U.S. patent application number 09/232359 was filed with the patent office on 2001-11-08 for method and system for modifying and densifying a porous film.
Invention is credited to HUANG, RICHARD, PANGRLE, SUZETTE K., PRAMANICK, SHEKHAR.
Application Number | 20010038889 09/232359 |
Document ID | / |
Family ID | 22872793 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010038889 |
Kind Code |
A1 |
PANGRLE, SUZETTE K. ; et
al. |
November 8, 2001 |
METHOD AND SYSTEM FOR MODIFYING AND DENSIFYING A POROUS FILM
Abstract
The invention provides a system and a method for densifying a
surface of a porous film. By reducing the porosity of a film, the
method yields a densified film that is more impenetrable to
subsequent liquid processes. The method comprises the steps of
providing a film having an exposed surface. The film can be
supported by a semiconductor substrate. When the film is moved to a
processing position, a focused source of radiation is created by a
beam source. The exposed surface of the film is then irradiated by
the beam source at the processing position until a predetermined
dielectric constant is achieved. The film or beam source may be
rotated, inclined, and/or moved between a variety of positions to
ensure that the exposed surface of the film is irradiated
evenly.
Inventors: |
PANGRLE, SUZETTE K.;
(CUPERTINO, CA) ; HUANG, RICHARD; (CUPERTINO,
CA) ; PRAMANICK, SHEKHAR; (FREMONT, CA) |
Correspondence
Address: |
BRINKS HOFER GILSON & LIONE
P.O. BOX 10395
CHICAGO
IL
60610
US
|
Family ID: |
22872793 |
Appl. No.: |
09/232359 |
Filed: |
January 15, 1999 |
Current U.S.
Class: |
427/551 ;
257/E21.241; 257/E21.273; 427/496; 427/503; 427/526; 427/596;
438/778; 438/788; 438/792; 438/798 |
Current CPC
Class: |
H01L 21/31695 20130101;
H01L 21/02126 20130101; H01L 21/3105 20130101; H01L 21/02351
20130101; H01L 21/02203 20130101 |
Class at
Publication: |
427/551 ;
427/496; 427/503; 427/526; 427/596; 438/798; 438/778; 438/788;
438/792 |
International
Class: |
B05D 003/06; C08J
007/04; C08J 007/18 |
Claims
1. A method of reducing the porosity of a tunable dielectric having
a thermal stability and a plurality of small pore sizes, comprising
the steps of: providing a film having an exposed surface;
positioning the film at a processing position; forming a beam from
a radiation source; and irradiating a select area of the exposed
surface with the beam at the processing position until a
predetermined dielectric constant is achieved.
2. A method of reducing the porosity of a tunable dielectric,
according to claim 1, further comprising the step of rotating the
film about a rotational axis as the select area of the exposed
surface is irradiated.
3. A method of reducing the porosity of a tunable dielectric,
according to claim 1, wherein the beam is an electron beam radiated
along a beam axis transverse to a film axis.
4. A method of reducing the porosity of a tunable dielectric,
according to claim 1, wherein the beam is an electron beam radiated
along a beam axis, the beam axis forming an acute angle with a film
axis.
5. A method of reducing the porosity of a tunable dielectric,
according to claim 1, further comprising the step of: rotating the
film about a rotational axis as the select area of the exposed
surface is irradiated; wherein the beam is an electron beam
radiated along a beam axis, the beam axis forming an acute angle
with a film axis.
6. A method of reducing the porosity of a tunable, according to
claim 5, further comprising the step of inclining the film having a
film axis, the film axis forming an acute angle with a horizontal
surface.
7. A method of reducing the porosity of a tunable dielectric,
according to claim 5, wherein the tunable dielectric is a
dielectric thin film selected from the group consisting of xerogels
and aerogels.
8. A method of reducing the porosity of a tunable dielectric,
comprising the steps of: providing a supporting device that
supports a thin film having an exposed surface; positioning the
supporting device at a processing position; forming a plurality of
electron beams from a plurality of electron sources; and
irradiating a select area of the exposed surface with the plurality
of electron beams at the processing position until a predetermined
dielectric constant is attained.
9. The method of claim 8, further comprising the step of: rotating
the supporting device and the electron sources about a rotational
axis and a plurality of beam axes respectively as the select area
of the exposed surface is irradiated.
10. The method of claim 8, wherein the plurality of electron beams
are radiated along a plurality of beam axis transverse to a film
axis.
11. The method of claim 8, wherein the plurality of electron beams
are radiated along a plurality of beam axes, the beam axes forming
a plurality of acute angles with a film axis.
12. The method of claim 8, further comprising the step of: rotating
the supporting device about a rotational axis as the select area of
the exposed surface is irradiated; wherein the plurality of
electron beams are radiated along a plurality of beam axes, the
beam axes forming a plurality of acute angles with a film axis.
13. The method of claim 8, further comprising the step of inclining
the supporting device and the electron sources so that a plurality
beam axes form an acute angle with a horizontal surface and a film
axis forms an acute angle with a horizontal surface.
14. A system for fabricating a tuned dielectric, comprising: a
radiation source for emitting a focused beam of radiation; a
positioning device for positioning a thin film at a location that
will receive the focused beam of radiation in a select area; and a
controlling device that manipulates the positioning device such
that the focused beam of radiation irradiates only the select area
of the thin film until a dielectric constant is attained.
15. A system for fabricating a tuned dielectric according to claim
14, further comprising rotating means coupled to a support device,
the support device being coupled to the positioning device for
rotating the thin film in response to the controlling device.
16. A system for fabricating a tuned dielectric according to claim
14, further comprising rotating means coupled to the radiation
source for rotating the radiation source in response to the
controlling device.
17. A system for fabricating a tuned dielectric according to claim
14, further comprising inclining means coupled to a support device,
the support device being coupled to the positioning device for
inclining the thin film in response to the controlling device.
18. A system for fabricating a tuned dielectric according to claim
14, further comprising inclining means coupled to the radiation
source for inclining the radiation source in response to the
controlling device.
19. A system for fabricating a tuned dielectric according to claim
14, wherein the focused source of radiation is an electron
beam.
20. A system for fabricating a tuned dielectric according to claim
14, wherein the focused source of radiation is an ion implantation
beam.
21. A system for fabricating a tuned dielectric according to claim
14, further comprising: inclining means coupled to a support
device, the support device being coupled to the positioning device
for inclining the thin film in response to the controlling device
and rotating means coupled to the support device for rotating the
thin film in response to the controlling device.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field of the Invention
[0002] The invention relates to a method and a system for altering
the porosity of thin films, and more particularly, to a method and
a system for creating a dielectric film having a low dielectric
constant.
[0003] 2. Description of Related Art
[0004] Microelectronic circuits perform a variety of functions in
small designs. With growing circuit speeds and miniaturization,
smaller circuit layouts stacked in a multilayer structure are
susceptible to the parasitic effect of capacitive coupling.
[0005] One solution that controls the effect of capacitive coupling
employs an interlayer dielectric having a low dielectric constant.
The integration of low dielectric constant materials between
integrated circuits isolate conductors, reduces power consumption,
and lowers the parasitic effect of capacitive coupling.
[0006] Several materials can be used as dielectrics. One insulator
used in microelectronic circuits is silicon dioxide (SiO.sub.2).
Silicon dioxide has a dielectric constant of about four. One of the
lowest known dielectric materials is air having a dielectric
constant of about one. Unfortunately, air does not lend itself to
multilayered design as it offers no underlying structure to support
layered circuits.
[0007] Accordingly, there is a need for a method and a system that
can achieve a low dielectric constant and also support multilayered
circuits. One class of tunable dielectric constant materials having
these properties is xerogels. Xerogels achieve a low dielectric
constant through the integration of nanometer size pores within a
silicon dioxide film. By applying a well-controlled evaporation
process, the xerogels can achieve a tuned dielectric constant by
tailoring the size and number of its pores. Xerogels can require
strict atmospheric controls to achieve the desired pore size, pore
distribution, and dielectric density. Accordingly, the preparation
of xerogels can require considerable time.
[0008] In light of the above described problems, there is a need
for a simple and timely method and system that creates a material
having a predetermined dielectric constant that is capable of
supporting the feature sizes of integrated circuits and lends
itself to a multilayered design.
SUMMARY OF THE INVENTION
[0009] The invention provides a system and a method for densifying
a surface of a porous film. By reducing the porosity of a film, the
method yields a densified film that is more impenetrable to
subsequent processes. The method comprises the steps of providing a
film having an exposed surface. The film can be supported by a
semiconductor substrate. When the film is moved to a processing
position, a focused source of radiation is created by a beam
source. The exposed surface of the film is then irradiated by the
beam source at the processing position until a predetermined
dielectric constant is achieved. The film or beam source may be
rotated, inclined, and/or moved between a variety of positions to
ensure that the exposed surface of the film is irradiated
evenly.
[0010] Another aspect of this invention involves a system for
fabricating a tuned dielectric film. The tuned dielectric
fabricating system comprises a radiation source, a positioning
device, and a controlling device. The radiation source emits a
focused beam of radiation, which for example, may comprise an
electron beam or ion implantation beam. The positioning device
places the film at a location that can receive the focused beam of
radiation. Preferably, the positioning device and radiation source
are coupled to rotating and inclining devices. The controlling
device can manipulate the radiation source, the positioning device,
the rotating devices, and/or the inclining devices such that the
focused beam of radiation irradiates the film until a predetermined
dielectric constant is attained.
[0011] The radiation source may be rotated, inclined, and/or moved
and may comprise a plurality of sources of radiation. The sources
of radiation may irradiate select areas of the film from different
positions to ensure even coverage. For example, where trenches are
formed in the dielectric film, the plurality of radiation sources,
which may be rotated, inclined, and/or positioned apart, will
irradiate the sides and bottom of the trench uniformly. Adjacent
surfaces can also be irradiated as can more than one trench.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a cross-sectional view of a semiconductor
substrate having a porous dielectric layer thereon;
[0013] FIG. 2 is a cross-sectional view of a semiconductor
substrate having in-laid copper leads formed in the porous
dielectric layer shown in FIG. 1;
[0014] FIG. 3 is a cross-sectional view of a film being prepared
according to a first embodiment of the invention;
[0015] FIG. 4 is a cross-sectional view of a film being prepared
according to a second embodiment of the invention;
[0016] FIG. 5 is a cross-sectional view of a film being prepared
according to a third embodiment of the invention; and
[0017] FIG. 6 is a block diagram of a system in accordance with the
invention for implementing the embodiments of FIGS. 3-5.
[0018] In the drawings, depicted elements are not necessarily drawn
to scale and the same reference numbers through several views may
designate alike and similar elements.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
[0019] The advantages of the present invention can be readily
comprehended through a description of a process for fabricating
in-laid copper leads in a dielectric film. Shown in FIG. 1, in
cross-section, is a portion of a semiconductor substrate 10 having
a dielectric layer 12 overlying the surface of semiconductor
substrate 10. Dielectric layer 12 is a silicon dioxide material
formed using the xerogel process previously described. To
accommodate in-laid copper leads, dielectric layer 12 includes a
first trench 14 and a second trench 16.
[0020] To form first and second trenches 14 and 16 in dielectric
layer 12, a plasma etching process is preferably carried out that
preferentially etches silicon dioxide, while not substantially
etching other materials, such as single silicon and polycrystalline
silicon, and the like. It is often necessary to apply a wet
cleaning process to remove polymer etching residue overlying the
surface areas of dielectric layer 12. Preferably, after completing
the plasma etching process, an organic cleaning solution is applied
to remove polymer fragments from the surface of dielectric layer
12.
[0021] To prevent the diffusion of copper into semiconductor
substrate 10, a barrier layer 18 is deposited to overlie the upper
surface of dielectric layer 12. Barrier layer 18 is preferably a
tantalum (Ta) metal film, or alternatively, a metal nitride, such
as tantalum nitride (TaN), titanium nitride (TiN), tungsten nitride
(WN), and the like. Preferably, barrier layer 18 is deposited by a
physical-vapor-deposition (PVD) or by a
plasma-enhanced-chemical-vapor-(PECVD) deposition process to a
thickness of about 300 angstroms.
[0022] After forming barrier layer 18, a copper seed layer 20 is
deposited to overlie barrier layer 18. Copper seed layer 20
provides electroplating imitation sites for the subsequent
formation of a copper layer overlying semiconductor substrate 10.
Preferably, copper seed layer 20 is 2000 .ANG. formed by a PVD or
PECVD of copper.
[0023] Once copper seed layer 20 is formed, a copper electroplate
deposition process is carried out to form a copper layer 22
overlying semiconductor substrate 10. During the deposition
process, copper selectively deposits on the copper seed layer 20.
As the deposition process continues, successive layers of copper
are deposited and eventually fill first and second trenches 14 and
16, and cover the remaining surfaces of semiconductor substrate
10.
[0024] After forming copper layer 22, a planarization process is
carried out to form in-laid copper leads 24 and 26 in first and
second trenches 14 and 16, respectively. Preferably, a
non-selective planarization process, such as
chemical-mechanical-polishing (CMP) is used to form a planar
surface 28. Alternatively, a non-selective plasma etching process
can also be used. The non-selective planarization process removes
substantially all layers overlying the upper surface of dielectric
layer 12. Also, depending upon the polishing resistance or etching
resistance of dielectric layer 12, a surface portion of dielectric
layer 12 can also be removed during the planarization process. Once
completed, in-laid copper leads 24 and 26 are defined by the shape
of first and second trenches 14 and 16, respectively. In-laid
copper leads 24 and 26 can extend in a variety of directions over
the surface of semiconductor 10 in order to electrically
interconnect various circuit components commonly used in an
integrated circuit device.
[0025] Upon completion of the planarization process and the
formation of in-laid copper leads 24 and 26, a silicon nitride
layer 30 is deposited to overlie planar surface 28. Preferably,
silicon nitride layer 30 is deposited using a PECVD process to a
thickness of about 500 angstroms. Silicon nitride layer 30 seals
the upper surface of in-laid copper leads 24 and 26 to prevent the
diffusion of unwanted contaminants, such as oxygen, and the like,
into the copper leads. Although the foregoing process is described
in the context of the formation of copper leads, those skilled in
the art will recognize that other structures, such as metallized
vias, and the like, can also be formed using the processing steps
described above.
[0026] The use of a xerogel to obtain a dielectric film having a
low dielectric constant can provide a convenient means for the
formation of such a film, however, numerous processing interactions
can function to increase the dielectric constant of a xerogel.
Although xerogel, as formed, has a dielectric constant in the range
of about 1.5 to 2.5, process interactions can increase the
dielectric constant to a value similar to thermally deposited
silicon dioxide (about 4.0). For example, during the formation of
trenches, such as first and second trenches 14 and 16, moisture can
be absorbed by the xerogel from the cleaning solution used to
remove polymer fragments from the surface of the dielectric layer.
Because the dielectric film is porous, solvents, such as water, and
the like, in the cleaning solution can be absorbed into the
dielectric film. In the case of water this is specially problematic
because water has a dielectric constant of about 85.
[0027] In addition to the deleterious effects of chemical
absorption, metallic atoms from barrier layer 18 can diffuse into
the porous xerogel. The diffused elements can react with the carbon
in the xerogel and sever the carbon-silicon bonds within the
xerogel. Further, nitrogen from silicon nitride layer 30 can
diffuse into the xerogel and form silicon nitride and silicon
oxynitride. These compounds have dielectric constants ranging from
of about 6, to about 7. Thus, while the porosity of the xerogel
leads to a beneficial low dielectric constant, the porosity also
provides diffusion pathways for the diffusion of unwanted materials
into the dielectric film. These materials react with the chemical
constituents of the xerogel to form high dielectric constant
compounds.
[0028] In addition to providing diffusion pathways for chemical
species contained in fabrication materials and processing
compounds, the porous nature of xerogel renders this material
easily removable by planarization processes, such as CMP. Those
skilled in the art will appreciate that precise control of the
resistivity of in-laid copper leads requires that a specified
cross-sectional area be maintained throughout the length of the
copper lead. Accordingly, it is undesirable to remove substantial
amounts of the dielectric material during the planarization
process. In an ideal case, the thickness of the in-laid copper lead
will be determined by the deposition thickness of the dielectric
layer. If substantial portions of the dielectric layer are removed
during the planarization process, or non-uniformly removed, the
thickness of the subsequently formed in-laid copper leads will vary
at different locations in the integrated circuit device. The
accompanying change in resistance can deleteriously affect the
function of the integrated circuit.
[0029] The process and material induced deleterious effects on the
dielectric constant of a dielectric film formed with a xerogel can
be reduced by the process and system of the present invention. By
controllably reducing the porosity of the dielectric film, the
present invention enables the formation of a densified dielectric
film that resists the inter-diffusion of fabrication materials and
process chemicals, and increases the hardness of the film, such
that an improved planarization process can be carried out.
[0030] The tunable dielectric process preferably includes a
positioning and an irradiating method. The method preferably
employs a radiation source 160 and/or a supporting device 250, as
shown in FIG. 6. The radiation source 160 and the supporting device
250 can be rotated, inclined, and/or moved. Rotating device 270 and
serves as a means for rotating a supporting device 250 such as a
susceptor 160. The rotating device 270 can attain a range of
rotational rates that allow a film 105 to be irradiated evenly.
Exemplary rotation rates can range from 0 to 100 revolutions per
mm. Similarly, inclining devices 290 and 300 serve as means for
inclining the supporting device 250 and the radiation source 160
separately. Preferably, one of the inclining devices 290 can
incline the film 105 to a plurality of inclining angles formed
between the supporting device 250 and a level horizontal surface
305 (shown in FIG. 5). A device that rotates and inclines the
supporting device 250 and radiation source 160 integrally is
envisioned in alternative embodiments.
[0031] FIG. 3 illustrates a cross-sectional view of the film 105
being prepared according to an embodiment of the invention. Here, a
thin film 105 is being prepared. As shown, the thin film 105 has an
exposed surface comprising a plurality of trenches or vias within a
plurality of substantially horizontal surfaces. In particular, the
thin film 105 comprises first, second, and third substantially
plane surfaces 110, 130, and 150, separated by a first 155 trench
and a second trench 158. The first trench 155 comprises a first
sidewall 115 and a second sidewall 125 connected to a first base
wall 120. The second channel 158 comprises a third sidewall 135 and
a fourth sidewall 145 connected to a second base wall 140. As
workers skilled in the art will appreciate, the shapes of the first
and second channels 158 and 260 are not necessarily uniform nor are
the channel shapes necessarily rectangular. The characteristics of
the trenches and vias may comprise any variety of geometric shapes,
such as, for example, a "U" or a "V" shape.
[0032] 1. First Embodiment
[0033] A tunable dielectric comprising the film 105 having a
plurality of pores is shown in FIG. 3. Preferably, the film 105,
which may be a thin film, is supported by an underlying structure
185, such as a semiconductor substrate with or without underlying
process layers. Utilizing a radiation source 160 that can be
rotated, inclined, and/or moved, one or more electron beams 165 are
formed. In a first embodiment, an "Electron Cure 30" manufactured
by Allied Signal Incorporated of San Diego, Calif. provides the
radiation source 160. The electron beams 165 preferably radiate
along one 175 or more beam axes. When the thin film 105 is placed
at a processing position 100, the electron beams 165 irradiate one
or more select areas of the thin film 105. In FIG. 3, the select
areas comprise the second side wall 115 and the second
substantially plane surface 130. In these areas 115 and 130, the
electron beams 165 preferably form an acute radiating angle between
the beam axes 175 and a film axis 170. The observed radiating
angle, however, may comprise an angle between zero and one hundred
and eighty degrees. Furthermore, although an electron beam 165 is
used in the first embodiment, other sources of radiation may be
used in alternative embodiments without departing from the spirit
or scope of the invention, such as, for example, ion beams.
[0034] In the above process, the radiation source 160 and the thin
film 105 may be rotated or inclined. FIG. 3 shows the radiation
source 160 and the thin film 105 being rotated about the beam axes
175 and rotational axis 180, respectively. As the select areas 115
and 130 are irradiated, the radiation source 160 and the thin film
105 are rotated ensuring an even exposure. Moreover, inclining
devices 290 and 300 may adjust the position and slope of the
radiation source 160 and the thin film 105. FIG. 5 shows the thin
film 105 inclined forming an acute angle between the film axis 170
and a level horizontal surface 305. Preferably, the inclination of
the thin film 105 ensures a uniform irradiation of the select areas
of the thin film 105. Workers skilled in the art will readily
appreciate that the rotation and inclination of the radiation
source 160 and/or the thin film 105 can be employed or eliminated
for any particular application to attain desired dielectric
constants.
[0035] The intensity of electron beams 165 and there emitted
duration are dependent on the current and desired properties of the
thin film 105. Specifically, the chemical composition, the pore
distribution, dielectric density, thickness, and desired dielectric
constant will determine the intensity and duration of the process.
As workers skilled in the art will appreciate, this list is not
exhaustive and many other properties can be considered when
selecting the intensity of electron beams 165 and this emitted
duration. Thus, it should be clear that other present and desired
properties of the thin film 105 are considered in alternative
embodiments.
[0036] 2. Second Embodiment
[0037] FIG. 4 shows a second embodiment that also reduces the
porosity of thin film 105. Only those parts of the second
embodiment that are different from the first embodiment will be
described. As shown, the exposed surfaces of thin film 105 are
irradiated from three distinct sources of radiation 205, 210, and
220. The three sources 205, 210, and 220 that are shown are focused
at specific surfaces 110, 115, 120, 125, 130, 135, 140, 145, and
150 that collectively comprise the exposed surface. The second
embodiment allows for the rotation of the radiation sources 205,
210, and 220 and the thin film 105 about a plurality of beam axes
225, 230, and 235 and a rotational axis 180, respectively.
Moreover, the second embodiment allows the radiation sources 205,
210, and 220 and the thin film 105 to be inclined through a
plurality of angles measured between the level horizontal surface
305 (shown in FIG. 5) and the beam axes 225, 230, and 235 and the
level horizontal surface and the film axis 170.
[0038] 3. Third Embodiment
[0039] FIG. 5 depicts a modification of the first embodiment as it
shows both a single movable radiation source 160 and illustrates
the thin film 105 in an inclined and rotating state. As explained
above, as the select areas of the thin film 105 are irradiated, the
radiation source 160 and the thin film 105 are rotated to ensure
even coverage of select areas 110, 115, 120, and 130. Likewise, the
radiation source 160 and the thin film 105 may be inclined.
Moreover, the rotation and the inclination of the radiation source
160 and the thin film 105 may continuously change, as the exposed
surface is irradiated to ensure that the select areas 110, 115,
120, and 130 attain a predetermined dielectric constant.
[0040] Porous silica xerogels and aerogels were used as
representative dielectric films in the above-described embodiments.
However, those skilled in the art will appreciate that the
invention envisions the use of other porous materials, such as, for
example, materials that have a high thermal stability and a low
thermal expansion coefficient or organic porous materials using low
energy, low dosage, radiation sources. The disclosed embodiments
enjoy utility in any semiconductor fabrication environment.
[0041] The concepts and embodiments previously illustrated may be
implemented through a tuned dielectric fabricating system
comprising a radiation source 160, a commercially available
handling system supporting device 250, rotating device 270,
inclining devices 290 and 300, and a controlling device 310, as
illustrated in FIG. 6. The radiation source 160, emits one or more
focused beams of radiation. Preferably, the focused beams may
comprise an electron beam or an ion implantation beam. The handling
system places water and film 105 with or without underlying process
layers. Preferably, the supporting device 250 and the radiation
source 160, are coupled to rotating device 270 and inclining
devices 290, 300 to rotate and/or incline the thin film 105 and
radiation source 160, respectively. The controlling device 310 can
manipulate the supporting device 250, rotating devices 270 and 280,
and inclining devices 290 and 300 such that the focused source of
radiation irradiates the select areas of the film 105 entirely
until a desired dielectric constant is attained.
[0042] Those skilled in the art will implement the steps necessary
to provide the device and methods disclosed. It is understood that
the process parameters including the rotational rates, inclining
angles, sources of radiation, radiation intensity, and radiation
duration are to be selected according to the properties of the film
105 and the desired dielectric constant to be attained.
[0043] Variations and modifications of the embodiments disclosed
herein may be made without departing from the scope of the
invention. The aforementioned description is intended to be
illustrative rather than limiting and it is understood that the
following claims and all equivalents set forth the scope of the
invention.
* * * * *