Fluid handling – Systems
Reexamination Certificate
1999-01-29
2001-04-24
Chambers, A. Michael (Department: 3753)
Fluid handling
Systems
C118S715000
Reexamination Certificate
active
06220286
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to improvements in semiconductor processing equipment, and in particular, in a preferred embodiment, to an improved nitrogen blanket distributor for an atmospheric pressure chemical vapor deposition (APCVD) apparatus.
BACKGROUND
Atmospheric pressure chemical vapor deposition (APCVD) is a semiconductor processing technique that is well known in the art. Several companies make APCVD apparatus for sale to semiconductor manufacturing companies. The present invention is an improvement to a prior art APCVD arrangement, as is described in detail in this specification.
U.S. Pat. No. 4,834,020 (Bartholomew, et al.) discloses a conveyorized atmospheric pressure chemical vapor deposition apparatus. This patent is assigned to Watkins-Johnson Company of Palo Alto, Calif. The apparatus described in this patent discloses use of nitrogen blanketing apparatus surrounding each deposition chamber to separate the ambient atmosphere from the deposition environment and to ensure that deposition chemicals do not escape from the immediate vicinity of the deposition chamber. Nitrogen distribution plenums are positioned on the entry side of each deposition chamber and on the exit side of each deposition chamber.
U.S. Pat. No. 5,304,398 (Krusell, et al.) also is assigned to Watkins-Johnson Company. This patent also discloses an atmospheric pressure chemical vapor deposition apparatus, which includes a gas injection assembly (indicated at reference
310
in
FIG. 1
of the present specification, which is a reproduction of FIG. 3 of the Krusell, et al. patent) through which process gases and nitrogen are introduced onto the surface of wafer
315
that is processed by the apparatus. This is the type of system in which the preferred embodiment of the present invention is intended to be used. Referring to
FIG. 1
, the structures
12
,
14
a
and
14
b
on either side of exhaust passages
336
and
338
are nitrogen distributors which provide a nitrogen blanket around the process area and the gas injection assembly
310
. The function of these nitrogen distributors is to provide a steady flow of nitrogen to the regions surrounding the process gas injection operation to remove excess or spent process gasses and to prevent introduction of foreign materials into the process area. The nitrogen that is fed through these distributors is removed from the process area via exhaust passages
336
and
338
, thus forming a continuous flow of inert gas surrounding the process area. The aforementioned patents are hereby incorporated by reference into this specification.
FIG. 2A
shows the construction of a prior art nitrogen distributor assembly over which the present invention provides a number of improvements. Nitrogen distributor assembly
10
comprises primary nitrogen distributor
12
and secondary nitrogen distributors
14
. Each distributor
12
,
14
comprises a solid shell
20
and a perforated screen
24
that form an enclosed space into which nitrogen may be introduced. Nitrogen supply tubes
16
are provided to convey nitrogen from an external nitrogen source to the nitrogen distributor assembly. Inside of nitrogen distributors
12
and
14
, these tubes
16
are perforated to release nitrogen within the distributors. Referring to the prior art primary distributor
12
, each nitrogen tube
16
enters the distributor and is bent at a 90° angle as shown at point
18
and then welded at selected points along its length to shell
20
of primary distributor
12
beneath screen
24
. A number of holes are drilled in nitrogen tube
16
proximate shell
20
in order to allow nitrogen to flow from the tube
16
into the enclosed space formed between shell
20
and screen
24
of primary nitrogen distributor
12
. Baffle
22
is constructed from a thin strip of metal and attached to tube
16
at one edge and to shell
20
at the other edge. Baffle
22
is provided in order to block the direct flow of nitrogen out of the perforations in tube
16
, to slow down the nitrogen flow and to allow it to evenly disperse within primary distributor
20
beneath primary screen
24
. A similar structure is employed in forming secondary nitrogen distributors
14
by using a corresponding tube having holes drilled therein positioned between a secondary shell a secondary stainless steel screen.
The prior art nitrogen distributor assembly shown in
FIGS. 2A and 2B
employs topographic features
26
in the primary screen
24
that are intended to control temperature-cycling related failures. Because these features exist only in the planar section of the primary screen
24
and do not extend around the curve that is formed by the screen as it passes around the lateral sides of primary distributor
12
, they tend to ensure that thermal-cycling failures occur primarily in the specific region of the features, rather than preventing such failures.
FIG. 2B
shows a typical prior art version of a APCVD injection assembly including gas blanket distribution apparatus. A work piece, which is typically a semiconductor wafer
210
, may be conveyed past the operative assembly on conveyor belt
212
. Injector head
214
receives the reactant process gasses and furnishes them through injector nozzle
216
, which extends through a window formed in primary nitrogen distributor
218
, and onto the surface of work piece
210
as it passes beneath nozzle
216
. Secondary nitrogen distributors
220
are provided on each side of primary nitrogen distributor
218
. The sides of primary nitrogen distributor
218
and secondary nitrogen distributors
220
that face each other and that face toward the work piece comprise perforated screen that may be made of stainless steel, which allow nitrogen to flow from the interiors of primary distributor
218
and secondary distributors
220
and into the vicinity of work piece
210
and injector nozzle
216
such that excess and spent process gasses are diluted and carried by the nitrogen flow away from the process area and up through the exhaust channels provided between primary nitrogen distributor
218
and secondary nitrogen distributors
220
. The flow of nitrogen is generally shown by the arrows in FIG.
2
B.
Nitrogen supply tubes
222
are operatively connected to a source of nitrogen (or other selected blanket gas) to provide a steady flow of nitrogen into primary nitrogen distributor
218
and secondary nitrogen distributors
220
. Additional tubes
224
may be used to provide reactant gasses into injector head
214
. First, the secondary distributor seals used in prior art devices are subject to leaking and failure. This is due in part to the design of prior art sealing elements and in part to inadequate structural rigidity in the distributor assembly. Second, prior art devices are prone to cause “powdering,” which can introduce harmful particulate contaminants into the processing area. Third, the prior art nitrogen distributor assemblies are difficult to manufacture. Finally, the perforated screens in prior art devices are known to experience stress cracking due to differential rates of thermal expansion between distributor components. Each of these deficiencies is discussed further below.
In the atmospheric pressure chemical vapor deposition (APCVD) machines that are known to the applicant, the nitrogen blanketing apparatus that is employed has several deficiencies which are corrected by the present invention.
Secondary seals
226
may be provided on the outboard side of each secondary distributor
220
. Each secondary seal
226
provides a seal between secondary nitrogen distributor
220
and the wall of the enclosure into which this assembly is placed during operation, which is not shown in this illustration. (See
FIG. 7
) In the prior art, as shown in
FIG. 2B
, secondary seal
226
is a strip of flexible stainless steel, one edge of which is welded to the back of secondary nitrogen distributor
220
, and the other edge of which is bent away from secondary distributor
220
in order to contact the enclosure when the distributor assembly is inserted therein. O
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