U.S. patent application number 14/327449 was filed with the patent office on 2015-03-19 for protection of porous substrates before treatment.
The applicant listed for this patent is IMEC VZW. Invention is credited to Mikhail Baklanov.
Application Number | 20150076109 14/327449 |
Document ID | / |
Family ID | 49165658 |
Filed Date | 2015-03-19 |
United States Patent
Application |
20150076109 |
Kind Code |
A1 |
Baklanov; Mikhail |
March 19, 2015 |
PROTECTION OF POROUS SUBSTRATES BEFORE TREATMENT
Abstract
A method is provided for treating a surface of a porous material
in an environment, the method comprising the steps of contacting a
porous material with an organic gas in an environment having a
pressure P1 and a temperature T1, wherein the organic gas is such
that at the pressure P1 and at the temperature T1 it remains a gas
when outside of the porous material but condenses as an organic
liquid when in contact with the porous material, thereby filling
pores of the porous material with the organic liquid, cooling down
the filled porous material to a temperature T2 such that the
organic liquid freezes within the pores, thereby sealing the pores
with an organic solid, thereby providing a protected porous
material, and performing a treatment on the surface.
Inventors: |
Baklanov; Mikhail;
(Veltem-Beisem, BE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
IMEC VZW |
Leuven |
|
BE |
|
|
Family ID: |
49165658 |
Appl. No.: |
14/327449 |
Filed: |
July 9, 2014 |
Current U.S.
Class: |
216/56 |
Current CPC
Class: |
H01L 21/31138 20130101;
H01L 21/31116 20130101; H01L 21/76826 20130101; H01L 21/76802
20130101; H01L 21/3105 20130101; H01L 21/76814 20130101 |
Class at
Publication: |
216/56 |
International
Class: |
H01L 21/02 20060101
H01L021/02; H01L 21/308 20060101 H01L021/308; H01L 21/3065 20060101
H01L021/3065 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 17, 2013 |
EP |
13184718.8 |
Claims
1. A method for treating a surface of a porous material in an
environment, the method comprising: I. contacting a porous material
with an organic gas in an environment having a pressure P1 and a
temperature T1, wherein the organic gas is such that at the
pressure P1 and at the temperature T1 it remains a gas when outside
of the porous material but condenses as an organic liquid when in
contact with the porous material, thereby filling pores of the
porous material with the organic liquid, thereafter II. cooling
down the porous material to a temperature T2 such that the organic
liquid freezes within the pores, thereby sealing the pores with an
organic solid, thereby providing a protected porous material, and
thereafter III. performing a treatment on a surface of the
protected porous material.
2. The method of claim 1, further comprising, after step III: IV.
removing the organic solid from the porous material.
3. The method of claim 2, wherein the removing comprises contacting
the organic solid with an auxiliary liquid miscible with the
organic liquid.
4. The method of claim 2, wherein the removing comprises raising
the temperature of the protected porous material to a temperature
T3 so as to vaporize the organic solid.
5. The method of claim 1, wherein the pressure P1 is lower than an
equilibrium vapor pressure PO of the organic gas at temperature T1
but equal to or higher than a critical pressure Pc at temperature
T1, wherein the critical pressure Pc is a pressure at which a
liquid phase and a vapor phase of the organic gas are at
equilibrium within the porous material.
6. The method of claim 1, wherein the temperature of the porous
material is equal to T1 at the time of the performance of step
I.
7. The method of claim 1, wherein the treatment is an etching.
8. The method of claim 7, wherein the etching is etching to form a
recess, wherein the method further comprises, after step Ill and
before or after step IV: V. filling at least partially the recess
with a metal.
9. The method of claim 1, wherein the treatment is a plasma
treatment.
10. The method of claim 1, wherein the plasma treatment is a plasma
etching.
11. The method of claim 1, wherein step II is delayed until the
porous material and the organic liquid are at equilibrium.
12. The method of claim 1, wherein the porous material is a
nanoporous material.
13. The method of claim 1, wherein the porous material is a
silicon-containing porous material.
14. The method of claim 4, wherein T3 is lower or equal to
250.degree. C.
15. The method of claim 4, wherein T3 is from 10 to 40.degree.
C.
16. The method of claim 1, wherein T2 is higher than -130.degree.
C.
17. The method of claim 1, wherein T2 is from -50.degree. C. to
-10.degree. C.
18. The method of claim 1, further comprising, before step I: VI.
providing a porous material having a surface bearing a resist
layer; and VII. patterning the resist layer so as to expose a
surface of the porous material, thereby providing the surface of
the porous material, wherein the treatment of the surface is an
etching of the surface, thereby forming a recess in the protected
porous material.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] Any and all priority claims identified in the Application
Data Sheet, or any correction thereto, are hereby incorporated by
reference under 37 CFR 1.57. This application claims the benefit of
European Application No. EP 13184718.8 filed Sep. 17, 2013. The
aforementioned application is incorporated by reference herein in
its entirety, and is hereby expressly made a part of this
specification.
TECHNICAL FIELD OF THE INVENTION
[0002] A method is provided for protecting porous materials against
damages upon etching or modification of a surface thereof. In
particular, the method relates to the field of semiconductor
devices and to the protecting of low-k dielectrics against plasma
induced damages.
BACKGROUND OF THE INVENTION
[0003] When a porous substrate needs to be treated by etching or
modification of a surface thereof, damage of the substrate often
occurs. This is particularly true with plasma mediated treatments.
This is presumably caused by active plasma radicals penetrating
deeply into the porous substrate and reacting therewith, thereby
changing its composition and its porosity. Both oxidative and
reductive plasmas have such detrimental effects. These problems for
instance occur in the field of microelectronics during integration
of low-k dielectrics.
[0004] Low-k dielectrics (materials having a dielectric constant
lower than the dielectric constant of SiO.sub.2, i.e. lower than
4.0) are necessary to decrease capacitance between nearby
conductive portions of high density integrated circuits and thereby
avoiding loss of speed and cross-talk. In order to decrease the
dielectric constant of low-k dielectrics as much as possible, low-k
dielectrics are made porous. Thereby, the dielectric constant can
be lowered down to about 2.0 or even less. Integrated circuit
fabrication processes on dielectrics involve plasma etching and
expose therefore the dielectrics to the damages mentioned
above.
[0005] US2005/0148202 describes a method for sealing or protecting
porous materials used in semiconductor fabrication. It describes
sealing the pores of a porous material by applying a mixture of a
polymer compound and an organic solvent. The sealing layer thus
formed is further dried resulting in evaporation of organic
solvents and volatile constituents (if any), and securing of the
polymer compound on the surface as a sealing material. Such a
sealing method has however several drawbacks. The long contact time
between a hot solvent and the substrate makes dissolution or damage
of the substrate possible.
[0006] Furthermore, the method is rather complicated, tedious and
labour-intensive since it involves synthesising a particular
polymer having well defined end-groups, preparing a particular
polymer solution, applying it homogeneously on the substrate (this
implies good wettability and elaborated application techniques),
and heating the solution to evaporate solvent and/or dry the
polymer. Furthermore, polymer deposition typically generates
stresses in porous substrates. Also, the polymer being retained in
the pores in the final product, it potentially influences the
properties of the dielectrics making them harder to control. It
also raises the question of mechanical stability when there is a
mismatch between the thermal coefficient expansion of the polymer
and of the porous material. Last but not least, polymers tend to
have difficulties completely filling pores and/or entering the
smallest pores, resulting in a filling which is not optimally dense
(see FIG. 7 (P)).
[0007] Dubois et al (Adv. Mater. 2011, 23, 25, 2828-2832) discloses
a similar method for sealing porous low-k dielectrics with an
organic polymer. The polymer is degraded by thermal treatment once
the etching and other processing steps are performed. This
presumably permits the patterned dielectric in the final structure
to have comparable properties to its pristine equivalent. However,
removing a polymer by thermal means implies degrading it and
thereby the possibility of leaving polymer residues in the pores.
Also, it is energy intensive. Furthermore, the other drawbacks
proper to the use of polymers remain as mentioned above for
US2005/0148202.
[0008] EP2595182 discloses a method for treating a surface of a
porous material in an environment, the method comprising the steps
of setting the temperature of the surface to a value T2 and setting
the pressure of the environment to a value P1, contacting the
surface with a fluid having a solidifying temperature at the
pressure value P1 above the value T2 and having a vaporizing
temperature at the pressure value P1 below 80.degree. C., thereby
solidifying the fluid in pores of the material, thereby sealing the
pores, treating the surface, wherein the treatment is preferably an
etching or a modification of the surface, and setting the
temperature of the surface to a value T3 and setting the pressure
of the environment to a value P2 in such a way as to vaporize the
fluid.
[0009] Although this method is effective at preventing much damage
to porous substrates, some damages still occurs.
SUMMARY OF THE INVENTION
[0010] There is therefore a need in the art for a way to prevent
damage to porous substrates upon treatment of the substrate (e.g.,
via etching or surface modification), which avoids the above
drawbacks.
[0011] An object of the embodiments is to provide a method which
permits the treatment of a porous material surface while protecting
it from excessive damages.
[0012] It is an advantage of embodiments that it may ease the
cleaning of the porous material after the treatment.
[0013] It is an advantage of embodiments that a particularly good
protection of the porous material can be obtained.
[0014] It is an advantage of embodiments that pores of very small
dimensions (e.g., micropores) can be filled and protected.
[0015] It is an advantage of embodiments that plasma-induced
fluorine diffusion within the porous material may be avoided or
limited.
[0016] It is an advantage of embodiments that the method may
protect the porous material against vacuum ultraviolet (VUV)
induced damage.
[0017] It is an advantage of embodiments that it may allow
treatments (such as, e.g., plasma treatment) at non-cryogenic
temperature (e.g., at -50.degree. C. or above), thereby reducing
costs.
[0018] It is an advantage of embodiments that it may involve a
moderate deprotecting temperature after the treatment, thereby
reducing costs and increasing compatibility with temperature
sensitive substrates.
[0019] It is an advantage of embodiments that it is an organic gas
that is used for contacting a porous material, thereby permitting
the contacting to occur in a vacuum chamber wherein the porous
substrate is easily delivered and wherein plasma etch can be
performed.
[0020] The above objectives are accomplished and advantages
achieved by a method as provided.
[0021] In a first aspect, a method is provided for treating a
surface of a porous material in an environment, the method
comprising the steps of: contacting a porous material with an
organic gas in an environment having a pressure P1 and a
temperature T1, wherein the organic gas is such that at the
pressure P1 and at the temperature T1 it remains a gas when outside
of the porous material but condenses as an organic liquid when in
contact with the porous material, thereby filling pores of the
porous material with the organic liquid, cooling down the filled
porous material to a temperature T2 such that the organic liquid
freezes within the pores, thereby sealing the pores with an organic
solid, and performing a treatment on the surface.
[0022] This method permits a particularly efficient filling of the
pores (e.g., including micropores), since the organic gas diffuses
easily within the porous material (even in the micropores), then
liquefies upon contact with the porous material and diffuses still
to some extent by capillarity. This permits a filling of pores that
compares favorably to a direct capillary filling by a liquid (which
enters micropores with more difficulty) or to a filling with a gas
that freezes upon contact with the porous material.
[0023] In a second aspect, a device is provided comprising a
treated porous material obtainable by a method according to any
embodiment.
[0024] Particular and preferred aspects are set out in the
accompanying independent and dependent claims. Features from the
dependent claims may be combined with features of the independent
claims and with features of other dependent claims as appropriate
and not merely as explicitly set out in the claims.
[0025] The above and other characteristics, features and advantages
of the present invention will become apparent from the following
detailed description, taken in conjunction with the accompanying
drawings, which illustrate, by way of example, the principles of
the invention. This description is given for the sake of example
only, without limiting the scope of the invention. The reference
figures quoted below refer to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a diagrammatic illustration of a process according
to an embodiment wherein the pores of a porous substrate are filled
and thereby sealed before treating (etching) the surface of the
porous substrate.
[0027] FIG. 2 is a diagrammatic illustration of a process according
to another embodiment wherein the pores of a porous material are
filled and sealed, but wherein the resist layer is stripped in situ
after sealing the pores.
[0028] FIG. 3 is a diagrammatic illustration of a process according
to yet another embodiment wherein the pores of a porous material
are filled and sealed, but wherein the resist layer is stripped in
situ after the pores have been filed and after the porous material
has been etched.
[0029] FIG. 4 is a diagrammatic illustration of a process according
to yet another embodiment wherein a hard mask is provided on the
porous material.
[0030] FIG. 5 is a diagrammatic illustration of a process according
to yet another embodiment, similar to that depicted in FIG. 3 but
wherein no hard mask layer is used.
[0031] FIG. 6 is a diagrammatic illustration of a process according
to yet another embodiment wherein the pores of a porous substrate
are filled and thereby sealed before treating (etching) the surface
of the porous substrate.
[0032] FIG. 7 is a diagrammatic illustration comparing a method of
the prior art (P) with that of an embodiment (E).
[0033] In the different figures, the same reference signs refer to
the same or analogous elements.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0034] The present invention will be described with respect to
particular embodiments and with reference to certain drawings but
the invention 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 correspond to actual reductions to
practice of the invention.
[0035] Furthermore, the terms "first", "second", "third" and the
like, are used for distinguishing between similar elements and not
necessarily for describing a sequence, either temporally,
spatially, in ranking or in any other manner. It is to be
understood that the terms so used are interchangeable under
appropriate circumstances and that the embodiments of the invention
described herein are capable of operation in other sequences than
described or illustrated herein.
[0036] Moreover, the terms "top", "bottom", "over", "under" and the
like are used for descriptive purposes and not necessarily for
describing relative positions. It is to be understood that the
terms so used are interchangeable under appropriate circumstances
and that the embodiments of the invention described herein are
capable of operation in other orientations than described or
illustrated herein.
[0037] It is to be noticed that the term "comprising", used in the
claims, should not be interpreted as being restricted to the means
listed thereafter; it does not exclude other elements or steps. It
is thus 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 means A and B"
should not be limited to devices consisting only of components A
and B. It means that with respect to the present invention, the
only relevant components of the device are A and B.
[0038] Reference throughout this specification to "one embodiment"
or "an embodiment" means that a particular feature, structure or
characteristic described in connection with the embodiment is
included in at least one embodiment of the present invention. Thus,
appearances of the phrases "in one embodiment" or "in an
embodiment" in various places throughout this specification are not
necessarily all referring to the same embodiment, but may.
Furthermore, the particular features, structures or characteristics
may be combined in any suitable manner, as would be apparent to one
of ordinary skill in the art from this disclosure, in one or more
embodiments.
[0039] Similarly it should be appreciated that in the description
of exemplary embodiments of the invention, various features of the
invention are sometimes grouped together in a single embodiment,
figure, or description thereof for the purpose of streamlining the
disclosure and aiding in the understanding of one or more of the
various inventive aspects. This method of disclosure, however, is
not to be interpreted as reflecting an intention that the claimed
invention requires more features than are expressly recited in each
claim. Rather, as the following claims reflect, inventive aspects
lie in less than all features of a single foregoing disclosed
embodiment. Thus, the claims following the detailed description are
hereby expressly incorporated into this detailed description, with
each claim standing on its own as a separate embodiment of this
invention.
[0040] Furthermore, while some embodiments described herein include
some but not other features included in other embodiments,
combinations of features of different embodiments are meant to be
within the scope of the invention, and form different embodiments,
as would be understood by those in the art. For example, in the
following claims, any of the claimed embodiments can be used in any
combination.
[0041] In the description provided herein, numerous specific
details are set forth. However, it is understood that embodiments
of the invention may be practiced without these specific details.
In other instances, well-known methods, structures and techniques
have not been shown in detail in order not to obscure an
understanding of this description.
[0042] Where a range of values is provided, it is understood that
the upper and lower limit, and each intervening value between the
upper and lower limit of the range is encompassed within the
embodiments.
[0043] All numbers expressing quantities of ingredients, reaction
conditions, and so forth used in the specification are to be
understood as being modified in all instances by the term `about.`
Accordingly, unless indicated to the contrary, the numerical
parameters set forth herein are approximations that may vary
depending upon the desired properties sought to be obtained. At the
very least, and not as an attempt to limit the application of the
doctrine of equivalents to the scope of any claims in any
application claiming priority to the present application, each
numerical parameter should be construed in light of the number of
significant digits and ordinary rounding approaches.
[0044] All references cited herein are incorporated herein by
reference in their entirety. To the extent publications and patents
or patent applications incorporated by reference contradict the
disclosure contained in the specification, the specification is
intended to supersede and/or take precedence over any such
contradictory material.
[0045] In the present description, reference will be made to
"organic compounds".
[0046] In the context of the embodiments, an organic compound is
any compound which contains carbon atoms. This includes
organometallic compounds. Some embodiments however exclude
organometallic compounds. In the embodiments, organic compounds are
the compounds that are contacted in their gas phase with the porous
material, wherein they will transition to their liquid phase before
being frozen to their solid phase. In function of the specific
context, the term organic compound will therefore sometimes be
substituted by a more precise term where the phase of the compound
is made explicit (organic gas, organic liquid or organic solid).
Each of these more specific terms however always refer to a same
organic compound and can be substituted by the terms "organic
compound in the gas phase", "organic compound in the liquid phase"
or "organic compound in the solid phase".
[0047] In a first aspect, a method is provided for treating a
surface of a porous material in an environment, the method
comprising the steps of: [0048] I. Contacting a porous material
with an organic gas in an environment having a pressure P1 and a
temperature T1, wherein the organic gas is such that at the
pressure P1 and at the temperature T1 it remains a gas when outside
of the porous material but condenses as an organic liquid when in
contact with the porous material, thereby filling pores of the
porous material with the organic liquid, [0049] II. Cooling down
the porous material to a temperature T2 such that the organic
liquid freezes within the pores, thereby sealing the pores with an
organic solid, thereby providing a protected porous material, and
[0050] III. Performing a treatment on the surface.
[0051] In an embodiment, the method may further comprise a step IV
after step III of removing the organic solid.
[0052] In an embodiment, the removing may comprise contacting the
organic solid with an auxiliary liquid miscible with the organic
liquid. This is advantageous because if the treated (e.g., etched)
sample is contacted with such an auxiliary liquid, the organic
solid (e.g., in which waste products may be entrapped or on which
waste products may be present) can be dissolved in the auxiliary
liquid and the waste can thereby be removed together with the
organic solid by a simple washing process. This is especially
useful to clean the substrate from metal wastes which are more
difficult to remove and more detrimental to the performance of
semiconductor devices than other types of wastes. Contacting the
substrate with the auxiliary liquid can, for instance, be performed
by dipping the substrate in the auxiliary liquid. Optionally, the
temperature of the substrate and/or the auxiliary liquid can be
raised sufficiently to permit the dissolution of the organic solid
in the auxiliary liquid. For instance, the temperature can be
raised to a temperature above the melting point of the organic
solid at the condition of pressure involved (e.g., atmospheric
pressure).
[0053] In an alternative embodiment, the removing may comprise
raising the temperature of the protected porous material 4 to a
value T3 in such a way as to vaporize the organic solid. This
embodiment does not require an auxiliary liquid and is more
straightforward than the embodiment involving an auxiliary liquid.
This embodiment is especially advantageous when the level of waste
in the pores or on the surface of the substrate is low or does not
include metal wastes.
[0054] In an embodiment, the temperature of the porous material may
be equal to T1 at the time of the performance of step I. In other
embodiments, at the time of the performance of step I, it may be
lower than T1 but higher than the melting temperature of the
organic liquid.
[0055] In an embodiment, step II may be delayed until the porous
material and the organic compound are at equilibrium. This
typically results in all accessible pores to be entirely filled
with the organic liquid. The exact conditions can be selected by
using, for instance in situ ellipsometry.
[0056] In an embodiment, T3 may be 250.degree. C. or less,
preferably from 10 to 40.degree. C.
[0057] In an embodiment, T2 may be higher than -130.degree. C.,
preferably from -50.degree. C. to -10.degree. C.
[0058] In an embodiment, T1 may be 250.degree. C. or less,
preferably from 10 to 40.degree. C. Most preferably, T1 may be from
18 to 25.degree. C.
[0059] In an embodiment, the method may further comprise:
[0060] before step I, [0061] VI. Providing a porous material having
a surface bearing a resist layer, and [0062] VII. Patterning the
resist layer so as to expose a surface of the porous material,
thereby providing the surface of the porous material, wherein the
treatment of the surface is an etching of the surface, thereby
forming a recess in the porous material.
[0063] The porous material may be any porous material. The material
can, for instance, take the form of a layer supported on a
substrate or can be self-supported.
[0064] The porous material may, for instance, be a nanoporous
material, i.e., a material with pores having on average a diameter
of between 0.2 and 1000 nm, or may be a material with pores having
on average a diameter equal to or larger than 1 .mu.m. Preferably,
the porous material is a nanoporous material.
[0065] Nanoporous materials can be subdivided into three
categories, the macroporous materials, the mesoporous materials and
the microporous materials.
[0066] Macroporosity refers to pores greater than or equal to 50 nm
and smaller than 1000 nm in diameter.
[0067] Mesoporosity refers to pores greater than or equal to 2 nm
and smaller than 50 nm in diameter.
[0068] Microporosity refers to pores greater than 0.2 nm and
smaller than 2 nm in diameter.
[0069] The embodiments can be used with nanoporous materials
belonging to any of these three categories. However, a family of
materials for which the method according to embodiments is
particularly useful is mesoporous materials, and in particular
mesoporous low-k materials, in particular those with a pore size of
between 2 and 10 nm.
[0070] These materials have repeatedly been demonstrated to suffer
from plasma induced damage, making their etching an ongoing
challenge which the embodiments help to meet.
[0071] The porous material is preferably a porous low-k
material.
[0072] In embodiments of the first aspect, the material may have a
dielectric constant lower than 3.9, preferably lower than 3.5, more
preferably lower than 3.0 and most preferably lower than 2.4. The
method according to embodiments is advantageously applied to such
low-k materials, in particular prior to plasma treatment (e.g.,
etching). The use of plasma etching on such low-k materials has
been shown to cause damages and waste products and embodiments help
to prevent such damages and to clean such waste products.
[0073] In embodiments of the first aspect, the porosity of the
porous material may be interconnected (at least partly
interconnected, preferably fully interconnected). When the porous
material is interconnected, the method of the embodiments permits
the very efficiently filling of all pores of the surface or
material with liquid, thereby assuring that, e.g., during the
etching of a cavity in the material, all walls of the cavity are
sealed with the solidified liquid.
[0074] A material having a fully interconnected porosity is
advantageous because an organic compound as defined in any
embodiment can fill all pores of a 1 .mu.m thick material film in 2
minutes or less by contacting its top surface (if the top surface
is free, i.e., has no hard mask, resist or other layer
thereon).
[0075] In embodiments, the porous material may have a porosity of
10% or more, preferably 20% or more, more preferably 30% or more
and most preferably 40% or more. In embodiments, the porous
material may have a porosity of 80% or less. A porosity of 10%
means that the pores amounts for 10% of the volume of the porous
material. A greater porosity is advantageous as it increases the
speed of diffusion of the organic compound in the porous material.
It therefore shortens the contacting step of the method and
increases its efficiency.
[0076] In an embodiment, the thickness of the porous material is
600 nm or less, preferably 400 nm or less, most preferably 300 nm
or less. Embodiments permit to fill the pores of a 200 nm layer in
only a few seconds.
[0077] In embodiments, the material may be a porous
silicon-containing material.
[0078] Porous silicon-containing materials include for instance
porous silica materials (e.g., not containing carbon atoms or
containing less than 1% wt. carbon atoms) and porous organosilicate
materials (e.g., containing more than 1% wt. carbon atoms).
Examples of porous silica materials are silica aerogels, silica
xerogels, silsesquioxanes such as hydrisosilsesquioxane (HSQ),
silicalite-based films, dendrite-based porous glass and mesoporous
silica amongst others.
[0079] Examples of porous organosilicates are porous carbon-doped
silicon dioxides and silsesquioxanes such as alkylsilsesquioxane
(e.g., methylsilsesquioxane (MSSQ)), amongst others. Preferably the
porous silicon-containing material is a porous organosilicate
glass.
[0080] In a preferred embodiment, the porous material (e.g., a
low-k material) may be prepared as follow before to perform step I:
[0081] a surface of the porous material is optionally provided with
a hard mask (e.g., comprising TaN, TiN, SiN, or amorphous carbon)
covering the surface, [0082] the hard mask (if present) or a
surface of the porous material (if no hard mask is present) is
provided with a resist covering the hard mask (if present) or the
surface of the porous material (if no hard mask is present), [0083]
openings are performed in the resist, [0084] if a hard mask is
present, openings are performed in the hard mask by etching through
the openings in the resist. The plasma can for instance be an F
(fluor)-containing plasma. In embodiments, the plasma etching can
be done at the temperature T2 and pressure P1. The result is a
porous material having an exposed surface.
[0085] In this preferred embodiment, the treatment of the surface
is preferably a plasma etching treatment. FIGS. 1-5 and their
corresponding description exemplify such embodiments.
[0086] The environment can be any environment but is typically a
chamber (e.g., comprising a bearing for the porous material).
Preferably it is a chamber in which the temperature can be set
below room temperature. Preferably it is a chamber in which the
pressure can be set below 1 atm. A cryogenic chamber for plasma
treatment is a typical example. Instead of cooling the whole
chamber to temperature T2, a bearing within this chamber can be
cooled down to the temperature T2.
[0087] In embodiments, the porous material may be placed in the
environment on a bearing. In the field of semiconductor processing,
the bearing is typically a chuck. During step I, the porous
material may be placed in thermal contact with the bearing in such
a way that the surface faces away from the bearing. During step I,
the temperature of the bearing may be set at T1. During step II,
the bearing can be cooled down to temperature T2. This is
advantageous because controlling the temperature of the bearing is
more efficient for controlling the temperature of the porous
material surface than controlling the temperature of the entire
environment (e.g., a chamber).
[0088] In embodiments, the bearing may have retractable pins and
the bearing may, for instance, be at temperature T2. This is
advantageous as it permits the porous substrate to be 1) placed on
the pins in the environment at temperature T1, without cooling it
down to T2, 2) contacting a surface of the substrate with the
organic gas at T1 and P1 (this permits a good fill by capillarity
of the porous material with the organic liquid), and 3) lowering
the substrate on the bearing by retracting its pins, thereby
establishing a good thermal contact between the bearing at T2 and
the substrate and thereby lowering the temperature of the surface
to the temperature T2.
[0089] In embodiments, the temperature T1 can be set actively or
passively. Setting the temperature T1 passively is simply using the
temperature of the environment (typically room temperature),
without increasing or decreasing it to a target temperature and
without performing particular acts to maintain it. Typically,
setting the temperature passively will be performed by choosing an
environment having the desired temperature. Setting the temperature
actively implies increasing or decreasing the temperature of the
environment to a target value or value range and maintaining the
temperature at this value or within this range.
[0090] Both types of setting can be used with the embodiments.
[0091] In embodiments of the first aspect, the value T2 may be
below 20.degree. C., preferably below 15.degree. C., preferably
below 10.degree. C., more preferably below 0.degree. C., still more
preferably below -5.degree. C., yet more preferably below
-10.degree. C.
[0092] There is no theoretical lower limit for T2 but for economic
reasons, it is usually not necessary to use T2 temperature lower
than -130.degree. C. Preferably, T2 is above -100.degree. C.
Preferably T2 is above -50.degree. C.
[0093] In an embodiment, the pressure P1 may be lower than the
equilibrium vapor pressure of the organic gas at temperature T1 but
equal to or preferably higher than the critical pressure Pc at
temperature T1, wherein the critical pressure Pc is the pressure at
which the liquid phase and the vapor phase of the organic gas are
at equilibrium within the porous material.
[0094] Without being bound by theory, the critical pressure Pc may
relate to the equilibrium vapor pressure P.sub.0 of the organic gas
via the following expression:
ln ( P c P 0 ) = - f .gamma. V L r K RT ##EQU00001##
[0095] Wherein f is a proportionality constant equal to cos
.theta., wherein .theta. is determined experimentally by measuring
the contact angle of the organic liquid on the porous material,
wherein .gamma. is the surface tension of the organic liquid,
wherein V.sub.L is the molecular volume of the organic liquid,
wherein r.sub.K is the average radius of the pores, wherein R is
the gas constant, and wherein T is the temperature of the porous
material (typically T1).
[0096] P1 is typically lower than 1 atm.
[0097] The contact between the surface of the porous material and
the organic gas is typically operated by introducing the gas
directly as such in the environment where the porous material
is.
[0098] In an embodiment, when the treatment step is an etching
step, the contacting step between the surface of the porous
material and the organic gas may lead to the gas liquefying at
contact with the porous material and diffusing within the porous
material down to a depth at least equal to the depth of the recess
that will be etched in the material during the etching step. This
vertical diffusion is advantageous as it permits the porous
material to have its pores filled down to the depth. The contacting
of the surface of the porous material and the organic compound also
usually leads to lateral diffusion under an optionally present mask
(resist or hard mask). This vertical and/or lateral diffusion
protects the pores of the recess walls during the entire etching
process. This has a clear advantage over simply sealing the surface
of the substrate with a coating not penetrating in the porous
material. Indeed, the protection conferred by a simple
non-penetrating coating does not extend to the walls of the
recesses being created.
[0099] The solidification of the organic liquid in pores of the
material is preferably the result of a process wherein the liquid
formed upon contacting the porous material and at least partly
filling the pores, solidifies within the pores, thereby sealing the
pores.
[0100] In embodiments, the organic compound may be a solid at
temperature T2 and pressure P1 or may solidify at temperature T2
and pressure P1. The vaporization temperature of the organic liquid
is preferably below 250.degree. C., preferably below 200.degree.
C., yet more preferably below 150.degree. C., still more preferably
below 80.degree. C., and most preferably below 40.degree. C. at the
pressure P1 at which the contacting step between the surface and
the organic gas is operated. This is advantageous as it permits to
vaporize the organic compound after the treatment and therefore
restore the porosity of the material with a relatively low
energetic budget.
[0101] In embodiments of the first aspect, the organic liquid may
have a vaporizing point below 250.degree. C. at 1 atm, more
preferably below 235.degree. C. at 1 atm, yet more preferably below
220.degree. C. at 1 atm and most preferably below 205.degree. C. at
1 atm.
[0102] In an embodiment, the organic compound may have a melting
point at P1 lower than 25.degree. C., preferably lower than
15.degree. C., preferably lower than 10.degree. C.
[0103] Particularly well suited organic compounds have a melting
point at P1 lower than 5.degree. C., more preferably lower than
0.degree. C. and most preferably lower than -5.degree. C. The
melting point of these fluids is preferably higher than
-130.degree. C., more preferably higher than -100.degree. C. at
P1.
[0104] In embodiments of the first aspect, the organic compound may
have a melting point -50.degree. C. or higher at P1. In an
embodiment, the liquid may have a melting point at 1 atm lower than
25.degree. C., preferably lower than 15.degree. C., preferably
lower than 10.degree. C.
[0105] Particularly well suited liquids have a melting point at 1
atm lower than 200.degree. C., more preferably lower than
100.degree. C. and most preferably lower than 50.degree. C. The
melting point of these fluids is preferably higher than -50.degree.
C., more preferably higher than -30.degree. C. at 1 atm.
[0106] In embodiments of the first aspect, the liquid may have a
melting point higher or equal to -50.degree. C. at 1 atm.
[0107] In an embodiment, the organic compound may be selected from
hydrocarbons, fluorocarbons, hydrofluorocarbons, alcohols,
aldehydes, ketones, organosilicon compounds and mixtures
thereof.
[0108] In an embodiment, the organic compound may be selected from
hydrocarbons, fluorocarbons, hydrofluorocarbons, alcohols,
aldehydes, ketones, and mixtures thereof.
[0109] Suitable hydrocarbons may for instance be C.sub.6-12
hydrocarbons. These hydrocarbons can be linear, branched or cyclic
(e.g., cyclooctane, cyclodecane). These hydrocarbons may be
saturated (e.g., nonane, decane) or not (e.g., 1-decene). They are
advantageous because they confer some protection against vacuum UV
(VUV) during plasma treatment. For this purpose, longer
hydrocarbons are better.
[0110] Suitable fluorocarbons may for instance be C.sub.4-10
fluorocarbons (e.g., C.sub.4F.sub.8, C.sub.8F.sub.18). These
fluorocarbons can be linear, branched or cyclic. These
fluorocarbons may be saturated or not.
[0111] Suitable hydrofluorocarbons may for instance be C.sub.4-10
hydrofluorocarbons. These hydrofluorocarbons can be linear,
branched or cyclic. These hydrofluorocarbons may be saturated or
not.
[0112] Suitable organosilicon compounds are for instance siloxanes
such as tetramethylcyclotetrasiloxane. Such compounds may help
repairing the porous substrate in addition to protect it from
damages.
[0113] In an embodiment, the organic compound may be selected from
alcohols, aldehydes, ketones and mixtures thereof. Such organic
compounds are advantageous for various reasons. First, in their
liquid phase, they wet particularly well typical substrates used as
low-k dielectrics (e.g., organosilicate glasses). These good
wetting properties permit the organic liquid to fill efficiently
(e.g., completely) the pores of the porous material, thereby, upon
solidification, efficiently (e.g., completely) sealing the pores.
Second, such organic liquids help cleaning the treated porous
material from waste products generated during the treatment.
[0114] Cleaning of a porous surface is not always easy because
waste products tend to remain entrapped in the pores. In an
embodiment, after the treatment and the resulting generation of
waste product at the surface and within the pores below the
surface, the vaporization of such organic liquids (alcohols,
aldehydes and ketones) may drive the waste products out of the
pores toward the surface. Once at the surface, they are more easily
removed, e.g., by cleaning with an auxiliary liquid. Alternatively,
in another embodiment, instead of vaporizing the organic liquid,
the porous surface can be directly contacted with an auxiliary
liquid miscible with the organic compound used to fill the
pores.
[0115] Independently of the cleaning method used, it is noted that
alcohol, aldehyde and ketone organic compounds are particularly
efficient in cleaning the pores at and directly below the surface.
Their affinity for the substrate provides these organic compounds
with a good affinity for the waste products generated during the
treatment of the substrate surface. This permits the organic
compounds to attach to the waste product and to transport the waste
products toward the surface either during the vaporization step or
the auxiliary liquid contacting step.
[0116] In embodiments, the organic compound may be selected from
alcohol, aldehydes, ketones having either a single hydroxyl group
or carbonyl group and having from 6 to 12 carbon atoms, or two
functions selected from hydroxyl and carbonyl functions and having
from 2 to 5 carbon atoms.
[0117] In embodiments, the alcohol may be selected from monohydric
alcohols and diols.
[0118] Illustrative examples of suitable alcohols are C.sub.6-11
linear saturated monohydric alcohols such as but not limited to
1-hexanol, 1-octanol or 1-decanol, C.sub.7-11 branched saturated
monohydric alcohols such as but not limited to
2,2-dimethyl-3-pentanol or 2-decanol, C.sub.6-8 aromatic monohydric
alcohols such as but not limited to benzyl alcohol, C.sub.2-5
linear diols such as but not limited to ethylene glycol or 1,
4-butane diol, C.sub.5-6 cyclic saturated monohydric alcohols such
as but not limited to cyclopentanol or cyclohexanol, and linear or
branched unsaturated monohydric alcohols such as but not limited to
geraniol.
[0119] Illustrative examples of suitable aldehydes are C.sub.7-11
linear saturated aldehydes such as but not limited to octanal or
nonanal, C.sub.9-11 branched saturated aldehydes, C.sub.7-9
aromatic aldehydes such as but not limited to benzaldehyde and
phenyl acetaldehyde.
[0120] Illustrative examples of suitable ketones may have the
general formula R.sub.1COR.sub.2 wherein R.sub.1 and R.sub.2 either
form a 6 or a 7 member cyclic moiety or are independently selected
from phenyl and C.sub.1-10 alkyl chains. Preferably the total
number of carbons in the ketone is from 6 to 12.
[0121] Illustrative examples of suitable ketones are cyclohexanone,
4-heptanone, 2-decanone and phenyl propyl ketone.
[0122] Alcohols, aldehydes, and ketones having longer alkyl chains
have the advantage to confer some protection against VUV.
[0123] In embodiments of the first aspect, the treatment may be any
treatment susceptible to damage the porous material. In embodiments
of the first aspect, the treatment may be any treatment susceptible
to damage the porous material and produce waste at the surface of
the porous material or within the pores of the porous material.
[0124] The treatment of the surface may be an etching of the
surface, a modification of the surface, or a combination of both.
It can also be an etching or a modification of a structure (e.g., a
resist layer) present on the surface.
[0125] Although the treatment is operated on the surface, it can
also have effects in the bulk of the material. For instance, the
etching of the surface may create trenches extending within the
bulk.
[0126] The etching of the surface can be any kind of etching. For
instance it can be an isotropic etching, an anisotropic etching or
a combination of both. It can be a chemical etching, a physical
etching or a combination of both. In an embodiment, the
modification of the surface may be a coating of the surface. For
instance it can comprise creating a layer of a second material on
the porous material or it can comprise plasma treating the surface
to change its properties. For instance it can involve changing the
hydrophilicity of the surface, cleaning the surface or forming
functional groups on the surface. For instance, coating a low-k
porous material with a metal such as gold is in some cases promoted
by the treatment of the low-k porous material substrate with a
plasma. This process is, for instance, useful in the preparation of
substrates for plasmon resonance measurements.
[0127] In a preferred embodiment, the treatment is a plasma
treatment such as, for instance, a plasma etching, a plasma surface
modification or a plasma enhanced deposition. It is noteworthy that
a plasma treatment aimed at a structure present on the surface will
also lead to a contact between the plasma and the surface. This is
also encompassed as an etching or a modification of the
surface.
[0128] In embodiments of the first aspect, the treatment may be a
plasma treatment, preferably a plasma etching. Embodiments
advantageously prevent plasma-induced damage. It is an advantage of
embodiments that, due to the diffusion of the organic liquid in the
pores, the protection of the pores toward the treatment extends to
a certain depth below the surface of the porous material. This
permits creation of recesses via etching in the porous material
while benefiting from the protective effect of the solidified
organic compound during the whole etching process.
[0129] In embodiments of the first aspect, the treatment may be an
etching of the surface so as to form a recess (e.g., a trench). In
embodiments, the method further comprises the steps of: [0130] V.
filling at least partially the recess with a metal, wherein step V
is performed after step III and before or after step IV. This is
advantageous since the sealed pores of the recess walls prevent
penetration of the metal in the pores.
[0131] In embodiments, optionally no hard mask is used prior to
form the recess.
[0132] In embodiments of the first aspect, the method of anyone of
the above embodiments may further comprises: before step i, [0133]
VI. Providing a porous material having a surface bearing a resist
layer, and [0134] VII. Patterning the resist layer so as to expose
a surface of the porous material, thereby providing the surface of
the porous material, wherein the treatment of the surface is an
etching of the surface, thereby forming a recess in the porous
material.
[0135] In embodiments, the temperature T3 may be 10.degree. C. or
higher, preferably 15.degree. C. or higher. In embodiments, T3 may
be 250.degree. C. or lower, preferably 200.degree. C. or lower,
more preferably 150.degree. C. or lower, yet more preferably
80.degree. C. or lower, still more preferably 40.degree. C. or
lower. In embodiments, the value T3 may be in the range 10.degree.
C.-250.degree. C., preferably 10.degree. C.-200.degree. C., more
preferably 10.degree. C.-150.degree. C., yet more preferably
10.degree. C.-80.degree. C., still more preferably 10.degree.
C.-40.degree. C. Preferably, T3 is room temperature, i.e.,
typically a temperature ranging from 20 to 25.degree. C.
[0136] In embodiments, T3 may be at least equal to the vaporization
temperature of the fluid at the pressure value P1. In practice, T3
can be somewhat higher than T1, for instance from 5 to 50.degree.
C. higher. It is also possible to reduce the pressure of the
environment below P1 during step IV. This permits to use lower
temperatures T3.
[0137] In an embodiment, step I may precede step II, step II may
precede step III, and step III may precede step IV.
[0138] In a second aspect, a device is provided comprising a
treated porous material obtainable by the method according to any
embodiment of the first aspect.
[0139] In embodiments, the device obtained by the method of the
first aspect may comprise trenches in a surface thereof, the porous
material having a k-value lower than 2.5, preferably lower than
2.3.
[0140] In an embodiment, the k-value exists at the level of the
trenches.
[0141] The invention will now be described by a detailed
description of several embodiments of the invention. It is clear
that other embodiments of the invention can be configured according
to the knowledge of persons skilled in the art without departing
from the technical teaching of the invention, the invention being
limited only by the terms of the appended claims.
Referring to FIG. 1:
[0142] FIG. 1 illustrates an embodiment where the pores of a porous
substrate are filled and thereby sealed before treating (here
etching) the surface of the porous substrate.
[0143] In step (1a), a multilayer is provided comprising a porous
low-k material 3. A hard mask 2 is provided on the porous low-k
material 3 and a resist layer 1 is provided on the hard mask 2 by
standard lithographic techniques. The hard mask 2 can for instance
be made of TaN, TiN, SiN or amorphous carbon.
[0144] In step (Ib), an opening is performed in the resist layer 1
by a standard lithographic technique (for instance involving
fluorocarbons), thereby making accessible a surface of the hard
mask 2.
[0145] In step (Ic) the opened multilayer is transferred to a
chamber at a reduced pressure P1 and at a temperature T1, wherein
P1 is lower than P0 but higher than Pc at T1 for a selected organic
gas 11g. The hard mask 2 is then etched by fluorine containing
plasma, thereby making accessible a surface 5 of the porous
material 3.
[0146] In step (II), the porous material 3 is contacted with the
selected organic gas 11g, which penetrates the pores 12 (not
depicted) of the porous material 3 and liquefies within, thereby
providing an at least partly filled porous material. The
temperature is then reduced to T2, i.e. below the freezing
temperature of the organic liquid 11L at P1, thereby providing a
protected porous material 4.
[0147] In step (11l), the protected material 4 is then etched with
a fluorine containing plasma 7 down to the appropriate depth. The
etching creates waste 10 at the surface 5 of the protected material
4.
[0148] In step (IV), the plasma treatment 7 is then stopped, the
temperature is allowed to increase to a temperature T3 sufficient
to vaporize the organic solid (eventually via a transition to a
liquid state). This temperature T3 can for instance be above T1 in
such a way that P1 is below Pc at T3. The result of this exemplary
embodiment is a patterned porous low-k material 3 which is not
damaged and which is cleaned from at least some of its waste
10.
Referring to FIG. 2:
[0149] FIG. 2 illustrates an embodiment similar to FIG. 1 where the
pores 12 (not depicted) of a porous material 3 are filled and
sealed, thereby providing a protected material 4 before treating 7
(here removing the resist 1 and etching) the surface 5 of the
protected material 4. However, in this embodiment, the resist layer
1 is stripped in situ during a step (11b) after that the pores 12
of the material 3 have been sealed with the organic compound 11.
The stripping step uses oxygen or hydrogen plasma which is a source
of damage for the porous material 3 and an indirect source of waste
10 due to the reaction with the material 3 during etching.
Performing the stripping step after that the pores 12 of the
material 3 have been sealed has therefore the advantage of avoiding
damaging the porous material 3 during the resist 1 removal
step.
Referring to FIG. 3:
[0150] FIG. 3 illustrates an embodiment similar to FIG. 2 where the
pores 12 (not depicted) of a porous material 3 are filled and
sealed before treating (here etching 7) the surface 5 of the
protected porous material 4. However, in this embodiment, the
resist layer 1 is stripped in situ during a step (IIIb) after that
the pores 12 of the material 3 have been filled and after the
protected porous material 4 has been etched with a fluorine
containing plasma 7 down to the appropriate depth. The advantages
are the same as for the embodiment of FIG. 2, i.e. avoiding
damaging the porous material 3 during the resist 1 removal
step.
Referring to FIG. 4:
[0151] FIG. 4 shows a variant applicable to the embodiments of
FIGS. 1-3. In FIG. 4, steps (Ia) and (Ib) are identical to the
steps described in FIG. 1.
[0152] In step (Ia), a multilayer is provided comprising a porous
low-k material 3. A hard mask 2 is provided on the porous low-k
material 3 and a resist layer 1 is provided on the hard mask 2 by
standard lithographic techniques. The hard mask 2 can for instance
be made of TaN, TiN, SiN or amorphous carbon.
[0153] In step (Ib), an opening is performed in the resist layer 1
by a standard lithographic technique, thereby making accessible a
surface 5 of the hard mask 2.
[0154] In step (Ic) the opened multilayer is transferred to a
chamber at a reduced pressure P1 and at a temperature T1, wherein
P1 is lower than PO but higher than Pc at T1 for a selected organic
compound 11, and is positioned on retractable pins 8 of a bearing 9
(a chunk) having a temperature T2 below the freezing temperature of
the organic compound 11 at P1. The hard mask 2 is then etched by
fluorine containing plasma. Due to the presence of the pins 8,
there is a certain distance between the material 3 and the cooled
bearing 9, assuring that the temperature of the material 3 remains
above T2 and above the temperature at with the liquid 11l freezes
at P1.
[0155] In step (Id), the material 3 is contacted with the organic
compound in the gas phase 11g, which penetrates pores 12 (not
depicted) of the porous material 3 and liquefies within.
[0156] In step (II), the porous material 3 at least partly filled
with the organic liquid 11l is lowered against the cooled bearing
9, thereby establishing thermal contact between the porous material
3 and the cooled bearing 9, thereby permitting the freezing of the
liquid 11l within the pores 12 of the material 4. In step (III),
the now protected material 4 is then etched with a fluorine
containing plasma 7 down to the appropriate depth. The etching
creates waste 10 at the surface 5 of the porous material 3.
[0157] In step (IV), the plasma treatment 7 is then stopped, the
temperature is allowed to increase to a temperature T3 sufficient
to vaporize the organic solid (eventually via a transition to a
liquid state). This temperature T3 can for instance be above T1 in
such a way that P1 is below Pc at T3. This raising of the
temperature is made faster by lifting the protected material 4 away
from the bearing 9. The result of this exemplary embodiment is a
patterned porous low-k material 3 which is not damaged and is
cleaned from at least some of its waste 10. An advantage of using
the retractable pins 8, is that only the chunk needs to be at
temperature T2 while the chamber can remain at T1.
Referring to FIG. 5:
[0158] FIG. 5 illustrates a particularly advantageous embodiment.
It is similar to FIG. 3 where the pores 12 of a porous material 3
are filled and thereby sealed before treating 7 (here etching) the
surface 5 of the protected porous material 4. However, in this
embodiment, no hard mask layer 2 is used. A hard mask 2 is
typically used to avoid low-k damage during the resist 1 strip in
O.sub.2 and H.sub.2 plasma. In the embodiment of FIG. 5, no hard
mask 2 is needed anymore because of ability to strip the resist 1
without damaging the low-k material 3. This is a big advantage
because normally the hard mask 2 generates stress which is one of
the reasons for line wiggling when working with small
dimensions.
[0159] In step (Ia), a multilayer is provided comprising a porous
low-k material 3. No hard mask 2 is provided on the porous low-k
material 3 and a resist layer 1 is provided directly on the low-k
material 3 by standard lithographic techniques.
[0160] In step (Ib), an opening is performed in the resist layer 1
by a standard lithographic technique (for instance involving
fluorocarbons), thereby making accessible a surface 5 of the porous
material 3.
[0161] In step (II) the opened multilayer is transferred to a
chamber at a reduced pressure P1 and at a temperature T1, wherein
P1 is lower than P0 but higher than Pc at T1 for a selected organic
gas 11g, and the porous material 3 is contacted with the selected
organic gas 11g, which penetrates the pores 12 (not depicted) of
the porous material 3 and liquefies within, thereby providing a
porous material 3 at least partly filled with the organic liquid
11l. The temperature is then reduced to T2, i.e. below the freezing
temperature of the organic liquid 11l at P1.
[0162] In step (IIIa), the now protected substrate 4 is then etched
with a fluorine containing plasma 7 down to the appropriate
depth.
[0163] The resist layer is stripped in situ in O.sub.2 and H.sub.2
plasma during a step (IIIb). The advantages are the same as for the
embodiment of FIG. 4, i.e. avoiding damaging the porous material 3
during the resist 1 removal step and this advantage is achieved
without the use of a hard mask 2. The etching creates waste 10 at
the surface of the protected material 4.
[0164] In step (IV), the plasma treatment 7 is then stopped, the
temperature is allowed to increase to a temperature T3 sufficient
to vaporize the organic solid (typically via a transition to a
liquid state). This temperature T3 can for instance be above T1 in
such a way that P1 is below Pc at T3. The result of this exemplary
embodiment is a patterned porous low-k material 3 which is not
damaged and which is cleaned from at least some of its waste
10.
[0165] In the embodiments of FIGS. 1-5, the organic compound 11 is
always chosen in such a way that it has a cleaning effect on the
wastes 10 generated by the treatment 7. These are however only
preferred embodiments. Embodiments where the organic compound 11
has little or no cleaning effect (but for instance otherwise
identical to the embodiments of FIGS. 1-5) are equally parts of the
embodiments.
Referring to FIG. 6:
[0166] FIG. 6 illustrates an embodiment where the pores 12 of a
porous substrate 3 are filled and thereby sealed before treating 7
(here etching) the surface 5 of the porous substrate 3.
[0167] In step (Ia), a porous low-k material 3 having a surface 5
is provided in an environment having a pressure P1 and a
temperature T1. An organic gas 11g is provided in the environment.
The organic gas 11g is such that at the pressure P1 and at the
temperature T1 it remains a gas when outside of the porous material
3 but condenses as an organic liquid 11l when in contact with the
porous material 3.
[0168] In step (Ib) shows the result of the contacting between the
porous material 3 and the organic gas 11g. The organic gas 11g
condensed within the pores 12 of the porous material 3 and filled
the pores 12 with a liquid 11l.
[0169] In step (II), the pressure is maintained at P1 but the
temperature is reduced to T2, i.e. below the freezing temperature
of the organic liquid 11l at P1.
[0170] In step (III), the protected porous material 4 is then
etched with a fluorine containing plasma 7 down to the appropriate
depth. The etching creates a trench 6.
[0171] In step (IV), the plasma treatment 7 is then stopped, the
temperature is allowed to increase to a temperature T3 sufficient
to vaporize the organic solid (typically via a transition to a
liquid state). This temperature T3 can for instance be above T1 in
such a way that P1 is below Pc at T3. The result of this exemplary
embodiment is a patterned porous low-k material 3 which is not
damaged.
[0172] FIG. 7 (P) schematically shows an embodiment of the prior
art. It depicts an enlarged portion of a porous material 3
comprising a pore 12. The material 3 is shown to comprise Si atoms
and CH.sub.3 groups. One such CH.sub.3 group is depicted within the
pore 12 and bound to a Si atom of the material 3. Polymer 13 is
depicted within the pore 12. It is visible that the pore 12 is not
completely filled by the polymer 13, allowing for instanced the
CH.sub.3 group to detach (double arrow) during a subsequent
treatment, leading to an alteration of the structure of the
original porous material 3.
[0173] FIG. 7 (E) schematically shows an embodiment. It depicts an
enlarged portion of a porous material 3 comprising a pore 12. The
material 3 is shown to comprise Si atoms and CH.sub.3 groups. One
such CH.sub.3 group is depicted within the pore 12 and bound to a
Si atom of the material 3. An organic solid 11s is depicted within
the pore 12. It is visible that the pore 12 is completely filled by
the organic solid 13s, preventing for instanced the CH.sub.3 group
to detach during a subsequent treatment, leading to preservation of
the structure of the original porous material 3.
[0174] It is to be understood that although preferred embodiments,
specific constructions and configurations, as well as materials,
have been discussed herein for devices according to the present
invention, various changes or modifications in form and detail may
be made without departing from the scope of this invention. For
example, any formulas given above are merely representative of
procedures that may be used. Functionality may be added or deleted
from the block diagrams and operations may be interchanged among
functional blocks. Steps may be added or deleted to methods
described within the scope of the present invention.
* * * * *