Coating apparatus – Gas or vapor deposition
Reexamination Certificate
2000-06-21
2002-11-19
Mills, Gregory (Department: 1763)
Coating apparatus
Gas or vapor deposition
C118S726000, C118S712000, C427S250000
Reexamination Certificate
active
06482266
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a chemical vapor deposition method and apparatus and, more particularly, to a metal organic chemical vapor deposition method and apparatus using an organic metal as a source to form on a substrate a thin film made of a metal constituting the source.
There is a conventionally known chemical vapor deposition method such as MOCVD (Metal Organic Chemical Vapor Deposition) for forming a thin film of a metal or metal oxide on a substrate using chemical reaction of the vapor phase.
FIG. 8
shows an example of a conventional MOCVD apparatus (Metal Organic Chemical Vapor Deposition apparatus). The MOCVD apparatus shown in
FIG. 8
forms a PZT film on a substrate
10
in an evacuated reactor
9
. Source vessels
1
a
,
1
b
, and
1
c
are respectively heated by temperature controllers
801
a
,
801
b
, and
801
c
to predetermined temperatures, thereby gasifying a lead dipivaloyl methanato complex Pb(DPM)
2
, an organometallic compound source Ti(O-i-Pr)
4
, and an organometallic compound source Zr(O-t-Bu)
4
.
The Pb(DPM)
2
, Ti(O-i-Pr)
4
, and Zr(O-t-Bu)
4
gases are introduced into the reactor
9
together with an oxide gas such as NO
2
or O
2
gas to form a PZT film on the substrate
10
using chemical reaction of the vapor phase.
At this time, the flow rates of Pb(DPM)
2
, Ti(O-i-Pr)
4
, Zr(O-t-Bu)
4
, and NO
2
gases are respectively controlled by mass-flow controllers (MFCs)
7
a
,
7
b
,
7
c
65
, and
7
d
arranged midway along gas supply paths extending to the reactor
9
.
In the MOCVD apparatus shown in
FIG. 8
, the respective source gases must be introduced to corresponding MFCs at predetermined vapor pressures in order to cause chemical reaction of the vapor phase in the reactor
9
. To obtain necessary source vapor pressures, the source vessels
1
a
,
1
b
, and
1
c
are kept at predetermined temperatures.
However, the temperatures are set when respective sources are fully filled in the source vessels
1
a
,
1
b
, and
1
c
. As the sources in the source vessels
1
a
,
1
b
, and
1
c
are gasified and supplied to the reactor
9
, the amounts of sources gradually decrease. As the amounts of sources in the source vessels
1
a
,
1
b
, and
1
c
decrease, the source vessels fail to maintain the necessary source vapor pressures.
The same problem arises even when a carrier gas such as He, Ar, or N
2
gas is introduced into the source vessel to carry source gases to the reactor
9
by this carrier gas in order to assure predetermined source flow rates. That is, as the amounts of sources in the source vessels decrease upon use, necessary source vapor pressures cannot be maintained, and control of the source flow rates becomes unstable.
To compensate for variations in supply vapor pressure caused by residue variations in the source vessel, for example, an MOCVD apparatus disclosed in Japanese Patent Laid-Open No. 4-362176 is proposed. The MOCVD apparatus described in this reference will be explained with reference to a basic arrangement shown in FIG.
9
. In this MOCVD apparatus shown in
FIG. 9
, pentaethoxy tantalum (Ta(OC
2
H
5
)
5
) serving as an organometallic source bubbled with oxygen and nitrogen for forming an oxygen atmosphere is introduced into a reactor
51
evacuated by a vacuum pump
54
. In this case, the flow rate of oxygen introduced into the reactor
51
and that of nitrogen introduced into a material vessel
55
are controlled by signals sent from a flow controller
61
to mass-flow controllers
58
.
Pentaethoxy tantalum used in the MOCVD apparatus of
FIG. 9
, which is a liquid at room temperature, is introduced as a vapor into the reactor
51
by heating the whole material vessel
55
to a temperature of, e.g., 100° C. by thermostatic heaters
57
, and bubbling pentaethoxy tantalum with nitrogen introduced into the material vessel
55
. To prevent pentaethoxy tantalum and nitrogen from liquefying through a gas supply path or pipe extending from the material vessel
55
to the reactor
51
, the gas supply path or pipe is heated by gas pipe heaters
56
. The gas pipe heaters
56
and the thermostatic heaters
57
are respectively controlled by temperature controllers
59
and
60
which receive outputs from a quadrupole spectrometer
62
(to be described below).
Oxygen and pentaethoxy tantalum introduced into the reactor
51
thermally react by heat energy supplied from an electric furnace
53
surrounding the reactor
51
. As a result, a tantalum oxide film Ta
2
O
5
is formed on a substrate
52
placed inside the reactor
51
.
The quadrupole spectrometer
62
connected to the reactor
51
detects the concentrations of oxygen and pentaethoxy tantalum introduced into the reactor
51
, and outputs an electrical signal when the mass number of pentaethoxy tantalum is around “405”. If the concentration of pentaethoxy tantalum represented by the magnitude of the electrical signal is higher than a predetermined value, the temperature controller
59
of the gas pipe heaters
56
and the temperature controller
60
of the thermostatic heaters
57
decrease the temperature of the gas pipe heaters
56
and that of the thermostatic heaters
57
. At the same time, the flow controller
61
causes the mass-flow controller
58
to decrease the flow rate of bubbling nitrogen, thereby decreasing the supply amount of pentaethoxy tantalum to the reactor
51
. The operation of decreasing the supply amount of pentaethoxy tantalum to the reactor
51
is kept performed until the concentration of pentaethoxy tantalum represented by an electrical signal from the quadrupole spectrometer
62
reaches a desired concentration.
To the contrary, if the concentration of pentaethoxy tantalum represented by an electrical signal from the quadrupole spectrometer
62
is lower than a desired concentration, the supply amount of pentaethoxy tantalum to the reactor
51
is increased under reverse control.
However, various limitations are imposed on the MOCVD apparatus shown in
FIG. 9
owing to the use of the quadrupole spectrometer
62
as a measuring device. The usable vacuum degree of the quadrupole spectrometer is structurally limited to a high vacuum range of about 10
−5
torr or more. The vacuum degree, although it depends on the process, in the reactor during chemical vapor deposition need not be so high, and is as high as about 10
−1
torr at most. To use the quadrupole spectrometer in this pressure range, a high-vacuum pump such as a turbo molecular pump must be adopted in addition to a reactor exhaust pump to differentially evacuate the reactor.
Hence, when the source concentration in the reactor during the chemical vapor deposition process is to be measured using the quadrupole spectrometer, like the apparatus shown in
FIG. 9
, the exhaust structure around the reactor becomes inevitably complicated. Even if the quadrupole spectrometer is installed using this structure, a gas component in the reactor is not necessarily the same as a gas component which reaches the quadrupole spectrometer. In addition, some of sources introduced into the reactor are decomposed by a high-temperature wafer heating device, which must be considered. For this reason, it is not practical to compensate for residue variations in the reactor by measuring the source concentration in the reactor during chemical vapor deposition using the quadrupole spectrometer.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a metal organic chemical vapor deposition method and apparatus capable of forming a desired organometallic film by supplying a necessary organometallic source gas more stably than the conventional apparatus.
To achieve the above object, according to one aspect of the present invention, there is provided a metal organic chemical vapor deposition method, comprising the steps of detecting a parameter convertible into the number of moles of gas of an organometallic source supplied from at least one source vessel, heating a source contained in the source vessel when the parameter becomes smaller than a minimum value
Matsumoto Kenji
Shinriki Hiroshi
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Tokyo Electron Limted
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