Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to apparatus for
transferring semiconductor wafers, from one holder to another,
and to a method of transfer using such apparatus.
In the processing, and storage, of semiconductor
wafers, they have to be transferred back and forth between
etch boats to furnace boats, and possibly to and from storage
boxes. It is essential that absolute cleanliness be observed
to avoid contamination and toward this end it is important
to handle the wafers as little as possible - indeed handling,
except with special implements, is to be avoided.
Also, wafers are treated in bulk, to reduce
costs and to obtain a reasonable throughput. It is therefore
; desirable that the transfer of wafers be in bulk, to the
extent: that one batch of wafers to be transferred at one time.
It has been proposed to use a transfer cassette to which the
wafers are transferred, for example from a storage box or etch
boat, the wafers then being transferred from the transfer
cassette to, for example, a furnace boat. A transfer cassette
is used to transfer wafers from a furnace boat back to an etch
boat. During such transfers edge chipping can occur. Also,
; alignment between the various items is difficult. Movement
can occur during turning over of cassette and boat, and, with
3" wafers, the apparatus is di-fficult to hold.
In accordance with the present invention, an
etch boat is modified to form a holder and to accept a
transversely extending rod or tube, inserted aFter wafers are
in the boat~ which retains the wafers in position. The holder or
etch boat is then turned over, and positioned over a furnace
boat, the wafers fitting in slots or grooves in the furnace
boat, and the rod or tube then removed - allowing removal of
the etch boat. To return the wafers to the holder or etch boat,
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it is positioned over the furnace boat holding the wafers.
The rod or tube inserted and the holder or etch boat lifted
of-f. The rod or tube, when in position, always retains the
wafers in the holder or etch boat.
The invention will be readily understood by
the following description in conjunction with the accompanying
drawings, in which:-
Figure 1 is a perspective view of an etchboat in accordance with the present invention,
Figure 2 is a cross-section on the line II-II
of Figure 1, with rod in position;
Figure 3 is a similar cross-section to that of
Figure 2, but with the etch boat turned upside down and wafers
positioned in a furnace boat,
Figure 4 is a similar cross-section to that of
Figure 2, but with a storage box positioned on the etch boat,
Figure 5 is a cross-section similar to that of
Figur~ 4, illustrating the transfer of wafers from etch boat
to storage box.
~-~ 20 As illustrated in Figure 1, an etch boat 10,
for example molded of a plastic material such as polytetra-
fluoroethylene (Teflon TM) to resist etchants, is in the form
of a trough, open at the bottom and with parallel sides, the
sides having a plurality of Vee shaped grooves 11 formed in the
inner surfaces thereof. The grooves 11 are dimensioned to hold
wafers, a wafer in each groove. Externally, the etch boat 10
has a flat top surface l2. The external shape may vary, but
normally the boat is provided with a flat base to the sides,
with a foot 13 at each corner. An end wall 14 connects the
sides of the boat at one end and a bar 15 connects the sides
at the other end. In use, wafers are placed i n the etch boat
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and the whole inserte(l into the etch chamber.
The etch boat 10, can be a conventional boat,
modified by the boring of a hole 16 longitudinally of the boat,
breaking through into the Vee grooves 11 at a position above
the maximum diameter of the wafers - as seen in Figure 2. A
rod or tube - not shown in Figure 1, is inserted into the hole
16.
Figure 2 illustrates the position of wafers 17
in the etch boat 10 and a rod 18 in the hole 16. As will be
10 seen, the rod 18, which can also be a tube, projects into ~ ~;
the grooves 11 at one side, just clear of the wafers 17.
For one particular transfer operation,
transfer of wafers to a furnace boat, the rod 18 is inserted,
as in Figure 2, and then the etch boat 10 inverted and
positioned over a furnace boat, usually of quartz. This is
illustrated in Figure 3, the quartz furnace boat shown at 20.
On inversion of the etch boat 10 the wafers 17 drop down a
very small amount until they contact the rod 18. The etch
boat is positioned over the furnace boat which has a series
of transverse grooves or slots 21. The grooves 21 are Vee
shaped looking in a direction parallel to the longitudinal axis
of the boat, as seen in Figure 3, and are also of Vee shaped
cross-section when viewed normal to the longitudinal axis.
This both centers and holds the wafers 17.
As the etch boat 10 is lowered onto the furnace ~ -
boat 20, the wafers 17 enter the slots 21 and eventually are
lifted slightly. The rod 18 is then removed and the etch boat
lifted up virtually, leaving the wafers 17 standing in the
furnace boat. ;
~emoval of the wafers from the furnace boat is
the reverse of the above - positioning the etch boat over the
wafers, insertion of the rod 18 and lifting the etch boat up
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and then turning over.
The operation of transferring wafers to a furnace
boat and from a furnace boat is very quick and easy. The
particular cross-sectional form of the grooves 11 and slots 21
provides for easy alignment. Edge chipping is avoided and no
contamination From handling occurs.
The invention is also applicable to the transfer
of wafers to and from other items, such as for example,
storage boxes. Figures 4 and 5 illustrate such a transfer. In
Figure 4, the wafers 17 are shown in the etch boat 10. The
rod 18 is shown inserted although this is not essential. The
storage box 25 is positioned on top of the boat 10 with the
grooves 11 of the boat 10 aligned with similar grooves 26 in
the storage box 25. The whole assembly is turned sideways, the
rod 18 removed and then the assembly turned slightly farther
until the storage box 25 is lower than the etch boat 10, as
illustrated in Figure 5. The wafers 17 then roll or slide from
the etch boat 10 into the storage box 25.
Wafers can be transferred from a storage box
to an etch boat by the reverse of the above. The etch boat
is aligned on top of the storage boat and then the whole rotated
until the storage box is slightly higher than the etch boat,
when the wafers will move down into the etch boat. The wafers
can then be processed in the etch boat or transferred to, for
example, a furnace boat. The use of the rod 18 occurs, as
described previously. Thus the etch boat - 10 can also be used
as a transfer device. Thus there is provided an arrangement
for extremely easy and simple transferring wafers, with the
minimum of apparatus, particularly without any additional items
other than those actually used in processing, except for the
rod 18.
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Alignment between the etch boat and other items
can be by sight, as for example between etch boat and furnace
boat, or small projections on the etch boat can be aligned with
recesses in the other item, for example the storage box, as
illustrated at 27 and 28 respectively in Figures 4 and 5.
The hole 16 is positioned in the wall of the
etch boat such that when the rod 18 is inserted it overlaps ~ ~
the wafers 17 in all cases, even if it should happen that the ~:.
flat 30 - normally formed on wafers to provide orientation -
: 10 should be at the side where the wafers is in the etch boat.
The actual steps carried out in using the ~ :
etch boat, as described above~ are illustrative only and
VariatiDnS in a particular sequence of steps, and in the steps
themselves, can occur, depending upon intentions and require~
ments.
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