Rigid gas collector for providing an even flow of gasses

Details Rigid gas collector for providing an even flow of gasses Rigid gas collector for providing an even flow of gasses

2001-11-27

2004-04-06

Lund, Jeffrie R. (Department: 1763)

Coating apparatus

Gas or vapor deposition

Chamber seal

C118S715000, C156S345290

Reexamination Certificate

active

06716289

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to epitaxial reactors and, more particularly, to a gas collector for epitaxial reactors.
BACKGROUND OF THE INVENTION
Continuing advances in the semiconductor industry have resulted in the development of highly complex thin-film deposition processes for fabricating semiconductor devices that are packaged for use in the manufacture of sophisticated electronic devices. The thin films of material that are deposited on the semiconductor wafers are often referred to as epitaxial layers. High speed electronic transistors, quantum-well diode lasers, light-emitting diodes, photodetectors, and optical modulators incorporate structures composed of numerous epitaxial layers ranging in thickness from several microns to as thin as a few tenths of a nanometer. These epitaxial layers are typically deposited, or grown, on a single-crystal substrate, i.e., the semiconductor wafer.
One method of forming epitaxial layers on a semiconductor wafer is known as chemical vapor deposition (CVD). In a typical manufacturing process of a wafer, for example, silicon or gallium arsenide in extremely pure crystalline form is overlaid sequentially with numerous layers of materials, which function as conductors, semiconductors, or insulators. Each subsequent layer is ordered and patterned such that the sequence of layers forms a complex array of electronic circuitry. The semiconductor wafer can then be subsequently cut along predetermined scribe lines into individual devices, commonly referred to as “chips.” These chips ultimately function as key components in electronic devices ranging from simple toys to complex supercomputers.
CVD processes normally take place within a reaction chamber. Initially, the semiconductor wafer is placed within a reaction chamber containing an inert atmosphere, and the temperature within the reaction chamber is elevated. Reaction gasses containing the compound or element to be deposited are then introduced to react with the surface of the semiconductor wafer, which results in deposition of the required film onto the semiconductor wafer. The reacted gasses are continually introduced and removed from the reaction chamber until a requisite film thickness has been achieved.
An example of an epitaxial reactor is described in U.S. Pat. No. 4,961,399, to Frijlink, which is incorporated herein by reference. This patent describes a reactor into which reaction gasses are introduced via a quartz funnel that is located at the center of the reactor. The reaction gasses then flow radially outward towards a quartz ring that bounds the reactor. Along the circumference of the quartz ring are equidistant slits, which collect the reacted gasses. Bounding the upper portion of the reaction chamber is a quartz disk. The quartz disk seals against O-rings, witch are positioned behind the quartz ring. Because quartz is a brittle and inflexible material, the quartz disk does not seal against the quartz ring. Instead, a gap is provided between the quartz disk and the quartz ring to prevent chipping of either.
This gap between the quartz disk and the quartz ring can cause problems within the reactor. For example, reaction gasses can escape through the gap and can form deposits outside the reaction chamber, and these deposits can interfere with the working of the reaction chamber and can also flake off and act as contaminants. Although a narrower gap can be provided, if a hard foreign body wider than the gap is introduced into the gap, such as during the opening of the reaction chamber, the foreign body could prevent the quartz disk from sealing properly over the reaction chamber or can cause chipping of either the quartz disk or the quartz ring.
An attempted solution to the above-described problems is disclosed in U.S. Pat. No. 4,976,217 to Frijlink, which is incorporated herein by reference. This patent describes a collecting crown or gas collector, which is both used to collect reaction gasses from the reaction chamber and also to provide a seal between the reaction chamber and a quartz disk or cover.
The gas collector and reaction chamber of the prior art is illustrated in
FIGS. 1 and 2
. The gas collector
1
is mounted on a supporting platform
4
by a horizontal plate
10
that rests upon the supporting platform
4
. The supporting platform
4
is typically formed from quartz and is positioned within a cylindrical body
19
of the reactor that surrounds the reaction chamber and the gas collector
1
. The cover
8
of the reaction chamber bounds the top of the reaction chamber and seals against the upper ridge
6
of the gas collector
1
and against toric joints
20
within the cylindrical body
19
.
The gas collector
1
is further illustrated in FIG.
3
. The gas collector
1
is formed from a folded plate of molybdenum having elastic properties. The molybdenum plate is folded along horizontal folding lines
13
and vertical folding lines
14
to form multiple flat plates
17
,
5
,
18
,
9
,
3
,
10
that are connected to one another along the folding lines
13
,
14
. Also, two plates
2
,
3
are touching without being fixed to each other. The combination of plates
17
,
5
,
18
,
9
,
3
,
10
form a conduit
30
that encircles the reaction chamber. One of the plates
17
includes regularly spaced inlets holes
12
that collect the reaction gasses from the reaction chamber. Instead of the inlet hole
12
, as shown below on the right-hand side of
FIG. 3
, the wall plate
17
can be provided with folded lower projections
15
, which separate the movable lower edge
2
away from the fixed edge
3
to leave a slot between the edges
2
,
3
through which the reaction gas can then pass.
The '217 patent states that an essential element of the gas collector
1
is the vertical baffle plate, which is constituted by plates
17
,
3
with the lower edge
2
of the upper plate
17
being pressed with a sliding motion against the upper edge of the lower plate
3
. The horizontal plates
10
that are connected to the lower plates
3
serve to place the gas collector
1
on the edge of the platform
4
. Furthermore, the top plate
5
is inclined and includes an upper ridge
6
.
The disclosed gas collector
1
suffers several problems. A non-exhaustive list of these problems include contamination of the periphery
11
of the platform, the top plate
5
, and the cylindrical body
19
; uneven gas flow and gas density of the reaction gasses through the reaction chamber; and contamination within the reaction chamber. Many of these problems stem from the gas collector
1
being completely formed from a sheet of molybdenum, which is folded along folding lines
13
,
14
. Sheet metal structures are very difficult to manufacture to a high degree of dimensional precision. For example, the bending of the sheet metal along the folding lines
13
,
14
is imprecise at best. Furthermore, the gas collector
1
is constructed using small screws and nuts, which do not lend themselves to maintaining a high degree of dimensional precision.
The gas collector
1
being formed by sheet metal, therefore, provides poor dimensional precision or tolerances for both the horizontal plate
10
extending over the platform
4
; the positions of the inlets
12
in the upper plate
17
; the connections of the upper plates
17
with one another, and the ridges
6
of the top plate
5
. Another reason for the poor dimensional tolerances of the gas collector
1
results from thermal stressing of the sheet metal during the deposition process. As the thin molybdenum sheet metal of the gas collector
1
expands and contracts during each process cycle, the gas collector
1
eventually buckles and warps, thereby destroying the dimensional integrity of the gas collector
1
.
The result of these poor dimensional tolerances is that the gas collector
1
, although purporting to seal the reaction gasses within the reaction chamber except through the inlets holes
12
, provides numerous locations for the reaction gasses to escape the reaction chamber. For example, the ridge
6
often fails to

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