U.S. patent number 3,661,253 [Application Number 04/882,179] was granted by the patent office on 1972-05-09 for retaining trays for semiconductor wafers and the like.
This patent grant is currently assigned to Monsanto Company. Invention is credited to Paul W. Cronkhite.
United States Patent |
3,661,253 |
Cronkhite |
May 9, 1972 |
RETAINING TRAYS FOR SEMICONDUCTOR WAFERS AND THE LIKE
Abstract
A series of marginally registrable plastic trays having a
plurality of wells for accommodating semiconductor wafers and
similar elements. The retaining wells are provided with a wall
having a surface configuration such that the critical surface of
the wafer does not contact the well. A removable cap is disposed
over each of the retaining wells and is provided with means for
engaging the upwardly presented surface of the semiconductor wafer.
Each of the trays is registrable with like trays so that a series
of these trays can be stacked, wrapped, and shipped as a unit.
Inventors: |
Cronkhite; Paul W. (St.
Charles, MO) |
Assignee: |
Monsanto Company (St. Louis,
MO)
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Family
ID: |
25380052 |
Appl.
No.: |
04/882,179 |
Filed: |
December 4, 1969 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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764472 |
Oct 2, 1968 |
3482682 |
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644966 |
Jun 9, 1967 |
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Current U.S.
Class: |
206/712;
229/406 |
Current CPC
Class: |
B65D
73/0035 (20130101); H01L 21/67346 (20130101) |
Current International
Class: |
H01L
21/673 (20060101); B65D 73/00 (20060101); H01L
21/67 (20060101); B65d 081/00 (); B65d
085/30 () |
Field of
Search: |
;206/65R,65K,72,1,18,45.14,46H,46FR,1.7 ;220/6R,97R
;229/2.5,43,14C |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
IBM Technical Disclosure Bulletin "Wafer Package," L. Hershoff,
Vol. 8, No. 11 April 1966, page 1642..
|
Primary Examiner: Dixson, Jr.; William T.
Parent Case Text
This application is a continuation-in-part of my copending
application Ser. No. 764,472, filed Oct. 2, 1968 (U.S. Pat. No.
3,482,682), which is in turn, a continuation-in-part of my
copending application Ser. No. 644,966, filed June 9, 1967, now
abandoned
Claims
Having thus described my invention, what I desire to claim and
secure by Letters Patent is:
1. A tray for retaining relatively thin flat semiconductor wafers
which have a critical surface and a surface opposed to said
critical surface, said tray comprising a supporting member having a
boss thereon which forms a recess sized to accommodate
semiconductor wafers, said recess having a wall which is
operatively connected to said supporting member and forming a
recess opening larger than the wafer to be supported in said
recess, said wall being of such size and shape to support a wafer
with the critical surface presented away from the opening and in
such manner that only the marginal edge portions of said wafer
contact said wall when oriented in substantially any position with
respect to said wall, cover means removably disposed over said
recess, and means operatively associated with said cover means for
engaging the surface of the wafer opposed to said critical
surface.
2. The tray of claim 1 further characterized in that a plurality of
recesses are operatively formed on said supporting member.
3. The tray of claim 1 further characterized in that an annular
bead is operatively associated with the upper end of said boss and
is sized to engage the cover means disposed thereon.
4. The tray of claim 3 further characterized in that each bead is
somewhat circular in vertical cross section.
5. The tray of claim 1 wherein said cover means is a caplike cover
member which has a dish-shaped wall including a downwardly
projecting surface which engages the wafer at a point somewhat
centrally thereof.
6. The tray of claim 1 further characterized in that said wall has
a bottom portion which is substantially flat and that a wafer is
disposed in substantially parallel relationship to said bottom wall
portion when located in said recess.
7. The tray of claim 1 further characterized in that said wall is
arcuately shaped.
8. The tray of claim 1 further characterized in that said wall has
a pair of tapered wall sections for supporting the wafer and a
bottom wall section, the latter being diametrally smaller than the
tapered wall sections so that a wafer may be disposed in spaced
relationship with respect to said bottom wall section.
9. A tray for retaining relatively thin flat semiconductor wafers
which have a critical surface and a surface opposed to said
critical surface, said tray comprising a supporting member having a
boss thereon which forms a recess sized to accommodate a
semiconductor wafer, said recess having a wall which is operatively
connected to said supporting member and forming a recess opening
larger than the wafer to be supported in said recess, a thin flat
semiconductor wafer disposed in said recess with its critical
surface presented away from the opening and having only its
marginal edge portions in contact with said recess when oriented in
substantially any position with respect to said wall, cover means
removably disposed over said recess, and means operatively
associated with said cover means for engaging the surface of the
wafer opposed to said critical surface.
10. The tray of claim 9 further characterized in that said wall is
arcuately shaped.
Description
This invention relates in general to certain new and useful
improvements in devices for storing and transporting semiconductor
wafers, and more specifically to a plurality of registrable trays
which are capable of accommodating a plurality of wafers.
In recent years, semiconductor devices such as silicon controlled
rectifiers have found widespread use in the electronics industry.
These semiconductor devices are made from semiconductor materials
which may have a plurality of layers of semiconductor material
having different conductivities and separated by a transition zone.
Semiconductor materials of this type having at least two layers of
different conductivities with a transition region therebetween are
very suitable for use in the formation of electronic members such
as diodes, transistors, switches and similar types of electronic
structure. One very effective method of producing semiconductor
materials is by the epitaxial deposition of silicon on a substrate
wafer formed of like material. Generally, the wafers involved must
be formed of single crystal silicon with precisely controlled
concentrations of doping impurities.
Frequently, the semiconductor wafers have a highly polished surface
which must remain free from contact with any foreign surface
whatsoever during storage and transporting thereof. It has
generally been found that when this polished surface contacts any
foreign surface, the surface tends to become contaminated and
marred. These slight marrings of the surface and the impurities
often materially interfere with effective further processing of the
wafers such as growth of epitaxial layers or fabrication of
semiconductor devices. In the past, transporting of the wafer
between steps in processing thereof has often caused serious
problems since it was not always possible to maintain the wafers in
a substantially clean atmospheric environment. Furthermore,
accidental contact with the surface of the wafer often occurred
through inadvertence which, in effect, made subsequent processing
steps futile and destroyed the value of the semiconductor
wafer.
These problems were even more severe during shipping of the wafers
to the purchasers thereof. Generally, each of the wafers had to be
enclosed in a specially designed bag of plastic or paper which was
treated in order to eliminate impurities. Even in this type of
container, it was impossible to prevent contact of the wafer
surface with the bag, per se. It was necessary to wrap these wafers
and stack them in such manner that a minimum of movement could be
obtained. However, due to this technique, the surface of a number
of wafers was often contaminated by the time they were received by
the user thereof. Accordingly, the various methods heretofore
employed for the handling, shipment and storage of semiconductor
wafers have not been very effective.
It is, therefore, the primary object of the present invention to
provide a series of marginally registrable nestable trays which are
capable of carrying semiconductor wafers in such manner that the
critical surfaces of the semiconductor wafers do not contact any
foreign surface.
It is another object of the present invention to provide a series
of retaining trays of the type stated which can be manufactured in
a mass-production operation and are capable of being constructed
with desired tolerance so that adverse surface conditions are not
created on the semiconductor wafers carried therein.
It is also an object of the present invention to provide a
retaining tray of the type stated for a plurality of wafer
diameters.
It is a further object of the present invention to provide
retaining trays of the type stated which are specifically designed
so that inadvertent handling of the wafers will not cause injury
thereof in the retaining trays.
It is an additional object of the present invention to provide
retaining trays of the type stated which are disposable and which
can be manufactured at a relatively low unit cost.
With the above and other objects in view, my invention resides in
the novel features of form, construction, combination, and
arrangement of parts presently described and pointed out in the
claims.
In the accompanying drawings:
FIG. 1 is a perspective view of a retaining tray which is
constructed in accordance with and embodies the present invention,
and showing a plurality of wafers disposed therein and caps
removably disposed over some of the retaining wells;
FIG. 2 is a fragmentary vertical sectional view taken along line
2--2 of FIG. 1;
FIG. 3 is a vertical sectional view similar to the sectional view
of FIG. 2 and showing portions of one of the retaining wells with a
cap disposed thereabove;
FIG. 4 is a fragmentary vertical sectional view similar to the
sectional view of FIG. 2 and showing portions of the retaining
wells of a pair of stacked trays with wafers disposed therein;
FIG. 5 is a fragmentary vertical sectional view similar to the
sectional view of FIG. 2 and showing a modified form of wafer
retaining tray constructed in accordance with an embodying the
present invention;
FIG. 6 is a fragmentary vertical sectional view similar to the
sectional view of FIG. 5 with a cap secured to the tray and
engaging a wafer disposed in the retaining well;
FIG. 7 is a fragmentary vertical sectional view similar to the
sectional view of FIG. 2 and showing a modified form of wafer
retaining tray having a somewhat arcuate bottom wall constructed in
accordance with and embodying the present invention;
FIG. 8 is a fragmentary vertical sectional view similar to the
sectional view of FIG. 2 and showing another modified form of wafer
retaining tray constructed in accordance with an embodying the
present invention;
FIG. 9 is a fragmentary vertical sectional view of a wafer tray
similar to the tray described in FIG. 8 and showing a wafer
disposed therein in such manner that it is not parallel to the
bottom wall of the retaining well;
FIG. 10 is a fragmentary vertical sectional view showing a wafer
tray similar to that of FIG. 8 with a wafer disposed therein in
another angulated position with respect to the bottom wall of the
retaining tray;
FIG. 11 is a fragmentary vertical sectional view similar to the
sectional view of FIG. 2 and showing another modified form of wafer
retaining tray having an arcuate wafer retaining wall which is
constructed in accordance with and embodies the present
invention;
FIG. 12 is a perspective view of an insert provided for removable
interposition between the cap and a wafer in the tray of FIG.
1;
FIG. 13 is a side elevational view of the insert of FIG. 12;
FIG. 14 is a fragmentary vertical sectional view, similar to FIG. 2
and showing the employment of the insert of FIG. 12 in the wafer
tray;
FIG. 15 is a vertical sectional view similar to the sectional view
of FIG. 2 and showing a wafer tray with a modified form of cap used
thereon; and
FIG. 16 is a perspective view of an insert which can be disposed
between a cap and the wafer disposed in the tray.
GENERAL DESCRIPTION
The present invention relates to a series of registrable retaining
trays which are designed to carry semiconductor wafers having a
highly polished or epitaxial surface. Each of the retaining trays
is preferably made of a somewhat rigid but yet sufficiently
flexible material to absorb shock loads during shipment. The trays
are formed with a plurality of upstanding circular bosses which are
substantially hollow in the provision of wafer retaining wells. In
one embodiment of the tray of the present invention, the retaining
wells include an inwardly extending shoulder which merges into an
inwardly tapered wall section, which is designed in such manner
that a wafer disposed within the well with the critical surface
presented in a generally downward position does not contact any
surface of the well. In essence, the tapered wall section is
so-designed that only the peripheral margins of the wafer come into
contact with any portion of the well. When the wafer is disposed in
a substantially horizontal position, the peripheral margins of the
entire surface of the wafer will frictionally engage the tapered
wall section at the proper diametral cross section. In this
position, the wafer is spaced from the bottom wall of the retaining
well.
Each of the bosses is provided with an annular bead at its upper
end and is adapted to receive a snap-fitting lid or cover member.
Each of the lids is provided with a circular annular shoulder for
engaging the boss and an inwardly struck engaging finger so that
the lid may be snap-fitted over the bead of the boss in a fairly
tight position. Furthermore, the lid is provided with a downwardly
extending central portion which engages the upwardly presented
surface of the wafer and, thereby holds the same in a substantially
immobile position in the retaining well. The portions of the
supporting surface extending between each of the retaining wells is
sized to fit snugly between the upwardly extending bosses of a
marginally registered tray disposed therebeneath. In this manner,
it is possible to marginally align each of the trays during a
vertical stacking operation. Furthermore, the portions of the trays
which extend between adjacent bosses will fit snugly therein so
that each of the trays can be stacked in marginal registration.
The present invention also provides a modified form of wafer
retaining tray which includes a support plate and a plurality of
upstanding bosses, each being hollowed in the form of a wafer
retaining well. In this embodiment of the wafer retaining tray, the
upstanding boss is provided with an annular bead which is somewhat
rectangular in horizontal cross section. The upstanding boss is
provided with an annular groove for engaging an inwardly extending
annular finger formed on a removable cap.
The present invention also provides a modified form of wafer
retaining tray which includes a tapered wall section and a somewhat
arcuately shaped bottom wall as opposed to a flat bottom wall.
Another embodiment of the wafer retaining tray of the present
invention includes a pair of tapered walls for supporting
semiconductor wafers of different diametral sizes. In this type of
wafer retaining tray, the bottom wall may be either flat or
arcuately shaped.
The wafer retaining tray of the present invention can also be
constructed in a manner where the wall of the recess is
hemispherical or arcuately shaped, there being no provision for a
tapered wall. In this manner, the wafer is supported in the
arcuately shaped wall. The only criterion for the type of wall is
that the wafer must be supported with the critical surface
presented downwardly and the wall must have a shape and size such
that the critical surface of the wafer does not contact any portion
of the retaining wall.
A number of cap systems can be used with wafer trays of the present
invention. One of these cap systems provides for an insert
removably disposed between the cap and the wafer so that the insert
holds the wafer into contact with the wall of the recess. The
insert may be fastened to the cap or removably interposed between
the cap and the wafer.
DETAILED DESCRIPTION
Referring now in more detail and by reference characters to the
drawings, A designates a retaining tray constructed in accordance
with the present invention. The retaining tray A generally
comprises a relatively flat sheet or so-called "support plate" 1
which is integrally formed with two rows of upstanding bosses 2
having a total of five bosses in the manner as illustrated in FIG.
1. It should be recognized, however, that the sheet 1 could be
preformed with any desired number of bosses and the invention is
not limited to the number of bosses illustrated or to the specific
pattern in which they are formed in the retaining sheet 1.
Each of the bosses 2 is formed with an inwardly and upwardly
extending annular side wall 3 which integrally merges into an
enlarged annularly extending somewhat circular bead 4 at its upper
end in the manner as illustrated in FIG. 2. The circular bead 4, in
turn, merges into an inwardly presented annular shoulder 5, which
is in turn integrally formed with a downwardly and inwardly
extending tapered wall 6. By reference to FIG. 2, it can be seen
that the tapered wall 6 is diametrally larger than a wafer W at its
upper end and is diametrally smaller than the wafer W at its lower
end. The tapered wall 6, in turn, merges at its lower end into a
slightly convex bottom wall 7. Thus, it can be seen that the
hollowed portion of the boss 2 serves as a retaining well 8 for
accommodation of wafers W of a specific size.
The bottom wall 7 is slightly diametrally smaller than a
semiconductor wafer W, which is to be disposed within the retaining
well 8. Accordingly, it can be seen that a wafer W which is
disposed therein in a position substantially parallel to the bottom
wall 7 is supported on the tapered wall 6. It should also be
understood that the bottom wall 7 could be hemispherical in shape
in accordance with the present invention.
Generally, the retaining tray A of the present invention was
designed for use with polished silicon semiconductor wafers.
However, the invention is by no means limited to these types of
wafers and the various applications thereof are set forth in more
detail hereinafter. For purposes of illustration and description of
the present invention, it may be assumed that the wafers are, for
example, silicon wafers with an epitaxial silicon coating formed
thereon. This epitaxial silicon surface is the critical surface
which must be maintained in a dust-free atmosphere. The preparation
of the epitaxial silicon surface involves a great deal of
time-consuming preparations and is very costly. It has been found
that even slight contact with this surface is often sufficient to
abrade the surface to an extent where it is no longer usable for
the manufacture of semiconductor devices. In addition, it has also
been found that mere momentary touching of the wafer by a fingertip
will also create sufficient contamination on the surface thereof
that it may be rendered unusable. The same problems hold true for
semiconductor wafers with highly polished surfaces. These treated
surfaces, which must be protected, are herein referred to as the
"critical surfaces." The retaining tray A of the present invention
was designed to specifically overcome these problems.
By reference to FIG. 9, it can be seen that each of the retaining
wells 8 is so constructed that a wafer W disposed therein can be
oriented in substantially any position and the substantial position
of the epitaxial surface thereof will still remain out of contact
with any portion of the walls 6 or 7 in the well 8. In essence, if
the tray A should be inadvertently tipped slightly so that the
wafer W is no longer supported on the tapered wall 6, it may shift
to a position substantially as illustrated in FIG. 9. For example,
it can be seen that the peripheral margin of the wafer W is
actually supported in the manner as illustrated in FIG. 7 and on
the spaced points (labeled "X"). It can be seen that the epitaxial
surface of the wafer W will remain out of contact with any portion
of the wall of the well 8 and only the peripheral margin of the
wafer will contact any portion of the wall of the well 8 at any one
time.
In FIG. 10, it can be seen that the wafer W may be oriented in a
slightly different position and again, the wafer is supported on
the spaced points (labeled "X"). While the shape of the retaining
trays illustrated in FIGS. 9 and 10 are slightly different than the
other retaining trays described in connection with the present
invention, it should be recognized that the wafer W can be oriented
in substantially any position in any of the embodiments of the
present invention in such manner that the critical surface does not
contact any portion of the recessed walls.
In order to maintain brevity, only one of the retaining wells 8 has
been described herein and only one has been illustrated in detail
in the accompanying drawings. However, it should be recognized that
each of the other retaining wells are substantially identical in
construction and are, therefore, neither illustrated nor described
in detail herein.
A removable cap C is provided for coverwise disposition over each
of the retaining wells 8 in the manner as illustrated in FIG. 3.
The cap C generally comprises a relatively flat top sheet 9, which
is slightly frusto-conical or "dish-shaped" so that it forms a
downwardly projecting central pressure point 10 which is designed
to bear against the upper surface of the wafer W in the manner as
illustrated in FIG. 3. Furthermore, the sheet 9 of the cap C may be
hemispherically shaped in accordance with the present invention.
The cap C is also provided with a somewhat circular annular
peripheral shoulder 11 which integrally merges into the flat sheet
9 and is sized to extend over the annular bead 4. Furthermore, the
cap C is formed of the same material as the tray A and is,
therefore, sufficiently flexible to become snap-fitted over the
bead 4 in the manner as illustrated in FIG. 3. The annular shoulder
11 merges into an inwardly extending annular finger 12 which
engages the underside of the bead 4 at its point of integral merger
with the side wall 3. Furthermore, the cap C is provided with an
annular outwardly flaring flange 13 in the manner as illustrated in
FIG. 3. Thus, it can be seen that the cap C can be engaged by the
flange 13 and urged upwardly from its closurewise position on the
boss 2 and can be easily reinserted thereon in tight-fitting
coverwise disposition. Furthermore, when the cap C is disposed over
the well 8 in coverwise disposition, it engages the wafer W and
holds the same in a fairly immobile position in the retaining well
8, by urging the same against the tapered wall 6.
By further reference to FIGS. 1 and 2, it can be seen that the side
walls 3 of each of the bosses 2 merge into the support plate 1
through an arcuate section 14. By reference to FIG. 4, it can be
seen that a series of the trays can be stacked in marginal
registration so that the arcuate sections 14 of one tray fit snugly
between the annular beads 4 on a tray disposed immediately
therebeneath. This is true even though cover members C are disposed
over each of the retaining wells 8. This type of construction also
serves to space the retaining wells of one tray from the bottom
wall of the tray disposed immediately thereabove. Nevertheless, the
trays A can be stacked in marginal registration in the manner as
illustrated.
It is possible to provide a modified form of wafer tray B,
substantially as illustrated in FIGS. 5 and 6, and which is
substantially similar to the wafer retaining tray A. The wafer
retaining tray B generally comprises a relatively flat sheet 20
with a plurality of upstanding bosses 21 having a relatively flat
annular side wall 22. At its upper end, the annular side wall 22
integrally merges into an annular bead 23 which is substantially
rectangular in horizontal cross section. The bead 23 is provided on
its interior surface with a vertical shoulder 24, which in turn,
merges into an inwardly and downwardly extending tapered side wall
25, for retaining a wafer W thereon. At its lower end, the side
wall 25 integrally merges into a slightly convex bottom wall 26.
The size and shape of the tapered wall 25 and the bottom wall 26 is
substantially similar to the tapered wall 6 and bottom wall 7
respectively of the retaining tray A. However, it is to be noted
that the upstanding bead 23 is not rounded in the same manner as
the bead 4 in the wafer retaining tray A. Furthermore, each of the
bosses 21 is provided with an annular groove 27 in the side wall 22
for reasons which will presently more fully appear. Thus, it can be
seen that the recessed portion in each of the upstanding bosses 21
provides a wafer retaining well 28, which is substantially similar
to the wafer retaining well 8 in the retaining tray A.
A cap C', which is substantially similar to the previously
described cap C is provided for coverwise disposition over each of
the retaining wells 28. The cover member C' generally comprises a
relatively flat sheet 29, which is slightly frusto-conical in shape
and provides a downwardly projecting center pressure point 30,
which engages the central portion of the upper surface of the wafer
W, in the manner as illustrated in FIG. 7. Furthermore, the flat
sheet 29 integrally merges into a downwardly extending relatively
vertical side wall 31, which is provided with a somewhat V-shaped
annular finger 32, the latter being snap-fitted in the groove 27 in
the manner as illustrated in FIG. 7. The vertical side wall 31
integrally merges into an outwardly extending annular flange 33.
Thus, it can be seen that the cap C' can be easily removed from the
upstanding boss 21 by merely engaging the flange 33 and pulling the
cap C' from the boss 21. In like manner, the cap C' can be easily
disposed over the wafer retaining well 28 by snap-fitting the same
so that the annular finger 32 extends into the annular groove 27 on
the boss 21.
The wafer retaining tray B is substantially similar in all other
respects to the wafer retaining tray A and is also nestable and
marginally registrable with like trays.
It is possible to provide a modified form of wafer tray B.sub.2
substantially as illustrated in FIG. 7 and which is similar to the
wafer tray A, illustrated in FIG. 1. The wafer tray B.sub.2 differs
from the wafer tray A in that an arcuately shaped bottom wall 34 is
provided in place of the flat bottom wall 7 of the tray A. In all
other respects, the wafer tray B.sub.2 is similar to the tray A. In
like manner, the cap C may also be used on the wafer tray B.sub.2
for retaining the wafer W therein.
It is also possible to provide another modified form of wafer tray
B.sub.3 which is more fully illustrated in FIGS. 8 and 10. The
wafer tray B.sub.3 generally comprises a support plate 35 having an
upstanding boss 36 integrally formed thereon. The boss 36 is
substantially identical to the boss 2 in the tray A and has a
somewhat arcuate recess 37 formed by a vertical wall 38 integrally
merging into a somewhat arcuately shaped tapered wall 39. The
arcuately shaped tapered wall 39, in turn, merges into an arcuately
shaped tapered wall 40 and thence into a relatively flat bottom
wall 41. It can be seen that a wafer W can be supported on either
of the tapered wall 39,40. Thus, the wafer retaining tray B.sub.3
is sized to accommodate a number of wafers W having different
diametral sizes. A cap C is also removably disposed over the boss
36 in the same manner as the cap C was used in the wafer tray A.
The present invention also contemplates a wafer tray B.sub.4
substantially as illustrated in FIG. 9. The wafer tray B.sub.4
differs from the wafer tray B.sub.3 in that an arcuately shaped
bottom wall 42 is used in place of the flat bottom wall 41. A
removable cap C is also provided for use with each of the recesses
in the tray B.sub.4. Furthermore, the tray B.sub.4 is used in
substantially the same manner as the tray B.sub.3.
The present invention further provides for another modified form of
wafer retaining tray B.sub.5 (FIG. 11) which is constructed in
accordance with and embodying the present invention. The wafer tray
B.sub.5 is similar to the wafer tray B.sub.2 and generally
comprises a support plate 43 having an upstanding boss 44
integrally formed thereon. The boss 44 is substantially identical
to the boss 2 in the tray A and has a recess 45 which is formed by
an arcuately shaped recess forming wall 46. It can be observed that
the arcuately shaped wall 46 may have any desired radius which is
limited only in such manner that it is capable of retaining a wafer
W in a position where the critical surface of the wafer is disposed
in spaced relation to a bottom portion of the wall 46. Thus, the
wafer W should be capable of being oriented in substantially any
position, such as that illustrated in FIGS. 9 and 10, without
having the critical surface thereof contact the upwardly presented
surface of the arcuate wall 46. It should be observed, furthermore,
that the wafer trays of the present invention are not necessarily
limited by the shape of the wall which retains the wafer. The only
important criterion is that the wall must be designed in such
fashion that the critical surface of the wafer W does not contact
the wall when oriented in substantially any position with respect
to the wall. The removable cap C is also provided for coverwise
disposition over the recess 45 in the manner as illustrated in FIG.
11.
It is possible to provide another modified form of wafer tray D,
substantially as illustrated in FIG. 14. The wafer tray D is
similar to the wafer tray A and generally comprises a support plate
50, having an upstanding boss 51 integrally formed thereon. The
boss 51 is substantially identical to the boss 2 in the tray A and
has a recess 52 which is formed by a tapered wall 53 and a bottom
wall 54 which are substantially identical in all respects to the
similar components in the tray A. In like manner, a removable cap
C" is provided for coverwise disposition over each of the recesses
52 in the manner as illustrated in FIG. 14. The cap C" is
substantially identical to the cap C and includes a top sheet 55
which is slightly frusto-conical or "dish-shaped" so that it forms
a downwardly projecting central pressure point 56. In like manner,
the cover member C could have a flat top sheet with no downwardly
projecting portion whatsoever.
Provided for interposition between the lower surface of the top
sheet 55 and the upper surface of the wafer W which is disposed in
the recess 52 is a disc-like insert 57. By reference to FIGS. 12
and 13, it can be seen that the insert is somewhat in the form of
an inverted cup and generally comprises a relatively flat top wall
58 formed with an annular downwardly and outwardly flaring skirt
59. The insert 57 is preferably formed of the same material as the
tray D and, therefore, is slightly resilient. Thus, when the flat
sheet 55 of the cap C" bears against the top wall 58 of the
disc-like insert 57, the lower peripheral margin of the skirt 59
will engage the upper surface of the wafer W and urge the same
downwardly against the tapered wall 53 of the recess 52.
It is also possible to provide a wafer tray E as illustrated in
FIG. 15 which is similar to the wafer tray illustrated in FIG. 2.
The tray E differs from the tray A in that a different type of cap
F is provided. The cap F generally comprises a relatively flat top
sheet 60 which is provided with a somewhat circular annular
peripheral shoulder 61. The shoulder 61 integrally merges into the
flat sheet 60 and is sized to extend over the annular bead 4.
Furthermore, the cap F is formed of the same material as the tray E
and is, therefore, sufficiently flexible to be snap-fitted over the
bead 4 in the manner as illustrated in FIG. 15. The annular
shoulder 61 merges into an inwardly extending annular finger 62
which engages the underside of the bead 4 at its point of integral
merger with the side wall 3. Furthermore, the cap C is provided
with an annular outwardly flaring flange 63 in the manner as
illustrated in FIG. 15. Thus, it can be seen that the cap C can be
engaged by the flange 63 and urged upwardly from its closurewise
position over the boss 2 on the tray E and can be easily reinserted
thereon in a tight-fitting coverwise disposition.
Adhesively or otherwise secured to the underside of the flat sheet
60 is a downwardly projecting circular retaining flange 64 which
engages the upper surface of the wafer W in order to hold the wafer
into snug fitting position against the tapered wall of the tray E.
The circular flange 64 is sized to extend near the peripheral
margin of the wafer W. It should be observed that the cap F can be
used with essentially any of the other wafer trays described
herein. It should be recognized that the retaining flange 64 may be
secured to the underside of the flat sheet 60 by means of a
snap-fitting engagement. Furthermore, the flange 64 can be
fabricated in the form of a ring as illustrated in FIG. 16 for
removable interposition between the cap F and the wafer disposed in
the wafer tray E.
The concept of using a cylindrical ring for engagement against a
wafer has been found to be highly effective. While the employment
of a disc 47 (FIG. 12) is indeed effective, the manufacture of the
disc must be carefully controlled both with regard to critically of
dimension and the composition of the material employed. When the
disc is employed, there is a tendency for the disc to spread out
from the resultant vertical forces imposed by the cap. This wiping
action across the upwardly presented surface of the wafer W in many
cases has undesirable effects. The concept of the ring obviates
this particular problem. There is no wiping action whatsoever in
connection with the ring and hence, the deleterious effects to the
wafer W are thereby avoided.
Many of the various embodiments of caps and capping systems
described herein can be used with any of the embodiments of the
trays of the present invention. For example, the cap C can
adequately be used with the tray B.sub.5. also be
This method of transporting each of the wafers W has been found to
be highly successful and has substantially eliminated the problems
of contacting the surfaces of the wafer W with any foreign matter,
thereby maintaining a high degree of purity and eliminating any
surface abrasion. While the trays of the present invention were
specifically designed for use with polished silicon wafers and
silicon wafers having epitaxial silicon or oxide coatings thereon,
they are also successfully employed with other types of
semiconductor wafers, such as gallium arsenide wafers and gallium
arsenide phosphide wafers. Furthermore, the trays are equally
suitable to hold and transport and store similar slice-shaped
objects which have critical surfaces prepared by methods other than
machine polishing, objects with critical surfaces which have been
prepared by cleaning, chemically etching, vapor etching, deposition
from the vapor phase, sputtering, or other thin film techniques,
crystallization from the melt, chemical or electrolytical
precipitation from solution can also be successfully used in the
retaining trays of the present invention. Furthermore, the tray is
capable of handling slices of any regular shape, preferably in the
form of a flat disc and may consist of materials other than
semiconductor materials, such as solid metal and metal alloys and
minerals. The wafers which may be used in the trays of the present
invention may be formed of glass, quartz, ceramics, sapphire and
other precious and semiprecious stones.
When transporting a series of marginally registered stacked trays,
the trays may be stored in a hermetically sealable container or
simply wrapped in a substantially self-sealing dust-proof foil or
plastic film. The trays may then be properly stacked and placed in
a suitable shipping container as desired. It should be observed
that the wafers W would not be damaged even if the trays A were
inadvertently turned over. It can be observed that after the wafers
W have been properly inserted into each of the wells 8, they are
held in place by the cap C. This type of condition eliminates any
possibility of contamination or abrasion to the critical surface of
the wafer.
It should be understood that changes and modifications in the form,
construction, arrangement and combination of parts presently
described and pointed out may be made and substituted for those
herein shown without departing from the nature and principle of my
invention.
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