U.S. patent application number 12/945625 was filed with the patent office on 2012-05-17 for process for lowering adhesion layer thickness and improving damage resistance for thin ultra low-k dielectric film.
This patent application is currently assigned to APPLIED MATERIALS, INC.. Invention is credited to MAHENDRA CHHABRA, Alexandros T. Demos, Kang Sub Yim.
Application Number | 20120121823 12/945625 |
Document ID | / |
Family ID | 46048004 |
Filed Date | 2012-05-17 |
United States Patent
Application |
20120121823 |
Kind Code |
A1 |
CHHABRA; MAHENDRA ; et
al. |
May 17, 2012 |
PROCESS FOR LOWERING ADHESION LAYER THICKNESS AND IMPROVING DAMAGE
RESISTANCE FOR THIN ULTRA LOW-K DIELECTRIC FILM
Abstract
An improved method for depositing an ultra low dielectric
constant film stack is provided. Embodiments of the invention
minimize k (dielectric constant) impact from initial stages of
depositing the ultra low dielectric constant film stack by reducing
a thickness of an oxide adhesion layer in the ultra low dielectric
film stack (<2 k.ANG.) to about or less than 200 .ANG., thereby
lowering the thickness non-uniformity of the film stack to less
than 2%. The improved process deposits the oxide adhesion layer and
the bulk layer in the ultra low dielectric film stack at lower
deposition rate and lower plasma density in combination with higher
total flow rate, resulting in better packing/ordering of the
co-deposited species during film deposition which causes higher
mechanical strength and lower porosity. The improved adhesion layer
provides high adhesion energy for better adhesion with ultra low
dielectric constant films to underlying barrier/liner layers. The
resulting low dielectric film has nanometer-sized pores and tighter
pore-size distribution, yielding a low dielectric constant film
with a dielectric constant of about 2.5 or less.
Inventors: |
CHHABRA; MAHENDRA;
(Stanford, CA) ; Yim; Kang Sub; (Palo Alto,
CA) ; Demos; Alexandros T.; (Fremont, CA) |
Assignee: |
APPLIED MATERIALS, INC.
Santa Clara
CA
|
Family ID: |
46048004 |
Appl. No.: |
12/945625 |
Filed: |
November 12, 2010 |
Current U.S.
Class: |
427/585 |
Current CPC
Class: |
C23C 16/56 20130101;
C23C 16/45523 20130101; C23C 16/401 20130101; C23C 8/10
20130101 |
Class at
Publication: |
427/585 |
International
Class: |
C23C 8/06 20060101
C23C008/06 |
Claims
1. A method of processing a substrate disposed within a processing
chamber, comprising: flowing into the processing chamber a gas
mixture comprising a flow rate of one or more organosilicon
compounds and a flow rate of one or more porogen compounds to
deposit an initiation layer on the substrate by applying a radio
frequency (RF) power to the processing chamber; ramping-up the flow
rate of the one or more organosilicon compounds until reaching a
final flow rate of the one or more organosilicon compounds to
deposit a first transition layer on the initiation layer; and while
flowing the final flow rate of the one or more organosilicon
compounds, ramping-up the flow rate of the one or more porogen
compounds until reaching a final flow rate of the one or more
porogen compounds to deposit a second transition layer on the first
transition layer, wherein the depositions of the initiation layer
and the first and second transition layers are performed at a ratio
of the RF power to a total flow rate between about 0.1 W/sccm and
about 0.3 W/sccm.
2. The method of claim 1, wherein the deposition of the initiation
layer is performed over a time period in the range of between about
0.5 second and about 5 seconds.
3. The method of claim 1, wherein the deposition of the first and
second transition layers is performed over a time period in the
range of between about 1 second and about 5 seconds and between
about 1 second and about 10 seconds, respectively.
4. The method of claim 1, wherein the one or more organosilicon
compound are introduced into the chamber at a flow rate between
about 200 mgm and about 700 mgm and the one or more porogen
compounds are introduced into the chamber at a flow rate between
about 200 mgm and about 1600 mgm.
5. The method of claim 1, wherein the depositions of the initiation
layer and the first and second transition layers are performed at a
deposition rate between 1000 .ANG./min. and about 3500 .ANG./min
and at a low RF power between about 350 W and about 500 W.
6. The method of claim 5, wherein the initiation layer and the
first and second transition layers are deposited to provide an
overall thickness in a range of about 50 .ANG. to about 300
.ANG..
7. The method of claim 1, wherein the ramping-up the flow rate of
the one or more organosilicon compounds is performed at a ramp-up
rate between about 600 mgm/sec. and about 1500 mgm/sec.
8. The method of claim 1, wherein the ramping-up the flow rate of
the one or more porogen compounds is performed at a ramp-up rate
between about 200 mgm/sec. and about 600 mgm/sec.
9. The method of claim 1, wherein the gas mixture further comprises
one or more oxidizing gases selected from the group consisting of
ozone, oxygen, carbon dioxide, carbon monoxide, water, nitrous
oxide, 2,3-butanedione, and combinations thereof.
10. The method of claim 1, further comprising introducing into the
processing chamber a flow rate of an inert gas selected from the
group consisting of helium, argon, or nitrogen.
11. The method of claim 1, wherein the one or more organosilicon
compounds is selected from the group consisting of
methyldiethoxysilane (mDEOS), tetramethylcyclotetrasiloxane
(TMCTS), octamethylcyclotetrasiloxane (OMCTS), trimethylsilane
(TMS), pentamethylcyclopentasiloxane, hexamethylcyclotrisiloxane,
dimethyldisiloxane, tetrasilano-2,6-dioxy-4,8-dimethylene,
tetramethyldisiloxane, hexamethyldisiloxane (HMDS),
1,3-bis(silanomethylene)disiloxane,
bis(1-methyldisiloxanyl)methane, bis(1-methyldisiloxanyl)propane,
hexamethoxydisiloxane (HMDOS), dimethyldimethoxysilane (DMDMOS),
dimethoxymethylvinylsilane (DMMVS), and derivatives thereof.
12. The method of claim 1, wherein the one or more porogen
compounds is selected from the group consisting of norbornadiene
(BCHD, bicycle(2.2.1)hepta-2,5-diene),
1-methyl-4-(1-methylethyl)-1,3-cyclohexadiene (ATP or
alpha-Terpinene), vinylcyclohexane (VCH), phenylacetate, butadiene,
isoprene, cyclohexadiene, bicycloheptadiene,
1-methyl-4-(1-methylethyl)-benzene (Cymene), 3-carene, fenchone,
limonene, cyclopentene oxide, vinyl-1,4-dioxinyl ether, vinyl furyl
ether, vinyl-1,4-dioxin, vinyl furan, methyl furoate, furyl
formate, furyl acetate, furaldehyde, difuryl ketone, difuryl ether,
difurfuryl ether, furan, 1,4-dioxin, and fluorinated carbon
derivatives thereof.
13. A method of processing a substrate disposed within a processing
chamber, comprising: providing a substrate bearing a liner/barrier
layer; depositing a carbon-containing oxide adhesion layer over the
liner/barrier layer at a deposition rate between about 1000
.ANG./min and about 3500 .ANG./min, comprising: flowing into the
processing chamber a gas mixture comprising a flow rate of one or
more organosilicon compounds and a flow rate of one or more porogen
compounds to deposit an initiation layer on the substrate by
applying a radio frequency (RF) power level of about 300 W to about
600 W at 13.56 MHz to the processing chamber; ramping-up the flow
rate of the one or more organosilicon compounds until reaching a
final flow rate of the one or more organosilicon compounds to
deposit a first transition layer on the initiation layer; and while
flowing the final flow rate of the one or more organosilicon
compounds, ramping-up the flow rate of the one or more porogen
compounds until reaching a final flow rate of the one or more
porogen compounds to deposit a second transition layer on the first
transition layer; depositing a low K film over the adhesion layer;
and curing the deposited low K film to form nanopores therein.
14. The method of claim 13, wherein the deposition of the
initiation layer is performed over a time period in the range of
between about 0.5 second and about 5 seconds.
15. The method of claim 13, wherein the deposition of the first
transition layer is performed over a time period in the range of
between about 1 second and about 5 seconds, and the deposition of
the second transition layer is performed over a time period in the
range of and between about 1 second and about 10 seconds.
16. The method of claim 13, wherein the one or more organosilicon
compounds are introduced into the chamber at a flow rate between
about 200 mgm and about 700 mgm and the one or more porogen
compounds are introduced into the chamber at a flow rate between
about 200 mgm and about 1600 mgm.
17. The method of claim 13, wherein the initiation layer and the
first and second transition layers are deposited to provide an
overall thickness in a range of about 50 .ANG. to about 300
.ANG..
18. The method of claim 13, wherein the ramping-up the flow rate of
the one or more organosilicon compounds is performed at a ramp-up
rate between about 600 mgm/sec. and about 1500 mgm/sec, and the
ramping-up the flow rate of the one or more porogen compounds is
performed at a ramp-up rate between about 200 mgm/sec. and about
600 mgm/sec.
19. The method of claim 13, wherein the depositions of the
initiation layer and the first and second transition layers are
performed at a ratio of the RF power to a total flow rate between
about 0.1 W/sccm and about 0.3 W/sccm.
20. The method of claim 13, wherein the gas mixture further
comprises an inert gas selected from the group consisting of
helium, argon, and nitrogen, and one or more oxidizing gases
selected from the group consisting of ozone, oxygen, carbon
dioxide, carbon monoxide, water, nitrous oxide, 2,3-butanedione,
and combinations thereof.
21. The method of claim 13, wherein the one or more organosilicon
compounds is selected from the group consisting of
methyldiethoxysilane (mDEOS), tetramethylcyclotetrasiloxane
(TMCTS), octamethylcyclotetrasiloxane (OMCTS), trimethylsilane
(TMS), pentamethylcyclopentasiloxane, hexamethylcyclotrisiloxane,
dimethyldisiloxane, tetrasilano-2,6-dioxy-4,8-dimethylene,
tetramethyldisiloxane, hexamethyldisiloxane (HMDS),
1,3-bis(silanomethylene)disiloxane,
bis(1-methyldisiloxanyl)methane, bis(1-methyldisiloxanyl)propane,
hexamethoxydisiloxane (HMDOS), dimethyldimethoxysilane (DMDMOS),
dimethoxymethylvinylsilane (DMMVS), and derivatives thereof.
22. The method of claim 13, wherein the one or more porogen
compounds is selected from the group consisting of norbornadiene
(BCHD, bicycle(2.2.1)hepta-2,5-diene),
1-methyl-4-(1-methylethyl)-1,3-cyclohexadiene (ATP or
alpha-Terpinene), vinylcyclohexane (VCH), phenylacetate, butadiene,
isoprene, cyclohexadiene, bicycloheptadiene,
1-methyl-4-(1-methylethyl)-benzene (Cymene), 3-carene, fenchone,
limonene, cyclopentene oxide, vinyl-1,4-dioxinyl ether, vinyl furyl
ether, vinyl-1,4-dioxin, vinyl furan, methyl furoate, furyl
formate, furyl acetate, furaldehyde, difuryl ketone, difuryl ether,
difurfuryl ether, furan, 1,4-dioxin, and fluorinated carbon
derivatives thereof.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] Embodiments of the present invention generally relate to the
fabrication of integrated circuits. More particularly, the
embodiments relate to process for depositing low dielectric
constant films for integrated circuits.
[0003] 2. Description of the Related Art
[0004] Semiconductor device geometries have dramatically decreased
in size since such devices were first introduced several decades
ago. Since then, integrated circuits have generally followed the
two year/half-size rule (often called Moore's Law), which means
that the number of devices that will fit on a chip doubles every
two years. Today's fabrication plants are routinely producing
devices having 65 nm and even 45 nm feature sizes, and tomorrow's
plants soon will be producing devices having even smaller
geometries.
[0005] The continued reduction in device geometries has generated a
demand for films having lower dielectric constant (k) values
because the capacitive coupling between adjacent metal lines must
be minimized to further reduce the size of devices on integrated
circuits in Cu dual damascene interconnect process technology. One
of the approaches that has been used to obtain an ultra low
dielectric constant (k<2.5) is to fabricate hybrid films of a
silicon matrix and an organic porogen by depositing the hybrid
films from a gas mixture comprising an organosilicon compound and a
compound comprising thermally labile species or volatile groups
(porogen) and then post-treat the deposited films with UV curing or
thermal treatment to remove the thermally labile species or
volatile groups of porogen from the deposited films, resulting in
nanometer-sized voids in the films which lowers the dielectric
constant of the films.
[0006] The nanoporous films are known to have less adhesion to
underlying barrier/liner layers than silicon oxides. Improvement of
adhesion may be obtained by depositing an adhesion layer of oxide,
which can enhance adhesion at the interface. To further improve
adhesion, it has been suggested to use a gradient layer with
increasing carbon content gradually between adhesion and main low-K
film deposition step. However, uncontrolled transition of both
silicon and porogen flow in this gradient layer can cause
undesirable gas phase reaction (due to variable changes of RF
power, pressure, and flow rate etc.), causing particle clusters on
the film or/and carbon bumps to form in the films or at the
interfaces.
[0007] In addition, it has been reported that ultra low dielectric
constant films developed as described above exhibit less than
desirable mechanical properties, such as poor mechanical strength
(modulus.apprxeq.4 GPa), which renders the films susceptible to
damage during subsequent semiconductor processing steps. Moreover,
since an oxide adhesion layer that is currently used for better
adhesion with ultra low dielectric constant films to underlying
barrier/liner layers constitutes major portion for the dielectric
film stack and typically has higher dielectric constant
(k.apprxeq.3.5) and very high thickness non-uniformity, the overall
dielectric constant and thickness non-uniformity of the resulting
dielectric film stack have not been reduced as expected.
[0008] Therefore, there is a need for a process of making ultra low
dielectric constant materials with improved mechanical strength,
lowered thickness non-uniformity, and minimize k (dielectric
constant) increase from initial stages of depositing the ultra low
dielectric constant materials, without compromising the
controllability for lower application thickness.
SUMMARY OF THE INVENTION
[0009] Embodiments of the present invention generally provide a
method for depositing an ultra low dielectric constant film with
novel process parameters. In one embodiment, the method includes
flowing into the processing chamber a gas mixture comprising a flow
rate of one or more organosilicon compounds and a flow rate of one
or more porogen compounds to deposit an initiation layer (oxide
layer) on the substrate by applying a radio frequency (RF) power to
the processing chamber, ramping-up the flow rate of the one or more
organosilicon compounds until reaching a final flow rate of the one
or more organosilicon compounds to deposit a first transition layer
on the initiation layer, and while flowing the final flow rate of
the one or more organosilicon compounds, ramping-up the flow rate
of the one or more porogen compounds until reaching a final flow
rate of the one or more porogen compounds to deposit a second
transition layer on the first transition layer, wherein the
depositions are performed at a low RF power between about 350 W and
about 500 W, and a ratio of the RF power to a total flow rate is
between about 0.1 W/sccm and about 0.3 W/sccm. Various processing
parameters and precursors are further discussed in the detailed
description.
[0010] In another embodiment, the method includes providing a
substrate bearing a liner/barrier layer, depositing a
carbon-containing oxide adhesion layer over the liner/barrier layer
at a deposition rate between about 1000 .ANG./min and about 3500
.ANG./min, comprising flowing into the processing chamber a gas
mixture comprising a flow rate of one or more organosilicon
compounds and a flow rate of one or more porogen compounds to
deposit an initiation layer on the substrate by applying a radio
frequency (RF) power level of about 300 W to about 600 W at 13.56
MHz to the processing chamber, ramping-up the flow rate of the one
or more organosilicon compounds until reaching a final flow rate of
the one or more organosilicon compounds to deposit a first
transition layer on the initiation layer, and while flowing the
final flow rate of the one or more organosilicon compounds,
ramping-up the flow rate of the one or more porogen compounds until
reaching a final flow rate of the one or more porogen compounds to
deposit a second transition layer on the first transition layer,
depositing a low K film over the adhesion layer, and curing the
deposited low K film to form nanopores therein. Various processing
parameters and precursors are further discussed in the detailed
description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] So that the manner in which the above recited features of
the present invention can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to embodiments, some of which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this invention and are therefore not to be considered limiting of
its scope, for the invention may admit to other equally effective
embodiments.
[0012] FIG. 1A is a cross-sectional view of a dielectric film stack
formed according to embodiments of the invention.
[0013] FIG. 1B is a close up of the cross-section of a portion of
the film stack shown in FIG. 1A.
[0014] FIG. 2 is a process flow diagram illustrating a method of
depositing an ultra low K nanoporous film stack according to one
embodiment of the invention.
[0015] FIG. 3 is a cross-sectional diagram of an exemplary
processing chamber that may be used for practicing embodiments of
the invention.
[0016] FIG. 4 illustrates a depth profile of element concentrations
in an organosilicate dielectric film stack by SIMS analysis.
DETAILED DESCRIPTION
[0017] The present invention provides a method of depositing a low
dielectric constant film. The low dielectric constant film
comprises silicon, oxygen, hydrogen and carbon. Embodiments of the
invention have been proved to be able to significantly lower the K
impact (dielectric constant) of an adhesion layer to an ultra low
dielectric constant film stack by reducing the thickness of the
adhesion layer. By lowering the adhesion layer thickness to about
or less than 200 .ANG., the thickness non-uniformity for an ultra
low dielectric film stack (<2 k.ANG.) is also reduced to less
than 2%. As will be discussed below, the improved oxide adhesion
layer is deposited at lower deposition rate and lower plasma
density in combination with higher total flow rate, resulting in
better packing/ordering of the co-deposited species during film
deposition which causes higher mechanical strength and lower
porosity. The improved adhesion layer provides high adhesion energy
for better adhesion with ultra low dielectric constant films to
underlying barrier/liner layers. The resulting low dielectric film
has nanometer-sized pores and tighter pore-size distribution. The
low dielectric constant film has a dielectric constant of about 3.0
or less, preferably about 2.5 or less. The low dielectric constant
film may have an elastic modulus of at least about 6.5 GPa or
above.
[0018] FIG. 1A schematically illustrates a cross-sectional view of
a dielectric film stack 100 formed according to embodiments of the
present invention. While not shown here, it is contemplated that
the dielectric film stack 100 of the present invention can be used
as an inter-metal dielectric layer in a dual damascene structure,
which may generally include one or more nanoporous inter-metal
dielectric layers (not shown) and one or more etch stop layers (not
shown) of silicon oxide, silicon nitride, silicon oxynitride, or
amorphous hydrogenated silicon carbide that are deposited in an
alternating or desired order. An anti-reflective coating (not
shown) and a trench photomask (not shown) comprising a photoresist
layer are then respectfully deposited over the deposited film
layers and patterned by conventional photolithography techniques in
a manner to develop a metallization structure to be filled with a
desired metal such as copper. The dual damascene formation process
may be repeated to deposit a desired number of interconnection
levels. An exemplary dual damascene structure that may be benefited
from the present invention is further described in the commonly
assigned U.S. Pat. No. 7,547,643 issued on Jun. 16, 2009 to
Francimar Schmitt et al., which is incorporated by reference in its
entirety.
[0019] Generally, the dielectric film stack 100 as shown in FIG. 1A
comprises a substrate 102 bearing a liner/barrier layer 104, which
acts as an isolation layer between a subsequent adhesion layer 106
and the underlying substrate surface 103 and metal lines 108 formed
on the substrate surface 103. A low K layer 110 is deposited over
the adhesion layer 106, which is capped by a capping layer 112.
Methods of depositing such a dielectric film stack 100 according to
various embodiments of the invention will be described briefly with
respect to FIG. 2 in conjunction with FIG. 1B.
Exemplary Process for Deposition of Organosilicate Layers
[0020] FIG. 2 is a process flow diagram 200 illustrating a method
of depositing a dielectric film stack 100 according to one
embodiment of the invention. Generally, a typical porous dielectric
film requires simultaneous deposition of one or more organosilicon
compounds, which becomes Si backbone, and one or more unsaturated
non-silicon compounds having thermally labile groups, which acts as
a sacrificial porogen. In step 202, a substrate 102 bearing a
liner/barrier layer 104 is positioned on a substrate support in a
processing chamber capable of performing Plasma-Enhanced Chemical
Vapor Deposition (PECVD) process. The liner/barrier layer 104 may
be deposited by a PECVD process from a plasma comprising a
organosilane compound, ammonia, oxygen and inerts. The deposition
process can include a capacitively coupled plasma or both an
inductively and a capacitively coupled plasma in the processing
chamber according to methods known in the art. The plasma can be
generated using inert gases, such as He, Ar, and N.sub.2. An inert
gas such as helium is commonly used in the PECVD deposition to
assist in plasma generation.
[0021] In step 204, a gas mixture having a composition including
one or more organosilicon compounds, one or more porogen compounds,
and one or more oxidizing gases is introduced into the processing
chamber through a gas distribution plate, such as a showerhead. An
initial gas composition of oxygen and/or helium may be introduced
into the processing chamber before initiation of the RF power to
stabilize the conditions for the subsequent depositions.
[0022] In one embodiment, the one or more organosilicon compounds
are introduced into the chamber at a flow rate between about 200
milligrams/minute to about 5000 milligrams/minute, for example,
between about 350 milligrams/minute and about 2500
milligrams/minute; the one or more oxidizing gases are introduced
into the chamber at a flow rate between about 100 sccm and about
1000 sccm, for example, between about 125 sccm and about 550 sccm;
and the one or more porogen compounds are introduced into the
chamber at a flow rate between about 50 milligrams/minute to about
5000 milligrams/minute, for example, between about 150 grams/minute
and about 1500 grams/minute. A radio-frequency (RF) power is
applied to an electrode, such as the showerhead, in order to
provide plasma processing conditions in the chamber. Suitable RF
power may be a power in a range of about 10 W to about 2000 W, such
as about 300 W to about 600 W at a frequency of about 13.56 MHz.
The gas mixture is reacted in the chamber in the presence of RF
power to deposit an initiation layer 106a comprising an oxide layer
that adheres strongly to the underlying liner/barrier layer
104.
[0023] The gas mixture may optionally include one or more carrier
gases. Typically, one or more carrier gases are introduced with the
one or more organosilicon compounds and the one or more porogen
compounds into the processing chamber. Examples of carrier gases
that may be used include helium, argon, carbon dioxide, and
combinations thereof. In one embodiment where helium is used as the
carrier gas, the helium gas are introduced into the chamber along
with one or more organosilicon compound at a flow rate between
about 1500 sccm and about 8000 sccm, for example, between about
3500 sccm and about 5500 sccm. With one or more porogen compounds,
helium gas are introduced into the chamber at a flow rate between
about 300 sccm and about 1800 sccm, for example, between about 700
sccm and about 1250 sccm.
[0024] The initiation layer 106a generally includes a silicon oxide
layer. As will be discussed below, the initiation layer 106a and a
first and second transition layers 106b, 106c (FIG. 1B) constitute
the adhesion layer 106 that enhances adhesion between the
underlying liner/barrier layer 104 and the subsequent low K layer
110. In one embodiment, the initiation layer deposition may have a
time range of between about 0.5 seconds and about 10 seconds, as
long as the deposition period is long enough to ensure cohesion of
the entire film. In one example, the initiation layer deposition
may last for about 1 second. The initiation layer 106a may be
deposited to a thickness in a range of about 5 .ANG. to about 100
.ANG., preferably about 10 .ANG. to about 50 .ANG.. It is
contemplated that the times for the various periods described in
this disclosure may be adjusted depending on the needs of
particular embodiments. For example, while a time range of about
0.5 seconds to about 10 seconds is described, in some embodiments,
the initiation period may last for 0 seconds. An initiation period
of 0 seconds means that changing flow rates of gas streams begins
immediately upon introducing them to the chamber. Thus, embodiments
with no initiation period are contemplated.
[0025] Prior to deposition of the low K layer 110, a separate
transition step is performed to prevent any unwanted particle
clusters from forming in the films due to undesirable gas phase
reaction of both silicon and porogen flows occurring at the gas
distribution plate. It has also been observed that the smooth
transition of the liquids into the chamber can significantly reduce
the occurrence of carbon bumps. These issues may be addressed by
separating the transition of two liquid precursors (i.e.,
organosilicon compounds and porogen compounds) at a desired ramping
rate. In a first period of the separate transition step 206, or
simply referring to step 206, the flow rate of the one or more
organosilicon compounds is gradually increased at a ramp-up rate
between about 100 mgm/sec. and about 5000 mgm/sec., for example,
between about 800 mgm/sec. and about 1200 mgm/sec., such as about
1000 mgm/sec., in the presence of the RF power, to deposit a first
transition layer 106b (see FIG. 1B, which is a close up of the
cross-section of the film stack shown in FIG. 1A) on the initiation
layer 106a until reaching a predetermined organosilicon compound
gas mixture. In embodiments where a helium carrier gas is used, the
flow rate of the one or more organosilicon compounds and the helium
gas may be decreased to a range between about 2500 sccm and about
4000 sccm. In one embodiment, the first transition layer deposition
may have a time range of between about 0.5 second and about 10
seconds. In one example, the first transition layer deposition time
may be about 1 second. The first transition layer 106b may be
deposited to a thickness in a range of about 10 .ANG. to about 300
.ANG., for example, about 50 .ANG. to about 200 .ANG..
[0026] In a second period of the transition step 208, or simply
referring to step 208, while keeping the predetermined
organosilicon compound gas mixture constant, the flow rate of the
one or more porogen compounds is gradually increased at a ramp-up
rate between about 100 mgm/sec. and about 5000 mgm/sec., for
example, between about 200 mgm/sec. and about 350 mgm/sec., such as
about 300 mgm/sec., to deposit a second transition layer 106c (FIG.
1B) onto the first transition layer 106b until reaching a
predetermined final gas mixture. In embodiments where a helium
carrier gas is used, the flow rate of the one or more porogen
compounds and helium gas may be increased to a range between about
800 sccm and about 2000 sccm. In one embodiment, the second
transition layer deposition may have a time range of between about
1 second and about 180 seconds. In one example, the second
transition layer deposition time may be about 3 seconds. The second
transition layer 106c may be deposited to a thickness in a range of
about 10 .ANG. to about 600 .ANG., preferably, about 100 .ANG. to
about 400 .ANG..
[0027] The deposition periods of the initiation layer 106a and the
first and second transition layers 106b, 106c preferably result in
deposition of a thin portion 106 of the film stack (106a, 106b,
106c) as shown. This thin portion 106 of the film stack serves as
an adhesion layer for better adhesion with ultra low dielectric
constant films to underlying barrier/liner layers. In most
embodiments, the thickness of this portion is reduced by almost
half, e.g., less than about 200 Angstroms. Deposition of the thin
portion 106 of the film stack (106a, 106b, 106c) may be achieved
through relatively short duration and/or low deposition rate. In
one embodiment, the deposition rate for the thin portion of the
film stack is between about 1000 Angstroms/minute to about 3500
Angstroms/minute, such as about 2500 Angstroms/minute. As the thin
portion 106 of the film stack (106a, 106b, 106c) constitutes
significant portion of an ultra low K nanoporous film stack (106a,
106b, 106c, 110) having a thickness less than 2000 Angstroms, the
thickness non-uniformity for the dielectric film stack 100 can be
reduced to less than 2% by lowering the thickness of the thin
portion of the film stack. Most importantly, the reduced thickness
of the thin portion 106 of the film stack (106a, 106b, 106c)
minimizes the K impact to the overall nanoporous film stack.
[0028] In step 210, upon reaching the final gas mixture
composition, a plasma of the final gas mixture comprising a flow
rate of one or more organosilicon compounds and a flow rate of the
one or more porogen compounds is formed to deposit a
porogen-containing organosilicate dielectric layer, i.e., the low K
layer 110. In one embodiment, the low K layer deposition may have a
time range of between about 15 second and about 180 seconds. In one
example, the final layer deposition time may be about 130 seconds.
The low K layer 110 may be deposited to a thickness in a range of
about 200 .ANG. to about 10,000 .ANG. until the RF power is
terminated. Not wishing to be bound by theory, it is believed that
by separating the ramp-up rates of the organosilicon compounds and
the porogen compounds, a more stable and manufacturable process can
be obtained, yielding organosilicate dielectric layers with
significantly less defect issues, such as carbon bumps.
[0029] Alternatively, step 208, depositing the second transition
layer 106c, may be combined with step 210, depositing the final
porogen silicon oxide layer. In such an embodiment, the porogen
compound flow rate is continuously ramped-up while flowing the
predetermined organosilicon compound gas mixture during the porogen
silicon oxide layer deposition. The combination of step 208 with
step 210 may have a time range of between about 1 second and about
180 seconds. In this manner, the final porogen silicon oxide layer
may have a gradient concentration of porogen where the
concentration of porogen in the silicon oxide layer increases as
the porogen silicon oxide layer is deposited. This gradient layer
may be deposited to a thickness in a range of about 50 .ANG. to
about 10,000 .ANG., preferably, about 100 .ANG. to about 5000
.ANG., until the RF power is terminated.
[0030] During the processes described above, the substrate is
typically maintained at a temperature between about 100.degree. C.
and about 400.degree. C., for example between about 200.degree. C.
and about 350.degree. C. The chamber pressure may be between about
1 Torr and about 20 Torr, for example between about 7 Torr and
about 9 Torr, and the spacing between a substrate support and the
chamber showerhead may be between about 200 mils and about 1500
mils, for example, between about 280 mils and about 450 mils. A RF
power level of between about 100 W and about 600 W for a 300 mm
substrate may be used. The RF power is provided at a frequency
between about 0.01 MHz and 300 MHz, such as about 13.56 MHz. The RF
power may be provided at a mixed frequency, such as at a high
frequency of about 13.56 MHz and a low frequency of about 350 kHz.
The RF power may be cycled or pulsed to reduce heating of the
substrate and promote greater porosity in the deposited film. The
RF power may also be continuous or discontinuous, depending upon
application.
[0031] In certain embodiments, lower plasma density in combination
with higher total flow rate is used. To obtain a lower plasma
density, a RF power level of between about 300 W and about 600 W,
for example, between about 350 W and about 500 W, may be used. In
cases where the RF power level of between about 350 W and about 500
W is used, a RF power/total flow rate of about 0.1 W/sccm to about
0.3 W/sccm is preferred. Alternatively, a RF power/total volume
flow of about 0.2 W/cm.sup.3 to about 0.5 W/cm.sup.3 is preferred.
The term "total flow rate" or "total volume flow" as used herein is
intended to refer to the flows/volumes of the gas mixture and
optional carrier gases introduced into the processing chamber
during the deposition, as discussed previously. It has been
observed by the present inventors that the use of lower plasma
density in combination with higher total flow rate may allow for a
denser packing of the co-deposited species during film deposition,
resulting in higher mechanical strength, smaller pore size (<10
.ANG.), and tighter pore-size distribution. This leads to
significant improvement in the mechanical integrity of the film by
increasing the damage resistance of the film to subsequent device
manufacturing processes.
[0032] In any of the embodiments described herein, a
porogen-containing organosilicate dielectric layer is deposited
from a process gas mixture comprising an organosilicon compound and
a porogen. The organosilicate layer may be used as a dielectric
layer. The dielectric layer may be used at different levels within
a dual damascene structure or a suitable device. For example, the
dielectric layer may be used as a premetal dielectric layer, an
inter-metal dielectric layer, or a gate dielectric layer. The
organosilicate layer deposited in accordance with various
embodiments of the present invention has been proved to be able to
provide a low dielectric constant less than 3.0, for example, about
2.5.
[0033] A wide variety of process gas mixtures may be used to
deposit the organosilicate dielectric layer, and non-limiting
examples of such gas mixtures are provided below. Generally, the
gas mixture includes one or more organosilicon compounds (e.g., a
first and a second organosilicon compound), one or more porogen
compounds, a carrier gas, and an oxidizing gas. These components
are not to be interpreted as limiting, as many other gas mixtures
including additional components such as hydrocarbons (e.g.,
aliphatic hydrocarbons) are contemplated.
[0034] The term "organosilicon compound" as used herein is intended
to refer to silicon-containing compounds including carbon atoms in
organic groups. The organosilicon compound may include one or more
cyclic organosilicon compounds, one or more aliphatic organosilicon
compounds, or a combination thereof. Some exemplary organosilicon
compounds include methyldiethoxysilane (mDEOS),
tetramethylcyclotetrasiloxane (TMCTS), octamethylcyclotetrasiloxane
(OMCTS), trimethylsilane (TMS), pentamethylcyclopentasiloxane,
hexamethylcyclotrisiloxane, dimethyldisiloxane,
tetrasilano-2,6-dioxy-4,8-dimethylene, tetramethyldisiloxane,
hexamethyldisiloxane (HMDS), 1,3-bis(silanomethylene)disiloxane,
bis(1-methyldisiloxanyl)methane, bis(1-methyldisiloxanyl)propane,
hexamethoxydisiloxane (HMDOS), dimethyldimethoxysilane (DMDMOS),
and dimethoxymethylvinylsilane (DMMVS), or derivatives thereof. The
one or more organosilicon compounds may be introduced into the
processing chamber at a flow rate in a range of about 200
milligrams/minute to about 5000 milligrams/minute, for example,
between about 350 milligrams/minute and about 2500
milligrams/minute.
[0035] The term "porogen compound" as used herein is intended to
refer to compounds that comprise thermally labile groups. The
thermally labile groups may be cyclic groups, such as unsaturated
cyclic organic groups. The term "cyclic group" as used herein is
intended to refer to a ring structure. The ring structure may
contain as few as three atoms. The atoms may include carbon,
nitrogen, oxygen, fluorine, and combinations thereof, for example.
The cyclic group may include one or more single bonds, double
bonds, triple bonds, and any combination thereof. For example, a
cyclic group may include one or more aromatics, aryls, phenyls,
cyclohexanes, cyclohexadienes, cycloheptadienes, and combinations
thereof. The cyclic group may also be bi-cyclic or tri-cyclic. In
one embodiment, the cyclic group is bonded to a linear or branched
functional group. The linear or branched functional group
preferably contains an alkyl or vinyl alkyl group and has between
one and twenty carbon atoms. The linear or branched functional
group may also include oxygen atoms, such as in a ketone, ether,
and ester. The porogen may comprise a cyclic hydrocarbon compound.
Some exemplary porogens that may be used include norbornadiene
(BCHD, bicycle(2.2.1)hepta-2,5-diene),
1-methyl-4-(1-methylethyl)-1,3-cyclohexadiene (ATP or
alpha-Terpinene), vinylcyclohexane (VCH), phenylacetate, butadiene,
isoprene, cyclohexadiene, bicycloheptadiene,
1-methyl-4-(1-methylethyl)-benzene (Cymene), 3-carene, fenchone,
limonene, cyclopentene oxide, vinyl-1,4-dioxinyl ether, vinyl furyl
ether, vinyl-1,4-dioxin, vinyl furan, methyl furoate, furyl
formate, furyl acetate, furaldehyde, difuryl ketone, difuryl ether,
difurfuryl ether, furan, and 1,4-dioxin, and fluorinated carbon
derivatives thereof. The one or more porogen compounds may be
introduced into the processing chamber at a flow rate in a range of
about 50 milligrams/minute to about 5000 milligrams/minute, for
example, between about 150 milligrams/minute and about 1500
milligrams/minute.
[0036] As discussed previously, the gas mixture may optionally
include one or more carrier gases. Typically, one or more carrier
gases are introduced with the one or more organosilicon compounds
and the one or more porogen compounds into the processing chamber.
Examples of carrier gases that may be used include helium, argon,
carbon dioxide, and combinations thereof. The one or more carrier
gases may be introduced into the processing chamber at a flow rate
less than about 20,000 sccm, depending in part upon the size of the
interior of the chamber. Preferably the flow of carrier gas is in a
range of about 500 sccm to about 5000 sccm. In some processes, an
inert gas such as helium or argon is put into the processing
chamber to stabilize the pressure in the chamber before reactive
process gases are introduced.
[0037] The gas mixture also includes one or more oxidizing gases.
Suitable oxidizing gases include oxygen (O.sub.2), ozone (O.sub.3),
nitrous oxide (N.sub.2O), carbon monoxide (CO), carbon dioxide
(CO.sub.2), and combinations thereof. The flow of oxidizing gas may
be in a range of about 100 sccm to about 3,000 sccm, depending in
part upon the size of the interior of the chamber. Typically, the
flow of oxidizing gas is in a range of about 100 sccm to about
1,000 sccm, for example about 450 sccm. Disassociation of oxygen or
the oxygen containing compounds may occur in a microwave chamber
prior to entering the deposition chamber and/or by RF power as
applied to process gas within the chamber.
Post Treatment Process
[0038] After the low dielectric constant film is deposited, the
film is post-treated. The film may be post-treated with a thermal
annealing, alone or assisted by UV radiation to remove the organic
labile and create pore inclusions into the final material. In one
embodiment, the low dielectric constant film is post-treated with a
UV curing process. The UV post-treatment may be performed in-situ
within the same processing chamber or system, for example,
transferred from one chamber to another without a break in vacuum.
Exemplary UV post-treatment conditions that may be used include a
chamber pressure of between about 1 Torr and about 10 Torr and a
substrate support temperature of between about 350.degree. C. and
about 500.degree. C. The source of ultraviolet radiation may be
between about 100 mils and about 1400 mils from the substrate
surface. Optionally, a processing gas may be introduced during the
ultraviolet curing process. Suitable processing gases include
oxygen (O.sub.2), nitrogen (N.sub.2), hydrogen (H.sub.2), helium
(He), argon (Ar), water vapor (H.sub.2O), carbon monoxide, carbon
dioxide, hydrocarbon gases, fluorocarbon gases, and fluorinated
hydrocarbon gases, or combinations thereof.
[0039] The UV radiation may be provided by any UV source, such as
mercury microwave arc lamps, pulsed xenon flash lamps, or
high-efficiency UV light emitting diode arrays. The ultraviolet
radiation may comprise a range of ultraviolet wavelengths, and
include one or more simultaneous wavelengths. Suitable ultraviolet
wavelengths include between about 1 nm and about 400 nm, and may
further include optical wavelengths up to about 600 or 780 nm.
Additionally or alternatively, the ultraviolet radiation may be
applied at multiple wavelengths, a tunable wavelength emission and
tunable power emission, or a modulation between a plurality of
wavelengths as desired, and may be emitted from a single UV lamp or
applied from an array of ultraviolet lamps. Examples of suitable UV
lamps include a Xe filled Zeridex.TM. UV lamp, a Ushio Excimer UV
lamp, a DSS UV lamp, or a Hg Arc Lamp. The deposited low dielectric
constant film is exposed to the ultraviolet radiation for between
about 10 seconds and about 600 seconds, for example between about
60 seconds and about 600 seconds. The UV radiation may have a
wavelength of between about 170 nm and about 400 nm, for example.
Further details of UV chambers and treatment conditions that may be
used are described in commonly assigned U.S. patent application
Ser. No. 11/124,908, filed on May 9, 2005, which is incorporated by
reference herein. The NanoCure.TM. chamber from Applied Materials,
Inc. is an example of a commercially available chamber that may be
used for UV post-treatments.
[0040] In another embodiment, the low dielectric constant film is
post-treated with a thermal or plasma enhanced annealing process.
The film may be annealed at a temperature between about 200.degree.
C. and about 400.degree. C. for about 2 seconds to about 1 hour,
preferably about 30 minutes, in a chamber. A non-reactive gas such
as helium, hydrogen, nitrogen, or a mixture thereof may be
introduced at a rate of about 100 sccm to about 10,000 sccm. The
chamber pressure is maintained between about 1 Torr and about 10
Torr. The RF power during the annealing is about 200 W to about
1,000 W at a frequency of about 13.56 MHz, and the preferable
substrate spacing is between about 300 mils and about 800 mils.
Annealing the low dielectric constant film at a substrate
temperature of about 200.degree. C. to about 400.degree. C. after
the low dielectric constant film is deposited volatilizes at least
some of the organic groups in the film, forming voids in the
film.
[0041] In yet another embodiment, the low dielectric constant film
is post-treated with an electron beam treatment. Exemplary electron
beam conditions that may be used include a chamber temperature of
between about 200.degree. C. and about 600.degree. C., e.g. about
350.degree. C. to about 400.degree. C. The electron beam energy may
be from about 0.5 keV to about 30 keV. The exposure dose may be
between about 1 .mu.C/cm.sup.2 and about 400 .mu.C/cm.sup.2. The
chamber pressure may be between about 1 mTorr and about 100 mTorr.
The gas ambient in the chamber may be any of the following gases:
nitrogen, oxygen, hydrogen, argon, a blend of hydrogen and
nitrogen, ammonia, xenon, or any combination of these gases. The
electron beam current may be between about 0.15 mA and about 50 mA.
The electron beam treatment may be performed for between about 1
minute and about 15 minutes. Although any electron beam device may
be used, an exemplary electron beam chamber that may be used is an
EBk.TM. electron beam chamber available from Applied Materials,
Inc. of Santa Clara, Calif.
[0042] The e-beam curing process improves mechanical strength of
the deposited film network and also lowers the k-value. The
energized e-beam alters the chemical bonding in the molecular
network of the deposited film and removes at least a portion of the
molecular groups, such as organic components from the ring of the
one or more oxygen-free hydrocarbon compounds comprising one ring
and one or two carbon-carbon double bonds in the ring, from the
film. The removal of the molecular groups creates voids or pores
within the film, lowering the K value.
Exemplary Hardware
[0043] FIG. 3 shows a cross-sectional, schematic diagram of a
chemical vapor deposition (CVD) chamber 300 for depositing a
carbon-doped silicon oxide layer. This figure is based upon
features of the PRODUCER.RTM. chambers currently manufactured by
Applied Materials, Inc. The PRODUCER.RTM. CVD chamber (200 mm or
300 mm) has two isolated processing regions that may be used to
deposit carbon-doped silicon oxides and other materials. A chamber
having two isolated processing regions is described in U.S. Pat.
No. 5,855,681, which is incorporated by reference herein.
[0044] The deposition chamber 300 has a chamber body 302 that
defines separate processing regions 318, 320. Each processing
region 318, 320 has a pedestal 328 for supporting a substrate (not
seen) within the chamber 300. The pedestal 328 typically includes a
heating element (not shown). Preferably, the pedestal 328 is
movably disposed in each processing region 318, 320 by a stem 326
which extends through the bottom of the chamber body 302 where it
is connected to a drive system 303. Internally movable lift pins
(not shown) are preferably provided in the pedestal 328 to engage a
lower surface of the substrate. The lift pins are engaged by a lift
mechanism (not shown) to receive a substrate before processing, or
to lift the substrate after deposition for transfer to the next
station.
[0045] Each of the processing regions 318, 320 also preferably
includes a gas distribution assembly 308 disposed through a chamber
lid 304 to deliver gases into the processing regions 318, 320. The
gas distribution assembly 308 of each processing region normally
includes a gas inlet passage 340 through manifold 348 which
delivers gas from a gas distribution manifold 319 through a blocker
plate 346 and then through a showerhead 342. The showerhead 342
includes a plurality of nozzles (not shown) through which gaseous
mixtures are injected during processing. An RF (radio frequency)
supply 325 provides a bias potential to the showerhead 342 to
facilitate generation of a plasma between the showerhead and the
pedestal 328. The deposition process performed in the deposition
chamber 300 can be either a non-plasma process on a cooled
substrate pedestal 328 or a plasma enhanced process. In a plasma
process, a controlled plasma is typically formed adjacent to the
substrate by RF energy applied to the showerhead 342 from RF power
supply 325 (with pedestal 328 grounded). Alternatively, the RF
power supply 325 can be provided to the pedestal 328, or to
different components at different frequencies.
[0046] The plasma may be generated using high frequency RF (HFRF)
power, as well as low frequency RF (LFRF) power (e.g., dual
frequency RF), constant RF, pulsed RF, or any other known or yet to
be discovered plasma generation technique. The RF power supply 325
can supply a single frequency RF between about 5 MHz and about 300
MHz. In addition, the RF power supply 325 may also supply a low
frequency RF between about 300 Hz to about 1,000 kHz to supply a
mixed frequency to enhance the decomposition of reactive species of
the process gas introduced into the process chamber. The RF power
may be cycled or pulsed to reduce heating of the substrate and
promote greater porosity in the deposited film. Suitable RF power
may be a power in a range of about 10 W to about 5000 W, for
example in a range of about 200 W to about 600 W. Suitable LFRF
power may be a power in a range of about 0 W to about 5000 W, for
example in a range of about 0 W to about 200 W.
[0047] A system controller 334 controls the functions of various
components such as the RF power supply 325, the drive system 303,
the lift mechanism, the gas distribution manifold 319, and other
associated chamber and/or processing functions. The system
controller 334 executes system control software stored in a memory
338, which in the preferred embodiment is a hard disk drive, and
can include analog and digital input/output boards, interface
boards, and stepper motor controller boards. Optical and/or
magnetic sensors are generally used to move and determine the
position of movable mechanical assemblies.
[0048] The above CVD system description is mainly for illustrative
purposes, and other plasma processing chambers may also be employed
for practicing embodiments of the invention.
Examples
[0049] The embodiments of the present invention demonstrate
deposition of ultra low K nanoporous films having dispersed
microscopic gas voids. In any of the embodiments described
previously, the following process parameters and ranges are
generally beneficial to main and/or adhesion layer deposition
process:
TABLE-US-00001 Parameters Range Heater temperature (.degree. C.)
200-350 Deposition time (s) 15-360 Pressure (Torr) 7-9 Spacing
(mils) 280-450 HF RF (Watt) 300-600 mDEOS (mgm) 200-2500 BCHD (mgm)
200-1600 O.sub.2 (sccm) 125-500 mDEOS He carrier gas flow rate
(sccm) 500-5000 mBCHD He carrier gas flow rate (sccm) 500-1250
[0050] During the deposition of an adhesion layer, ramp-up rates
for one or more organosilicon compounds and one or more porogen
compounds in various transitions are generally between 800 mgm/sec
and 1200 mgm/sec and between about 200 mgm/sec. and about 350
mgm/sec., respectively. Preferably, only one of the flows of the
organosilicon compounds and the porogen compounds is changing
during various transition steps to prevent any defects in the
films, as discussed previously.
[0051] In one specific embodiment described above with respect to
FIGS. 1A and 1B, porogen-containing organosilicate dielectric
layers were deposited on a substrate. The film was deposited using
a PECVD chamber (i.e., CVD chamber) on a PRODUCER.RTM. system,
available from Applied Materials, Inc. of Santa Clara, Calif.
During deposition the chamber pressure was maintained at a pressure
of about 6.5 Torr and the substrate was maintained at a temperature
of about 270.degree. C. The substrate was positioned on a substrate
support disposed within a process chamber. The substrate was
positioned 450 mils from the chamber showerhead.
[0052] The process gas mixture having an initial gas composition of
300 sccm oxygen and 3800 sccm helium was introduced into the
chamber and flow rates stabilized before initiation of the RF
power. Subsequently, a RF power level of about 600 W at 13.56 MHz
was applied to the showerhead to form a plasma of a gas mixture
including a methyldiethoxysilane (mDEOS) introduced into the
chamber at a flow rate of about 600 mgm to deposit a silicon oxide
initiation layer. After initiation of the RF power for about 1
second, the flow rate of mDEOS was increased to 2200 mgm. at a
ramp-up rate of about 1000 mgm/sec. for about 1 second. In
addition, the flow of helium was decreased to about 3000 sccm.
[0053] Upon reaching and keeping a final mDEOS flow rate of about
2200 mg/min, a flow of BCHD was introduced into the chamber at a
ramp-up rate of about 400 mgm/sec. for about 3 seconds to reach a
porogen deposition flow rate of about 1300 mgm. The final gas
mixture composition also includes 3000 sccm helium and 225 sccm
oxygen. Upon reaching the desired thickness of the
porogen-containing organosilicate dielectric layer, the RF power is
terminated to stop further deposition. After RF power termination,
the chamber throttle valve is opened to allow the process gas
mixture to be pumped out of the chamber. The separate transition of
the liquid precursors into the chamber reduces the defects in the
films. A secondary-ion mass spectrometry (SIMS) analysis was
performed to analyze the depth profile of element concentrations in
a dielectric film stack, as shown in FIG. 4. The depth distribution
of carbon shows a smooth phase shift of carbon in the films,
suggesting that no carbon bumps occurred in the films using the
exemplary process.
[0054] It is contemplated that many variations of the above example
may be practiced. For example, other organosilane precursors,
porogen precursors, oxidizing gases, and inert gases may be used.
In addition, different flow rates and/or ramp rates may be
employed. Depending upon application, the flow rates of the various
precursors may be adjusted to change the carbon content as portions
of the film (e.g., initiation layer 106a and/or transition layers
106b, 106c) are deposited, such that an initial portion of the
deposited film has a low carbon content, and is therefore
oxide-like, while successive portions have higher carbon content,
becoming oxycarbide-like.
[0055] Embodiments of the invention have been proved to be able to
significantly lower the K impact of an oxide adhesion layer to an
ultra low dielectric film stack by reducing the thickness of the
adhesion layer that is deposited with novel process parameters. By
lowering the adhesion layer thickness to about or less than 200
.ANG., the thickness non-uniformity for an ultra low dielectric
film stack (<2 k.ANG.) is also reduced to less than 2%. The
improved oxide adhesion layer is deposited at lower deposition rate
of about 2400 .ANG./min. and lower plasma density in combination
with higher total flow rate (RF power/total flow between about 0.1
W/sccm and about 0.3 W/sccm), resulting in better packing/ordering
of the co-deposited species during film deposition which causes
higher mechanical strength of about 6.9 GPa. The improved adhesion
layer provides good enough adhesion energy (.about.4.5 J/m.sup.2)
for better adhesion with ultra low dielectric constant films to
underlying barrier/liner layers. The resulting ultra low K
nanoporous films has smaller pore radius of between about 7 .ANG.
and about 10 .ANG. and tighter pore-size distribution with porosity
in the range about 15% and about 25%.
[0056] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
* * * * *