U.S. patent application number 10/065861 was filed with the patent office on 2004-05-27 for drying process for low-k dielectric films.
This patent application is currently assigned to Axcelis Technologies, Inc.. Invention is credited to Berry, Ivan, Escorcia, Orlando, Hallock, John, Han, Qingyaun, Margolis, Ari, Waldfried, Carlo.
Application Number | 20040099283 10/065861 |
Document ID | / |
Family ID | 32323603 |
Filed Date | 2004-05-27 |
United States Patent
Application |
20040099283 |
Kind Code |
A1 |
Waldfried, Carlo ; et
al. |
May 27, 2004 |
Drying process for low-k dielectric films
Abstract
A method for drying and removing contaminants from a low-k
dielectric film of an integrated circuit wafer, the method
comprising exposing the low k dielectric layer to photons; and
simultaneously with, prior to, or subsequent to the photon
exposure, exposing the substrate to a process effective to remove
the contaminants without causing degradation of the low k
dielectric layer, wherein the process is selected from the group
consisting of a heat process, a vacuum process, an oxygen free
plasma process, and combinations thereof.
Inventors: |
Waldfried, Carlo; (Falls
Church, VA) ; Han, Qingyaun; (Columbia, MD) ;
Hallock, John; (Potomac, MD) ; Berry, Ivan;
(Ellicott City, MD) ; Margolis, Ari; (Hollywood,
FL) ; Escorcia, Orlando; (Falls Church, VA) |
Correspondence
Address: |
CANTOR COLBURN, LLP
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
|
Assignee: |
Axcelis Technologies, Inc.
55 Cherry Hill Drive
Beverly
MA
01915
|
Family ID: |
32323603 |
Appl. No.: |
10/065861 |
Filed: |
November 26, 2002 |
Current U.S.
Class: |
134/1.2 ;
257/E21.241; 257/E21.242; 257/E21.251; 257/E21.252 |
Current CPC
Class: |
H01L 21/3105 20130101;
H01L 21/31058 20130101; G03F 7/42 20130101; H01L 21/31111 20130101;
H01L 21/31116 20130101 |
Class at
Publication: |
134/001.2 |
International
Class: |
C25F 001/00 |
Claims
1. A drying process for removing contaminants from a substrate
having a low k dielectric layer thereon in a process chamber, the
process comprising: exposing the low k dielectric layer to photons;
and simultaneously with, prior to, or subsequent to the photon
exposure, exposing the substrate to a process effective to remove
the contaminants without causing degradation of the low k
dielectric layer, wherein the process is selected from the group
consisting of a heat process, a vacuum process, an oxygen free
plasma process, and combinations thereof.
2. The drying process of claim 1, wherein the photons are generated
by ultraviolet light radiation or x ray radiation.
3. The drying process of claim 1, wherein the low k dielectric
layer comprises a porous or non-porous doped oxide material, and
wherein the heat process comprises heating the substrate to a
temperature of about 20.degree. C. to about 400.degree. C.
4. The drying process of claim 1, wherein the low k dielectric
layer comprises a porous or non-porous doped oxide material, and
wherein the heat process comprises heating the substrate to a
temperature of about 100.degree. C. to about 300.degree. C.
5. The drying process of claim 1, wherein the low k dielectric
layer comprises an organic material, and wherein the heat process
comprises heating the substrate to a temperature of about
80.degree. C. to about 180.degree. C.
6. The drying process of claim 1, wherein the photons incident to
the substrate have an energy density of about 10 milliwatts per
square centimeter to about 1 watt per square centimeter.
7. The drying process of claim 1, wherein the vacuum process
comprises decreasing a pressure about the substrate to about 1 to
about 10 millitorr.
8. The drying process of claim 1, further comprising purging the
process chamber with an inert gas.
9. A process for removing contaminants adsorbed, adhered, or
trapped within a low k dielectric layer, wherein the contaminants
comprise residual water, moisture, silanols, residual plasma or wet
etch chemistries residuals of wet clean chemistries, acids, bases,
and solvents, the process comprising: exposing the low k dielectric
layer in a process chamber to radiation comprising a wavelength of
about 150 nanometers to about 500 nanometers; and exposing the
substrate to an oxygen free plasma or heat or a vacuum or a
combination thereof to remove the contaminants without causing
degradation of the low k dielectric layer.
10. The process of claim 9, wherein the low k dielectric layer
comprises a porous material or doped oxide material, and wherein
heating the substrate comprises a temperature of about 20.degree.
C. to about 400.degree. C.
11. The process of claim 9, wherein the low k dielectric layer
comprises a porous material or doped oxide material, and wherein
heating the substrate comprises a temperature of about 100.degree.
C. to about 300.degree. C.
12. The process of claim 9, wherein the low k dielectric layer
comprises an organic material, and wherein heating the substrate
comprises a temperature of about 80.degree. C. to about 180.degree.
C.
13. The process of claim 9, wherein reducing the pressure comprises
lowering the pressure in the process chamber to less than about 1
to about 10 milliTorr.
14. The process of claim 9, wherein exposing the low k dielectric
layer to the radiation comprises a time of less than about 120
seconds.
15. The process of claim 9, wherein exposing the low k dielectric
layer to the radiation comprises a time of less than about 60
seconds.
16. The process of claim 9, wherein the plasma is formed from a gas
composition comprising a hydrogen bearing gas and an inert gas.
17. A drying process for removing contaminants from a substrate
having a low k dielectric layer thereon in a process chamber, the
process comprising: exposing the low k dielectric layer to
electromagnetic radiation; and simultaneously with, prior to, or
subsequent to the radiation exposure, exposing the substrate to a
process effective to remove the contaminants without causing
degradation of the low k dielectric layer, wherein the process is
selected from the group consisting of a heat process, a vacuum
process, an oxygen free plasma process, and combinations thereof.
Description
BACKGROUND
[0001] This disclosure relates generally to a method for drying and
removing contaminants from low-k dielectric films.
[0002] Recently, much attention has been focused on developing low
k dielectric thin films for use in the next generation of
microelectronics. As integrated devices become smaller, the
RC-delay time of signal propagation along interconnects becomes one
of the dominant factors limiting overall chip speed. With the
advent of copper technology, R has been pushed to a practical
lowest limit so attention must be focused on reducing C. One way of
accomplishing this task is to reduce the average dielectric
constant k of the thin insulating films surrounding interconnects.
The dielectric constant of traditional silicon dioxide insulative
materials is about 3.9. Lowering the dielectric constant below 3.9
will provide a reduced capacitance.
[0003] The low k dielectric materials used in advanced integrated
circuits typically comprise organic polymers or oxides and have
dielectric constants less than about 3.5. The low k dielectric
materials can be spun onto the substrate as a solution or deposited
by a chemical vapor deposition process. Important low k film
properties include thickness and uniformity, dielectric constant,
refractive index, adhesion, chemical resistance, thermal stability,
pore size and distribution, coefficient of thermal expansion, glass
transition temperature, film stress, and copper diffusion
coefficient.
[0004] In fabricating integrated circuits on wafers, the wafers are
generally subjected to many process steps before finished
integrated circuits can be produced. Low-k dielectric materials can
be sensitive to some of these process steps. For example, plasma
used during an "ashing" step can strip both photoresist material as
well as remove a portion of the low-k dielectric film. Ashing
refers to a plasma stripping process by which residual photoresist
and post etch residues are stripped or removed from a substrate
upon exposure to the plasma. The ashing process generally occurs
after an etching or implant process has been performed in which a
photoresist material is used as a mask for etching a pattern into
the underlying substrate or for selectively implanting ions into
the exposed areas of the substrate. The remaining photoresist and
any post etch or post implant residues on the wafer after the etch
process or implant process is complete must be removed prior to
further processing for numerous reasons generally known to those
skilled in the art. The ashing step is typically followed by a wet
chemical treatment to remove traces of the residue, which can cause
further degradation of the low k dielectric and may cause increase
in the dielectric constant.
[0005] Alternatively, the photoresist can be removed by the use of
wet strippers. Wet strippers include acids, bases, and solvents as
are known to those skilled in the art. The particular wet strippers
used are well within the skill of those in the art. For example,
nitric acid, sulfuric acid, ammonia are commonly employed as wet
strippers. In operation, the substrate is immersed, puddled,
streamed, sprayed or the like by the wet stripper and subsequently
rinsed with deionized water.
[0006] After ashing or wet stripping of the photoresist, a rinsing
step is typically employed to remove the stripper, contaminants
and/or photoresist residuals. Typically, the rinsing step employs
deionized water.
[0007] It is important to note that ashing processes significantly
differ from etching processes. Although both processes may be
plasma mediated, an etching process is markedly different in that
the plasma chemistry is chosen to permanently transfer an image
into the substrate by removing portions of the substrate surface
through openings in a photoresist mask. The plasma generally
includes high energy ion bombardment at low temperatures to remove
portions of the substrate. Moreover, the portions of the substrate
exposed to the ions are generally removed at a rate equal to or
greater than the removal rate of the photoresist mask. In contrast,
ashing processes generally refer to selectively removing the
photoresist mask and any polymers or residues formed during
etching. The ashing plasma chemistry is much less aggressive than
etching chemistries and is generally chosen to remove the
photoresist mask layer at a rate much greater than the removal rate
of the underlying substrate. Moreover, most ashing processes heat
the substrate to temperatures greater than 200.degree. C. to
increase the plasma reactivity. Thus, etching and ashing processes
are directed to removal of significantly different materials and as
such, require completely different plasma chemistries and
processes. Successful ashing processes are not used to permanently
transfer an image into the substrate. Rather, successful ashing
processes are defined by the photoresist, polymer and residue
removal rates without affecting or removing underlying layers,
e.g., low k dielectric layers.
[0008] Solvents, such as those comprising the wet chemical
treatment or wet strippers, can adhere, become adsorbed and/or
trapped in pores of the low k dielectric film. This entrainment can
cause an increase in the dielectric constant of the film, thus
defeating the purpose of using the low-k dielectric. An increase in
dielectric constant undesirably affects interconnect capacitance
and cross talk. Moreover, trapped cleaning chemicals can also lead
to metal corrosion and reduced device reliability since a surface
of the dielectric layer typically abuts a conductive metal layer.
These problems are exacerbated for those low k dielectrics that
contain pores.
[0009] These prior art chemical formulations include strong
reagents such as strong inorganic acids, strong bases and/or
reactive amine containing compounds. However, such strong reagents
can cause unwanted further removal of metal or insulator layers
remaining on the wafer and are therefore undesirable in many
instances. Additionally, strippers containing both amine
component(s) and water may corrode metal, particularly copper,
aluminum and aluminum-copper alloys.
[0010] Various methods have been disclosed in the art for removing
or reducing the amounts of solvent trapped within the low k
dielectric film. For example, You et al., in U.S. Pat. No.
6,235,453, describe a plasma treatment at the end of the ashing
process, (employs a different plasma chemistry than the ashing
process) that seals the surface of the low k dielectric film layer
to prevent solvent adsorption in a subsequent wet chemical
treatment. However, it has been found that the so-called protective
layer provided by the plasma treatment does not eliminate solvent
adsorption and as such does not eliminate the need for a drying
step. Moreover, the use of the plasma treatment increases the
dielectric constant of the dielectric film layer method by virtue
of the treatment. You et al. also describe a method for removing or
reducing trapped solvents by employing heat and/or a vacuum.
However, the described drying process is relatively slow and relies
on the volatility of the contaminants being sufficiently volatile
to be outgassed from the low k dielectric film layer. As previously
described, some of the contaminants are residual photoresist
materials, which are based on polymers and typically are not
sufficiently volatile to be removed by the heat and/or vacuum
processing by itself.
BRIEF SUMMARY
[0011] Disclosed herein is a drying process for removing moisture
and contaminants from a substrate having a low k dielectric layer
thereon in a process chamber. The process comprises exposing the
low k dielectric layer to photons; and simultaneously with, prior
to, or subsequent to the photon exposure, exposing the substrate to
a process effective to remove the contaminants without causing
degradation of the low k dielectric layer, wherein the process is
selected from the group consisting of a heat process, a vacuum
process, an oxygen free plasma process, and combinations
thereof.
[0012] In another embodiment, a process for removing contaminants
adsorbed, adhered, or trapped within a low k dielectric layer,
wherein the contaminants comprise residual water, moisture,
silanols, residual plasma or wet etch chemistries residuals of wet
clean chemistries, acids, bases, and solvents is described. The
process comprises exposing the low k dielectric layer in a process
chamber to radiation comprising a wavelength of about 150
nanometers to about 500 nanometers; and exposing the substrate to
oxygen free plasma, or heat, or a vacuum, or a combination thereof
to remove the contaminants without causing degradation of the low k
dielectric layer.
[0013] The above described and other features are exemplified by
the following figures and detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Referring now to the figures, which are exemplary
embodiments and wherein the like elements are numbered alike:
[0015] FIG. 1 illustrates a cross section of an exemplary exposure
tool for drying a low k dielectric layer; and
[0016] FIG. 2 is a FTIR spectra of before and after drying results
for a porous doped oxide low-k dielectric film.
DETAILED DESCRIPTION
[0017] A process for drying and removing contaminants from low-k
dielectric films is described herein. The drying process generally
comprises exposing a surface of the low k dielectric film to
photons, and simultaneously, prior to, or subsequently applying
plasma, or heat or a vacuum, or a combination of two or more of the
foregoing processes to remove the contaminants adhered to,
adsorbed, and/or trapped by the low k dielectric layer. The photons
could be included in ultraviolet (UV), x-ray, and/or other forms of
electromagnetic radiation. In a preferred embodiment, the source of
photons is from a UV light exposure.
[0018] Preferably, the drying process follows an ashing and/or wet
stripping process to remove residues and solvents adhered to,
adsorbed, or trapped by the low k dielectric layer. While not
wanting to be bound by theory, it is believed that upon photon
exposure of the low k dielectric layer, excitation, scission and/or
fragmentation of molecular bonds of the contaminants contained
therein or thereon occurs, which facilities the removal of these
contaminants. The species generated by excitation, scission and/or
fragmentation exhibit greater volatility and can be removed with
the plasma or heat or vacuum treatment or the combination of two or
more of the foregoing processes applied to the substrate
simultaneous with or subsequent to the photon exposure.
[0019] Low k dielectrics are hereinafter defined as those
insulating materials suitable for use in the manufacture of
integrated circuits or the like having a dielectric constant less
than about 3.5. Low k dielectrics can generally be categorized as
one of two types: organic, and doped oxides. Examples of organic
low k dielectric materials include polyimides, benzocyclobutene,
parylenes, diamond-like carbon, poly(arylene ethers), cyclotenes,
fluorocarbons and the like, such as those dielectrics commercially
available under the trademarks SiLK, or BCB. Examples of doped
oxide low k dielectric materials include methyl silsesquioxane,
hydrogen silsesquioxanes, nanoporous oxides, carbon doped silicon
dioxides, and the like, such as, for example, those dielectrics
commercially available under the trademarks CORAL, BLACK DIAMOND
and AURORA. Both types of low-k materials exist in dense and porous
versions. Porous versions thereof are commercially known under
trademarks such as LKD, ORION, BOSS, or porous SiLK. Other low k
dielectric materials will be apparent to one of ordinary skill in
the art in view of this disclosure.
[0020] As previously disclosed, the photons could be included in
ultraviolet (UV), x-ray, and/or other forms of electromagnetic
radiation. For exemplary purposes, reference will now be made in
detail to the preferred embodiments, wherein the photon source is a
UV light source. The use of other proton sources will be well
within the skill of those in the art in view of this
disclosure.
[0021] The wavelength of the UV light exposure can be emitted as a
narrow wavelength or as a broadband spectrum. Preferably, the UV
light exposure is emitted as a broadband spectrum. As used herein,
the term "broadband spectrum" refers to a radiation source having
at least one wavelength band having a full-width half-maximum
greater than about 10 nanometers (nm), with preferably greater than
about 100 nm more preferred, and with greater than 200 nm even more
preferred. The term full-width half-maximum (FWHM) is hereinafter
defined as the width across a wavelength profile when it drops to
half of its peak, or maximum value.
[0022] Preferably, the UV radiation comprises wavelengths of about
150 nanometers (nm) to about 500 nm, with about 200 nm to about 400
nm more preferred. The energy incident to the low k dielectric
surface is preferably, on average, about 10 milliwatts per square
centimeter (mW/cm.sup.2) to about 1 watt (W/cm.sup.2). The exposure
times are directly dependent on the intensity of the light source
(as well as other factors). In terms of throughput, the exposure
times are preferably less than about 180 seconds, with less than
about 60 seconds more preferred, and with less than about 30
seconds even more preferred.
[0023] Simultaneously with, or subsequent to the UV light exposure,
it is preferred that the substrate is subjected to plasma, or heat
or vacuum or a combination comprising two or more of the foregoing
processes. The plasma is preferably an oxygen free plasma such as
is described in U.S. Pat. No. 6,281,135 to Han et al., herein
incorporated by reference in its entirety. Preferably, the oxygen
free plasma is generated from a gas composition comprising an inert
gas and optionally, a hydrogen bearing gas.
[0024] The hydrogen bearing compounds include those compounds that
contain hydrogen, such as for example, hydrocarbons,
hydrofluorocarbons, hydrogen precursor gas, hydrogen gas, and
hydrogen gas mixtures. Preferably, the hydrogen bearing compound is
a non-flammable hydrogen gas mixture containing an inert gas such
as nitrogen.
[0025] Preferred hydrogen precursor gases are those that exist in a
gaseous state and release hydrogen to form reactive hydrogen
species such as free radical or hydrogen ions under plasma forming
conditions. The gas may be a hydrocarbon that is unsubstituted or
may be partially substituted with a halogen such as bromine,
chlorine or fluorine, or with oxygen, nitrogen, hydroxyl and amine
groups. Preferably, the hydrocarbon has at least one hydrogen and
from one to twelve carbon atoms, and more preferably has from three
to ten carbon atoms. Examples of suitable hydrogen bearing gases
include methane, ethane, ammonia, and propane.
[0026] Preferred hydrogen gas mixtures are those gases that contain
hydrogen gas and an inert gas. Examples of the inert gas include
argon, nitrogen, neon, helium or the like. Especially preferred
hydrogen gas mixtures are so-called forming gases that consist
essentially of hydrogen gas and nitrogen gas or hydrogen gas and
helium, or hydrogen gas and argon. Particularly preferable is a
forming gas, wherein the hydrogen gas ranges in an amount from
about 3 to about 5 percent by volume of the total forming gas
composition due to safety considerations.
[0027] Plasma asher devices particularly suitable for use in the
present disclosure are downstream plasma ashers, such as for
example, those microwave plasma ashers available under the trade
names GEMINI ES, ES3, or ES31, and commercially available from
Axcelis Technologies. Portions of the microwave plasma asher are
described in U.S. Pat. Nos. 5,498,308 and 4,341,592, and PCT
International Application No. WO/97/37055, herein incorporated by
reference in their entireties. The disclosure is not limited to any
particular plasma asher in this or in the following embodiments.
For instance, an inductively coupled plasma reactor can be
used.
[0028] The amount of heat applied to the substrate will depend on
the thermal stability of the particular low k dielectric layer as
well as the other layers and components already formed in the
substrate. The substrate is preferably exposed to heat of
sufficient intensity and duration to cause the contaminants to
diffuse out of the low-k dielectric layer and volatize without
causing degradation of any other components or layers in the
substrate. Preferably, for porous or non-porous doped oxide low k
materials the wafer is heated from about 20.degree. C. to about
400.degree. C., with about 100.degree. C. to about 300.degree. C.
more preferred. Preferably, for organic low k materials the wafer
is heated from about 80.degree. C. to a maximum of about
180.degree. C. The maximum temperatures for organic dielectrics are
dependent on the intrinsic properties of the organic low k material
used and can be determined by thermal analysis techniques known to
those skilled in the art. The temperature may be step-wise
increased during processing or remain static throughout the drying
process.
[0029] A vacuum, if employed, is preferably operated at about 1
mTorr to about 100 mTorr, with about 1 mTorr to about 50 mTorr more
preferred, and with about 1 mTorr to about 10 mTorr even more
preferred.
[0030] FIG. 1 illustrates an exemplary exposure tool 10 suitable
for practicing the drying process. The exposure tool 10 generally
includes a process chamber 12 and a radiation source chamber 14.
The process chamber 12 includes a chuck 16 on which a substrate 18
is disposed. Optionally, the chuck 16 or process chamber 12 may be
adapted to provide a heat source (not shown) for heating the wafer
during processing. An example of optional heating is a heated
chuck. The exposure tool 10 further includes a radiation source 20
and a plate 22 may be disposed between the radiation source 18 and
the chuck 16. Conduits 24 are disposed in fluid communication with
the process chamber 12 for purging the chamber 12, regulating a
pressure within the process chamber 12, and the like. The exposure
tool 10 may further include additional features such as the
structural features described in U.S. Pat. No. 4,885,047 to
Matthews et al., incorporated herein by reference in its entirety,
for providing a uniform exposure of light to the wafer surface.
[0031] The drying process includes loading the substrate 18 into
the process chamber 12 and exposing the substrate 18 to UV
radiation emitted by the radiation source 20. Preferably, the
process chamber 112 is configured for automatic handling such that
manual handling of the substrate 18 is eliminated. In a preferred
embodiment, the process includes purging the process chamber 12
with one or more inert gases to remove the air within the process
chamber 12 and then exposing the substrate 18 to UV radiation.
Suitable inert gases for purging air from the process chamber 12
include, but are not limited to, nitrogen, argon, helium, forming
gas, combinations comprising at least one of the foregoing gases,
and the like. Simultaneous with or subsequent to the UV radiation
exposure, the substrate may be subjected to heat and/or a vacuum
for removing the volatile components from the low k dielectric
layer.
EXAMPLES
[0032] In this example, a porous doped oxide low k dielectric layer
with a thickness of approximately 1 micrometer was spin coated onto
a silicon substrate, cured, and exposed to ambient moisture. The
peaks associated with moisture and contaminant absorption can be
readily observed in an FTIR spectra of the substrate at wavelengths
of about 3000 to about 3400 angstroms and at about 1400
angstroms.
[0033] The substrate was then placed in a UV process chamber having
features similar to that shown in FIG. 1 and purged with nitrogen.
The substrate was then exposed to a UV radiation having a broadband
wavelength spectrum ranging from 220 to 400 nm. The exposure time
was 30 seconds and the wafer was heated to 240.degree. C. during
the exposure.
[0034] Referring now to FIG. 1, an FTIR was obtained of the
substrate before and after the UV drying process. The results
clearly show that moisture is removed from the low k dielectric
surface as demonstrated by the absence of peaks at about 3000 to
about 3400 and about 1400 cm.sup.-1.
[0035] Advantageously, the process can be used to remove
contaminants from a low k dielectric layer, thus avoiding
degradation that can occur because of the adhered, adsorbed, and/or
trapped contaminants. The photon mediated drying process is
believed to more efficiently remove contaminants since large
molecules can be fragmented to form volatile compounds upon
exposure to the UV radiation.
[0036] While the disclosure has been described with reference to an
exemplary embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the disclosure. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
disclosure without departing from the essential scope thereof.
Therefore, it is intended that the disclosure not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this disclosure, but that the disclosure will include
all embodiments falling within the scope of the appended
claims.
* * * * *