded to at least
one hydrogen atom.
[0021] Use herein of the term "silanes" refers to
silicon-containing compounds containing at least one silicon atom
bonded to at least one hydrogen atom or bonded to at least one
carbon atom. Exemplary silanes include SiH.sub.4,
SiH.sub.3(CH.sub.3), and SiH.sub.3(CF.sub.3).
[0022] The term "aliphatic C--H bond" refers to a C--H bond where
the carbon atom bonded to the hydrogen atom is not in an aromatic
ring; thus, "aliphatic C--H bond", as used herein, includes
alicyclic C--H bonds. Similarly, an "aliphatic hydrogen" is a
hydrogen atom bound to a carbon through an aliphatic C--H bond.
[0023] By use of the interchangeable terms "low k" or "low
dielectric constant" herein is meant a dielectric constant below
the dielectric constant of silicon oxide or silicon nitride.
Preferably, a low dielectric constant is a dielectric constant
below about 3.5, and more preferably below about 3.
[0024] The term "oxidizing agent" refers to an oxygen-containing
compound capable of reacting with an organofluoro silane to form
one or more Si--O bonds. Exemplary oxidizing agents include
hydrogen peroxide, ozone (O.sub.3), oxygen (O.sub.2), oxides of
nitrogen (N.sub.2O, NO, NO.sub.2), and mixtures thereof.
[0025] By use of the term "mild oxidizing agent" is meant an
oxidizing agent, such as a peroxide, capable of oxidizing an
organofluoro silane reactant at a low temperature, and which will
not oxidize sufficiently vigorously to cause the Si--C bonds to
break in preference to Si--H bonds, since cleavage of Si--C bonds
can interfere with the film-forming capabilities of the reaction
product. Typically, a mild oxidizing agent will cause cleavage of
Si--H bonds in preference to Si--C bonds. An exemplary mild
oxidation agent is hydrogen peroxide.
[0026] The term "strong oxidizing agent" means an oxidizing agent
capable of forming Si--O bonds more readily than hydrogen peroxide.
Exemplary strong oxidizing agents include ozone (O.sub.3), oxygen
(O.sub.2), oxides of nitrogen (N.sub.2O, NO, NO.sub.2), and
mixtures thereof.
[0027] The term "silicon-bonded moiety" as used herein refers to an
atom or group of atoms, containing at least one atom bonded to a
silicon atom.
[0028] By use of the term "low temperature" is meant a temperature
not exceeding about 25.degree. C., preferably not exceeding about
10.degree. C., and most preferably not exceeding about 5.degree. C.
Typically, this temperature will be measured by reference to the
temperature of the substrate support.
[0029] Organofluoro Silane
[0030] In one embodiment of the invention, at least one silicon
atom of the organofluoro silane is bonded to at least one hydrogen
atom. Reacting such an organofluoro silane with an oxidizing agent
causes cleavage of Si--H bonds and formation of one Si--O bond for
each Si--H bond cleaved. Other moieties that can be bonded to each
silicon atom include: oxygen atoms bonded to either another silicon
atom or a carbon atom; or organofluoro moieties containing carbon
atoms bonded to fluorine atoms but not containing aliphatic C--H
bonds; or both. By not containing aliphatic C--H bonds, the
fluorine and carbon-containing moiety is less susceptible to
oxidation by the oxidizing agent when the organofluoro silane is
reacted with the oxidizing agent. An organofluoro silane
characterized by the lack of aliphatic C--H bonds will preferably
contain at least one hydrogen atom bound to a silicon atom and at
least one carbon atom bound to a silicon atom. Exemplary
organofluoro silanes which may be used in the method of the
invention include (H).sub.3Si(CF.sub.3),
(H).sub.3Si(CF.sub.2CF.sub.3), (H).sub.3Si(CF(CF.sub.3).sub.2),
(H).sub.3Si(C(CF.sub.3).sub.3), (H).sub.3Si(CF.sub.2)Si(H).sub.3,
(H).sub.3Si(CF.sub.2)Si(CF.sub.3)(H).sub.2,
(H).sub.2(CF.sub.3)Si(CF.sub.- 2)Si(CF.sub.3)(H).sub.2,
((CF.sub.3)(H)SiO).sub.4, and
((CF).sub.3(H)Si(CF.sub.2)).sub.4.
[0031] At least one silicon-bonded moiety will contain at least one
carbon atom bound to one or more fluorine atoms. Typically, this
carbon and fluorine-containing moiety will be a saturated
fluorocarbon containing only carbon atoms and fluorine atoms and
having the general formula C.sub.xF.sub.2x+1, where x ranges from 1
to 5; for example, --CF.sub.3, --CF.sub.2CF.sub.3,
--CF(CF.sub.3).sub.2, --CF.sub.2CF.sub.2CF.sub.3,
--CF.sub.2CF.sub.2CF.sub.2CF.sub.3, --CF.sub.2CF(CF.sub.3).sub.2,
and --C(CF).sub.3, and the like. While x can range from 1 to 5, x
preferably ranges from 1 to 4, more preferably ranges from 1 to 3,
most preferably ranges from 1 to 2, and typically is 1. An
organofluoro silane having such a silicon-bonded organofluoro
moiety will typically also contain a hydrogen atom bonded to a
silicon atom. In one embodiment, an organofluoro silane will
contain only: one or more silicon atoms; one or more carbon atoms;
one or more fluorine atoms; one or more hydrogen atoms, where the
hydrogen atoms are bonded only to silicon atoms; and, optionally,
one or more oxygen atoms.
[0032] An example of a family of such compounds has the general
formula for single-silicon atom-containing compounds:
(H).sub.ySi(C.sub.xF.sub.2x- +1).sub.4-y, where y is 1 to 3 and x
is 1 to 5. An example of a family of multiple-silicon
atom-containing organofluoro silanes has the formula:
R.sub.1((R.sub.2)Si(L)).sub.nSi(R.sub.3) where R.sub.1.dbd.(H) or
(C.sub.xF.sub.2x+1), R.sub.2.dbd.(H).sub.2 or
(C.sub.xF.sub.2x+1)(H), R.sub.3.dbd.(H).sub.3 or
(C.sub.xF.sub.2x+1)(H).sub.2, L=--(O)-- or
--(C(R.sub.4).sub.2).sub.m--, n=0 to 5, x=0 to 5, m=1 to 4, and
each R.sub.4 is independently F or (C.sub.xF.sub.2x+1). While n can
range from 1 to 6, n preferably ranges from 1 to 4, more preferably
ranges from 1 to 3, most preferably ranges from 1 to 2, and
typically is 1. Also, m can range from 1 to 4, and preferably
ranges from 1 to 3, more preferably ranges from 1 to 2, and
typically is 1. An example of a family of cyclic organofluoro
silanes has the formula: ((C.sub.xF.sub.2x+1).sub.pSi(H).sub-
.2-p(L)).sub.q where L=--(O)-- or --(C(R).sub.2).sub.r, each R is
independently F or (C.sub.xF.sub.2+1), p=1 to 2, q=3 to 6, r 1 to
4, and x=1 to 5. While q can range from 3 to 6, q preferably ranges
from 4 to 5, and typically is 4. As with m above, r can range from
1 to 4, and preferably ranges from 1 to 3, more preferably ranges
from 1 to 2, and typically is 1.
[0033] Alternatively, a carbon and fluorine-containing
silicon-bonded moiety can contain one or more aromatic rings, so
long as it also contains at least one carbon atom bonded to a
fluorine atom. In one such case, the carbon atom bonded to the
fluorine atom is an aliphatic carbon. For example,
carbon-containing moieties having one or more aromatic rings can
include --Ph--CF.sub.3, --CF.sub.2--Ph, --CF.sub.2--Ph--CF.sub.3,
and the like, where Ph is a six carbon aromatic ring. Since
aromatic C--H bonds are more resistant to oxidation relative to
aliphatic C--H bonds, the aromatic C--H bond will not be readily
oxidized by the oxidizing agent used in the method of the
invention. Similarly, an organofluoro silane may contain an
aromatic moiety bound to silicon, which aromatic moiety does not
contain fluorine atoms, so long as the aromatic moiety contains no
aliphatic hydrogens, and at least one other silicon-bonded moiety
of the organofluoro silane contains at least one carbon atom bonded
to at least one fluorine atom.
[0034] Moieties Linking Si Atoms
[0035] An organofluoro silane used in the method of the invention
contains at least one silicon atom, but can contain up to 6 silicon
atoms. Organofluoro silanes containing more than one silicon atom,
including cyclic organofluoro silanes, will have either an oxygen
atom or a --(C(R).sub.2).sub.r-- moiety (where each R is
independently F or (C.sub.xF.sub.2x+1); r=1 to 4; and x=1 to 5)
linking the two or more silicon atoms. It is within the scope of
the invention that an organofluoro silane containing three or more
silicon atoms may have an oxygen atom linking a first set of two
silicon atoms and a --(C(R).sub.2).sub.r-- moiety linking a second
set of two silicon atoms; however, an organofluoro silane will
typically contain only oxygen atoms linking silicon atoms or only
--(C(R).sub.2).sub.r-- moieties linking silicon atoms. Preferably,
--(C(R).sub.2).sub.r-- is CF.sub.2.
[0036] In one embodiment, it is desirable that some carbon atoms be
incorporated into the backbone of the polymer to enhance the
thermal conductivity of the resultant dielectric film. Thus a
silicon oxide containing carbon and fluorine atoms and may have the
structure: 1
[0037] where one or more carbon atoms are incorporated into the
silicon/oxygen chain. Such materials can be formed, for example,
using organofluoro silanes having a --CF.sub.2-- linking two
silicon atoms. For example, the organofluoro silane used to form
the material of structure I can be
H.sub.2CF.sub.3SiCF.sub.2SiCF.sub.3H.sub.2.
[0038] Oxidizing Agent
[0039] The oxidizing agent used in the method of the invention can
be any oxygen-containing compound capable of reacting with an
organofluoro silane to form a Si--O bond. Typically, the oxidizing
agent will be capable of reacting with a Si--H bond in forming the
Si--O bond. Exemplary oxidizing agents capable of such a reaction
include hydrogen peroxide, oxygen, ozone, and oxides of nitrogen
(N.sub.2O, NO, NO.sub.2). Preferably, the oxidizing agent
selectively cleaves Si--H bonds in preference over cleaving Si--C
bonds, Si--O bonds, or C--F bonds. In one embodiment, the oxidizing
agent also selectively cleaves Si--H bonds in preference over
cleaving aromatic C--H bonds.
[0040] In another embodiment, an oxidizing agent for use in the
method of the invention is a mild oxidizing agent, for example,
hydrogen peroxide. A mild oxidizing agent reactant preferably
comprises a vaporous source of peroxide. Such a peroxide can be
conveniently obtained by flash evaporation of concentrated (30 vol.
% or more) liquid hydrogen peroxide. By the term "source of
peroxide" is meant any material capable of being heated (such as
liquid hydrogen peroxide), or decomposed and heated (such as
calcium peroxide or barium peroxide), to provide a vaporous
hydrogen peroxide (H.sub.2O.sub.2) oxidizing agent.
[0041] In yet another embodiment, the oxidizing agent is more
reactive than hydrogen peroxide, for example, ozone.
[0042] Reaction Conditions
[0043] The organofluoro silane and the oxidizing agent can be
reacted together by introducing them into a reaction chamber and
carrying out chemical vapor deposition. For example, an
organofluoro silane and hydrogen peroxide are introduced into a
reaction chamber containing a cooled substrate support therein on
which is mounted a semiconductor substrate such as a silicon
substrate on which the reaction product will deposit. For such a
reaction, the reaction chamber is advantageously maintained at a
pressure of from about 0.1 Torr to about 50 Torr, preferably from
about 1 Torr to about 10 Torr, and most preferably from about 1
Torr to about 5 Torr. Both the organofluoro silane and the hydrogen
peroxide are introduced into the chamber in a gaseous or vaporous
phase. The delivery system for the reactants is preferably
maintained at a temperature which ensures delivery of the reactants
into the chamber as gases or vapors, typically from about
70.degree. C. to about 100.degree. C. Flow rates of the individual
reactants will depend upon chamber size and will also vary with the
particular reactants. During the reaction and deposition, the
temperature of the substrate support in the reaction chamber is
maintained at a low temperature not exceeding about 25.degree. C.,
preferably not exceeding about 10.degree. C., and most preferably
not exceeding about 5.degree. C. The reaction and deposition is
carried out for a period of time sufficient to form the layer of
low k fluorine and carbon-containing silicon oxide dielectric
material to the desired thickness over the integrated circuit
structure already formed on the silicon substrate. Usually this
thickness will range from a minimum of about 300 nm to ensure
sufficient electrical insulation between underlying conductive
regions and conductive regions to be formed over the low k
dielectric material up to a maximum of about 800 nm or more.
Thicker layers can be formed, but are deemed unnecessary and merely
add to the bulk of the structure. Such a reaction method forms a
low k film having excellent via-filling properties, yields a
dielectric layer with low adhesion stress, and can be preferable
when using silane compounds that, under particular conditions, can
be oxidized by mild oxidizing agents such as peroxide.
[0044] In another embodiment, the organofluoro silane and oxidizing
agent reactants can be reacted together by introducing gaseous or
vaporous organofluoro silane or an organofluoro silane-containing
mixture and a strong oxidizing agent into a chamber at about 40
Torr to about 1000 Torr, preferably from about 700 Torr to about
800 Torr. The reaction can then be carried out at a temperature
from about 250.degree. C. to about 450.degree. C., preferably from
about 250.degree. C. to about 400.degree. C., and typically about
350.degree. C. The strong oxidizing reagent used in the reaction
can be any oxygen-containing oxidizing reagent capable of reacting
with an organofluoro silane to form a low k fluorine and
carbon-containing silicon oxide dielectric material, such as ozone
(O.sub.3), oxygen (O.sub.2), oxides of nitrogen (N.sub.2O, NO,
NO.sub.2), and the like. The reaction and deposition is carried out
for a period of time sufficient to form the layer of low k fluorine
and carbon-containing silicon oxide dielectric material to the
desired thickness over the integrated circuit structure already
formed on the silicon substrate. Usually this thickness will range
from a minimum of about 300 nm to ensure sufficient electrical
insulation between underlying conductive regions and conductive
regions to be formed over the low k dielectric material up to a
maximum of about 800 nm or more.
[0045] In yet another embodiment, a plasma-enhanced chemical vapor
deposition (PECVD) can be carried out. A plasma-activated strong
oxidizing agent and a gaseous or vaporous organofluoro silane or an
organofluoro silane-containing mixture and a carrier gas such as
helium can be introduced into a chamber at about 1 Torr to about 40
Torr, preferably from about 5 Torr to about 20 Torr. The reaction
can then be carried out at a temperature from about 50.degree. C.
to about 450.degree. C., preferably from about 200.degree. C. to
about 300.degree. C., and typically about 250.degree. C. The strong
oxidizing reagent used in the reaction can be any oxygen-containing
oxidizing reagent capable of reacting with an organofluoro silane
to form a low k fluorine and carbon-containing silicon oxide
dielectric material, such as ozone (O.sub.3), oxygen (O.sub.2),
oxides of nitrogen (N.sub.2O, NO, NO.sub.2), and the like.
Typically, the strong oxidizing agent will be oxygen. The reaction
and deposition is carried out for a period of time sufficient to
form the layer of low k fluorine and carbon-containing silicon
oxide dielectric material to the desired thickness over the
integrated circuit structure already formed on the silicon
substrate. Usually this thickness will range from a minimum of
about 300 nm to ensure sufficient electrical insulation between
underlying conductive regions and conductive regions to be formed
over the low k dielectric material up to a maximum of about 800 nm
or more.
[0046] While not intending to be limited to the following theory,
it is thought that, as the polymer forms, bonds of the organofluoro
moieties to the silicon atoms of the silicon oxide polymer will not
be oxidized as readily as bonds of unsubstituted alkyl moieties to
the silicon atoms of the silicon oxide polymer. Furthermore, the
dielectric constant of the resulting dielectric material having
fluorocarbon groups substituted for alkyl groups should not be
adversely affected by the higher polarizability of the fluorocarbon
groups because of the higher volume of the fluorocarbon group over
the alkyl group, since the dielectric constant is obtained by
dividing the polarizability (.alpha.) by the volume (v) in the
formula k=.alpha./v and increases in polarizability tend to be
canceled out by increases in volume.
[0047] Silane Mixtures
[0048] While the product of the process of the invention
principally comprises a low dielectric constant (low k) silicon
oxide dielectric material containing organofluoro groups, it is
within the scope of the invention to utilize, in the process of the
invention, mixtures of the organofluoro silanes with non-fluoro
silanes, including SiH.sub.4. In one embodiment, it may be
desirable to use as one component of the mixture an organofluoro
silane containing aliphatic C--H bonds. Such materials can be
blended with one or more of the above-described organofluoro
silanes to enhance other physical properties of the resultant film
of low k dielectric material. Exemplary physical properties include
dielectric constant, adhesion capabilities, via filling
capabilities, surface stress, and the like.
[0049] For example, to enhance the film forming properties of the
low dielectric constant fluorine and carbon-containing silicon
oxide dielectric material of the invention, one or more
organofluoro silanes can be blended with one or more of the
following non-fluoro silanes:
[0050] a) silanes having no silicon atoms bonded to
carbon-containing groups;
[0051] b) organo silanes containing silicon atoms bonded to one or
more carbon-containing groups having aliphatic C--H bonds (such as
methyl silane used in the Trikon Flowfill process);
[0052] c) organo silanes that do not contain aliphatic C--H bonds,
such as organo silanes containing a silicon atom bonded to an
aromatic carbon group; and
[0053] d) mixtures of any two or more of a), b), and c).
[0054] Such a mixture of silanes which includes one or more
organofluoro silanes may be reacted, for example, with hydrogen
peroxide (H.sub.2O.sub.2) in forming a low k fluorine and
carbon-containing silicon oxide dielectric material. For example, a
mixture of silanes corresponding to mixture a) above could contain
a mixture of silane (SiH.sub.4) and an organofluoro silane having
the formula (H).sub.ySi(C.sub.xF.sub.2x+1).sub.4-y, where y ranges
from 1 to 3, x is an integer from 1 to 5. A mixture of silanes
corresponding to mixture b) could contain methyl silane combined
with the organofluoro silane
(H).sub.ySi(C.sub.xF.sub.2x+1).sub.4-y. To form a mixture including
both a) and b), one could use both silane and methyl silane in
combination with the organofluoro silane having the formula
(H).sub.ySi(C.sub.xF.sub.- 2x+1).sub.4-y. Other examples of
substituted silanes which can be used either singly or in
combination to form mixtures of silanes containing organofluoro
silanes include dimethyl silane, ethyl silane, isopropyl
(1-methylethyl) silane, n-butyl silane, isobutyl (2-methyl propyl)
silane, phenyl silane, and methylenebis-silane.
[0055] As stated above, the amount of such silanes which may be
combined with one or more organofluoro silanes in the method of the
invention will typically be combined as minor components. By use of
the term "minor component" is meant that the one or more
non-fluorosilanes used in a mixture of silanes will comprise less
than 50 volume % of the total volume of the compounds in the
mixture, ensuring that the major component of the mixture comprises
one or more organofluoro silanes. However, it is recognized that in
some instances the enhancement of other properties of the resulting
mixture, e.g., the film forming properties, may justify the use of
more that 50 volume % of other silanes, that is, up to about 70
volume % of other silanes and 30 volume % of one or more
organofluoro silanes, even though such usage may raise the
dielectric constant of the resulting dielectric material.
[0056] When using such mixtures the average dielectric constant of
the dielectric material formed using a mixture of silanes can be
determined for the particular proportions of such dielectric
materials using the formula:
k.sub.av=.SIGMA..sub.ix.sub.ik.sub.i
[0057] where x.sub.i is the volume fraction of dielectric component
i and k.sub.i is the dielectric constant of the pure dielectric
component. Thus, for example, dielectric materials (a) and (b)
might be added to the low dielectric constant fluorine and
carbon-containing silicon oxide dielectric material of the
invention to enhance the film forming properties of the resulting
mixture. If a mixture is formed comprising 10 volume % of
dielectric material (a), 15 volume % of dielectric material (b),
and 75 volume % of the low dielectric constant fluorine and
carbon-containing silicon oxide dielectric material, the average
dielectric constant of the mixture will comprise the sum of the
products of the dielectric constant of each of the materials times
its volume % in the mixture. If the dielectric constant of the low
dielectric constant fluorine and carbon-containing silicon oxide
dielectric material is 2.4, the dielectric constant of dielectric
material (a) is 3.5, and the dielectric constant of dielectric
material (b) is 3.4, the average dielectric constant k.sub.av would
equal (2.4.times.75)+(3.5.times.0.10)+- (3.4.times.0.15)=2.7.
[0058] In Combination with Other Layers
[0059] While the low k fluorine and carbon-containing silicon oxide
dielectric material formed in the method of the invention will have
increased oxidation resistance relative to carbon-doped silicon
oxide dielectric material, it may be desirable to form a thin
conventional (standard k) silicon oxide (SiO.sub.2) or silicon
nitride base layer over the substrate to act as a moisture barrier
layer for such low k fluorine and carbon-containing silicon oxide
dielectric material subsequently formed thereon. A similar moisture
barrier layer may also be formed over such a low k fluorine and
carbon-containing silicon oxide dielectric layer for the same
reasons. Such a barrier layer adjacent the layer of low k fluorine
and carbon-containing silicon oxide dielectric material can be
formed to a thickness of about 50 nanometers (nm) to provide
adequate protection (if deemed necessary) for the low k fluorine
and carbon-containing silicon oxide dielectric layer to be formed
thereon. Thicknesses exceeding this minimum may be used, but are
probably unnecessary and may negatively contribute to an undesired
rise in the overall dielectric constant of the resulting composite
layer. Such barrier layers may then serve to protect the low k
dielectric material during subsequent processing steps.
[0060] Similarly, the low k fluorine and carbon-containing silicon
oxide dielectric material formed in the method of the invention may
find utility, for example, as one or more of the low k dielectric
layers described in Ser. Nos. 09/425,552; 09/346,493; 09/426,056;
09/426,061; 09/605,380; 09/607,512; 09/704,164; 09/704,200; all
assigned to the assignee of this invention.
[0061] Product--Dielectric Material
[0062] The low dielectric constant fluorine and carbon-containing
silicon oxide dielectric material produced by the method of the
invention will be suitable for use in integrated circuit
structures. This fluorine and carbon-containing silicon oxide
dielectric material will contain silicon atoms bonded to oxygen
atoms, silicon atoms bonded to carbon atoms, and carbon atoms
bonded to fluorine atoms. In one embodiment of the invention, the
fluorine and carbon-containing silicon oxide dielectric material
will be characterized by the absence of aliphatic C--H bonds. A
fluorine and carbon-containing silicon oxide dielectric material
produced by the method of the invention will have a dielectric
constant below the dielectric constant of silicon oxide or silicon
nitride. Preferably, the dielectric constant of the fluorine and
carbon-containing silicon oxide dielectric material will be below
about 3.5, more preferably below about 3.
[0063] Additionally, the fluorine and carbon-containing silicon
oxide dielectric material will demonstrate superior resistance to
degradation in subsequent processing steps such as, for example,
via etch and photoresist removal steps. While not wishing to be
limited by a particular theory, it is considered that organofluoro
compounds, particularly those that do not contain aliphatic C--H
bonds, will have an increased resistance to oxidation. This
resistance will decrease the susceptibility of the fluorine and
carbon-containing silicon oxide dielectric material to physical
degradation which can occur in a variety of manners, such as
thermal instability, solvent absorption, and the like.
[0064] In one embodiment, the fluorine and carbon-containing
silicon oxide dielectric material will contain as principal
components only silicon atoms, carbon atoms, fluorine atoms, and
oxygen atoms. Such a fluorine and carbon-containing silicon oxide
dielectric material will not contain a significant number of
hydrogen atoms, and, consequently, will not contain a significant
number of bonds susceptible to oxidation during deposition or
subsequent processing steps.
[0065] In another embodiment, the fluorine and carbon-containing
silicon oxide dielectric material will have a ratio of carbon atoms
to silicon atoms of C:Si greater than about 1:3. As described
above, the introduction of carbon atoms into a dielectric material
has been useful for lowering the dielectric constant of silicon
oxide dielectric materials. By introducing a greater ratio of
carbon atoms to silicon atoms, the dielectric constant can be
lowered even further. A particular choice of C:Si ratio will depend
not only upon the desired dielectric constant, but also upon other
desired physical properties of the dielectric material. Thus, a
desired C:Si ratio can be greater than about 2:3, greater than
about 1:1 or greater than about 3:2.
[0066] Similarly, because several components can be combined in a
silane mixture used to form the fluorine and carbon-containing
silicon oxide dielectric material, some silicon atoms may not be
bonded to any carbon atoms, while some carbon atoms may be bonded
solely to other carbon atoms and other fluorine atoms. For example,
a silane mixture can contain SiH.sub.4 and
H.sub.3Si(CF.sub.2CF.sub.3); in this example, the ratio of C:Si
will be a function of the ratio of H.sub.3Si(CF.sub.2CF.sub.3):
SiH.sub.4 in the silane mixture. Such a ratio will typically be
greater than about 1:3, greater than about 2:3, greater than about
1:1, or greater than about 3:2. Regardless, such a dielectric
material will be characterized by the presence of C--C bonds.
[0067] Thus, the invention provides a low temperature process for
forming a low k fluorine and carbon-containing silicon oxide
dielectric material exhibiting superior resistance to oxidation
than conventional carbon-doped low k silicon oxide dielectric
materials while also providing good gap-filling capabilities and
low stress adhesion not always found in other fluorine and
carbon-containing silicon oxide dielectric materials.
[0068] The following example serves to further illustrate the
process of the invention.
EXAMPLE
[0069] Trifluoromethyl silane (CF.sub.3SiH.sub.3) and hydrogen
peroxide can be introduced into a reaction chamber containing a
cooled substrate support therein on which is mounted a silicon
substrate on which the reaction product will deposit. The reaction
chamber is advantageously maintained at a pressure of about 1-5
Torr. Both the trifluoromethyl silane and the hydrogen peroxide are
introduced into the chamber in a gaseous or vaporous phase. The
delivery system for the reactants is maintained at about
100.degree. C., which ensures delivery of the reactants into the
chamber as gases or vapors. Flow rates of the individual reactants
will depend upon chamber size and will also vary with the
particular reactants. During the reaction and deposition, the
temperature of the substrate support in the reaction chamber is
maintained at a low temperature of about 0-10.degree. C. The
reaction and deposition is carried out for a period of time
sufficient to form the layer of low k fluorine and
carbon-containing silicon oxide dielectric material to the desired
thickness over the integrated circuit structure already formed on
the silicon substrate. Usually this thickness will be a minimum of
about 300 nm to ensure sufficient electrical insulation between
underlying conductive regions and conductive regions to be formed
over the low k dielectric material. Such a reaction method forms a
low k film having excellent via-filling properties, yields a
dielectric layer with low adhesion stress.
[0070] While a specific embodiment of the process of the invention
has been illustrated and described for carrying out the invention,
modifications and changes of the apparatus, parameters, materials,
etc. used in the process will become apparent to those skilled in
the art, and it is intended to cover in the appended claims all
such modifications and changes which come within the scope of the
invention.
* * * * *