Ultrasonic jet semiconductor wafer cleaning apparatus

An ultrasonic jet semiconductor wafer cleaning apparatus for removing debris from a surface of a semiconductor wafer as the wafer is rotated about a prescribed axis in a cleaning plane is disclosed. The apparatus comprises a housing having a principal axis, an inlet port, and an outlet port; a means for producing focused ultrasonic waves of acoustic energy concentric with and incident the outlet port to form a jet stream of cleaning liquid released through the outlet port; a focal point positioning means for adjustably positioning a focal point of the focused ultrasonic wave producing means between a first focal point position and a second focal point position along an axis; and a means coupled to the housing for sweeping the housing in an reciprocating manner along a sweep path.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to semiconductor wafer cleaning 
apparatus, and more particularly, to an ultrasonic jet cleaning apparatus 
for cleaning of semiconductor wafers. 
2. Discussion of the Related Art 
During the manufacture of semiconductor devices, there are many stages that 
require cleaning of a silicon wafer or microelectronic parts. A common 
method for cleaning of silicon wafers or microelectronic parts is to use 
spin clean systems or tools. These spin clean systems involve the use of a 
high pressure water jet, on the order of 1200 psi., the high pressure 
water jet being vertically directed and incident upon a rotating part to 
be cleaned, the part being positioned therein below. The part is typically 
disposed in a plane which is at right angles to the incident jet stream. 
The nozzle of the jet is attached to a reciprocating arm so that the 
entire part can be accessed. Often, the high pressure of the water column 
causes damage, particularly when repaired circuits are subjected to the 
jet stream. A mathematical analysis of the forces exerted by the 
conventional spin clean tool indicates very large horizontal forces in the 
region of the boundary layer of the jet at the cleaning plane. These 
forces are at times strong enough to destroy a repair metallurgy of the 
repaired circuit since typical circuit lines are vulnerable to shear 
forces. High pressure water jets are further disadvantageous in that high 
water pressure greatly increases the buildup of electrostatic charge, 
which, if sufficiently high, is followed by a discharge. Such discharges, 
if allowed to occur can destroy circuit elements on a wafer. 
Another disadvantage of such high pressure spin clean tools is that they 
are not economically well suited for a high volume manufacturing 
environment. That is, such spin clean tools require relatively expensive 
use of large quantities of ultra-pure deionized (DI) water and the use of 
high pressure filters necessary to maintain both a high pressure and a 
purity of the water. Additionally, nozzles of such high pressure spin 
clean tools are subject to considerable wear under the high water 
pressures and generally require frequent replacement. Furthermore, 
additional disadvantages of using such high pressure spin clean tools 
include relatively high costs associated with both replacement parts and 
physical labor required for replacement installation, not to mention, 
problems generated as a result of process down time. 
In "Spin-Clean Ultrasonic Jet Cleaner", IBM Technical Disclosure Bulletin, 
Vol. 34, No. 1, June 1991, pp. 449-450, a modified spin-clean device is 
disclosed. The modified spin-clean device provides a low pressure water 
jet operating at pressures on the order of 7.5 psi. A transducer contained 
within a chamber of the device provides ultrasonic energy which is 
directed into the water jet near an output nozzle. A disadvantage of such 
a modified spin-clean device is that the device is not well suited for a 
variety of cleaning applications. That is, the use of the acoustic energy 
is not easily optimized for the cleaning of parts having various cleaning 
requirements. Furthermore, the modified spin-clean device suffers from 
ill-effects of undue water turbulence within the chamber of the device, 
whereby optimal transfer of acoustic energy to the workpiece via a liquid 
jet is not attainable. The modified spin-clean device does not include 
means for optimizing or measuring an acoustic energy, nor does it provide 
for control of a cleaning liquid flow pattern. 
There is thus needed an apparatus for cleaning semiconductor wafers or 
microelectronic parts providing a low pressure liquid jet capable of 
highly efficient energy transfer from an ultrasonic transducer for 
enhanced cleaning efficiency. Such an apparatus should further be well 
suited for providing a desired cleaning performance as needed according to 
the particular requirements of the part being cleaned. Still further, such 
an apparatus should be well suited for use in a high volume manufacturing 
environment. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a spin-clean apparatus 
which overcomes the above-mentioned problems and disadvantages. 
Another object of the present invention is to provide an optimal low 
pressure liquid jet produced by a highly efficient transfer of focused 
ultrasonic waves of acoustic energy into the liquid jet and more 
particularly, onto the surface of the workpiece. 
According to the invention, a semiconductor wafer cleaning apparatus, for 
removing debris from a surface of a semiconductor wafer as the wafer is 
rotated about a prescribed axis in a cleaning plane, comprises a housing, 
a focused ultrasonic wave producing means, a focal point positioning 
means, and a sweeping means. The housing has a principal axis, an inlet 
port for receiving a cleaning liquid from a supply, and an outlet port 
concentric about the principal axis for releasing the cleaning liquid 
therethrough. The focused ultrasonic wave producing means is located 
within the housing along the principal axis thereof for producing 
ultrasonic waves of acoustic energy focused to a focal point wherein 
acoustic energy density is maximum at the focal point. The focused 
ultrasonic waves of acoustic energy are concentric with and incident the 
outlet port to form a jet stream of cleaning liquid released through the 
outlet port, wherein the jet stream of cleaning liquid is characterized by 
longitudinal forces and non-cavitation of the cleaning liquid. The focal 
point positioning means adjustably positions the focal point of the 
focused ultrasonic wave producing means between a first focal point 
position and a second focal point position along the principal axis of the 
housing. Lastly, a sweeping means coupled to the housing sweeps the 
housing in a reciprocating manner along a prescribed sweep path over the 
cleaning plane, wherein the outlet port is positioned in a direction of 
the cleaning plane and the principal axis is substantially perpendicular 
to the cleaning plane.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIGS. 1 and 2, a cleaning apparatus 10 according to the 
present invention shall be described. Cleaning apparatus 10 shall be 
described with reference to the cleaning or removing of debris from a 
surface on a semiconductor wafer or workpiece 12 as the wafer is rotated 
about a prescribed axis in a cleaning plane (indicated by numeral 11 in 
FIG. 3). Wafer 12 is securably held in the cleaning plane on a rotatable 
platen or the like, as is well known in the art, wafer 12 further being 
positioned within a basin 4. A motor 5 provides rotational motion to wafer 
12 as controlled by a controller 6. Controller 6 may comprise a suitable 
control means such as a computer controller or the like, programmed for 
the desired operation of motor 5. Programming of a computer controller is 
well known in the art and therefore not discussed in detail herein. While 
the discussion to follow makes reference to the cleaning of a wafer 12, it 
should be noted that cleaning apparatus 10 may be suitable for cleaning of 
other similar objects, such as magnetic disks for example. Cleaning 
apparatus 10 includes a liquid jet cell 13 and comprises a housing 14, a 
focused ultrasonic wave producing means 16, a focal point positioning 
means 18, and a sweeping means 20. 
Cleaning liquid from a supply (not shown) can typically be fed into liquid 
Jet cell 13 via a valve 7, a pressure regulator 8, and a filter 9. Valve 7 
can comprise any suitable electronically controllable valve, electrically 
connected to controller 6 for control thereof. Regulator 8 comprises any 
suitable regulator for regulating the pressure of the cleaning liquid to 
be in a low pressure range of approximately 1 to 25 psi. Filter 9 can 
comprise any suitable known filter for filtering the cleaning liquid 
therethrough. A flexible tubing 3 connects between filter 9 and housing 14 
of liquid jet cell 13. 
Referring now to FIG. 3, housing 14 of liquid jet cell 13 comprises a 
chamber having a principal axis 15 and is further characterized by first 
and second portions, 22 and 24, respectively. Housing 14 may be 
constructed out of any suitable material, for example, metal, for 
providing at a minimum the desired features described hereinafter. First 
portion 22 constitutes an upper portion of housing 14 and includes an 
inlet port 26 for receiving a cleaning liquid via flexible tubing 3 from a 
supply (not shown). Inlet port 26 is preferably positioned on portion 22 
so as to minimize any turbulent flow of a cleaning liquid as the cleaning 
liquid is introduced into housing 14 during operation and use. 
Second portion 24 constitutes a lower portion of housing 14 and includes an 
outlet port 28 for releasing cleaning liquid therethrough. Second portion 
24 is characterized by an inner wall 25 having a tapered shape in the form 
of an inverted cone. More particularly, the inner wall 25 of portion 24 
substantially matches an inner wall 23 of portion 22 at a boundary 
therebetween, and inner wall 25 is thereafter tapered down to a dimension 
substantially matched to the size of the outlet port 28. The conically 
tapered shape of the inner wall 25 of portion 24 assists in the reduction 
of turbulent flow of liquid within housing 14 to a minimum. 
Outlet port 28 is preferably concentric about the principal axis 15. Outlet 
port 28 comprises a nozzle having a cross-sectional diameter on the order 
of between 0.5 and 1.0 mm (i.e., 500 to 1,000 microns). Outlet port 28 is 
a suitable nozzle for promoting laminar flow, such as is well known in the 
art. Outlet port 28 preferably comprises a conically shaped tapered 
machined orifice in a metal plate 29, as shown in FIG. 3. The orifice 
further comprises a highly polished smooth surface. 
Focused ultrasonic wave producing means 16 is located within said housing 
14 along the principal axis 15 thereof. Focused ultrasonic wave producing 
means 16 produces ultrasonic waves of acoustic energy focused to a focal 
point 30 wherein an acoustic energy density is maximum at the focal point 
30. Preferably, focused ultrasonic wave producing means 16 comprises an 
ultrasonic transducer having a concave surface 32 for providing focused 
ultrasonic waves of acoustic energy with an acoustic focal length of 1.6 
cm and capable of an acoustic power density of 5,000 Watts per square 
centimeter (W/cm.sup.2). Transducer 16 may comprise a suitable transducer 
such as is commercially available from Precision Acoustic Devices, Inc. of 
Fremont, Calif. Focused ultrasonic wave producing means 16 should be 
operable at a frequency within the range of 0.1 MHz to 100 MHz. 
Focused ultrasonic wave producing means 16 is energized by a suitable radio 
frequency (RF) generator 17, generator 17 being electrically connected to 
means 16. RF generator 17 is preferably controlled by controller 6 for 
providing a desired RF signal output to means 16. That is, RF generator 17 
is controlled by controller 6 for enabling focused wave generating means 
16 to be operable at a frequency within the range of 0.1 MHz to 100 MHz. 
Focused ultrasonic wave producing means 16 is suitably positioned within 
housing 14, as will be discussed in further detail herein below, such that 
the focused ultrasonic waves of acoustic energy produced thereby are 
concentric with and incident the outlet port 28. That is, the concave 
surface of transducer 16 for producing focused ultrasonic waves is 
oriented within housing 14 towards outlet port 28. 
A focal point positioning means 18 adjustably positions the focal point 30 
of focused ultrasonic wave producing means 16 along the principal axis 15 
of housing 14, as indicated by arrow 34, and more particularly, between a 
first focal point position (as shown in FIG. 3) and a second focal point 
position (as shown in FIG. 4). That is, the focal point 30 of transducer 
16 may be positioned by means 18 at any desired position over the range 
between the first focal point position and the second focal point 
position. Preferably, positioning means 18 comprises a suitable means for 
translating ultrasonic transducer 16 between a first transducer position 
and a second transducer position along the principal axis of said housing 
to correspondingly position the focal point of ultrasonic transducer 16 
between a first focal point position within housing 14 along the principal 
axis 15 proximate to the outlet port 28 and a second focal point position 
beyond housing 14 along the principal axis 15. For instance, positioning 
means 18 may comprise any suitable positioning means attached to 
ultrasonic wave producing means 16 and housing 14 for translating 
transducer 16, such as, a controllable screw mechanism, a hydraulicly 
controlled linear spacer, a piezoelectric device spacer, or the like. 
Referring again to FIG. 3, further included within housing 14 is a means 36 
coupled within housing 14 for reducing turbulent flow of the cleaning 
liquid within the housing 14 to a minimum. Turbulent flow reduction means 
36 is positioned within housing 14 to be intermediate portions 22 and 24. 
The turbulent flow reduction means 36 preferably comprises an aperture 
plate coupled within housing 14 substantially perpendicular to the 
principal axis 15 thereof. Aperture plate 36 includes a series of 
apertures therein, one aperture being a central aperture for receiving the 
focused ultrasonic wave producing means 16 therebetween. The remainder of 
apertures are of a suitable size and are arranged around the focused 
ultrasonic wave producing means 16 to promote laminar flow of the cleaning 
liquid within portion 24 of housing 14. A suitable means, such as an 
0-ring gasket, is provided between the aperture plate 36 and transducer 
16, to provide a substantially leak-proof seal therebetween while allowing 
for relative movement between the two parts to occur, as will be explained 
herein below. 
Referring once again to FIGS. 1, 2, and 3, sweeping means 20 is suitably 
coupled to housing 14 for sweeping housing 14 in a reciprocating manner, 
as indicated by arrow 39, along a prescribed sweep path 38 over the 
cleaning plane 11 of wafer 12. Sweeping means 20 maintains housing 14 in a 
desired orientation, wherein the outlet port 28 is positioned in a 
direction of the cleaning plane 11 and wherein the principal axis 15 of 
housing 14 is substantially perpendicular to the cleaning plane 11. 
Sweeping means 20 further provides an appropriate vertical spacing of 
housing 14 above cleaning plane 11 (and thus, wafer 12) according to the 
requirements of a particular cleaning operation (e.g., a spacing distance 
on the order of 0.05 to 5 centimeters). Sweeping means 20 can comprise, 
for example, a sweep arm 40 attached to a reciprocating motor 42, the 
sweep arm 40 being of suitable dimension to provide travel of housing 14 
along the desired sweep path 38, and further attached suitably to 
reciprocating motor 42 to provide a desired vertical spacing of housing 14 
above cleaning plane 11, as discussed above. Reciprocating motor 42 is 
electrically connected to controller 6 for suitable control thereof, that 
is, for controlling the sweeping of housing 14 in a desired manner, as 
will be discussed further below. 
Referring now to FIGS. 1, 2, and 5, a calibration signal means 44 is 
positioned at a calibration position 46 along the prescribed sweep path 
38, the calibration signal means 44 having a top surface thereof located 
at the cleaning plane 11. Calibration signal means 44 preferably comprises 
an ultrasonic transducer having a substantially planar detection surface 
45. Transducer 44 is for use in a detection mode, that is, for generating 
a calibration signal representative of an acoustic energy intensity 
contained in the jet stream at the cleaning plane. An electrical output 
signal wire 48 of calibration signal means 44 is connected to controller 
6. Controller 6 is suitably programmed to be responsive to the calibration 
signal for controlling focal point positioning means 18 to position the 
focal point to a desired position, as will be further explained below, 
whereby the acoustic energy intensity within the jet stream produced by 
apparatus 10 at the cleaning plane 11 is adjustable to a desired level. 
In operation, a wafer 12 having a surface to be cleaned is rotated by motor 
5 controlled by controller 6. Controller 6 operates valve 7 to allow 
cleaning liquid, for example, deionized water, to flow under low pressure 
into inlet port 26 of housing 14. The water fills both portions 22 and 24 
of housing 14. Turbulent flow of the cleaning liquid is minimized as the 
liquid passes from portion 22 into portion 24 via aperture plate 36. That 
is, aperture plate 36 encourages laminar flow of the liquid, in the 
direction of the ultrasonic waves of acoustic energy, to thereby avoid the 
bouncing of the liquid off the inner wall 25 of portion 24. In other 
words, undesirable reflections giving rise to turbulence in the liquid are 
minimized. As a result, with minimum turbulence, the phase of the 
ultrasonic waves is advantageously maintained and energy from the focused 
ultrasonic wave producing means 16 in the cleaning liquid is optimized. 
Controller 6 energizes RF generator 17 to energize focused ultrasonic wave 
producing means 16. Upon energization of means 16, focused ultrasonic 
waves of acoustic energy are produced, focusing to focal point 30. The 
orientation of means 16 within housing 14 produces a low pressure 
insonified ultrasonic jet of cleaning liquid released through outlet port 
28, the jet having a cross-sectional area substantially equal to the 
cross-sectional area of outlet port 28. The jet of cleaning liquid 50, or 
liquid jet stream, provides a column of cleaning liquid to clean the 
surface of wafer 12, the jet of cleaning liquid also confining the 
ultrasonic waves of acoustic energy at the cleaning liquid/air interface. 
This occurs due to the acoustic impedance mismatch at the cleaning 
liquid/air interface which gives rise to a high acoustic reflection 
coefficient, preventing acoustic energy from escaping from the liquid out 
into the air. Furthermore, the acoustic energy propagates in a direction 
that is co-linear with the jet stream 50. In addition, as the cleaning 
liquid leaves outlet port 28, acoustic energy confined within jet stream 
50 propagates co-linearly within jet stream 50 between the outlet port 28 
and the cleaning plane 11 (or wafer 12). 
The present invention advantageously achieves excellent cleaning capability 
with the jet stream 50 of cleaning liquid while avoiding undesirable 
cavitation of the cleaning liquid. In addition to the previously discussed 
problems in the art, cavitation in a cleaning liquid may not be desirable 
when cleaning highly delicate parts. That is, cavitation is the implosion 
of air within a liquid, resulting in uncontrollable collapsing or break-up 
of the liquid. Such cavitation, when present in a cleaning liquid during 
the cleaning of delicate microelectronic parts, or the like, subjects the 
parts to an undue risk of damage to the same. Cavitation in the cleaning 
liquid can be further characterized by a non-uniform acoustic energy 
distribution at the cleaning surface which in turn gives rise to surface 
erosion and other possible damage. 
According to the present invention, means 16 is operated at a high 
frequency in the range of 0.1 MHz to 100 MHz to advantageously reduce the 
probability for cavitation of the cleaning liquid to occur. In a preferred 
embodiment, means 16 is operated at 10 MHz to provide a power density of 
5,000 W/cm.sup.2 at the focal point 30 and thereby avoid exceeding a 
cavitation threshold, the cavitation threshold for 10 MHz energization 
occurring at approximately 100,000 W/cm.sup.2, the threshold further being 
a minimum limit at which cavitation can begin to occur. Thus, the liquid 
jet 50 produced by jet cell 13 presents no undue hazard to delicate parts 
being cleaned. 
Controller 6 can operatively position the focal point 30 of means 16 
between a first focal point position and a second focal point position, 
according to the requirements of a particular object or wafer being 
cleaned. Varying the position of focal point 30 effectively adjusts an 
intensity of acoustic energy at the cleaning plane to achieve various 
desired cleaning results. 
In a first focal point position, as shown in FIG. 3, the jet of cleaning 
liquid 50 is characterized by longitudinal forces and non-cavitation of 
the cleaning liquid at the cleaning plane. The focal point 30 is proximate 
to outlet port 28 wherein, the focused ultrasonic waves of acoustic energy 
are efficiently transmitted via the cleaning liquid onto the wafer 12, the 
cleaning liquid effectively functioning as an energy waveguide. The 
intensity of the acoustic energy at the cleaning surface will be a 
function of the internal energy reflections within the jet stream. In 
addition, acoustic energy within jet stream 50 is spread or distributed 
over an effective area approximately equal to the cross-sectional area of 
the jet stream prior to contacting wafer 12 or the cleaning plane 11. 
In a second focal point position, as shown in FIG. 4, the jet of cleaning 
liquid 50 is also characterized by longitudinal forces and non-cavitation 
of the cleaning liquid at the cleaning plane. The focal point 30 is beyond 
to outlet port 28 wherein, the focused ultrasonic waves of acoustic energy 
are efficiently transmitted via the cleaning liquid onto the wafer 12. 
With the focal point 30 located at the wafer 12 in the cleaning plane 11, 
the cleaning liquid no longer serves to reflect the acoustic energy along 
its length. Under this condition, the jet stream acts as a medium for 
transmitting the acoustic energy to the workpiece surface but not for 
reflecting the energy therein in order to confine it which is typical for 
a waveguide. The acoustic energy within jet stream 50 is concentrated 
within a cross-sectional area smaller than the cross-sectional area of the 
jet stream prior to contacting waver 12 or the cleaning plane 11. For 
example, the cross-sectional area of concentrated acoustic energy may have 
a diameter of 150 microns, whereas, the cross-sectional area of the jet 
stream 50 may have a diameter of 500 microns. The smaller cross-sectional 
area (i.e., 150 micron diameter) has an acoustic energy density 
approximately eleven (11) times greater than that of the larger 
cross-sectional area (i.e., 500 micron diameter). Such a smaller 
cross-sectional area of acoustic energy presented to the cleaning plane 
advantageously provides for more localized cleaning without cavitation or 
the occurrence of any undesirable lateral forces from the jet boundary 
layer. The intensity of the ultrasonic waves of acoustic energy is thus 
maximized at the cleaning plane 11, as a result of the focal point 30 
being positioned there. Furthermore, the increased energy density at the 
cleaning plane has a significant effect in making the removal capability 
of the jet stream 50 considerably more effective. 
To calibrate the intensity of acoustic energy at the cleaning plane, 
controller 6 moves the ultrasonic jet cell 13 to the calibration position 
46 along sweep path 38. With the ultrasonic jet cell 13 positioned over 
calibration means 44, controller 6 controls valve 7 to introduce cleaning 
liquid into housing 14 and energizes focused ultrasonic wave producing 
means 16. A jet stream 50 is produced, enabling the intensity of acoustic 
energy at the cleaning plane to be determined via calibration means 44. In 
response to the calibration signal provided by calibration means 44, 
controller 6 transmits an appropriate signal or signals to focal point 
position adjusting means 18 and the focal point position of means 16 is 
adjusted accordingly. Calibration means 44 may also be used for alignment 
purposes, i.e., for aligning jet cell 13 upon an initial set-up of 
apparatus 10 and/or during any routine maintenance thereof. 
According to the particular requirements of a cleaning operation, a 
cleaning procedure using the present invention may be as follows. Wafer 12 
is placed upon the wafer platen within basin 4 and rotated. Ultrasonic jet 
cell 13 is placed in the calibration position 46, wherein controller 6 
controls appropriate components, as described above, for adjusting the 
intensity of acoustic energy in the jet stream 50 at the cleaning plane to 
a first intensity, 5,000 W/cm.sup.2 at 10 MHz, for example. A cleaning 
operation may be conducted solely at this first intensity, wherein 
controller 6 controls i) the rotation of the wafer 12; ii) the functioning 
of ultrasonic jet cell 13 to produce the jet stream 50; and iii) the 
reciprocating motion of jet cell 13 along sweep along path 38 until the 
entire wafer has been cleaned. Alternatively, other intensities different 
from the first intensity may be used in a sequence, as necessary, for a 
particular cleaning operation. As a result of low pressure operation, 
problems associated with electrostatic discharge are advantageously 
eliminated. Furthermore, apparatus 10 is operable for relatively low cost, 
as a result of significantly reduced quantities of expensive DI water at 
low pressure necessary to perform a cleaning operation, for example. 
Referring now to FIGS. 6 and 7, in an alternate embodiment, the ultrasonic 
jet cell 13 is substantially similar to that of the preferred embodiment 
with the following exceptions. Focused ultrasonic wave producing means 16 
comprises an array of flat ultrasonic transducers 116, the array of 
ultrasonic transducers arranged and phased in a prescribed manner such 
that a proper time sequence energization of said array produces focused 
ultrasonic waves of acoustic energy focused to a focal point 30. In lieu 
of separate RF generating means 18 and positioning means 17, a positioning 
means for this alternate embodiment can comprise a signal generating means 
suitable for energizing the array 116 in such a manner for adjustably 
positioning the focal point 30 of the array of ultrasonic transducers 
between a first focal point position within housing 14 along the principal 
axis 15 proximate to the outlet port 28 and a second focal point position 
beyond the housing 14 along the principal axis. In this latter instance, 
the second focal point position is preferably at the cleaning plane 11. In 
operation, the alternate embodiment functions similarly to that of the 
preferred embodiment. 
Referring now to FIGS. 8 and 9, in another alternate embodiment of the 
present invention, the ultrasonic jet cell 13 is substantially similar to 
that of the preferred embodiment with the following exceptions. Housing 
14' includes first and second portions, 22' and 24', respectively. Second 
portion 24' constitutes a lower portion of housing 14' and includes a 
plurality of outlet ports 28' for releasing cleaning liquid therethrough. 
Second portion 24' is characterized by a plurality of inner walls 25', 
each having a tapered shape in the form of an inverted cone. More 
particularly, each inner wall 25' is tapered from a first larger diameter 
dimension down to a dimension substantially matched to the size of the 
respective outlet port 28'. The conically tapered shape of each inner wall 
25' of portion 24' assists in the reduction of turbulent flow of liquid 
within housing 14' to a minimum. The plurality of outlet ports 28' are 
concentric about a corresponding plurality of outlet port axes, each of 
the outlet port axes being parallel to the principal axis 15. 
A plurality of means 16' are located within housing 14 along respective 
axes corresponding to the plurality of outlet port axes. The plurality of 
means 16' produce ultrasonic waves of acoustic energy focused to a 
respective focal point 30' wherein acoustic energy density is maximum at 
the respective focal point. The focused ultrasonic waves of acoustic 
energy of each focused ultrasonic wave producing means 16' are concentric 
with and incident a respective outlet port 28' to form a respective jet 
stream of cleaning liquid 50' released through the respective outlet port, 
the respective jet stream of cleaning liquid characterized by longitudinal 
forces and non-cavitation of the cleaning liquid at the cleaning plane 11. 
An angular orientation .alpha. and spacing S between each respective 
focused ultrasonic wave producing means 16' of the plurality of means 16' 
is determined by the requirements of a particular cleaning requirement and 
the type of transducers used. That is, the angular orientation a and 
spacing S should at least be sufficient to ensure non-interference between 
adjacent transducers 16'. 
A means similar to positioning means 18 of the preferred embodiment may be 
utilized for positioning each respective focal point of said plurality of 
focused ultrasonic wave producing means along the respective outlet port 
axis, indicated by arrow 34', between a first focal point position and a 
second focal point position. 
A means 36' is coupled within housing 14' for reducing turbulent flow of 
the cleaning liquid within housing 14' to a minimum, wherein the turbulent 
flow reduction means 36' comprises an aperture plate coupled within 
housing 14' intermediate portions 22' and 24', and further substantially 
perpendicular to the principal axis 15. The aperture plate comprises a 
corresponding plurality of apertures for receiving the plurality of 
focused ultrasonic wave producing means 16' therethrough and a series of 
apertures arranged around said plurality of focused ultrasonic wave 
producing means. Suitable means, such as O-rings, are provided between the 
aperture plate 36' and transducers 16' to provide substantially leak-proof 
seals therebetween while allowing for relative movement between the parts 
to occur. 
In the second alternate embodiment, a calibration means similar to 
calibration means 44 can be located in the cleaning plane and positioned 
at a calibration position 46 along a prescribed sweep path 38 for 
providing a calibration signal of an acoustic energy intensity contained 
in a desired jet stream, of the plurality of jet streams, at the cleaning 
plane. Controller 6 can be made responsive to the calibration signal for 
controlling the focal point positioning means to position a respective 
focal point corresponding to the desired jet stream to a desired position, 
whereby acoustic energy intensity of the desired jet stream at the 
cleaning plane is adjusted to a desired level. In operation, the second 
alternate embodiment functions similarly to that of the preferred 
embodiment. 
There has thus been shown a cleaning apparatus for cleaning semiconductor 
wafers or microelectronic parts providing an optimal low pressure liquid 
jet capable of highly efficient energy transfer from an ultrasonic 
transducer for enhanced cleaning efficiency. The present invention is well 
suited for providing a desired cleaning performance as necessary for the 
particular requirements of the part being cleaned. Still further, the 
present invention is well suited for use in a high volume manufacturing 
environment. The present invention thus provides a spin-clean apparatus 
which overcomes the previously-mentioned problems and disadvantages. 
While the invention has been particularly shown and described with 
reference to the preferred embodiment thereof, it will be understood by 
those skilled in the art that various changes in form and detail may be 
made therein without departing from the spirit and scope of the invention. 
For example, the present invention may likewise be suitable for the 
cleaning of other objects, such as, the cleaning of magnetic disks, for 
example.