Note: Descriptions are shown in the official language in which they were submitted.
CA 02303979 2000-03-16
WO 99/15845 PCT/US98/19793
1
IMPROVED CHEMICAL DRYING AND CLEANING SYSTEM
Field of the Invention
This invention relates to a chemical system for drying and/or
cleaning semiconductor, optical, electronic and other surfaces.
Background of the Invention
In fabrication of a semiconductor wafer, an electrical or optical
component or a printed circuit board, a workpiece will be subjected to one
or more cleaning and drying processes in which, ideally, all foreign
substances that are not intended to be incorporated in the workpiece are
removed. Chenucal baths containing strong acids, strong bases or
oxidizers, such as HCI, H2SOq,, HN03, H2P03, HF, NHq,OH and H202,
are often used as part of a cleaning process. These substances are often
toxic, chemically reactive, corrosive and/or bioaccumulative and must be
handled and disposed of as hazardous substances.
Several workers have disclosed methods for drying parts, including
integrated circuits, by use of heated or superheated gases. One attractive
method uses a drying vapor of heated isopropanol (IPA), which forms a
minimum boiling azeotrope with water and is believed to displace water
2o from the wafer surfaces, and the vapor flows into the vessel at one end and
simultaneously flows out of the vessel at another end.
Other workers have disclosed use of a plurality of megasonic beam
transducers, located at staggered positions, for cleaning wafers. Each
transducer emits a vibratory megasonic beam with an unspecified (very
high) frequency in a fixed direction, and the transducer locations are
chosen so that the collection of beams irradiate, and thereby clean, all
wafer surfaces in a chamber, no matter how the wafers are arranged.
Use of ultrasonic transducers in a chemical cleaning bath to
cooperatively remove contaminants and unwanted material layers from
semiconductor wafers, medical instruments and other objects of interest is
disclosed by other workers. Still other workers have disclosed use of
ultrasonic transducers to coat, spray, deposit or otherwise apply a desired
material to an object surface, or for ultrasonic fogging.
CA 02303979 2000-03-16
WO 99/15845 PCT/US98/19793
2
These approaches use heated or superheated gases or direct beam
irradiation to dry or clean an object surface; or they use cooperative
action by an ultrasonic beam and an active chemical bath to remove
contaminants from, or to apply a desired material to, an object surface.
These approaches are complex, usually require operation at high
temperatures, often require processing times of one to several minutes,
and often require use of specially resistant chamber walls for the
processing chamber. The chemicals used are often designated as hazardous
substances, requiring special handling.
What is needed is a system that uses non-hazardous substances for
chemically cleaning and/or drying workpieces and that is reasonably
effective for removing substantially all foreign substances with diameters
above a range of sizes, such as 0.1 - 0.5 ~.m. Preferably, the system should
also be effective for removing liquids from and drying and cleaning
workpieces in relatively short time intervals. Preferably, the chemicals
used should be recyclable and the energy requirements for the cleaning or
drying process should be modest.
Summary of the Invention
These needs are met by the invention, which provides a system for
2o drying and/or cleaning foreign substances from selected surfaces of a
workpiece, such as a semiconductor wafer, an electrical or optical
component, or a printed circuit board, including a selected liquid such as
hydrofluoroether (HFE), ethylated hydrofluoroether (denoted eth-HFE) or
a mixture of hydrofluoroether or ethylated hydrofluoroether with one or
more other chemicals. A first processing liquid is prepared at a
temperature in a selected range, such as T(bath) = 10-90 oC, in a tank or
other liquid housing, and the workpiece is fully immersed in a first liquid
processing bath, or otherwise exposed to the first processing liquid, for a
selected time interval. The invention works well, for example, at room
temperature. Optionally, the processing liquid is subjected to wave motion
through ultrasonic waves at one or more selected frequencies introduced
into the liquid. The workpiece is drawn through a second processing liquid
at a selected linear withdrawal rate, such as 0.5-5 cm/sec, or slower or
CA 02303979 2000-03-16
WO 99/15845 PCT/US98/19793
3
faster if desired. The workpiece may be substantially stationary, or may be
rotating at a selected angular velocity, as the second processing liquid is
transferred to the workpiece.
The second processing liquid has a very low surface tension, much
lower than water and most other liquids, and has a higher liquid density
than water so that, as the exposed surface area of the workpiece increases,
foreign substances are removed from the exposed surfaces) and water and
other liquids with higher surface tension are displaced by the second
liquid. One result of this procedure is that the workpiece surface can be
to cleaned and simultaneously dried, often within a time interval of length
about 1-60 sec, or longer, if desired.
Brief Description of the Drawings
Figure 1 illustrates use of the invention in one embodiment.
Figures 2A-2D illustrate possible chemical configurations for HFE.
Figure 3 is a flow chart illustrating a drying procedure according to
the invention.
Figures 4A-4F illustrate a suitable procedure for drying
workpieces.
Figure 5 is a side view of a suitable dispenser for HFE or eth-HFE
liquid, to be used with the process shown in Figures 4A-4F.
Figure 6 illustrates one apparatus for transferring HFE or eth-HFE
liquid to a workpiece.
Figure 7 illustrates layers of four-zone drying according to the
invention.
Figures 8A-8C illustrate another process for practicing the
invention.
Figures 9, 12, 13, 14, 15 and 16 illustrate alternative apparatus for
dispensing the HFE or eth-HFE liquid onto a workpiece that is moved
vertically or horizontally.
Figure 10 is a graph schematically illustrating improvement of
drying with increased pressure head used to spray or transfer HFE or eth-
HFE liquid.
CA 02303979 2000-03-16
WO 99/15845 PCT/US98/19793
4
Figure 11 is a graph schematically illustrating variation of minimum
aperture width Ow0 with surface tension of a spraying liquid.
Figures 17A-I7E illustrate other approaches for transferring the
HFE or eth-HFE liquid to a workpiece.
Description of Best Modes of the Invention
In Figure 1, a chemical bath housing or container 11 contains a
selected first processing liquid 13 that is prepared at a selected bath
temperature in a range T(bath) = 10-90 °C, optionally using a container
heater 15. The (first) processing liquid 13 may be DI water or some other
suitable liquid. The first liquid 13 is preferably inert and preferably has a
relatively high surface tension. DI water, with a surface tension (room
temperature) of about 80 dynes/cm, works well here. IPA, with a
relatively low surface tension of 17.6 dynes/cm, also works well here. One
or more workpieces 17A, 17B, 17C is fully immersed or submerged in the
liquid 13 for a selected time interval of length in the range ~t = 1-600
seconds. Alternatively, the workpiece(s) need not be immersed in the first
processing liquid. The first liquid 13 is optionally subjected to ultrasonic
vibrations generated by one or more ultrasonic transducers 19A, 19B
located at an outside wall or at an inside wall or on a bottom wall of the
housing 1 l, or that is located within the first liquid 13 itself. The
ultrasonic vibration frequency or frequencies is preferably in the range
between 20 kHz and 750 kHz but may be higher if desired. An ultrasonic
transducer available from Ney Ultrasonics is capable of generating a
sequence of ultrasonic frequencies, including 40, 72, 104 and 136 kHz.
Other ultrasonic transducers can generate higher ultrasonic frequencies,
and some devices can also generate ultrasonic frequencies as low as 20
kHz.
A workpiece 17A, 17B, 17C is upwardly withdrawn from the first
processing liquid 13, and an exposed surface of the workpiece is sprayed
with a sheet of a second processing liquid (not explicitly shown in Figure
1 ) to achieve rapid workpiece drying and/or cleaning. The second liquid
preferably includes a hydrofluoroether (methyl nonafluorobutyl ether or
methoxy nonaflurobutane, referred to here as HFE for ease of reference),
CA 02303979 2000-03-16
WO 99/15845 PCT/US98/19793
or an ethylated hydrofluoroether (eth-HFE), available from 3M Company
as HFE-7100 or HFE-7200, or as a mixture of a hydrofluoroether or
ethylated hydrofluoroether and one or more other chemicals, such as
traps-1,2-dichloroethylene, H2C1C-CC1H2 (producing an HFE azeotrope)
5 or another halogen-containing alkene. The hydrofluoroether has a
chemical composition that is either
CF3-CF2-CF2-CF2-O-CF3 or
(CF3)2-CF-CF2-O-CF3 or
CF3-CF2-CF2-O-CF2-CF3 o r
l0 (CF3)2-CF-O-CF2-CF3 or
CSOF12 (generic formula)
or a mixture of these compositions. The first four of these compositions
are illustrated in Figures 2A-2D, respectively, and the first two of these
four compositions together appear to provide close to 100 percent of the
fractions. The freezing point and boiling point of HFE are approximately
T = -135 °C and T = 60 °C, respectively. HFE has density
and surface
tension of 1.52 gm/cm3 and 13.6 dynes/cm, respectively. Other HFE
formulations have boiling points ranging from 38 °C up to about 80
°C.
By contrast, isopropyl alcohol (IPA) and water have surface tensions of
about 17.6 dynes/cm and 80 dynes/cm, respectively. Thus, HFE can
displace IPA, water and most other liquid substances with moderate to
high surface tensions from the surface of a workpiece, as the workpiece is
withdrawn from a bath or spray of the second liquid. The second liquid
may be provided as a conventional liquid or as a vapor, mist, "fog" or
other suitable fluid form (collectively referred to here as a second
"liquid"), although the conventional liquid form is preferred.
The eth-HFE has a chemical composition that is either
CF3-CF2-CF2-CF2-O-CH2-CF3 or
CF3-CF2-CF2-CF2-CH2-O-CF3 o r
CF3-CF2-CF2-CH2-CF2-O-CF3 o r
CF3-CF2-CH2-CF2-CF2-O-CF3 o r
CF3-CH2-CF2-CF2-CF2-O-CF3 o r
(CF3)2-CF-CF2-O-CH2-CF3 or
CA 02303979 2000-03-16
WO 99/15845 PCT/US98/19793
6
(CF3)2-CF-CF2-CH2-O-CF3 o
r
(CF3)2-CF-CH2-CF2-O-CF3 or
CF3-CF2-CF2-O-CF2-CH2-CF3 o
r
CF3-CF2-CF2-O-CH2-CF2-CF3 o
r
CF3-CF2-CF2-CH2-O-CF2-CF3 o
r
CF3-CF2-CH2-CF2-O-CF2-CF3 o
r
CF3-CH2-CF2-CF2-O-CF2-CF3 o
r
(CF3)2-CF-O-CF2-CH2-CF3 or
(CF3)2-CF-O-CH2-CF2-CF3 or
(CF3)2-CF-CH2-O-CF2-CF3 or
C6H20F12 (generic formula)
or a mixture of these compositions. The first four of these compositions
are illustrated in Figures lA-1D, respectively, and the first and sixth of
these sixteen compositions together appear to provide close to 100 percent
of the fractions.
The linear rate of drawing the workpiece through or from the
second liquid is preferably in the range 0.5-10 cm/sec, but may be
somewhat faster or slower, and the second liquid is optionally subjected to
ultrasonic vibrations while the workpiece is immersed. The molecular
weight of HFE and of eth-HFE are about 364 and 378, respectively, which
are much higher than the molecular weight of water (18, with 364/18 =
20.2 » 1 ) or of IPA (60), so that, as the workpiece is drawn through the
second liquid, the higher density and lower surface tension of the second
liquid cause this liquid ( 1 ) to easily displace any liquid droplets with
higher surface tension parameters from the workpiece surfaces) and (2)
to move down the (partly) exposed surfaces) of the workpiece into the
first liquid-second liquid mix below. The workpiece surfaces) is dry
within 30 sec after the workpiece is removed from the second liquid, if
ultrasonic vibrations are used, and within a somewhat longer time, such as
30-45 sec, after the workpiece is removed from the second liquid, if no
ultrasonic vibrations are used. The workpiece is also cleaned by removal
of residues from the exposed surface(s), using this approach.
CA 02303979 2000-03-16
WO 99/15845 PCT/US98/19793
7
When the second liquid (including HFE or eth-HFE) is held at a
temperature in the range 10 °C <_ T < 80 °C, at most a few
milliliters/minute of this liquid are lost due to volatilization, for a tank
with a normal exposed liquid surface. The second liquid can be drawn
from the container 11, passed through a filter 21 and returned to its
container, to remove the residues and to recycle the second liquid for
reuse in drying and/or cleaning.
Figure 3 is a flow chart illustrating one embodiment of a suitable
procedure for practicing the invention. In step 31, a workpiece (electronic
part or parts) is fully immersed in a (preferably inert) first processing
liquid, such as deionized (DI) water or IPA that is prepared in a selected
temperature in the range T = 10-90 °C, for an immersion time interval
(optional) of selected length in the range Ot = 0-600 seconds. In step 33,
the first liquid is optionally subjected to ultrasonic wave motion at one or
more selected ultrasonic frequencies in the range 20-750 kHz for most or
all of the immersion time interval. In step 35, after the time interval of
immersion is completed, the workpiece is slowly withdrawn from the bath
of the first processing liquid, preferably at a linear rate of withdrawal of
between 0.5 and 5 cm/sec and preferably in a clean room or inert
environment. In step 37, a selected second processing liquid, such as HFE
or eth-HFE, is transferred to the workpiece exposed surfaces) and
removed. In step 39 (optional), the selected liquid is filtered or otherwise
cleaned and returned to the container or to another container for reuse in
another chemical bath. The procedure shown in Figure 2 will provide
some cleaning of the workpiece and will usually dry the workpiece in no
more than 1-30 seconds after exposure to the HFE or eth-HFE (1-60 sec
for the full process). If only workpiece drying is desired, step 33 can be
omitted.
Transfer of the second liquid in step 37 may proceed by spraying
the second liquid onto the exposed surfaces) of the workpiece, for
example, as a line or strip of sprayed liquid, or by dribbling the liquid
onto one or more of the exposed surfaces by a source of the liquid that is
positioned above, at the side of or adjacent to the workpiece.
CA 02303979 2000-03-16
WO 99/15845 PCT/US98/19793
8
Figures 4A-4F illustrate a suitable process for using HFE or eth-
HFE and recycling most or all of this liquid in electronic parts wafer
drying and cleaning. In Figures 4A and 4B, one or (preferably) many
workpieces 41, such as semiconductor wafers, printed circuit boards or
the like are picked up by one or more workpiece arms 43A and 43B, and
the workpieces are positioned in a first housing or tank 45 that is open at
the top and that has a drain aperture 47 at the bottom thereof. Preferably,
the housing initially contains deionized (DI) water 49, preferably at a
temperature in the range 10-90 oC, and the workpiece 41 is completely
immersed in the DI water. Preferably, the DI water is filled to the top of,
and slightly overflowing from, the first housing 45, in order to minimize
accumulation of unwanted material in the DI water through removal by
spillover. Alternatively, the workpiece arms) 43A and 43B may be
replaced by one or more vacuum chucks (preferred) or magnetic or
adhesive disks that temporarily grasp and hold the workpiece 41.
In Figure 4C, a second housing or tank 51 containing a second
liquid 50 (e.g., HFE or eth-HFE or azeotrope thereof), preferably
maintained at a pressure p of between 10 and 100 psi relative to the
environment and maintained at a temperature in the range 10-80 oC for
eth-HFE {or 10-60 °C for HFE), is positioned above, at the side of or
adjacent to the first housing 41.
The second housing 51 is connected to one, two or more thin plates
53 with slotted apertures or other suitable apertures 55 therein (shown in
side view in Figure 5). The apertures 55 are oriented so that, when the
pressurized second liquid 50 is allowed to flow from the second housing
51, the second liquid is sprayed (with or without atomization) from these
apertures, in an approximately horizontal, vertical or diagonal pattern.
Any object that is located in front of the apertures 55 will be sprayed or
otherwise covered with a liquid, vapor or mist from the second liquid 50.
Alternatively, the second housing 51 can be positioned above the
first housing 41, and the second liquid can be dribbled onto the exposed
surfaces of the workpiece as the workpiece emerges from the first liquid
bath, taking care that the volume of second liquid delivered to the
CA 02303979 2000-03-16
WO 99/15845 PCTNS98/19793
9
workpiece exposed surfaces is sufficient to cover these surfaces before the
second liquid runs off these surfaces.
HFE liquid has a specific density of about 1.52 gm/cm3, which is
much heavier than the specific density of the DI water (~ 1.0 gm/cm3), the
HFE is a relatively nonpolar molecule (as compared to a highly polar
water molecule), and the HFE surface tension, 13.6 dynes/cm, is much less
than that of water (~ 80 dynes/cm). Ethylated HFE may have a slightly
higher specific density. As a result of these differences, if HFE or eth-HFE
is used as the second liquid 50 in Figure 3C, most of the HFE or eth-HFE
that falls into the first liquid 49 will ultimately sink to the bottom of the
(mixed) liquid in the first housing 45. The portion of the HFE or eth-HFE
liquid that passes along the exposed surfaces of the workpiece 41 above the
first liquid bath can clean and/or dry the workpiece exposed surfaces.
In Figures 4D and 4E, the workpieces 31 are now pushed upward
within the first liquid by one or more "pusher" arms 53. When
approximately half of the workpiece 41 is above the upper surface of the
first liquid, the workpiece is gripped by the workpiece arms) 43A and
43B (or vacuum chuck or magnetic or adhesive disks) and is pulled slowly
upward from the first liquid 49 in the first housing 45, at a preferred
linear rate in the range 0.5-10 cm/sec. As the workpiece 41 moves
upward, it passes through a region where the workpiece is subjected to the
transfer (by spraying, dribbling or other suitable transfer process) of the
second liquid 50 thereto from the slotted apertures 55. Because the surface
tension of the second liquid, such as HFE or eth-HFE, is much smaller
than the surface tension of the first liquid (e.g., DI water or IPA), the
second liquid will displace the first liquid from the surface of the
workpiece 41. HFE (or eth-HFE) and similar second liquids are also fairly
volatile, with a relatively low heat of vaporization (around 30 cal/gm for
HFE and for eth-HFE) and high vapor pressure (about 195 mm Hg) so that
any portion of the second liquid that displaces the first liquid on the
workpiece surfaces will ultimately evaporate and will thereby quickly dry
a contiguous portion of an exposed surface of the workpiece 41. In Figure
CA 02303979 2000-03-16
WO 99/15845 PCT/US98/19793
4F, the workpiece 41 has been pulled completely from the first liquid in
the first housing 45.
Most or all of the second liquid (HFE or eth-HFE) that does not
evaporate from the exposed surfaces of the workpiece 41 will fall into the
5 first liquid and will sink to and collect at the bottom of the first
housing,
where this (primarily second) liquid can be removed, using the bottom
aperture of the first housing, for recycling of the second liquid. If the
atmosphere in which the apparatus shown in Figures 4A-4F is maintained
dry and inert, for example, by use of cool dry N2 or CO, the portion of
10 the second that evaporates from the workpiece surfaces can also be
recovered, recycled and reused. Reuse may be possible even where the
atmosphere is not dry and inert.
Figure 6 indicates a suitable arrangement of apparatus for use of the
second liquid to dry and clean electronic parts. Two hollow cylinders 61A
and 61B are positioned with their longitudinal axes approximately parallel.
Each of the cylinders 61A and 61B has one or more longitudinally
oriented slotted apertures 63A and 63B, respectively, therein, with a slot
width h that is preferably in the range 0.02 - 0.5 mm. Each cylinder 61 A
and 61B is connected to a source 65 of pressurized HFE or eth-HFE or
other suitable second liquid. If this pressure is sufficiently high, the
second
liquid is forced through the slotted apertures and emerges as a thin sheet
or spray 67, in the shape of a sheet or a sector of a cylinder, and these
sprays collide with and cover a workpiece 69 that is positioned between
the two slotted apertures 63A and 63B. The HFE or eth-HFE or other
suitable second liquid can be heated modestly (e.g., to T ~ 30-50 °C)
as it
emerges from the slotted apertures 63A and 63B so that, when the second
liquid collides with the surfaces of the workpiece 69, the second liquid will
more quickly evaporate and thereby dry the workpiece. If the spray
velocity is made large enough, the HFE or eth-HFE spray can also remove
unwanted residues from portions of the exposed surfaces of, and thereby
clean, the workpiece 69. The hollow cylinders 61A and 61B are
preferably rotated in the same direction or in opposite directions around
CA 02303979 2000-03-16
WO 99/15845 PCT/US98/19793
11
their respective longitudinal axes at an angular velocity cu in the range 2rt-
100rc radians per second, using a mechanical rotator 71.
Cleaning a workpiece surfaces) with HFE or eth-HFE or HFE
azeotrope liquids according to the preceding procedure appears to remove
most or all the contaminant particles with sizes greater than about 0.1 ~,m,
as is presently required for a surface cleaning process for semiconductor,
optical and electronic surfaces. In tests according to the preceding
procedure, the workpiece surfaces were observed to become dry shortly
after the workpieces were removed from the first liquid so that workpiece
surface drying and cleaning occurred approximately simultaneously.
According to product specifications provided by the developer of
HFE, 3M company, each of HFE and eth-HFE is intended to be a non-toxic
replacement for the CFCs and similar chemicals used in various
applications over the past 30 years. HFE is substantially non-toxic with an
acute lethal inhalation concentration that exceeds 100,000 parts per
million. HFE is not presently classified as a hazardous substance. However,
a mixture of HFE and another chemical may be more active. The HFE
azeotrope, for example, is volatile, and disposal of HFE azeotrope into a
water supply may require compliance with hazardous waste regulations.
No corresponding figures have yet been released for eth-HFE.
DI water and either HFE or eth-HFE readily form a liquid/liquid
two-component system with little mixing (20 ppm of HFE in DI water; 90
ppm of DI water in HFE, for example), due in part to the high polarity of
water and the relatively lower polarity of the HFE or eth-HFE and the
differences in molecular weight. The HFE or eth-HFE is thus easily
separated from the DI water, or any other inert, lighter, higher polarity
liquid, such as IPA, for filtering and reuse or for disposal of the HFE or
eth-HFE.
The process of the invention has three or four zones of drying, as
illustrated on a surface of a workpiece 81 shown in Figure 7. As the
workpiece is withdrawn from the first liquid, the bottom zone 81A is still
immersed in the first liquid. A second zone 81B, adjacent to the bottom
zone 81 A, has risen above the first liquid but has particles of air and/or
CA 02303979 2000-03-16
WO 99/15845 PCTNS98/19793
12
processing liquid on the surface. A third zone 81C, adjacent to the second
zone 81B, has the second liquid transferred thereto by spraying or
dribbling, and the second liquid forms a fluid sheet (liquid and/or
atomized gas particles) of the second liquid, mixing with and displacing
S the air and/or processing liquid particles that remain on the exposed
surface. In a fourth zone 81 D, adjacent to the third zone 81 C, the fluid
sheet of second liquid has volatilized, usually in 30 sec or less, leaving a
dry workpiece surface in this zone. The second zone 81B can be
eliminated, if desired, by forming the second liquid fluid sheet in a region
slightly above the exposed surface of the processing liquid in the tank.
Another procedure for practicing the invention is illustrated in
Figures 8A-8C. In Figure 8A, a workpiece 91, which has recently been
removed from a first processing liquid (e.g., DI water or IPA, not
shown), is immersed in a tank 93 containing a second processing liquid 95,
such as HFE or eth-HFE or HFE azeotrope, which is heated to a
temperature below its boiling point (T~60-80 °C for HFE in general).
The
workpiece 91 is immersed in the second liquid 95 for a selected immersion
time interval, preferably in the range 5-120 sec, or longer if desired. For
at least a portion of the immersion time interval (e.g., at least 5-10 sec),
the workpiece 91 is subjected to ultrasonic vibrations generated by an
ultrasonic wave generator 97 that is positioned inside, or outside and
contiguous to, the tank 93. The ultrasonic vibrations help the low surface
tension second liquid 95 displace material residues, air and first liquid on
exposed surfaces of the workpiece 91. After the immersion time interval
ends, the workpiece 91 is withdrawn from the second liquid 95, as shown
in Figure 8B, at a linear withdrawal rate in a preferred range of 0.5-10
cm/sec, into a controlled atmosphere, such as a vacuum, a clean room or
an atmosphere containing primarily N2 or CO. Any of the second liquid
remaining on the exposed surfaces) of the workpiece 91 after the
3o workpiece is fully withdrawn (Figure 8C) will usually volatilize within 1
sec after the workpiece is withdrawn from the second liquid 95.
As illustrated in Figure 9, a workpiece 101 can be withdrawn
vertically (in the direction of the vector v) between two plenums 103A
CA 02303979 2000-03-16
WO 99/15845 PCT/US98/19793
13
and 1038, with longitudinally oriented apertures, 104A1, 104A2, 104B1
and 104B2, that spray HFE or eth-HFE liquid onto one side or two
opposed sides of the workpiece at a selected incidence angle ~ relative to
the workpiece surface. The HFE or eth-HFE liquid 105 is held in a fluid
reservoir 107 that is connected to the apertures through a pressurized
pump 109 or other suitable device, which delivers the HFE or eth-HFE
liquid to the apertures 103A and 1038 with a controllable pressure head
Op. Unvolatilized spray liquid and any other processing liquid (e.g.,
water) and other residues removed from the workpiece surface are
collected in a collector 110, located below the workpiece 101, for possible
cleaning and recycling or for disposal.
Alternatively, the workpiece 101 can be oriented at an angle a
relative to the vertical (indicated as a workpiece 101' in Figure 9), where
a ranges from a few degrees to about 80°, with all other aspects
remaining the same.
We have found that, with an aperture width or gap 0w of the order
of 0.05 mm, a pressure head value ~p of the order of 40 psi for HFE or
eth-HFE is sufficient to dry a workpiece surface that is exposed to the HFE
or eth-HFE spray in as little as S-7 sec. We estimate that the aperture
width Ow could be reduced to as low as 0.02 mm and the HFE or eth-HFE
liquid would still form an acceptable, continuous spray after passing
through the apertures 103A and 1038, because of the low surface tension
and other features associated with the HFE or eth-HFE liquid. If the HFE
or eth-HFE liquid were replaced by another liquid with a higher surface
tension, such as IPA or DI water, we estimate that the aperture width Ow
could not be reduced below about 0.05 mm, if a continuous spray is to be
maintained at a modest pressure head of the order of 40 psi.
Where HFE or eth-HFE liquid, maintained at an elevated
temperature such as 40 °C, is used with this configuration, we find
that we
can withdraw a 200 mm diameter semiconductor wafer from the liquid in
5-7 sec (linear withdrawal rate of about 29 mm/sec). At the end of this
second withdrawal period, we find that most of the wafer is fully dry,
based on "bare eye" examination, and within a few seconds after removal
CA 02303979 2000-03-16
WO 99/15845 PCT/US98/19793
14
of the last of the wafer from the HFE liquid, the wafer is fully dry. We
believe that, if the HFE or eth-HFE liquid temperature is raised to a
higher temperature, such as 50-56 °C, the wafer can be withdrawn in a
shorter time interval, such as 3-5 sec, and the wafer will be fully dry as
soon as the wafer has cleared the liquid. The relatively high vapor
pressure of the HFE or eth-HFE liquid at room temperature (210 mm Hg)
ensures that any HFE or eth-HFE liquid that remains but cannot be seen
with a "bare eye" examination after removal of the wafer will be very
quickly volatilized.
Several parameters are available to optimize the drying and the
cleaning characteristics of the HFE, applied in the configuration shown in
Figure 9. First is the temperature, already discussed in the preceding. As
the HFE liquid temperature is raised, the drying process and, separately,
the cleaning process appear to occur more quickly. A second optimizing
parameter is the angle ~ at which the spray {one-sided or two-sided) is
directed at and strikes the workpiece 101. We believe that an angle ~
somewhere between grazing incidence (~ ~ 0°) and near-normal incidence
(~ ~ 90°) is optimal here.
A third optimizing parameter is the pressure head 0p imposed on
the HFE liquid behind the aperture(s). Workpiece drying and/or cleaning
appears to improve as the pressure head 0p is increased, but the
improvement appears to be saturating, as suggested in the schematic graph
of a selected drying characteristic ~ (time to dry) versus 0p shown in
Figure 10.
A fourth optimizing parameter is the aperture width 0w. As Ow is
decreased, the amount of HFE or eth-HFE liquid directed at the workpiece
surface will decrease, if the pressure head Op is held constant, no matter
what liquid is used. When the aperture width 0w decreases below what is
believed to be a threshold or minimum value, OwO, which depends upon
liquid temperature, liquid surface tension, pressure head and possibly
other variables, the continuous spraying action will give way to erratic and
uncontrollable spurts of the liquid. The threshold aperture width ~w0 at
which this transition occurs will decrease approximately monotonically
CA 02303979 2000-03-16
WO 99/15845 PCT/US98/19793
with decreasing surface tension, as suggested by the schematic graph of
Ow0 versus liquid surface tension in Figure 11. Thus, the threshold
aperture width Ow0 for HFE liquid should be lower than Ow0 for IPA,
which should be lower than Ow0 for DI water. Thus, HFE or eth-HFE
5 liquid has a greater range of relevant operating parameters, such as Ap
and Ow, for drying and/or cleaning than does a liquid such as IPA or DI
water.
A fifth optimizing parameter is the rate r of linear withdrawal of
the workpiece through the liquid spray. Here, a given drying and/or
10 cleaning characteristic will continue to improve as the withdrawal rate r
is
decreased, but this must be balanced by consideration of the desired drying
and/or cleaning time for the workpiece, which time will be approximately
proportional to 1/r as the rate r is decreased.
A sixth optimizing parameter is the number N of apertures used to
15 spray HFE or eth-HFE liquid onto the workpiece on one side. In Figure 8,
N = 2 sprays are provided for each side. One can choose N = 1, 2, 3 or
any other reasonable number, and the drying and/or cleaning
characteristic should improve with increasing N, if the sprays on a given
side are kept far enough apart that they do not interfere with each other. If
2o two adjacent sprays are located close enough to interfere with each other,
this may increase the effective workpiece drying time, although the
cleaning characteristic may be improved or degraded, depending on the
workpiece and the circumstances.
As illustrated in Figure 12, a sequence of workpieces 111-1, 111-2,
111-3 can be drawn more or less vertically (in the direction of the path
vectors v) in a curvilinear path P between two plenums 113A and 113B,
with longitudinally oriented apertures, 114A1, 114A2, 114B1 and 114B2,
that spray HFE or eth-HFE liquid onto one side or two opposed sides of
the workpiece at a selected incidence angle ~ relative to the workpiece
surface. The HFE or eth-HFE liquid 115 is held in a fluid reservoir 117
that is connected to the apertures through a pressurized pump 119 or other
suitable device, which delivers the HFE liquid to the apertures 113A and
113B with a controllable pressure head Op.
CA 02303979 2000-03-16
WO 99/15845 PCT/US98/19793
16
As illustrated in Figure 13, a workpiece 121 can be drawn
horizontally (in the direction of the vector v) between two plenums 123A
and 123B, each having one or more vertically oriented apertures, 124A
and 124B, that spray HFE or eth-HFE liquid onto one side or two opposed
sides of the workpiece at a selected incidence angle relative to the
workpiece surface. The HFE or eth-HFE liquid 125 is held in a fluid
reservoir 127 that is connected to the apertures through a pressurized
pump 129 or other suitable device, which delivers the HFE or eth-HFE
liquid to the apertures 124A and 124B with a controllable pressure head
Op. Unvolatilized spray liquid and any other processing liquid (e.g.,
water) and other residues removed from the workpiece surface are
collected' in a collector 130, located below the workpiece 121, for possible
cleaning and recycling or for disposal.
The choices of pressure head Op, aperture width Ow, liquid
temperature T, linear rate r of horizontal movement of the workpiece and
the other parameters are substantially as in Figure 9 or 12. One advantage
of the configuration in Figure 12 or 13, vis-a-vis the vertical
configuration in Figure 9, is that two or more workpieces 121 can be
moved through the spray serially so that the drying and/or cleaning
processes) can be operated as a single workpiece continuous process, in
which the workpieces move through a region where spraying occurs
serially. One possible disadvantage of the horizontal processing shown in
Figure 13 is that the sprayed HFE or eth-HFE liquid that does not
immediately volatilize upon striking the workpiece may vertically run
down the workpiece and interact with or interfere with another portion of
the HFE or eth-HFE liquid being sprayed on an adjacent portion of the
workpiece at about the same time.
This possible disadvantage is minimized, if not eliminated, by the
horizontal movement/diagonal spray configuration illustrated in Figure
14. In this configuration, the workpiece 131 is drawn horizontally at a
linear rate r (in the direction of the vector v) between a first diagonally
oriented apertures 134A and a second diagonally oriented aperture (not
shown) that spray HFE or eth-HFE liquid onto one side or two opposed
CA 02303979 2000-03-16
WO 99/15845 PCTNS98/19793
17
sides of the workpiece. The liquid spray on each side of the workpiece
contacts the workpiece along a diagonal line having an associated diagonal
angle 8 as shown. The HFE or eth-HFE liquid 135 is held in a fluid
reservoir 137 that is connected to the apertures through a pressurized
pump 139 or other suitable device, which delivers the HFE or eth-HFE
liquid to a first plenum 133A and to a second plenum (not shown) having
the respective first and second apertures, with a controllable pressure head
Op through apertures having aperture widths 0w. Unvolatilized spray
liquid and any other processing liquid (e.g., water) and other residues
removed from the workpiece surface are collected in a collector 140,
located below the workpiece 131, for possible cleaning and recycling or
for disposal. The choices of pressure head Op, aperture width Ow, liquid
temperature T, linear rate r of horizontal movement of the workpiece and
the other parameters are substantially as in Figure 9, 12 or 13. The
configuration of Figure 14 allows single workpiece processing and batch
processing, as in Figure 13, but the unvolatilized HFE or eth-HFE liquid at
one portion of the sprayed workpiece does not substantially interfere with
spraying of HFE or eth-HFE liquid onto an adjacent portion of the
workpiece.
The configuration of Figure 14 has a seventh optimizing parameter,
the diagonal angle 8 for application of the sprayed liquid. An optimum
diagonal angle A(opt) will likely depend upon the linear rate r at which the
workpiece is drawn horizontally through the spray and upon a
representative rate s(vert) at which unvolatilized HFE or eth-HFE liquid
can vertically run down a surface of the workpiece 131: as s{vert)
increases, a minimum diagonal angle 8, at which this process can be
operated without liquid-liquid interference, will likely increase.
Figure 15 illustrates another alternative configuration for drying
and/or cleaning a workpiece 141. The workpiece 141 is transported
through a processing region 142 where one or more approximately
circular moving currents) (spray or bulk liquid) C1, C2 of the second
liquid move across each surface of the workpiece to be processed. A
nominal center cl, c2 of each of the approximately circular moving
CA 02303979 2000-03-16
WO 99/15845 PCT/US98/19793
18
currents C1, C2 is preferably located away from the workpiece surface so
that each point on the workpiece surface experiences a current C1, C2
with a non-zero liquid velocity. Alternatively, the nominal center cl, c2
for the current C1, C2 can be located on an exposed surface of the
workpiece 141.
Each circularly moving current C1, C2 is provided by a circulation
mechanism 143, partly or fully immersed in the second liquid, such as a
mechanically-driven or magnetically-driven liquid stirrer. The liquid
angular velocity c~ associated with each approximately circular flow
pattern C1, C2 may be chosen in the range from a fraction of a radian per
sec (e.g., 0.2 rad/sec) up to several hundred radians per sec (e.g., 500
rad/sec). The second liquid 144 is preferably held in a fluid reservoir 145
and is delivered by a pump 14b at selected time intervals to the workpiece
processing region 142, where the circulation mechanism 143 causes the
second liquid to move in an approximately circular pattern.
The workpiece 141 is moved through the processing region 142 by
one or more mechanical arms 147A and 147B (or a vacuum chuck or
magnetic or adhesive disk workpiece gripper) and is subjected to the
circularly moving current C1, C2 of the second liquid. Alternatively, the
workpiece 141 can be held stationary and the circularly moving currents)
C1, C2 can be caused to sweep across the workpiece surfaces) to be
processed. After the workpiece surfaces) has been processed by the
second liquid, the second liquid used for this purpose is optionally drained
into or otherwise deposited in a spent liquid plenum 148 and is either
dumped or (preferably) cycled through a liquid filtering mechanism 149
and redeposited in the fluid reservoir 145.
Where the workpiece 141 is subjected to only one circularly moving
current, C1 or C2, of the second liquid, the nominal radius, rl or r2, of
this current pattern is preferably greater than the diameter of the
workpiece surfaces) to be processed. Where the workpiece 141 is
subjected to two or more circularly moving currents, C1 and C2, the
nominal radius, rl and/or r2, of one or both of these current patterns is
optionally chosen to be somewhat greater than one-half of the diameter of
CA 02303979 2000-03-16
WO 99/15845 PCT/US98/19793
19
the workpiece, and the two currents, C1 and C2, cooperate to move
across and fully cover the workpiece surfaces) to be processed, as
illustrated in Figure 14. The nominal centers, c1 and c2, of the currents,
C1 and C2, are then located so that the workpiece surfaces) to be
processed moves between these nominal centers.
Two or more workpieces 151 and 152 may be positioned close to
and adjacent to each other, as illustrated in apparatus shown in Figure 16,
and three pressure heads 153A, 1538 and 153C may be positioned adjacent
to these workpieces, as shown, in order to clean and dry the workpiece
exposed surfaces. Each of the outer pressure heads 153A and 153C has one
or more spray apertures, 154A and 154C, respectively, to provide drying
and/or cleaning of one exposed surface of the adjacent workpiece. The
middle or inner pressure head 1538 has one or more spray apertures
154B 1 and 154B2 located on each side thereof to spray an exposed surface
of the adjacent workpiece, 151 and 152, respectively. The apparatus 150
also includes a reservoir or supply tank 157 of second liquid 155 and a
pressure pump 159 that delivers pressurized second liquid to the pressure
heads 153A, 1538 and 153C. A liquid collector 160, located below the
workpieces 151 and 152 in the spraying region, collects liquid that drips
off the workpieces for possible recycling and reuse.
Proceeding in the manner illustrated in Figure 16, two or more
workpieces, located adjacent to each other, can be simultaneously dried
and/or cleaned, as might occur in a true batch process. A separation
distance, DI and/or D2, between two adjacent workpieces, 151 and 152,
that is at least equal to a selected minimum separation distance D(min)
should be maintained in order to provide sufficient clearance distance,
D(clear;l) and D(clear;2), for a pressure head 153B and associated spray
apertures, 1548 1 and 154B2, to pass between the adjacent workpieces, 151
and 152. These clearance distances preferably include an adequate backoff
distance of each spray aperture, 1548 1 and 154B2, from the
corresponding exposed surface of an adjacent workpiece.
The spray patterns defined by the spray apertures 154A, 15481,
154B2 and 154C may be horizontally oriented, vertically oriented or
CA 02303979 2000-03-16
WO 99/15845 PCTNS98/19793
diagonally oriented, as illustrated in Figures 9, 13 and 14, and may be
independently chosen for each spray pattern. For example, because of the
different nature of the two exposed surfaces of the workpiece 151, the
spray patterns formed by the apertures 154A and 154B 1 might be vertical
5 and diagonal, respectively. The spray patterns defined on each of the two
exposed surfaces for the workpieces in Figures 6, 9, 12, 13, 14, 15 and 16
may be independently chosen. Optionally, only one exposed surface or side
of the workpieces in Figures 6, 9, 12, 13, 14, 15 and I6 may be dried
and/or cleaned, if desired.
10 Figures 17A-17E illustrate other approaches to transferring the
HFE or eth-HFE liquid to a workpiece. In Figure 17A, an exposed surface
of the workpiece 161 is spinning at a selected angular frequency cu about a
selected rotation axis that passes through the exposed surface, and one or
more sheets 163-n (n = 1, 2, 3, ...) of HFE-based liquid (e.g., HFE or eth-
15 HFE liquid), shown schematically as lines on the surface, are sprayed onto
the workpiece surface as the surface rotates. Each of the sheets 163-n may
have the same HFE-based liquid. Alternatively, two or more of the sheets
163-n may use different HFE-based liquids as the spray material, in order
to take advantage of different responses of contaminants on the workpiece
20 surfaces) to different HFE-based liquids.
Two or more of the sheets 165-n of HFE-based liquid in Figure 17A
need not be parallel to each other and may be planar sheets ( 165-1 ) or
curvilinear sheets (165-2, 165-3) or a mixture of planar sheets and
curvilinear sheets; and if these sheets are not parallel to each other, as
illustrated in Figures 17B, the sheets need not intersect each other at or
near the center of rotation of the workpiece 161.
In Figure 17C, two or more sheets 167-1 and 167-2 of different
HFE-based liquids are sprayed onto a surface of a rotating workpiece 161
along different line segments that preferably each cover the entire
workpiece surface as the workpiece surface rotates at a selected angular
velocity w about a selected rotation axis that passes through the exposed
surface. As in Figure 17A, the two sheets 167-1 and 167-2 may have the
same HFE-based liquid as a spray. Alternatively, the two sheets 167-1 and
CA 02303979 2000-03-16
WO 99/15845 PCT/US98/19793
21
167-2 may each have a different HFE-based liquid, in order to take
advantage of different responses of contaminants on the workpiece
surfaces) to different HFE-based liquids.
In Figure 17D, one or more liquid streams 169 of HFE-based liquid
is deposited onto a selected location on a surface of a rotating workpiece
161 as the workpiece surface rotates at a selected angular velocity w about
a selected rotation axis that passes through the exposed surface, and the
HFE-based liquid is allowed to spread across part or all of the workpiece
surface by action of rotation (centrifugal force, etc.) of the workpiece
surface.
In Figure 17E, an exposed surface {not shown) of the workpiece
161 that is to be cleaned is placed in contact with an exposed surface of, or
immersed in, a pool of HFE-based liquid 171. The exposed surface is
rotated at a selected angular velocity w about a selected rotation axis that
passes through the exposed surface. A combination of ( 1 ) exposure of the
exposed surface to the HFE-based liquid and (2) a shear force developed
between the rotating exposed surface and the contiguous HFE-based liquid
171. The shear force may become reduced by the tendency of the HFE-
based liquid 171 to "spin up" to the rotational velocity of the exposed
surface. The shear force magnitude may be kept high by moving the
workpiece exposed surface around within the pool of HFE-based liquid so
that the presently contiguous liquid does not have time to fully "spin up" to
the angular velocity of the rotating exposed surface.
