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BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
This invention relates to methods and apparatus for treating wafer-like
articles; and, more particularly, for treating thin, fragile, wafer-like
articles, such as semiconductor wafers. Such treatment may include, but is
not limited to, cleaning, scrubbing, abrading, grinding, and coating.
Although the invention will be described particularly with reference to an
embodiment adapted for scrubbing and cleaning semiconductor wafers, it
will be appreciated that the invention is not so limited. For example, the
invention may be employed for treating, e.g., scrubbing and cleaning,
other thin, fragile articles, such as photolithographic masks.
In the field of semiconductor manufacture, considerable attention has been
directed toward reducing manual processing steps by replacing those steps
with automatic machinery. Such attention is motivated not only by a desire
to reduce cost, but also to improve quality by eliminating such factors as
breakage and variation in the degree of treatment from article to article.
2. DESCRIPTION OF THE PRIOR ART
Prior to this invention, some mechanized apparatus has been available for
treatments such as scrubbing semiconductor wafers. An early form of such
apparatus is disclosed in U.S. Pat. No. 3,585,668 issued June 22, 1971 to
R. J. Jaccodine et al. The Jaccodine et al. apparatus includes a
substantially horizontally disposed, rotatable holder. Wafers are inserted
into pockets in the holder, and rotation of the holder brings one side of
the wafers to rotating brushes and detergent and rinsing mechanisms. In
such apparatus the wafers are initially loaded and then scrubbed on one
side, after which the wafers must be turned over if scrubbing on the other
side is desired. It is generally desirable to eliminate such multiple
handling.
An improvement over the above-described apparatus is disclosed in U.S. Pat.
3,664,872 issued May 23, 1972 and 3,748,677 issued July 31, 1973 to G. A.
Frank et al. The Frank et al. apparatus is adapted for simultaneously
scrubbing and cleaning both sides of a semiconductor wafer, inasmuch as
the wafers are held in generally open slots in a vertically rotating disc.
The disc conveys the wafers between a pair of opposed counter-rotating
brushes within a detergent spray. The wafers are held in the disc by
pockets formed by ledges overhanging the periphery of each slot.
It is advantageous to eliminate such overhanging ledges to prevent masking
of those portions of the wafers which are covered by such ledges to
thereby improve the cleaning of the entire surfaces of the wafers. Also,
to improve the cleaning of the wafers, it is preferable not to use pockets
which can trap cleaning residues and thereby detract from the cleaning of
the wafers. Another reason for eliminating such pockets is that they
support the wafers, which are fragile, only by small portions of the
peripheries and therby subject the wafers to stresses produced by the
brushes and by the water and detergent streams.
SUMMARY OF THE INVENTION
In accordance with this invention, wafer-like articles are treated by
inserting the articles into open slots in a substantially plane conveying
member disposed between a pair of closely spaced, immobile, parallel
plates which laterally retain the articles in the slots. The member
conveys the articles in succession to a first aperture in one of the
plates, through which one side of each article is exposed to a first
treatment. Further conveyance brings each article in succession to an
aperture in the other plate, through which the other side of each article
is exposed to a second treatment.
In a particular disclosed embodiment, the conveying member is a
substantially plane rotatable disc having a slotted periphery. As the disc
is rotated, each article is urged between the plates to an aperture in one
of the plates, through which one side of the article is exposed for the
desired treatment while the opposed side of the article is supported by
the opposed plate. Further rotation of the disc brings each article to an
aperture in an opposing plate through which the other side of the article
is exposed to a desired treatment, while the first side of the article is
supported by the first plate.
In the particular disclosed embodiment, the apparatus is adapted so that
still further rotation of the disc brings each article to an exit port
which is arranged in relation to the slots for gravity discharge of the
articles form the disc.
For cleaning treatments, which typically may involve scrubbing and
introduction of water and detergent streams, the disc advantageously is at
least partially submerged in a liquid so that articles emerging from the
disc are never exposed to air. Rather, the emerging articles exit from the
disc in the liquid to avoid any drying which could result in formation of
undesirable residues on the surfaces of the articles. Also for such
cleaning treatments, a water-bearing mechanism advantageously is used at
the input and exit ports to avoid adherence of the wet articles to the
opposed plates due to surface tension.
For treatments such as cleaning semiconductor wafers, the wafers
advantageously are inserted directly and automatically into the slots from
a multi-slotted magazine, which is indexed synchronously with the rotation
of the disc to permit wafers to transfer to the slots in the disc in
sequence. Also, for such treatments, the submerged container for receiving
the exiting articles advantageously is a multi-slotted magazine which also
is indexed in synchronism with the rotation of the disc to avoid any
manual handling of the articles whatsoever during the treatment process.
BRIEF DESCRIPTION OF THE DRAWING
The aforementioned and other features, characteristics, and advantages, and
the invention in general, will be better understood from the following
detailed description taken in conjunction with the accompanying drawing in
which:
FIG. 1 is an elevational view of one embodiment for treating articles; and
FIG. 2 is an exploded isometric view of the apparatus of FIG. 1.
DETAILED DESCRIPTION
As was alluded to hereinabove, the invention will be described in detail
with respect to a particular embodiment adapted for advantageously
scrubbing and cleaning wafers of silicon semiconductor material. However,
it is to be understood that the method and apparatus will function quite
successfully for other types of articles, such as photolithographic masks,
and for other types of treatment.
With current technology, silicon semiconductor material typically is
processed in the form of substantially circular wafers having a diameter
of one to three inches and a thickness from a few mils (10.sup..sup.-3
inches) to several tens of mils.
Referring now to the figures, wafers 11 are transferred from a wafer
container, such as a multi-slotted wafer magazine 12, into a slot 13 in a
disc 14. The transfer from magazine 12 to slot 13 may be accomplished
manually, or preferably, by an automatic technique such as will be
described later with reference to FIG. 1.
Disc 14 is a multi-slotted, plane, essentially circular member having a
plurality of slots 13 open to the periphery thereof. As illustrated, slots
13 are completely open laterally, in the sense that there are no
overhanging protrusions at the peripheral edges thereof. Disc 14 is
mounted on a shaft 15 by a conventional slot and key arrangement 16. Shaft
15 is coupled conventionally to a motor or gear train arrangement (not
shown) for imparting rotation to disc 14 via shaft 15.
Wafers 11 are retained laterally in the slots by a pair of opposed,
immobile, parallel plates 17 and 18 which are spaced sufficiently closely
to disc 14 so that the wafers cannot fall therebetween. In a particular
application, the wafers 11 may be approximately 20 mils thick, in which
case disc 14 may be typically of thickness about 25 mils and plates 17 and
18 would be spaced a few mils (in practice as close as feasible) from disc
14.
In operation, rotation of disc 14 brings each slot 13 and wafer 11 therein
to a first aperture 19 through which one entire side or face of wafer 11
is exposed to a rotating brush 20 as the wafer traverses aperture 19. A
nozzle 21, coupled to a manifold 22 to which can be selectively applied a
detergent solution D through port 23 and water W through a port 24, is
disposed so as to direct the appropriate solution onto brush 20 and
aperture 19. Brush 20, as shown, is coupled to a shaft 25 which is driven
by any suitable rotating means (not shown). An arrow 26 indicates a
preferred, but not necessary, direction of rotation for shaft 25 and brush
20.
Further rotation of disc 14 brings each wafer successively to an aperture
27 in plate 18, through which another entire side of wafers 11 are exposed
to another brush 28 and appropriate cleaning fluids. The fluids are
directed onto brush 28 and aperture 27 via another nozzle 29, which also
is coupled to a simple manifold 30 adapted to receive selectively a
variety of solutions W and D through ports 31 and 32. As seen, brush 28 is
mounted on a shaft 33 which is also coupled to and driven by rotation
means (not shown). An arrow 34 indicates a preferred but not necessary
direction of rotation for brush 28.
Apertures 19 and 27, as shown, advantageously are smaller in lateral extent
than the articles (wafers 11) to be cleaned, to avoid any tendency for the
articles to become dislodged from disc 14. However, of course, such
smaller size is not necessary to the practice of this invention.
It will be seen that the slots 13 in disc 14 are inclined toward the
direction of rotation of disc 14. Such direction of rotation is indicated
by an arrow 35. Such inclination of the slots 13 is, of course, not
necessary, but is preferred for the purpose of aiding in retaining the
wafers radially in the slots as treatments proceed; and such inclination
typically may be of about 30.degree. from a radial line extending from the
center of disc 14.
As assembled, plates 17 and 18 are held apart by a flat ring-like member
36, which is just slightly (a few mils) larger in internal diameter 37
than the external diameter of disc 14, and which includes an input opening
38 and an exit opening 39. Openings 38 and 39, of course, must be at least
as large as the wafers being treated. Member 36 also serves to retain the
wafers in the slots as they approach exit opening 39.
Opening 38, in combination with a slot 13 aligned therewith, may be thought
of as an input passageway. Similarly, opening 39, in combination with a
slot aligned therewith, may be thought of as a exit passageway. Aligned
with the input passageway and disposed in both plates 17 and 18 are a
plurality of openings, designated generally 40. The openings 40, which are
inclined at an acute angle relative to the longitudinal direction of the
input passageway, are for directing a fluid at that acute angle to act as
a water-bearing mechanism for urging a wafer into the slot. Such
directional fluid introduction is desirable to avoid sticking of wafers 11
to the wet inner surfaces of plates 17 and 18 due to surface tension.
Otherwise, such sticking could be a problem due to the nearly perfectly
flat wafers and internal surfaces of plates 17 and 18.
A similar plurality of openings, designated generally 41, in plates 17 and
18, are aligned with the exit passageway for urging the wafers from the
slots for similar reasons. Of course, the openings 40 and 41 are not
visible on the inner surface of plate 18 in FIG. 2, but as will be
understood, are disposed directly across from those of plates 17. Water or
other suitable fluid under pressure is introduced to openings 40 and 41
via conventional tubing 42' and 43' (FIG. 1) and input ports 42 and 43,
respectively, in plates 17 and 18. As will be appreciated, the water and
other solutions introduced via nozzles 21 and 29 will wet the entire inner
surfaces of plates 17 and 18 and of disc 14 as operation proceeds.
As shown, at least a lower portion of the apparatus including most of the
exit passageway is submerged in a suitable solution 44, such as water, in
a reservoir 45 so that wet slices emerging from the apparatus need not
come in contact with air. Such contact could cause undesirable drying and
residue formation. Disposed in solution 44 is a wafer magazine 46 having
one of its slots aligned with the exit passageway, as indicated by arrow
47. A suitable indexing mechanism, designated generally 48, is
synchronized with the rotation of shaft 15 so that the carrier 46 is
indexed to provide the next slot aligned with passageway 47 to
successively receive wafers from disc 14.
Indexing means 48 may include, for example, a sequential advancing pawl in
the form of a flexible pin 49 connected to a rigid member 50. The lower
end of member 50 is pivotally mounted on a pin 51; and the upper end of
member 50 is pivotally connected to an air cylinder 52 or other suitable
actuating means. Magazine 46 is slidably held in a track 53 in reservoir
45 so that the top of magazine 46 is in sliding contact or nearly in
contact with the bottom edge of plates 17 and 18. Pin 49 engages slots
(not shown) in the edge of magazine 46, which are aligned with the
wafer-receiving slots, so that when air cylinder 52 is actuated
synchronously with the rotation of shaft 15 and disc 14, magazine 46 is
moved sufficiently to present an empty slot in magazine 46 aligned with
exit passageway 47 when a wafer 11 exits from disc 14.
As mentioned above, wafers advantageously are also inserted automatically
from magazine 12 into disc 14. Exemplary apparatus for such automatic
insertion may include an indexing mechanism, designated generally 54,
analogous to indexing mechanism 48. As shown, mechanism 54 includes a
sequential advancing pawl in the form of a flexible pin 55 which engages
slots in the edge of magazine 12. Pin 55 is connected to a rigid member 56
which is pivotally mounted at one end on a pin 57 and which is pivotally
connected at the other end to an air cylinder 58.
Magazine 12 is slidably held in a track 59. Actuation of cylinder 58
synchronously with the rotation of shaft 15 and disc 14 allows wafers to
fall in sequence through void 38 and into empty receiving slots 13 aligned
with void 38.
It is important to the successful practice of a cleaning operation that the
degree of scrubbing achieved is sufficient to remove tenacious particles,
but not be so vigorous to result in scratching of the wafers or dislodging
them from disc 14. While the proper amount of scrubbing is to some extent
dependent upon such factors as time of scrubbing, speed of rotation of the
brushes, speed of rotation of the disc, and speed of advancement of the
disc past the brushes, it may generally be achieved in large measure by
the proper choice of brushes and distance between the brush and slice
surfaces.
It will be appreciated that such factors as brush stiffness and brush
quality are difficult of description, being dependent upon the type,
density, length, cross section and width of the bristles and upon the size
and shape of the brush. By way of example only, it has been found
satisfactory to use cylindrical nylon brushes, having circular cross
sections of from one to four inches and bristles from one-half to one and
one-half inches in length, with the bristles having a circular cross
section of from 0.006 to 0.012 inch. Spacing the brush such that 1/16 to
one-fourth inch of the ends of the bristles come in contact with the
wafers has been found to be appropriate.
With such brushes and spacings, a speed of rotation of about 2 to 10
revolutions per minute of the disc and a brush rotation speed of
approximately 10 to 350 revolutions per minute has provided suitable
scrubbing with brushes of the type mentioned hereinabove. Of course, such
speeds are only suggested and are not in any way required for the practice
of this invention.
At this point, it is believed the principles of the invention have been
described in sufficient detail to enable one skilled in the art to
practice the invention. Although the invention has been described in part
by making detailed reference to a specific embodiment, such detail is
intended to be and will be understood to be instructive rather than
restrictive. It will be appreciated that many variations may be made in
the structure and in the modes of operation without departing from the
spirit and scope of the invention as disclosed in the foregoing teachings.
For example, of course, a plurality of staggered openings may be provided
in either both plates 17 and 18 to enable successive treatments on either
or both sides of the articles. Similarly, a plurality of treating media,
such as a plurality of brushes, may be provided in each or any of the one
or more openings in each plate, as may appear desirable to a worker in the
art for particular treating operations.
Further, the conveying member need not be a rotatable disc. It may, for
example, be a substantially plane rectangular strip having a plurality of
openings for receiving and conveying articles between a pair of opposed
parallel plates having staggered apertures through which the articles are
exposed to desired treatments. Other suitably configured members for
conveying wafer-like articles between stationary, opposed lateral
retaining and supporting members will no doubt occur to workers in the
art, all within the spirit and scope of this invention as disclosed herein
.
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