U.S. patent application number 11/785754 was filed with the patent office on 2007-10-25 for plating apparatus.
This patent application is currently assigned to NEC ELECTRONICS CORPORATION. Invention is credited to Yoichi Togashi.
Application Number | 20070246350 11/785754 |
Document ID | / |
Family ID | 38618451 |
Filed Date | 2007-10-25 |
United States Patent
Application |
20070246350 |
Kind Code |
A1 |
Togashi; Yoichi |
October 25, 2007 |
Plating apparatus
Abstract
A plating apparatus includes a bath configured to reserve a
plating solution for plating a substrate and a holder configured to
hold the substrate. The bath includes an anode electrode provided
inside the bath. The holder includes a cathode electrode for
applying a voltage to the substrate. The bath is equipped with
first and second discharge portions. The plating apparatus includes
a first path, a supply path, a second path and a flow rate control
valve. The first path circulates the plating solution, which is
discharged from the first discharge portion, to the bath. The
supply path supplies the plating solution, which is provided from
the first path, into the bath. The second path provides the plating
solution, which is discharged from the second discharge portion
after flowing on the anode electrode, to the first path. The flow
rate control valve controls a flow rate of the plating solution
flowing from the second path to the first path.
Inventors: |
Togashi; Yoichi; (Yamagata,
JP) |
Correspondence
Address: |
MCGINN INTELLECTUAL PROPERTY LAW GROUP, PLLC
8321 OLD COURTHOUSE ROAD
SUITE 200
VIENNA
VA
22182-3817
US
|
Assignee: |
NEC ELECTRONICS CORPORATION
Kawasaki
JP
|
Family ID: |
38618451 |
Appl. No.: |
11/785754 |
Filed: |
April 19, 2007 |
Current U.S.
Class: |
204/237 |
Current CPC
Class: |
C25D 17/002 20130101;
C25D 17/02 20130101; C25D 17/001 20130101; C25D 5/08 20130101; H01L
21/2885 20130101 |
Class at
Publication: |
204/237 |
International
Class: |
C25B 15/00 20060101
C25B015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 21, 2006 |
JP |
2006-117711 |
Claims
1. A plating apparatus comprising: a plating treatment bath
configured to reserve a plating solution for plating a substrate
and including an anode electrode provided inside said plating
treatment bath; a substrate holder provided above said plating
treatment bath, configured to hold said substrate and including a
cathode electrode for contacting said substrate to apply a voltage
to said substrate; a first flow path configured to circulate said
plating solution, which is discharged from said plating treatment
bath via a first discharge portion, to said plating treatment bath;
a supply path configured to supply said plating solution, which is
provided from said first flow path, into said plating treatment
bath; a second flow path configured to provide said plating
solution, which is discharged from said plating treatment bath via
a second discharge portion after flowing on said anode electrode,
to said first flow path; and a flow rate control valve provided
between said first flow path and said second flow path, wherein
said flow rate control valve is configured to control a flow rate
of said plating solution provided from said second flow path to
said first flow path.
2. The plating apparatus according to claim 1, wherein said plating
treatment bath includes: an anode chamber provided above said anode
electrode and equipped with said second discharge portion; a
membrane diffuser plate chamber provided above said anode chamber
and equipped with said first discharge portion; and a membrane
provided between said anode chamber and said membrane diffuser
plate chamber, said anode chamber is configured to provide said
plating solution, which is supplied via said supply path, to said
flow rate control valve via said second discharge portion and said
second flow path, and said membrane diffuser plate chamber is
configured to provide said plating solution, which is supplied via
said supply path, to said first flow path via said first discharge
portion.
3. The plating apparatus according to claim 1, wherein said flow
rate control valve is configured to control a flow rate of said
plating solution flowing along said second flow path between 60 and
100 ml/min.
4. The plating apparatus according to claim 3, wherein said supply
path includes a first supply path and second supply path, said
first supply path is equipped with a first outlet port configured
to supply said plating solution, which is provided from said first
flow path, to said anode chamber, said second supply path is
equipped with a second outlet port configured to supply said
plating solution, which is provided from said first flow path, to
said membrane diffuser plate chamber, and said first supply path is
configured to supply said plating solution from said first outlet
port such that said flow rate of said plating solution flowing
along said second flow path is between 60 and 100 ml/min.
5. The plating apparatus according to claim 1, wherein said
substrate holder is configured to hold said substrate such that
said substrate can rotate in a horizontal plane.
6. The plating apparatus comprising: a plating treatment bath
configured to reserve a plating solution for plating a substrate
and including an anode electrode provided inside said plating
treatment bath; a substrate holder provided above said plating
treatment bath, configured to hold said substrate and including a
cathode electrode for contacting said substrate to apply a voltage
to said substrate; a first flow path configured to circulate said
plating solution, which is discharged from said plating treatment
bath via a first discharge portion, to said plating treatment bath:
a supply path configured to supply said plating solution, which is
provided from said first flow path, into said plating treatment
bath; and a second flow path configured to provide said plating
solution, which is discharged from said plating treatment bath via
a second discharge portion, to said first flow path, wherein said
plating treatment bath includes: an anode chamber provided above
said anode electrode and equipped with said second discharge
portion; a membrane diffuser plate chamber provided above said
anode chamber and equipped with said first discharge portion; and a
membrane provided between said anode chamber and said membrane
diffuser plate chamber, said supply path includes: a first supply
path equipped with-a first outlet port configured to supply said
plating solution to said anode chamber; and a second supply path
equipped with a second outlet port configured to supply said
plating solution to said membrane diffuser plate chamber, and said
supply path is configured to supply said plating solution from said
first outlet port such that a flow rate of said plating solution
flowing along said second flow path is between 60 and 100
ml/min.
7. The plating apparatus according to claim 6, wherein said
substrate holder is configured to hold said substrate such that
said substrate can rotate in a horizontal plane.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a plating apparatus for use
in a plating process for manufacturing semiconductor devices.
[0003] 2. Description of the Related Art
[0004] Some of conventional plating apparatuses are known as
facedown type plating apparatuses. The facedown type plating
apparatus adopts a form (referred to as facedown form) of arranging
a substrate such as silicon wafer above a plating solution bath and
forms a plated layer such as a copper layer on the substrate. In
the facedown type plating apparatus, there is provided the plating
solution bath having an anode electrode disposed at the bottom
thereof and a plating solution filled therein. The substrate is
arranged such that the surface thereof, on which plating treatment
is executed, faces the solution surface of the plating solution. In
the facedown type plating apparatus, the plating treatment is
executed by applying voltage between the substrate and the anode
electrode in this condition. The facedown form has been
increasingly widely used since it is advantageous in, for example,
downsizing the plating apparatus.
[0005] Hereinafter, a conventional plating apparatus will be
described. FIG. 1 shows a configuration of the conventional plating
apparatus 101 in a cross sectional view. Referring to FIG. 1, the
conventional plating apparatus 101 includes a plating treatment
chamber 102, a tank 103, a pump 104, and a constant current power
source 105. The tank 103 holds a plating solution flowed out from
the plating treatment chamber 102. The pump 104 circulates the
plating solution held in the tank to the plating solution chamber
102. The pump 104 circulates the plating solution through the tank
103 and the plating treatment chamber 102. The constant current
power source 105 supplies DC current to wafer holders 111 and an
anode contact plate 119, which are described later.
[0006] Referring to FIG. 1, the plating treatment chamber 102
includes the wafer holders 111 for holding a wafer 107 and a
plating treatment chamber inner bath 112 for holding the plating
solution. The plating treatment chamber 102 is provided with
circulation drains 113, which are connected to the plating
treatment chamber inner bath 112 via respective anode chamber drain
nozzles 114. The plating treatment chamber inner bath 112 includes
the anode contact plate 119, an anode 115, a membrane 117, and a
diffuser plate 118. The plating treatment chamber inner bath 112
configures an anode chamber 121 between the anode 115 and the
membrane 117. Similarly, the plating treatment chamber inner bath
112 configures a membrane diffuser plate chamber 122 above the
membrane 117.
[0007] The anode contact plate 119 supplies to the anode 115, a
current outputted from the constant current power source 105. The
anode 115 acts as a bottom electrode in correspondence with the
current supplied via the anode contact plate 119. The membrane 117
filters additive decomposition products contained in the plating
solution. The diffuser plate 118 supplies the plating solution to
the wafer 107 such that the plating solution flows uniformly to the
wafer 107.
[0008] As a plating solution supply path, a plating solution supply
nozzle 116 is configured which penetrates through the anode contact
plate 119, the anode 115, and the membrane 117. Referring to FIG.
1, the plating solution supplied into the membrane diffuser plate
chamber 122 passes through the diffuser plate 118 and then is
discharged through the circulation drains 113. The plating solution
supplied into the anode chamber 121 is discharged from the
circulation drains 113 via the anode chamber drain nozzles 114
provided for the anode chamber 121.
[0009] Here, as for the conventional plating treatment chamber 102,
when the plating treatment is executed on the wafer 107 which is
set on the wafer holders 111, the plating solution is supplied from
the plating solution supply nozzle 116 at a rate of 61/min. During
the plating treatment, a current of 1 to 10 A is supplied to the
anode 115 for approximately two to five minutes.
[0010] Japanese Laid Open Patent Application (JP-P-2001-316887)
discloses a face down type plating apparatus. United States Patent
Document (U.S. Pat. No. 6,890,416) discloses another plating
apparatus. The another plating apparatus is provided with a pump,
anode chamber and membrane diffuser plate chamber. The rotation
rate and stroke of the pump is increased to control the flow rates
of plating solution flowing to the entire of the anode chamber,
membrane diffuser plate chamber and surface of a wafer to be
plated.
[0011] To form a thick copper (Cu) film by plating the wafer 107
with copper, as described above, it is required to provide a
current of approximately 10 A for a long period of time. In this
case, Cu concentration in the plating solution flowing on the anode
115 may become high. A small flow rate of the plating solution
flowing on the anode 115 in this condition may cause deposition of
crystals of copper sulfate on the anode 115. The crystals of copper
sulfate on the anode 115 increase the electric resistance between
the plating solution and the anode 115. This may make it difficult
to maintain the current of approximately 10 A for a long period of
time, which may in turn result in failure to perform an appropriate
plating treatment.
[0012] Conventionally, a power supply, which can supply high
voltage, has been used as the constant current power source to
secure desired current, thereby coping with the problem of the
increased resistance.
[0013] In formation of the thick Cu film, the flow rate of the
plating solution flowing on the anode 115 has been increased by
increasing the amount of the plating solution supplied to the
plating treatment chamber 102. As described above, when the thicker
film is formed by plating, it is required to increased flow rate of
the plating solution flowing on the anode 115 (in order to prevent
Cu deposition on the anode).
[0014] As for the plating apparatus disclosed in United States
Patent Document (U.S. Pat. No. 6,890,416), the pump increases the
flow rate of the plating solution and thereby enables suppressing
the deposition of crystals of copper sulfate on an anode of the
plating apparatus.
SUMMARY
[0015] It has now been discovered that an increased amount of the
plating solution to be supplied results in an increased amount of
the plating solution flowing to the surface of the membrane 117.
Thus, the plating solution flowing on the surface of the wafer 107
flows faster. This may make it difficult to form a plated film with
a uniform film thickness over the surface of the wafer 107.
Moreover, the increased amount of the plating solution raises the
consumption of various components contained in the plating
solution, resulting in the increased cost for plating the
wafer.
[0016] In an aspect of the present invention, a plating apparatus
includes a plating treatment bath and a substrate holder. The
plating treatment bath is configured to reserve a plating solution
for plating a substrate. The substrate holder is provided above the
plating treatment bath and configured to hold the substrate such
that the substrate can rotate in a horizontal plane. The plating
treatment bath includes an anode electrode provided inside the
plating treatment bath. The substrate holder includes a cathode
electrode for contacting the substrate to apply a voltage to the
substrate. The plating apparatus includes a first flow path, a
supply path, a second flow path and a flow rate control valve. The
first flow path is configured to circulate the plating solution,
which is discharged from the plating treatment bath via a first
discharge portion, to the plating treatment bath. The supply path
is configured to supply the plating solution, which is provided
from the first flow path, into the plating treatment bath. The
second flow path is configured to provide the plating solution,
which is discharged from the plating treatment bath via a second
discharge portion after flowing on the anode electrode, to the
first flow path. The flow rate control valve is provided between
the first flow path and the second flow path. The flow rate control
valve is configured to control a flow rate of the plating solution
provided from the second flow path to the first flow path.
[0017] In this case, the flow rate control valve controls the flow
rate of the plating solution flowing along the second flow path
such that the deposition of copper sulfate crystals on the anode
electrode can be suppressed. Moreover, the flow rate control valve
adjusts its valve opening not to increase a flow speed of the
plating solution flowing along the substrate surface.
[0018] The present invention is effective in optimally controlling
only the flow rate of the plating solution flowing to an anode
chamber without changing the amount of the plating solution to be
supplied. That is, the present invention enables a variable flow
rate of the plating solution flowing to the anode chamber while
keeping constant the flow rate of the plating solution flowing on a
surface of the wafer. The present invention enables a plating
treatment for forming plated films of various thickness from thin
film thickness to thick film thickness while keeping constant the
flow rate of the plating solution flowing on the surface of the
wafer.
[0019] According to the present invention, when a thin film is
plated, a flow rate of the plating solution flowing on the anode
electrode can be reduced to smaller flow rate than when a thick
film is plated. The reduction in the flow rate of the plating
solution can suppress the consumption of additives and also
increase in cost.
[0020] According to the present invention, a plating treatment can
be executed without configuring a constant current power source
that can supply high voltage. This permits execution of an
appropriate plating treatment without increasing facility-related
costs.
[0021] According to the present invention, an increase in a flow
speed of the plating solution on the wafer surface can be
suppressed to thereby provide a plated film of uniform film
thickness over the surface of the wafer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The above and other objects, advantages and features of the
present invention will be more apparent from the following
description taken in conjunction with the accompanying drawings, in
which:
[0023] FIG. 1 is a sectional view illustrating a configuration of a
conventional plating apparatus;
[0024] FIG. 2 is a sectional view illustrating a configuration of a
plating apparatus according to a first embodiment of the present
invention; and
[0025] FIG. 3 is a sectional view illustrating a configuration of a
plating apparatus according to a second embodiment of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] The invention will be now described herein with reference to
illustrative embodiments. Those skilled in the art will recognize
that many alternative embodiments can be accomplished using the
teachings of the present invention and that the invention is not
limited to the embodiments illustrated for explanatory purpose.
[0027] The embodiments of the present invention will be described
below with reference to the accompanying drawings. The embodiments
to be described below refer to, as an example, a case where a
plating apparatus 1 according to the present invention is an
apparatus which plates a silicon wafer with copper to thereby form
the Cu film. This does not mean that the present invention is only
applicable to plating treatment for forming the Cu film.
First Embodiment
[0028] FIG. 2 is a sectional view that illustrates configuration of
a plating apparatus 1 according to the first embodiment of the
present invention. Referring to FIG. 2, the plating apparatus 1 of
the first embodiment includes a plating treatment chamber 2, a tank
3, a pump 4, a constant current power source 5, and flow rate
control valves 6.
[0029] The plating treatment chamber 2 is a treatment bath in which
the plating treatment on a wafer 7 is executed. The plating
treatment chamber 2 reserves a plating solution for use in
performing the plating treatment on the wafer 7. The tank 3 holds
the plating solution discharged from the plating treatment chamber
2. The pump 4 supplies the plating solution held in the tank 3 to
the plating treatment chamber 2. Thus, the plating solution
discharged from the plating treatment chamber 2 returns to the
plating treatment chamber 2. This enables circulative supply of the
plating solution. The constant current power source 5 provides an
electric power required for the plating treatment performed by the
plating treatment chamber 2. The flow rate control valve 6 controls
the flow rate of the plating solution flowing to the anode chamber
while keeping constant the flow rate of the plating solution
flowing on the wafer surface.
[0030] Referring to FIG. 2, the plating treatment chamber 2
includes a plating treatment chamber inner bath 12. The plating
treatment chamber 2 is also provided with circulation drains 13.
Wafer holders 11 hold the wafer 7. As shown in FIG. 2, the wafer
holders 11 are in contact with the wafer 7 which is arranged with
the surface thereof subjected to plating treatment facing downward.
The wafer holders 11 hold the wafer 7 such that the wafer 7 can
rotate. The wafer holders 11 are connected to the constant current
power source 5 via a first node N1.
[0031] Inside the plating treatment chamber inner bath 12, an anode
15 is configured. As shown in FIG. 2, the anode 15 is connected to
an anode contact plate 19, which is provided outside the plating
treatment chamber inner bath 12. The anode contact plate 19 is
connected to the constant current power source 5 via a second node
N2. Therefore, the anode 15 acts as an anode electrode (bottom
electrode) in correspondence with a current supplied via the anode
contact plate 19.
[0032] The circulation drains 13 are configured in the plating
treatment chamber 2, and each serve as a flow path for circulating
the plating solution flowing out from the plating treatment chamber
inner bath 12. As shown in FIG. 2, the plating apparatus 1
according to the present embodiment configures a plating solution
circulating flow path 8 (first flow path) with the circulation
drains 13, the tank 3, and the pump 4.
[0033] The plating treatment chamber inner bath 12 described above
includes anode chamber drain nozzles 14, a plating solution supply
nozzle 16, a membrane 17, and a diffuser plate 18. The anode
chamber drain nozzle 14 is an outlet port for discharging the
plating solution contained in an anode chamber 21. As shown in FIG.
2, the anode chamber drain nozzles 14 according to the present
embodiment are connected to the flow rate control valves 6. The
membrane 17 filters additive decomposition products contained in
the plating solution. The diffuser plate 18 supplies the plating
solution such that the plating solution flows uniformly to the
wafer 107.
[0034] The plating solution supply nozzle 16 is a plating solution
supply path in the plating apparatus 1 according to the present
embodiment. The plating solution supply nozzle 16 penetrates
through the anode contact plate 19, the anode 15, and the membrane
17. As shown in FIG. 2, the plating solution supplied into a
membrane diffuser plate chamber 22 passes through the diffuser
plate 18, and is discharged from the circulation drains 13. The
plating solution supplied into the anode chamber 21 is supplied
from the anode chamber drain nozzles 14, which are provided in the
anode chamber 21, to the circulation drains 13 via the flow rate
control valves 6.
[0035] As described above, in the plating treatment for forming the
Cu film or the like, it is required to reduce the amount of the
plating solution flowing to the membrane diffuser plate chamber 22
to appropriately form the Cu film. In order to prevent formation of
crystals of copper sulfate or the like on the anode 15 in this
condition, the plating apparatus 1 according to the present
embodiment is provided with the anode chamber drain nozzles 14 of
large nozzle diameter size. The anode chamber drain nozzles 14 of
large nozzle diameter size ensure a sufficient amount of the
plating solution flowing to the anode chamber drain nozzles 14.
That is, the large nozzle diameter size of the anode chamber drain
nozzles 14 reduces the flow resistance of the nozzles 14, thereby
permitting a sufficient amount of the plating solution to flow to
the anode chamber drain nozzles 14.
[0036] Here, the flow rate control valve 6 according to the present
embodiment controls valve opening such that the flow rate of the
plating solution flowing through the anode chamber drain nozzle 14
is between 60 and 100 ml/min. An experiment has proved that, in the
plating treatment for forming the Cu film or the like, controlling
this flow rate between 60 and 100 ml/min provides favorable
results. That is, controlling the flow rate of the plating solution
flowing through the anode chamber drain nozzle 14 between 60 and
100 ml/min by use of the flow rate control valve 6 prevents the Cu
concentration in the plating solution flowing on the anode 15 from
becoming high. In the plating apparatus 1 according to the present
embodiment, the flow rate control valves 6 controls the flow late
of the plating solution. Thus, the plating apparatus 1 suppresses
formation of the crystals of copper sulfate on the anode 15 and
thus prevents an increase in the electrical resistance between the
anode 15 and the plating solution.
[0037] The flow rate control valve 6 can vary the flow rate of the
plating solution flowing to the anode chamber 12 while keeping
constant the flow rate of the plating solution flowing on the
surface of the wafer 7, thereby avoiding stagnation of the flow on
the anode 15. Thus, upon formation of the thicker Cu film,
deposition of copper sulfate on the anode 15 is suppressed. The
plating apparatus 1 can form an appropriate Cu film. On the other
hand, upon formation of a thinner Cu film, the flow rate of the
plating solution flowing on the anode 15 can be reduced smaller
than that for forming the thicker Cu film. Thereby, the plating
apparatus 1 suppresses the consumption of additive and thus
increase in the cost.
[0038] In this condition, the flow rate of the plating solution
supplied to the membrane diffuser plate chamber 22 is controlled at
an optimum level, thus permitting the thickness of the film to be
uniform over the surface of the wafer 7. Further, there is no
increase in the electrical resistance, thus permitting
configuration of the plating apparatus which forms the appropriate
Cu film without being provided with a power supply which can supply
high voltage. This permits reduction in the costs spent on
facilities for the plating apparatus.
Second Embodiment
[0039] Hereinafter, referring to the drawings, a second embodiment
of the present invention will be described. FIG. 3 is a sectional
view that illustrates configuration of the plating apparatus 1
according to the second embodiment of the present invention. In the
drawing used for the following description, components provided
with the same numerals as those in the first embodiment have the
same configuration and operation as those in the first embodiment.
Therefore, the descriptions for the overlapping components are
omitted from the following description.
[0040] Referring to FIG. 3, in the plating apparatus 1 according to
the second embodiment, the pump 4 in the plating solution
circulating flow path 8 is provided with an anode chamber pump 31
and a membrane diffuser plate chamber pump 32. The plating solution
supply nozzle 16 includes a membrane diffuser plate chamber plating
solution supply nozzle 33 and anode chamber plating solution supply
nozzles 34. As shown in FIG. 3, the anode chamber pump 31 is
connected to the anode chamber plating solution supply nozzles 34.
The membrane diffuser plate chamber pump 32 is connected to the
membrane diffuser plate chamber plating solution supply nozzle
33.
[0041] The anode chamber plating solution supply nozzle 34 supplies
the plating solution to the anode chamber 21. The membrane diffuser
plate chamber plating solution supply nozzle 33 supplies the
plating solution to the membrane diffuser plate chamber 22. As
shown in FIG. 3, the membrane diffuser plate chamber plating
solution supply nozzle 33 and the anode chamber plating solution
supply nozzles 34 are configured independently from each other.
Here, the anode chamber pump 31 supplies the plating solution to
the anode chamber plating solution supply nozzles 34, and the
membrane diffuser plate chamber pump 32 supplies the plating
solution to the membrane diffuser plate chamber plating solution
supply nozzle 33. Therefore, controlling the flow rates of the
plating solution supplied by the anode chamber pump 31 and the
membrane diffuser plate chamber pump 32 permits highly accurate
control of flow rates of the plating solution flowing in the anode
chamber 21 and in the membrane diffuser plate chamber 22.
[0042] The plating apparatus 1 according to the second embodiment
can control independently the flow rates of the plating solution
supplied to the anode chamber 21 and the membrane diffuser plate
chamber 22. This permits supplying a minimum necessary amount of
the plating solution to each of the chambers, thus achieving cost
reduction by suppressing the plating solution consumption.
Third Embodiment
[0043] Hereinafter, referring to the drawings, a third embodiment
of the present invention will be described. The plating apparatus 1
according to the third embodiment is provided with the plating
solution supply nozzle 16 having outlet ports of nozzle diameter
sizes such that the plating solution flows through the anode
chamber drain nozzle 14 at a flow rate of 60 to 100 ml/min. In this
case, the plating solution supply nozzle 16 controls the nozzle
diameter size of the outlet port for supplying the plating solution
to the membrane diffuser plate chamber 22 or controls the nozzle
diameter size of the outlet port for supplying the plating solution
to the anode chamber 21. Thus, the plating solution supply nozzle
16 controls the flow rate through the anode chamber drain nozzle
14. The plating apparatus 1 according to the third embodiment, when
the flow rate of the plating solution discharged from the anode
chamber drain nozzle 14 is desired to be fixed, can control the
flow rate of the plating solution flowing through the anode chamber
drain nozzle 14 while suppressing an increase in the
facility-related costs. Moreover, providing the flow rate control
valve 6 described above permits variably controlling, with higher
accuracy, the flow rate of the plating solution flowing through the
anode chamber drain nozzle 14.
[0044] The plurality of embodiments described above can be
practiced in combination within the range consistent with the
configuration and operation thereof. The flow rate control valve of
the present invention maybe provided with, for example, a flow
meter and thereby may control the valve.
[0045] It is apparent that the present invention is not limited to
the above embodiment, but may be modified and changed without
departing from the scope and spirit of the invention.
* * * * *