Electric heating – Metal heating – By arc
Reexamination Certificate
1998-06-22
2001-08-07
Walberg, Teresa (Department: 3742)
Electric heating
Metal heating
By arc
C118S7230VE, C216S074000, C427S255320
Reexamination Certificate
active
06271498
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of cleaning an MOCVD (Metal Organic Chemical Vapor Deposition) apparatus or another CVD apparatus having a vaporizer for vaporizing a liquid raw material by applying heat and a processing chamber for forming a thin film on a substrate by a CVD (Chemical Vapor Deposition) method using the raw material vaporized in the vaporizer. More specifically, the present invention relates to a method of removing residues in the vaporizer and the processing chamber.
2. Description of the Related Art
In general, a liquid material, which is liquid at room temperatures, is generally sent in a vaporized state by a method disclosed in Japanese Patent Laid-Open No. 50-211072 and using a so-called bubbler or a bubbling apparatus. Also in a process for manufacturing semiconductors, the above-mentioned method is employed in a multiplicity of film forming apparatuses including those for forming TEOS (tetraethoxyorthosilane) films or those for forming superconductive thin films.
On the other hand, dielectric thin films have attracted attention in recent years as an important technique for manufacturing next-generation DRAM (Dynamic Random Access Memory) and FRAM (Ferroelectric Randam Access Memory) apparatuses, the dielectric or ferroelectric thin films including, for example, BST (BaSrTiO
3
, that is, barium strontium titanate) films, SrTiO
3
(strontium titanate) films and PZT (PbZrTIO
3
) films.
When a dielectric thin film is formed by a CVD apparatus, a metal organic material, such as Ba(DPM)
2
, Sr(DPM)
2
or Pb(DPM)
2
, is employed (DPM: dipivaloyl methane). Since each of the above-mentioned materials is solid in room temperatures, the material must be maintained at a hot state not lower than about 200° C. and thus maintained in a liquid state when the material in a gas state is sent by the bubbling apparatus. However, a fact is known that the raw material is quickly decomposed and allowed to deteriorate in the above-mentioned hot state.
To realize a liquid state at relatively low temperatures, a method has been developed with which the metal organic material (a solid raw material) is dissolved in an adduct (a type of a solvent) such as THF (tetrahydrofuran). If the vaporized material is sent by the bubbling apparatus, the pipe arranged from the bubbling apparatus to the processing chamber must be maintained at 200° C. or higher to prevent condensation and liquefaction of the material. Therefore, the hot pipe state must be maintained. In this case, there arises a problem in that only the adduct, such as the THF, is decomposed and vaporized and thus a required material, such as Sr(DPM)
2
, is condensed and fixed to the inner portion of the pipe and the like.
To solve the above-mentioned problem, research of a method has begun recently, with which a liquid raw material obtained by dissolving the above-mentioned required solid raw material in a solvent is, in the liquid state, sent, and then the raw material is heated in a vaporizer formed at the front of the processing chamber so as to be vaporized and immediately supplied to the inside portion of the processing chamber.
A CVD apparatus having the above-mentioned vaporizer has been disclosed in Unexamined Japanese Patent Publication (kokai) No. Hei 7-268634. An example of the CVD apparatus is shown in FIG.
4
.
A liquid raw material
4
obtained by dissolving a required solid raw material, such as Sr(DPM)
2
, in a solvent, such as THF, is supplied from a liquid raw-material supply apparatus
2
to a vaporizer
8
through a liquid raw-material pipe
6
in a predetermined quantity.
The liquid raw-material supply apparatus
2
according to this example has a liquid raw-material container
42
for accommodating the liquid raw material
4
, valves
44
to
47
, a flow-rate adjustment unit
48
and pipes for connecting the above-mentioned elements. The liquid raw-material container
42
is, through a valve
44
, supplied with an inert gas
50
for sending the liquid raw material
4
with pressure. The inert gas
50
is composed of at least a nitrogen gas or a rare gas (that is, He, Ne, Ar, Kr, Xe or Rn which is applied hereinafter). When the liquid raw material
4
is sent under pressure, the valves
44
,
45
and
47
are opened and the valve
46
is closed.
The vaporizer
8
has a structure in which a gas introducing pipe
16
is connected to a vaporizing container
10
. Moreover, a nozzle
14
is, coaxially with the gas introducing pipe
16
, inserted into the vaporizing container
10
. In addition, a heater
12
is disposed to surround the vaporizing container
10
. The nozzle
14
is connected to the liquid raw-material pipe
6
. The gas introducing pipe
16
is supplied with an inert gas
18
through a flow-rate adjustment unit
17
. Also the inert gas
18
is composed of at least either of the nitrogen gas or the rare gas.
The liquid raw material
4
supplied to the vaporizer
8
is, at the leading end of the nozzle
14
, roughly particulated by the high speed inert gas
18
flowing around the leading end. Thus, the liquid raw material
4
is dispersed and allowed to collide with a wide range of the inner wall of the vaporizing container
10
heated to temperatures not lower than 250° C. so that the liquid raw material
4
is immediately vaporized. A vaporized raw material
20
is allowed to pass through a vaporized raw-material pipe
22
and a valve
24
, and then supplied to the inside portion of the processing chamber
26
.
In the processing chamber
26
, a holder (also called a susceptor)
36
for holding a substrate
34
on which a film will be formed and a gas diffusing plate
32
having a multiplicity of small openings and arranged to diffuse a gas introduced into the processing chamber
26
are disposed. The holder
36
and the substrate
34
disposed above the holder
36
are heated by a heating means (not shown). A vacuum exhausting unit
40
for vacuum-exhausting the inside portion of the processing chamber
26
is connected to the processing chamber
26
through a valve
38
. In addition to the vaporized raw material
20
, a gas
30
arranged to react with the vaporized raw material
20
is introduced into the processing chamber
26
. When a thin film made of SrTiO
3
is formed, the gas
30
is a mixed gas of TTIP {Ti (O-i-C
3
H
7
) and an oxide gas (O
2
or the like). The vaporized raw material
20
and the gas
30
are mixed in the processing chamber
26
. The mixed gas is dispersed to have a uniform flow velocity by the gas diffusing plate
32
, and then diffused in the processing chamber
26
vacuum-exhausted by the vacuum exhausting unit
40
. Then, the mixed gas is brought into contact with the heated surface of the substrate
34
. As a result of CVD reactions, a thin film made of SrTiO
3
or the like is formed. The mixed gas which has not been used to form the thin film is discharged to the outside through the vacuum exhausting unit
40
.
The above-mentioned raw material, such as Sr(DPM)
2
or Ba(DPM)
2
, is easily bonded to trace impurities, such as H
2
O, CO, CO
2
or the like, and precipitated. If the environmental temperature is high, the raw material is gradually decomposed and precipitated because of variation with time. Residues of the raw material are accumulated in the vaporizer
8
(specifically, the vaporizing container
10
of the vaporizer
8
which applies hereinafter), causing a variety of problems to arise. For example, residues are fixed to the inner wall of the vaporizing container
10
, causing the efficiency to vaporize the liquid raw material
4
to deteriorate or the state of fixation to become nonuniform. As a result, the vaporization becomes instable. Moreover, residues sometimes cause the nozzle
14
to be clogged. If fixed residues are separated, there is apprehension that the downstream valve or the pipe is clogged.
To prevent this, a cleaning solution (for example, nitric acid) capable of dissolving residues is used to periodically clean the inside portion of the vaporizing container
10
. The exhaus
Hayashi Tsukasa
Kuwahara Hajime
Miyake Koji
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Nissin Electric Co., LTD
Van Quang
Walberg Teresa
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