Batteries: thermoelectric and photoelectric – Thermoelectric – Processes
Utility Patent
1999-05-21
2001-01-02
Gorgos, Kathryn (Department: 1741)
Batteries: thermoelectric and photoelectric
Thermoelectric
Processes
C136S230000, C374S208000, C118S715000
Utility Patent
active
06169244
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to semiconductor process equipment, and more particularly, to a thermocouple sheath cover suitable for use in a semiconductor reactor.
2. Description of the Related Art
Semiconductor processing typically involves the formation of one or more layers on a semiconductor substrate. For example, silicon epitaxy, sometimes called epi, is a process in which one or more layers of single-crystal (monocrystalline) silicon are deposited on a monocrystalline silicon wafer.
Unavoidably, these deposited layers are not only deposited on the substrate but are also undesirably deposited on other parts of the epi reactor.
FIG. 1
is a schematic representation of an epi reactor
10
which illustrates the accumulation of undesirable deposits on a thermocouple sheath in accordance with the prior art.
As shown in
FIG. 1
, reactor
10
includes a quartz dome
12
which forms a reactor enclosure
14
with a reactor base section
16
. Located within enclosure
14
are one or more substrates
18
, typically monocrystalline silicon wafers, supported by a susceptor
20
.
During processing, substrates
18
are heated typically with an external radiation source
22
such as tungsten halogen lamps, resistive heating elements and/or RF heaters. A reactive gas is introduced into enclosure
14
through one or more injector ports
24
. The reactive gas typically includes trichlorosilane although other reactive gases besides trichlorosilane can be used depending upon the particular type of layer to be deposited. The reactive gas reacts with heated substrates
18
resulting in the deposition of layers on substrates
18
as those skilled in the art understand. The spent process gas may then be exhausted through a vacuum pump
17
. Typically, vacuum pump
17
is also used to produce a subatmospheric pressure in enclosure
14
during processing. However, depending upon the particular process, enclosure
14
may be maintained at atmospheric pressure during processing.
Of importance, to insure uniformity of thickness and quality of the deposited layer, the temperature to which substrates
18
are heated during the epi process must be accurately measured and controlled.
To allow accurate measurement of the temperature of substrates
18
, reactor
10
includes a thermocouple tip
26
located in a thermocouple sheath
28
and in enclosure
14
. To prevent reactive gas from escaping, thermocouple sheath
28
forms a seal with port
30
of base section
16
using conventional techniques such as the use of an O-ring. The temperature measured by thermocouple tip
26
is displayed on a temperature readout unit
32
which is coupled to thermocouple tip
26
by leads
27
. Thermocouple tip
26
is typically located near the sealed end of thermocouple sheath
28
. See U.S. Pat. No. 5,710,407 issued to Moore et al, herein incorporated by reference in its entirety, which discusses temperature control in a reactor in more detail.
During the epi process, deposits
40
, e.g. silicon, are inevitably formed on thermocouple sheath
28
. Over time, deposits
40
flake and fall off of thermocouple sheath
28
thus introducing particulates
42
into enclosure
14
. Particulates
42
can contaminate substrates
18
and cause defects in the layer deposited on substrates
18
. High quality layers, such as those required for integrated circuits, must be free from these defects.
To reduce generation of particulates
42
, conventional practice is to clean or replace thermocouple sheath
28
during periodic scheduled maintenance of reactor
10
. However, during the time period between scheduled maintenance, substantial accumulation and flaking of deposits
40
and the associated contamination from particulates
42
occurs. Accordingly, the art needs a method for preventing particulate contamination from occurring between periodic scheduled maintenance.
SUMMARY OF THE INVENTION
In accordance with the present invention, a cover mounted about an article used in a substrate processing reactor is presented. The cover has an outer surface which has a greater adherence to deposits than the article. In one embodiment, the article is a quartz thermocouple sheath, and the outer surface of the cover includes silicon carbide which has a greater adherence to deposits than the quartz of the thermocouple sheath.
By having a greater adherence to deposits, the cover impedes and essentially eliminates deposit flaking. Thus, the cover avoids the particulate contamination associated with conventional quartz thermocouple sheaths. Decreasing or eliminating particulate contamination advantageously improves the yield.
Further, to the extent deposit accumulation does become significant on the cover, an etch process can be used to remove the deposits. For example, an etch process using hydrogen chloride (HCl) as the etch gas can be performed to remove deposits from the cover although other etch gases can be used depending upon the particular deposits to be removed. Alternatively, the cover is easily removed and replaced with a new clean cover. The removed cover can then be cleaned and saved for use at a later time while the reactor remains online processing substrates.
Preferably, the cover is formed of a material such as silicon carbide which has essentially no effect on the response time or the measured temperature compared to the use of a conventional quartz thermocouple sheath. As used herein, the response time is the time in which temperature changes in the reactor are measured by a thermocouple in the quartz thermocouple sheath. In this manner, the cover is thermally invisible and the thermocouple measures temperature the same as not having the cover in place.
In one embodiment, the cover includes first and second half sections and a slip ring. The cover is installed over the thermocouple sheath by placing the half sections around the thermocouple sheath and then sliding the slip ring into place around the half sections. Further, by forming the cover and thermocouple sheath with corresponding bends, such as 90° bends, the cover is prevented from slipping or moving relative to the thermocouple sheath. The cover is also easily removed from the thermocouple sheath by sliding the slip ring off and removing the half sections.
Also in accordance with the present invention, a thermocouple assembly is presented which includes a thermocouple sheath and a sheath cover, the sheath cover having an outer surface with a greater adherence to deposits than the sheath. In one embodiment, the sheath has a sealed end and a thermocouple tip is located within the sheath adjacent the sealed end.
These and other objects, features and advantages of the present invention will be more readily apparent from the detailed description set forth below taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4978567 (1990-12-01), Miller
patent: 5053247 (1991-10-01), Moore
patent: 5207835 (1993-05-01), Moore
patent: 5444217 (1995-08-01), Moore et al.
patent: 5580388 (1996-12-01), Moore
patent: 5710407 (1998-01-01), Moore et al.
patent: 5802099 (1998-09-01), Curran et al.
patent: 5820686 (1998-10-01), Moore
patent: 5872632 (1999-02-01), Moore
patent: WO 99/23276 (1999-05-01), None
Carlos Thomas F.
Moore Gary M.
Gorgos Kathryn
Gunnison McKay & Hodgson, L.L.P.
Hodgson Serge J.
Moore Epitaxial Inc.
Parsons Thomas H
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