U.S. patent application number 16/230674 was filed with the patent office on 2019-05-09 for method for pore sealing of porous materials using polyimide langmuir-blodgett film.
The applicant listed for this patent is IMEC, St. Petersburg Electrotechnical University. Invention is credited to Mikhail Baklanov, Svetlana Goloudina, Alexey Ivanov, Mikhail Krishtab, Victor Luchinin, Vyacheslav Pasyuta.
Application Number | 20190135998 16/230674 |
Document ID | / |
Family ID | 47900922 |
Filed Date | 2019-05-09 |
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United States Patent
Application |
20190135998 |
Kind Code |
A1 |
Luchinin; Victor ; et
al. |
May 9, 2019 |
Method for Pore Sealing of Porous Materials Using Polyimide
Langmuir-Blodgett Film
Abstract
Method for pore sealing a porous substrate, comprising: forming
a continuous monolayer of a polyimide precursor on a liquid
surface, transferring said polyimide precursor monolayer onto the
porous substrate with the Langmuir-Blodgett technique, and
imidization of the transferred polyimide precursor monolayers,
thereby forming a polyimide sealing layer on the porous substrate.
Porous substrate having at least one surface on which a sealing
layer is provided to seal pores of the substrate, wherein the
sealing layer is a polyimide having a thickness of a few monolayers
and wherein there is no penetration of the polyimide into the
pores.
Inventors: |
Luchinin; Victor; (St.
Petersburg, RU) ; Goloudina; Svetlana; (St.
Petersburg, RU) ; Pasyuta; Vyacheslav; (St.
Petersburg, RU) ; Ivanov; Alexey; (St. Petersburg,
RU) ; Baklanov; Mikhail; (Veltem-Beisem, BE) ;
Krishtab; Mikhail; (St. Petersburg, RU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
IMEC
St. Petersburg Electrotechnical University |
Leuven
St. Petersburg |
|
BE
RU |
|
|
Family ID: |
47900922 |
Appl. No.: |
16/230674 |
Filed: |
December 21, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15285445 |
Oct 4, 2016 |
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16230674 |
|
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13847457 |
Mar 19, 2013 |
9492841 |
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15285445 |
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61613295 |
Mar 20, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B32B 2305/07 20130101;
Y10T 428/249991 20150401; B82Y 40/00 20130101; B32B 2457/00
20130101; H01L 21/02318 20130101; B32B 2260/046 20130101; C08J 5/18
20130101; B05D 1/208 20130101; B05D 1/204 20130101; B32B 18/00
20130101; C08J 2379/08 20130101; B32B 2305/026 20130101; C08J
2483/02 20130101; H05K 2201/0104 20130101; Y10T 428/249979
20150401; H05K 2201/0154 20130101; H05K 1/03 20130101; B32B 27/281
20130101; H01L 23/5329 20130101; H05K 2201/01 20130101; H05K
2201/0116 20130101; B05D 2505/50 20130101; H01L 21/02285 20130101;
B32B 27/04 20130101; B32B 2307/204 20130101; H05K 2201/0162
20130101; H05K 3/143 20130101; C08G 73/1067 20130101; B32B 2307/00
20130101; B32B 37/15 20130101; B32B 2379/08 20130101; C09D 179/08
20130101; B05D 1/20 20130101; B82Y 30/00 20130101; C09D 179/08
20130101; C08K 5/175 20130101 |
International
Class: |
C08J 5/18 20060101
C08J005/18; B05D 1/20 20060101 B05D001/20; H01L 23/532 20060101
H01L023/532 |
Claims
1. A porous substrate having at least one surface on which a
sealing layer is provided to seal pores of the porous substrate,
wherein the porous substrate is an ultra-low .kappa. dielectric
material having a dielectric constant .kappa. lower than 2.3 and
the porous substrate has a pore size of 1 to 5 nm, and wherein the
sealing layer comprises a continuous monolayer of a polyimide
precursor.
2. The porous substrate of claim 1, wherein the sealing layer has a
thickness lower than 5 nm.
3. The porous substrate of claim 1, wherein the polyimide precursor
is polyamic acid alkylamine salt.
4. The porous substrate of claim 1, wherein the sealing layer does
not penetrate into pores of the porous substrate.
5. The porous substrate of claim 1, wherein the dielectric constant
.kappa. is lower than 2.1.
6. The porous substrate of claim 1, wherein the porous substrate
has an average pore size of 2 nm.
7. The porous substrate of claim 1, wherein the substrate is a
porous organosilicate.
8. The porous substrate of claim 7, wherein the porous
organosilicate comprises SiOCH material having a .kappa.-value of
2.3 and an average pore size of 2 nm.
9. The porous substrate of claim 1, wherein the sealing layer has a
dielectric constant of 3.3 or less.
10. The porous substrate of claim 1, wherein a combination of the
porous substrate and the sealing layer has a refractive index of
between 1.33 and 1.36 as obtained by ellipsometric porosimetry.
11. The porous substrate of claim 1, wherein the continuous
monolayer of a polyimide precursor is compatible with a
Langmuir-Blodgett deposition technique.
12. An integrated circuit comprising: a substrate, wherein the
substrate is an ultra-low .kappa. dielectric material having a
dielectric constant .kappa. lower than 2.3, wherein a surface of
the substrate comprises a plurality of pores with pore sizes
between 1 and 5 nm; and a sealing layer directly overlaying the
surface of the substrate and sealing at least a portion of the
pores of the surface such that the sealing layer does not penetrate
into the pores, wherein the sealing layer comprises a continuous
monolayer of polyimide.
13. The integrated circuit of claim 12, wherein the sealing layer
has a thickness lower than 5nm.
14. The integrated circuit of claim 12, wherein a dielectric
constant .kappa. of the substrate is lower than 2.1.
15. The integrated circuit of claim 12, wherein the substrate has
an average pore size of 2 nm.
16. The integrated circuit of claim 12, wherein the substrate is a
porous organosilicate.
17. The integrated circuit of claim 16, wherein the porous
organosilicate comprises SiOCH material having a dielectric
constant .kappa. of 2.3 and an average pore size of 2 nm.
18. The integrated circuit of claim 12, wherein the sealing layer
has a dielectric constant of 3.3 or less.
19. The integrated circuit of claim 12, wherein a combination of
the substrate and the sealing layer has a refractive index of
between 1.33 and 1.36 as obtained by ellipsometric porosimetry.
20. The integrated circuit of claim 12, wherein the continuous
monolayer of polyimide is compatible with a Langmuir-Blodgett
deposition technique.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/285,445, entitled "Method of Pore Sealing
of Porous Materials Using Polyimide Langmuir-Blodgett Film", filed
on Oct. 4, 2016, which is a divisional of U.S. patent application
Ser. No. 13/847,457, entitled "Method for Pore Sealing of Porous
Materials Using Polyimide Langmuir-Blodgett Film", filed on Mar.
19, 2013, which claims priority to U.S. Patent App. No. 61/613,295,
entitled "Method for Pore Sealing of Porous Materials Using
Polyimide Langmuir-Blodgett Film", filed on Mar. 20, 2012, the
contents of all of which are fully incorporated by referenced
herein for all purposes.
TECHNICAL FIELD
[0002] The present disclosure relates to methods for pore sealing
of porous materials. The present disclosure further relates to pore
sealed porous materials.
BACKGROUND OF THE DISCLOSURE
[0003] Continual decreasing of feature size of transistors in
modern integrated circuits constrains thickness of auxiliary
dielectric layers such as barrier layers or etch-stop layers in
interconnects because of their relatively high dielectric constant
reducing efficiency of low-.kappa. material integration. For
example, dielectric materials used today as barrier or etch-stop
layers are usually silicon nitride (SiN, .kappa. value of about
7.0) and silicon-carbonitride (SiCN, .kappa. value of about 4.8),
dielectric constants which noticeably exceed that of advanced ultra
low-.kappa. materials (.kappa. lower than 2.1).
[0004] In general, a low-.kappa. dielectric is a material with a
small dielectric constant relative to silicon dioxide. Further an
ultra-low .kappa. dielectric material is characterized by
dielectric constant .kappa. lower than 2.3, more preferably lower
than 2.1. Usually the pore size of such a material is between 1 and
5 nm.
[0005] Deposition of a thin layer on a porous material without
penetrating the pores is often nontrivial and represents a
difficult task especially for chemical vapor deposition (CVD) and
atomic layer deposition (ALD) techniques which are both using
gaseous precursors which can diffuse inside the net of pores thus
increasing the effective thickness of the top layer and
deteriorating properties of pristine material.
SUMMARY OF THE DISCLOSURE
[0006] It is an aim of this disclosure to present a method for pore
sealing a porous substrate which does not show the drawbacks of the
prior art discussed above.
[0007] This aim is achieved by the method comprising the steps of
the first independent claim.
[0008] It is another aim of this disclosure to present a pore
sealed porous substrate with improved surface characteristics.
[0009] This other aim is achieved by the substrate comprising the
technical characteristics of the second independent claim.
[0010] According to this disclosure, the drawbacks of the prior art
are alleviated by constructing, by means of the Langmuir-Blodgett
technique, a polyimide sealing film on the surface of the porous
substrate. The resulting sealing film comprises one or more
continuous monolayers consisting of close packed polymer
chains.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] All drawings are intended to illustrate some aspects and
embodiments of the present disclosure. The drawings described are
only schematic and are non-limiting.
[0012] FIG. 1A represents the structural formula of polyimide
prepolymer--polyamic acid alkylamine salt.
[0013] FIG. 1B represents the structural formula of polyimide
prepolymer--polyimide (PI).
[0014] FIG. 2A represents the AFM-profile of pristine SiOCH.
[0015] FIG. 2B represents the AFM-profile of pristine SiOCH after
deposition of PI film.
[0016] FIG. 3A represents the Scanning Electron Microscopy (SEM)
images of cross-sections of a Si/SiOCH structure. All samples are
covered with a Pt layer.
[0017] FIG. 3B represents the Scanning Electron Microscopy (SEM)
images of cross-sections of a Si/SiOCH/PI structure wherein the
imidization temperature is 250.degree. C. All samples are covered
with a Pt layer.
[0018] FIG. 3C represents the Scanning Electron Microscopy (SEM)
images of cross-sections of a Si/SiOCH/PI structure wherein the
imidization temperature is 400.degree. C. All samples are covered
with a Pt layer.
[0019] FIG. 4 shows the adsorption isotherms for Si/SiOCH/PI
structures differentiated by conditions of PI film formation.
[0020] FIG. 5 shows the adsorption and desorption isotherms for
Si/SiOCH/PI structure.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0021] The present disclosure will be described with respect to
particular embodiments and with reference to certain drawings but
the disclosure is not limited thereto but only by the claims. The
drawings described are only schematic and are non-limiting. In the
drawings, the size of some of the elements may be exaggerated and
not drawn on scale for illustrative purposes. The dimensions and
the relative dimensions do not necessarily correspond to actual
reductions to practice of the disclosure.
[0022] Furthermore, the terms first, second, third and the like in
the description and in the claims, are used for distinguishing
between similar elements and not necessarily for describing a
sequential or chronological order. The terms are interchangeable
under appropriate circumstances and the embodiments of the
disclosure can operate in other sequences than described or
illustrated herein.
[0023] Moreover, the terms top, bottom, over, under and the like in
the description and the claims are used for descriptive purposes
and not necessarily for describing relative positions. The terms so
used are interchangeable under appropriate circumstances and the
embodiments of the disclosure described herein can operate in other
orientations than described or illustrated herein.
[0024] Furthermore, the various embodiments, although referred to
as "preferred" are to be construed as exemplary manners in which
the disclosure may be implemented rather than as limiting the scope
of the disclosure.
[0025] The term "comprising", used in the claims, should not be
interpreted as being restricted to the elements or steps listed
thereafter; it does not exclude other elements or steps. It needs
to be interpreted as specifying the presence of the stated
features, integers, steps or components as referred to, but does
not preclude the presence or addition of one or more other
features, integers, steps or components, or groups thereof. Thus,
the scope of the expression "a device comprising A and B" should
not be limited to devices consisting only of components A and B,
rather with respect to the present disclosure, the only enumerated
components of the device are A and B, and further the claim should
be interpreted as including equivalents of those components.
[0026] The present disclosure relates to a method for pore sealing
of a porous substrate using films of rigid-chain polyimide
deposited by Langmuir-Blodgett technique, herein referred to as
LB-films. The method is suitable for pore sealing applications of
porous materials such as ultra-low-.kappa. dielectric materials
which are used in interconnect applications of advanced integrated
circuits.
[0027] Further the present disclosure also relates to the sealing
layer obtained by the method of the disclosure which comprises a
rigid-chain polyimide and has a dielectric constant (.kappa.-value)
of about 3.2-3.3.
[0028] In general, a low-.kappa. dielectric is a material with a
small dielectric constant relative to silicon dioxide. Further an
ultra-low .kappa. dielectric material is characterized by
dielectric constant .kappa. lower than 2.3, more preferably lower
than 2.1. Usually the pore size of such a material is between 1 and
5nm.
[0029] Deposition of a thin layer on a porous material without
penetrating the pores is often nontrivial and represents a
difficult task especially for chemical vapor deposition (CVD) and
atomic layer deposition (ALD) techniques which are both using
gaseous precursors which can diffuse inside the net of pores thus
increasing the effective thickness of the top layer and
deteriorating properties of pristine material. The method of the
disclosure solves this problem by using LB films which are
deposited on the surface of a porous material such as for example
SiOCH as one or more continuous monolayers of strongly interacting
macromolecules and which subsequently form close packed polymer
chains in the polyimide film.
[0030] A Langmuir-Blodgett (LB) film contains one or more
monolayers of an organic material, deposited from the surface of a
liquid onto a solid by immersing (or emersing) the solid substrate
into (or from) the liquid. A monolayer is adsorbed homogeneously
with each immersion or emersion step, thus films with very accurate
thickness can be formed. This thickness is accurate because the
thickness of each monolayer is known and can therefore be added to
find the total thickness of a Langmuir-Blodgett film. The
monolayers are assembled vertically and are usually composed of
amphiphilic molecules with a hydrophilic head and a hydrophobic
tail.
[0031] Polyimide (abbreviated PI) is a polymer of imide monomers.
In embodiments of the disclosure the polyimide film was obtained by
thermal imidization (e.g.
[0032] at a temperature within the range of 250-400 .degree. C.) of
Langmuir-Blodgett films of precursor alkylammonium salts of
polyamic acid (PAA) based on dianhydride of
3,3',4,4'-biphenyltetracarboxylic acid and o-tolidine (BPDA-oTD)
and tert-amine o, o', o''-trihexadecanoyltriethanolamine as
illustrated in FIG. 1. Other polyimide precursors, known to the
person skilled in the art, may however also be used.
[0033] Advantageously the thickness of the polyimide film deposited
by the Langmuir-Blodgett technique can be made as thin as several
monolayers. Moreover, intermolecular interaction of precursor
macromolecules densely packed within a monolayer before transfer on
the porous substrate makes it possible to avoid penetration of
precursor material inside the pores. The latter peculiarity of the
deposition process may also lead to achievement of a pore sealing
effect with about 4 nm of PI film in one of the specific
embodiments.
[0034] The polyamic acid alkylamine salt (PAAS) was synthesized in
two steps. Initially, individual solutions of polyamic acid and
tertiary amine with a concentration of 1 mmol/l were prepared in a
1:1 DMA-benzene solvent mixture. Then these solutions were mixed in
a ratio of 1:2 immediately before using it for preparation of the
PAAS monolayer on the surface of deionized water filling the LB
trough. The PAAS solution was disposed dropwise onto the water
surface at 5-10 min intervals for 1 h. A surface pressure as a
function of an area related to a repeating unit of polymer chains
on the water surface (a compression isotherm) evidenced formation
of close packed polymer chains in the monolayer. After controlled
formation the PAAS monolayer was subsequently transferred onto the
porous substrate.
[0035] Prepared monolayers of PAAS were transferred onto the layer
of porous SiOCH material having a .kappa.-value of 2.3. The pore
structure of the pristine material was evaluated with ellipsometric
porosimetry and found to have an open porosity of about 30% and a
pore size of about 2 nm. The method of the disclosure is suitable
to seal porous dielectrics having a pore size of 1 to 5 nm, without
any penetration of the sealing material into the pores.
[0036] Formation of PI films was accomplished at different
conditions of PAAS LB films deposition such as surface pressure and
the number of layers in LB film. Monolayers of PAAS on the
water-air interface were formed at a surface pressure
(.pi..sub.dep) of 25, 30 and 35 mN/m, respectively, and then
underwent a transfer procedure repeated 8 or 20 times. The rate of
immersion and withdrawal of the substrate was kept constant at 0.2
cm/min for all the experiments. The transport coefficient was used
to control the quality of transferred monolayer and was calculated
as a ratio between the area of monolayer decreased in the course of
deposition and the area of the substrate used. This coefficient was
close to 1.0 when the surface pressure of monolayer was fixed at 25
and 30 mN/m, while the value of 1.1 was obtained at a surface
pressure of 35 mN/m.
[0037] The imidization step (thermal treatment) of the PAAS LB film
was carried out after the transfer of the LB film on the substrate
comprising the porous material at two temperatures of 250.degree.
C. and 400.degree. C. The imidization took place in vacuum at a
pressure lower than 10.sup.-1 Torr, preferably about 10.sup.-3
Torr, or in inert atmosphere such as N.sub.2 or noble gases to
prevent oxidation. The duration of the imidization process is from
about 1 hour to several hours. In the preferred embodiments the
duration was 4 to 6 hours.
[0038] The sealing film was examined in terms of thickness and
refractive index, roughness and impermeability of polyimide layer
to external chemicals such as toluene.
[0039] The thickness and refractive indices of the sealing LB films
were determined by reflection ellipsometry within the framework of
one-layer optical model. The surface morphology was inspected with
an atomic force microscope Nanoscope V in a tapping mode in air.
Ellipsometric porosimetry was used to test integrity of the sealing
LB film. The latter technique is based on in-situ recording of
ellipsometric angles during increase of toluene vapor pressure in
the chamber. Then the values of angles at certain pressure are
recalculated into values of refractive index by using of one-layer
model, thus forming adsorption and desorption curves which are to
be analyzed. Such a measurement was performed with EP-10 equipped
with spectroscopic ellipsometer 801SE (.lamda.=350-850 nm). In
addition cross-section of samples was made with Helios NanoLab 400
combining ion and electron beams.
[0040] Initially, the measurement techniques mentioned above were
applied to pristine samples composed of a thin layer of SiOCH
low-.kappa. dielectric on silicon substrate. Surface analysis with
AFM demonstrates a profile with peak-to-peak value of about 2 nm as
shown in FIG. 2A which is a measure of the pore openings. According
to ellipsometric measurement the thickness of the low-.kappa. layer
is equal to 193 nm and refractive index is close to 1.33. As a
supplementary layer, the sealing polyimide film on top of the
porous low-.kappa. material is designed to minimize a rise of the
.kappa.-value of the whole structure comprising the low-.kappa.
material with the sealing layer on top.
[0041] Results of the ellipsometric evaluation of SiOCH samples
covered with LB polyimide film (sealing layer) at different
conditions are presented in the Tables 1 and 2 below. As can be
seen from these data, refractive index of the 2-layer structure
deviates from the pristine one by less than 2% regardless of number
of PI layers and parameters of film formation.
[0042] The thickness of the polyimide film can be estimated as an
increase of the initial thickness of SiOCH layer. The lower
temperature of the imidization step leads to the higher values of
effective film thickness which relates to the processes of removal
of aliphatic segments in the PAAS molecule and ordering of polymer
chains constituting the film.
[0043] Thickness (d) and refractive index (n) of SiOCH/PI structure
with polyimide film formed at T.sub.a=250.degree. C. are shown in
Table 1 below.
TABLE-US-00001 TABLE 1 .pi..sub.dep, mN/m N d, nm (d-d.sub.i), nm 8
PI layers 25 1.33 200 7 30 1.34 200 7 35 1.35 201 8 20 PI layers 25
1.35 208 15 30 1.36 212 19 35 1.36 214 21
[0044] Thickness (d) and refractive index (n) of SiOCH/PI structure
with polyimide film formed at T.sub.a=400.degree. C. are shown in
Table 2 below.
TABLE-US-00002 TABLE 2 .pi., mN/m N d, nm (d-d.sub.i), nm 8 PI
layers 25 1.35 197 4 30 1.34 196 3 35 1.34 197 4 20 PI layers 25
1.33 202 9 30 1.34 203 10 35 1.33 204 11
[0045] Based on the analysis of AFM-images and profiles made after
deposition of PI film one can conclude that the roughness of the
sealed porous material is influenced by the surface pressure within
PAAS monolayer on the water-air interface, the number of PI layers
and the imidization temperature. The smallest peak-to-peak value of
about 3 nm (as shown in FIGS. 3A-3C) was observed on the sample
with 8 PI layers formed at a surface pressure of 25 mN/m which were
annealed at 400.degree. C.
[0046] The surface of sealed porous material became rougher than
pristine one. However, further smoothing of LB films can be
achieved by changing the deposition conditions such as lowering the
rate of PAAS monolayer transfer or by using a PI precursor selected
to lead to an increased density of the LB film before the transfer
to the substrate.
[0047] Without wishing to be bound by theory it is believed that
the intermolecular interaction in the continuous PAAS monolayer
allows transferring a continuous monolayer instead of separate
molecules which results in an effective pore sealing preventing the
PI film (sealing layer) or parts thereof from going inside the
pores. Visual proof of the latter effect is presented in FIGS. 3B
and FIG. 3C which show cross-section SEM-images of two structures
with top layers deposited by LB technique and different imidization
temperatures of 250.degree. C. and, respectively, 400.degree. C.,
The measure of sealant pores penetration can be estimated visually
through the contrast in the SEM-image at the interface between the
layer of low-k material (SiOCH) and the top PI film. The interface
between PI and SiOCH layer is in both cases sharp and proves the
absence of pores penetration.
[0048] Analysis of toluene adsorption and desorption isotherms
obtained from ellipsometric porosimetry (as shown in FIGS. 4 and 5)
proves the efficiency of pore sealing with PI films of the
disclosure. All tested samples show isotherms similar to that in
FIG. 5. According to these data the refractive index of the
two-layer structure SiOCH/PI is almost constant within a broad
range of toluene pressure which suggests that pores of low-k
material are still filled with air which means that the surface
pores are sealed. However there are two small areas namely at low
and high pressures of adsorbate where the refractive index changes.
We believe that an initial insignificant rise of refractive index
is related to the intrinsic microporosity of polyimide film which
is caused by its domain structure. The fact of abrupt increase in
the end of the adsorption process may be a consequence of toluene
condensation on the PI film surface owing to its roughness which is
confirmed with an absence of any hysteresis loop in that region of
pressures.
[0049] In a specific embodiment it was found that films of about 4
nm comprising 8 polyimide monolayers are able to seal the surface
of porous material with average pore size of 2 nm without
significant deterioration of its pristine properties. The thickness
and the number of monolayers may vary upon changing the
experimental conditions.
[0050] In various embodiments of the disclosure an effective pore
sealing is obtained with a thickness lower than 5 nm of sealant due
to intermolecular forces between polymer chains in precursor
monolayer which allows transferring a continuous monolayer instead
of separate molecules.
* * * * *