U.S. patent application number 11/230841 was filed with the patent office on 2006-01-19 for stacked via-stud with improved reliability in copper metallurgy.
This patent application is currently assigned to INTERNATIONAL BUSINESS MACHINES CORPORATION. Invention is credited to Birendra N. Agarwala, Conrad A. Barile, Hormazdyar M. Dalal, Brett H. Engel, Michael Lane, Ernest Levine, Xiao Hu Liu, Vincent McGahay, John F. McGrath, Conal E. Murray, Jawahar P. Nayak, Du B. Nguyen, Hazara S. Rathore, Thomas M. Shaw.
Application Number | 20060014376 11/230841 |
Document ID | / |
Family ID | 32325713 |
Filed Date | 2006-01-19 |
United States Patent
Application |
20060014376 |
Kind Code |
A1 |
Agarwala; Birendra N. ; et
al. |
January 19, 2006 |
Stacked via-stud with improved reliability in copper metallurgy
Abstract
A multilevel semiconductor integrated circuit (IC) structure
including a first interconnect level including a layer of
dielectric material over a semiconductor substrate, the layer of
dielectric material comprising a dense material for passivating
semiconductor devices and local interconnects underneath; multiple
interconnect layers of dielectric material formed above the layer
of dense dielectric material, each layer of dielectric material
including at least a layer of low-k dielectric material; and, a set
of stacked via-studs in the low-k dielectric material layers, each
of said set of stacked via studs interconnecting one or more
patterned conductive structures, a conductive structure including a
cantilever formed in the low-k dielectric material. The dielectric
layer of each of the multiple interconnection levels includes a
soft low-k dielectric material, wherein the cantilever and set of
stacked via-studs are integrated within the soft low-k dielectric
material to increase resistance to thermal fatigue crack formation.
In one embodiment, each of the set of stacked via-studs in the
low-k dielectric material layers is provided with a cantilever,
such that the cantilevers are interwoven by connecting a cantilever
on one level to a bulk portion of the conductor line on adjacent
levels of interconnection, thereby increasing flexibility of
stacked via-studs between interconnection levels.
Inventors: |
Agarwala; Birendra N.;
(Hopewell Junction, NY) ; Barile; Conrad A.;
(Wappingers Falls, NY) ; Dalal; Hormazdyar M.;
(LaGrangeville, NY) ; Engel; Brett H.; (Hopewell
Junction, NY) ; Lane; Michael; (Cortlandt Manor,
NY) ; Levine; Ernest; (Poughkeepsie, NY) ;
Liu; Xiao Hu; (Croton-on-Hudson, NY) ; McGahay;
Vincent; (Poughkeepsie, NY) ; McGrath; John F.;
(Somerville, MA) ; Murray; Conal E.; (Yorktown
Heights, NY) ; Nayak; Jawahar P.; (Wappingers Falls,
NY) ; Nguyen; Du B.; (Danbury, CT) ; Rathore;
Hazara S.; (Stormville, NY) ; Shaw; Thomas M.;
(Peekskill, NY) |
Correspondence
Address: |
SCULLY SCOTT MURPHY & PRESSER, PC
400 GARDEN CITY PLAZA
SUITE 300
GARDEN CITY
NY
11530
US
|
Assignee: |
INTERNATIONAL BUSINESS MACHINES
CORPORATION
ARMONK
NY
|
Family ID: |
32325713 |
Appl. No.: |
11/230841 |
Filed: |
September 20, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10306534 |
Nov 27, 2002 |
6972209 |
|
|
11230841 |
Sep 20, 2005 |
|
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|
Current U.S.
Class: |
438/622 ;
257/E21.576; 257/E21.582; 257/E23.145; 438/672; 438/763 |
Current CPC
Class: |
H01L 23/5286 20130101;
H01L 23/5283 20130101; H01L 21/76807 20130101; H01L 21/76829
20130101; Y10T 428/24917 20150115; H01L 21/76838 20130101; H01L
23/5226 20130101; H01L 2924/0002 20130101; H01L 23/53295 20130101;
H01L 2924/0002 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
438/622 ;
438/763; 438/672 |
International
Class: |
H01L 21/4763 20060101
H01L021/4763; H01L 21/44 20060101 H01L021/44; H01L 21/31 20060101
H01L021/31 |
Claims
1-8. (canceled)
9. A method of forming a multilayer semiconductor integrated
circuit structure comprising the steps of: a) forming a first layer
of dielectric material over a semiconductor substrate, the layer of
dielectric material comprising a dense material for passivating
semiconductor devices and local interconnects underneath; b)
forming multiple interconnect layers of dielectric material formed
above the layer of dense dielectric material, each layer of
dielectric material including at least a layer of low-k dielectric
material; and, c) forming a set of stacked via-studs in the low-k
dielectric material layers, each of said set of stacked via studs
interconnecting one or more patterned conductive structures, a
conductive structure comprising a cantilever formed in said low-k
dielectric material.
10. The method as claimed in claim 9, wherein a dielectric layer of
each said multiple interconnect layers includes a soft low-k
dielectric material, said cantilever being integrated within said
soft low-k dielectric material at a level to increase resistance to
thermal fatigue crack formation.
11. The method as claimed in claim 10, wherein said soft low-k
dielectric material includes SiLK, Aerogels, fluoridized polyimide,
polymeric compound or air.
12. The method as claimed in claim 9, wherein said cantilever
structures are interwoven by connecting a cantilever on one level
of interconnection to a bulk portion of a semiconductor line on an
adjacent level of interconnection, thereby increasing flexibility
of stacked via-studs between interconnection levels.
13. A multilevel semiconductor integrated circuit (IC) structure
comprising: a semiconductor substrate layer having formed therein a
metal feature, a first interconnect layer including low-k
dielectric material formed over said substrate; a first via stud in
said first interconnect dielectric layer connecting said metal
feature formed in said semiconductor substrate to a first metal
interconnection line segment formed in said first dielectric layer;
a second interconnect layer including low-k dielectric material
formed over said first interconnect dielectric layer; a second via
stud in said second interconnect dielectric layer aligned with and
connecting said first metal interconnection line segment with a
second metal interconnection line segment formed in said second
dielectric layer, said second metal interconnection line segment of
rectangular shape and at a selected location such that one end of
the second metal line segment is above the first metal line segment
of the same length and the width; a third interconnect layer
including low-k dielectric material formed over said second
interconnect dielectric layer; and, a third via stud in said third
interconnect dielectric layer connecting said second metal
interconnection line segment of rectangular shape at an opposite
end thereof with a third metal interconnection line segment formed
in said third dielectric layer, said first, second and third
integrated via-studs and said second metal line segment forming a
stacked via-stud arrangement with said second metal line segment
comprising a cantilever structure.
14. The multilevel IC structure as claimed in claim 9, wherein a
dielectric material of each said first, second and third
interconnection dielectric layers includes a soft low-k dielectric
material, said cantilever being integrated within said soft low-k
dielectric material at a level to increase resistance to thermal
fatigue crack formation.
15. The multilevel IC structure as claimed in claim 13, further
including a fourth interconnection dielectric level including low-k
dielectric material above said third interconnection level and a
fourth level integrated via-stud connecting said third metal line
segment with a fourth metal interconnection line segment formed in
said fourth dielectric layer, said third metal line segment
comprising a second cantilever structure formed in said low-k
dielectric material of said third dielectric layer.
16. A multilevel semiconductor integrated circuit (IC) structure
including: a first interconnect level including a layer of
dielectric material over a semiconductor substrate, the layer of
dielectric material comprising a dense material for passivating
semiconductor devices and local interconnects underneath; multiple
interconnect layers of dielectric material formed above the layer
of dense dielectric material, each layer of dielectric material
including at least a layer of low-k dielectric material; and, a set
of stacked via-studs in the low-k dielectric material layers, each
of said set of stacked via studs interconnecting one or more
patterned conductive structures, a conductive structure comprising
a cantilever formed in said low-k dielectric material.
17. The multilevel IC structure as claimed in claim 16, wherein
said cantilever comprises a high conductivity metal, said
cantilever disposed between two stacks of via-studs from said set
of stacked via-studs.
18. A redundant system for interconnecting conductive layers of a
multiple layer semiconductor integrated circuit (IC), said
redundant system comprising: a plurality of interlaced metal
via-studs for interconnecting a first conductive structure at a
lower level interconnect structure lying over a substrate to a
second conductive structure formed in an upper interconnect level,
each said conductive structures lying in a layer of dielectric
material; a third conductive structure in an interconnect level
between said lower and upper interconnect levels, said interconnect
level including a low-k dielectric material, at least one of said
metal via-studs connecting said first conductive structure to said
third conductor structure at a bulkhead region end of said third
conductive structure; a gap being formed in said third conductive
structure to result in one or more cantilever structures in said
third conductive structure; and, at least one of said metal
via-studs connecting a free end of said cantilever structure a
distance from said first metal via-stud to a bulkhead region formed
in said second conductive structure at said upper level; wherein
said third conductive structure lies in a perpendicular fashion
with respect to said upper and lower conductive structures to
facilitate redundant paths connecting said first and second
conductive layers via said third conductive layer.
19. The redundant system as claimed in claim 18, wherein said
second conductive layer includes a further cantilever structure,
said cantilever structures of said second and third conductive
structures being interwoven by connecting a cantilever on one
conductive structure at a level of interconnection to a bulk
portion of a conductive structure on an adjacent level of
interconnection, thereby increasing flexibility of stacked
via-studs between interconnection levels.
20. A flexible system for a multilevel interconnection including a
bus line at one interconnection level, said system comprising: a
semiconductor substrate having metal features; multiple layers of
dielectric material over said substrate, each layer comprising at
least a layer of a low strength low-k dielectric material; a
multilevel interconnection disposed within multilayers of
dielectric, the multilevel interconnection comprising a flexible
patterned structure; the flexible patterned structure includes at
least one cantilever structure formed by removing U-shaped metal
formation within the width of a line, and at selected regions along
a bus line; a set of stacked via-studs formed substantially in said
low strength low-k dielectric material for connecting the free end
of the cantilever on one level of interconnection to the bulk of
said bus line on another interconnection level.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to a new
semiconductor process and integrated circuit structure, and more
particularly, to a new process and structure which provides stacked
via-studs, in multilevel interconnection wiring of semiconductor
devices with high conductivity copper metallurgy and low-k
dielectric, with improved mechanical stability under large thermal
excursions.
[0003] 2. Description of the Prior Art
[0004] In order to meet the ever increasing demand for increased
device density and performance, a semiconductor technology
consisting of a low-k dielectric material and an interconnection
wiring of copper metallurgy, defined by a dual damascene method, is
the present day choice. Because, dry air has the theoretically
lowest dielectric constant of one (1), most low-k materials such as
aerogels, hydrogen silsesquioxane (HSQ), fluorinated organic
polymers (e.g., SiLK, a trade mark of Dow chemical Co., Midland,
Mich.), among others, have high porosity and, thereby, a negligibly
small mechanical strength. A schematic cross-section of the present
day high performance interconnection structure is shown in FIG.
1(a). Such schemes generally have semiconductor devices (not shown)
formed in silicon substrate 10 and locally interconnected by
tungsten or polysilicon interconnection 101 which is imbedded in a
passivation layer 103 of boro-phosphosilicate glass (BPSG)
deposited just above the silicon substrate 10 to prevent any ionic
migration into the device junctions. The high performance
interconnection is formed with wirings of high conductivity
metallurgies 131, 231, 331 on different levels, insulated from each
other with layer 112, 212, 312 of low-k dielectric and
interconnected at desired points by metal filled via-studs 132,
232, 332. In order to prevent, or to reduce, the corrosive impurity
ingression into interconnection wiring structure, as well as to
impart mechanical stability, at least one layer of the top most
layer of interconnection wiring 431 and via stud 432 is imbedded in
one or more layers 412 of previous standard insulators such as
silicon oxide, e.g., deposited by the plasma enhanced chemical
vapor deposition (PECVD) using silane (SiH.sub.4) or
tetraethylorthosilicate (TEOS) precursors. Accordingly, the present
day high performance interconnection is comprised of one or more
layers of high conductivity copper interconnections, imbedded in
the low-k dielectric SiLK, and bounded on top and bottom by much
denser layers of PECVD oxide and BPSG, respectively.
[0005] A reliability evaluation of such integrated circuit
structures shown in FIG. 1(a) revealed excessive and premature
failures due to circuit opens caused by development of cracks in
the wiring upon thermal cycling. FIG. 1(a) shows a typical crack
formed in the stacked via-stud, in this example, at the interface
of via-stud 332 and interconnection wiring 331, after 1000 thermal
cycles between -65.degree. C. and 150.degree. C. Unlike the well
known circuit open problem caused by electromigration, these cracks
are not current flow dependent and may occur at any location beyond
the interface of via-stud 332 and interconnection wiring 331. These
cracks are generated upon thermal cycling alone; further, the
propensity of crack generation is much greater in stacked
via-studs, as shown in FIG. 1(a). Stacked via-studs are essential
in high circuit density interconnections to feed power directly
from the bus lines on the upper most wiring level to the local
interconnects of semiconductor devices on lower most wiring level.
In an interconnection terminology, the stacked via-studs are
comprised of alternatively stacked metal filled via studs 132, 232,
and 332 and interconnect metal lines 131, 231, and 331. For the
purposes of making stacked via-studs, the cross-sectional area of
interconnection line segments 131, 231, 331 are made the same as
the cross sectional areas of corresponding via-studs 132, 232, 332.
One, or a set of redundant, stacked via-studs provide a direct
connection from the top most level to the lower most level of
interconnection. The greater the ratio of stacked via-stud height
(H) to diameter of the via-studs (D), the greater is the propensity
for crack formation. The continuing trend of dimensional shrinkage
(smaller D) and increased wiring levels (larger H) in multilevel
interconnections lead to much higher H to D ratios, thereby making
the stacked via-studs of present and future interconnection wiring
schemes increasingly more prone to cracks. It should be emphasized
that propensity of crack formation is much less in an
interconnection scheme where the porous dielectric material (e.g.,
SiLK) is replaced by the previous standard dense dielectric
material (e.g., PECVD oxide). The crack propensity also increases
with the range of temperature cycles and the number of cycles,
showing that cracks are generated by metal fatigue, a phenomenon
not seen before in integrated circuit wiring. During thermal
cycling of the substrate, the stacked via-stud undergoes
compressive/tensile stresses generated, respectively, by thermal
expansion/contraction of the stacked via-stud due to mismatch in
coefficients of thermal expansion between the metal and the
surrounding dielectric. Because the stacked via-stud is
mechanically pinned by the relatively much denser, and stiffer,
layer of PECVD oxide at the top, and by the silicon substrate at
the bottom, the difference in thermal expansion/contraction between
the metal and the surrounding dielectric causes the stresses in the
stacked via-stud. It should be noted that the thermal coefficient
of expansion mismatch between copper and SiLK is several times
higher than that between copper and PECVD oxide, thereby making the
stacked via-stud of copper and low-k dielectric, e.g., SiLK,
interconnection wiring scheme much more prone to crack formation
than in stacked via-studs of present day multilevel
interconnections comprised of a dense dielectric, e.g., PECVD
oxide, at all levels of the interconnection. The crack formation in
copper-SiLK interconnection wiring scheme is further aggravated due
to nearly absent compressive stresses in SiLK dielectric material.
Fatigue crack initiation is a surface phenomenon; it is well known
that a surface coating improves the fatigue life. Dense oxide
films, in deposited thin film form, have high intrinsic compressive
stress, thereby exerting a lateral compressive force on via-studs.
These compressive forces on the via-stud surface help delaying, or
preventing, the thermal fatigue failure in present day wiring
schemes with a dense dielectric, e.g., PECVD oxide, material. The
negligibly small compressive stress in low-k materials, along with
the large thermal expansion mismatch between copper and low-k
dielectric, e.g., SiLK, are root causes for the observed fatigue
failure.
[0006] One of the major applications of stacked via-studs is to
directly transfer large amount of current from power buses on the
top most level of interconnection wiring to power buses on lower
levels. Invariably, a scheme of redundant stacked via-studs is used
to carry a large amount of current. FIG. 1(b) shows a perspective
view of a set of four redundant stacked via-studs in present day
technology, formed between fat metal lines of power buses on
different layers of interconnection wiring. In such cases, the
propensity of fatigue crack formation is greatly increased in
multilevel interconnection schemes with low-k dielectric, e.g.
SiLK, due to additional compressive stresses arising from the
rigidity of fat metal lines acting on the stacked via-stud
column.
[0007] Accordingly, methods must be sought to mechanically
strengthen the tall, thin stacked via-stud structures imbedded in a
soft low-k dielectric material.
[0008] U.S. Pat. No. 6,143,396 to Saran, the disclosure of which is
incorporated by reference herein, provides an architecture of
reinforced wire bond pads to prevent cracking of pads during
mechanical loading, such as electrical testing, wire bonding or
solder ball joining. A multiple of metal studs underneath bond pads
are provided to make the bond pads more mechanically stable.
[0009] U.S. Pat. No. 6,232,662 B1 to Saran, the disclosure of which
is incorporated by reference herein, enhances the architecture in
his earlier patent by interconnecting the reinforcing metal studs
and adding a layer of metal wiring, such that the reinforcing metal
studs form a part of an active interconnection pattern and,
thereby, the real estate underneath the bond pads is conserved. All
of Saran's schemes involve short length metal studs bounded on top
and bottom by a dense dielectric material; such schemes are not
beneficial when the studs are long, for example, in the case of
stacked via-studs as discussed above.
[0010] Bearing in mind the problems and deficiencies of the prior
art, it would be beneficial to provide a semiconductor device
having copper interconnections and low strength low-k dielectric
with a stacked via-stud which is resistant to cracking upon large
thermal excursions.
SUMMARY OF THE INVENTION
[0011] It is therefore an object of the present invention to
provide a semiconductor device having copper interconnections and
low strength low-k dielectric with a stacked via-stud which is
resistant to cracking upon large thermal excursions.
[0012] It is a further object of the present invention to provide a
semiconductor device having copper interconnections and low
strength low-k dielectric with a stacked via-stud that is
mechanically flexible at top end of the stack.
[0013] It is another object of the present invention to provide a
semiconductor device having copper interconnections and low
strength low-k dielectric with a stacked via-stud that is
mechanically flexible.
[0014] It is yet another object of the present invention to provide
a semiconductor device having copper interconnections and low
strength low-k dielectric with a stacked via-stud that includes at
least one cantilever structure, integrated with the stacked
via-stud, to allow the mechanical flexibility.
[0015] It is still another object of the present invention to
provide a semiconductor device having copper interconnections and
low strength low-k dielectric with a stacked via-stud that provides
at least one stacked via-stud with more than one integrated
cantilever structure, where each of the provided cantilevers is
formed on a different level of the interconnection wiring
scheme.
[0016] It is a further object of the present invention to provide a
semiconductor device having copper interconnections and low
strength low-k dielectric with a stacked via-stud that includes a
set of redundant stacked via-studs where each stack is provided
with at least one integrated cantilever structure, and interwoven
to conserve wiring real estate.
[0017] Thus, according to a first aspect of the present invention,
there is provided, a multilevel semiconductor integrated circuit
(IC) structure and process method for forming. The structure
comprises: [0018] a semiconductor substrate layer having formed
therein a metal feature, [0019] a first interconnect layer
including low-k dielectric material formed over the substrate;
[0020] a first via stud in the first interconnect dielectric layer
connecting the metal feature formed in the semiconductor substrate
to a first metal interconnection line segment formed in the first
dielectric layer; [0021] a second interconnect layer including
low-k dielectric material formed over the first interconnect
dielectric layer; [0022] a second via stud in the second
interconnect dielectric layer aligned with and connecting the first
metal interconnection line segment with a second metal
interconnection line segment formed in the second dielectric layer,
the second metal interconnection line segment of rectangular shape
and at a selected location such that one end of the second metal
line segment is above the first metal line segment of the same
length and the width; [0023] a third interconnect layer including
low-k dielectric material formed over the second interconnect
dielectric layer; and, [0024] a third via stud in the third
interconnect dielectric layer connecting the second metal
interconnection line segment of rectangular shape at an opposite
end thereof with a third metal interconnection line segment formed
in the third dielectric layer, [0025] the first, second and third
integrated via-studs and the second metal line segment forming a
stacked via-stud arrangement with the second metal line segment
comprising a cantilever structure.
[0026] Preferably, a dielectric material of each the first, second
and third interconnection dielectric layers includes a soft low-k
dielectric material, the cantilever being integrated within the
soft low-k dielectric material at a level to increase resistance to
thermal fatigue crack formation.
[0027] According to a second aspect of the present invention, there
is provided a multilevel semiconductor integrated circuit (IC)
structure and process method for forming. The structure comprises:
[0028] a first interconnect level including a layer of dielectric
material over a semiconductor substrate, the layer of dielectric
material comprising a dense material for passivating semiconductor
devices and local interconnects underneath; [0029] multiple
interconnect layers of dielectric material formed above the layer
of dense dielectric material, each layer of dielectric material
including at least a layer of low-k dielectric material; and,
[0030] a set of stacked via-studs in the low-k dielectric material
layers, each of the set of stacked via studs interconnecting one or
more patterned conductive structures, a conductive structure
comprising a cantilever formed in the low-k dielectric
material.
[0031] Preferably, the cantilever comprises a high conductivity
metal and is disposed between two stacks of via-studs from the set
of stacked via-studs.
[0032] According to a third aspect of the present invention, there
is provided a redundant system for interconnecting conductive
layers of a multiple layer semiconductor integrated circuit (IC),
the redundant system comprising: [0033] a plurality of interlaced
metal via-studs for interconnecting a first conductive structure at
a lower level interconnect structure lying over a substrate to a
second conductive structure formed in an upper interconnect level,
each the conductive structures lying in a layer of dielectric
material; [0034] a third conductive structure in an interconnect
level between the lower and upper interconnect levels, the
interconnect level including a low-k dielectric material, at least
one of the metal via-studs connecting the first conductive
structure to the third conductor structure at a bulkhead region end
of the third conductive structure; [0035] a gap being formed in the
third conductive structure to result in one or more cantilever
structures in the third conductive structure; and, [0036] one of
the metal via-studs connecting a free end of the cantilever
structure a distance from the other at least one metal via-stud to
a bulkhead region formed in the second conductive structure at the
upper level.
[0037] In this third embodiment, the third conductive structure
lies in a perpendicular fashion with respect to the upper and lower
conductive structures to facilitate redundant paths connecting the
first and second conductive layers via the third conductive layer.
Furthermore, the second conductive layer includes a further
cantilever structure, the cantilever structures of the second and
third conductive structures being interwoven by connecting a
cantilever on one conductive structure at a level of
interconnection to a bulk portion of a conductive structure on an
adjacent level of interconnection, thereby increasing flexibility
of stacked via-studs between interconnection levels.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] The features of the invention believed to be novel and the
elements characteristic of the invention are set forth with
particularity in the appended claims. The figures are for
illustration purposes only and are not drawn to scale. The
invention itself, however, both as to organization and method of
operation, may best be understood by reference to the detailed
description which follows taken in conjunction with the
accompanying drawings in which:
[0039] FIG. 1(a) is a cross-sectional side view of a prior art
semiconductor device showing a fatigue crack, formed upon thermal
cycling, in a stacked via-stud of copper metallurgy in SiLK low-k
material.
[0040] FIG. 1(b) is a perspective view of a set of four redundant
stacked via-studs in present day art.
[0041] FIGS. 2 through 5 are sequential partial cross-sectional
side views of a semiconductor substrate illustrating one embodiment
of the present invention where one cantilever is provided.
[0042] FIG. 6 is a schematic cross-section through a stacked
via-stud, of present invention, containing a cantilever.
[0043] FIG. 7 is a schematic cross-section through a stacked
via-stud containing two cantilevers.
[0044] FIG. 8 is a planar top view of a portion of first level of
high conductivity metal interconnection in low-k dielectric,
SiLK.
[0045] FIG. 9 is a top planar view of a portion of second level of
high conductivity metal interconnection atop the same portion as in
FIG. 8.
[0046] FIG. 10 is a cross-sectional view of a set of stacked
via-studs at section A-A' of drawings in FIGS. 8 and 9.
[0047] FIG. 11 is a cross-sectional view of a set of stacked
via-studs at section B-B' of drawings in FIGS. 8 and 9.
DETAILED DESCRIPTION OF THE INVENTION
[0048] The present invention is generally related to methods for
forming metal filled via-studs and conductor lines on a substrate
where the via-studs and conductor lines are formed using a dual
damascene method, and preferably copper metallurgy and low-k
dielectric material. The present invention has particular relevance
to stacked via-stud schemes which particularly use low strength
low-k dielectric materials and incorporate a cantilever structure
within the stacked via-stud which may serve as an effective thermal
fatigue crack stop.
[0049] Particularly referring to FIG. 2, there is shown a
semiconductor substrate 10 above which a sequence of dielectric
layers 111, 112, 113 is deposited, subsequently patterned and
metallized to form a first level of interconnection. It should be
understood that a plurality of semiconductor devices may be formed
in the substrate and, although not shown, are provided with a local
interconnect line 101, typically tungsten with underlayers of
titanium and titanium nitride (not shown). The semiconductor
devices and the local interconnects are provided with a passivation
layer 103, typically deposited boro-phosphosilicate (BPSG) glass or
like dense doped silicate glass.
[0050] The dielectric layers 111, 112, 113 comprise a bottom
dielectric layer 111 of approximate thickness 20 to 50 nm, which
may be PECVD deposited silicon nitride (Si.sub.3N.sub.4) or the
like, a thicker low-k dielectric layer 112, and a top dielectric
layer 113 of a hard mask layer of approximate thickness 20 to 90
nm, e.g., BLOk.RTM. or BLOk.RTM. and silicon nitride, to act as a
moisture barrier. BLOk.RTM. (trademark of Applied Materials Inc.)
is a PECVD deposited silicon carbide film. Layer 112 is a low-k
dielectric material which may be deposited by any of number of well
known techniques such as sputtering, spin-on, or PECVD. Preferably,
the low-k dielectric layer 112 is spun-on SiLK.
[0051] Referring to FIG. 3, a via-stud pattern is defined atop
layer 113 followed by sequential etching of hard mask layer 113 and
partially etching low-k dielectric 112 with suitable conventional
etchants. The pattern for the high conductivity metal
interconnection lines is next defined followed by further etching
of hard mask 113, the remainder of low-k dielectric 112, and bottom
dielectric 111 to form trenches 121 (for interconnection lines) and
holes 122 (for via-studs) to expose metal line 101. For the
purposes of forming a stacked via-stud, the cross-sectional area of
metal line 121 is made approximately same as the cross sectional
area of via-stud 122.
[0052] Referring to FIG. 4, a sequence of metal liner layers 130 is
next deposited to line the etched trench and via-stud hole 121,
122. The metal liner layers 130 comprise refractory materials
tantalum, tantalum nitride, chromium/chromium oxide, titanium,
titanium nitride, tungsten, tungsten silicide, or the like, and a
seed layer of copper deposited using any of the known deposition
methods, such as, for example, CVD, hollow cathode magnetron
sputtering, deposit-etch (dep.-etch) process, or any combination of
these or, other similar methods. The liner deposition process is
preferably a hollow cathode magnetron sputtering combined with
dep.-etch process. This is followed by deposition of high
conductivity metal such as copper for via-studs 132 and
interconnection lines 131 using electroplating methods. For certain
applications it may be advantageous to follow the copper deposition
by deposition of a refractory metal (not shown), particularly using
a CVD process, to act as a polish stop and to prevent copper
corrosion. Any excess metal materials are next removed in a
singular step or in a sequence of steps, such as, by
chem.-mechanical polishing (CMP) to leave the integrated via-studs
132 and the interconnection lines 131, imbedded in, and
substantially planar with, the surrounding low-k dielectric 112 and
BLOk.RTM. layer. 113, as shown in FIG. 4. The foregoing steps are
initial process steps of the method conventionally known in the art
as a dual damascene method.
[0053] Next, a second level of combined via-stud and
interconnection line segment are formed at the point in the
process. Referring to FIG. 5, there is first formed the sequential
deposition of dielectric layers 212 and 213, the dielectric layer
212 comprising a low-k dielectric material and a dielectric layer
213 of a denser dielectric material formed above layer 212. It
should be understood that the material of the low-k dielectric
layer 212 in the second level may be the same low-k dielectric
material or different than the low-k dielectric material in the
first layer. Then, there is formed the second level of
interconnection comprised of via-stud 232 and interconnection line
segment 231, where the line segment 231 is designed to be a
rectangle in shape such that, the width of the rectangle is
approximately the same as the diameter `D` of the corresponding via
stud 232, and the length `L` of the rectangle is at least three
times the width. Preferably, the length of the rectangle line
segment `L` is four to eight times its width. Thus, the via-stud
232 is situated at one end of the rectangular line segment 231. It
should be noted that according to conventions known in the art, the
line segment 231 would have been of same cross-sectional area as
that of the corresponding via-stud 232.
[0054] Referring to FIG. 6, dielectric layers 311, 312 and 313 are
next sequentially deposited to form the last level of
interconnection. The layer 311 is PECVD silicon nitride of
thickness ranging from 20 to 50 nm; layer 312 is a dielectric
material of porous texture, like SiLK or fluorosilicate glass
(FSG), of thickness ranging from 50 nm to 500 nm; and layer 313 is
a dense dielectric, such as PECVD silicon oxide or polyimide, of
thickness ranging from 50 nm to 500 nm which forms the final
passivation layer. It should be noted that the purpose of adding a
layer 312 of porous material, like SiLK, is to provide cushioning
to the stacked via-stud 231-232-131-132. The last interconnection
level, comprised of via-stud 332 and interconnection line segment
331, is next formed, as above, by the dual damascene method. The
via-stud 332 is designed to align with the other end of the
rectangle line segment 231. The last interconnection level,
comprised of via-stud 332 and interconnection line 331 is imbedded
in, and substantially planar with, the dense dielectric layer
313.
[0055] It should be noted that the stacked via-stud
132-131-232-231-332-331 now has an integrated cantilever 231 and a
layer of soft material 312 above and below the end of the stacked
via-stud as noted above. The integrated cantilever 231, having a
soft material above and below it, is able to move up or down with
least resistance; effectively reducing any strain induced in the
stacked via-stud and preventing thermal fatigue cracking of the
stacked via-stud.
[0056] FIG. 7 illustrates another embodiment of the present
invention. As shown in FIG. 7, there is depicted a schematic
cross-section through stacked via-studs and interconnection wiring
layers, where the interconnection wiring is comprised of at least
three levels in soft dielectric SiLK. Here, cantilevers 231 and 331
are provided to a stacked via-stud, where each of the cantilevers
is formed on a different level of the wiring scheme. Such increased
robustness becomes of increasing importance as the stud diameter
decreases below 0.1 micron. Thus, as shown in FIG. 7, implementing
the processes described herein, dielectric layers 411, 412 and
passivation layer 413 are sequentially formed on top of the
interconnect layer comprising cantilever 331. Using the processes
as described herein, via-stud 432 is formed through a damascene
method through dielectric layer 412 to connect with the cantilever
331 on a side of the cantilever opposite the location of the
underlying via-stud 332 connection. Finally, a top level
interconnect 431 is formed in layer 413.
[0057] In yet another embodiment of the present invention, an array
of four redundant stacked via-studs is provided with cantilevers to
increase the flexibility between fat bus lines on adjacent wiring
levels. The progress of making the interwoven stacked via-stud of
the present invention is sequentially shown in FIGS. 8 to 11.
[0058] FIG. 8 particularly illustrates a planar top view of a
portion of first level of high conductivity interconnection. The
first level of interconnection, imbedded in low-k dielectric 112,
is comprised of metal lines 131 and via-studs 132x (where, x is 1,
2, 3 or 4, representing four redundant via-studs according to this
embodiment). The bus line 131 is designed to provide two
cantilevers, 1311 and 1312. Thus, a portion of bus lines on each
level of interconnection has two cantilever structures, 1311 and
1312, and bulkheads (the remaining width of the bus line 131) 1310.
It should be noted that different numerals, 1310, 1311 and 1312,
are used merely to indicate various associated sections formed in
the bus line 131. It should also be noted that different via-stud
numerals, 1321, 1322, 1323 and 1324, indicate four particular
via-studs, of via-stud family 132x, which make contact to local
interconnections 101 on lower level of wiring (not shown).
[0059] FIG. 9 illustrates a planar view of a portion of the next
level of wiring, where the bus lines 231 run in a direction
perpendicular to the direction of bus lines 131 of the previous
level. Two cantilevers, 2311 and 2312, are provided in the bus line
231. The four redundant via-studs, 2321, 2322, 2323 and 2324,
formed with this level of interconnection, are selectively situated
such that two of the via-studs, 2321 and 2322, connect the bulk
head 2310 to the free end of cantilevers 1312 and 1311,
respectively, of the previous level (FIG. 8). The other two studs
2323 and 2324 connect the end of cantilevers 2312 and 2311,
respectively, to bulk head 1310 of the bus line 131 of previous
level. This is more clearly illustrated in FIG. 10 which depicts a
cross-sectional view of a set of stacked via-studs at section A-A'
of drawings in FIGS. 8 and 9 and, in FIG. 11 which is a
cross-sectional view of a set of stacked via-studs at section B-B'
of drawings in FIGS. 8 and 9.
[0060] The foregoing steps form cantilevers in wide metal lines,
and respectively connect the formed cantilevers and bulkheads in
one level of bus line to bulk heads and cantilevers formed in the
bus line of the adjacent levels of interconnection.
[0061] The foregoing steps can be repeated to form the redundant
stacked via studs of the invention with increased flexibility and,
thereby, improved fatigue life.
[0062] It should be apparent to those skilled in the art that given
the teachings above, other embodiments of designs to reduce the
strain in a stacked via-stud, imbedded in a soft media and capped
at top and at bottom by relatively denser media; or other
modifications of this invention, such as, for example, the
cross-sectional area of the via-stud could be enlarged; a set of
neighboring dummy studs may be provided; or, a stronger liner for
high conductivity metals may be provided without departing from the
spirit of the invention. Accordingly, such modifications are
considered within the scope of the invention as limited solely by
the appended claims.
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