U.S. patent application number 12/548487 was filed with the patent office on 2010-01-14 for structure and method for sicoh interfaces with increased mechanical strength.
This patent application is currently assigned to INTERNATIONAL BUSINESS MACHINES CORPORATION. Invention is credited to Alexandros Demos, Daniel C. Edelstein, Stephen M. Gates, Alfred Grill, Steven E. Molis, Vu Ngoc Tran Nguyen, Steven Reiter, Darryl D. Restaino, Kang Sub Yim.
Application Number | 20100009161 12/548487 |
Document ID | / |
Family ID | 39775025 |
Filed Date | 2010-01-14 |
United States Patent
Application |
20100009161 |
Kind Code |
A1 |
Edelstein; Daniel C. ; et
al. |
January 14, 2010 |
STRUCTURE AND METHOD FOR SiCOH INTERFACES WITH INCREASED MECHANICAL
STRENGTH
Abstract
Disclosed is a structure and method for forming a structure
including a SiCOH layer having increased mechanical strength. The
structure includes a substrate having a layer of dielectric or
conductive material, a layer of oxide on the layer of dielectric or
conductive material, the oxide layer having essentially no carbon,
a graded transition layer on the oxide layer, the graded transition
layer having essentially no carbon at the interface with the oxide
layer and gradually increasing carbon towards a porous SiCOH layer,
and a porous SiCOH (pSiCOH) layer on the graded transition layer,
the porous pSiCOH layer having an homogeneous composition
throughout the layer. The method includes a process wherein in the
graded transition layer, there are no peaks in the carbon
concentration and no dips in the oxygen concentration.
Inventors: |
Edelstein; Daniel C.;
(Yorktown Heights, NY) ; Demos; Alexandros;
(Dublin, CA) ; Gates; Stephen M.; (Hopewell
Junction, NY) ; Grill; Alfred; (Yorktown Heights,
NY) ; Molis; Steven E.; (Patterson, NY) ;
Nguyen; Vu Ngoc Tran; (San Jose, CA) ; Reiter;
Steven; (Santa Clara, CA) ; Restaino; Darryl D.;
(Hopewell Junction, NY) ; Yim; Kang Sub; (Santa
Clara, CA) |
Correspondence
Address: |
INTERNATIONAL BUSINESS MACHINES CORPORATION;DEPT. 18G
BLDG. 321-482, 2070 ROUTE 52
HOPEWELL JUNCTION
NY
12533
US
|
Assignee: |
INTERNATIONAL BUSINESS MACHINES
CORPORATION
Armonk
NY
APPLIED MATERIALS, INC.
Santa Clara
CA
|
Family ID: |
39775025 |
Appl. No.: |
12/548487 |
Filed: |
August 27, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11690248 |
Mar 23, 2007 |
7615482 |
|
|
12548487 |
|
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|
Current U.S.
Class: |
428/310.5 |
Current CPC
Class: |
H01L 21/31695 20130101;
H01L 21/76835 20130101; H01L 21/76834 20130101; Y10T 428/24851
20150115; H01L 2221/1047 20130101; H01L 21/76832 20130101; C23C
16/0272 20130101; H01L 21/7682 20130101; Y10T 428/249961 20150401;
H01L 21/02216 20130101; H01L 21/02304 20130101; H01L 21/02274
20130101; C23C 16/029 20130101; C23C 16/401 20130101; H01L 21/02203
20130101; H01L 21/02126 20130101 |
Class at
Publication: |
428/310.5 |
International
Class: |
B32B 5/14 20060101
B32B005/14 |
Claims
1. A SiCOH film structure comprising: a substrate having a layer of
dielectric or conductive material; a layer of oxide on the layer of
dielectric or conductive material, the oxide layer having
essentially no carbon; a graded transition layer on the oxide
layer, the graded transition layer having essentially no carbon at
the interface with the oxide layer and gradually increasing carbon
towards a porous SiCOH layer; and a porous SiCOH (pSiCOH) layer on
the graded transition layer, the porous pSiCOH layer having an
homogeneous composition throughout the layer.
2. The structure of claim 1 wherein in the oxide layer, the
concentration of carbon is less than up to 3 atomic percent.
3. The structure of claim 1 wherein in the oxide layer, the
concentration of carbon is less than 0.1 atomic percent.
4. The structure of claim 1 wherein the thickness of the oxide
layer is in the range of about 1 to 100 Angstroms.
5. The structure of claim 1 wherein the thickness of the oxide
layer is about 20 Angstroms.
6. The structure of claim 1 wherein in the graded transition layer,
there are no peaks in the carbon concentration.
7. The structure of claim 1 wherein in the graded transition layer,
there are no dips in the oxygen concentration.
8. The structure of claim 1 wherein in thickness of the graded
transition layer is in the range of from 50 to 300 Angstroms.
9. An electronic structure comprising: a substrate having a layer
of dielectric material; a plurality of copper damascene conductors
within said layer of dielectric material, wherein said dielectric
material includes: a layer of oxide on the layer of dielectric
material, the oxide layer having essentially no carbon; a graded
transition layer on the oxide layer, the graded transition layer
having essentially no carbon at the interface with the oxide layer
and gradually increasing carbon towards a porous SiCOH layer; and a
porous SiCOH (pSiCOH) layer on the graded transition layer, the
porous pSiCOH layer having an homogeneous composition throughout
the layer.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of currently co-pending
U.S. patent application Ser. No. 11/690,248, filed on Mar. 23,
2007, the subject matter of which is incorporated herein by
reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] The present invention generally relates to a semiconductor
electronic device structure comprising at least one porous SiCOH
(pSiCOH, carbon-doped oxide) layer having improved interfacial
strength (adhesive and cohesive strength near the interface) to a
dielectric or conducting layer. The improved interfacial strength
is caused by the presence of transition layers that are formed
between the porous SiCOH layer and the dielectric or conducting
layer. The transition layers are formed in the present invention by
starting the deposition of a specific layer, while a surface
preparation plasma is still present and active in the reactor.
[0003] The continuous shrinking in dimensions of electronic devices
utilized in ULSI circuits in recent years has resulted in
increasing the resistance of the BEOL metallization without
concomitantly decreasing the interconnect capacitances. Often
interconnects are even scaled to higher aspect ratios to mitigate
the resistance increases, leading to increased capacitances. This
combined effect increases signal delays in ULSI electronic devices.
In order to improve the switching performance of future ULSI
circuits, low dielectric constant (k) insulators and particularly
those with k significantly lower than silicon oxide are being
introduced to reduce the capacitance.
[0004] The low-k materials that have been considered for
applications in ULSI devices include polymers containing Si, C and
O, such as methylsiloxane, methylsilsesquioxanes, and other organic
and inorganic polymers which are fabricated by spin-on techniques
or, Si, C, O and H containing materials (SiCOH, SiOCH, carbon-doped
oxides (CDO), silicon-oxycarbides, organosilicate glasses (OSG))
deposited by plasma enhanced chemical vapor deposition (PECVD)
techniques. In an effort to decrease the dielectric constant
further, Grill et al. U.S. Pat. No. 6,312,793, the disclosure of
which is incorporated by reference herein, discloses porous low-k
dielectrics such as porous SiCOH. The incorporation of the low-k
dielectrics in the interconnect structures of integrated circuits
(IC) often requires the use of other dielectric materials as
diffusion barrier caps or etch-stop and chemo-mechanical polishing
(CMP) hardmasks. The adhesion among the different layers in the
complex structures of an IC device is often too low, resulting in
delaminations during the processing of the device, dicing into
chips, or reduced reliability in response to mechanical stresses
imposed by typical chip packaging materials. Often even when the
adhesion is adequate, the deposited low-k film may possess degraded
cohesive strength near the initial interface that is formed during
deposition, and adhesion testing leads to fracture within this
initial layer, which may be from single to tens of nm thick.
Without careful failure analysis, the low failure energies from
adhesion testing of such cases may be mistakenly attributed to poor
interfacial adhesion, rather than substandard cohesive strength of
the near-interface low-k film. This is especially true for
interfacial strength (adhesive and cohesive strength near the
interface) of a carbon doped oxide dielectric comprised of Si, C, O
and H (SiCOH) to other hardmask or diffusion barrier cap
dielectics, such as SiN, SiC(H) or SiCN(H).
[0005] It would thus be highly desirable to provide a semiconductor
device comprising an insulating structure including a multitude of
dielectric and conductive layers with good interfacial strength
among the different layers, and a method for manufacturing such
semiconductor devices.
[0006] Various solutions have been proposed for increasing the
interfacial strength of low-k dielectrics to the previous
layer.
[0007] Conti et al. U.S. Pat. Nos. 6,570,256 and 6,740,539, the
disclosures of which are incorporated by reference herein, disclose
a carbon-graded layer which can be employed within the initial
region of a carbon-containing organosilicate layer to improve
adhesion to the underlying substrate. However, the so-called
carbon-graded layer consists of successive distinct layers with the
concentration of carbon increasing in steps from layer to layer.
Thus, each carbon-graded layer is in actuality a layer of constant
carbon concentration.
[0008] Edelstein et al. U.S. Pat. No. 7,067,437, the disclosure of
which is incorporated by reference herein, discloses a
carbon-graded transition layer between the underlying dielectric or
conducting layer and the dense SiCOH layer. The carbon-graded
transition layer may be oxygen rich and/or carbon depleted.
[0009] The foregoing references developed structures containing
dense dielectric layers. The present inventors have found that
porous dielectric layers present certain difficulties in their
formation, particularly due to the carbon generated by the porogen
used to form the pores in the dielectric. Another difficulty arises
when the precursors used to form porous dielectric layers react
rapidly in the gas phase, forming particulates which settle on the
manufacturing substrate, an occurrence known as gas phase
nucleation (GPN). Particles then cause patterning defects and other
manufacturing failures. The present inventors have analyzed those
methods (conditions) that produce GPN and the preferred methods
(conditions) that do not produce GPN.
[0010] Accordingly, it is a purpose of the present invention to
provide a semiconductor device structure and method for
manufacturing an insulating structure comprising a multitude of
dielectric and conductive layers with improved interfacial
strengths between at least one porous SiCOH layer and other layers
in the interconnect structure.
[0011] It is another purpose of the present invention to achieve
these improved interfacial strengths by a process which would allow
continuous grading of the interfaces.
[0012] Further purposes and advantages of the present invention
will become apparent after referring to the following description
of the invention considered in conjunction with the accompanying
drawings.
BRIEF SUMMARY OF THE INVENTION
[0013] The purposes and advantages of the invention have been
achieved by providing, according to a first aspect of the
invention, a method for improving the interfacial strength between
different layers, the method comprising the steps of: [0014] a)
providing a substrate having a layer of dielectric or conductive
material; [0015] b) forming a layer of oxide on the layer of
dielectric or conductive material, the oxide layer having
essentially no carbon; [0016] c) forming a graded transition layer
on the oxide layer, the graded transition layer having essentially
no carbon at the interface with the oxide layer and gradually
increasing carbon and towards a porous SiCOH layer; and [0017] d)
forming a porous SiCOH layer on the graded transition layer, the
porous SiCOH layer having an homogenous uniform composition
throughout the layer.
[0018] According to a second aspect of the invention, there is
provided a method for improving the interfacial strength between
different layers, the method comprising the steps of: [0019] a)
providing a substrate having a layer of dielectric or conductive
material; [0020] b) introducing a flow of oxygen and SiCOH
precursor into a chamber for a first time period so as to form a
layer of oxide on the layer of dielectric or conductive material,
the oxide layer having essentially no carbon; [0021] c) maintaining
the flow of oxygen while gradually increasing the flow of the SiCOH
precursor to a predetermined amount while also introducing and
gradually increasing the flow of a porogen precursor to a
predetermined amount into the chamber for a second time period so
as to form a graded transition layer on the oxide layer, the graded
transition layer having essentially no carbon at the interface with
the oxide layer and gradually increasing carbon a porous SiCOH
layer; and [0022] d) maintaining the flow of SiCOH precursor and
porogen precursor at the predetermined amount in the chamber for a
third time period while abruptly reducing the flow of oxygen to a
predetermined value so as to form a porous SiCOH layer on the
graded transition layer, the porous SiCOH layer having an
homogenous composition throughout the layer.
[0023] According to a third aspect of the invention, there is
provided a method for improving the interfacial strength between
different layers, the method comprising the steps of: [0024] a)
providing a substrate having a layer of dielectric or conductive
material; [0025] b) introducing a flow of oxygen and a flow of
SiCOH precursor into a chamber for a first time period so as to
form a layer of oxide on the layer of dielectric or conductive
material, the oxide layer having essentially no carbon, the flows
of oxygen and SiCOH precursor being independently adjustable as to
start time, end time and ramp rate during the first time period;
[0026] c) maintaining the flow of oxygen while gradually increasing
the flow of the SiCOH precursor to a predetermined amount while
also introducing and gradually increasing the flow of a porogen
precursor to a predetermined amount into the chamber for a second
time period so as to form a graded transition layer on the oxide
layer, the graded transition layer having essentially no carbon at
the interface with the oxide layer and gradually increasing carbon
towards a porous SiCOH layer, wherein the flows of oxygen, SiCOH
precursor and porogen precursor being independently adjustable as
to start time, end time and ramp rate during the second time
period; and [0027] d) maintaining the flow of SiCOH precursor and
porogen precursor at the predetermined amount in the chamber for a
third time period while abruptly reducing the flow of oxygen to a
predetermined value so as to form a porous SiCOH layer on the
graded transition layer, the porous SiCOH layer having an
homogeneous composition throughout the layer, wherein the flows of
oxygen, SiCOH precursor and porogen precursor being independently
adjustable as to start time, end time and ramp rate during the
third time period.
[0028] According to a fourth aspect of the invention, there is
provided a SiCOH film structure comprising: [0029] a substrate
having a layer of dielectric or conductive material; [0030] a layer
of oxide on the layer of dielectric or conductive material, the
oxide layer having essentially no carbon; [0031] a graded
transition layer on the oxide layer, the graded transition layer
having essentially no carbon at the interface with the oxide layer
and gradually increasing carbon towards a porous SiCOH layer; and
[0032] a porous SiCOH (pSiCOH) layer on the graded transition
layer, the porous pSiCOH layer having an homogeneous composition
throughout the layer.
[0033] According to a fifth aspect of the invention, there is
provided an electronic structure comprising: [0034] a substrate
having a layer of dielectric material; [0035] a plurality of copper
damascene conductors within said layer of dielectric material,
wherein said dielectric material includes: [0036] a layer of oxide
on the layer of dielectric material, the oxide layer having
essentially no carbon; [0037] a graded transition layer on the
oxide layer, the graded transition layer having essentially no
carbon at the interface with the oxide layer and gradually
increasing carbon towards a porous SiCOH layer; and [0038] a porous
SiCOH (pSiCOH) layer on the graded transition layer, the porous
pSiCOH layer having an homogeneous composition throughout the
layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] The features of the invention believed to be novel and the
elements characteristic of the invention are set forth with
particularity in the appended claims. The Figures are for
illustration purposes only and are not drawn to scale. The
invention itself, however, both as to organization and method of
operation, may best be understood by reference to the detailed
description which follows taken in conjunction with the
accompanying drawings in which:
[0040] FIG. 1 is a cross sectional view of a prior art interconnect
substrate.
[0041] FIG. 2 is a cross sectional view of an interconnect
substrate according to the present invention in which there is an
interfacial layer to improve a SiCOH dielectric layer to the
preceding layer.
[0042] FIG. 3 is an enlarged cross sectional view of the
interfacial layer and SiCOH layer.
[0043] FIG. 4 is a graph of flow rate versus time for the formation
of a dense SiCOH layer.
[0044] FIG. 5 is a graph of flow rate versus time for the formation
of a porous SiCOH layer.
[0045] FIG. 6 is a graph of flow rate versus time for the formation
of a porous SiCOH layer according to the first embodiment of the
present invention.
[0046] FIG. 7 is a graph of flow rate versus time for the formation
of a porous SiCOH layer according to the present invention
according to the second embodiment of the present invention.
[0047] FIG. 8 is a block diagram illustrating the various steps of
the process of forming a porous SiCOH layer according to the
present invention.
[0048] FIGS. 9 to 11 are TOF-SIMS analysis graphs for porous SiCOH
formed according to the flow rates versus time shown in FIGS. 5 to
7, respectively.
DETAILED DESCRIPTION OF THE INVENTION
[0049] The present invention discloses a structure with improved
interfacial strength between different layers of insulating or
conductive materials. The improved interfacial strength is obtained
in the present invention by forming thin transition layers between
the different pairs of layers. The transition layer is formed while
the plasma of a surface pretreatment step is still present and
active in the reactor chamber at the same time the precursors of
the film that is being deposited are introduced into the reactor
chamber.
[0050] Referring to the Figures in more detail, and particularly
referring to FIG. 1, there is shown a prior art semiconductor
structure, generally indicated by 10. Semiconductor structure 10
comprises the underlying semiconductor material 12 having one or
more metallization layers comprising dielectric material 14 and
metallization 16. It should be understood that there could be one
or more metallization layers between dielectric material 14 and
semiconductor material 12.
[0051] On top of dielectric material 14 is another layer of
dielectric material 20 representing the next metallization layer.
There could be further metallization layers on top of dielectric
material 20 until the required number of metallization layers are
fabricated. Such further metallization layers are not shown for
purposes of clarity and are not necessary to the understanding of
the present invention. Between dielectric material 20 and
dielectric material 14 is a capping layer 18. The capping layer 18
is typically used when the dielectric materials 14, 20 are
so-called low-k dielectric materials. Capping layer 18 is opened at
24 during the processing of semiconductor structure 10 to permit
electrical connection between metallization 16 and via 22. Capping
layer 18 is typically a silicon carbide based material such as SiCH
or SiCHN.
[0052] Modern day semiconductor structures often mix and match
dielectric materials so as to obtain the maximum in performance and
reliability. As noted above, low-k dielectric materials are
preferred because of their lower dielectric constant which enhances
the electrical performance of the interconnect structure.
Dielectric material 14 may be any commonly used low-k dielectric
material as referenced previously. Dielectric material 20, however,
is a SiCOH dielectric material. It has been found that there is
poor adhesion between SiCOH and the material of the capping layer
18, often resulting in delamination of the metallization layer.
[0053] The adhesion problems found between SiCOH (so-called dense
SiCOH) and the underlying capping layer 18 are exacerbated when the
dielectric material 20 is a porous SiCOH (pSiCOH). Porous SiCOH is
preferred because of its lower dielectric constant and is being
integrated into state of the art semiconductor structures. The
present inventors have found, however, that porous SiCOH presents
certain difficulties in its formation due to the interaction of two
precursors and O2 (oxygen) used to form porous dielectric layers in
the processing reactor. Under some conditions, the precursors react
rapidly in the gas phase forming particulates on the manufacturing
substrate, an occurrence known as gas phase nucleation (GPN).
[0054] Turning now to FIG. 2, there is shown a preferred embodiment
of the present invention. Semiconductor structure 100 includes
semiconductor material 12 and multiple metallization layers, one of
which is indicated by dielectric material 14 having metallization
16. Dielectric material 14 may be any low-k dielectric material
including porous SiCOH. On top of dielectric material 14 is capping
layer 18 which again has been opened at 24 to allow connection to
via 22 (such as a copper damascene connector or other
metallization) in dielectric material 20. In practice, the typical
semiconductor structure 100 will have many such vias 22. Dielectric
material 20 is a porous pSiCOH. To improve the interfacial strength
between porous SiCOH 20 and capping layer 18, there is an
interfacial structure 26 which dramatically, surprisingly and
unexpectedly improves the interfacial strength between the porous
SiCOH 20 and capping layer 18.
[0055] Interfacial structure 26 is shown in greater detail in FIG.
3 where it can be seen that interfacial structure 26 is actually
made up of two separate layers 28 and 30. Layer 28 is an oxide
layer having essentially no carbon. What is meant by "essentially
no carbon" is that no detectible carbon is measured in the layer,
measured for example by x-ray photoelectron spectroscopy (XPS) or
time-of-flight secondary ion mass spectrometry (TOF SIMS). While
having no carbon present is preferred for purposes of the present
invention, it is believed that carbon in amounts up to 0.1 to 3
atomic percent may not adversely affect the present invention.
Layer 30 is a graded transition layer which has essentially no
carbon and no porosity at the interface with oxide layer 28 and
gradually increases both the amount of carbon and porosity until
predetermined levels are reached. At that point, an homogeneous
porous SiCOH layer 20 is formed on the graded transition layer
30.
[0056] It is desirable to keep layers 28 and 30 as thin as possible
because they increase the dielectric constant of the integrated
structure. It is preferred that oxide layer be about 1 to 100
Angstroms in thickness (20 Angstroms being highly preferred) while
the graded transition layer be about 50 to 300 Angstroms in
thickness.
[0057] It is desirable that the concentration profile of the carbon
in graded transition layer 30 experience no spikes or peaks
(hereafter collectively referred to as peaks) and that the oxygen
concentration in graded transition layer 30 experience no dips or
valleys as either of these conditions can lead to a weakness in the
transition layer 30. The present inventors have found that such
weakness can lead to delamination of porous SiCOH within
interfacial structure 26, and have found that depth profiling with
TOF SIMS is a preferred method to detect the carbon and oxygen
concentration profile.
[0058] The inventors believe that there are three conditions which
are important to the formation of a robust interfacial layer 26.
There must be essentially no carbon in oxide layer 28, the
concentration of the carbon in graded transition layer 30 must have
no peaks and the oxygen concentration in graded transition layer 30
must have no dips or valleys.
[0059] Referring now to FIG. 4, there is shown a diagram of flow
rate versus time for a prior art process. The dielectric precursor
(a SiCOH precursor) is flown into a plasma enhanced chemical vapor
deposition (PECVD) chamber for a time T1, usually 1-2 seconds.
Thereafter, the dielectric precursor is ramped up while the oxygen
concentration is ramped down for a time T2, usually 2 seconds. For
a time T3, usually 50 seconds, the dielectric precursor is held at
a high flow rate while the oxygen is held at a low flow rate. The
resultant structure is a carbon graded transition layer formed
during the T1-T2 interval in which carbon gradually increases while
the formation of the SiCOH gradually increases as well followed by
a dense homogenous layer of dielectric SiCOH in the T2-T3
interval.
[0060] Referring to FIGS. 4 to 7 the actual precursors flows have
rounded, gradual, transitions as is known in the art while the
Figures schematically show discrete, sharp transitions. As noted
above, it is currently desired to form at least one layer of porous
SiCOH. A person skilled in the art might assume that the porogen
precursor should be introduced when the dielectric precursor is
ramped up as shown in FIG. 5. The present inventors, however, have
found that such a process sequence results in a large carbon peak
in the carbon graded transition layer formed during the T1-T2
interval, eventually resulting in a mechanically weak interfacial
layer.
[0061] According to a first embodiment of this invention, the
porogen precursor is introduced later in the process flow, such as
during the T2-T3 interval, as shown in FIG. 6. The time difference
from T1 to T2 is called an "offset" for porogen introduction, and
the offset improves the process but still results in a carbon peak
and an oxygen dip, both of which lead to a mechanically weak
interfacial layer.
[0062] The process according to the second embodiment of the
present invention is illustrated in FIG. 7. Oxygen and the
dielectric precursor are flown into a PECVD chamber for a time T1,
usually 1-4 seconds. Helium or argon may be optionally introduced
into the reactor chamber with the oxygen. The oxygen flow rate is
kept high while the dielectric precursor flow rate is kept low so
that an oxide layer having essentially no carbon (as defined above)
is formed on the substrate. During a time T2, usually 2-4 seconds,
the dielectric precursor is ramped up to a predetermined level
while the oxygen flow rate is kept high. T2 is the time at which
the dielectric precursor flow is stable. The porogen precursor is
introduced during the T1-T2 interval. T3 is the time at which the
porogen precursor flow is stable. Two methods may be used to have
T3>T2. Either an offset or delay by 1-2 seconds is used as was
shown in FIG. 6, or the ramp rate of the porogen may be lower than
that of the dielectric. This case is shown as 36 in FIG. 7 with a
lower slope for the porogen versus the dielectric. During the T1-T2
interval, a carbon graded transition layer is formed in which both
carbon and porosity gradually and uniformly increase. There are no
carbon peaks or oxygen dips formed during T2. It is preferred that
the interval 38 between T2 and T3 be as short as possible. The
present inventors have found that it is preferred to ramp down
oxygen flow at T3 and not earlier in the process. Ramping down
oxygen early in the process was shown with respect to FIGS. 5 and
6, and this leads to a carbon peak and/or oxygen dip and resulting
weaker adhesion strength. Further, an objective during the T1-T2
interval is to form SiCOH first so the oxygen is kept high during
the T1-T2 interval. At the beginning of T3, or possibly just before
the beginning of T3, the oxygen flow rate is ramped steeply down
while the dielectric precursor and porogen precursor are held
approximately constant until the process terminates. The time T4 is
when all flows are stabilized at values to deposit the porous SiCOH
film. The T4 time period is typically in the range of 10 to 200
seconds. During T4, an homogenous porous SiCOH layer is formed. The
various flows of oxygen, dielectric precursor and porogen may be
independently adjusted so as to obtain the best dielectric layer.
Each of the foregoing stages are performed without interruption of
the plasma in the reactor but by adjusting the gas mixtures and
plasma parameters at each stage.
[0063] Referring now to FIG. 8, the inventive method begins with
the first step 40 of positioning a substrate such as an
interconnect structure into a reactor chamber in which a plasma can
be generated. Suitable reactors include: plasma enhanced chemical
vapor deposition reactors, high-density plasma reactors, sputtering
chambers, and ion beam chambers. The reactor is evacuated and then
the substrate is heated to a temperature of about 400.degree. C. or
less. Preferably, the substrate is heated to a temperature of from
about 200.degree. C. to about 400.degree. C.
[0064] In the next step 42, the substrate is subjected to an
optional surface pretreatment step in which at least one surface
pretreatment gas is flown into the reactor at which time it is
converted into a plasma. The at least one surface pretreatment gas
that can be used in the surface pretreatment step includes an inert
gas such as Ar, Ne, He, Xe and Kr; H.sub.2; NH.sub.3; O.sub.2;
SiH.sub.4 and O.sub.2; and mixtures thereof. In some embodiments, F
atoms may also be introduced into the feed gas. The flow rate of
the surface pretreatment gas may vary depending on the reactor
system and the type of gas being introduced. The chamber pressure
can range anywhere from 0.05 to 20 torr, but the preferred range of
pressure operation is 1 to 10 torr. The surface pretreatment step
occurs for a first period of time, which is typically from about
0.08 to about 2 min.
[0065] An RF power source is typically used to generate a plasma of
the surface pretreatment gas. The RF power source typically
operates at 13.6 MHz, although other frequencies may be used.
Optionally, a low frequency RF component (less than 1 MHz) may be
used, or a combination thereof may be employed. The high frequency
power density can range anywhere from 0.1 to 2.0 W/cm.sup.2 but the
preferred range of operation is 0.2 to 1.0 W/cm.sup.2. The low
frequency power density can range anywhere from 0.0 to 1.0
W/cm.sup.2 but the preferred range of operation is 0.0 to 0.5
W/cm.sup.2.
[0066] At this point of the process, the next step 44 commences
wherein a flow of precursor gases for the formation of the carbon
depleted layer of oxide, such as that shown, for example, in FIG. 3
as oxide layer 28 are introduced into the reactor. The reactor at
this point thus contains a plasma of the surface pretreatment gases
still present and active within the reactor, yet the next layer's
precursor gases of oxygen and SiCOH dielectric precursor are being
introduced. The flows of the precursor gases into the reactor may
vary and are dependent on the chemical and physical make-up of the
layer that is being deposited. The flows of precursor reactants
into the reactor occur for a second period of time, which is
typically from about 1 to 4 seconds. During the transition of these
process steps, it is preferred, although may not be absolutely
critical, to maintain a constant chamber pressure by allowing the
throttle valve position to adjust due to the change of process gas
flows. It is also preferred, but again may not be absolutely
critical, to maintain the same power levels during the transition
of these process steps in order to provide a more reproducible
layered film.
[0067] The next step 46 is forming a carbon graded transition layer
on the carbon depleted layer such as that shown, for example, in
FIG. 3 as graded transition layer 30. The interconnect substrate
remains in the reactor chamber and step 46 is performed without
interruption of the plasma in the reactor. The precursor gases of
oxygen and SiCOH dielectric precursor are adjusted for the
formation of this layer while the porogen precursor gas is
introduced into the reactor chamber. This step 46 occurs for 2-4
seconds. During this step, the O2 flow is kept at a relatively high
value, as shown in FIGS. 6 and 7, while the flows of the dielectric
and porogen precursors are increased.
[0068] The last step 48 in the process of FIG. 8 is forming a
porous SiCOH layer on the graded transition layer such as that
shown, for example, in FIG. 2 as porous SiCOH layer 20. In the
transitioning between step 46 and 48, the interconnect substrate is
maintained in the plasma in the reactor chamber but the plasma
parameters and precursor gases of oxygen, dielectric precursor and
porogen precursor are adjusted to form the porous SiCOH layer. The
length of time is variable depending upon the desired thickness of
the porous SiCOH layer but should be about 50 seconds. The porous
SiCOH has an ultralow dielectric constant (k<2.6) and the
substrate is an interconnect structure having an upper layer of a
dielectric material such as SiCHN on which the interfacial
structure and then the SiCOH type dielectric are formed
thereon.
[0069] The above processing steps of the present invention may be
repeated any number of times to provide a multilayered structure in
which each successively deposited layer has an interfacial layer
therebetween.
[0070] Qualitatively, the interfacial strength provided by the
transition layer of the present invention is strong enough to
prevent delamination or cohesive failure near the interface between
the interconnect dielectric and the dielectric cap layer during
fabrication and reliability testing.
[0071] The dielectric precursor utilized may be any alkoxysilane.
For example, this precursor may be selected from the group
consisting of diethoxymethylsilane, dimethyldimethoxysilane,
octamethylcyclotetrasiloxane, tetramethylcyclotetrasiloxane, with
one preferred precursor being diethoxymethylsilane (DEMS). The
porogen precursor may be selected from the group consisting of
bicycloheptadiene (BCHD), hexadiene (HXD), or other molecules
described in U.S. Pat. Nos. 6,147,009, 6,312,793, 6,441,491,
6,437,443, 6,441,491, 6,541,398, 6,479,110 B2, and 6,497,963, the
disclosures of which are incorporated by reference herein. One
preferred precursor is 2,5-norbornadiene (or bicycloheptadiene
BCHD).
EXAMPLES
Example 1
[0072] A Si wafer containing a layer of SiCNH alloy was used to
simulate an interconnect substrate with the same SiCNH alloy
capping a pre-formed patterned interconnect layer. A Si wafer
containing a layer of SiCNH alloy was placed in a PECVD chamber and
a porous SiCOH layer was prepared according to the flow rates of
oxygen, dielectric precursor and porogen precursor illustrated in
FIG. 5. Particulars of the process are described in the following
Table 1.
TABLE-US-00001 TABLE 1 Step Label in Figure 0 to T1 T1 to T2 T3
Duration (seconds) 1 to 4 1 to 4 30 to 60 RF Power, General Low
High High Description Example RF Power (W) 300-500 600-700 600-700
Dielectric Precursor Flow Low Ramping Low High to High Porogen
precursor Flow Zero Ramping High to High O2 Flow High Low Low
[0073] A TOF-SIMS analysis was done of the completed structure. The
result is illustrated in FIG. 9.
[0074] The X axis of FIG. 9 is the sputter time, which is
proportional to depth into the sample with zero of the X axis being
the top surface of the sample and the time beyond 200 s being the
SiCNH layer. The Y axis is signal intensity for the secondary ions
detected by TOF-SIMS. The signal versus depth for carbon is
labelled 60. The signal versus depth for SiO is labelled 62. The
signal versus depth for SiN is labelled 64.
[0075] The sample illustrates a significant carbon peak and oxygen
dip for this particular sample indicating a mechanically weak
sample. The sample had a measured adhesive strength of 2.0
J/m.sup.2.
Example 2
[0076] A second Si wafer containing a layer of SiCNH alloy
(simulating an interconnect substrate) was placed in a PECVD
chamber and a porous SiCOH formed according to the flow rate
profiles of oxygen, DEMS dielectric precursor and BCHD porogen
precursor as illustrated in FIG. 6. The particulars of the process
are illustrated in Table 2 below.
TABLE-US-00002 TABLE 2 Step Label in Figure 0 to T1 T1 to T2 T2 to
T3 T4 Duration (seconds) 1 to 4 1 to 4 1 to 4 30 to 60 RF Power,
General Low High High High Description Example RF Power (W) 300-500
600-700 600-700 600-700 Dielectric Precursor Flow Low Ramping Low
High High to High Porogen precursor Flow Zero Zero Ramping High to
High O2 Flow High Low Low Low
[0077] It was found advantageous by the inventors to decrease the
power density of the plasma such that steps 0 to T2 are performed
with a reduced power density and steps after T2 are performed with
a higher power density. It was found advantageous by the inventors
that a SiCOH precursor ramp rate between 500 to 1500 milligrams per
minute/second and a porogen precursor ramp rate between 100 to 600
milligrams per minute/second be used.
[0078] A TOFS-SIMS analysis for example 2 is illustrated in FIG.
10. The signal versus depth for carbon is labelled 70. The signal
versus depth for SiO is labelled 72. The signal versus depth for
SiN is labelled 74 As can be seen, the sample exhibits both a
carbon peak and an oxygen dip indicating a mechanically deficient
sample. This was verified by mechanical testing results which
showed delamination in the area of the carbon peak and oxygen dip.
The sample exhibited an adhesive strength of 2.5 J/m.sup.2.
Example 3
[0079] A third interconnect substrate was prepared by placing the
substrate in a PECVD chamber and flowing oxygen, DEMS dielectric
precursor and BCHD porogen precursor according to the flow rate
profile illustrate in FIG. 7. The particulars of the process are
illustrated in Table 3 below.
TABLE-US-00003 TABLE 3 Step Label in Figure 0 to T1 T1 to T2 T2 to
T3 T4 Duration (seconds) 1 to 4 1 to 4 4 30 to 60 RF Power, General
Low High High High Description Example RF Power (W) 300-500 600-700
600-700 600-700 Dielectric Precursor Flow Low Ramping Low High High
to High Porogen precursor Flow Zero Ramping Ramping High to High to
High O2 Flow High High High Low
[0080] It was found advantageous by the inventors to decrease the
power density of the plasma such that steps 0 to T2 are performed
with a reduced power density and steps after T2 are performed with
a higher power density. It was found advantageous by the inventors
that a SiCOH precursor ramp rate between 500 to 1500 milligrams per
minute/second and a porogen precursor ramp rate between 100 to 600
milligrams per minute/second be used.
[0081] The TOFS-SIMS analysis for Example 3 is shown in FIG. 11.
The signal versus depth for carbon is labelled 80. The signal
versus depth for SiO is labelled 82. The signal versus depth for
SiN is labelled 84. The signal versus depth for carbon, 80, shows a
smooth carbon and the oxygen signal versus depth 82 has no distinct
dip or valley. This profile indicates an interfacial structure
without weak points, as would be the case if there were carbon
peaks or oxygen dips as in Examples 1 and 2. Mechanical testing of
Example 3 verified the robustness of the interfacial layer and
strong adhesion of the porous SiCOH wherein the sample had a
measured adhesive strength of 3.5-3.7 J/m.sup.2. The increase in
adhesive strength between Examples 1, 2 and Example 3 as well as
the magnitude of the increase in adhesive strength was both
surprising and unexpected.
[0082] It will be apparent to those skilled in the art having
regard to this disclosure that other modifications of this
invention beyond those embodiments specifically described here may
be made without departing from the spirit of the invention.
Accordingly, such modifications are considered within the scope of
the invention as limited solely by the appended claims.
* * * * *