U.S. patent application number 10/008623 was filed with the patent office on 2002-04-04 for potted transducer array with matching network in a multiple pass configuration.
This patent application is currently assigned to INTERSIL CORPORATION. Invention is credited to Caravaggio, Michael A., Fenstermacher, Terry L., Grebs, Thomas E., Longenberger, Robert F., Ridley, Rodney S., Schuler, Malcolm R., Trost, Jason R., Webb, Raymond J..
Application Number | 20020038662 10/008623 |
Document ID | / |
Family ID | 23352398 |
Filed Date | 2002-04-04 |
United States Patent
Application |
20020038662 |
Kind Code |
A1 |
Schuler, Malcolm R. ; et
al. |
April 4, 2002 |
Potted transducer array with matching network in a multiple pass
configuration
Abstract
The invention provides a pair of parallel megasonic transducers
that generate parallel columns of megasonic waves across a cleaning
container. Semiconductor wafers move back and forth transverse to
the columns. The transducers have their back side potted with a
silicone elastomer to prevent corrosion. In another embodiment
megasonic waves from in-line transducers are dispersed with a
cylindrical quartz rod. Water is enriched with ozone by pumping
ozone under pressure through a filter into sealed housing of
deionized water.
Inventors: |
Schuler, Malcolm R.;
(Mountaintop, PA) ; Longenberger, Robert F.;
(Shickshinny, PA) ; Ridley, Rodney S.;
(Mountaintop, PA) ; Grebs, Thomas E.;
(Mountaintop, PA) ; Trost, Jason R.; (Drums,
PA) ; Webb, Raymond J.; (Mountaintop, PA) ;
Caravaggio, Michael A.; (Mountaintop, PA) ;
Fenstermacher, Terry L.; (Nescopeck, PA) |
Correspondence
Address: |
JAECKLE FLEISCHMANN & MUGEL, LLP
39 State Street
Rochester
NY
14614-1310
US
|
Assignee: |
INTERSIL CORPORATION
|
Family ID: |
23352398 |
Appl. No.: |
10/008623 |
Filed: |
December 6, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10008623 |
Dec 6, 2001 |
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09829634 |
Apr 10, 2001 |
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09829634 |
Apr 10, 2001 |
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09344867 |
Jun 28, 1999 |
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Current U.S.
Class: |
134/1.3 ;
134/184; 210/760; 261/DIG.42; 422/186.1 |
Current CPC
Class: |
Y10S 134/902 20130101;
C02F 1/36 20130101; C02F 2103/346 20130101; C02F 2201/782 20130101;
C02F 1/78 20130101; B08B 3/12 20130101 |
Class at
Publication: |
134/1.3 ;
134/184; 422/186.1; 210/760; 261/DIG.042 |
International
Class: |
B08B 003/12 |
Claims
1. A megasonic cleaning apparatus comprising: a container for
holding a cleaning fluid and a plurality of semiconductor wafer,
said container having a rectangular configuration with a floor,
four wall, and an open top; a megasonic transducer array mounted to
the floor of the container, said array comprising a frame for
holding one or more transducers, each transducer comprising a
piezoelectric element bonded to transmitting plate for coupling
megasonic energy from the piezoelectric elements into the cleaning
fluid; one or more electrical cables connected to the piezoelectric
elements and extending from the element to a source of electrical
energy wherein said quartz plates, piezoelectric elements and said
connections to the cables all encapsulated in a material that
resists intrusion from liquid in the container.
2. The megasonic cleaning apparatus of claim 1 wherein the
encapsulating material comprises silicone.
3. The megasonic cleaning apparatus of claim 1 wherein the
megasonic transducers comprise a piezoelectric element bonded to a
odd quarter wave length quartz plate, said odd quarter wave length
quartz plate having first and second planar surfaces separated from
each other by the thickness of the quartz plate, said first planar
surface facing the floor of the tank for coupling sonic energy from
the transducers into the cleaning fluid in the tank and the second
planar surfaces bonded to the piezoelectric element.
4. The megasonic cleaning apparatus of claim 1 wherein the
transducers are parallel to each other.
5. The megasonic cleaning apparatus of claim 1 wherein the
transducers are in line with each other.
6. A megasonic cleaning apparatus comprising: a container for
holding a cleaning fluid and a plurality of semiconductor wafer,
said container having a rectangular configuration with a floor,
four wall, and an open top; a megasonic transducer array mounted to
the floor of the container, said array comprising a frame for
holding two or more transducers, said transducers arranged in
parallel and aligned transverse to the intended direction of the
wafers, each transducer comprising a piezoelectric element bonded
to a odd quarter wave length quartz plate, said odd quarter wave
length quartz plate having first and second planar surfaces
separated from each other by the thickness of the quartz plate,
said first planar surface facing the floor of the tank for coupling
sonic energy from the transducers into the cleaning fluid in the
tank and the second planar surfaces bonded to the piezoelectric
element; and one or more electrical cables connected to the
piezoelectric elements and extending from the element to a source
of electrical energy.
7. The megasonic cleaning apparatus of claim 6 wherein said quartz
plates, piezoelectric elements and said connections to the cables
all encapsulated in a material that resists intrusion from liquid
in the container.
8. The megasonic cleaning apparatus of claim 7 wherein the
encapsulating material comprises silicone.
9. The megasonic cleaning apparatus of claim 6 wherein the
transducer array further comprises a rectangular frame for
supporting the quarter wave plates and the piezoelectric
elements.
10. The megasonic cleaning apparatus of claim 6 further comprising
an odd quarter wave plate coupled to the surface of the transducers
and having a thickness that is an odd quarter wave length of sound
waves transmitted by the transducers.
11. The megasonic cleaning apparatus of claim 6 further comprising
a megasonic generator for generating megasonic electrical signals,
an odd quarter wave plate coupled to the surface of the transducers
and having a thickness that is an odd quarter wave length of
selected megasonic waves transmitted by the transducers, and means
for adjusting the megasonic generator to generate electrical
signals that correspond to the selected sound waves.
12. The megasonic cleaning apparatus of claim 6 further comprising
a class D amplifier and a matching transformer for generating
electrical signals that are matched to electro-sonic
characteristics of the transducers for generating megasonic sound
waves in the cleaning fluid.
13. A method for megasonic cleaning semiconductor wafers comprising
the steps of: generating two or more parallel sets of megasonic
waves in a cleaning fluid; immersing semiconductors in the cleaning
fluid; moving the wafers in the cleaning fluid along a path
transverse to the megasonic waves and traversing said path two or
more times.
14. The method of claim 13 wherein the megasonic waves are
generated across parallel regions of the fluid and the step of
moving the wafers comprises reciprocating the wafers through said
parallel regions.
15. A method for megasonic cleaning semiconductor wafers comprising
the steps of: generating megasonic waves with a laminar energy wave
front in a cleaning fluid in a container; and intercepting the
generated waves inside the container and dispersing the waves in a
divergent manner.
16. A megasonic cleaning apparatus comprising: a container for
holding a cleaning fluid and a plurality of semiconductor wafer,
said container having a rectangular configuration with a floor,
four wall, and an open top; a megasonic transducer array mounted to
the floor of the container, said array comprising a frame for
holding one or more transducers, each transducer comprising a
piezoelectric element bonded to transmitting plate for coupling
megasonic energy from the piezoelectric elements into the cleaning
fluid; a cylindrical rod disposed in the container above the
transducers for intercepting laminar sonic energy transmitted from
the transducers in a regular pattern and re-distributing said sonic
energy to the rest of the container in a divergent pattern; one or
more electrical cables connected to the piezoelectric elements and
extending from the element to a source of electrical energy.
17. The megasonic cleaning apparatus of claim 16 wherein the
transmitting plates, piezoelectric elements and said connections to
the cables all encapsulated in a material that resists intrusion
from liquid in the container.
18. The megasonic cleaning apparatus of claim 16 wherein the
encapsulating material comprises silicone.
19. The megasonic cleaning apparatus of claim 16 wherein the
transmitting plates comprises quartz plates having a thickness
corresponding to an odd quarter wave length of the megasonic
energy.
20. A megasonic cleaning apparatus comprising: a container for
holding a cleaning fluid and a plurality of semiconductor wafer,
said container having a rectangular configuration with a floor,
four wall, and an open top; a megasonic transducer array mounted to
the floor of the container, said array comprising a frame for
holding one or more transducers, each transducer comprising a
piezoelectric element bonded to transmitting plate for coupling
megasonic energy from the piezoelectric elements into the cleaning
fluid and an electrical cable connected to the piezoelectric
elements; each transmitting plate comprising a quartz plates having
a thickness corresponding to an odd quarter wave length of the
megasonic waves generated by the piezoelectric elements.
21. The megasonic cleaning apparatus of claim 20 wherein the
transmitting plates, piezoelectric elements and said connections to
the cables all are encapsulated in a material that resists
intrusion from liquid in the container.
22. The megasonic cleaning apparatus of claim 20 wherein the
encapsulating material comprises silicone.
23. An apparatus for generating ozonated water comprising: a
housing for holding fluid and having first and second inlets; a
first inlet for receiving water; an ozone dispersion filter
connected to the second inlet and disposed in the container for
dispersing ozone into the water in the container; and an outlet
coupled to the container for removing ozonated water from the
container.
24. The apparatus of claim 23 wherein the filter comprises
polytetrafluroethylene.
25. A method for generating ozonated water comprising the steps of;
pumping deionized water into a sealed housing; pumping ozone into a
filter in the housing at a pressure greater than the pressure of
the water; withdrawing ozonate water from the housing through a
restricted orifice in order to maintain the pressure in the housing
for dissolving the ozone into the water in an amount equal to or
greater than 7 parts per million.
26. The method of claim 25 wherein the temperature of the water is
approximately 20 degrees centigrade.+-.two degrees centigrade.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 09/829,634, filed Apr. 10, 2001 (Attorney
Docket No. 87552.99R093/SE-1395PD.B), which is a divisional of U.S.
patent application Ser. No. 09/344,867, filed Jun. 28, 1999
(Attorney Docket No. 87552.99R091).
BACKGROUND OF THE INVENTION
[0002] This invention relates in general to transducer assemblies
and, in particular, to improvements in methods and apparatus for
megasonic semiconductor wafer cleaning.
[0003] Megasonic energy and waves are used to clean and remove
particles from the surface of semiconductor wafers during wafer
processing into devices and integrated circuits. High frequency
acoustic energy is termed megasonic for frequencies in the range of
0.5 MHZ and 2 MHZ or higher. Acoustic energy is termed ultrasonic
when frequencies range from 20 KHZ to 0.5 MHZ.
[0004] Megasonic cleaning is used at many stages in the fabrication
process for removing particles, photoresist, dewaxing and
degreasing using different solvents and stripping solutions. It has
also been shown that megasonic energy will aid in the removal of
particulates (.gtoreq.0.1 micron) that are tightly adhered to the
wafer surface. The primary advantages of using megasonic cleaning
is that it saves in the cost of chemical cleaners, provides
superior cleanliness and simultaneously cleans both sides of the
wafers, thereby requiring less handling.
[0005] Existing megasonic cleaning systems have several drawbacks.
In a typical megasonic transducer, a monoclinic quartz
piezoelectric crystal is mounted on a quartz plate. The megasonic
energy from the crystal is transmitted through the quartz plate
into the cleaning solution. The quartz plate may be exposed to the
cleaning solution or may transmit the megasonic energy through the
tank floor. A typical tank is made of natural polypropylene that
does not readily transmits megasonic waves. The thickness of the
quartz plate is critical for maximum transmission of the megasonic
energy into the cleaning solution.
[0006] The back side of the quartz piezoelectric crystal has a bus
bar for receiving electrical energy from a cable. The bus bar and
the cable connection are typically left open and uninsulated. It
has been observed that over time, corrosive fumes escaping from the
cleaning solution in the open tank corrode the bus bar and cable
connection. While others have completely encapsulated the quartz
piezoelectric element, the encapsulation of the surface of the
piezoelectric element that faces the quartz plate requires
substantial modifications in the size of the plate so that acoustic
energy is properly transmitted to the cleaning solution. See, for
example, U.S. Pat. No. 5,355,048.
[0007] In a typical megasonic cleaning apparatus, one or more
transducers are placed at the bottom of the cleaning tank and are
substantially in line with one another. These transducers generate
columns of standing wave megasonic energy that extend from the
bottom of the tank to the top. Studies have revealed that these
standing waves often have dead zones or stagnant zones where the
megasonic energy has reduced power. If the wafers or portions of
the wafers are disposed in those stagnant zones, those wafers or
portions of the wafers will not be cleaned as well as the rest of
the wafers. In order to remedy this problem, others have proposed
moving the wafers from side to side or rotating the wafers. See,
for example, U.S. Pat. Nos. 5,427,662 and 5,520,205. Still others
have fashioned hollow cylindrical quartz plates with corresponding
cylindrical piezoelectric crystals or have provided solid half
cylindrical quartz plates fixed to the bottom of the tank for
dispersing the sonic energy. See, for example, U.S. Pat. Nos.
4,869,278 and 4,998,549.
[0008] Once the wafers have been cleaned, it is important to
provide a thin native oxide layer on the wafers as soon as possible
in order to prevent contamination of the wafer during its
fabrication. Native oxide readily forms on bare silicon wafer
surfaces with or without ozone. However when it is formed slowly or
in a uncontrolled manner it will tend to incorporate high levels of
SiOx particles or other contaminants. Using high levels of ozone
(.gtoreq.7 ppm) helps to form a quick and clean native oxide. Such
a native oxide layer can be provided by subjecting the wafers to a
bath of ozone-rich water. However, current techniques for ozonating
water are inadequate. The ozone quickly leaves the water bath and
so the wafers do not receive the desired native oxide layer.
SUMMARY
[0009] The invention provides solutions for the above described
shortcomings of the prior art. One of the features of the invention
is a silicon elastomer to pot or encapsulate the back surface only
of the connection between the bus bar and the cable. This invention
avoids the difficulties of providing insulation between the
piezoelectric crystal and the quartz plate. By potting only the
back surface of the bus bar and cable connection, the transmission
structure of the quartz wave plate and the quartz crystal remain
unaltered. The potting prevents the fumes from corroding or
otherwise damaging the electrical connection between the cable and
the bus bar itself and the quartz transducer.
[0010] The invention provides two solutions for dispersing sonic
energy over the wafers. The first solution provides a double pass
structure and method. In this solution, the transducers comprise
two or more transducers arranged parallel to each other along the
bottom of the tank and orthogonal to the vertical position of the
wafers or product to be cleaned. The wafers are inserted into the
tank and then are moved reciprocally at least twice along a path
that is substantially perpendicular to the columns of megasonic
energy created by the parallel transducers. This method ensures
that each wafer passes through the maximum megasonic energy at some
point during their transfer through the megasonic energy.
[0011] The second solution for dispersing the megasonic energy
provides in a structure that uses typical in-line transducers and a
cylindrical quartz rod. The cylindrical quartz rod is disposed in
the cleaning apparatus and above and separated from the
transducers. The cylindrical rod intercepts megasonic waves
emanating from the quartz plate at the bottom of the tank and
disperses and re-directs the waves away from their intended
vertical path.
[0012] Finally, the invention provides an ozone-capturing apparatus
and method. This apparatus and method uses a reverse
polytetrafluroethylene (Teflon) filter. The filter is immersed in a
housing of water. Ozone is pumped into the filter under pressure
with a check valve to prevent the back flow of ozone. The receiving
housing is filled with water and is likewise sealed. The ozone
under pressure is forced out of the Teflon filter and into the
surrounding water. The ozonated water is withdrawn from the base of
the housing and is passed to a wafer ozone bath for applying the
ozonated water to the wafer. With the ozonated water applied to the
wafer, the wafers quickly acquire a thin layer of virtually
contaminant free native oxide. That layer of native oxide aides in
protecting the wafers from further contaminants during the further
wafer processing. Note that native oxide is self-limiting in its
growth, with the final thickness (usually <50.ANG.) dependant on
the ambient, temperature and pressure under which it is formed.
DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a sectional view showing a potted transducer and
megasonic apparatus with parallel transducers.
[0014] FIG. 2 is a top view of the megasonic apparatus of FIG.
1.
[0015] FIG. 3 is an expanded sectional view of the transducer of
FIG. 1.
[0016] FIG. 4 is an expanded top view of the transducer shown in
FIG. 3.
[0017] FIG. 5 is a partial perspective view of in-line potted
transducers.
[0018] FIG. 6 is a sectional view of the transducer shown in FIG.
5.
[0019] FIG. 7 is a sectional view of a megasonic apparatus with a
cylindrical dispersion rod.
[0020] FIG. 8 is a partial perspective view of the dispersion rod
and the transducer of FIG. 7.
[0021] FIG. 9 is an end view showing the wafer and the dispersed
megasonic waves produced by the transducer in the cylindrical
rod.
[0022] FIG. 10 is a schematic diagram of the ozonated water
apparatus.
DETAILED DESCRIPTION OF THE DRAWINGS
[0023] With reference to FIGS. 1 and 2, there is shown a megasonic
apparatus 10 that includes a container 5 with endwalls 12, 14 and
sidewalls 13F, 13R. The container is filled with a cleaning fluid
9. A plurality of semiconductor wafers 22 are held in a wafer boat
20 that is supported above the tank by a conventional carriage or
robotic arm (not shown). The transducer 30 is mounted to the floor
16 of the container. As shown in FIG. 2, a pair of quartz plates
52, 54 face the floor of the container 16. Quartz plates are
mounted to piezoelectric transducers 42, 44. Those transducers
convert electrical energy into megasonic sound waves. Electrical
energy is supplied to the transducers by bus bars 18, 19,
respectively. The bus bars are coupled via cables 38, 39 to
oscillators that generate electrical signals for actuating the
piezoelectric crystals 42, 44. Screws 33a, 33b and 32a, 32b couple
the transducer frame 30 to the floor 16.
[0024] With reference further to FIGS. 3 and 4, there is shown a
gasket 45 that is disposed around the periphery of the top surface
of the transducer 30. The transducer 30 includes sidewalls 31, 35,
endwalls 36, 37 and a center wall 34. The gasket 45 is preferably
made of any suitable, flexible insulating material. The preferred
gasket is made of Gortex.RTM.. The quartz plate, crystal and bus
bar assembly is mounted on the top side of the frame. The remaining
cavity behind the bus bars 18, 19 is filled with a suitable
insulation material 55. The insulation material 55 may be any
suitable potting material, for example, a silicone elastomer. The
silicone elastomer material seals the bus bar and the cable
connection from corrosive fumes that escape the open top of the
container 5.
[0025] In operation, the megasonic transducers 30 generate parallel
columns of standing megasonic waves. The wafers 22 are lowered in
their wafer boat 20 into the cleaning fluid 9. The carriage or
robotic arm translates the wafers in the direction shown by arrow
6. This direction is transverse to the column of standing megasonic
waves. By passing through the standing columns of megasonic waves
in a first direction and then in the opposite direction, the wafers
are all exposed to substantial megasonic energy and no one wafer is
permanently resident in a stagnant zone.
[0026] An alternate potted embodiment of the invention is shown in
FIGS. 5 and 6. There, in-line transducers 60.1, 60.2 include
piezoelectric elements 61.2, 61.2. On top of the piezoelectric
elements are, respectively, quartz plates 62.1 and 62.2. Bus bars
63.1 and 63.2 carry electrical energy from cables 64.1 and 64.2 to
the piezoelectric elements 61.1, 61.2. Potting materials such as
silicone elastomer 65 fills the back side of the cavity of the
transducer frame.
[0027] In both of the above embodiments, the quartz plates are
sized to a thickness that corresponds to an odd quarter wavelength
of the megasonic wave. By an odd quater wavelength is meant a
number of quarter wavelengths where the number is one of a sequence
of natural numbers beginning with one and counting by twos and are
not divisible by two. In these embodiments, it is preferred that
the odd quarter wavelength be a number of 0.177 inches and is
preferably in a range of 0.150 inches to 0.200 inches or a multiple
thereof The quartz plate is chosen to be an odd quarter wavelength
in order to provide a desired acoustic matching between the
piezoelectric crystal, the megasonic waves, and the cleaning fluid
9. By choosing an odd quarter wavelength maximum energy transfer is
obtained with little or no absorption of the energy by the quartz
plate.
[0028] Turning now to FIGS. 7-9, there is shown an alternate
embodiment for dispersing the megasonic energy throughout the
container. In this embodiment, a cylindrical rod 72 is spaced from
the floor of the tank 71 and is supported by supports 74, 73
located at opposite ends of the rod. A transducer 75 with a quartz
plate 76 is located beneath the rod 72. Although only one
transducer is shown in the figures, those skilled in the art will
appreciate that two or more transducers may be arranged in line
with each other as shown in FIGS. 5 and 6. In operation, megasonic
energy emitted from the quartz plate 76 is intercepted by the rod
72. As shown in FIG. 9, the rod 72 is located in the cleaning fluid
and between the floor of the tank and the wafers 86. When the rod
72 intercepts the megasonic waves, it disperses them throughout the
cleaning fluid 9. This dispersion avoids the problems inherent in
standing waves. Thus, the megasonic energy is dispersed throughout
the cleaning fluid 9 and all of the wafers 86 are substantially,
evenly cleaned but at a lower power density than can be realized by
the first solution of a very focused laminar power dispersion.
[0029] Turning to FIG. 10, there is shown an improved apparatus for
dissolving ozone into water. In prior art techniques, surface
passivation is provided by hydrogen peroxide. However, it has been
found that hydrogen peroxide may contain metallic contaminants
which are undesirable. It is desired that the ratio of ozone to
water should be more than 7 parts per million in order to achieve a
rapid silicon surface conversion to a native oxide. Improper ozone
levels result in silicate particulates.
[0030] In the inventive apparatus, a polytetrafluroethylene
(Teflon) filter 103 is immersed in a sealed water housing 102.
Ozone is introduced through an inlet line 104 that has an in-line
check valve 101. The Teflon filter allows the ozone 103 to dissolve
into the water in the housing 102. The ozonated water is then
discharged through discharge outlet 105. That water is then placed
into a container where the wafers are rapidly oxidized leaving a
thin oxide layer with virtually no metallic or organic
contamination. The inlet 104 carries highly deionized water. The
ozone is introduced into the water through a high purity Teflon
filter housing that contains a 0.1 micron Teflon filter cartridge.
The filter openings must be large enough to permit ozone to flow
from through the openings and into the housing 102. Since the ozone
and the water are mixed in a sealed environment 102, there is
little or no free ozone in the discharge fluid. The ozonating
operation is normally carried out at a temperature of about 20
degrees C.,.+-.2 degrees C. Lower temperatures will result in more
ozone dissolving in the water. In the preferred emboidiment, the
discharge fluid from orifice 130 is at least 7 parts per million of
ozone.
[0031] The above examples are not intended to limit the spirit and
scope of the invention. Those skilled in the art understand that
further additions, modifications and changes may be made to the
invention without department from the appended claims.
* * * * *