U.S. patent application number 11/175647 was filed with the patent office on 2005-11-17 for methods for producing an electronic device having microscopically small contact areas.
This patent application is currently assigned to Infineon Technologies AG. Invention is credited to Hacke, Hans-Jurgen.
Application Number | 20050255633 11/175647 |
Document ID | / |
Family ID | 7638211 |
Filed Date | 2005-11-17 |
United States Patent
Application |
20050255633 |
Kind Code |
A1 |
Hacke, Hans-Jurgen |
November 17, 2005 |
Methods for producing an electronic device having microscopically
small contact areas
Abstract
A method for producing an electronic device, which has at least
one microscopically small contact area for an electronic circuit
having interconnects on a surface of a substrate. A
three-dimensionally extending microscopically small contact element
is integrally connected to the contact area in one piece.
Inventors: |
Hacke, Hans-Jurgen;
(Munchen, DE) |
Correspondence
Address: |
LERNER AND GREENBERG, PA
P O BOX 2480
HOLLYWOOD
FL
33022-2480
US
|
Assignee: |
Infineon Technologies AG
|
Family ID: |
7638211 |
Appl. No.: |
11/175647 |
Filed: |
July 6, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11175647 |
Jul 6, 2005 |
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09833260 |
Apr 10, 2001 |
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6946725 |
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Current U.S.
Class: |
438/106 ;
257/E21.506; 257/E23.021; 257/E23.078 |
Current CPC
Class: |
H01L 2224/13655
20130101; H01L 24/11 20130101; H01L 2224/13644 20130101; H01L
2924/01006 20130101; H01L 2924/014 20130101; H01L 2924/14 20130101;
H01L 2924/01033 20130101; H01L 2924/00013 20130101; H01L 24/13
20130101; H01L 2924/12042 20130101; H01L 2224/13644 20130101; H01L
2924/01005 20130101; H01L 21/4853 20130101; H01L 2924/181 20130101;
H01L 2924/00013 20130101; H01L 2224/13582 20130101; H01L 2224/13147
20130101; H01L 2924/01322 20130101; H01L 2924/00014 20130101; H01L
2924/00 20130101; H01L 2224/13099 20130101; H01L 2924/00014
20130101; H01L 2924/00014 20130101; H01L 2224/1147 20130101; H01L
2924/00 20130101; H01L 2224/13147 20130101; H01L 2924/01013
20130101; H01L 2924/01079 20130101; H01L 2924/01029 20130101; H01L
2924/181 20130101; H01L 2924/01082 20130101; H01L 2924/12042
20130101; H01L 2924/01327 20130101; H01L 2224/13655 20130101 |
Class at
Publication: |
438/106 |
International
Class: |
H01L 021/44 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 10, 2000 |
DE |
100 17 746.8 |
Claims
We claim:
1. A method for producing an electronic device having
microscopically small contact areas and interconnects formed on a
surface of a substrate being one of a semiconductor chip and a
semiconductor wafer, the contact areas having microscopically small
contact elements respectively integrally connected to the contact
areas in one piece and extending three-dimensionally at an oblique
angle, the method which comprises: patterning a conductive layer on
a surface of a substrate to form interconnects and microscopically
small contact areas; applying a passivation layer to the patterned
conductive layer; opening contact windows in the passivation layer
in order to uncover the contact areas; applying a closed conductive
layer in order to connect the contact areas; applying a masking
layer to the closed conductive layer; patterning the masking layer
with through openings that extend to the closed conductive layer
near the contact areas; filling the through openings with
conductive material to form three-dimensionally extending
microscopically small contact elements that are respectively
integrally connected to the contact areas in one piece; removing
the masking layer; and removing the closed conductive layer.
2. The method according to claim 1, which comprises using
photolithography methods to perform the steps of patterning the
conductive layer and opening the contact windows in the passivation
layer.
3. The method according to claim 1, which comprises performing the
step of applying the closed conductive layer using a technology
selected from the group consisting of vapor-deposition technology,
sputtering technology and deposition technology.
4. The method according to claim 1, which comprises using a copper
alloy layer as the closed conductive layer.
5. The method according to claim 1, which comprises performing the
step of applying the masking layer to the closed conductive layer
using a process selected from the group consisting of spinning on,
spraying on, and immersion.
6. The method according to claim 1, which comprises using a
photosensitive dielectric as the masking layer.
7. The method according to claim 6, which comprises exposing the
masking layer made of the photosensitive dielectric at a solid
angle with respect to the contact areas in order to produce
three-dimensionally angled contact elements.
8. The method according to claim 1, which comprises using
photolithography to perform the step patterning of the masking
layer.
9. The method according to claim 1, which comprises using a resin
layer as the masking layer that is applied to the closed conductive
layer.
10. The method according to claim 1, which comprises using a
process selected from the group consisting of laser removal
technology, ion beam sputtering, and plasma etching to perform the
step of patterning the masking layer with through openings.
11. The method according to claim 1, which comprises using
electro-deposition to perform the step of filling the through
openings with conductive material.
12. The method according to claim 1, which comprises using
electroless deposition technology to perform the step of filling
the through openings with conductive material.
13. The method according to claim 1, which comprises using etching
technology to perform the step of removing the closed conductive
layer.
14. The method according to claim 1, which comprises forming
contact heads using a process selected from the group consisting of
electrodeposition and an electroless process.
15. The method according to claim 1, which comprises potting spaces
between the contact elements.
16. The method according to claim 15, which comprises performing
the step of potting the spaces using a technology selected from the
group consisting of spraying technology and injection-molding
technology.
17. The method according to claim 1, which comprises: forming
contact heads using a process selected from the group consisting of
electrodeposition and an electroless process; potting interspaces
between the contact elements; and uncovering the contact heads
after performing the step of potting of the interspaces between the
contact elements.
18. The method according to claim 17, which comprises using laser
removal technology to perform the step of uncovering the contact
heads.
19. The method according to claim 1, which comprises coating the
contact heads with a metal selected from the group consisting of
nickel and gold.
20. A method for producing an electronic device having at least one
microscopically small contact area, which comprises: providing a
substrate having a surface and a plurality of contact areas that
are integrally connected to a plurality of three-dimensional
microscopically small contact elements, the plurality of the
contact areas being for at least one electronic circuit having
interconnects located on the surface of the substrate; patterning a
metal sheet to produce a plurality of uncovered contact spring
contours having breaking locations that are connected to the metal
sheet and having uncovered ends which correspond in size,
configuration and position to the plurality of the contact areas of
the substrate; aligning and pressing the patterned metal sheet onto
the substrate so that the uncovered ends of the plurality of the
contact spring contours are pressed onto the plurality of the
contact areas; heating the metal sheet and the substrate to bond
the uncovered ends of the plurality of the contact spring contours
to the plurality of the contact areas; and cooling and
stripping-off of the metal sheet, leaving behind
three-dimensionally extending, bonded or soldered contact springs
on each of the plurality of the contact areas.
21. The method according to claim 20, which comprises, before
pressing the metal sheet onto the substrate, coating the uncovered
ends of the plurality of the contact spring contours with a layer
that is selected from the group consisting of a nickel layer and a
gold layer.
22. The method according to claim 20, which comprises coating the
plurality of the contact spring contours with a solderable metal
alloy near the breaking locations.
23. The method according to claim 20, which comprises: providing a
spring-elastic material having a thickness between 30 and 100 .mu.m
with a solderable tin layer; and then providing the material as the
metal sheet that is patterned.
24. The method according to claim 20, which comprises, before
pressing the metal sheet onto the substrate, soft annealing regions
of the plurality the contact spring contours.
25. The method according to claim 24, wherein the regions are
central regions of the plurality the contact spring contours.
26. The method according to claim 20, which comprises: using a soft
metal sheet as the metal sheet that is patterned; and after the
metal sheet has been stripped off, heat-treating the
three-dimensionally extending contact springs to obtain a desired
spring property.
27. The method according to claim 20, which comprises providing the
metal sheet as a copper alloy metal sheet having patterns.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional of application Ser. No. 09/833,260,
filed Apr. 10, 2001; the application also claims the priority,
under 35 U.S.C. .sctn.119, of German patent application No. 100 17
746.8, filed Apr. 10, 2000; the prior applications are herewith
incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The invention relates to a method for producing an
electronic device having microscopically small contact areas.
[0003] In the course of miniaturization of IC housings, housing
packages have been disclosed which are the same size as the
semiconductor chips of a semiconductor substrate or are only
insignificantly larger than the semiconductor chips. They are
called CSP housings (Chip Size Packages). On the semiconductor chip
itself there are arranged microscopically small contact areas,
which are usually arranged in a central row or in the edge region
of the semiconductor chip, microscopically small meaning that the
structure can be discerned and measured under a light microscope.
Although rewiring from the central or edge region distribution of
the microscopically small contact areas to the outwardly leading
external connections that are distributed in rows and/or columns
over the entire area of the extensive housing of the electronic
device can be effected in different ways, expansion compensation
between the expansion of the semiconductor chip and of an
intermediate carrier which carries the rewiring and the external
connections must be made possible. In order to further reduce the
production costs for such extensive housings, the aim is for the
realization already to be implemented, with great effectiveness, at
the wafer level. In this case, the term wafer level CSP housing is
used.
[0004] There are numerous possibilities for carrying out the
rewiring at the wafer level and using a relatively thick dielectric
instead of an intermediate carrier, the rewiring being carried out
by means of thin-film wiring.
[0005] In order to carry out a test of the electronic circuits on
the wafer, a method is known in which a wire connection is
successively placed as first bond on each unwired chip connection
by means of thermocompression bonding. This wire connection is then
severed, and the wire stubs are electroplated with spring-tempered
material to produce elastic contact tips which can be used to make
contact for electrical testing and for burn-in.
[0006] Such a sequential production of test connections by way of
wire stubs that are subsequently electroplated for producing
elastic contact tips made of spring-tempered material is extremely
cost-intensive and cannot be realized directly on the
microscopically small contact areas, but rather only after rewiring
via interconnects that bring about the expansion compensation, and
after the production of the outwardly led connections arranged in
rows and columns.
SUMMARY OF THE INVENTION
[0007] It is an object of the invention to specify an electronic
component having at least one microscopically small contact area
and a method for producing it which overcomes the disadvantages in
the prior art and makes it possible to simultaneously produce a
multiplicity of contacts which are suitable both for compensating
areal unevennesses and for enabling expansion compensation in the
event of thermal cycling of an electronic device.
[0008] To that end, the electronic device comprises a contact area
which additionally has a three-dimensionally extending
microscopically small contact element which is connected to the
contact area in one piece and integrally.
[0009] This electronic device has the advantage that its contact
area with the three-dimensionally extending microscopically small
contact element can be realized simultaneously for a multiplicity
of integrated circuits on a wafer. Furthermore, this electronic
device has the advantage that, for test purposes, a test head with
correspondingly arranged contact connection areas on an
intermediate carrier can simultaneously make contact with the
three-dimensionally extending microscopically small contact
elements, without a bonded connection already having to be
produced. As a result, it is advantageously possible to test the
electronic devices still prior to encapsulation in a plastic
housing directly on a wafer without rewiring and intermediate
carrier.
[0010] Finally, the electronic device according to the invention,
with its contact areas which additionally carry a
three-dimensionally extending microscopically small contact
element, can compensate all expansion differences between the
electronic circuit having interconnects on the surface of a
substrate or semiconductor and the intermediate carrier belonging
to the housing. This avoids conventional form-flexible contact
connection lugs between microscopically small contact areas on the
surface of the substrate and contact connection areas on an
intermediate carrier. Furthermore, this electronic device has the
advantage that the three-dimensionally extending microscopically
small contact elements can compensate unevennesses of the surface
of the substrate. Finally, it is also possible to compensate for
tolerances of a distance between the surface of the substrate and
the contact connection areas arranged on the surface of an
intermediate carrier, by virtue of the three-dimensionally
extending microscopically small contact pins.
[0011] In a preferred embodiment of the invention, in the
electronic device, a contact connection area of an intermediate
carrier with flat conductors is arranged opposite the contact area.
In the course of rewiring, such flat conductors distribute the
microscopically small contact areas arranged on the edge regions of
the surface of the substrate, or the microscopically small contact
areas arranged in a row through the center of the surface of the
substrate, over the entire area of the electronic device and
provide a connection to corresponding outwardly led electrical
connections of the electronic device. The outwardly led electrical
connections are, for example, contact bumps distributed in rows
and/or columns on the extensive housing of the electronic device.
In a preferred embodiment of the invention, the substrate is a
semiconductor chip or a semiconductor wafer, and the electronic
circuit is at least one integrated circuit in that region of the
semiconductor chip or of the semiconductor wafer which is near the
surface.
[0012] On account of the invention's design of the electronic
device with contact areas which have a three-dimensionally
extending microscopically small contact element which is connected
to the contact area in one piece and integrally, it is
advantageously possible to equip all contact areas of a
semiconductor chip with contact elements of this type and/or to
populate an entire semiconductor wafer with a multiplicity of
electronic circuits and a multiplicity of contact areas with these
contact elements simultaneously in one production method and thus
to use the contact elements not only for expansion compensation or
for compensating unevennesses in the course of rewiring to
electronic external connections, but rather to utilize the contact
elements in order to check the function of the electronic circuit
still prior to encapsulation of the electronic devices with
housings and still prior to separation of a semiconductor wafer
into individual electronic devices.
[0013] In a further preferred embodiment of the invention, the
electronic circuit with interconnects has a multiplicity of contact
areas which are each arranged on an end of the interconnects. These
interconnects situated on the surface of the substrate serve for
connection between contact areas and the electrodes of the active
and passive components of the electronic circuit in that region of
the substrate which is near the surface, and, unlike the flat
conductors on an intermediate carrier, do not have the task of
realizing rewiring.
[0014] In a preferred embodiment of the invention, the contact
element has not only plastic deformability, which is given for each
metal, but also elastic deformability, with the result that an
advantageous spring stiffness of the contact pin is available.
[0015] In a further preferred embodiment of the invention, the
contact element is preformed at a solid angle which deviates from
the orthogonal orientation. Such an inclined orientation of the
contact element relative to the contact area has the advantage of
facilitating elastic adaptation to unevennesses of the surface of
the substrate and plastic expansion compensation, since the
microscopically small contact elements are already preformed at a
corresponding solid angle.
[0016] In a further preferred embodiment of the invention, the
contact element is prebent at a solid angle which deviates from the
orthogonal orientation. In this preferred embodiment, the
microscopically small contact element firstly extends in the
orthogonal direction and is plastically deformed using a tool, with
the result that it is permanently bent and, in this prebent form,
is available for the various further requirements made of the
electronic device.
[0017] The length of the contact element can be adapted to the wide
variety of requirements which are imposed on the electronic device.
Thus, preferably the length of the contact element is at least 5%
greater than the largest bulging of the surface of the substrate,
which advantageously ensures that even the largest bulging of the
surface of the substrate can be compensated by the contact pin.
Furthermore, the length of the contact element may be at least 5%
greater than the largest distance between contact area and contact
connection area, in order to ensure that the contact element
reliably bridges even the largest distance between the contact area
and an opposite contact connection area, preferably of an
intermediate carrier or of a test head.
[0018] Finally, the length of the contact element may be at least
5% greater than the largest length difference with regard to the
centrally located neutral point of the substrate in the event of
maximum thermal cycling. In the case of this preferred embodiment,
it is additionally ensured that, for all instances of thermal
cycling, the length of the contact element suffices to ensure
expansion compensation for the different external dimensions of the
substrate and the thermal cycling.
[0019] Furthermore, the length of the contact element may be at
least 5% greater than the largest length difference between
substrate and intermediate carrier relative to the centrally
located neutral point of the substrate in the event of maximum
thermal cycling. This advantageously also enables expansion
compensation taking account of the different thermal expansion of
substrate material and intermediate carrier material by means of
the adapted length of the contact element.
[0020] Preferably, the contact area and the contact element are
produced from an identical metal alloy. This embodiment has the
advantage that no diffusion area layers at all have to be provided
in order to avoid electromigration and other material migration at
the junction between contact area and contact element. However,
this embodiment cannot be implemented for all customary contact
area materials.
[0021] Therefore, in a further preferred embodiment of the
invention, the contact area is produced from an aluminum alloy,
while the contact element is produced from a gold alloy. This
combination has the advantage that it provides a high-quality,
non-oxidizing contact element which additionally has the advantage
that its free end can enter into intermetallic compounds, with
isothermal solidification, with a contact connection area made of
an aluminum alloy and, consequently, the contact pin can be
connected to the rewiring that leads further.
[0022] In a further preferred embodiment of the invention, the
contact areas are made of an aluminum alloy and the contact element
is made of a copper alloy. This has the advantage that, in order to
further connect the contact pin to the rewiring of an intermediate
carrier, conventional connection technologies which work with
copper alloys can directly be used.
[0023] In a preferred embodiment of the invention, the
microscopically small contact elements are designed as
microscopically small contact pins. These contact pins are
preferably mushroom-shaped and bear a rounded mushroom-cap-shaped
contact head. The contact pins are preferably arranged
simultaneously on a semiconductor wafer with the contact areas as
integral one-piece element by means of specially adapted method
steps appertaining to planar technology.
[0024] In a further preferred embodiment of the invention, the
contact pin has a diameter which is less than or equal to half the
shortest linear dimension of the contact area. In this case, the
contact area may be of rectangular, circular or elliptical design,
and the restriction of the diameter of the contact pin to the
preferred magnitude less than or equal to half the shortest linear
dimension of the contact area advantageously serves to impart to
the three-dimensionally extending microscopically small contact
pin, over a relatively large contact connection area, sufficient
adhesion on the surface of the substrate in order that elastic
bending and plastic deformations of the microscopically small
contact pin become possible without the one-piece integral
component comprising contact area and contact pin lifting off from
the surface of the substrate or even tearing off from the adjoining
interconnects.
[0025] In a further preferred embodiment, the contact pin has a
contact head on its end which is remote from the contact area. As a
result, the contact pin acquires a mushroom-shaped configuration as
an integral part of the contact area. This mushroom-shaped
configuration has the advantage that sliding relative to the
contact connection areas of an intermediate carrier is facilitated,
and that, for fixed connections between the rewiring of an
intermediate carrier and the contact pins, the material of the
contact head can be adapted to the material properties of the
contact connection area to which the contact head is connected.
[0026] The contact head of the contact pin may be produced from the
same metal alloy as the contact pin and, for the various
applications, may additionally have either a coating made of nickel
and/or gold or a solderable metal alloy coating, or the entire
contact head may possibly be composed of solder. This embodiment of
the contact head, in particular the optimal choice of material for
the contact head, depends on the construction of the housing of the
electronic device. If only a pressure contact is demanded for the
rewiring, a friction- and oxidation-resistant coating of nickel or
gold on the contact head will certainly be advantageous. However,
if a bonded connection is required, then this essentially depends
on the eutectic melts which can be formed between the material
combinations comprising contact head and rewiring that leads
further. Finally, if the aim is to effect a soldered connection
preferably for the contact head, if external connections such as
contact bumps made of soldering balls are also to be produced, then
it is advantageously possible to use a single burn-in process to
produce both the connection of the rewiring to the external contact
bumps and the internal soldered connection between contact head and
rewiring for an electronic device.
[0027] In a further preferred embodiment of the invention, the
microscopically small contact elements are designed as
microscopically small contact springs having a leaf-spring-like
configuration, one end of the contact spring being integrally
connected to the contact areas of the substrate or of the
semiconductor chip, and the other end extending three-dimensionally
from the contact area. The width of the contact spring toward the
free end is preferably tapered in such a way that a virtually
square contact area of the contact leaf spring is arranged in a
three-dimensionally offset manner above the connection to the
contact area of the substrate or semiconductor chip.
[0028] The contact springs are preferably produced by means of
synchronous method steps for all the contact springs of a wafer
simultaneously by means of multiple bonding or diffusion soldering
from a patterned metal sheet, the three-dimensionally extending
elastic contact springs with their free-standing contact area ends
being formed at prepared desired breaking points in the structures
of the metal sheet during the lifting-off of the metal sheet from
the bonded or diffusion-soldered points.
[0029] The contact spring preferably extends with its free end at a
solid angle .alpha. which is smaller than the orthogonal with
respect to the contact area. Such a contact spring which is angled
with respect to the contact area has the advantage that, by means
of its free-standing ends, surface unevennesses between a measuring
head with multiple contact connection areas for measuring the
function of the semiconductor chip can be compensated more easily
by elastic deformation and, during the packaging of the
semiconductor chip, contact to the multiple contact connection
areas of an intermediate carrier can be produced more easily since
surface unevennesses between semiconductor chip and intermediate
carrier can be compensated.
[0030] In a further preferred embodiment of the invention, the
width of the contact leaf springs corresponds to the width of the
contact areas on a substrate or semiconductor chip. This has the
advantage that during bonding, the entire contact area on the
semiconductor chip is available for the one-piece integral
connection of contact area and contact spring and, as a result, an
intensive, stable connection with a large area on a microscopic
order of magnitude can be constructed.
[0031] In a further preferred embodiment of the invention, the
contact spring is provided with gold and/or with a nickel coating
at its free end. In this case, the nickel coating serves as a
diffusion-inhibiting layer between the material of the contact
spring and the gold coating in order to ensure that the contact
spring material does not diffuse through as far as the material of
the contact area on the semiconductor chip.
[0032] The metal sheet is preferably made of an elastic material
such as a spring bronze or a copper alloy, with the result that
leaf-spring-like contact springs are directly produced when the
metal sheet is stripped off from the substrate or a semiconductor
wafer. In a further preferred embodiment of the invention, however,
it is also possible to use a soft-annealed sheet of spring bronze
which then attains its spring stiffness by means of heat treatment
of the wafer or of the semiconductor chip after the residual sheet
has been lifted off from the substrate or a semiconductor
wafer.
[0033] A metal sheet made of spring-elastic material is preferably
used, which is selectively soft-annealed preferably by means of a
laser beam in the region where the contact spring bends to the
greatest extent, in order advantageously to prevent the contact
spring from being torn off from the contact area of the substrate,
or to avoid damage to the contact connection area, by virtue of the
fact that small bending forces have to act on the connection
between contact spring end and contact area. In this case, too, the
spring stiffness of the contact spring is established after bonding
by means of subsequent heat treatment.
[0034] A method for producing an electronic device having at least
one microscopically small contact area for an electronic circuit
having interconnects on a surface of a substrate, the contact area
additionally having a three-dimensionally extending microscopically
small contact element which is connected to the contact area in one
piece and integrally, comprises the following method steps:
[0035] a) Patterning of a conductive layer on a surface of a
substrate to form interconnects and microscopically small contact
areas,
[0036] b) Application of a passivation layer to the patterned
conductive layer,
[0037] c) Opening of contact windows in the passivation layer in
order to uncover the contact areas,
[0038] d) Application of a closed conductive layer in order to
connect the contact areas,
[0039] e) Application of a masking layer to the closed conductive
layer,
[0040] f) Patterning of the masking layer with through openings to
the contact areas,
[0041] g) Filling of the through openings with conductive
material,
[0042] h) Removal of the masking layer,
[0043] i) Removal of the closed conductive layer.
[0044] These method steps according to the invention make it
possible for there to be produced, directly on the microscopically
small contact areas, in addition three-dimensionally extending
microscopically small contact pins and/or contact springs as
contact elements which are connected to the contact areas in one
piece and integrally. This method furthermore has the advantage
that by varying the thickness of the masking layer during
application to the closed conductive layer, it is possible
simultaneously to vary the length for all the contact elements. The
thicker the masking layer is applied, the longer the contact
elements that are being formed become, since the through openings,
which are finally filled with conductive material and form the
contact elements, have a length which is governed by the thickness
of the masking layer.
[0045] The masking layer itself is an essential aid for producing
contact elements which are connected to the contact area in one
piece and integrally, and is removed again in a concluding method
step. Moreover, the application of a closed conductive layer after
interconnects have already been patterned on the surface of the
substrate serves merely to short-circuit all the microscopically
small contact areas in order to enable, for example,
electrodeposition of metal from the closed conductive layer through
the through openings. After electrodeposition of conductive
material to fill the through openings and after removal of the
masking layer, the short circuit between the contact areas can also
be cancelled by removing the closed conductive layer.
[0046] The patterning of a conductive layer is preferably effected
by means of photolithography. The application of a passivation
layer, preferably made of Si.sub.3N.sub.4, is carried out by means
of sputtering technology. The opening of windows to the contact
areas may again be effected by means of photolithography. The
application of a closed conductive layer may preferably be effected
by means of vapor deposition technology, sputtering technology or
deposition technology. The patterning of a conductive layer, the
application of a passivation layer, the opening of windows to the
contact areas and also the subsequent application of a closed
conductive layer may be effected simultaneously for a multiplicity
of electronic devices and directly on a substrate or semiconductor
wafer in order thus to form the precondition for simultaneously
producing a multiplicity of contact elements on a multiplicity of
contact areas.
[0047] To subsequently fill a through opening to a contact pin by
electrodeposition, a closed conductive layer is preferably produced
from a copper alloy. For electroless deposition of the contact
element material on the surface of the contact areas in the through
openings of the masking layer, it is possible, in another preferred
embodiment of the invention, to dispense with the application of a
closed conductive layer since it is not necessary to short-circuit
all the contact areas in the case of electroless metal deposition.
However, electroless deposition methods are often not selective
enough, with the result that a relatively thick deposited
conductive layer may be produced on the masking layer at the same
time as the through openings are filled.
[0048] The masking layer itself is preferably applied by means of
spinning on, spraying on or by means of an immersion technology. In
a preferred implementation of the invention, for the formation of
through openings, the masking layer may be composed of a
photosensitive dielectric, such as preferably of a viscous
photoresist whose viscosity can be adapted to the requirements for
the electronic device depending on the required length of the
contact element and thus in accordance with the required thickness
of the masking layer. For selective precuring of the photosensitive
dielectric, the masking layer is preferably covered by means of a
mask that is blackened at the positions of the contact elements or
of the through openings to be developed, and the remainder of the
masking layer made of photosensitive dielectric is exposed.
[0049] In a subsequent development step, the unexposed region of
the photosensitive dielectric layer is dissolved out, thereby
producing through openings to the closed conductive layer in the
region of the contact areas on the surface of the substrate during
development. However, such through openings may also preferably be
produced in a resin layer by means of laser removal technology, ion
beam sputtering or plasma etching, in particular if the required
length of the contact elements exceeds the exposable thickness of
photosensitive dielectrics. The advantage of resin layers in
conjunction with laser removal technology, ion beam sputtering or
plasma etching is that said masking layer made of resin can be
applied in any desired thickness and can be produced with through
openings.
[0050] After the through openings have been made in the masking
layer, the through openings are preferably filled with conductive
material by means of electrodeposition. To that end, in a
corresponding electrodeposition bath, the closed conductive layer
is put at cathode potential and an electrode made of the material
of the contact elements to be formed is connected to the anode
potential, with the result that the anode material is removed via
metal ion exchange and a contact element made of metal grows on
contact areas in the through openings.
[0051] When the masking layer is removed, a three-dimensionally
extending microscopic small contact element which is connected to
the underlying contact area in one piece and integrally is produced
at the position of each filled through opening. The removal of the
closed conductive layer can be effected by means of etching
technology only if the masking layer has been completely removed
beforehand.
[0052] After the removal of the masking layer and of the closed
conductive layer, the contact element can move freely with its free
end, and it can bend elastically and plastically with a change in
its solid angle, with the result that it is advantageously possible
for the three-dimensionally extending contact element to bridge
different distances and unevennesses and to compensate different
expansions.
[0053] Furthermore, with the method specified above, it is
possible, after the filling of the through openings, to carry out a
further deposition on the masking layer in order to produce a
mushroom-cap-like outgrowth on the tip of the contact element, with
the result that a contact head is preferably formed by means of
electrodeposition. This contact head can additionally be refined by
deposition preferably of a relatively noble contact surface coating
made preferably of a nickel and/or gold layer.
[0054] The masking layer can also readily be removed after
formation of a contact head, by the masking layer being dissolved
in suitable solvents. Another preferred method for dissolution of
the masking layer is incineration by means of plasma
technology.
[0055] A wafer whose contact areas are equipped with such
three-dimensionally extending contact elements can directly be
tested at the wafer level, still prior to separation into
individual semiconductor chips or into individual electronic
devices, by a test head being used to press an intermediate carrier
with contact connection areas onto the contact elements of an
integrated circuit of an individual electronic device in order to
check the functionality of the electronic circuit of the electronic
device. Such test heads with a corresponding number of contact
connection areas on an intermediate carrier material simplify the
hitherto customary functional testing before, during and after
burn-in. Furthermore, the microscopically small three-dimensionally
extending contact elements on the wafer can be used for being
connected with a large-area intermediate carrier for rewiring the
contact areas with connections passing out of a housing. In this
case, the intermediate carrier may have the same dimensions as the
wafer and, opposite each contact area on the surface of the wafer,
have a contact connection area which is connected via flat
conductors to the outwardly led connections of the electronic
device.
[0056] In order to achieve reliable simultaneous soldering or
ultrasonic bonding of the multiplicity of contact elements to the
contact connection areas of the intermediate carrier, the
interspaces between the contact elements are preferably potted by
means of spraying technology or injection-molding technology, and,
if necessary, the contact heads are subsequently uncovered after
the potting of the interspaces, with the result that the positions
of the contact heads relative to the contact connection areas of
the intermediate carrier are stabilized by means of these method
steps. By means of a corresponding contact pressure and a thermal
treatment or corresponding frictional heating using ultrasound, it
is subsequently possible to effect either a soldered connection by
means of a contact head made of solder or a connection by means of
ultrasonic bonding of all the contact heads of a wafer
simultaneously to the contact connection areas of an intermediate
carrier.
[0057] The choice of correspondingly elastic and plastically
deformable injection-molding compounds in the interspaces between
the contact elements makes it possible to compensate unevennesses
of the surface of the substrate and the surface of the intermediate
carrier, and to realize a housing technology at the wafer level,
with the result that, with the simultaneous division of the wafer
with the connected intermediate carrier with rewiring and external
connections, the wafer with its multiplicity of integrated circuits
can efficiently be separated into electronic devices.
[0058] In the preferred implementation of the method, the patterned
conductive layer, the contact elements and the contact heads are
produced from a material which has already been discussed above for
the individual applications.
[0059] A further method for producing an electronic device having
at least one microscopically small contact area for an electronic
circuit having interconnects on a surface of a substrate, the
contact area additionally having a three-dimensionally extending
microscopically small contact element which is connected to the
contact area in one piece and integrally, comprises the following
method steps:
[0060] a) Patterning of a metal sheet preferably made of a copper
alloy with patterns, the structure having a multiplicity of
etched-free contours of contact springs which are connected to the
metal sheet by a desired breaking point, the uncovered end of the
contact spring contour corresponding in size, arrangement and
position to the contact areas of a substrate,
[0061] b) Alignment and pressing of the patterned metal sheet onto
a substrate with a multiplicity of contact areas, the uncovered
ends of the contact spring contours being pressed onto the contact
areas,
[0062] c) Heating of the metal sheet and of the substrate for the
purpose of bonding the uncovered ends of the contact spring
contours to the contact areas,
[0063] d) Cooling and stripping-off of the metal sheet, leaving
behind three-dimensionally extending, bonded contact springs on
each of the contact areas.
[0064] This method advantageously produces microscopically small
contact springs which extend three-dimensionally from contact areas
on a substrate, the contact springs being connected to the contact
areas in one piece and integrally. In this case, the simultaneous
formation of contact springs is not limited in terms of numbers,
with the result that a multiplicity of contact springs can
advantageously be formed simultaneously using this method.
[0065] The contact springs on the contact areas have the advantage
that they lengthen the contact areas three-dimensionally, with the
result that subsequent components, for example of a housing of an
electronic device, can be placed onto these resilient connections
or be soldered to the uncovered ends of the contact springs or be
bonded to them. The spring action of these contact springs makes it
possible to compensate unevennesses in the plane of the contact
areas and unevennesses in the plane of contact connection areas of
an adjoining intermediate carrier of a housing.
[0066] Furthermore, it is possible, directly after the production
of the integrated circuits on a semiconductor wafer, to test these
circuits with their multiple contact areas by means of a test head
with correspondingly arranged contact connection areas, which is
simply placed onto the free ends of the contact springs by its
contact connection areas and can then test the functionality of
each individual integrated circuit. During this test, the contact
springs compensate differences in distance between the test head
and the substrate and ensure that a resilient frictional contact
with the contact connection areas of the test head can be
established.
[0067] The patterning of a metal sheet with contact spring contours
is preferably carried out by means of an etching technology. To
that end, the metal sheet is covered with a protective layer in the
regions that are not to be etched. This covering can be effected by
means of photoresist technology, screen-printing technology or
stencil masking technology.
[0068] In another preferred implementation of the patterning, the
contours of the contact springs are introduced into the metal sheet
by means of laser removal technology. Dry etching methods such as
plasma etching are also suitable for introducing the contact spring
contours into a metal sheet.
[0069] In a preferred implementation of the method, the uncovered
ends of the contact spring contours are coated with a nickel and/or
a gold layer before being pressed onto the contact areas of a
substrate. This coating has the advantage that, in particular, the
gold layer forms intermetallic phases, with isothermal
solidification, with the contact areas made, preferably, of an
aluminum alloy, said phases ensuring a high temperature resistance
of the compound.
[0070] In a further preferred implementation of the method, the
contact spring contours are coated with a solderable metal alloy in
the region of the desired breaking points. This selective metal
coating has the advantage that after the desired breaking points
have been torn, the contact connection areas formed have a solder
coating which is suitable for connection to adjoining contact
connection areas.
[0071] In a further preferred implementation of the method, a
spring-elastic material having a thickness between 30 and 100 .mu.m
is used as the metal sheet, which material is additionally provided
with a tin layer. This has the advantage that, after the patterning
of the metal sheet, the contact spring contours are already
provided with a tin layer which enables a soldered connection to
the contact areas.
[0072] In a further preferred implementation of the invention,
before the pressing-on of the metal sheet, the contact spring
contours are soft-annealed in predetermined regions, preferably in
their central region. This method has the advantage that, during
the subsequent stripping-off of the metal sheet from the substrate,
the force on the contact area is minimized and the bending-over of
the contact spring into a three-dimensional extent of its free end
only minimally loads the contact areas and the connection between
contact areas and contact springs. The soft-annealing of the metal
sheet made of spring-elastic material in the central region of the
contact spring contours may preferably be effected by laser
scanning over the corresponding regions.
[0073] In a further preferred implementation of the method, the
metal sheet used is a soft material such as a soft copper alloy,
after the metal sheet has been stripped off, the residual
three-dimensionally extending contact structures being heat-treated
to desired spring properties of the contact springs. In the case of
this method variant, the actual spring force is produced only after
the connection to the contact area and/or the shaping of the
contact spring are concluded. In the case of this method variant,
the connection between contact spring and contact area is loaded
the least in the case of the shaping.
[0074] The invention is explained in more detail using exemplary
embodiments together with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0075] FIG. 1 shows a partial cross-sectional perspective view of a
first embodiment of the invention with a contact pin extending
orthogonally in a three-dimensional manner from a contact area.
[0076] FIG. 2 shows a partial cross-sectional perspective view of a
second embodiment of the invention with a contact pin that is
preformed at a solid angle which deviates from the orthogonal
orientation.
[0077] FIGS. 3 to 9 show preferred method steps of an
implementation of a method of the invention using cross sections
through an electronic device.
[0078] FIG. 10 shows a cross section through a preferred embodiment
of an electronic device after potting of the interspaces between a
multiplicity of contact pins.
[0079] FIG. 11 shows a cross section through a preferred embodiment
of an electronic device after the contact heads have been
uncovered.
[0080] FIG. 12 shows a plan view of a metal sheet patterned with
contact spring contours.
[0081] FIG. 13 shows an enlarged detail from FIG. 12.
[0082] FIG. 14 shows a perspective partial view of an arrangement
of a multiplicity of microscopically small contact springs after
the metal sheet has been stripped off.
[0083] FIG. 15 shows a partial cross-sectional perspective view of
a microscopically small contact spring which is connected to a
contact area in one piece and integrally.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0084] FIG. 1 shows a partial cross-sectional perspective view of a
first embodiment of the invention with a contact element 5
extending orthogonally in a three-dimensional manner from a contact
area 1 and having the form of a contact pin 16. This
three-dimensionally extending contact pin 16 has a microscopically
small length and has a contact head 8 in this embodiment. The
microscopically small contact area 1 is part of an electronic
circuit having interconnects 2 on a surface 3 of a substrate 4. In
this embodiment, the interconnects 2 and the contact area 1 are
composed of an aluminum alloy, while the contact pin 16 has a
copper alloy which also forms the contact head 8, the surface of
the contact head 8 being refined with a nickel and a gold
coating.
[0085] Electronic devices of this type have the advantage that
unevennesses of the surface 3 of the substrate 4 can be compensated
over the length of the contact pins 16, by virtue of the fact that
the contact pin 16 can match the unevennesses by bending under
plastic and elastic forces. This is particularly advantageous if
the contact pin 16 is intended to serve for testing the function of
an electronic device on a wafer before the wafer is separated into
individual electronic devices or semiconductor chips having an
integrated circuit by means of a separation technique. To that end,
a test head having contact connection areas which are held by an
intermediate carrier and are arranged spatially opposite the
contact areas may be pressed onto the contact heads 8 of the
contact pins 16, the contact pressure compensating the unevennesses
of the substrate 4 and of the intermediate carrier and hence the
different distances between the two.
[0086] FIG. 2 shows a partial cross-sectional perspective view of a
second embodiment of the invention with a contact element 5 that is
preformed at a solid angle .alpha., which deviates from the
orthogonal orientation. This pin-like contact on the contact area 1
obliquely to the substrate surface allows tolerance-noncritical
contact-making for test purposes both in the wafer format and in
the component format. This embodiment of the invention is
tolerance-noncritical because the inclination of the contact pin 16
and its deviation from the orthogonal orientation allow a certain
spring action and, as a result, height differences can be
compensated.
[0087] Furthermore, the lateral movement of the obliquely arranged
contact pin 16 of FIG. 2, which is triggered when pressure is
exerted, is also particularly advantageous. The movement
contributes to reliable contact-making as a result of the contact
point rubbing freely on an opposite contact connection area (not
shown) of an intermediate carrier.
[0088] The contact pin 16 of FIG. 1 or FIG. 2 can be used not just
for testing technology with regard to the functionality of an
individual electronic device but also for connecting the contact
area 1 to a contact connection area of an intermediate carrier
which carries a rewiring to external connections of the housing. In
this case, the intermediate carrier is part of a housing for
packaging the electronic devices. On this intermediate carrier,
rewiring from the contact connection areas to external connections
distributed on the entire area of the intermediate carrier is
performed via flat conductors. In order to stabilize the position
of the contact pin 16 during the connection of the contact pin 16
to a contact connection area (not shown) of an intermediate
carrier, the interspace between a multiplicity of contact pins 16
can be filled by an elastic potting compound 13, preferably made of
silicone, as is shown in cross section by FIG. 10, for example.
[0089] FIGS. 3 to 9 show preferred method steps of an
implementation of a method of the invention using cross sections
through an electronic device.
[0090] In FIG. 3, a patterned metal layer with passivation layer 15
and uncovered contact areas 1 is applied on the surface 3 of a
substrate 4. This patterning of the metal layer and the uncovering
of the contact areas 1 may preferably be effected by means of
photoresist technology of a closed conductive layer or of a closed
passivation layer 15 made of SI.sub.3N.sub.4. As is shown by FIG.
4, a closed conductive layer 10 is applied to this passivation
layer 15 with uncovered contact areas 1. The layer 10 short
circuites all the contact areas 1.
[0091] After the application of the closed conductive layer, a
masking layer 11 is applied to the closed conductive layer 10 by
means of spinning on, spraying on or by means of immersion
technology. In this implementation of the method, a photosensitive
dielectric is applied as masking layer 11, which is shown in FIG.
5. A photomask 14 is placed over the dielectric, as can be seen in
FIG. 6. At a solid angle .alpha., with parallel light irradiation,
the photoelectric dielectric is exposed in the regions in which the
photomask 14 is not blackened, with the result that these regions
of the photosensitive dielectric are precrosslinked and the
precrosslinked exposed regions remain during the subsequent
development process, while through openings 12 are formed from the
surface of the masking layer 11 to the closed conductive layer 10
during the subsequent development process of the photosensitive
dielectric.
[0092] As shown by FIG. 7, the through openings 12 are filled with
metal by means of electrodeposition, thereby producing a
three-dimensionally extending microscopically small contact element
5 which is connected to the contact area 1 in one piece and
integrally. In the embodiment as shown by FIG. 7, the closed
conductive layer 10 is made of a copper alloy and an
electrodeposited contact pin 16 has a contact head 8 that is made
of an adapted copper alloy. The contact head 8, after being formed,
is refined by coating with nickel and a gold coating, which are
likewise electrodeposited.
[0093] After the production of contact pin (16) and contact head
(8) by electrodeposition, the masking layer (11) is removed, and a
structure as shown in cross section in FIG. 8 remains. The thin
closed conductive layer 10 is then briefly etched, leaving behind
the structure (shown in FIG. 9) with free-standing microscopically
small contact pins 16 which are connected to corresponding contact
areas 1 in one piece and integrally. These contact pins 16 can be
produced simultaneously on an entire wafer surface and are thus
available for making contact with a test head in order to test the
functionality of the electronic devices before the substrate 4 is
separated into electronic devices.
[0094] Afterward, the contact pins 16 with their heads 8 may be
enclosed in a potting compound made, preferably, of silicone, in
order to stabilize and to support the contact pins 16, as is shown
in FIG. 10. During the potting process, however, as shown by FIG.
10, the contact heads 8 may be covered by the potting compound, so
that, in a further step, the contact heads 8 are uncovered
preferably by laser removal, as is shown in FIG. 11. The contact
heads 8 may then either be coated with a solderable coating in a
soldering wave bath, or they may be used together with their
refined coatings of nickel and/or of gold for ultrasonic
bonding.
[0095] A solder coating placed on the contact heads 8 is preferably
used for enabling the contact heads 8 to contact connection areas
of an intermediate carrier, which carries the rewiring, to external
electrical connections that are distributed on an area. The
electrical connections are usually contact bumps which are formed
from solder balls and project in rows and/or columns on one side of
the housing, while the housing carries the semiconductor chip on
the other side. The connection of the intermediate carrier with
rewiring to the contact heads 8 can also be carried out for a
multiplicity of contact heads 8 on a wafer and the separation of
this assembly into electronic devices can then take place.
[0096] FIG. 12 shows a plan view of a metal sheet 21 patterned with
contact spring contours 25. In this embodiment, this metal sheet is
the same size as a semiconductor wafer having, for example, 32
semiconductor chips. The metal sheet 21 is between 30 and 100 .mu.m
thick and has a multiplicity of contact spring contours 25, the
number of which corresponds to the contact areas on the
semiconductor wafer. The contact spring contours 25 are etched into
the metal sheet 21 or cut into the metal sheet 21 using a laser
beam.
[0097] FIG. 13 shows an enlarged detail from FIG. 12. This detail
is intended to show only in principle the structure of the contact
spring contours 25. Such a contour comprises an uncovered end 24, a
central region 26 and a desired breaking point 23, with which the
contact spring contour 25 is connected to the metal sheet 21. The
central region 26 of the contact spring contour tapers toward the
desired breaking point, with the result that the cross section with
which contact spring contours are suspended from the metal sheet 21
is extremely small and can easily be torn away.
[0098] FIG. 14 shows a perspective partial view of an arrangement
of a multiplicity of microscopically small contact springs 17 after
the metal sheet 21 which is shown in FIG. 12 has been stripped off.
It can clearly be seen that the contact spring contours 25, as are
shown in FIG. 13, have now been formed into a contact area with a
first contact spring end 19, which is fixedly connected on the
substrate surface, and a free, second contact spring end 20. To
that end, the contact spring contours 25 of FIG. 13 with their
uncovered ends 24 have been bonded or soldered onto the contact
areas of a substrate, and have subsequently been bent to form
contact springs during the tearing-off of the metal sheet 21.
[0099] FIG. 15 shows a partial cross-sectional perspective view of
a microscopically small contact spring 17 which is connected to the
contact area 1 in one piece and integrally. The contact spring of
this exemplary embodiment has the form of a leaf spring which is
tapered toward the free end and can be connected by this free end
to an intermediate carrier with contact connection areas of a
rewiring or can make contact with a test head having
correspondingly arranged contact connection areas.
* * * * *