U.S. patent application number 11/252477 was filed with the patent office on 2006-02-16 for device for connecting two wafers in a planar manner for grinding down and cutting up a product wafer.
This patent application is currently assigned to Infineon Technolgies AG. Invention is credited to Franz Hecht, Werner Kroninger, Melanie Lutzke.
Application Number | 20060032587 11/252477 |
Document ID | / |
Family ID | 7658501 |
Filed Date | 2006-02-16 |
United States Patent
Application |
20060032587 |
Kind Code |
A1 |
Hecht; Franz ; et
al. |
February 16, 2006 |
Device for connecting two wafers in a planar manner for grinding
down and cutting up a product wafer
Abstract
A device for connecting two wafers in a planar manner for
grinding down and cutting up a product wafer has a vacuum chamber,
a chuck for receiving a carrier wafer, a heating device for heating
up the chuck and a vacuum-chamber cover with a vacuum-holding
device, on which a product wafer can be arranged suspended above
the carrier wafer. After the evacuation of the vacuum chamber, the
active surface of the product wafer is dropped onto a double-sided
adhesive film on the carrier wafer and is pressed into place by the
rising pressure during air admission. The result is that the wafers
are connected together.
Inventors: |
Hecht; Franz;
(Bernhardswald, DE) ; Kroninger; Werner;
(Neutraubling, DE) ; Lutzke; Melanie; (Ingolstadt,
DE) |
Correspondence
Address: |
LERNER AND GREENBERG, PA
P O BOX 2480
HOLLYWOOD
FL
33022-2480
US
|
Assignee: |
Infineon Technolgies AG
|
Family ID: |
7658501 |
Appl. No.: |
11/252477 |
Filed: |
October 18, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
10403877 |
Mar 31, 2003 |
6972069 |
|
|
11252477 |
Oct 18, 2005 |
|
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PCT/DE01/03683 |
Sep 26, 2001 |
|
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10403877 |
Mar 31, 2003 |
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Current U.S.
Class: |
156/382 |
Current CPC
Class: |
H01L 21/6838 20130101;
H01L 21/67132 20130101; H01L 21/67092 20130101 |
Class at
Publication: |
156/382 |
International
Class: |
B32B 37/00 20060101
B32B037/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 29, 2000 |
DE |
100 48 881.1 |
Claims
1. A device for connecting two wafers one on top of another in a
planar manner, the device comprising: a vacuum chamber having a
chamber volume and an evacuating device for said chamber volume; a
chuck having an evacuating device for receiving a carrier wafer
having a surface with a double-sided adhesive film or an adhesive
layer; a heating device for heating up said chuck; and a
vacuum-chamber cover having a vacuum-holding device for holding a
product wafer having a surface; said vacuum-holding device
configured on said vacuum-chamber cover for suspending the product
wafer in said vacuum chamber at a distance above the carrier wafer
such that the surface of the product wafer and the surface of the
carrier wafer are congruent before being connected.
2. The device according to claim 1, wherein: said vacuum-holding
device has a surface and a plurality of guiding pins protruding
perpendicularly from said surface of said holding device; and said
plurality of guiding pins being conically shaped.
3. The device according to claim 2, wherein each of said plurality
of guiding pins has a conical base area positioned on said
vacuum-holding device and a cone tip protruding from said
vacuum-holding device.
4. The device according to claim 2, in combination with the product
wafer, wherein: the product wafer has an edge region and is being
held on said vacuum-holding device; and said plurality of guiding
pins are configured near the edge region of the product wafer.
5. The device according to claim 2, wherein said vacuum-holding
device has a plurality of guiding pins configured, in relation to
said chuck, for ensuring that when the carrier wafer is on said
chuck and when the product wafer is being received on the
double-sided adhesive film or on the adhesive layer of the carrier
wafer, the product wafer is received in a precise and aligned
manner.
6. The device according to claim 1, further comprising: a first
vacuum valve, a second vacuum valve, and a third vacuum valve; said
vacuum-holding device having an evacuating device; said first
vacuum valve configured between said evacuating device of said
vacuum-holding device and said vacuum-chamber cover; said second
vacuum valve configured between said evacuating device of said
vacuum chamber and said vacuum chamber; and said third vacuum valve
configured between said evacuating device of said chuck and said
chuck.
7. The device according to claim 1, wherein said vacuum-holding
device includes at least three guiding pins.
8. The device according to claim 1, wherein said vacuum-holding
device includes at least five guiding pins.
9. The device according to claim 1, in combination with the product
wafer and the carrier wafer, wherein: the product wafer has a
thickness; said vacuum-holding device has a surface; said chuck has
a surface; said vacuum-holding device includes a plurality of
guiding pins that have a length of at least the thickness of the
product wafer plus a distance between the product wafer and the
double-sided adhesive film or the adhesive layer of the carrier
wafer on said chuck; and said length of each of said plurality of
said guiding pins of said vacuum-holding device is less than a
distance between said surface of said vacuum-holding device of said
vacuum-chamber cover and said surface of said chuck.
10. The device according to claim 1, wherein: said vacuum-holding
device includes a plurality of guiding pins; and each of said
plurality of said guiding pins of said vacuum-holding device has a
conical base area with a diameter of 200 to 1200 micrometers.
11. The device according to claim 1, wherein: said vacuum-holding
device includes a plurality of guiding pins; and each of said
plurality of said guiding pins of said vacuum-holding device has a
cone tip with a diameter of 100 to 500 micrometers.
12. The device according to claim 1, wherein: said vacuum-holding
device has a first vacuum valve and a plurality of depressions; and
said vacuum-holding device has an evacuating device; and said first
vacuum valve is for connecting said plurality of depressions of
said vacuum-holding device to said evacuating device of said
vacuum-holding device.
13. The device according to claim 12, wherein: said plurality of
depressions are concentric grooves formed in said vacuum-holding
device; and each of said plurality of depressions has a groove base
with a drilled hole communicating with said evacuating device of
said vacuum-holding device.
14. The device according to claim 1, wherein: said chuck has a
surface; and said chuck includes a plurality of positioning pins
protruding perpendicularly from said surface of said chuck.
15. The device according to claim 14, wherein: said plurality of
positioning pins are conically shaped; and each of said plurality
of positioning pins has a cone base area positioned on said surface
of said chuck and a cone tip protruding from said surface of said
chuck.
16. The device according to claim 14, in combination with the
carrier wafer, wherein: the carrier wafer has an edge region and is
being held on said chuck; and said plurality of positioning pins of
said chuck are configured near the edge region of the carrier
wafer.
17. The device according to claim 14, wherein said positioning pins
of said chuck are configured, in relation to said vacuum-holding
device, for ensuring that when the carrier wafer is on said chuck
and when the product wafer is being received on the double-sided
adhesive film or on the adhesive layer of the carrier wafer, the
product wafer is received in a precise and aligned manner.
18. The device according to claim 14, in combination with the
carrier wafer, wherein: the carrier wafer has a thickness; and each
of said plurality of positioning pins of said chuck has a length
that is less than or equal to the thickness of the carrier
wafer.
19. The device according to claim 14, in combination with the
carrier wafer and the product wafer, wherein: the carrier wafer has
an edge and is being held on said chuck; the product wafer has an
edge and is being held by said vacuum holding device; the carrier
wafer and the product wafer will be connected together; said
vacuum-holding device includes a plurality of guiding pins; and
said plurality of positioning pins are configured offset from said
plurality of guiding pins with respect to the edge of the carrier
wafer and the edge of the product wafer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional of application Ser. No. 10/403,877,
filed Mar. 31, 2003; which was a continuing application, under 35
U.S.C. .sctn.120, of International application PCT/DE01/03683,
filed Sep. 26, 2001; the application also claims the priority,
under 35 U.S.C. .sctn.119, of German patent application DE 100 48
881.1, filed Sep. 29, 2000; the prior applications are herewith
incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a device for connecting two wafers
in a planar manner for grinding down and cutting up a product
wafer.
[0004] U.S. Pat. No. 6,045,073 discloses a method for grinding down
semiconductor chips, in which the active surfaces of the chips are
initially connected electrically to a contact surface of a
leadframe via contact bumps and the edge regions thereof are
encapsulated in a silicone composition. Subsequently, the silicon
remains are removed from the rear side of the chips and the rear
side of a chip is subjected to a plasma etching process, in order
to etch the chip down to a few .mu.m.
[0005] This method has the disadvantage that the etching down
cannot be used simultaneously for many chips on a wafer of a large
surface area, but is merely restricted to relatively small surface
areas of an individual chip. The restriction of the previous
solutions to the etching down of individual chips is essentially
attributable to the fact that it is problematic for a carrier of a
large surface area to be connected in a planar manner to a wafer of
a large surface area. Even minor deviations in the parallelism of
the carrier and the wafer result in considerable differences in
thickness from one edge region of the wafer to the other edge
region, so that uniform etching down of the entire wafer to a few
.mu.m cannot be accomplished with the previously known method,
especially since commercially available wafers have a diameter of
150 to 300 mm.
[0006] 2. Summary of the Invention
[0007] It is accordingly an object of the invention to provide a
device for connecting two wafers in a planar manner for grinding
down and cutting up a product wafer, which overcomes the
above-mentioned disadvantages of the prior art apparatus and
methods of this general type.
[0008] In particular, it is an object of the invention to provide a
device and a method for connecting two wafers in a planar manner
such that a product wafer can be ground down and then cut up
without having to first cut up the product wafer into chips and
then etch the rear sides of the chips while each chip is in a
corresponding carrier material or in a corresponding semiconductor
package. In addition, the invention is intended to provide a method
with which it is possible for two wafers to be connected in a
planar manner with high precision, without instances of warpage,
bowing, sloping, or other large-area defects occurring during the
connection.
[0009] With the foregoing and other objects in view there is
provided, in accordance with the invention, a device for connecting
two wafers one on top of another in a planar manner. The device
includes: a vacuum chamber having a chamber volume and an
evacuating device for the chamber volume; a chuck having an
evacuating device for receiving a carrier wafer having a surface
with a double-sided adhesive film or an adhesive layer; a heating
device for heating up the chuck; and a vacuum-chamber cover having
a vacuum-holding device for holding a product wafer having a
surface. The vacuum-holding device is configured on the
vacuum-chamber cover for suspending the product wafer in the vacuum
chamber at a distance above the carrier wafer such that the surface
of the product wafer and the surface of the carrier wafer are
congruent before being connected.
[0010] With the foregoing and other objects in view there is also
provided, in accordance with the invention, a method for connecting
a product wafer and a carrier wafer in a planar manner. The method
includes steps of: attaching a double-sided adhesive film or an
adhesive layer onto the carrier wafer; placing the carrier wafer
between positioning pins on a chuck of a vacuum chamber; placing
the product wafer between guiding pins of a vacuum-holding device
of a vacuum-chamber cover and fixing the product wafer by opening a
first vacuum valve connecting the vacuum-holding device to an
evacuating device; closing the vacuum chamber and evacuating the
vacuum chamber to an equal or higher vacuum than a vacuum of the
vacuum-holding device by opening a second vacuum valve; and after
closing at least the first vacuum valve and the second vacuum valve
and opening air-admitting orifices, admitting air into the vacuum
chamber such that the carrier wafer and the product wafer are
simultaneously pressed onto each other in a planar manner by rising
pressure in the vacuum chamber.
[0011] According to the invention, the device for connecting two
wafers one on top of the other in a planar manner includes a vacuum
chamber with an evacuating device for the chamber volume, a chuck
with an evacuating device for receiving a carrier wafer with
double-sided adhesive film or an adhesive layer provided on one
side of the carrier wafer, a heating device for heating up the
chuck, and a vacuum-chamber cover with a vacuum-holding device for
a product wafer. The vacuum-holding device is arranged on the
vacuum-chamber cover in such a way that the product wafer is
arranged suspended in the vacuum chamber at a distance above the
carrier wafer, with congruent surface areas, before the product
wafer and the carrier wafer are connected.
[0012] This device has the advantage that the distance or
intermediate space between a product wafer held by the
vacuum-holding device and the adhering surface of the double-sided
adhesive film on the carrier wafer, arranged underneath the product
wafer on a chuck and having a double-sided adhesive film, can be
evacuated completely, so that no contamination and no microscopic
gas bubbles can impair the planarity between the two wafers. A
further advantage of this device is that the product wafer held by
a vacuum-holding device is arranged in a suspended manner, and
consequently with its active surface directed downward, so that no
dust or other contamination particles can settle on the surface
before the surface comes into contact with the double-sided
adhesive film. A further advantage of this invention is that, at
the instant at which extraction pumping causes the vacuum in the
vacuum chamber to become less than the vacuum by which the product
wafer is held suspended over the carrier wafer, the product wafer
automatically falls down from its vacuum securement and can be set
down flat on the double-sided adhesive film without any gas pocket.
A further advantage of this device is that the product wafer can
overcome the distance between the product wafer and the
double-sided adhesive film in free fall without any canting and
falls onto the film in a planar manner.
[0013] To ensure reliable setting down of the product wafer on the
double-sided adhesive film of the carrier wafer, in one embodiment
of the invention, the vacuum-holding device has guiding pins, which
protrude perpendicularly from its surface and are conically shaped.
These cone bases area of the guiding pins are positioned on the
vacuum-holding device, while the cone tips protrude from the
vacuum-holding device. This arrangement has the advantage that the
product wafer can fall down unhindered, and yet guided, by the
guiding pins from the vacuum-holding device on the vacuum-chamber
cover automatically and in a plane-parallel manner, without canting
or catching on the guiding pins, since in this embodiment they are
conically shaped.
[0014] To ensure this reliable guidance, the guiding pins of the
vacuum-holding device are arranged in the edge region of the
product wafer. At the same time, the guiding pins of the
vacuum-holding device are arranged with respect to the chuck which
carries the carrier wafer in such a way that precise and aligned
setting-down and receiving of the product wafer on the double-sided
adhesive film or on the adhesive layer of the carrier wafer on the
chuck is ensured. This is achieved on the one hand by the
vacuum-chamber cover being precisely brought together with the
vacuum chamber and on the other hand by the product wafer being
placed exactly between the guiding pins.
[0015] For controlling the individual method steps, vacuum valves
are provided in the vacuum lines and in the connections between one
or more evacuating devices.
[0016] In a further embodiment of the invention, the device
includes a first vacuum valve configured between an evacuating
device of the vacuum-holding device and the vacuum-chamber cover, a
second vacuum valve configured between the evacuating device for
the chamber volume and the vacuum chamber, and a third vacuum valve
configured between the evacuating device of the chuck and the
chuck. With these vacuum valves, the individual process steps can
be controlled and the positions both of the carrier wafer and of
the product wafer can be reliably handled.
[0017] In one embodiment of the invention, at least three guiding
pins are arranged on the vacuum-holding device, since three guiding
pins allow clear fixing to take place in the X and Y directions. An
improved version of the device provides that at least five guiding
pins are arranged on the vacuum-holding device. With five guiding
pins for one wafer in each case, the latter is reliably secured
against slipping, canting, shifting or becoming displaced in some
other way.
[0018] A further embodiment of the invention provides that the
guiding pins are of a length which corresponds at least to the
thickness of the product wafer plus the distance between the
product wafer and the double-sided adhesive film or the adhesive
layer, and which is less than the distance between the surface of
the vacuum-holding device of the vacuum cover and the surface of
the chuck. In this case, the distance between the product wafer
suspended from the vacuum-holding device and the carrier wafer
lying on the chuck is dimensioned in such a way that reliable
vacuum-drying of the opposing surfaces is possible, so that the
surface of the double-sided adhesive film can completely outgas,
and the opposite side of the product wafer has a completely dry
surface and, after the evacuation of the vacuum chamber, there are
no gases between the surfaces to be adhesively bonded. The distance
depends, furthermore, on the size of the opposing surface areas.
The larger these surface areas are, the greater the
extraction-pumping cross section must be chosen, and consequently
the greater the distance between the wafers must be set. In a
further embodiment of the invention, the distance for 6 to 12-inch
wafers (150 to 300 mm) lies between 3 and 15 millimeters. In the
case of wafers of up to 6 inches, the distance can be reduced to
one millimeter.
[0019] A further embodiment of the invention provides that the cone
base areas of the guiding pins have a diameter of 200 .mu.m to 1200
.mu.m and at the cone tips have a diameter of between 100 and 500
.mu.m. Such slender and thin pins have the advantage that they are
extremely compliant and induce the lowest possible stresses in the
product wafer during the guidance of the product wafer.
[0020] In a further embodiment of the invention, the vacuum-holding
device has depressions that can be connected to an evacuating
device via a first vacuum valve. Depressions of this type are
formed in the vacuum-holding device as concentric grooves and have,
in their groove base, drilled holes that communicate with the
evacuating device for the vacuum-holding device. With this
embodiment it is ensured that the rear side of the product wafer is
subjected to a vacuum over a large surface area and is suspended
from the vacuum-chamber cover in a planar manner on the surface of
the vacuum-holding device.
[0021] A further embodiment of the invention provides that the
chuck has positioning pins, which protrude perpendicularly from the
surface of the chuck. These positioning pins may be designed in a
way similar to the guiding pins for the product wafer, whereby the
same advantages are also obtained for the carrier wafer. On the
other hand, the carrier wafer does not have to be guided over the
distance between the carrier wafer and the product wafer. To this
extent, the positioning pins may also have cylindrical shapes and
be of a length that is less than or equal to the thickness of the
carrier wafer. Conical forming of the positioning pins allows them
to protrude beyond the carrier wafer and contribute to the guiding
into place of the product wafer. For this purpose, the positioning
pins of the chuck are arranged with respect to the vacuum-holding
device in such a way that precise and aligned setting-down and
receiving of the product wafer on the double-sided adhesive film or
on the adhesive layer of the carrier wafer on the chuck is
ensured.
[0022] In particular if both guiding pins and positioning pins
protrude beyond the respective wafer surfaces, they are not only
conically shaped in an advantageous way, but should not exceed the
thickness of the respective wafer plus the distance lying between
the wafers, to ensure that neither the guiding pins nor the
positioning pins touch the surfaces of the chuck lying opposite or
the vacuum-holding device lying opposite.
[0023] In a preferred embodiment, the positioning pins are
cylindrically formed and are of a smaller length than the thickness
of the carrier wafer. This is permissible, since in this embodiment
they do not contribute to the guiding of the product wafer, but
align the carrier wafer in relation to the product wafer exactly
and with congruent surfaces.
[0024] If the sum of the lengths of the positioning pins and
guiding pins together exceeds the distance between the surface of
the chuck and the surface of the vacuum-holding device, in a
further embodiment of the invention, the positioning pins are
arranged offset from the guiding pins with respect to the edge of
the wafers to be connected. It is consequently ensured at the same
time that positioning and guiding pins cannot collide with one
another. Both the chuck and the vacuum-holding device have
fastening possibilities for the positioning pins and guiding pins,
which allow adaptation to the respective size of a wafer.
[0025] In a further embodiment of the invention, the device has a
heater, which is arranged on the chuck and permits heating of the
chuck to between 60 and 200.degree. C. The vacuum-holding device
may also have a further heater, to assist outgassing of the surface
of the product wafer.
[0026] A method for connecting two wafers in a planar manner for
grinding down and cutting up a product wafer, the one wafer being a
carrier wafer with a double-sided adhesive film or with an adhesive
layer and the second wafer being a product wafer, has the following
method steps:
[0027] drawing the double-sided adhesive film or the adhesive layer
onto the carrier wafer;
[0028] placing the carrier wafer between positioning pins on a
chuck of a vacuum chamber;
[0029] placing the product wafer between guiding pins of a
vacuum-holding device of a vacuum-chamber cover and fixing the
product wafer by opening a first vacuum valve that connects the
vacuum-holding device to an evacuating device;
[0030] closing the vacuum chamber and evacuating the vacuum chamber
to an equal or higher vacuum than the vacuum of the vacuum-holding
device by opening a second vacuum valve;
[0031] admitting air into the vacuum chamber after closing the
vacuum valves and opening air-admitting orifices, with the wafers
simultaneously being pressed one onto the other in a planar manner
by the rising pressure in the vacuum chamber.
[0032] This method has the advantage that, without mechanical aids,
after closing the vacuum chamber and evacuating the vacuum chamber
to the same or a higher vacuum than the vacuum of the
vacuum-holding device, the product wafer, held in a suspended
manner by the vacuum-holding device on the vacuum-chamber cover,
falls down from the vacuum-holding device and drops in a planar
manner onto the surface facing it of the double-sided adhesive film
on the carrier wafer. During this falling, the product wafer is
guided by the guiding pins arranged around its edge, so that it is
neither laterally displaced nor canted as it falls down. For this
purpose, the guiding pins, as stated above, are conically shaped
and, on account of their length, bridge the distance between the
vacuum-holding device and the surface of the double-sided adhesive
film on the carrier wafer. Furthermore, this method has the
advantage that the active surface of the product wafer can be held
at a distance from the surface of the double-sided adhesive film on
the carrier wafer, which for its part is arranged on the chuck, so
that during the evacuation phase of the vacuum chamber the
intermediate space between the two surfaces can outgas completely
and the surfaces of the product wafer and the double-sided adhesive
film to be brought together are vacuum-dried.
[0033] The pumping cross section between the two surfaces for the
applied and increasing vacuum of the vacuum chamber can be adapted
by the distance between the two surfaces to the requirements of the
outgassing and vacuum drying and to the requirement for complete
evacuation of the intermediate space between the product wafer and
the double-sided adhesive film. The extraction-pumping cross
section is in this case the generated surface of the intermediate
space between the surface of the product wafer and the surface of
the double-sided adhesive film along the outer edge of the product
wafer. Consequently, the extraction-pumping cross section is
determined by the distance between the product wafer surface and
the double-sided adhesive film and also the size of the product
wafer. A further advantage of the inventive device is that the
extraction-pumping cross section can be adapted to the requirements
of the process by increasing the distance between the product wafer
and the double-sided adhesive film. For instance, to reduce the
extraction-pumping time and consequently the production time, it is
possible to increase the extraction-pumping cross section by
increasing the distance when there is adequate capacity of the
evacuating device and reduce the extraction-pumping cross section
when the extraction-pumping time lasts longer on account of a
reduced capacity of the evacuating device.
[0034] In an example of how the method is carried out, the step of
grinding down the product wafer, which has been adhesively attached
in a planar manner, to a thickness below 100 .mu.m is additionally
carried out. On account of the method of connecting a carrier wafer
to the product wafer to be ground down, with thickness variations
limited to a few .mu.m over the size of the product wafer surface
area, this grinding down can be performed in a corresponding
automatic grinding-down machine. Every deviation during the
connecting of the two wafers in a planar manner from their
plane-parallelism has an effect on the uniformity of the thickness
of the ground-down wafer. Since, however, on account of the method,
the active surface area of the product wafer is brought onto the
double-sided adhesive film under a vacuum, there is no possibility
of causing gas bubble formations between the wafers by residual gas
pockets. These gas bubble formations if present could be the cause
of a non-planar connection between the product wafer and the
carrier wafer.
[0035] In a further example of how the invention is carried out,
the product wafer that has been ground-down to below 100 .mu.m is
etched down to a thickness of as little as 15 .mu.m. This method
variant has the advantage that, with wafers becoming increasingly
thinner, etching/mechanical grinding down is no longer carried out
much below 100 .mu.m and instead there is a trend toward thinning
down purely by etching, without any mechanical loading, for
thinning to 15 .mu.m. After etching down the product wafer, it is
still connected, as before, to the carrier wafer, so that it is
mechanically supported by the carrier wafer.
[0036] Cutting up the product wafer into individual chips can be
performed both with and without the adhesively attached carrier
wafer. If the carrier wafer is separated from the product wafer
before the cutting or sawing of the product wafer into individual
chips, the product wafer connected to the carrier wafer is still
adhesively fixed beforehand onto a saw frame covered with film, and
then the carrier wafer is heated by heating up a chuck above the
release temperature for the film or the adhesive, for example, to
at least 120.degree. C., for detaching the double-sided adhesive
film and for removing the carrier wafer. After that, the
ground-down and etched product wafer in the covered saw frame can
be cut up into individual chips. The release temperature is
understood as meaning a temperature at which the adhesiveness
subsides and the product wafer can be detached from the carrier
wafer. The release temperature may well be below the melting
temperature of the double-sided adhesive film or the adhesive
layer.
[0037] In the case of a variant of the method for cutting up the
ground-down product wafer into individual chips, initially the
wafer assembly including a ground-down and etched-down product
wafer and a carrier wafer undergoes a cutting-up step, in which the
ground-down and etched-down product wafer is cut up into chips, and
subsequently the entire composite wafer is adhesively fixed onto a
carrier film. The ground-down and etched-down, and now separated,
chips are adhesively fixed onto the carrier film. To remove the
carrier wafer holding the chips, the assembly including the
composite wafer and the double-sided adhesive film is heated up to
the melting temperature of the double-sided adhesive film and the
carrier wafer is pulled off from the complete assembly, so that
subsequently the ground-down and etched-down chips stuck on a
carrier film are available for further processing. This method has
the advantage that the cutting up of the ground-down and
etched-down product wafer into chips can be carried out by sawing
cutting-up methods, in which a wafer is divided into chips.
[0038] A further variant provides that, even before it is
introduced into the device for connecting it to a carrier wafer,
the surface of the product wafer is provided with sawing grooves
that already divide up the surface of the product wafer into
individual chip areas to a depth of down to 100 .mu.m, so that
after the grinding-down and etching-down of the product wafer the
latter is automatically in a form in which it is cut up into
individual chips on the carrier wafer.
[0039] Consequently, the method has the advantage that all three
variants of cutting up a product wafer into chips involving
grinding down and etching down the product wafer can be carried
out. The method for connecting a product wafer to a carrier wafer
in a planar manner by a double-sided adhesive film consequently
improves the prospects of successfully grinding-down, etching-down,
and cutting up a product wafer into individual ground-down and
etched-down chips.
[0040] Consequently, with the method, the product wafer and the
carrier wafer are bonded by a double-sided adhesive film in a
vacuum chamber. A ground dummy wafer may be used as the carrier
wafer. The double-sided adhesive film is used as the connecting
adhesive. First, a carrier wafer with the adhesive which will later
connect the device wafer or product wafer and the carrier wafer is
introduced into the chamber.
[0041] To center the product wafer and the carrier wafer without
any offset, conical pins are used. The device wafer is sucked into
place on the wafer rear side by a vacuum (vacuum 1). The chamber is
then evacuated (vacuum 2). By equalizing the pressure, vacuum 1
loses its holding force and the product wafer falls onto the
carrier, guided by the conically tapering pins or guiding pins. By
subsequently admitting air, the product wafer is then uniformly
loaded and pressed onto the carrier wafer, which leads to a firm
connection. No punch is used for pressing the device wafer.
[0042] Thinning the product wafers far below 100 micrometers
requires a carrier wafer that is firmly connected to the product
wafer during the thinning, and gives it the necessary stability.
Dummy wafers or ceramic wafers may be used as materials for the
carrier wafer. It is least expensive to use a pre-ground dummy
wafer as the carrier wafer. The pre-grinding ensures a constant
thickness, uniformity, and surface quality of the carrier
wafer.
[0043] The product wafer and the carrier wafer are adhesively
attached one on top of the other by a double-sided adhesive,
thermally releasable film. After the thinning of the carrier wafer,
the product wafer is released again by heat exposure. At about 120
degrees Celsius, the double-sided adhesive film loses its adhesive
force. This film can be stored in the rolled-up state with two
covering films.
[0044] As the first product wafer, finger-tip wafers were thinned
to 80 micrometers, 60 micrometers and 40 micrometers. The wafers
were sawn into beforehand (bevel cut before thinning). In this
case, the separated chips were subsequently supplied on
leadframes.
[0045] The basic module of the device is a vacuum chamber, which is
equipped for vacuum-connecting two wafers. The device for
connecting wafers in a planar manner permits carrier wafers on
product wafers to be handled with a throughput of about 15 wafers
per hour. The composite wafers produced by the device can still be
handled when the product wafer is in an extremely thin state. The
product wafer on the composite wafer can be ground down to about 70
micrometers. Further removal of the product wafer can be performed
by etching.
[0046] Other features which are considered as characteristic for
the invention are set forth in the appended claims.
[0047] Although the invention is illustrated and described herein
as embodied in a device for connecting two wafers in a planar
manner for grinding down and cutting up a product wafer, it is
nevertheless not intended to be limited to the details shown, since
various modifications and structural changes may be made therein
without departing from the spirit of the invention and within the
scope and range of equivalents of the claims.
[0048] The construction and method of operation of the invention,
however, together with additional objects and advantages thereof
will be best understood from the following description of specific
embodiments when read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0049] FIG. 1 is a basic diagram of a device for connecting two
wafers one on top of the other in a planar manner;
[0050] FIG. 2 is a portion of a device for connecting two wafers
one on top of the other in a planar manner; and
[0051] FIG. 3 is a flow diagram showing the method steps of an
example of how to carry out the method for connecting two wafers in
a planar manner for grinding down and cutting up a product
wafer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0052] Referring now to the figures of the drawing in detail and
first, particularly, to FIG. 1 thereof, there is shown a basic
diagram of a device for connecting two wafers 1, 2 one on top of
the other in a planar manner. In FIG. 1, the reference numeral 3
designates a vacuum chamber, which is connected to an evacuating
device 104 for the chamber volume. The reference numeral 4
designates a chuck, which is likewise connected to an evacuating
device 102 and can receive a carrier wafer 2 on its surface 12. The
carrier wafer 2 has an edge region 14. The reference numeral 5
shows a double-sided adhesive film, which in FIG. 1 is connected by
one of its adhesive surfaces to the carrier wafer 1. Numeral 8
designates a heating device, which is capable of heating up the
chuck 4 to the melting temperature of the double-sided adhesive
film 5.
[0053] The vacuum chamber 3 is closed off in the downward direction
by a vacuum base plate 29 having a number of lead-throughs. The
lead-throughs 30 and 31 are power lead-throughs for the heating
device 8 of the chuck 4. Arranged in the center of the vacuum base
plate 29 is a lifting-turning lead-through 32 that can be used to
adjust the height of the chuck 4 and, if required, to turn the
chuck 4. This lifting-turning device has a piece of pipe 33 which
leads from a vacuum valve 22 to the evacuating device 102 of the
chuck 4. The pipe 33 also serves as a vacuum line 34. Air can be
admitted to the interior of the piece of pipe 33 via an
air-admission orifice 28, when the vacuum valve 22 is closed, and
consequently the connection to the evacuating device 102 is
interrupted.
[0054] The vacuum base plate 29 additionally has a pipe connector
35, via which the vacuum chamber 3 can be connected to the
evacuating device 104 via a vacuum line 45 after the vacuum valve 7
has been opened. Air can be admitted to the vacuum chamber 3 via an
air-admission orifice 27 when the vacuum valve 7 is closed.
Arranged on the vacuum base plate 29 is a piece of pipe 37 with a
lower flange 38 and an upper flange 39, which forms a vacuum
chamber wall 35. The lower flange 38 is connected in a vacuum-tight
manner to the vacuum base plate 29 by means of an O-ring 40. The
upper flange 39 carries a vacuum-chamber cover 18, which for its
part is connected in a vacuum-tight manner to the upper flange 39
by means of an O-ring 41.
[0055] Arranged on the vacuum-chamber cover 18 is a vacuum-holding
device 19 having a surface 20 on which the rear side of a product
wafer can be held suspended so that its active surface 42 is at a
distance a from the second adhesive surface of the double-sided
adhesive film 5. The vacuum-holding device 19 is connected to an
evacuating device 106 via a vacuum line 44, a pipe connector 43,
and a vacuum valve 6, and these components are used to evacuate the
vacuum-holding device 19. Air can be admitted to the vacuum-holding
device 19 via an air-admission orifice 26 when the vacuum valve 6
is closed.
[0056] Arranging a vacuum-holding device 19 on a vacuum-chamber
cover 18 makes it possible to arrange a product wafer 1 with its
active surface 42 lying opposite a carrier wafer at a distance a,
so that the intermediate space formed by the distance a between the
product wafer 1 and the carrier wafer 2 can be completely evacuated
and outgassed and, if required, the surfaces of the product wafer
to be connected to one of the surfaces of the double-sided adhesive
film 5 can be vacuum-dried before connecting. It is consequently
possible to bring these surfaces onto each other only after this
vacuum preparation of the surfaces, in that for example extraction
pumping via the vacuum valve 7 and the vacuum line 45 causes the
vacuum in the vacuum chamber 3 to become greater than the vacuum
which is acting on the vacuum-holding device 19 via the vacuum line
44 and the vacuum valve 6. This is because, with an equal or
greater vacuum in the vacuum chamber in comparison with the vacuum
of the vacuum-holding device 19, the product wafer falls from its
suspended position with its active surface onto the double-sided
adhesive film 5 and, during the subsequent admission of air to the
vacuum chamber via the air-admission orifice 27 with the vacuum
valves 5, 7 and 22 closed at the same time, is pressed by the
rising pressure in the vacuum chamber 3 onto the carrier wafer.
[0057] FIG. 2 shows a detail A of a device for connecting two
wafers 1 and 2 one on top of the other in a planar manner. For this
purpose, the carrier wafer 2 is arranged with its thickness D on
the chuck 4 shown in FIG. 1, which is shown here in the form of a
detail and partly in cross section. The chuck 4 can be heated up by
a heating device 8. Furthermore, the chuck 4 can be evacuated in
the direction of the arrow B, so that the carrier wafer 2 can be
held on the chuck 4 using the drilled vacuum holes 17. The exact
position of the carrier wafer 2 on the chuck 4 is determined by
means of positioning pins 23, 24, of which one positioning pin 24
is shown in this detail A. A positioning pin 24 of this type may
have a cylindrical shape, as long as its length does not exceed the
thickness D of the carrier wafer 2 plus the thickness h of the
double-sided adhesive film 5. In the embodiment depicted in the
detail A, the positioning pin 24 has a conical shape and is located
with its cone base area 25 on the surface 12 of the chuck 4 and
protrudes with its cone tip 47 from the surface 12. The conical
configuration of the positioning pin 24 has the advantage that the
cone tip 47 can contribute to the guiding and positioning of the
product wafer 1.
[0058] The detail A additionally shows a partial cross section of
the vacuum-holding device 19, with which a product wafer 1 can be
held with its rear side 48 on the vacuum-chamber cover 18, which is
shown in FIG. 1. The vacuum-holding device 19 is evacuated in the
direction of the arrow C, whereby the rear side 48 of the product
wafer 1 is pressed onto the surface 20 of the vacuum-holding
device. For this purpose, the vacuum-holding device 19 has drilled
vacuum holes 17 (also identified with numerals 15 and 16 in FIG.
1), which, in an embodiment not shown, can be made in the
vacuum-holding device 19 in concentrically arranged grooves. Exact
positioning of the product wafer 1 during the holding by the
vacuum-holding device 19 and during the method of connecting two
wafers is achieved by conical guiding pins 9 and 10, of which the
conical guiding pin 10 is shown in the detail A. Its length bridges
the distance a between the surface 42 of the product wafer 1 and
the surface of the double-sided adhesive film 5. The conical form
of the guiding pin 10 ensures that, when the product wafer falls
down onto the double-sided adhesive film 5, canting of the wafer on
the guiding pin 10 is avoided. Furthermore, the detail A shows that
the guiding pin 10 of the holding device 20 is arranged offset from
the positioning pin 24 on the circumference of the wafer, so that
the pins are not a hindrance during the adhesive attachment and
connecting of the product wafer 1. The guiding pin 10 has a cone
tip 13.
[0059] Since the device which is shown in FIG. 1 has the
possibility of adjusting the height of the chuck 4 via the lifting
and turning lead-through 32, it may well be of advantage to align
the guiding pins and the positioning pins exactly with one another,
so that it is ensured that, when the chuck 4 is moved up in the
direction of the vacuum-holding device 19, a minimum distance a is
ensured and the two wafers 1, 2 are not inadvertently pressed onto
each other before the evacuation.
[0060] A further advantage of the device shown in FIGS. 1 and 2 is
that the distance a can be varied during the operation of
connecting two wafers 1, 2 for grinding down and subsequently
cutting up a product wafer 1. For instance, the extraction-pumping
cross section can be kept large at the beginning of the operation,
in that the lifting device of the chuck 4 is arranged in its lowest
position, and the distance a can be reduced to a few millimeters,
by raising the chuck using the lifting-turning device 32, before
the falling down of the product wafer 1, i.e. as long as the vacuum
in the vacuum chamber 3 has not yet reached the vacuum of the
vacuum-holding device 19. By bringing the two surfaces to be
connected together, that is the active surface 48 of the product
wafer 1 and the free surface of the double-sided adhesive film 5,
the risk that the falling-down product wafer 1 will undergo canting
is minimized when there is an equal or higher vacuum in the vacuum
chamber 3 in comparison with the vacuum of the vacuum-holding
device 19.
[0061] FIG. 3 is a flow diagram showing the steps of an example of
a method for connecting two wafers in a planar manner for grinding
down and cutting up a product wafer 1. In a first method step 50,
the first covering film of the two covering films of a double-sided
adhesive film 5 is removed. In the next method step 51, the exposed
surface of the double-sided adhesive film 5 can be drawn onto the
carrier wafer 2. This drawing of a double-sided adhesive film onto
a carrier wafer may already be carried out fully automatically
under a vacuum. The drawing of the double-sided adhesive film 5
onto the carrier wafer 2 is followed by method step 52, in which
the carrier wafer 2 with the double-sided adhesive film is placed
between the pins or positioning pins 23, 24 onto a chuck 4 of a
semi-automatic machine, as shown in FIG. 1.
[0062] In the next step 53, the second covering film, which is
still located on the double-sided adhesive film, can be removed
from the latter. For this purpose, the carrier wafer 2 may already
be fixed on the chuck 4 by evacuating the chuck 4. In step 54, the
product wafer 1 to be ground is then sucked into place between the
pins or guiding pins of the vacuum-chamber cover 18 of the
semi-automatic machine, as shown in FIG. 1. After closing and
evacuating the vacuum chamber 3 in step 55, the product wafer 1,
which was held suspended from the vacuum-holding device 19, falls
onto the adhesive surface of the double-sided adhesive film 5. By
admitting air to the vacuum chamber 3, in method step 56, the
product wafer 1 is deposited with its active surface 42 on the
carrier wafer 2 via the double-sided adhesive film 5.
[0063] After removing the composite wafer produced in this way,
including the product wafer 1 and the carrier wafer 2 with the
double-sided adhesive film 5 lying in between, there may follow
further method steps, for example, grinding down the product wafer,
separating the product wafer and the carrier wafer, and cutting up
the product wafer into chips. For this purpose, in method step 57
the wafer is ground down to <100 .mu.m and in method step 58 the
product wafer 1 is etched to a minimum of 40 .mu.m. This minimum of
40 .mu.m does not constitute a limit, but is reached in this
example of how the method is carried out. Etching down can be
carried out over a large surface area, even down to thicknesses of
15 .mu.m and below. Subsequently, in method step 59, the wafer
assembly including the product wafer 1 and the carrier wafer 2 is
adhesively attached with the ground-down wafer 1 on a saw frame
covered with film, with the double-sided adhesive film 5 lying in
between. After that, separating the product wafer 1 and the carrier
wafer 2 is performed using a heatable chuck 4, at 120.degree. C.
for example, in method step 60, and finally the ground-down product
wafer 1 is sawn into chips in the saw frame covered with a
film.
[0064] Apart from this example of how to carry out a method for
connecting two wafers in a planar manner for grinding down and
cutting up a product wafer 1 into chips, there are further
variants, which have already been described above. In particular,
with the device shown in FIG. 1, the pumping cross section can be
varied during the closing and evacuating of the vacuum chamber in
step 55 by using a lifting lead-through 32 in the vacuum base plate
29 of the device shown in FIG. 1 to make the chuck 4 be kept
initially in a position away from the vacuum-holding device 19 and
brought into position so that the distance a only has a few
millimeters between the product wafer 1 and the carrier wafer 2
only shortly before the falling down of the product wafer 1.
[0065] The positioning of the positioning pins and of the guiding
pins at the edges of the wafers may be variable and respectively
adapted to the size and shape of the wafers to be connected. The
cutting up of the product wafer 1 into chips may be performed
before separating the product wafer 1 from the carrier wafer 2, so
that, when the product wafer 1 is separated from the carrier wafer
2, this already has the effect that only chips are obtained for
further processing. Other variations, obvious to a person skilled
in the art, are possible without departing from the scope of
invention as defined by the claims.
* * * * *