U.S. patent application number 11/431000 was filed with the patent office on 2006-09-14 for material for forming insulating film with low dielectric constant, low dielectric insulating film, method for forming low dielectric insulating film and semiconductor device.
This patent application is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Hideo Nakagawa, Masaru Sasago.
Application Number | 20060202356 11/431000 |
Document ID | / |
Family ID | 29416829 |
Filed Date | 2006-09-14 |
United States Patent
Application |
20060202356 |
Kind Code |
A1 |
Nakagawa; Hideo ; et
al. |
September 14, 2006 |
Material for forming insulating film with low dielectric constant,
low dielectric insulating film, method for forming low dielectric
insulating film and semiconductor device
Abstract
A material for forming an insulating film with low dielectric
constant of this invention is a solution including a fine particle
principally composed of a silicon atom and an oxygen atom and
having a large number of pores, a resin and a solvent.
Inventors: |
Nakagawa; Hideo; (Shiga,
JP) ; Sasago; Masaru; (Osaka, JP) |
Correspondence
Address: |
McDermott Will & Emery LLP
600 13th Street, N.W.
Washington
DC
20005-3096
US
|
Assignee: |
Matsushita Electric Industrial Co.,
Ltd.
Osaka
JP
|
Family ID: |
29416829 |
Appl. No.: |
11/431000 |
Filed: |
May 10, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10437299 |
May 14, 2003 |
|
|
|
11431000 |
May 10, 2006 |
|
|
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Current U.S.
Class: |
257/783 ;
257/E23.144; 257/E23.167 |
Current CPC
Class: |
H01L 24/48 20130101;
H01L 2224/04042 20130101; H01L 2924/01029 20130101; H01L 2924/01006
20130101; H01L 2924/12044 20130101; H01L 2224/45099 20130101; H01L
24/03 20130101; H01L 2224/05556 20130101; H01L 21/02203 20130101;
H01L 21/312 20130101; H01L 2224/05599 20130101; H01L 2924/01005
20130101; H01L 21/02216 20130101; H01L 24/05 20130101; H01L
2924/00014 20130101; H01L 21/31695 20130101; H01L 21/7682 20130101;
H01L 2221/1047 20130101; H01L 2224/27416 20130101; H01L 2224/85424
20130101; H01L 2224/05093 20130101; H01L 2224/451 20130101; H01L
21/02282 20130101; H01L 23/5329 20130101; H01L 23/5222 20130101;
H01L 2224/48463 20130101; H01L 2224/451 20130101; H01L 2924/01013
20130101; H01L 21/02126 20130101; H01L 2924/01014 20130101; H01L
2924/01074 20130101; H01L 2224/48463 20130101; H01L 21/316
20130101; H01L 2924/00014 20130101; H01L 2924/00014 20130101; H01L
2924/01019 20130101; H01L 2224/85447 20130101; H01L 2924/00
20130101; H01L 2224/05599 20130101; H01L 2924/00014 20130101 |
Class at
Publication: |
257/783 |
International
Class: |
H01L 23/48 20060101
H01L023/48 |
Foreign Application Data
Date |
Code |
Application Number |
May 14, 2002 |
JP |
2002-137893 |
Claims
1-37. (canceled)
38. A low dielectric constant film comprising a fine particle
having a crystal structure including a bonding of a silicon atom
and an oxygen atom, wherein the fine particle includes a pore.
39. The low dielectric constant film of claim 38, wherein the fine
particle has a size equal to or more than 1 nm and equal to or less
than 30 nm.
40. The low dielectric constant film of claim 38, wherein the pore
in the fine particle has a size equal to or more than 0.5 nm and
equal to or less than 3 nm, and wherein the size of the fine
particle is bigger than the size of the pore.
41. The low dielectric constant film of claim 38, wherein the fine
particle has a zeolite crystal.
42. The low dielectric constant film of claim 38, wherein a rate of
the fine particle in the low dielectric constant film is higher
than 30 wt %.
43. A semiconductor device comprising: a low dielectric constant
film formed on a substrate; and an interconnect formed in the low
dielectric constant film, wherein the low dielectric constant film
includes a fine particle having a crystal structure including a
bonding of a silicon atom and an oxygen atom, and the fine particle
includes a pore.
44. The semiconductor device of claim 43, wherein the fine particle
has a size equal to or more than 1 nm and equal to or less than 30
nm.
45. The semiconductor device of claim 43, wherein the pore in the
particle has a size equal to or more than 0.5 nm and equal to or
less than 3 nm, wherein the size of the fine particle is bigger
than the size of the pore.
46. The semiconductor device of claim 43, wherein the fine particle
has a zeolite crystal.
47. The semiconductor device of claim 43, wherein a rate of the
fine particle in the low dielectric constant film is higher than 30
wt %.
48. The semiconductor device of claim 43, wherein a pad is formed
in the low dielectric constant film, and the pad is connected to
the interconnect.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a material for forming an
insulating film with low dielectric constant, an insulating film
with low dielectric constant, a method for forming an insulating
film with low dielectric constant and a semiconductor device
including an insulating film with low dielectric constant.
[0002] Recently, a multilayer interconnect structure including an
insulating film with low dielectric constant is necessary for
realizing refinement, a high-speed operation and a low power
consuming operation of a semiconductor device.
[0003] A conventional insulating film used in a multilayer
interconnect structure is, for example, a silicon oxide film having
a dielectric constant of approximately 4.2 or a silicon oxide film
doped with fluorine having a dielectric constant of approximately
3.7. Also, in order to further lower the low dielectric constant,
an organic component-containing silicon oxide film doped with a
methyl group (CHF.sub.3) is recently under examination.
[0004] It is, however, very difficult to lower the dielectric
constant of an organic component-containing silicon oxide film
below 2.5, and therefore, an insulating film having pores, namely,
what is called a porous film, is necessary.
[0005] Now, conventional technique for a porous film will be
described.
[0006] First, a first conventional example and a second
conventional example disclosed in Japanese Laid-Open Patent
Publication No. 2001-294815 will be described.
[0007] In the first conventional example, a porous film is formed
by baking a thin film made from a solution including a silicon
resin and an organic solvent. In this example, open pores are
randomly formed in portions where the organic solvent has been
vaporized in baking the thin film. In this case, the organic
solvent has a function as a solvent as well as a function to form
the pores. In general, a spin coating method is employed for
forming the thin film by applying the solution on a substrate, and
a hot plate and a furnace (electric furnace) are used for baking
the thin film.
[0008] In the second example, a porous film is formed by baking a
thin film made from a solution including not only a silicon resin
and an organic solvent but also a porogen of an organic substance.
In this example, not only open pores but also closed pores can be
formed through selection of the porogen. In this case, the porogen
is naturally vaporized to disappear from the resultant film.
[0009] Next, a third conventional example disclosed in Japanese
Laid-Open Patent Publication No. 8-181133 will be described.
[0010] A porous film of the third conventional example has
conceptually the most general structure and is formed by using a
solution as shown in FIG. 9. Specifically, as shown in FIG. 9, a
solution in which a silicon resin 102, a porogen 103 and a solvent
104 are mixed is contained in a vessel 101.
[0011] In the third conventional example, which is disclosed in
Japanese Laid-Open Patent Publication No. 8-181133, a porous film
is formed by baking a thin film made from a solution including a
fullerene such as C60 or C70, a silicon resin and an organic
solvent. In this case, a hollow portion of the fullerene becomes a
pore of the porous film.
[0012] As the silicon resin used in the first, second and third
conventional examples, an organic silicon resin such as
methylsilsesquioxane capable of lowering the dielectric constant as
compared with an inorganic silicon resin is used.
[0013] Now, an exemplified conventional method for forming a thin
film from a solution will be described with reference to FIGS. 10A
through 10F. In general, a substrate on which a thin film has been
formed by the spin coating method is baked with a hot plate or an
electric furnace.
[0014] First, as shown in FIG. 10A, a semiconductor wafer 112 is
placed on a spindle 111 connected to a rotation mechanism, and
thereafter, an appropriate amount of solution 114 used for forming
a porous film is dropped on the semiconductor wafer 112 from a
solution supply tube 113.
[0015] Next, as shown in FIG. 10B, the spindle 111 is rotated so as
to rotate the semiconductor wafer 112, and thus, the solution 114
is spread so as to form a thin film 115.
[0016] Then, as shown in FIG. 10C, the semiconductor wafer 112 on
which the thin film 115 has been formed is placed on and annealed
with a hot plate 116 so as to vaporize the solvent. This procedure
is generally designated as pre-bake and is performed at a
temperature of approximately 100.degree. C. for approximately 1
through 3 minutes.
[0017] Next, as shown in FIG. 10D, the semiconductor wafer 112 is
placed on a hot plate 117 to be annealed at a temperature of
approximately 200.degree. C. for 1 through 3 minutes. This
procedure is generally designated as soft bake.
[0018] Thereafter, as shown in FIG. 10E, the resultant
semiconductor wafer 112 is placed in an electric furnace 118, and
then, the temperature of the electric furnace 118 is increased to
approximately 400.degree. C. through 450.degree. C., so that
annealing can be performed at the highest set temperature for
approximately 1 hour. This procedure is generally designated as
hard bake, and when this procedure is completed, a porous film 115A
is formed on the semiconductor wafer 112. The hard bake can be
performed by using a hot plate. Also, in using some solution,
annealing is preferably performed, between the soft bake and the
hard bake, with a hot plate at an intermediate temperature between
the temperatures of the soft bake and the hard bake for
approximately 1 through 3 minutes.
[0019] FIG. 10F is an enlarged view of a portion surrounded with an
alternate long and short dash line in FIG. 10E. As is understood
from FIG. 10F, pores 119 (white portions in the drawing) are formed
in the porous film 115A formed on the semiconductor wafer 112.
[0020] The mechanical strength of the porous film 115A obtained
through nano-indentation evaluation is at most approximately 5 GPa
in the Young's modulus. With respect to insulating films that are
currently actually used in semiconductor devices, the modulus of a
silicon oxide film is approximately 78 GPa, the modulus of a
fluorine-containing silicon oxide film is approximately 63 GPa and
the modulus of an organic component-containing silicon oxide film
is approximately 10 GPa. Thus, the mechanical strength of the
porous film 115A is smaller than that of any other insulating film
used in a multilayer interconnect structure of a current
semiconductor device, and accordingly, a porous film with larger
mechanical strength is desired to be developed.
[0021] FIG. 11 shows the cross-sectional structure obtained in
bonding a wire to a semiconductor device that has a three-layer
interconnect structure and uses a conventional porous film as an
insulating film. In FIG. 11, a reference numeral 120 denotes a
semiconductor wafer, a reference numeral 121 denotes a porous film,
reference numerals 122, 124 and 126 denote metal interconnects,
reference numerals 123, 125, 126 and 128 denote via plugs and a
reference numeral 129 denotes a pad to be connected to an external
interconnect.
[0022] As shown in FIG. 11, when a wire 130 is bonded to the upper
face of the pad 129, a crack is caused in the pad 129 and the
multilayer interconnects.
[0023] The mechanical strength of the porous film 115A is necessary
for retaining multilayered interconnects stacked for forming a
multilayer structure as well as in bonding for mounting a chip of a
semiconductor device in a package as described above. In the case
where an organic component-containing silicon oxide film is used as
an insulating film, the mechanical strength is at a level of the
very limit of breakdown obtained in employing the current bonding
technique, and although the bonding technique is expected to be
further developed in the future, development of a porous film with
large mechanical strength is of urgent necessity.
[0024] In the first and second conventional examples, the open
pores are randomly formed. Therefore, in order to realize an
insulating film with a dielectric constant k of 2.2 through 2.3,
the Young's modulus of approximately 5 GPa or less in the
nano-indentation evaluation can be attained at most. This
mechanical strength depends upon the method for forming the film in
the first or second example. Specifically, the porogen and the
solvent are not present but the silicon resin alone is present in
the porous film after the bake, and therefore, the mechanical
strength of the porous film depends upon the original strength of
the silicon resin and the porosity (a ratio occupied by pores in a
unit volume). In the first or second conventional example, when the
dielectric constant is to be further lowered, the porosity is
increased, which further lowers the mechanical strength.
[0025] In the third conventional example, although the fullerene
remains in the porous film after the bake, the mechanical strength
basically depends upon the strength of the silicon resin including
the fullerene and hence is at the same level as that attained in
the first or second conventional example. Also, when the content of
the fullerene exceeds approximately 30 wt %, the fullerenes are
connected to each other, and therefore, the mechanical strength is
further lowered.
[0026] As described so far, a practically usable rigid film cannot
be obtained by any of the conventional methods for forming a porous
film because there is a limit in the mechanical strength of the
structure itself of the porous film of a silicon resin.
[0027] Also, a conventional porous film can attain merely
mechanical strength much lower than the mechanical strength
necessary for a semiconductor device, and when the dielectric
constant of the porous film is to be lowered, the mechanical
strength is disadvantageously lowered.
[0028] As a result, in the case where a conventional porous film is
actually used in a multilayer interconnect structure of a
semiconductor device, there arise a problem that a semiconductor
device with sufficient strength cannot be fabricated and a problem
that even when a semiconductor chip can be fabricated, the
semiconductor device cannot be completed because it is broken in
mounting the chip in a package.
SUMMARY OF THE INVENTION
[0029] In consideration of the aforementioned conventional
problems, an object of the invention is increasing the mechanical
strength of an insulating film with low dielectric constant made of
a porous film.
[0030] In order to achieve the object, the first material for
forming an insulating film with low dielectric constant of this
invention includes a solution containing a fine particle that is
principally composed of a silicon atom and an oxygen atom and has a
large number of pores; a resin; and a solvent.
[0031] In using the first material for forming an insulating film
with low dielectric constant, an insulating film having a low
dielectric constant and large mechanical strength can be easily and
definitely formed.
[0032] In the first material for forming an insulating film with
low dielectric constant, the fine particle preferably has a size
more than approximately 1 nm and less than approximately 30 nm.
[0033] Thus, when the resultant low dielectric insulating film is
provided between metal interconnects, an interconnect groove with a
good cross-sectional shape can be formed in the low dielectric
insulating film if the metal interconnects are buried
interconnects, and a smooth insulating film free from a gap can be
formed if the metal interconnects are patterned interconnects.
[0034] In the first material for forming an insulating film with
low dielectric constant, each of the pores in the fine particle
preferably has a size more than approximately 0.5 nm and less than
approximately 3 nm.
[0035] Thus, a large number of pores can be definitely formed
within the fine particle.
[0036] In the first material for forming an insulating film with
low dielectric constant, the pores in the fine particle may be
partially confined or isolated.
[0037] In the first material for forming an insulating film with
low dielectric constant, the fine particle is preferably formed by
mechanically crushing a substance having a plurality of open pores
randomly distributed.
[0038] Thus, the fine particle having a large number of open pores
can be definitely obtained.
[0039] In the first material for forming an insulating film with
low dielectric constant, the fine particle is preferably formed by
mechanically crushing a substance having a large number of closed
pores substantially uniformly dispersed.
[0040] Thus, the fine particle having a large number of closed
pores can be definitely obtained.
[0041] In the first material for forming an insulating film with
low dielectric constant, the fine particle is preferably
synthesized through a chemical reaction.
[0042] Thus, the fine particle with a uniform size can be
definitely obtained.
[0043] In the first material for forming an insulating film with
low dielectric constant, the resin is preferably a silicon
resin.
[0044] Thus, the mechanical strength of the resultant low
dielectric insulating film can be further increased.
[0045] In this case, the silicon resin preferably includes organic
silicon.
[0046] Thus, the mechanical strength can be increased as well as
the dielectric constant can be lowered in the resultant low
dielectric insulating film.
[0047] In the first material for forming an insulating film with
low dielectric constant, the resin is preferably an organic
polymer.
[0048] Thus, the dielectric constant of the resultant low
dielectric insulating film can be further lowered.
[0049] In the first material for forming an insulating film with
low dielectric constant, the solution preferably further includes a
compound for reinforcing bond between the resin and the fine
particle.
[0050] Thus, the mechanical strength of the resultant low
dielectric insulating film can be further increased.
[0051] The second material for forming an insulating film with low
dielectric constant of this invention includes a fine particle, and
the fine particle is formed by mechanically crushing a substance
that is principally composed of a silicon atom and an oxygen atom
and has a plurality of open pores randomly distributed, and the
fine particle has a large number of pores formed by the plurality
of open pores.
[0052] In using the second material for forming an insulating film
with low dielectric constant, an insulating film having a low
dielectric constant and large mechanical strength can be formed. In
this case, conditions in the temperature, the pressure and the
fabrication atmosphere, which are restricted in using a
conventional porous film, are not restricted in the fabrication
process for a semiconductor device. Therefore, the degree of
freedom in producing the substance having randomly distributed open
pores is increased, so that a fine particle with large mechanical
strength can be obtained.
[0053] The third material for forming an insulating film with low
dielectric constant of this invention includes a fine particle, and
the fine particle is formed by mechanically crushing a substance
that is principally composed of a silicon atom and an oxygen atom
and has a large number of closed pores substantially uniformly
dispersed, and the fine particle has a large number of pores formed
by the closed pores.
[0054] In using the third material for forming an insulating film
with low dielectric constant, an insulating film having a low
dielectric constant and large mechanical strength can be formed. In
this case, conditions in the temperature, the pressure and the
fabrication atmosphere, which are restricted in using a
conventional porous film, are not restricted in the fabrication
process for a semiconductor device. Therefore, the degree of
freedom in producing the substance having substantially uniformly
dispersed closed pores is increased, so that a fine particle with
large mechanical strength can be obtained.
[0055] The fourth material for forming an insulating film with low
dielectric constant of this invention includes a fine particle, and
the fine particle is synthesized through a chemical reaction, is
principally composed of a silicon atom and an oxygen atom and has a
large number of pores.
[0056] In using the fourth material for forming an insulating film
with low dielectric constant, an insulating film having a low
dielectric constant and large mechanical strength can be formed. In
this case, conditions in the temperature, the pressure and the
fabrication atmosphere, which are restricted in using a
conventional porous film, are not restricted in the fabrication
process for a semiconductor device. Therefore, the degree of
freedom in producing a substance having a large number of pores is
increased, so that a fine particle with large mechanical strength
can be obtained.
[0057] The method for forming an insulating film with low
dielectric constant of this invention includes the steps of forming
a thin film by applying, on a substrate, a solution including a
fine particle principally composed of a silicon atom and an oxygen
atom and having a large number of pores, a resin and a solvent; and
annealing the substrate for evaporating the solvent, whereby
forming an insulating film with low dielectric constant out of the
thin film.
[0058] In the method for forming an insulating film with low
dielectric constant of this invention, the low dielectric
insulating film is formed by evaporating the solvent from the thin
film made from the solution including the fine particle, the resin
and the solvent by annealing the substrate. Therefore, the low
dielectric insulating film has a structure in which the fine
particle having a large number of pores is introduced into a
structure of the resin and hence attains a low dielectric constant
and large mechanical strength. Also, when the ratio of the fine
particle in the solution is increased, the dielectric constant can
be lowered without lowering the mechanical strength.
[0059] In the method for forming an insulating film with low
dielectric constant, the fine particle preferably has a size more
than approximately 1 nm and less than approximately 30 nm.
[0060] Thus, when the resultant low dielectric insulating film is
provided between metal interconnects, an interconnect groove with a
good cross-sectional shape can be formed in the low dielectric
insulating film if the metal interconnects are buried
interconnects, and a smooth insulating film free from a gap can be
formed if the metal interconnects are patterned interconnects.
[0061] In the method for forming an insulating film with low
dielectric constant, each of the pores in the fine particle
preferably has a size more than approximately 0.5 nm and less than
approximately 3 nm.
[0062] Thus, a large number of pores can be definitely formed
within the fine particle.
[0063] In the method for forming an insulating film with low
dielectric constant, the resin is preferably a silicon resin.
[0064] Thus, the mechanical strength of the resultant low
dielectric insulating film can be further increased.
[0065] In this case, the silicon resin preferably includes organic
silicon.
[0066] Thus, the mechanical strength can be increased as well as
the dielectric constant can be lowered in the resultant low
dielectric insulating film.
[0067] In the method for forming an insulating film with low
dielectric constant, the resin is preferably an organic
polymer.
[0068] Thus, the dielectric constant of the resultant low
dielectric insulating film can be further lowered.
[0069] In the method for forming an insulating film with low
dielectric constant, the solution preferably further includes a
compound for reinforcing bond between the resin and the fine
particle.
[0070] Thus, the mechanical strength of the resultant low
dielectric insulating film can be further increased.
[0071] In the method for forming an insulating film with low
dielectric constant, the step of annealing the substrate preferably
includes a sub-step of bonding the fine particle to the resin.
[0072] Thus, the mechanical strength of the low dielectric
insulating film can be further increased.
[0073] The low dielectric insulating film of this invention
includes a fine particle principally composed of a silicon atom and
an oxygen atom and having a large number of pores; and a resin
bonded to the fine particle.
[0074] Since the low dielectric insulating film of this invention
has a structure in which the resin and the fine particle having a
large number of pores are bonded to each other, it attains a low
dielectric constant and large mechanical strength.
[0075] In the low dielectric insulating film, the fine particle
preferably has a size more than approximately 1 nm and less than
approximately 30 nm.
[0076] Thus, when the low dielectric insulating film is provided
between metal interconnects, an interconnect groove with a good
cross-sectional shape can be formed in the low dielectric
insulating film if the metal interconnects are buried
interconnects, and a smooth insulating film free from a gap can be
formed if the metal interconnects are patterned interconnects.
[0077] In the low dielectric insulating film, each of the pores in
the fine particle preferably has a size more than approximately 0.5
nm and less than approximately 3 nm.
[0078] Thus, a large number of pores can be definitely formed
within the fine particle.
[0079] In the low dielectric insulating film, the resin is
preferably a silicon resin.
[0080] Thus, the mechanical strength of the low dielectric
insulating film can be further increased.
[0081] In this case, the silicon resin preferably includes organic
silicon.
[0082] Thus, the mechanical strength can be increased as well as
the dielectric constant can be lowered in the low dielectric
insulating film.
[0083] In the low dielectric insulating film, the resin is
preferably an organic polymer. Thus, the dielectric constant of the
low dielectric insulating film can be further lowered.
[0084] In the low dielectric insulating film, the solution
preferably further includes a compound for reinforcing bond between
the resin and the fine particle.
[0085] Thus, the mechanical strength of the low dielectric
insulating film can be further increased.
[0086] The semiconductor device of this invention includes a
plurality of metal interconnects; and an insulating film with low
dielectric constant formed between the plurality of metal
interconnects, and the low dielectric insulating film includes a
fine particle principally composed of a silicon atom and an oxygen
atom and having a large number of pores, and a resin bonded to the
fine particle. The plural metal interconnects herein may be a lower
metal interconnect and an upper metal interconnect or adjacent
metal interconnects formed in one interconnect layer.
[0087] In the semiconductor device of this invention, even when the
dielectric constant of the low dielectric insulating film is
lowered, its mechanical strength is large, and therefore, cracks
can be prevented from being caused in the metal interconnects.
[0088] In the semiconductor device, the fine particle preferably
has a size more than approximately 1 nm and less than approximately
30 nm.
[0089] Thus, an interconnect groove with a good cross-sectional
shape can be formed in the low dielectric insulating film if the
metal interconnects are buried interconnects, and a smooth
insulating film free from a gap can be formed if the metal
interconnects are patterned interconnects.
[0090] In the semiconductor device, each of the pores in the fine
particle preferably has a size more than approximately 0.5 nm and
less than approximately 3 nm.
[0091] Thus, a large number of pores can be definitely formed
within the fine particle.
[0092] In the semiconductor device, the resin is preferably a
silicon resin.
[0093] Thus, the mechanical strength of the low dielectric
insulating film can be further increased.
[0094] In this case, the silicon resin preferably includes organic
silicon.
[0095] Thus, the mechanical strength can be increased as well as
the dielectric constant can be lowered in the low dielectric
insulating film.
[0096] In the semiconductor device, the resin is preferably an
organic polymer.
[0097] Thus, the dielectric constant of the low dielectric
insulating film can be further lowered.
[0098] In the semiconductor device, the low dielectric insulating
film preferably further includes a compound for reinforcing bond
between the resin and the fine particle.
[0099] Thus, the mechanical strength of the low dielectric
insulating film can be further increased.
BRIEF DESCRIPTION OF THE DRAWINGS
[0100] FIG. 1 is a cross-sectional view of a solution that is a
material for forming an insulating film with low dielectric
constant according to Embodiment 1 of the invention;
[0101] FIGS. 2A and 2B are cross-sectional views of a fine particle
of a material for forming an insulating film with low dielectric
constant according to Embodiment 2 of the invention;
[0102] FIGS. 3A and 3B are cross-sectional views of a fine particle
of a material for forming an insulating film with low dielectric
constant according to Embodiment 3 of the invention;
[0103] FIGS. 4A, 4B and 4C are cross-sectional views of fine
particles of a material for forming an insulating film with low
dielectric constant according to Embodiment 4 of the invention;
[0104] FIGS. 5A, 5B, 5C, 5D and 5E are cross-sectional views for
showing procedures in a method for forming an insulating film with
low dielectric constant according to Embodiment 5 of the
invention;
[0105] FIGS. 6A and 6B are cross-sectional views of low dielectric
insulating films according to Embodiment 6 of the invention;
[0106] FIGS. 7A and 7B are cross-sectional views of the low
dielectric insulating film according to Embodiment 6 of the
invention;
[0107] FIG. 8 is a cross-sectional view of a semiconductor device
according to Embodiment 7 of the invention;
[0108] FIG. 9 is a conceptual diagram of a solution used for
forming a conventional porous film;
[0109] FIGS. 10A, 10B, 10C, 10D, 10E and 10F are cross-sectional
views for showing procedures in a method for forming a conventional
porous film; and
[0110] FIG. 11 is a cross-sectional view for explaining a problem
occurring in a semiconductor device using the conventional porous
film.
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1
[0111] Embodiment 1 of the invention will now be described with
reference to FIG. 1. In Embodiment 1, a material for forming an
insulating film with low dielectric constant is embodied as a
solution.
[0112] As shown in FIG. 1, the solution according to Embodiment 1
is contained in a vessel 1, and includes a silicon resin 2
corresponding to a resin, fine particles 3 each having a large
number of pores and a solvent 4.
[0113] As the silicon resin 2, inorganic silicon, organic silicon
or a mixture of them can be used. When organic silicon is used, the
dielectric constant of a resultant low dielectric insulating film
can be further lowered.
[0114] The fine particles 3 having a large number of pores are made
from a compound principally formed through bonding between a
silicon atom and an oxygen atom, and the pores may be communicated
with or independent of one another.
[0115] First, a method for preparing the fine particles 3 having a
large number of open (communicated) pores will be described.
[0116] Such fine particles 3 can be prepared by crushing
meso-porous silica or a zeolite crystal with regularity such as a
honeycomb structure. Alternatively, the bake temperature (the hard
bake temperature) employed in forming a porous film or a porous
structure described in the first or second conventional example is
increased to be higher than in the first or second conventional
example, so as to obtain a porous film or a porous structure in
which the crosslinkage between silicon resins is reinforced, and
this porous film or porous structure can be crushed to give the
fine particles 3. Alternatively, colloidal silica, and spherical
colloidal silica in particular, obtained through hydrolysis of
alkoxysilane, such as tetramethoxysilane or tetraethoxysilane, can
be used as the fine particles 3.
[0117] Next, a method for preparing the fine particles 3 having a
large number of closed (independent) pores will be described.
[0118] Such fine particles can be prepared by crushing a porous
film or a porous structure formed by using fine particles of an
organic polymer as a porogen. Also in this case, the bake
temperature employed in forming a porous film or a porous structure
described in the first or second conventional example is increased
to be higher than in the first or second conventional example, so
as to obtain a porous film or a porous structure in which the
crosslinkage between silicon resins is reinforced, and this porous
film or porous structure can be crushed to give the fine particles
3. Alternatively, the fine particles 3 may have a structure in
which colloidal silica, and spherical colloidal silica in
particular, is adhered around an organic polymer working as a
nuclear.
[0119] In either case, the fine particle 3 preferably has a size
more than approximately 1 nm and less than approximately 30 nm, and
each pore of the fine particle 3 preferably has a size more than
approximately 0.5 nm and less than approximately 3 nm.
[0120] The solvent 4 may be a solvent that is substantially
completely evaporated at the temperatures of the pre-bake and the
soft bake, and examples are alcohols such as methanol, ethanol and
isopropyl alcohol; and organic solvents such as cyclohexane, NMP
(N-methylpyrolidone), PGMEA (propylene glycol monomethyl ether
acetate), PGME (propylene glycol monomethyl ether) and PGMPE
(propylene glycol monopropyl ether).
Embodiment 2
[0121] Embodiment 2 of the invention will now be described with
reference to FIGS. 2A and 2B. In Embodiment 2, a material for
forming an insulating film with low dielectric constant is embodied
as a fine particle.
[0122] FIG. 2A shows a porous structure 5 used for preparing fine
particles 6, and FIG. 2B shows the fine particles 6 prepared by
crushing the porous structure 5.
[0123] The porous structure 5 has a plurality of open pores
randomly distributed therein, and the fine particles 6 each having
a large number of pores can be obtained by mechanically crushing
the porous structure 5. In order to mechanically crush the porous
structure 5, the porous structure 5 may be crushed through
collision with a rapidly rotating blade or the porous structure 5
contained in a sealed vessel is allowed to collide with the inner
wall of the sealed vessel. When the fine particles 6 are prepared
in such a manner, the resultant fine particles are in a variety of
sizes, and therefore, the fine particles 6 are preferably selected
from these fine particles so as to be in a size more than
approximately 1 nm and less than approximately 30 nm.
[0124] As the porous structure 5, meso-porous silica or zeolite
crystal with regularity such as a honeycomb structure can be used.
Alternatively, the bake temperature (the hard bake temperature)
employed in forming a porous film or a porous structure described
in the first or second conventional example is increased to be
higher than in the first or second conventional example, so as to
obtain a porous film or a porous structure in which the
crosslinkage between silicon resins is reinforced, and this porous
film or porous structure may be used as the porous structure 5.
[0125] Each pore of the fine particle 6 preferably has a size more
than approximately 0.5 nm and less than approximately 3 nm.
Embodiment 3
[0126] Embodiment 3 of the invention will now be described with
reference to FIGS. 3A and 3B. In Embodiment 3, a material for
forming an insulating film with low dielectric constant is embodied
as a fine particle 8.
[0127] FIG. 3A shows a porous structure 7 used for preparing fine
particles 8 and FIG. 3B shows the fine particles 8 prepared by
crushing the porous structure 7.
[0128] The porous structure 7 has a large number of closed pores
substantially uniformly dispersed therein, and the fine particles 8
each having a large number of pores can be obtained by mechanically
crushing the porous structure 7. In order to mechanically crush the
porous structure 7, the porous structure 7 may be crushed through
collision with a rapidly rotating blade or the porous structure 7
contained in a sealed vessel is allowed to collide with the inner
wall of the sealed vessel. When the fine particles 8 are prepared
in such a manner, the resultant fine particles are in a variety of
sizes, and therefore, the fine particles 8 are preferably selected
from these fine particles so as to be in a size more than
approximately 1 nm and less than approximately 30 nm.
[0129] The porous structure 7 may be a porous film or a porous
structure formed by using fine particles of an organic polymer as a
porogen. Also in this case, when the bake temperature is set to be
higher than that employed in the first or second conventional
example, the resultant porous structure 7 can attain large
mechanical strength. Each pore of the fine particle 8 preferably
has a size more than approximately 0.5 nm and less than
approximately 3 nm.
Embodiment 4
[0130] Embodiment 4 of the invention will now be described with
reference to FIGS. 4A through 4C. In Embodiment 4, a material for
forming an insulating film with low dielectric constant is embodied
as a fine particle synthesized through a chemical reaction.
[0131] FIG. 4A shows a first fine particle 10A that is synthesized
through a chemical reaction and has a large number of pores. The
first fine particle 10A is a fine particle 9a of colloidal silica,
and particularly spherical colloidal silica, produced through
hydrolysis of alkoxysilane such as tetramethoxysilane or
tetraethoxysilane, and the fine particle 9a has a large number of
pores. The fine particle 9a may be a fine particle of meso-porous
silica or zeolite crystal instead of the colloidal silica.
[0132] FIG. 4B shows a second fine particle 10B that is synthesized
through a chemical reaction and has a large number of pores. The
second fine particle 10B has a structure in which fine particles 9a
each having a large number of pores are substantially uniformly
adhered around an organic polymer 10a with a relatively small
diameter. The fine particle 9a may be colloidal silica produced
through the hydrolysis of alkoxysilane such as tetramethoxysilane
or tetraethoxysilane. Alternatively, the fine particle 9a may be a
fine particle of meso-porous silica or zeolite crystal instead of
the colloidal silica. Furthermore, the fine particle 9a and the
organic polymer 10a may be in a spherical or polyhedral shape.
[0133] FIG. 4C shows a third fine particle 10C that is synthesized
through a chemical reaction and has a large number of pores. The
third fine particle 10C has a structure in which fine particles 9a
each having a large number of pores are substantially uniformly
adhered around an organic polymer 10b with a relatively large
diameter. The fine particle 9a may be colloidal silica produced
through the hydrolysis of alkoxysilane such as tetramethoxysilane
or tetraethoxysilane. Alternatively, the fine particle 9a may be a
fine particle of meso-porous silica or zeolite crystal instead of
the colloidal silica. Furthermore, the fine particle 9a and the
organic polymer 10b may be in a spherical or polyhedral shape.
Moreover, the fine particles 9a are preferably adhered around the
organic polymer 10b not substantially uniformly but in special
arrangement for increasing the mechanical strength of the third
fine particle 10C.
[0134] The first, second or third fine particle 10A, 10B or 10C
preferably has a size more than approximately 1 nm and less than
approximately 30 nm, and each pore of the fine particle 9a
preferably has a size more than approximately 0.5 nm and less than
approximately 3 nm.
Embodiment 5
[0135] Embodiment 5 of the invention will now be described with
reference to FIGS. 5A through 5E. In Embodiment 5, an insulating
film with low dielectric constant and a method for forming the same
by using the solution according to Embodiment 1 are embodied.
[0136] First, as shown in FIG. 5A, the solution according to
Embodiment 1 is prepared. Specifically, a solution including a
silicon resin 2, fine particles 3 described in any of Embodiments 2
through 4 and a solvent 4 is contained in a vessel 1. Then, a
semiconductor wafer 12 is placed on a spindle 11 connected to a
rotation mechanism, and an appropriate amount of solution 14 is
dropped on the semiconductor wafer 12 from a solution supply tube
13 connected to the vessel 1.
[0137] Then, as shown in FIG. 5B, the spindle 11 is rotated so as
to rotate the semiconductor wafer 12, and thus, the solution 14 is
spread to form a thin film 15.
[0138] Next, as shown in FIG. 5C, the semiconductor wafer 12 on
which the thin film 15 has been formed is placed on a hot plate 16
and annealed for evaporating the solvent. This procedure is
generally designated as pre-bake, and is performed at a temperature
of approximately 100.degree. C. for approximately 1 through 3
minutes.
[0139] Thereafter, as shown in FIG. 5D, the semiconductor wafer 12
is placed on a hot plate 17 and annealed at a temperature of
approximately 200.degree. C. for approximately 1 through 3 minutes.
This procedure is generally designated as soft bake.
[0140] Next, as shown in FIG. 5E, after placing the semiconductor
wafer 12 in an electric furnace 18, the temperature of the electric
furnace 18 is increased to approximately 400.degree. C. through
450.degree. C., and then, annealing is performed at the highest set
temperature for approximately 1 hour. This procedure is generally
designated as hard bake, and when this procedure is completed, an
insulating film with low dielectric constant 15A including the
silicon resin 2 and the fine particles 3 is formed on the
semiconductor wafer 12. The hard bake may be performed by using a
hot plate. Also, annealing is preferably performed with a hot plate
between the soft bake and the hard bake at an intermediate
temperature between the temperatures of the soft bake and the hard
bake for approximately 1 through 3 minutes.
[0141] In Embodiment 5, the silicon resin 2 is substantially
stabilized in its structure because a basic siloxane structure is
almost formed during the soft bake, and siloxane skeletons are
crosslinked during the subsequent hard bake, so that the low
dielectric insulating film 15A can be rigid and attain large
mechanical strength. In other words, the silicon resins 2 are
bonded to one another during the soft bake and the fine particles 3
each having a large number of pores and the silicon resin 2 are
bonded to each other.
[0142] In this manner, the low dielectric insulating film 15A of
Embodiment 5 has a structure in which the silicon resin 2 and the
fine particles 3 having pores are rigidly bonded to each other.
Accordingly, the low dielectric insulating film 15A is a porous
film with toughness and large mechanical strength as compared with
a siloxane structure made from a silicon resin alone.
Embodiment 6
[0143] Embodiment 6 of the invention will now be described with
reference to FIGS. 6A, 6B, 7A and 7B. Also in Embodiment 6, an
insulating film with low dielectric constant and a method for
forming the same by using the solution according to Embodiment 1
are embodied.
[0144] When an insulating film with low dielectric constant is
formed by the method described in Embodiment 5, the state in which
the pores are formed in the low dielectric insulating film is
varied depending upon the molecular structure of the solvent.
Specifically, in the case (1) where a solvent that is substantially
completely evaporated through the pre-bake; such as alcohol, is
used, substantially no pores other than a large number of pores
present within the fine particles is formed. However, in the case
(2) where a solvent that is not completely evaporated during the
pre-bake but is completely evaporated during the soft bake is used
and the solvent is composed of straight chain molecules or
molecules with a structure approximate to a straight chain, open
pores are likely to be formed in a portion corresponding to the
silicon resin in addition to a large number of pores present within
the fine particles. In this manner, the state of pores formed in an
insulating film with low dielectric constant depends upon the kind
of solvent. This will now be described with reference to FIGS. 6A
and 6B.
[0145] FIG. 6A shows the cross-sectional structure of a first low
dielectric insulating film 21 formed on a semiconductor wafer 20,
and the first low dielectric insulating film 21 includes a silicon
resin 21 having pores and fine particles 23 each having a large
number of pores. In the drawing, a white portion inside the silicon
resin 21 corresponds to a pore. In the first dielectric insulating
film 21, there are a large number of pores present within the fine
particles 23 and open pores formed in the silicon resin 21, and
hence, the first dielectric insulating film 21 is a porous film
having open pores as a whole.
[0146] FIG. 6B shows the cross-sectional structure of a second low
dielectric insulating film 24 formed on a semiconductor wafer 20,
and the second low dielectric insulating film 24 includes a silicon
resin 24 having no pores and fine particles 23 each having a large
number of pores. In the second low dielectric insulating film 24,
there is no pore in the silicon resin 24, and hence, the second low
dielectric insulating film 24 is a porous film having a large
number of closed pores as a whole.
[0147] FIG. 7A shows a first state of the first low dielectric
insulating film 21 of FIG. 6A, and the first state is obtained by
using a material for forming an insulating film with low dielectric
constant in which the ratio of the fine particles 23 in the solute
is lower than approximately 30 through 50 wt %. In the first state,
a structure of the silicon resin 22 is the majority, the fine
particles 23 having pores are present in this structure, and the
structure of the silicon resin 22 is rigidly bonded to the fine
particles 23 having pores. In the case where the fine particles 23
with larger mechanical strength than the silicon resin 22 are
introduced into the structure of the silicon resin 22 as in the
first state, the resultant film can attain much larger mechanical
strength than a structure composed of the silicon resin 22
alone.
[0148] FIG. 7B shows a second state of the first low dielectric
insulating film 21 of FIG. 6A, and the second state is obtained by
using a material for forming an insulating film with low dielectric
constant in which the ratio of the fine particles 23 in the solute
is higher than approximately 30 through 50 wt %. In the second
state, the fine particles 23 having pores correspond to the main
skeleton of the first low dielectric insulating film 21, and the
adjacent fine particles 23 are bonded to each other through a
structure of the silicon resin 22. In the second state, the fine
particles 23 with larger mechanical strength than the silicon resin
22 are introduced into the structure of the silicon resin 22
similarly to the first state. Therefore, the resultant film can
attain much larger mechanical strength than the structure composed
of the silicon resin 22 alone, and in addition, since the ratio of
the fine particles 23 having pores is higher than in the first
state, the low dielectric constant is further lowered.
[0149] As described so far, in the low dielectric insulating film
according to Embodiment 5 or 6, fine particles each having a large
number of pores are introduced into a structure of a silicon resin,
and therefore, the low dielectric insulating film can be formed as
a porous film having a dielectric constant as low as approximately
2.5 or less and large mechanical strength. The mechanical strength
of the low dielectric insulating film according to Embodiment 5 or
6 is approximately 6 GPa or more in the Young's modulus.
[0150] In other words, in the low dielectric insulating film of
Embodiment 5 or 6, the fine particles having a large number of
pores and introduced for forming pores in the film do not disappear
during the formation but remain in the resultant porous film and
are strongly bonded to the structure of the silicon resin.
Therefore, when the ratio of the fine particles having pores in the
solution is increased to 30 wt % or more so as to further lower the
dielectric constant by increasing the porosity of the low
dielectric insulating film, the mechanical strength is not lowered
differently from the case where a fullerene is used but rather
increased.
[0151] When organic silicon in which silicon and an organic group
such as a methyl group are bonded to each other or a silicon resin
including organic silicon is used as the silicon resin, the
dielectric constant of the resultant low dielectric insulating film
can be further lowered.
[0152] Also, when an organic polymer such as a polymer formed
through an aryl-ether bond or an aryl-aryl bond is used instead of
the silicon resin, the dielectric constant of the resultant
dielectric insulating film can be further lowered. This is because
MSQ in a bulk has a dielectric constant of approximately 2.9 while
the organic polymer in a bulk has a dielectric constant as low as
2.6. Therefore, since this relationship holds also in a porous film
in which a silicon resin and an organic polymer have pores, the
dielectric constant can be easily lowered by using an organic
polymer instead of the silicon resin.
[0153] Also, in the first state of the first low dielectric
insulating film 21 shown in FIG. 7A, when a compound for
reinforcing the bond between the silicon resin and the fine
particles is additionally used, the mechanical strength can be
further increased.
[0154] Furthermore, in the second state of the first low dielectric
insulating film 21 shown in FIG. 7B, when a compound for
reinforcing the bond between the fine particles included in the
silicon resin is additionally used, the mechanical strength can be
further increased.
[0155] An example of the compound for reinforcing the bond between
the silicon resin and the fine particles is alkoxysilane. For
example, two methyl groups (CH.sub.3--) and two methoxy groups
(CH.sub.3O--) are bonded to silicon (Si) in
dimethyldimethoxysilane, and therefore, the crosslinkage between
the silicon resin and the fine particles can be accelerated in the
soft bake and the hard bake performed in forming the film. Also,
since alkoxysilane can accelerate the crosslinkage between fine
particles as well as the crosslinkage between an organic polymer
and fine particles, it can be suitably used as the compound for
reinforcing the bond in this invention.
Embodiment 7
[0156] Embodiment 7 of the invention will now be described with
reference to FIG. 8.
[0157] In Embodiment 7, a semiconductor device including an
insulating film with low dielectric constant is embodied.
[0158] FIG. 8 shows the cross-sectional structure obtained in
bonding a wire to a semiconductor device that has a multilayer
interconnect structure, for example, a three-layered interconnect
structure and uses the low dielectric insulating film of Embodiment
5 or 6 as an insulating film. In FIG. 11, a reference numeral 30
denotes a semiconductor wafer, a reference numeral 31 denotes an
insulating film with low dielectric constant, reference numerals
32, 34 and 36 are metal interconnects, reference numerals 33, 35,
36 and 38 denote via plugs, and a reference numeral 39 denotes a
pad to be connected to an external interconnect. The metal material
for the metal interconnects 32, 34 and 36 may be copper or aluminum
alloy. In using copper interconnects, copper can be used for the
via plugs, and in using aluminum interconnects, tungsten may be
used for the via plugs.
[0159] As shown in FIG. 8, when a wire 40 is bonded to the top face
of the pad 39, the semiconductor device is mounted in a package not
shown.
[0160] In Embodiment 7, since the low dielectric insulating film 31
has larger mechanical strength than a conventional porous film, no
cracks are caused in the pad 39 and the metal interconnects 32, 34
and 36. Also, since the low dielectric insulating film 31 has large
strength for holding the metal interconnects 32, 34 and 36, the
resultant semiconductor device can be stabilized.
* * * * *