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BACKGROUND OF THE INVENTION
The invention relates to fluid application systems for subjecting
substantially planar objects to fluids for cleaning, etching, developing
of photoresist and the like.
DESCRIPTIION OF THE PRIOR ART
Automatically controlled wet processing of thin semiconductor wafers by
immersing in various fluids, liquid and gases, has been used. These wafers
are commonly a few mils in thickness and up to several inches in diameter.
The semiconductor wafers are made of silicon, germanium or III-V
semiconductor compounds and are extremely brittle and fragile. In the
fabrication of semiconductor devices, a series of fluid applications
involving cleaning, etching, photoresist development and so forth are
important to these processes. Following the fabrication of semiconductor
devices such as transistors, diodes and integrated circuits in the
semiconductor wafer, the wafer is cut into many chips which each contain
the desired transistor, diodes or integrated circuits. These chips are
then mounted on typically a ceramic substrate and electrically and
physically attached thereto. These resulting modules require cleaning
procedures so as to remove residual solder fluxes and the like which
remain on the module after the physical and electrical joining processes.
Where the flip chip type of semiconductor joining technique is used such
as described in the L. F. Miller U.S. Pat. No. 3,429,040, issued on Feb.,
25, 1969, the cleaning of solder fluxes and the like which are between the
semiconductor chip and the ceramic substrate is particularly difficult.
Workers in the semiconductor field have designed techniques for treating
semiconductor wafers in automated systems. U.S. Pat. No. 3,489,608, to
Bernard Jacobs, issued Jan. 13, 1970, describes an apparatus for
chemically treating a plurality of semiconductor wafers. The wafers are
placed on a carrier which rotates within a chamber. As the carrier
rotates, liquid or gaseous chemicals are sprayed onto the wafers. The
movement of the wafers relative to the spray brings about an intimate
contact between the chemicals and the wafers to produce the desired
chemical treatmemts.
U.S. Pat. No. 3,779,179, to Gertrude L. Thomas, issued Mar. 26, 1974,
describes another technique for fluid treatment of semiconductor wafers.
In one preferred embodiment a container is utilized to hold a quantity of
the processing solution. A carrier holding a plurality of components is
immersed in the processing solution to enable the desired treatment of the
components. The processor has a plurality of apertures located below the
components in the carrier tray when the tray is immersed in the processing
solution. The plurality of apertures release a precisely controlled amount
of gas into the processing solution below the components being processed
to provide precisely controlled agitation of the solution in contact with
the component to thereby effect the desired treatment.
U.S. Pat. No. 3,071,178 to M. S. Howeth, issued Jan. 1, 1963, describes an
apparatus for the controlled etching of metal. This apparatus includes an
autoclave wherein the etching or corrosion solution is applied therein by
vapor form within an atmosphere, the temperature and pressure of which are
controlled at their optimum values for the etching process.
U.S. Pat. No. 3,760,822 to Arthur Evans, issued Sept. 25, 1973, describes a
machine for cleaning semiconductor wafers wherein the cleaning solvent is
dispensed under pressure using nitrogen for this purpose. After dispensing
the solvent, the solvent line is closed by a suitable valve and nitrogen
alone is used to blow off to dry the wafers while they are spinning in a
specifically designed semiconductor wafer holder. The wafer on each vacuum
chuck is held thereto by the vacuum drawn through a pattern of grooves on
the top surface of the chuck whereas the solvent and gas blow-off with
respect to the wafer held on the particular chuck is dispensed from the
underface of the vacuum chuck above the wafer in question.
SUMMARY OF THE PRESENT INVENTION
A fluid application system has been developed which includes a specifically
designed agitation mechanism which allows the performance of the various
fluid application techniques onto a plurality of stationary semiconductor
wafers or modules in a standard carrier. The prior art techniques almost
universally have required the movement of the objects to be treated as an
important part of the treatment process. The present agitation mechanism
is so efficient and effective that the movement of the objects is not
required and therefore there is a reduced possibility for the injury to
the objects being treated. Further, the agitation mechanism is positioned
closely adjacent to the objects and since it does not take up a great deal
of room, a series of these agitation mechanisms can be positioned one over
the other with additional of the objects to be treated placed under each
of the series of these agitation mechanisms. This structure then makes for
an efficient system to treat large numbers of either semiconductors wafers
or modules.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows bench mounted module cleaning chambers of one embodiment of
the invention;
FIG. 2 illustrates a close-up view of a module cleaning chamber with a
module carrier outside the chamber;
FIG. 3 shows a partially sectioned side view of the fluid application
system with the chamber open and the module carrier outside of the
agitation mechanisms;
FIG. 3A illustrates a sectional view of FIG. 3 along line 3--3.
FIG. 4 shows a partial exploded view along its front to back centering of
the agitation mechanism;
FIGS. 5A, 5B, 5C and 5D illustrate the operation of the agitation
mechanism;
FIG. 6 shows a schematic representation of the electrical and fluid flow
connections of the fluid application system shown in FIGS. 1-5D;
FIG. 7 shows a chamber which is constructed by having each internal surface
of the chamber made of an agitator mechanism;
FIG. 8 illustrates schematically a modification of the agitation mechanism;
and
FIG. 9 shows a portable type agitation mechanism.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The equipment may include in one embodiment three bench mounted cleaning
chambers, as shown in FIG. 1, each chamber being assigned to one of the
three cleaning categories. The three cleaning process categories are:
1. General Cleaning - Removal of general contaminents resulting from
storage and handling.
2. Flux cleaning - Removal of flux residues after chip joinings.
3. Pre-encapsulation cleaning - Removal of particulates and moisture.
The fundamental operating principle of the chamber is analogous to the
small home dishwasher appliance. It requires an introduction of parts into
an enclosure where they remain stationary while the various liquids and
gases are introduced in sequential steps. A metered amount of cleaning
fluid, liquid or gas, is used for each step and upon completion, drained
into a waste reservoir for reclaimation.
The following description relating to the operation of the module cleaning
embodiment may be understood with the help of FIGS. 1, 2 and 3. The
modules are introduced into the chamber 1 in batched groups contained in a
standard manufacturing carrier 2. Within the carrier are four module
pallets 3, spaced apart in a vertical array, each containing a horizontal
matrix of modules 4. The carrier 2 is manually placed on a support
platform 5 attached to the chamber door 6. A cycle start button is
manually depressed. All operations hereon can be automatically sequenced
and controlled via a pre-programmed process controller. The chamber door 6
is closed by a two way air cylinder 7, as seen in FIG. 3, the door being
supported by two shafts 8, as seen in FIG. 2, each guided by a pair of
bearing blocks 9 containing linear ball bushings 10. As the door is closed
against a compressable seal 11, four door locks 12, one at each corner,
pass through their respective slots 13 in the door 6, rotate
counterclockwise as the pin 14 bears and wedges the door against the seal
11 resulting from the cumulative force of the pressure angle of the cam
insert pairs 15 located at each corner of the door 6. The position of the
carrier 2 completely encompasses the four agitation mechanisms 16 and the
mass member 17, such that each agitator 16 is above and parallel to the
substrate plane established by the four pallets 3. The operation and
description of the agitation mechanism 16 is given hereinafter.
Solvent is supplied through input port 18 and out each nozzle plate of the
four agitation mechanisms 16, filling the chamber with a premeasured and
temperature conditioned solvent. The process engineer has the option of an
initial soak step or an initial agitation step or a combination of both,
applied intermittently. When the time interval for this process step is
completed, the solvent is drained through port 19 into a holding tank for
reclaiming. The step can be repeated or spray rinsed through the
agitators, or both, or gas dried (nitrogen or air) through the agitator,
or any combination the process engineer desires. During gas drying, the
chamber is exhausted via port 20. At the completion of the process cycle,
the door locks 12 rotate clockwise, aligning the pins 14 with the slots 13
and the double acting cylinder 7 pushes the door open allowing the carrier
2 to be removed.
The agitation mechanism 16 is made up of twelve basic parts. FIG. 4 shows a
partial exploded view cut along its front to back centering. The mechamism
is assembled as follows. First, the nozzle plate 27 having a square matrix
of closely spaced holes 38 and two piston locator pins 29 is mounted and
sandwiching an elastomer gasket seal 26 to the countersunk surface 39 of
the piston frame 24 fastened in place at its perimeter by screws 31. The
square piston 25 having a countersunk slot 40 on one side edge and a
series of long parallel holes 37 drilled perpendicular to slot 40 and
having the same centering spacing as the rows of holes contained in the
nozzle plate 27 along the Y--Y axis. Spray holes 42 are drilled
intersecting the long holes 37 and having the same centering spacing as
the rows of holes contained in the nozzle plate 27 along the X--X axis.
Six blind clearance holes are drilled in the bottom surface of the piston
25. Four of which pocket the four compression springs 28 and the remaining
two locate the piston hole matrix to the nozzle plate hole matrix via the
two locating pins 29. The square piston 25 is then mounted to the bottom
surface of the elastomer diaphram 22 and retained by plate 23 and fastened
together with screws 32. The assembly as described is placed on top of the
piston frame 24. The piston 25 fits within the square opening of the
piston frame 24. The elastomer diaphram 22 rests on top of the piston
frame 24 and is sandwiched and held down by the pneumatic chamber plate 21
and fastened together at the perimeter with screws 30. The four agitator
mechanisms 16 are mounted to a manifold plate 43, as seen in FIG. 3, which
is mounted to the back surface of chamber 1 and sealed with an elastomer
gasket 44. The manifold plate 43 permits communication of the solvent and
gases input at ports 18 and 18' respectively with the agitator mechanism
16.
The agitator mechanism 16 which is a form of a diaphram pump is shown in
FIGS. 5A. 5B, 5C, and 5D. The pmup has a pneumatic chamber 33 and a fluid
chamber 34 separated by an elastomer diaphram 22. It's operation is as
follows: The parts to be cleaned, in this case the modules 4 contained in
pallets 3 parallel and under the agitator mechanism 16, are all submerged
in the cleaning solvent contained in chamber 1, as previously described.
The agitation cycle begins when compressed air is allowed through inlet
port 35 via port 18' as shown in FIG. 3A. The air pressure forces the
diaphram/piston 25 down urging the solvent contained in the fluid chamber
34 through the holes in the nozzle plate 27 thereby impinging by spraying
the module surfaces and flushing the dissolved contaminate away.
Exhausting the compressed air as shown in FIG. 5B, the four springs 28
having been compressed, restore the piston 25 in the up position pulling
in the solvent and filling the fluid chamber 34. The action described is
repeated many times during the agitation process step. Frequencies of up
to 200 cycles/minute can be obtained. The gauge air pressure can be
adjusted permitting either a gentle or forceful agitation cycle as
determined by the product being cleaned.
During the solvent spray rinse process step, the solvent is removed from
the chamber by draining as described earlier. Compressed air is allowed
through inlet port 35, for this purpose a lower pressure, sufficient to
depress the four compression springs and allowing the piston 25 to rest on
the nozzle plate 27 as shown in FIG. 5C. In this position the chemical
supply port 36 of the piston frame 24 is aligned with the distribution
slot 40 and holes 37 of the piston 25 permitting solvent to flow under
pressure through the circuit described and out the smaller spray holes 42
and through the larger nozzle plate holes 38. The piston 25 having been
prealigned with the nozzle plate 27 via the locating pins 29, therefore
superimposing the smaller spray holes 42 directly over the larger nozzle
plate holes 38. The spray holes 42 are designed such to impede the solvent
flow thereby creating a fine spray mist used for rinsing the modules 4.
The same procedure is used for filling the chamber 1 with solvent as that
described for spray rinsing, however, with the drain 19 in a closed
position.
During the gas drying process step, shown in FIG. 5D, heated nitrogen or
air is used to purge the solvent and eventually drying the modules 4 using
the same procedure defined for spray rinsing. During this time the drain
19 and exhaust port 20 are opened as shown in FIG. 3.
FIG. 6 in a self-explanatory manner illustrates the electrical controls for
agitation, spray and nitrogen dry of the present fluid application system.
The fluid plumbing is also shown therein.
The arrangement of the agitator mechanism can be modified in many ways. Its
use is not limited to substrate or module cleaning. It can be applied to
photolithographic process, acid etching, etc. for semiconductor wafer
processing. An example of its use and arrangements can be best described
by reference to FIG. 7 which shows each internal surface of a tank made up
of agitator mechanisms 16'.
A further example of a possible modification is shown in FIG. 8 wherein the
agitator piston is driven with a mechanical or electrical oscillator. The
FIG. 8 shows a chamber 50 to hold the fluid to be agitated, a drain 52
constructed with the frame of the chamber, and a motor driven oscillating
means 54 suitably connected to the piston (not shown). In this embodiment
the agitation mechanism 56 is in the bottom of the chamber.
FIG. 9 shows a portable agitation mechanism unit 60 having two agitation
mechanisms 62 and means 64 between the two mechanisms for holding an
object or objects 66 to have fluid applied thereto. The mechanisms 62 each
have the orificed plate positioned on one side of the object or objects 66
to be subjected to the fluid. A handle 68 allows for easy movement of the
unit. Flexible tubes 70 connects the agitation mechanisms to a gas source
for activation of the cyclical agitation of the mechanism. The unit 60 can
be successively moved through a series of chemical fluid applications, 71,
72, 73, 74 and 75. For example, in a photoresist developing process (after
light exposure), the chambers could contain the following 71 -- an
alkaline solution pH 7, 72 -- deionized water, 73 -- alkaline solution, 74
-- deionized water and 75 -- dry-nitrogen gas. In chemical etching or
machining the chambers could contain 71 -- acid or alkaline solution, 72
-- deionized water immersion agitated, and 73 -- deionized water sprayed.
While the invention has been particularly shown and described with
reference to the preferred embodiments thereof, it will be understood by
those skilled in the art that various changes in form and details may be
made therein without departing from the spirit and scope of the invention.
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