U.S. patent application number 11/872229 was filed with the patent office on 2008-02-07 for method to create flexible connections for integrated circuits.
This patent application is currently assigned to INTERNATIONAL BUSINESS MACHINES CORPORATION. Invention is credited to Leena Paivikki Buchwalter, Russell A. Budd, Chirag S. Patel.
Application Number | 20080029889 11/872229 |
Document ID | / |
Family ID | 36911819 |
Filed Date | 2008-02-07 |
United States Patent
Application |
20080029889 |
Kind Code |
A1 |
Buchwalter; Leena Paivikki ;
et al. |
February 7, 2008 |
METHOD TO CREATE FLEXIBLE CONNECTIONS FOR INTEGRATED CIRCUITS
Abstract
A method of producing flexible interconnections for integrated
circuits, and, in particular, the forming of flexible or compliant
interconnections preferably by a laser-assisted chemical vapor
deposition process in semiconductor or glass substrate-based
carriers which are employed for mounting and packaging multiple
integrated circuit chips and selectively, other devices in the
technology.
Inventors: |
Buchwalter; Leena Paivikki;
(Hopewell Junction, NY) ; Budd; Russell A.; (North
Salem, NY) ; Patel; Chirag S.; (Peekskill,
NY) |
Correspondence
Address: |
SCULLY, SCOTT, MURPHY & PRESSER, P.C.
400 GARDEN CITY PLAZA
SUITE 300
GARDEN CITY
NY
11530
US
|
Assignee: |
INTERNATIONAL BUSINESS MACHINES
CORPORATION
New Orchard Road
Armonk
NY
10504
|
Family ID: |
36911819 |
Appl. No.: |
11/872229 |
Filed: |
October 15, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11063449 |
Feb 23, 2005 |
|
|
|
11872229 |
Oct 15, 2007 |
|
|
|
Current U.S.
Class: |
257/737 ;
257/E21.511; 257/E23.068; 257/E23.194; 438/613 |
Current CPC
Class: |
H01L 2924/01033
20130101; H01L 2924/14 20130101; H01L 2924/01074 20130101; H01L
2924/01005 20130101; H01L 2924/00 20130101; H01L 2924/00 20130101;
H01L 2924/00 20130101; H01L 2924/014 20130101; H01L 2924/01073
20130101; H01L 2224/81801 20130101; H01L 2924/01029 20130101; H01L
2924/351 20130101; H01L 2924/10253 20130101; G01R 1/07307 20130101;
H01L 2924/01042 20130101; H01L 23/49811 20130101; H01L 2924/01013
20130101; H01L 2924/01079 20130101; H01L 2924/01078 20130101; H01L
21/4853 20130101; G01R 1/06716 20130101; H01L 2924/01006 20130101;
H01L 2924/01044 20130101; H01L 2924/14 20130101; H01L 23/562
20130101; H01L 2924/351 20130101; H01L 2924/10253 20130101; G01R
1/0408 20130101; H01L 24/81 20130101; H01L 2924/01082 20130101 |
Class at
Publication: |
257/737 ;
438/613; 257/E21.511; 257/E23.068 |
International
Class: |
H01L 23/48 20060101
H01L023/48; H01L 21/44 20060101 H01L021/44 |
Claims
1. A semiconductor package assembly comprising a substrate and at
least one integrated circuit chip mounted on said substrate, said
at least one flexible interconnect forming a compliant electrical
connection between said substrate and said at least one integrated
circuit chip.
2. A method of fabricating a compliant probe substrate, comprising
of a substrate and said at least one flexible interconnect forming
a compliant probe lead (interconnect).
3. A compliant probe substrate as claimed in claim 2, wherein a
substrate is made of semiconductor, ceramic, organometallic
materials in a passive form or having active or passive components
assembled onto it.
4. A compliant probe substrate as claimed in claim 3, wherein the
compliant interconnect or the tip of it comprises of mechanically
and electrically durable and/or physically abrasive materials.
5. A semiconductor package assembly as claimed in claim 1, wherein
said compliant flexible interconnect is constituted of a material
deposited by laser-assisted chemical vapor deposition (LCVD).
6. A semiconductor package assembly as claimed in claim 1, wherein
said compliant flexible interconnect comprises a generally upright
C-shaped member extending between facing surfaces of said substrate
and said at least one integrated circuit chip.
7. A semiconductor package assembly as claimed in claim 6, wherein
a tip of said C-shaped member, which supports said at least one
integrated circuit chip is provided with a solder wettable
metallurgical material.
8. A semiconductor package assembly as claimed in claim 7, wherein
said solder wettable metallurgical material comprises an Ni
adhesion layer and solder wettable gold (Au).
9. A semiconductor package assembly as claimed in claim 6, wherein
a plurality of said C-shaped members are spaced in x-y planar
dimensions at varied spacings from a neutral point so as to
compensate for differences in coefficients of expansion between
said substrate and said at least one integrated circuit chip
encountered responsive to heat generated during operation of said
semiconductor package assembly.
10. A semiconductor package assembly as claimed in claim 8, wherein
said adhesion layer and said solder wettable metallurgical material
are deposited by laser-assisted chemical vapor deposition.
11. A semiconductor package assembly as claimed in claim 8, wherein
said adhesion layer and said solder wettable metallurgical material
are deposited through selective surface plating.
12. A semiconductor package assembly as claimed in claim 8, wherein
said adhesion layer and said solder wettable metallurgical material
are surrounded by an insulator for maintaining the solder within
the flexible interconnect tip.
13-15. (canceled)
16. A method as claimed in claim 15, wherein said spirally-shaped
complaint flexible interconnect is formed on a motor-driven
goniometer arrangement in conjunction with a focused laser beam
projected through said optical system and LCVD.
17-20. (canceled)
21. A method as claimed in claim 19, wherein said adhesion layer
and said solder wettable metallurgical material are deposited by
laser-assisted chemical vapor deposition.
22. A method as claimed in claim 19, wherein said adhesion layer
and said solder wettable metallurgical material are deposited
through selective surface plating.
23. A method as claimed in claim 19, wherein said adhesion layer
and said solder wettable metallurgical material are surrounded by
an insulator for maintaining the solder within the flexible
interconnect tip.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a novel method of producing
flexible interconnections for integrated circuits, and, in
particular, although not limited thereto, to the provision of
forming flexible or compliant interconnections in semiconductor or
glass substrate-based carriers which are employed for mounting and
packaging multiple integrated circuit chips and selectively, other
devices in the technology. In particular, the integrated circuit
chip or the plurality of chips, which are mounted on a carrier, is
or are connected to a next level package or a circuit board, and
wherein the next level package may be constituted of a ceramic or
an organic composite depending upon particular intended
applications.
[0003] Basically, in the formation of integrated circuits employing
organic chip carriers, the provision of a flexible or compliant
interconnection assumes great importance in maintaining the
operative integrity of the integrated circuits, due to the
differences, which are frequently encountered in the mismatches in
the thermal coefficients of expansion (CTE), which are present
between the organic chip carrier and the chip or chips, or a
silicon carrier (Si-carrier), which is bonded thereto.
[0004] In essence, when the applicable chip or the Si-carrier is,
or chips or carriers, are of a large size or sizes, the mismatch
between the respective CTEs is further increased, inasmuch as the
flexible interconnection size must be specifically designed to take
cognizance of the differences in the absolute physical movement or
displacement between the respective components as a function of the
displacement or distance which is measured from a so-called neutral
point of the overall semiconductor structure.
[0005] Generally, the differences or mismatches which may be
present in the coefficients of thermal expansions between the
components create problems in the fatigue life of the
interconnection in response to an increase in the difference or
mismatch between the CTEs of the substrate and the chip or chips.
In the prior art, and in current state of the technology,
cognizance has been given to such differences or CTE mismatches in
the x and y-directions or planes of the integrated circuit
structure. However, although the movements in the x and y plane to
which considerations have been given in improvising solutions in
the formation of the compliant or flexible connections between a
chip and carrier, and have been extensively treated in the prior
art, and have also been addressed in applicants' co-pending U.S.
patent application Ser. No. 10/686,640, filed on Oct. 17, 2003
(Attorney Docket No. YOR920030192), the disclosure of which is
incorporated in its entirety herein by reference, that application
being commonly assigned to the assignee of the present
application.
[0006] In order to provide a compliant or essentially flexible
interconnection, which will take cognizance of the CTE mismatches
which are encountered between the chip or chips and the substrate
or carrier components, utilization has been implemented of methods
of laser assisted chemical vapor deposition (LCVD) of the
conductors which form the electrical interconnections. Thus, for
instance, in order to form the interconnections, any metal which is
suitable for that purpose can be deposited by means of laser
assisted chemical vapor deposition (LCVD), wherein such metal
forming the interconnection may be suitably constituted of, but not
limited to, tungsten, molybdenum, tantalum and platinum, although
tungsten is preferably the most widely employed of these types of
metals.
[0007] For example, pertaining to the basic concept of chemical
vapor deposition (CVD), a solid material is deposited from gaseous
reactants through chemical reactions onto or in the vicinity of a
heated surface. The resulting properties of the deposited material
can be readily controlled by appropriate regulation of the process
conditions, and which normally entails a multi-step process in
order to form the interconnections. In implementing the LCVD, a
laser is employed in order to thermally or photochemically activate
the CVD process, whereby laser frequencies are selected such that
the gaseous reactants do not absorb the radiation, and a focused
laser may be utilized as a localized heat source. The laser may be
either a continuous wave laser or, alternatively, a pulsed laser,
wherein the use of such LCVD processes, including the thermally
activated CVD process, is known in the current state of the
technology. The CVD techniques may be employed to deposit various
solid materials, such as metals, alloys and non-metals and
compounds comprising carbides, nitrides and oxides, whereby
deposition of the material may be in the form of thin films,
fibers, powders, rods or other three-dimensional structures.
[0008] For the purpose of testing integrated circuit chips in
wafer, singulated, carrier, or package form, it is important for a
probing substrate to have a compliant or flexible probe tip or
interconnect, due to non-planarity of surface pads or solder bumps
that are present on the surface of the wafer, chip, carrier, or
package. Furthermore, it is desirable to have a probe tip surface
to be mechanically and chemically durable and physically abrasive
such that upon physical contact with the device under test (i.e.,
wafer, chip, carrier, or package), any existing surface oxides and
residues that may have formed on the surface of a pad or a solder
bump are effectively removed to assure a low resistance electrical
contact during testing.
[0009] Heretofore, in the current state of the technology, either
no consideration or only a limited degree of consideration has been
given to the forming of flexible interconnects in integrated
circuit structures which take cognizance of compliance in the
z-direction, in addition to compliance in the x and y planes.
[0010] For instance, especially in the case of an organic chip
carrier, is a matter of extreme importance, that in connection with
the use of a flexible interconnection there must be accounted for
differences or mismatches in the thermal coefficients of expansion
(CTEs) between the interconnection and the chip or the Si-carrier
which is bonded thereto.
[0011] As indicated in a chart hereinbelow, which sets forth
fatigue life-cycles versus coefficients of thermal expansion of the
substrate, there is a clear correlation of the interrelationship in
the fatigue life-cycle with regard to the differences which are
evident between the substrate and chip coefficients of thermal
expansion.
[0012] Furthermore, the stress and strain, which is created by the
interconnection due to the physical dimensions of the chip or
carrier and the height of the interconnection, have an important
bearing on the provision of a compliant or flexible interconnection
in the z-direction. Although ceramic chip carriers are attractive
from the standpoint of their thermal characteristics, they are
expensive to produce and in order to reduce manufacturing costs,
extensive considerations are being given to the use of chip
carriers, which are constituted of polymeric materials.
Nevertheless, the difference in the coefficients of thermal
expansion (CTEs) between the chip and the carrier is evident to a
degree so as to cause significant problems with regard to the
integrity and service life expectancy of standard C4
connections.
[0013] 2. Discussion of the Prior Art
[0014] For example, in effecting formation of a compliant
connection between a chip and carrier allowing for movements in the
x- and y-plane, which take into consideration compensating for CTE
differences or mismatches, prior art publications, such as Patel,
et al., U.S. Pat. No. 6,528,349 B1; Takiar, et al., U.S. Pat. No.
6,521,970 B1; Khandros, et al., U.S. Pat. No. 6,372,527 B1;
Fjelstad, et al., U.S. Pat. No. 6,211,572 B1; DiStefano, et al.,
U.S. Pat. No. 6,104,087; and Bezuk, et al., U.S. Pat. No.
4,845,542, each disclose diverse methods and structures directed to
the build up of compliant or flexible interconnections and are
primarily concerned with complicated multi-step and consequently,
expensive processing procedures in the manufacture of integrated
circuits or the like structures.
SUMMARY OF THE INVENTION
[0015] More specifically, the present invention relates to an
obtention in a cost reduction of the compliant interconnect build
by, in a novel and inventive manner, devising a method of replacing
the complicated processing required in the prior art with simple
laser assisted chemical vapor deposition (LCVD) of the
interconnect. Hereby, in contrast with the invention, Bezuk, et
al., U.S. Pat. No. 4,845,542 teaches the employment of (LCVD) to
deposit rigid post interconnects. The interconnect design of Bezuk,
et al. does not concern itself with z-direction compliance, and
only a minimal x-y direction compliance, and is adapted to be used
between adjacent wafers, in the absence of any CTE difference, and
contemplates the no use of any masks or lens-arrays, in effect, a
single interconnect build at any one time. The interconnect shapes
described in that patent are all subject to fatigue related issues
due to a lack of spring characteristics in the build. Aluminum, as
disclosed therein, also has the drawback of creep, thus opening a
possibility of permanent deformation during joining and/or thermal
stressing. Also noted is that the applied solder in Bezuk, et al.
has a tendency to wick away, particularly onto the Ni post,
reducing the solder volume in an uncontrolled manner causing
problems in the process of chip joining.
[0016] The present invention concerns itself with eliminating or
ameliorating the problems delineated above with regard to the prior
art, and more specifically is concerned with a two-fold method
using thermally activated chemical vapor deposition (TACVD) adapted
to deposit the conductor forming the compliant or flexible
interconnect structure facilitating z-direction as well as x- and
y-reaction compliance. The thermal activation of metal deposition
is accomplished using for example, an Ar+ (Argon) laser (laser
assisted chemical vapor deposition, (LCVD). The deposition
temperatures are <1000K utilizing either pulsed and/or
continuous wave laser heating of a substrate constituted of a laser
energy absorbing material.
[0017] Pursuant to a first embodiment, the invention provides for
x-, y-, and z-directional movement of the laser with well defined
focal point to directly `write` or produce a spring-structure type
of interconnect which is flexible but non-collapsible in nature.
Several interconnects can be `written` or formed simultaneously by
a unique usage of microlenses, focusing, and/or masking as taught
in co-pending U.S. patent application Ser. No. 10/686,640, filed on
Oct. 17, 2003 (Attorney Docket YOR920030192), which is commonly
assigned to the present assignee, and the entire disclosure of
which is incorporated herein by reference.
[0018] In accordance with a further embodiment of the invention,
there is entailed a reduction in the amount of lithography in order
to first build a z-direction compressible polymeric base with
via-hole opening to the wiring, as taught, for example, in Patel,
U.S. Pat. No. 6,528,349 B1, the disclosure of which is incorporated
herein by reference in its entirety. In this embodiment, a blanket
conductor film is deposited onto the organic surface. The localized
heating effected by the laser exposure is now performed through a
mask opening, or is directly `written` or produced using a focused
laser beam through a matrix of microlenses and pre-determined x-,
y-, and z-movements of the sample, or the laser/mask or a
laser/microlens system as disclosed in above-mentioned U.S. patent
application Ser. No. 10/686,640.
[0019] Concerning the foregoing features and embodiments, in
particular, there are in evidence a number of aspects to which the
invention is directed, and which are unique from the standpoint of
providing a simple solution in the formation of a compliant and
flexible interconnection for preferably integrated circuits, and
which is resilient in x-, y- and z-directions and planes.
[0020] Accordingly, it is an object of the present invention to
provide a flexible interconnect comprising of laser absorbing base,
LCVD deposited interconnect of certain shape, and solder wettable
pad at the tip of the flexible interconnect.
[0021] An object of the present invention resides in providing a
barrier against solder migration down the flexible interconnect
made of glassy inorganic or organic material, whereas a further
aspect of the invention contemplates providing a barrier against
solder migration made of silica or of another insulator using an
LCVD process.
[0022] An object of the present invention is to provide a flexible
interconnect on a substrate comprising of laser absorbing base,
LCVD deposited interconnect of certain shape, and having
mechanically and chemically durable and/or physically abrasive
surface characteristics such that repetitive electrical and
physical contact can be made to the device under test.
[0023] Another object of the present invention provides for a
flexible interconnect matrix with varied x-y dimensions accounting
for a difference in the distance from a neutral point.
[0024] A further object of the present invention pertains to the
provision of a method of flexible interconnect orientation relative
to the neutral point so as to allow an optimum orientation for
maximum needed deflection of given interconnect which will account
for a CTE mismatch between a substrate and the therewith connected
Si-element.
[0025] Yet another object of the present invention provides a
method to directly `write` or generate the free-standing flexible
interconnects using a unique combination of LCVD with lasermasks or
microlens arrays. In this instance, the method is adapted to
deposit the flexible interconnect onto a laser absorbing material
on a compressible polymer base which has been previously
patterned.
[0026] Still another object of the present invention provides for a
method adapted to simultaneously cause a localized release of the
flexible interconnect base of the compressible polymer base so as
to allow free x-y movement of the flexible interconnect after the
excess of the blanket interconnect base metallurgy has been removed
using techniques known in the art.
[0027] None of the foregoing objects, aspects and features are
known or in existence in the current state-of-the-art, whereby the
present invention is unique in the provision of a concept of a
build up of an integrated circuit structure or electronic package
providing for x-, y- and z-directionally, compliant and/or flexible
interconnections utilizing a thermal LCVD approach, as described
hereinbelow in more specific detail.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Reference may now be made to the following detailed
description of preferred embodiments of the invention, taken in
conjunction with the accompanying drawings; in which:
[0029] FIG. 1A through 1D disclose aspects in the build up of a
free-standing complex microstructure without the use of masking,
with regard to two specific embodiments thereof pursuant to the
invention;
[0030] FIG. 2 illustrates a modification representative of an
alternate physical orientation of a laser employed in implementing
the inventive method, whereby a spiral connect microstructure is
being fabricated utilizing the LCVD concept;
[0031] FIGS. 3A through 3D illustrate sequential steps in the
forming of C-shaped compliant interconnections shown in the
z-direction, whereby FIG. 3A represents a first step showing the
interconnection of a base adhesion layer and LCVD metal deposition
initiation layer;
[0032] FIG. 3B illustrates solder deposited on solder wettable
metal metallurgy on the compliant C-shaped interconnection;
[0033] FIG. 3C illustrates a chip with a solder wettable bottom
surface metallurgy positioned onto a substrate via the
interposition of flexible interconnections;
[0034] FIG. 3D illustrates, on an enlarged scale, the encircled
detail from FIG. 3A of the drawings;
[0035] FIG. 4 illustrates, generally schematically, a preferred
orientation of a plurality of flexible interconnects with respect
to a neutral point on a chip or Si-carrier, with the interconnects
being arranged radially spaced about the neutral point;
[0036] FIG. 5A through 5F illustrate sequential steps in
implementing the formation of another embodiment of compliant
interconnects pursuant to the invention, wherein in FIG. 5A the via
hole has been opened to access a metal pad on an organic chip
carrier pursuant to prior art methods;
[0037] FIG. 5B illustrates a laser deposited blanket metal film,
which has been provided on a polymer surface;
[0038] FIGS. 5C through 5D illustrate various steps in removing and
coating the material;
[0039] FIG. 5E illustrates a side view of the finished compliant
interconnection, as shown also in a plan view of FIG. 5F; and
[0040] FIG. 6 illustrates two different shapes of compliant
interconnects formed pursuant to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0041] In specific detail, the invention concept is directed to
interconnecting Si-components to CTE mismatched Si-component
carriers and establishing a temporary contact between Si-components
and a probe substrate for electrical and burn-in tests. The
Si-component may be stacked silicon, Si-chips bonded to Si-carrier
or combination of both which then are bonded to the next level
packaging made of inorganic or organic material or material
combination.
[0042] LCVD interconnect material may be readily selected from the
list of typical materials which are available for LCVD and wherein
Table 1 shows presently available materials. TABLE-US-00001 TABLE 1
Typical LCVD metals and their properties Resistivity Max writing
Metal/precursor Material properties .mu..OMEGA.cm rate .mu.m/s
W/WF6/H2 .alpha.-phase, low stress 12-25 200 Ni/Ni(CO)5 micro - or
polycrystalline 15-70 200 Co/Co2(CO)10 microcrystalline 13-25 50
Pt/Pt(PF3)4 microcrystalline 11-15 200 Al/TMAA polycrystalline 4
200 Cu/Cu(TMVS)hFac) microcrystalline 7 10 Mo microcrystalline 24
100 Au/AuAcAc polycrystalline 3 10
[0043] The foregoing does not in any manner limit the materials of
consideration such as are set forth in Table 1. Metal properties
which are generally of interest are listed in Table 2 herein below.
TABLE-US-00002 TABLE 2 General metal properties Thermal Resis-
Conduc- Mate- E .DELTA.E/.DELTA.T .sigma..sub.y CTE tivity tivity
Poisson rial (Gpa) MPa/C (MPa) (ppm/C) .mu..OMEGA.cm (W/mK) ratio
Cu no -39 320 16.5 1.73 380 0.35 Au 79 -19 210 14.2 3 317 0.35 Al
72 -31 110 23.1 4 237 0.345 Ni 207 320 13.4 6.4 91 0.31 Co 211 78
13.0 6.2 100 0.32 W 411 -42 1800 4.5 5.39 180 0.28 Mo 300 43 840
4.8 5.7 140 0.321 Pt 168 -23 160 8.8 10.6 72 0.38 Ru 422 550 6.4
7.1 117 0.25
[0044] Selection of the interconnect material is effected by the
required spring characteristics, in essence, flexibility and
compliance which, in turn, are effected by the dimensions of the
Si-component, .DELTA.CTE between the Si-component and the
substrate, and the encountered temperature range.
[0045] Any thermally activated CVD process can be activated using
laser as the heat source. Thus insulators, such as Si.sub.3N.sub.4,
and alloys (to tailor flexible interconnect properties) can be
deposited by using LCVD.
[0046] For instance, the dimensions of the interconnect are
determined by the Si-component x-y dimensions, Si-component and
substrate .DELTA.CTE, the location of interconnect relative to a
neutral point, requires z-dimension compliance.
[0047] Referring in detail to the drawings, and particularly FIGS.
1A and 1B, there is provided an arrangement 10 for the forming or
fabrication of a flexible or compliant interconnect 12, which is in
essentially in the shape of a spiral, as shown in enlarged detail
in FIG. 1B. In this instance, the flexible interconnect 12 is
formed through the intermediary of a laser beam 14 and a microlens
army 16 (only a single lens being illustrated) and which, if
desired, may be optionally combined with substrate movement or
rotation. In this instance, there is provided a goniometer 18,
which is rotated in the direction of Arrow A through the
intermediary of a suitable drive motor 20, and wherein a vertical
displacement is implemented in the direction of Arrow B in order to
form the flexible interconnect 12 in the spiral shape in the
z-direction of an integrated circuit structure (not shown).
Pursuant to this aspect, the foregoing method of fabrication of the
flexible interconnect may be also implemented through a dielectric
mask rather than a microlens array, with the employment of either
the laser, as mentioned hereinabove, or through imparting a
substrate micromovement, or by a combination of these particular
features and/or movements.
[0048] As illustrated in FIG. 1A, which produces the spiral shape
of the flexible interconnect 12 of FIG. 1B, it is also possible to
contemplate a modification, as shown in FIGS. 1C and 1D, wherein
rather than the spiral of FIG. 1B, there is provided a spiral 22 in
the form of deposition about a rod shaped structure 24 through the
intermediary of a microlens and laser beam, which is similar to the
previous embodiment. In this structure, the goniometer 18 is
rotated in an opposite direction, as shown by arrow C, so as to
produce a series of coil-like bands 26 about the vertically
extending structure 24 in producing the spiral flexible
interconnect 22.
[0049] As shown in FIG. 2 of the drawings, in this instance there
may be provided a somewhat different arrangement of the laser beam
14 and microlens array 16 relative to the goniometer, as shown in
FIGS. 1A and 1C of the drawings. For the remainder, the fabrication
method, with the exception of the orientation, is similar to that
of FIG. 1A, in order to produce the spirally shaped flexible
interconnect. Basically, the embodiments illustrated in FIGS. 1A
through 1D are directed to the formation or fabrication of flexible
or complaint interconnects built up of complex free-staining
microstructures without the application of masking, and wherein the
alternative physical orientation of the lasers and the spiral
microstructures being fabricated employ the unique LCVD approach
pursuant to the invention. This also applies to the alternative
arrangement for the laser beam and microlens arrangement, as shown
in FIG. 2 of the drawings.
[0050] As illustrated in the embodiment of FIGS. 3A through 3D,
showing stages or steps in the formation of C-shaped interconnects
30, which are essentially of a flexible or compliant nature
especially in the z-direction and wherein these are illustrated as
being positioned on an interconnect base 32 on a substrate 33,
which base is constituted of an adhesion layer 34 and an LCVD metal
deposition layer 36. Basically, the tip 38 of each C-interconnect
is comprised of an adhesion layer 39, and where solder wettable
material or metal 42 and inorganic or organic solder barrier 41 is
arranged thereon.
[0051] As illustrated in FIG. 3B, the interconnects 30 are shown
with solder deposited on the solder wettable metallurgy 42, for
instance, in the nature of solder balls 46 located proximate the
free tip end 38 of the C-shaped interconnect 30. As illustrated in
FIG. 3C of the drawings, in that instance, a chip 48 has been
positioned on the solder wettable metallurgy 42 by means of solder
wettable bottom surface metallurgy, known in the technology as
being bonded to the substrate or base 32 through the flexible
C-shaped interconnects 30. This is shown in further enlarged detail
in FIG. 3D of the drawings, wherein it becomes readily apparent
that the solder may also be deposited on the chip solder wettable
metallurgy, as opposed to being deposited on the flexible C-shaped
interconnect tip 38.
[0052] Reverting to FIG. 4 of the drawings, this illustrates a
preferred orientation of a plurality of C-interconnects 30 arranged
mutually spaced on a chip or silicon carrier 50 relative to a
neutral point or axis 52 to compensate for CTE mismatch-caused
stresses. In that manner, the C-shaped flexible interconnects 30
may be readily oriented radially about the neutral point or at
particular spacings relative to the neutral point. Available in the
arrangement of the C-interconnects 30 relative to distances from
the neutral point 52 is the possibility of shaping the structures
thereof so as to be tailored in order to match encountered CTE
mismatches to thereby compensate for the fact that the
C-interconnect 30 nearer the central or neutral point can be
thinner or skinnier in its construction requiring a lesser x-y
compliance, in comparison to the further outermost spaced
C-interconnects, which are subjected to higher stresses. This, in
essence, provides for a satisfactory balancing of CTE mismatches,
which are frequently encountered in the technology and whereby the
particular diverse spacing of the various radially offset
C-interconnects 30 relative to the neutral point or axis is adapted
to compensate for such variations in the CTE mismatches, as the
distance of the interconnect increases from the neutral point or
axis.
[0053] Reverting to the configuration, as shown in FIGS. 5A through
5F of the drawings, there is disclosed a further embodiment of the
invention in which a polymer film 60 is utilized to supply a
z-direction control in compliance so as to compensate for CTE
mismatches. A via hole 62 is opened so as to provide access to a
metal pad 64 on an organic chip carrier 66, which may employ
fabrication methods known in the art. A thin laser-absorbing
blanket metal film 68 of a focused laser-beam applied nature (LCVD)
is deposited on the polymer film surface 60. Thereafter, a
dielectric mask 70 may be utilized with the focused laser beam in
order to deposit a compliant interconnect 72 onto the blanket metal
coating film 68, as shown in FIGS. 5C and 5D. The blanket metal
coating film 68 is then removed through the employment of either
wet or dry processing methods, both of which are well known in the
art, as represented in the further process step of FIG. 5E. This
structure is also illustrated in a plan view, as shown in FIG. 5F.
In essence, in this manner, there is provided an alternative method
to the fabrication structures, as represented in FIGS. 1A and 1D of
the drawings.
[0054] Reverting to FIG. 6 of the drawings, there are illustrated
two different shapes for compliant interconnects, in which one is
essentially of a rod shaped element 80 extending from a via 82,
whereas a further one provides a snake-like or winding compliant or
flexible interconnect 84. Readily, it is apparent that numerous
other configurations of flexible and compliant interconnects can be
employed by the present invention, and the drawings only represent
typical embodiments thereof, not limited thereto.
[0055] In summation, since LCVD is based on thermally activated
chemical vapor deposition, and since the laser selected couples
with the metals selected thus only heating that area it is focused
on, then it is possible to effect LCVD of different shapes with
clever mechanical movement of the substrate without the need to
keep the laser parallel to the direction of surface of growth, but
can be positioned perpendicular to the direction of growth when
necessary. A large area simultaneous deposition of C-shaped
interconnects is possible by either moving a mask, laser/microlens
system, or in a computer controlled path consistent with the
desired interconnect shape.
[0056] Moreover, the present invention provides a method to
selectively delaminate the metal bound to the polymer surface
during the initial steps of laser deposition, where the duration of
the laser at the PVD metal on the polymer surface is extended long
enough so that slight thermal decomposition is effected at the
interfacial region of the metal-polymer stack. The polymer is
selected from thermal stable materials such as polyimides,
polyphenylenes, and so forth. Pursuant to a method, it is possible
to build a solder wettable metallurgy at the tip of the flexible
interconnect where the solder is contained at the tip. A LCVD
insulator, such as Si3N4, is deposited on the tip of the flexible
interconnect. This is then followed by adhesion layer deposition,
such a Ni, and then Au deposition using LCVD process. Another
aspect of the present invention is to use selective plating of Ni
at the tip of the flexible interconnects followed by immersion in
Au.
[0057] Moreover, the present invention provides a method to build a
probe substrate with flexible temporary connections for electrical
and burn-in tests. Pursuant to this method, it is possible to build
a flexible connection with surface roughness by tailoring the
deposition conditions thus allowing effective abrasion of contact
pad on test device to result in good electrical contact. Moreover,
pursuant to this method is coating of the rough, preferably
tungsten (or another conductor with high yield stress), surface
with a noble hard metal such as, but not limited to, ruthenium
using LCVD or plating resulting in rough, hard, inert, and
electrically conductive flexible probe.
[0058] While it is apparent that the invention herein disclosed is
well calculated to fulfill the objects stated above, it will be
appreciated that numerous modifications and embodiments may be
devised by those skilled in the art, and it is intended that the
appended claims cover all such modifications and embodiments as
fall within the true spirit and scope of the present invention.
* * * * *