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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to thin-film coatings of semiconductor wafers
and flat panel displays, and in particular to spin coating large surfaces
with photoresist and similar high-viscosity chemicals.
2. Description of the Prior Art
In the fabrication of semiconductor devices, a wafer is coated with
photoresist or a similar high-viscosity liquid chemical by spinning the
wafer and applying an amount of the chemical to the center of the spinning
wafer. (As used herein, the term "liquid" is not limited to fluids of
low-viscosity and, in fact, can refer to highly viscous chemical
substances.) Until recently, spin coating has been mostly confined to
coating circular surfaces or small square mask plates. However, spin
coating is now used to apply chemicals to thin film heads, multi-chip
modules, and flat panel displays which are square or rectangular and are
often very large. Spin coating such surfaces presents primarily two
problems.
First, the corners of a square or rectangular surface are poorly covered.
The chemical being applied to the surface is spun to the edge where excess
is thrown from the surface by centrifugal force. Chemical leaving the
center of an edge is struck by the corner of the spinning surface as the
corner is further from the center of the surface than is the center of an
edge. Such a collision disrupts the even flow of chemical from the center
of the surface to the corners of the surface.
Secondly, evaporation of solvent from the chemical and the cooling of the
chemical as a result of such evaporation increases the viscosity of the
chemical. Therefore, as the chemical spreads toward the edges of the
spinning surface, the thickness of the coating of chemical on the surface
increases. Such thickening over time causes a "bowl" shaped coating in
which the coating is thinner near the center of the surface and thicker
near the edges of the surface.
One solution to the latter problem of the chemical drying too soon on the
spinning surface is to apply the chemical to a surface spinning at a
normal speed and then to ramp up, i.e., gradually increase, the speed of
the spinning surface as the chemical spreads. Increasing the spin rate
spreads the chemical more quickly and potentially before the chemical
thickens substantially. However, increasing the spinning speed of the
surface creates another problem.
The surface tension of the chemical on the spinning surface is what causes
the chemical to spread evenly during spinning. However, as the spinning
rate is increased, the centrifugal force overcomes the surface tension of
the chemical. This is especially true on larger surfaces such as large
flat panel displays. When the surface tension is overcome, the smooth
circular shape of the spreading chemical bursts like a bubble and the
chemical then streams linearly toward the edges of the spinning surface in
multiple radial paths. These multiple radial paths form striations in the
coating of the spinning surface.
The radial gaps in coating between the striations are filled in by applying
an excess of the chemical to the center of the spinning surface until
radial flow of the chemical from the center of the surface, as a result of
the extreme centrifugal force, fills in the uncoated area. Thus, the
surface is coated by saturating the surface with chemical, most of which
is discarded as waste. Furthermore, the uniformity of the coating is poor
as a result of the striations in and drying of the chemical coating.
Excessive use of photoresist in particular is a significant problem in the
art. Photoresist accounts for approximately 5% of the cost of materials
for semiconductor devices and generally costs as much as $1,000 per
gallon. Thus, excessive waste of photoresist significantly affects the
cost of manufacturing semiconductor devices. Additionally, disposal of
photoresist waste presents a substantial environmental burden on
communities in which semiconductor devices are manufactured and on
surrounding ecological systems. The problem is exacerbated when coating
larger surfaces.
One solution found in the prior art is illustrated by FIG. 1. An object 102
to be coated with a chemical on surface 104 was placed on a spinning chuck
106 which was spun by a motor 108. A chemical was deposited on the center
of surface 104 through a tube 110. The drying of the chemical during
spreading of the chemical by centrifugal force was slowed by containment
of solvent vapors evaporating from the chemical. Containment of some of
the solvent vapor was accomplished by placing a lid 112 over and in close
proximity to surface 104 during spinning.
The apparatus of FIG. 1 did not stop drying of the chemical altogether, but
rather slowed the drying by trapping solvent vapors evaporating from the
chemical. The apparatus of FIG. 1 provided no way to control the rate of
drying of the chemical. Furthermore, excess chemical was thrown by
centrifugal force from surface 104 to the inner surface of lid 112.
Therefore, it was necessary to periodically clean lid 112 and such
cleaning increased substantially the introduction of particle contaminants
into the system and reduced the feasibility of automatic, high-speed
manufacturing.
FIG. 2 shows another apparatus used in the prior art to slow the drying of
a chemical in the spin coating of large or non-circular surfaces. Chemical
202 was placed at the center of surface 104 and a plate 204 was brought
into close proximity to surface 104 during spinning. The object of having
plate 204 in close proximity to surface 104 was to contain the solvent
vapors evaporating from surface 104. The apparatus of FIG. 2 was only
partially effective as plate 204 was stationary, causing surface effects
and vortices in the air directly adjacent to surface 104, thereby causing
chemical 202 to dry unevenly and failing to adequately slow the drying of
chemical 202.
What is needed is a method and apparatus which allows greater control of
the evaporation of solvent from a chemical as the chemical is applied to
and spreads over a spinning surface. What is further needed is a method
and apparatus by which drying of a chemical during spin coating is
substantially slowed without substantially increasing the risk of
contamination of the coated surface.
SUMMARY OF THE DISCLOSURE
An apparatus and method are provided for controlling the rate of drying of
a high-viscosity, liquid chemical applied to a substantially flat surface
of a spinning article. The chemical dries as centrifugal force spreads the
chemical over the surface of the spinning article. The drying of the
chemical results from the evaporation of a solvent from the chemical. The
rate of drying of the chemical is controlled by controlling the saturation
level of the solvent, i.e., the amount of solvent vapor, in the local
atmosphere in which the article is spinning, i.e. in the airspace adjacent
to the surface of the article. To control the saturation level of the
solvent in the local atmosphere, a solvent vapor is introduced through a
showerhead which is positioned in close proximity to the spinning surface.
By spinning the article in a solvent-laden vapor, the evaporation of
solvent from the chemical is slowed and therefore the rate at which the
chemical dries and thickens is also slowed. No lid or cover is used around
the periphery of the spinning article which would be splattered by
chemical spilling off the edge of the article and which would necessitate
cleaning and the increased potential for surface contamination.
According to a second aspect of the invention, spreading of the chemical is
facilitated and premature drying of the chemical is avoided by applying to
the surface of the article a thin layer of the solvent prior to
application of the chemical. The chemical flow is enhanced locally at the
surface of the spinning article causing the chemical to flow more smoothly
and evenly toward the edges of the surface, even when using slower spin
speeds.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram of a spin coating apparatus of the prior art.
FIG. 2 is a diagram of a spin coating apparatus of the prior art.
FIG. 3 is a diagram of a spin coating apparatus constructed in accordance
with the present invention.
FIG. 4A is a view of the underside of a showerhead constructed in
accordance with the present invention.
FIG. 4B is a top view of a showerhead constructed in accordance with the
present invention.
FIG. 4C is a cross-sectional view of a showerhead constructed in accordance
with the present invention.
FIGS. 4D and 4E are views of respective undersides of showerheads
constructed in accordance with second and third embodiments of the present
invention.
FIGS. 5A and 5B are top views of a showerhead and a spinning article in
accordance with the present invention.
FIG. 6 is a diagram of a spin coating apparatus constructed in accordance
with a second embodiment of the present invention.
FIG. 7 is a diagram of a spin coating apparatus constructed in accordance
with a third embodiment of the present invention.
FIG. 8 is a cross-sectional view of a showerhead constructed in accordance
with the third embodiment of the present invention.
FIG. 9 is a cross-sectional view of a solvent vapor source constructed in
accordance with the present invention.
FIG. 10 is a cross-sectional view of a combination solvent vapor source and
showerhead constructed in accordance with a fourth embodiment of the
present invention.
FIGS. 11A and 11B are cross-sectional views of a spin-coating assembly
formed in accordance with a fifth embodiment of the present invention.
FIGS. 12A and 12B are plan views of a portion of the spin-coating assembly
of FIGS. 11A and 11B.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
An apparatus and method are provided for controlling the rate of drying of
a chemical applied to a substantially flat surface of a spinning article.
The rate of drying of the chemical is controlled by controlling the
saturation level of a solvent in the local atmosphere in which the article
is spinning. The solvent in the local atmosphere is a solvent present in
the chemical, the drying of the chemical being accomplished by the
evaporation of the solvent from the chemical. By spinning the article in a
solvent-laden gas, the evaporation of solvent from the chemical is slowed
and therefore the rate at which the chemical dries and thickens is also
slowed. No lid or cover is used around the periphery of the spinning
article, since such a lid or cover would be splattered by chemical
spilling off the edge of the article and which would necessitate cleaning
and the increased potential for surface contamination. In one embodiment,
which is described below, article 302 is covered while spinning. However,
no lid or cover extends below surface 304 which could therefore be
contaminated during the spin-coating of surface 304. Since there is
positive solvent-laden gas flow from the center of the surface and no air
from beyond the spinning surface is pulled into the air space adjacent the
surface, complete control of the environment adjacent to the surface is
attained.
An article 302 (FIG. 3) having a surface 304 is securely held by a chuck
306. In one embodiment, article 302 is securely held to chuck 306 by
applying a vacuum to the underside of article 302 as is done routinely in
the art. Chuck 306 and article 302 are spun by a motor 308 at a
controllable rate. An amount of a chemical containing a solvent is placed
on the center of surface 304 through a chemical tube 310. In another
embodiment, which is described below, the chemical is introduced through a
hollow arm which is moved to a position between showerhead 312 and surface
304. The centrifugal force resulting from the spinning of surface 304 of
article 302 spreads the chemical evenly and uniformly over surface 304. As
the solvent evaporates from the chemical, the chemical dries on surface
304.
During the spinning of surface 304, a vapor source 316 creates a gaseous
mixture of nitrogen, or some other generally non-reactive gas, and the
solvent, which is introduced into a showerhead 312 through a gas tube 314.
Vapor source 316 is described in greater detail below. As used herein, the
term "non-reactive" means that the gas does not generally react with
either the solvent or the chemical at room temperature. Another
non-reactive gas is ordinary air. The gaseous mixture is sometimes
referred to herein as "the solvent vapor". The solvent vapor is dispersed
through showerhead 312 into the area immediately adjacent to surface 304.
As the airspace adjacent to surface 304 has an increased saturation level
of the solvent, evaporation of the solvent from the chemical deposited on
surface 304, and hence the drying of the chemical, is slowed. As a result,
the chemical flows more smoothly in response to the centrifugal force of
the spinning of surface 304 and coats surface 304 more smoothly and
uniformly. Additionally, as described more completely below, surface 304
can be spun at a slower speed and the chemical can spread to cover the
entirety of surface 304 before drying. Thus, the chemical spreads smoothly
and evenly toward the edge of surface 304. No striations are formed in the
chemical coating on surface 304.
Showerhead 312 (FIG. 4A) has a hole 402 therethrough at the center so that
the viscous chemical can be introduced through chemical tube 310 (FIG. 3)
during operation. As discussed below, the chemical can be introduced
through an arm, which can be positioned between showerhead 312 and surface
304. Showerhead 312 (FIG. 4A) has in its underside a number of
perforations 404 through which solvent vapor is dispersed. In one
embodiment, perforations 404 have a diameter of 0.002 inches and are
spaced approximately one-half inch apart. On the topmost side of
showerhead 312 (FIG. 4B) is an opening 406 through which solvent vapor is
introduced into showerhead 312. While a circular shape is shown for
showerhead 312 (FIGS. 4A-4E), the showerhead can be any shape, e.g.,
rectangular, as long as showerhead 312 covers a substantial portion of
surface 304, as described more completely below.
Solvent vapor is introduced through opening 406 (FIG. 4C) into a chamber
408 of showerhead 312. Chamber 408 is an annular airspace which is filled
with solvent vapor. The solvent vapor then flows through perforations 404
so as to be uniformly dispersed through the underside of showerhead 312.
When article 302 (FIG. 5A) is spun in close proximity to showerhead 312 in
the direction of arrow A, vortices are formed as shown by arrows 500A,
500B, 500C and 500D. Such vortices move solvent vapor from between
showerhead 312 and surface 304 and move surrounding air to the space
between showerhead 312 and surface 304. Moving the surrounding air into
close proximity to surface 304 can cause premature drying of the chemical
and undesirable thickening in the chemical coating of surface 304. This is
prevented by ensuring (a) that showerhead 312 (i) is in sufficiently close
proximity to surface 304 and (ii) covers substantially the entirety of
surface 304 and (b) that the amount of solvent vapor dispersed through
showerhead 312 is sufficient to replace the amount of air spun from
surface 304, as described below.
As discussed above, the prevention of vortices between showerhead 312 and
surface 304 depends on the distance between showerhead 312 and surface 304
and the rate at which surface 304 spins. Additionally, if showerhead 312
is positioned too closely to surface 304, solvent vapor emanating from
perforations 404 (FIG. 4B) can erode chemical from surface 304 (FIG. 5A),
causing ring-shaped erosion of chemical from spinning surface 304. Good
results have been obtained with showerhead 312 spaced from surface 304
one-half of an inch.
While satisfactory results are obtained when the surface area of the
underside of showerhead 312 covers at least a substantial part of surface
304, it is preferred that the entirety of surface 304 is covered by the
underside of showerhead 312 including some overhang as a margin of safety.
For example, surface 304 (FIG. 5B), when spun in the direction of arrow A,
occupies an area defined by circle 502. Showerhead 312 is circular and
occupies a concentric circular area exceeding the are of circle 502 by a
10% safety margin. Good results are obtained when showerhead 312 occupies
a concentric circular area which is 100% to 110% of the area defined by
surface 304 as it spins, i.e., of the area of circle 502.
It is preferred that the amount by which the diameter of showerhead 312
exceeds the diameter of the space occupied by surface 304 during spinning
does not exceed approximately 10%. As chemical is thrown from the edge of
surface 304, the chemical collides with air surrounding surface 304 and
travels in paths which deviate from the plane in which surface 304 spins.
Some of this chemical leaves surface 304 on upward trajectories with
angles as high as 15.degree. from the plane in which surface 304 spins. If
showerhead 312 is excessively large, chemical is more likely to contact
showerhead 312, thereby requiring cleaning of showerhead 312 and
increasing the likelihood of particle contaminants being introduced during
the spin coating process. Thus, it is preferred that the diameter of
showerhead 312 does not exceed the diameter of the area occupied by
surface 304 during spinning by more than approximately 10%.
Thus, if showerhead 312 is sufficiently large and sufficiently close to
surface 304, the likelihood that "dry" air, i.e., air which is not laden
with solvent vapor, will be pulled into contact with chemical spreading
over surface 304 is substantially reduced. However, air in the local
atmosphere adjacent to surface 304 is thrown from the area adjacent to
surface 304 by centrifugal force similar to the force which spreads
chemical over surface 304. The throwing of air from the local atmosphere
leaves a reduced pressure in the airspace adjacent to surface 304. This
reduced pressure creates the vortices described above.
Such a reduced pressure over surface 304 is avoided by dispersing a
sufficient volume of solvent vapor through showerhead 312 to compensate
for the volume of air thrown from the airspace adjacent to surface 304. In
other words, the flow rate of the solvent vapor through showerhead 312 is
equal to the rate at which air is thrown from the local atmosphere plus
some additional amount included as a margin of safety. For example, the
flow rate of solvent vapor can be increased by 20% to provide this safety
margin. In one embodiment, solvent vapor is introduced into showerhead 312
at a rate of 25-50 SCFH (standard cubic feet per hour).
While FIG. 4A shows that the entire underside of showerhead 312 is
perforated with perforations 404, such is not necessary for satisfactory
performance of the present invention. Alternative embodiments of
showerhead 312 are shown in FIGS. 4D and 4E. FIG. 4D shows a showerhead
312-1 in which perforations 404 are located within a circular region of
the underside of showerhead 312-1. The circular region is concentric with
the center of rotation of surface 304 (not shown in FIG. 4D) and has a
diameter which is substantially less than the diameter of showerhead
312-1.
Showerhead 312-1 produces satisfactory results as solvent vapor dispersed
at the center of spinning surface 304 (FIG. 3) is moved out toward the
outer edges of spinning surface 304 by the same centrifugal force which
spreads the chemical over surface 304. No dry air comes into contact with
surface 304 (a) as showerhead 312-1 (FIG. 4D) is positioned in close
proximity to surface 304 (FIG. 3) and covers substantially the entire area
of surface 304 and (b) as the flow rate of solvent vapor through
showerhead 312-1 is sufficient to replace air thrown from the airspace
adjacent to surface 304.
Showerhead 312-2 (FIG. 4E) has perforations 404 positioned in the underside
of showerhead 312-2 to form a ring which is concentric with the center of
rotation of surface 304 (not shown in FIG. 4E). Showerhead 312-2 functions
as described above with respect to showerhead 312-1 (FIG. 4D). However,
since there is less solvent vapor dispersed inside the ring of
perforations 404 (FIG. 4E), chemical near the center of surface 304 (FIG.
3) is allowed to dry at a faster rate than the center would dry if solvent
vapor is dispersed directly over the center. Since chemical placed at the
center of surface 304 initially has not dried appreciably, it is not as
important to slow the drying of the chemical at the center of surface 304.
Showerhead 312-2 (FIG. 4E) allows the center of surface 304 (FIG. 3) to
dry at a faster rate while allowing the rate of drying of surface 304 away
from the center of surface 304 to be controlled as described herein.
The disclosed embodiment of the present invention represents a significant
improvement over the prior art as the rate of drying of the chemical on
spinning surface 304 can be varied widely. The placement of showerhead 312
in close proximity to surface 304 inhibits the evaporation of solvent from
the chemical. Introducing solvent vapor through showerhead 312 slows
drying of chemical on surface 304 even further. Introducing larger amounts
of solvent vapor through showerhead 312 can minimize the drying process
and prevent admixture of dry air in the airspace adjacent to surface 304.
By slowing the drying of chemical, surface 304 can be spun at slower speeds
even when spin coating rather large surfaces. Favorable results have been
obtained in coating surfaces as large as 14 inches by 16 inches. Slower
spin speeds allow improved process control since the chemical spreads
evenly toward the edges of surface 304 without uneven drying.
Additionally, slower spin speeds allows chemical leaving the center of an
edge of a square surface to fall sufficiently to avoid colliding with the
corner of a square or rectangular surface. Furthermore, back splash is
prevented, yielding a cleaner process. "Back splash" refers to
contamination of the underside of article 302 (FIG. 3), which extends
beyond chuck 306, by a mist of chemical which is caused by the turbulence
of spinning article 302 and the chemical thrown from spinning surface 304.
Thus, slower spin speeds improve the coating of corners of square and
rectangular surfaces and reduce the likelihood of contamination.
The particular spin speed which provides a particularly good coating
depends on the following factors: (1) the size of surface 304, (2) the
particular solvent contained by the chemical, (3) the amount of the
solvent in the chemical, (4) the temperature of the chemical, and (5) the
desired thickness of the chemical coating. One embodiment of the present
invention coats a 14-inch by 16-inch rectangular substrate with a coating
of Shipley Microposit XP-90190-21 photoresist chemical with a thickness of
1.5 microns. Shipley Microposit XP-90190-21 is available from The Shipley
Company of Newton, Mass. The disclosed embodiment of the present invention
can accurately coat surfaces to any of a wide range of thicknesses. The
thickness that is desired is determined by the particular application for
which the surface is coated. In the particular use of the present
invention described herein, 1.5 microns is defined as the desired
resulting thickness of the coating of surface 304.
For the particular solvent and the amount of solvent in the Shipley
Microposit XP-90190-21 chemical when the chemical is at a temperature of
approximately 20.degree. to 22.degree. C., particularly good results are
obtained with a spin speed of 1000 rpm to 1500 rpm. To properly coat the
14-inch by 16-inch surface, showerhead 312 is circular and approximately
21 inches in diameter.
In particularly large surfaces, good results have been obtained by wetting
surface 304 with solvent prior to application of chemical. Solvent is
introduced as solvent vapor through showerhead 312 which then condenses on
surface 304 or is deposited directly on surface 304 through chemical tube
310. Surface 304 is spun until the solvent is about 1,000 .ANG. thick. A
series of circular interference fringes flowing from the center of surface
304 can be visually observed when the solvent approaches 1,000 .ANG..
Chemical is applied to surface 304 with 1,000 .ANG. thick layer of solvent
coating surface 304. As chemical comes into contact with surface 304, the
layer of solvent facilitates chemical flow. Thus, coating of surface 304
can be accomplished at substantially reduced spin speeds as less
centrifugal force is required to draw the chemical to the edges of surface
304. Additionally, since very little solvent is present on surface 304
when chemical is introduced, the solvent is quickly absorbed by the
chemical and therefore has no detectable effect on the thickness of the
coating of chemical produced.
An embodiment of the invention in which surface 304 is wetted with solvent
immediately prior to applying chemical to surface 304 is shown in FIG. 6.
Solvent is introduced to the center of surface 304 through a solvent tube
602 and an amount of chemical is subsequently introduced through chemical
tube 310. Solvent tube 602 is displaced from the center of surface 304 and
is therefore angled at an open end such that solvent introduced through
the open end will be deposited on the center of surface 304.
FIG. 7 shows the embodiment of FIG. 6 wherein solvent tube 602 and chemical
tube 310 are used in conjunction with showerhead 312B. Showerhead 312B
(FIG. 8) is as described above with respect to showerhead 312 with the
exception that showerhead 312B has a hole 802 for receiving solvent tube
602.
Vapor source 316 (FIG. 3) is shown in greater detail in FIG. 9. A tank 902
is partially filled with a solvent 910. For example, in conjunction with
Shipley Microposit XP-90190-21, solvent 910 can be Shipley EBR-10 or
Shipley EC11, both of which are available from The Shipley Company of
Newton, Mass. A seal 904 is used to seal in an airspace 914 above solvent
910 in tank 902. A gaseous diffusion tube 906 passes through seal 904 and
extends to near the bottom of tank 902. Gaseous diffusion tube 906 has a
fritted glass end 908 which is emersed in solvent 910. An output tube 916
also passes through seal 904 but, unlike gaseous diffusion tube 906, does
not reach solvent 910. Instead, an open end of output tube 916 is in
airspace 914.
Vapor source 316 operates as follows. Nitrogen gas, or other generally
non-reactive gas such as ordinary air, is introduced through a tube 920
into gaseous diffusion tube 906. For example, tube 920 can be connected to
an air pump or nitrogen gas source (neither shown). The nitrogen gas
passes through gaseous diffusion tube 906 to fritted glass end 908 at
which point the nitrogen gas passes through fritted glass end 908 into
solvent 910 thereby forming bubbles 910. As bubbles 912 are formed in
solvent 910 and pass through solvent 912 to airspace 914, bubbles 912
become saturated with solvent vapor. Seal 904 is air-tight such that
solvent vapor from airspace 914 flows through output tube 916 at the same
rate at which nitrogen gas is introduced through tube 920. Solvent vapor
passes through output tube 916 to gas tube 314 and therethrough to
showerhead 312 (FIG. 3).
Thus, by introducing nitrogen gas through tube 920 (FIG. 9) of vapor source
316 at a specific rate, solvent vapor flows through gas tube 314 at that
same specific rate. The amount of solvent vapor that can be produced by
vapor source 316 is limited by the rate at which nitrogen gas can flow
through fritted glass end 908. For some applications of the present
invention which require particularly heavy flow of solvent vapor, a second
embodiment of a vapor source (FIG. 10) provides increased solvent vapor
capacity.
Inside chamber 408 of showerhead 312C, immediately above perforations 404,
is a solvent-absorbent, gas permeable, annular filter 1006. Also inside
chamber 408 of showerhead 312C is a drip tube 1002. Drip tube 1002 has
perforations 1004 along a length near an end 1002E of drip tube 1002. End
1002E is sealed. Perforations 1004 are all within chamber 408 and a port
1002P through which drip tube 1002 passes through the outer wall of
showerhead 312 is sealed such that no gas can pass through port 1002P.
A solvent in liquid form is introduced through drip tube 1002 into chamber
408 of showerhead 312C. The solvent drips through perforations 1004 and
saturates filter 1006. Gas tube 314 (FIG. 3) is connected to a source of
nitrogen gas or of any other generally non-reactive gas. In this
illustrative example, gas tube 314 is connected to a source of nitrogen.
Nitrogen gas is introduced through opening 406 (FIG. 10) into chamber 408.
Nitrogen gas passes through filter 1006. As nitrogen gas passes through
filter 1006, which is saturated with liquid solvent as described above,
the nitrogen gas becomes saturated with solvent vapor. The solvent-laden
nitrogen gas then passes through perforations 404 as described above.
Thus, FIG. 10 illustrates a second embodiment of a vapor source in
accordance with the present invention in which solvent vapor is formed by
passing nitrogen gas through a solvent saturated, gas permeable filter.
Another embodiment of the present invention is shown in FIGS. 11A, 11B,
12A, and 12B. Article 302 is secured to chuck 306-11 by applying a vacuum
through chuck 306-11 to the underside of article 302 as is commonly done
in the art. As a safety precaution, article 302 is held in place on chuck
306 by several retaining pins 306P (FIG. 12A). Chuck 306-11 (FIG. 11A) is
raised to receive article 302 as bearing 1112 allows chuck 306-11 to be
moved in the vertical direction. Dispensing head 310A is positioned over
the center of surface 304 of article 302 as shown in FIGS. 11A and 12A.
Dispensing head 310A and dispensing arm 310B (FIG. 12A) are hollow and are
connected so as to permit chemical to be dispensed through dispensing arm
310B to dispensing head 310A and therethrough onto surface 304. Once
chemical is dispensed onto surface 304, dispensing arm 310B and dispensing
head 310A are moved along track 310T in the direction of arrow A to the
position indicated in FIG. 12B.
Above surface 304 (FIG. 11A) is showerhead 312C. Showerhead 312C is curved
so as to redirect solvent vapor from the edge of spinning surface 304 to
the center of spinning surface 304. Since chemical is dispensed through
dispensing head 310A, there is no need for a hole in the center of
showerhead 312C to perform this function (see hole 402 (FIG. 4A) of
showerhead 312). Showerhead 312C (FIG. 11A) is supported by solvent vapor
supply channel 314C through which solvent vapor is introduced to
showerhead 312C. Solvent vapor supply channel 314C is connected to solvent
vapor supply channel 314B and therethrough to solvent vapor supply channel
314A. Positioned between showerhead 312C and solvent vapor supply channel
314B are a primary containment 1102A and a secondary containment 1102B
which contain chemical and solvent vapor for the protection of human
operators of the apparatus shown in FIGS. 11A and 11B. Solvent vapor
supply channel 314A is movable in the vertical direction. As solvent vapor
supply channel 314A is connected to solvent vapor supply channels 314B and
314C, primary containment 1102A, secondary containment 1102B, and
showerhead 312, movement of solvent vapor supply channel 314A causes
corresponding movement of solvent vapor supply channels 314B and 314C,
primary containment 1102A, secondary containment 1102B, and showerhead
312C. Solvent vapor supply channels 314A, 314B, and 314C; showerhead 312C;
primary containment 1102A; and secondary containment 1102B are shown in
the "up" position in FIG. 11A.
After chemical is dispensed through dispensing head 310A through dispensing
arm 310B, dispensing head 310A and dispensing arm 310B are moved along
track 310T to the position shown in FIGS. 12B and 11B. Solvent vapor
supply channels 314A, 314B and 314C are then lowered as shown in FIG. 11B.
Primary containment 1102A is positioned against a bowl liner 1104 so as to
form a primary sealed chamber 1118A. Bowl liner 1104 can be made of
plastic inexpensively and can therefore be made disposable. Secondary
containment 1102B contacts a support structure 1116 to thereby form a
secondary sealed chamber 1118B which surrounds primary sealed chamber
1118A. Additionally, the lowering of solvent vapor supply 314C lowers
showerhead 312C into close proximity with surface 304.
Using bearing 1112, chuck 306-11 is lowered so as to position surface 304
below lip 1104A of bowl liner 1104. Bowl liner 1104 is shaped such that
chemical thrown from surface 304 which strikes bowl liner 1104 below lip
1104A is directed toward a drain 1106 through which excess chemical is
collected. Additionally, excess solvent vapor and chemical mist are drawn
through an exhaust port 1108 and an exhaust manifold 1110. By directing
excess chemical to drain 1106 and by directing excess solvent vapor and
chemical mist through exhaust port 1108 to exhaust manifold 1110, the
likelihood of back splash on the underside of article 302 is reduced. To
further reduce the likelihood of back splash on the underside of article
302, ends 306-11A of chuck 306-11 extend beyond the underside of article
302. Any vapors of chemical escaping the seal between bowl liner 1104 and
primary containment 1102A are drawn from secondary containment chamber
1118B through port 1114 in support structure 1116. Thus, human operators
operating the apparatus shown in FIGS. 11A, 11B, 12A and 12B are protected
from any ill effects of chemical mist or solvent vapor.
While specific embodiments are disclosed herein, the disclosed embodiments
are illustrative only and are not to be limiting of the present invention.
The present invention is therefore limited only by the claims which
follow.
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