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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device having a multilayer
interconnection structure and a method of fabrication thereof, and more
particularly to the semiconductor device having an interlayer insulating
film including a silicone ladder series resin film, and the method of
fabrication thereof.
2. Description of the Prior Art
Because of higher integrated semiconductor devices such as LSI, their
interconnection have been developed to have a multilayer structure as well
as a higher density structure. Hence, an upper layer of the multilayer
interconnection has a large variation in a step level, a fine wiring
pattern formed on the upper layer causes a problem of damaged reliability
due to disconnection and so forth.
Therefore, flattening of an interlayer film is an important technique to
facilitate the multilayer interconnection, and various methods have been
developed as the flattening technique.
Above all, an SOG (spin on glass) coating method is often employed because
of an easy process, to coat a surface of a semiconductor substrate having
the variation in the step level with liquid insulating material so as to
form an interlayer insulating film having a flat surface.
However, in this method, a failure may occur in a wiring made of aluminium
(Al) or the like due to, for example, moisture emitted from the material
(hereinafter referred to as SOG material) which is used in the SOG coating
method. Thus, long-term reliability may be damaged due to degraded
electric characteristics and so forth.
In order to avoid the problem, one method is employed in which the
interlayer film has a three-layer structure so as not to directly contact
the wiring with a coating film (hereinafter referred to as SOG film)
formed by the SOG coating method.
For example, as disclosed in Japanese Patent Publication (Kokai) No.
3-62554, an interlayer insulating film having the three-layer structure is
formed to have a structure in which the SOG film is interposed between
oxide films formed by plasma vapor phase epitaxy.
A brief description will now be given of a method of fabrication of the
interlayer insulating film having the three-layer structure.
As shown in FIG. 5(a), a pattern serving as a first Al wiring layer 3 is
initially formed on a semiconductor substrate 1 and an insulating film 2.
Subsequently, as shown in FIG. 5(b), a silicon oxide (SiO.sub.2) film 4 is
deposited by a plasma CVD (chemical vapor deposition) method on the first
aluminium (hereinafter abbreviated Al) wiring layer 3. Further, a surface
of the silicon oxide film 4 is coated by a spin coater with an SOG film 8.
Thereafter, as shown in FIG. 5(c), a silicon oxide film 6, deposited by the
plasma CVD method, is formed on a surface of the SOG film 8.
Next, according to an RIE (reactive ion etching) method, a contact hole is
provided by etching in the interlayer insulating film having the
three-layer structure at a predetermined position.
As shown in FIG. 5(d), a second Al wiring layer 7 is formed by using, for
example, a sputtering method to provide patterning for a desired form.
In this case, it is necessary to provide a flat primary coat so as to form
the second Al wiring layer 7 with high accuracy.
The SOG film 8 is formed for the flattening to serve as an intermediate
layer in the interlayer insulating film having the three-layer structure.
When an inorganic SOG material is used to form the thick SOG film 8 by
only one coating, there is a problem in that the SOG film 8 is easily
cracked due to shrinkage or the like at a time of thermosetting.
Hence, the thermostting must be performed after applying the inorganic SOG
material so as to form a thin film. Further, in order to improve flatness,
it is necessary to repeat the coating of the thin SOG film several times
so as to form the multilayered SOG film 8.
However, the process inevitably results in the increased number of steps
for the flattening. In addition, it is naturally difficult to form a thick
film made of the inorganic SOG material by only one coating.
As compared with the above, when organic SOG materials such as silicone
resin are employed, a thick film can be easily formed by only one coating,
and even a thick film by one coating can offer the advantage of good
resistance to crack at the time of thermosetting.
However, though the conventional organic SOG material enables one coating
and can provide more improved flatness by the coating than that in the
inorganic SOG material as described before, it is impossible to provide
sufficient flatness required in the multilayer interconnection structure.
Further, the conventional organic SOG material discharges substantially the
same amount of gases such as moisture in the film as that in the inorganic
SOG material. When the organic SOG film is employed as a single layer
film, the gases such as moisture adversely affect upper and lower
semiconductor layers or a metallic layer in the SOG film.
Therefore, as set forth above, the organic SOG material is employed as an
interlayer film which is vertically interposed between the inorganic
silicon oxide films to form the three-layer structure.
Even in case of the interlayer insulating film having the three-layer
structure, the SOG film serving as the intermediate layer is exposed by
providing the through-hole for wiring.
This interferes with the wiring such as Al in the through-hole to generate
degraded electric characteristics, resulting in a disadvantage for the
long-term reliability.
In order to avoid the disadvantage, etch back is typically carried out to
remove the remaining SOG film on a flattened wiring pattern of a lower
wiring layer so as to expose no organic SOG film in the through-hole which
is provided above the wiring pattern of the lower layer.
From this point of view, if silicone ladder series resins are employed as
the organic SOG material, it is possible to obtain a sufficiently thick
film by the one coating. It is also possible to reduce the amount of
discharged gases such as moisture generated by dehydrating condensation
because of a small amount of --OH group.
That is, even when the silicone ladder series resins are exposed in the
through-hole, no failure occurs in the Al wiring, thereby eliminating
restriction on a structure of a semiconductor device and reducing the
number of steps.
This type of silicone ladder series resin is disclosed in, for example,
Japanese Patent Publication (Kokai) No. 56-49540.
Though the silicone ladder series resin employed in the publication
discharges a small amount of gases, such as moisture, and it can provide
excellent reliability of the wiring, the silicone ladder series resin has
a poor bond performance between the resin film and adjacent layers
consequently, the resin film may be easily separated from a primary coat
or an upper film.
Particularly, resins frequently exhibiting the poor bond performance may
include resins having a --CH.sub.3 group or a --C.sub.2 H.sub.5 group at
an end of a molecular chain at which an --OH group is absent, and resins
having a molecular weight exceeding 100,000 and having an extremely small
amount of --OH group.
However, resins having --OH groups in side chains of molecular chains
discharge a large amount of gases.
Meanwhile, in the process to form the interlayer insulating film having the
three-layer structure in the above multilayer interconnection structure,
the inorganic silicon oxide film formed by, for example, the plasma CVD
method and the organic SOG film are concurrently etched in the etch back
or in the process to form the through-hole.
Hence, it is necessary to reduce the difference between etching rates of
the organic SOG film and the silicon oxide film. The organic SOG film and
the silicon oxide film are formed as adjacent interlayer films, and are
finally treated as the same layer.
In the etching process thereof, if two types of layers are concurrently
etched and two materials have considerably different etching rates, etched
surfaces of the two materials do not conform to each other. As a result,
it is impossible to provide a desired processed form.
For example, when the lower layer is flattened by the etch back method, it
is necessary to provide the same etching rate in upper and lower layers.
In reality, the etching rate of the organic SOG film is generally slower
than that of the inorganic SOG film in dry etching.
This is why the organic SOG film contains carbon. That is, in the dry
etching for etching inorganic materials, as the etched material has a
larger amount of carbon, the etching rate becomes more slowly.
Here, it is possible to provide a higher etching rate of carbon-containing
organic SOG film by using an oxygen-containing etching gas in the dry
etching.
As described before, if the same etching rate can be set in the dry etching
for the silicon oxide film made of the inorganic material and for the
organic SOG film made of organic material, the interlayer films in a
two-layer structure can be concurrently etched.
Further, a large amount of oxygen must be added to the etching gas in order
to etch resins such as silicone ladder series resins containing a large
amount of carbon at the same dry etching rate as that of the silicon oxide
film containing no carbon.
However, if a larger amount of oxygen is added, a greater amount of the
resist used as a mask is etched to form a pattern, resulting in a low
selection ratio of the silicone ladder series resins serving as the
etching target and the resists serving as the mask.
Consequently, since patterning such as formation of the through-hole is
interfered, an amount of added oxygen should be limited.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to
provide a semiconductor device having a multilayer interconnection
structure in which long-reliability of a wiring material, electric
characteristics, and so forth can be improved, and to provide a method of
fabrication thereof.
It is another object of the present invention to provide a method of
fabrication of a semiconductor device in which a process can be
simplified.
It is still another object of the present invention to provide a method of
fabrication of a semiconductor device in which a contact hole can be
successfully provided even when an interlayer insulating layer is formed
by a combination of an inorganic silicon oxide film and a flattening film
made of a silicone ladder polymer.
It is a further object of the present invention to provide a method of
fabrication of a semiconductor device in which etching can be carried out
by using a gas containing no oxygen.
It is a still further object of the present invention to provide a method
of fabrication of a semiconductor device in which it is possible to
provide the same etching selection ratio of a film and other layers, or
provide largely different selection ratios of the film and a resist mask
used at a time to form a pattern by the etching.
According to the first aspect of the present invention, for achieving the
above-mentioned objects, there is provided a semiconductor device in which
an interlayer insulating layer includes a flattening film made of silicone
ladder series resins, and the flattening film is a cured film made of
resin materials containing at least one of silicone ladder polymers which
are represented by the chemical formula:
(HO).sub.2 (R.sub.2 Si.sub.2 O.sub.3).sub.n H.sub.2
(where n denotes an integer which is sufficient to obtain a weight average
molecular weight of the compound in the range of 2,000 to 100,000; and R
represents any one of a hydrogen atom, a lower alkyl group, and a phenyl
group).
As stated above, in the semiconductor device according to the first aspect
of the present invention, the interlayer insulating layer includes the
flattening film (i.e., a cured film) made of the silicone ladder series
resins. Though the silicone ladder polymer can provide a good bond
performance to a primary coat because of "--OH" at its end of a molecular
chain, the silicone ladder polymer causes little gas discharge (i.e.,
little outgassing) adversely affecting other layers since "--OH" is absent
in its side chains.
According to the second aspect of the present invention, there is provided
a semiconductor device in which the resin material contains hydrogen
silsesquioxane.
According to the third aspect of the present invention, there is provided a
semiconductor device in which the flattening film contains a silicone
polymer containing hydroxy groups in side chains.
According to the fourth aspect of the present invention, there is provided
a semiconductor device in which the resin material contains a silane
coupling agent in the range of 150 to 100,000 ppm.
As stated above, in the semiconductor device according to the second to
fourth aspects of the present invention, the resin material contains
hydropen silsesquioxane, the silicone polymer containing the hydroxy
groups in the side chains, or the silane coupling agent in the range of
150 to 100,000 ppm. As a result, it is possible to improve a bond
performance between the cured film and an upper or lower layer.
According to the fifth aspect of the present invention, there is provided a
method of fabrication of a semiconductor device in which a resin material
is used containing silicone ladder polymers which are represented by the
chemical formula: (HO).sub.2 (R.sub.2 Si.sub.2 O.sub.3) .sub.n H.sub.2, an
organic solvent is added to the resin material to prepare and apply a
resinous solution having a resin concentration of 5 to 30 wt % so as to
form a coating film, and a flattening film is formed by thermosetting the
coating film.
As stated above, in the method of fabrication of the semiconductor device
according to the fifth aspect of the present invention, since the resinous
solution having the resin concentration of 5 to 30 wt % is used, it is
possible to provide a cured film having excellent flatness and a good
plugging performance.
According to the sixth aspect of the present invention, there is provided a
method of fabrication of a semiconductor device in which the resinous
solution contains one silicone ladder polymer having a high molecular
weight of 30,000 or more, and the other silicone ladder polymer which has
a low molecular weight less than 30,000 and is 20 wt % or more with
respect to the one silicone ladder polymer having the high molecular
weight.
As stated above, in the method of fabrication of the semiconductor device
according to the sixth aspect of the present invention, the resinous
solution is employed in which the one silicone ladder polymer having the
high molecular weight of 30,000 or more is mixed with the other silicone
ladder polymer having the low molecular weight less than 30,000.
Consequently, it is possible to enhance a bond performance of the silicone
ladder polymer to a primary coat. Further, it is thereby possible to
improve flatness and a plugging performance during coating.
According to the seventh aspect of the present invention, there is provided
a method of fabrication of a semiconductor device in which a resinous
solution contains hydrogen silsesquioxane.
According to the eighth aspect of the present invention, there is provided
a method of fabrication of a semiconductor device in which a resinous
solution contains a solution in which a silicone polymer containing
hydroxy groups in side chains is dissolved with a concentration in the
range of 5 to 40 wt %.
As stated above, in the method of fabrication of the semiconductor device
according to the seventh and eighth aspects of the present invention,
hydrogen silsesquioxane, or the silicone polymer containing hydroxy groups
in the side chains is used as the resinous solution. As a result, it is
possible to improve a bond performance to a primary coat, flatness and a
plugging performance of a cured film.
According to the ninth aspect of the present invention, there is provided a
method of fabrication of a semiconductor device in which a resinous
solution contains a silane coupling agent in the range of 150 to 100,000
ppm with respect to a resin content.
As stated above, in the method of fabrication of the semiconductor device
according to the ninth aspect of the present invention, the resinous
solution is used containing the silane coupling agent in the range of 150
to 100,000 ppm, resulting in an improved bond performance to a primary
coat.
According to the tenth aspect of the present invention, there is provided a
method of fabrication of a semiconductor device in which a carbon content
of a resinous solution is controlled to a predetermined value.
As stated above, in the method of fabrication of the semiconductor device
according to the tenth aspect of the present invention, the carbon content
is controlled to the predetermined value, thereby enabling control of an
etching rate. When an interlayer insulating layer includes an inorganic
silicon oxide film and a flattening film made of silicone series resin,
the same etching rate can be provided for the two films. The etching rate
can be held even in case of an etching gas containing a small amount of
oxygen or no oxygen.
According to the eleventh aspect of the present invention, there is
provided a method of fabrication of a semiconductor device, including the
additional step of modifying a surface of a resin film by decarbonization
processing.
As stated above, in the method of fabrication of the semiconductor device
according to the eleventh aspect of the present invention, the
decarbonization processing is carried out so that a surface of a silicone
ladder series resin film is modified to form an inorganic oxide film,
thereby enabling use of an etching gas containing no oxygen. It is thereby
possible to carry out highly accurate patterning, and provide a
through-hole in an interlayer film in a process employing typical dry
etching using the gas containing no oxygen.
According to the twelfth aspect of the present invention, there is provided
a method of fabrication of a semiconductor device, including the
additional step of forming an inorganic film made of silicon oxide on at
least any one of an upper layer and a lower layer of a resin film.
As stated above, in the method of fabrication of the semiconductor device
according to the twelfth aspect of the present invention, the inorganic
film is made of the silicon oxide so that an etching rate can be
controlled. Further, a contact hole can be formed by only one etching
process to have a side wall which is free from irregularity even when an
interlayer film has a multilayer structure including a silicone ladder
series resin film and the inorganic film made of silicon oxide.
The above and further objects and novel features of the invention will more
fully appear from the following detailed description when the same is read
in connection with the accompanying drawings. It is to be expressly
understood, however, that the drawings are for purpose of illustration
only and are not intended as a definition of the limits of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1(a) to 1(d) are sectional views showing a structure of a
semiconductor device according to one embodiment of the present invention;
FIGS. 2(a) to 2(d) are sectional views showing, in the order of process, a
method of fabrication of the semiconductor device according to one
embodiment of the present invention;
FIG. 3 is an explanatory view showing a relationship between a carbon
content of silicone resin and an etching rate;
FIGS. 4(a) to 4(d) are sectional views showing, in the order of process, a
method of fabrication of a semiconductor device according to another
embodiment of the present invention; and
FIGS. 5(a) to 5(d) are sectional views showing, in the order of process, a
method of fabrication of a conventional semiconductor device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A schematic description will now be given of the present invention.
The present invention is characterized by that a silicone ladder series
resin film is used as an interlayer insulating film in a multilayer
interconnection structure on a semiconductor substrate, and that a cured
film made of silicone ladder polymers which are represented by the
following chemical formula (I):
##STR1##
(where: R respectively denote the same or different hydrogen atoms, lower
alkyl groups, or phenyl groups; and n is an integer which is sufficient to
obtain a weight average molecular weight of 2,000 to 100,000) is employed
as silicone series resin. It is thereby possible to provide the interlayer
insulating film causing little outgassing and having excellent flatness by
only one coating.
Though the silicone ladder polymer can provide a good bond performance to a
primary coat because of "--OH" at an end of a molecular chain, the
silicone ladder polymer causes little gas discharge (i.e., little
outgassing) adversely affecting other layers since "--OH" is absent in its
side chains.
Further, the silicone ladder polymer exhibits poor resistance to crack in
case of molecular weight less than 2,000, and exhibits a poor plugging
performance in case of the molecular weight exceeding 100,000.
In this case, the cured film may contain hydrogen silsesquioxane, or a
silicone polymer containing hydroxyl groups in side chains. Alternatively,
the cured film may contain a silane coupling agent in the range of 150 to
100,000 ppm. It is thereby possible to improve a bond performance to upper
and lower layers.
On the other hand, according to the present invention, a flattening film is
formed by applying and thermosetting a resinous solution. The resinous
solution has such a composition that an organic solvent is added to the
silicone ladder polymer represented by the chemical formula (I) so as to
provide a concentration in the range of 5 to 30 weight percent
(hereinafter abbreviated wt %).
This is why the flatness becomes poor when a solid content concentration is
less than 5%, and the plugging performance is degraded in case of the
concentration exceeding 30%.
As the organic solvent, a solution may be used to contain any one of or
mixture of an aromatic series organic solvent, an alcohol series organic
solvent, an ester series organic solvent, an ether series organic solvent,
and a ketone series organic solvent.
As the aromatic series organic solvent, a solution may be used to contain
any one of or mixture of methoxybenzene, ethoxybenzene, toluene,
1,2,3,4-tetrahydronaphthalene, and so forth. As the alcohol series organic
solvent, a solution may be used to contain any one of or mixture of
methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol,
tert-butanol, and so forth. As the ester series organic solvent, a
solution may be used to contain any one of or mixture of methyl acetate,
ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl
acetate, sec-butyl acetate, pentyl acetate, isopentyl acetate, and so
forth.
Further, as the ketone series organic solvent, a solution may be used to
contain any one of or mixture of acetone, methyl ethyl ketone, methyl
isobutyl ketone, and cyclohexanone. As the ether series organic solvent, a
solution may be used to contain any one of or mixture of ethylene glycol
dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl
ether, diethylene glycol diethyl ether, and so forth.
According to the present invention, one silicone ladder polymer material
having a high molecular weight and the other silicone ladder polymer
having a low molecular weight are mixed together for the purpose of
improvement of a bond performance of the silicone ladder polymer to the
primary coat.
Preferably, one silicone ladder polymer having a weight average molecular
weight of 30,000 or more is mixed with another silicone ladder polymer
having a low molecular weight less than 30,000.
A type of the mixed silicone ladder polymer having the low molecular weight
may be identical with or different from a type of the silicone ladder
polymer having the high molecular weight. An amount of addition of the low
molecular weight material is preferably more than or equal to 20 wt % with
respect to the high molecular weight material.
The addition of the low molecular weight material is effective in, as well
as the bond performance to the primary coat, the flatness and the plugging
performance at the time of coating because of a variation generated in a
coating characteristic.
For the above purpose, it is also effective to add another inorganic or
organic solution (hereinafter referred to as inorganic SOG solution or
organic SOG solution) used for the SOG coating method, employing hydrogen
silsesquioxane, or a silicone polymer containing hydroxyl groups in side
chains.
An amount of addition of the hydrogen silsesquioxane is preferably in the
range of 20 to 60 wt % with respect to the silicone ladder polymer. The
amount less than 20 wt % can not provide an effect, and the amount
exceeding 60 wt % causes poor resistance to crack.
An amount of addition of the inorganic SOG solution or the organic SOG
solution is preferably in the range of 5 to 40 wt % with respect to
silicone ladder series resin coating liquid. The amount less than 5 wt %
can not provide an effect, and the amount exceeding 40 wt % may cause a
problem of wiring reliability due to a large amount of discharged gases.
The inorganic SOG solution used herein may include commercially available
OCD T-2 (produced and sold by Tokyo Ohka Kogyo Co., Ltd., available in
Japan: the same shall apply hereinafter), SF2700 (Sumitomo Chemical Co.,
Ltd.), HSG-2000 (Hitachi Chemical Co., Ltd.), and so forth.
Further, the organic SOG solution may include commercially available OCD
T-7 (Tokyo Ohka Kogyo Co., Ltd.), SF1000 (Sumitomo Chemical Co., Ltd.),
HSG-2200 (Hitachi Chemical Co., Ltd.), and so forth.
In addition, according to the present invention, a silane coupling agent in
the range of 150 to 100,000 ppm with respect to a resin content is added
to the silicone ladder series resin coating liquid in order to improve a
bond performance.
When an amount of addition of the silane coupling agent is less than 150
ppm, it is impossible to provide an effect of an improved bond
performance. The amount exceeding 100,000 ppm results in degraded film
quality of the silicone ladder series resin film after thermosetting and
forming the film.
As set forth above, in a method of patterning the silicone series resin
film, a dry etching is generally employed in which an oxygen-containing
gas mixed CF.sub.4 with CHF.sub.3 is used, and an etching rate ratio is
controlled by an amount of addition of the oxygen.
However, in this method, a variation in an oxygen content of the etching
gas may cause a major problem in selectivity of a resist used during the
patterning, and may adversely affect other processes.
For example, the silicone ladder polymer having the phenyl groups in side
chains of the chemical formula represented by the chemical formula (I) can
be effectively used for the interlayer film requiring heat resistance.
However, because of a high carbon content of the silicone ladder polymer,
a gas containing a large amount of oxygen is required as the etching gas
during the patterning.
Hence, since it is impossible to provide a large etching ratio of the
silicone ladder polymer and the resist mask used during the patterning,
accuracy of the patterning is lost.
After having studied a solution to overcome the problem, the present
inventors could find that the etching rate could be controlled by the
carbon content of the interlayer film.
This shows that, when a film is formed by the same process, the etching
rate of the silicone series resin depends upon only the carbon content of
the silicone resin, and is not affected by, for example, a structure of an
organic group forming the silicone resin.
That is, it is possible to control the carbon content by selecting a type
of the side chain of the silicone ladder polymer represented by the
chemical formula (I). The control can be also made by mixing two or more
types of silicone ladder polymers having different carbon contents.
Further, it is possible to adjust the carbon content by a mixing ratio of
the silicone ladder polymer and inorganic hydrogen silsesquioxane, or by
an amount of the inorganic SOG solution or the organic SOG solution which
is added to the silicone ladder series resin coating liquid.
On the other hand, for the above purpose, decarbonization processing may be
carried out to etch the organic SOG such as silicone ladder series resins
having a high carbon content. The processing includes plasma processing
using an inactive gas, and so forth.
The decarbonization processing modifies a surface of the silicone ladder
series resin film to form an inorganic oxide film so that an etching gas
containing no oxygen can be used in the dry etching for forming a pattern.
As a result, it is possible to provide a large etching ratio of the
silicone ladder series resin film and the resist mask used during the
patterning so as to enable highly accurate patterning, and to provide a
through-hole in the interlayer film by the process employing the typical
dry etching using the gas containing no oxygen.
Even when the interlayer film has a multilayer structure including the
silicone ladder series resin film and an inorganic film made of silicon
oxide by CVD, the same etching ratio can be provided for the silicone
ladder series resin film and the inorganic film by controlling the etching
rate as described above.
It is thereby possible to provide, by only one etching processing, a
contact hole whose side wall has no irregularity even in the interlayer
film having the multilayer structure including the silicone ladder series
resin film and the inorganic film made of the silicon oxide.
A detailed description will now be given of one embodiment of the present
invention referring to the accompanying drawings.
EXAMPLE 1
FIGS. 1(a) to 1(d) are sectional views partially showing a semiconductor
device according to one embodiment of the present invention.
In the drawings, reference numeral 1 means a silicon semiconductor
substrate with circuit elements, 2 is an insulating film formed on the
semiconductor substrate 1, 3 is a first Al wiring layer formed on the
insulating film 2, 4 is a silicon oxide film made by a plasma CVD method
to cover the first Al wiring layer 3, 5 is a resin film which was formed
on the silicon oxide film 4 and was made of the silicone ladder series
resins represented by the chemical formula (I) as described above, 6 is a
silicon oxide film formed on the resin film 5, and 7 is a second Al wiring
layer formed on the silicon oxide film 6.
The first Al wiring layer 3 and the second Al wiring layer 7 are connected
through a contact hole which was provided in an interlayer film at a
predetermined position, including the silicon oxide film 4, the resin film
5, the silicon oxide film 6, and so forth.
FIG. 1(a) shows a state in which the first Al wiring layer 3 and the second
Al wiring layer 7 are separated by the interlayer film having a
three-layer structure including the silicon oxide film 4, the resin film
5, the silicon oxide film 6, and so forth.
FIG. 1(b) shows a state in which the first Al wiring layer 3 and the second
Al wiring layer 7 are separated by the interlayer film having a two-layer
structure including the resin film 5, and the silicon oxide film 6.
FIG. 1(c) shows a state in which the first Al wiring layer 3 and the second
Al wiring layer 7 are separated by the interlayer film having a two-layer
structure including the silicon oxide film 4 and the resin film 5.
FIG. 1(d) shows a state in which the first Al wiring layer 3 and the second
Al wiring layer 7 are separated by the interlayer film including one
layer, i.e., the resin film 5.
The silicon oxide film was formed on or under the resin film 5 by the CVD
method or the like, thereby improving reliability of the semiconductor
device such as strength, or electric characteristic.
A description will now be given of a method of fabrication of the
semiconductor device shown in FIG. 1(a) referring to FIGS. 2(a) to 2(d).
In the first step, the insulating film 2 was formed on the semiconductor
substrate 1, and an Al film was deposited on the semiconductor substrate
by a sputtering method or the like. Further, a given photolithography
technique was used for patterning to form the first Al wiring layer 3.
Subsequently, the silicon oxide film 4 was formed by the plasma CVD method
on the first Al wiring layer 3 which was formed on the semiconductor
substrate 1.
The silicon oxide film 4 was spin-coated with a silicone ladder polymer
solution.
A main dissolved substance in the silicone ladder polymer solution was a
silicone ladder polymer which had a weight average molecular weight of
20,000, and is represented by the following chemical formula (II):
##STR2##
(where n denotes an integer which is sufficient to obtain the weight
average molecular weight of 20,000)
An n-butyl acetate/1-butanol (4/1) mixed solution was used as solvent of
the silicone ladder polymer solution, and the above substance is dissolved
to provide a concentration of 15 wt %.
Glycidoxypropyltrimethoxysilane (Model:"KBM-403E", a product of Shin-Etsu
Chemical Co., Ltd.) was employed as an additive to serve as a silane
coupling agent with a concentration of 1,000 ppm with respect to a
silicone ladder polymer resin content.
The silane coupling agent may be later added to the silicone ladder polymer
resinous solution as described above, or the silane coupling agent may be
initially dissolved in the solvent and thereafter the silicone ladder
polymer resin may be dissolved in the solvent. Alternatively, it is also
possible to mix one solution of the silane coupling agent with another
solution of the silicone ladder polymer resin.
The silicone ladder polymer solution was spin-coated, and was thereafter
heat-treated for thirty minutes at each of temperatures of 150.degree. C.
and 250.degree. C. The silicone ladder polymer solution was further
heat-treated at the temperature of 400.degree. C. for one hour, thereby
thermostting the applied silicone ladder polymer film to form the resin
film 5.
The silicone ladder polymer containing the hydroxyl groups in side chains,
represented by the chemical formula (II), is a method disclosed in
Japanese Patent Application No. 4-340638 which is incorporated herein in
its entirety.
The silicone ladder polymer produced according to the method was a
high-purity silicone ladder polymer containing 1 ppm or below of each of
sodium, potassium, iron, copper, lead and hydrogen chloride, and 1 ppb or
below of each of uranium and thorium, that is, having an extremely low
impurity content.
Hence, the interlayer insulating film made of the silicone ladder polymer
could exhibit excellent heat resistance, and contributed to improvement of
reliability b cause of good controllability and a little variation in
characteristics in a molecular weight distribution of 10 or less.
Next, as shown in FIG. 2(b), isotropic etching was made to the resin film 5
by a CF.sub.4 series gas to improve its flatness and eliminate or reduce a
thickness thereof above a wiring pattern of the first Al wiring layer 3.
Subsequently, the silicon oxide film 6 was formed on the resin film 5 by
the CVD method to form the interlayer insulating film having the
three-layer structure. As shown in FIG. 2(c), a predetermined position of
the interlayer insulating film having the three-layer structure was etched
according to a typical method to provide a con | | |
