U.S. patent number RE36,890 [Application Number 08/535,680] was granted by the patent office on 2000-10-03 for gradient chuck method for wafer bonding employing a convex pressure.
This patent grant is currently assigned to Motorola, Inc.. Invention is credited to Frank T. Secco d'Aragona, Raymond C. Wells.
United States Patent |
RE36,890 |
Wells , et al. |
October 3, 2000 |
**Please see images for:
( Certificate of Correction ) ** |
Gradient chuck method for wafer bonding employing a convex
pressure
Abstract
An apparatus and method for improved wafer bonding by scrubbing,
spin drying, aligning, and pressing the polished wafers together.
The first wafer (13) is mounted on a flat wafer chuck (11) and a
second wafer (14) is mounted on a convex pressure gradient chuck
(10). Wafers are scrubbed until a polished contamination free
surface is obtained and pressed together. The convex pressure
gradient chuck exerts a higher pressure at the center of the wafer
than at the periphery of the wafer.
Inventors: |
Wells; Raymond C. (Scottsdale,
AZ), Secco d'Aragona; Frank T. (Scottsdale, AZ) |
Assignee: |
Motorola, Inc. (Schaumburg,
IL)
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Family
ID: |
26957835 |
Appl.
No.: |
08/535,680 |
Filed: |
September 28, 1995 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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276189 |
Jul 15, 1994 |
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Reissue of: |
565761 |
Jul 31, 1990 |
05131968 |
Jul 21, 1992 |
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Current U.S.
Class: |
156/153;
148/DIG.135; 156/281; 156/285; 156/87; 438/455 |
Current CPC
Class: |
B32B
37/0007 (20130101); B32B 37/10 (20130101); B32B
38/162 (20130101); H01L 21/2007 (20130101) |
Current International
Class: |
H01L
21/20 (20060101); H01L 21/02 (20060101); B32B
031/16 (); H01L 021/304 () |
Field of
Search: |
;451/388,41,55,289
;156/153,281,212,87,285,286 ;279/3 ;437/62,225,921,974
;148/DIG.12,DIG.159,DIG.135 ;438/455 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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62-71215 |
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Jan 1987 |
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JP |
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575923 |
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Mar 1946 |
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GB |
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Other References
Parker, Sybil, editor, McGraw-Hill Dictionary of Scientific and
Technical Terms, 3.sup.rd Ed, 1984, p. 1274. .
Lehman, V. et al, "Contamination Protection of Semiconductor
Surfaces by Wafer Bonding," Solid State Technology, Apr. 1, 1990,
pp. 91-92. .
Haisma, J., et al, "Silicon-on-Insulator Wafer Bonding-Wafer
Thinning Technological Evaluations," Japanese Journal of Applied
Physics, vol. 28, No. 8. Aug. 1989 pp 1427-1443. .
Shimbo, M. et al, "Silicon-to-Silicon Direct Bonding Mehtod,"
Journal of Applied Physics, vol. 60, No. 8, Oct. 15, 1986, pp
2987-2989. .
Black, R.D., et al, "Silicon and Silicon dioxide thermal bonding
for Silicon-insulator applications," Journal of Applied Physics,
vol. 63 No. 8, Apr. 15, 1988, pp. 2773-2777. .
Lasky, J.B, "Wafer Bonding for Silicon-on-Insulator Technologies,"
Applied Physics Letters, vol. 48, No. 1, Jan. 6, 1986, pp.
78-80..
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Primary Examiner: Aftergut; Jeff H.
Attorney, Agent or Firm: Cooper; Kent J. Barbee; Joe E.
Parent Case Text
.Iadd.This application is a continuation of reissue application
Ser. No. 08/276,189 filed Jul. 15, 1994, now abandoned, which is a
reissue application of Ser. No. 07/565,761, filed Jul. 31, 1990,
now U.S. Pat. No. 5,131,968..Iaddend.
Claims
We claim:
1. A method for bonding a first and a second semiconductor wafer
together, which comprises:
mounting the first semiconductor wafer on a flat chuck and mounting
the second semiconductor wafer on a convex pressure gradient
chuck;
scrubbing a surface of the first and second semiconductor wafer to
obtain polished surfaces; and
pressing the polished surfaces of the first and second
semiconductor wafers together by using the flat chuck and the
convex pressure gradient chuck to press them together by applying a
convex pressure gradient by using pressurized fluid across a
surface of the second semiconductor wafer that is in contact with
the convex pressure gradient chuck, thereby applying a greater
pressure centrally located which gradually decreases to a periphery
of the convex pressure gradient chuck by interconnecting a series
of pressure reduction orifices, plenums, and channels which create
a convex pressure gradient on the second semiconductor wafer during
the pressing of the polished surfaces together.
2. The method of claim 1 further including spin-drying the
semiconductor wafers after the scrubbing step.
3. The method of claim 1 further including providing the convex
pressure gradient chuck with a soft malleable head.
4. The method of claim 2 further including accomplishing all steps
sequentially.
5. A method of bonding a first and a second semiconductor wafer
together, comprising:
polishing a surface of the first semiconductor and a surface of the
second semiconductor wafer to obtain clean surfaces;
pressing the clean surfaces of the first and the second
semiconductor wafer together by applying a convex pressure gradient
across at least a surface opposite the clean surface of the first
semiconductor wafer; and
creating the convex pressure gradient by using a pressurized fluid
through orifices and channels to create a greater pressure
centrally located which gradually decreases to a periphery of the
convex pressure gradient chuck to bond the first and second
semiconductor wafers together.
6. A method for bonding a first and a second semiconductor wafer
together which comprises the steps of:
scrubbing a surface of the first semiconductor wafer and a surface
of the second semiconductor wafer to obtain clean surfaces;
spin drying the surface of the first and the second semiconductor
wafer to obtain at least a monolayer of liquid left on the surface
of at least one wafer;
pressing the surface of the first and the second semiconductor
wafer together by exerting a convex pressure gradient on at least
the first semiconductor wafer; and
creating the convex pressure gradient by using a pressurized fluid
through orifices and channels to create a greater pressure
centrally located which gradually decreases to a periphery of the
convex pressure gradient chuck to bond the first and second
semiconductor wafers together. .Iadd.
7. A method for processing a semiconductor wafer comprising the
steps of:
providing the semiconductor wafer, the semiconductor wafer having a
frontside and a backside;
providing a rotatable polishing chuck for holding the semiconductor
wafer;
mounting the semiconductor wafer on the rotatable polishing chuck
by applying a vacuum to the backside of the semiconductor
wafer;
placing the rotatable polishing chuck next to a surface such that
the frontside of the semiconductor wafer is in contact with the
surface; and
exerting a positive pressure on the backside of the semiconductor
wafer by exposing the backside of the semiconductor wafer to a
pressurized fluid, while the frontside of the semiconductor wafer
is pressed against the surface by the rotatable polishing
chuck..Iaddend..Iadd.8. The method of claim 7, wherein the step of
exerting the positive pressure is further characterized as exposing
the backside of the semiconductor wafer to a gas..Iaddend..Iadd.9.
The method of claim 7, wherein the step of exerting the positive
pressure is further characterized as exposing the backside of the
semiconductor wafer to a liquid..Iaddend..Iadd.10. The method of
claim 7, wherein the step of exerting the positive pressure is
further characterized as applying a convex pressure gradient to the
backside of
the semiconductor wafer..Iaddend..Iadd.11. A method for processing
a frontside of a semiconductor wafer comprising the steps of:
providing the semiconductor wafer, the semiconductor wafer having a
frontside and a backside;
providing a rotatable polishing chuck for holding the semiconductor
wafer;
mounting the semiconductor wafer onto the rotatable polishing
chuck;
using the rotatable polishing chuck to press the frontside of the
semiconductor wafer against a surface;
exposing the backside of the semiconductor wafer to a pressurized
fluid to apply a positive pressure to the backside of the
semiconductor wafer, wherein the rotatable polishing chuck
continues to press the frontside of the semiconductor wafer against
the surface while the pressurized fluid is applied to the backside
of the semiconductor wafer..Iaddend..Iadd.12. The method of claim
11, wherein the step of exposing the backside of the semiconductor
wafer to the pressurized fluid is further characterized as exposing
the backside of the semiconductor wafer to a gas..Iaddend..Iadd.13.
The method of claim 11, wherein the step of exposing the backside
of the semiconductor wafer to the pressurized fluid is further
characterized as exposing the backside of the semiconductor wafer
to a liquid.
Description
BACKGROUND OF THE INVENTION
This invention relates, in general, to the bonding of two surfaces,
and more particularly, to an apparatus and method for bonding two
semiconductor wafers.
The bonding of two semiconductor wafers together offers many
advantages in the manufacturing of semiconductor devices. Devices
that are manufactured in this manner offer higher performance for
high density CMOS, high voltage, and high frequency devices. Many
theories have been discussed in the literature about actual bonding
mechanisms for joining two wafers together. One such theory is Van
der Waals bonding or dipole bonding. Van der Waals bonding is
caused by an electrical interaction of dipoles in two bodies. This
theory as well as others are discussed in greater detail by J.
Haisma, G. A. C. M. Spierings, U. K. P. Biermann and J. A. Pals,
"Silicon-on-Insulator Wafer Bonding-Wafer Thinning Technological
Evaluations," Japanese Journal of Applied Physics, Vol. 28, No. 8,
August, 1989, pages 1426-1443. Generally, the conventional process
of wafer bonding is achieved by quickly cleaning the surfaces to be
bonded, manually placing the surfaces in contact with each other,
and further pressing the surfaces together by a hand rolling pin
device. This process results in poor bonding and many voids due to
contamination.
Contamination of the bonding surface is a major concern in being
able to achieve void free bonding of the two surfaces. Organic film
and particle contamination are two main contamination types that
prevent manufacturing high quality void free bonded surfaces.
Organic contamination of semiconductor surfaces has been shown to
occur by simple storage of surfaces as described by V. Lehmann, U.
Gosele, and K. Mitani, "Contamination Protection of Semiconductor
Surfaces by Wafer Bonding." Solid State Technology, April 1990,
pages 91-92. Particles, another form of contamination that is well
known in the industry also has been shown to participate in the
void formation of bonded surfaces. Therefore, a method that enables
the removal of contamination and prevents the occurrence of
recontamination of the bonding surfaces is highly desirable.
SUMMARY OF THE INVENTION
The objects and advantages of the present invention are provided by
an improved apparatus and method for bonding a first and a second
wafer together. The first wafer is mounted on a convex pressure
gradient chuck. Wafers that are mounted on the flat and convex
pressure gradient chucks are scrubbed or polished until a
contamination free surface is achieved on both wafers. After the
wafers have been scrubbed clean of contamination and before
recontamination of the surfaces can occur the wafers are joined.
The joining of the wafers is accomplished by moving the chucks
together. The convex pressure gradient chuck applies a pressure
gradient to the wafer surfaces, further pressing the surfaces
together and exerting a higher pressure in the central portion of
the wafer than at the peripheral portion to prevent self sealed
bubbles or voids.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of wafers mounted on chucks;
FIG. 2 pictorially illustrates a chuck mounted with a wafer being
scrubbed/polished in accordance with an embodiment of the present
invention.
FIG. 3 is a cross-sectional view showing contact of the wafers up
against a scrubbing pad; and
FIG. 4 is a cross-sectional view of convex pressure gradient
chuck.
DETAILED DESCRIPTION OF THE DRAWINGS
A cross-sectional side view of a flat wafer vacuum chuck 11 and a
convex pressure gradient wafer chuck 10 is illustrated in FIG. 1.
Flat wafer chuck 11 is illustrated as having a large circular head
15 and a vacuum shaft 17. Wafer 13 is mounted on head 15. Vacuum
shaft 17 extends from the middle of vacuum head 15 of flat vacuum
chuck 11. Vacuum shaft 17 further contains a vacuum port 12 which
extends though shaft 17 and head 15. It should be understood that
vacuum shaft 17 is connected to a rotational means which can rotate
head 11 and wafer 13 at high RPM. Vacuum port 12 transfers a
negative pressure to wafer 13 which holds wafer 13 in place for
subsequent processing. Additionally, it should be further
understood that chuck 11 is attached to an apparatus that possesses
freedom of movement so that direction, speed, and force can be
specified.
Chuck 10 is composed of a large circular head 20 and vacuum shaft
16. Circular head 20 is manufactured so that convex pressure
gradient 24 is transferred from circular head 20 to wafer 14.
Physical properties of head 20 can range from a hard flat surface
to a soft malleable or flexible surface. Selection of specific
surfaces is determined by process requirements. The circular head
20 is used to distribute pressure gradient 24 across wafer 14 when
the wafers are bonded. This action squeezes out any possible
bubbles or voids that might occur during bonding. Vacuum shaft 16
extends from the middle of vacuum head 20. Vacuum shaft 16 further
contains a vacuum port 26 which extends through vacuum shaft 16 and
head 20. It should be understood that vacuum shaft 16 is connected
to a rotational means which can rotate head 10 and wafer 14 at high
RPM. Vacuum port 26 transfers a negative pressure to wafer 14 to
hold the wafer in place for subsequent processing. In one
embodiment, vacuum port 26 can also serve as a pressure inlet for
creating a pressure gradient 24. Additionally, it should be further
understood that chuck 10 is attached to an apparatus that possesses
the freedom of movement so that direction, speed, and force can be
specified.
Convex pressure gradient 24 is illustrated by a multiplicity of
arrows 24 shown in chuck 10. Larger and smaller arrows illustrate
the relative magnitude of pressure gradient 24 that is transferred
to wafer 14 on chuck 10. Larger arrows indicate a greater pressure
with smaller arrows indicating less pressure, thus a greater
pressure is shown in the middle of wafer 14 with gradual diminution
of pressure to the outside edges. Pressure gradient 24 is provided
by a head 20 which is attached to shaft 16.
FIG. 2 pictorially illustrates one embodiment of the polishing or
scrubbing operation of the present invention. Driving means 19
rotates a double sided scrubbing pad 23 so that any selected
rotational speed or rotational direction can be obtained for pad
23. In this embodiment pad 23 is capable of being swung away from
chuck 11 and chuck 10 for subsequent processing. A multiplicity of
pads with a variety of surfaces is capable of being swung in and
out from between chuck 11 and chuck 10. This variety of surfaces
offers process capability from polishing, scrubbing, planarizing,
or the like. Chuck 11, wafer 13, wafer 14, and chuck 10 are
symmetrically aligned to center points such that wafer 13, wafer 14
and chuck 10 are hidden from view. Additionally, chuck 11 and wafer
13 are on one side of scrubbing pad 23, and chuck 10 and wafer 14
are on the other side of pad 23. Wafer chuck 11 is shown only
partially contacting scrub pad 23. It should be understood by
someone skilled in the art that this is only one configuration and
that it would be possible to have wafer 13 in total contact with
pad 23. Vacuum shaft 17 is shown with vacuum port 12. It should be
understood that vacuum shaft 17 can provide a rotational means for
chuck 11 that is separate and independent from rotational means 19.
Rotation of shaft 17 and shaft 16 can also be left to idle or free
wheel if desired. It will also be understood that chuck 11 and
chuck 10 are symmetrical and can be independent from each other. It
should be further understood that the mechanical attributes of
chuck 11 can be applied to chuck 10 on the opposite side of pad 23.
Dispense nozzle 21 is shown so that ultra pure deionized water or
other materials can be dispensed while scrubbing of wafer 13 and
wafer 14 is in progress. Dispensing of deionized water onto wafer
13, wafer 14, and pad 23 serves to cleanse wafer 13, wafer 14 and
pad 23 free of contamination.
In yet another embodiment, wafer 14 and wafer 13 are scrubbed on
the same side of pad 23.
Once the scrubbing of wafer 13 and wafer 14 is completed, polished,
contamination free wafers are produced. Wafer 13 and wafer 14 are
then spin dried to remove excess moisture. Spin drying is achieved
by rotating wafer 13 and wafer 14 at high RPM. To enhance the spin
drying process an ultra pure gas such as nitrogen or the like, can
be blown on the polished surfaces.
Determination of crystal orientation of wafer 13 and wafer 14 is
accomplished by observation of major and minor flats of wafer 13
and wafer 14. The identification of the major and minor flats is
well known in the art and commercial equipment for doing this
procedure is readily available. Knowing the orientation of wafer 13
and wafer 14 allows for the proper placement of wafer 13 and wafer
14 for bonding purposes.
After scrubbing, spin drying, and crystal orientation wafer 13 and
wafer 14 are joined by moving flat wafer chuck 11 and convex
pressure gradient chuck 10 together until wafer 13 and wafer 14 are
in contact with each other thereby pressing the two scrubbed wafers
together. The pressing of
these wafers together is further enhanced by the use of pressure
gradient 24 of chuck 10. Convex pressure gradient chuck 10 (see
FIG. 1) causes a greater bonding force to be applied at the center
of the wafers and radiate out to the periphery of the wafer thereby
forming any air or contaminants out from the bonding surfaces on
the wafers.
Preferably, the wafers are bonded or pressed together immediately
following the drying step; however, some delay may be permissible
between drying and pressing. If the delay results in the
recontamination the wafers, polishing will have to be repeated
unless other steps have been taken to protect the surfaces of the
wafers from contaminants.
It should be understood that in some applications the joining of
surfaces that are clean and have some amount of liquid still on the
surfaces to be joined is advantageous. Amounts of liquid may range
from at least one monolayer to having the surface flooded with
liquid. Excess liquid that is between the bonding surfaces is then
squeezed out by convex pressure gradient 24 as the bonding surfaces
are pressed together producing a void free bond.
In the preferred embodiment of this invention the scrubbing, spin
drying, crystal orientation and joining are accomplished in one
enclosure in a continuous operation.
FIG. 3 is a cross-sectional view of a portion of FIG. 2. Chuck 11
and chuck 10 squeeze wafer 13 and wafer 14 respectively up against
scrub pads 23 from opposite sides. The squeezing force is generated
by applying a force on chuck 11 and chuck 10 perpendicular to scrub
pad 23. Wafer 13 and wafer 14 are held firmly on head 20 and head
15 by applying a negative pressure though vacuum port 12 and vacuum
port 26. In another embodiment wafers are held firmly in place by
frictional forces. Scrub pads 23 are supported by a flat disc 22
which is attached to rotating means 19 illustrated in FIG. 2. Pad
23 is preferably a synthetic suede leather material. One such
material is Corfam (a trade name used by Dupont).
FIG. 4 is a cross-sectional view of one embodiment of a convex
pressure gradient chuck 10. It should be understood that this is
just one embodiment and other embodiments can be used to achieve a
convex pressure gradient 24 shown in FIG. 1. Convex pressure
gradient chuck 10 is a symmetrical device, therefore only one half
of convex pressure gradient chuck 10 is described in detail since
the other half is a mirror image. Vacuum port 26 is located in
convex pressure gradient shaft 16. Vacuum port 26 is not only used
to provide vacuum to hold wafer 14 to convex pressure gradient
chuck 10 but, also to provide a means to input pressure so as to
create a pressure gradient. Pressure supplied though port 26 can
either be a liquid or a gas. Use of either a gas or a liquid is
determined by processing conditions. Pressure supplied though port
26 is directed between orifice 39 and orifice 34. Orifice 39
transfers pressure from port 26 to wafer 14 though channels 38.
This is the highest pressure position and is centered on wafer 14.
Channels 38 are concentric grooves and receive pressure from
orifice 39. Channels 38 are connected to orifice 39 by a slot (not
shown). Concentric channels 38 may receive pressure from two or
more orifices 39.
Pressure reduction orifice 34 reduces pressure from incoming port
26. Plenum 33 receives reduced pressure from pressure reduction
orifice 34. Pressure in plenum 33 is directed between orifice 36
and orifice 41. Orifice 36 transfers pressure from plenum 33 to
channels 37. Channels 37 then direct pressure to wafer 14. This is
the second highest pressure position on wafer 14. Pressure from
plenum 33 is further reduced by pressure reduction orifice 41.
Orifice 41 provides pressure for plenum 42 which is directed
between orifice 43 and orifice 46. Pressure from plenum 42 is
directed toward wafer 14 by orifice 43. Pressure coming from
orifice 43 is directed into channels 44. These channels apply
pressure to wafer 14. This is the third highest pressure position
on wafer 14. Pressure from plenum 42 is directed into pressure
reduction orifice 46. Pressure reduction orifice 46 further reduces
pressure from plenum 42 into plenum 47. Pressure in plenum 47 is
directed between orifice 48 and orifice 51. Pressure from plenum 47
is directed into orifice 48 which transfers pressure to channels
49. Channels 49 subsequently transfer pressure to wafer 14. This is
the fourth highest pressure position on wafer 14. Orifices 34, 39,
41, and 46 provide for a gradual decrease in pressure, with a
greater pressure centrally located on wafer 14 and gradually
decreasing to the periphery of chuck head 20. This decline in
pressure is pictorially illustrated by convex pressure gradient 24
in FIG. 1. Pressure from plenum 47 is also directed through orifice
51. Pressure coming though orifice 51 comes up against flexible
flap 32. Flexible flap 32 is held in place by at least one screw or
pin 31. Flexible flap 32 is made in such a manner that when excess
pressure is pressed up against flap 32, flap 32 flexes as shown in
phantom by lines 30. Movement by flap 32 can expel excess pressure
either in a gaseous or a liquid form. Once excess pressure has been
released flap 32 then resumes its normal shape. Once flap 32 is in
its normal position a vacuum can be drawn though all plenums,
orifices, and channels.
Channels 37, 38, 44, and 49 are formed as grooves of concentric
rings around convex pressure gradient chuck. Grooves 37 are
interconnected to orifice 36 by a slot (not shown) cut between the
two grooves and though orifice 36. Grooves 37 may recieve pressure
from two or more orifices. By way of example, grooves 38, 44, and
49 are interconnected to their respective orifices in a similar
manner as grooves 37. It should be understood that it is possible
to have as many plenums and orifices as necessary to accommodate
any wafer size. It should be further understood that convex
pressure gradient chuck 10 can be manufactured from a variety of
materials such as metal, rubber, or the like.
By now, it should be appreciated that there has been provided a
novel apparatus and method for bonding wafers that eliminates voids
and bonding defects between the bonded wafers.
* * * * *