Gas separation: processes – Selective diffusion of gases – Selective diffusion of gases through substantially solid...
Reexamination Certificate
2001-09-14
2003-08-12
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Selective diffusion of gases
Selective diffusion of gases through substantially solid...
C095S096000, C096S009000, C096S111000, C096S130000, C096S136000
Reexamination Certificate
active
06605134
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for collecting a rare gas in particular, a method and an apparatus for collecting the (are gas contained in an exhaust gas exhausted from a rare gas using apparatus operated under decompression, such as a plasma sputtering apparatus, a plasma oxidation apparatus, a plasma CVD apparatus, a reactive ion etching apparatus or the like.
2. Description of the Prior Art
In a process for manufacturing a semiconductor device such as a semiconductor integrated circuit, an active matrix type liquid crystal panel, a solar cell and a panel thereof, a magnetic disk or the like, there has been used an apparatus such as a sputtering apparatus an oxidation apparatus, a plasma CVD apparatus, a reactive ion etching apparatus or the like for generating plasma in a rare gas atmosphere under decompression in order to carry out various processes for the semiconductor device by the plasma.
For example, in the sputtering apparatus, while introducing the rare gas into a process chamber with a flow rate of about 500 cc/minute, an inside of the chamber is exhausted by a vacuum exhaust apparatus, and a high frequency is applied to an electrode in the chamber in order to generate plasma in a state that a pressure of the chamber is maintained at about 1 Pa. Then, a solid film forming material provided in the chamber is sputtered by the plasma, to thereby form a thin film by deposition on a wafer surface.
Furthermore, in the oxidation apparatus, while introducing a mixed gas of the rate gas and oxygen into the process chamber with a flow rate of about 1000 cc/minute, plasma is generated in a state that a pressure of the chamber is maintained at about 100 Pa by the vacuum exhaust apparatus similar to the sputtering apparatus. Oxygen is made as a quasi-exited state by using the plasma. Oxide film is formed by the quasi-exited oxygen on the wafer surface which is heated to about 400° C.
Furthermore, in the plasma CVD apparatus) while introducing a mixed gas of a film forming gas and the rare gas into the process chamber with a flow rate of about 1000 cc/minute, plasma is generated in a state that a pressure of the chamber is maintained at about 100 Pa by the vacuum exhaust apparatus similar to the sputtering apparatus. The film forming gas is exited by using the plasma. The thin film is formed by deposition on the wafer surface which is heated to about 300° C.
Moreover, in the reactive ion etching apparatus, while introducing a mixed gas of an etching gas and the rare gas into the process chamber, plasma is generated in a state that a pressure of the chamber is maintained at several Pa. The etching gas is exited by using the plasma, to thereby carry out etching by using the exited ion.
In the above-described various apparatuses, since a process is carried out by using plasma having a high energy, if there exists in a processing atmosphere a gas such as nitrogen, oxygen, moisture or the like that does not contribute to film formation, there happen such problems that a predetermined thin film is not formed, or etching can not be carried out.
For example, in case of carrying out forming metallic interconnection for semiconductor integrated circuit by using the sputtering apparatus, if there exist moisture, oxygen or the like in the atmosphere, metallic film is oxidized, to thereby increase an electric resistivity of the metallic interconnection. Furthermore, there is even such a case that a crystal structure is changed similar to the case of tantalum. Moreover, if there exist oxygen, moisture, organic impurities or the like in the atmosphere where a polycrystalline silicon film is formed by the plasma CVD apparatus, there occur various problems.
In addition, if there exist impurities when etching is carried out by the reactive ion etching apparatus, a selectivity for materials can not be determined, to thereby cause inferior etching, or to damage a wafer. Therefore, the amount of the impurities contained in the rare gas introduced into the plasma using apparatus is necessarily to be reduced to a level of below several ppb.
FIG. 3
is a schematic diagram showing a sputtering apparatus as an embodiment of a plasma processing apparatus. Generally, this type of the sputtering apparatus is provided with a loading chamber
12
for conveying the wafer at the front of the process chamber
11
, to thereby convey the wafer one by one.
The loading chamber
12
is maintained as decompressed state by a vacuum exhaust apparatus
13
connected to the loading chamber
12
via a valve, in a purge gas atmosphere of nitrogen gas or the like supplied from a purge gas supply device (not shown). After the loading chamber
12
and the process chamber
11
are vacuum-exhausted, the wafer before processing which is maintained in the loading chamber
12
is positioned on a wafer susceptor
15
in the process chamber
11
passing through a gate valve
14
for separating both the chambers
11
,
12
.
After the gate valve
14
is closed, the rare gas which is supplied from a rare gas cylinder
16
and removed of impurities by a purifier
17
, is introduced into the process chamber
11
via a gas supply apparatus
18
. Generally in order to make an inside of the process chamber
11
as the rare gas atmosphere, a cycle comprising pumping the inside of the process chamber
11
by the vacuum exhaust apparatus
19
connected to the process chamber
11
and introducing the rare gas from the gas supply apparatus
18
is repeatedly carried out more than one time by an instruction from a control means.
After the inside of the process chamber
11
is made as the rare gas atmosphere, plasma is generated in the process chamber
11
by applying high frequency thereto from a high frequency electric source
21
via a matching circuit
20
. Solid film forming material is sputtered by the generated plasma, to thereby deposit thin film on the wafer. The wafer formed with a predetermined thin film is conveyed from the process chamber
11
to the next process via the loading chamber
12
for next processing. In the above-described process, taking-in and taking-out of the wafer are carried out about 30 times per hour. In addition, nitrogen gas is introduced from nitrogen gas supply line
22
into the vacuum exhaust apparatus
19
for preventing back diffusion of the exhaust gas.
However, whether the exhaust gas vacuum exhausted from the sputtering apparatus via the vacuum exhaust apparatus is for purging the inside of the process chamber, or for being used in film formation, the exhaust gas is exhausted from an exhaust line
23
to an outside of a system as it is. On the other hand, the rare gas supplied from the rare gas supply cylinder
16
exists as a very small amount in the atmosphere, for example, the existence concentration of xenon is about 0.086 ppm in the atmosphere. The rare gas is manufactured by further purifying the rare gases concentrated in oxygen gas by cryogenic separation of the air, and is difficult to be obtained in a larger amount, and the cost thereof becomes higher in proportion to the existence ratio thereof.
Thus, it has been proposed a method for collecting the rare gas contained in the exhaust gas from the vacuum exhaust apparatus
19
by a closing loop. This method comprises compressing the exhaust gas by connecting the vacuum exhaust apparatus
19
and a compressor, providing a pair of switching valves in an outlet passage of the compressed gas, and opening and closing the switching valves according to the concentration of the rare gas, to thereby collect the exhaust gas from the process chamber with the rare gas collecting apparatus. The collected exhaust gas is removed of impurities in the appropriate purifier to be recycled.
However, since in this method nitrogen gas is introduced into the vacuum exhaust apparatus
19
for preventing back diffusion of the exhaust gas, it was difficult to collect the rare gas as having high concentration. Furthermore, even in case of collecting the rare gas as having some degree of high
Hayashida Shigeru
Ishihara Yoshio
Kimijima Tetsuya
Nagasaka Toru
Merchant & Gould P.C.
Nippon Sanso Corporation
Spitzer Robert H.
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