U.S. patent application number 09/966208 was filed with the patent office on 2002-02-07 for fill material for dual damascene processes.
Invention is credited to Lamb, James E. III, Shao, Xie.
Application Number | 20020016057 09/966208 |
Document ID | / |
Family ID | 23514719 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020016057 |
Kind Code |
A1 |
Lamb, James E. III ; et
al. |
February 7, 2002 |
Fill material for dual damascene processes
Abstract
An improved via and contact hole fill composition and method for
using the composition in the dual damascene production of circuits
is provided. Broadly, the fill compositions include a quantity of
solid components including a polymer binder and a solvent system
for the solid components. The boiling point of the solvent system
is less than the cross-linking temperature of the composition.
Preferred solvents for use in the solvent system include those
selected from the group consisting of alcohols, ethers, glycol
ethers, amides, ketones, and mixtures thereof. Preferred polymer
binders are those having an aliphatic backbone and a molecular
weight of less than about 80,000, with polyesters being
particularly preferred. In use, the fill composition is applied to
the substrate surfaces forming the contact or via holes as well as
to the substrate surfaces surrounding the holes, followed by
heating to the composition reflow temperature so as to cause the
composition to uniformly flow into and cover the hole-forming
surfaces and substrate surfaces. The composition is then cured, and
the remainder of the dual damascene process is carried out.
Inventors: |
Lamb, James E. III; (Rolla,
MO) ; Shao, Xie; (Rolla, MO) |
Correspondence
Address: |
HOVEY WILLIAMS TIMMONS & COLLINS
2405 GRAND BLVD., SUITE 400
KANSAS CITY
MO
64108
|
Family ID: |
23514719 |
Appl. No.: |
09/966208 |
Filed: |
September 27, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09966208 |
Sep 27, 2001 |
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09460162 |
Dec 13, 1999 |
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09460162 |
Dec 13, 1999 |
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09383785 |
Aug 26, 1999 |
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Current U.S.
Class: |
438/618 ;
257/E21.259; 257/E21.579 |
Current CPC
Class: |
Y10T 428/12556 20150115;
H01L 21/312 20130101; Y10T 428/24802 20150115; H01L 21/76808
20130101 |
Class at
Publication: |
438/618 |
International
Class: |
H01L 021/4763 |
Claims
We claim:
1. A method of applying a fill composition to a contact or via hole
having a bottom and sidewalls and formed in a substrate, said
composition being useful for protecting the substrate during
etching processes, said method comprising the steps of: providing a
quantity of a fill composition including a quantity of solid
components including a polymer binder and a solvent system for said
solid components, said composition being at least about 70% removed
from the base material when subjected to a pre-bake thermal
stability test, and said composition having less than about 15%
shrinkage when subjected to a film shrinkage test; and applying
said composition to at least a portion of said bottom and
sidewalls.
2. The method of claim 1, wherein said composition is capable of
being cross-linked at a cross-linking temperature, and further
including the step of heating said composition to its reflow
temperature so as to cause at least some of the composition to flow
into the contact or via hole, said reflow temperature being less
than the cross-linking temperature of said composition.
3. The method of claim 2, wherein said heating step comprises
heating said composition to a temperature of less than about
120.degree. C.
4. The method of claim 2, further including the step of curing said
composition by heating the composition to at least about its
cross-linking temperature after said reflow heating step.
5. The method of claim 4, said hole having a depth and wherein the
height of the cured fill composition in the contact or via hole is
at least about 50% of the depth of the hole.
6. The method of claim 4, said hole having a depth and wherein the
meniscus height of the cured fill composition is less than about
10% of the depth of the contact or via hole.
7. The method of claim 4, said hole having a diameter and having an
upper circumferential edge defining an opening, said substrate
presenting a surface adjacent said circumferential edge, wherein
said applying step comprises contacting a quantity of said
composition with said substrate surface to form a film, said film
having a thickness T at a distance from said circumferential edge
approximately equal to the diameter of the hole and a thickness t
adjacent the edge of the hole, and wherein after said curing step,
t is at least about 40% of T.
8. The method of claim 1, wherein said applying step comprises spin
coating said composition to the surface of the substrate and to the
bottom and sidewalls of the contact or via hole.
9. The method of claim 1, said solvent system having a flash point
of greater than about 85.degree. C.
10. The method of claim 1, wherein said polymer binder has a
molecular weight of less than about 80,000.
11. The method of claim 1, wherein said polymer binder comprises
polyacrylate.
12. The method of claim 1, wherein said solvent system includes a
solvent selected from the group consisting of alcohols, ethers,
glycol ethers, amides, esters, ketones, and mixtures thereof.
13. The method of claim 12, wherein said solvent is PGME.
14. The method of claim 1, wherein said composition further
includes a cross-linking agent.
15. The method of claim 1, wherein said polymer binder includes a
cross-linking moiety.
16. The method of claim 14, wherein the cross-linking temperature
of said composition is from about 150-220.degree. C.
17. The method of claim 1, wherein said solid components, when
mixed together, have a melting point of less than about 200.degree.
C.
18. The method of claim 1, said composition and said substrate each
having respective etch rates, said composition etch rate being
approximately equal to said base material etch rate.
Description
RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/460,162, filed Dec. 13, 1999, incorporated
by reference herein, which is a divisional of U.S. patent
application Ser. No. 09/383,785, filed Aug. 26, 1999, now
abandoned.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention is broadly concerned with fill
compositions and methods useful for protecting the surfaces forming
the contact and via holes during dual damascene processes for the
production of integrated circuits. More particularly, the
compositions of the invention comprise a quantity of solid
cross-linkable components including a polymer binder, and a solvent
system for the solid components. The boiling point of the solvent
system is preferably sufficiently lower than the cross-linking
temperature of the composition so that essentially all of the
solvent system is evaporated during the first stage bake without
the fill composition being cross-linked to any appreciable degree.
In use, the fill compositions are applied to a substrate previously
patterned with contact or via hole according to conventional
methods followed by heating the composition to its reflow
temperature in order to evaporate the solvent system and cause the
composition to flow into the hole for uniform coverage. The
composition is then cured and the remainder of the dual damascene
process carried out in the usual fashion.
[0004] 2. Description of the Prior Art
[0005] The damascene process, or the process of forming inlaid
metal patterning in preformed grooves, is generally a preferred
method of fabricating interconnections for integrated circuits. In
its simplest form, the dual damascene process starts with an
insulating layer which is first formed on a substrate and then
planarized. Horizontal trenches and vertical holes (i.e., the
contact and via holes) are then etched into the layer corresponding
to the required metal line pattern and hole locations,
respectively, that will descend down through the insulating layer
to the device regions (if through the first insulating layer, i.e.,
a contact hole) or to the next metal layer down (if through an
upper insulating layer in the substrate structure, i.e., a via
hole). Metal is next deposited over the substrate thereby filling
the trenches and the holes, and thus forming the metal lines and
the interconnect holes simultaneously. As a final step, the
resulting surface is planarized using the known chemical-mechanical
polish (CMP) technique, and readied to accept another dual
damascene structure.
[0006] During the dual damascene process, the contact and via holes
are typically etched to completion prior to the trench etching.
Thus, the step of trench etching exposes the bottom and sidewalls
(which are formed of the insulating or dielectric layer) of the
contact or via holes to over-etch which can deteriorate the contact
with the base layer. An organic material is therefore used to
partially or completely fill the via or contact holes and to
protect the bottom and sidewalls from further etch attack. These
organic fill materials can also serve as a bottom anti-reflective
coating (BARC) to reduce or eliminate pattern degradation and
linewidth variation in the patterning of the trench layer, provided
the fill material covers the surface of the dielectric layer.
[0007] Fill materials have been used for the past several years
which have high optical density at the typical exposure
wavelengths. However, these prior art materials have limited fill
properties. For example, when the prior art compositions are
applied to the via or contact holes formed within the substrate and
to the substrate surface, the films formed by the compositions tend
to be quite thin on the substrate surface immediately adjacent the
holes, thus leading to undesirable light reflection during
subsequent exposure steps. Also, because the prior art compositions
etch more slowly than the dielectric layer, the unetched fill
compositions provide a wall on which the etch polymer will deposit.
This etch polymer build-up then creates undesirable resistance
within the metal interconnects of the final circuit. These problems
are explained in more detail below.
[0008] There is a need in the art for contact or via hole fill
materials which provide complete coverage at the top of via and
contact holes. Furthermore, this material should provide adequate
protection to the base of the via and contact holes during etching
to prevent degradation of the barrier layer and damage to the
underlying metal conductors. In order to prevent sidewall polymer
buildup, the etch rate of the material should be equal to or
greater than the etch rate of the dielectric material, or the
contact or via holes should be filled partially so that the fill
material in the holes does not extend above the base of the trench
following trench etch.
SUMMARY OF THE INVENTION
[0009] The instant invention overcomes the problems in the art by
providing a fill material or composition which can be applied to
via and/or contact holes during damascene processing to provide
complete surface coverage while avoiding undue buildup of the etch
polymer around the top edge of the holes at the base of the trench
of the damascene structure.
[0010] In more detail, the compositions (fill material and fill
composition are used interchangeably herein) of the invention
comprise a quantity of solid components including a polymer binder
or resin, and a solvent system (either single or multiple solvents)
for the solid components. The inventive compositions are superior
to prior art compositions in that they are formulated to achieve
two requirements: the inventive composition will freely and evenly
flow into the contact or via holes with minimal or no cross-linking
of the composition during the pre-bake stage (i.e., first stage
bake); and during the pre-bake stage essentially all of the solvent
is evaporated so that the composition incurs very little shrinkage
during the final bake stage. These two requirements are quantified
by subjecting the composition to the "pre-bake thermal stability
test" and the "film shrinkage test" set forth in detail below.
[0011] There are numerous factors which affect the ability of the
fill composition to meet the foregoing requirements. For example,
the polymer binder or resin preferably comprises an aliphatic
backbone and has a molecular weight of less than about 80,000,
preferably less than about 25,000, and more preferably from about
2000-7500. Suitable polymer binders include polyesters,
polyacrylates, polyheterocyclics, polyetherketones,
polyhydroxystyrene, polycarbonates, polyepichlorohydrin, polyvinyl
alcohol, oligomeric resins (such as crown ethers, cyclodextrins,
epoxy resins), and mixtures of the foregoing. The solvent systems
utilized in the composition of the invention preferably have a
boiling point of less than about 160.degree. C., more preferably
less than about 140.degree. C., and most preferably less than about
120.degree. C. The solvent system should also have a flash point of
greater than about 85.degree. C., and more preferably greater than
about 100.degree. C. When more than one solvent is utilized in the
solvent system, the boiling point or flash point of the solvent
system refers to the boiling point or flash point of the highest
boiling or lowest flashing solvent. It is also important that the
solvent system be compatible with the resist system chosen for the
particular damascene process. That is to say, an air-dried film of
the fill composition should redissolve in the chosen resist solvent
system within 30 seconds with essentially no undissolved residue
being visible in the solution.
[0012] The concentrations of the solvent system and other volatile
species present in the composition is not critical, so long as the
total concentration of the solvent system and volatile species in
the film just prior to cross-linking of the film (i.e., just prior
to the second stage bake) is less than about 5% by weight, and
preferably less than about 2% by weight, based upon the total
weight of the fill composition taken as 100% by weight. This
solvent system and volatile weight percent in combination with the
above solvent system boiling and flash points is important to
ensure that minimal shrinking of the composition occurs during the
second stage bake. Preferred solvents for use in the solvent system
include alcohols, ethers, glycol ethers, amides, esters, ketones,
water, propylene glycol monomethyl ether (PGME), propylene glycol
monomethyl ether acetate (PGMEA), ethyl lactate, and PCBTF
(p-chlorobenzotrifluoride), with PGME being particularly
preferred.
[0013] The fill compositions of the inventions preferably
cross-link at a temperature of from about 150-220.degree. C., and
more preferably about 180.degree. C. It is important that the fill
compositions cross-link at a temperature higher than the
temperature to which the composition is heated during the first
stage reflow baking so as to avoid undue crosslinking of the
composition during the reflow step. Such premature cross-linking
would prevent the composition from completely and uniformly flowing
into the contact or via holes. Cross-linking of the polymer binder
in the composition can be accomplished by the use of a
cross-linking agent in the composition or by the selection of
polymer binders which include "built in" cross-linking moieties.
Preferred cross-linking systems include acid or base catalyzed,
thermal catalyzed, and photocatalyzed systems such as aminoplasts,
epoxides, blocked isocyanates, acrylics, and mixtures thereof.
[0014] All solid components utilized in the fill compositions of
the invention should form a free-flowing liquid at a first stage
reflow bake temperature of less than about 200.degree. C., and
preferably less than about 120.degree. C., thus preventing the
composition from adhering to the hole sidewalls and forming a steep
meniscus. All components must remain chemically stable at these
reflow temperatures for at least about 15 seconds, and preferably
at least about 30 seconds. By chemically stable, it is meant that
the components only undergo changes in their physical state and not
in their chemical state (such as by cross-linking of their
components). The chemical stability can be determined by UV/VIS or
FTIR analysis, both before and after the first stage bake.
[0015] In order to avoid the etch polymer buildup problems of the
prior art, the etch rate of the fill composition should be
approximately equal to the base material or dielectric material
etch rate. Furthermore, the fill composition should have a faster
etch rate than the etch rate of the photoresist. The ratio of the
composition etch rate to the photoresist etch rate should be at
least about 1.5:1, preferably at least about 3:1, and more
preferably at least about 4:1. One way to achieve such fill
composition etch rates is through the selection of the polymer
binder. Highly oxygenated or halogenated species will result in an
increased etch rate.
[0016] The compositions can also be formulated to include optional
ingredients as necessary. Optional ingredients include wetting
agents (such as fluorinated surfactants, ionic surfactants,
non-ionic surfactants, and surface active polymer additives) and
dyes or chromophores. Examples of suitable dyes include any
compound that absorbs at the electromagnetic wavelength used for
the particular process. Examples of dyes which can be used include
compounds containing anthracene, naphthalene, benzene, chalcone,
phthalimides, pamoic acid, acridine, azo compounds, and
dibenzofuran. The dyes may be physically mixed into the
composition, or alternately, may be chemically bonded to the
polymer binder. For e-beam exposure, conductive compounds can be
used.
[0017] The method of applying the fill compositions to a substrate
with a contact or via hole simply comprises applying a quantity of
a composition hereof to the substrate surfaces forming the hole by
any conventional application method (including spin coating). After
the composition is applied to the hole, it should be heated to its
reflow temperature (as set forth above) during the first stage bake
so as to cause the composition to flow into the contact or via
hole(s), thus achieving the desired hole and substrate surface
coverage. After the desired coverage is achieved, the resulting
fill composition film should then be heated to at least the
cross-linking temperature of the composition so as to cure the
film.
[0018] In partial fill processes, the height of the cured fill
material in the hole should be from about 35-65%, and preferably at
least about 50% of the depth of the hole. In complete fill
processes, the height of the cured fill material in the hole should
be at least about 95%, and preferably at least about 100% of the
depth of the hole. The height of the meniscus of the cured fill
composition should be less than about 15% of the depth of the hole,
and preferably less than about 10% of the hole depth. Although a
meniscus is conventionally deemed to be a concave surface or
"valley" which forms on the top surface of a flowable substance in
a container (i.e., the via or contact hole), as used herein the
term meniscus is also intended to include convex surfaces or
"hills" formed on the top surface of a substance in a container or
hole. The meniscus height as used herein refers to the distance
from the highest point at which the composition contacts the
sidewalls of the contact or via holes to the lowest point in the
concave surface of the meniscus, or for a convex meniscus, the
distance from the highest point at which the composition contacts
the sidewalls of the contact or via holes to the highest point on
the convex surface.
[0019] The thickness of the cured fill material film on the surface
of the substrate adjacent the edge of the contact or via hole
should be at least about 40%, preferably at least about 50%, and
more preferably at least about 70% of the thickness of the film on
the substrate surface a distance away from the edge of the contact
or via hole approximately equal to the diameter of the hole.
Finally, the percent of solids in the compositions should be
formulated so that the thickness of the film formed on the
substrate surface is from about 35-250 nm. Following the methods of
the invention will yield precursor structures for the dual
damascene process having the foregoing desirable properties.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1A depicts a starting substrate structure for use in a
partial fill process using a prior art partial planarizing bottom
anti-reflective coating (BARC) as the contact or via hole fill
material;
[0021] FIG. 1B depicts the structure of FIG. 1A after a photoresist
has been applied to the dielectric layer, exposed, and developed,
and the contact or via hole pattern has been etched;
[0022] FIG. 1C depicts the structure of FIG. 1B after a prior art
BARC has been applied to the structure and cured;
[0023] FIG. 1D depicts the structure of FIG. 1C after a photoresist
has been applied to the structure, exposed, and developed;
[0024] FIG. 1E depicts the structure of FIG. 1D after the trench
patterns have been etched;
[0025] FIG. 1F depicts the structure of FIG. 1E after the
photoresist and fill material have been removed from the
structure;
[0026] FIG. 1G depicts the structure of FIG. 1F after the barrier
layer has been removed;
[0027] FIG. 1H depicts the structure of FIG. 1G after a metal has
been deposited into the contact or via holes;
[0028] FIG. 1I depicts the final damascene structure formed during
the steps shown in FIGS. 1A-1H;
[0029] FIG. 2A depicts a starting substrate structure for use in a
complete fill process using a prior art planarizing BARC as the
contact or via hole fill material;
[0030] FIG. 2B depicts the structure of FIG. 2A after a photoresist
has been applied to the dielectric layer, exposed, and developed,
and the contact or via hole pattern has been etched;
[0031] FIG. 2C depicts the structure of FIG. 2B after a prior art
BARC has been applied to the structure and cured;
[0032] FIG. 2D depicts the structure of FIG. 2C after a photoresist
has been applied to the structure, exposed, and developed;
[0033] FIG. 2E depicts the structure of FIG. 2D after the trench
patterns have been etched;
[0034] FIG. 2F depicts the structure of FIG. 2E after the
photoresist and fill material have been removed from the
structure;
[0035] FIG. 2G depicts the structure of FIG. 2F after the barrier
layer has been removed;
[0036] FIG. 2H depicts the structure of FIG. 2G after a metal has
been deposited into the contact or via holes;
[0037] FIG. 2I depicts the final damascene structure formed during
the steps shown in FIGS. 2A-2H;
[0038] FIG. 3A depicts a starting substrate structure for use in a
fill process using a prior art conformal type BARC as the contact
or via hole fill material;
[0039] FIG. 3B depicts the structure of FIG. 3A after a photoresist
has been applied to the dielectric layer, exposed, and developed,
and the contact or via hole pattern has been etched;
[0040] FIG. 3C depicts the structure of FIG. 3B after a prior art
conformal BARC has been applied to the structure and cured;
[0041] FIG. 3D depicts the structure of FIG. 3C after a photoresist
has been applied to the structure, exposed, and developed;
[0042] FIG. 3E depicts the structure of FIG. 3D after the trench
patterns have been etched;
[0043] FIG. 3F depicts the structure of FIG. 3E after the
photoresist and fill material have been removed from the
structure;
[0044] FIG. 3G depicts the structure of FIG. 3F after the remainder
of the barrier layer has been removed;
[0045] FIG. 3H depicts the structure of FIG. 3G after a metal has
been deposited in the contact or via holes;
[0046] FIG. 3I depicts the final damascene structure formed during
the steps shown in FIGS. 3A-3H;
[0047] FIG. 4A depicts a starting substrate structure for use in a
complete fill process using a fill material of the invention;
[0048] FIG. 4B depicts the structure of FIG. 4A after a photoresist
has been applied to the dielectric layer, exposed, and developed,
and the contact or via hole pattern has been etched;
[0049] FIG. 4C depicts the structure of FIG. 4B after a fill
material according to the invention has been applied to the
structure to completely fill the via or contact holes and
cured;
[0050] FIG. 4D depicts the structure of FIG. 4C after a photoresist
has been applied to the structure, exposed, and developed;
[0051] FIG. 4E depicts the structure of FIG. 4D after the trench
patterns have been etched;
[0052] FIG. 4F depicts the structure of FIG. 4E after the
photoresist and fill material have been removed from the
structure;
[0053] FIG. 4G depicts the structure of FIG. 4F after the barrier
layer has been removed;
[0054] FIG. 4H depicts the structure of FIG. 4G after a metal has
been deposited into the contact or via holes;
[0055] FIG. 4I depicts the final damascene structure formed during
the steps shown in FIGS. 4A-4H;
[0056] FIG. 5A depicts a starting substrate structure for use in a
partial fill process using a fill material of the invention;
[0057] FIG. 5B depicts the structure of FIG. 5A after a photoresist
has been applied to the dielectric layer, exposed, and developed,
and the contact or via hole pattern has been etched;
[0058] FIG. 5C depicts the structure of FIG. 5B after a fill
material according to the invention has been applied to the
structure to partially fill the contact or via holes and cured;
[0059] FIG. 5D depicts the structure of FIG. 5C after a photoresist
has been applied to the structure, exposed, and developed;
[0060] FIG. 5E depicts the structure of FIG. 5D after the trench
patterns have been etched;
[0061] FIG. 5F depicts the structure of FIG. 5E after the
photoresist and fill material have been removed from the
structure;
[0062] FIG. 5G depicts the structure of FIG. 5F after the barrier
layer has been removed;
[0063] FIG. 5H depicts the structure of FIG. 5G after a metal has
been deposited into the contact or via holes;
[0064] FIG. 5I depicts the final damascene structure formed during
the steps shown in FIGS. 5A-5H;
[0065] FIG. 6A depicts a starting substrate structure for use in a
complete fill process using a fill material of the invention
followed by applying a thin BARC over the via/contact fill
material;
[0066] FIG. 6B depicts the structure of FIG. 6A after a photoresist
has been applied to the dielectric layer, exposed, and developed,
and the contact or via hole pattern has been etched;
[0067] FIG. 6C depicts the structure of FIG. 6B with a fill
material according to the invention applied to the structure to
completely fill the contact or via holes and subsequent curing of
the fill material, followed by the application of a thin film BARC
to the cured fill material and subsequent curing of the thin
film;
[0068] FIG. 6D depicts the structure of FIG. 6C after a photoresist
has been applied to the structure, exposed, and developed;
[0069] FIG. 6E depicts the structure of FIG. 6D after the trench
patterns have been etched;
[0070] FIG. 6F depicts the structure of FIG. 6E after the
photoresist, fill material, and thin film BARC have been removed
from the structure;
[0071] FIG. 6G depicts the structure of FIG. 6F after the barrier
layer has been removed;
[0072] FIG. 6H depicts the structure of FIG. 6G after a metal has
been deposited into the contact or via holes;
[0073] FIG. 6I depicts the final damascene structure formed during
the steps shown in FIGS. 6A-6H;
[0074] FIG. 7 depicts the meniscus height of a precursor structure
in the dual damascene process utilizing a prior art fill
composition in a contact or via hole;
[0075] FIG. 8 depicts the meniscus height of a precursor structure
in the dual damascene process utilizing a fill composition
according to the instant invention in a contact or via hole;
[0076] FIG. 9 depicts the thickness of a film formed from a prior
art fill composition and applied to the surface surrounding a
contact or via hole in a precursor structure in the dual damascene
process;
[0077] FIG. 10 depicts the thickness of a film formed from the
inventive fill composition and applied to the surface surrounding a
contact or via hole in a precursor structure in the dual damascene
process;
[0078] FIG. 11 is an SEM photograph (50,000.times.) showing a fill
material of the invention applied to a via hole and cured;
[0079] FIG. 12 is an SEM photograph (50,000.times.) showing a fill
material of the invention applied to a via hole and cured with a
thin film of anti-reflective coating applied to the top of the
material followed by curing of the thin film;
[0080] FIG. 13 is an SEM photograph (50,000.times.) showing a cured
fill material of the invention applied to a via hole according to
partial via fill processes;
[0081] FIG. 14 is an SEM photograph (60,000.times.) showing a prior
art BARC in a via hole after curing;
[0082] FIG. 15 is an SEM photograph (50,000.times.) showing a
different prior art BARC material in a via hole after curing;
and
[0083] FIG. 16 is an SEM photograph (50,000.times.) showing a prior
art cured BARC partially filling a via hole.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0084] 1. The Problems with Prior Art Processes and
Compositions
[0085] FIGS. 1A-1I show various stages of a partial via fill
process using prior art organic fill materials. In FIG. 1A a
starting damascene structure 11 includes a dielectric material 10
applied to a substrate 12 and interspersed with a pattern of gate
or metal conductors 16. A protective barrier layer 18 covers and
thus protects dielectric material 10 and conductor 16 during
further etching. A dielectric material 20 is applied immediately
adjacent barrier layer 18. Referring to FIG. 1B, a photoresist 22
is then applied to the dielectric layer 20 followed by exposure and
developing of the resist contact or via hole patterns onto the
dielectric layer 20 and subsequent etching to form the contact or
via holes 24.
[0086] In FIG. 1C, a prior art BARC fill material 26 is applied to
holes 24 to partially fill the holes to a level of from 35-65% of
the original hole depth followed by curing of the material 26. One
notable prior art shortcoming can be seen in FIG. 1C. First, at top
edge 28 of the holes 24 the BARC material 26 thins and may
completely dewet leaving little or no BARC material 26 to prevent
reflections which will negatively impact the trench patterning step
as shown in FIG. 1D where the trench patterning of a photoresist 30
is degraded at location 32. After the trench patterning, trenches
34 are etched in the dielectric material 20 and part of the
dielectric material is eroded between adjacent trench lines at
location 36 (see FIG. 1E) due to the degraded trench pattern. Other
problems with the prior art materials is that the cured material
forms a steep meniscus (the meniscus height being represented by
"M" in FIG. 1C), and the etch rate of the BARC material 26 is
slower than that of the dielectric layer 20. This slower etch rate
combined with the steep meniscus results in the formation of peaks
38 of the BARC material 26 which allow etch polymer 40 to deposit
and build up on top of the dielectric layer 20.
[0087] Referring to FIG. 1F, the photoresist 30 and the BARC
material 26 are then removed from structure 11. However,
conventional BARC material stripping compositions will not remove
the polymer 40, and the processes that do remove the polymer 40
tend to attack the dielectric layer 20 and/or protective barrier
layer 18. Therefore, the polymer 40 is generally left on the
structure 11 and the damascene process continued.
[0088] In FIG. 1G, the barrier layer 18 is removed followed by the
deposition of the metal or gate material 42 in the holes 24 and
trenches 34 (FIG. 1H). After the dual damascene metallization step
shown in FIG. 1H, conventional CMP processes are carried out,
resulting in a completed damascene structure 44.
[0089] Upon examining structure 44 in FIG. 1I, the problems created
by the above-described prior art fill material shortcomings can be
readily seen. For example, the eroded trench line locations 36
often result in a short at point 46. Also, the buildup of the etch
polymer 40 (which is an insulating material) leads to higher
contact/via resistivities where the metal to metal contact area
between the metals in the trenches 34 and the holes 24 is reduced
by the presence of the polymer 40. Furthermore, the buildup of the
polymer 40 will cause increased stress in the metal around the
polymer 40, thus occasionally leading to the cracking of the metal
around the holes 24 and/or trenches 34 resulting in defects in the
final circuit.
[0090] FIGS. 2A-2I depict a prior art damascene process very
similar to the process depicted in FIGS. 1A-1I except that FIGS.
2A-2I show the "complete" fill (i.e., greater than 95%) of the
prior art BARC fill material 26 in the contact or via holes 24 as
shown in FIG. 2C. The use of the complete fill process eliminates
the thinning problem as discussed above with respect to the top
edge 28 of the holes 24 in FIG. 1C. However, the slower etch rate
of the BARC material 26 still causes the buildup of the etch
polymer 40 as shown in FIGS. 2E-2I. Again, this leads to higher
resistivities and metal stress around the polymer buildup.
[0091] FIGS. 3A-3I illustrate a prior art process for forming
damascene structures which is very similar to the processes
discussed above except that the prior art BARC fill material 26 is
applied to the via or contact holes 24 in what is known as a
"conformal" fashion. Referring to FIG. 3C, the conformal
application is illustrated wherein a thin film of the BARC material
26 is coated over top surface 48 of the dielectric layer 20, down
edge surfaces 50 of the holes 24, and on bottom surfaces 52 of the
holes 24. When conformally applied, the BARC material 26 maintains
nearly uniform thickness, providing good reflectivity control and
minimizing damage to the trench pattern integrity. However, the
slower etch rate of the BARC material 26 again leads to the problem
of the etch polymer 40 building up on the dielectric layer 20 as
shown in FIGS. 3E-3I.
[0092] Another problem with using prior art BARC materials in a
conformal fashion is that the bottom surfaces 52 of the holes 24
often do not have sufficient protection from the etch gas during
the etching process. Referring to FIG. 3E, the barrier layer 18 can
be breached during etching, thus exposing the conductors 16 to
attack. The etch gas utilized during the trench etching process or
the resist strip removal process may also attack the conductors 16
as shown in FIG. 3F. The resist strip process generally consists of
several steps including: oxygen plasma strip, ozone plasma strip,
and various wet chemistries such as ozonated water, sulfuric
peroxide, hydrogen peroxide, and dilute HF followed by water
rinses. For most metal conductors 16, the wet chemistries will
directly etch the metal and cause metal corrosion during the
following rinse step, absent the protective barrier layer 18. The
oxygen radical-based plasma strip process can also form stable
metal oxides on the surface of the metal, thus degrading the via or
contact reliability. This in turn will lead to high via or contact
resistance and/or complete failure of the interconnect at point 54
(FIG. 3I) after via or contact dual damascene metallization.
[0093] 2. The Present Invention
[0094] FIGS. 4A-4I, 5A-5I, and 6A-6I illustrate the improved
damascene structures that can be obtained utilizing fill materials
formulated according to the instant invention.
[0095] FIGS. 4A-4I show a complete via fill process using organic
fill materials having the properties described above. In FIG. 4A, a
starting damascene structure 56 includes a dielectric material 58
applied to a substrate 60 and interspersed with a pattern of gate
or metal conductors 64 (formed of aluminum, copper, tungsten, or
other conducting material). The substrate 60 can be formed of
silicon, GaAs, or other semiconductor materials with regions of
doping to provide source and drain areas or any other electrical
element. A protective barrier layer 66 covers and thus protects the
dielectric material 58 and conductors 64 during further etching
steps. The barrier layer 66 can be formed of silicon, tantalum, and
titanium nitrides, as well as titanium and tantalum oxides. A
dielectric layer 68 is applied immediately adjacent the barrier
layer 66. The dielectric material 58 and the dielectric material 68
may be formed of most insulating materials, including silicon
dioxide, silicon nitrides, fluorinated oxides, and titanium oxides.
Referring to FIG. 4B, a photoresist 70 is applied to the dielectric
layer 68 followed by exposure and developing of the contact or via
hole pattern onto the dielectric layer 68 and subsequent etching to
form the contact or via holes 72.
[0096] In FIG. 4C, a BARC fill material 74 formulated according to
the instant invention is applied to the holes 72, preferably by the
spin coat or spray coat methods, to essentially completely (i.e.,
at least 95% of the holes' depth) fill the holes 72. The material
74 is then cured by heating to its cross-linking temperature.
During the deposition of material 74, the substrate to which the
material 74 is applied may be static, or it may be spinning with a
rotation of from about 200-5000 rpm. The material 74 can be applied
in either a radial or reverse radial manner. Alternately, the
material 74 can be applied by a spray atomization method. If
necessary, in order to improve via or contact fill depth, a second
or third fill composition layer can be applied after spinning the
previous coat for about 15-60 seconds at a rotational speed of at
least about 1500 rpm. Finally, the material 74 can also be applied
utilizing the spike spin method wherein the material 74 is applied
to the substrate while the substrate is accelerated to a rotational
speed of about 3000-7000 rpm for about 1-3 seconds followed by
deceleration to a rotational speed of from about 200-3000 rpm and
spun until dry. After the application of one or more coats of the
via or contact fill composition and spin drying to remove the
solvent(s), the film of material 74 is ready to bake.
[0097] The initial bake step (or first stage bake) removes the
volatile byproducts and solvent systems from the fill composition
film and heats the film to a temperature above the reflow point of
the combined solid components present in the material 74. When
heated to the reflow point, the material 74 will liquify and
readily flow into the via or contact holes 72 under the force of
gravity, capillary forces, or surface wetting dynamic forces to
provide the desired coverage and hole fill levels and to displace
trapped air, solvents, and volatiles evolving from the material 74.
The initial bake temperature should be less than about 200.degree.
C., preferably less than about 140.degree. C., and more preferably
less than about 120.degree. C. The initial bake step should not
result in a chemical change in the liquified fill material 74
(e.g., the material should not cross-link). The initial bake step
may be carried out in any number of ways including but not limited
to a contact hotplate, a proximity hotplate with a gas pillow
between the substrate and hotplate surface, a proximity hotplate
with proximity pins between the substrate and the hotplate surface,
convection oven, infrared oven, or halogen rapid thermal processing
oven. Upon being liquified during the initial bake step, the
material 74 will reach the desired coverage in less than about 60
seconds, preferably less than about 15 seconds, and more preferably
less than about 1 second.
[0098] Once the material 74 has flowed sufficiently to achieve the
desired coverage, the material 74 is cured in a second stage bake.
The second stage bake cross-links the film of the material 74 to
prevent the material 74 from interfering with subsequent resist
coating and processing. Once the material 74 is cured, a
photoresist 76 is applied, exposed, and developed to form patterns
for trenches 78 which are subsequently etched. Because the material
74 has an etch rate equal to or greater than the etch rate of the
dielectric layer 68, the problem of etch polymer buildup on the
layer 68 prevalent in the prior art is eliminated as can be seen in
FIGS. 4E-4I.
[0099] Referring to FIG. 4F, the photoresist 76 and the BARC
material 74 are removed from structure 56 without damage to the
barrier layer 66. This is typically accomplished by plasma etch,
ozone strip, ozonated water strip, organic solvent strip, sulfuric
peroxide cleaning, hydrogen peroxide cleaning or any combinations
of the foregoing strip and clean processes. In FIG. 4G, the barrier
layer 66 is then removed (such as by plasma etch) followed by the
deposition of a metal or gate material 80 (with appropriate barrier
and seed layers, if necessary) in the holes 72 and trenches 78
(FIG. 4H). After the dual damascene metallization step shown in
FIG. 4H, conventional CMP processes are carried out resulting in a
completed damascene structure 82. Unlike the prior art, the
resulting structure 82 is formed without any via or contact hole
fill residues, sidewall polymer buildup or crowns around the top of
the via or contact holes, or pattern distortions leading to
shorting of adjacent trenches.
[0100] The process shown in FIGS. 5A-5I is similar to the process
described above with respect to FIGS. 4A-4I except that FIGS. 5A-5I
illustrate the partial fill process utilizing fill materials
according to the instant invention. FIGS. 6A-6I depict an alternate
embodiment wherein a thin film of a BARC 84 is spin coat-applied
over the cured fill material 74, followed by curing of the BARC
film. The film 84 can be tailored to the electromagnetic wavelength
used for subsequent resist exposure. The second film protects the
subsequent resist pattern from electromagnetic wave variations
which lead to a degraded resist pattern. Alternately, a conductive
film for e-beam exposure can be applied in place of the film 84 to
reduce the impact of charging within the substrate which would
cause degradation of the e-beam resist pattern. A resist film 76 is
then applied and patterned as described previously.
[0101] FIGS. 7-10 compare damascene structures utilizing fill
compositions according to the invention to structures utilizing
prior art fill compositions. In FIG. 8, the meniscus formed by a
fill composition 86 formulated according to the instant invention
and applied to a via or contact hole 88 is much less steep than the
meniscus formed by a prior art fill material 90 applied to a via or
contact hole 92 and shown in FIG. 7. Thus, relative to the height H
of the via or contact hole, the fill compositions of the instant
invention have a meniscus height M of less than about 15% of H, and
preferably less than about 10% of H. For example, if the height H
of a via hole was 200 nm, the meniscus height M should be less than
about 30 nm, and preferably less than about 20 nm. This meniscus
height M in combination with the etch rate of the fill composition
prevents the polymer buildup problems of the prior art, thus
yielding metal conductors within the contact or via holes without
increased resistance.
[0102] FIG. 9 shows the thickness of the prior art film 90 on a
surface 94 of a dielectric material 96 adjacent a via or contact
hole opening 98. FIG. 10 illustrates the thickness of an inventive
film 100 on a surface 102 of a dielectric material 104 adjacent a
via or contact hole opening 106. In both FIGS. 9 and 10, the
respective films 90, 100 have a thickness "T" at a distance from
the edge of the hole approximately equal to the diameter of the
hole. Each film also has a thickness "t" at areas on or closely
adjacent the hole edge. The thickness t of the inventive film 100
is greater than the thickness t of the prior art prior art film 90.
When using the inventive fill compositions in the dual damascene
processes, t should be at least about 40% of T, preferably at least
about 50% of T, and more preferably at least about 70% of T. For
example, if a given hole has a diameter of 200 nm, then at about
that distance from the edge of the hole, t should be at least about
0.4 T.
Composition Testing
[0103] In order to determine whether a particular composition meets
the requirements of the invention, the composition is subjected to
the following tests:
[0104] 1. Pre-bake Thermal Stability Testing
[0105] The fill material should be reflowable and densified during
the pre-bake step in order to achieve the desired fill level and
fill profile. To accomplish this, the substrate and fill material
must be heated to a temperature that will remove the casting
solvent from the film and allow the film to flow and densify prior
to cross-linking of the fill material. With the onset of
cross-linking, the film viscosity and flow point increase as the
film's solubility in the solvent decreases and the chemical links
become rigid, thus reducing the potential density of the film.
[0106] As used herein, a "pre-bake thermal stability test"
determines the degree of cross-linking during the pre-bake stage
and is conducted as follows. The via fill material is spin-coated
onto a flat silicon wafer followed by a 30 second pre-bake at a
temperature that is either: the standard pre-bake temperature
recommended by the manufacturer of the particular prior art fill
material; or, above the boiling point of all solvents present in
the inventive fill material. Following the pre-bake, the film
thickness is measured with an ellipsometer and recorded. A solution
of a casting solvent or solvents (selected for the particular fill
composition being tested) is then applied to the surface of the
wafer for 5 seconds followed by spin drying at 5000 rpm for 30
seconds. Finally, the sample is baked at 100.degree. C. for 30
seconds, and the film thickness is measured again to determine the
percent of the fill material removed by the casting solvent. The
percent of material removed corresponds to the quantity of
noncross-linked fill composition. The inventive fill compositions
are at least about 70% removed, preferably at least about 85%
removed, and more preferably essentially completely removed during
this test.
[0107] 2. Final Bake Film Solvent Resistance Testing
[0108] In order for a fill material to perform properly as a
sublayer for a photoresist layer, the cured fill material must be
relatively insoluble in the solvent system from which the
particular photoresist is cast. This is necessary to avoid the
mixing of the fill material with the photoresist which typically
degrades the performance of the photoresist. As used herein, to
determine whether a particular cured fill material is insoluble in
the preferred resist solvent system, a "final bake film solvent
resistance test" is conducted as follows. The via fill material is
spin-coated onto a flat silicon wafer followed by a pre-bake for 30
seconds at a temperature that is either: the standard pre-bake
temperature recommended by the manufacturer of the particular prior
art fill material; or above the boiling point of all solvents
present in the inventive fill material. The sample is then
subjected to a final bake for 60-90 seconds at a temperature above
the material's cross-linking temperature. After the final bake, the
film thickness is measured (with an ellipsometer) and recorded.
PGME is applied to the surface of the wafer for 5 seconds followed
by spin-drying at 5,000 rpm for 30 seconds and a 30 second bake at
100.degree. C. The film thickness is measured again. The final film
should remain intact with little loss or increase in thickness.
Thus, the film thickness after the solvent contact should change
less than about .+-.3%.
[0109] 3. Film Shrinkage Testing
[0110] To obtain the desired fill material profile in a via or
contact hole, the shrinkage of the fill material film between the
pre-bake and final bake should be minimal. As used herein, a "film
shrinkage test" is conducted as follows. The fill material is
spin-coated onto a silicon wafer followed by a 30 second pre-bake
at a temperature that is either: the standard pre-bake temperature
recommended by the manufacturer of the particular prior art fill
material; or above the boiling point of all solvents present in the
inventive fill material. After the pre-bake, the film thickness is
measured (with an ellipsometer) and recorded. The coated wafer is
then subjected to a final bake at a temperature that is at least
the cross-linking temperature of the material, after which the film
thickness is determined. The percent shrinkage is calculated as
follows:
% shrinkage=[(pre-bake thickness-final thickness)/pre-bake
thickness].times.100
[0111] The inventive fill compositions have less than about 15%
shrinkage, and preferably less than about 10% shrinkage during this
test.
EXAMPLES
[0112] The following examples set forth preferred methods in
accordance with the invention. It is to be understood, however,
that these examples are provided by way of illustration and nothing
therein should be taken as a limitation upon the overall scope of
the invention.
Example 1
[0113] 1. Copolymer Syntheses
[0114] Using a mantle for heating, the instant reaction was carried
out in a three liter, 4-necked flask equipped with a mechanical
stirring rod, thermometer, nitrogen inlet plus thermocouple, and a
condenser having a nitrogen outlet. Under ambient conditions, the
following compounds were charged: 13.59 g of glycidyl methacrylate;
25.25 g of hydroxyl propyl methacrylate; 1.17 g of
2,2'-azobisisobutyronitrile; and 1.17 g of 1-dodecanethiol in
158.83 g of PGME. The resulting solution was stirred under nitrogen
for 15 minutes to remove oxygen, followed by stirring under
nitrogen for 24 hours at 70.degree. C. The heat and nitrogen were
turned off, and the reaction mixture was allowed to cool to room
temperature.
[0115] 2. Mother Liquor Syntheses
[0116] Using a mantle for heating, the instant reaction was carried
out in a three liter, 4-necked flask equipped with a mechanical
stirring rod, thermometer, nitrogen inlet plus thermocouple, and a
condenser having a nitrogen outlet. Under ambient conditions, the
following compounds were charged: 65 g of the copolymer prepared in
Part 1 of this example (20 weight % in PGME); 6.85 g of
9-anthracenecarboxylic acid; 0.173 g of benzyltriethylammonium
chloride; and 27.75 g of PGME. The reaction mixture was then
refluxed under nitrogen for 24 hours, after which the heat was
turned off and the nitrogen disconnected, allowing the mixture to
cool to room temperature.
Example 2
Preparation of Full Fill Via or Contact Fill Material
[0117] A via or contact fill material was prepared by mixing 27.62%
by weight of the mother liquor prepared in Part 2 of Example 1 with
1.73% by weight Cymel 303LF (cross-linking material available from
Cytech Industries, Inc.), 27.35% of PGMEA, and 43.3% by weight of
PGME. The mixture was stirred for about 1 hour to give a clear
solution after which it was exchanged for 15 hours with 7.24%
(based on the weight of the mixture) of 650 C exchange resin. The
resulting mixture was then filtered through 2.times.0.1 .mu.m
(absolute) end-point filters. This material was coated onto two
silicon wafers at a spin speed of 2500 rpm for 60 seconds followed
by baking at 160.degree. C. for 1 minute and then a 215.degree. C.
bake for 90 seconds. The resulting film had a thickness of
approximately 1560 .ANG..
[0118] This composition was then applied by spin coating to two
silicon wafers. The via fill material was static applied then
ramped with an acceleration of 20,000 rpm/second to 2500 rpm and
held for 60 seconds. The wafers were pre-baked at 160.degree. C.
for 60 seconds in contact hotplate mode. Wafer 1 had a film
thickness of 1701 .ANG. and wafer 2 had a film thickness of 1702
.ANG..
[0119] The pre-bake thermal stability test set forth in the testing
section above was conducted on wafer 1. The film thickness after
stripping was 0 .ANG.. Thus, the film remained completely soluble
at the pre-bake stage, indicating that essentially no cross-linking
had occurred. Wafer 2 was then baked at 215.degree. C. for 90
seconds in contact hotplate mode. The resulting film thickness was
1561 .ANG., a decrease of 141 .ANG. (a shrinkage of 8.3%). Finally,
wafer 2 was subjected to the final bake film solvent resistance
test described previously. The post-strip thickness was 1,563
.ANG., an increase of 2 .ANG. or 0.13%. Thus, this composition met
the minimum film requirements of the fill composition of the
invention.
Example 3
Preparation of Partial Fill Via or Contact Fill Material
[0120] The material prepared above in Example 2 was diluted with
PGME and PGMEA to produce a via or contact fill material which
would provide a film of about 550-600 .ANG.. This fill material was
applied to two silicon wafers at a spin speed of 2500 rpm for 60
seconds, followed by a 160.degree. C. bake for 1 minute and a
215.degree. C. bake for 60 seconds to form a film having a
thickness of about 590 .ANG., confirming that the material was
properly diluted.
[0121] The diluted fill material was then spin-coated onto two
silicon wafers with static application followed by an acceleration
of 20,000 rpm/second to 2500 rpm which was held for 60 seconds.
Both wafers were pre-baked at 160.degree. C. for 60 seconds in
contact hotplate mode. The thicknesses of the films on wafers 1 and
2 were 639 .ANG. and 644 .ANG., respectively. The pre-bake thermal
stability test was conducted on wafer 1. The film thickness after
stripping was 0 .ANG.. The film remained completely soluble after
the pre-bake, indicating that essentially no cross-linking had
occurred. Wafer 2 was then baked at 215.degree. C. for 60 seconds
in contact hotplate mode. The resulting film thickness was 593
.ANG., a decrease of 51 .ANG. which corresponds to a 7.9% film
shrinkage. Finally, wafer 2 was subjected to the final bake film
solvent resistance test, resulting in a post-strip thickness of 587
.ANG., a loss of 6 .ANG. (or 1%) after the final bake. Thus, the
fill material met the minimum requirements.
Example 4
Full Fill Via or Contact Fill Applications
[0122] The composition prepared in Example 2 was coated over an
oxide film with 1 .mu.m deep, 0.35 .mu.m diameter holes patterned
on a silicon wafer. The composition was coated by dynamic
dispensing on the substrate at a 400 rpm spin speed held for 5
seconds, followed by a 20,000 rpm/second acceleration to the final
spin speed of 1500 rpm which was held for 30 seconds. The film was
then pre-baked in contact hotplate mode at 160.degree. C. for 60
seconds followed by a contact hotplate final bake at 215.degree. C.
for 60 seconds. The wafer was then cross-sectioned for SEM analysis
(50,000.times.) of the fill composition profile in the hole (see
FIG. 11). The fill material completely filled the hole, and had a
thickness of 104 nm at the top edge of the hole and 113 nm
approximately 350 nm away from the edge of the hole. The meniscus
height M was about 66 nm.
[0123] Thus, the fill material completely filled the hole as is
required in full via or contact hole fill applications. The
difference in fill levels between the edge of the hole and the
center of the hole should be less than about 15% of the original
hole depth. In this case the difference was less than 6.6%. The
film thickness of the fill composition at the edge of the hole
should be at least about 40% of the film thickness at a distance
from the edge of the hole about equal to the diameter of the hole.
In this example, the film thickness at the hole edge was 92% of the
thickness one hole diameter of (i.e., 350 nm) away from the hole
edge. Thus, this composition met the specifications.
Example 5
Full Fill Via or Contact Fill Material with Second Layer of a Thin
Anti-reflective Coating
[0124] The steps of Example 4 were repeated using a thin,
industry-standard anti-reflective coating (DUV30-6 ARC.RTM. which
provides approximately a 600 .ANG. thick film on flat silicon when
used according to manufacturer's specifications, available from
Brewer Science, Inc., Rolla, Mo.) was applied over the via fill
material. The DUV30-6 was applied by dynamic dispensing on the
cured via fill material at a spin speed of 400 rpm held for 5
seconds, followed by an acceleration of 20,000 rpm/second to a
final spin speed of 3000 rpms which was held for 30 seconds. The
film was then given a contact hotplate pre-bake at 100.degree. C.
for 30 seconds followed by a contact hotplate final bake of
175.degree. C. for 60 seconds. The wafer was then cross-sectioned
for SEM analysis (50,000.times.) to examine the fill composition
profile in the hole (see FIG. 12). The fill material completely
filled the hole as required. The thickness of the film at the top
edge of the hole was 150 nm, while the thickness of the film
approximately 350 nm from the edge of the hole was 150 rim. The
meniscus height M was 31 nm. The difference between the fill depth
at the edge of the hole and the fill depth at the center of the
hole was 3.1% of the original hole depth. The thickness of the film
350 nm away from the hole was the same as the thickness at the edge
of the hole, meeting all of the requirements for the film.
Example 6
Partial Fill Via or Contact Fill Applications
[0125] The composition prepared in Example 3 was coated over an
oxide film with 1 .mu.m deep, 0.35 .mu.m diameter holes patterned
on a silicon wafer. The composition was coated by dynamic
dispensing on the substrate at a 400 rpm spin speed held for 5
seconds, followed by a 20,000 rpm/second acceleration to the final
spin speed of 1500 rpm which was held for 30 seconds. The film was
then pre-baked in contact hotplate mode at 160.degree. C. for 60
seconds followed by a contact hotplate final bake at 215.degree. C.
for 60 seconds. The wafer was cross-sectioned for SEM analysis
(50,000.times.) of the fill composition profile in the hole (see
FIG. 13). The fill material filled the hole to 535 nm, and had a
thickness of 38 nm at the top edge of the hole and 59 nm
approximately 350 nm away from the edge of the hole. The meniscus
height M was about 129 nm.
[0126] In partial via or contact hole fill applications, the fill
material should fill the hole to between 35% and 65% of the hole
depth. In this example, the hole was filled to 53%. The difference
in fill levels between the edge of the hole and the center of the
hole was 12.9%. The film thickness of the fill composition at the
edge of the hole was 64.4% of the thickness 350 nm away from the
hole. Thus, this composition met the specifications.
Example 7
Full Fill Via or Contact Fill Applications with a Prior Art
BARC
[0127] A prior art BARC (DUV30-16) was utilized to demonstrate the
performance of prior art compositions. The DUV30-16 was applied to
two silicon wafers by dynamic dispensing on the wafers at a spin
speed of 400 rpm which was held for 5 seconds, followed by an
acceleration of 20,000 rpm/second to a final spin speed of 1500 rpm
which was held for 30 seconds. Both wafers were subjected to a
100.degree. C. pre-bake in contact hotplate mode for 30 seconds.
The film thicknesses on wafers 1 and 2 were 1710 .ANG. and 1758
.ANG., respectively. The pre-bake thermal stability test was
conducted on wafer 1, with the post-strip thickness being 1484
.ANG.. The film was substantially insoluble after the pre-bake,
indicating that significant cross-linking had occurred.
[0128] Wafer 2 was then baked at 175.degree. C. for 60 seconds in
contact hotplate mode. The resulting film thickness was 1605 .ANG.,
a decrease of 153 .ANG. which corresponds to a film shrinkage of
8.7%. Wafer 2 was then subjected to the final bake film solvent
resistance test. The post-strip thickness of wafer 2 was 1610
.ANG., an increase of 5 .ANG. (or a shrinkage of -0.31%) after the
final bake. Thus, the prior art BARC passed the final bake solvent
resistance test and the film shrinkage test. However, the prior art
BARC failed the pre-bake stability test in that only 13.2% of the
fill composition was removed by the solvent after the pre-bake,
which is substantially below the minimum requirement of at least
about 70% removal.
[0129] The DUV30-16 was coated over an oxide film with 1 .mu.m
deep, 0.35 .mu.m diameter holes patterned on a silicon wafer. The
composition was coated by dynamic dispensing on the substrate at a
400 rpm spin speed held for 5 seconds, followed by a 20,000
rpm/second acceleration to the final spin speed of 1500 rpm which
was held for 30 seconds. The film was then pre-baked in contact
hotplate mode at 100.degree. C. for 30 seconds followed by a
contact hotplate final bake at 175.degree. C. for 60 seconds. The
wafer was cross-sectioned for SEM analysis (60,000.times.) of the
fill composition profile in the hole (see FIG. 14). The fill
material did not completely fill the hole, but instead only had a
fill height of 908 nm. The film thickness was 93 nm at the top edge
of the hole and 157 nm approximately 350 nm away from the edge of
the hole. The meniscus height M was about 220 nm.
[0130] Thus, the fill material only filled the hole to 93% of the
hole depth rather than to at least about 95% as is required in full
via or contact hole fill applications. Also, the difference in fill
levels between the edge of the hole and the center of the hole
(i.e., the meniscus height M) should be less than about 15% of the
original hole depth. In this case the difference was 22%, which is
greater than the allowable 15% meniscus height M. The film
thickness of the fill composition at the edge of the hole should be
at least about 40% of the film thickness at a distance from the
edge of the hole about equal to the diameter of the hole. In this
example, the film thickness at the hole edge was 59.5% of the
thickness one hole diameter (i.e., 350 nm) away from the hole edge.
Thus, this composition met this latter specification.
[0131] In sum, the film substantially cross-linked during the
pre-bake step and did not achieve the full fill requirements for
full fill application, resulting in a meniscus height M in excess
of the maximum allowable height.
Example 8
Full Fill Via or Contact Fill Material Applications with a Prior
Art BARC
[0132] A prior art BARC (EXP97053, available from Brewer Science,
Inc.) was utilized to demonstrate the performance of prior art
compositions. The EXP97053 was applied to two silicon wafers by
dynamic dispensing on the wafers at a spin speed of 400 rpm which
was held for 5 seconds, followed by an acceleration of 20,000
rpm/second to a final spin speed of 2500 rpm which was held for 30
seconds. Both wafers were subjected to a 100.degree. C. pre-bake in
contact hotplate mode for 30 seconds. The film thicknesses on
wafers 1 and 2 were 2281 .ANG. and 2272 .ANG., respectively. The
pre-bake thermal stability test was conducted on wafer 1, with the
post-strip thickness being 138 .ANG.. Thus, the film remained
mostly soluble after the pre-bake, indicating that a small amount
of cross-linking had occurred.
[0133] Wafer 2 was then baked at 175.degree. C. for 60 seconds in
contact hotplate mode. The resulting film thickness was 1888 .ANG.,
a decrease of 384 .ANG. which corresponds to a film shrinkage of
16.9%. Wafer 2 was then subjected to the final bake film solvent
resistance test. The post-strip thickness of wafer 2 was 1877
.ANG., a loss of 11 .ANG. (or a shrinkage of 0.6%) after the final
bake. Thus, the prior art BARC passed the final bake solvent
resistance test and the pre-bake thermal stability test. However,
the prior art BARC failed the film shrinkage test in that the film
thickness decreased by 16.9% during the final bake.
[0134] The EXP97053 was coated over an oxide film with 1 .mu.m
deep, 0.35 .mu.m diameter holes patterned on a silicon wafer. The
composition was coated by dynamic dispensing on the substrate at a
400 rpm spin speed held for 5 seconds, followed by a 20,000
rpm/second acceleration to a final spin speed of 2500 rpm which was
held for 30 seconds. The film was then pre-baked in contact
hotplate mode at 100.degree. C. for 30 seconds followed by a
contact hotplate final bake at 175.degree. C. for 60 seconds. The
wafer was cross-sectioned for SEM analysis (50,000.times.) of the
fill composition profile in the hole (see FIG. 15). The fill
material did not completely fill the hole, but instead only had a
fill height of 745 nm. The film thickness was 102 nm at the top
edge of the hole and 124 nm approximately 350 nm away from the edge
of the hole. The meniscus height M was about 412 nm.
[0135] The fill material only filled the hole to 74.5% of the hole
depth rather than to at least about 95% as is required in full via
or contact hole fill applications. The difference in fill levels
between the edge of the hole and the center of the hole was 41.2%,
which is greater than the allowable 15% meniscus height M. The film
thickness of the fill composition at the edge of the hole was 82.3%
of the thickness one hole diameter of (i.e., 350 nm) away from the
hole edge. Thus, this composition meets the latter
specification.
[0136] In sum, the film did not achieve all of the full fill
requirements for full fill applications. Rather, the film had a
large amount of shrinkage between the pre-bake and final bake,
leading to a large meniscus height M and an inability to fully fill
the hole.
Example 9
Partial Fill Via or Contact Fill Material Applications with a Prior
Art BARC
[0137] A prior art BARC (EXP97053, which was formulated to provide
an approximately 800 .ANG. thick film) was utilized to demonstrate
the performance of prior art compositions. The EXP97053 was applied
to two silicon wafers by dynamic dispensing on the wafers at a spin
speed of 400 rpm which was held for 5 seconds, followed by an
acceleration of 20,000 rpm/second to a final spin speed of 2500 rpm
which was held for 60 seconds. Both wafers were subjected to a
100.degree. C. pre-bake in contact hotplate mode for 30 seconds.
The film thicknesses on wafers 1 and 2 were 799 .ANG. and 805
.ANG., respectively. The pre-bake thermal stability test was
conducted on wafer 1, with the post-strip thickness being 345
.ANG.. The film remained partially soluble after the pre-bake,
indicating that some cross-linking had occurred with a stripping of
56.8%.
[0138] Wafer 2 was then baked at 175.degree. C. for 60 seconds in
contact hotplate mode. The resulting film thickness was 662 .ANG.,
a decrease of 143 .ANG. which corresponds to a film shrinkage of
17.8%. Wafer 2 was subjected to the final bake film solvent
resistance test. The post-strip thickness of wafer 2 was 657 .ANG.,
a loss of 5 .ANG. (or a shrinkage of 0.7%) after the final bake.
Thus, the prior art BARC passed the final bake solvent resistance
test. However, the prior art BARC failed the film shrinkage test in
that the film thickness decreased by 17.8% during the final bake.
The prior art BARC also failed the pre-bake thermal stability test
in that only 56.8% of the fill composition was removed.
[0139] The EXP97053 was coated over an oxide film with 1 .mu.m
deep, 0.35 .mu.m diameter holes patterned on a silicon wafer. The
composition was coated by dynamic dispensing on the substrate at a
400 rpm spin speed held for 5 seconds, followed by a 20,000
rpm/second acceleration to the final spin speed of 2500 rpm which
was held for 30 seconds. The film was then pre-baked in contact
hotplate mode at 100.degree. C. for 30 seconds followed by a
contact hotplate final bake at 175.degree. C. for 60 seconds. The
wafer was then cross-sectioned for SEM analysis (50,000.times.) of
the fill composition profile in the hole (see FIG. 16). The fill
material filled the hole to 426 nm, with the thickness of the film
being 14 nm at the top edge of the hole and 32 nm approximately 350
nm away from the edge of the hole. The meniscus height M was about
257 nm.
[0140] In partial fill applications, the material should fill the
hole to between 35% and 65%. In this example, the material filled
the hole to 42.6%. The difference in fill levels between the edge
of the hole and the center of the hole was 25.7%, which is greater
than the allowable 15% meniscus height M. The film thickness of the
fill composition at the edge of the hole was 43.8% of the thickness
one hole diameter of (i.e., 350 nm) away from the hole edge, just
meeting this requirement.
[0141] In sum, this composition had significant cross-linking and a
large amount of shrinkage between pre-bake and final bake (leading
to a large meniscus) and did not meet the minimum requirements.
* * * * *