U.S. patent application number 13/493244 was filed with the patent office on 2012-10-04 for silicon oxycarbide, growth method of silicon oxycarbide layer, semiconductor device and manufacture method for semiconductor device.
This patent application is currently assigned to FUJITSU SEMICONDUCTOR LIMITED. Invention is credited to Shun-ichi Fukuyama, Kengo Inoue, Tamotsu Owada, Atsuo Shimizu, Hirofumi Watatani.
Application Number | 20120252227 13/493244 |
Document ID | / |
Family ID | 35506448 |
Filed Date | 2012-10-04 |
United States Patent
Application |
20120252227 |
Kind Code |
A1 |
Owada; Tamotsu ; et
al. |
October 4, 2012 |
SILICON OXYCARBIDE, GROWTH METHOD OF SILICON OXYCARBIDE LAYER,
SEMICONDUCTOR DEVICE AND MANUFACTURE METHOD FOR SEMICONDUCTOR
DEVICE
Abstract
A method of manufacturing a semiconductor device includes the
steps of: preparing an underlying structure having a silicon
carbide layer covering a copper wiring, and growing silicon
oxycarbide on the underlying structure by vapor deposition using,
as source gas, tetramethylcyclotetrasiloxane, carbon dioxide gas
and oxygen gas, a flow rate of said oxygen gas being at most 3% of
a flow rate of the carbon dioxide gas. The surface of the silicon
carbide layer of the underlying structure may be treated with a
plasma of weak oxidizing gas which contains oxygen and has a
molecular weight larger than that of O.sub.2 to bring the surface
more hydrophilic. Film peel-off and cracks in the interlayer
insulating layer decrease.
Inventors: |
Owada; Tamotsu; (Kawasaki,
JP) ; Fukuyama; Shun-ichi; (Kawasaki, JP) ;
Watatani; Hirofumi; (Kawasaki, JP) ; Inoue;
Kengo; (Kawasaki, JP) ; Shimizu; Atsuo;
(Kawasaki, JP) |
Assignee: |
FUJITSU SEMICONDUCTOR
LIMITED
Yokohama-shi
JP
|
Family ID: |
35506448 |
Appl. No.: |
13/493244 |
Filed: |
June 11, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12314036 |
Dec 3, 2008 |
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13493244 |
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11206955 |
Aug 19, 2005 |
7485570 |
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12314036 |
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10694826 |
Oct 29, 2003 |
6949830 |
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11206955 |
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Current U.S.
Class: |
438/778 ;
257/E21.24 |
Current CPC
Class: |
H01L 21/76826 20130101;
H01L 21/76834 20130101; C23C 16/30 20130101; H01L 21/02227
20130101; H01L 21/76832 20130101; H01L 21/02274 20130101; H01L
21/31633 20130101; H01L 21/02315 20130101; H01L 21/0234 20130101;
H01L 21/76808 20130101; H01L 21/02126 20130101; H01L 21/02216
20130101; H01L 21/76801 20130101; H01L 21/02304 20130101 |
Class at
Publication: |
438/778 ;
257/E21.24 |
International
Class: |
H01L 21/31 20060101
H01L021/31 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 30, 2002 |
JP |
2002-315900 |
Claims
1. A method of manufacturing a semiconductor device comprising the
steps of: preparing an underlying structure having a semiconductor
substrate, a copper wiring formed above said semiconductor
substrate and a silicon carbide layer covering said copper wiring;
making hydrophilic a surface of the silicon carbide layer of said
underlying structure by using plasma of oxidizing gas which
contains oxygen and has a molecular weight larger than a molecular
weight of O2; and forming a low dielectric constant insulating
layer on the surface of said hydrophilic silicon carbide layer,
said low dielectric constant insulating layer having a specific
dielectric constant lower than a specific dielectric constant of
silicon oxide.
2. The method of manufacturing a semiconductor device according to
claim 1, wherein said step of making hydrophilic by using the
plasma is a step of exposing said underlying structure to down-flow
of plasma.
3. The method of manufacturing a semiconductor device according to
claim 1, wherein said step of making hydrophilic by using the
plasma is performed in a same chamber as used by said step of
forming said low dielectric constant layer.
4. The method of manufacturing a semiconductor device according to
claim 1, wherein said weak oxidizing gas is CO.sub.2.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional application of U.S.
application Ser. No. 12/314,036 filed on Dec. 3, 2008, which is a
divisional application of U.S. application Ser. No. 11/206,955
filed on Aug. 19, 2005, now U.S. Pat. No. 7,485,570, which is a
divisional application of U.S. application Ser. No. 10/694,826
filed Oct. 29, 2003, now U.S. Pat. No. 6,949,830, which was based
on and claimed priority to Japanese Patent Application No.
2002-315900 filed on Oct. 30, 2002, the entire contents of which
are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] A) Field of the Invention
[0003] The present invention relates generally to a low dielectric
constant insulator having a low specific dielectric constant, a
method of growing a low dielectric constant insulating layer, a
semiconductor device having a low dielectric constant insulating
layer, and a method of manufacturing a semiconductor device having
a low dielectric constant insulating layer. The invention relates
specifically to a low dielectric constant insulator suitable for
use with a semiconductor integrated circuit having multi-layer
wirings, a method of growing a low dielectric constant insulating
layer, a semiconductor device having multi-layer wirings and low
dielectric constant insulators, and a method of manufacturing such
a semiconductor device.
[0004] B) Description of the Related Art
[0005] Semiconductor integrated circuit devices are becoming highly
integrated, and there is the tendency that the scale of wirings of
each device increases one generation after another. As the wiring
scale becomes large, the number of wiring layers increases so that
a multi-layer wiring structure is adopted. High integration of a
semiconductor integrated circuit device results in a narrow wiring
space.
[0006] There is the tendency that the wiring space is narrowest at
lower level wiring layers and broadens toward upper level wiring
layers. Many of lower level wirings are used for transmitting
signals, whereas many of upper level wirings are used for power
source lines. Because of this characteristic difference, the
conditions required for multi-layer wirings are not the same.
[0007] A transmission speed of a signal in a wiring is governed by
wiring resistance and wiring parasitic capacitance. It is desired
for a high speed operation to lower a wiring resistance and reduce
a wiring parasitic capacitance.
[0008] In order to lower a wiring resistance, Cu wirings are used
nowadays in place of Al wirings. It is difficult to use wiring
material having a resistivity lower than that of Cu. As the
reduction in a wiring resistance reaches near its limit, it becomes
necessary to reduce a wiring parasitic capacitance. When Cu wirings
are used, a diffusion preventive film of SiN, SiC or the like is
formed covering each Cu wiring in order to prevent oxidation and
diffusion of Cu.
[0009] A parasitic capacitance between wirings increases if the
wiring space becomes narrow assuming the same wiring thickness. The
influence of a parasitic capacitance upon a device operation speed
is small if the device has a wiring space of 1 .mu.m or broader,
whereas this influence becomes large if the device has a wiring
space of 0.5 .mu.m or narrower. It can be expected that if a device
has a wiring space of 0.2 .mu.m or narrower, the parasitic
capacitance greatly influences the device operation speed.
[0010] The parasitic capacitance between wirings can be reduced if
the wiring thickness is made thin and the confronting area of
adjacent wirings is made small. However, as the wiring thickness is
made thin, the wiring resistance increases so that the operation
speed as a whole cannot be improved.
[0011] The most effective means for reducing the wiring parasitic
capacitance is to make an insulating layer between wirings have a
low dielectric constant. Insulating materials having a lower
specific dielectric constant have been used in place of silicon
oxide (USG) having a specific dielectric constant of about 4.1,
P-doped silicon oxide (PSG) and B- P-doped silicon oxide
(BPSG).
[0012] Other materials now in use include: organic insulating
materials having a very low specific dielectric constant (such as
SiLK (registered trademark) and FLARE (registered trademark)); and
porous materials such as porous silicon oxide. These materials have
characteristics largely different from those of silicon oxide and
are difficult to be used as the material of an interlayer
insulating film for multi-layer wirings because of their mechanical
strength, reliability and the like. These materials are therefore
used mainly for lower level wiring layers.
[0013] Silicon oxycarbide (SiOC) has been paid attention as another
insulating material having a low specific dielectric constant. A
vapor-grown silicon oxycarbide film available from Novellus
Systems, Inc., called CORAL (registered trademark), is manufactured
at a deposition speed of about 1000 to 1200 nm/min by plasma
enhanced chemical vapor deposition (CVD) under the conditions of
source gas of tetramethylcyclotetrasiloxane (TMCTS), oxygen
(O.sub.2) and carbon dioxide (CO.sub.2), a flow rate
TMCTS:O.sub.2:CO.sub.2=5:250:5000 (ml/min, sccm), a gas pressure of
4 torr, an HF (13.56 MHz) power of 600 W and an LF (1 MHz or lower)
power of 400 W.
[0014] This insulating material called CORAL has Si--O--C as its
main skeleton and a specific dielectric constant of 2.9 which is
considerably lower than that of silicon oxide. This insulating
material is promising as an interlayer insulating layer material
for multi-layer wirings.
[0015] It has been proposed that a silicon oxycarbide layer is used
partially as a hard mask layer and thereafter the silicon
oxycarbide layer is left as a portion of an interlayer insulating
film having a low dielectric constant (refer to Japanese Patent
Laid-open Publication No. 2003-218109, family of U.S. patent
application Ser. No. 10/053,288 filed on Jan. 17, 2002).
[0016] A low specific dielectric constant material is generally has
low adhesion to, for example, an underlying layer formed as a
diffusion preventive film for Cu. If the number of wiring layers is
increased by using interlayer insulating films having low adhesion,
a film peel-off occurs at the interface to the underlying
layer.
[0017] It is desired that the multi-layer wiring structure uses a
lamination of a plurality of low dielectric constant insulating
layers having different thermal expansion coefficients. The
material having a low specific dielectric constant has generally
the tendency of a low density and a low mechanical strength. If
there exists a mismatch of a thermal coefficient between interlayer
insulating layers, a large stress is generated at the interface so
that cracks may be formed in the insulating layer having a low
relative dielectric factor.
SUMMARY OF THE INVENTION
[0018] An object of this invention is to prevent peel-off and
cracks of interlayer insulating layers for multi-layer wirings.
[0019] Another object of the invention is to provide insulating
material having a low dielectric constant suitable for use as the
material of multi-layer wirings of a semiconductor device.
[0020] Still another object of the invention is to provide a method
of growing a low dielectric constant insulating layer on an
underlying layer.
[0021] Further object of the invention is to provide a
semiconductor device of high reliability having multi-layer wirings
with low dielectric constant insulating material, and a method of
manufacturing such a semiconductor device.
[0022] According to one aspect of the present invention, there is
provided silicon oxycarbide which contains hydrogen and has a
carbon content of at least about 18 at % and a specific dielectric
constant of at most about 3.1.
[0023] According to another aspect of the present invention, there
is provided silicon oxycarbide whose hydrogen content is at most 30
at % and whose specific dielectric constant is at most about
3.1.
[0024] According to another aspect of the present invention, there
is provided a method of growing a silicon oxycarbide layer
comprising the steps of: preparing an underlying layer; and growing
a silicon oxycarbide layer on the underlying layer by vapor
deposition using, as source gas, tetramethylcyclotetrasiloxane,
carbon dioxide gas and oxygen gas, a flow rate of said oxygen gas
being at most 3% of a flow rate of the carbon dioxide gas.
[0025] According to another aspect of the present invention, there
is provided a semiconductor device comprising: a semiconductor
substrate; a copper wiring formed above the semiconductor
substrate; a silicon carbide layer covering the copper wiring; and
a first silicon oxycarbide layer covering the silicon carbide
layer, the first silicon oxycarbide layer containing hydrogen and
having a carbon content of at least about 18 at % (at least 17 at
%) or a hydrogen content of at most 30 at %, and a specific
dielectric constant of at most about 3.1.
[0026] According to another aspect of the present invention, there
is provided a method of manufacturing a semiconductor device
comprising the steps of: preparing an underlying structure having a
semiconductor substrate, a copper wiring formed above the
semiconductor substrate and a silicon carbide layer covering the
copper wiring; and growing a silicon oxycarbide layer on the
underlying structure by vapor deposition using, as source gas,
tetramethylcyclotetrasiloxane, carbon dioxide gas and oxygen gas, a
flow rate of said oxygen gas being at most 3% of a flow rate of the
carbon dioxide gas.
[0027] According to another aspect of the present invention, there
is provided a method of manufacturing a semiconductor device
comprising the steps of: preparing an underlying structure having a
semiconductor substrate, a copper wiring formed above the
semiconductor substrate and a silicon carbide layer covering the
copper wiring; making hydrophilic a surface of the silicon carbide
layer of the underlying structure by using plasma of weak oxidizing
gas which contains oxygen and has a molecular weight larger than a
molecular weight of O.sub.2; and forming a low dielectric constant
insulating layer on the surface of the hydrophilic silicon carbide
layer, the low dielectric constant insulating layer having a
specific dielectric constant lower than a specific dielectric
constant of silicon oxide.
[0028] SiOC having novel characteristics can be manufactured.
Adhesion can be improved by depositing this SiOC on an SiC layer.
It is also possible to increase a physical strength and prevent
cracks and the like. By incorporating these merits, a semiconductor
device having high reliability and high performance can be
provided.
[0029] The surface of an SiC layer can be made further hydrophilic.
An SiOC layer having the conventional structure can be formed on
the surface of a enhanced hydrophilic SiC layer with enhanced
adhesion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIGS. 1A to 1C show a table and graphs explaining the
results of experiments made by the present inventors.
[0031] FIGS. 2A and 2B show a table and a graph explaining the
results of experiments made by the present inventors.
[0032] FIG. 3 is a graph showing the results of stud-pull tests
checking adhesion of SiOC layers.
[0033] FIGS. 4A to 4D are cross sectional views of a semiconductor
substrate illustrating the processes of forming a multi-layer
wiring structure of a semiconductor integrated circuit device
according to an embodiment of the invention.
[0034] FIGS. 5A and 5B are cross sectional views of a semiconductor
substrate illustrating the processes of forming multi-layer wirings
according to another object of the invention.
[0035] FIGS. 6A and 6B are cross sectional views of a semiconductor
substrate illustrating the processes of forming multi-layer wirings
according to still another embodiment of the invention.
[0036] FIG. 7 is a cross sectional view of a semiconductor
substrate illustrating the processes of forming a multi-layer
wiring structure according to another embodiment of the
invention.
[0037] FIG. 8 is a schematic cross sectional view showing the
structure of a semiconductor integrated circuit device having a
multi-layer wiring structure.
[0038] FIG. 9 is a perspective view schematically showing the
structure of a plasma CVD system.
[0039] FIG. 10 is a table showing the film forming conditions and
measurement results of samples.
[0040] FIG. 11 is a table showing the compositions of selected
samples.
[0041] FIG. 12 is a graph showing infrared absorption spectra of
selected samples.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0042] With reference to the accompanying drawings, description
will be made on the experiments made by the present inventors and
the results thereof and on the embodiments of the invention.
[0043] A vapor-grown silicon oxycarbide (registered trademark
CORAL) film available from Novellus Systems, Inc., has a low
relative dielectric factor of about 2.9. However, it has weak
adhesion to an SiC layer or the like and is rather insufficient in
terms of the physical strength such as hardness and elastic
constant or Young's modulus.
[0044] The present inventors have developed new CVD conditions to
improve tight adhesion of a vapor-grown silicon oxycarbide film and
increase the physical strength. In the following, a conventional
vapor-grown silicon oxycarbide film is called CORAL, and a
vapor-grown silicon oxycarbide film developed by the present
inventors is called TORAL or new SiOC. TORAL or new SiOC is
considered having Si--O--C as its main skeleton.
[0045] FIG. 1A is a table showing growth parameters of a CORAL film
and a TORAL film. CORAL is grown by flowing, as source gas, TMCTS
at 5 ml/min, O.sub.2 gas at 250 sccm and CO.sub.2 gas at 5000 sccm,
as described earlier, under the conditions of a pressure of 4 torr,
an HF power of 600 W and an LF power of 400 W.
[0046] The present inventors have tried if the physical strength
can be improved by lowering a deposition speed. In order to lower
the deposition speed, the flow rate of the source gas TMCTS was
reduced to 1 ml/min or by one fifth, and the HF and LF powers were
lowered to 300 W and 200 W or by one second, respectively. The flow
rate of O.sub.2 gas was reduced more than that of CORAL in the
range of 0 to 200 sccm. The O.sub.2 gas flow was set to 0, 50, 80,
100, 120, 150 and 200 (sccm).
[0047] The deposition speed of TORAL was lowered to 300 to 350
nm/min which is about 1/4 to 1/3 that of CORAL. The density of
TORAL increased apparently to about 1.6 to 1.7 as compared to the
density of about 1.4 of CORAL.
[0048] FIGS. 1B and 1C are graphs showing the physical constants of
TORAL films deposited in the manner described above.
[0049] FIG. 1B is a graph showing a change in hardness and elastic
constant (modulus) relative to the oxygen flow rate. The abscissa
of FIG. 1B represents an oxygen flow rate in the unit of sccm, and
the ordinate represents hardness in the unit of GPa and the modulus
in the unit of GPa. Measurement points coupled by solid lines
indicate hardness data, and measurement points coupled by broken
lines indicate modulus data. White circles indicate hardness and
modulus of CORAL given for the purpose of comparison. The abscissa
has no meaning for CORAL (because the oxygen flow rate is constant
at 250 sccm).
[0050] As seen from FIG. 1B, hardness and modulus are generally
constant irrespective of the O.sub.2 flow rate, although they
change more or less at the O.sub.2 flow rates of 100 and 120
(sccm). As compared to the hardness of about 2 GPa of CORAL, the
hardness of TORAL increased to about 3 GPa. The elastic constant is
about 13 GPa for CORAL whereas the elastic constant for TORAL
increases to about 20 GPa. TORAL increases the physical strength
greatly as compared to that of CORAL. It is therefore expected that
the generation of cracks is suppressed. Reducing the flow rates of
source gas, TMCTS and oxygen, is effective for lowering the
deposition speed and improving the physical strength.
[0051] Dependency of physical strength on the oxygen flow rate is
low. From the view point of physical strength, it is considered
that the flow rate of oxygen can be decreased as desired.
[0052] FIG. 1C is a graph showing a change in the specific
dielectric constant with an oxygen flow rate. The abscissa
represents an oxygen flow rate in the unit of sccm and the ordinate
represents a specific dielectric constant. As seen from FIG. 1C, as
the oxygen flow rate reduces, the specific dielectric constant
lowers. At the oxygen flow rate larger than 100 sccm, particularly
larger than 150 sccm, the specific dielectric constant increases
remarkably. In order to maintain the specific dielectric constant
low, it is preferable to set the oxygen flow rate to 150 sccm (3%
of the CO.sub.2 gas flow rate) or smaller, particularly to 100 sccm
(2% of the CO.sub.2 gas flow rate) or smaller. The specific
dielectric constant is required to be 3.1 or smaller in order to
satisfy the capacitance design value of devices under the technical
state of current developments. TORAL satisfying this condition
corresponds to samples having the oxygen flow rate of 50 sccm or
the oxygen flow rate of 0. In order to set the specific dielectric
constant to about 3.1 or smaller, it is preferable to set the
oxygen flow rate to 50 sccm (1% of the CO.sub.2 gas flow rate) or
smaller. The specific dielectric constants of these samples are
approximately equal to or slightly higher than the specific
dielectric constant of about 2.9 of CORAL. The hardness and modulus
are increased considerably as compared to those of CORAL, as shown
in FIG. 1B.
[0053] FIG. 2A is a table showing the compositions of films
measured by Rutherford backward scattering or the like. There
exists a measurement error of .+-.2%. Even if the precision is
raised through averaging, an error of .+-.1% may still exist. TORAL
samples were made at the oxygen flow rates of 0, 50 and 150 (sccm).
For the comparison purpose, measurements were also conducted for
CORAL and ESL3 which is silicon carbide (SiC) available from
Novellus Systems, Inc. A vapor-grown silicon carbide film contains
Si, C and in addition a fairly large amount of H and O. Since
silicon carbide has Si--C as its main skeleton, H and O are
expected to be coupled to outer positions of the main skeleton.
[0054] As compared to ESL3, the silicon oxycarbide film CORAL has
apparently an increased amount of oxygen and a decreased amount of
other components. Silicon oxycarbide is considered having the main
skeleton Si--O--C. It can be considered that although silicon
carbide (ESL3) contains Si, O and C at about 20%, it has
substantially no Si--O--C skeleton. As compared to the compositions
of CORAL, the compositions of TORAL has an increased amount of Si,
a slightly increased amount of at least O, and a decreased amount
of H. As compared to CORAL, TORAL having the oxygen flow rate of 50
sccm or smaller has carbon (C) more by about 2 at % or higher and
hydrogen (H) less by about 12 at %.
[0055] The composition of carbon (C) of TORAL increases as the
oxygen flow rate is lowered. An increase in the C contents may be
ascribed to an increased influence of CO.sub.2. By considering that
the oxygen flow rate is preferably set to 50 sccm in order to
realize the specific dielectric constant of about 3.1, it is
preferable that the composition of the carbon (C) is set to about
18 at % or larger (or 17 at % or larger). According to the
experiment results, the C composition is preferably about 18 to 21
at % (17 to 22 at %). Although it can be expected that the larger
the C composition, the lower the specific dielectric constant, the
state that the amount of C is larger than that of Si may pose a
problem of characteristics. The C composition is therefore
preferably about 25 10 at % (26 at %) or smaller.
[0056] The composition of hydrogen (H) is about 20 at % (21 at %)
which is far larger than about 32 at % of CORAL. Hydrogen is not an
essential element for silicon oxycarbide, but it is the component
accompanied when TMCTS is used as the source gas. Hydrogen is
considered having a function of reducing cross links by terminating
the bonds of Si, C and O. The amount of hydrogen contents is
therefore preferably as small as possible. Even if oxygen is flowed
at 150 sccm, the hydrogen composition exists at about 11 at % so
that it is difficult to lower the hydrogen composition to about 11
at % or lower when the oxygen flow rate is set to 50 sccm.
[0057] FIG. 2B is a graph showing infrared absorption spectra of a
CORAL film and a TORAL film. The abscissa represents a wave number
in the unit of cm.sup.-1 and the ordinate represents an absorption.
Absorption, which can be considered being caused by Si--H near at a
wave number of 2200 to 2300 cm.sup.-1, can be observed clearly for
CORAL, whereas such absorption is as small as it is hardly observed
for TORAL. As compared to CORAL, absorption caused by C--H near at
a wave number 3000 cm.sup.-1 is reduced for TORAL. A decrease in
Si--H and C--H may be ascribed to a reduction of terminated bonds
and an increase in bridge density (cross links). If the cross links
increase, it can be expected that the physical strength such as
hardness and modulus can be improved. This expectation matches the
increase in C composition and the decrease in H composition.
[0058] Although SiC to be used as a copper diffusion preventive
film is hydrophilic in strict speaking, the surface of the film is
rather water-repellent (hydrophobic). SiC/SiOC/SiC structures
having a silicon oxycarbide film sandwiched between silicon carbide
films were formed and stud-pull tests using Sebastian tester were
conducted.
[0059] FIG. 3 is a graph showing the stud-pull test results. The
ordinate represents a strength applied during the stud-pull test,
the strength being in the unit of MPa. A sample c has a
conventional CORAL layer sandwiched between SiC layers. A sample s1
has a TORAL layer in place of an SiC layer, sandwiched between SiC
layers. It can be seen that the tight adhesion is improved clearly
in the latter case. Although the CORAL sample had many peel-off at
the interface of underlying SiC/CORAL, the TORAL sample had no
peel-off at the interface.
[0060] A sample s2 has a lower SiC layer, a TORAL layer of 50 nm in
thickness formed at an HF power of 90 W on the lower SiC layer, a
CORAL layer formed on the TORAL layer and an SiC layer formed on
the CORAL layer. In this case, it cannot be said necessarily that
the tight adhesion is improved.
[0061] A sample s3 has the structure similar to that of the sample
s2, but the TORAL layer was formed by raising the HF power from 90
W to 200 W. It can be said that the tight adhesion is improved
fairly to the extent similar to or greater than the conventional
CORAL sample. Raising the HF power applied when the TORAL layer is
formed is considered preferable in order to improve the tight
adhesion.
[0062] The SiC layer has a surface like a water repellent surface.
It can be considered that if a silicon oxycarbide film is formed on
the surface like a water repellent surface, the tight adhesion may
be degraded. If the surface of an SiC layer is changed more
hydrophilic, the tight adhesion is expected to be improved. In the
experiments, the surface of an SiC layer was changed hydrophilic by
CO.sub.2 plasma. The CO.sub.2 plasma process was performed by a
down-flow process of microwave excited plasma under the conditions
of a CO.sub.2 flow rate of 5000 sccm, a pressure of 4 torr, an RF
power of 100 (90 to 200) W and a process time of 5 seconds.
[0063] A sample s4 shown in FIG. 3 was formed by processing the
surface of a lower SiC layer with CO.sub.2 plasma (changing the
surface hydrophilic), thereafter depositing a CORAL layer and
depositing an SiC layer on the CORAL layer. A strength of nearly 70
MPa or larger was obtained and it can be said that the tight
adhesion is improved apparently. Also in this case, peel-off at the
interface SiC/CORAL was not observed.
[0064] According to the test results shown in FIG. 3, the tight
adhesion is improved most when the SiC surface is subjected to a
hydrophilic process by CO.sub.2 plasma. This may be ascribed to the
underlying SiC layer surface changed more hydrophilic.
[0065] When the underlying SiC layer surface was processed by
O.sub.2 plasma instead of CO.sub.2 plasma, the tight adhesion was
degraded. The O.sub.2 plasma processing conditions were an O.sub.2
flow rate of 500 sccm, a pressure of 2 torr, a power of 200 W and a
process time of 2 seconds.
[0066] The result of the stud-pull test of a sample without a
CO.sub.2 plasma process showed a strength of 55 MPa, whereas the
result of the stud-pull test of a sample with a CO.sub.2 plasma
process showed a strength of 70 MPa, indicating definite
improvement on the tight adhesion. No peel-off was observed at the
SiC/CORAL interface similar to that described above. The result of
the stud-pull test of the sample subjected to the O.sub.2 plasma
process showed a degraded tight adhesion of 45 MPa. Peel-off was
observed mainly at the SiC/CORAL interface. This may be ascribed to
that excessive oxidation by the O.sub.2 plasma process degrades the
tight adhesion due to surface decomposition.
[0067] In order to perform a plasma process without excessive
oxidation, it may be preferable to use a down-flow process of
microwave excited plasma or other processes.
[0068] When the oxygen flow rate is reduced to 0 to 50 sccm when a
TORAL layer is formed, plasma of the source gas in a chamber
contains a decreased O.sub.2 composition and a relatively increased
CO.sub.2 composition. It can be considered in other words that
plasma of the source gas becomes approximately CO.sub.2 plasma. It
may be considered that high tight adhesion of the TORAL film to the
SiC film matches high tight adhesion of the SiC film subjected to
the CO.sub.2 plasma process to the CORAL film formed on the SiC
film. Good results can be obtained by using plasma of gas which
contains CO.sub.2 and does not contain oxygen or plasma with an
oxygen flow rate restricted small relative to a CO.sub.2 flow
rate.
[0069] It can be considered from these results that it is effective
for tight adhesion improvement to gently oxidize the
near-water-repellent or water repellent surface of an SiC film or
the like. From the fact that O.sub.2 plasma showed bad results and
CO.sub.2 plasma showed good results, it can be considered
preferable to process the surface by plasma of gas which has a
molecular weight larger than that of O.sub.2 and contains oxygen.
Gas of NO.sub.2 or the like may be used in addition to
CO.sub.2.
[0070] Studies made by the present inventors have been directed
further to the conditions of forming a silicon oxycarbide film
having a proper physical strength and a low specific dielectric
constant by selecting the plasma CVD conditions.
[0071] FIG. 9 is a schematic diagram showing the structure of a
plasma CVD system used. A lower electrode 50 severs also as a
suceptor for placing thereon six 8-inch wafers. The susceptor is
provided with a transport mechanism for transporting each wafer.
Six upper electrodes 51a, 51b, 51c, 51d, 51e and 51f are disposed
facing the lower electrode 50 to constitute six pairs of diode
parallel plate electrodes. These parallel plate electrodes
constitute six stages S0 to S5.
[0072] The upper electrodes are connected to high frequency (HF)
power sources 52a, 52b, . . . , 52f, respectively. The lower
electrode 50 is connected to a high frequency power source 53
having a frequency (LF) lower than the high frequency (HF). The
upper electrodes also have the function of shower heads for
supplying source gas. The lower electrodes 50 contain heater
blocks. When a high frequency power is supplied to all the stages,
the total high frequency power is equally divided to six parts and
supplied to the respective stages. It is also possible to supply
high frequency power selectively to a selected stage. By applying a
predetermined high frequency voltage between the lower electrode 50
and a predetermined upper electrode 51, plasma can be generated
above a predetermined wafer.
[0073] A transported wafer is placed on a first stage under the
first upper electrode 51a and undergoes a proper process.
Thereafter, the wafer undergoes processes sequentially at a second
stage S1, a third stage S2, a fourth stage S3, a fifth stage S4 and
a sixth stage S5, and thereafter is ejected out. Experiment results
of silicon carbide films will be described which were subjected to
the same process at each stage. Unless specifically denoted, the
amounts of gas supply and high frequency power are total values for
six stages.
[0074] FIG. 10 shows the conditions and results of each
experimental sample. Some samples are excluded which have a large
irregularity of film thickness. Source gas used is TMCTS of 1
ml/min, (O.sub.2 :0 sccm) and CO.sub.2 of 5000 sccm for all
samples. A deposition speed, an irregularity of intra-wafer film
thickness and a refractive index were measured by changing a
chamber inner pressure, a high frequency power HF applied to the
upper electrode and a high frequency power LF applied to the lower
electrode. The irregularity of film thickness was measured at 49
points of each wafer and represented by % of a half of a difference
between maximum and minimum average values. There is a relation
that a square of a complex refractive index (n+ik) is equal to the
complex dielectric constant. The refractive index n is measured as
a physical quantity having a close relation to the dielectric
factor. The refractive index n is, however, measured at a frequency
of light which is greatly different from a frequency of an electric
signal at which the dielectric constant is measured.
[0075] A sample 1 uses TORAL formed at the oxygen flow rate of 0
described above. The chamber inner pressure is gradually lowered at
the same HF and LF powers to obtain samples 1 to 4. As the chamber
inner pressure is lowered, the deposition speed gradually lowers.
This may be ascribed to that as the pressure lowers, the amount of
source gas supplied to the wafer reduces. As the deposition speed
lowers, the irregularity of film thickness reduces and the
regularity is improved. The refractive index gradually increases as
the deposition speed lowers.
[0076] Paying attention to the sample 2 which has a relatively good
regularity of film thickness, not so large an increase in
refractive index and a good stability of plasma, a hardness, a
modulus and a specific dielectric constant were measured. According
to the experiment results, the sample 1 has the hardness of 3,
modulus of about 20 GPa and specific dielectric constant of about
3.0. The hardness of the sample 3 increases to about 4.0 and the
modulus increases to about 23.6. The specific dielectric constant
maintains about 3.0. It can be said that the sample 3 is an
excellent low dielectric constant insulating layer having an
increased physical strength and maintaining the same specific
dielectric constant, as compared to the sample 1. In the following,
this novel SiOC is called SiOC-A.
[0077] For samples 5 to 9, the pressure was fixed to 3.5 torr and
HF and LF powers were raised. As both the HF and LF powers are
raised, the deposition speed gradually increases, excepting the
sample 6. It appears that there is no definite rules of the film
thickness irregularity and refractive index. The physical
properties of the samples 6 and 9 were measured by taking into
consideration the plasma stability and the like. The sample 6 has a
hardness of 3.5, a Young's modulus of 24.7 and a specific
dielectric constant of 3.2. The sample 9 has a hardness of 4.4, a
Young's modulus of 30.1 and a specific dielectric constant of 3.3.
Although the physical strength of the hardness and Young's modulus
is superior to that of TORAL, the application field of a low
dielectric constant insulating film may be restricted at a specific
dielectric constant of 3.2 or larger. It can be supposed that if
the high frequency power is simply raised, the specific dielectric
constant increases.
[0078] For samples 10 to 14, the chamber inner pressure is fixed to
3.5 torr, the LF power applied to the lower electrode is fixed to
200 W and only the HF power applied to the upper electrode is
raised to 600 W starting from 400 W. Although the sample 10 shows
exceptionally a high deposition speed and a low film thickness
irregularity, the samples 11 to 14 gradually increase the
deposition speed as the HF power is raised. The film thickness
irregularity is low particularly for the samples 13 and 14. It
seems there is the tendency that the refractive index lowers as the
HF power is raised. The refractive index is low particularly for
the sample 14. The physical properties of the sample 14 were a
hardness of 3.6 GPa, a Young's modulus of 23.4 GPa and a specific
dielectric constant of 3.2. Although the hardness and Young's
modulus are high, the specific dielectric constant is also high so
that the application field of a low dielectric constant insulating
layer is restricted.
[0079] For samples 15 to 18, the chamber inner pressure is fixed to
4.0 torr and the HF and LF powers are changed. Although the sample
15 is formed in the same conditions as those of the sample 1, the
deposition speed is slightly high and the film thickness
irregularity is reduced. This is considered to show a kind of
variation in a process of the same condition. For the samples 16 to
18, the HF power applied to the upper electrode is fixed to 600 W
and the LF power is changed from 0, 200 to 400 W. For the sample
16, the LF power applied to the lower electrode is set to 0. The
deposition speed considerably lowers to 89. The samples 16, 17 and
18 show an abrupt increase in deposition speed and a reduced film
thickness irregularity as the LF power is raised. It seems that the
refractive index increases as the deposition speed increases. It
can be understood that the LF power applied to the lower electrode
greatly influences film formation.
[0080] For samples 19 to 22, the chamber inner pressure is
increased to 4.5 torr. For the samples 19 to 21, the LF power
applied to the lower electrode is fixed to 200 W and the HF power
applied to the upper electrode is raised from 600, 800 to 900 W. As
the HF power applied to the upper electrode is raised, the
deposition speed increases. As compared to the sample 19, the
samples 20 and 21 reduce the film thickness irregularity
considerably. The samples 19 to 21 have the refractive index lower
than that of the samples 1 to 18. The physical properties of the
sample 20 having a low film thickness irregularity and an excellent
plasma stability were measured, which showed a hardness of 2.0, a
Young's modulus of 17.3 and a specific dielectric constant of 2.85.
Although the hardness of 2.0 is almost equal to that of CORAL, the
Young's modulus of 17.3 is superior to that of CORAL and the
specific dielectric constant of 2.85 is lower than that of CORAL.
Since the specific dielectric constant is low and the Young's
modulus is improved, this low dielectric constant insulating layer
is expected to be used in various application fields. In the
following description, this novel SiOC is called SiOC-B.
[0081] For a sample 22, the LF power applied to the lower electrode
is raised by 100 W more than that of the sample 21. The deposition
speed increases largely, and the refractive index increases
although the film thickness regularity is good.
[0082] For samples 23 and 24, the chamber inner pressure is
increased further to 5.0 torr and the LF power applied to the lower
electrode is set to 200 W. The HF power applied to the upper
electrode was set to 1100 W and 1200 W. As the HF power is raised,
although the deposition speed increases and the film thickness
irregularity increases, the refractive index lowers gradually.
[0083] It has been found that an insulating layer having a low
specific dielectric constant can be formed by using TMCTS and
CO.sub.2 without using oxygen. The samples 3 and 20 among others
have a low specific dielectric constant and provide excellent low
dielectric constant insulating layers. The sample 3 is, however,
associated with some instability of a plasma state so that
particles are deposited on the wafer due to flowing source gas when
the plasma is being quenched or extinguished.
[0084] To avoid this, following the plasma CVD process, only
CO.sub.2 gas was supplied to generate CO.sub.2 plasma to terminate
the plasma CVD and slightly oxidize the CVD film surface by
switching over plasma CVD to CO.sub.2 plasma treatment. The
CO.sub.2 plasma generation conditions are a CO.sub.2 flow rate of
5000 sccm, a pressure of 1 torr and an HF power of 150 W. Several
ten thousands of particles having a diameter of 0.1 .mu.m are
deposited on a wafer of the sample 3 having a diameter of 20 cm.
However, by generating CO.sub.2 plasma at the time of plasma
quenching, the number of particles having a diameter of 0.1 .mu.m
was able to be reduced to several hundreds, and in better
conditions, to about 100 particles. In the plasma CVD system shown
in FIG. 9, the SiOC film is deposited at six stages. The CO.sub.2
plasma process was performed at each stage following the deposition
of the SiOC film.
[0085] The compositions of films were measured, the films including
a film SiOC-A made of the sample 3, a film SiOC-A:PDX made of a
film formed under the same conditions as those of the sample 3 and
subjected to CO.sub.2 plasma at the time of plasma quenching, and a
film SiOC-B made of the sample 20. The composition measurement
precision has an approximate error of .+-.2 at %.
[0086] FIG. 11 is a table showing the compositions of the films
SiOC-A, SiOC-A:PDX and SiOC-B, with those of CORAL. The specific
dielectric constants are also shown. SiOC-A has the same
compositions as those of TORAL at the oxygen flow rate of 0. As
compared to SiOC-A, SiOC-B reduces carbon and silicon by 3 at % and
increases hydrogen by 7 at %. It appears that there exists the
phenomenon different from the carbon composition dependency of
TORAL observed when the oxygen flow rate is lowered. A possibility
of existence of a different phenomenon cannot be negated because
the pressure is set higher and the HF power is raised much higher
than those of SiOC-A. As compared to CORAL, the pressure and HF
power are raised and the LF power is lowered.
[0087] As compared to SiOC-A, it can be considered that cross links
are reduced due to an increase in hydrogen and the mechanical
strength is lowered. However, as compared to CORAL, the hydrogen
contents are remarkably small (about 5 at %) and the carbon
contents are large by about 2 at %. The measured carbon content
values were 17.8 and 17.9. When the measurement errors are
considered, these measurement values fall in the above-described
preferable range of about 18 at % or higher (17 at % or higher). It
can be said that the carbon contents are larger than those of CORAL
by about 1 at % or larger. The mechanical strength is higher than
that of CORAL and the specific dielectric constant of 2.85 is lower
than that of CORAL.
[0088] The hydrogen composition is about 27 at % which is
apparently lower than about 32 at % of CORAL. This is considered
corresponding to the mechanical strength far more excellent than
CORAL. Silicon oxycarbide can therefore be realized which has the
hydrogen composition of about 27 at % or smaller (28 at % or
smaller) and is excellent in the mechanical strength and has a
specific dielectric constant of about 3.1 or smaller. Low
dielectric constant silicon oxycarbide is expected to be realized
at a hydrogen composition of about 29 at % or smaller (30 at % or
smaller), which silicon oxycarbide has a mechanical strength
superior to that of CORAL and a specific dielectric constant of
about 3.1 or smaller.
[0089] SiOC:PDX is obtained by growing SiOC-A and thereafter
processing the SiOC-A surface by a CO.sub.2 plasma process for 2
seconds at each of the six stages shown in FIG. 9. The compositions
of SiOC-A:PDX is considered the same as those of SiOC-A. The
measured compositions are considerably different from those of
SiOC-A. This may be ascribed to absorption of water contents or the
like in the oxidized surface layer after SiOC-A:PDX is exposed to
the atmospheric air. Although the specific dielectric constant
increases, the number of particles on the wafer surface is reduced
greatly.
[0090] FIG. 12 is a graph showing spectra of infrared absorption of
SiOC-A and SiOC-B, being compared to infrared absorption of a
reference (CORAL). The abscissa represents a wave number in the
unit of cm.sup.-1 and the ordinate represents an absorption. As
compared to the reference Ref, C-H absorption reduces near at the
wave number of 3000 cm.sup.-1. Similarly, C--H absorption reduces
also near at the wave number of 1270 cm.sup.-1. Conversely,
Si--CH.sub.2--Si absorption near at 1360 cm.sup.-1 increases more
than that of the reference Ref. It can be understood from these
absorption spectra that as compared to the reference Ref, SiOC-A
and SiOC-B have an increased umber of C--H bonds and a decreased
number of cross links. It can be considered that an increase in
cross links improves the physical strength.
[0091] FIGS. 4A to 4D are cross sectional views illustrating a
manufacture method for a semiconductor integrated circuit device
according to an embodiment of the invention.
[0092] As shown in FIG. 4A, after an element isolation region, an
element structure including MOS transistors, and the like are
formed on a silicon substrate 100, a phosphosilicate glass (PSG)
layer 11 is formed by vapor deposition to a thickness of about 1.5
.mu.m at a substrate temperature of 600.degree. C. The surface of
the PSG layer 11 is planarized by chemical mechanical polishing
(CMP) and thereafter a resist layer is deposited on the surface of
the PSG layer 11 to form a resist pattern having electrode lead
openings. By using the resist pattern as a mask, the PSG layer 11
is etched to form via holes exposing the contact areas on an
underlying region. The resist pattern is removed thereafter. After
a barrier layer such as Ti or the like is formed, a W layer is
formed by CVD or the like to bury the electrode lead via holes. The
W layer and the like deposited on the PSG layer 11 are removed by
CMP to form tungsten plugs 12.
[0093] An SiC layer 14 as an etch stopper layer is formed to a
thickness of about 70 nm, covering the tungsten plug 12, the etch
stopper layer having an oxygen shielding function and being made of
ESL3 (registered trademark) of Novellus Systems, Inc. Next, a
silicon oxycarbide (SiOC) layer 15 of TORAL is deposited to a
thickness of 550 nm. The oxycarbide layer 15 having improved tight
adhesion and physical strength is therefore formed on the SiC layer
14.
[0094] An SiC layer 17 functioning as a middle stopper layer is
deposited on the surface of the SiOC layer 15 to a thickness of
about 30 nm, the SiC layer being made of ESL2 (registered
trademark) of Novellus Systems, Inc. An SiC layer 18 of TORAL is
deposited on the SiC layer 17 to a thickness of about 370 nm. The
SiOC layer 18 has also improved tight adhesion to the SiC layer 17
and having improved physical strength. An antireflection film ARC1
is formed on the surface of the SiC layer 18.
[0095] On this antireflection film ARC1, a photoresist layer PR1
having a via hole opening pattern is formed. By using the
photoresist pattern PR1 as an etching mask, the antireflection film
ARC1, SiOC layer 18, SiOC layer 17 and SiOC layer 15 are
etched.
[0096] As shown in FIG. 4B, the photoresist pattern PR1 is removed
and a photoresist layer PR2 having a wiring pattern opening is
newly formed. A filler F is buried in a via hole already formed.
The filler F is made of resist material removed with
photosensitivity. By using the photoresist layer PR2 having the
wiring pattern opening as an etching mask, the antireflection film
ARC1 and SiOC layer 18 are etched. Thereafter, the photoresist
pattern PR2 and filler F are removed and the exposed SiC layers 17
and 14 are selectively etched to thereby form a dual damascene
trench.
[0097] As shown in FIG. 4C, a TaN barrier layer 19a of about 30 nm
in thickness and a Cu seed layer 19b of about 30 nm in thickness
are formed by sputtering on the inner surface of the dual damascene
trench. The Cu seed layer 19b is used for plating Cu thereon. On
the surface of the Cu seed layer 19b, a Cu layer 19c is plated. In
this manner, the dual damascene trench is filled with copper
wiring. An unnecessary Cu layer and the like deposited on the SiOC
layer (including the antireflection film ARC1) are removed by CMP.
In this case, the antireflection film ARC1 can be used as a
stopper. The antireflection film is also removed by the CMP or
etching.
[0098] As shown in FIG. 4D, an SiC layer 24 of ESL3 (registered
trademark) of Novellus Systems, Inc. is formed to a thickness of
about 70 nm, covering the Cu wiring 19. This SiC layer has a
function of a copper diffusion preventive film.
[0099] An SiOC layer 25 of TORAL similar to that described earlier
is formed to a thickness of about 550 nm as an interlayer
insulating film for an upper wiring. On this SiOC layer 25, an SiC
layer 27 is formed to a thickness of about 30 nm, and an SiOC layer
28 of TORAL is formed to a thickness of about 370 nm on the SiC
layer 27. On the surface of the SiOC layer 28, an antireflection
film ARC2 is formed to complete a lamination structure. By
performing the processes similar to those shown in FIGS. 4A, 4B and
4C, a dual damascene wiring is formed buried in the interlayer
insulating films 24, 25, 27 and 28.
[0100] If necessary, similar processes are repeated to form the
necessary number of wiring layers. An interlayer insulating film of
silicon oxide is formed and aluminum (Al) pads are formed thereon.
With this structure, a wiring having a capacitance of 180 fF/mm was
able to be formed, for example, in the second wiring layer. Whether
there is any film peel-off was checked by repeating heat treatment
for 30 minutes at 400.degree. C. five times. Film peel-off was not
observed at all.
[0101] Heat cycle tests were conducted for a multi-layer wiring
structure made of pairs of an SiC layer and a conventional silicon
oxycarbide film (of CORAL (registered trademark) of Novellus
Systems, Inc.) formed on the SiC layer and having the same film
thickness as that of the embodiment structure. Peel-off was
observed between the underlying SiC layer and the CORAL layer.
[0102] Other novel silicon oxycarbide films may also be used.
[0103] As a modification, a multi-layer structure was formed by
using an SiOC-A layer having a thickness of 350 nm as the silicon
oxycarbide layers 15 and 25 and an SiOC-A layer having a thickness
of 550 nm as the silicon oxycarbide layers 18 and 28. The SiOC-A
forming conditions are a TMCTS flow rate of 1 ml/min, a CO.sub.2
flow rate of 5000 sccm, a pressure of 3.5 torr, an HF power of 300
W and an LF power of 200 W. Also with this multi-layer structure,
film peel-off was not observed at all even if heat treatment for 30
minutes at 400.degree. C. was repeated five times. The capacitance
of the second wiring layer was about 180 fF/mm. At the interface
between an oxycarbide layer made of CORAL of Novellus Systems, Inc.
and the underlying SiC layer, peel-off was observed after heat
cycle tests.
[0104] When SiOC-A is manufactured, the chamber inner pressure is
relatively low, 3.5 torr, and plasma is likely to become unstable.
Particles are likely to be formed at the time of plasma quenching.
At the time of plasma quenching, the supply of source gas is
stopped and CO.sub.2 gas is introduced to generate CO.sub.2 plasma
for 2 seconds. It is possible in this manner to prevent particles
from being generated. Although there is a possibility that a
specific dielectric constant increases slightly, an insulating
layer without particles can be formed.
[0105] In the above-described modification, after each SiOC-A film
is formed, in six-stage SiOC deposition process, the surface of the
SiOC film was processed for 2 seconds at each plasma quenching by
using CO.sub.2 plasma generated under the conditions of a CO.sub.2
flow rate of 5000 sccm, a pressure of 1 torr and an HF power of 150
W. In other words, the SiOC films 15, 18, 25, and 28 are formed of
SiOC-A:PDX. Also in this case, film peel-off was observed not at
all after repeating heat treatment for 30 minutes at 400.degree. C.
for five times. The capacitance of the second wiring layer measured
was about 180 fF/mm.
[0106] SiOC-B may also be used. For example, in the modification,
as the silicon oxycarbide layers 15, 18, 25 and 28, a silicon
carbide layer of SiOC-B was used which was manufactured under the
conditions of a TMCTS flow rate of 1 ml/min, a CO.sub.2 flow rate
of 5000 sccm, a pressure of 4.5 torr, an HF power of 800 W and an
LF power of 200 W. The capacitance of the second wiring layer
measured was about 180 fF/mm. Film peel-off was observed not at all
after repeating heat treatment for 30 minutes at 400.degree. C. for
five times.
[0107] When SiOC-B is manufactured, the chamber inner pressure is
relatively high so that plasma can be made stable and the
generation of particles can be suppressed. In addition, the
specific dielectric constant can be lowered further, which is
effective for reducing the capacitance between wirings.
[0108] In the above embodiment, the interlayer insulating film
other than the etch stopper layer (copper diffusion preventing
film) is made of the silicon oxycarbide layer of TORAL. The TORAL
layer may be used as an intermediate layer combined with other
layers. The material of the TORAL layer may be silicon oxycarbide
formed at an oxygen flow rate of 50 to 0 sccm.
[0109] FIGS. 5A and 5B are cross sectional views illustrating a
wiring forming process for a semiconductor integrated circuit
device according to another embodiment of the invention.
[0110] As shown in FIG. 5A, on the surface of a silicon substrate
10, an interlayer insulating film 11 and a lower wiring 12
respectively made of PSG similar to the embodiment described above
are formed. An etch stopper SiC layer 14 is formed to a thickness
of about 50 nm by using ESL3 (registered trademark) of Novellus
Systems, Inc, the SiC layer covering the surface of the lower level
wiring 12.
[0111] On the SiC layer 14, an SiOC layer 15x of TORAL is deposited
to a thickness of about 50 nm. As described earlier, this SiOC
layer 15x has improved tight adhesion to the underlying SiC layer.
On the SiOC layer 15x of TORAL, an SiOC layer 15y of CORAL similar
to a conventional example is formed to a thickness of about 500 nm.
Next, an SiC layer 17 as a middle stopper is formed to a thickness
of about 30 nm by using ESL2 (registered trademark) of Novellus
Systems, Inc. On this SiC layer, an SiOC layer 18x of TORAL is
formed as a liner to a thickness of about 50 nm. On the SiOC layer
18x of TORAL, an SiOC layer 18y of CORAL is formed to a thickness
of about 320 nm. On the SiOC layer 18y, an antireflection film ARC1
of SiN or the like is formed.
[0112] Thereafter, similar to the processes shown in FIGS. 4A to
4C, a dual damascene trench is formed by photoresist mask forming
and etching processes.
[0113] As shown in FIG. 5B, a TaN layer and a Cu seed layer are
formed by sputtering on the inner surface of the dual damascene
trench, and a Cu layer 19 is plated on the Cu seed layer. By
planarizing the surface of the Cu layer by CMP, a dual damascene
copper wiring 19 is formed. An SiC layer 24 as a copper diffusion
preventive layer is formed covering the copper wiring 19, the SiC
layer having a thickness of 70 nm and being made of ESL3 of
Novellus Systems, Inc.
[0114] Processes similar to the above processes are repeated to
form a desired number of wiring layers. The capacitance of, e.g.,
the second wiring layer of the multi-layer structure constructed as
above was about 180 fF/mm.
[0115] Whether there is any film peel-off was observed by repeating
heat treatment for 30 minutes at 400.degree. C. five times. Film
peel-off was observed not at all.
[0116] Other novel SiOC materials may be used in place of TORAL. A
silicon oxycarbide layer having a thickness of 50 nm and made of
SiOC-A was used as the SiOC layers 15x and 18x. The parasitic
capacitance of the second wiring layer of the multi-layer structure
was about 180 fF/mm. Film peel-off was observed not at all after
repeating heat treatment for 30 minutes at 400.degree. C. five
times.
[0117] It has been found that the tight adhesion can be improved by
interposing an SiOC layer of TORAL or SiOC-A between the SiOC layer
of CORAL and the SiC layer as the underlying etch stopper
layer.
[0118] In this embodiment, on the surface like a water repellent
surface of the SiC layer having the copper diffusion preventive
function, the SiOC layer of TORAL is formed to form a multi-layer
wiring structure having improved tight adhesion between the SiC and
SiOC layers.
[0119] Tight adhesion can be improved also by the surface
processing of an SiC layer.
[0120] FIGS. 6A and 6B are cross sectional views of a silicon
substrate illustrating the process of forming a multi-layer wiring
structure of a semiconductor integrated circuit device according to
a further embodiment of the invention. Similar to the embodiment
described above, an interlayer insulating film 11 and a lower
wiring 12 are formed on the surface of a semiconductor substrate
10. An SiC layer 14 having a thickness of about 70 nm and made of
ESL3 (registered trademark) of Novellus Systems, Inc. is formed
covering the surface of the lower wiring 12. The surface of the SiC
layer 14 is subjected to a process using CO.sub.2 plasma. By using
the CVD system shown in FIG. 9, the CO.sub.2 process was performed
at the first stage SO. The process conditions were a CO.sub.2 flow
rate of 5000 sccm, a pressure of 4 torr, an RF power of 200 W and a
process time of 5 seconds. It can be considered that this plasma
process forms a hydrophilic surface 14x on the surface of the SiC
layer 14.
[0121] On the hydrophilic surface of the SiC layer 14, an SiOC
layer 15y is formed to a thickness of about 550 nm by using CORAL
(registered trademark) of Novellus Systems, Inc. On this SiOC layer
15y, an SiC layer 17 as a middle stopper is formed to a thickness
of about 30 nm by using ESL2 (registered trademark) of Novellus
Systems, Inc. The surface of the SiC layer 17 is processed by
CO.sub.2 plasma, similar to that described before, to form a
hydrophilic surface 17x. On this hydrophilic surface 17x, an SiOC
layer 18y of CORAL of Novellus Systems, Inc. is formed to a
thickness of about 370 nm. On the surface of the SiOC layer 18y, an
antireflection film ARC1 of SiN or the like is formed.
[0122] Thereafter, photolithography, etching and the like are
performed in a manner similar to the above-described embodiment to
form a dual damascene trench.
[0123] As shown in FIG. 6B, a TaN layer and a Cu seed layer are
formed on the inner surface of the dual damascene trench by
sputtering to a thickness of about 30 nm, respectively. A Cu layer
is plated on the Cu seed layer. An unnecessary wiring layer on the
surface of the SiOC layer 18y is removed by CMP or the like to
complete a dual damascene copper wiring 19. An SiC layer 24 as a
copper diffusion preventive layer is formed covering the copper
wiring 19, to a thickness of 70 nm by using ESL3 of Novellus
Systems, Inc.
[0124] Similar to the above-described embodiment, the necessary
number of wiring layers is formed by repeating similar processes.
The capacitance of, for example, the second wiring layer of the
multi-layer structure constructed as above was about 180 fF/mm.
Film peel-off was observed not at all after repeating heat
treatment for 30 minutes at 400.degree. C. five times.
[0125] In the multi-layer wiring structure, it is desired in some
cases that as the material of the interlayer insulating film for
lower wiring layers having a high wiring density, an organic
insulating film (e.g., SiLK (registered trademark) having a
specific dielectric constant of about 2.6) is used in place of SiOC
having a specific dielectric constant of about 2.9 to 3.1.
[0126] FIG. 7 is a cross sectional view showing the structure of a
multi-layer wiring structure according to another embodiment of the
invention. After a necessary structure is formed on a silicon
substrate 100, a PSG layer 11 having a thickness of about 1.5 .mu.m
is formed and a tungsten plug 12 is buried in the PSG layer 11.
[0127] Covering the surface of the W plug 12, an SiC layer 21 is
deposited to a thickness of about 30 nm. On this SiC layer, an
organic insulating layer 22 (made of SiLK-J150 (registered
trademark of the Dow Chemical Company)) is formed to a thickness of
about 450 nm. The surface of the organic insulating film 22 is
covered with a silicon oxide layer 23 having a thickness of about
100 nm. This lamination structure forms first interlayer insulating
layers 21, 22 and 23.
[0128] A wiring groove is formed through the first interlayer
insulating layers and a copper wiring 34 is buried therein. After
the surface of the copper wiring 34 is planarized, an SiC layer 36
of about 50 nm in thickness, an organic insulating layer 37 (made
of SiLK-J350 (registered trademark of the Dow Chemical Company)) of
about 450 nm in thickness and a silicon oxide layer 38 of about 100
nm in thickness are formed. On the surface of the silicon oxide
layer 38, a hard mask layer HM of SiN is formed to a thickness of
about 50 nm.
[0129] A dual damascene trench is formed by using a photoresist
mask and the pattern of the hard mask HM. After the dual damascene
trench is formed, a barrier metal layer and a seed layer are formed
by sputtering, and a Cu layer is plated to bury the dual damascene
trench and form a dual damascene Cu wiring 29. The hard mask layer
HM may be removed during CMP of planarizing the surface of the dual
damascene wiring 29.
[0130] Covering the surface of the dual damascene wiring 29, an SiC
layer 14 having a thickness of about 70 nm is formed by using ESL3
(registered trademark) of Novellus Systems, Inc. On the SiC layer
14, an SiOC layer 15 of TORAL is formed to a thickness of about 350
nm. On the surface of the SiOC layer, an SiC layer 17 of about 30
nm in thickness and an SiOC layer (Toral layer) 18 of about 550 nm
in thickness are formed.
[0131] By photolithography and etching, a dual damascene trench
similar to that described above is formed, and a copper wiring is
buried therein. By repeating similar processes, a fourth wiring
layer can be formed on the third wiring layer by using an SiOC
layer as an interlayer insulating layer. Wiring layers can be
stacked as necessary.
[0132] Heat treatment for 30 minutes at 400.degree. C. was repeated
five times for the multi-layer wiring structure formed in the above
manner. No film peel-off was observed.
[0133] Other novel SiOC layers may be used in place of TORAL. For
example, the SiOC layers 15 and 18 of the above-described structure
were formed by using SiOC-B. The film forming conditions are the
same as those described above. Film peel-off was observed not at
all after repeating heat treatment for 30 minutes at 400.degree. C.
five times.
[0134] Large thermal stress is considered to be applied to the
boundary region between the organic insulating layer 27 having a
large thermal expansion coefficient and the SiOC layer 15 having a
relatively small thermal expansion coefficient. However, no crack
was formed in the third interlayer insulating film.
[0135] When an SiOC layer of CORAL was used in place of the novel
SiOC layer, peel-off was observed at the interface between the SiC
layer and the SiOC layer of CORAL after similar heat cycle tests,
and crack was formed which is supposed resulting from the third
layer wiring layer.
[0136] When the number of layers of a multi-layer wiring structure
increases, various types of interlayer insulating films can be used
depending upon the type of each wiring layer.
[0137] FIG. 8 is a schematic diagram showing the structure of a
semiconductor integrated circuit device having a multi-layer wiring
structure. Formed on the surface of a silicon substrate 1 are an
element isolation region 2 by shallow trench isolation, a gate
electrode 3 on the active region surface and a MOS transistor
structure. A PSG layer 4 is formed burying the gate electrode 3 and
a W plug 5 is buried in the PSG layer. A silicon oxide layer 6 is
formed on the surface of the PSG layer and a via conductor 7 is
buried in the silicon oxide layer.
[0138] On the silicon oxide layer 6, a first interlayer insulating
film IL1 made of organic insulator is formed and a copper wiring W1
is buried therein. On the first interlayer insulating film IL1, a
second interlayer insulating film IL2, a third interlayer
insulating film IL3 and a fourth interlayer insulating film IL4 are
formed by using organic insulator. Copper wirings W2, W3 and W4 are
buried in the respective interlayer insulating films.
[0139] On the fourth wiring layer, an interlayer insulating film
IL5 of SiOC is formed and a copper wiring W5 is buried therein. On
the fifth interlayer insulating film IL5, a sixth interlayer
insulating film IL6, a seventh interlayer insulating film IL7 and
an eighth interlayer insulating film IL8, of similar structure as
the fifth interlayer insulating film, are sequentially stacked and
copper wirings W6, W7 and W8 are buried therein.
[0140] An interlayer insulating film IL9 of silicon oxide is formed
covering the eighth copper wiring W8, and a copper wiring W9 is
buried therein. On the interlayer insulating film, an interlayer
insulating film IL10 of silicon oxide and a copper wiring W10 are
formed, which are covered with an interlayer insulating film IL11a
of silicon oxide. In the interlayer insulating film IL11a, via
conductors are embedded, and then covered with another interlayer
insulating film IL11b. openings for pads are formed through the
interlayer insulating film IL11b, and aluminum pads PD (and upper
most wirings) are formed on the via conductors embedded in the
interlayer insulating film IL11. A protective film PS is formed
covering the pads PD.
[0141] In this multi-layer wiring structure, the organic interlayer
insulating films are used for the first to fourth wirings having
the narrowest wiring space, the SiOC interlayer insulating films
are used for the fifth to eighth wiring layers, and the silicon
oxide layers are used for the ninth to eleventh interlayer
insulating films. Proper interlayer insulating films are selected
depending upon the wiring space so that the multi-layer wiring
structure can be formed which has high reliability and high
performance.
[0142] The present invention has been described in connection with
the preferred embodiments. The invention is not limited only to the
above embodiments. For example, the number of wiring layers can be
determined as desired. Material other than Cu may be used as the
wiring material. If a higher specific dielectric constant is
permitted, a TORAL layer having a specific dielectric constant of
about 3.1 or higher may also be used. It will be apparent to those
skilled in the art that other various modifications, improvements,
combinations, and the like can be made.
* * * * *